3G科普之W-CDMA

W-CDMA
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Wideband Code Division Multiple Access 宽带CDMA) 是一种3G蜂窝网络。WCDMA UMTS使用的部分协议与2G GSM 标准一致。
具体一点来说，W-CDMA是一种利用码分多址复用(或者CDMA 通用 复用技术，不是指CDMA标准)方法的宽带扩频3G移动通信空中接口。

历史概要

历史上，欧洲电信标准委员会 (ETSI) 在 GSM 之后就开始研究其 3G 标准，其中有几种备选方案是基于直接序列扩频CDMA的，而日本的第三代研究也是使用宽带CDMA技术的，其后，以二者为主导进行融合，在3GPP组织中发展成了第三代移动通信系统UMTS，并提交给国际电信联盟(ITU)。
国际电信联盟最终接受WCDMA作为IMT-2000 3G标准的一部分。

误解

名字跟CDMA很相近，同时WCDMA跟CDMA关系也很微妙。两者都基于码分多址技术，都使用了美国高通（Qualcomm）的部分专利技术。一般认为WCDMA的提出是部分厂商为了绕开专利陷阱而开发的，其方案已经尽可能地避开高通专利。

在移动电话领域，术语 CDMA 可以代指码分多址扩频复用技术，也可以指美国高通（Qualcomm）开发的包括IS-95/CDMA1X和CDMA2000(IS-2000)的CDMA标准族。

在Qualcomm为IS-95协议使用它之前，CDMA复用技术已经存在了很长时间。然而，由于采用CDMA复用方法是IS-95协议区别于当时的GSM（采用TDMA）等其它协议的主要特征，现在通常将该协议也称为CDMA。

WCDMA 也使用CDMA的复用技术而且它跟Qualcomm的标准也很相似。但是WCDMA不仅仅是复用标准。它是一个详细的定义移动电话怎样跟基站通讯，信号怎样调制，数据帧怎么构建等的完整的规范集。

总之:

* 术语CDMA在移动通讯领域通常特指Qualcomm开发的CDMA标准族。它们定义了一组移动通讯协议。
* CDMA作为复用技术，既用于W-CDMA空中接口协议，也用于Qualcomm的CDMA协议。
* W-CDMA专指在IMT-2000中定义的移动电话协议。
* W-CDMA协议与Qualcomm开发的CDMA无关。
* CDMA标准族(IS-95/cdmaOne和CDMA2000)不兼容W-CDMA标准族。

当前状况

2001年，日本NTT DoCoMo公司的FOMA是世界上第一个商业运营W-CDMA服务。 FOMA不兼容UMTS。

J-Phone 日本电话(现沃达丰)已经继推出基于W-CDMA服务后，声称“沃达丰全球标准”兼容UMTS (尽管2004年时还有争议)。

2003年初，和记黄埔 逐步在全球运营他们的UMTS网络(简称3，参见en:3)。

大多数欧洲GSM运营商计划未来某个时间推出UMTS服务，尽管有几个已经把此服务提到日程上来，有一些甚至从2003年底就开始运营UMTS网络。

沃达丰于2004年2月在欧洲多个UMTS网络投入运行。沃达丰还打算在其他国家（包括澳大利亚及新西兰）建设UMTS网络。

AT&T 无线 (现属于Cingular Wireless) 在一些城市开通了UMTS。尽管因为公司兼并使得网络建设进度被延迟，但Cingular已宣布计划在2005年与HSDPA一起部署W-CDMA。

TeliaSonera于2004年10月13日开始在芬兰提供384kbps速率的W-CDMA服务。服务只是在主要城市可用。通讯费率大约2美元每兆字节。

产品认证

* GCF (Global Certification Forum)：现时是世界主要的2G及3G认证机构。
* PTCRB: 在北美为GSM移动设备（ME）类型认证提供框架。

技术

W-CDMA可以使用非成对或者成对频段，虽然所有当前W-CDMA设备（例如FOMA and UMTS）使用两个5MHz频段，一个用于上行一个用于下行。更多信息请参看扩频。

与其他标准比较

* 最初CDMA2000计划使用多个1.25MHz载波，但后来放弃了，而WCDMA则使用单一5MHz带宽载波。
* 在ITU的IMT-2000标准中，WCDMA被看作CDMA直接序列扩频，而CDMA2000被称作"多载波CDMA"。
* WCDMA 标准族(例如FOMA、UMTS)与CDMA标准族(例如IS-95和CDMA2000)不一致。


W-CDMA
From Wikipedia, the free encyclopedia

W-CDMA (Wideband Code Division Multiple Access) is a type of 3G cellular network. W-CDMA is the technology behind the 3G UMTS standard and is allied with the 2G GSM standard with the International Telecommunication Union - ITU.

