改进的增量中继多载波传输速率优化策略

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"这篇研究论文探讨了如何最大化增量式中继多载波传输的可实现速率策略，专注于提高合作传输的频谱效率。通过利用改进的放大转发(AMF)正交频分复用(OFDM)方案，提出了几种优化资源分配的策略，以达到最大传输速率。尽管优化问题的高计算复杂性需要寻求次优解决方案，但搜索过程的复杂性仍然较高。因此，文章发展了一种低复杂度的替代方法，旨在在性能和复杂性之间找到更好的平衡。此外，还分析了该方法的平均无条件信噪比(SNR)中断概率。数值结果证明了提案的优势并验证了理论的正确性。" 在无线通信领域，增量式中继是一种有效的提升通信效率的技术，特别是在多载波传输系统如OFDM中。OFDM因其对频率选择性衰落的抵抗能力而被广泛应用于4G和5G网络。论文中的"增量策略"可能指的是动态地增加或减少参与中继节点的数量，以适应不断变化的信道条件，从而提高系统的总体数据速率。论文提出了一种改进的AF协议，其中中继节点不仅转发信号，还通过智能放大和转发来增强信号质量。这种策略可以有效地减少错误传播，提高信号的传输效率。然而，资源的优化分配（如功率、带宽和中继选择）是关键挑战，因为这直接影响到系统的可实现速率。为了解决优化问题的高计算复杂性，论文探索了次优的资源分配策略，这些策略可能基于启发式算法或者简化模型，能够在保持相对高性能的同时，降低计算需求。这些策略对于实时性和计算资源有限的移动通信环境尤其重要。论文进一步分析了低复杂度替代方法的平均无条件SNR中断概率，这是衡量系统可靠性的一个关键指标。通过理论分析，可以更好地理解在不同信道条件下的系统性能，并为系统设计提供指导。数值模拟和结果验证了提出的策略在实际应用中的优势，展示了如何通过这些策略在不显著增加系统复杂性的情况下，有效提升传输速率。这为未来无线网络的设计和优化提供了有价值的理论依据和技术参考。

5820 IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, VOL. 65, NO. 7, JULY 2016

Maximizing Achievable Rate Strategies for

Incremental-Relay Multicarrier Transmission

Yang Zhang, Lihua Pang, Fengkui Gong, Guangliang Ren,

Xiao Liang, Bin Li, Jianwu Dou, and Jiandong Li

Abstract—This paper develops an improved amplify-and-forward (AF)

orthogonal frequency-division multiplexing (OFDM) scheme, where an

incremental policy is fully utilized to promote the spectrum efﬁciency of co-

operative transmission, and presents several achievable-rate-maximizing

resource allocation strategies. The high computational complexity for op-

timization necessitates our investigation of suboptimal approaches. How-

ever, the associated computational burdens are still intensive due to the

exhaustive search nature. As a consequence, a low-complexity alternative

evolves to achieve a better tradeoff between performance and complexity.

Moreover, its average unconditional signal-to-noise ratio (SNR) outage

probability is analytically derived. Numerical results are shown to illus-

trate the beneﬁts of the proposals and verify the validity of the theoretical

analysis.

Index Terms—Achievable rate, amplify-and-forward (AF), cooperative

communication, incremental-relaying, orthogonal frequency division mul-

tiplexing (OFDM), outage probability, resource allocation.

I. INTRODUCTION

The essential idea of cooperative transmission is that spatial diver-

sity is obtained through antenna sharing by wireless network users. As

a basic collaborative scheme, amplify-and-forward (AF) has attracted

extensive attention since detection and decoding are not required on

the relays.

Capacity optimization is the most fundamental problem faced by

user cooperation. It is well known that due to the half-duplex nature of

the relay nodes, channel capacity of the cooperative systems will drop

to one half in contrast to direct transmission. Thus, it is imperative

Manuscript received June 13, 2014; revised April 18, 2015; accepted July 2,

2015. Date of publication July 7, 2015; date of current version July 14, 2016.

This work was supported in part by the Natural Science Basic Research Plan

in Shaanxi Province under Grant 2015JQ6221 and Grant 2015JQ6259; by

the Fundamental Research Funds for the Central Universities under Grant

JB140109; by the National Natural Science Foundation of China under Grant

61401321, Grant 61372067, and Grant 61510505; by the National High Tech

R&D Program of China under Grant 2014AA01A704; by the National Basic

Research Program of China under Grant 2014CB340206; by the Open Project of

the State Key Laboratory of Integrated Service Networks under Grant ISN16-01;

and by the Science and Technology Research and Development Program of

Shaanxi Province under Grant 2014KJXX-49. The review of this paper was

coordinated by Prof. S. Muhaidat.

