A New Framework for Designing Power-Efficient Resource Allocation under Rate Constraints

In this paper, we discuss resource management in modern wireless communications with the objective of minimizing power consumption, and carry out an analysis of simultaneous transmission and orthogonal transmission schemes in an FDMA (Frequency Division Multiple Access) framework. Based on a two-link line model with path-loss only, the performance of these two schemes for network power minimization under the specified rate constraints is investigated. It is found that ST (Simultaneous Transmission) consumes less power than OT (Orthogonal Transmission) close to the base station, but much more power in the cell-edge area. This illustrates that the ST/OT selection criterion for sum power minimization is location- dependent. Further, numerical results suggest that the ST/OT selection margins are generally dominated by their network rate constraints rather than the rate proportions between the two links. New definitions of power-utility and fairness metrics are further proposed, following by the design of weighted resource allocation approaches based on efficiency-fairness tradeoffs. I. Introduction With the expansion of the global population and the preva- lence of wireless devices, interference among multiple active links is becoming a dominant problem, causing serious QoS degradation for future wireless communications (1). Although various interference mitigation techniques are designed to im- prove QoS, these methods generally require high-complexity transceiver devices. Meanwhile, wireless resources are often wasted during the mutually-interfered transmission processes. Taking these issues into consideration, modern communication industries have shifted their interests to looking for economical system-design strategies rather than simply improving QoS with more advanced radio techniques (2). 'Economical design' takes into account both the network operation requirements and the requirement to minimize en- ergy consumption for environmental reasons, which could be interpreted together with geographic demographics. In high- density city areas, huge energy consumption may reach system energy constraints, causing serious interference and excessive CO2 emissions (3) (4). The energy loss due to enabling and maintaining communications takes a great portion of the total energy consumption compared with the required RF (Radio Frequency) energy. Recently, the concept of 'green radio' is proposed, aiming at the 'economical and environmental design' of wireless communication systems (5). Regarding implementations, intelligent resource allocation and scheduling algorithms are needed under the definition of power-efficiency metrics. Compared with the throughput maximization problem which employs capacity as an effective measure, designing new power-efficient resource allocation strategies is still an open problem. In this paper, several power-efficiency metrics are suggested. One simple form is to minimize the sum power consumption in the network. In this paper, by ignoring the power consumed in transceiver circuits and only considering the RF power components, we investigate FDMA-based ST and OT schemes for sum power minimization under the assumed network architecture and QoS requirements. In order to simplify this problem, firstly a mutually-interfered two-link model is assumed in Section II. After that, the performance of ST and OT with the same QoS requirements is compared and analyzed in Section III and Section IV. A discussion on their properties under sum rate constraints is also provided, resulting in an optimum ST/OT selection criterion for sum power reduction. In Section V, the resource allocation problem is discussed in the broader framework of defining proper tradeoffs and constraints. A new power-utility metric is proposed, indicating the design of weighted resource allocation approaches based on efficiency- fairness tradeoffs.