Half-duplex Mode Research Articles

Deep Reinforcement Learning for Optimizing RIS-Assisted HD-FD Wireless Systems

This letter investigates the reconfigurable intelligent surface (RIS)-assisted multiple-input single-output (MISO) wireless system, where both half-duplex (HD) and full-duplex (FD) operating modes are considered together, for the first time in the literature. The goal is to maximize the rate by optimizing the RIS phase shifts. A novel deep reinforcement learning (DRL) algorithm is proposed to solve the formulated non-convex optimization problem. The complexity analysis and Monte Carlo simulations illustrate that the proposed DRL algorithm significantly improves the rate compared to the non-optimized scenario in both HD and FD operating modes using a single parameter setting. Besides, it significantly reduces the computational complexity of the downlink HD MISO system and improves the achievable rate with a reduced number of steps per episode compared to the conventional DRL algorithm.

Cross-Cycled Uplink Resource Allocation over NB-IoT.

Before each user equipment (UE) can send data using the narrowband physical uplink shared channel (NPUSCH), each UE should periodically monitor a search space in the narrowband physical downlink control channel (NPDCCH) to decode a downlink control indicator (DCI) over narrowband Internet of Things (NB-IoT). This monitoring period, called the NPDCCH period in NB-IoT, can be flexibly adjusted for UEs with different channel qualities. However, because low-cost NB-IoT UEs operate in the half-duplex mode, they cannot monitor search spaces in NPDCCHs and transmit data in the NPUSCH simultaneously. Thus, as we observed, a percentage of uplink subframes will be wasted when UEs monitor search spaces in NPDCCHs, and the wasted percentage is higher when the monitored period is shorter. In this paper, to address this issue, we formulate the cross-cycled resource allocation problem to reduce the consumed subframes while satisfying the uplink data requirement of each UE. We then propose a cross-cycled uplink resource allocation algorithm to efficiently use the originally unusable NPUSCH subframes to increase resource utilization. Compared with the two resource allocation algorithms, the simulation results verify our motivation of using the cross-cycled radio resources to achieve massive connections over NB-IoT, especially for UEs with high channel qualities. The results also showcase the efficiency of the proposed algorithm, which can be flexibly applied for more different NPDCCH periods.

Performance analysis of antenna selection scheme in dual-hop NOMA HD and FD energy harvesting relay networks

In this paper, the outage probability (OP) performance of antenna selection schemes is investigated in downlink non-orthogonal multiple access based energy harvesting amplify-and-forward relay network. In this network, base station with multiple antennas simultaneously communicates with multiple-antenna users via the relay, which is equipped with single transmit and multiple receive antennas and operates in half-duplex (HD) or full-duplex (FD) mode. The joint transmit-receive antenna selection and receive antenna selection schemes are employed in the first and second hops, respectively. For the proposed system, the closed-form expressions for the exact OP are derived jointly for HD and FD modes over Nakagami-m fading. Then, the corresponding asymptotic OP expressions are obtained. Finally, accuracy of our analyses is verified by simulations.

Performance analysis of legitimate UAV surveillance system with suspicious relay and anti-surveillance technology

We propose a legal Unmanned Aerial Vehicle (UAV) surveillance system to perform passive surveillance or active jamming while in the presence of a suspicious relay or source, where a UAV works in half-duplex mode and the relay/source deploys artificial noise to prevent monitoring. Three schemes are considered for a Multiple-Input Multiple-Output (MIMO) UAV: surveilling followed by jamming; jamming followed by surveilling; and two-stage surveilling. For each scheme, a closed-form expression of surveilling non-outage probability is derived, and surveilling performance under different system configurations is analyzed. Monte Carlo (MC) simulation validates derivation correctness.

