JP4476154B2 - DSSS / OFDM duplex waiting reception method and wireless LAN apparatus - Google Patents

Description

  The present invention relates to a DSSS / OFDM duplex waiting reception method and a wireless LAN device in a wireless LAN device.

  Wireless LAN technology has been 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.

  The IEEE 802.11 standard targets burst signals, but a preamble signal for performing signal detection, synchronization processing, and the like is added to the head of the burst signal. The 11g standard realizes upward compatibility with the 11b standard, and supports OFDM modulation in addition to the DSSS / CCK modulation used in 11b in order to perform high-speed communication.

  In the 11g standard, in order to realize upward compatibility with 11b, it is specified in the protocol whether DSSS / CCK or OFDM signal is transmitted, and if there is an 11b terminal in the same network, DSSS / CCK The time for occupying the network is notified in advance by packet transmission using a modulated signal, and OFDM communication is performed within that time.

  Thus, since the 11g standard-compliant receiver needs to receive both DSSS / CCK and OFDM modulation at the same time, both demodulators need to be operated in parallel at the same time. However, for the purpose of reducing power consumption, it is not preferable to operate both demodulators simultaneously. Therefore, it is desirable to operate only both signal detectors and operate the demodulator selected by detection after detecting the signal.

  However, since both signal detectors must be considered including AGC processing and antenna switching, it is difficult to operate both processes in parallel, and RF control such as AGC needs to be processed sequentially.

  An OFDM preamble detector can realize an initial trigger by RSSI detection when the power is high, but it is also necessary to detect a signal with a low power at high speed by a correlation detector. Therefore, the initial signal detection is performed by an initial trigger by correlation detection at 1 symbol 0.8 μsec. Therefore, the correlation process is performed by cross-correlation. Also, the detection threshold is not increased too much to ensure that a trigger is applied. For the time being, a trigger is set up to make a reliable decision in post-processing.

  After the initial detection, the OFDM receiver performs AGC processing at high speed using the RSSI signal value. Also, antenna switching is performed every time a burst wave is received. OFDM AGC processing and antenna switching processing must be performed in a time of about 5 μsec out of 0.8 μsec short preamble period × 10 = 8 μsec. When the AGC is determined, detailed correlation detection and synchronization processing and frequency offset sparse adjustment are performed in the remaining 3 μsec.

  The DSSS reception preamble detector performs a Berker code correlation process. In general, the Berker correlator is resistant to noise, so that the discrimination capability is high even if the input signal is an OFDM preamble signal.

  Since the AGC process of the DSSS unit is a feedback system that does not use the DSSS, the process takes time. In addition, there is a problem of frequency offset, and when obtaining AGC accuracy, it is necessary to increase the number of feedbacks.

  Since one symbol time of DSSS is 1 μsec and one symbol time of OFDM is 0.8 μsec, the OFDM detector makes a decision first.

  Now, consider a case where a DSSS signal is input. Since the DSSS input signal has a waveform like a square wave and the OFDM correlator is a cross-correlator, it is easy to erroneously detect a waveform like a square wave. For this reason, if the initial trigger is erroneously detected by the OFDM that the initial trigger makes a decision first, after the OFDM AGC / ANT process, the synchronization detection process is performed. Move.

  However, since it is necessary to perform AGC processing by 20 μsec of signal input, considering that it takes 8 μsec to transition from the OFDM processing due to a synchronization error, it is more desirable to move faster by DSSS processing.

  SUMMARY OF THE INVENTION In view of such problems, it is an object of the present invention to provide a DSSS / OFDM double-sided waiting reception method and a wireless LAN apparatus that can realize DSSS AGC processing with high accuracy.

