time-frequency and spatial processing
error correcting coding
blind signal processing
This article is about ways to build HF-band high speed data transfer systems. Traditionally two ways of building these systems are used: consequent and parallel. Each of them uses various ways to address intersymbol interference which appears due to multiple beams. Each approach has its ipsides and downsides.
Nowadays consequent and parallel data transfer systems (DTS) show close speeds. In fact they reached the limit of increasing speed by repetition factor.
Further increase of speed is possible by building a system with multiple inputs and outputs (MIMO). Theoretically with MIMO one can achieve increase of data transfer speed by a factor equal to the number of antennas. That is achieved by using iterative decoding algorithms. However to work with this system one needs to know exact complex transfer coefficient for each subchannel. Some resources are used to estimate these. Besides subchannels should be uncorrelated which is hard in HF-band.
Employees of Samara NIIR branch suggested method of forming separate subchannels to use MIMO by using phased antenna array. Separate subchannels are formed by forming radiation patterns having maximum at the same azimuth but different elevation. Besides in order to form extra subchannels polarization processing is used.