Self-interference Channel Estimation Research Articles

LoneSTAR: Analog Beamforming Codebooks for Full-Duplex Millimeter Wave Systems

This work develops LONESTAR, a novel enabler of full-duplex millimeter wave (mmWave) communication systems through the design of analog beamforming codebooks. LONESTAR codebooks deliver high beamforming gain and broad coverage while simultaneously reducing the self-interference coupled by transmit and receive beams at a full-duplex mmWave transceiver. Our design framework accomplishes this by tolerating some variability in transmit and receive beamforming gain to strategically shape beams that reject self-interference spatially while accounting for digitally-controlled analog beamforming networks and self-interference channel estimation error. By leveraging the coherence time of the self-interference channel, a mmWave system can use the same LONESTAR design over many time slots to serve several downlink-uplink user pairs in a full-duplex fashion without the need for additional self-interference cancellation. Compared to those using conventional codebooks, full-duplex mmWave systems employing LONESTAR codebooks can mitigate higher levels of self-interference, tolerate more cross-link interference, and demand lower SNRs in order to outperform half-duplex operation—all while supporting beam alignment. This makes LONESTAR a potential standalone solution for enabling simultaneous transmission and reception in mmWave systems, from which it derives its name.

An Adaptive-Iterative Nonlinear Interference Cancellation in Time-Varying Full-Duplex Channels

In this paper, first, the sensitivity of traditional Full-Duplex (FD) communication systems to time variation in the self-interference (SI) channel is demonstrated via performance analysis. It is seen that conventional schemes are not capable of providing efficient operation regarding practical concerns such as spectral efficiency, SI channel aging and learning accuracy, and the contamination of signal-of-interest (SoI). Then, in regard to the aforementioned concerns, a practical FD operation together with a novel iterative SoI-contamination-aware digital SI cancellation (DSIC) algorithm that relieves the sensitivity against time variation considerably is proposed. The proposed scheme, namely <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Turbo</i> DSIC, is practical in terms of training and computational complexity thanks to its two-stage structure such that complex nonlinear parameter learning (NPL) is conducted very rarely in the first stage, and linear processing is performed adaptively at symbol-rate in the second stage, where SoI is iteratively estimated at each data block and eliminated from the received signal to improve SI channel estimation accuracy. Finally, the performance of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Turbo</i> DSIC, under hardware impairments and time-varying (TV) propagation, is evaluated via both computer simulation environment and actual experimental hardware setup in terms of bit error rate (BER) and achievable information rate (AIR) metrics.

A Digital Self-Interference Cancellation Scheme for In-Band Full-Duplex-Applied 5G System and Its Software-Defined Radio Implementation

The development of mobile communication technology toward 6G is difficult because the required spectrum resources have already been allocated to existing systems. Therefore, new communication systems must have high spectral efficiency to effectively utilize the available resources. This article proposes a digital self-interference (SI) canceller that can be applied to full-duplex cellular systems based on the current 5G signal format (5G-FDC) to introduce in-band full-duplex systems beyond 5G. Specifically, we reorganize the 5G demodulation reference signal (DMRS) and define a novel DMRS configuration, in which the DMRSs for uplink and downlink communications do not interfere with each other. The proposed DMRS configuration effectively improves the accuracy of the SI channel estimation. Moreover, we propose a channel extrapolation scheme that suppresses the channel estimation degradation, which deteriorates the block error rate performance. Additionally, we propose a noise estimation method to improve the low-density parity check decoding performance of the desired signal in 5G-FDC systems. The effectiveness of the proposed method is demonstrated through computer simulations and experimentally by using our developed and implemented software-defined radio-based 5G-FDC prototype. Digital SI cancellation performances of 50 dB and 30.6 dB are observed in the simulation and experimental evaluations, respectively.

Impacts of Residual Self-Interference, Hardware Impairment and Cascade Rayleigh Fading on the Performance of Full-Duplex Vehicle-to-Vehicle Relay Systems.

