Parallel preamble search architectures and methods

• US 20080273634A1
• Filed: 05/02/2008
• Published: 11/06/2008
• Est. Priority Date: 05/03/2007
• Status: Active Grant

• Current Assignee: Mbit Wireless Inc.
• Original Assignee: Mbit Wireless Inc.
• Inventors: Govindswamy, Arumugam, Patel, Bhaskar
• Granted Patent: US 7,953,190 B2
• Time in Patent Office: Days
• US Class Current: 375/343
• CPC Class Codes: H04L 27/2666 Acquisition of further OFDM parameters, e.g. bandwidth, subcarrier spacing, or guard interval length
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT

Abstract

The present invention provides architectures and methods which enables faster and more power efficient detection of channel parameters used by a communication system. Various parallel preamble correlator structures are able to perform searches for multiple preambles in parallel. The received samples are correlated with different delays between the samples corresponding to the different possible channel parameters that may be used by the communication system. Processing elements used in the preamble search may be shared among the parallel preamble search sections of a given architecture to reduce costs and power consumption. Decimation and filtering may also be used to reduce the interference from adjacent channels.

Claims

1. A mobile station having a parallel sliding window correlator apparatus for preamble searching in a wireless network, comprising:

a delay line device for receiving an input signal representative of a received signal from the wireless network, the delay line device providing a plurality of outputs including a first output r(n), a second output r(n−

D), a third output r(n−

2D), a first filtered output r₂(m), a second filtered output r₂(m−

D/2) and a third filtered output r₂(m−

D);

a first FFT section coupled to the delay line device and receiving the first output, the second output and the third output, the first FFT section including a plurality of nodes for processing the first, second and third outputs, a first one of the plurality of nodes of the first FFT section for obtaining a first correlation magnitude signal, a second one of the plurality of nodes for obtaining a first energy level signal corresponding to a first energy level of the received signal, a third one of the plurality of nodes for scaling the first energy level signal by a predetermined first threshold to obtain a first scaled signal, and a fourth one of the plurality of nodes for taking the difference between the first correlation magnitude signal and the first scaled signal to generate a first delay correlation detection indication signal; and

a second FFT section coupled to the delay line device and receiving the first filtered output, the second filtered output and the third filtered output, the second FFT section including a plurality of nodes for processing the first, second and third filtered outputs, a first one of the plurality of nodes of the second FFT section for obtaining a second correlation magnitude signal, a second one of the plurality of nodes for obtaining a second energy level signal corresponding to a second energy level of the received signal, a third one of the plurality of nodes for scaling the second energy level signal by a predetermined second threshold to obtain a scaled signal, and a fourth one of the plurality of nodes for taking the difference between the second correlation magnitude signal and the second scaled signal to generate a second delay correlation detection indication signal;

wherein the first FFT section is an N-size FFT section and the second FFT section is an N/2 size FFT section, the N-size FFT section searches for a first preamble associated with a first channel bandwidth and the N/2 size FFT section searches for a second preamble associated with a second channel bandwidth, and processing to obtain the first and second delay correlation detection indication signals is performed in parallel.

2. The mobile station of claim 1, wherein the first threshold corresponds to a ratio of the first correlation magnitude signal and the first energy level signal, and the second threshold corresponds to a ratio of the second correlation magnitude signal and the second energy level signal.

3. The mobile station of claim 1, wherein the first channel bandwidth is an integral multiple of the second channel bandwidth.

4. The mobile station of claim 3, wherein a sampling rate for the first channel bandwidth is an integral multiple of a sampling rate of the second channel bandwidth.

5. The mobile station of claim 1, wherein the delay line device includes a decimation filter to reduce a sampling rate or filter out unwanted signals to generate the first, second and third filtered outputs.

6. The mobile station of claim 5, wherein coefficients of the decimation filter are obtained dynamically depending on the first and second channel bandwidths and the sampling rate.

