Wireless green technologies for smart cities

Abstract

In this chapter, radio frequency (RF) energy harvesting (EH) technologies like wireless power transfer (WPT) and simultaneous wireless information and power transfer (SWIPT) are discussed. Among the various wireless green technologies, SWIPT technique has gained a lot of attention among the researchers, and it is suitable for smart cities. The unique advantage of SWIPT gives communication nodes to harvest energy from the RF signal and also at the same time to decode information from the signal. Therefore, the transmitting nodes allocate resources for both EH and information decoding (ID). In SWIPT, the most famous resource allocation schemes are either based on power or time resource allocation, or in some cases hybrid power and time resource allocation schemes are implemented. If the power or time resource is not sufficient for the information symbols in the signal, then this can lead to performance degradations. Therefore, an alternative approach is allocating a specific set of symbols for EH, and remainder is used for ID. In this chapter, two novel methods are discussed based on the SWIPT techniques with symbol-wise resource allocation, they are modulation-based SWIPT (M-SWIPT) and frequency-splitting-based SWIPT (FS-SWIPT). In FS-SWIPT, the symbols belonging to specific frequency are used for EH without disturbing the remainder of the symbols in the signal. M-SWIPT allocates specific modulation for EH, preferably higher modulation and the power of modulated symbols are changed by using hybrid constellation shaping (HCS) and therefore, M-SWIPT is much more adaptable. The performances of both the SWIPT techniques are discussed and further in FS-SWIPT, the non-linear distortion (NLD) effects due to variation in transmit power of symbols at transmitter side are analysed. HCS is a novel constellation shaping and the approach of using this constellation shaping gives M-SWIPT to allocate resources in a flexible manner. Over performance of M-SWIPT is analysed in the presence of this shaping scheme.M-SWIPT and FS-SWIPT techniques are designed for improving the energy efficiency and improving the reliability of the low-power sensor devices at very low signal-to-noise regions.