Optimal Maximum Likelihood Receiver Research Articles

Improved Pair-Wise Detections of Differential Quasi-Orthogonal Space-Time Modulation with Four Transmit Antennas

In this paper, we propose new complex and real pair-wise detection for conventional differential space–time modulations based on quasi-orthogonal design with four transmit antennas for general QAM. Since the new complex and real pair-wise detections allow the independent joint ML detection of two complex and real symbol pairs, respectively, the decoding complexity is the same as or lower than conventional differential detections. Simulation results show that the proposed detections exhibit almost identical performance with an optimum maximum-likelihood receiver, as well as improved performance compared with conventional pair-wise detections, especially for higher modulation order.

Optical Energy-Constrained Slot-Amplitude Modulation for Dimmable VLC: Suboptimal Detection and Performance Evaluation

Energy-constrained slot-amplitude modulation (ECSAM) enables light dimming, eliminates light flicker and constrains the peak optical power while providing robust communication links. However, the complexity of the maximum-likelihood (ML) based ECSAM receiver increases exponentially with required spectral efficiency. This paper provides a comprehensive performance evaluation of ECSAM for the indoor visible light communication (VLC) channel with multipath propagation under realistic illumination constraints and imperfect channel estimation. A sub-optimal receiver that employs a slot-by-slot detection algorithm followed by a slot-correction mechanism for reducing the receiver complexity is proposed. Additionally, the method for optimal selection of parameters when designing the signal waveform is presented. The analytical upper bound on the symbol error rate of ECSAM is derived using the union-bound technique. The results show that the error performance of the sub-optimal receiver are comparable to that of the optimal ML receiver. Compared with conventional power or bandwidth efficient VLC modulation techniques such as multiple pulse position modulation (MPPM) and pulse amplitude modulation (PAM), ECSAM provides complete flexibility in modifying the signal constellation for a desired dimming level to maximise the spectral efficiency and provide a robust bit error rate performance especially in the multipath propagation channel induced intersymbol interference.

A hybrid free space optical-millimeter wave cooperative system

In this paper, a hybrid free space optical (FSO)–millimeter wave (mmWave) cooperative system is proposed. Specifically, a cooperative dual-hop decode-and-forward (DF) relaying system coexists with a direct communication link and two scenarios are considered. In the first scenario, the direct link is used for FSO transmission while the DF dual-hop relaying system is used for mmWave transmission. On the contrary, in the second scenario, the direct link is used for mmWave communication whereas the relaying link is used for FSO communication. In both scenarios, the mmWave link experiences Nakagami-m fading while the FSO link suffers gamma–gamma turbulence fading. At the destination, the two signals, i.e., the mmWave and the FSO signals, are jointly detected using an optimum maximum likelihood receiver. To investigate the performance of the proposed systems, novel analytical expressions for the overall average bit error rate (BER) and outage probability are derived. The impact of different system and channel parameters on the overall average BER is investigated. Additionally, the performance of the proposed systems is compared with other setups where only direct mmWave or FSO link exists. Monte Carlo simulation results are provided to corroborate the accuracy of the analysis.

Characterization on Practical Photon Counting Receiver in Optical Scattering Communication

We characterize the practical photon-counting receiver in optical scattering communication with a finite-sampling rate and electrical noise. Finite-small pulse width incurs dead time effect that may lead to sub-Poisson distribution on the recorded pulses. We analyze the first-order and second-order moments on the number of recorded pulses with a finite-sampling rate at the receiver side under two cases, where the sampling period is shorter than or equal to the pulse width as well as longer than the pulse width. Moreover, we adopt the maximum likelihood (ML) detection. In order to simplify the analysis, we adopt binomial distribution approximation on the number of recorded pulses in each slot. A tractable holding time and decision threshold selection rule is provided to maximize the minimal Kullback-Leibler (KL) distance between the two distributions. The performances of proposed sub-Poisson distribution and the binomial approximation are verified by the experimental results. The equivalent photon arrival rate and pulse holding time predicted by the sub-Poisson model and the associated proposed binomial distribution are well validated by the simulation results, where the finite-sampling rate and electrical noise are considered. The proposed holding time and decision threshold selection rule performs close to the optimal ML receiver.

Error Rate Analysis of GF(q) Network Coded Detect-and-Forward Wireless Relay Networks Using Equivalent Relay Channel Models

This paper investigates simple means of analyzing the error rate performance of a general q-ary Galois Field network coded detect-and-forward cooperative relay network with known relay error statistics at the destination. Equivalent relay channels are used in obtaining an approximate error rate of the relay network, from which the diversity order is found. Error rate analyses using equivalent relay channel models are shown to be closely matched with simulation results. Using the equivalent relay channels, low complexity receivers are developed whose performances are close to that of the optimal maximum likelihood receiver.

