Co-frequency Co-time Full Duplex Research Articles

Movable Antenna-Enabled Co-Frequency Co-Time Full-Duplex Wireless Communication

Movable Antenna-Enabled Co-Frequency Co-Time Full-Duplex Wireless Communication

Improved Fractional Delay Method for Canceling the Self-Interference of Full Duplex

For achieving the high spectral efficiency of the co-frequency co-time full duplex (CCFD), the self-interference (SI) should be cancelled drastically using the signal processing techniques. The radios frequency (RF) canceler uses the reconstructed SI symbol to cancel that arriving from the air interface, where the accurate time-alignment of the two symbols is required so that the cancellation is made at per entire symbol basis. Though using the variable fractional delay (VFD) method allows the exact time-alignment, it deforms inevitably the waveform of the reconstructed SI symbols in the practical application. Actually, the waveform deformation of the reconstructed SI symbol can impair the quality of the cancellation performance. To address this problem, we propose a new cost function that converts the mathematical error of the conventional VFD to the residual SI power directly. The sufficiency of the new cost function is proved and the superior performance is conformed by the simulation results.

Digital SI Cancellation Based on LSTM for Co-frequency Co-time Full Duplex Communication Systems

To address the high self-interference (SI) in co-frequency co-time full duplex (CCFD) communication systems, a digital SI suppression method based on deep learning is proposed. A memory polynomial is firstly utilized to simulate the SI channel. Then a long short-term memory network (LSTM) is used to reconstruct the SI signal. The clean signal after interference suppression can be achieved by subtracting the SI signal at the receiver. To better reflect the changes of the SI signals after being transmitted through the multiple channels and reduce dependence on data volume, feature preprocessing and feature reconstruction are performed at the input of the LSTM. We use the multi-segment delayed transmitted signal as the multiple features and utilize the brainstorm optimization (BSO) technique to estimate the ideal time delay. We verify the proposed SI suppression scheme in the OFDM transmission system. The experimental results show that compared with the traditional least squares estimation (LS) and adaptive filter least mean square (LMS) algorithms, the proposed scheme has a significant performance boost. A SI signal suppression capability of 47.19 dB is achieved.

Ray-Tracing Simulation and Verification of Full-Duplex Self-Interference Channels in an Urban Scenario

Compared with the half-duplex (HD), co-time co-frequency full-duplex (CCFD) technology can effectively improve spectrum utilization. Self-interference (SI) is one of the major factors limiting full-duplex (FD) performance. In this letter, we build the same scattering environment as the field measurement campaign, and simulate the FDSI and the conventional base station-to-base station (B2B) channels using ray-tracing technology. We simulate all the multi-path components (MPCs) and observe the power delay profiles (PDPs), received power, and delay spreads (DS) by changing the angular gap between and the height of the transmitting (Tx) and the receiving (Rx) antennas. The parameters and profiles of the simulated SI channel are consistent with and thus verify the measurement results. To further compare the FD channels and the conventional base station-to-user equipment (B2U) channel, we also compare the measured and simulated SI channels with the 3GPP channel model. It is interesting to find out that the channel characteristics are quite similar in the same scenario.

Energy-efficient resource management for CCFD massive MIMO systems in 6G networks

This paper presents a co-time co-frequency full-duplex (CCFD) massive multiple-input multiple-output (MIMO) system to meet high spectrum efficiency requirements for beyond the fifth-generation (5G) and the forthcoming the sixth-generation (6G) networks. To achieve equilibrium of energy consumption, system resource utilization, and overall transmission capacity, an energy-efficient resource management strategy concerning power allocation and antenna selection is designed. A continuous quantum-inspired termite colony optimization (CQTCO) algorithm is proposed as a solution to the resource management considering the communication reliability while promoting energy conservation for the CCFD massive MIMO system. The effectiveness of CQTCO compared with other algorithms is evaluated through simulations. The results reveal that the proposed resource management scheme under CQTCO can obtain a superior performance in different communication scenarios, which can be considered as an eco-friendly solution for promoting reliable and efficient communication in future wireless networks.

A Wire-Line Secure Communication System Based on CCFD Self-Interference Cancellation

This paper presents a design scheme of wire-line telephone system using self-interference (SI) cancellation technology in co-frequency co-time full-duplex (CCFD) system to realize absolute secure communication at the physical layer. This scheme can hide the target signal by skillfully releasing the high-power artificial noise to the whole link at the receiving node, and then make use of the receiver’s knowledge of the SI signal to achieve high dB SI cancellation with the help of analog domain SI cancellation technology in CCFD domain, so that the signal-to-noise ratio (SNR) received by the eavesdropper at any position of the link is far lower than that of the legitimate receiver, so as to realize the absolutely secure communication in the sense of Wyner principle. This paper not only puts forward the specific design scheme of absolutely secure communication telephone, but also analyzes the calculation of security capacity under different eavesdropping positions, different SI cancellation capability and different system parameters according to Shannon theory.

