Polarization diversity for HF data transmission

There has been considerable effort devoted to increasing data rates over 3 kHz HF channels. The two most commonly employed serial-tone waveform standards, Mil-Std 188-110A and STANAG 4285, provide user data rates of 2400 bps after coding. Both permit data rates greater than this, but without forward error correction they have only limited utility in the difficult HF environment. Data rates approaching 9600 bps may be feasible on HF channels with good signal-to-noise ratios (SNR). However, in order to support these data rates on long-haul circuits, some means more effective than those currently employed must be found for dealing with the fading which is experienced on these circuits. In Serinken et al. (1996), the advantages of using polarization diversity on a sky-wave link between St. John's, Newfoundland and Ottawa, Ontario were demonstrated not only for diversity reception, but also for the case where diversity is employed in the transmission. Receive diversity was accomplished by introducing a combiner prior to the modem, a less-than-ideal approach for a fading frequency-dispersive channel. This paper represents a continuation of the work in Serinken et al. using a modem developed at the Communications Research Centre (CRC) which treats diversity combining and equalization as a joint optimization problem. In this work, the emphasis has been placed on using polarization diversity to achieve high data rates over a long-haul HF link.