Multiplex communication
First Claim
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1. A signal broadcasting RF transmitter apparatus comprising means for generating an RF frequency-multiplexed signal comprising a plurality of frequency-spaced subcarriers in a band, characterised by means for periodically inserting data specifying the subcarriers present onto a first, predetermined, subcarrier.
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Abstract
An OFDM communications system comprises broadcast providers 400, earth stations 100, repeater satellites 200, and receivers 300 (for example mobile receivers). The size of the multiplex can be increased by adding extra channels. Two channels are provided, on the in phase and quadrature components of each subcarrier.
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Citations
94 Claims
- 1. A signal broadcasting RF transmitter apparatus comprising means for generating an RF frequency-multiplexed signal comprising a plurality of frequency-spaced subcarriers in a band, characterised by means for periodically inserting data specifying the subcarriers present onto a first, predetermined, subcarrier.
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14. A frequency-multiplexed RF signal comprising a plurality of frequency-spaced subcarriers, characterised in that it includes a first subcarrier at a predetermined frequency and in that said first subcarrier carries periodic data specifying the other subcarriers present in the frequency multiplexed signal.
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15. An orthogonal frequency multiplexed RF signal carrying a first plurality of channels on a second, smaller, plurality of subcarriers, each channel modulating a quadrature component of one of said subcarriers.
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17. An RF receiver apparatus comprising means for receiving an RF frequency multiplexed signal comprising a plurality of frequency-spaced subcarriers in a band, characterised by means for reading data specifying the subcarriers present from a first, predetermined, subcarrier and for configuring the receiver to receive said subcarriers.
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19. An OFDM receiver comprising a demodulator for demodulating a first plurality of channels from a second, smaller, plurality of subcarriers, said demodulator being arranged to demodulate each channel from one quadrature component of one subcarrier.
- 20. A frequency multiplexed RF signal comprising a plurality of frequency-spaced subcarriers each being modulated in a succession of data symbol periods, at least one said subcarrier being a reference subcarrier carrying orthogonal data and reference sequences of data and reference symbols respectively, in reference symbol repetition periods each of a duration of a multiple of the data symbol period duration, characterised in that, in at least first and second symbol periods within each reference symbol repetition period, the symbols carried on said reference subcarrier comprise combined symbols comprising respectively first and second different combinations of the same, repeated, data and reference symbols, said first and second combinations providing said orthogonality and permitting the separation of said data and reference symbols.
- 24. A signal broadcasting RF transmitter apparatus comprising a modulator arranged to modulate a plurality of frequency-spaced subcarriers with information in a succession of data symbol periods, said modulator being arranged to receive orthogonal sequences of data and reference information and to modulate at least one said subcarrier as a reference subcarrier with combined symbols comprising respectively first and second different combinations of the same, repeated, data and reference symbols, in different symbol periods, said first and second combinations providing orthogonality between said data and reference symbols and permitting the separation of said data and reference symbols at a receiver.
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28. A receiver for a frequency multiplexed RP signal comprising a plurality of frequency-spaced subcarriers each being modulated in a succession of data symbol periods, a least one said subcarrier being a reference subcarrier carrying orthogonal data and reference sequences of data and reference symbols respectively, in reference symbol repetition periods each of a duration of a multiple of the data symbol period duration, the receiver comprising means for combining the symbols received on said reference subcarriers in at least first and second symbol periods within each reference symbol repetition period to generate first and second combinations therefrom, a first combination recovering a data symbol and a second combination recovering a reference symbol, said first and second combinations providing orthogonality and permitting the separation of said data and reference symbols.
- 30. A frequency-multiplexed signal generator generating a frequency multiplexed signal which may have, selectively, either a first format comprising at least one subcarrier or a second format comprising more subcarriers than said first format, the signal generator comprising a first signal processing circuit generating said first format, a second signal processing circuit generating said second format, and a selection circuit selecting one or other of said first or second signal processing circuits.
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42. A method of generating a frequency multiplexed signal, comprising the steps of selecting either a first signal format comprising a relatively small number of frequency multiplexed subcarriers or a second format comprising a larger number of subcarriers than the first;
- and either;
filtering one or more subcarrier input data signals using filters arranged to apply a relatively high degree of attenuation to the sidelobes of said subcarriers to produce said first format;
orgenerating a plurality of subcarriers in such a manner as to pass at least part of the first sidelobe of each said subcarrier to produce said second format.
- and either;
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43. A method of generating a frequency multiplexed signal comprising:
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selecting the number of subcarriers in said signal; and
, in dependence on said selection, eitherapplying pulse shaping filtering to a small number of input subcarrier modulating data signals to generate a first multiplexed format signal comprising a relatively small number of subcarriers;
orapplying an Inverse Fourier Transform to a relatively large number of input subcarrier modulating data signals, to generate a frequency multiplexed signal in a second format comprising relatively large number of said subcarriers.
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44. A frequency multiplexed signal generator comprising:
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one or more pulse shaping filters;
a Inverse Fourier Transformer; and
a selector operatively coupled to interconnect input subcarrier modulating signals to either said one or more pulse shaping filters or said Inverse Fourier Transformer. - View Dependent Claims (46, 48, 49)
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45. A frequency multiplexed signal receiver comprising a first signal processing circuit for receiving a frequency multiplexed signal in a first format consisting of a small number of subcarriers, and a second signal processing circuit for receiving a frequency multiplexed signal in a second format comprising a larger number of subcarriers.
