JP2008259198A - Moving channel tracking and signal detecting method and receiving side - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately perform signal detection by tracking channel change at high speed. <P>SOLUTION: The disclosed method includes the steps of: defining a channel coefficient corresponding to a preceding OFDM symbol as an estimate of a channel coefficient of a current OFDM symbol; detecting the current OFDM symbol using the estimate of the channel coefficient corresponding to the current OFDM symbol; correcting the detected current OFDM symbol using finite alphabet characteristics of the OFDM symbol itself; and updating the channel coefficient corresponding to the current OFDM symbol based on the corrected current OFDM symbol. A receiving side mainly including a channel tracking means, a signal detecting means and an OFDM symbol correcting means is disclosed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to channel tracking and signal detection technology, and more particularly, to a method for performing channel tracking and signal detection in a radio channel that fluctuates at high speed, and a receiver.

  In order to guarantee the reliability of the radio link, the mobile communication system must have a relatively high capability for channel fading, interference and noise immunity. However, when the user terminal moves at high speed, the radio channel between the user terminal and the base station changes considerably within the duration of one data symbol. Such a channel that changes at high speed in the time domain is also referred to as a rapid time-varying channel. In such a radio channel environment that fluctuates at high speed, it is necessary for the receiving side to be able to track a channel that changes at high speed in order to realize accurate signal detection.

  However, at the present stage, a signal detection method based on a quasi-static channel condition is usually adopted on the receiving side. Since such a signal detection method is based on the premise that the channel is assumed to be a quasi-static channel, the receiving side cannot normally effectively track a channel that changes at high speed in the time domain. Therefore, accurate signal detection cannot be performed in a high-speed time-variable channel environment, and as a result, reception performance of the high-speed mobile communication system is degraded. Therefore, how to perform channel tracking and signal detection in a high-speed time-varying channel environment is a problem to be solved in order to guarantee the reception performance of the system.

  In order to solve the above-mentioned problems, the present invention provides a channel tracking and signal detection method in a high-speed time-varying channel and a receiving side so as to track a channel change at high speed and accurately perform signal detection.

The channel tracking and signal detection method in the high-speed time-varying channel according to the present invention is as follows.
Step A where the channel coefficient corresponding to the previous OFDM symbol is an estimate of the channel coefficient of the current OFDM symbol;
Detecting a current OFDM symbol using an estimate of a channel coefficient corresponding to the current OFDM symbol; and
Step C modified from the detected current OFDM symbol to an optimal OFDM symbol selected from a finite set of signals that the OFDM symbol can take;
Updating a channel coefficient corresponding to the current OFDM symbol based on the modified current OFDM symbol.

 Here, the channel coefficient updated in step D is set as an estimated value of the channel coefficient corresponding to the current OFDM symbol, and the process further includes returning to step B.

 In step C, if there is no change in the current OFDM symbol before and after modification, the channel coefficient update for the channel corresponding to the current OFDM symbol and the signal detection process for the current OFDM symbol are terminated.

 If the transmitting side has encoded the OFDM symbol to be transmitted, Step C further includes performing secondary correction using the encoding rule on the detected current OFDM symbol.

 If the current OFDM symbol is an OFDM symbol used for training and synchronization, the current OFDM symbol is directly used to determine a channel coefficient corresponding to the current OFDM symbol.

  As can be seen, according to the channel tracking and signal detection method of the present invention, the OFDM symbol finite alphabet characteristic in the process of detecting the OFDM symbol without assuming that the channel state information is known on the receiving side. Is fully used to constantly modify the detected OFDM symbol, and the tracking result of the channel is updated using the modified OFDM symbol. As shown from experiments, the channel tracking and signal detection method according to the present invention can realize high-speed channel tracking and signal detection, and has relatively high accuracy.

 In order to further clarify the object and solution of the present invention, the present invention will be described below in more detail with reference to the accompanying drawings.

 One embodiment of the present invention illustrates a method for channel tracking and signal detection on the receiving side in an orthogonal frequency division multiplexing (OFDM) system in a fast time varying channel environment.

 In the normal case, when defining the configuration of the OFDM signal to be transmitted in order to achieve accurate recovery of data transmitted on the high-speed time-varying channel at the receiving side of the OFDM system, the time and frequency between the radio channel and The influence on the OFDM signal due to the change should be fully considered. However, considering the compatibility of the configuration of the traditional OFDM signal defined in the conventional wireless local area network (WLAN), as shown in FIG. 1, the OFDM defined in this embodiment is used. The configuration of the signal is almost the same as the configuration of the OFDM signal defined in the conventional WLAN.

