White Paper and Test Report
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ZigBee – WiFi
Coexistence
White Paper and Test Report
Gilles Thonet
Patrick Allard-Jacquin
Pierre Colle
Schneider Electric
Innovation Department
37 Quai Paul Louis Merlin
38000 Grenoble, France
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Table of Contents
EXECUTIVE SUMMARY ........................................................................................ 3
1
INTRODUCTION ............................................................................................ 4
1.1
B
ACKGROUND
............................................................................................................................4
1.2
P
URPOSE OF THE
D
OCUMENT
..........................................................................................................4
1.3
R
EFERENCES
..............................................................................................................................4
1.4
A
CRONYMS
................................................................................................................................5
2
COEXISTENCE IN ZIGBEE .............................................................................. 6
2.1
IEEE
802.15.4
L
AYERS
...............................................................................................................6
2.2
Z
IG
B
EE
L
AYERS
..........................................................................................................................8
3
SUMMARY OF PREVIOUS STUDIES ................................................................ 9
3.1
S
CHNEIDER
E
LECTRIC
...................................................................................................................9
3.2
D
AINTREE
N
ETWORKS
(Z
IG
B
EE
A
LLIANCE
) ....................................................................................... 10
3.3
D
ANFOSS
(Z-W
AVE
A
LLIANCE
) ..................................................................................................... 12
3.4
E
MBER
................................................................................................................................... 13
3.5
F
REESCALE
.............................................................................................................................. 15
3.6
U
NIVERSITY OF
C
OOPERATIVE
E
DUCATION
L
ÖRRACH
............................................................................ 15
3.7
S
UMMARY
............................................................................................................................... 16
4
RESIDENTIAL TESTS ................................................................................... 18
4.1
H
OUSE
1 ................................................................................................................................ 18
4.2
H
OUSE
2 ................................................................................................................................ 20
5
LABORATORY TESTS ................................................................................... 24
5.1
D
ESCRIPTION OF
T
EST
E
NVIRONMENT
.............................................................................................. 24
5.2
W
I
F
I
T
RAFFIC
P
ATTERNS
............................................................................................................. 26
5.3
R
ESULTS
................................................................................................................................ 31
6
CONCLUSIONS AND RECOMMENDATIONS ................................................... 37
White Paper and Test Report
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Executive Summary
ZigBee is a very attractive technology for implementing low-cost, low-power wireless
control networks requiring high flexibility in node placement. Supported by an underlying
IEEE specification, ZigBee can benefit from an increasingly large ecosystem that is being
built around the standard. Although using the license-free 2.4 GHz band is a strong cata-
lyst for fast and worldwide market deployments, the presence of other wireless technolo-
gies across the same spectrum has risen concerns about potential coexistence issues.
Most of the worries have concentrated on IEEE 802.11 transmitters (commonly desig-
nated as WiFi transmitters in their commercial off-the-shelf versions) since they are now
largely spread in both residential and office environments. The present report aims at as-
sessing this potential risk in an unbiased way through both laboratory and real-
environment experiments. It also attempts to summarize test results collected by other
research groups so as to derive an overall and consensual conclusion on this issue.
Although previous test results seem to have delivered somewhat inconsistent conclu-
sions, a closer look reveals that most of them are on the same line at equivalent experi-
mental conditions (IEEE 802.11b/g mode, power level, traffic type, …). Based on meas-
urements carried out in Schneider Electric’s wireless laboratory and real houses, the fol-
lowing conclusions can be formulated:
• ZigBee operating in a real residential environment is not affected by today’s most
typical WiFi usage patterns, even in the most severe interference conditions
(overlapping frequency channels, real-time video traffic). ZigBee packets may ex-
perience an increased latency under WiFi interference but delivery is not im-
pacted.
• Laboratory experiments show that WiFi could have a significant impact on ZigBee
when increasing WiFi’s power level or duty cycle above what is used or reachable
in today’s applications (file transfer, audio and video streaming). This is especially
true when operating in IEEE 802.11b mode. Better coexistence properties in IEEE
802.11g mode can be explained by less time spent by interfering packets on air.
