Link Adaptations in Wireless LAN for Energy Minimization and Service Differentation

1. Link Adaptations in Wireless LAN for Energy Minimization and Service Differentation Naomi Ramos Debashis Panigrahi Sujit Dey Embedded System Design Automation and Test Lab http://esdat.ucsd.edu

2. Introduction Objectives: To enable adaptability within wireless protocol stacks to adjust to current conditions, application, and node requirements Current Research Progress: MAY 2002: Identified and evaluated effect of some adaptable parameters in IEEE 802.11b MAC Layer NOV 2002: Designed dynamic adaptation policies on fragmentation threshold parameter MAY 2003: Continued work on dynamic adaptation policies for energy-efficiency using link layer parameters. Began investigation of dynamic link adaptations for Quality of Service (QoS) differentiation.

3. Outline Presentation Outline: Motivation & Background Topics to be covered Energy-Efficient Link Adaptations in IEEE 802.11b Quality of Service (QoS) Link Adaptations in IEEE 802.11b QoS Link Adaptation in IEEE 802.11e Conclusions & Future Work

4. Wireless LAN: Usage & Challenges

5. Research Approach Identify adaptable parameters available in IEEE 802.11 Evaluate effects of parameters on energy and throughput Develop dynamic runtime adaptation policies

6. IEEE 802.11 Background Fragmentation Threshold - Threshold used to determine whether higher level packet is partitioned into smaller units Retry Limit - The maximum number of retransmissions allowed for each transmitted packet Transmission Power - Power level used to send data packets. Backoff Period - Determines the waiting period prior to transmission BckPeriod = rand(0, CWi ) * SlotDuration where CWi = 2 i * CWmin

7. Energy-Efficient Adaptations: Fragmentation Analysis Goal: To save energy by choosing appropriate fragmentation threshold Analysis: Energy = No of Fragments * No of Attempts * Energy per Attempt Given the following variables: packet size (X), fragmentation threshold (F), header size (H), data rate (DR), transmit power (Ptx), and bit error rate (BER)

8. Energy-Efficient Adaptations: Fragmentation Policy

9. Energy-Efficient Adaptation: Retry Limit Goal: To save energy by choosing appropriate retry limit Retry Limit Impact: Increases the probability of a packet being received successfully Leads to energy savings by preventing wasteful retransmissions in extremely bad channel conditions Analysis: Given a packet X, a current value of BER, and a tolerable packet loss rate of Pmax,, the average number of retransmissions required is given by the following

10. Energy-Efficient Adaptation: Transmission Power Goal: To save energy by choosing appropriate transmission power Transmission Power Impact: Improves signal strength and reduces BER Reduces % of retransmission and packet loss Increases total energy consumption Transmission Power Adaptation: Increase transmission power when experiencing numerous packet drops Decrease transmission power when experiencing periods without packet drops

11. Energy-Efficient Adaptations: OPNET Setup Network Infrastructure Mode of IEEE 802.11 Data Rate: 11 Mb/s Physical Layer: DSSS Channel Model Opnet Channel Model Fixed Channel Model Gilbert-Elliot Model Energy Model Introduced into OPNET simulation model1 Transmit : {1.25, 1.5, 1.65, 1.75, 1.9} W * packet tx time Receive : 1 W * packet rx time

12. Energy-Efficient Adaptations: Results

13. Energy-Efficient Adaptations: Results

14. QoS Adaptations: Backoff Factor & Offset Description: Determines the waiting period prior to transmission BckPeriod = rand(0, CWi ) * SlotDuration where CWi = 2 i * CWmin Two parameters Backoff Factor: the factor by which the CW increases Backoff Offset: a fixed additional waiting period BckPeriod = BckOffset + rand(0, CWi ) * SlotDuration where CWi = (BckFactor) i * CWmin Backoff Period Impact: Can insure prioritization by setting the offset value Can prioritize at the packet level during retransmission Goals: To achieve prioritization by setting the backoff offset and the backoff factor

15. QoS Adaptations: Backoff Policy & Results

16. QoS Adaptations: IEEE 802.11e Service Differentiation Efforts - IEEE 802.11e Evolving standard to provide service differentiation Mechanism for static prioritization between different traffic classes (tc), e.g. video, voice, ftp Enhanced Distributed Coordination Function Arbitration Inter Frame Spacing (AIFS) Contention Window (CWmin) Persistence Factor (PF)

17. QoS Adaptations: Network-Aware IEEE 802.11e IEEE 802.11e Limitations Static class-based priority inefficient to support time-varying application requirements Class based prioritization may not provide required throughput in presence of varying channel conditions Example

18. QoS Adaptations: Network-Aware IEEE 802.11e Goal: To provide and maintain service differentiation in the presence of channel conditions Adaptable Parameters: Persistence Factor, Fragmentation Threshold, Defer Count

19. QoS Adaptations: Network-Aware IEEE 802.11e

20. Conclusions & Future Work Investigated available parameters in IEEE 802.11b Data Link Layer Analyzed effects of parameters on energy and service differentiation Developed dynamic adaptation policies Showed that significant energy savings and prioritization can be achieved through a dynamic link layer Evaluated scope of network-aware service differentiation in IEEE 802.11e Further investigations of parameters available in IEEE 802.11b/e Investigate the implications of adaptivity in ad-hoc network Develop methodology for mapping applications to adaptation policies Implement the framework with Linux machines