KR20080050244A - Apparatus and method for channel equalizing using absolute value of channel coefficient - Google Patents

Abstract

A method and an apparatus for channel equalization are provided to prevent a noise from being amplified by decreasing a variance of a channel equalization signal. A channel estimation apparatus includes a channel interpolator(41), a mapper(42), and an equalizer(43). The channel interpolator delivers an estimated channel coefficient for a sub-carrier of a symbol to the equalizer. The mapper delivers the estimated basic layer symbol to the equalizer. The equalizer equalizes the channel by using the received symbol, the channel coefficient received from the channel interpolator, and the basic layer symbol received from the mapper.

Description

Apparatus and method for channel equalizing using absolute value of Channel Coefficient}

The present invention relates to a channel-based channel equalizer and a method thereof, and more particularly, to an OFDM-based hierarchical modulation transmission system using an additional layer signal modulation method using Mary PSK (Phase Shift Keying). The present invention relates to a channel-based channel equalizer and a method for reducing the probability of noise amplification by reducing the variance of the channel equalization result signal by combining the channel estimation result with a decision-based method.

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-017-01, Task name: Terrestrial DMB transmission advancement technology] .

In general, hierarchical modulation is a technique for synchronously modulating at least two signals modulated by different modulation schemes together to be transmitted and used to increase data rate.

As an example of a digital audio broadcasting (DAB) or terrestrial digital multimedia broadcasting (DMB) system, a signal transmitted on each subcarrier includes a phase reference symbol (PRS) transmitted at the beginning of each transmission frame, and thus an even numbered OFDM therefrom. The symbol interval has a constellation as shown in FIG. 1 (a) and the odd OFDM symbol interval has a constellation as in FIG. 1 (b).

An example of a constellation in which hierarchical modulation is applied to a signal having the constellation as described above is as shown in FIGS. 2A and 2B. In this case, π / 4-DQPSK modulation is applied to the base layer signal and QPSK modulation is applied to the additional layer signal.

를 하기의 [수학식 1]과 같이 정의한다.Variables that determine the characteristics of a hierarchically modulated system

Is defined as in Equation 1 below.

Here, the value of a means the interval between minimum additional layer signals between adjacent "quadrants" and the value of b is the interval between adjacent additional layer signals within one "quadrants".

값이 작을수록 추가계층 신호 성분의 전력이 상대적으로 증가하므로 추가계층 신호의 수신 성능은 개선되지만, 서로 다른 기본계층 심벌에 해당하는 성상도 군간의 거리가 짧아지므로 기본 계층 신호의 수신 성능 열화가 증가한다. 반대로,

값이 커지게 되면 추가계층 신호의 수신 성능 열화는 증가하고 기본계층 신호의 수신 성능 열화는 감소한다.At this time,

The smaller the value, the higher the power of the additional layer signal component, so that the reception performance of the additional layer signal is improved, but the deterioration in reception performance of the base layer signal is increased because the distance between constellation groups corresponding to different base layer symbols is shorter. do. Contrary,

As the value increases, the reception performance degradation of the additional layer signal increases and the reception performance degradation of the base layer signal decreases.

The receiver needs to perform channel estimation and channel equalization to properly reconstruct the hierarchically modulated signal. To this end, the transmitter periodically inserts a pilot signal (symbol) for channel estimation into a transmission signal or transmits it periodically or aperiodically.

The LS (Least-Squares) method is the most common method for estimating a channel through such a pilot symbol, and the channel estimation of the LS method is expressed by Equation 2 below.

)가 파일럿에 대한 것임을 나타내며, n은 OFDM 심벌 번호, 그리고 k는 파일럿의 부반송파 위치를 나타낸다. Where p is the variable (

) Denotes a pilot, n denotes an OFDM symbol number, and k denotes a pilot subcarrier position.

은 n번째 OFDM 심벌의 파일럿 부반송파 위치에서 수신된 파일럿 심벌 벡터를 의미하며,

은 수신된 파일럿 심벌들에 대한 추정 값들로 이루어져 있는 벡터를 의미한다. therefore

Denotes a pilot symbol vector received at a pilot subcarrier location of an n th OFDM symbol,

Denotes a vector consisting of estimated values for the received pilot symbols.

The receiver estimates channel coefficients for all subcarriers other than the pilot through interpolation based on the estimated channel coefficient as shown in [Equation 2], and the result is used for channel equalization.

Hereinafter, a channel equalization method of a conventional zero-forcing (ZF) method will be described with reference to FIG. 3.

