Spectral Efficiency Tradeoff Research Articles

Energy Efficiency and Spectral-Efficiency Tradeoff in Amplify-and-Forward Relay Networks

The tradeoff between energy efficiency (EE) and spectral efficiency (SE) in amplify-and-forward relay networks is studied. Three kinds of transmission strategies are considered: 1) noncooperative transmission; 2) relay transmission without a direct link; and 3) relay transmission with a direct link. The tradeoff between EE and SE is formulated as an optimization problem in which the objective is to maximize EE while satisfying the SE requirement. In the noncooperative transmission strategy, the optimization problem is solved by seeking the optimal source transmission power P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> . It is proven that EE is a strictly quasi-concave function of P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> . In the relay transmission with/without a direct link, the optimization problem is solved by jointly seeking the optimal source transmission power P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> and the optimal relay amplification gain β. It is proven that EE is a strictly quasi-concave function of either P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> or β. An optimal but highly complex 1-D searching (ODS) method and a near-optimal but lower complexity alternate optimization (AOP) method are proposed. Simulation results show that the ODS results are consistent with the 2-D exhaustive searching results. The AOP method can achieve an EE close to that obtained by 2-D exhaustive searching. Moreover, the transmission strategies are compared in terms of EE under the same SE constraint.

Energy Efficiency and Spectral Efficiency Tradeoff in Interference-Limited Wireless Networks

This letter investigates the fundamental tradeoff between energy efficiency (EE) and spectral efficiency (SE) for interference-limited wireless networks (IWNs), which is a nonconvex optimization and NP-hard problem. A general algorithm procedure (GAP) embedded with an iterative power allocation algorithm (IPAA) is proposed, which has good performance with the advantages of fast convergence, low complexity and insensitivity to initial values. Simulation results explicitly depict the EE-SE tradeoff curve for IWNs.

Energy- and Spectral-Efficiency Tradeoff for Distributed Antenna Systems with Proportional Fairness

Energy efficiency(EE) has caught more and more attention in future wireless communications due to steadily rising energy costs and environmental concerns. In this paper, we propose an EE scheme with proportional fairness for the downlink multiuser distributed antenna systems (DAS). Our aim is to maximize EE, subject to constraints on overall transmit power of each remote access unit (RAU), bit-error rate (BER), and proportional data rates. We exploit multi-criteria optimization method to systematically investigate the relationship between EE and spectral efficiency (SE). Using the weighted sum method, we first convert the multi-criteria optimization problem, which is extremely complex, into a simpler single objective optimization problem. Then an optimal algorithm is developed to allocate the available power to balance the tradeoff between EE and SE. We also demonstrate the effectiveness of the proposed scheme and illustrate the fundamental tradeoff between energy- and spectral-efficient transmission through computer simulation.

A Unified Energy Efficiency and Spectral Efficiency Tradeoff Metric in Wireless Networks

In this letter, we propose a unified metric for energy efficiency (EE) and spectral efficiency (SE) tradeoff design in wireless networks. Different from previous EE-based or SE-based design, we simultaneously optimize both EE and SE. First, we formulate our design problem as a multi-object optimization (MOO) problem, in which the Pareto optimal set is characterized. After normalizing EE and SE to make them comparable, we then convert the MOO problem into a single-object optimization (SOO) problem by the weighted product scalarization method. We further show that the objective function of this SOO problem, i.e., our proposed EE and SE tradeoff (EST) metric, is quasi-concave with the transmit power and a unique globally optimal solution is derived. Numerical results validate the effectiveness of the proposed unified EST metric.

Energy Efficiency and Spectral Efficiency Tradeoff in Downlink Distributed Antenna Systems

This letter investigates the tradeoff between energy efficiency (EE) and spectral efficiency (SE) in downlink multiuser distributed antenna systems (DAS). Given the SE requirement and maximum power limit, a constrained optimization problem is formulated to maximize EE. Because of the multi-dimensional and non-convex nature of the problem, we first transform the multicriteria optimization problem with high complexity into a simpler single objective optimization problem. Then a novel power allocation algorithm is proposed to achieve maximum EE. Simulation results demonstrate the effectiveness of the proposed scheme as well as illustrate the fundamental tradeoff between energy efficient and spectral efficient transmission in downlink multiuser DAS.

Energy- and Spectral-Efficiency Tradeoff in Downlink OFDMA Networks

Conventional design of wireless networks mainly focuses on system capacity and spectral efficiency (SE). As green radio (GR) becomes an inevitable trend, energy-efficient design is becoming more and more important. In this paper, the fundamental tradeoff between energy efficiency (EE) and SE in downlink orthogonal frequency division multiple access (OFDMA) networks is addressed. We first set up a general EE-SE tradeoff framework, where the overall EE, SE and per-user quality-of-service (QoS) are all considered, and prove that under this framework, EE is strictly quasiconcave in SE. We then discuss some basic properties, such as the impact of channel power gain and circuit power on the EE-SE relation. We also find a tight upper bound and a tight lower bound on the EE-SE curve for general scenarios, which reflect the actual EE-SE relation. We then focus on a special case that priority and fairness are considered and suggest an alternative upper bound, which is proved to be achievable for flat fading channels. We also develop a low-complexity but near-optimal resource allocation algorithm for practical application of the EE-SE tradeoff. Numerical results confirm the theoretical findings and demonstrate the effectiveness of the proposed resource allocation scheme for achieving a flexible and desirable tradeoff between EE and SE.

Automatic Request for Cooperation (ARC) and Relay Selection for Wireless Networks

Recently, there has been growing interest in the design of wireless cooperative protocol to achieve higher diversity-multiplexing tradeoff among single antenna devices. We propose an automatic request for cooperation (ARC) scheme for wireless networks which can achieve higher order diversity by selecting the best relay. In this scheme, a source transmits a data packet towards a destination and a group of relays. The destination tries to decode the information from the source and if the detection is correct the process will stop. Otherwise, the destination transmits an ARC towards the relays. We utilize this ARC signal for selecting the best relay from the set of relays that have successfully decoded the source packet. The selected relay generates and transmits redundant information for the source packet. The destination combines the two packets received from the source and the best relay to improve the reliability of the packet. We analyze the packet error rate, spectral efficiency and diversity-multiplexing tradeoff of our proposal and compare them with some existing protocols. Analysis shows that our proposal can achieve higher diversity multiplexing tradeoff than conventional cooperative protocols.