In order to solve the above problems, in the present invention,
A reception method in a wireless LAN device that supports both the DSSS system and the OFDM system,
An OFDM correlation detection stage for detecting a correlation in the OFDM scheme for the received signal;
A DSSS correlation detection step of detecting a correlation in the DSSS scheme with respect to the received signal;
And OFDM demodulation step for demodulating the OFDM scheme by the occurrence of an OFDM search trigger due to the fact that the correlation in the OFDM scheme is detected by the OFDM correlation detection step,
When the DSSS search trigger due to the fact that the previous SL DSSS correlation detecting step a correlation in DSSS scheme has been detected is generated, and the OFDM demodulation interruption phases to interrupt the OFDM demodulation step,
A DSSS demodulation stage in which a DSSS demodulation is performed by generating a DSSS search trigger when a correlation in the DSSS system is detected by the DSSS correlation detection stage ;
Ru equipped with.

In the present invention,
In the DSSS correlation detection step, the threshold level for detecting the correlation in D SSS scheme's threshold level before the OFDM demodulation step is started, the threshold level after the OFDM demodulation step is started Higher threshold level .

In the present invention,
In the DSSS correlation detection step, the threshold level after the OFDM demodulation step is started is set to be a higher threshold level than the threshold level for detecting the correlation in the DSSS scheme in the DSSS reception step .

In the present invention,
A wireless LAN device that supports both DSSS and OFDM systems,
OFDM correlation detection means for detecting the correlation in the OFDM system for the received signal;
DSSS correlation detection means for detecting a correlation in the DSSS scheme for the received signal;
OFDM demodulation means for demodulating the OFDM scheme by the occurrence of an OFDM search trigger due to the detection of correlation in the OFDM scheme by the OFDM correlation detection means ;
DSSS demodulation means for performing demodulation of the DSSS method,
The OFDM demodulating means interrupts demodulation of the OFDM when a DSSS search trigger is generated due to detection of correlation in the DSSS system by the DSSS correlation detecting means during demodulation of the OFDM system,
The DSSS demodulator unit, when DSSS search trigger due to the fact that the correlation in the DSSS scheme is detected by the DSSS correlation detection means has occurred, performs the demodulation of the DSSS scheme.

In the present invention,
The DSSS correlation detection unit shall be the variable threshold level for detecting the correlation in the DSSS scheme.

  ADVANTAGE OF THE INVENTION According to this invention, the DSSS / OFDM double-sided waiting reception method and wireless LAN apparatus which implement | achieve ASS process of DSSS accurately 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 detection unit 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 ends 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 DS generated when DSSS signal is detected by correlation detection unit 342 of DSSS unit 34 SS_END_TRIG: Trigger signal generated when demodulation is completed in the demodulator 343 of the DSSS unit 34. Further, the BB / MAC unit 3 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, when a carrier is detected, the correlation detection unit 332 of the OFDM unit 33 and the correlation detection unit 342 of the DSSS unit 24 start correlation detection. In this correlation detection, the correlation detection unit 342 of the DSSS unit 24 performs Barker detection. Since this Barker detection is resistant to noise and has a high discrimination capability with respect to the OFDM preamble, it is desirable to prioritize the detection result of the correlation detection unit 342.

  Therefore, even if a DSSS signal is input and an OFDM_SEARCH_TRIG signal is generated, if Barker detection is performed before determining an OFDM synchronization error, the input signal is determined to be a DSSS signal and immediately sent to the DSSS unit 34. By shifting the processing, it is possible to take time for the AGC processing in the DSSS unit 34, and it is possible to realize the AGC processing with higher accuracy.

  This will be specifically described with reference to FIG. FIG. 2 is a diagram illustrating processing of the OFDM unit and the DSSS unit. Both the OFDM part and the DSSS part first perform correlation detection. The OFDM unit generates an OFDM_SEARCH_TRIG signal and starts OFDM processing. At this time, the DSSS unit continues the correlation detection. When the DSSS unit detects a barker, a DSSS_SEARCH_TRIG signal is generated and the barker detection is prioritized. Therefore, the OFDM unit interrupts the OFDM process, and the DSSS unit executes the DSSS process.

  Next, processing for changing the threshold level will be described with reference to FIG. In this description, the lower the threshold level, the harder it is to determine whether the input signal is a DSSS signal. That is, an input signal determined as a DSSS signal at a lower threshold level has a higher probability of being a DSSS signal.

