IMA Wireless Workshop 6/05 – 1 Wireless Local Area Network Simulation Abstract: We describe a software system that simulates wireless local area networks supporting heterogeneous services and multiple protocols. We present applications of this system in three areas: analysis of voice capacity, maximization of data throughput while protecting voice quality of service, and the design and evaluation of scheduling algorithms in a polling-based system. Martin Eiger, Moncef Elaoud, David Famolari, Raquel Morera Telcordia Technologies Piscataway, NJ
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IMA Wireless Workshop 6/05 – 1 Wireless Local Area Network Simulation Abstract: We describe a software system that simulates wireless local area networks.
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IMA Wireless Workshop 6/05 – 1
Wireless Local Area Network Simulation
Abstract: We describe a software system that simulates wireless local area networks supporting heterogeneous services and multiple protocols. We present applications of this system in three areas: analysis of voice capacity, maximization of data throughput while protecting voice quality of service, and the design and evaluation of scheduling algorithms in a polling-based system.
Martin Eiger, Moncef Elaoud, David Famolari, Raquel Morera
Telcordia Technologies
Piscataway, NJ
IMA Wireless Workshop 6/05 – 2
Overview
Multi-year collaborationModel and analyze many configurations
–Existing standards–Possible future standards
Several IEEE 802.11 variations–One queue/separate queues–Contention-based/contention-free
C/UNIX with CSIM simulation package
IMA Wireless Workshop 6/05 – 3
Wireless Local Area Network
Heterogeneous services Shared transmission medium
access point
IMA Wireless Workshop 6/05 – 4
Listen-Before-Talk Protocol
Transmit only after idle medium for appropriate IFS (interframe space) interval
Random backoff after every transmission–Pick random integer, decrement periodically, transmit when counter reaches 0
–Suspend countdown on busy medium, resume after idle IFS
–Promotes fairness Increase random backoff range after collision; restore on success
IMA Wireless Workshop 6/05 – 5
Simulator “Knobs”
Time to simulate802.11 standardNumber of nodesMobilityTransmission ratesService mixPacket sizesPacket arrival ratesDelay thresholds
Interframe spacingContention windows
Queue limitsScheduling policyDesired output
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IMA Wireless Workshop 6/05 – 6
Voice Capacity (IEEE 802.11b)
Conclusions: QoS degrades
for all users concurrently
Packetization interval is key determinant of max capacity (reason: fixed overhead per packet)
0
10
20
30
40
50
60
1 6 11 16 21 26 31 36 41 46 51 56
Active Voice Users
Supp
orte
d V
oice
Use
rs
10ms 20ms 30ms 40ms
50ms 60ms 70ms 80ms
packet-ization
intervals:
IMA Wireless Workshop 6/05 – 7
Multiple Queues
Several queues at each node
Each queue senses medium, backs off independently
Motivation: set each queue’s interframe space and contention window parameters separately to assure quality of service
IMA Wireless Workshop 6/05 – 8
voiceAIFS CW
voice UDP voice UDP
1 50 70 1 8
2 50 90 1 8
3 30 90 1 8
4 30 30 1 16
5 30 30 1 16
6 30 50 1 16
7 30 110 1 8
8 30 70 1 16
9 30 110 1 16
10 30 70 1 32
Voice and Data
Conclusion: Failing to adapt AIFS and contention window values can cost ~20% of data throughput
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
1 2 3 4 5 6 7 8 9 10
voice supported
UD
P t
hrou
ghpu
t (M
b/s)
max throughputfixed AIFS and CW
IMA Wireless Workshop 6/05 – 9
Contention-Free Scheduling
Access point grants Transmission Opportunities
Uplink Downlinkpoll
pkt1 … pktn
block ack req
block ack
pkt1 … pktn
block ack req
block ack
The big question: Scheduling
IMA Wireless Workshop 6/05 – 10
Scheduling Problem
Inputs–Traffic stream specifications (packet size, average packet arrival rate, …)