Bluetooth anti-jamming technology

1. Bluetooth adaptive frequency hopping (AFH) technology

The Bluetooth system works in the 2.4GHz ISM (ie industrial, scientific, medical) frequency band. Many devices work in this frequency band. Working in such a frequency band, mutual interference must be relatively serious. Therefore, the Bluetooth system uses frequency hopping technology to prevent fading and Suppress distractions. Before the connection is established, the Bluetooth device selects a frequency hopping frequency in a fixed frequency band, quickly exchanges time and address handshake information, and then quickly obtains time and frequency synchronization. After the connection is established, the two devices change the channel frequency according to the hopping sequence, so that the frequency hopping frequency appears random.

Bluetooth defines 32 frequency points as a frequency band, which is divided into 79 sub-frequency bands. The lowest 28 bits of the Bluetooth master clock CLK and the master device address determine the frequency band and frequency hopping sequence of Bluetooth work, as shown in Figure 2.10; Bluetooth system definition Frequency hopping sequences under 5 working states: paging, paging response, inquiry, inquiry response and connection frequency hopping sequence. There are different strategies to generate frequency hopping sequence in different states.

Figure 2.11 shows the generation principle of the frequency hopping sequence of the Bluetooth system; the input X is determined by the clock information bit, which determines the phase of the hopping frequency point in the 32 frequency sequences of a certain frequency band -- the offset of the frequency sequence in the segment At the same time, the speed of changing the frequency hopping frequency point is also determined by it; A to F determine the order of the frequency hopping sequence. value; in the query/paging scanning state, the input sequence from A to F is only related to the address, so its frequency hopping sequence is uniquely determined. In other states, A~F is controlled by the clock and the Bluetooth address, and its frequency hopping The sequence jumps accordingly with the change of the clock; Y1 and Y2 control the selection of the transceiver frequency hopping sequence, Y1 ensures that the transceiver frequency will not be repeated, and Y2 makes the transceiver frequency in different frequency bands; PERM5 is a The butterfly arithmetic unit controlled by C, D, and Y1 plays the role of disturbance.

(1) Paging/paging scanning state: Bluetooth devices search for other devices to join their piconets through paging; paging devices select a new frequency hopping point every 312.5µs to initiate paging, during paging scanning, The paged device selects a new frequency point to monitor every 1.28s. The paging and the paged device use the lower 28 bits of the paged device address. The paging hopping sequence generated is a well-defined periodic sequence, which The 32 frequency points are evenly distributed on 79 frequency channels.

(2) Query/query scanning status: Bluetooth devices search for other devices around by querying. The querying device selects a new frequency to send query messages every 312.5µs, and the queried device selects a new frequency to monitor every 1.28s; query Use the universal inquiry access code as the inquiry address with the inquired device. The generated 32 query hopping sequences are evenly distributed on 79 frequency channels.

(3) Connection state: Using the lowest 28 effective bits of the master device address, the two sides of the Bluetooth communication device change a frequency every 625µs, and the resulting channel hopping sequence period is very long, and 79 hopping sequences are in any short period of time It is close to the uniform distribution, which can meet the requirements of the frequency hopping system.

The algorithm of adaptive frequency hopping is added in the Bluetooth 1.2 protocol; when a certain channel signal quality is found to be poor during Bluetooth communication, that is, it becomes a "bad" channel, these bad channels can be discarded during frequency hopping and other channels can be selected Frequency hopping channels with good quality are used instead, thereby avoiding communication interference on certain frequency points, thereby enhancing its anti-interference ability.

2. Bluetooth baseband error correction mechanism

Bluetooth technology adopts forward error correction FEC and automatic repeat request (Automatic Repeat-reQuest, ARQ) technology, and the error correction mechanism adopted is relatively simple. Among them, the forward error correction (FEC) is that the sending end encodes the data information according to certain rules to form a code with error correction capability; the receiving end receives the encoded data and performs corresponding decoding according to the predetermined rules to determine the received data. Whether there is an error in the data information, if there is an error, determine its location and correct it. This coding method is more suitable for real-time transmission systems, but the disadvantage of this technology is that the error correction capability is limited.

Autonomous retransmission request is also called decision feedback. It uses confirmation and timeout to realize reliable information transmission on the basis of unreliable service; The error detection capability; after receiving the encoded information, the receiving end decodes it and makes a judgment to detect whether there is a certain bit error, and then sends the judgment result back to the sending end through the feedback channel; the sending end according to the feedback judgment result, Decide whether to retransmit the data; but the retransmission is not unlimited. After multiple retransmissions, the system will not retransmit after the time specified by the system.

The specific error correction methods in the Bluetooth baseband include: 1/3 ratio FEC, 2/3 ratio FEC and ARQ. Among them, the 1/3 ratio FEC codes each bit of information three times, the coding method is relatively simple, and the length of the coding sequence is three times the length of the original sequence. The 2/3 ratio FEC encoding uses a generator polynomial to encode 10-bit data into 15 bits, which is a (15, 10) truncated Hamming code, and the data receiver performs the corresponding reverse operation, according to the error detection and error correction mechanism provided by the algorithm restore the original data. In the ARQ mode, the data packet has been retransmitted until the final acknowledgment is received or the retransmission times out.

The above are the details of the Bluetooth anti-interference technology introduced by Shenzhen Zuchuang Microelectronics Co., Ltd. for you. If you have Bluetooth product design and development needs, you can trust us. We have rich experience in custom development of smart electronic products. We can evaluate the development cycle and IC price as soon as possible, and can also calculate the PCBA quotation. We are a number of chip agents at home and abroad: Songhan, Yingguang, Jieli, Ankai, Quanzhi, realtek, with MCU, voice IC, BLE Bluetooth IC, dual-mode Bluetooth module, wifi module. We have hardware design and software development capabilities. Covering circuit design, PCB design, single-chip microcomputer development, software custom development, APP custom development, WeChat official account development, voice recognition technology, Bluetooth development, wifi technology, etc. It can also undertake the research and development of smart electronic products, the design of household appliances, the development of beauty equipment, the development of Internet of Things applications, the design of smart home solutions, the development of TWS earphones, the development of Bluetooth earphone speakers, the development of children's toys, and the research and development of electronic education products.