Full-duplex Relay System Research Articles

Analyzing error probability in aerial full-duplex relay systems: Exact formulations and optimization techniques

In this study, we investigate the performance of aerial full-duplex relay (AFDR) systems. In particular, we examine two practical scenarios: one where there is no direct link between the transmitter and user, and another where such a link exists. For both scenarios, we develop mathematical models to calculate the closed-form expressions of symbol error probabilities (SEPs) for AFDR systems, using a realistic channel aligned with the fifth generation (5G) and beyond yardsticks. To take care of residual self-interference (RSI) in AFDR, we propose an optimal power allocation strategy. Our numerical findings indicate that the performance in the case with a direct link is considerably higher than that in the case without this link. Additionally, we analyze thoroughly the effects of key parameters such as transmit power, RSI levels, carrier frequencies, and AFDR positions. The effect of RSI is significantly strong, and our proposed optimal power allocation method substantially improves system performance, especially in high transmit power scenarios where error floors may occur. Importantly, the optimal power level is dramatically lower than the conventional value where the optimal power cannot be found. Thus, besides reducing the SEPs, optimal power also helps to prolong the time of operation of AFDR. Monte-Carlo simulations are performed to confirm the accuracy of our derived expressions and demonstrate the efficacy of the proposed approaches in practical scenarios.

Joint wireless energy transmission and dynamic power management for full-duplex relay system

The rapid deployment of fifth-generation (5G) mobile communication systems demands sustainable power solutions. This paper introduces a novel joint design for wireless energy transmission and dynamic power management in full-duplex relay systems, aiming to ensure a continuous power supply for relay nodes. Our approach integrates energy harvesting from RF signals and dynamic battery management, focusing on optimizing throughput via energy allocation and precoding design. Simulation results demonstrate that our scheme significantly outperforms conventional non-battery half-duplex schemes in system throughput. Notably, we observe performance increments in throughput compared to all mentioned traditional methods, highlighting the efficacy of our design in enhancing 5G network sustainability and efficiency. This innovative approach presents a promising solution for effective power management in next-generation mobile networks.

Intelligent Reflecting Surface Assisted Full-Duplex Relay Systems: Deployment Design and Beamforming Optimization

Intelligent Reflecting Surface Assisted Full-Duplex Relay Systems: Deployment Design and Beamforming Optimization

Analog-Circuit Domain Cancellation with Optimal Feedback Path Selection on Full-Duplex Relay Systems

This paper proposes a scheme that reduces residual self-interference significantly in the analog-circuit domain on wireless full-duplex relay systems. Full-duplex relay systems utilize the same time and frequency resources for transmission and reception at the relay node to improve spectral efficiency. Our proposed scheme measures multiple responses of the feedback path by changing the direction of the main beam of the transmitter at the relay, and then selecting the optimal direction that minimizes the residual self-interference. Analytical residual self-interference is derived as the criterion to select the optimal direction. In addition, this paper considers the target of residual self-interference power before the analog-to-digital converter (ADC) dependent on the dynamic range in the analog-circuit domain. Analytical probability that the residual interference exceeds the target is derived to help in determining the number of measured responses of the feedback path. Computer simulations validate the analytical results, and show that in particular, the proposed scheme with ten candidates improves the residual self-interference by approximately 6 dB at the probability of 0.01 that the residual self-interference exceeds target power compared with a conventional scheme with the feedback path modeled as Rayleigh fading.

Cooperative Key Establishment Protocol for Full-Duplex Relay Systems

Using the fading channel characteristics, as a randomness source, for the secret key generation earns significant attention because of it’s computational less power and low energy consumption. Current researches focus on point-to-point reciprocal-based key extraction from these randomness sources. Most practical communication situations are non-line of sight, so endpoints use a relaying channel to improve communication performance. Besides that, in the upcoming 5G systems, the full-duplex (FD) communications will be one of the main techniques, which will remove the advantage of using the reciprocal feature in the randomness source common observation. In this paper, we consider the challenge of generating a symmetric secret key between two legitimate parties in the relaying channel with FD capability. We suggest an efficient key extraction protocol that accomplished an acceptable shared secret key rate compared to the direct channel traditional approach. Unlike similar schemes, we provide full statistical analysis for the construction of randomness source from the relaying channel with FD capability. Additionally, we investigate the performance analysis of the suggested key agreement protocol. We also analyze the effect of the curious-but-honest relay and an eavesdropper on the proposed protocol.

