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

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

Overview and objectives Exploiting path diversity Originator Final destination - 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

Opportunistic versus deterministic Overview and objectives 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

Overview and objectives Exploiting path diversity Originator Final destination 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? e.g ) : deterministic best path : opportunistic best path

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.

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

Opportunistic Forwarding Initial path - 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 S D 4 Originator Final destination 5 RREP 6

Opportunistic Forwarding First data transmission - 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. S D 4 5 Cooperative network range 6 DATA

Preferred node(s) Target node Backup node(s) P5P5 P4P4 P3P3 - P i is the probability that a transmission from node 2 will be correctly decoded by node i - P target is transmission probability threshold Target node –The node such that P i >= P target 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 P target 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 P target S D

Preferred node(s) Target node Backup node(s) P5P5 P4P4 P3P3 S D 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 > P target - 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.

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

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

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

Opportunistic Forwarding J-Broadcast - Relay-set 3 = {S} - Node S has two relay-set 3 D 4 5 *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-go S = max(JVia {1,2} ) = 18 Target node = 2 Backup node = 1 - As a member of relay-set 2, worst-SNR-to-go S = 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-go 1 ) Combined priority node list = {3,2,1} S 1 2 JBC

Opportunistic Forwarding J-Broadcast - Relay-set 3 = {S} - Node S has two relay-set S D 4 5 *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-go S = max(JVia {1,2} ) = 18 Target node = 2 Backup node = 1 - As a member of relay-set 2, worst-SNR-to-go S = 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-go 1 ) Combined priority node list = {3,2,1} Backup node Target node Preferred node 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. Use hop count for each node to construct better priority nodes. Using hop count makes node receives more various JBCs (from different hops)

Opportunistic Forwarding J-Broadcast S D 4 5 RS0RS1RS2 RS3 - Now, each node in relay-set knows target node(s), preferred node(s), and backup node(s).

Opportunistic Forwarding J-Broadcast S D 4 5 : 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

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

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)

Opportunistic Forwarding PEP/SNR relationship Prob. of packet error SNR (dB) nominal steep steepest shallowest shallower shallow Mbps Black : shallowest Blue : nominal Red : steepest Dotted : 1Mbps Solid : 2Mbps

Opportunistic Forwarding PEP/SNR relationship 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) Prob. of packet error SNR (dB) nominal steep steepest shallowest shallower shallow Mbps Black : shallowest Blue : nominal Red : steepest Dotted : 1Mbps Solid : 2Mbps

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

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

Opportunistic Forwarding Second data transmission 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. Bit rate constraint to transmit data : target

Opportunistic Forwarding Second data transmission S D 4 5 ACK - 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.

Opportunistic Forwarding Second data transmission S D 4 5 ACKACK 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.

Opportunistic Forwarding Second data transmission S D 4 5 ACK - 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 Obstacle *Example of the communication range covered only in one direction

Opportunistic Forwarding Second data transmission S D 4 5 DATA 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. *What if the first priority node cannot decode the data?

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

Opportunistic Forwarding Second data transmission S D 4 5 ACKACK

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

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

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.

Deterministic Forwarding Path quality monitoring S D 4 5 : Deterministic best path - 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.

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

Deterministic Forwarding Path quality monitoring S 1 3 D : New deterministic best path

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

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

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

Simulation Environment UDel Models – Map models Downtown Chicago

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

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

Simulation Environment UDel Models – Website

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

Simulation Results # of nodes Deterministic forwardingOpportunistic forwarding Bit rate (Mbps) nominal steep steepest shallowest shallower shallow Second data (before nodes move) - 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

Simulation Results nominal steep steepest shallowest shallower shallow - The smoother curve, the lower received power. - Lower averaged power, but still achieve good bit rate. Received power (dBm) Deterministic forwardingOpportunistic forwarding Second data (before nodes move) # of nodes

Simulation Results - The higher node density, the smaller number of hops. - Each point represents for both approaches and all different steepness. Second data (before nodes move) # of hops Deterministic and opportunistic forwarding # of nodes

Simulation Results - 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. Performance before the first route failure Deterministic forwardingOpportunistic forwarding Bit rate (Mbps) nominal steep steepest shallowest shallower shallow # of nodes

Simulation Results - 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. Performance before the first route failure Deterministic forwardingOpportunistic forwarding Bit rate (Mbps) nominal steep steepest shallowest shallower shallow When node does not move When node moves # of nodes

Simulation Results - 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. Performance before the first route failure Deterministic forwardingOpportunistic forwarding Bit rate (Mbps) nominal steep steepest shallowest shallower shallow When node does not move When node moves # of nodes

Simulation Results Performance before the first route failure nominal steep steepest shallowest shallower shallow # of hops Deterministic forwardingOpportunistic forwarding - DF is 0.5% shorter on average. The result is quite close. # of nodes

Simulation Results Performance during the connection lifetime nominal steep steepest shallowest shallower shallow - Path monitoring and route updates are more critical to maintain a path than allowing opportunistic forwarding. - The smoother curve in PEP/SNR relationship, the better performance. Deterministic forwarding Packet delivery ratio Opportunistic forwarding # of nodes

Simulation Results Performance during the connection lifetime nominal steep steepest shallowest shallower shallow - Again, path monitoring and route updates are crucial to reduce route failure rate. - Degree of the PEP/SNR relationship curve impacts more on performance of OF than DF because W2 is wider than W1. 1/Route duration Deterministic forwarding Opportunistic forwarding W1 W2 # of nodes

Simulation Results Performance during the connection lifetime nominal steep steepest shallowest shallower shallow - Efficiency = duration for data pkts / duration for any packet including overhead. - Overhead for DF = JBC frames used in highly efficient J-Broadcast process, less AODV pkts - Overhead for OF = ACK, ACKACK frames per every data transmission, more AODV pkts. Deterministic forwarding Opportunistic forwarding Efficiency # of nodes

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

Conclusions DeterministicOpportunistic Bit rateSlowerFaster Rx powerLargerSmaller # of hopsLongerShorter When nodes are stationary Opportunistic forwarding is preferred

Conclusions DeterministicOpportunistic Bit rateFasterSlower Rx powerLargerSmaller # of hopsShorterLonger PDRHigherLower Route failure rateLowerHigher EfficiencyHigherlower When nodes move Deterministic forwarding is preferred

Conclusions - Opportunistic forwarding has good opportunism when nodes do not move, but when nodes move, opportunism begins to be disappeared due to losing channel information within cooperative network range. - Deterministic forwarding has no opportunism when nodes do not move, but when nodes move, the performance in various metrics is better than opportunistic forwarding due to regaining channel information. - When nodes are stationary, opportunistic forwarding is preferred. - When nodes are not stationary, deterministic forwarding is preferred. - The smoother curve in PEP/SNR relationship, the more opportunism. - Degree of the PEP/SNR relationship curve impacts more on performance of opportunistic forwarding than deterministic forwarding.

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

Future Work - Impacts of signal interferences on the performance - Explore the broader range of local cooperative network - Explore any opportunism in deterministic forwarding e.g. opportunism during repairing link failure by using nodes within the same relay-set and the next relay-set

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