JP2006295465A - Input signal discrimination method, and wireless lan apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an input signal discrimination method for discriminating whether a received signal adopts the OFDM or the DSSS with high accuracy and to provide a wireless LAN apparatus. <P>SOLUTION: The input signal discrimination method discriminating whether the received signal is a DSSS signal or an OFDM signal includes a cross-correlation power output step for outputting a cross-correlation power of an input signal; a peak detection step for detecting a peak value within one-symbol time of the cross-correlation power output in the cross-correlation power output step; an accumulation calculation step of calculating an accumulated value within the one symbol time of the cross-correlation power outputted from the cross-correlation output step; and a discrimination step of discriminating whether the input signal is the DSSS signal or the OFDM signal on the basis of the peak value and the accumulated value. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an input signal determination method and a wireless LAN apparatus that determine whether a signal is a DSSS signal or an OFDM signal.

  Wireless LAN technology is being standardized in IEEE 802.11 (Institute of Electrical and Electronics Engineers 802.11), and the introduction of wireless LAN is progressing in place of a conventional wired network or coexisting with a wired network.

  IEEE 802.11b (hereinafter referred to as 11b) defines a DSSS (Direct Sequence Spread Spectrum) system, and IEEE 802.11a defines an Orthogonal Frequency Division Multiplexing (OFDM) system, which is referred to as IEEE 802.11g (hereinafter referred to as 11g). ) Stipulates contents corresponding to both the DSSS system and the OFDM system.

  When the DSSS signal is input in such a state of waiting for both signals, it is necessary to accurately issue a correlation error and shift to the DSSS process even when the OFDM initial detector is erroneously operated and operates until the synchronization process. Therefore, there is a method in which a Barker correlator, which is a DSSS signal detector, is supplementarily used to shift to DSSS processing when the Barker correlation value exceeds a certain threshold.

  However, depending on the setting of the Barker detection threshold, the state of noise, and the like, the Barker detector threshold may not be exceeded during a short preamble in which processing such as AGC processing and synchronization processing is performed after OFDM initial trigger detection.

  In that case, it is necessary for the OFDM receiver to perform discrimination from the DSSS signal by itself. After initial detection is activated in OFDM, AGC and antenna switching are performed, but the time needs to end within approximately 5 μsec. After the AGC is determined, 3 symbols are required in the short preamble to perform the synchronization process and the frequency offset correction.

  That is, it is necessary to leave the last 3 × 0.8 = 2.4 μsec in the short preamble period of 8 μsec. In this section, the AGC process is completed and the input amplitude should be within the expected level. Therefore, it is desirable to perform auto-correlation and cross-correlation processing again in this section to further improve the accuracy of detection results and discriminate from DSSS and noise.

  However, the cross-correlation is weak to a square wave such as DSSS, and with 3 symbols, only 2 symbols can be used for determination for autocorrelation. Also, depending on the autocorrelation threshold setting, there is a possibility of causing a determination error.

  In view of such problems, an object of the present invention is to provide an input signal determination method and a wireless LAN apparatus that accurately determine whether an input signal is OFDM or DSSS.

  In order to solve the above problems, the present invention provides an input signal determination method for determining whether an input signal is a DSSS signal or an OFDM signal, and outputs the cross-correlation power of the input signal. A cross-correlation power output stage, a peak detection stage for detecting a peak value within one symbol time of the cross-correlation power output in the cross-correlation power output stage, and a cross-correlation power output in the cross-correlation power output stage A cumulative calculation step of calculating a cumulative value within one symbol time, and a determination step of determining whether the input signal is a DSSS signal or an OFDM signal based on the peak value and the cumulative value. It is characterized by having.

  In the present invention, the peak detection step detects the peak value of the maximum peak and the second largest peak.

  In the present invention, the cumulative calculation step calculates a cumulative value of cross-correlation power excluding the peak value detected in the peak detection step.

  According to the present invention, there is provided a wireless LAN apparatus compatible with both the DSSS scheme and the OFDM scheme, wherein the cross-correlation power output means outputs the cross-correlation power of the input signal, and the cross-correlation power output means. Peak detecting means for detecting the peak value within one symbol time of the cross-correlation power output in step 1, and cumulative calculation means for calculating the cumulative value within one symbol time of the cross-correlation power output from the cross-correlation power output means And determining means for determining whether the input signal is a DSSS signal or an OFDM signal based on the peak value and the accumulated value.

