Performance Prediction of Future V-band

Earth-space Link in the Tropics

1A.F. Ismail

#,

1N.W. Md Saad,

1K. Badron,

2W. Hashim and

1K. Abdullah

1Dept. of ECE, Faculty of Engineering, International Islamic University Malaysia, Kuala Lumpur, Malaysia.

2MIMOS Berhad, Technology Park Malaysia, Kuala Lumpur, Malaysia.

af_ismail@iium.edu.my, 0816280@live.iium.edu.my, khairayu@iium.edu.my, wahidah.hasim@mimos.my and

khaizuran@iium.edu.my

Abstract—Higher capacity systems demand for increased of

bandwidths. Higher bandwidth can be achieved by means of

increasing the frequency, and hence greater the capacity of a

channel to carry information. The Ka-band satellite rollouts in

the tropics are still growing. However, the higher frequencies

such as V-band do present a more substantial potential for

increased system capacity and are now starting to draw

attention. Although the bandwidths are theoretically higher at V-

band links, there are many aspects that are harder to achieve

than of those of at lower frequencies. V-band frequencies

certainly have higher RF losses, higher atmospheric propagation

losses and certainly much higher losses due to precipitation.

While the required V-band technological advancements are being

pursued, it is would be in the interest of the satellite designers

and engineers alike to evaluate the viability of such links

especially in the tropics where heavy rains are copious

Keywords—rain attenuation; V-band; tropical region;

impairment

I. INTRODUCTION

A quarter century ago, the operating frequencies of most

available satellites in the tropics were C-band or S-band.

During those days, Ku-band and Ka-band satellite links were

initially confined mainly to temperate regions [1]. Recently

however, there has been significant proliferation of bandwidth-

intensive High Definition Television (HDTV) broadcasting

worldwide including the tropical regions. What lies just beyond

the horizon is the next generation HDTV, a more bandwidth

hungry service; the Ultra High Definition Television

(UHDTV). The 8K UHDTV will at least have 16 times the

number of pixels of the existing 1080p HDTV. In the future,

new satellites in the tropical and equatorial regions will also

have no alternative but to operate at higher than Ku-band

frequencies due to spectrum limitations. Contrary to popular

belief that the future in TV broadcasting will be Internet

Protocol Television (IPTV), one must admit that bandwidth of

fibre optic networks is not unlimited or infinity. Hence, super

high frequency satellite broadcasts might be a more workable

option. The fibre network that have been used for decades to

transmit large volumes of traffic across the country will one

day come to a halt when the number of its users reached

maximum [2].

Performance predictions are an essential step in the design

of all new satellite links. Performance is usually defined as the

expected quality of the channel for a very high percentage of

time (at least a month and usually a year). For satellite

systems, it is usually that level achieved in what is called “clear

sky”. It is very critical to be able to predict accurately the likely

impairment to be encountered on a given link in order to plan

the services economically. The predicted value of signal loss

and fading are used to determine the design parameters [3].

Examples of design parameter are the power requirements of

the equipment, the antenna characteristics and the service range

or the hop length. These design parameters can be determined

and from them the performance of a service is specified for a

particular percentage of the time. The performance can be

specified for example, at availability of 99% of time at a given

receiving location or at a specified percentage of locations

within a reception area. Availability is the ratio typically

associated with the percentage of the total time a service is

capable of being used, or is available to be used during a given

interval to the length of the interval.

Fig. 1. Basic segment of a satellite broadcast link

In satellite communication terms, the link availability is

usually expressed as a percentage of a year when the link will

perform as per the required Bit Error Rate (BER). As an

example, 99% availability for a year, states that the link will be

available for 867.24 hours and unavailable for 87.6 hours

(8760 – 87.6 hours / 8760 hours x 100). Equally important,

other attribution such as the level of interfering signals

exceeded for some small percentage of the time, for instance at

0.1%, also need to be predicted, again at the reception point or

1st IEEE International Symposium on Telecommunication Technologies

978-1-4673-4786-0/12/$31.00 ©2012 IEEE 187

area of concern. Predictions are employed in order to know

whether a satisfactory service will be provided at the required

reception point or area and also for planning to avoid mutual

interference with other systems sharing the same frequency

band.

