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I was wondering if there was a way that I could detect the exact frequency of a BLE signal with an iphone. I know it will be in the 2.4 GHz range but i would like to know the difference down to the 1 Hz range between the transmitted frequency and the received frequency. The difference would be caused by the doppler effect meaning that the central or the peripheral would have to be moving. Also is there an exact frequency that iphones transmit BLE at or does it depend on the iphone's antenna?
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Bluetooth operates at frequencies between 2.402 and 2.480 GHz, or 2.400 and 2.4835 GHz, including guard bands 2 MHz wide at the bottom end and 3.5 MHz wide at the top.
Bluetooth uses 2.4 GHz. Bluetooth is a standard wireless communication protocol. It's a "language" that lets multiple devices talk to each other wirelessly. Bluetooth protocols use the 2.4 GHz as the method to transmit or communicate that language between the devices.
Indoors, obstacles like concrete walls will attenuate the radio signal and the effective range will be drastically reduced. In normal use, ten meters is a good guide to what can be achieved between two Bluetooth devices indoors.
The signal strength is typically expressed in units of dBm, which is the logarithm of the power in milliwatts with a reference level of 1 milliwatt (mW). In Wi-Fi and Bluetooth chipsets the signal power is converted to an integer value known as the Received Signal Strength Indication (RSSI) and is used internally.
Bluetooth doesn't have one particular frequency it operates on. Via bluetooth.com:
Bluetooth technology operates in the unlicensed industrial, scientific and medical (ISM) band at 2.4 to 2.485 GHz, using a spread spectrum, frequency hopping, full-duplex signal at a nominal rate of 1600 hops/sec.
… adaptive hopping among 79 frequencies at 1 MHz intervals gives a high degree of interference immunity and also allows for more efficient transmission within the spectrum.
So there'll be a wide spread of frequencies in use for even a single connection to a single device. There's hardware on the market like the Ubertooth that can do packet captures and spectrum analysis.
To my knowledge, iOS doesn't offer API to find out this information. OS X does at some level, probably via SPI or an IOBluetooth API, because Apple's Hardware Tools (search for "Bluetooth") offer a way to monitor spectrum usage of Bluetooth Classic devices on OS X.
As to your desire to detect movement via the Doppler effect on the radios, my instincts say that it's going to be very, very difficult to do. I'm not sure what the exact mathematics behind it would look like, but you'll want to examine what the Doppler effect on a transmission at 2.4 GHz would be as a result of low-to-moderate rates of motion. (A higher rate of motion or relative speed, say, over a few tens of miles an hour, will be quickly make Bluetooth the wrong radio technology to use because of its low transmit power.)
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