Re: [Discuss-gnuradio] Digital Communication using GNU Radio.

[Eric Blossom]

On Thu, Jun 02, 2005 at 09:21:59AM -0700, Sachi wrote:
> Hi, all
> I am still studying the codes of the FSK_R(T)X.py.
> It's a little bit confusing because the comments are
> rather limited. 
> Which algorithm or book chapter does the author refer
> to when he wrote the codes, especially for the time
> synchronization part? I think that information can
> help me understand the code line by line much better.
> 
> Thanks in advance
> 
> Sachi 

Hi Sachi,

The time synchronization method is a standard open loop technique that
works fine for many uses.  It results in establishing both bit timing
and frame alignment.  Fundamentally we start with a signal that is
oversampled 8 times, and then look for a particular synchronization
pattern at every possible offset.  When we find the best one, we
declare that we are synchronized, and use that alignment for the
duration of the current frame.  It's similar to the oversampling
techinque used in UARTs to find the middle of the start bit.

Synchronization is generally not well covered in intro comms texts.

Frerking, "Digital Signal Processing in Communication Systems" is full
of practical digital comms techniques, including some having to do
with synchronization.

Meyr, Moeneclaey and Fechtel, "Digital Communications Receivers:
Synchronization, Channel Estimation, and Signal Processing" is pretty
much all about synchronization, but is pretty heavy going.

Eric