In Band Full Duplex (IBFD) Technology for Next Generation Wireless Networks: A Survey in Cellular Networks

Next-Generation(NextG)wireless communication networks with their widespread applications require high data rates,seamless connectivity and high quality of service(QoS).To cope up with an unprecedented rise of data hungry applications,users demand more spectral resources imposing a limitation on available wireless spectrum.One of the potential solutions to address the spectrum scarce issue is to incorporate in band full duplex(IBFD)or full duplex(FD)paradigm in next generation networks including 5G new radio(NR).Recently,FD has gained the research interest in cellular networks for its potential to double the wireless link capacity and enhancing spectral efficiency(SE).In half duplex(HD)cellular networks,base stations(BSs)can either perform uplink(UL)or downlink(DL)transmission at a particular time instant leading to reduced throughput levels.Due to the advancement in the self interference reduction(SIR)techniques,full duplex base stations(FD-BSs)can be employed to allow simultaneous UL and DL transmissions at the same time–frequency resources as compared to its HD counterpart.It ideally achieves twice the throughput without any additional complexity at user-equipment(UE).This paper covers a detailed survey on FD cellular networks.A series of SIR approaches,UE-UE mitigation techniques are summarized.Various existing MAC protocols and antenna architectures for FD cellular networks are outlined.An overview of security aspects for FD in cellular networks is also presented.Lastly,various open issues and possible research directions are brought up for FD cellular networks.

Analysis of RF Feedback Chain Isolation in Wireless Co-Time Co-Frequency Full Duplex

By employing a radio frequency(RF) feedback chain, the self-interference can be canceled efficiently in co-time co-frequency full duplex(CCFD). However, the evitable signal crosstalk which is caused by the imperfect RF feedback chain isolation usually damages the self-interference cancelation(SIC) performance. To deal with this problem, firstly, we analyze the impact of RF feedback chain isolation on SIC performance. Then a digital preprocessing scheme with RF feedback chain is proposed in the multiple-antenna CCFD architecture. Using both analytical and experimental methods, we find that the proposed scheme achieves a better performance on SIC.

Wireless Relay Communication on High Speed Railway：Full Duplex or Half Duplex？

In this paper,we introduce one full-duplex(FD) relaying transmission scheme for high speed railway and compare its ergodic capacity and outage performance with half-duplex(HD) relaying scheme. Both decode-and-forward(DF) amplify-and-forward(AF) relay modes are considered. Moreover,the carriage penetration loss(CPL) and the self-interference(SI) cancellation ratio are investigated. We derive the closed-form expressions for the outage probability and ergodic capacity of both HD and FD relay transmission schemes. It is shown that when CPL is larger than a certain level,the FD relay can achieve better performance in terms of capacity and keep the outage probability in a low level. It is also found that three factors: AF or DF modes,CPL and SI cancellation ratio,can have impact on capacity performance,and that CPL is one decisive factor. Our results can provide theoretical supports for development and deployment of future wireless communication systems on high speed railways.

Robust Digital Non-Linear Self-Interference Cancellation in Full Duplex Radios with Maximum Correntropy Criterion

Full duplex radio increases the frequency efficiency but its performance is limited by the self-interference （SI）. We first analyze the multiple noises in the full duplex radio system and model such noises as an α - stable distribution. Then we formulate a novel non-Gaussian SI problem. Under the maximum correntropy criterion （MCC）, a robust digital non-linear self-interference cancellation algorithm is proposed for the SI channel estimation. A gradient descent based algorithm is derived to search the optimal solution. Simulation results show that the proposed algorithm can achieve a smaller estimation error and a higher pseudo signal to interference plus noise ratio （PSINR） than the well-known least mean square （LMS） algorithm and least square （LS） algorithm.

Polarization Oblique Projection Based Self-Interference Cancellation against PA Nonlinear Distortion in MIMO Full Duplex System

In MIMO full duplex system,power amplifier(PA) nonlinearity limits the self-interference(SI) cancellation seriously. Most existing methods need to model and estimate the PA nonlinearity in order to reconstruct the SI,however the estimation error caused by the mismatch between the estimated PA model and the actual PA property still impacts the cancellation ability,especially when the transmit power is high. In this paper we propose a polarization oblique projection based self-interference cancellation method which does not need to estimate the PA nonlinearity coefficients. It exploits the polarization state information of the signals which is immune to the PA nonlinearity,and establishes an oblique projection operator to cancel the SI. Numerical results and analysis demonstrate that it can cancel the nonlinear SI effectively. Moreover the signal to interfere plus noise ratio(SINR) and the achievable sum rate do not deteriorate when the transmit power is high. Further,the upper bound of the achievable sum rate can be more than twice that of the half duplex.

