An empirical relation for path diversity gain as a function of terminal separation distance and single site fade depth is presented. This relation is based on existing 15.3 GHz ATS-5 attenuation data and 16.0 GHz radiometric temperature data for earth-space propagation paths. Preliminary 30 GHz ATS-6 diversity data are presented and are found to agree well with this empirical relation

Hodge, D. B.

Theobold, D. M.

English

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ATS-6 MILLIMETER WAVELENGTH
PROPAGATION EXPERIMENT
D. B. Hodge and D. M. Theobold
TV  Ohio State UnivP; city
ElectroScience laboratory
Department of El*ctrlcal Enginewinp
Columbus, Ohio 43212
(NASA-CI- 143P14 )	 A'IS-6 MILLIMETEF
kkV F LFNGTH fROPAGA'IICN EXPERIMENT Cuaiterly
FeFOLt, 15 Jan. - 14 Apr. 1975 (0hio State
Univ.)	 14 F HC $3. 25 	CSCL 17L•
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Report 3863-5
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June 1975
N75- 28279
Quarterly Report for Period 15 January 1975-14 April 1975
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GODDARD SPACE FLIGHT CENTER
Greenbelt, Maryland 20771
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NASS-21983
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Quarterly Report
15 Jan,'75-14 Aor.'75
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TFCHNICAL REf't1RT STANDARD TITLE PACE
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_R•pon No ---- - -	 '7 G.,.e,e..	 1 Ac,@%%-,,., W,	 7 Ret.0.ent s (,)tnlog No
1 f.11e and Su1.1,11e
ATS-6 MILLIMETER WAVELENGTH
PROPAGATION EXPERIMENT
1 Aurho.lsl
D. Q. Hot'ge and D. M. Theobold
9 Pe,fo,­q O,gan.tn t ,an Name anti Add,eas
The Ohio State University ElectroScience
Laboratory, Department of Electrical
Engineering, Co l umbus, Ohio 43212
12 Sponso­q Agency Nome and Address
,NASA, GSFC
Greenbelt, Maryland 20771
E. Hirschmann, Code 951, Technical Cfficer
1S Supple,eentnry Notes
16 Abst,ort
An empirical relation for path diversity gain as a function of
terminal separation distance and single site fade depth is pre-
sented. This relation is based on existing 15.3 GHz ATS-5
attenuation data and 16.0 GHz radiometric temperature data for earth-
space propagation paths. Preliminary 30 GHz ATS-6 diversity data
are presented and are found to agree well with this empirical re-
lation.
The current status and summary of operations are also reviewed,
118 D,str,butcan StatementI17. Key wo,ds (Selected by Aurhur(s))
li ATS-6
i Millimeter Wave
Propagation
Diversity
14. Security Classif. (of th.s report)
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! 20 Security elnss. l (of rh.a page)
	
