In-band Full-duplex Communication Research Articles

MIMO In-Band-Full-Duplex PLC: Design, Analysis and First Hardware Realization of the Analog Self-Interference Cancellation Stage

In-band full-duplex (IBFD) is an attractive solution for increasing the throughput of Power Line Communication (PLC) systems. In IBFD, each network node is allowed to transmit and receive simultaneously in the same frequency band. This paper discusses the importance of defining figures of merit to analyze IBFD performance, which is often forgotten by the literature that addresses IBFD from a pure system level and signal processing perspective. This is because in IBFD hardware-related aspects are of great importance. The focus is then given to the first self-interference (SI) cancellation stage, namely the analog coupling and self-interference cancellation stage (ASICS). Two architectures are considered. A detailed analysis is offered by taking into account circuit-level aspects. A broadband multiple conductor PLC scenario is assumed to enable multiple-input multiple-output (MIMO) IBFD communication. The first considered architecture performs SI subtraction exploiting operational amplifiers. The second proposed architecture exploits the characteristics of a three ports magnetic circuit together with a signal generator to remove the SI. Design, analysis, and hardware realization of these circuits have been done to compare and show the practical feasibility of the ASICS for PLC, well known to be challenged by its line impedance matching problems and severe frequency selective channel characteristics. This paper is the first documented contribution of the IBFD ASICS for 2×2 MIMO broadband PLC physically realized and tested in the field.

Blind Source Separation For Full-Duplex Systems: Potential and Challenges

Full-duplex communications systems that transmit and receive simultaneously suffer self-interference due to the mixing of the transmitted signal and the weaker received signal at the same node. The problem becomes compounded in Multi-Input Multi-Output (MIMO) systems, where considerable overhead is dedicated to training. In this article, we discuss using blind source separation techniques, namely Independent Component Analysis (ICA) to reduce training overhead in MIMO in-band full-duplex wireless communication systems. Practical limitations are discussed and experimental results that compare ICA to traditional Least Square approaches are presented, showing the superiority of ICA, especially in low SNR regimes.

RF self-interference cancellation by using photonic technology [Invited

Radio frequency (RF) self-interference is a key issue for the application of in-band full-duplex communication in beyond fifth generation and sixth generation communications. Compared with electronic technology, photonic technology has the advantages of wide bandwidth and high tuning precision, exhibiting great potential to realize high interference cancellation depth over broad band. In this paper, a comprehensive overview of photonic enabled RF self-interference cancellation (SIC) is presented. The operation principle of photonic RF SIC is introduced, and the advances in implementing photonic RF SIC according to the realization mechanism of phase reversal are summarized. For further realistic applications, the multipath RF SIC and the integrated photonic RF SIC are also surveyed. Finally, the challenges and opportunities of photonic RF SIC technology are discussed.

Analog Self-Interference Cancellation Using Auxiliary Transmitter Considering IQ Imbalance and Amplifier Nonlinearity

In-band full-duplex communication, which transmits and receives simultaneously on the same frequency, causes self-interference (SI). In this paper, to cancel SI present in the radio frequency (RF) domain, we propose a novel nonlinear SI cancellation approach using an auxiliary transmitter which is effective in the presence of IQ imbalance and nonlinear distortion. The proposed approach estimates the local transceiver channel by using a time-domain least squares method and creates a signal for SI cancellation based on estimation results and a finite impulse response filter, whose coefficients are derived in this paper. Additionally, we theoretically calculate the SI cancellation limit of the proposed approach. Information about the SI cancellation limit due to phase noise is important for meeting SI cancellation requirements and being able to compare the effects of RF impairments such as IQ imbalance and nonlinear distortion. From simulation results, we show that the proposed approach outperforms the conventional approach and the case of using a general adaptive algorithm for the proposed approach. Furthermore, the SI cancellation limit is improved by adjusting the propagation delay of the SI signal and the canceling signal in addition to sharing one local oscillator in the local transceiver.

Application of ICA on Self-Interference Cancellation of In-Band Full Duplex Systems

In this letter, we propose a modified version of Fast Independent Component Analysis (FICA) algorithm to solve the self-interference cancellation (SIC) problem in In-band Full Duplex (IBFD) communication systems. The complex mixing problem is mathematically formulated to suit the real-valued blind source separation (BSS) algorithms. In addition, we propose a method to estimate the ambiguity factors associated with ICA lumped together with the channels and residual separation error. Experiments were performed on an FD platform where FICA-based BSS was applied for SIC in the frequency domain. Experimental results show superior performance compared to least squares SIC by up to 6 dB gain in the SNR.

