Anshul Jaiswal

Transceiver hardware impairments (THI) significantly affect the performance of communication systems, necessitating their analysis for realistic performance evaluation and robust system design. Furthermore, integrating channel coding is imperative for enhancing error resilience under diverse fading environments. However, the joint impact of THI and channel coding on error performance in downlink rate-splitting multiple access (RSMA) systems remains unexplored. This paper investigates the impact of THI on the symbol error rate (SER) and explores the effectiveness of block codes in mitigating these impacts in RSMA systems. More precisely, a detailed analysis of the constellation-based SER is conducted for a multi-user RSMA setup, considering both transmitter and receiver hardware impairments with perfect and imperfect detection events of the common stream. Moreover, closed-form expressions for the coded average SER (ASER) are derived under both zero and non-zero THI for multi-user RSMA systems over Nakagami-m fading with varying shape parameters in single-input single-output (SISO) scenarios. This study also presents asymptotic ASER expressions with diversity order analysis under both zero and non-zero THI. The accuracy of these derived ASER expressions is verified through Monte Carlo simulations. Furthermore, the SISO analytical framework is extended to the multiple-input multiple-output scenario, with comparative evaluations against the SISO scenario to demonstrate the practical applicability of the proposed coded RSMA system.

This paper presents two asymmetric one-way full-duplex (FD) cooperative communication systems that incorporate advanced multiple access schemes. Both systems are formed using a mixed free-space optical (FSO)/millimeter wave (mmWave)-radio-frequency (RF) configuration, where the first hop employs a hybrid FSO/mmWave and the second hop utilizes RF links to support mobile connectivity for multiple users. The first system employs rate-splitting multiple access (RSMA) to minimize successive interference cancellation (SIC) operations, termed the FD asymmetric cooperative-RSMA (C-RSMA) system. In contrast, the second system adopts quadrature RSMA (QRSMA) to eliminate SIC, termed the FD asymmetric C-QRSMA system. For comprehensive analysis, the FSO, mmWave, and RF links are modelled using Málaga-M distribution with pointing error, Nakagami-m, and κ − μ fading, respectively. Unlike existing works that focus on sum rate or signal-to-interference-plus-noise ratio, this study derives outage probability, coverage probability, average sum rate, and energy efficiency. These metrics, derived in multi-user environments with imperfect SIC and signal space diversity, are validated through Monte Carlo simulations. Finally, the proposed systems are compared with state-of-the-art schemes, revealing that the systems not only enhance spectral efficiency but also significantly reduce system complexity.

Rate-splitting multiple access (RSMA) has emerged as a promising solution for managing multi-user interference in wireless communication systems. However, a significant challenge persists in mitigating high interference during private stream detection in conventional RSMA and quadrature-RSMA (Q-RSMA), particularly in multi-user scenarios. To address this issue, this work proposes a rate-splitting technique called private stream interference-management RSMA (P-RSMA), which leverages coordinate interleaving among combinations of private streams to reduce the number of interfering symbols. To analyze and compare P-RSMA with RSMA and Q-RSMA, a constellation-based analytical framework is presented to derive symbol error rate (SER) expressions for multi-user P-RSMA, RSMA, and Q-RSMA schemes under the single-input single-output (SISO) setting, considering both perfect and imperfect detection events of the common stream. A detailed power-bound analysis is also performed to resolve the constellation ambiguity problem in all considered schemes for arbitrary modulation orders of the common and private streams, emphasizing the strategic importance of adapting modulation orders for different symbols. Closed-form uncoded and coded average SER (ASER) expressions are then derived under Rayleigh fading channels with channel ordering. This work further incorporates a diversity order evaluation for the constellation-based framework to characterize asymptotic performance and benchmark against SINR- based methods. Additionally, the analytical framework is extended to the multiple-input multiple-output (MIMO) setting, and results are compared with those from the SISO scenario to demonstrate the performance gains and practical relevance of the proposed P-RSMA scheme. Numerical results demonstrate the superiority of P-RSMA over RSMA and Q-RSMA, which are corroborated through Monte Carlo simulations.

This paper introduces a multi-user mixed free-space optical (FSO)/radio-frequency (RF) system for a non-terrestrial network, where satellite collaborates via a high-altitude platform system (HAPS) to enhance user connectivity. By employing a one-way full-duplex decode-and-forward HAPS (OW-FDH) as a relay, the proposed system enhances spectral efficiency while significantly reducing the successive interference cancellation (SIC) through the use of quadrature non-orthogonal multiple access (NOMA). For comprehensive analysis, the system is investigated considering the Málaga$-\mathcal {M}$ channel with a pointing error for FSO link and Nakagami-$m$ for RF links. Considering the effects of hardware impairment and imperfect SIC, the closed-form unified expressions of outage probability (OP) and ergodic capacity (EC) are derived and validated via Monte Carlo simulations. To gain deeper insights, asymptotic analyses of OP and EC are performed to reveal key trends at high power, along with evaluations of SIC requirements. As special cases, performance metrics are determined for Q-NOMA with half-duplex HAPS and standard NOMA with both full-dupex and half-duplex HAPS. The proposed system is further examined under a hybrid FSO/RF link, an amplify-and-forward HAPS relay, and practical conditions such as imperfect channel state information and non-zero boresight pointing errors.

