180 research outputs found
Joint Design of Overlaid Communication Systems and Pulsed Radars
The focus of this paper is on co-existence between a communication system and
a pulsed radar sharing the same bandwidth. Based on the fact that the
interference generated by the radar onto the communication receiver is
intermittent and depends on the density of scattering objects (such as, e.g.,
targets), we first show that the communication system is equivalent to a set of
independent parallel channels, whereby pre-coding on each channel can be
introduced as a new degree of freedom. We introduce a new figure of merit,
named the {\em compound rate}, which is a convex combination of rates with and
without interference, to be optimized under constraints concerning the
signal-to-interference-plus-noise ratio (including {\em signal-dependent}
interference due to clutter) experienced by the radar and obviously the powers
emitted by the two systems: the degrees of freedom are the radar waveform and
the afore-mentioned encoding matrix for the communication symbols. We provide
closed-form solutions for the optimum transmit policies for both systems under
two basic models for the scattering produced by the radar onto the
communication receiver, and account for possible correlation of the
signal-independent fraction of the interference impinging on the radar. We also
discuss the region of the achievable communication rates with and without
interference. A thorough performance assessment shows the potentials and the
limitations of the proposed co-existing architecture
A comparison of processing approaches for distributed radar sensing
Radar networks received increasing attention in recent years as they can outperform
single monostatic or bistatic systems. Further attention is being dedicated
to these systems as an application of the MIMO concept, well know
in communications for increasing the capacity of the channel and improving
the overall quality of the connection. However, it is here shown that radar
network can take advantage not only from the angular diversity in observing
the target, but also from a variety of ways of processing the received signals. The
number of devices comprising the network has also been taken into the analysis.
Detection and false alarm are evaluated in noise only and clutter from a theoretical
and simulated point of view. Particular attention is dedicated to the statistics
behind the processing. Experiments have been performed to evaluate practical
applications of the proposed processing approaches and to validate assumptions
made in the theoretical analysis. In particular, the radar network used for
gathering real data is made up of two transmitters and three receivers. More than
two transmitters are well known to generate mutual interference and therefore
require additional e�fforts to mitigate the system self-interference. However,
this allowed studying aspects of multistatic clutter, such as correlation, which
represent a first and novel insight in this topic. Moreover, two approaches for
localizing targets have been developed. Whilst the first is a graphic approach, the
second is hybrid numerical (partially decentralized, partially centralized) which
is clearly shown to improve dramatically the single radar accuracy. Finally the
e�ects of exchanging angular with frequency diversity are shown as well in some
particular cases. This led to develop the Frequency MIMO and the Frequency
Diverse Array, according to the separation of two consecutive frequencies. The
latter is a brand new topic in technical literature, which is attracting the interest
of the technical community because of its potential to generate range-dependant
patterns. Both the latter systems can be used in radar-designing to improve the
agility and the effciency of the radar
A simulation of the single scan accuracy of a two-dimensional pulsed surveillance radar
Bibliography: leaves 194-198.The following dissertation considers the single-scan two-dimensional positional accuracy of a pulsed surveillance radar. The theoretical aspects to the positional accuracy are considered and a generalized analytical approach is presented. Practical position estimators are often complex, and theoretical predictions of their performance generally yield unfriendly mathematical equations. In order to evaluate the performance of these estimators, a simulation method is described based on replicating the received video signal. The accuracy of such a simulation is determined largely by the accuracy of the models applied, and these are considered in detail. Different azimuth estimation techniques are described, and their performances are evaluated with the aid of the signal simulation. The best azimuth accuracy performance is obtained with the class of analogue processing estimators, but they are found to be more susceptible to interference than their binary processing counterparts. The class of binary processing estimators offer easily implemented techniques which are relatively insensitive to radar cross-section scintillation characteristics. A hybrid estimator, using both analogue and binary processing, is also evaluated and found to give an improved accuracy performance over the binary processing method while still maintaining the relative insensitivity to radar cross-section fluctuation
Study to investigate and evaluate means of optimizing the Ku-band combined radar/communication functions for the space shuttle
The performance of the space shuttle orbiter's Ku-Band integrated radar and communications equipment is analyzed for the radar mode of operation. The block diagram of the rendezvous radar subsystem is described. Power budgets for passive target detection are calculated, based on the estimated values of system losses. Requirements for processing of radar signals in the search and track modes are examined. Time multiplexed, single-channel, angle tracking of passive scintillating targets is analyzed. Radar performance in the presence of main lobe ground clutter is considered and candidate techniques for clutter suppression are discussed. Principal system parameter drivers are examined for the case of stationkeeping at ranges comparable to target dimension. Candidate ranging waveforms for short range operation are analyzed and compared. The logarithmic error discriminant utilized for range, range rate and angle tracking is formulated and applied to the quantitative analysis of radar subsystem tracking loops
Study to investigate and evaluate means of optimizing the Ku-band combined radar/communication functions for the space shuttle
The Ku band radar system on the shuttle orbiter operates in both a search and a tracking mode, and its transmitter and antennas share time with the communication mode in the integrated system. The power allocation properties and the Costa subloop subcarrier tracking performance associated with the baseline digital phase shift implementation of the three channel orbiter Ku band modulator are discussed
Adaptive detection of distributed targets in compound-Gaussian noise without secondary data: A Bayesian approach
In this paper, we deal with the problem of adaptive detection of distributed targets embedded in colored noise modeled in terms of a compound-Gaussian process and without assuming that a set of secondary data is available.The covariance matrices of the data under test share a common structure while having different power levels. A Bayesian approach is proposed here, where the structure and possibly the power levels are assumed to be random, with appropriate distributions. Within this framework we propose GLRT-based and ad-hoc detectors. Some simulation studies are presented to illustrate the performances of the proposed algorithms. The analysis indicates that the Bayesian framework could be a viable means to alleviate the need for secondary data, a critical issue in heterogeneous scenarios
Study to investigate and evaluate means of optimizing the radar function
The investigations for a rendezvous radar system design and an integrated radar/communication system design are presented. Based on these investigations, system block diagrams are given and system parameters are optimized for the noncoherent pulse and coherent pulse Doppler radar modulation types. Both cooperative (transponder) and passive radar operation are examined including the optimization of the corresponding transponder design for the cooperative mode of operation
Detection of Gaussian Signal Using Adaptively Whitened Data
The adaptive matched filter, like many other adaptive detection schemes, uses in its test statistic the data under test whitened by the sample covariance matrix S of the training samples. Actually, it is a generalized likelihood ratio test (GLRT) based on the conditional (i.e., for given S) distribution of the adaptively whitened data. In this letter, we investigate detection of a Gaussian rank-one signal using the marginal (unconditional) distribution of the adaptively whitened data. A first contribution is to derive the latter and to show that it only depends on a scalar parameter, namely the signal to noise ratio. Then, a GLRT is formulated from this unconditional distribution and shown to have the constant false alarm rate property. We show that it bears close resemblance with the plain GLRT based on the whole data set (data under test and training samples). The new detector performs as well as the plain GLRT and even better with multiple cells under test and low training sample support
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