Impact Of Residual Self-interference Research Articles

Full/half-duplex unmanned aerial vehicles assisted wireless systems: Performance analysis and optimization

In this paper, we explore the utilization of both full-duplex (FD) and half-duplex (HD) transmission modes on unmanned aerial vehicles (UAVs) to enhance wireless system performance. We consider two practical scenarios: one without a direct transmitter-user link and the other with such a link. For both cases, we derive mathematical expressions of outage probabilities (OPs) and throughputs of FD-UAV and HD-UAV systems, employing a realistic channel model aligned with the fifth and beyond generations (5G-B5G) standards. In cases where imperfect self-interference cancellation (SIC) occurs in FD-UAV systems, we introduce an optimal power allocation approach to enhance system performance. Numerical results underscore the benefits of cooperative communications, particularly when combining the direct link with the UAV link at the user, leading to an overall enhancement in system performance. Furthermore, we conduct a comprehensive analysis of various system parameters, including predefined rates, residual self-interference (RSI) levels, high carrier frequencies of Wi-Fi networks, and high altitudes of UAVs. The impact of RSI is particularly notable, and the proposed optimal power allocation approach significantly improves system performance in such cases. Specifically, the introduced scheme helps avoid error floors in regions of high transmit power, enabling throughputs to reach desired targets in FD-UAV systems. Crucially, the optimal power value is considerably lower than the traditional value often used without optimal power allocation, extending the operational duration of FD-UAV. Finally, to validate the derived mathematical expressions and affirm the effectiveness of the proposed approaches, we conduct Monte-Carlo simulations.

Adaptive Channel Detection for Full-Duplex IAB Systems on Unlicensed Bands

The integration of integrated access and backhaul (IAB) and full-duplex communications on unlicensed bands can improve the spectrum efficiency and mitigate the spectrum resource shortage. To guarantee fair coexistence on unlicensed spectrum, the listen-before-talk mechanism needs to be executed at the IAB nodes, where the clear channel assessment (CCA) is applied before transmission. However, the residual self-interference (RSI) brought by the full-duplex communication may degrade the CCA detection performance tremendously. Therefore, in this paper we propose an adaptive channel detection scheme for the full-duplex IAB network to minimize the impact of RSI on the CCA detection, which can enhance the spectrum efficiency. In particular, the closed-form expressions of false alarm probability and detection probability are derived. Accordingly, the energy detection (ED) threshold applied in CCA is adjusted adaptively to improve the system throughput. Then, a novel timing sequence with respect to the self-interference cancellation and CCA detection is proposed. The corresponding optimal initial threshold is also derived to realize the adaptive ED threshold. Furthermore, an enhanced request to send/clear to send mechanism is proposed to solve the hidden terminal problem. Simulation results demonstrate that the proposed schemes can effectively reduce the impact of RSI on the CCA detection accuracy and significantly improve the system throughput.

Performance of SWIPT-Enabled FD TWR Network With Hardware Impairments and Imperfect CSI

Cooperative communication with energy harvesting capability increases network coverage and provides a green and sustainable solution for future wireless technologies. In this article, we analyze the performance of a two-way relay network, where bidirectional information exchange between two nodes takes place via simultaneous wireless information and power transfer-enabled relay node, operating in full-duplex (FD) mode over generalized Nakagami- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$m$</tex-math></inline-formula> fading channels. Different nonlinear power amplifier (NLPA) models, such as solid-state power amplifier, traveling wave tube amplifier, and soft envelope limiter, are considered at the relay node. The effect of practical constraints, such as imperfect channel state information (CSI) and transceiver hardware impairments (HIs), is considered. Further, we consider the impact of residual self-interference (RSI) due to imperfect successive interference cancellation in the FD mode. For performance analysis, the closed-form expressions of outage probability (OP), asymptotic OP, system throughput, energy efficiency, ergodic capacity, and asymptotic ergodic capacity are derived. The diversity order of the considered network is evaluated. Further, the impact of imperfect CSI, NLPA, HIs, RSI, and other parameters are highlighted on the system performance. The performance of FD and half-duplex mode is also compared. Monte Carlo simulations confirm the accuracy of the derived closed-form expressions.

