Hi ALex well ETSI can say what they like, but unless the system is long delay multipath tolerant, it will be a poor performer with respect to analog if a hill gets in the way with another hill behind it...
This is not a rayleigh flat fading scenario, this is a frequency selective fast fading scenario. I see it in all the narrowband digital systems, P25, DMR, Tetra. It is VERY difficult to fix with an equaliser in a narrow band environment . If the multipath was stationary, then it is fixable, but in a mobile environment, the results are poor unless there is alot of overhead. The only real fix is slowing down the symbol rate. The 700 sps I think is slow enough, anything more than 2000 sps is trouble So, if you want to go faster than say 2000 sps, use of OFDM ! lots of low symbol rate carriers... as for doppler shift, well that depends on the frequency, speed etc sure. cheers glen. On 18/09/2017 7:00 PM, Adrian Musceac wrote: > Hi, > > Helmut, for me RTL-SDR support is required. I will not be testing with > another SDR hardware for reception as my application is meant to work > with the USB stick (small dynamic range or not). > > Glen, have a look at > http://www.etsi.org/deliver/etsi_etr/300_399/30001/01_60/etr_30001e01p.pdf > specifically section 6.2.2 and below. Faces exactly the same issues. > FM is also affected by fast Rayleigh fading.. > Anyway, Doppler shift will be a bigger issue than multipath. > > Cheers, > Adrian > > > On 9/18/17, glen english <g...@cortexrf.com.au> wrote: >> HI Adrian >> >> good stuff! >> >> OK, now try the analog versus the digital, with a copy of the TX signal >> at 30uS delay and -10dB with respect to the wanted signal.... (a common >> multipath ) , and also 30uS delay and 0dB. >> >> Let me know... >> >> >> On 15/09/2017 9:10 PM, Adrian Musceac wrote: >>> Hi, >>> >>> I present a three way comparison between narrow band FM (5 kHz), QPSK >>> Codec2 1300 (2.4 kHz) and QPSK Opus 19 kbit/s (16 kHz): >>> >>> https://www.youtube.com/watch?v=vApRe6R1gnk >>> >>> The comparison is taking place in the ISM band of 433 MHz with >>> interference present from some temperature sensors in an adjacent >>> channel. >>> >>> Conditions: same antenna locations, same RX chain gain, varying >>> transmit gain (LCD like number on the top left of the screen) >>> >>> Results: both digital modes cope better with interference and are more >>> intelligible than FM. The numbers on top left of RX application are >>> expressed in dB of amplification in the SDR transmitter chain. >>> >>> Hardware: for transmit one USRP B200 with 433 MHz filter installed, >>> for RX one RTL-SDR filter with 433 filter installed. >>> Software: QRadioLink running on top of Gnuradio (GNU/Linux): >>> https://github.com/kantooon/qradiolink >>> >>> 73, >>> Adrian YO8RZZ >>> >>> >>> ------------------------------------------------------------------------------ >>> Check out the vibrant tech community on one of the world's most >>> engaging tech sites, Slashdot.org! http://sdm.link/slashdot >>> >>> >>> _______________________________________________ >>> Freetel-codec2 mailing list >>> Freetel-codec2@lists.sourceforge.net >>> https://lists.sourceforge.net/lists/listinfo/freetel-codec2 >> >> >> ------------------------------------------------------------------------------ >> Check out the vibrant tech community on one of the world's most >> engaging tech sites, Slashdot.org! http://sdm.link/slashdot >> _______________________________________________ >> Freetel-codec2 mailing list >> Freetel-codec2@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/freetel-codec2 >> > ------------------------------------------------------------------------------ > Check out the vibrant tech community on one of the world's most > engaging tech sites, Slashdot.org! http://sdm.link/slashdot > _______________________________________________ > Freetel-codec2 mailing list > Freetel-codec2@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Freetel-codec2 mailing list Freetel-codec2@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/freetel-codec2
