KR100887928B1 - Method for searching synchronization symbol of wireless usb system - Google Patents

Abstract

A method for searching symbol synchronization of a wireless USB(Universal Serial Bus) system is provided to improve reception performance by tracking an error when obtaining an accurate symbol start point and tracking the synchronization. A cross correlation is calculated by comparing a signal inputted to a wireless USB system and a complex code of a reference symbol(S10). An initial symbol start point is calculated by comparing the cross correlation with a critical value(S12,S14). The frequency hopping synchronization is searched when using the frequency hopping(S16,S18). An analog effect is minimized(S20). The symbol synchronization is tracked by tracking the maximum value generated based on the initial symbol start point(S24). The final symbol start point is calculated by tracking the position of the maximum value(S30).

Description

Symbol Synchronization Search Method for Wireless USB System {METHOD FOR SEARCHING SYNCHRONIZATION SYMBOL OF WIRELESS USB SYSTEM}

The present invention relates to a synchronous search method of a wireless USB system, and more particularly, to search for an initial symbol starting point by inputting a predetermined number or more of cross-correlation values above a reference value in a multiband OFDM baseband modem. The present invention relates to a symbol synchronization search method of a wireless USB system which calculates and applies a starting point of a final synchronization symbol by tracking symbol synchronization by accumulating a position where a maximum correlation value is obtained in a predetermined region based on a starting point.

In general, USB (Universal Serial Bus) is a serial port that solves the problem of slow speed and limited device connectivity of existing external expansion ports (serial or parallel). And a plug and play interface for connecting the computer with a peripheral device such as a printer.

Unlike external expansion ports used to connect only devices such as modems, printers, and scanners, USB can be connected to peripheral devices such as keyboards, monitors, mice, printers, and modems at once. If your PC has only one USB connector, you can connect up to 127 peripherals in a molded or radial form.

In recent years, wireless USB (WUSB) based on Ultra Wide Band (UWB) technology has been standardized in an effort to eliminate the need for USB cables to connect computer systems and external peripherals. Wireless USB is aiming for communication speeds comparable to the USB 2.0 standard (eg, up to 480 Mbps) over distances up to 10 meters.

Among the baseband modem methods for implementing wireless personal area networks (PANs) for short-range communication of portable devices such as wireless USB, multi-band orthogonal frequency division multiplexing (OFDM) is used for wireless USB (WUSB), Wireless 1394, and next-generation Bluetooth. It is used as baseband communication method.

In the multi-band OFDM scheme (MB-OFDM), the packet transmission includes a PLCP header including 30 or 18 PLCP preambles, MAC headers, packet lengths, and a modulation method of the PSDU, as shown in FIG. It consists of PSDU part including actual data to be transmitted. PLCP preamble is specifically a packet / frame synchronization sequence part having 24 or 12 repeated symbols and 6 channel estimation sequence. It is composed of parts.

The multiband OFDM scheme consists of 128 multiple tones and uses an FFT of size 128. One OFDM symbol has 165 samples consisting of 128 valid samples and 37 zero-valued samples in the time domain. In this case, the packet synchronization sequence part is the most important part for packet reception, and is a process of determining the start of the transmitted packet and the range of samples to which the FFT is applied.

In the case of WUSB, 37 samples having zero values for each symbol are added to 128 sample values generated after IFFT to reduce the influence of inter-symbol interference caused by transmission delay. Therefore, it uses a zero padding method different from the Cycle-Prefix method attached to the front or the back of the symbol.

In the case of the zero padding method, a sample window for applying a more accurate FFT is required. In this case, inaccurate symbol synchronization induces a result of incorrectly generating an OFDM symbol to be restored, thereby inducing a packet transmission. This false symbol synchronization process is caused by the characteristics of the radio channel, the AWGN and other errors, along with the error due to the inconsistency of the transmitter and the receiver.

After all, finding the correct symbol synchronization is the starting point for the accurate restoration of PLCP header and PSDU information and is one of the most important blocks in baseband modem design.

In the case of a communication system using an OFDM modulation method, a cycle-prefix method is generally used. In this case, the FFT operation of the received sample is processed using the characteristics of the Cyclic-Prefix without finding an accurate OFDM symbol start point. An OFDM demodulation process may be performed through the process.

For example, in the case of a 802.11a / g system, which is a typical packet transmission using OFDM modulation, since the Cyclic-Prefix method is used, the performance can be satisfied by the approximate search method rather than the exact symbol synchronization search method.

However, the zero-padding method used in Wireless USB requires exact symbol start point search.

In addition, since the starting point of the transmission packet is not known in the initial search process, there are inherent reception gain mismatch, DC-offset, frequency offset, and the like, and a search error due to AWGN may occur.

The error of the symbol start point search process may cause not only packet loss but also power loss when used in a portable device. Therefore, an error warning is required.

Meanwhile, the MB-OFDM scheme adopted in Wireless USB also uses four types of center frequency hopping as shown in FIG. 2 according to the channel in the TFI mode.

