Research On Initial Ranging Algorithms In WiMAX System

Initial ranging is a process in the wireless access, in which the Base Station detectsthe initial ranging user, estimates the timing offset and the power of the detected user,and feeds back these parameters to the detected user, and then makes the detected userto adjust its timing offset and power according to the feedback. To meet therequirements of the synchronization and power adjustment in the uplink of the wirelessOFDMA communication system, and obtain a high transmission efficiency, it is veryimportant to improve the performance of the initial ranging.In this work, the initial ranging algorithms in the WiMAX OFDMA system aremainly researched. Firstly, the OFDMA ranging system and the initial rangingalgorithms in the SISO-OFDMA system are introduced. And then the initial rangingmethods in the MIMO-OFDMA system are studied. In the MIMO-OFDMA system, aninitial ranging algorithm based on the multi-user diversity is discussed, but it has a badperformance. To further improve the performance of the initial ranging, a modifiedinitial ranging algorithm based on the ESPRIT is proposed. The proposed methodovercomes the disadvantage of the MDL algorithm, and improves the performance ofthe initial ranging.Finally, the initial ranging methods using the beam-forming are also researched inthe paper, and an improved initial ranging method based on the beam-forming isproposed. Simulation results show that the performance of the proposed method isbetter than that of the method based on the multi-user diversity and the method basedon beam-forming in the MIMO-OFDMA ranging system.