K. S. Shanmugan

A Model for Radar Images and Its Application to Adaptive Digital Filtering of Multiplicative Noise

Standard image processing techniques which are used to enhance noncoherent optically produced images are not applicable to radar images due to the coherent nature of the radar imaging process. A model for the radar imaging process is derived in this paper and a method for smoothing noisy radar images is also presented. The imaging model shows that the radar image is corrupted by multiplicative noise. The model leads to the functional form of an optimum (minimum MSE) filter for smoothing radar images. By using locally estimated parameter values the filter is made adaptive so that it provides minimum MSE estimates inside homogeneous areas of an image while preserving the edge structure. It is shown that the filter can be easily implemented in the spatial domain and is computationally efficient. The performance of the adaptive filter is compared (qualitatively and quantitatively) with several standard filters using real and simulated radar images.

Crop Classification Using Airborne Radar and Landsat Data

Airborne radar data acquired with a 13.3-GHz scatterometer over a test site near Colby, KS, were used to investigate the statistical properties of the scattering coefficient of three types of vegetation cover and of bare soil. A statistical model for radar data was developed that incorporates signal fading and natural within-field variabilities. Estimates of the within-field and between-field coefficients of variation were obtained for each cover type and compared with similar quantities derived from Landsat images of the same fields. The second phase of this study consisted of evaluating the classification accuracy provided by Landsat alone, radar alone, and both sensors combined. The results indicate that the addition of radar to Landsat improves the classification accuracy by about 10 percentage points when the classification is performed on a pixel basis and by about 15 points when performed on a field-average basis. As with all crop-classification studies, these results pertain to the specific dates, geographic region, and crop categories.

The rapidly deployable radio network

The rapidly deployable radio network (RDRN) is an architecture and experimental system to develop and evaluate hardware and software components suitable for implementing mobile, rapidly deployable, and adaptive wireless communications systems. The driving application for the RDRN is the need to quickly establish a communications infrastructure following a natural disaster, during a law enforcement activity, or rapid deployment of military force. The RDRN project incorporates digitally controlled antenna beams, programmable radios, adaptive protocols at the link layer, and mobile node management. This paper describes the architecture for the RDRN and a prototype system built to evaluate key system components.

Block-oriented network simulator (BONeS)

Provides an overview of the BONeS network modelling philosophy and structure. BONeS can be viewed as an integrated system that provides a complete graphical environment for the description and simulation of communications networks. The integrated environment of BONeS includes the capability to describe protocol functions, layers of the ISO Open Systems Interconnection model, and network transmission effects in a hierarchical fashion using block diagrams; configure and execute a discrete-event simulation of the network; perform design iterations; and analyze the system performance. Each of these capabilities is provided through a consistent user interface that relies on the extensive use of graphics, windows, and consistency checking to provide a visual environment for describing networks and their protocols.<<ETX>>

Hidden Markov models for burst errors in GSM and DECT channels

Digital communication systems operating over fading radio channels suffer burst errors which can be modeled by a hidden Markov process model. An approach is presented for constructing HMM models for GSM and DECT channels using waveform level simulation and the resulting set of HMM models are tabulated for realistic values of the fading channel parameters. The use of the HMM model for protocol design and evaluation is also illustrated along with a comparison of the computational requirements for the HMM model versus a detailed waveform level simulation approach. While the actual savings in computations that is possible with the use of HMM models depends on how often the parameters of the model have to be computed from waveform level simulation, it is shown that typical savings of two or more orders of magnitude are possible.

The influence of sensor and flight parameters on texture in radar images

Texture is known to be Important in the analysis of radar images for geologic applications. It has previously been shown that texture features derived from the grey-level co-occurrence matrix (GLCM) can be used to separate large-scale texture in radar images. Here the influence of sensor parameters, specifically the spatial and radiometric resolution and flight parameters, i.e., the orientation of the surface structure relative to the sensor, on the ability to classify texture based on the GLCM features is investigated. It was found that changing these sensor and flight parameters greatly affects the usefulness of the GLCM for classifying texture on radar images.

RDRN: a rapidly deployable radio network-implementation and experience

A proof-of-concept implementation for an experimental wireless ATM network developed within the project RDRN (rapidly deployable radio network) is presented. The RDRN architecture consists of two types of transportable nodes, remote nodes (RNs) and edge nodes (ENs), which utilize GPS-derived location information to rapidly configure themselves into a high-capacity adaptive wireless network operating at 1-10 Mb/s over distances as far as 10 kilometers. The initial prototype has been deployed and early experiments have been conducted to validate hardware, software, and protocol design and implementation. In addition to describing the RDRN architecture and protocols, this paper presents preliminary performance results obtained from the actual implementation.

Simulation-based estimation of intermodulation distortion and C/IM

A technique for simulating and analyzing intermodulation (IM) distortion in multicarrier systems operating over nonlinear channels is presented. A cross-correlation technique is used to estimate and isolate the signal components and intermodulation products and to obtain estimates of carrier-to-intermodulation (C/IM) power ratio over any bandwidth of interest. Details of the estimation procedure along with examples are presented from a C/IM point of view.<<ETX>>

Dual diversity combining and equalization for indoor radio channels

The data rate and performance of digital transmission systems operating over indoor radio channels are limited by the frequency selective fading in the channel. Appropriate combinations of diversity, modulation, equalization, coding, and spreading techniques can be used to mitigate the effects of frequency selective fading and improve throughput and performance. A dual diversity combining and equalization scheme for high data rate transmission over indoor radio channels is presented. The performance of the proposed scheme is evaluated using discrete multipath models for line of sight and obstructed topography indoor radio channels.<<ETX>>

COEDS: a CAAD tool for shipboard communication system engineering

The authors describe COEDS (communication engineering design system), a new CAAD (computer-aided analysis and design) tool developed for shipboard communication systems. COEDS aids in EMI (electromagnetic interference) analysis, system degradation prediction, and interference mitigation. COEDS tools are used to build block diagrams of communication systems, calculate power and frequency of cosite interference, predict the degree of performance, and evaluate alternative designs. The application of these tools is shown by an example of an HF system design and interference analysis. The example demonstrates the block diagram interface, automated program operation, generation of graphical output, and ease of use in changing the design to meet performance criteria.<<ETX>>