功率控制的技術在無線通訊系統上是相當重要的機制，它是用來管理基地台及行動台發射功率的技術，期望用最小的發射功率達到正常或最佳品質的通訊服務。反向鏈路功率控制是針對行動台而順向鏈路功率控制是針對基地台，特別在提升分碼多重存取的容量、效能是更加明顯。然而無線通訊系統最大通訊阻礙來自衰減的通道環境，使得分碼多重存取系統的容量受限於多路徑效應、影子效應以及近-遠效應。對於分碼多重存取蜂巢式系統之反向鏈路而言，由於近-遠效應的干擾特別敏感，功率控制是必要的技術。 在第二代無線通訊系統的順向鏈路最初未考慮快速功率控制，導致其系統容量效率受限於此。為了提高順向鏈路容量效率，在cdma2000順向鏈路系統中，使用了快速(800Hz)閉迴路功率控制可以突破第二代無線通訊系統順向鏈路的容量瓶頸。不過傳統上，功率控制的步階大小是固定在1dB，對於行動載具的可變速度而言，並非最佳化。故此，利用行動載具速度的都卜勒效應產生都卜勒頻率來建造一行動載具測速機制。依據行動載具測速機制測出行動載具速度區段，並選擇適合的功率控制步階大小與通道估測濾波器參數使其達到最佳匹配，藉以提升第三代分碼多重存取(3G CDMA)效能，其發射功率可節省1.6dB，此相似方法也可適用於反向鏈路之功率控制上。 Power control technique is the most important device unit in wireless communication systems. This technique for managing the transmit power in the base stations and mobiles to a minimum level needed for the normal or best performance. The reverse link power control is applied to the base stations and the forward link power control to the mobiles. Especially, the CDMA capacity is significant improved. However, the most deterioration results from rapid fluctuating channel environment in wireless communication systems such that the capacity of CDMA systems is limited by the multipath fading, the shadowing fading, and the “near-far” effect. The power control for the reverse link of a CDMA cellular system is a necessary technique due to the near-far effect. The original 2G CDMA-based wireless communication system does not have the fast power control, so it limits the system capacity. For improving the forward link capacity, a fast(800Hz) power control is used for the forward link of cdma2000. In convention, however, the power control step size for a fixed value of 1dB cannot be optimal in any mobile speed along with a carrier frequency. Thus, the design of the mobile speed estimation unit is developed based on Doppler frequency spectrum induced by Doppler effect of the mobile speed. The estimation of the mobile speed zones is based on the mobile speed estimation device. The power control step sizes and the parameters of the channel estimation filter are optimally selected to improve the forward link performance of the 3G CDMA systems. The simulation results indicate that the transmit power can save up to1.6dB for the single path case in the forward link. The similar approach will be suitable for the design of the power control at the other channel conditions and the reverse link.
