Hi Simon, Good questions. It's nice to see someone actually looking at the spec :)
Q1: The DD (Digital Data or Data-Only) mode, is specified in the header, as you noted. This mode is currently only implemented at 128kbps on 23cm in the Icom ID-1. The payload of the D-STAR DD frame is an Ethernet Packet. If you were to take two ID-1 radios and plug Ethernet cables into them they form an over the air, half duplex, Ethernet bridge. There are no additional optimizations beyond this on DD. As a side note, at least one experimenter has sent DD frames over the 6.25 kHz 4800 baud GMSK "channel" on VHF or UHF, but commercial radios do not support this nor are they adversely affected by the signal based on reports from the experimenter. Q2: On DV (Digital Voice mode) The voice component is compressed and encoded down to 2400 bps and supplemented with a 1200 bps FEC, the remaining 1200 bps of the 4800 bps (6.25 kHz wide GMSK) data stream is available for auxiliary "data" and used to convey certain manufacturer (Icom) enhancements, GPS strings, and raw "short message" data with no error detection or correction in the protocol. Some applications such at D-RATS (http://www.d-rats.com) add these features at the application level. On May 13, 2009, at 9:19 AM, mungewell wrote: > > > Hi, > I'm relatively new to the HAM scene and have been getting > increasingly interested in D-Star (although don't have any D-Star > capable equipment). > > In the protocol spec I see that there is a flag (Flag 1:bit 7) which > denotes data-only or voice+data modes, but otherwise information is > a bit sparse on the data side. > > Q1. In the case of the data-only mode, is the data packed into 96 > byte (72+24) frames and sent across the link until complete? > > I do note that every xx frames is a required to be a sync frame to > ensure receiver lock. > > Q2. Is there any encoding scheme (not the scrambling/line coding) to > compress the data to make better use of airwaves and provide FEC? > > By this I mean a scheme where x byte of ASCII (binary, C40, etc) can > be compressed into <x bytes in order to shorten transmission time. > > Cheers, > Simon > VA6SDW > > > John Hays Amateur Radio: K7VE [email protected] [Non-text portions of this message have been removed]
