Methods for Spatiotemporal Signal Coding in Non‑Stationary Frequency‑Selective MIMO‑OFDM Channels

The article investigates methods of spatio‑temporal encoding of signals in MIMO-OFDM systems during transmission in non‑stationary frequency‑selective channels. The limitations of traditional approaches (STBC, SFBC) at high levels of Doppler shift and frequency selection are considered. The relevance of the study is due to the need to increase the spectral efficiency and stability of wireless communication systems to intersymbol interference and Doppler distortion.

Methods used. The article proposes the structure of a combined spatial encoding algorithm WHSTBC‑CC based on combined suppression and Walsh‑Hadamard transformation. Mathematical models of transmitting and receiving signals are constructed, taking into account the influence of channel distortions and additive white Gaussian noise. To analyze the effectiveness, modeling methods were applied taking into account the normalized values of the Doppler shift and the coefficients of time and frequency correlation.

Results. It is shown that the use of WHSTBC‑CC provides an increase in transmission stability and a reduction in the probability of errors at fdT < 0.01. The energy gain coefficient of the method is 5-12 dB compared with the classical STBC and is practically independent of the frequency abundance of the channel. The modification of spatial coding developed in the work using the Walsh-Hadamard transform and the conjugate suppression algorithm partially compensates for these disadvantages, increasing the stability of the system and providing an energy gain of up to 12 dB compared with the classical STBC. Experimental measurements on a mobile SDR platform have confirmed the operability of the proposed approach in a real radio environment, including scenarios with and without direct visibility.

The novelty of the work lies in the development of an adaptive spatial coding algorithm that integrates various schemes (STBC, SFBC) depending on the channel parameters.

Practical significance. The results obtained can be used in the design and optimization of MIMO‑OFDM systems for mobile communications and broadband access networks, as well as in specialized radio networks operating in conditions of high instability and exposure to electronic jamming.

1. Nizamaldeen S.A., Al-Qaradaghi T.M. A comparison between STBC-OFDM and SFBC-OFDM. International Journal of Arts and Sciences. 2014;6(5):157–166.

2. Hanzo L., Akhtman J., Wang L. MIMO-OFDM for LTE, WiFi and WiMAX: Coherent versus Non-coherent and Cooperative Turbo Transceivers. IEEE; 2011.

3. Yeh H.G. Architectures for MIMO-OFDM System in Frequency Selective Mobile Fading Channels. IEEE Transactions on Circuits and Systems II: Express Briefs. 2015;62(12):1189–1193. DOI:10.1109/TCSII.2015.2498300

4. Al-Dweik A., Kalbat F., Muhaidat S. Filio O., Ali S.M. Robust MIMO-OFDM System for Frequency Selective Mobile Wireless Channels. IEEE Transactions on Vehicular Technology. 2014;64(5):1739‒1749. DOI:10.1109/TVT.2014.2340736

5. Medina C.A., Sampaio-Neto R. Frequency domain equalization space-time block-coded CDMA transmission system. Journal on Wireless Communications and Networking. 2011;2011:80. DOI:10.1186/1687-1499-2011-80

6. Solodovnyk V.I., Naumenko N.I. Space-Frequency Block Coding with Two-Mode Index Modulation OFDM and Increased Stability to Channel Frequency Selectivity. Radioelectronics and Communications Systems. 2020;63(4):186‒200. DOI:10.20535/s0021347020040020. EDN:SWLRPQ

7. Youssefi M., Bounouader N., Guennoun Z., El Abbadi J. Adaptive Switching between Space-Time and Space-Frequency Block Coded OFDM Systems in Rayleigh Fading Channel. International Journal of Communications, Network and System Sciences. 2013;6(6):318‒320. DOI:10.4236/ijcns.2013.66034

8. Kumar R.R., Indumathi P., Pandian R., Jacob T.P., Pravin A., Prasad K.M. Adaptive modulation and coding in a changing wireless environment. AIP Conference Proceedings. 2024;2850(1):030011. DOI:10.1063/5.0208281

9. Lee N., Kang J., Lee N., Kang J. Adaptive switching between space-time and space-frequency block coded OFDM Systems. Proceedings of the Military Communications Conference, 16‒19 November 2008, San Diego, USA. IEEE; 2008. DOI:10.1109/MILCOM.2008.4753221

10. Azza M.A., El Yahyaoui M., El Moussati A. Adaptive Modulation and Coding for the IEEE 802.15.3c High Speed Interface Physical Layer Mode. Proceedings of the Mediterranean Conference on Information & Communication Technologies, MedCT 2015, 7‒9 May 2015, Saïdia, Morocco. Lecture Notes in Electrical Engineering, vol.380. Cham: Springer; 2016. p.365–371. DOI:10.1007/978-3-319-30301-7_38

11. Kyritsi P., Chizhik D. Capacity of multiple antenna systems in free space and above perfect ground. IEEE Communications Letters. 2002;6(8):325–327. DOI:10.1109/LCOMM.2002.802049

12. Tikhvinsky V.O., Volodina E.E. Mobile communications of the third generation. Economics and quality of services. Moscow: Radio and Communications Publ., 2005. p.240. (in Russ.)

13. Balabanov I.V., Sidorin V.V. Ensuring the availability of services in mobile communication networks. Internet-zhurnal naukovedenie. 2014; 2(21):95. EDN:SJFMHD