Based On The Wimax Ofdma Uplink Interference Cancellation And Downlink Multi-antenna Technology

With the fast development of multimedia communication, large capacity data communication is much required than traditional voice communication. Wireless communication is developing with higher data rate, wider range and better mobility. And the appearance of WiMAX (World Interoperability for Microwave Access) meets the trend of development. WiMAX is a broadband wireless communication technology based on IEEE802.16 standard, supporting higher data rate, voice and video communication in fixed and mobile environment. OFDM and OFDMA technology are widely applied in WiMAX physical layer as the main technology in IEEE802.16 standard. Especially OFDMA supports mobile IEEE802.16e standard. So researches on OFDMA are important.OFDMA technology theories and OFDMA in WiMAX technology are introduced firstly. Transmitting data is achieved by exploiting the orthogonality of the sub-carriers in OFDMA. However in uplink channel, each user has its own frequency offset which leads to a loss of orthogonality among the sub-carriers and multiuser interference at the base station receiver. This paper focuses on carrier frequency offset estimation (CFO) and multiuser interference elimination in uplink OFDMA system based on generalized carrier assignment schemes. Maximum likelihood estimation algorithm is investigated in CFO estimation. The exact solution to this problem turns out to be too complex for practical purposes as it involves a search over a multi-dimensional domain. However, to make use of the alternating-projection technique, we replace the above search with a sequence of mono-dimensional searches. Then, we present a low-complexity algorithm using iterative signal processing to compensate for the CFO in OFDMA systems. Matlab simulation shows that the proposed algorithm could eliminate multiuser interference and improve the uplink performance of OFDMA.Furthermore, broadband wireless technology provides large capacity in downlink, and MIMO technology can enhance capacity and spectrum efficiency without increasing bandwidth. So this dissertation also researches multi-antenna technology in downlink based on OFDMA. To support high speed communication and largest system capacity, a downlink model based OFDMA and D-STTD is proposed. An algorithm about inverse matrix is proposed at the base station receiver, so that the complexity of receiver computation has been reduced. At last, through simulation, we analyses the downlink performance in frequency selective channels and correlative channels.