KR100776678B1 - Apparatus and Method for Channel Coefficient Estimation in the Wireless Pico cell Communication Systems - Google Patents

Abstract

1. TECHNICAL FIELD OF THE INVENTION

The present invention relates to an apparatus and method for estimating channel coefficients in a wireless picocell communication system of direct sequence spread spectrum.

2. The technical problem to be solved by the invention

The present invention compares the sum operation result calculated by the complex sum / difference operation of the first symbol with the second symbol and the difference operation result, and sets a large value as a reference value for the third symbol. In the wireless picocell communication system of the direct sequence spread spectrum method having high performance and low complexity, the channel coefficient is estimated by averaging the final result obtained by repeating the above process up to N symbols by the number of symbols (N). An object of the present invention is to provide an apparatus and method for estimating channel coefficients.

3. Summary of Solution to Invention

In the present invention, in the channel coefficient estimating apparatus, a sum value obtained by a complex sum / difference operation of a first symbol and a second symbol is compared with a difference operation result, and a large value is referred to as a reference value for the third symbol. Initial reference value determining means for determining; Reference value storing means for storing an initial reference value determined by said initial reference value determining means and a reference value selected by said reference value selecting means; Despreading means for compensating for frequency offset by performing despreading on the preamble interval of the third symbol; Sum calculation means for adding up a reference value stored in the reference value storing means and a complex value of a symbol despread by the despreading means; First magnitude value calculating means for calculating a first magnitude value of a result calculated by the sum calculating means; Difference calculating means for difference calculating a complex value of a reference value stored in said reference value storing means and a symbol despread by said despreading means; Second magnitude value calculating means for calculating a second magnitude value of a result calculated by the difference calculating means; Reference value selecting means for comparing the first magnitude value with the second magnitude value and selecting a large value as a reference value; And channel coefficient estimating means for estimating the coefficient of the corresponding channel by dividing the final reference value selected by the reference value selecting means by the total number of symbols.

4. Important uses of the invention

The present invention is used for channel coefficient estimation.

Wireless Pico Cell System, Channel Estimation, Delay Spread, Despread, Reference Value, Complex Sum / Difference Calculation

Description

Apparatus and Method for Channel Coefficient Estimation in the Wireless Pico Cell Communication Systems}

1 is a diagram illustrating an embodiment of a wireless picocell communication system of a direct sequence spread spectrum method to which the present invention is applied;

2 is a diagram illustrating an embodiment of a received signal model based on a fading channel in a wireless picocell communication system of a direct sequence spread spectrum method to which the present invention is applied;

3 is a configuration diagram of an apparatus for estimating channel coefficients in a wireless picocell communication system using a direct sequence spread spectrum method according to the present invention;

4 is a diagram illustrating an exemplary embodiment of an apparatus for estimating channel coefficients in a wireless picocell communication system using a direct sequence spread spectrum method according to the present invention;

5 is a flowchart illustrating a channel coefficient estimating method in the apparatus for estimating channel coefficients according to the present invention.

* Explanation of symbols for the main parts of the drawings

31: initial reference value determination unit 32: reference value storage unit

33 despreader 34 sum operation

35: first size value calculator 36: difference calculator

37: second size value calculator 38: reference value selector

39: channel coefficient estimation unit

The present invention relates to an apparatus and method for estimating channel coefficients in a wireless picocell communication system using a direct sequence spread spectrum method, and more particularly, a sum operation calculated through a complex sum / difference operation of a first symbol and a second symbol. Compares the result value with the difference value, sets the large value as the reference value for the third symbol, and then repeats the above process from the third symbol to N symbols and averages the final result value obtained by symbol number (N). The present invention relates to an apparatus and method for estimating a channel coefficient in a wireless picocell communication system of a direct sequence spread spectrum method having high performance and low complexity.

In general, the Direct Sequence Spread Spectrum (DSSS) method refers to a method in which one signal symbol is spread in a predetermined sequence for communication.

