MARCHING TOWARDS PERSONAL COMMUNICAITION
Mirza Shahidul Islam
The future success of mobile communication can be built on solutions that meet the personal needs or requirements of the users. The concept of communication to reach any where at any time will generate further development in the area of mobile communication. The aim of telecommunication to provide UPT (universal personal telecommunication) using universal personal number throughout the globe is not far away.
In traditional telephone communication the call set-up is actually made between the end terminals (telephone handsets/machines). Similarly, in conventional data communication the same is done between two computer or/and terminals. But in personal communications this concept is going to be changed. Personal communications is to provide a link between end users.
Theme of personal communications is to provide service to any person, at any time and anywhere. And it is a vehicle to offer global services for voice, data, video, image etc. In the scheme, for identification purpose, a person is to have a unique and universal identification, i.e. worldwide a single telephone or E-mail address etc. In order to meet the theme, personal communication shall operate the world over and it will support man and machine mobility.
As it will operate globally, and as the unique and universal identification of person through UTN (universal telephone number/personal number) are essential in the concept, the required switching system will be complex and an extended one. Therefore, intelligent capabilities of switching are essential. Hence two important issues required for personal communication are:
- Wireless communication to support man and machine mobility.
- Intelligent capability of switching system to support complex and huge switching the world over with a universal code or number.
In comparison with conventional communication, personal communications will provide better and wider flexibility and independence like that available to a person on tour in a personal car rather than a person availing public transport for a tour.
Components of PCN
Personnel communications as of today offer viable and wide services. Different industries see the personal communications from different angles like cellular radio communication, VSAT (very small aperture satellite), wireless PBX (private branch exchange), wireless LAN (local area network), wireless access to CENTREX, paging cordless telephone, and ever intelligent PSTN (public switched telephone network) etc. As such PCN (personal communication network) will he a hybrid network (Fig. I).
PCS (personal communication services) otter both terminal mobility and personal mobility. The present trend of PCS offers a convergence of public wireless services (like cellular and paging) and private radio services (like police radio network). PCS will mainly consist of cellular and cordless wireless services, i.e. PCS=C+C. However, cellular and cordless services differ from the point of terminal mobility management. Whereas in cellular it is the high-powered base stations which support mobility with hand-over facilities among base stations, cordless is based on low-powered private or public system with no handover facilities. Examples of cellular are GSM (global standard for mobile systems) and paging, whereas those of Cordless are CT-2 (cordless telecommunication-version 2) and cordless (table I).
But this is not all. PCS are being defined and designed by several vendors in several directions starling from several points. Yet, PCS has found a solid ground in communication era.
The wireless world of communication was introduced in America around mid- I 930s, when the American police departments began using radio telephones lot communication with field stations, Public radio applications like PLMR (public land mobile radio services) and SLMR (special land mobile radio services) are extensions of police radio service. In early- 1980s, tour more wireless services were introduced:
AMPS (advanced mobile phone services) developed by Bell Laboratory in [98(1. This concept was changed to cellular concept in 1984. However, early days’ cellular communication is analogue in nature and is known as first. Generation cellular. In early days of I 99(1. the second generation cellular communication known as digital cellular communication had emerged.
Airphone services where terrestrial cells and/or satellite based connectivity to main telephone network are used. Major applications of these services are in aircraft and space nail routes.
— Cordless service for limited mobility is another class.
— Telepoint provides wireless PCO (Public Call Office) services to customers’ owned telephone handsets within a limited range of base stations in public places. The basic standard of telepoint is CT-2. 01-2 uses ADPCM (adaptive differential pulse code modulation) with 32 kbps encoding to digitalis voice. It. uses CFS K (gaussian frequency shift keying) for modulation and FDMA (frequency division multiple access) architecture. It. also supports data transmission up to 2.4 kbps through speech codes.
Cellular radio has evolved from wide area radio transmission techniques. The objectives 01 early conventional wide area mobile radio system was to cover a large area (as large as possible) with a fixed base station with high radiated power and high tower antenna. The system configuration once designed was fixed.
Today’s cellular systems, on the other hand, are targeted towards smaller cells having low—powered base stations. By this new scheme, frequency reuses concept. Is implemented and high capacity is achieved. Small power radiated by base stations enable nonadjacent cells to use the same frequency for operation. This in turn increases the number of subscribers. When a cell becomes congested, it is split (cell splitting) 1.0 increase the number of subscribers.
