中兴CDMA蜂窝移动通信系统.PPT

CDMA Key Technology ZTE Corporation CDMA Division CDMA Key Technology Power Control Near-far problem If all mobiles transmitted at the same power level, the base station would receive unnecessarily strong signals from mobiles nearby and extremely weak signals from mobiles that are far away. This will reduce the capacity of the system. Power Control Power control is a CDMA feature that enables mobiles to adjust the power at which they transmit. This ensures that the base station receives all signals at the appropriate power. Both forward and reverse links uses power control techniques. Power Control (Continued) Reverse Link Open Loop Power Control An initial estimation of required transmission power by the mobile Coarse measure of path loss based upon total receive power at mobile Receive Power+Transmitted Power=-73(dbm)+Parameter Power Control (Continued) Reverse Link Closed Loop Power Control Used to compensate for asymmetries in forward/reverse links Up/down commands sent to mobile based upon SNR measured at Base Station compared to a specified threshold Transmitted 800 times per second at 1dB increments Power Control (Continued) Reverse Outer Loop Power Control Setpoint is varied according to FER on reverse link (measured at the Base Station Controller) Sampled at 50 frames per second rate (20msec) Setpoint adjusted every 1-2 seconds Power Control (Continued) Forward Link Power Control Base station slowly decreases power to each mobile As FER (measured at the mobile) increases, the mobile requests a raise in forward link power Power Control (Continued) All types of power control work simultaneously to minimize transmit power Diversity Time Diversity Frequency Diversity Space Diversity Diversity (Continued) Diversity (Continued) Diversity (Continued) Soft Handoff A soft handoff establishes a connection with the new BTS prior to breaking the connection with the old one. This is possible because CDMA cells use the same frequency and the