21 No of Page%	 1 22 P,,,•.•
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TABLE OF CONTENTS
I. EMPIRICAL DIVERSITY GAIN RELATION
II. PRELIMINARY ATS-6 30 GHz DIVERSITY DATA
III. SUMMARY OF OPERATIONS
IV. CURRENT STATUS
V. REFERENCES
VI. PUBLICATION SUMMARY
i
Page
1
5
12
13
13
14
Footnote:
Parts I and II of this report were presented at the USNC/URSI
meeting, Urbana, Illinois, 3-5 June 1975. Part I of this report has
also been submitted to the IEEE Transactions on Antennas and Propagation
for publication.
ii
f -^
I.	 LMPIK T.:A. DIVERSITY GAIN RELATION
Only a limited amount of diversity gain data exists for millimeter
wavelength earth-space propagation paths. These data, consisti.rg of
measurements performed by The Ohio State University and Bell Telephone
Laboratories, were collected and presented in an earlier publication [1].
The OSU data were obtained using the ATS-5 15.3 GHz downlink for-
attenuation measurements; and the BTL data were generated from 16 Gllz
radiometric temperature measurements along a nominal ATS-5 propagation
path. In both cases the ground term'nals were separated along a baseline
oriented in approximately the NW-SF direction; the nominal look angles
were 220° azimuth and 35° elevation. Even though these data were collected
in different locations, the OSU data in Ohio and the BTL data in New Mersey,
and over different time periods, the resultinq diversity gain data %-)rre
remarkably consistent.
Diversity gain is defined here as the difference between the path
attenuations associated with the single termina l
 an,' diversity modes of
operation for a given percentage time. Thus, 0 versity gain, G, is a
function cF the single terminal fade depth, A, as well as the terminal
separation distance, D.
These data were used to generate an empirical relationship for
diversity gain as a function of both separation distance and single
terminal fade depth. first, it was recognized that the diversity gain
data, Fiq. 1, behavL, as
(1) G = all_e'bD)
for each value of single terminal fade depth. Consequently, a minimum
RMS error fit was performed for each fade depth; this procedure yielded
a family of coefficients, a and b, which de pended only upon the fade
depth. These coefficients, Figs. ? and 3, were also fit to closz-d
form analytic expression:
(2) a = A - 3.6 (1-e-0.24A)
(3) b = 0.46 (1-e-0.26A)
where G and A are expressed in dB and D is expressed in kilometers. Now,
using Eqs. (1), (2), and (3), diversity gain was calculated as a function
of terminal separation distance and single terminal fade depth. The
results of these caiculat.ons are shown in Fig. 1; it may be seen that
the agreement between the empirical calculation and the data points is at
r-qT
- I
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2	 4	 6	 8	 10	 12	 14
A , SINGLE SITE ATTENUATi( V (dB)
12
10--
8
a
6
4
I 2
0
0
Fig. 2. :.oefficient a versus single
site attenuation, A.
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worst approximately 0.75 dB. This agreement is well within the experimental
accuracy of the experiment and emphasizes the consistency of thesE
experimental data.
It is of interest to note that the linear portion of the curve
relating the coefficient a to the single terminal fade depth intercepts
the ordinate at about -3.6 dB. This coefficient may be interpreted as
'	 the difference between the diversity gain reached for large separation
'	 distances and the ideal diversity gain. Therefore, this result indicates
that the diversity gain approaches a level approximately 3.6 dB below the
ideal diversity gain as the terminal separation distance becomes large.
This behavior is in accord with the concept of optimum diversity gain
presented earlier [1].
It is also of interest to
value: of approximately 0.4 for
be interpreted as the decay ra
terminal separation distance.
formance is largely determined
the order of 2.5 km.
note that the coefficient b approaches a
large fade depths. This coefficient may
Le for diversity gain as a function of
Thus, one may conclude that diversity per-
by storm cell cores having diameters on
Finally, the empirically calculated diversity gain is presented as
a function of single terminal fade depth in Fig. 4. These curves show
that the diversity gain has app.,oached its optimum value, i.e., that
value associated with an infinitely large separation distance, within
1 dB for terminal separation distances over 8 km.
II. PRELIMINARY ATS-6 30 GHz DIVERSITY DATA
The OSU participation in the ATS-6 Millimeter Wavelength Propagation
has been described in an earlier •eport [2] and will only be summarized
here. The primary objective of this experiment consists of 20 and 30 GHz
downlink attenuation and radiometric temperature measurements at two
spatially separated ground terminals. These terminals, the OSU Fixed and
Transportable Terminals, were described in detail in earlier reports [3,4].
20 GHz radiometric temperature measurements were also made at a third
spatially separated ground terminal, the OSU unmanned Terminal. In
addition, a Comsat 12/16 GHz uplink terminal was colocated at the OSU
Fixed Terminal along with three remote 18 GHz uplink Comsat terminals.
The relative locations of these ground terminals are shown in Fig. 5.
The nominal look angles to the ATS-6 synchronous satellite were 40° ele-
vation and 200° azimuth.
Although a considerable amount of data has been collected at the
present time, only initial results for 30 GHz diversity behavior have
been analyzed to date. Hence, the following discussion covers only
30 Gliz downlink attenuation data from the Fixed and Transportable
Terminals.
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A, SINGLE SITE FADE DEPTH (dB)
Fig. 4.	 Diversity gain, G, versus single
site fade depth, A.
25	 30
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ASamples of the raw data frali these terminals are presented in Fig.
6. These curves represent the sampled outputs of the 30 GHz receivers
e
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(MIN)
Fig. 6. 30 GHz raw receiver data (28 April 1975).
before processing. The receiver outputs were sampled at a rate of 10 Hz
although the plots were generated using 10 sample, i.e., 1 sec., average's.
It should be noted that at approximately 22 minutes into this data period
a 10 dB pad was switched out of the receiver input at the Transportable
Terminal, The received signal at that terminal subsequently dropped
below threshold for approximately 1 minute, and the 10 dB pad was
reinserted at about 32 minutes into the data period. This same segment
of data is shown in Fig. 7 after conversion to a decibel scale and
compensation for the pad changes. Finally, fade dist; • ibutions were
generated for this same data segment; these curves are shown in Fig. 8.
A set of cumulative tade distribution for seven fade events which
occurred during early Spring, 1975, are presented in Fig. 9.
	
