Ofdm frequency offset

GNU Radio
1

Dear all:
Thank you in advance.
1.
I want to ask a question about the new ofdm example.And
I know the receiver have used the SCA(schmidl and cox algorithm)
algorithm.Now in my application,maybe this algorithm isn’t enough.And I
want to ask whether have other good frequency offset correction
algorithm which have been implemented.
2.What is the algorithm used by the old version of the
ofdm example?Thanks.

Best regards,
zs

2

Hi zs,

this reminds me very much of OFDM radar technologies, as your problem
boils down to finding a good estimator for the spectral properties of
your OFDM frame as well as the time it reached you.
I think you should have a look at chapter 3, “OFDM Radar Algorithms” of
[1]; you might find that considering the unknown timing being a result
of the time it took a OFDM signal to reach you (and hence an effect of
range) a useful approach. You can find some shorter information on the
accuracy of these estimates in [2].
The difference in the algorithms described in [1] and your problem is
that you don’t a priori know the transmitted signal – you’ll have to
figure that out by using something like S&C to receive and decode the
OFDM symbol prior to “clean” reconstruction; you could then use the
parameters (range == timing, doppler == frequency) that the radar
estimators give you to model the symbol like you received it, and
subtract it from your incoming signal. Of course, the mistakes you make
when decoding the incoming symbol will have an influence on the accuracy
of your estimates.

Best regards,
Marcus

[1] Braun, Martin. /OFDM Radar Algorithms in Mobile Communication
Networks/. Diss. Karlsruhe, Karlsruher Institut f??r Technologie (KIT),
Diss., 2014, 2014;

[2] Braun, Martin, Christian Sturm, and Friedrich Jondral. “On the
single-target accuracy of OFDM radar algorithms.” /PIMRC/. 2011.;

3

Dear Marcus M.:

Actually my problem is:
y=useful information+x*h(channel)*cfo(carrier offset
due to the local oscillator between the interference and the
radar)+noise.
I want to turn y to
new_y=useful information+noise.
So I need know the channel(h) and the cfo exactly(I know the x in
advance while I don’t know the cfo and h.So I have to estimate them).The
root question I faced is the cfo estimated from the SCA isn’t enough.

Thank you so much. I will read the paper you mentioned.Maybe
helpful.Thanks.
Best regards,
zs

At 2015-06-24 17:08:16, “Marcus M.” [email protected] wrote:
Hi zs,

this reminds me very much of OFDM radar technologies, as your problem
boils down to finding a good estimator for the spectral properties of
your OFDM frame as well as the time it reached you.
I think you should have a look at chapter 3, “OFDM Radar Algorithms” of
[1]; you might find that considering the unknown timing being a result
of the time it took a OFDM signal to reach you (and hence an effect of
range) a useful approach. You can find some shorter information on the
accuracy of these estimates in [2].
The difference in the algorithms described in [1] and your problem is
that you don’t a priori know the transmitted signal – you’ll have to
figure that out by using something like S&C to receive and decode the
OFDM symbol prior to “clean” reconstruction; you could then use the
parameters (range == timing, doppler == frequency) that the radar
estimators give you to model the symbol like you received it, and
subtract it from your incoming signal. Of course, the mistakes you make
when decoding the incoming symbol will have an influence on the accuracy
of your estimates.

Best regards,
Marcus

[1] Braun, Martin. OFDM Radar Algorithms in Mobile Communication
Networks. Diss. Karlsruhe, Karlsruher Institut fr Technologie (KIT),
Diss., 2014, 2014;

[2] Braun, Martin, Christian Sturm, and Friedrich Jondral. “On the
single-target accuracy of OFDM radar algorithms.” PIMRC. 2011.;

On 06/24/2015 10:29 AM, zs wrote:

Dear Marcus M.:

Thank you so much for your kindly reply.

The SCA is adequate for a correct demodulation of the signal while maybe
inadequate for estimate the precise frequency shift.I don’t have the
synchroniztion device.In my application,I need to reconstruct one
transmit signal in time domain,and remove it from the received
signal.For example,y=x1+x2,and I want to remove x2 from the baseband
recevied signal.

Now my idea is no only used the SCA algorithm mentioned in the new ofdm
example, but also use other similar finer carrier frequency estimation
algorithm.I want to combined the algorithms.So I ask the question in the
maillist.

Thank you so much.

