Master Thesis Electrical Engineering Thesis no: MEE xx-xx June 2011

Master Thesis Electrical Engineering Thesis no: MEE xx-xx June 2011

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Master Thesis

Electrical Engineering

Thesis no: MEE xx-xx

June 2011

COEXISTENCE OF WLAN AND WWAN

IN A NOTEBOOK

Emmanuel O. Owolabi and

Vivien I. Ibiyemi

June 22, 2011

Supervisors:

Dr. Leif. R. Wilhelmsson

Research Department, Ericsson AB, Sweden

Prof. Abbas Mohammed

School of Electrical Engineering, BTH,

Sweden

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Dedication

To the almighty God and to my loving husband who has been a strong pillar by my side all through the period of this program and gave me strong motivation to carry on. To my lovely kids; Olaide Olivea-Janet,

Oluwatomide David and Oluwabisade Jenny who bore with my absence from home with a welcoming smile and a mummy we are proud of you countenance and to you Mum. Also in memory of my father Funsho

Oke.

Ibiyemi Vivien Ibironke,

Lund, Sweden.

June 2011.

To the El Shaddai, my teachers, my family and specially to my precious beauty Ruth.

Owolabi Emmanuel Olusegun,

Lund, Sweden.

June 2011.

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Abstract

A modern notebook can be equipped with several devices of wireless network access technologies, such as Wireless Local Area Network

(WLAN), Wireles Wide Area Network (WWAN), Wireless Personal

Area Network (WPAN), and radio based navigation systems, such as

GNSS (Global Navigation Satellite System). Future mobile devices will have different radio technologies such as Long Term Evolution (LTE),

Wideband Code Division Multiple Access (WCDMA) and WLAN transceivers co-existing on the same module that enables such a device to connect to the different radio technologies.

With these radio technologies present in the same device, care must be taken to minimize the interference between them.

In this master thesis, we analyze the co-existence of WLAN in the 2.4GHz ISM band, GSM 1800MHz/900MHz, and WCDMA FDD in the 800MHz and 2.1GHz band when they are embedded in a notebook. Different coexistence scenarios have been considered during this work, with focus on realistic power levels for the victim system as well as the aggressor system, and the actual antenna coupling measured for different notebooks. These measurements and the realistic power levels computed are results that will be a factor to consider when designing WLAN/WWAN coexistence module.

This work is divided into seven major parts.

Chapter 1 is an introduction to coexistence, and a description of the different radio access technologies considered.

Chapter 2 is the state of the art. This is a brief discussion of previous related work on coexistence.

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Chapter 3 is the problem statement definition describing the research problems and hypothesis.

Chapter 4 describes the measurement plan, devices and parameters considered in developing the test environment and the different measurement scenarios.

Chapter 5 presents the measurement setup and procedures undertaken in achieving the measurement.

Chapter 6 is the result analysis.

Chapter 7 presents conclusion and future work.

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Acknowledgment

Many thanks Ericsson Research for giving us an opportunity work on this thesis. We also want to use this medium to express our appreciation to our supervisor Dr. Leif Wilhelmsson. Thank you so much for your support throughout the duration of this thesis. Your technical knowledge and valuable experience was of great help to us. You impacted and inspired us in a way that we will not forget in a long while. Thank you for believing in us and for giving us the opportunity to be part of Ericsson research Lund, Sweden. Our gratitude also goes the MBM team in Ericsson Lindholmen, our co-supervisors, Lars Persson and Torbjorn Elfstrom. There are not enough words to describe how useful and significant your contribution was towards the successful completion of this work. Thanks you so much. Hakan Svensson and

Lars Calen thanks for your contribution. You were there to help and to give us some guidiance during each visit to the Ericsson Lindholmen lab. Thank you so much.

We appreciate Fredrik Tillman, technical manager, Ericsson research in Lund, Pierre Gildert, MBM Manager Ericsson Lindholmen,

Stefan Lingren, MBM Manager Ericsson Lindholmen. Thank you for your support during the thesis period.

Also we would like to express our gratitude to all the staff at research department, who helped us throughout this work and made this experience a pleasant and an unforgettable one. To everyone at Scheelevagen thank you.

Prof. Abbas Mohammed, our supervisor and examiner at BTH.

Your effort, support and recommendation is much appreciated and we vii

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To all our friends and families, thank you so much for being there when it matters.

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List of Abbreviation

ARIB: Association of Radio Indurstries and Businesses

CDMA: Code Division Multiple Access

CSMA/CA: Carrier Sense Multiple Access with Collision Avoidance

ETSI: European Telecommunication Standards Institute

E-UTRA: Evolved Universal Terestrial Radio Access

FDMA: Frequency Division Multiple Access

TDMA: Time Division Multiple Access

GSM: Global System of Mobile Communication

QAM: Quadrature Amplitude Modulation

QPSK: Quadrature Phase Shift Keying

BPSK: Binary Phase Shift Keying

GPRS: General Packet Radio Services

GPS: Global Positioning System

GLONASS: Global Navigation Satellite System

MBM: Mobile broadband module

OFDM: Orthogonal Frequency Division Multiple Access

SNR: Signal to Noise Ration

WWAN: Wireless Wide Area Network

WCDMA: Wideband Code Division Multiple Access

WLAN: Wireless Local Area Network

Wi-Fi: Wireless Fidelity

WCTS: Wirelss Communication Test Set

3GPP: Third Generation Partnership Project

ETSI: European Telecommunication Standards Institute ix

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Contents

1 Wireless Technologies and Coexistence 1

1.1

Wireless Technologies . . . . . . . . . . . . . . . . . . . .

1

1.1.1

Introduction 1

1.2

Coexistence Theory . . . . . . . . . . . . . . . . . . . . .

3

1.3

WCDMA Overview

. . . . . . . . . . . . . . . . . . . . .

8

1.4

WCDMA Characteristics . . . . . . . . . . . . . . . . . . .

10

1.5

WCDMA protocol Architecture . . . . . . . . . . . . . . .

12

1.5.1

The physical layer

1.5.2

The Medium Access Control

13

13

1.5.3

The Radio Resource Control protocol 14

1.6

WCDMA Frame Structure . . . . . . . . . . . . . . . . . .

15

1.6.1

Uplink Link Frame Structure 15

1.6.2

Downlink Frame Structure 16

1.6.3

Synchronization Channel 17

1.7

Cell search . . . . . . . . . . . . . . . . . . . . . . . . . .

18

1.8

Spreading and Modulation . . . . . . . . . . . . . . . . . .

19

1.9

Wireless Local Area Network . . . . . . . . . . . . . . . .

19

1.9.1

PHY Layer

1.9.2

Packet Structure-Frame Format

1.9.3

The various WLAN standards

1.9.4

Transmission Range and data flow 27

1.10 WLAN Performance . . . . . . . . . . . . . . . . . . . . .

28

22

24

25

2 State of the art 29 xi

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3 Research question and problem statement 31

3.1

Motivation . . . . . . . . . . . . . . . . . . . . . . . . . .

31

3.2

Problem Statement . . . . . . . . . . . . . . . . . . . . .

32

3.3

Main Contribution . . . . . . . . . . . . . . . . . . . . . .

33

4 Measurement Requirement 35

4.1

Measurement plan . . . . . . . . . . . . . . . . . . . . . .

35

4.2

Evaluation criteria definition . . . . . . . . . . . . . . . . .

35

4.2.1

Throughput 36

4.2.2

Jitter 37

4.2.3

4.2.4

4.2.5

Signal to Noise Ratio

Packet loss

Attenuation

39

40

40

4.2.6

Spurious emission 41

4.2.7

Out of band emission 41

4.3

Coexistence Measurement Procedures

. . . . . . . . . . .

41

4.4

Brief description of the tools and devices used . . . . . . .

42

4.4.1

Possible risk associated with measurement 48

4.4.2

Link Budget Analysis 48

5 Measurement Set-Up 53

5.1

Setup and characterization . . . . . . . . . . . . . . . . .

53

5.1.1

5.1.2

5.1.3

WWAN/WLAN

Aggressor: WWAN Victim: WLAN

Aggressor: GSM, Victim: WLAN

53

58

60

5.1.4

Aggressor: WLAN, Victim: WWAN 62

6 Results Presentation and Analysis 69

6.1

Coexistence Measurement Results . . . . . . . . . . . . . .

69

6.1.1

Antenna Coupling Measurement Results 69

6.1.2

Aggressor: WCDMA and Victim: WLAN 71

6.1.3

6.1.4

Aggressor:GSM 1800MHz/900MHz, Victim:WLAN

Aggressor:WLAN, Victim: WCDMA

75

79

7 Conclusion and Future research

Bibliography

83

85 xii

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List of Figures

1.1

Spurious Emission and Out of Band Emission [2]. . . . .

4

1.2

Coexistence of Access Technologies on a Notebook. [9]. .

5

1.3

E-UTRA Operating Bands [3].

. . . . . . . . . . . . . .

7

1.4

wcdma communication model [4]. . . . . . . . . . . . . .

9

1.5

HSPA evolution path . . . . . . . . . . . . . . . . . . . .

9

1.6

3G Evolution Path [4]. . . . . . . . . . . . . . . . . . . .

10

1.7

WCDMA Protocol Architecture[6]. . . . . . . . . . . . .

12

1.8

WCDMA Uplink Frame Structure [6].

. . . . . . . . . .

15

1.9

WCDMA Downlink Frame Structure [6]. . . . . . . . . .

17

1.10 Spectral Mask 802.11g [17]. . . . . . . . . . . . . . . . .

21

1.11 PHY and MAC Layer Architecture.[26] . . . . . . . . . .

23

1.12 DSSSOFDM Frame Structure breakdown. [27]. . . . . .

25

1.13 Power levels for some modulation [4]. . . . . . . . . . . .

28

4.1

Devices used in Coexistence Measurement . . . . . . . .

42

4.2

Process of identifying where degradation starts and interferer is being introduced . . . . . . . . . . . . . . . .

49

4.3

Link Budget for Coexistence of WLAN and WWAN . .

50

4.4

Diagrammatic representation to show point at which C and I were taken . . . . . . . . . . . . . . . . . . . . . .

51

5.1

WCDMA FDD BAND I Settings . . . . . . . . . . . . .

55

5.2

Measurement setup . . . . . . . . . . . . . . . . . . . . .

56

5.3

Setup: WWAN BAND I Aggressor to WLAN. . . . . . .

59

5.4

WWAN GSM as Aggressor to WLAN. . . . . . . . . . .

60

5.5

GSM Settings Screen shot. . . . . . . . . . . . . . . . . .

61

5.6

WLAN interfering WWAN. . . . . . . . . . . . . . . . .

62

5.7

WCTS setup screen . . . . . . . . . . . . . . . . . . . .

63 xiii

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5.8

Typical iperf MBM Client Screen . . . . . . . . . . . . .

65

5.9

Typical Measurement Screen with cell power of -60 . . .

66

5.10 Lab Pictures . . . . . . . . . . . . . . . . . . . . . . . .

67

5.11 Lab Pictures . . . . . . . . . . . . . . . . . . . . . . . .

68

6.1

Antenna Characterization Results . . . . . . . . . . . . .

70

6.2

WWAN Aggressed WLAN . . . . . . . . . . . . . . . . .

71

6.3

WCDMA Interferer Budget Link . . . . . . . . . . . . .

73

6.4

WCDMA Tx Power and WLAN Throughput . . . . . .

74

6.5

GSM Aggressed WLAN. . . . . . . . . . . . . . . . . . .

75

6.6

Antenna Coupling Type1 and Type2 at 2.4GHz . . . . .

76

6.7

GSM1800MHz link budget . . . . . . . . . . . . . . . . .

77

6.8

WLAN Throughput and GSM1800MHz Power . . . . .

