Selecting Cellular Radio Protocols for Cross-Border Asset Trackers
Select LTE Cat-M1 for balanced mobility and power, or Cat 1bis for universal global roaming at the cost of higher battery capacity.
Desensitization
Meaning
Interference phenomenon where the sensitivity of a radio receiver is reduced by the presence of high-power signals from nearby transmitters. Receiver desensitization occurs when noise floor levels rise because an internal transmitter operates in close physical proximity to a sensitive receiving antenna. This coupling of electromagnetic energy effectively masks low-power signals that the device would otherwise capture easily.
Interference Mechanism
Radiant energy from local oscillators or power amplifiers leaks into the sensitive reception path of a co-located radio module. While a system typically operates within its own frequency band, harmonics and wideband noise from a cellular modem can overlap with the narrow window of a global positioning system receiver. This interaction lowers the signal to noise ratio until the receiver can no longer distinguish the intended data from the background interference.
Mitigation Strategy
Physical separation of traces on the printed circuit board and the addition of metal shielding cans help reduce the coupling between the noisy and sensitive sections. High-performance band-pass filters are installed at the antenna port to block out-of-band energy that contributes to the desensitization effect during simultaneous operation. A receiver that usually detects weak signals at negative 110 dBm might only see them at negative 98 dBm when the local cellular modem is active at full power, creating a performance gap that must be closed through careful component placement and trace isolation.
System Verification
Final product testing includes radiated measurements to ensure that the cellular and navigation radios operate together without losing signal locks. These tests measure the total isotropic sensitivity of the device while all internal transmitters are active. The results confirm that the mechanical enclosure and board layout prevent the desensitization from reaching levels that would trigger a service disconnect.