Thanks Mel,
Funny you should mention that. A couple days ago, I put together a
spreadsheet of all the FreeDV-like modems out there. Here is a summary:
Modem Number of Carriers Carrier Sep (Hz) Symbol length (ms) Guard
Interval (ms) Symbol Rate (Hz) % Guard Lobe width (Hz) Total BW (Hz)
Comments: FreeDV 17 75 20 6.666666667 50 33.33% 100 1275 FDM. Guard
numbers are OFDM equivalent ARD9800 36 62.5 20 4 50 20.00% 100 2250 WinDRM
A 57 41.666667 26.66666667 2.666666667 37.5 10.00% 75 2375 Based on
DRM A WinDRM
B 51 46.875 26.66666667 5.333333333 37.5 20.00% 75 2390.625 Based on
DRM B WinDRM
E 45 46.875 26.66666667 5.333333333 37.5 20.00% 75 2109.375 Based on DRM B
I mainly wanted to see how FreeDV compares to the other modes developed for
voice. I haven't read all of the DRM spec, but I did look at the WinDRM
info and source to see how fancy that is.
I'd like to start by doing an 'apples-to-apples' OFDM modem which matches
the FDMDV one, so that the comparison in meaningful.
I actually like the KISS philosophy of the FDMDV modem a lot, But I can
see that the OFDM modes have gained some robustness by spreading sync
across time and frequency, etc.
-Frank
On Wed, Jun 5, 2013 at 5:24 PM, Mel Whitten <[email protected]> wrote:
> Might be worth the time to review how Digital Radio Mondiale configures
> their
> robust modes using OFDM. The DRM spec is here:
>
> http://www.etsi.org/deliver/etsi_es/201900_201999/201980/03.01.01_50/es_201980v030101m.pdf
>
> Mel
>
> ----- Original Message -----
> From: "Bruce Perens" <[email protected]>
> To: <[email protected]>
> Sent: Wednesday, June 05, 2013 3:22 PM
> Subject: Re: [Freetel-codec2] Building on Windows
>
>
> > Add "4) Is the linearity of Amateur equipment intended for SSB voice and
> > lacking in headroom beyond its rated power really adequate for this
> > modulation?"
> >
> > On 06/05/2013 01:16 PM, Frank Palazzolo wrote:
> >>
> >>
> >> The questions I am trying to answer are:
> >> 1) Will the orthogonality of the OFDM carriers be degraded
> >> significantly by the HF channel, compared to FDM?
> >> 2) If not, can we take advantage of that spectrum 'between the
> >> carriers' that FDMDV is not using?
> >> 3) If we keep a symbol rate of 50Hz with a carrier spacing of 75Hz,
> >> this is equivalent to a 6.67ms guard band. Will having this guard
> >> band in time rather than spacing between carriers be more robust to
> >> multipath?
> >>
> >
> >
> >
> ------------------------------------------------------------------------------
> > How ServiceNow helps IT people transform IT departments:
> > 1. A cloud service to automate IT design, transition and operations
> > 2. Dashboards that offer high-level views of enterprise services
> > 3. A single system of record for all IT processes
> > http://p.sf.net/sfu/servicenow-d2d-j
> > _______________________________________________
> > Freetel-codec2 mailing list
> > [email protected]
> > https://lists.sourceforge.net/lists/listinfo/freetel-codec2
> >
>
>
>
> ------------------------------------------------------------------------------
> How ServiceNow helps IT people transform IT departments:
> 1. A cloud service to automate IT design, transition and operations
> 2. Dashboards that offer high-level views of enterprise services
> 3. A single system of record for all IT processes
> http://p.sf.net/sfu/servicenow-d2d-j
> _______________________________________________
> Freetel-codec2 mailing list
> [email protected]
> https://lists.sourceforge.net/lists/listinfo/freetel-codec2
>
------------------------------------------------------------------------------
How ServiceNow helps IT people transform IT departments:
1. A cloud service to automate IT design, transition and operations
2. Dashboards that offer high-level views of enterprise services
3. A single system of record for all IT processes
http://p.sf.net/sfu/servicenow-d2d-j
_______________________________________________
Freetel-codec2 mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/freetel-codec2
