KR20000001049A - Apparatus and method to estimate channel within c.d.m.a. cellular mobile telecommunication system - Google Patents

Abstract

PURPOSE: An apparatus and a method are provided to accurately estimate a channel which is continuously varied within CDMA cellular mobile telecommunication system. CONSTITUTION: The apparatus comprises pilot code correlators(110, 210, 310), code determiners(120, 220, 320) and impulse response filters(130, 230, 330). The pilot code correlators(110, 210, 310) perform correlation between a pilot bit and added information bit by a pilot pseudo noise code, and acquire a correlation value. The code determiners(120, 220, 320) determine a sign according to the correlation value of added information bit. The impulse response filters(130, 230, 330) estimate a CDMA channel according to the sign of the correlation value of added information bit.

Description

Channel Estimation Apparatus and Method in CDM Cellular Mobile Communication System

The present invention relates to a channel estimating apparatus and method for a CDMA cellular mobile communication system. In particular, in a cellular mobile communication system using the CDMA scheme, the present invention continues by transmitting a pilot bit and an additional information bit other than the pilot bit in each frame on a pilot channel. A channel estimating apparatus and method for a CDMA cellular mobile communication system for estimating a changing CDMA channel more accurately.

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 coherent 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 a noncoherent method of detecting 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 coherent methods using pilot signals.

Recently, a proposal has been made that in a CDMA cellular mobile communication system, a pilot signal as well as another side information bit may be added on a pilot channel of a reverse link. Accordingly, a more accurate channel estimation apparatus and method are required.

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

Referring to FIG. 1, a received signal through a multipath input to a conventional CDMA channel estimating apparatus is delayed and outputted by a predetermined time through delay units 10, 20, and 30, respectively.

The pilot signals transmitted through the pilot channel among the received signals delayed by a predetermined time are correlated by using the pilot PN codes in the pilot code correlators 11, 21, and 31.

The correlation values calculated by taking the correlation in the pilot code correlators 11, 21, and 31 are used as the CDMA channel estimates.

Finite impulse response filter (FIR filter) (12, 22, 32) for accurate CDMA channel estimation increases the CDMA channel interval to be estimated, that is, pilot code correlator (11, 21). And increase the correlation interval of (31).

In addition, the FIR filters 12, 22, and 32 delay and accumulate the correlation values output from the pilot code correlators 11, 21, and 31, and use the average values accordingly to estimate the CDMA channel.

The traffic code correlators 13, 23, and 33 correlate the traffic signal received through the traffic channel among the received signals delayed by a predetermined time with the traffic PN code. At this time, the correlation values calculated from the traffic code correlators 13, 23, 33 are combined with the output values of the FIR filters 12, 22, 32 through the multipliers 14, 24, 34.

The combined values of the respective multipliers 14, 24 and 34 are summed in the adder 40.

The pilot signal through the pilot channel mentioned above is a bit string sent by multiplying a pilot PN code by a signal that is already known by the same bit string that is periodically repeated or by the receiver.

As described above, the CDMA channel estimating apparatus according to the prior art is designed considering only the case in which only a pilot signal exists on the pilot channel. Therefore, when additional information bits other than the pilot bit are added and transmitted on the pilot channel, the channel is estimated. There is a problem that the performance of the estimation apparatus may be degraded.

That is, if more specific additional information about a CDMA channel such as general call data bits or power control bits is transmitted along with the pilot bits on the pilot channel, the conventional CDMA channel estimator can only know the received pilot bits. In other words, it is difficult to estimate the correct CDMA channel because the additional information bits other than the pilot bits are unknown.

Disclosure of Invention The present invention has been made to solve such a problem, and provides an apparatus and method for CDMA channel estimation modified and adapted to be suitable for a case where additional information bits other than pilot bits exist on a pilot channel. have.

A feature of the channel estimating apparatus of the CDMA cellular mobile communication system according to the present invention for achieving the above object is that by using both the pilot bits present in each frame on any pilot channel and another additional information bits other than the pilot bits In estimating the CDMA channel, a pilot code correlator for correlating the pilot bits transmitted to the pilot channel with the additional information bits and calculating a correlation value according thereto, and the additional information bits calculated by the pilot code correlator A code determining unit for determining a sign of a correlation value for a finite element, and a finite shock response filter for using the correlation value for additional information bits to estimate a CDMA channel according to the code determined by the code determining unit. It is composed.

