Wireless ad hoc networks: cross layer opportunities NSF workshop Washington DC Aug 27-28

1. Wireless ad hoc networks: cross layer opportunities NSF workshopWashington DC Aug 27-28 Mario Gerla Computer Science Dept, UCLA www.cs.ucla.edu

2. Ad hoc networkingCurrent Status Leading Applications • Tactical battlefield: • no infrastructure • Civilian emergency: • infrastructure, if present, was destroyed • Critical Requirements: scalability, survivability, 100% reliable, QoS, jam protection, etc • Non critical: Cost, Standards, Privacy

3. SURVEILLANCE MISSION AIR-TO-AIR MISSION STRIKE MISSION RESUPPLY MISSION FRIENDLY GROUND CONTROL (MOBILE) SATELLITE COMMS SURVEILLANCE MISSION UAV-UAV NETWORK COMM/TASKING COMM/TASKING Unmanned UAV-UGV NETWORK Control Platform COMM/TASKING Manned Control Platform Tactical Ad Hoc Network

4. Emerging Landscape : “Opportunistic” Ad Hoc networks Recreational, commercial, education applications • Vehicle networks • Workgroups (eg, sharing 3G via Bluetooth) • Massive Network games • Patient monitoring Access to Internet? • available, but - “bypass it” with “ad hoc” if too costly or inadequate Tolerant to delays: DTNs Critical:Cost, Privacy, security, standards

5. Car to Car communications for Safe Driving Vehicle type: Cadillac XLRCurb weight: 3,547 lbsSpeed: 65 mphAcceleration: - 5m/sec^2Coefficient of friction: .65Driver Attention: YesEtc. Vehicle type: Cadillac XLRCurb weight: 3,547 lbsSpeed: 75 mphAcceleration: + 20m/sec^2Coefficient of friction: .65Driver Attention: YesEtc. Alert Status: None Alert Status: None Alert Status: Inattentive Driver on Right Alert Status: Slowing vehicle ahead Alert Status: Passing vehicle on left Vehicle type: Cadillac XLRCurb weight: 3,547 lbsSpeed: 45 mphAcceleration: - 20m/sec^2Coefficient of friction: .65Driver Attention: NoEtc. Vehicle type: Cadillac XLRCurb weight: 3,547 lbsSpeed: 75 mphAcceleration: + 10m/sec^2Coefficient of friction: .65Driver Attention: YesEtc. Alert Status: Passing Vehicle on left

6. Co-operative Download: Car Torrent Internet Vehicle-Vehicle Communication Exchanging Pieces of File Later

7. Vehicular Sensor Network (VSN)

8. B B B C C C A A A D D D Personal Networking: BlueTorrent

9. Patient Monitoring Nurses upload patient data; share data files in P2P mode

10. 1. Future expectations on wireless network research • Network layer more tightly coupled with applications • Content sharing, environement sensing • Besides data forwarding, additional services: • Location aware service discovery, • content based routing; • P2P networking • Data collection, processing, filtering, storage, dissemination • Network layer design must interact with: • applications • PHY Layer

11. 2. Major recent advances/breakthroughs in the physical layer • Cognitive radios (spectrum scavenging) • MIMOs (for flexible topology designs; interference mitigation etc) • Cooperative radios • Multi radio devices (BT, 802.11, 3G, etc)

12. 3. Algorithms must adjust to PHY layer “PHY layer aware” MAC, Network and Transport designs Examples (based on MIMO): • Topology control • A MIMO aware MAC protocol: SPACE-MAC • Multi-path Routing & MIMO • TCP & MIMO

13. MIMO Topology Control/Routing • Topology control: • Exploit mode flexibility to dynamically shape topology • Meet different customer requirements Topology with high capacity links: disconnected network Topology with low capacity links: fully connected network 300Mbps 10Mbps

14. SPACE2 MAC • A sends RTS to B; F and D learn about A • B responds with CTS; F and D learn about B When A wishes to transmit to B B F D A

15. SPACE MAC (cont) • After A and B pair is established, F and D pair also can talk • F and D beamform such that signals from/to B and A are nulled; then, A and B start talking B F D A

16. Two-Path Routing using MIMO relay nodes • S sends two independent streams simultaneously to R • Assume 2 antennas at each node (but extendible to systems with more antennas). S R sender receiver

17. MIMO yields 6-fold throughput gain • In the traditional relay mode, the capacity is C/3. • Simulcast achieves 6-fold throughput increase. S R sender receiver

18. TCP and MIMO in Ad Hoc Networks • Consider three flows in the same wireless domain • As the flows get closer to each other: • Interference builds up • Throughput decreases • Fairness suffers • Can MIMO Help?

