THE ROLE OF SERVICE AREAS IN THE OPTIMIZATION OF

FSS ORBITAL AND FREQUENCY ASSIGNMENTS

The Ohio State University by

Curt A. Levis

Coil-Way Wang

Yoshikazu Yamamura

ElectroScience Laboratory, Department of Electrical Engineering

and

Charles H. Reilly

David J. Gonsalvez

Department of Industrial and Systems Engineering

The Ohio State University

Columbus, Ohio 43210

The Ohio State University

ElectroScience Laboratory

Department of Electrical Engineering

Columbus, Ohio 43212

Technical Report 716548-3

Grant NAG 3-159

December 1985

(HASA-CB-176488) THE BOLE OFISEBVlfeE AREAS

IN THE OPIIMIZATICJN OF FSS OfifiXXAL A»J>

FBEQDENCY: ASSIGKHENTS^ |0hio State UniVv,, ;

Columbus. J,-,. ;31 p HC A03/MF A01 CSCLl JI7B ? Unclas

63/17 ; 05391 ,

National Aeronautics and Space Administration

Lewis Research Center

21000 Brookpark Rd.

Cleveland, Ohio 44135
NOTICES

When Government drawings, specifications, or other data are

used for any purpose other than in connection with a definitely

related Government procurement operation, the United States

Government thereby incurs no responsibility nor any obligation

whatsoever, and the fact that the Government may have formulated,

furnished, or in any way supplied the said drawings, specifications,

or other data, is not to be regarded by implication or otherwise as

in any manner licensing the holder or any other person or corporation,

or conveying any rights or permission to manufacture, use, or sell

any patented invention that may in any way be related thereto.
50771-1 Ql

REPORT DOCUMENTATION

PAGE

I. RETORT NO.

716518-3

4. Title and Subtitle

THE ROLE OF SERVICE AREAS IN THE OPTIMIZATION OF FSS ORBITAL

AND FREQUENCY ASSIGNMENTS

7. Autnorft)

Levis, Hang. Yamamura. Reilly, Gonsalvez

t. Performing Onjanliatlon Nam* end Addrm

The ElectroScience Laboratory

Department of Electrical Engineering

The Ohio State University

1320 Kinnear Road

Columbus, Ohio 43210

12. Sponsoring Organization Name and Addmt

NASA - Lewis Research Center

21000 Brookpark Rd.

Cleveland, Ohio 44135 .

1. Recipient's Accession No.

ft. Report Date

December 1985

S. Performing Organization Rept. No.

716548-3

10. PrOfOCt/TeskSWor* Unit No.

II. CentrKt(C) or Grant(G) No.

(O

'!' NA£

 3

:1_5_9

IS. Typ* of Report 4 Period Covered

Technical

14.

IS. Supplementary Note*

ORIGS^SAL PAGE IS

OF POOR QUAUTY

It. Abstract (Limit: 200 words)

A relationship is derived, on a single-entry interference basis, for the

minimum allowable spacing between two satellites as a function of electrical

parameters and service-area geometries. For circular beams, universal curves

relate the topocentric satellite spacing angle to the service-area separation

angle measured at the satellite. The corresponding geocentric spacing depends

only weakly on the mean longitude of the two satellites, and this is true also

for elliptical antenna beams.

As a consequence, if frequency channels are preassigned, the orbital

assignment synthesis of a satellite system can be formulated as a mixed-integer

programming (MIP) problem or approximated by a linear programming (LP) problem,

with the interference protection requirements enforced by constraints while some

linear function is optimized. Possible objective-function choices are discussed

and explicit formulations are presented for the choice of the sum of the absolute

deviations of the orbital locations from some prescribed "ideal" location set.

A test problem is posed consisting of six service areas, each served by one

satellite, all using elliptical antenna beams and the same frequency channels.

Numerical results are given for three "ideal" location prescriptions for both the

MIP and the LP formulations. The resulting scenarios also satisfy reasonable

aggregate interference protection requirements.