In practice, self-interference (SI) in full-duplex (FD) wireless communication systems cannot be completely eliminated due to imperfections in different factors, such as the SI channel estimation and hardware circuits. Therefore, residual SI (RSI) always exists in FD systems. In addition, hardware impairments (HIs) cannot be avoided in FD systems due to the non-ideal characteristics of electronic components. These issues motivate us to consider an FD-HI system with a decode-and-forward (DF) relay that is applied for vehicle-to-vehicle (V2V) communication. Unlike previous works, the performance of the proposed FD-HI-V2V system is evaluated over cascaded Rayleigh fading channels (CRFCs). We mathematically obtain the exact closed-form expressions of the outage probability (OP), system throughput (ST), and ergodic capacity (EC) of the proposed FD-HI-V2V system under the joint and crossed effects of the RSI, HIs, and CRFCs. We validate all derived expressions via Monte-Carlo simulations. Based on these expressions, the OP, ST, and EC of the proposed FD-HI-V2V system are investigated and compared with other related systems, such as ideal hardware (ID) and half-duplex (HD) systems, as well as a system over traditional Rayleigh fading channels (RFCs), to clearly show the impacts of negative factors.

Full-Duplex Transceiver Design in the Presence of Phase Noise and Performance Analysis

Phase noise introduced by oscillators shows significant impacts on full-duplex (FD) transceivers, even for the architecture in which the transmitter and receiver share the same oscillator. In this paper, an FD transceiver design is proposed to mitigate the phase noise contained in the multipath self-interference (SI) components. This design is featured by deploying two receive chains whose oscillator signals are originated from the transmit oscillator signal but with different delays. To work with the proposed design, an SI cancellation algorithm is developed, where the phase noise contained in the multipath SI components are extracted by dividing the two received signals. The cancellation capabilities of the proposed transceiver, as well as two typical conventional transceivers, are derived in closed-forms. The impacts of oscillator delay adjustment errors and SI channel estimation errors on the cancellation capability are also analyzed to reveal guidelines for FD transceiver designs. Simulation results show that the proposed transceiver design can expand the transmission power and relax the requirement for the analog canceller, which shows advantages in the long-range communication with high transmission power, or in the scenario where analog cancellations are not applicable.

Iterative Self-Interference Mitigation in Full-Duplex Wireless Communications

This paper considers a full-duplex wireless communication system in which detection of the desired signal is hindered not only by the self-interference (SI), but also phase noise, in-phase and quadrature-phase imbalance and power amplifier’s nonlinearity distortion. An iterative algorithm is proposed in which the processes of SI cancellation and detection of the desired signal aid each other in each iteration. In each iteration, the SI cancellation process performs widely linear estimation of the SI channel and compensates for physical impairments to improve the detection performance of the desired signal. The detected desired signal is in turn removed from the received signal to improve SI channel estimation and SI cancellation in the next iteration. Simulation results show that the proposed algorithm significantly outperforms existing algorithms in SI cancellation and detection of the desired signal.

Distribution of the Residual Self-Interference Power in In-Band Full-Duplex Wireless Systems

This paper derives the distribution of the residual self-interference (SI) power in an analog post-mixer canceler adopted in a wireless in-band full-duplex communication system. We focus on the amount of uncanceled SI power due to SI channel estimation errors. Closed form expressions are provided for the distribution of the residual SI power when Rician and Rayleigh fading SI channels are considered. Moreover, the distribution of the residual SI power is derived for low and high channel gain dynamics, by considering the cases when the SI channel gain is time-invariant and time-variant. While for time-invariant channels the residual SI power is exponentially distributed, for time-variant channels the exponential distribution is not a valid assumption. Instead, the distribution of the residual SI power can be approximated by a product distribution. Several Monte Carlo simulation results show the influence of the channel dynamics on the distribution of the residual SI power. Finally, the accuracy of the theoretical approach is assessed through the comparison of numerical and simulated results, which confirm its effectiveness.

On the Feasibility of Full-Duplex Large-Scale MIMO Cellular Systems

This paper concerns the feasibility of full-duplex large-scale multiple-input-multiple-output cellular systems. We first derive the analytic model of the ergodic achievable sum-rate for cell-boundary users. The model is derived by applying a simple linear filter, i.e., matched filter or zero-forcing filter, to the base-station (BS). In the analytic model, we consider large-scale fading, pilot contamination, transmitter noise, and receiver distortion. In addition, to solve the critical pilot overhead problem induced by self-interference channel estimation, we propose a pilot transmission scheme—the simultaneous pilot transmission (SPT)—and assess its performance, in terms of the ergodic sum-rate. In considering two multicell scenarios, cooperative and non-cooperative multicell systems, we obtain the ergodic achievable sum-rate by reflecting the characteristic of each scenarios, such as limited front-haul capacity and procedures of channel estimation. With all derived results, to investigate the feasibility, we observe the tradeoffs between the full- and half-duplex systems, between the SPT and conventional scheme, and between the two multicell scenarios with respect to various system parameters and environment. In the end, we confirm the tightness of our analytic model and advantages of full-duplex, SPT, and cooperation of BSs in our system model.

