Frequency-selective Rician Fading Research Articles

LOS-Based Equal Gain Transmission and Combining in General Frequency-Selective Ricean Massive MIMO Channels

In general frequency-selective Ricean fading environments with doubly-ended spatial correlation, this paper investigates the spectral efficiency of a broadband massive multiple-input multiple-output (MIMO) system. In particular, in order to reduce overhead of channel estimation effectively, it proposes a scheme of equal gain transmission and combining, which is only based on line- of-sight (LOS) component and has low hardware complexity. With the scheme, several interesting transmit power scaling properties without and with spatial correlation are derived when the number of antennas at the transmitter or the number of antennas at the receiver grows in an unlimited way. Furthermore, the asymptotical rate analysis is extended to the cooperative relaying scenarios with decode-and-forward and amplify-and-forward protocols, respectively, and then two novel power scaling laws are given.

Interference Cancellation in CDMA Systems Employing Complementary Codes Under Rician Fading Channels

The ideal correlation properties of single user code division multiple access (CDMA) systems with complementary codes (CC) are lost by multiple access interference and near–far effects in downlink frequency selective fading channels. This severity in interference has motivated to develop ways to overcome the threats with suitable suboptimal interference cancellation schemes. In this paper, we propose successive interference cancellation (SIC) for downlink CDMA systems with CC to improve the system capacity and reduce error rate under near–far situations. Theoretical study and extensive simulations were conducted to verify the effectiveness of proposed SIC under frequency selective Rician fading channels in achieving frequency diversity gain, close to theoretical lower bound in complementary coded CDMA (CC-CDMA) systems.

Distributed polar-coded OFDM based on Plotkin’s construction for half duplex wireless communication

ABSTRACTA Plotkin-based polar-coded orthogonal frequency division multiplexing (P-PC-OFDM) scheme is proposed and its bit error rate (BER) performance over additive white gaussian noise (AWGN), frequency selective Rayleigh, Rician and Nakagami-m fading channels has been evaluated. The considered Plotkin’s construction possesses a parallel split in its structure, which motivated us to extend the proposed P-PC-OFDM scheme in a coded cooperative scenario. As the relay’s effective collaboration has always been pivotal in the design of cooperative communication therefore, an efficient selection criterion for choosing the information bits has been inculcated at the relay node. To assess the BER performance of the proposed cooperative scheme, we have also upgraded conventional polar-coded cooperative scheme in the context of OFDM as an appropriate bench marker. The Monte Carlo simulated results revealed that the proposed Plotkin-based polar-coded cooperative OFDM scheme convincingly outperforms the conventional polar-coded cooperative OFDM scheme by 0.5 ~ 0.6 dBs over AWGN channel. This prominent gain in BER performance is made possible due to the bit-selection criteria and the joint successive cancellation decoding adopted at the relay and the destination nodes, respectively. Furthermore, the proposed coded cooperative schemes outperform their corresponding non-cooperative schemes by a gain of 1 dB under an identical condition.

Adaptive Relay Selection and Power Allocation for OFDM Cooperative Underwater Acoustic Systems

The increasing use of relays in underwater acoustic (UWA) communications is a driving force to explore efficient techniques that can significantly improve the system performance. To fully exploit the benefits of cooperative systems, efficient management of resources including relays and power is required. In this paper, both optimal relay selection and power loading issues are investigated for an orthogonal frequency division multiplexing (OFDM) cooperative transmission over UWA channel. In our analysis, we consider amplify-and-forward (AF) relaying with perfect channel state information (CSI) at the source, relay, and destination nodes. Moreover, we assume sparse and frequency-selective Rician fading in the presence of colored Gaussian ambient noise. Unlike previous works on this topic, in our study, the power of noise is not identical for all subcarriers at both the relay and destination nodes. We solve two optimization problems that rely on the minimization of the bit error rate (BER) and maximization of the system capacity. In each problem, both optimal relay selection and power loading issues are addressed in two dependent phases. In the first phase, an unconstrained optimization problem is solved to determine the optimal relay out of multiple relays vertically located at different depths of water. We adopt all-subcarrier (AS) basis approach in our OFDM-based transmission model in which a single relay is engaged to transmit the entire OFDM block to the destination. In the second phase, after selecting the optimal relay, another optimization problem is solved to obtain the optimal power allocation. This is jointly done at both the source and relay nodes under total power constraint and fixed subcarrier rate. Extensive simulations are conducted to evaluate the performance of proposed algorithms under different scenarios.

