KR20050067328A - Apparatus for acquiring multi-path in wireless packet communication system and method thereof - Google Patents

Abstract

The present invention relates to an apparatus and method for multi-path acquisition for short-range wireless packet communication system. The Barker Code despreader of the multipath obtaining apparatus performs cross correlation of the received signal and the Barker code to calculate a cross correlation function value. The adder adds the cross-correlation function value calculated by the Barker code despreader for each sample position, and the expander extends the add result output from the adder to a specific length. The average value calculation and comparator outputs a comparison result obtained by averaging the result value output from the expander with respect to the total number of estimated symbols and comparing the result with a specific threshold value. Multiple paths are detected by identifying the sample location with the largest magnitude value among the larger values. According to the present invention, accurate information on a communication channel is obtained in a receiver of a CCK-type wireless LAN system, and thus can be operated at an optimal transmission efficiency. In addition, performance can be maintained in the multipath acquisition process, and implementation complexity can be simplified.

Description

Multipath Acquisition Apparatus and Method for Local Wireless Packet Communication System {APPARATUS FOR ACQUIRING MULTI-PATH IN WIRELESS PACKET COMMUNICATION SYSTEM AND METHOD THEREOF}

The present invention relates to an apparatus and method for multipath acquisition for a near field wireless packet communication system. More specifically, the present invention relates to a symbol of a preamble that is periodically repeated in a wireless LAN system of a CCK (Complementary Code Keying) scheme. The present invention relates to an apparatus and a method for acquiring a multipath.

Wireless communication is rapidly evolving in recent years due to user mobility, system flexibility, frequency free use and high speed data transmission. Wireless systems can be classified into LANs and WANs according to their range of use, and the recent proliferation of notebooks and personal digital assistants (PDAs) has increased the need for wireless LANs. HiperLAN (High Performance Local Area Network) series established in Europe in 1992 as a standard for wireless LAN and IEEE 802.11 series which have been evolving to 802.11b, 802.11a, and 802.11g since the IEEE final draft was approved in 1997. .

The IEEE 802.11 series is emerging as a standard for wireless LAN products by sharing a medium access control (MAC) layer and supporting various data rates for multimedia services. The 802.11b specification is the single-carrier system that supports up to 11 Mbps using Direct Sequence Spread Spectrum (DSSS) and Complementary Code Keying (CCK) in the 2.4 ㎓ ISM band. a is a multi-carrier system supporting various data rates of up to 54 Mbps by applying Orthogonal Frequency Division Multiplexing (OFDM) in the 5 GHz U-NII band. The 802.11g standard, currently under discussion, can be viewed as a baseband aspect that incorporates the features of 802.11 DSSS, 802.11b, and 802.11a. That is, the 2.4GHz ISM band is used for compatibility with 802.11b, and DSSS, CCK, PBCC, OFDM, DSSS-OFDM, etc. are supported as transmission modes, and 54Mbps high-speed data transmission is possible.

While much discussion is underway today on whether 802.11a or 802.11g will be the next-generation high-speed wireless LAN standard, many studies have anticipated 802.11g, which has advantages in compatibility with 802.11b, the mainstream of wireless LAN. It's going on.

On the other hand, CCK (complementary code keying) is a DSSS coding scheme used in the 802.11b WLAN standards of 5.5 and 11 Mbps. The slower 1 to 2 Mbps specification uses Barker coding, which provides up to 64 CCKs and overlaps transmissions using multiple different codes, whereas Barker coding provides only one coding pattern. Unlike CDMA, which uses CMC, CCK uses several different codes to serially transmit a larger amount of data in a TDM manner.

The receiver of the CCK system requires a process of estimating channel characteristics and correcting a received signal distorted by a possible channel. When a packet transmitted from a transmitter arrives at a receiver through a fading channel, transmission packets of various paths are received at random time delay intervals. This multipath signal generates a signal strength or randomness. A change in frequency, time dispersion, and so on can occur. Therefore, a technique for improving receiver performance by accurately finding a multipath of a signal and setting the coefficient value of a channel matched filter (CMF) is required.

