MATLAB Central Newsreader - bug?

bug?

Balachander Narasimhan — Wed, 06 Feb 2008 17:56:01 -0500

the rayleighchan command always gives the same tap weights
whenever invoked. Even if I restart matlab, it gives the
same tap values. isnt this a bug?

Re: bug?

roberson@ibd.nrc-cnrc.gc.ca (Walter Roberson) — Wed, 06 Feb 2008 18:09:54 -0500

In article <focsbh$9p6$1@fred.mathworks.com>,
Balachander Narasimhan <balxxxxxchand@whatever.com> wrote:
>the rayleighchan command always gives the same tap weights
>whenever invoked. Even if I restart matlab, it gives the
>same tap values. isnt this a bug?

I see nothing in the documentation to indicate that it should
give different tap weights each time.

In the link 'Simulation of Multipath Fading Channels Methodology'
I do see that,

1.A complex uncorrelated (white) Gaussian process with zero mean
and unit variance is generated in discrete time.

But I don't see anything in there that indicates that it must or
should generate a different Gaussian process each time.
--
This is a Usenet signature block. Please do not quote it when replying
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Re: bug?

Roger Stafford — Wed, 06 Feb 2008 18:50:04 -0500

"Balachander Narasimhan" <balxxxxxchand@whatever.com> wrote in message
<focsbh$9p6$1@fred.mathworks.com>...
> the rayleighchan command always gives the same tap weights
> whenever invoked. Even if I restart matlab, it gives the
> same tap values. isnt this a bug?
----------
As Walter has hinted, there is probably a random element involved in
rayleighchan, which would imply that the pseudo-random functions 'rand' or
'randn' have been called upon. If so, you would need to reset their initial "seed"
or "state" settings to something that is truly random, such as the time of day
when matlab was loaded, in order to achieve different results. See some of the
numerous cssm threads on this subject.

Roger Stafford

Re: bug?

Balachander Narasimhan — Thu, 07 Feb 2008 20:03:03 -0500

Thanks for the reply. But rayleighchan function returns a
channel object. There would be circumstances in which one
needs multiple channel objects which behave independently.
Here, the function becomes useless.

regs
bala

roberson@ibd.nrc-cnrc.gc.ca (Walter Roberson) wrote in
message <foct5i$a0b$1@canopus.cc.umanitoba.ca>...
> In article <focsbh$9p6$1@fred.mathworks.com>,
> Balachander Narasimhan <balxxxxxchand@whatever.com> wrote:
> >the rayleighchan command always gives the same tap weights
> >whenever invoked. Even if I restart matlab, it gives the
> >same tap values. isnt this a bug?
>
> I see nothing in the documentation to indicate that it should
> give different tap weights each time.
>
> In the link 'Simulation of Multipath Fading Channels
Methodology'
> I do see that,
>
> 1.A complex uncorrelated (white) Gaussian process with
zero mean
> and unit variance is generated in discrete time.
>
> But I don't see anything in there that indicates that it
must or
> should generate a different Gaussian process each time.
> --
> This is a Usenet signature block. Please do not quote it
when replying
> to one of my postings.
> http://en.wikipedia.org/wiki/Signature_block

Re: bug?

Balachander Narasimhan — Thu, 07 Feb 2008 20:04:01 -0500

Thanks for the reply. But setting the states of rand or
randn did not help.

regs
bala

"Roger Stafford" <ellieandrogerxyzzy@mindspring.com.invalid>
wrote in message <focvgs$qjo$1@fred.mathworks.com>...
> "Balachander Narasimhan" <balxxxxxchand@whatever.com>
wrote in message
> <focsbh$9p6$1@fred.mathworks.com>...
> > the rayleighchan command always gives the same tap weights
> > whenever invoked. Even if I restart matlab, it gives the
> > same tap values. isnt this a bug?
> ----------
> As Walter has hinted, there is probably a random element
involved in
> rayleighchan, which would imply that the pseudo-random
functions 'rand' or
> 'randn' have been called upon. If so, you would need to
reset their initial "seed"
> or "state" settings to something that is truly random,
such as the time of day
> when matlab was loaded, in order to achieve different
results. See some of the
> numerous cssm threads on this subject.
>
> Roger Stafford
>

Re: bug?

Jane schimit — Wed, 05 Mar 2008 08:44:02 -0500

You can use:
chan = rayleighchan(...,...);
seed = randseed(..,..);
reset(,seed);

to set rayleighchan's initial state.