Full-duplex Nodes Research Articles

Power Optimization of a Three-Node Two-Way Relay-Assisted Power-Line Communication System

A smart grid system requires two-way communication links. Because power-line infrastructure is widely available, power-line communication (PLC) is preferred as the communication technology in smart grid systems. A power-line, on the other hand, was not designed to carry data and thus suffers from disturbances that attenuate the transmitted signal. Therefore, it is beneficial to provide spatial diversity to improve the system performance. Optimal power allocation has always been an issue to be solved in relay-aided communication systems. Using a two-way multicarrier relay configuration, this paper investigates power optimization of a relay-assisted PLC system with the consideration of the quality of service (QoS) constraints. Further, we investigate the combination of half-duplex and full-duplex nodes. Since the QoS constrained power allocation problem is highly non-convex, an alternating optimization (AO) algorithm is proposed to decompose the optimization problem into sub-problems. The AO algorithm is an iterative algorithm where it uses the newly obtained parameters (e.g., power) to find a new set of other parameters. Simulation results show that the proposed system successfully reduces the total power required by the system compared to the conventional bidirectional direct transmission (BDT) system and the relay-assisted two-way information exchange (R2WX) system under the same QoS requirement.

Bit Error Rate Analysis of Physical Layer Network Coding Spatially Modulated Full-Duplex Nodes Based Bidirectional Wireless Relay Network

In this paper, Physical Layer Network coding (PLNC)-Spatially Modulated Full-Duplex (SMFD) nodes based two-way/bidirectional cooperative wireless relay network is proposed. The PLNC-SMFD-based system is a viable technology in the field of next-generation wireless networks to enhance spectral efficiency. In the proposed system model, both the source nodes and relay nodes are employed with 2 × 2 antenna configurations where 2 bits of information are exchanged between the source nodes through a relay node. Transmit antenna selection at the source nodes is based on the incoming bitstreams. For instance, the transmit antenna is selected at PLNC-SMFD nodes based on the data symbols of the Most Significant Bit (MSB). Whereas the selected transmit antenna sends the Least Significant Bit (LSB) bit of data symbol at any time instance. Further, the self-interference at the transmitting and receiving nodes is modeled as Gaussian with the thermal noise power as a variance. The Bit Error Rate (BER) analytical expressions for both the upper and lower bound are derived in a Rayleigh Fading channel background. It has been graphically shown that the BER performance of the proposed system analyzes the effect of self-interference.

Design and analysis of IEEE 802.11 based Full Duplex WLAN MAC protocol

Full-Duplex (FD) communication is a promising technique that can be used in 5G to potentially double the system throughput compared to conventional Half Duplex (HD) transmission. Recent experiments have demonstrated near-perfect self-interference suppression techniques in the PHY layer to aid the possibility of FD communication. This paper presents a Synchronized Mode Full-Duplex (SM-FD) wireless LAN MAC protocol with appropriate modification of the IEEE 802.11 standard. The proposed SM-FD MAC protocol maintains synchronization between nodes and Access Point (AP) to increase efficiency. SM-FD MAC protocol supports WLAN having both FD and HD capable nodes by establishing both symmetrical links (Node1 ↔ AP) and asymmetrical links (Node1 → AP → Node2). To this end, we have utilized the packet-alignment-based capture effect in an efficient way. The proposed SM-FD MAC protocol has been analyzed using a Markov chain model. The analytical results for RTS and data collision probability, saturated throughput, delay, and energy spent per packet transmission have been derived and validated against simulation.

Centralized Dynamic-Time Division Duplex Utilizing Interference Alignment

In this paper, we combine centralized dynamic-time division duplex (D-TDD) with interference alignment (IA) for a wireless network comprised of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula> full duplex nodes. We maximize the performance of the proposed centralized D-TDD scheme utilizing IA in terms of rate region by optimizing the reception, transmission, simultaneous reception and transmission, and silence at each node in each time slot in addition to the choice of whether a node should treat the interference as noise or it should use IA. The problem of the rate region maximization of the wireless network is formulated as a non-convex optimization problem, whose optimal solution is found. The simulation results demonstrate that the proposed centralized D-TDD scheme utilizing IA achieves significant gains over the existing D-TDD schemes.

