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ANTIUM Informe resumido

Project ID: IST-2000-26222
Financiado con arreglo a: FP5-IST
País: France

Space-time algorithms for DVB-T synchronisation, channel estimation and TPS demodulation

During the deployment of a new DVB-T network, the network operator has to check that it does not generate interference on the existing networks. If it is the case, it must identify the transmitter that generates this interference. This identification issue will become more difficult and critical with the densification of the DVB-T networks since on the one hand the number of DVB-T signals that may interfere will increase, and on the other hand, when we consider a portable reception, there is a multi path environment with no direct path from the transmitter to the receiver. When we consider a classical configuration for the DVB-T signal such as the 8K mode, a guard interval of 1/32 and a 64 QAM constellation with a code rate of 2/3, the objective is to detect and to identify all the DVB-T signals that are in a given channel for C/I down to -20dB.

To reach this performance, a multi-antenna receiver is mandatory and space-time algorithms have been developed in the field of the ANTIUM project:
- The first step of the ANTIUM receiver consists in detecting all the DVB-T signals that are present in a given channel, and in doing the coarse-time synchronization, which corresponds to find for each of them the beginning of the useful part of the OFDM symbols. This is achieved by doing at each instant the correlation between a reference sequence and the output of the spatial filter matched to this reference sequence. When this statistics is higher than a pre-determined threshold, the detection is effective. Moreover, the reference sequence we have chosen also provides the location of the scattered pilots.
- The second step consists in doing for each detected signal the OFDM demodulation (FFT of the useful part of the OFDM symbols) on each antenna and in doing the channel estimation. A new channel estimator, able to deal with co-channel interference, has been designed. After a preliminary rough estimation, at the scattered pilot location, of the channel in the time-frequency domain, the estimation is transformed to the time-delay domain where a parametric model is considered. The estimation is then improved using a MMSE algorithm based on the estimated statistics of the channel. This channel estimation allows providing an estimation of the level of the considered DVB-T signal as well as its SINR.
- The last step consists in demodulating the TPS bits for each detected DVB-T signal. The TPS provides some information and more specifically the Cell_id, which is an identifier of the cell to which the transmitter belongs. To achieve a reliable TPS demodulation even for C/I down to -20dB, MMSE space-time combining is used and we take profit from the frequency diversity of the TPS.

All these algorithms are detailed in the D3031b deliverable. They have been implemented in the ANTIUM demonstrator, and their performance have been assessed not only by simulation, but also with lab tests and during field trials whose results are detailed in the D5021 deliverable.

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Denis MASSE, (R&D expert)
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