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SIMPLY COOPERATIVE

SIMPLY COOPERATIVE. Anthony Ephremides Pompeu Fabra University April 29, 2010 Barcelona, Catalunia. THE “COAT OF ARMS”. S : source. D : destination. THE “COAT OF ARMS”. R : relay. S : source. D : destination. THE “COAT OF ARMS”. l 2. R : relay and source. l 1. S : source.

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SIMPLY COOPERATIVE

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  1. SIMPLY COOPERATIVE Anthony Ephremides Pompeu Fabra University April 29, 2010 Barcelona, Catalunia

  2. THE “COAT OF ARMS” S: source D: destination

  3. THE “COAT OF ARMS” R: relay S: source D: destination

  4. THE “COAT OF ARMS” l2 R: relay and source l1 S: source D: destination

  5. THE “COAT OF ARMS” l2 R: relay and source l1 S: source D: destination “ether” medium

  6. THE “HISTORY”

  7. THE “HISTORY” • Key differences • No “source” traffic fromR • No “ether” • Classical information-theoretic quest for capacity – backlogged S • “RELAY” CHANNEL (Van der Meulen ’60’s) R reservoir S D

  8. THE “HISTORY” • Key differences • No “source” traffic fromR • No “ether” • Classical information-theoretic quest for capacity – backlogged S • “RELAY” CHANNEL (Van der Meulen ’60’s) R reservoir S D • “REVISED” RELAY CHANNEL • (wireless) ( • Laneman/Tse/Wornell • Sendonaris /Erkip/Aazhang • Kramer/ Gastpar/Gupta • Kramer/Maric/Yates …………………… ) Basic idea: Cooperative Diversity (variety of schemes) Objective: Again, Capacity (backlogged S)

  9. A “WIRELESS” NETWORK PERSPECTIVE

  10. A “WIRELESS” NETWORK PERSPECTIVE • “PACKETS” THROUGHPUT

  11. A “WIRELESS” NETWORK PERSPECTIVE • “PACKETS” THROUGHPUT • “BURSTY TRAFFIC” DELAY

  12. A “WIRELESS” NETWORK PERSPECTIVE • “PACKETS” THROUGHPUT • “BURSTY TRAFFIC” DELAY • STABLE Throughput

  13. A “WIRELESS” NETWORK PERSPECTIVE • “PACKETS” THROUGHPUT • “BURSTY TRAFFIC” DELAY • STABLE THROUGHPUT • COGNITION • (sensing)

  14. A “WIRELESS” NETWORK PERSPECTIVE • “PACKETS” THROUGHPUT • “BURSTY TRAFFIC” DELAY • STABLE THROUGHPUT • COGNITION • (sensing) Q: CAN’T WE STILL CO-OPERATE?

  15. 1 2 M DIGRESSION: THE VIRTUE OF THE SINGLE QUEUE (STATISTICAL MULTIPLEXING) or SM S1 D S2 S D 1+ 2+…+ M “VIRTUAL” QUEUE

  16. 1 2 M i THE “PRIMITIVE” IDEA (Sadek, Liu, Ephremides 2007) Source Terminals • NO CONTENTION (e.g. TDMA) • PERFECT CHANNEL SENSING • INSTANT ERROR-FREE “ACKs” • SINR > b • FADING CHANNELS (i.e. packet erasure channels) S1 S2 Relay R D hrd hir Si Destination hid SM

  17. Cooperation Method 1 • Each terminal transmits HOL packet in its assigned slot (if empty, slot is free) • If D receives successfully, it sends ACK (heard by both the relay and the user) • If D does not succeed but R does: at first sensed empty slot R transmits to D the failed packet • If neither D nor R succeed, packet gets retransmitted by the terminal in next frame • Relay does not keep packets after the end of the frame Remarks: Idle slots are utilized! • Relay has always a finite queue (M packets Max) • Terminal queues “interact”

