Research On The Key Technologies Of MAC Cross-layer Optimization In OFDM-Based WLAN

It gets more and more popular to send and receive data via WLAN,such as Wi-Fi,and people require higher throughput.With the development of physical technology,the data transmission rate of WLAN becomes higher and higher,yet the channel efficiency becomes lower and lower.The reason of this situation is that,there is too much control data produced by channel access contention on the very limited channel,and the transmission time of control data did not reduce with the improvement of data transmission rate.Hence,it is very meaningful to optimize traditional access control method and increase network throughput.In this paper,we list and analysis the different optimization methods to date,and choose the cross-layer method as our main idea,which means using physical technology to optimize traditional MAC protocol.Firstly,we propose PACTON protocol based on synchronous network.The main idea is using one of the OFDM subcarrier to contend and others to transmit data.A contention algorithm is presented.The advantage of PACTON is that,it sacrifices little channel resource to parallel the channel contention and data transmission,which improve the network throughput obviously.Secondly,we propose DF-CD protocol based on asynchronous network.There are two parts,one is defer-frozen method and the other is collision detection method.The former defers the backoff counter frozen process to decrease the contention overhead,and the latter uses frozen signal on different subcarriers to detect packets collision.According to rigorous theoretical analysis and plentiful simulations,it is revealed that our proposed PACTON scheme and DF-CD scheme can reduce contention overhead dramatically,thus network throughput is improved significantly.However,we did not achieve measurement in a testbed,which will be the main work of our future research.