Page 171 - ITU Journal Future and evolving technologies – Volume 2 (2021), Issue 2

ITU Journal on Future and Evolving Technologies, Volume 2 (2021), Issue 2

EQUAL‑GAIN COMBINING WITH INTERFERENCE MITIGATION FOR MOLECULAR TYPE
HOPPING ASSISTED MOLECULAR SHIFT KEYING SYSTEMS

Weidong Gao, Terrence Mak and Lie‑Liang Yang 1
1
School of Electronics and Computer Science, University of Southampton, SO17 1BJ, UK.
NOTE: Corresponding author: Lie‑Liang Yang, lly@ecs.soton.ac.uk

Abstract – In multiple access molecular diffusive communications, many nano‑machines exchange information and fuse

data through a common Diffusive Molecular Communication (DMC) channel. Hence, there is Multiple‑Access Interference
(MAI), which should be suf iciently mitigated so as to achieve reliable communications. In this paper, we propose a novel low‑
complexity detection scheme, namely Equal‑Gain Combining with Interference Mitigation (EGC‑IM), for signal detection in the
Molecular Type Hopping assisted Molecular Shift Keying (MTH‑MoSK) DMC systems. By removing a number of entries from

each row of the detection matrix formed during detection, the EGC‑IM scheme shows its potential to signi icantly mitigate
MAI and hence, outperform the conventional EGC scheme. Furthermore, the EGC‑IM scheme has lower complexity than the

conventional EGC scheme and therefore, it is bene icial for practical implementation.

Keywords – Diffusive molecular communications, equal‑gain combining, interference mitigation, molecular shift keying,
multiple‑access
1. INTRODUCTION individual nano‑machine to send its information to a
common receiver. Hence, MDMA differentiates different
Because of the manufacturing and size limitations, in‑
dividual nano‑machines are only capable of inishing nano‑machines via molecular types.
simple missions. To enhance the capability of nano‑ In [8], we have introduced a multiple‑access Diffusion‑
machines, nano‑networking built on the basis of individ‑ based Molecular Communication (DMC) system based on
ual nano‑machines via information exchange and coop‑ molecular type hopping and molecular shift‑keying mod‑
eration is required to complete relatively complex tasks. ulation, referred to as the MTH‑MoSK DMC system. As
in MDMA systems, a MTH‑MoSK DMC system also ex‑
Molecular Communications (MC) has been recognized
to be a promising solution to implement communica‑ ploits multiple types of molecules. However, an MTH‑
tion between nano‑devices, and has received a lot of re‑ MoSK DMC system dose not work on the principle of
MDMA systems, in which each transmitter nano‑machine
search interest in recent years [1]. In nano‑networking,
uses one exclusive type of molecule. Instead, in MTH‑
multiple‑access communications constitute an important
technique, which considers information transmission be‑ MoSK DMC systems, all transmitter nano‑machines share
tween multiple transmitter nano‑machines and one com‑ all types of molecules. In more detail, in MTH‑MoSK
DMC systems, each transmitter nano‑machine is assigned
mon receiver [2, 3, 4, 5, 6].
a unique address code to control the Molecular‑Type Hop‑
According to different information particles and the
mechanisms of propagation, various types of multiple‑ ping (MTH) over, say, chips (or slots) of one symbol du‑
ration, so as to transmit the same symbol times using
access techniques have been proposed/introduced to
different types of molecules. This processing allows to
MC in literature. For instance, in [2, 3], the authors
mitigate Inter‑Symbol Interference (ISI) and simultane‑
introduced Molecular Code‑Division Multiple‑Access
ously support multiple nano‑machines. At the receiver,
(MCDMA), which assigns different signature codes to
different nano‑machines, for supporting them to trans‑ the information received from different nano‑machines
is detected by invoking the MTH codes of different nano‑
mit information simultaneously with a common access
point. At the receiver, the signature codes of different machines for molecular type dehopping and with the aid
nano‑machines are invoked again to recover the received of some other processing.
information. In [4, 5, 6], the concept of Molecular Time‑ In multiple access DMC systems, all nano‑machines share
Division Multiple‑Access (MoTDMA) was proposed to one DMC channel, resulting in Multiple Access Inter‑
assist multiple nano‑machines to transmit information ference (MAI), which makes reliable detection challeng‑
to one common receiver. In MoTDMA, different nano‑ ing [3, 9]. In literature, various detection schemes have
machines are scheduled to transmit information within been proposed and studied in the context of different
different time slots, and hence implement multiple multiple‑access schemes and channel environments [2,
access MC. Moreover, Molecular Division Multiple Access 4, 6, 7]. Speci ically, the authors of [2] proposed a chip
(MDMA) was studied in [7], where a speci ic type of detection scheme, which employs an adaptable thresh‑
molecule or a set of molecular types is employed by each old derived from the number of molecules received within

© International Telecommunication Union, 2021 157