WiMAX: The Innovative Broadband Wireless Access

WiMAX: The Innovative Broadband Wireless Access
JOURNAL OF COMMUNICATIONS, VOL. 3, NO. 2, APRIL 2008
53
WiMAX: The Innovative Broadband Wireless
Access Technology
Abdulrahman Yarali
Industrial and Engineering Technology, Murray State University, Murray, USA
Email: abdul.yarali@murraystate.edu
Saifur Rahman and Bwanga Mbula
Virginia Polytechnic and State University, Murray State University, Murray, USA
Email: Srahman@vt.edu , bwanga.mbula@murraystate.edu
Abstract—The telecommunication industry has been
through disruptive times, but data networking service
revenue has continued to rise. The telecom industry is
expected to continue to grow as demand increases for cable
and high-speed Internet in previously unserviced locations
and as local telephone companies upgrade their lines in
response to increasing competition. This paper presents an
extended overview of the Worldwide Interoperability for
Microwave Access (WiMAX) and its applications in higher
generation wireless networks as a cost effective solution to
answering the challenges posed by the digital divide. It
looks at the technology behind WiMAX and networks
design and deployment factors that impact WiMAX
coverage. A cell site coverage simulation at different
frequency bands using Wireless simulation tool is presented.
Also the paper makes a comparison of WiMAX with two
enhanced third generation (3G) technologies that are
potential competitors to WiMAX. It then goes on describe
the business models in WiMAX and states some of the
benefits and drawbacks of a mobile WiMAX network.
access to Information and Communication Technologies
(ICTs), where the least developed countries are separated
from the developed countries because of a lack of
technology particularly information and communication
technology [2].
The digital divide has persisted due to the relatively
high cost of putting up modern telecommunications
infrastructure. This is compounded by the fact that there
are a number of different services available and each
service requires its own technology and network [3].
Therefore existing technologies such as Wireless Fidelity
(WiFi), Digital Subscriber Line (DSL), Global System
for Mobile communications (GSM), Integrated Services
Digital Network (ISDN), and the relatively new 3G
technologies have not been able to provide a total
solution to closing the digital divide. Fig. 1 illustrates the
main network types and the prevalent technologies
associated with each, mapped against usage models and
access modes.
Index Terms — Broadband Access, Digital Divide,
WiMAX, , OFDM, MIMO, Cell Coverage, 3G and 4G.
I. INTRODUCTION
Telecommunications has grown at a tremendous rate in
the last ten to twenty years. Improved semiconductor and
electronics manufacturing technology, and the growth of
the internet and mobile telecommunications have been
some of the factors which have fueled this growth in
telecommunications. The deployment of state of the art
telecommunications infrastructure and services has
however been restricted to the developed world. The least
developed countries have been left in the technological
dark ages with few or none of the next generation
networks installed. Developed countries now boast high
speed connections with a large percentage of homes
having access to the internet and broadband services at an
affordable fee. The underdeveloped countries are yet to
enjoy such facilities. This is referred to as the digital
divide [1]. During the first World Summit on the
Information Society (WSIS) held in Geneva in December
2003, the Digital Divide was defined as the unequal
© 2008 ACADEMY PUBLISHER
Figure 1. Wireless network type and range.
MAN - Metropolitan Area Network (Citywide, Rural Area) LAN Local Area Network (Office, Home, Campus) WAN- Wide Area
Network (countrywide, International)
WiMax earned an important seal of approval recently
when the Radio communication sector of the
54
JOURNAL OF COMMUNICATIONS, VOL. 3, NO. 2, APRIL 2008
International Telecommunication Union (ITU-R)
certified it as a 3G (third-generation) mobile data
technology.
Fig. 2 shows the standard history for
802.16.
mostly the changes will be in components and
software.
x Readiness of the current wireless fixed and mobile
market and waiting on new technology.
x As carriers built out wireless networks, most of the
questions in this field have been answered and can
now be applied to the development of a mirror
network that provides WiMAX access.
802.16
(Dec 2001)
802.16c
(2004)
802.16
Amendment
WiMAX System
Profiles
10 - 66 GHz
802.16a
(Jan. 2003)
Original fixed wireless broadband
air Interface for 10 – 66 GHz:
Line-of- sight only, Point-to
-Multi-Point applications
Extension for 2-11 GHz:
Targeted
for non-line-ofsight, Point-to-Multi-Point
applications like “last mile”
broadband access
802.16d
(Oct. 2004)
Adds WiMAX System
Profiles
802.16e
(Dec.2005)
MAC/PHY Enhancements to
support subscribers moving a
vehicular speeds
Figure 2. 802.16 Standard Evolution
WiMAX will have a larger impact long term than we
have seen from cellular phones in the past two decades.
Initial rollouts of WiMAX will begin mostly by
competitive local phone service carriers and rural Internet
service providers. Larger carriers will utilize fixed
WiMAX to deliver services to residential customers
many of whom are in underserved markets. WiMAX
adoption in these underserved markets will be high due to
lack of availability of high-speed data access. These
deployments will generate capital to be reinvested for
future deployments. Larger customer base will begin
driving both the cost of carrier and customer equipment
down. As the economy of scale makes deployment less
expensive mobile platforms will begin to appear. This
development will be spread between high population
centers and the rural markets that already have fixed
platforms deployed. Fixed platform will act as a
springboard for mobile deployment.
Then
interconnections will begin to form between rural
markets and metropolitan markets as carriers form
cooperative agreements to share network resources. The
economy of scale will increase exponentially at this point
and we will notice a negative impact on traditional
cellular, Internet and voice services.
Once the
implementation of initial hot underserved rural markets
and high-density metro areas are completed, springboard
deployments will quickly take WiMAX coverage to the
level of coverage offered by traditional wireless today.
