PHLAME: A Physical Layer Aware MAC protocol for Electromagnetic nanonetworks in the Terahertz Band

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Abstract

Nanonetworks will enable advanced applications of nanotechnology in the biomedical, industrial, environmental and military fields, by allowing integrated nano-devices to communicate and to share information. Due to the expectedly very high density of nano-devices in nanonetworks, novel Medium Access Control (MAC) protocols are needed to regulate the access to the channel and to coordinate concurrent transmissions among nano-devices. In this paper, a new PHysical Layer Aware MAC protocol for Electromagnetic nanonetworks in the Terahertz Band (PHLAME) is presented. This protocol is built on top of a novel pulse-based communication scheme for nanonetworks and exploits the benefits of novel low-weight channel coding schemes. In PHLAME, the transmitting and receiving nano-devices jointly select the optimal communication scheme parameters and the channel coding scheme which maximize the probability of successfully decoding the received information while minimizing the generated multi-user interference. The performance of the protocol is analyzed in terms of energy consumption, delay and achievable throughput, by taking also into account the energy limitations of nano-devices. The results show that PHLAME, by exploiting the properties of the Terahertz Band and being aware of the nano-devices’ limitations, is able to support very densely populated nanonetworks with nano-devices transmitting at tens of Gigabit/second.

Introduction

Nanotechnology is providing a new set of tools to the engineering community to design and manufacture novel electronic components, just a few cubic nanometers in size, which can perform only very specific tasks, such as computing, data storing, sensing and actuation. The integration of several of these nano-components into a single entity will enable the development of more advanced nano-devices. By means of communication, these nano-devices will be able to achieve complex tasks in a distributed manner [1], [2], [3], [4]. The resulting nanonetworks will enable more advanced applications of nanotechnology in the biomedical, environmental, industrial and military fields, such as intrabody health monitoring and drug delivery systems, or wireless nanosensor networks for biological and chemical attack prevention at the nanoscale, amongst others.

For the time being, the communication options for nano-devices are very limited. The miniaturization of a conventional metallic antenna to meet the size requirements of the nano-devices would impose the use of very high operating frequencies (several hundreds of Terahertz), thus limiting the feasibility of nanonetworks. Alternatively, nanomaterials enable the development of plasmonic nano-antennas which can operate at much lower frequencies. Amongst others, ongoing research on the characterization of the EM properties of graphene, lately referred to as the wonder material of the 21st century [11], [22], points to the Terahertz Band (0.1–10.0 THz) as the radiation frequency band of novel nano-antennas [11], [22], [17]. Interestingly enough, novel graphene-based RF components for nano-transceivers are also envisioned to operate in this frequency band [14], [16], [15].

The Terahertz Band (0.1–10.0 THz) is one of the least explored communication frequency ranges in the EM spectrum [6]. In [8], [12], we developed a new channel model for Terahertz Band communications and showed how the absorption from several molecules in the medium attenuates and distorts the traveling waves and introduces colored Gaussian noise. Despite these phenomena, this band can theoretically support very large bit-rates, up to several Terabit/second. However, it is not likely that very limited nano-devices will require these very high transmission bit-rates. Alternatively, and probably more importantly, having a very large bandwidth enables new simple communication and medium sharing mechanisms suited for the expectedly very limited capabilities of nano-devices.

In this direction, we have recently introduced a new communication scheme for nano-devices based on the exchange of very short pulses spread in time called TS-OOK (Time Spread On–Off Keying) [9]. Indeed, due to the size and energy constraints of nano-devices, it is currently not feasible to generate a high-power carrier signal in the nanoscale at Terahertz frequencies. As a result, classical communication paradigms based on the transmission of continuous signals cannot be used. On the other hand, very short pulses can be generated and efficiently radiated in the nanoscale [17]. In particular, femtosecond-long pulses, which have their main frequency components in the Terahertz Band, are already being used in several applications such as nanoscale spectroscopy and biological imaging [20].

Due to the expectedly very high nano-device density in nanonetworks, novel Medium Access Control (MAC) protocols are needed to regulate the access to the channel and to coordinate concurrent transmissions among nano-devices. Classical MAC protocols cannot directly be used in nanonetworks because they do not capture either the limitations of nano-devices or the peculiarities of the Terahertz Band:

  • First, the majority of existing MAC protocols for wireless networks have been designed for band-limited channels. This is not the case of nanonetworks because, as shown in [8], [12], the Terahertz channel provides nano-devices with an almost 10 THz wide window. This is the main difference between graphene-enabled wireless communication for nanonetworks in the Terahertz Band and the classical wireless paradigms.

  • Second, classical MAC protocols which are based on carrier-sensing techniques cannot be used in pulse-based communication systems. Only some solutions proposed for Impulse Radio Ultra Wide Band (IR-UWB) networks [7] could be considered, but their complexity limits their usefulness in the nanonetwork scenario. For example, it does not seem feasible to generate and distribute orthogonal time hopping sequences among nano-devices as in IR-UWB.

  • Third, the main limitation for nano-devices results from the very limited energy that can be stored in nano-batteries, which requires the use of novel energy-harvesting systems [18], [21]. As a result, the energy of nano-devices has both positive and negative temporal fluctuations which change the availability of the nano-device to communicate over time.