A WDM-PON compatible wavelength-reused bidirectional in-band full-duplex radio-over-fiber system

A bidirectional in-band full-duplex radio-over-fiber system for the WDM-PON architecture is proposed and experimentally demonstrated. To deploy a simplified and low-cost optical network unit (ONU), the downlink optical carrier at the ONU is reused for uplink connection by employing a polarization modulator (PolM) as the transmitter at the center office (CO). Meanwhile, at the CO the wideband optical self-interference cancellation (SIC) is implemented while coping the output of the PolM as the reference signal, to harvest the in-band full-duplex communication and further facilitate a compact ONU. Also, a simple digital SIC algorithm based on the least mean square (LMS) method is introduced to compensate for the delay and amplitude fluctuations arising from fiber transmission. In experiments, simultaneous transmissions of 3.6 Gb/s 16-QAM OFDM downstream and 1.8 Gb/s 16-QAM OFDM upstream signals over the 6.15-km down and up fiber links are successfully demonstrated, wherein both downlink and uplink signals are centered at the same frequency from 3 to 8 GHz. The uplink transmission demonstration is accompanied by the emulated self-interference signal from the 3.6 Gb/s downstream signal. With the existence of 6.15-km fiber transmission, over 20.1-dB cancellation depth for the 1-GHz wideband SIC is experimentally achieved. The error-vector magnitude (EVM) performance of the uplink transmission thereby is improved from over 45.8% to below 9.9%.

Analog Least Mean Square Loop for Self-Interference Cancellation: A Practical Perspective.

Self-interference (SI) is the key issue that prevents in-band full-duplex (IBFD) communications from being practical. Analog multi-tap adaptive filter is an efficient structure to cancel SI since it can capture the nonlinear components and noise in the transmitted signal. Analog least mean square (ALMS) loop is a simple adaptive filter that can be implemented by purely analog means to sufficiently mitigate SI. Comprehensive analyses on the behaviors of the ALMS loop have been published in the literature. This paper proposes a practical structure and presents an implementation of the ALMS loop. By employing off-the-shelf components, a prototype of the ALMS loop including two taps is implemented for an IBFD system operating at the carrier frequency of 2.4 GHz. The prototype is firstly evaluated in a single carrier signaling IBFD system with 20 MHz and 50 MHz bandwidths, respectively. Measured results show that the ALMS loop can provide 39 dB and 33 dB of SI cancellation in the radio frequency domain for the two bandwidths, respectively. Furthermore, the impact of the roll-off factor of the pulse shaping filter on the SI cancellation level provided by the prototype is presented. Finally, the experiment with multicarrier signaling shows that the performance of the ALMS loop is the same as that in the single carrier system. These experimental results validate the theoretical analyses presented in our previous publications on the ALMS loop behaviors.

Simultaneous Transmitting–Receiving–Sensing for OFDM-based Full-Duplex Cognitive Radio

In this paper, a Transmitting–Receiving–Sensing (TRS) mode of OFDM-based Full-Duplex Cognitive Radio (FD-CR) is proposed. The new mode aims at monitoring the Primary User (PU) activities on the operating channel while establishing an in-band full-duplex communication between two communicating Secondary Users (SUs), i.e. SUs transmit and receive simultaneously on the same frequency band. Assuming that the primary activity covers all the operating band when PU is active, Spectrum Sensing is performed on some Sub-Carriers (SCs) which are neutralized by the two communicating SUs. Letting some SCs null by both SUs helps to accurately performing the spectrum sensing on these SCs since no residual self-interference neither secondary transmission are present. When PU is detected on these SCs, then we consider that he becomes active again; Then SUs should vacate the channel. For the proposed mode, false alarm, detection and collision probabilities are derived in addition to the throughput rate. An optimal selection of the sensing SCs per OFDM symbol is derived with respect to a maximal tolerable rate of collision between PU and SU transmission. Numerical results corroborate the effectiveness of our proposed mode in terms of the PU awareness and the secondary throughput rate.

