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Last Update: 06 Feb 2008
Mobile Satellite Systems and Services

Feasibility Study of a Mobile Ku-band System


   

Objectives

The objective of this study was to analyse the technical feasibility of Ku Band Broadcasting to mobile users making use of end of life satellites. One very interesting aspect of this approach is the low development cost for the space segment.

The effort during the study was devoted to defining very low cost terminals. The study results included the identification of the regulatory aspects, the services offered to users and the general system architecture. System performances analyses were consolidated through detailed propagation analysis (including simulations and measurements results) of the Ku band channel and different waveforms were investigated to outline system capacity which are ranked according to the waveform selection and antenna performances.

System recommendations have been issued from these trade-off analyses and a preferred concept has been proposed for the receiver and antenna architecture taking into account the system transmission infrastructure (interleaving, signal spreading, use of FEC in different layers, etc.). The final part of this study was concerned with the high level specifications for both user antenna and receiver and the definition of an associated development plan for the next phases keeping in mind the low cost objectives for mass market applications.

Features

The following figure presents a candidate architecture using end of life Ku-band GEO satellite for mobile applications. This end-to-end system architecture is composed of:

1. A contribution segment (CS) aiming at delivery multimedia content through a distribution/contribution network to the GW cache server.

2. A ground control segment (GCS) aiming at controlling the satellite operation and managing the resource allocation.

3. A gateway segment (GS) including cache server and the gateway feeding the satellite.

4. A satellite segment (SS) with a single end-of-life Ku-band GEO satellite in nominal and a second satellite ensuring time/space diversity, if required.

5. A user terminal segment (UTS) defined either as an individual receiver or collective receiver configuration.

6. An optional gap-filler segment (GFS) either on existing terrestrial infrastructures (T-DAB or T-DVB) or dedicated retransmission segment to provide reliable communications over dense urban/suburban areas.

7. An optional GPRS/T-UMTS cellular network allowing mainly interactive services.

Project Plan

The study has been completed.

Challenges

The ESA Mobile Feasibility Study has allowed the analysis of a complete system including all contributing segments. One main assumption from the beginning of this study was to make use of existing satellites or more precisely to take benefit of very low cost space segments using end of life satellites of the Ku Band fleet. A major challenge and the critical item for the system is the Dedicated Received Box (D.R.B.) including antenna and receiver. The other segments can take benefit of existing hardware (ground segment, satellite segment) or of synergies with existing technologies (push and store approach for the hub, carrousel mechanisms, FEC mechanisms at transport layer, T-DAB/T-DVB terrestrial repeaters if necessary in urban zones, etc.).

One major issue concerns the antenna which has to cope with tough constraints from an electronic and mechanical point of view: very small size is requested for car implementation, while on the other hand sufficient gain and G/T performances are requested to provide attractive services.

Another key feature concerns the Dedicated Receiver Box that must integrate the following functions at a very low cost for a mass market application:

  • a digital receiver dedicated to receive the satellite signals 
  • MMI functionality to access the contents (radio receiver + cache server means + physical interface to connect the MMI) 
  • An optional wireless interface to connect to 2G/3G handset to provide interactive services.

Therefore the main challenges that have been outlined in the proposed development plan concerns: 

  • the uplink station aspect including the cache server and hub functionality
  • the D.R.B. including receiving antenna, receiver and associated interfaces with the in car MMI

Benefits

As the intention is to make use of end of life satellites, one very interesting feature of the analyses performed during this study has been to demonstrate parametric values for the achievable capacity, taking into account realistic satellite EIRP and choosing a large panel of potential air interfaces.

The situation in certain cases is such that for specific waveforms we could achieve several hundred of kb/s throughput per transponder. Assuming a reasonable number of active transponders in operation, this leads to several Mb/s capacity per satellite.

Therefore, the system in Ku band could really compete against projects that use different technologies such as: S-DAB, T-DAB, S-DVB, T-DVB. Systems based on end of life Ku band satellites could be proposed to offer a large class of services and will also take benefit of techniques available to improve quality of reception such as interleaving at radio layer or FEC techniques at transport layer.

Once the challenges associated with the car antenna and receiver are solved, the system can be operational immediately due to the Ku band transponder capacity in orbit and at a very low deployment cost.

What we can say is that a real business opportunity is in front of us and the Ku Band broadcast/multicast system can be a very attractive low cost concept for applications like: 

  • NRT services 
  • QRT services Low data rate streaming services

Current Status (dated: 28 Jan 2003)

The first months of the activity were dedicated to market and services analysis to be able to define mission recommendations to support a system definition and following analyses.

An important part of the study was the analysis of the Ku band propagation channel. This task consisted in simulating the channel for different typical end user scenario. The analysis was also supported by a test campaign in Ku band during which important parameters were measured and identified. After these computations, signal availability was determined and theoretical throughput was defined. From above it was stated that the urban situation is very critical without the addition of terrestrial repeaters.

A system definition was proposed and system performances were analysed according to trade-off investigation for the selected waveform. Four waveforms were investigated parametrically and the results are available for different scenarios and different user speed. System throughput and synchronisation have been largely discussed. Recommendations were proposed in the trade-off evaluation and two candidates were maintained: W-CDMA and a proprietary air interface with additional criteria being necessary to definitely select the most appropriate concept solution.

After six months study, a general system review enabled the selection of the antenna design and the waveform: complexity/availability/development cost being integrated in the selection.

The last study months were dedicated to a final iteration in the antenna design, the definition of the modulator and the user terminal and to outline the development plan for the equipment.

A final review was held in presence of the two teams by the end of year 2002. This review proved constructive in terms of merging ideas and proposing the scheme for the next phases.

Presently, ESA is preparing the next activities that consist in User Antenna Development and User Terminal Development and the expected schedule is to issue the ITTs by first quarter of 2003.


Last Update: 06 Feb 2008
 
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