CABLE AND EARTH STATIONS - A BUSINESS CONNECTION

Guy W. Beakley and Alex B. Best

Scientific-Atlanta, Inc.

ABSTRACT with cable television distribution sys­ tems offers many new opportunities as the In practically every cable franchise information society emerges. being awarded today, the recipient is required to install an "institutional B Business Communications Needs cable" to serve the communication needs of the business community. Although to date A number of large businesses are very little use is being made of this non­ essentially information-based. Included entertainment cable, industry predictions are banks, insurance companies, invest­ indicate an explosive growth for business ment companies, and stock exchanges. Their communications over the next ten years. principal business depends on gathering The purpose of this paper is to identify and assimilating large amounts of data. and explain the characteristics of this This is currently being done by process­ potentially large business market, and ing large amounts of paper, but office to give an overview of the techniques and automation will allow the information to equipment requirements for the business/ be processed and stored electronically cable and cable/earth station inter­ with only summary information being re­ connect. It seeks to alert franchise corded on paper. Communication and operators that the time to prepare for transfer of this information will be serving this market is now, when they are accomplished by the interconnected cable applying for franchises and building and and satellite systems described in this rebuilding their cable system. paper.

Introduction Although productivity improvements have occurred in agriculture, manufact­ Much has been said about the evolu­ uring and service industries, product­ tion of the United States from an indus­ ivity improvement in the office has been trial society to an information society. slow. Very little has been done to bring Just as the number of people working in spiraling office cost under control. industry outnumbered the people working However, office tools are now being put in agriculture in the early 1900's, the in place to change this situation. These people working in information occupations include communicating word processors, now outnumber those working in industrial facsimile devices, computer-to-computer occupations. links, voice messages stored in digital format, integrated voice and data PABX, Information and the way it is used and intrafacility communication networks. will be the key strategic variable in many A sophisticated business communication businesses. For this to happen, effective system will allow charts, budgets, last­ information transfer can no longer be minute schedules changes, press releases, constrained by a communication system that contracts, and photographs to be trans­ was designed for voice transmission. mitted quickly and reliably. Many people will be able to work at home connected by With the advent of the communication cable to their office. Executives attend­ satellite, large amounts of information ing out-of-town meetings and salespeople can be sent easily from one city to anoth­ on the road will be able to have immedi­ er. Cable operators need to know tha~ the ate and accurate access to information satellite carriers are well along on their back at the home office. In the future, plans and their investment in intercity a person will be able to substitute tele­ distribution of information. The bottle­ conferencing for some business travel. neck lies in the local distribution. The The possibilities seem unlimited. cable that is now being laid for distribu­ tion of television can be used for a sub­ With office automation moving ahead, stantial part of this local distribution. satellite common carriers have recognized The linking of satellite earth stations business communications as a viable

