In-Band Full-Duplex Wireless: Challenges and Opportunities

Although in-band full-duplex (IBFD) radios promise to double the throughput of a wireless link, they are more vulnerable to jamming attacks than their out-of-band full-duplex (OBFD) counterparts. For two communicating OBFD nodes, a jammer needs to attack both the uplink and the downlink channels to completely break the communication link. In contrast, only one common channel needs to be jammed in the case of two IBFD nodes. Even worse, a jammer with self-interference suppression (SIS) capabilities (the underlying technique of IBFD radios) can learn the transmitters' activity while injecting interference, allowing it to react instantly to the transmitter's strategies. In this work, we consider a power-constrained IBFD “reactive-sweep” jammer that sweeps through the set of channels by jamming a subset of them simultaneously. We model the interactions between the IBFD radios and the jammer as a stochastic constrained zero-sum Markov game in which nodes adopt the frequency hopping (FH) technique as their strategies to counter jamming attacks. Beside the IBFD transmission-reception (TR) mode, we introduce an additional operation mode, called transmission-detection (TD), in which an IBFD radio transmits and leverages its SIS capability to detect jammers. The aim of the TD mode is to make IBFD radios more cognitive to jamming. The nodes' optimal defense strategy that guides them when to hop and which operational mode (TD or TR) to use is then established from the equilibrium of the stochastic Markov game. We prove that this optimal policy has a threshold structure, in which IBFD nodes stay on the same channel up to a certain number of time slots before hopping. Simulation results show that our policy significantly improves the throughput of IBFD nodes under jamming attacks.

Recent advances in the design of in-band full-duplex (IBFD) radios promise to double the throughput of a wireless link. However, IBFD-capable nodes are more vulnerable to jamming attacks than their out-of-band full-duplex (OBFD) counterparts, and any advantages offered by them over the OBFD nodes can be jeopardized by such attacks. A jammer needs to attack both the uplink and the downlink channels to completely break the communication link between two OBFD nodes. In contrast, he only needs to jam one channel (used for both uplink and downlink) in the case of two IBFD nodes. Even worse, a jammer with the IBFD capability can learn the transmitters' activity while injecting interference, allowing it to react instantly with the transmitter's strategies. In this paper, we investigate frequency hopping (FH) technique for countering jamming attacks in the context of IBFD wireless radios. Specifically, we develop an optimal strategy for IBFD radios to combat an “IBFD reactive sweep jammer”. First, we introduce two operational modes for IBFD radios: transmission reception and transmission-detection. These modes are intended to boost the anti-jamming capability of IBFD radios. We then jointly optimize the decision of when to switch between the modes and when to hop to a new channel using Markov decision processes. Numerical investigations show that our policy significantly improves the throughput of IBFD nodes under jamming attacks.

In-Band Full-Duplex (IBFD) operation allows simultaneous transmission of data over the same frequency band. However, IBFD operation experiences a strong Self-Interference (SI) due to its TX-signal leaking to the receiver. This paper presents a compact dual port antenna (footprint about 0.33λ × 0.33λ) with high isolation between TX/RX ports designed using an accurate and fast tool for full-wave electromagnetic analysis based on the Method of Moments, and global/local search algorithms for design optimization. The resulting antenna works at 2.6GHz in IBFD mode providing measured passive isolation on the order of 20-30 dB at indoor environments, supporting the potential of these complex dense structures that depart from designs found in literature.

Performance analysis of distributed coordination function with early collision detection in In-band Full-duplex wireless networks

In-band Full-duplex (IBFD) wireless communication allows improved throughput for wireless networks. The current Half-duplex (HD) medium access mechanism Request to Send/Clear to Send (RTS/CTS) has been directly applied to IBFD wireless networks. However, this is only able to support a symmetric dual link, and does not provide the full advantages of IBFD. To increase network throughput in a superior way to the HD mechanism, a novel three-way handshaking access mechanism RTS/SRTS (Second Request to Send)/CTS is proposed for point to multipoint (PMP) IBFD wireless networks, which can support both symmetric dual link and asymmetric dual link communication. In this approach, IBFD wireless communication only requires one channel access for two-way simultaneous packet transmissions. We first describe the RTS/SRTS/CTS mechanism and the symmetric/asymmetric dual link transmission procedure and then provide a theoretical analysis of network throughput and delay using a Markov model. Using simulations, we demonstrate that the RTS/SRTS/CTS access mechanism shows improved performance relative to that of the RTS/CTS HD access mechanism.