In the earlier concept of mobile communication, a fixed base station was used 10 cover a typical geographical range of 80 square kms (Fig. 2 (a)). -The base station had a powerful transmitter and a sensitive receiver, It also had connectivity with conventional wire lines. A frequency hand was used to cover communication in the lull area.
In Cellular system, the total geographic coverage of a base station is sub-divided into a number of cells (Fig. 2 (h)). In theory, cells are hexagonal, hut in practice, they are quite irregular in shape (Fig. 2 (c)). Instead of using high-powered base station as in the earlier concept, a number of low-powered transceivers, one hr each cell is used in the cellular concept.
A typical architecture of a digital cellular network is shown in fig.3
This is a standard architecture adopted by CEPT (Conference European Post. & Telecommunication). The name the standard is CSM (global standard for mobile-communication) There are other standards also like ADC (Japanese digital cellular), and JDC (Japanese digital cellular). But GSM is used in most of the European and Asian countries including India (Table-II). CJSM may actually he defined as
CSM = Cellular technology + Digital communication + Computer communication.
In GSM, a mobile user is allotted a identification number under a ASS. This number is maintained in he HLR (home location register) of MSC as well as it BSS. When the user goes to other area under other BSS.s, the information of his mobility is broadcast to other BSSs and MSCs by a technique known as ‘hand off; and his identification is monitored through a record in VLR (visiting location register) of MSC. VLR allocated a temporary number to roaming user. Users using GSM network can communicate within the network as well as to other national/international network through otter conventional network like P&T networks and data network depending on purposes.
Under GSM. there are two frequency hands
-890-915 MHz for mobile to base station communication/uplink communication,
-935-960 MHz for base station to mobile communication/downlink communication.
These hands are divided into 124 pairs of carrient spaced by 200 KHz, beginning with 890.2 MI-It. Each cell has a minimum of one carrier and a maximum of 15. Cell size ranges from one to several kms. TDMA technique is used for connectivity between, a mobile and base station, Eight time slots, each of 0.5 msec length, are used (Fig. 4),
Design of any cellular system has to tackle the floorings:
- Channel characteristics/propagation characteristics of the reunion.
- Cell size/consideration of growth of customer,
- Channel assignments.
- Modulation technique.
- System integration problems.
Standard technique for re-use 01 frequency follows an algorithm as flows:
1. Move i number of cells from a reference cell along any chain of hexagons,
2. Turn 60 degrees left and move j number of cells.
Now, the new site and reference cell are co-channels where frequency re-use is possible Here, i and j are integers and i > j. The number of cells, k, with non-repeating channels (i. e. number of cells per cluster) is: K = i2+j2+ij (Fig. 5). The ratio D/R where D is the distance between the centers of nearest neighboring co-channels and R is the cell radius, is know n as co-channel ratio or normalized re-use ratio.
Pagers are One-way message systems. They provide transfer of message on wireless networks. A message can he sent by any bod y to a person having a pager without any constraint of mobility.
Thus, it allows freedom to people on movement. Paging is like cellular telephone but without tow-way online interactive communication. Paging is useful to doctors, journalists, professionals, politicians, airlines etc. For example, if a specialist doctor is associated with live hospitals, it will be quite difficult for patients/nurses of any hospital to surely contact the doctor when he is attending any other hospital. With cellular telephone, Although it may he possible but it may not he warranted because of some peculiar requirements (for example, when and if the doctor is engaged in operation). In such cases, if lie doctor is carrying a pager, the message may he left with his pager by any nurse/patent in question.
Paging support mobility enhanced productivity and backup support to telephone. Pagers work on stipple technique. The calling person may simply dial the paging Centre through a usual telephone and leave message with the operator along with the pager number. The operator wi I send the message to cal led pager and I he message will he flashed on he pager along with an activating signal.
There are two types of standards for paging transmission (a) POCSAC (post o 111cc code standards advisory group), and (h) RDS (radio data system).
The frequency allocation for POCSAG is 134-168 MHz hand. A typical ROS paging system is shown in Fig. 6.
RDS service requires users to register under on company in different cites. RDS pagers are costlier and bulkier than POCSAG pagers.
Paging services can he classified into two groups On-sight paging (ONSP) and off-sight paging (OFSP).Loosely speaking, ONSP is realized through the dedicated transmission system. Therefore, investment wise it is costly hut communication is easier, speedier and uninterrupted. Due to the government restriction, transmitter power cannot exceed 5 watts; and hence its coverage is only about 3 kms in diameter.
