Research On The Bit And Subcarrier Dynamic Allocation Algorithms For OFDMA System

Orthogonal Frequency Division Multiplexing (OFDM) technique is capable of confronting multipath fading and suppressing inter-symbol interference (ISI) caused by multipath propagation. Besides, finite spectrum resource could also be efficiently utilized. Thus OFDM is considered to be the preferred scheme of the next generation wireless communication system.Bit and subcarrier dynamic allocation technique is one of the key techniques in OFDM. As the characteristics of time-varying and frequency-selective fading of wireless channel, spectrum resource can be utilized more efficiently by adopting the dynamic allocation algorithm, which allocates bit and subcarrier according to channel characteristic of each subcarrier. Hence the bit and subcarrier dynamic allocation algorithms is emphasized in this thesis.Wireless channel fading status information is the basis of allocating bit and subcarrier in the dynamic allocation algorithm. Therefore the characteristics of wireless channel fading are analyzed firstly in the thesis. Then the principle of the bit allocation base on single user OFDM system is introduced in detail. Performances of some typical bit allocation algorithms, including greedy algorithm, Chow, Cioffi, and Bingham algorithm and Fischer algorithm, are analyzed and compared. Based on these, an improved bit allocation algorithm with less computational complexity is proposed. Numerical results show that the performance of the improved algorithm is close to that of greedy algorithm, while the computational complexity is much lower. Meanwhile, inner relationships among various optimize rules are discussed in the thesis. By converting to MA rule, the typical algorithms are compared. Also the characteristics of bit allocation algorithm under the RA rule are analyzed. Base on the multiuser OFDM system, the principle of the subcarrier allocation algorithm isintroduced. The performances of some typical subcarrier allocation algorithms, such as Wongl algorithm-. Wong2 algorithm and Zhang algorithm and so on, are analyzed and compared. Then the corresponding improved methods are proposed. At last, multiuser OFDMA simulation system is built. The system performance based on two typical bit and subcarrier dynamic allocation algorithms respectively are compared by simulation. The system performances under the channel estimate error and maximum Doppler Shift are also analyzed by simulation.