In FIG. 1, TS (Training and Synchronization OFDM Symbol) represents an OFDM symbol used for training and synchronization. The TS symbol transmitted from the transmission side is known to the reception side, and the reception side is transmitted from the transmission side. After receiving the TS symbols, operations such as synchronization and channel estimation can be realized based on the known TS symbols. D represents an OFDM symbol of transmission data (Data). T ₀ represents the time at which the TS symbol is transmitted, and t ₁ , t ₂ ,..., T _n ,.

 Based on the OFDM frame structure shown in FIG. 1, the specific process of the method for performing channel tracking and signal detection on the receiving side shown in the present embodiment mainly includes the following steps as shown in FIG.

 In step A, the receiving side determines a channel coefficient corresponding to the first OFDM symbol in the OFDM frame based on the first OFDM symbol in the OFDM frame, ie, the TS symbol, and the first OFDM symbol in the OFDM frame. A time-varying channel impulse response (TV-CIR) corresponding to the symbol is further determined.

 Details of a method for determining a channel coefficient corresponding to the first OFDM symbol in the OFDM frame based on the first OFDM symbol in the OFDM frame in this step will be described later. In addition, since the channel coefficient is a coefficient expressed by a TV-CIR exponential sequence expansion formula, the receiving side determines a channel coefficient corresponding to one OFDM symbol in the OFDM frame, and then corresponds to a different OFDM symbol. TV-CIR can be easily obtained.

 In step B, the channel coefficient corresponding to the first OFDM symbol in the determined OFDM frame is set as the channel coefficient corresponding to the second OFDM symbol in the OFDM frame, and the TV− corresponding to the second OFDM symbol in the OFDM frame is An estimated value of CIR is calculated and used to detect the signal of the second OFDM symbol in the OFDM frame.

 Details of the signal detection method in this step will also be described later.

 In step C, based on the finite alphabet (FA) characteristic of the OFDM symbol itself, the second OFDM symbol detected in step B is modified, and the second OFDM symbol in the OFDM frame is redetermined. .

 If the signal detected in step B does not belong to the set of OFDM symbol values because only one OFDM symbol can be transmitted in the OFDM system in the finite alphabet, in order to realize a correction to the detected symbol, By symbol determination, the closest symbol can be found from the set of symbol values and can be determined as a redetermined symbol.

 In this step, when the information symbol transmitted from the transmission side is encoded, a part of redundancy is added so as to obtain a coding gain by normal encoding. Based on the encoding rule on the transmitting side, the OFDM symbol determined in the determination can be subjected to secondary correction by the redundancy generated in the encoding, and the OFDM symbol can be determined again.

 Those skilled in the art can realize the correction to the received signal by using the FA characteristic of the information symbol itself and the redundancy generated by the encoding on the receiving side, so that the symbol determined after the correction is transmitted from the transmitting side. It can be understood that it is closer to the original information symbol.

 In step D, based on the second OFDM symbol in the re-determined OFDM frame, the channel coefficient corresponding to the second OFDM symbol in the OFDM frame is updated, and the second OFDM symbol in the updated OFDM frame The TV-CIR corresponding to the second OFDM symbol in the OFDM frame is further determined based on the channel coefficient corresponding to.

 In this step, the method of updating the channel coefficient corresponding to the second OFDM symbol in the OFDM frame is based on the first OFDM symbol in the OFDM frame in the step A, and the first OFDM symbol in the OFDM frame is changed to the first OFDM symbol in the OFDM frame. This is roughly the same as the method for determining the corresponding channel coefficient.

 In the present embodiment, in order to realize accurate channel tracking and signal detection, the above steps B to D may be repeatedly executed. That is, after the channel coefficient corresponding to the second OFDM symbol in the OFDM frame determined in step D is set again as the TV-CIR estimate corresponding to the second OFDM symbol in the OFDM frame, in step B Applied to the signal detection of the second OFDM symbol in the OFDM frame, and then detected in step C using the FA characteristic of the information symbol itself, or further using the symbol coding rule. The second OFDM symbol is modified, the second OFDM information symbol is re-determined, and finally the channel of the second OFDM symbol using the second OFDM symbol in the re-determined OFDM frame in step D The coefficients are updated again and the TV-CIR of the second OFDM symbol is redetermined. The second OFDM symbol in the OFDM frame re-determined in step C is the same as the second OFDM symbol in the OFDM frame detected before modification, ie, the second OFDM symbol in the OFDM frame before and after modification. Steps B to D are repeated as described above until the OFDM symbols are the same. The second OFDM information symbol in the OFDM frame determined by the above method is approximately close to the original information symbol of the second OFDM symbol transmitted from the transmission side, and the second OFDM obtained by the above procedure is used. The symbol TV-CIR is also already close to the actual channel impulse response. At this time, the execution of the steps B to D is further repeated.

