Difference between revisions of "Smartphone Wireless"

Revision as of 10:22, 23 May 2021

Full Title or Meme

There are a large number of radios on a Smartphone. This wiki looks at those that are not part of the cellular network.

Context

Terminology

• RF = Radio Frequency
• HF = High Frequency
• UHF = Ultra High Frequency
• IR = Infrared - typically read by a IR sensor, but can also be an IR camera
• Light is even higher, but that is handled by the camera and not radios
• Exciter = an antenna that is designed to send energy to a passive RFID tag

Existing Bands

The distance measures here are for a "smart chip" to an antenna tuned to find and query the chip.

RFID

RF Identifier

• Passive = no battery, typically a tag applied to a inventory item - read range has been 12-15 originally now 30+ feet
• Battery Assisted Passive = typically a monitored sensor that is polled by RF
• Active = has battery and dual antenna - read range 300 feet
• Low Frequency 120 to 150 kHz. - near touch scanning
• HF/NFC 13.56 MHz - range in centimeters
• UHF = 300 MHz to 3 GHz - older
• UHF Gen2 = 860 to 960 MHz - range several meters (works through rain)

NFC

Near Field Communications

• Apple Pay
• Android Pay
• Smart card with build in antenna
• 13.56 MHz
• widely held limit of one meter can be extended.

BLE

Bluetooth low energy + battery powered

• Also excited by a stationary antenna that causes the smartphone to respond
• Needs to have an app on a smartphone that is powered up and has bluetooth enabled that responds to the message with a UUID
• Operations at 2.4 GHz at about 70 meters between device and antenna.
• It is easy to test the range of BLE by seeing how far away from the the phone an ear bud will work. Typically that is about one room away.
• Here is some raw data on testing BLE
• BLE connections may be used in ISO 18013-5 between mDL and reader, but security sessions are not required. The mDL can enable either peripheral or central roles.

WiFi

• Generally used for local internet connections. Can also be enabled by one of the above to send a UUID.
• Originally just used 2.4 GHz now also uses 5 GHz

It can be seen that the 2.4 GHz band is widely used for other applications including microwave ovens (as a result of the signal absorption in water) as well as Bluetooth, and many other wireless communications applications. Sometimes using other bands can improve the WLAN performance as a result of the lower interference levels.

Use Cases

Contact Tracing

uses Bluetooth as it’s the most widely available technology. Bluetooth Low Energy devices are designed to be always on and, as the name implies, use very little battery. Depending on the scenario you can add in extra power management tricks. i.e. if there’s no accelerometer changes for many minutes, or contacts are constant, then you’re probably at home in bed, so check much less often for ‘contacts’. Wearables take this approach for example. Depending if you’re trying to “accurately measure risk” or “detect a contact or not” determines the level of data you need, and thus your scanning frequency. Generally though these apps will register a ‘background service’ - this enables the app user interface and non-bluetooth components to be removed from memory, and only the network contacts/logging to operate. This saves battery consumption. 1-2% battery per hour, depending on age of device, is usual. That’s approx half the battery use of WhatsApp just sitting in the background!

References