More technically, W-CDMA is a wideband spread-spectrum 3G mobile telecommunication air interface that utilizes code division multiple access (or CDMA the general multiplexing scheme, not to be confused with CDMA the US standard).

History

W-CDMA was developed by NTT DoCoMo as the air interface for their 3G network FOMA. Later NTT DoCoMo submitted the specification to the International Telecommunication Union (ITU) as a candidate for the international 3G standard known as IMT-2000. The ITU eventually accepted W-CDMA as part of the IMT-2000 family of 3G standards. Later, W-CDMA was selected as the air interface for UMTS, the 3G data part of GSM. Attempts were made to unify W-CDMA (3GPP) and CDMA-1X (3GPP2) standards in order to provide a single worldwide standard. However, divergent requirements resulted in the two incompatible standards being retained.

Features

Only key features are cited below.

* Supports two basic modes of duplex: FDD (frequency division duplex) and TDD (time division duplex) modes
* Employs coherent detection on uplink and downlink based on the use of pilot symbols
* Inter-cell asynchronous operation
* Variable mission: on a 10 ms frame basis
* Multicode transmission
* Adaptive power control based on SIR
* Multiuser detection and smart antennas can be used to increase capacity and coverage
* Multiple types of handoffs between different cells including soft handoff, softer handoff and hard handoff

Misconceptions

W-CDMA is based on the Direct Spread CDMA technique. Code Division Multiple Access has been developed by a number of companies, and in the US this is dominated by Qualcomm. However, the ITU standard is not a Qualcomm implementation, but one where Qualcomm has been invited to participate. Other standards, such as TD-SDMA/TD-CDMA, have been developed by Siemens and Chinese companies independent of both the ITU and Qualcomm and bears no relationship with the US technology other than the name others have assigned to it.

In the mobile phone world, the term CDMA can refer to either the Code Division Multiple Access spread spectrum multiplexing technique, or the CDMA family of standards developed by Qualcomm, including cdmaOne (IS-95) and CDMA2000 (IS-2000 and IS-856).

The CDMA multiplexing technique existed long before Qualcomm used it for its IS-95 protocol. However, this protocol is now widely referred to as "CDMA" for its principal characteristic of using the CDMA multiplexing scheme to share multiple connections divided by different codes (PN sequences) over the same spectrum channel, as opposed to other spectrum division schemes

Qualcomm was able to introduce the first mobile protocol relying upon the CDMA multiplexing technique, associating the multiplexing technique with the name of the protocol.

W-CDMA is used in 3G as a political compromise made by the more advanced non-US companies to allow the US to participate in the rollout of 3G services. Since it now is part of the International Telecommunication Union's standards it is part of a larger suite of standards. W-CDMA is a complete set of specifications, a detailed protocol that defines how a mobile phone communicates with the tower, how signals are modulated, how datagrams are structured, and system interfaces are specified allowing free competition on technology elements.

In summary:

* The term CDMA in the mobile world typically refers to the CDMA family of standards developed by Qualcomm. They are protocols, sets of defined specifications of mobile communications
* CDMA (the multiplexing technique) is used as the principle of the W-CDMA air interface protocol, as well as Qualcomm's CDMA protocols
* W-CDMA strictly refers to a mobile phone protocol with detailed specifications, as defined in IMT-2000
* The W-CDMA protocol was developed independently of the CDMA protocol developed by Qualcomm.
* The CDMA family of standards (including cdmaOne and CDMA2000) are not compatible with the W-CDMA family of standards that are based on ITU standards.

Implementations

The world's first commercial W-CDMA service, FOMA, was launched by NTT DoCoMo in Japan in 2001. FOMA is compatible with standard UMTS. But the effort for migrating the FOMA specifications to UMTS are indicated by Japan.

J-Phone Japan (now Vodafone) soon followed by launching their own W-CDMA based service, originally branded "Vodafone Global Standard" and claiming UMTS compatibility. The name of the service was changed to "Vodafone 3G" in December 2004.

Beginning in 2003, Hutchison Whampoa gradually launched their upstart UMTS networks.