This process will move much faster than the
deployment of cellular networks and devices for the
following key reasons:
x The manufacturing process for WiMAX devices
will be quite similar to that of wireless devices and
© 2008 ACADEMY PUBLISHER
II. NETWORK ARCHITECTURE
WiMAX has a flexible architecture. The Mobile
WiMAX End-to-End network architecture is based on an
All-IP platform, all packet technology and no circuit
switch telephony.
The open IP architecture gives network operators great
flexibility when selecting solutions that work with legacy
networks or that use the most advanced technologies, and
in determining what functionality they want their network
to support. They can choose from a vertically integrated
vendor that provides a turnkey solution or they can pick
and choose from a dense ecosystem of best-of-breed
players with a more narrow focus. The architecture
allows modularity and flexibility to accommodate a broad
range of deployment options such as small scale to large
scale, urban, suburban and rural coverage, mesh
topologies , flat , hierarchical and their variant, and
finally, co-existance of fixed , nomadic portable and
mobile usage models [4].
Mobile WiMAX adds both the mobility and Multiple
Input Multiple Output (MIMO) functionalities to the
IEEE 802.16- 2004 standard. It is one of two standards
adopted by the WiMAX forum with the other one being
the IEEE 802.16 – 2004. Mobile WiMAX network
architecture mainly has three components. These include
the Access Services Network (ASN), the Core Services
Network (CSN) and the Application Services Network
(AS). Fig. 3 illustrates the interconnection of these
networks. The WiMAX network supports the following
key functions:
x All IP Access and core service networks
x Support for fixed, nomadic and mobile access
x Interoperability with existing networks via
internetworking functions
x Open interfaces between ASN’s and between the
ASN and the CSN
x Support for differential quality of service
depending on the application
x Unbundling of the Access, core and application
service networks
A. ASN
The ASN is the access network of WiMAX and it
provides the interface between the user and the core
service network. Mandatory functions as defined by the
WiMAX forum include the following:
JOURNAL OF COMMUNICATIONS, VOL. 3, NO. 2, APRIL 2008
Figure 3. WiMAX Network Architecture [5].
x
x
x
x
x
Handover
Authentication through the proxy authentication,
authorization and accounting (AAA) server
Radio resource management
Interoperability with other ASN’s
Relay of functionality between CSN and MS,
e.g. IP address allocation
55
AAA system and also contains the IP servers, gateways
to other networks i.e. Public Switched Telephone
Network (PSTN), and 3G.
WiMAX has five main open interfaces which include;
reference points R1, R2, R3, R4 and R5 interface [7]. The
R1 interface interconnects the subscriber to the base
station in the ASN and is the air interface defined on the
physical layer and Medium Access Control (MAC) sub
layer. The R2 is the logical interface between the mobile
subscriber and the CSN. It is associated with
authorization, IP host configuration management,
services management, and mobility management. The R3
is the interface between the ASN and CSN and supports
AAA, policy enforcement and mobility management
capabilities. The R4 is an interface between two ASN’s.
It is mainly concerned with coordinating mobility of
Mobile Stations (MS’s) between different ASN’s. The R5
is an interface between two CSN’s and is concerned with
internetworking between two CSN’s. It is through this
interface that activities such as roaming are carried out.
The unbundling of WiMAX divides the network based
on functionality. The ASN falls under the Network
Access Provider (NAP). The NAP is a business entity
that provides WiMAX network access to a Network
Service Provider (NSP). The NSP is a business entity that
provides core network services to the WiMAX network
and consists of the CSN. The Applications services fall
under the Applications Services Provider (ASP).
III. TECHNOLOGIES EMPLOYED BY WIMAX
Base Station (BS). The cell equipment comprises the
basic base station equipment, radio equipment and a base
station link to the backbone network. The base station is
what actually provides the interface between the mobile
user and the WiMAX network. The coverage radius of a
typical base station in urban areas is around 500 to 900
meters [6]. In rural areas the operators are planning cells
with a radius of 4 kilometer (Km). This is quite a realistic
number now and quite similar to the coverage areas of
GSM and UMTS/HSDPA base stations today.
Deployment is driven either by the bandwidth required
to meet demand, or by the geographic coverage required
to cover the area. Based on the cell planning of other
previous technologies, urban and suburban segments cell
deployment will likely be driven by capacity. Rural
segment deployment will likely be driven by the cell
radius.
ASN Gateway. The ASN Gateway performs
functions of connection and mobility management and
inter-service provider network boundaries through
processing of subscriber control and bearer data traffic. It
also serves as an Extensible Authentication Protocol
(EAP) authenticator for subscriber identity and acts as a
Remote Authentication Dial in User Service (RADIUS)
client to the operator’s AAA servers.
B. Core Services Network
The CSN is the transport, authentication and switching
part of the network. It represents the core network in
WiMAX. It consists of the home agent (HA) and the
© 2008 ACADEMY PUBLISHER
Mobile WiMAX operates in licensed frequency bands
in the range of 2 to 6 MHz. The technologies employed
by mobile WiMAX include the following:
x Scalable Orthogonal Frequency Division
Multiple Access (SOFDMA) on the physical
layer
x MIMO
x IP (Internet Protocol)
x Adaptive antenna systems (AAS)
x Adaptive Modulation schemes (AMS)
x Advanced Encryption Standard (AES) encryption
A. Physical Layer
Mobile WiMAX will initially operate in the 2.3 GHz,
2.5 GHz, 3.3 GHz, and 3.4-3.8 GHz spectrum bands [8]
using SOFDMA.
OFDMA is perhaps the most
important technology associated with WiMAX.
SOFDMA is based on OFDMA which in turn is based on
OFDM [9].