Wideband Full-Duplex Phased Array With Joint Transmit and Receive Beamforming: Optimization and Rate Gains

Full-duplex (FD) wireless and phased arrays are both promising techniques that can significantly improve data rates in future wireless networks. However, integrating FD with transmit (Tx) and receive (Rx) phased arrays is extremely challenging, due to the large number of self-interference (SI) channels. Previous work relies on either RF canceller hardware or on analog/digital Tx beamforming (TxBF) to achieve SI cancellation (SIC). However, Rx beamforming (RxBF) and the data rate gain introduced by FD nodes employing beamforming have not been considered yet. We study FD phased arrays with joint TxBF and RxBF with the objective of achieving improved FD data rates. The key idea is to carefully select the TxBF and RxBF weights to achieve wideband RF SIC in the spatial domain with minimal TxBF and RxBF gain losses. Essentially, TxBF and RxBF are repurposed, thereby not requiring specialized RF canceller circuitry. We formulate the corresponding optimization problem and develop an iterative algorithm to obtain an approximate solution with provable performance guarantees. Using SI channel measurements and datasets, we extensively evaluate the performance of the proposed approach in different use cases under various network settings. The results show that an FD phased array with 9/36/72 elements can cancel the total SI power to below the noise floor with sum TxBF and RxBF gain losses of 10.6/7.2/6.9dB, even at Tx power level of 30dBm. Moreover, the corresponding FD rate gains are at least 1.33/1.66/1.68 ×.

Optimal Centralized Dynamic-Time-Division-Duplex

The study of optimal properties of centralized dynamic-time-division-duplex (D-TDD) employed at a wireless network consisting of multiple nodes is a highly challenging and partially understood problem in the literature. In this paper, we develop an optimal centralized D-TDD scheme for a wireless network comprised of K full-duplex nodes impaired by self-interference and additive white Gaussian noise. As a special case, we also propose the optimal centralized D-TDD scheme when part or all nodes in the wireless network are half-duplex. Thereby, we derive the optimal adaptive scheduling of the reception, transmission, simultaneous reception and transmission, and silence at every node in the network in each time slot such that the rate region of the network is maximized. The performance of the optimal centralized D-TDD can serve as an upper-bound to any other TDD scheme, which is useful in qualifying the relative performance of TDD schemes. The numerical results show that the proposed centralized D-TDD scheme achieves significant rate gains over existing centralized D-TDD schemes.

JavaSim-IBFD-CRNs: Novel java simulator for in-band Full-Duplex cognitive radio networks over Internet of Things environment

Multi-channel non-time-slotted cognitive radio ad hoc networks are attractive to researchers nowadays; because they utilize the spectrum efficiently and represent a useful network design for Internet of Things (IoT) applications. From this point, a simulator that mimics these networks is developed using Java language. Further, researchers have proven that many problems facing these networks can be solved by using Full Duplex (FD) nodes. Thus, the proposed simulator is extended to support FD cognitive radio nodes. Each one of these nodes is allowed to receive in a sweeping pattern from various nodes, while transmitting to another node. In an alternative scenario, the node can transmit in a sweeping pattern to various nodes while receiving from one node in a specific direction. Both scenarios are adopted in the route request packet broadcasting phase. However, in the route reply packet delivery, the nodes are allowed to operate in FD transmit and sense or in FD transmit and receive modes. Interestingly, the simulator is tested using FD protocol, also introduced in this paper, that can be useful for IoT applications. Besides the proposed protocol is compared with very recent and close related routing protocol called Probabilistic and Deterministic Path Selection (PDPS). The results are logical; as they are compatible with the theoretical expectations, and the FD protocol surpassed PDPS by almost doubling the throughput.

Secure Degrees of Freedom of MIMO Two-Way Wiretap Channel With no CSI Anywhere

This article considers a two-way multiple-input multiple-output (MIMO) Rayleigh block fading wiretap channel with two full-duplex nodes (Alice and Bob) exchanging messages simultaneously and wiretapped by a $ {N}_{ {e}}$ -antennas eavesdropper (Eve). The channel state remains unchanged over a coherence interval T and is unknown to all terminals, including Alice, Bob, and Eve, at the beginning of the coherence interval. We first show the expression of the optimal signal waveform for Alice and Bob, which maximizes the sum secrecy rate, should be the products of independent random diagonal matrices and isotropically distributed unitary matrices. Then, conditioned on large T and small $ {N}_{ {e}}$ , the upper-bound for the secure degree of freedom (s.d.o.f.) of the two-way wiretap channel is derived, and a constant-norm-signaling (CNS) scheme is presented to achieve this theoretical bound. Finally, we formulate an optimization problem of the s.d.o.f. achieved by the CNS scheme for general cases with arbitrary T and $ {N}_{ {e}}$ , and solve this problem by exploring the monotonicity of the achievable s.d.o.f.. Our result shows that the optimal s.d.o.f. can be independent of coherence time T and becomes the product of the numbers of legitimate nodes’s transmitter antennas (NLNTA) for large $ {N}_{ {e}}$ and small NLNTA.

