1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)
Submission Title: [QoS Support in Wireless BANs]
Date Submitted: [November, 2008]
Source: [Feng Shu and Guido Dolmans]
Company: [Holst Centre / IMEC-NL]
Address [High Tech Campus 31, Eindhoven, the Netherlands]
Voice:[ ], FAX: [ ],
[{feng.shu,
Abstract: [Presentation for QoS support in wireless BANs.]
Purpose: [To discuss QoS support issues for BAN]
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2. QoS Support in Wireless BANs
Feng Shu and Guido Dolmans
IMEC-NL
November, 2008, Dallas

3. QoS support in wireless BANs
Outline
QoS support in wireless BANs
QoS differentiation – gives priority to critical nodes (two examples based on CSMA-CA protocol)
latency differentiation scheme (LDS)
reliability differentiation scheme (RDS)
Simulation and evaluation

4. QoS support in wireless BANs
As technical requirement document (TRD) specifies, major QoS for wireless BANs include
Latency
Reliability
When critical & non-critical app’s co-exist, give priorities to critical ones
QoS differentiation mechanisms needed
Reliability def.: BER, packet loss, packet success rate
Critical
Non-critical
Reliability
Latency
Two examples of QoS differentiation based on CSMA-CA

5. Traffic Class Definition
Type  : traffic has stricter QoS of latency and/or reliability
usually less amount of traffic
treated with higher priority
Type  : traffic has less strict QoS of latency and/or reliability
usually more amount of traffic
treated with lower priority

6. Energy Conserving CSMA-CA Protocol
W0 = 8
W1 = 16 4 3 2 1 11 10 9 8 7 6 5 4 3 2 1
packet
transmission
Type  /  nodes:
W0 / W0 : initial backoff windows
M / M : maximum # of attempts in a single backoff process
R / R : maximum # of collisions before a packet is aborted

7. Latency Differentiation Scheme (LDS)
LDS – prioritize by adjusting backoff window sizes
Type  nodes start with smaller initial backoff window
W0 ≤ W0
In case of collision, type  nodes restart with maximum backoff window Wmax to reduce contention level

8. Reliability Differentiation Scheme (RDS)
RDS – prioritize by giving more transmission attempts
Type  nodes are given more backoff attempts when channel is sensed busy
M > M
In case of collisions, type  nodes are given more opportunities of retransmissions
R > R

9. Performance Evaluation
Implemented a C++ based simulator
PHY layer: IEEE , 2.4 GHz
Node generate packets based on Poisson arrivals, let  indicate the average packet arrival rate
packet length L = 60 bytes, ie, 6 backoff slots
# of type  nodes: three
# of type  nodes: variable
Backoff parameters are taken from default values of standard
Simulations run 100,000 time slots, and each point is averaged over 10 independent simulation runs

10. Latency – LDS When initial backoff window is smaller, latency is lower
 = 28.5
Critical nodes have much lower average latency
When initial backoff window is smaller, latency is lower

11. Packet Success Rate - LDS
W0 = 16
 = 28.5
LDS does not give priority to critical nodes for transmission reliability

12. Packet Success Rate – RDS & LDS
M = 8, M = 4
R = 6, R = 3
W0=4, W0 =16
 = 12.5
When LDS & RDS implemented, reliability of critical nodes is increased

13. Latency – RDS & LDS M = 8, M = 4 R = 6, R = 3 W0=4, W0 =16
 = 12.5
Critical nodes can have larger latency when traffic load gets heavy
This reveals an intrinsic trade-off between latency & reliability

14. Conclusions Major QoS of wireless BANs are latency & reliability
QoS differentiation needed when critical & non-critical app’s competing for resources
Latency differentiation scheme (LDS)
Reliability differentiation scheme (RDS)
It reveals that an intrinsic trade-off exists between requirements such as latency & reliability