kdjk-04

# Line coding

Misal jika data yang dikirim seperti berikut, maka penerima akan sulit
menentukan berapa jumlah bit yang dikirim.
00000000 00000000 00000000 00000000

Solusi:
+ clock     Manchester          Eth 10Mbps
+ scramble  4B/5B + NRZI        Fast Eth
            8B/10B + NRZI       Gigabit Eth, HDMI, SATA, ...


# Modulasi

Contoh: WiFi 2.4 GHz
        - baseband: 20 MHz
        - carrier : 2400-2500 MHz
            - channel 1:  2412 MHz (center freq), range: 2402-2422 MHz
            - channel 6:  2437 MHz (center freq), range: 2427-2447 MHz

# Checksum

 Sender                                 Receiver
 ------                                 --------
322                                    3
 FFFF                                   FFFF
 FF00                                   FF00
 F0F0                                   F0F0
 C0C0                                   C0C0
 0000   checksum empty                  4F4D   checksum received
 ---- +                                 ---- +
 B0AF                                   FFFC
    3   carry                              3   carry
 ---- +                                 ---- +
 B0B2   sum                             FFFF   sum

 4F4D   checksum (komplemen n-1)        0000   checksum (komplemen n-1)
                                               --> correct


# CRC

Sender                                  Receiver
------                                  --------
g = 1011                                g = 1011
i = 1100                                b = 1100010
r = 000 (belum dihitung)
b = 1100000
      ________                                ________
1011 / 1100000                          1011 / 1100010
       1011                                    1011
       ------- xor                             ------- xor
        1110                                    1110
        1011                                    1011
        ------ xor                              ------ xor
         1010                                    1011
         1011                                    1011
         ----- xor                               ----- xor
           010      --> r = 010                    000      --> r = 000
b = i,r                                                     --> OK
b = 1100010