A High Spectral Efficiency System Enabled by Free Window with Full Duplex

This paper studies the capacity issues of a wireless communication system that implements single channel full duplex(SCFD) communication at the base station(BS), thereby the mobile stations share the channel via time division duplex(TDD). The system makes use of the same setup as has been used in previous studies of SCFD, but unlike these previous systems, the new system uses water-filling to maximize the spectral efficiency of the uplink channel. The concept of a free window is introduced to the duplex model for measuring, intuitively, the effective bandwidth of the bi-directional communication. The capacity gain is calculated and numerical results show the advantage of the proposed system over that of conventional TDD.

On distributed power control in full duplex wireless networks

In this paper, we first consider the problem of distributed power control in a Full Duplex （FD） wireless network consisting of multiple pairs of nodes, within which each node needs to communicate with its corresponding node. We aim to find the optimal transmition power for the FD transmitters such that the network-wide capacity is maximized. Based on the high Signal-to-Interference-Plus-Noise Ratio （SINR） approximation and a more general approximation method for logarithm functions, we develop effective distributed power control algorithms with the dual decomposition approach. We also extend the work to the general FD network scenario, which can be decomposed into subproblems of isolated nodes, paths, and cycles. The corresponding power control problem is then be solved with the distributed algorithm. The proposed algorithms are validated with simulation studies.

Co-Channel Interference Suppression Techniques for Full Duplex Cellular System

Co-frequency and co-time full duplex(CCFD) is a promising technique for improving spectral efficiency in next generation wireless communication systems. However, for the applications of CCFD in a cellular network, severe co-channel interference is an essential problem. Specifically, there are two significant interferences, i.e., inter-terminal interference(ITI) and inter-cell interference(ICI), which lead to an obvious performance degradation. In this paper, two techniques are proposed for suppressing the ITI and ICI in a CCFD cellular system, respectively. The first technique is obtained by modeling the three-node CCFD system as the Z-channel. After deriving the sum-capacity of the Z-channel, a sum-capacity-achieving scheme based on successive interference cancellation(SIC) is proposed. The second technique is designed by combining the fractional frequency reuse scheme with CCFD. The performance gains of the proposed two techniques in terms of signalto-interference plus noise ratio(SINR) and sumcapacity are analyzed. Simulation results show that the proposed scheme can achieve significant interference suppression performance and higher system capacity, especially for cell edge users.

Time-Hopping Sequence Design for Virtual Full Duplex via Rapid On-Off-Division Duplex

To achieve virtual full-duplex(VFD)communication using half-duplex radios,the rapid on-off-division(RODD)technique has been proposed in recent years.The time-hopping(TH)sequence is critical to controlling self-interference introduced in the paradigm.By constructing the collision model with a symbol level time scale,the periodic collision correlation function properties are introduced as the performance metric for the TH sequence in the RODD system.To achieve the best VFD performance,an optimization-based method for TH sequence design is proposed.In addition,the conventional TH frame structure design for RODD system is improved.Numerical simulations are presented to demonstrate that the proposed approach can significantly increase system performance.Results indicate that the TH sequence design is very effective for the RODD system.

Asymptotic Analysis and Precoding Design of Integrated Access and Backhaul in Full-Duplex mmWave Networks

In this paper,we consider a full-duplex(FD)millimeter wave(mmWave)multiuser integrated access and backhaul(IAB)system with massive MIMO,and the system asymptotic performance and interference cancellation schemes are investigated.First,the asymptotic performance of the IAB system with massive MIMO is analyzed.As the number of macro base station(MBS)and small base station(SBS)antennas approaches infinity,the FD selfinterference(SI),inter-tier interference and noise can be eliminated,which means that only multiuser interference remains in the system.Then,multiuser interference can be suppressed by the base band(BB)precoders.Since all interference and noise are suppressed,the spectral efficiency of the SBS and users are infinite in theory.Then,two interference suppression precoding schemes are proposed.A block diagonalization(BD)-based interference cancellation scheme is designed based on the channel characteristics and null space projection.The FD SI,intertier interference and multiuser interference are eliminated by BB precoders.Instead of eliminating interference completely,a signal to leakage and noise ratio(SLNR)-based precoding scheme is derived to suppress both interference and noise.By utilizing the Rayleigh-Ritz theorem,the SLNRs of the SBS and users are optimized.Simulation results show that all the interference can be effectively eliminated by the BD-based scheme at the cost of spectral efficiency performance loss,while the SLNR-based scheme can balance interference and noise and achieve higher spectral efficiency with comparatively low interference level.Therefore,the BD-based scheme is more suitable for interference elimination cases,and the SLNRbased scheme can improve the system performance in low interference scenarios.