ASER Analysis of Hybrid Receiver Based SWIPT Two-Way Relay Network

In this paper, we investigate the performance of a hybrid receiver-based simultaneous wireless information and power transfer (SWIPT) two-way relay network over Nakagami- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> faded channels. A hybrid receiver is adopted at the relay node that utilizes both the time switching (TS) and power splitting (PS) protocols for energy harvesting and information transmission. Amplify-and-forward relaying protocol is utilized at the relay node to process the information in half-duplex mode. In the considered network, impact of a practical non-linear power amplifier (NLPA) at the relay node is considered. Selection combining is performed at the destination node to utilize the direct-link and relay assisted signals. For the considered system, the analytical expressions of outage probability (OP) and asymptotic OP are derived over Nakagami- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> faded channels for both the integer and non-integer value of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> . The analytical expression of the system throughput and energy efficiency of the considered network are also derived. Further, the analytical expression of ergodic capacity is derived in terms of the Meijer-G function. By utilizing a cumulative distribution function based approach, analytical expressions of average symbol error rate (ASER) for general order hexagonal quadrature amplitude modulation (QAM), general order rectangular QAM, and 32-cross QAM schemes are derived. For different QAM constellations, a comparative ASER analysis is also illustrated. Furthermore, the impact of TS factor, PS ratio, energy conversion efficiency, NLPA, and threshold data-rates on the considered network is also highlighted. Finally, Monte-Carlo simulations are performed for validation of the derived analytical expressions.

Covert Rate Maximization in Wireless Full-Duplex Relaying Systems With Power Control

This paper investigates the fundamental covert rate performance in a wireless relaying system consisting of a source-destination pair, a full-duplex (FD) relay and a warden, where the relay can work at either the FD mode or the half-duplex (HD) mode. We first provide theoretical modeling for the instantaneous/average covert rate when the system works solely under the FD mode or HD mode, and then explore the corresponding optimal transmit power control of relay for the covert rate maximization. For an improvement of covert rate, we further propose a joint FD/HD mode that flexibly switches between the FD and HD modes depending on channel state of the relay self-interference channel. Under the joint FD/HD mode, we also examine the related problems of theoretical modeling for covert rate and optimal transmit power control of relay for covert rate maximization. Finally, extensive numerical results are provided to illustrate the covert rate performances of the relaying system under the FD, HD and joint FD/HD modes.

On Performance of Energy Harvested Cooperative NOMA Under Imperfect CSI and Imperfect SIC

With the advent of 5G and the need for energy-efficient massively connected wireless networks, in this work, we consider an energy harvesting (EH) based multi-relay downlink cooperative non-orthogonal multiple access (NOMA) system with practical constraints. The base station serves NOMA users with the help of decode-and-forward based multiple EH relays, where relays harvest the energy from the base station's radio frequency. A relay is selected from the multiple K-relay by using a partial relay selection protocol. The system is considered to operate in half-duplex mode over a generalized independent and identical Nakagami$-m$ fading channel. The closed-form expression of outage probability and ergodic rate are derived for users, under the assumption of imperfect channel state information (CSI) and imperfect successive interference cancellation (SIC) at the receiver node. Expression of outage probability and ergodic rate for both users under the assumption of perfect CSI and perfect SIC are also presented. Further, the asymptotic expression for the outage probability is also shown. The derived analytical expressions are verified through Monte-Carlo simulations.

Age of Information of Dual-Sensor Information Update System With HARQ Chase Combining and Energy Harvesting Diversity

A novel status update information system is designed by jointly considering wireless energy harvesting diversity, status update transmission diversity, and hybrid automatic repeat request with chase combining (HARQ-CC) diversity, which consists of two sensors and one destination. The two sensors, which have finite-sized batteries, harvest energy from a Bernoulli process, and cooperatively deliver the status update to the destination by sharing a common information source. In addition, the two sensors synchronously operate in half-duplex (HD) mode and are triggered by a common control center. We first propose the sensor energy harvesting model that can be represented by Markov chain (MC) and develop the construction method of the transition matrix of sensor battery energy states as well as the stationary distributions. Secondly, the average age of information (AoI) of the proposed dual-sensor status update system is derived in terms of a closed-form expression by accurately calculating the statistical descriptions of the maximal number of the retransmissions of an update packet and the service time of one packet. Compared with traditional single-sensor system, the proposed dual-sensor system not only harvests more energy, but also has a smaller average AoI.

Hardware Impairments Aware Full-Duplex NOMA Networks Over Rician Fading Channels

A cooperative full duplex (FD) nonorthogonal multiple access (NOMA) scheme over Rician fading channels is considered. The practical, imperfect successive interference cancellation and residual hardware impairments at transceivers are taken into account. To evaluate the performance of the considered system, the analytical approximate expressions for the outage probability and the ergodic rate of the considered system are derived, and the asymptotic performance is also explored. Simulation results manifest that the FD cooperative NOMA can improve the ergodic sum rate of the system compared to the half-duplex mode.

