KR100924171B1 - Symbol Boundary Detection in High Speed Wireless Local Area Network - Google Patents

Abstract

The present invention relates to a symbol boundary detection method and apparatus for detecting a reliable symbol boundary by improving a problem of a conventional peak detection method for symbol synchronization in a next generation wireless local area communication system for high speed data transmission. CLAIMS 1. A symbol boundary detection method for symbol synchronization in a communication system, comprising: (a) calculating a difference between a first peak value (previous peak value) and a second peak value (current peak value) retrieved by a maximum peak value search; (b) comparing the calculated peak difference with a first threshold, which is a value arbitrarily set to determine a previous peak value as a symbol boundary; (c) if the peak difference is less than the first threshold, determining the location where the previous peak occurred as a symbol boundary; And (d) if the peak difference is greater than the first threshold, determining a location where the current peak value occurs as a symbol boundary.

Next Generation, High Speed, Wireless, Near Field, Communication, WLAN, Symbol, Synchronous, Perimeter, Detection, Peak

Description

Symbol boundary detection method and apparatus in high speed wireless local area network

The present invention relates to a method and apparatus for detecting a symbol boundary in a high speed wireless local area network (WLAN), and improves a problem of a conventional peak detection method for symbol synchronization in a next generation wireless local area communication system for high speed data transmission. The present invention relates to a symbol boundary detection method and apparatus capable of detecting a reliable symbol boundary.

The present invention is derived from the research conducted as part of the IT new growth engine core technology development project of the Ministry of Information and Communication and the Ministry of Information and Communication Research and Development. [Task Management Number: 2006-S-014-02, Title: 200Mbps IEEE 802.11n Modem] And RF chipset development].

In IEEE 802.11a, a standard of the existing wireless local area network, a physical layer convergence protocol (PLCP) preamble field is defined for synchronization. The preamble consists of 10 short preamble symbols and 2 long preamble symbols.

1 shows a packet structure in 802.11a of a typical wireless local area network. The PLCP preamble is followed by a signal field and data.

The total preamble length is 16 us, and the short preamble symbol is a form in which a signal of 0.8 us is repeated 10 times. This repeated form is determined by testing the correlation characteristics in the frequency domain of the short preamble symbol. The short preamble symbol in the frequency domain uses 12 subcarriers, and there are three unused subcarriers between used subcarriers. The short preamble sequence is represented by Equation 1 below.

The signal in the time domain can be obtained after taking an Inverse Fast Fourier Transform (IFFT), and can be expressed by Equation 2 below.

The long preamble symbol consists of 53 subcarriers and is assigned values as shown in Equation 3 below.

The long preamble symbol in the time domain is obtained by an IFFT relation as shown in Equation 4 below.

The guard interval (T _GI2 ) is 1.6 kHz. The long preamble symbol is repeated twice, which is used for channel estimation and fine frequency error estimation as well as symbol synchronization.

The symbol synchronization detecting apparatus obtains a cross correlation value of a repeating pattern reception signal of each preamble, and correlates each cross correlation value to calculate a power value of a channel. Then, the moving average value of the power value of the channel is obtained within a predetermined window, and the symbol synchronization is calculated based on the time when the obtained moving average value exceeds the threshold or when the obtained moving average value becomes the highest. That is, symbol synchronization is obtained at two preamble boundary points having different repetition patterns.

2 is a graph showing the correlation between the short preamble and the long preamble and the product of the two correlations. As shown in FIG. 2, the symbol synchronization detecting apparatus obtains a correlation peak between a short preamble and a long preamble using a correlation between a received signal and a known preamble, and multiplies the short preamble correlation by 32 samples to multiply the largest peak value. Find.

The next generation wireless short-range communication system for high-speed data transmission uses multiple antennas and incorporates various techniques to reliably transmit and receive. In particular, in the next generation wireless short-range communication system, Cyclic Delay Diversity (CDD) and spatial spreading (Spatial Spreading) are major technologies of transmission methods. Cyclic Delay Diversity (CDD) is a technique for preventing unintended beamforming effects in a multi-antenna environment, resulting in frequency selectivity, resulting in greater performance gains in flat channels. have.

However, the channel response of a wireless channel varies from moment to moment, and when transmitting using cyclic delay diversity, it is more difficult to find an accurate symbol boundary by delay spread when receiving a signal passing through various wireless channel environments. .

