Reconfigurable intelligent surface (RIS) has emerged as a promising technique for enhancing the performance of wireless networks. However, the traditional reflecting‐only RIS requires that the ...transmitter and receiver ought to be on the same side of the RIS, limiting the flexibility of RIS deployment. To overcome this drawback, a new simultaneous transmission and reflection reconfigurable intelligent surface (STAR‐RIS) has been proposed. Different from STAR‐RIS assisted half‐duplex systems in the existing literature, this work investigates a novel STAR‐RIS aided full‐duplex (FD) communication system. An FD base station (BS) communicates with an uplink (UL) user and a downlink user simultaneously over the same time‐frequency dimension assisted by a STAR‐RIS. The authors aim to maximise the energy efficiency by jointly optimising the transmit power of the BS and the UL user and the passive beamforming at the STAR‐RIS. The authors decouple the non‐convex problem into two subproblems and optimise them iteratively. The Dinkelbach's method is used to solve the power optimisation subproblem, whereas the penalty‐based method and successive convex approximation are applied to design the passive beamforming. The convergence and complexity of the proposed algorithm are also analysed. The simulation results demonstrate the superior performance of the proposed scheme compared with other baseline schemes.
This work investigates a novel STAR‐RIS aided full‐duplex (FD) communication system. The authors aim to maximise the system energy efficiency by jointly optimising the transmit power of the BS and UL user, and passive beamforming at the STAR‐RIS. The authors decouple the non‐convex problem into two subproblems and optimise them iteratively. Simulation results demonstrate the superior performance of the authors' proposed scheme compared to other baseline schemes.
The sixth generation advocates green communications, thus energy efficiency (EE) has become an important metric. In this study, a method to increase the EE of a reconfigurable intelligent surface ...(RIS) aided point‐to‐point communication system is proposed, where both sources are equipped with multi‐antenna and operate in the full‐duplex (FD) mode. The extra power consumption for self‐interference cancellation in the FD mode is considered and modelled as a linear function of the transmission power. The EE maximisation problem is divided into an active beamforming subproblem for the two multi‐antenna sources and a passive beamforming subproblem for RIS, and an alternative optimisation framework is adopted to solve them iteratively. Dinkelbach's method is used to address the fractional objective function in the active beamforming optimisation problem. The penalty method and successive convex approximation are exploited for passive beamforming design. Simulation results show that the scheme can greatly boost the EE performance compared with the half‐duplex mode and is superior to the sum‐rate‐maximisation scheme in larger transmission power settings. The proposed method can be used to extend the lifetime of communication devices without deteriorating communication performance.
In this paper, we have studied a multi‐antenna point‐to‐point full‐duplex system, where the communication is assisted by an RIS. Simulation results show our scheme can greatly boost the energy efficiency performance compared with the half‐duplex mode and our proposed scheme is superior to the sum‐rate‐maximisation scheme in larger transmission power setting.
Reconfigurable intelligent surface (RIS) has been proven to be a promising technology for improving the performance of future wireless systems. However, since conventional RIS can only reflect or ...transmit (i.e., refract) incident signals, it limits the applications of RISs. Fortunately, a novel simultaneous transmission and reflection reconfigurable intelligent surface (STAR-RIS) is proposed to improve the convenience of communication. By altering the electromagnetic properties of the STAR-RIS elements with a smart controller, it can split the incident signal into transmission and reflection signals, achieving 360° coverage. This work demonstrates the effectiveness of STAR-RIS aided full-duplex (FD) communication system, where a FD base station (BS) communicates with an uplink (UL) user and a downlink (DL) user simultaneously over the same time-frequency dimension assisted by a STAR-RIS. The objective is to minimize the total transmit power subject to the given minimal data rate requirement. We decouple the original problem into power optimization and STAR-RIS passive beamforming subproblems and adopt the alternating optimization (AO) framework to solve them iteratively. Specifically, in each iteration, we derive the closed-form expression for the optimal power design, then use the successive convex approximation (SCA) method and semidefinite program (SDP) to solve the passive beamforming optimization subproblem. Simulation results verify the convergence and effectiveness of the proposed algorithm and further reveal the performance gain compared with the half-duplex (HD) and conventional RIS.
Oscillator phase noise is one of the bottlenecks that limits the self-interference (SI) cancellation capability of full-duplex systems. In this paper, we propose a method for the suppression of ...common phase error (CPE) and intercarrier interference (ICI) induced by the phase noise in full-duplex orthogonal frequency division multiplexing (OFDM) systems. First, we regard the effect of CPE as a portion of the SI channel and perform estimation, reconstruction and elimination in the time domain. Then, the ICI signal is estimated and suppressed in the frequency domain. Additionally, by analysing the performance of proposed algorithm, we further develop an iterative mechanism to reduce the parameter estimation error and improve SI cancellation capability. Simulation results show that the proposed method has a significant SI cancellation capability improvement over the traditional SI cancellation schemes.
