Wireless Resource Management And Cross-layer Design For Wlan

As data rate in physical (PHY) layer of wireless networks has been improved with the advantage of OFDM, Adaptive Modulation and Coding (AMC) and MIMO techniques, medium access control (MAC) layer can promote network performance. In this dissertation, by using cross-layer design which combines PHY and MAC layer, wireless resource management and optimization of for wireless local area network (WLAN) are deeply investigated.Firstly, based on OFDM PHY layer, combined with the parameters such as channel, nodes, network, traffic and others, the throughput and delay of traffic are modeled and analyzed. It shows that in a stable network, performance is closely related to the arrival of traffic. Thus different methods must be provided for variable bit rate and constant rate rate traffic. Meanwhile performance of the traffic can be accurately analyzed with Poisson process in dynamic network. An AMC rate control algorithm integrated with channel, collision, buffer size and traffic requirements to ensure average packet error rate is presented. Optimal performance can be archived by adjusting the signal to noise ratio (SNR) threshold of data rate. The different performance requirements can be satisfied by a simple weighted optimization algorithm.Then, a cross-layer traffic access control and scheduling algorithm with quality of service (QoS) performance is presented. Utilizing the resource coefficient describing the resource effect of scheduling policy, an access control algorithm providing the average QoS and long-term fairness is proposed, and optimal resource allocation can be archived with the help of AMC. Using the moving-average of serviced traffic, scheduling policy tunes delay as the traffics’requirements, decreases delay jitter and guarantees the short-term fairness. System throughput is enhanced by scheduling other traffic when the SNR is smaller than its lowest threshold but still bigger than others.Subsequently, the performance improvements under rate control are studied. An enhanced Stop and Wait Distributed Coordination Function (DCF) is proposed to promote the transmission efficiencies. Backoff process of DCF stops when the SNR is below the lowest threshold of transmission, and waits to begin till the SNR becomes big enough again, so both the transmission error and collision can be decreased. Maximized throughput can be archived at the tradeoff of channel time, collision probability and frame error rate that are changed differently when the SNR threshold is tuned. Aiming to enhance energy efficiency, an analysis model of energy efficiency and throughput guaranting the BER requirement of traffic is derived. According to the analysis results, a simple and effective method of optimizing the energy efficiency based on optimal constant transmission power is provided, which completes the task of two dimensional selection of transmission power and data rate, archives the target of improving energy efficiency and guaranting system throughput, and also avoides the problem of the varied hidden terminals caused by dynamically changed transmission power.Again, an analysis model of frame aggregation under unsaturated traffic and limited buffer which integrates with channel access, frame average service time and queue theory is proposed. The model can get the stable result with a recursive algorithm, and further derive the throughput and latency of frame aggregation in steady state. Impact of traffic, frame length, collision probability, buffer size, aggregation size and interactive effects are taken into consideration, so this model can be used in the optimation of waiting time or buffer size in different situation.Finally, it is the study of MAC optimization for MIMO system. A cross-layer rate control algorithm integrated with channel prediction in order to maximize the MAC throughput is presented. The algorithm selects MIMO mode and other parameters adaptively, thereby enhances the throughput of traffic. It can be used in close-loop control with feedback of every frame and other scenario such as traffic scheduling and frame retransmission. A frame aggregation optimizing algorithm which tunes the number of spatial streams, modulation and coding schemes, aggregation size is presented. This algorithm is implemented with a simplified lookup table and SNR thresholds calculated using Link Quality Metric. It shows the throughput can be enhanced maximally and the BER is reduced taking advantage of diversity of MIMO mode. Suitability of application, simplicity of implementation, efficiency of run-time made it be used in MIMO and SISO systems widely.