KR100686046B1 - Apparatus and Method of channel estimating in Digital receiver - Google Patents

Abstract

The present invention relates to an apparatus and method for channel estimation of a digital receiver. The present invention provides a noise estimator for estimating noise of a received signal located on each path of a received signal, a filter for calculating the average of the estimated noise, and a channel separated from the obtained average noise and the received signal. Provided is a channel estimating apparatus for a digital receiver including a channel estimator for receiving a channel estimate. Therefore, according to the present invention, the noise is extracted and removed from the original signal, thereby accurately recovering the original signal from the distorted signal.

Satellite DMB, channel estimator, noise estimator, IIR filter, synthesizer

Description

Apparatus and Method of channel estimating in Digital receiver

1 is a view showing for explaining the principle of a general MRC

2 is a block diagram illustrating a configuration of a channel estimating apparatus including a noise estimator according to the present invention.

3 illustrates a Walsh code extension method for explaining a noise estimation method according to the present invention.

4 illustrates a Walsh code of 128 length in accordance with the present invention.

5 is a block diagram showing the overall configuration of a satellite DMB according to the present invention.

-Explanation of symbols for the main parts of the drawings-

100 (n): Noise Estimator 200 (n): IIR Filter

300 (n): Channel estimator

The present invention relates to a noise estimator, and more particularly, to a channel estimating apparatus and method for effectively estimating a channel by removing noise of a signal received from a satellite DMB receiver.

Digitalization of broadcasts has made Digital Multimedia Broadcasting (DMB) possible, encompassing data transmission and multimedia services. The DMB is robust against noise and distortion on a transmission channel, has a high transmission efficiency and has an advantage of enabling a multimedia service.

The satellite DMB broadcast adopted in Korea is based on the Japanese system E system and consists of performance equipment, earth station, satellite, terrestrial relay equipment and subscriber receiver.

The satellite DMB broadcasting system transmits multimedia contents from the earth station transmission center to the satellite, and the user receives the data directly from the satellite or from a terrestrial auxiliary relay called a gap filter in a shaded area where the signal strength is weak. It will work.

In this case, the transmission channel of the satellite DMB is a wireless mobile reception channel, and the amplitude of the received signal is not only time-varying, but also the Doppler shift of the received signal spectrum occurs due to the mobile reception. .

Therefore, in consideration of the transmission and reception in such a channel environment, the satellite DMB transmission method adopts a code division multiplexing (CDM) transmission method.

As such, the CDM transmission scheme used in satellite DMB uses the same frequency spreading scheme as that used in the code division multiple access (CDMA) scheme, which is much more than the band required to transmit a desired signal. By transmitting a signal using a wide band, it is resistant to jamming or interference of other signals.

The frequency spreading method transmits a desired symbol by multiplying a spreading signal having a much higher frequency. The period of the spreading signal is called a chip, and one symbol is composed of several chips.

Therefore, in the frequency spreading method, the multipath components can be extracted as much as the resolution of the chip. Thus, by adding each multipath component that eliminates the phase error, instead of removing the multipath components as in other transmission schemes. Signal to Noise Ratio (SNR) is increased to improve reception performance.

Such methods include MRC (Maximum Ratio Combining) technique and EGC (Equal Gain Combining) technique. Among them, MRC is more widely used because of its superior performance.

Referring to Figure 1 attached to the principle of the MRC as follows.

는 다음의 수학식 1과 같이 표현된다.As shown in FIG. 1, the original signal u (t) to be restored is received through L paths at the input terminal of the receiver, and the channel gains are multiplied by each channel, and the noise (AWGN, white noise) is added to the signal x (t). Each signal received in the L paths

Is expressed by Equation 1 below.

는 k번째 경로의 채널 이득이고,

는 k번째 수신단의 잡음이다.In Equation 1

Is the channel gain of the kth path,

Is the noise of the k-th receiver.

Therefore, the output of the combiner (combiner) of Figure 1 can be expressed as shown in the following equation (2) plus each of the received signals.

는 수신기에서 곱해지는 계수이다. 상기 계수

는 MRC에서 순시치 SNR 비율이 최대가 될 수 있도록, 즉 합성기(combiner)의 출력단에서 에러 확률이 최소가 될 수 있도록 설정되어야 한다.In Equation 2

Is the coefficient to be multiplied at the receiver. The coefficient

The MRC should be set such that the instantaneous SNR ratio in MRC can be maximized, that is, the error probability is minimized at the output of the combiner.

To this end, the output of the synthesizer can be expressed as Equation 3 below by dividing the signal component and the noise component.

가 독립적이라 가정하면, 순시치 SNR은 다음의 수학식 4와 같이 표현된다.Noise

Assuming that is independent, the instantaneous value SNR is expressed as in Equation 4 below.

는 잡음

의 분산을 의미한다. 상기 수학식 4의 Schwarz inequality는 수학식 5와 같이 표현된다.In Equation 4

The noise

Means dispersion. Schwarz inequality of Equation 4 is expressed as Equation 5.

