A Most Promising HAPs Technology for Next Generation Wireless Communication Systems

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1 Computing For Nation Development, February 25 26, 2010 Bharati Vidyapeeth s Institute of Computer Applications and Management, New Delhi A Most Promising HAPs Technology for Next Generation Wireless Communication Systems Sankit R. Kassa 1, Koushik Barman 2 and Deman Kosale 3 1,2 E&CE Departments, 3 EE Departments, NIT, Hamirpur 1 kassasankit@gmail.com, 2 nith.barman@gmail.com and 3 demankosale@yahoo.co.in ABSTRACT High Altitude Platform Stations (HAPs) is a new and promising technology, useful for Next Generation Wireless Networks, which can serve a large number of users at low-cost and quick access to modern wireless communication services. This paper reviews on the system structure, the advantages of HAPs over terrestrial and satellite architectures and possible communications applications of HAPs. It also presents an overview about some underway HAPs projects worldwide. Finally, it focuses on the technical challenges and critical issues of energy source, platform station keeping, modulation, coding, antennas design, propagation, diversity, interference and handoff issues. KEYWORDS Introduction, Types, Applications, Frequency allocation and projects of HAPs worldwide. 1. INTRODUCTION In today s world, we use mobile communication technology everywhere in all over the world for making a call. But this cellular technology is very much costly and not so much reliable. And it has not reach up to the rural areas. So a new technology called HAP is proposed by scientists all over the world for communication purpose. HAP technology has been established for the past several years, although the reality shows that its progress is being done in a very slow mechanism. HAP is a type of plane or balloon, in a stratosphere, which is unmanned and which will be in the altitude of 17 to 22 KM above the ground. For delivering the communication link, HAPs can absolutely play a key role to combine the features of ground based mobile towers and that of the satellite. Researches show that HAPs can cover the area of up to 100 KM diameter area with an altitude of about 20 KM above the ground. At this altitude (which is well above commercial aircraft height), they can maintain a quasistationary position and support payloads to deliver a range of services: principally communications, and remote sensing. Communications services including broadband, WiMAX, 3G, and emergency communications, as well as broadcast services, are under consideration. A recent HAP trial in Sweden has successfully tested the usage of HAP at 24 km altitude, operating in the mm-wave band to send data via Wi-Fi (802.11b) to a coverage area of 60 km in diameter, with the goal of demonstrating the potential of this novel technology. HAP can provide the best features of both terrestrial masts (which may be subject to planning restrictions and/or related environmental/health constraints) and satellite systems (which are usually highly expensive). This makes HAP a viable competitor/complement to conventional terrestrial infrastructures and satellite systems. In particular, HAPs permit rapid deployment, and highly efficient use of the radio spectrum (largely through intensive frequency reuse). The relatively close range of HAPs compared to satellites means that data rates can be significantly higher for the same size antennas, and imaging and remote sensing are highly effective, offering low cost and high resolution. A variety of hybrid applications may also be envisaged, such as traffic management, navigation, security management, and so on. HAPs differ from other means of communications delivery in the fact that HAP movement and limited mission durations must be taken into consideration in order to ensure that communication services are maintained. Innovative solutions including mechatronic antenna beam steering techniques, smart and MIMO antenna technologies, intra/inter HAP handoff processes, and diversity techniques could play an important role. Multiple bearer systems, using multiband wireless and free space optic technologies, including hybrid terminals can exploit the advantageous propagation environment. Integrated networks containing HAP, terrestrial, and satellite components can be further used to enhance the user experience and exploit the best features of each segment. 2. TYPES OF HAPS There are 3 types of HAPs. 2.1 Type 1: Balloon type HAPs Balloon type HAPs used for communication These can range from micro-vehicles to substantive craft, and may be powered by fuel or solar energy. Most have limited mission duration with propulsion systems, which are semi-rigid or non-rigid, huge and mainly solar-powered balloons, over 100 m long with a payload of about 800 kg or more. The achievable mission duration is hoped to be about 5 years. The Fig. 1s shown below. Use of electric motors and propellers as propulsion, while solar cells mounted on the wings and stabilizers provide power