II. PERFORMANCE PREDICTION

Radiowave propagation plays a very significant part in

the design and eventually dictates performance of space

communication systems. The IEEE defines V-band as between

40 to 75 GHz, but for communications satellites this frequently

means transmit (down-link) signals in the range of 40-46 GHz

and receive (up-link) signals in the range of 48-56 GHz. The

challenge in operating at such high frequencies for

communication purposes is that there exist stronger

electromagnetic interaction between the radio signals and

atmospheric hydrometeors [4]. These instances will without

doubt distort the performance of such high frequency satellite

communication systems. Several procedures have been

proposed for predicting rain induced attenuation statistics.

Among currently available prediction methods are the models

recommended by the radiocommunications sector of the

International Telecommunication Union (ITU-R) [5], the

Dissanayake, Allnutt and Haidara (DAH) rain induced

attenuation model [6], the Crane-Global model [7] and the

Crane-Two Component model [8].

Fig. 2. World climate map [9]

In this paper, performance prediction of a future V-band

Earth-space link for Malaysia, operating in tropical climate

environment was produced using the latest ITU-R model in

force, published in October 2009. This is the most up-to-date

published ITU-R method to predict attenuation due to

precipitation along a slant propagation path, identified as

Recommendation ITU-R P.618-10 - ‘Propagation Data and

Prediction Methods Required for the Design of Earth-Space

Telecommunication Systems’. The procedure currently

adopted in ITU-R prediction model is based on the estimation

of the attenuation exceeded at 0.01% of the time A0.01, which

is derived from the rainfall rate exceeded at the same time

exceedance percentage, R0.01. From a theoretical point of view,

the concept of equiprobable analysis is not consistent with

meteorological information and not entirely satisfying.

Nonetheless, the accuracy obtained in previous cases when

using the prediction method is somewhat consistent with the

quality and variability of available rain intensity data [10].

For a given value of rainfall rate at 0.01 time exceedance

percentage R0.01, the specific attenuation R is calculated. When

multiplied with the effective path length LE, the corresponding

attenuation value at 0.01% time exceedance A0.01 is produced.

The schematic presentation of an Earth-space path outlining the

parameters to be included into the attenuation prediction

procedures is portrayed in Fig. 3.

Fig. 3. Schematic presentation. A: frozen precipitation, B: rain height, C:

liquid precipitation, D: Earth-space path, LG: horizontal projection, LS: slant-

path length, hr: rain height, hs: station height, : elevation angle [2]

The set expression for the estimation of A0.01 is based on

two assumptions. With reference to the above figure, the first

assumption is that the spatial structure of rain can be modelled

by equivalent rain cell; with a rectangular cross-section of

equivalent length LG and effective height hR-hS in the plane of

the path. The subsequent assumption is that the equivalent rain

cell can assume any position with respect to the path with

equal probability.

III. PREDICTION OF PROPAGATION

A variety of propagation parameters needed in planning

Earth-space systems operating in either the Earth-to-space or

space-to-Earth direction, have to be predicted reliably. For a

likely future satellite-Earth link to be operating in Johor

Bahru, Malaysia, the estimations of its performance were

calculated methodically through the following procedures.

