Memory reduction in digital broadcast receivers

• US 7,664,187 B2
• Filed: 04/22/2006
• Issued: 02/16/2010
• Est. Priority Date: 04/25/2005
• Status: Expired due to Fees

• Current Assignee: CSR Technology Incorporated (Qualcomm, Inc.)
• Original Assignee: SIRF Technology Incorporated (Qualcomm, Inc.)
• Inventors: Chen, Steven, Luu, Howard K.
• Primary Examiner(s): Tran; Khanh C
• Application Number:
  US11/379,786
• Publication Number:
  US 20070064821A1
• Time in Patent Office: 1,396 Days
• Field of Search: 375260-261, 375/340, 375/343, 370/208, 370/210, 708403-405
• US Class Current: 375/260
• CPC Class Codes: H04L 27/265 Fourier transform demodulators, e.g. fast Fourier transform [FFT] or discrete Fourier transform [DFT] demodulators H04L27/26524 takes precedence
• CPC Class Codes: H04L 27/2651 Modification of fast Fourier transform [FFT] or discrete Fourier transform [DFT] demodulators for performance improvement

Abstract

An input random access memory (RAM) module of a fast Fourier transform (FFT) engine of a DVB receiver is used to store, during a first time period, delayed versions of an input signal that includes a first orthogonal frequency division multiplexed (OFDM) symbol and a cyclic prefix therefor received at the receiver, and samples for a second OFDM symbol to be demodulated using the FFT engine during a second time period. Delayed versions of the input signal are stored in the input RAM module of the FFT engine in a first-in-first-out (FIFO) fashion for signal acquisition and for FFT processing. Similarly, an output RAM module of the FFT engine is used to store moving averages of an autocorrelation of the input signal with its cyclic prefix computed over presumed guard intervals and over multiple symbols.

Claims

1. A method comprising:

sharing an input random access memory (RAM) module of a fast Fourier transform (FFT) engine of a receiver so as to store, during a period of signal acquisition, delayed versions of an input signal including a first orthogonal frequency division multiplexed (OFDM) symbol and a cyclic prefix therefor received at the receiver, and samples for a second OFDM symbol to be demodulated using the FFT engine after the period of signal acquisition; and

storing, in an output RAM module of the FFT engine, moving window averages of an autocorrelation of the input signal computed over one or more presumed guard intervals thereof.

2. The method of claim 1, further comprising storing, in the output RAM modules of the FFT engine, recursive integration over multiple symbols of the moving window averages of the input signal computed over the one or more presumed guard intervals.

3. A method comprising:

sharing an input random access memory (RAM) module of a fast Fourier transform (FFT) engine of a receiver so as to store, during a period of signal acquisition, delayed versions of an input signal including a first orthogonal frequency division multiplexed (OFDM) symbol and a cyclic prefix therefor received at the receiver, and samples for a second OFDM symbol to be demodulated using the FFT engine after the period of signal acquisition; and

storing intermediate signal processing results obtained during acquisition of the input signal in an output RAM module of the FFT engine.

4. The method of claim 3, further comprising storing, in the output RAM of the FFT engine, an FFT of the input signal computed by the FFT engine.

5. A method comprising:

sharing an input random access memory (RAM) module of a fast Fourier transform (FFT) engine of a receiver so as to store, during a period of signal acquisition, delayed versions of an input signal including a first orthogonal frequency division multiplexed (OFDM) symbol and a cyclic prefix therefor received at the receiver, and samples for a second OFDM symbol to be demodulated using the FFT engine after the period of signal acquisition,

wherein the input signal has a duration comprising a total period and the cyclic prefix has a duration comprising a guard interval, the method further comprising determining the guard interval.

6. The method of claim 5, wherein determining the guard interval comprises, for each of a plurality of possible guard intervals:

selecting one of the plurality of possible guard intervals;

delaying the input signal by a difference between the total period and a corresponding selected guard interval;

storing the delayed signal in the input RAM module;

calculating a moving window average of an autocorrelation for the delayed signal over the selected guard interval;

storing the moving window average in an output RAM module of the FFT engine;

storing the recursive integration of the moving window average in an output RAM module of the FFT engine;

determining a first recursively integrated moving window average from a plurality of stored recursively integrated moving window averages; and

determining the guard interval based on the first recursively integrated moving window average.

7. The method of claim 5, wherein the delayed versions of the input signal are stored in the input RAM module of the FFT engine in a first-in-first-out (FIFO) fashion.

8. A receiver comprising:

an input random access memory (RAM) coupled to a signal acquisition module of the receiver so as to store, while acquiring a signal, delayed versions of an input signal including a first orthogonal frequency division multiplexed (OFDM) symbol and a cyclic prefix therefor received at the receiver, and samples for a second OFDM symbol to be demodulated using a fast Fourier transform (FFT) engine of the receiver during a after the signal is acquired; and

an output RAM coupled to the FFT engine so as to store moving window averages of an autocorrelation of the input signal computed over one or more presumed guard intervals thereof.

9. The receiver of claim 8, wherein the output RAM is further coupled to the FFT engine so as to store recursive integration results of the moving window averages of the input signal computed over the one or more presumed guard intervals.