Impacts of Imperfect CSI and Transceiver Hardware Noise on the Performance of Full-Duplex DF Relay System With Multi-Antenna Terminals Over Nakagami-m Fading Channels

In this paper, we investigate the performance of a full-duplex (FD) relay system where multi-antennas are exploited at source and destination. Unlike previous works, the impacts of imperfect channel state information (I-CSI), transceiver hardware noise (THN), and residual self-interference (RSI) are taken into account. We mathematically derive the exact closed-form expressions of the outage probability (OP), symbol error rate (SER), and ergodic capacity (EC) of the FD relay system with I-CSI, THN, and RSI over 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. From the derived expressions, the performance of the considered system under the effects of three negative factors (I-CSI, THN, and RSI) is compared with that system in the case of all ideal factors (perfect channel state information (P-CSI), perfect transceiver hardware (P-TH) and perfect self-interference cancellation (P-SIC)), two ideal factors (P-CSI and P-TH, P-CSI and P-SIC, P-TH and P-SIC), or one ideal factor (P-CSI or P-TH or P-SIC). Numerical results show a strong impact of three negative factors on the OP, SER, and EC of the considered FD relay system, especially when the data transmission rate of the system and signal-to-noise ratio (SNR) are high. In particular, OP, SER, and EC go to the floors in the high SNR regime due to the three negative factors. Therefore, when I-CSI, THNs, and RSI exist in the FD relay system, we should use suitable source and relay transmission power to obtain excellent performance while saving energy consumption. Moreover, when two of the three negative factors are large enough, the remaining factor’s impact becomes weaker and may be neglected in certain circumstances.

SER performance of MIMO full-duplex relay system with channel estimation errors and transceivers hardware impairments

In practice, traditional wireless communication systems are often affected by various negative factors such as channel estimation errors (CEE) and transceiver hardware impairments (THI). For in-band full-duplex (FD) communication systems, besides CEE and THI impacts, imperfect self-interference cancellation will significantly degrade the system performance because of residual self-interference (RSI). This paper aims to investigate the performance of a multiple-input multiple-output (MIMO) FD relay (FDR) system in realistic scenarios where the impacts of CEE, THI, and RSI are taken into account. We mathematically derive the exact closed-form expression of symbol error rate (SER) of the considered MIMO-FDR system and validate the derived expression by Monte-Carlo simulations. Numerical results indicate that the impacts of three imperfect factors (CEE, THI, and RSI) are remarkable. Specifically, with the considered values of CEE, THI, and RSI, the impact of CEE on the SER is most substantial. Additionally, compared with the ideal system (perfect channel estimations, transceiver hardware, and self-interference cancellation), the SER of the considered system is significantly higher and goes to the error floor fast. Therefore, it is crucial to apply all solutions for reducing the CEE, THI, and RSI in the considered MIMO-FDR system.

