6 Replies Latest reply on Jun 22, 2018 7:45 AM by LJYe_2922526

    BLE scan rssi with CYW20706

    LJYe_2922526

      Hi forum experts,

       

      I'm using CYW20706 to scan for BLE beacons, and I'm noticing the RSSI value provided by the stack changes erratically between +93 and -38.

       

      Beacon[0], id=1369100000, batt=0, power=5, zone=88, rssi=-32

      Beacon[0], id=1369100000, batt=0, power=5, zone=88, rssi=-36

      Beacon[0], id=1369100000, batt=0, power=5, zone=88, rssi=-33

      Beacon[0], id=1369100000, batt=0, power=5, zone=88, rssi=-36

      Beacon[0], id=1369100000, batt=0, power=5, zone=88, rssi=90

      Beacon[0], id=1369100000, batt=0, power=5, zone=88, rssi=90

      Beacon[0], id=1369100000, batt=0, power=5, zone=88, rssi=-32

       

      I use the wiced_bt_ble_scan() API, and in my wiced_bt_ble_scan_result_cback_t callback hander, I'm printing the 'rssi' field in the provided wiced_bt_ble_scan_results_t directly.

       

      Is this behavior expected?

       

      Thanks!

        • 1. Re: BLE scan rssi with CYW20706
          ZhengbaoZ_96

          Hi  LJ:

           

              what is your test environment now?  for the issue clarification, the best test environment is:

          1.  test with a conductive antenna, this will has a very accurate results about the signal

          2.   if test the environment on the air,  please test it with a open area which has less reflections.

          1 of 1 people found this helpful
          • 2. Re: BLE scan rssi with CYW20706
            ZhengbaoZ_96

            Hi Lj:

             

               Actually, I can duplicate this RSSI issue in 20706 demo.   and did a lot of tests like setting the high duty adv into indefinite mode in slave side.

            but only can reduce the ratio for the wrong value.   but find the regular :

            1. The wrong value is always a positive value which is not reasonable in user cases,   we can ignore it .

            2.  the actual rssi value like -50 ,-56, -60,  fluctuate in a normal range .

             

            so if you need to collect the rssi value , please ignore the positive value , thanks.

            • 3. Re: BLE scan rssi with CYW20706
              LJYe_2922526

              Hi zhez,

               

              We use the RSSI value to estimate location(20706 act as a BLE beacon scanner), so dropping the beacon kind of defeats the purpose.

               

              Questions:

              1) Is it possible to find out the max possible valid RSSI? I think I've seen -25. Reason I'm asking is I'm only seeing positive values when the scanner is very very close to the source, (maybe the radio is getting saturated somehow at this point?), and I can simply treat anything above -25 as -25.

              2) Could you check the BLE stack source code and see if there is any sign extension bug (If I change 7th bit of 90 to 1, it becomes -38)? If this is the issue we can simply fix it in my app code for now

              3) Can we expect a bug fix in the next patch? When is next patch roughly?

               

              Thanks!

              • 4. Re: BLE scan rssi with CYW20706
                ZhengbaoZ_96

                Hi LJ:

                 

                sorry for reply late, Actually , we are looking into this issue .   but really need more time to have a fix.

                and When the rssi is going to be a positive value , it means the distance is very close, that is just as you described .

                So I think you can judge the distance according the value captured..  

                1 of 1 people found this helpful
                • 5. Re: BLE scan rssi with CYW20706
                  LJYe_2922526

                  Hey zhez,

                   

                  We are pretty convinced that the issue is just a missing sign bit. We often see sequence like -37, -37, -38, 90, -38, -37, 89, -39.... And if we just add the sign bit back in, it becomes -37, -37, -38, *-38*, -38, -37, *-39*, -39...., which looks very reasonable.

                   

                  For now we are going to add the bit in our firmware and we look forward to an official fix.

                   

                  Thanks.

                  • 6. Re: BLE scan rssi with CYW20706
                    LJYe_2922526

                    Also just as a guess, I saw a define for 0x7F as invalid RSSI values. Maybe somehow the stack & it with 0x7F when it wanted to set it to 0x7F? Just a guess.