OFDM is a form of Frequency Division Multiplexing,
but it has higher spectral efficiency and resistance to
multi path fading and path loss compare to other
multiplexing methods. It divides the allocated frequency
spectrum into sub carriers which are at right angles to
each other. This reduces the possibility of cross channel
interference thereby allowing the sub – carriers to
overlap. This reduces the amount of frequency spectrum
required, hence the high spectral efficiency. The reduced
data rate of each stream reduces the possibility of inter
56
symbol interference because there is more time between
the arrival of symbols from different paths. This feature
of OFDM makes it resistant to multi path fading and ideal
for non line of site applications. In OFDMA each
frequency sub – carrier is divided into sub – channels
which can be accessed by multiple users hence increasing
the capacity of OFDM [10].
Scalable OFDMA is a form of OFDMA which allows
variable channel bandwidth allocation from 1.25 MHz to
20 MHz. SOFDMA has capabilities which make it ideal
for the implementation of IP and Hybrid Automatic
Repeat Request (HARQ). WiMAX also uses other
features to enhance the performance of OFDMA. They
include dynamic frequency shifting, MIMO, Adaptive
Antenna Systems (AAS) and software defined radios.
Dynamic frequency shifting monitors the signal and
changes frequencies to avoid interference. Software
defined radios are controlled by changing software
settings and this gives the equipment more flexibility
when switching frequencies.
MIMO is a technology that has already found use in
WiFi (IEEE 802.11n). MIMO multiplies the point-topoint spectral efficiency by using multiple antennas and
RF chains at both the BS and the MS. MIMO achieves a
multiplicative increase in throughput compared to Single
Input, Single Output (SISO) architecture by carefully
coding the transmitted signal across antennas, OFDM
symbols, and frequency tones. These gains are achieved
at no cost in bandwidth or transmit power [11].
AAS are spatial processing systems which combine
antenna arrays with sophisticated signal processing. They
reduce the effects of interference from multiple signal
paths thereby also contributing to high capacity of the
system and the use of mobile WiMAX in NLOS
environments.
B.Mac Sub Layer
The 802.16 Medium Access Control (MAC) sub layer
uses a scheduling algorithm for which the subscriber
station only needs to compete for initial entry into the
network. The scheduling algorithm also allows the base
station to control QoS parameters by balancing the timeslot assignments among the application needs of the
subscriber stations.
WiMAX supports Quality of Service (QoS)
differentiation for different types of applications. The
802.16 standard defines the following types of services
[12]:
Unsolicited Grant Services (UGS): UGS is designed to
support Constant Bit Rate (CBR) services, such as T1/E1
emulation, and Voice over IP (VoIP) without silence
suppression.
Real-Time Polling Services (rtPS): rtPS is designed to
support real-time services that generate variable size data
packets on a periodic basis, such as MPEG video or VoIP
with silence suppression.
Non-Real-Time Polling Services (nrtPS): nrtPS is
designed to support non-real-time services that require
variable size data grant burst types on a regular basis.
Best Effort (BE) Services: BE services are typically
provided by the Internet today for Web surfing.
© 2008 ACADEMY PUBLISHER
JOURNAL OF COMMUNICATIONS, VOL. 3, NO. 2, APRIL 2008
IV. NETWORK DIMENSIONING AND
DESIGN
There is a large range of possible scenarios for the
deployment of mobile WiMAX, but main four categories
are [13]:
x Fixed and Mobile operator with Enhanced Data
for GSM Evolution (EDGE)/3G who uses mobile
WiMAX as a complementary extension for data
services
x Mobile only operator with EDGE/3G who uses
mobile WiMAX as a complementary extension
for data services
x Fixed operator who uses mobile WiMAX to
compete with 3G operators for data and voice
services
x New entrant who uses mobile WiMAX to move
into mobile market – threat to incumbent mobile
operator.
WiMAX operates in a mixture of licensed and
unlicensed bands. The unlicensed bands are typically the
2.4 GHz and 5.8 GHz bands. Licensed spectrum provides
operators control over the usage of the band, allowing
them to build a high-quality network. The unlicensed
band, on the other hand, allows independents to provide
backhaul services for hotspots. Typical area licensed
WiMAX spectrum allocations are:
x Lower 700 MHz (US) with 2x6 MHz channels
x 2.5 GHz Multichannel Multipoint Distribution
Service with 15.5 MHz in US and 72 MHz in
Canada
x 3.5 GHz Wireless Local Loop with 2 x 2hMHz
channel blocks
x 5.8 GHz UNI (license exempt) with 80 MHz
allocation
WiMAX access networks are often deployed in pointto-multipoint cellular fashion where a single base station
provides wireless coverage to a set of end users stations
within the coverage area. The technology behind
WiMAX has been optimized to provide both large
coverage distances of up to 30 kilometers under Line Of
Sight (LOS) situations and typical cell range of up to 8
kilometers under No LOS (NLOS) [14]. In a NLOS, a
signal reaches the receiver through reflections, scattering,
and diffractions. The signals arriving at the receiver
consists of many components from direct and indirect
paths with different delay spreads, attenuation,
polarizations, and stability relative to the direct path.
WiMAX technology, solves or mitigates the problem
resulting from NLOS conditions by using OFDMA, Subchannelization,
directional
antennas,
transceiver
diversity, adaptive modulation, error correction and
power control [15]. The NLOS technology also reduces
installation expenses by making the under-the-eaves
Customer Premise Equipments (CPE) installation a
reality and easing the difficulty of locating adequate CPE
mounting locations.
Both LOS and NLOS coverage conditions are
governed by propagation characteristics of their
environment, radio link budget and path loss. In both
JOURNAL OF COMMUNICATIONS, VOL. 3, NO. 2, APRIL 2008
cases relays help to extend the range of the base station
footprint coverage allowing for a cost-efficient
deployment and service [16].
