Research On Adaptive Bit And Energy Allocation Algorithm In OFDM System

With the development of modem mobile communication, the spectral resource is being scare because of the people’s desire for the multimedia and interconnection with Internet in the mobile service. So it has been an urgent task to purse new wireless technology with spectral efficiency.The prominent advantages of OFDM system are the high efficiency spectrum and anti-multi-path delayed ability, and the OFDM technology is suitable for the applications of future high-speed bandwidth wireless communication. The adaptive resource allocation of OFDM system allocates the sub-carrier, bit and power based on the real-time channel information.Firstly, the paper introduces the development and basic principle of OFDM system and the wireless channel environment; then several adaptive bit and power allocation classical algorithms for single user OFDM system are researched. A kind of adaptive bit and power allocation algorithm for the single user OFDM system based on MA criterion is designed because of the high complexity for the greedy algorithm. The improved algorithm deletes the sub-channels that are not suitable for transmitting the data information and allocates the bit according to channel capacity, and then adjusts the bit using greedy algorithm with changeable steps, the BER and transmitting power performances are very similar between the improved algorithm and greedy algorithm, but the CPU running time of improved algorithm decreases doubled, and effectively reduces the complexity of the resource allocation algorithm. Then the paper studies adaptive resource allocation of multi-user OFDM system, and mainly analyzes the optimal algorithm and two-step algorithm,. An improved algorithm based on user need degree is given in order to decrease the complexity of two-step algorithm. Although the improved algorithm has the similar performance with the two-step algorithm, the CPU running time of the improved algorithm decreases a lot. At the same time, the transmission power of the improved algorithm has about5dB lower than OFDM-TDMA fixed resource allocation. The main achievements of this paper are:according to the disadvantages of the existing algorithms, the paper gives simplified adaptive resource allocation algorithms for the single user and multi-user OFDM systems, and simulates the two improved algorithms using MATLAB. The simulation results verify the correctness and effectiveness of the improved algorithm. Therefore the improved algorithm can actually more effective and flexibility to solve adaptive resource allocation problems, and then makes up some existing defects.