HIGH ALTITUDE PLATFORMS: SERVICES AND OPPORTUNITIES Lenin ...repositorio.educacionsuperior.gob.ec/bitstream/28000/2481/1/T-SENESCYT-01331.pdf · HIGH ALTITUDE PLATFORMS: SERVICES

1 INTRODUCTION

HIGH ALTITUDE PLATFORMS: SERVICES AND

OPPORTUNITIES

Lenin Jara Olmedo

September 2010

MSc in Communication Engineering Project Report

2 INTRODUCTION

ABSTRACT

This Report describes the fundamentals of High Altitudes Platforms (HAPs) and produces

a comprehensive review of the platform, payload, standards, communication channel and

link budget principles related to this technology. The concept and trends of HAPs are

analyzed to produce basic assumptions about the platform. From this starting point, a basic

design of a WiMAX system to provide internet service is developed. The possible

performance of the system is obtained to discuss the benefits and limitation of the

technology.

3 INTRODUCTION

ACKNOWLEDGEMENTS

I just want to say thanks,

To Tim Tozer, more than an academic supervisor.

To John Dawson, a high level reader.

To John Thornton, short but enjoyable supervision.

To Dave Pearce, “How to write a report”.

To Sofia, my wife, peace in hard times.

4 INTRODUCTION

GLOSSARY

ACTD HAA Advanced Concept Technology Demonstration High-Altitude Airship

ADSL Asymmetric Digital Subscriber Line

ARQ Automatic Repeat Request

BER Bit Error Rate

BS Base Station

CAGR Compound Annual Growth Rate

CAPANINA Communications from Aerial Platform Networks delivering

CONATEL Ecuadorian telecommunications national authority

COST European Cooperation in Science and Technology

CPE Customer Premise Equipment

DARPA Defense Advanced Research Projects Agency

DVB Digital Video Broadcasting

DVB-H DVB-Handheld

DVB-S Digital Video Broadcast via satellite

EIRP Equivalent isotropically radiated power (in dBW)

FS Fixed Service

FSPL Free Space Path Loss

GBP Great British Pound

GloPac Global Hawk Pacific

HAA High Altitude Airship

HAAP High Altitude Aeronautical Platform

HALE High Altitude Long Endurance

HALE-D High Altitude Long Endurance –Demonstrator

HAP High Altitude Platform

HAPS High Altitude Platform Station

HTA Heavier Than Air

HULA Hybrid Ultra Large Aircraft

ICT Information and communication technologies

IEEE 802.16 Institute of Electrical and Electronics Engineers

IMT 2000 International Mobile Telecommunications-2000

http://es.wikipedia.org/wiki/Automatic_Repeat_Request

http://www.ieee.org/

5 INTRODUCTION

INEC Instituto Nacional de Estadisticas y Censos

ITS Intelligent Transportation Systems

ITU International Telecommunication Union

ITU-R International Telecommunication Union Recommendation

JAXA Japan Aerospace Exploration Agency

LOS Line Of Sight

LTA Lighter Than Air

MAN Metropolitan Area Networks

NASA National Aeronautics and Space Administration

NICT National Institute of Information and Communications Technology

ODU Outdoor Unit

PC Personal Computer

PGA Plataforma de Gran Altura ( High Altitude Platform)

PTDS Persistent Threat Detection System

RPV Remote Piloted Vehicle

SNR Signal to Noise Ratio

SPF Stratospheric Platform

TARS Tethered Aerostat Radar System

UAV Unmanned Airplane Vehicles

USASMDC U.S. Army Space and Missile Defense Command

VoIP Voice over IP

WiMAX Worldwide Interoperability for Microwave Access

WRC-07 World Radio Conference 2007

WRC-11 World Radio Conference 2011

http://en.wikipedia.org/wiki/International_Telecommunication_Union

http://en.wikipedia.org/wiki/International_Telecommunication_Union

6 INTRODUCTION

TABLE OF CONTENTS GLOSSARY ................................................................................................... 4

1 INTRODUCTION ............................................................................................ 8

2 HIGH ALTITUDE PLATFORM, CONCEPT AND FUTURE ....................................... 10

2.1 HAP DEFINITION ................................................................................... 10

2.2 HAP PROJECTS ..................................................................................... 11

2.3 TYPES OF HIGH ALTITUDE PLATFORMS .................................................... 13

2.3.1 BALLOONS ...................................................................................... 13

2.3.2 AIRSHIPS ....................................................................................... 15

2.3.3 AIRPLANES ..................................................................................... 16

2.4 APPLICATION AND SERVICES ROAD MAP ....... ¡Error! Marcador no definido.

3 SCENARIO AND SERVICES ........................................................................... 19

3.1 SCENARIO ............................................................................................ 19

4 TECHNICAL ASPECTS .................................................................................. 22

4.1 PLATFORMS .......................................................................................... 22

4.2 ARCHITECTURE ..................................................................................... 23

4.3 FREQUENCIES ...................................................................................... 28

4.4 STANDARS ........................................................................................... 29

4.5 PAYLOAD ............................................................................................. 30

4.6 CHANNEL MODEL .................................................................................. 35

4.7 LINK BUDGET ....................................................................................... 38

5 PROJECT MANAGEMENT ............................................................................... 49

5.1 PROJECT PLANNING .............................................................................. 49

5.2 PROCESS ............................................................................................. 50

5.3 PROBLEMS ........................................................................................... 52

5.4 ROLES AND TASKS ................................................................................ 53

5.5 IMPROVEMENT IN PLANNING .................................................................. 54

6 CONCLUSION ............................................................................................. 55

7 REFERENCES .............................................................................................. 57

7 INTRODUCTION

8 INTRODUCTION

1 INTRODUCTION

The idea of using a high altitude platform ( HAP) for communications has been around for

almost 50 years, since the first attempts to bounce rays for telephone communications from

a balloon in 1960 [1]; the last ten years seem to be the most prolific period in studies and

programs around the world [2]. The initial concept of a High Altitude Platform (HAP)

presents a relatively fixed position at 17 to 22 km, at stratosphere level, above any normal

aircraft but below orbiting satellites. The concept claims benefits like large coverage,

mobility on demand or payload reconfiguration.

This report is about services and opportunities from High Altitude Platforms. The purpose

of the project is to understand the state of the art of HAPs and their advantages and

disadvantages to present the opportunities and benefits in a clear way. The aim is the

production of a straw man or deployment scenario as a proposal intended to generate

discussions of limitations against benefits and to provoke the generation of new and better

proposals about this technology.

This report is written by a group of five M.Sc. Communication Engineering students at the

University of York, England, as a Final Project and an academic requirement of the Master

Program.

The Group will critically examine the High Altitude Platform technology and its practical

applications for scenarios in Nigeria and Ecuador. The report will cover most of the

essential aspects on HAPs systems such as platforms, payloads, standards, channel

model and link budget. One of this specialized areas and scenarios will be covered in more

detail in each report submitted by each member of the group. This report analyses in

general Nigeria and Ecuador’s scenarios focusing the results on the South American

country and comments on Nigeria’s results from other reports; a complete idea of HAP

technology will be presented emphasizing on the platform and payload considerations.

Information about HAPs can be found in journal papers, official recommendations,

technical documents, conferences reports and few books. It is necessary to research

sources to produce adequate background for further discussion and support the

alternatives, the options and the constraints in the application of the technology in the

proposed scenarios. The basis of the report is to determine the relation between previous

studies and limitations or opportunities in the proposed scenarios. Furthermore continuous

9 INTRODUCTION

interaction, studies and analysis of alternatives, provides comments and ideas as the main

result of the report.

The structure of this report presents the technology in a comprehensible way to understand

the technology from different angles and viewpoints. Chapter II is a literature review about

definitions, types and applications of HAPs, producing an analysis of future possibilities of

HAP availability. Chapter III establishes the scenarios and services to be provided,

including some economical and political comments. Technical aspect based in parameters

as platforms, payload, standards or link budgets are analyzed for the case in Chapter IV as

multi-subject issues with possible alternatives or solutions. A final discussion is presented

in Chapter V with the establishment of the potential benefits, limitations, vulnerabilities and

suggested actions for the use of HAP technology. Chapter VI presents the project

management of the investigation.

