Donald R. Ucci

Communication techniques using monopulse waveforms

This paper studies wireless communication systems using technology that does not require a carrier signal. The vehicle used for transmission is a monopulse waveform. Such waveforms possess a bandpass nature, having no DC content. The short time duration of these waveforms, typically nanoseconds, provides has an ultrawide bandpass characteristic, with a spectrum in the range of hundreds of megahertz, making them ideally suited for a spread spectrum communication system. The temporal representations of several monopulse signals are illustrated, and the power spectral densities of the Gaussian and Rayleigh monopulse waveshapes are presented. The relationship between effective time duration, peak-to-RMS value, and bandwidth is detailed. The spectral effect of pulse amplitude modulated data and pulse position modulated data is compared. A methodology for efficient data transmission and a technique for rate doubling at no cost in bandwidth is described. Diversity methods to mitigate a harsh environment, such as those encountered in fading channels, jamming, and multipath situations, are introduced.

Packet radio performance of inhibit sense multiple access with capture

Current portable and land-mobile radio systems employ frequency modulation which exhibits a distinct capture effect. Furthermore, multipath propagation, shadowing, and the spatial distribution of the terminal units create data packets with varying signal strength. We investigate the performance of nonpersistent inhibit sense multiple access (ISMA) applied to the forward channel of packet radio communication networks. We show that the aggregate capacity of ISMA substantially increases compared to the noncapture case for small capture ratios. The mean packet delay of ISMA is also reduced with capture. The effect of different signal strength distribution is explored, and the capacity and delay improvements discussed.

Microwave Oven Signal Modelling

The microwave oven (MWO) is a commonly available appliance that does not transmit data but still radiates signals in the unlicensed 2.4 GHz Industrial, Scientific and Medical (ISM) band. The MWO thus acts as an unintentional interferer for IEEE 802.11 Wireless Fidelity (Wi-Fi) communication signals. An analytic model of the MWO signal is developed and studied in this paper. The models efficacy is studied via simulation and experimental emulation.

Interference temperature limits of IEEE 802.11 protocol radio channels

Interference temperature is a measure of how well a radio operating with a particular protocol and modulation scheme can tolerate interference in its spectrum space. We consider this tolerance metric for the IEEE 802.11 protocol for wireless networking. In experiments with off-the-shelf devices in the laboratory, we characterize the tolerance of the protocol to interference at various frequencies and power levels. Using the results of the experiment, we compute the interference temperature limit that the system will tolerate. We find that the interference temperature limit of the devices is much lower than the upper bound predicted by theory. The interference temperature limit of the protocols is not proportional to the data capacity, hence factors in the physical implementation play an important role in the robustness of the channel.

The effect of a finite distance source on an Applebaum array

The effect of the finite distance of the signal source on the performance of a far-field steering Applebaum type adaptive array is examined. The output signal-to-noise ratio (SNR) is expressed in terms of 1) the distance between the signal and the array center, 2) the input SNR, 3) the element number and locations, and 4) the signal direction. From that expression a rule of thumb is drawn to determine the distance between the signal source and the array center at which the degradation of the output SNR is 1 dB. That distance is in general much larger than the far-field range of a conventional beam forming array.

Location Estimation of Isotropic Transmitters in Wireless Sensor Networks

There are several techniques available for determining the location of wireless transmitters in a network of receivers. The simplest technique for use in sensor networks, is to interpolate the position of the transmitter in the network using the received signal strength (RSS). In this paper we review the RSS geometric locating process. We consider the model for the propagation path to determine an optimal estimate of the location of an isotropic transmitter. We apply a location estimation algorithm to experimental data taken in the field. The experiments involved locating GSM cellular transmitters within a network of power sensors which we emulated with GSM handsets. We analyze the performance of the algorithm in light of the the field tests. We consider modifications of the model to encompass the more nuanced nature of real directional transmitters. We conclude with some remarks on applications of this process to intrusion detection and locating mobile users for emergency services

Spectral signatures and interference of 802.11 Wi-Fi signals with Barker code spreading

This paper characterizes interference in 802.11 Wireless Fidelity (Wi-Fi) systems that utilize Barker codes as spreading sequences. Particularly, detailed spectral analyses are performed. These studies result in exact power spectral densities (PSDs) for 1 Mbps and 2 Mbps signaling schemes that define their spectral signatures. Investigation of the leakage of interference power into adjacent 802.11 channels, which can be useful for the deployment of cognitive radios, is presented The theoretical and computer simulation results for the Wi-Fi signal PSDs are verified through experimental measurements and emulation

Characterization of an Unintentional Wi-Fi Interference Device - the Residential Microwave Oven

Some devices not used for data communications radiate in the 2.4 GHz wireless-fidelity (Wi-Fi) band, thus causing unintentional interference that degrades the performance of IEEE 802.11 wireless systems. An analytical model for radio emissions from one of the most common unintentional interferers, the residential microwave oven, is developed from laboratory measurements. Simulation of the analytical model results in a power spectral density and spectrogram that are in good agreement with experimental data. An interference mitigation technique is proposed for the microwave oven emission

Robust quality of service backbone for mobile ad hoc networks

Mobile ad hoc networks (MANETs) are a rapidly growing field today. Unlike conventional wireless networks, MANETs have no physical backbone infrastructure and no administrative support. Generally, these networks are characterized by scarce resources (e.g. bandwidth, power, etc.), high error rates, and a dynamic topology. In MANETs, the quality of service (QoS) aspect, in general, and QoS routing, in particular, need more attention as a result of the rising popularity and necessity- of real-time multimedia applications. Currently, no robust QoS backbone algorithm can efficiently serve a MANET environ. This paper proposes a novel QoS backbone construction algorithm for MANETs. The backbone nodes are mainly selected based on individual node stability and available bandwidth for each node. Then, these nodes are implicitly connected using link bandwidth and delay as QoS metrics. The proposed algorithm, its performance analysis, and simulation results are presented in this paper

Use of the Tapped Delay Line Adaptive Array to Increase the Number of Degrees of Freedom for Interference Suppression

A conjecture is made that a tapped delay line adaptive array of K elements can be used to suppress more than K - 1 noncoincidentcenter frequency interferers when the interferers operate within afraction of the signal bandwidth. This is possible because of theavailability in the increased number of degrees of freedom. Asimulation study is made verifying this conjecture for the case of atwo-element array and two interferers. Three and five tap sectionsare used in the simulation. The study indicates that the performanceimproves with increasing number of taps.