  18. Cooperation Method 2 • Each terminal transmits HOL packet in its assigned slot (if empty, slot is free) • If Dreceives successfully, it sends ACK (heard by both the relay and the user) • If D does not succeed but R does: at first sensed empty slot R transmits to D the failed packet • If neither D nor R succeed, packet gets retransmitted by the terminal at next opportunity • Relay keeps all packets it receives correctly Remarks: Again: Idle slots are utilized! • Relay has a possibly growing queue • Terminal queues do not interact

  19. THE CRITERION STABLE THROUGHPUT: arrival rate service rate  m Q(t): queue size at time t ~ “positive recurrence” Loynes: If arrival process and service process are jointly stationary, the queue is stable iff  < m max stable throughput

  20. 1 2 THE CRITERION (cont.) 2 Q1(t) Set of ’s such that Q1 and Q2 are stable service Q2(t) 1 Problem: When Q1(t) and Q2(t) “interact”, stationary “service rate” cannot be identified. Q2 2 2 m2' 1 1 1 2 m1 m1 m1 m2' m1 '≠m1 m2 '≠m2 2 2 2 m2 m2 1 1 1 m1 m1 m1 m2' 2 2 2 m2 m2 1 1 1 m1' m1' m1' Q1 Solution: STOCHASTIC DOMINANCE (Rao, Ephremides 1988)

  21. BACK TO THE “PRIMITIVE” SYSTEM • COOP METHOD 1 • COOP METHOD 2 • RANDOM ACCESS • TDMA • SELECTIVE “DECODE-AND-FORWARD” ---NETWORK VIEW no cooperation i.e. EVERY PACKET USES TWO SLOTS OR EVERY PACKET USES TWO “HALF-SLOTS” AS TWICE THE RATE

  22. BACK TO THE “PRIMITIVE” SYSTEM • COOP METHOD 1 • COOP METHOD 2 • RANDOM ACCESS • TDMA • SELECTIVE “DECODE-AND-FORWARD” ---NETWORK VIEW no cooperation i.e. EVERY PACKET USES TWO SLOTS OR EVERY PACKET USES TWO “HALF-SLOTS” AS TWICE THE RATE attention

  23. 0.5 0.45 TDMA 0.4 COOP2 DF ALOHA 0.35 0.3 2 l 0.25 0.2 0.15 0.1 0.05 0 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 l 1 Result for 2-users COOP1 Comparison

  24. 1 1 TDMA COOP2 0.9 0.9 DF ALOHA TDMA=COOP1 COOP2 0.8 0.8 DF ALOHA 0.7 0.7 0.6 0.6 0.5 0.5 Aggregate Maximum Stable Throughpt Aggregate Max Stable Throughput 0.4 0.4 0.3 0.3 0.2 0.2 0.1 0.1 0 0 0 5 10 15 20 25 30 35 1 2 3 4 5 6 7 8 9 10 SNR Thresold (b) [dB] R [b/s/Hz] DF: Relay transmits at twice the rate and utilizes one time slots. (Rate and SNR-threshold are related through the Gaussian mutual information formula. DF: Relay transmits at the same rate and utilizes two time slots.

  25. 5 10 TDMA COOP1 4 10 COOP2 DF ALOHA 3 10 Average Delay 2 10 1 10 0 10 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 l 1 Delay • Notoriously difficult for interacting queues • Symmetric System: 2-users

  26. 1 2 M WHY? VIRTUE OF THE SINGLE QUEUE S1 S2 R D SM PARTIAL CONCENTRATION INTO SINGLE QUEUE IN METHOD 2

  27. BUT S1 S2 R D SM

  28. BUT S1 S1 S2 S2 D R D SM SM

  29. BUT S1 S1 S2 S2 D R D SM SM TANDEM IS BORN piD piN pND i N D =(N+1) 1 2 Pij: Packet success probability from i to j (increasing in i, decreasing in j, for i < j) or, simply (PiD increasing in i) ANY TERMINAL COULD PLAY THE ROLE OF THE RELAY

