Uncorrelated Rayleigh Fading Channels Research Articles

Developing Laboratory Experiments to teach Undergraduate Engineering Students Multi-User Massive MIMO Technology for 5G Cellular Networks

An effective method of facilitating student learning in a laboratory environment is “practice by doing”. The study of modules related to signal-processing for digital communications requires deep mathematical and theoretical foundations but the practice goal is not really emphasized in the undergraduate curriculum at the University of Mauritius. This causes the students to lose interest in the corresponding modules resulting in high rate of failures. In this work, we propose to develop laboratory experiments with a view to bridge the gap between theoretical and practical aspects in the field of Massive Multiple-Input Multiple-Output (MIMO) systems for 5G cellular networks. Various laboratory scenarios are set up that consider a Maximum Ratio Combining (MRC) receiver in the uplink with an uncorrelated Rayleigh fading channel. Moreover, from a signal processing perspective to enhance the student’s understanding, we analyze the efficiency and error performance of Massive MIMO systems with MPSK and MQAM modulation schemes as well as perfect and imperfect channel estimates. The leading industry software package MATLAB R2022 is used to develop all laboratory experiments and the codes are elaborated in this analysis. Data collected from the experiments are used to generate spectral efficiency and error performance curves which can be used for future research. The findings underscore the significance of accounting for both scenarios and illuminate promising avenues for future research in the realm of massive MIMO education and learning. The assimilation of MATLAB® flowcharts for each MRC receiver, MPSK, and MQAM with perfect and imperfect Channel State Information (CSI) adds further depth to the study, ensuring a comprehensive understanding of the intricacies of massive MIMO systems. Ultimately, this contribution helps in the nurturing of expertise such that future generations of wireless communication pioneers can be inspired.

An Analytical Reliability Performance Assessment of Cell-Free Massive MIMO Systems for 5G and Beyond Cellular Networks

In today‟s realm, the 5G cellular networks offer a new era of fully digital environment by connecting people anywhere anytime. This era requires inspiring demands to the networks in terms of spectral and energy efficiencies, low-latency and ultra-reliable communications. A major development to deal with these unparalleled demands is the introduction of Cell- Free Massive MIMO (CF mMIMO) systems to the cellular network. In recent years, mathematical foundations have been laid for a CF mMIMO communication system to evaluate the spectral and energy efficiencies given the number of access points. Various existing literatures have adopted mathematical models to formulate closed-form expressions for these efficiencies using uncorrelated Rayleigh fading for simple linear processing detectors. In this paper, we try to address a compelling and interesting question which has not received much attention lately. The question is how to evaluate the reliability of a connected user terminal in both a CF mMIMO and conventional mMIMO system? We answer this question by first analyzing the signal models for both systems assuming exact channel estimates and consider an uncorrelated Rayleigh fading channel model. The exact Bit Error Rate, as a reliability assessment, in closed-form are then derived based on strong mathematical foundations, which are simple to numerically evaluate in Matlab R2022, for MPSK and MQAM modulation schemes. The mathematical models presented in this work can be used in 5G and Beyond 5G networks to evaluate the distributions of error rates for a user given the number of Access points or Base Station antennas and modulation scheme. Machine Learning algorithms can be applied to the analytical expressions with a view to predict the error performance of a user terminal given the fading characteristic of the propagation environmen

User Subgrouping and Power Control for Multicast Massive MIMO Over Spatially Correlated Channels

Massive multiple-input-multiple-output (MIMO) is unquestionably a key enabler of the fifth-generation (5G) technology for mobile systems, enabling to meet the high requirements of upcoming mobile broadband services. Physical-layer multicasting refers to a technique for simultaneously serving multiple users, demanding for the same service and sharing the same radio resources, with a single transmission. Massive MIMO systems with multicast communications have been so far studied under the ideal assumption of uncorrelated Rayleigh fading channels. In this work, we consider a practical multicast massive MIMO system over spatially correlated Rayleigh fading channels, investigating the impact of the spatial channel correlation on the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">favorable propagation</i> , hence on the performance. We propose a subgrouping strategy for the multicast users based on their channel correlation matrices’ similarities. The proposed subgrouping approach capitalizes on the spatial correlation to enhance the quality of the channel estimation, and thereby the effectiveness of the precoding. Moreover, we devise a max-min fairness (MMF) power allocation strategy that makes the spectral efficiency (SE) among different multicast subgroups uniform. Lastly, we propose a novel power allocation for uplink (UL) pilot transmission to maximize the SE among the users within the same multicast subgroup. Simulation results show a significant SE gain provided by our user subgrouping and power allocation strategies. Importantly, we show how spatial channel correlation can be exploited to enhance multicast massive MIMO communications.

