Michael J. Ready

Blind equalization based on radius directed adaptation

A blind equalization algorithm, termed radius directed equalization (RDE), for quadrature amplitude modulation (QAM) signals based on the known modulus of the constellation symbol radii is described. For example, 16 QAM has three radii and 32 QAM has five radii. The algorithm uses the error between the equalizer output modulus and the nearest symbol radius to update the equalizer weights. The RDE algorithm provides faster convergence than the constant modulus algorithm (CMA) for QAM signals and is independent of the carrier offset. The algorithm is described in the context of blind carrier and baud clock recovery schemes.<<ETX>>

Automatic noise floor spectrum estimation in the presence of signals

This paper describes a technique for automatically estimating the noise floor spectrum in the presence of signals. The technique works equally well for both flat and non-flat noise floor spectra. The technique is based on applying morphological binary image processing operators to a binary image of the received power spectrum. It is related to rank-order filters but is more computationally efficient. The performance is illustrated on the detection of radio signals.

Optimum and reduced complexity multiuser detectors for asynchronous CPM signaling

Maximum likelihood detector algorithms are developed for the matrix of transmitted symbols in a multiuser system in which the received signal is the sum of K cochannel continuous phase modulated (CPM) signals and additive white Gaussian noise. We illustrate that the maximum likelihood matrix detector, which provides optimum detector performance, consists of K sets of front-end matched filters followed by a Viterbi algorithm. We also derive two reduced complexity receivers, demonstrating through simulation that they perform within 1-2 dB of the optimal while substantially reducing complexity. The paper demonstrates how performance can be traded off against complexity, giving particular attention to cochannel Gaussian minimum shift keyed (GMSK) signals

Demodulation of cochannel FSK signals using joint maximum likelihood sequence estimation

This paper describes a technique for demodulating cochannel Manchester-encoded, frequency-shift-keyed (MEFSK) signals even when the two signals have equal power. Both data sequences are recovered. The technique is based on joint maximum likelihood sequence estimation (JMLSE). The Viterbi algorithm is used to minimize the computational requirements. Adaptive loops track the transmitter carrier and filtering characteristics. The demodulator performance is evaluated as a function of baudrate offset, carrier power separation and additive noise.<<ETX>>

Performance improvements achieved by equalizing intermediate rate FSK signals

FSK modems are commonly used for transmission of intermediate data rate signals (1-8 Mbps) in the microwave bands. Link performance can be limited when operating in multipath environments. This paper investigates the performance gains achieved by using equalization and post FM discriminator adaptive filtering for FSK signals to mitigate the effects of multipath. Performance is compared to nonequalized transmissions over a variety of multipath channels.

Architecture considerations for frequency domain adaptive equalizers

Fractionally-spaced frequency domain equalizer (FDE) designs are motivated by reviewing specific applications. Several FDE architectures m e discussed including both baseband and p a s band designs. Techniques are discussed which reduce the complexity of :-spaced FDEs.

The demod-remod technique for demodulating co-channel FSK signals

The authors describe the demod-remod method of demodulating two cochannel MEFSK (Manchester-encoded frequency shift keying) signals. The technique uses a conventional demodulator to obtain an estimate of the primary data sequence. The primary data are then remodulated and subtracted from the received signal to obtain an estimate of the secondary signal. The secondary signal is demodulated using conventional demodulation techniques. The authors present a description of phase noise, its effect on demod-remod performance, and methods used to mitigate it. Experimental results showing the range of signal power separations and carrier-to-noise ratios over which the demod-remod technique works are also presented.<<ETX>>

Simulation study of a successive interference cancellation receiver for signal monitoring on a CDMA downlink

A successive interference cancellation (SIC) algorithm is developed for the interception of signals transmitted on a CDMA forward link. The system is modelled after the IS-95 standard but the results are also applicable to other CDMA systems such as the wideband CDMA (W-CDMA) and IS-2000 standards. In realistic systems, the different forward link channels are de-orthogonalised, leading to performance degradation in conventional matched filter (CMF)-type receivers. Simulation results indicate that the proposed SIC receiver ameliorates the detrimental effects of de-orthogonalisation, interference and multipath, exhibiting significant gains in traffic capacity over the capacity of a CMF. The numerical simulations also show that the proposed receiver is relatively insensitive to system imperfections. The techniques developed in this paper can be used for interception, surveillance, reconnaissance or monitoring of CDMA signals; to relax the strict requirements on power control; and to improve the capacity of CDMA systems. Copyright

Analysis of Post-Demodulator Adaptive Filter Behavior to Compensate for Multipath Channels for FSK Signals

Analysis of adaptive filters positioned after FSK demodulators and the statistics of their non-Gaussian noise environment are used to extend previous analytical and simulation studies. Equalization of multipath channels for FSK signals is typically accomplished with an adaptive filter at the receiver before demodulation. Motivated by a desire to reduce computation, a post-demodulator adaptive filter was proposed, and simulations using multipath models derived from physical channel measurements showed promise. However, previous systematic simulation and theoretical analysis of short multipath channels have led to ambiguous results. This paper analyzes the non-Gaussian statistics of the filter input and, for longer multipath channels, shows why increasing the filter length does not improve performance and why the converged LMS filter produces a BER higher than the minimum achievable by a linear filter.

Post FM-Discrimination Multipath Equalization of MSK Signals

This paper provides an early look at the performance of a post FM-discriminator equalizer of MSK signals. The results build on earlier work for FSK signals that showed a computational and performance advantage over pre FM-discriminator equalization. The BER performance is explored for several multipath channels, and the frequency response of the filters after convergence is compared. While these results confirm that the behavior for MSK signals is similar to previous observations for FSK, they also raise many new questions. Full characterization of post FM-discrimination equalization is the subject of on-going investigation