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A Comparison of Opportunistic and Deterministic Forwarding in Mobile Wireless Networks

A Comparison of Opportunistic and Deterministic Forwarding in Mobile Wireless Networks. Jonghyun Kim Stephan Bohacek. Electrical and Computer Engineering University of Delaware. Outline. Overview and objectives Opportunistic Forwarding Deterministic Forwarding Simulation Environment

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A Comparison of Opportunistic and Deterministic Forwarding in Mobile Wireless Networks

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  1. A Comparison of Opportunistic and Deterministic Forwarding in Mobile Wireless Networks Jonghyun Kim Stephan Bohacek Electrical and Computer Engineering University of Delaware

  2. Outline Overview and objectives Opportunistic Forwarding Deterministic Forwarding Simulation Environment Simulation Results Conclusions Future Work

  3. Overview and objectives Exploiting path diversity Final destination Originator • - Many different paths exist • - Deterministic and opportunistic best path exist • - Deterministic best path is found in advance and it is not changed until • the next deterministic best path update • Opportunistic best path is found on-the-fly and it is changed if a chance is • arised

  4. Overview and objectives Opportunistic versus deterministic • In deterministic forwarding, the route can be continually monitored. If the • route degrades, refinement is triggered. • Overhead to find refine routes • However, in opportunistic forwarding, it is difficult to determine the quality • of the route, and hence difficult to trigger refinement • There is no single route whose quality can be monitored • The goal of opportunistic forwarding is to use weak links. Thus the path that a • particular packet uses is typically (hopefully) bad. (compare this to deterministic case) • Overhead to coordinate which node will forward the packet

  5. Overview and objectives Exploiting path diversity e.g ) : deterministic best path : opportunistic best path 2 7 10 5 3 Final destination 1 9 6 Originator 8 11 4 When nodes are stationary, - Opportunistic best path : shorter hop, lower SNR, faster bit rate - Deterministic best path: longer hop, higher SNR, slower bit rate When nodes are moving, what will happen to the performance in various metrics?

  6. Overview and objectives Objectives - Compare the performance between opportunistic and deterministic forwarding 1)when nodes are moving and 2)by considering various steepness of the relationship between SNR and packet error probability. - Observe how much opportunism is varying according to various steepness.

  7. Outline Overview and objectives Opportunistic Forwarding Deterministic Forwarding Mixed Forwarding Simulation Environment Simulation Results Conclusions Future Work

  8. Opportunistic Forwarding Initial path RREP 1 5 D 2 4 S Final destination 3 Originator 6 - A slightly modified AODV is used to find the initial path above. - Initially, originator’s priority node : node1 node1’s priority node : node5 node 5’s priority node : final destination

  9. Opportunistic Forwarding First data transmission Cooperative network range DATA 1 5 D 2 4 S 3 6 - During first data transmission through the initial path, node 2, 3, and 4 can be aware of this communication by overhearing packets, so they will join J-Broadcast process, but node 6 will not join. - Thus, searching for path diversity is localized.

  10. Preferred node(s) P5 1 5 P4 D 2 4 S Target node 3 P3 Backup node(s) - Pi is the probability that a transmission from node 2 will be correctly decoded by node i - Ptarget is transmission probability threshold • Target node • The node such that Pi >= Ptarget and makes the most progress to the destination • Preferred nodes • Nodes that make better progress to the destination • By definition, the probability of reaching a preferred node is less than Ptarget • Back-up nodes • Nodes that make some progress to the destination, but not as much as the target node. • In many cases, the probability of reaching a back up node is greater than Ptarget

  11. Preferred node(s) P5 1 5 P4 D 2 4 S Target node 3 P3 Backup node(s) Node A makes better progress to the destination than node B if - node A has few hops to the destination and each hop has a probability of success > Ptarget - node A and B have the same number of hops, but node A has a higher worst-SNR-to-go, where worst-SNR-to-go is the worst SNR to go to final destination along the path.