78

6.9

WLAN Interferes WCDMA . . . . . . . . . . . . . . . .

79

6.10 WLAN Tx Power Distribution. . . . . . . . . . . . . . .

80

6.11 WCDMA Coexistence Throughput . . . . . . . . . . . .

81 xiv

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Chapter

1

Wireless Technologies and Coexistence

1.1

Wireless Technologies

1.1.1

Introduction

The world’s first wireless telephone conversation occurred in 1880, when

Alexander Graham Bell and Charles Sumner Tainter invented and patented the photophone, a telephone that conducted audio conversations wirelessly over modulated light beams (which are narrow projections of electromagnetic waves).

Wireless telecommunications can be described as transfer of information between two or more points that are physically not connected.

Distances can be short, as a few meters as in television remote control; or long, ranging from thousands to millions of kilometers for deep-space radio communications. It encompasses various types of fixed, mobile, and portable two-way radios, cellular telephones, personal digital assistants (PDAs), and wireless networking. Other examples of wireless technology include GPS units, and garage door openers, wireless computer mice, keyboards and headsets, satellite television and cordless telephones, etc.

There are several technoques of accessing a wireless communication system(s), these are called access technologies. Below are some examples of systems and their access technologies; e.g

• Wi-Fi using CCK/OFDMA.

• Bluetooth using FHSS.

• GSM using TDMA/FDMA.

1

2

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Wireless Technologies and Coexistence

• WiMAX using OFDMA.

• UMTS/3G using WCDMA/CDMA.

• Satellite Communication using FDMA/CDMA/TDMA variant.

• LTE using OFDMA, SC-FDMA etc.

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Wireless Technologies and Coexistence 3

1.2

Coexistence Theory

The quest for communication anywhere anytime has fueled an enormous growth in wireless communication. With increase in demand for wireless devices such as notebooks, PDAs, gaming devices and the increase in network based applications, it has become necessary for the telecommunication industry to proffer a one stop solution that caters for the demand for data intensive applications as well as real time access to corporate data services while providing seamless mobility and high bandwidth to all users. There is need to support available access technologies on a single module (such as Wi-Fi/WLAN, LTE, WCDMA,

GSM, etc.) to provide seamless roaming between the schemes. Therefore coexistence of the existing wireless access technologies with a view to providing mobility and seamless coverage (3G), capacity and high bandwidth (WLAN) has become a topic of interest for operators and vendors alike.

An MBM (Mobile Broadband Module, a mobile wireless access device) will usually house several different technologies like GSM, WCDMA,

LTE, GLONAS, GPS, and Galileo. An integrated solution offers a number of advantages over external solutions predominantly regarding convenience, security, hardware and software compatibility and expanded functionality e.g. Sim Based Solution [12].

So far, the use of mobile devices is on the increase, both in private and public places. However, development of new ways or new functionalities to the use of these mobile devices such as notebooks is equally on the increase and connectivity to the Internet and other networks is becoming a priority for most notebook users. The combination of these two trends is giving rise to new requirements for the modern notebook users which can be characterized by the quest and need to be on line real-time at any chosen location.

As the notebook user requirement is changing, it has become necessary for the industry to offer an integration of WWAN (3G, LTE, GSM) technologies into notebooks in order to meet this growing demand.

With the roll-out of 3G and LTE networks being accelerated across continents and additional media enhanced capabilities that are supported by HSPA upgrades, notebooks with built-in connectivity to mobile network represent a major step towards achieving an all-emcompassing

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Wireless Technologies and Coexistence 4 and unlimited connectivity in an all communicating world.

While there is so much excitement and optimism about the topic on coexistence of WLAN and WWAN, the telecommunication industry is yet faced with the challenge of interference such as out of band and spurious emissions (Figure 1.1) due to the close range of frequencies at which these access technologies operates and high output transmit power radiated by these systems. In as much as the MBM module is usually embedded in a host together with WLAN as shown in Figure 1.2, the coexistence between IEEE802.11b/g/n and GSM/WCDMA/LTE could be further challenging. For example the ISM band (WLAN),

Evolved Universal Terestrial Radio Access (E-UTRA) LTE and UTRA

(WCDMA) are quite close in the 2GHz range. So also is WiMax and the

ISM band. Implementing these technologies on a module in a notebook such that they can successfully coexist together or independent of one another without one impacting negatively on the other is the point of interest in coexistence.

Coexistence here could be in two forms namely; Proximity and Collocation. Proximity is when the two system operates without dependent conditions such as physical closeness, meaning the system operate in the same area. Collocation is the pyhsical presence of the two systems in a module embedded in a device, i.e physical collocation or reside side by side [1].

Figure 1.1: Spurious Emission and Out of Band Emission [2].

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Wireless Technologies and Coexistence 5

Figure 1.2: Coexistence of Access Technologies on a Notebook. [9].

Figure 1.2 shows a typical laptop device equiped with multiple access technologies, the different antennas is a representaion of each of them.

In this research work, we analyze coexistence between WLAN and

WCDMA when both systems are integrated into a notebook. We evaluate under what conditions both systems can operate independently and when collaboration is needed. Setting up a network of WLAN connections in Ad-hoc mode, interfered by WCDMA/GSM traffic and vice versa, we analyzed the performance of these access technologies from coexistence point of view. Iperf test tool was used to observe the impact of one access technology (the aggressor) on the other (the victim) in terms of throughput, SNR (C/I), jitter, and packet loss. Using this tool, we observed the effect of interfering WLAN traffic with WWAN traffic.

The results from the analysis are used to determine the transmit

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Wireless Technologies and Coexistence 6 power values of the aggressor access technology and the expected corresponding throughput of the victim access technology that are suitable for coexistence. This provides a basis for selecting appropriate transmit power and RF requirement needed in the design of the MBM that will coexist the different access technologies that are discussed.

Figure 1.3 [3] shows the operating bands of the E-UTRA.

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Wireless Technologies and Coexistence 7

Figure 1.3: E-UTRA Operating Bands [3].

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Wireless Technologies and Coexistence 8

1.3

WCDMA Overview

The outcome of the ETSI process in early 1998 was the selection of wideband CDMA as the technology for UMTS in the paired spectrum(FDD) and TD-CDMA (Time Division CDMA) for the unpaired spectrum (TDD). There was also a decision to harmonize the parameters between the FDD and the TDD components. Therefore 3G is an umbrella term for the third generation radio technologies developed within 3GPP and it refers to UMTS/WCDMA technology.

The standardization of WCDMA went on in parallel with ETSI and ARIB until the end of 1998 when the Third Generation Partnership

Project(3GPP) was formed by standards-developing organizations from all regions of the world. The present organizational partners of 3GPP are ARIB (Japan), CCSA (China), ETSI (Europe), ATIS(USA), TTA

(Korea and TTC (Japan)). W-CDMA was specified in Release 99 and

Release 4 of the specifications. High Speed Packet Access (HSPA) was introduced in Releases 5 (Downlink) and 6 (Uplink) giving substantially greater bit rates and improving packet-switched applications.

The third generation of mobile phone technology(3G) is the beginning of broadband technology convergence enhanced with the features to deliver high data throughput as well as voice quality to users. This evolution from the traditional networks also known as 1G is as result of user requirement for high quality, high throughput and wide range of inter connectivities.

3G proves to be a good successor to GSM, building upon GSM proven Subscriber Identity Module card roaming model, yet offering much more spectrum for voice services whilst enabling a much wider variety of data and multimedia services.

Another advantage of 3G network is that it can be deployed along side a GSM network or can be deployed as an overlay networks to support both data and voice with the existing GSM networks.

At the birth of the 3G network with the promise of high data throughput many were of the opinion that it will die a natural death due to the existence of WLAN. As the wireless local area network (WLAN) offers much more and it’s marketability does have promising future, though it will not provide the same geographical coverage and mobility as we have today in 3G. Hence, the two technologies were definitely go-

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Wireless Technologies and Coexistence 9 ing to be complementary as we already have it [4]. Figure 1.4 shows the communication model of a typical WCDMA system while Figure 1.5 is the HSPA evolution [4].

Figure 1.4: wcdma communication model [4].

Figure 1.5: HSPA evolution path

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Wireless Technologies and Coexistence 10

1.4

WCDMA Characteristics

WCDMA uses a digital wideband spread spectrum technology to transmit multiple independent conversations across single or multiple 5MHz segments of radio spectrum. WCDMA operates at 2GHz range of frequencies.

Within 3GPP, WCDMA is called UTRA (Universal Terrestrial Radio Access) and the radio access specifications provide for

Frequency Division Duplex (FDD) and Time Division Duplex (TDD) variants, several chip rates are provided for in the TDD option, allowing

UTRA technology to operate in a wide range of bands and to co-exist with other radio access technologies.

Figure 1.6 shows the evolution in the 3G networks. It operates with a 3.84Mcps on a 5MHz band spectrum. WCDMA supports a data rate of 384kbps at hot spots and 144kbps in wide coverage for circuit switched and 2Mbps for packet switched.

Figure 1.6: 3G Evolution Path [4].

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Wireless Technologies and Coexistence 11

Channel Bandwidth

Chip Rate

WCDMA Chracteristics

5MHz

3.84Mcps

Convolutional and turbo codes Channel Codeing

Channel Multiplexing in downlink

Channel multiplexed in uplink

Data and control channels time multiplexed

Control and pilot channel time multiplexed

Coherent Detection

Spreading downlink

I and Q multiplexing for data and control channel

User dedicated time multiplexed pilot (downlink and uplink) with common pilot in the downlink

QPSK (Downlink) Data modulation

BPSK (uplink)

Downlink RF channel structure Direct spread

Duplex Mode FDD and TDD

Frame Length 10ms

Soft handover

Handover

Multirate

Power Control

Interfrequency handover

Variable spreading and multicode

Open and fast closed loop (1.6KHz)

Balanced QPSK (downlink)

Spreading modulation

Dual-channel QPSK (uplink)

Complex spreading sircuit

Spreading factors 4-256 (uplink), 4-512 (uplink)

OVSP sequences for channel sepration

Spreading (uplink)

Gold sequences for cell and user separation (truncated cycle 10ms)

OVSP sequences, Gold sequence for user separation (different time shift in I and Q channel, truncated cycle 10ms)

Table 1.1: WCDMA Characteristics table [5].

12

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Wireless Technologies and Coexistence

1.5

WCDMA protocol Architecture

To Core Network

Control Plane

Layer 3

User Plane

Radio Access Bearers

RNC

Logical Channels

Layer 2 MAC

Transport Channels

Layer1

NodeB

Figure 1.7: WCDMA Protocol Architecture[6].

The layered approach in Figure 1.7 highlights the different protocol layers in WCDMA. Each layer is responsible for a specific part of the radio-access functionality.

The Packet Data Convergence Protocol (PDCP) processes the User’s data from the core network, for example IP packets. It performs (optional) header compression to save radio-interface resources, because IP packets have a relatively large header, 40 bytes for IPv4 and 60 bytes for IPv6 [4].

The Radio Link Protocol (RLC) segments the IP packets into smaller units known as RLC Protocol Data Units (RLC PDUs)and it equally reassembles the received segments back to IP packets at the receiving end. Error free delivery of data is of high priorityfor packet-data services, therefore the RLC in addition to the above assignment is shouldered with the responsibility of handling the ARQ protocol such that the RLC can be configured to place a request for retransmission of each

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Wireless Technologies and Coexistence 13 erroneous RLC PDUs (Packet Data Units)received.The RLC entity at the receiving end indicates the need for a retransmission to the RLC entity at the transmitting end by use of status report [4].

1.5.1

The physical layer

Right below the MAC layer is the physical layer. The physical layer offers different transport channels to MAC. A transport channel is characterized by how the information is transferred over the radio interface.