In-band full duplex (IBFD) radio represents one of the key technologies for future wireless communication and radar applications. A major challenge of this technology is to mitigate the strong self-interfer-ence (SI) so that the residual SI level falls below the receiver's noise floor. Radio frequency (RF) self-inter-ference cancellation (SIC) is essential for preventing an IBFD receiver from becoming saturated by the SI. We commence with an in-depth review of the promising analog least mean square (ALMS) adaptive filtering architecture, conceived for RF SIC in the IBFD radio RF front-end. The cancellation circuits employing this architecture can be implemented purely by analog components without any involvement of more power-thirsty digital signal processing. The behaviors, performance, and implementation of the ALMS loop are presented. Finally, their applications in various IBFD radios are discussed, and future research directions are provided.

In In-band Full-duplex (IBFD) wireless networks, the RTS/CTS mechanism is unable to establish an asymmetric dual link and to recognize the transmission mode of communication nodes to capture more opportunities of IBFD transmission, which limits total network throughput. In this paper, we propose a novel distributed IBFD MAC mechanism to establish symmetric/asymmetric dual link in wireless networks. Here we fully consider the two modes of asymmetric dual transmission. By medium access, the neighbors of communication nodes can clearly know network transmission status, which will provide extra opportunities of asymmetric IBFD dual communication. Finally, we develop a Markov model to characterize the non-saturation throughput of our proposed mechanism in IBFD wireless networks. The numerical results show that the throughput of IBFD network with our scheme nearly doubles that of HD network with RTS/CTS. Moreover, the non-saturation degree of the network has little influence on the throughput of our mechanism.

In-band full-duplex (IBFD) operation can potentially double the spectral efficiency of wireless networks. For IBFD operation, self-interference is a critical issue. In addition, in full-duplex cellular (FDC) networks, particularly when the cell size is small, inter-user interference would be another limiting factor for the performance. To overcome these issues, the scheduling scheme proposed in this paper is to adaptively utilize bidirectional IBFD in addition to half-duplex (HD) and unidirectional IBFD in FDC networks according to the residual self-interference after interference cancellation and inter-user interference. The proposed scheme is based on generalized proportional fair scheduling by using a fairness parameter. Extensive simulations are conducted to analyze the impact of the cell size. Simulation results revealed that the use of bidirectional IBFD is extremely effective for a small cell with few users if self-interference is sufficiently canceled because inter-user interference is large in small cell and the scheduler tends to select bidirectional IBFD in the cell with few users.

Recent advances in self-interference cancellation techniques enable in-band full-duplex wireless systems, which transmit and receive simultaneously in the same frequency band with high spectrum efficiency. As a typical application of in-band full-duplex wireless, in-band full-duplex relaying (FDR) is a promising technology to integrate the merits of in-band full-duplex wireless and relaying technology. However, several significant research challenges remain to be addressed before its widespread deployment, including small-size full-duplex device design, channel modeling and estimation, cross-layer/joint resource management, interference management, security, etc. In this paper, we provide a brief survey on some of the works that have already been done for in-band FDR, and discuss the related research issues and challenges. We identify several important aspects of in-band FDR: basics, enabling technologies, information-theoretical performance analysis, key design issues and challenges. Finally, we also explore some broader perspectives for in-band FDR.

CMOS-integrated in-band full-duplex (IBFD) operation in wireless links and cryogenic quantum platforms was previously enabled by magnetic-free circulators using the phase non-reciprocity from spatial-temporal modulation. In this article, we present an alternative and simple integrated circuit scheme, which not only realizes non-reciprocal signal flows required for IBFD operations but also improves the isolation performance by completely eliminating any chip-level transmit (TX)-to-receive (RX) coupling. The above functions are enabled by performing a direction/frequency-independent, single-sideband down-conversion to the counter-propagating TX and RX signals, which creates opposite deviations of on-chip TX and RX frequencies with respect to the antenna (ANT) frequency. Such a principle also broadens the isolation bandwidth and enables integrated receiver down-mixing function. As a proof-of-concept, a 3.4-4.6-GHz (30% fractional bandwidth) IBFD interface is implemented using a 65-nm bulk CMOS technology. The measured TX-to-RX isolation of the circuit is 32-51 dB at 300 K, and 14-29 dB at 4.2 K. The measured TX-to-ANT and ANT-to-RX insertion losses are 3.0 and 3.2 dB at 300 K, and 1.9 and 2.0 dB at 4.2 K. At 300 K, the measured TX-to-ANT and ANT-to-RX IIP3 are 29.5 and 27.6 dBm, respectively. The IBFD core of the chip occupies an area of 0.27 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and has a dc power (nominally consumed in an on-chip modulation clock generator) of 48 mW at 300 K and 42.6 mW at 4.2 K.

