ORBIT-SPECTRUM SHARING BETWEEN THE FIXED-SATELLITE AND BROADCA G-SATELLITE SERVICES WITH AP ICATIONS TO 12 GHz DO ESTI SYSTEMS PREPARED FOR THE NATIONAL AERON UTICS AND S ACE ADMINISTRATION, EDWARD E.REINHART R-463-NA A MAY 1974 N7517548 S AING :(N ASBtCR- L-3688) ORBIT-SPECTRUM ,BETW'EEI THE .FIXED-SATELLITE AND WIT Unclas BROADCASTING-SATELLIT SERVICES TO 12 GHz DmESTIC SYST S 1733 0 AppLICARTfIONS 250 H $ .50 3 32 inal- Reo°r.t ( AND Corp. This research was sponsored by the National Aeronautics and Space Ad- ministration under Contract No. NAS 5-21722. Views or conclusions con- tained in this study should not be interpreted as representing the official opinion or policy of the National Aeronautics and Space Administration. Published by The Rand Corporation /A",/1 / " ORBIT-SPECTRUM SHARING BETWEEN THE FIXED-SATELLITE AND BROADCASTING-SATELLITE SERVICES WITH APPLICATIONS TO 12 GHz DOMESTIC SYSTEMS PREPARED FOR THE NATIONAL AERONAUTICS AND SPACE ADMINISTRATION EDWARD E.REINHART R-1463-NASA MAY 1974 Reproduced by NATIONAL TECHNICAL INFORMATION SERVICE US Department of Commerce Springfield, VA. 22151 land SANTA MONICA, CA. 90406 PRiCES SUBJEc TO C PREFACE This is the final report on Tasks 1, 2, and 3 of a modification to NASA contract NAS5-21722--titled "A Study of Spectrum and Orbit Sharing Between the Broadcasting-Satellite Service and the Fixed-Satel- lite Service in the 11.7 to 12.2 GHz Band." The final report on other tasks of this contract will appear as Rand report R-1300-NASA, Plan- ning and Coordination of Broadcasting-Satellite Systems.. The study reported here was sponsored by NASA as a part of their technical consultation program. It was motivated by an FCC request to NASA for technical guidance regarding preferred methods for sharing the 11.7 to 12.2 GHz band between the fixed-satellite and broadcasting- satellite services. The results of the study should be useful to the FCC in connection with its domestic regulatory responsibilities in this frequency band. The analytic techniques and results are also relevant to the formulation of U.S. positions in preparation for the 1977 planning conference of the International Telecommunication Union (ITU), which will develop international plans for the use of the 12 GHz broadcasting-satellite band and for the 1979 ITU World Administrative Radio Conference, which will revise the entire frequency allocation table. Although the emphasis is on domestic systems in the 11.7 to 12.2 GHz band, the report provides a systematic, tutorial analysis of the general problem of orbit-spectrum sharing among inhomogeneous satellite systems. Building upon the pioneering studies of orbit- spectrum utilization sponsored by the Office of Telecommunictions Policy and upon the NASA analysis of domestic fixed-satellite system compatibility, it gives all of the equations needed in the analysis and summarizes and interprets the relevant experimental data. Par- ticular attention is paid to the problem of extrapolating and applying the available data on rain attenuation and to reconciling differences in the results of various measurements of the subjective effects of interference on television picture quality. -iv- An analytic method is presented to replace "trial-and-error" for determining the approximate values of the intersatellite spacings required to keep mutual interference levels within prescribed limits when many dissimilar satellites share the orbit. Another powerful and essential analytic tool developed for this study is an efficient new computer model for assessing the interference compatibility of arbitrary configurations of large numbers of geostationary satellite systems. Although the computer model presently is restricted to telephone and television signals that employ frequency modulation, it is not restricted to the 12 GIHz band, and could easily be extended to include other modulation techniques. New concepts and terminology are introduced for describing and evaluating sharing strategies. For example, the terms "spectrum divi- sion" and "orbit division" are used to distinguish between strategies in which each satellite service can use only an assigned share of the spectrum or orbit, respectively, while enjoying unrestricted access to the other components of the orbit-spectrum resource. The concept of "utilization factor" is defined as a dimensionless measure of the effectiveness with which a service utilizes its share of the resource. The sum of the utilization factors for the sharing services then yields the "total utilization factor," which affords a useful figure-of-merit for the sharing strategy under investigation. Each section of the report is complete in itself. Readers who are not interested in the technical basis for the analysis may safely omit Secs. III, IV, V, and