일때 최대값을 갖게 되므로, 계수

는 다음의 수학식 6일때 SNR이 최대가 된다.In Equation 5

Is the maximum value when

Is the maximum SNR in the following equation (6).

로 나눈값을 곱해주면 된다.Therefore, in order to obtain the maximum SNR at the output of the synthesizer, a conjugate of channel gain is recalled on the incoming input signal.

Multiply by.

를 백색 잡음으로 가정하고, 상기 값은 각 핑거마다 동일하다고 가정하여

를 계산할때 고려하지 않는다.In this case, in general, the synthesizer of each finger (Finger)

Is assumed to be white noise, and the value is assumed to be the same for each finger.

Is not taken into account when calculating.

는 백색 잡음이 아니고, 각 핑거마다 다른 값을 가질 확률일 높다. 따라서, 정확한 신호의 합성을 위해서는 상기 잡음이 고려된 채널 추정을 하여야 한다.But remind

Is not white noise and is likely to have a different value for each finger. Therefore, in order to synthesize the correct signal, the channel estimation considering the noise should be performed.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide an apparatus and method for estimating the noise of a received signal and removing the estimated noise for effective channel estimation. will be.

In order to achieve the above object, the present invention provides a noise estimator for estimating noise of a received signal located on each path of a received signal, a filter for calculating an average of the estimated noise, the obtained average noise and a received signal. Provided is a channel estimator for a digital receiver including a channel estimator for receiving a channel classified from a signal and estimating a channel.

The noise estimator is characterized by estimating noise by a despreading technique using a Walsh code.

The Walsh code is preferably 128 in length.

According to an aspect of the present invention, there is provided a digital reception method, comprising: dividing a channel in each path of a received signal having multiple paths, estimating noise in each path of the received signal, obtaining an average of the estimated noise, and And receiving a channel separated from the obtained average noise, and estimating a channel.

The channel estimating may include removing the average noise from the divided channels.

Therefore, according to the present invention, the noise is extracted from the original signal through the despreading technique, and thus the original signal is accurately recovered from the distorted signal.

Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention that can specifically realize the above object will be described.

In addition, the terminology used in the present invention was selected as a general term widely used as possible now, but in some cases, the term is arbitrarily selected by the applicant, in which case the meaning is described in detail in the corresponding description of the invention, The present invention is to be understood as the meaning of terms rather than names.

2 is a block diagram illustrating a configuration of a channel estimating apparatus including a noise estimator according to the present invention.

As shown in FIG. 2, a channel estimating apparatus according to the present invention includes a noise estimator 100 (1),..., 100 (n) located on each path of a received signal and estimates noise of the received signal. Infinite Impulse Response (IIR) filters (200 (1), ..., 200 (n)) for calculating the average of the estimated noise, and a channel estimator that receives the obtained average noise value and removes it from the received signal to estimate an accurate channel. (300 (1), ..., 300 (n)).

Referring to the channel estimation method of the channel estimating apparatus configured as described above, first, the Walsh despreader uses the Walsh code to distinguish the channels of the satellite DMB. Do this.

The Walsh despreader is present in each path of the received signal, that is, in each finger to distinguish the channel of the received signal. The Walsh code is an orthogonal code, and in the case of different codes, since the cross correlation value is '0', a desired code, that is, a channel can be extracted.

The Walsh code can be extended from the code of length 2 by the method shown in FIG. 3, and in the case of satellite DMB, the Walsh code having a length of 64 is used.

That is, FIG. 3 is a diagram illustrating a Walsh code extension method, and as shown in FIG. 3, the code may be sequentially expanded from a code of 2 to a code of 4 and a code of 8. In this case, a method similar to the following Equation 7 is used.

Therefore, the Walsh code having a length of 64 among the codes extended by the above method is used in the satellite DMB to distinguish the channels, and the total 64 channels can be distinguished.

Meanwhile, the noise estimators 100 (1), ..., 100 (n) according to the present invention, which exist in each path of the received signal, estimate noise from the received signal. In this case, the noise estimators 100 (1), ..., 100 (n) use Walsh codes to estimate noise included in the received signal.

The noise estimators 100 (1), ..., 100 (n) use Walsh codes of length 128. This is because when the Walsh code having a length of 64 is used, the channel component is always extracted regardless of 64 codes, and thus only the desired noise component cannot be extracted.

The Walsh code having a length of 128 is illustrated in the accompanying FIG. 4, and as shown in FIG. 4, the Walsh code having a length of 128 may be extended by one more extension.

From the Walsh codes of length 128, 0 to 63 codes can be obtained through Walsh despreading, and since the remaining Walsh 64 to Walsh 127 are orthogonal to the 64 code words, they are correlated. The value is '0'.

를 구할 수 있다.In this case, the first 64 Walsh and the next 64 Walsh of the Walsh 64 to Walsh 127 of Walsh having a length of 128 may be the same size and have the same sign. Since they have opposite values, they cancel each other out to find the noise component n _k . Is a variance value from the noise component n _k

Can be obtained.

