Forum: GNU Radio Zero Forcing (ZF) and MMSE Equalizer

Bc643d76db2b57e5e0d9f20bf6aad26d?d=identicon&s=25 ZaInzAiN Jj (Guest)
on 2013-08-13 08:23
(Received via mailing list)
Hi all,
I am new to gnuradioand I want to implement Zero Forcing (ZF) and MMSE
equalizer in OFDM communication using gnuradio.
Which part need reconfiguration to implement them?
I use usrp bus series and gnuradio 3.7.0.

Thanks,
Zai
Ad80d352eb445a3d7dccd5a779db0e43?d=identicon&s=25 Martin Braun (CEL) (Guest)
on 2013-08-13 10:13
(Received via mailing list)
On Tue, Aug 13, 2013 at 02:21:43PM +0800, ZaInzAiN Jj wrote:
> Hi all,
>
> I am new to gnuradio and I want to implement Zero Forcing (ZF) and MMSE
> equalizer in OFDM communication using gnuradio.
>
> Which part need reconfiguration to implement them?
>
> I use usrp bus series and gnuradio 3.7.0.

With 3.7, it's quite simple. OFDM signals are equalized using blocks of
type ofdm_frame_equalizer_vcvc. This block doesn't actually do the
signal processing; instead, you drop in an instance of a
ofdm_equalizer_base class.

So all you need to do is derive from ofdm_equalizer_base and pass it to
ofdm_frame_equalizer_vcvc.

Of course, in a practical system, you have two components for your
equalization: The channel estimation and the actual equalization.
You probably need to work on both. However, if you stick to the current
OFDM frame structure, you will get an initial estimate of the channel.
If you have a static channel, zero forcing will work out of the box with
the available equalizers.

For MMSE, you will need a way to estimate the SNR inside the equalizer.
IIRC, you need the symbol alphabet for that. Simply make it an argument
for the equalizer class.

If you finish a working MMSE implementation, I'd love to see the code.

Cheers,
MB

--
Karlsruhe Institute of Technology (KIT)
Communications Engineering Lab (CEL)

Dipl.-Ing. Martin Braun
Research Associate

Kaiserstra├če 12
Building 05.01
76131 Karlsruhe

Phone: +49 721 608-43790
Fax: +49 721 608-46071
www.cel.kit.edu

KIT -- University of the State of Baden-W├╝rttemberg and
National Laboratory of the Helmholtz Association
Bc643d76db2b57e5e0d9f20bf6aad26d?d=identicon&s=25 ZaInzAiN Jj (Guest)
on 2013-08-13 11:33
(Received via mailing list)
Thanks Martin,
your information very helpful.
for current, what is equalizer which used on gnuradio 3.7 ?

from gnuradio 3.7 API there are three equalizer. cma, kurtotic and lms
equalizer.
what is equalizer which used?


Thanks,
Zai


________________________________
 From: Martin Braun (CEL) <martin.braun@kit.edu>
To: discuss-gnuradio@gnu.org
Sent: Tuesday, August 13, 2013 3:11 PM
Subject: Re: [Discuss-gnuradio] Zero Forcing (ZF) and MMSE Equalizer


On Tue, Aug 13, 2013 at 02:21:43PM +0800, ZaInzAiN Jj wrote:
> Hi all,
>
> I am new to gnuradio and I want to implement Zero Forcing (ZF) and MMSE
> equalizer in OFDM communication using gnuradio.
>
> Which part need reconfiguration to implement them?
>
> I use usrp bus series and gnuradio 3.7.0.

With 3.7, it's quite simple. OFDM signals are equalized using blocks of
type ofdm_frame_equalizer_vcvc. This block doesn't actually do the
signal processing; instead, you drop in an instance of a
ofdm_equalizer_base class.

So all you need to do is derive from ofdm_equalizer_base and pass it to
ofdm_frame_equalizer_vcvc.

Of course, in a practical system, you have two components for your
equalization: The channel estimation and the actual equalization.
You probably need to work on both. However, if you stick to the current
OFDM frame structure, you will get an initial estimate of the channel.
If you have a static channel, zero forcing will work out of the box with
the available equalizers.

For MMSE, you will need a way to estimate the SNR inside the equalizer.
IIRC, you need the symbol alphabet for that. Simply make it an argument
for the equalizer class.

If you finish a working MMSE implementation, I'd love to see the code.

Cheers,
MB

--
Karlsruhe Institute of Technology (KIT)
Communications Engineering Lab (CEL)

Dipl.-Ing. Martin Braun
Research Associate

Kaiserstrae 12
Building 05.01
76131 Karlsruhe

Phone: +49 721 608-43790
Fax: +49 721 608-46071
www.cel.kit.edu

KIT -- University of the State of Baden-Wrttemberg and
National Laboratory of the Helmholtz Association
C539637020fd56193dd6daec746c4a84?d=identicon&s=25 Tom Rondeau (Guest)
on 2013-08-14 23:40
(Received via mailing list)
On Tue, Aug 13, 2013 at 5:31 AM, ZaInzAiN Jj <zain_zain_jj@yahoo.com>
wrote:
> Zai
Those equalizers are designed for narrowband (or non multi carrier)
systems and are not (necessarily or directly) appropriate for OFDM.
Best look at the OFDM receiver (gr-digital/examples/ofdm/rx_ofdm.grc)
for the equalizer structure used there.

--
Tom
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