Partner und Internationale Organisationen
(Englisch)
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CEA-LETI (F),Mitsubishi Electric (F),ETHZ (CH), IMST GMBH (D), Institute for Telecomunications (P), Technical University Lisbon-IST (P)
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Abstract
(Englisch)
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The European third generation terrestrial mobile system (UMTS-UTRA) is currently being standardised. It aims at offering a large variety of services (circuit and packet services, low to high bit rates), as well as greater capacity and coverage compared to second generation systems (e.g. GSM). First commercial networks will be launched at the beginning of the year 2001 and will mainly provide basic UMTS functionality, using today's technology.
Despite the high capacity offered by UMTS, the expected demand is likely to outstrip the projected capacity. Therefore, the need to develop more advanced UMTS systems will be fuelled by capacity requirements and the need to offer customers more attractive features (2 Mbit/s services).
The objective of the project is thus to define and validate new concepts maximising link capacity of the UMTS standard. To achieve this task, it is foreseen to deeply evaluate new system architecture based on joint Smart Antenna (SA) concepts and Multi-User Detector (MUD) schemes. The work will start from the current specifications of UTRA for both FDD and TDD modes, in order to ensure a complete compatibility with existing standards.
The expected results of the project are the following :
· Improve link capacity of both FDD and TDD modes, by means of digital signal processing techniques : MUD and smart antenna techniques located both at the base station and the terminal.
· Optimise overall complexity of the transceivers (terminal and base station).
· Support of standardisation efforts.
According to ETSI evaluation reports, coverage is limited by the uplink. The only reason is that the available transmit power of a terminal is lower than the one of a base station. When downlink antenna diversity is applied, capacity is limited by the uplink for all but speech services. These limitations are caused by intra and inter-cell Multiple Access Interference (MAI). The project will focus on mitigating intra-cell interference.
Two classical solutions are used to face this problem :
· Multi-User Detectors do not regard interference as noise, but estimate and then cancel the influence of co-channel interference on the signal of interest. The resulting signal is less corrupted by MAI, thus improving performances.
· Smart Antennas algorithms allow the system to combat efficiently MAI through spatial discrimination of interfering signals on both up and down links.
Both techniques have been widely explored in the past years, but they have usually been studied separately. The main objective of the project is thus to define, implement and evaluate new solutions combining the potentialities of MUD and SA techniques.
To reach this objective, the project will develop a link level simulation platform, and increase the potentiality of a system simulator already built by a partner of the consortium. This methodology has been chosen in order to, first, validate the foreseen benefits of some concepts, and then check the capacity improvements. This will provide clear figures to compare different potential solutions.
The link level simulation platform, that will be will set up during the project, will model both up and down links of FDD and TDD modes. It will be used to compare on the same basis the proposed algorithms. It will be developed on a modular basis, including the following building blocks :
a new time-space channel model, which is mandatory to evaluate the benefit of joint MUD and SA algorithms. This model will be based on COST259 SWG2.1 recommendations.
Basic MAC layer functionality (e.g. power control mechanisms).
Synchronisation mechanisms : acquisition and tracking for the FDD mode, middamble detection and burst splitting for the TDD mode.
Implementation constraints : radio and antennas impairments, chip sampling, quantization effects.
The system simulator will evaluate capacity increase of both FDD and TDD modes. To perform this task, the interface between link and system level simulations will be carefully designed, in order to accurately model the influence of the proposed concepts.
In parallel to the task presented above, the project undertakes a more implementation oriented work. This consists in determining the overall complexity of the algorithms, and their sensitivity to system impairments (e.g. non-linear power amplifier, quantization effects). The objective of this work is to ensure an efficient implementation.
As many members of the consortium are involved in standardisation bodies (ETSI, 3GPP), results of the project will be used, if needed, to propose contributions to the standards.
The ASILUM project was a 2 year project and concluded in December 2001. The outcomes of the project in summary were· collection of directional channel measurements results from two field measurement campaigns· development of a wideband directional channel model (WDCM) (software simulation) that was validated against the measurements· study and implementation of a link level simulation platform (single cell simulation) for advanced 3G/UMTS receiver techniques with multiple antennas supporting multiple receivers using the WDCM.· study and implementation of a system level tool for evaluating the link level results at the system level (multiple cells) and reporting the improvement in cell size and cell capacity by using such advanced 3G/UMTS receivers.· documentation to 3GPP standardisation meetings to report the results · public release of documentation and research paper publication showing the resultsAccording to the Dec. 2001 final review the project achieved a 'successful completion' and scored an average result of 3.6/4, which is regarded as a very good score.In measurable terms the ASILUM project results are significant and indicate that large savings can be made in the number of basestations needed by 3G operators, only by changing the relatively inexpensive signal processing receiver units running in the basestations. This means operators can become profitable sooner. The work also showed that 3G service providers could reap large improvements in revenue compared to a normal network due to the additional capacity that interference cancelling receivers offer.Due to the success of the project, encouragement at the EC, and discussion with other partners Ascom is preparing to submit a follow-up EC project called TURBO-ASILUM. The aim is to research implementation methods and then build these receivers in real-time hardware to demonstrate the feasibility of the schemes.
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