108 market. These satellite carriers are NTSC color video can be digitized at shaping intercity business communications the rate of about 90 Mbps with no visible with their new concept of shared earth degradation. Removing redundancy allows a stations. Digital satellite carriers video signal to be sent at 20 Mbps with offer business customers a capability to insignificant loss in video quality. When transmit vast amounts of data, voice, the motion is limited and the camera is electronic mail and other business signals fixed, it is possible to reduce the bit from the earth station up to the satellite rate to 6 Mbps with limited loss in qual­ and back down to another earth station. ity. The challenge is to reduce the bit Cable is a logical choice for a medium to rate to 1.5 Mbps and maintain reasonable distribute this data from the earth cost in the video source coding equip­ station to the businesses in each city. ment. As more devices for video coding are invented and as the cost of travel Business Communications Services increases, business teleconferencing will become a common event. Satellite and cable systems offer increased communications capabilities for Consider next data transmission. text, facsimile, data transmission, inte­ Large computers can manipulate data at greated voice and visual aids and video rates of one Mbps or faster. Efficient conferencing. In the past, text trans­ resource sharing, computer back-up, file mission has been handled principally by protection, core diagnosis and other telex which is slow and has a rudimentary factors make it necessary for distant character set. Telex is being replaced computers to communicate with each other. with communicating word processors which Transmission at Mbps rates is required for allow typewritten material to go from one computer communications in the future. machine to another at high speed. Much of the transmission and storage is accomp­ The office of the future will be lished electronically, thus creating tre­ integrated electronically. A number of mendous communications needs. With a scenarios for linking the equip~ent and satellite/cable communications system, people become evident. One scenario sees a secretary can type a letter, attach the the hub of the automated office being an appropriate electronic "address" and send integrated voice and data PABX. The PABX a copy directly to another terminal at a permits users to transmit, switch, and distant facility. store voice, data and images. Another possibility has local networks connecting Graphs, pictures and photographs do not office machines, digital telephones, and lend themselves to character transmission intelligent terminals or work centers. and are better sent by facsimile. In These terminals process and display data, order to obtain high resolution and trans­ text, pictures, and graphs. Regardless mit at a rate of one page per second, the of the method, there will be a need for bit rate needs to be of the order of 256 rapid communication of information within Kbps. This high data rate is available the office and from office to office. on the satellite. It creates the need for a high capacity local distribution Satellite Business Communications system such as cable can provide. Satellite business carriers have made The next step beyond communicating by great strides in the intercity portion of voice and still pictures is conferencing satellite business communications. Car­ using full- motion video. Point-to-multi­ riers such as RCA, Western Union, and point video conferencing now makes econo­ American Satellite Company have provided mic sense. Many national sales meetings increasingly sophisticated business com­ have been set up with regional salespeople munications facilities for their cust­ coming to local auditoriums where earth omers. American Satellite through its stations are installed or have been temp­ satellite data exchange (SDX) service has orarily set up. The salespeople view the specialized in providing voice and data program material on large television communications to small earth stations screens and respond to the presenter by located on end-users premises. American phone. Point-to-point teleconferencing is Satellite now has over 50 earth stations very costly when using full-motion video operating and another 34 under contract. because of the large bandwidth required. RCA Communications is providing a data, Analog video requires one quarter to one voice, facsimile, slow scan TV and tele­ full transponder of satellite. The use of print service called "56 Plus". Western this much capacity for a normal business Union also offers a similar data service meeting would be excessively expensive, to its customers. hence there is a need to digitize the information and reduce the data.

109 A typical customer-premises earth The telephone system normally restricts station may have a 5, 7, or 10 meter ant­ data transmission to speeds of 9.6 Kbps enna, redundant GaAs FET low noise amp­ and below. Data rates of one to forty lifiers, redundant 5 watt to 125 watt high Mbps can be transmitted by satellite. The power amplifiers, 56 to 1544 Kbps digital telephone network can be expected to modems, and a modem protection switch. produce on the average, one error per Scientific-Atlanta furnishes this equip­ 100,000 (105) bits transmitted. Elabo­ ment and a microprocessor-based monitor rate error checking and correcting and control unit in a complete earth schemes, which reduce efficiency, have terminal which is calls DET-56. A block been developed to overcome this problem. diagram of this system is shown in Figure Error rates of fewer than one error per 1. Each 56 Kbps channel can carry a 56 10,000,000 (107) bits are easily accomp­ Kbps data circuit or can be multiplexed lished using satellite communications. to carry many data circuits of different speeds. Voice channels can be provided Satellite Business Systems (SBS), using PCM or CVSD encoding. Data from a partnership among wholly-owned sub­ computers, terminals, and facsimile can sidiaries of Comsat General Corporation, also be transmitted over the DET-56. IBM and AETNA Life and Casualty Company, Figure 2 shows the DET-56 earth stations is implementing an extensive digital time that have been installed to date in the division multiple access (TDMA) system United States. for transmitting voice, data, and image. The $7 billion intracompany business com­ Communication of business data by munications market is SBS's principal tar­ satellite offers a number of advantages. get. The company offers complete voice,

DOWNLINK

System Monitor and Control

UPLINK

Control and Stetus-FNdback Interconnections with System Monitor and Control

Simplified Block Diagram of Digital Earth Terminal Figure 1

110 data, facsimile, and teleconferencing earth station in Wausau, Wisconsin and one services. in St. Louis, Missouri in early 1981. ISACOMM is now building earth stations in Baltimore, Atlanta, Houston and Sacramento and anticipates a total network of 40 earth stations by early 1984. DET·56 Earth Stations for Business Communications LOCAL DISTRIBUTION BY CABLE

Digital Headend

In several articles which have been published recently reference has been made to the "digital headend". This dig­ ital headend will process signals that are somewhat different from video signals and will use modulation methods that may be unfamiliar. Nevertheless, the analogy to the classical cable television headend is apparent.

