Results 1  10
of
214
Channel identification: Secret sharing using reciprocity in UWB channels
 IEEE Transactions on Information Forensics and Security
, 2007
"... To establish a secure communications link between any two transceivers, the communicating parties require some shared secret, or key, with which to encrypt the message so that it cannot be understood by an enemy observer. Using the theory of reciprocity for antennas and electromagnetic propagation, ..."
Abstract

Cited by 89 (0 self)
 Add to MetaCart
(Show Context)
To establish a secure communications link between any two transceivers, the communicating parties require some shared secret, or key, with which to encrypt the message so that it cannot be understood by an enemy observer. Using the theory of reciprocity for antennas and electromagnetic propagation, a key distribution method is proposed that uses the ultrawideband channel pulse response between two transceivers as a source of common randomness that is not available to enemy observers in other locations. The maximum size of a key that can be shared in this way is characterized by the mutual information between the observations of two radios, and an approximation and upper bound on mutual information is found for a general multipath channel and examples given for UWB channel models. The exchange of some information between the parties is necessary to achieve these bounds, and various information sharing strategies are considered and their performance simulated. The vulnerability of such a secret sharing system to attack from a radio in a nearby location is briefly considered in an example.
Energy efficient communications in ad hoc networks using directional antennas
 in Proc. IEEE Infocom’2002
, 2002
"... Abstract — Directional antennas can be useful in significantly increasing node and network lifetime in wireless ad hoc networks. In order to utilize directional antennas, an algorithm is needed that will enable nodes to point their antennas to the right place at the right time. In this paper we pres ..."
Abstract

Cited by 80 (2 self)
 Add to MetaCart
(Show Context)
Abstract — Directional antennas can be useful in significantly increasing node and network lifetime in wireless ad hoc networks. In order to utilize directional antennas, an algorithm is needed that will enable nodes to point their antennas to the right place at the right time. In this paper we present an energyefficient routing and scheduling algorithm that coordinates transmissions in ad hoc networks where each node has a single directional antenna. Using the topology consisting of all the possible links in the network, we first find shortest cost paths to be energy efficient. Then, we calculate the amount of traffic that has to go over each link and find the maximum amount of time each link can be up, using endtoend traffic information to achieve that routing. Finally, we schedule nodes’ transmissions, trying to minimize the total time it takes for all possible transmitterreceiver pairs to communicate with each
Capacity Bounds For AdHoc Networks Using Directional Antennas
, 2003
"... Directional antennas can be useful in significantly increasing the capacity of wireless ad hoc networks. With directional antennas, independent communications between nodes can occur in parallel, even if the nodes are within range of each other. However, mutual interference by simultaneous transmis ..."
Abstract

Cited by 41 (3 self)
 Add to MetaCart
Directional antennas can be useful in significantly increasing the capacity of wireless ad hoc networks. With directional antennas, independent communications between nodes can occur in parallel, even if the nodes are within range of each other. However, mutual interference by simultaneous transmissions limits the maximum number of such concurrent communications. Furthermore, it poses bounds on the amount of capacity gain one can achieve by using directional antennas instead of omnidirectional ones. These bounds depend on the specific antenna type and its parameters, as well as higher layer protocol requirements. In this paper we calculate interferencebased capacity bounds for a generic antenna model as well as a realworld antenna model and analyze how these bounds are affected by important antenna parameters like gain and beamwidth.
A substrate for small patch antennas providing tunable miniaturization factors
 IEEE Trans. Microwave Theor. Tech
, 2006
"... Abstract—Magnetic properties were imparted to a naturally nonmagnetic material by metallic inclusions. A patch antenna tested the performance of the magnetic metamaterial as a substrate and validated that a single substrate can achieve a range of miniaturization values. The effective medium metamate ..."
Abstract

Cited by 36 (0 self)
 Add to MetaCart
Abstract—Magnetic properties were imparted to a naturally nonmagnetic material by metallic inclusions. A patch antenna tested the performance of the magnetic metamaterial as a substrate and validated that a single substrate can achieve a range of miniaturization values. The effective medium metamaterial substrate employed electromagnetically small embedded circuits (ECs) to achieve permeability and permittivity greater than that of the host dielectric. Geometric control of the ECs allowed and to be tailored to the application. The magnetic metamaterial exhibited enhanced and with acceptable lossfactor levels. Models for predicting and are presented, the benefits of employing metamaterial substrates are discussed, and the results in this antenna experiment are presented. The metamaterial exhibits performance characteristics not achievable from natural materials. Of particular significance is that with the permeability varying strongly and predictably with frequency, the miniaturization factor may be selected by tuning the operating frequency. Simulations indicate that such performance can be extended to several gigahertz with current technology. Relative permeability values in the aI–Srange are achievable for moderately lowloss applications. Representative antenna miniaturization factors on the order of 4–7 over a moderate (approximately 10%) transmission bandwidth and efficiencies in a moderate range (20%–35%) are demonstrated with the possibility of higher efficiencies indicated. Index Terms—Magnetic materials, metamaterials, microstrip antennas.
A direct derivation of a singleantenna reciprocity relation for the time domain
 IEEE Transactions on Antennas and Propagation
, 2004
"... Abstract—In this paper, a singleantenna reciprocity relation is derived for the time domain. First, the antenna is considered on transmission; next, the same antenna is considered when it is receiving an incident plane wave. The two states, transmission and reception, are related by the application ..."
Abstract