In this paper, we present a PHysical Layer Aware MAC protocol for Electromagnetic nanonetworks in the Terahertz Band (PHLAME). This protocol is built on top of the Rate Division Time-Spread On–Off Keying (RD TS-OOK), which is a revised version of our recently proposed pulse-based communication scheme for nano-devices, and it exploits the benefits of novel low-weight channel coding schemes. PHLAME is based on the joint selection by the transmitter and the receiver of the optimal communication parameters and channel coding scheme which minimize the interference in the nanonetwork and maximize the probability of successfully decoding the received information. Moreover, the fluctuations in the energy of the nano-devices are taken into account. To the best of our knowledge, this is the first MAC protocol for EM nanonetworks that captures the peculiarities of the Terahertz Band as well as the expected capabilities of graphene-based nano-devices.

The main contributions in this paper are summarized as follows:

  • We describe the Rate Division Time Spread On–Off Keying (RD TS-OOK), which is a revised version of the communication scheme based on the exchange of femtosecond-long pulses that we introduced in [9], in order to support variable symbol rates.

  • We propose a PHysical Layer Aware MAC protocol for EM nanonetworks (PHLAME), which adapts the RD TS-OOK coding parameters according to the transmitter and the receiver perceived channel quality and available resources.

  • We analytically study the performance of the proposed protocol in terms of energy consumption, delay and achievable throughput, by using accurate models of the Terahertz channel (path-loss and molecular absorption noise) and the interference.

The remainder of this paper is organized as follows. In Section 2, we describe the new pulse-based communication scheme which is considered in our analysis. In Section 3, we present our new MAC protocol for EM nanonetworks and highlight the novelties of this solution. In Section 4, we analytically investigate the performance of the presented protocol in terms of energy consumption, delay and throughput. In Section 5, we provide numerical results for the performance of PHLAME. Finally, we conclude the paper in Section 6.

Section snippets

Rate division time spread on–off keying

The Rate Division Time Spread On–Off Keying (RD TS-OOK) is a new modulation and channel access mechanism for nano-devices based on the asynchronous exchange of femtosecond-long pulses, which are transmitted following an on–off keying modulation spread in time. A simplified version of this mechanism was first introduced in [9], [10].

The functioning of this communication scheme is as follows. Assuming that a nano-device needs to transmit a binary stream (e.g., the output of a nanosensor),

  • A

PHysical Layer Aware MAC Protocol for Electromagnetic nanonetworks

The PHysical Layer Aware MAC Protocol for Electromagnetic nanonetworks (PHLAME) is a novel MAC protocol tailored to the peculiarities of the Terahertz Band and which takes into account the limitations of future electronic nano-devices. The protocol is built on top of RD TS-OOK, and it is split in two stages, namely, the handshaking process and the data transmission process, which we describe next.

Performance analysis

In this section, we analyze the performance of PHLAME in terms of energy consumption, packet latency and normalized throughput.

Numerical results

In this section we provide numerical results on the performance of PHLAME in terms of energy consumption, packet latency and normalized throughput.

Conclusions

Wireless communication among nano-devices will boost the applications of nanotechnology in many fields of our society, ranging from healthcare to homeland security and environmental protection. However, enabling the communication among nano-devices is still an unsolved challenge. We acknowledge that there is still a long way to go before having an integrated nano-device, but we believe that hardware-oriented research and communication-focused investigations will benefit from being conducted in

Acknowledgment

This work was supported by Fundación Caja Madrid.

Josep Miquel Jornet received the Engineering Degree in Telecommunication Engineering and the Master of Science in Information and Communication Technologies from the School of Electrical Engineering, Universitat Politècnica de Catalunya (UPC), Barcelona, Spain, in 2008. From September 2007 to December 2008, he was a visiting researcher at the MIT Sea Grant, Massachusetts Institute of Technology, Cambridge. Currently, he is pursuing his Ph.D. degree in the Broadband Wireless Networking

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    Josep Miquel Jornet received the Engineering Degree in Telecommunication Engineering and the Master of Science in Information and Communication Technologies from the School of Electrical Engineering, Universitat Politècnica de Catalunya (UPC), Barcelona, Spain, in 2008. From September 2007 to December 2008, he was a visiting researcher at the MIT Sea Grant, Massachusetts Institute of Technology, Cambridge. Currently, he is pursuing his Ph.D. degree in the Broadband Wireless Networking Laboratory, School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, with a fellowship from “Fundación Caja Madrid”. He is a student member of the IEEE and the ACM. His current research interests are in Nanonetworks and Graphene-enabled Wireless Communication.

    Joan Capdevila Pujol received the Engineering Degree in Telecommunication Engineering from the School of Electrical Engineering, Universitat Politècnica de Catalunya (UPC), Barcelona, Spain, in December 2010. From February 2010 to November 2010, he was a visiting researcher at the Broadband Wireless Networking Lab, School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta. His research interests are in electromagnetic nanonetworks.

    Josep Solé Pareta obtained his M.Sc. degree in Telecom Engineering in 1984, and his Ph.D. degree in Computer Science in 1991, both from the Universitat Politècnica de Catalunya (UPC). In 1984 he joined the Computer Architecture Department of the UPC. Currently he is Full Professor with this department. He did a Postdoc stage (summers of 1993 and 1994) at the Georgia Institute of Technology. He is co-founder of the UPC-CCABA (http://www.ccaba.upc.edu/). His publications include several book chapters and more than 100 papers in relevant research journals (>25), and refereed international conferences. His current research interests are in Nanonetworking Communications, Traffic Monitoring and Analysis and High Speed and Optical Networking, with emphasis on traffic engineering, traffic characterization, MAC protocols and QoS provisioning. He has participated in many European projects dealing with Computer Networking topics.

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    This work was completed during his stay in the Broadband Wireless Networking (BWN) Laboratory.

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