Lecture3-SignalsEncoding.ppt

Coding of analog signals For example voice and video Analog signal is measured at equal intervals Sampling Quantization in time PAM—pulse amplitude modulation 脉冲幅度调制 Aliasing– 混叠[?eili?si?] PCM Examples PCM: From Analog to Digital Types of Polar encoding Polar signal (two levels) NRZ-level (NRZ-L) and NRZ-inverse phase (NRZ-I) Average signal level reduced Synchronization could still a problem Synchronization even for long strings of 1s or 0s Two signal-changes per bit—more bandwidth “Differential RZ” Manchester Encoding Two signal levels Higher pulse rate requires larger bandwidth Differential Manchester Encoding Block Coding Bit stream is divided into m-bit groups Groups are encoded as n-bit codes 4B/5B: 5-bit codes represent 4-bit groups 8B/10B: 10-bit codes represent 8-bit groups Substitution in 4B/5B Block Coding Chose codes in such a way that synchronization is ensured In 4B/5B, there can never be more than three consecutive 0s Error detection Control information Disadvantage: higher bandwidth 4B/5B Control Characters 8B/6T Encoding Programming Exercise 1 B8ZS Encoding Rule Example for B8ZS HDB3 (High-Density Bipolar 3-factorial) ——It applies in Europe , Japan and China. In HDB3, if 4 0s come one after another, we put 000V or B00V in the place of four 0s based on the polarity of the previous 1 and the previous destroyer (破坏点). V is the destroyer ( it destroys the alternation rule of polarity) B is the bit according with the alternation rule of polarity and cooperates with V. Substitution Rule: If the number of 1s since last substitution is odd, B00V is used . If the number of 1s since last substitution is even, 000V is used. V is the same polarity as last non-zero polarity, B is the contrast polarity of the last no-zero polarity. 3阶高密度双极性码 Substitution arithmetic of HDB3: 000V B00V The pattern 000+ 000- +00+ -00- HDB3 code + - - + polarity of the previous 1 even even odd odd Number of 1s since last substitution Ide