Full-duplex Multiple-input Multiple-output Research Articles

A Microwave Photonic 2 × 2 IBFD-MIMO Communication System with Narrowband Self-Interference Cancellation.

Combined in-band full duplex-multiple input multiple output (IBFD-MIMO) technology can significantly improve spectrum efficiency and data throughput, and has broad application prospects in communications, radar, the Internet of Things (IoT), and other fields. Targeting the self-interference (SI) issue in microwave photonic-based IBFD-MIMO communication systems, a microwave photonic self-interference cancellation (SIC) method applied to the narrowband 2 × 2 IBFD-MIMO communication system was proposed, simulated, and analyzed. An interleaver was used to construct a polarization multiplexing dual optical frequency comb with a frequency shifting effect, generating a dual-channel reference interference signal. The programmable spectrum processor was employed for filtering, attenuation, and phase-shifting operations, ensuring amplitude and phase matching to eliminate the two self-interference (SI) signals. The simulation results show that the single-frequency SIC depth exceeds 45.8 dB, and the narrowband SIC depth under 30 MHz bandwidth exceeds 32.7 dB. After SIC, the desired signal, employing a 4QAM modulation format, can be demodulated with an error vector magnitude (EVM) as low as 4.7%. Additionally, further channel expansion and system performance optimization are prospected.

Secure MIMO NOMA transmission with energy harvesting-aided full-duplex jammer under erroneous channel information

NOMA allows for the simultaneous transmission of multiple user signals and full-duplex (FD) communication enables concurrent transmit-and-receive operations, both improving spectral efficiency. Additionally, NOMA networks utilize energy harvesting (EH) to efficiently harvest energy from radio frequency sources, contributing to improved energy efficiency. In addition, deploying multiple antennas at NOMA users facilitates energy transfer and harvesting, as well as reliable information transmission through antenna array processing. Moreover, jamming is presented as a useful method to secure wireless transmission. Therefore, multiple-input multiple-output (MIMO) NOMA transmission with EH-aided FD jammer (MMnOehFD) is envisioned to acquire high performance like energy efficiency, security, reliability, and throughput. The paper numerically assesses the reliability and security of MMnOehFD where evaluation metrics include energy efficiency, throughput, and outage probability. Further, practical factors such as erroneous channel information (ECI) and multi-antenna users are taken into account in the evaluation. Results indicate that the ECI significantly degrades system performance, and this degradation is influenced by multiple parameters. Also, the proposed MMnOehFD can avoid complete outage and attain optimal performance with appropriate system configuration. The performance of the MMnOehFD is notably improved with an increasing number of antennas. Further, the MMnOehFD outperforms two baseline schemes (MIMO OMA transmission with EH-aided FD jammer and MIMO NOMA transmission without jammer), highlighting the effectiveness of combining jammer and NOMA.

Isolation Improvement Using the Field-Circuit Combined Method for In-Band Full-Duplex MIMO Antenna Arrays

This paper proposes a field-circuit combined decoupling method for co-polarized in-band full-duplex multiple-input multiple-output (MIMO) antenna arrays. The proposed field-circuit combined method is composed of decoupling network and neutralization-based decoupling. An in-band full-duplex antenna with high isolation and low cross-polarization level is designed and extended to a 1 × 4 linear array. The decoupling network and ADS are applied for the array to alleviate the mutual coupling by rebuilding the neutralization wave paths in the circuit and field domains. Thus, low coupling (< −25 dB) among the transmitting/receiving antennas and high isolation (> 47 dB) between the transmitting and receiving antennas are achieved at 2.6 GHz, exhibiting a superior decoupling performance.

In-band full-duplex MIMO PLC systems for relaying networks

In Power Line Communications (PLC), there are regulatory masks that restrict the transmit power spectral density for electromagnetic compatibility reasons, which creates coverage issues despite the not too long distances. Hence, PLC networks often employ repeaters/relays, especially in smart grid neighborhood area networks. Even in broadband indoor PLC systems that offer a notable data rate, relaying may pave the way to new applications like being the backbone for wireless technologies in a cost-effective manner to support the Internet-of-things paradigm. In this paper, we study Multiple-Input Multiple-Output (MIMO) PLC systems that incorporate in-band full-duplex functionality in relaying networks. We present several MIMO configurations that allow end-to-end half-duplex or full-duplex operations and analyze the achievable performance with state-of-the-art PLC systems. To reach this analysis, we get channel realizations from random network layouts for indoor and outdoor scenarios. We adopt realistic MIMO channel and noise models and consider transmission techniques according to PLC standards. The concepts discussed in this work can be useful in the design of future PLC relay-aided networks for different applications that look for a coverage extension and/or throughput: smart grids with enhanced communications in outdoor scenarios, and “last meter” systems for high-speed connections everywhere in indoor ones.