It is
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Fig. 7. ereprocessed 30 GHz receiver data (28 April 1975).
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0	 5	 10	 15	 20	 25	 30
ATTENUATION (dB)
Fig. 8. 30 GHz fade distribution (28 April 1975).
10
TRANS
ED
5	 10	 15	 20	 25	 30
ATTENUATION (dB)
100
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Fig. 9. Cumulative 30 GHz fade distributions (7 events).
11
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interesting to note that the character of the diversity fade distri-
bution has changed little from that shown i ,, Fiq. 8 even though six
additional fade events are included. Bot k, terminals expe-ienced fades
to depths of 30 dB or more during one or more of these events.
Diversity gain data were extracted from the curves shown in Fig. 9;
I	 these 30 G11z diversity gain data points arc shown in Fig. 1 along with
i
	
	
+hP PmDi r ?rally derived diversity gain curves. The agreement is excep-
tional; in fact, although not shown in this figure, the 30 GHz data
points and the 15 GHz empirical results egree within 0.2 1) dB for all fade
depths up to 30 dB. The calculations were not carried beyond this fade
depth due to lack of data.
This preliminary result indicates that diversity gain is not a
sensitive function of frequency. Alternatively, this result. indicates
that terminal separation distances of 8-10 km, which provide nearly
optimum diversity gain at 15 GHz, will provide the same diversity improve-
ment at 30 GHz. Clearly, thi s, preliminary conclusion rests on a limited
data base at the present time; nevertheless, the close a-3reement with
earlier results tends to strengthen the credibility of th 4 s conclusion.
III. SUMMARY OF OPERATIONS
All three OSU ground terminals remain operational. The total
operating times as of 15 May 1975 were
Transportable 20 GHz 5,087 min.
30 GHz 7,078
Fixed 20 GHz 3,957
30 GHz 5,387
Unmanned 2,272
total	 time 23,781	 min.
Margin measurements were perfo rnied on 6 June 1975 with the satellite
antennas directed toward VPI. The margins were
	
20 GHz	 30 GHz
Transportable	 46 dB	 34 dB
Fixed	 47 dB	 37 dB
for the 20 GHz cw/Dish and 30 GHz cw/Dorn modes.
12
r
IV. CURRENT STATUS
Data collection is continuing at all terminals; it is anticipated
that data collection will cease on about 13 June 1975 as the satellite
moves out of view of the OSU terminals. Data processing is underway and
will continue.
V. REFERENCES
1. D. Q. Hodge, "Path Diversity for Reception of Satellite Signals,"
Journal de Recherches Atmospheriques, V. 8, p. 443, June, 1974.
2. D, Q. Hodge, "ATS-F Millimeter Wavelength Propagation Experiment,"
Report 3863-1, July 1974, The Ohio State University ElectroScience
Laboratory, Department of Electrical Engineering; prepared under
Contract NAS5-21983 for National Aeronautics and Space Administration
(NASA Goddard).
3. D. B. Hodge and R. C. Taylor, "ATS-6 Millimeter Wavelength
Propagation Experiment," Report 3863-2, September 1974, The Ohio
State University ElectroScience Laboratory, Department of Electrical
Engineering; prepared under Contrac t_ 14AS5-21983 for National
Aeronautics and Space Administration (NASA Goddard).
4. D. Q. Hodge and R. C. Taylor, "ATS-6 Millimeter Wavelength Propa-
gation Experiment," Report 3863-3, March 1975, The Ohio State
University ElectroScience Laboratory, Department of Electrical
Engineering; prepared under Contract NAS5-21983 for National
Aeronautics and Space Administration (NASA Goddard).
M
13
VI. PUBLICATION SUMMARY
This summary includes all reports, oral presentations, and publi-
cations generated under NASA Contract No. NAS5-21983.
' 1. 3863-1, July 1974
2. 3863-2, September 1974
i
3. 3863-3, March 1975
4. 3863-4, April 1975
5. "An f_mpirical Relationship for Path Diversity Gain,"
0. B. Hodge, submitted to the IEEE Transactions on
Antennas and Propagation for publication.
6. "Initial Results of OSU 20 and 30 GHz ATS-6 Propagation
Measurements," D. B. Hodge and D. M. Theobold, presented at
USNC/URSI Meeting, Urbana, Illinois, 3-5 June 1975.
I
14
I,


ATS-6 millimeter wavelength propagation experiment

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