  12. Opportunistic Forwarding J-Broadcast Communication range *Consider only node 5 worst-SNR-to-goD = inf SNRD = 20 JViaD = min (SNRD, worst-SNR-to-goD) = 20 worst-SNR-to-go5 = JViaD = 20 Target node = D Priority node list = {D} JBC 1 5 D 2 4 S 3 - JBC packet contains worst-SNR-to-goD. - Node 3, 4, and 5 within D’s radio range receive JBC and compute worst-SNR-to-go. - Relay-set 1 = {3, 4, 5}

  13. Opportunistic Forwarding J-Broadcast *Consider node 2 worst-SNR-to-go{3,4,5} = {15, 18, 20} SNR{3,4,5} = {23, 20, 17} JVia{3,4,5} = min (SNR{3,4,5}, worst-SNR-to-go{3,4,5}) = {15, 18, 17} worst-SNR-to-go2 = max(JVia{3,4,5}) = 18 *Consider node S worst-SNR-to-go3 = 15 SNR3 = 13 JVia3 = min (SNR3, worst-SNR-to-go3) = 13 worst-SNR-to-goS = 13 Target node = 3 Priority node list = {3} JBC 1 5 D 2 4 S 3 - Relay-set 2 = {1, 2, S} - Priority node list ={preferred node(s), target node(s), backup node(s)}

  14. Opportunistic Forwarding J-Broadcast *Consider node 2 worst-SNR-to-go{3,4,5} = {15, 18, 20} SNR{3,4,5} = {23, 20, 17} JVia{3,4,5} = min (SNR{3,4,5}, worst-SNR-to-go{3,4,5}) = {15, 18, 17} worst-SNR-to-go2 = max(JVia{3,4,5}) = 18 Target node = 4 (maximum JVia index) Preferred node = 5 (larger worst-SNR-to-go5) Backup node = 3 (smaller worst-SNR-to-go3) Priority node list = {5, 4, 3} *Consider node S worst-SNR-to-go3 = 15 SNR3 = 13 JVia3 = min (SNR3, worst-SNR-to-go3) = 13 worst-SNR-to-goS = 13 Target node = 3 Priority node list = {3} Preferred node(s) 1 5 D 2 4 S Target node 3 Backup node(s) - Relay-set 2 = {1, 2, S} - Priority node list ={preferred node(s), target node(s), backup node(s)}

  15. Opportunistic Forwarding J-Broadcast *Consider node S - As a member of relay-set 3, worst-SNR-to-go{1,2} = {17, 18} SNR{1,2} = {21, 22} JVia{1,2} = min (SNR{1,2}, worst-SNR-to-go{1,2}) = {17, 18} worst-SNR-to-goS = max(JVia{1,2}) = 18 Target node = 2 Backup node = 1 - As a member of relay-set 2, worst-SNR-to-goS = 13 Target node = 3 Combined target node = 2 (maximum JVia index) Combined preferred node = 3 (shorter hop) Combined backup node = 1 (smaller worst-SNR-to-go1) Combined priority node list = {3,2,1} JBC 1 5 D 2 4 S 3 - Relay-set 3 = {S} - Node S has two relay-set

  16. Opportunistic Forwarding Can only S join multiple relay-sets? Yes What about other nodes? No They cannot because if a node receive a burst on JBCs, it joins a certain relay-set and it does not process JBC with the same sequence number any more. J-Broadcast *Consider node S - As a member of relay-set 3, worst-SNR-to-go{1,2} = {17, 18} SNR{1,2} = {21, 22} JVia{1,2} = min (SNR{1,2}, worst-SNR-to-go{1,2}) = {17, 18} worst-SNR-to-goS = max(JVia{1,2}) = 18 Target node = 2 Backup node = 1 - As a member of relay-set 2, worst-SNR-to-goS = 13 Target node = 3 Combined target node = 2 (maximum JVia index) Combined preferred node = 3 (shorter hop) Combined backup node = 1 (smaller worst-SNR-to-go1) Combined priority node list = {3,2,1} Backup node 1 5 Target node D 2 4 S 3 Preferred node Use hop count for each node to construct better priority nodes. Using hop count makes node receives more various JBCs (from different hops) - Relay-set 3 = {S} - Node S has two relay-set

  17. Opportunistic Forwarding J-Broadcast RS2 RS1 RS0 RS3 1 5 D 2 4 S 3 - Now, each node in relay-set knows target node(s), preferred node(s), and backup node(s).

