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

[Sachi]

Hi Eric and other friends

Today I tried a lot on the FSK TX/RX, by connecting
the BasicTX and BasicRX on the same USRP board via a
sma-sma cable.

I am wondering, what is a good and correct reception?
Ideally, I thought it should be, if I send a file, it
should be received exactly the same as the original
one.  However, this is not the case in my experiments.
Sometimes, even I didn't send anything, the receiver
can still "receive" something and write them into the
file.  Sometimes, although it is synchronized at the
receiver, (the seq no. is correct, going
increasingly), the receiving file is still much
different with the original one, (might be larger).

So what happens? Is there anything wrong with my
setting? What can be done for a reliable transmission?

Thanks for all your help
Sachi

--- Sachi <address@hidden> wrote:

> Hi, Eric
>  
> Thanks very much for your information. It really
> helps me a lot. But I still have a couple of
> questions:
> 1. Does this synchronization algorithm have any
> specific name?
> 2. I notice that at the TX side, a payload file need
> to be sent. So what kind of file should I use here?
> Any file? Does it have any special format? On the
> other hand, at the RX side, what should be observed
> to convince me that the file has been received
> correctly? Receiving a same file? If possible, could
> you please give me more information about the how to
> run the experiments (the command, arguments)
> 3. I directly use 29.xMHz for transmission and
> reception (without freq. tuner) with two USRP boards
> at two PCs, because I think the DAC and ADC can work
> well for this frequency. I just use two amplifiers
> at both ends to increase the SNR. So do you think
> this scenario could work well?
>  
> Thanks very much for your time
>  
> Regards
>  
> Sachi
> 
> Eric Blossom <address@hidden> wrote:
> 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
> 
> 
> 
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