Frequency-flat Rayleigh Fading Channels Research Articles

SYMBOL ERROR PROBABILITY PERFORMANCE FOR GENERALIZED SELECTION COMBINING DIVERSITY RECEPTION OF M-QAM OVER RAYLEIGH FADING CHANNEL

The performance of generalized selection combining (GSC) diversity reception symbol error probability (SEP) of square M-ary quadrature amplitude modulation (M-QAM) signals over frequency-flat Rayleigh fading channels is investigated in this work. The combining techniques considered in this paper are maximum ratio combining and selection combining (SC). We present closed-form approximate expressions for the average combined signal-to-noise ratio (SNR) and SEP in the fading channel for M-QAM signal reception in the GSC using diversity pathways that are independently, identically distributed. The simulation results validate the SEP expressions and demonstrate that, for a given number of accessible diversity paths, combining the strongest paths results in the majority of the diversity gain, and that the SNR declines as the number of combined paths increases. On the other hand, the numerical results demonstrate that, for a certain number of combined paths, increasing the number of available diversity paths can lead to a significant performance improvement.

Error performance analysis of generalized quadrature spatial modulation using H-8QAM

Motivated to enhance the error performance (EP) of generalised complex quadrature spatial modulation (GCQSM) systems, this study proposes a scheme that builds on GCQSM and uses hexagonal quadrature amplitude modulation (H-QAM) constellations which have the advantages of a maximised Euclidean distance with relatively low peak-to-average power ratio, compared to conventional QAM (C-QAM) systems. This in turn, leads to an enhancement of the EP of GCQSM schemes. The proposed scheme utilises a rotated hexagonal 8QAM (H-8QAM) set. Thus, the proposed scheme is herein named; Generalised QSM using H-8QAM (GQSM-H-8QAM). In this study, the EP of the proposed GQSM-H-8QAM scheme is investigated over Rayleigh frequency flat-fading channels with additive white Gaussian noise. Additionally, a theoretical average bit error probability (ABEP) expression of the GQSM-H-8QAM scheme is formulated and validated using Monte Carlo simulations. Compared to simulation results, the ABEP proves to be increasingly tight at high signal-to-noise ratio values. Obtained simulation results also show an improvement in the EP of the GQSM-H-8QAM scheme over various SM schemes like GCQSM, C-QSM and conventional-generalized spatial modulation (C-GSM), at the same spectral efficiency (SE). An improvement in the EP of 0.61 dB with SE of 8 bits/s/Hz is seen in 4times 4 GQSM-H-8QAM over 4times 4 GCQSM using C-8QAM, 2.58 dB over 4times 4 C-QSM-C-64QAM and a gain of 4.85 dB over 4times 4 C-GSM-C-64QAM.

Secrecy Performance of Eigendecomposition-Based FTN Signaling and NOFDM in Quasi-Static Fading Channels

In this paper, we investigate the information-theoretic secrecy performance of recent precoded faster-than-Nyquist signaling (FTN) with the aid of optimal power allocation in eigenspace. More specifically, the secrecy rate and secrecy outage probability of a fading wiretap channel, which was derived for classical Nyquist-based orthogonal signaling transmission, is extended to those of our eigendecompsition-based FTN (E-FTN) signaling for a quasi-static frequency-flat Rayleigh fading channel. Our performance results demonstrate that the proposed E-FTN signaling scheme exhibits improvements in secrecy rate and secrecy outage probability over conventional Nyquist-based and FTN signaling transmission, assuming employment of a root-raised cosine filter. We also show that the same benefits as those of single-carrier E-FTN signaling are attainable by its non-orthogonal multicarrier counterpart, where subcarrier spacing is set lower than that of orthogonal frequency-division multiplexing.

Study On Early Warning Systems (EWS) for Indonesia Digital Terrestrial Television

Early warning system (EWS) via digital television (TV) in Indonesia is still un-optimal in design and implementation due to the absent of clear standard/guidance to follow across the country. This paper studies various EWS based on digital TV of Japan, Korea, and the United States of America (USA). Although the systems look like different, the EWS can be simplified into 3 nodes representing (i) Emergency Agency, (ii) TV broadcaster, and (iii) TV receiver. Beside the 3-node-based EWS, this paper evaluates the possibilities of EWS having 4 nodes. We perform computer simulations to evaluate the latency and bit error rate (BER) performances under additive white Gaussian noise (AWGN) and frequency-flat Rayleigh fading channels. We found that the system latency and BER performances of EWS are highly affected by (i) the distance of one node to another and (ii) the number of nodes, where EWS with 3 or 4 nodes found to be enough and suitable for Indonesia digital TV. We propose a criterion of good EWS, i.e., total delay T <= t + 4.delta.t with t and delta.t being the propagation delay and processing time, respectively, and BER less than Pb=10-3. The result of this paper are expected to be used as a reference for the Indonesia EWS systems.

