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multiple transmissions approximately at the same time received by one CC1120

Harry
Expert 2920 points
Other Parts Discussed in Thread: CC1190, CC1120

I am using a TrxEB development board along with a CC1120 + CC1190 on carrier frequency 868MHz, RX filter bandwidth 25KHz, modulation format 2-FSK, 1.2Kbps bit rate, 10dBm output power, with all sync registers set to D3 91 D3 91 in SYNC 3,2,1,0 registers respectively on all boards. 

I have a have a scenario I would like to know the expected output for. 

Suppose there are 10 transmitters set to the said configurations and one single receiver. If all ten CC1120s transmit at the same time ten different packets,  would the receiver receives the packets? would it receive partially some packets? would all packets be useless as they shared the same channel; 868 MHz? 

I would so much appreciate an explanation if possible.

Thank you . 

  • 0
    TI__Guru**** 317180 points
    The receiver will not receive anything (or just noise)

    You will see why if you try to draw 10 different wave on top of each other with a small timelag between them. In the resulting drawing you won't be able to recognize any of the original waves, with luck just some partial bits.
  • 0 in reply to TER
    Expert 2920 points
    Thank you TER.

    Question 1 :

    Is there a way I could have transmissions by multiple transmitters and still recover the message ?
    Is it only possible if I tune a receiver and a transmitter to the same exact channel and no one else transmits with high enough power to superimpose with my packet? Would OFDM play a role in this scenario?

    If I need to have multiple transmissions at the same time using CC1120 how do you advice I solve this issue? How many maximum transmissions would I be able to have? (at least using different channels). My data rate is 1.2kbps.

    Question 2 :

    If I am to transmit on a channel a receiver is not yet tuned into, is there at the receiver end to guess the transmission frequency at the time sensing the packet in the air and still fully receive the packet? My problem is, If I do not know on which channel a transmitter transmits, what would be the fastest/easiest to receive a message from such a transmitter?

    please be kind enough to shred some of your knowledge regard to this matter.
  • 0 in reply to Harry
    Expert 1740 points

    Question 2:

    If your transmitters have long enough preamble and transmit on 10 different frequencies, receiver could scans all possible channels during preamble and eventually to get packet on the channel with best signal strength. 

  • 0 in reply to Harry
    TI__Guru**** 317180 points
    Q1: Regulations normally don't let you send with more than one transmitter in a channel. Implement CCA or LBT (see 6.11 and 6.12 in www.ti.com/.../swru295e.pdf)
  • 0 in reply to TER
    Expert 2920 points

    for the large number of nodes my network will have, I guess I'm left with only one option. That is to allow any node to talk to any other node by transmitting through any channel; I just have to make sure that all nodes are listening in to all channels around 868MHz.

    i.e. If there are 10 channels, a node wanting to talk to node "J" will transmit through any "free" channel and expect its expected receiver node "K" to capture its request and tune into that frequency and receive rest of the full data or continue the conversation. I hope my idea is correct and this option is supported by CC1120+CC1190 combination.

    I apologize if answers seem obvious on users guide. I am 12 days away from submission of a long project document in which I am supposed to roughly explain an algorithm. I can only expect to get married to the swru295 in next month.

    Thank you TER and Oleg for your support and time.