That is, when the transmitting side inputs a signal to be transmitted to a pseudo-random noise sequence, acquires a spread spectrum signal having a low power density per frequency, and transmits it to the receiving side, the receiving side has the same pseudo noise. The original signal is reproduced using the sequence.

This direct sequence spreading method has the advantages of good modulation efficiency, fast signal synchronization, and low in-band interference due to low power density, which has been used for code division multiple access (CDMA), and has recently been introduced in ZigBee. It is also used for communication.

On the other hand, in a fading channel environment that changes constantly, accurate information about a communication channel through which data is transmitted is required in order for a wireless communication network to operate at an optimal transmission efficiency. That is, the receiver needs to estimate the characteristics of the correct channel to correct the distorted received signal.

Therefore, a design of an algorithm for estimating channel characteristics is required, and the channel coefficient obtained through the estimation becomes a characteristic value of a channel for operating a channel matched filter or an equalizer.

As a result, since accurate estimation of channel characteristic values is an important factor in system performance, a method for estimating accurate channel characteristic values is urgently needed to obtain satisfactory receiver performance.

The present invention has been proposed to meet the above requirements, and compares the sum operation result calculated by the complex sum / difference operation of the first symbol and the second symbol with the difference operation result, and sets a large value for the third symbol. By setting the reference value and repeating the above process from the third symbol to N symbols, the final result obtained is averaged by the number of symbols (N) to estimate the channel coefficient, thereby spreading the direct sequence band with high performance and low complexity. An object of the present invention is to provide an apparatus and method for estimating channel coefficients in a wireless picocell communication system.

That is, the present invention compares the sum operation result calculated by the complex sum / difference operation between the first symbol and the second symbol with the difference operation result, and sets a large value as a reference value for the third symbol. Comparing the sum operation result calculated through the complex sum / difference operation of the reference value with respect to the third symbol with the difference operation result value, the large value is set as the reference value for the fourth symbol, and obtained by performing the Nth symbol. By estimating a channel coefficient by averaging a final result value by the number of symbols (N), an apparatus and method for estimating channel coefficients in a direct sequence spread spectrum wireless picocell communication system having high performance and low complexity are provided. There is a purpose.

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.

In the apparatus of the present invention for achieving the above object, in the channel coefficient estimating apparatus, a large value by comparing the sum operation result value and the difference operation result value calculated through the complex sum / difference operation of the first symbol and the second symbol Initial reference value determining means for determining a as a reference value for a third symbol; Reference value storing means for storing an initial reference value determined by said initial reference value determining means and a reference value selected by said reference value selecting means; Despreading means for compensating for frequency offset by performing despreading on the preamble interval of the third symbol; Sum calculation means for adding up a reference value stored in the reference value storing means and a complex value of a symbol despread by the despreading means; First magnitude value calculating means for calculating a first magnitude value of a result calculated by the sum calculating means; Difference calculating means for difference calculating a complex value of a reference value stored in said reference value storing means and a symbol despread by said despreading means; Second magnitude value calculating means for calculating a second magnitude value of a result calculated by the difference calculating means; Reference value selecting means for comparing the first magnitude value with the second magnitude value and selecting a large value as a reference value; And channel coefficient estimating means for estimating the coefficient of the corresponding channel by dividing the final reference value selected by the reference value selecting means by the total number of symbols.

Meanwhile, in the method of estimating a channel coefficient in an apparatus for estimating a channel coefficient, the method of the present invention compares the sum operation result calculated by the complex sum / difference operation of the first symbol and the second symbol with the difference operation result. An initial reference value determining step of storing a large value as a reference value for a third symbol; A compensation step of compensating for frequency offset by performing despreading on the preamble interval of the third symbol; A first calculating step of calculating the sum of the stored reference value and the complex value of the spread symbol; A first calculating step of calculating a first magnitude value of the result of the sum operation; A second operation step of calculating a difference between the stored reference value and the complex value of the despread symbol; A second calculating step of calculating a second magnitude value of the result of the difference calculation; Selecting a large value as a reference value of a next symbol by comparing the first magnitude value with the second magnitude value; And repeating the compensating step, the first calculating step, the first calculating step, the second calculating step, the second calculating step, and the selecting step with respect to all symbols, and dividing the selected final reference value by the total number of symbols. And a channel coefficient estimating step of estimating a coefficient of the channel.

