What is inside SYNC Channel Message in CDMA

The sync channel messages include the CDMA protocol revision supported by the cell site, the minimum protocol revision supported by a CDMA mobile in order to work with the cell site, the system and network identification numbers for the cell site, the PN offset of the cell site, the paging channel data rate, and all of the timing parameters including such items as local time offset from system time and a flag for indicating if daylight savings time is active in the area.

The Long Code State parameter contains the 42 bits the phone needs to place into its Long Code generator to become synchronized with the base station. This information is valid 320 ms in the future. How then does the phone use this information to get synchronized? Remember that at this point the mobile has decoded the Pilot channel from the base station.

In decoding the Pilot, the mobile has synchronized its Short Code generator to match that of the received Pilot channel from the base station. The Pilot consists of the just the Short Codes that repeat every 26.6666 ms. The Long Code State information is valid 320 ms in the future.

The phone simply counts the repetitions of the short code to determine the 320 ms period that it needs to wait before beginning to clock its Long Code generator: 320 ms/ 26.66 ms = 12 repetitions of the Short Code.

The Long Code generator is driven by the same 1.2288 MHz clock that drives the Pilot Channel’s Short Codes. So the phone simply lodes the 42 bits into its Long Code generator, counts 12 repetitions of the Pilot Short Codes, and then begins to clock its Long Code generator with the 1.2288 MHz clock it derived from the Pilot Channel’s Short Codes.

Simple Sync Channel Message Contains the Following Data:
  • Base Station Protocol Revision
  • Min Protocol Revision Supported
  • SID, NID of Cellular System
  • Pilot PN Offset of Base Station
  • Long Code State
  • System Time
  • Leap Seconds From Start of System Time
  • Local Time Offset from System Time
  • Daylight Savings Time Flag
  • Paging Channel Data Rate
  • Channel Number
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