Preferably, the pilot code correlation unit correlates a pilot bit and an additional information bit by using a pilot pseudo noise code, and the code determining unit is further configured to repeat the additional information bit for an arbitrary period. The cumulative correlation value for is used.

A feature of the channel estimation method of the CDMA cellular mobile communication system according to the present invention for achieving the above object is that by using both the pilot bit present in each frame on any pilot channel and another additional information bit other than the pilot bit In estimating the CDMA channel, calculating a correlation value for the pilot bit and the additional information bits, estimating the channel from the correlation value for the pilot bits, and extracting the channel from the correlation value for the additional information bits. Estimating.

Preferably, the step of estimating the channel from the correlation value for the information bits, the sum of the correlation value for the additional information bits accumulated to any point in the past and the correlation value for the additional information bits transmitted on the current pilot channel And determining a sign according to the summed correlation value, wherein the correlation value for the additional information bits accumulated up to a certain point in the past and the correlation value for the additional information bits transmitted in the current pilot channel are determined. In the summing step, the correlation value for the additional information bits accumulated up to a certain point in the past and the correlation value for the additional information bits transmitted in the current pilot channel are correlated for the same additional information bits.

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

2 is a block diagram showing the configuration of a CDMA channel estimating apparatus according to the present invention;

3 is a flowchart showing a code determination method according to CDMA channel estimation according to the present invention;

4 is a diagram illustrating some components of a transmitting side and a frame configuration on a pilot channel for CDMA channel estimation according to the present invention.

Explanation of symbols for main parts of the drawings

100,200,300: delay unit 110,210,310: pilot code correlator

120,220,320: code determination unit 130,230,330: finite shock response filter

140,240,340: Traffic Code Correlator

150,250,350: time delay

400: sum

Hereinafter, a preferred embodiment of an apparatus and method for estimating a CDMA channel according to the present invention will be described with reference to the accompanying drawings.

2 is a block diagram showing the configuration of the CDMA channel estimation apparatus according to the present invention.

Referring to FIG. 2, the received signal through the multipath input to the CDMA channel estimating apparatus according to the present invention is delayed and output by a predetermined time through the delay units 100, 200, and 300, respectively.

The pilot bits and the additional information bits transmitted through the pilot channel among the received signals delayed by a predetermined time are correlated by using the pilot PN codes in the pilot code correlators 110, 210, and 310.

Here, the pilot bits and the additional information bits are transmitted through the pilot channel.

The pilot code correlators 110, 210, and 310 set a time offset in units of PN chips to take a correlation, and the resulting correlation value is used as a CDMA channel estimation value.

At this time, the correlation value for the pilot bit which already knows the sign at the receiving side is used as the CDMA channel estimation value as it is in the conventional CDMA channel estimating apparatus, and the correlation value for the additional information bit unknown at the receiving side. Sign Decision process for.

Other data sign decision (120,220,320) determines whether the pilot code correlator (110,210,310) has a sign of '0' or '1' for the correlation value for the additional information bits output by the FIR The filter 130, 230, 330 will be notified.

If the code determiner 120, 220, or 320 determines that the sign of the correlation value of the additional information bit is '1', the FIR filters 130, 230, and 330 process the same as the pilot bit and apply the correlation value of the additional information bit. If it is determined that the sign (sign) is '0', the FIR filters 130, 230, and 330 reverse the sign and process the same.

In addition, the FIR filters 130, 230, and 330 for accurate CDMA channel estimation increase the CDMA channel interval to be estimated as in the prior art. That is, the correlation intervals of the pilot code correlators 110, 210, and 310 are increased.

The FIR filters 130, 230, and 330 delay and accumulate the correlation values output from the pilot code correlators 110, 210, and 310, and use the average values according to the channel values.

The traffic code correlators 140, 240, and 340 correlate the traffic signal received through the traffic channel among the received signals delayed by a predetermined time with the traffic PN code and output a correlation value accordingly. In this case, the correlation values calculated from the traffic code correlators 140, 240, and 340 are combined with the output values of the FIR filters 130, 230, and 330 through the multipliers 160, 260, and 360 through the time delay units 150, 250, and 350 for accurate compensation.