As described above, when the noise estimator 100 (1),..., 100 (n) uses a Walsh code having a length of 128, an instantaneous noise is obtained through despreading with one code of Walsh 64 to Walsh 127. Tooth noise is input to an IIR filter (200 (1), ..., 200 (n)) to find the average noise in the filter.

The n average noises obtained by the IIR filters 200 (1), ..., 200 (n) are input to the channel estimators 300 (1), ..., 300 (n), respectively.

The channel estimators 300 (1), ..., and 300 (n) respectively receive the signal despread from the Walsh despreader and the average noise, and estimate an accurate channel by subtracting the average noise from the despread signal. Done.

Channels estimated by the respective channel estimators 300 (1), ..., 300 (n) are synthesized by a combiner to recover the original signal.

On the other hand, Figure 5 is a block diagram showing the overall configuration of the satellite DMB to which the technical idea according to the present invention is applied.

As shown in FIG. 5, a received signal input through an antenna is converted into a baseband signal through a tuner 1, and the converted signal is an automatic gain controller (AGC) 3. Its size remains constant. The signal having a relatively constant magnitude through the automatic gain control unit 3 is converted into a digital signal by an analog-to-digital converter (A / D) 5.

In the CDM transmission method, in order to demodulate a signal, the acquisition of a pseudo-noise sequence (PN) used for signal spreading should be prioritized. This process involves two steps of signal acquisition and tracking. Is made of.

Acquisition of the signal is a process of securing signal synchronization within ± 1/2 chips at the receiver, and is performed by a searcher 7. In this case, the chip refers to a division unit of a pseudo noise sequence.

The tracking of the signal refers to fine tuning of the captured signal and is performed in the trackers 9 (1), ..., 9 (n).

The synchronized signal is despread by multiplying the pseudonoise sequence generated by the receiver in the PN despreading and Walsh despreading units 15 (1), ..., 15 (n), and the Walsh code used to distinguish the CDM channels. Extract the desired CDM channel by multiplying by.

On the other hand, the synchronized signal is input to the noise estimators 11 (1), ..., 11 (n) according to the present invention and has a length of 128 in the noise estimators 11 (1), ..., 11 (n). The Walsh code is used to estimate the noise. The estimated noise is averaged in the IIR filters 13 (1), ..., 13 (n).

The process is performed in all the multiple paths found by searcher 7, each of which is called a finger. The finger has been described above.

The extracted channel and the average noise are input to channel estimators 17 (1), ..., 17 (n), respectively, to estimate and output an accurate channel by removing the average noise from the extracted channel.

Meanwhile, the frequency offset estimator 19 estimates the frequency offset for each finger, synthesizes the frequency offset, and feeds back the tuner 1 to correct the frequency offset.

The channels estimated by the respective channel estimators 17 (1), ..., 17 (n) whose frequency offsets are corrected are input to the RAKE synthesizer 21 and synthesized. The RAKE synthesis is performed on all CDM channels to be demodulated. In particular, the pilot channel, which is a control channel, contains information on interleaved size and convolutional coding rate and must be demodulated.

Thereafter, timing is extracted from the frame and super frame timing extracting circuit 23 using the pilot channel, and Viterbi decoding, deinterleaving, RS decoding, and the like are performed in the corresponding blocks 25, 27, and 29, respectively. Through the decoded signal, the data mode detector 31 obtains information on the interleave size and the convolutional coding rate and uses the decoded data channel.

On the other hand, the data channel is displayed on the screen by A / V decoding through a process such as time deinterleaving, Viterbi decoding, byte deinterleaving, RS decoding, etc. through the information obtained from the pilot signal.

The present invention is not limited to the above-described embodiments, and can be modified by those skilled in the art as can be seen from the appended claims, and such modifications are within the scope of the present invention. .

The channel estimation apparatus and method according to the present invention described above has the effect of accurately reconstructing the original signal from the distorted signal by extracting and removing noise from the original signal through a despreading technique.

Claims (9)

In a digital receiver, With multiple paths A noise estimator positioned on each path of a received signal to estimate path-specific noise of the signal; A filter for calculating an average of the estimated noise for each path; And A channel estimator for estimating a channel associated with the received signal using the average of the noise and a signal despread the received signal, And the noise estimator, the filter, and the channel estimator are included in each of a plurality of fingers included in the digital receiver. The method of claim 1, And the noise estimator estimates the noise for each path of the signal by a despreading technique using a Walsh code. The method of claim 2, And the Walsh code has a length of 128. The method of claim 1, And a signal obtained by despreading the received signal is a signal obtained by despreading the received signal using a Walsh code. delete In the digital receiving method, Dividing a received signal having multiple paths for each path; Estimating noise for each path of the received signal; Obtaining an average of the estimated noise; And Estimating a channel associated with the received signal using the average of the noise and a signal despread the received signal Channel estimation method of the digital receiver comprising a. The method of claim 6, And estimating the noise using a despreading technique using a Walsh code. The method of claim 7, wherein And the Walsh code has a length of 128. The method of claim 6, And estimating the channel comprises estimating a channel associated with the received signal by removing the average noise from the despread signal of the received signal.

Images