7. The mobile station of claim 1, wherein:

the first FFT section further includes nodes for squaring the first and second outputs and the second node of the first FFT section subtracts the squared second output from the squared first output; and

the second FFT section further includes nodes for squaring the first and second filtered outputs and the second node of the second FFT section subtracts the squared second filtered output from the squared first filtered output.

8. The mobile station of claim 7, wherein:

the first FFT section further includes a fifth node for multiplying the first output with a conjugate of the second output, a sixth node for multiplying the second output with a conjugate of the third output, and a seventh node for subtracting a signal received from the sixth node from a signal received from the fifth node and outputting a first resultant signal; and

the second FFT section further includes a fifth node for multiplying the first filtered output with a conjugate of the second filtered output, a sixth node for multiplying the second filtered output with a conjugate of the third filtered output, and a seventh node for subtracting a signal received from the sixth node from a signal received from the fifth node and for outputting a second resultant signal.

9. The mobile station of claim 8, wherein the first correlation magnitude is obtained by taking an absolute value of the first resultant signal and the second correlation magnitude is obtained by taking an absolute value of the second resultant signal.

10. A mobile station having a parallel sliding window correlator apparatus for preamble searching in a wireless network, comprising:

a delay line device for receiving an input signal representative of a received signal from the wireless network, the delay line device providing a plurality of outputs including a first output r(n), a second output r(n−

D₁), a third output r(n−

2D₁), a fourth output r(n−

D₂) and a fifth output r(n−

2D₂), wherein D₁ is a first distance between repeating sections of the input signal and D₂ is a second distance between repeating sections of the input signal;

a first FFT section coupled to the delay line device and receiving the first output, the second output and the third output, the first FFT section including a plurality of nodes for processing the first, second and third outputs, a first one of the plurality of nodes of the first FFT section for obtaining a first correlation magnitude signal, a second one of the plurality of nodes for obtaining a first energy level signal corresponding to a first energy level of the received signal, a third one of the plurality of nodes for scaling the first energy level signal by a predetermined first threshold to obtain a first scaled signal, and a fourth one of the plurality of nodes for taking the difference between the first correlation magnitude signal and the first scaled signal to generate a first delay correlation detection indication signal; and

a second FFT section coupled to the delay line device and receiving the first output, the fourth output and the fifth output, the second FFT section including a plurality of nodes for processing the first, fourth and fifth outputs, a first one of the plurality of nodes of the second FFT section for obtaining a second correlation magnitude signal, a second one of the plurality of nodes for obtaining a second energy level signal corresponding to a second energy level of the received signal, a third one of the plurality of nodes for scaling the second energy level signal by a predetermined second threshold to obtain a scaled signal, and a fourth one of the plurality of nodes for taking the difference between the second correlation magnitude signal and the second scaled signal to generate a second delay correlation detection indication signal;

wherein the first FFT section is an N-size FFT section and the second FFT section is also an N-size FFT section, the first FFT section searches for a first preamble associated with a first channel bandwidth and the second FFT section searches for a second preamble associated with a second channel bandwidth, and processing to obtain the first and second delay correlation detection indication signals is performed in parallel.

11. The mobile station of claim 10, wherein:

the first FFT section further includes nodes for squaring the first and second outputs and the second node of the first FFT section subtracts the squared second output from the squared first output; and

the second FFT section further includes nodes for squaring the first and fourth outputs and the second node of the second FFT section subtracts the squared fourth output from the squared first output.

12. The mobile station of claim 11, wherein:

the first FFT section further includes a fifth node for multiplying the first output with a conjugate of the second output, a sixth node for multiplying the second output with a conjugate of the third output, and a seventh node for subtracting a signal received from the sixth node from a signal received from the fifth node and outputting a first resultant signal; and

the second FFT section further includes a fifth node for multiplying the first output with a conjugate of the fourth output, a sixth node for multiplying the fourth output with a conjugate of the fifth output, and a seventh node for subtracting a signal received from the sixth node from a signal received from the fifth node and for outputting a second resultant signal.