17. Document Analysis •. Deecrlpten

Satellite

Orbit

Assignment

b. ld*ntlfl*rs/Ope«-end*d T«rrm

Interference

Fixed Service

Regulation

e. COSATI new/Croup

IS. Availability Statement 1». Security Cle»» (Tr.it Report)

.Unclassified

Security Clan (This Pet*)

Unclassified

21. No. of

25

22. Price

(See ANS»-Z3«.1« > flwfrvcMatt* <

ii

OPTIONAL rORM 272 (4-77)

(Formerly NTIS-3S)

Department of Commerce
TABLE OF CONTENTS

ABSTRACT ii

LIST OF TABLES iv

LIST OF FIGURES v

I. INTRODUCTION 1

II. REQUIRED SATELLITE SEPARATIONS 1

III. SEPARATIONS FOR CIRCULAR BEAMS 4

IV. SEPARATIONS FOR ELLIPTICAL BEAMS ' 10

V. LINEAR PROGRAMMING FORMULATION 14

VI. MIXED INTEGER PROGRAMMING FORMULATION . 17

VII. NUMERICAL RESULTS 19

VIII. CONCLUSIONS 22

REFERENCES 23

111
LIST OF TABLES

Table

1 A* VALUES IN DEGREES •

2 As VALUES IN DEGREES

14

3

 SOLUTIONS TO TEST PROBLEMS 2Q

4 MMm:D or TrcT pjjj^s CORRESPONDING TO A

;E

21

iv
LIST OF FIGURES

Figure Page

1. Interference geometry between down-link networks. 2

2. Universal curves for the minimum al low-able satellite

spacing angle i|>3 as function of the normalized

off -axis angle iL ip is the half -power beam width of

the satellite antenna, d/X the diameter-to-wavelength

ratio of the EViR antenna. g

3. Minimum geocentric satellite spacing when earth

stations are separated in longitudinal direction.

35 dB, GSIT =40 dB, GEWR = 50 dB. 8

4. Minimum geocentric satellite spacing when earth

stations are separated in latitudinal direction.

RDN = 35 dB, GSIT = 40 dB, GEWR = 50 dB. 9

5. Geography of the six-service-area scenario. Dots

indicate test points. 12
I. INTRODUCTION

Satisfactory scenarios of orbit and spectrum allocations for

communications satellites must achieve sufficient protection for the

desired signals relative to interfering ones. Since the protection

ratio is a highly non-linear function of the satellite locations and the

frequencies to be assigned, it is natural to formulate the optimization

of these assignments in terms of non-linear programming techniques

[1-4]. The resulting codes place heavy demands on computational

resources [5]. Here we shall introduce an intermediate step: from an

estimate of the required single-entry protection we shall first

calculate the required satellite separations and then use these as

constraints in a linear-programming optimization, which should require

less computational effort. To do so, it is first necessary to derive

quantitative relationships between the required satellite separations,

the service-area geography, the protection ratios, and other system

parameters.

II. REQUIRED SATELLITE SEPARATIONS

Consider the single-entry interference between two down-link

satellite communications circuits. The up-link calculation has been

shown to be dual, i.e., of precisely the same form [6], The geometry is

shown in Figure .1. The following notation is used: S - satellite,

E - earth station, W - wanted network, I - interfering network, T -

transmit, R - receive. These symbols will also be used as subscripts in

the equations below. It should be noted that the angle 4», is a

1
EARTH

(a) Overall geometry

SW

GROUND AIM

POINT OF SW

GROUND AIM

POINT OF SI

COVERAGE AREA OF SW

•WANTED SIGNAL PATHS

INTERFERING SIGNAL PATHS

(b) Detail with Earth radius exaggerated for clarity

Figure 1. Interference geometry between down-link networks.
two-dimensional vector since, for elliptical or shaped beams, not only

its magnitude is important, but also the orientation of its plane with

respect to the plane defined by the beam axis and the beam-maximum (or

other reference) direction, e.g., the ellipse major axis for elliptical

patterns. Similarly the angle ty* is

 a vector, but ip., can be treated as

a scalar since there is no incentive for earth stations to use

non-circular beams.

The carrier and interference powers can be determined by means of

the Friis transmission formula [7] and combined to give a

well-approximated single-entry carrier-to-interference ratio

EWR

 " ESIT

where E denotes effective isotropic radiated power, n antenna

discrimination relative to the beam maximum, and G antenna gain in the

beam-maximum direction [8]. For satisfactory performance the

carrier-to-interference ratio must equal or exceed the required

protection ratio, which is the product of a co-channel protection ratio

P and a relative protection ratio p(f), where f denotes the frequency

offset from co-channel [9], Therefore Equation (1) shows that the

minimum allowable satellite spacing is implied in

'

 DSIT<V GSIT>
where -

RDN = P P(f> ESWT ESIT Dsl (V GSWT>

The first four factors in RON are known system parameters. Also since

calculations will always be performed at test points on the boundary of

a service area and since, in practice, satellite beams will be shaped to

give a-- reduction of approximately 3 dB at these test points, one can set

-»• DSNT^I'^SMT)

 a !/2« Tne left side of Equation (2) can therefore be

considered known in an orbit synthesis procedure.

