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XIX IMEKO World Congress
Fundamental and Applied Metrology
September 6!11, 2009, Lisbon, Portugal
BASIC CHARACTERISTICS OF ZIGBEE AND SIMPLICITI MODULES
TO USE IN MEASUREMENT SYSTEMS
L. Skrzypczak1), D. Grimaldi2), R. Rak3)
1)
Department of Electronics, Computer and System Sciences, University of Calabria, Rende – CS, Italy,
[email protected]
2)
Department of Electronics, Computer and System Sciences, University of Calabria, Rende – CS, Italy,
[email protected]
3)
Institute of the Theory of Electrical Engineering, Information and Measurement Systems,
Electrical Engineering Faculty, Warsaw University of Technology, Warsaw, Poland, [email protected]
Abstract – The main goal of this paper is to
experimental examine some of the properties of two
different wireless communication modules, ZigBee and
SimpliciTI, which are employing two different transmission
standards. This paper is a part of wider research aimed to
examine and evaluate the different wireless transmission
standards to use in distributed measurement systems.
Keywords
:
ZigBee;
Measurement Systems
SimpliciTI;
Distributed
1. INTRODUCTION
The use of new wireless transmission standards in
measurement systems is described by some requirements of
industrial applications such those presented in [1] which are
(i) integration into existing measurement systems, (ii)
coordination of the advanced and traditional monitoring
structures, and (iii) design of innovative measurement
systems. This paper is an attempt to examine two different
wireless transmission standards named ZigBee and
SimpliciTI in order to meet those requirements.
SimpliciTI is Texas Instruments proprietary network
protocol [2] for low-power radio frequency wireless
communication. Main properties of SimpliciTI are [2]:
Low cost which means that SimpliciTI network protocol can
be implemented in systems with small memory capacity.
According to [2] as low as 8 kB of ROM and 1 kB of RAM
is needed to implement SimpliciTI.
Flexibility which is achieved by multiple network topologies
namely star and peer-to-per (p2p) [2].
The basic Application Programmers Interface (API) makes
SimpliciTI simple to be used.
Wide selection of transceiver chips made to work with
SimpliciTI operating in sub-1GHz frequencies and in 2.4
GHz band [3] makes this protocol versatile.
Finally very low current consumption in sleep state [2]
makes SimpliciTI very well suited for battery powered
applications.
ZigBee is wireless communication standard managed by
the ZigBee Alliance and is based on the standard IEEE
ISBN 978-963-88410-0-1 © 2009 IMEKO
802.15.4 physical and Media Access Control (MAC) layers
[4].
Main properties of ZigBee are [5]:
Flexible network topology. Simple star topology as well as
more complicated mesh topology are possible. This makes
ZigBee easy to install because when using mesh topology
network range is not limited to maximum range of the single
device.
ZigBee scalability is also achieved by static and dynamic
star and mesh topology allowing mode than 65000 nodes
with low latency to be connected to the same network [5].
Low power is achieved by allowing long periods of noncommunication without the need for re-synchronisation [5].
Because ZigBee Alliance is not limited to one company
many manufacturers produce ZigBee modules and
equipment such antennas. This makes competition on the
market which means low prices.
The cause of choosing these two transmission standards
is that they were designed for monitoring and control
applications [5], [2]. Such applications are closely related to
measurement systems field.
This paper is a presentation of characteristics of both
standards in the area of measurement systems.
The following sections describe the measured
parameters, the methodology of making presented
measurements, used wireless modules and environmental
conditions under which all presented measurements were
made.
At the end the conclusion is made on the basis of
experimental results.
2. RESEARCH OVERVIEW
Characteristics of tested modules is based on Quality of
Service (QoS) parameters. These parameters derived from
[6] are listed in Table 1.
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As concerning the quantization of the Jitter, it is defined
in [6] as delay variability. Therefore, it can be evaluated by
measuring differences between each measurement of DOF.
Another parameter that must be added to the previous
ones is the value of current taken from the power source in
different states of the wireless module (Sleep/Idle, Receive,
transmission).
Table 1. QoS parameters.
Category
Timeliness
Bandwidth
Reliability
Parameters
Delay
Response time
Jitter
System-level data rate
Application-level data rate
Transaction time
Mean time to failure (MTTF)
Mean time to repair (MTTR)
Mean time between failures (MTBF)
Percentage of time available
Packet loss rate
Bit error rate
4. MODULES USED
In this research only three parameters have been selected
namely packet loss rate, delay, and jitter. This is because the
goal of this research is to evaluate the basic characteristics
of two wireless data transmission modules of two different
standards. The QoS parameters does not include power
consumption of the module and signal strength measured as
the power of signal received by the receiver. Both tested
modules are designed to by battery powered so the power
consumption is very important parameter.
