Energy efficiency in multiaccess fading channels under QoS constraints

Qiao Deli, Gursoy Mustafa, Velipasalar, Velipasalar Senem

Description

In this article, transmission over multiaccess fading channels under quality-of-service (QoS) constraints is studied in the low-power and wideband regimes. QoS constraints are imposed as limitations on the buffer violation probability. The effective capacity, which characterizes the maximum constant arrival rates in the presence of such statistical QoS constraints, is employed as the performance metric. A two-user multiaccess channel model is considered, and the minimum bit energy levels and wideband slope regions are characterized for different transmission and reception strategies, namely time-division multiple-access (TDMA), superposition coding with fixed decoding order, and superposition coding with variable decoding order. It is shown that the minimum received bit energies achieved by these different strategies are the same and independent of the QoS constraints in the low-power regime, while they vary with the QoS constraints in the wideband regime. When wideband slope regions are considered, the suboptimality of TDMA with respect to superposition coding is proven in the low-power regime. On the other hand, it is shown that TDMA in the wideband regime can interestingly outperform superposition coding with fixed decoding order. The impact of varying the decoding order at the receiver under certain assumptions is also investigated. Overall, energy efficiency of different transmission strategies under QoS constraints are analyzed and quantified.

Sujets

• Energy efficiency
• Quality of service
• Time division multiple access

Informations

• Publié par: biomed
• Publié le: 01 janvier 2012
• Nombre de lectures: 12
• Langue: English

Extrait

Qiaoet al.EURASIP Journal on Wireless Communications and Networking2012,2012:136 http://jwcn.eurasipjournals.com/content/2012/1/136

R E S E A R C HOpen Access Energy efficiency in multiaccess fading channels under QoS constraints 1* 22 Deli Qiao, Mustafa Cenk Gursoyand Senem Velipasalar

Abstract In this article, transmission over multiaccess fading channels under qualityofservice (QoS) constraints is studied in the lowpower and wideband regimes. QoS constraints are imposed as limitations on the buffer violation probability. The effective capacity, which characterizes the maximum constant arrival rates in the presence of such statistical QoS constraints, is employed as the performance metric. A twouser multiaccess channel model is considered, and the minimum bit energy levels and wideband slope regions are characterized for different transmission and reception strategies, namely timedivision multipleaccess (TDMA), superposition coding with fixed decoding order, and superposition coding with variable decoding order. It is shown that the minimum received bit energies achieved by these different strategies are the same and independent of the QoS constraints in the low power regime, while they vary with the QoS constraints in the wideband regime. When wideband slope regions are considered, the suboptimality of TDMA with respect to superposition coding is proven in the lowpower regime. On the other hand, it is shown that TDMA in the wideband regime can interestingly outperform superposition coding with fixed decoding order. The impact of varying the decoding order at the receiver under certain assumptions is also investigated. Overall, energy efficiency of different transmission strategies under QoS constraints are analyzed and quantified. Keywords:effective capacity, energy efficiency, energy per information bit, lowpower regime, multipleaccess fad ing channels, quality of service, superposition coding, timedivision multiple access, wideband regime, wideband slope

1. Introduction Energy efficiency is an important consideration in wire less systems and has been rigorously analyzed from an informationtheoretic perspective. In [1], Verdú has extensively studied the spectral efficiencybit energy tra deoff in the wideband regime, considering the Shannon capacity as the performance metric. For the Gaussian multiaccess channel, Caire et al. [2] have shown that time division multipleaccess (TDMA) is in general a subopti mal transmission scheme in the lowpower regime unless one considers the asymptotic scenario in which the power vanishes. It is also shown that fading channel makes the superposition strategy more favorable. In this analysis, Shannon capacity formulation is again adopted as the main performance metric. However, Shannon

* Correspondence: [e-mail] 1 Department of Electrical Engineering, University of NebraskaLincoln, NE 68588, USA Full list of author information is available at the end of the article

capacity does not quantify the performance in the pre sence of qualityofservice (QoS) limitations in the form of constraints on queueing delays or queue lengths. Indeed, most communication and informationtheoretic studies, while providing powerful results, do not generally concentrate on delay and QoS constraints [3]. At the same time, providing QoS guarantees is one of the key requirements in the development of next genera tion wireless communication networks since data traffic with multimedia content is expected to grow significantly and in realtime multimedia applications, such as voice over IP (VoIP) and interactivevideo (e.g., videoconferen cing), latency is a key QoS metric. Many efforts have been made to incorporate the delay constraints in the perfor mance analysis [47]. In [4], delay limited capacity has been proposed as a performance metric, which is defined as the rate that can be attained regardless of the values of the fading states. In [6], the tradeoff between the average transmission power and average delay has been analyzed

© 2012 Qiao et al; licensee Springer. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.