In-band full duplex (IBFD) wireless is of utmost interest to future wireless communication and networking due to great potentials of spectrum efficiency. IBFD wireless, how- ever, is throttled by its key challenge, namely self-interference. Therefore, effective self- interference cancellation is the key to enable IBFD wireless. This paper proposes a real-time non- linear self-interference cancellation solution: Deep learning based Self-Interference Cancellation (DSIC) to enable IBFD wireless. In this solution, a self-interference channel is modeled by a deep neural network (DNN). Synchronized self- interference channel data is first collected to train the DNN of the self-interference channel. Afterwards, the trained DNN is used to cancel the self-interference at a wireless node. This solution has been implemented on a USRP SDR testbed and evaluated in real world in multiple scenarios with various modulations in transmitting information including numbers, texts as well as images. It results in the performance of 17dB in digital cancellation, which is very close to the self-interference power and nearly cancels the self- interference at a SDR node in the testbed. The solution yields an average of 8.5% bit error rate (BER) over many scenarios and different modulation schemes.

The fifth-generation wireless system framework provides the option to evaluate the performance of in-band full-duplex (IBFD) operation through flexible duplexing. The resulting self-interference, however, must be mitigated within a fraction of a symbol duration for successful communication. This paper introduces the use of machine learning to accelerate the tuning of multi-tap adaptive RF cancellers. The tuning performance of a prototype system using a two-tap canceller was measured over a 20 MHz bandwidth centered at 2.5 GHz, and demonstrated more than 38 dB of cancellation with less than 10 tuning iterations. This tuning speed is significantly faster than previous approaches, and illustrates that this novel application of machine learning to RF canceller tuning can enable IBFD operation in dynamic interference environments.

By current medium access control mechanisms designed for Half-duplex (HD), a node in distributed In-band Full-duplex (IBFD) wireless networks cannot identify the HD or IBFD transmission modes of the other nodes. This will decrease IBFD transmission opportunities by preventing simultaneous transmission in asymmetric dual link. In this paper, we propose a novel in-band Full-duplex Distributed Medium Access (FD-DMA) mechanism for wireless networks. Using this mechanism, both symmetric dual link and asymmetric dual link can be established by only one channel access. Moreover, all the neighbor nodes of primary transmitter and primary receiver can know exactly the IBFD transmission modes, which will increase the opportunity of IBFD communication and solve hidden nodes problem. The performance analysis and simulations show that the throughput of IBFD networks with FD-DMA mechanism nearly doubles that of the HD networks with RTS/CTS mechanism, and is much higher than that of IBFD networks with RTS/CTS mechanism.

In-band full-duplex (IBFD) transmission represents an attractive option for increasing the throughput of wireless communication systems. A key challenge for IBFD transmission is reducing self-interference. Fortunately, the power associated with residual self-interference can be effectively canceled for feasible IBFD transmission with combinations of various advanced passive, analog, and digital self-interference cancellation schemes. In this survey paper, we first review the basic concepts of IBFD transmission with shared and separated antennas and advanced self-interference cancellation schemes. Furthermore, we also discuss the effects of IBFD transmission on system performance in various networks such as bidirectional, relay, and cellular topology networks. This survey covers a wide array of technologies that have been proposed in the literature as feasible for IBFD transmission and evaluates the performance of the IBFD systems compared to conventional half-duplex transmission in connection with theoretical aspects such as the achievable sum rate, network capacity, system reliability, and so on. We also discuss the research challenges and opportunities associated with the design and analysis of IBFD systems in a variety of network topologies. This work also explores the development of MAC protocols for an IBFD system in both infrastructure-based and ad hoc networks. Finally, we conclude our survey by reviewing the advantages of IBFD transmission when applied for different purposes, such as spectrum sensing, network secrecy, and wireless power transfer.

In band full duplex (IBFD) is an emerging transceiver technology that facilitates simultaneous transmission and reception on the same frequency to double spectral efficiency. Self-interference (SI) from its own transmitter is the biggest challenge in IBFD radios causing significant degradation to its receiver performance. SI cancellation (SIC) techniques proposed in literature involve considerable hardware and software complexities for practical realization of IBFD radios. In this letter, a hybrid cellular architecture is proposed composing of IBFD base station and legacy half duplex user equipments (UEs), thus avoiding complex SIC requirement at UE. A novel frequency allocation scheme is proposed for this hybrid architecture that allows sharing of carrier frequencies among UEs based on distance criteria. As the number of UEs increases, chances of finding UEs that satisfy the distance criteria also increase steadily. Simulation results reveal that the probability of 100% frequency reuse exceeds 0.9 for as few as 8 UEs itself, demonstrating the potential of the proposed idea.