 | Issue: | India 1998 |
| Article no.: | 7 | |
| Topic: | Wireless Technologies and Services | |
| Author: | Mr. N. K. Sinha | |
| Title: | Member (Technology) | |
| Organisation: | Telecom Commission of India | |
| PDF size: | 40KB |
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Article abstract
The Telecom Commission of India is looking towards wireless solutions for a fast and cost-effective services delivery for the high rate data and fax traffic, leased line digital service and Internet access. By the year 2000 and beyond, mobile wide band applications are expected to become more and more important. The technology for the speed of communication that a customer needs has to be developed while integrating the various technologies that are being inducted into the network at present. A developing country like India cannot afford to retire a technology within a very short span of its induction.
Full Article
Wireless technologies provide an important link to the telecommunication networks for the connectivity between various network elements and access to customers. This is a complex problem. In suburban and urban areas, networks of densities lying between a thousand or several thousands lines/km have to be built whereas, in rural areas, there would be a need to connect scattered groups of potential users. Today, the Telecom Commission is looking towards wireless solutions, not merely as a replacement for Plain Old Telephony Services (POTS) but also for the fast and cost-effective services delivery for the high rate data and fax traffic, leased line digital service and Internet access. Apart from the services, straightforward provisioning and simple installation procedures are important tools. A subscriber expects a light, compact and portable handset with a provision i of a high degree of security against interception of calls. The Telecom Commission cannot afford to neglect the authentication and fraudulent call prevention features in wireless communication. New Wireless Technologies Speed of deployment, start-up costs and quick revenue returns are significant factors in the favour of wireless technology. Wireless technology can also be used to complement fibre in the network over adverse terrains, for spur routes, and where fast deployment or lower initial cost is required. Satellite and terrestrial systems using microwave frequencies support both the traditional plesiochronous digital hierarchy of transmission speeds used in most installed equipment today, and synchronous digital hierarchy which runs at a higher speed and provides the standard multiplexing technique for the high-speed networks of the future. The future trend includes the migration to higher frequencies and also extensive use of infrared transmissions for intra-office communications or substantial use ofmillimetre waves for satellite services. A number of new wireless technologies which are expected to be useful in the rapid expansion of telecommunications networks, are presented below: Local Loop and Cordless Terminal Mobility A Point to Multipoint (P-MP) system using Multi-Access Rural Radio (MARR) can be deployed in rural networks. MARR is a cost-effective method compared to the current use of open wire or copper pair in a rural scenario. A digital P-MP system based on Time Division Multiple Access (TDMA) is now available, providing wire line speech quality and 64 kbps data connectivity. Other technologies available in Wireless Local Loop (WLL) are categorised as Digital Cellular Mobile Technologies. At present, wireless access technologies like Global System for Mobile Communicati9ns (GSM), Code Division Multiple Access (CDMA:), TDMA support only low data rate up to 96 kbps. A number of proprietary wireless access systems have been developed with a view to provide Integrated Services Digital Network (ISDN) connectivity to subscribers. User requirements are, however, not limited to 144 kbps but increasing with the growing need and popularity of wireless, cable TV, multimedia, etc. At the basis of Cordless Terminal Mobility (CTM) are the improved facilities of the second-generation systems together with the possibility of providing mobility management functions in the network. CTM will allow personal cordless terminals to be used to communicate via any compatible base station, using a single service registration. CTM Network Architecture is designed to keep capital and operation cost per subscriber at a moderate level. The quality of the CTM service will be the same as in wire-based networks, in terms of the grade of access and transmission characteristics and will open the possibility of providing ‘a mobile telecommunication service suitable for a mass market. Wideband Access Efforts are being made to develop Wideband communications using Wideband Code-Division Multiple Access (W-CDMA) and Wideband Time-Division Multiple Access (W-TDMA) for multimedia applications over mobile telephone networks. This third-generation system is