Spectral Efficiency Performance Research Articles

Optimized DM-RS Configuration for Improved 5G New Radio Network Capacity and Performance

Network load in mobile networks is continuously growing, putting pressure on mobile operators to deliver target network performance and user experience. This paper focuses on network capacity improvement through increased spectral efficiency, which can be achieved with overhead reduction by optimizing the demodulation reference signal (DM-RS) configuration, which is one of the channels/reference signals with the largest contribution to overhead. In a high-speed scenario, the Doppler effect noticeably influences the temporal nature of the channel such that a channel interpolation process is required within a slot. However, increasing the number of symbols used for DM-RS has a negative impact on capacity. The Doppler effect was analyzed for various 5G NR configurations of operating frequency and subcarrier spacing (SCS), and various use cases were considered using user equipment (UE) speed as the main parameter. For suitable use cases, the DM-RS configuration was optimized in networks with live traffic. The impact of the configuration change on 5G/NR spectral efficiency, user experience and link adaptation performance was assessed through a deep-dive analysis of active measurements, available performance Management (PM) counters and key performance indicators. An optimized DM-RS configuration is proposed, and it is demonstrated to achieve gains of 5–15%, depending on the metric used, use case analyzed, network load, traffic mix and other relevant network characteristics such as topology and clutter type.

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.

Metamaterial Inspired Varactor-Tuned Antenna with Frequency Reconfigurability and Pattern Diversity.

A metamaterial-inspired varactor-tuned antenna with frequency reconfigurability and pattern diversity is designed. Two different versions of a reconfigurable structure are integrated into a single antenna to excite two different orthogonal patterns, which realizes pattern diversity for MIMO applications. The outer annular Composite Right-/Left-Handed Transmission Line (CRLH-TL) works at the 1 mode and provides a broadside pattern, and the inner circular radiator loaded with split ring resonators (SRR) operates at the 0 mode and radiates an omnidirectional pattern, which realizes pattern diversity. By using surface-mounted varactors, the operating frequencies for the two radiation patterns can be tuned over a wide frequency range, from 1.7 GHz to 2.2 GHz, covering the 1.71-2.17 GHz LTE band, and a low mutual coupling between the two radiators is achieved. The antenna has also been prototyped. The measured results are in good agreement with the simulation results, verifying the proposed concept. The dual-mode MIMO system equipped with the proposed antenna elements is discussed within the context of a 3-D channel model, and it shows a superior array compactness and spectral efficiency (SE) performance compared to scenarios with single-mode elements.

Analysis of Carrier Aggregation as a Diversity Technique for Improved Spectral Efficiency and Secrecy Performance in Mobile Communications

Carrier aggregation (CA) was introduced in mobile communication systems in response to the demand for higher network capacity. CA was conceived as a technique to achieve higher data rates by aggregating multiple blocks of spectrum from the same or different frequency bands. This work explores a different point of view, where CA is employed not as a way to increase capacity through using more bandwidth, but as a diversity technique in order to increase the spectral efficiency of the existing spectrum, and therefore, achieve higher capacity without needing additional spectrum. A mathematical model and set of closed-form expressions are provided, which can be used to characterise the performance of CA as a diversity technique (in terms of both ergodic capacity and secrecy capacity) and determine the impact of various relevant configuration parameters. The numerical results obtained by evaluating the mathematical expressions derived in this work are in line with our previous simulation studies and demonstrate that CA can be effectively exploited as a diversity technique to improve the capacity and performance of mobile communication systems compared to the case of single-carrier transmission over the same amount of bandwidth.

Performance analysis of FSO communications over a generalized turbulence fading channel with pointing error

SummaryQuantitatively assessing the performance of free space optical (FSO) communication systems requires an accurate description of turbulence induced fading. However, it is well known that common irradiance distributions inaccurately model intensity tail regions. Recently, a general fading model as the product of arbitrary number of Gamma with inverse Gamma was proposed and shown to accurately predict measurements, besides containing many well‐known models as special cases. This paper is concerned with analyzing the effect of discrepancies among different fading distributions on optical system performance in terms of bit error rates and capacity. Based on the general fading model a unified analysis of the channel structure effects on FSO communications in the presence of turbulence and pointing error is presented. The outage probability is investigated for both homodyne and direct detection schemes. Closed form expressions for the average probability of bit error for intensity modulation, phase shift keying and polarization shift keying, single‐input‐single‐output systems are given and verified by Monte‐Carlo simulations. Spatial diversity is also studied through single‐input‐multiple‐output systems. Also, the ergodic capacity is derived. Comparisons between the proposed distributions and other widely used distributions are carried out and show significant differences among existing fading models. This suggests possible improvements in the spectral efficiency and error performance design of optical wireless communication systems.

