Amir Masoud Rabiei

Multiple symbol differential detection of MPSK in the presence of frequency offset

The conventional multiple-symbol differential detection (MSDD) of differential phase-shift keying (DPSK) signals is studied in the presence of frequency offset. It is shown that in the case of nonzero frequency offset, the performance of the conventional MSDD receiver degrades by increasing the number of observed samples. A double DPSK (DDPSK) modulation scheme is then introduced and it is shown that in the presence of nonzero frequency offset, an MSDD receiver with DDPSK modulation outperforms a conventional MSDD receiver with DPSK modulation, when both receivers use a large number of received samples. Examples lead to a conjecture that the performance of an optimum MSDD receiver with DDPSK modulation and an infinite number of received samples, approaches that of a conventional DPSK demodulator with two received samples.

A simple, intuitive expression for the BER of a jointly optimal single cochannel interferer BPSK receiver

A simple and intuitive new expression for the bit error rate (BER) performance of a synchronous jointly optimum receiver is derived. The receiver is used to detect a binary phase-shift keying (BPSK) signal in the presence of an identical cochannel interferer and additive white Gaussian noise (AWGN). The new expression separates into the BER of BPSK in AWGN plus a term due to the interference. The term due to interference approaches zero when the interference power or its correlation with the desired signal tends to zero, as expected.

Cochannel interference mitigation using whitening receiver designs in bandlimited microcellular wireless systems

The problem of cochannel interference (CCI) suppression using a noise-plus-interference whitening matched filter (WMF) is addressed. Binary phase-shift keying modulated transmission over a Nakagami-m fading channel is considered in a bandlimited microcellular wireless system. It is shown that the signal-to-interference-plus-noise ratio (SINR) of the WMF can not exceed that of the conventional matched filter (CMF) receiver for synchronous CCI, but in the asynchronous channel, CCI whitening can be used to improve receiver performance. The SINR-maximizing filter (SINRMF) in an asynchronous channel is derived and shown to be composed of a WMF followed by a discrete time filter. The SINRs of the WMF and SINRMF receivers are analytically evaluated for a standard raised-cosine (RC) and a Beaulieu-Tan-Damen pulse. It is shown that for the RC pulse, the WMF can achieve a SINR gain as large as 1.76 dB over the CMF receiver provided that the transmission is free of intersymbol interference (ISI). The SINR of the ISI-impaired system is also evaluated and the conditions under which this system can achieve close to ISI-free SINR are studied. The SINR is evaluated for the SINRMF and it is shown that this filter can restore much of the SINR loss incurred due to ISI introduced by the WMF.

Exact error probability of a bandlimited single-interferer maximum-likelihood BPSK receiver in AWGN

An exact expression for the bit error rate of a synchronous maximum-likelihood receiver used to detect a bandlimited binary phase-shift keying (BPSK) signal in the presence of a similar BPSK signal, additive white Gaussian noise and imperfect carrier phase recovery is derived. The users are assumed to employ pulse-shaping filters whose impulse responses satisfy Nyquists first criterion. The receivers error probability is compared with that of the perfect phase recovery case to show its sensitivity to carrier phase errors. It is shown that the receiver is more robust to carrier phase mismatch at high signal-to-interference ratios (SIRs) than low SIRs

Optimal 100% Excess Bandwidth Signaling in Cochannel Interference

The problem of transmitter-receiver (T-R) filter design for detection of a binary phase-shift keying signal in asynchronous cochannel interference and Gaussian noise is considered. It is shown that maximum signal-to-interference-plus-noise ratio (SINR) can be achieved only if the T-R filters have a flat spectrum with 100% excess bandwidth. The bit error probability (BEP) performance of a system with the proposed filters is compared to that of a system with conventional root raised-cosine filters both for perfect and imperfect timing recovery cases. It is shown that the proposed filter design is superior to the conventional root raised-cosine filters both in having larger SINR and smaller BEP