Study on Error Correction Capability of Simple Concatenated Polar Codes

Polar codes ware mathematically proven to achieve the Shannon limit, where the error probability is reduced with the help of frozen bits. Since the frozen bits are detrimental in terms of transmission efficiency, this paper investigates the importance of the frozen bits and the possibility of being replaced by other protected bits via a concatenation with other outer channel coding schemes. We evaluate the impact of frozen bits to the capability of error correction of original Polar codes (OPC) and the concatenated Polar codes (CPC) in short block-length in terms of bit-error-rate (BER) performances. Repetition codes are used as outer channel encoder prior to the Polar codes and are divided into two schemes, i.e., (i) irregular repetition-CPC (IR-CPC) codes and (ii) regular repetition-CPC (RR-CPC) codes. We evaluate BER performances using computer simulations based on Log-Likelihood Ratio (LLR) with the modulation of Binary Phase Shift Keying (BPSK) under Additive White Gaussian Noise (AWGN) and frequency-flat Rayleigh Fading channels. We found that the OPC is better than the IR-CPC codes or RR-CPC codes for the same channel coding rate and block-length. This finding indicates that the frozen bits in OPC has strong contribution to the error correction capability of the Polar codes and may not be replaced by other bits even though the bits are protected by other channel coding schemes.

Labeling Diversity for Media-Based Space-Time Block Coded Spatial Modulation

Media-based space-time block coded spatial modulation (MBSTBC-SM) combines the advantages of media-based modulation (MBM) and STBC-SM. Meanwhile, labelling diversity (LD) has been applied to STBC-SM and improve the error performance. Hence, this paper proposes the application of LD to MBSTBC-SM in the form of MBSTBC-SM-LD over a fast, frequency-flat Rayleigh fading channel, without channel estimation. The proposed MBSTBC-SM-LD demonstrates an improved average bit error rate (BER) performance over MBSTBC-SM and STBC-SM. For example, a 4 × 4, m <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rf</sub> = 2 MBSTBC-SM-LD demonstrates a 2 dB gain in signal-to-noise ratio (SNR) over MBSTBC-SM. Furthermore, the analytical framework for the union bound on the average BER of MBSTBC-SM-LD is formulated, and validates the Monte Carlo simulation results for the MBSTBC-SM system over a fast, frequency-flat Rayleigh fading channel. In addition, a low-complexity detector, which is able to achieve 73% reduction in computational complexity of MBSTBC-SM-LD, while maintaining a near-ML error performance is proposed.

Low-complexity Detectors for Cyclic Structured Space-time Block Coded Spatial Modulation over a Slow Rayleigh Fading Channel

This paper presents low-complexity detectors for space-time block coded spatial modulation with cyclic structured (STBC-CSM) codeword over a quasi-static frequency-flat Rayleigh fading channel. Two low-complexity detectors are proposed, which reduce the computational complexity of the STBC-CSM maximum-likelihood (ML) detector and demonstrate near-ML error performance of STBC-CSM. Furthermore, Monte-Carlo simulation results for the proposed schemes are presented to validate the theoretical Average Bit Error Probability (ABEP) of STBC-CSM. The proposed low-complexity detectors can achieve a 99% reduction in computational complexity, when high order M-ary (M &gt; 64) amplitude and/or phase modulation symbols are employed for STBC-CSM.

Average power allocation based sum-rate optimization in massive MIMO systems

This paper exploits variations in the average channel gains in multi-cell multi-user massive multiple input multiple output (MIMO) systems. An average transmit power-control-based sum-rate optimization scheme is presented for the uplink of the system. The matched filtering (MF) and the zero forcing (ZF) processors are considered with perfect and imperfect channel state information at receiver (CSIR) under frequency flat Rayleigh fading channel. An average power-control-based system model is constructed for analyzing the sum-rate and formulating an optimization problem. A discrete level combinatorial optimization is performed for MF and ZF sum-rate under perfect and imperfect CSIR. The numerical results show a significant improvement in the sum-rate and power consumption. A low complexity algorithm for numerical optimization of the sum-rate is proposed. The performance of algorithm is quantified with different scenarios including different number of users, macro cells, and micro cells with low and high inter-cell interference powers. The evaluation results show that the improvement in sum-rate and energy efficiency increases with inter-cell interference power and the number of MTs.

Uncoded Space-Time Labeling Diversity—Application of Media-Based Modulation With RF Mirrors

In this letter, we apply the concept of media-based modulation with radio frequency mirrors to uncoded space-time labeling diversity (USTLD). Several configurations are investigated. Results demonstrate a significant improvement in the error performance over USTLD and the recently proposed space-time channel modulation for fast frequency-flat Rayleigh fading channels with and without channel estimation error. Improvement is also shown for the quasi-static channel case. The analytical average bit error probability is formulated for the scheme and is shown to agree well with Monte Carlo simulation results at moderate-to-high signal-to-noise ratios. Furthermore, the detection computational complexity of each configuration is analyzed in terms of the number of real operations.