Performance analysis of OSSK-UWOC systems considering pointing errors and channel estimation errors.

In this paper, we present the bit error rate (BER) performance of the underwater wireless optical communication (UWOC) systems using the optical space shift keying (OSSK) on the gamma-gamma turbulent fading channel, which also considers pointing errors and channel estimation errors. Firstly, we develop the new expressions for the probability density function (PDF) based on the Gamma-Gamma distribution with error factors. Subsequently, we analyze the statistical characteristic of the difference in attenuation coefficients between two channels in the OSSK system, by which we provide analytical results for evaluating the average BER performance. The results show that the effective improvement of spectral efficiency (SE) and BER performance is achieved by rationally allocating the number of lasers and detectors in the system. The OSSK-UWOC system performs better when a narrow beam waist is used. Furthermore, the presence of channel estimation error brings the BER performance advantage to the system, and the system with a high channel estimation error (ρ = 0.7) shows a 4 dB improvement in signal-to-noise ratio (SNR) gain compared to the system with a low channel estimation error (ρ = 0.95). The findings in this paper can be used for the UWOC system design.

Clustered jamming in U-V2X communications with 3D antenna beam-width fluctuations

Jamming is the disruption of wireless communication signals, rendering them unreadable or degraded, typically caused by jamming devices. Clustered jamming in vehicular communications is a highly sophisticated attack technique characterized by the coordinated deployment of multiple jammers with the strategic intent to deliberately disrupt and incapacitate communication links, thereby presenting a formidable challenge to the reliability and security of vehicular networks. It is critical to address the intricate challenges imposed by clustered jamming in the context of vehicle-to-everything (V2X) communications augmented by unmanned aerial vehicles (UAVs), given their critical role in facilitating essential vehicle-to-vehicle and vehicle-to-UAV communication links. In this paper, we examine UAV-V2X (U-V2X) communications within the context of clustered jamming and the variations in the 3D beam-width of antennas. Also, mitigation techniques for clustered jamming in V2X communications are addressed. We consider the distribution of UAVs is governed by the Poisson point process, the distribution of vehicular-nodes (VNs) is governed by the Poisson line process, and the distribution of jammers is governed by the Matern Cluster Process. The analytical equations for the association probability and the success probability (SP) of a typical VN with the UAV and near-by VN, along with the presence of jammers and the variations of antenna beam-width are provided. Furthermore, we investigate the SP and spectral efficiency performance of the U-V2X network under different network configurations of UAVs, VNs, roads, jamming clusters, and transmit power of jamming devices. Our findings reveal that clustered jammers influence U-V2X network’s performance, further compounded by UAV beam-width fluctuations. Moreover, in low-density areas, UAVs demonstrate superior reliability for connectivity compared to VNs, despite clustered jamming. Also, lower UAV antenna fluctuations enhance UAVs’ dependability in U-V2X networks amidst clustered jamming. Specifically, for a given setup with τ= -5 dB, U-V2X link’s SP with jamming drops to one-quarter due to 2-degree beam-width fluctuations. Consequently, it is imperative to design and implement anti-jamming strategies, particularly as the number of jamming clusters and variations of antenna beam-width increase.

A hybrid digital self-interference cancellation method with attention-based TCN-GRU for full-duplex systems

Full-duplex (FD) technology is expected to be widely used in future communication systems due to its excellent performance in spectral efficiency. Self-interference (SI) is the main problem affecting the transmission quality of the FD systems, thus it is crucial to research the SI cancellation (SIC) techniques. In this paper, we present an innovative hybrid digital SIC method named sliding time window, temporal convolutional network (TCN), gated recurrent unit (GRU) and attention mechanism (AM)-based deep learning network (STGAN). The proposed method can extract complete features and time information from the input sequence, and accurately estimate the SI in FD systems. We first present a preprocessing module that utilizes sliding time windows to handle the original signal sequence. Then, we utilize the TCN and GRU to extract the short-term features and long-term dependencies within the sequence. Finally, the AM is adopted to explore the significance of the information conveyed by the sequence at different time steps. The effectiveness of the STGAN is verified in multiple experimental scenarios. Simulation results indicate that the interference cancellation ratio (ICR) of the STGAN is significantly higher than existing methods.

