A Survey on Implementation and Applications of Full Duplex Wireless Communications

Abstract

Nowadays, wireless networks play an important role in our daily life. Hence, radio frequency (RF) spectrum which is required to support the large number of users of these networks, have become a very valuable resource. Full Duplex (FD) communications, in which data can be sent and received using the same frequency band at the same time, is a promising solution for satisfying, at least in part, the ever increasing demand for wireless spectrum. Theoretically, FD could double the spectral efficiency and capacity. However, in order to harvest these benefits, it has to combat/suppress self-interference (SI) caused by transmitting and receiving data, simultaneously. FD systems should use SI cancellation methods to deal with this important challenge. Due to the significant benefits of FD communication, this research area has recently attracted much attention among the research community. In this paper, we review the applications and implementation challenges of FD communication in different subject areas such as energy harvesting, vehicular communication, massive Multiple-Input Multiple-Output (MIMO), small cells, practical implementation, millimeter wave and military applications. We also study the tradeoffs in deploying FD communication in each of the applications.

Introduction

Full Duplex (FD) communication is a promising solution to satisfy the increasing demand of mobile data traffic by potentially doubling the system capacity. FD enables wireless systems to simultaneously transmit and receive signals in the same frequency band at the same time. Theoretically, FD transmission can double the spectral efficiency compared to its Half Duplex (HD) counterpart. In traditional systems, where HD mode is used, time division duplex or frequency division duplex are used and this leads to a relatively low spectral efficiency [1]. In contrast, the main advantages of FD transmission can be listed as follows [1], [2]:

• Doubling the ergodic capacity

• Feedback delay reduction

• End-to-end delay reduction

• Network secrecy improvement

• Improving the efficiency of ad hoc network protocols

• Increasing the spectrum usage flexibility

• Increase in throughput

• Collision avoidance

• Solving the hidden terminal problem

• Reducing congestion with the aid of Medium Access Layer (MAC) scheduling

In spite of these benefits, utilizing FD communication has some challenges which can be summarized as follows [1], [2]:

• Self-interference (SI) and imperfect interference cancellation

• Degraded link reliability

• Higher packet loss ratio

• Higher buffer size requirement

• Increased inter-user interference

• Increased power consumption and complexity.

In addition, exploitation of FD capability requires consideration of two important factors: costly equipment capable of delivering FD functionality and coexistence of both uplink (UL) and downlink (DL) transmission on the same channel [3]. Furthermore, FD systems may not always outperform their HD counterpart, and therefore, hybrid schemes developed for adaptively exploiting FD and HD modes should also be considered [2].

The abbreviations which are used in this paper are collected in Table 1.

FD communication has been quite well studied for various types of wireless networks. In this subsection, we review the existing surveys conducted on FD in order to differentiate our work from the existing papers. Our survey investigates the state-of-the-art applications of FD communication. Table 2 presents a comparative summary of existing surveys on FD communication.

A brief review of recent research activities of in-band FD relaying and a discussion on related research issues and challenges have been provided in [6]. The authors explored basics, enabling technologies, information-theoretical performance and key design challenges of in-band FD relaying. The embedding of FD radios in OBUs of future vehicles is discussed in [10]. By considering the effects of imperfect SIC, the authors investigated the design implications of FD devices at higher-layer protocols of future vehicular networks and compared with HD mode.

The authors in [11] provided a detailed overview ofFD-enabled dynamic spectrum sharing and have studied some of the most recent advances in this domain. The authors have also proposed a communication protocol for enabling concurrent sensing and transmission in dynamic spectrum sharing environment. The supporting network architectures and the various transmit and receive antenna designs for FD Cognitive Radio (CR) network communications is reviewed in [9]. The authors classified SI suppression methods for FD CR networks and reviewed the spectrum sensing approaches and security requirements. In addition, major advances in FD MAC protocols, open issues and challenges for supporting FD operations in CR networks are discussed. The authors in [1] studied basic concepts of in-band FD with shared and separated antennas and advanced SIC methods. In addition, research challenges, opportunities and effects of in-band FD on system performance are discussed in the context of bidirectional, relay and cellular networks. Furthermore, development of MAC protocol for an in-band FD system and advantages of in-band FD for spectrum sensing, network secrecy and wireless power transfer are discussed in [1].

