4 Replies Latest reply on Nov 8, 2008 1:30 AM by vinay.dand

    Multiple CyFi in a building / hall

    vinay.dand
              Hello,   
         
      We have an application, in which, two trans-receiver are paired with unique address, master quering the slave for it's presence, say every one second or so. If link is broken due to one of the device forming the pair move out of RF link range (150 ft. line of sight - outdoor, reduced inside the building) then alarm action is activated.   
         
      We want to know, is it posiible to have 300 or more such pair operating inside same building or an hall area of 3000 sq. ft., with out interfering with each other's operation.   
         
      Both Master and slave will be battery operated and carried by two different persons, accomping each other.   
         
      Please suggest practical solution and applicability of CyFi in above application   
         
      Regards   
      Vinay Dand   
         
      Mumbai   
      electrocentre@vsnl.com   
         
        • 1. Re: Multiple CyFi in a building / hall
          content.librarian
                  Hi Vinay,   
             
          A master-slave pair in your application forms a single network. The question is how many networks can you fit in that space.   
             
          A CyFi network is differentiated from other CyFi networks using three parameters: its operating frequency, its pseudo-noise (PN) code, and its CRC seed. Doing some quick math, there are 78 channels to choose from, multiplied by 10 possible PN codes to choose from, is already 780 different networks, not counting differentiation from the different CRC seeds.   
             
          This means that yes, you can in fact have several hundred CyFi networks operating in close proximity without interfering with each other, especially if they are transmitting infrequently.   
             
          One issue you do have to keep in mind is that other 2.4-GHz sources in the vicinity will reduce the number of available channels, and thus also reduce the number of networks. But that will depend on how much activity you expect those interferers to have. For example, if you have three Wi-Fi networks, each occupying 22-MHz of bandwidth, totaling 66-MHz, then you only have 14-MHz left of clear spectrum to choose from. The truth is though, a CyFi network may still be able to operate on the same channel as a Wi-Fi network because its DSSS modulation can provide a first line of defense against interference.   
             
          As for applicability to this application, the one issue I see is that the Hub in a CyFi network is assumed to be a wall-powered device, because it must remain on all the time to receive data from Nodes in the network. How much battery life do you need?   
          • 2. Re: Multiple CyFi in a building / hall
            vinay.dand
                    Hello Hanna,   
               
            Thanks for prompt reply.   
               
            One trans-receiver out of one pair, do not have size and battery power restriction, as there is a 6volts, 1.5Ah battery available. We expect an eight hour operation. Hub can be implemented there.   
               
            Slave need to be thin with low power consumption, if possible, operting from a single 3v lithium cell or couple of NiMhcells!   
               
            As I have not studied the CyFi, is it possible to get approximate Hub implementation power consumption? (with no transmission activity, only waiting in receive mode and discriminating between signals from adjacent hubs and other non CyFi networks (Wi-Fi) till own network slave is recognised).   
               
            Meanwhile, let me download all relavent documents etc. and study them. We are also considering Chipcon RF solution (TI) or modules from RFM.   
               
            Regards   
            Vinay   
            • 3. Re: Multiple CyFi in a building / hall
              content.librarian
                      Hi Vinay,   
                 
              A Hub that is always listening means that the CyFi transceiver would be constantly in receive mode, which consumes 22mA.   
                 
              Have you taken the CyFi training on www.cypress.com/training? If not, I would highly recommend that you do so. The CyFi 101 and CyFi 102 courses will answer a lot of these questions.   
              • 4. Re: Multiple CyFi in a building / hall
                vinay.dand
                        Thanks,   
                   
                You have got me hooked on CyFi. Our team will study them on this weekend.   
                   
                Regards   
                Vinay