how other srw affect your wlan performance abdullah a. al-asmari saudi aramco/ it copyright © saudi...
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How other SRW affect your WLAN Performance
Abdullah A. Al-AsmariSaudi Aramco/ ITCopyright © Saudi Aramco 2005
2Copyright © Saudi Aramco 2005.
Agenda Wireless Landscape
Short Range Wireless WLAN & Bluetooth
WLAN & Bluetooth coexistence Solving WLAN & Bluetooth coexistence
Conclusion
3Copyright © Saudi Aramco 2005.
Wireless Landscape
Data Rate (Mbps)
Ran
ge
ZigBeeUWBWPAN
10M
WLAN30M
WMAN(Fixed)
Cellular(Mobile)
WiFi
IEEE 802.16
2G
0.01 0.1 1 10 100 1000
Bluetooth
3G
Source: WiMedia
RFID
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SRW Short Range Wireless refers to a group of technologies that enable
wireless data communication across distances of between one and a few hundred meters
WLAN, Bluetooth, UWB, ZigBee , and RFID
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WLAN 802.11b
Standard for 2.4GHz ISM band (80 MHz) Direct Sequence Spread Spectrum (DSSS) 11 Mbps, 500 ft range
802.11a Standard for 5GHz U-NII band (300 MHz) OFDM 54 Mbps
802.11g Standard in 2.4 GHz OFDM up to 54 Mbps
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Bluetooth Cable replacement RF technology (low cost) Short range (10m, to 100m) 2.4 GHz band (crowded) One Data (700 Kbps) and three voice channels Widely supported by telecommunications PC and consumer electronics companies Few applications beyond cable replacement
2400 MHz 2483.5 MHz1 MHz
79 hopping channels in 83.5 MHz
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UWB UWB a broad technology solution for creating high-speed, low-cost
and low-power WPANs Excellent ranging capability Very high data rates possible
500 Mbps at ~10 feet under current regulations 7.5 Ghz of “free spectrum” in the U.S.
FCC legalized UWB for commercial use Spectrum allocation overlays existing users, but its allowed power level
is very low to minimize interference
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ZigBee Promoted by the ZigBee Alliance Very low power, low rate, and short distance transmission standard
for wireless sensors network Operates in 868/918 MHz, and 2.4GHz bands using IEEE 802.15.4 Low power means low cost and very long (up to years!) battery life
making “place and forget” device applications feasible
BAND COVERAGE DATA RATE # OF CHANNEL(S)
2.4 GHz ISM Worldwide 250 kbps 16
868 MHz Europe 20 kbps 1
915 MHz ISM Americas 40 kbps 10
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RFID RADIO FREQUENCY IDENTIFICATION uses a semiconductor
(micro-chip) in a tag or label to transmit stored data when the tag or label is exposed to radio waves of the correct frequency
Very short range (10 meters) sensor technology used to supplement bar-code reader type applications
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Wireless Bands
Frequency (GHz)
128k 13.56M 1 2 3 4 5 6 7 8 9 10 11868M
915M
RFIDZigBeeBluetooth802.11b/g802.11aUWB
U-NII Band
ISM
Ban
d
ISM
Ban
d
2.4G
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Frequency interference
3
2
1
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Frequency interference
2400 MHz2483.5 MHz
Wi-Fi channel (802.11b/g)
1600 hops/s
Bluetooth channel
RFI
D
Zig
Bee
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WLAN & Bluetooth Two of the most popular wireless standards – IEEE 802.11b/g
wireless LAN (WLAN) and Bluetooth – absolutely must play together because they are increasingly co-located in the same handheld device
BLUETOOTH AND WLAN ARE ON A COLLISION COURSE—NOT IN THE MARKET, BUT IN THE AIRWAVES
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WLAN & Bluetooth Marriage of these two popular technologies is quickly becoming a
problem because of four interrelated facts: IEEE 802.11b/g & Bluetooth use the same 2.4 GHz ISM frequency band
(although they use different access mechanisms) Standards bodies did not fully anticipate the range of scenarios in which
WLAN and Bluetooth would compete for the same spectrum. As a result, they did not include comprehensive, robust, and cooperative mechanisms in their respective standards to mitigate interference
Intense bandwidth utilization when Bluetooth and WLAN transceivers are simultaneously in use can easily overwhelm the error correction mechanisms implemented in the two standards to manage typical interference scenarios
Co-location (the presence of Bluetooth and WLAN in the same handheld device) adds the problem of desensitized receivers to the basic spectrum access issues
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WLAN “802.11g” vs. “802.11a” Pros of 802.11a - fastest maximum speed; supports more
simultaneous users; regulated frequencies prevent signal interference from other devices
Cons of 802.11a - highest cost; shorter range signal that is more easily obstructed
Pros of 802.11g - fastest maximum speed; supports more simultaneous users; signal range is best and is not easily obstructed
Cons of 802.11g - appliances may interfere on the unregulated signal frequency
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WLAN “802.11g” vs. “802.11a” The 2.4 GHz band and the power outputs specified for
802.11b/802.11g have more worldwide acceptability, which may make these networks a better choice for global deployments
Current state of PDAs cannot make use of the 802.11a station adapters due to bus limitations on the PDAs
802.11g is the most promising option to consider (2.4GHz)
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WLAN 802.11b/g It employs three specific, non-overlapping, 22-MHz wide channels.
