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How to listen to multiple RF transmissions at once

Former Member

I'm trying to build a small scale internal GPS of sorts, for tracking people inside an empty room as a prototype. The plan is that each person will have a receiver on them and there will be multiple transmitters (from the same device/controller) around the room that will communicate with the receivers in order to calculate the persons location by working out the distance between them like GPS does.

 

The problem I'm currently having is trying to work out how transmission should work. Since there are going to be multiple transmitters I think I'd like them to communicate on separate frequencies/channels to avoid collisions between them, is this possible with only one receiver per person?

 

I did wonder whether it was possible to get the receiver to listen on a large bandwidth picking up all the channels that the transmitters are transmitting on then it might be possible to filter out the data for each transmitter. Is this something that might work or would it just have the same collision issues as having transmitters on the same frequency and channel?

 

Any help on this issue would be extremely useful, many thanks :-)

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    This is called a real time location system (RTLS).  I know only the basics about them.  I know the simplest ones operate on received signal strength indication (RSSI).  You can walk around the area with the RTLS transmitter and record the RSSI values at all the fixed receivers.  When you see that "signature" of RSSI's, you know roughly where the transmitter is.  It's good enough to tell which room someone's in.  More sophisticated systems operate like GPS based on the time delay.  I don't know much about them.

     

    It is very common for multiple wireless devices to following one another along a hopping sequence.  Hopping makes it easier to comply with FCC rules on the ISM bands.  You could get an eval board that uses BLE or Zigbee.  If it needs to be a custom protocol, which probably means more work for you, you could the CC430 series from TI, which have a whole radio built into a chip that has a small embedded processor.  One chip can run your application and do communication, while sleeping and pulling a few uA most of the time.  They make good eval boards in the form factor of a key fob, wrist watch, etc. 

     

    Don't get hung up on frequency and physical layer.  You don't want to rely on separate frequencies to keep communications channels separate.  You want to rely on the multiple access scheme that comes with a standard.  The idea of a board band receiver listening to multiple signals at once is certainly possible.  It's what software defined radio (SDR) is about.  You sample the IF and pull out the individual msg signals in software.  That's fine, but as the bandwidth you sample increases, dynamic range becomes an issue.  You should not have to dig into these nuts-and-bolts physical layer issues.

     

    I would instead find an eval board that already does some of what you want with the test code and try to modify their stuff.