A comprehensive list of FD techniques and their pros and cons are presented in [2]. The authors classified various SIC techniques and compared their advantages and disadvantages. In addition, the main impairments that degrades the SIC is analyzed. Furthermore, FD-based MAC protocol design have also been studied. In addition, the challenges related to implementation, performance enhancement and optimization of FD systems are discussed. The potential of FD systems with passive suppression, active analogue cancellation and active digital cancellation for 5G cellular networks have been investigated in [5]. The authors have surveyed the use of FD MAC protocol in order to address challenges such as end-to-end delay and network congestion. In [8], technical challenges and solutions for Long Term Evolution (LTE) compatible FD cellular networks is provided. The authors, by considering features such as wide-band and wide dynamic range support for RF SIC, studied a robust and efficient SI channel estimation technique for digital SIC.

The main concepts of in-band FD wireless is reviewed in [4]. The authors studied a wide range of in-band FD SI mitigation methods and also investigated the design and analysis of research challenges and opportunities in in-band FD wireless systems. In [3], the authors have discussed challenges such as scenarios where FD networking is applicable, effects of interference caused by FD, and more importantly, have also discussed how much improvement could be achieved compared to HD mode when advanced interference management solutions are used. Building on shared-antenna-based transceiver architecture, the challenges of transmitter–receiver isolation in mobile FD devices, have been studied in [7]. The authors provided comprehensive Radio Frequency(RF) measurement results with the aid of complete demonstrator implementation.

From the existing surveys, we can conclude that theresearchers have investigated the FD communication in terms of FD relaying [6], vehicular communication [10], spectrum sensing/sharing [1], [9], [11], MAC protocol design [1], [2], [5], [9], and the most important challenge of FD communication, i.e. SIC [1], [2], [4], [5], [7], [8], [9]. To the best of our knowledge, there is not a survey to investigate FD communication by its applications, while several technologies can exploit FD to improve their performance. Therefore, we aim to classify the applications of FD communication in this paper.

FD communication has attracted many researchers recently [12]. As mentioned before, to the best of our knowledge, there is no survey about applications of FD communication. Therefore, in this paper, we aim to classify the applications of FD communication. In fact, FD communication has a vast variety of applications in different subject areas, such as energy harvesting [13], vehicular communications [14], massive Multiple-Input Multiple-Output (MIMO) [15], small cells [16], millimeter wave [17], military [18], Device-to-Device (D2D) communications [19], relaying [20], network localization [21], cognitive radio [22] and so on. In this paper, we explore some of these important applications to show the tradeoffs that are considered to improve the performance of the system. Topics which are covered in this survey are summarized as:

• Energy Harvesting (EH)

• Vehicular Communications

• Massive MIMO

• Small Cells

• Millimeter Wave

• Military

• Practical Implementation

We describe some important research areas in the field of FD wireless communications. Each topic can exploit FD capabilities according to its use-case. For example, in vehicular communications, an important challenge is to reduce the delay of the system. Hence, FD capability could be used to reduce the delay by simultaneously sensing the environment and sending information. In some other applications, where throughput may be the main performance metric, FD can be used provided SIC and FD-associated problems are taken into consideration. Therefore, we can conclude that for each application, a tradeoff should be considered to use the benefits of FD communication to deal with imposed challenges.

Major topics and performance criteria for FD communication are summarized in Table 3, Table 4, respectively.

The rest of the paper is organized as follows: in Sections 3–7, we review applications of FD communication. At the beginning of each section, the considered application is explained, then existing works considering networking problems, scenarios and performance metrics are reviewed. Finally at the end of each section, challenges of considered application is summarized. In Section 8, future works are introduced and finally paper is concluded.