KR20030055652A - Rake receiver capable of compensating channel estimating delay - Google Patents

Abstract

PURPOSE: A rake receiver capable of compensating channel estimation delay is provided to use a finite impulse response filter, and to install a data buffer for buffering data during channel estimation and compensation periods, thereby according a channel value by a pilot signal from a shared pilot channel or a dedicated physical control channel with demodulated data. CONSTITUTION: Many fingers(100) estimate and compensate channels by spreading receiving signals, and output symbols. A combiner(200) combines the outputted symbols. A decoder(300) decodes output data of the combiner(200). Each of the fingers(100) comprises as follows. A despreader(110) receives wireless signals including a shared pilot signal and a traffic signal, and despreads the wireless signals. A channel estimating device(A) selectively outputs a channel estimation value estimated by the shared pilot signal and a dedicated physical control pilot signal, and buffers a traffic signal of the despread signals to output the buffered signal. An multiplier(160) multiplies the channel estimation value by the buffered value, and outputs a data value whose channel influence is compensated.

Description

RAKE RECEIVER CAPABLE OF COMPENSATING CHANNEL ESTIMATING DELAY}

The present invention relates to a rake receiver, and more particularly to a rake receiver capable of channel estimation delay compensation.

When transmitting data through the wireless mobile communication system, the received signal is distorted due to multipath, fading, etc. due to various factors of the transmission channel.

In the asynchronous IMT-2000 system, a signal known as a common pilot channel or a pilot signal is inserted into data (pilot in a dedicated physical control channel) to transmit a signal, and the signal is coherently detected to compensate for signal distortion. do.

One common pilot channel is assigned to each base station to provide a phase reference to the terminal and to provide a means for comparing the signals of neighboring base stations to determine handoff. As such, the channel estimation and compensation device is necessary for demodulation of the transmitted data and for improving receiver performance.

1 is a block diagram illustrating an example of a conventional channel estimator.

As shown in FIG. 1, the conventional channel estimator includes a pilot channel estimator 100, a traffic channel estimator 110, a first multiplier 120, a second multiplier 130, and an adder 140.

In the above configuration, the pilot channel estimator 100 estimates the channel using the pilot channel, and the traffic channel estimator 110 estimates the channel using the traffic channel. The first and second multipliers 120 and 130 multiply predetermined values by the estimated values output from the pilot channel estimator 100 and the traffic channel estimator 110, respectively, and the adder 140 adds the multiplied result. .

As described above, the conventional technology improves performance over channel estimation using only the pilot channel by performing channel estimation using a pilot channel and a traffic channel together without time delay.

However, this channel estimator has a disadvantage in that since the pilot channel estimator and the traffic channel estimator use an infinite impulse response filter, they do not have a linear phase response characteristic due to the characteristics of the infinite impulse response filter. That is, in the channel estimation and compensation method using the infinite impulse response filter, a phase error occurs in the estimated value after the filtering.

In addition, this method uses forgetting factors to determine the amount of averaging, so that the exact number cannot be averaged. In addition, there is a problem that the filter delay is not free.

Another example of a conventional channel estimation and compensation method is Korean Patent No. 2001-0077512 (name: "Channel Estimation Apparatus and Method of Code Division Multiple Access System", 2000. 2.3). The channel estimating apparatus described in this patent includes a channel integrator that integrates a received signal by an integer multiple of a channel orthogonal code period, and a demodulation period that compensates the total amount of channel change delayed by demodulating a period by calculating a channel change rate per hour of the channel-integrated received signal. A delay compensator and a complex multiplier configured to complex-compensate the demodulated-period delay-compensated channel and the received signal by performing a channel compensation, wherein a demodulation cycle delay occurs during an integration period of a receive channel during channel estimation of a code division multiple access system. By compensating for the channel error according to the present invention, an accurate channel integration value can be obtained at an arbitrary time point, thereby improving the error of channel estimation.

However, this channel estimating apparatus does not consider channel estimation by a common traffic channel and does not consider the delay during the channel estimation period, so there is a problem in that the performance improvement of the receiver cannot be expected.

Accordingly, an object of the present invention is to solve the above-mentioned problems, and uses a finite impulse response filter having a linear phase response characteristic, and uses data during channel estimation and compensation periods to remove distortion of despread data. A rake receiver capable of channel estimation delay compensation that reduces the overall error probability by matching a demodulated data with a channel value of a pilot signal of a common pilot channel or a dedicated physical control channel by having a buffering data buffer. .

1 is a block diagram illustrating an example of a conventional channel estimator.

