Role of WCDMA in 3G Mobile Communication
Introduction to 3G:
The Third Generation (3G) will be digital mobile multimedia offering broadband mobile communications with voice, video, and graphics, audio and other information.
The mobile communications industry has evolved in three stages, and correspondingly three generations of mobile phones have emerged thus far. Each one has provided more flexibility and usability than the previous ones.
o (1G) Analog: Analog phones helped to make voice calls inside one’s country without roaming facilities.
o (2G) Digital mobile phone systems added fax, data and messaging capabilities as well as voice telephone service in many countries offering worldwide roaming.
o (3G) Multimedia services add high speed data transfer to mobile devices, allowing new video, audio and other applications (including Internet services) through mobile phones.
3G, based on WCDMA technology, will bring these incompatible standards together.
Features of 3G:
1. With 3G, the information is split into separate but related packets before being transmitted and reassembled at the receiving end. Packet switched data formats are much more common than their circuit switched counterparts.
2. The World Wide Web (WWW) is becoming the primary communications interface. People access the Internet for entertainment, services, and information collection, the intranet for accessing enterprise information and connecting with colleagues and the extranet for accessing customers and suppliers. These are all derivatives of the World Wide Web aimed at connecting different communities of interest. Information and other resources are being stored in remote Web servers, which serve the various needs of human beings through Web browsers at their ends.
3. Speeds of up to 2 Megabits per second (Mbps) are achievable with 3G. The data transmission rates will depend upon the environment, the call is being made in, however, only indoors and in stationary environments that these types of data rates will be available. For high mobility, data rates of 144 kbps are expected to be available.
Implementation of WCDMA in 3G:
Wideband Code-Division Multiple-Access (W-CDMA) is one of the main technologies for the implementation of third-generation (3G) cellular systems.
The implementation of W-CDMA will be a technical challenge because of it’s complexity and versatility. The complexity of W-CDMA systems can be viewed from different angles: the complexity of each single algorithm, the complexity of the overall system and the computational complexity of a receiver. W-CDMA link-level simulations are over 10 times more compute-intensive than current second-generation simulations. In W-CDMA interface different users can simultaneously transmit at different data rates and data rates can even vary in time. UMTS networks need to support all current second generation services and numerous new applications and services.
Different modes of operation in WCDMA:
In WCDMA, there are two different modes of operation possible:
o TDD: In this duplex method, uplink and downlink transmissions are carried over the same frequency band by using synchronized time intervals. Thus time slots in a physical channel are divided into transmission and reception part.
o FDD: The uplink and downlink transmissions employ two separated frequency bands for this duplex method. A pair of frequency bands with specified separation is assigned for a connection. Since different regions have different frequency allocation schemes, the capability to operate in either FDD or TDD mode allows for efficient utilization of the available spectrum
Key Features of WCDMA:
The key operational features of the WCDMA radio interface are listed below:
1. Support of high data rate transmission: 384 Kbps with wide area coverage, 2 Mbps with local coverage.
2. High service flexibility: support of multiple parallel variable rate services on each connection.
3. Both Frequency Division Duplex (FDD) and Time Division Duplex (TDD).
4. Built in support for future capacity and coverage enhancing technologies like adaptive antennas, advanced receiver structures and transmitter diversity.
5. Support of inter frequency hand over and hand over to other systems, including hand over to GSM.
6. Efficient packet access.
WCDMA Technical Specifications
Multiple Access Scheme: DS-CDMA
Duplex Scheme: FDD/TDD
Packet Access Dual mode: (Combined and dedicated channel)
Multirate/Variable rate scheme: Variable spreading factor and multi-code
Chip Rate: 3.84 Mcps
Carrier Spacing: 4.4-5.2 MHz (200 kHz carrier raster)
Frame Length: 4.4-5.2 MHz (200 kHz carrier raster
Inter Base Station synchronization: FDD: No synchronization needed
TDD: Synchronization required
3G mobile communication Technology with WCDMA:
Providing good in-building coverage plays an important role in attracting and retaining mobile subscribers. Ordinarily, coverage from the macro network extends into buildings but should be complemented by dedicated in-building systems. Greater data capacity and the ability of third-generation networks to provide high-speed data services increase the demands put on the cellular network. Subscribers have great expectations regarding third-generation services.
Therefore, when introduced, the new services must (at very least) be available everywhere second-generation services can be found. Notwithstanding, many third-generation networks deployed to date have been designed primarily to provide good coverage in outdoor environments-not inside buildings. As a consequence, users of early implementations of wideband code-division multiple access (WCDMA) rate third-generation services poorly compared to second-generation services.
The major advantage is increased capacity through more efficient use of the spectrum. Greater capacity enables the WCDMA wireless network to handle higher call density at a lower cost. Implementation of WCDMA improved the voice quality, system performance and Mobile battery life.
1. Rakesh Arora, “Recent advances in wireless data networking”.
2. Hans Beijner, “The Importance Of In-Building Solutions In Third-Generation Networks”.
3. Juha Korhonen, “Introduction to 3G Mobile Communications”.
4. Ramjee Prasad, “Towards a Global 3G System”
5. Jeffrey Bannister, Paul Mather, Sebastian Coope, “Convergence Technologies for 3G”
6. MR Karim, Mohsen Sarraf, “W CDMA and Cdma2000 for 3G Mobile Networks”
7. Keiji Tachikawa, “W CDMA Mobile Communications System”
8. R Ramachandran, “Evolution to 3G mobile communication”
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