Rick et. al., The commercial HF folks already have higher throughput data modes...close to 9600 bps user throughput (now RAW throughput) but the signal is 6-8 KHz wide and they give this throughput at 0 to -5 dB SNRs.
Thus far DV hasn't made such progress but Thompson CSF and their New Generation HF Modem (http://www.argreenhouse.com/society/TacCom/papers98/11_04i.pdf#search=%22NEW%20STUDIES%20ABOUT%20A%20HIGH%20DATA%20RATE%20HF%20PARALLEL%20MODEM%22)may improve data and DV capability.* I would assume that Thales is looking at Thompson's work. * User Available Data Rate Modulation and Coding Symbol Rate 9600 bps Turbo Code QAM 64 3/4 2133 baud 4800 bps Turbo Code QAM 16 3/5 2000 baud 2400 bps Turbo Code QPSK 3/5 2000 baud There is a great difference in real time voice and data but what is the definition of real time voice? Can we wait 5-10 seconds between the time the sender stops and we start receiving? We can't even wait for the curtsey tone on repeaters...how can we wait for a DV epoch to demodulate? When I speak of an HF signal, I always assume a poor CCIR signal with much fading, etc. The best HF SSB signal is still a poor POTS signal. Things to do...push until we start seeing the Shannon Limit. Start "training" our transmissions/packets/data. Define/determine the best receive filter(s). Determine which modulation technique is best (this research may have already been done.) Push bandwidth. test and retest the signal coding and interleaving. Determine the balance between the amount of FEC to be used vs. ARQ. Determine if broadcast and messages modes are needed and if different are needed, what parts of the code are reusable/common. The same for DV. Can we reuse the code for V/UHF communications? Define a standard test simulation model, i.e. the KC7WW channel simulator or Moe Wheatly's channel simulator. Set a standard test text and test binary. I believe that when we get DV with the quality as good or better than the current AOR DV and operating at a 0 or less SNR, we will replace current analog SSB. I also believe that this will not be done until we start seeing more SDR hardware on the market. I have but a little time left to see all this come to true...I hope I do get to see it. 73, Walt/K5YFW -----Original Message----- From: digitalradio@yahoogroups.com [mailto:[EMAIL PROTECTED] Sent: Wednesday, October 11, 2006 3:54 PM To: digitalradio@yahoogroups.com Subject: Re: [digitalradio] Re: Digital Voice: Some thoughts after one week. The one common theme I see with much of the digital modes that require the higher level of speed is that the required minimum S/N ratio hovers around 10 db S/N. It seems to be true with DV voice, with SCAMP, and also with high baud rate modes (such as trying to exceed a few hundred baud on HF). To me there is a dividing line between real time voice and high speed digital texting vs. slower modes that get through under difficult conditions. Actually, difficult conditions tend to be more of the norm on HF. Does anyone have any "inside" information that would suggest that we will be able to lower the required S/N ratios for a given speed or are we already too close to the Shannon Limit as it is? If we can not do this, I don't see how any of the higher speed digital modes will ever be able to replace analog communications for weak signal and general amateur radio communications with modest power levels and modest antennas. In other words, what most of us do most of the time. Of course this would not be true for VHF and up, only for the restricted BW's of HF. 73, Rick, KV9U DuBose Walt Civ AETC CONS/LGCA wrote: >Ed, > >Back in the fall of 1989, we started using a unit called the TacTerm for DV. >The best modem was a 39 parallel tone modem (Mil-Std-188-110?) and 2400 BPS. >On HF it sounded funny...robotic like...and while it did work on about the >same SNR as a ~S3 SSB signal ...the SNR had to be about 10 dB, it worked much >better on VHF and UHF FM as well as UHF AM. > >In Jan-Feb 1990, after Operation Just Cause, I got to play with a Harris >Mil-Std-188-110? modem and DV at 2400 BPS AND 4800 BPS. The 2400 bps DV still >sounded a bit robotic but worked quite well at S2-S3 signals and even when the >SNR was at or I think slightly below 10 dB. The modem had ALE and provided a >SNR figure and