The figure above shows WiPry-Combo Spectrum Analyzer measuring the frequency-hopping signal from a Jawbone Bluetooth earpiece. Since the earpiece did not pair with another device, it continued transmitting the pairing initiation signals that are captured on the iPod’s display. WiPry’s Heat Map view shows frequencies where the earpiece hopped, the duration at each frequency, and the transmit power level.
Typical Bluetooth Radio & Modulation
There’s a lot of work required to convert digital ones and zeroes into the 1 MHz-wide RF pulses. Here are some Bluetooth radio basics and interesting specifications:
- Bluetooth devices operate in Master/Slave pairs
- Communication between devices occurs in time slots of 625 us
- The master device transmits on the odd number 625 us time slots
- The slave device transmits on the even number 625 us time slots
- Receiver sensitivity: -70 dBm @ 0.1% Bit Error Rate (BER)
- Transmit power: 0 dBm typical, up to +20 dBm with power control
- Modulation types (converting bits into symbols)
- Gaussian Frequency-Shift Keying (GFSK)
- Differential Phase-Shift Keying (DPSK)
Frequency-Hopping shown in WiPry-Combo Spectrum Analyzer's Heat Map
Modulation in the Frequency Domain
Modulation in the Time Domain
Whitepaper On Pulse Shaping In Modulation
This is a terrific white paper about pulse shaping. Making a rectangular pulse look more like a Gaussian curve reduces the power spectrum. A SIMPLE SIGNAL SHAPER FOR GMSK/GFSK AND MSK MODULATOR BASED ON SIGMA-DELTA LOOK-UP TABLE Tomislav SVEDEK Marijan HERCEG Tomislav MATIC Department of Communicationr, Faculty of Engineering J.J. Strossmayer University of Osijek Osijek, Croatia Published in Radio Engineering, Vol. 18, No. 2, June 2009
WhitePaper_Simple_Signal_Shaper_GFSK.pdf