Photonics-Assisted Analog Wideband Self-Interference Cancellation for In-Band Full-Duplex MIMO Systems With Adaptive Digital Amplitude and Delay Pre-Matching

A photonics-assisted analog wideband RF self-interference (SI) cancellation and frequency downconversion approach for in-band full-duplex (IBFD) multiple-input multiple-output (MIMO) systems with adaptive digital amplitude and delay pre-matching is proposed based on a dual-parallel Mach–Zehnder modulator (DP-MZM). In each MIMO receiving antenna, the received signal, including different SI signals from different transmitting antennas and the signal of interest, is applied to one arm of the upper dual-drive Mach–Zehnder modulator (DD-MZM) of the DP-MZM, the reference signal is applied to the other arm of the upper DD-MZM, and the local oscillator signal is applied to one arm of the lower DD-MZM. The SI signals are canceled in the optical domain in the upper DD-MZM and the frequency downconversion is achieved after photodetection. To cancel the SI signals, the analog reference signal is constructed in the digital domain, while the amplitude and delay of the constructed reference are adjusted digitally by upsampling with high accuracy. Experiments are performed when two different SI signals are employed. The genetic algorithm or least squares algorithm is combined with segmented search respectively for the SI signal reconstruction and amplitude and delay pre-matching. A cancellation depth of around 20 dB is achieved for the 1-Gbaud 16 quadrature-amplitude modulation orthogonal frequency-division multiplexing signal.

Hybrid Beamforming Design for Self-Interference Cancellation in Full-Duplex Millimeter-Wave MIMO Systems with Dynamic Subarrays.

Full-duplex (FD) millimeter-wave (mmWave) multiple-input multiple-output (MIMO) communication is a promising solution for the extremely high-throughput requirements in future cellular systems. The hybrid beamforming structure is preferable for its low hardware complexity and low power consumption with acceptable performance. In this paper, we introduce the hardware efficient dynamic subarrays to the FD mmWave MIMO systems and propose an effective hybrid beamforming design to cancel the self-interference (SI) in the considered system. First, assuming no SI, we obtain the optimal fully digital beamformers and combiners via the singular value decomposition of the uplink and downlink channels and the water-filling power allocation. Then, based on the obtained fully digital solutions, we get the dynamic analog solutions and digital solutions using the Kuhn-Munkres algorithm-aided dynamic hybrid beamforming design. Finally, we resort to the null space projection method to cancel the SI by projecting the obtained digital beamformer at the base station onto the null space of the equivalent SI channel. We further analyze the computational complexity of the proposed method. Numerical results demonstrate the superiority of the FD mmWave MIMO systems with the dynamic subarrays using the proposed method compared to the systems with the fixed subarrays and the half-duplex mmWave communications. When the number of RF chains is 6 and the signal-to-noise ratio is 10 dB, the proposed design outperforms the FD mmWave MIMO systems with fixed subarrays and the half-duplex mmWave communications, respectively, by 22.4% and 47.9% in spectral efficiency and 19.9% and 101% in energy efficiency.

Joint Analog and Digital Transceiver Design for Wideband Full Duplex MIMO Systems

In this paper, we propose a wideband Full Duplex (FD) Multiple-Input Multiple-Output (MIMO) communication system comprising of an FD MIMO node simultaneously communicating with two multi-antenna UpLink (UL) and DownLink (DL) nodes utilizing the same time and frequency resources. To suppress the strong Self-Interference (SI) signal due to simultaneous transmission and reception in FD MIMO systems, we propose a joint design of Analog and Digital (A/D) cancellation as well as transmit and receive beamforming capitalizing on baseband Orthogonal Frequency-Division Multiplexing (OFDM) signal modeling. Considering practical transmitter impairments, we present a multi-tap wideband analog canceller architecture whose number of taps does not scale with the number of transceiver antennas and multipath SI components. We also propose a novel adaptive digital cancellation based on truncated singular value decomposition that reduces the residual SI signal estimation parameters. To maximize the FD sum rate, a joint optimization framework is presented for A/D cancellation and digital beamforming. Finally, our extensive waveform simulation results demonstrate that the proposed wideband FD MIMO design exhibits higher SI cancellation capability with reduced complexity compared to existing cancellation techniques, resulting in improved achievable rate performance.

