Demetre, Correction SCS says..."On an average channel, PACTOR-III is around 3.5 times faster than PACTOR-II. On good channels, the effective throughput ratio between PACTOR-III and PACTOR-II can exceed 5. PACTOR-III achieves slightly higher robustness at the low SNR edge compared to PACTOR-II."
The URL to look at is http://www.scs-ptc.com/pactor.html and http://www.scs-ptc.com/download/PACTOR-III-Protocol.pdf Pactor III has several things going for it but also makes some considerations to be compatible with Pactor II and I that degrade the potential performance of Pactor III. Note in KN6KB's chart. The HF channel simulator used by KN6KB was the KC7WW Real-Time CCIR-520 Compliant HF Channel Simulator (http://www.johanforrer.net/simulr.htm). Simulated conditions includes several modes: pass through, flat fading, multipath For flat fading and multipath conditions, the Watterson model for simulating ionospheric effects is applied. This effectively simulates the compounded effects on several incident rays (typically two) due to influence of Earth's magnetic field, refraction in the ionosphere, and the dynamic motion of the ionosphere (Doppler). This results in the production of realistic amplitude fading and phasing effects with controlled statistical properties. Behavior of the model is controlled by user-supplied parameters for operating mode, fading rate, Doppler bandwidth. In addition, any level of Gaussian noise may be specified to achieve a particular signal to noise ratio (SNR). The figures in KN6KBs chart are an average of White Gaussian Noise, Multi-path Good (conditions), Multi-path (poor conditions) and Flat Fading. Again, note that above -5 dB SNR, the only difference that KN6KB shows is a change in throughput. The BER is not addressed. To achieve the higher thoughput of Pactor III, the number of tones (carriers/sub-carriers) is increased at the expense of a wider bandwidth...500 Hz for Pactor II and a maximum occupied bandwidth: 2.4 kHz @ -40 dB, audio passband: 400-2600 Hz (at Speed Level 6). SCS's use of Huffman and pseudo Markov coding (can be considered as double Huffman coding) is interesting and may be something that other coders may want to look at. Additionally the use of CCIR-CRC16 is nice. While ARQ is nice, it does have a transmission distance limit of 40,000 km. However for most, this is not a problem unless you are primarily going to use the mode for short haul NVIS operation...even at the 20,000 km ARQ setting. Perhaps the inclusion of a pilot tone(s) and tones with some other form fix modulation would have made the mode better. Also, IMHO the frame format is mode complicated that it needs to be. However, the adaptive qualities of the mode make it valuable. The use of DQPSK in speed levels 6, 5, 4 are questionable in that for QPSK modulation, you have a -3 dB loss...so the question is do you gain more using QPSK or not? Would have adding more DBPSK tones and a doppler tone proved better. And it goes without saying that using a real Viterbi decoder with soft decision provides a good coding gain. The features of Pactor III are the results of the cooperative and concerted efforts of several individuals who were not simply writing code to see what they could come up with. Rather they had a specific goal or set of speculations to work toward. The combination of cooperative effort and specific outcome goals has made Pactor III a very successful HF data transmission protocol. With the opensource soundcard protocols commonly referred to on this list, it is a shame that there is not more cooperative and collaborative coding efforts and a consensus of what outcome specifications hams are looking for in an HF data modem. 73, Walt/K5YFW -----Original Message----- From: digitalradio@yahoogroups.com [mailto:[EMAIL PROTECTED] Behalf Of Demetre SV1UY Sent: Thursday, January 11, 2007 10:44 AM To: digitalradio@yahoogroups.com Subject: [digitalradio] Re: Pactor versus Olivia --- In digitalradio@yahoogroups.com, "DuBose Walt Civ AETC CONS/LGCA" <[EMAIL PROTECTED]> wrote: > > Again, may I inject my 2 cents worth. > > SCS says that Pactor III is 4 times faster than Pactor II and the code would indicate such. Thus the raw channel throughput IS faster and the BER should be better. But as far as performance goes at varying SNRs will make a difference in throughput. > > At a -5 dB SNR on the KC7WW channel simulator KN6KB measured the throughput of Pactor I/II/II as about the same. At a + 10 dB SNR, the maximum throughput of Pactor I was measured as ~ 100 NetBytes/minute. Pactor II measures as ~3000 NetBytes/minute and Pactor III measures as ~11,000 NetBytes/minute....almost 4 times that of Pactor II. > > 73, > > Walt/K5YFW Hi Walt, Thanks for reply. As I understand it if I need the speed it is a very good idea to upgrade to PACTOR III. I have PACTOR I and II at the moment and I am very happy with it. If the measurements are also true in real conditions too, then perhaps it is a good idea to upgrade to PACTOR III since when conditions are good the 4 times increase is great and one would hold an HF channel busy for shorter periods. 73 de Demetre SV1UY