A. WiMAX Cell Site Design
One of the most important technical and business
issues of any wireless technology is efficiently (cost and
performance) providing coverage and capacity, while
avoiding the build-out of a large number of new base
stations. The first step in designing a wireless system is
to develop a link budget. Link budget is the loss and gain
sum of signal strength as it travels through different
components in the path between a transmitter and
receiver. The link budget determines the maximum cell
radius of each base station for a given level of reliability
and is comprised of two types of components: system
related components and non-system related components
[17].
These components are important factors when
evaluating the complexity and speed in deploying at
higher frequency bands, especially in unlicensed bands
such as 5.8 GHz (licensed in some countries such as
Russia). Other factors like interference from other
surrounding networks will also impact network
performance and quality of service.
Path loss, shadow margin, environmental effects, and
morphology are important factors when planning for an
optimum coverage.
The morphology and physical
surroundings of a cell site play a very important role in
determining the cell footprint. A cell site footprint can
shrink from 7km in a mostly flat area with light tree
densities to 3 km in a hilly terrain with moderate–toheavy tree densities [17].
Traditional RF planning remains the fundamental
limiting factor in system performance in WiMAX. With
adaptation of Erceg Model [18], the cell size for several
carrier frequencies from 450MHz to 3.5GHz is estimated
for WiMAX systems using path loss propagation models
for flat rural, hilly rural and urban environment.
Equation (1) is used to estimate total path loss.
57
budget of 142 dB which provides approximately a 3km
cell coverage at 1900MHz has been assumed [18]. Based
on the results to obtain the same cell radius of 3km with
2.5 GHz frequency band an additional 4dB for link
budget is needed. In a coverage limited design scenario,
this 4dB corresponds to about 22 percent reduction in cell
coverage footprint and almost 70 percent increase in the
20
Cell
Radius,
18
km
700MHz
16
1.5GHz
1.9GHz
14
2.5GHz
12
3.5GHz
10
5.8GHz
8
6
4
2
0
Path Loss, dB
Figure 4. Path loss vs. WiMAX cell radius
cell count. Table I shows cell count calculation for
1900MHz to 3.5 GHz to illustrate the impact that path
loss can have, especially when deploying in higher
frequency bands. Fig. 5 and 6 show the results of cell
count estimation in a flat rural area for frequency
operation of 450 MHz and 3.5GHz. Assuming the equal
distribution of the coding modulation schemes inside the
cells and the probability of terrain coverage of 95%, the
system capacity is lower for WiMAX systems at 450MHz
frequency, due to large cell size. Compared with existing
cellular systems, WiMAX systems implement advanced
radio features that compensate for the extra attenuation
resulting from higher carrier frequency, larger
transmission bandwidth, and deep indoor penetration.
TABLE I.
L = A + 10
J
log ( d / d0) + S
A = 20 log (
4Sd 0
O
(1)
)
(2)
J = a –bhb+ c/ hb
(3)
In these equations: L is the total path loss in dB, d0 is
the close-in reference distance and d is the TransmitterReceiver separation distance in Km, S is a random
variable ,
O is
the wavelength of the carrier, A is free
J
space path loss, hb= base station height,
is path loss
exponent and a, b and c are constant depending on
morphology type.
Fig. 4 illustrates a comparison of a path loss
simulation for a WiMAX system for different frequency
bands using EDX SignalPro wireless planning and design
tool. In this EDX simulation study, a scenario with a link
© 2008 ACADEMY PUBLISHER
Freq.
Band
1900
MHz
2.5GHz
3.5GHz
WIMAX CELL COUNT VS. FREQUENCY
Cell
Radius
km
3
Link
Budget(dB)
3
3
146
151
Cell
radius
Reduction
Cell count
increase
21-24%
42-46 %
62-75%
200-250%
142
The radio enhancement feature applicable to fixed and
mobile WiMAX is subchannelisation.
Other
enhancement features that are only applicable to mobile
WiMAX are convolutional turbo coding, repetition
coding ( 3dB gain), and Hybrid Automatic Repeat
Request (HARQ).
Applying smart antennas or MIMO configuration in
the different topologies will enhance the cell site
coverage footprint. Cell planning options and WiMAX
technology features also allow interference and noise
handling so that WiMAX can provide sufficient coverage
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JOURNAL OF COMMUNICATIONS, VOL. 3, NO. 2, APRIL 2008
[19]. Fig. 7 shows global percentage of WiMAX
deployment per frequency band.
Figure 5.Cell radius for 450 MHz
Source: Jozef Stefan Institute
Figure 6. Cell radius for 3.5 GHz
services, improve bandwidth efficiency and offer realtime applications like VoIP and other streaming services
over an IP-based network. . It is a disruptive technology
that, after matching the incumbent technology, has
qualities of its own that will allow it to supersede the
incumbent’s legacy infrastructure. WiMAX, unlike
incumbent circuit-switched infrastructure, is a technology
that can be quickly and cheaply deployed anywhere in the
world. The North American telephony market (services)
is estimated to do almost $1.2 trillion in business
annually.
WiMAX potentially strikes at the very heart of
incumbent telco business paradigm that relied on a high
barrier to entry to the voice market. The biggest
challenges to deploying WiMAX–based services are
business related. Carriers need financial capability to
implement infrastructure. The WiMAX business model
can be looked from several perspectives. These include
the equipment vendors, service providers and application
providers and customers.
A. Equipment Vendors
As a standard-based technology, WiMAX enables
inter-vendor interoperability which brings lower costs,
greater flexibility and freedom, and faster innovation to
operators.
Within the WiMAX industry there is a strong
commitment to ensuring full interoperability through
certification and ad-hoc testing between vendors. It is
important for network operators to realize how
interoperability is established and what it covers so that
they understand how different products, solutions and
applications from different vendors can coexist in the
same WiMAX network.
