Re: [Discuss-gnuradio] Bandwidth switching per symbol

[Matthias Wilhelm]

Hi,

this seems really strange, some ideas for debugging:

1) the demod process works fine at first but adds or drops a few samples such 
that some chips a shifted a bit, and as the chip seqs of 802.15.4 are just 
shifted/inverted version of each other so that you see many different symbols 
in the end.
You can print the input to the packet_sink (after slicing) and see if they 
resemble shifted version of the sequences you expect. The debug messages also 
mention how many chip errors were found, if the receiver had too many chip 
errors and restarted, etc. 

2) Is the problem always after 32 symbols? (32 symbols * 32 chips, ...) This 
would suggest a "digital" problem. Buffers too small or something?

3) The error may be at the sender, shifting the symbols a bit in the middle of 
the packet so that the receiver has problems with sync (or just sends bogus 
after 32 symbols). You can monitor (scope sink) with a second USRP if the 
signal looks alright. 

Regards,
Matthias


Am 29.07.2011 um 14:36 schrieb address@hidden:

> Hi,
> 
> Well its the first case (strange behavior)
> (g means good symbol, b means bad): gggggggggggggbbbbbbbbbbbb
> 
> more precisely, Preamble, SFD, packet length (PHR) is all received correctly. 
> Additionally, also a part of the payload is received correctly. Here an 
> example:
> 
> I send the following packet:
> ['0x0', '0x0', '0x0', '0x0', '0xa7', '0x19', '0x1', '0x0', '0xff', '0xb', 
> '0xb', '0xb', '0xb', '0xb', '0xb', '0xb', '0xb', '0xb', '0xb', '0xb', '0xb', 
> '0xb', '0xb', '0xb', '0xb', '0xb', '0xb', '0xb', '0xb', '0x68', '0x44', '0x0']
> 
> and receive the following:
> ['0x0', '0x0', '0x0', '0x0', '0xa7', '0x19', '0x1', '0x0', '0xff', '0xb', 
> '0xb', '0xb', '0xb', '0xb', '0xb', '0xb', '0xca', '0x8f', '0x45', '0xa5', 
> '0x79', '0xab', '0x35', '0x9a', '0x8c', '0x32', '0xf9', '0x8c', '0xa0', 
> '0xba', '0x2']
> 
> If this would be during the packet_sink, then the error would occur somewhere 
> in the middle of decode_chips()...
> 
> best regards, and thanks again
> Bjorn
>