Channel Estimation And Signal Detection In Broadband Wireless Access Systems

Broadband wireless access(BWA) technology is a very competitive technology for broadband access, it has such advantages as cheap price, rapid deployment, high scalability, lower maintenance and upgrade costs. Along with the evolution of Internet services, customers have a great demand for high rate, high performance and interoperable BWA products.According to this requirement, IEEE developed and published 802.16 standard on fixed broadband wireless access systems. In this standard, WirelessMAN-OFDMA, which combines orthogonal frequency division multiplexing(OFDM) and frequency division multiple access technologies, is the main physical layer scheme for 2GHz-11GHz non-line-of-sight transmission. In this thesis, OFDM channel estimation and signal detection techniques in broadband wireless environment are investigated based on that WirelessMAN-OFDMA specification.WirelessMAN-OFDMA specification is introduced in detail at first, including symbol parameters, frame structure, modulation scheme and multiple antennas configuration. Then, the reference channel model of fixed BWA systems is described, mainly about the parameters'concepts in this channel model.As to single-in-single-output OFDM systems, two kinds of channel estimation methods, frequency domain and time domain, are investigated respectively. A time domain linear minimum mean square error (LMMSE) channel estimation algorithm is derived, and its computation complexity can be greatly lowered by matrix transform without degrading performance. It also can avoid interpolation which is needed in frequency domain algorithms, and the correspondence interpolation error. Then, signal detection methods for single-in-single-output OFDM systems are analyzed.As to multiple antennas OFDM systems, frequency domain and time domain least square (LS) channel estimation algorithms are presented. Time domain algorithm has better performance, considering performance and complexity, channel estimation for this system should use time domain LS algorithm. Then, for two and four transmitter diversity schemes in the standard, the detection algorithms of these space time codes are given. The algorithms'performances are analyzed by simulations. Correlated channels'impact on system is also simulated and analyzed. A Maximum A posteriori (MAP) receiver for concatenated space time block code and convolutional code is designed, through which optimal bit error rate performance is achived, and the system can get diversity gain and coding gain at the same time.