Differential Coding and Scrambling Six Meeting Channel coding
Differential Coding and Scrambling Six Meeting
Channel coding for error correction
Channel coding by scrambling
Differential coding
Differential Coding Example Last Output: 1011 10 110010 011 100
Differential Coding Example 2 Last Output: 1001 00 101101 001
Scrambling: Shift Register
Self-synchronizing Scrambler An n-stage scrambler An n-stage descrambler
Scrambler: Example Stage 1 2 3 4 5 Initial code 0 1 1 1 0 0 0 0 0
Scrambler: Example Stage 1 2 3 4 5 Initial code 0 1 1 1 0 0 0 0 0
Self-synchronizing Descrambler + +
Tap Polynomial l l Self-synchronizing. l scramblers do not need the frame synchronization, l The x in the polynomial can be interpreted as a shift operator Pseudo-random binary sequences (PRBS) l Put the shift register stages into a known start-up condition
Set–reset scrambling l Sending l l Receiving l l Combining the input data with a PRBS in an exclusive-OR gate. Combining, in an exclusive-OR gate, the coded data with the identical pseudo-random sequence used at the transmitter, synchronization. l Frame alignment must take place
Error Detection: Cyclic Redundancy Checks l Original message = X l l Divide this message number by G, l l X = 7654321. G = 99 X = 7654321 = 77316 × 99 + 37 Reminder = 37 Sent message = Y l Y = 765432137
Modulo-2 Cyclic Redundancy Checks Orig. Message: 11100110 Sent Message: 11100110
Org = 0110 l Div = 01 1110 10 | 01100000 10 111 10 010 10 00 l
CRC With Shift Register (Nice View)
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