  In the present invention, the peak detecting means detects a peak value of a maximum peak and a second largest peak.

  In the present invention, the cumulative calculation means calculates a cumulative value of cross-correlation power excluding a peak value detected by the peak detection means.

  ADVANTAGE OF THE INVENTION According to this invention, the input signal determination method and wireless LAN apparatus which determine accurately whether the input signal is OFDM or DSSS can be provided.

  Hereinafter, preferred embodiments of the present invention will be described.

  FIG. 1 is a diagram illustrating a configuration example of a wireless LAN device according to an embodiment of the present invention. Only functional units related to reception are shown, and functional units related to transmission are omitted.

  In FIG. 1, the wireless LAN device includes antennas 1A and 1B, an RF unit 2 composed of a single IC chip, and a BB / MAC unit 3 composed of another single IC chip. The MAC unit 3 is connected to a host CPU 4 such as a PC (Personal Computer) or a printer, which is a higher-level device including an application that communicates via a wireless LAN.

  The BB / MAC unit 3 also indicates the I component (RX I), Q component (RX Q), and received signal strength of the received signal after conversion (mixing with a carrier frequency signal) output from the RF unit 2. An interface between the RF unit 2 and the A / D conversion unit 31 that inputs an RSSI (Receive Signal Strength Indication) signal and converts it into a digital value is performed, and the operations of the OFDM unit 33 and the DSSS unit 34 described below are controlled. An RF interface unit 32, an OFDM unit 33 that performs demodulation of the OFDM scheme, and a DSSS unit 34 that performs demodulation of the DSSS scheme are provided. The OFDM unit 33 and the DSSS unit 34 include AGC processing units 331 and 341 that control the gain of the RF unit 2, correlation detection units 332 and 342 that detect whether the signal is a desired scheme, and data demodulation. Demodulating sections 333, 343 and the like are provided.

  As signals exchanged between the RF interface unit 32, the OFDM unit 33, and the DSSS unit 34, those relating to the present invention are the following signals.

R _X I, Q: digitized received signal RSSI_TRIG: trigger signal generated during carrier detection OFDM_ACT: signal generated during operation of OFDM unit 33 OFDM_SEARCH_TRIG: OFDM signal detected by correlation detector 332 of OFDM unit 33 OFDM_SYNC_TRIG: trigger signal generated when a synchronization error occurs in the demodulation unit 333 of the OFDM unit 33 OFDM_END_TRIG: trigger signal generated when demodulation is completed in the demodulation unit 333 of the OFDM unit 33 DSSS_ACT: DSSS Signal generated during operation of unit 34 DSSS_SEARCH_TRIG: Trigger signal generated when DSSS signal is detected by correlation detection unit 342 of DSSS unit DS SS_END_TRIG: Trigger signal generated when demodulation is completed in the demodulator 343 of the DSSS unit 34. The BB / MAC unit 3 further includes a MAC interface unit 35 that interfaces with the MAC unit 36 described below, and a CSMA / CA. And a MAC unit 36 that performs media access control (MAC) such as (Carrier Sense Multiple Access with Collision Avoidance).

  The configuration of the wireless LAN device in the embodiment of the present invention is as described above. Next, specific processing will be described. First, in the present embodiment, a correlation value output of cross-correlation is used from the viewpoint of considering discrimination from a DSSS signal.

  The cross-correlation power when a DSSS signal and an OFDM preamble signal are input will be described with reference to FIG. FIG. 2 shows input signals 401 and 402, OFDM cross-correlation power 403, and DSSS cross-correlation power 404. The input signal 401 is a DSSS signal. The input signal 402 is an OFDM signal.

  The OFDM cross-correlation power 403 indicates the cross-correlation power of the OFDM preamble signal, and the DSSS cross-correlation power 404 indicates the cross-correlation power of the DSSS signal.

  As shown in FIG. 2, when an OFDM preamble signal is input, there is one peak in one symbol. On the other hand, when a DSSS signal is input, due to the nature of the signal (square wave), the cross-correlation power has a number of peaks instead of once in one symbol time, and cannot be determined only by the correlation threshold.