The two categories of equipment vendors include the
network equipment vendors and the terminal equipment
vendors. Network equipment includes ASN and CSN
equipment. Terminal equipment includes mobile phones,
CPE, modems, laptops, smart phones and PDA’s.
Source: Jozef Stefan Institute
Percentage of WiMAX Deployments per Frequency
Band
57%
60%
50%
40%
30%
20%
13%
18%
12%
10%
0%
2.3-2.4GHz
2.5-2.7GHz
3.3-3.8GHz
4.9-6GHz
Figure 7. WiMAX deployment per band.
Source: wimaxcounts.com
V. The WiMAX Business Model
This technology offers an attractive package that
promises to minimize costs of delivering wireless data
© 2008 ACADEMY PUBLISHER
B. Service Providers
The business aspect of the service providers can also
be looked at from two perspectives. The first one is
where the service provider owns the whole system
including the core network and the access network. The
second option is the unbundled option where the access
network and core networks exist as independent business
entities.
The service providers are expected to gain profits
through the sale of the different services and applications
that WiMAX is capable of carrying. The different
services that can be offered on WiMAX networks include
best effort VoIP, carrier class IP telephony through the IP
multimedia core, music, video conferencing, streaming
video, interactive gaming, mobile instant messaging
(IM), IP Television (IPTV), basic broadband wireless
internet, and other application based services to corporate
customers. The concept of unbundling the network
reduces the barriers of entry into the mobile
JOURNAL OF COMMUNICATIONS, VOL. 3, NO. 2, APRIL 2008
telecommunications industry because a provider does not
need to own the whole network.
In emerging markets such as Africa, and south Asia
where telecom investment is still nascent and 3G yet to
be launched, WiMAX makes complete business sense
even at equal cost - better speeds, better spectrum
utilization and the promise of broadband to a much
sparsely spread population. The low cost of
BWA/WiMAX spectrum compared to 3G is a clear driver
for service providers to enter the field of wireless services
with WiMAX.
Fig 8 shows a global WiMAX
deployment by region.
Global WiMAX Deployment by Region
45
40
35
30
25
20
39
34
15
10
areas offer the highest density of customers with more
business establishments. In such cases a higher number of
cells which are small in size are required to meet the
capacity requirements. These are the areas more
competition is expected. Rural areas are expected to have
a lower penetration of customers, less corporate
customers, and bigger cell sizes because emphasis is on
coverage rather than capacity. Individual subscribers will
use WiMAX for music downloads, interactive gaming,
and personal broadband internet, and will form a large
percentage the total subscribers.
Corporate subscribers are also expected to contribute
to revenues of WiMAX, and their interest will be in
applications and services which will enhance their
organizations apart from the basic telecommunications
services.
Companies are poised to compete with each other in
WiMAX network deployment, which will ensure that the
prices will be competitive.
17
13
5
59
VI. COMPARISON WITH COMPETING TECHNOLOGIES
0
APAC
CALA
Europe
North America
Figure 8.Global WiMAX networks.
Source: wimaxcount.com. APAC= Asia Pacific, CALA= Caribbean
and Latin America.
C. Application Providers
WiMAX has already revolutionized the broadband
wireless market by standardizing broadband wireless
access market, by opening up new service opportunities
and by creating the environment for ubiquitous
broadband services. The aim is to provide the service that
best fits the individual’s needs. Applications can be
developed in house by the service providers, outsourced
from other companies or developed and sold directly to
the end user by an independent applications development
company.
Applications are based on Internet Protocol (IP), and
IP applications are sent back or forth via WiMAX. This
allows the users to develop applications independently
from the underlying network infrastructure. Some
applications will still be developed by operators but the
vast majority will come from those working directly in
the internet crowd. For them and for the end users
competing wireless technologies are very beneficial.
Competition spurs network roll outs, offers possibility for
new players in the market, and creates competition
between device manufacturers. Also, new applications
will be introduced more easily and much more quickly as
they are no longer forced into a tight framework that
takes long time to develop and from which it is difficult
to get out again.
D. WiMAX Customers
Prospective WiMAX customers can be grouped either
geographically or by the level or volume of services.
Geographical categories range from urban to rural
customers, while categories according to size include
individual customers and the corporate customers. Urban
© 2008 ACADEMY PUBLISHER
At some point current 2G and 3G network operators
will migrate to a 4G network technology. Mobile
WiMAX is likely to face competition from third and 4G
technology enhancements. They include the Code
Division Multiple Access (CDMA) variants CDMA2000
and
Wideband-CDMA
(WCDMA)
and
their
enhancements which are 1x Evolution Data Optimized
(1xEVDO) and High Speed Downlink Packet Access
(HSDPA) respectively. Unlike in the early days of the
CDMA vs. GSM competition, this higher generation
competition will be quite different and fruitful since for
these new generations networks and the applications are
separated and do not depend on each other. 4G networks
will go far beyond 2G and 3G by mainly improving three
things:
x Interface Technology: 4G standards will make a
radical change and will use OFDM [9]. The new
modulation itself will not automatically bring an
increase in speed but very much simplifies the
following two enhancements:
x Channel Bandwidth: 4G systems will use a
bandwidth of up to 20 MHz, i.e. the channel
offers four times more bandwidth than channels
of current systems. As 20 MHz channels might
not be available everywhere, most 4G systems
will be scalable, for example in steps of 1.25
MHz. It can therefore be expected that 4G
channel sizes will range from 5 to 20 MHz.
x MIMO: The idea of MIMO is to use the
multipath phenomena. While this behavior is
often not desired, MIMO makes active use of it
by using several antennas at the sender and
receiver side, which allows the exchange of
multiple data streams, each over a single
individual wave front. Two or even four
antennas are foreseen to be used in a device.
How well this works is still to be determined in
practice but it is likely that MIMO can increase
60
throughput by a factor of two in urban
environments.
