D2D大规模MIMO系统中的导频复用与功率优化策略

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本文主要探讨了在D2D(设备到设备)底层大规模MIMO系统中，如何优化导频分配和功率控制以提升系统效率并降低开销。大规模MIMO技术通过使用大量天线提高无线通信的容量和可靠性，而D2D通信则允许直接设备间的通信，无需经过基站，这在5G网络中尤为重要。首先，研究者针对D2D用户（DU）的信号干扰加噪声比(SINR)提出了一个下限分析，这是评估系统性能的关键指标。通过这个分析，他们确定了在大规模MIMO环境下，为了保证有效通信，DU所需的最低 SINR 水平。这一部分的工作有助于理解在导频分配时应考虑的必要条件，以确保每个DU能够接收到足够的信号而不受过多干扰。接下来，针对导频污染问题，他们提出了一种改进的基于图着色的飞行员分配算法(RGCPA)，即Revised Graph Coloring based Pilot Allocation。图着色理论在这里被巧妙地应用于无线网络的资源管理，通过优化DU之间的导频复用，避免或至少显著减小了由于共享相同导频导致的信号干扰。RGCPA算法旨在通过有效地利用可用的导频资源，提升整个系统的效率。随后，文章关注的是D2D链路的数据传输功率控制问题。为了最小化数据传输功率，研究者设计了一个优化模型，并采用了迭代方法来解决。通过合理的功率控制，可以平衡信号强度和能耗，确保在满足服务质量的同时，最大程度地节省能源。仿真结果显示，引入导频重用策略显著减少了导频开销，而RGCPA算法在实际应用中表现出强大的效果，几乎消除了飞行员污染对系统性能的影响。此外，文中提出的功率控制方案展示了快速收敛性，这意味着系统可以在短时间内达到稳定状态，这对于实时通信场景来说是非常重要的。本研究为大规模MIMO背景下D2D通信系统中的关键问题提供了创新解决方案，包括优化的导频分配策略和高效的数据传输功率控制，这些都将有助于提高整体系统的性能、可靠性和能效。这项研究成果对于设计未来的无线通信网络具有重要参考价值。

112 IEEE COMMUNICATIONS LETTERS, VOL. 21, NO. 1, JANUARY 2017

Pilot Allocation and Power Control in D2D Underlay Massive MIMO Systems

Hao Xu, Nuo Huang, Zhaohui Yang, Jianfeng Shi, Bingyang Wu, and Ming Chen

Abstract—In this letter, we propose pilot reuse among

device-to-device (D2D) users (DUs) in a D2D underlay massive

MIMO system to shorten pilot overhead. First, we derive a

lower bound on the average signal-to-interference-plus-noise

ratio of DUs. Then, a revised graph coloring-based pilot allo-

cation (RGCPA) algorithm is proposed to mitigate the pilot

contamination. Finally, a power control problem to minimize

D2D links’ data transmit power is formulated and an iterative

scheme is adopted to solve the problem. The simulation results

show that pilot overhead can be shortened greatly by pilot reuse,

and the effect of pilot contamination can be almost cancelled

using the proposed RGCPA algorithm. In addition, the power

control scheme converges rapidly.

Index Terms— Massive MIMO system, device-to-device com-

munication, pilot allocation, power control.

I. INTRODUCTION

URRENTLY, massive MIMO has triggered considerable

interest since it can achieve high network capacity and

reduce transmit powers [1]. With perfect channel state infor-

mation (CSI), the effect of small-scale fading, uncorrelated

noise and intra-cell interference can be averaged out com-

pletely in massive MIMO systems.

Due to its distinct advantages such as high spec-

trum efﬁciency, short packet delay and low energy

consumption [2], [3], device-to-device (D2D) communication

which enables nearby devices to communicate directly has

been introduced to massive MIMO systems [4]. To obtain

perfect CSI of all links, orthogonal pilots should be used

by all transmitters. This will increase pilot overhead greatly,

especially in a system with plenty of D2D users (DUs). Pilot

resources can be saved by reusing pilots among DUs, but it

will result in pilot contamination.

