Hi! - To my background there's to say - before you read this - I'm just a software-dev. I have little expertise when it comes to hardware.
I support the development of a real-time application that uses 802.15.4 on an AT86230RF Chip. That RF chip is IEEE 802.15.4-2003 compliant. It has got a data-rate of 250 kBit/s. Let's say I want to send 10 Byte. 2 Bytes CRC are added, and 6 Bytes from the Physical Layer (Preambel + Length Field + Delimeter). So I send 144 Bits (12 Byte PSDU are 12 *8 and 48 Bytes Physical Layer due 6 * 8). Theoretically I get 0,576 ms per transmission using 250 Kbit/s: 1/250k*144*10^3. Now... I use my USRP with an XCVR, start the sender, and record some transmissions into cfiles. I plot the Q channel, and calculate the transmission lengh: like how many samples do I see with a high amplitude relative to the sample-rate. That's when the RF chip is active. I get 3,45 ms. So the difference between what I theoretically can assume as TX time, and what I see in reality is abnormally high. My questions: 1.) Can I use an Oscilloscope to find out whether there's signal on IF. The Oscilloscope operates on something like 100 MHz, so I want the down-scaled frequency. I read that the RF frontend down-scales to the ADC. I can pin-point the microcontroller with the chip. Can I also pin-point the USRP2 with the XCVR (or RFX)? I could correlate the state-changes of the RF Chip that way. 2.) I suspect the differences result from state-changes on the RF chip (PLL_ON -> TX). Is anybody aware of a similar performance analysis on Zigbee for real-time applications? As I stated out I'm not a hardware-expert. 3.) I use the Gnuradio Companion, and record from the USRP2 directly into a cfile. Is there any way to apply a filter to be able to automatically detect the start and end point of a high-amplitude that represents sending activity? I tried to use the integrator to lower the amplitude (I'm not interested in demodulation at this point, just tx start and end). But that doesn't work very well. I hope my terminology isn't too crude ;) Best, Marius _______________________________________________ Discuss-gnuradio mailing list [email protected] https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