Increasing channel size and using MIMO will increase
throughput by about 8-10 times. Thus speeds of 40
MBit/s per sector of a cell are thus possible. Using a
commonly accepted evaluation methodology for 3G
systems, Mobile WiMAX has been simulated against the
3G enhancements [20]. These simulations have shown
that:
x Mobile WiMAX peak data rates are up to 5x
better than 3G+ technologies and
x Mobile WiMAX spectral efficiency is 3x better
than any 3G+ technology
x Lower equipment cost for WiMAX due to
certified products (compare with WiFi)
x WiMAX require new infrastructure while HSPA
rides on UMTS
x Roughly the same coverage (average ~5 km)
x Roughly the same performance (average ~2 Mb/s
per user)
x HSDPA launches in 2006 while HSUPA will
come in 2008
x WiMAX standard set end of 2005 and first
products in 2006
x HSPA has a higher acceptance with mobile
operator
A. 1xEVDO
This standard is developed by the Third Generation
Partnership Project 2 (3GPP2), the body responsible for
CDMA and EVDO. 1xEV-DO is an enhanced version of
CDMA2000-1x. There are four versions that have been
released; namely Rev. 0, Rev. A, Rev. B and Rev C.
1xEV-DO is a high-speed data only specification for
1.25 MHz Frequency Division Duplex (FDD) channels
with a peak Downlink (DL) data rate of 2.4 Mbps.
Improvements to CDMA2000 – 1x in the 1xEV-DO
Rev.0 specification include [9]:
Downlink channel is changed from Code Division
Multiplex (CDM) to Time Division Multiplex (TDM) to
allow full transmission power to a single user.
Downlink power control is replaced by closed loop
downlink rate adaptation.
Adaptive modulation and coding (AMC)
HARQ
Fast downlink scheduling
Soft handoff is replaced by a more bandwidth efficient
“virtual” soft handoff
1xEV-DO-Rev 0 however, was designed to support
only packet data services and not conversational services.
In 1xEVDO-Rev A, and EVDO Rev C (also dubbed
DORC) additional enhancements were added to the
1xEV-DO specification. They include the following [8]:
Downlink: Smaller packet sizes, Higher DL peak data
rate (up to 3.1 Mbps), and Multiplexing packets from
multiple users in the MAC layer.
Uplink (UL) : Support of HARQ, AMC, Higher peak
rates of 1.8 Mbps, and Smaller frame size
These enhancements in both the UL and DL of 1xEVDO Rev.A allow it to support conversational services.
© 2008 ACADEMY PUBLISHER
JOURNAL OF COMMUNICATIONS, VOL. 3, NO. 2, APRIL 2008
B. HSDPA/HSPA
The WCDMA specification was enhanced to create the
High Speed Downlink Packet Access (HSDPA) and then
High Speed Packet Access (HSPA) specifications. The
enhancements in HSDPA include, AMC, Multi-code
operation, HARQ, Higher DL peak rates (up to 14 Mbps),
and De-centralized architecture where scheduling
functions are moved from the Radio Network Controller
(RNC) to Node-B thus reducing latency and enabling fast
scheduling.
HSPA adds enhancement to the uplink of the WCDMA
specifications. In reference [9] a quantitative comparison
of Mobile WiMAX, 1xEVDO and HSPA system
performance, was conducted based on the commonly
accepted 1xEV-DV evaluation criterion. The Mobile
WiMAX system configuration was based on the WiMAX
Forum baseline minimum configuration. Table II
illustrates a Comparison of Mobile WiMAX with 3G
enhancements [21].
These technologies i.e. EVDO, HSPDA and Mobile
WiMAX have several performance enhancing features
such as AMC, HARQ, fast scheduling, and bandwidth
efficient handoff in common [22].
From the end-user point of view, HSPA and WiMAX
are close substitutes; both are enabling same types of
services for the same devices and contexts. Differences in
the technological performance are also considered to be
quite small. This suggests that the technologies will
engage in a technological battle, rather than coexist and
complement each other.
TABLE II.
COMPARISON OF MOBILE WIMAX WITH 3G
ENHANCEMENTS
rameter
Duplex
Occupied spectrum
(MHz)
Channel
DL
bandwidth
UL
(MHz)
Spectral
DL
Efficiency
UL
Net
DL
Information
Throughput
UL
per
channel/Sect
or (Mbps)
3xEVDO
Rev. B
HSDPA
HSUPA
Mobile
WiMAX
FDD
2.5
FDD
10
FDD
10
FDD
10
TDD
10
1.25
1.25
5
5
5
5
5
5
DL/UL
=3
0.85
0.36
1.06
0.93
0.28
4.65
0.78
0.14
3.91
0.78
0.30
3.91
1.91
0.84
14.1
0.45
1.39
0.7
1.50
2.20
1xEVDO
Rev. A
C. WiFi
WiMAX is different from WiFi in many respects. The
WiFi MAC layer uses contention access. This causes
users to compete for data throughput to the access point.
WiFi also has problems with distance, interference, and
throughput and that is why triple play (voice, data, video)
technologies cannot be hosted on traditional WiFi. In
contrast 802.16 uses a scheduling algorithm. This
algorithm allows the user to only compete once for the
access point. This gives WiMAX inherent advantages in
throughput, latency, spectral efficiency, and advanced
antenna support.
JOURNAL OF COMMUNICATIONS, VOL. 3, NO. 2, APRIL 2008
Companies developing radical innovations may adopt
different stances; not only based on the strategic interests
of the company but also they taking into other
considerations such as the market and its needs and
requirements, as well as other products it may carry.
When comparing WiFi and WiMAX, one is comparing
their substitutability and complementary to existing
technologies and how different companies have and will
view them. WiMAX and WiFi can offer some potentially
significant cost savings for mobile network operators by
providing an alternate means to backhaul base station
traffic from cell site to the base station controllers.
