Downlink signal evaluation of haps m 55 aircraft above malaysian skies

International Journal of Electronics and Communication Engineering & TechnologyAND
INTERNATIONAL JOURNAL OF ELECTRONICS (IJECET), ISSN
0976COMMUNICATION ENGINEERING &2,TECHNOLOGY (IJECET)
– 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue July-September (2012), © IAEME

ISSN 0976 – 6464(Print)
ISSN 0976 – 6472(Online)
Volume 3, Issue 2, July- September (2012), pp. 336-345
IJECET
© IAEME: www.iaeme.com/ijecet.html
Journal Impact Factor (2012): 3.5930 (Calculated by GISI) ©IAEME
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DOWNLINK SIGNAL EVALUATION OF HAPS M-55 AIRCRAFT
ABOVE MALAYSIAN SKIES

Wanis A Hasan and Ahmad N Abdulfattah
Communication Engineering Department, Higher and Intermediate Institute of
Comprehensive Professions, P.O. Box 0283-11, Bani Walid, +218, Libya, 0917329250,
algazalat@yahoo.com
Communication and Computer Engineering Department, CIHAN University, P.O. Box
0383-23, Erbil, Kurdistan Region, +964, Iraq, 07701606662,
msc.ahmedaldabbagh@gmail.com

ABSTRACT

HAPS is a promising technology, uses airborne ships for providing narrow and broadband
wireless communication and broadcasting services from the sky to users and end terminals on
the ground. It is considered as the most viable and cost-effective solution for communication
service providers by complementing their existing terrestrial and satellite network
investments, to allow their customers have more freedom and convenience to get connected
to different communication networks nationwide and worldwide. Malaysia has made
significant efforts in the research of HAPS M-55 aircraft deployment and applications in
cooperation with some international partners. In this paper, the downlink signal of HAPS M-
55 aircraft will be evaluated within two different reception scenarios in terms of rain
attenuation and signal multipath fading, while hovering above Malaysian skies. Racian
channel will be introduced as a multipath fading channel. All results will be obtained based
on theoretical assumptions and settings and by using the MATHLAB as a simulation tool.

336

International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 2, July-September (2012), © IAEME

KEYWORDS: HAPS M-55 aircraft, elevation angle, radio link budget calculation, rain
attenuation, signal multipath fading, Racian fading channel.

I. INTRODUCTION
The necessity of finding a reliable wireless communication infrastructure, which can ensure
high quality of service (QoS) and meet the customers’ communication needs in Malaysia, has
shifted the attention to search deeply in HAPS technology and applications [1],[2]. In 2007,
the mile stone was created when the federal government of Malaysia signed an agreement
with QucomHaps Co. of Ireland and the Russian owner and designer of M-55 GN
stratospheric aircraft. That agreement aims to fly the M-55 aircraft above the Malaysian skies
to provide a nationwide wireless access to a broadband connectivity at subscription rates
lower than anything commercially offered in the local competitive market [1], [2].

Fig.1. Several communication services provided by a HAPS M-55-based system

HAPS M-55 is a piloted aircraft manufactured and developed by the Geoscan International
Agency (GIA) projects [1]. It is designed to fly at the Stratosphere layer and lasts for about
five-hour-time interval for each flight. It hovers in a circular path at an altitude of nearly 21

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km high. It has a body weights approximately 24 tons and 37m wingspan long. It can
accommodate carriage of payloads of 2 tons and consumes power supply of 40kW. It is a
single-seated aircraft and can operate at day and night time, even in critical weather
conditions while taking off or landing statuses as stated in. A single M-55 aircraft can form
ground coverage of about 400 km radius. This coverage is equivalent to approximately 258
ground terrestrial base stations coverage. It is supposed that only five M-55 aircrafts will be
launched and flown concurrently to provide wireless broadband coverage for the entire
Malaysian territory [1],[2].

II.SCENARIOS AND ASSUMPTIONS

The downlink signal of HAPS M-55 aircraft (service signal) will be evaluated based on two
different reception scenarios in terms of rain attenuation and signal multipath fading. It is
assumed that the HAPS M-55 aircraft will be flown at an altitude of 21 km above Johor state,
which is a part of Malaysian territory. The elevation angle of downlink signal reception will
be a vital parameter in both scenarios.