10 HIGH ALTITUDE PLATFORM, CONCEPT AND FUTURE


2.1 HAP DEFINITION

The concept of a new platform for establishing wireless communications has a vital

beginning with the paper of Goran, Djuknic and Freindefelds (1997) [3]. The concept

presents an airborne platform which could operate at stratospheric altitudes for significant

periods of time, with a low cost and a capacity of carrying multipurpose and sizable

communications payloads. This new concept promises to offer advantage over the well

established terrestrial and satellite communications systems while at the same time some

of their pitfalls are avoided. The concept is known as High Altitude Aeronautical Platform

(HAAP), Stratospheric Platform (SPF) or simply High Altitude Platform (HAP). The ITU

presented in 2001 a definition for High Altitude Platform Station (HAPS) as part of the

vocabulary of terms for wireless access, and stated this technology as “A station located or

an object at an altitude of 20 to 50 km and at a specified nominal, fixed point relative to the

Earth [4]”. In practice, aerial platforms will operate in a quasi stationary position at altitudes

between 17 and 22 km, where the stratospheric winds indicate their minimum velocities.

Platforms may carry a payload for communication systems either a complete base station

or a simple transparent transponder, depending on the system configuration.

HAPs are claimed to provide some advantages compared with other communications

configurations. In comparison with terrestrial systems HAPs provide large coverage area

or better propagation in some scenarios; in relation with satellite systems, advantages are

relatively good link budgets, lower cost, rapid deployment and large system capacity. Yet,

some constraints have to be considered, principally the capability of station keeping,

availability of HAP frequencies, and upgrading of power systems.

A High Altitude Platform is a flying component of a communication system, a concept

which implies new considerations including the parameters of operation e.g. endurance,

size, weight, and critical power supply limitations for platform and payload. These

parameters are related in the categorizations of the different types of high altitude

platforms, each one of them with their own advantages and disadvantages.


2.2 HAP PROJECTS

A starting point for this technology could be the publishing of two of the most cited papers

about HAPs are wireless communications system at the end of the 90’s and beginning of

the new century [3], [5] . From those years onward, research and investigation on this topic

have been spreading and updating around the world [2] e.g. HeliNet, CAPANINA,

HAPCOS and Osiris in Europe, HALO in USA or Skynet in Japan. Taking into

consideration a chronological order, the relevance and impact of the results, appropriate

documentation and a balance in the geographical location of the program, the Japanese

Skynet, European CAPANINA and American Vulture will be presented as examples of the

world research, preponderance and collaboration on this new technology.

In Japan a national HAPs R&D (Research and Development) national project started in

1998 with the participation of the Japan Aerospace Exploration Agency (JAXA) for the

aeronautical study and the National Institute of Information and Communications

Technology (NICT) for the communications systems [6] . JAXA from 2000 to 2004

performed several experiments in a Stratospheric Platform (SPF) during a Phase 1 that

included technology familiarisation and the development of scaled prototypes. One of the

remarkable achievements of this project is station-keeping flight tests of the Stratospheric

Platform (SPF) at Taiki-cho, Hokkaido, from July to November 2004. Focusing just on

Earth-observation experiments, the platform was an airship almost 47 meters long and

reaching 16 km height. According to JAXA, the project was not a large scale program

standard and the Phase 2, for the completion of a full scale platform, was not achieved.

At the same time NICT developed trials on communications, broadcasting and

radiolocation payloads. The potential to provide various services to users in a wide area at

a reasonable cost encouraged the realisation and achievement of some successful

experiments. In June and July 2002 third generation mobile communications systems [7]

and TV broadcasting [8] were successfully conducted in the Kauai Island, Hawaii with the

collaboration of a U.S. flight mission team for the NASA´s Pathfinder Plus solar powered

aircraft. The Pathfinder Plus reached an altitude of 20 km and a flight of 13.5 hours during

the last mission, transmitting for more than 3 hours. Video phone connection at 64 kbps

with a commercial mobile phone and internet connection at 384 kbps using a PC card with

an external antenna were established in the IMT-2000 test. Clear high-definition TV picture


and voice were successfully received in the digital TV test, with a transmission rate up to

20Mbps. The project at an overall review achieved notable goals materializing some

concepts, establishing concerns and testing the theory.

While the Japanese program was being developed, a new project was conceived in the

European continent. Communications from Aerial Platform Networks delivering Broadband

Communication for All (CAPANINA) [9] was a project that included partners from UK, Italy,

Japan, Hungary, Switzerland, Germany, Slovenia and Spain. This project was partially

funded by the European Union Framework and existed from late 2003 until late 2006. The

aim of the project was to develop a broadband wireless communications capability, at

speeds up to 120 Mbits, from High Altitude Platforms to stationary users on the ground,

especially those who could be marginalized by geography or distance from actual

infrastructure, and to users on moving vehicles at high speeds up to 300 km/h [10]. The

project was looking to demonstrate that aerial platforms could support broadband users

through theoretical studies and practical trials, even though the test vehicles, including

tethered aerostat, stratospheric balloon or potentially HAPs were not developed as part of

the project. CAPANINA project was closely related with other European initiatives as COST

297 (European Cooperation in Science and Technology 297) and Heliplat. COST 297 [11]

provided a forum for research and technological development, increasing the knowledge

and understanding of HAPs, looking for cohesion among the community; this action

commenced in 2005 and formally completed its 4 year tenure in late 2009. Helinet [12]

was a European project based on Heliplat, a 70 m wing span aeroplane, that aimed to

examine delivery of broadband communications via HAPs. The project was headed by

Politecnico di Torino (Italy), but the University of York undertook the study of broadband

communications payload. CAPANINA is a well documented project and the deliverables

are totally available to the public in its website [13] as rich source of HAP knowledge.

In parallel to the research in HAPs for civil applications, the United States of America has

been developing special interest for military applications due to the necessity of supporting

systems in areas at a long distance from their own country. The concept leads to growing

needs for communications and surveillance systems which can be deployed around the

world or permit wide area coverage. Under the circumstances, the Defense Advanced

Research Projects Agency (DARPA) has managed programs to pioneer High Altitudes

Platforms like the cargo platform Walrus, Navy‘s Hybrid Ultra Large Aircraft (HULA) or the


Advanced Concept Technology Demonstration High-Altitude Airship (ACTD HAA) [14].

Currently, DARPA [15] is developing the Vulture program which intends for an unmanned

aerial system to remain on-station uninterrupted for a period of five years, providing

surveillance and communication services. Boeing, Aurora Flight Sciences, and Lockheed

Martin were selected on April 2008 as contractors for Phase 1 of the program [16], where a

conceptual system definition should be done. Phase 2 is expected at the end of 2012. A

contractor will be selected to build a near full scale prototype with a flying endurance up to

three months. The final goals for the program establish 450 kg payload and 5 kW of

onboard power for a flight above 18 km altitude, i.e. basically an aircraft performing like a

satellite without the launching costs.

Neither civilian nor military HAP are commercially available at the moment. However, the

programs and projects previously presented show that High Altitude Platforms began to be

treated as a new convenient technology and advantages of this platform are clearly

understood and studied.

2.3 TYPES OF HIGH ALTITUDE PLATFORMS

The term HAP has no rigid definition and could be taken to mean airplanes or airships,

manned or unmanned with autonomous operation, capable of long endurance on station,

at altitudes from 17 to 22 km. One of the first categorization of High Altitude Platform types

was presented by Tozer and Grace (2001) [5]; the platforms were classified as Airships

(essentially balloons) or Airplanes, in a manned or unmanned operation.

2.3.1 BALLOONS

Balloons are considered the earliest aerial platforms with a history going back to ancient

China with hot air balloons, made of oiled rice paper on a bamboo frame, used as military

signals. The activity for balloons nowadays includes small balloons for meteorological use

and tethered aerostats. Balloons are very straightforward to construct and launch, and not

expensive. Yet they don’t have the capability of relatively stationary position because they

are at mercy of the winds. On the other hand, tethered balloons with a limitation on the

altitude reached can be used as fixed platforms.

One of the most advanced projects with balloons is the Tethered Aerostat Radar System

(TARS) operated by the United States of America [17]. This is a tethered balloon-borne


radar system, which has been operating since 1980. The purpose of the system is to

provide low level radar surveillance data in support of drug interdiction programs. The

aerostat is an envelope, aerodynamically shaped balloon of approximately 70 meters long

by 22 meters across the hull, filled with helium and capable of rising up to 5 km tethered by

a single cable. The payload for this platform is between 550 and 1,000 kg.

A similar system to TARS is the Persistent Threat Detection System (PTDS) in use by

the Army since 2004. The PTDS provides communications, surveillance, intelligence, and

reconnaissance for long endurance and it is currently deployed in Iraq and Afghanistan

[18]. An actual photography of the system is presented in Fig. 1. During the last months of

2009, Lockheed Martin, the company in charge of the TARS and PTDS received a 133

million USD award to provide the U.S. Army with eight additional PTDS to support coalition

forces, showing the growing interest in the development of surrogate satellite capability.

