How other SRW affect your WLAN Performance Abdullah A. Al-Asmari Saudi Aramco/ IT Copyright © Saudi Aramco 2005.

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


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


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


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


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


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


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


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


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


Frequency interference

3

2

1


Frequency interference

2400 MHz2483.5 MHz

Wi-Fi channel (802.11b/g)

1600 hops/s

Bluetooth channel

RFI

D

Zig

Bee


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


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


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


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)


WLAN 802.11b/g It employs three specific, non-overlapping, 22-MHz wide channels.


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


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


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


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


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


WLAN & Bluetooth Coexistence Interference occurs when a Bluetooth and a WLAN device are in

close proximity and simultaneously transmit and receive wireless signals


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


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


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


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


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)


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


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


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


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


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


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


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


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


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


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

Q&A

[email protected]

How other SRW affect your WLAN Performance Abdullah A. Al-Asmari Saudi Aramco/ IT Copyright © Saudi Aramco 2005.

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