Flat Rayleigh Fading Channels Research Articles

On the block error rate performance of cooperative non‐orthogonal multiple access short‐packet communications with full‐duplex relay and partial relay selection

AbstractIn this paper, we mathematically investigate a downlink non‐orthogonal multiple access (NOMA) system for short‐packet communications (SPC) in which the near users are used as full‐duplex (FD) relays to forward intended signals from the source to a far user. In addition, partial relay selection is employed to enhance the performance of the FD relays under the impact of imperfect interference cancellation. At the far user, selection combining (SC) or maximal ratio combining (MRC) is employed to combine the signals received from the source and the selected FD relay. The analytical expressions for the average block error rate (BLER) of two users over flat Rayleigh fading channels are derived. Furthermore, closed‐form asymptotic expressions of the average BLERs at the near and far users in high signal‐to‐noise ratio (SNR) regimes are obtained. The numerical results show that the analytical BLERs of the near user and far user closely match the simulation results.

Gain of Spatial Diversity with Conjoint Signals in Arbitrarily Correlated Rayleigh Fading Channels

Coding gains for arbitrarily correlated signals in a spatial diversity system with conjoint signals are presented in this study. The basic form of the proposed signal synthesizer evenly produces phase changes in the output signals. The mixer is an orthogonal transformation matrix, which is energy preserving and blind to the channel correlation matrix. The idea is to synthesize additional conjoint signal copies from the received signals that would be received if there were more antennas. However, these conjoint signals contain a level of correlation with the received signals. With the assumption of flat Rayleigh fading channels, simulation results for symbol error probability (SEP) are presented for different numbers of receive branches and varying correlation conditions. It is shown that under binary phase shift keying (BPSK), the synthesizer achieves decorrelation coding gains of about 1 dB when selection combining (SC) or equal gain combining (EGC) is used. The synthesizer’s performance across M-ary quadrature amplitude modulation (MQAM) signals is also tested. In addition, analytical frameworks are derived for BPSK and MQAM, which are tightly bound by the Monte Carlo simulation results obtained using Matlab. The correlation analysis is performed for different numbers of antennas and varied antenna spacings.

Performance Enhancement of LDPC Codes Based on Protograph Construction in 5G-NR Standard

To meet the high throughput demands, the 3rd Generation Partnership Project has specified the low-density parity check (LDPC) codes in the fifth generation-new radio 5G-NR standard with rate and length compatibility and scalability. This paper presents an extensive performance evaluation and enhancement of LPDC using the protograph-based construction defined in the 5G-NR standard. Firstly, the protograph-LDPC with layered offset min-sum (OMS) decoding, polar with successive cancellation list (SCL), and block turbo code are implemented and compared. Puncturing and shortening are applied to maintain block length at 1024 and code rate at 1/2 for all codes for comparison fairness. The results showed that P-LDPC outperforms its counterparts in terms of bit/ frame error rate (BER/ FER) behavior for given signal-to-noise ratios. Then, different P-LDPC settings were realized to study the effects of base graph selection (Graph1 or Graph2), code rate change (1/3 - 2/3), and block lengths increase (260 – 4160 bits). The simulation outcomes proved that BER performed better for lower coding rates or higher block lengths. Furthermore, P-LDPC behavior was examined over a Rayleigh flat-fading channel to achieve a 12.5 dB coding gain at 0.001 BER compared with uncoded transmission.

Confidentiality Enhancement Using Spread Spectrum Modulation Technique for Aggregated Data in Wireless Sensor Networks