The use of tethered balloons for HAPs are constrained by the tether, with needs for a

further development in materials research to produce one light and strong enough to keep

the high altitude range over 17 km. However, the use of aerostats generates interest in

capabilities of HAPs holding stationary positions.

Fig. 1 Photo of the Persistent Threat Detection Systems (PTDS) (taken from http://www.army.mil/-news/2009/06/18/22954-ptds-serves-as-surveillance-force-

multiplier)


2.3.2 AIRSHIPS

The next steps in the development of HAPs from balloons are unmanned airships, which

have had resurgence in recent years through the development of new technologies

applicable in their structures, such as certain types of plastics and more resistant and

lightweight hulls. Since the beginning, the concept of HAPs aims for airships with very large

semi rigid or non rigid containers, of the order of 100 meters or more of length. Air

stationary position is achieved by the use of electric motors and propellers allowing the

shuttle to fly against the wind. Actual efforts and larger projects are aimed to develop

unmanned airships with longer endurance and greater payload capacity; the length of

some of these platforms should reach above 150 meters, 1,000 or 2000 Kg of payload and

a mission duration about 5 years [19].

NASA’s Glenn Research Center presents in 2002 a detailed study about the performance

capabilities and the requirements for a High Altitude Airship [20]. The baseline for this

study was positioning an observational platform for coastal security at 21.5 km along the

east and west coasts of the United States of America. The configuration is an elliptical

shaped vehicle, one of the most popular shapes due to the good drag characteristics and

the previous knowledge about performances with low altitude airships. The report analysed

power, propulsion and airships models to generate sizing result for different mission

parameters and goals. Several factors were included such as wind, latitude, seasonal

power availability, efficiencies of technologies, etc. Some results includes lifting capacity,

flight duration or latitude range. The selected design point was an airship 185 m in length

and 46 m in diameter; this design might provide payload mass of 2000 / 4000 kg, payload

power of 1 kW, and a year coverage for the lower limit payload mass.

One of the biggest airship project planned is the Lockheed Martin High Altitude Airship

(HAA) [21], developed by the Lockheed Martin Company in its facilities located in Akron,

Ohio, United States of America. Lockheed Martin was taking advantage of its experience in

the aeronautical field, and the purpose was the development of an affordable, long

endurance, and stratospheric platform. The specifications of the airship include the ability

to fly at 20,000 km, carriage of multi-mission payload, and geostationary position. An

artistic representation of the HAA is presented in Fig. 2.


Fig. 2 Artistic representation of the Lockheed Martin High Altitude Airship (HAA) (taken from http://www.lockheedmartin.com/products/HighAltitudeAirship/

According to Lockheed Martin, the company has a contract to build a subscale prototype

airship system, named High Altitude Long Endurance –Demonstrator (HALE-D). The

performance for the prototype is initial progress to certify the feasibility of the High Altitude

Airship; the Army expects a sustained operation for at least two weeks at 21km altitude,

500 watts of power, and a useful payload of 23 kg. Minimizing the weight with strength

fabrics, using high efficiency thin film solar panels, and moving the platform with lightweight

propulsion units can lead to accomplish the milestones in this project. However, there are

factors such as uncertainty about performance and control at big scale, nonexistent

industrial base or light gas problems which contributes to make this airship a difficult

challenge.

2.3.3 AIRPLANES

Airplanes as HAPs can be presented as manned or unmanned technologies. The use of

manned airplanes is a well developed alternative with large payload capacity, but limited by

the constraints on fuel and human factors, in addition to high operating costs. Manned

airplanes are being used for experimental trials [22], but are hardly considered as a final

component of a long term HAP network due to the non stationary conditions of these

platforms.


The alternative option is unmanned airplanes. The option for stationary position is flying

against the wind or in circular tight paths, but one of the biggest drawbacks is the short

duration of the missions and high cost of operation. Again, the prime challenge is the

power balance related to the capacity of storing energy for persistent missions. This

constraint was especially important with the initial approach of unmanned solar-powered

plane, where the aircraft should store energy to keep flying throughout the night.

From the beginning, AeroVironment is an American company with a strong relationship

with the development of this technology for this type of platform. AeroVironment was the

manufacturer of NASA’s Pathfinder, Pathfinder Plus [23], Centurion [24] and Helios

Prototype [25], a series of solar powered aircrafts initiated by the U.S. government in the

early 1980's, which have achieved flight endurance trials up to demonstrating solar power

technology for high-altitude, long-duration flights. In fact, Helios Prototype reached an

altitude of 29.5 km, on August 14th 2001, a world record for sustained horizontal flight by a

winged aircraft. The company at the moment is developing the Global Observer unmanned

aircraft system, to provide persistent communications and remote sensing for civil and

commercial applications. The characteristic of the Global Observer are an endurance up to

1 week, payload up to 180 kg, operation altitude around 20 km and a liquid hydrogen

powered propulsion system. An artistic representation of the Global Observer is presented

in Fig. 3. Unmanned Airplane Vehicles (UAVs) were initially considered as another

category of aerial platforms due to the short mission durations and the operation at

generally modest altitudes. But at this moment, this technology is one of the most

developed, particularly in the military field and could be considered as an upgrade of the

initial concept of unmanned aero plane. UAV are increasing their capabilities, especially in

operation altitudes, with several of them reaching altitudes above 18-20 km; therefore, they

could be an alternative platform for some short term applications. During the last few years,

the unmanned airships are being focused on surveillance rather than as part of a

communication network, but they have served as principal platform in several trials

worldwide [26] .


Fig. 3 Artistic representation of a Global Observer flight. (Taken from http://avinc.com/uas/stratospheric/global_observer/

19 SCENARIO AND SERVICES


3.1 SCENARIO

The first step of the project was the establishment of a scenario for the proposal. The group

decided to define two scenarios, one in Nigeria and the other in Ecuador. The scenario in

Ecuador is the main scenario where this report will be developed, and Nigeria will be an

alternative scenario where some additional issues will be discussed and related.

The Republic of Ecuador is situated in South America and positioned over the Equatorial

line, occupying the latitude and longitude of 2°S and 77°30°W respectively, with a total

area of 283,561 km2. Ecuador has a population estimated in 2010 [35] at 14,204,900

inhabitants , distributed as 66.2% urban and 33.7 % rural , with a population density of 50.1

people per square kilometre. Ecuador’s economy is heavily dependent on exporting

resources, especially crude oil which produces the main income.

The Federal Republic of Nigeria is situated in the West African region on the Gulf of

Guinea, the main latitude is 10°N and the main longitude is 8°E, with a total area of

923,768 km2. Nigeria has a huge population estimated in 2009 by the United Nations at

154,950,000 inhabitants, distributed as 48.3% urban and 51.7% rural, with a population

density of 167.5 people per square kilometer [36]. Nigeria could be the largest market in

sub Saharan Africa, but the economy has over-dependence on oil which constitutes about

95% of generated revenue and faces social and economic problems. [37].

These two scenarios present developing countries where the first step of the road map

could be generated. Therefore, a study of the conditions for these specific countries

achieves an important discussion in this new technology. Besides, the HAPs projects, as

suggested in Section 2.2, are considered to developed countries, yet applications for

specific nations have not been largely covered. For a scenario in a developing country, the

Stand Alone Architecture of the HAP can be considered as convenient for applications

such as broadband, environment and disaster surveillance. Because of the expensive and

sometimes inefficiency to deploy terrestrial networks in rural or remote areas, and the cost

of satellite system for the small traffic demand, a HAP system may be deployed with

economic and efficiency advantages such as large-area coverage, low cost, broadband

capability and rapid deployment [38].


Starting with the analysis of terrestrial networks in both countries, a basic analysis of

communications networks is necessary. According to the ITU ICT Statistics Database ITU

[39], the fixed telephones lines present in Nigeria 0.75 lines per 100 inhabitants, while in

Ecuador this number rises to 12.31, still far away from the statistics of 35.28 or 57.67 in

Hungary and United Kingdom respectively. The complete statistics are shown in Table 2.

What is common for all four countries is a small and even negative Compound Annual

Growth Rate (CAGR) for the fixed lines. That is a logical result from the world tendency to

replace fixed lines with wireless communications.

Table 1 Fixed infrastructure in some countries related to the project (based in [39]).

The absence of fixed lines could be related to the low penetration rate of internet in the

scenario countries. The fixed line was the precursor of internet access through the dial-up

and ADSL connections, the first technologies for internet connections. Nigeria for the year

2009 presents 0.59 internet subscriptions per 100 inhabitants, 28.43 users for 100

inhabitants, and 0.05 broadband subscriptions per 100 inhabitants. Ecuador for the same

year presents 4.13 internet subscriptions per 100 inhabitants, 15.06 users for 100

inhabitants, and 1.77 broadband subscriptions per 100 inhabitants. These numbers are far

away from the statistics of European countries, for example the United Kingdom with 31.65

internet subscriptions per 100 inhabitants or 83.56 users for 100 inhabitants.

