主题：【注意】手机的疑问 -- 淡山客

感谢各位的热心帮助，我现在有了初步的概念。真的好感谢大家,每人鲜花一朵，聊表谢意

copy from wikipedia

IS-54 and IS-136 are second-generation (2G) mobile phone systems, known as Digital AMPS (D-AMPS). It is used throughout the Americas, particularly in the United States and Canada. D-AMPS is considered end-of-life, and existing networks are in the process of being replaced by GSM/GPRS and CDMA2000 technologies. Although most often referred to as TDMA, this is an incorrect reference to the protocols. IS-54 and IS-136 do, however, use Time Division Multiple Access as an air interface.

D-AMPS uses existing AMPS channels and allows for smooth transition between digital and analog systems in the same area. Capacity was increased over the preceding analog design by dividing each 30 kHz channel pair into three time slots and digitally compressing the voice data, yielding three times the call capacity in a single cell. A digital system also made calls more secure because analog scanners could not access digital signals. Calls were encrypted, although the algorithm used (CMEA) was later found to be weak. [1]

IS-136 added a number of features to the original IS-54 specification, including text messaging, circuit switched data (CSD), and an improved compression protocol. SMS and CSD were both available as part of the GSM protocol, and IS-136 implemented them in a nearly identical fashion.

Large IS-136 networks include Cingular Wireless and U.S. Cellular in the United States, and Rogers Wireless in Canada. Cingular (who purchased AT&T Wireless in October 2004) and Rogers Wireless are upgrading their existing IS-136 networks to GSM/GPRS, while US Celluar is migrating most of their network to CDMA2000. Rogers Wireless removed all 1900 MHz IS-136 in 2003, and is slowly doing the same with their 800 MHz spectrum as the equipment fails. It is not unusual for a Rogers D-AMPS customer to have coverage in a specific location one day, and then none in that same area the next.

Mobile phone standards

1G

AMPS

2G

GSM

D-AMPS

2.5G

GPRS

2.75G

CDMA2000 1xRTT

EDGE

3G

W-CDMA (UMTS,FOMA)

CDMA2000 1xEV

TD-SCDMA

总结:北美最先使用的是AMPS协议,为analog信号,然后发展到D-AMPS协议 (数字通信了),俗称"TDMA".最近(应不早于2002年,我2002/2003年用的手机还是用"TDMA"协议的)部分运营商逐步转到第二代的gsm和2.5代的gprs,部分转到cdma2000.刚才又查了点资料,Verizon Wireless 和 Bell Canada 采用的是第三代的技术,不过还在第一阶段,即 cdma2000 1xEV-DO, EV-DO=Evolution data optimized. sprint pcs 在2004/7, 号称直接要在美国建全国性的符合第二阶段cdma网络,即cdma2000 1xEV-DV, EV-DV = evolution data and voice.

中国大陆目前主要是gsm/gprs(移动),联通好象是在2002年开始主推cdma2000,不过那个时候是采用的2.5G(或者叫2.75G)的技术,不知道现在升级了没有.

所以如果你的手机是在2002年以前在美国买的,回国也没法改装.国内能改装的是gsm手机，一般是欧洲的.因为欧洲已经使用gsm系统很长时间了.2004年开始在美国买的gsm手机可以带回国用了.因为美国的运营商要照顾欧洲的生意,而中国的gsm频段和欧洲一样.

比如同是gsm网络,美国和中国采用的频段不一样,这时可以买一个三频的手机.其次,通讯协议不同.美国以前常用的是tdma,中国一开始就建设的是gsm的.这个时候不仅频点不同,编码寻址也不同,改造手机很麻烦,有时候不仅要加解码芯片,还要看RF部分的指标等等,不如干脆买个新的.另外gsm手机用的是sim卡作为个人身份认证,tdma把类似的号码做死在手机中了,所以两者间可能还改不? 我曾经认识一个人,回国就去改装手机,结果把手机烧了,回来后还得买个新的,亏大发了.

俺的就是三频的（纽约中国城买的），回国在设定（setting）里换个频段（band）就成了