 After determining the TV-CIR corresponding to the second OFDM symbol in the OFDM frame by the above iterative procedure, by analogy with this, the channel coefficient corresponding to the second OFDM symbol in the OFDM frame determined by the above method is further determined. Is the channel coefficient estimation value corresponding to the third OFDM symbol in the OFDM frame, and the signal detection of the third OFDM symbol in the OFDM frame is performed, while the channel coefficient of the third OFDM symbol in the OFDM frame and the TV -CIR can be determined.

 Here, a method for determining a TV-CIR of a third OFDM symbol using a channel coefficient corresponding to the second OFDM symbol in the determined OFDM frame for the third OFDM symbol in the OFDM frame, and the OFDM The signal detection method is substantially the same as the steps B to D described above, the first OFDM symbol in the steps B to D is changed to the second OFDM symbol, and the second OFDM symbol in the third OFDM symbol is changed to the third OFDM symbol. It is only necessary to change to the OFDM symbol.

 In this manner, the above method can be widely used for detecting other OFDM symbols in the OFDM frame and tracking to channels corresponding to the other OFDM symbols. That is, Step E shown in FIG. 2 is repeatedly executed. In step E, the channel coefficient and TV-CIR corresponding to the (n + 1) th OFDM symbol in the OFDM frame are updated based on the nth (n is a natural number) OFDM symbol in the re-determined OFDM frame.

 In normal cases, a relatively large sudden change does not occur within the duration of two preceding and following OFDM symbols in a high-speed time-varying channel, so that the channel coefficient corresponding to the previous OFDM symbol is sufficiently large as described above. Methods that utilize to achieve TV-CIR tracking and signal detection of the current symbol channel typically have relatively high accuracy.

 Hereinafter, a method for determining a channel coefficient corresponding to the first OFDM symbol in the OFDM frame based on the first OFDM symbol in the OFDM frame in the step A, and a second OFDM in the OFDM frame in the step D A method for updating the channel coefficient corresponding to the symbol will be described in detail. The above two methods are substantially the same in the problem solved, and when the OFDM symbol transmitted from the transmitting side is known or determined, the channel corresponding to the OFDM symbol based on the signal received by itself It may be abstracted to a method of determining the coefficients.

In the OFDM system, it is known that the transfer function of the radio channel may be expressed as Equation 1 below.

here,

Ｑの値はチャネル変化を再現する指数部分の最大値を表し、ＱとＲ_１の比はユーザ端末の最大の移動速度によって設定され、ｎ＝１，…，Ｎは時間係数を表し、Ｎは１つのＯＦＤＭシンボルの持続時間内の総サンプリング数であり、

は雑音信号を表し、

は送信側から送信された情報シンボルであり、

は受信側で受信されたＯＦＤＭシンボルの時間領域表示であり、

はチャネル係数であり、Ｋはチャネル遅延時間の長さの最大値である。 and,

The value of Q represents the maximum value of the exponent part that reproduces the channel change, the ratio of Q and R ₁ is set by the maximum moving speed of the user terminal, n = 1,..., N represents the time coefficient, The total number of samplings in the duration of one OFDM symbol,

Represents the noise signal,

Is an information symbol sent from the sender,

Is the time domain representation of the OFDM symbol received on the receiving side,

Is a channel coefficient, and K is the maximum value of the length of the channel delay time.

Thereby, the following formula 2 is obtained by deriving from the above formula 1.

The above formula 2 is further simplified to obtain the following formula 3.

はチャネル係数行列と呼ばれ、

はＯＦＤＭのプレフィックス（ｐｒｅｆｉｘ）を生成するものであり、

は送信側の送信待ちの情報データである。 here,

Is called the channel coefficient matrix,

Is to generate an OFDM prefix,

Is information data waiting for transmission on the transmission side.

The above formula 3 is further simplified to obtain the following formula 4.

であり、

は送信側から送信された情報シンボルからなる対角行列を表す。 here,

And

Represents a diagonal matrix composed of information symbols transmitted from the transmission side.

When the transmitted OFDM symbol is known or determined by the above derivation, a method for determining a channel coefficient corresponding to the OFDM symbol based on the received signal is expressed as a solution of Equation 5 below. May be.