Meanwhile, US Pat. No. 6,233,273 discloses a "Rake receiver with decision feedback equalizer", which uses a CMF or Rake receiver to improve the performance of a receiver by reducing the effects of interference of noise or spreading codes as much as possible. It is characterized by. However, the prior art does not disclose precisely obtaining multiple paths to improve receiver performance as described above.

An object of the present invention for solving the above problems is, by applying a cross-correlation technique to the symbols of the preamble that is periodically repeated, multi-path acquisition apparatus for a short-range wireless packet communication system to simplify the performance and implementation complexity And a method thereof.

According to one aspect of the present invention for achieving the above object, a multi-path acquisition device,

A multi-path acquisition device for a CCK (Complementary Code Keying) wireless LAN system,

A Barker code despreader for performing cross correlation between a received signal and a Barker code to calculate a cross correlation function value; An adder configured to add the cross-correlation function values calculated by the Barker code despreader for each sample position and output the sample values; An expansion unit which extends the addition result output from the adder to a specific length and outputs the result; An average value calculator and comparator for outputting a comparison result obtained by averaging the result value output from the expander with respect to the total number of estimated symbols and comparing with a specific threshold value; And a maximum value position detector for detecting a multi-path by detecting a sample position having a maximum magnitude value among values larger than the specific threshold value from the average value calculation and the comparison result output from the comparator.

Here, the Barker code despreader may perform cross correlation with the Barker code for a preamble section of the received signal.

In addition, the Barker code despreader cross-correlates a specific number of symbol intervals, the adder performs an addition operation on the specific number of symbol intervals, and the average value comparator and the comparator perform the specific number of symbol intervals. It characterized in that the averaging for.

Multi-path acquisition method according to another feature of the present invention,

A multipath acquisition method for a CCK (Complementary Code Keying) wireless LAN system,

a) performing a cross correlation between a received signal and a Barker code to output a cross correlation function value; b) comparing the cross-correlation function value with a particular threshold value; c) detecting a cross-correlation function value greater than the particular threshold as a result of the comparison; And d) detecting a multi-path by identifying a sample position having a maximum value among the detected cross-correlation function values.

Here, step b) comprises the steps of: i) adding and outputting the cross-correlation function value for each sample position; ii) expanding and outputting the output addition result to a specific length; iii) averaging the result of the extended output with respect to the total number of estimated symbols; And iv) comparing the averaged value with the particular threshold.

Hereinafter, with reference to the accompanying drawings, it will be described in detail a multi-path acquisition apparatus and method for a short-range wireless packet communication system according to an embodiment of the present invention.

1 is a diagram illustrating a demodulator structure in a CCK wireless LAN system according to an embodiment of the present invention.

Referring to FIG. 1, in a CCK wireless LAN system according to an exemplary embodiment of the present invention, a received packet signal is amplified by the amplifier 11 and then converted into a digital signal through an analog-to-digital converter (ADC) 12. . In this case, the digital signal is controlled by the automatic gain control unit 13.

In addition, the signal capturing unit 14 detects an enable signal from the received packet signal, and the multipath obtaining unit 15 is operated by the enable signal and output from the ADC 12. Acquire multiple paths from the signal. Thereafter, the frequency offset estimator 16 estimates the frequency offset of the received packet signal with respect to the multipath obtained by the multipath obtainer 15.

The frequency offset estimated by the frequency offset estimator 16 and the digital signal output from the ADC 12 are multiplied by the multiplier 17 and then input to a down sampling unit 20 that performs a demodulation algorithm. .

Meanwhile, the channel coefficient estimator 18 estimates and outputs channel coefficients for the digital signals output from the multiplier 17.

Next, the digital signal output from the ADC 12 and the channel coefficient estimated by the channel coefficient estimator 18 are input to the downsampler 20 and demodulated, where the downsampler 20 is a channel matched filter (Channel). Matched Filter (CMF) 21, switch 22, and Decision Feedback Equalizer (DFE) 23, which uses a demodulation algorithm to downsample the digital signal output from multiplier 17. A demodulation process is performed on the received packet signal.

