KR100364758B1 - Apparatus and method channel estimation in communication system - Google Patents

Abstract

The present invention relates to channel estimation of a communication system, and more particularly, to an apparatus and method for channel estimation of a communication system capable of accurate demodulation when a pilot signal and a forward power control bit are transmitted to a pilot channel used for channel estimation. The channel estimation apparatus of such a communication system detects a signal transmitted through a target channel by correlating with a Walsh code of a pilot channel and a pilot channel correlator to detect a transmitted signal. Adding and outputting first and second filter units for performing channel estimation using a target channel correlator, additional information bits, and output signals of the pilot channel correlator, and output signals of the second filter unit and the first filter unit. A plurality of fingers comprising an adder, a power control demodulator for demodulating the output signal of the pilot channel correlator and the output signal of the second filter unit, and a traffic channel demodulator for demodulating the output signal of the adder and the output signal of the target channel correlator, Combining the output of each power control demodulator of the finger to output the additional information bits (PCB) 1 Tu combiner, combines the output of each traffic channel of said plurality of demodulator fingers and consist of a second combiner for transmitting to the decoder.

Description

Apparatus and method channel estimation in communication system

The present invention relates to channel estimation of a communication system, and more particularly, to an apparatus and method for channel estimation of a communication system capable of accurate demodulation when a pilot signal and a forward power control bit are transmitted to a pilot channel used for channel estimation. .

In general, in a CDMA scheme, in a forward link in which a base station communicates with a mobile station, the base station can transmit the same signal through one pilot channel, and thus each mobile station can obtain information about the channel using the same signal. Using this information, the forward link detects a signal using a synchronous method.

On the other hand, in the reverse link communicating from the mobile station to the base station, the pilot channel is not used because the power consumption is large when using the pilot channel. As such, since pilot information of the pilot channel is not available, it is difficult and complicated to find out the channel information. Therefore, the reverse link uses an asynchronous method that detects a signal without information about a channel.

The asynchronous reception method has the advantage of being simple, but has the disadvantage of poor performance. In addition, in the current cellular mobile communication system, the radius of the cell is gradually decreasing, and the burden on the output signal size required by the mobile station is also reduced. Accordingly, many cellular systems currently under development tend to use pilot channels on the reverse link, and signal detection tends to use a synchronous method using pilot signals.

Recently, a proposal has been made that in a CDMA cellular mobile communication system, not only a pilot signal but also additional side information bits may be added on a pilot channel of a reverse link. Accordingly, a more accurate channel estimation apparatus and method are required.

Hereinafter, an apparatus and method for estimating a channel of a conventional communication system will be described with reference to the accompanying drawings.

FIG. 1 is a block diagram showing a CDMA channel estimating apparatus according to the prior art, and FIG. 2 is a diagram showing an internal structure of the FIR filter shown in FIG.

1 shows a patent registered with the U.S. Patent Office as 5,737,327 (April 7, 1998). The conventional CDMA channel estimating apparatus 20 is made in consideration of the case where only a pilot signal exists in a pilot channel. The filter circuit unit 10, the despreader 21, the pilot channel correlator 22, the first filter unit 24 which is an anti-Causal filter, and the second filter unit 25 that is a common filter ), Adder 30, first and second conjugates 29 and 31, target channel correlator 23, first and second delay units 26 and 27 as delay elements, power control demodulator 32 And a traffic channel demodulator 33 and combiner 40.

Here, the first and second filter units 24 and 25 are each composed of finite impulse response filters (hereinafter, abbreviated as FIR filters).

In the conventional channel estimator, the pilot signal is correlated to the pilot signal using the FIR filter of the second filter unit 25 and the FIR filter of the first filter unit 24. Phase shift and attenuation components generated by the E-Stimulation are estimated and applied to a target channel, that is, a corresponding traffic channel.

