Research And Implementation Of OFDM Adaptive Resource Allocation Scheme

With the increasing demand for high-speed data transmission and multimedia services,higher requirements for the transmission rate and quality of wireless communication are put forward.However,wireless communications are limited by scant spectrum resources.Therefore,improving band utilization and system capacity is a central issue in current research.OFDM divides the available channe l into multiple independent subchannels,and adaptively allocates bits or power to these subchannels reasonably,which can improve system performance and make full use of spectrum resources.This thesis focuses on the OFDM adaptive resource allocation prob lem,mainly to complete the following work:1.In the single-user OFDM adaptive resource allocation,in order to reduce Hughes-Hartogs algorithm's high computational complexity,an improved adaptive resource allocation scheme based on the MA criterion is proposed.In the improved scheme,subchannels higher than the average channel gain are first screened,and the average number of bits is directly allocated to these subchannels.After the pre-allocation is completed,the remaining bits are allocated to the sub-channel which increasing power is smallest each time according to the idea of the Hughes-Hartogs algorithm.After analysis,it can be known that the number of improved power calculations is(_bR-MR)?N and the number of power comparisons is(N-M).The corresponding Hughes-Hartogs algorithm power calculation number is _bR?N and the number of power comparisons is N.Therefore,the improved adaptive resource allocation scheme has lower computational complexity.The simulation results show that the improved adaptive resource allocation scheme is consistent with the performance of the Hughes-Hartogs algorithm.This shows that the improved adaptive resource allocation scheme guarantees the performance of the scheme while reducing the computational complexity.2.In the multi-user adaptive resource allocation,classic schemes exist some problems,such as low search accuracy,multiple iterations,user fairness and system capacity,an improved multi-user adaptive resource allocation scheme is proposed.Firstly,introduce the concept of fairness by referring to the literature.Then,by introducing the crossover and mutation behavior patterns of differential evolution algorithm into the artificial fish swarm algorithm,the random behavior of artificial fish is improved.In the process of resource allocation,subcarriers in the system are first allocated to users under a certain fairness threshold,and then the system power is allocated by using an improved artificial fish swarm algorithm to improve the transmission capacity of the system.The simulation results show that the system resource capacity is improved by 0.057bit/s/Hz and 0.122bit/s/Hz compared with the AFSA algorithm and the Shen algorithm when the fairness is 0.99 and the number of users is 14.When the fairness is 0.95 and number of users is 14,the system capacity is increased by 0.132 bit/s/Hz and 0.198 bit/s/Hz,compared to the above two algorithms.When the number of users is 8,the improvement scheme is iterated 5 times to obtain a convergence value,which is 15 times lower than the AFSA algorithm.Therefore,the improved adaptive resource allocation scheme improves the system capacity and reduces the number of iterations while ensure users'fairness.3.In view of the current problems of lacking implementing adaptive resource allocation schemes,this thesis designs and implements an improved single-user adaptive resource allocation scheme.In order to be applicable in practical OFDM systems,this thesis designs a resource allocation module and a source module.Then based on the FPGA tool and ISE software,with reference to the OFDM baseband transmission system,some system modules are designed and implemented,including a modulation module,an insertion pilot module,an IFFT transformation module,an insertion cyclic prefix module,short training sequence and long training sequence module.In this way,after processing by these modules,the bit data to be sent out through the subsequent modules can form a complete OFDM frame.Finally,this paper implements these modules and compares exported data with the data generated by matlab.According to the data analysis,the absolute error of the real part between the two sets of data is 0.016%of the amplitude value,and the absolute error of the imaginary part is about 0.017%of the amplitude value.This verifies the accuracy of the data.