1.Co-Channel sites; shift parameters i=3;j=2
3. Co-Channel Re-Use=D/2
Fig:-5 Standard Technique for re-use of frequency
OFSP uses fewer or non-dedicated transmission towers. Initial investment in low and coverage is high (about 50 kms in diameter). There is ample chance of message congestion and loss. Moreover, high-rise and obstructive regions may not be served by DFSP. TOP
Different type of pagers are in vogue in the market like numeric, alphanumeric and even English type Developed countries are trying to develop to way pagers.
Very small aperture satellite (VSAT communication is an important wing of personal communication for huge organization. VSAT is a small (60cm or 120 cm) dish antenna which communicates with the central sub stallion via satellites, Thereby providing time communication Over a distributed organization, and that too without using costly high power antenna of conventional earth station.
Now -a-days, VSAT can provide voice, data and video communication. The transmission tale is low 1200 bps. VSAT provides two-way direct communication hr all purposes like voice. Data and video, VSAT networks will be cheaper and. therefore, more attractive than terrestrial communication networks, VSAT provides a unique solution to the corporate network and a cost-effective solution or rural communication.
VSAT Is a cheaper alternative 1.0 conventional earth stations used In satellite communication. VSAT usually uses a star topology and a VSAT network consists oF a control Centre, remote station equipment. and transponders. The control Centre is usually located at central office of The telephone network,
VSAT can provide cost-effective rural telephone and fax services,
PCS Personal communication services
Personal communication services are being planned to he introduced in the USA, PCS has been defined purely as a concept without reference to any specific technology.
PCS will provide terminal in mobility, personal mobility and service profile management. It. will to I low the personal number concept i.e. one number at any place and any time.
Personal mobility is the ability of the end users to access their telecommunications services of any terminal, in any location, and ability of the network to locate arid ideate end users as They move.
Terminal mobility refers to the ability of a terminal to access telecommunications services from any location, while in motion and the capability of the network o locate and identify this terminal as! Moves.
Services mobility refers to the ability to associate services with an end user rather than with particular equipment and for those services to follow end users as they move with respect, to the network.
PCS is made, possible largely for lie integration of wireless technology will intelligence network
In its notice of Enquirer, the FCC describes PCS as encompassing a broad range of radio communication services that free individuals from The constraints of the wireline PSTN and enable them to communicate when they are away from their home or office telephone. The concept embraces a wide range of mobile communication systems and technologies as well as their possible integration with existing and future fixed networks.
The goal is to allow a person to use a lightweight portable phone at home, in the office and in an outdoor environment. Users could then he reached under one number at any place and ally hum. PCS is treated as two and a half generation system.
FCC allocated 140 MHz frequency spectrum PCS, 120 MHz for licensed and 20 MHz for unlicensed services. Licensed 1850-191() MHz
3 slots of 15 MHz
3 slots 01 5 MHz
Unlicensed 1910-1930 MHz
The choice of the technology for PCS may he based on DCS-1900 (TDMA based system) or CDMA. TDMA based systems are likely to he deployed first due to the availability of the equipment.
The key attributes of PCS are:
- Terminal mobility by wireless accesses.
- Personal mobility by persona] telecommunication services.
- Service profile management using IN concepts.
- Provide validation and authentication procedures to facilitate billing and accounting.
FPLMTS Future public land mobile telecom systems
Task Group 8/i of ITU-R is finalizing the recommendations on FPLMTS aiming to provide mobile telecommunications-anywhere-anytime. FPLMTS are third generation mobile systems, which are scheduled to start, service around he year 2000, subject to market considerations.
The concept of a small lightweight and convenient pocket considerations is a fundamental part of FPLMTS, and provides terminal mobility, which is complementary to the personal mobility and service profile management provided by UPT.
FPLMTS will provide access, by means of one or more radio links, to a wide range of communications supported by fixed telecom networks, and to otter services, which are specific to mobile users.
Services will he available in all situations in which a user may he found, indoor or outdoor, and ranging from denseurban situations through suburban and rural areas. Land, maritime and aeronautical situations are included so that the user in a vehicle, on a ship, or in an aircraft will have continuous availability or services.
The range of service includes voice telephony, wide area paging, data services and video communication services. FPLMTS will cover the application areas presently provided by separate systems such as cellular, cordless, telepoint, mobile data, and paging.
