Wireless Wide Area Networks continued
Second-Plus Generation Technologies
The second-generation technologies provide data transfer rates only up to 14.4 Kbps. The high data speeds that are needed for video and graphic image transmission are not available on most of the today’s mobile phone systems. Such capabilities require a highly complex and robust technology platform that will not be available in most of the countries until few years from now. An interim step to the next generation technologies is second-plus generation or 2.5G technologies as shown in Figure 4. These technologies support data transfer rates of 57.6 Kbps and higher and offer subscribers access to the Internet at speeds that are comparable to a wire-line ISDN connection or even faster. These include HSCSD, GPRS and EDGE. An overview of these technologies is given next:
HSCSD (High Speed Circuit Switched Data):
HSCSD is a circuit-switched mobile data standard that gives a single user simultaneous access to multiple channels, up to four, at the same time. In comparison, GSM supports only one user per channel per time slot. Assuming a standard data transmission rate of 14.4 Kbps, using four timeslots with HSCSD allows theoretical speeds of up to 57.6 Kbps. This is broadly equivalent to providing the same transmission rate as that available over one ISDN B-Channel.
HSCSD does not disrupt voice service availability. In fact, HSCSD can be pre-empted by voice calls- such that HSCSD calls can be reduced to one channel if voice calls are seeking to occupy these channels. In networks where HSCSD is deployed, GPRS (discussed in next section) may only be assigned third priority, after voice as number one priority and HSCSD as number two. HSCSD is therefore more likely to be deployed in start up networks or those with plenty of spare capacity – since it is relatively inexpensive to deploy and can turn some spare channels into revenue streams. It is however easier to implement in mobile networks than GPRS because some GSM vendor solutions require only a software upgrade of base stations and no new hardware.
HSCSD is expensive for end users as they have to pay for multiple simultaneous calls. However, being a circuit-switched standard, HSCSD could be the best way of communicating with other circuit switched communications media such as the PSTN and ISDN.
Figure 4: Evolution of 2G Networks to 2.5G and 3G
GPRS (General Packet Radio Service):
GPRS is a new packet-based bearer that is being introduced on many GSM and TDMA mobile networks from the year 2001 onwards. It is a non-voice value added service that allows a subscriber to send and receive data in an end-to-end packet transfer mode, without using any network resources in circuit-switched mode. It also permits the user to receive voice calls simultaneously when sending or receiving data calls.
GPRS facilitates instant connections (no dial-up) whereby information can be sent or received immediately as the need arises. This is why GPRS users are sometimes referred to be as being “always connected”. A GPRS mobile device displays a mobile portal service all the time, but it is only activated, and the user is only charged, when information is being transmitted. The main feature of GPRS is that it reserves radio resources only when there is data to send and that these radio resources are shared by all Mobile Stations (Mess) in a cell. It handles data transfer rates from 14.4 Kbps, using just one TDMA slot, up to 115.2 Kbps, using all eight TDMA slots. This will allow it to handle all types of transmission from slow-speed short messages, to the higher speeds needed for browsing complex web pages with high graphics content.
GPRS fully enables a true “Mobile Internet” scenario by allowing integration between the existing Internet and the GPRS network, via interfaces to TCP/IP. Its network can be viewed as a sub-network of the Internet with GPRS capable mobile phones being viewed as mobile hosts. This means that each GPRS terminal can potentially have its own IP address and will be addressable as such. Any service that is used over the fixed Internet today – web browsing, file transfer, chat, email, telnet – will also be available over mobile network via GPRS. In addition, higher data rates will allow users to take part in video conferencing and interact with multimedia websites and similar applications as well.
Enhanced Data rates for Global Evolution (EDGE):
EDGE is a radio based high-speed mobile data standard that was first proposed to the European Telecommunications Standards Institute (ETSI) in 1997 as an evolution of GSM. In fact, it was formerly called GSM384. It is the result of a joint effort between TDMA industry association and the GSM Alliance to develop a common set of third generation wireless standards which supports high-speed modulation. EDGE allows mobile operators to offer 3G services without having to purchase a 3G license. It allows data transmission speeds from 48 Kbps, using just one timeslot, up to 384 Kbps, using all eight timeslots. It supports 800/900/ 1800/1900 MHz frequency bands. Although it reuses the GSM carrier bandwidth and timeslot structure, it is by no means restricted to use within GSM cellular systems. In fact, by enhancing the capability of existing GSM or TDMA systems, it facilitates an evolution of existing cellular systems towards third-generation capabilities.
Implementation of EDGE by network operators has been designed to be simple. Only one EDGE transceiver unit will need to be added to each cell. The new EDGE capable transceiver can also handle standard GSM traffic and will automatically switch to EDGE mode when needed. EDGE capable terminals will also be needed since the existing mobile phone or terminals do not support the new modulation techniques and will need to be upgraded to use EDGE network functionality. EDGE provides the most cost-effective means to provide IP-based multimedia services and applications within existing spectrum. The advantages of EDGE include rapid availability, the reuse of existing GSM and TDMA infrastructure, and support for gradual introduction. In addition, it allows the full advantages of GPRS to be explored, with fast connection set-up, higher bandwidth, and data rates as high as 384 Kbps.