On the other hand, when a packet transmitted from a transmitter arrives at a receiver through a fading channel, transmission packets of various paths are received at random time delay intervals. Such multipath signals generate a signal strength or a random frequency change, and Time scattering and the like may appear.

The reason why the signal is received through the multipath is because the transmission signal is reflected by an obstacle around it or the altitude of the antenna is lower than that of the surrounding object. As a result, the transmission packet arriving at the receiver is received at different times. A tendency appears.

Accordingly, the multipath acquisition algorithm used by the multipath obtainer 15 captures the relative delay profile of packets received through the multipath to determine how far the path of the currently received packet is.

CCK wireless LAN system adopts DSSS signal model and captures delay type of received packet using 11-chip Barkder sequence, which is a kind of PN code applied when generating spread signal from transmitter. The path acquisition algorithm is configured. At this time, the complex gain value of each captured path can be set to the coefficient value of the CMF 20, but the coefficient value reliable for the channel response by an error value such as an frequency offset. Since it is too difficult to apply the result, a more accurate coefficient value measurement process must be performed after the frequency offset estimation algorithm by the frequency offset estimator 16 is performed.

Thus, the information captured in this algorithm process is limited to the relative delay type of the currently received signal, which can be utilized in the frequency offset estimation algorithm. The basic structure of this algorithm is very similar to that of the channel coefficient estimation algorithm, except that the channel coefficient estimation algorithm calculates channel coefficient values for each path.

2 is a view for explaining a received signal model in consideration of a transmission signal and a fading channel in a CCK wireless LAN system according to an embodiment of the present invention.

First, the packet transmitted from the transmitter 25 ( ) Is assumed as in [Equation 1] and [Equation 2] below.

here, = 0,1,2,... Represents a sample index.

Where N represents the total number of samples for one packet.

Under the above assumption, the packet signal received at the receiver 27 through M paths can be designed as follows. That is, when there is an arbitrary time delay between each path, a signal transmitted from the transmitter 25 and passing through the fading channel 29 may be expressed as Equation 3 below. have.

Where M is the total number of paths, Is a random time delay from the first received packet. Therefore, the received packet at the receiver 27 becomes the following [Equation 4].

On the other hand, due to various obstacles such as the transmission signal is reflected by the surrounding obstacles or the altitude of the antenna is lower than the surrounding object, the receiver 27 receives a signal passing through the multi-path. The generation of such a multipath causes a random change in signal strength, time scattering, or the like, thereby degrading the demodulation process in the receiver 27.

The multipath acquisition algorithm performed in the multipath obtainer 15 is an algorithm for capturing the relative delay time of a signal received through this multipath, which is the process of finding the starting position of the Barker code in the received signal. Can be interpreted as

3 is a diagram illustrating a structure of a multipath obtainer for a CCK wireless LAN system according to an embodiment of the present invention.

Referring to FIG. 3, the multipath obtainer 15 for a CCK wireless LAN system according to an embodiment of the present invention includes N Barker code despreaders 30-1,..., 30 -N, N adders. (40-1, ..., 40-N), expander 50, average value calculation and comparator 60, and maximum position detector 70.

The Barker code despreaders 30-1,..., 30 -N calculate and output a cross-correlation of the received signal and the Barker code. In this case, N barker code despreaders are provided to calculate a cross-correlation function value with the Barker code for the N signal intervals for the received signal r (n).

Adder ( , 40-1,... , 40-N) calculates the magnitude (Magnitude) of the cross-correlation function values calculated by the Barker code despreaders 30-1,. At this time, N adders are provided to perform an addition process on the cross correlation function values output from the N Barker code despreaders 30-1, ..., 30-N.

Expander ( , 50 is twice the result calculated by the adders 40-1,…, 40-N because the addition results output from the adders 40-1,…, 40-N may be difficult to capture smooth multipath. Output by length. For example, when the over-sampling factor is O _k , the cross-correlation function values respectively calculated by the Barker code despreaders 30-1,. When calculated for a total of 11 × O _k sample positions and outputted by the adders 40-1,…, 40-N, for a total of 11 × O _k sample positions, the dilator 50 has a total of 2 × 11. × O Expands to the result at _k sample positions and outputs.

