Ofdma Wireless Access Technology In A Timely Manner The Frequency Synchronization Is Estimated That

Motivated by the increasing demand of the modern society for high-speed reliable information exchanges anytime and anywhere, broadband wireless systems (BWS) are envisioned for future mobile communication networks. It has been widely acknowledged that the terrestrial BWS faces a formidable challenge due to the frequency-selective multipath fading propagation environment. Multi-carrier modulation (MCM) is a preferable physical layer technology for BWS, since it can efficiently mitigate the frequency-dependent distortion across a wide frequency band and simplify the equalization in a multipath fading environment. BWS also relies on the multiple access technique to divide the common transmission medium among multiple users. As a unique multiple access system based on the MCM technology, the orthogonal frequency division multiple access (OFDMA) is a promising technology for BWS.This dissertation first introduces OFDMA systematically. Second, a maximum likelihood estimator (MLE) that jointly estimates the carrier frequency offset (CFO) and the channel response of each user in uplink OFDMA systems based on generalized carrier assignment schemes is investigated in this research. 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, making use of the alternating-projection technique, we replace the above search with a sequence of mono-dimensional searches. At last, this dissertation present an algorithm that performs joint frequency offset acquisition, channel estimation and data detection for each active user. Users'separation is accomplished at the base station through space-alternating generalized-expectation (SAGE) techniques.After theoretical analysis, we analysis and compare the efficiency and feasibility of these algorithms with Matlab software simulation. Motivated by the increasing demand of the modern society for high-speed reliable information exchanges anytime and anywhere, broadband wireless systems (BWS) are envisioned for future mobile communication networks. It has been widely acknowledged that the terrestrial BWS faces a formidable challenge due to the frequency-selective multipath fading propagation environment. Multi-carrier modulation (MCM) is a preferable physical layer technology for BWS, since it can efficiently mitigate the frequency-dependent distortion across a wide frequency band and simplify the equalization in a multipath fading environment. BWS also relies on the multiple access technique to divide the common transmission medium among multiple users. As a unique multiple access system based on the MCM technology, the orthogonal frequency division multiple access (OFDMA) is a promising technology for BWS. This dissertation first introduces OFDMA systematically. Second, a maximum likelihood estimator (MLE) that jointly estimates the carrier frequency offset (CFO) and the channel response of each user in uplink OFDMA systems based on generalized carrier assignment schemes is investigated in this research. 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, making use of the alternating-projection technique, we replace the above search with a sequence of mono-dimensional searches. At last, this dissertation present an algorithm that performs joint frequency offset acquisition, channel estimation and data detection for each active user. Users'separation is accomplished at the base station through space-alternating generalized-expectation (SAGE) techniques. After theoretical analysis, we analysis and compare the efficiency and feasibility of these algorithms with Matlab software simulation.