Pronounced fading occurring in the line of sight radio links at frequencies below 10 GHz can be traced to the effects of multipath propagation. Modulation disturbances depend on travel time differences between the direct wave and the wave which is reflected at atmospheric layers. A method described for the determination of the time delay is based on an indirect approach which utilizes the difference in fading at various frequencies. The method was employed in measurements involving a distance of 181 km. The results obtained in the measurement are discussed

Gilroi, H. G.

English

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NASA TECHMCAL *MDRANDUM	 NASA TM-75378
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DETMUNATION OF THE TIME DELAY IN THE CASE OF
J	 u 1-TWO-PATH PROPAGATION ON THE BASIS OF ME 	 r.	 c Co
ATTENTUATION CHARACTERISTICS FOR TWO AWACENT 	 y
FREQUENCIES N
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H. G. Gilroi	 c^
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Translation of	 Bestimmung der Laufzeitdifferenz bei w x z N
Zweiwegausbreitung aus dem Daempfungsverlauf' fuer
y
w
benachbarte Frequenzen," Kleinheubacher Berichte, Vol. -.4w c
19, 1976 , pp. 261 - 265 x `i H u .6
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NATIONAL AERONAUTICS AND SPACE ADMINIS'IIiATION
WASHINGTON, D. C. 	 JANUARY 1979
STANDARD TITLE PAGE
1.	 Report No.
.. NA;,A TM- 75378
I. Government Accession No. 1.	 Recipient's Coteleg No.
Tltl	 n	 1H1
1TEF
S.	 Report Date
l I
	 O^ OF THE TIME MAY IN THE CAM OF .January 1979
TWO - PATH PROPAGATION ON THE BASIS OF THF t.	 Porlerming Otg.ni.ation Cade
ATTENTUATION CIIARACTEh.L- STICS FOR TWO
1.	 Performing Organisation Report No.7.	 Auther(.)
H. G. Gilroi 10,	 work unit Me.
11.	 Contract or Grant No.9 .	P.,lo,m ng O , gon uet,on Nome end Add,...
------- 13,	 Type of Report and Period CovoreA
Translation 
12.	 Sponsoring Ay•ncy Now	 end Addr•es
National Aeronautics and Space Adtainistration
Washington, D. C.	 20546 14•	 Sponsoring Agenc y Code 
IS.	 Supplomentery Notes
Translation of "Bestimmung der Laufzeitdifferenz bei
Zweiwegausbreitung P-is dem Daempfunrsverlauf fuer
benachbarte Frequenzen," Kleinhe-,Abacher Berichte,
Vol.	 19, 1976, pp. 261 - 265
,A
	
2 o 7-1)
16 	 Absr,ect
17.	 Key Wards (Selected by Author(s)) 11.	 Di.tribution Statement
Unclassified - Unlimited
19.	 Security Clesslf. (of this report)
Unclassified
20.	 Security Cl.ssif. (o) this page)
Unclassified
21• Ne. of Pages
9
22.
DETERMINATION OF THE TIME DELAY IN THE CASE OF
TWO-PATH PROPAGATION 0:4 THE BASIS OF THE
ATTENUATION CHARACTERISTICS FOR TWO ADJACEti"
FREQUENCIES
H. G. Gilroi*
ABSTRACT. Pronounced fading occurring; in
the line of si;-:,t radio links at frequencies
below 1010 GHz can be ;..aced to the effects of
multipath propagation. Modulation disturbances
depend on travel time differences between the
direct gave and the wave which is reflected at
at:.,osphe.^ J' c layers. n method described for the
deter-urination of the time delay is based on a;n,
indirect approach which utilizes the differ-
;	 once in fading at various frequencies. The
.:.echod was employed in nneasurements involving
a distance of 181 km. The results obtained
in tre measurement are discussed.
'	 :ult'_nath fading
Pronounced fading in lire of sight radio links is attributed
	 /?ol**'
in the case of frequencies below 10 G11z to multipath propagation.
Transmission factor and transrr,ission angle depend on the frequency
when the direct wave and the waves reflected on atmospheric layers
interfere. In the broad frequency bands of the multichannel radio
i
•
r_	
_.,
link, level fluctuations and in.termodulation noise occur in the
modulated signal. According to the two-path model, these modulation
disorders depend on the time delay T between direct and reflected
wave.
2	 ,othod for deter miriation of the time delay
The time delays here are ton short to be measured directly for
the available band width as the distance between a pulse and its
echo. Only indirect methods are applicable. In the following;
studies, the different fading for different frequencies is used.
For tae ratio a of the reception level U to its free space
value U.:	 ..
t;
a	
Uo	
(1)
we airs for the two-path propagation Lr1]:
e ?
	1- 2 R r-ob 
y 
d R2	 (2)
::ere, .i is the reflection factor: 	 /262
R s 'f
and p is the difference of phase between direct and reflected wave.M
he average of a2 is
	