Wireless Sensor Networks (WSN) play a crucial role in transmitting bulk data remotely on Internet of Things (IoT). The data transmitted by the tiny sensor nodes of the network are basically the physical parameters of the environment like temperature, vibration, pressure etc. There exists a huge co-relation in the data sent by the nodes. This bulk data needs to be aggregated in order to conserve the energy of the network and thereby enhance the network lifetime. Although the aggregation might lead to loss of actual data, aggregating helps in reducing energy requirement during transmission which is of primary importance and hence is considered as a suitable method in WSN. Adding confidentiality to aggregated data helps in sending the data more securely. Spread spectrum modulation is a widely used technique to provide confidentiality in communication systems. In this research work, we implement a data aggregation technique and apply the spread spectrum modulation technique to provide confidentiality to the aggregated data that needs to be transmitted from the cluster head node to the gateway. Here, data aggregation process consists of averaging the number of data that are sensed by a sensor node and transmitting only its average value to the gateway. This reduces the amount of data transmission and helps in conserving energy. Further, the spread spectrum technique implements Binary Phase Shift Keying (BPSK) method with Frequency Hopping Spread Spectrum (FHSS) carried out using six different frequencies on MATLAB 2020a. The simulation results evaluate the performance of the system. The graphs are plotted for modulated and demodulated signals, spread and de-spread sequences, Bit Error Rate (BER) of BPSK/ FHSS over Rayleigh flat fading channel, Power Spectral Density (PSD) and Fast Fourier Transform (FFT) of frequency hopped signal. The results show that BER value decreases with increase in Signal to Noise Ratio (SNR). The maximum power consumption in the network is 7.518 mW at 5MHz frequency, for adding confidentiality to the aggregated data to be transmitted. Thus, the proposed work promises efficient energy consumption, longer network lifetimes with added confidentiality.

Distributed totally decomposed cumulative Goppa coded-cooperative communication with optimized selection in the relay

In this paper, powerful induced-cyclic totally decomposed cumulative Goppa (TDCG) codes are selected and used for coded-cooperative diversity, which can fit wireless communication applications. Two TDCG codes employed at the source and relay nodes establish the joint design of the destination channel code. In the cooperation phase, we consider an optimized relay channel code which improves the overall bit-error-rate (BER) performance. Two methods of optimization are explored. The most practical method for optimization in terms of reduced processing complexity is proposed. We use a joint decoding which exploits all the resources gained by the cooperation scheme at the destination. The BER performance is evaluated through Monte-Carlo simulations with BPSK modulation and coherent detection over the flat Rayleigh fading channel. The proposed TDCG coded-cooperative diversity scheme exhibit a better BER performance than the non-cooperation scheme and other existing coded cooperation methods of similar code rates under similar channel conditions.

Stochastic Models for the Fading Channel Success Rate of Sub-6G UWB Systems

This paper presents different stochastic models for entangled UWB fading channels. Closed-form canonical expressions are derived for the statistical distribution of the fading power difference of interfering independent and dependent mixture of flat-fading Rayleigh and Rician channels. The link success probability is derived in terms of the cumulative distribution function of the channel fading power differences. An alternative metric for link success rate (LSR) is developed in terms of the statistical distribution of the ratio of the diffuse powers. Under this alternative formulation, and for the case of 2 independent Rayleigh paths, the LSR statistical distribution was consistent with the heavy-tail Lomax distribution. The scope of future research includes the validation of theoretical and simulated models with real measurements on actual multi-user massive multiple-input-multiple-output (MU-mMIMO) beam-forming sub-6G physical systems.

BER performance analysis of asynchronous NOMA with arbitrary phase offset

An asynchronous transmission scenario for non-orthogonal multiple access (NOMA) user signals with arbitrary phase offset is investigated in this paper. To improve the system performance in the user power-balanced conditions, we adopt a synthetic detection method at the receiver, i.e., the jointly optimal maximal likelihood detection aided triangular successive interference cancellation (JO ML-TSIC) method. Analytical bit error rate (BER) solutions are obtained for a two-user case with the optimal, intentional one-half symbol period time delay implemented between the user signals. Furthermore, closed-form BER solutions for the case using the triangular successive interference cancellation (TSIC) detection method are also derived for comparisons. Numerical results show that the JO ML-TSIC receiver for the asynchronous system outperforms the TSIC receiver as well as the synchronous successive interference cancellation (SIC) receiver in all the conditions concerned. The results also show that the superiority of the JO ML-TSIC receiver is strengthened when the signals experience flat Rayleigh fading channels compared to the TSIC and the synchronous SIC receivers.