  As shown in FIG. 3, the initial threshold level at which the correlation detection is started is set to a relatively high threshold level with a weak decision to detect without missing the DSSS signal. Since the correlation detection during OFDM processing after the generation of the OFDM_SEARCH_TRIG signal is used as an auxiliary, it must be determined that it is a DSSS signal, so it is made lower than the initial threshold level to make the determination stricter. .

  Next, after an OFDM_SYNCLOSS_TRIG signal is generated due to a synchronization error in OFDM processing and the processing moves to the DSSS unit, the threshold level is further set to a lower threshold value. The AGC process is performed after the process is transferred to the DSSS unit. At this time, it is intended to determine the disappearance of the DSSS signal rather than determining whether the signal is a DSSS signal.

  When the DSSS signal disappears, it is necessary to immediately return to the initial state (OFDM and DSSS enter the initial trigger detection wait state). The reason is that the DSSS preamble signal is very long and corresponds to the change in state during that time. Thus, the threshold level of the wireless LAN device according to the present embodiment is variable. In particular, as described above, there may be three threshold levels, and these threshold levels may be variable.

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 the process of an OFDM part and a DSSS part. It is a figure which shows the example which makes a threshold level (three steps) variable.

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

Claims (5)

A reception method in a wireless LAN device that supports both the DSSS system and the OFDM system,
An OFDM correlation detection stage for detecting a correlation in the OFDM scheme for the received signal;
A DSSS correlation detection step of detecting a correlation in the DSSS scheme with respect to the received signal;
And OFDM demodulation step for demodulating the OFDM scheme by the occurrence of an OFDM search trigger due to the fact that the correlation in the OFDM scheme is detected by the OFDM correlation detection step,
When the DSSS search trigger due to the fact that the previous SL DSSS correlation detecting step a correlation in DSSS scheme has been detected is generated, and the OFDM demodulation interruption phases to interrupt the OFDM demodulation step,
A DSSS demodulation stage in which a DSSS demodulation is performed by generating a DSSS search trigger when a correlation in the DSSS system is detected by the DSSS correlation detection stage ;
DSSS / OFDM duplex waiting reception method characterized by Ru with a. The DSSS / OFDM duplex waiting reception method according to claim 1,
In the DSSS correlation detection step, the threshold level for detecting the correlation in D SSS scheme's threshold level before the OFDM demodulation step is started, the threshold level after the OFDM demodulation step is started A DSSS / OFDM double-sided waiting reception method, wherein the threshold level is set to be higher than the threshold level . In the DSSS / OFDM duplex waiting reception method according to claim 2,
In the DSSS correlation detection step, the threshold level after the OFDM demodulation step is started is set to be a higher threshold level than the threshold level for detecting the correlation in the DSSS scheme in the DSSS reception step A DSSS / OFDM duplex waiting reception method characterized by the above. A wireless LAN device that supports both DSSS and OFDM systems,
OFDM correlation detection means for detecting the correlation in the OFDM system for the received signal;
DSSS correlation detection means for detecting a correlation in the DSSS scheme for the received signal;
OFDM demodulation means for demodulating the OFDM scheme by the occurrence of an OFDM search trigger due to the detection of correlation in the OFDM scheme by the OFDM correlation detection means ;
DSSS demodulation means for performing demodulation of the DSSS method,
The OFDM demodulating means interrupts demodulation of the OFDM when a DSSS search trigger is generated due to detection of correlation in the DSSS system by the DSSS correlation detecting means during demodulation of the OFDM system,
The wireless LAN apparatus according to claim 1, wherein the DSSS demodulation unit performs demodulation of the DSSS method when a DSSS search trigger is generated when a correlation in the DSSS method is detected by the DSSS correlation detection unit . The wireless LAN device according to claim 4,
The wireless LAN apparatus, wherein the DSSS correlation detection means makes a threshold level for detecting a correlation in the DSSS system variable.

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