The average value calculator and comparator 60 averages the result value output from the expander 50 to N, which is the total number of estimated symbols, compares the result with a threshold value, and outputs a comparison result.

The maximum position detector 70 grasps the sample position information whose average value is greater than the threshold value and the comparison result output from the comparator 60, and then detects the sample position having the largest magnitude value among the relative values. Multiple paths are detected by identifying the path delay type.

Hereinafter, a multi-path acquisition method for a CCK wireless LAN system according to an embodiment of the present invention will be described in detail.

First, the N Barker code despreaders 30-1, ..., 30-N calculate cross-correlation with the Barker code for the N signal intervals for the received signal r (n). do.

First, the cross-correlation function value for a symbol can be expressed as shown in Equation 5 below.

Here, k denotes a sample index in one symbol interval when the over-sampling factor O _k is 4, and C (i) represents an 11-chip Barker code sequence. That is, as shown in Equation 5, the result of calculating the cross-correlation function at each sample position of one symbol interval is the same as the despreading result of applying the Barker code to two symbol intervals of the received signal. Therefore, the cross correlation function value for one symbol interval has a total of 44 results.

Using these results, the magnitude (Magnitude) of the cross-correlation function value is calculated for each symbol for a total of N estimated symbols and expressed as a column vector, as shown in Equation 6 below.

Here, X _k refers to the magnitude vector of the autocorrelation function value for each sample position with respect to the k th symbol. N adders (40-1, ..., 40-N) are sample positions of the zero to 43 th value of the sample position of each symbol represented by [Equation 6]. Adding as much as Equation 7 below.

By multiplying the sum of the column vectors for the total N estimated symbols represented by Equation 7 to capture the multipath of the received signal, if the form of the multipath delay is found at the boundary of the symbol, that is, Since it is difficult to measure the exact path delay when there is a path with a gain, it is difficult to achieve a smooth path acquisition with the magnitudes of the cross-correlation function values at 44 sample positions. Therefore, size information at 88 sample positions corresponding to twice the length of the result value calculated by Equation 7 is required. This assumes that the maximum path delay exists within one symbol period, and the path delay of the received signal can be seen to be repeated at the same position for each symbol. In view of this fact, the expander 50 obtains the result of [Equation 7]. The value is extended to the result at 88 sample positions and applied as in Equation 8 below.

Next, the average value calculation and comparator 60 finally averages the size information at 88 sample positions by the total number of estimated symbols N as represented by Equation 8, which is expressed as Equation 9 below. do.

Therefore, the average value calculation and comparator 60 compares the result of [Equation 9] with a threshold value and outputs the comparison result, and the maximum position detector 70 obtains sample position information having a magnitude value higher than the threshold value. In particular, the relative path delay type is identified by extracting the sample position having the largest magnitude value among them.

In this way, the multipath acquisition algorithm uses the principle of calculating the cross-correlation function value with the 11-chip Barker code for the preamble section of the received signal and capturing the start position of each path through the multipath acquisition algorithm. In addition, in order to reduce the influence of interference of noise or spreading code as much as possible, averaging of N symbol intervals is performed to reduce false alarm probability.

4 is a diagram illustrating a performance analysis of multipath signal acquisition probability according to a threshold of a multipath acquisition algorithm for a CCK wireless LAN system according to an embodiment of the present invention.

Referring to FIG. 4, for performance analysis of the multipath acquisition algorithm, the capture probabilities of the multipaths are compared with the threshold values for the path acquisition and the SNR. Accurate multipath acquisition was assumed to accurately capture two paths with a set two-chip path delay and a path delay, and it can be seen that the smaller the threshold, the better the acquisition probability.

However, if the threshold value is small, the probability of false alarms captured by three or more paths is increased when the SNR is low, and the threshold value is 2.0 in FIG. 4 on the assumption that accurate path acquisition is not performed for such false alarms. In case of, the probability of path acquisition is rather low.

On the other hand, the multi-path acquisition method according to an embodiment of the present invention as described above is implemented as a program and stored in a recording medium (CD-ROM, RAM, ROM, floppy disk, hard disk, magneto-optical disk, etc.) in a computer-readable form Can be.