Mobile network operators typically utilize some type of
wired infrastructure that they must buy from an
incumbent operator. A WiFi or WiMAX mesh can offer
a much more cost-effective backhaul capability for base
stations in metropolitan environments.
The results of the comparison show that mobile
WiMAX has better performance in all the areas listed
above (where it shares performance enhancing features
with EVDO and HSDPA/HSPA). Furthermore, the
technologies on which mobile WiMAX is based result in
lower equipment complexity and simpler mobility
management due to the all-IP core network. They also
provide Mobile WiMAX systems with many other
advantages over CDMA based systems such as:
x Tolerance to Multipath and Self-Interference
x Scalable Channel Bandwidth
x Orthogonal Uplink Multiple Access
x Support for Spectrally-Efficient TDD
x Frequency-Selective Scheduling
x Fractional Frequency Reuse
x Improved variable Quality of Service (QoS)
x Advanced Antenna Technology
WiMAX gained its expected acceptance by the ITU as
an official IMT2000 wireless standard – removing many
potential regulatory barriers to its adoption in cellular
bands may push the CDMA giant further towards
adopting 802.16e.
Many governments dictate
technologies when they allocate wireless spectrum, and
they typically look to the ITU, which is affiliated with the
United Nations, to say what technologies qualify. WiMax
will now be one of their choices when faced with a
requirement for 3G, which the ITU calls IMT-2000. With
the prospects for introduction of multimode starting in
2008, WiMAX will become an exceptional enhancement
to existing cellular 3G networks. Operators who adopt
WiMAX multimode are not pressed into either replacing
or displacing service to customers. Instead, they have an
evolutionary alternative to provide higher bandwidth
services and a ”personal broadband everywhere” triple or
quadruple play of services, which will help retain and
attract customers.
VII. APPLICATIONS
The WiMAX standard has been developed to address a
wide range of applications. Based on its technical
attributes and service classes, WiMAX is suited to
© 2008 ACADEMY PUBLISHER
61
supporting a large number of usage scenarios. Table III
address a wide range of applications [23].
TABLE III. SUMMARY OF WIMAX APPLICATIONS
CLASS
DESCRIPTION
Interactive Gaming
REAL
TIME
Yes
VoIP, Video
Conferencing
Yes
Streaming Media
Yes
Information
Technology
No
Media Content
download (store and
forward)
No
APPLICATION
TYPE
Interactive
Gaming
VoIP
BANDWIDTH
Videophone
32-384 Kbps
Music/Speech
Video clips
Movies
streaming
Instant
Messaging
Web browsing
Email (with
attachments)
Bulk data,
Movie
download
Peer to Peer
5-128 Kbps
20 – 384 Kbps
> 2 Mbps
50-85 Kbps
4-64 Kbps
< 250 byte
messages
> 500 Kbps
> 500 Kbps
> 1 Mbps
> 500 Kbps
VOIP & IP
Mobile WiMAX is an all IP network. The use of
OFDMA on the physical layer makes it capable of
supporting IP applications. It is a wireless solution that
not only offers competitive internet access, but it can do
the same for telephone service.
Voice over Internet Protocol (VoIP) offers a wider
range of voice services at reduced cost to subscribers and
service providers alike .VoIP is expected to be one of the
most popular WiMAX applications. Its value proposition
is immediate to most users. While WiMAX is not
designed for switched cellular voice traffic as cellular
technologies as are CDMA and WCDMA, it will provide
full support for VoIP traffic because of QoS functionality
and low latency. IPTV enables a WiMAX service
provider to offer the same programming as cable or
satellite TV service providers. IPTV, depending on
compression algorithms [24], requires at least 1 Mbps of
bandwidth between the WiMAX base station and the
subscriber. In addition to IPTV programming, the service
provider can also offer a variety of video on demand
(VoD) services. IPTV over WiMAX also enables the
service provider to offer local programming as well as
revenue generating local advertising.
VIII.
BENEFITS OF WIMAX
WiMAX is a global technology. Different countries
refer to their systems by different names for example;
WiBro is the name of 802.16e standard in South Korea
and HIPERMAN(High Performance Radio Metropolitan
Are Network) in Europe. The Widely used international
broadband spectrum range is 3.5 GHz. The followings
are some of the advantages of WiMAX.
Wireless.
By using a WiMAX system,
companies/ residents no longer have to rip up buildings
or streets or lay down expensive cables.
62
JOURNAL OF COMMUNICATIONS, VOL. 3, NO. 2, APRIL 2008
High Bandwidth. WiMAX can provide shared data
rates of up to 70 Mb/s. this is enough bandwidth to
support more than 60 businesses at once with T1-type
connectivity. It can also support over a thousand homes at
1 Mb/s DSL-level connectivity Also, there will be a
reduction in latency for all WiMAX communications.
Long Range. The most significant benefit of WiMAX
compared to existing wireless technologies is the range.
WiMAX has a communication range of up to 40 Km[25].
Multi-Application. WiMAX uses the Internet protocol
and is therefore capable of efficiently supporting all
multimedia services from VoIP to high speed internet and
video transmission. It also supports a differentiated
quality of service enabling it offer dynamic bandwidth
allocation for different service types. WiMAX has the
capacity to deliver services from households to small and
medium enterprises, small office, home office (SOHO),
Cybercafés, Multimedia Tele-centers, Schools and
Hospitals.
Flexible Architecture. WiMAX supports several
systems architectures, including Point-to-Point, Point-tomultipoint, and ubiquitous coverage.
High Security. The security of WiMAX is state of the
art. WiMAX supports advanced encryption standard
triple data encryption standard. WiMAX also has built-in
VLAN support, which provides protection for data that is
being transmitted by different users on the same base
station. Both variants use Privacy Key Management
(PKM) for authentication between base station and
subscriber station. WiMAX offers strong security
measures to thwart a wide variety of security threats.