Performance of Spectral and Energy Efficiency in Cell-free Massive MIMO-aided URLLC System with Short Blocklength Communications

Performance of Spectral and Energy Efficiency in Cell-free Massive MIMO-aided URLLC System with Short Blocklength Communications

Numerical Evaluation of the MU-MIMO Beamforming Performance with Channel Estimation

This paper presents the numerical evaluation of the ZF beamforming algorithm and DFT precoding using the LS channel estimation in the multiuser multiantenna (MU-MIMO) downlink system. The sum rate performance depending on a number of users are presented. The arising inter user correlation degrades the sum rate (spectral efficiency) performance of multiuser MIMO system especially in scenarios where the number of users is larger than the number of antennas at the BS. For MIMO channel simulation the QuaDRiGa channel model reflecting the real propagation conditions is used. The obtained performance of MU-MIMO ZF precoding in spatially correlated channel are compared with DFT precoding based on the empirical cumulative density function of the sum rate of multiple users. Numerical results show that the ZF precoder outperforms the DFT precoder in channel with less spatial correlation. The DFT precoder in spatially more correlated channel has advantage over ZF precoder.

MCIK-NOMA: A novel index modulation based approach to improve spectral efficiency and error performance over generalized [formula omitted] and [formula omitted] fading channels with imperfect CSI

Non-orthogonal multiple access (NOMA) scheme has emerged as a promising multiple access technology in future wireless communications as it provides massive connectivity than the existing orthogonal multiple access (OMA) methods. Index modulation (IM) permits additional information to be conveyed through the indices of active sub carriers along with the M-ary data symbols thereby increasing the spectral efficiency through selection diversity gain. The union of NOMA and IM called a novel multi-carrier index keying based non-orthogonal multiple access (MCIK-NOMA) system is proposed in this paper and its performance is analyzed over generalized α−μ and k−μ fading environments. The impact of various fading factors such as non-linearity (α), ratio of powers (k) and number of multi-path clusters (μ) on the system performance is investigated and discussed through simulations. Furthermore, the error performance of Rayleigh, Weibull, Gamma, exponential and Nakagami-m fading environment is investigated by changing the fading parameters of generalized fading channels. The impact of perfect, fixed and variable channel state information (CSI) conditions on the proposed system is explored. Simulation results verify the theoretical expressions. The results demonstrate that the proposed MCIK-NOMA system outperforms the existing NOMA and OMA systems in terms of bit error rate (BER), spectral efficiency, and energy efficiency.

Discrete Hartley transform-based dual-mode index modulation OFDM for visible light communications

Using discrete Hartley transform (DHT) instead of discrete Fourier transform (DFT) in the optical index modulation (IM) aided orthogonal frequency division multiplexing (OFDM) systems for visible light communications (VLC) results in improvement in terms of the spectral efficiency, energy efficiency, peak-to-average power ratio, and bit error rate (BER) performance with a lower computational complexity, benefiting from the removal of the Hermitian symmetry. In this paper, by employing dual-mode (DM) index modulation in the DHT-based OFDM systems, more spectral efficient schemes for VLC are proposed. A reduced-complexity maximum likelihood (ML) detector and a simple log-likelihood ratio (LLR) detector for the DM-OFDM-IM systems are presented, achieving a better performance with a lower complexity over the traditional detectors. The spectral efficiency and the average BER are analyzed. The minimum distance between different transmitted subblock vectors is calculated for characterizing the performance. The simulation results demonstrate that the DHT-based DM-OFDM-IM systems achieve significant performance gains over the DHT-based OFDM-IM counterparts and perform better than the DFT-based counterparts in terms of the spectral efficiency and BER performance.