In addition, the present invention improves the performance and simplifies the complexity of the direct sequence spread spectrum wireless picocell communication system through a crosscorrelation technique using symbols of a preamble that is periodically repeated.

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.

1 is a diagram illustrating an embodiment of a wireless picocell communication system of a direct sequence spread spectrum method to which the present invention is applied.

In general, a signal received by a fading channel varies in amplitude unstable and also has a frequency error due to the Doppler shift.

As shown in FIG. 1, a packet transmitted by a transmitter is delivered to a receiver through a multipath by a fading channel, and packets received in each path have different channel characteristics. In terms of receiver performance, it causes interference between signals.

Therefore, the interference should be removed in consideration of the channel characteristics of the packet received in each path. To this end, the delay profile included in the received packet is captured, and the channel characteristic value is estimated for each signal of the captured path.

In this case, the channel characteristic value is a coefficient value of a channel matched filter (CMF) which minimizes the influence of signal interference by the channel.

2 is a diagram illustrating an embodiment of a received signal model based on a fading channel in a wireless picocell communication system of a direct sequence spread spectrum method to which the present invention is applied.

First, it is assumed that the transmission signal symbol T [n] from the transmitter 21 is expressed by Equations 1 and 2 below.

In this case, a packet signal received at the receiver through M channel paths, that is, a signal passing through a fading channel having an arbitrary time delay between each path is represented by Equation 3 below.

는 첫 번째 수신된 패킷의 랜덤 시간 지연(random time delay)을 나타낸다.Where M represents the total number of paths (paths),

Denotes a random time delay of the first received packet.

As a result, the packet received by the receiver 22 is expressed by Equation 4 below.

Here, W [n] means AWGN (Additive White Gaussian Noise).

On the other hand, the process of estimating the channel characteristic value for each path for the signal received through the multi-path is essential, this process is preferably performed after minimizing the effect of the frequency offset (offset).

The channel coefficient estimating apparatus estimates channel characteristic values for each path of the received signal and provides them to a channel matching filter or equalizer.

3 is a diagram illustrating an embodiment of an apparatus for estimating channel coefficients in a wireless picocell communication system using a direct sequence spread spectrum method according to the present invention.

As shown in FIG. 3, the channel coefficient estimator in the direct sequence spread spectrum wireless picocell communication system according to the present invention includes a sum operation calculated through a complex sum / difference operation of a first symbol and a second symbol. An initial reference value determiner 31 for determining a large value as a reference value for the third symbol by comparing a result value and a difference operation result value, and an initial reference value and reference value selector 38 determined by the initial reference value determiner 31 A reference value storage unit 32 for storing the reference value selected in FIG. 32, a despreader 33 for compensating for frequency offset by performing despreading on the preamble interval of the third and subsequent symbols, and the reference value storage unit ( The sum value calculated by the sum operation unit 34 and the sum operation unit 34 for calculating the sum value of the reference value stored in 32) and the complex value of the symbol despread by the despreader 33 is calculated. A difference calculating section 36 for calculating a difference between a complex value of a reference value stored in the reference size storage section 32 and the reference value storing section 32 and a symbol despread by the despreading section 33 Calculating a size value and the second size value calculated by the second size value calculator 37 and the first size value calculator 35 for calculating the size value of the result calculated by the difference calculator 36. A reference value selecting section 38 for comparing the magnitude value calculated by the section 37 to select a large value as a reference value, and dividing the final reference value selected by the reference value selecting section 38 by the total number of symbols to estimate the channel coefficient. And a channel coefficient estimator 39.

