Broadband Applications, Services and Infrastructure
The project will enable high rate communications (of up to 120 MBit/s) to be delivered directly to a user anywhere in line of sight of a HAP within a coverage area up to 60 km wide, making it economically viable to deliver services typically offered to big corporations, to users who may be marginalized by geography, distance from physical infrastructure, or those travelling inside high-speed public transport vehicles.
Such technologies complement future broadband infrastructure (either as backhaul or fronthaul communications), with a key requirement that such an infrastructure will seamlessly integrate with other delivery platforms (e.g. satellite, terrestrial) and standards, allowing (mobile and fixed) users to select the most suitable infrastructure and standards.
Applications and Services SelectionCAPANINA is specifically about HAPs providing two-way broadband communications to communities where it is not possible or not feasible to offer terrestrial alternatives such as xDSL. Examples of target communities are rural, mobile (such as trains) and disaster sites. But provision of broadband (say > 64 kbit/s) is not enough – it is also necessary to offer a compelling range of applications and services.
Typical services include:
In addition to the services, there is the question of connectivity. The position of the HAP in the end-to-end path can be, in order of decreasing per-user value:
Each of these scenarios has a value chain, with the top scenario having few but high value links and the bottom scenario having many low value links. Therefore the integration and automation of service provision and maintenance becomes more important as the use migrates towards the access network.
The final ingredient to this work is value chains, where for each scenario the revenue share and responsibility boundary is worked out, which in turn depends upon the size of the market that will be addressed.
This work is on-going, but initial results are that e-tainment, data networking and subscribed information are the three largest likely money earning services for HAPs and this will be evaluated for each of the roles and actors in the scenarios.
Aerial Platform Configurations and Spectrum SharingBesides using a single platform the potential of multiple HAP constellations combined with highly directional user antennas is also investigated to enhance capacity by means of overlapped or co-located regions of coverage and to exploit site diversity to increase service availability. In particular, the arrangement and number of aerial platforms has a considerable effect on the flexibility and eventual system capacity of such networks.
Recent work has highlighted the potential of allowing multiple high altitude platforms to serve a common service area, while sharing a common frequency allocation. A typical example is shown in below. Such configurations allow the system capacity to be increased incrementally over time. The technique works by exploiting the directionality of the user antenna (which is required in order to provide the link budget needed to deliver high rate broadband links). The directionality allows spatial discrimination to occur. A user points to the chosen HAP, with other HAPs sharing the same resources appearing as interference, normally in the side lobes of the user antenna ensuring that it is attenuated with respect to the wanted beam.
Such deployment techniques have both economic and technical benefits. From an economic perspective it means that initial coverage can be provided quickly and cheaply with just a single platform. When the platform becomes full (and the concept proven), additional platforms can be deployed tailoring the capacity to the needs of the market, and thereby removing the need for organisations to risk large amounts of capital by deploying a full constellation of platforms.
Such options could prove instrumental in kick-starting aerial platform technologies, especially in this risk averse climate following the Iridium and 3G financial setbacks. The technology benefits are twofold:
It is expected that these will be made up of a combination of mm-wave and free space optical links, which are discussed in more detail later. It is also expected that such connectivity will enhance the ability of delivering spatial diversity as a way of overcoming outages to rain (mm-wave links) and cloud (free-space optical links).
This work will also assist the spectrum sharing work underway as part of the project. The ITU has assigned frequency allocation in the 47/48 GHz bands for use on a worldwide basis and 31/28 GHz to up to 40 countries worldwide.
Europe is currently excluded from the latter allocation due to inadequate spectrum sharing studies being carried out in Europe taking into account the concerns of the terrestrial broadband fixed wireless access operators that share the same bands. Currently, the ITU defines a coordination distance, which it defines as the minimum distance two operators must be separated before they can share the same allocation.
Such definitions are no longer appropriate for situations where users have high directionality, and where appropriate levels of interference can be tolerated. Interoperability issues will be examined to determine the viability of the coexistence of HAP systems with other terrestrial and satellite technologies.
Such technologies will require an appropriate link transmission standard. HeliNet established that no single standard was appropriate to a HAP architecture, but for transmission to fixed users the IEEE 802.16 was the most appropriate.
CAPANINA will examine in more detail the most appropriate radio resource management and handoff schemes that will be required to deliver broadband from a moving multi-cell platform, when part of the multiple platform configuration.
End-to-end networking and interworking with other technologies will be of paramount importance when delivering broadband. Users will wish to see a common set of applications, services and configurations when they are in the office, at home in a rural area, or on board a high-speed train.
These issues will be tackled here, and a network architecture that maintains diverse quality of service requirements will be developed based on existing/future standards such as IPv6. This will be based on work undertaken in HeliNet that considered network provision for the fixed user applications.
Optical Link CapabilityOptical communications will considerably enhance platform - network (backhaul) and inter-platform communications. HeliNet identified that one of the main constraints of HAP communications systems is dealing with the aggregation of traffic (up to 14 Gbit/s per platform). To cope with this amount of traffic will require 10-12, mm-wave, backhaul ground stations over the coverage area. For the sake of cost/environmental impact the objective is to limit the number of backhaul ground stations.
Optical communication systems will allow data rates in excess of that available using mm-wave bands based links (622 Mbit/s up to 2.5 Gbit/s per link is under development).
Additionally, inter-platform links can replace terrestrial infrastructure (or be used in areas where no infrastructure exists) and ensure that configurations of multiple platforms can realise their full potential in terms of capacity per sq km. Inter-platform links, the major application for optical communications, will not suffer outages due to rain/cloud as they will be used well above cloud height (a HAP will be situated at altitudes between 17-22 km).
Even the worst case cloud ceiling of 13 km for midlatitude locations still allows link distances between 450 and 680 km without limitations subject to appropriate pointing and stabilisation.
Optical inter-platform links can help to deliver spatial diversity and as such enhance platform – ground backhaul availability in clear air conditions (cloud cover diversity). E.g. if it is cloudy at one platform site, traffic can be diverted to a clear site and backhauled to an alternative ground station and on into the network.
Additionally, HAP-network backhaul optical links can be used to augment, but not replace, the mm-wave backhaul links for connection the ground station. Optical links can only be used in non-cloudy conditions and hence will have a lower availability than the corresponding mm-wave links for that case.
CAPANINA is also examining the potential of non-mechanical beam steering. Initially numerical simulations are being used, and a selection of options are being compared assuming a selection of 2D phased arrays of lasers, optical amplifiers, or phase (electro-optical) modulators. Additionally, the compatibility of non-mechanical beam steering with modulation at GHz rates will be assessed, allowing a pointing and tracking system (PAT) design recommendation to be made.
Whereas current free space optical systems work at near-IR wavelength, the feasibility for the HAP application of using a quantum-cascade based infrared source operating in the mid-IR atmospheric window of 5 – 8 µm will also be assessed.
A possible receiver construction to work with such a transmitter, and the applicability of non-mechanical PAT design in this wavelength range will be developed.