【正文】 right code, this process is reversed and the original signal is extracted. Using unique codes means that the same frequency is repeated in all cells. which is monly referred to as a frequency reuse of 1.WCDMA is a step further in the CDMA technology. It uses a 5MHz wide radio signal and a chip rate of , which is about three times higher than the chip rate of CDMA2000. The main benefits of a wideband carrier with a higher chip rate are:● Support for higher bit rates ● Higher spectrum efficiency thanks to improved trunking efficiency (. a better statistical averaging) ● Higher QoS Further, experience from secondgeneration systems like GSM and CDMA One has enabled improvements to be incorporated in WCDMA. Focus has also been put on ensuring that as much as possible of WCDMA operators39。 investments in GSM equipment can be reused. Examples are the reuse and evolution of the core network, the focus on cositing and the support of GSM handover. In order to use GSM handover, the39。different actions can be taken. First, congestion control is activated and reduces the bit rate of non realtime applications, to resolve the overload. Second, if the reduced bit rate activity is not sufficient, the congestion control triggers the inter or intrafrequency handover, which moves some subscribers to less loaded frequencies. Third, handover of some subscribers to GSM and fourth action is to discontinue connections, and thus protect the quality of the remaining connections. Synchronization One of the basic requirements when WCDMA was standardized was to avoid dependence on external systems for accurate synchronization of base stations. This has been achieved by a mechanism, where the handset, when needed, measures the synchronization offset between the cells and reports this to the network. In addition, there is also an option to use an external source, such as GPS, for synchronizing the nodes, . to always provide the best solution both asynchronous and synchronous nodes are supported.4. Basic architecture concepts/ System overview Radio Access Network (RAN) Architecture The main purpose of the WCDMA Radio Access Network is to provide a connection between the handset and the core network and to isolate all the radio issues from the core network. The advantage is one core network supporting multiple access technologies.The WCDMA Radio Access Network consists of two types of nodes:Radio Base Station (Node B)The Radio Base Station handles the radio transmission and reception to/from the handset over the radio interface (Iu). It is controlled from the Radio Network Controller via the Iub interface. One Radio Base Station can handle one or more cells.Radio Network Controller (RNC)The Radio Network Controller is the node that controls all WCDMA Radio Access Network functions. It connects the WCDMA Radio Access Network to the core network via the Iu interface. There are two distinct roles for the RNC, to serve and to control. The Serving RNC has overall control of the handset that is connected to WCDMA Radio Access Network. It controls the connection on the Iu interface for the handset and it terminates several protocols in the contact between the handset and the WCDMA Radio Access Network.The Controlling RNC has the overall control of a particular set of cells, and their associated base stations. When a handset must use resources in a cell not controlled by its Serving RNC, the Serving RNC must ask the Controlling RNC for those resources. This request is made via the Iur interface, which connects the RNCs with each other. In this case, the Controlling RNC is also said to be a Drift RNC for this particular handset. This kind of operation is primarily needed to be able to provide soft handover through