Joint User Selection and Transceiver Design for Cell-Free With Network-Assisted Full Duplexing

In this paper, we investigate the problem of sum rate maximization by guaranteeing the quality of service (QoS) of both uplink and downlink in cell-free with network-assisted full Duplexing (NAFD), where the users operate in half-duplex mode and access points (APs) operate in either full-duplex mode or half-duplex mode. In the considered network, the central processor unit (CPU) sends the compressed beamformed signals to the transmit-APs (T-APs) over the downlink fronthaul, and the T-APs forward the signals to downlink users. At the same time, the receive-APs (R-APs) compress the signals transmitted by uplink users and forward them to the CPU via uplink fronthaul. We aim to maximize the spectral efficiency and the number of users that should be admitted by the network, where users’ requirements of both downlink and uplink signal-to-interference-plus-noise (SINR) constraints, fronthaul capacity constraints, energy harvesting constraints and simultaneous wireless information and power transfer (SWIPT) ratio design are considered. A successive convex approximation-based algorithm is proposed to solve the highly coupled problem, which is guaranteed to converge to the Karush-Kuhn-Tucker (KKT) conditions. We conduct a comprehensive comparison between the NAFD scheme and the traditional co-frequency co-time full duplex (CCFD) scheme and time division duplex (TDD) scheme and offer some valuable opinions about the system design.

Joint Antenna Selection and Power Allocation for Secure Co-Time Co-Frequency Full-Duplex Massive MIMO Systems

In this paper, we design a co-time co-frequency full-duplex (CCFD) massive multiple-input multiple-output (MIMO) network to improve the utilization of time–frequency resources and physical layer security. Simultaneous information transmissions of the base station and the users are regarded as same-frequency interference against interception by eavesdroppers. To promote energy conservation and improve utilization of system resources, we propose a joint antenna selection and power allocation (JASPA) strategy for CCFD massive MIMO networks. Considering the trade-off between secrecy performance and system communications quality, we formulate optimization functions based on JASPA for two security concerns. We design a quantum-inspired backtracking search algorithm (QBSA) to obtain the optimal JASPA scheme. Simulation results show that the performance of the proposed QBSA is superior to previous intelligent algorithms in CCFD massive MIMO systems. The effectiveness of the proposed JASPA scheme is demonstrated under various communications scenarios, and can be considered a cornerstone for future research in wireless communications domain.

A Prototype of Co-Frequency Co-Time Full Duplex Networking

Radio FD has emerged as an attractive technique capable of doubling the spectral efficiency over half duplex. However, for signal reception, an FD node needs to suppress its transmitter's signals quite significantly. In point to point communication systems, these transmitter signals are termed self-interference. When working with an FD mobile network, the self-interference problem becomes much more complicated because the receiver of an FD base station (BS) receives interference not only from its BS transmitter in its cell, but also from those in the surrounding cells. For the UL channel, self-interference extends to the problem of multiple interference. And, a similar interference problem can be found among the MSs over a DL channel. In both cases, the interference owing to the FD implementation spreads beyond the scope of the self-interference. This article describes the development of FD BSs that use antenna arrays to deal with the BSs' interference, and thus enable FD communication over the UL channel, where the theoretical focus is placed on how to use the antenna array to nullify the multiple interference and receive the signals of the desired MSs simultaneously. To complete the system construction, FD MSs have also been developed to enable DL transmission. A prototype system is described for the scenario of two cells and one FD MS for tests of FD communication over UL channels and DL channels in terms of video performance. Good video quality is demonstrated at both the BS and MS.

Microwave photonic RF front-end for co-frequency co-time full duplex 5G communication with integrated RF signal self-interference cancellation, optoelectronic oscillator and frequency down-conversion.

A novel RF front-end, which could simultaneously realize wideband RF signal self-interference cancellation (SIC), local oscillator (LO) generator based on optoelectronic oscillator (OEO) and frequency down-conversion has been proposed and experimentally demonstrated. In our microwave photonic RF front-end, only one single-polarization optical in-phase and quadrature-phase (IQ) modulator are required. The upper Mach-Zehnder modulator (MZM) of this optical IQ modulator works as a mixer; the lower MZM works as a reference arm; the parent Mach-Zehnder interferometer (MZI) is used to combine two output optical signals of these two child MZMs. In this way, not only self-interference signal is cancelled in optical domain but also frequency down-conversion is realized at the same time. On the other hand, the upper MZM is also shared to form an OEO by using a self-polarization-stabilization technique. By this means, no external LO signal for frequency down-conversion and electrical attenuator for SIC are needed in our scheme, contributing to compact structure and cost reduction. In our proof-of-concept experiment, a LO signal with central frequency of 10 GHz and phase noise of -108.66 dBc/Hz@10kHz is generated. By optimizing the bias points of the used optical IQ modulator, a 5×20MHz 64-ary quadrature amplitude modulation-orthogonal frequency division multiplexing (64QAM-OFDM) LTE-A signal with central frequency of 12.6 GHz is down-converted to 2.6 GHz, and about 28 dB cancellation ratio is achieved. The proposed scheme is suitable for wideband, integrated co-frequency co-time full duplex 5G communication.

