The presence of the O and X modes in the HF skywave propagation has previously been investigated experimentally for their role in providing polarization diversity and improving channel capacity when a MIMO structure is employed. A mathematical treatment of MIMO channel modelling and capacity improvement has also been reported but limited to NVIS links only. This paper reports the mathematical derivation of the HF 2×2 polarized MIMO channels when cross-dipoles, i.e., a pair of orthogonally polarized horizontally-oriented dipoles, are used at both ends to examine the cross-polarization property and the capacity improvement factor (CIF), with the transmitter-receiver range being near enough to allow single-hop paths only but also distant enough to make the trajectory oblique. Results on the cross-polarization property suggest that the power contributions of the waves from the two transmitters that arrive at each receiver are equal. In addition, the signal from any one of the transmitters is received by the two receivers with unbalanced powers that depend on the phase shift difference between the O and X paths. It is also observed that on average the MIMO channels with oblique paths have lower capacity than the NVIS MIMO channels due to the reduced orthogonality between polarizations of antennas in the dual-antenna system at each end. The above hypotheses are confirmed through ray-tracing simulation and field measurement over a 575 km HF radio link.
1. Athukorala, C. P. and B. P. Resosudarmo, "The Indian Ocean tsunami: Economic impact, disaster management, and lessons," Asian Economic Papers, Vol. 4, No. 1, 1-39, 2005. doi:10.1162/asep.2005.4.1.1
2. Lu, B. W., "A unified theory of ionospheric propagation of short radio waves with special emphasis on long-distance propagation," Progress In Electromagnetics Research, Vol. 13, 87-114, 1996.
3. ITU-R Rec. F.1761, Characteristics of HF Fixed Radiocommunication Systems, Intern. Telecomm. Union, Radio Sector, Geneva, Switzerland, 2006.
4. Molisch, A. F., M. Z. Win, Y. Choi, and J. H. Winters, "Capacity of MIMO systems with antenna selection," IEEE Transactions on Wireless Communications, Vol. 4, No. 4, 2005. doi:10.1109/TWC.2005.850307
5. Shafi, M., M. Zhang, A. L. Moustakas, P. J. Smith, A. F. Molisch, F. Tufvesson, and S. H. Simon, "Polarized MIMO channels in 3-D: Models, measurements and mutual information," IEEE Journal on Sel. Areas in Comm., Vol. 24, No. 3, 514-527, 2006. doi:10.1109/JSAC.2005.862398
6. Strangeways, H. J., "Estimation of signal correlation at spaced antennas for multi-moded ionospherically re°ected signals and its e®ect on the capacity of SIMO and MIMO HF links," IRST, 306-310, London, UK, 2006.
7. Ndao, P. M., Y. Erhel, D. Lemur, and J. Le Masson, "Design of a high-frequency (330 MHz) multiple-input multiple-output system resorting to polarisation diversity," IET Microwave Antennas Propag., Vol. 5, No. 11, 1310-1318, 2012. doi:10.1049/iet-map.2010.0165
8. Abbasi, N., "Capacity estimation of HF-MIMO systems," IET Microwave Antennas Propag., 11th International Conference of Ionospheric Radio Systems and Techniques, IRST, Edinburgh, 2009.
9. Witvliet, B. A., "The importance of circular polarization for diversity reception and MIMO in NVIS propagation," IET Microwave Antennas Propag., EuCAP, The Hague, The Netherlands, 2014.
10. Erhel, Y., D. Lemur, M. Oger, J. Le Masson, and F. Marie, "Evaluation of ionospheric HF MIMO channels: Two complementary circular polarizations reduce correlation," IEEE Antennas and Propagation Magazine, Vol. 58, No. 6, 38-48, 2016. doi:10.1109/MAP.2016.2609799
11. Gunashekar, S. D., E. M. Warrington, S. M. Feeney, S. Salous, and N. M. Abbasi, "MIMO communications within the HF band using compact antenna array," Radio Science, Vol. 45, No. RS603, 1-16, 2010.
12. Witvliet, B. A. and R. M. Alsina-Pages, "Radio communication via near vertical incidence skywave propagation: An overview," Telecommunication Systems, Vol. 66, No. 2, 295-309, 2017. doi:10.1007/s11235-017-0287-2
13. Ndao, P. M., Y. Erhel, D. Lemur, M. Oger, and J. Le Masson, "Development and test of a trans-horizon communication system based on a MIMO architecture," EURASIP Journal on Wireless Communications and Networking, Vol. 2013, No. 167, 2013.
14. Enserink, S., C. Kse, M. Fitz, M. Urie, and R. McCourt, "A model for dual polarized HF MIMO communications," IEEE Military Communications Conference, Tampa, FL, USA, Oct. 26-28, 2015.
15. Balanis, C. A., Antenna Theory Analysis and Design, John Wiley and Sons, New York, USA, 2005.
16. Manalu, S. L., G. Hendrantoro, and A. Mauludiyanto, "Design of measurement system for HF MIMO NVIS channel," 4th IEEE Int. Conf. on Infor. Technol., Comp., and Elect. Eng., Semarang, Indonesia, 2017.