2 is a block diagram illustrating an entire rake receiver having a data estimating apparatus according to an exemplary embodiment of the present invention.

3 is a diagram illustrating a channel estimating apparatus for restoring data according to an embodiment of the present invention.

4A and 4B are diagrams comparing the performance of the channel estimator averaging four symbols and the channel estimator averaging eight symbols.

5 is a diagram illustrating a bit error probability characteristic according to an embodiment of the present invention.

Rake receiver of the present invention for achieving the above object,

A plurality of fingers for spreading a received signal to estimate and compensate a channel to output a symbol; A combiner for combining the symbols output from the plurality of fingers; And a decoder for decoding the output data of the combiner, wherein the plurality of fingers include a despreader for receiving and despreading a radio signal including a common pilot signal and a traffic signal; A channel estimating apparatus for selectively outputting channel estimates respectively estimated by a common pilot signal and a dedicated physical control pilot signal among the despread signals, and buffering and outputting a traffic signal among the despread signals; And a multiplier for multiplying the channel estimation value selectively output from the channel estimating apparatus and the buffered output value to output a data value compensated for by the channel.

The channel estimating apparatus includes: a common pilot channel estimator for estimating and compensating a channel in symbol units based on a common pilot signal among the despread signals; A dedicated physical control signal channel estimator for estimating and compensating a channel in slot units by separating a dedicated physical control pilot signal from the despread signal with a traffic signal; A selector for selecting one of the signal compensated by the common pilot channel estimator and the signal compensated by the dedicated physical control signal channel estimator; And a data buffer for buffering a traffic channel among the despread signals.

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

In the following description of the present invention, if it is determined that the detailed description of related known functions or configurations may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

2 is a block diagram illustrating an entire rake receiver having a channel estimating apparatus for recovering data according to an embodiment of the present invention.

In FIG. 2, the rake receiver includes a finger 100, a combiner 200, and a decoder 300. There are several fingers 100 inside the receiver, and in this embodiment, four are set.

Each finger 100 includes a despreader 110, a channel estimator A and a multiplier 160, and the channel estimator A estimates and compensates the channel in symbols by the despread pilot signal. The common pilot channel estimator 120 separates the dedicated physical control signal from the traffic signal and estimates and compensates the channel in slot units, and then buffers the received traffic signal during the channel estimation period. A data buffer 140 and a selector 150 for selectively outputting the outputs of the channel estimators 120 and 130.

Each finger 100 is assigned a path signal through different channels. In the asynchronous IMT-2000 system, a common pilot signal is transmitted simultaneously with a traffic signal for phase reference. The multiple code division multiple access signals thus transmitted are despread while passing through the despreader 110.

The despread signal passes through the channel estimator to compensate for the estimation of the transmission channel and the deviation of the estimate, while the data of the traffic channel is buffered during the channel estimation and compensation periods so that the pilot signal of the common pilot channel or the dedicated physical control channel The channel value by and the data of the traffic channel match.

In detail, the common pilot signal among the despread signals is estimated by the common pilot channel estimator 121 in the symbol unit of the common pilot channel estimator 120, and the channel compensation filter (WMA filter) 123 is used. By averaging several symbols, we reduce the deviation of the estimate. Meanwhile, the pilot of the dedicated physical control signal for the closed loop transmission diversity among the despread signals includes the dedicated physical control channel estimator 131 and the channel compensation filter (WMA filter) in units of slots of the dedicated physical control signal channel estimator 130. Through 133). The outputs of the two channel estimators 121 and 131 which have passed through the channel compensation filters 123 and 133 respectively are selected and output by the selector 160.

The two channel estimators 120 and 130 among the components of the channel estimating apparatus will be described later with reference to FIG. 3.

As such, while estimating a channel using a pilot of a common pilot signal and a dedicated physical control signal, the traffic channel is buffered in the data buffer 140 and multiplied by the multiplier 160 by a channel estimate value output from the selector 150. The data value whose influence is compensated for is output. This data value is the value of the first finger, and the remaining fingers (not shown) also output data values through the same process as above, and the output data values are combined in the combiner 200 and in the decoder 300. Decoded.

Hereinafter, two channel estimators 120 and 130 of the channel estimating apparatus will be described.

As shown in FIG. 2, the common pilot channel estimator 120 includes a common pilot channel estimator 121 and a channel compensation filter 123, and the dedicated physical control signal channel estimator 130 includes a dedicated physical control channel. An estimator 131 and a channel compensation filter 133. Since the two channel estimators 120 and 130 have the same configuration except that they are processed in symbol units and slot units, respectively, in FIG. 3, the full pilot channel estimator 121 and the channel for the common pilot channel estimator 120 are shown. The specific configuration of the compensation filter 123 is shown.

