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.

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.

The demand for high data rate wireless services has grown tremendously. The demand is expected to grow further at an increased pace. The scarcity of the usable radio frequency spectrum is a major bottleneck to cater to the growing demand for high data rate wireless services. Current cellular wireless networks rely on deploying small cells as a possible solution to cater to the growing demand. However, this practice has resulted in severe co-channel interference (CCI) levels in cellular networks. The first phase of this thesis investigates the impact of CCI on relay networks and distributed antenna systems, which are included in recent wireless standards such as long-term evolution advanced (LTE-A). The analytical results derived for system performance metrics, such as the outage probability and the ergodic rate, are used to obtain valuable insights for system design. The second stage of this thesis research proposes interference reduction schemes for wireless relay networks operating in the presence of CCI and analytically investigates the performance of each scheme. The analytical results are used to obtain crucial design insights such as the feedback rate and position of the relay nodes. Another approach to compensate for the spectrum scarcity is through improving the spectral efficiency (SE) of the wireless networks. As a step towards increasing SE, recently, there has been research efforts to implement full-duplex (FD) wireless communications. The main challenge in FD is the interference on the reception by its own transmission. Recent advances in self-interference reduction schemes have made FD communications feasible for short range communications. This thesis develops a theoretical framework to study the average data rate of FD communications for short range communications using device-to-device networks.