The three major features of Bluetooth low energy technology contribute to ULP performance. These three major features are maximized standby time, fast connection and low peak transmit/receive power consumption.
Battery life will be drastically reduced if the wireless is "on" for any short period of time, so any necessary sending or receiving tasks need to be completed quickly. The first trick used by Bluetooth Low Energy technology to minimize wireless on time is to use only 3 "advertisement" channels to search for other devices, or announce its presence to devices seeking to establish a connection. In comparison, standard Bluetooth technology uses 32 channels.
This means that Bluetooth low energy technology only needs 0.6 to 1.2ms to "turn on" to scan other devices, while standard Bluetooth technology requires 22.5ms to scan its 32 channels. As a result, Bluetooth low energy technology requires 10 to 20 times less power to locate other wireless devices than standard Bluetooth technology.
It is worth noting that using 3 advertising channels is somewhat of a compromise: it is a compromise between "on" time (corresponding to power consumption) and robustness in a very crowded part of the spectrum. This is a trade-off (the fewer advertising channels, the more opportunities there are for another wireless device to broadcast on the selected frequency, making it easier to cause signal conflicts). But the designers of the specification are quite confident in balancing this compromise - for example, the advertising channel they choose will not conflict with the Wi-Fi default channel
Once the connection is successful, Bluetooth Low Energy technology will switch to one of 37 data channels. During the brief period of data transmission, the wireless signal will switch between channels in a pseudo-random manner using adaptive frequency hopping (AFH) technology pioneered by standard Bluetooth technology (although standard Bluetooth technology uses 79 data channels).
Another reason why Bluetooth low energy technology is required to have the shortest wireless on time is that it has a raw data bandwidth of 1Mbps - larger bandwidth allows more information to be sent in less time. For example, another wireless technology with 250kbps bandwidth would need to be on eight times longer (consuming more battery power) to send the same information.
Bluetooth low energy technology "completes" a connection (i.e., scans for other devices, establishes the link, sends data, authenticates, and ends appropriately) in just 3ms. Standard Bluetooth technology takes hundreds of milliseconds to complete the same connection cycle. Again, the longer the wireless is on, the more battery energy is consumed.
Bluetooth Low Energy technology can also limit peak power consumption in two other ways: using more "relaxed" radio frequency parameters and sending very short data packets. Both technologies use Gaussian Frequency Shift Keying (GFSK) modulation, but the modulation index used by Bluetooth Low Energy technology is 0.5, while standard Bluetooth technology is 0.35. The index of 0.5 is close to the Gaussian Minimum Frequency Shift Keying (GMSK) scheme, which can Reduce the power consumption requirements of wireless devices (the reasons for this are more complicated and will not be discussed in this article). Lower modulation index also has two benefits, namely improved coverage and enhanced robustness.
Standard Bluetooth technology uses longer packet lengths. When sending these longer packets, the wireless device must remain in a relatively high-power state for a longer period of time, which tends to heat the silicon. This heating will change the physical properties of the material, thereby changing the transmission frequency (breaking the link) unless the wireless device is frequently recalibrated. Recalibration consumes more power (and requires a closed-loop architecture, making wireless devices more complex and thus driving up device prices).
In contrast, Bluetooth Low Energy technology uses very short data packets - which keeps the silicon cool. Therefore, Bluetooth low energy transceivers do not require energy-intensive recalibration and closed-loop architecture.