Most countries have since the ITU approved of the 3G mobile service either "auctioned" the radio frequencies to the company willing to pay the most, or conducted a "beauty contest" - asking the various companies to present what they intend to commit to if awarded the licenses. This strategy has been criticised for aiming to drain the cash of operators to the brink of bankruptcy in order to honour their bids or proposals. Most of them have a time constraint for the rollout of the service - where a certain "coverage" must be achieved within a given date or the license will be revoked.

Vodafone launched several UMTS networks in Europe in February 2004. MobileOne of Singapore commercially launched its 3G (W-CDMA) services in February 2005. New Zealand in August 2005 and Australia in October 2005.

AT&T Wireless (now a part of Cingular Wireless) has deployed UMTS in several cities. Though advancements in its network deployment have been delayed due to the merger with Cingular, Cingular began offering HSDPA service in December 2005.

Rogers in Canada is currently trialing HSDPA on W-CDMA at 1900MHz and plan the launch the service commercial in Q3, 2006.

TeliaSonera opened W-CDMA service in Finland October 13th 2004 with speeds up to 384 kbit/s. Availability only in main cities. Pricing is approx. 2€/MB. SK Telecom and KTF, two largest mobile phone service providers in South Korea, have each started offering W-CDMA service in December 2003. Due to poor coverage and lack of choice in handhelds, the W-CDMA service has barely made a dent in the Korean market which was dominated by CDMA2000. By October 2006 both companies are covering more than 90 cities while SK Telecom has announced that it will provide nationwide coverage for its WCDMA network in order for it to offer SBSM (Single Band Single Mode) handsets by the first half of 2007. KT Freecel will thus cut funding to its CDMA2000 network development to the minimum.

In Norway, Telenor introduced W-CDMA in major cities by the end of 2004, while their competitor, NetCom, followed suit a few months later. Both operators have 98 % national coverage on EDGE, but Telenor has parallel WLAN roaming networks on GSM, where the UMTS service is competing with this. For this reason Telenor is dropping support of their WLAN service in Austria (2006).

Maxis Communications and Celcom, two mobile phone service providers in Malaysia, started offering W-CDMA services in 2005.

In Sweden, Telia introduced W-CDMA March 2004.

Technology

W-CDMA may use unpaired or paired spectrum, though the current implementations of W-CDMA (i.e. FOMA and UMTS) all use a pair of 5MHz spectrum, one for uplink and one for downlink. See Spread spectrum for more information. FOMA uses sixteen slots per radio frame, where as UMTS uses 15 slots per radio frame.

3G科普之综述

3G
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第三代移动通讯技术（英语：3rd-generation，3G），是指以UMTS和CDMA2000为代表的，支持高速数据传输的蜂窝移动通讯技术。3G服务能够同时传送声音﹙通话﹚及数据信息﹙电子邮件、即时通讯等﹚。3G的代表特征是提供高速数据业务，速率一般在几百kbps以上。

3G规范是由国际电信联盟（ITU）所制定的IMT-2000规范的最终发展结果。原先制定的3G远景：是能够以此规范达到全球通信系统的标准化。但目前3G存在三种标准，UMTS, CDMA2000, TD-SCDMA。

3G的含义
3G能将无线通信与国际互联网等多媒体通信结合的新一代移动通信系统。能够处理图像、音乐、视频形式，提供网页浏览、电话会议、电子商务信息服务。无线网络必须能够支持不同的数据传输速度，也就是说在室内、室外和行车的环境中能够分别支持至少2Mbps、384kbps以及144kbps的传输速度。

UMTS
UMTS的全名是Universal Mobile Telephone System，中文译为全球移动通讯系统，是基于W-CDMA科技所发展出来的。用在以GSM为主流，要进化到3G的地区，例如欧洲。UMTS目前由3GPP组织负责标准化规范的制定。3GPP所负责的2G或2.5G规范有GSM, GPRS 和EDGE。

FOMA
由日本最大的电信系统商Ntt DoCoMo在2001年提出的规范名称，一般来说就是最早的3G规范。一样基于W-CDMA的规范发展原理，它却与UMTS不兼容。目前正在开发互相兼容的补救方法。

CDMA2000
CDMA2000是3G规范中最重要也是最早开发的规范，它由2G系统中的IS-95规范演化而来，并与之存在相当程度的兼容。CDMA2000主要应用于中国、美洲、日本和韩国。目前由3GPP2组织负责制定规范标准。3GPP2组织与UMT规范中3GPP组织是互相独立的。