In this method, since the channel estimation is not accurate when the channel observation interval for channel estimation is small, the observation interval for channel estimation is increased by using an FIR filter. For the data portion of the target channel, the second filter unit 25 More accurate channel estimation is possible by adding an FIR filter for the common portion.

As shown in the figure, when the FIR filter is used in the second filter unit 25, the delay for the data path must be delayed. Therefore, the anti-coal of the first filter unit 24 is applied to the additional information bit (PCB). Only using the FIR filter results for the potion can be applied quickly without delay.

FIG. 3 is a diagram illustrating some configurations of a transmitter and a frame configuration of a pilot for general CDMA channel estimation. In particular, FIG. 3 illustrates a configuration of a pilot channel of a reverse link of a CDMA-2000 system. The first three quarters send a pilot signal, while the other quarter multiplexes the power bits for the forward power bits.

For the CDMA channel estimating apparatus, the transmitting side separately transmits pilot bits and other additional information bits (PCBs) other than the pilot bits to four PN chips per frame through a pilot channel. Here, the additional information bits are within a number (1 to 2 bits) bits, and contain more specific information on the CDMA channel such as general call data bits or power control bits.

The pilot bits and additional information bits necessary for CDMA channel estimation are multiplexed and transmitted through the multiplexer 42. The pilot bits usually have a sign of '+1', and the additional information bits are pilot channels to increase reliability. The same bit is repeated multiple times for each frame through multiplexing.

The channel estimating apparatus and method of the conventional communication system are made in consideration of the case in which only a pilot signal exists in a pilot channel. Therefore, when the pilot signal and the forward power control bit exist in the pilot channel, the performance of the channel estimator may be degraded. Can be. In other words, since the receiver knows what information is loaded on the pilot channel, it is correlated with the pilot code and used as the channel information. However, when a pilot channel contains a signal other than a pilot, the receiver does not know what information the information has, and there is a problem in that performance is degraded when the existing channel estimator is used as it is.

An object of the present invention has been devised in view of the above-mentioned problems of the prior art, and a channel estimation apparatus of a communication system capable of accurate demodulation when a pilot signal and a forward power control bit are transmitted to a pilot channel used for channel estimation. It is to provide a method.

According to an aspect of the present invention for achieving the above object, a pilot channel correlator that detects a transmitted signal by correlating with a Walsh code of a pilot channel, and correlates with a Walsh code of a corresponding target channel to target a target channel. A target channel correlator for detecting a signal transmitted through the first channel filter, a first and second filter unit for performing channel estimation using the additional information bits and the output signal of the pilot channel correlator, and the second filter unit and the first filter unit An adder for adding and outputting an output signal, a power control demodulator for demodulating the output signal of the pilot channel correlator and the output signal of the second filter unit, and a traffic channel demodulator for demodulating the output signal of the adder and the output signal of the target channel correlator And the additional information by combining the output of the power control demodulator of each of the plurality of fingers (Finger) Bit (PCB) a first combiner for outputting a Tu, to combine an output of each traffic channel of said plurality of demodulator fingers is comprised of a second combiner for transmitting to the decoder.

According to another aspect of the present invention for achieving the above object, receiving a radio frequency signal and despreading with a pseudo noise (PN) code to output a transmission signal, despreading the transmission signal with a Walsh code Detecting an additional information bit and a pilot channel signal, despreading the transmission signal with a Walsh code, detecting a signal of a target channel, and filtering the detected pilot channel signal and the additional information bit for channel estimation And demodulating the signal of the target channel by using the result of filtering the pilot channel signal and the additional information bits.

1 is a block diagram showing a CDMA channel estimation apparatus according to the prior art

FIG. 2 is a diagram showing an internal structure of the FIR filter shown in FIG.

3 is a diagram illustrating some components of a transmitter and a frame structure of a pilot for general CDMA channel estimation;

4 is a block diagram illustrating a CDMA channel estimating apparatus according to a first embodiment of the present invention.

5 is a view showing the internal structure of the FIR filter according to the present invention

6 is a block diagram illustrating a CDMA channel estimating apparatus according to a second embodiment of the present invention.

7A to 7D are diagrams for explaining the determination of the provisional determination value in the CDMA channel estimation method of the present invention.

* Description of the symbols for the main parts of the drawings *

50: filter circuit 51: despreader

52: pilot channel correlator 53: target channel correlator

54, 55: filter section 56, 58, 63: delay section

57, 60: conjugate 59: adder

61: power control demodulator 62: summer

64: traffic channel demodulator 65: finger portion

66,68: Combiner 67: Decision unit

Hereinafter, a configuration and an operation according to an exemplary embodiment of the present invention will be described with reference to the accompanying drawings.

4 is a block diagram illustrating a CDMA channel estimating apparatus according to a first embodiment of the present invention, FIG. 5 is a diagram illustrating an internal structure of an FIR filter according to the present invention, and FIGS. 7A to 7D illustrate the present invention. It is a figure for demonstrating provisional determination value determination in a method.

The CDMA channel estimating apparatus according to the first embodiment of the present invention includes a filter circuit unit 50 for converting a radio frequency (RF) signal received from an antenna into a baseband signal, and a baseband signal of the filter circuit unit 50. The first finger portion 65a of the plurality of finger portions 65a, 65b ... 65k that demodulates is described as an example, and the baseband signal converted by the filter circuit portion 50 is illustrated by a local oscillator (not shown). A despreader 51 despreading the PN code generated through the PN code, and a pilot channel correlator 52 correlating the despread signal with the Walsh code of the pilot channel to detect the transmitted signal. And a target channel correlator 53 which receives the despread signal and takes a correlation with the Walsh code of the target channel to detect a signal transmitted through the target channel, and an output of the pilot channel correlator 52. Pilot symbol that is a signal First and second filter units 54 and 55 for performing channel estimation through respective FIR filters, and a first conjugate for conjugating the output signal of the second filter unit 55. 57, a third delay unit 58 for outputting the output signal of the second filter unit 55 after a delay for a predetermined time, an output signal of the third delay unit 58, and a first filter unit ( An adder 59 for adding and outputting the output signal of 54, a second conjugate 58 for conjugating the output signal of the adder 59, and an output signal of the pilot channel correlator 52; The first delay unit 56 for outputting after a delay for a set time, the power control demodulator 61 for demodulating the output signal of the first delay unit 56, and the output signal of the first conjugate (57); A summator 62 for summing output signals of the power control demodulator 61, and a first combiner 66 for combining the outputs of the summator 62; And a second delay unit for determining an additional information bit (PCB) according to an output value of the first combiner 66 and a second delay outputting the output value of the target channel correlator 53 after a predetermined time delay. A traffic channel demodulator 64 for demodulating the output signal of the second delay unit 63 and the second conjugate 60, and a second combiner that combines the outputs of the traffic channel demodulator. It consists of 68.

In the channel estimation apparatus of the present invention, the received radio frequency signal is converted into a baseband signal through the filter circuit unit 50, and the converted signal is pseudo noise generated through a local oscillator (not shown). ) Despreading with code

Then, the pilot channel correlator 52 receives the despread signal, that is, the output signal, takes a correlation with the Walsh code of the pilot channel, and transmits it through the pilot channel, that is, the additional information bit (PCB) and the pilot channel signal. Detect (pilot symbol)

The target channel correlator 53 receives the despread signal and performs correlation with the Walsh code of the target channel to detect a signal transmitted through the target channel. At this time, the additional information bit (PCB) and the pilot channel signal (pilot symbol) include phase shift and attenuation components caused by various channel environments. In order to remove such components, channel estimation is performed on the pilot symbols that are the outputs of the pilot channel correlator 52 through two FIR filters. That is, the filtering is performed. Here, the first filter unit 54 performs FIR filtering with a signal component of an anti-common portion without delay compared to a symbol of a delayed target channel, whereas the second filter is performed. The unit 55 performs FIR filtering with the signal component of the common portion by using the same delay as the symbol of the delayed target channel.

