Half-duplex Networks Research Articles

Ergodic Rate Analysis for Full-Duplex and Half-Duplex Networks with Energy Harvesting

Considering energy harvesting, the ergodic data rates for both in band full-duplex (FD) and half-duplex (HD) wireless communications were studied. The analytic expressions of downlink and uplink ergodic rates for the proposed system were first derived with independent and identically distributed (i.i.d.) Rayleigh fading link. It was revealed that the uplink data rate can be improved by decreasing the downlink data rate. Furthermore, the uplink/downlink data rates are also shown to be influenced by some significance parameters, for example, the power split parameter and signal-to-noise ratio (SNR) (i.e., PS/σ2) of each link. Additionally, unlike the HD, the proposed FD node is capable of harvesting energy during the communication process; however, this is at the cost of performance loss induced by the residual self-interference (RSI), which is caused by the essence of simultaneous uplink and downlink transmissions in a single frequency band.

Sum-Rate Optimization in Flexible Half-Duplex Networks With Transmitter/Receiver Scheduling

In this paper, we focus on the problem of transmitter and receiver scheduling to maximize the achievable sum-rate of a flexible half-duplex network where nodes have the flexibility to either transmit, receive or be silent in a given time slot. We consider a network with multiple transmitters and receivers where each transmitter has specific information it needs to send to a set of receiving nodes. First, we conduct some structural analysis and show that the achievable sum-rate is maximized when each transmitter only transmits to a single receiver at a given time. Next, we consider one instance of the flexible network and by reducing the symmetric multiple receiver network to a single receiver network, we also show that the achievable sum-rate is maximized when either one transmitter or all the transmitters transmit. In fact, there exists a unique received signal-to-noise ratio at which the optimality changes from all-to-one. Finally, we design a novel low-cost algorithm that gives a sub-optimal solution to the achievable sum-rate maximization problem in a flexible half-duplex network. We also provide a comprehensive comparison of the proposed algorithm with respect to existing resource allocation techniques, and observe that our proposed algorithm provides significant sum-rate gains.

Buffer State Based Relay Selection for Half-Duplex Buffer-Aided Serial Relaying Systems

This work investigates multi-hop serial relaying half-duplex (HD) networks comprising one source, one destination and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K$ </tex-math></inline-formula> decode-and-forward (DF) relays. Buffer-aided (BA) relays are considered where finite size buffers are added to relays. For this setup, we propose a novel BA relaying strategy that selects the node that must transmit over one epoch in a block fading environment. Selecting a node depends on the buffer state information of all relays and on the availability of the hops. Moreover, the proposed relaying scheme is controlled by an adjustable parameter that allows the system to achieve multiple levels of tradeoff between the average packet delay (APD) and the outage probability (OP). A Markov chain model is adopted to evaluate the system’s performance and simple closed-form expressions were derived for the APD and OP based on an asymptotic analysis. The performance analysis proves the ability of the suggested relaying scheme to achieve significant OP and APD gains with small buffer sizes. Two variants of the proposed relaying scheme are particularly appealing. The APD-prioritizing variant achieves the smallest APD of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2K$ </tex-math></inline-formula> without improving the diversity order. The second OP-prioritizing variant reaches the full diversity order of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K+1$ </tex-math></inline-formula> while increasing the asymptotic APD to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K(K+3)$ </tex-math></inline-formula> .

A Novel MAC Protocol with Fusion Center and Adaptive Full-Duplex Communication for Cognitive Radio Networks

Cognitive radio network is an intelligent and adaptive communication technology used to effectively utilize the radio spectrum to provide better communication. It enables the secondary (unlicensed) users to communicate over vacant channels without disrupting the communication of the primary (licensed) users. This paper proposes a novel contention-free MAC protocol for full-duplex and half-duplex cognitive radio networks. A novel concept of a fusion center-based channel allocation scheme is proposed to provide better channel allocation and reduced energy consumption. The proposed technique is compared with the existing techniques in terms of the average number of channels being sensed by each user, average wait time, collisions, throughput, and average energy consumption. The number of collisions increases as the maximum allotted time of communication increases in existing approaches. The experiment is performed with 20, 40, 60, and 80 s. The existing approaches show for 20 s, the number of collisions is 65, 61, 68, and 62; for 40 s, the number of collisions is 93, 96, 95, and 92; for 60 s, the number of collisions is 122, 126, 133, and 130; for 80 s, the number of collisions is 176, 170, 173, and 175. The proposed method approaches the number of collisions will become zero as the maximum allotted time of communication increases. The experimental results show that the proposed approach performs better than existing approaches. Moreover, it can be observed that the average waiting time of secondary users when a collision occurs is reduced with the application of a fusion center-based channel allocation scheme.