13. The mobile station of claim 12, wherein the first correlation magnitude is obtained by taking an absolute value of the first resultant signal and the second correlation magnitude is obtained by taking an absolute value of the second resultant signal.

14. A mobile station having a parallel sliding window correlator apparatus for preamble searching in a wireless network, comprising:

delay means for receiving an input signal representative of a received signal from the wireless network and for providing a plurality of outputs;

first FFT means operatively coupled to the delay means for obtaining a first correlation magnitude signal, for obtaining a first energy level signal corresponding to a first energy level of the received signal, for scaling the first energy level signal by a predetermined first threshold to obtain a first scaled signal, and for taking the difference between the first correlation magnitude signal and the first scaled signal to generate a first delay correlation detection indication signal; and

second FFT means operatively coupled to the delay means for obtaining a second correlation magnitude signal, for obtaining a second energy level signal corresponding to a second energy level of the received signal, for scaling the second energy level signal by a predetermined second threshold to obtain a second scaled signal, and for taking the difference between the second correlation magnitude signal and the second scaled signal to generate a second delay correlation detection indication signal;

wherein the first FFT means searches for a first preamble associated with a first channel bandwidth and the second FFT means searches for a second preamble associated with a second channel bandwidth, and the first and second FFT means operate in parallel.

15. The mobile station of claim 14, wherein the first FFT means operates on an N-size FFT and the second FFT means operates on an N/2 size FFT.

16. The mobile station of claim 14, wherein the first FFT means operates on an N-size FFT and the second FFT means operates on the N-size FFT.

17. The mobile station of claim 14, further comprising:

third FFT means operatively coupled to the delay means for obtaining a third correlation magnitude signal, for obtaining a third energy level signal corresponding to a third energy level of the received signal, for scaling the third energy level signal by a predetermined third threshold to obtain a third scaled signal, and for taking the difference between the third correlation magnitude signal and the third scaled signal to generate a third delay correlation detection indication signal;

wherein the third FFT means operates in parallel with the first and second FFT means.

18. The mobile station of claim 17, wherein the first FFT means operates on a first distance between repeating sections of the input signal, the second FFT means operates on a second distance between repeating sections of the input signal, and the third FFT means operates on decimated and filtered versions of the input signal.

19. A mobile station having a sliding window correlator apparatus for preamble searching in a wireless network, comprising:

a delay line device for receiving an input signal representative of a received signal from the wireless network, the delay line device providing a plurality of outputs including a first output r(n), a second output r(n−

N_cp1), a third output r(n−

N₁), a fourth output r(n−

N₁−

N_CP1), a fifth output r(n−

N_CP2), a sixth output r(n−

N₂) and a seventh output r(n−

N₂−

N_CP2) wherein N₁ is a first distance between repeating sections of the input signal and N₂ is a second distance between repeating sections of the input signal;

a first FFT section coupled to the delay line device and receiving the first output, the second output, the third output and the fourth output, the first FFT section including a plurality of nodes for processing the first, second, third and fourth output signals, a first one of the plurality of nodes of the first FFT section for obtaining a first correlation magnitude signal, a second one of the plurality of nodes for obtaining a first energy level signal corresponding to a first energy level of the received signal, a third one of the plurality of nodes for scaling the first energy level signal by a predetermined first threshold to obtain a first scaled signal, and a fourth one of the plurality of nodes for taking the difference between the first correlation magnitude signal and the first scaled signal to generate a first CP correlation detection indication signal; and

the second FFT section including a plurality of nodes for processing the first, fifth, sixth and seventh outputs, a first one of the plurality of nodes of the second FFT section for obtaining a second correlation magnitude signal, a second one of the plurality of nodes for obtaining a second energy level signal corresponding to a second energy level of the received signal, a third one of the plurality of nodes for scaling the second energy level signal by a predetermined second threshold to obtain a second scaled signal, and a fourth one of the plurality of nodes for taking the difference between the second correlation magnitude signal and the second scaled signal to generate a second CP correlation detection indication signal; and

wherein the first FFT section is an N-size FFT section and the second FFT section is also an N-size FFT section, the first FFT section searches for a first preamble associated with a first channel bandwidth and the second FFT section searches for a second preamble associated with a second channel bandwidth, and processing to obtain the first and second delay correlation detection indication signals is performed in parallel.

