There are three characteristics of Bluetooth low energy technology that underlie its ULP performance: maximized standby time, fast connection, and low peak transmit/receive power.
Switching the radio “on” for anything other than very brief periods dramatically reduces battery life, so any transmitting or receiving that has to be done needs to be done quickly. The first trick Bluetooth low energy technology uses to minimize time on air is to employ only three “advertising” channels to search for other devices or promote its own presence to devices that might be looking to make aconnection. In comparison, Classic Bluetooth technology uses 32 channels.
This means Bluetooth low energy technology has to switch “on” for just 0.6 to 1.2ms to scan for other devices, while Classic Bluetooth technology requires 22.5ms to scan its 32 channels. Consequently, Bluetooth low energy technology uses 10 to 20 times less power than Classic Bluetooth technology to locate other radios.
Switching the radio “on” for anything other than very brief periods dramatically reduces battery life, so any transmitting or receiving that has to be done needs to be done quickly. The first trick Bluetooth low energy technology uses to minimize time on air is to employ only three “advertising” channels to search for other devices or promote its own presence to devices that might be looking to make aconnection. In comparison, Classic Bluetooth technology uses 32 channels.
This means Bluetooth low energy technology has to switch “on” for just 0.6 to 1.2ms to scan for other devices, while Classic Bluetooth technology requires 22.5ms to scan its 32 channels. Consequently, Bluetooth low energy technology uses 10 to 20 times less power than Classic Bluetooth technology to locate other radios.
Once connected, Bluetooth low energy technology switches to one of its 37 data channels. During the short data transmission period the radio switches between channels in a pseudo-random pattern using the Adaptive Frequency Hopping (AFH) technology pioneered by Classic Bluetooth technology (although Classic Bluetooth technology uses 79 data channels).
Another reason why Bluetooth low energy technology spends minimal time on air is because it features a raw data bandwidth of 1Mbps – greater bandwidth allows more information to be sent in less time. An alternative technology that features a bandwidth of 250kbps, for example, has to be “on” for eight times as long (using more battery energy) to send the same amount of information.
Bluetooth low energy technology can “complete” a connection (i.e. scan for other devices, link, send data, authenticate, and “gracefully” terminate) in just 3ms. With Classic Bluetooth technology, a similar connection cycle is measured in hundreds of milliseconds. Remember, more time on air requires more energy from the battery.
Another reason why Bluetooth low energy technology spends minimal time on air is because it features a raw data bandwidth of 1Mbps – greater bandwidth allows more information to be sent in less time. An alternative technology that features a bandwidth of 250kbps, for example, has to be “on” for eight times as long (using more battery energy) to send the same amount of information.
Bluetooth low energy technology can “complete” a connection (i.e. scan for other devices, link, send data, authenticate, and “gracefully” terminate) in just 3ms. With Classic Bluetooth technology, a similar connection cycle is measured in hundreds of milliseconds. Remember, more time on air requires more energy from the battery.
Classic Bluetooth technology uses a long packet length. When these longer packets are transmitted the radio has to remain in a relatively high power state for a longer duration, heating the silicon. This changes the material’s physical characteristics and would alter the transmission frequency (breaking the link) unless the radio was constantly recalibrated. Recalibration costs power (and requires a closed-loop architecture, making the radio more complex and pushing up the device’s price).
In contrast, Bluetooth low energy technology uses very short packets - which keeps the silicon cool. Consequently, a Bluetooth low energy transceiver doesn’t require power consuming recalibration and a closed-loop architecture.
In contrast, Bluetooth low energy technology uses very short packets - which keeps the silicon cool. Consequently, a Bluetooth low energy transceiver doesn’t require power consuming recalibration and a closed-loop architecture.
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