针对无线Ad hoc 网络的拥塞问题，提出了一种基于媒质共享的公平拥塞控制( MCFCC) 算法，并与典型算法LRED 进行了比较． 在MCFCC 算法中，节点根据竞争共享信道时的退避次数计算退避率，据此进一步得出分组丢弃概率，从而能合理控制源节点的分组发送速率，并可通过快速准确地判断节点和网络的拥塞程度，解决共享媒质冲突和拥塞导致的吞吐量下降问题．另外，该算法通过请求发送、清除发送捎带的方式把拥塞信息发送给邻节点，使得每个节点可以及时获得周围网络的拥塞信息，并据此更新自身的拥塞信息和分组丢弃概率，从而改善各节点上业务流之间的公平性． 仿真结果表明，MCFCC 算法对IEEE 802. 11 DCF 协议的改进效果明显，可以大大提高网络的吞吐量，改善节点间的公平性，从媒质接入控制层上有效地避免了网络拥塞．

In order to overcome the congestion in wireless Ad hoc networks,a novel congestion control algorithm,namely,medium contention-based fair congestion control ( MCFCC) algorithm,is proposed and compared with the typical algorithm LRED. In the MCFCC algorithm,the backoff ratio of the node is calculated according to the backoff times in competing for shared channels,and the corresponding packet dropping probability is further obtained. Thus,the packet transmission rate of the source nodes can be reasonably controlled,and both the collision of shared media and the throughput degradation caused by the congestion can be solved with the help of the fast and accurate judgements on the congestion statuses of nodes and networks. Moreover,the congestion information are sent to the neighbor nodes by means of request to send or clear to send frame,so that each node can know the congestion information about its neighbors and then adjust its congestion information and packet dropping probability,thus improving the fairness among traffic flows. Simulation results show that the MCFCC algorithm can significantly improve the performance of IEEE 802.11 DCF,greatly increase the network throughput,ameliorate the fairness among nodes and effectively avoid the network congestion at the medium access control layer.