Analysis and Compensation of Tx and Rx IQ Imbalances in Uplink IM-OFDMA Systems

Index modulation-based orthogonal division multiple access (IM-OFDMA) has recently been proposed as a potential technique for future wireless communication systems due to its superior spectral efficiency and error performance over conventional multiple access schemes. However, its performance is still under investigation by researchers in light of a variety of scenarios and assumptions. Following this direction, in this paper, the individual and joint effects of the transmitter (Tx) and receiver (Rx) in-phase and quadrature imbalances (IQI) on the bit-error-rate (BER) performance of the uplink IM-OFDMA scheme are investigated by considering whether each user's RF front-end is identical or not. Moreover, to reduce the detrimental effect of IQI, a preamble-based estimation and compensation method is proposed for IM-OFDMA. Closed-form expressions for the average BER of IM-OFDMA are obtained by considering the physical effect of the Tx and Rx IQI. Also, using Monte Carlo simulations, the derived expressions are verified under different system configurations. Analytical and simulation results reveal that Tx and Rx IQI cause an error floor in the BER performance of IM-OFDMA schemes. However, the proposed estimation and compensation method not only reduces the impact of IQI but also leads to a better BER performance compared to the case of no IQI, which mainly refers to the frequency diversity caused by the IQI.

Spectral Efficiency Improvement Using Bi-Deep Learning Model for IRS-Assisted MU-MISO Communication System.

The intelligent reflecting surface (IRS) is a two-dimensional (2D) surface with a programmable structure and is composed of many arrays. The arrays are used to supervise electromagnetic wave propagation by altering the electric and magnetic properties of the 2D surface. IRS can influentially convert wireless channels to very effectively enhance spectral efficiency (SE) and communication performance in wireless systems. However, proper channel information is necessary to realize the IRS anticipated gains. The conventional technique has been taken into consideration in recent attempts to fix this issue, which is straightforward but not ideal. A deep learning model which is called the long short-term memory (Bi-LSTM) model can tackle this issue due to its good learning capability and it plays a vital role in enhancing SE. Bi-LSTM can collect data from both forward and backward directions simultaneously to provide improved prediction accuracy. Because of the tremendous benefits of the Bi-LSTM model, in this paper, an IRS-assisted Bi-LSTM model-based multi-user multiple input single output downlink system is proposed for SE improvement. A Wiener filter is used to determine the optimal phase of each IRS element. In the simulation results, the proposed system is compared with other DL models and methods for the SE performance evaluation. The model exhibits satisfactory SE performance with a different signal-to-noise ratio compared to other schemes in the online phase.

A New NOMA-Based Two-Way Relaying Scheme

Two-Way Relaying (TWR) has been widely investigated in the literature as an efficient relaying scheme for dual-hop cooperative transmissions. In TWR, two nodes exchange data through an intermediate relay, where both nodes simultaneously send signals towards the relay in the first time slot. The relay, in turn, combines both received signals into one signal and sends it back to both nodes on the second time slot. In this paper, the spectral efficiency is further enhanced in TWR scheme by adopting Non-Orthogonal Multiple Access (NOMA) technique. Specifically, the transmitted signals from the nodes in the first time slot are composed based on NOMA transmission and intended to multiple intermediate relay-nodes. Consequently, each relay will extract its own symbols, combine them and send them in the second time slot. The improvement of the spectral efficiency in our system, as compared to the Conventional TWR, is linearly proportional to the number of relay-nodes that can be installed. The performance of the proposed scheme is mathematically analyzed in terms of the spectral efficiency and error performance, shown significant gain when compared to the conventional TWR scheme.

A Deep Reinforcement Learning Approach to Two-Timescale Transmission for RIS-Aided Multiuser MISO systems

Reconfigurable intelligent surface (RIS) has drawn great attention recently as a promising technology for future wireless networks. In this letter, considering the two-timescale transmission protocol, we investigate the joint design of the transmit beamforming at the base station (BS) with instantaneous channel state information (CSI) and the RIS phase shifts with statistical CSI. Due to the large number of RIS elements, this design issue usually suffers from high computational complexity. To resolve the non-convexity issue with low complexity, we propose a novel deep reinforcement learning (DRL) framework, which contains two agents applying proximal policy optimization (PPO) based algorithm. Experiment results demonstrate that the proposed algorithm has comparable spectral efficiency performance to the state-of-the-art methods with substantially reduced computational delay.

