Imperfect Self-interference Research Articles

Hybrid Duplex Wireless Peer Discovery With Imperfect Self-Interference Cancellation

This letter investigates the hybrid duplex wireless peer discovery (Hyb-WPD) that increases the average number of discovered peers (ADP), through arbitrating between half duplex and full duplex (FD) operations. FD allowing simultaneous tranceiving inherently introduces residual self-interference (RSI) due to non-ideal implementation; thus, this impairment yields a new design issue for transmission probability, which determines whether a peer receives or tranceives. This letter proposes the design principles for the Hyb-WPD depending on RSI through mathematically analyzing the ADP, and the numerical results demonstrate their performance.

Half-Duplex or Full-Duplex Communications: Degrees of Freedom Analysis Under Self-Interference

In-band full-duplex (FD) communication provides a promising alternative to half-duplex (HD) for wireless systems, due to increased spectral efficiency and capacity. In this paper, HD and FD radio implementations of two way, two hop and two way two hop communication are compared in terms of degrees of freedom (DoF) under a realistic residual self-interference (SI) model. DoF analysis is carried out for each communication scenario for HD, antenna conserved (AC) and RF chain conserved (RC) FD radio implementations. The DoF analysis indicates that for the two way channel, the achievable AC FD with imperfect SI cancellation performs strictly below HD, and RC FD DoF trade-off is superior when the SI can be sufficiently cancelled. For the two hop channel, FD is better when the relay has large number of antennas and enough SI cancellation. For the two way two hop channel, when both nodes require similar throughput, the achievable DoF pairs for FD do not outperform HD. FD still can achieve better DoF pairs than HD, provided the relay has sufficient number of antennas and SI suppression.

Secure Communications for the Two-User Broadcast Channel With Random Traffic

In this paper, we study the stability region of the two-user broadcast channel (BC) with bursty data arrivals and security constraints. It is assumed that one of the receivers has a secrecy constraint, i.e., its packets need to be kept secret from the other receiver, which is defined based on signal to interference noise ratio. The receiver with secrecy constraint has full-duplex capability to send a jamming signal for improving its service rate. The stability region of the two-user BC with secrecy constraint is characterized for the general decoding case. Then, assuming two different decoding schemes, the respective stability regions are derived. The full-duplex operation of receiver results in self-interference, and the effect of imperfect self-interference cancelation on the stability region is also investigated. The stability region of the BC with a secrecy constraint, where the receivers do not have full duplex capability can be obtained as a special case of the results derived in this paper. In addition, the paper considers the problem of maximizing the saturated throughput of the queue for which there is no secrecy constraint under minimum service guarantees for the other queue. The results provide new insights on the effect of the secrecy constraint on the stability region of the BC. It is found that the stability region with secrecy constraint is sensitive to the degree of self-interference cancelation.

Capacity Improvement for Full Duplex Device-to-Device Communications Underlaying Cellular Networks

In this paper, the capacity improvement of full-duplex (FD) device-to-device (D2D) underlaying cellular networks (CNs) is analyzed. A single-cell environment is considered with one half-duplex (HD) base station, multiple HD cellular user equipments (CUEs), and one pair of FD D2D user equipments (DUEs). The BS is equipped with ${M}$ multiple antennas, and one pair of FD DUEs is permitted to share the same resource with ${M}$ out of ${K}$ uplink HD CUEs, which will lead to a more complex interference environment. First, a novel interference-limited area-based (ILA-based) scheme is proposed to manage the co-channel interference from CN CUEs to FD DUEs. The ILA-based scheme does not allow the coexistence of HD CUEs and FD DUEs if the HD CUEs are located in any region of the two ILAs. Next, a senior ILA-based (SILA-based) scheme is proposed to reduce the complexity of the ILA-based scheme, in which only a common ILA is designed for both FD DUEs instead of the two ILAs in the ILA-based scheme. Then, the lower bounds of the ergodic capacity for FD D2D communications with imperfect self-interference cancellation (SIC) are derived in closed-forms with the ILA-based scheme and the SILA-based scheme. Furthermore, the capacity gain of the FD D2D communications is analyzed, and the numerical results show that the capacity improvement of the FD D2D communications is much greater than the traditional HD D2D communication if the sufficient SIC is achieved.