Performance analysis of two tier HetNets with massive MIMO enabled wireless backhauling

Dense deployment of small cells escalates the network capacity, making it a candidate technology for the future wireless network. However, backhauling of such a large number of small cells becomes a major challenge in its successful deployment. In this paper, a framework for massive MIMO enabled wireless backhauling in a two-tier heterogeneous network is developed. The framework considers massive MIMO enabled macro base station and in-band full-duplex (IBFD) small cell base station. Massive MIMO system provides high spectral efficiency and high energy efficiency. Besides, due to IBFD capability, the small cells can utilize the same frequency band to communicate over the access link and the backhaul link simultaneously. Tools from the stochastic geometry are utilized to model and derive the analytical expressions of coverage probability and area spectral efficiency (ASE). Furthermore, a trade-off between ASE and coverage probability is observed. All the analytical results are verified by simulation. Simulation results show that massive MIMO and IBFD communication may be useful technologies from the backhauling perspective in the dense small cell network. It is observed that the proposed framework provides 42.30% improvement in the coverage performance over the other existing framework for rate threshold of 1 bps/Hz. Furthermore, optimal performance for the proposed model can be achieved by tuning of bandwidth allocation factor.

Energy Efficiency Maximization via Joint Sub-Carrier Assignment and Power Control for OFDMA Full Duplex Networks

In this paper, we develop an energy efficient resource allocation scheme for orthogonal frequency division multiple access (OFDMA) networks with in-band full-duplex (IBFD) communication between the base station and user equipments (UEs) considering a realistic self-interference (SI) model. Our primary aim is to maximize the system energy efficiency (EE) through a joint power control and sub-carrier assignment in both the downlink (DL) and uplink (UL), where the quality of service requirements of the UEs in DL and UL are guaranteed. The formulated problem is non-convex due to the non-linear fractional objective function and the non-convex feasible set which is generally intractable. In order to handle this difficulty, we first use fractional programming to transform the fractional objective function to the subtractive form. Then, by employing Dinkelbach method, we propose an iterative algorithm in which an inner problem is solved in each iteration. Applying majorization-minimization approximation, we make the inner problem convex. Also, by introducing a penalty function to handle integer sub-carrier assignment variables, we propose an iterative algorithm for addressing the inner problem. We show that our proposed algorithm converges to the locally optimal solution which is also demonstrated by our simulation results. In addition, simulation results show that by applying the IBFD capability in OFDMA networks with efficient SI cancellation techniques, our proposed resource allocation algorithm attains a 75% increase in the EE as compared to the half-duplex system.

A Framework for 5G Networks with In-Band Full-Duplex Enabled Drone-Mounted Base-Stations

Drone-mounted base-stations (DBSs) characterized by high mobility and low cost intrinsic attributes can be deployed to enhance the network capacity in order to relieve the mismatch between the large amount of user demands and the limited wireless resources. In this article, we propose a DBS-assisted in-band full-duplex (IBFD) HetNet framework for 5G networks. We then discuss the problem of DBS-assisted heterogeneous networks (DBSH) with IBFD communications, which can be decomposed into three sub-problems: the DBS placement problem, the UE assignment problem, and the bandwidth and power allocation problem (including bandwidth and power allocation for backhaul links and access links). We propose a greedy algorithm, named DBSH-IBFD, to solve three sub-problems as follows: 1) All DBSs are deployed one by one. The horizontal location of a DBS is determined by the area with the maximum aggregated weight (the weight is defined by the number, the location, and SINR of a UE) and then the altitude of a DBS is determined by which the maximum network throughput is achieved. 2) Each UE is associated with the BS that provides the best signal-to-noise-ratio. 3) The power and bandwidth of the MBS are allocated to all DBSs based on the workload, and all BSs allocate power and bandwidth to their associated UEs. DBSH-IBFD is demonstrated to achieve better throughput performance than benchmark algorithms, and IBFD-enabled DBSs are the most spectrum efficient as compared to the MBS and HD-enabled DBSs.

Flexible backhaul-aware DBS-aided HetNet with IBFD communications

Abstract Drone-mounted base-stations (DBSs) are promising complements and substitutes of the terrestrial base-stations. We investigate the problem of P lacement and c O mmunications in the D BS-aided heterogeneous network (POD) with tier-1 backhaul using free space optics communications and tier-2 backhaul utilizing in-band full-duplex communications to provide ubiquitous connections and high spectrum efficiency. The POD problem is shown to be NP-hard, and thus we simplify the POD problem by decomposing it into three sub-problems. Finally, we propose an approximation algorithm to solve the POD problem, and demonstrate that the proposed algorithm is superior to two baseline algorithms.

