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CC1100 RSSI / CS
I have two CC1100 nodes spaced some distance apart on my desk, transmitting at 315 MHz at -10 dBm, with 433 MHz antennas. I don't believe saturation could be an issue because of the low output power and mismatched antennas. I have also tried the same setup with CC1101 radios with the same results.
I am attempting to implement a manual duty cycling mechanism in software (long preamble transmissions for transmitters, energy based receive checks on the receivers). I can get it to work flawlessly with CC2500 radios, but the CC1100 radios are a different story: when a CC1100 radio wakes up in the presence of another transmitter, the carrier-sense line goes high and intermittently remains high (or toggles rapidly) even after nearby transmitters are gone. This CS line remains high until the node receives a valid packet or about 5+ seconds of waiting around. Because the node thinks there is a carrier on the channel when there isn't, I cannot transmit any packets or even go back to sleep in my custom low power communications strategy - the node thinks there's something on the channel it should stay awake for.
I started reporting RSSI values to see what was going on. The noise floor is about -45, and jumps to about 19 to 70 in the true presence of a transmitter. In the case where the carrier sense line gets stuck high even when there are no transmitters nearby, the RSSI readout stays at around -1, which is well above the noise floor so would be interpreted as valid energy on the channel. I observe with a spectrum analyzer there is nothing on the channel.
Ideally, I'd like the RSSI value to go back down to the noise floor when no transmitters are on the channel :) I've just had no luck in doing so. What work-arounds can I attmept to get the radio to read the "correct" RSSI value and unstick that CS line?
My AGC registers are setup as follows:
CC1100_AGCTRL2 = 0xC7, CC1100_AGCTRL1 = 0x20, CC1100_AGCTRL0 = 0xB0,
Hi there,Are you observing this on a TI reference design (CC110xEM), or is it just occuring on a custom design ?Cheers,RF4ALL
Yes - using TI eval modules. The problem occurs on both the CC1100EM and the CC1101EM, but not the CC2500EM.
By the way, I managed to sufficiently work around the problem, although it's not the most optimal solution.
In my CSMA implementation I'm sampling the CS line to see if there's energy on the channel. If the line is high, I then also check the preamble quality threshold and sync byte by reading PKTSTATUS. If the preamble quality threshold is low and no sync byte was found, I kick the radio into IDLE and back into RX mode. When the radio comes back up in RX mode, the CS line is typically correct and the RSSI values are back to the noise floor where they should be.
I am working on a cellular network project. I will use 5 cc1100 modules which I was designed up to reference design. There will be 3 base stations which will evaluted by just MSP430 AND CC1100. Then the othe two modules will have an extra LCD and keypad. Firstly, I need to calculate or check the signal strength. When my mobile wants to send data it has to know the strongest signal strength how I can do this. Please help me
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