Line coding - NTNU

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Decoding of partial response ? c k - c k-1 c k - c k-1 c k - c k-1 c k-1 c k-1 Digital Communication, Line codes and scrambling IET, NTNU 27 Precoding of partial response (duobinary) Precoder Convert to bipolar b k = 0,1 d k = 0,1 0 to -1 c k = ±1 a k ˆ + 1 to +1 z -1 z -1 Digital Communication, Line codes and scrambling Duobinary coding b k = 0 d k = d k1 c k = c k1 a k = c k + c k1 =±2 b ˆ k = 0 b k =1 d k d k1 c k c k1 a k = c k + c k1 = 0 b ˆ k =1 3-level decision Decoding depends only on current received signal sample ): no error propagation. Precoding may be used also for modified duobinary and dicode. IET, NTNU b k 28
Scrambling • Most transmission systems are based on an assumption of random input data ): statistically independent bits and p(“0”) = p(“1”) = 1/2 • Practical input data often differ from this assumption and may for instance contain long strings of ones or zeroes • Scrambling is a way to ensure approximately random data • Scrambling is based on pseudorandom sequences generated by linear feedback shift registers. Digital Communication, Line codes and scrambling IET, NTNU 29 Linear feedback shift register Number of states in a shift register of length n: 2 n The output sequence is periodic, and for a maximum length shift register the period is: 2 n -1 Digital Communication, Line codes and scrambling IET, NTNU 30
Page 1 and 2: Presentation in course TTT4130 Digi
Page 3 and 4: Example, 4B3T code The 4B3T code is
Page 5 and 6: DC-balance Most transmission system
Page 7 and 8: Eye curve for AMI code with DC cuto
Page 9 and 10: Power spectrum AMI code Digital Com
Page 11 and 12: One alternative of a 4B3T code Digi
Page 13: Duobinary partial response y k = c
Page 17 and 18: Applications of scrambling • Echo

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