TABLE I. EARTH STATION AND SATELLITE INFORMATION

Possible Earth station Potential Satellite Location

longitude (degree),

les : 103.38 E

longitude (degree),

lst : 91.5 E

latitude (degree),

: 1.33 N

frequency (GHz),

f : 38

station height above mean sea level of the (km),

hs : 0.018

polarisation: vertical

188

The below transcript involves and includes adaptations of

the ITU-R P.618-10 for the sake of readability and clarity. In

the latest version of ITU-R prediction procedure, the vertical

structure of rain is taken into account by the use of an

effective rain height hR, derived from experimental data, in the

expression of LS. For vertical paths, the effective path length

coincides with the effective rain height, which at any latitude

may differ from the 00

C isotherm height hFR, as specified in

ITU-R Recommendation, P.839-3 - ‘Rain Height Model for

Prediction Methods’ [11]. Varying techniques have been

proposed by researchers in order to include the vertical

structure of rain into account. Some of techniques can be

considered as an extension of those previously developed for

terrestrial paths [12]. Whereas others proposed rain height

derivation based on extensive studies on the rain structure

itself [13].Malaysian investigators did carry out elementary

studies at various local locations using the TRRM and

meteorology radars in the hope to uncover the actual effective

rain height. [14, 15]. The rainfall rates R0.01 at time

exceedance of 0.01% from the new climatic zone map of ITU-

R Recommendation P.837-6 [16] that equals to 100 mm hr-1

was used in calculating predicted attenuation values.

1) Calculation of the elevation angle , for the earth-space

link:

)cos()(cos1

45.0)cos()cos(tan

2

1

esst

esst

ll

ll (1)

2) Calculation of the polarisation angle :

tan

sintan 1 esst ll

(2)

3) The effective rain height, hR, for the latitude of the

station was determined according to ITU-R

recommendation:

kmhhR 36.00 (3)

The ITU-R Recommendation P.839-3 states that h0 for

Malaysia equals to 4.5 km

4) For 5 computation of the slant-path length Ls,

below the rain height is as follows:

(4)

5) Calculation of the horizontal projection, LG of the

slant-path length from:

(5)

6) Determination of the k and values using the

frequency-dependent coefficients, kH, kV, H, and V from

Table 1 of the ITU-R P.838-3.

Based on assumption of spherical drops, values of k and

have been calculated at various frequencies between 1 and

1000 GHz for several drop temperatures and drop size

distributions. The calculations were computed by assuming

oblate spheroidal drops, aligned with a vertical symmetry axis

and with dimensions related to equal volume spherical drops.

Values of k and coefficients based on the Laws and Parson’s

rain dropsize distribution and a drop temperature of 200 C have

also been calculated and included in Table 1 of

Recommendation ITU-R P.838-3[17]. The table also includes

values for horizontal and vertical polarisation of k and at

various frequencies.

Values of k and at frequencies other than those in the

table can be estimated by interpolation using logarithmic scale

for frequency f, a logarithmic scale for k, and a linear scale for

. For linear and circular polarisation, and for all path

geometries, the k and coefficients for the specific

attenuation equation can be calculated from using the

following equations:

(6)

(7)

where is the path elevation angle and is the

polarisation tilt angle relative to the horizontal as in (2) ( =

45 for circular polarisation).

7) The specific attenuation, R, using the frequency-

dependent coefficients calculated above and the rainfall rate,

R0.01 was obtained by using (1).

Researchers [18] have reported that the relationship

between specific attenuation ‘A’ or ‘R’ and rainfall rate R can

be approximated by using the power-law.

)( 01.0RkR (8)

8) Calculation of the horizontal reduction factor, r0.01, for

0.01% of the time:

(9)

9) Calculation of the vertical adjustment factor, v0.01, for

0.01% of the time:

sin

)( SRs

hhL

cosSG LL

2/2coscos)( 2 VHVH kkkkk

kkkkk VVHHVVHH 2/2coscos)( 2

GRG L

f

Lr

2–01.0

e–138.0–78.01

1

189

01.0

1– –tan

rL

hh

G

sR (10)

Since the > , therefore the reduced length LR was

determined according to;

(11)

In the case of Malaysia, its < 36, hence

= 36 – | | (12)

(13)

10) Calculation of the effective path length is:

01.0vLL RE (14)

11) The predicted attenuation exceeded for 0.01% of an

average year is then calculated using:

(15)

where the effective path length LE is the product of slant

path length, horizontal path reduction factor r0.01 and vertical

path reduction factor v0.01. The empirical expression of (15) is

then used for scaling the other time percentage, in order to

provide a complete prediction of rain induced attenuation

distribution.