Low Complexity Optimal and Suboptimal Detection at Spatial Modulation MIMO Receivers

This paper develops three low-complexity detection schemes for the spatial modulation (SM) Multiple Input Multiple Output (MIMO) systems. We first propose a reduced complexity maximum likelihood (RC-ML) detection scheme. For the practical values of the modulation index, the proposed RC-ML method is simpler than the existing hard-limiting-based ML schemes. The two other proposals are based on a suboptimal Maximum Ratio Combining (MRC) detection method. We present a new analysis of the MRC detector in the uncorrelated Rayleigh fading channel and identify the system operational scenarios for which the MRC performance is nearly identical to the ML performance. Our proposals — a hybrid MRC-ML method and an MRC scheme with rank reduction — are inspired by this analysis. The analytical and simulation results show that the proposed MRC-based schemes can attain a near-optimal performance while reducing the complexity of the ML-based SM receiver.

Downlink Multi-User Hybrid Beamforming Systems With Receiver IQ Imbalance: Pre-Compensation and Performance Analysis

We consider the downlink (DL) of a multi-user hybrid beamforming system having receiver IQ imbalance (Rx-IQI). For a generic channel model and any IQI unaware hybrid precoder, we derive a generalized expression of the DL signal-to-interference-and-noise-ratio (SINR) using which we show that the corresponding DL sum-rate is limited by the Rx-IQI parameters. Therefore, we propose a novel Rx-IQI pre-compensation algorithm and we derive a generalized DL SINR expression for the Rx-IQI pre-compensation scenario. Using the derived SINR expressions, we provide closed-form sum-rate expressions of the zero-forcing hybrid precoder for uncorrelated Rayleigh fading and sparse mm-wave channels. Through analysis and numerical simulations, we show that the proposed algorithm almost achieves the performance of an IQI-free system.

On the Distribution of SINR for Widely Linear MMSE MIMO Systems With Rectilinear or Quasi-Rectilinear Signals

Although the widely linear least mean square error (WLMMSE) receiver has been an appealing option for multiple-input-multiple-output (MIMO) wireless systems, a statistical understanding on its pose-detection signal-to-interference-plus-noise ratio (SINR) in detail is still missing. To this end, we consider a WLMMSE MIMO transmission system with rectilinear or quasi-rectilinear (QR) signals over the uncorrelated Rayleigh fading channel and investigate the statistical properties of its SINR for an arbitrary antenna configuration with $N_t$ transmit antennas and $N_r$ receive ones. We first derive an analytic probability density function (PDF) of the SINR in terms of the confluent hypergeometric function of the second kind, for WLMMSE MIMO systems with an arbitrary $N_r$ and $N_t=2, 3$. For a more general case in practice, i.e., $N_t>3$, we resort to the moment generating function to obtain an approximate but closed form PDF under some mild conditions, which, as expected, is more Gaussian-like as $2N_r-N_t$ increases. The so-derived PDFs are able to provide key insights into the WLMMSE MIMO receiver in terms of the outage probability, the symbol error rate, and the diversity gain, all presented in closed form. In particular, its diversity gain and the gain improvement over the conventional LMMSE one are explicitly quantified as $N_r-(N_t-1)/2$ and $(N_t-1)/2$, respectively. Finally, Monte Carlo simulations support the analysis.