TD-SCDMA
向ITU提交的第三种3G方案，获得ITU通过。2004年12月西门子宣布与中国的华为技术有限公司成立合资公司TDTech，就是开发此系统的技术公司。
TD-SCDMA实验网络已建成，网络支撑的各种业务也在试验中，据中国信息产业部公报，2005年该项目组获得较大突破，预计2006年能够在中国正式开通。
当前的研发状态还不是很明朗。主要参与企业为中国的大唐电信、中兴电子、华为。其中大唐电子主要负责终端和交换设备研发。其他两家在此标准上也投入很大资金，专注于基站设备和交换设备研发。

3G与科技泡沫
欧洲3G执照和无线电频谱的拍卖在1990年代3G与科技泡沫事件中扮演了重要的角色。由于确信3G的采纳与普及会相当快速，欧洲的电信公司总计投入了3000亿欧元在标准化规范、购买设备与拓展市场上面。
但预期获利却无法使3G的普及具体化。于是研发者留下了负债和几近无用的3G执照就离开了。许多公司放弃了执照和研发计划、以降低负债。有些公司还试图与发放执照的政府打官司。

德国和奥地利运营商的一些历史数据

* 采用3G标准: WCDMA
* 可用频率:

1. 1.900 MHz – 1.920 MHz (TDD)
2. 1.920 MHz – 1.980 MHz (FDD-上行链路)
3. 2.020 MHz – 2.025 MHz (TDD)
4. 2.110 MHz – 2.170 MHz (FDD-下行链路)

* 通道带宽: 5 MHz
* 片速 : 3,84 Mcps
* Nutzertrennung: 编码(CDMA); 频率(FDMA)
* 移动终端最大发射功率: 0.125–0.25 瓦 (GSM: 1–2瓦)

在德国以下6个可用FDD－频带被发给以下运营商:

运营商 上行链路 下行链路 当时价格
沃达丰德国 D2 1.920,3 MHz – 1.930,2 MHz 2.110,3 MHz – 2.120,2 MHz 164.7亿德国马克 (84.2亿欧元)
未知 1.930,2 MHz – 1.940,1 MHz 2.120,2 MHz – 2.130,1 MHz (164.5亿马克给3G工作组, 后来返还)
E-Plus 1.940,1 MHz – 1.950,0 MHz 2.130,1 MHz – 2.140,0 MHz 164.2亿马克 (83.9亿欧元)
未知 1.950,0 MHz – 1.959,9 MHz 2.140,0 MHz – 2.149,9 MHz (163.7亿马克 给Mobilcom)
O₂－DE 1.959,9 MHz – 1.969,8 MHz 2.149,9 MHz – 2.159,8 MHz 165.2亿马克 (84.5亿欧元)
T-Mobile D1 1.969,8 MHz – 1.979,7 MHz 2.159,8 MHz – 2.169,7 MHz 165.8亿马克(84.8亿欧元)

