High data rate HF communication system

Dynamic variations in ionospheric channels result in fading, dispersion, Doppler, multipath and other effects, limiting the performances of a communication system. The HF band is also highly congested and it is difficult to obtain a relatively clear channel with large bandwidth. International regulations also restrict the channels to 3 kHz slots. Even if a wide bandwidth channel were available, the ionospheric distortions would not be uniform over the large bandwidth, making adaptive equalization and other improved techniques difficult to implement. A fully adaptive high data rate (64 kbps) communication system is being developed using multiple 3 kHz slots operating in parallel. The adaptation of the choice of frequencies as well as the communication parameters is performed dynamically. A novel equalizer has also been implemented. The equalizer allows superior performance in combating multipath. The weights for the equalizer taps also provide information about channel parameters. The DSP based software modem is being built as a basic building block for each slot. This software modem allows various adaptations of bit-rate, coding, modulation, frame size, interleaver depth, power control, etc. It is believed that this versatile software modem will find immediate use in various applications