Transport channels are channel coded and then mapped to the physical channels specified in the physical layer. There exist two types of transport channels:

1. Dedicated channels

2. Common channels

There is one dedicated transport channel, the dedicated channel (DCH), which is a downlink or uplink transport channel. The DCH is transmitted over the entire cell or over only a part of the cell using beam-forming antennas. The DCH is enabled with capability to do fast rate change

(every 10ms), fast power control, and inherent addressing of mobile stations. The physical layer is responsible for coding, spreading, modulation of the radio-frequency carrier and data modulation. Spreading of the data to be transmitted to the chip rate of 3.84 Mchip/s in WCDMA is the primary assignment of the physical layer. Its other functions include coding, transport-channel multiplexing, and modulation of the radio-frequency carrier [6].

1.5.2

The Medium Access Control

The Medium Access Control (MAC) layer provides data transfer services to the RLC of layer 2 in the form Logical Channels. How a logical channel is described depends on the type of information that is being transfered because different logical channel set exist or can be defined for different kinds of data transfered services as offered by the MAC.

There are two types of logical channel groups namely control channels for transfer of control plane information and traffic channels for

14

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Wireless Technologies and Coexistence the transfer of user plane information. The MAC layer also has the capability to multiplex data from multiple logical channels [6].

Just before data transmission, and for each Transmission Time Interval (TTI), minimum of one transport block is fed from the MAC layer to the physical layer for each Transmission Time Interval (TTI) where coding, interleaving, multiplexing, spreading, etc., is performed.

For WCDMA, the TTI is the time which the interleaver spans and the time it takes to transmit the transport block over the radio interface.[]

Therefore a larger TTI depicts better time diversity, but also a longer delay. In the first release, WCDMA relies on TTI lengths of 10ms,20ms,

40ms, and 80ms. But HSPA introduces additional 2ms TTI to reduce latency [4].

To support different data rates, The MAC has the capability to vary the transport format between consecutive TTIs. The transport format consists of several parameters describing how the data shall be transmitted in a TTI and different data rates can be achieved if the transport-block size or the number of transport blocks is varied [4].

1.5.3

The Radio Resource Control protocol

This is responsible for the configuration of PDCP, RLC, MAC, and physical layer. It equally handles admission control, handover decisions,and active set management for soft handover. With accurate setting of the parameters of the RLC, MAC, and physical layers, RRC will yield the required quality of service (QoS) requested by the core network for a particular service. On the network side, the MAC, RLC and RRC entities in Release 99 are all located in the RNC while the physical layer is mainly located in the NodeB. The same entities also exist in the UE. For example, the MAC in the UE is responsible for selecting the transport format for uplink transmissions from a set of formats configured by the network. However, the handling of the radio resources in the cell is controlled by the RRC entity in the network and the UE obeys the RRC decisions taken in the network [4].

In the interface of W-CDMA, the different interface users can immediately transmit at varying information rates, with the data rates even varying in time. Networks of the UMTS are required to support every 2G service, plus new services and applications.

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1.6

WCDMA Frame Structure

1.6.1

Uplink Link Frame Structure

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Figure 1.8: WCDMA Uplink Frame Structure [6].

There are two uplink dedicated physical and two common physical channels:

1. The uplink dedicated physical data channel (uplink DPDCH) and the uplink dedicated physical control channel (uplink DPCCH).

2. The physical random access channel (PRACH) and physical common packet channel (PCPCH).

The uplink DPDCH is used to carry dedicated data generated at layer 2 and above (i.e. the dedicated transport channel (DCH)). There may be zero, one, or several uplink DPDCHs on each layer 1 connection.

The uplink DPCCH is used to carry control information generated at layer 1 [6].

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Control information consists of known pilot bits to support channel estimation for coherent detection, transmit power-control (TPC) commands, feedback information (FBI), and an optional transportformat combination indicator (TFCI). The transport-format combination indicator/identifier informs the receiver about the instantaneous parameters of the different transport channels multiplexed on the uplink DPDCH, and corresponds to the data transmitted in the same frame. For each layer 1 connection there is only one uplink DPCCH [6].

Figure 1.8 shows the principal frame structure of the uplink dedicated physical channels. Each frame of length 10ms is split into 15 slots, each of length Tslot = 2560 chips, corresponding to one power-control period.

The parameter k in figure 1.8 determines the number of bits per uplink DPDCH/DPCCH slot. It is related to the spreading factor (SF) of the physical channel as SF = 256/2k. The DPDCH spreading factor may thus range from 256 down to 4. An uplink DPDCH and uplink

DPCCH on the same layer 1 connection generally are of different rates and thus have different spreading factors [6].

1.6.2

Downlink Frame Structure

The frame structure of WCDMA downlink is as shown in Figure 1.9.

There is one downlink dedicated physical channel, one shared and five common control channels;

1. Downlink dedicated physical channel (DPCH);

2. Physical downlink shared channel (DSCH);

3. Primary and secondary common pilot channels (CPICH);

4. Primary and secondary common control physical channels (CCPCH);

5. Synchronization channel (SCH).

Figure 1.9 shows the frame structure of the DPCH. On the DPCH, the dedicated transport channel is transmitted time multiplexed with control information generated at layer 1 (known pilot bits, power-control commands, and an optional transport-format combination indicator).

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Figure 1.9: WCDMA Downlink Frame Structure [6].

DPCH can contain several simultaneous services when TFCI is transmitted or a fixed rate service when TFCI is not transmitted.

The network determines if a TFCI should be transmitted. When the total bit rate to be transmitted exceeds the maximum bit rate for a downlink physical channel, multicode transmission is employed (i.e., several parallel downlink DPCHs are transmitted using the same spreading factor). In this case, the layer 1 control information is put on only the first downlink DPCH [6].

1.6.3

Synchronization Channel

A user equipment has to perform synchronization during the search for a cell after power on. Primary Synchronization:the user equipment synchronizes with the help of a 256 chip primary synchronization code.

This code is the same for all the cells, and it helps to synchronize with the time slot structure.

Secondary Synchronization; the user equipment receives a secondary synchronization code which defines the group of scrambling codes within the group of codes to find the right code with the help of a correlator.

After these three steps, the user equipment can receive all further data over a broadcast channel [6].

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Wireless Technologies and Coexistence 18

1.7

Cell search

During cell search, the mobile station searches for a cell and determines the downlink scrambling code and common channel frame synchronization of that cell. Because the radio frame timing of all common physical channels is related to the timing of P-CCPCH, it is enough to find the timing of P-CCPCH only.

The cell search is typically carried out in three steps: slot synchronization; frame synchronization and code-group identification; and scrambling-code identification. An example procedure from the 3GPP specification TS25.214 is described as follows:

• Step 1: Slot synchronization. During the first step of the cell search procedure, the mobile station uses the SCH’s primary synchronization code to acquire slot synchronization to a cell.

This can be done with a single matched filter matched to the primary synchronization code that is common to all cells. The slot timing of the cell can be obtained by detecting peaks in the matched filter output.

• Step 2: Frame synchronization and code-group identification. During the second step of the cell search procedure, the mobile station uses the SCHŠs secondary synchronization code to find frame synchronization and identify the code group of the cell found in the first step.

This is done by correlating the received signal with all possible secondary synchronization code sequences and identifying the maximum correlation value. Because the cyclic shifts of the sequences are unique, the code group and the frame synchronization are determined.

• Step 3: Scrambling-code identification. During the third and last step of the cell search procedure, the mobile station determines the exact primary scrambling code used by the found cell. The primary scrambling code is typically identified through symbolby-symbol correlation over the CPICH with all codes within the code group identified in the second step.

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After the primary scrambling code has been identified, the primary CCPCH can be detected. So much that the system and cell specific BCH information can be read. In case the mobile station has received information about which scrambling codes to search for, steps 2 and 3 above can be simplified [6].

1.8

Spreading and Modulation

WCDMA applies a two-layered code structure consisting of a orthogonal spreading codes and pseudo-random scrambling codes.

Spreading is performed using channelization codes, which transforms every data symbol into a number of chips, thus increasing the bandwidth of the signal. Orthogonality between the different spreading factors can be achieved by the tree-structured orthogonal codes. WCDMA and HSPA employs a higher order modulation such as 8PSK, BPSK in the uplink and QPSK, M-QAM in the downlink. In the uplink, either short or long spreading

(scrambling) codes are used. The short codes are used to ease the implementation of advanced multiuser receiver techniques; otherwise, long spreading codes can be used. In the downlink, the same orthogonal channelization codes are used as in the uplink.

Gold codes of length 218 are used for scrambling, but they are truncated to form a cycle of a 10ms frame (i.e., 384,000 chips).

Scrambling is also used for cell separation in the downlink and user separation in the uplink [6].

1.9

Wireless Local Area Network

IEEE 802.11 also known as Wi-Fi is the fundamental building block of wireless local area networks (WLAN).

These set of standards consist of protocols and transmission schemes which are today one of the most remarkable standardization achievement. The technology has it’s origin in a 1985 ruling by the US federal communication commission that released the ISM band for unlicensed use. The year 1991 witnessed the invention of a

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Wireless Technologies and Coexistence lifetime,the precursor to the 802.11 in Nieuwegein, the Netherlands by NCR corporation AT and T (Now Alcatel-Lucent and

LSI corporation).

The patent of the Wi-Fi has it’s genesis dated back to the 1977 paper written by CSIRO [18] researcher O’Sullivan who wrote a set of mathematical equations for telescopic image sharpening and later develop what is to be called Wi-Fi at the Commonwealth Scientific and Industrial Research Organization (CSIRO), the Australia’s national science agency [24].

The 802.11 family consists of a series of over-the-air modulation techniques that use the same basic protocol.

The most popular are those defined by the 802.11b and 802.11g protocols, which are amendments to the original standard.

802.11-1997 was the first wireless networking standard among the 802.x, but

802.11b was the first widely accepted one, followed by 802.11g and

802.11n. Security was originally purposefully weak due to export requirements of some governments, and was later enhanced via the

802.11i amendment after governmental and legislative changes.

802.11n is a new multi-streaming modulation technique. Other standards in the family are service amendments and extensions or corrections to the previous specifications.

802.11b and 802.11g use the 2.4GHz ISM band, operating in the

United States under Part 15 of the US Federal Communications

Commission Rules and Regulations. Because of this choice of frequency band, 802.11b and g equipment may occasionally suffer interference from microwave ovens, cordless telephones and Bluetooth devices.

802.11b and 802.11g control their interference and susceptibility to interference by using direct-sequence spread spectrum (DSSS) and orthogonal frequency-division multiplexing (OFDM) signaling methods, respectively as well as a probabilistc Media Access

Control (MAC) call Carrier Sense Multiple Access with Collison Aviodance (CSMA/CA). 802.11a uses the 5GHz U-NII band, which, for much of the world, offers at least 23 non-overlapping channels rather than the 2.4GHz ISM frequency band, where all channels overlap. Better or worse performance with higher or

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Wireless Technologies and Coexistence 21 lower frequencies (channels) may be realized, depending on the environment.

The segment of the radio frequency spectrum used by 802.11

varies between countries. In the US, 802.11a and 802.11g devices may be operated without a license, as allowed in Part 15 of the

FCC Rules and Regulations. Frequencies used by channels one through six of 802.11b and 802.11g fall within the 2.4GHz amateur radio band. Licensed amateur radio operators may operate

802.11b/g devices under Part 97 of the FCC Rules and Regulations, allowing increased power output but not commercial content or encryption.

The spectral mask does define the output restriction of the 802.11g

up to +/-11MHz from any channel’s center frequency up to a point of -50dBr of attenuation. Figure 1.10 [17] shows the overview of overlapping and non overlapping channels from the spectral mask point of view. From the diagram, we observe that if transmitters are closer together than channels 1, 6, and 11 (for example, 1, 4, 7, and 10), overlap between the channels may cause unacceptable degradation of signal quality and throughput [17].