每个频带有2个信道带宽。中间频率由运营商自定,至少要有4个200KHz分配。除此之外还要预留保护带防止信道干扰。
部署3G的国家

目前已拥有商用3G网络的国家(和地区)和使用标准为：

* 阿根廷 (CDMA2000 1x)
* 澳大利亚 (W-CDMA) (CDMA2000 1x, EVDO)
* 奥地利 (W-CDMA)
* 阿塞拜疆 (CDMA2000 1x)
* 白俄罗斯 (CDMA2000 1x)
* 百慕大群岛 (CDMA2000 1x)
* 巴西 (CDMA2000 1x)
* 加拿大 (CDMA2000 1x)
* 智利 (CDMA2000 1x)
* 中国 (CDMA2000 1x : 中国联通) 未取得牌照
* 中国（WCDMA 中国移动）未取得牌照
* 哥伦比亚 (CDMA2000 1x)
* 丹麦 (W-CDMA)
* 多米尼加共和国(CDMA2000 1x)
* 厄瓜多尔 (CDMA2000 1x)
* 格鲁吉亚 (CDMA2000 1x)
* 德国 (W-CDMA)T-Mobile、沃达丰 O2-DE ePlus
* 希腊 (W-CDMA)
* 危地马拉(CDMA2000 1x)
* 中国香港(W-CDMA)
* 印度 (CDMA2000 1x)
* 印尼 (CDMA2000 1x)
* 以色列 (W-CDMA)
* 意大利 (W-CDMA)
* 牙买加(CDMA2000 1x)
* 日本 (W-CDMA, CDMA2000 1x)
* 哈萨克斯坦(CDMA2000 1x)
* 韩国 (CDMA2000 1x) (W-CDMA in testing)
* 吉尔吉斯斯坦(CDMA2000 1x)
* 马来西亚(W-CDMA) 明讯, Celcom, MiTV, TimeCell)
* 墨西哥 (CDMA2000 1x)
* 摩尔多瓦(CDMA2000 1x)
* 荷兰(W-CDMA)
* 新西兰(CDMA2000 1x) (W-CDMA in testing)
* 尼加拉瓜(CDMA2000 1x)
* 尼日利亚 (CDMA2000 1x)
* 挪威 (W-CDMA)
* 巴基斯坦(CDMA2000 1x)
* 巴拿马(CDMA2000 1x)
* 秘鲁 (CDMA2000 1x)
* 波兰(CDMA2000 1x)
* 罗马尼亚(CDMA2000 1x)
* 俄罗斯(CDMA2000 1x)
* 斯罗文尼亚(W-CDMA)
* 韩国 (CDMA2000 1x)
* 南非 (W-CDMA in testing)
* 西班牙 (W-CDMA)
* 瑞士 (W-CDMA)
* 台湾 (CDMA2000 1x : 亚太电信) (W-CDMA : 中华电信、台湾大哥大、威宝电信、远传电信)
* 泰国 (CDMA2000 1x)
* 阿拉伯联合酋长国 (W-CDMA)
* 英国 (W-CDMA)
* 美国 (CDMA2000 1x) (W-CDMA in testing)
* 乌兹别克斯坦(CDMA2000 1x)
* 委内瑞拉(CDMA2000 1x)
* 越南 (CDMA2000 1x)

3G
From Wikipedia, the free encyclopedia

3G (or 3-G) is short for third-generation technology. It is used in the context of mobile phone standards. The services associated with 3G provide the ability to transfer simultaneously both voice data (a telephone call) and non-voice data (such as downloading information, exchanging email, and instant messaging). In marketing 3G services, video telephony has often been used as the killer application for 3G.

3G networks are not upgrades of 2G networks and do not operate on the same frequency spectrum; rather, entirely new networks need to be built and new frequencies need to be assigned to mobile operators. Induced euphoria led to huge spectrum-licensing fees in many countries, especially in Europe, where spectrum auctions went into the billions of euros. These spectrum licensing fees which were collected years before actual 3G development, together with the enormous investments necessary to build the all-new 3G networks, financially strained a number of mobile operators, delaying 3G roll-out worldwide except in Japan and South Korea, where such spectrum licensing fees were non-existent as the priority in those countries was set on national IT infrastructure development.

The first country which introduced 3G on a large commercial scale was Japan. In 2005, about 40% of subscribers used 3G networks only, with 2G being on the way out in Japan. It was expected that during 2006 the transition from 2G to 3G would be largely completed in Japan, and upgrades to the next 3.5G stage with 3 Mbit/s data rates were underway.

The successful 3G introduction in Japan showed that video telephony was not the killer application for 3G networks after all. The real-life usage of video telephony on 3G networks was found to be a small fraction of all services. On the other hand, downloading of music found strong acceptance by customers. Music download services in Japan were pioneered by KDDI with the EZchakuuta and Chaku Uta Full services.

Technically, 3G networks are not IEEE 802.11 networks. IEEE 802.11 networks are short range, primarily internet access networks, while 3G networks are wide area cellular telephone networks which evolved to incorporate high-speed internet access and video telephony to these networks.

Background

It is estimated that there are about 60 3G networks in 25 countries around the world. In Asia, Europe and the USA, telecommunication companies use WCDMA technology with the support of around 100 terminal designs to operate 3G mobile networks.

In 2001, NTT DoCoMo - one of the giant telecommunication companies in Japan - was the first telecommunication company to launch a commercial WCDMA network. The introduction of 3G services within Europe began in early 2003.

The official 3G mobile network is the systems and services based on the ITU family of standards under the International Mobile Telecommunications programme, 'IMT-2000'. A boost was given to 3G mobile networks in Europe when the EU council suggested that the 3G operators should cover 80% of the European national populations by the end of 2005.

