[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Discuss-gnuradio] The GMSK demodulation

From: Sylvain Munaut
Subject: Re: [Discuss-gnuradio] The GMSK demodulation
Date: Fri, 28 Feb 2014 16:31:16 +0100

Also as a side note, you can't demod GSM and then slice it. You have
to demod it burst by burst so that you can lock to the training
sequence of each. So the demod block of GR is pretty much useless

airprobe has a viterbi demod (which is probably one of the few good
part of airprobe to re-use).



On Fri, Feb 28, 2014 at 4:27 PM, Tom Rondeau <address@hidden> wrote:
> On Fri, Feb 28, 2014 at 10:12 AM, Marcus Müller <address@hidden> wrote:
>> Hi Zhenhua,
>> as Aditya pointed out: Viterby is /not/ a demodulator.
>> You should read something on digital communication that explains the
>> difference between channel coding and modulation, then everything will be
>> clearer to you.
>> Greetings,
>> Marcus
>> On 02/28/2014 04:04 PM, zhenhua han wrote:
>> What confused me is the Viterbi algorithm. I saw it can be used to
>> demodulate GMSK in more than one place (such as here:
>> http://www.mathworks.cn/cn/help/comm/ref/comm.gmskdemodulatorclass.html )
>> I think it's better for me to read some materials of Viterbi and find out
>> what really it is.
>> Cheers
>> Zhenhua
>> 2014-2-28 下午10:40于 "Aditya Dhananjay" <address@hidden> 写道:
>>>> As I have known, GSM uses GMSK modulation which BT = 0.3 and it uses
>>>> Viterbi algorithm for demodulation. And I took a look at the code of GMSK
>>>> demod code in GNU Radio, it use quadrature_demod but not Viterbi as
>>>> demodulation method. So which one is better in doing demodulating GMSK?
>>>> Moreover, GSM uses Viterbi algorithm to decode the convolution encoding.
>>>> Would it be possible to use quadrature_demod to demodulate GSM signal
>>>> instead of Viterbi? What about the convolution decoding part (maybe by some
>>>> other method)?
>>> I think you are mixing up the modulation and coding components.
>>> At the transmitter, you first code (convolutional code), and then you
>>> modulate (GMSK).
>>> At the receiver, you first demodulate (quadrature demodulate) and then you
>>> decode (Viterbi).
>>> Coding takes a stream of bits and converts it to another stream of bits.
>>> Modulation refers to the process of converting the post-coded bits into
>>> "symbols" that you will then send over-the-air.
>>> best,
>>> aditya
> Actually, guys....
> http://www.ittc.ku.edu/~prescott/kcp/HPRC-GMSK-Demod.pdf
> You can demodulate GMSK using the Viterbi algorithm.
> Zhenhua,
> We don't implement this method in our GMSK demodulator, though I have
> wanted to see someone do it. The Viterbi is the maximum likelihood
> detector for GMSK, but it's more complicated to implement. The
> quadrature method we use is simple and intuitive but suboptimal.
> Tom
> _______________________________________________
> Discuss-gnuradio mailing list
> address@hidden
> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio

reply via email to

[Prev in Thread] Current Thread [Next in Thread]