Channel Coding – RAYmaps

November 20, 2021June 3, 20225G, BER Performance, Channel Coding, Simulation

Low Density Parity Check Codes

LDPC codes were first proposed by Robert Gallager in 1960 but they did not get immediate recognition as they were quite cumbersome to code and decode. But in 1995 the interest in these codes was revived, after discovery of Turbo Codes. Both these codes achieve the Shannon Limit and have been adopted in many wireless communication systems including 5G.

November 5, 2021June 3, 2022BER Performance, Channel Coding

Convolutional Codes and Viterbi Decoding

Convolutional codes when decoded using Viterbi Algorithm (VA) provide significant gains over the no coding case. The performance is further improved by using soft metrics instead of hard metrics (Euclidean distance is used in this case instead of Hamming distance). In fact, the performance is even better than brute force ML decoded Hamming (7,4) Code discussed in the previous section.

November 5, 2021June 3, 2022BER Performance, Channel Coding

Hamming Codes

In this post we discuss Hamming (7,4) Code which transmits 4 information bits for every 7 bits transmitted, resulting in a code rate of 4/7. The 3 additional bits are called parity bits and these protect against single bit errors in the channel. This is called a systematic code since after performing the coding operation the information bits are preserved, parity bits are only appended to the information bits.