Secure full duplex OFDM wireless communication based on phase relay between the legitimate nodes

This study proposes a scheme to realise secure orthogonal frequency-division multiplexing (OFDM) wireless communication between two full duplex nodes—node A and node B. If node A wants to send secret messages to node B, node A and node B transmit the training signal to each other to acquire channel state information (CSI) in the first time frame. Node A acquires the phases of the received signal from node B (no need to decode). In the second time frame, node A then sends secret messages to node B with the phases of the modulated signal being added to the random phases of the signal from node B in the previous time frame, i.e node A relaying the phases of the signal from node B. Node B can recover the secret messages from node A, but eavesdroppers cannot because they do not know the CSI of the main channel. The secrecy capacity is irrelevant to the CSI of the eavesdropper channel, which is a big advantage over other schemes. The scheme can guarantee secrecy capacity to be positive in all circumstances and work well for single-input single-output systems. A computation efficient algorithm is presented to optimally allocate power over sub-carriers for secrecy capacity maximisation.

Hybrid Scheduling in Heterogeneous Half- and Full-Duplex Wireless Networks

Full-duplex (FD) wireless is an attractive communication paradigm with high potential for improving network capacity and reducing delay in wireless networks. Despite significant progress on the physical layer development, the challenges associated with developing medium access control (MAC) protocols for heterogeneous networks composed of both legacy half-duplex (HD) and emerging FD devices have not been fully addressed. Therefore, we focus on the design and performance evaluation of scheduling algorithms for infrastructure-based heterogeneous HD-FD networks (composed of HD and FD users). We first show that centralized Greedy Maximal Scheduling (GMS) is throughput-optimal in heterogeneous HD-FD networks. We propose the Hybrid-GMS (H-GMS) algorithm, a distributed implementation of GMS that combines GMS and a queue-based random-access mechanism. We prove that H-GMS is throughput-optimal. Moreover, we analyze the delay performance of H-GMS by deriving lower bounds on the average queue length. We further demonstrate the benefits of upgrading HD nodes to FD nodes in terms of throughput gains for individual nodes and the whole network. Finally, we evaluate the performance of H-GMS and its variants in terms of throughput, delay, and fairness between FD and HD users via extensive simulations. We show that in heterogeneous HD-FD networks, H-GMS achieves 16-30x better delay performance and improves fairness between HD and FD users by up to 50% compared with the fully decentralized Q-CSMA algorithm.

Throughput improvement by mode selection in hybrid duplex wireless networks

Hybrid duplex wireless networks, use half duplex (HD) as well as full duplex (FD) modes to utilize the advantages of both technologies. This paper tries to determine the proportion of the network nodes that should be in HD or FD modes in such networks, to maximize the overall throughput of all FD and HD nodes. Here, by assuming imperfect self-interference cancellation (SIC) and using ALOHA protocol, the local optimum densities of FD, HD and idle nodes are obtained in a given time slot, using Karush–Kuhn–Tucker (KKT) conditions as well as stochastic geometry tool. We also obtain the sub-optimal value of the signal-to-interference ratio (SIR) threshold constrained by fixed node densities, using the steepest descent method in order to maximize the network throughput. The results show that in such networks, the proposed hybrid duplex mode selection scheme improves the level of throughput. The results also indicate the effect of imperfect SIC on reducing the throughput. Moreover, it is demonstrated that by choosing an optimal SIR threshold for mode selection process, the achievable throughput in such networks can increase by around 5%.

Delay-Optimal Cooperation Policy in a Slotted Aloha Full-Duplex Wireless Network: Static Approach

We consider a cooperative wireless communication network comprising two full-duplex (FD) nodes transmitting to a common destination based on slotted Aloha protocol. Each node has exogenous arrivals and also may relay some of the unsuccessfully transmitted packets of the other node. In this article, we find the optimal static policies of nodes in order to minimize the sum of the average transmission delays, while the average transmission delay of each node is constrained. The static policy of each node specifies the probability of accepting an unsuccessfully transmitted packet of the other node and how the node prioritizes its transmissions. We show that in the optimal policies, just the node with the better link to destination may relay the packets of the other node. We derive optimal acceptance probability of the relaying node in closed form, and show that it should transmit the packets of the other node first. Moreover, we prove that the noncooperation policy is optimal if the ratio of successful transmission rates of nodes does not exceed the Golden ratio. We also show that FD capability of nodes is helpful only when full-acceptance is the optimal policy. Efficiency of the attained optimal policy is illustrated by numerical results.