Best regards,
zs

At 2015-06-24 15:54:30, “Marcus M.” [email protected] wrote:
Dear zs,

basically, Schmidl and Cox is a very good algorithm, because it can
achieve the same quality of synchronization with half of the
synchronization overhead compared to other approaches, or a better
performance with the same amount.
I must admit that from the top of my head, there’s probably not much
that’s better than S&C in a real world OFDM receiver, but I must admit
that I haven’t implemented many OFDM synchronizers myself.

However, you say

Now in my application,maybe this algorithm isn’t enough.

which means that you have a mathematical measure that’s not OK for S&C,
I guess. So in what way doesn’t S&C suffice? What is it about your
application that makes S&C insufficient or impossible to use?

Best regards,
Marcus

On 06/24/2015 09:00 AM, zs wrote:

Dear all:
Thank you in advance.
1.
I want to ask a question about the new ofdm example.And
I know the receiver have used the SCA(schmidl and cox algorithm)
algorithm.Now in my application,maybe this algorithm isn’t enough.And I
want to ask whether have other good frequency offset correction
algorithm which have been implemented.
2.What is the algorithm used by the old version of the
ofdm example?Thanks.

Best regards,
zs

4

Dear Marcus M.:

Thank you so much.So kindly of you.Thanks.I will read the papers you
mentioned.

Best regards,
zs

At 2015-06-24 17:08:16, “Marcus M.” [email protected] wrote:
Hi zs,

this reminds me very much of OFDM radar technologies, as your problem
boils down to finding a good estimator for the spectral properties of
your OFDM frame as well as the time it reached you.
I think you should have a look at chapter 3, “OFDM Radar Algorithms” of
[1]; you might find that considering the unknown timing being a result
of the time it took a OFDM signal to reach you (and hence an effect of
range) a useful approach. You can find some shorter information on the
accuracy of these estimates in [2].
The difference in the algorithms described in [1] and your problem is
that you don’t a priori know the transmitted signal – you’ll have to
figure that out by using something like S&C to receive and decode the
OFDM symbol prior to “clean” reconstruction; you could then use the
parameters (range == timing, doppler == frequency) that the radar
estimators give you to model the symbol like you received it, and
subtract it from your incoming signal. Of course, the mistakes you make
when decoding the incoming symbol will have an influence on the accuracy
of your estimates.

Best regards,
Marcus

[1] Braun, Martin. OFDM Radar Algorithms in Mobile Communication
Networks. Diss. Karlsruhe, Karlsruher Institut fr Technologie (KIT),
Diss., 2014, 2014;

[2] Braun, Martin, Christian Sturm, and Friedrich Jondral. “On the
single-target accuracy of OFDM radar algorithms.” PIMRC. 2011.;

On 06/24/2015 10:29 AM, zs wrote:

Dear Marcus M.:

Thank you so much for your kindly reply.

The SCA is adequate for a correct demodulation of the signal while maybe
inadequate for estimate the precise frequency shift.I don’t have the
synchroniztion device.In my application,I need to reconstruct one
transmit signal in time domain,and remove it from the received
signal.For example,y=x1+x2,and I want to remove x2 from the baseband
recevied signal.

Now my idea is no only used the SCA algorithm mentioned in the new ofdm
example, but also use other similar finer carrier frequency estimation
algorithm.I want to combined the algorithms.So I ask the question in the
maillist.

Thank you so much.

Best regards,
zs

At 2015-06-24 15:54:30, “Marcus M.” [email protected] wrote:
Dear zs,

basically, Schmidl and Cox is a very good algorithm, because it can
achieve the same quality of synchronization with half of the
synchronization overhead compared to other approaches, or a better
performance with the same amount.
I must admit that from the top of my head, there’s probably not much
that’s better than S&C in a real world OFDM receiver, but I must admit
that I haven’t implemented many OFDM synchronizers myself.

However, you say

Now in my application,maybe this algorithm isn’t enough.

which means that you have a mathematical measure that’s not OK for S&C,
I guess. So in what way doesn’t S&C suffice? What is it about your
application that makes S&C insufficient or impossible to use?

Best regards,
Marcus

On 06/24/2015 09:00 AM, zs wrote:

Dear all:
Thank you in advance.
1.
I want to ask a question about the new ofdm example.And
I know the receiver have used the SCA(schmidl and cox algorithm)
algorithm.Now in my application,maybe this algorithm isn’t enough.And I
want to ask whether have other good frequency offset correction
algorithm which have been implemented.
2.What is the algorithm used by the old version of the
ofdm example?Thanks.

Best regards,
zs