Additional Channel is CDMA1x RTT system.

Here fundamental channels pilot, paging, sync, traffic, access channel are same as CDMA IS95 which are described in previous post. In CDMA 1x RTT few channels are introduced which are described below:

1). Forward Quick Paging Channel(F-QPCH)

2). Forward Supplemental Channel (F-SCH)

3). Reverse Pilot Channel (R-PICH)

4). Reverse Supplement Channel(R-SCH)

1). Forward Quick Paging Channel(F-QPCH)

Mobile monitors incoming calls on paging channel. The mobile station continuously monitors the Paging Channel on both slotted and non slotted mode. The mobile station can “sleep” or reduce power consumption (for the power conservation) during non-active states (during the slots when the paging channel is not being monitored).

Since battery consumption is high in paging channel mode so QPCH channel (quick paging channel) is introduce to save battery of mobile. Mobile monitors QPCH to determine if there is a paging forthcoming on paging channel in its slot (looks at 1-bit paging indicator). If no flag, then mobile continues to sleep; if have flag, the mobile monitor appropriate slot and decodes general page message

Without QPCH, mobile must monitor regular paging channel slot and decode several fields to determine whether page is for it or not; this drains mobile batteries quickly.

2). Forward Supplemental Channel (F-SCH)

F-SCH Assigned for high-speed packet data (>9.6 kbps) in the forward direction; (FCH is always assigned to each call). Up to 2 F-SCH can be assigned to a single mobile. SCH cannot exist without having a fundamental channel established.

3). Reverse Pilot Channel (R-PICH)

It is used to Implement Quick Power Control on the Forward Link. It Allows base station to do timing corrections without having to guess where mobile is (in search window). Mobile can transmit at lower power, reducing interference to others. The Reverse Pilot Channel is unmodulated spread spectrum signal used to assist the base station in detecting a mobile station transmission.

4). Reverse Supplement Channel(R-SCH)

R-SCH is used for high-speed packet data (>9.6 kbps) in reverse direction. Difference between F-SCH and R-SCH is in Walsh code based spreading. F-SCH supports Walsh code lengths of 4 to 128 (1xRTT) or 1024 (3xRTT) depending on data rate and chip rate. R-SCH uses either a 2-digit or 4-digit Walsh code; rate matching done by repetition of encoded and interleaved symbols. Walsh code allocation sequence is pre-determined and common to all mobiles. Users are differentiated using long PN code with user mask.