MIMO system capacity based on different numbers of antennas

This paper analyzed and compared the ergodic channel capacities of several typical channel systems (SISO, SIMO, MISO, MIMO) in independent identically distributed flat Rayleigh fading channels. The theoretical and simulation results show that the ergodic capacity of the MIMO channel increases linearly with the number of antennas.

Pilot Design of the 1-Bit Massive MIMO in Rayleigh-Fading Channel

In the wireless communication system, the pilot is essential for channel estimation. This paper study the pilot design of the 1-bit massive multi-input multi-output system with the flat Rayleigh fading channel. This paper aims to design the pilot matrix minimizing the estimation error of the Bussgang linear minimum mean squared error (BLMMSE) channel estimator, of which the estimation error is given by a closed-form formula. An approximate BLMMSE channel estimation error is derived in the low signal-to-noise ratio (SNR) region. The lower bound of the approximate channel estimation error for all possible pilot matrices is derived. The analysis shows that the pilot matrix with pairwise orthogonal and equal-norm row vectors and equal-norm column vectors is optimal in terms of approximate channel estimation error. The hypersphere-based steepest descent (HSD) algorithm is proposed to design the pilot matrix by optimizing the performance of the BLMMSE estimator. The numerical results show that the proposed HSD algorithm has a noticeable improvement in channel estimation compared with the DFT pilot and the random pilot. The HSD algorithm is also valid for the near maximum likelihood estimator and SNR mismatch.

Partial Self-Concatenation Structure and Performance Analysis of Spinal Codes Over Rayleigh Fading Channel

Spinal codes are a new family of rateless codes which have been proved to be capacity-achieving over both the additive white Gaussian noise (AWGN) channel and the binary symmetric channel (BSC). However, over the Rayleigh fading channel between the vehicle nodes, the error performance of Spinal codes is not satisfactory since the tail message blocks of Spinal codes are prone to error. To solve this issue, this paper proposes a new practical partial self-concatenation coding structure of Spinal codes, named <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$N$</tex-math></inline-formula> tail-protected Spinal codes, to pointedly protect tail message blocks of Spinal codes over the flat Rayleigh fading channel. Theoretical performance analysis and simulation results are also provided to validate and verify the effectiveness of the proposed <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$N$</tex-math></inline-formula> tail-protected Spinal codes.

Approximation of Capacity in MIMO Systems

This paper introduces functional approximations to the MIMO capacity over flat Rayleigh fading channels, which allow for analytical solutions to network resource optimization problems. This approximation allows to solve the problem of resource allocation optimization in radio networks and in other systems used to transfer information. The precision of the suggested approximations is assessed and is shown to provide a very close match to the exact capacity expression.

Improving Bit Error Rate of MIMO-OFDM System Using Discrete Wavelet Transformation

This paper has developed a discrete wavelet transform (DWT) for multicarrier modulation in MIMO-OFDM system. The proposed system used additive Gaussian white noise (AGWN) and Rayleigh flat fading channel with respect to SNR using binary phase shift keying (BPSK). The algorithms for various scenarios of MIMO-OFDM system have been developed and simulated in MATLAB environment. The performance metric of the system was based on bit error ratio (BER) variation over values of signal to noise ratio (SNR) for different transmit and receive antennas including single input multiple output (SIMO) arrangement. The simulation results showed that the performance of DWT based MIMO-OFDM outperformed DFT based MIMO-OFDM. For the 2×1, 2×2, 2×3 MISO and MIMO systems, the DWT scheme offered reduced BER of 1.803e-05, 1.502e-05, and 1.413e-05 against 0.005847, 0.005361, and 0.005325 for the DFT scheme with respect to signal to noise ratio (SNR) at 10 dB. Generally, the results showed that using DWT scheme in OFDM for wireless communication system does not require an extra subcarrier to provide cyclic prefix function that serves as additional cost burden and reduces bandwidth.

