[理学]信息与通信工程专业英语02part1.ppt

The IMT-2000 mobile spectrum is around 2 GHz around 800~900 MHz and at 2.6 GHz. The WCDMA system is specified in 3GPP for all the frequency bands. There are further frequencies where WCDMA specification and deployment are also considered, including the 700 MHz band in USA, the 2.3 GHz (Wireless Communication Services (WCS)) band in the USA and part of the existing broadcast frequencies between 400 and 700 MHz. Requirements for Third-Generation Systems The second-generation systems were built mainly to provide speech services in macro cells. To understand the background to the differences between second-generation systems, we need to look at the new requirements of the third-generation systems, which are listed below:8 GSM is the foundation for the Digital Cellular System 1800 (DCS 1800), and the Personal Communications System 1900 (PCS 1900). GSM 900 is the original system that was first implemented in Europe in the early to mid-1980s. DCS 1800 is an upbanded version of GSM 900. PCS 1900 is also based on GSM and is the North American version. It is quite similar to GSM, with only minor differences. In 1997, DCS 1800 was renamed GSM 1800. A variety of data services built into the GSM standard allow the user to directly access fax, data and in the future even Internet services. Short message services enable the user of a GSM phone to combine traditional cellular voice services with paging services in a single unit. GSM has been defined as a platform, which is adaptable to a variety of new market requirements. This will enable the user to utilize a maximum of personal communication — a must for the modern cellular subscriber. Compared to older cellular transmission standards GSM includes a variety of network access, voice, and data services. Features like seamless roaming and handover provide a maximum level of f