A Novel Self-Interference Cancellation Method Using an Optimized LMS Algorithm in CCFD Systems for a 5G Communication Network

The Co-frequency Co-time Full Duplex (CCFD) is a key concept in 5G wireless communication networks. The biggest challenge for CCFD wireless communication is the strong self-interference (SI) from near-end transceivers. Aiming at cancelling the SI of near-end transceivers in CCFD systems in the radio frequency (RF) domain, a novel time-varying Least Mean Square (LMS) adaptive filtering algorithm which is based on step-size parameters gradually decrease with time varying called the DTV-LMS algorithm is proposed in this paper. The proposed DTV-LMS algorithm in this paper establishes the non-linear relationship between step factor and the evolved arct-angent function, and using the relationship between the time parameter and error signal correlation value to coordinately control the step factor to be updated. This algorithm maintains a low computational complexity. Simultaneously, the DTV-LMS algorithm can also attain the ideal characteristics, including the interference cancellation ratio (ICR), convergence speed, and channel tracking, so that the SI signal in the RF domain of a full duplex system can be effectively cancelled. The analysis and simulation results show that the ICR in the RF domain of the proposed algorithm is higher than that in the compared algorithms and have a faster convergence speed. At the same time, the channel tracking capability has also been significantly enhanced in CCFD systems.

Analysis of Desired Receive Signal Impact in Wireless Co-time Co-frequency Full Duplex

With self-interference cancellation (SIC), a wireless full duplex terminal is allowed to transmit and receive signal simultaneously in the same frequency band. This paper focuses on the analysis of desired receive signal impact on the radio frequency (RF) SIC performance. The full-duplex system model is rst given, and the principle of radio frequency self-interference cancellation is introduced. Then, from the perspective of the convex function, the in uence of the desired signal on the RF SIC is analyzed when the total power of the signal after RF SIC is taken as the objective function. It is found that when there is no desired signal, the objective function is a convex function, and the residual self-interference power can converge to the minimum value by the gradient descent method. If the desired signal exists and the channel is constant, the objective function is also a convex function, and the residual self-interference power can also converge to the minimum value. However, in the presence of the desired signal and the channel uctuates, the target is not a convex function, and the residual self-interference power cannot be converged to the minimum value by the gradient descent method.

Spatial full-duplex light communication achieved with a monolithic non-suspended multicomponent system.

The multiple-quantum-well diode (MQW-diode) inherently exhibits simultaneous behavior because of the overlap between the emission spectra and spectral responsivity of the MQW-diode. This feature makes it feasible to form a full-duplex light communication system when two identical MQW-diodes separately function as a transmitter and a receiver at the same time. To verify spatial full-duplex light communication, we fabricated and characterized a monolithic multicomponent system by integrating two InGaN waveguide-based MQW-diodes into a single chip. A 5-μm-wide air gap between two MQW-diodes was manufactured for precise alignment, which could yield spatial light transmission and coupling. Spatial co-time co-frequency full-duplex (CCFD) light communication was experimentally demonstrated using the monolithic multicomponent system, a self-interference cancellation scheme was used to extract the superimposed signals, and a full-duplex audio transmission experiment was performed, opening a promising route toward parallel information processing via free space based on the simultaneous light-emitting and light-detecting phenomenon of the MQW-diode.

Self Interference Cancellation in Co-Time-Co-Frequency Full Duplex Cellular Communication

The performance of co-time co-frequency full duplex (CCDF) communication systems is limited by the self-interference (SI), which is the result of using the same frequency for transmission and reception. However, current communication systems use separate frequencies for transmission and reception, respectively. Therefore, SI is an important issue to be fixed for future-generation systems. As the radio frequency (RF) spectrum is very scared and a CCDF system has the potential to reduce the current spectrum use by half. In this paper, a CCDF communication system is modeled and a combination of RF and digital cancellations is used to mitigate the SI. The simulation results reveal that the proposed combination of RF and digital cancellation achieve the bit-error-rate of 10-11 at an interference-to-signal ratio of 10 dB, which is satisfying value for CCDF communication. The achieved efficiency of the proposed system is 13 bits/sec/Hz at a signal-to-noise ratio of 50 dB. The antenna separation of 35 dB is considered for the proposed model to keep the data loss as minimum as possible. The performance can be improved further by increasing digital-to-analog converter bits but with added complexity.

Analysis and Experimental Verification of Digital Self-Interference Cancelation for Co-time Co-frequency Full-Duplex LTE

In the communication mechanism of co-time co-frequency full-duplex (CCFD), digital self-interference cancellation (SIC) is used for suppressing residual self-interference (SI) after antenna and radio frequency (RF) SICs, as well as low-power multipath SI. In this study, the CCFD LTE verification experiment is presented, which adopts digital SIC with the SI signal reconstructed in frequency domain. For the multipath Rayleigh SI channel, the expression of digital SIC capability is derived and the relationship among the channel estimation error, the received SI power, and digital SIC capability is analyzed. Experimental results show that the digital SIC ability is 31.2 dB for a 20 MHz 16QAM modulated LTE SI signal with frequency centered at 2.6 GHz and the interference-to-noise ratio of 40 dB.