MIMO Hybrid PD-SCMA NOMA Uplink Transceiver System

The application of multiple-input multiple-output (MIMO) on power domain sparse code multiple access (PD-SCMA) systems would enhance their performance by increasing the multiplexing and diversity gains. However, this is at a cost of increased detection complexity, as more users and antennas are deployed. This work develops and investigates the performance of spatial multiplexing MIMO based hybrid PD-SCMA system (M-PD-SCMA) transceiver on an uplink heterogeneous network over Rayleigh flat-fading channels. The aim is to strike a balance on the number of antennas and capacity/spectral efficiency. The system capacity and outage robustness of the proposed transceiver in imperfect channels is evaluated and the bit error rate (BER) performance analysed. The link-level simulation results demonstrate that M-PD-SCMA achieves performance benchmark with PD-SCMA schemes. The proposed receiver achieves guaranteed BER performance with an increase in the number of transmit and receive antennas. Besides, the results highlight the impact of the codebook size, number of layers and power level distinctiveness on the outage bounds at each receive antenna at different SNR levels. Thus, the feasibility of an M-PD-SCMA system is validated.

Design a New Time-Diversity System Using Orthogonal Mapping Matrix and Symbols Interleaving for Rayleigh Flat-Fading Channels

A time-diversity system is implemented in this work using a time-diversity encoder. The diversity encoder uses an orthogonal matrix to map vectors of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula> modulated symbols to vectors of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula> diversity symbols. Each modulated symbol is implicitly transmitted <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula> times in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula> successive periods when the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula> diversity symbols are transmitted. No changes in the symbols’ transmission rate occur due to the proposed time-diversity scheme. The diversity symbols are transmitted with the same transmission rate of modulated symbols in the systems with no signal diversity. The proposed system uses the same bandwidth of the system with no signal diversity too. In the receiver, the outputs of the matched filter are stored in a buffer of length <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula> during the diversity period. After filling the buffer, its contents are multiplied with the inverse of the fading matrix. A diversity detector remaps the diversity symbols to the modulated symbols. It also combines the corresponding modulated symbols in one decision variable. The noise samples in the decision variables are uncorrelated. A maximum-likelihood (ML) detector and a linear detector are used as diversity detectors in this work. The performance of the proposed system achieves the same performance as the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula> diversity channels system with a unity-gain-combiner (UGC) receiver.

Secure Communication for Cognitive Networks Based on MIMO and Spreading LDPC Codes

The existing cognitive radio (CR) systems lack the ability to deal with the attack of a pretended primary user (PPU), which can palsy cognitive network. To solve the problem, in this paper, a secure cognitive radio (CR) system is proposed. The proposed systems combines MIMO and spread spectrum techniques as well as low density parity check (LDPC) codes to cancel the electronic interference of PPU. The simulation results in Rayleigh flat-fading channel show that, comparing with MIMO cognitive system without the proposed method, the proposed approach can effectively cancel electronic interference from enemy and channel noises interference, and obtain about 9dB gain.

Design and performance analysis of modern communications systems based on Multicarrier compression technique

This paper shows how to enhance the bandwidth and bit error rate (BER) performance of modern communications system in multicarrier modulation systems by including a compression technique in frequency dimensional after multicarrier modulation. The proposed system design for multi-carrier systems was implemented using a standard system based on Fast Fourier Transform (FFT). This proposed idea of the multicarrier modulation system done by adding the Discrete Wavelet Transform (DWT) as compression stage to multicarrier coefficients. This operation will be done by sending the approximation coefficients of DWT and discard the details coefficients. The details coefficients in receiver side will compensate with zeros in IDWT stage. The simulation results were examined using additive white Gaussian noise (AWGN), flat Rayleigh fading and selective fading channels showing that the proposed additional compression scheme after DWT can double the data rate and reduce the bit error rate (BER).