Joint Antenna and Device Scheduling in Full-Duplex MIMO Wireless-Powered Communication Networks

In this article, we study a joint antenna and Internet of Things device (ID) scheduling problem in the full-duplex (FD) multiple-input–multiple-output (MIMO) wireless-powered communication network (WPCN) over time-varying fading channels. We first formulate an optimization problem to maximize the average sum rate of IDs while satisfying their minimum average data rate requirements by jointly scheduling ID selection for uplink data transmission, antenna switching, and beamforming. To deal with the problem, we propose a scheduling algorithm based on Lagrangian duality and the stochastic optimization theory. The proposed scheduling algorithm necessitates solving per-time-slot problems, each of which aims at maximizing the weighted sum of the selected ID’s uplink data rate and the nonselected IDs’ harvested power from the downlink by jointly optimizing ID selection, antenna switching between uplink and downlink, and beamforming at that time slot. To solve the per-time-slot problem, we develop a joint ID selection, antenna switching, and beamforming (Joint-IAB) algorithm based on the block coordinate descent (BCD) and successive convex approximation (SCA) methods. Through simulation, we demonstrate that our scheduling algorithm with the proposed Joint-IAB algorithm provides better performance than the other scheduling algorithms while well satisfying the given minimum average data rate requirements of IDs.

Digitally assisted photonic analog domain self-interference cancellation for in-band full-duplex MIMO systems via the LS algorithm with adaptive order.

A digitally assisted photonic analog domain self-interference cancellation (SIC) and frequency downconversion method is proposed for in-band full-duplex multiple-input multiple-output (MIMO) systems using the least square (LS) algorithm with adaptive order. The SIC and frequency downconversion are achieved in the optical domain via a dual-parallel Mach-Zehnder modulator, while the downconverted signal is processed by the LS algorithm with adaptive order that is used to track the response of the multipath self-interference (SI) channel and reconstruct the reference signal for SIC. The proposed method can overcome the reconstruction difficulty of the multipath analog reference signal for SIC with high complexity in the MIMO scenario and can also solve the problem that the order of the reference reconstruction algorithm is not optimized when the wireless environment changes. An experiment is carried out to verify the concept. SIC depths of 30.2, 26.9, 23.5, 19.5, and 15.8 dB are achieved when the SI signal has a carrier frequency of 10 GHz and baud rates of 0.1, 0.25, 0.5, 1, and 2 Gbaud, respectively. The convergence of the LS algorithm with adaptive order is also verified for different MIMO multipath SI signals.

A Full-Duplex MIMO System Based on CP-Free OFDM in Sensor Network

Recently, results have shown that full-duplex (FD) system based on orthogonal frequency division multiplexing (OFDM) is potential for wireless sensor networks. However, extending FD to further improve spectral efficiency by removing cyclic prefix (CP) with optimal canceling self-interference (SI) remains a challenge. In this paper, we analytically study the conventional FD OFDM system and proposed a CP-free system on this basis. The key point of the proposed scheme is the symbols transmitted in a unit of two identical symbols without CP. To eliminate the intersymbol interference, the disturbed part are replaced by the repeated signal at the receiver, which has the same effect as CP. Finally, an SI cancellation is down to restore the transmitted symbols. As a key of analysis, a multiple-input multiple-output (MIMO) FD simulation model is carried to show that our proposed scheme is effectiveness in terms of the bit error ratio (BER).

Low complexity full duplex MIMO systems: Analog canceler architectures, beamforming design, and future directions

The hardware complexity of the analog Self-Interference (SI) canceler in conventional full duplex Multiple Input Multiple Output (MIMO) designs mostly scales with the number of transmit and receive antennas, thus exploiting the benefits of analog cancellation becomes impractical for full duplex MIMO transceivers, even for a moderate number of antennas. In this paper, we provide an overview of two recent hardware architectures for the analog canceler comprising of reduced number of cancellation elements, compared to the state of the art, and simple multiplexers for efficient signal routing among the transceiver radio-frequency chains. The one architecture is based on analog taps and the other on AUXiliary (AUX) Transmitters (TXs). In contrast to the available analog cancellation architectures, the values for each tap or each AUX TX and the configuration of the multiplexers are jointly designed with the digital transceiver beamforming filters according to desired performance objectives. We present a general optimization framework for the joint design of analog SI cancellation and digital beamforming, and detail an example algorithmic solution for the sum-rate optimization objective. Our representative computer simulation results demonstrate the superiority, both in terms of hardware complexity and achievable performance, of the presented low complexity full duplex MIMO schemes over the relative available ones in the literature. We conclude the paper with a discussion on recent simultaneous transmit and receive operations capitalizing on the presented architectures, and provide a list of open challenges and research directions for future FD MIMO communication systems, as well as their promising applications.