my old ham radio ear figured an S2-3 signal. > >When we switched to 4800 bps, the DV sounded just like the individual speaking >over a telephone...better than SSB voice but it required a slightly better SNR. > >Data with the TacTerm 39 tone modem was really good...text came through at >about a page a minute with a signal that you could hear. When the signal got >down close to the noise...where you had to strain to hear it, the throughput >went down to maybe 20-30 lines per minute....but still near 100% copy (could >have been typing errors). The actual computer software was KA9Q NOS running >on a BIG military laptop computer. > >When we went to the Harris modem and 2400 BPS/4800 BPS, the copy at 2400 BPS >was about the same with a good signal but better than the TacTerm with lower >qualitity signals. > >4800 bps screemed unless the signal got below 10 dB SNR or so. > >During Operations Desert Shield and Desert Storm, the U.S. Marine Corp used a >Hughes RT-1209 and Harris AM-6545A 400 watt amplifier to make up the GRC-193A >(http://www.nj7p.org/millist/pic/grc-193.gif) used in some of the last >productions Jeeps and Humvees. Most were using a 15-16 ft fold over whip. >The whip went up just about 18" higher then the Humvee top and then tilted >over and ran horizontal the remainder of the length. This provided a good >NVIS antenna radiation pattern. > >The Marine Corp did connect the Harris MIL-STD-188-110x modem to the GRC-193 >and used a computer to send data from the field back to their command center. > >For digital voice I believe that some units used the Navy's version of the >TacTerm and some may have been using the later ITT MinTerm DV unit. The >TacTerm (KY-57) can accept signal fades of up to 12 seconds without losing >synchronization with the transmitting station. > >I never noticed any delays or words that were not understandable using the >TacTerm or MinTerm or Harris Modem using LCP-10 and UG-??? encryption unit. >There were of course a second or two between transmissions, but certainly not >enough to prevent artillary spotting or fire control. > >The PRC-109/GRC-193 systems were used at least in 1985 and perhaps before with >the TacTerm. The TacTerm was used in the Viet Nam war on HF SSB, VHF and UHF >AM and as far as I know without problems. The C-130s tracking and Navy vessel >captured by North Korea used Tacterm's on HF and the crew of the C-130 never >mentioned to me that there were communications using the TecTerm. > >So when the Marine Corp have problems with DV must have been shortly after the >capture of the USS Pubelo which I believe was in 1968. > >A good reference on the ANDVT modem may be _HF modem evaluations for the >Advanced Narrowband Digital Voice Terminal (ANDVT)_ by Chase, D.; Bello, P. >A.; Boardman, C.; Pickering, L.; Pinto, R. published in Nov 1978 > >Abstract: >"During this program, the specifications for the ANDVT HF modem have been >refined and detailed evaluation and simulation of the new technical features >within this modem have been conducted. These include a multiple-tone signal >detection format with an adaptive threshold, a multiple-tone/multiple-stage >Doppler estimation algorithm, a matched filter frame estimation algorithm >utilizing PN correlation properties, a low-rate error-correction coding >approach for protection of the KG sync sequences, an error-correction coding >approach specifically designed to protect the critical speech parameters, use >of soft-decision (channel measurement) information obtained from the >demodulator, and decision-directed Doppler tracking utilizing information from >all data tones. The analytical and simulation results provide the desirable >result that the preamble can be successfully received at a lower SNR than is >required for the reception of high-quality 2400-b/s digitized voice." > >Walt/K5YFW > > > Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) Yahoo! Groups Links Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/digitalradio/ <*> Your email settings: Individual Email | Traditional <*> To change settings online go to: http://groups.yahoo.com/group/digitalradio/join (Yahoo! ID required) <*> To change settings via email: mailto:[EMAIL PROTECTED] mailto:[EMAIL PROTECTED] <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