Improvement of Pilot Symbol Orthogonal Sequences in 2×2 to 4×4 MIMO Wireless Communication Systems with Channel State Estimation

AbstractMIMO wireless communication systems with channel state estimation, in which 2 to 4 transmit-receive antenna pairs are employed, are simulated. The channel estimation is fulfilled by the orthogonal pilot signal approach, where the Walsh Hadamard-ordered sequences are commonly used for piloting. The signal is modulated by applying the quaternary phase shift keying method. Maximum 250 000 packets are transmitted through flat-fading Rayleigh channels, to which white Gaussian noise is added. Based on simulating 10 subcases of the frame length and number of pilot symbols per frame, it is ascertained that pilot symbol orthogonal sequences in 2×2 to 4×4 MIMO systems can be improved by substituting Walsh functions with partially unsymmetrical binary functions constituting the eight known orthogonal bases. The benefit is that the bit-error rate is substantially decreased, especially for 2×2 MIMO systems. Considering three cases of the pilot signal de-orthogonalization caused by two indefinite and definite pilot sequence symbol errors, the relative decrement varies from 0.123 % to 14.7 %. However, the decrement becomes less significant as the number of transmit-receive antenna pairs is increased.

Successive interference cancelation‐inspired channel estimation for downlink non‐orthogonal multiple access

AbstractThis paper proposes a channel estimation (CE) scheme composed of two successive interference cancelation‐inspired approaches for a two‐user power domain downlink non‐orthogonal multiple access system. One approach is intended for the weaker user, and the other approach is intended for the stronger user. Both CE approaches employ a constant step‐size least mean squares (CSS‐LMS) algorithm, using partial pilots to estimate a Rayleigh flat fading channel with a Jake's Doppler spectrum. Closed‐form analytical expressions for the CE error variance are presented for each approach and the mean square error (MSE) is used as the performance metric. Through simulation, the CE performance of the stronger user and the weaker user is assessed for different probabilities of error in detection of the unknown pilot. A reasonable probability of error in detection is then selected and employed in evaluating the CE performance of both schemes against their theoretical analyses. Overall, the theoretical analysis matches the simulation results.

A Novel Concatenated LWT and WHT Based UFMC Waveform Design for the Next Generation Wireless Communication Systems

A novel concatenated Lifting Wavelet Transform (LWT) and Walsh Hadamard Transform (WHT) with Universal Filtered Multi Carrier (UFMC) waveform is suggested as an alternative to Orthogonal Frequency Division Multiplexing (OFDM) waveform for the next generation wireless telecommunication systems in this paper. The suggested waveform is composed of LWT and WHT with UFMC waveform. Both the elimination the disadvantages of OFDM and the improvement the achievement of UFMC waveform, from the fifth generation waveform candidates, has been aimed with the suggested waveform. In order to verify the performance of the suggested waveform and compare with the traditional OFDM, UFMC, and LWT‐UFMC waveform computer simulation studies are performed in additive white Gaussian noise and flat Rayleigh fading channel environments. The acquired computer simulation results exhibit that the achievement of the suggested waveform has better than the achievement of the traditional OFDM, UFMC, and LWT‐UFMC waveform. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

A Novel GFDM Waveform Design Based on Cascaded WHT-LWT Transform for the Beyond 5G Wireless Communications.

In this paper, a new WHT-LWT-GFDM waveform obtained by combining Walsh–Hadamard Transform (WHT), Lifting Wavelet Transform (LWT), and Generalized Frequency Division Multiplexing (GFDM) is presented for use in next-generation wireless communication systems. The proposed approach meets the requirement of 5th-generation (5G) and beyond communication schemes in terms of low latency, low peak-to-average-power ratio (PAPR), and low bit-error rate (BER). To verify the performance of the presented waveform, PAPR and BER simulation results were obtained in additive white Gaussian noise (AWGN) and flat Rayleigh fading channels, and the performance of the proposed system was compared with conventional Orthogonal Frequency Division Multiplexing (OFDM), GFDM, and Walsh–Hadamard transform-based GFDM (WHT-GFDM). Simulation results show that the proposed waveform achieves the best BER and PAPR performances and it provides considerable performance gains over the conventional waveforms.