Approximate Algorithms for 3-D Placement of IBFD Enabled Drone-Mounted Base Stations

The future 5G network is expected to provide throughput 1000 times and spectrum efficiency 10 times those of the current 4G network. In-band full-duplex (IBFD) is a promising technique for 5G that can conceivably improve spectrum efficiency. Drone-mounted base stations (DBSs) provide high mobility and high flexibility, and leveraging DBSs to provision services to UEs can facilitate the quality of service of the wireless network and enlarge the coverage area. Therefore, the throughput and the spectrum efficiency can be improved by leveraging IBFD-enabled DBSs. We formulate the drone-mounted base station placement with IBFD communications ( DBSP-IBFD ) problem, which consists of two sub-problems: the joint bandwidth, power allocation and UE association ( joint-BPU ) problem and the DBS placement problem. We first propose an approximate algorithm to solve the joint-BPU problem that provides guaranteed performance. Then, an exhaustive search method is employed to obtain the optimal locations for DBSs. After that, we propose a $\frac{1}{2}(1-\frac{1}{2^{l}})$ -approximation algorithm to solve the DBSP-IBFD problem, where $l$ is the number of simulation runs. Simulation results have demonstrated that the throughput of the proposed approximate algorithm is superior to benchmark algorithms in solving the DBSP-IBFD problem.

Full-Duplex Enabled Time-Efficient Device Discovery for Public Safety Communications

Device-to-device (D2D) communications is the integral part of public safety (PS) communications. However, the most important requirement is the users’ rapid discovery to timely communicate the emergency information. The existing half-duplex (HD) results in large time delays because it cannot transceive during same time slot. In-band full duplex (IB-FD) communications is an enabler to quickly discover the user because of simultaneous transmission and reception during same time-frequency block. In this paper, we proposed the frame structure for IB-FD system with prioritized PS users in resource allocation. Moreover, to improve spectral efficiency, time-efficient device discovery resource allocation (TE-DDRA) scheme has been proposed as well, where a user can switch the transmission mode from HD to IB-FD when the demand exceeds the available resources in HD mode. The proposal is validated by system-level simulations in terms of discovery time with conventional random access mode. The simulation results shows that with PS priority mode around 37% discovery time as compared with random access mode.

Compact Co-Horizontally Polarized Full-Duplex Antenna With Omnidirectional Patterns

This letter presents a compact co-horizontally polarized (HP) in-band full-duplex (IBFD) antenna with omnidirectional patterns. The Tx antenna is a variant turnstile antenna with four 90° progressively phased T-shaped monopoles, whereas the Rx antenna is an in-phase loop antenna with four symmetrically excited dipoles. The polarizations and radiation patterns of both antennas are horizontally polarized and omnidirectional patterns in the azimuth plane. Nevertheless, a high measured isolation of more than 37 dB across the desired band is achieved with an orthogonal spatial phase diversity approach. To the best of our knowledge, this is the first time two co-HP omnidirectional antennas are integrated with a high isolation for the IBFD communication. The proposed antenna has the potential to double the spectral efficiency of wireless communication systems and to combat the polarization variations in the rich multipath environments.

Uplink Power Control and Ergodic Rate Characterization in FD Cellular Networks: A Stochastic Geometry Approach

Simultaneous co-channel transmission and reception, denoted as in-band full-duplex (FD) communications, has been promoted as a solution to improve the spectral efficiency in wireless networks. For cellular networks, in addition to the existing aggregate interference in half-duplex transmission, the residual self-interference and cross-mode interference [i.e., between uplink (UL) and downlink (DL)] impose major obstacles for FD communications’ deployment. Although the FD communication’s promising impact on the overall network data rate has been established in the literature, the rate gains are achieved in the DL transmissions at the expense of marginal gain, or even degradation, for the UL transmissions. This paper, therefore, focuses on the analysis of UL ergodic rate in FD cellular networks where a minimum distance between BSs using the same time-frequency resource block is imposed. Hence, the mutually interfering BSs’ locations are modeled by Matern hard core point process. The distribution of the aggregate interference and the channel-to-interference-plus-noise ratio at the UL of a typical user are characterized using a stochastic geometry analysis. Several UL power control techniques are presented and their resulting ergodic rates are derived and compared. The simulation results suggest that the UL performance highly depends on the network parameters and the UL power control techniques.

