Re: [Discuss-gnuradio] 802.15.4 Frame sync confusion

[Bastian Bloessl]

Hi,

On 10/18/2017 01:24 PM, sumit kumar wrote:
> Hi,
>
>
> If my understanding is correct, most of the 802.15.4 receiver 
> implementations perform frame synchronization i.e. find the start of the 
> frame using the preambles which are nothing but 8 zeros(each of which is 
> further converted to 32 bit chip).
>
> This is done after the OQPSK symbols (complex samples) are already 
> decoded to bits. Same does the gr-ieee 802.15.4

It's actually working with the chip sequences not the data bits. When 
the receiver is not synchronized is searches for the chip sequence that 
corresponds to the zero data bits, i.e., the preamble. Once the sequence 
is found (when the chip sequence matches reasonably well), it continues 
to decode chip sequences with the known alignment (and looks for the SFD 
data bits).

That means the algorithm works already on a rather deep layer. I'm sure 
it could be much improved. It is just a simple approach that presents a 
tradeoff between performance and complexity (in terms of CPU time and 
implementation complexity).

Best,
Bastian