Third Generation Technologies
Two shortcomings of the second generation bearer networks are low bandwidth and limited network capacity which negatively impact the user experience and the reliability of the service. Third generation or 3G technology is a new technological evolution that will offer far more bandwidth and greater data and voice call capacity than today's digital mobile networks allow. It is a next giant step in mobile technology development with its goal being full interoperability and inter-working of mobile systems. The idea behind 3G is to unify the disparate standards that today's second generation wireless networks use.
With 3G technology, portable bandwidth will rise to the level of wired broadband connections and the data transfer rates of up to 2 Mbps will be possible (128 Kbps in a car, 384 Kbps when a device is stationery or moving at pedestrian speed and 2 Mbps in fixed applications). When this speed is achieved, wireless technology will find a new audience that is interested in Internet browsing, wireless gaming, and listening to music. Current mobile networks are only designed for voice and text messaging, whereas 3G networks will allow faster and more complex data transmission such as streaming video and audio, video conferencing, satellite navigation and interactive application sharing. These networks will provide packet switched data access to the Internet with an end-to-end IP connection. This means that when the mobile phone is activated it is automatically connected to the Internet via a normal browser. Subscribers will then enjoy capabilities similar to today’s fixed-line Internet services with significant add-ons such as location-based and highly personalized services.
Third generation technology allows handsets to be left permanently connected to the network and use capacity only when they receive or transmit packages. Subscribers can thus pay for the volume of data transmitted, not how long they talk.
Although the technology behind 3G may seem complicated, the ways in which 3G will affect all of our lives are easy to imagine. Just imagine having a combined camera, computer, stereo, and radio included in your mobile phone. Rich-media information and entertainment will be at your fingertips whenever and wherever you want. Being able to do so much, the end user device is no longer just a mobile phone, and will be referred to as a terminal.
Standardization of third generation mobile communications began in the mid-1990s under supervision of the International Telecommunications Union (ITU). The goal was full interoperability and inter-working of mobile systems capable of providing value-added services. In 1998, the ITU called for Radio Transmission Technology (RTT) proposals for IMT-2000 (International Mobile Telecommunications-2000), the formal name for the third generation standard. Under the brand IMT-2000, it approved three standards to achieve this: W-CDMA, CDMA2000 and TD-SCDMA. W-CDMA (Wideband Code Division Multiple Access) was backed by the European Telecommunications Standards Institute (ETSI) and the GSM operators in Europe and elsewhere; while the CDMA2000 was backed by the North American CDMA community, led by the CDMA Development Group (CDG). The third standard won the support in the other parts of the world. Earlier, in January 1998, the W-CDMA standard was also incorporated by ETSI in the specification of
UMTS (Universal Mobile Telecommunications system) Terrestrial Radio Access; hence W-CDMA and UMTS are often used synonymously.
IMT-2000 is to ensure that these technologies can work in different networks, primarily in IP networks, but for the sake of backwards compatibility, in the GSM and the American ANSI networks as well. Most major network operators in Europe and Asia are committed to the W-CDMA standard for 3G mobile communications. Nevertheless, other standards are being implemented in other parts of the world. In North America and Asia Pacific, the next generation wireless network is going to be mainly based on CDMA2000 and China, the world's largest market for mobile communication, will be using TD-SCDMA standard for 3G networks.
Upgrading from 2G to 3G requires significant capital investment. In the UK, for example, five 3G mobile licenses were auctioned off at a total of $35 billion with the expectation that it will cost each license-holder between $4 billion and $9 billion to build out their 3G network. For this reason carriers have been reluctant to upgrade their networks before they see a real demand for high-speed wireless data and many view 2.5G as more than just an interim solution as it delivers significant bandwidth improvements at greatly reduced cost.
Today, however, as major wireless service providers assess the high costs of deploying 3G services and the accompanying technical difficulties such as 3G handset and network infrastructure readiness, a few are already working on deployment of W-CDMA in Europe and Japan. Table 3 shows market snapshot and status of deployment of mobile Internet technologies in some of these countries. NTT DoCoMo in Japan has already released a third generation phone service FOMA (Freedom Of Mobile multimedia Access) in major urban areas of the country. FOMA receives data at 384 Kbps and transmit at 64 Kbps, and delivers everything from movie trailers and sports highlights to music, video clips and news feeds.
The Strategies Group predicts that there will be 9.5 million 3G mobile high-speed data subscribers by 2005 and UMTS Forum predicts that by 2010 data services will represent $300 billion or 66% of all worldwide 3G revenues.
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