Conventional wireless local area communication systems are designed to find this symbol boundary using the preamble correlation, but cyclic delay diversity (CDD) and spatial spreading at the transmitting end of a high-speed wireless local area communication system such as IEEE 802.11n system. If data is transmitted by using and is placed in a wireless channel environment having a large delay spread, the reliability of the conventional peak detection method is deteriorated. In other words, the values of correlations are each one of the largest and slightly smaller peaks, followed by smaller peaks, which can cause errors in the detection process for two large ones.

Accordingly, the present invention has been proposed to solve the above-mentioned problems of the prior art, and improves the problem of the conventional correlation-based peak detection method in the next generation wireless local area network for high-speed data transmission to detect reliable symbol boundaries. It is an object of the present invention to provide a symbol boundary detection method and apparatus.

Other objects and advantages of the present invention can be understood by the following description, and will be more clearly understood by the embodiments of the present invention. Also, it will be readily appreciated that the objects and advantages of the present invention may be realized by the means and combinations thereof indicated in the claims.

A method according to the present invention for achieving the above object, in the symbol boundary detection method for symbol synchronization in a high-speed wireless local area communication system, (a) the first peak value (previous peak value) and the second peak value retrieved by the maximum peak value search; Calculating a difference of (current peak values); (b) comparing the calculated peak difference with a first threshold, which is a value arbitrarily set to determine a previous peak value as a symbol boundary; (c) if the peak difference is less than the first threshold, determining the location where the previous peak occurred as a symbol boundary; And (d) if the peak difference is greater than the first threshold, determining a location where the current peak value occurs as a symbol boundary.

In addition, an apparatus according to the present invention for achieving the above object comprises: a symbol boundary detection device for symbol synchronization in a high-speed wireless local area communication system, the peak value searching means for searching for the maximum peak value; First storage means for storing a first detected peak value (previous peak value); Second storage means for storing a second detected peak value (current peak value); Peak difference calculation means for calculating a difference between a previous peak value stored in the first storage means and a current peak value stored in the second storage means; And comparing means for comparing the peak difference calculated by the peak difference calculating means with a first threshold value and determining, as a symbol boundary, a position where the previous peak value is generated or a position where the current peak value is generated according to the comparison result. Include.

Preferably, the comparing means, when the peak difference is less than the first threshold value, determines the position where the previous peak value is generated as a symbol boundary, and when the peak difference is greater than the first threshold value, the current peak value is generated. Determined locations are symbol boundaries.

Preferably, the comparing means compares the previous peak value and the current peak value with a second threshold value, respectively, to determine the position where the previous peak value is generated or the position where the current peak value is generated as a symbol boundary.

Preferably, the comparing means controls the peak value stored in the second storage means to be stored in the first storage means when the previous peak value or the current peak value is less than the second threshold.

As described above, the present invention compares a difference between a previously detected peak value and a currently detected peak value with a threshold for determining a current peak value as a symbol synchronization position in order to improve the problems of the conventional correlation-based peak detection method. The symbol boundary can be reliably detected by determining the previous peak value or the current peak value with symbol synchronization.

The above objects, features and advantages will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, whereby those skilled in the art may easily implement the technical idea of the present invention. There will be. In addition, in describing the present invention, when it is determined that the detailed description of the known technology related to the present invention may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 3 is a detailed block diagram illustrating a correlation value calculator for calculating a general correlation value, and FIG. 4 is a circuit diagram for extracting a general symbol boundary.

The symbol synchronizer is for indicating a symbol boundary of a received packet. For this purpose, as shown in FIG. 3, the correlation calculation unit of the symbol synchronizer uses a 32 tap FIR filter, which is a matched filter, to calculate the coefficients in the reverse order of time in the complex conjugate of two short training signal sequences. Determine. Then, the correlation calculation unit determines the coefficients in the reverse order of time of the complex coupling of the second half of the long training signal sequence using the 16 tap FIR filter. The correlation calculator computes cross-correlation with each filter result. These two cross-correlation values accumulate, resulting in a maximum peak at the end of the short training signal sequence. This peak value is approximately the channel power value.

As shown in FIG. 4, the synchronization block performs synchronization using this cross-correlation value and programmed register bits channel enable value. In FIG. 4, the synchronization block includes a selector 41, an accumulation calculator 42, a carrier frequency error compensator 43, a maximum peak value detector 44, a counter 45, and a comparator 46. do.