Y. Zhang is with the State Key Laboratory of Integrated Service Networks,

Xidian University, Xi’an 710071, China, with the School of Information Engi-

neering, Xi’an University of Science and Technology, Xi’an 710054, China, and

also with the National Mobile Communications Research Laboratory, Southeast

University, Nanjing 210096, China (e-mail: yangzhang1984@gmail.com).

L. Pang is with the State Key Laboratory of Integrated Service Networks,

Xidian University, Xi’an 710071, China, and also with the School of Informa-

tion Engineering, Xi’an University of Science and Technology, Xi’an 710054,

China.

F. Gong, G. Ren, and J. Li are with the State Key Laboratory of Integrated

Service Networks, Xidian University, Xi’an 710071, China.

X. Liang is with the National Mobile Communications Research Laboratory,

Southeast University, Nanjing 210096, China.

B. Li and J. Dou are with the System Simulation Department, ZTE Corpora-

tion, Shanghai 201203, China.

Color versions of one or more of the ﬁgures in this paper are available online

at http://ieeexplore.ieee.org.

Digital Object Identiﬁer 10.1109/TVT.2015.2453213

to promote the capacity of cooperative transmission. In particular,

some protocols committed to improve spectrum efﬁciency have been

proposed, such as incremental relaying and two-way and two-path re-

laying. Incremental relaying enhances spectrum efﬁciency by invoking

relays to help only when necessary, i.e., when the direct transmission

from the source to the destination fails. In two-way and two-path

relaying, capacity is upgraded through reducing the number of slots

used in the exchange of information data and through employing

different relays in adjacent time slots, respectively. However, most

of these spectrum-efﬁcient strategies in the literature focus on ﬂat-

fading relay channels. Alternatively, power assignment between the

source and the relay nodes has attracted a considerable amount of

attention in recent years since transmission power, on one hand, can

be deemed as a scarce radio resource particularly in some battery-

operated cooperative relaying applications and, on the other hand, has

to be kept at a reasonable level to comply with the criterion of future

green communications. It has been proved that by optimally assigning

limited power to the nodes involved in cooperative transmission, sys-

tem performance such as power consumption with quality-of-service

(QoS) constraints, capacity, bit error rate, or outage probability can be

signiﬁcantly boosted [1]. Meanwhile, it has been recently shown that

the maximum beneﬁt of cooperative relaying would be achieved with

minimum overhead if a single best relay can be chosen for a particular

node pair. Speciﬁcally, Krikidis et al. in [2] proposed a classical max-

min relay selection mechanism for AF networks, in which a bottleneck

was deﬁned as the smaller signal-to-noise ratio (SNR) of the dual-

hop links, and the relay with a maximum bottleneck was selected to

help. Afterward, this scheme received extensive investigation. Four

single-relay selection mechanisms, including the max-min scheme,

were put forward based on the instantaneous or average SNR received

for broadcast networks in [3]. It is worth mentioning that the potential

relay nodes and the transmitting power can be regarded as resources

and be jointly optimized with distinct optimization objectives [4].

Building on the given observations, we investigate broadband or-

thogonal frequency-division multiplexing (OFDM) communications

with incremental AF relaying and optimize the available resources

with a total sum-power constraint in the considered scenario to obtain

higher spectrum efﬁciency. The result in this work is an attempt

to review resource allocation problems in a brand new application

scenario and can probably make the research around the topic of

relay more comprehensive. Our speciﬁc contributions are threefold:

1) A new cooperative protocol for incremental-relay multicarrier AF

cooperative transmission is proposed to improve the network achiev-

able rate. Speciﬁcally, this protocol is made of two signaling periods,

and it absorbs the advantages of the incremental relaying strategy in

which subcarriers with a high-quality direct link are fully utilized.

2) Given that an optimal solution for the resource allocation is difﬁcult

to obtain even with numerical techniques, we thus propose subop-

timal step-by-step strategies including incremental policy decision,

power loading, and relay selection algorithms to further enhance the

spectrum efﬁciency. Speciﬁcally, binary incremental policies can be

ﬁrst determined by instantaneous channel state information (CSI), and

subsequent power allocation results can be mathematically obtained

by standard Lagrange techniques. Ultimately, relay selection would

be conducted in either a global or an independent way based on

the algorithm ﬂexibility. 3) Although satisfactory performance can be

achieved, the proposals are still not easy to implement. Therefore, we

further simplify the algorithm and derive the corresponding average

unconditional SNR outage probability at the subcarrier level. Simu-

lation results indicate that a good tradeoff can be realized between

performance and complexity.

See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.

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