On the customer's premises, racks of equipment consisting of digital multi­ Figure 2 plexers and standard bandwidth modems are installed. The output of the modems are frequency multiplexed on a two-way system with the output from other modems. At the The earth stations, which are shown earth station, there will be much larger in Figure 3, operate in the 12/14 GHz "Digital headends" receiving the modem RF frequency band so that they can be located signals and processing them to a format in cities without frequency interference compatible with the satellite equipment. problems. The system offers private net­ For installations where the digital earth works that are fully switchable and allow station is not co-located with the cable capacity expansion on demand. Facilities headend, data translators may be required are provided to enable the companies to to allow full access to any location in dynamically monitor and control the use of the system. In many respects this their networks. The terminals are small "digital headend" is less complex than (5.5 meter and 7.7 Meter antennas) and some of the very sophisticated cable head­ can be located on customer premises or at end systems which are being installed cable headends. The satellite's capacity today. is so large that users will be able to send information between locations at rates hundreds of times those used today.

In addition to private networks with dedicated facilities, SBS will offer shared services between two or more users whose traffic volume does not justify customer premises facilities. SBS is also planning an exchange services network bet­ ween 150 metropolitan areas served by 20 SBS switching centers. A twenty earth station network is to be completed by January 1982. Twenty-five earth stations are to be added by May 1982 and 50 more by January 1983. The shared and exchange services require local data transfer facilities that can be ideally provided by cable.

The need of insurance companies to share data has stimulated the formation of a resale common carrier of SBS service. Figure 3 ISACOMM, a communications subsidiary of Insurance Systems of America, is selling communications services to smaller users, principally in the insurance industry. ISACOMM initiated service through an

111 Distribution Basically, a station wishing to transmit using CSMA/CD listens to the circuit. If The type of distribution systems used the link is idle, it transmits. If two to carry the data signals can be any one stations should transmit simultaneously of several types. In practice, most sys­ (collide), each attempts to transmit again tems installed primarily to handle data after a random delay. have been of the mid-split type. This equipment is readily available and offers TABLE 1 approximately equal bandwidth in either Commonly Used Data Rates for direction. Typical band edges for mid­ Satellite and Terrestrial Services split amplifiers are 5MHz-108MHz upstream and 174MHz-300MHz downstream. Several Multiples of 1.2 Kbps 1.2, 2.4, 4.8, manufacturers have recently introduced new 9.6, 19.2 Kbps amplifiers which take advantage of the 400 MHz technology to extend the data handling Multiples of 56 Kbps 56,112,224, capacity beyond that of the mid-split 448 Kbps system. This system is referred to as a Tl 1544 Kbps hi-split system and provides a bandwidth of lOMHz-172MHz in the upstream direction 2Tl 3088 Kbps and 234MHz-400MHz downstream. It should TIC 3152 Kbps be pointed out however that for limited data applications, data signals can co­ T2 6312 Kbps exist on the same cable with entertain­ ment and other services as long as suf­ Modulation ficient spectrum is available. As is well known, the majority of these sys­ In addition to the multiplexing and tems are designed around a sub-split accessing method, one also has to consider concept (5-30MHz, 54-300/400MHz) with its the modulation that is to be used. The obvious lack of equality in bi-directional basic possibilities are amplitude shift capacity. keying (ASK), phase shift keying (PSK), and frequency shift keying (FSK). An Regardless of the type of system, attractive method for transmitting on non­ the broadband cable with its inherent high linear systems (satellites) is PSK. PSK signal to noise ratio and linearity offers transmission can take place using any num­ an ideal environment for the transmission ber of phases, e.g., two phases (hi-phase, of data signals. BPSK), four phases (quad-phase, QPSK), etc. BPSK and QPSK are widely used in Multiplexing/Access satellite SCPC circuits. When transmit­ ting at high data rates on cables, the The information that is to be sent frequency spectrum must be conserved. by cable can be multiplexed using time Since the cable is relatively linear and division multiplexing (TDM) or frequency the signal-to-noise ratios are high, an division multiplexing (FDM). Some com­ attractive modulation method is a com­ bination of time and frequency division bination of amplitude and phase shift key­ access will probably be used for most ing. The measure of transmission effici­ applications. Consider the data rates ency normally used is called bits/Hz. which are commonLy used in satellite This is the number of bits per second that circuits (Table 1). If many low data rate can be transmitted in one Hz bandwidth. ports are available at one location, the The number of bits/Hz for BPSK is one, most cost effective method of transmitting QPSK is two and for a combination of amp­ the signals is to time division multiplex litude and phase shift keying, can be 3 before modulation. On the other hand, the or more. For data rates of Tl or larger, higher data rate services are usually a combination of amplitude and phase shift sent single channel per carrier (SCPC) keying should be considered for use on the using frequency divison multiplex on the cable in order to conserve spectrum. coax or satellite. On the other hand, consider the case Another item that needs to be men­ of a large number of users at different tioned is changing access according to locations, each user having a relatively the changing needs of different users low data rate, and each user transmitting (multiple access). Pure time division occasionally. Here a modulation method systems may be made multiple access by can be employed that uses spectrum less allowing different users to occupy differ­ efficentl~ but yields less costly hard­ ent time slots on demand (TDMA). Like­ ware, e.g. FSK. In addition, the system wise, freqency division multiplex systems could employ CSMA/CD, giving all users can be extended to demand access (TDMA or access to the same channel. In most DAMA). Another method that is commonly cases, it is evident which type of mod­ used is called carrier sense multiple ulation method should be employed. For access/collison detection (CSMA/CD). further information on data modems for