Analog Self-Interference Cancellation in Dual-Polarization Full-Duplex MIMO Systems

Full-duplex (FD) technology combined with dual-polarization (DP) multiple-input multiple-output (MIMO) systems is attractive to improve spectral efficiency and to enhance link capacity. Cancelling self-interference (SI) in such DPFD MIMO systems using beamforming techniques is very challenging due to a significant difference of the co-polarization and cross-polarization SI channels. In this letter, an analog adaptive filter structure is proposed to mitigate both co-polarization and cross-polarization SIs in DPFD MIMO systems. Stationary analysis is applied to evaluate the performance of the proposed structure. Simulation results show that about 45 dB to 55 dB of SI cancellation can be achieved regardless of the isolation differences between cross-polarization and co-polarization channels.

SER performance of MIMO full-duplex relay system with channel estimation errors and transceivers hardware impairments

In practice, traditional wireless communication systems are often affected by various negative factors such as channel estimation errors (CEE) and transceiver hardware impairments (THI). For in-band full-duplex (FD) communication systems, besides CEE and THI impacts, imperfect self-interference cancellation will significantly degrade the system performance because of residual self-interference (RSI). This paper aims to investigate the performance of a multiple-input multiple-output (MIMO) FD relay (FDR) system in realistic scenarios where the impacts of CEE, THI, and RSI are taken into account. We mathematically derive the exact closed-form expression of symbol error rate (SER) of the considered MIMO-FDR system and validate the derived expression by Monte-Carlo simulations. Numerical results indicate that the impacts of three imperfect factors (CEE, THI, and RSI) are remarkable. Specifically, with the considered values of CEE, THI, and RSI, the impact of CEE on the SER is most substantial. Additionally, compared with the ideal system (perfect channel estimations, transceiver hardware, and self-interference cancellation), the SER of the considered system is significantly higher and goes to the error floor fast. Therefore, it is crucial to apply all solutions for reducing the CEE, THI, and RSI in the considered MIMO-FDR system.

Transmit Beamforming for Communication and Self-Interference Cancellation in Full Duplex MIMO Systems: A Trade-Off Analysis

The performance of transmit beamforming for both optimized precoding and self-interference cancellation (SIC) in full duplex multiple input multiple output (MIMO) transceivers is analysed in this paper. With sub-space dimension larger than that of the null-space of the self-interference channels, the precoding error is reduced but the interference suppression ratio (ISR) is degraded, resulting in a trade-off between multibeam communication and MIMO SIC. An analytical approach for the ISR evaluation is proposed assuming known eigenvalue distribution of the self-interference channels, and a closed-form ISR expression is derived after applying a uniform distribution approximation. The ISR and precoding error trade-off curves are also formulated. Joint SIC by transmit beamforming and beam-based analog adaptive filters over both propagation and analog domains is proposed to achieve better SIC performance and enable more flexible receive antenna selection. Simulation results verify the theoretical analyses.

Resource Allocation for MIMO Full-Duplex Backscatter Assisted Wireless-Powered Communication Network With Finite Alphabet Inputs

With practical finite alphabet inputs, usually the throughput of a practical communication system cannot reach the capacity based on assumption of Gaussian inputs. In this paper, we study the resource allocation strategy for multiple-input multiple-output (MIMO) full-duplex backscatter assisted wireless-powered communication network (FD-BAWPCN) with finite alphabet inputs, to maximize the sum-throughput. Firstly, we propose a gradient-based resource allocation strategy (GBRA), which alternately optimizes the precoder and time allocation based on the two-block alternating direction method of multipliers (ADMM). Secondly, to reduce the computational complexity and improve the feasibility of the strategy in practical applications, we further propose a codebook-based resource allocation strategy (CBRA), which can run more than three orders of magnitude faster than GBRA at the expense of a small sum-rate degradation. Then, the performance of the full-duplex (FD) and half-duplex (HD) system with or without backscatter assistance using GBRA are compared and analyzed. Numerical results demonstrate that the GBRA strategy has great robustness under various conditions but suffers a high computational complexity, and the CBRA strategy is effective and converges speedily.

Impacts of Imperfect Channel State Information, Transceiver Hardware, and Self-Interference Cancellation on the Performance of Full-Duplex MIMO Relay System.

