Low complexity wireless sensors for power-efficient communiation and energy harvesting

The modern communication goes towards the direction of green, sustainable solutions; this raises many issues such as better usage of spectrum, lower system complexity, or lower energy consumption. MIMO transmission provides a promising solution with better spectral efficiency, but the required large antenna spacing and additional RF chains hinder its application to compact and battery powered devices. Wireless sensor networks are composed of such battery-powered devices, which require better energy efficiency in order to have a longer lifetime. Thus low complexity wireless sensors for power efficient communications are necessary.
The beam space MIMO transmission approach was proposed recently for energy efficient communication; it uses only one RF chain and maps the MIMO data streams onto orthogonal basis radiation patterns. The resulting data streams appear at the receiver as originating from conventional MIMO transmitters. In this thesis, the constraint of beam space MIMO to operate with only PSK modulation was waived; a higher order modulation was attained, e.g., 16-QAM, with the use of only one parasitic element for the ESPAR antenna. The developed smart antenna load generation and switching mechanism ensures the required pattern composition for such higher order modulation schemes. The beam space MIMO approach is also adopted for wireless sensor networks, where the energy efficiency is analyzed and it is shown to perform better than other schemes. Finally, as an additional source of energy savings, energy harvesting was considered for wireless sensor networks, applied to structural monitoring applications. The analysis shows how this approach can further increase the lifetime of wireless sensor networks.