Page 58 - 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

expected error probability with respect to the threshold put (MISO), and MIMO. Further, the work in [84] derived
and substituting the resulting expression equal to zero. approximate analytical expression of hitting probability
Further, in [78], equal gain combining was used at the i‑ considering the the presence of two fully absorbing re‑
nal destination which could sense the molecules sent by ceivers in 3‑D medium. Based on this expression, authors
both the transmitter and the decode‑and‑forward relay demonstrated that a signaling molecule has higher hitting
node. In this work, the optimal position of the relay and probability if two fully absorbing receivers at a distant lo‑
optimal detection threshold at each of the receivers were cation are used instead of a single fully absorbing receiver.
derived by using a Block Coordinate Descent Algorithm Further, considering null and alternative hypotheses with
(BCDA) which minimizes the end‑to‑end probability of er‑ OOK modulated symbols, the area under the ROC curve
ror. Note that single type of molecules transmission at was derived to analyze the detection performance at both
both the nodes causes ILI that in turn decreases the chan‑ receivers. The insights developed in this work can be fur‑
nel capacity. Thus, to improve the channel capacity of a ther used for designing the detection schemes with two
decode‑and‑forward relay‑assisted‑based MC system, dif‑ receivers.
ferent types of molecules were used for transmission at
the source and the relay in [79]. For decoding, a joint op‑ 2.1.4 Distributed detection‑based MC systems
timal detection threshold problem was also solved using
the Gradient Descent algorithm, which minimizes the er‑ The work in [85] considered cooperative detection where
ror probability with respect to thresholds at the interme‑ more than one receiver detects the OOK modulated trans‑
diate relay and the inal destination. mitted bit and send their decision to an FC, which makes
a global decision using the majority, AND, and OR rules.
Simulation results demonstrated that the error probabil‑
2.1.3 MIMO‑based MC systems
ity for the majority rule was the lowest. In the noisy sce‑
The work in [80] proposed a binary ASK modulation nario, the OR rule performed better for high threshold
scheme for the MIMO‑MC system. For the proposed values. A square pulse transmission based on OOK was
system, a Zero‑Forcing (ZF)‑based equalizer, as well as proposed in [86] for abnormality detection. In this work,
ixed and adaptive threshold‑based detection schemes, the abnormality detection scheme considered a two‑tier
have been proposed. Simulation results demonstrated structure, where several sensor nano‑machines sensed
that both ZF and adaptive threshold‑based detectors had theabnormalityand senttheirdecisions toanFCtodecide
identical BER performance, however, the ixed threshold‑ the presence or absence of abnormality. The NP criterion‑
based detection experienced the worst BER performance based generalized likelihood ratio test was used for detec‑
at the receiver. tion in the irst tier and the OR‑based fusion rule [85] was
used at FC in the second tier.
Derivative‑based detection for 2×2 MIMO‑MC consider‑
ing OOK modulation was proposed in [81]. In this work, Authors in [87] formulated a convex optimization prob‑
the detection was based on the premise that when a bit‑1 lem to determine the threshold at each of the receivers
was transmitted the received signal had consecutive pos‑ and FC, which minimizes the expected end‑to‑end prob‑
itive derivative values due to an initial rise in the num‑ ability of error. The performance of the system was eval‑
ber of received molecules, and in the case of bit‑0, the re‑ uated under perfect and noisy reporting by the receivers
ceived signal either had consecutive negative slope values to the FC. A similar system of sensor nano‑machines send‑
or small positive values due to a weak rising edge caused ing molecular signals to an FC for cooperative abnormal‑
by the Inter‑Link Interference (ILI). Further, for detection ity detection was proposed in [88]. In this work, two dif‑
in a severe ILI scenario, a ZF detection scheme was pro‑ ferent transmission schemes emitting the same type of
posed in [82] assuming asymmetric topology (different molecules and different types of molecules by sensors to
number of transmit/receive antennas). The received sig‑ the FC were considered. For detection, LLR was compared
nal was multiplied by the Moore‑Penrose pseudo inverse against the threshold to decide whether an abnormality is
of the channel matrix to counter the ILI and also to yield present or not. In addition to this, suboptimal detection
an estimate of the transmitted signal. Simulation results schemes for different types of molecules were proposed,
showed that ZF detection with signal sampling at peak where only the maximum value inside the logarithm func‑
times of respective receive antennas achieved lower BER tion was considered. Moreover, the maximal ratio com‑
than the ZF detection with signal sampling at the same bining of the sensor outputs and two‑stage detection were
time for all receive antennas. also proposed therein.
A MIMO‑MC system where a transmitter could send differ‑ Further, to reduce the number of samples and subse‑
ent types of molecules was proposed in [83]. In this work, quently decision delay at the FC, a detection technique
optimizing the drug dosage (i.e., number of molecules was proposed in [89]. This technique used a sequential
emitted by the transmitter) was considered. For perfor‑ average probability ratio test, which employed two differ‑
mance analysis, BER was evaluated for four different con‑ ent thresholds for binary hypothesis testing. A decision
igurations i.e., Single‑Input Single‑Output (SISO), Single‑ was made in favor of the irst hypothesis if LLR was less
Input Multiple‑Output (SIMO), Multiple‑Input Single Out‑ than the lowerthresholdotherwisethe second hypothesis

46 © International Telecommunication Union, 2021