Re: question on FIR channel


"philgo" <philgo@xxxxxxxxx> wrote in message
news:1155700345.187970.125490@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

robert bristow-johnson wrote:
philgo wrote:
hi, suppose I have the FIR channel with 10 taps.
My target sampling rate is, for example, 50MHz, i.e., the sampling
period is 20ns.
But my channel taps do not fall on integer units of the sampling
period, say they fall on
33, 44, 55, 66, 77, 88, 99, 111, 122, 133 ns respectively.

are you sure that is not 110, 121, and 132 ns? everything else was a
multiple of 11 ns.

I actually wanted to give some random numbers that are not integers of
20ns.


What shall I do to create a FIR channel with taps falling exactly on
integer number of samplings? thank you in advance.

so what you're trying to do is scale an existing FIR design from an FIR
filter that ran at a sampling rate of about 90.9 MHz or 1/(11 ns) to a
not-yet-existing FIR design that is meant to run at 50 MHz? is that
it?

I do not get it. Basically, I am given an FIR channel at non-integer
samples and want to convert the FIR channel with only integer delayed
samples , but without changing the channel characteristics.

I suppose you mean that you have either a real FIR filter that you are
calling a "channel" or you have a multipath channel that is well
approximated by a FIR filter with arbitrary delays between the paths.

Here are some suggestions for modeling such a "channel":

1) Carefully examine just how accurate the delays can be measured/specified.
Then consider moving the delays within the range of error so that they fall
on a regular grid - perhaps a sparsely populated regular grid. That is,
there can be lots of zero FIR coefficients.

2) Carefully consider sampling at a very high rate and then quantizing the
times at which each of the nonzero FIR coefficients lie - such that the
error introduced by quantizing delays is negligible. Sort of the same thing
as #1 but taken from slightly another perspective.

3) Consider randomizing the delays (or, if narrowband signals, the phase) to
simulate channel behavior on a statistical basis. This may be the most
realistic simulation of all if the delays really aren't known that well or
if they vary due to relative motion or a time-varying channel.

If the signal is narrowband then the original objective is may not be
completely achievable.
If the signal is broadband then the original objective may be reasonably
achievable.

Fred



.

Relevant Pages

  • Re: Nyquist Sampling
    ... By sampling say a 3.1 kHz band-limited voice channel at the Nyquist rate ...
    (comp.dsp)
  • Rayleighchan function in matlab
    ... communications toolbox and so neither the raileighchan function. ... FIR discrete channel is correct. ... Where I heuristically approximate the number of taps in the channel as ...
    (comp.dsp)
  • implementing rayleighchan in OFDM
    ... I am doing my M.SC thesis on the topic "ICI cancellation in OFDM". ... I can implement the OFDM structure in AWGN channel, ... Which parameters determine the sampling time of x_t and sampling ... it is a basic question sorry but I am confused...) ...
    (comp.soft-sys.matlab)
  • implementing rayleighchan in OFDM
    ... I am doing my M.SC thesis on the topic "ICI cancellation in OFDM". ... I can implement the OFDM structure in AWGN channel, ... Which parameters determine the sampling time of x_t and sampling ... it is a basic question sorry but I am confused...) ...
    (comp.dsp)
  • implementing rayleighchan in OFDM
    ... I am doing my M.SC thesis on the topic "ICI cancellation in OFDM". ... I can implement the OFDM structure in AWGN channel, ... Which parameters determine the sampling time of x_t and sampling ... it is a basic question sorry but I am confused...) ...
    (sci.math.symbolic)