- 47. An OFDM transmitter comprising an OFDM generator for generating an ensemble of orthogonal, information-carrying frequency subcarriers, and a transmit filter for passing the subcarriers and at least a portion of the first sidelobes of the highest and lowest frequency subcarriers, and attenuating the second and subsequent sidelobes of said highest and lowest frequency subcarriers.
- 51. A method of receiving an OFDM signal comprising filtering said signal to pass all the OFDM subcarriers and at least a portion of the first outer sidelobes of the highest and lowest frequency information-carrying subcarriers, and to attenuate frequencies outside the frequency of the second outer sidelobes of the said highest and lowest frequency subcarriers.
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52. A method of filtering an orthogonal frequency division multiplexed signal comprising a plurality of orthogonal, information-carrying subcarriers each having a (sin x/x) spectral form, consisting of filtering said plurality of subcarriers so as to pass all said subcarriers and at least a portion of the first sidelobe of the highest and lowest subcarriers, and to attenuate the second and further sidelobes of said highest and lowest frequency subcarriers.
- 55. A receiver for receiving an OFDM signal comprising a filter with a pass band arranged to pass the subcarriers of said OFDM signal and at least a portion of the first outer sidelobes of the highest and lowest subcarriers present therein, and to attenuate frequencies corresponding to the spectral positions where the second and further outer sidelobes of said highest and lowest frequency subcarriers would be.
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59. An OFDM signal comprising a plurality of orthogonal information-bearing subcarriers, the first outer sidelobes of the highest and lowest frequency said subcarriers being partially attenuated by filtering.
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60. A method of processing an orthogonal frequency multiplexed signal modulated in symbol periods comprising:
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a first step of reducing the magnitude of the signal over a symbol period so as to maintain orthogonality, and where necessary, a second step of reducing the magnitude of particular temporal portions of the signal relative to others so as to reduce the peak-to-mean ratio of the multiplexed signal. - View Dependent Claims (61, 62, 63, 64)
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65. An OFDM transmitter comprising:
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a symbol power attenuator circuit (132) operable to evenly attenuate all successive samples of an OFDM symbol of excessive magnitude or peak to average ratio; and
a sample attenuator circuit (136) operable to selectively attenuate relatively high magnitude samples within the symbol period.
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- 66. A receiver for a frequency multiplexed signal comprising a plurality of frequency subcarriers carrying information in symbol periods and having intervals of predetermined amplitude between said symbol periods, the receiver comprising a signal timing circuit arranged to generate a timing signal permitting the recovery of the information, said signal timing circuit being responsive to said intervals, said recovery being carried out on said multiplexed signal independently of the recovery of said subcarriers.
- 71. A method of acquiring the timing within a frequency multiplexed signal which comprises a plurality of subcarriers each modulated synchronously with information in symbol periods separated by intervals of a predetermined magnitude, the method comprising the step of detecting said intervals prior to separation or demultiplexing said signal.
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74. A frequency acquisition circuit for acquiring the frequency of a signal modulated in a succession of symbol periods, and including first and second symbol periods, comprising:
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a sampling circuit sampling over a fraction of each said symbol period;
a first frequency phasor circuit arranged to generate, responsive to said samples, an output signal indicative of the phase advance due to frequency offset between said first and second symbol periods over a first interval which is not an integral number of said symbol periods; and
a second frequency phasor circuit arranged to generate, responsive to said samples, an output signal indicative of the phase advance due to frequency offset over a second interval which is not equal to said first interval. - View Dependent Claims (75, 76, 77, 78, 79, 80, 81)
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82. A method of frequency acquisition for a signal modulated in symbol periods;
- comprising the steps of;
sampling symbol periods over fractions of their lengths, so as to pass frequencies higher than the reciprocal of the symbol period;
estimating the phase advance due to frequency offset over a first number of said samples and the phase advance due to frequency offset over a second number of said samples, said first and said second numbers corresponding to time periods which differ by an amount which is not an integer number of said symbol periods; and
forming a measure of the difference between the first and second phase advances to provide a frequency error estimate. - View Dependent Claims (83)
- comprising the steps of;
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84. A method of decoding a convolutionally encoded and interleaved signal comprising the steps of:
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sampling the signal;
reading each signal sample into a deinterleaver circuit in a first order;
reading each sample into a control circuit arranged to generate one or more control signals responsive to the level of each sample;
reading the samples out of the deinterleaver in a second order;
quantizing the samples; and
decoding the quantized samples;
characterised by reading said samples into said control circuit in parallel with the reading thereof into said deinterleaver circuit, and by the step of aligning the range of the quantizer with that of the samples prior to reading the samples out of the deinterleaver circuit.
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85. A decoder circuit for an interleaved and convolutionally encoded signal comprising a deinterleaver arranged to receive successive samples of the received signal;
- a quantizer arranged to receive samples read out from the deinterleaver circuit; and
a decoder arranged to decode the quantized samples;
characterised by a range control circuit operably connected to receive the samples in parallel with the deinterleaver circuit and to derive control signals for aligning the range of the quantizer and that of the samples read into the deinterleaver circuit, prior to read out of the samples from the deinterleaver circuit.
- a quantizer arranged to receive samples read out from the deinterleaver circuit; and
- 86. A satellite broadcasting system comprising a ground based broadcasting system transmitting an orthogonal frequency multiplexed signal and a repeater satellite in non geostationary orbit.
Specification