Dual antenna with nrf51822 to detect exact position of BLE device

[jitu]

I am working on a device where i need to sense proximity of a smart phone and then judge its exact position and then take action depending on the position. Below is my theoretical solution...

the two antennas in the diagram can be switched using a RF switch and then RSSI values can be measured from the two antennas and after comparing the value an estimate can be made about the position of the smart phone.The antenna rf pattern is such that there is a difference RSSI values when measured from outside or inside for an antenna.

I want to know if this technique will work or any suggestions and is there any support in the BLE soft devices for such a technique?

[endnode]

Yes, it will work (= it works). Just be careful, there are already bunch of patents around such solution. Unless you don't care...

[FormerMember]

From what I can see, this question consists of two parts:

1. How to control the RF switching.
2. How to use BLE in this scenario.

RF switching: You will want to switch between the two antennas before a RX event.

nRF51: Radio notifications can be used to konw whether the radio is being used or not, using a software interrupt; it will send an ACTIVE signal prior to a radio event, and a nACTIVE signal after a radio event. The ACTIVE signal will tell you if a radio event is coming up, however, you cannot know whether it is a TX or RX event. To distinguish between TX and RX events, you will have to use the VDD_PA pin. VDD_PA will go to 1.8 V 130 us before a TX operation starts. Note that a radio event can consist of multiple RX and TX.

nRF52: With the softdevice S132 it is possible to use the LNA configuration to control the RF switching; it will toggle a GPIO to know when to turn on/off a LNA. In your case, you can use this information to switch between the two antennas.

The LNA configuration is enabled using sd_ble_opt_set(..) with the option BLE_COMMON_OPT_PA_LNA and configuration parameters of the type ble_opt_t -> common_opt --> pa_lna (ble_common_opt_pa_lna_t)

BLE: If the nRF5 device is in a connection with a smart phone, it can alternate between the two antennas between connection each events, each connection interval. In BLE, the central/master has to transmit a packet each connection interval.

[Chris Fog]

@endnode, how would I search for those patents? We are also looking at a similar solution! I googled without success.

[endnode]

Hi Chris, patent search is discipline on its own (which gives business to various lawyers and other free-loaders) and I cannot advice on that as I'm luckily not in charge of it in our group. However just by simple look it should be evident that trying to patent this in 2016 is coming like 2-10 years after the party. Here is one example from locksmith/access control business, it should lead to many older applications not by this company only: www.freshpatents.com/-dt20130711ptan20130176107.php

Cheers Jan

[Chris Fog]

@endnode: Thanks! We met with Philip Dumas from Unikey last week, and are considering using them as a supplier :)