Ivor's interest in this, if I understand correctly, is that it simplifies the analogue electronics and processing. Since one needs the FH capability in any case for the main message, why not use it also for the detection preamble?
Dale's motivation is from the signal processing perspective, that an orthogonal set of FH chips can be used without a guard time with superior detection and estimation performance, if properly handled.
Our original concern was that the Doppler performance of the FH sequence seemed inferior to that of the HFM, but this now seems like an artifact of our coherent detector processing, rather than a fundamental signal processing constraint. Indeed, from an information theory point of view, there should be nothing that can be done with a 4 or 6-chip HFM that cannot be done better with a 32-chip FH sequence.
Paul vanWalree is working with us to make comparative transmissions on our semi-permanent modem farm in which we will be using two different channel probe signals, bracketing both ver 0.3 and 1.0 JANUS signals and two types of DSSS signals with similar bandwidth and baud rates for comparison.
It is our intention to provide detector implementation examples in the ver 1.0 release that will transparently handle either the ver 1.0 standard or the older ver 0.3 for legacy purposes.