가 n번째 OFDM 심벌의 k번째 부반송파 위치에서 수신된 심벌이라 하고,

가 그에 해당하는 송신 심벌이라고 하면, 하기의 [수학식 3]을 이용하여 채널 등화를 수행한다.

Is a symbol received at the k th subcarrier position of the n th OFDM symbol,

Is a transmission symbol corresponding thereto, channel equalization is performed using Equation 3 below.

는 n번째 OFDM 심벌의 k번째 부반송파의 채널 등화 결과를 의미하고,

는 LS 방식과 보간 등에 의해 추정된 n번째 OFDM 심벌의 k번째 부반 송파의 채널계수를 의미하며,

는 채널과 상관관계가 없는 가우시안(Gaussian) 잡음 벡터를 의미한다. here,

Denotes a channel equalization result of the k th subcarrier of the n th OFDM symbol,

Denotes the channel coefficient of the kth subcarrier of the nth OFDM symbol estimated by the LS method and interpolation, etc.

Denotes a Gaussian noise vector that is not correlated with the channel.

값이 작은 부분(채널의 널(null) 부분)에서는 잡음 증폭을 야기시켜 등화 성능을 열화시키는 문제점이 있다.The conventional channel equalization method of ZF (Zero-Forcing) method as shown in [Equation 3],

In a small portion (a null portion of the channel), there is a problem of degrading equalization performance by causing noise amplification.

In summary, the conventional ZF channel equalization method can theoretically recover a received signal without distortion, but in reality, it is difficult to expect good performance due to noise amplification problem, especially in a frequency selective fading channel environment.

That is, when nulls with very small channel gains in the frequency dimension exist within the signal band, multiplying each subcarrier signal of the received signal by the inverse of the estimated channel gain for each subcarrier channel results in the original signal component. Although the signal is recovered in the same shape as, the noise component in the subcarrier channel corresponding to null is also amplified so that a reception error occurring in the subcarrier channel causes a problem of significantly reducing the overall reception performance.

In OFDM-based hierarchical modulation transmission systems using M-ary phase shift keying (PSK) as an additional layer signal modulation method, channel estimation results are combined with decision-based methods to equalize the channel, thereby improving channel equalization result distribution. Provided are a channel coefficient sized channel equalizer and a method for reducing the probability of noise amplification.

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. It will also be readily appreciated that the objects and advantages of the present invention can be realized by the means and combinations thereof indicated in the claims.

In accordance with an aspect of the present invention, there is provided an apparatus for channel-based channel equalization, comprising: channel interpolation means for transferring an estimated channel coefficient for a subcarrier of a symbol to an equalization means; Mapping means for transferring an estimated base layer symbol to the equalization means; And the equalizing means for equalizing a channel using a received symbol, a channel coefficient received from the channel interpolation means, and a base layer symbol received from the matching means.

In addition, the method of the present invention for solving the above problems, in the channel-based size equalization method of the channel coefficient, receiving the estimated channel coefficient for the subcarrier of the symbol; Receiving an estimated base layer symbol; And a channel equalization step of equalizing a channel by using a received symbol, the received channel coefficient, and the estimated base layer symbol.

The foregoing problems, features, and advantages will become more apparent from the following detailed description of the invention in connection with the accompanying drawings, and as a result, those skilled in the art to which the present invention pertains the technical idea of the present invention. It will be easy to do. 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.

According to the present invention, the channel equalization result is combined with the decision-based method in an OFDM-based hierarchical modulation transmission system using M-ary phase shift keying (PSK) as an additional layer signal modulation method, thereby channel equalization result. By reducing the variance of the signal, it is possible to reduce the probability of noise amplification.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In an embodiment of the present invention, an OFDM-based hierarchical modulation transmission system is described as an example, and the OFDM-based hierarchical modulation transmission system includes a digital audio broadcasting (DAB) or a terrestrial digital multimedia broadcasting (DMB) system.

Prior to the description of the present invention, a technique related to the channel estimation process, that is, the process of estimating the base layer symbol, is a widely used technique and is not a subject matter of the present invention, and thus the detailed description thereof will not be provided.

4 is a diagram illustrating an embodiment of an apparatus for channel based size equalization of channel coefficients according to the present invention.

