On Congestion Control Algorithm In Multi-hop Wireless Networks

With the rapid development of wireless communication technology, multi-hop wirelessnetworks have been widely applied in various areas. However, in multi-hop wirelessnetworks, the traditional TCP suffers from misjudgment of congestion status caused bymany factors such as network noise, node mobility, and hidden terminal etc, which leads toserious degradation of TCP’s performance. Therefore, it is desirable to design a congestioncontrol algorithm that adapts to multi-hop wireless networks.In this thesis, we propose a novel hop-by-hop congestion control algorithm based onacknowledgment mechanism in the context of semi-TCP. The main ideas of the algorithmare described as follows:1) The original ACK frame in the MAC layer is extended to carrythe congestion information;2) A node can broadcast or acquire information on congestionstatus by transmitting or receiving this ACK frame;3) Nodes adapt the transmission rateaccording to the congestion information, and coordinate to relieve a congestion when ithappens.Our proposed algorithm is implemented with the IEEE802.11MAC for performancestudy. In the implementation, the original binary back-off algorithm is modified and thecross-layer cooperation between MAC and routing layers is introduced to further improvethe performance of the algorithm. Through simulation studies in NS-2, we demonstrate thatthis approach can significantly improve the performance of TCP in multi-hop wirelessnetworks in terms of throughput and delay.