Research on Key Technology of Full Duplex Cognitive Radio Network

In traditional half duplex cognitive radio networks, secondary users can only sense the spectrum or transmit at a given time. This kind of half duplex network limits the throughput of users, because the user unit can’t transmit data in spectrum sensing. However, with the development of self-interference suppression (SIS) technology, full duplex cognitive radio network allows spectrum sensing and data transmission on a given channel at the same time. Compared with traditional half duplex network, full duplex network improves throughput and reduces conflicts. In order to explore the future development direction of spectrum sensing technology, in the context of full duplex cognitive radio, a comprehensive study of radio network is carried out, including key technologies, current challenges and future research directions.

Optimal and Approximation Algorithms for Joint Routing and Scheduling in Millimeter-Wave Cellular Networks

Millimeter-wave (mmWave) communication is a promising technology to cope with the exponential increase in 5G data traffic. Such networks typically require a very dense deployment of base stations. A subset of those, so-called macro base stations, feature high-bandwidth connection to the core network, while relay base stations are connected wirelessly. To reduce cost and increase flexibility, wireless backhauling is needed to connect both macro to relay as well as relay to relay base stations. The characteristics of mmWave communication mandates new paradigms for routing and scheduling. The paper investigates scheduling algorithms under different interference models. To showcase the scheduling methods, we study the maximum throughput fair scheduling problem. Yet the proposed algorithms can be easily extended to other problems. For a full-duplex network under the no interference model, we propose an efficient polynomial-time scheduling method, the {\em schedule-oriented optimization}. Further, we prove that the problem is NP-hard if we assume pairwise link interference model or half-duplex radios. Fractional weighted coloring based approximation algorithms are proposed for these NP-hard cases. Moreover, the approximation algorithm parallel data stream scheduling is proposed for the case of half-duplex network under the no interference model. It has better approximation ratio than the fractional weighted coloring based algorithms and even attains the optimal solution for the special case of uniform orthogonal backhaul networks.

Self-Optimizing Wireless Networks on Structures

This brief proposes half-duplex wireless networks that use acoustic guided waves traveling on or through structures for physically-secure long-range power and data telemetry. It also develops a protocol for such networks to optimize their power and data delivery to compensate for slowly-varying factors like temperature and structural damage. Specifically, near-maximum power point tracking (nMPPT) is implemented by searching for the optimal transmission frequency in complex acoustic channels. Binary frequency shift keying (BPSK) modulated on the power waveform is proposed for downlink. A power-efficient fast uplink is achieved by using Non Return to Zero - Inverted (NRZ-I) data encoding. Data security is naturally ensured by the unique channel responses defined by the transceivers’ physical locations. Miniature smart sensor nodes with a quiescent power of 4.8 $\mu \text{W}$ and a peak power of $\sim 200~\mu \text{W}$ have been developed for such sparse networks. The proposed half-duplex telemetry approach is experimentally evaluated on a structural health monitoring (SHM) test bed and achieves a power transfer of $\sim 181.8~\mu \text{W}$ at 0.5 m and a BER of 10−4 for a 80 bps downlink driven at 20 $\text{V}_{pp}$ , and a BER of 10−4 for a 2 Mbps uplink driven at $\sim 2~\text{V}_{pp}$ .

Successive Relaying for Two-Hop Two-Destination Multicarrier Relay Channels

We propose a successive relaying decode-and-forward protocol for the half-duplex 2-relay 2-destination multicarrier channel. The proposed protocol performs significantly better than existing protocols and achieves sum rates close to the cutset upper bound. We also prove that the linear program that describes the cutset upper bound for sum capacity is optimized using only 3 of the 4 possible states of the half-duplex network. Of these 3 states, successive relaying uses the two states in which one of the relays is receiving from the source while the other relay is transmitting to the destinations. In simulations under a Rayleigh fading model, the gap between the cutset upper bound and the proposed protocol is observed to be bounded.

Inter-Client Interference Cancellation for Full-Duplex Networks With Half-Duplex Clients

Recent studies have experimentally shown the gains of full-duplex radios. However, due to its relatively higher cost and complexity, we can envision a more practical step in the network evolution is to have a full-duplex access point (AP) but keep the clients half-duplex. Unfortunately, the full-duplex gains can hardly be extracted in practice as the uplink transmission from a half-duplex client introduces inter-client interference to another downlink client. To address this issue, we present the design and implementation of IC2 (Inter-Client Interference Cancellation), the first physical layer solution that exploits the AP’s full-duplex capability to actively cancel the interference at the downlink client. Such active cancellation not only improves the achievable capacity, but also better tolerates imperfect user pairing, simplifying the MAC design as a result. We build a prototype of IC2 on USRP-N200 and evaluate its performance via both testbed experiments and large-scale trace-driven simulations. The results show that, without IC2 , about 60% of client pairs produce no gain from full-duplex transmissions, while, with IC2 the median gain of the achievable rate over conventional half-duplex networks can be $1.65\times $ and $1.47\times $ for 1- and 2-antenna scenarios, respectively, even when clients are simply paired randomly.

