Determining signal channel impulse response using subcarrier pilot signals

Patent metadata

Field	Value
Publication number	US-10050811-B2
Application number	US-201414505674-A
Country	US
Kind code	B2
Filing date	Oct 3, 2014
Priority date	Oct 17, 2013
Publication date	Aug 14, 2018
Grant date	Aug 14, 2018

Abstract

Distortion caused by spurious components in a determined channel impulse response (CIR) is reduced. In an OFDM (orthogonal frequency-division multiplexing) system pilot signals are applied to different subcarriers of different symbols in accordance with a pilot transmission scheme. Channel estimates are determined by time-interpolation for some of the data slots of the received signal which do not already include a pilot signal. For each of a sequence of symbols, a respective Inverse Fast Fourier Transform is performed on the pilot signals and interpolated channel estimates in the data slots of that symbol, thereby determining a sequence of estimated CIRs for the sequence of symbols. Spurious channel components will vary across the sequence of estimated CIRs, whereas the true channel peaks will tend not to significantly vary across the sequence of estimated CIRs. Therefore the sequence of estimated CIRs can be filtered (e.g. with a low-pass filter) to attenuate the spurious components, thereby determining a CIR for the signal for which the distortion caused by the spurious components is reduced.

First claim

The invention claimed is:

1. A method of processing a signal to determine a channel impulse response for the signal, the signal adhering to a frequency-division multiplexing scheme in which the signal comprises a plurality of symbols, each of the symbols comprising a plurality of distinct data slots for transmitting data using a respective plurality of subcarriers which are distinct in the frequency domain, wherein pilot signals are applied to data slots of at least some different symbols using different subcarriers in accordance with a pilot transmission scheme, the method comprising:
receiving the signal over a channel, wherein the pilot signals in the received signal are indicative of channel estimates for the data slots of the received signal which include the pilot signals;
for at least some of the data slots of the received signal which do not include a pilot signal, determining channel estimates by time-interpolation of received pilot signals in other data slots of the received signal; and
determining a channel impulse response for the signal using a plurality of the channel estimates, by:
performing at least one inverse Fourier transform on said plurality of channel estimates to determine a sequence of estimated channel impulse responses for a sequence of symbols, and
filtering the sequence of estimated channel impulse responses to attenuate components of the sequence of estimated channel impulse responses which vary with identified particular frequencies over the sequence of estimated channel impulse responses, wherein the particular frequencies are identified so as to correspond to frequencies with which spurious components vary over time, said spurious components being peaks which occur in the channel impulse response for the signal due to imperfections in said determination of channel estimates by time interpolation.

2. The method of claim 1 wherein
a respective inverse Fourier transform is performed for each symbol of the sequence of symbols on the channel estimates for a plurality of the data slots of that symbol, thereby determining the sequence of estimated channel impulse responses for the sequence of symbols.

3. The method of claim 1 wherein each of the estimated channel impulse responses comprises values at a plurality of bin positions, and wherein the method further comprises:
for each of a plurality of the bin positions of the estimated channel impulse responses, performing a Fourier transform over the sequence of estimated channel impulse responses; and
analysing the results of the Fourier transform to identify said particular frequencies by finding peaks in the results of the Fourier transform corresponding to components which vary over the estimated channel impulse responses at frequencies which are indicative of spurious components.

4. The method of claim 1 further comprising identifying said particular frequencies by determining frequencies at which spurious components are likely to occur based on the pilot transmission scheme.

5. The method of claim 3 further comprising controlling said filtering of the sequence of estimated channel impulse responses to attenuate components which vary with said identified particular frequencies over the sequence of estimated channel impulse responses.

6. The method of claim 1 wherein the pilot signals are applied to data slots of the symbols in a regular repeating pattern across the different subcarriers in accordance with the pilot transmission scheme, thereby setting a number of different patterns of channel estimate phases in the symbols, wherein the regular repeating pattern is a diagonal repeating pattern across the different subcarriers of the symbols in the signal.

7. The method of claim 6 wherein said filtering comprises integrating a number of the estimated channel impulse responses, said number of integrated estimated channel impulse responses being equal to a positive integer multiplied by the number of different patterns of channel estimate phases in the symbols.

8. The method of claim 1 wherein said sequence of symbols for which estimated channel impulse responses are determined includes either (i) a set of consecutive symbols in the received signal, or (ii) some but not all of a set of consecutive symbols in the received signal.

9. A receiver configured to process a signal to determine a channel impulse response for the signal, the signal adhering to a frequency-division multiplexing scheme in which the signal comprises a plurality of symbols, each of the symbols comprising a plurality of distinct data slots for transmitting data using a respective plurality of subcarriers which are distinct in the frequency domain, wherein pilot signals are applied to data slots of at least some different symbols using different subcarriers in accordance with a pilot transmission scheme, the receiver comprising:
a receive module configured to receive the signal over a channel, wherein the pilot signals in the received signal are indicative of channel estimates for the data slots of the received signal which include the pilot signals;
an interpolation module configured to determine channel estimates for at least some of the data slots of the received signal which do not include a pilot signal, by time-interpolation of received pilot signals in other data slots of the received signal; and
a processing block configured to determine a channel impulse response for the signal using a plurality of the channel estimates, the processing block comprising:
an inverse Fourier transform module configured to perform at least one inverse Fourier transform on said plurality of channel estimates to determine a sequence of estimated channel impulse responses for a sequence of symbols, and
a filter module configured to filter the sequence of estimated channel impulse responses to attenuate components which vary with identified particular frequencies over the sequence of estimated channel impulse responses, wherein the particular frequencies are identified so as to correspond to frequencies with which spurious components vary over time, said spurious components being peaks which are created in the channel impulse response for the signal by imperfections in the time-interpolation of the interpolation module.

10. The receiver of claim 9 wherein the inverse Fourier transform module is configured to perform a respective inverse Fourier transform on the channel estimates for a plurality of the data slots of each symbol of a sequence of the symbols, to thereby determine the sequence of estimated channel impulse responses.

11. The receiver of claim 9 wherein the filter module is configured to filter the plurality of the channel estimates over a sequence of the symbols to attenuate components which vary with particular frequencies over the sequence of symbols, thereby determining a set of filtered channel estimates for a respective set of the subcarriers; and
wherein the inverse Fourier transform module is configured to perform an inverse Fourier transform on the set of filtered channel estimates, thereby determining the channel impulse response for the signal.

12. The receiver of claim 9 further comprising a Fast Fourier Transform block configured to sample the symbols of the received signal, wherein the Fast Fourier Transform block is configured to use the determined channel impulse response for the signal to position a Fast Fourier Transform window for sampling the symbols of the received signal.

13. The receiver of claim 12 wherein the Fast Fourier Transform block is configured to:
use the determined channel impulse response for the signal to estimate inter-symbol interference as a function of the position o

Assignees

• Imagination Tech Ltd

Inventors

• Murrin Paul

Classifications

• H04L27/2665 Primary

  Fine synchronisation, e.g. by positioning the FFT window · CPC title

• H04L25/0212 Primary

  of impulse response · CPC title

• H04L25/0232

  by interpolation between sounding signals · CPC title

• H04L27/2647

  Arrangements specific to the receiver only (equalisation H04L27/01) · CPC title

• H04L27/2675

  Pilot or known symbols · CPC title