Fast-Forward Mitigation Schemes for Cognitive Adversary

We address a denial of service attack on low-latency communication, wherein a cognitive adversary, armed with a full-duplex radio, can simultaneously measure the energy levels on the victim’s frequency band besides jamming it. First, we show that traditional countermeasures such as frequency hopping cannot mitigate such attacks. To circumvent this problem, we propose two cooperative relaying schemes, namely: semi-coherent fast-forward half-duplex and semi-coherent fast-forward full-duplex relaying schemes, wherein the victim node seeks the assistance of a helper node in its vicinity, that can either work in half-duplex or full-duplex mode, to instantaneously multiplex the victim’s messages in its message to the destination. In the former scheme, the victim is required to continue transmission on the jammed band, whereas the helper node is asked to overhear the victim’s frequency band to multiplex their information in its frequency band. In the latter scheme, the victim and the helper node cooperatively pour fraction of their power on both frequency bands so as to reliably communicate their messages on the helper’s frequency band. Extensive analysis on the choice of the power splitting factor between the frequency bands is presented besides proving that both schemes successfully engage the adversary on the jammed frequency band.

Full-Duplex MAC Protocol Based on CSMA/CA for Switching Transmission Mode

Full-duplex (FD) radios can transmit and receive packets simultaneously in the same frequency band. Although this potentially doubles the spectral efficiency, it also causes inter-node interference, which was not an issue for half-duplex (HD) radios and can significantly reduce FD radio throughput. This paper proposes a hybrid transmission switching algorithm to reduce performance degradation due to inter-node interference. In contrast to previous studies that only considered channel capacity, we determine the transmission mode by considering the modulation and coding scheme (MCS). The access point compares the required transmission time for HD, FD, and hybrid mode and selects the mode with the best network throughput. We also designed an analytical model to evaluate network throughput for the proposed algorithm. In particular, we consider FD pair probability, which has not been addressed previously. Analytical and simulation results verify that the proposed algorithm improves network performance.

Cooperative Relaying for Multi-User MIMO Wireless Backhaul Networks

With the increasing deployment of more short-range small cells using mmWave technologies, backhaul becomes a bottleneck and wireless backhaul is relatively attractive compared to wired backhaul due to lower cost and efficient operation. As such, cooperative relaying for multi-user multiple-input multiple-output (MU-MIMO) wireless backhaul networks is studied, in which the source sends independent messages to $K$ destinations with the help of $N$ relays where the relays operate in full- or half-duplex mode. Herein, we focus on a line-of-sight dominant environment in which each of the channel matrices between nodes becomes rank-deficient due to the lack of multi-paths. In such cases, the multiplexing gain from using multiple antennas is severely limited, and the capacity cannot be improved with the number of antennas. To overcome the rank deficiency, we develop a novel cooperative relaying scheme that utilizes relays as active reflectors. In the proposed scheme, the source distributes the streams over the relays as uniformly as possible, and the relays extract the streams of each destination based on their received signals and forward them to their corresponding destinations, while any inter-user and inter-relay interference is also properly nulled out. We analyze the achievable sum degrees of freedoms (DoFs) and sum rates with full-duplex and half-duplex relays, and derive an upper bound on the sum DoF, which is tight when the relays operate in full-duplex mode. The results demonstrate that our scheme offers significant improvement to system throughput in comparison with direct transmission without cooperative relaying.

A Distributed Resource Allocation Scheme for Self-Backhauled Full-Duplex Small Cell Networks

Full-duplex (FD) radio with wireless backhauling, is a key technology for dense small cell deployments in fifth generation (5G) cellular networks. In this paper, the problem of joint user scheduling, operation mode selection and power allocation in a two-tier cellular network with FD-capable small basestations is considered. The objective is to maximize the network sum rate under quality-of-service requirements and backhaul capacity constraints. In order to solve the problem, a distributed algorithm is developed which divides the original problem into two subproblems, viz., (i) user scheduling and mode selection; and (ii) power allocation. For the first subproblem, a low-complexity search method is proposed for opportunistically finding the best user scheduling and operation modes. In the second subproblem, an iterative successive convex approximation method is proposed to transform the nonconvex power allocation problem into a sequence of convex subproblems. The proposed solution provides a hybrid strategy which opportunistically selects FD or half-duplex (HD) operation modes for access and backhaul links. It is observed that the proposed algorithm converges in few iterations and mitigates the interferences by properly adjusting the transmission powers. Numerical results demonstrate the superiority of the proposed scheme over other possible scenarios. In particular, the proposed algorithm can achieve up to 44% gain in overall sum rate compared to a network that solely uses HD.