Full Duplex Communications for Next Generation Cellular Networks:The Capacity Gain

Full duplex communication highly improves spectrum efficiency of a wireless communication link.However, when it is applied to a cellular network, the capacity gain from this technology remains unknown. The reason is that full duplex communication changes the aggregate interference experienced by each communication link in cellular networks. In this paper, the capacity gain from full duplex communication is studied for cellular networks of 4G and beyond, where the same frequency channel is adopted in each cell. A two-layer Poisson point process(PPP) is adopted to model the network topology, and stochastic geometry is employed to derive the coverage probability and the average capacity of typical link in a cellular network. On the basis of these derived parameters, the capacity gain from full duplex communication is determined. Numerical results reveal that without mutual interference cancellation(MIC), the capacity gain is small under various power levels; with perfect MIC at base stations, the capacity gain can exceed 60%; with imperfect MIC at base stations, the capacity gain decreases quickly even with a slight drop of MIC performance.

Rate-Energy Tradeoff for Wireless Simultaneous Information and Power Transfer in Full-Duplex and Half-Duplex Systems

In this paper,we study the rate-energy tradeoff for wireless simultaneous in-formation and power transfer in full-duplex and half-duplex scenarios.To this end,the weighting function of energy efficiency and transmission rate,as rate-energy tradeoff metric is first introduced and the metric optimization problem is formulated.Applying Karush-Kuhn-Tucker(KKT)conditions for Lagrangian optimality and a series of mathematical approximations,the metric optimization problem can be simplified.The closed-form solution of the power ratio is obtained,building direct relationship between power ratio and the rate-energy tradeoff metric.By choosing power ratio,one can make the tradeoff between information rate and harvested power in a straightforward and efficient way.Using the method similar to the half duplex systems,the optimal power ratio can be obtained in the full duplex systems,so as to balance the information transmission rate and energy transmission efficiency.Simulation results validate that the information rate is non-increasing with harvested power in half-duplex systems and the tradeoff of information rate and harvested power can be simply made.In the full duplex systems,the power ratio solution of the rate-energy tradeoff metric optimization problem can be used as the approximate optimal solution of the optimization problem and the approximation error is negligible.

The Full-Duplex Artificial Noise Scheme for Security of a Cellular System

This paper focuses on the problem of secure transmission in a cellular system. A full-duplex base station using artificial noise is adopted to improve both the uplink and downlink secrecy rate via pairing terminals which reverses the downlink and uplink of each other. We give the designs of artificial noise and the user's desired signal, and derive the pairing prin-ciple between terminals. Moreover, the influence of self-interference cancellation on secrecy rate is ex-plored. Simulation results show that the secrecy rate can get much better performance by adopting full-duplex artificial noise scheme and proposed pair-ing method. The downlink secrecy rate decreases with the distance between terminals. Besides the uplink secrecy rate is sensitive to the ability of self-interference cancellation.

Joint Transceiver Designs for Full-Duplex MIMO SWIPT Systems Based on MSE Criterion

For the simultaneous wireless information and power transfer(SWIPT), the full-duplex MIMO system can achieve simultaneous transmission of information and energy more efficiently than the half-duplex. Based on the mean-square-error(MSE) criterion, the optimization problem of joint transceiver design with transmitting power constraint and energy harvesting constraint is formulated. Next, by semidefinite relaxation(SDR) and randomization method, the SDRbased scheme is proposed. In order to reduce the complexity, the closed-form scheme is presented with some simplified measures. Robust beamforming is then studied considering the practical condition. The simulation results such as MSE versus signal-noise-ratio(SNR), MSE versus the iteration number, well prove the performance of the proposed schemes for the system model.

Channel Estimation for Full-Duplex Relay Transmission in Cloud Radio Access Networks

Relay in full-duplex(FD) mode can achieve higher spectrum efficiency than that in half-duplex mode,while it is crucial to suppress relay self-interference to ensure transmission quality which requires instantaneous channel state information(CSI). In this paper,the channel estimation issue in FD amplify-andforward relay networks is considered,where the training-based estimation technique is adopted. Firstly,the least square(LS) estimation is implemented to obtain composite channel coefficients of source-relay-destination(SRD) channel and relay loop-interference(LI) channel in order to assist destination in performing data detection. Secondly,both LS and maximum likelihood estimation methods are utilized to perform individual channel estimation aiming at supporting successive interference cancelation at destination. Finally,simulation results demonstrate the effectiveness of both composite and individual channel estimation,and the presented ML method can achieve lower MSEs than LS solution.

