CDMA Power Control, Smart Antenna

Power Control in CDMA All the mobiles communicate on the same frequency. Therefore, internal interference is developed within the system which causes problems in determination of system capacity and voice quality The Tx power from each mobile must be controlled to limit interference. Even the power level should be adequate for satisfactory voice quality.

Objective of Power Control To limit transmitted power on the forward and reverse channels while maintaining link quality. To minimize the Near-Far Problem

Reverse Link Power Control The Reverse link power control affects the access and reverse traffic channels. It is used for establishing the link during the origination a call. The reverse link power includes the open-loop and closed loop power control

Forward Link Power Control The BTS independently adjusts the power for each forward traffic channel based on information received from the mobile. Power control commands are send in the form of Power Control bits (PCBs)

Power control bits are transmitted continuously on the forward traffic 800 bits(0 or 1) per second i.e each bit is transmitted at 1.25 ms intervals A ‘0’ indicates the MS to increase its power, ‘1’ indicates MS to decrease the power Tx If the received signal is low, a ‘0’ is transmitted there by instructing the mobile station to increase its mean output power level. If the received signal is high, a ‘1’ is transmitted to indicate that the mobile station should decrease its power level.

Smart Antennas Smart antennas used digital signal processing to pin point location of users Decides exact path of transmission between MS and BTS All CDMA mobiles use smart antennas

CDMA Network Architecture In CDMA architecture, network components are similar to that in a GSM network like BTS, BSC, MSC, HLR, VLR, AUC, EIR (termed as ESN) etc., GPS antenna is added to the tower for time synchronization. PDSN (Packet data serving node) handles data traffic with in the CDMA network

The PDSN does the role of gateway also. The PDSN does the following activities: Manage the radio-packet interface between the BSS (Base Station Subsystem = BTS + BSC) and the IP network by establishing, maintaining and terminating link layer to the - Initiate, terminate, authenticate session initiated by the subscriber. Provide IP add to the subscriber, perform packet routing with in and to external networks. So in one word it manages every issue related to data traffic.