3G Technology


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INTRODUCTION


3G technology is the latest in mobile communications. 3G stands for "third generation" -- this makes analog cellular technology generation one and digital/PCS generation two. 3G technology is intended for the true multimedia cell phone -- typically called smartphones -- and features increased bandwidth and transfer rates to accommodate Web-based applications and phone-based audio and video files.
So-called 3G wireless networks are capable of transferring data at speeds of up to 384Kbps. Average speeds for 3G networks will range between 64Kbps and 384Kbps, quite a jump when compared to common wireless data speeds in the United States that are often slower than a 14.4Kb modem. 3G is considered high-speed or broadband mobile Internet access, and in the future 3G networks are expected to reach speeds of more than 2Mbps.
The 3G technologies are turning phones and other devices into multimedia players, making it possible to download music and video clips. The new service is called the "freedom of mobile multimedia access" (FOMA), and it uses wideband code division multiple access (W-CDMA) technology to transfer data over its networks. W-CDMA sends data in a digital format over a range of frequencies, which makes the data move faster, but also uses more bandwidth than digital voice services. W-CDMA is not the only 3G technology; competing technologies include CDMAOne, which differs technically, but should provide similar services.


Evolution from 2G to 3G

2G networks were built mainly for voice data and slow transmission. Due to rapid changes in user expectation, they do not meet today's wireless needs. Evolution from 2G to 3G can be sub-divided into following phases:
• From 2G to 2.5G (GPRS)
The first major step in the evolution to 3G occurred with the introduction of General Packet Radio Service (GPRS). So the cellular services combined with GPRS became' 2.5G.'GPRS could provide data rates from 56 kbit/s up to 114 kbit/s. It can be used for services such as Wireless Application Protocol (WAP) access, Short Message Service (SMS), Multimedia Messaging Service (MMS), and for Internet communication services such as email and World Wide Web access. GPRS data transfer is typically charged per megabyte of traffic transferred, while data communication via traditional circuit switching is billed per minute of connection time, independent of whether the user actually is utilizing the capacity or is in an idle state.
GPRS is a best-effort packet switched service, as opposed to circuit switching, where a certain Quality of Service (QoS) is guaranteed during the connection for non-mobile users. It provides moderate speed data transfer, by using unused Time division multiple access (TDMA) channels. It was originally standardized by European Telecommunications Standards Institute (ETSI), but now by the 3rd Generation Partnership Project (3GPP).



Network standardization

The International Telecommunication Union (ITU) defined the demands for 3G mobile networks with the IMT-2000 standard. An organization called 3rd Generation Partnership Project (3GPP) has continued that work by defining a mobile system that fulfills the IMT-2000 standard. This system is called Universal Mobile Telecommunications System (UMTS).

IMT-2000 standards and radio interfaces

International Telecommunications Union (ITU): IMT-2000 consists of six radio interfaces among them one is
• W-CDMA also known as UMTS
Micro Cells, Micro Cells, and Pico Cells
The 3G network might be divided up in hierarchical fashion:
• Macro cell - the area of largest coverage, e.g., an entire city.
• Micro cell - the area of intermediate coverage, e.g., a city centre.
• Pico cell - the area of smallest coverage, e.g., a "hot spot" in a hotel or airport.



TECHNOLOGIES USED BEFORE


TDMA vs. CDMA
We have considered how a mobile phone can send and receive calls at the same time (via an uplink and a downlink). Now we will examine how many users can be multiplexed into the same channel (i.e., share the channel) without getting interference from other users, a capability called multiple accesses. For 3G technology, there are basically two competing technologies to achieve multiple accesses: TDMA and CDMA.
TDMA is Time Division Multiple Access. It works by dividing a single radio frequency into many small time slots. Each caller is assigned a specific time slot for transmission. Again, because of the rapid switching, each caller has the impression of having exclusive use of the channel.
CDMA is Code Division Multiple Access. CDMA works by giving each user a unique code. The signals from all the users can then be spread over a wide frequency band. The transmitting frequency for any one user is not fixed but is allowed to vary within the limits of the band. The receiver has knowledge of the sender's unique code, and is therefore able to extract the correct signal no matter what the frequency.