25-08-2014, 01:10 PM
CDMA TECHNOLOGY
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. INTRODUCTION
We are moving into a new era of communications and information technology. Personal competitiveness in business in relies more and more on increase personal productivity and responsiveness. Today everybody is on the move and mobile is the only way to keep contact with that person. But now a days peoples want multimedia facilities from their mobile handset. But it requires high data rate, hi efficiency and many more technical things, which are available in third generation. (CDMA) so the CDMA TECHNOLOGY makes existing mobile handset more efficient and attractive.
CDMA (3G) mobile devices and services will transform wireless communications into on-line, real-time connectivity. 3G wireless technology will allow an individual to have immediate access to location-specific services that offer information on demand. The first generation of mobile phones consisted of the analog models that emerged in the early 1980s. The second generation of digital mobile phones appeared about ten years later along with the first digital mobile networks. During the second generation, the mobile telecommunications industry experienced exponential growth both in terms of subscribers as well as new types of value-added services. Mobile phones are rapidly becoming the preferred means of personal communication, creating the world's largest consumer electronics industry.
The rapid and efficient deployment of new wireless data and Internet services has emerged as a critical priority for communications equipment manufacturers. Network components that enable wireless data services are fundamental to the next-generation network infrastructure. Wireless data services are expected to see the same explosive growth in demand that Internet service and wireless voice services have seen in recent years
The Cellular Challenge
The world's first cellular networks were introduced in the early 1980s, using analog radio transmission technologies such as AMPS (Advanced Mobile Phone System). Within a few years, cellular systems began to hit a capacity ceiling as millions of new subscribers signed up for service, demanding more and more airtime. Dropped calls and network busy signals became common in
many areas.
To accommodate more traffic within a limited amount of radio spectrum, the industry developed a new set of digital wireless technologies called TDMA (Time Division Multiple Access) and GSM (Global System for Mobile). TDMA and GSM used a time-sharing protocol to provide three to four times more capacity than analog systems. But just as TDMA was being standardized,
an even better solution was found in CDMA.
2.2 Commercial Development
The founders of QUALCOMM realized that CDMA technology could be used in commercial cellular communications to make even better use of the radio spectrum than other technologies. They developed the key advances that made CDMA suitable for cellular, then demonstrated a working prototype and began to license the technology to telecom equipment manufacturers.
The first CDMA networks were commercially launched in 1995, and provided roughly 10 times more capacity than analog networks - far more than TDMA or GSM. Since then, CDMA has become the fastest-growing of all wireless technologies, with over 100 million subscribers worldwide. In addition to supporting more traffic, CDMA brings many other
2 The CDMA Revolution
Historically, the capacity was calculated using simple arguments. Reality, of course, is much more complicated than the idealized models. Real cell coverage areas are highly irregular, not the neat hexagons found in textbook models. Offered load is not spatially uniform, changes dramatically with time-of-day, and is often subject to other uncontrollable influences.
4.3 Background
An idealized multiple access mobile radio system consists of a family of base stations, or "cells," geographically distributed over the service area, and mobile stations. We use the term "mobile" generically to mean any subscriber station, whether it moves or not. The majority of new cellular sales are now in fact hand held portable units, and the market outlook is for that trend to continue for the foreseeable future.
Communication between base stations and mobile stations is established by a negotiation upon call origination. Once communication is established between base and mobile, movement of the mobile is detected and the service is handed over from one base station to another. One cell at a time services each mobile in the narrowband services. The concept of handoff is extended to a multi-way simultaneous "soft" handoff
TRANSMIT DIVERSITY
Transmit diversity consists of de-multiplexing and modulating data into two orthogonal signals, each of them transmitted from a different antenna at the same frequency. The two orthogonal signals are generated using either Orthogonal Transmit Diversity (OTD) or Space-Time Spreading (STS). The receiver reconstructs the original signal using the diversity signals, thus taking advantage of the additional space and/or frequency diversity.
7.6 VOICE AND DATA CHANNELS
The CDMA2000 forward traffic channel structure may include several physical channels:
• The Fundamental Channel (F-FCH) is equivalent to functionality Traffic Channel (TCH) for IS-95. It can support data, voice, or signaling multiplexed with one another at any rate from 750 bps to 14.4 kbps.
• The Supplemental Channel (F-SCH) supports high rate data services.
• The Dedicated Control Channel (F-DCCH) is used for signaling or bursty data sessions. This channel allows for sending the signaling information without any impact on the parallel data stream.
CONCLUSION
In view of the explosive growth of wireless communication over recent decades and the lead-time required for the introduction of new technologies, the time has come to develop a clear perspective of CDMA(3G) wireless systems and services. This CDMA(3G) vision should exploit to complementary approaches. One based on evolution though a network centric view and the other based on the recently introduced user centric view. The person to person communication concept needs to be enhanced to include person to machine and machine to machine networking for ubiquitous connectivity to Internet services.
Interworking between access networks implementing enhanced versions of current technologies for broadcast cellular and short-range communications should provide a good first solution for CDMA(3G) services. This technology map can be extended to include access technologies for transmission at more than 50 Mbit/s for fast moving users as well as ultra wide band systems for wide area coverage. However several interesting technologies challenges ad regulatory issues need to be addressed before the CDMA(3G) vision becomes a reality.