3. MEASURED PARAMETERS
4.1. SimpliciTI
The SimpliciTI module used in this research is EZ430RF2500 from Texas Instruments [7]. This module was
chosen because of its simplicity, small dimensions and low
price. It consists of the following devices:
- 2 boards with MSP430F2274 microcontroller and
CC2500 transceiver with chip antenna, two leds and
pushbutton,
- USB interface for programming and communication
with PC,
- Battery holder with connector to transceiver board
This module is thought as a development tool for
wireless sensor networks and can be used as a standalone
device or incorporated into an existing project [7].
There is demonstration application available for this
module but for this research it was needed to create custom
application to be able to measure all given parameters.
As concerning the quantization of the packet loss rate,
the following parameter is defined: PER (Packet Error
Rate) or Packet Loss Rate. It describes what fraction of all
sent packets were corrupted or lost and can be calculated as:
PER =
Pcorr
"100%
Ptotal
(1)
where Pcorr is number of corrupted or lost packets and Ptotal is
number of all packet sent.
! this parameter it is easy to determine the
By measuring
characteristics of examined wireless module in different
environmental conditions such as distance between devices
or interference with other devices of the same or different
standard. The increase of PER according to [6] may be
caused by collision or weak signal. In this research collision
is not the case because only receiver and transmitter are in
range. This means that only weak signal is the cause of PER
increase. However the increase of PER because of collision
will be investigated in further research. As an addition to
PER, power of signal received by the receiver is measured.
By correlating increase of PER with signal strength it is
easier to determine the cause of PER increase as the result of
weak signal or interference from other devices.
As concerning the quantization of the delay, the
following parameter is defined: DOF (Delay of Frame). It
describes the delay between writing data frame to the
transmitter output buffer and reading it from receiver input
buffer. This parameter is especially important in high speed
systems where the low response time is needed [6].
Fig. 1. EZ430-RF2500 – SimpliciTI evaluation module.
4.2. ZigBee
The ZigBee module used in this research is RZ RAVEN
from Atmel [8]. This module was chosen because it contains
all hardware and software needed to complete this research
without the need to create custom software. The low price
was advantage as well. There are following devices in the
kit:
- LCD module (AVRRAVEN)
- USB module (RZUSBSTICK)
This development kit is aimed for various applications –
simple point-to-point communication, sensor networks and
human interface devices [8].
Application named Radio Evaluation Software (RES)
provided by Atmel lets user to perform certain tests [6]:
! PER/Range Characterization Test
! RF Characterization Test
! DC Characterization Test
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PER/Range Characterization Test provides possibility
to test how the distance between transmitter and receiver
and environmental conditions (such as presence of another
radio device nearby) affects data transmission. This test also
provides information about the signal strength.
RF Characterization Test is convenient to test characteristics
of radio transmitter/receiver in terms of different radio
frequency related tests [9].
DC Characterization Test provides important information
about current consumption of the device in different
working states such as transmission, reception or idle state.
For this research, only PER/Range test and DC
characteristics are important because RF performance is not
subject of this research. RF performance test is used to test
transmitter output (modulation and carrier frequency)
compliance with regulatory agency requirements [9].
Digital oscilloscope and series resistor was used to
monitor current consumed by the battery operated remote
module in different operation states (Idle/Sleep, Reception,
Transmission). DC characteristics measurement circuit is
shown in Fig. 4. This circuit is used to test current
consumption of the device.
Fig. 4. DC characteristics measurement circuit.
Digital Sampling Oscilloscope was used to measure
DOF parameter described in section 3. DOF measurement
circuit is shown in Fig. 5. DOF is measured with
oscilloscope as a time between start of frame transmission in
the transmitter and reception of the complete frame in the
receiver.
Fig. 2. RZ RAVEN ZigBee evaluation kit.
5. TESTING EQUIPMENT AND PROCEDURES
5.1. Testing equipment
Testing equipment consists of :
!
PC,
!
USB module with SimpliciTI or ZigBee interface,
!
Remote wireless device of respective standard,
SimpliciTI or ZigBee,
!
Digital Oscilloscope – HP 1652b.
The PC with terminal emulation software is used for
communication with USB module of different modules.
Both SimpliciTI and ZigBee modules use simple commands
for configuration and performing tests as well as to display
results of the test.
Remote module was fixed to the portable tripod to
ensure its unchanged orientation and reduce human body
interference. This also makes it easier to position module
exactly at the needed distance from PC. The concept of test
setup for PER measurement is shown on Fig. 3.
Fig. 3. PER test setup.
Fig. 5. DOF measurement circuit
5.2. Test Procedure
Following tests were performed:
! PER/signal strength
! maximum range (maximum distance between
transmitter and receiver where no transmission
errors occur)
! DC characteristics
! DOF
In PER test the battery operated remote module was used
as a transmitter to easily move it in the testing ground and
PC with wireless USB module was used as a receiver as in
Fig. 3. The parameter itself was measured in terms of
distance between remote device and USB module. There
were three measurements made at each spatial position and
average value of PER was calculated.
