Timing synchronization and retrieval in mobile communications

Pao Yue-kong Library Electronic Theses Database

Timing synchronization and retrieval in mobile communications

 

Author: Lam, Yiu-wa
Title: Timing synchronization and retrieval in mobile communications
Degree: M.Sc.
Year: 2000
Subject: Code division multiple access
Mobile communication systems
Synchronization
Hong Kong Polytechnic University -- Dissertations
Department: Multi-disciplinary Studies
Dept. of Electronic and Information Engineering
Pages: vii, 65, [86] leaves : ill. ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1517712
URI: http://theses.lib.polyu.edu.hk/handle/200/4705
Abstract: Accuracy of the timing algorithm directly affects the performance of the system in the transmission of digital data. A small drift the clock frequencies can drastically increase the probability of detecting error. In CDMA mobile communication systems, timing must be established in the receiver before any attemption to detect the digital signal. This project presents a novel source coding method that is resistant to timing jitter for CDMA systems. By assigning appropriate Walsh functions, used for orthogonal modulation in the uplink IS-95, to the text, the performance is improved by 100% in the presence of timing jitter with very little added overhead. One of the difficulties in the design of CDMA systems is timing synchronization between the base station (BS) and the mobile station (MS). Any deviation from the correct timing reduces the quality of the received signal and may render the system totally unusable. Walsh symbols are used in the IS-95 uplink for orthogonal modulation, as they are ideal for use to identify the correct data under perfect conditions. However, the presence of timing errors undermines their usefulness. Even a 10% shift of a chip interval (Tc) causes significant degradation in performance. Furthermore, the Bit Error Rate (BER) increases dramatically for timing errors of more than 10% Tc. For large shifts of 50% Tc or more, ambiguities in the timing instants exist that make the retrieval of timing information extremely difficult. Complex timing synchronization algorithm is required when timing error is in the form of jitter, especially in multi-path Rayleigh fading conditions. The aim of the project is to investigate the possibility of coding algorithm for source coding of English text in CDMA mobile communications by using the MATLAB program to simulate and evaluate the symbol error performance of the system. Therefore, simulation and analysis of various Walsh coding schemes for source coding in different signal to noise rate (SNR) are necessary. Also, Rayleigh fading channel will be applied for the simulation of transmission channel. Moreover, a suitable source coding method will be found out for English text by utilization of Walsh codes. The coding algorithm incurs very little overhead but an unexpected bonus for the CDMA systems can be acquired. Moreover, a paper was prepared and submitted to Wireless Personal Communications, Kluwer Academic Publishers for publishing. The Kluwer Academic Publishers is an international journal locates in Netherlands.

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