Scenario I: two users (uA and uB) receive the downlink signals with 20o and 90o elevation
angles respectively. That is to evaluate the downlink signal level when one user is at the end
of coverage whereas the other is in the center. 20o was chosen as the lowest elevation angle,
at which the user is supposed to receive the downlink signal with the lowest quality. If the
lowest elevation angle is assumed, the larger the service coverage can be formed, but the rain
propagation path, however, becomes longer and larger fade margin may be needed [3]. Also
90o was also chosen as the highest elevation angle, at which the user centralizes directly
under the Sub-Platform Point (SPP), and can receive the downlink signal with better quality
[3]. Communication links of the downlink signals received by both users are considered Line-
of-Sight (LOS) paths. While travelling between the HAPS M-55 aircraft and the two users, it
is assumed that those signals will experience a rainfall event (rainy sky weather condition).

Just for a comparison purpose, they will be first evaluated under clear sky weather condition.
Settings of the two users were calculated and inserted in Table (1) as below:

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Table (1) Settings of the two users (uA & uB)
Elevation Altitude Distance Propagation Total Antenna Feeder
angle (m) to SPP path length signal gain Loss
(Degree) (km) (km) path No. (dBi) (dB)
uA 20` 25 57.70 61.39 1 28 0.7
uB 90 25 0 21 1 28 0.7

Fig.2. Two users receive HAPS M-55 downlink signal with 20o and 90o elevation angles

Operational parameters of HAPS M-55 aircraft were assumed for both downlink signals
while travelling under a clear sky condition and inserted in Table (2) as below:

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Table (2) Operational parameters of HAPS M-55 aircraft
Parameter Downlink

Elevation angle (degrees) 20 90
Altitude (Km) 21 21
Frequency (GHz) 28 28
Data Rate (Mbit/s) 2 2
Modulation Scheme QPSK QPSK
Output power (dBW) -12.1 -13.2
Feeder loss (dB) 0.7 0.7
Gain (dBi) 26.6 18.3
EIRP (dBW) 13.8 4.4
Propagation path length (Km) 61.93 21
Free space loss (dB) 157.1 147.7
Atmospheric gas loss (dB) 0.4 0.4
Rain attenuation (dB) 0 0

In order to evaluate the downlink signal under a rainy sky condition, data of rainfall rate of
Johor was collected and used to predict the overall rain attenuation based on [4], [5], [6] as
shown in Table (3) below:

Table (3) Rain attenuation predicted in Johor State
Elevation angle Service reliability Rain rate Rain attenuation predicted
(degree) (%) (mm/h) (dB)
20 103.6
99 120.35
90 13

The equation, which is used in the calculations, is the basic simplified received signal power
equation as shown below [4]:

P୰ = P୲ − L୤ୣୣୢୣ୰ + G୲ − L୤ୱ୪ − L୥ୟୱ − L୰ୟ୧୬ + G୰ − L୤ୣୣୢୣ୰ (1)

Where:

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P୰ : Downlink received signal power (dBW)
P୲ : Transmitted signal power (dBW)
L୤ୣୣୢୣ୰ : Transmitted signal power loss because of feeder inefficiency (dB).

G୲ : Transmitting antenna gain (dBi)
L୤ୱ୪ : Free space loss (dB)
L୥ୟୱ : Power loss because of Atmospheric gas (dB).
L୰ୟ୧୬ : Rain attenuation loss (dB)
G୰ : Receiving antenna gain (dBi)
L୤ୣୣୢୣ୰ : Received power loss because of feeder inefficiency (dB).

Scenario II: only one user, uA, receives the downlink signal through direct and diffuse
propagation paths due to the nature of vicinity. It is assumed that one Line-of-Sight path
(LOS) and five delayed paths (NLOS) will be absorbed by the uA’s antenna. In this scenario,
the downlink signal which is received by the uB will be ignored, because it is supposed to
have only one Line-of-Sight path (direct path) [3], [7]. The vicinity of the user, uA, includes
many clutters and obstructions whose locations relative to the user uA will determine the time
delay length the diffuse downlink signal may experience [7], [8], [9]. It is known that the
most delayed path will travel the longest distance from the HAPS M-55 aircraft to the uA and
the vise-versa. For this purpose, the time delay of the five paths will be set based on into two
assumptions; assuMax specifies the maximum time delay of the last diffuse path (the fifth
delayed path) does not exceed the time duration of the transmitted symbol, and the maximum
range of the surrounding clutter is less than 300 m. Also assuMin specifies that the minimum
time delay of the first diffuse path (the first delayed path) is longer than the time duration of
the transmitted symbol, and the minimum range of surrounding clutter is more than 300 m.
This scenario will focus on the multipath effects on the downlink signal based on this
manner, and by using the Racian multipath fading channel [2], [8], [10], [11], [12]. Settings
used for the user, uA, in this scenario are shown in Table (4) as below:

