W-CDMA(Wideband Code Division Multiple Access)는?

엠파스 경제사전 – 용어설명
통화자 개개인의 음성 및 영상 정보를 디지털로 바꿔 고유의 코드를 부여해
전송할 수 있는 차세대 이동통신 기술
이다. 협대역 CDMA는 주파수대역이 1.25MHz지만, 광대역은 5-15MHz로 넓다.이는 1차선 도로와 4-8차선 고속도로의 차이로서 그만큼 광대역으로는 멀티미디어 정보를 많이 초고속으로 보낼 수 있다. 우리나라가 새로운 시내전화방식으로 검토하고 있는 무선가입자망(WLL)분야에도 적용 할 수 있어 상용화에 성공할 경우 상당한 규모의 수입대체는 물론 해외시장 진출 효과를 거둘 수 있을 것으로 전망된다.

W-CDMA is a type of 3G cellular network. W-CDMA is the higher speed transmission protocol used in the Japanese FOMA system and in the UMTS system, an advanced 3G system, designed as a replacement for the aging 2G GSM networks deployed worldwide.

More technically, W-CDMA is a wideband spread-spectrum mobile air interface that utilizes the direct sequence Code Division Multiple Access signalling method (or CDMA) to achieve higher speeds and support more users compared to the older TDMA signalling method of GSM networks. W-CDMA is a competitor to CDMA2000.



Technical features
 -Radio channels are 5MHz wide.
 -Chip rate of 3.84 Mcps
 -Supports two basic modes of duplex, frequency division and time division.
   Current systems use frequency division, one frequency for uplink and one for downlink.
   For time division, FOMA uses sixteen slots per radio frame, where as UMTS uses 15 slots
   per radio frame.
 -Employs coherent detection on uplink and downlink based on the use of pilot symbols.
 -Supports inter-cell asynchronous operation.
 -Variable mission on a 10 ms frame basis.
 -Multicode transmission.
 -Adaptive power control based on SIR (Signal-to-Interference Ratio).
 -Multiuser detection and smart antennas can be used to increase capacity and coverage.
 -Multiple types of handoff between different cells including soft handoff, softer handoff and
   hard handoff.



Development

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, as an alternative to CDMA2000, EDGE, and the short range DECT system. Later, W-CDMA was selected as the air interface for UMTS, the 3G successor to GSM.


Code Division Multiple Access communication networks have been developed by a number of companies over the years, but development of cell-phone networks based on CDMA (prior to W-CDMA) was dominated by Qualcomm, the first company to succeed in developing a practical and cost-effective CDMA implementation for consumer cell phones, its early IS-95 air interface standard. IS-95 evolved into the current CDMA2000 (IS-856/IS-2000) standard.


In the late 1990s, NTT DoCoMo began work on a new wide-band CDMA air interface for their planned 3G network FOMA. FOMA’s air interface, called W-CDMA, was selected as the air interface for UMTS, a newer W-CDMA based system designed to be an easier upgrade for European GSM networks compared to FOMA. FOMA and UMTS use essentially the same air interface, but are different in other ways; thus, handsets are not 100% compatible between FOMA and UMTS, but roaming is supported.


Qualcomm created an experimental wideband CDMA system called CDMA2000 3x which unified the W-CDMA (3GPP) and CDMA2000 (3GPP2) network technologies into a single design for a worldwide standard air interface. Compatibility with CDMA2000 would have beneficially enabled roaming on existing networks beyond Japan, since Qualcomm CDMA2000 networks are widely deployed, especially in the Americas, with coverage in 58 countries in 2006. However, divergent requirements resulted in the W-CDMA standard being retained and deployed.


Despite incompatibilities with existing air-interface standards, the late introduction of this 3G system, and despite the high upgrade cost of deploying an all-new transmitter technology, W-CDMA has been adopted and deployed rapidly, especially in Japan, Europe and Asia, and is already deployed in over 55 countries with ????? subscribers in 2006.[1]



Rationale for W-CDMA
W-CDMA transmits on a pair of 5 Mhz wide radio channels, while CDMA2000 transmits on one or several pairs of 1.25 MHz radio channels. Though W-CDMA does use a direct sequence CDMA transmission technique like CDMA2000, W-CDMA is not simply a wideband version of CDMA2000. The W-CDMA system is a new design by NTT DoCoMo, and it differs in many respects from CDMA2000. From an engineering point of view, W-CDMA provides a different balance of costs vs. capacity vs. performance vs. density, and promises to achieve a benefit of reduced cost for video phone handsets. W-CDMA may also be better suited for deployment in the very dense cities of Europe and Asia. And cross-licencing of patents between Qualcomm and W-CDMA vendors has eliminated possible patent issues due to the features of W-CDMA which remain covered by Qualcomm patents.


W-CDMA has been developed into 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.

출처 : 위키백과

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