PHY

Wireless rates change. A device may use a high rate near the AP and fall back near the coverage edge. BLE can choose between 1M PHY, 2M PHY, and LE Coded PHY. NB-IoT accepts low speed to improve coverage and power behavior.

The underlying issue is not simply “strong signal is fast, weak signal is slow.” PHY, modulation, and coding make the same trade-off: how much useful information can be carried with the current channel condition, and how much failure risk is acceptable.

A device can sit next to a router and report 866 Mbps, while real application throughput is only a few hundred megabits or less. BLE has the same trap: the PHY may say 2M, but GATT notifications do not deliver 2 Mbps of application data. The gap is not always marketing abuse. Bandwidth, rate, and throughput are different layers.

The common mistake is treating a larger advertised rate as a promise that application data will arrive at that speed.