Page 172 - ITU Journal Future and evolving technologies – Volume 2 (2021), Issue 2

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

Binary
the previous chip. In [4], the detection method presented &,(
input
Bit-to-
X " " MoSK % ( )
symbol +
in [10] was considered for MoTDMA systems. In this mapping modulation
detection scheme, the number of received molecules is
MTH
compared with a variable threshold, which is directly set address Diffusive
channel
as the number of molecules of the same type that are
received in the previous transmission period. For the Binary �
output Receiver 0,( ( ) Interference from
MTH‑MoSK DMC system proposed in [8], two detection Sampling -
processing other nanomachines
schemes using the principles of majority vote and Equal‑ �
Gain Combining (EGC) were designed and studied. It was Fig. 1 – System diagram showing the components of MTH‑MoSK DMC
shown that the detection performance of both detection systems.
schemes is severely affected by MAI.
ing joint MTH‑assisted multiple access and MoSK modula‑
Therefore, in this paper, we introduce a low‑complexity
tion, where each transmitted symbol conveys log bits.
2
detection scheme which has an MAI mitigation capabil‑ In an MTH‑MoSK DMC system, the symbol duration of

ity for MTH‑MoSK DMC systems. Speci ically, we in‑ seconds is divided into chips of each lasting = /
vestigate and compare two types of low‑complexity de‑ ℎ
seconds. We assume that the system supports ≤
tection schemes. As the baseline, the irst one is the
nano‑machines and they have a similar distance from a
above‑mentioned EGC assisted detection [8], which has
common Access Point (AP), which may be connected with
low complexity but experiences MAI. The second one is
other communication networks.
also in the principle of EGC but assisted by interference
mitigation processing, which is therefore referred to as As illustrated in Fig. 1, log bits of binary in‑
2
EGC‑IM for convenience of description. Our further dis‑ formation are mapped to a ‑ary symbol ∈
course will show that the EGC‑IM scheme only imposes {0, 1, … , − 1} to be transmitted by the th nano‑
a slight increase of computation on the EGC scheme, but machine. Using the unique MTH address code assigned
employs the capability to effectively mitigate MAI. Our to the nano‑machine, which is expressed as =
simulation results show that MAI dominates the achiev‑ [ , , … , ( −1) ], ( ) ∈ [0, − 1], the symbol is
(1)
(0)

able performance, when Signal‑to‑Noise Ratio (SNR) is signed to give
relatively high. In this case, the EGC‑IM scheme can sig‑
ni icantly outperform the conventional EGC scheme.
(1)
(0)
The contribution of this paper can be brie ly summarized =[ , , … , ( −1) ]
as follows:
= ⋅ 1 1 1 (1× ) ⊕

• An EGC‑IM detection scheme is proposed for MTH‑ (0) (1) ( −1)
=[ ⊕ , ⊕ , … , ⊕ ],

MoSK DMC systems. The EGC‑IM scheme has low
= 1, 2, … , (1)
complexity, which is similar to the conventional EGC
scheme. However, the EGC‑IM scheme employs the
capability of MAI mitigation.
where ⊕ presents the addition operation in the Galois
• The detection performance of an EGC‑IM scheme ield GF ( ) [11] and 1 1 1 (1× ) is an all‑one‑element row
is investigated and compared with that of the con‑ vector of length . Therefore, the elements of take

ventional EGC scheme, showing that the EGC‑IM values in {0, 1, … , − 1}. After the MTH processing,
scheme is a high‑ef iciency detection scheme for ‑ary MoSK modulation is implemented, as shown in
MTH‑MoSK DMC to simultaneously support multiple Fig. 1, and the corresponding types of molecules are suc‑
nano‑machines. cessively emitted into the DMC environment from = 0
to = − 1. To explain the principles in more de‑
The remainder of the paper is presented as follows. Sec‑

tail, we consider an MTH‑MoSK DMC system supporting
tion 2 introduces the DMC channel model and the princi‑
= 2 nano‑machines, whose MTH address codes are
ple of MTH‑MoSK DMC. In Section 3, we present the prin‑
= [6, 2, 5, 7, 3, 4] and = [0, 1, 7, 3, 6, 2], respectively.
2
1
ciples of the conventional EGC and the proposed EGC‑IM The symbols transmitted by the two nano‑machines are

schemes. Performance results are demonstrated in Sec‑ = 7 and = 2, respectively. Then, after the ad‑
1
2

tion 4. Finally, the main conclusions from research are dition operations in the Galois ield, we obtain 1 =

summarized in Section 5.
[1, 5, 2, 0, 4, 3] and = [2, 3, 5, 1, 4, 0], which determine
2
which type of molecule is emitted within a chip of a sym‑
2. SYSTEM MODEL bol duration.
Speci ically, if within the th chip of the th symbol du‑
2.1 Transmitted signal ration, the type‑ molecules is emitted by the th nano‑
machine to transmit information, according to Fick’s
The system diagram for the MTH‑MoSK system is shown law [12, 13], the concentration of the th type of infor‑
in Fig. 1. We assume that the MTH‑MoSK DMC system em‑ mation molecules sampled at time ≥ ( + ) can be
ℎ

ploys types of information molecules for implement‑ expressed as
158 © International Telecommunication Union, 2021