An Optimized Congestion Control and Error Management System for OCCEM

In this paper, a new OCCEM congestion control mechanism is introduced in multi-homing mode. Congestion in each route can be avoided or can be controlled, based on an Active Queue Management (AQM) method. Also, routers compute probability of congestion for the sources on the paths and then notify them. Therefore, the sources can adjust their sending rates on each path effectively and if necessary, can switch to an alternate path to prevent congestion. Simulations have been conducted with Opnet linked with NS2. The simulation shows that the new method can decrease packet loss, increase the amount of transmissions and stabilize queue length, as compared with standard OCCEM. Keywords: OCCEM; AQM; congestion contro

Routing and Broadcast Development for Minimizing Transmission Interruption in Multi rate Wireless Mesh Networks using Directional Antennas

Using directional antennas to reduce interference and improve throughput in multi hop wireless networks has attracted much attention from the research community in recent years. In this paper, we consider the issue of minimum delay broadcast in multi rate wireless mesh networks using directional antennas. We are given a set of mesh routers equipped with directional antennas, one of which is the gateway node and the source of the broadcast. Our objective is to minimize the total transmission delay for all the other nodes to receive a broadcast packet from the source, by determining the set of relay nodes and computing the number and orientations of beams formed by each relay node. We propose a heuristic solution with two steps. Firstly, we construct a broadcast routing tree by defining a new routing metric to select the relay nodes and compute the optimal antenna beams for each relay node. Then, we use a greedy method to make scheduling of concurrent transmissions without causing beam interference. Extensive simulations have demonstrated that our proposed method can reduce the broadcast delay significantly compared with the methods using omnidirectional antennas and single-rate transmission. In addition, the results also show that our method performs better than the method with fixed antenna beams. Keywords: Multihop, Wireless, Mesh, Omnidirectional 

Hop-by-hop Channel - Alert Routing to Congestion Control in Wireless Sensor Networks

One of the major challenges in wireless sensor networks (WSNs) research is to prevent traffic congestion without compromising with the energy of the sensor nodes. Network congestion leads to packet loss, throughput impairment, and energy waste. To address this issue in this paper, a distributed traffic-aware routing scheme with a capacity of adjusting the data transmission rate of nodes is proposed for multi-sink wireless sensor networks that effectively distribute traffic from the source to sink nodes. Our algorithm is designed through constructing a hybrid virtual gradient field using depth and normalized traffic loading to routing and providing a balance between optimal paths and possible congestion on routes toward those sinks. The simulation results indicate that the proposed solution can improve the utilization of network resources, reduce unnecessary packet retransmission, and significantly improve the performance of WSNs. Keywords: Wireless sensor networks; Traffic-aware; Routing; Data transmission rate; Congestion; Gradien