It is important to note that Equation (2) is an implicit equation

relating the required satellite separation to the separation of the two

service areas. The existence of such a relationship has long been

recognized qualitatively [10,11], Equations (2) and (3) state

quantitatively that, when frequency isolation is insufficient, the

system requires antenna discrimination to achieve a required protection

level, and that this is obtained as the product of the earth and

satellite antenna discriminations.

III. SEPARATIONS FOR CIRCULAR BEAMS

For circular beams, the angle ^2

 in Equation (2) becomes scalar and

it is possible to solve explicitly for 1^3 as a function of i|>2 when the

discrimination patterns DsiT>

 nEWR are specified. The relationship can

be plotted conveniently as a universal set of contour curves, with R^

as parameter and normalized values of ^.^ as coordinates. The need

for normalization is implied in Equation (2) by the presence of the
gains G as arguments in the antenna discriminations. For example, when

GEWR is large, corresponding to a narrow Earth-station beam, a given

value of DEHR is reached with a smaller value of ^3 than when GE^R is

small. The universal curves are shown in Figure 2 for discrimination

pattern envelopes recommended by the CCIR for co-polarized FSS

antennas [12,13], Unfortunately, no corresponding cross-polarized

patterns have been recommended as yet. Two sets of curves are required

because of the piecewise specifications of DC^). At first sight it

might appear that four sets would be required since four "pieces" are

used in the CCIR specification of Earth-station discrimination.

However, it turns out that the far side-lobe and back-lobe regions imply

so much discrimination that the interference can be neglected, while the

constant part of the pattern, representing the near-sidelobe envelope,

is accounted for by the discontinuity in the ^3 values which results

from switching between Figures 2a and 2b in accordance with the

directions given below them.

The expression of the universal curves in terms of the

antenna-centered "off-axis" angles \|>2 and t3 is natural and also useful:

for example, it shows that the "separation" of service areas, measured

by i|>2» is rigorously the distance from the aimpoint of the interfering

satellite antenna to that test point of the area suffering interference

which is on the highest discrimination contour of the interfering

satellite antenna pattern on the Earth surface. For circular beams and

high satellite elevations this would be the test point nearest to the

interfering satellite aim point. Nevertheless, for many system
ORIGINAL PAGE IS

OF POOR QUALITY

0 3 (a) Use for t- > 26.3 G^un degrees or above appropriate

Earth station antenna gain line. Unless dB are

specified G-n means the numerical gain value.

0.0 20.0

(b) Use for *, < 20 (d/X)"[5.35 + 5 Iog10(d/X)]1/2 or below

appropriate Earth station antenna gain line

Figure 2. Universal curves for the minimum allow-able satellite spacing

angle i|»3 as function of the normalized off-axis angle i|»?>

ip is the half-power beam width of the satellite antenna"! d/x

tne diameter-to-wavelength ratio of the EWR antenna.
calculations it is more useful to find the geocentric satellite

separation A<|> instead of the topocentric angle tp-, directly as a

function of the longitude differences and latitudes of EWR, EIR, and SI

instead of \P2. Actually the angle i|»o turns out to be a rather good

approximation for A<J>, which can be improved sufficiently for all

practical purposes by

A* = i|>3 [1.023-0.302 cos(<j>M-<|.E)coseE]

1

/2 racj (4)

where ta is the longitude of the midpoint between the wanted and

interfering satellites (SW,SI) and <|>r, 9- are the longitude and latitude

of the test point (EWR), respectively.