Channel capacity of TAS/MRC system with adaptive transmission and channel estimation errors

This correspondence presents the impact of channel estimation error (CEE) on the channel capacity analysis of multiple-input multiple-output (MIMO) system employing transmit antenna selection and maximal ratio combining (TAS/MRC) under adaptive transmission (ADT) techniques over frequency-flat Rayleigh fading channels. In this paper, we evaluated exact closed-form expressions of channel capacity for TAS/MRC system with CEE under different variable power and variable rate adaptation techniques: (i) optimal power and rate adaptation (opra) (ii) constant power with rate adaptation (cpra) (iii) channel inversion with fixed rate (cifr). The channel state information (CSI) consisting of the signal-to-noise ratio (SNR) level is estimated by the decoder and fed back to the transmitter. Further, the ADT schemes can be operated frame by frame, hence permitting for distinct compromises among the attainable capacity and the corresponding implementation complexity. Numerical outcomes illustrate the impact of CEE on the link capacity and outline the performance characteristics among the distinctive adaptation techniques.

Outage probability analysis for a cognitive amplify‐and‐forward relay network with single and multi‐relay selection

The authors evaluate the outage probability of a cognitive amplify-and-forward relay network with cooperation between certain secondary users, chosen by single and multi-relay (two and four) selection, based on the underlay approach, which requires adherence to an interference constraint on the primary user. The relay selection is performed either on the basis of a max-min strategy or one based on maximising exactly the end-to-end signal-to-noise ratio. To realise the relay selection schemes within the secondary networks, a predetermined threshold for the power of the received signal in the primary receiver is assumed. To assess the performance advantage of adding additional secondary relays, we obtain analytical expressions for the probability density function and cumulative density function of the received SNR and thereby provide closed form and near closed form expressions for outage probability over Rayleigh frequency flat fading channels. In particular, the authors present lower and upper bound expressions for outage probability and then provide a new exact expression for outage probability. These analytical results are verified by numerical simulation.

Two- and four-relay selection schemes for application in interference limited legacy networks

The limiting effect of multi-user interference from an adjacent cell upon the relays used for cooperative transmission is considered in the context of legacy networks which adopt max(min(·,·)) type relay selection policies. We extend previous work which considered single relay selection to the selection of two or four such relays, as is required in distributed space–time coding. We obtain new analytical expressions for outage probability over Rayleigh frequency flat fading channels for two signal-to-noise ratio regimes. We confirm by simulation that such a relay selection scheme has robustness to relay selection feedback error and outperforms a single relay selection scheme.

On the Power Amplifier Nonlinearity in MIMO Transmit Beamforming Systems

In this paper, single-carrier multiple-input multiple-output (MIMO) transmit beamforming (TB) systems in the presence of high-power amplifier (HPA) nonlinearity are investigated. Specifically, due to the suboptimality of the conventional maximal ratio transmission/maximal ratio combining (MRT/MRC) under HPA nonlinearity, we propose the optimal TB scheme with the optimal beamforming weight vector and combining vector, for MIMO systems with nonlinear HPAs. Moreover, an alternative suboptimal but much simpler TB scheme, namely, quantized equal gain transmission (QEGT), is proposed. The latter profits from the property that the elements of the beamforming weight vector have the same constant modulus. The performance of the proposed optimal TB scheme and QEGT/MRC technique in the presence of the HPA nonlinearity is evaluated in terms of the average symbol error probability and mutual information with the Gaussian input, considering the transmission over uncorrelated quasi-static frequency-flat Rayleigh fading channels. Numerical results are provided and show the effects on the performance of several system parameters, namely, the HPA parameters, numbers of antennas, quadrature amplitude modulation modulation order, number of pilot symbols, and cardinality of the beamforming weight vector codebook for QEGT.

Outage probability in distributed transmission based on best relay pair selection

Cooperative diversity has been recently proposed as a way to form virtual antenna arrays and thereby mitigate the deleterious effect of fading channels in transmission. In an environment where multiple relays are available, selection of a subset of such relays may be required as, for example, in distributed space-time coding. In this study, the authors therefore use local measurements of the instantaneous channel conditions to select the best relay pair from a set of N available relays, which both come from the same cluster or different clusters, and then use these best relays for cooperation between the source and the destination. The authors also show that the best relay pair selection scheme has robustness against feedback error and outperforms a scheme based on selecting only the best single relay. The authors obtain analytical expressions for the probability density function, cumulative density function and the moment generating function of the received signal-to-noise ratio to derive closed-form expressions for outage probability over Rayleigh frequency flat-fading channels. The analytical results are supported by simulation studies.