However, overlapping channels may be used under certain circumstances. This way, more channels are available. The 802.11

Figure 1.10: Spectral Mask 802.11g [17].

standard reserves the low levels of the OSI model for a wireless connection that uses electromagnetic waves, i.e.:

– The physical layer (sometimes shortened to the "PHY" layer), which offers three types of information encoding.

– The data link layer, comprised of two sub-layers: Logical

Link Control (or LLC) and Media Access Control (or MAC).

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1.9.1

PHY Layer

The physical layer defines the radio wave modulation and signalling characteristics for data transmission, while the data link layer defines the interface between the machine’s bus and the physical layer in particular an access method close to the one used in the Ethernet standard and rules for communication between the stations of the network.

The 802.11 standard comprises of two sublayers namely;

– the Physical Layer Convergence Protocol (PLCP) sublayer and

– the physical medium dependent (PMD) sublayer

Below are some of the the functions of the PLCP.

– The PLCP also provides the interface for transfer of data octets between MAC and the PMD.

– The MAC layer communicates with the Physical Layer Convergence Protocol (PLCP) sublayer via primitives (a set of instructive commands) through a service access point (SAP).

– It also minimizes the dependence of the MAC layer on the

PMD sublayer by mapping MPDUs into a frame format suitable for transmission by the PMD.

– The PLCP also delivers incoming frames from the wireless medium to the MAC layer. The PLCP sublayer as illustrated in Figure 1.11 [26].

– The PLCP also delivers incoming frames from the wireless medium to the MAC layer.

– The PLCP sublayer is illustrated in Figure 1.11 [26].

– The PLCP appends a PHY-specific preamble and header fields to the MPDU that contain information needed by the

Physical layer transmitters and receivers.

The 802.11 standard refers to this composite frame (the MPDU with an additional PLCP preamble and header) as a PLCP protocol data unit (PPDU). The MPDU is also called the PLCP

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Wireless Technologies and Coexistence 23

Figure 1.11: PHY and MAC Layer Architecture.[26]

Service Data Unit (PSDU), and is typically referred to as such when referencing physical layer operations.

The frame structure of a PPDU provides for asynchronous transfer of PSDUs between stations. As a result, the receiving station’s Physical layer must synchronize its circuitry to each individual incoming frame while the PMD under the direction of the

PLCP sublayer provides transmission and reception of Physical layer data units between two stations via the wireless medium.

To provide this service,the PMD interfaces directly with the wireless RF medium and provides modulation and demodulation of the frame transmissions. The PLCP and PMD sublayers communicate via primitives, through a SAP, to govern the transmission and reception functions. The PMD sublayer is seen as illustrated in Figure 1.11 [26] IEEE 802.11 in its original form operate three different types of PHYs called:

1. 2.4GHz Frequency Hopping Spread Spectrum is described as when there is a switching of frequency of a single carrier so as not to interfere with and not be interfered by another carrier.

2. Direct Spread Spectrum (DSSS) is the energy in a single carrier is spread over a wider spectrum by multiplying data

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Wireless Technologies and Coexistence bit(s) with a special 11-bit pattern, called a Barker key.

This is done at a chip rate of 11MHz. This technique can help reduce interference from narrow-band sources. The IEEE

802.11b -1999 and

3. Infrared IR

1.9.2

Packet Structure-Frame Format

Below is a typical frame structure for all IEEE 802.11. PREAM-

BLE: The preamble is PHY dependent and it includes the following;

– SYNCH is an 80-bits sequence alternating zeros and ones,which is used by the PHY circuitry to select the appropriate antenna if diversity is used and to reach a steady-state frequency offset correction and synchronization with the received packet timing and

– SFD a start frame delimiter that consist of the 16-bit binary pattern 0000 1100 1011 1101, which is used to define the frame timing

PLCP HEADER: The PLCP header is always transmitted at

1Mbits/s and contains Logical information that will be used by the PHY Layer to decode the frame, and consists of those earlier discussed elements.

– PLCP-PDU LENGTH WORD: This represent the number of bytes contained in the packet, this is useful for the PHY to correctly detect the end of packet.

– PLCP SIGNALLING FIELD: This contains only the rate information and its encoded and

– HEADER ERROR CHECK FIELD: This is a 16bits CRC error detection field

Figure 1.12

[27] below shows the frame structure breakdown

FSBD of the general frame structure to the PHY layer as well as the MAC.

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Figure 1.12: DSSSOFDM Frame Structure breakdown. [27].

Any high-level protocol can be used on a WLAN network the same way it can be used on an Ethernet network and there are several standards in the WLAN categories.

1.9.3

The various WLAN standards

The IEEE 802.11 standard is the earliest standard in it’s group thats supports between 1-2Mbps of bandwidth. Over the years there are modifications made to enhance bandwidth (these modifications includes the 802.11a, 802.11b and 802.11g standards, which are called 802.11 physical standards) or to better specify components in order to ensure improved security or compatibility. Below is the various amendments to the 802.11 standard and their significance:

– 802.11a: Is a standard that allows higher bandwidth, up to

54Mbps maximum throughput, about 30Mbps in practice.

The 802.11a standard provides 8 radio channels in the 5 GHz frequency band.

– 802.11b: The 802.11b standard is currently the most widely used one. It offers a maximum throughput of 11Mbps about

6Mbps in practice and could reach up to 300 meters in an open environment. It uses the 2.4 GHz frequency range, with

3 radio channels available.

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– 802.11c-Bridging: The 802.11c called bridging standard is probably of no great interest to people. However the amendment of 802.1d standard allows it to be compatible with

802.11-devices at the data link layer.

– 802.11d: A supplement to the 802.11 standard which is meant to allow international use of local 802.11 networks. It lets different devices trade information on frequency ranges depending on what is permitted in the country where the device is manufactured.

– 802.11e: Improving service quality,the 802.11e standard is meant to improve the quality of service at data link layer.

The standard’s goal is to define the requirements of different packets in terms of bandwidth and transmission delay so as to allow optimized transmission of voice and video.

– 802.11f: The 802.11f is a recommendation standard for Access Point manufacturers that allows products compatible.

It uses the Inter-Access Point Roaming Protocol (IAPRP), which allows a roaming user to transparently switch from one access point (AP) to another AP when mobile without infrastructure hardware limitation.

– 802.11g: The 802.11g standard offers high bandwidth (54

Mbps maximum throughput theoretically on the 2.4 GHz frequency range. The 802.11g standard is backwards-compatible with the 802.11b standard, meaning that devices that support the 802.11g standard can also work with 802.11b.

– 802.11h: The 802.11h standard is intended to bring together the 802.11 standard and the European standard (HiperLAN

2, hence the h in 802.11h) while conforming to European regulations related to frequency use and energy efficiency.

– 802.11n: is the ammendment on the existing standards but this time to provide higher data rate in the range of 600Mbit/s over the 802.11a/g with 54Mbits/s.

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1.9.4

Transmission Range and data flow

The 802.11a, 802.11b and 802.11g standards, called "physical standards" are amendments to the 802.11 standard. Depending on their range, the standards offers different data transfer rates.

Standard Frequency Speed Range

WiFi a (802.11a) 5 GHz 54 Mbit/s 10 m

WiFi B (802.11b) 2.4 GHz 11 Mbit/s 100 m

WiFi G (802.11b) 2.4 GHz 54 Mbit/s 100 m

802.11g

2.4 GHz 54 Mbit/s 27 m

Table 1.2: Transmission range

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1.10

WLAN Performance

WLAN peformance study and analysis in [13] shows the relationship between the different supported modulation schemes such as BPSK, QPSK, 16QAM, 64QAM and respective SNR-BER of

802.11g.

It shows the nominal values of the SNR and BER for the different modulation schemes, however it is seen that the 64QAM produced higher throughput for the WLAN system all things being equal(i.e

cosidering a very good radio channel condition).

However the adaptability of the commercial WLAN module used ensure automatic adaptation of the the different modulation schemes to the prevailing condition of the radio environment. The Figure

1.13 shows the graph modulation schemes SNR vs BER curve.

Figure 1.13: Power levels for some modulation [4].

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Chapter

2

State of the art

Several work and considerations has been carried out on this very important and interesting topic that defines different radio technologies coexistence and inter radio access technologies. This is in an attempt to increase the way we communicate both with voice and data which will further enhance convergence in broadband, seamless coverage and mobility.

Emerging heterogeneous multi-radio networks with focus on interference issues due to simultaneous operation of multiple radio has been a point of interest.

There are different perspectives and bottlenecks to consider in the coexistence of different access technologies amongst are; Interference in the radio layer-physical layer,end to end seamless mobilty, handover, etc. The radio access must be critically analyzed so also is the core networks.

If the radio access must coexist favourably, there must be a sync effort with their core networks. Analysis of WLAN and UMTS handover have been considered in [14], with empahasis on overlay modelling handover with possible delays in the core network.

A comprehensive review of sources of coexistence interference with efforts proposing a media independent service(MICE) layer with suggestion of improvement through air interface as well as protocol was considered in [1].

Various effort were analzed in [15] with consideration in the FEM design for multiradio capabilities.

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Chapter

3

Research question and problem statement

3.1

Motivation

The demand for higher data throughput, seamless coverage, mobility and generally a data centric network is a motivating factor for the study of coexistence as operators and vendors are charged with the responsibility of providing a solution that will satisfy the user’s requirements in terms of availability, reliability and quality of service enabling seamless traffic offloading from one access technologies to another.

As we consider coexistence of the different access technologies as the solution to satisfying these requirements, interference such as spurious emission and out of bound emission is a foreseen challenge in its implementation particularly coexistence of IEEE

802.11b/g/n and GSM/WCDMA/LTE which are envisioned to be challenging due to their output transmit power, close range of operating frequencies and harmonics.

The purpose of this master thesis is to analyze under what operating conditions WLAN and WWAN can coexist together when both systems are integrated in a notebook.

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3.2

Problem Statement

Our research question is based on coexistence capability of mobile devices such as laptop, phones, PDA, etc.

How would different access technologies such as WLAN, WCDMA and LTE coexist on a modern notebook?

We evaluate the coexistence of WLAN, WCDMA, and GSM radio access technologies considering the effect of interference from one to the other, by analysing IP throughput degradation, SNR, losses as a function of spurious emission and jitter. These will form the criteria and basis for different use cases (e.g network router and handover scenarios) the will be evaluated. We also evaluate the effect of antenna coupling on each of these radio technologies as it is the system component point of access, hence the effect of coupling between the system is a factor in desensing.

Antennas coupling, signal strength, spurious emission e.t.c are parameters at layer one of the system. For this reason we have focused on the physical (PHY) layer transmission of the technologies under consideration.

We computed a transmit power distribution as well as coupling effect analysis that forms a basis for the selection of RF requirements which will guide designers in the development and integration of WLAN and WWAN into a notebook.

Within this work, coexistence is considered from collocation perspective, a scenario where the module that houses WLAN and

WWAN (WCDMA, GSM) technologies is embedded in the laptop.The foreseen circumstance is that these access technologies operates within close range of frequency. WCDMA at 2.1GHz, the WLAN in the Industrial Scientific and Medical (ISM) Band at 2.4GHz, and GSM at 1800MHz.

Two use cases considered in analysing coexistence of these technologies are the network router and WLAN/WWAN handover, when WWAN and WLAN operates simultaneously with maintained sensitivity for WWAN and WLAN respective receivers.

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Research question and problem statement 33

The first is when WWAN is implemented as an access to the Internet while the WLAN is use to distribute these accessed resources to connected devices and the foreseen problem is such that there are disturbances between WWAN and WLAN that in turn affect their respective throughput.