Improvement on Age of Information for Information Update Systems With HARQ Chase Combining and Sensor Harvesting-Transmitting Diversities

The age of information (AoI) has attracted increasing attentions as a new metric and tool to capture the timeliness of reception and freshness of data, which is different from the conventional metric such as outage, delay, and throughput. While most existing works focused on AoI analysis and optimizing method, the information update system design by utilizing diversity to reduce AoI is not fully exploited so far. Inspired by this fact, a novel information status update system is designed by jointing wireless energy harvesting diversity, status update transmitting diversity, and hybrid automatic repeat request (HARQ). Specially, the update system consists of two sensors that can be seen as an unified entity from the destination's perspective, and one destination. The two sensors, which have finite-size batteries and synchronously operate in half-duplex mode, harvest energy from a Bernoulli process source, and cooperatively deliver the status update to destination by sharing a common information source. To exploit the information of the unsuccessfully decoding update packet, the HARQ and chase combining (HARQ-CC) are jointly used at destination so that the HARQ-CC receiving diversity is also exploited. By using Bernoulli process energy arrival probability and sensor transmission probability, we first propose one novel sensor energy harvesting and update delivering model that can be represented by Markov Chain (MC) and develop one novel construction method of the transition matrix of sensor battery energy states. Considering the developed energy state transmission matrix column stochastic, irreducible, and aperiodic, we obtain the stationary distribution of sensor battery energy states so that the steady transmitting power is derived. Secondly, the average AoI of the dual-sensor status update system is derived in terms of a closed-form expression by accurately calculating the statistical descriptions of the maximum retransmission number (time) in HARQ-CC and the service time of one packet. The analytical results are validated by using the comparison from simulations. Moreover, compared with traditional single sensor system, the dual-sensor system not only harvests more energy, but also has smaller average AoI because of the joint exploitation of multi-diversity. Besides, the impact of the system parameters on harvested energy and average AoI is provided, which provides insights in terms of the optimal design of Internet of things system.

Alternate-Jamming-Aided Wireless Physical-Layer Surveillance: Protocol Design and Performance Analysis

In this article, we develop an alternate-jamming-aided wireless physical-layer surveillance protocol where two devices (M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> and M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) work cooperatively to eavesdrop on and intervene in a suspicious transmission link from a source (S) to a destination (D). Unlike existing approaches which rely on the use of a multi-antenna full-duplex radio as the monitor, in our protocol, M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> and M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> are both single-antenna nodes operating in half-duplex mode, which alternately perform proactive eavesdropping and jamming to mimic the behavior of a full-duplex monitor. Within any time slot, M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> sends a jamming signal to deteriorate the signal reception at D and M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> eavesdrops on the transmission from S. During the next slot, M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> overhears the signal sent from S, and M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> forwards its received signal during the previous slot to realize jamming. In this manner, the jamming signal received at M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> can be perfectly removed after self-interference cancellation, and the signals from S during the two consecutive slots are jointly decoded with high reliability, thus enabling successful surveillance. On the other hand, the detection performance at D is heavily degraded due to the injection of the jamming signal, thereby preventing information leakage from S to D. The performance of the proposed protocol is analyzed in terms of the eavesdropping non-outage probability, the surveillance success probability, as well as the symbol error probability. Theoretical analysis and simulation results demonstrate the superiority of our design compared to competing solutions in the literature.

Special Section on Full-Duplex Transceivers for Future Networks: Theory and Techniques

Conventional wireless communication systems operate in a half-duplex mode, i.e., current radios cannot transmit and receive at the same time and on the same frequency. Full-duplex wireless operation was generally assumed to be impossible due to the great difference in transmit and receive signal power levels. However, recent advances in antenna, hardware, and signal processing techniques have shown that full-duplex operation is practically feasible. Thanks to novel combinations of antenna, analog, and digital cancellation techniques, self-interference suppression of 80–110 dB can be made possible. The feasibility in building a practical full-duplex radio using off-the-shelf hardware and software-defined radios therefore alleviates many problems in wireless network design.

