CHE (Channel Encoder)

Introduction:

Channel Encoder (CHE) is a digital signal processing block used in communication systems to convert information bits into symbols that can be transmitted over the communication channel. The main purpose of CHE is to add redundancy to the transmitted symbols, which improves the system's ability to detect and correct errors that may occur during transmission.

In this article, we will discuss the working principle of the Channel Encoder, its types, and their applications in various communication systems.

Working Principle of Channel Encoder:

The Channel Encoder takes a stream of input bits and converts them into a sequence of symbols. These symbols are usually represented by the amplitude and phase of the transmitted signal. The number of symbols generated by the Channel Encoder depends on the modulation scheme used to transmit the data.

The Channel Encoder adds redundancy to the symbols by including additional bits that help detect and correct errors. The additional bits are generated using an error-correcting code. The most commonly used error-correcting codes are convolutional codes and block codes.

Convolutional codes are generated using feedback shift registers. The shift registers generate a sequence of bits that are combined with the input data to generate the encoded output. The encoded output consists of the input data and the additional redundancy bits generated by the convolutional code. The encoder's output is a sequence of symbols that are transmitted over the channel.

Block codes, on the other hand, generate additional redundancy bits by dividing the input data into blocks and adding parity bits to each block. The parity bits are generated using a predetermined algorithm and are used to detect and correct errors in the received data.

Types of Channel Encoder:

There are two main types of Channel Encoders: Convolutional Encoders and Block Encoders. Both types of encoders have their advantages and disadvantages.

Convolutional Encoder:

A Convolutional Encoder is a type of Channel Encoder that uses a linear feedback shift register to generate the redundant bits. The feedback shift register is a shift register that generates a sequence of bits based on the input data and the previous output.

The Convolutional Encoder has a constraint length that determines the number of previous inputs used to generate the current output. The constraint length is denoted by K. The output of the Convolutional Encoder depends on the current input bit and the previous K-1 input bits.

The Convolutional Encoder has a rate that determines the ratio of the input bits to the output bits. The rate is denoted by R = k/n, where k is the number of output bits generated by the Convolutional Encoder, and n is the number of input bits.

The Convolutional Encoder's advantages are that it provides a good trade-off between the encoding complexity and error-correcting performance. The Convolutional Encoder is widely used in digital communication systems such as satellite communication, wireless communication, and digital television.

Block Encoder:

A Block Encoder is a type of Channel Encoder that divides the input data into blocks and adds redundant bits to each block. The redundant bits are used to detect and correct errors in the received data.

The most commonly used Block Encoder is the Reed-Solomon Encoder. The Reed-Solomon Encoder adds redundant bits to the input data by dividing the input data into blocks and generating a polynomial for each block. The polynomial is used to generate the redundant bits that are added to the block.

The Reed-Solomon Encoder's advantages are that it provides a high level of error-correcting performance, making it suitable for applications that require high reliability, such as data storage and digital communication systems.

Applications of Channel Encoder:

The Channel Encoder is widely used in digital communication systems. Some of the applications of Channel Encoder are:

Digital Television:

In digital television, the Channel Encoder is used to encode the digital video and audio signals. The encoded signals are then transmitted over the air or through a cable.

Wireless Communication:

In wireless communication systems, the Channel Encoder is used to encode the digital data transmitted over the wireless channel. The Channel Encoder improves the system's ability to detect and correct errors that may occur during transmission.

Satellite Communication:

In satellite communication systems, the Channel Encoder is used to encode the digital data transmitted from the earth to the satellite and from the satellite to the earth. The Channel Encoder is used to improve the system's ability to detect and correct errors that may occur during transmission.

Data Storage:

In data storage systems, the Channel Encoder is used to encode the digital data stored on the disk or other storage media. The Channel Encoder is used to improve the system's ability to detect and correct errors that may occur during storage.

Conclusion:

In conclusion, the Channel Encoder is an essential block in digital communication systems. It improves the system's ability to detect and correct errors that may occur during transmission. The two main types of Channel Encoders are Convolutional Encoder and Block Encoder. The Convolutional Encoder provides a good trade-off between encoding complexity and error-correcting performance, while the Block Encoder provides a high level of error-correcting performance. The Channel Encoder is used in various communication systems, such as digital television, wireless communication, satellite communication, and data storage systems.