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INTRODUCTIONWireless ad hoc communication on the nanoscale will requirethinking outside of the traditional radio spectrum. New appli-cations will utilize new forms of wireless communication chan-nels. For example, nanoscale communication will enableprecise mechanisms for directly interacting with cells in vivo.Information may be sent to and from specific cells within thebody, allowing detection and healing of diseases on the cellu-lar scale. From a medical standpoint, the use of current wire-less techniques to communicate with implants is unacceptablefor many reasons, including bulky size, inability to use mag-netic resonance imaging after implantation, potential radia-tion damage, surgical invasiveness, need to recharge/replacepower, post-operative pain and long recovery times, andreduced quality of life for the patient. Better, more humane invivo implant communication is needed. Development of bothbiological and engineered nanomachines is progressing; suchmachines will need to communicate [1]. Unfortunately, net-working vast collections of nanoscale sensors and robots usingcurrent techniques, including wireless techniques, is not possi-ble without communication mechanisms that exceed nanoscalevolumes.

Three ad hoc networking approaches are briefly outlined:• Those based on the use of nanostructures such as nano-

tubes• Biological approaches• A brief mention of quantum mechanical approaches

NANOSTRUCTURESIt may be productive to reconsider how nano-materials areused within devices. The single carbon nanotube (CNT) radio,a radio receiver constructed from a single carbon nanotube,made news many years ago. However, technology has contin-ued to focus on utilizing CNT networks as semiconductingmaterial to construct a single transistor or field effect transis-tor (FET). Consider the fact that many such transistors arerequired to build today’s network equipment. The result isthat nanoscale networks are embedded within each communi-cation device; that same nanoscale network technology mightotherwise be more effectively and directly utilized for ad hoccommunication. Consider rethinking the communicationarchitecture such that the CNT network itself is the communi-cation media and individual nanotubes are the links. Muchresearch has gone into understanding how to align nanotubes.Unfortunately, cost and separation of impurities (metallictubes) are still expensive problems. Lower-cost randomly ori-ented tubes are directly utilized as a communication media[2–6].

BIOLOGICALBiological approaches leverage nature’s own cellular informa-tion transport techniques. The biological inspiration for thiscomes from the cells’ own nanotube network, microtubules. Infact, microtubules and carbon nanotubes have many similari-ties [7]. A clear similarity is their common structure; both arehollow thin-walled tubes with a high aspect ratio and very effi-cient for bearing loads. Microtubules are cytoskeletal biopoly-mers that play a critical role in all phases of the cell’s lifecycle. Carbon nanotubes are suggested to be the closest non-

biological counterpart of microtubules. CNTs are extremelystiff, with a Young’s modulus five times higher than steel.Similar to microtubules, they are also highly resilient. Whilethe chemical composition of microtubules, comprising pro-teins and non-covalent bonds, differs from CNTs, which com-prise carbon and covalent bonds, their mechanical behavior isquite similar. Both microtubules and CNTs spontaneouslyassemble into bundles.

In addition, microtubules and CNTs share electrical prop-erties: both have conductances that have been carefully mea-sured. The flow of current through microtubules and CNTs isdifferent: microtubules use an ion channel, while CNTs areeither semi-conducting or metallic. Current flow throughmicrotubules was measured in [8] to be approximately 9 nS(nano-Seimens) at a rate of approximately 1.0 m/s and exhibitsan amplification effect. Thus, we could even draw the analogyfurther to say that both microtubules and CNTs can act astransistors. Suda et al. [9] have alluded to the fact that electricfields may be used to control the movement of microtubules.Also, both are impacted by magnetic fields, and free-floatingmicrotubules can be steered via a magnetic field. Micro-tubules naturally self-assemble, while controlled self-assemblyof CNTs is possible by coating with amino acids. One signifi-cant difference is that microtubules are more dynamic thancurrently engineered CNT networks. Microtubules switchbetween phases of assembly and disassembly on the timescaleof seconds, thus constantly growing and shrinking in size anddynamically changing the communication paths for molecularmotor transport.

Clearly, there are a myriad of other nanoscale biologicalmechanisms for signaling, from diffusion of chemical waves(e.g., calcium), DNA and cell conjugation, hormones, andpheromones, to many others as yet undiscovered.

QUANTUMQuantum phenomena are another avenue that industry isexploring for small-scale networking [10, 11]. Certainly, the tiebetween quantum mechanics and biology is growing. Whetherphotonics or something closer to matter waves is ultimatelyused for nanoscale networking is yet to be determined. How-ever, the idea of coupling quantum dots with smart materialsis certainly enticing [12, 13].

FUTURE DIRECTION AND ACTIVITIESOne of the greatest needs for nanoscale networking isadvances in theory:• Whether one might achieve an information rate through a

nanotube network that approaches the maximum flowthrough the equivalent network graph; in other words, net-work coding at the level of individual nanoscale particles[14].

