The Resampling Methods Direct Sequence Spread Spectrum Signal’s Demodulator Implementation

Relevance. The direct spread spectrum signals are widely used in navigation and communication systems recently. These signals prevail in modern satellite navigation systems and are used in various communication systems with code division multiplexing in particularly. In this regard, the tasks of building direct spread spectrum signals’ demodulators have the key importance. Mach importance in the construction of demodulators is the problem chip rate variability.

The purpose of the study is to propose a demodulator structure focused on solving this problem.

Methods. The research is based on computer modeling methods.

Decision. The paper proposes an approach to the construction of the direct spread spectrum signal’s demodulators based on modern methods of digital signal processing. It is shown that the main advantage of the proposed approach is the possibility of rebuilding the variable chip rate demodulators. Based on the results obtained, a scheme for the direct spread spectrum signals demodulator using resampling methods is proposed. Resampling, in turn, is implemented on the basis of polynomial interpolation using Lagrange polynomials. The structure of the resampler is proposed, similar to the structure of an interpolating filter with a finite impulse response. The presented simulation results show the effectiveness of the proposed approach.

Novelty. It seems that the currently common methods of implementing direct spread spectrum signal in terms of delay synchronization do not sufficiently meet modern requirements. The implementation of delay synchronization schemes based on resampling is practically not discussed in well-known works. At the same time, modern methods and devices of digital signal processing make it possible to ensure an effective hardware implementation of the scheme in question. In this context, the approach proposed in the paper to the construction of demodulators seems to be very relevant.

Significance. The results of the work can be used in the construction with direct spread spectrum signals’ demodulators for a wide range of communication and navigation systems. The synchronous sampling structure proposed in this paper is very promising, especially for variable chip rate demodulators.

1. Gardner F.M. Interpolation in digital modems. Part I: Fundamentals. IEEE Transactions on Communications. 1993;41(3): 501‒507. DOI:10.1109/26.221081

2. Erup L., Gardner F.M., Harris R.A. Interpolation in digital modems. Part II: Implementation and performance. IEEE Transactions on Communications. 1993;41(6):998‒1008. DOI:10.1109/26.231921

3. GLONASS. Principles of Construction and Functioning. Edited by A.I. Perov, V.N. Kharisov. Moscow: Radiotekhnika Publ.; 2010. 800 p. (in Russ.)

4. Kinkulkin I.E. Global Navigation Satellite Systems. Functioning Algorithms of Consumer Equipment. Moscow: Editoriia URSS Publ.; 2018. 325 p. (in Russ.)

5. Rec. ITU-R TF.1153-4. The operation use of two-way satellite time and frequency transfer employing pseudorandom noise code. August 2015.

6. Gardner F.M. Phaselock Techniques. John Wiley & Sons; 2005. 450 p.

7. Mengali U., D’Andrea A.N. Synchronization Technique for Digital Receivers. New York: Plenum Press; 1997.

8. Meyer H., Moeneclaey M., Fechtel S.A.H. Digital Communication Receivers. New York: John Wiley & Sons; 1998

9. Farrow C.W. A continuously variable digital delay element. Proceedings of the IEEE International Symposium on Circuits and Systems, 7‒9 June 1988, Espoo, Finland. IEEE; 1988. p.2641‒2645. DOI:10.1109/ISCAS.1988.15483

10. Hogenauer E. An economical class of digital filters for decimation and interpolation. IEEE Transactions on Acoustics, Speech, and Signal Processing. 1981;29(2):155‒162. DOI:10.1109/TASSP.1981.1163535

11. Brusin E. Implementation Direct Spread Spectrum Signals Demodulator Acquisition Using Automatic Frequency Control. Proceedings of the XIIIth International Conference on Infotelecommunications in Science and Education, 27‒28 February 2024, St. Petersburg, Russian Federation. St. Petersburg: The Bonch-Bruevich Saint-Petersburg State University of Telecommunications Publ.; 2024. p.504‒509. (in Russ.) EDN:ZGFNZS

12.