WARC 92 has identified the following frequency hands for FPLMTS
The satellite component of the PPLMTS are:
The duplex techniques considered for use by FPLMTS include into division duplex and frequency division duplex. A FDD spacing of 190 MHz has been specified for the satellite component of FPLMTS. WARC92 resolved that. administrations which implement FPLMTS
(a) should make necessary frequencies available for system development
(b) should use these frequencies when FLMPTS are implemented:
(c) should use the relevant international technical characteristics, as identified by the recommendation of ITU-R and ITU-T to facilitate worldwide use and roaming;
It is anticipated that, the detailed recommendation will be available by the end of I 997. The following recommendations have been approved:
816 - Frame work in services supported by FPLMTS
817 - Network architectures FPLMTS
818 - Satellite operation within FPLMTS
819 - FPLMTS for developing countries
1034 - Requirements for the radio interfaces for FPLMTS
1035 - Framework for the radio interface (s) and radio subsystem Functionality for FPLMTS
1036 — Spectrum considerations for implementation of FPLMTS in the bands 1885-2025 MHz and 2110-2200 MHz.
UMTS : Universal mobile telecommunication system
In Europe, a similar concept to FPLMTS called the Universe Mobile Telecommunication System is currently being defined by ETSI, The research work is pioneered by RACE (Research on Advanced Communication [or Europe) Programme under MONET (Mobile Network) Project.
UMTS is intended to he a third generating mobile communication system which will integrate mobile services (like cellular telephony, Paging, PMR etc) I Mo a single syst.eni so halall ki lids of terminals can he used in all environments (at. home, in the olce and in the public environment MONET has chosen to lirsl desigii UMTS as part of B—ISBN, hut also to address flue possibility to use pro B-ISBN networks as backbone network br UMTS.
UMTS will use the same frequency spectrum as identified for FPLMTS in WARC-92. The UMTS ~vill follow the migration path from GSM, CT-2, DECT, DCS-18(X) etc.
UMTS is viewed as a system completely in the B—ISBN cotitoxt for which the basic htictional ties oft he core network will be reused as mud, as possible. UMTS design will make excessive use on IN concept, services and infrastructure. The radio access part of UMTS will have a flexible architecture to cope with a variety of application environnients and possibly with different radio access technologies, e.g. TDMA and CDMA.
UPT: Universal personal telecommunications
UPT as defined by ITU-T study group is a telecommunication service which enables telecommunication services by allowing personal mobility. It enables each UPT’ user to participate in a user defined set of subscribed services and to initiate and receive calls on he basis of a unique network-transparent personal telecommunications number (PTN) across multiple networks, public and private, at any terminal fixed, movable or mobile, irrespective of geographical location
-Limited only by terminal and network capabilities and restrictions by the network provider.
UPT is a feature by which the services, the routing and charging can he related to personal mobility, subscription which can he moved freely between terminals and networks. UPT involved the network capability of uniquely ideating a UPT user by means of UPT number. UPT service also provides service profile management. U PT is currently being defined by IFUT as an advanced concept for personal telecommunications. It includes personalized service profile with variable routing tables and routing filters.
FPLMTS and UPT provide essentially complementary mobility and PPLMTS is defined to support UPT. i. e. a UPT’ user using FPLMTS terminal is able to receive UPT services as agreed between UPT subscriber and UPT service provider. There is no technical requirement that this FI’LMTS network operator needs .0 he a UPT service provider. In this case the FPI.2YITS network acts as an intermediate link between the LJPT user and the UPT service provider.
Quick adoption of PCS should be a sound strategy for development. In this respect, it should he mentioned that cellular radio communication and cordless telephony seem to provide he foundation. PCS will revolutionize the communication services, Wireless PCS has occupied niainstrean, status. Only cellular telephony growth till 1993 in countries like Australia amid Asia, Western Europe and North America are respectively 71 per cent, 63 percent and 47 percent. With PCS, telecommunication is in a total transition, phase.
Developing countries must try to catch up or a brighter future, As PCN service is basically wireless service, 1 is attractive for developing countries due 10 advantages like easy installation and updating, small capital need, loss maintenance cost etc.
But we need urgently standardization of PCN equipment and services. Also The cost. of PCN equipment has to he hi ) ought down to make it attractive to the common people.
Electronics for you, Sep & Dec 95
|Engr. Mirza Shahidul Islam was born in Jessore. He obtained his B. Sc. Engg. (Electrtcal), in 1970 from Bangladesh University of Engg. & Technology, Dhaka. He joined as ADE in Bangladesh Telegraph & Telephone Board in 1972 and became Divisional Engineer in 1976. He look training on different subjects on Telecommunications in Germany. Finland, United Kingdom and Thailand, He worked as Director Phones, Dhaka Telecom Region (South). Now retired.|