Although the preferred embodiment of the present invention has been described in detail above, the present invention is not limited thereto, and various other changes and modifications are possible.

According to the present invention, accurate information on a communication channel is obtained in a receiver of a CCK-type wireless LAN system, and thus can be operated at an optimal transmission efficiency.

In addition, performance can be maintained in the multipath acquisition process, and implementation complexity can be simplified.

1 is a diagram illustrating a demodulator structure in a CCK wireless LAN system according to an embodiment of the present invention.

2 is a view for explaining a received signal model in consideration of a transmission signal and a fading channel in a CCK wireless LAN system according to an embodiment of the present invention.

3 is a diagram illustrating a structure of a multipath obtainer for a CCK wireless LAN system according to an embodiment of the present invention.

4 is a diagram illustrating a performance analysis of multipath signal acquisition probability according to a threshold of a multipath acquisition algorithm for a CCK wireless LAN system according to an embodiment of the present invention.

Claims (11)

In the multi-path acquisition device for a wireless LAN system of the CCK (Complementary Code Keying) method, A Barker code despreader for performing cross correlation between a received signal and a Barker code to calculate a cross correlation function value; An adder configured to add the cross-correlation function values calculated by the Barker code despreader for each sample position and output the sample values; An expansion unit which extends the addition result output from the adder to a specific length and outputs the result; An average value calculator and comparator for outputting a comparison result obtained by averaging the result value output from the expander with respect to the total number of estimated symbols and comparing with a specific threshold value; And A maximum value position detector for detecting a multi-path by detecting a sample position having a maximum magnitude value among values greater than the specific threshold value from the average value calculation and the comparison result output from the comparator Multipath acquisition device comprising a. The method of claim 1, And the Barker code despreader performs cross correlation with the Barker code for a preamble section of the received signal. The method of claim 1, The Barker code despreader performs cross correlation on a specific number of symbol intervals, The adder performs an addition operation on the specific number of symbol intervals, The average value calculator and the comparator perform averaging on the specific number of symbol intervals. Multipath acquisition device, characterized in that. The method according to claim 1, wherein When the symbol is an over-sampling factor O _k , the symbols are cross-correlated for each 11 × O _k sample positions, and the expander is a cross-correlation function at the 11 × O _k sample positions. And multiplying the value to output a cross-correlation function at 2 x 11 x O _k sample positions. In the multi-path acquisition method for a wireless LAN system of the CCK (Complementary Code Keying) method, a) performing a cross correlation between a received signal and a Barker code to output a cross correlation function value; b) comparing the cross-correlation function value with a particular threshold value; c) detecting a cross-correlation function value greater than the particular threshold as a result of the comparison; And d) detecting a multi-path by identifying a sample position having a maximum value among the detected cross-correlation function values Multi-path acquisition method comprising a. The method of claim 5, B), i) adding and outputting the cross-correlation function value for each sample position; ii) expanding and outputting the output addition result to a specific length; iii) averaging the result of the extended output with respect to the total number of estimated symbols; And iv) comparing the averaged value with the specific threshold value Multi-path acquisition method comprising a. The method of claim 6, And in step a), performing cross-correlation with the Barker code for a preamble section of the received signal. The method of claim 7, wherein And in step a), performing cross-correlation with the Barker code during a specific number of symbol intervals, and outputting each cross-correlation function value. The method of claim 7, wherein The cross-correlation function value R (n) is represented by Here, k is a sample index in one symbol interval when the over-sampling factor O _k is 4,            C (i) is an 11-chip Barker code sequence. Multipath acquisition method characterized in that follows. The method of claim 9, The cross-correlation function value is expressed in the form of a column vector for the specific number of symbols, and the column vector form (X ₀ , X ₁ , ..., X _N-1 ) is represented by X _k is the magnitude vector of the cross-correlation function value of each sample position for the k th symbol. Follow The addition result (Sum) in step i) is as follows Multipath acquisition method characterized in that follows. The method of claim 10, The result value (Sum _exp. ) That is expanded and output in the step iin) is the following relational expression Multipath acquisition method characterized in that follows.