UHF RFID Handheld Device Encoding and Decoding

In the RFID system, the RFID handheld terminal emits electromagnetic waves in a specific area, and the size of the area depends on the antenna size and operating frequency. The LC series resonant circuit is arranged in the radio frequency card, and its frequency is the same as the frequency emitted by the handheld terminal. When the radio frequency card passes through this area, under the influence of electromagnetic waves, the LC resonant circuit resonates, so that charges are generated in the capacitor. At the other end of the capacitor, an electronic pump transfers the charge in the capacitor to another capacitor for storage. When the charge reaches 2V, this capacitor can be used as a power supply to provide working voltage for other circuits, transmit data in the card or receive data from the handheld terminal. After receiving the data in the card, the handheld terminal decodes and performs error checking to determine the validity of the data, and transmits the data to the computer network through RS232, RS422, RS485 or wirelessly.

RFID handheld device encoding is a transformation of the signal to achieve a certain purpose, and its inverse transformation is called decoding or decoding. According to the history of coding, coding theory has three branches: source coding, channel coding and security coding. Coding theory is widely used in digital communication, computing technology, automatic control and artificial intelligence.

1. RFID handheld device source encoding and decoding

Source coding is the transformation of the signal output by the source, including the discretization of continuous signals (that is, the analog signals are converted into digital signals through sampling and quantization), and the coding of data compression to improve the effectiveness of signal transmission. Source decoding is the inverse process of source encoding.

Source coding has two main functions:

(1) Complete the analog/digital conversion

When the information source gives an analog signal, the source encoder converts it into a digital signal to realize the digital transmission of the analog signal.

(2) Improve the effectiveness of information transmission

This requires trying to reduce the number of symbols and the rate of symbols through some kind of data compression technique. The symbol rate determines the bandwidth occupied by the transmission, and the transmission bandwidth reflects the effectiveness of the communication.

2. Channel coding and decoding of RFID handheld devices

Channel coding is to re-transform the signal output by the source coder, including coding for distinguishing channels, adapting to channel conditions and improving communication reliability. Channel decoding is the inverse process of channel coding.

The main purpose of channel coding is forward error correction to enhance the anti-interference ability of digital signals. When the digital signal is affected by noise and other influences during channel transmission, errors will be caused. In order to reduce errors, the channel encoder adds protection components (supervisory elements) to the transmitted information symbols according to certain rules to form an anti-interference code. The channel decoder at the receiving end decodes according to the corresponding inverse rules, and finds errors or corrects them to improve the reliability of the communication system.

3. Secure encoding and decoding of RFID handheld devices

Security coding is to re-transform the signal, that is, to make the information difficult to be stolen and deciphered during the transmission process. In the occasion where confidential communication needs to be realized, in order to ensure the security of the transmitted information, artificially scramble the transmitted digital sequence, that is, add a password. This process is called encryption. Security decoding is the reverse process of security encoding. Security decoding uses the same password copy as the sending end to decrypt the received data at the receiving end to reStore the original information. The purpose of secret coding is to hide sensitive information, which is often achieved by replacing, shuffling, or both. A cryptographic system usually includes two basic parts: an encryption (decryption) algorithm and a key that can change the control algorithm.

According to its structure, ciphers are divided into sequence ciphers and block ciphers. Sequence cipher is a random sequence generated by the algorithm under the control of the key, and mixed with plaintext bit by bit to obtain ciphertext. Its main advantage is that there is no error diffusion, but it has high requirements for synchronization. It is widely used in in the communication system. Block cipher is an algorithm that encrypts plaintext by group under the control of a key. The ciphertext bits generated in this way generally have interdependence with the corresponding plaintext group and bits in the key, which can cause error diffusion. It is mostly used for message encryption. Confirmation and digital signature.

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