CDMA CALL PROCESSING
To process a call, MS goes through the following stages to get traffic channel.
SYSTEM INITIALISATION STATE
SYSTEM IDLE STATE
SYSTEM ACCESS STATE
TRAFFIC CHANNEL STATE
CALL PROCESSING
CALL PROCESSING STATE
In system initialization state the mobile acquires a pilot channel by searching the PN off sets and selects the strongest pilot signal. Then it acquires synchronization channel using W 32 and detecting timing offset of pilot and detecting timing offset of pilot channel. Then mobile acquires the system configuration and timing information. Then the MS enters the system idle state where it monitors the paging channel. Now the mobile can receive necessary message to initiate or receive a call.
If a call is placed or received, MS enters the system access state exchanging necessary parameters. MS transmits its response on access channel and BS transmits on paging channel. On access, the MS enters traffic channel state and communicate. It also transmits control messages replacing speech by signaling. Power control messages are sent on forward link channel.
SYSTEM INITIALIZATION STATE
System determination sub state: Mobile can select analog or CDMA, if the system selects CDMA, the mobile sets the CDMA channel parameters to channel number. Pilot channel acquisition sub state: Mobile acquires pilot channel of CDMA system and tunes to CDMA channel and sets its code channel for the pilot channel and searches for pilot channel within 20 msec, the mobile should acquire pilot channel, else mobile enters system determination sub state indicating failure. Synchronization acquisition sub state: Mobile acquires the sync channel and obtains system configuration and timing information for CDMA system and sets its code channel for sync channel if mobile does not receive a sync channel message within 21 msec, mobile enters the sync determination sub state with a protocol mismatch indication. If it receives within 21 msec, mobile stores system configuration and timing information. Timing change sub state:
A mobile synchronizes its long code timing of system timing to those of CDMA system after receiving and processing sync messages. After sync channel is acquired and sync message is received, it stores the following information like system identification, network identification, system time, long code at system time, paging channel data rate etc. Idle State
Mobile monitors pagging channel. Mobile can receive message from base station to initiate or receive a call. It can also initiate a registration process, message transmission. After entering idle state, mobile sets its Walsh code to the primary paging channel and sets its rate to the rate obtained from sync message. Paging channel is subdivided into 80 msec slots are called paging channel slots. In slotted mode, the mobile monitors only certain assigned slots. When paging channel is not monitored, mobile can stop or reduce its processing activities to save battery power. In the non slotted mode, paging and control data can be received on any of this slot. The mobile monitors all the slots on continuous basis.
Idle Hand off:
Idle hand off or change of paging channel occurs when a mobile has moved to coverage of another, during idle state. Hand off should occur when it detects new pilot that is stronger than current pilot.
Pilots are identical by short PN offsets. These pilot sets are maintained by active, candidate, neighbor, remaining. If neighbor set or remaining set is stronger than active set and candidate set, pilot hand off is performed. On receiving new message, from new paging channel, it resumes operations. SYSTEM ACCESS STATE:
It includes following sub states. 1. Update overhead information 2. Mobile State origination Attempt 3. Page Response 4. Registration Access sub state 5. Mobile Station Transmission. Traffic channel sub state:
Speech communication takes associated with control messages. There are 5 sub states in this. 1. Traffic Channel initialization: In this state, mobile verifies it can receive forward traffic channel and starts transmit on reverse link. 2. Waiting for order sub state: In this, MS waits for an alert with information message. 3. Waiting for MS answer sub state: In this state, the MS waits for user to answer the call. 4. Conversation sub state: Here, the MS exchange primary traffic data packets with base station. 5. Release Sub state: In this case, MS disconnects a call. CDMA REGISTRATION
Registration is a process in which the MS tells the base station about the whereabouts. It notifies base station of its location status, identification, slot cycle and other characteristics. Purpose of registration is to enable the base station to page the mobile in case of an incoming call.
CDMA supports 9 types of registration.
1. Power up registration: The mobile registers, when it powers up. 2. Power down registration: The mobile registers, when it powers down informing the system that it is no longer active. 3. Time based registration: the mobile registers at regular intervals of time. Its use also alerts the system to automatically deregister mobile stations that did not perform a successful power down registration. 4. Distance based registration: Mobile performs a registration when distance between current base station and the base station which it has previous registered exceeds the threshold. 5. Zone based registration: Mobile registers when it enters a new zone. 6. Parameter changed registration: Mobile does a registration when it enters a new system or some of its stored parameters change. 7. Ordered registration: mobile registers when a base station asks for it. 8. Implicit registration: When a MS sends a successful origination message or page response message, base station can ask a mobile of its location. 9. Traffic channel registration: Base station tells the mobile, it is registered. Only power up, power down, time based, location based registrations are presently supported.
CALL PROCESSING (Mobile Station to Base Station)
Mobile originated call
CALL PROCESSING (Base Station to Mobile Station)
Mobile Terminated call
Mobile initiated call disconnect
Base Station initiated call disconnect
CALL PROCESSING DURING SOFT HAND OFF
