ASK and FSK transmission on same channel

To be able to demodulate an incoming RF signal the CC1101 needs a given SNR. If a different device is sending on the same channel at the same time CC1101 will not be able to decode if the other signal is not much weaker than the signal you want to demodulate.

One way to get around this is by using LBT (listen before talk). The sensors should check if the channel is free before sending the data. Also by using a two way system sending ack the sensor will know if the data was received or not.

TER said:

To be able to demodulate an incoming RF signal the CC1101 needs a given SNR. If a different device is sending on the same channel at the same time CC1101 will not be able to decode if the other signal is not much weaker than the signal you want to demodulate.

Even if one device is using ASK and the other device FSK? The sensors are sending on 433,92Mhz +- 28Khz and the disturbing device (in this case a crane remote controll) ist sending just on 433,92Mhz. So they are not using the same frequency. Does 433,92Mhz has to be free if the data is transmitted on 433,92+-28Khz, when using FSK?

TER said:

One way to get around this is by using LBT (listen before talk). The sensors should check if the channel is free before sending the data. Also by using a two way system sending ack the sensor will know if the data was received or not.

If you look at the spectrum for FSK and ASK you will see that the ASK spectrum is fairly wide and have a fair amount of energy even at +/- 28 kHz offset.

I understand that you can't do something with the interfering device but if you implement LBT on your sensors you will avoid sending data when you have something else on the air.

TER said:

If you look at the spectrum for FSK and ASK you will see that the ASK spectrum is fairly wide and have a fair amount of energy even at +/- 28 kHz offset.

First i have to correct something, the deviation is about 41Khz. I attached an image containing a waterfall diagram. There seems to be not much energy at +/- 41kHz offset. However when the disturbing signal appears, i do not receive any data from the sensors.

Here my register configuration. Maybe you see something wrong.

0x0D,  // IOCFG2              GDO2 Output Pin Configuration
    0x2E,  // IOCFG1              GDO1 Output Pin Configuration
    0x0D,  // IOCFG0              GDO0 Output Pin Configuration
    0x47,  // FIFOTHR             RX FIFO and TX FIFO Thresholds
    0xD3,  // SYNC1               Sync Word, High Byte
    0x91,  // SYNC0               Sync Word, Low Byte
    0xFF,  // PKTLEN              Packet Length
    0x04,  // PKTCTRL1            Packet Automation Control
    0x32,  // PKTCTRL0            Packet Automation Control
    0x00,  // ADDR                Device Address
    0x00,  // CHANNR              Channel Number
    0x06,  // FSCTRL1             Frequency Synthesizer Control
    0x00,  // FSCTRL0             Frequency Synthesizer Control
    0x10,  // FREQ2               Frequency Control Word, High Byte
    0xB0,  // FREQ1               Frequency Control Word, Middle Byte
    0x71,  // FREQ0               Frequency Control Word, Low Byte
    0xB9,  // MDMCFG4             Modem Configuration
    0x93,  // MDMCFG3             Modem Configuration
    0x00,  // MDMCFG2             Modem Configuration
    0x22,  // MDMCFG1             Modem Configuration
    0xF8,  // MDMCFG0             Modem Configuration
    0x45,  // DEVIATN             Modem Deviation Setting
    0x07,  // MCSM2               Main Radio Control State Machine Configuration
    0x30,  // MCSM1               Main Radio Control State Machine Configuration
    0x18,  // MCSM0               Main Radio Control State Machine Configuration
    0x16,  // FOCCFG              Frequency Offset Compensation Configuration
    0x6C,  // BSCFG               Bit Synchronization Configuration
    0x43,  // AGCCTRL2            AGC Control
    0x40,  // AGCCTRL1            AGC Control
    0x91,  // AGCCTRL0            AGC Control
    0x87,  // WOREVT1             High Byte Event0 Timeout
    0x6B,  // WOREVT0             Low Byte Event0 Timeout
    0xFB,  // WORCTRL             Wake On Radio Control
    0x56,  // FREND1              Front End RX Configuration
    0x10,  // FREND0              Front End TX Configuration
    0xE9,  // FSCAL3              Frequency Synthesizer Calibration
    0x2A,  // FSCAL2              Frequency Synthesizer Calibration
    0x00,  // FSCAL1              Frequency Synthesizer Calibration
    0x1F,  // FSCAL0              Frequency Synthesizer Calibration
    0x41,  // RCCTRL1             RC Oscillator Configuration
    0x00,  // RCCTRL0  
    0x59,
    0x7F,
    0x3F,
    0x81,
    0x35,
    0x09,	

TER said:

I understand that you can't do something with the interfering device but if you implement LBT on your sensors you will avoid sending data when you have something else on the air.

The disturbing signal is continuous and appears for a pretty long time, so the sensors would just listen and send nothing, but they have to send updates in short intervalls.