Research Of Adaptive Resource Allocation Algorithms And LDPC Coding In Multicarrier Systems

The next-generation mobile communication systems are required to provide high data-rate, high reliable transmission. How to provide these services and guarantee end-to-end QoS under abominable channel environment has been one challenge of the future wireless communication systems. OFDM can resist multipath fading and increase the transmission rate; MIMO can improve the system performance and capacity; adaptive technology which automatically adjusts the transmission parameters and structure to meet the wireless environment can improve the spectral efficiency and the system performance. So, OFDM, MIMO and adaptive technology are regarded to be key technologies of the future wireless mobile communication system.This dissertation researches on adaptive bit and power allocation algorithms in multicarrier systems. Several adaptive bit and power allocation algorithms are proposed according to different constraints. Based on the analysis of MIMO-OFDM system model, the proposed algorithms are extended to MIMO-OFDM systems. The performance of combined LDPC coding and adaptive allocation algorithms in multicarrier systems is studied. Furthermore, the effect of the imperfect channel state information on the adaptive algorithms is studied, and an adaptive algorithm is presented which can lower the effect. The dissertation also researches on the performance of LDPC coding, OFDM and adaptive algorithms in image transmission.Section I is the preface of this dissertation, which introduces the background knowledge and the current researching status. The organization and main contributions of this paper are presented also.As a theoretical foundation, In Section II, the principle of OFDM, adaptive technology and MIMO-OFDM is introduced and their advantages and disadvantages are analyzed. In this Section, several mathematical models of adaptive algorithms are given according to different service requests.In Section III, adaptive bit and power allocation algorithms in multicarrier systems are researched. An adaptive bit and power allocation algorithm is presented which minimize the BER under the constraints of total transmission rate and total power. Firstly, the algorithm constructs Lagrange function containing bit and power values, then obtains the optimal bit and power values of each subcarrier by the differential of Lagrange function. Simulation results show that the proposed algorithm can improve the system performance greatly with low computational complexity. Based on the analysis of MIMO-OFDM system, the proposed algorithm is extended to SM-OFDM system. The simulation results show that the algorithm is still effectiveIn Section IV, two bit and power allocation algorithms are presented, which can maximize the system capacity under the constraints of target BER and total power. One reallocates power based on the fact that BER value of each subcarrier is lower than the target BER; another one reallocates power based on the fact that the average BER of all subcarriers is lower than the target BER. The simulation results show that two algorithms can implement high throughput. Based on the analysis of MIMO-OFDM system model in Section III, the performance of two algorithms in SM-OFDM system is studied. The results show that two algorithms are effective and reliable in SM-OFDM system. In this Section, the effect of imperfect channel state information on adaptive algorithms is researched, and an adaptive algorithm which can lower this effect is presented. The results show that this algorithm is effective to resist the channel mismatch result form feedback delay and estimation error.In Section V, the performance of combined LDPC coding and adaptive bit power allocation algorithms in multicarrier system is researched. Firstly, the basic principle of LDPC codes is introduced. Then, the performance of combined LDPC coding with two adaptive algorithms (one is to minimize the BER and another is to minimize the transmission power) in multicarrier system is researched respectively. The simulation results show that the performance with combined LDPC coding and adaptive algorithm is better than LDPC coding or adaptive algorithm alone. This indicates that the combination of LDPC coding and adaptive algorithm is effective in multicarrier system. The results also show that the gain result from LDPC coding is higher than that result from adaptive algorithm. In Section VI, the performance of adaptive bit power allocation algorithm, LDPC coding and OFDM in image transmission is researched. Image transmission scheme which use the combination technology of adaptive bit and power allocation algorithm,LDPC coding and OFDM is proposed. The performance of two image transmission schemes is studied respectively. One scheme ues LDPC coding,OFDM and adaptive algorithm which is to minimize the BER, another scheme uses LDPC coding,OFDM and adaptive algorithm which is to minimize the transmission power. The simulation results show that the performance of image transmission with OFDM, LDPC and adaptive algorithm is better than that with OFDM+LDPC or OFDM+adaptive algorithm or OFDM. This indicates that the combination of OFDM, LDPC and adaptive algorithms is effective in image transmission.In Section VII, the dissertation is summarized and some problems need to be further researched are presented.