BLE Range Claims Measured against Real Link Budgets
Real Bluetooth range requires subtracting antenna detuning, body loss, and indoor path loss exponents from marketing budgets before ordering silicon.
Human Body Loss
Meaning
Wireless signal attenuation occurs when a transmitter or antenna is placed in close proximity to organic tissue. To account for human body loss, product engineers must measure how much electromagnetic energy is absorbed by organic tissue during normal device operation. This attenuation is a major factor in the design of wearable smart sensors and wrist-worn tracking devices.
Radiation Pattern
Proximity to organic tissue alters the direction and strength of the radio signals emitted by an antenna. To characterize human body loss, engineers use phantom body models in anechoic chambers to map the changes in the antenna radiation lobes. The body acts as a reflector and absorber, which dampens the signal in certain directions.
This distortion can lead to intermittent connectivity when the wearable is positioned away from the receiver.
Antenna Tuning
Electrical impedance of the antenna shifts when placed against the skin, which detunes the radio frequency circuit. When managing human body loss, developers often employ dynamic tuning circuits to adjust the impedance of the antenna on the fly. This adjustment prevents the transmitter from reflecting power back into the radio frequency amplifier, which would cause overheating.
By using adaptive matching networks, the system maintains its radiated output power even when the device is handled. This active mitigation is tested extensively during the prototype evaluation phase.
Power Budget
Compensating for signal absorption requires a clear understanding of the maximum power limits allowed by safety regulations. Factoring in human body loss ensures that the battery can support the higher output power required to maintain a connection. This extra power consumption reduces the overall battery life of the smart device.