Robert D. Wilson

Channel Identification: Secret Sharing Using Reciprocity in Ultrawideband Channels

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 (UWB) 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 is simulated. A qualitative assessment of the vulnerability of such a secret sharing system to attack from a radio in a nearby location is also given.

UWB radio deployment challenges

The challenges related to the deployment of ultrawideband (UWB) radios are posed in terms of interference issues that UWB radio systems will encounter. The problem of coexistence with a Global Positioning System (GPS) receiver is used as an experimental example. Calculation of an upper bound to the UWB transmitter power illustrates the effect of one possible type of regulation for a given UWB antenna system. The interference environment for a UWB receiver is used to lower bound the UWB transmitter power necessary for a given data rate. Sample measurements are provided.

Comparison of CDMA and modulation schemes for UWB radio in a multipath environment

This paper investigates three different performance metrics for three candidate combinations of multiple access and modulation schemes in ultra wideband radio. The schemes are compared for a single user, multipath channel at a fixed data rate. First, semianalytic expressions are developed for the probability of error with arbitrary multiple-access coding and amplitude or pulse position modulation, which are then reduced for the special cases of time hopped with bit flipping modulation, time hopped with pulse-position modulation and direct sequence with bit flipping modulation. Using Monte-Carlo simulation the bit error rate, probability of outage and probability of best performance are found. The results show that the bit flipped schemes have a consistently lower average bit error rate and outage probabilities and the direct sequence, bit flipped, scheme has highest probability of outperforming both other schemes. In addition, the effect of multipath arrival clustering in channel models was examined and it was found that the same performance curves could be generated with nonclustered arrivals, and hence channel models with nonclustered arrivals can safely be used in performance prediction.

Template estimation in ultra-wideband radio

The short duration of transmitted pulses in ultra-wideband (UWB) impulse radio enables fine time resolution in the receiver and therefore the opportunity to take great advantage of multipath diversity. However, unlike narrowband channels, many UWB channels are frequency selective even if the channel consists of only a single path, significantly altering the shape of the pulse. In this paper we present a least squares approach to finding a suitable correlation template in a UWB receiver based on our knowledge of the transmitted waveform and some properties of the channel. It is shown that the template increases energy capture in the receiver when compared to a template with the same shape as the transmitted pulse, and is more resistant to narrowband interference than a transmitted reference system.

Channel Identification: Secret Sharing using Reciprocity in Ultrawideband Channels

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 on mutual information is found for a general multipath channel and examples given for UWB channel models. Simulation results of key lengths achieved using the proposed key sharing techniques over some ultrawideband channel models are presented.

Ultra wideband interference effects on an amateur radio receiver

This paper illustrates the complexity of issues that arise in the accurate measurement and interpretation of ultra wideband (UWB) interference effects in narrowband receivers. The behavior of an amateur radio receiver in the presence of sinusoidal and UWB interference is studied. We characterize antenna response and receiver nonlinearities, which lead to an understanding of UWB effects on the receiver output during outdoor response measurements as a function of range and antenna orientation.

The flexible geometry of the [HW2(CO)10]− anion

Abstract It is found that the [HW 2 (CO) 10 ] − anion exists in both linear and bent forms: in [Et 4 N] + [HW 2 (CO) 10 ] − the anion adopts a linear D 4 h structure with eclipsed equatorial carbonyl groups, but in [(Ph 3 P) 2 N] + [HW 2 (CO) 10 ] − the anion has a bent backbone and staggered equatorial carbonyl groups.

The crystal structure of Mn(NO)3P(C6H5)3: The first x-ray analysis of a mononuclear metal trinitrosyl complex

Abstract The structure of Mn(NO)3PPh3 has been analyzed by single-crystal X-ray diffraction. It shows a tetrahedral geometry with essentially linear nitrosyl groups, and an eclipsed configuration around the MnP bond. Average distances and angles are: MnN 1.686(7) A, MnP 2.315(2) A, NO 1.165(10) A, PC 1.815(4) A, MnNO 177.2(7)°, PMnN 103.6(2)°, NMnN 114.7(4)°. Final R factor 7.3% for 2064 non-zero reflections. The structure of the five-coordinate nitrito complex Mn(NO)2(ONO)(PEt3)2 is also mentioned briefly.

On the dependence of UWB impulse radio link performance on channel statistics

An important set of applications for ultra-wideband radio involves high data rate communication in indoor, and thus highly cluttered, multipath environments. Hence the statistical model of the multipath channel is an important factor in the evaluation of radio designs. The model should be realistic enough to provide accurate performance estimates, while also simple enough to facilitate rapid simulation and tractable analysis. In this paper we present two simplifications to the standard multipath model and show that both closely reproduce the performance of the standard model for a variety of radio configurations, thus providing lower complexity alternatives for radio simulation or analysis. The characteristics of each model are then compared to gain some insight into the impact of different channel metrics on radio performance.