Page 66 - 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

background concerning these protocols that we are Note that because of the way the coordinates are
using together: the routing protocol (SLR), the de ined,they can be shared by multiple nodes (which
belongs to the same SLR zone). Consequently, SLR is a
nano‑sleep mechanism itself, and the density estimation
protocol (DEDeN). protocol that routes a packet to the correct zone
instead of a speci ic node.
It is important to note that the choice of the routing pro‑
tocol here is mostly inconsequential to the contribution.
In this paper we do not present a new routing protocol.
In regard to the very speci ic concurrent transmission be‑
haviour of wireless nano‑network(s), we instead present
a mechanism to reduce the load on each node. This mecha‑
nism can be adapted to various routing protocols and
here we choose SLR for the sake of convenience.
3.1 SLR protocol

Stateless Linear‑path Routing (SLR) is a spatial rou-
Fig. 7 – SLR initial phase (left) and SLR routing phase (right).
ting/addressing protocol. It implements a
coordinate‑based routing, in which data packets are
routed in a linear routing path. Coordinates are 3.2 Sleeping mechanism
de ined as an integer number of hops from special nodes
called anchors (Fig. 6). All nanonodes are assumed to be We start be emphasizing that the nano‑sleep we present
placed in a cubic space, where anchors’ nodes are placed at in this section is different in both means and objectives
the vertexes (two anchors for a 2D area / three anchors from the sleep mechanism (often call duty‑cycle) that we
for 3D area). commonly ind in traditional networks.
The SLR protocol has two phases: (1) addressing/initial In traditional networks, making a node sleep and wake up
phase and (2) routing phase. in de ined intervals aims at preserving energy and thus
increasing the life span of the network. A node always
wakes up for a duration long enough to allow the recep‑
tion of one or more frames. It processes the received
packets and then goes back to sleep by turning off most
of its reception and processing capabilities. By doing so,
it preserves a substantial amount of energy. As the
packets are sent sequentially over the channel, the longer
the awaken duration, the larger the number of packets
received. We could also say that while it is awake, a
node has to be able to process the full throughput of the
network. It then completely ignores packets sent while it
is sleeping.
Our proposed nano‑sleeping mechanism differs from
those used in a macro‑scale network by its ine granula-
Fig. 6 – SLR addressing phase.
rity, asynchronicity, and decentralization. The main
In the initial phase, addressing, as shown in Fig. 7, two problem it solves is the potential overwhelming of a node
anchor nodes (placed at the vertexes of 2D network) when too many packets coexist on the channel. With
broadcast a packet (beacon) to the whole network. TS‑OOK, multiple nodes targeting different receivers
Beacon mes‑ sages include a hop distance ield can indeed transmit at the same time, and there is no
initialized to 0, which increments with each hard limit to how many packets can concurrently
retransmission. The node coordinates are the hop coexist on the channel. Because of that, using a
counter in those beacons and correspond to the traditional awaken duration may cause a node to be
distance to the anchors. This phase will be performed overwhelmed when the number of packets concurrently
only once at the network deployment. transmitted exceed its decoding capabilities. Nano‑
In the routing phase (Fig. 7), packets contain the SLR ad‑ sleeping is designed to tackle this problem, by allowing
dress of the sender and receiver. A greedy approach is a node to concentrate on a small number of packets
used to route the packets to their intended destination. while completely (and safely) discarding the others.
When a node receives a message, it checks if it is located A nanonode does not stay awake for the duration of one
on the path from the source to the destination. If and only or several packets, but for a much shorter duration, a
if it is the case, the node forwards the message. This check fraction of the value. In our proposed sleeping

uses basic integer computation appropriate for the low mechanism, all nodes have the same awake‑sleep cycle,
nanonode computation capabilities. equal to . Inside the cycle, all the nodes have the same

54 © International Telecommunication Union, 2021