Abstract:
The present invention relates to a receiver for use in an OFDM type transmission system, in which data is transmitted in frames. Each frame has a cyclic prefix which is a repetition of part of the frame. Control means are provided and the control means controls a sampling oscilator. The control means include estimation means for estimating timing deviations of the sampling clock. The estimation means operates entirely on frequency domain input data.
Abstract:
Modern multi-carrier transmission systems, using orthogonal carriers with high order QAM constellations for the transmission of multiple bits per carrier and symbol, place high demands on the synchronisation of the receiver with the transmitter. The maximum permitted deviation from exact synchronisation is usually a small fraction of a sampling interval. A reserved carrier, the pilot carrier, which is given a fixed phase, is usually used as the reference to achieve this high accuracy. The receiver sampling clock oscillator is phase-locked to the pilot carrier. It is, therefore, necessary to estimate the phase of the pilot carrier. Using a bandpass filter to recover the pilot carrier, regardless of the frame structure of the DMT signal, does not eliminate the influence of neighbouring carriers on the pilot carrier.
Abstract:
Modern multi-carrier techniques using orthogonal carriers with high order QAM constellations for the transmission of a plurality of bits per carrier and symbol, use some method for the determination of an inverse channel model to be used in an equalisation process. In the frequency domain, this is normally based on an estimate of the channel attenuation and phase for each carrier. The present invention provides a simplified method of equalisation that uses data at the symbol detector input and output to adaptively estimate an inverse channel model.
Abstract:
In a two-way multi-carrier transmission system, such as a DMT system, in which there can be dynamic changes in the transmission parameters, some means must be provided for maintaining synchronisation between transmitter and receiver when the transmission parameters change. The first stage of such a process requires that changes of parameter be notified by one transceiver to the other, involved in an active communication process, over a slow transmission channel, the control channel. Subsequently the synchronisation of the transceivers is adjusted simultaneously, i.e. from a predetermined DMT symbol. Such adjustements in time synchronisation must be achieved with a minimum of overhead.