QoS-Based Linear Transceiver Optimization for Full-Duplex Multiuser Communications

In this paper, we consider a multiuser wireless system with one full duplex (FD) base station (BS) serving a set of half duplex (HD) mobile users. To cope with the in-band self-interference (SI) and co-channel interference, we formulate a quality-of-service (QoS) based linear transceiver design problem. The problem jointly optimizes the downlink (DL) and uplink (UL) beamforming vectors of the BS and the transmission powers of UL users so as to provide both the DL and UL users with guaranteed signal-to-interference-plus-noise ratio performance, using a minimum UL and DL transmission sum power. The considered system model not only takes into account noise caused by nonideal RF circuits, analog/digital SI cancellation but also constrains the average signal power at the input of the analog-to-digital converter (ADC) for avoiding signal distortion due to finite ADC precision. The formulated design problem is not convex and challenging to solve in general. We first show that for a special case with a worst case SI channel estimation error, the QoS-based linear transceiver design problem is globally solvable by a polynomial time bisection algorithm. For the general case, we propose a suboptimal algorithm based on alternating optimization (AO). The AO algorithm is guaranteed to converge to a Karush–Kuhn–Tucker solution. To improve the computational efficiency of the AO algorithm, we further develop a fixed-point method by extending the classical uplink–downlink duality in HD systems to the FD system. Simulation results are presented to demonstrate the performance of the proposed algorithms and the comparison with HD systems.

Self-Interference Channel Estimation Algorithm Based on Maximum-Likelihood Estimator in In-Band Full-Duplex Underwater Acoustic Communication System

To efficiently cancel the self-interference (SI) caused by the simultaneous transmission and reception in in-band full-duplex (IBFD) underwater acoustic (UWA) communication system, we propose a novel channel estimation approach to estimate the sparse SI channel, the proposed channel estimation algorithm has a better estimation performance than the traditional channel estimator. In the IBFD radio communication system, the SI and intended channels are estimated through using training symbols in different time slots, and therefore, the effect of intended signal can be avoided in SI channel estimation. Because of the time variable and longtime delay in the UWA channel, we cannot estimate the SI and intended channel in different time slots. The intended signal is treated as additive noise when estimating SI channel in the IBFD-UWA communication system, and thus, the SI channel estimation is affected by non-Gaussian noise and the traditional algorithms designed for Gaussian noise typically perform poor. In view of this situation, we propose a maximum likelihood (ML) with sparse constraint to estimate the sparse SI channel. The ML with sparse constraint is derived via combining a sparse constraint into conventional ML cost function and using stochastic gradient algorithm to get the iterative formula, thereby resulting in a better performance. Extensive simulations and experimental results show that the proposed algorithm has faster convergence and better cancelation performance compared with traditional ML and least square. We also present the convergence and steady-state mean-squared error analysis of the proposed algorithm.

Achievable Rates of Full-Duplex Massive MIMO Relay Systems Over Rician Fading Channels

We analytically study the achievable rates of full-duplex massive multiple-input multiple-output (MIMO) relay systems over Rician fading channels. The decode-and-forward protocol is adopted at the relay station, where the channel state information (CSI) is assumed to be imperfect. We demonstrate that the system bottleneck, self-interference (SI), can be significantly canceled by zero-forcing (ZF) processing at the relay station, which is equipped with massive receive and transmit arrays. Because no active SI cancellation is deployed at the relay station, there is no need for SI channel estimation. We derive an approximate closed-form achievable rate expression for ZF processing with statistical CSI. When the number of antennas of the transmit and receive arrays at the relay station is sufficiently large, the transmit powers of each source and the relay station can be significantly scaled down proportionally to the number of antennas. Since Rayleigh fading is a special case of Rician fading, the results in this paper hold for Rayleigh fading channels. The theoretical analysis is verified by the numerical results.