Performance analysis of full‐duplex cellular two‐way relay networks with the Nth worst relay selection under channel estimation error and cochannel interference

AbstractThis paper considers a full‐duplex (FD) cellular multiuser two‐way multirelay network, wherein one Na‐antenna base station communicates bidirectionally with M single‐antenna users via L single‐antenna amplify‐and‐forward relays. A practical scenario where cochannel interference (CCI) and channel estimation error (CEE) present in the network is considered for the investigation. Considering the CEE and interferers at the relays, we formulate the Nth worst relay selection scheme, which consists the best relay selection as a special case. With such relay selection strategy, we derive the tight lower bound (LB) expressions for the overall outage probability, average bit error rate, and ergodic sum rate with CEE and CCI under Rayleigh fading. Furthermore, we deduce the asymptotic expressions for the overall outage probability and average bit error rate at high signal‐to‐noise ratio. Based on the asymptotic outage expression, we present some practical cases of interest, from which the impacts of CCI, CEE, and residual self‐interference (RSI) (imposed on the FD nodes) on system diversity order are presented. It is shown via the numerical results that CEE, CCI, and RSI have detrimental impact on the system performance. Our results also reveal that the impacts of CEE, CCI, and RSI can be alleviated by increasing the number of relays. We also obtain some insights on the self‐interference cancelation requirements for the FD mode. The numerical and simulation results verify our theoretical analysis.

Self-interference cancellation in full-duplex wireless devices: A survey

Full-duplex wireless nodes can transmit and receive at the same time and in the same frequency band, thus effectively doubling the data rate. In these systems, the transmit signal interferes with the receive signal, a phenomena termed as self-interference. Self-interference is a major impediment to realising a full-duplex wireless node. In the recent years, there has been significant research on self-interference mitigation. In this paper, we survey important techniques for self-interference cancellation from the past few years. In particular, we focus on the various RF and baseband self-interference cancellation techniques for realising an ideal full-duplex node.

On the Performance of Distributed MIMO With Full-Duplex Jamming

In this paper, we consider a distributed MIMO system with a set of geographically distributed nodes forming a multi-antenna source $S$ , and a set of geographically distributed full duplex (FD) nodes forming a multi-antenna destination $D$ . $S$ and $D$ each forms a transmit and a receive cluster, respectively. $D$ uses FD mode to jam the signal from $S$ at eavesdropper $E$ , incurring some residual self-interference. We assume that neither $S$ nor $D$ has knowledge of their instantaneous channel state information to $E$ . Furthermore, to simplify the system design, especially for the mobile case, we assume as well that $S$ has no knowledge of the ICSI of its channel to $D$ . Hence, adopting ergodic secrecy rate (ESR) as the performance metric, we are interested in evaluating the ESR averaged over the nodes’ locations, i.e., cluster averaged ESR. To accomplish this, we obtain a lower bound (LB) and an upper bound of the ESR. As part of our work, we also obtain bounds on the cluster averaged ergodic rate between the two clusters. We demonstrate by simulations that the LB can act as a good approximation of the ESR for practical purposes.

Power Allocation for Multi-Hop Transmission Using Unsaturated Full-Duplex Relay Network Model

In a half-duplex relay system, the end-to-end performance decreases significantly as the number of relay nodes increases because each relay node cannot forward a packet until packet reception is completed. In-band full-duplex transmission is considered a promising technology to improve the end-to-end performance of the multi-hop relay system. However, the transmission of full-duplex relay nodes experiences interference from that of other simultaneous relay nodes as well as residual self-interference. We consider a decode-and-forward relay scenario and derive an unsaturated full-duplex relay model that considers packet drops during relay forwarding. We also propose centralized and distributed power adjustment schemes for improving the end-to-end outage performance of the relay system by adjusting the transmit power at each node.

