METHOD FOR SWITCHING BETWEEN A LONG GUARD INTERVAL AND A SHORT GUARD INTERVAL AND MODULE USING THE SAME

• US 20100202301A1
• Filed: 06/17/2009
• Published: 08/12/2010
• Est. Priority Date: 02/12/2009
• Status: Abandoned Application

• Current Assignee: Ralink Technology Corporation (MediaTek, Inc.)
• Original Assignee: Ralink Technology Corporation (MediaTek, Inc.)
• Inventors: TU, YUNG SZU, LIAO, YEN CHIN, WEN, CHUN HSIEN, CHEN, JIUNN TSAIR
• Application Number:
  US12/486,503
• Publication Number:
  US 20100202301A1
• Time in Patent Office: Days
• US Class Current: 370/252
• CPC Class Codes: H04L 25/0216 with estimation of channel length
• CPC Class Codes: H04L 25/0222 Estimation of channel variability, e.g. coherence bandwidth, coherence time, fading frequency
• CPC Class Codes: H04L 25/0228 with direct estimation from sounding signals
• CPC Class Codes: H04L 27/2607 Cyclic extensions
• CPC Class Codes: H04L 43/16 Threshold monitoring
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT

Abstract

The module for switching between a long guard interval and a short guard interval comprises a signal processing unit, a measurement unit, a comparison unit and a switching unit. The module receives a first data symbol, and the data symbol has one of a long guard interval and a short guard interval. The signal processing unit is configured to generate a second data symbol in accordance with the first data symbol. The measurement unit is configured to measure a portion of the first and second data symbols in order to generate a first measurement value and a second measurement value. The comparison unit is configured to generate an output signal by comparing the first and second measurement values with a threshold value. The switching unit is configured to selectively switch guard intervals of subsequent data symbols in accordance with the output signal.

Claims

1. A method for switching between a long guard interval and a short guard interval, comprising the steps of:

receiving a first data symbol, the first data symbol including a cyclic preamble and an effective data;

generating a second data symbol in accordance with the cyclic preamble, the second data symbol including an effective data;

respectively measuring portions of the first and second data symbols to generate a first measurement value and a second measurement value; and

comparing the first and second measurement values with a threshold value to generate an output value, wherein the output value is used to choose a long guard interval or a short guard interval.

2. The method of claim 1, wherein the cyclic preamble includes a long guard interval, a first portion of the long guard interval includes i samples, a second portion of the long guard interval includes j samples, and k samples in a tail portion of the second data symbol are the same as the j samples, wherein i, j and k are integers.

3. The method of claim 1, wherein the cyclic preamble includes a short guard interval, the short guard interval includes m samples, and k samples in a tail portion of the second data symbol are the same as the m samples, wherein m and k are integers.

4. The method of claim 1, wherein the portions of the first and second data symbols are the effective data of the first and second data symbols.

5. The method of claim 1, wherein the first and second measurement values represent signal-to-noise ratio (SNR) or error vector magnitude (EVM).

6. The method of claim 1, wherein the comparing step comprises comparing an absolute value of a difference between the first measurement value and the second measurement value with the threshold value.

7. The method of claim 6, wherein when the absolute value is smaller than the threshold value, guard intervals of subsequent data symbols are switched to a short guard interval;

when the absolute value is greater than the threshold value, guard intervals of subsequent data symbols are switched to a long guard interval.

8. A method for switching from a long guard interval to a short guard interval, comprising the steps of:

receiving a preamble to generate a channel estimation parameter;

calculating a cross-correlation of channels between adjacent subcarriers in accordance with the channel estimation parameter;

determining whether the cross-correlation is greater than a threshold value; and

switching guard intervals of subsequent data symbols to a short guard interval if the determination is affirmative.

9. The method of claim 8, wherein the calculating step comprises the steps of:

calculating a minimum value of a coherence bandwidth in accordance with the short guard interval;

calculating the number of adjacent subcarriers in accordance with the minimum value of a coherence bandwidth;

calculating the cross-correlation in accordance with the number of adjacent subcarriers and the channel estimation parameter.

10. The method of claim 9, wherein the step of calculating the number of adjacent subcarriers is performed in accordance with a frequency spacing of the subcarriers.

11. The method of claim 8, wherein the preamble and the short guard interval comply with the Institute of Electrical and Electronics Engineers (IEEE) 802.11a or IEEE 802.11n standard.

12. A module for switching between a long guard interval and a short guard interval, the module receiving a first data symbol, the data symbol having one of a long guard interval and a short guard interval, the module comprising:

a signal processing unit configured to generate a second data symbol in accordance with the first data symbol;

a measurement unit configured to measure portions of the first and second data symbols in order to generate a first measurement value and a second measurement value;

a comparison unit configured to generate an output signal by comparing the first and second measurement values with a threshold value; and

a switching unit configured to selectively switch guard intervals of subsequent data symbols in accordance with the output signal.

13. The module of claim 12, wherein the signal processing unit includes:

a replica unit configured to replicate a plurality of samples in a guard interval of the first data symbol; and

a replacement unit configured to generate a second data symbol by replacing a plurality of samples in a tail portion of the first data symbol through the replica unit.

14. The module of claim 12, wherein the portions of the first and second data symbols are respectively the effective data of the first and second data symbols.

15. The module of claim 12, wherein the measurement unit is a signal analyzer, and the first and second measurement values represent an error vector magnitude (EVM).

16. The module of claim 15, wherein the comparison unit further comprises an operation unit for comparing an absolute value of a difference between the first measurement value and the second measurement value with the threshold value.

17. The module of claim 16, wherein when the absolute value is smaller than the threshold value, guard intervals of subsequent data symbols are switched to a short guard interval;

when the absolute value is greater than the threshold value, guard intervals of subsequent data symbols are switched to a long guard interval.