Digital Alias-free Signal Processing (DASP) technology and applications

The knowledge accumulated in this area over a long period of time represents the theoretical basis for R&D carried out in this direction.  While the term “Digital Alias-free Signal Processing” places emphasis on the alias suppressing capability of the DASP technology, it offers much more. Actually the basic point of this technology is the approach to analog signal digitising and to processing of the digitised signals. The dominating role of signal digitising is duly recognized and the process of system design typically starts by analysis of the conditions for signal digitising dictated by the given application. The required signal sampling and quantising modes, best fitting to the specifics of this application, are defined at this stage. The algorithms for processing the digital signal then have to be matched to the technique used for the signal digitising.   Theory of DASP technology for signal encoding and digital processing is summarised in the monograph:

I. Bilinskis. “Digital Alias-free Signal Processing”, Wiley, 2007.

Massive data acquisition from real life objects and supplying of computers with this information in an effective way evidently is vital to realizing full potential of computer system applications in many areas. DASP technology represents a powerful tool for such system development. Specifically, the R&D ERAF project “Development of multi-channel systems for acquisition of data from biomedical, ecological and industrial systems and transferring them to computerized systems”, completed in 2008, is focused on achieving progress in this direction by finding ways how to avoid some typical data acquisition bottlenecks. Thus the project is dedicated to resolving key problems in the area of interfacing sensors and sensor networks with computers. To reach the goal of this project and to create competitive multi-channel data acquisition systems for supplying computers with information gathered from the real world objects, a flexible approach to complexity-reduced multi-channel data acquisition from a large quantity of sensors has been developed and used. The developed methods, systems and algorithms for data acquisition from wideband, event timing and large distributed clusters of signal sources are discussed with emphasis on data gathering from a large quantity of signal sources. Special signal digitising techniques, including pseudo-randomised multiplexing, time-to-digital conversions and signal sample value taking at time instants when the input signal crosses a sinusoidal reference function, are used for that. The versatility of the considered data acquisition systems is achieved by using modular system design. Development of the discussed massive data acquisition systems is based on the knowledge accumulated over a long period of time in the area of Digital Alias-free Signal Processing.


Innovative technology for high-precision event timing (Lat, Eng, Rus)

There is important problem in development of high-performance event timers, namely to combine picosecond precision, high measurement rate and reasonable cost of realisation. Traditional technologies for high-precision event timing actually cannot provide that.

To solve this problem, at the end of 1990s we have offered a novel DSP-based technology for event timing. General idea of this technology is to generate a specific analog signal at instant determined by the input event, digitise such signal and then digitally process it [link to PDF0]. When the processing is made in a proper way, it results in an estimate of the analog signal position (and the input event position respectively) on the time axis. This technology not only provides for excellent performance characteristics of event timers but it also leads to almost full replacement of the highly specialized hardware by typical DSP facilities, reducing the hardware realisation cost.

Specific methods for event timing based on this approach mainly differ in regard to the best practice of analog signals generation and to the matched algorithms for their digital processing. Our researches are focused mainly on solution of the problem: to achieve the best precision using a limited amount of the analog signal samples to increase the measurement rate. Specifically, recently developed method for such event timing provides picosecond measurement precision, using only four samples of the analog signal.

Relevant publications:

  • Yu. Artyukh, V. Bespal’ko, E. Boole. (2009) Potential of the DSP-based Method for Fast Precise Event Timing // Electronics and Electrical Engineering. – Kaunas: Technologija, 2009. – No. 4(92). – P. 19–22.
  • Yu.Artyukh. (2001) A method for continuous extreme precise time-interval measurement. Automatic Control and Computer Sciences, 2001, Vol.35, No.5, pp.11-18.
  • Yu. Artyukh. (2002) High-resolution Event Timing Based on Analog Signal Digitizing. Proceedings of the 8th Biennial Electronics Conference, October 6-9, 2002, Tallinn, Estonia, p. 237-238.
  • Yu. Artyukh, A. Ribakov, V. Vedin. (1998) A new Approach to High Performance Continuous Time Interval Counting. Proceedings of the XI Polish National Conference “Application of Microprocessors in Automatic Control and Measurements, October, 1998, Warsaw, Poland, p. 139-143.
  • Yu. Artyukh, A. Ribakov, V. Vedin.(1997) Modulation Domain Analyzer of the DASP-Lab System. Proceedings of the 1997 International Workshop on Sampling Theory and Application, June, 1997, Aveiro, Portugal, p.379-383.