QoS. WiMAX can be dynamically optimized for a mix
of traffic that is being carried.
Multi Level Service. QoS is delivered generally
based on the service level agreement between the end
user and the service provider.
Interoperability. WiMAX is based on international,
vendor-neutral standard. This protects the early
investment of an operator since it can select the
equipments from different vendors.
Low Cost and Quick deployment. WiMAX requires
little or no external plant construction compared with the
deployment of wired solutions.
Base stations will
cost under $20,000 but will still provide customers with
T1-class connections [26].
Worldwide Standardization. WiMAX is developed
and supported by the WiMAX forum (more than 470
members). The WiMAX forum collaborates with
different international standards organizations that are
developing broadband wireless standards with the intent
to provide interoperability among the standards. Some of
the other broadband wireless standards include
HiperMAN/HiperLAN (Europe) and WiBRO (South
Korea). These standards are compatible with WiMAX at
the physical layer. WiMAX will become a truly global
technology based standard for broadband and will
guaranty interoperability, reliability and evolving
technology and will ensure equipment with very low cost.
IX. DRAWBACKS OF WIMAX
© 2008 ACADEMY PUBLISHER
Broadband wireless in general and WiMAX in
particular face a number of challenges that could impede
their adoption in the marketplace. The most significant
challenge is that WiMAX is a new technology with
emerging support.
Hesitancy. Companies are very hesitant of setting up
WiMAX base stations today since it has not yet reached
widespread use. Intel has made their Centrino laptop
processors WiMAX enabled. All laptops are expected to
have WiMAX by 2008[27].
Exclusion of Start-Up Companies. Even though cost
provides a low barrier to entry, none of the startup
companies are projected to be major players in the
development of WiMAX. Intel and Cisco seem to have
an obvious advantage today, and by the time it reaches
widespread use, large operators will find WiMAX to be a
very attractive new way of raising revenues.
Research and Development.
For
WiMAX
to
succeed, new products must be researched and developed
to incorporate WiMAX. Without the help of major
companies investing in this R&D, WiMAX could be
gravely underutilized.
X. CONCLUSION
Broadband wireless is a significant growth marketplace
for the telecom industry to deliver a variety of
applications and services to both mobile and fixed users.
The combination of both advanced radio features and
flexible end-to-end architecture makes WiMAX attractive
solution for diverse operators. It provides many different
services on one network, services which required
different networks in the past. It also provides
convergence of fixed and mobile networks. It provides
high speed access to the subscriber at a reasonable cost,
thereby enabling the service provider to make a profit
from the technology, using economies of scale. It offers
the advantage of reduced total cost of ownership during
the lifetime of a network deployment.
We compared WiMAX with other 3G technologies.
While it is clear that WCDMA has the advantage when
referring to voice and soft handoff of voice, these
advantages disappear for data-centric applications. There
are some additional advantages of WCDMA in
equipment performances; however, these advantages are
not sufficient to overcome the advantages of OFDMA.
As data traffic continues to grow, there will be an
increasing need to offload data from 3G to and OFDMA
based network optimized for data. Mobile WiMAX
(802.16e) provides the only standards-based OFDMA
WAN technology. WiMAX is an excellent complement
to other wireless technologies that are designed to work
in the LAN (WiFi) or that offer wider coverage but with
more limited capacity (GSM, CDMA, UMTS, EV-DO).
Recent inclusion of WiMAX in IMT2000, and the ITU
decision may push the CDMA giant further towards
adopting 802.16e
In regard to WiMAX cell design and coverage, the
radio enhancement feature applicable to fixed and mobile
WiMAX compensate for the extra attenuation resulting
JOURNAL OF COMMUNICATIONS, VOL. 3, NO. 2, APRIL 2008
from higher carrier frequency, larger transmission
bandwidth, and deep indoor penetration.
WiMAX is expected take prominence in about five
years (2012). The strengths of WiMAX lie in its ability to
address the requirements of modern telecommunications
networks and the commitment that has been shown to its
development and wide acceptance by a number of leading
equipment vendors and service providers. WiMAX could
potentially be deployed in a variety of spectrum bands:
2.3 GHz, 2.5 GHz, 3.5 GHz and 5.8 GHz. The biggest
challenges to deploying WiMAX–based services do not
stem very much from the spectrum, but from business
case issues.
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© 2008 ACADEMY PUBLISHER
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A. Yarali (S’92, M’96-IEEE) is a faculty member of
Telecommunication Systems Management and Industrial
Engineering Technology at Murray State University where he
has developed a wireless option program. He has worked as a
technical advisor in wireless industry since 1995. Dr. Yarali is
currently conducting research program in wireless mobile
systems design and implementation at Murray State University.
Saifur Rahman (S’75, M’78, SM’83, F’98 – IEEE) is the
director of the Advanced Research Institute at Virginia Tech
where he is the Joseph Loring Professor of electrical and
computer engineering. He also directs the Center for Energy
and the Global Environment at the University. Professor
Rahman has served as a program director in engineering at the
US National Science Foundation between 1996 and 1999. He
has served on the IEEE Power Engineering Society Governing
Board as VP of industry relations, and VP of publications
between 1999 and 2003. In 2006 he served as the vice president
of the IEEE Publications Board, and a member of the IEEE
Board of Governors. He is also a member-at-large of the IEEEUSA Energy Policy Committee. He has published over 300
papers on conventional and renewable energy systems, load
forecasting, uncertainty evaluation and infrastructure planning.
Bwanga Mbula is a graduate student at Murray State
University. He has worked in telecommunication field for
several years. Bwanga’s research interest is in wireless mobile
communication filed.
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