外文翻譯---寬帶cdma無線接入網(wǎng)的基本概念(編輯修改稿)
2025-02-14 00:01 本頁面
【文章內(nèi)容簡介】 is handover between the new (WCDMA) network and the existing (GSM) network, which can be triggered by coverage, capacity or service requirements. Handover from WCDMA to GSM, for coverage reasons, is initially expected to be very important since operators are expected to deploy WCDMA gradually within their existing GSM network . When a subscriber moves out of the WCDMA coverage area, a handover to GSM has to be conducted in order to keep the connection.Handover between GSM and WCDMA can also have a positive effect on capacity through the possibility of load sharing. If for example the numbers of subscribers in the GSM network is close to the capacity limit in one area, handover of some subscribers to the WCDMA network can be performed.Another function that is related to intersystem handover is the pressed mode. When performing handover to GSM, measurements have to be made in order to identify the GSM cell to which the handover will be made. The pressed mode is used to create the measurement periods for the handset to make the required measurements. Interfrequency handover (intrasystem handover)The need for interfrequency handover occurs in high capacity areas where multiple 5MHz WCDMA carriers are deployed. Interfrequency handover, which is handover between WCDMA carriers on different frequencies, has many similarities with GSM handover, for example the pressed mode functionality. Channel type switchingIn WCDMA there are different types of channels that can be used to carry data in order to maximize the total traffic throughput. The two most basic ones are mon channels and dedicated channels. Channel type switching functionality is used to move subscribers between the mon and the dedicated channel, depending on how much information the subscriber needs to transmit. The dedicated channel is used when there is much information to transmit, such as a voice conversation or downloading a web page. It utilizes the radio resources efficiently as it supports both power control and soft handover. Admission controlAs there is a very clear tradeoff between coverage and capacity in WCDMA systems, the admission control functionality is used to avoid system overload and to provide the planned coverage. When a new subscriber seeks access to the network, admission control estimates the network load and based on the new expected load, the subscriber is either admitted or blocked out. By this the operator can maximize the network usage within a set of network quality levels, . levels depending on what kind of service/information the subscriber wants to use. Congestion control Even though an efficient admission control is used, overload may still occur, which is mainly caused by subscribers moving from one area to another area. If overload occurs, four 39。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 asy
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