System Access: When the mobile first turns on, it must find the best base station. This is similar to analog where the phone scans all the control channels and selects the best one.
In CDMA, the mobile unit scans for available Pilot signals, which are all on different time offsets. This process is made easier because of the fixed nature of these offsets. The timing of any base station is always an exact multiple of 64 system clock cycles (called chips) offset from any other base station.
The mobile selects the strongest pilot tone and establishes a frequency and time reference from this signal. The mobile then demodulates the sync channel, which is always on Walsh 32. This channel provides master clock information by sending the state of the 42 bit long code shift register 320 milliseconds in the future.
Once the mobile has read the sync channel and established system time, the mobile uses the parameters from the sync channel to determine the long code mask being used by the cell site it is acquiring.
- Find All Receivable Pilot Signals: Choose Strongest One
- Establish Frequency and PN Time Reference (Base Station I.D.)
- Demodulate Sync Channel
- Establish System Time
- Determine Paging Channel Long Code Mask