が、求めるべき既知のまたは決定されたＯＦＤＭシンボルに対応するチャネル係数となる、ということが理解できる。上記の数式５において、

はシステムによって設定された総変化規制係数（Ｔｏｔａｌ−Ｖａｒｉａｔｉｏｎ Ｒｅｇｕｌａｔｉｏｎ Ｃｏｅｆｆｉｃｉｅｎｔ）であり、

は勾配演算行列である。 Those skilled in the art will understand that the channel coefficient at which the calculation formula in the brace of Equation 5 above has the minimum value.

Is the channel coefficient corresponding to the known or determined OFDM symbol to be determined. In Equation 5 above,

Is the Total-Variation Regulation Coefficient set by the system,

Is a gradient calculation matrix.

に対して勾配を求め、次に、勾配が０となる際のチャネル係数値を求める。このとき、解を求めて得られたチャネル係数値が、上記の数式５のブレース内の計算式が最小値となる際のチャネル係数となる。具体的に下記のステップを含む。

The method for obtaining the solution of Equation 5 specifically includes the following steps. That is, first, the calculation formula in the brace of Equation 5 above.

Next, the channel coefficient value when the gradient becomes 0 is obtained. At this time, the channel coefficient value obtained by obtaining the solution becomes the channel coefficient when the calculation formula in the brace of the above formula 5 becomes the minimum value. Specifically, the following steps are included.

 As can be seen, if the transmitted OFDM symbol is known or determined, the receiving side can calculate the channel coefficient of the current radio channel based on the received signal.

 Next, the channel coefficient corresponding to the first OFDM symbol in the OFDM frame determined in step B is set as the channel coefficient corresponding to the second OFDM symbol in the OFDM frame, and the second OFDM symbol in the OFDM frame is used. A method for calculating an estimated value of TV-CIR for the second OFDM symbol in the OFDM frame using the estimated TV-CIR value will be described in detail. Without losing generality, the method uses the channel coefficient corresponding to the previous OFDM symbol in the OFDM frame determined in the present embodiment as the channel coefficient estimate corresponding to the current OFDM symbol in the OFDM frame. As an example, the present invention may be applied to the process of detecting the signal of the current OFDM symbol, and the TV-CIR estimate of the current OFDM symbol is calculated using the channel coefficient corresponding to the current OFDM symbol in the corrected OFDM frame. However, the present invention may be applied to a process for performing signal detection of the current OFDM symbol.

As shown in Equation 3 above, the channel transfer function of the OFDM system may be expressed by the following equation.

 After determining the channel coefficient corresponding to one OFDM symbol, the OFDM symbol transmitted from the transmission side can be calculated by the above Equation 3. As can be seen from the above description, the channel coefficient corresponding to the determined one OFDM symbol may be a channel coefficient corresponding to the previous OFDM symbol, and the current OFDM symbol determined in the previous step. May be a channel coefficient corresponding to.

A specific process for obtaining a solution may be calculated by the following Equation 6.

はノルム（ｎｏｒｍ）算出を表す。 A person skilled in the art understands that [s ₁ s ₂ ... S _N ] when the calculation formula in the brace of Equation 6 is the minimum value is the OFDM symbol transmitted from the transmission side to be obtained. it can. Where the operator

Represents a norm calculation.

Specifically, the following steps are included.

 As can be seen, after determining the channel coefficient corresponding to the current OFDM symbol, the receiving side can estimate the OFDM symbol transmitted from the transmitting side based on the signal received by itself.

 Correspondingly, the present invention also provides a receiver including channel tracking means, signal detection means and OFDM symbol correction means. Its internal configuration is as shown in FIG.

  The above are only preferred embodiments of the present invention and do not limit the protection scope of the present invention. All the improvements made in the algorithm and signal processing flow of the present invention should be included in the protection scope of the present invention.

It is a figure which shows the frame structure of the OFDM signal by the Example of this invention. 3 is a flowchart of a method for realizing channel tracking and signal detection according to an embodiment of the present invention; It is a figure which shows the internal structure of the receiving side by the Example of this invention.