Here, the initial reference value determiner 31 performs a despreading on the preamble interval of the first symbol symbol 1 to compensate for the frequency offset, and thus the second despreader 301 and the second symbol. a second despreader 302 for performing a despreading on the preamble section of symbol 2 to compensate for the frequency offset, and a first symbol despread by the first despreader 301 and the first symbol A complex sum operator 303 for performing a complex sum operation of the second symbol despread by the second despreader 302, and a first magnitude value for calculating a magnitude value of the result of the complex sum operator 303. A calculator 304 and a complex arithmetic operator 305 for performing a complex arithmetic operation of the first symbol despread by the first despreader 301 and the second symbol despread by the second despreader 302. , The result of the calculation by the complex arithmetic operator 305 The second size value calculator 306 for calculating the size value, and the size value calculated by the first size value calculator 304 and the size value calculated by the second size value calculator 306 are compared. A reference value selector 307 for selecting a large value as a reference value for the third symbol.

In the present invention, a process of estimating a channel coefficient for one channel for the purpose of understanding (path 1) has been described, but the present invention is not limited thereto. That is, the number of channel coefficient estimation paths does not affect the present invention.

Hereinafter, the operation of the channel coefficient estimation apparatus having the above components will be described in more detail.

First, the channel coefficient estimating apparatus preferentially performs a despreading process for the preamble section of the reception symbol r (n) in order to minimize the influence of the frequency offset.

)은 하기의 [수학식 5]와 같이 복소수의 형태를 갖는다.This frequency offset compensated symbol (

) Has the form of a complex number as shown in Equation 5 below.

이고, 이때

는 일 구간(일예로 11-chip 구간 : 역확산을 위해 곱하는 11비트 데이터)에 해당되는 L개의 심볼 주기를 의미하고,

는 추정된 위상파 오프셋을 의미한다. here,

, Where

Denotes L symbol periods corresponding to one section (for example, 11-chip section: 11-bit data multiplied for despreading).

Denotes the estimated phase wave offset.

Then, up to N symbols of the k-th path are extracted through Equation 6 below.

는 k번째 경로의 경로 지연을 의미하며, M은 chip의 길이에 해 당하는 심볼 주기를 의미한다. 이때, '11-chip'은 확산 또는 역확산인 경우 심볼당 11 chip 개수를 의미한다.here,

Denotes a path delay of the k-th path, and M denotes a symbol period corresponding to the length of the chip. In this case, '11 -chip 'refers to the number of 11 chips per symbol in the case of spreading or despreading.

Subsequently, add and subtraction operations are performed on the extracted N symbols in order to calculate a magnitude value that minimizes the influence of noise. In this case, the symbol is in the form of a complex value, and calculates the complex sum / difference result of the first symbol and the second symbol for the operation after the third symbol. This is shown in Equation 7 below.

,

의 크기(Magnitude)값을 비교하여, 큰 값에 해당하는 연산 결과를 다음 심벌에 대한 참조값(Reference value)으로 선택한다. 이를 표현하면 하기의 [수학식 8]과 [수학식 9]와 같다.Since, calculated above

,

Magnitude values are compared, and the operation result corresponding to the large value is selected as a reference value for the next symbol. This is expressed as Equation 8 and Equation 9 below.

는 두 연산 결과값 중 큰 값이 된다.here,

Is the larger of the two result values.

와 세 번째 심벌의 복소수 합/차 연산을 수행한다. 이러한 과정은 N개 심벌까지 반복적으로 수행한다.Thereafter, as shown in Equation 10 below.

Perform the complex sum / difference operation of and the third symbol. This process is performed repeatedly up to N symbols.

값에 대하여 추정 심벌 수(N)로 평균을 취하여, 하기의 [수학식 11]과 같이 k번째 채널에 대한 채널 계수 추정값(

)을 구한다.After, final

By taking the average as the estimated symbol number (N) with respect to the value, the channel coefficient estimation value for the k-th channel (Equation 11)

)

In this way, the channel coefficient estimation value can be estimated for each path (per channel).

