Why the Qam modulation cannot work well in ofdm benchmark example?

GNU Radio
1

Hi guys,

Recently, I have conducted a project based on ofdm benchmark. However,
when
I use the high modulation rate like qam16 and qam64, the packet error
rate
increase significantly. I guess the reason is that the preamble in
gunradio
is too weak to do channel estimation, thereby raising the packet error
rate.

Furthermore, even though I test the example offline without going
through
the channel, the packet error rate still very high, which make me feel
confused. It is supposed to perform normally offline, without any
decoding
error right?

Best,
Kay

2

On Fri, Nov 01, 2013 at 07:23:33PM -0700, Yingjie C. wrote:

Recently, I have conducted a project based on ofdm benchmark. However, when I
use the high modulation rate like qam16 and qam64, the packet error rate
increase significantly. I guess the reason is that the preamble in gunradio is
too weak to do channel estimation, thereby raising the packet error rate.

Furthermore, even though I test the example offline without going through the
channel, the packet error rate still very high, which make me feel confused.
It is supposed to perform normally offline, without any decoding error right?

In order to do QAM over OFDM, you will need a good equalizer; we
currently don’t have good ones implemented.

MB

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

Dipl.-Ing. Martin B.
Research Associate

Kaiserstraße 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-Württemberg and
National Laboratory of the Helmholtz Association

3

On Sun, Nov 3, 2013 at 5:09 AM, Martin B. (CEL)
[email protected]wrote:

through the

channel, the packet error rate still very high, which make me feel
confused.
It is supposed to perform normally offline, without any decoding error
right?

In order to do QAM over OFDM, you will need a good equalizer; we
currently don’t have good ones implemented.

MB

Thanks for the clarification. I’ve been grappling with the high packet
error rates for a while now. :slight_smile:

Aditya