Dear all,
I have been stuck with a synchronisation problem for a long time. Here
is my problem: I am implementing frequency hopping on both Tx and Rx
ends. At the Tx end, Tx starts changing its transmission frequency from
channel 11 to channel 26 after the its first packet is sent and then
keeps sending all the time. At the Rx end, Rx is probably switched on
later on at the different time. We need the Rx to listen to the incoming
packets and then lock itself to the transmission frequency of the Tx by
hopping its receiving frequency.
Currently, the Tx frequency is changed every 1 second with transmission
interval of 0.25 s, and the Rx frequency is changed every 1 second
immediately after it receives first packet. Somehow, I can't have the Rx
has the exactly same frequency change rate as the Tx since some packets
have been lost. The program on the Tx is written based on the
**CountDual* *and that running on Rx is written based on the
**TOSBase*B*, and I am using TinyOS 1.1.15.
*
*The core code is listed below for *TOSBase:
*event TOS_MsgPtr RadioReceive.receive(TOS_MsgPtr Msg) {
dbg(DBG_USR1, "TOSBase received radio packet.\n");
if ((!Msg->crc) || (Msg->group != TOS_AM_GROUP))
return Msg;
/*
* The frequency is changed at predefined
* time interval.
*
*/
if(( (Msg->data[0]) == 4 ) &&
enableStart){ // The loop for changing
frequency will not start until the Rx receives some specific packets.
freq_int++;
call CC2420Control.TunePreset(freq_channel[freq_int]);
// set the Rx frequency to channel 12.
if(enableChange){
call Timer1.start(TIMER_REPEAT, period_Timer1);
enableChange = FALSE;
}
enableStart = FALSE;
}
...
}
The reason why I manually set the Rx frequency to channel 12 is because
I don't know how to keep the Rx synchronised with the Tx in the very
beginning. The Rx quite easily lose the synchronisation with the Tx, but
I really dont know any reasons for this. Could any one give me some
hints please?
Thank you!
Shui
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