expected to allow for the exchange of audio, video and data information at up to 2 Mbps with ‘anyone’, ‘anywhere’ and ‘anytime’ at a low cost using handy devices. Wideband systems under development are expected to be frequency efficient. The system will offer important capacity advantages since the system allows handoff between different radio frequencies. Operators can use hierarchical cell structures to create layered cell systems, which will increase capacity in densely populated areas with high traffic volumes. Broadband Access Local Multichannel Distribution Systems (LMDS) is the generic wireless technology for TV distribution in possible direct competition with cable TV. Higher frequency bands are especially useful, antennas being smaller They can also merge aesthetically with walls/windows/facade of buildings. It is important to note that LMDS is not a true line of sight system. In fact, buildings and other structures that would normally obstruct signals, act as active or passive repeaters because the signals are bounced off around them. This unique trait makes the LMDS system particularly suited to densely populated urban areas with tall buildings and skyscrapers. Wireless Data The phenomenal growth of personal computers, laptop and notebook computers has created a need for wireless data services to mobile users. Most mobile data systems operate in various mobile bands from 100 to 200 MHz. The simplest application for wireless data communication is using facsimile or terminal voice band modems available at transmission rates of 9.6 or 14.4 kbps. Mobile Data systems provide a variety of services to business users and public safety organisations. The basic services supported are electronic mail (email), enhanced paging, modem, facsimile, remote access to host computers, Local Area Networks (LAN) and information broadcasting services. Broadband Wireless Access A form of Broadband Wireless access is a technology for Wireless Local Area Network (W-LAN), which has emerged primarily as a tool for business applications. It is mainly aimed at data transaction rather than video or voice, effectively connecting portable computers and data entry systems to local network via high data rate wireless access support from 2 to over 50 Mbps transmission rates and low coverage of tens of metres in the majority of applications. Satellite Satellite communication started with Geosynchronous Earth Orbit satellites (GEOs), which orbit the earth 35,680 km above the equator taking exactly 24 hours to complete each orbit. The advent of Very Small Aperture Terminal (VSAT) has opened a reliable option for the business users in linking up their far flung units over a vast geopgraphical area. These networks use CDMA and TDMA techniques. Satellite communication technology has advanced dramatically from 30m diameter earth stations operating under INTELSAT systems to handheld terminals under Global Mobile Personal. Communications by Satellite (GMPCS) systems. An opportunity has been opened up for meeting the new and latest communication needs using the non geostationary satellite systems which are expected to play a big part in untethering computer and communication users. The orbit of Medium Earth Orbit Satellites (MEOs) is significantly closer to earth than a GEO satellite at 2500km to 10,000 km. Although this reduces signal delays, it also means a MEO’s signal area is smaller than a GEO. In other words, more MEOs are needed to cover the same area as a GEO. Low Earth Orbit Satellites (LEOs) operate 600km to 2500km above the earth and consequently, there are negligible transmission delays between end users and satellites. The advantage of LEOs technology is that power requirements are relatively low, meaning that small, handheld cellular type units can transmit signals to and from LEOs. Low earth orbit satellites also present valuable savings to the satellite builder. The so-called ‘little LEOs’ will provide lower-rate data services than their big LEO counterparts. Little LEOs are designed to provide store-and-forward data as well as vehicle tracking, status monitoring, data acquisition, paging, email, security monitoring and emergency alerting. Meteor Burst Communication System A Meteor Burst Communications System (MBCS) uses ionised meteor trails as a means of radio signal propagation. Billions of ionised meteor trails are produced daily in the region of the earth’s atmosphere from 80 to 120km above the earth. These trails diffuse rapidly and usually disappear within a few seconds. However, during their existence, they reflect radio waves and provide a reliable communication channel. Meteors appear at random, but are in fact very predictable. The primary propagation mechanisms used by the network are extended range line-of-sight at short ranges out to about 150km and meteor scatter using for long range coverage out to 200-800km. In areas where the nodal density is sparse this technology represents a very cost-effective alternative