外文翻譯---通用分組無線服務(wù)技術(shù)-其他專業(yè)-在線瀏覽
2025-03-24 09:46本頁面
【正文】 oice and packet data, with the work coordinating to ensure that it is not required to transmit on two different frequencies at the same time. Such mobiles are considered pseudoClass A, sometimes referred to as simple class A. Some works are expected to support DTM in 2021. USB GPRS modems use a terminallike interface USB and later, data formats , and RFC 1144 and external antennas. Modems can be added as cards (for laptops) or external USB devices which are similar in shape and size to a puter mouse. Coding schemes and speeds The upload and download speeds that can be achieved in GPRS depend on a number of factors such as: the number of BTS TDMA time slots assigned by the operator the maximum capability of the mobile device expressed as a GPRS multislot class the channel encoding used summarised in the following table. The least robust, but fastest, coding scheme (CS4) is available near a base transceiver station (BTS), while the most robust coding scheme (CS1) is used when the mobile station (MS) is further away from a BTS. Using the CS4 it is possible to achieve a user speed of kbit/s per time slot. However, using this scheme the cell coverage is 25% of normal. CS1 can achieve a user speed of only kbit/s per time slot, but has 98% of normal coverage. Newer work equipment can adapt the transfer speed automatically depending on the mobile location. In addition to GPRS, there are two other GSM technologies which deliver data services: circuitswitched data (CSD) and highspeed circuitswitched data (HSCSD). In contrast to the shared nature of GPRS, these instead establish a dedicated circuit (usually billed per minute). Some applications such as video calling may prefer HSCSD, especially when there is a continuous flow of data between the endpoints. The following table summarises some possible configurations of GPRS and circuit switched data services. Coding scheme Speed (kbit/s) CS1 CS2 CS3 CS4 畢業(yè)設(shè)計說明書（英文翻譯） 5 Technology Download (kbit/s) Upload (kbit/s) TDMA Timeslots allocated CSD 1+1 HSCSD 2+1 HSCSD 3+1 GPRS (Class 8 amp。 ., packet mode munication, which makes it possible for several users to share the same frequency channel. The packets have constant length, corresponding to a GSM time slot. The downlink uses firste firstserved packet scheduling, while the uplink uses a scheme very
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