Forums

BER of multipath channel

Started by Richard_K December 29, 2006
I wrote a program to calculate the BER of LMS equalizer in AWGN and
multipath channel. The tap weights of the mobile radio channels are
normalized to 1 (the exact value is 1.0062).

Surprisingly, I found out that the performance of the equalizer in
multipath channel is better than the one in AWGN. Is this acceptable? Or
anything that might be wrong in my simulation? Or the performance gain of
the receiver in multipath is due to the channel tap weights that has a
normalized value which is slightly greater than 1?

Please help. Thanks.

Richard_K wrote:

> I wrote a program to calculate the BER of LMS equalizer in AWGN and > multipath channel. The tap weights of the mobile radio channels are > normalized to 1 (the exact value is 1.0062). > > Surprisingly, I found out that the performance of the equalizer in > multipath channel is better than the one in AWGN. Is this acceptable? Or > anything that might be wrong in my simulation? Or the performance gain of > the receiver in multipath is due to the channel tap weights that has a > normalized value which is slightly greater than 1? > > Please help. Thanks.
For the fair comparison, the sum of the absolute weights of all taps in the multipath channel should be equal to 1. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
I agreed with you. 

So in this case where the tap weights normalized value is slightly greater
than 1 (which is 1.0062), is this one of the possible reason that can lead
to better performance in multipath channel as compared to AWGN channel?

Thanks.

> > >Richard_K wrote: > >> I wrote a program to calculate the BER of LMS equalizer in AWGN and >> multipath channel. The tap weights of the mobile radio channels are >> normalized to 1 (the exact value is 1.0062). >> >> Surprisingly, I found out that the performance of the equalizer in >> multipath channel is better than the one in AWGN. Is this acceptable?
Or
>> anything that might be wrong in my simulation? Or the performance gain
of
>> the receiver in multipath is due to the channel tap weights that has a >> normalized value which is slightly greater than 1? >> >> Please help. Thanks. > > >For the fair comparison, the sum of the absolute weights of all taps in >the multipath channel should be equal to 1. > > >Vladimir Vassilevsky > >DSP and Mixed Signal Design Consultant > >http://www.abvolt.com > > >
On Fri, 29 Dec 2006 13:37:45 -0600, "Richard_K" <ngyh80@hotmail.com>
wrote:

>I agreed with you. > >So in this case where the tap weights normalized value is slightly greater >than 1 (which is 1.0062), is this one of the possible reason that can lead >to better performance in multipath channel as compared to AWGN channel?
Depending on exactly what you're doing I'd guess that the problem may be in how you're measuring SNR or Eb/No. Since multipath allows you to integrate more power than just the direct path, this gets confusing sometimes. Are you measuring SNR at the constellation or some other way? FWIW, 10log(1.0062) is less than 0.3dB, so I don't think that's the only problem (unless that's the difference that you're seeing). SNR, IMHO, should be measured with all of the power in the multipath profile integrated to compute Ps before computing SNR. Scaling it so that the profile total power is unity (which it sounds like you're close already) should do that. You could try measuring SNR at the constellation to see if it gets a different result.
> >Thanks. > >> >> >>Richard_K wrote: >> >>> I wrote a program to calculate the BER of LMS equalizer in AWGN and >>> multipath channel. The tap weights of the mobile radio channels are >>> normalized to 1 (the exact value is 1.0062). >>> >>> Surprisingly, I found out that the performance of the equalizer in >>> multipath channel is better than the one in AWGN. Is this acceptable? >Or >>> anything that might be wrong in my simulation? Or the performance gain >of >>> the receiver in multipath is due to the channel tap weights that has a >>> normalized value which is slightly greater than 1? >>> >>> Please help. Thanks. >> >> >>For the fair comparison, the sum of the absolute weights of all taps in >>the multipath channel should be equal to 1. >> >> >>Vladimir Vassilevsky >> >>DSP and Mixed Signal Design Consultant >> >>http://www.abvolt.com >> >> >> >
Eric Jacobsen Minister of Algorithms, Intel Corp. My opinions may not be Intel's opinions. http://www.ericjacobsen.org
I have came across with the same problem too. Can anyone please help?

> >I wrote a program to calculate the BER of LMS equalizer in AWGN and >multipath channel. The tap weights of the mobile radio channels are >normalized to 1 (the exact value is 1.0062). > >Surprisingly, I found out that the performance of the equalizer in >multipath channel is better than the one in AWGN. Is this acceptable? Or >anything that might be wrong in my simulation? Or the performance gain
of
>the receiver in multipath is due to the channel tap weights that has a >normalized value which is slightly greater than 1? > >Please help. Thanks. >