Pilot contamination mitigation has been widely studied

in multi-cell systems [5], [6]. To model the pilot assign-

ment problem, [5] proposed two game-theoretic approaches in

which a centralized coordinator was not needed. [6] proposed a

graph coloring based pilot allocation (GCPA) scheme to reduce

pilot contamination. However, these works mainly focused

on pilot allocation in conventional wireless communication

systems. To the best of the authors’ knowledge, there is a

Manuscript received April 25, 2016; revised June 8, 2016; accepted

July 24, 2016. Date of publication August 2, 2016; date of current version

January 6, 2017. This work was partially supported by the National 863 High

Technology Development Project under Grant 2014AA01A701, the National

Nature Science Foundation of China under Grants 61372106, 61223001,

61571125, the China Scholarship Council (CSC), the Program Sponsored for

Scientiﬁc Innovation Research of College Graduate in Jiangsu Province under

Grant KYLX15_0074, and the Fundamental Research Funds for the Central

Universities. The associate editor coordinating the review of this letter and

approving it for publication was O. Amin.

The authors are with the National Mobile Communications Research

Laboratory, Southeast University, Nanjing 210096, China (e-mail:

xuhao2013@seu.edu.cn; huangnuo@seu.edu.cn; yangzhaohui@seu.edu.cn;

shijianfeng@seu.edu.cn; wubingyang@seu.edu.cn; chenming@seu.edu.cn).

Digital Object Identiﬁer 10.1109/LCOMM.2016.2597236

lack of studies on pilot reuse (PR) and pilot contamination

mitigation in D2D underlay massive MIMO systems.

In this letter, we propose pilot reuse among DUs in a single-

cell D2D underlay massive MIMO system to shorten pilot

overhead. CUs use a set of orthogonal pilots to obtain perfect

CSI of cellular links. It is assumed that all transmitters use

the same time-frequency resource block to transmit signals.

We ﬁrst derive a lower bound on DU’s average signal-to-

interference-plus-noise ratio (SINR). Then, we propose a low-

complexity revised GCPA (RGCPA) algorithm to mitigate

pilot contamination caused by pilot reuse. Finally, an iterative

power control algorithm is adopted to minimize D2D links’

data transmit power. Both the RGCPA algorithm and the

power control algorithm are performed based on the averaged

slowly varying metric. Therefore, the algorithms can be run

periodically at a coarser frame level granularity, and the

computational overhead can be decreased greatly. Simulation

results show that pilot overhead can be shortened greatly

by PR, and the effect of pilot contamination can be almost

cancelled by using the proposed RGCPA algorithm. In addi-

tion, the power control process converges rapidly.

II. M

ATHEMATICAL MODELS

A. Network and Baseband Channel Models

Consider a single-cell D2D underlay massive MIMO system

with one base station (BS), T CUs and K D2D pairs. The set

of CUs and D2D pairs are denoted by T and K , respectively.

Assume that the BS has a large number of antennas and each

CU has one antenna. As for D2D communication, we consider

the SIMO transmission in [4], i.e., each D2D transmitter

(D2D-Tx) is equipped with one antenna, and each D2D

receiver (D2D-Rx) is equipped with M antennas. Note that the

analysis and results in this letter can be directly extended to

MIMO transmission. In this system, cellular uplink resources

are shared by DUs, and all transmitters use the same time-

frequency resource block to transmit signals, leading to

co-channel interference. The received data vector of D2D-Rx k

is given by



i=1

1/2

s,i



t=1

1/2

s,t

+ n

, ∀k ∈ K , (1)

where p

s,i

and x

denote the data transmit power and zero-

mean unit-variance data symbol of D2D-Tx i, respectively.

 v

1/2

is the channel vector from D2D-Tx i to

D2D-Rx k with v

denoting the real-valued large-scale fad-

ing coefﬁcient. Each entry of f

represents the fast fading

coefﬁcient from D2D-Tx i to the corresponding antenna at

D2D-Rx k. Assume that v

is constant and known as a priori,

and f

∼ C N(0, I

) with I

denoting the M dimensional

identity matrix. Similarly, q

s,t

, s

and h

 ¯v

1/2

are deﬁned

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

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