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.

WLAN

WLAN technology is a term used for a wide range of Wireless Local Access Network technologies. Those technologies aim to provide connectivity and wireless access at a high bandwidth to IP-based networks in a similar way or better than wired connections (e.g. Ethernet) provide nowadays. The different options that are currently available in the market have appeared accordingly to the progressive increase of higher bandwidths.The first WLAN standard was created within the IEEE in 1997, the reference for this one is 802.11 (Table 2.4) [25]. The possibilities provided by this standard were to support a maximum of 2Mbps using the unregulated radio-signaling frequency of 2.4 GHz. A drawback when using this unregulated radio-signaling frequency is that WLAN radio signals can be interfered by other equipment working in the same frequency range such as microwaves oven, cordless phones, etc.; in any case, by keeping these at a reasonable distance interference can be avoided. The benefit of using this unregulated radio frequency band is that the cost of the equipment can be lowered as there is no need to pay radio
frequency licenses. The 2Mbps provided by 802.11 were appropriated but are too slow for lots of applications. This triggered the creation of a new IEEE standard, the 802.11b as an extension of 802.11. In September 1999, 802.11b was already supporting up to 11Mbps, providing a bandwidth comparable to traditional Ethernet. 802.11b uses also the same radio frequency band (i.e. 2.4 GHz) as 802.11, having the same drawbacks and benefits derived from free spectrum, but providing a much more convenient bandwidth enough for the majority of applications.

WLAN Standard version

· IEEE 802.11 Standard for WLAN operations at data rates up to 2Mbps in the 2.4GHz ISM Industrial, Scientific and Medical (ISM) band.

· IEEE 802.11a Standard for WLAN operations at data rates up to 54Mbps in the 5GHz Unlicensed National Information Infrastructure (UNII) band.

· IEEE 802.11b Standard for WLAN operations at data rates up to 11 Mbps in the 2.4GHz ISM band.

· IEEE 802.11g High-rate extension to 802.11b allowing for data rates up to 54Mbps in the 2.4 GHz ISM band.

At the same time that 802.11b was being standardized in IEEE, another standard 802.11a was generated as an extension of the 802.11. The 802.11a standard was released in September 1999 supporting a bandwidth of 54Mbps, providing a bandwidth more than enough for the majority of applications; actually, it provided enough bandwidth for several users at the same time. However, 802.11a needs the utilization of a higher frequency band to provide higher bandwidth, and it uses the 5GHz radio frequency band, which is a regulated frequency band. The utilization of a higher frequency has several drawbacks: the achieved distance range is smaller compared to 802.11b, and also penetration of walls and obstacles is more difficult. Despite of providing higher bandwidth, 802.11a products came into the market later than 802.11b because the equipment was more expensive due to regulated band usage constrains. Commonly, 802.11b technology is used in domestic market and 802.11a is used in business market. Between 2002 and 2003, a new standard called 802.11g was generated in IEEE. The 802.11g tries to combine the main advantages of 802.11a and 802.11b, so it is able to support a bandwidth up to 54Mbps using the 2.4 GHz frequency band. The new standard was created to be backward compatible with 802.11b access points, so old devices can still work with new equipment, but at lower rates. All the 802.11 technologies are commonly known as Wi-Fi (Wireless Fidelity). Wi-Fi Alliance
is an entity that certifies that vendor’s products follows the different 802.11 specifications. It certifies 802.11, 802.11a, 802.11b and 802.11g.

Bluetooth is another wireless network technology developed in a different path than 802.11 technologies. Bluetooth supports a very short range of approximately 10 meters, providing up to 1Mbps. The most attractive point of Bluetooth is its low manufacturing cost, otherwise it is not a technology that can be considered for general-purpose networking due to the coverage and bandwidth restrictions. However, the range of application for controlling and messaging remote device is very wide. Nowadays it starts to be very common in cell phones or computers as a fast and easy way to connect with remote devices such as earphones,GPS, PDAs, etc.

Complementary WLAN Access Technology for Cellular Networks

The high data rates provided by WLAN technologies are very attractive for different purposes, and cellular network industry has started to put an eye on it as a good possibility to increase data rates provided to their customers. Maximum data rates provided by traditional cellular network technologies are poor compared to maximum data rates provided by any of the 802.11 families. As an example, the maximum throughput that can be achieved by an MS using legacy 2.5G EGPRS terminals is 59.2 kbps in single slot mode, or up to roughly 220 kbps with current 4 TSLs devices in best conditions. For WCDMA, this limit is set up to 384 kbps for current starting networks, although 2Mbps would be also possible. This fact makes the WLAN technology very attractive for new upcoming 3G services that in general would require a high throughput. However, the main limitation is the coverage provided by WLAN equipment, which is remarkably shorter than the one provided by traditional cellular networks. This led to the conclusion that WLAN could be used to access upcoming new set of 3G services, but with a different scope as that of the so-called 3G cellular networks. Based on these assumptions, WLAN AN was also raised as a new complementary access technology to provide 3G services.

WLAN ANs are well suited to hotspot coverage, where there is a high density of high data rate services, such as 3G services, requiring a limited mobility (e.g. located in airports, cafeterias,etc.). But looking at the other side of the coin, 3G systems allow voice, support wide coverage area and provide high possibilities to mobility; 3G systems are more suitable for wider areas with
relatively low to moderate demand of high data rate services but with more mobility needs. This implies that WLAN ANs and 3G systems may compete in certain market niche but more often the market niche for WLAN AN and 3G systems are complementary, which should enable a nice and soft interworking between these two types of technologies when accessing 3G services. After understanding the complementary characteristics of WLAN and 3G cellular technologies, the next step is to provide multi-access functionalities to the terminals, and furthermore, to make multi-access solution work smoothly by providing seamless mobility mechanism.