Cross-Layer Adaptivere Source Allocation For OFDM System

Multi-carrier OFDM (Orthogonal Frequency Division Multiplexing) is selected as a key technology of LTE system for its ability to overcome multipath fading. Meanwhile, OFDM can be better combined with the link adaptation to realize the system capacity's enhancement through fully unearthing the system time-frequency resources.The layered resource allocation scheme increases performance of one-layer under the foundation of optimizing each layer, but it can not improve performance of overall system. Through considering the coupler among layer, cross-layer design combines the intersected layer in a network as a whole to optimize, sothat it can entirely promote the system performance. Therefore, studying the cross-layer resource allocation for OFDM system has larger significance in practice.A layered resource allocation algorithm based on the LTE system is proposed, while introduces basic structure and related key technologies of LTE system. On that basis, firstly, the importance of cross-layer design is discussed and the structure chart of cross-layer resource allocation is gived for LTE downlink OFDM system. Secondly, the process of cross-layer resource allocation is analysed, and then, the user transmission speed constraint and the priority function of different types of traffic are derived. Finally, a QoS-guaranteed cross-layer resource allocation strategy is proposed for OFDM system, which realizes the interaction of information among layer in a network as well as ensures the validity and reliability of network transmission by taking wireless channel's time-variable characteristic at physical layer, user buffer queue's inherent dynamic characteristic at MAC layer, traffic arrival's randomness at application layer and user's fairness under the application of multiuser diversity into account in scheduling and resource allocation. Simulation results indicate that the proposed algorithm can effectively reduce the overall system latency and improve the system spectral efficiency, while guarantees proportional fairness among user.