Features

The most significant features offered by third generation (3G) mobile technologies are the momentous capacity and broadband capabilities to support greater numbers of voice and data customers - especially in urban centres - plus higher data rates at lower incremental cost than 2G.

By using the radio spectrum in bands identified, which is provided by the ITU for Third Generation IMT-2000 mobile services, it subsequently licensed to operators. 3G uses 5 MHz channel carrier width to deliver significantly higher data rates and increased capacity compared with 2G networks.

The 5 MHz channel carrier provides optimum use of radio resources for operators who have been granted large, contiguous blocks of spectrum. On the other hand, it also helps to reduce the cost to 3G networks while being capable of providing extremely high-speed data transmission to users.

It also allows the transmission of 384kbps for mobile systems and 2Mbps for stationary systems. 3G users are expected to have greater capacity and improved spectrum efficiency, which will allow them to access global roaming between different 3G networkings.

Standard 3G

International Telecommunications Unit (ITU): IMT-2000 consists of five radio interfaces

* W-CDMA
* CDMA2000
* CDMA2001
* TD-CDMA / TD-SCDMA
* UWC-136
* DECT+

Issues

Even though 3G has successfully been introduced to European mobile users, there are some issues that are debated by 3G providers and users.

* High input fees for the 3G service licenses;
* Great differences in the licensing terms;
* Current high debt of many telecommunication companies, making it more of a challenge to build the necessary infrastructure for 3G;
* Member State support to the financially troubled operators;
* Health aspects of the effects of electromagnetic waves;
* Expense and bulk of 3G phones;
* Lack of 2G mobile user buy-in for 3G wireless service;
* Lack of coverage because it is still new service;
* High prices of 3G mobile services in some countries.

SK Telecom Co Ltd overview

他家的open question不好答，先从Reuter上弄了些资料：

SK Telecom Co., Ltd. (SK Telecom), incorporated in March 1984, is a wireless telecommunications services provider in Korea. The Company had approximately 19.8 million subscribers as of April 30, 2006. SK Telecom provides digital cellular services to its subscribers using code division multiple access (CDMA) technology. The Company provides wireless Internet services under its NATE brand name, which allow its wireless subscribers to access various Websites designed for cellular use, such as access to entertainment-related contents and services and online financial services. SK Telecom provides satellite digital multimedia broadcasting (DMB) service, which enables satellite broadcasting to mobile devices. The Company also provides telematics service and Digital Home service. SK Telecom provides various services outside of Korea, including in the United States, China, Vietnam and Mongolia. In March 2005, the Company acquired a 21.7% equity interest in iHQ Inc., an entertainment management firm producing films, managing entertainers and operating online game services. In August 2005, SK Telecom acquired a 60% stake in YBM Seoul Records Inc., a Korean music recording company. In July 2005, the Company sold a 60% equity interest in SK Teletech to Pantech & Curitel, reducing its equity interest from 89.1% to 29.1%.

Cellular Services

As of April 30, 2006, approximately 18.9 million owned handsets capable of accessing the Company's CDMA 1xRTT network. SK Telecom also provides wideband code division multiple access (WCDMA) services. During the year ended December 31, 2005, the Company completed development of high-speed downlink packet access (HSDPA) technology. By May 2006, SK Telecom had expanded HSDPA service to 25 cities, including Busan and Incheon.

The value-added services offered by SK Telecom include Call Keeper service, COLORing service, Auto COLORing service and Perfect Call service. As of December 31, 2005, 8. 5 million users had subscribed to the Company's COLORing service, 4.6 million users had subscribed to its Perfect Call service and 3.5 million users had subscribed to its Call Keeper service.

As of May 31, 2006, SK Telecom offered CDMA roaming services in 18 countries including the United States, Japan, China, Thailand, Canada, New Zealand and Australia. The Company's global system for mobile communications (GSM) roaming services are available in 78 countries, including countries in Europe and Africa. SK Telecom's WCDMA voice roaming service is available in Japan, Hong Kong, Singapore, Italy, France and Germany. In addition, the Company's global data roaming service is available in six countries, including China, Japan and Thailand. SK Telecom had approximately two million global roaming service users as of December 31, 2005.