On Blind Channel Estimation in Full-Duplex Wireless Relay Systems

We investigate the feasibility of second-order statistics-based blind channel estimation in the context of two-hop full-duplex relay systems. To that end, the performance of blind and traditional pilot-based (training sequence based) channel estimation approaches are compared. This is accomplished by deriving the Cramer-Rao Lower Bound (CRLB) expressions for both blind and pilot-based schemes, and comparing them to each other and to the mean-squared error (MSE) values measured via simulation. Post-equalization SINR expressions are also derived for both blind and pilot-based methods. Furthermore, a modified post-equalization SINR expression, where the channel estimation error is replaced by the inverse of the Fisher information matrix (FIM) is proposed, providing an upper bound for the post-equalization SINR. These analytically-predicted SINR values for the blind approach are compared to the SINR measured via link simulation. The performance of the two channel estimation methods is analyzed by comparing the CRLB, post-equalization SINR, and BER performance for two significantly different transmission packet sizes. All of the above metrics indicate that blind estimation provides clear performance advantages relative to the pilot-based counterpart. Additionally, the blind approach eliminates the overhead associated with the pilot-based method, where a portion of the system resources is allocated to the pilot sequence. To quantify this, the spectral efficiency of the FD relay system employing blind and pilot-based channel estimation methods are compared, indicating that at high SNR, the blind approach provides around 2-bps/Hz spectral efficiency gain relative to a typical pilot-based method. Finally, the computational complexity of the two channel estimation techniques are evaluated and compared. The blind approach has a clear computational advantage for larger packet sizes.

Combining Power Allocation and Superposition Coding for an Underlay Two-way Decode-and-forward Scheme

Combining Power Allocation and Superposition Coding for an Underlay Two-way Decode-and-forward Scheme

Toward URLLC: A Full Duplex Relay System with Self-Interference Utilization or Cancellation

Ultra-reliable low-latency communication (URLLC) is one of the key use cases of 5G wireless communications to facilitate specific application scenarios with stringent latency and reliability demands, such as industrial automation and Tactile Internet. A full duplex (FD) relay with simultaneous transmission and reception in the same frequency band is an effective approach to enhance the reliability of cell-edge user terminals by significantly suppressing self-interference (SI). However, the signal processing latency at FD relay due to SI cancellation, referred to as relaying latency, takes a significant part in the end-to-end latency, and therefore should be minimized, while guaranteeing high reliability. In this article, we first present an up-to-date overview of the end-to-end latency for an FD relay system, addressing physical layer challenges. We investigate the possible solutions in the literature to achieve the goal of URLLC. The efficient solution is to allow a simple amplify-and-forward FD relay mode with low-complexity SI radio frequency and analog cancellations, and process the residual SI alongside the desired signal at the base station in an adaptive manner, rather than being cancelled at relay in the digital domain. Also, the residual SI can be utilized at the base station to enhance the reliability and degree of freedom in signal processing, not necessarily being cancelled as much as possible. The FD relay assisted system with adaptive SI utilization or cancellation enables extended network coverage, enhanced reliability, and reduced latency compared to the existing overview work.

On the Performance of MIMO Full-Duplex Relaying System With SWIPT Under Outdated CSI

In this paper, we propose a full-duplex (FD) relaying system with multi-input multi-output (MIMO) with simultaneous wireless information and power transfer (SWIPT), where the communication from source to destination is assisted by a full-duplex decode-and-forward (DF) relay. The time switching (TS) protocol is used at the relay to harvest the energy of radio-frequency (RF) signals transmitted from the source. To improve both system performance and the amount of harvested energy, multiple antennas are used at source and destination. Transmit antenna selection (TAS) is employed at the source with an assumption that the feedback of channel state information (CSI) is outdated. Meanwhile, both selection combining (SC) and maximal ratio combining (MRC) techniques are applied at the destination. The closed-form expressions of the outage probability (OP), optimal throughput, and symbol error probability (SEP) are derived subject to the outdated CSI over Rayleigh fading channels. We also make a comparison between the performance of the proposed MIMO-FD relaying system with SWIPT and that of MIMO half-duplex (HD) relaying systems with and without SWIPT. The validity of derived mathematical expressions is verified by Monte-Carlo simulations. Numerical results show that the TAS/MRC scheme gives better system performance than the TAS/SC scheme. Moreover, higher energy harvesting time is needed to maximize the throughput than to minimize the OP.