19. TCP over SPACE MAC (MIMO)Distance = 400m (interference range)

20. TCP over SPACE MAC (MIMO)Distance = 350m (tx range)

21. Identify gaps • Question: How to exploit the wealth of PHY emerging technology? • Do not limit your scope to LINK capacity gains • Look for cross layer optimization opportunities at all layers: • MAC • Network (routing, topology control, multicast, bandwidth scavenging, etc) • transport, • applications and PHY layer

22. The End Thank You

23. Simul-Cast Brian Choi Mario Gerla

24. MIMO System Model weight vector w1 = [w11 w21 … wm1] W V s(t)WHVH = r(t)

25. Assumptions • Fading is flat (i.e. freq. independent). • Channel is symmetric and quasi-static. • Two subchannels - control channel and data channel • Rich scattering - H is full-rank • Antenna’s capable of transmitting and receiving signals simultaneously. • We ignore additive channel noise. • Perfect sychronization between nodes

26. Two Path Routing Problem relay nodes • S sends two independent streams under two paths simultaneously to R. • Assume 2 antennas at each node (but extensible to systems with more antennas). S R sender receiver

27. The 6-fold Benefit of MIMO • If C = (capacity of a point-to-point link) in the traditional relay mode, the capacity is C/3. • Simulcast achieves 6X throughput increase. S R sender receiver

28. Sender • A wants to send a stream (s1(t)) to B and another stream (s2(t)) to C simultaneously. s(t) = [s1(t) s2(t)] B A s1(t) s2(t) C

29. Sender: Linear Coding WB • B receives rB(t) = s(t)WAHABWBH. • For B to recover s1(t), B must consume 2 degrees of freedom. s(t) = [s1(t) s2(t)] HAB B rB1(t) A rB2(t) s1(t) s2(t) C rC1(t) WA HAC rC2(t)

30. Sender: Pre-coding B rB1(t) A rB2(t) s1(t)   s2(t) C rC1(t) rC2(t) • If A knows the channel and the steering matrices of B and C, then A can precode its data such that s1(t) is received at rB1(t), s2(t) is received at rC1(t), without interfering each other. • B and C needs to comsume only one DOF each.

31. Dirty Paper Coding wB1 B rB1(t) A rB2(t) s1(t)   wC1 s2(t) C rC1(t) rC2(t) HABwB1H HACwC1H Let H = = QR QR factorization, Q = unitary, R = upper triangular

32. Dirty Paper Coding • Let r(t) = [rB1(t) rC1(t)]. Thenr(t) =s(t)H. • Multiply s(t) by QH, such that s’(t) = s(t)QH. • Then r(t) = s’(t)H = s(t)QHH = s(t)QHQR = s(t)R • rB1(t) = s1(t)R1,1 (no interference) • rC1(t) = s1(t)R1,2 + s2(t)R2,2 • Sender can estimate this interference and subtract it from s(t) before transmitting. (interference!)

33. Relay Node • There is one DOF left for us to use. We use it to simultaneously relay the received data to the next node. • We set weight vectors such that they are orthogonal to each other. used to send a stream to the next node used to receive data from the previous node

34. Receiver A HAR • This reduces to the problem of spatial multiplexing. • If R knows the channels and the weight vectors used for both streams, then R can decode the received data. R HBR B

35. Network-wise Benefit • If C = (capacity of a point-to-point link) in the traditional relay mode, the capacity is C/3. • Simulcast achieves 6X throughput increase. S R sender receiver

36. Multiple Paths • We can run OLSR-type of routing protocol for the nodes to pre-determine the paths. • This suggests a cross-layer approach (between network layer and MAC layer).

37. Summary • With MIMO and Pre-coding techniques, one can effectively reduce the DOF consumption at the receiving nodes. • We can utilize the idle DOF to relay the data simultaneously. • With two independent simultaneous paths, we can achieve up to 6X throughput increase.