10. A receiver comprising:

an input random access memory (RAM) coupled to a signal acquisition module of the receiver so as to store, while acquiring a signal, delayed versions of an input signal including a first orthogonal frequency division multiplexed (OFDM) symbol and a cyclic prefix therefor received at the receiver, and samples for a second OFDM symbol to be demodulated using a fast Fourier transform (FFT) engine of the receiver during a after the signal is acquired; and

an output RAM coupled to the FFT engine so as to store intermediate signal processing results obtained during acquisition of the input signal at the receiver.

11. The receiver of claim 10, wherein the output RAM is further coupled to the FFT engine so as to store an FFT of the input signal computed by the FFT engine.

12. A receiver comprising:

a fast Fourier transform (FFT) engine including an input random access memory (RAM) module;

a signal acquisition module; and

a demodulator;

wherein the signal acquisition module is configured to store, during an acquisition period, in the input RAM module of the FFT engine, a delayed version of an input signal including a first orthogonal frequency division multiplexed (OFDM) symbol and a cyclic prefix therefor received at the receiver,

wherein the FFT engine is configured to store, in the input RAM module of the FFT engine, samples of a second OFDM symbol from the input signal, and

wherein the demodulator is configured to use the FFT engine, during a time period other than the acquisition period, to demodulate the second OFDM sample stored in the input RAM module of the FFT engine,

wherein the FFT engine further includes an output RAM module, and wherein the signal acquisition module is further configured to store, in the output RAM module of the FFT engine, moving window averages of an autocorrelation of the input signal computed over one or more presumed guard intervals thereof.

13. The receiver of claim 12, wherein the delayed version of the input signal is stored in the input RAM module of the FFT engine in a first-in-first-out (FIFO) fashion.

14. The receiver of claim 12, wherein the signal acquisition module is further configure to store, in the output RAM module of the FFT engine, recursive integration over multiple symbols of the moving window averages of the input signal computed over the one or more presumed guard intervals.

15. A receiver comprising:

a fast Fourier transform (FFT) engine including an input random access memory (RAM) module;

a signal acquisition module; and

a demodulator;

wherein the signal acquisition module is configured to store, during an acquisition period, in the input RAM module of the FFT engine, a delayed version of an input signal including a first orthogonal frequency division multiplexed (OFDM) symbol and a cyclic prefix therefor received at the receiver,

wherein the FFT engine is configured to store, in the input RAM module of the FFT engine, samples of a second OFDM symbol from the input signal, and

wherein the demodulator is configured to use the FFT engine, during a time period other than the acquisition period, to demodulate the second OFDM sample stored in the input RAM module of the FFT engine,

wherein the FFT engine further includes an output RAM module, and wherein the signal acquisition module is further configured to store intermediate signal processing results obtained during the acquisition period in the output RAM module of the FFT engine.

16. A receiver comprising:

a fast Fourier transform (FFT) engine including an input random access memory (RAM) module;

a signal acquisition module; and

a demodulator;

wherein the signal acquisition module is configured to store, during an acquisition period, in the input RAM module of the FFT engine, a delayed version of an input signal including a first orthogonal frequency division multiplexed (OFDM) symbol and a cyclic prefix therefor received at the receiver,

wherein the FFT engine is configured to store, in the input RAM module of the FFT engine, samples of a second OFDM symbol from the input signal, and

wherein the demodulator is configured to use the FFT engine, during a time period other than the acquisition period, to demodulate the second OFDM sample stored in the input RAM module of the FFT engine,

wherein the input signal has a duration comprising a total period and the cyclic prefix has a duration comprising a guard interval, and the signal acquisition module is further configured to determine the guard interval.

17. A receiver comprising:

a fast Fourier transform (FFT) engine including an input random access memory (RAM) module;

a signal acquisition module; and

a demodulator;

wherein the signal acquisition module is configured to store, during an acquisition period, in the input RAM module of the FFT engine, a delayed version of an input signal including a first orthogonal frequency division multiplexed (OFDM) symbol and a cyclic prefix therefor received at the receiver,

wherein the FFT engine is configured to store, in the input RAM module of the FFT engine, samples of a second OFDM symbol from the input signal, and

wherein the demodulator is configured to use the FFT engine, during a time period other than the acquisition period, to demodulate the second OFDM sample stored in the input RAM module of the FFT engine,

wherein the input signal has a duration comprising a total period and the cyclic prefix has a duration comprising a guard interval, and the signal acquisition module is further configured to determine the guard interval by;

selecting one of the plurality of possible guard intervals;

delaying the input signal by a difference between the total period and a corresponding selected guard interval;

storing the delayed signal in the input RAM module;

calculating a moving window average of an autocorrelation for the delayed signal over the selected guard interval;

storing the moving window average in an output RAM module of the FFT engine;

storing the recursive integration of the moving window average in an output RAM module of the FFT engine;

determining a first recursively integrated moving window average from a plurality of stored recursively integrated moving window averages; and

determining the guard interval based on the first recursively integrated moving window average.