DC characteristics was measured in different setup. The
main difference was that remote device was powered from
internal battery with series resistor connected. Digital
oscilloscope was used to measure the voltage drop on series
resistor which was proportional to current consumed by the
device. The circuit is shown in Fig. 4.
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DOF was measured by using general Input/Output ports
of the microcontrollers used in the remote and USB devices.
Two probes of the digital sampling oscilloscope were
connected to respective modules to measure time between
writing packet to output buffer in the transmitter (this was
indicated by the change of microcontroller pin state) and
reading transmitted packet in receiver (this was also
indicated by the change of general Input/Output port pin
state). The DOF circuit is shown in Fig. 5.
Packet Error Rate was fluctuating up to about 24 m
and rapidly risen at the distance over 24 m. The maximum
distance where all packets were lost was about 30 m.
Table 2. SimpliciTI current consumption in different states.
6. EXPERIMENTAL RESULTS
6.1. SimpliciTI
Results of transmission power loss due to distance
increasing between transmitter and receiver are shown in
Fig. 6.
Idle
19 mA
Receive
19.4 mA
Transmit
23 mA
The current consumption, shown in Tab.2 is about the
same as in [10] in reception mode and transmission mode. It
is different in idle mode (1.5 mA [10]) because in [10]
device is in sleep state during idle and in this research
device it is in active state to avoid any delay caused by the
need to wake up device from sleep state before receiving
frame.
The measured Delay of Frame was 4.5 ms and it was
stable in all measurements meaning that there was no jitter
[6].
6.2. ZigBee
Fig 6. SimpliciTI transmission power loss due to distance
increasing between transmitter and receiver.
The maximum distance at which most data packets were
transmitted is about 30 m which is lower than 50m
mentioned in [7]. Also [7] explains that the maximum
transmission distance can be affected by the orientation of
antennas of both transmitter and receiver. In this research
the parallel orientation of on-board chip antennas was
chosen basing on experiments with different antenna
orientations.
Fig. 9. ZigBee transmission power loss due to distance increase
between transmitter and receiver
The measured maximum distance between transmitter
and receiver with almost no data loss was 100 m which fully
comply with [5].
Fig. 7. SimpliciTI Packet Error Rate increase due to distance
increase between transmitter and receiver
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Table 3. ZigBee current consumption in different states.
Idle
4 mA
Receive
5.3 mA
Transmit
18.5 mA
[7]
eZ430-RF2500 Development Tool User’s Guide (Rev. C),
Texas Instruments, 2008
[8] AVR2016: RZRAVEN Hardware User’s Guide (rev. A),
Atmel, 2008
[9] AVR2002: Raven Radio Evaluation Software (rev. A), Atmel,
2008
[10] M.Morales Wireless Sensor Monitoring Using the eZ430RF2500, Texas Instruments 2008
The current consumption of RZ-RAVEN, shown in
Table.3, is lower than eZ430-RF2500 in reception and
transmission modes, Especially in reception mode where
eZ430-RF2500 (SimpliciTI) consumes four times as much
current as RZ-RAVEN (ZigBee).
The measurement of Delay of Frame varied from 1 ms to
about 100 ms. This may be due to the very complex ZigBee
stack. This variation of Delay of Frame or jitter [6] limits
the use of tested ZigBee modules in DMS because of
potential problems with time synchronisation between
devices.
7. CONCLUSIONS
This research is the part of wider work aimed to extend
the use of different wireless transmission standards in
measurement systems. The approach is based on the use of
set of QoS parameters (usually used to characterize
telecommunication applications), in the field of
measurement systems.
Both SimpliciTI and ZigBee modules have slightly
different characteristics. RZ RAVEN (ZigBee) has greater
range but power consumption in sleep state is higher than
SimpliciTI module (EZ430-RF2500). Both modules can be
battery powered and both are small in size. EZ430-RF2500
has the advantage of 16 bit microcontroller and SimpliciTI
API is smaller. However RZ RAVEN has more peripherals.
The results of this research shown that some parameters
especially the maximal range of SimpliciTI module is lower
than declared by the manufacturer.
The complete research over these wireless modules will
give information of how and where and in what application
can these wireless transmission standards can be used in the
field of measurement systems.
REFERENCES
[1]
[2]
[3]
[4]
[5]
[6]
A. Aiello, D.L. Carni, D. Grimaldi, G. Guglielmelli,
Wireless Distributed Measurement System by Using Mobile
Devices, IEEE-IDAACS, 2005
SimpliciTI Overview (Rev. B), Texas Instruments, 2008
Low-Power RF Selection Guide, Texas Instruments, 2008
Maximizing Throughput in ZigBee Wireless Networks
through Analysis, Simulation and Implementations, T. Ryan
Burchfield, S. Venkatesan, D. Weiner
ZigBee Overview, ZigBee Alliance, 2007
VOIP Performance Measurement using QoS Parameters,
A.H. Muhamad Amin, IIT 2005
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