Efficient cooperative multicarrier underwater acoustic communication over the Persian Gulf channel

Real-time and reliable transmission with high data rate is one of the most crucial design issues in underwater acoustic (UWA) communications. This paper is part of an operational project in the Persian Gulf which is known as a shallow water channel worldwide. Building on the promising combination of cooperative and multicarrier techniques, we first address the design of an efficient UWA communication system over the Persian Gulf channel. We assume sparse and frequency-selective Rician fading, non-white correlated Gaussian ambient noise, and non-uniform Doppler distortion among subcarriers. Based on the extensive field measurements, we adopt a comprehensive channel model including modified sound speed profile, modified absorption coefficient, reflections from the surface and bottom of the sea, and modified ambient noise model. In our work, carrier frequency is efficiently determined based on the system and environmental parameters. In addition, a simple criterion for Doppler scale calculation is proposed. Moreover, based on the approximate auto-correlation function of the ambient noise, whitening filter is utilized at the receiver. In many applications of underwater acoustic sensors network (UW-ASN), nodes may not be big enough to have more than one antenna. Therefore, to achieve spatial diversity, cooperation between nodes can be a proper alternate method. In another part of this research, toward a proper approach that each node operates under full-duplex mode, we address a cooperative virtually-aided transmission scenario which is called cooperative multiple input single output. Simulation results demonstrate that our proposed models can significantly improve the bit error rate performance of UW-ASN in the Persian Gulf channel.

Specular component‐based beamforming for broadband massive MIMO systems with doubly‐ended correlation

Beamforming (BF) transmission for broadband massive MIMO systems in frequency-selective Ricean fading environments is investigated. By treating the scattered component as interference in order to reduce the heavy overhead for estimating channel state information, a transmit/receive BF scheme only based on the specular component is presented. It is shown by analytical results that the ergodic achievable rate for the scenario with doublyended spatial correlation can be asymptotically equal to that of the one without correlation when the transmit power is scaled down by the multiplication of the two numbers of antennas at the transmitter and the receiver. It is also shown by simulation results that different from the traditional point of view, spatial correlation can improve the rate performance of the proposed BF scheme.

Information theoretical performance analysis and optimisation of cooperative underwater acoustic communication systems

In this study, the authors investigate the information theoretical limits on the performance of single-carrier cooperative underwater acoustic communication systems in the presence of intersymbol interference. The authors assume decode-and-forward relaying and consider orthogonal half-duplex cooperation. Under the assumptions of sparse and frequency-selective Rician fading channel and non-white correlated Gaussian ambient noise, the authors derive expressions for bounds on the individual and achievable rates for both cases where channel state information is available at the transmitter or not. Using these expressions, the authors optimise input signalling and relay location to maximise average achievable rates.

Information theoretical performance limits of single‐carrier underwater acoustic systems

In this study, the authors investigate the information theoretical limits on the performance of point-to-point single-carrier acoustic systems over frequency-selective underwater channels with intersymbol interference. Under the assumptions of sparse and frequency-selective Rician fading channel and non-white correlated Gaussian ambient noise, the authors derive an expression for channel capacity and demonstrate the dependency on channel parameters such as the number, location and power delay profile of significant taps, as well as environmental parameters such as distance, temperature, salinity, pressure and depth. Then, the authors use this expression to determine the optimal carrier frequency, input signalling and bandwidth for capacity maximisation.

A Novel Receiver Design for Single-Carrier Frequency Domain Equalization in Broadband Wireless Networks with Amplify-and-Forward Relaying

In this paper, we propose an efficient receiver design for single carrier frequency-domain equalization (SC-FDE) for relay-assisted transmission scenario over frequency selective channels. Building upon our earlier work, we propose a novel minimum mean square error (MMSE)-based receiver design tailored to broadband cooperative networks. We show that, by incorporating linear processing techniques, our MMSE-based receiver is able to collect full antenna and multipath diversity gains, while maintaining low complexity implementation. Specifically, under the assumption of perfect power control and high signal-to-noise ratio (SNR) for the underlying links and assuming either of source-to-relay (S → R) or relay-to-destination (R → D) links to be frequency selective Rician fading, our performance analysis demonstrates that the proposed receiver is able to achieve a maximum diversity order of min (LSR,LRD) + LSD + 2, where LSR, LRD, and LSD are the channel memory lengths for S → R, R → D, and source-to-destination (S → D) links, respectively. Simulation results demonstrate that our proposed receiver outperforms the conventional cooperative MMSE-SC-FDE receiver by performing close to the matched filter bound (MFB).

