On Thu, 21 Feb 2008 02:35:33 -0800 (PST), Bob <
[email protected]>
wrote:
>On 21 Feb, 08:14, c...@claysturner.com wrote:
>> On Feb 20, 4:38*pm, Bob <sten...@yahoo.com> wrote:
>>
>>
>>
>>
>>
>> > On 20 Feb, 20:41, Mark <makol...@yahoo.com> wrote:
>>
>> > > > So now I see something,,,notice the small peak to the left of the
>> > > > cursor on the second and fourth traces. Should this not be the same as
>> > > > the peaks beside it?
>>
>> > > remember you are looking at the RRC filter..which is only 1/2 the
>> > > picture
>>
>> > > pass this output though another RRC filter so that you have the full
>> > > RC filter and you will see what the receiver sees...
>>
>> > > the Rx and Tx have matched filters and the NYquist filter is both of
>> > > them in cascade,
>>
>> > > you are looking 1/2 way through the cascade..
>>
>> > > Mark
>>
>> > Hi Mark,
>>
>> > The pulses you see on the first link is what happens when I pass the
>> > data through the RRC on the TX link. On the demod side links 2 and 3
>> > are when the data from the modulator is passed through idential RRCs.
>> > So, in effect I already have the RC response at the receiver. But is
>> > it correct...that's what I would like to know?
>>
>> > Bob- Hide quoted text -
>>
>> > - Show quoted text -
>>
>> Hello Bob,
>>
>> The feeding of pulses into the RRC filter (via convolution) assumes
>> your pulses become Kronecker deltas. Don't feed rectangular pulses,
>> instead feed spikes into the RRC filter. Then after going through two
>> of these in sucession, you will see a nice looking signal. You are
>> currenly getting a bunch of ringing resulting from the rectangular
>> pulse's response comingled (convolved) with the RRC's response. For
>> simplifying the testing, just try an RC filter and look at its output.
>> Two RRCs convolved is an RC. Try it!
>>
>> IHTH,
>>
>> Clay- Hide quoted text -
>>
>> - Show quoted text -
>
>Hi Clay,
>
>I did already try it. I fed the output of one RRC into another and
>you're correct...I did get a nice RC pulse output.
>In the test case, this was done for spikes well seperated. However,
>for real test data, I don't have much choice as I have strings of 1's
>and in most cases very few 0's between them. In this case, what are my
>options?
>
>Regards
>Bob
I haven't looked at your latest plots, but I'm a little confused by
your last statement. How many samples per symbol are there going
into the transmit RRC filter? If the answer is one, then you don't
have to worry about the rectangular symbol problem. If the answer is
more than one, then only one of those samples per symbol should be
non-zero if you want to avoid an additional sinx/x response in the
filtering.
Eric Jacobsen
Minister of Algorithms
Abineau Communications
http://www.ericjacobsen.org