20. The mobile station of claim 19, wherein:

the first FFT section further includes nodes for squaring the first and second outputs and the second node of the first FFT section subtracts the squared second output from the squared first output; and

the second FFT section further includes nodes for squaring the first and fifth outputs and the second node of the second FFT section subtracts the squared fifth output from the squared first output.

21. The mobile station of claim 20, wherein:

the first FFT section further includes a fifth node for multiplying the first output with a conjugate of the third output, a sixth node for multiplying the second output with a conjugate of the fourth output, and a seventh node for subtracting a signal received from the sixth node from a signal received from the fifth node and outputting a first resultant signal; and

the second FFT section further includes a fifth node for multiplying the first output with a conjugate of the sixth output, a sixth node for multiplying the fifth output with a conjugate of the seventh output, and a seventh node for subtracting a signal received from the sixth node from a signal received from the fifth node and outputting a second resultant signal.

22. The mobile station of claim 21, wherein the first correlation magnitude is obtained by taking an absolute value of the first resultant signal and the second correlation magnitude is obtained by taking an absolute value of the second resultant signal.

23. A method of preamble searching by a mobile station in a wireless network, the method comprising:

in a first processing section of the mobile station;

generating a first correlation magnitude signal;

generating a first energy level signal corresponding to a first energy level of the received signal;

scaling the first energy level signal by a predetermined first threshold to obtain a first scaled signal; and

generating a first delay correlation detection indication signal by taking the difference between the first correlation magnitude signal and the first scaled signal;

in a second processing section of the mobile station;

generating a second correlation magnitude signal;

generating a second energy level signal corresponding to a second energy level of the received signal;

scaling the second energy level signal by a predetermined second threshold to obtain a second scaled signal; and

generating a second delay correlation detection indication signal by taking the difference between the second correlation magnitude signal and the second scaled signal;

wherein the first processing section searches for a first preamble associated with a first channel bandwidth and the second processing section searches for a second preamble associated with a second channel bandwidth, and wherein the first and second processing sections operate in parallel.

24. The method of claim 23, wherein the first processing section operates on an N-size FFT and the second processing section operates on an N/2 size FFT.

25. The method of claim 23, wherein the first processing section operates on an N-size FFT and the second processing section operates on the N-size size FFT.

26. The method of claim 23, further comprising:

receiving an input signal representative of a received signal from the wireless network in a delay line device;

the delay line device providing a plurality of outputs based upon the received input signal, including a first output r(n), a second output r(n−

D), a third output r(n−

2D), a first filtered output r₂ (m), a second filtered output r₂(m−

D/2) and a third filtered output r₂(m−

D);

in the first processing section, obtaining the first energy level signal by squaring the first and second outputs and taking the difference between the squares of the first and second outputs;

in the second processing section, obtaining the second energy level signal by squaring the first and second filtered outputs and taking the difference between the squares of the first and second outputs;

in the first processing section, obtaining the first correlation magnitude signal by;

multiplying the first output by a conjugate of the second output to obtain a first multiplied signal;

multiplying the second output by a conjugate of the third output to obtain a second multiplied signal; and

subtracting the second multiplied signal from the first multiplied signal;

in the second processing section, obtaining the second correlation magnitude signal by;

multiplying the first filtered output by a conjugate of the second filtered output to obtain a first multiplied signal;

multiplying the second filtered output by a conjugate of the third filtered output to obtain a second multiplied signal; and

subtracting the second multiplied signal from the first multiplied signal.