Secure Audio Transmission Over Wireless Uncorrelated Rayleigh Fading Channel

Audio communications and computer networking play essential roles in our daily lives, including many domains with different scopes. Developments in these technologies are quick. In consequence, there is a dire need to secure these technologies up to date. This paper presents an efficient model for secure audio signal transmission over the wireless noisy uncorrelated Rayleigh fading channel. Also, the performance of the utilized multiple secret keys-based audio cryptosystem is analyzed in different transformation domains. The discrete cosine transform (DCT), the discrete sine transform (DST), and the discrete wavelet transform (DWT) are investigated in the utilized multiple secret key-based audio cryptosystem. Simulation results show consistent results with the wireless noisy channel. The performance of the proposed multiple secret keys-based audio cryptosystem can be ranked concerning the employed domain as DWT, DCT, and DST transform techniques. The simulation experiments proved that the presented multiple secret keys-based audio cryptosystem for audio signals transmitted over the wireless noisy uncorrelated Rayleigh fading channel achieves reliable and secure wireless link utilizing combined multi security layers.

RCSA Protocol with Rayleigh Channel Fading in Massive-MIMO System

Introduction: Massive MIMO is a process where cellular BSs a large number of antennas. In this study, we concern about the end-to-end massive-MIMO system under the Rayleigh channel fading effect. Also, it includes both inter-channel interference and intra channel interference in an m-MIMO network system. Method: The major aim is to increase the throughput and network capacity as well as minimizing the channel collision in between the associated pilots. Here, we proposed an RCSA protocol with Rayleigh channel fading effect in the m-MIMO network to create a network like a real-time scenario. Here we have focused on the deployment of urban scenarios with the small timing variation and provided our novel RAP for the UEs, where the UEs want to access the network. To validate the performance of our proposed scheme we are going to compare with the state-of-art technique in the result analysis section. Result: We provide the analysis based upon the two considered scenarios; such as scenario-A considered at intra-channel interference and whereas in scenario-B considered both intra-cell channel interference as well as inter-cell channel interference. Where our RCSA approach is proposed with uncorrelated Rayleigh fading channels (URFC) that used to increase the capacity of network and decrease the collision probability. Conclusion: Here, we proposed the RCSA approach and it consist of four major steps such as; system initialization and querying; response queuing; resource contention and channel state analysis and, resource allocation. The system performs in the TDD mode of operation and the resources of time-frequency are divided into the coherent blocks of channel Discussion: In order to compare our RCSA-URFC approach, here we consider the state-of-art technique such as vertex graph-coloring-based pilot assignment (VGCPA) [35] under URFC. In addition we also consider the bias term randomly to make decision on particular UE. It very difficult to guess the strong probability of UE, therefore as per information obtained via

Novel detection schemes for generalized quadrature spatial modulation

SummarySpatial Modulation (SM) is a technology that incorporates digital modulation and coding with multiple antennas to achieve high data rates along with improved energy efficiency. Quadrature spatial modulation (QSM), which extends the transmitted signals to in‐phase and quadrature domains, has recently been proposed to improve spectral efficiency (SE) for SM. In this paper, we have considered a combination of Generalized QSM (GQSM) and Quasi Orthogonal Space Time Block Codes (QOSTBC). We propose a new detection scheme for the GQSM and use three different prevailing detection schemes for QOSTBC. We present Bit Error Rate (BER) versus average SNR performance for the combined system using M‐QAM constellations with quasi‐static spatially uncorrelated Rayleigh fading channels and computational complexity in terms of numbers of addition/multiplication and search time. We have compared the considered system with prevailing GQSM system and shown that the prevailing system, as per active antenna permutation (AAP) in GQSM, offers number of transmitted bits ranging from 2 to 9 whereas the proposed system offers number of transmitted bits ranging from 6 to 16 in the same bandwidth. Thus, there is a visible gain in SE. Furthermore, we have compared the BER performance of the considered system with the performance of maximum likelihood detector (MLD) and spatial modulation (SM). In the considered system, the QOSTBC improves the diversity gain. Hence, we have shown that the considered Scheme 3 substantially outperforms the SM. Further, the considered system with Scheme 3 has nearly similar BER performance with the maximum likelihood detector (MLD), which has higher computational complexity.