  18. Opportunistic Forwarding J-Broadcast 1 5 D 2 4 S 3 : deterministic best path going though target nodes : opportunistic better paths over deterministic best path in terms of shorter hops or better progress to destination. : opportunistic worst path going through backup nodes. Jonghyun Kim and Stephan Bohacek, Exploiting Multihop Diversity through Efficient Localized Searching with CDMA and Route Metric-based Power Control, MSWiM’06, Torremolinos, Malaga, Spain, October 2006

  19. Opportunistic Forwarding J-Broadcast The constraint to broadcast JBC : Probability of successful transmission to downstream nodes (PST) must exceed target transmission probability (TTP). = lowest bit-rate = probability of successful transmission to downstream node i depends on the steepness of the relationship between SNR and packet error probability Need to explain the equation using graphical view

  20. Opportunistic Forwarding J-Broadcast The constraint to broadcast JBC : Probability of successful transmission to downstream nodes (PST) must exceed target transmission probability (TTP). Downstream nodes (JBC senders)

  21. Opportunistic Forwarding PEP/SNR relationship 0 0 10 10 -1 -1 10 10 2 Mbps steepest -2 -2 Dotted : 1Mbps 10 10 steep Prob. of packet error Solid : 2Mbps nominal -3 shallow Red : steepest -3 10 10 shallower Blue : nominal shallowest Black : shallowest -4 -4 10 10 -5 0 5 10 15 20 25 -5 0 5 10 15 20 25 SNR (dB)

  22. Opportunistic Forwarding PEP/SNR relationship 0 0 10 10 -1 -1 10 10 2 Mbps steepest -2 -2 Dotted : 1Mbps 10 10 steep Prob. of packet error Solid : 2Mbps nominal -3 shallow Red : steepest -3 10 10 shallower Blue : nominal shallowest Black : shallowest -4 -4 10 10 -5 0 5 10 15 20 25 -5 0 5 10 15 20 25 SNR (dB) In case of steepest curve, when BR = 2Mbps, SNR >= 20.5  always F(BR, SNR) = 1 when BR = 2Mbps, SNR < 20.5  always F(BR, SNR) = 0 Thus, opportunism is disappeared because F(BR, SNR) is deterministic (i.e. there is no randomness of the probability of successful transmission)

  23. Opportunistic Forwarding PEP/SNR relationship 0 0 10 10 -1 -1 10 10 2 Mbps steepest -2 -2 Dotted : 1Mbps 10 10 steep Prob. of packet error Solid : 2Mbps nominal -3 shallow Red : steepest -3 10 10 shallower Blue : nominal shallowest Black : shallowest -4 -4 10 10 -5 0 5 10 15 20 25 -5 0 5 10 15 20 25 SNR (dB) In case of shallowest curve, maximum opportunism occurs because randomness of the probability of successful transmission becomes high.

  24. Opportunistic Forwarding Second data transmission 1 DATA 5 D 2 4 S 3 Priority node list = {3,2,1} - Node 1, 2 and 3 buffer the received data.

  25. Opportunistic Forwarding Second data transmission Bit rate constraint to transmit data : target Backup nodes are not included into the bit rate calculation because the maximum bit rate would be set to reach these backup nodes and hence the preferred nodes would have little chance to receive the data packet.

  26. Opportunistic Forwarding Second data transmission 1 5 ACK D 2 4 S 3 - Assume that highest priority node 3 successfully decoded the data. - Lower priority node 1 and 2 overhear ACK, so they discard the buffered data because they know that node 3 will transmit the data.

  27. Opportunistic Forwarding Second data transmission 1 ACKACK 5 D 2 4 S 3 Why is ACKACK needed? To avoid collisions that happen when the communication range of either ACK sender (node 3) or ACKACK sender (node S) can cover a lower priority node (node 1 or 2) only in one direction. Thus, bi-directional ACK and ACKACK collision avoidance is needed.

  28. Opportunistic Forwarding Second data transmission *Example of the communication range covered only in one direction 1 5 ACK D 2 4 S 3 Obstacle - Node 2 cannot receive ACK due to an obstacle. - Without ACKACK, node 2 will send its buffered data which causes collision with node 3’s data

  29. Opportunistic Forwarding Second data transmission *What if the first priority node cannot decode the data? 1 DATA 5 D 2 4 S 3 Priority node list = {3,2,1} - If the first priority node 3 could not decode the data, the second priority node 2 waits for a predefined time. During that time, if node 2 does not overhear ACK or ACKACK, node 2 transmits ACK.

  30. Opportunistic Forwarding Second data transmission 1 5 D ACK 2 4 S 3 - Lowest priority node1 discards its buffered data.

  31. Opportunistic Forwarding Second data transmission 1 ACKACK 5 D 2 4 S 3

  32. Opportunistic Forwarding Second data transmission *What if the first priority node cannot decode the data? 1 DATA 5 D 2 4 S 3 Priority node list = {5,4,3} - Repeat this until a route failure occurs. - After route failure, repeat this procedure performed so far.