Throughput Analysis of In-Band Full-Duplex Transmission Networks With Wireless Energy Harvesting Enabled Sources

In this paper, we investigate a two-hop communication system in which the source utilizes radio frequency (RF) energy harvesting for the transmission of information. An intermediate relay works in a half-duplex (HD) mode in the energy harvesting (EH) phase to provide energy to the source. In the information transmission phase, the relay works in a full-duplex (FD) mode to receive information signals from the source and simultaneously transmit information signals to the destination in the same frequency band. The paper provides the analysis of outage probability and throughput of a FD relaying system and two HD relaying systems. The first HD system ( $HD_{1}$ ) has the same EH duration as the FD system while the second HD one ( $HD_{2}$ ) has the same transmitting power from the source as the FD one. The results show that the throughput with respect to the time split between the EH phase and the information transmission one is a concave function and the optimal time split can be calculated numerically. Besides, the polarization dissimilarity factor of the antennas used has an influence on the system throughput, which is maximized when polarization states are orthogonal. The FD system can double the system throughput while having the outage probability as low as that of the $HD_{1}$ system, at a cost of adopting the extra polarization-enabled digital cancellation (PDC) scheme. Meanwhile, the FD system can nearly double the system throughput while having the outage probability superior to that of the $HD_{2}$ system. Simulations are run to confirm the above analyses.

Joint Optimization of Power and Location in Full-Duplex UAV Enabled Systems

Unmanned aerial vehicles (UAVs) can be used as aerial base stations (BSs) for future small cells. They can increase the spectral efficiency of the small cells due to their higher probability to have line-of-sight (LOS) connections and their mobility as a BS. In this article, in order to show the effectiveness of using full-duplex (FD) technology in UAV networks, we consider a UAV equipped with FD technology (FD-UAV) with imperfect self-interference cancelation as an aerial BS that serves both uplink (UL) and downlink (DL) users simultaneously in a small cell network. We aim to maximize DL sum-rate, whilst prescribing a certain quality of service for UL users, by optimizing the location of FD-UAV and available resources. The problem is nonconvex; so we propose an iterative method by exploiting the difference of convex functions programming to jointly optimize transmission power of users, FD-UAV location, and FD-UAV transmission power. Simulation results are illustrated to show the effectiveness of the proposed method for FD-UAV in comparison with ground BS, in both FD and half-duplex modes.

Outage Probability Analysis of Decode-and-Forward Two-Way Relaying System with Energy Harvesting Relay

In this paper, we evaluate a two-way relay system consisting of two terminals and an intermediate relay. In this model, two terminals do not have a direct link but exchange data with each other via the relay in three phases. The relay utilizes energy harvesting technology to collect energy from the received signals of two terminals in the first two phases and then uses the obtained energy for signal transmission in the third phase. Each node is equipped with a single antenna and operates under a half-duplex mode. All wireless channels are influenced by reversible independent flat Rayleigh fading. Using analytical methods, we provide the exact and approximate closed-form expressions of user outage probability and system outage probability. The approximate expressions of these outage probabilities are more explicit and straightforward, providing a better understanding of the influences of network parameters on the system quality. Monte-Carlo simulations are used to confirm the correctness of mathematical analyses.

Beamforming and Resource Allocation for Multiuser Full-Duplex Wireless-Powered Communications in IoT Networks

For a self-sustaining wireless communication system in the Internet-of-Things (IoT) networks, energy harvesting (EH) can be implemented at each user node as a constant renewable power supply source. Hence, an investigation into the use of wireless-powered communication network (WPCN) protocols to facilitate communication between an access point (AP) and multiple mobile users (MUs) is presented in this article. The AP has multiple antennas and operates in the full-duplex (FD) mode. The MUs, on the other hand, have single antennas and works in the half-duplex (HD) mode. Each MU communicating with the FD-AP is assigned to one of two groups, based on the time allocation and channel access for either uplink (UL) or downlink (DL) communication. The channel assignment, time resource, and power resource allocations are optimized to maximize the UL weighted sum rate. The sum-rate optimization problem is found to be nonconvex. Therefore, an iterative algorithm is investigated to optimize the UL weighted sum rate of the proposed FD-WPCN system. Next, the proposed FD-WPCN algorithm is modified for HD-WPCN-enabled communication between the AP and multiple MUs. Extensive simulations are conducted to verify the proposed algorithm for FD-WPCN and compare its performance with the HD-WPCN counterpart. From the simulation results, FD-WPCN outperformed HD-WPCN at a low AP transmit signal-to-noise ratio (SNR) region. The opposite behavior is observed for high AP transmit SNR due to increasing residual self-interference at the FD-AP.