The relationship between ^ and the geocentric variables can be found

by substituting suitable expressions obtained from Figure 1 into the

cosine law

cosily = (b2+c2-g2)/2bc , (5)

but for many purposes the relationships

9 9

rad

 •

where Rj: is the earth radius, give a sufficiently good estimate. The

correct value is close to the upper limit for high satellite SI

elevations and to the lower for low elevations, as viewed from the aim

point EIR. The variation of the required separation A<f> for various

system parameters and configurations in terms of longitude and latitude

is shown in Figures 3 and 4. From these and more such computations the

following results emerge [14]:
ORIGINAL PAGE !S

OF POOR QUALITY

LMCfTUOE OF E3X RELATIVE TO CWtt

"*L'ONGlfuDE OF SM RELBmE TO

U) C*M AT 0-K

(a)

-u. -io. o. ». n. «.

LONGITUDE OF SM RELATIVE TO EHR

(el CWR AT 40* H .

!LONGITUDE Or CR KCumvc TO EWB 1

 I i- •

LONCITUOE OF iti RELftHVE TO "MR

JM IVM AT tO*M

(b)

:LON6ITUOE OF EIR RELATIVE TO :WR

(0. -U. 0. U. U.

LONGITUDE OF SM RELATIVE TO EUR

<«| EWR AT WN

(c) (d)

Figure 3. Minimum geocentric satellite spacing when earth stations are

separated in longitudinal direction. RON = 35 dB, G$IT = 40

dB, GEWR = 50 dB.

8
ORIGSMAL PAGE IS

OF POOR QUALITY

ct

is

o-r bJ

-SO. -30. 0. 90. 60.

LONGITUDE OF SH RELflTIVE TO EHR

(a) EWR AT 0*N

(a)

LATITUDE OF EIR

28*N

SO. -10. 0. 10. 10.

LONGITUDE OF SH RELATIVE TO EHR

(b) EWR AT 20* N

(b)

-60. -10. ' 0. 10. 60.

LONGITUDE OF SH RELflTIVE TO EHR

(C) EWR AT 40' N

(c)

-60. -30. 0. 10. 60

LONGITUDE OF SH RELflTIVE TO EHR

(dl EWR AT 60* N

(d)

Figure 4. Minimum geocentric satellite spacing when earth stations are

separated in latitudinal direction. RDN = 35 dB, 6517 =40

dB, GEWR = 50 dB.
(a) the smallest required separation occurs for practical geometries

when the wanted satellite is near the longitude of the center of

its service area,

(b) for a substantial range of orbital locations about this longitude

the required separation varies little.

This last result, which appears to be true also for elliptical beams

(see Section IV), is very important in the synthesis procedure discussed

in Section V, because it reduces or eliminates the need to recalculate

the required satellite separations as satellite orbit assignments are

changed.

IV. SEPARATIONS FOR ELLIPTICAL BEAMS

For elliptical beams, the required satellite separations can be

calculated by the following procedure:

(1) For each service area choose test points on the periphery and

calculate the orientation and axial ratio Ar of the minimum

projected ellipses which enclose them, using 2° increments in

satellite longitude [15],

(2) Choose a wanted and an interfering satellite and a longitude

within the orbital arc under consideration, and consider the

desired and interfering satellites collocated at that longitude.

By incrementally increasing A<{>, with the satellites located

symmetrically on each side of the initially chosen central

10
longitude, calculate the required satellite separation from

Equation (2) with

where \|»0 is the half-power beamwidth in the direction of the major

axis and 6 is the angle between the plane in which ^ is measured

and the plane determined by the SIT beam axis and the SIT ellipse

major axis. Equation (5) is used for evaluating ^ in this

calculation.

(3) Repeat step (2) for other central longitudes. The result for the

worst test point for each service area shown in Figure 5 is shown

in Table 1 for a sequence of central longitudes. For each pair of

satellites two separation values can be obtained, depending on

which service area is considered protected, with the satellite of

the other area considered interfering. The larger of these

appears as A<|> in Table 1. Notice the slow variation of A<|> with

the mean satellite longitude, provided that this longitude is not

too different from that of the protected service area. One

satellite per service area was assumed in these calculations.

(4) Choose the largest of all the A<J> values obtained in this process

over the allowable orbital arc for each satellite pair and denote

it AS. The triangular matrix of As elements corresponding to

Table 1 is shown in Table 2 for all satellites constrained to the

11
SERVICE AREA

ARGENTINA

BOLIVIA

CHILE

PARAGUAY

PERU

URUGUAY

Figure 5. Geography of the six-service-area scenario,

test points.