  33. Outline Overview and objectives Opportunistic Forwarding Deterministic Forwarding Simulation Environment Simulation Results Conclusions Future Work

  34. Deterministic Forwarding Most of the protocols for opportunistic forwarding are still used here, but the main differences are as follows - Packets go through only target nodes - - - Dose not use ACK, and ACKACK packets - Path quality monitoring is performed target Usually, In case of steepest curve, equality occurs.

  35. Deterministic Forwarding Path quality monitoring : Deterministic best path 1 5 D 2 4 S 3 - S maintains the last worst-SNR-to-go obtained from the J-Broadcast process - Whenever S receives implicit ACK, it updates worst-SNR-to-go.

  36. Deterministic Forwarding Path quality monitoring 1 5 D 2 4 S 3 2 moved here - S will detect that the path quality goes bad, so it invokes the J-Broadcast process to find a new deterministic best path.

  37. Deterministic Forwarding Path quality monitoring : New deterministic best path 1 5 D 4 S 3 2

  38. Outline Overview and objectives Opportunistic Forwarding Deterministic Forwarding Simulation Environment Simulation Results Conclusions Future Work

  39. Simulation Environment # of scenarios : 5 # of nodes : 64, 128, 256, 512, 1024 # of steepness : 6 # of trials : 60 City map : Chicago downtown CBR traffic : 512 byte per 50 ms Simulation time : 5 minutes Mobility : UDel mobility simulator Channel gain : UDel channel simulator Packet simulator: Qualnet

  40. Simulation Environment UDel Models – Simulation methodology performed once per city real city map: GIS shapefiles or image Map builder Base station editor map data Process map data Channel simulator1 processed map data channel gain matrix Mobility simulator Channel simulator2 channel gain trace mobility trace Packet simulator e.g., Qualnet, ns, Opnet Statistics

  41. Simulation Environment UDel Models – Map models Downtown Chicago

  42. Simulation Environment UDel Models – Mobility models Pedestrian crosswalk at a traffic light General view Office workers inside a building Pedestrian flow from a subway

  43. Simulation Environment UDel Models – Channel models Communication connectivity(11Mbps ) Variable nature of communication

  44. Simulation Environment UDel Models – Website http://udelmodels.eecis.udel.edu

  45. Outline Overview and objectives Opportunistic Forwarding Deterministic Forwarding Simulation Environment Simulation Results Conclusions Future Work

  46. Simulation Results Second data (before nodes move) nominal steep steepest shallowest shallower shallow 4 4 Deterministic forwarding Opportunistic forwarding 3.5 3.5 3 3 Bit rate (Mbps) 2.5 2.5 2 2 1.5 1.5 64 128 256 1024 512 64 128 256 1024 512 # of nodes - The smoother curve in PEP/SNR relationship and the higher node density, the more opportunism utilized. - The performance is same in steepest case as expected.

  47. Simulation Results Second data (before nodes move) nominal steep steepest shallowest shallower shallow Deterministic forwarding Opportunistic forwarding -76 -76 -77 -77 Received power (dBm) -78 -78 -79 -79 -80 -80 64 128 256 1024 64 128 256 1024 512 512 # of nodes - The smoother curve, the lower received power. - Lower averaged power, but still achieve good bit rate.

  48. Simulation Results Second data (before nodes move) 2.7 Deterministic and opportunistic forwarding 2.65 2.6 2.55 # of hops 2.5 2.45 2.4 2.35 2.3 64 128 256 1024 512 # of nodes - The higher node density, the smaller number of hops. - Each point represents for both approaches and all different steepness.

  49. Simulation Results Performance before the first route failure nominal steep steepest shallowest shallower shallow Deterministic forwarding Opportunistic forwarding 3.5 3.5 3 3 Bit rate (Mbps) 2.5 2.5 2 2 1.5 1.5 64 128 256 1024 64 128 256 1024 512 512 # of nodes - Deterministic forwarding (DF) is between 5% and 10% better. - When nodes move, channel information begins to be not correct. DF will trigger J-broadcast process if path quality is degraded, so it will obtain new channel information. But opportunistic forwarding (OF) will not.

  50. When node moves When node does not move Simulation Results Performance before the first route failure nominal steep steepest shallowest shallower shallow Deterministic forwarding Opportunistic forwarding 3.5 3.5 3 3 Bit rate (Mbps) 2.5 2.5 2 2 1.5 1.5 64 128 256 1024 64 128 256 1024 512 512 # of nodes - Deterministic forwarding (DF) is between 5% and 10% better. - When nodes move, channel information begins to be not correct. DF will trigger J-broadcast process if path quality is degraded, so it will obtain new channel information. But opportunistic forwarding (OF) will not.

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