Cited by 29 (0 self)
 Add to MetaCart
Abstract—In this paper, a singleantenna reciprocity relation is derived for the time domain. First, the antenna is considered on transmission; next, the same antenna is considered when it is receiving an incident plane wave. The two states, transmission and reception, are related by the application of a modified form of the reciprocity theorem for electromagnetic fields with general time dependence due to Cheo. The derivation of the reciprocity relation for the antenna makes use of simple geometric arguments to evaluate the spatial/temporal integrals that occur in the theorem. A few extensions of the reciprocity relation are also described. Index Terms—Antenna theory, reciprocity relation, time domain. I.
The Foster reactance theorems for antennas and radiation Q
 IEEE Trans. Antennas Propag
, 2000
"... Abstract—The calculation of antenna has been an interesting and a controversial topic for years. In this paper, we first give a rigorous study of antenna by introducing a complete description of the complex power balance relation for an antenna system. Using the complex Poynting theorem, we have sho ..."
Abstract

Cited by 22 (5 self)
 Add to MetaCart
(Show Context)
Abstract—The calculation of antenna has been an interesting and a controversial topic for years. In this paper, we first give a rigorous study of antenna by introducing a complete description of the complex power balance relation for an antenna system. Using the complex Poynting theorem, we have shown that the antenna is essentially equivalent to a one port lossy network. The Foster reactance theorem is usually stated for a lossless network. The main purpose of this paper is to determine whether the Foster reactance theorem holds for antennas. By making use of a complex frequency domain version of the Poynting theorem, we have shown that the Foster reactance theorem is valid for an antenna. Finally, the Foster reactance theorem for the antenna has been applied to demonstrate the widely held assumption 1, provided 1, where stands for the fractional bandwidth of an arbitrary antenna. Index Terms—Antenna input impedance, energy storage, factor. I.
Accurate modeling of dual dipole and slot elements used with photomixers for coherent terahertz output power,” Microwave Theory and Techniques
 IEEE Transactions on
, 2001
"... Abstract—Accurate circuit models derived from electromagnetic simulations have been used to fabricate photomixer sources with optimized highimpedance antennas. Output powers on the order of 1 W were measured for various designs spanning 0.6–2.7 THz. The improvement in output power ranged from 3 to ..."
Abstract

Cited by 12 (0 self)
 Add to MetaCart
(Show Context)
Abstract—Accurate circuit models derived from electromagnetic simulations have been used to fabricate photomixer sources with optimized highimpedance antennas. Output powers on the order of 1 W were measured for various designs spanning 0.6–2.7 THz. The improvement in output power ranged from 3 to 10 dB over more conventionally designed photomixers using broadband logspiral antennas. Measured data on single dipoles, twin dipoles, and twin slots are in good agreement with the characteristics predicted by the design simulations. Index Terms—Equivalent circuits, modeling, photoconducting devices, submillimeterwave antennas, submillimeterwave mixers. I.
Directional versus Omnidirectional Antennas for Energy Consumption and kConnectivity of Networks of Sensors
, 2004
"... A network is kconnected if it remains connected after the removal of any k − 1 of its nodes. Assume that n sensors, modeled here as (omni)directional antennas, are dropped randomly and independently with the uniform distribution on the interior of a unit length segment or a unit square. We derive s ..."
Abstract

Cited by 11 (4 self)
 Add to MetaCart
(Show Context)
A network is kconnected if it remains connected after the removal of any k − 1 of its nodes. Assume that n sensors, modeled here as (omni)directional antennas, are dropped randomly and independently with the uniform distribution on the interior of a unit length segment or a unit square. We derive sufficient conditions on the beam width of directional antennas so that the energy consumption required to maintain kconnectivity of the resulting network of sensors is lower when using directional than when using omnidirectional antennas. Our theoretical bounds are shown by experiment to be accurate under most circumstances. For the case of directional antennae, we provide simple algorithms for setting up a kconnected network requiring low energy. 1
Benefit of Pattern Diversity via TwoElement Array of Circular Patch Antennas in Indoor Clustered
 MIMO Channels,” IEEE Trans. Commun
, 2006
"... ..."
(Show Context)
Asympotic Capacity Bounds for Adhoc Networks Revisited: The Directional and Smart Antenna Cases
"... Abstract — Directional and smart antennas can be useful in increasing the capacity of wireless ad hoc networks. A number of media access and routing protocols have been recently proposed for use with such antennas, and have shown significant performance improvements over the omnidirectional case. H ..."
Abstract

Cited by 10 (0 self)
 Add to MetaCart
Abstract — Directional and smart antennas can be useful in increasing the capacity of wireless ad hoc networks. A number of media access and routing protocols have been recently proposed for use with such antennas, and have shown significant performance improvements over the omnidirectional case. However, it is important to explore if and how different directional and smart antenna designs affect the asymptotic capacity bounds, derived by Kumar and Gupta [11]. These bounds are inherent to specific adhoc network characteristics, like the shared nature of the wireless media and multihop connectivity, and may pose major scalability limitations for such networks. In this paper, we look into how directional and smart antennas can affect the asymptotic behavior of an adhoc network’s capacity. Specifically, we perform a capacity analysis for an ideal flattopped antenna, a linear phasedarray antenna, and a fully adaptive array antenna model. Finally, we explain how an adhoc network designer can manipulate different antenna parameters to mitigate the scalability problem of adhoc networks. Keywordscomponent; — capacity; adhoc; directional antennas; smart antennas; I.