SWIPT MIMO Relaying in with Spectrum Sharing Networks with Interference Cancellation
Authors: Al-Qahtani Fawaz 
Published: July 2019

Simultaneous wireless information and power transfer (SWIPT) is a promising solution to increase the lifetime of wireless nodes and hence alleviate the energy bottleneck of energy constrained wireless networks. To recent days, there are three different designs of SWIPT system which includes integrated SWIPT, closed-loop SWIPT, decoupled SWIPT. Integrated SWIPT is the simplest design where power and information are extracted by the mobile from the same modulated microwave transmitted by a base station (BS). For this scheme, the information transfer (IT) and power transfer (PT) distances are equal. For the closed loop scenario, it splits IT and PT between uplink and downlink wherein PT is in downlink and IT is for dedicated for uplink. The last one is to add additional special base station (BS) called a power beacon PB in which PT and IT are orthogonalized by using different frequency bands or time slots to avoid interference. Therefore, powering a cognitive radio networks through RF energy harvesting can be efficient in terms of spectrum usage and energy limits for wireless networking. The RF energy harvesting technique also is applicable in cooperative networks wherein an energy constrained relay with limited battery depends on external charging mechanism to assist the transmission of source information to the destination. In an effort to further improve spectrum sharing network performance, a number of works has suggested the idea of incorporating the multiple antenna technique into cognitive relaying. In particular, transmit antenna selection with receive maximal ratio combining (TAS/MRC) is adopted as a low complexity and power efficient approach which achieves full transmit/receive diversity.

Since the SUs and PUs share the same frequency band, there will be inevitably interference between the SUs and PUs. Therefore, reducing the effect of PU interference on the performance of secondary receiver is of significance important. Consequently, smart antennas can be employed to mitigate the PU interference. With knowledge of the direction of arrival (DoA), the receive radiation pattern can be shaped to place deep nulls in the directions of some of interfering signals. By doing so, two null-steering algorithms were proposed in the literature i.e., dominant interference reduction algorithm, and adaptive arbitrary interference reduction algorithm. The first algorithm requires perfect predication and statistical ordering of the interference signals instantaneous power, and the later algorithm does not need prior knowledge of the statistical properties of interfering signals. In this work, we limit our analysis to the dominant interference reduction algorithm.

In this work, we consider a dual-hop relaying with amplify-and-forward (AF) scheme where the source, relay, and the destination are equipped with multiple antennas. The relay node is experiencing co-channel interference. The purpose of array processing at the relay is to provide interference cancellation. Therefore, the energy constrained relay collects energy from ambient RF signals, cancel CCI, and then forward the information to the destination. In particular, we provide a comprehensive analysis for the system assuming selection at the source, and the destination. We derive the end-to-end exact and asymptotic outage probability for the proposed system model. A key parameters are also obtained featuring the diversity and coding gains.