Performance of Optimum and Suboptimum Receivers for Space-Time Coded Systems in Correlated Fading

We consider a space-time coded system in a correlated Rayleigh flat fading environment with imperfect channel estimation. Two receiver structures are considered: a suboptimum receiver and the optimum maximum likelihood receiver. The system performance of both receivers is analyzed in terms of the pairwise error probability.

Disjoint detection in polarization multiplexed communication systems affected by polarization dependent loss

We study the performance of a simple optical receiver for use with polarization multiplexed transmission in the presence of polarization dependent loss (PDL). The receiver is based upon filtering of each of the channels with a polarizer that is orthogonal to the other channel, such that interference due to loss of orthogonality is avoided at the expense of a reduction in the detected signal to noise ratio. In spite of its simplicity, this receiver is shown to perform almost as well as the optimal maximum likelihood receiver, and much better than receivers that are based on conventional polarization splitting.

Optimum detection of non-orthogonal QAM signals with spectral overlapping

The authors evaluate and propose two approaches for the detection of two non-orthogonal m-QAM signals with spectral overlapping through an AWGN channel. Some previously reported works are revisited and alternative solutions in order to permit their application in practical communication systems are proposed. The subject method is proved to be relevant because it does not obey the Riesz basis condition for performing signal separation. The optimum maximum-likelihood receiver for this detection problem is also derived and the performance analysis is presented, including some analytical and Monte Carlo simulation results.

Performance Analysis and Multi-Stage Iterative Receiver Design for Concatenated Space- Frequency Block Coding Schemes

This paper presents performance analysis and computationally efficient receiver design for concatenated space-frequency block coded orthogonal frequency division multiplexing (SFBC-OFDM) systems. Firstly, we present a simple method to approximate the theoretical bit error rate performance of the optimal maximum likelihood (ML) receiver for concatenated SFBC-OFDM systems. Next, we propose a low complexity multistage iterative QR decomposition based successive interference cancellation (QR-SIC) detector for OFDM systems employing the concatenated SFBC strategy. The proposed detector utilizes a Turbo-like iterative QR-SIC algorithm that exploits both spatial and frequency diversities inherent in multi-input multioutput (MIMO) multi-path fading channels. The performance of the proposed QR-SIC receiver is evaluated via Monte Carlo simulations. Our results show that the performance of the proposed receiver can approach the theoretical BER performance of the optimal ML receiver at high signal-to-noise ratios. In addition, we also compare the performance and complexity of the proposed QR-SIC detector with a Turbo-based maximum aposteriori (MAP) demodulator. These comparisons show that the proposed QR-SIC scheme performs reasonably well with respect to the MAP demodulator at higher iterations while attaining a much lower complexity than the MAP demodulator.

Performance of multiple access channels with asymmetric feedback

Channel state feedback at the transmitter is extensively used to increase the reliability of wireless transmissions. In multiuser systems, the downlink capacity to different users is often different due to the near-far effect. We capture this asymmetry by introducing an asymmetric feedback model where different users get a different amount of feedback from the base station. First, we derive the outage probability for the optimum maximum-likelihood receiver which forms an upper bound on the diversity-multiplexing performance. This is accompanied by the conditions under which these bounds can be achieved. Second, we analyze the performance of two popular suboptimal receivers: the spatial decorrelator and the successive interference cancellation receiver. As a special case, when there is no asymmetry, the performance matches feedback-based single-user performance in many scenarios.

The Diversity Order of the Semidefinite Relaxation Detector

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In this paper, we consider the detection of binary (antipodal) signals transmitted in a spatially multiplexed fashion over a fading multiple-input–multiple-output (MIMO) channel and where the detection is done by means of semidefinite relaxation (SDR). The SDR detector is an attractive alternative to maximum-likelihood (ML) detection since the complexity is polynomial rather than exponential. Assuming that the channel matrix is drawn with independent identically distributed (i.i.d.) real-valued Gaussian entries, we study the receiver diversity and prove that the SDR detector achieves the maximum possible diversity. Thus, the error probability of the receiver tends to zero at the same rate as the optimal ML receiver in the high signal-to-noise ratio (SNR) limit. This significantly strengthens previous performance guarantees available for the semidefinite relaxation detector. Additionally, it proves that full diversity detection is also possible in certain scenarios when using a noncombinatorial receiver structure. </para>

Preselection-based iterative multiuser detector for DS-CDMA systems

A low-complexity iterative multiuser detector is presented that uses adaptive preselection to minimise complexity while maintaining system performance very similar to that achieved when using the optimal maximum likelihood receiver.