This paper explores the limitations of a conventional reconfigurable intelligent surface-assisted spatial modulation (RIS-SM) system by analyzing the signal-spatial constellation diagram. These limitations include closely packed signalspatial points and a lack of flexibility in adjusting their positions, negatively affecting system performance. To address these challenges, this work proposes a unified RIS-SM (U-RIS-SM) system that utilizes optimal RIS reflector phases and a modified modulation scheme with a tuning parameter. The proposed U-RIS- SM system facilitates the constellation redesigning of signalspatial points by adjusting the tuning parameter. Additionally, the optimal tuning parameter value is determined to achieve the best possible performance of U-RIS-SM. Closed-form expressions for the symbol error rate (SER), average SER (ASER), and average mutual information (MI) of the proposed U-RIS-SM system under the Nakagami-m fading channel are derived and validated through Monte-Carlo simulations. Moreover, since the proposed U-RIS-SM system can be transformed into existing RIS-SM and RIS-assisted space shift keying (RIS-SSK) systems by varying the tuning parameters and RIS reflector phases, the performance metrics for existing RIS-SM/SSK systems are derived from expressions for U-RIS-SM. The U-RIS-SM system is compared with existing RIS-SSK and RIS-SM systems across various parameters, demonstrating its superior performance. Furthermore, to assess its effectiveness under practical conditions, its performance is examined using a low-complexity two-stage maximum likelihood detector, as well as under RIS phase errors and discrete RIS phase shifts.

In recent years, several emerging multiple-access (MA) schemes have been proposed, each offering distinct advantages. Non-orthogonal MA (NOMA) and quadrature NOMA (Q-NOMA) are widely recognized for their ability to reduce inter-user interference through successive interference cancellation (SIC). Rate-splitting MA (RSMA) enhances interference management by partially decoding interference and treating the remaining interference as noise. Quadrature RSMA (Q-RSMA) builds on RSMA by leveraging quadrature dimensions to enable interference-free detection of the common stream, achieving an ever-increasing average sum-rate (ASR) as the signal-to-noise ratio improves, even under imperfect SIC conditions. Building upon these strengths, this paper proposes a novel MA scheme that integrates the quadrature separation approach of Q-RSMA, the stream-splitting method of RSMA, and the SIC-based interference reduction technique of NOMA/Q-NOMA, and therefore termed the quadrature stream-splitting integrated SIC-driven MA (Q-SSMA). To demonstrate the enhanced performance of Q-SSMA, closed-form expressions for outage probability (OP) and ASR are derived and corroborated through simulations. Numerical results show that Q-SSMA outperforms RSMA, Q-RSMA, NOMA, and Q-NOMA in both OP and ASR, while offering computational complexity comparable to NOMA.

In this work, a novel signal-space-diversity-based full-duplex (FD) cooperative non-orthogonal multiple access (SFD-CNOMA) system is introduced for a multi-user scenario. In the proposed system, cell-centered and cell-edge users’ information will be multiplexed in the superimposed signal’s inphase and quadrature components. This reduces successive-interference-cancellation (SIC) operations, detection delay, and complexity compared to conventional FD cooperative NOMA (CFD-CNOMA). An analytical framework is introduced to assess the average sum rate, outage probability, and diversity order for both perfect and imperfect SICs, considering order statistics. Comparative analysis demonstrates that SFD-CNOMA outperforms CFD-CNOMA under both perfect and imperfect SICs.

Multi-carrier power-domain non-orthogonal multiple access (MC-PD-NOMA) has been considered a key technology for next-generation wireless networks. In MC-PD-NOMA, the available channel bandwidth is divided into several sub-carriers in order to serve the multiple users in each sub-carrier. In this work, to reduce the number of successive interference cancellation (SIC) operations, detection delay, SIC complexity and to enhance the SIC stability of the MC-PD-NOMA, a system, namely, MC-quadrature-NOMA (MC-Q-NOMA), is proposed. Furthermore, the proposed MC-Q-NOMA follows the essential upconversion architecture to provide orthogonality in the pass-band. Moreover, a novel analytical framework is introduced to evaluate analytical expressions of average sum-rate (ASR), outage probability (OP), and diversity order for the proposed system under the generalized α - μ channel for perfect and imperfect SICs. In addition, the proposed framework is utilized to determine the analytical expression of ASR, OP, and diversity order for MC-PD-NOMA. Comparative analysis indicates that under imperfect SIC, MC-Q-NOMA outperforms the MC-PD-NOMA due to the lesser number of SICs. However, under perfect SIC, MC-Q-NOMA demonstrates comparable performance with the MC-PD-NOMA. Furthermore, the analytical expression of the average bit-error-rate is evaluated for the MC-Q-NOMA. Numerical results demonstrate that the error performance of MC-Q-NOMA is superior to MC-PD-NOMA for all signal-to-noise ratio values.