the Appendix and concentrate on the detailed description of the problem contained in Sec. II, the evaluation of sharing strategies in Sec. VI, and the discussion of conclusions in Sec. VII. _v_ SUMIARY In the United States, the band 11.7 to 12.2 GHz was recently allocated to both the fixed-satellite and broadcasting-satellite ser- vices. For these services to share the allocation equitably and effi- ciently, the design and deployment of future systems will have to be carefully regulated. To provide a technical basis for developing the necessary rules and regulations, this report identifies and evaluates a number of strategies for sharing the orbit-spectrum resource con- sisting of the 500 1fMHz of spectrum in the band and a nominal 75 deg segment of the geostationary orbit. The analytic approach begins with the design of a set of four baseline system models to represent the two services, taking care to ensure that the choice of parameters for these systems is based on consistent design assumptions. Alternative sharing strategies are applied to various mixes of the baseline systems using computer simu- lation to verify the interference compatibility of the assumed satel- lite system configurations. The strategies are evaluated in terms of the effectiveness with which each service utilizes its share of. the orbit-spectrum resource. The measure of effectiveness is the "utili- zation factor," defined as the capacity that a service can provide when using an assigned share of the resource relative to the capacity it could provide if granted an exclusive allocation of the entire resource. The sum of the utilization factors for the two services is the "total utilization factor," which is taken as a figure-of-merit for the sharing strategy. Two types of sharing strategies are considered. In a spectrum- division strategy, each service can occupy the entire orbital segment but is assigned only part of the frequency band. In an orbit-sharing strategy, the reverse is true. The principal conclusions to be drawn from a comparison of these strategies are as follows: The fixed-satellite and broadcasting-satellite services can share the orbit-spectrum resource equitably and effectively. Both orbit- division and spectrum-division strategies permit total utilization -vi- factors close to 100 percent, indicating that sharing does not sig- nificantly jeopardize orbit-spectrum utilization. With spectrum-division there is no interservice interference so that the utilization factor for each service is very nearly pro- portional to the fraction of spectrum allocated to it and the total utilization factor is always near 100 percent. The spectrum may be divided between the services in any desired proportion independent of the characteristics of the satellite systems. With orbit-division, interservice interference is controlled by careful separation of satellites in the orbit and the preferred satel- lite deployment depends on both the equipment and signal parameters of the sharing systems. However, the problem differs only in degree from that of finding compatible spacings for intraservice sharing and, for any given combination of systems, a deployment can be found for which the utilization factor of the corresponding orbit-division strategy approaches 100 percent. For certain combinations of systems, the total utilization can significantly exceed 100 percent, although in these cases, there is a limitation on the relative size of the orbit shares that can be assigned. Compared with an orbit-division strategy using the same types of systems, spectrum-division imposes a serious economic penalty: each service has to use more satellites to provide the same total capacity. Since an orbit-division strategy can provide equally high and in some cases higher utilization factors, it is concluded that orbit-division is to be preferred to spectrum division. The satellite deployment that characterizes the preferred orbit- division strategy for a given set of systems depends on the degree of inhomogeneity among those systems. When satellite eirps, earth-sta- tion antenna diameters, or signal modulation indices are quite dif- ferent, a clustered deployment in which two or more satellites of the less powerful system are "clustered" between adjacent satellites of the more powerful system yields the highest total utilization. When the system parameters are more homogeneous, the deployment becomes less critical, and in most cases, somewhat higher utilization factors -vii- are obtained by gathering satellites of the same kind together in clusters and minimizing the number of interfaces between clusters. The use of sharing tactics such as frequency interleaving, crossed-polarization operation, and crossed-beam operation, do not normally affect the values