Energy Harvesting in Cooperative Communications

Cooperative communications is a promising technique used to combat the multipath propagation in wireless networks. It can also extend the network coverage and provide the diversity gain by using the existing infrastructure. In practice, this is often achieved by using idle nodes in the network as relays. The multiple access relay system and parallel relay system are appealing candidates for emerging wireless cooperative networks due to bandwidth efficiency and improved power consumption. The amplify and forward (AF) and decode and forwards (DF) protocols are basic cooperative relay protocols used over the relay channels. In this thesis, we study parallel relays in AF cooperative communication networks using QPSK signalling over the Rayleigh fast fading with additive Gaussian noise channels. The maximum ratio combining (MRC) method is employed to detect the received signals at the destination. By simulating the symbol error rate (SER) of the combined received signal at the destination, we study a trade-off between the number of relays and the quality of the communications. The energy efficiency of a system determines its operational sustainability. Energy harvesting (EH) is a crucial technology for a variety of wireless systems that have limited access to a reliable electricity supply or recharging sources. In this thesis, the design of a multiple access relay system (MARS) using EH is considered. We assume that the sources and the relay have no embedded power supply but rechargeable energy storage devices. Thus, each node is powered by harvesting the energy from the RF signals broadcasted by an access point (AP), and it operates in store-then-cooperate (STC) mode. We simulate the link level performance by using the physical layer network coding in the presence of EH with DF protocol. The thesis presents energy harvesting schemes (EH and STC) and outage probability analysis. The schemes presented in this thesis achieve SER performance approaching that of a fixed power supply and contribute significantly to sustaining the energy in the system while maintaining a constant throughput.