Full-Duplex MAC Protocol for CSMA/CA-Based Single-Hop Wireless Networks.

Full-duplex (FD) communication provides new opportunities for improving the throughputs of networks. However, this condition means that the number of senders increases from one to two within a certain range. We have to arrange the two nodes to send frames simultaneously in the media access control (MAC) layer. For the single-hop network model, using the FD features of the nodes and the cut-through mechanism, we propose an FD MAC protocol. The protocol improves the throughput of the network from the following two aspects. On the one hand, during the transmission of each node, based on the information of the received frame’s header, the protocol can detect collisions in the network, preventing the channel from being ineffectively occupied for a long time. On the other hand, the protocol can provide the FD with as many opportunities as possible for the nodes. According to the working process of the protocol, we modeled the states (“active” and “passive” transmission, back-off) of each node and their transitions to a Markov chain. We solved the “active” transmission probability of the node and further modeled the analytical performance of the protocol. The simulation results showed that the system throughput produced by our protocol was at least twice that of the conventional CSMA/CA protocol used in the half-duplex networks.

Outage behaviour and SCK‐based power allocation for analogue network coding protocol in cooperative networks

In this study, the authors consider the communication scenario where two sources communicate with the help of a single relay, modelled as a half-duplex butterfly network. Closed-form expressions of the outage probabilities are derived in the high signal-to-noise ratio (SNR) regime for the orthogonal amplify-and-forward and non-orthogonal amplify-and-forward protocols. Then the expressions are approximated to enable power allocation. Closed-form power allocation schemes are proposed for each protocol, where only statistical channel knowledge is required. It is shown that the authors analyses match well with simulation results and the approximated versions are very close to the simulation results. The proposed power allocation schemes achieve a large SNR gain over the equal-power strategies and approach the optimal power allocation schemes.

Hybrid full-/half-duplex cellular networks: user admission and power control

We consider a single-cell network with a hybrid full-/half-duplex base station. For the practical scenario with N channels, K uplink users, and M downlink users (max{K,M} ≤ N ≤ K + M), we tackle the issue of user admission and power control to simultaneously maximize the user admission number and minimize the total transmit power when guaranteeing the quality-of-service requirement of individual users. We formulate a 0–1 integer programming problem for the joint-user admission and power allocation problem. Because finding the optimal solution of this problem is NP-hard in general, a low-complexity algorithm is proposed by introducing the novel concept of adding dummy users. Simulation results show that the proposed algorithm achieves performance similar to that of branch and bound algorithm and significantly outperforms the random pairing algorithm.

A Dynamic Addressing Protocol on Code Messages for an Underwater Wireless Half Duplex Networks of Autonomous Sensors

This paper presents the new protocol for the organization of dynamic addressing nodes in the underwater wireless networks. In view of the extremely limited frequency band and significant delays inherent in the underwater acoustic data transmission channel, as well as the nonlinearity of the propagation paths of the acoustic signal in water, an approach is proposed for constructing a dynamic addressing protocol based on avoiding collisions at the receiving point. The protocol takes into account the peculiarities of the physical layer of the data transmission and is designed for servicing the network of autonomous non-synchronized nodes.

A Dynamic Addressing Protocol on Code Messages for an Underwater Wireless Half Duplex Networks of Autonomous Sensors

This paper presents the new protocol for the organization of dynamic addressing nodes in the underwater wireless networks. In view of the extremely limited frequency band and significant delays inherent in the underwater acoustic data transmission channel, as well as the nonlinearity of the propagation paths of the acoustic signal in water, an approach is proposed for constructing a dynamic addressing protocol based on avoiding collisions at the receiving point. The protocol takes into account the peculiarities of the physical layer of the data transmission and is designed for servicing the network of autonomous non-synchronized nodes.

The Value of Full-Duplex for Cellular Networks: A Hybrid Duplex-Based Study

Recent work has demonstrated the gain of full-duplex (FD) network over half-duplex (HD) network in bidirectional sum throughput under the assumption of symmetric uplink-downlink traffic demands and perfect self-interference suppression (SIS). In this paper, we study the performance gain of FD network over HD network under asymmetric bidirectional traffic demands and non-ideal SIS. To this end, we investigate the traditional static time division duplex (TDD) transmission mode and the advanced dynamic TDD transmission mode to obtain the performance of HD network, and investigate the pure FD transmission mode and a flexible HD-FD hybrid transmission mode, namely, XD mode, to obtain the performance of FD network. We use the number of users supported by a network as performance metric, which is defined as the minimum of the weighted numbers of users supported in uplink and downlink given random traffic demands of users. To maximize the number of users, we optimize the bidirectional transmit power for pure FD mode, bidirectional time slot configuration for dynamic TDD mode, and both for XD mode. Numerical results show an evident gain of pure FD mode and XD mode over static TDD mode for different levels of traffic asymmetry, but the gain over dynamic TDD mode is marginal, which cannot justify the application of FD technology in cellular systems without advanced interference control mechanisms.