Therefore, new ways to provide internet connections should be presented to achieve better

Internet connections and reduce the digital gap. One of these alternatives could be a HAP

Country Fixed

telephone

lines in

2004

Fixed

telephone

lines in

2009

CAGR

(%)

Fixed

telephone

lines per

100

inhabitants

2004

fixed

telephone

lines per

100

inhabitants

2009

CAGR

(%)

Ecuador 1,590,800 2,004,200 4.7 12.31 14.71 3.6

Nigeria 1,027,500 1,419,000 6.7 0.75 0.92 4.2

Hungary 3,564,400 3,068,700 -2.9 35.28 30.71 -2.7

UK 34,576,500 33,614,500 -0.6 57.67 54.60 -1.1


communication system but must be presented as an adequate and sustainable business

model. A cost effective model in terms of openness and neutrality is presented in [38]. The

HAP provides services as an individual network operator, coexisting with major broadband

and mobile network operators,and not involving the end users . This model could be used

to provide internet services for suburban or rural areas where the population density is low

or where the deployment of terrestrial networks is expensive. These characteristics could

led to the deployment of the HAP with success , taking in consideration the amazing

increase of mobile services in both countries with rates of 125 % and 102% in Nigeria and

Ecuador respectively.

The scenario in Nigeria includes the provision of services to the areas of most populated

cities in the country [40]. In Ecuador, provision of internet to multiple points, isolated and

with a long distance will be considered. The provision of data transfer for military forces will

be discussed. A point related was a discussion in regards to military operational

considerations, but the point is over the scope of this project and taking into consideration

an allocation inside the own territory and air space the issue was overcome.

22 TECHNICAL ASPECTS

4 TECHNICAL ASPECTS

4.1 PLATFORMS

The development and trend of platforms is discussed in section ¡Error! No se encuentra

el origen de la referencia. ¡Error! No se encuentra el origen de la referencia.,

which presents unmanned planes solar powered and airships (when available) as most

suitable platforms for developing countries scenarios. Some payload capacity and power

available specifications are presented in Table 2. These specifications generally are for

unmanned solar powered aircraft but they could be easily reached by small airships. This

baseline and further analysis was released to be considered in the different areas of the

project. The baseline was established after the analysis of general platform parameters of

operation, size/weight, and critical power supply limitations for platform and payload, and

specific additional information for the case in Ecuador.

Source Year Payload

(kg)

Power

available

(W)

Volume

occupied

(m3)

Helinet Project [47] 2001 100 400 2

Experiment IMT-200 from Helios [26] 2002 50 500 Not

available

HAP Survey [48] 2005 50 to 300 3000 Not

available

CAPANINA Project Road Map [27] 2007 250 500 0.25

Table 2 Solar power aircraft specifications in some projects / studies

An airship or a powered airplane positioned in the stratosphere needs to be in a relatively

fixed position with respect to the ground. ITU-R F.1501 recommended a location sphere of

500m radius but this is more feasible for an airship than for an airplane. Other technologies

as HALO airplanes [32] suggested a toroidal volume of radius 4-6 km and Helinet project

[47] choose a cylinder with radius 4-2.5 km, and height +/- 1.5/0.5 km height for 99.9 / 99


% tolerances respectively. For the project platform, an assumption similar to the Helinet is

selected, due to that, a solar airplane would be the worst case scenario in the platform

stationary keeping requirements, then a cylinder of 2.5 km radius (an horizontal

displacement) and +/- 0.5 km altitude variation is the limitation established as presented in

Fig. 4.

Fig. 4 Assumed HAP location cylinder

The baseline platform is just an initial limitation for the study. The general characteristics

will be constant but specifications about weight or payload could be adjusted depending on

the needs of different scenarios or perspectives.

4.2 ARCHITECTURE

In the context of HAPs topology, a complete description of topology configuration for HAP

networks is presented in CAPANINA Project [27]; payload configuration options can be

seen in HeliNet Project [57]. Regarding to connectivity for Internet Provision, the project

can be considered as Access Network, where the HAP connects the end users to the core

network edge. A variation of this configuration may be a HAP Private Network with the HAP

connecting two or more users; this may be applied for organizations such as oil companies,

government organizations or military units. In a Private Network connectivity, security

issues need to be well thought-out because data should not be decoded by unauthorized

users. Access Network and Private Network schemes are presented in Fig. 5. For an

Access Network a core network link might be based on terrestrial infrastructure or through

a satellite. However, if the independence from non proprietary technology is a requirement

i.e. not depending on the satellite owner, the core terrestrial network is mandatory.


a) b)

Fig. 5 HAP connectivity schemes ( adapted from [27])

The platform considered for the case has limitations about payload capacity, therefore a

size/mass efficient configuration is suggested with hardware placed wherever as possible

on ground stations. The lightness solution may be a transparent transponder, i.e. no

onboard processing on telecommunication payload. This configuration presents

advantages related to weight and size of the communications payload, which adjusts to

constraint from the platform. On the other hand, network traffic should be handled from

ground station increasing the delay. Terminals providing connectivity to the core network

may require more power, bigger antenna size and more complex equipment to give an

appropriate service but this might be easily allocated in ground stations connecting to the

core.

The network architecture of HAP Communication System for Ecuador and Nigeria is shown

in figure 1. It is proposed an integrated terrestrial-HAP system with core networking ground

station, either under the same coverage beam than users or connected via dedicated link .

The first option has been tested in WiMAx trials [58] but presents the constraint of

congestion when traffic increases, a condition that based on the low demanding of rural

areas could be overlooked for specific sectors. The second alternative implies that the

backhaul with a dedicated line which adds more weight to payload but allows allocation of

ground station far from the edge of beam coverage area. These alternatives are presented

in Fig. 6.


a) b)

Fig. 6 Integrated terrestrial HAP system a) Gateway station under coverage beam b) Gateway far from coverage beam (based on [38]).

The architecture presented is one of the simplest, but would be suitable according to

platform limitations and services proposed. For military purposes, light and simple

communications payload presents fewer concerns about survivability of the payload i.e.

consequences of payload lost in case of failures or accident of the platform. Other benefit

from light payload is the possibility of extra space for surveillance payload when possible.

For military purposes a whole ground station for core network could be easily displaced to

adequate positions to operate with the HAP system.

Coverage is one of the best advantages presented by HAPs systems and is a parameter

than can be calculated using simple mathematical and well known expressions. The

diameter of coverage, i.e. the distance on ground that HAP could present a LOS (Line Of

Sight) link is calculated using the relation presented in [59]:

( (

( )) )

Where is the diameter of coverage area, is the radius of the Earth in km, is the height

of the HAP in km, and is the elevation angle in radians (angle between horizontal and

maximum communication line). Maximum communication distance is called the direct LOS

between HAP and user in the edge of the coverage area. Table 3 presents coverage and

maximum communication distance for different angles for HAP at 22, 20 and 17 km. 5

degrees angle is considered the minimum elevation angle for this communication link.


Diameter of

coverage (km)

Maximum communication

distance (km)

Elevation

angle (◦ )

Altitude

22 km

Altitude

20 km

Altitude

17 km

Altitude

22 km

Altitude

20 km

Altitude

17 km

0 1057 1008 930 529 504 465

2 702 657 586 352 329 293

5 422 388 337 212 195 169

10 236 215 185 120 110 94

15 160 146 124 83 76 64

30 76 69 59 44 40 34

Table 3 HAP coverage and maximum communication distance for different elevation angle at altitudes of 22, 20 and 17 km.

These results are similar to the ones obtained by the use of ICS Telecom nG by Line of

Sight Coverage; a HAP was represented as a transmitter station at 17, 20 and 22 km

height in the available maps of Nigeria. Results from the visibility tool, i.e. the lowest

possible angle of elevation, for a HAP at 20 km high, are shown in Fig. 7. The HAP is

represented by the station (green square) allocated in the center of the coverage area

(blue area around the HAP). Receiver stations are allocated around the country, some of

them on the edge of the coverage area. The longest ground distance, radius of the

coverage area, is 607 km from central station (HAP) to station A. This is just a line of sight

coverage and do not represents a communication coverage. In the figure obtained from

ICS Telecom nG, the border of Nigeria has been drawn with a black line to present a

general idea of the relation coverage area / country area.


Fig. 7 Line of sight coverage from a station at 20 km high using ICS Telecom nG (border line

and names has been enhanced for visualization)

Similar analysis, without the software tool and based in Table 3 results, is presented for

Ecuador. In this case, with HAPs at 22 km high and elevation angle of 5 degrees, three

HAPs should be deployed to cover the whole country. This coverage is presented in Fig.