On Performance of Full-Duplex Decode-and-Forward Relay Systems with an Optimal Power Setting under the Impact of Hardware Impairments

In this paper, we analyze the performance of in-band full-duplex (IBFD) relay systems that use the decode-and-forward (DF) protocol at the relay under the impact of imperfect self-interference cancellation and hardware impairments. Three practical relay scenarios are considered in our analysis: (i) there is no direct link from the source to the destination; (ii) there is a direct link, but the signal from the source is considered interference; and (iii) there is a direct link, and the signal from the source is cooperatively combined with that from the relaying path. Specifically, we derive exact and asymptotic expressions for the outage probability (OP) of the IBFD system. Based on the OP, the exact expression for symbol error probability (SEP) is also derived. Moreover, in order to cope with the effect of imperfect self-interference cancellation (SIC) due to the full-duplex mode, we propose optimal and suboptimal power calculation methods for the relay to minimize the OP and SEP. A performance evaluation shows that the IBFD relay system is significantly affected by both imperfect SIC and hardware impairments. However, the optimal power values can help to improve the system performance, significantly.

Finite-Order Source and Relay Filtering Design for Wideband Full-Duplex Amplify-and-Forward Relaying Networks

Compared with half-duplex relaying, the full-duplex relay (FDR) system provides higher spectral efficiency due to the concurrent transmission and reception at the relay node. As known, the full-duplex operation will introduce the self-interference (SI) that significantly degrades the system performance. Conventionally, SI is treated as a harmful signal that needs to be removed from the system as completely as possible. The conventional design concept, however, may not be efficient since SI is in fact a delayed version of the desired signal. Specifically, it is possible to have further performance improvement if SI can be exploited appropriately. In this paper, we will investigate the source/relay filter design problem where the source and relay are considered as finite impulse response (FIR) and infinite impulse response (IIR) filters, respectively. The design goal is to optimize the end-to-end performance for the linear minimum mean-square error (MMSE) and nonlinear MMSE decision-feedback equalizers. To reduce the implementation cost, we further propose a finite-order filter design for the source and relay precoders. Simulations demonstrate that our designs outperform the conventional ones.

Non-Time-Switching Full-Duplex Relay System with SWIPT and Self-Energy Recycling

Non-Time-Switching Full-Duplex Relay System with SWIPT and Self-Energy Recycling

Cooperative Key Establishment Protocol for Full-Duplex Relay Systems

Using the fading channel characteristics, as a randomness source, for the secret key generation earns significant attention because of it’s computational less power and low energy consumption. Current researches focus on point-to-point reciprocal-based key extraction from these randomness sources. Most practical communication situations are non-line of sight, so endpoints use a relaying channel to improve communication performance. Besides that, in the upcoming 5G systems, the full-duplex (FD) communications will be one of the main techniques, which will remove the advantage of using the reciprocal feature in the randomness source common observation. In this paper, we consider the challenge of generating a symmetric secret key between two legitimate parties in the relaying channel with FD capability. We suggest an efficient key extraction protocol that accomplished an acceptable shared secret key rate compared to the direct channel traditional approach. Unlike similar schemes, we provide full statistical analysis for the construction of randomness source from the relaying channel with FD capability. Additionally, we investigate the performance analysis of the suggested key agreement protocol. We also analyze the effect of the curious-but-honest relay and an eavesdropper on the proposed protocol.

Performance analysis of full duplex relay assisted mixed RF/FSO system

In this paper, we analyze the performance of a full duplex (FD) relay assisted mixed radio frequency (RF)/free space optical (FSO) system with self-interference. The RF links follow Nakagami-m distribution, and FSO links adopt Gamma–Gamma atmospheric turbulence model. We derive the exact and asymptotic outage probability (OP) expressions of the system. Based on the cumulative distribution function (CDF), the bit error rate (BER) and average capacity expressions are further presented. To verify the superiority of FD relay system, we deduce the average capacity of half duplex (HD) relay system and investigate the performance differences between FD relay system and HD relay system. Furthermore, the residual self-interference condition is discussed in this paper. Simulation results show that, when the self-interference coefficient (SIC) is large, the capacity of FD relay system declines severely and behaves even worse than HD relay system. Moreover, there is a tradeoff between SIC and system performance, because the transmission power of the second hop RF link is also the self-interference of the first hop.

