外文翻譯---理論研究通用分組無線業(yè)務(wù)(編輯修改稿)
2025-06-26 09:06 本頁面
【文章內(nèi)容簡介】 ensures each user transmits and receives at a proper energy level to convey information successfully while reducing the interference to other users. Power control is needed in FDMA and TDMA systems because of the cochannel interference management. This type of interference is caused by the frequency reuse in the limited available spectrum. Via a proper power level adjustment, the cochannel interference can be reduced. This allows a higher frequency reuse factor and thus increases the system capacity. ower control is the most essential requirement in CDMA systems. Without power control, all the mobiles transmit to the base station with the same power not taking into account path loss and fading effect. Mobiles close to the base station will cause significant interference to mobiles that are farther away from the base station. This effect is the socalled near/far effect. Therefore, a welldesigned power control algorithm is crucial for proper operation of a CDMA system. In the absence of power control, the system capacity is very low pared to other systems. Another advantage of power control is that it can prolong battery life by using a minimum required transmission power. Power control on a reverse link is more stringent than on a forward link because of the near/far effect. On a forward link, power control is still necessary to reduce the intercell interference. Power control can be operated in a centralized form or a distributed form. A centralized controller obtains the information of all the established connections and channel gains, and controls the transmission power level. The centralized approach can optimize the power usage of the entire or part of the work and thus is very efficient. It requires extensive control signaling in the work, however, and is difficult to apply in practice. 3 GPRS architecture GPRS is considered as a service or feature of GSM. It was designed by ETSI to be implemented over the existing infrastructure of GSM without interfering with the already existing services. The aim is quick GPRS deployment with minor impact on existing GSM PLMN ponents. Fig. 1 illustrates the logical architecture of a GSM work supporting GPRS. Figure 1. Architecture of GPRS work Mobile Station GPRS and GSM systems provide interworking and sharing of resources dynamically between users. For this reason, three types of terminals have been defined: a classA MS can carry a circuitswitched and a packet switched connection simultaneously enabling the subscriber to initiate or receive a voice call without interrupting a data transmission or reception activity. This type of terminal probably will not be available when GPRS is initially deployed due to its plexity and high cost. An MS of classB is able to connect to both GSM and GPRS at the same time but an ining voice call requires GPRS data transactions in progress to be suspended for the duration of the call. GPRS data transactions can then resume at the end of the voice call. Finally, a classC MS allows subscribers to access one service type only at a given time in an exclusive manner. The GPRS MS has two ponents: a MT (Mobile Terminal) which is typically a handset used to access the radio interface as a radio modem, and a TE (Terminal Equipment) which is typically a laptop or a PDA (Personal Digital Assistant). GPRS MSs will also e as one unit bining the functionalities of an MT and a TE. Base Station Subsystem GPRS has minor impact on the existing GSM BSS making it easy to reuse existing ponent and links without major modifications. This is possible because GPRS uses the same frequency bands and hopping techniques, the same TDMA frame structure, the same radio mod
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