Francesco De Palo

Generation of pseudo-random sequences for noise radar applications

Noise Radar Technology (NRT) is nowadays a promising tool in radar systems. It is based on the transmission of waveforms composed of many noisy samples, which behave as LPI (Low Probability of Intercept) and antispoofing signals. Each noisy sequence is theoretically uncorrelated with the others. In the paper we propose a scheme to generate a “tailored” pseudo-random sequences (limited in amplitude). It will be followed by an analysis of the main performances in terms of the Peak Side Lobe Ratio (PSLR) of the autocorrelation function, cross-correlation analysis to evaluate the orthogonality, bandwidth and energy efficiency.

Noise radar technology: Pseudorandom waveforms and their information rate

The well-known LPI (Low Probability of Intercept) and antispoofing capabilities of some radar waveforms as well some other desirable feature such as a low sidelobes level of their autocorrelation function can be enhanced by “tailored” pseudo-random sequences, whose phase is made up by a deterministic part plus a variable random term. With such an approach it is possible to design a virtually unlimited number of noisy waveforms with good auto-correlation properties (PSLR, i.e. Peak to Side Lobe Ratio) and, for MIMO applications, good orthogonality between them. In this paper the LPI characteristic are analyzed by evaluation of the variation of their information rate with their “randomness” varying. It results that an ad-hoc tradeoff between the different requirements (LPI, PSLR) is required in most cases.

Orthogonal waveforms for multiradar and MIMO radar using noise radar technology

In many radar applications, including marine, automotive and MIMO, there is a need for orthogonal transmission from different radar sets to mitigate mutual interference; the same applies to the different channels in a MIMO radar. New techniques, belonging to the cyclic algorithm family, might be used to generate orthogonal signals with, in addition, low sidelobes in their autocorrelation function in order to mitigate both interference and masking effects due to dynamic range problem. Their performance analysis is shown.

Design of a Noise Radar Demonstrator

The NATO SET-225 Research Group is planning a series of live trials of Noise Radar technology to be performed in summer, 2016 at the Fraunhofer FHR Institute in Wachtberg (near Bonn). The preliminary architecture of the Demonstrator to be used in these trials is described starting from aims and requirements and arriving to define the main system functions, the parameters and the signal processor. It results that this low-cost demonstrator, although mostly implemented using commercial (or anyway, available) equipment and components, will be functionally close enough to a fully-developed operational Noise Radar system as much as to allow us to assess the potential performance of the operational radar, together with the potential plan and effort required to deliver such a system.

Interference problems expected when solid-state marine radars will come into widespread use

The increasing environmental consciousness and the better attention being paid to the primary resources (especially oil and raw materials) is one of the main drivers of the increase in vessel traffic. Moreover, sea shipping is characterized by a good delivery rate and by affordable operating costs in comparison with other transport means, i.e. by road, rail or air. For this reasons, the continuous increase of vessel traffic requires a high degree of control and an adequate assistance to the navigation, in order to ensure safety, reduction of risks for the environment, as well as an efficient, quick and comfortable navigation. The paper describes the evolution of the marine radar systems pointing out the advantages and the potential drawbacks due to the implementation of solid state technology in the incoming, new generation solid-state, high duty cycle marine radars.

Potential applications of noise radar technology and related waveform diversity

The advantages of Noise Radar Technology over more conventional radars using deterministic, although sophisticated, waveforms are twofold: Low Probability of Interception/Exploitation of radar signals and mitigation of mutual interference in marine crowded environments. In this frame, the potential applications of Noise Radar Technology are many: two of them are considered in some detail, i. e. battlefield radar and marine radar. Key elements of the design of the transmitted waveforms in both applications are discussed.

The NATO SET-184 noise radar trials

In the frame of the research activities of the NATO SET-184 group, and thanks to the NATO SET Panel support, experimental tests of the Noise Radar Technology have been carried out in (and near to) Warsaw, in the Autumn of 2013. The paper describes why the particular experiments were made, placing them within the context of previous noise radar trials and with those which will be carried out in summer, 2016 in the frame of the ensuing SET 225 research group. The experimental data set and some representative results are critically described.

A Statistical Model for Vessel-to-Vessel Distances to Evaluate Radar Interference

The maritime traffic is significantly increasing in the recent decades due to its advantageous features related to costs, delivery rate and environmental compatibility. With the advent of the new generation of marine radars, based on the solid state transmitter technology that calls for much longer transmitted pulses, the interference problem can become critical. Knowing the positions and the heights of the ships the mean number of the vessels in radar visibility can be estimated to evaluate the effects of their mutual radar interferences. This paper aims to estimate the probability density function of the mutual distances. The truncation of the density function, within a limited area related to the horizon visibility, leads to a simple single-parameter expression, useful to classify the ships as either randomly distributed or following a defined route. Practical results have been obtained using AIS data provided by the Italian Coast Guard in the Mediterranean Sea.

Analysis and Possible Mitigation of Interferences Between Present and Next-Generation Marine Radars

The maritime traffic is significantly increasing in the recent decades due to its advantageous features related to costs, delivery rate and environmental compatibility. For this reasons it requires a high degree of control and an adequate assistance to the navigation. The related systems are the Vessel Traffic System (VTS), mainly using radar and the Automatic Identification System (AIS). In the recent years a new generation of marine radars with a lower cost of maintenance is being developed. They are based on the solid-state transmitter technology and uses coded “long pulse” in transmission, i.e. high “duty-cycle”, with “pulse compression” in reception. The main drawbacks of these apparatuses are the interference effects that they might cause on existing marine radars, becoming critical when the traffic density increases. The AIS data (identity, location, intention and so on) can be useful to estimate the mutual distances among ships and the mean number of surroundings vessels, that is the number of marine radars in visibility. Using suitable models it is shown that the high duty-cycle of solid-state marine radars can generate severe interference to all marine radar sets in visibility with a significant reduction, well below the international regulations, of their detection capability. The mitigation of these damaging effects, not an easy task, can be achieved by changing the radar waveforms, i.e. resorting to Noise Radar Technology.

Maritime Traffic Models for Vessel-to-Vessel Distances

The maritime traffic is significantly increasing in the recent decades due to its advantageous features related to costs, delivery rate and environmental compatibility. The Vessel Traffic System (VTS), mainly using radar and AIS (Automatic Identification System) data, provides ship’s information (identity, location, intention and so on) but is not able to provide any direct information about the way in which ships are globally positioned, i.e. randomly distributed or grouped/organized in some way, e.g. following routes. This knowledge can be useful to estimate the mutual distances among ships and the mean number of surroundings vessels, that is the number of marine radars in visibility. The AIS data provided by the Italian Coast Guard show a Gamma-like distribution for the mutual distances whose parameters can be estimated through the Maximum-Likelihood method. The truncation of the Gamma model is a useful tool to take into account only ships in a relatively small region. The result is a simple one-parameter distribution able to provide indications about the traffic topology. The empirical study is confirmed by a theoretical distribution coming from the bi-dimensional Poisson process with ships being randomly distributed points on the sea surface.