8. HAPs have been allocated in points to fit the shape of the country with a LOS coverage

represented by the blue circles.


Fig. 8 Line of sight coverage for HAP altitude 22 km and elevation angle of 5 degrees.

4.3 FREQUENCIES

ITU have been conducting technical and regulatory studies on HAPs in order to establish

regulatory procedures taking into account the impacts in other system specially in

neighbouring countries [60]. The World Radio Conference 2007 (WRC-07) reviewed some

resolutions [61] to create an adequate frame for the deployment of HAPs. In regards to

Resolution 122, ITU invites administrations that intend to deploy HAPS systems in the

Fixed Services to use 47.2/ 47.5 GHz and 47.9/ 48.2 GHz. For Resolution 145, ITU

identifies an additional frequency allocation for HAPs on Ka bands: 27.5/ 28.35 GHz in the

HAPS-to-ground direction and 31/ 31.3 GHz in the ground-to-HAPS direction. This

allocation was formerly designated to 12 countries in Asia-Pacific region due to the higher

rain attenuation; later, the allocation was extended to other countries, including Region 2


(North and South America). The use of HAPS as base station for a terrestrial IMT 2000 has

been considered an option for some countries therefore the review of Resolution 221

specifies for this purpose the bands 1,885-1,980 MHz, 2,010-2,025 MHz and 2,110-2,170

MHz in Regions 1 and 3 and 1,885-1,980 MHz and 2,110-2, 160 MHz in Region 2. The

systems base on new technologies using HAPS for future applications was considered in

the Resolution 734 which resolved to extend the studies to identify two channels of 80

MHz each for gateway links for HAPS in the range from 5,850 to 7,075 MHz, in bands

already allocated to the FS, while ensuring the protection of actual services; this issue will

be discussed in WRC-11.

4.4 STANDARS

For this project two standards were proposed in the tender: Digital Video Broadcasting

(DVB) and Worldwide Interoperability for Microwave Access (WiMAX). Specifications and

detailed features of both are presented in the Project Report referenced in [64]; this section

presents basic concepts of both standards and the advantages of the standard selected for

this project.

DVB refers specifications for digital media delivery including broadcast. This standard is

supported by the DVB Project [65], a consortium of around 250 organizations including

manufactures, broadcasters, regulatory bodies and others in over 35 countries. DVB

Project aims to provide standardization for data, voice, and multimedia as video

broadcasting and has identified the media as terrestrial, satellite and cable. DVB includes

DVB-S, DVB-S2, DVB-H, and DVB-RCS which differs in the modulation scheme. DVB-S

(Digital Video Broadcast via satellite) and DVB-S2 are capable of delivering TV and other

broadcast services, DVB-H(DVB-Handheld) is as choice for portable devices in

movement to receive broadcast services, DVB-RCS is intended to provide bi-directional

and asymmetric traffic Base Station- Subscriber Units. DVB is a valid option to provide

internet and data related services, aim of this project, e.g. in Europe fast internet access

services are offered by DVB data broadcasting [66].

Another alternative is WiMAX, an air interface defined by the IEEE 802.16 wireless

standard. This is intended for Metropolitan Area Networks (MAN) i.e. for large computer

networks that usually covers a city or a large campus, and it is mainly configured for a


Point to Multipoint topology. The standard is supported by The WiMAX Forum, an

organization formed to “certify and promote the compatibility and interoperability of

broadband wireless products based upon the harmonized IEEE 802.16/ETSI HiperMAN

standard [67]”. This standard can be used to provide home/office broadband connectivity

across whole cities or large areas.

WiMAx was selected as a priori option until the service in the scenario would be decided

but without in-depth analysis. However, the selection was maintained after the definition of

internet provision because of the background of this study area at that time. Some of the

specifications are important features for a broadband wireless access deployment

presented in Sections 4.2 ARCHITECTURE and 4.7 LINK BUDGET.

According to WiMAX Forum, full featured base station may cover cell radius from 30 to 50

km for a 3.5 GHz system with line of sight conditions. However, full featured base station

means that besides the mandatory capabilities this equipment is using higher RF (radio

frequency) output than a standard BS (base station), sub-channelling, transmit and

receive diversity, and automatic repeat request (ARQ) as error correction technique, i.e.

the BS requires several improvements aimed by this standard. For the maximum

communication distances considered in this project, around 40 km, the standard may

comply with the requirements.

WiMAX allows an adaptative modulation to adjust the signal modulation scheme based on

the SNR (Signal to Noise Ratio) condition of the link. A high quality radio link uses a high

modulation scheme as 64 QAM and a low quality radio link uses a lower modulation

scheme such as QPSK. The edge of the coverage area will present the weakest signal,

then the range of the coverage area can be increased since the system can adjust to

fading conditions.

4.5 PAYLOAD

Equipment for the system may be divided in two groups: HAP equipment and Ground

Equipment. HAP equipment presents several constraints due to weight, size, power and

movement of the platform. On the other hand, ground equipment needs to be compatible

with HAP alternatives, but presents few constraints in comparison with the platform

equipment.


HAP equipment is usually called Payload; this includes the electronic equipment and

components located in the platform. Payload applications include telecommunications,

remote sensing, meteorological measurement, agricultural support, real-time monitoring of

coastal regions, integrated navigation / communication systems or pollution monitoring. For

this project, Platform Navigation and Control equipment which will be considered as a

component of the platform; consequently, any definition of payload or HAP equipment is

strictly referred to the Application payload.

For WiMAX standard one of the first documented payload trials was in 2007 for the project

StratXX [58], when WiMAX payload, based on commercially available equipment, was

intended to be used in stratospheric HAPs and demonstrated the feasibility of links at

communications distances of 24.4 km. This trial utilizes a topology similar to that presented

in Fig. 6 a), with a PC server inside the beamwidth of the HAP, therefore some constraints

have been already considered and the project is aware of that. WiMAX is intended as a

point to multipoint Wireless Metropolitan Area Network, consequently the base station was

allocated in the HAP. With this topology one of the CPE (Customer Premise Equipment)

was used as a backhaul station, which may cause a problem if the system is heavily

loaded. This project does not intend to design a payload; the aim is to present a general

idea of constraints about dimension/weight/power analysis.

Based on a payload similar to that used in trials for StratXX, Table 4 presents individual

dimensions and weight for main equipment based in commercial providers [68] [69] [70]

[71] . Design of the payload is a complex process which considers frequencies, standards,

link availability and parameters of the service to be provided [72] in an interactive process

to finally select specific equipment adjusted to this parameters. Payload is different for a

system with a simple transponder than for on-board processing system. The first

alternative may consider items such as 1,2,5,6; the total weight is 27.4 kg and volume

occupied is 0,05 m3 .On-board processing may consider additionally items 3 and 4; the

total weight is 104.9 kg and the volume occupied is 0,11 m3. Weight and size

considerations will be more complex for system with multiple HAPs interconnected by

optical link or when additional surveillance equipment is implemented.

Item Description Dimensions[mm] Weight (kg)

1 WiMAX base station 481 / 444 x 125 x 280 6.9


2 WiMAX ODU (Outdoor Unit) 420 x 340 x 270 15

3 PC server 175 x 439 x 750 77

4 Ethernet switch 25 x 20 x 20 0,5

5 Antenna 1 80 (Length) 0.5

6 Antenna 2 600 (Diameter) 5

Table 4 Basic WiMAX payload weight/ size with commercial components (based in configuration from [58])

In a solar powered system, the power available is a real limitation. For provision of service

over a long period, power is obtained not only from the main system but also from the

backup batteries for night operation. If we just consider a single equipment such as the

base station, the analysis presents some interesting results. The initial assumption is a 43

dBm radiated power which implies a consumption of 200 W based on 10 % power amplifier

efficiency. The base station should be working 24 hours per day, then is required 200W *

24 hours= 4,800 watt-hours per day. Average solar availability of 12 hours, due to the

location near to equatorial line, and a solar panel generating 70 milliwats per square inch

produce 700 milliwatts hours per day. Then, it is necessary about 3.7 m2 (5,800 square

inches) of solar panels. This would represent 7- 8% of available wings area to install the

panels in the solar powered airplanes, Zephyr and Solar Impulse, presented in Section 4.1

PLATFORMS. Using commercial light and flexible solar panels [73], 3.7 m2 area would

require around 5 units, for a total weight of 8 kg, similar weight than the base station.