High-performance event timer system design

There is a whole line of Riga event timers developed and made on the basis of DSP approach to high-precision event timing. Over many years application area for Riga event timers is focused mainly on Satellite Laser Ranging (SLR) where high performance of measurement equipment is especially needed. In this area IECS closely collaborates with “International Laser Ranging Service” (ILRS) [link to ILRS site] that coordinates operation of the global network of SLR stations and related institutions. Specifically, about 30 units of the recent Event Timer A032-ET and completed timing systems for SLR have been developed in years 2006-2008 on requests of the ILRS partners from various countries.
In line with development of our technology for event timing, we continuously are advancing the performance characteristics of Riga event timers. Specifically, the latest model A033-ET Riga event timer provides <4 ps single shot RMS resolution, combining it with the measurement at rate up to 25 MHz. This is twice as better that for the previous model A032-ET.
In addition to SLR, other possible applications of Riga timing instruments also are being studied. In particular, the time-of-flight spectrometry is currently studied as a primary subject of interest for such applications.

Relevant publications:

  • Yu.Artyukh, V.Bespal’ko, E.Boole. (2000) High Resolution Modular Time Interval Counter. Proceedings of the 12th International Workshop on Laser Ranging. Matera, Italy, 13-17 November 2000.
  • Yu. Artyukh, V. Bespal’ko, E. Boole. (2002) A new line of timing systems for Satellite Laser Ranging. Proceedings of the 8th Biennial Electronics Conference, October 6-9, 2002, Tallinn, Estonia, p.239-240.
  • V.Bespal’ko, E.Boole, V.Vedin. (2008) The model A032-ET of Riga event timers. Proceedings of the 15th International Workshop on Laser Ranging, Canberra, Australia, 2008, Vol.2, pp. 321-326.
  • Yu. Artyukh, V. Bespal’ko, E. Boole, K. Lapushka. (2002) A010 Family of Time Interval Counters adapted to SLR application. Proceedings of the 13th International Laser Ranging Workshop. Washington D.C. October 07-11, 2002.
  • Yu.Artyukh, V.Bespal’ko, K.Lapushka, A.Rybakov. (2008) Event timing system for Riga SLR station. Proceedings of the 15th International Laser Ranging Workshop, Canberra, Australia, Vol.2, pp. 306-310.


Methods for testing and specification of picosecond-precision event timers

At a time we are dealing with the problems of reliable testing of Riga event timers. The matter is that these timers provide extremely high precision, exact determining of which in commonly certified way is impossible or, at least, very difficult. For example, the common-used comparison method needs a reference instrument with much higher certified precision than that for the A032-ET. There are only a few such instruments in world and they are accessible only in exceptional cases. For this reason particular methods are being developed for reliable precision testing of Riga event timers in process of their prototyping and further manufacturing.  In view of that there are two basic problems for research. The first is to clearly define the timer’s errors, specification of which can be really useful for practical applications (such as single-shot resolution, differential linearity, interval linearity, offset drift etc). The second related problem is to develop the testing methods providing a reliable evaluation of these errors for any specific implementation of Riga event timers.
As for the testing methods, the main research task is to evaluate the precision parameters with sub-picosecond resolution and make that without applications of highly specialised test equipment. Mostly we are solving this task on the basis of statistical approach to the tests. In many respects the methods developed up to now confirm the mentioned requirements.


Relevant publications:

  • Yu.Artyukh, V.Bespal’ko, E.Boole. (2008) Non-linearity errors of high-precision event timing. Automatic Control and Computer Sciences, Vol. 42, No.4, pp.191-196.
  • Yu.Artyukh, V.Bespal’ko, E.Boole. (2006) Statistical approach to linearity evaluation of high-precision event timers. Electronics and Electrical Engineering, Kaunas: Technologija, No. 4(68), pp. 73-76.


Development and design of event timer systems

We offer our experience and accumulated engineering know-how in the area of event timing to resolve specific scientific tasks in this area and to create various customized application-specific event timer systems as well on the basis of long-term contracts. Designing of Event Timing System RTS-2006 represents an example of similar service. The RTS-2006 was made for Riga SLR station on special request and represents a multimode fully completed instrument for Satellite Laser Ranging (SLR) at 10 Hz repetition rate. The RTS-2006 can support millimetre accuracy of SLR, providing a good basis for improving the Riga SLR station performance. Note that, despite our best practice in SLR, other areas of applications for Riga timing systems are familiar for us as well.