to expensive satellite systems. For links used for inter-nodal communication, the average waiting time to communicate to a vehicle via meteor scatter will be between 3 to 8 minutes. In the line of sight mode, it will be almost instantaneous. Meteor communications systems generally operate using probe and listen type protocol. In this mode of operation, centrally located master stations broadcast a probing signal, which consists of some overhead information and who should respond, along with differential Global Positioning System (GPS) update information. If a unit receives the probe signal and it is part of the group of units which have been allowed to respond, it will transmit its position information and any message information located in its message queue. High Density Fixed Systems The majority of current worldwide High Density Fixed Systems (HDFS) deployments are in the 38 GHz band, with a primary focus on urban and suburban business and industrial areas. Future HDFS deployment is expected to extend to residential areas, spearheaded by local distribution of television programmes in competition to cable TV and other new broadband fixed services offered to the home. The variety of possible current HDFS network configurations includes: conventional Point to Point (P-P), P-MP, and combinations thereof. The densest HDFS deployment cases have reached the range of 1 to 10 stations per square kilometre, and are expected to increase dramatically within a few years. High Altitude Platform Station (Stratospheric System) A stratospheric high-density system in the fixed service may consist of one or more high altitude (approximately 23 km) regenerative repeaters, one or more ground switching/control stations and a large number of subscriber access terminals which provide broadband services such as video telephony. The technology is presently under study and the International Telecommunication Union (ITU) has provisionally allocated the frequencies in 47 GHz band for this service. As each stratospheric station can cover an area of greater than 500 km radius, it is possible to have a coverage of the entire country by using a small number of such systems. Global Positioning System GPS uses a constellation of 24 satellites in six inclined orbits at about 17,600 km above the earth. This constellation of satellite orbits the earth in 12 hours in such a way that at least four satellites are visible to a user at any point. Total GPS consists of a space element of the satellites,’ control element for monitoring and control, and a user element.. Another constellation of Navigation Satellites is the GLONASS (Global Orbiting Navigation Satellite System) of the Russian Federation, also consisting of 24 satellites. Integrated use of both constellations can provide almost double visibility and more redundancy leading to higher precision. GPS is poised to influence a variety of application areas. As costs drop, it will be possible to mount GPS receivers in each and every vehicle. The future of smart highways and smart automobiles that relieve the strain of driving may now be closer than one can imagine. Radio Frequency Ids Radio Frequency identification systems, simply called RF IDs, are small, low-cost tags that can be attached to objects or persons so as to track their position. Low power consumption is especially critical here as the tag’s lifetime may be determined by that of a single small battery. RF ID products in the 900-MHz and 2.4 GHz range have recently appeared in the market. RF ID is an upcoming technology, but is far from perfect. Some issues will require resolving, or at least substantial progress, before RF ID can be introduced to a wider audience. Natural Evolution Path By the year 2000, mobile wideband applications are expected to become more and more important. Advances in technology will make it possible to implement WLL in urban, suburban and rural areas providing fully featured, cost-effective services, such as: Ÿ a transparent air interface that provides wireline quality and services; Ÿ greater subscriber density for a given bandwidth allocation; Ÿ greater Data capacity for advanced services such as Basic Rate ISDN and Video transmission; Ÿ improved service reliability at reduced operating cost; Ÿ replacement of deteriorated wireline infrastructure; Ÿ augmentation of existing access infrastructure to increase the serving capacity; and, Ÿ reduction in cost to subscriber with greater security against interception. As demands for higher bit-rate services increase, narrow-band communication migrating to broadband will be the natural evolution path. Conclusion Today, the industry requires a vision beyond the year 2000. The technology for the speed of communication that a customer needs, has to be developed while integrating the various technologies that are being inducted into the network at present. A developing country like India cannot afford to retire a technology within a very short span of its induction.