Additionally, batteries are required for the base station night operation. A procedure similar

to one presented in [74] is followed to calculate battery specifications. The required power

is 200 W and the nighttime is assumed to be 12 hours, then the batteries output requires

12 hours x 200 W = 2,400 W-hr energy. Regenerative fuel cells’ efficiency can be consider

50%, therefore input energy to this fuel cells needs to be 4.8 kW-hr. Suppose fuel cell’s

energy density as 0.3 kW-hr/kg then the total weight of the fuel cells is 16 kg. This weight is

more than two times the weight of the base station. As it can be seen, power transmitted

from the payload implies solar panel areas and weight considerations, not only from the

main power system but also from the back up batteries required.


Location and operation of the antennas have special restrictions due to the pitch, roll, yaw

and displacement of the platform. These considerations influence the selection of the type

of antenna, which must cope with the normal considerations regarding the frequency range

and special requirements to maintain the link with the ground. The platform antenna

should be able to maintain its position with respect to the ground as the platform flies

against the wind or in circles, and ground equipment antenna needs a enough to keep

tracking the HAP. The analysis of these conditions can be complex on a multicell layout,

but for a single cell and hence single beam the procedure may be simpler. An analysis for

single beam is presented in [58] where the airship platform movement is mitigated by an

steered antenna and the station keeping target is assumed as a 5 km radius position

sphere and maximum +/- 5 grades pitch or roll. For that specific case an optimal 3 dB

beamwidth of 32.6◦ was required for the ground station antenna. Pitch, roll ,yaw and the

platform position keeping sphere can be seen in Fig. 9 Pitch, roll, yaw and the StratXX

platform position keeping sphere.

Fig. 9 Pitch, roll, yaw and the StratXX platform position keeping sphere.

Finally, some environmental requirements are presented. Altitudes about 20 km produce

additional constraints for the equipment, specially pressure and temperature. The pressure

at these regions is 1/20 times the pressure at sea level [75],which implies that the payload

must be pressurized. Temperature in the stratosphere is about -55◦C, then the equipment

should be specifically designed for extreme cold temperatures or a climatic system needs


to be implemented. For this project the last alternative is mandatory due to the assumption

of commercial equipment usage with operation temperatures between -40 to 50◦C [68]

[69].

Planning tools such as ICS Telecom nG or Satmaster Pro can be used for Link Budget

calculation and analysis as be detailed in Section 4.7 LINK BUDGET. Additionally, these

tools present some accessories to ease the data input from equipment specifications. ICS

Telecom nG provides Equipment and Pattern tabs for the Microwave parameters; these

are useful tools for basic payload design. However, link simulations were based in general

input values assumed in Chapter 4 TECHNICAL ASPECTS. SatMaster Pro Graph / Table

menu plot and present useful relationships between parameters; they are good references,

but most of them are designated for antenna parameters.

Fig. 10 Equipment tab as presented in a HAP Microwave Link Simulation in ICD Telecom nG.

From this section is concluded that performances in a HAP system design may be

constrained by limitations in the payload capacity, which also depends on the platform

selected. Then, the system design has to consider a tradeoff between requirements and


availability; availability means space, weight, power or in some cases equipment

specifications.

4.6 CHANNEL MODEL

Propagation model aims to predict the average received signal power from the transmitter

in a given distance (large-scale fading) and as fluctuation of the received power over very

short distances or short time duration ( small-scale fading). In this process fading occurs

when there is no line of sight between transmitter and receiver. When there is line of sight,

multipath creates small scale fading [76]. For satellite to ground station transmission,

propagation takes place via many paths. A direct wave carries significant portion of

energy, but specular ground reflected wave and diffusive wave takes the remaining energy

as represented in Fig. 11. Then, the signal is received by multiple paths, with the replicas

being the same transmitted signal with different phase, amplitudes, delays and arrival

angles in a constructive or destructive way.

Fig. 11 Multipath signal from a satellite ( adapted from [76])

HAP propagation model can be considered similar to satellite communications link [48];

both are conceived under free space propagation. ICS Telecom nG as a tool, for planning

telecommunication networks, presents several options to set the propagation model;

option ITU 525/526 is based in recommendations ITU-R P.525-2 - Calculation of free-

space attenuation and ITU-R P.526-10 - Propagation by diffraction; therefore, this option is

selected for simulation of HAPs system.

In a free space propagation the receiver power decays as the square of the distance

between the transmitter and receiver as it can be seen in the well known equation 1:

(

)

(1)

Where,

http://www.itu.int/rec/R-REC-P.525/en

http://www.itu.int/rec/R-REC-P.526/en


: free space path loss

: distance HAP-user (in meters)

: frequency (in hertz)

: speed of light in a vacuum ( 3 x 10^8 m/s)

For HAP channel model small-scale fading is usually described by Ricean distribution. This

distribution assumes a main fixed component such as the line of sight link and a large

number of varying rays of lower power. One critical parameter is the Ricean factor,

which is defined as the ratio of signal power in dominant component to the scattered power

contribution. For HAP system values goes from 0 to 20 dB; in terrestrial systems usually

it is close to zero. The larger its value, the highest the HAPs system energy gain in

comparison with a terrestrial system.

An interesting evaluation of WiMAX services over HAPs communication channel is

presented in [77]. The environment of the experiment was similar to a suburban area, with

open areas, trees and some constructions. The analysis describes a prediction of for a

HAP wireless channel based on experimental data simulating the floating position of HAP

as it can be seen in Fig. 12, and two estimation methods for Ricean factor. From the

curves obtained, it is concluded than frequency and elevation angle affect the value of .

For the frequencies used in the experiment, Ricean factor was bigger at 1.2 GHz rather

than 2.4 GHz, therefore the multipath signal would contribute more power in higher

frequency. Also, value increases when the elevation angle is higher and better

performance is obtained for higher than lower angles due to the major scattered signal in

lower angles. With these results WiMax performance was simulated under the channel

characteristics. This simulation shows, in general, HAPs channels perform well for WiMAX

applications when the elevation angle is higher than 40◦. Consequently, the coverage area

might not be as high as initially expected due to the SNR required for lower angles i.e. at

more distant points, as it can be seen in Fig. 13 . These limitations will be considered for

coverage area service by the HAP WiMAX system.


Fig. 12 Experimental model of data measurement (taken from [77])

Fig. 13 Perfomance of WiMAX service under HAPs channel model in 2.4 GHz (taken from [77])


Rain attenuation effects are negligible at the range of frequencies less than 10 GHz

selected for this project. However, for the frequencies suggested by ITU for HAPs systems,

i.e. over 10 GHz, rain produces a high impact with the attenuation of the signal by

scattering or absorbing radiation. Rain attenuation can be obtained by hand calculation

according to ITU-R P838-3 equations and tables, or by the calculators incorporated in the

planning tools described in previous section.

A more complete Channel Model description can be found in the Project Report referenced

in [78] , but with the basic considerations presented in this section a general understanding

of the topic for the project has been presented.

4.7 LINK BUDGET

Link budget deals with the calculation of the expected received signal to noise ratio in order

to assess the success of implementing a communication system. Based in the Link budget

analysis, the designer decides about power transmitted, antenna size and gain, and link

availability among others. The aim of the Link Budget in this project is to determine the

system performance according to the limitations and analysis previously presented.

Parameters such as transmit and receive antennas gain, noise figure, losses, etc, will be

assumed according to the goals and considerations of the project. Project Report

referenced in [79] presents the Link Budget details; this section presents Link Budget

basic equations, assumptions considered for the calculation and the relation with the

analysis previously done. For calculation of the Link Budget, well known equations will be

employed, and the geometry considered can be seen in Fig. 14.

Fig. 14 HAP link budget geometry


The basic objective of the calculation is to determine the Link Margin of the system, i.e. the

system ability to support the communication link. It will be calculated as the difference

between the available carrier to noise density ratio ( (

)

) to the required carrier to

noise density ratio((

)

):

(

)

(

)

(2)

In a basic Link Budget analysis , the r(

)

can be obtained from the relation:

(

)

(3)

where

: Equivalent isotropically radiated power (in dBW)

: free-space path loss (in dB)

: rain attenuation (in dB)

: receiver gain (in dB)

: Boltzmann’s constant (J/K)

: temperature of the system (in K)

The (

)

can be obtained from the equation:

(

)

(4)

Where

: Bit energy per noise spectral density (in dB); it is taken for a particular BER (Bit Error

Rate)

: Data Rate (in dB)


For the HAP system some special assumptions were considered specially related to

antenna gain, power transmitted and required performance. The user’s worst case is the

edge of the coverage area; therefore the analysis of a basic link budget is done for this

point.