The other way is the offload, when a WLAN and WWAN capable device changes seamlessly from a WWAN to a WLAN cell during a session or vice versa. In this case the WLAN device is configured as an ad-hoc or infrastructure device on a linux machine. Thus the foreseen problem here is that the device will not be able to detect the other cell due to de-sensing of the receiver.

3.3

Main Contribution

The main contribution of this thesis work is the characterization and computatuion of transmit power distribution system for an aggressor system in the coexistence of WLAN and WWAN on a device, that will give radio module designers a basis for determining optimal power/RF requirement for coexistence of these technologies.

It’s also to show the under which condition both systems will operate favourably.

We design a realistic RF test environment that simulates real life scenarios in which coexistence measurement is carried out.

Antenna characterization measurements were taken to analyze the effect of coupling in the coexistence of WLAN and WWAN targeting realworld commercial products/devices.

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Chapter

4

Measurement Requirement

Understanding and highlighting the specific requirement for the coexistence measurement is important in a research work in order to have a good sense of direction. Therefore from our problem statement we identified the specific requirements for the WLAN,

WWAN,and GSM coexistence measurement and measurement plans.

4.1

Measurement plan

Here we determine what is to be measured and how it will be achieved. A procedure definition on how the activities will be achieved is mapped out. We also define our completion criteria and control yardsticks to enable us measure the progress against the plan and make necessary adjustment where and when necessary.

4.2

Evaluation criteria definition

To effectively analyze coexistence, it’s important to identify parameters that impact on the performance of WLAN, WCDMA and GSM technologies. Listed below are evaluation criteria or parameters and terms that we have considered including their brief description and importance in this measurement.

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– Throughput.

– Jitter/delay round-trip-time (RTT).

– Packet loss.

– Signal to noise/interference ratio.

– Attenuation and signal strength.

– Losses in cables and connectors.

– Spurious Emission

– Out of Band Emission

4.2.1

Throughput

In telecommunication networks such as Ethernet or packet radio, throughput or network throughput can be defined as the average rate of successful message delivery over a communication channel.

This data may be delivered over a physical or logical link, or passed through a certain network node. The throughput is usually measured in bits per second (bit/s or bps), and sometimes in data packets per second or data packets per time slot. The system throughput or aggregate throughput is the sum of the data rates that are delivered to all terminals in a network. The throughput can be analyzed mathematically by means of queueing theory, where the load in packets per time unit is denoted as arrival rate and the throughput in packets per time unit is denoted departure rate . Throughput is essentially synonymous to digital bandwidth consumption.

Users of telecommunications devices, systems designers, and researchers into communication theory are often interested in knowing the expected performance of a system. From a user perspective, this is often phrased as either "which device will get my data there most effectively for my needs", or "which device will deliver the most data per unit cost". Systems designers are often interested in selecting the most effective architecture or design constraints for a system, which drive its final performance. In most cases, the benchmark of what a system is capable of, or its ’maximum performance’ is what the user or designer is interested in.

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Measurement Requirement 37

Maximum theoretical throughput is closely related to the maximum possible quantity of data that can be transmitted under ideal circumstances. In some cases this number is reported as ideal, though this can be deceptive. Maximum theoretical throughput is more accurately reported to take into account format and specification overhead with best case assumptions. This number, like the closely related term ’maximum achievable throughput’ below, is primarily used as a rough calculated value, such as for determining bounds on possible performance early in a system design phase.

Throughput degradation is a function of spurious emission level, if there is an effect on the physical layer, it will have a ripple effect on the IP network layer as well as application layer.

In this measurement, the main factor affecting our throughput is interference from other technologies which drives the victim into the receiver noise level.

4.2.2

Jitter

Jitter could relate to delay or round trip time in a network. Jitter is of interest for broadband connection. It is applicable to real time network applications. It is the amount of variation in latency/response time. Reliable connections consistently report back the same latency over and over again. Lots of variation (or

’jitter’) is an indication of problems. Jitter shows up as different symptoms, depending on the application being used. Web browsing is fairly resistant to jitter, but any kind of streaming media

(voice, video, music) is quite suceptible to Jitter.

Jitter is a symptom of other problems. It’s an indicator that there might be something else wrong. Often, this ’something else’ is bandwidth saturation (sometimes called congestion) - or not enough bandwidth to handle the traffic load [32]. Jitter is the variation in timing of some event against a clock. It is properly used when describing the variation in bit arrival times against the regenerated clock at a receiver, but it is also loosely used to describe the variation of IP packet arrival times. However, with

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IP packets there is no clock to directly compare the packet arrival times to, so we need to consider differences in delay, as worked out from packet time stamps.

In RFC 3393 the IETF define this packet jitter as the Instantaneous Packet Delay Variation (IPDV) and deprecate the use of the term jitter. The IPDV is defined as the difference in one way delay between sucessive packets, ignoring any lost packets, and with the one way delay being from the start of the packet being transmitted at the source address to the end of the packet being received at the destination.

If a part of the packet switching process always takes the same time, then obviously its effect will be cancelled out when taking the difference in delay. For example, assuming it always takes the same time from receipt of the start of a packet at the receiver to the whole packet being assembled (which clearly assumes constant packet lengths), we could use the time when the start of the packet arrives at the destination as our destination timestamp.

Given a sequence of packets transmitted at times t(1), t(2), t(3),

... t(n) and received at times t’(1), t’(2), t’(3), ... t’(n), then the sequence of delays is d(1), d(2), d(3), ... d(n), where d(i) = t’(i)

- t(i) and d(i) >= 0. Thus the IPDV, or jitter as defined by the

IETF, is the sequence d(2) - d(1), d(3) - d(2), ... d(n) - d(n-1).

and the maximum jitter: jmax = maxabs[d(2) - d(1)], abs[d(3) d(2)], ... abs[d(n) - d(n-1)]

This is unsigned, but it is possible to sign it by giving jmax the sign of the selected maximum term in the sequence. In the discrete event simulation tool OPNET the definition of jitter is the time difference between the instances when successive packets are received at the destination minus the time difference between the instances when these packets are sent at the source, thus the IPDV is: [t’(n) - t’(n-1)] - [t(n) - t(n-1)], ... [t’(3) - t’(2)] - [t(3) - t(2)],

[t’(2) - t’(1)] - [t(2) - t(1)] = [t’(n) - t(n)] - [t’(n-1) - t(n-1)], ...

[t’(3) - t(3)] - [t’(2) - t(2)], [t’(2) - t(2)] - [t’(1) - t(1)] = d(n) d(n-1), ... d(3) - d(2), d(2) - d(1)

This gives n-1 data points for n packets, which could be rather a

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Measurement Requirement 39 lot [30].

Jitter calculations are continuously computed by the server, as specified by RTP in RFC 1889. The client records a 64 bit second/microsecond timestamp in the packet. The server computes the relative transit time as (server’s receive time - client’s send time). The client’s and server’s clocks do not need to be synchronized; any difference is subtracted out in the jitter calculation.

Jitter is the smoothed mean of differences between consecutive transit times [31].

4.2.3

Signal to Noise Ratio

When performing a RF site survey, it’s important to define the range of boundaries of an access point based on signal to noise

(SNR) ratio, which is the signal level (in dBm) minus the noise level (in dBm). For example, a signal level of -55dBm measured near an access point and typical noise level of -90dBm yields a

SNR of 35dB, which is a 90 percent success probability level for

1000byte frame for wireless LANs which is considered a healthy value for a WLAN connection [19].

The SNR relating to a user device communicating with an access point and vice versa, decreases as the seperation between them in terms of distance and the applicable free space loss between the user and the access point increases. This has an impact on the signal level. An increase in noise level due to an increase in RF interference from other devices operating at same frequency with a user device for example microwave ovens, cordless phones,etc could further degrade the SNR.

SNR directly impacts the performance of a wireless connection, therefore it is a key parameter for evaluating the performance of a wireless device like WWAN and WLAN devices. A higher SNR depicts a stronger signal strength in relation to the noise levels, which allows higher data rates and fewer retransmissions - all of which offers better throughput. A lower SNR makes it impossible for the wireless devices to sustain high data rate hence the device will have to operate at lower data rates, causing a decrease in

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Measurement Requirement throughput. For example, an SNR of 35dB may allow an 802.11g

client radio and access point to communicate at about 24 Mbps

(maximum achievable practically); whereas, a SNR of 18dB may only provide for 6Mbps [29].

Within thesis, we have considered SNR as C/I. This is because the equipment used did not give us access to the firmware of the module, therefor it was not possible to fix the data rate of WLAN.

4.2.4

Packet loss

Packet loss occurs when one or more packets of data traveling across a computer network fail to reach their destination.

Packet loss can arise from a number of factors including signal degradation over the network medium due to multi-path fading, packet drop because of channel congestion, corrupted packets rejected in-transit, faulty networking hardware, faulty network drivers or normal routing routines (such as DSR in ad-hoc networks).

In addition to this, packet loss probability is also affected by signal-to-noise ratio and distance between the transmitter and receiver.

When caused by network problems, lost or dropped packets can result in highly noticeable performance issues or jitter with streaming technologies, voice over IP, online gaming and videoconferencing, and will affect all other network applications to a degree.

Packet loss is closely associated with quality of service considerations, and is related to the Erlang unit of measure [33].

4.2.5

Attenuation

Attenuation is the decrease in strength of a radio wave between a transmitter and a receiver; it could be as a result of pathloss or interference.

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Measurement Requirement 41

Within this work, we used step attenuators to vary interference level of the aggressor as well as to attain the required signal strength for the victim access technology.

4.2.6

Spurious emission

This is the unwantedemissions that can occur outside the necessary bandwith and which can be reduced without impeding or causing harmful interference to the transmission of information [2].

4.2.7

Out of band emission

This is unwanted emissions that may occur outside the necessary bandwidth in the course or process of modulation, excluding spurious emission [2].

4.3

Coexistence Measurement Procedures

In determining how the measurement will be achieved, we identified relevant devices for the coexistence measurement setup, and setting up of a test/measurement environment,test tools that are required, the procedures, guidelines for the measurement and what scenarios will be effective in actualizing the best measurement results.

Below are the selected devices for the measurement setup and

Figure: 4.1 is a picture of some of the devices .

1. Lenovo Laptop housing WLAN modules model: 49654AGN

MM1, MAC: 001DE0ABF6E3 as transmitter.

2. Toshiba laptop housing WLAN modules model: 4965AG

MM2, MAC: 0013E843507F as receiver.

3. WCDMA Server.

4. CMU 200 (WWAN base station).

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Measurement Requirement

Figure 4.1: Devices used in Coexistence Measurement

5. Agilent 8960 wireless Communication Test Set (WCTS).

6. WCDMA module (Housed on cradle).

7. Couplers and Splitters.

8. Network Analyzer.

9. Variable Attenuators: 69dB, 60dB, 10dB

10. Spectrum Analyzer

11. Momentum Nanometer

12. Cables and Connectors

13. Test tool: iperf

14. Operating system: ubuntu Linux

15. UDP Traffic

4.4

Brief description of the tools and devices used

1. Lenovo T61 Laptop (Transmitter).

We used this as our transmitter and iperf client. The WLAN modules is embedded in the laptop with the following specification:

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Measurement Requirement 43

– linux version: GNUBash version 4.15(1)

-release(i686-pc-linux-gnu)

– HDD: 150G

– RAM: 1024mB

– Form factor: SODIMM

– Processor: intel (R) Core(TM)2 Duo CPU T7300 2.00GHz

2. Toshiba TECRA M9 laptop (Receiver).

We used this as our receiver and iperf server. The WLAN modules is embedded in the laptop with the following specification:

– linux version: GNUBash version 4.15(1)

-release(i686-pc-linux-gnu)

– HDD: 80G

– RAM:2048MB

– Form Factor: SODIMM

– Processor: intel (R) CPU 1.80GHz

3. RhodesShwartz CMU 200 (as WWAN Base station):

This equipment can offer for WCDMA / HSPA measurements the following key functionalities: Non-Signaling measurements, Reduced signaling measurements (Tx and Rx),

Signaling measurements , application testing therefore it has an advantage of QPSK / WCDMA Modulation analysis providing most relevant measurements, power, Modulation, Spectrum, and CDP in many different application, BER, BLER,

DBLER measurements and Update requirements for hardware and software installation . For GSM(GPRS), the CMU

200 offers functionalities for Signaling and non-signaling measurements , channel coder support, reduced signaling mode for research and development, fast mobile production and application testing therefore it offers the following advantages for RX/TX measurements:

– It Provides all RX/TX measurements necessary for GPRS

– It Allows GPRS RX/TX testing in reduced signaling mode

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For Power vs Slot:

– It Provides Multislot Power measurements

– It allows power measurements for all 8 slots at the same time

For GPRS attach/detach:

– It Provides all attach and detach signaling functionality

– It allows GPRS attach and detach mobile functionality to test GPRS capabilities [20].