Schneider Electric’s investigations suggest that WiFi today does not constitute a
threat to satisfactory ZigBee communications in real residential environments.
However, technical evolutions of WiFi technology and possible new application patterns in
the future could in theory have more impact on ZigBee. This leads Schneider Electric to
recommend, as an additional safety net, having the possibility of changing ZigBee’s fre-
quency channel while in operation. This functionality, called Frequency Agility, is provided
by the ZigBee PRO stack specification. We believe that, equipped with that feature, Zig-
Bee-based devices will be able to operate in a reliable and future-proof way.
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1 Introduction
1.1 Background
Well-accepted wireless communication technologies generally operate in frequency bands
that are shared among several users, often using different RF schemes. This is true in
particular for WiFi, Bluetooth, and more recently ZigBee. They all three operate in the
unlicensed 2.4 GHz band, also known as ISM band, which has been key to the develop-
ment of a competitive and innovative market for wireless embedded devices. But, as with
any resource held in common, it is crucial that those technologies coexist peacefully to
allow each user of the band to fulfill its communication goals.
Despite efforts made by standardization bodies to ensure smooth coexistence it may oc-
cur that communication technologies transmitting for instance at very different power
levels interfere with each other. In particular, it has been pointed out that ZigBee could
potentially experience interference from WiFi traffic given that while both protocols can
transmit on the same channel, WiFi transmissions usually occur at much higher power
level.
1.2 Purpose of the Document
This report aims at providing a comprehensive and objective evaluation of ZigBee/WiFi
coexistence. Building on previous studies led by other research groups, it reviews the
main techniques implemented in ZigBee to ensure adequate RF coexistence. Both theo-
retical and practical tests are then carried out in laboratory and residential environments.
Contrary to investigations led by other companies, the present study seeks to assess the
coexistence limits of both technologies in order to formulate ZigBee development rec-
ommendations.
1.3 References
[1] Schneider Electric Internal Report. ZigBee Coexistence with WiFi. February 2006.
[2] G. Thonet and M. Bruel. ZigBee: The Journey Toward Deployment in Industrial Appli-
cations. ST Journal of Research. Vol. 4. No. 1. May 2007.
[3] ZigBee Alliance. ZigBee and Wireless Radio Frequency Coexistence. Document
075026r02. May 2007.
[4] Z-Wave Alliance. WLAN Interference to IEEE 802.15.4. White Paper. March 2007.
[5] Ember Presentation to the 2006 ZigBee Developers Conference. ZigBee / 802.11 Co-
existence – Testing and Recommendations. June 2006.
[6] Freescale Semiconductor Application Note. MC1319x Coexistence. AN2935. July 2005.
[7] A. Sikora. Compatibility of IEEE 802.15.4 (ZigBee) with IEEE 802.11 (WLAN), Blue-
tooth, and Microwave Ovens in 2.4 GHz ISM-Band – Test Report. Steinbeis-Transfer
Center, University of Cooperative Education Lörrach. September 2004.
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1.4 Acronyms
ADSK Asymmetric Digital Subscriber Line
APS Application Sublayer
CFI Call For Interest
CSMA/CA Carrier Sense Multiple Access with Collision Avoidance
CSMA/CD Carrier Sense Multiple Access with Collision Detection
DSP Digital Signal Processor
DSSS Direct Sequence Spread Spectrum
FHSS Frequency Hopping Spread Spectrum
FTP File Transfer Protocol
HDTV High Definition Television
HDV High Definition Video
IC Integrated Circuit
IEEE Institute of Electrical and Electronics Engineers
IP Internet Protocol
ISM Industrial, Scientific and Medical
ITU International Telecommunications Union
JPEG Joint Picture Expert Group
MAC Medium Access Control
MPEG Motion Picture Expert Group
MTU Maximum Transmission Unit
PCM Pulse Code Modulation
PCR Program Clock Reference
PDA Personal Digital Assistant
PER Packet Error Rate
PLC Programmable Logic Controller
PHY Physical
RF Radio Frequency
RTP Real-Time Transport Protocol
UDP User Datagram Protocol
VAD Voice Activity Detection
VoIP Voice over Internet Protocol
WLAN Wireless Local Area Network