Compensation of Transmitter IQ Imbalance in Multi-User Hybrid Beamforming Systems

In this paper, we consider the uplink (UL) communication of a massive multi-user (MU) multiple-input multiple-output (MIMO) hybrid beamforming system (HBFS) in which the transmitting user-equipments are affected by IQ imbalance (IQI). We first show that if the transmitter IQI is not compensated, it will result in a finite ceiling of the UL achievable sum-rate at high signal-to-noise ratio, which only depends on the transmitter IQI matrices and is independent of the propagation channel and the choice of the hybrid combining matrices. This justifies the need for transmitter IQI compensation in massive MU-MIMO HBFS. Therefore, we propose a novel zero-forcing based transmitter IQI compensation algorithm to be implemented at the base station which effectively mitigates the undesired effects of transmitter IQI and is applicable for any channel model and any choice of the number of RF chains. For uncorrelated Rayleigh fading channel, we derive an approximate closed-form expression of the UL sum-rate achieved by the massive MU-MIMO HBFS with the proposed transmitter IQI compensation. Finally, numerical results are presented which confirm the effectiveness of the proposed transmitter IQI compensation algorithm in mitigating the undesired effects of transmitter IQI in different channel environments.

Physical layer security for multiuser multi‐eavesdropper multi‐input multi‐output (MIMO) system in the presence of imperfect feedback

SummaryIn this work, we analyze the physical layer security (PLS) for a multiuser (MUS) multi‐input multi‐output multi‐eavesdropper (MIMOME) wireless network using selection transmission (ST) at the base station (BS) with maximum ratio combining (MRC) at both of the receivers, receivers of legitimate users (LUs) as well as the receivers of illegitimate users over an uncorrelated Rayleigh fading channel. In this scenario, multiple users communicate to a BS at the same time multiple eavesdropper user may intercept the transmission. Next, we drive exact closed‐form expression for probability of nonzero secrecy capacity (PNZSC) and secrecy outage probability (SOP) in the presence of imperfect channel state information (ICSI). At last, we present the simulation results to authenticate the analytical results and analyze the impact of ICSI on PLS of MUS‐MIMOME system.

Quadrature spatial modulation based multiuser MIMO transmission system

This study presents a multiuser (MU) multiple-input multiple-output (MIMO) downlink transmission scheme based on the quadrature spatial modulation (QSM) concept, which uses the indices of the non-zero entries in its transmission vector to modulate and transmit an independent sequence of bits for each user in the system. The MU interference is removed by using a matrix precoding technique based on channel state information (CSI) known as block diagonalisation (BD). The performance of the proposed scheme is compared with the conventional MU–MIMO–BD system for uncorrelated Rayleigh fading channels and correlated fading channels with imperfect CSI in the reception. Additionally, a low-complexity near maximum likelihood (ML) detection algorithm for the MU–MIMO–QSM signal's detection is proposed. For the considered cases, the proposed MU–MIMO–QSM scheme exhibits gains up to 1 dB in bit error rate performance and a reduction in detection complexity up to 93% as compared to the conventional MU–MIMO–BD scheme for the optimal ML detection. The proposed algorithm performs very near to the optimal ML detector whilst achieving a complexity reduction of up to 58%.

Spectral efficiency enhancement in Massive MIMO system under pilot contamination

SummaryMassive multiple‐input, multiple‐output (MIMO) system is an effective technique to develop the spectral efficiency of the wireless communication systems. Since the number of users is much higher than the available number of orthogonal pilot sequences, the users in the neighboring cells can reuse the same pilots of the home cell. Thus, pilot contamination occurs, which restricts the system throughput. In this paper, Laplacian centralized scattering‐spatially correlated Rayleigh fading channel model with multi‐cell minimum mean square error (M‐MMSE) combining and precoding to mitigate pilot contamination and enhance cell throughput. This model gives a more accurate description, especially for cell‐edge users. It results in an accurate spatial channel correlation matrix calculation that enhances the channel estimation quality under pilot contamination. Simulation results indicate that the proposed Laplacian scattering‐spatially correlated Rayleigh fading model achieves better pilot contamination mitigation and larger spectral efficiency, as compared with both the one‐ring scattering‐spatially correlated Rayleigh fading and the uncorrelated Rayleigh fading channel models for different combining and precoding schemes at different pilot reuse factors. The cost of interference rejection and spectral efficiency enhancement is an increase in the system computational complexity.

