Optical FiberL9.pptx

Reproducing the original analog telephone signal from

  • No School
  • AA 1
  • 91

This preview shows page 62 - 76 out of 91 pages.

Reproducing the original analog telephone signal from the PAM signal through a LPF.
Image of page 62

Subscribe to view the full document.

Line Code A code chosen for use within a communication systems for transmission purposes. A line code may differ from the code generated at a user terminal, and thus may require translation
Image of page 63
WHY LINE CODE? Long sequence of 0s and 1s may disguise Error detection capability No reduction in data rate
Image of page 64

Subscribe to view the full document.

Line Codes for PCM Unipolar NRZ -- Stays positive and does not return to level 0 during binary 1 cell. Bipolar NRZ -- 2 non zero voltages i.e. positive for 1 and negative for 0 and does not return to 0. Unipolar RZ -- there is always a return to level 0 between individual bits during binary 1 cell. Bipolar RZ -- 2 non zero voltages i.e. positive for 1 and negative for 0 and returns to level 0 as well.
Image of page 65
Line Codes for PCM CMI -- 1s represented by alternate + and - states and 0s always represented by a - state during first half and + in second half of bit interval. AMI -- 1s represented by alternate + and - states and 0s always represented by zero voltage.
Image of page 66

Subscribe to view the full document.

Line Codes for PCM HDB3 (High density Bipolar 3) -- used to eliminate series of more than 3 0s in the AMI. The last zero of 4 consecutive zeroes is replaced by a violation (V) pulse that violates the AMI rule. The first zero may be replaced by a 1 to prevent two V’s to have the same polarity.
Image of page 67
Regenerative Repeater The advantage of PCM lies chiefly in the fact that it is a digital process . it is much easier for a receiver to distinguish between a 1 and a 0 than to reproduce faithfully a continuous wave signal. Transmission media carrying PCM signals employ regenerative repeaters that are spaced sufficiently close to each other (approximately 2kms ) to prevent any ambiguity in the recognition of the binary PCM pulses
Image of page 68

Subscribe to view the full document.

Regenerative Repeater The regenerative repeater conditions the received (attenuated and distorted) pulses through preamplifiers and equalizer circuits . The signal is then compared against a voltage threshold Above the threshold is a logic 1, and below the threshold is a logic 0. The resulting signal is said to be threshold detected.
Image of page 69
Regenerative Repeater Timing circuits within the regenerative repeater are synchronized to the bit rate of the incoming signal. The threshold detected signal is sampled at the optimum time to determine the logic level of the signal. The resulting code is used to regenerate and retransmit the new equivalent signal
Image of page 70

Subscribe to view the full document.

Regenerative Repeater
Image of page 71
Formats for 30-channel PCM systems (E1) A time slot: 8 bits A frame lasts 125 s and is divided into 32 slots, numbered slot 0 to slot 31, transmission rate 2.048 Mbps Time slot 0: frame alignment Time slot 16 for multiframe alignment and signaling, the remaining 30 slots for data transmission (voice channel) A multiframe consists of 16 frames numbered frame 0 to 15
Image of page 72

Subscribe to view the full document.

Formats for 30-channel PCM systems (E1) TS 0 for even frames: Y0011011-- frame sync. word (FAW) for odd frames: Y1ZXXXX TS 16 for frame 0: 0000XZXX (0000 multiframe alignment signal, Y:international use, Z: frame alignment loss indicator, X: not used) TS 16 for frames 1 to 15: signaling for 30 channels
Image of page 73
Image of page 74

Subscribe to view the full document.

PCM 30 Pulse Frame
Image of page 75
Image of page 76
  • Fall '19
  • Bell Systems

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern