25-08-2017, 09:32 PM
3G Cellular Systems
3G Cellular Systems.doc (Size: 33 KB / Downloads: 20)
wireless systems into universal mobile telecommunication system. Work is continuing in European research consortium, RACE, and in ETSI towards developing UMTS (Universal Mobile Telecommunication System) on an joint European basis. At the same time ITU is working globally towards IMT-2000 (International Mobile Communication-2000) with mutual agreements and information exchange.
One of the main objective of 3G systems is that they will gather existing mobile services (cellular, cordless, paging etc.) into one single network. The multiplicity of services and features of the system will make it possible for the users to choose among multiple terminals and service provides. Terminals will become smarter and will be able to support several radio interface with the help of software radio technology. Among the objectives that have been assigned to 3G system designers are : voice quality as with fixed networks, satellite services for non covered areas, low terminal and services costs, high bit rate mobile multi-media services (2 Mbps for indoor and reduced mobility users, 384 Kbps for urban outdoor , and 144 Kbps for rural outdoor), multiple services per user (speech at 8 Kbps, data at 2,4 or 6 x 64=384 Kbps, video at 384 Kbps and multimedia, security and antifraud features against access to data by non-authorized people or entities.
This Paper explains how the next generation of mobile (UMTS) can be launched and then carries on to propose how the networks can be evolved to deliver the voice and data application based upon IP technologies.
The architectural starting point
The allocation in the early 1990s of spectrum for third generation mobile really spurred on the technology solutions to deliver higher bit rate communications in the mobile arena which had been restricted to low-rate voice and simple (<10 Kbit/s) circuit-switched data. A variety of drivers and enabling technologies were tabled to provide the high-bandwidth network capabilities to support the greater bandwidths expected from the advanced third generation radio technologies. The protocol included the use of B-ISDN based techniques with ATM, use of pure N-ISDN technology from both wired and wireless network, along with enhancements of the GSM architecture.
The issue of incorporating new radio technology has been a significant one for operators who have had to migrate from first generation (analogue) systems to second generation (digital) systems such as GSM. The development of the W-CDMA and TDD radio technologies and their associated radio access networks (RANs) would take a significant amount of time and effort. This factor, combined with proposals to develop completely new core networks and architectures would have severely delayed the availability of third generation communications and consequently a pragmatic approach to the core network architecture was taken . The ensuing architecture grafted the new UTRAN aspects on to the ‘front end’ of an ‘evolved’ GSM/GPRS phase 2 + core network, comprising mobile switching centers (MSCs) and GPRS support nodes (GSNs). This resulted in the concept architectures of Figure. This solution enables operator who have GSM networks, and also suppliers who have core network product lines offering GSM capability, to minimize the technical changes from the contemporary GSM infrastructure. This approach also re-applies the tried and tested GSM roaming, charging, signaling and service mechanisms to UMTS.
The UMTS launch architecture
The detailed technical developments added to the GSM core network architecture were predominantly to support the UTRAN aspects which, within the 1999 Release of 3GPP standards (3GPP R99, also known as 3GPP R3) support the W-CDMA radio aspects .
The UTRAN elements
A completely new access network architectures was developed for the revolutionary radio access mechanisms which took on board the high-speed switching capabilities of ATM, the evolvable support for both W-CDMA and TDMA, as well as delivering standard open interfaces.
The basic functional blocks of the UTRAN architectures are the node B and the radio network controller (RNC). The node B can be said to be roughly equipment to the GSM BTS in linking the antenna site to the network. The node B functions include the radio and modulation/spreading aspects along with channel coding( forward error correction) and some of the combining/splitting functions for soft handover. It should be noted that soft handover and micro-diversity is where multiple, differently located receivers are added/removed and used to provide gain in the received signal. The principal requirement with the node B is to minimize the cost/functionality as the network could comprise a large number of node B nodes. The naming of the node B is a result of compromise in the standard process.