Power allocation and routing for full-duplex multi hop wireless networks under full interference

When traditional half-duplex (HD) radios are employed in indoor wireless mesh networks, such as home networks, interference among mesh nodes is a major impairment, as the end-to-end throughput is to be shared between all transmitting nodes. Full-duplex (FD) relaying can improve the end-to-end throughput, as simultaneous transmissions and receptions, hence simultaneous links are enabled, but FD nodes are subject to self-interference (SI) in addition to inter-node interference, resulting in a more complicated, full interference scenario. In this work, a power allocation solution is proposed along with routing for enabling FD in such multi hop wireless networks subject to full interference. First, an optimization problem is formulated for maximizing the end-to-end throughput of FD relaying on a given, known path, considering the full interference model. A linear programming based solution is devised to obtain the optimal transmit power levels for FD relaying nodes on the path. Then, for joint power allocation and routing in an FD mesh network, Dijkstra’s algorithm is modified by applying the proposed power allocation in the calculation of the path metrics. Via detailed numerical experiments considering different system parameters, such as network size, SI cancellation capability, maximum power level per node, it is shown that the proposed FD relaying with power control based on full interference model outperforms not only HD relaying, but also an existing FD relaying solution based on a single hop interference model. The amount of improvement by FD relaying depends on the system settings. For instance, for low power budget systems, HD throughput can be tripled, while for systems with high power budget, FD relaying achieves 80% higher throughput over HD relaying. When power control is combined with routing, the end-to-end throughput performance of the proposed FD routing solution again outperforms the existing solutions. Depending on the power budget, up to two times higher throughput is achieved over FD routing based on single hop interference, and HD routing can be improved by up to five times even for moderate SI cancellation levels. Our results suggest that employing proposed joint power allocation and routing scheme, migration to FD can be beneficial for home wireless mesh networks under full interference, especially for bandwidth-hungry applications, such as video streaming, gaming.

Hardware Impairments Aware Transceiver Design for Bidirectional Full-Duplex MIMO OFDM Systems

In this paper, we address the linear precoding and decoding design problem for a bidirectional orthogonal frequency-division multiplexing communication system, between two multiple-input multiple-output (MIMO) full-duplex (FD) nodes. The effects of hardware distortion as well as the channel state information error are taken into account. In the first step, we transform the available time-domain characterization of the hardware distortions for FD MIMO transceivers to the frequency domain, via a linear Fourier transformation. As a result, the explicit impact of hardware inaccuracies on the residual self-interference and inter-carrier leakage is formulated in relation to the intended transmit/received signals. Afterwards, linear precoding and decoding designs are proposed to enhance the system performance following the minimum-mean-squared-error and sum rate maximization strategies, assuming the availability of perfect or erroneous channel state information. The proposed designs are based on the application of alternating optimization over the system parameters, leading to a necessary convergence. Numerical results indicate that the application of a distortion-aware design is essential for a system with a high hardware distortion, or for a system with a low thermal noise variance.

Energy efficient MAC protocol for wireless full-duplex networks

The wireless full-duplex (FD) nodes can transmit and receive at the same time using the same frequency-band. Currently, the latest FD media access control (MAC) protocols mainly focus on how to convert the physical layer gains of FD nodes to the throughput gain of wireless FD networks, but pay little attention to the energy consumptions of FD nodes. In this paper, we propose an energy efficient FD MAC protocol. According to the values of self-interference cancellation coefficients corresponding to the nodes of each FD pair and the signal propagation attenuation, the proposed protocol can adaptively select the communication mode of the FD pair between the full-duplex and half-duplex. Also, the minimum transmit power for FD nodes can be obtained to achieve high energy efficiency. We develop an analytical model to characterize the performance of our protocol. The numerical results show that the proposed MAC protocol can optimize the system throughput and reduce the transmission energy consumptions of nodes simultaneously as compared with those of the existing works.

A Stochastic Geometry Approach to Asynchronous Aloha Full-Duplex Networks

In-band full-duplex is emerging as a promising solution to enhance throughput in wireless networks. Allowing nodes to simultaneously send and receive data over the same bandwidth can potentially double the system capacity, and a good degree of maturity has been reached for physical layer design, with practical demonstrations in simple topologies. However, the true potential of full-duplex at a system level is yet to be fully understood. In this paper, we introduce an analytical framework based on stochastic geometry that captures the behaviour of large full-duplex networks implementing an asynchronous random access policy based on Aloha. Via exact expressions we discuss the key tradeoffs that characterise these systems, exploring among the rest the role of transmission duration, imperfect self-interference cancellation and fraction of full-duplex nodes in the network. We also provide protocol design principles, and our comparison with slotted systems sheds light on the performance loss induced by the lack of synchronism.