Performance Analysis of Matched-Filter Detector for MIMO Spatial Multiplexing Over Rayleigh Fading Channels With Imperfect Channel Estimation

The matched-filter (MF) detector is the lowest complexity linear detector in practical MIMO spatial multiplexing systems. Its performance is significantly affected by the number of available antennas and an operating channel SNR. In this paper, we analyze the exact performance of the MF detector without any restrictions on the numbers of the transmit and receive antennas. To this end, we first develop the exact, closed-form expression of the MF detector output over uncorrelated Rayleigh fading channels with an arbitrary number of antennas. Based on this result, we derive the exact closed-form bit error rate expressions for uncoded BPSK, QPSK, and $M$ -ary QAM signaling, which can be seen as the generalized forms of the conventional receiver diversity based on maximum ratio combining. We also elucidate the conditions on the numbers of antennas and channel SNR, where the use of MF detector should become effective. Furthermore, in the case of coded MIMO systems, we develop the optimal metric derived from the exact MF output. The corresponding mutual information justifies the simulated performance of LDPC-encoded MIMO spatial multiplexing with the MF detector over ideally interleaved Rayleigh fading channels. Finally, we extend our analysis to more practical systems with imperfect channel estimation.

Two-Layer Coded Spatial Modulation With Block Markov Superposition Transmission

This paper is concerned with the spatial modulation (SM), a multiple-input multiple-output (MIMO) transmission technique, that maps information bits not only into the conventional two-dimensional signal points but also into the indices of active transmit antennas. We present a two-layer coded SM scheme, in which the spatial bits carried by the antenna indices and the signal bits carried by the conventional signals are protected separately by two error correction codes. For the ease of decoding process, the code rates are allocated according to the chain rule of the mutual information. We choose block Markov superposition transmission (BMST) codes for each layer, since they are easily designed for any given code rate with a predictable performance lower bound. An iterative sliding-window decoding algorithm is also presented by exchanging messages iteratively between the two BMST decoders and the soft-in soft-out (SISO) demapper of the SM. To reduce the computational complexity, we propose to implement the SISO demapping algorithm by employing only partial soft inputs. Numerical results show that the BMST-SM system performs well over uncorrelated Rayleigh fading channels.

Reordered Elias Gamma Error Correction Codes for the Near-Capacity Transmission of Multimedia Information

A novel joint source and channel coding (JSCC) scheme is proposed, which we refer to as the reordered Elias gamma error correction (REGEC) code. Like the recently proposed unary error correction (UEC) code and EGEC code, the proposed code facilitates the practical near-capacity transmission of source symbol values that are randomly selected from a large or infinite alphabet. However, in contrast to the UEC code, both the EGEC and our proposed REGEC codes are universal codes, facilitating the transmission of source symbol values that are randomly selected using any monotonic probability distribution. However, the EGEC code has a complicated structure comprising two parts, where unequal error protection is required to balance the two parts with the aid of a specific parameterization that must be tailored to the source distribution, preventing its employment for unknown or non-stationary sources. By contrast, the proposed REGEC code does not need unequal error protection, and hence its parameterization does not have to be tailored to the particular source distribution, and thus the REGEC code is a more attractive scheme. More explicitly, our REGEC code has a simple structure comprising only a single part, which does not suffer from the delay and loss of synchronization that are associated with the two parts of the EGEC code. In a particular practical scenario, where the source symbols obey a specific Zeta probability distribution, our REGEC scheme is shown to offer gains of up to 0.9 dB over the best of JSCC and separate source and channel coding (SSCC) benchmarkers, when QPSK modulation is employed for transmission over an uncorrelated narrowband Rayleigh fading channel. In the scenario where the source symbols obey the distribution produced by the H.265 video codec, our REGEC scheme is shown to offer a gain of 0.7 dB over the SSCC benchmarker. These gains are achieved for free, without increasing the required transmit-duration, transmit-bandwidth, transmit-energy, or decoding complexity.