In millimeter wave (mmWave) communications, the beamforming gains of large-scale antenna arrays are used to combat severe path losses and improve communication link quality. This requires beam ...training (BT) to determine the optimal beam direction and achieve beam alignment. The hierarchical codebook with multi-resolution training beams is widely used in BT to reduce training overhead. Unfortunately, due to hardware restrictions, the transition area between two adjacent training beams often leads to error propagation in a traditional BT scheme, which limits the accuracy of beam alignment. In this paper, we propose an improved BT scheme under hierarchical codebook. First, we define an index to measure the power difference of the received signals. Once the index is lower than the predefined threshold, the optimal beam direction is considered to be in the transition area, and an extra interval that contains the transition area is proposed for further beam searching. Then, we analyze the optimal threshold and the probability of beam misalignment based on the ideal beam pattern, proving that the error rate exponentially decreases with the signal-to-noise ratio (SNR) under a single-path channel with constant gain. Finally, simulation results demonstrate that the proposed scheme can significantly improve the accuracy of beam alignment and is applicable to most existing beam patterns.
Channel estimation for millimeter wave (mmWave) systems is challenging due to their large antenna arrays. Owing to the sparse scattering nature of the mmWave channel, channel estimation can be ...performed by estimating the directions and the gains of paths. Most existing schemes assume that a wideband mmWave channel exhibits a common sparsity in the frequency domain. Unfortunately, they ignore the beam squint effect caused by the wide bandwidth, resulting in severe performance loss. In this paper, we investigate the wideband channel estimation problem with beam squint. Specifically, by utilizing measurement signals at all subcarriers, we propose a spatial spectrum-based scheme for a subarray architecture that requires only a single training slot. We first prove that the scheme can accurately obtain the spatial spectrum from a theoretical perspective. Then, we design the beamforming weights of the subarray to avoid pseudo peaks and analyze the inherent spectrum ambiguity phenomenon under the subarray architecture. Finally, to cope with beam squint, we divide the entire bandwidth into multiple subbands and design a combination criterion for the spatial spectrum of each subband. During this process, we prove that the spectrum ambiguity is eliminated, and the joint estimation of the path directions can be obtained. Simulation results demonstrate that the proposed scheme has better estimation accuracy than other methods and significantly reduces the required number of training slots.
A hybrid beamforming structure, which consists of digital precoding and analog beamforming, is a low-cost solution to millimeter wave (mmWave) large-scale antenna systems. In this letter, we study ...the sum rate maximization problem where an analog beamformer is selected from a discrete codebook. A two-stage scheme is proposed in order to avoid an exhaustive search. First, the lower bound of the sum rate is derived, and the trace inverse of the equivalent channel is determined as a novel metric for beam selection. Based on this metric, we formulate a convex problem to derive an initial beam set. Finally, an iterative algorithm is designed to update beams for further performance improvement. Simulation results demonstrate that the proposed scheme achieves a near-optimal sum rate performance and outperforms existing schemes.
Simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) offers a promising solution for achieving full space coverage. In this letter, we focus on a STAR-RIS assisted ...downlink communication system, where we jointly optimize the locations, passive transmitting and reflecting beamforming (BF) of the STAR-RISs, and the active BF at the base station (BS), to maximize the sum rate of users in non-line-of-sight (NLoS) areas. We propose a joint deployment and beamforming design algorithm to address the formulated non-convex optimization problem. Simulation results validate the superiority of our proposed algorithm.
In this letter, we investigate the joint beamforming optimization for a reconfigurable intelligent surface (RIS)-aided multi-antenna full-duplex communication system. Our goal is to minimize the ...total transmit power by jointly optimizing the active beamforming at the sources and the passive beamforming at the RIS, subject to the minimum data rate requirements at the sources. To solve the non-convex problem, an efficient algorithm is proposed by utilizing the alternating optimization framework to iteratively optimize variables. Specifically, in each iteration, the active beamforming vectors are obtained by using the semidefinite relaxation (SDR) method and the optimality of the solution is proved, while the successive convex approximation (SCA) method and semidefinite program (SDP) are used to solve the passive beamforming optimization problem. Numerical results verify the convergence and effectiveness of the proposed algorithm, and further reveal the performance gain compared with the RIS assisted half-duplex system.
Simultaneously transmitting and reflecting RISs (STAR-RISs) can serve users positioned on either side of the surface by means of transmitting and reflecting the incident signal. The deployment angle ...of the STAR-RIS is pivotal to the gain of the received and transmitted signals, and the STAR-RIS with rotatable angles has the potential to boost the spectral efficiency (SE). In this paper, the power allocation, transmission and reflection coefficients (TARCs), and deployment angle of the STAR-RIS is jointly optimized to maximize the SE. However, since the non-convex of the objective function and the manual coupling of variables, it is challenging to solve this problem. To this end, we propose a low-complexity algorithm, where the deployment angle of the STAR-RIS is obtained by using deep learning (DL) according to channels from the BS to STAR-RIS and from the STAR-RIS to users. Then, the power allocation and TARCs are iteratively optimized in an alternating manner. Numerical results reveal that the proposed algorithm can effectively achieve superior system's SE.
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