Mr. Aamir Jelani
Over the past decade, wireless communications has seen an exponential growth and will certainly continue to witness spectacular developments due to the emergence of new interactive multimedia applications and highly integrated systems driven by the rapid growth in information services and microelectronic devices. So far, most of the current mobile systems are mainly targeted to voice communications with low transmission rates. In the near future, however, broadband data access at high transmission rates will be needed to provide users packet-based connectivity to a plethora of services. It is also almost certain that the neXt Generation (XG) wireless systems will consist of complementary systems with a set of different standards and technologies along with different requirements and complementary capabilities that will offer users ubiquitous wireless connectivity between mobile and desktop computers, machines, game systems, cellular phones, consumer electronic products, and other hand-held devices. A key requirement in future wireless system is their ability to provide broadband connectivity with end-to-end Quality of Service (QoS), a high network capacity, and throughput at a low cost. To support the above services, a host of new issues and problems have to be addressed. This talk will discuss the challenges facing the 3G communication networks and at some of the important issues pertaining to the evolution of mobile communication networks from GSM (Global System for Mobile Communications) to GPRS (General Packet Radio Service) to 3G (Third Generation) and to CDMA and WCDMA. And also describe some of the leading enabling technologies and comparison of CDMA2000 and WCDMA
Third generation (3G) is the generic term used for the next generation of mobile communications systems. These have been created to support the effective delivery of a range of multimedia services. In addition, they provide more efficient systems for the over-the-air transmission of existing services, such as voice, text and data that are available today.
Electromagnetic waves were first discovered as a communications medium at the end of the 19th century. The first systems offering mobile telephone service (car phone) were introduced in the late 1940s in the United States and in the early 1950s in Europe. Those early single cell systems were severely constrained by restricted mobility, low capacity, limited service, and poor speech quality. The equipment was heavy, bulky, expensive, and susceptible to interference. Because of those limitations, less than one million subscribers were registered worldwide by the early 1980s.
The introduction of cellular systems in the late 1970s and early 1980s represented a quantum leap in mobile communication (especially in capacity and mobility). Semiconductor technology and microprocessors made smaller, lighter weight and more sophisticated mobile systems a practical reality for many more users. These 1G cellular systems still transmit only analog voice information. The most prominent 1G systems are Advanced Mobile Phone System (AMPS), Nordic Mobile Telephone (NMT), and Total Access Communication System (TACS). With the 1G introduction, the mobile market showed annual growth rates of 30 to 50 percent, rising to nearly 20 million subscribers by 1990.
The development of 2G cellular systems was driven by the need to improve transmission quality, system capacity, and coverage. Further advances in semiconductor technology and microwave devices brought digital transmission to mobile communications. Speech transmission still dominates the airways, but the demands for fax, short message, and data transmissions are growing rapidly. Supplementary services such as fraud prevention and encrypting of user data have become standard features that are comparable to those in fixed networks. 2G cellular systems include GSM, Digital AMPS (D-AMPS), code division multiple access (CDMA), and Personal Digital Communication (PDC). Today, multiple 1G and 2G standards are used in worldwide mobile communications. Different standards serve different applications with different levels of mobility, capability, and service area (paging systems, cordless telephone, wireless local loop, private mobile radio, cellular systems, and mobile satellite systems). Many standards are used only in one country or region, and most are incompatible. GSM is the most successful family of cellular standards (GSM900, GSM–railway [GSM–R], GSM1800, GSM1900, and GSM400), supporting some 250 million of the world’s 450 million cellular subscribers with international roaming in approximately 140 countries and 400 networks. 2G to 3G: GSM Evolution Phase 1 of the standardization of GSM900 was completed by the European Telecommunications Standards Institute (ETSI) in 1990 and included all necessary definitions for the GSM network operations. Several tele-services and bearer services have been defined (including data transmission up to 9.6 kbps), but only some very basic supplementary services were offered. As a result, GSM standards were enhanced in Phase 2 (1995) to incorporate a large variety of supplementary services that were comparable to digital fixed network integrated services digital network (ISDN) standards. In 1996, ETSI decided to further enhance GSM in annual Phase 2+ releases that incorporate 3G capabilities. GSM Phase 2+ releases have introduced important 3G features such as intelligent network (IN) services with customized application for mobile enhanced logic (CAMEL), enhanced speech compression/decompression (CODEC), enhanced full rate (EFR), and adaptive multi-rate (AMR), high–data rate services and new transmission principles with high-speed circuit-switched data (HSCSD), general packet radio service (GPRS), and enhanced data rates for GSM evolution (EDGE). UMTS is a 3G GSM successor standard that is downward-compatible with GSM, using the GSM Phase 2+ enhanced core network.
