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About this book

This book provides and assesses the techniques required for the realization of practical wireless-powered backscatter systems for large-scale and intelligent IoT networks. It explores the deployment, reliability, and security aspects of backscatter devices for both indoor and outdoor environments. The book also sheds light on some of the recently evolving technologies such as artificial intelligence/ machine learning, non-orthogonal multiple access (NOMA), and multi-tone carrier techniques and identifies their application in backscatter communications. In addition, it offers a valuable blueprint for future studies in the domains of intelligent reflective surfaces, ambient backscatter communications and massive IoT networks.

Table of Contents

Frontmatter

Cooperative Communication Techniques in Wireless-Powered Backscatter Communication: Preambles and Technical Perspective

Abstract
User cooperation is considered as a key enabling technology in wireless-powered backscatter communication (BaKcom) to improve the energy efficiency of the overall network while comparing to a traditional non-cooperative system. In light of the literature on BaKcom, most researchers consider such scenarios, where they backscatter the information directly to the receiver. The channel fading limits the system throughput between each transmitter and receiver pair. The limitation in system throughput motivates us to provide an introductory guideline and technical perspective of cooperative communication in the backscatter scenario. While this chapter mainly focuses on the technical aspects and potential applications of cooperative BaKcom, a brief historical perspective of cooperation techniques in general for wireless communications along with their implementation details, applications and research challenges is described. Section  2 of this chapter focuses on the role and uses of low powered Internet of Things (IoT) devices in future wireless communications and shows how BaKcom technology benefits such devices. In Section  3, we start our discussion by designing a system model and explaining the basic working of cooperative communication in backscatter scenarios. Based on the available literature, some potential cooperative techniques are provided, along with their comparative analysis. Finally, Section  4 concludes the chapter by providing future research directions.
Muhammad Ali Jamshed, Haris Pervaiz, Syed Hassan Ahmed, Atm Shafiul Alam

Physical-Layer Security for Ambient Backscattering Internet-of-Things

Abstract
The pursuit of tiny computing and sensor devices become a big challenge in the Internet of Things (IoT) era. The process of powering such small-size wireless nodes becomes more difficult as the battery adds extra weight, size, and cost. Additionally, batteries replacement is impractical for the expected massive IoT connectivity especially in inaccessible environments, while recharging is very difficult in multiple scenarios. Ambient backscatter communication (AmBC) solves this problem by leveraging existing radio-frequency transmissions for wirelessly powering battery-free nodes. Due to the limited computational power of such nodes, high-complexity security and authentication protocols are infeasible. Consequently, it is imperative to exploit low-complexity techniques such as physical-layer security (PLS). PLS is a key-less security technique that relies on the randomness of the communication channel between the transceiver nodes for securing the transmitted message. In this work, we consider the PLS of an ambient backscattering IoT (AmBC-IoT) system. In AmBC-IoT system, backscattering IoT devices (BDs) form a symbiotic system, in which the access point (i.e., radio frequency source) supports not only the conventional legacy receiver but also the IoT transmission. Specifically, we derive closed-form expressions for the secrecy outage probability and the ergodic secrecy rate under passive eavesdropping. Additionally, we provide asymptotic analysis for both metrics to gain insights on the effect of different parameters on the performance. The accuracy of the analytical results has been validated by extensive simulations.
Basem M. ElHalawany, Ahmad A. Aziz El-Banna, Kaishun Wu

Multi-tone Carrier Backscatter Communications for Massive IoT Networks

Abstract
Backscatter communications is rapidly evolving with each passing year. Due to a great amount of research interest in this technology, backscatter communications have found its application in healthcare, intelligent transportation systems, industrial automation, and supply management. Moreover, it is considered as one of the most promising technology for enabling massive and low-powered Internet of Things (IoT). Due to such revolutionary and transformative characteristics of backscatter communications, it is extensively used in radio frequency identification (RFID) systems. The performance of backscatter RFID systems is notably characterized by the overall system throughput. Since the next generation IoT networks are expected to have high data rate requirements, the conventional backscatter RFID systems may not be feasible. It is because the conventional system can only make use of slots with a single backscatter tag response and the data from the slots with multiple backscatter tag responses (collision slots) is discarded. Thus, the collision slots present in the system decrease not only the overall throughput but also increase the inventory time required for the system. To overcome this issue, this work combines frequency division multiple access (FDMA) and time division multiple access (TDMA) techniques. Specifically, a multi-tone carrier is exploited to recover the signal from multiple backscatter tags in collision slots. The numerical results indicate that the performance in terms of the expected throughput is significantly improved. These results can pave the way for high data rate IoT networks that use multi-tone backscatter communications.
Furqan Jameel, Muhammad Nabeel, Wali Ullah Khan

