rssi | Ruby-like simple string interpolation for Node.js

1. How do I get the RSSI value (RSU side) from the message sent from a vehicle? Answer: Check: https://stackoverflow.com/a/54594801/7215379 has a similar Q & A.
2. How to send multiple messages from the same vehicle simultaneously? Answer: Are you talking about sending multiple copies of the same message or sending message of different type.

I figured out two bugs in my code.

1. I was calling startScanning() when centralManagerDidUpdateState() was called with central.state == .poweredOn. This causing scanning to start again right after calling myCentral.connect(connectedPeripheral!, options: nil)
2. Calling myCentral.stopScan() after myCentral.connect(connectedPeripheral!, options: nil) was causing disconnections

I don't understand why either of those were happening, but fixing them allowed me to now connect and get services and characteristics!

This may be a bug fixed in 12.3.

However, if possible, you should be scanning for your specific list of services rather than nil. Scanning for nil is generally only appropriate for general-purpose BLE scanners. I expect CoreBluetoth on macOS to continue to move towards the iOS approach, where scanning for nil service is very restricted, so if you don't need it, now would be a good time to remove it.

The rssi value is good for making signal strength comparisons between different nodes. The rssi value in typically given in dB, but with an arbitrary reference. You'd need a noise measurement in dB with the same reference to convert rssi to SNR -- something that is specific to the implementation of a modem or simulation model. For example, Subnero modems publish the noise value in the same units (but potentially a larger bandwidth) as phy.noise.

You can also use CoreBluetooth APIs to detect beacons, which give you a separate RSSI measurement for each packet detected. For a beacon advertising at 10 times per second, this would give you an RSSI update approximately every 100ms.

There are two big catches to using CoreBluetooth:

1. It cannot detect iBeacon because Apple blocks it. CoreBluetooth can detect AltBeacon and Eddystone.

2. The API is harder to use with beacons — you have to parse out the identifiers from the packets manually.

Also, be aware that the RSSI value returned by CoreLocation once per second is actually an average based on all packets received over the previous second, so it is more stable than individual samples taken at a higher frequency. Depending on what you want the samples for, you may find the higher variation is a problem.

Finally, be aware that the max rate at which you get samples with CoreBluetooth depends on the beacon transmission rate. Some beacons advertise only once per second. If you are working with such a beacon, you will not get any more samples with CoreBluetooth.

I found an answer. I had to add line:

I wouldn't call this noise, there is clearly a pattern. Since a myriad of factors can influence the received signal, one can only speculate without further information/measurements.

An example: Bluetooth LE uses three channels for advertising (37, 38 and 39) which are spread over the frequency band. Since the receiver can only receive on one channel at a time, the picture you showed could indicate that the deviations are caused by the different channels/frequencies that find completely different propagation paths in your environment.

The magic word is filtering. You have to average your RSSI measurements over a longer period of time and then use the obtained values to triangulate the position.

Bluetooth Low Energy was added to Bluetooth version 4.0. Since your device uses Bluetooth 3.0, it must be a Bluetooth Classic device.