The main characteristics of 3G systems, known collectively as IMT–2000, are a single family of compatible standards that have the following characteristics:
Cdma2000 specification was developed by the Third Generation Partnership Project 2 (3GPP2), a partnership consisting of five telecommunications standards bodies: ARIB and TTC in Japan, CWTS in China, TTA in Korea and TIA in North America. Cdma2000 has already been implemented to several networks as an evolutionary step from CDMAOne as cdma2000 provides full backward compatibility with IS-95B. Cdma2000 is not constrained to only the IMT-2000 band, but operators can also overlay acdma2000 1x system, which supports 144 kbps now and data rates up to 307 kbps in the future, on top of their existing CDMAOne network. The evolution of cdma2000 1x is labeled cdma2000 1xEV. 1xEV will be implemented in steps: 1xEV-DO and 1xEV-DV. 1xEV-DO stands for "1x Evolution Data Only". 1xEVDV stands for "1x Evolution Data and Voice". Both 1xEV cdma2000 evolution steps will use a standard 1.25 MHz carrier. 1xEV-DO probably will be available for cdma2000 operators during 2002 and 1xEV-DV solutions will be available approximately late 2003 or early 2004.
Some of the Concepts which should e considered in order to understand the further details of the of CDMA2000 and WCDMA are discussed in the following section
The transmission from a base station to a mobile phone is considered as the forward link. The reverse link is from the mobile phone to the base station.
Channel access methods are used in point to multipoint networks such as cellular networks for dividing forward and reverse communication channels on the same physical communications medium, they are known as duplexing methods, such as
Time division duplex (TDD) is the application of time-division multiple access to separate outward and return signals. Time division duplex has a strong advantage in the case where the asymmetry of the uplink and downlink data speed is variable. As the amount of uplink data increases, more bandwidth can be allocated to that and as it shrinks it can be taken away. Another advantage is that the uplink and downlink radio paths are likely to be very similar in the case of a slow moving system. This means that techniques such as beam forming work well with TDD systems.
Frequency division duplex (FDD) is the application of frequency-division multiple access to separate outward and return signals. The uplink and downlink sub-bands are said to be separated by the "frequency offset". Frequency division duplex is much more efficient in the case of symmetric traffic. In this case TDD tends to waste bandwidth during switchover from transmit to receive, has greater inherent latency, and may require more complex, more power-hungry circuitry. Another advantage of FDD is that it makes radio planning easier and more efficient since base stations do not "hear" each other (as they transmit and receive in different sub bands) and therefore will normally not interfere each other. With TDD systems, care must be taken to keep guard bands between neighboring base stations (which decreases spectral efficiency) or to synchronize base stations so they will transmit and receive at the same time (which increases network complexity and therefore cost, and reduces bandwidth allocation flexibility as all base stations and sectors will be forced to use the same uplink/downlink ratio)
There are major two type of spread spectrum techniques. Direct Sequence Spread spectrum and Frequency hoping spread Spectrum. CDMA is a multiple-access scheme based on spread-spectrum communication techniques. It spreads the message signal to a relatively wide bandwidth by using a unique code that reduces interference, enhances system processing, and differentiates users. CDMA does not require frequency or timedivision for multiple access; thus, it improves the capacity of the communication system.