NB-IoT: 10 Anos en Papel, 18 Meses Real
· 7 min read · Technical Whitepapers
Huawei: 2 anos teoricos -> 6 meses reales. Registro de red es la brecha.
Las matematicas del marketing: bateria 5 Wh, corriente de sueno PSM 3 µA, 1 transmision por dia a 200 mJ. Resultado: 10.2 anos. Las matematicas de campo: misma bateria, mismo dispositivo, pero la red sobrescribe el temporizador PSM a 10 segundos. El dispositivo se vuelve a conectar desde cero 4 veces al dia. Cada reconexion quema 100-200 mA·s — equivalente a 12 horas de presupuesto de sueno PSM. El dispositivo muere en 18 meses.
Las Matematicas de Bateria Corregidas
Un solo evento de registro de red NB-IoT consume 100-200 mA·s. A 3 µA de sueno PSM, eso equivale a 9-18 horas de presupuesto de sueno. Si la sesion persiste: energia diaria ~5,736 mJ. Si la sesion se corta en cada transmision (24 reconexiones): ~10,536 mJ — un aumento del 84%.
Los Comandos AT Que Realmente Activan PSM
PSM no esta activo automaticamente. Tres comandos AT deben enviarse. La red puede sobrescribir los valores solicitados. La unica forma de verificar el comportamiento PSM real es medir el consumo de corriente en la bateria con una herramienta como Otii Arc durante un ciclo completo de transmision+sueno.
Preguntas frecuentes
Why does my NB-IoT device die in 18 months when the datasheet says 10 years?
The datasheet assumes: PSM sleep at 3 µA, session persists between transmissions, signal is strong, and the network honors the device's requested PSM timer values. In the field: PSM is often overridden by the network to 10 seconds, the session drops between transmissions, the device re-attaches 4-24 times per day, and each re-attach burns 100-200 mA·s — equivalent to hours of sleep budget. The gap is carrier configuration, not hardware.
How do I verify that PSM is actually active on my device?
Do not trust AT command acknowledgments. Measure current draw at the battery with a tool like Otii Arc (100 nA resolution). Send AT+CPSMS to request PSM. Wait for the device to enter sleep. If the measured current is above 10 µA, the device is in idle — not PSM sleep. The network may have overridden the requested timer values or the module firmware may not support the specific PSM configuration the network granted.
PSM or eDRX — which saves more battery?
PSM saves more — sleep current <5 µA vs 50-200 µA for eDRX. But PSM makes the device unreachable during sleep. eDRX keeps the device reachable within a known wake window. Use both: eDRX for the post-transmission listening period (so the server can reach the device if needed), then PSM for deep hibernation until the next scheduled transmission.