Introduction to android Bluetooth Low-energy (LBE) Technology

Introduction to android Bluetooth Low-energy (LBE) Technology

Bluetooth Low-energy (BLE) technology is a low-cost, short-distance, and interoperable Robust Wireless Technology that works in a licensed 2.4 GHz ism rf band. It was designed as an ultra-low power (ULP) wireless technology from the very beginning. It uses many smart means to minimize power consumption.

Bluetooth Low energy technology uses a variable connection interval, which can be set to milliseconds to seconds depending on the specific application. In addition, because BLE technology uses a very fast connection mode, it can be in a "non-connection" status (Saving Energy) at ordinary times. At this time, the two ends of the link only know each other, enable the link only when necessary, and then close the link as soon as possible.

The working mode of BLE technology is ideal for transmitting data from micro-wireless sensors (data is exchanged every half second) or from other peripherals such as remote controls that use completely asynchronous communication. These devices send a very small amount of data (usually several bytes), and the number of sending times is very small (for example, several times to every minute, or even less ).

Ultra-Low Power Wireless Technology

The three features of Bluetooth Low-energy technology achieve ULP performance. These three features are the maximum standby time, fast connection, and low-peak transmission/receiving power consumption.

Wireless "enable" will greatly reduce the battery life as long as it is not very short, so any necessary sending or receiving tasks need to be completed quickly. The first technique used by Bluetooth Low Energy Technology to minimize the time needed to enable wireless connection is to search for other devices using only three "ad" channels, or to advertise itself to devices seeking to establish connections. In contrast, the standard bluetooth technology uses 32 channels.

This means that the Bluetooth Low Energy Technology only needs to "enable" 0.6 to Ms, while the Standard bluetooth technology requires MS to scan its 32 channels. Results The power consumption required by Bluetooth Low Energy Technology to locate other wireless devices is 10 to 20 times lower than that of standard bluetooth technology.

It is worth noting that using three ad channels is a compromise to some extent: this is the "on" Time (corresponding to power consumption) in the very crowded part of the spectrum) A compromise with robustness (the fewer AD channels, the more opportunities another wireless device can broadcast on the frequency of choice, the more likely it will cause signal conflict ). However, designers of the specification are quite confident in balancing this compromise-for example, the ad channel they choose will not conflict with the default Wi-Fi channel (see Figure 1)

Figure 1: The Advertising channel of Bluetooth Low Energy Technology is carefully selected to avoid conflicts with Wi-Fi.

Once the connection is successful, the Bluetooth Low Energy Technology will switch to one of 37 data channels. During a short period of data transmission, wireless signals will use the Adaptive Frequency Hopping (AFH) proposed by the standard bluetooth technology) technology switches between channels in a pseudo-random manner (although the standard bluetooth technology uses 79 data channels ).

Another reason for requiring the Bluetooth Low-energy technology to enable wireless connection for the shortest time is that it has 1 Mbps of original data bandwidth-a larger bandwidth allows more information to be sent in a shorter period of time. For example, another wireless technology with kbps bandwidth needs to be enabled eight times (consuming more battery energy) to send the same information ).

Bluetooth Low-energy technology "Completes" one connection (scanning other devices, establishing links, sending data, authentication, and appropriate termination) only takes 3 ms. It takes several hundred milliseconds for the standard Bluetooth Technology to complete the same connection cycle. Again, the longer the wireless connection is enabled, the more battery energy is consumed.

Bluetooth Low Energy Technology can also limit peak power consumption in two other ways: using more "loose" RF parameters and sending short packets. Both technologies use Gaussian Frequency Shift Keying (GFSK) modulation, but Bluetooth Low energy technology uses a modulation index of 0.5, while the Standard bluetooth technology is 0.35. 0.5 of the exponent is close to the Gaussian minimum frequency shift keying (GMSK) solution, which can reduce the power consumption requirements of wireless devices (this reason is complicated and will not be repeated here ). The lower modulation index has two benefits: improved coverage and enhanced robustness.

The standard bluetooth technology uses a long packet length. When these long data packets are sent, wireless devices must maintain a longer period of time in a relatively high power consumption state, so that the wafer may heat up easily. This fever will change the physical properties of the material, thereby changing the transmission frequency (interruption link) unless the wireless device is frequently re-calibrated. Re-calibration will consume more power (and require closed-loop architecture, making wireless devices more complex and pushing up device prices ).

On the contrary, Bluetooth Low-energy technology uses very short data packets-This keeps the silicon wafers low. Therefore, Bluetooth Low-energy transceiver does not require more energy-consuming re-calibration and closed-loop architecture.

 

BLE's two chip Architectures

Bluetooth Low-energy architecture consists of two chips: Single-Mode chip and dual-mode chip. A single-mode bluetooth device is a new chip that only supports Bluetooth Low-energy technology. It is part of a technology dedicated to ULP operation optimization. The Bluetooth Single-Mode chip can communicate with other single-mode chips and dual-mode chips. In this case, the latter needs to use the Bluetooth Low-energy technology in its own architecture to send and receive data (see figure 2 ). Dual-mode chips can also communicate with standard bluetooth technology and other dual-mode chips using the traditional Bluetooth architecture.

Dual-mode chips can be used in any use of standard bluetooth chips. In this way, mobile phones, PCs, and personal navigation devices with dual-mode chips are installed (PND) or other applications can communicate with all traditional standard Bluetooth devices that are already in use on the market and all future Bluetooth Low-energy devices. However, because these devices require standard Bluetooth and Bluetooth Low-energy tasks, the dual-mode chips are not optimized for ULP operations as high as single-mode chips.

A single-mode chip can work with a single button battery (such as CR2032 of 3 V and 220mAh) for a long time (several months or even a few years ). On the contrary, standard Bluetooth Technology (and Bluetooth Low-energy dual-mode devices) usually requires at least two AAA batteries (10 to 12 times the power of the button battery, can tolerate a much higher peak current ), in more cases, you can only work for days or weeks at most (depending on the specific application ). Note that there are also some highly specialized standard Bluetooth devices that can work with a battery with a lower capacity than AAA battery.

Figure 2: A dual-mode chip uses the Bluetooth Low-energy part in its architecture to communicate with a single-mode device.