Wireless Internet Services

The Company offers a variety of Internet content and services, in addition to providing its wireless subscribers access to the Internet. Under its brand name NATE, SK Telecom offers its wireless subscribers access to the Internet, where subscribers can access a variety of content, including current news, stock quotes and other information, as well as get access to a variety of services, including securities trading and online banking services. Subscribers can purchase goods and services through their wireless devices, send and receive e-mail and gain access to various third-party Internet websites configured to work with wireless technology. Subscribers access NATE using wireless application protocol (WAP) technology. As of April 30, 2006, approximately 19.1 million, or 96.5%, of the Company's subscribers owned WAP-enabled handsets capable of accessing its CDMA 1xRTT network.

Multimedia

In November 2002, SK Telecom introduced June, a wireless data service that provides streaming content. Content provided through the June service includes video on demand, (VOD) and music on demand (MOD); television programs, which can be viewed real time, and multimedia messaging. In addition, June subscribers can access the Internet through NATE. As of December 31, 2005, June had 6.7 million subscribers.

Music Portal Service

In November 2004, the Company introduced a music portal service called MelOn, a music service concept from a combined wireless and wired network. This service allows subscribers to access digital music through cellular phones on a wireless network. This service also offers access to real time streaming from online Websites and digital music downloads to Moving Picture Experts Group Layer-3 Audio (MP3) players and MP3 phones. As of December 31, 2005, SK Telecom had 4.2 million subscribers to its MelOn Service.

Community Portal Service

The Company's subsidiary, SK Communications Co., Ltd. offers Cyworld, which is an online community portal service. As of December 31, 2005, SK Telecom's Cyworld portal service had 16.6 million subscribers. In March 2004, the Company launched Mobile Cyworld, allowing its subscribers to access the Cyworld portal community site through their cellular phones. In 2005, approximately 1.25 million subscribers accessed Mobile Cyworld service, with the average number of monthly users reaching 585,000.

Wireless Entertainment Services

In April 2005, SK Telecom launched GXG, a three-dimensional (3D) mobile game portal, through which subscribers can download mobile games to their cellular phones. As of December 31, 2005, GXG offered 62 mobile games from domestic and foreign game publishers and more than 300,000 of its subscribers owned handsets equipped with a mobile gaming-specific chip. In November 2003, the Company launched Cizle, a wireless Internet movie portal. Cizle allows subscribers to purchase movie tickets using their cellular phones.

M-Commerce

In April 2002, the Company introduced Moneta, a wireless credit and payment system, which allows subscribers to make credit card payments using their cellular phones. As of December 31, 2005, 4.3 million Moneta-enabled handsets had been sold in Korea. In May 2002, SK Telecom entered into a technological cooperation agreement with Visa, pursuant to which Visa agreed to adopt the Company's wireless credit and payment system as the international standard for Visa's worldwide operations. In addition, SK Telecom has established payment systems with department stores and discount stores (such as Family Mart) and affiliated merchant stores (such as Starbucks and TGI). The Company is also developing other uses for mobile payment technology to provide other services, such as payment for transportation services and to serve as a means of identification.

In August and November 2003, SK Telecom launched Mobile Trading System and Stock Investment Information Service, respectively. The Mobile Trading System service provides a program that permits customers to carry out a variety of stock trading, including futures, options and electronic communications network (ECN) trading transactions.

As of December 31, 2005, the Company provided chip-based mobile banking services, under the brand name M-Bank, in conjunction with 17 commercial banks in Korea. M-Bank offers a range of mobile banking services, allowing subscribers to conduct a variety of banking transactions, including money transfers and account inquiries, through their mobile phones. As of December 31, 2005, M-Bank had approximately 760,000 subscribers.

Under its NATE.com brand name, SK Telecom offers a portal service at its Website, www.NATE.com. NATE.com offers a variety of content and services, including an Internet search engine, as well as access to free e-mail accounts. The Company offers an instant messaging service to its Nate.com and NATE users called NATE-ON. This service allows users to chat online through a variety of devices, including personal computers, wireless handsets and personal digital assistants. As of December 31, 2005, the number of NATE-ON subscribers reached approximately 10.3 million. Under its NATE Auction brand name, launched in June 2006, SK Telecom offers its wireless subscribers access to a real time auction platform, where subscribers can sell or bid on items using their cellular phones.