Full-Duplex Cooperative Non-Orthogonal Multiple Access With Beamforming and Energy Harvesting

In this paper, a novel communication scheme that combines beamforming, energy harvesting, and cooperative non-orthogonal multiple access (NOMA) system is introduced. In the proposed scheme, NOMA is first combined with beamforming to serve more than one user in each beamforming vector. Later, simultaneous wireless information and power transfer (SWIPT) technique is exploited to encourage the strong user to relay the weak user’s information messages in full-duplex (FD) manner. However, one major drawback of FD communications is the self-interference (SI) signal due to signal leakage from terminal’s output to the input. Three different cases are adopted. In the first case, the SI signal is assumed to be fully cancelled at the strong user using SI cancellation techniques. In the second case, SI is only cancelled at the information decoding circuits, while being harvested in the energy harvester to provide extra energy. The third case investigates the impact of imperfect SI cancellation on system performance is investigated. It is proved that introducing SWIPT doesn’t only motivate users to collaborate, but also mitigates the impact of the SI signal. In addition, the problem of total sum rate maximisation is formulated and solved locally by means of two-step difference of convex functions (DC)-based procedure. Furthermore, the outage probability of both weak and strong user is derived and provided in closed-form expressions. Numerical simulations are presented to illustrate the sum rate gain of the proposed scheme if compared with existing schemes, and to verify the derived formulas.

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.

On User Association in Multi-Tier Full-Duplex Cellular Networks

We address the user association problem in multi-tier in-band full-duplex (FD) networks. Specifically, we consider the case of decoupled user association (DUA), in which users (UEs) are not necessarily served by the same base station (BS) for uplink (UL) and downlink (DL) transmissions. Instead, UEs can simultaneously associate to different BSs based on two independent weighted path-loss user association criteria for UL and DL. We use stochastic geometry to develop a comprehensive modeling framework for the proposed system model, where BSs and UEs are spatially distributed according to independent point processes. We derive closed-form expressions for the mean rate utility in FD, half-duplex (HD) DL, and HD UL networks as well as the mean rate utility of legacy nodes with only HD capabilities in a multi-tier FD network. We formulate and solve an optimization problem that aims at maximizing the mean rate utility of the FD network by optimizing the DL and UL user association criteria. We investigate the effects of different network parameters, including the spatial density of BSs and power control parameter. We also investigate the effect of imperfect self-interference cancellation (SIC) and show that it is more severe at UL, where there exist minimum required SIC capabilities for BSs and UEs, for which FD networks are preferable to HD networks; otherwise, HD networks are preferable. In addition, we discuss several special cases and provide guidelines on the possible extensions of the proposed framework. We conclude that DUA outperforms coupled user association, in which UEs associate to the same BS for both UL and DL transmissions.

Full-duplex Multi-Antenna Relay Assisted Cooperative Non-Orthogonal Multiple Access

We consider a cooperative non-orthogonal multiple access (NOMA) network in which a full-duplex (FD) multi-antenna relay assists transmission from a base station (BS) to a set of far users with poor channel conditions, while at the same time the BS transmits to a set of near users with strong channel conditions. We assume imperfect self-interference (SI) cancellation at the FD relay and imperfect inter-user interference cancellation at the near users. In order to cancel the SI at the relay a zero-forcing based beamforming scheme is used and the corresponding outage probability analysis of two user selection strategies, namely random near user and random far user (RNRF), and nearest near user and nearest far user (NNNF), are derived. Our finding suggests that significant performance improvement can be achieved by using the FD multi-antenna relay compared to the counterpart system with a half-duplex relay. The achieved performance gain depends on network parameters such as the user density, user zones, path loss and the strength of the inter-user interference in case of near users. We also show that the NNNF strategy exhibits a superior outage performance compared to the RNRF strategy, especially in the case of near

