OFDM认知无线电系统能效优化：水填充因子辅助搜索策略

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"基于OFDM的认知无线电系统的能效优化：一种注水因子辅助搜索方法" 本文主要探讨了在能源效率（EE）日益重要的背景下，如何优化基于正交频分复用（OFDM）技术的认知无线电（CR）系统的能效。传统的OFDM-CR系统设计主要考虑系统吞吐量，但随着对无线通信系统能源消耗的关注增加，提升单位能量消耗的系统吞吐量成为了一个关键问题。研究中，作者关注了在总功率约束、干扰功率约束以及速率约束下的节能功率分配策略。 OFDM-CR系统的能效优化问题是一个非凸问题，这使得寻找最优功率分配策略变得复杂。为了解决这一问题，文章提出了一种创新的算法——水填充因子辅助搜索（Water-Filling Factor Aided Search，WFAS）。WFAS算法借鉴了经典的水填充思想，即在不同的信道条件和约束下，动态分配功率，以最大化EE。这一方法针对多约束条件下的EE优化问题，能够有效地寻找近似最优解。论文中，作者证明了WFAS算法具有全局ε-最优性和良好的收敛性，即在一定容差范围内，算法可以收敛到接近最优解的状态。通过数值模拟，论文展示了WFAS算法在不同约束条件下的性能，与传统的功率分配策略如频谱效率优先的分配进行了对比。结果表明，WFAS算法在保持系统性能的同时，显著提高了能效，尤其是在有严格功率和干扰限制的情况下。此外，本文的贡献还在于为OFDM-CR系统的能效优化提供了一个实用的解决方案，这不仅有助于理论研究，也为实际无线通信系统的设计提供了指导。通过对多种约束条件的分析，WFAS算法显示了其在复杂无线环境中的适应性和有效性。 "基于OFDM的认知无线电系统的能效优化：一种注水因子辅助搜索方法"这篇文章为无线通信领域的能效提升提供了新的视角和方法，其提出的WFAS算法有望成为未来CR系统设计中的一个重要工具，以实现更绿色、更高效的无线通信。

2366 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, VOL. 12, NO. 5, MAY 2013

Energy Efﬁciency Optimization for

OFDM-Based Cognitive Radio Systems:

A Water-Filling Factor Aided Search Method

Junling Mao, Gang Xie, Member, IEEE, Jinchun Gao, Member, IEEE, and Yuanan Liu, Member, IEEE

Abstract—Conventional designs of OFDM-based cognitive ra-

dio (CR) systems mainly focus on the system throughput. Since

nowdays the energy efﬁciency (EE) of wireless systems becomes

more and more important, this paper intends to improve the

system throughput for unit-energy consumption in OFDM-based

CR systems. The energy-efﬁcient power allocation problem of

OFDM-based CR systems is studied under the total power

constraint, the interference power constraint and the rate con-

straint. Since the energy-efﬁcient power allocation problem is

non-convex, in order to ﬁnd the optimal power allocation at

each subcarrier, we propose a novel method named water-

ﬁlling factors aided search (WFAS) to solve the EE optimization

problems with multiple constraints. The global ε-optimality

and the convergence of the proposed method are presented.

The numerical results conﬁrm the theoretical conclusions. The

comparisons of the energy-efﬁcient power allocation and the

spectrum-efﬁcient power allocation in OFDM-based CR systems

are given under different constraints via numerical simulations

as well.

Index Terms—Energy efﬁciency, Cognitive radio, OFDM,

Power allocation.

I. INTRODUCTION

OGNITIVE Radio (CR) techniq ue h as drawn consider-

able attentions due to its advantages of spectrum reusing

[1]. In CR networks, the secondary users (SUs) communicate

over the bandwidth originally allocated to the primary network

while assuring that the resulted performance degradation of the

active primary transmissions is tolerable [2].

One popular transmission scheme of CR networks is called

opportunistic spectrum access (OSA), which allows SUs com-

municate over the spectrum hole where the primary trans-

mission is de tected to be inactive [2]. Since the primary

transmission state usually changes with time, to support the

OSA scheme, the orthogonal frequency division multiplexing

(OFDM) technique has been adopted in broadband CR net-

works due to its ﬂexibility in dynamic spectrum access [3].

Manuscript received July 12, 2012; revised November 13, 2012; accepted

January 9, 2013. The associate editor coordinating the review of this paper

and approving it for publication was S. Affes.

This work was supported in part by Canada-China Scientiﬁc and Techno-

logical Cooperation (No. 2010DFA11320), the Natural Science Foundation of

China (Nos. 60973111 and 61170275), and Important National Science and

Technology Scientiﬁc Projects (No. 2012ZX03003001-004).

J. Mao, J. Gao, and Y. Liu are with the Beijing Key Laboratory of Work

Safety Intelligent Monitoring, Beijing University of Posts and Telecommuni-

cations, Beijing 100876, China (e-mail: maojunling@bupt.edu.cn).

G. Xie is with the Beijing Key Laboratory of Network System Architecture

and Conv e rgence, Beijing Uni versity of Posts and Telecommunications.

Digital Object Identiﬁer 10.1109/TWC.2013.013013.121013

However even though SUs transmit over the spectrum hole in

OFDM-based CR systems, the mutual interference between

the secondary systems and the primary systems still exists

when the primary bands and the CR bands are side-by-side [4].

Thus, the power control for OFDM-based CR systems should

be adopted to ensure the interference caused by secondary

transmission below a pre-deﬁned value.

In previous works, most power allocation schemes for

OFDM-based CR systems intend to improve the system

throughput (or spectrum efﬁciency (SE)) [5]-[10]. [5] and

[6] give the optimal and suboptimal power allocation for

OFDM-based CR systems under the single interference power

constraint. [7] gives the optimal power allocation for overlay

and underlay OFDM-based CR systems under multiple in-

terference p ower constraints. [8] studies the joint power and

bits allocation schemes. [9] considers the power allocation for

OFDM-based CR systems with imperfect spectrum sensing.

[10] studies the joint optimization of detection threshold and

the power allocation.

Besides the SE, the energy efﬁciency (EE) has been consid-

ered more and more important in future wireless systems [11]-

[15]. It is reported that wireless and mobile communications

account for more than 9% of the global carbon dioxide

emissions originated from information and communication

technologies (ICT) [11] and more than 50% of the total energy

consumption is consumed by the radio access part, where 50-

80% is used for the power ampliﬁer (PA) [15]. Therefore, the

transmit power adaption is very important to improve the EE

of wireless systems. The EE optimization for OFDM-based

non-CR systems has been studied in [16]-[23]. [16] solves the

EE optimization problem via seeing the transmit power as a

function of transmit rate. [17] points that the EE optimization

problem can also be solved via seeing the transmit rate as a

function of transmit power. [18] gives another way for EE op-

timization, which is named fractional programming [19]. [20]

further introduces the fractional programming method into

EE optimization. [21] and [22] consider th e EE optimization

of OFDM-based non-CR systems with additional minimum

rate constraint. [23] considers the EE optimization of non-CR

OFDMA systems with minimum rate constraint for each user.

Owing to the importance of EE, in OFDM-based CR

systems, the EE optimization should also be considered. [24]

studies an energy-efﬁcient power allocation f or OFDM-based

CR systems, where the objective function is not the system

throughput for unit-energy consumption [25] as in [16]-[23]

1536-1276/13$31.00

 2013 IEEE

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