2 during the day and charge the on-board fuel cells. Some proposals make claims of continuous flight up to six months or more as shown in fig.2 below. This unmanned aircraft can play a major role in the progress of HAP because there is nothing any man in it, so it can go anywhere in the world and can give its service everywhere in all over the world. Fig Type 2: Unmanned aircraft Fig.2: 2.3 Type 3: Manned aircraft as HAP This is not fit in the definition of HAP but it can also be considered as HAP. The aircraft will circle above commercial airline traffic to serve as the hub of communication network. It has average flight duration of several hours due to fuel constraints and human factors as in fig.3 Fig. 3: 3. HAPS APPLICATIONS: 3.1 HAPS Broadband Fixed Wireless Access One possible application of HAPS is fixed, broadband wireless access (BWA), which provides potentially very high data rates in terms of mega bits per second. The spectrum allocation for HAPS worldwide for the provision of BWA services consists of a pair of 300MHz bands in the 7/48GHz band, although the 28/31GHz is also specified in much of Asia. Many services can be provided, including but not limited to T1 access, ISDN access, web browsing, high-resolution video conferencing, large file transfers, and Ethernet LAN bridging. A BWA communications system typically supports various types of user terminals fixed, portable and mobile. The typical bit rate of the access link is a few Mbps for most fixed and portable terminals, while a several hundred Mbps link is available for limited fixed terminals with antennas larger than typical ones. As BWA communications systems operate in the millimeter wave band, the size of the antenna in the terminal can be made as small as several centimeters in radius. A number of HAPS may be deployed in a network to cover an entire region. Inter- HAPS optical links may used to interconnect a number of platforms for greater area coverage. 3.2 High Altitude Platform Station UMTS In addition to broadband wireless access at 47/48GHz and 28/31GHz, ITU has also endorsed the use of HAPS in the IMT- 2000/UMTS spectrum for the provision of 3G mobile services. HAPS UMTS systems will use the same RTTs and provide the same functionality and meet the same service and operational requirements as traditional terrestrial owner-based UMTS systems. The HAPS systems can be designed to serve as the sole station in a stand-alone infrastructure (essentially, replacing the tower base station network with a base station network in the sky ) or can be integrated into a system that employs traditional terrestrial base station towers, satellites and HAPS. A terrestrial mobile system using HAPS supports most of the same environments as traditional networks. 3.3 High Altitude Platform Station Although the delivery platform for HAPS (base stations consolidated on a geostationary platform in the stratosphere) is very different from traditional systems (base stations distributed on towers and rooftops), the mobile network operates in the same fundamental manner transparent to the user. Only very small Pico-cell (< 100m) and indoor highspeed operations are not supported by HAPS. Although comparable in many ways to traditional terrestrial systems, the HAPS system offers certain additional features. Firstly, single HAPS can serve a footprint that extends over an entire 500km radius footprint. Secondly, the delivery of service from the stratosphere enables a softer handoff operation from cell to cell. All the cell antennas in the system are collocated on the platform thereby eliminating the need to use time delay correction to synchronize the codes used by the beams involved in the handoff operation. Thirdly, the system executes handoff operations in several chip times thereby enabling service to extremely fast moving vehicles. Fourthly, dynamic beam assignment allows the system to provide service to traffic hot spots throughout the footprint and also enables point-to-point high speed coverage throughout the coverage area. Lastly, the HAPS system provides an improved radiation pattern for beams than the R x law (x 4) used by terrestrial base station antennas. This may enable higher spectrum efficiency across the entire coverage area since other cell interference is greatly

3 A Most Promising HAPs Technology for Next Generation Wireless Communication Systems reduced. The HAPS system can employ joint-detectiondemodulation or interference cancelling for both intra-cell interference mitigation and adjacent cells to achieve even higher spectrum efficiency. 3.4 High Altitude Platform Station for DVB or DAB: DVB-T has started in operation. DVB-H, handheld version of DVB-T, has been demonstrated in Oxford, UK. Similar to any other terrestrial-based wireless systems, the reception quality of DVB-T and DVB-H is highly dependent on the terrain. To reduce the percentage of outage Areas (blank spots), higher communication link margin and/or higher tower and/or larger number of towers are required. HAPS located at high altitude could potentially be used as an alternative solution for DVB/DAB repeater/transmitter. Sky Tower has proven that delivering broadcasting services over HAPS requires much less power. From the test, Sky Tower shows that it requires only 1w transmit power for HDTV compared to 1000 watt in terrestrial system. A feasibility study of HAPS-DVB/DAB has been conducted also by ESA under STRATOS project. 4. FREQUENCY ALLOCATION: The ITU-R has wide ranging activities concerning spectrum regulation for HAPs. A number of frequency bands have been specified by ITU-R for HAPS [8], and these are included in the successive WRC resolutions: /47 GHz 300 MHz bandwidth in both directions worldwide /28 GHz revised at WRC 07 to 300 MHz in both directions for use in over 40 countries worldwide (include all countries in North and South America but excluding all of Europe) GHz worldwide to support IMT-2000 from HAPS GHz is also under consideration as a WRC 11 Agenda item for Gateway link use for IMT-2000 use. 5. MAJOR PROJECTS OF HAPs WORLDWIDE: 5.1 StratXX AG X-Station This project is developing a solar powered airship based HAP, the X-Station [9]. They are striving to commercialize stratospheric communication platforms through the innovative application of advanced technologies, including the rapid provision of communications systems using