The Research On Subcarrier Allocation Algorithms In OFDM-Based Cooperative Communication Systems

As a new spatial diversity technology, cooperation diversity has attracted more attention from the industry for it could be combined with other diversity technologies without occupying extra time or bandwidth. The combination between Orthogonal frequency division multiplexing (OFDM) and cooperative can not only combat multipath interference, increase the system's information transmission rate and provide space multiplexing gain, which greatly increase the channel capacity, improve system performance and communication quality, but also become more practical. For this reason, this paper studies the distribution subcarrier allocation strategy and channel estimation algorithm of OFDM cooperative communication system.First, this paper introduces the principle, classification, advantages and disadvantages of cooperative diversity, and then introduces the model of traditional cooperative communication system. The principles and key technologies of OFDM are discussed.Second, channel estimation algorithms of two-hop OFDM cooperative communication system with single relay are discussed, which are mainly based on block pilot. The paper gives the Jakes Rayleigh fading model, and then discusses the multi-path frequency-selective fading channel modeling method based on Jakes model; And the paper introduces time-division duplex and frequency division duplex model of OFDM cooperative communication system, then designs three kinds of channel estimator, LS, LMMSE and LrMMSE, based on block pilot symbol; At last, the paper does lots of Monte Carlo simulations used for discussing the impact of different parameters on the performance of estimator.Finally, this paper analyzes the subcarrier allocation algorithms of two-hop OFDM cooperative communication system with single relay; Based on TDD mode, fixed subcarrier allocation (FSA) and adaptive subcarrier allocation (ASA) algorithm are presented for the AF-OFDM model, also based on the FDD mode, fixed distributed subcarrier allocation (FDSA) and adaptive distributed subcarrier allocation (ADSA) algorithm are presented for the DF-OFDM model; the performance of the proposed subcarrier allocation algorithms are analyzed in theory; Then, the paper does lots of simulations used for analyzing the performance of different subcarrier allocation algorithms, and discusses the impact of different parameters.