Compatability:
Bluetooth Low Energy is not backward-compatible with the previous (often called "classic") Bluetooth Basic Rate/Enhanced Data Rate (BR/EDR) protocol. The Bluetooth 4.0 specification permits devices to implement either or both of the LE and BR/EDR systems.
Bluetooth Low Energy uses the same 2.4 GHz radio frequencies as classic Bluetooth, which allows dual-mode devices to share a single radio antenna. BLE does, however, use a simpler modulation system.