Adaptive Transmission Protocols for Fountain-Coded Multicast in Packet Radio Networks

Fountain coding is a valuable tool for multicast transmissions in half-duplex packet radio networks if it is supported by an adaptive transmission protocol that compensates for fluctuations in the propagation losses on the radio links. Our goal is to devise low-complexity packet-by-packet adaptive modulation and channel coding protocols that provide high throughput for a broad range of multicast channels and operate with limited feedback and no knowledge of the fade levels or even the probability distribution for the fading on the radio links. The only control information for the protocols is derived from simple receiver statistics that are obtained by the demodulators and channel decoders in the receiving radios. Performance results are presented for practical fountain coding with low-complexity adaptive modulation and channel coding. Results on ideal fountain coding with adaptive transmission based on hypothetical perfect channel-state information are employed as performance benchmarks.

Impact of Full Duplex Scheduling on End-to-End Throughput in Multi-Hop Wireless Networks

There have been some rapid advances on the design of full duplex (FD) transceivers in recent years. Although the benefits of FD have been studied for single-hop wireless communications, its potential on throughput performance in a multi-hop wireless network remains unclear. As for multi-hop networks, a fundamental problem is to compute the achievable end-to-end throughput for one or multiple communication sessions. The goal of this paper is to offer some fundamental understanding on end-to-end throughput performance limits of FD in a multi-hop wireless network. We show that through a rigorous mathematical formulation, we can cast the multi-hop throughput performance problem into a formal optimization problem. Through numerical results, we show that in many cases, the end-to-end session throughput in a FD network can exceed 2x of that in a half duplex (HD) network. Our finding can be explained by the much larger design space for scheduling that is offered by removing HD constraints in throughput maximization problem. The results in this paper offer some new understandings on the potential benefits of FD for end-to-end session throughput in a multi-hop wireless network.

Buffer-Aided Diamond Relay Network With Block Fading and Inter-Relay Interference

A simple diamond half-duplex relay network composed of a source, two decode-and-forward half-duplex relays, and a destination is considered, where a direct link between the source and the destination does not exist. For this network, we study the case of buffer-aided relays, where the relays are equipped with buffers. Each relay can receive data from the source, store it in the buffer, and forward it to the destination, when the channel conditions are advantageous. Thereby, buffering enables adaptive scheduling of the transmissions and receptions over time, which allows the network to exploit the diversity offered by the fading channels. For the considered half-duplex network, four transmission modes are defined based on whether the relay nodes receive or transmit. In this paper, we derive the locally optimal scheduling of the transmission modes over time and investigate the achievable average rate, when the relays are affected by inter-relay interference. Since the proposed buffer-aided transmission policies introduce unbounded delay, we provide a sub-optimal buffer-aided transmission policy with limited delay. Moreover, for inter-relay interference cancellation, we consider two coding schemes with different complexities. In the first scheme, we employ dirty paper coding, which entails a high complexity, whereas in the second scheme, we adopt a low-complexity technique based on successive interference cancellation at the receiving relay nodes and optimal power allocation at the transmitting nodes. Our numerical results show that the proposed protocols, with and without delay constraints, outperform existing protocols for the considered network from the literature.

On the Capacity Gain from Full Duplex Communications in a Large Scale Wireless Network

Compared to half duplex communications, full duplex communications can significantly improve link capacity. However, in a large scale wireless network such as a wireless mesh network, the capacity gain from full duplex communications has not been fully investigated. To this end, a metric of network capacity called transmission capacity is studied in this paper for a full duplex wireless network. It captures the maximum transmission throughput in a unit area, subject to a certain outage probability. The key challenge of deriving transmission capacity is to characterize the aggregate interference of the typical link in a full duplex wireless network, which is completely different from that in a half duplex wireless network. In this paper, stochastic geometry is employed to model the network topology as a Thomas cluster point process and then the aggregate interference is characterized as a shot-noise process. Based on these models, the transmission capacity is derived. Analytical results show that under the same network density the distribution of aggregate interference in a full duplex wireless network is more dispersed than that in a half duplex wireless network. Comparisons of transmission capacity between a full duplex network and a half duplex network reveal that the capacity gain from full duplex communications is limited due to severe aggregate interference. This result implies that self-interference cancellation alone cannot ensure scalable full duplex wireless networking.

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