In the case of the common pilot channel estimator, when the despreader 110 despreads the received signal r (t) by the pilot known and outputs it to the common pilot channel estimator 121, the integrator 121a integrates the symbols at a symbol period. The sampler 121b samples the symbol unit and outputs the channel estimate Chest_Out scaled by the combiner 121c.

The output Chest_Out of the common pilot channel estimator 121 is multiplied by the orthogonal spreading code and despread the signal received in symbol units (256 chips), and then multiplied by the conjugate complex of the common pilot pattern.

Here, Scr_OVSF is an orthogonal spreading code in an asynchronous IMT-2000 system, r_chip represents a received signal passing through a digital front end (DFE), and CPICH_pilot is a common pilot pattern known to the receiver.

Although not illustrated, the dedicated physical control channel estimator 130 also outputs the channel estimate Chest_Dpch through the same process as the common pilot channel estimator 120 and the dedicated physical control channel estimator 131.

At this time, the channel estimator 130 output Chest_Dpch may be obtained through a bonding group of slots after the pilot signal (r_pilot) Pilot (pilot) known by the receiver, after extracting from the dedicated channel complex multiplied, Equation (2) This is illustrated.

As such, the estimated Chest_Out obtained from the channel estimation is passed through the channel compensation filter 123 to reduce the deviation and improve the performance of the modulator. Likewise, the output Chest_Dpch of the channel estimator 130 also reduces its deviation by passing through the channel compensation filter 133 although its detailed configuration is not shown.

In the present invention, a finite impulse response filter is used as the channel compensation filter 123 to compensate for the problem of nonlinearity of the conventional infinite impulse response filter and to average the correct number of symbols. In particular, in the present embodiment, an optimal filter was designed in terms of complexity-performance by averaging eight symbols with a length of eight.

4A and 4B compare the performance of a channel compensation filter that averages four symbols (K = 4) and a channel compensation filter that averages eight symbols (K = 8), and compares the overall power to the power of other cells. When the received power ratio (Ior / Ioc) is 9 dB, a channel compensation filter that averages eight symbols for the case where the speed of the mobile station is 120 km / h (Fig. 2a) and 300 km / h (Fig. 2b) 0.5 to 0.6 dB shows better performance. Therefore, in the present invention, a channel compensation filter that averages eight symbols is used.

In other words, the channel compensation filter 123 is composed of a finite impulse response filter having eight taps of length consisting of seven delayers 123a, eight weight multipliers 123b, and an accumulator 123c.

In the channel compensation filter input, eight symbols are inputted through a delay-free input and seven delayers 123a connected in series, each of which is multiplied by a weight multiplier 123b, and accumulates the accumulator 123c. Channel estimation compensation value Outputs Equation 3 is an equation representing the channel estimation compensation value.

Here, Chest_Out (x) represents a state of the filter delayed in symbol units as a channel estimate, and Wx represents a weight of the filter. In the present invention, the weights of the filters used are shown in Table 1.

W ₀ W _One W ₂ W ₃ W ₄ W ₅ W ₆ W ₇ weight One 4 12 15 15 12 4 One

That is, in the present invention, a symmetric finite impulse response filter using filter weights as shown in Table 1 is used.

During such channel estimation and channel estimation compensation filtering, the traffic signal is stored in the data buffer 140 mentioned in FIG. 1 and multiplied by this value in accordance with the channel estimation compensation filter output time. The data buffer becomes a function of the spreading factor and the signal type (channel estimation mode) for estimating the channel, and Table 2 shows the most suitable data buffer amount according to the optimum complexity-performance.

Channel Estimation Mode Diffusion factor Data buffer amount (symbol unit) Common pilot signal 512 2.5 Common pilot signal 256 5 Common pilot signal 128 10 Common pilot signal 64 20 Common pilot signal 32 40 Common pilot signal 16 40 Common pilot signal 8 40 Common pilot signal 4 40 Dedicated physical control signal 512 5 Dedicated physical control signal 256 10 Dedicated physical control signal 128 20 Dedicated physical control signal 64 40 Dedicated physical control signal 32 40 Dedicated physical control signal 16 40 Dedicated physical control signal 8 40 Dedicated physical control signal 4 40

As shown in Table 2, the optimum results in terms of complexity and performance when the spreading factor is 40 symbols in consideration of performance and complexity at spread rates of 16, 8, 4, etc. Seems.

