Research On Packet Scheduling And MAC Protocol Model Of WLAN

Wireless network communications are an emerging technology and are becoming an essential feature of everyday life.The wireless LAN was the combination product of computer network and wireless communication technology in the 1990's.It provided the access to network via wireless channel.Compared with the traditional Ethernet,it has many advantages,such as convenient installation,flexible usage,saving money and easy to extend.It could be a potential method for the future telecommunication: mobility,personality and multimedia application,and it also came to be an efficient broadband wireless access mechanism.The IEEE 802.11 standard is the most widely used wireless LAN standard today. Firstly,the first chapter briefly introduces the history,status in quo,standard and features of wireless LAN.In chapter 2,the structure and physical layer of wireless LAN is briefly introduced,but introducing the MAC layer in detail,especially for the mechanism of distributed coordination function.Because all of the nodes in the wireless LAN which is a single hop network share the wireless channel,it leads to the collision of data packets which are from different nodes.The collision of data packets which is caused by the nodes that are sending data packets in the same slot restrain the performance of the network system.When there are few nodes in the network,the data packets rarely collide with each other,but as the number of the nodes increases,the load of network becomes heavier,the collision of data packets is more and more severe which will badly affect the performance of network.Corresponding to the above-mentioned question,in the chapter 4,the performance of network in highly loaded network is researched based on the network model which is a single hop network.Aiming at the situation of the inefficient utilization of channel in highly loaded network,we propose a packet scheduling algorithm based on contention window and its improved algorithm,both of which greatly improve the performance of the network.The distributed access scheme based on CSMA/CA is the main feature of the MAC layer.There have been few models to analysis the network performance based on distributed access scheme,but we propose a new model which considers more conditions,and also compare the network performance in several analytical models. According to the new model,we study the initial contention window how to affect the network performance of both basic and RTS/CTS access mechanisms.Moreover,we propose the Markov chain model in non-saturated case.The impact of non-saturation degree on the throughput of both basic and RTS/CTS access mechanisms are analyzed and compared.We also study the throughput of IEEE 802.11 in presence of non ideal transmission channel.At last,we propose a simple method to improve network performance,which is to change the recovery scheme of backoff counter.In the last chapter,the main research results are concluded,and the further research prospect is pointed out.