A Hybrid TDMA/FDMA MAC Scheme for The Internet of Nano

A Hybrid TDMA/FDMA MAC Scheme for The Internet of Nano-Things
Anish Prasad Shrestha, Anup Thapa and Kyung Sup Kwak*
Inha University
*
( Email: [email protected])
Abstract
We propose a hybrid TDMA/FDMA Medium Access Control scheme to provide contention-free
interconnection of nanodevices within electromagnetic nanonetwork which would eventually lead to the
Internet of Nano-Things. It is a simple yet novel scheme appropriate for computation limited nanodevices
arranged in star topology. Our proposed scheme implements modulo and division operations to assign
frequency band and timeslots and further uses beacon signal to implement dynamic TDMA.
Ⅰ. Introduction
The term “Internet of Nano-Things” was
introduced by Akylildiz et al. in [1]. The Internet of
Nano-Things (IoNT) integrates nanoscale devices with
existing communication networks and ultimately to the
Internet.
Although
communication
approach
at
nanoscale could be molecular or electromagnetic (EM),
we refer only EM communication in this paper. Recent
advancements in carbon electronics have opened door
to a new generation of electronic nano-components
such as nanobatteries, nanomemories, nanological
circuits and even nanoantennas making it possible to
manufacture a complete nanodevice [2]. A network of
such nanodevices form an EM nanonetwork which
communicate using EM radiation. The miniaturized
form of a classical antenna imposes the use of very
high radiation frequencies in EM nanonetwork. Due to
such antenna resonant frequency, the available
transmission bandwidth ranges from a few hundreds
of gigahertz to almost ten terahertz (0.1-10THz).
Nanodevices proposed in the literature are expected
to store around 800-900 of picoJoule [3], while fully
charged. This could last for only few transmission
rounds. Once the battery is drained, it would require
to harvest energy from surrounding environment which
would take about one minute to recharge 80%. As
such, EM nanonetwork cannot afford any collision. A
careful transmission using deterministic approach is
required. Hence, we propose a simple yet novel hybrid
TDMA/FDMA Medium Access Control (MAC) scheme
which will provide collision free but efficient way to
use vast available bandwidth.
Ⅱ. Network Architecture
We show a typical network architecture for the
IoNT in Fig. 1. Regardless of the application, it is
expected that each element in the desired environment
will be equipped with nanodevices which will be
connected to the Internet through series of components
like nano-routers, nano-micro interface devices and
gateway [1]. The network architecture is based on
star topology where each nanodevices will try to
connect to the nanorouter which have comparatively
larger computational resources than nanodevices.
Fig. 1 Network Architecture for the Internet of NanoThings
Ⅲ. Proposed Scheme
We assume there are K number of nanodevices within
a coverage of each nanorouter. As molecular
absorption in channel severely limits the transmission
distance, frequency reuse factor becomes one i.e. entire
bandwidth will available for each nanorouter. Therefore,
bandwidth is divided into W subbands to deploy
FDMA. We propose the assignment of a temporary
identity IDi (which is an integer number) to each
nanodevice where, i ϵ {0,1,2,…,K}. This temporary
identity will be unique within the domain of each
nanorouter.
Assume two integer numbers n and d. We define
two functions mod and div such that‘n mod d ’
provides the integer remainder and ‘n div d ’
provides integer quotient when n is divided by d.
Then, we can assign specific subband to ith nanodevice
as
IDi mod W ≡ BGj
(1)
where, BGj represents the designated subband and j ϵ
{0,1,2,…,W-1}. As such, nanodevices are uniformly
distributed within each subband. We allocate timeslot
for each nanodevices which are grouped within that
particular subband. The timeslot for ith nanodevice can
Fig. 2 Flow diagram of dynamic TDMA within a specific subband
be assigned as
IDi div W≡TSt
(2)
where, TSt represents the designated timeslot within a
specific subband and t ϵ {0,1,2,..,T}. T is given by
ceiling of K/W. For example, a nanodevice with
temporary identity 95 in nanonetwork with 9 subbands
will be grouped to bandgroup 5 and timeslot 10.
For the efficient use of timeslots, we further
implement dynamic TDMA using beacon signal. A
beacon signal is always transmitted at the beginning
of each TDMA transmission cycle as shown in fig. 2.
A beacon signal informs
i.
Number of slots in each TDMA transmission
cycle
ii.
Which timeslots are free, occupied and
reserved?
iii.
For how many cycles will the occupied
timeslot be busy?
A nanodevice IDi will wait for beacon signal
whenever it has something to transmit. After listening
the beacon signal, it will first find out if the timeslot
TSt designated for it is free or not. If the timeslot is
occupied, it will sleep till the timeslot is busy. The
nanorouter reserves the timeslot TSt for one
transmission cycle to nanodevice IDi once it is free.
This prevents other nanodevices from reusing the
same timeslot again. Once the nanodevice IDi can
access the designated timeslot TSt, it can also request
access to any vacant timeslots for P number of cycles.
After P number of cycles, nanorouter will reserve the
timeslot used by nanodevice IDi to other designated
nodes in the following transmission cycle. As such,
any nanodevice does not need to wait for more than P
number of cycles with the implementation of dynamic
TDMA.
V. Discussion
In this section, we highlight the benefits and
limitations of the proposed scheme in the context of
IoNT.
Limited
energy
in
nanodevices
restrict
the
transmission capacity, although entire bandwidth is
available to it. Therefore, our scheme uses FDMA for
increasing spectrum efficiency. It also guarantees
contention-free transmission in time domain to ensure
minute amount of energy stored in nanodevices is not
wasted in collision. To comply with the limited
computation requirement of nanodevices, we use only
one modulo operation and one division operation.
However, it should be noted that total number of
supported device is given by product of number of
subbands and number of timeslots. Considering vast
available bandwidth, we expect reasonable number of
devices will be supported under this scheme. Moreover,
all participating devices are required to have oscillator
generating equal duration of clock cycles for
synchronization. This is because duration of each
timeslot should be integer multiple of the clock
duration.
V. Conclusion and Future Works
In this paper, we proposed a MAC scheme based on
TDMA and FDMA that could address the strictest
requirement of nanonetworks. We also discussed the
pros and cons of the proposed scheme.
In future, we intend to analyze performance of the
proposed scheme in terms of throughput and delay.
ACKNOWLEDGMENT
This work was supported by the National Research
Foundation of Korea (NRF) grant funded by the Korea
government (MEST 2010-0018116).
References
[1] I. F. Akyilidiz, and J. M. Jornet, “The internet of
Nano-Things,”IEEE Wireless Communications, vol.
17, no. 6, pp.58-63, 2010.
[2] I. F. Akyilidiz, J. M. Jornet, “ Electromagnetic
wireless
nanosensor
networks,”Nano
Communication Networks, vol 1, no. 1, pp. 3-19,
2010.
[3] J. M. Jornet, and I. F. Akyilidiz, “Joint energy
harvesting and communication analysis for perpetual
wireless nanosensor networks in the terahertz
band,”IEEE Trans. on NanoTech., vol. 11, no. 3, pp.
570-580, 2012.

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