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Characteristics of Nanonetworks

By Vandana Sharma, on July 14, 2017

In the Paper titled "Channel Modeling and Capacity analysis for electromagnetic Wireless Nanonetworks in the Terahertz Band" by Joseph Miquel Jornet et al, the state of the art in molecular electronics is reviewed to motivate the study of the terahertz Band (0.1-10THz) for electromagnetic communication among nanodevices.

Characteristics of Nanonetworks

A novel propagation model for EM communication in the Terahertz Band is emerged, which is grounded on radiative transfer theory and in light of molecular absorption. This model accounts for the total path loss and the molecular absorption noise that a wave in the Terahertz Band suffers when propagating over very short distances. Terahertz Band’s Channel Capacity is suggested by using this model for different power allocation schemes, including a scheme based on the transmission of femtosecond long pulses. The results show that for very short transmission distances in the order of several tens of millimeters, the Terahertz channel supports very large bit rates, up to few terabits per second, which enables a radically different communication paradigm for nanonetworks.

Amongst others, one of the early applications of nanonetworks is in the field of nanosensing. Nanosensors are not just tiny sensors, but nanomachines that take advantage of the properties of novel nanomaterials to identify and measure new types of events in the nanoscale. ,Graphene Nanoribbons (GNRs) or Carbon Nanotubes (CNTs), has ignited the emergence of nano-batteries, nano-processors, nano-memories as well as nano-sensors/actuators . In order to determine the frequency band of operation of future graphene-based EM nano-transceivers, it is necessary to characterize the radiation properties of this nanomaterial. Basically two approaches are there to study frequency band of operation. In the RF approach, according to the classical antenna theory, the reduction of the antenna size down to a few hundreds of nanometers would impose the use of drastically high resonant frequencies. However, at the nanoscale, the propagation of EM waves in graphene is mainly governed by two quantum effects, namely, the quantum capacitance and the kinetic inductance . The possibility to define an antenna with atomic precision working at relatively low resonant frequencies opens the door to EM communication for nanonetworks.

OPTICAL PERSPECTIVE

The emission of photons from nano-structures due to electron photon interaction i.e the interaction between electrons and vibrating ions in the materials , motivates the study of nanotubes and nanoribbons as optical emitters or detectors. From this perspective, the EM radiation is obtained when single electrons collide with the edges of the material in which they are travelling or the other particles that can be found in it, releasing the photons as a result. Mathematically it is demonstrated that a quasi-metallic CNT emits Terahertz radiation when a potential difference is applied to its ends. The absorption of infrared radiation in a nanotube is experimentally demonstrated. CNTs have been proposed as potential optical antennas operating in the Terahertz Band(0.1-10.0 THz).So all these results are basic building blocks for graphene based EM nanonetworks in the Terahertz Band.

The performance of novel nano-patch antennas based on GNR’s and that of nano-dipole antenans based on CNTs are compared and it was shown that a 1 micrometer long grapheme based naono antenna can efficiently radiate EM waves in the Terahertz Band (0.1-10 THz).This resut matches the initial predictions for the frequency of operation of grapheme based RF transistors.

In this paper, focus is mainly on EM communications among nano-devices and develop a physical channel model for wireless communication in the Terahertz Band (0.1-10.0 THz). This model allows us to compute the signal path loss, the molecular absorption noise and, ultimately, the channel capacity of EM nanonetworks.

The main contributions of work are the development of a channel model for EM nanocommunications in the Terahertz Band by revising the concept of molecular absorption and formulations for the total path loss and molecular absorption noise. Proposal of different power allocation patterns for the Terahertz Band and the evaluation of the performance of the Terahertz Band in terms of channel capacity.

In second section of this paper, a new channel model for Terahertz communication by using radiative transfer theory is developed. In third section the capacity of the Terahertz channel and different power allocation patterns are formulated. In fourth section of this paper, numerical results for the channel path loss, molecular absorption noise and capacity are provided and discussed.

TERAHERTZ PROPAGATION MODEL

Graphene based EM nanotransceivers will operate in the Terahertz Band, the frequency range in the EM spectrum that spans the frequencies between 10 GHz and 10 THz. The frequency regions below and above microwave and infrared is still one of the least explored zones of EM spectrum. The extreme path loss observed for such transmission distances, which is mainly affected by molecular absorption, reduces the total bandwidth to just a few transmission windows, which are several gigahertz wide each. Because of this, current efforts both on device development and channel characterization are focused on the communication in the absorption-defined window around 300 GHz. However, thinking of the short transmission range of nano machines, there is a need to understand and model the entire Terahertz Band from 0.1 to 10.0 THz for distances below one meter.

CONCLUSION

In summary, graphene is both quantitatively and qualitatively different from any other material conventionally used in electronic applications. Not only does it have room temperature electron and hole nobilities more than 100 times higher than those of Si, as well as excellent mechanical properties, but also, its ambipolar transport properties, ultra thin and flexible structure, and electrostatic doping offer a new degree of freedom for the development of advanced electronic.

From the preliminary device results currently available, graphene offers great potential to impact RF communication electronics in areas as diverse as low noise amplifiers, frequency multipliers, mixers and resonators. However, in order to take advantage of the full potential of graphene devices, more basic research needs to be combined with improved material growth and device technology. A better understanding of parameters such as breakdown voltage, electron velocity, and saturation current is needed to allow a complete benchmark of this material and an evaluation of its potential performance. In addition, these new applications will have to overcome the limitations of graphene that arise from the lack of bandgap. Once the growth and fabrication technology of these new devices matures, their integration with conventional Si electronics, and/or flexible and transparent substrates has the potential to transform communications. Advanced graphene devices could enable the introduction of advanced RF communication systems in a broad array of new applications. Graphene, the ultimate nanomaterial, is therefore in an excellent position to help RF communication systems become even more ubiquitous and versatile than they are today.