The automatic recognition of the modulation format of a detected signal, the intermediate step between signal detection and demodulation, is a major task of an intelligent receiver, with various civilian and military applications. Obviously, with no knowledge of the transmitted data and many unknown parameters at the receiver, such as the signal power, carrier frequency and phase offsets, timing information and so on, blind identification of the modulation is a difficult task. This becomes even more challenging in real-world scenarios with multipath fading, frequency-selective and time-varying channels. With this in mind, the authors provide a comprehensive survey of different modulation recognition techniques in a systematic way. A unified notation is used to bring in together, under the same umbrella, the vast amount of results and classifiers, developed for different modulations. The two general classes of automatic modulation identification algorithms are discussed in detail, which rely on the likelihood function and features of the received signal, respectively. The contributions of numerous articles are summarised in compact forms. This helps the reader to see the main characteristics of each technique. However, in many cases, the results reported in the literature have been obtained under different conditions. So, we have also simulated some major techniques under the same conditions, which allows a fair comparison among different methodologies. Furthermore, new problems that have appeared as a result of emerging wireless technologies are outlined. Finally, open problems and possible directions for future research are briefly discussed.

Survey of automatic modulation classification techniques: classical approaches and new trends

Frequency modulated continuous wave (FMCW) radar uses a very low probability of intercept waveform, which is also well suited to make good use of simple solid-state transmitters. FMCW is finding applications in such diverse fields as naval tactical navigation radars, smart ammunition sensors and automotive radars. The paper discusses some features of FMCW radar which are not dealt with in much detail in the generally available literature. In particular, it discusses the effects of noise reflected back from the transmitter to the receiver and the application of moving target indication to FMCW radars. Some of the strengths and weaknesses of FMCW radar are considered. The paper describes how the strengths are utilised in some systems and how the weaknesses can be mitigated. It also discusses a modern implementation of a reflected power canceller, which can be used to suppress the leakage between the transmitter and the receiver, a well known problem with continous wave radars.

Linear FMCW radar techniques

At the watershed scale, soil moisture is the major control for rainfall–runoff response, especially where saturation excess runoff processes dominate. From the ecological point of view, the pools of soil moisture are fundamental ecosystem resources providing the transpirable water for plants. In drylands particularly, soil moisture is one of the major controls on the structure, function, and diversity in ecosystems. In terms of the global hydrological cycle, the overall quantity of soil moisture is small, ∼0.05%; however, its importance to the global energy balance and the distribution of precipitation far outweighs its physical amount. In soils it governs microbial activity that affects important biogeochemical processes such as nitrification and CO2 production via respiration. During the past 20 years, technology has advanced considerably, with the development of different electrical sensors for determining soil moisture at a point. However, modeling of watersheds requires areal averages. As a result, point measurements and modeling grid cell data requirements are generally incommensurate. We review advances in sensor technology, particularly emerging geophysical methods and distributed sensors, aimed at bridging this gap. We consider some of the data analysis methods for upscaling from a point to give an areal average. Finally, we conclude by offering a vision for future research, listing many of the current scientific and technical challenges.

/pdf/soil-moisture-measurement-for-ecological-and-hydrological-1jak2uhu52.pdf

Soil Moisture Measurement for Ecological and Hydrological Watershed-Scale Observatories: A Review

Interferometric radar techniques often necessitate two-dimensional (2-D) phase unwrapping, defined here as the estimation of unambiguous phase data from a 2-D array known only modulo 2pi rad. We develop a maximum a posteriori probability (MAP) estimation approach for this problem, and we derive an algorithm that approximately maximizes the conditional probability of its phase-unwrapped solution given observable quantities such as wrapped phase, image intensity, and interferogram coherence. Examining topographic and differential interferometry separately, we derive simple, working models for the joint statistics of the estimated and the observed signals. We use generalized, nonlinear cost functions to reflect these probability relationships, and we employ nonlinear network-flow techniques to approximate MAP solutions. We apply our algorithm both to a topographic interferogram exhibiting rough terrain and layover and to a differential interferogram measuring the deformation from a large earthquake. The MAP solutions are complete and are more accurate than those of other tested algorithms.

