卫星物联网中的高效前向链路多路复用新方案

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本文主要探讨了"基于卫星的物联网中的一种新颖的前向链路多路复用方案"这一主题，发表在2018年4月的《IEEE物联网杂志》(Volume 5, Issue 2)上。随着卫星通信技术在物联网（IoT）领域的潜力日益显现，该研究着重于提升卫星系统在支持大量用户时的频谱效率问题。传统上，一个卫星系统通常只为单个用户服务，为了同时服务多个用户，会采用时间分复用(TDMA)或频率分复用(FDMA)等技术。作者Die Hu、Lianghua He和Jun Wu提出了一个创新的前向链路多路复用策略。其核心思想是通过将不同用户的星座点映射到更高阶的星座点，这种方法称为星座编码，使得这些用户可以在同一频段内同时发送信号。具体操作流程是：在发射端，每个用户的信号组合被转换为更高阶的调制信号，然后进行传输。接收端，每个用户在接收到并检测到混合信号后，利用相应的解码技术分离出各自的数据，实现了在同一频率带内的多用户数据传输。这种新颖的方案克服了传统方法的限制，提高了频谱利用率，对于那些需要大规模覆盖或者难以部署地面基础设施的地区，如偏远地区、海上或者空中的物联网应用具有显著的优势。通过星座编码和多用户同时传输，卫星通信在物联网中的角色得到了进一步增强，有望在未来为物联网的广泛应用提供更为高效和经济的解决方案。该研究不仅对卫星通信理论有所扩展，也对实际的物联网网络设计和优化提供了有价值的参考。

IEEE INTERNET OF THINGS JOURNAL, VOL. 5, NO. 2, APRIL 2018 1265

A Novel Forward-Link Multiplexed Scheme in

Satellite-Based Internet of Things

Die Hu , Member, IEEE, Lianghua He, and Jun Wu , Senior Member, IEEE

Abstract—Satellite communication has the potential to play a

key role in many applications of Internet of Things (IoT). In this

paper, we consider a satellite-based IoT and investigate the tech-

nology that can improve the spectral efﬁciency. In general, one

beam in satellite systems serves one user. To serve multiple users,

time division multiplexing or frequency division multiplexing is

usually used. In this paper, we propose a novel forward-link

multiplexed scheme, by which the signals of different users can

be transmitted simultaneously using the same frequency band.

Speciﬁcally, at the transmitter, we ﬁrst map each combination

of the users’ constellation points to a higher-order constellation

point, which is referred to as constellation coding, and then trans-

mit such higher-order modulation signals. At the user side, after

receiving and detecting the transmitted signal, each user obtain

its own signal by the corresponding demapping, which is referred

to as constellation decoding. The total system capacity over an

additive white Gaussian noise channel is analyzed in this paper.

Simulation results demonstrate that the proposed scheme can

greatly improve the spectral efﬁciency.

Index Terms—Constellation coding, forward link, frequency

division multiplexing (FDM), multiplexing, satellite communica-

tions, time division multiplexing (TDM).

I. INTRODUCTION

HE CONCEPT of Internet of Things (IoT) points out one

of the directions in the evolution of the Internet, where a

large number of different and heterogeneous end systems can

be incorporated transparently and seamlessly [1], [2].

There are many applications based on the IoT paradigm. In

recent years, the use of the satellite is found to be of paramount

importance in some applications of IoT (e.g., smart grid, envi-

ronmental monitoring, and emergency management), because

satellite communications have unique merits such as large-

scale coverage, superb ability to support emerging communi-

cations services, and cost effectiveness for broadcast/multicast

connectivity [3]–[7]. However, to make an effective IoT via

satellite, there are several issues needed to be answered. In [5],

an integrated view of satellite-based IoT is provided, and

Manuscript received November 21, 2017; revised January 11, 2018;

accepted January 21, 2018. Date of publication January 30, 2018; date of

current version April 10, 2018. This work was supported by the National

Natural Science Foundation of China under Grant 61771144, Grant 61772369,

and Grant 61571329. (Corresponding author: Lianghua He.)

D. Hu is with the Key Laboratory of EMW Information, Fudan University,

Shanghai 200433, China (e-mail: hudie@fudan.edu.cn).

L. He and J. Wu are with the Department of Computer Science

and Technology, Tongji University, Shanghai 201804, China (e-mail:

helianghua@tongji.edu.cn; wujun@tongji.edu.cn).

Digital Object Identiﬁer 10.1109/JIOT.2018.2799550

some relevant topics, such as heterogeneous networks inter-

operability, quality of service management, and group-based

communications are discussed. In [6], the architecture of the

low earth orbit satellite constellation-based IoT is discussed.

In [7], the use of protocol stack on a satellite random access

channel is investigated.

In satellite-based IoT, one satellite generally serves a huge

number of smart objects. Therefore, the spectral efﬁciency of

the whole system is an important performance criterion that

needs to be considered. In this paper, we will focus on the

technology that can remarkably improve the spectral efﬁciency

of the satellite systems.

Beam techniques have been explored in almost all the satel-

lite mobile systems. In order to deliver broadband interactive

data trafﬁc, satellite systems are currently implementing a

multibeam architecture. Compared with a single global beam

transmission, the use of a multibeam architecture can bring

several advantages, such as sending different symbols simul-

taneously to geographically separated areas. Furthermore, by

allowing to reuse the available bandwidth in sufﬁciently

separated beams, the user bandwidth can be increased [8].

However, the frequency reuse schemes cannot dramatically

increase the channel capacity [9]. To further improve the spec-

tral efﬁciency, full frequency reuse is applied to the multibeam

satellite systems [10], [11]. As a consequence, interference

mitigation techniques need to be implemented in the forward

link to mitigate interbeam interference. Many interference mit-

igation techniques have been proposed in the literature. These

techniques can be implemented either at the transmitter (i.e.,

through precoding) [8], [10]–[14] or at the user terminal (i.e.,

through multiuser detection) [15]–[18].

In multibeam satellite systems, one beam generally serves

one user. To serve different users, one can employ time divi-

sion multiplexing (TDM) or frequency division multiplexing

(FDM) [9]. In this paper, we propose a new multiplexed

scheme, by which, different users using the same frequency

band can be served simultaneously. The spectral efﬁciency can

be greatly improved by using the proposed scheme.

The key technique in the proposed scheme is referred to

as constellation coding. Speciﬁcally, given the user number

and each user’s constellation, we map each combination of the

users’ constellation points to a higher-order constellation point.

In stead of transmitting each user’s constellation at different

time slots (i.e., using TDM) or different frequency bands (i.e.,

using FDM), the proposed multiplexed scheme transmits the

higher-order constellation obtained by constellation coding. At

the user side, after the received higher-order modulation signal

2327-4662

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