  30. HENCE, BACK TO THE ‘COAT OF ARMS” 2 2 NEW ISSUE: ACCESS POLICY: p12 p23 1 p13 3=D 1 • PRIORITY ORDER IN SERVING QUEUES AT “2” • AFFECTS DELAY (NOT THROUGHPUT) • “ANY” CONFLICT-FREE “WORK-CONSERVING” • TDMA • (MAXIMUM STABLE THROUGHPUT REGION: SAME) • RANDOM OR SCHEDULED ACCESS WITH MULTIPACKET • RECEPTION • (B. Rong, A. Ephremides 2009)

  31. STABLE THROUGHPUT REGION • Both policies yield same stable throughput regions under cooperation • N users simultaneously increase stable throughput rates • lkmax , 1 ≤ k ≤ N-1 • lNmax • p1,2 increases  region increases

  32. LESSON TAUGHT • GAIN BY ALL USERS BECOMES MOTIVATION FOR COOPERATION

  33. LESSON TAUGHT • Gain by all users becomes motivation for cooperation or • It is in the interest of the rich to help the poor

  34. LESSON TAUGHT • Gain by all users becomes motivation for cooperation or • It is in the interest of the rich to help the poor Deeper and Far-reaching Interpretation: FOR BURSTY TRAFFIC IN SHARED CHANNELS, REDUCTION OF THE PRESENCE OF COMPETITION IS BENEFICIAL

  35. SEQUEL vs • STABLE THROUGHPUT REGION “BACKLOGGED” THROUGHPUT REGION (FOR SCHEDULED ACCESS AND PRIORITY TO “NOT-TO-RELAY”) • COMMON PHENOMENON • FOR RANDOM ACCESS (q1,q2) ON COLLISION CHANNEL, COOPERATION MAY HELP IF (B. Rong, A. Ephremides ISIT 2009)

  36. MULTI-PACKET RECEPTION CAPABILITY (B. Rong, A. Ephremides 2009) • CRITERION: SINR > g (simplest) • NEW SET OF SUCCESS PROBABILITIES • NO SIMULTANEOUS “TRANSMIT” AND “RECEIVE” BY R (initially) • PSRAS BEFORE • PRD > PRD/S new PSD > PSD/Rnew and of course PRD > PSD (Denote these probabilities by ) • R KNOWS WHETHER QS=0 R “Standard” channel (J. Luo & A. Ephremides 2006) S D COOPERATION POLICY: R MIXES OWN AND S’s PACKETS IF QS=0, R TRANSMITS w.p. 1 (IF QR>0) IF QS>0, S TRANSMITS w.p. 1 AND R w.p. q (IF QR>0)

  37. RESULT (MPR) A REGION OF VALUES OF THE PACKET SUCCESS PROBABILITIES, ,SUCH THAT • IF • IF for q=0 for suitable values of q (i.e., scheduled transmission or “conventional” cooperation )

  38. RESULT (cont.) Resulting stability regions If , opportunistic scheme results in improved stability region If , the optimal strategy is the conventional cognitive cooperation

  39. --- AND MORE • Similar results for full tandem (more than two source terminals) • Enhancement with physical-layer improvements • Combine with dynamic decode-and-forward (K. Azarian, H. El Gamal, P. Schniter 2005) • Combine with ADAPTIVE superposition coding (T. Cover 1972) (B.Rong, I. Krikidis, A. Ephremides 2009)

  40. RESULT NC: no cooperation CC: conventional cooperation S-CC: conventional cooperation with superposition coding NC-DDF: non-cognitive DDF C-DDF: cognitive DDF SC-DDF: cognitive DDF with superposition coding

  41. WHAT ABOUT NETWORK CODING? QR1 R: • transmits random linear combinations of contents of QR1 , QR2(packet-by-packet) • NO IMPROVEMENT 2 R QR2 1 D S --BUT: (i) IF THERE ARE MULTIPLE DESTINATIONS AND / OR (ii) CONTENTS OF BUFFERS ARE COMBINED IN THEIR ENTIRETY • possible improvement • (under investigation)

  42. CONCLUSION • Relay-based cooperation at the packet level can be beneficial for different reasons (not diversity-related)

  43. CONCLUSION • Relay-based cooperation at the packet level can be beneficial for different reasons (not diversity-related) • TERMINALS CAN BE SIMPLY COOPERATIVE

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