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Bluetooth Bluetooth wireless technology provides cable-free connections to a
wide range of computing and telecommunication devices, including notebook computers, mobile phones and personal digital assistants (PDAs)
Bluetooth can support up to three synchronous voice channels, one asynchronous data channel or a channel that simultaneously carries asynchronous data and synchronous voice
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Bluetooth The Bluetooth radio chip separates the 2.4GHz frequency band into
79 hops, 1MHz apart, starting with 2.402 and ending with 2.480 Randomly hop at a rate up to 1,600 hops per second The gross data rate of Bluetooth is 1Mbps
2400 MHz 2483.5 MHzWi-Fi channel (802.11b)
1600 hops/s
Bluetooth channel
30 dBm
-80 dBm
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Bluetooth When a Bluetooth-enabled device is turned on, it sends omni-
directional radio signals asking for a response from any units with an address in a particular range
A Piconet is formed if another device within the range responds Any unit within a Piconet can establish a connection with another
Piconet to form a Scatternet When a Piconet is established, the initiating unit acts as a master
and the others act as slaves for the duration of the connection A Piconet consists of one master and up to seven slave units
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Bluetooth The Bluetooth Special Interest Group (SIG) commissioned Millward
Brown Group to conduct a study on consumer awareness, attitude and usage of Bluetooth wireless technology compared with other wireless technologies. The study polled 1,300 consumers from ages 18 to 70 in the US, UK and Japan during the autumn of 2003 and again in the autumn of 2004
It is encouraging to see how consumer awareness mirrors the rise in volumes of Bluetooth products over the last year
Select which technology allows mobile devices to connect wirelessly?
Bluetooth USA UK Japan
2003 22 47 43
2004 41 77 61www.touchbriefings.com
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Bluetooth
0
50
100
150
200
250
300
350
400
Mil
lio
ns
of
Un
its
2002 2003 2004 2005
Year
Wi-Fi
BT
Source: In-Stat/Philips
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WLAN & Bluetooth Coexistence Interference occurs when a Bluetooth and a WLAN device are in
close proximity and simultaneously transmit and receive wireless signals
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WLAN & Bluetooth Coexistence The two technologies use different methods for signal transmission:
carrier sense multiple access (CSMA) and frequency hopping spread spectrum
CSMA is used by an 802.11b/g transceiver to listen for a clear channel before transmitting a signal that is approximately 20MHz wide and typically occupies one to three possible non-overlapping channels spaced 25MHz apart
A simple calculation demonstrates that a Bluetooth transmitter will output a signal that collides with an 802.11b/g signal about 25 percent of the time
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WLAN & Bluetooth Coexistence Distance between Wi-Fi and Bluetooth tends to prevent them from
interfering, but in a PDA this is not possible. When Bluetooth and Wi-Fi are put into the same device, the transmitted signals from one network appear on the receiver of the other making them interfere with the each other (Collocation Interference)
If the traffic in the cell is light enough, the problem can be corrected within the existing standards. Both standards define error correction protocols that basically require the system to fall back and retransmit the data
If, however, traffic in the cell is heavy, retransmission only makes matters worse by creating even more traffic. Valid data throughput can drop dramatically
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Performance with WLAN & Bluetooth Coexistence In the case of WiFi, a separation of 10 m results in minimal impact
for short-range WiFi use, with increasing impact over longer ranges A separation of only 2 cm, has a much more profound impact. In
that situation, Bluetooth can shut down WiFi for all but short-range use
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Performance with WLAN & Bluetooth Coexistence In the case of Bluetooth, the effect is different. Wi-Fi has minimal
impact on Bluetooth when separated by 10 m, regardless of range A 2 cm separation, drastically reduces Bluetooth throughput even
for short ranges and quickly shuts it down with increasing range
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Solving WLAN & Bluetooth Coexistence The IEEE 802.15.2 recommended practices. The mechanisms fall
into two categories: collaborative and non-collaborative Non-collaborative mechanisms require that Bluetooth or WLAN take
independent means to avoid interference: Adaptive Frequency Hopping (AFH) Adaptive Packet Selection And Scheduling (APSS)
Collaborative mechanisms require that Bluetooth and WLAN exchange information when accessing the medium: Packet Traffic Arbitration (PTA) Alternating Wireless Medium Access (AWMA) Deterministic Spectral Excision (DSE)
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Adaptive Frequency Hopping (AFH) Bluetooth 1.2 specification includes Adaptive Frequency Hopping
(AFH) to help Bluetooth devices find and avoid interference Using AFH, a channel can be classified as good or bad, so that bad
channels are avoided and replaced in the hopping sequence by pseudo-randomly selecting out of the remaining good channels
Once a Bluetooth device determines that a WLAN device is operating within the 2.4 GHz band, the frequency hopping channels that overlap are designated as bad and avoided
