Lsi Logic Corporation

Andrew Corporation

Steven Richard Ring

Peter Kenington

Richard Michael Bennett

A lineariser () for reproducing distortion present in the output of an amplifier () (or other signal handling device) generates a predistortion signal from the amplifier input. The predistortion signal is mixed into the amplifier input signal using, for example, a vector modulator (). The predistortion signal may be derived in a quadrature format, the orthogonal components of the predistortion signal being mixed into separate mixers of the vector modulator. The predistortion signal is generated by multiplying the input signal with itself repeatedly to generate components of distortion which are susceptible of independent control. The predistortion signal is generated digitally using DSP (). A multiplier or mixer may be used to square the sampled input signal to produce a reduced frequency signal which the DSP can use to gennerate the predistortion signal. Another lineariser mixes the predistortion signal into the input signal during up conversion.

Lineariser for a signal handling apparatus

The input and output of amplifier () are sampled and downconverted in frequency and filtered at (and) to produce sub-band signals. The input signal sub-band () is then subtracted from the output signal sub-band () at () to produce a residual signal () containing any distortion present in the sub-band selected by the downconversion oscillator (). Signal analyser () compares the input and output signal energy to deduce the amount of distortion in the output signal, to provide signals for controlling a distortion reduction mechanism such as a predistorter operating on amplifier (). Alternatively, the input signal sub-band () and the output signal sub-band () are Fourier transformed (and) to produce spectrums which can be analysed to determine the presence of distortion in the output of amplifier ().

Distortion detection for a power amplifier

Phase shifting network ( ) predistorts the input to non-linear amplifier ( ) to counteract AM-PM distortion. The input signal is sampled at ( ) and its amplitude is detected at ( ). The amplitude signal is then used to index a lookup table ( ) which contains corresponding data for controlling the phase shifting network ( ). The input signal may be digital and the phase shifting process may be implemented in the digital domain.

Distortion reduction

In a multi-directional orthogonal frequency division modulation (OFDM) communication system, for example, on a digital subscriber line, an uplink channel is provided by a first group of the OFDM sub-channels (sub-carriers), and a downlink channel is provided by a second group of the OFDM sub-channels (sub-carriers). In one aspect, communication efficiency is improved by controlling the relative number of sub-channels allocated to each group, and hence controlling the capacity of the channels dynamically. Preferably, the relative capacities are controlled in response to demand for channel capacity. In another aspect, the orthogonality of the sub-carriers generated by different transmitters is improved by providing a frequency and/or time synchronising signal for providing reference frequency and timing. In a further aspect, multiplex communication over a network between three or more stations is provided by distributing the OFDM sub-channels (sub-carriers) between the stations to provide three or more channels within the OFDM bandwidth.

Relating to multidirectional communication systems

In a multi-directional orthogonal frequency division modulation (OFDM) communication system, for example, on a digital subscriber line, an uplink channel is provided by a first group of the OFDM sub-channels (sub-carriers), and a downlink channel is provided by a second group of the OFDM sub-channels (sub-carriers). In one aspect, communication efficiency is improved by controlling the relative number of sub-channels allocated to each group, and hence controlling the capacity of the channels dynamically. Preferably, the relative capacities are controlled in response to demand for channel capacity. In another aspect, the orthogonality of the sub-carriers generated by different transmitters is improved by providing a frequency and/or time synchronizing signal for providing reference frequency and timing. In a further aspect, multiplex communication over a network between three or more stations is provided by distributing the OFDM sub-channels (sub-carriers) between the stations to provide three or more channels within the OFDM bandwidth.

Multidirectional communication systems

An analogue to digital converter system for digitizing a stream of analogue symbols, the analogue to digital converter system includes an analogue to digital converter for sampling the symbols at predetermined sample timings and a feedback loop for adjusting the sample timings. The feedback loop includes an eye opening detector connected to an output of the analogue to digital converter and responsive to successive digitized symbol samples to determine eye opening signals. The eye opening detector includes a deviation detector for determining a deviation signal representative of a deviation of a digitized symbol sample value with respect to a mean sample value. Preferably, a variance measurement calculator calculates the variance of these deviations. A feedback control is responsive to successive eye opening signals to generate timing control signals for adjusting the sample timings. The deviation detector can employ a fixed means sample value or can determine the mean sample value from a plurality of digitized sample values over a predetermined period. A variance calculator calculates a variance signal representative of a variance of a deviation signal value with respect to a mean deviation value. The variance calculator can determine the mean deviation value from a plurality of digitized sample values over a predetermined period. Successive variance values form the eye opening signals and an eye opening signal is output in response to each digitized symbol sample.

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Bristol, United Kingdom

Steven Richard Ring