• Whether given a network resistance (as well as minimalinformation regarding tube characteristics), one can gener-ate a set of feasible tube networks with the given resistance;that is, infer the underlying network structure, which maybe approached via the inverse eigenvalue problem.

• Determine the fundamental relationship between computa-tion and communication; in other words, quantifying theminimal amount of computation necessary to perform rout-ing at the nanoscale. For example, active networking [15]

WIRELESS AD HOC NANOSCALE NETWORKINGSTEPHEN F. BUSH, GE GLOBAL RESEARCH

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has been proposed for use at the nanoscale [16]. Theresearch related to ad hoc nanoscale networking would filla book [17]; hopefully, with the limited space available inthis column, you have seen enough to pique your interest.One way to get involved is to join the IEEE EmergingTechnologies Committee on this topic at http://www.com-soc.org/nano.

REFERENCES[1] A. Cavalcanti et al., “Nanorobot Communication Techniques: A Compre-

hensive Tutorial,” ICARCV ’06, Dec. 2006, pp. 1–6; available at http://iee-explore.ieee.org/stamp/stamp.jsp? arnumber=4150242&isnumber=4126184

[2] S. F. Bush and S. Goel, “Graph Spectra of Carbon Nanotube Networks,”1st Int’l. Conf. Nano-Networks, Lausanne, Switzerland, Sept. 2006; availableat http://www.research.ge.com/_bushsf/ pdfpapers/04152817 Graph-Spectra.pdf

[3] S. F. Bush and Y. Li, “Graph Spectra of Carbon Nanotube Networks:Molecular Communication,” Materials Research Soci. 2006 Fall Proc., no.0951-E04-06, 2006.

[4] S. F. Bush and Y. Li, “Network Characteristics of Carbon Nanotubes: AGraph Eigenspectrum Approach and Tool Using Mathematica,” GE Glob-al Research, tech. rep. 2006GRC023, 2006; available at http://www.research.ge.com/_bushsf/ pdfpapers/2006GRC023 Final ver.pdf

[5] S. F. Bush and S. Goel, “Graph Spectra of Carbon Nanotube Networks,”Proc. NanoNet ’06, 2006, pp. 1–10.

[6] S. Bush and Y. Li, “Nano-Communications: A New Field? An Explorationinto A Carbon Nanotube Communication Network,” GE Global Researchtech. rep., 2006; available at http://www.research.ge.com/_bushsf/ pdf-papers/2006GRC066 Final ver.pdf

[7] F. Pampaloni and F. Ernst-Ludwig, “Microtubule Architecture: Inspirationfor Novel Carbon Nanotube-based Biomimetic Materials,” Trends in Biotech.,vol. 26, no. 6, 2008, pp. 302–10.

[8] W. H. Goldmann, “Actin: A Molecular Wire, an Electrical Cable?” Cell BiolInt, vol. 32, no. 7, July 2008, pp. 869–70; available at http://dx.doi.org/10.1016/j.cellbi.2008.03.015

[9] T. Suda et al., “Exploratory Research in Molecular Communicationbetween Nanomachines,” Proc. Genetic and Evolutionary Comp., 2005; avail-able at http://www.ece.gatech.edu/research/labs/bwn/NANOS/papers/Suda2005.pdf

[10] R. Van Meter et al., “System Design for a Long-Line Quantum Repeater,”2007; available at http://www.citebase.org/abstract?id=oai:arXiv.org:0705.4128

[11] S.-T. Cheng, C.-Y. Wang, and M.-H. Tao, “Quantum Communication forWireless Wide-Area Networks,” IEEE JSAC, vol. 23, no. 7, 2005, pp. 1424–32.

[12] A. Dorn et al., “Electronic Transport through a Quantum Dot network,” Phys.Rev. B, vol. 70, 2004, pp. 205–306; available at http://www.citebase.org/abstract?id=oai:arXiv.org:cond-mat/0411300

[13] W. McCarthy, Hacking Matter: Levitating Chairs, Quantum Mirages, andthe Infinite Weirdness of Programmable Atoms, free multimedia editioned. Basic Books, 2003; available at http: //www.wilmccarthy.com/Hack-ingMatterMultimediaEdition.pdf

[14] G. Kramer and S. Savari, “Edge-Cut Bounds on Network Coding Rates,”J. Network and Sys. Mgmt., Special Issue on Management of Active andProgrammable Networks, vol. 14, no. 1, Mar. 2006, pp. 49–67; availableat http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.87.4827.

[15] S. F. Bush and A. B. Kulkarni, Active Networks and Active Network Man-agement: A Proactive Management Framework, Kluwer, 2001.

[16] J. P. Patwardhan et al., “Nana: A Nanoscale Active Network Architec-ture,” ACM J. Emerging Technologies in Comp. Sys., vol. 3, no. 2, Jan2006, pp. 1–31, available at http: //www.cs.duke.edu/_jaidev/papers/nana.pdf

[17] S. F. Bush, Nanonetworks, to be published, Artech House, 2010.

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