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Blind Equalization and Differential Modulation in Aero-based Wireless Communication

Author: LiJiang
Tutor: YuSongZuo
School: Shanghai Jiaotong University
Course: Communication and Information System
Keywords: intersymbol interference blind equalization variable step-size excess mean square error convergence speed
CLC: TN92
Type: Master's thesis
Year: 2008
Downloads: 31
Quote: 4
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Abstract


In the field of wireless communications, the primary problem is intersymbol interference (ISI) in multipath transmission. Equalizers are often used to combat the influence of channels for improving communication quality and decreasing ISI in receivers. Comparing with traditional equalizers, blind equalizers are widely used to combat the distortion of communication channels because of their special advantages. Training sequences are necessary in traditional equalizers for channel equalizing. In wireless communications, especially in aero-based wireless communications, the channels are time variant. So we must transmit many training sequences frequently to converging traditional equalizers. However, these training sequences will decreases the effective data bit rate and waste much bandwidth. The blind adaptive equalizations, which don’t need any training sequences, can achieve more efficient channel bandwidth usage. Therefore, blind adaptive equalizations have attracted more and more interest since they are regarded as more efficient equalizations in wireless communications. On the basis of studying on wireless communication channels, this paper discusses the comparability and differences between mobile channels and aero-based wireless channels in order to analyze the character of aero-based wireless channels and find the next research direction. This paper quotes an aero-based wireless channel: Rural channel. Then this paper demonstrates howπ/4-DQPSK could rectify Doppler frequency offset, and explains thatπ/4-DQPSK should be used in aero-based wireless communications. This paper gives emphasis on blind equalizations, especially constant modulus algorithm, multiple modulus algorithm, variable step-size algorithm and modified constant modulus algorithm.π/4-DQPSK and blind equalization are demonstrated to be effective in static Brazil A channel and dynamic Rural channel. After comparing the advantages and disadvantages of these algorithms, this paper gives a new blind equalization algorithm, which could correct phase offset ofπ/4-DQPSK signals after blind equalization. Especially, contrasting with existing algorithm the new algorithm can work under worse phase noise in dynamic channel. The feasibility and efficiency of the new algorithm are illuminated by simulations in this paper.

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CLC: > Industrial Technology > Radio electronics, telecommunications technology > Wireless communications
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