Delivery of Broadband to High Speed Vehicles

Delivery of broadband services to high speed vehicles from aerial platform network, essentially based on state-of-the-art mobile broadband wireless access system, is most future oriented part of the research and innovation work in CAPANINA project.

It is concentrating on a scenario of delivering broadband to trains equipped with a collective terminal interfacing with on-board wireless LAN base stations.
This scenario is graphically depicted on the right, where the main issues to be investigated are also identified.
high speed vehicles delivery scenario
Detailed Overview of the train scenario.
(click to enlarge).

The main challenges in developing broadband wireless access system for high-speed mobile users with collective access lie in the definition of a suitable radio interface for a mobile user link, including the selection of the most appropriate modulation and coding techniques, development of resource and mobility management procedures, design of network and application layer protocols to support adequate quality of service (QoS), as well as the development of train antenna capable of fast steering to adapt to high-speed movement of the train.

The ultimate target of this scenario is to support data rates of up to 120 Mbit/s to vehicles travelling up to 300 km/h.

Propagation Impairments

While offering wide bandwidth and hence the potential to provide very high capacity the mm-wave bands assigned by ITU are severely affected by rain attenuation and scattering despite the relatively short and uncluttered links between mobile vehicles and a HAP.

The addition of the doppler effect and possibility of multipath transmission (caused by reflections) in the case of non-LOS operation on fast moving vehicles requires a detailed understanding of the propagation environment and characterisation of the propagation channel to support design of an efficient radio interface, as well as analysis of short-term rain outage mitigation strategies, such as time diversity and caching.

Due to lack of propagation measurements specific for the HAP operation environment the work is taking into account relevant measurements in satellite and terrestrial links, and is strongly based on the outcomes of the HeliNet project, which has carried out a detailed assessment of the rain attenuation mechanisms and how they affect fixed nodes.

Channel characterisation and verification will be supported by a series of measurements taken from the system testbed during the trail campaigns, and a suitable numerical channel model will be implemented as a FIR filter with time-variant coefficients including spatial information.

Radio Interface

The numerical channel model will be used for detailed analysis of suitability of modulation schemes and coding techniques proposed in selected candidate standards (i.e. QPSK, M-QAM, OFDM and concatenated Reed-Solomon and convolutional coding), similar to that done for the fixed wireless application in HeliNet project.

In addition, cutting edge technologies are explored including the use of MIMO as a platform diversity technique and advanced signal processing algorithms that
  1. minimise the processing power requirements,
  2. are computationally efficient, and
  3. cope with the high aggregate data rates and with the envisaged multipath/Doppler environment.
The performance gains of these technologies achievable for aerial platform applications will be assessed through the implementation of selected algorithms on a DSP platform.

Resource and Mobility Management

The combination of high-speed mobility and platform movement present a significant challenge for resource and mobility management in maintaining adequate communication links in the high speed train scenario, with rapid and frequent handover required to maintain adequate QoS for delay sensitive broadband applications.

Based on the resource management supporting broadband communications to fixed users, proposed in the HeliNet project novel resource allocation strategies are developed for both the user and backhaul links of a single HAP, to mitigate the effects of mobility and interference and provide both efficient spectrum utilisation and adequate QoS.

These strategies encompass resource and mobility management, i.e. interaction of channel assignment, medium access control, inter-beam and inter-platform handoff, caching, and prioritisation, and are designed to integrate in the selected broadband transmission standard.

Resource and mobility management procedures also have to provide suitable mechanisms, which guarantee required QoS level on the radio interface and mapping of QoS parameters on to the higher layers, similar as studied in the HeliNet project for the radio interface based on the IEEE 802.16 standard.