Input from unused channels is set to zero. The cumulative operation implemented by the IIR filter is a function of 0.25 / (1-0.75D). The carrier frequency error compensator 43 compensates for an estimated carrier frequency offset (CFO) value at the output of the accumulated value. The maximum peak value detector 44 detects the maximum value with respect to the error compensated real component. That is, the real component whose carrier frequency error is compensated represents the channel power at the end of the short training signal sequence, and the real component of all outputs is compared with the previous maximum to determine whether the current real component is the new maximum. . When a new maximum value is found, the value of the counter 45 is reset to zero.

When the counter value reaches a specific value syn_delay_rx (programmable register value), the comparator 46 outputs a synchronizing signal Syn to signify completion of symbol synchronization. This programmable register value has a value that is suitable for symbol synchronization at the beginning of the second long training signal sequence.

This symbol synchronization operation is limited to a fixed time period of the counter to prevent endless operation. This counter is initialized when a carrier is detected for a finite period of time by a given programmed register value.

The present invention focuses on the fact that the peak according to the cyclic delay diversity (CDD), the spatial spreading and the channel response of the transmission signal can be diversified in the symbol synchronization device, thereby improving reliability in the following manner.

FIG. 5 is a diagram for describing a peak difference (PD) among correlation peaks.

Typically, the values of correlation occur one after each of the largest and slightly smaller peaks, followed by successive small peaks. Here, the peak difference PD means a difference between the magnitude of the first peak and the magnitude of the second peak.

6 is a process flow diagram of an improved symbol boundary detection method according to the present invention.

The present invention provides an absolute value for the difference PD between a previously detected peak value (first peak value) and a presently detected peak value (second peak value) than a threshold value (first threshold value) for determining a previously detected peak value as a symbol boundary. If small, the symbol boundary is determined by the previously detected peak value (first peak value), and if the absolute value of the peak difference PD is greater than the first threshold value, the symbol boundary is determined by the present detected peak value (second peak value).

The existing method determines the position where the maximum peak value occurs as a symbol boundary. As a result, the conventional method determines the symbol boundary at the second peak value, which is the maximum peak, even if the first peak value is large, which may result in performance degradation.

The present invention compares the magnitude of the first two peaks, which are the largest in terms of correlation, so that when the first peak is smaller than the second peak and the magnitude difference is smaller than the threshold, the symbol peak is selected as the symbol boundary. The reliability of the edge detection can be improved.

Hereinafter, the present invention will be described in more detail with reference to FIG. 6.

First, the symbol synchronizer calculates a cross correlation value for the received preamble (101). The maximum peak value is then retrieved for the error compensated real component (102). The first peak value thus retrieved is stored in the A register (103). The detected second peak value is then stored 104 in the B register.

Then, the difference PD between the first peak value stored in the A register and the second peak value stored in the B register is obtained (105). The absolute value of the peak difference thus obtained is compared with a threshold value (first threshold value) for determining the first peak value stored in the A register (ie, this means a previously detected peak value) as a symbol boundary. .

As a result of the comparison, if the peak difference is less than the first threshold, it is checked whether the previous peak stored in the A register is greater than the existing peak search threshold (second threshold) for determining with symbol synchronization (107). If the previous peak value stored in the A register is greater than the second threshold, the position where the previous peak value stored in the A register is generated is determined as a symbol boundary for symbol synchronization (108). On the other hand, if the previous peak value stored in the A register is less than the second threshold value, the current peak value (second peak value) stored in the B register is stored in the A register to be used as the previous peak value (109).

On the other hand, as a result of comparing the absolute value of the peak difference PD with the first threshold value, if the peak difference is greater than the first threshold value, it is checked whether the peak value stored in the B register is larger than the second threshold value for determining symbol synchronization (see FIG. 110). If the current peak value stored in the B register is greater than the second threshold, the position where the current peak value stored in the B register is generated is determined as a symbol boundary for symbol synchronization (111). On the other hand, if the current peak value stored in the B register is less than the second threshold, the current peak value (second peak value) stored in the B register is stored in the A register to be used as the previous peak value (112).

Next, a symbol boundary detection apparatus according to the present invention will be described.