4 is a diagram illustrating an exemplary embodiment of an apparatus for estimating channel coefficients in a wireless picocell communication system using a direct sequence spread spectrum method according to the present invention.

As shown in FIG. 4, the performance analysis diagram measures normalized channel coefficient error of the channel coefficient and the estimated channel coefficient given to the fading channel having one path.

In order to measure the normalized channel coefficient error, the following process was performed. That is, when the error between the channel coefficient given by the channel and the channel coefficient estimated by the channel coefficient estimation algorithm is expressed, Equations 12 and 13 below.

는 채널에서 부여한 채널계수를 의미하고,

는 추정한 채널계수를 의미하며, L은 시뮬레이션에서의 패킷 반복 횟수를 의미한다.here,

Means channel coefficient assigned by channel,

Denotes the estimated channel coefficient, and L denotes the number of packet repetitions in the simulation.

The normalized channel coefficient error is squared with the magnitude squared of the channel coefficient given by the channel as shown in Equation 14 below.

As can be seen from this, the signal-to-noise ratio (SNR) is reduced to about 1% in normalized channel coefficient error at 14dB.

5 is a flowchart illustrating a channel coefficient estimating method in the apparatus for estimating channel coefficients according to the present invention.

First, the initial reference value determiner 31 compares the sum operation result value and the difference operation result value calculated through the complex sum / difference operation of the first symbol and the second symbol, and converts the large value into a reference value for the third symbol. The determination is made and stored in the reference value storage unit 32 (501).

Thereafter, the despreader 33 compensates for the frequency offset by performing despreading on the preamble section of the third and subsequent symbols.

Subsequently, the sum calculator 34 sums the stored reference value and the complex value of the spread symbol (503).

Thereafter, the first size value calculator 35 calculates a first size value of the result of the sum operation (504).

Subsequently, the difference calculator 36 calculates a complex value between the stored reference value and the despread symbol (505).

Thereafter, the second size value calculator 37 calculates a second size value of the result of the difference operation (506).

Thereafter, the reference value selector 38 compares the first magnitude value with the second magnitude value and selects a large value as a reference value of a next symbol (507).

Subsequently, the channel coefficient estimator 39 repeats the processes 502 to 507 for all symbols, and then estimates coefficients of the corresponding channel by dividing the selected final reference value by the total number of symbols.

This channel coefficient estimation process is performed for all channels.

Hereinafter, the initial reference value determination process will be described in more detail.

First, the frequency offset is compensated by performing despreading on the preamble section of the first symbol.

Thereafter, despreading is performed on the preamble section of the second symbol to compensate for the frequency offset.

Thereafter, a complex sum operation of the despread first symbol and the despread second symbol is performed.

Thereafter, a third magnitude value of the result of the complex sum operation is calculated.

Thereafter, a complex difference operation of the despread first symbol and the despread second symbol is performed.

Thereafter, a fourth magnitude value of the result of the complex difference calculation is calculated.

Thereafter, the calculated third magnitude value is compared with the calculated fourth magnitude value, and a large value is selected as a reference value for the third symbol.
This process determines the initial reference value.

As described above, the method of the present invention may be 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. Since this process can be easily implemented by those skilled in the art will not be described in more detail.

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.

As described above, the present invention compares the sum operation result calculated by the complex sum / difference operation of the first symbol with the second symbol and the difference operation result, and sets a large value as a reference value for the third symbol. By repeating the above process from the first symbol to N symbols, the final result obtained is averaged by the number of symbols (N) to estimate the channel coefficient, thereby improving system performance and implementing a system having a low complexity. have.