Multicarrier-Division Duplex for Solving the Channel Aging Problem in Massive MIMO Systems

The separation of training and data transmission as well as the frequent uplink/downlink (UL/DL) switching make time-division duplex (TDD)-based massive multiple-input multiple-output (mMIMO) systems less competent in fast time-varying scenarios due to the resultant severe channel aging. To this end, a multicarrier-division duplex (MDD) mMIMO scheme associated with two types of well-designed frame structures are introduced for combating channel aging when communicating over fast time-varying channels. For comparison, the corresponding TDD frame structures related to the 3 rd Generation Partnership Project (3GPP) standards and their variant forms are presented. The MDD-specific general Wiener predictor and decision-directed Wiener predictor are introduced to predict the channel state information, respectively, in the time domain based on UL pilots and in the frequency domain based on the detected UL data, considering the impact of residual self-interference (SI). Moreover, by applying the zero-forcing precoding and maximum ratio combining, the closed-form approximations for the lower bounded rate achieved by TDD and MDD frame structures over time-varying channels are derived. Our main conclusion from this study is that the MDD, endowed with the capability of full-duplex but less demand on SI cancellation than in-band full-duplex (IBFD), outperforms both the conventional TDD and IBFD in combating channel aging.

Optimal power allocation for non‐orthogonal multiple access enabled full‐duplex underlay cognitive relay networks under partial relay selection

AbstractThis article considers non‐orthogonal multiple access (NOMA) enabled full‐duplex (FD) underlay cognitive relay networks (ie, NOMA‐FDCRNs) with partial relay selection scheme. The secondary network, where NOMA is used, consists of a secondary base station (SBS) sending messages to two secondary users (SUs), that is, a near SU (SU1) and a far SU (SU2), by utilizing a dedicated relay selected from a set of FD decode‐and‐forward nodes. We obtain analytical expressions for the outage probabilities (OPs) of the SUs and then deduce the asymptotic OP expressions as well. Further, expressions are obtained for the optimal power allocation (OPA) coefficients at the SBS and at the relay that separately maximizes the throughput of the secondary network in NOMA‐FDCRN. Furthermore, the jointly optimal power allocation (JOPA) coefficients that maximize the throughput are also determined. The analyses consider (i) imperfect successive interference cancelation conditions, (ii) the tolerable interference limit of the primary receiver, (iii) the secondary nodes' maximum transmit power values, (iv) interference generated by the primary transmitter, and (v) the residual self‐interference (RSI) at the FD relay. It is shown that the proposed OPA coefficients at the SBS and the JOPA can mitigate the impact of RSI and significantly improve the OP and throughput performance. The numerical results show that the proposed JOPA approach provides 32% and 106% improvement of throughput compared to random power allocation (RPA) and equal power allocation (EPA) strategies, respectively. The OP of SU1 and SU2 reduce by 68% and 73%, respectively, under the proposed JOPA compared to RPA, while compared to EPA, the OP of SU1 and SU2 reduce by 96% and 97%, respectively.

Transmit antenna selection – An effective method for improving the performance of spatial modulation full-duplex relay networks with wireless energy harvesting

Full-duplex (FD) communications have been proved as an inevitable techniques to obtain high quality of service in modern wireless communications. In this paper, an integrated communication scheme using spatial modulation (SM) with transmit antenna selection (TAS) and wireless energy harvesting (EH) is proposed to enhance the overall spectral efficiency and diversity order of full-duplex relaying (FDR) networks as well as to overcome the battery shortage problem at the intermediate relay nodes. The performance of this EH-SM-FDR system is investigated thoroughly by deriving the exact-form expressions of the outage probability (OP) and network throughput. The impact of residual self-interference (RSI) at FD relay and the EH time-switching ratio is also analyzed, from which the optimal value of EH time-switching ratio to minimize the OP and maximize the network throughput of the system is obtained. It is recommended from our analysis that more receive antennas should be equipped at the relay than at the destination to achieve better OP performance. This analysis also recommends best suitable data transmission rate depending on the source transmit power to reach lowest OP and highest throughput. Finally, Monte Carlo simulations are conducted to validate all analytical results.