Hybrid Analog-Digital Channel Estimation and Beamforming: Training-Throughput Tradeoff

This paper designs hybrid analog-digital channel estimation and beamforming techniques for multiuser massive multiple input multiple output (MIMO) systems with limited number of radio frequency (RF) chains. For these systems, first we design novel minimum mean square error (MMSE) hybrid analog-digital channel estimator by considering both perfect and imperfect channel covariance matrix knowledge cases. Then, we utilize the estimated channels to enable beamforming for data transmission. When the channel covariance matrices of all user equipments (UEs) are known perfectly, we show that there is a tradeoff between the training duration and throughput. Specifically, we exploit that the optimal training duration that maximizes the throughput depends on the covariance matrices of all UEs, number of RF chains and channel coherence time ($T_c$). We also show that the training time optimization problem can be formulated as a concave maximization problem {for some system parameter settings} where its global optimal solution is obtained efficiently using existing tools. In particular, when the base station equipped with $64$ antennas and $1$ RF chain is serving one single antenna UE, $T_c=128$ symbol periods ($T_s$) and signal to noise ratio of $10$dB, we have found that the optimal training durations are $4T_s$ and $20T_s$ for highly correlated and uncorrelated Rayleigh fading channel coefficients, respectively. The analytical expressions are validated by performing numerical and extensive Monte Carlo simulations.

Development of a MATLAB Toolbox for Mobile Radio Channel Simulators

A profound knowledge of mobile radio channels is required for the development, evaluation, and also assessment at practical conditions of present and future mobile radio communication systems. The modelling, analysis, and simulation of mobile radio channels are important key area in current context. In addition to that, knowledge of channel behaviour in mobile radio communication is extensively recommended for the study of transmitter/receiver performances under different propagation scenarios. Our intention in this research work was to develop various kinds of mobile fading channel simulators using MATLAB and embed them into MATLAB software as a toolbox. Implemented channel simulators were combined MATLAB as a toolbox which users can easily select well-known channel models to test and to study the performance of mobile communication systems. It gives better support for the new users to work on the developed channel simulators, run the test procedures as well as parameter computation. The toolbox contains channel simulators for simulating non-stationary land mobile satellite channel, spatial shadowing processes, MIMO channels, multiple uncorrelated Rayleigh fading channels, mobile to mobile channel, frequency hopping channels etc. Set of test procedures were developed such as the autocorrelation function ACF, average duration of fades ADF, the probability density function PDF, and the level-crossing rate LCR etc., in order to test and to confirm the correctness of the implemented channel simulators. Proposed new algorithms to compute the model parameters of the channel simulators were also implemented in the toolbox to enable the parameterization of the channel simulators under specific propagation conditions. Some of the simulation models were implemented based on specification of GSM system by CEPT-COST 207. DOI: http://dx.doi.org/10.4038/jur.v2i1-2.7853 J. Univ. Ruhuna 2014 2:40-45

Block Markov Superposition Transmission with Spatial Modulation

Spatial modulation (SM) is a multiple-input multiple-output (MIMO) transmission technique that maps the information into both antenna indices and signals from a conventional signal constellation. Block Markov superposition transmission (BMST) is a recently proposed coding scheme which has a good performance and a predictable performance lower bound. In this letter, we propose to combine the BMST with the SM, resulting in a system, which is acronymized as BMST-SM for convenience. Also presented is a sliding-window decoding executed iteratively between the BMST decoder and the soft-in soft-out (SISO) SM demapper. To evaluate the performance of the BMST-SM system, the mutual information is derived for the SM with multiple receive antennas under uniformly distributed input constraint. Simulation results show that the BMST-SM scheme performs around one dB away from the Shannon limit at the bit-error-rate (BER) around 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> over uncorrelated Rayleigh fading channels.

Unequal error protection by partial superposition transmission using low‐density parity‐check codes

In this study, the authors consider designing low-density parity-check (LDPC) coded modulation systems to achieve unequal error protection (UEP). They propose a new UEP approach by partial superposition transmission (PST) called UEP-by-PST. In the UEP-by-PST system, the information sequence is distinguished as two parts, the more important data (MID) and the less important data (LID), both of which are coded with LDPC codes. The codeword that corresponds to the MID is superimposed on the codeword that corresponds to the LID. The system performance can be analysed by using discretised density evolution. Also proposed in this study is a criterion from a practical point of view to compare the efficiencies of different UEP approaches. Numerical results show that, over both additive white Gaussian noise channels and uncorrelated Rayleigh fading channels, (i) UEP-by-PST provides higher coding gain for the MID compared with the traditional equal error protection approach, but with negligible performance loss for the LID; and (ii) UEP-by-PST is more efficient with the proposed practical criterion than the UEP approach in the digital video broadcasting system.