Exact outage probability analysis for cooperative AF relay network with relay selection in presence of inter-cell interference

Analysed is the outage probability of an amplify-and-forward relay network which adopts a relay selection policy to maximise end-to-end signal to interference plus noise (SINR) performance in the presence of inter-cell interference. The analysis considers the effect of adjacent cell interference, both at the relay and at the destination nodes, upon cooperative transmission. New exact analytical expressions for the probability density function, and cumulative density function of the received SINR are obtained and thereby closed form expressions for outage probability in the high signal-to-noise ratio region over Rayleigh frequency flat-fading channels are provided, which are verified by numerical simulation.

Error Probability of DF Relaying with Pilot-Assisted Channel Estimation over Time-Varying Fading Channels

In this paper, we investigate the error rate performance of a cooperative network with adaptive decode-and-forward (DF) relaying over time-selective frequency-flat Rayleigh-fading channels. We assume pilot-symbol-assisted modulation (PSAM) for the estimation of time-varying fading channel coefficients. For the system under consideration, we derive an exact closed-form expression for the average bit/symbol error rate, which is further validated through Monte Carlo simulations. Such closed-form solutions are highly desirable because they allow for rapid and efficient performance evaluation. Through the derived expression, we also demonstrate the effect of various system parameters such as the number of relays, Doppler values, and filter length on system performance.

Power-efficient-coded architecture for distributed wireless sensing

Most distributed wireless sensor systems avoid using error correction codes because of the added complexity and power consumption of the decoders. Therefore these uncoded sensor systems are not capable of providing a robust communication link in noisy environments. This leads to a high packet loss, limits the communication range and increases the number of sensors required to cover a region. A novel architecture with several simple sensors and a few sensors with complex decoders is proposed. This approach is power efficient, practical and at the same time provides better coverage and link quality. Several coding schemes are studied with the overall goal of maximised performance, while minimising the decoding complexity, hence saving sensor nodes&apos; power. Furthermore, in both additive white Gaussian noise and frequency-flat Rayleigh fading channels a code is optimised to provide the lowest possible bit error rate for a specific memory constraint. It is demonstrated that overall power consumption for a coded wireless sensor system can be less than its uncoded counterpart, even considering the decoding power consumption. The proposed approach is targeted at real-time wireless environmental monitoring, where the information flow is unidirectional, justifying the usage of complex decoders in a few super-nodes.

List-Based Group-Wise Symbol Detection for Multiple Signal Communications

Co-channel interference (CCI) occurs in a wireless receiver when multiple signals are present. The receiver experiences excessive CCI under overload which occurs when there are more signals than receive antennas. This makes separation and estimation of the transmitted data signals difficult. We develop a novel reduced-complexity receiver structure for the separation and symbol detection of multiple co-channel signals in frequency-flat Rayleigh fading channels. Moreover, we show that list-based group-wise processing can achieve better performance at low and moderate signal-to-noise ratios than existing group-wise soft information processing schemes. The receiver is equipped with multiple antennas and developed to work under overload. Its structure consists of a linear preprocessor followed by a nonlinear reduced-complexity symbol detector. The proposed list group-search detection (LGSD) algorithm relies on list feedback and reduces complexity by iteratively searching over groups of transmitted symbols. It outputs a list of likely data symbols which is well suited to further processing using soft input error control decoders. Simulation shows that LGSD can achieve near optimum joint maximum likelihood performance under overload at significantly lower complexity.

On Optimum Regenerative Relaying With Imperfect Channel Knowledge

This correspondence is concerned with the performance of a regenerative relaying protocol on fading wireless channels with imperfect channel knowledge at the receivers. Assuming a single source and a single destination with multiple relay nodes, using binary modulation at the source, we present optimum receiver at the destination on frequency-flat Rayleigh fading channels by taking into account the effects of imperfect channel knowledge at the receivers. Since exact performance analysis of the optimal receiver is complicated due to the non-linear nature of the log-likelihood ratio contribution from the relay, upon using a standard technique in the literature, we present a simple approximate receiver and derive closed-form expression for the average bit error rate (BER) at the destination with a single relay node. We also present a simple analytical technique that allows us to numerically evaluate the average BER for an arbitrary number of relay nodes. Finally, with perfect channel estimation our proposed receiver subsumes the coherent receivers whereas with a minimum mean-square error channel estimation it reduces to the non-coherent receiver in the work of Chen and Laneman (2006).

On bounding the performance of group-wise multiuser detectors

We develop a union bound on the error performance of group-wise symbol detectors in frequency-flat Rayleigh fading channels. The bound is applicable to detectors that search over a subspace of the total symbol space. It provides a means to investigate tradeoffs among system parameters such as group size versus error performance.