HAP antenna

One of the aims of the system is to provide the wider coverage area for urban population in

Lagos and rural population in Ecuador. Therefore using the following equations, it was

necessary to determine a HAP antenna beamwidth to illuminate such area from the

platform fixed at 20 km high:

(

)

(5)

(6)

Combining (5) and (6)

√

(7)

where

: gain of the HAP antenna.

: antenna efficiency, typically 0.6 to 0.7. For this case 0.7 will be assumed

D: antenna diameter

: 3 dB beamwidth in degrees of the antenna

A better coverage ( or illuminated area) is reached by a low antenna gain as it can be seen

in Table 5, where the antenna gain and the diameter of a circular coverage area is

presented. However, 6 and 5 dB are among the lowest gain found in commercial antennas

[80], therefore the maximum coverage proposed is 50 km. With this coverage diameter the

elevation angle is around 39 ◦, and an adequate performance for a WiMAX system is

expected as it was discussed in section 4.6 CHANNEL MODEL. The maximum

communication distance would be around 35 km which may be reached for the WiMAX

equipment according to section 4.4 STANDARS.


Antenna Gain

(dBi)

Coverage diameter

(km)

5 50.7

6 41.6

7 34.9

8 29,7

9 25,6

12 17,1

15 11,7

18 8,2 Table 5 HAP coverage related with antenna gain and 3dB

HAP power transmitted.

In the configuration of the system, the base station might be allocated in the HAP. Typical

values for WiMAX base stations power transmission are from 1W to 20 W, which are

commonly used in link budgets analysis and offered by commercial equipment vendors [68]

[69] [70]. In coverage simulation with ICS Telecom nG, bigger areas were reached if

transmitted power was increased from 20 W to 50W; however an increase in power

transmitted means that higher power availability and constraints in size and weight exists

from the payload, as discussed in Section 4.5 PAYLOAD . This alternative, during the

discussion of Link Budget parameters, was rejected due to the relatively small platform

selected for the project which may present few areas to allocate panels and the assumed

payload capacity.

Receiver antenna

The receiver antenna deals with the movement of the platform. Antenna’s gain is

calculated from a beam enough to keep pointing the relatively stationary platform.

Considering a movement of 2.5 km radius, the antenna’s gain is obtained in a simplification

of the approach detailed in Section 4.5 PAYLOAD. The basic geometry is presented in Fig.

1Fig. 15; just the horizontal displacement is considered with the assumption of level

altitude constant and no pitch, roll or yaw. To cover this displacement, the widest


beamwidth is required for the user exactly under initial HAP point; then the antenna

requires a 3 dB beamwidth of 15 degrees. Using equation (7) and efficiency of 0.7 antenna

gain is calculated in 22 dB. The solution addresses a fixed antenna in a way that users do

not have to care about alignment of the ground antenna with the HAP

Fig. 15 Basic geometry for horizontal displacement

Performance of the system

The worst case for signal is the edge of the coverage area. WiMAX allows an adaptative

modulation, then to maintain the quality of the link the requirement assumed is a C/No ratio

of 9 dB is for a QPSK modulation scheme [63].

From the analysis of the scenario in Nigeria presented by Project Report referenced in [40],

the data rate was assumed as 300 Mbps to cover the metropolitan area of Lagos. This data

rate is assumed for 10,000 home users with 1 Mbps using a contention ratio 50:1 and 100

companies with links of 1 Mbps. For the uplink a data rate of 200 Mbps and a frequency of

3.55 GHz were considered.


With the assumptions previously discussed the Link Budget is calculated in an Excel

spreadsheet developed for this section as presented in Table 6 and Table 7. These results

are similar to those obtained in the Project Report referenced in [79].

DOWNLINK

Parameter Unit Values

HAP

Height km 20.0

Antenna gain dBi 5.0

Antenna gain W 3.2

Antenna efficiency 0.7

3dB Beamwidht degrees 103.5

Coverage diameter km 50.7

Displacement of HAP km 2.5

Transmit power W 20.0

Transmit power dBm 43.0

EIRP dBm 48.0

Transmit losses dB 1.0

Frequency Ghz 3.5

Communication distance Km 34.3

Speed of ligth km/s 300000.0

FSPL dB 134.0

Ar (rain attenuation) dB 0.0

RECEIVER GROUND STATION The Boltzman Constant dBJ/K -228.6

Noise temperature K 300.0

Thermal noise density dBm/Hz -173.8



Engineering margin dB 2.0

Rx Losses dB 2.0

C/No Available dB-Hz 102.8

Data Rate Mbps 300.0

Data Rate dB 84.8

Eb/No 9.0

C/No required dB- Hz 93.8


Link Margin dB 9.0

Table 6 Excel spreadsheet with the Downlink calculation

UPLINK

Parameter Unit Values

GROUND STATION Height HAP km 20.0


Antenna gain W 100.0


3dB Beamwidht 18.4

Coverage diameter km 6.5

Displacement of HAP km 2.5

Transmit power W 20.0

Transmit power dBm 43.0

EIRP dBm 63.0

Transmit losses dB 2.0

Frequency Ghz 3.6

Communication distance Km 34.3

Speed of ligth km/s 300000.0

FSPL dB 134.1

Noise Figue dB 5.0

Ar (rain attenuation) dB 0.0

RECEIVER HAP The Boltzman Constant dBJ/K -228.6

Noise temperature K 300.0

Thermal noise density dBm/Hz -173.8


Rx Noise figure dB 4.0

Engineering margin dB 2.0

C/No Available dB-Hz 100.7

Data Rate Mbps 200.0

Data Rate dB 83.0

Eb/No 9.0

C/No required db-Hz 92.0


Link Margin dB 8.7

Table 7 Excel spreadsheet with the Uplink calculation

According to the discussion presented in Section 4.2 ARCHITECTURE, a backhaul is used

to connect the core network with the HAP. This backhaul generally operates at higher

frequencies than 3.5 GHz and transmit high data rate over long distances. The backhaul

station for the project is positioned 10 km out of the coverage edge. From this point, a

beam of 4 degrees is required to cover the possible movement of the HAP presented in

Fig. 16. Commercial equipment may provide around 300 Mbps at 15 GHz [70], therefore

the link budget for the backhaul can be done with similar consideration as the previous

links. Link margins of 4.3 dB were obtained for the backhaul in the Report referenced in

[79]. The geometry for the worst case can be seen in Fig. 16 .

Fig. 16 HAP Backhaul geometry for the worst case in the link budget.

ICS Telecom nG was used to simulate and analyze the HAP – user link. For Section 4.2

ARCHITECTURE, simulations dealt with the ability to include maps and create coverage

areas. However, maps were available just for Nigeria scenario. Coverage simulation with

the HAP at 20,000 m high, user at 10 m high, and input parameters assumed in the link

budget, are presented in Fig. 17 a). Different sensitivity coverage areas are represented

by the concentric circles of different color; blue represents 36 dbu threshold sensitivity. For

this Section, Path Profile results and graph were obtained from input parameters assumed

for the link budget . One of these simulations can be seen in Fig. 17 b). The Microwave

Link produces a Path Budget summary that includes Attenuations, Gains, Losses, and

Reliability as main results. ICT Telecom nG includes those features, but presents a not


very friendly interface, which converts the simulations in a time consuming task for non

expert users. Input parameters, not considered in the basic analysis, were assumed to

generate and produce adequate margins in the scenario. From these manipulations, it can

be concluded that more parameters may produce detailed simulations, but it is necessary a

reason for these assumptions. Therefore, the simulations create path budget and

microwaves links, used to modify power values, modulations or availability to generate

better links as an exercise of parameter discussion.

a)


b)

Fig. 17 Coverage (a) and Path calculation (b) from the HAP simulated at 20,000 m, user at 10

m, for a threshold at 36 dbu

Satmaster Pro is a tool designed principally for link budgets in satellite communications,

but can be used for HAP analysis. The tool is simpler than ICS Telecom nG, is easy to use

and presents a friendly interface. On the other hand, the results are just calculation of link

budget parameters. However, more inputs can be filled with the Link Budget assumptions

presented in this Section, and similar margins that those calculated with the Excel

spreadsheet are obtained. The HAP can be simulated as a non GEO satellite, with their

own name, altitude, range and longitude. Other features include simple but useful graphics,

tables and calculations that make easier the design of the link. A fragment of the results for

a simulation of the HAP is presented in Fig.21.


Fig. 18 Results from one simulation of the HAP-user link presented in this Section.

49 PROJECT MANAGEMENT


5.1 PROJECT PLANNING

This project was divided in two phases: preliminary study and strawman scenario. The

preliminary study includes a literature review of 15 days in April. During May and June, the

preliminary study established five areas: platform and payloads; propagation; link budget;

standards; and scenarios. The purpose was that each member gets a real understanding

of principles and state of the art technologies in one of these areas. Supervision meetings

and occasional group meetings was the main way to inform about findings and concerns. A

basic knowledge in the use of ICS Telecom nG was developed in this period.