Dots indicate

12
TABLE 1

A<f> VALUES IN DEGREES

Single-entry protection ratio = 30 dB. The discrimination

patterns of refs. 16,17 were used for the Earth antennas with

d/X = 60 and 0.6 aperture efficiency. Those of ref. 18 were

used for the satellite antennas with beam width as determined

by the minimum ellipse. It was assumed that SW and SI produce

the same power density at their respective aim points,

corresponding to RnN « 33 dB.

Satellite

pairs

AR6

ARG

ARG

ARG

ARG

BOL

BOL

BOL

BOL

CHL

CHL

CHL

PRG

PRG

PRU

BOL

CHL

PRG

PRU

URG

CHL

PRG

PRU

URG

PRG

PRU

URG

PRU

URG

URG

Mean Satellite Longitude

70°W

4.00

4.18

4.24

0.94

4.18

4.13

4.00

3.87

0.39

1.08

3.84

0.42

0.49

2.16

0.40

80°W

4.02

4.05

4.28

1.04

4.14

4.20

3.99

3.95

0.38

1.14

3.83

0.41

0.49

2.19

0.37

90°W

4.05

4.00

4.32

1.15

4.06

4.28

4.00

3.99

0.38

1.25

3.85

1.03

0.50

2.20

0.37

100°W

4.12

4.02

4.28

1.25

4.06

4.39

4.03

4.10

0.84

1.46

3.89

1.28

0.85

2.34

0.33

110°W

4.17

4.19

4.32

1.41

3.94

4.57

4.04

4.26

0.94

2.00

3.94

1.59

1.10

2.46'

0.32

13
80°W to 110°W orbital arc. These separations will be used as

constraints in the synthesis procedures of the next section.

TABLE 2

AS VALUES IN DEGREES

BOL CHL PRG PRU URG

ARG

BOL

CHL

PRG

PRU

4.17 4.19

4.57

4.32

4.04

2.00

1.41

4.26

3.94

1.10

4.14

0.94

1.59

2.46

0.37

V. LINEAR PROGRAMMING FORMULATION

The FSS synthesis problem can now be formulated as a linear program

with a set of nonlinear side constraints. The set of satellite

locations which satisfy the constraints constitutes the feasible region.

A variety of linear functions can be selected to be optimized. Three

functions have occurred to us:

(a) to search only for some point in the feasible region by setting

the function to be minimized equal to zero;

(b) to minimize the occupied orbital arc;

(c) to minimize the sum of the absolute deviations of the satellite

locations from a specified set of locations.

14
The last objective has been implemented in the formulation described

below. The following parameters and non-negative variables are used:

ej(wj) - easternmost (westernmost) feasible location for satellite

j, in °W,

dj - desired location for satellite j,

AS-JJ - required minimum separation between satellites i and j, as

in Table 2,

Xj - relative location (in degrees west of ej) of satellite j,

Xj+(xj~) - degrees west (east) of dj that satellite j is located,

pij(nij) - degrees west (east) of satellite j that satellite i is

located (defined for i < j).

The FSS orbit assignment synthesis is then formulated as follows:

Minimize

z = I (Xj

+ + xj-) (8)

J

subject to

Xj - Xj+ + Xj- = dj for all j , (9)

x-j - Xj - p-jj + n-jj = 0 for all i,j

where i < j , (10)

Pij + njj > ASfj for all i,j

where i < j , (11)

15
Xj < Wj - ej for all j , (12)

Xj, xj+, Xj- > 0 for all j , (13)

Plj»

 nij > ° for all i,j

where i < j , (14)

and

where i < j . (15)

The objective function, Equation (8), computes the sum of the

absolute deviations of the prescribed satellite locations Uj's) from

the desired or ideal locations (dj's). These absolute deviations are

measured in the first set of constraints, Equation (9). The actual

separations between all pairs of satellites (p^j + n-jj) are computed in

the second set of constraints, Equation (10), and are compared to the

minimum required satellite separations in the third set of constraints,

Equation (11). The constraints of Equation (12) guarantee that the

location prescribed for each satellite is feasible. Constraint Equations

(13) and (14) indicate that all of the variables in the problem are

restricted to non-negative values. Finally the complementary

relationships between pairs of variables p^j and n^j are enforced by the

constraints of Equation (15).