)를 등화기(43)로 전달하기 위한 채널 보간기(41), 추정된 기본계층 심벌(

)을 등화기(43)로 전달하기 위한 π/4-DQPSK 맵퍼(42), 및 상기 채널 보간기(41)로부터 전달받은 채널계수, 상기 π/4-DQPSK 맵퍼(42)로부터 전달받은 기본계층 심벌 및 수신 심벌(

)을 이용하여 채널을 등화하기 위한 등화기(43)를 포함한다.As shown in FIG. 4, the size-based channel equalizer of the channel coefficient according to the present invention includes a channel coefficient of the k-th subcarrier of the estimated n-th OFDM symbol.

), The channel interpolator 41 for passing the equalizer 43 to the equalizer 43,

Π / 4-DQPSK mapper 42 for transmitting the equalizer 43 to the equalizer 43, and the channel coefficient received from the channel interpolator 41, and the base layer received from the π / 4-DQPSK mapper 42. Symbol and received symbol (

Equalizer 43 for equalizing the channel using < RTI ID = 0.0 >

인 부분, 즉 채널계수의 크기가 임계치(

)보다 작은 부분에서는 수신 심벌과 추정된 기본계층 심벌의 평균을 이용하여 등화한다.Here, the equalizer 43 is

, That is, the magnitude of the channel coefficient is the threshold (

For parts smaller than), equalization is performed using the average of received symbols and estimated base layer symbols.

That is, the equalizer 43 equalizes the channel using Equation 4 below.

는 추정된 기본계층 심벌을 의미하고,

는 적용할 채널 등화 방식을 선택하기 위한 임계치를 의미한다. here,

Means the estimated base layer symbol,

Denotes a threshold for selecting a channel equalization scheme to apply.

The equalization method according to the present invention allows a symbol with reduced noise variance to be used as an input of a channel decoder, which is a block next to the channel equalizer, in a small portion of the channel size.

On the other hand, assuming the channel and base layer symbol estimation is correct, the output of the equalizer 43 is expressed by Equation 5 below.

는 정확한 기본계층 심벌에 대한 송신 심벌을 나타내고,

는 수신 심벌을 나타내고,

은 수신 심벌에 대한 송신 심벌을 나타내고,

는 채널과 상관관계가 없는 가우시안(Gaussian) 잡음 벡터를 나타내며,

는 정확한 채널 계수를 나타낸다.here,

Denotes the transmission symbol for the correct base layer symbol,

Denotes a received symbol,

Denotes a transmit symbol for the received symbol,

Represents a Gaussian noise vector that is not correlated with the channel,

Represents the exact channel coefficients.

에 바이어스(bias)되어 있음을 알 수 있다.The output of the equalizer 43 through Equation 5

It can be seen that the bias is (biased).

Hereinafter, with reference to FIG. 5, in order to examine the performance of the channel-based channel equalization method of the channel coefficient according to the present invention, the equalization according to the constellation and inverse filtering method of the equalizer output symbol according to the method of the present invention Compare the constellations of the output symbols.

인 부분에서 본 발명(제안된)에 따른 등화기 출력 심벌의 성상도 및 인버스 필터링 방법을 적용한 등화기 출력 심벌의 성상도를 나타내며, 도 5의 (b)는

인 부분에서 등화기 출력 심벌의 성상도를 나타낸다.(A) of FIG.

In Fig. 5 shows the constellation of the equalizer output symbol according to the present invention (proposed) and the constellation of the equalizer output symbol to which the inverse filtering method is applied.

The constellation of the equalizer output symbol at

값은 0.5이다.At this time, the channel used to represent the constellation of the equalizer output symbol is the COST-207 TU6 channel model, the considered moving speed is 120 km / h, SNR 24dB,

The value is 0.5.

인 경우의 성상도 가

인 경우보다 넓게 퍼져 있는 것을 볼 수 있다. As shown in Figure 5, due to noise amplification

If constellation is

You can see that it is wider than.

인 경우 본 발명의 방법은 심벌의 성상도가 기본계층 심벌값 주변으로 모여 있는 반면, 인버스 필터링 방법은 분산되어 있는 것을 볼 수 있다.Also,

In the method of the present invention, the constellations of the symbols are gathered around the base layer symbol values, while the inverse filtering method is distributed.

As a result, the variance of noise is reduced to one quarter, so that the equalizer output with reduced noise amplification in the small part of the channel, i.e., the inaccuracy of the estimated channel coefficient or the amplification of noise, is used as the next block, the channel decoder input. Can be.

Figure 6 is an exemplary view showing the results of the simulation to evaluate the performance of the receiver for receiving the hierarchical modulation signal used in the present invention.

The channel used in this experiment is the COST-207 TU6 channel model, the center frequency is 200MHz, and the considered moving speed is 120km / h. The code rate of the convolutional encoder used for the BER (Bit Error Rate) analysis is applied to 1/2 of the base layer signal and the additional layer signal.