HAPs in regions currently not well served or lacking infrastructure. They plan to deploy a number of services on their platform, capable of providing, TV and radio, broadcast, mobile telephony, Voice over Internet Protocol (VoIP), remote sensing and local GPS. To date they have developed lower altitude airship-based platforms, including PhoeniXX and XBUGS, and a photograph of one of their airships in development is shown in Figure 4. The test program involved testing both the craft and the communications and remote sensing payloads. StratXX is located in Switzerland, and it uses a number of European strategic partners from industry and academia, including CSEM (Switzerland), DLR (Germany), EPFL (Switzerland), RUAGAerospace (Switzerland), and University of York (UK), as well as its own in-house expertise. Fig CAPANINA The European Commission supported the CAPANINA project (FP6-IST ) [10] as part of the 6th Framework Programme, to further develop the state of-the-art in broadband from aerial platforms. The project ran from November 2003 until January 2007, involving a consortium of 13 partners, representing a mixture of large industry, SMEs, and academia/research organisations. The aim of the project was to exploit this future wireless technology to deliver burst data rates to users of up to 120 Mbps anywhere within a 60 km coverage area. Both mm-wave band and free space optical communications technologies were considered. The project adopted a three-strand approach: Identification of appropriate applications and services and associated business models. This included establishing the most appropriate integrated network architectures, and included wireless and free space optical link technologies, and multiple platform technologies and spectrum sharing The development of a system testbed that allowed nearer-term tests of broadband services/applications to fixed users, including backhaul for terrestrial WLAN, corporate communications and video-on-demand, along with an evaluation of free space optical technology Longer-term state-of-the-art research and innovation that examined advanced mobile broadband wireless access. Outline system design and critical hardware was developed for a scenario that delivered broadband to trains, integrating with on-board wireless LAN base stations.

4 (Fig. 5) 5.3 HeliNet One of the early HAP projects was HeliNet (IST ) [26, 27], which ran between January 2000 and March 2003 funded by the European Commission s FP5 programme. The project examined aeronautical issues and three prototype applications: Broadband telecommunications; Environmental monitoring; and Vehicle localisation. A design for a scale size prototype stratospheric aircraft, Heliplat, was developed and key components built. 5.4 Angel Technologies HALO Angel Technologies developed a manned stratospheric plane in the late 1990s. It was planning to deliver continuous services to users using a fleet of these craft that would have mission duration of 8 h, where they would circle above the coverage area. The project is not thought to be currently active, and was almost certainly a casualty of the dot.com boom and bust. One of the main reasons for inactivity could be down to the fact that the business model was not appropriate to the type of HAP vehicle. Such a vehicle may be much better suited to shortrange missions, such as event servicing and disaster relief. Fig COMPARISON OF HAPS: HAPS do not require any launch vehicle, they can move under their own power throughout the world or remain stationary, and they can be brought down to earth, refurbished and redeployed. Once a platform is in position, it can immediately begin delivering service to its service area without the need to deploy a global infrastructure or constellation of Platforms to operate. HAPS can use conventional base station technology - the only difference is the antenna. Furthermore, customers will not have to use different handsets. The relatively low altitudes enable the HAPS systems to provide a higher frequency reuse and thus higher capacity than satellite systems. The low launching costs and the possibility to repair the platforms gateway could lead to cheap wireless infrastructures per subscriber. Joint venture companies and government authorities located in each country will control the Sky Station platforms serving their region to ensure the best service offerings tailored to the local market. Offerings can change as a region develops. Each platform can be retrieved, updated, and re-launched without service Interruption. 7. PROBLEMS IN IMPLEMENTING HAPS: 7.1 Energy Source: HAPs station usually need to take off, fly, landing, correct the position and all these movement beside for airships as well as for aircraft, the movement is a problem to be faced. Aircraft usually fly on a tight circle (about 2 km radius or more), while airships can theoretically stay still and they only need to compensate for the winds. The ITU has specified that HAP should be kept within a circle of 400 m radius; with height variations of +700 m. GPS can play an important role in the precise positioning of HAPs. The ability of HAPs to maintain position reliably in the face of variable winds is a major challenge Antenna The antenna system is one of the most critical performance factors in a HAPs configuration. It is summarized below: The payload equipment consumed power. So the choice of energy source is a fundamental issue. One approach concerns sending energy from the earth in the form of microwave beams.however, the transmission efficiency is low, the cost of the ground station is quite high, and the radiation to other flying objects can be considerable. Another alternative is to carrying fuel reserves on the board. In this case the platform becomes heavy and expensive beside the bad environmental impact due to the gases exhausted by engines. Capturing solar energy is one of the solutions used by numbers of proposed projects. At higher latitudes both the variation in the angle of the sun relative to the solar panels between summer and winter, and the short winter days will limits the power. Large and heavy stored batteries which used to store the power during days and used at night have an additional significant effect payload with electric power. At very low altitudes around 5 km, we can use a cabletether to supply onboard systems and the Communication