Optimal Training-Based Scheme for MIMO Full-Duplex Wireless Links

In a multiple-input-multiple-output (MIMO) full-duplex (FD) wireless link, training-based schemes are the most effective with digital self-interference (SI) cancellation methods after antenna and analog SI cancellations, and they help receiver to know responses of both residual SI channel for digital cancellation and transmission channel for demodulation. In this situation, the open issue is that how much training is needed in MIMO FD wireless links-too little training will cause the imperfect digital SI cancellations and the transmission channels are also improperly learned, too much training and the links have no time left for the data transmission before the fading channel changes. We compute a capacity lower bound of a MIMO FD channel that is learned at the receiver by training without any feedbacks, and maximize the bound as a function of the received signal-to-noise ratio $\rho $ , fading coherence time $T$ , and numbers of link antennas $M$ , $N$ . When training power is equal to data power, numerical results show that the optimal number of training symbols $T_{o}$ is $T_{o}\geq 2\mathrm {max}(M,N)$ if $T \gg \mathrm {max}(M,N)$ under appropriate $\rho $ . Conversely, if $T\approx 2\max (M,N)$ , $T_{o} .

Asymptotic Analysis of MIMO Multi-Cell Full-Duplex Networks

We study a multi-cell multi-user MIMO full-duplex network, where each base station (BS) has multiple antennas with full-duplex capability supporting single-antenna users with either full-duplex or half-duplex radios. We characterize the up- and downlink ergodic achievable rates for the case of linear precoders and receivers. The rate analysis includes practical constraints, such as imperfect self-interference cancellation, channel estimation error, training overhead, and pilot contamination. We show that the $2\times $ gain of full duplex over half-duplex system remains in the asymptotic regime, where the number of BS antennas grows infinitely large. We numerically evaluate the finite SNR and antenna performance, which reveals that full-duplex networks can use significantly fewer antennas to achieve spectral efficiency gain over the half-duplex counterparts. In addition, the overall full-duplex gains can be achieved under realistic 3GPP multi-cell network settings despite the increased interference introduced in the full-duplex networks.

Full-duplex radios for vehicular communications

Recent significant advances in self-interference cancellation techniques pave the way for the deployment of full-duplex wireless transceivers capable of concurrent transmission and reception on the same channel. Despite the promise to theoretically double the spectrum efficiency, full-duplex prototyping in off-the-shelf chips of mobile devices is still in its infancy, mainly because of the challenges in mitigating self-interference to a tolerable level and the strict hardware constraints. In this article, we argue in favor of embedding full-duplex radios in onboard units of future vehicles. Unlike the majority of mobile devices, vehicular onboard units are good candidates to host complex full-duplex transceivers because of their virtually unlimited power supply and processing capacity. Taking into account the effect of imperfect self-interference cancellation, we investigate the design implications of full-duplex devices at the higher-layer protocols of next-generation vehicular networks and highlight the benefits they could bring with respect to half-duplex devices in some representative use cases. Early results are also provided that give insight into the impact of self-interference cancellation on vehicle-to-roadside communications, and showcase the benefits of FD-enhanced medium access control protocols for vehicle-to-vehicle communications supporting crucial road safety applications.

On the Analog Self-Interference Cancellation for Full-Duplex Communications With Imperfect Channel State Information

This paper studies the performance of the analog multi-tap (MT) canceller, where the tap coefficients are calculated based on the estimated self-interference (SI) channel state information (CSI). In this paper, both the time-invariant and the time-varying SI channels scenarios are investigated, considering the dynamic range of the analog-to-digital converter (ADC) and the linearity of the receiver chain. Closed-form expressions are first developed to calculate the residual SI power after the MT cancellation, characterizing the joint effects of the imperfect SI CSI, reconstruction errors on the estimated SI CSI, and the variation of the SI channels. Then, the achievable rate of the full-duplex transceivers is derived as a function of the residual SI power after the MT cancellation, dynamic range of the ADC, and the linearity of the receiver chain. Theoretical and simulated results show that with imperfect SI CSI, deploying more taps may harm the amount of analog SI cancellation. The sensitivity of the canceller to the doppler frequency shift reduces the amount of analog SI cancellation, and thus brings rate gain loss even with a doppler negligible in conventional communications.