a2 - t • R2	( 3 )
For the frequencies fl and f2 , the expressions al and a2 differ
1	 according to Equation (2) in Q by
	
A )D= 2w (f1 - f2 ) 11 	 (4)
The statistical relationship between a 2 and a2 is obtained
according to-Equation (2) and (3) from the autocorrelation fun,:tion:
2
-I co.
	 con (T.G y) C v
	
2	 (i)
^R cos G
.T
This gives the standardized autocorrelation function:
4, • cos A	 (b )
r om the recording  of the two quantities aia nd a2 (example in
Figure 1), the correlation coefficient r t is calculated from the
times with fading for time intervals t. Taking:
f'. U rt	 (7)
we obtain from (4) and (6):
arc co:. r.
_^ 	 Zit (f^ - f2,`	 (8)
an average time delay over the period t.
Other methods apply for the determination of the time delay
statistics of the base level fluctuations or the inter:ao:ulation
noise [2 - 91. As compared with these methods, the above-described
one has the advantage that the technical arrangements are very
si::ple. We do without the demodulator and other equipment causing
errors in the case of deep fading.
3. %:easurement layout
The measurements were carried out over the distance between
Hornisgrinde (Schwarzwald) and Feldberg (Taunus). The distance of
181 k.;, is far above the usual radio link distances. The radio beam
travels so high above the Rhine level (rig re 2) that time delays
up to 7 ns are possible with the geometrical layout.
#,•.AIA.P 6ft
4. Resu+ts
I
From the registrations of the
reception level for f l
 and f 2 from
:'arch to July 1975, a pair of values
.ras taken in times with fading per
::inuLe and the correlation coeffi-
ciant for time intervals of 1 hour
and 5 hours was calculated. From
these we obtained according to Equa-
tion (b) the time delays 
T 1 h
for I hour and i 5 for 5-hour inter-
val5 .
Fro:; Table 1 and 2, the ranges
may be seen contalnin6 the calcu-
lated values as well as the range of
f
^•i^1'^^ ;17 ;^^ ,.	 . ► t; X1,1
r	 o"	 r
WI
ti
Figure 1. Example of
registration
T:anslator'^i note.
The text in t:z° figure is
illegible.
-i\
i^^	 Iill)
s•
i
y	 v	 r	 a	 ac	 as	 as	 au	 oc^s
Figure 2. Ground section of the test radio
link distance. The carrier frequencies of
both radio link units were:
f2	 6315,35 r:-:z.
Translator's note. Text in the figure is
illegible.
reliability for 95p probability. In the ease of the averages fro:
spring to summer, a decrease in time delay is found.
4
'AMC	 • ^, .r
TABLE 1.	 TIME DELAY T l / nsh
No.	 or Mcasur4im,,nt Reliability :Maximum Reliability Average
evaluated results low- range value range
hours e6t, value
:larch tU	 ^ 0,E+2	 ^ (O, f.4-1,0;)	 ! 1,71 (^,^^ : ; 12)  t, ^ 0
April. ^ '0 0,51 (o.4.3-0,C:.; }:. 2(	 ,1 r,. J.3) 1,:2
May ?O O,EO (0,0-0,77) 1,`: (1,51-',y1) •`i
June 3U G,:7	 ( C. 26-0, 1,37	 I (i,r:_,e. .'O)
July 3,0	 i 0,42 (G.33-v,:o) 2.; a (1,3i-;,75)	 ; 1,:3
I
TABLE 2. TIME DELAY T5h/ns
Minimum	 Reliability	 Maximum	 Reliability	 Average
value
	 range	 value
	 range
:larch I.v7 (0,97 -
	