Linear programs are much more readily solvable than nonlinear

programs and integer programs. They are most often solved by the simplex

method [19], This technique examines a sequence of basic solutions to

the constraints of the linear program. Each solution examined has an

16
objective function value no less favorable than that of the previous

solution. The algorithm terminates when it is determined that no

improved solution can be found.

The presence of the nonlinear side constraints of Equation (15)

prevents us from using the simplex method in its most common form. The

method can be modified to handle these additional constraints through the

use of restricted basis entry: p-jj can not be a basic variable if njj is

a basic variable, and vice versa [20], When employing the simplex method

with restricted basis entry, we are certain to find a local, but not

necessarily a global, optimum. As formulated, the problem has m(m+2)

variables, where m is the number of satellites, and m2 constraints, not

counting the simple bound constraints of Equations (12) to (14) and

complementarity constraints of Equation (15). The formulation is similar

to one suggested by Ignizio for the N-job, single-machine scheduling

problem [21],

VI. MIXED INTEGER PROGRAMMING FORMULATION

The same problem can also be formulated as a mixed integer program

[22], A global optimum is guaranteed when this formulation is employed.

However, the computational effort required to find a final solution can

be immensely greater than it would be with the linear programming

formulation. In any case, this formulation is helpful in assessing the

quality of the solutions found using the linear programming formulation

on small test problems.

17
To complete this formulation, we need the following definitions:

e =

 mi.n {e.} , (16)

J

 J

w =

 max {w.} , (17)

J

 J

1 if satellite i is located west of

satellite j

0 otherwise .

xij = f satellite j. (18)

The objective function and the constraints (9), (10), (11), (13) and

(14) appear in this formulation precisely as they did in the linear

programming formulation. The complementarity constraints (15) are

replaced by two new constraints:

< 0 (15a)

(w-e)x1j + ni . < (w-e) (15b)

which, together with the nonnegativity restrictions on p^j and njj,

constraints (14), guarantee that either PJJ = 0 or n-jj = 0 for all pairs

of satellites i and j.

If there are m satellites, the mixed integer formulation entails

m(m+2) continuous variables, m(m+l)/2 binary variables, and 2m2-m

constraints specified by Equations (9), (10), (11), (15a), (15b). The

time required to solve an FSS synthesis problem with this formulation

will be most heavily dependent upon the number of binary variables. For

large problems (many satellites), this formulation may involve

prohibitive solution times.

18
VII. NUMERICAL RESULTS

The FSS synthesis minimizing the sum of absolute deviations of

orbital positions from a prescribed "desired" set was solved, both as a

linear program with the simplex method with restricted basis entry and

as a mixed integer program via branch-and-bound [23]. The service areas

and test points were those of Figure 5 with one satellite per service

area. The available orbital arc for each satellite was specified as

80°W to 110°W. It was assumed that each satellite would carry a full

complement of frequency channels, so that a co-channel calculation is

appropriate. A single-entry C/I value of 30 dB was chosen with the

intent of achieving a 25 dB aggregate co-channel C/I ratio. With these

assumptions the As values of Table 2 are pertinent. Three problems were

run, differing only in the specified "desired" satellite locations. In

problem 1, this "desired" location was specified for every satellite as

95°W, the center of the arc. In problem 2, all "desired" locations were

specified at 110°W, the westernmost end of the arc. In problem 3, each

was specified near the central longitude of the ellipse circumscribing

the service area to be served; these "desired" longitudes are indicated

in the column labeled DL in Table 3, which shows the solutions obtained

for all three problems by both methods. The LP formulations required 48

variables and 36 constraints, while 63 variables, 15 of them binary, and

66 constraints were needed for the MIP formulation.

The solutions to these test problems illustrate some important

points. First of all, the solution of a synthesis problem by means of

an integer program can require a substantially greater amount of

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20
computer time than by means of a linear program. Secondly, the two

approaches used can produce strikingly different solutions. (See the

results for Problems 1 and 2.) It may also happen that the same

solution will be found with both methods, even though this is not

evident from the results presented here. Finally, acceptable solutions,

in terms of aggregate co-channel C/I ratios, are obtained even when the

objective function value for the linear programming solution differs

substantially from the mixed integer programming solution, the global

optimum. This is not unexpected because the AS constraints guarantee

acceptable single-entry C/I ratios. Table 4 shows the distributions of

aggregate co-channel C/I ratios for the two methods and three problems.