Analysis of Outage Probability and Throughput for Energy Harvesting Full-Duplex Decode-and-Forward Vehicle-to-Vehicle Relay System

In this paper, we evaluate the performance of a vehicle-to-vehicle (V2V) system where full-duplex relay (FDR) harvests the energy from source and uses decode-and-forward (DF) protocol to forward data from source to destination. Unlike existing works about FDR systems, we consider the scenario that both relay and destination are moving vehicles, leading to the channel between relay and destination characterized by double (cascade) Rayleigh fading. We successfully obtain the closed-form mathematical expressions of the outage probability (OP) and throughput of the considered energy harvesting- (EH-) FDR-V2V system. Based on these expressions, the system performance is investigated through various scenarios. Numerical results indicate that the performance of the considered system is reduced compared with that of the system over Rayleigh fading channels. We also observe that there is an optimal EH time duration that minimizes the OP and maximizes the throughput. This value depends on the transmission power of source. Furthermore, the OP goes to outage floor faster due to the impact of the residual self-interference (RSI), especially when RSI is high. All analysis results are verified by Monte-Carlo simulations.

Software-Based Real-Time Full-Duplex Relaying: An Experimental Study

Relaying in wireless networks is one of the most important concepts to improve the overall communication performance and to increase coverage. Relay systems can work in either half or full-duplex mode. Half-duplex relaying unfortunately increases the overall latency and also causes spectral losses. On the other hand, in-band full-duplex relaying helps to overcome such issues by simultaneously receiving packets from the source and forwarding them towards the destination. We present a software-based real-time full-duplex relaying system, which we implemented in GNU Radio. The system supports running simulations using an abstract channel model as well as over-the-air experiments using Software Defined Radios (SDRs). A major challenge in developing such a system is dealing with self-interference. For this, we constructed a new looped self-interference cancellation system and integrated it with the GNU Radio implementation. In an experimental study, we validated and evaluated our system to characterize the practical performance of the proposed full-duplex relay system. Our main focus is on the impact of the residual looped self-interference, for which we show analytical and simulation results to confirm the experimental study.

Outage Probability and Throughput Analyses in Full-Duplex Relaying Systems With Energy Transfer

In this article, we consider a dual-hop full-duplex (FD), amplify-and-forward, orthogonal frequency division multiplexing (OFDM) relaying network, where the relay operates based on a time-switching architecture to harvest energy from radio frequency signals. We use a polarization-enabled digital self-interference cancellation (PDC) scheme to cancel the self-interference signal at the relay in order to achieve FD communications. The paper provides a comprehensive analysis of the system performances in terms of outage probability and throughput over multipath Rayleigh fading channels. Furthermore, the optimal time split between the duration of energy harvesting and signal transmission to maximize the system throughput is numerically calculated. We also derive the asymptotic lines to simplify the expressions of outage probability and throughput at high transmit signal-to-noise ratios (SNR). Our analysis and simulation results show that the proposed FD relaying system by utilizing a proper time split fraction can boost the system throughput significantly over an appreciable range of transmitting SNR values, compared to half-duplex (HD) relaying systems.

Improving the Performance of Spatial Modulation Full-Duplex Relaying System With Hardware Impairment Using Transmit Antenna Selection

This paper aims to study the impact of hardware impairments (HI) on the performance of spatial modulation (SM) system with full-duplex relay (FDR), namely SM-FDR system. To combat the negative effect of HI, a transmit antenna selection (TAS) scheme is applied at transmitter. The system performance in terms of outage probability (OP) and symbol error rate (SER) in case of HI and ideal hardware are compared. Furthermore, the impact of TAS on the system performance is also considered. This study derives successfully the exact expression of the OP and the approximate expression of the SER with TAS under the impact of both HI and residual self-interference (RSI). Both HI and RSI have strong influence on the performance of the SM-FDR system, especially at high data transmission rate, and the influence of the former is higher. However, the system performance is significantly enhanced, i.e. the SER is reduced, when TAS is applied. Therefore, it is recommended to apply TAS to improve the performance of SM-FDR systems when both HI and RSI exist in reality. Finally, all analytical expressions are validated by Monte Carlo simulation.