Claims (6)

In the channel coefficient estimation apparatus, Initial reference value determining means for comparing a sum operation result calculated through a complex sum / difference operation of the first symbol and the second symbol with a difference operation result, and determining a large value as a reference value for the third symbol; Reference value storing means for storing an initial reference value determined by said initial reference value determining means and a reference value selected by said reference value selecting means; Despreading means for compensating for frequency offset by performing despreading on the preamble interval of the third symbol; Sum calculation means for adding up a reference value stored in the reference value storing means and a complex value of a symbol despread by the despreading means; First magnitude value calculating means for calculating a first magnitude value of a result calculated by the sum calculating means; Difference calculating means for difference calculating a complex value of a reference value stored in said reference value storing means and a symbol despread by said despreading means; Second magnitude value calculating means for calculating a second magnitude value of a result calculated by the difference calculating means; Reference value selecting means for comparing the first magnitude value with the second magnitude value and selecting a large value as a reference value; And Channel coefficient estimating means for estimating the coefficient of the corresponding channel by dividing the final reference value selected by the reference value selecting means by the total number of symbols An apparatus for estimating channel coefficients in a wireless picocell communication system of a direct sequence spread spectrum method comprising a. The method of claim 1, The initial reference value determination means, A first despreader for compensating a frequency offset by performing despreading on a preamble section of a first symbol; A second despreader for compensating a frequency offset by performing despreading on a preamble section of a second symbol; A complex sum calculator for performing a complex sum operation of the first symbol despread by the first despreader and the second symbol despread by the second despreader; A first magnitude value calculator for calculating a magnitude value of a result calculated by the complex sum calculator; A complex difference operator for performing a complex difference operation between a first symbol despread by the first despreader and a second symbol despread by the second despreader; A second magnitude value calculator for calculating a magnitude value of a result calculated by the complex difference calculator; And A reference value selector for comparing a magnitude value calculated by the first magnitude value calculator with a magnitude value calculated by the second magnitude value calculator and selecting a large value as a reference value for a third symbol Channel coefficient estimation apparatus in a wireless picocell communication system of the direct sequence spread spectrum method comprising a. The method of claim 2, The channel coefficient estimator, An apparatus for estimating channel coefficients in a direct sequence spread spectrum wireless picocell communication system having a channel coefficient estimation path corresponding to a total channel number. In the channel coefficient estimation method in the channel coefficient estimation apparatus, An initial reference value determining step of comparing a sum operation result calculated through a complex sum / difference operation of the first symbol and the second symbol with a difference operation result, and storing a large value as a reference value for the third symbol; A compensation step of compensating for frequency offset by performing despreading on the preamble interval of the third symbol; A first calculating step of calculating the sum of the stored reference value and the complex value of the spread symbol; A first calculating step of calculating a first magnitude value of the result of the sum operation; A second operation step of calculating a difference between the stored reference value and the complex value of the despread symbol; A second calculating step of calculating a second magnitude value of the result of the difference calculation; Selecting a large value as a reference value of a next symbol by comparing the first magnitude value with the second magnitude value; And After repeating the compensation step, the first calculation step, the first calculation step, the second calculation step, the second calculation step, and the selection step for all symbols, the selected final reference value is divided by the total number of symbols for the corresponding channel. Channel coefficient estimating step of estimating the coefficient of Channel coefficient estimation method in the channel coefficient estimation apparatus comprising a. The method of claim 4, wherein The initial reference value determination step, Compensating for the frequency offset by performing despreading on the preamble section of the first symbol; Compensating for the frequency offset by performing despreading on the preamble section of the second symbol; Performing a complex sum operation of the despread first symbol and the despread second symbol; Calculating a third magnitude value of the result of the complex sum operation; Performing a complex difference operation between the despread first symbol and the despread second symbol; Calculating a fourth magnitude value of the result of the complex difference calculation; And Comparing the calculated third size value with the calculated fourth size value and selecting a large value as a reference value for a third symbol Channel coefficient estimation method in the channel coefficient estimation apparatus comprising a. The method of claim 5, The channel coefficient estimating step, The channel coefficient estimating method of the channel coefficient estimating apparatus, characterized in that for each channel, if there are a plurality of channels.

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