Android Bluetooth Low Energy (LBE) Technology Introduction

Bluetooth Low Energy (BLE) technology is a low-cost, short-distance, interoperable and robust wireless technology. Work on a license-free 2.4GHz ISM RF band. It has been designed for ultra-low power (ULP) wireless technology from the start.

It uses many intelligent means to minimize power consumption.

Bluetooth low energy technology is used in variable connection intervals. This interval can be set from a few milliseconds to a few seconds depending on the detailed application.

In addition, BLE technology is used in a very high-speed connection mode. So usually can be in a "non-connected" state (save energy), at this time the link between the two sides only know each other. The link is only opened if necessary. Then close the link within the shortest possible time.

The working mode of BLE technology is ideal for transmitting data from micro wireless sensors (exchanging data once every half-second) or with other peripherals such as remote controls with fully asynchronous communication.

The amount of data sent by these devices is very small (usually several bytes). And the number of sends is very small (for example, several times per second to every minute). or less).

Ultra-low power wireless technology

The three characteristics of Bluetooth low energy technology have achieved ULP performance. Each of these three features is the maximum standby time, high-speed connection, and low-peak transmit/receive power.

The wireless "on" time is only too short to dramatically reduce battery life, so no matter what the required send or receive task needs to be done very quickly. The first technique used by Bluetooth low-energy technology to minimize the time of wireless switching is to search for other devices with only 3 "ad" channels, or to announce that they exist for devices seeking to establish a connection. Compared with. Standard Bluetooth technology uses 32 channels.

This means that Bluetooth low-power technology scans other devices just "on" for 0.6 to 1.2ms of time, while standard Bluetooth technology requires 22.5ms of time to scan its 32 channels.

Results Bluetooth Low energy technology is 10 to 20 times times less power required to locate other wireless devices than standard Bluetooth technology.

It's worth noting that. Using 3 ad channels is a compromise of some degree: This is a tradeoff between "on" time (corresponding to power consumption) and robustness in a very congested part of the spectrum (the fewer ad channels, the more chances the other wireless device will broadcast on the chosen frequency, the easier it will be to cause a signal conflict). Only the designer of the specification is quite confident in balancing such compromises-for example, the ad channel they choose does not conflict with the Wi-Fi default channel (see Figure 1)

Figure 1: The advertising channel for Bluetooth low energy technology is carefully chosen. Ability to avoid collisions with Wi-Fi

Once the connection is successful. Bluetooth Low energy technology will switch to one of 37 data channels.

During a short period of data transfer. Wireless signals will switch between channels in a pseudo-random manner using adaptive frequency hopping (AFH) technology advocated by standard Bluetooth technology (although standard Bluetooth technology uses 79 data channels).

Bluetooth low power technology is required the shortest time to open a wireless switch is also due to the fact that it has 1Mbps of raw data bandwidth--greater bandwidth agrees to send a lot of other information in a shorter period of time. For example, there is a wireless technology with 250kbps bandwidth that sends the same information 8 times times longer (consumes a lot of other battery energy).

Bluetooth Low energy technology "over" a single connection (that is, scanning other devices, establishing links, sending data, authenticating, and ending appropriately) requires only 3ms. The same connection period is hundreds of milliseconds after standard Bluetooth technology has been completed.

Again, the longer the wireless is on, the more energy the battery consumes.

Bluetooth low-Power technology can also limit peak power consumption in two other ways: by using more "loose" RF parameters and sending very short packets. Both technologies use high Spenn shift keying (GFSK) modulation. But Bluetooth low-energy technology uses a modulation index of 0.5, while standard Bluetooth technology is 0.35.

The 0.5 index approaches the Gaussian minimum frequency shift keying (GMSK) scheme, which reduces the power consumption requirements of wireless devices (this is more complicated, this is not a part of this article). The lower modulation index also has two advantages, namely improved coverage and enhanced robustness.

Standard Bluetooth technology uses a longer packet length.

When these longer packets are sent, the wireless device must remain in a relatively high power state for a longer period of time. So easy to make silicon wafer heat. Such a fever will change the physical properties of the material, thus changing the transmission frequency (interrupt link), unless the wireless device is frequently re-calibrated.

Calibrating again will consume a lot of other power (and requires a closed-loop architecture.) Make wireless devices more complex. thereby pushing up the price of the equipment).

Instead. Bluetooth low-energy technology uses very short packets-which keeps the silicon at a low temperature. Therefore, Bluetooth low power transceivers do not require a more energy-efficient re-calibration and closed-loop architecture.

Two kinds of chip architectures for BLE

Bluetooth low-Power architecture together has two kinds of chip composition: single-mode and dual-mode chip. Bluetooth single-mode devices are a new type of chip in the Bluetooth specification that only supports Bluetooth low-energy technology-part of a technology optimized for ULP operations. Bluetooth single-mode chip can communicate with other single-mode chips and dual-mode chips, the latter need to use the Bluetooth low-energy technology in their own architecture to send and receive data (refer to Figure 2). Dual-mode chips can also communicate with standard Bluetooth technology and other dual-mode chips using traditional Bluetooth architectures.

The dual-mode chip can be used in any situation where standard Bluetooth chips are used at the moment. This allows mobile phones, PCs, personal navigation devices (PND) or other applications with dual-mode chips to communicate with all traditional standard Bluetooth devices already in use in the market and all future Bluetooth low power devices.

However, because these devices require running standard Bluetooth and Bluetooth low-power tasks, the dual-mode chip is not optimized for ULP operations as high as a single-mode chip.

Single-mode chips can be used for a very long time (months or even years) with one-button batteries (e.g. 3V, 220mAh CR2032).

In contrast, standard Bluetooth technology (and Bluetooth low-energy dual-mode devices) typically requires at least two AAA batteries (10 to 12 times times the power of the coin cell, which can tolerate a much higher peak current), and in many other cases it can only work for a few days or weeks (depending on the detailed application). Note that there are also some highly specialized standard Bluetooth devices. They can work with batteries that are lower in capacity than AAA batteries.

Figure 2: The dual-mode chip communicates with the single-mode device using the Bluetooth low energy portion of its architecture.

Android Bluetooth Low Energy (LBE) Technology Introduction