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)