Method of determining the location of the FFT window and the delay spread for the platinum broadcast channel estimator

• US 8,094,740 B2
• Filed: 10/26/2009
• Issued: 01/10/2012
• Est. Priority Date: 04/18/2005
• Status: Expired due to Fees

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Bhushan, Naga, Namgoong, June, Black, Peter John
• Primary Examiner(s): Tran, Khanh C
• Application Number:
  US12/606,009
• Publication Number:
  US 20100039925A1
• Time in Patent Office: 806 Days
• Field of Search: None
• US Class Current: 375/260
• CPC Class Codes: H04L 25/022 of frequency response
• CPC Class Codes: H04L 27/2662 Symbol synchronisation
• CPC Class Codes: H04L 27/2665 Fine synchronisation, e.g. by positioning the FFT window

Abstract

In one embodiment, the invention comprises a channel estimation method, comprising determining a FFT window position, and calculating a delay spread. In another embodiment, the step of determining a FFT window position comprises setting an initial position of the FFT window, computing an energy for each tap, time averaging said energy for each tap, comparing an average energy of each tap with a first threshold multiplied by the average energy of all taps, comparing the average energy of each tap with a second threshold multiplied by a maximum average energy in alias components, updating the set of paths if the average energy of the tap is greater than said second threshold multiplied by the maximum average energy in alias components; and refining the FFT window position.

Claims

1. A method comprising:

receiving a code divisional multiplexed (CDM) waveform in a signal;

receiving an orthogonal frequency division modulation (OFDM) waveform in the signal, wherein the CDM waveform and the OFDM waveform are time multiplexed; and

transforming the signal from a time domain to a frequency domain by applying a fast Fourier transform (FFT), wherein transforming the signal from the time domain to the frequency domain comprises;

setting an initial position of an FFT window based upon an estimated channel impulse response, wherein the FFT window is to be applied to a digital representation of the signal; and

adjusting a position of the FFT window whenever any tap of the FFT window has an energy less than either a first threshold or a second threshold multiplied by a maximum average energy.

2. The method of claim 1, wherein the OFDM waveform includes pilot tones that are staggered with respect to each other.

3. A non-transitory computer readable medium storing instructions that, when executed by a processor, cause the processor to:

receive a signal that includes a code divisional multiplexed (CDM) waveform time multiplexed with an orthogonal frequency division modulation (OFDM) waveform; and

transform the signal from a time domain to a frequency domain by executing instructions to further cause the processor to;

set an initial position of a fast Fourier transform (FFT) window based upon an estimated channel impulse response, wherein the FFT window is to be applied to a digital representation of the signal; and

adjust a position of the FFT window whenever any tap of the FFT window has an energy less than either a first threshold or a second threshold multiplied by a maximum average energy.

4. A method for comprising:

receiving a signal that includes a radio frequency (RF) orthogonal frequency division modulation (OFDM)-modulated waveform time multiplexed with a code divisional multiplexed (CDM) waveform;

down-converting the signal to provide an intermediate frequency (IF) signal;

digitizing the IF signal to provide a digital signal;

if the digitized signal includes a cyclic prefix, removing the cyclic prefix to recover a time-domain signal;

transforming the time-domain signal in a fast Fourier transform (FFT) to recover frequency domain symbols;

determining timing of a beginning of each of the frequency domain symbols;

determining a starting point for the FFT;

measuring a frequency response on an OFDM pilot tone of the signal; and

estimating a channel impulse response, including determining a first significant component and a last significant component in an estimated channel impulse response.

5. The method of claim 4, further comprising:

calculating the channel impulse response from the frequency response over a window between the first significant component and the last significant component;

computing energy for each of 2P tap time-domain channel estimates of the channel impulse response;

computing an average energy for each of the 2P tap time-domain channel estimates with respect to an infinite impulse response (IIR) filter;

computing a second signal using each of the 2P tap time-domain channel estimates that is greater than both a first threshold and a second threshold; and

calculating a delay spread for the 2P tap time-domain channel estimates.

6. An apparatus for transforming a signal from a time domain to a frequency domain by applying a fast Fourier transform (FFT), the apparatus comprising:

a receiver operative to receive a signal that includes a code divisional multiplexed (CDM) waveform time multiplexed with an orthogonal frequency division modulation (OFDM) waveform; and

a processor coupled to the receiver, the processor configured to transform the signal from a time domain to a frequency domain by executing instructions to further cause the processor to;

set an initial position of a fast Fourier transform (FFT) window based upon an estimated channel impulse response, wherein the FFT window is to be applied to a digital representation of the signal; and

adjust a position of the FFT window whenever any tap of the FFT window has an energy less than either a first threshold or a second threshold multiplied by a maximum average energy.

