7 research outputs found

    COSSAP simulation model of DS-CDMA indoor microwave ATM LAN

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    This thesis presents an original work in the area of designing and implementing a simulation testbed for modelling a high speed spread spectrum Asynchronous Transfer Mode (ATM) Local Area Network (LAN). The spread spectrum technique used in this LAN model is Direct Sequence Code Division Multiple Access (DS-CDMA). The simulation model includes at least a physical layer of such a LAN, embedded into the COSSAP1 simulation environment, and has been fully tested. All the newly developed building blocks are comprised of standard blocks from the COSSAP libraries or compatible user-built primitive blocks (only where it is absolutely necessary), and are flexible enough to allow the modification of simulation or model parameters; such as the number of signal channels, modulation method used, different spreading code sequences and so on. All these changes can be made with minimal effort. Another significant contribution made in this thesis is the extended research into evaluating the Bit Error Rate (BER) performance of different spread spectrum COMA coding schemes for an indoor microwave A1M LAN [8]. Different spread spectrum CDMA coding schemes are compared for their transmission error rate in Additive White Gaussian Noise (AWGN) channel with varying transmitted signal power and at different channel Signal to Noise Ratio (SNR) levels. Since a wireless microwave channel is very prone to transmission errors, a major contribution of the simulation testbed developed in this thesis is its use in the finding of an optimal physical layer transmission scheme with the best Bit Error Rate (BER) performance in an indoor environment

    Second year technical report on-board processing for future satellite communications systems

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    Advanced baseband and microwave switching techniques for large domestic communications satellites operating in the 30/20 GHz frequency bands are discussed. The nominal baseband processor throughput is one million packets per second (1.6 Gb/s) from one thousand T1 carrier rate customer premises terminals. A frequency reuse factor of sixteen is assumed by using 16 spot antenna beams with the same 100 MHz bandwidth per beam and a modulation with a one b/s per Hz bandwidth efficiency. Eight of the beams are fixed on major metropolitan areas and eight are scanning beams which periodically cover the remainder of the U.S. under dynamic control. User signals are regenerated (demodulated/remodulated) and message packages are reformatted on board. Frequency division multiple access and time division multiplex are employed on the uplinks and downlinks, respectively, for terminals within the coverage area and dwell interval of a scanning beam. Link establishment and packet routing protocols are defined. Also described is a detailed design of a separate 100 x 100 microwave switch capable of handling nonregenerated signals occupying the remaining 2.4 GHz bandwidth with 60 dB of isolation, at an estimated weight and power consumption of approximately 400 kg and 100 W, respectively

    Collaborative coding multiple access communications

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    This thesis investigates collaborative coding multiple access (CCMA) channel communication schemes. The CCMA schemes potentially permit efficient simultaneous transmission by several users sharing a common channel, without subdivision in time, frequency or orthogonal codes. The main areas of investigation include the information transmission capacity for single and multiple access channels, coding/decoding techniques and practical system design for CCMA schemes. The information transmission capacity of a sampled and quantised single access AWGN channel is developed. It is determined and optimised when the channel input and output are limited by certain practical constraints. These investigations have led to the development and determination of the information transmission capacity of multiple access channels. The capacity of a multiple access channel is studied for two different classes of T-user channel models from both theoretical and practical points of view. It is shown, in principle, that higher transmission rates or, equivalently, more reliable communication than with time sharing is achievable employing the same signalling alphabet. The CCMA schemes, in addition to providing the multiple access function, can also incorporate a certain degree of error control capability. Two main decoding techniques, hard decision and maximum likelihood soft decision, are presented with uniquely decodable CCMA schemes. A new low complexity maximum likelihood decoding technique is described and analysed. Reliability performance of various collaborative codes is studied by simulation employing these decoding techniques. It is shown that uniquely decodable schemes permit the multiple access function to be combined with forward error correction. It is also found that soft decision decoding can provide an energy gain over hard decision decoding. The final area of investigation is a practical CCMA modem system design to combine collaborative coding and modulation. An M-ary frequency shift keying based modulation scheme is described for the T-user CCMA schemes. Three particular types of demodulation techniques, square-law, zerocrossing counting, and quadrature receiver, are described. These techniques are developed in software, tested and evaluated over noiseless and noisy channels

    Investigation of pre-detection signal processing of pseudonoise communication signals in the presence of additive white gaussian noise and CW and bursty interference

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    By comparison to conventional communication systems, spread-spectrum systems are known to be less affected by interference because of their large dimensionality in signal space. Nevertheless, significant performance degradation is experienced when large interference exists in a few or even one signal coordinates. In this case, interference reduction techniques are also known to provide additional processing gain. A novel class of pseudonoise (PN) invariant algorithms is derived to reduce the impact of interference and restore much of the structure of PN signals received in the presence of interference and noise. A PN signal received by a pre-detection signal process (PDSP) implementing a PN invariant algorithm remains unchanged at the output. When an interference waveform is added to the PN signal, most of the DC bias as well as other smooth components of the interference may be significantly reduced at the output of the same PDSP. If n is the longest run in the PN sequence of maximal length N, and Ro is the chip rate, it is shown that the algorithms work well when the interference is sinusoidal with a frequency deviation from the carrier up to Ro/N. At such a low frequency deviation, the processing gain is observed to be relatively high and independent of the phase deviation. As the frequency deviation Increases to nRo/N, the performance of the spread-spectrum system decreases to the level that would have been obtained in the absence of the PDSP

    Sequential detection methods for spread-spectrum code acquisition

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    Intelligent Sensor Networks

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    In the last decade, wireless or wired sensor networks have attracted much attention. However, most designs target general sensor network issues including protocol stack (routing, MAC, etc.) and security issues. This book focuses on the close integration of sensing, networking, and smart signal processing via machine learning. Based on their world-class research, the authors present the fundamentals of intelligent sensor networks. They cover sensing and sampling, distributed signal processing, and intelligent signal learning. In addition, they present cutting-edge research results from leading experts
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