Hence, we made a choice of CMU 200 for the GSM as aggressor and WCDMA as aggressor scenario measurements.

4. Agilent 8960 wireless Communication Test Set:

Agilent 8960 wireless Communication Test Set is a Cellular mobile station (handset) manufacturing test set. It can resolve phone design problems earlier and test beyond typical network conditions with simultaneous Tx/Rx at the highest data rates. Agilent 8960 can perform real world stress test to functionally verify SMS, MMS, data throughput, video, inter-RAT hand- overs, and other services in the presence of realistic network impairments. It has the capability to ensure high-quality introductions of new phones and mobile devices testing with the fastest, most complete, and stable

3GPP-compliant TS 34.121-1 TX/Rx measurements in an integrated UMTS/HSPA manufacturing test solution. For these reason we have selected this equipment to simulate

WCDMA base station for the WCDMA as victim measurement scenario.

5. WCDMA module (Housed on cradle):

We mounted the MBM module F5521gw on cradle to simulate a real life scenario case where it’s embedded in the laptop. The Mobile Broadband Module is an embedded PCI

Express Full-Mini Card, which enables end users to have mobile access to the internet or corporate network with flexibility and high speed, including Śalways onlineŠ capability. It supports data services HSPA Evolution (F5521gw), HSPA,

UMTS, EDGE, GPRS, and SMS. Selected modules also have

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Measurement Requirement 45 a GPS receiver, which can be used by positioning applications. The Ericsson Mobile Broadband Module is a solution designed as an add-in option for various host devices such as notebooks, netbooks, tablets etc [21].

6. Couplers and Splitters:

Nadar and Merrimac couplers, combiners and splitters were used in the coexistence measurement setup. combiners and splitters were used to appropriately channel the signal in the desired direction as indicated in the hardware setup while the couplers were used to create proper isolation between nodes within the coexistence network.

7. Network Analyzer:

We used the Network analyzer to calibrate the equipments used in the setup. All devices ranging from cables to attenuators, couplers, splitters, were calibrated to validate the accuracy of the measurement. Details of this are documented in the appendix.

8. Variable Attenuators:

69dB, 60dB, 30dB and 10dB Nadar and Broadwave variable attenuators were used to depict a varying distance of the

Wi-Fi receiver from its access point and its distance from the WCDMA base station to WCDMA UE as well as to create proper isolation between . Each level of attenuation corresponds to particular distance in this regard.

9. Spectrum Analyzer:

A spectrum analyzer is used analyze the spectra characteristic of a signal. We used the spectrum analyzer to confirm that the WLAN, GSM and WCDMA signals being generated corresponds to the theoretical characteristics.

10. Momentum Nanometer:

This is a tool used to obtain the right momentum when connecting devices in the lab. We used this to ensure all cables were properly connected without any leakages.

11. Cables and Connectors:

Cables and connectors were used to establish end to end connection between the devices.

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Measurement Requirement

12. iperf Test tool:

Iperf is a commonly used network testing tool that can create

TCP and UDP data streams and measure the throughput on a network. Iperf is a modern tool for network performance measurement written in C++.

Iperf allows the user to set various parameters that can be used for testing a network, or alternately for optimizing or tuning a network. Iperf has a client and server functionality, and can measure the throughput between the two ends, either unidirectonally or bi-directionally. It is open source software and runs on various platforms including Linux, Unix and Windows. It is supported by the National Laboratory for Applied Network Research. When used in UDP mode,

Iperf allows the user to specify the datagram size and provides results for the datagram throughput and the packet loss.While in TCP mode,Iperf measures the throughput of the payload.

Typical Iperf output contains a timestamped report of the amount of data transferred and the throughput measured.

Iperf is significant as it is a cross-platform tool that can be run over any network and output standardized performance measurements. Thus it can be used for comparison of wired and wireless networking equipment and technologies in an unbiased way. Since it is also open source, the measurement methodology can be scrutinized by the user as well.

There are two versions of Iperf being maintained, Iperf 2.x

and Iperf3. This qualities motivated our decision on using iperf as the test tool for the coexistence measurement. In this measure Iperf3 was used [22].

13. Operating system: ubuntu Linux:

14. UDP (User Datagram Protocol):

User Datagram protocol UDP provides a connectionless packet service that offers unreliable ’best effort’ delivery. This is means that the arrival of packest is not guaranteed, nor is the correct sequencing of delivered packets.

It is use for

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Measurement Requirement 47 applications that do not require an acknowledgment of the receipt of data. Several Internet applications use UDP for transmission, for example audio or video broadcasting uses

UDP so also does the Simple Network Management Protocol

(SNMP), the Routing Information Protocol (RIP) and the

Dynamic Host Configuration Protocol (DHCP).

UDP provides a mechanism that application programs use to send data to other application programs.

Since TCP does not report loss to the user, UDP tests is helpful to see packet loss along a path. We are also able to read the jitter and the transfered packets on iperf for UDP traffic.

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4.4.1

Possible risk associated with measurement

We foresee the following measurement risk which are possible source of errors that we have controllably minimized in our effort to ensure measurement accuracy during the measurement in the lab.

– Risk of leakage from the nodes. We mitigated this risk by having the right momentum on all the connection.

– Risk of isolation problems between connecting ports was mitigated by using the right couplers, splitters and combiners.

– Risk of inaccurate evaluation losses in cables and connectors. This we mitigated by calibrating all devices used in the setup.

– Risk of other laboratory equipment interference: the possibility of other interferers within the test environment and the air interface. Therefore we mitigated this risk by eliminating the air interface communication through the use of coaxial cables. We also confirmed from the network analyzer that there were no interference at the frequencies we were operating at.

– We evaluated link budget analysis for each of the scenarios to determine the level of interference power that will possibly impact on the aggressed system and we analyzed the points at which degradation is expected comparing it with the theoretical expectation to ensure measurement were being done in the right direction.

Figure 4.2 is a diagramatic description of the point at which degradation of the victim is speculated i.e., the region outside its stabilty and it is at this point that the interferer is introduced to aggress the network of the victim.

4.4.2

Link Budget Analysis

A link budget is the accounting of all of the gains and losses from the transmitter, through the medium (free space, cable, waveg-

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Measurement Requirement 49

Throughput

Point where degradation sets in

C/N

Figure 4.2: Process of identifying where degradation starts and interferer is being introduced uide, fiber, etc.) to the receiver in a telecommunication system.

It accounts for the attenuation of the transmitted signal due to propagation, as well as the antenna gains, feedline and miscellaneous losses. Randomly varying channel gains such as fading are taken into account by adding some margin depending on the anticipated severity of its effects. The amount of margin required can be reduced by the use of mitigating techniques such as antenna diversity or frequency hopping.

A simple link budget equation looks like this:

Received Power (dBm) = Transmitted Power (dBm) +

Gains (dB) - Losses (dB).

Figure: 4.3 represents the link budget analysis used within this thesis.

Within this thesis, we have analyzed our link budget as follows:

I = Aggressor Transmit power + Cable and Connector Losses + attenuation.

C = desired signal strength.

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Measurement Requirement

TX power, e.g 14 dBm

Degradation due to Interference

Required C with interference

C/I

Required C without interference

Receiver noise floor = N

C/N

Interference = I

Noise Figure (NF)

Thermal Noise Floor

Figure 4.3: Link Budget for Coexistence of WLAN and WWAN

C/I = C-I.

What we have basically did within this measurement is to vary

C/I, this results in an increase or reduction in the degradation region which is the green region.

An increase in C/I depicts a bad quality of signal likewise a decrease in C/I depicts a good quality of signal. We refer to C/I as our SNR because the firmware of the equipment used did not give us access to change fix the data rate and modulation of the modules used. Therefore, C and I were taken for both WLAN,

GSM and WCDMA at the antenna as described in the schematic diagram in Figure 4.4 below.

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Measurement Requirement 51

Figure 4.4: Diagrammatic representation to show point at which C and I were taken

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Chapter

5

Measurement Set-Up

5.1

Setup and characterization

5.1.1

WWAN/WLAN

In this use-case WWAN and WLAN operates simultaneously with maintained sensitivity performance for respective receiver.

There are two different sub use-cases to be investigated:

– The network router use-case which is defined by simultaneous operation of WWAN and WLAN. WWAN will be used as access to Internet through a network operator while WLAN will be used to share internet access to different devices locally. In this case the network router is a notebook equipped with a WWAN module or a network router equipped with

WWAN module.In this case the WLAN device will operate as an access-point. The foreseen problem is that the WWAN and WLAN are disturbing each other with throughput decrease as result.

– In the handover use-case the host can choose appropriate access technology determined by locally available network capacity. The handover use case is that a WLAN and WWAN capable device changes seamless from a WWAN to a WLAN cell during a session. In this case the WLAN device must be configured as an ad-hoc or infrastructure device. The fore-

53

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Measurement Set-Up seen problem is that the device will not be able to detect the other cell due to de-sensing of the receiver.

Based on this we came up with the following scenarios:

– WLAN -> WCDMA, WLAN as Interferer

– GSM -> WLAN, GSM as Interferer

– WCDMA -> WLAN, WCDMA as Interferer

Hence there is a need to review the necessary parameters of each of the systems. The table below is the WLAN link parameter settings for the measurement analysis and –Intel Ultimate WLAN

Link 5300 [8] used for the WLAN network setup.

System Channel Mode Modulation Tx Power

WLAN Module 2.412GHz

Ad hoc OFDM/CCK 14dBm

Table 5.1: WLAN Parameter Settings

WLAN

802.11b

802.11g (with 11b)

802.11g (11g-only)

802.11a

Channel Modulation Max.UDP rate

3 CCK 7.1Mbps

3

3

19

OFDM/CCK

OFDM/CCK

OFDM

19.5Mbps

30.5Mbps

30.5Mbps

Table 5.2: Maximum attainable application-level throughput [8].

Type Freq(MHz) Tx.Power

802.11g

2412 14-16dBm

Modulation

OFDM/CCK

Max.UDP rate

21.9Mbps

Table 5.3: Maximum practical application-level throughput

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Measurement Set-Up 55

Figure 5.2 shows the block diagram for the coexistence measurement setup and it consists of a WLAN transmitter side and a receiver side, both set up in Ad-Hoc modes and at channel 1

(2.412GHz) as well as a WCDMA or GSM base station simulator connected to the Ericsson MBM F5521gw module. The WLAN link is aggressed/interfered by WCDMA or GSM link and vice versa. The transmitter and the receiver of the WLAN system,

WCDMA/GSM base station and user equipment (UE) were connected through coaxial cables. In other words, all devices and equipments used have been connected through coaxial cables, therefore the setup depicts an end to end cable connection and all cables, attenuators and connectors were calibrated on the network analyzer before commencement of measurement to capture their losses. Attenuators were used to simulate the space propagation through distance.

