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The first generation of mobile phones was analog; the second generation was digital. Just as there was no worldwide standardization during the first generation,there was also no standardization during the second, either. Four systems are in use now: D-AMPS, GSM, CDMA, and PDC. Below we will discuss the first three. PDC is used only in Japan and is basically D-AMPS modified for backward compatibility with the first-generation Japanese analog system.

D-AMPS—The Digital Advanced Mobile Phone System
The second generation of the AMPS systems is D-AMPS and is fully digital.It is described in International Standard IS-54 and its successor IS-136. D-AMPS was carefully designed to co-exist with AMPS so that both first- and secondgeneration mobile phones could operate simultaneously in the same cell. In particular, D-AMPS uses the same 30 kHz channels as AMPS and at the same frequencies so that one channel can be analog and the adjacent ones can be digital.
When D-AMPS was introduced as a service, a new frequency band was made available to handle the expected increased load. The upstream channels were in the 1850–1910 MHz range, and the corresponding downstream channels were in the 1930–1990 MHz range, again in pairs, as in AMPS. In this band, the waves are 16 cm long, so a standard ¼-wave antenna is only 4 cm long, leading to
smaller phones. However, many D-AMPS phones can use both the 850-MHz and 1900-MHz bands to get a wider range of available channels.

The first generation of mobile phones was analog; the second generation was digital. Just as there was no worldwide standardization during the first generation,there was also no standardization during the second, either. Four systems are in use now: D-AMPS, GSM, CDMA, and PDC. Below we will discuss the first three. PDC is used only in Japan and is basically D-AMPS modified for backward compatibility with the first-generation Japanese analog system.
第一代手机是模拟制式的，第二代是数字制式的。正如在模拟时代没有世界通用标准一样，数字时代同样没有这样的标准。现在使用的有四种系统：D-AMPS, GSM, CDMA, 和PDC.下面我们将讨论前三种。PDC只在日本通行，它是为了对日本第一代模拟系统向下兼容而在D-AMPS的基础上修改而来。

D-AMPS—The Digital Advanced Mobile Phone System
The second generation of the AMPS systems is D-AMPS and is fully digital.It is described in International Standard IS-54 and its successor IS-136. D-AMPS was carefully designed to co-exist with AMPS so that both first- and secondgeneration mobile phones could operate simultaneously in the same cell. In particular, D-AMPS uses the same 30 kHz channels as AMPS and at the same frequencies so that one channel can be analog and the adjacent ones can be digital.
D-AMPS——数字式高级移动电话服务系统
第二代高级移动电话服务系统简称D-AMPS，它是全数字式的。它在国际标准IS-54及其继任者IS-136范围之内。D-AMPS经过仔细设计以使其与AMPS（Advanced Mobile Phone System 高级移动电话系统）共存，这样第一代和第二代系统就能同时在一部手机上运行。尤其特别的是，D-AMPS与AMPS采用相同的30kHz频道，这样在频率相同时一个通道可以是模拟的，相邻的通道可以设成数字的。

When D-AMPS was introduced as a service, a new frequency band was made available to handle the expected increased load. The upstream channels were in the 1850–1910 MHz range, and the corresponding downstream channels were in the 1930–1990 MHz range, again in pairs, as in AMPS. In this band, the waves are 16 cm long, so a standard ¼-wave antenna is only 4 cm long, leading to smaller phones. However, many D-AMPS phones can use both the 850-MHz and 1900-MHz bands to get a wider range of available channels.
当D-AMPS作为一项服务引进时，一个新的频率范围被开发出来以应对将要增长的负荷。这个上行信道范围在1850–1910 MHz，相对应的下行信道范围在1930–1990 MHz，就像AMPS，它也是成对出现的。在这个频率范围内，波长为16厘米，所以一个标准的1/4行波天线长度仅为4厘米，由此产生了更小的手机。然而许多D-AMPS手机可以使用850-MHz和1900-MHz两种波段以获得更宽的可用频道范围。

手机的第一代模拟；第二代是数字。正如在第一代没有全球标准化，也有在第二没有标准化，要么。四系统的使用：GSM，CDMA，D-AMPS，PDC。下面我们将讨论前三。PDC是用于在日本，基本上是D-AMPS修改为与第一代日本模拟系统的向后兼容性。 d-amps-the数字高级移动电话系统 AMPS系统的第二代D-AMPS和完全的数字。这是国际标准的描述和它的继任者IS-136 IS-54。D-AMPS是经过精心设计的共存与放大器使第一和第二代移动电话可以在同一个细胞同时操作。特别是，D-AMPS使用相同的30千赫频道放大器，在相同的频率，一个通道可以是模拟和相邻的可数字。 当D-AMPS是作为一种服务，一个新的频带提供了处理预期增加的负载。上行通道在1850–1910 MHz频率范围内，和相应的下游渠道，在1930–1990 MHz范围，再对，如放大器。在这一带，波长16厘米，所以标准的¼波天线只有4厘米长，导致 较小的手机。然而，许多D-AMPS手机可以同时使用850兆赫和1900兆赫的频带更宽范围的可用信道。

真牛，这都行

第一代移动手机是模拟的，第二代是数字式的。正如在第一代手机期间没有在世界范围内标准化，在第二代期间也没有标准化。现在使用的有四个系统：D-AMPS, GSM, CDMA, and PDC.下面我们将谈论前三个。PDC仅在日本使用，基于D-AMPS改进的，能与日本的第一代模拟系统后向兼容。 D-AMPS——先进的数字式移动电话系统 AMPS系统的第二代是D-AMPS且是全数字式的。符合国际标准Is-54和后续标准IS-136。为了第一代和第二代手机能在同一机体上同时运行D-AMPS和AMPS系统，D-AMPS被仔细设计。D-AMPS使用了与AMPS相同的频道30KHZ，这样在同一频率下，一个通道可以是模拟的，邻近的通道可以是数字式的。 当D-AMPS作为一种系统被引进时，一个新的频段被用来处理所期望的增加的下载量。向上的频道在1850—1910MHZ范围内，相对应的向下的频道在1930－1990MHZ范围内，AMPS也是如此。在这个频段里，波长16厘米长，因此一个标准的1／4波长天线仅有4厘米长，这引导做更小的手机。然而，许多D－AMPS系统手机能使用850MHZ和1900MHZ带来获得更宽范围的可用频道