Page 68 - 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

Two methods of adaptive threshold detection for OOK Further, a signal detection scheme with initial distance
transmission were proposed in [118]. The adaptive estimation was proposed in [137]. In this scheme, a pi‑
threshold calculation was based on determining the aver‑ lot signal was released before information transmission
age distance variation within a symbol interval. The dis‑ which assisted to estimate the stochastic distance based
tance was calculated using the diffusion equation (6). The on maximizing the likelihood of the received signal in the
irst adaptive detection scheme was based on a compari‑ irst step. In the second step, maximum likelihood esti‑
son of received concentration with the adaptive threshold. mation was used to ind the initial distance by maximiz‑
In this scheme, the adaptive threshold was selected as half ing the likelihood function based on the PDF of distance.
of the maximum value of the reconstructed signal during Authors employed a MAP‑based detection scheme at the
the interval where the last bit‑1 was detected. Thus, the receiver and based on this, the expression for optimal
decision rule to detect the transmitted bit in the jth bit threshold was obtained. Furthermore, an adaptive detec‑
interval can be expressed as tion scheme for OOK modulation was proposed in [138],
where the decision threshold in the current bit‑interval
{ was selected as the weighted sum of the received signals
1 if h j,peak ≥ h ∗,peak /2,
ˆ (13) in the previous two bit‑intervals. The weights were ob‑
b j =
0 otherwise, tained by minimizing the error rate at the receiver nano‑
machine. Also, a pre‑coding scheme was presented to
where ∗ denotes the index of the last bit‑1 detected, and combat ISI, where the transmitter scaled the number of
h j,peak is the peak value of reconstructed signal using av‑ released molecules if two consecutive bit‑1 were trans‑
erage distance between the transmitter and the receiver mitted. The probability of error was further minimized to
in jth bit interval. determine the optimal scaling factor. The proposed tech‑
nique outperformed the ixed threshold technique and the
The second detection scheme was peak time‑based de‑ one presented in [47] where the received signal in the pre‑
tection in which the peak time of the current bit‑interval vious bit‑interval was considered as an adaptive thresh‑
was compared with 1.6 times the peak time of the recon‑ old.
structed signal where the last bit‑1 was detected. More‑
over, ISI mitigation was also performed by subtracting the Optimal LLR based decision rule was derived at the re‑
reconstructed signals of previous bit‑intervals from the ceiver in [139]. Based on the derived optimal rule, the
total received signal in the current bit‑interval. Simula‑ probability of error with respect to the number of trans‑
tion results demonstrated that these detection schemes mitted molecules and channel capacity with increasing
perform well if the coherence time of the channel is large, external interference was also evaluated. A detection
however they fail to give satisfactory performance if the scheme based on slope values within a symbol interval
coherence time is small (i.e., around 1‑bit interval). was proposed in [140] considering OOK based transmis‑
sion at the transmitter. In this work, Einsteins’ law of dif‑
To overcome the limitations of this work, another de‑
fusion was used to ind the CIR. Moreover, the detection
tection scheme was proposed in [136] in which mod‑
threshold was set to zero as the slope value was positive
i ied concentration shift keying was used where some
for bit‑1 and negative for bit‑0. Cell‑to‑cell communica‑
molecules for bit‑0 were also transmitted. This could
tion based on calcium signaling was proposed in [141].
help the receiver to ind the distance using the diffusion
In this work, intra‑cellular and intercellular calcium sig‑
equation even when bit‑0 was transmitted and the adap‑
naling was studied for mobile cells in an environment
tive threshold was calculated based on the reconstructed
composed of cytoplasm. Based on the external diffusion
signals of previous bit duration unlike [118] where the
model of calcium, the transmission of calcium‑based on
threshold calculation based on the bit duration in which concentration and waveform was also studied. Moreover,
the last bit‑1 was transmitted. The detection rule in [136] the decay of calcium signals in the environment and the
is given by number of activated cells as a percentage of sender cells
 were analyzed.
f 1,max (j−1,t)−f 0,max (j−1,t)
 1 if max(x r k ,k [j]) ≥ ;
ˆ b j = ln f 1,max (j−1,t)
f 0,max (j−1,t)
0 otherwise.
 The work in [142] studied cluster formation by a set
(14) of mobile nano‑machines using the attractant molecules.
This work considered that the angular movement of nano‑
where x r k ,k [j] is the ISI mitigated signal in jth bit inter‑
machines was in the direction of the maximum concen‑
val, r k is the distance between the transmitter and the re‑ tration gradient and the concentration sensed by nano‑
ceiver at kth sample, f 1,max (j −1, t) and f 0,max (j −1, t) are machines was governed by their sensitivity. The number
the peak values of the reconstructed signals for bit‑1 and and size of clusters were shown to be controlled by the
bit‑0 respectively in (j − 1)th bit interval. It is shown that sensitivity of nano‑machines to the concentration of at‑
the detection scheme in [136] performs well for a coher‑ tractants. An MMC system for drug delivery was proposed
ence time of ≈ 2‑bit duration. in [143] where drug carriers and diseased cells were con‑
sidered as transmitters and receivers, respectively. Using
the PDF of stochastic CIR and the reception probability

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