Adaptive PN code synchronisation in DS-CDMA systems

Spread Spectrum (SS) communication, initially designed for military applications, is now the basis for many of today's advanced communications systems such as Code Division Multiple Access (CDMA), Global Positioning System (GPS), Wireless Local Loop (WLL) , etc. For effective communication to take place in systems using SS modulation, the Pseudo-random Noise (PN) code used at the receiver to despread the received signal must be identical and be synchronised with the PN code that was used to spread the signal at the transmitter. Synchronisation is done in two steps: coarse synchronisation or acquisition, and fine synchronisation or tracking. Acquisition involves obtaining a coarse estimate of the phase shift between the transmitted PN code and that at the receiver so that the received PN code will be aligned or synchronised with the locally generated PN code. After acquisition, tracldng is now done which involves maintaining the alignment of the two PN codes. This thesis presents results of the research calTied out on a proposed adaptive PN code acquisition circuit designed to improve the synchronisation process in Direct Sequence CDMA (DS-CDMA) systems. The acquisition circuit is implemented using a Matched Filter (MF) for the correlation operation and the threshold setting device is an adaptive processor known as the Cell Averaging Constant False Alarm Rate (CA-CFAR) processor. It is a double dwell acquisition circuit where the second dwell is implemented by Post Detection Integration (PDI). Depending on the application, PDI can be used to mitigate the effect of frequency offset in non-coherent detectors and/or in the implementation of multiple dwell acquisition systems. Equations relating the performance measures - the probability of false alarm (Pra ), the probability of detection (P d) and the mean acquisition time (E {Tacq}) - of the circuit are deri ved. Monte Carlo simulation was used for the independent validation of the theoretical results obtained, and the strong agreement between these results shows the accuracy of the derived equations for the proposed circuit. Due to the combination of PDI and CA-CFAR processor in the implementation of the circuit, results obtained show that it can provide a good measure of robustness to frequency offset and noise power variations in mobile environment, consequently leading to improved acquisition time performance. The complete synchronisation circuit is realised by using this circuit in conjunction with a conventional code tracking circuit. Therefore, a study of a Non-coherent Delay-Locked Loop (NDLL) code tracking circuit is also calTied out.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Adaptive PN code synchronisation in DS-CDMA systems.

Spread Spectrum (SS) communication, initially designed for military applications, isnow the basis for many of today's advanced communications systems such as CodeDivision Multiple Access (CDMA), Global Positioning System (GPS), Wireless LocalLoop (WLL) , etc. For effective communication to take place in systems using SSmodulation, the Pseudo-random Noise (PN) code used at the receiver to despread thereceived signal must be identical and be synchronised with the PN code that was used tospread the signal at the transmitter. Synchronisation is done in two steps: coarsesynchronisation or acquisition, and fine synchronisation or tracking. Acquisitioninvolves obtaining a coarse estimate of the phase shift between the transmitted PN codeand that at the receiver so that the received PN code will be aligned or synchronisedwith the locally generated PN code. After acquisition, tracldng is now done whichinvolves maintaining the alignment of the two PN codes.This thesis presents results of the research calTied out on a proposed adaptive PN codeacquisition circuit designed to improve the synchronisation process in Direct SequenceCDMA (DS-CDMA) systems. The acquisition circuit is implemented using a MatchedFilter (MF) for the correlation operation and the threshold setting device is an adaptiveprocessor known as the Cell Averaging Constant False Alarm Rate (CA-CFAR)processor. It is a double dwell acquisition circuit where the second dwell isimplemented by Post Detection Integration (PDI). Depending on the application, PDIcan be used to mitigate the effect of frequency offset in non-coherent detectors and/or inthe implementation of multiple dwell acquisition systems. Equations relating theperformance measures - the probability of false alarm (Pra ), the probability of detection (P d) and the mean acquisition time (E {Tacq}) - of the circuit are deri ved. Monte Carlosimulation was used for the independent validation of the theoretical results obtained,and the strong agreement between these results shows the accuracy of the derivedequations for the proposed circuit. Due to the combination of PDI and CA-CFARprocessor in the implementation of the circuit, results obtained show that it can providea good measure of robustness to frequency offset and noise power variations in mobileenvironment, consequently leading to improved acquisition time performance. Thecomplete synchronisation circuit is realised by using this circuit in conjunction with aconventional code tracking circuit. Therefore, a study of a Non-coherent Delay-LockedLoop (NDLL) code tracking circuit is also calTied out

SIMULINK Implementation of a CDMA Transmitter

An implementation of a Code Division Multiple Access (CDMA) transmitter has been developed using SIMULINK and MATLAB. This transmitter uses a modified carrier in modulation. This modified carrier, which is frequency modulated, has been shown to reduce intersymbol interference (ISI) and multiple access interference (MAl). These two types of interference are caused by multipath propagation which results in delayed versions of the original signal. The benefits of this modified modulation technique are apparent when there are delays involved. The spreading sequences used are 7- bit Gold codes which allow a maximum of nine users. The initial trials of the transmitter indicate that it is functioning correctly

Engineering evaluations and studies. Volume 3: Exhibit C

High rate multiplexes asymmetry and jitter, data-dependent amplitude variations, and transition density are discussed

The payload/shuttle-data-communication-link handbook

Communication links between the Orbiter, payloads, and ground are described: end-to-end, hardline, S-band, Ku-band, TDRSS relay, waveforms, premodulation, subcarrier modulation, carrier modulation, transmitter power, antennas, the RF channel, system noise, received signal-to-noise spectral density, carrier-tracking loop, carrier demodulation, subcarrier demodulation, digital data detection, digital data decoding, and tandem link considerations

Proceedings of the Second International Mobile Satellite Conference (IMSC 1990)

Presented here are the proceedings of the Second International Mobile Satellite Conference (IMSC), held June 17-20, 1990 in Ottawa, Canada. Topics covered include future mobile satellite communications concepts, aeronautical applications, modulation and coding, propagation and experimental systems, mobile terminal equipment, network architecture and control, regulatory and policy considerations, vehicle antennas, and speech compression