27. The method of claim 26, further comprising:

scaling the first energy level signal by a first predetermined threshold value;

scaling the second energy level signal by second a predetermined threshold value;

if the first correlation magnitude signal is greater than or equal to the scaled first energy level signal, then outputting a positive first delay correlation detection indication signal;

if the first correlation magnitude signal is less then the scaled first energy level signal, then outputting a negative first delay correlation detection indication signal;

if the second correlation magnitude signal is greater than or equal to the scaled second energy level signal, then outputting a positive second delay correlation detection indication signal; and

if the second correlation magnitude signal is less then the scaled second energy level signal, then outputting a negative second delay correlation detection indication signal.

28. The method of claim 23, further comprising:

receiving an input signal representative of a received signal from the wireless network in a delay line device;

the delay line device providing a plurality of outputs based upon the received input signal, including a first output r(n), a second output r(n−

D₁), a third output r(n−

2D₁), a fourth output r(n−

D₂) and a fifth output r(n−

2D₂);

in the first processing section, obtaining the first energy level signal by squaring the first and second outputs and taking the difference between the squares of the first and second outputs;

in the second processing section, obtaining the second energy level signal by squaring the first and fourth outputs and taking the difference between the squares of the first and fourth outputs;

in the first processing section, obtaining the first correlation magnitude signal by;

multiplying the first output by a conjugate of the second output to obtain a first multiplied signal;

multiplying the second output by a conjugate of the third output to obtain a second multiplied signal; and

subtracting the second multiplied signal from the first multiplied signal;

in the second processing section, obtaining the second correlation magnitude signal by;

multiplying the first output by a conjugate of the fourth output to obtain a first multiplied signal;

multiplying the fourth output by a conjugate of the fifth output to obtain a second multiplied signal; and

subtracting the second multiplied signal from the first multiplied signal.

29. The method of claim 28, further comprising:

scaling the first energy level signal by a first predetermined threshold value;

scaling the second energy level signal by second a predetermined threshold value;

if the first correlation magnitude signal is greater than or equal to the scaled first energy level signal, then outputting a positive first delay correlation detection indication signal;

if the first correlation magnitude signal is less then the scaled first energy level signal, then outputting a negative first delay correlation detection indication signal;

if the second correlation magnitude signal is greater than or equal to the scaled second energy level signal, then outputting a positive second delay correlation detection indication signal; and

if the second correlation magnitude signal is less then the scaled second energy level signal, then outputting a negative second delay correlation detection indication signal.

30. A method of preamble searching by a mobile station in a wireless network, the method comprising:

providing a delay line device for receiving an input signal representative of a received signal from the wireless network;

the delay line device generating a plurality of outputs including a first output r(n), a second output r(n−

N_cp1), a third output r(n−

N₁), a fourth output r(n−

N₁−

N_CP1), a fifth output r(n−

N_CP2), a sixth output r(n−

N₂) and a seventh output r(n−

N₂−

N_CP2), wherein N₁ is a first distance between repeating sections of the input signal and N₂ is a second distance between repeating sections of the input signal;

receiving the first output, the second output, the third output and the fourth output at a first FFT section, the first FFT section;

obtaining a first correlation magnitude signal;

obtaining a first energy level signal corresponding to a first energy level of the received signal;

scaling the first energy level signal by a predetermined first threshold to obtain a first scaled signal; and

taking the difference between the first correlation magnitude signal and the first scaled signal to generate a first CP correlation detection indication signal;

receiving the first, fifth, sixth and seventh outputs at a second FFT section, the second FFT section;

obtaining a second correlation magnitude signal;

obtaining a second energy level signal corresponding to a first energy level of the received signal;

scaling the second energy level signal by a predetermined second threshold to obtain a second scaled signal; and

taking the difference between the second correlation magnitude signal and the second scaled signal to generate a second CP correlation detection indication signal.

31. The method of claim 30, wherein the first FFT section is an N-size FFT section and the second FFT section is also an N size FFT section, and the first FFT section searches for a first preamble associated with a first channel bandwidth and the second FFT section searches for a second preamble associated with a second channel bandwidth.

32. The method of claim 30, wherein the first and second FFT sections operate in parallel to generate the first and second CP correlation detection indication signals.