Performance Evaluation of Multiple IEEE 802.11b WLAN Stations in the Presence of Bluetooth Radio

Overview

 Evaluation of the performance of IEEE 802.11b WLANs with Bluetooth devices.

 Evaluation of multiple WLANs and one Access Point in the presence of Bluetooth.

 Competition between Bluetooth and WLAN stations can cause degradation of performance.

Modeling of the IEEE 802.11b MAC

Key factors that will impact system performance  Presence of hidden stations.

 Use of carrier sensing.

 Decentralized nature of multiple access methods.

Modeling of the IEEE 802.11b MAC

Assumptions  Ignore effects of framer error due to bit errors from channel noise  There is limited station mobility

Successful Transmissions

 No station in the Rx’s capture area that is not hidden from the Rx, transmits in the time interval (

t

β,

t

+ β)

Successful Transmission

 No station in the Tx’s capture area that is not hidden from the Tx, receives successfully a data frame whose transmission was initiated in the time interval (

t

β,

t

+ β)

Successful Transmission

 No station in

H

ij(

d

’ij) transmits during the interval (

t

,

t

+

l

)

Successful Transmission

 No station in

H

ji(

d

’ij) transmits in the interval (

t

+

l

+ DIFS,

t

+

l

+ max{DIFS, SIFS +

l

ack}).

Renews Intervals [ T

s

]

The average time the channel is sensed busy because of successful transmission.

Basic Access Method [bs] With RTS/CTS [rc]

Time During Collision [ T

c

]

The average time the channel is sensed busy by each station during collision.

Basic Access Method [bs] With RTS/CTS [rc]

Throughput of 802.11

Interference Modeling

 Propagation Model  2 Parts   Line of Sight (LOS) for the first 8 meters Path Loss > 8 meters

Higher Packet Reception w/ Time Coincidence

By using multiple time slot packets in Bluetooth, you  Reduce the Bluetooth hop rate  Increase throughput.

= Reduced transmission time and results in longer gaps in Bluetooth interference, which increases the successful reception of WLAN packets

Higher Packet Reception w/ Frequency Coincidence

 802.11 can provide reliable service in the presence of narrow-band interferer such as Bluetooth transmitters.

 This will work if the Signal-to-Interference (SIR) is 10 greater than 10 dB.

Collisions

Probability of collision with “n” slot overlap The overall probability of collision Probability of interference of m Piconets

Important Points

 With a light and heavy Bluetooth user scenario, the throughput of multiple WLAN STAs systems will degrade no matter what the data rate.

 Hidden Stations, Carrier Sensing, & a Decentralized nature of multiple access methods impact a systems performance.

 As long as the IEEE 802.11(b) receiver gets a desired signal that is 10dB stronger than the in-channel interference tone, the activity of a BT device does not harm.

 For a Bluetooth transmission to disrupt an 802.11b packet, there must be an overlap in time and in frequency.

Appendix

                

Ai(d):

a set of stations in a circular area of radius

d

around station

i

.

Xi:

a location of station

i

Dij: α:

a distance between station i and station

j

capture parameter, α ≥ 1

d

’ij:

α

d

ij

Hj(d):

a set of stations that are hidden from station

j

and are in a circle of radius

d

around

j

Hij(d):

a set of stations that are hidden from station

i

but not from station

j

in a circle of radius

d

around station

j

β:

propagation delay including carrier sensing delay (in wireless networks the propagation delay is dominated by the carrier sensing delay given the small diameter of BSSs, i.e., less than 100m)

l :

the length of a pay load – this does not include PHY and MAC header. l “type” is the length of a “type” frame.