Time Slot Management in Backscatter Systems for Large-Scale IoT Networks

Abstract
Backscatter communication is considered as a key enabler of the Internet of Things (IoT). It has recently emerged as an alternative of active RF source transmission which enables devices to communicate at a very low power budget. This can be partly attributed to the information transmission configuration of the backscatter tags which makes use of ambient RF signals for reflecting the information to the receiver. Due to these characteristics, the backscatter communications have found many applications in smart homes and transportation systems. In this regard, passive and semi-passive radio frequency identification (RFID) backscatter tags are commonly available in the market. However, these backscatter systems not tags use ALOHA based anti-collision algorithms and make use of slots with a single tag response (singleton) only. The slots with multiple backscatter tag responses (collision) along with slots having no backscatter tag response (empty) are of no use and directly affect the overall throughput as well as the inventory time of the system. Though some anti-collision protocols have been proposed that try to eliminate the empty slots, such systems are still inefficient because of neglecting the transmission capability of other backscatter tags. Specifically, if multiple backscatter tag signals colliding in a single slot are decoded successfully, only the strongest of them proceed with the identification process and the rest of the recovered tag signals are discarded. The present protocol allows only single tag identification per slot. In this chapter, a novel technique is proposed to use some of the unreadable slots (i.e., empty and unsuccessful collision slots) by using the recovered RFID backscatter tags data from previous collision slots that have not proceeded with the identification process. The simulation results show improved throughput and reduced inventory time.
Furqan Jameel, Muhammad Nabeel, Wali Ullah Khan

Age of Information in Backscatter Communication

Abstract
Age of Information (AoI) has been introduced to characterize the newness of data which is observed in real time. In other words, it is the measure of time elapsed since the generation of last received update about a process and is a vital metric in networks such as Internet of things (IoTs), especially when the application demands fresh updates. Most of the applications require fresh data e.g., applications related to environmental monitoring, smart agriculture, body area networks etc. On the other hand backscatter communication promises to resolve one of the most challenging issues of IoT devices, i.e., making them capable for communication without the batteries. The importance of AoI in backscatter communication is paramount to gauge performance of backscatter IoT networks. This chapter addresses the significance of AoI in backscatter communication and suggests some techniques to design a communication system with minimum AoI, maximum energy efficiency, and minimum outage.
Qamar Abbas, Shah Zeb, Syed Ali Hassan

Enhancing Backscatter Communication in IoT Networks with Power-Domain NOMA

Abstract
Internet of Things (IoT) networks are being designed to connect billions of sensors/devices for an application-specific environment to provide services and carry out special tasks. It enables the virtual connection of the real-world physical devices with Internet cyberspace. While, there is an exponentially growing trend in the use of IoT technology for diverse applications such as smart agriculture, smart industries, smart hospitals, smart homes, etc., there are pressing design issues which affect the IoT network performance in the long run, for example, replacement of batteries for increasing the lifetime of devices to maintain the network longevity. To tackle this challenge, various wireless powered-based energy transfer paradigms were proposed over time. Backscatter communication (BackCom) is likewise one of the energy-efficient solutions proposed, which can satisfy the stringent green communication aspects of IoT networks. To achieve massive connectivity in BackCom-enabled IoT network, selecting a suitable multiple access scheme is also a crucial part. Most multiple access schemes proposed for BackCom systems are based on frequency or timeslots sharing techniques. Multiple access techniques proposed for BackCom IoT system can reap the gain of non-orthogonal multiple access (NOMA) principle. In NOMA, multiple end nodes (ENs) of sensors network is served in the same resource block, thereby, increasing the spectrum efficiency of BackCom IoT system. In this chapter, we discuss the prospects of backscatter technique with application of NOMA for green communication in IoT network.
Shah Zeb, Qamar Abbas, Syed Ali Hassan, Aamir Mahmood, Mikael Gidlund

NOMA-enabled Wireless Powered Backscatter Communications for Secure and Green IoT Networks

Abstract
Non-orthogonal multiple access (NOMA) is becoming one of the promising technologies for the fifth generation (5G) and beyond 5G (B5G) communications due to its ability of connecting massive wireless devices. Meanwhile, backscatter communication (BSCom) is emerging as a key solution to the Internet of Things (IoTs) due to its energy efficiency. In this chapter, we first provide a brief introduction of NOMA technology, discuss its fundamental concepts, and outline its applications. Then, we discuss the basic concepts of BSCom systems in brief, describe its different configurations, highlight the challenges of NOMA-enabled BSCom systems, and discuss the recent solutions. Moreover, we provide the basics of physical layer security (PLS) in wireless communication systems. Using the aforementioned backgrounds, we formulate an optimization problem for secrecy rate maximization in NOMA-enabled BSCom in the presence of multiple eavesdroppers. The problem is subjected to backscatter device (BSD) reflection coefficient and base station (BS) power according to NOMA protocol. To efficiently solve the optimization problem, we exploit the duality theory. For the purpose of comparison, we also present a conventional orthogonal multiple access (OMA)-enabled BSCom system as a benchmark. Finally, we present the simulation results and conclude this chapter with future research directions.
Wali Ullah Khan, Guftaar Ahmad Sardar Sidhu, Xingwang Li, Zeeshan Kaleem, Ju Liu
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