Analysis of throughput and error rate of 16-QAM, 64-QAM, and 256-QAM O-NOMA waveforms

Abstract This study presents a comprehensive analysis of the throughput performance, spectrum efficiency, and block error rate (BLER) of optical non-orthogonal multiple access (O-NOMA) waveforms using 16-quadrature amplitude modulation (QAM), 64-QAM, and 256-QAM modulation schemes. The aim is to assess the trade-offs between data rate, spectral efficiency, and error performance in O-NOMA systems. The analysis reveals that higher-order modulations, such as 64-QAM and 256-QAM, offer higher data rates and improved spectrum efficiency compared to 16-QAM. Furthermore, the study investigates the spectrum performance of the O-NOMA waveforms. The results indicate that higher-order modulations may utilise the spectrum more efficiently, maximising the data throughput within the available bandwidth. Moreover, the BLER analysis provides insights into the error performance of the O-NOMA waveforms. It quantifies the probability of errors occurring in a block of transmitted data and evaluates the system’s reliability. The analysis reveals that 256-QAM O-NOMA achieves lower BLER and high throughput in uplink and downlink as compared with the 16 and 64-QAM O-NOMA frameworks.

User grouping and resource management in efficient NOMA‐OMA transmission scheme for infotainment message dissemination in VANETs

AbstractThe data distribution for infotainment services at vehicular ad‐hoc networks (VANETs) has become a research hotspot in recent years. Non‐orthogonal multiple access (NOMA) is accepted as an enabling technology for 5G and beyond due to its improved spectral efficiency. In this work, we consider a VANET communication scenario where users have common data demands such as high‐density maps, local entertainment/shopping options or other popular media content. For such a scenario, we propose an efficient clustering scheme together with a hybrid NOMA‐OMA scheme for improved spectral and power efficiency. For this setup, we also develop an optimal bandwidth allocation strategy to improve the power efficiency further. We formulate a one dimensional nonlinear power minimization problem such that the bandwidth allocation for the system can be optimized. The complexity and optimality analysis of optimization algorithms used for power minimization are performed. The improved performance of the proposed scheme in terms of power efficiency, spectral efficiency and latency performance is showcased in comparison to conventional NOMA and OMA approaches.

Non-linear companding scheme for PAPR reduction in OFDM systems

Abstract High peak-to-average power ratio (PAPR) is one of the critical drawbacks of orthogonal frequency division multiplexing (OFDM). Companding is an efficient scheme to limit the PAPR. Companding operation distorts the shape of OFDM signal, therefore reducing the PAPR with slight degradation in BER performance of OFDM signal. This paper proposes a non-linear companding transform, which transforms the ‘αth’ power of OFDM signal magnitude into a trigonal distribution. In the proposed scheme, design parameter ‘α’ is used to realize a better trade-off between PAPR and BER performance. Proposed scheme provides improved spectral efficiency and BER performance with a reduction in PAPR. We have also calculated the optimal value of design parameter ‘α’ to achieve the optimal BER.

Performance Evaluation of Full Array, Sub-Array and Overlapped-Sub-Array Hybrid Beamforming Architectures for Massive Mimo Systems

The technological advancement in wireless communication, promises high data rate for end users. This has led to the possibility of smart cities, inter connected vehicles, and virtual reality applications. One of the recent technologies in wireless communication is massive MIMO where large number of antennas are deployed at the transmitter or receiver. This is possible due to the use of mmWave in wireless communication. With massive MIMO, beamforming technique can be employed in the communication system. Beamforming is the ability of communication system to direct power to the intended users and to cancel power at non-intended users and thus significantly improving communication system performance. Digital beamforming was initially used in MIMO systems. However, for massive MIMO systems it leads to high power consumption due to large number of dedicated radio frequency chain in each antenna. To address this challenge, hybrid beamforming techniques were introduced. There are three architectures for hybrid beamforming: Fully array architecture (FAA), overlapped sub-array architecture (OSA) and sub-array architecture (SAA). This paper has analysed three performance parameters of the mentioned hybrid beamforming architectures. The simulation results show that, FAA architecture has high performance in outage probability and spectral efficiency. However, its energy efficiency is lower compared to OSA and SAA. Specifically, SAA has the highest energy efficiency in comparison to FAA and OSA. It can also be observed that, with only 25% increased number of elements in OSA, the energy efficiency can be slightly lower compared to SAA, while achieving appreciable spectral efficiency performance with respect to FAA. Additionally, this work has derived an outage probability expression, which has not been covered in most of the studies. This study gives an insight of selecting the best architecture based on the performance requirement.