Power and time allocation for two-way cooperative relaying systems with superposed signal transmissions

Abstract

In this dissertation, resource allocation schemes for two-way cooperative relaying systems were studied in a three-node scenario consisting of a base station, a near user having better channel quality, and a far user who cannot communicate with the base station directly.

The first study deals with half-duplex based two-way cooperative non-orthogonal multiple access (NOMA) system inspired by straightforward network coding. As the advent of power domain NOMA, cooperative NOMA systems, in which near user communicate with a base station, while simultaneously support the far user transmission, have been studied recently. To enhance spectral efficiency, we intro-duce a two-way cooperative NOMA system which can support two users’ bidirectional communications during three phases. The closed form expression of outage probability is derived and validated by Monte Carlo simulation. Also, an optimal joint power and time allocation algorithm is provided to minimize system outage probability. Performance evaluation shows that the proposed joint power and time al-location algorithm can enhance outage performance significantly compared with both fixed power and equal time allocation and optimal power and equal time allocation. Moreover, the proposed two-way cooperative NOMA scheme has superior system outage performance rather than conventional one-way relay based cooperative NOMA scheme adopting optimal power and time allocation, regardless of users’ positions and target rates. Also, it is shown that the proposed scheme improves the near user’s energy efficiency over the conventional scheme by reducing the number of relay transmissions. It is worth noting that the proposed two-way cooperative NOMA scheme and resource allocation algorithm can enhance outage performance and users’ energy efficiency over conventional scheme without additional successive interference cancellation process or synchronization process.

In the second study, an in-band full-duplex based two-way cooperative relaying system is proposed to further improve spectral efficiency. Considering residual self-interference and asymmetric uplink-downlink traffic requirements, we propose an opportunistic power allocation algorithm with dynamical switching relay mode to enhance uplink reliability and downlink rate. To evaluate system performance, we provide performance comparison with conventional in-band full-duplex based one-way cooperative NOMA scheme. The exact analysis on outage probability and ergodic rate for each signal was derived and verified by Monte Carlo simulation. Results show that the proposed scheme guarantee uplink outage probability gain over conventional scheme regardless of residual self-interference and user’s target rates. Also, it is shown that the proposed scheme can enhance downlink ergodic rate than conventional scheme by removing downlink power sharing between two users’ downlink signals.