Filter for impulse response shortening with additional spectral constraints for multicarrier transmission
First Claim
1. A digital filter for a multiple carrier, multi-channel, communication system, the digital filter comprising:
- a digital filter structure configured to apply a frequency characteristic according to a filter characteristic, g(n), to a digital Orthogonal Frequency Division Multiplexing (OFDM) signal;
taps coupled to the digital filter structure and configured to receive digital filter coefficients,the number of digital filter coefficients being less than or equal to a number of coefficients to set an effective length of convolution of the filter characteristic with an impulse response of the communication channel, g(n)*h(n), less than a target length; and
the filter structure configured to apply, via the taps, coefficients adjusted according to a cost function, to minimize a difference between a desired spectral response, Gd(ω
), and an actual spectral response, G(ω
), of the digital filter to adjust the filter characteristic, g(n).
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Accused Products
Abstract
A channel in a multiple carrier communication system is equalized by computing a desired spectral response, shortening the impulse response of the channel so that a significant part of an energy of the impulse response is confined to a region that is shorter than a target length and filtering the signal based on the desired spectral response. A multiple carrier communication system may include a primary impulse shortening filter that receives an output signal of an analog to digital converter and accepts coefficients. A secondary impulse shortening filter may receive the output signal of the analog to digital converter, output an output signal, and pass coefficients to the primary impulse shortening filter. A reference signal generator may output a reference signal. A comparator may compare the output signal and the reference signal and output a resulting error signal. An adaptive processor may compute coefficients for the secondary impulse shortening filter based on the error signal.
237 Citations
21 Claims
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1. A digital filter for a multiple carrier, multi-channel, communication system, the digital filter comprising:
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a digital filter structure configured to apply a frequency characteristic according to a filter characteristic, g(n), to a digital Orthogonal Frequency Division Multiplexing (OFDM) signal; taps coupled to the digital filter structure and configured to receive digital filter coefficients, the number of digital filter coefficients being less than or equal to a number of coefficients to set an effective length of convolution of the filter characteristic with an impulse response of the communication channel, g(n)*h(n), less than a target length; and the filter structure configured to apply, via the taps, coefficients adjusted according to a cost function, to minimize a difference between a desired spectral response, Gd(ω
), and an actual spectral response, G(ω
), of the digital filter to adjust the filter characteristic, g(n). - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A method for adapting a digital filter in a multicarrier, multi-channel, communication system, the method comprising:
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applying a frequency characteristic according to a filter characteristic, g(n), to a digital Orthogonal Frequency Division Multiplexing (OFDM) signal; producing the filter characteristic, g(n), through use of digital filter coefficients, received via taps, the number of coefficients being less than or equal to a number of coefficients to set an effective length of convolution of the filter characteristic with an impulse response of a communication channel, g(n)*h(n), less than a target length; and adjusting the digital filter coefficients, via the taps, by applying a cost function to minimize a difference between a desired spectral response, Gd(ω
), and an actual filter spectral response, G(ω
), of the digital filter to adjust the filter characteristic g(n). - View Dependent Claims (14, 15, 16, 17, 18, 19, 20)
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21. A non-transitory computer readable medium having stored thereon instructions that, when loaded and executed by a digital signal processor, cause the processor to:
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apply a frequency characteristic according to a filter characteristic, g(n), to a digital Orthogonal Frequency Division Multiplexing (OFDM) signal; select digital filter coefficients to produce the filter characteristic, g(n), the number of coefficients being less than or equal to a number of coefficients to set an effective length of convolution of the filter characteristic with an impulse response of a communication channel, g(n)*h(n), less than a target length; and adjust the digital filter coefficients by applying a cost function to minimize a difference between a desired spectral response, Gd(ω
), and an actual filter spectral response, G(ω
), of the digital filter to adjust the filter characteristic g(n).
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Specification