Here, the outputs of the two FIR filters (the first and second filter parts 54 and 55) are added by the adder 59, and then sent to the second conjugate 60, and the second conjugate 60 produces a complex conjugate. By taking a complex multiplex with the signal of the target channel, the above-mentioned phase shift and attenuation components can be effectively removed.

In this case, the additional information bit (PCB) received through the pilot channel is estimated by using only the output of the FIR filter of the second filter unit 55 using the common portion. The reason for the channel estimation using only the common potion is that determining the additional information bits without delay can increase the power control effect, thereby improving the performance of the entire system.

And the additional information bits (PCB) received from the respective finger portions 65a, 65b ... 65k are determined via the first combiner 66. The determined additional information bit (PCB) is used to up / down the transmit power of the transmitting end, and is also used as information of the coefficient of the FIR in this patent. One example thereof is described in FIG.

The CDMA channel estimating apparatus according to the first embodiment of the present invention is similar to the conventional configuration, but has a different portion from which the additional information bits (PCB) are input. Referring to FIG. 5 showing the FIR configuration, the output values of the plurality of delay elements Z ⁻¹ are equal to a (a1, a2, There is an adder part that multiplies the values of an) and sums the result of the multiplier.

That is, in general, when data other than the pilot signal is added to the pilot channel, the data is added to a predetermined area so that the receiver can know whether the data to be processed is a pilot signal or other information signal.

However, it is impossible to know what information is sent like a pilot signal. In other words, it is possible to distinguish whether the data transmitted now is a pilot signal or not, but if the information is not a pilot signal, it is not known whether the information of 1 or 0 is sent.

If the information of 1 is sent, the process is the same as that of the pilot signal. If the information of 0 is sent, the sign is reversed. Therefore, the FIR filters (first and second filter units 54 and 55) need to reverse the processing. do. Therefore, when a signal other than a pilot signal is input, the sign must first be determined and informed by the FIR filters (first and second filter units 54 and 55) to estimate the correct channel.

Thus, in the present invention, after combining the information of the additional information bits (PCB) from the finger portions 65a, 65b ... 65k, the determined result is applied to a (k). That is, the value of a (k) is applied to the drawings shown in Figs. 7A to 7D.

That is, FIG. 7A illustrates a case where the PCB enters into the FIR filter for the first time. In this case, FIR filtering is performed by taking a (k) as zero for the first additional information bit (PCB) area to be introduced, so that the decision on the additional information bit (PCB) has not yet been completed. The additional information bit (PCB) area is not applied to the FIR filter.

However, since the decision on the value of the additional information bit (PCB) has already been made for the additional information bit (PCB) existing in the previous power control group (PCG), the result of the determination is a (k). ) To drive the FIR filter and apply a value of a (k) = 1 to the pilot signal region.

In FIG. 7B, as in FIG. 7A, all the additional information bits (PCB) have not been introduced to the receiver, and thus the additional information bit (PCB) decision has not been completed. Corresponding a (k) vector value Is shown in Figure 7b.

In FIG. 7C and FIG. 7D, all additional information bits (PCBs) have already been introduced and a decision thereof has been completed. Therefore, the result of the additional information bit (PCB) decision is applied to a (k).

As a result, in the section in which the additional information bits PCB are input in FIG. 4, the channel state is determined through signals introduced into two filters (the first and second filter units 54 and 55) with respect to the additional information bits PCB. The estimation compensates for the phase shift and the attenuation components of the target channel.

After all, when the length of the filter is n, the FIR filter is driven only for (n- (number of taps into which the PCB is introduced + 1)), and all of the additional information bits (PCB) for the PCG interval are FIR filters. After the decision is made, the decision of the additional information bit (PCB) is completed, and the result of the decision of the additional information bit (PCB) is applied to the weighting value of the corresponding part, and the FIR filter is again applied to the entire section. Drive for (span).