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Table (4) Settings of the user, uA
Coverage area Propagation Total signal path User speed Max Doppler shift K-Factor
environment No. (m/s) (Hz)
Suburban Outdoor 6 1.3 121.3 4

III. RESULTS AND DISCUSSION
• Downlink signal level
The downlink signal was simulated under two different weather conditions (clear & rainy)
and plotted in Fig.3. as shown below:

Fig.3. Downlink signal versus elevation angle of reception

It is observed that the downlink signal level varies as a function of the elevation angle of
reception and the weather condition. In other words, its level drops while a rainfall event is
taking place, especially when the elevation angle of reception decreases. uA will only enjoy
the same downlink signal level as the uB does when the sky is clear, but will not do during
the rainfall events; regardless their downlink signals experience the same rainfall rate.

• Downlink signal experience
The downlink signal was simulated based on the assuMax multipath assumption and plotted
in Fig.4. as shown below:

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Fig.4. Magnitude of downlink signal versus time delay and frequency

It is noticed that the downlink signal received by the user, uA experiences a frequency-flat
fading, caused due to the time dispersion phenomena. The scattering and reflection of the
downlink signal on the surfaces and edges of the clutters, which are located at not farther than
300 m from the user, uA, produced several replicas of the downlink signal. Those replicas
were delayed and received at irresolvable time points within the time duration of the direct
received symbol. It seen that the five delayed components combine and get clustered at
approximately the time zero second as shown in Fig.4.

Also the downlink signal was simulated based on the assuMin multipath assumption and
plotted in Fig.5. as shown below:

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Fig.5. Magnitude of downlink signal vs. time delay and frequency

It is seen in this time that the downlink signal received by the user, uA experiences a
frequency-selective fading, resulted from the delayed signals which were received randomly
at different time points higher than time duration of the direct received symbol. It is clear that
the five delayed components are aligned to the time line relative to their locations (at
distances farther than 300 m) to the user, uA as shown in Fig.5.

IV. CONCLUSION
It can be concluded that the downlink signal of the HAPS M-55 aircraft (service signal) may
be affected by several propagation impairments such as the rain attenuation, especially in
Malaysia, where the rainfall events are dominant weather conditions along the year. Also the
signal multipath fading is a matter of importance that can affect the downlink signal level
either with flat or selective fading unless proper fade mitigation techniques (FMTs) are
applied.

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V. REFERENCES
1. GEOSCAN (UK) Plc., et al. (2004), “project profile”, Moscow, Russia
2. Alejandro .A.Z., et. al. (2008), “High-Altitude Platforms for Wireless Communications”,
1st ed, John Wiley & Sons Ltd, Chichester, UK,
3. International Telecommunication Union (2002), “Technical and operational characteristics
for the fixed service using high altitude platform stations in the bands 27.5-28.35 GHz and
31-31.3 GHz,” Rec. ITU-R F.1569, Geneva, Switzerland
4. Wanis .A.H. (2010), “Evaluation of potential interference and rain effects on 21.4-22 GHz
downlink broadcasting satellite signal in Malaysia,” Johor, Malaysia
5. Cheblil .J (1997) “Rain rate and rain attenuation distribution for Microwave study in
Malaysia,” Johor, Malaysia
6. International Telecommunication Union (2007), “Propagation Data and Prediction
Methods Required for the Design of Earth-Space Telecommunications Systems,” Rec. ITU-R
P.618-9, Geneva, Switzerland
7. José .L. C., et. al. “Channel Modeling and Simulation in HAPS Systems,” Catalonia, Spain
8. Fabio .D., et. al. (2002), “Small-Scale Fading for High-Altitude Platform (HAP)
Propagation Channels,” IEEE Journal on Selected Areas in Communications, vol. 20, No. 3,
April 2002
9. International Telecommunication Union (2012), “Propagation data required for the design
of Earth-space aeronautical mobile telecommunication systems,” Geneva, Switzerland
10. Vogel, W. J. and J. Goldhirsh (1995), “Multipath Fading at L-Band for Low Elevation
Angle, Land Mobile Satellite Scenarios,” IEEE Journal on Selected Areas in
Communications, Vol. 13, No. 2, February 1995
11. International Telecommunication Union (2001), “Propagation data required for the design
of Earth-space land mobile telecommunication systems,” ITU-R P.682-3, Geneva,
Switzerland
12. Fernando U-V. and Delgado-P, “Performance simulation in high altitude platforms
(HAPS) communications systems,” Catalonia, Spain

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Downlink signal evaluation of haps m 55 aircraft above malaysian skies

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