Enabling Technologies toward Fully LTE-Compatible Full-Duplex Radio

Full-duplex radio has potential to double spectral efficiency by simultaneously transmitting and receiving signals in the same frequency band, but at the expense of additional hardware and power consumption for self-interference cancellation. Hence, the deployment of a full-duplex cellular network can be realized by employing full-duplex functionality only at an eNodeB, which is supposed to have sufficient computation and power resources, and by scheduling pairs of half-duplex UEs that are in either downlink or uplink. By doing so, fast and smooth full-duplex deployment is possible while minimally affecting the legacy UEs and the rest of the network entities. In this article, we provide technical challenges and solutions for an LTE-compatible full-duplex cellular network, featuring wideband and wide dynamic range support for RF self-interference cancellation, and robust and efficient self-interference channel estimation for digital self-interference cancellation. Based on a realistic LTE-based cellular model, our full-duplex radio design is evaluated through system-level simulations and real-world testbed experiments. Simulation results show that a significant throughput gain can be achieved by the full-duplex technique despite the existence of physical limiting factors such as path loss, fading, and other-cell interference. Testbed measurements reveal that at a bandwidth of 20 MHz, self-interference cancellation up to 37 dB is achieved in the RF domain, and most of the residual self-interference is further cancelled down to the noise floor in the subsequent digital domain.

Channel estimation and self-interference cancelation in full-duplex communication systems

This paper presents a two-stage self-interference (SI) cancelation for full-duplex multi-input–multi-output (MIMO) communications systems. By exploiting the SI channel sparsity, a compressed-sensing-based SI channel estimation technique is developed and used in the first SI-cancelation radio-frequency (RF) stage to reduce the SI power prior to the receiver low-noise amplifier (LNA) and the analog-to-digital converter (ADC) to avoid overloading. Subsequently, a subspace-based algorithm is proposed to jointly estimate the coefficients of both the residual SI and intended channels and transceiver impairments for the second SI-cancelation baseband stage to further reduce the residual SI. Unlike other previous works, the intended signal is taken into consideration during the estimation process to reduce the overhead. It is demonstrated that the SI channel coefficients can be perfectly estimated with no knowledge of the intended signal, and only a few training symbols are needed for ambiguity removal in intended-channel estimation. Simulation results show that the proposed algorithms outperform the least square (LS) algorithms and offer the remarkable signal-to-residual-SI-and-noise ratio (SINR) approaching the signal-to-noise ratio (SNR).

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.

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.

Channel Estimation for Self-Interference Cancellation in Full-Duplex Wireless Systems

In this paper, analog cancellation with a self-interference channel estimation scheme is proposed for full-duplex wireless systems. The aim of the proposed scheme is to cancel the self-interference...

스펙트럼 효율 향상을 위한 동일대역 동시 통신 (Simultaneous Single Band Duplex) 시스템

본 논문에서는 동일 대역 동시 이중 통신(SSD)을 위한 시스템 모델과 간섭 채널 추정을 통한 효율적인 Digital Cancellation 방법을 제안한다. 본 논문에서는 RF Cancellation이 효과적으로 이루어 졌다고 가정한다. SSD 시스템에는 자국의 송신 신호가 자국의 수신기에 간섭 신호로 작용하는 문제가 있다. 자기 간섭 신호 제거를 위해 자기 간섭 채널을 추정하고 이를 바탕으로 자기 간섭 신호를 제거해야 한다. 효과적인 자기 간섭 채널 추정을 위해 제안하는 시스템은 시간 프레임에 추정 구간을 두었다. 또한 최적의 계수 선택을 위해 신호 전력의 세기를 계산하여 자기 간섭 신호를 가장 잘 제거하는 계수를 선택하여 자기 간섭 신호를 제거하는 방법을 사용한다. 추가로 남아있는 자기 간섭 신호의 영향을 최소화하기 위해 LDPC 부호를 사용하였다. 제안하는 시스템은 자기 간섭 신호를 제거하면서 LDPC 부호의 5회 반복을 통해 20dB에서 <TEX>$10^{-4}$</TEX>의 성능을 낸다. 즉, 제안하는 방법은 자기 간섭채널이 심하게 변하지 않는 상황에서 신호를 효과적으로 제거 하면서 SSD 통신을 할 수 있다. In this paper, we propose a SSD (simultaneous single-band duplex) system using Digital Cancellation. Also, we propose a method for Digital Cancellation when RF Cancellation is effectively performed. The proposed system has estimation frame for effective self-interference channel estimation in time-domain. The proposed system calculates signal power for selection of optimal coefficient after digital cancellation. Then, the proposed system selects coefficient of minimum signal power. Further, the proposed system uses LDPC code to minimize the effects of remaining self-interference signal. The proposed system shows BER performance of at 20dB by cancelling self-interference and iterating LDPC code. That is, the proposed system shows that the SSD communication is possible in static self-interference channel.