Since all four types begin in the low band, the search for the symbol starts with the low band. Since frequency hopping occurs in units of 3 symbols or 6 symbols, when the preamble is made of 24 symbols as shown in FIG. 1, only 8 symbol search opportunities are given. In addition to the symbol search process, AGC, DC-offset, frequency Since the process of offset (Frequency Offset) must also be made, the maximum opportunity interval must be used, and in the case of TFI mode, the synchronization process must consider the synchronization of the frequency hopping together with the synchronization of the OFDM symbol start point.

The present invention was created to solve the above needs, and an object of the present invention is to search for an initial symbol starting point by inputting a predetermined number or more consecutive values of a reference value or more in a baseband modem of a multiband OFDM method and then initial symbol. Provides a synchronization search method of a wireless USB system that calculates and applies a final symbol start point by tracking symbol synchronization through accumulation of positions where the maximum correlation value occurs in a predetermined region in a preamble repeated based on a starting point. Is in.

In order to achieve the above object, the present invention provides a synchronous search method of a wireless USB system for searching for a symbol start point in a wireless USB system employing a multiband OFDM scheme. Comparing the first step of calculating the cross-correlation degree, the second step of calculating the initial symbol start point by comparing the calculated cross-correlation and the threshold value, and after calculating the initial symbol start point, the frequency hopping synchronization according to whether or not to use the frequency hopping Tracking the symbol synchronization by tracking the position of the maximum value generated based on the initial symbol start point after minimizing the analog effect after minimizing the analog effect after searching for frequency hopping synchronization. And a sixth step of tracking the symbol synchronization and calculating and applying a final symbol start point. Characterized in that binary.

The second step of calculating the initial symbol start point in the present invention is to calculate the initial symbol start point by detecting the maximum value of the cross-correlation for a certain number of input signals from the time when the cross-correlation degree is detected above the threshold value It is done.

In the present invention, the fourth step of minimizing the analog effect is characterized by applying AGC, DC offset, and frequency offset.

In the fifth step of tracking symbol synchronization in the present invention, if the cross-correlation degree generated in a predetermined interval region before and after the position where the maximum value of the cross-correlation degree predicted by calculating based on the initial symbol start point is to be generated, the corresponding position is greater than or equal to the threshold value. It is characterized by calculating the hit ratio of.

In the present invention, when the maximum value of the cross-correlation degree is below the threshold or the maximum value of the cross-correlation outside the constant interval region occurs by comparing the input signal with the reference symbol in the fifth step of tracking symbol synchronization. The error alarm count value is increased to generate an error and return to the first step when the error alarm count value is greater than or equal to the reference set value.

At this time, the value of False Alarm coefficient is increased when the maximum value of cross-correlation is lower than the threshold in a certain section area or when the maximum value of cross-correlation is generated outside a certain section. If the value exceeds the threshold is characterized in that for reducing.

In the present invention, the fifth step of tracking symbol synchronization is repeated until the boundary of the synchronization sequence is found.

As described above, the present invention searches for an initial symbol start point by continuously inputting a predetermined number or more of cross-correlation values above a reference value in a multiband OFDM baseband modem in a preamble repeated based on the initial symbol start point. The symbol synchronization is traced through the accumulation of the position where the maximum correlation value is obtained in a certain area, and the final symbol start point is calculated and applied to obtain the correct symbol start point and to improve the reception performance through the error tracking process during the synchronization tracking process. There is an advantage in that hardware complexity can be reduced.

Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings, and the same parts as in the prior art use the same reference numerals and names. In addition, the present embodiment is not intended to limit the scope of the present invention, but is presented by way of example only and those skilled in the art will be capable of many modifications within the technical spirit of the present invention.

3 is a flowchart illustrating a synchronous search method of a wireless USB system according to the present invention.

First, in a wireless USB system employing a multiband OFDM scheme, a symbol search is started to calculate a cross correlation by comparing an input signal with a reference symbol (S10). At this time, cross-correlation is calculated by using only complex code values of the input signal and the reference symbol to minimize hardware use.

When the cross-correlation degree calculated by calculating the cross-correlation between the input signal and the reference symbol exceeds the threshold, the initial symbol start point is calculated by calculating the position where the cross-correlation is the maximum value for a certain number of input signals from this point. It is calculated (S12) (S14).

That is, if the cross-correlation degree exceeds the threshold, it is assumed that a valid symbol for the input signal has begun to be received, and then the cross-correlation degree is observed for a predetermined number of input signals. If the correlation is high, the location of the maximum value is found by updating the stored correlation.

The position having the maximum value determined as described above determines that the reference symbol and the input signal match, and calculates an initial symbol start point therefrom.

As described above, after calculating the initial symbol start point, it is determined whether the frequency hopping is used as shown in FIG. 2, and the frequency hopping synchronization is searched when the frequency hopping is used (S16).