It will be remembered that a 30 dB single-entry constraint was used to

calculate the As table on which all these calculations are based.

TABLE 4

NUMBER OF TEST POINTS CORRESPONDING

TO A GIVEN AGGREGATE CO-CHANNEL

C/I RATIO RANGE FOR EACH PROBLEM AND METHOD

Problem

1

1

2

2

3

3

Method

LP

MIP

LP

M IP

LP

M IP

<27

0

0

0

0

0

0

C/I

27-28

1

1

0

4

0

0

Interval

28-30

8

6

5

10

4

9

(dB)

30-35

16

18

20

25

16

14

>35

29

29

29

15

34

31

21
VIII. CONCLUSIONS

An implicit relationship has been derived which relates the

topocentric separation of two satellites as required for a given level

of single-entry protection to the separation and orientation of their

service areas. For circular beams and topocentric angles the results

are presented explicitly; a computational approach is given for

elliptical beams and for use with longitude and latitude variables. It

is found that the geocentric separation depends primarily on the service

area separation, secondly on a parameter RQN which characterizes the

electrical design, and only slightly on the mean orbital position of the

satellites. Both linear programming (LP) and mixed integer programming

(MIP ) algorithms have been implemented, with the sum of the absolute

deviations of the orbital locations from a prescribed "ideal" set as

objective function. Three "ideal" sets were used. A single-entry

protection ratio of 30 dB was specified with the intent of satisfying an

aggregate co-channel C/I ratio of 25 dB. The set of orbital locations

chosen by the LP and MIP methods differed substantially in two cases

and, to a lesser degree, in the third. Still, all six solutions which

were found provided acceptable protection ratios at all 54 test points.

The worst aggregate co-channel C/I ratio found was 27 dB.

The results are encouraging with respect to applying the LP

procedure to larger scenarios. The MIP formulation may result in

excessive computation times when many satellites are involved, but it is

guaranteed to arrive at a global optimum; it will therefore be useful

for evaluating the efficacy of the LP approach via smaller test

problems, such as the three presented here.

22
REFERENCES

[1] Y. Ito, T. Mizuno, T. Muratani, "Effective Utilization of

Geostationary Orbit through Optimization", IEEE Trans, on

Communications, Vol. COM-27, No. 10, pp. 1551-1558, Oct. 1979.

[2] C.H. Reilly, C.H. Martin, D.J. Gonsalvez, C.A. Mount-Campbel1,

C.A. Levis, C.W. Wang, "Broadcasting Satellite Service Synthesis

Using Gradient and Cyclic Coordinate Search Procedures", Eleventh

AIAA Communications Systems Conference, San Diego, March 1986.

[3] C.H. Martin, D.J. Gonsalvez, C.A. Levis, C.W. Wang, "Engineering

Calculations for Communications Satellite Systems Planning",

Interim Report 713533-4, 1/15/83-7/15/83, The ElectroScience

Laboratory^ The Ohio State University, Columbus, Ohio 43212, on

Grant No. NAG 3-159, for NASA/Lewis Research Center, 21000

Brookpark Road, Cleveland, Ohio 44135.

[4] C.A. Levis, C.H. Martin, C.H. Reilly, D.J. Gonsalvez, Y. Yamamura,

"Engineering Calculations for Communications Satellite Systems

Planning", Interim Report 713533-5, 7/15/83-7/14/84, The

ElectroScience Laboratory, The Ohio State University, Columbus, OH

43212, on Grant No. NAG 3-159, for NASA/Lewis Research Center,

21000 Brookpark Road, Cleveland, Ohio 44135.

[5] C.H. Reilly, C.A. Levis, D. Gonsalvez, C.W. Wang, Y. Yamamura,

"Engineering Calculations for Communications Satellite Systems

Planning", Interim Report 716548-2, 7/15/84-7/14/85, The

ElectroScience Laboratory, The Ohio State University, Columbus,

Ohio 43212, on Grant No. NAG 3-159, for NASA/Lewis Research

Center, 21000 Brookpark Rd., Cleveland, Ohio 44135.

[6] Y. Yamamura, C.A. Levis, "Calculation of Allowable Orbital

Spacings for the Fixed-Satellite Service", Technical Report

716548-1, Chapter III, The ElectroScience Laboratory, The Ohio

State University, Columbus, OH 43212, on Grant No. NAG 3-159, for

NASA/Lewis Research Center, 21000 Brookpark Road, Cleveland, Ohio

44135.