As shown in FIG. 6, HP (High Priority) represents a base layer reception performance through π / 4-DQPSK demodulation in a layer modulation system, and LP (Low Priority) represents a layer modulation signal received from a layer modulation system. Receive performance of the additional layer demodulated in-phase by the receiver.

7 to 9 are exemplary views showing the results of a simulation for the performance evaluation of the channel-based channel equalization method of the channel coefficient according to the present invention.

값은 3,

값은 0.5를 적용하였다.The channel used in this experiment is the COST-207 TU6 channel model, the center frequency is 200 MHz, and the considered travel speeds are 80 km / h, 120 km / h and 200 km / h. The code rate of the convolutional encoder used for the BER (Bit Error Rate) analysis is applied to 1/2 of the base layer signal and the additional layer signal.

The value is 3,

A value of 0.5 was applied.

As shown in Figs. 7 to 9, reception performance when there is only a base layer when the moving speeds are 80 km / h, 120 km / h, and 200 km / h, respectively, and the base layer for the layer-modulated signal The reception performance of and the additional performance of the additional layer for the layer modulated signal are shown.

That is, "no LP" indicates performance when no hierarchical modulation is applied, HP indicates reception performance of the base layer through π / 4-DQPSK demodulation in the layer modulation system, and LP indicates channel equalization in the layer modulation system. It shows the reception performance of the additional layer coherent demodulation through.

In this case, the reception performance of the additional layer is shown by comparing the equalization method (LP: Pro.) And ZF equalization method (LP: Con) of the present invention.

Through this, it can be seen that the channel-based channel equalization method of the channel coefficient improves the BER performance.

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 carried out by those skilled in the art will not be described in detail any more.

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 an exemplary view showing a constellation of a signal transmitted through a subcarrier in a DAB or terrestrial DMB system;

2 is an exemplary view illustrating a constellation diagram of applying layer modulation to a signal transmitted through a subcarrier in a DAB or terrestrial DMB system;

3 is a diagram illustrating an exemplary embodiment of a channel equalization method of a conventional zero-forcing (ZF) method.

4 is a block diagram of an embodiment of a channel-based channel equalization apparatus according to the present invention;

5 is an exemplary view illustrating the performance of a channel coefficient size-based channel equalization method according to the present invention;

6 is an exemplary view showing a result of performing a simulation for performance evaluation of a receiver for receiving a hierarchical modulated signal used in the present invention;

7 to 9 are exemplary views showing the results of a simulation for the performance evaluation of the channel-based channel equalization method of the channel coefficient according to the present invention.

* Explanation of symbols for the main parts of the drawings

41: channel interpolator 42: mapper

43: equalizer

Claims (8)

In the size-based channel equalizer of the channel coefficient, Channel interpolation means for conveying an estimated channel coefficient for a subcarrier of a symbol to equalization means; Mapping means for transferring an estimated base layer symbol to the equalization means; And The equalization means for equalizing a channel using a received symbol, a channel coefficient received from the channel interpolation means, and a base layer symbol received from the matching means Size based channel equalizer of the channel coefficient comprising a. The method of claim 1, The equalization means, And channel equalization using an average of the received symbol and the estimated base layer symbol in a portion where the magnitude of the channel coefficient received from the channel interpolation means is smaller than a threshold value. The method of claim 1, The equalization means, And a channel coefficient equalization using the received symbol and the estimated channel coefficient in a portion where the channel coefficient received from the channel interpolation means is larger than a threshold. The method of claim 2 or 3, The threshold is Size-based channel equalizer of the channel coefficient, characterized in that 0.5. In the size-based channel equalization method of the channel coefficient, Receiving an estimated channel coefficient for a subcarrier of a symbol; Receiving an estimated base layer symbol; And A channel equalization step of equalizing a channel by using a received symbol, the received channel coefficient, and the estimated base layer symbol Size based channel equalization method of the channel coefficient comprising a. The method of claim 5, wherein The channel equalization step, And equalizing a channel using an average of the received symbol and the estimated base layer symbol in a portion where the magnitude of the channel coefficient is smaller than a threshold. The method of claim 5, wherein The channel equalization step, And channel equalization using the received symbol and the estimated channel coefficient in a portion where the magnitude of the channel coefficient is greater than a threshold. The method according to claim 6 or 7, The threshold is A magnitude-based channel equalization method of channel coefficients, characterized in that 0.5.

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