On Performance of Two-Way Full-Duplex Communication System With Reconfigurable Intelligent Surface

In this paper, we apply a reconfigurable intelligent surface (RIS) to a two-way (TW) full-duplex (FD) wireless communication system, where a RIS has N reflecting elements and operates as a relay station forwarding signals between two FD terminals. To demonstrate the advantages of RIS compared with traditional relay, we also present the system and signal models of the TW-FD amplify-and-forward relay (AFR) system. We mathematically analyze the performance of the TW-FD-RIS system by deriving the exact closed-form expressions of the average outage probability (AOP) and the average symbol error rate (ASER) in the case N=1, and approximate expressions of the AOP and the ASER in the case N ≥ 2. Besides, we provide the exact closed-form expression of the AOP and approximate expression of the ASER of the TW-FD-AFR system. Monte-Carlo simulations validate all derived mathematical expressions. Numerical results demonstrate that using the RIS greatly improves the TW-FD communication system's performance compared with using amplify-and-forward (AF) relay. Specifically, even the RIS with one element ( N=1), the AOP and ASER of the TW-FD-RIS system are still lower than those of the TW-FD-AFR system in the low signal-to-noise ratio (SNR) regime. However, in the high SNR regime, the AOP and ASER of the TW-FD-RIS system are higher. In the case N ≥ 2, the AOP and ASER of the TW-FD-RIS system are significantly reduced. On the other hand, the impact of residual self-interference (SI) due to FD transmission mode on the performance of TW-FD-RIS and TW-FD-AFR systems is remarkable, making the AOP and ASER of these two systems reach the error floor in the high SNR regime. Fortunately, the usage of RIS with N ≥ 2 can greatly reduce this impact and avoid the error floor for the TW-FD-RIS system.

Power Adaptation for Enhancing Spectral Efficiency and Energy Efficiency in Multi-Hop Full Duplex Cognitive Wireless Relay Networks

This work investigates the energy efficiency (EE) and the spectral efficiency (SE) performance of multi-hop full duplex cognitive relay networks (MH-FDCRNs) operating in the spectrum sharing mode, under the influence of interference from the primary source. We formulate three distinct optimization problems for finding the optimal power allocation (OPA) for the secondary nodes in MH-FDCRN: (i) EE optimization with minimum SE requirement; (ii) SE optimization with minimum EE requirement; and (iii) EE-SE trade-off optimization. The impact of residual self-interference (RSI) arising due to full duplex operation at the relay nodes and the inter relay interference (IRI) arising due to frequency re-use are considered. For the EE/SE optimization problems, we transform the original non-convex optimization problems to their convex forms by expressing the numerator of the objective function as the difference of concave functions, and by using parametric transformation. For the EE-SE trade-off optimization problem, we first transform the original multi objective optimization problem into a single objective form; and then into its convex form by introducing an auxiliary variable. Computationally efficient algorithms are proposed to solve the considered problems. The convergence properties of the proposed algorithms are established through mathematical analysis as well as through computer simulation studies. We prove that the points of convergence of the proposed iterative algorithms are the Karush-Kuhn-Tucker (KKT) points of the initial non-convex problems. With the help of detailed numerical results, the best trade-off among EE and SE can be achieved by proper selection of priority factor, compared to the individual optimization approaches.

Full-duplex amplify-and-forward relay system with direct link: Performance analysis and optimization

In this paper, we analyze the performance of a full-duplex (FD) amplify-and-forward (AF) relay system under various cases of relaying gains and channel state information conditions. Specifically, we consider the case that the FD relay node uses either fixed or variable gain for relaying under perfect and imperfect channel state information (CSI). For the case of imperfect CSI (I-CSI), we derive the exact expressions for the outage probability (OP), throughput, and symbol error probability (SEP) of the considered system. For the case of perfect CSI (P-CSI), we can provide approximate expressions of OP, throughput, SEP, and ergodic capacity. We also propose an effective power allocation scheme for the FD relay node to reduce the effect of residual self-interference (RSI). Both analytical and simulation results show a significant impact of RSI on the system performance. In particular, when RSI is small the variable-gain relaying can provide better performance than the fixed gain. However, when RSI becomes large these two relaying schemes have similar performance. In this situation, using the proposed optimal power allocation scheme can improve the system performance, especially for the case with weak direct link.