The symbol boundary detection apparatus according to the present invention includes a correlation value calculator for calculating a cross correlation value for a received preamble, a peak value search unit for searching a maximum peak value for an error-compensated real component, and a first detected peak value ( A first register for storing the previous peak value), a second register for storing the second detected peak value (current peak value), a peak difference calculator for calculating a difference between the previous peak value and the current peak value, a peak difference and a first threshold value; Comparing the values, the comparison unit for determining the position where the previous peak value or the current peak value is generated as a symbol boundary according to the result.

The comparison unit determines the symbol boundary with the previous peak value (first peak value) if the absolute value for the peak difference PD is less than the first threshold value, and the current peak value if the absolute value of the peak difference PD is greater than the first threshold value. The symbol boundary is determined by (the second peak value).

On the other hand, the method of the present invention as described above can be written in a computer program. And the code and code segments constituting the program can be easily inferred by a computer programmer in the art. In addition, the written program is stored in a computer-readable recording medium (information storage medium), and read and executed by a computer to implement the method of the present invention. The recording medium may include any type of computer readable recording medium.

The present invention described above is capable of various substitutions, modifications, and changes without departing from the technical spirit of the present invention for those skilled in the art to which the present invention pertains. It is not limited by the drawings.

1 is a diagram illustrating a packet structure of a general high speed wireless local area communication system;

2 is a graph showing the correlation between a typical short preamble and a long preamble, and a correlation between two correlations;

3 is a block diagram of a general correlation value calculator;

4 is a diagram illustrating a symbol boundary extraction circuit of a general symbol synchronization device;

5 is a view for explaining a peak difference,

6 is a process flowchart of a symbol boundary detection method according to the present invention.

Claims (8)

A symbol boundary detection method for symbol synchronization in a high speed wireless local area communication system, (a) calculating a difference between the first peak value (previous peak value) and the second peak value (current peak value) retrieved by the maximum peak value search; (b) comparing the calculated peak difference with a first threshold, which is a value arbitrarily set to determine a previous peak value as a symbol boundary; (c) if the peak difference is less than the first threshold, determining the location where the previous peak occurred as a symbol boundary; And (d) if the peak difference is greater than the first threshold, determining a location where the current peak is generated as a symbol boundary; Symbol boundary detection method comprising a. The method of claim 1, Before step (a) above, And storing the first peak value (previous peak value) searched by the maximum peak value search in a first register, and storing the second peak value (current peak value) in a second register. . The method of claim 2, In step (c), If the peak difference is less than the first threshold, comparing the previous peak value with a second threshold for determining symbol synchronization; If the previous peak value is greater than the second threshold, determining a location where the previous peak value occurs as a symbol boundary; And And storing the peak value stored in the second register in the first register if the previous peak value is less than the second threshold. The method of claim 2, In step (d), If the peak difference is greater than the first threshold, comparing the current peak value with a second threshold for determining symbol synchronization; If the current peak value is greater than the second threshold, determining a location where the current peak value is generated as a symbol boundary; And And storing the peak value stored in the second register in the first register if the current peak value is less than the second threshold. An apparatus for detecting a symbol boundary for symbol synchronization in a high speed wireless local area communication system, Peak value searching means for searching for a maximum peak value; First storage means for storing a first detected peak value (previous peak value); Second storage means for storing a second detected peak value (current peak value); Peak difference calculation means for calculating a difference between a previous peak value stored in the first storage means and a current peak value stored in the second storage means; And Comparison means for comparing the peak difference calculated by the peak difference calculating means with a first threshold value and determining, as a symbol boundary, a position where the previous peak value is generated or a position where the current peak value is generated according to the comparison result; Symbol boundary detection apparatus comprising a. The method of claim 5, wherein The comparison means, If the peak difference is less than the first threshold, the position at which the previous peak value is generated is determined as a symbol boundary. If the peak difference is greater than the first threshold, the position at which the current peak value is generated is determined as a symbol boundary. Symbol boundary detection device, characterized in that. The method of claim 6, The comparison means, And comparing the previous peak value and the current peak value with a second threshold value to determine a position where the previous peak value is generated or a position where the current peak value is generated as a symbol boundary, respectively. The method of claim 7, wherein The comparison means, And the peak value stored in the second storage means is stored in the first storage means when the previous peak value or the current peak value is smaller than the second threshold value.

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