A Novel Forwarding Method for Full-Duplex Two-Way Relay Networks

An estimate-and-forward(EF) scheme for single-input single-output(SISO) and multiple-input multiple-output(MIMO) full-duplex two-way relay networks is proposed and analyzed. The relay estimates the received signal from two terminal nodes by a minimum mean squared error(MMSE) estimation and forwards a scaled version of the MMSE estimate to the destination. The proposed EF outperforms conventional amplify-and-forward(AF) and decode-and-forward(DF) across all signal-to-noise ratio(SNR) region. Because its computational complexity is high for relays with a large number of antennas(large MIMO) and/or high order constellations, an approximate EF scheme, called list EF, are thus proposed to reduce the computational complexity. The proposed list EF computes a candidate list for the MMSE estimate by using a sphere decoder, and it approaches the performance of the exact EF relay at a negligible performance loss. The proposed forwarding approach also could be used to other relay networks, such as half-duplex, one-way or massive MIMO relay networks.

Secure Power and Subcarrier Auction in Uplink FullDuplex Cellular Networks

We consider a cellular network with a full-duplex base station, multiple uplink users and an eavesdropper. The full-duplex base station transmits jamming signals to degrade the eavesdropper channel when receiving secure multi-user signals. To maximize the secrecy rate of uplink communications, we propose a distributed ascending-clock auction(ACA) algorithm to allocate subcarriers and jamming power. Specifically, the impact of the self-interference of the full-duplex base station on the secrecy rate is considered. The proposed algorithm consists of two parts. Firstly, subcarriers and the jamming power are respectively priced by the base station. Secondly, users select the subcarrier and the jamming power based on the price. Moreover, the convergence of the proposed auction algorithm is mathematically proved. Simulation results show that the proposed auction algorithm is more beneficial to improve the uplink secrecy performance compared to traditional auction algorithms.

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.

High-Performance Beamformer and Low-Complexity Detector for DF-Based Full-Duplex MIMO Relaying Networks

In this paper, we consider a full.duplex multiple.input multiple.output(MIMO) relaying network with the decode.and.forward(DF) protocol. Due to the full.duplex transmissions, the self.interference from the relay transmitter to the relay receiver degrades the system performance. We thus propose an iterative beamforming structure(IBS) to mitigate the self.interference. In this method, the receive beamforming at the relay is optimized to maximize the signal.to.interference.plus.noise.ratio(Max.SINR), while the transmit beamforming at the relay is optimized to maximize the signal.to.leakage.plusnoise.ratio(Max.SLNR). To further improve the performance, the receive and transmit beamforming matrices are optimized between Max.SINR and Max.SLNR in an iterative manner. Furthermore, in the presence of the residual self.interference, a low.complexity whitening.filter(WF) maximum likelihood(ML) detector is proposed. In this detector, a WF is designed to transform a colored interference.plus.noise to a white noise, while the singular value decomposition is used to convert coupled spatial subchannels to parallelindependent ones. From simulations, we find that the proposed IBS performs much better than the existing schemes. Also, the proposed low.complexity detector significantly reduces the complexity of the conventional ML(CML) detector from exponential time(an exponential function of the number of the source transmit antennas) to polynomial one while achieving a slightly better BER performance than the CML due to interference whitening.

Secure Beamforming Design for SWIPT in MISO Full-Duplex Systems

This paper investigates the problem of bi-directional secure information exchange for a multiple-input single-output(MISO)broadcast channel in presence of potential and external eavesdroppers capable of decoding the confidential messages.Specifically,a multi-antenna base station(BS)simultaneously sends wireless information and power to a set of dual-antenna mobile stations(MSs)using power splitters(PSs)in the downlink and receives information in the uplink in full-duplex(FD)mode.We address the joint design of the receiver PS ratio and the transmit power at the MSs,the artificial noise covariance,and the beamforming matrix at the BS in order to guarantee the individual secrecy rate and energy harvesting constraints at each receiver,and the signal-tointerference plus noise ratio(SINR)at the BS and MSs.Using semidefinite relaxation(SDR)technique,we obtain solution to the problem with imperfect channel state information(CSI)of the self-interfering channels.Simulation results are presented to demonstrate the performance of our proposed scheme.