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Adaptive Frequency Hopping (AFH) Bluetooth 1.2 can reduce its hopping sequence from 79 1MHz bands
to as few as 15 The throughput of the Bluetooth link using AFH is at 100% at a
distance of 2 m. When their distance is closer than 0.5 m, the Bluetooth throughput - even using AFH – decreases
AFH as a standalone technique is insufficient when Bluetooth and 802.11 devices are co-located in the same design
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Adaptive Packet Selection And Scheduling (APSS) Bluetooth provides a wide range of packet types to select from, with
various payload lengths and forward error correction (FEC) options Using shorter packets, for instance, reduces the amount of data
needed to be present when interference occurs and can actually improve throughput compared to larger packets
Dropping the use of FEC when a Wi-Fi system is the cause of interference can also help
Developers can implement the APSS technique predominantly in the MAC layer, while keeping the hardware structure virtually unchanged
APSS is an inappropriate technique for Bluetooth voice applications
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Packet Traffic Arbitration (PTA) The PTA technique uses a control entity that receives per-
transmission transmit requests from each network stack and issues transmission-confirmation signals to the stacks to indicate whether the transmission can proceed
Does not require that either network device be a master device The PTA controller can simply deny any requests that would result
in a collision Requires a number of status signals from the two wireless devices The controller needs to know the traffic priority of each packet It needs to know the Bluetooth frequency in use to determine
whether a collision is likely Requires at least two additional wires to communicate Designers can implement the approach only when the hardware
designs of the two wireless chips are compatible
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Alternating Wireless Medium Access (AWMA) AWMA is a simple procedure that divides the time interval for
transmission and reception into a Bluetooth interval and an 802.11 interval
For this technique to work, the WLAN and Bluetooth devices must be connected, implying that they are collocated in the same physical unit
In addition, all nodes in the WLAN must connect to the same access point so that they are synchronized
The Bluetooth device must be in its master mode The slave device can transmit only if it receives permission from the
master This mechanism has the substantial disadvantage of requiring in-
field upgrades to all access points already in use
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Deterministic Spectral Excision (DSE) DSE starts from the perspective that Bluetooth be considered a
narrowband interferer for the 22 MHz wide 802.11b/g signal It puts a null in the 802.11b/g’s receiver at the frequency of the
Bluetooth signal the 802.11b/g receiver needs to know the frequency hopping pattern
as well as the timing of the Bluetooth transmitter This additional signal processing adds significant complexity to
existing WLAN receivers and does not solve the collocation issue
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Other Practices AIM (adaptive-interference management); control the direction of
the antennas in use Inter-Digital, an RF-component company, has developed AIM (adaptive-
interference management) technology that can enable Wi-Fi networks to adapt their operating frequencies in response to interference
The company also offers an AIM antenna that uses beam forming to create a directional antenna that has a strong null in one direction which allows the system to switch among omni-directional and two opposite- pointing directional antennas to find the pattern that minimizes interference
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TI coexistence solution TI has developed a coexistence solution for simultaneous
functionality of 802.11b/g and Bluetooth in small form factors, including cell phones, laptop computers, PDAs, web tablets and other types of mobile terminals
It provides intelligent and seamless coordination between TI’s WLAN and Bluetooth technologies at MAC layer
No RF isolation is needed between the 802.11 and Bluetooth antennas
Takes advantage of the general purpose coexistence interface BUS connection between TI’s 802.11 MAC processors and TI’s advanced Bluetooth system on-a-chip
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TI coexistence solution Software monitors WLAN and Bluetooth traffic patterns and, when
both 802.11 and Bluetooth require bandwidth, it uses multiplexing techniques to allocate the bandwidth for simultaneous functions
At any time, all of the available bandwidth can be dedicated to either 802.11 or Bluetooth, as long as one or the other is idle
The coexistence solution can intelligently set different priorities depending on the time-sensitive nature of the communication
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Conclusion 2.4GHz is a crowded band All wireless technologies that reside in 2.4GHz can co-exist without
interference except with Bluetooth presence RFID and ZigBee occupying very narrow bandwidth which allow
them to co-exist with 802.11b/g without interference Since Bluetooth using Frequency Hopping scheme, it will interfere
with any occupying wireless at 2.4GHz band Bluetooth and Wi-Fi must coexist The techniques that designers can apply depend on the chip sets in
use, but the greatest flexibility comes from devices that can coordinate their activities