KR20010083463A - Channel estimation for space-time transmit diversity receiver - Google Patents

Abstract

PURPOSE: A channel predicting apparatus for a space-time diversity receiver and a method thereof are provided to enhance channel prediction performance and overall system performance by solving a pilot pattern of orthogonal noise and reducing a delay in wideband CDMA(Code Division Multiple Access) mobile communication system. CONSTITUTION: The first integrator(12) integrates inputted signals in according with a chip clock. A pilot pattern generator(13) is synchronized with a symbol clock under controlling by a frame initiating signal generator(11) and generates a pilot pattern. A mixer(14) receives the output from the first integrator(12) and mixes the output with the generated pilot pattern. The second integrator(15) integrates the output from the mixer(14) according to the symbol clock. An adding and accumulating unit(16) adds the output from the second integrator with a previously accumulated value, and outputs a phase distortion prediction value for each channel.

Description

Channel predictor for space-time diversity receiver and its method {CHANNEL ESTIMATION FOR SPACE-TIME TRANSMIT DIVERSITY RECEIVER}

The present invention relates to a channel predictor for a space-time diversity receiver and a method thereof, and more particularly, to a channel predictor for a space-time diversity receiver adopted in an asynchronous wideband code division multiple access (CDMA) mobile communication system. It's about how.

In a base station asynchronous broadband mobile communication system using a code division multiple access (CDMA) spread spectrum scheme, Space-Time Transmit Diversity (STTD) is used as a method for increasing forward capacity. In this method, two consecutive symbols of the modulator output contain the same symbol information by using space-time coding. However, two orthogonal signals are generated and transmitted to each of two antennas. By compensating for the channel phase distortion of the signal along the channel path, it demodulates the transmitted symbol. The demodulation of the received signal determines the performance of the system according to how accurately the channel phase distortion of signals passing through different channel paths for each antenna is predicted. To this end, the base station transmits a pilot, which is a data pattern previously agreed with the data, and extracts the channel distortion information by receiving it from the mobile station. In this case, in order to distinguish two antenna pilots, a special pattern orthogonal to each antenna is used. Due to the characteristics of the pattern, a channel prediction scheme commonly used in a conventional synchronous CDMA system is degraded due to performance degradation. Can not use it.

In other words, the structure of the channel prediction method used in the existing spread spectrum system is roughly divided into two types, one method is to de-spread or de-scrambling pilot data chip chip (chip) It is a method of extracting channel distortion information by processing in a clock unit, and another method is to integrate despread or descrambled pilot data in a chip clock unit for a data symbol period, and then process a symbol clock to process a channel. A method of extracting distortion information. Here, the chip clock processing has an advantage of low processing delay. On the other hand, orthogonal noise exists due to incomplete orthogonality between the pilot symbol and the data (traffic) symbol. In a typical CDMA spread spectrum mobile communication system, such a problem is not large. However, the asynchronous CDMA spread spectrum mobile communication system employing a space-time diversity scheme uses a special orthogonal pilot pattern to distinguish two transmit antennas. Using predictive methods leads to performance degradation.

Accordingly, an object of the present invention is to solve the problems of the prior art as described above, and an object of the present invention is to solve orthogonal noise of a pilot pattern per antenna in a wideband CDMA mobile communication system employing a space-time diversity scheme, and to reduce delay. Accordingly, an object of the present invention is to provide a channel predicting apparatus and a method for improving channel prediction performance and improving the performance of the entire system.

1 is a block diagram of a space-time diversity receiver of an asynchronous spread spectrum communication system.

2 is a block diagram of a channel prediction apparatus according to the present invention;

3 is a detailed block diagram of one channel processor according to the present invention;

4 is an operation timing diagram according to the present invention.

5 is a graph showing the results of computer simulations performed to compare the performance of the channel prediction method and the conventional channel prediction method according to the present invention.

* Explanation of symbols for main parts of the drawings

11: frame start signal generator 12, 15: integrator

13: pilot pattern generator 14: mixer

16: adder and accumulator 17: shift register

According to an aspect of the present invention, there is provided a channel prediction apparatus in a space-time diversity reception system, comprising: means for generating a frame start signal; And an I channel processing means and a Q channel processing means corresponding to each antenna, wherein each channel processing means comprises: first integrating means for integrating an input signal according to a chip unit clock; Means for generating a pilot pattern in synchronization with a symbol unit clock according to the control of the frame start signal generating means; Means for receiving the output of the first integration means as a symbol unit clock and mixing the generated pilot pattern; Second integrating means for integrating the output of the mixing means according to a symbol unit clock; And an adding and accumulating means for adding the output of the second integrating means to the accumulated previous value and outputting a phase distortion prediction value for each channel.

In addition, the channel prediction method according to the present invention, in the channel prediction method applied to the space-time diversity reception system, for the input signal in synchronization with the chip unit clock for each of the I channel and Q channel corresponding to each antenna A first step of integrating; A second step of synchronizing a pilot pattern corresponding to each channel of each antenna to a symbol unit clock at a frame start time; A third step of mixing the value integrated in the first step and the pilot pattern generated in the second step in synchronization with the symbol unit clock; A fourth step of integrating the mixed signal of the third step in synchronization with the symbol unit clock; And a fifth step of adding the integrated signal of the fourth step in synchronization with a previously accumulated value and a two-symbol unit clock to output a channel phase distortion prediction value.

