An Efficient Flow Control and Medium Access in Multihop Ad Hoc Networks with Multi-Channels

Abstract

In multihop MANETs, nodes have to cooperate to forward each other's packets through the networks. Every node, including source and intermediate nodes, has a fair opportunity to transmit a packet Thus, the hot spot may suffer traffic congestion. The packet loss rate and the transmission delay are increased, but the throughput is decreased Due to the contention for the shared channel, the throughput of each single node is limited not only by the channel capacity, but also by the transmissions in its neighborhood (intraflow/interflow contention problem). Furthermore, the network throughput still restrict by the channel capacity. Some other related works using multiple channels simultaneously to transmit packets without interfering each other increases the throughput But if the traffic load is heavy, these schemes may induce more serious packet loss on the contrary because they do not consider the congestion problem especially in multihop MANETs. In this paper, we propose a new multichannel MAC protocol using multichannel transmission, and develop a hop- by-hop congestion control scheme, which is named "Efficient Flow Control with Multichannels" (EFCM). The EFCM scheme modifies the IEEE 802.11 RTS/CTS frame format to reserve bandwidth in different channels. It also solves the hidden terminal problem in the multichannel environment The intermediate nodes have a higher priority than the source (or leaf) nodes to contend for the right of transmission to solve the intraflow contention. In order to solve the interflow contention, congestion control is taken in every node to construct a flow table, which restricts the number of packets of every flow passing by congested nodes. According to the simulation results, the whole network throughputs of EFCM are improved significantly.