Performance study of a maximum-likelihood receiver for FFH/BFSK systems with multitone jamming

We derive the optimum structure of a maximum-likelihood (ML) receiver for a fast frequency-hopped binary frequency-shift-keying (FFH/BFSK) spread-spectrum (SS) communication system operating in the presence of multitone jamming (MTJ) and additive white Gaussian noise (AWGN). It is shown that the side information of noise variance, signal tone amplitude, and multiple interfering tone amplitude at each hop, as well as the computation of nonlinear modified Bessel function are required to implement the optimum ML receiver. We have also derived and analyzed two suboptimum receivers-namely, the ML-I and ML-II receivers-for large and small signal-to-noise ratio (SNR), respectively. Performance comparisons among various receivers show that the ML receiver gives the best performance, while the ML-I and ML-II receivers also outperform the other existing methods under both high and low SNR conditions.

Multilevel polarization shift keying: optimum receiver structure and performance evaluation

Multilevel digital coherent optical modulation schemes based on the state of polarization of a fully polarized lightwave are proposed and analyzed. Based on the complete statistical characterization of the Stokes parameters, extracted through appropriate signal processing in the presence of shot and additive Gaussian noise, the optimum maximum likelihood receiver operating symbol by symbol is derived. The exact performance in terms of the average symbol error probability is found. Optimum constellations for the case of equipower 4, 8, 16 and 32 signals are found on the basis of the minimization of the error probability for a given average power. Their performance turns out to be promising as compared to other standard modulation techniques. The spectral analysis of polarization modulated signals is presented. A new receiver structure, which solves the problem of the excess penalties incurred in the presence of channel dichroism, is proposed and analyzed. >

Phase-coherent digital communications for underwater acoustic channels

High-speed phase coherent communications in the ocean channel are made difficult by the combined effects of large Doppler fluctuations and extended, time-varying multipath. In order to account for these effects, we consider a receiver which performs optimal phase synchronization and channel equalization jointly. Since the intersymbol interference in some underwater acoustic channels spans several tens of symbol intervals, making the optimal maximum-likelihood receiver unacceptably complex, we use a suboptimal, but low complexity, decision feedback equalizer. The mean squared error multiparameter optimization results in an adaptive algorithm which is a combination of recursive least squares and second-order digital phase and delay-locked loops. The use of a fractionally spaced equalizer eliminates the need for explicit symbol delay tracking. The proposed algorithm is applied to experimental data from three types of underwater acoustic channels: long-range deep water, long-range shallow water, and short-range shallow water channels. The modulation techniques used are 4- and 8-PSK. The results indicate the feasibility of achieving power-efficient communications in these channels and demonstrate the ability to coherently combine multiple arrivals, thus exploiting the diversity inherent in multipath propagation. >

On orthogonal signaling over the slow nonselective Rician fading channel with unknown specular component

Orthogonal signaling over the slow nonselective Rician fading channel is considered. Previous receiver designs have all assumed the amplitude and phase of the specular component of the received carrier to be known completely, but this assumption is entirely unrealistic. The problem is reformulated with unknown random amplitude and phase of the specular component. The optimum maximum likelihood receiver is obtained for equally likely equal-energy orthogonal signals and is shown to be identical to the quadratic receiver for the purely unknown phase channel and the pure Rayleigh fading channel. The error probability performance is analyzed for a fixed known specular amplitude. When specialized to the binary signaling case this error probability result exhibits a performance that is very close to and asymptotically approaches that of the conventional coherent-specular-component case for high SNR. Thus, knowledge of the specular component phase is not important to the optimum receiver. >

Neural net-based continuous phase modulation receivers

The authors propose feedforward neural networks (NNs) as receivers for partial-response continuous-phase-modulation (CPM) systems. Their approach is to replace the entire receiver structure, excluding timing recovery, with a neural net unit whose inputs are time samples of the incoming baseband signals, and whose outputs are the decoded symbols. Simulation results for coherent and incoherent NN-based receivers are presented, and their performance is compared with that of the optimum maximum-likelihood receiver. The performance of NN-based receivers at large SNR is analyzed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Integrated multielement receiver structures for spatially distributed interference channels

The structure and performance of a maximum likelihood (ML) receiver for reception in spatially distributed interference channels when a multielement array capability is available are described. Under the assumption of Gaussian interference, the receiver consists of an optimum ML array processor followed by a sequence estimator implemented using the Viterbi Algorithm. Numerical results are provided to illustrate the symbol error probability performance of this optimum ML receiver. A completely adaptive realization of this scheme is described with performance illustrated through simulation.

Optimal receiver design for convolutional codes and channels with memory via control theoretical concepts

The optimum maximum likelihood receiver for estimating the information sequence that passes through a convolutional encoder and a channel with a known finite memory part followed by a noisy memoryless part is derived using control theoretic concepts. The problem is modeled as a regulator control problem in which the plant under consideration is a finite state machine with the information symbols as inputs. It is in a form in which dynamic programming can be applied to obtain a general solution. The case of sending pulse amplitude modulated (PAM) signals over a linear channel with additive white Gaussian noise is analyzed in detail and upper and lower bounds are derived for the performance criterion, the probability of an information sequence error. Applying the coding concept of concatenation, a suboptimum solution for overcoming the “curse of dimensionality” is discussed.