We also offer our latest timing products such as high-performance event timers on the basis of short-term contracts (like usual purchasing). Currently we offer Event Timer A033-ET. Distinguishing feature of this instrument is extremely high precision combined with high measurement rate. In particular, single-shot RMS resolution better than 5 ps and measurement rate up to 25 MHz make the A033-ET one of a few best event timers currently available. Combining the A033-ET with application-specific software, a number of top-quality and reasonably priced event timer systems can be created.



Relevant publication:

  • Yu.Artyukh, E.Boole, V.Vedin. (2008) Instrumentation for creating KHz SLR timing systems. Proceedings of the 15th International Workshop on Laser Ranging, Canberra, Australia, 2008, Vol.2, pp.311-315.
  • Yu. Artyukh, V. Bespal'ko, K. Lapushka, A. Rybakov. (2008) Event Timing System for Riga SLR Station. Proceedings of the 15th International Workshop on Laser Ranging, Canberra, Australia, 2008, Vol.2, pp. 306-310.


Event Timer A033-ET

The Event Timer A033-ET is a computer-based instrument that measures time instants when input events (represented by NIM logic pulses) occur. Distinguishing feature of the A033-ET is extremely high precision combined with high measurement rate. In particular, single-shot RMS resolution better than 5 ps and measurement rate up to 25 MHz make the A033-ET one of a few best event timers currently available. Combining the A033-ET with application-specific software, a number of top-quality and reasonably priced event timer systems can be created. Especially the A033-ET is well suited for applications related to Satellite Laser Ranging.

Main features:

- Single-shot RMS resolution:    3.5 - 4 ps typically
- Dead time:    40 ns
- Maximum burst rate: up to 25M Event/s
- Maximum average rate: up to 30K Event/s


See more details in Data Sheet [link to PDF1] and Manual [link to PDF2].
The A033-ET is a custom instrument manufactured in a limited quantity and only on special request [link to PDF3]. Modifications of the A033-ET that provide certain special user’s requirements are possible on agreement basis. More info by e-mail:  artyukh@edi.lv



Image processing and pattern recognition

Research results in pattern recognition and development experience of digital image processing systems accumulated in IECS are used to re-establish this topic as one of the main research directions of the institute now. Recent activities were related with joint European project MODULINSPEX sponsored by the European Commission within the 6th Framework Programme.
Development of image processing algorithms and their implementation as software library is performed. The main application task considered is detection of foreign bodies in food. Development of algorithms is mainly oriented towards real time applications where images are obtained e.g. from the conveyor system and are to be processed in real time mode within rather limited time frame. Therefore simplest algorithms suitable for really fast operation are mainly considered.
The following algorithms are proposed to solve object detection problems in grayscale images:

  • Compensation of large background objects for the detection of smaller ones using median and morphological filtering
  • Image thresholding for separation of contaminant objects
  • Connectivity analysis of thresholded images
  • Finding objects of different size and shape in thresholded images by searching for structural elements
  • Calculation of statistical coefficients matched to characteristics of specific objects to be found
  • Object classification based on regression analysis


Illustration of image processing for finding small metal objects:

•    Initial image
•    Image after background compensation
•    Image of covariance coefficients calculated from fragments
•    Thresholded image indicating fragments with foreign objects


Proposed algorithms and their combinations solve several application tasks and provide the base for more sophisticated analysis of images in real time mode. Hardware solutions for object detection in grayscale images suitable for implementation using FPGA technology are patented.


Hyperspectral image processing

Hyperspectral images are processed for classification of objects on the basis of their spectral signatures obtained in multiple bands covering the visible light and near infrared regions. Research in this area is triggered by applications in forestry, e.g. discrimination of tree species in mixed Baltic forest, sponsored by Forest Owners Consulting Center (www.mikc.lv) and performed in collaboration with Institute for Environmental Solutions (www.videsinstituts.lv) and Latvian State Forest Research Institute "Silava" (www.silava.lv).

Classification results of tree species performed in pixel and tree crown level


Processing results of hyperspectral images are combined with LiDAR data obtained for the same region in order to ensure proper segmentation of tree crowns and build 3D intensity and height models of the forest.

LiDAR data over the hyperspectral image                           3D height model of the forest developed from

                                                                                                    LiDAR data


Research in this area is headed by Dr.sc.comp. Ints Mednieks ( mednieks@edi.lv ).

Relevant publications:

  • Latvian Patent No.13857. Digital X-ray image analyser for real-time detection of foreign bodies. Inventors: I.Mednieks, A.Skageris. Bulletin 2009/3.