There are many factors that make BLE low power, and I have attempted to address as many of them as possible. In order to better understand the power consumption differences between Bluetooth classic and BLE, it would helpful to look at some of the differences between the Bluetooth technologies. This would help appreciate the difference in power consumption. For starter Bluetooth classic consist of Bluetooth 1.0-3.0. These include Bluetooth BR (Basic Rate) round 1.2Mbit/sec, Bluetooth EDR (Enhance Data Rate) at 3Mbits/Sec and Bluetooth HS. Bluetooth operates in 2.4 GHz ISM band, with Bluetooth classic uses 79 channels from 2.4GHz to 2.4835 GHz each spaced 1Hhz apart whereas BLE uses 40 channels from 2.402 GHz 2.480 GHz each spaced 2MHz apart. Of the 40 channels 3 of them are dedicated to advertising requests. Initial parameters are exchanged using same channel used for the connection request. Upon successful discover and connection, regular data channels are used for communication. Also note that advertising channels don’t overlap with Wifi [Direct-sequence spread spectrum (DSSS)][1] channels 1, 6, and 11. So Bluetooth uses a 2.4 GHz frequency band but implements a simpler Gaussian Frequency Shifting Protocol to **reduce power** as well as DSSS modulation. [![advertising and data channels][2]][2] [![Bluetooth LE channel arrangements][3]][3] BLE has many different modes of which the main modes of operation are advertising mode, scanning mode, master device, and slave device. In the advertising mode the BLE base device will receive responses from other BLE devices for advertising events. On the scan mode the BLE device will scan for advertising request from other BLE devices and will respond with additional information depend on the status of the active scan status. There is also the passive mode, scanner only as well as advertiser only in which case the receiver and transmitter function of the RF module is required respectively. Some understanding of the Link Layer State machine is beneficial to understanding management of **power consumption**. There are five states and they are 1. **Standby**: Can be entered into from any other state and no transmitting or receiving packets 2. **Advertising**: This state can be entered from standby state. In this state the link layer will be transmitting advertising packets as well as responding to advertising related data exchanges 3. **Scanning**: Scanning state can be entered from standby state, which listens for advertising channel packets from devices 4. **Initiating**: The link layer in this state initiates a connection with another device responding to advertising channel packets from specific devices 5. **Connection**: The connection state has two defined roles, namely master and slave. A device in the master role will define timing for transmission [![State Diagram][4]][4] A connection is established by one device being in advertiser mode and other in initiator mode. The initiator becomes the master and the advertiser becomes the slave. This master slave data exchange defines critical connection parameters such as defining the channel and timing, which includes connection interval and salve latency. The slave latency is important because this determines the number of connection intervals the slave can ignore without losing connection. This helps the slave to optimize and preserve power consumption. The slave can request to update the communication parameters to better fit the slave’s application. [1]: https://en.wikipedia.org/wiki/Direct-sequence_spread_spectrum [2]: https://i.sstatic.net/2apaO.png [3]: https://i.sstatic.net/uQcI9.png [4]: https://i.sstatic.net/kmapO.jpg