Hi Andy. Let's say one works with Olivia 1000/32. Olivia sends/receives 7bit ASCII letters. Each 7 bit letter is coded by Walch-Hadamard transformation into 2^(7-1)=64 bits. One of 32 tones modulation codes 32=2^5 combinations, which equals to 5 binary bits. Olivia is spreading 5 7bit letters over 64 MFSK32 tones. It takes 64/31.25=2.048 seconds to transmit one block of 5 letters. I hope this explains why the received letters appear in groups of five and why there is a considerable lag, which cannot be lower than 2 seconds for any decoder.
Olivia receiver searches for the Walch-Hadamard coded blocks in time and space. Pawel Jalocha's code is running matrix of decoders spaced by one half of Olivia tone spacing in frequency and one half of tone spacing in time. He is calculating signal level (or quality, correlation or whatever one wants to name it) of each of the decoder in the matrix to check, whether and/or where a valid Olivia block was received. I believe the difference between Patrick's MultiPSK and Pawel's original Olivia code is in the way how the sync time is adjusted after the initial sync is reached. Partick's code locks in time and only slightly adjusts the sync time to cope with differences in RX/TX sound card clock callibration the same way his or any other MFSK16 decoder works. Pawel's code is always looking up one half of block time after the expected sync time. While Pawel's strategy is good for initial synchronization and for decoding very weak signal, additionaly introduced 1 second lag in case of Olivia1000/32 is annoying. I believe Pawel's code may be improved to decrease time lag in case the decoder is already locked to a strong signal. Also if a strong correlation is detected, one does not need to wait another 1 second for even stronger signal, because this is highly improbable. I believe Patrick's MFSK is doing both. Also if the signal is very strong, then one may break into a middle of a block and the block will be detected correctly with the prerequisity that the decoder will be flushed at the time one changes frequency either on waterfall or by tuning knob. I don't think any Olivia decoder is flushed at tuning change. It sounds like a challenge for my PocketDigi code, but don't tell my wife I have a new project :-) 73, Vojtech OK1IAK --- In digitalradio@yahoogroups.com, "Andrew O'Brien" <[EMAIL PROTECTED]> wrote: > > Folks, when Simon was first adding Olivia to DM780 he studied Pawel > Jalocha's coding and consulted with him about the correct implementation. > The lag noticed in DM780 is reportedly as the Pawel Jalocha intended. What > I am looking for is people to get on the air with Olivia and see if the > applications that may have less lag , have any noticeable decoding > degradation. Since I know Olivia in MixW and Multipsk work well, I am > wondering if the "proper" implimentation of Olivia in DM780 is worth the > delay and issues this causes during a QSO (those not knowing about the lag > think we are not coming back to them and start a transmission again ) > > Andy > > On Thu, Nov 20, 2008 at 3:18 AM, Simon Brown (KNS) <[EMAIL PROTECTED]>wrote: > > > The lag is in the software - it's part of the design for the error > > correction. Where error correction is part of the design then *in general* > > with Ham modes you have to wait a while before text is decoding is the > > error > > correction is applied. The lag is not caused by CPU load. > > > > To really understand this it's best to analyse the Olivia design although > > this can be rough for the brain :-) > > > > > > Simon Brown, HB9DRV > > www.ham-radio-deluxe.com > > > > ----- Original Message ----- > > From: "captcurt2000" <[EMAIL PROTECTED] <captcurt%40flash.net>> > > > > > Sooo. a 500Mhhz machine running at 20% is going to perform the > > > integrations and decoding same delay as a 2 Ghz machine running at 20%?? > > > > > > That seems counter intuitive to me.. > > > > > > I'm sure you're right but I don't understand how that can be. > > > > > > I thought the load information talked about resources not speed of > > > execution. > > > > > > Help me understand.. > > > > > > > > > > -- > Andy K3UK >