7. The apparatus of claim 6, further comprising:

a transmitter operative to provide the code divisional multiplexed (CDM) waveform in a transmit signal,

wherein the transmitter is also operative to provide the orthogonal frequency division modulation (OFDM) waveform in the transmit signal.

8. The apparatus of claim 7, wherein the transmitter is operative to include, within the OFDM waveform, pilot tones that are staggered with respect to each other.

9. An apparatus comprising:

a receiver operative to receive a signal that includes a radio frequency (RF) orthogonal frequency division modulation (OFDM)-modulated waveform time multiplexed with a code divisional multiplexed (CDM) waveform;

a down-converter operative to down-convert the signal to provide an intermediate frequency (IF) signal;

a digitizer operative to digitize the IF signal to provide a digital signal;

a cyclic prefix remover operative to remove any cyclic prefix within the digitized signal to recover a time-domain signal;

a fast Fourier transform (FFT) module operative to transform the time-domain signal to recover frequency domain symbols; and

a processor operative to;

determine a timing of a beginning of each of the frequency domain symbols;

adjust a window of the FFT module;

determine a starting point for a FFT;

measure a frequency response of an OFDM pilot tone of the signal; and

estimate a channel impulse response, including determining a first significant component and a last significant component in an estimated channel impulse response.

10. The apparatus of claim 9, wherein the processor is further operative to:

calculate the channel impulse response from the frequency response over a window between the first significant component and the last significant component;

compute energy for each of 2P tap time-domain channel estimates of the channel impulse response;

compute an average energy for each of the 2P tap time-domain channel estimates with respect to an infinite impulse response (IIR) filter;

compute a second signal using each of the 2P tap time-domain channel estimates that is greater than both a first threshold and a second threshold; and

calculate a delay spread for the 2P tap time-domain channel estimates.

11. An apparatus comprising:

a receiver means operative to receive a signal that includes a code divisional multiplexed (CDM) waveform time multiplexed with an orthogonal frequency division modulation (OFDM) waveform; and

a processor means operative to transform the signal from a time domain to a frequency domain by executing instructions to;

set an initial position of an FFT window based upon an estimated channel impulse response, wherein the FFT window is to be applied to a digital representation of the signal; and

adjust a position of the FFT window whenever any tap of the FFT window has an energy less than either a first threshold or a second threshold multiplied by a maximum average energy.

12. The apparatus of claim 11, further comprising:

transmitter means operative to provide the code divisional multiplexed (CDM) waveform in a transmit signal,

wherein the transmitter means is also operative to provide the orthogonal frequency division modulation (OFDM) waveform in the transmit signal.

13. The apparatus of claim 12, wherein the transmitter means is operative to include, within the OFDM waveform, pilot tones that are staggered with respect to each other.

14. An apparatus comprising:

receiver means operative to receive a signal that includes a radio frequency (RF) orthogonal frequency division modulation (OFDM)-modulated waveform time multiplexed with a code divisional multiplexed (CDM) waveform;

down-converter means operative to down-convert the signal to provide an intermediate frequency (IF) signal;

digitizer means operative to digitize the IF signal to provide a digital signal;

cyclic prefix remover means operative to remove any cyclic prefix within the digitized signal to recover a time-domain signal;

fast Fourier transform (FFT) means operative to transform the time-domain signal to recover frequency domain symbols; and

processor means operative to;

determine a timing of a beginning of each of the frequency domain symbols;

adjust a window of the FFT means;

determine a starting point for a FFT;

measure a frequency response of an OFDM pilot tone of the signal; and

estimate a channel impulse response, including determining a first significant component and a last significant component in an estimated channel impulse response.

15. The apparatus of claim 14, wherein the processor means is further operative to:

calculate the channel impulse response from the frequency response over a window between the first significant component and the last significant component;

compute energy for each of 2P tap time-domain channel estimates of the channel impulse response;

compute an average energy for each of the 2P tap time-domain channel estimates with respect to an infinite impulse response (IIR) filter;

compute a second signal using each of the 2P tap time-domain channel estimates that is greater than both a first threshold and a second threshold; and

calculate a delay spread for the 2P tap time-domain channel estimates.

16. An apparatus comprising a processor to:

receive a signal that includes a code divisional multiplexed (CDM) waveform time multiplexed with an orthogonal frequency division modulation (OFDM) waveform; and

transform the signal from a time domain to a frequency domain by executing instructions to further cause the processor to;

set an initial position of a fast Fourier transform (FFT) window based on an estimated channel impulse response, wherein the FFT window is to be applied to a digital representation of the signal; and

adjust a position of the FFT window whenever any tap of the FFT window has an energy less than either a first threshold or a second threshold multiplied by a maximum average energy.