Energy-Efficiency-Oriented Cross-Layer Resource Allocation for Multiuser Full-Duplex Decode-and-Forward Indoor Relay Systems at 60 GHz

Energy-efficiency (EE)-oriented green communication design is an important issue at 60 GHz due to high power consumption of devices working at such a high frequency. In this paper, we investigate EE-oriented resource allocation for full-duplex (FD) decode-and-forward relay-assisted 60-GHz multiuser indoor systems. In contrast to the existing spectral efficiency (SE)-oriented designs, our scheme maximizes the EE for a FD relaying system under cross-layer constraints, addressing the typical problems at 60 GHz, such as the intermittent signal blockage caused by the small wavelength of millimeter-wave. A low-complexity EE-orientated resource allocation algorithm is proposed, by which the transmission power allocation, subcarrier allocation, and throughput assignment are performed jointly across multiple users. Simulation results verify our analytical results and confirm that the FD relaying with the proposed algorithm achieves a higher EE than the FD relaying with SE-oriented approaches, while offering a comparable SE. In addition, a much lower throughput outage probability is guaranteed by the proposed resource allocation algorithm, showing its robustness against channel estimation errors. A full range of power consumption sources and imperfect self-interference cancellation are considered to rationalize our analysis.

Resource Allocation for a Full-Duplex Wireless-Powered Communication Network With Imperfect Self-Interference Cancelation

We consider a full-duplex wireless powered communication network, supporting wireless power transfer of a hybrid access point in the downlink and time-division multiple-access devices in the uplink simultaneously. By considering the residual self-interference (SI), we formulate the problems of power allocation (PA) and time allocation (TA) to maximize the sum rate of the uplink subject to the energy causality as well as the peak and average power constraints. The non-convex optimization problems of the joint PA-TA and the PA are approximated as second-order cone programs to be solved with successive convex approximation. The results show that the proposed PA-TA (PA) algorithm outperforms the conventional PA-TA when the SI exists at any (severe) level.

On the Stability of a Full-Duplex Aloha Network

This letter offers the first characterization of the stability for full-duplex (FD) large size networks. Through stochastic geometry tools, key performance metrics such as delay and maximum stable arrival rate are derived for the nonsaturated system and compared with a half-duplex counterpart, also accounting for imperfect self-interference cancellation. This analysis better identifies that the FD advantage is prominent for sparse networks, whereas in dense topologies, residual self-interference may hinder achievable gains.

Non-Orthogonal Multiple Access With Cooperative Full-Duplex Relaying

We propose a full-duplex (FD) cooperative non-orthogonal multiple access (NOMA) system with dual users, where a dedicated FD relay assists the information transmission to the user with weak channel condition. Under the realistic assumption of imperfect self-interference cancellation, the achievable outage probability of both users and ergodic sum capacity are investigated, and exact analytical expressions are derived. Simulation results demonstrate that the proposed FD cooperative NOMA system attains better performance than the half-duplex cooperative NOMA system in the moderate signal-to-noise ratio regime.

Transmit Power Allocation for Physical Layer Security in Cooperative Multi-Hop Full-Duplex Relay Networks.

In this paper, we consider a transmit power allocation problem for secure transmission in multi-hop decode-and-forward (DF) full-duplex relay (FDR) networks, where multiple FDRs are located at each hop and perform cooperative beamforming to null out the signal at multiple eavesdroppers. For a perfect self-interference cancellation (PSIC) case, where the self-interference signal at each FDR is completely canceled, we derive an optimal power allocation (OPA) strategy using the Karush-Kuhn-Tucker (KKT) conditions to maximize the achievable secrecy rate under an overall transmit power constraint. In the case where residual self-interferences exist owing to imperfect self-interference cancellation (ISIC), we also propose a transmit power allocation scheme using the geometric programming (GP) method. Numerical results are presented to verify the secrecy rate performance of the proposed power allocation schemes.

