October 2001

Steve Shellhammer, Symbol TechnologiesSlide 1

doc.: IEEE 802.15-01/482r0

Submission

IEEE P802.15 Working Group for Wireless Personal Area NetworksTM

Summary of IEEE 802.15.2WLAN/WPAN Coexistence Mechanisms

October 2001

Steve Shellhammer, Symbol TechnologiesSlide 2

doc.: IEEE 802.15-01/482r0

Submission

Coexistence Mechanisms• Since some WLANs (e.g. IEEE 802.11b

“Wi-Fi”) and WPANs (e.g. IEEE 802.15.1 “Bluetooth”) operate in the same band they interfere with one another.

• A Coexistence Mechanism is a technique to minimize that interference.

• Initial Focus on 802.11b and Bluetooth

October 2001

Steve Shellhammer, Symbol TechnologiesSlide 3

doc.: IEEE 802.15-01/482r0

Submission

Coexistence Mechanisms• Collaborative Mechanisms

– Some form of communication exists between the WLAN and WPAN.

– Use this link to provide fair sharing of medium (i.e. air waves)

• Non-Collaborative Mechanisms– No communication between WLAN and

WPAN exists.– Techniques to minimize the effects of the

mutual interference

October 2001

Steve Shellhammer, Symbol TechnologiesSlide 4

doc.: IEEE 802.15-01/482r0

Submission

Collaborative Coexistence Mechanism

• Intended to be used when 802.11b and Bluetooth are in the same physical unit.

• There are two modes– Alternating Wireless Medium Access (AWMA)– META

• Both are techniques to schedule WLAN and WPAN transmission to avoid interference.

October 2001

Steve Shellhammer, Symbol TechnologiesSlide 5

doc.: IEEE 802.15-01/482r0

Submission

Collaborative Mechanism

• The Collaborative Coexistence Mechanism relies on physical signals between the two radios within a common unit (e.g. laptop).

• These physical signals are used to coordinate timing of the WLAN and WPAN transmissions to avoid interference.

October 2001

Steve Shellhammer, Symbol TechnologiesSlide 6

doc.: IEEE 802.15-01/482r0

Submission

Alternating Wireless Medium Access

• The IEEE 802.11b beacon interval is divided into two subintervals– One subinterval is for WLAN operation– One subinterval is for WPAN operation

October 2001

Steve Shellhammer, Symbol TechnologiesSlide 7

doc.: IEEE 802.15-01/482r0

Submission

Alternating Wireless Medium Access

Time

IEEE 802.11b beacon interval

BT-WLAN boundary

WPAN

WLAN

October 2001

Steve Shellhammer, Symbol TechnologiesSlide 8

doc.: IEEE 802.15-01/482r0

Submission

Alternating Wireless Medium Access

• Since each radio has its own subinterval, both radios will operate properly, with no interference.

• This works even if the two radio are very close to one another, for example, in the same hand-held computer or PDA. The two radios can be separated from one another by only a few centimeters.

October 2001

Steve Shellhammer, Symbol TechnologiesSlide 9

doc.: IEEE 802.15-01/482r0

Submission

Alternating Wireless Medium Access

• Only the Bluetooth radio in the portable unit needs to be modified. That Bluetooth radio needs to be the master of the Piconet.

• Standard Bluetooth-enabled devices work with this approach. Since they are slaves they only speak when spoken to. They naturally stay within Bluetooth interval.

October 2001

Steve Shellhammer, Symbol TechnologiesSlide 10

doc.: IEEE 802.15-01/482r0

Submission

Alternating Wireless Medium Access

• This approach solves interference from nearby 802.11 and Bluetooth devices, since all the systems are synchronized.– During the 802.11 interval, no Bluetooth

devices transmit.– During Bluetooth interval, no 802.11

devices transmit.

October 2001

Steve Shellhammer, Symbol TechnologiesSlide 11

doc.: IEEE 802.15-01/482r0

Submission

META

• The META acts as a “Traffic Cop” between the WLAN and WPAN Medium Access Control (MAC) layers.

• META controls which wireless systems has access to the medium on a packet-by-packet basis.

