Research On Dynamic Subcarrier Bit Allocation Algorithms For OFDM Systems

With the rapid development of wireless communication services,there is a higher demand for the speed and quality of communications,besides,the scarcity of wireless spectrum resources hinders the development of wireless communication technology.Therefore,how to realize the transmission of information at high speed reliably has become an urgent matter which is needed to be solved under the condition of limited bandwidth.The channel is divided into several independent sub-channels by the Orthogonal Frequency Division Multiplexing(OFDM)technology,and then adaptive technologies are used to implement dynamic bit and power allocation on the sub-channels based on actual channel conditions of each sub-channel,which can make use of the spectrum resources fully,and improve system transmission performance.This thesis,for the issues that dynamic subcarrier bit allocation technology in OFDM system,mainly completed the following work:1.In dynamic bit power allocation for single-user OFDM systems,according to the defects of the classical greedy algorithm such as the excessive iterations and the heavy computation,an improved greedy algorithm based on the margin adaptive criterion is proposed.Compared with the Greedy algorithm,the proposed algorithm can reduce the calculation amount by means of the pre-allocation and the iterative allocation.A new function of the power utilization rate is used in the improved algorithm to pre-allocate a portion of the bits to the subchannel with the good condition in the pre-allocation.Then,in the process of the iterative allocation,the power variation of the subchannels,based on the concept of classification and sort,would be stored in a form,thus the complexity of the improved greedy algorithm is reduced.Simulation results show that,under the same conditions,the improved algorithm and the greedy algorithm have almost the same bit-error performance,but the improved algorithm is better in terms of the running time.Then it shows the improved greedy algorithm can reduce the complexity of the algorithm while ensuring its performance.2.In dynamic sub-carrier bit allocation for multi-user OFDM systems,in order to solve the non-compatible problems of the system capacity and the user fairness adaptive resource allocation based on the Rate Adaption criterion,a novel adaptive resource allocation scheme with the high fairness is proposed.This scheme is achieved by thesubcarrier allocation algorithm based on the high fairness and the power allocation algorithm based on the simulated annealing and improved artificial bee colony algorithm.The scaling factor b is introduced into the subcarrier allocation algorithm,the subcarriers is divided into two parts,firstly the bN subcarriers are allocated to the users with the lower ratio to ensure the high fairness among the users;then the remaining subcarriers are allocated to the users with the maximum channel gain,and every user can at most be assigned a subcarrier in order to improve the system capacity.In the power allocation algorithm,the power optimization among all the users is achieved by taking the advantage of the improved artificial bee colony algorithm based on the simulated annealing in order to achieve the greater system capacity.The simulation results show that the proposed scheme can not only ensure the high fairness among the users but also improve the system capacity effectively.Therefore,the effectiveness of the proposed scheme has been proved.