ISI-Free Cochannel Interference Whitening for Bandlimited Fading Channels

The problem of cochannel interference mitigation using interference-plus-noise whitening receiver design in the presence of intersymbol interference (ISI) is considered. The effect of ISI on the signal-to-interference-plus-noise ratio (SINR) of the interference whitening receiver is examined. Then, two methods are proposed to maximize the SINR without introducing ISI. In the first method, the transmitter and receiver filters are designed to maximize the SINR while their overall spectrum maintains a given Nyquist spectrum to avoid ISI. In the second method, the transmitter filter is assumed to be fixed and only the receiver filter is designed to achieve maximum SINR without introducing ISI. The SINR of the ISI-free SINR-maximizing filter is then analytically compared with that of the conventional matched filter receiver and the interference whitening receiver. Numerical results are presented for the cases when standard raised-cosine and Beaulieu-Tan-Damen pulses are used in the system.

Cochannel Interference Whitening Receiver Designs for BPSK in Nakagami-m/Rayleigh Fading

The detection of a binary phase-shift keying signal distorted by like-modulated cochannel interference and noise using a noise-plus-interference whitening matched filter (WMF) is considered. The interfering signals are assumed to be independent and Rayleigh-faded. It is shown that in a synchronous channel, the signal-to-interference-plus-noise ratio (SINR) at the output of a WMF can not exceed that of the conventional matched filter (CMF) receiver. It is observed that in a synchronous channel, an interference WMF degrades the performance both through decreasing the SINR and introducing intersymbol interference (ISI). In contrast, in an asynchronous channel an optimal WMF can improve the SINR relative to the CMF receiver. It is shown that for a standard raised-cosine pulse the maximum achievable SINR gain over the CMF receiver is 1.76 dB. The SINR of the WMF receiver in asynchronous CCI is also evaluated for the case when a linear equalizer is used to mitigate the ISI caused by the WMF.

SINR-Maximizing Transmitter Designs for Multiaccess Interference Suppression

The problem of transmitter pulse-shaping design for suppressing multiple access interference in bandlimited multiaccess communication systems is considered. The design is laid out in such a way that the transmitter-receiver (T-R) combination maximizes the signal-to-interference-plus-noise ratio (SINR). It is shown that the optimum transmitter filter is composed of a sum of two sinc functions with different gains and bandwidths. An exact expression for the output SINR of the proposed T-R combinations is derived and compared to that of the conventional matched filter (CMF) receiver with a root raised-cosine transmitter filter. The SINRs of the proposed T-R pairs and the CMF receiver in the presence of timing error are also analyzed and accurate expressions for them are derived.

Two Multiuser Combining Receiver Diversity Structures

Two multiuser combining receiver structures for space diversity reception of a signal distorted by cochannel interference and additive white Gaussian noise are derived. The desired and interfering signals are assumed to be binary phase- shift keying modulated and Rayleigh-faded. The first receiver concurrently minimizes the error probability for all users and is composed of a bank of maximal ratio combiners (MRCs) followed by a maximum-likelihood detector. In the second receiver, the error probability is minimized only for the desired user and it is shown that the receiver comprises an MRC bank followed by a likelihood ratio tester that picks the globally best hypothesis. Simulation results illustrate the superiority of the proposed detection strategies over a receiver which makes use of optimum combining, especially for small values of signal-to- interference power ratios.

BER of A Bandlimited Single-Interferer Maximum-Likelihood BPSK Receiver With Carrier Phase Error

An exact expression for the bit error probability of a maximum-likelihood receiver used to detect two bandlimited binary phase-shift keying signals in a synchronous additive white Gaussian noise channel in the presence of carrier phase recovery errors is derived. The users employ pulse-shaping filters whose impulse responses satisfy Nyquists first criterion for zero intersymbol interference. The receivers error probability is compared with that of the perfect phase recovery case for various values of signal-to-interference ratio (SIR) to show its sensitivity to carrier phase errors. It is shown that the receiver is more robust to carrier phase mismatch at large values of SIR than at small values of SIR.