Dmitry Kiryashov writes:

[big barker code snip]

>
> So you send/receive signal with Barker modulation and search maximum of
> ACF(Send_Packet,Recv_Packet). If you know n (in Bn ACF function) you can
> measure distance .
>
> WBR Dmitry.
>
> P.S. Any additional information see at textbook about radiolocation .
>

This is essentially what is done in RADAR systems, too. Ideally, and
for best time/distance resolution, you would like to transmit an
impulse. But because of bandwidth and peak power constraints you
can't. So instead, you transmit a signal whose autocorrelation
function is an impulse. In RADAR the transmitted signal is a chirp (FM
modulation) and with a digital modulation scheme you can use the
Barker codes that Dmitry describes. After the cross-correlation of
received signal with transmitted signal all you have is an easily
identifiable peak corresponding to the reception of the return
signal. There is more than one Barker code for a given number of
symbols and separate devices can operate near each other if they use
different Barker codes. This system has good noise immunity too. This
is all very similar to spread-spectrum modulation or code-division
multiplexing. Longer Barker codes are better but require more
computing for the cross correlation and take longer to transmit, so
you have to be sure you will finish transmitting before the reflection
returns.

Mal Goris
--
http://www.nfra.nl/~mgoris/