Haesoon Lee

A Survey of In-Band Full-Duplex Transmission: From the Perspective of PHY and MAC Layers

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.

Bidirectional Full-Duplex Systems in a Multispectrum Environment

Our investigation focuses on the performance of full-duplex systems where both nodes simultaneously exchange their signals using a single spectrum for two-way communication. To maximize the achievable sum rate (ASR) for full-duplex systems in multispectrum environments, we address a new selection strategy that considers the channel state of both nodes. The ASR for a multispectral bidirectional full-duplex (M-BFD) system is obtained using the proposed selection strategy and compared with conventional multispectral bidirectional half-duplex (M-BHD) systems. We derive the ASR as closed-form expressions and quantify the effect of selection diversity on the ASRs for M-BFD and M-BHD systems. In addition, we present practical-case Monte Carlo simulation results by considering the effects of self-interference (SI) and channel correlation. The numerical results show that the ASR gain for M-BFD is larger than that for M-BHD.

A New In-band Full-duplex SIC Scheme Using a Phase Rotator

How well the self-interference cancellation (SIC) technique performs is a primary issue in realizing an in-band full-duplex (FD) wireless communication system. One factor affecting its performance is channel estimation error on the self-interference channel. We propose a new analog SIC scheme which is robust to channel estimation error. It uses phase rotators in the radio frequency (RF) chain. We also derive closed-form equations for the residual self-interference of the proposed and the conventional schemes. The analytical and numerical results show that the residual self-interference under the proposed SIC scheme is less than that using the conventional scheme, even though channel estimation error is present.

A new frame structure for asynchronous in-band full-duplex systems

In in-band full-duplex employing conventional frame structure, pilot contamination is inevitable due to asyn-chronism between the nodes. Asynchronism can occur for several reasons such as propagation delay and synchronization error. Pilot contamination increases channel estimation error for both the desired and self-interference channels. We propose a new frame structure that avoids interference during pilot transmission. The proposed frame structure utilizes maximum time offset information in order to cover all the possible time offsets. We then derive the mean square error (MSE) of the channel estimation when the proposed frame structure is employed. Furthermore, based on the MSE analysis, we deliver superior conditions for the proposed frame structure compared to the conventional one. Finally, we show that sacrificing pilot length to avoid interference during pilot transmission guarantees channel estimation performance when the power of the interference is large.

Capacity analysis of outdated relay selection in opportunistic relaying system using an adaptive transmission technique

In this paper, we investigate the impact of outdated channel state information (CSI) on the channel capacity of an opportunistic relaying system in conjunction with adaptive transmission techniques. We derive the closed-form expressions of the channel capacity and its associated outage probability for four adaptive transmission techniques: (1) optimal rate adaptation with constant transmit power, (2) optimal transmit power and rate adaptation, (3) channel inversion with fixed rate, and (4) truncated channel inversion with fixed rate. Analytical and numerical results show the effects of outdated CSI on the capacity of the optimal power and rate adaptation and the sub-optimal channel inversion techniques. In addition, we compare the channel capacity among various adaptive transmission techniques in the presence of outdated CSI, thereby illustrating the intuitive tradeoff between the achievable capacity and implementation complexity.

Rotated precoder based self-interference cancellation in full-duplex communication

We propose a new method for full-duplex self-interference cancellation. The proposed scheme uses a precoder to align the self-interference channel with orthogonal direction of detection axis. The simulation result shows that the proposed RP-SIC enhances the average throughput of user equipment compared to the conventional scheme in high residual self-interference region.

Impact of Time and Frequency Misalignments in OFDM Based In-Band Full-Duplex Systems

When two nodes communicate using in-band full-duplex (FD) with orthogonal frequency division multiplexing (OFDM), the self-interference (SI) and desired signals experience a time and frequency misalignment problem. In this article, we introduce the effect of timing and frequency offsets in FD systems. A conventional FD node simultaneously receives two signals: the desired signal and the SI. The FD node then synchronizes based on the desired signal, and the SI is distorted by timing and frequency offsets. These timing and frequency offsets break orthogonality and create inter-symbol interference and inter-channel interference that degrade the performance of the self-interference cancellation (SIC). To address this, we design a modified digital SIC approach that considers the timing and frequency offset and synchronizes the desired signal and the SI in consecutive order.

Mode selection in multi-user full-duplex systems considering inter-user interference

This paper focuses on multi-user full-duplex (FD) systems. When multiple users share the same resources, using FD degrades the sum capacity compared to using half-duplex (HD) because of the inter-user interference (IUI) that arises between two FD users. This factor highlights the need for a good strategy for switching between FD and HD modes. We address this first by considering a two-user case and deriving the sum capacities. We then consider the general case of K users and compare the average sum capacities for all-FD mode, all-HD mode and the optimal mode case.

FDR and HDR for AF relaying with QoS guarantees

In this paper, we consider a full-duplex amplify-and-forward (AF) relaying with guaranteeing quality of service (QoS). In order to evaluate the QoS guaranteeing ability of FDR, we derive the effective capacity with considering residual self-interference. Based on the analysis and numerical results, it is verified that the stringent QoS constraint degrades effective capacity performance of full-duplex relay (FDR) more severely than that of half-duplex relay. The simulation results also show that the better link quality at S-R link is required in order to guarantee QoS constraint at FDR.