  In the present embodiment, the above-described two cross-correlation power properties are used to compare the peak power of the cross-correlation power within one symbol time with the accumulated addition value other than the peak power. In this comparison, if the difference or ratio is more than a certain value, it means that the peak power in one symbol is strong, and there is a strong possibility that it is an OFDM signal. In the opposite case, a plurality of peak powers exist in one symbol, and there is a strong possibility of being a DSSS signal.

  In the case of FIG. 2, three determinations can be made over three symbols. A configuration for this comparison will be described with reference to FIG. FIG. 3 shows a cross-correlator 410, a peak detector 411 within a symbol time, a power accumulator 412 within a symbol time, amplifiers 413 and 414, and a comparator 415. The configuration shown in FIG. 3 is provided in the RF interface unit 32.

  The cross correlator 410 outputs a cross correlation power from the input signal. The peak detector 411 within symbol time detects a peak within one symbol time. A power accumulator 412 within symbol time accumulates cross-correlation power within symbol time excluding power at the maximum peak and the second peak. The amplifier 413 adds the cross correlation powers of the maximum peak and the second peak in one symbol. This is because a cross-correlation peak may appear between samples depending on the sampling timing of the input signal. The amplifier 414 multiplies the accumulated cross-correlation power by α. This α is a threshold value. The comparator 415 compares the outputs from the amplifiers 413 and 414.

  When the output from the amplifier 413 is large, there is a strong possibility that it is an OFDM signal. When the output from the amplifier 414 is large, there is a strong possibility that it is a DSSS signal.

  Thus, it is characterized by determining whether an input signal is an OFDM signal using the output of a comparator.

  In the above description, the cross correlator 410 corresponds to the cross correlation power output means. The peak detector 411 corresponds to peak detection means. The power accumulator 412 corresponds to accumulation calculation means. The comparator 415 corresponds to determination means.

It is a figure which shows the structural example of the wireless LAN apparatus concerning one Embodiment of this invention. It is a figure which shows a cross correlation power. It is a figure which shows the example of judgment using a comparator.

Explanation of symbols

1A, 1B Antenna 2 RF unit 3 BB / MAC unit 31 A / D conversion unit 32 RF interface unit 33 OFDM unit 331 AGC processing unit 332 Correlation detection unit 333 Demodulation unit 34 DSSS unit 341 AGC processing unit 342 Correlation detection unit 343 Demodulation unit 35 MAC interface part 36 MAC part 4 Host CPU
401, 402 Input signal 403 OFDM cross-correlation power 404 DSSS cross-correlation power

Claims (6)

An input signal determination method for determining whether an input signal is a DSSS signal or an OFDM signal,
A cross-correlation power output stage for outputting a cross-correlation power of the input signal;
A peak detection step of detecting a peak value in one symbol time of the cross correlation power output in the cross correlation power output step;
A cumulative calculation step of calculating a cumulative value of the cross correlation power output in the cross correlation power output step within one symbol time;
A determination step of determining whether the input signal is a DSSS signal or an OFDM signal based on the peak value and the accumulated value. The method of claim 1, wherein the peak detecting step detects a peak value of a maximum peak and a second largest peak. 3. The input signal determination method according to claim 1, wherein the cumulative calculation step calculates a cumulative value of cross-correlation power excluding the peak value detected in the peak detection step. A wireless LAN device that supports both DSSS and OFDM systems,
Cross-correlation power output means for outputting the cross-correlation power of the input signal;
Peak detection means for detecting a peak value within one symbol time of the cross-correlation power output by the cross-correlation power output means;
Cumulative calculation means for calculating a cumulative value of the cross correlation power output by the cross correlation power output means within one symbol time;
A wireless LAN device comprising: a determination unit that determines whether the input signal is a DSSS signal or an OFDM signal based on the peak value and the accumulated value. 5. The wireless LAN apparatus according to claim 4, wherein the peak detecting unit detects a peak value of a maximum peak and a second largest peak. The wireless LAN apparatus according to claim 4 or 5, wherein the cumulative calculation unit calculates a cumulative value of cross-correlation power excluding a peak value detected by the peak detection unit.

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