The combined values of the respective multipliers 160, 260, and 360 are summed in the adder 400.

The above-mentioned pilot bit through the pilot channel is a bit string transmitted by multiplying a pilot PN code by the same bit string that is periodically repeated or a signal already known by the receiving side, and the receiving side transmits additional information bits through the pilot channel. Although it is known that the additional information bit is not known, a sign decision on a correlation value is required.

Also, for accurate CDMA channel estimation, not only the current data coming into the traffic channel but also the data coming later are stored in a random memory and used for channel estimation. Since the CDMA channel estimation is not only accurate, but also the data detection on the traffic channel can be accurately performed.

3 is a flowchart illustrating a code determination method for CDMA channel estimation according to the present invention.

Referring to FIG. 3, additional information bits transmitted together with pilot bits on a pilot channel are generally transmitted several times for reliable CDMA channel estimation.

When a correlation value for repeated additional information bits is first inputted, the code determiner described in FIG. 2 determines a sign only by the current correlation value inputted.

However, after that, the code can be determined more accurately by using the past correlation value for the repeated additional information bits without using the current correlation value for the repeated additional information bits.

In other words, the past correlation value for the additional information bits is continuously accumulated, and the previously accumulated correlation value and the current correlation value are summed (S2), and it is determined whether the summed correlation value exceeds '0' (S3). ).

According to the determined result, if the summed correlation value exceeds '0', the sign determiner informs the FIR filter of '+1' sign (S4), and if the summed correlation value is less than '0', the sign judge The determiner informs the FIR filter of the '-1' sign (S5).

Here, the accumulated correlation value for the additional information bits is accumulated only the number of times repeatedly transmitted for one additional information from the transmitting side, and when new additional information is transmitted, the process returns to the initial code determination process.

4 is a diagram illustrating some configurations of a transmitting side and a frame configuration on a pilot channel for CDMA channel estimation according to the present invention.

For the CDMA channel estimating apparatus, the transmitting side transmits the pilot bits and other additional information bits other than the pilot bits, usually separated into four PN chips per frame through the 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 500. 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.

As described above, in addition to the pilot bits and the additional information bits, more accurate CDMA channel estimation is possible in case the additional information bits other than the pilot bits exist on the pilot channel. Through this, the call quality of the CDMA cellular mobile communication system is improved.

Claims (6)

In estimating a CDMA channel using both the pilot bits present in each frame on any pilot channel and another additional information bit other than the pilot bits, A pilot code correlator for correlating the pilot bits transmitted to the pilot channel with the additional information bits and calculating a correlation value accordingly; A sign determining unit for determining a sign of a correlation value for the additional information bit calculated by the pilot code correlation unit; And a finite shock response filter for using the correlation value for the additional information bits to estimate the CDMA channel according to the code determined by the code determination unit. . 2. The apparatus of claim 1, wherein the pilot code correlator takes a correlation between the pilot bit and the additional information bit using a pilot pseudo noise code. . 2. The apparatus of claim 1, wherein the code determining unit uses the accumulated correlation value for the additional information bits repeated for a certain period of time. In estimating a CDMA channel using both the pilot bits present in each frame on any pilot channel and another additional information bit other than the pilot bits, Calculating a correlation value for the pilot bit and the additional information bit; Estimating a channel from the correlation value for the pilot bit; Estimating a channel from the correlation value for the additional information bits. The method of claim 4, wherein estimating a channel from a correlation value for the additional information bits includes: Summing a correlation value for the additional information bits accumulated up to a point in time in the past and a correlation value for the additional information bits currently transmitted in the pilot channel; And determining a sign according to the summed correlation value. 6. The method of claim 5, wherein in the step of adding a correlation value for the additional information bits accumulated up to the past arbitrary time point and a correlation value for the additional information bits currently transmitted in the pilot channel, accumulating up to the past arbitrary time point And a correlation value for the additional information bits and a correlation value for the additional information bits currently transmitted in the pilot channel. The correlation value of the additional information bits is correlated with the same additional information bits.