3G -WCDMA

3G - Third Generation mobile telephone networks are the latest stage in the development of wireless communications technology. Significant features of 3G systems are that they support much higher data transmission rates and offer increased capacity, which makes them suitable for high-speed data applications as well as for the traditional voice calls. In fact, 3G systems are designed to process data, and since voice signals are converted to digital data, this results in speech being dealt with in much the same way as any other form of data. Third Generation systems use packet-switching technology, which is more efficient and faster than the traditional circuit-switched systems, but they do require a some what deferent infrastructure to the 2G systems.

Compared to earlier mobile phones a 3G handset provides many new features, and the possibilities for new services are almost limitless, including many popular applications such as TV streaming, multimedia, video conferencing, Web browsing, e-mail, paging, fax, and navigational maps. Japan was the First country to introduce a 3G system, which was largely because the Japanese PDC networks were under severe pressure from the vast appetite in Japan for digital mobile phones. Unlike the GSM systems, which developed various ways to deal with demand for improved services, Japan had no 2.5G enhancement stage to bridge the gap between 2G and 3G, and so the move into the new standard was seen as a solution to their capacity problems. It is generally accepted that CDMA is a superior transmission technology, when it is compared to the old techniques used in GSM/TDMA. WCDMA systems make more efficient use of the available spectrum, because the CDMA technique enables all base stations to use the same frequency. In the WCDMA system, the data is split into separate packets, which are then transmitted using packet switching technology, and the packets are reassembled in the correct sequence at the receiver end by using the code that is sent with each packet. WCDMA has a potential problem, caused by the fact that,as more users simultaneously communicate with a base station, then a phenomenon known as cell breathing can occur. This effect means that the users will compete for the finite power of the base station s transmitter, which can reduce the cell s range V W-CDMA and cdma2000 have been designed to alleviate this problem.

The operating frequencies of many 3G systems will typically use parts of the radio spectrum in the region of approximately 2GHz (the IMT-2000core band), which were not available to operators of 2G systems, and so are away from the crowded frequency bands currently being used for 2G and 2.5G networks. UMTS systems are designed to provide a range of data rates, depending on the user circumstances, providing up to 144 kbps formoving vehicles (microcellular environments), up to 384 kbps for pedestrians (microcellular environments) and up to 2 Mbps for indoor or stationary users (Pico cellular environments). In contrast, the data rates supported by the basic 2G networks were only 9.6 kbps, such as in GSM, which was inadequate

Radio Access Technology

Radio Access Technology is the base of Mobile Communication.

Basic Multiple Access schema's in Cellular Systems

A cellular system generally consists of base stations (BS) provided by operators and a number of mobile stations (MS is a mobile phone) that transmit and receive radio signals to and from a BS. Since there are many MSs in a cell (the coverage area of a BS), multiple access technologies to ensure the transmission of each MS are fundamental for cellular communications.
Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), and Code Division Multiple Access (CDMA) are three basic multiple access methods that maintain the orthogonally among MSs in frequency, time and code domains respectively.

• In FDMA systems, each MS tunes its frequency synthesizer to the channel (frequency carrier) assigned by the BS and then transmits signals on this dedicated channel.
• In TDMA systems, a channel with a relatively wide bandwidth is divided into non overlapping time slots. All MSs tune their frequency synthesizers to the same frequency carrier, but each MS transmits in a dedicated time slot assigned by the BS.
• In CDMA systems, in contrast, orthogonal spreading codes are assigned to MSs. MSs can transmit in the same frequency and time domains, and their signals are distinguished by these orthogonal spreading codes.

Since the frequency spectrum is a very limited resource, reuse of the same frequency spectrum in different cells is always an important issue when designing a cellular system.

Radio Access Technologies in Wideband CDMA

Wideband CDMA (W-CDMA) inherits the merits of DS-CDMA technologies that are used in IS-95. The W-CDMA system also includes additional new technologies, such as highly accurate TPC, Rake combining, asynchronous cell operation, OVSF and code multiplexing, and Turbo coding. These technologies are keys to the success of the W-CDMA.