Study On The Multiple Access Protocol With Perfect Scheduling Transmission In WLAN

Recently, as a cheap and convenient wireless local access method, wireless LAN has aroused the interests of more and more people. The wireless LAN access technologies have also greatly attracted the attention of industrial and academic researchers. With the rapid development of wireless data service and the increasing demand of multimedia application, developing a medium access protocol with high throughput, good fairness and providing quality of service (QoS) is defiant and attractive.This thesis mainly discusses the multiple access technique in wireless LAN. The main research works and results are listed as follows:1. Based on the idea of contention access and perfect scheduling transmission, User-and-Traffic-dependent Perfect-scheduling Multiple Access (UTPMA) protocol is presented. In the contention access period, based on the information about the effective usage and the collision of the contention access slot(s), a collision resolution strategy of adaptive adjusting the number of contention access slots is proposed, which makes a node to access channel quickly while reduces the overhead of contention access. In the non-collision transmission period, the central access point schedules the transmission of each node with its partial feedback information, which reduces the transmission overhead while insures the packets to be transmitted as soon as possible. On the platform of IEEE 802.11, the realizable scheme is proposed by introducing the self-organized algorithm and designing management packets, control packets, and data packets of UTPMA.2. An analysis model is presented to analysis the throughput, access delay and access rejection probability of UTPMA protocol. The analytical and the simulation results almost coincide. With the analysis model, the optimal frame length of UTPMA is obtained. In addition, a study on the influence of different protocol parameters and traffic types on the properties of UTPMA protocol is conducted. The comparison results of UTPMA and IEEE 802.11 DCF show UTPMA has better performance.3. Base on UTPMA, an enhanced UTPMA protocol supporting QoS is presented. In this protocol, both the contention access algorithm and the transmission schedule scheme are based on the differentiation of priority. The contentionaccess slots are divided into independent and consecutive slots groups. The number of contention access slots in each group can be adjusted adaptively with the collision information of such slots, thus guarantees the traffic with high priority access channel first while makes the traffic with low priority not be starved. By perfectly scheduling the traffic in one node to be transmitted on the order of the priority, the traffic with high priority can be transmitted first. In addition, to lessen the traffic overstocked in the network, an overstock resolve scheme is provided. It provides different slot allocation schemes to the nodes with different overload state, thus reduces the dropping probability in the case of satisfy the delay requirement.