Digital Convergence and New Businesses

The Company launched a DMB satellite in March 2004. In October 2004, SK Telecom granted the right to use its satellite, satellite orbit and frequency to TU Media, an affiliate in which the Company held a 29.6% equity stake as of December 31, 2005. In May 2005, TU Media began to provide commercial satellite DMB service, offering seven video and 20 audio channels. As of December 31, 2005, TU Media offered a range of broadcast content, including education, games, drama, music, news and culture over more than 37 channels. As of April 30, 2006, TU Media had over 500,000 subscribers.

In February 2002, SK Telecom introduced a Telematics service called NATE Drive. NATE Drive is an interactive navigation service that provides driving directions, real time traffic updates and emergency rescue assistance through voice and graphic messaging. In December 2004, the Company added new services to NATE Drive, including a tourist guide and cultural information. As of December 31, 2005, SK Telecom had approximately 285,000 NATE Drive subscribers. In April 2002, the Company entered into an agreement with Renault Samsung Motors and Samsung Electronics to jointly develop a Telematics business. Pursuant to the agreement, the Company provides the cellular phone network and NATE Drive service, while Samsung Electronics provides Telematics-enabled terminals for vehicles and Renault Samsung Motors installs the Telematics-enabled terminals in certain vehicles it sells.

Provision of Wireless Internet Platforms and Cellular Network Solutions to Foreign Code Division Multiple Access (CDMA) Network Operators

In April 2002, the Company entered into an agreement with Pelephone Communications Ltd., an Israeli CDMA operator, to supply its NATE wireless Internet platform to Pelephone on a turnkey basis. In May 2002, SK Telecom entered into a memorandum of understanding with Openwave, a wireless Internet-based communication software and application provider, to form an alliance in order to carry out co-marketing of its NATE wireless Internet platform solutions in overseas markets. In December 2002, the Company entered into an agreement with Asia Pacific Broadband Wireless Communications (APBW), to provide a wireless Internet solution on a turnkey basis. In July 2004, SK Telecom signed a contract with TA Orange, a GSM-based mobile communications operator in Thailand to provide wireless Internet platforms, including the NATE portal platform and NATE service solutions and contents.

Overseas Operations

SK Telecom has operations in the United States, China, Vietnam and Mongolia. On March 24, 2005, the Company and EarthLink completed the formation of SK-EarthLink to market wireless voice and data services in the United States. In October 2005, SK EarthLink changed its name to HELIO. HELIO is a non-facilities-based nationwide mobile virtual network operator (MVNO) offering cellular voice and data services to wireless consumers located in the United States. It commercially launched its MVNO services in May 2006. Since December 2004, SK Telecom has been offering its COLORing solution to Verizon Wireless, a mobile phone service provider in the United States.

In February 2004, the Company and China Unicom established a joint venture company called UNISK Information Technology Co., Ltd. (UNISK). SK Telecom owns a 49% stake of UNISK and China Unicom holds a 51% stake. UNISK offers wireless Internet service in China. In July 2004, the Company acquired ViaTech, an Internet portal service and mobile contents provider in China, to enhance its wireless Internet contents and expand its service area. Through ViaTech, SK Telecom offers a Chinese-language version of Cyworld to subscribers in China. ViaTech had approximately 1.3 million Cyworld subscribers as of January 31, 2006.

In October 2000, SK Telecom along with LG Electronics and Dongah Elecomm established a joint venture company, SLD Telecom PTE. In July 2003, SLD Telecom entered into a business cooperation contract with Saigon Postal Telecommunication Services Corporation to establish a joint venture company, S-Telecom, to provide cellular mobile communications services and commercial CDMA cellular service under the brand name S-Fone. As of December 31, 2005, the S-Fone service was offered in 39 provinces in Vietnam, including HoChiMin and Hanoi. The number of S-Fone subscribers had surpassed 370,000 as of December 31, 2005.

In July 1999, the Company acquired a 27.8% equity interest in Skytel, a Mongolian cellular service provider. As of May 31, 2006, Skytel had approximately 100,000 subscribers. As of December 31, 2005, SK Telecom's equity interest in Skytel was 28.6%.

Other Products and Services

Until the sale of a controlling interest in SK Teletech in July 2005, the Company designed, marketed and sold digital handsets through, SK Teletech, under the brand name SKY. Through its 90.8%-owned subsidiary, SK Telink Co., Ltd., SK Telecom provides international telecommunications services, including direct-dial, as well as pre-and post-paid card calling services, bundled services for corporate customers, voice services using Internet protocol, Web-to-phone services and data services.

The Company competes with KT Corporation and LG Telecom, Ltd.