Page 57 - ITU Journal Future and evolving technologies Volume 2 (2021), Issue 3 – Internet of Bio-Nano Things for health applications

ITU Journal on Future and Evolving Technologies, Volume 2 (2021), Issue 3

bit-1 bit-0 bit-1 bit-0

t t
t peak, A
t peak, A t peak, B
Proposed OOK OSK

Type-A molecules
Type-B molecules

Fig. 15 – A variant of OOK and OSK modulation schemes.

For better ISI mitigation in comparison with [71], a compared to the conventional MoSK modulation [33].
scheme based on non‑linear mapping was proposed in The generalized MoSK can transmit ⌊log (M!/(M I !(M −
2
[72]. This scheme irst calculated the peak time of the CIR M I !))⌋ bits per symbol where M I out of M types of
and then the CIR before peak time was multiplied by a fac‑ molecules were required to send a symbol. While the
tor such that the peak value of the CIR should increase. MoSK scheme can only transmit ⌊log (M)⌋ bits per sym‑
2
Also, for ISI mitigation, the CIR after peak time was mul‑ bol using M types of molecules. For example, M=16 is re‑
tiplied by a different factor to reduce the CIR tail. Fur‑ quired in MoSK while M=6 and M I =3 is required in gen‑
ther, for OOK‑based transmission, a threshold‑based de‑ eralized MoSK to achieve a data rate of 4 bits per symbol.
tection was performed using signal energy as a decision Apart from this, maximum likelihood detection consider‑
metric. In this case, the threshold at the receiver was se‑ ing the presence/absence of ISI from previous one symbol
lected as the mean of the signal energies of the previous P duration was used at the receiver. The simulation results
bit‑intervals. Note that this selection of threshold is valid demonstrated that the proposed modulation scheme with
only if P is signi icantly large. Simulation results demon‑ a maximum likelihood detector achieves better error per‑
strated that this non‑linear mapping scheme had better formance compared to MoSK, CSK and D‑MoSK schemes.
BER performance compared to the scheme proposed in
[71]. 2.1.2 Relay‑assisted‑based MC systems

In [73] CSK modulation similar to [74] was used at the
The work in [74] proposed CSK modulation where Q 1
transmitter. The detection was done by maximizing the molecules were emitted to transmit bit‑1 and Q 0 (< Q 1 )
Probability Mass Function (PMF) of the number of re‑ molecules were emitted to transmit bit‑0. This re‑
ceived molecules. A similar detection procedure was duces the Peak‑to‑Average‑Molecule Ratio that is suit‑
also presented considering the presence of an additional able for nano‑machines having limited storage. Further,
source. This additional source generated interference an estimate‑and‑forward relaying scheme was proposed,
which was modeled using a uniformly distributed ran‑ which was shown to perform better than the decode‑and‑
dom variable for mathematical analysis. Also, an optimal forward, and amplify‑and‑forward relaying schemes. In
detection interval was found, which minimized the error contrast to decode‑and‑forward relaying, this improve‑
probability. It was shown that the optimal detection inter‑ ment arises since the estimate‑and‑forward relay trans‑
val was less than the transmission bit‑interval. Authors mits a soft decision. Also, the estimate‑and‑forward re‑
in [75] proposed coded modulation for binary OOK and lay does not amplify the noise as seen in the amplify‑and‑
4‑ary CSK. Moreover, at the receiver, threshold‑less de‑ forward relaying scheme. The maximum likelihood esti‑
tection of data symbols was proposed since the thresh‑ mation of the number of transmitted molecules was per‑
old was set to zero due to the orthogonal coding scheme. formed at the intermediate relay node which was also
7
However, the data rate was limited for the proposed sys‑ used to ind the error probability at the destination re‑
tem due to channel coding. ceiver. The optimization of the decision threshold in [74]
was similar to the one proposed in [51].
Further, a generalized MoSK modulation was proposed in
[76] to improve the data rate using less types of molecules The work in [77] considered an amplify‑and‑forward re‑
laying scheme to increase the communication range. In
7 Since the channel coding schemes append some coded bits to the infor‑ this work, a detection scheme based on the MAP rule has
mation bits, the amount of information transmitted in a given time is
reduced in comparison to the scenario which does not consider chan‑ been proposed for OOK modulated transmission. The de‑
nel coding. tection threshold was determined by differentiating the

© International Telecommunication Union, 2021 45