1,20) 104 (1,0; - 1,27)
April 1,07 (0,97 -
	
1,20) 1,12 (	 0,01	 -	 1,25) I	 '.C'9
::ay 0,76 (G,66 - 0,64) 1,24 (1.12
	
-	 1._.i) 1.03
June 0,79 (0,71 - 0,89) 1.05 (0,94 -	 1,1u) O,SO
July 0,73 (G,66 - 0,62) !	 1.75 E	 C1,59 -	 1,92) i	 1.C9
/?o'the histogram of Figure 3 shows the frequency distribution of
T  h for the total studied interval. In the 5-h,,ur sections, T1 h
fluctuates on the average by 0.3 ns. These fluctuations are also the
cause of the difference between the sum frequency curves for T1 h and
T5.. (Figure 4). The distributions deviate considerably from the
normal ones.
It is planned to compare the time delays determined according
to the method described here with the values obtained fro.,, pilot
level fluctuations and intel-modulation noise, to test how far t o
modulatlon disturbances In radio line: can be described by the two-
path propagation.
i• r 1 2 f Y it 11	 si w. i:. G S% Ta V Z.
P_
V1
t
"i
Figure 3. Frequency of T 	 Figure 4. Distribution of
in the total studied inter- T1 h and Tr	 yr
val	 Translator's note. Text in the
:figure is illegible.
References
1. Fehlhaber, H. Two-Path Propagation on Radio Fields with
Direct Sight and Free First Fresnel Zone. Techn. Ber. des
Forschungsinstitute der DBP Beim FTZ, A &+ 55 TBr 27, 1970.
2. Fehlhaber, L. Modulation Distortions in Fading in the Fre-
quency-Modulated ;Multichannel Radio Link. NTZ, Vol. 2e,
No. 2, 1973.
3. Fehlhaber, L. Fluctuations of the Base Band Levu in the
:,:-FD:: Radio Link on Radio Fields with Direct Sight as a
Result of Interference Fading. Techn. Ber. des Forshcungs-
instituts der DBP Beim FTZ, A 457 TBr 31, 1971.
4. Fehlhaber, H. The Probability Distribution of the rase Band
Level Fluctuations in the FM-FDM Radio Link with Twc-Path
Fading. Techn. Ber. des Forschungsinstituts der DBP beim
FTZ, A 455 TBr 29, 1973.
5. Fehlhaber,	 Intermodulation Noises In the FM-FDM Radio
Link, on Radio Fields with Direct Sight as a Result of inter-
]	 fererce Fading. Tech. Ber. des. Forschungsinstituts tier
-BP beam FTZ, A 455 TBr 29, 1971.
!	 6.	 Fehlhaber, L. The Probability Distribution of the Inter-
modulation Noise in the FM-FDM& Radio Link in Two-Path
Fading. Techn. Ber, des Forschungsinstituts der DBP beim
j	 FTZ, A 455, TBr 41, 1973.
1265
G
I7.	 Fetilhaber, L. Broad Band Propagation Measurements on a 138 km
Long Radio Field at 6 GHz. Teehn. Ber. des Forschun^;s-
instituts der DBP beim FTZ, A 455 TBr 40 0
 1973.
S.	 Fehlhaber, L. Transmission of Broad Frequency Bands through
the Troposphore on Sight Ranges. Kleinheubacherberichte,
Vol. 17, 1.974•
i	 9.	 uiloi, H. G. ;^easure.ment of Modulation Distortions lnducea
by Propagation on Broad Band Radio Line Distances.
Kleirheubacaer Be:ichte, Vol. 18, 1975.
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Determination of the time delay in the case of two-path propagation on the basis of the attenuation characteristics for two adjacent frequencies

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