| The idea of cross-layer design is a key theoretical innovation for next generation wireless communication systems.It discards the idea of layered design and views separate network layers as a whole to design,analyze,optimize,and control.At the same time,it makes full use of the closely related information between physical,MAC, and other layers to optimize the performance of wireless network protocol.With the idea of cross layer design,this thesis investigates several key problems in cross layer design of different protocols for next generation wireless communication networks. Through theoretical analysis and computer simulation,it verifies the advantage of cross-layer design over conventional layered design in throughput,packet loss,and average delay.The research results provide next generation wireless communication networks reference cross-layer optimization strategies and are helpful for the standardization.In this thesis,we mainly focus on cross-layer design,non-linear optimization,and dynamic resource allocation.We build the general mathematical model with parameters from different layers,and use non-linear optimization as a mathematical tool to combine cross-layer design and dynamic resource allocation together so as to improve the network performance.Our work and contributions include:1.We propose a new link adaptation mechanism based on cross-layer design.First we investigate the current link adaptation mechanisms including ARF,RBAR,MSDU based adaptive physical layer mode selection,and MPDU based link adaptation.We choose MPDU based link adaptation as the basis of our work,which is with best performance through comparison.It dynamically adjusts the data transmission rate of MPDU so that the system performance improves greatly.Based on the above analysis,we propose a cross-layer link adaptation based on IEEE 802.11a OFDM physical layer and DCF MAC layer.By detecting network load information and channel state information,it dynamically adjusts the frame length,contention window length,and physical layer mode so as to improve the goodput and reduce the network packet loss. 2.With the mathematical tool of non-linear optimization,we use the theoretical expression of goodput as the objective,and frame length,contention window length, and physical layer mode as the constraints.It is a convex optimization problem according to the proof.Therefore,based on the convex optimization theory with good characteristics,the solution is easily found.3.We propose a cross-layer adaptation subcarrier allocation,which is called CL_ARRA.Working in the base station(BS) of wireless mesh network,i.e., downlink,it uses IEEE 802.16e OFDMA technique to dynamically allocate the subcarriers to maximize system throughput and satisfy the quality of service requirement.It includes two steps:first the base station dynamically allocates the subcarriers according to CSI and QSI so as to obtain the strategy of subearrier allocation;then with the subcarrier allocation,it acheives dynamic power allocation to improve the throughput of downlink.Different from other methods,this scheme works in overlapped neighborhood cells using the same frequency.It allows neighborhood cells to share frequency resources and minimize the collision probability of mobile nodes in the overlapped region.Therefore,it improves the system throughput and reduces the average delay effectively.4.Based on the above downlink subcarrier allocation mechanism(CL_ARRA),we propose a new collision avoidance uplink MAC protocol,which uses the subcarrier resource allocated by CL_ARRA to access the BS and MS in the cell.Through the investigation on uplink transmission mechanism,we introduce a new subcarrier backoff algorithm,which dynamically adjusts the quantity of subcarriers of mobile nodes in the overlapped region to avoid collision.Using 2-D Markov Chain model, the analysis of the MAC protocol shows that the protocol effectively reduces the collision probability of mobile nodes in the overlapped region and improves the system throughput.
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