TAILIEUCHUNG - Communication Systems for the Mobile Information Society phần 6

Điều này không chỉ do thực tế rằng UMTS cung cấp đủ băng thông trên giao diện không khí cho các ứng dụng như vậy mà còn do một phương pháp mới để xử lý các thay đổi tế bào cho các kết nối gói. Với GPRS truy cập mạng GSM, roaming từ một tế bào khác (quản lý di động) cho các kết nối packetswitched được điều khiển bởi trạm di động. | Universal Mobile Telecommunications System UMTS 167 Figure Discontinuous transmission DTX on a dedicated channel reduces the interference for other subscribers While in the Cell-DCH state the mobile continuously measures the reception quality of neighboring cells and reports the results to the network. Based on these values the RNC can then decide to start a handover procedure when required. While the GSM radio network uses a static reporting interval a much more flexible approach was selected for UMTS. In the first step the RNC instructs the terminal similar to the GSM approach to send periodic measurement reports. The measurement interval itself is now flexible and can be set by the network between and 64 seconds. Furthermore the network can also instruct the terminal to send measurement reports only if certain conditions are met. This way it is possible to send measurement reports for neighboring cells to the network only if the measurement values reach a certain threshold. This removes some signaling overhead which can be used to send more user data over the bearer instead. Another advantage of this method for the RNC is the fact that it has to process fewer messages for each connection compared to periodical measurement reports. Depending on the requirements of the data to be sent different properties can be assigned to a dedicated channel. One property for example is the length of the spreading code which affects the maximum bandwidth available for user data. Therefore depending on the length of the spreading code data rates in the range of a few kilobits per second up to several hundred kilobits per second are possible for a single connection see Section . While the Idle and Cell-DCH RRC states are mandatory for the network all other states like the Cell-FACH Cell-PCH and URA-PCH states which are further described below are optional. The Cell-FACH state is mainly used when only a small amount of data needs to be transferred to or from a .

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