Novel self-interference suppression schemes based on Dempster-Shafer theory with network coding in two-way full-duplex MIMO relay

A two-way full-duplex multiple-input multiple-output (MIMO) relay provides effective spectral efficiency and system capacity improvement. However, self-interference (SI) as a serious problem limits the development of a full-duplex relay. In this paper, the novel SI suppression schemes based on the Dempster-Shafer (DS) evidence theory are proposed to suppress SI in the two-way full-duplex MIMO relay. DS evidence theory can appropriately characterize uncertainty and make full use of multiple evidence source information by DS combination rule to obtain reliable decisions. The first proposed DS network coding (DS-NC) scheme adopts DS evidence theory to detect the signal of each source node, considering SI suppression in the basic probability assignment computation in the multiple access phase. Moreover, different from the DS-NC scheme, the further proposed DS physical-layer network coding (DS-PNC) scheme considers SI suppression from the vector space perspective and combines the PNC mapping rule with the DS theory to obtain a network-coded signal without estimating each source node signal. In the broadcast phase, antenna selection is adopted at the relay and DS evidence theory is also applied at each source node for SI suppression. Meanwhile, the effects of imperfect SI channel estimation and the intended channel estimation on the proposed schemes are also studied. Finally, the proposed DS-PNC scheme is studied with the SI signal model which considers analog radio frequency cancellation, the effects of I/Q modulator imbalances, and power amplifier nonlinearity of the transmitter. Simulation results reveal that the proposed DS-PNC scheme is a little more sensitive to the channel estimation errors than the traditional spatial-domain schemes. However, with the perfect channel state information, the proposed DS-NC with one iteration and DS-PNC schemes outperform traditional spatial-domain schemes. Furthermore, considering the SI signal model with nonlinear distortion and radio frequency cancellation, the DS-PNC scheme is also superior to the traditional schemes. Meanwhile, the DS-PNC scheme is more robust to the SI and achieves the same diversity gain as the ideal cancellation.

Joint user scheduling and channel allocation for cellular networks with full duplex base stations

Full-duplex communication (FDC) can potentially double the network capacity by allowing a device to transmit and receive simultaneously on the same frequency band. In this study, a novel resource allocation and user scheduling algorithm is proposed to maximise the network throughput for a cellular network with full-duplex (FD) base stations (BSs). The authors consider that FDC is utilised at the BS with imperfect self-interference (SI) cancellation while user devices only work in the traditional half-duplex (HD) way. In addition, to potentially cancel co-channel interference caused by other users, the opportunistic interference cancellation (OIC) technique is applied at user side. Since FDC does not always perform better than HD due to residual SI (RSI), a joint mode selection, user scheduling, and channel allocation problem is formulated to maximise the system throughput. The optimisation problem is non-convex and NP-hard, thereby a suboptimal heuristic algorithm with low computational complexity is proposed. Numerical results demonstrate that user diversity gain, FD gain, and OIC gain can be achieved by the proposed algorithm, respectively. The performance of FDC depends on the intensity of RSI and the distribution of user devices.

Power Allocation for Buffer-Aided Full-Duplex Relaying With Imperfect Self-Interference Cancelation and Statistical Delay Constraint

This paper considers source and relay power allocation for buffer-aided full-duplex (B-FD) relaying network, assuming constant data rate arrivals at the source buffer. Statistical delay constraint is imposed, where the end-to-end queue length is allowed to exceed a pre-defined queue-length threshold with a maximum acceptable queue-length-outage probability. We assume imperfect self-interference (SI) cancelation, where the non-zero residual SI power is modeled to be proportional to the relay transmit power. We investigate two power allocation problems for source arrival rate maximization: 1) B-FD relaying with adaptive power allocation (B-FD-APA) when the instantaneous channel state information at the transmitters (CSIT) is available and 2) B-FD relaying with static power allocation (B-FD-SPA) when only the statistical CSIT is available. To solve the problems, we first employ asymptotic delay analysis to transform the statistical delay constraint into more tractable constraints. Then, the optimal solutions are derived using Lagrangian approach. In addition, solutions for various special cases of residual SI and delay constraint are presented. With B-FD-APA, the relay can opportunistically switch between half-duplex (HD) and FD operation modes according to the channel conditions. With B-FD-SPA, the relay always employs FD mode. Numerical results are performed to compare the capacities of the proposed B-FD, non-buffer FD, and buffer-aided HD relaying schemes, as well as direct transmission (DT) under various settings, demonstrating the effectiveness of B-FD relaying to support delay-constrained communications.