12) The estimated attenuation at other time percentages

of an average year, in the range from 0.001% up to 1%, is

deduced from value in step 11 above; in keeping with the

following conditions:

For p < 1% and | | < 36 and 25:

)36(005.0 (16)

and the predicted attenuation is:

(17)

Table II lists the parameters put together in accordance to

the ITU-R’s recommendations.

TABLE II. CALCULATED PARAMETERS USING ITU-R

RECOMMENDATIONS

Parameters Values

R0.01 (mm hr-1): ITU-R P.837-6 100

() 75.92

() 83.57

hR (km): ITU-R P.839-3 4.86

LS (km) 4.99

LG (km) 1.21

kH : ITU-R P.838-3 0.4001

KV : ITU-R P.838-3 0.3844

αH : ITU-R P.838-3 0.8816

αV : ITU-R P.838-3 0.8552

0.868

K 0.3919

R (dB/km) 21.34

r0.01 (mm hr-1) 0.77

() 79.07

() 34.67

v0.01 (mm hr-1) 1.3782

LR (km) 5.30

A0.01 (dB) 113.15

0.17335

IV. RESULTS AND OBSERVATIONS

In designing communications links, cumulative

distributions may be the most effective presentation format for

the long-term data. For instance, link availability or

exceedance at a point can be determined from its annual

cumulative distribution. Thus, appropriate rain induced

attenuation margins can be incorporated into the system in the

attempt to achieved the desired link performance.

Fig. 4. Plot of ITU-R predicted performance statistics

cos

01.0rLL G

R

45.0–e–131sin1

1

2

)1/(θ–

01.0

f

L RR

ER LA 01.0

)θsin)–1(–)(ln045.0–)(ln033.0655.0(–

01.001.0

01.0

pAp

p

pAA

190

TABLE III. SELECTED TIME PERCENTAGES AND PREDICTED VALUES

Time exceedance (%) ITU-R 618-6

Predicted Attenuation (dB)

1.000 14.10

0.300 41.52

0.100 67.42

0.010 113.15

0.001 128.81

Table III lists selected predicted attenuation values for the

likely future V-band satellite-Earth link in Malaysia. Initial

results of possible rain induce-attenuation impairment to be

experienced by a V-band link at Johor Bahru were generated.

The findings suggested that due to the severity of the rain

induced attenuation that will be encountered, commercial V-

band satellite operation in Malaysia and others in tropical

region may not be simply feasible to operate at 99.7%

availability (equivalent to 0.3% time exceedance) to abide the

broadcasting standard. Non realistic margin (by today’s

technological advancement) of somewhat above 41 dB has to

be incorporated into the wireless system to cope with rain

fading in such severe climate.

If V-band satellite communications is to be actually

realized, current [19] and impending researches should be

immediately focused on integrated solutions in the satellite’s

design i.e. increased transmission power level, larger reflector,

reconfigurable antennas, radiating antenna technologies, etc.

RF engineers can partake in the effort by exploring the use of

one or more countermeasure techniques to alleviate the effect

of rain induced attenuation.

V. CONCLUSION

It is not to be expected that spectrum congestion at Ku-

band will happen in the near future. The use of Ku-band

frequency band will be generalised for the next few years,

with an anticipated evolution towards Ka-band and eventually

the V-band for high data rate multimedia applications. The

main constraint will be the propagation impairment that is

expected to be quite severe in tropical climates, so standard

performances may be taxing to achieve in these regions.

Production of predicted impairment statistics as been

highlighted in this paper is therefore very important for the

future design and deployment of anticipated high frequencies

satellite systems in the tropics.

ACKNOWLEDGMENT

The authors acknowledge the Research Management

Centre of the International Islamic University Malaysia

(IIUM). The reported research findings are part of the

deliverables for the research funded under IIUM’s Endowment

Grant Type B.

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