In addition, for the additional information bit (PCB), the FIR filter is driven only for (n-(number of taps into which the PCB is introduced) + 1) for one filter to compensate for phase shift and attenuation components.

In order to increase the accuracy of the estimation of the channel, it is possible to estimate the correct value by observing the interval of the observed channel to both sides of the current value to be estimated. In order to make the observation section of the channel both sides, it is necessary to observe not only the first data but also the data coming later. To this end, the data entering the current target channel must be stored in the memory (second delay unit 63) and delayed.

In other words, if the half-delay of the channel change observation section is processed, the estimated channel value is obtained by observing and processing both channel changes at the time of channel estimation, so that the channel estimation value is accurate and data demodulation can be performed accordingly. . However, because data delay requires memory, the cost can be increased and problems can occur when processing in real time. Therefore, the delay length can be changed from 0 to the channel observation interval based on performance, cost, or service. Can be.

6 illustrates the use of two FIR filters (first and second filter parts 54 and 55) of FIG. 5 using one FIR filter (first filter part 74) and a common portion. In order to achieve this, the delay unit is implemented. The FIR filter internal structure is the same as in FIG.

In the channel estimation of the communication system according to the present invention as described above, when a signal other than the pilot signal is added to the pilot channel, the channel is estimated using not only the pilot signal but also all other signals, thereby obtaining accurate channel estimation. This can improve the quality of the receiver.

Claims (5)

A pilot channel correlator for detecting a transmitted signal by correlating with a Walsh code of a pilot channel, a target channel correlator for detecting a signal transmitted through a target channel by correlating with a Walsh code of a corresponding target channel, and adding A first and second filter unit for performing channel estimation using an information bit and an output signal of the pilot channel correlator, an adder for adding and outputting output signals of the second filter unit and the first filter unit; A finger comprising a power control demodulator for demodulating the output signal of the pilot channel correlator and the output signal of the second filter unit, and a traffic channel demodulator for demodulating the output signal of the adder and the output signal of the target channel correlator; A first combiner for outputting the additional information bits (PCB) by combining the outputs of the respective power control demodulators of the plurality of fingers; And a second combiner for combining the outputs of the respective traffic channel demodulators of the plurality of fingers and transmitting them to a decoder. 2. The apparatus of claim 1, wherein a first delay unit is arranged between the pilot channel correlator and the power control demodulator to delay and output an output signal of the pilot channel correlator for a predetermined time period, and between the target channel correlator and the traffic channel demodulator. And a second delay unit configured to delay the output signal of the target channel correlator for a predetermined time period and output the delayed signal, and between the second filter unit and the adder, delay the output signal of the second filter unit for a predetermined time and output the delayed signal. A third delay unit, and a first conjugate configured to output an output signal after conjugating the output signal of the second filter unit between the second filter unit and the power control demodulator, and the power control demodulator and the first combination Between the you are configured a summer for summing the output signal of the power control demodulator, And a second conjugate configured to conjugate an output signal of the adder between an adder and the traffic channel demodulator. Receiving a radio frequency signal and despreading with a pseudo noise (PN) code to output a transmission signal; Despreading the transmission signal with a Walsh code to detect an additional information bit and a pilot channel signal; Despreading the transmission signal with a Walsh code to detect a signal of a target channel; Filtering the detected pilot channel signal and side information bits for channel estimation; And demodulating the signal of the target channel by using the filtering result of the pilot channel signal and the additional information bits. 4. The method of claim 3, wherein the filtering comprises: a first step of performing filtering with a signal component of an anti-coal portion in a pilot symbol of a target channel; A second step of performing filtering with the signal components of the common portion using the same delay as the pilot symbol of the delayed target channel; And performing a composite conjugate by adding the filtered outputs in the first and second steps. In the receiver of a mobile communication system, A channel estimation method in a communication system, characterized in that channel estimation is performed by filtering a pilot signal and an additional information bit (PCB) received through a pilot channel.