The preliminary study would produce inputs to define the strawman scenario. During the

second phase in July and August, the group developed the scenario based in assumptions

presented and justified for the members; analysis and results are discussed to obtain

adequate conclusions. Software tools such as Excel, Matlab, ICS Telecom nG or

Satmaster are used and evaluated for calculation and/or simulation. A summary of the

Tender initial plan is presented in Fig. 19; some changes were done during the execution

and the Plan adjusted to the real time spent is presented in Fig. 20 .

Fig. 19 Initial Plan ( based in [83] )


Fig. 20 Plan executed

5.2 PROCESS

In order to fulfill the goals, a general process was presented in the Tender, as it can been

in Fig. 21 Now that the project is completed, comments about the achievements,

difficulties and problems for this process are discussed in this section.

Fig. 21 Project Process graph ( taken from Project Tender [83])

Understanding of requirements: The Tender presented some gaps in the aims of the

project and how to do it; a recapitulation of objectives and strategies were done after the

feedback of this document in April.


Definition of task: Definition of personal tasks during the phase of preliminary study was

the most difficult part. Sometimes, the members of the group felt overwhelmed with the

amount of information available, the correct selection, and sorting the right topics.

However, in supervision meetings important aspects were pointed to build a better

understanding of the area designated. Some areas defined adequately the tasks and got a

better background for the case study, and therefore the real understanding of the

technology to support the case. During the study case, strawman scenario, Specific tasks

were easily defined when the group worked together, specially in the initial parts of the

usage of ICS Telecom nG, and the evaluation of performance and link budget analysis

during the last month.

Requirement of group information: Information, data or inputs required from other

members of the group was fluently required and compared at the end of the project, but

during the preliminary research in the area designated, little information was evaluated

among the members.

Share information: Papers, files, results, comments were shared among members of the

group, but sometimes not among all the members. To correct this problem, the internal e-

mail was asked as mandatory for the process; this electronic document would keep

informed over findings and new approaches to the project.

Information back up: The group virtual disk was an additional and adequate alternative to

backup the information and make it available. There was no problem at all with files.

Group meeting: Undoubtedly, the most valuable part of the process. During the group

study case, problems and milestones were discussed among the members and excellent

ideas and conclusions were obtained.

Releasing of topics for supervision discussion: Every week a designated Chairman

was in charge of the supervision meeting. Before that, the Chairman had to prepare the

topics to be discussed. Yet sometimes these policy were not followed and consequently

supervision session rounds about random topics without any defined issue or preparation

from the group members.

Advance report: Supervision and group meetings, milestones and future task were

reported in the weekly email without any major problem. In February, a form for the weekly

email was released to cover all the aspects suggested by the Electronics Department.


Final Report: The ideas, solution and results will be included in the Final Report.

Additional a section with a summary of the system for the executive reader should be

included.

5.3 PROBLEMS

The Risk Management section of the Tender identified potential problems during the

development of the project. Some of them occurred and the analysis about them is

presented as following.

Incorrect estimation of task times: The task to define the scenario service was

discussed for several weeks when it was planned to be finished in a couple of days before

the division of areas. With some undefined initial assumptions some areas went ahead

trying to follow the initial plan and avoid delays but part of that work needed to be re done

after final assumptions was made. Another incorrect estimation was the assumption of

case parameters settled in 4 days, that was a continuous process during one month.

Task not well defined or not included: The research of antennas was included in the

Antennas and Propagation area in the beginning of the Tender, but then this area was

changed to Channel Model and the study of antennas was not included in the preliminary

research. When the Case analysis was being discussed issues related to this topic had to

be deal by areas such as Payloads and Link Budget without the previous background and

inputs.

Lack of communication: Occasionally some decisions about approaches to the project

were not shared with all the members, then particular efforts were wasted.

Misunderstanding of the tasks: Usage of ICS Telecom nG was considered a main task

during the preliminary study, but after some supervision meetings and feedback from the

first Draft Report this tool was defined as an accessory to get some results for the project.

Finally, the ICS Telecom nG was included as an alternative tool of the technical solution to

the project.

Misunderstanding of the scope of the project: The Project was planned from the

beginning as an open investigation aimed to provide a real understanding of HAP

technology. This approach facilitates the work in areas of real interest for group members,

e.g. platforms in my case. On the other hand, it was difficult to join all the interests in a


single body of work. A strawman scenario was a good frame to limit the project, but an

earlier definition of specific goals instead of a general understanding would produce more

deep results.

5.4 ROLES AND TASKS

Administrative roles for the members were proposed in the Tender but during the

development of the project some changes occurred. In my personal case, the role was

Team Coordinator; the function facilitated internal and external communication, proposed

and arranged meetings, coordinated work among the different members, distributed role

shifts and prepared forms for documents . Additionally, as member Communication Officer

in some weeks I was in charge of the several supervision meeting, presented the topics for

supervision and released the weekly email.

As member of the group study my main general task was provide an adequate

understanding of the technologies, benefits and limitations of Platforms and Payloads for

the development of the strawman scenario.

In the preliminary study specific task includes:

Investigation of trends in platforms.

Definition of assumptions for platform.

Definition of limitation and constraints of payload.

Establishment of architecture for the system.

During the group case some task includes:

Provision of link budget parameters related to platform.

Provision of link budget constraints and parameters from payload.

Evaluation of ICS Telecom nG and SatMaster Pro software, mainly related to

coverage and equipment.

Provision of sources and information for the development of a scenario in Ecuador.

Awareness of commercial equipment available and their limitation.

Analysis, review and some recalculation of Link Budget results.

Development and analysis of Ecuador scenario.


5.5 IMPROVEMENT IN PLANNING

Based in the analysis presented in this section, a suggested Plan for a similar study is

presented in Fig 27. This plan reduces one third of the time spent in the different

preliminary study areas and allows enough time to the discussion of the service to be

provided. This discussion presents specific goals for the strawman scenario and basic

assumptions. Then, the plan goes straight forward to the technical solution and feasibility at

the same time. With this change, all the parameters in doubt might be checked with

enough time. The most interactive process of link budget and performance is increased to

two months. The documentation keep the same initial point at the beginning of the

technical solution to not miss any details of the solution.

Fig. 22 Proposed plan

55 CONCLUSION

6 CONCLUSION

This project describes the state-of-the-art of High Altitude Platforms (HAP) technology, and

relates the fundamentals with a strawman scenario. HAPs are balloons, airplanes or

airships allocated around 20 km above ground, and are considered a valid alternative for

the deployment of communication systems. At the moment there is no HAP available, but

for this analysis the possible limitations and constraints were investigated. Then,

alternatives and solutions for the provision of internet service to urban and rural areas in

Nigeria and Ecuador were analyzed. For this report, the main analysis was focused on the

rural areas in Ecuador. Other Group Projects were focused in Nigeria and consequently

referenced for the user interested in.

A small platform, with capacity of 250 kg and power of 400 W for the application payload,

was assumed after an analysis of trends and technologies. In order to obtain a general

performance of the HAP system, a basic design was developed considering principles,

fundamentals and specifications for standards, payload, channel model and link budget.

One important point is the consideration of commercial equipment to relate the features

with a real implementation. The design was based in WiMAX technology and may provide

a data rate of 120 Mbps, serve 18,000 clients and cover a circular area of 50 km diameter.

For the project, different levels of software were used from basic Excel Spreadsheet or

Google Earth to more complex terrain coverage and link planning tools such as ICS

Telecom nG or Satmaster Pro. Some interesting results were presented and commented to

support the discussion of the concepts.

The strawman scenario in Ecuador presented opportunities and benefits in a simple and

clear way, but at the same time showed some limitations of the system. This Report

considered a scenario different than previous studies, a country where the rural population

presents particular characteristics in incomes, demography, distribution and required e-

services. Then, the HAP system is presented and supported as a social revenue concept,

different that the usual business model. To end with, the possibility to provide surveillance

service is suggested and analyzed in the final discussion.

Projects working with strawman scenarios should consider antennas as an additional or

separated area of research. An study approach, similar to that for platforms or standards in

56 CONCLUSION

this project, is required. With detailed assumptions, simulation and planning tools may

generate more realistic outputs.

For further work, systems combined in a single platform are a topic applicable in many

scenarios. Communication, surveillance, and remote sensing from the same HAP may

present interesting challenges to the researcher. Additionally, military applications are

usually named but valid information is difficult to find. Therefore, some good results and

alternatives from these topics would contribute to the kick off the HAP technology.

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