Imperfect channel state information (I-CSI) and imperfect transceiver hardware often happen in wireless communication systems due to the time-varying and random characteristics of both wireless channels and hardware components. The impacts of I-CSI and hardware impairments (HI) reduce not only the system performance but also the self-interference cancellation (SIC) capability of full-duplex (FD) devices. To investigate the system performance in realistic scenarios, in this paper, we consider the performance of an FD multiple-input multiple-output (MIMO) relay system under the effects of I-CSI, imperfect SIC (I-SIC), and imperfect transceiver hardware. We mathematically derive the exact closed-form expressions of the outage probability (OP) and ergodic capacity of the considered HI-FD-MIMO relay system over Rayleigh fading channels with the existence of I-CSI, I-SIC, and HI. Numerical results indicate that the performance in terms of OP and capacity reaches saturation faster, especially when the channel estimation error, the residual self-interference (RSI), and HI levels are remarkable. Therefore, various solutions for effectively reducing the channel estimation error, RSI, and HI levels in the HI-FD-MIMO relay system should be carried out to improve the system performance. All derived mathematical expressions are verified through Monte-Carlo simulations.

Joint Nullspace Projection-Based Interference Mitigation for Full-Duplex Relay-Assisted Multicell Networks

Full-duplex (FD) relaying is more spectrally efficient compared to its counterpart, conventional half-duplex (HD) relaying, since it allows simultaneous transmission and reception in the same frequency channel. Working in FD relaying scheme results in relay self-interference (SI) signal that degrades the system performance. Furthermore, in a multicell scenario, the FD relay is also subject to interrelay interference (IRI) and relay-to-destination interference (RDI) coming from co-channel relays in adjacent cells. Conventionally, zero-forcing (ZF) beamforming (BF) is adopted to mitigate either the SI, IRI, or RDI but not all of them simultaneously. In this article, beamforming (BF) matrices at the multiple-input–multiple-output (MIMO) relays are designed jointly to mitigate the SI, IRI, and RDI signals based on channel alignment and nullspace projection. In addition, joint power allocation for the source and relay is performed for maximizing the system performance in terms of ergodic capacity. Numerical results demonstrate and verify that the proposed scheme can achieve better outage probability and ergodic capacity compared to baseline schemes. Our findings reveal that MIMO FD relaying significantly improves the system performance compared to its counterpart conventional MIMO HD relaying.

Beam-Based Analog Self-Interference Cancellation in Full-Duplex MIMO Systems

Self-interference (SI) cancellation for full-duplex (FD) multiple input multiple output (MIMO) systems is challenging due to both hardware and signal processing complexity. In this paper, a beam-based adaptive filter structure with analog least mean square (ALMS) loops is proposed to significantly reduce the complexity of SI cancellation for FD MIMO systems. With this structure, the number of adaptive filters required for SI cancellation scales linearly with the number of transmit beams rather than quadratically with the number of antennas. Furthermore, to avoid additional transmit chains used to up-convert the beam signals to generate reference signals for the ALMS loops, a novel method is proposed to select the optimized reference signals from all transmitted signals. In addition, our stationary analysis shows that the proposed structure for FD MIMO systems outperforms the ALMS loop employed for an FD single input single output system. Simulations are conducted to confirm the theoretical analyses.

On the Performance of Full-Duplex Spatial Modulation MIMO System With and Without Transmit Antenna Selection Under Imperfect Hardware Conditions

Hardware impairments (HI) due to imperfect manufactured electronic parts degrade the performance of wireless systems. In this paper, we consider a bidirectional full-duplex (FD) spatial modulation (SM) multiple-input multiple-output (MIMO) system with non-ideal hardware and residual self-interference (RSI). We propose to use the transmission antenna selection (TAS) as a solution to mitigate this degradation. The performance of the considered system is analyzed using mathematical analysis. Specifically, we first derive the exact closed-form expressions of the outage probability (OP), symbol error probability (SEP), and achievable data rate (ADR) for two cases: with and without TAS. Given these expressions, we conduct a detailed evaluation of the system performance under various scenarios to gain insight into its behavior. Essential conclusions are then made on HI and RSI’s impacts, especially for the case with TAS and high transmission rates.

Effect of Doppler Shift on the Performance of Multicell Full-Duplex Massive MIMO Networks

This paper studies the uplink and downlink achievable rates for large-scale multiple-input–multiple-output (MIMO) systems, assuming perfect and imperfect channel state information under the effect of Doppler shift. Different from the previous relevant work, we consider a multiuser system scenario, where a full-duplex mode worked in the multicell base stations, and maximum-ratio combining/maximum-ratio transmission is applied at the receiver end. Then, we derive the asymptotic uplink and downlink sum rate by utilizing the large number theorem and considering the performance comparison between the perfect and imperfect channel. In addition, the impact of the Doppler shift on the system performance (e.g., the uplink and downlink sum rates) is analyzed via the simulation results.