5 A Most Promising HAPs Technology for Next Generation Wireless Communication Systems backhaul may also be provided through the tether via fiber optic link. 1. A large number of spot beams will be required; these may be produced either by a multi beam antenna or some form of phased array. 2. Use of high radio frequency in order to secure a sufficient bandwidth. 3. Directional antenna with a high gain to cope with attenuation in high frequencies. 4. Reduced weight, size, and power consumption of the mission payload. 7.3 Diversity Propagation from HAPs is not fully characterized at high frequency which allocated by the ITU for HAPs at 47/48 GHz worldwide and 28GHz in Asia. Rain fading, could cause serious degradations to some services. Real time services, such as TV and video streaming, would be most affected. So one of the main required is to develop rainfall attenuation, sandstone attenuation and scattering statistic. An important objective is to determine the most appropriate diversity techniques. Different diversity methods can be assigned to different traffic and user categories Handoff In mobile cellular schemes, handoff occur due to motion of the user, this is in contrast to HAPs schemes where handoff may occur due to platform motion which move the antenna beams. Delay for multimedia service may impose much more stringent constraints on the handoff process Interference Interference represents an issue of paramount importance for any communication system. The interference levels always affect the supported number of system users. In HAPs we can distinguish the following cases of interference paths: 1. Between HAPs ground stations and other terrestrial stations or satellite earth stations. 2. Between HAPs ground stations and satellites space stations. 3. Between HAPs on-board stations and other terrestrial stations. 4. Between HAPs on-board stations and space stations. 8. CONCLUSION HAP is a very good technology, through implementing, the way by which we can have benefits of both the satellites and terrestrial networks. And that s why the new era is absolutely of HAPs. By using some techniques shown above, we can implement it easily and use it in efficient way by reducing the problems which are challenges yet but the scientists will definitely reduce it in the nearby future. The main advantage of HAP is that it is not replacing the existing technologies of satellite or terrestrial networks but it is complementing it. But we can believe that, we will overcome by all the difficulties in the nearby future and the above shown some projects will soon come in working in real world. At last, 4G technology is also coming in existence in mobile communication technology mostly up to year 2012 and we can also take help of HAPs technology to improve it in real manner, so that s why the future of this technology is very bright ahead. 9. FUTURE SCOPE HAP is a good technology to be implemented. When 4G will come into existence near about 2015, at that time HAPs will be used in a real manner at large scale. Researchers must make HAPs technology compatible with 4G technologies like LTE, WiMAX networks etc., so that more and more people can get its use because A HAP can provide its service more, covering a very big area than that of covered by a single base station at a time. REFERENCES [1]. S. Karapantazis and F. Pavlidou "Broadband Comm. via High-Altitude Platforms: A survey "IEEE Communications Surveys & Tutorials, First Quarter 2005 vol.7, no. 1. [2]. T. C. Tozer and D. Grace, "High-Altitude Platforms for Wireless Communications," IEE Electronics & Com. Eng. J, vol. 13, no. 3, June 2001, pp [3]. G. M. Djuknic, J. Freidenfelds, and Y. Okunev, "Establishing Wireless Communications Services via High Altitude Platforms A Concept Whose Time Has Come," IEEE Com. Mag., vol. 35, no. 9, Sept. 1997, pp [4]. E. Falletti et al., Integration of a HAP Within a Terrestrial UMTS Network: Interference Analysis and Cell Dimensioning, Wireless Pers. Comm., Kluwer, vol. 24, no. 2, Jan. 2003, pp [5]. S. Karapantazis and F.-N. Pavlidou, "The Role of High Altitude Platforms in beyond 3G Networks", IEEE Wireleess Communications, pp , Dec [6]. Z. Elabdin et ai., "High Altitude Platform for Wireless Communications and Other Services", Proceedings of the International Conference on Electrical and Computer Engineering 2006 (lcece '06), pp , December [7]. A. Widiawan and R. Tafazolli, "High Altitude Platform Station (HAPS): A Review of New Infrstracture Development for future Wireless Communications", Wireless Personal Communications, 42: , [8]. ITU Recommendation ITU-R F.1500, Preferred Characteristics of Systems in the Fixed Service Using High Altitude Platforms Operating in the Bands GHz and GHz, International Telecommunications Union, Geneva, Switzerland, [9]. StratXX AG Website, [10]. D. Grace, M. Mohorcic, M. H. Capstick, M. Bobbio Pallavicini and M. Fitch, Integrating Users into the Wider

6 Broadband Network via High Altitude Platforms, IEEE Wireless Commun., October 2005, Vol. 12, No. 5, pp