Performance Analysis of Full-Duplex Amplify-and-Forward Relay System with Hardware Impairments and Imperfect Self-Interference Cancellation

In this paper, we analyze the performance of a full-duplex (FD) amplify-and-forward (AF) relay system with imperfect hardware. Besides the aggregate hardware impairments of the imperfect transceiver, we also consider the impact of residual self-interference (RSI) due to imperfect cancellation at the FD relay node. An analytical framework for analyzing the system performance including exact outage probability (OP), asymptotic OP, and approximate symbol error probability (SEP) is developed. In order to tackle these impacts, we propose an optimal power allocation scheme which can improve the outage performance of the FD relay node, especially at the high signal-to-noise ratio (SNR) regime. Numerical results are presented for various evaluation scenarios and verified using the Monte Carlo simulations.

Improper Gaussian Signaling for Hardware Impaired Multihop Full-Duplex Relaying Systems

In this paper, we analyze the performance degradation of a multi-hop decode-and-forward full-duplex relaying system caused by the residual self-interference (RSI) and hardware distortions (HWD) imposed by the FDR operation and imperfect hardware, respectively. In addition, we study the benefits of employing improper Gaussian signaling (IGS) in the MH-FDR system. Different from the traditional symmetric signaling scheme, i.e., proper Gaussian signaling (PGS), IGS has non-zero pseudo-variance that can limit the impact of RSI and HWD in the MH-FDR system. To evaluate the system performance gain using IGS, first we express the end-to-end achievable rate of the MH system as the minimum rate supported by all participating links. Then, we optimize the pseudo-variance of all participating transmitters, including source and relays to compensate the interference impact and improve the end-to-end achievable rate. We propose two network optimization schemes based on the system characteristics, i.e., joint optimization framework and distributed optimization scenario. Interestingly, IGS-based scheme outperforms its counterpart PGS-based scheme, especially at higher interference-to-noise ratio. Our findings reveal that using IGS in single-user detection systems that suffer from both RSI and HWD can effectively mitigate the degradation in the achievable rate performance.

Secure full-duplex two-way relaying networks with optimal relay selection

The secrecy outage probability (SOP) of cooperative communication systems with optimal relay selection (ORS) scheme in the presence of an eavesdropper is investigated by implementing decode-and-forward-based full-duplex (FD) two-way relayingmode. Under Rayleigh fading assumptions, the closed-form expressions for the distributions of end-to-end signal-to-interference-plus-noise ratio in each wireless link are derived. Furthermore, the closed-form expression for the exact SOP of the proposed ORS scheme is given out. Numerical results show that the SOP of the proposed system can be substantially impacted by several parameters involved, including the number of relays, the average signal-to-noise ratio (SNR) of eavesdropper links, and the average residual self-interference (SI) imposed on the FD relays. In particular, the impact of residual SI is shown to be more obvious in terms of eroding the system’s secrecy performance in a low-to-medium SNR regime than in a high-SNR regime. As long as the residual SI power is not beyond the background noise level, the proposed FD-TWC scheme can always outperform the conventional half-duplex mode in terms of SOP.

Power Allocation for Opportunistic Full-Duplex based Relay Selection in Cooperative Systems

In this paper, performance analysis of full-duplex (FD) relay selection under decode-and-forward (DF) relaying mode is carried out by taking into account several critical factors, including the distributions of the received signal-to-noise ratio (SNR) and the outage probability of wireless links. The tradeoff between the FD and half-duplex (HD) modes for relay selection techniques is also analyzed, where the former suffers from the impact of residual self-interference, but the latter requires more channel resources than the former (i.e., two orthogonal channels are required). Furthermore, the impact of optimal power allocation (OPA) on the proposed relay-selection scheme is analyzed. Particularly, the exact closed-form expressions for outage probability of the proposed scheme over Rayleigh fading channels are derived, followed by validating the proposed analysis using simulation. Numerical results show that the proposed FD based scheme outperforms the HD based scheme by more than 4 ㏈ in terms of coding gain, provided that the residual self-interference level in the FD mode can be substantially suppressed to the level that is below the noise power.