Yasir Ahmed

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Amir Manbachi

Johns Hopkins University

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University of Adelaide

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National Institute of Technology, Calicut

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Pontificia Universidad Catolica de Chile

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Univerzitet u Sarajevu, Filozofski fakultet

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A model-based approach to demodulation of Co-channel MSK signals

GLOBECOM '03. IEEE Global Telecommunications Conference (IEEE Cat. No.03CH37489)

Co-channel interference limits the capacity of cellular systems, reduces the throughput of wirele... more Co-channel interference limits the capacity of cellular systems, reduces the throughput of wireless local area networks, and is the major hurdle in deployment of high altitude communication platforms. It is also a problem for systems operating in unlicensed bands such as the 2.4 GHz ISM band and for narrowband systems that have been overlaid with spread spectrum systems. In this work we have developed model-based techniques for the demodulation of cochannel MSK signals. It is shown that MSK signals can be written in the linear model form, hence a minimum variance unbiased (MVU) estimator exists that satisfies the Cramer-Rao lower bound (CRLB) with equality. This framework allows us to derive the best estimators for a single-user and a two-user case. These concepts can also be extended to wideband signals and it is shown that the MVU estimator for Direct Sequence Spread Spectrum signals is in fact a decorrelator-based multiuser detector. However, this simple linear representation does not always exist for continuous phase modulations. Furthermore, these linear estimators require perfect channel state information and phase synchronization at the receiver, which is not always implemented in wireless communication systems. To overcome these shortcomings of the linear estimation techniques, we employed an autoregressive modeling approach. It is well known that the AR model can accurately represent peaks in the spectrum and therefore can be used as a general FM demodulator. It does not require knowledge of the exact signal model or phase synchronization at the receiver. Since it is a non-coherent reception technique, its performance is compared to that of the limiter discriminator. Simulation results have shown that model-based demodulators can give significant gains for certain phase and frequency offsets between the desired signal and an interferer. phase difference between the signal of interest and an interferer 4.7 Performance of model-based demodulator with LMS update 4.8 Performance of model-based demodulator using angle of filter coefficients 4.9 Comparison of various model-based demodulation schemes 4.10 Performance of limiter discriminator for various carrier frequency separations 4.11 Performance of model-based demodulator for various carrier frequency separations 4.12 Comparison of limiter discriminator and model-based demodulator for carrier frequency separation of 1/2T 4.13 Comparison of model-based demodulator and limiter discriminator in Rayleigh fading environment (FdT = 0.002, Eb/No = 20dB)

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