Queueing and channel access delay analysis in in-band full-duplex wireless networks

In-band full-duplex wireless communication, which supports a node to transmit and receive simultaneously in the same frequency band, is receiving growing interest. The latency of packets in an in-b...

USRP 장치를 이용한 동일대역 전이중 무선통신 연구

The implementation of an in-band full-duplex wireless communication system is demonstrated in this study. In the analog/RF domain, the self-interference(SI) signal is reduced using a separate antenna for the transmitter and receiver paths, and most of the SI signal is canceled in the digital domain. A software defined radio(SDR) is used to implement the in-band full-duplex wireless communication system. The USRP X310 device uses transmitting and receiving antennas. By adjusting the gain of the transmitting and receiving ends of the SDR device, the magnitude of the SI signal entering the receiving antenna, and the size of the received signal from the outside, are both set to −64 dB. To verify the in-band full-duplex wireless communication performance, the source data is image and orthogonal frequency-division multiplexing is used for modulation. A WiFi standard frame with a carrier frequency of 2.67 GHz and bandwidth of 20 MHz is used. In the received signal, the SI signal is canceled by digital signal processing and the SI signal is attenuated by up to 34 dB. OFDM demodulation was impossible when the SI signal was not removed. However, the bit error rate is reduced to 2.63×10−5 when the SI signal is attenuated by 34 dB, and no error is detected in the 100 Mbit data output as a result of passing through the Viterbi decoder.

Geometry-Based Statistical Channel Models of Reflected-Path Self-Interference in Full-Duplex Wireless

Self-interference (SI) channel characteristics are crucial for SI cancellation (SIC) techniques of in-band full-duplex (IBFD) wireless communications. This paper develops two geometry-based statistical channel models-geometry-based concentric ellipses model (GBCEM) and geometry-based concentric circles model (GBCCM)-for full-duplex systems in micro- and macrocell environments, respectively, to analyze the characteristics of reflected-path SI (RSI) compared with the desired signal (DS). The probability density functions of incident angle and path length are derived to identify the fading characteristics of RSI and DS. The simulations based on GBCEM and GBCCM intuitively present the signal characteristics by the signal envelope in the time domain, the statistics of signal envelope, the autocorrelation properties, and the power spectral density. We find that the fading characteristics of RSI and DS can be modeled as Rayleigh when reflectors sit far away from the receiver. We also find that RSI is still likely to be Rayleigh fading, even if DS is not when reflectors scatter in a specific region restricted by the range of incident angle. Our works on the characteristics of RSI and DS are generally helpful to explore a more efficient SIC mechanism for IBFD systems, and the developed models are useful for both simulation and analysis purposes.

In-Band Full-Duplex Relay-Assisted Millimeter-Wave System Design

Millimeter-wave (mmWave) communication is a promising technology for future wireless systems due to the availability of huge unlicensed bandwidth. However, the need for large number of radio frequency (RF) chains associated with the antenna array and the corresponding increase in hardware complexity and power consumption are major stumbling blocks to its implementability. In this paper, we propose a low-complexity in-band full-duplex relay-assisted mmWave communication system design. We obtain the proposed multiple-input multiple-output analog–digital hybrid transceivers and relay filters by minimizing the overall sum-mean-square-error while mitigating the effect of residual loopback self-interference (LSI) in the system. The number of RF chains required in the proposed design is less than the number of antennas. We first present a design assuming the availability of perfect channel state information (CSI) at all the nodes. Later, we extend it to a robust design assuming a more realistic scenario, where the available CSI is imperfect. Furthermore, the LSI channel knowledge is assumed to be imperfect for both the designs rendering them robust to errors in loopback CSI. We employ sparse approximation technique to reduce the hardware complexity in the proposed system designs. The proposed algorithms are shown to converge to a limit even though the global convergence is hard to prove since the overall problem is non-convex. The hardware complexity-performance tradeoff of the proposed design is analyzed. Furthermore, the resilience of the robust design in the presence of CSI errors and the performance of both the proposed designs over various parameters are illustrated via numerical simulations.