Energy and spectrum are two precious commodities for wireless communications. How to improve the energy and spectrum efficiency has become two critical issues for the designs of wireless communication systems. This dissertation is devoted to the development of energy and spectral efficient wireless communications. The developed techniques can be applied to a wide range of wireless communication systems, such as wireless sensor network (WSN) designed for structure health monitoring (SHM), medium access control (MAC) for multi-user systems, and cooperative spectrum sensing in cognitive radio systems. First, to improve the energy efficiency in SHM WSN, a new ultra low power (ULP) WSN is proposed to monitor the vibration properties of structures such as buildings, bridges, and the wings and bodies of aircrafts. The new scheme integrates energy harvesting, data sensing, and wireless communication into a unified process, and it achieves significant energy savings compared to existing WSNs. Second, a cross-layer collision tolerant (CT) MAC scheme is proposed to improve energy and spectral efficiency in a multi-user system with shared medium. When two users transmit simultaneously over a shared medium, a collision happens at the receiver. Conventional MAC schemes will discard the collided signals, which result in a waste of the precious energy and spectrum resources. In our proposed CT-MAC scheme, each user transmits multiple weighted replicas of a packet at randomly selected data slots in a frame, and the indices of the selected slots are transmitted in a special collision-free position slot at the beginning of each frame. Collisions of the data slots in the MAC layer are resolved by using multiuser detection (MUD) in the PHY layer. Compared to existing schemes, the proposed CT-MAC scheme can support more simultaneous users with a higher throughput. Third, a new cooperative spectrum sensing scheme is proposed to improve the energy and spectral efficiency of a cognitive radio network. A new Slepian-Wolf coded cooperation scheme is proposed for a cognitive radio network with two secondary users (SUs) performing cooperative spectrum sensing through a fusion center (FC). The proposed scheme can achieve significant performance gains compared to existing schemes.

Cellular services have been ineffective in providing defense and disaster recovery communications, no matter how important the user is. This has led to the emergence of Wireless Priority Services for disaster communication, which dynamically prioritizes some connections. Future generation Wireless Priority Services must support a large number of calls. This can be achieved by making the system spectrally efficient. We propose to use linear, higher order modulation techniques for priority services instead of the currently deployed non-linear modulation schemes for priority and non-priority services. The proposed modulation techniques increase spectrum efficiency as needed but suffer from increased Adjacent Channel Interference and Inter Symbol Interference. This work deals with modelling of Adjacent Channel Interference and methods to reduce the same using digital filters. Finally we cite references which help explain how to incorporate the linear modulation schemes and interference minimizing filters into the existing GSM system using Software Defined Radio.

Wireless communications have evolved significantly over the past few decades, and the current scenario is characterized by a widespread variety of wireless technologies, applications, and services. Some of the key trends and developments in wireless communications include: 5G Networks: 5G networks deployed in many countries around the world, offering enhanced data rates, reduced latency, and additional capacity compared to previous generations of wireless networks. 5G networks use massive MIMO, beamforming, and network slicing to provide high- quality, high-speed wireless connectivity to users. Internet of Things: It is a network for devices connected wirelessly, which can communicate with each other and with the internet. IoT devices include smart sensors, wearables, and home automation systems, among others. Wireless technologies for example Bluetooth, Wi-Fi, and Zigbee are commonly used for IoT applications. Smart Homes and Cities: Wireless communication plays significant part in the implementation of smart-homes and cities, which use interconnected devices and sensors to improve energy efficiency, safety, and quality of life. Wi-Fi, Zigbee, and Bluetooth are the technologies connect devices and sensors to the internet and to each other wirelessly. Autonomous Vehicles: Wireless communications are critical for the development of autonomous vehicles, which rely on high-speed, low-latency wireless networks to communicate with other vehicles, infrastructure, and the cloud. 5G networks and other advanced wireless technologies are being developed to support the communication needs of autonomous vehicles. Satellite Communications: Satellites are being used increasingly for wireless communications, particularly in areas where terrestrial networks are unavailable or unreliable. Satellite communications are used for applications such as remote sensing, navigation, and communication with remote locations. Cellular networks (e.g. 5G, 4G LTE), satellite communications, and near-field communication (NFC) also fall into connectionless communication. Wireless communication systems must constantly function at faster speeds while making use of the available spectrum. Error-correcting codes, modulation techniques, and multiple access techniques are essential for achieving high spectrum efficiency. Channel codes, significant part of communication system that enhances reliability of data transmission by adding redundancy to the data. They make the receiver enabled such that it can identify and correct errors if any in the received signal owing to interference, or other impairments that affect the signal during the transmission through the channel.

In June 2000, GTEL (Wireless Telecommunications Research Group) at the F- eral University of Ceara ́ was founded by Professor Rodrigo Cavalcanti and his c- leagues with the mission of developing wireless communications technology and impact the development of the Brazilian telecommunications sector. From the start, this research effort has been supported by Ericsson Research providing a dynamic environment where academia and industry together can address timely and relevant research challenges. This book summarized much of the research output that has resulted from GTEL’s efforts. It provides a comprehensive treatment of the physical and multiple access layers in mobile communication systems describing different generations of systems but with a focus on 3G systems. The team of Professor C- alcanti has contributed scienti cally to the development of this eld and built up an impressive expertise. In the chapters that follow, they share their views and kno- edge on the underlying principles and technical trade-offs when designing the air interface of 3G systems. The complexity of 3G systems and the interaction between the physical and m- tiple access layers present a tremendous challenge when modeling, designing, and analyzing the mobile communication system. Herein, the authors tackle this pr- lem in an impressive manner. Their work is very much in line with the developments in 3GPP providing a deeper understanding of the evolution of 3G and also future enhancements.

Taking a coherent and logical approach, this book describes the potential use of co-ordinated multipoint systems supported by radio over fiber. It covers an impressive breadth of topics, ranging from components, subsystem and system architecture, to network management and business perspectives. The authors show the importance of radio over fiber in eliminating or mitigating against the current, perceived barriers to the use of co-ordinated multipoint, and the drivers for standardisation activities in future mobile/wireless systems over the next few years. The book brings together the system concept for centralized processing, including what is required for co-existence with legacy wireless systems, the algorithms that can be used for improving wireless bandwidth utilization at physical and MAC layers and the radio over fiber network and link design necessary to support the wireless system. Other important research is also covered as the authors look at compensating for radio over fiber impairments and providing simple network management functions. A study of service provision and the business case for such a future wireless system is also fully considered. This book comes at an important time for future wireless systems with standardization of fourth generation wireless systems still ongoing. The content enables readers to make key decisions about future standardisation and their own research work. The business analysis also makes the book useful to those involved in deciding the future directions of telecoms organisations. This information will be core to their decision-making as it provides technical knowledge of the state-of-the-art but also system level assessments of what is possible in a business environment.