The WLAN equipment run on Linux operating system and they were both connected in Ad-hoc modes.

Figure 5.1: WCDMA FDD BAND I Settings

Table 5.2 shows configuration of the WLAN module while Figure 5.1 is the characteristics settings of the WCDMA. Introducing the WCDMA signal at the uplink (1920-1980)MHz into the WLAN receiver path-link which will work as an interferer will represent

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Measurement Set-Up

Figure 5.2: Measurement setup collocation coexistence that will help in the analysis of the coexisting WWAN with WLAN in same device.

Though our consideration is at the physical layer i.e layer 1 of the OSI (open system interconnect) model, however we have used iperf performance test tool evaluative capability at the application layer to measure the throughput, jitter, transfered and packet loss relative to the activities and effect of the physical layer. Iperf tool is installed on the machines that established the WLAN link system, one as a client which acts as transmitter and the other as server which act as a receiver. With iperf running on these systems we are able to measure the throughput, bit error rate as well as percentage packet loss of the data transmitted over the link, using the figure below as a guide to the setup; block

B (WLAN-Tx) is the transmitter running the client version of iperf tools while block C (WLAN-Rx) is the receiver running the

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Measurement Set-Up 57 server version of the iperf tools. The CMU 200 was employed as the WCDMA and GSM base station simulator which propagates

WCDMA signal towards the mobile broad band module (MBM) the user equipment.

The MBM supports higher data throughput on the WCDMA,HSPA and LTE networks.

In Figure 5.2, the (A-D link)represents the downlink of the WCDMA which is the WCDMA base station (CMU 200) transmitting towards the user equipment(MBM F5521gw) that resides on the cradle while the link (D-A) which is the user equipment (UE) transmitting to the base station, is the uplink, however this uplink is coupled with link (D-C) which is the interferer to the victim, the WLAN link (B-C). In between the link is a step attenuator to vary and regulate the amount of power from the WCDMA uplink which is the interference. This is simulation of the coupling effect between the WLAN antenna and the WCDMA antenna when collocated on a chip/module inserted in a device such as laptops in real network scenarios. It could also be used to evaluate the distance of WCDMA transmitter to the receiver of the WLAN link in other scenarios. Link (B-C) is the WLAN link and on this link we have used: an attenuator, a coupler and coaxial cable with which the distance can be adjusted or varied to evaluate the effect of separation to simulate the transmission across the distance that separates the transmitter from the receiver of the

WLAN system.

System

WCDMA Band I

WCDMA Band I

WCDMA Band V

WCDMA Band V

GSM

GSM

Frequency(MHz) Power

2100 24dBm

800

800

10dBm

25dBm

800

900

1800

10dBm

33dBm

30dBm

Table 5.4: Systems overview

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Measurement Set-Up

Wcdma Uplink Downlink Channels Power

Band I 1922.4MHz

2112.4MHz

9612/10562 24dBm

Band I 1922.4MHz

2112.4MHz

9612/10562 10dBm

Band V 826.4MHz

871.4MHz

4132/4357 25dBm

Band V 826.4MHz

871.4MHz

4132/4357 10dBm

Table 5.5: WCDMA parameters

5.1.2

Aggressor: WWAN Victim: WLAN

In this scenario WCDMA system is the aggressor while the WLAN is the victim. figure 5.3 is the diagrammatic representation of the setup. WLAN transmit and received link as well as the WCDMA base station simulator’s connection to Ericsson MBM F5521gw module embedded on a cradle. WLAN link is interfered by 5MHz spectrum of WCDMA HSPA signal delivered into the WLAN link at the configurations stated in Table 5.4. WCDMA Band I at

2.1GHz and Band V at 800MHz was simulated at different occasion of measurement to depict both the high and low band of the

WCDMA radio environment while the WLAN link radio environment was simulated at Channel 1 (2.4GHz) in the ISM band at different power levels.

Initiating the setting in Table 5.5 for FDD WCDMA Band I,

2.1GHz of the WCDMA FDD (HSUPA/HSDPA) on the CMU

200, enabling the connect UE CS with connect UE PS in the connect Control menu of the CMU 200 to establish signaling and paging mode. Thus, we are able to attach the module to the base station with 5MHz bandwidth WCDMA signal at a transmit power of 24dBm. The same procedure follows when WCDMA is reduced to 10dBm output power.

The generated signal is delivered to the UE (which consist of the

MBM F5521gw module and a test SIM, both housed on a cradle).

The targeted victim in this scenario is the receiving path of the

WLAN link hence, the aggressor which is the uplink of WCDMA

(the link from the MBM module to the CMU 200) is introduced

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Measurement Set-Up 59

Figure 5.3: Setup: WWAN BAND I Aggressor to WLAN.

to the receive path of the WLAN which is already up and running with connections as shown in figure 5.3.

In this setup iperf tool is used to generate, transmit and receive

UDP packets across the WLAN network. With these setup, measurement were taken and recorded to analyze the behavior of

WLAN when aggressed by WCDMA.

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Measurement Set-Up

5.1.3

Aggressor: GSM, Victim: WLAN

Figure 5.4: WWAN GSM as Aggressor to WLAN.

In this scenario GSM acts as the aggressor while WLAN is the victim. The set up and processes in this scenario is similar to the scenario where WCDMA acts as aggressor, but WCDMA parameters has been replaced with GSM simulation parameters. In evaluating coexistence of both WLAN and GSM technologies, we consider GSM 1800MHz and GSM 900MHz operating frequencies in order to analyze the effect of the out of band of

GSM on WLAN. GSM is configured to use 2-uplink channels and

1-Downlink channel with main service running GSM+GPRS and packet data service selection. Figure 5.5 is a screen shot of the

CMU settings that was used to simulate GSM radio environment in the setup and measurement and Figure 5.4 is the detailed setup

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Measurement Set-Up 61 diagram. With the setup running, the performance of WLAN when aggressed by GSM was observed. Measurement were taken and results are analyzed in the form of graphs and tables in chapter 6.

Figure 5.5: GSM Settings Screen shot.

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Measurement Set-Up

5.1.4

Aggressor: WLAN, Victim: WWAN

A

WCDMA SERVER, iperf Client

D

WCDMA CLIENT

STATION, iperf Server

WCTS

Nadar Splitter for diversity

[email protected]

[email protected]

[email protected]

RPM1134039/00750B cable

Path C-2

[email protected]

[email protected]

Narda Splitter

[email protected]

F

2

C

1

WCDMA UE

Tiger Splitter

[email protected]

[email protected]

Path C-1

Turquoise blue long cable

[email protected]

Orange Cable

[email protected]

[email protected]

B

C

WLAN RX, iperf Server

Narda coupler

-0.18dB @2.4GHzMHz

E

Broadway Tech. 0-

30dB attenuator

[email protected]

Narda coupler

[email protected]

[email protected]

SN22580 Navy Blue cable

[email protected]

[email protected]

Nadar step attenuator

Model 745-69dB

[email protected]

Nadar step attenuator

Model 745-60dB -

[email protected]

WLAN TX, iperf Client

Figure 5.6: WLAN interfering WWAN.

This setup depicts the scenario where WLAN acts as aggressor to

WWAN link. This is the reverse direction of the scenario where

WCDMA acts as the aggressor to WLAN. All the connected computers (the MBM client, WCTS window server, WLAN Rx and

Tx computers) in this setup run iperf tool to generate, transmit and receive UDP packets across the network. Figure 5.6 shows the setup which is the reverse form of

Figure 5.5, where the WWAN (WCDMA, GSM, LTE) is the aggressor to WLAN being the victim. The radio frequency path is controlled through the use of coaxial cables,couplers,attenuators as well as splitters. In this figure the Agilent wireless communication test set (WCTS) connected to a windows server with a level of control form the base station simulator for the WWAN

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Measurement Set-Up 63

(WCDMA and GSM in this case). This is to enable us push traffic from the windows server through the WCTS down to the UE

(MBM F5521gw). This forms the link A-F-D. Figure 5.7 shows call setup configuration screen shot for the WCTS equipment.

Figure 5.7: WCTS setup screen

The MBM is connected to a laptop called the MBM client station through the USB COM port,which runs the AT commands that controls the MBM and pull events on the module.

The splitter at F is used as an isolator for A-F-E such that there is no link propagation existing in the direction of A-F-E and vice versa. Link A-F-D is characterized with WCDMA BAND I or V or GSM 1800MHz or 900MHz with WCTS being the Transmitter

(iperf client) and MBM (iperf server) receiver respectively. The link propagation at A-F-D which is the downlink of the WWAN is the receiver path of the link propagation for the WWAN system and as such the point of interest for the coexistence study when

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Measurement Set-Up the WLAN is the aggressor during collocation.

Figure 5.6 shows the two laptops at point B (the WLAN Tx) and point C (the WLAN Rx) respectively. The link propagation at

B-E-C is maintained as the WLAN stable link with the WLAN module Tx power at 14dBm, channel 1 with data rate of 21.3Mbps

(64QAM). Iperf UDP script runs on the two laptops are running delivering UDP packets across the network with appropriate data rate measurement. The coupler used at point E is to ensure that there is proper RF isolation between the uplink traffic of the MBM

(mobile broadband module) at point D and the WLAN Rx path.

It is used to direct the WLAN Tx power into the Rx/Downlink path of the WWAN link.

After the setup and calibration of link A-F-D, we also calibrated and brought up link B-E-C with variable attenuators on the link

B-E to be able to introduce interference power at different levels.

These attenuators depicts the antenna coupling as well as attenuation due to distance between the access point and the WLAN module on the laptop. The interfering system (WLAN) hits the

Rx path of the WWAN through the splitter at F.

Iperf UDP packet data transmission is set up between WCTS iperf-client (running on WCDMA server) and MBM iperf-server

(running on MBM client) and also between the WLAN Tx and

WLAN Rx. Figure 5.8 is a screen shot of the iperf results on the

MBM client screen

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Measurement Set-Up 65

Figure 5.8: Typical iperf MBM Client Screen

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Measurement Set-Up

Figure 5.9 is a sample of the typical measurement screen for

WCTS which shows the throughput,cell power and other settings.

During the measurement, we varied the cell power at the WCTS base station simulator as well to achieve different sensitivity of the downlink path to the MBM module. This emulates radio propagation between the base station and the UE and the various data rate at different sensitivity were recorded. Results are presented

Figure 5.9: Typical Measurement Screen with cell power of -60 in the form of graphs to show the relation between C/I (the signal strength C measured at D and the interference power I measured at D) and those recorded data rates. The signal strength C is the cell power from the WCTS towards the MBM which is the

WWAN downlink and this is measured at the MBM i.e the power that hits the receiver after the losses on the RF link A-F-D has been deducted.

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Measurement Set-Up

Below are some of the real lab pictures.

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Figure 5.10: Lab Pictures

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Measurement Set-Up

Figure 5.11: Lab Pictures

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Chapter

6

Results Presentation and Analysis

6.1

Coexistence Measurement Results

This chapter presents results as described in chapter 5. The raw data of all measurement done within this thesis research are documented in appendix 1 of this report. However the processed data which forms the results is presented in this chapter in form of tables and graphs to create a clearer understanding of the effects of all the different scenarios.

From coexistence point of view, considering the interferer input power (I), Victim’s signal strength (C) and antenna coupling effect as parameters for analyses,the interferer/aggressor Tx power distributions are computed and resulting values presented in the form of tables and graphs.

