With no coding you won't be operating at very low SNRs in a relative
sense to coded systems. A second-order tracking loop works great to
obtain and maintain timing synchronization even for systems coded at
low rates operating near threshold, so it should be relatively easy to
get such a system to work for your application.
This seems to be what you described although the nonlinearity followed
by BPF can be a fairly noisy phase detector I can see that it might
work well for your case. There are better detectors in the
literature that operate reliably to far lower SNRs.
I don't know why your colleagues would think this wouldn't work, to my
knowledge it's how most low SNR continuous-stream demodulators are
implemented.
Cheers,
Eric
On 5 Mar 2005 12:13:47 -0800, "john" <
[email protected]> wrote:
>I can tolerate bit errors in this application (do not need perfect data
>recovery), but loss of synch raises havoc. There is no coding
>whatsoever.
>
>Thanks,
>
>John
>
>Eric Jacobsen wrote:
>> Geez, how low do you need to go? Are you using some kind of
>> seriously low code rates or something?
>>
>> Just using a second-order timing recovery loop with a well-known
>> timing phase detector and a reasonably narrow loop bandwidth will
>> track timing well below 0dB SNR. Satellite systems have been doing
>> this for years. I don't know what the deep space guys do, but it
>> might be insightful as well.
>>
>> Using pilot symbols helps since it removes ambiguity, but it requires
>> adding the overhead for the pilots and then requires obtaining synch
>> with the pilots (i.e., locating them). Both very doable if your
>> system allows such flexibility.
>>
>>
>>
>> On 4 Mar 2005 18:01:35 -0800, "john" <
[email protected]> wrote:
>>
>> >All,
>> >
>> >I'm curious about practical implementations of very low SNR clock
>> >synchronization for non-burst coherent BPSK. I have been doing some
>> >work in this area, and have found that a nonlinearity, narrow BPF,
>and
>> >2nd order transition tracking PLL works quite well to 20% SER and
>> >beyond. Some of my colleagues don't believe it, pointing to papers
>that
>> >claim MAP detectors fail well before that point. They claim that
>data
>> >aided techniques using pilot symbols are the way to go.
>> >
>> >Any comments are welcome.
>> >
>> >John
>> >
>>
>> Eric Jacobsen
>> Minister of Algorithms, Intel Corp.
>> My opinions may not be Intel's opinions.
>> http://www.ericjacobsen.org
>
Eric Jacobsen
Minister of Algorithms, Intel Corp.
My opinions may not be Intel's opinions.
http://www.ericjacobsen.org