Statistical Characteristics of OFDM Systems over Frequency-Selective Rician Fading Channels and Its Application to BER Study

Some statistical characteristics, including the means and the cross-correlations, of frequency-selective Rician fading channels seen by orthogonal frequency division multiplexing (OFDM) subcarriers are derived in this paper. Based on a pairwise error probability analysis, the mean vector and the cross-correlation matrix are used to obtain an upper bound of the overallbit-error rate (BER) in a closed-form for coded OFDM signals with and without inter-carrier interference. In this paper, the overall BER is defined as the average BER of OFDM signals of all subcarriers obtained by considering their cross-correlations. Numerical examples are presented to compare the proposed upper bound of the overall BERs and the overall BERs obtained by simulations.

Appropriate Algorithms for Estimating Frequency-Selective Rician Fading MIMO Channels and Channel Rice Factor: Substantial Benefits of Rician Model and Estimator Tradeoffs

The training-based channel estimation (TBCE) scheme in multiple-input multiple-output (MIMO) frequency-selective Rician fading channels is investigated. We propose the new technique of shifted scaled least squares (SSLS) and the minimum mean square error (MMSE) estimator that are suitable to estimate the above-mentioned channel model. Analytical results show that the proposed estimators achieve much better minimum possible Bayesian Cramér-Rao lower bounds (CRLBs) in the frequency-selective Rician MIMO channels compared with those of Rayleigh one. It is seen that the SSLS channel estimator requires less knowledge about the channel and/or has better performance than the conventional least squares (LS) and MMSE estimators. Simulation results confirm the superiority of the proposed channel estimators. Finally, to estimate the channel Rice factor, an algorithm is proposed, and its efficiency is verified using the result in the SSLS and MMSE channel estimators.

BER Analysis of OFDM Systems Impaired by Phase Noise in Frequency-Selective Fading Channels

In this paper, we study the effect of finite-power, phase-locked loop based phase noise on the bit-error-rate (BER) performance of orthogonal frequency division multiplexing (OFDM) systems in frequency-selective fading channels. It is well known the impact of phase noise on the performance of an OFDM system can be divided into a multiplicative term called common phase error (CPE) and an additive term called intercarrier interference (ICI). Based on the conditional Gaussian approximation technique, we first derive the BER formulas for BPSK, QPSK, 16-QAM, and 64-QAM modulated OFDM signals in frequency-selective Rayleigh fading channels. To further quantify the individual influence of the CPE and the ICI on system performance for different phase noise spectra, we derive the BER expressions for perfect CPE compensation cases. The analytical results obtained for frequency-selective Rayleigh fading channels are then generalized to frequency-selective Rician fading channels. Simulation results not only validate the accuracy of our analysis but also show the dependency of BERs on the shapes of phase noise spectra.

Doppler Spread Estimation for Broadband Wireless OFDM Systems Over Rician Fading Channels

In this paper, we present a new Doppler spread estimation algorithm for broadband wireless orthogonal frequency division multiplexing (OFDM) systems with fast time-varying and frequency-selective Rayleigh or Rician fading channels. The new algorithm is developed by analyzing the statistical properties of the power of the received OFDM signal in the time domain, thus it is not affected by the influence of frequency-domain inter-carrier interference (ICI) introduced by channel variation within one OFDM symbol. The operation of the algorithm doesn’t require the knowledge of fading channel coefficients, transmitted data, or signal-to-noise ratio (SNR) at the receiver. It is robust against additive noise, and can provide accurate Doppler spread estimation with SNR as low as 0 dB. Moreover, unlike existing algorithms, the proposed algorithm takes into account the inter-tap correlation of the discrete-time channel representation, as is the case in practical systems. Simulation results demonstrate that this new algorithm can accurately estimate a wide range of Doppler spread with low estimation latency and high computational efficiency.

