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发表于 2006-1-16 02:18:03| 字数 4,749| - 墨西哥
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http://en.wikipedia.org/wiki/CDMA2000
CDMA2000
From Wikipedia, the free encyclopedia.
CDMA2000 is a family of 3G mobile telecommunications standards that use CDMA, a multiple access scheme for digital radio, to send voice, data, and signaling data (such as a dialed telephone number) between mobile telephones and cell sites.
CDMA (Code Division Multiple Access) is a mobile digital radio system that transmits streams of bits and whose channels are divided using codes (PN sequences). CDMA permits many radios to share the same frequency channel. Unlike TDMA (Time Division Multiple Access), a competing system used in GSM and D-AMPS, all radios can be active all the time, because network capacity does not directly limit the number of active radios. Since larger numbers of phones can be served by smaller numbers of cell sites, CDMA-based standards have a significant economic advantage over TDMA-based standards, or the oldest cellular standards that used Frequency Division Multiple Access.
CDMA2000 has a relatively long technical history, and remains compatible with the older CDMA telephony methods (such as cdmaOne) first developed by Qualcomm, a commercial company, and holder of several key international patents on the technology.
CDMA2000 is an incompatible competitor of the other major 3G standard W-CDMA (UMTS). Since CDMA2000 is based on older standards, many authorities speculate that the incompatible CDMA standards exist so that US, European and other countries might assure a domestic market and patent protections for their mobile phone providers.
CDMA2000 is one of the approved radio interfaces for the ITU's IMT-2000 standard and a successor to 2G CDMA (IS-95, branded cdmaOne). It is standardized by 3GPP2.
CDMA2000 is a registered trademark of the Telecommunications Industry Association (TIA-USA) in the United States, not a generic term like CDMA. TIA has branded their 2G CDMA standard (aka IS-95) as cdmaOne.
There are many different types of CDMA2000. In order of increasing complexity:
Contents [hide]
1 CDMA2000 1x
2 CDMA2000 3x
3 CDMA2000 1xEV-DO
4 CDMA2000 1xEV-DV
5 External links
[edit]
CDMA2000 1x
CDMA2000 1x, also known as 1x, CDMA2000 1X, 1X, or 1xRTT (1x Radio Transmission Technology), is the core 3G CDMA2000 technology. The designation 1x is used to identify the version of CDMA2000 radio technology that operates in a pair of 1.25-MHz radio channels (one times 1.25 MHz, as opposed to three times 1.25 MHz in 3xRTT). 1xRTT almost doubles voice capacity over IS-95 networks. Although capable of higher data rates, most deployments have limited the peak data rate to 144 kbit/s. While 1xRTT officially qualifies as 3G technology, 1xRTT is considered by some to be a 2.5G (or sometimes 2.75G) technology. This has allowed it to be deployed in 2G spectrum in some countries which limit 3G systems to certain bands.
The air interface standard of this second generation of CDMA digital cellular is denoted as IS-2000. The main differences between IS-95 and IS-2000 signalling are: the use of a pilot signal on the IS-2000 reverse link to permit the use of coherent modulation, and 64 more traffic channels on the forward link that are orthogonal to the original set. Some changes were also made to the data link layer to accommodate the greater use of data services -- IS-2000 has media and link access control protocols and QoS control. In IS-95, none of these were present, and the data link layer basically consisted of a "best effort delivery" RLP -- this arrangement is still used for voice.
In the United States, Verizon Wireless, Sprint PCS, Alltel, and U.S. Cellular use 1x.
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CDMA2000 3x
CDMA2000 3x utilizes a pair of 3.75-MHz radio channels (i.e., 3 X 1.25 MHz) to achieve higher data rates. The 3x version of CDMA2000 is sometimes referred to as Multi-Carrier or MC. The 3x version of CDMA2000 has not been deployed and is not under development at present.
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CDMA2000 1xEV-DO
CDMA2000 1xEV-DO (1x Evolution-Data Optimized, originally 1x Evolution-Data Only), also referred to as 1xEV-DO, EV-DO, or just DO, is an evolution of CDMA2000 1x with High Data Rate (HDR) capability added and where the forward link is time-division multiplexed. This 3G air interface standard is denoted as IS-856.
CDMA2000 1xEV-DO in its latest revision, Rev. A, supports downlink (forward link) data rates up to 3.1 Mbit/s and uplink (reverse link) data rates up to 1.8 Mbit/s in a radio channel dedicated to carrying high-speed packet data. 1xEV-DO Rev. A was first deployed in Japan and will be deployed in North America in 2006. The Rev. 0 that is currently deployed in North America has a peak downlink data rate of 2.5 Mbit/s and a peak uplink data rate of 154 kbit/s.
Verizon Wireless, Sprint Nextel Corporation, Bell Canada, and TELUS are in the midst of nationwide deployment of 1xEV-DO in North America, and Alaska Communications Systems (ACS) is deploying 1xEV-DO in the main population centers of Alaska.
Japanese operator KDDI uses the brand "CDMA 1X WIN" for their CDMA2000 1xEV-DO network, but this is only in reference to its building on past marketing promotions.
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CDMA2000 1xEV-DV
CDMA2000 1xEV-DV (1x Evolution-Data and Voice), supports downlink (forward link) data rates up to 3.1 Mbit/s and uplink (reverse link) data rates of up to 1.8 Mbit/s. 1xEV-DV can also support concurrent operation of legacy 1x voice users, 1xRTT data users, and high speed 1xEV-DV data users within the same radio channel.
In 2005, Qualcomm put the development of EV-DV on an indefinite halt, due to lack of carrier interest, mostly because both Verizon Wireless and Sprint are using EV-DO. |
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