Claims (15)

A channel tracking and signal detection method in a high-speed time-varying channel,
A channel coefficient corresponding to a previous orthogonal frequency division multiplexing (OFDM) symbol is used as an estimate of the channel coefficient of the current OFDM symbol;
Detecting a current OFDM symbol using the estimate of the channel coefficient corresponding to the current OFDM symbol; and
Step C modified from the detected current OFDM symbol to an optimal OFDM symbol selected from a finite set of signals that the OFDM symbol can take;
Updating a channel coefficient corresponding to a current OFDM symbol based on the modified current OFDM symbol; and
A channel tracking and signal detection method comprising:   The channel tracking and signal detection according to claim 1, further comprising a step E of returning to step B using the channel coefficient updated in step D as an estimate of a channel coefficient corresponding to a current OFDM symbol. Method.   In step C, if there is no change in the current OFDM symbol before and after the modification, the channel coefficient update for the channel corresponding to the current OFDM symbol and the signal detection process for the current OFDM symbol are terminated. The channel tracking and signal detection method according to claim 1.   Step C further includes performing secondary correction using a coding rule on the detected current OFDM symbol when the transmitting side performs coding on the OFDM symbol to be transmitted, The channel tracking and signal detection method according to claim 1, 2 or 3. When the current OFDM symbol is an OFDM symbol used for training and synchronization,
Determining the channel coefficient corresponding to the current OFDM symbol directly using the current OFDM symbol;
The channel tracking and signal detection method according to claim 1, further comprising:  The determination includes: calculating a channel coefficient corresponding to a current OFDM symbol based on a signal received at a receiving side and a known OFDM symbol used for training and synchronization. 5. The channel tracking and signal detection method according to 5.  In step B, detecting the current OFDM symbol using an estimate of the channel coefficient corresponding to the current OFDM symbol is based on the signal received at the receiving side and the channel coefficient corresponding to the current OFDM symbol. 2. The channel tracking and signal detection method according to claim 1, comprising calculating a current OFDM symbol. The calculation of the current OFDM symbol is obtained by finding the solution of

Here, [s ₁ s ₂ ... S _N ] to be obtained is an OFDM symbol estimated to be transmitted from the transmission side,

Is the signal received on the receiving side,

Is a channel coefficient matrix containing channel coefficient information,

Generates a prefix for the OFDM symbol,

Is the Fourier transform matrix and the operator

Represents the norm calculation,
The channel tracking and signal detection method according to claim 7. Finding the solution

Initialize the variable as follows, where

Step B1 which is

If you decide whether to meet

Step B2

Step B3 and

Step B4 for calculating

And return to step B2 to repeat until the convergence condition is satisfied,

Step B5 and
The channel tracking and signal detection method according to claim 8, comprising:   The channel of claim 1, wherein in step C, the modification includes determining a symbol closest to the detected symbol from a set of OFDM symbol values to be a modified OFDM symbol. Tracking and signal detection methods.   In step D, updating the channel coefficient corresponding to the current OFDM symbol based on the modified current OFDM symbol includes updating the current OFDM symbol based on the signal received at the receiver and the current OFDM symbol. 2. The channel tracking and signal detection method according to claim 1, comprising calculating corresponding channel coefficients. The calculation of the channel coefficient corresponding to the current OFDM symbol is obtained by finding the solution of

Where you should ask

Is the channel coefficient corresponding to the current OFDM symbol,

Is the signal received on the receiving side,

Is the total change regulation factor set by the system,

Is the gradient operation matrix,

Of which

Represents an OFDM symbol transmitted from the transmitting side,

And

The value of Q represents the maximum value of the exponent part that reproduces the channel change, the ratio of Q and R ₁ is set by the maximum moving speed of the user terminal, and K is the maximum value of the length of the channel delay time. N = 1,..., N is a time factor, and N is the total number of samples within the duration of one OFDM symbol,
12. The channel tracking and signal detection method according to claim 6 or 11, wherein: Finding the solution

Initialize the variable as follows, where

Step D1 which is

If you decide whether to meet

Step D2

Step D3 and

Calculating step D4;

And return to step D2 to repeat until convergence, step D5,
13. The channel tracking and signal detection method according to claim 12, further comprising: The receiving side,
Channel estimation is performed based on the signal received at the receiving side and the corrected OFDM symbol fed back by the OFDM symbol correcting means, the channel coefficient corresponding to the current OFDM symbol is determined, and the determined current OFDM Channel tracking means for outputting a channel coefficient corresponding to the symbol to the signal detection means;
A signal for estimating the OFDM symbol transmitted from the transmission side based on the channel coefficient output from the channel tracking means and the signal received at the reception side, and outputting the estimated OFDM symbol to the OFDM symbol correction means Detection means;
An OFDM symbol correction unit that performs correction processing on the OFDM symbol output from the signal detection unit using a finite signal set that can be taken by the OFDM symbol, and outputs the corrected OFDM symbol to the channel tracking unit. When,
A receiving side characterized by including:   The OFDM symbol correction means further performs secondary correction on the OFDM symbol output from the signal detection means based on a coding rule when the transmission side encodes the OFDM symbol. Item 15. The receiving side according to Item 14.

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