[7] W.L. Stutzman, G.A. Thiele, Antenna Theory and Design, John Wiley

& Sons, 1981, page 60.

[8] Y. Yamamura, C.A. Levis, pp. cit., Chapter II. Although stated for

circular antenna beams, the derivation is valid generally when ^

and ^2 (in the notation of the present paper) are considered as

vectors.

23
[9] CCIR Report 634-2 "Broadcasting-Satellite Service (Sound and

Television)" , Recommendations and Reports of the CCIR, 1982, Vols.

X/XI , part 2, pp. 121-159, Figure 1. International

Telecommunication Union , Geneva, 1982. Also availabl e from

National Technical Information Service, Springfield, Virginia .

(It is assumed similar reference protection ratios will be

generated for the FSS).

[10] CCIR Report 453-3 "Technical Factors Influencin g the Efficiency of

Use of the Geostationary-Satellite Orbit by Radiocommunications

Satellites Sharing the Same Frequency Bands", Sections 2.3, 8.3.

Recommendations and Reports of the CCIR, 1982, Vol. IV, part 1,

pp. 272-306. International Telecommunication Union , Geneva, 1982.

Also availabl e from National Technical Information Service,

Springfield , Virginia .

[11] CCIR Report 663-2 "Orbit and Frequency Plannin g in the Broadcast

Satellite Service", Section 2.1.8. Recommendations and Reports of

the CCIR, 1982, Vol. X/XI, part 2, p. 95. International

Telecommunication Union , Geneva, 1982. Also availabl e from

National Technical Information Service, Springfield, Virginia .

[12] CCIR Report 391-4 "Radiation Diagrams of Antennas for Earth

Stations in the Fixed-Satellite Service for Use in Interference

Studies and for the Determination of a Design Objective", Annex I

"Reference Pattern of the WARC-79". Recommendations and Reports

of the CCIR. 1982, Vol. IV, part I, pp. 198-200. .International .

Telecommunication Union , Geneva, 1982. Also availabl e from

National Technical Information Service, Springfield, Virginia .

[13] CCIR Report 558-2 "Satellite Antenna Patterns in the FixedSatellite Service", Recommendations and Reports of the CCIR, 1982,

Vol. IV, part 1, p. 386, International Telecommunication Union,

Geneva, 1982. Also availabl e from National Technical Information

Service, Springfield, Virginia .

[14] Y. Yamamura, C.A. Levis, op. cit., Chapter II.

[15] H. Akima , "A Method for Determining the Mini-mum Elliptica l Beam

of a Satellite Antenna", NTIA Report 81-88, National

Telecommunications and Information Administration, US Dept. of

Commerce, October 1981. Minor modifications by J. Cesaites,

Federal Communications Cornm., Washington, D.C.

[16] CCIR Report 391-4, op. cit., modified by CCIR Recommendation 580

[17].

24
[17] CCIR Recommendation 580, "Radiation Diagrams for Use as Design

Objectives for Antennas of Earth Stations Operating with

Geostationary Satellites", Recommendations and Reports of the

CCIR, 1982, Vol. IV, part 1, pp. 184-185. International

Telecommunication Union, Geneva, 1982. Also available from

National Technical Information Service, Springfield, Virginia.

[18] Technical Bases for the Regional Administrative Radio Conference

1983 tor the Planning of the Broadcasting-satellite Service Tn"

Region 2. Report of the CCIR Conference Preparatory Joint Meeting

of Study Groups 4,5,9,10 and 11. pp. 112, Equation (5), with the

5th and 6th expressions for f deleted. International

Telecommunication Union, Geneva, 1982.

[19] D. Luenberger, Linear and Non-Linear Programming, Addison-Wesley,

1984. •J

[20] D. Phillips, A. Ravindrang, J. Solberg, Operations Research:

Principles and Practice. John Wiley & Sons, 197&.Chapter II.

[21] J. Ignizio, "A Generalized Goal Programming Approach to the

Minimal Interference, Multicriteria N x 1 Scheduling Problem", HE

Trans., Vol. 16, No. 4, pp. 316-322, December 1984.

[22] R. Garfinkel, G. Nemhauser, Integer Programming. John Wiley &

Sons, 1972.

[23] ibid.

25