For example, if the TFC value is 3 and 4, since the initial symbol may occur in the 1st and 2nd symbols of the frequency hopping pattern, the cross-correlation at the expected position of the input signal after calculating the initial symbol start point is calculated. If the degree is greater than the threshold value, it is determined that the first symbol is searched in the first symbol, and the symbol of the next input signal is judged to be the third symbol, and the frequency hopping is performed, and if it is small, the initial symbol is searched in the second symbol. By judging, the symbol of the next input signal is judged as the fourth symbol and frequency hopping.

After searching for the frequency hopping synchronization, AGC (Auto Gain Control), DC offset (DC-offset), and frequency offset (Frequency offset) are applied to minimize the analog effect (S20).

In order to minimize the analog effect, after applying AGC, DC offset, and frequency offset, the boundary of the packet synchronization sequence is started (S22).

In this way, the cross-correlation predicted from the initial symbol start point until the search of the boundary of the packet synchronization sequence and the boundary of the packet-synchronization sequence is performed is actually generated in the constant interval region before and after the position where the maximum value is to be generated. After tracking the symbol synchronization by tracking the position of the maximum value of the figure (S24), the final symbol start point is calculated and applied based on the frequency of the position where the maximum value occurs (S30).

In other words, based on the result obtained in the process of calculating the initial symbol start point, the maximum value that occurs when the cross-correlation calculated in the constant interval region before and after the center of the cross correlation is expected Increase the hit rate for that location.

In this way, the hit rate of the position having the maximum value and above the threshold value is counted, and the starting point of the final sync symbol is recalculated using the position of the maximum hit rate.

In this case, when the boundary of the packet synchronization sequence is searched (S28), the symbol synchronization tracking is terminated and the final symbol start point is calculated, and the cross-correlation diagram in the expected interval area is compared by comparing the reference signal with the signal input during synchronization tracking. If the maximum value of is below the threshold value or if the maximum value of cross-correlation is generated outside the expected interval area, increase the value of the False Alarm coefficient to detect the error when the value of the False Alarm is above the standard setting value. And the symbol is searched again (S26).

The false alarm coefficient for generating an error is increased when the maximum value of cross-correlation is below a threshold in a predetermined interval region or when the maximum value of cross-correlation occurs outside a certain interval region. If the maximum value of the cross-correlation diagram exceeds the threshold, the error warning count value is exceeded the reference value, so that the initial synchronous search is considered failed and the symbol is searched again.

1 is a diagram illustrating a packet configuration of a multiband OFDM scheme of a general wireless USB system.

2 is a diagram illustrating an example of frequency hopping in a general wireless USB system.

3 is a flowchart illustrating a synchronous search method of a wireless USB system according to the present invention.

Claims (7)

A synchronous search method of a wireless USB system for searching for a symbol start point in a wireless USB system employing a multiband OFDM scheme, A first step of calculating a cross-correlation degree by comparing a complex code of a signal input to the wireless USB system with a reference symbol; A second step of calculating an initial symbol start point by comparing the calculated cross-correlation with a threshold; A third step of searching for frequency hopping synchronization based on whether frequency hopping is used after calculating the initial symbol start point; A fourth step of minimizing analog effects after searching for the frequency hopping synchronization; A fifth step of tracking the repeat symbol synchronization until the boundary of the sync sequence is searched by tracking the position of the maximum value generated based on the initial symbol start point after minimizing the analog effect; A sixth step of calculating and applying a final symbol start point by tracking the position of the maximum value; Synchronous search method of a wireless USB system, characterized in that made. The method of claim 1, wherein the second step of calculating the initial symbol start point comprises: detecting a maximum value of the cross-correlation for a predetermined number of input signals from the time when the cross-correlation is detected above a threshold; A method for synchronous searching of a wireless USB system, characterized by calculating an initial symbol start point. The method of claim 1, wherein the fourth step of minimizing the analog effect is to apply AGC, DC offset, and frequency offset. The cross-correlation diagram of claim 1, wherein the fifth step of tracking the symbol synchronization is generated in a predetermined interval region before and after the position where the maximum value of the cross-correlation diagram predicted by calculating the initial symbol start point is generated. Is equal to or greater than the threshold value, the sync rate searching method of the wireless USB system, characterized in that for calculating the hit rate. The method of claim 1, wherein in the fifth step of tracking the symbol synchronization, the input signal and the reference symbol are compared to each other when the maximum value of the cross-correlation is less than or equal to a threshold value in a predetermined section region. When the maximum value of the cross-correlation degree occurs, the error warning count value is increased to generate an error when the error warning count value is equal to or greater than a reference set value and return to the first step. The method of claim 5, wherein the error warning coefficient is increased when the maximum value of the cross-correlation degree is less than or equal to a threshold value in the constant section area or when the maximum value of the cross-correlation degree occurs outside the constant section area. If the maximum value of the cross-correlation in the section area exceeds the threshold value, the synchronization search method of a wireless USB system. delete

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