Page 68 - ITU Journal Future and evolving technologies Volume 2 (2021), Issue 7 – Terahertz communications

ITU Journal on Future and Evolving Technologies, Volume 2 (2021), Issue 7

Algorithm 1 Packet retransmission algorithm executed
by all nodes at the destination zone except the destination
node.
alreadyseen = false
waitingTime
wT1ts = aD ‑ (pcktrecp ‑ aS)mod
wT2ts = ‑ (aD ‑ (pcktrecp ‑ aS))mod
if packet type is data and reach the destination zone
then
if Sleeping mechanism is used then
if packet !alreadyseen and the received node is
not the destination node then
if pcktrecp mod ≥ aS then

waitingTime = wT1ts
else pcktrecp mod < aS + aD ‑

waitingTime = wT2ts
end if
end if
end if
Fig. 9 – The effect of the retransmission algorithm at the destination
end if zone.
We recall that this algorithm works when the packet 4 are awake during the packet retransmission by Node 1.
reaches the destination zone. The algorithm works on ho‑ It happens that a node can receive several copies of the
mogeneous and heterogeneous networks, with equal or packet, which is the case for Node 4. This is due to the
different awaken durations. In this algorithm we took into simultaneous awake of the node with the
consideration the case when the awaken duration spans retransmission. Finally, the igure shows that the destination
over two time cycles. We describe the algorithm as fol‑ node awaken time does not overlap with any of the other
lows: nodes. Node 4 retransmits the packet at the end of his
awaken duration, and it is received by the destination Node 3.
• waitingTime: Represents the time the node should Therefore, in the absence of the retransmission
wait before packet retransmission at the end of its algorithm, the destination node would not have received
awaken duration. the packet in the case where it was in sleep mode.
• wT1ts: Formula to calculate the node waiting time if 5.
the awaken duration range is 1 . EVALUATION

• wT2ts: Formula to calculate the node waiting time In this section, we evaluate our proposed ideas through
when its awaken duration spans for 2 . simulations since a detailed analytical study is not possi‑

ble. BitSimulator [16] is used in our simulations due to its
• aD: Represents the node awaken duration. characteristics.
BitSimulator has been designed to allow simulations
• aS: Represents the node awaken starting time. of applications and routing protocols in wireless nano‑
• pcktrecp: Represents the time when the node re‑ networks. It differs from other network simulators by
ceives the packet. its accuracy as it can simulate every bit of payload and
their potential collisions. It also targets ultra‑dense nano‑
Fig. 9 depicts an example of a packet retransmission at networks (hundreds of thousands of nodes). It is highly
the destination zone. In our proposed algorithm, all the optimized for speed and accompanied by a VisualTracer,
nodes have the same awake‑sleep cycle . Inside the an interactive visualization and analysis tool that greatly

cy‑ cle, all the nodes are different in their awake duration helps in dense and complex scenarios. Technical details
aD (or percentage of ) , also the beginning of the awake and information about full reproducibility of our results

1
in‑ terval for each node aS are randomly determined. are provided on a separate website .
When a node receives the packet, the algorithm checks In our previous publication [14], we proposed a novel
whether the node is not the destination node. If this is sleeping mechanism in a homogeneous nano‑network
the case, the algorithm will be applied. which is totally different to the traditional sleeping mech‑
anism applied in ad hoc networks. We de ine a homoge‑
Node 3 represents the destination node. Node 1 receives
neous network as a network in which node density is con‑
the packet, and since it is not the destination node, it
stant. Therefore, all nodes will have the same awaken du‑
executed the algorithm. The algorithm computes the
ration. In this kind of network, the nano‑sleep mechanism
waiting time to retransmit the packet at the end of the
node awaken duration. By coincidence, nodes 2 and 1 \http://eugen.dedu.free.fr/bitsimulator

56 © International Telecommunication Union, 2021