Effect of Channel Estimation Error on Bit Error Probability in OFDM Systems over Rayleigh and Ricean Fading Channels

A characteristic function-based method is used to derive closed-form bit error probability (BEP) expressions for orthogonal frequency-division multiplexing (OFDM) systems in the presence of channel estimation error over frequency-selective Rayleigh fading channels and frequency-selective Ricean fading channels. Both single channel reception and diversity reception with maximal ratio combining (MRC) are examined. The BEP expressions are shown to be sums of several conditional probability functions which can be calculated by using proper complex Gaussian random variable theory and a characteristic function method. The closed-form BEP expressions can be used to accurately investigate the bit error rate performance degradation caused by channel estimation error under different wireless channel environment models. The performances of two interpolation methods, a sine interpolator with Hamming windowing and a Wiener interpolator, are compared.

EXACT PERFORMANCE MEASURES FOR DIRECT-SEQUENCE CODE SYNCHRONIZATION IN FADING CHANNELS

This paper presents an exact performance analysis for the evaluating a mean acquisition time in a cellular code division multiple access system. New expressions for the probabilities of detection, miss, and false alarm are derived in a frequency-selective Rician fading channel. From the numerical results, it is shown that our formula gives the accurate results of the mean acquisition time in the performance analysis of the parallel acquisition system with the reference filter.

Pairwise error probability of space-time codes in frequency selective Rician channels

In this letter, we investigate the performance of space-time codes in frequency selective correlated Rician channels. An exact expression has been derived for the pairwise error probability (PEP) of space-time trellis codes over frequency selective Rician fading channel, which is in the form of a single finite range integral. We also obtain a closed form expression for the PEP when the signal matrices are drawn from some special design and the performance upper bound.

BER Performance for Downlink MC-CDMA Systems over Rician Fading Channels

We consider downlink multicarrier code-division multiple-access (MC-CDMA) systems using binary phase-shift keying (BPSK) modulation scheme and maximal ratio combining (MRC) in frequency-selective Rician fading channels. A time-domain method to obtain bit error rate (BER) by calculating moment generating function (MGF) of the decision variable for a tapped-delay-line channel model is proposed. This method does not require any assumption regarding the statistical or spectral distribution of multiple access interference (MAI), and it is also not necessary to assume that the fading encountered by the subcarriers is independent of each other. The analytical formula is also verified by simulations.

A Simple Method of BER Calculation in DPSK/OFDM Systems over Fading Channels

In orthogonal frequency division multiplexing (OFDM) systems with differential phase shift keying (DPSK), it is possible to apply differential modulation either in the time or frequency domain depending on the condition of fading channels, such as the Doppler frequency shift and the delay spread. This paper proposes a simple calculation method, that is, an approximate closed-form equation of the bit error rate (BER) in DPSK/OFDM systems mentioned above over both time and frequency selective Rician fading channels. The validity of the proposed method is demonstrated by the fact that the BER performances given by the derived equation coincide with those by Monte Carlo simulation.

Nonparametric PN code acquisition using the signed-rank statistic for DS/CDMA systems in frequency-selective Rician fading channels

In this paper, signed-rank based nonparametric detectors are used for pseudonoise (PN) code acquisition in frequency-selective Rician fading channels. We first derive the locally optimum rank detector and then propose the locally suboptimum rank (LSR) and kth order modified signed-rank (MSR/sub k/) detectors using approximate score functions. We compare the hybrid parallel double-dwell scheme using the LSR and MSR/sub k/ detectors with that using the conventional squared-sum (SS) and modified sign (MS) detectors. From the simulation results, it is shown that the LSR and MSR/sub k/ detectors perform better than the SS detector using the cell averaging constant false-alarm rate processor and the MS detector by about 2-3 dB.

The zeros of random polynomials: further results and applications

We consider the density of the zeros of random polynomials with nonzero mean correlated Gaussian coefficients. We show that for most communication problems the original result by Hammersley (1956) can be expressed in a simpler form. In order to illustrate the usefulness of the presented theory, two applications are considered. First, the zeros of frequency-selective Ricean fading channels are investigated. Second, the zeros of the transfer function corresponding to channel impulse response estimates obtained by a least-squares approach are calculated. For both applications implications for equalizer design are discussed.