There’s a paper by Mariusz Kaczmarek, Jacek Ruminski and Adam Bujnowski of Gdansk University of Technology on the Accuracy analysis of the RSSI BLE SensorTag signal for indoor localization purposes (pdf).
They studied the radio signal from multiple Texas Instruments SensorTag CC2650 devices in order to determine if it could be used to determine location.
“Given the large number of factors governing the received RSSI, calibration is unlikely to be able to compensate for all of
them, leading us to conclude that there is an inherent limit to the accuracy of a BLE positioning system especially when multiple devices are used.”
…that instead of using a single RSSI measurement to estimate distance, try using the average or median value of N measurements collected on the same spot (at least N>20) so that you can reduce the effect of small scale fading.
The type of System on a Chip (SoC) can greatly affect beacon battery life. At one time it was only Dialog that had low power SoCs. TI, NXP and Nordic followed and now Toshiba has joined them with their new TC35678FSG, TC35678FXG and TC35679FSG (PDF).
Toshiba has more information on these products.
The BeaconZone store has a special category for low power SoC beacons.
We have been looking into the TI CC2640 SoC used in our latest PC062 beacon. The main advantage of the TI CC2640 is exceptional battery life. However, the CC2640 specification provides added features that we expect to be utilised in feature beacons.
The CC2640 has 3 processor cores so that the application (M3 core) and Bluetooth stack (M0 core) can run separately. Previously, they both ran on the same core preventing the beacon from doing additional CPU intensive tasks such as WiFi. The third core (SCE) deals with sensors/peripherals allowing the main core to spend longer time sleeping thus saving power.
Hence, in the near future we expect beacons to become much more capable, for example supporting multiple wireless protocols. IoT sensor beacons will also be able to be produced that will still able to be extra low power despite the extra sensors.
You can find the processor chip in the specification section of our beacon descriptions. Most people don’t know what this means or implies. This article will hopefully help you make a more informed choice and provide some insights into what’s coming in the near future.
There are currently three main chip families from Texas Instruments (CC254x), Dialog (DA14580) and Nordic (nrf51822). These chip manufacturers publish standard electronic circuit and printed circuit board layouts that beacon OEMs use for their beacons. Hence, most beacons, within a chip family, have very similar designs. However, small differences in implementation of board layout in areas such as the power supply, grounding, terminations, connectors and the antenna can cause electrical differences that can cause loss of power or noise that can affect operation. Hence the quality of the beacon radio signal is affected more by the quality of the implementation than the choice of chip. This is also evident in real world tests. We have performed RSSI strength and stability tests on the beacons we sell and haven’t yet found any correlation between signal quality and chip family.
The CPU type does significantly affect battery use. For the same transmit power and advertising interval configuration, the Dialog DA14580 provides 2x to 3x battery life of Nordic nrf51822 based (e.g. Estimote) beacons and up to x6 the battery life of TI CC254x based-beacons.
However, chip families are evolving ecosystems and there are also new contenders. In our talks with manufacturers, we know that the newer TI CC2640 is being used in new beacon designs and will provide a x3.5 battery life, at a compromise of a slightly reduced signal range, compared to the CC254x. NXP (used be part of Philips Semiconductors) also have the QN9020 that provides x3.5 battery power compared to the TI CC254x. We’ll be stocking beacons with these new processors in the near future.