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        Packet CDMA communication without preamble

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        Sajjad.pdf (2.115Mb)
        Date
        2007-01-02
        Author
        Rahaman, Md. Sajjad
        Type
        Thesis
        Degree Level
        Masters
        Abstract
        Code-Division Multiple-Access (CDMA) is one of the leading digital wireless communication methods currently employed throughout the world. Third generation (3G) and future wireless CDMA systems are required to provide services to a large number of users where each user sends data burst only occasionally. The preferred approach is packet based CDMA so that many users share the same physical channel simultaneously. In CDMA, each user is assigned a pseudo-random (PN) code sequence. PN codephase synchronization between received signals and a locally generated replica by the receiver is one of the fundamental requirements for successful implementation of any CDMA technique. The customary approach is to start each CDMA packet with a synchronization preamble which consists of PN code without data modulation. Packets with preambles impose overheads for communications in CDMA systems especially for short packets such as mouse-clicks or ATM packets of a few hundred bits. Thus, it becomes desirable to perform PN codephase synchronization using the information-bearing signal without a preamble. This work uses a segmented matched filter (SMF) which is capable of acquiring PN codephase in the presence of data modulation. Hence the preamble can be eliminated, reducing the system overhead. Filter segmentation is also shown to increase the tolerance to Doppler shift and local carrier frequency offset. Computer simulations in MATLAB® were carried out to determine various performance measures of the acquisition system. Substantial improvement in probability of correct codephase detection in the presence of multiple-access interference and data modulation is obtained by accumulating matched filter samples over several code cycles prior to making the codephase decision. Correct detection probabilities exceeding 99% are indicated from simulations with 25 co-users and 10 kHz carrier frequency offset or Doppler shift by accumulating five or more PN code cycles, using maximum selection detection criterion. Analysis and simulation also shows that cyclic accumulation can improve packet throughput by 50% and by as much as 100% under conditions of high offered traffic and Doppler shift for both fixed capacity and infinite capacity systems.
        Degree
        Master of Science (M.Sc.)
        Department
        Electrical Engineering
        Program
        Electrical Engineering
        Supervisor
        Dodds, David E.
        Committee
        McCrosky, Carl; Makaroff, Dwight; Gokaraju, Ramakrishna
        Copyright Date
        January 2007
        URI
        http://hdl.handle.net/10388/etd-01022007-084014
        Subject
        Code Acquisition
        PN Codephase Synchronization
        Packet CDMA
        CDMA
        Segmented Matched Filter
        Matched Filter
        Packet Throughput
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