Receiving issue when I try to transmit same data from two cc1120

Darshan Belanke

Other Parts Discussed in Thread: CC430F5137, CC1120

Hi,

I have two devices one is transmitting every time and another is receiving every time.

Transmitter will transmit data every second. If there is only pair of Transmitter-Receiver then receiver is able to receive the same data every second.

But when multiple Transmitter and one receiver comes in picture, the receiver will receive once in 10-15 sec. Here the transmitted data on each TX remains same.

I am not able to get to the problem.

I am using CC1120 as transmitter and CC430F5137 as receiver.

over 10 years ago

0 TER over 10 years ago

TI__Guru**** 317180 points

If you use more than one transmitter on the same channel you have to ensure that only one is transmitting at a given time either by having a time multiplexed system or using CCA or LBT.

0 Darshan Belanke over 10 years ago in reply to TER

Prodigy 140 points

Thanks for reply TER.

I have a doubt :
As the same code is running on both TX.
What happens when we are trying to send same data at same time on multiple TX.

And do you have any sample code for time multiplexed system?

0 TER over 10 years ago in reply to Darshan Belanke

TI__Guru**** 317180 points

If more than one transmitter is on on the same channel at the same time the resulting signal will be impossible to demodulate. (Draw to equal waves on two pieces of paper and offset them slightly and add the two waves. You will get a wave form that does not look like the original)

The easiest is to implement CCA or LBT, see 6.11 and 6.12 in the CC112x UserGuide.

0 Darshan Belanke over 10 years ago in reply to TER

Prodigy 140 points

Hi Ter,

Imagine a scenario where two RX, X is kept between two TX i.e. A & B and Y is kept in range of only A.

If we try to use CCA, LBT then Y may not receive the signal.

0 TER over 10 years ago in reply to Darshan Belanke

TI__Guru**** 317180 points

Why? The only thing LBT does is to check that nobody else is sending before sending.

0 Darshan Belanke over 10 years ago in reply to TER

Prodigy 140 points

Actual requirement is we X/Y should receive data every time from A/B

Consider above scenario, X will receive either from A or from B. As A & B are out of range so both will transmit. But at receiver side i.e. X side we are facing issue.

Any suggestions?

0 Darshan Belanke over 10 years ago in reply to Darshan Belanke

Prodigy 140 points

Attached the picture for reference.

0 TER over 10 years ago in reply to Darshan Belanke

TI__Guru**** 317180 points

Thank for the drawing, I think I understand now what you mean.

Ideally the nodes should be time multiplexed but since A and B not "see" each other they will not be able sync. If A and B sends with random intervals the probability for transmission at the same time is small. In addition X and Y should send an ack when they have received a packet giving A and B to retransmit if required.

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Receiving issue when I try to transmit same data from two cc1120