Bluetooth 5.2 Technology and Application

In order to understanding of Enhanced Attribute Protocol (EATT), Bluetooth protocol stack is mainly divided into three layers. The Apps layer is the application layer, and the middle layer is the Host layer, including Generic Access Profiles (GAT), Security Manager Protocol (SMP), Generic Attribute Profile (GATT), Attribute Protocol (ATT) and Logical Link Control and Adaption (L2CAP). The third layer is the control layer, including Host Control Interface (HCL), Link Layer (LL) and Physical Layer (PHY). The lower layer provides services to the upper layer by packaging from bottom to top. The following picture shows Bluetooth protocol stack.

Figure 3.

ATT mainly defines attribute parameters of different services, which are used for information exchange and negotiation between master and slave devices. L2CAP splits and assembles the upper data to match the ability of the Controller. EATT in Bluetooth 5.2 is an enhancement to ATT, which can handle concurrent transactions and adds flow control to improve the stability of EATT. In other words, EATT protocol allows different applications to execute concurrently on different L2CAP channels. And the size of the Maximum Transmission Unit (MTU) of ATT is allowed to be modified during connection. The ATT_MTU and LMPCAP_MTU in EATT protocol are independently configured. As shown in the following figure 4 (b).

Figure 4.

In Bluetooth 5.1 and earlier versions, things are processed sequentially, and concurrency is not supported. Transactions can only be executed after a complete PDU (Protocol Data Unit). The size of MTU between ATT and L2CAP is fixed. That is to say, once a connection is established, the MTU of a certain service cannot be changed, and there is a one-to-one correspondence between them. As shown in figure 4 (a).

In a word, The ATT protocol is executed sequentially, in that only one transaction can be executed. While EATT can execute multiple events simultaneously between Bluetooth client and server with low power consumption. Therefore, the main advantages of EATT in application include convenience, flexibility and faster processing speed, which greatly improves the process and delay of stack multiple access and responds well to the expectation of eliminating security vulnerabilities.

The purpose of adding LE Power Control function in Bluetooth 5.2 is to balance signal quality and power as well as reduce power consumption.

Bluetooth 5.2 integrates the bi-directional power control function of Bluetooth Low Energy (BLE). The low-power Bluetooth receiver can monitor the signal strength of the master device and request to change the transmission power, with the main purpose of balancing the signal quality and power. When the master device always transmits high-intensity signals, the link of the receiving device will fail and the power of the transmitting terminal will be wasted. On the contrary, when the signal strength is too low, the error rate of the receiving equipment is too high, resulting in transmission failure.

The LE Power Control function allows the Bluetooth controller to use the concept of “area” to monitor the change of path loss and report it to the Bluetooth host. Finally, this feature can also improve the coexistence of other wireless devices in the 2.4GHz frequency range in the environment.

Bluetooth 5.2 can realize dynamic management of signal transmission power. The master device be notified to modify the power by detecting the signal strength of the other party. Compared with the equipment whose distance often changes, it saves power consumption, and can modify the power appropriately to hide the application requirements. The user can also change the transmission power autonomously and send the change instruction to the slave device. The advantage of LE Power Control is the efficient utilization of battery power. In the field of battery-powered sensors, like many applications existing in the Internet of Things and smart homes, the new low-power Bluetooth 5.2 performance allows dynamic optimization of battery life while minimizing the need for power maintenance, thus greatly reducing costs.

Bluetooth 5.2 integrates the LE Isochronous channel for realizing the next generation of Bluetooth Low Power Audio (LE Audio). It defines a time-dependent data transmission channel and transmission strategy. Thereby ensuring that the data received by the receiver meets the timeliness requirements. It allows time-limited data to be transmitted to one or more devices for time synchronization.

LE Audio adopt a new Low Complexity Communication Code (LC3) with low complexity. Compared with the old Bluetooth audio coding SBC, it has the characteristics of good sound quality and low power consumption.

In the past, only connection-oriented asynchronous communication links and broadcast links in disconnected mode were supported. Bluetooth 5.2 supports synchronous audio stream transmission channel in connected mode and synchronous audio stream transmission channel in disconnected mode.

The Isochronous channel supports both connected mode and unconnected mode. In the one-to-one connection mode, Le-CIS (LE Connected Social Stream) is used to connect data streams synchronously, and the clearing mechanism flush the delayed data. Different LE-CIS form a CIG (Connected Isochronous Groups) synchronous connection group, and the CIS in the same CIG has the same time stamp to ensure that the data in the same group is synchronous. The most obvious application is headphones, and the left ear and the right ear are a CIS respectively. If they form a CIG, the time between them is synchronous.

Figure 5.

For the broadcast mode, it is called Broadcast Isochronous Stream (BIS), and multiple BIS can form a BIG synchronous broadcast group. Synchronization of broadcast mode is realized by a PDU broadcast in one cycle, which contains a time stamp for each BIS. Once synchronized, receiving convenience can be called synchronous receiver. In the same example, if a mobile phone plays, the left and right ears of each person in a group must also receive synchronous data streams, then the data of the left and right ears must belong to the same BIG.

Figure 6.

Because of the low-power Bluetooth, many smart devices rely on Bluetooth technology for no connection and data exchange, which reduces the power consumption of devices.

For example, in the gym, different fitness programs will be played on different screens, and there must be interference between the voices. At this time, different audio is divided into different groups, and the corresponding audio can be received by accessing the corresponding groups, thus reducing noise interference.

The flight train information in the waiting hall of the waiting hall is played in a big speaker mode, which is difficult to hear clearly for some people with hearing impairment or when the environment is noisy. If the flight train information is broadcast through LE Audio equipment and the passengers receive it through Bluetooth headset or corresponding mobile APP, it can greatly save time and energy.

Passengers on the plane can connect headphones to the flight information system, specify their favorite language, and hear flight information in this language.