Two-dimensional phase unwrapping with use of statistical models for cost functions in nonlinear optimization

Passive coherent location (PCL) systems are a variant of bistatic radar that exploit 'illuminators of opportunity' as their sources of radar transmission. Dispensing with the need for a dedicated transmitter makes PCL inherently low cost, and hence attractive for a broad range of applications. Although a number of experimental and development examples exist, relatively little has been reported on the detailed performance of these systems and the resulting effects that these will have on the interpretation of backscatter and exploitation of derived information. In the paper a bistatic form of the radar range equation specifically tailored to PCL systems is developed. Realistic examples are used to examine and compare variations in sensitivity and coverage for three candidate transmitters of opportunity. These are analogue FM radio, cellular phone base stations and digital audio broadcast (DAB). These examples show that a wide and extremely useful set of detection ranges are achievable and also highlight some of the key issues underpinning more detailed aspects of predicting detection performance.

Passive coherent location radar systems. Part 1: performance prediction

A radar system includes a radar transceiver for generating transmit signals and for receiving signals reflected by targets. The radar system includes a mixer for combining the transmit signals and the reflected signals into a mixer signal. A radar signal processor includes a sampling device, connected to the mixer, for sampling the mixer signal and for generating a sampled mixer signal. A spectrum estimation device, connected to the sampling device, generates a range profile signal including a plurality of range bins each containing a magnitude of a spectral component. A threshold device, connected to the spectrum estimation device, generates a target space array from the range profile signal. A target decision device, connected to the threshold device, generates estimated range and speed signals for a closest target from the target space array.

Radar signal processor

A prototype W-band all-weather automotive radar based on a single-chip 0.1-/spl mu/m AlGaAs-InGaAs-GaAs HEMT transceiver has been developed. This radar has the features of simple architecture and small size, with adequate performance. Owing to the maturity of HEMT MMIC technology, this radar is potentially low cost to implement in personal vehicles. The prototype radar used for autonomous intelligent cruise control in a passenger car is presented in this paper. The MMIC development, together with the radar system design, is also addressed. >

Forward-looking automotive radar using a W-band single-chip transceiver

This invention discloses a hearing aid including one or more amplification channels in which each amplification channel includes a bandpass filter establishing the frequency range of that particular channel. Each amplification channel further includes a variable gain amplifier, a short-term energy averaging circuit, a long-term energy averaging circuit and a difference amplifier. An acoustical signal sensed by a microphone associated with the hearing aid is applied to the bandpass filter which then applies a signal within the particular frequency range of that filter to the variable gain amplifier and the short-term energy averaging circuit. An output from the variable gain amplifier is applied to the long-term energy averaging circuit and an earphone for enabling a hearing aid user to perceive the sounds sensed by the microphone. Steady state signals perceived by the microphone are integrated by the long-term energy averaging circuit which causes the difference amplifier to reduce the gain of the variable gain amplifier, thus decreasing the steady state sound. A novel sound sensed by the microphone is integrated by the short-term energy averaging circuit which causes the difference amplifier to increase the gain of the variable gain amplifier. In this manner, the gain of the amplifier is increased for desirable sounds and decreased for background noise.

Hearing aid incorporating a novelty filter

An apparatus for correcting for nonlinearities in modulation systems includes a transmitter (24, 28, 48, 50, 52) for transmitting a time varying modulated radar signal (56). A receiver (58, 62) receives an echo signal (60) resulting from reflection of the transmitted modulated signal (56). A mixer (48) compares the transmitted signal against the echo signal and providing a comparison signal indicative of the comparison. The comparison signal is sampled by an A/D converter (74). The A/D convertor (74) provides a sampled comparison signal to a controller/DSP (22). Controller/DSP (22) resamples the sampled comparison signal at selected resample times and effectively varies the selected resample times to correct for nonlinearities in the comparison signal resulting from nonlinearities of the transmitted time varying modulated signal.

Method and apparatus for digital compensation of VCO nonlinearity in a radar system

Method and apparatus for digital compensation of VCO nonlinearity

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