There are Four channel in Forward direction in cdma.

  1. PILOT CHANNEL (1)
  2. SYNC CHANNEL (1)
  3. FORWARD TRAFFIC + PAGING CHANNELS (62)
  4. PAGING CHANNELS ( MAXIMUM 7)

PILOT CHANNEL

PILOT SIGNALS ARE TRANSMITTED BY EACH CELL SITE TO ASSIST MOBILE RADIO IN ACQUIRING AND TRACKING THE CELL SITE DOWNLINK SIGNAL

PILOT CHANNEL IS ASSIGNED CODE CHANNEL NUMBER ZERO

THE SIGNAL STRENGTH OF THE PILOT CHANNELS IS MEASURED BY Ec/Io

Ec/Io IS THE ENERGY PER CHIP PER INTERFERENCE DENESITY MEASURED ON THE PILOT CHANNEL

Ec/Io EFFECTIVELY DETERMINES THE FORWARD COVERAGE AREA OF A CELL OR A SECTOR

SYNC CHANNEL

SYNC CHANNEL IS GIVEN THE CODE CHANNEL NUMBER 32; FIXED DATA RATE 1200 KBPS

ALLOWS RECIEVER TO OBTAIN FRAME SYNCHRONIZATION ON SIGNAL

MESSAGES SENT ON SYNCH CHANNEL ARE

  • SYSTEM TIME
  • CHARACTERISTICS OF THE SYSTEM

FORWARD TRAFFIC AND PAGING CHANNELS

PAGING CHANNELS ARE GIVEN THE CODE CHANNEL NUMBER  1 THRU 7

FORWARD TRAFFIC CHANNELS GROUPED INTO RATE SET 1( 9.6, 4.8, 2.4 or 1.2 KBPS) AND RATE SET 2 (14.4, 7.2, 3.6 or 1.8 KBPS)

RATE SET 1 IS REQUIRED FOR IS-95 WHEREAS RATE SET 2 IS OPTIONAL

SPEECH IS ENCODED WITH VARIABLE RATE VOCODER TO GENERATE FORWARD TRAFFIC CHANNEL DATA DEPENDING ON VOICE ACTIVITY