An on-air evaluation of ALE for high speed data traffic

A trial of HF radio automatic link establishment (ALE) used in conjunction with 2400 bits/s MIL-STD-188-110A modems was conducted between Melbourne and Adelaide (650 kms) during August 1993. The results showed that the ALE technique was successful in automatically finding a propagating channel, establishing a link and passing data. In this regard it is shown that it clearly provided better links than would have been achievable from ionospheric prediction information alone. ALE´s success rate in selecting the best channel for the transmission of data, however, was not as high as expected at 64% for the single-tone modem, and 80% for the 39-tone data waveform when used with minimum interleaving. This was found to be attributable to the relatively poor correlation of the received BERs with the ALE link quality assessment (LQA) scores and demonstrates that this metric is not optimised for the two modem types examined. It was noted that the single-tone modem bit error rate (BER) was found to be superior to that of the 39-tone parallel modem at 2400 bits/s in all but a few incidences