6.1.1

Antenna Coupling Measurement Results

The principal function of an antenna is to convert an electromagnetic field into an induced voltage and vece versa. It is the point of contact to and from a device. In coexistence, the effect of the different antennae oer each other is of higher importance. Mutual coupling is well known in the antenna community,since coupling between antenna elements is one of the most important properties to consider in antenna design [35]. Within this Master’s thesis we

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Results Presentation and Analysis have carried out a practical measurement on antenna coupling effect between the several Tx/Rx ports on the laptop devices and documented our results. The results shows the isolation between the ports that are relevant to the coexistence analysis within the measurement scope of this thesis and this is a major factor in analyzing the effects of an aggressor power distribution over the victim in all the considered scenarios. Figure 6.1 shows is a picture of the antenna coupling measurement made in the laboratory with a network analyzer.

Figure 6.1: Antenna Characterization Results

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Results Presentation and Analysis 71

6.1.2

Aggressor: WCDMA and Victim: WLAN

Sequel to the setup and characterization done in Chapter 5, we have documented in an excel sheet the attenuation settings for both WLAN and WCDMA systems as well as losses in the cables,connectors etc. As explained in Chapter 5, the columns in the table depict the parameters with their units as used within the coexistence measurements: Attenuation measured in dB,power measured in dBm,jitter measured in ms and packet loss in percentage. Typically a WLAN link operating at 64QAM modulation scheme and using OFDM is at 54Mbps throughput with a transmit power of +14.5dBm and a receiver sensitivity of -76dBm

[34]. The resulting graph in figure 6.2 is the grahical representation of the result of measurement taken at two transmit power levels: 24dBm and 10dBm for WCDMA BAND I and 24dBm for

WCDMA Band V on the same graph. The Y-axis represents the

Figure 6.2: WWAN Aggressed WLAN

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Results Presentation and Analysis throughput of WLAN network/link operating with signal strength

C as a result of varying interference/input power I (with careful consideration of the attenuation, losses in cables and connectors) of WCDMA system when both are operated simultaneously, while the X-axis represents the relationship C/I which is the ratio of the desired signal strength to the interference caused by the unwanted signal both measured at the receiver of the desired system (in this case the WLAN). This can also be referred to as the SINR. The graph shows that a decrease in C/I results in a decrease in WLAN throughput. This is due to the following reason:

• A decrease or increase in the fraction C/I will be as a result of change in C or I. In this case the parameter that changes is the

Interferer (WCDMA) input power, while WLAN operating conditions remained the same.

• Decrease in SNR causes a decrease in WLAN throughput. This confirms the theoretical analysis on the impact of throughput on

C/I. This is the effect of interference caused by the WCDMA

BAND I spurious emission. On the contrary, while Band I interference on WLAN is obvious, there is no effect of Band V on the

WLAN system as the band is far away in frequency to the ISM band.

In Figure 6.3 we have computed an interferer budget link with parameters such as; WCDMA Tx power, WLAN signal strength, antenna coupling Type1/Type2, Interference power, and SINR

(Signal to Interference Noise Ratio). For antenna coupling 1 of

-32.7dB the green and grey colored region ranging from 16dBm to 0dBm of WCDMA transmit power and the corresponding C/I

(SINR) in the green region ranging from -44.45dBm to -28.45dBm

and the ash color region of 6dBm to 0dBm transmit power corresponding to the ash color region of -44.45dB to -28.45dB C/I for antenna coupling 2 are transmit power and C/I (SINR)values that will enhance successful coexistence without degradation effect on

WLAN when it is being interfered/coexisted with WCDMA .

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Results Presentation and Analysis 73

Interference power in the table is derived thus; I(dBm) is

I = T xP ower − AntennaCoupling

= T x(dBm) − AntC(dB) while signal to interference ration SINR is;

(6.1)

(6.2)

SIN R = Signalstrength − Interf erence

= C(dBm) − I(dBm)

(6.3)

(6.4)

We then relate the SINR to the C/I in figure 6.2 in order to arrive at the corresponding throughput for different transmit power.

Figure 6.3: WCDMA Interferer Budget Link

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Results Presentation and Analysis

Figure 6.4: WCDMA Tx Power and WLAN Throughput

Hence, Figure 6.8 shows the the expected throughput of WLAN at various transmit power of WCDMA relative to the desired signal strength. With a fixed WLAN signal strength, increase or decrease in WCDMA transmit power will result decrease or increase of WLAN throughput respectively.

Therefore, power control capability of WCDMA can be used in appropriating transmit power for effective coexistence with respect to the sensitivity of the WLAN.

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Results Presentation and Analysis

6.1.3

Aggressor:GSM 1800MHz/900MHz, Victim:WLAN

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Figure 6.5: GSM Aggressed WLAN.

Figure 6.5 is the graphical result from the GSM 900MHz and

1800MHz scenario where GSM acts as aggressor to WLAN. For

GSM at 900MHz frequency, there is no significant effect on WLAN.

This is as anticipated because GSM 900MHz is far away in frequency to WLAN in the ISM Band. For the GSM 1800MHz as aggressor scenario, degradation effect is observed on WLAN system/link performance. From Figure 6.5,using two time slot in the uplink and one time slot in the downlink for the GSM system, we observe that a decrease in C/I from -65dB to -79dB does not cause any degradation in WLAN performance as a steady throughput is observed in this region. Therefore, It is a good region to explore for optimal coexistence gain. However, as C/I further decreases

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Results Presentation and Analysis

Figure 6.6: Antenna Coupling Type1 and Type2 at 2.4GHz

below -80dB (i.e C/I < -80dB) as a result of interference from

GSM 1800MHz, WLAN performance is impacted resulting in a gradual degradation effect due to the interference created by the high band (1800MHz) of the GSM signal. However, the graph shows that GSM could not totally degrade WLAN performance as further increase in C/I resulted in a average throughput of

11Mbps between -84dB and -95dB. slot in the downlink for the

GSM system. This characterization is a valid input to the power distribution of the aggressor which is an indication of the degree or extent to which WLAN and GSM can successfully coexist without significant impact on the performance of WLAN. The two figures in 6.6 shows the antenna characteristics measurement done at GSM frequencies using two separate real life notebooks of type1 and type2. We have chosen antenna coupling within the

2.4GHz range for the GSM being the aggressor because it is the out of band of GSM that hits the WLAN.

Figure 6.7 is the tabulated interferer budget link developed with parameters such as; GSM Tx power, WLAN signal strength, antenna coupling Type12, Interference power, and SINR (signal to noise ratio). For antenna coupling 1 of -33.3dB the green colored region ranging from 30dBm to 0dBm GSM transmit power and the corresponding C/I (SNR) in the green region ranging from

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Results Presentation and Analysis 77

Figure 6.7: GSM1800MHz link budget

-67.85dBm to -37.85dBm and the green color region of 30dBm to 0dBm transmit power corresponding to the green color region of -62.05dB to -32.05dB C/I for antenna coupling 2 are transmit power and C/I (SNR) values that will enhance successful coexistence without degradation effect on WLAN when GSM is interfering/coexisting at 1800MHz frequency. Interference power is derived as in 6.2 as well as SINR 6.4 Transmit power distribution of the aggressor i.e GSM 1800MHz can then form a basis for the choice of power as well as the received signal strength of the

WLAN for a considerable throughput in coexistence scenario.

The graph in figure 6.8 shows the relation between the throughput of the WLAN and the transmit power of the aggressor (GSM in this case) at different points of the coexistence measurement with

WLAN sensitivity at -71.15dBm. This relation can be used to

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Results Presentation and Analysis

Figure 6.8: WLAN Throughput and GSM1800MHz Power find the distribution of the interferer transmit power (GSM) as well as the corresponding expected throughput of WLAN as it relates to coexistence.

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Results Presentation and Analysis

6.1.4

Aggressor:WLAN, Victim: WCDMA

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Figure 6.9: WLAN Interferes WCDMA

Figure 6.9 is the graphical representation of the result for this scenario.This result show that when WLAN in the 2.4GHz ISM

BAND acts as aggressor to WCDMA Band V, there is no significant degradable effect or impact. This is as expected because the difference in operating frequency of WLAN at 2.4GHz and

WCDMA BAnd V at 900MHz is quite large. However, WCDMA

Band I is heavily degraded by WLAN 2.4GHz (channel 1) as the result shows in figure 6.9 due to the fact that the operating frequencies of WLAN and WCDMA is close in this scenario as is the case with BAND V. The effect seen here is that of spurious emission from the WLAN on the WCDMA frequency. In order to keep the WLAN link well balanced at the a considerable peak rate of

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Results Presentation and Analysis

Figure 6.10: WLAN Tx Power Distribution.

21.3Mbps and provide maximum output set Tx power in the test environment, we attenuate the WLAN link by 20dB. The curve shows the characteristics of the WCDMA link to it’s throughput when aggressed by WLAN. For values of C/I less than or equal to

-42dBm, while values of C/I less than -42dBm, the resulting curve shows that there is no degradation in throughput for WCDMA band I. Coexistence success in this region is high. Further decrease in C/I, with C/I less than or equal to -42dBm,results in further degradation in throughput. This is an indication that a careful selection of the WLAN Tx power as well as exploration of the power control capability in WCDMA to appropriate the desired signal sensitivity will maximize coexistence success probabilty between WLAN and WCDMA system.

Therefore, characterizing the power distribution as well as the sensitivity levels in both the aggressor (WLAN) and the interfered

(WCDMA) respectively in figure

Figure 6.10 shows the table of WLAN Tx Power distribution,the desired signal strength (C), the antenna coupling types,interference power, as well as the calculated C/I. Figure 6.11 shows the relation between the Tx power of the aggressor to the expected throughput

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Results Presentation and Analysis 81

Figure 6.11: WCDMA Coexistence Throughput when both systems WLAN and WCDMA coexist. There are two curves on this graph, each for the two different antennas coupling measured for different notebooks. The curves shows the points reflecting the measurements we have carried out and one can could extended further, the distribution of the interfere transmit power relative to the victim throughput.It can be done through a suitable link budget calculations, antenna coupling and Tx power of the interferer.

With desired signal sensitivity C (dBm) where the system downlink signal is stable and of best throughput i.e the WCDMA throughput on the MBM F5521gw is 21Mbps with 64QAM modulation scheme. From the above we then calculated C/I for the desired WCDMA signal.

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Chapter

7

Conclusion and Future research

Within the coexistence measurement,various scenarios have been considered in analyzing coexistence of WLAN, WWAN with results.

WWAN as aggressor to WLAN scenarios’ results shows that the

WLAN will favourably coexist with WWAN-WCDMA band V without degradable impact while band I will impact WLAN. The impact of band I will not degrade WLAN when the C/I is greater than -45dB but WLAN will degrade otherwise.

GSM as aggressor to WLAN scenarios’ results show that the

WLAN will at all levels of GSM power distribution favourably coexist with WWAN-GSM as shown in Figure 6.8.

When WLAN aggresses WCDMA, this scenarios’ shows that there is degradable effect on WCDMA but the coexistence is favourable

(i.e., without degradation) at C/I greater than -42dB without degradation. Comparing the WWAN and WLAN results, it is observed that WWAN degrades WLAN more than WLAN degrades WWAN.

Looking through the concept of coupling effect earlier discussed and analyzed, we can conclude that as long as there is enough isolation between these access technolgies as they collocate, their coexistence will be favourable in close proximity which gives rise to their independent operation.

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Conclusion and Future research

While there is a need for a control system during collocation to enhance the system performance more than what is realizable with minimum isolation. Thus creating a more collaborative coexistence.

Expected future work will be to develop a scheduling algorithm that enhances the coexistence of GSM-WLAN, WCDMA-WLAN, the said algorithm could be of packet structure, power control exploring the different power levels etc. It will be good also to have these performance done for different modulation scheme on the WLAN

We recommend an adaptive power control mechanism for both

WCDMA and WLAN.

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