Towards third generation wireless technology

GOING BY the present indication, mobile telephone connections will supersede the fixed lines.

Demand for mobile phones has enhanced radio access technology capabilities to enable true multimedia services to be delivered at high bit rates. Demand has increased for miniaturised customer devices that will provide audio/video in a portable cum pocketable multimedia devices not only on fixed landline connection but also on a mobile line. The wireless terminal has the potential to become a generic platform for or gateway to the complete range of communication services, that is voice, data video and multimedia.

In the initial stages of wireless network development only the analog techniques such as AMPS, TACS were used and they form the group of first generation. The second generation of wireless technology came into being with the introduction of GSM (global system for mobile communications) in almost all the European countries, IS-95 in America and DAMPs in parts of North American States. The second generation systems were digital systems with overwhelming advantages over the analog systems.

Second generation wireless

technology

The present second generation GSM architecture is designed to meet the demand for voice and data at lower speed for the mobile subscribers.

The non-standardisation of the second generation mobile system to a global acceptance is one of the main reasons, the task force group has gone for a more comprehensive radio access technology which will suit the future environment in any part of the world and has now come out with a Third Generation System 3G or IMT- 2000 (international mobile telecommunication) or UMTS (universal mobile telecommunication system) which has been approved by ITU (international telecommunication union). The following services and application capabilities are envisaged to great extent in the third generation wireless system.

- Wide range of services from narrow band voice up to wideband real-time multimedia services.

- Support high speed packet-data transmission including internet applications

- Real time audio/video applications such as interactive video conferencing.

Specialised multimedia business applications such as telemedicine and remote security surveillance.

The third generation systems should be able to support, Data rate of 144 Kbps in moving vehicles, 384 Kbps in low mobility area (pedestrian), 2 Mbps in indoor environment (buildings), symmetrical and asymmetrical data items. It should also support circuit switched end packet switched services, superior voice quality comparable with fixed line quality and several simultaneous services to end-users and terminals.

However, the 3G technology must have the compatibility of co- existence and inter-operability with 2G systems.

Dedicated traffic channel is point-to-point bi-directional channel that transmits and receives user information like data or voice. The characteristics some of the IMT 2000 system are:

- Operational band - uplink 1920-1940 MHz; Downlink 2110-2130 MHz

- Frequency division duplex (FDD) 190 MHz duplex distance

Chip rate - 4096 Mega chips per second

- Carrier width - 5 MHz

- Long code, short code and transmission rate.

Upgradation to IMT-2000

The standardised 3G wireless technology from the existing 2G systems can be achieved in two or three stages of up gradation of the network technology to accommodate higher rate data transfer capability using packet switching technique and Internet Protocol (IP).

All GSM networks (2G) can easily be transformed to 3G networks by implementation of GPRS (General Packet Radio System) and EDGE (Enhanced Data Rate For GSM network evolution).

GPRS: Data rates are increased up to 160 Kbps (peak 384 Kbps) and all internet services made available for mobile stations for use at anytime anywhere. GPRS is an essential part of the mobile network revolution and key to mobile data growth. GPRS serves as a natural migration path needing only middleware for 2G data application. GPRS is the first step in the change over of circuit to packet switching with incremental cost addition in the existing infrastructure of GSM. This suits burst data applications especially WAP based E-mail, SMS and telemetry . This offers to the service providers (operators) new revenue stream opportunities.

The implementation of GPRS is by introducing serving GPRS support node (SGSN) and gateway GPRS support node (GGSN) which will interwork with home location register, the mobile switching centre, visitor location register and the base station subsystems GGSN, which is the interconnection point for packet data networks, is connected to the SGSN via IP backbone. To support efficient multiplexing of packet traffic to and from mobile terminals a new packet data channel has been defined for the air- interface. One such channel is mapped onto a single time slot, thereby utilizing the same physical structure as ordinary circuit switched GSM channels. By means of packet multiplexing the allocated channels can be shared by GPRS users in a cell. A new general purpose high performance packet switching platform is thus evolved using support nodes in GPRS.

EDGE: Enables networks operating in the 800,900,1800 and 1900 MHz frequency bands to provide third-generation capabilities. It can be regarded as generic air interface for efficiently providing high bit rates thereby facilitating the evolution of existing cellular systems toward third generation capabilities. Here a new modulation scheme called eight-phase - shift - keying (8PSK) is used to increase the gross bit rate on the air-interface. Normal GSM air interface uses rate of 22.8 kbps only. Using 8PSK the bit rate is increased to 69.2 kbps per time slot, which can go up to 271 Kbps also.

Introduction of EDGE has very little impact on the core network and needs no new hardware. Network operators will be able to introduce EDGE gradually by introducing Edge capable transceivers in a subset of cells where Edge Coverage is desired. An integrated mixture of circuit-switched GPRS and EDGE users will be allowed to co-exist in the same frequency band. Edge also achieves good spectral efficiency using only a limited amount of spectrum. It enables forthcoming wideband services in GSM also.

Wireless application protocol (WAP)

With a view to attract new customers and at the same time retaining the existing customers, the GSM network operators while upgrading the network to 3G workout new strategy to introduce some cutting edge technology like internet enabled wireless communications. This is called wireless application protocol (WAP), a standardised way of linking mobile phone and the internet with micro browser facility in the handset on a client- server approach. Here, by using WML (wireless markup language) instead of the well-known HTML, internet based applications like e-mail, phone banking, news broadcast reception, radio listening, hotels/restaurant/cinema bookings, online shopping etc are brought to the mobile station instrument of the customer. The customer devices are also required to be WAP enabled to enjoy this facility. PC/Laptop applications like video conferencing, accessing by corporate LAN, MP3 format audio are also possible using WAP.

The 3G system with the help of WAP aim at enriching the network content in order to promote leading edge image for the operators.

A. Ganesan

Divisional Engineer

Chennai Telephones

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