Page 105 - 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

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Fig. 1 – Classi ication of molecular communication based on scale, energy consumption and communication type

knowledge of the recipient’s processing capabilities. A results show that the negative feedback‑based method
more complex shape requires the transmitter to be able provides maximin strategy by changing the number of
to detect the losses of molecular frames. The transmitter transmitters, number of receivers, molecule degradation
may feel the existence or absence of expected chemical re‑ rate, diffusion coef icient and location, i.e. maximizes the
actions in the receiver in the environment and adjust the minimum throughput. The positive feedback method is
sending rate accordingly. also a maximin strategy for ef iciency by changing the
ii) Receiver‑initiated low control: When the recipient’s number of receivers, diffusion coef icient and degrada‑
molecular storage is illing up, the receiver informs the tion rate of molecules, i.e. maximizes the minimum ef i‑
transmitter by sending feedback. This form of low con‑ ciency.
trol is commonly used in traditional communication. So In [12], a TCP‑like protocol is proposed to ind the optimal
far, only one method of low control initiated by the re‑ transmission rate between the transmitter and receiver
ceiver has been studied in [20, 18]. In order to control the and prevent congestion in molecular communication. In
low of information in traditional networks, the recipient this method, the transmitter is assumed to be very simple
announces a window size to the sender, meaning that the and the receiver acts as a control node and sends the con‑
unacknowledged number of bytes of the sender should nection signal to the transmitter. This triggers the trans‑
not exceed that value at any given moment. If the recipi‑ mitter to release molecules. The transmitted molecules
ent reads the information as fast as it reaches, the window are released in the environment and are absorbed by the
will remain open, otherwise, the window size will be re‑ receptors on the receiver surface. When the receiver ab‑
duced by reaching each segment to eventually reach zero. sorbs the desired amount of the transmitter molecules,
In [18], senders and receivers are considered. it releases a disconnection signal to prevent the trans‑
First, an optimization problem is proposed to ind the mitter from continuing the transmission. Similar to the
maximum throughput and ef iciency according to the TCP transmitter, which is not already aware of the maxi‑
sender’s transmission rate. Throughput is the number mum network capacity, the transmitter irst increases the
of molecules processed by receptors per unit time. Ef i‑ transmission rate. In TCP, this increase is done exponen‑
ciency is throughput divided by the number of molecules tially in the irst step and in the stage of avoiding conges‑
sent per unit time. For simplicity, it is assumed that all tion linearly with the round trip time. In this scenario, for
transmitters are located at the origin and all receivers simplicity, only a linear rate increase is considered. Then,
are located at a similar location. With this assump‑ the receiver decides to halve or stop the transmission rate
tion, a mathematical expression is obtained for the up‑ according to the round trip time.
per bound of throughput and ef iciency. Then, the op‑
timal transmission rate that maximizes them is calcu‑ 2.2 Congestion control
lated numerically. It can be seen that there is a compro‑
mise between throughput and ef iciency. In the follow‑ Congestion control is used to regulate the number of
ing, [18] presents a method for controlling the transmis‑ molecular transfer data units in order to prevent conges‑
sion rate using positive and negative feedback. In this tion in the middle nodes. This can be done by setting
method, the receiver bio‑nanomachine releases feedback the sender’s transmission rate. By detecting an error, the
molecules in the environmentin response to the transmit‑ sender’s transmission rate can be reduced to a speci ied
ter. The transmitter bio‑nanomachine then regulates its predetermined value. It is also possible to calculate the
transmission rate based on the concentration of feedback new transmission rate according to the amount of conges‑
molecules. In the Negative Feedback (NF) the transmit‑ tion. Congestion can be detected from the error rate. Af‑
ter bio‑nanomachine reduces the transmission rate by in‑ ter the rate decreases, the sender may start to increase the
creasing the concentration of feedback molecules. In the sending rate again so that it can use the maximum channel
Positive Feedback (PF), the opposite is true. Simulation capacity. The amount of this increase can be constant or

© International Telecommunication Union, 2021 93