1 Energy Efficient Channel Access Scheduling For Power Constrained Networks Venkatesh Rajendran J.J. Garcia-Luna-Aceves Katia Obrackzka Dept. of Computer Engineering University of California Santa Cruz, CA Wireless Personal Multimedia Communication (WPMC) October , 2002

2 Outline Introduction Introduction DEANA DEANA Energy model Energy model Analysis Analysis Conclusion Conclusion

3 Introduction Power-constrained networks Energy-aware scheduling Energy-aware scheduling

4 Energy-aware scheduling Idle listening : Idle listening : a node is in receive mode even though it is not scheduled to receive or transmit any data.

5 DEANA (Distributed Energy Aware Node Activation) Using node activation to schedule conflict free transmissions. A TDMA-based MAC protocol Neighborhood-aware Contention Resolution (NCR) Node Activation Multiple Access (NAMA)

6 DEANA (Cont.) Using the Neighborhood-aware Contention Resolution (NCR) mechanism for collision-free channel access Selecting the state of the radio transceiver based on three different node states, namely transmitter, receiver, or idle in order to conserve energy.

7 NCR Avoid unintentional collisions. Fair sharing of network bandwidth for each node, so as to avoid the resource starvation problem present in contention-based schemes. Allow constant bandwidth utilization, even under heavy traffic load, so as to keep network data transmission live at all times.

8 Collision types

9 Time division structure for NAMA

10 NAMA`s Signal Format

11 NAMA`s Data Format

12 Time division structure for DEANA Time is divided into cycles of scheduled access and random access. The scheduled access period is used for data transmission using the scheme described above and The random access period is used for transmission of small packets of signaling information containing neighbor information.

13 Time division structure for DEANA (Cont.)

14 Rules of energy conservation heuristics If the winner of the current transmission slot is in a node A’s one-hop neighborhood, then set node A to receive mode during the control slot. If node A is selected as a receiver during the control slot, then keep node A in receive mode during the data slot; else switch node A to standby mode.

15 Rules of energy conservation heuristics (Cont.) If the winner of the current transmission slot is in node A’s two-hop neighborhood, then set node A to sleep mode for the entire transmission slot.

16 Rules of energy conservation heuristics (Cont.) If node A is the winner of the current transmission slot has packets to send, then set node A to transmit mode, inform the intended receiver(s) during the control slot, and transmit the data packet(s) during the data slot. does not have a packet for transmission, set node A to standby mode for the entire transmission period.

17 The notation used in the remainder of the paper N 2 : Node’s number of two-hop neighbors N 1 : Node’s number of one-hop neighbors q : Channel access probability p : Probability that the selected node has a packet to transmit p me : Probability that a node is selected as receiver by its one-hop neighbor T c : Length of the control slot in seconds T d : Length of the data slot in seconds T t : Length of the transition period between transmission slots

18 The notation used in the remainder of the paper (Cont.) P tx : Average power consumption in transmit mode P rx : Average power consumption in receive mode P st : Average power consumption in standby mode P x,y : Average power consumption in transition from mode x to mode y E c : Average power consumption during the control slot E d : Average power consumption during the data slot E t : Average power consumption during the transmission slot

19 Power consumption while in transition state P tx,st = (P tx +P st )/2 (1) P st,tx = P tx (2) P rx,st = (P rx +P st )/2 (3) P st,rx = P rx (4) P tx,rx = (P tx +P rx )/2 (5) P rx,tx = P tx (6)

20 Power consumption while in transition state (Cont.) (7) (7) E c = T c [(1-q) P rx +qP tx ] (8) E d = (1-q) {pp me TdP rx +(1- p me +1-p) [P st (T d -T t )+P rx,st T t ]} + q{pT d P tx +(1-p) [P st (T d -T t ) +P tx,st T t ]}(9) Et = Tt{q [p (q P tx +(1-q) Pt rx,rx ) +(1-p) (q P st,tx +(1-q)P st,rx ] +(1-q) [p me (p (q P rx,tx +(1-q) Pr x ) +(1-p) (q P st,tx +(1-q)P st,rx ) ) +(1-p me ) (q P st,tx +(1-q)P st,rx )]} (10)

21 Average energy consumption (11) (11) (12) (12)

22 Performance ComparisonMode Power consumption in mW Transmit24.75 Receive13.5 Standby 15*10 -3 Average power consumption in different modes

23 Transition time To From To FromTransmitReceiveStandby Transmit02010 Receive12010 Standby16200 Transition time in us

24 Fig 3a

25 Fig 3b

26 Fig 4a

27 Fig 4b

28 Fig 5

29 Conclusion By switch to low power, standby mode. DEANA can By switch to low power, standby mode. DEANA can achieve significant energy savings (up to 95%). One main One main disadvantages : frequent switching between radio modes can lead to unnecessary power consumption A link activation scheme could be used instead.