Research On Adaptive Bit Power Allocation Algorithms For OFDM Systems

With the diversification of wireless communication services,the traditional spectrum utilization technology can not guarantee the efficiency and reliability of communication transmission.Besides,the scarcity of frequency domain resources has become an important factor of restricting the development of wireless communication technology.Therefore,how to realize the transmission of information at high speed reliably has become an urgent problem which is needed to be solved under the condition of limited bandwidth.While the Orthogonal Frequency Division Multiplexing(OFDM)technology divides the actual channel into plenty of parallel sub-channels,so the adaptive bit and power allocation technology can be used to allocate a different number of information bits and transmit power for each sub-channel according to their real-time channel condition,which can make use of the spectrum resources fully,and ultimately achieves the purpose of improving the transmission performance of the whole communication system.This thesis,through the research on the adaptive bit power allocation technology in OFDM system,mainly completed the following work:1.Firstly,the channel attributes of wireless channel and the OFDM technology are analyzed in detail,and then the adaptive bit power allocation scheme in OFDM system is mainly analyzed by comparison with the traditional static bit power allocation scheme in OFDM system.2.In single-user OFDM system,after a through research on Greedy algorithm,this thesis puts forward an improved adaptive bit power allocation algorithm for single-user with reduced complexity based on the margin adaptive criterion,which is mainly composed of pre-allocation and iterative allocation.In the pre-allocation,the improved algorithm allocates partial information bits in advance according to the channel condition of each sub-channel;while in the iterative allocation,the improved algorithm reduces the times of calculation and comparison by increasing the memory cost.The simulation results show that the simulation results of the improved algorithm are basically the same as those of the Greedy algorithm in the same simulation environment,but the improved algorithm has a shorter running time,which shows that the improved bit power allocation algorithm for single-user has lower time complexity.3.In multi-user OFDM system,as for the problem that the rate adaptive criterion cannot balance the system capacity and user fairness,a novel scheme which adopts the two steps of the sub-channel allocation and the power allocation is proposed in this thesis.This scheme is mainly achieved by the sub-channel allocation algorithm based on fairness and the power allocation algorithm based on penalty function.In the sub-channel allocation algorithm,the capacity of the system can be improved when the fairness constraint is satisfied,otherwise the fairness of the user can be improved.However,the system capacity and user fairness can not be better balanced after the sub-channel allocation.In view of this,a novel power optimization strategy based on penalty function is proposed in the power allocation algorithm,and this strategy takes the advantage of the improved artificial bee colony algorithm based on the simulated annealing to achieve the tradeoff between the system capacity and user fairness.It can be seen from the simulation results,the proposed scheme in this thesis can not only improve the system capacity effectively but also achieve a given user fairness constraint,thus proving the effectiveness of the proposed scheme.