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Wednesday, 31 January 2018

Opportunistic Routing With Congestion Diversity in Wireless Ad Hoc Networks(2015)

Opportunistic Routing With Congestion Diversity in Wireless Ad Hoc Networks(2015)

We consider the problem of routing packets across a multi-hop network consisting of multiple sources of traffic and wireless links while ensuring bounded expected delay. Each packet transmission can be overheard by a random subset of receiver nodes among which the next relay is selected opportunistically. The main challenge in the design of minimum-delay routing policies is balancing the trade-off between routing the packets along the shortest paths to the destination and distributing the traffic according to the maximum backpressure. Combining important aspects of shortest path and backpressure routing, this paper provides a systematic development of a distributed opportunistic routing policy with congestion diversity (D-ORCD). D-ORCD uses a measure of draining time to opportunistically identify and route packets along the paths with an expected low overall congestion. D-ORCD with single destination is proved to ensure a bounded expected delay for all networks and under any admissible traffic, so long as the rate of computations is sufficiently fast relative to traffic statistics. Furthermore, this paper proposes a practical implementation of D-ORCD which empirically optimizes critical algorithm parameters and their effects on delay as well as protocol overhead. Realistic QualNet simulations for 802.11-based networks demonstrate a significant improvement in the average delay over comparable solutions in the literature.
  • The opportunistic routing schemes can potentially cause severe congestion and unbounded delay. In contrast, it is known that an opportunistic variant of backpressure, diversity backpressure routing (DIVBAR) ensures bounded expected total backlog for all stabilizable arrival rates. To ensure throughput optimality (bounded expected total backlog for all stabilizable arrival rates), backpressure-based algorithms do something very different: rather than using any metric of closeness (or cost) to the destination, they choose the receiver with the largest positive differential backlog (routing responsibility is retained by the transmitter if no such receiver exists).
  • E-DIVBAR is proposed: when choosing the next relay among the set of potential forwarders, E-DIVBAR considers the sum of the differential backlog and the expected hop-count to the destination (also known as ETX).
  1. The existing property of ignoring the cost to the destination, however, becomes the bane of this approach, leading to poor delay performance in low to moderate traffic.
  2. Other existing provably throughput optimal routing policies distribute the traffic locally in a manner similar to DIVBAR and hence, result in large delay.
  3. E-DIVBAR does not necessarily result in a better delay performance than DIVBAR.
  1. The main contribution of this paper is to provide a distributed opportunistic routing policy with congestion diversity (D-ORCD) under which, instead of a simple addition used in E-DIVBAR, the congestion information is integrated with the distributed shortest path computations .
  2. A comprehensive investigation of the performance of D-ORCD is provided in two directions:
  3. We provide detailed simulation study of delay performance of D-ORCD. We also tackle some of the system-level issues observed in realistic settings via detailed simulations.
  4. In addition to the simulation studies, we prove that D-ORCD is throughput optimal when there is a single destination (single commodity) and the network operates in stationary regime. While characterizing delay performance is often not analytically tractable, many variants of backpressure algorithm are known to achieve throughput optimality.
  1. We show that D-ORCD exhibits better delay performance than state-of-the-art routing policies with similar complexity, namely, ExOR, DIVBAR, and E-DIVBAR. We also show that the relative performance improvement over existing solutions, in general, depends on the network topology but is often significant in practice, where perfectly symmetric network deployment and traffic conditions are uncommon.
  2. We show that a similar analytic guarantee can be obtained regarding the throughput optimality of D-ORCD. In particular, we prove the throughput optimality of D-ORCD by looking at the convergence of D-ORCD to a centralized version of the algorithm. The optimality of the centralized solution is established via a class of Lyapunov functions proposed.
  • System                           :         Pentium Dual Core.
  • Hard Disk                      :         120 GB.
  • Monitor                         :         15’’ LED
  • Input Devices                 :         Keyboard, Mouse
  • Ram                               :         1GB.
  • Operating system                    :         Windows 7.
  • Coding Language           :         JAVA/J2EE
  • Tool                               :         Netbeans 7.2.1
Database                              :           MYSQL

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