October 2001

Steve Shellhammer, Symbol TechnologiesSlide 12

doc.: IEEE 802.15-01/482r0

Submission

META• Dynamic algorithm schedules traffic• Knowledge of time-frequency collisions is key

– Simultaneous transmission or reception allowed– Tx simultaneous with Rx allowed if not in-band (requires good LNA)– Critical for SCO operation-WLAN can work around in-band collisions

• This figure does not show polls/nulls, which often dominates Bluetooth traffic

Time

IEEE 802.11b beacon interval

(Packet widths are not to scale…)

WPAN

WLAN

October 2001

Steve Shellhammer, Symbol TechnologiesSlide 13

doc.: IEEE 802.15-01/482r0

Submission

META Block Diagram

METAEngine

FrequencyCollision

Map

WLAN Stack

WLAN FIFO2

WLAN FIFO1

WLANModem

WLANModem

DecisionLogic

DecisionLogic

Bluetooth Stack

Backoff &CCA

TxEvent

Enable

Enable

SwitchMatrix

Bluetooth FIFO

October 2001

Steve Shellhammer, Symbol TechnologiesSlide 14

doc.: IEEE 802.15-01/482r0

Submission

When to use AWMA and when to use META• Use AWMA

– When there is a high density of mobile users.

– Because AWMA eliminates all WLAN/WPAN interference, even nearby users

• Use META– When there is lower density of users– Better overall throughput, if limited nearby

interference

October 2001

Steve Shellhammer, Symbol TechnologiesSlide 15

doc.: IEEE 802.15-01/482r0

Submission

Non-Collaborative Coexistence Mechanisms

• Two approaches are being Standardized:

1. Bluetooth Packet Selection and Scheduling

2. Bluetooth Adaptive Frequency Hopping

October 2001

Steve Shellhammer, Symbol TechnologiesSlide 16

doc.: IEEE 802.15-01/482r0

Submission

Bluetooth Packet Selection & Scheduling• The this is a non-collaborative

mechanism in which the Bluetooth devices independently detect the presence of 802.11b and determine which channels are utilized by 802.11b.

• Then the Bluetooth piconet does not transmit when it hops into one of the channel occupied by 802.11b.

October 2001

Steve Shellhammer, Symbol TechnologiesSlide 17

doc.: IEEE 802.15-01/482r0

Submission

• Currently allowed under FCC rules, for both low-power and high-power Bluetooth devices

• This prevents Bluetooth from interfering with frequency-static systems like 802.11b

• This does not improve the Bluetooth performance.

Bluetooth Packet Selection & Scheduling

October 2001

Steve Shellhammer, Symbol TechnologiesSlide 18

doc.: IEEE 802.15-01/482r0

Submission

Adaptive Frequency Hopping• Just like the Bluetooth Packet Scheduling

technique, the this is a non-collaborative mechanism in which the Bluetooth devices independently detect the presence of 802.11b and determine which channels are utilized by 802.11b.

• In AFH the Bluetooth piconet remaps its hopping sequence to “hop around” the frequency band occupied by 802.11b

October 2001

Steve Shellhammer, Symbol TechnologiesSlide 19

doc.: IEEE 802.15-01/482r0

Submission

FCC NPRM

• Under Current FCC ruled Adaptive Frequency Hopping is only allowed for low-power (< 1 mw) Bluetooth devices.

• In May 2001 the FCC issued a Notice of Proposed Rule Making.

• If this Rule Making issues then Adaptive Frequency Hopping will be allowed under high-power Bluetooth devices.

October 2001

Steve Shellhammer, Symbol TechnologiesSlide 20

doc.: IEEE 802.15-01/482r0

Submission

Adaptive Frequency Hopping• This allows Bluetooth and 802.11b to

share the ISM band by minimizing interference.

• Both 802.11b and Bluetooth see improved performance.

• Requires modifications to Bluetooth Specification.

• Currently working with SIG to obtain specification modifications.

October 2001

Steve Shellhammer, Symbol TechnologiesSlide 21

doc.: IEEE 802.15-01/482r0

Submission

Adaptive Frequency Hopping• AFH consists of three components• Channel classification techniques to

determine which channels are “good” and which are “bad”

• Link Manager Commands to exchange information about “Good” and “Bad” channels

• Methods of remapping bad channels to good channels.

October 2001

Steve Shellhammer, Symbol TechnologiesSlide 22

doc.: IEEE 802.15-01/482r0

Submission

Status

• The Coexistence Mechanisms are currently being standardized in the Draft IEEE 802.15.2 Recommended Practice.