IoT-Based Coordinated Direct and Relay Transmission With Non-Orthogonal Multiple Access

IEEE WIRELESS COMMUNICATIONS LETTERS, VOL. 10, NO. 3, MARCH 2021 503

IoT-Based Coordinated Direct and Relay Transmission With

Non-Orthogonal Multiple Access

Tien-Tung Nguyen , Toan-Van Nguyen , Thai-Hoc Vu , Daniel Benevides da Costa , Senior Member, IEEE,

and Chung Duc Ho

Abstract—This letter studies an Internet-of-Things (IoT)-based

coordinated direct and relay transmission (CDRT) adopting

non-orthogonal multiple access (NOMA), where an information

source directly communicates with a strong user while a weak

user needs the help of an IoT master node. Different from tradi￾tional NOMA-CDRT systems, in which NOMA protocol is only

deployed at the information source to serve users, the proposed

novel system, i.e., IoT-assisted NOMA-CDRT, have two stages:

(1) information source transmits the information data to users

and (2) IoT master node operating as a relay to decode and for￾ward data of the weak user along with IoT-U. Under the consid￾ered system setup, we derive exact closed-form expressions for the

outage probability of users as well as approximated expressions

for the ergodic sum capacity. Our results show that the proposed

system may not perform well in terms of outage performance at

the strong user during the cooperative transmission phase, but

achieves higher ergodic sum capacity in whole communication

process, and enhances efficient spectrum usage, compared with

conventional CDRT and orthogonal multiple access systems.

Index Terms—Coordinated direct and relay transmission

(CDRT), non-orthogonal multiple access (NOMA), ergodic sum

capacities, Internet-of-Things (IoT).

I. INTRODUCTION

RECENTLY, with the exponential growth of the Internet￾of-Things (IoT), the fifth generation (5G) network is

envisioned to have the ability of interconnecting heterogeneous

IoT sensors or devices for various IoT services and applica￾tions [1]. However, from another point of view, the demand

of spectrum usage has increased dramatically. Due to the

spectrum shortage, non-orthogonal multiple access (NOMA)

technique has arisen as a promising solution for addressing this

Manuscript received October 14, 2020; revised November 1, 2020; accepted

November 1, 2020. Date of publication November 4, 2020; date of current

version March 9, 2021. This work was supported by Thu Dau Mot University

under Grant DT.20.2-017. The associate editor coordinating the review of this

article and approving it for publication was X. Lei. (Corresponding author:

Chung Duc Ho.)

Tien-Tung Nguyen is with the Telecommunication Division, Industrial

University of Ho Chi Minh, Ho Chi Minh City 700000, Vietnam (e-mail:

[email protected]).

Toan-Van Nguyen is with the Posts and Telecommunications Institute of

Technology, Hanoi, Vietnam (e-mail: [email protected]).

Thai-Hoc Vu is with the School of Electrical Engineering, University of

Ulsan, Ulsan 44610, South Korea (e-mail: [email protected]).

Daniel Benevides da Costa is with the Department of Computer

Engineering, Federal University of Ceará, Sobral 62010-560, Brazil (e-mail:

[email protected]).

Chung Duc Ho is with the Faculty of Electrical, Electronics Engineering

and Computer Sciences, Thu Dau Mot University, Thu Dau Mot 750000,

Vietnam, and also with the Electronics and Telecommunication Research

Group, Thu Dau Mot University, Thu Dau Mot 750000, Vietnam (e-mail:

[email protected]).

Digital Object Identifier 10.1109/LWC.2020.3035891

challenge. In principle, in order to achieve high spectral effi￾ciency, NOMA-based networks deploy superposition coding at

transmitting nodes to multiplex the signals of multiple users

and use successive interference cancellation (SIC) at receiving

nodes to decode the signals in power domain [2].

Along the years, some strategies applying cooperative

NOMA (CNOMA) have been proposed in the literature to

improve the spectral efficiency and expand the transmis￾sion coverage. In particular, a promising approach is to

embed NOMA into a coordinate direct and relay transmission

(CDRT), where strong user is directly served by the source

while weak user’s signal is transmitted from the source via

a half-duplex relay [3]. Relying on this idea, [4] investigated

outage performance and ergodic sum capacity (ESC) of a full￾duplex relaying system basing on a CNOMA-based CDRT

scheme. In [5], the outage and ergodic capacity performance

of the near and far users were analyzed in a CNOMA-assisted

CDRT system, where an energy harvesting (EH) relay was

deployed to help the base station data transmission to the

far user. The authors in [6] proposed an efficient relay selec￾tion scheme for a multi-relay scenario to obtain the maximum

successful decoding at the strong user. Very recently, assum￾ing a CNOMA-based CDRT satellite network with direct link

between source and far user, closed-form expressions for out￾age probabilities (OPs) were derived under shadowed-Rician

fading and Nakagami-m fading [7]. Furthermore, performance

analysis in terms of ESC and OP for CDRT with uplink

NOMA was carried out in [8], [9]. Considering an IoT system

setup, the authors in [10] investigated the outage performance

of a CNOMA network, where the IoT master node with role

of EH relay assisted the source to communicate with the des￾tination while simultaneously conveys data to its IoT user.

Later, the authors in [11] extended [10] by accounting for

interference signals as potential energy sources.

Differently from previous works,1 in this letter, we propose

a novel network combining two schemes, i.e., CNOMA-based

CDRT [3]–[9] and CNOMA IoT schemes [10], [11], which

will be termed as IoT-assisted CNOMA-CDRT scheme. The

proposed network enhances the spectrum utilization of con￾ventional CDRT in the cooperative transmission phase by

deploying NOMA stage at the relay. Based on this system

setup, exact closed-form for the users’ OP as well as approxi￾mated expressions for the ergodic sum capacity are derived and

compared with conventional CDRT and orthogonal multiple

access (OMA) systems. Simulation and analytical results show

that the proposed scheme achieves superior ESC in whole

communication process with slight OP loss in the cooperative

transmission phase, compared with the other benchmark

strategies.

1The studies [3]–[9] concern the CNOMA-based CDRT scheme consisted

of two users, while works [10], [11] simultaneously serve information node

and IoT-U node without CDRT strategy.

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