5 is a diagram illustrating bit error probability characteristics according to an exemplary embodiment of the present invention. In the case of the spreading factor 16, the data buffer amount K is almost the same as that of the 32 and 64 data buffers. The amount is 40 determined.

Although the present invention has been described with reference to the most practical and preferred embodiments, the present invention is not limited to the above disclosed embodiments, but also includes various modifications and equivalents within the scope of the following claims.

As described above, the channel estimating apparatus of the present invention uses a weighted averaging filter (finite impulse response filter) of eight symbols as a filter for compensating for channel estimation, and provides an optimal channel estimation by presenting a weight of the filter therefor. This is possible.

In addition, the overall error probability can be lowered by appropriately setting the size of the data buffer according to the spreading factor for the common pilot signal and the dedicated physical control signal with the data buffer.

In addition, when the channel estimation apparatus is employed in the rake receiver, the reception performance may be improved in a fading environment.

Claims (10)

A plurality of fingers for spreading a received signal to estimate and compensate a channel to output a symbol; A combiner for combining the symbols output from the plurality of fingers; And A decoder for decoding the output data of the combiner Including; The plurality of fingers, A despreading unit configured to receive and despread a radio signal including a common pilot signal and a traffic signal; A channel estimating apparatus for selectively outputting channel estimates respectively estimated by a common pilot signal and a dedicated physical control pilot signal among the despread signals, and buffering and outputting a traffic signal among the despread signals; And A multiplier for multiplying a channel estimate value selectively output from the channel estimating apparatus and the buffered output value to output a data value compensated for by the channel; Rake receiver each comprising a. The method of claim 1, The channel estimating apparatus A common pilot channel estimator for estimating and compensating a channel in symbol units based on a common pilot signal among the despread signals; A dedicated physical control signal channel estimator for estimating and compensating a channel in slot units by separating a dedicated physical control pilot signal from the despread signal with a traffic signal; A selector for selecting one of the signal compensated by the common pilot channel estimator and the signal compensated by the dedicated physical control signal channel estimator; And A data buffer buffering a traffic channel among the despread signals Rake receiver comprising a. The method of claim 2, The common pilot channel estimator A channel estimator for estimating a transmission channel in symbol units from the common pilot signal, wherein the channel estimator An integrating unit for integrating the common pilot signal in a symbol period; A sampling unit sampling the output of the integrator in symbol units; And A combiner for combining channel outputs to accumulate channel estimates Including; And A channel compensation filter comprising a finite impulse response filter in symbol units for reducing the deviation of the estimated value of the channel estimator Rake receiver comprising a. The method of claim 3, The channel estimate Chest_Out is obtained by multiplying the complex signal of the common pilot pattern after multiplying by orthogonal spreading code and despreading the received signal in symbol units. Here, Scr_OVSF is an orthogonal spreading code in a mobile communication system, r_chip is a received signal passing through the digital front end (DFE), CPICH_pilot is a common pilot pattern known to the rake receiver. Rake receiver, characterized in that follows. The method of claim 2, The dedicated physical control signal channel estimator A channel estimator for estimating a channel in slot units from the dedicated physical control signal, wherein the channel estimator An integrating unit for integrating the dedicated physical control signal at a slot period; A sampling unit sampling the output of the integrating unit in slot units; And A combiner for combining and outputting the sampling unit to accumulate and output a channel estimate Including; And A channel compensation filter comprising a finite impulse response filter in slot units to reduce the deviation of the estimate of the channel estimator Rake receiver comprising a. The method of claim 5, The channel estimate (Chest_Dpch) that becomes the pilot (pilot) known by the receiver after the extraction of the pilot signal (r_pilot) in a dedicated channel, obtained by the accumulation is multiplied by a complex number, the following equations Rake receiver, characterized in that follows. The method according to claim 3 or 5, The channel compensation filter is a finite impulse response filter that averages eight symbols, First to seventh delay units connected to each other in series by delaying and outputting an input symbol by a predetermined time; A first weight multiplier configured to receive an input symbol without delay and multiply the weight; Second to eighth weight multipliers configured to receive delayed symbols passing through the first to seventh delay units, respectively, and multiply predetermined weights; And An accumulator that accumulates an output of the first to eighth weight multipliers Rake receiver comprising a. The method of claim 7, wherein And the first to eighth weight multipliers have weights of 1, 4, 12, 15, 15, 12, 4, and 1, respectively. The method of claim 2, And the data buffer is sized as a function of spreading factor and channel estimation mode. The method of claim 9, And the size of the data buffer is approximately 40 symbols when the spreading factor of the channel estimation mode is 32 or less.