Energy-Efficient Transmission Strategy For Asymmetric Two-Way Relay System

With the rapid development of Mobile Internet and Internet of Things, the explosive growth of mobile data traffic and massive device connectivity have caused energy costs continuously rising and ecological environment deteriorating, which makes the green communication technology drawing more and more attention. As a very important performance indicator to measure energy consumption of the network, energy efficiency has become a hot topic.Relay technique plays a vital role in the IMT-2020 mobile network architecture evolution. Compared with traditional relay technology, two-way relay channel(TWRC) employing amplify-and-forward(AF) protocol is of high spectrum efficiency, easy to be implemented. With the increase of terminal density, the circuit power is close to or greater than transmission power, and it increases with transmission rate. Obviously, it's unreasonable that only transmission power is considered in the power consumption, where terminals are located in the short-distance transmission scenario. In order to provide various services, terminals require asymmetric Quality-of-service(QoS). Therefore, when rate-dependent circuit power is considered, how to improve energy efficiency for asymmetric AF-TWRC system is an urgent problem.To solve the problem above, this paper mainly studies the energy-efficient transmission strategy in AF-TWRC system, which is based on the different channel state information(CSI), different power consumption models and different energy efficiency models. The main contributions of this paper are as follows:(1) For the AF-TWRC system based on statistical CSI, considering the most general rate-dependent circuit power consumption model, we propose the energy-efficient transmission strategy while satisfying the total transmission power and asymmetric QoS requirements. Firstly, when the circuit power is modeled as a convex increasing function of transmission rate, the optimization problem that maximizes the energy efficiency GPE(Goodbit-Per-Energy) is formulated. Then, some algebraic manipulations are implemented by fractional programming theorem and convex optimization theorem. At last, the transmission power allocation algorithm is obtained. To provide valuable insights into practical system-designs, the closed-form solution of the optimal power allocation is provided when the circuit power is modeled as a linear function of transmission rate.(2) For the AF-TWRC system based on instantaneous CSI, considering the most general rate-dependent circuit power consumption model, we propose the energy-efficient transmission strategy while satisfying the total transmission power and asymmetric QoS requirements. Firstly, when the circuit power is modeled as a convex increasing function of transmission rate, the optimization problem that maximizes the energy efficiency TBPUE(Transmitted Bits Per Unit Energy) is formulated. Then, some algebraic manipulations are implemented by double layer optimization method, fractional programming theorem and convex optimization theorem. At last, the transmission power allocation algorithm is obtained. To provide valuable insights into practical system-designs, the closed-form solution of the optimal power allocation is proposed when the circuit power is modeled as a linear function of transmission rate.The simulation results are presented to verify the proposed power allocation algorithm, and the impacts of system parameters such as relay location, transmission power constraints and asymmetric rate requirements on the system energy efficiency are studied. Compared with the equal power allocation scheme and the traditional optimal power allocation scheme which ignored the circuit power, the optimal power allocation scheme proposed in this paper is significantly higher in energy efficiency.