摘要:
A multi-carrier transmission system, for example a DMT system. Channel information is transmitted between two transceivers using a plurality of subcarriers. Each subcarrier, or symbol, has a parameter associated with it. The transceivers are adapted to transmit the channel information as a sequence of n groups in which each of the n groups contains information concerning the number of adjacent subcarriers which have the same value as the parameter, together with the actual value of the parameter. The parameter which may have a plurality of discrete values, may be a bit-loading value, or a QAM constellation identifier.
摘要:
A multi-carrier transmission system, such as a DMT system. A receiver must be able to recover a sampling clock that is very accurately synchronized to a transmitter sampling clock. Typically, synchronization is achieved by using a reserved carrier, the pilot carrier, which is transmitted with a fixed phase. The receiver sampling clock is then phase locked to the pilot carrier. Frame timing can be recovered by using a correlation technique. Thus an improved method of recovering a sample clock and phase locking the sampling clock to a pilot carrier is provided.
摘要:
A multi-carrier transmission system has a plurality of transceivers, each having a receiver and a transmitter. Data is transmitted between the transceivers by modulating the data onto a multiplicity of carrier waves in the form of multi-bit symbols, wherein each carrier wave constitutes a channel, and wherein the number of bits per symbol (the bit loading), varies between channels and, within a channel, with time, so that each channel has associated therewith a bit loading parameter. In operation, the multi-carrier system is adapted to synchronously update, at the transceivers, the bit loading parameters associated with each channel by transmission of data over a control channel, in that the control channel is established, at system start-up, on a predetermined one of the multiplicity of carrier waves whose identity is known to the transceivers, and in that the control channel is, after start-up, changed from the predetermined channel to a further channel, selected by the first transceiver on the basis of channel characteristics.
摘要:
A transmission system using nQAM. A control channel is superimposed on a nQAM data channel. It is desirable to separate control channel data from user data without using a higher level protocol layer. In multi-carrier systems with variable bit-loading it is particularly desirable that the control channel data be separable from user data when the value of n. that is the bit-loading, or constellation identifier are unknown. Binary data is transmitted using nQAM modulation. The binary data includes both user data and control data. This means that a control channel is superimposed on a user data channel within the same nQAM constellation. Separation of the control data is facilitated by arranging control data points to have either a unique phase or unique amplitude values. These unique values are not employed for user data points.
摘要:
A multi-carrier transmission system. A received multi-carrier signal is sampled and digitized before FFT processing. Multi-carrier signals consist of many narrow band carrier waves which convey data via a wide band channel. The amplitude distribution of the sum of all the individual carriers is Gaussian. This means that high amplitudes occur with low probability. At the present time, analog to digital converters have a limited dynamic range. It is therefore normal practice to provide a compromise between cutting and quantization noise. The adverse affects of a course quantization have to be balanced between signal distortions caused by the loss of the low probability high amplitude signals.
摘要:
A multi-carrier transmission system using orthogonal carriers with high order QAM constellations for the transmission of a plurality of bits per carrier and symbol. The system uses some method for the determination of an inverse channel model to be used in the equalization process. In the frequency domain, this is normally based on an estimate of the channel attenuation and phase for each carrier. A simplified method of equalization is provided which uses data at the symbol carrier input and output to adaptively estimate an inverse channel model.
摘要:
A multi-carrier transmission system using DMT. It is known to recover a receiver sample and clock from a reserved carrier, a pilot carrier having a fixed phase. A sampling clock oscillator in a receiver is then phase locked to the pilot carrier. Multi-carrier receivers, such as DMT receivers, are normally equipped with an FFT processor. A complex number representing the pilot carrier is then available from the FFT processor output. If an FFT processor is not available, a one frequency DFT processor can be provided to produce a complex estimate of the pilot carrier. In a DMT system, frame synchronization is handled separately from sampling clock synchronization, although the two processes are intimately related and frame synchronization must be acquired before sampling clock synchronization.