112 cable networks see the reference below. for transmission on the cable. (Figure 4) It should be noted that Scientific-Atlanta Application for Cable modems can transmit TIC (3.152 Mbps) using slightly more than 1 MHz (1/6 of a video We have discussed the potentially channel). The 70 voice channel require­ large market for cable serving as the ment for Business B can be satisfied local distribution facility connecting using two D4 channel banks and two TIC businesses with satellite common carriers. modems. Both customer requirements can be We have discussed some of the technical satisfied economically using the config­ methods that are available for implement­ uration shown in Figure 4. ing this cable distribution system. Now let us consider an example of two current CONCLUSION business needs that Scientific-Atlanta is helping address. Business A wants to Cable television systems can play an establish a dedicated communication link important part in the intracity distribu­ to another city with 8 voice channels, tion of voice, data, electronic mail, and one 9.6 Kbps circuit, one 56 Kbps circuit other business communications. In only a and one 224 Kbps circuit. Business B few years, cable has gone from an auxili­ wishes to communicate with 70 voice chan­ ary system for areas with poor television nels through the same satellite communica­ reception to the most versatile and econo­ tions earth station. Forty-eight voice mical system for mass distribution of many channels can be digitized on a commercial­ channels of video entertainment. The next ly available D4 channel bank and sent on a step will be equally dramatic. It will TIC (3.152 Mbps) circuit. Data multiplex­ involve cable operators finding new busi­ ers can be added to one D4 channel bank in ness customers for using the cable system order to provide the 8 voice channels and to distribute business communications the various data circuits. The TIC out­ within the city. These customers will be put from the D4 channel bank is then fed satellite communications carriers, large into a spectrum efficient TIC modem and corporations, financial institutions, mun­ converted to the appropriate frequencies icipal agencies, and hospitals and univer­ sity complexes. ,------, ,------, 1 Earth Station 1 I Business A I I I I I I I I I I I I I I ll!RQI>,()IIAND C:N3LE. Izmbfoo 1 'r---'----' rf=f~~~---~Zl4kb,a ~ I~·• I '----+--- '!">l.k..,.l I I I I ~~~.... I 1 ~~ .... I I L ______j I I ,------, I 1 Business B 1 I I I 18 \IOIC( I 18\/0ICE. CHI\NNf.L'> I I I I CHI\NNELS. I I I I ZZ \/DICE zz \/DICE I CAANNELs. I I CIIMINl:L~ I 1 I L ______j L ______j

Cable Data Communications Link Equipment Configuration Figure 4

H.W. Katz, "Status Report on EIA Broadband Modem Standards," NCTA, 1980.

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