In general, the characteristics of the space-time diversity pilot pattern are four symbols in a group, but since the two symbol patterns are orthogonal, the present invention allows pilot filtering to an integral value during these two symbol intervals. In addition, the noise due to the orthogonality of the pattern is reduced. In addition, the present invention integrates the pilot in the chip unit by the symbol unit, and then obtains the autocorrelation value of the antenna pattern, takes the values corresponding to the two symbols and sends them to the input value of the pilot filter, thereby avoiding unnecessary chip unit operation. By performing symbol units and two symbol units, power consumption may be reduced in hardware implementation. In addition, in order to efficiently control power in terms of performance, fast demodulation is required. In order to minimize pilot filter delay, the present invention uses a method in which half of an output value is returned per signal to reduce the delay.

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

1 is a block diagram of a space-time diversity receiver of an asynchronous spread spectrum communication system to which the present invention is applied.

In the drawing, "1" represents a reception antenna, and "2-1 and 2-2" represent a scrambling code correlator for calculating a self correlation of a scrambling code, which is a kind of pseudo noise (PN) code. This scrambling code is used to distinguish the base station that the mobile station wishes to receive. In addition, the mobile station uses an orthogonal channelization code, which is a kind of orthogonal code, to distinguish the communication channel assigned to the mobile station from other channels, and “4” represents an autocorrelator for this. Each of the scrambling code correlators 2-1 and 2-2 performs autocorrelation using the code input from the scrambling code generator 3, and the correlator 4 for dechannelization is input from the orthogonal code generator 5 The generated code to perform correlation. In the figure, "7" denotes a demodulator which performs decoding, and "6" denotes a channel predictor which predicts the channel phase distortion value for each antenna of the present invention and provides it to the demodulator 7. FIG.

Fig. 2 is a block diagram of a channel predictor 6 according to the present invention, in which “11” is a frame start signal generator, “12, 15” is an integrator, “13” is a pilot pattern generator, and “14” is a mixer. "16" represents an adder and accumulator, and "17" represents a shift register, respectively.

In order to solve the orthogonal noise of the pilot pattern for each antenna, in the present invention, two symbol integration values are used, and time information for integrating the two symbols is received from the frame start signal generator 11. In addition, by integrating one symbol in the process of integrating two symbols, the auto-correlation value of the antenna pattern is obtained for each antenna after the output value is integrated, and then an integral value corresponding to the two symbols is obtained, thereby avoiding chip clock operation. Running on a clock saves power in the receiver. In order to reduce the delay according to the channel prediction, only 1/2 of the sum and accumulated output values are fed back, and the new input values are summed and accumulated to obtain new output values.

This will be described in more detail with reference to FIG. 2.

As shown in the figure, the channel prediction apparatus according to the present invention includes an I channel processor and a Q channel processor having the same structure corresponding to the frame start signal generator 11 and each antenna. That is, among the signals descrambled by the descrambler, an I-signal is simultaneously input into an I-channel processor for antenna 1 and an I-channel processor for antenna 2, and the Q-signal is a Q-channel processor for antenna 1 And simultaneously to the Q-channel processor for antenna 2.

In the following description, since the structures of the I channel and the Q channel processor are the same, only the I-channel processor will be described.

First, the input descrambling signal is integrated for one symbol period in the first integrator 11 and outputted in symbol units. The output value of this integrator 11 represents a pilot symbol value and contains information about antennas 1 and 2. In order to obtain the channel prediction value for the antenna 1, the mixer 14 synthesizes the signal integrated by the first integrator 12 and the pilot symbol pattern of the antenna 1 output from the pilot pattern generator 13, thereby inverse patterning ( de-patternizing). Likewise, in order to obtain a channel prediction value for antenna 2, the same procedure is performed in the channel processor for antenna 2. Here, since the pilot symbol pattern is repeated in units of frames, the pilot pattern generator 13 generates a pilot symbol pattern based on the frame start time signal input from the frame start signal generator 11. On the other hand, the signal output from the mixer 14 is integrated by the value of the two symbols by the second integrator 15, the output of the second integrator 15 is input to the adder and accumulator 16. The adder and accumulator 16 decreases the previous value in half from the shift register 17, receives a feedback value, receives an output of the second integrator 15, and adds the feedback value and the integrated value, Output the predicted channel phase distortion value for the I channel. The Q-channel processor also performs the same process.

Figure 3 shows a detailed block configuration of one channel processor according to the present invention.

Integrators 12 and 15 generally consist of one adder and a register. The input of the first integrator 12 is input as a clock in a chip unit, and the output is output as a clock in a pilot symbol unit. That is, the adder adds the value input by the chip unit clock and the previous value of the register operated by the chip unit clock, and the added value is input to the mixer 14 in synchronization with the pilot symbol unit clock. As such, a dump A is provided to compensate for a mismatch between the clock in the chip unit and the clock in the pilot symbol unit.

Mixer 14 and pilot pattern generator 13 operate on a pilot symbol unit clock. Meanwhile, the input of the second integrator 15 is performed by the pilot symbol unit clock Ts, and the output is performed by two pilot symbol unit clocks 2Ts. That is, the adder of the second integrator 15 adds the value input as the symbol unit clock and the previous value of the register operated as the symbol unit clock, and the added value is synchronized with the pilot symbol unit clock to add and accumulate ( 16). To this end a dump B is likewise provided.

Adder and accumulator 16 and shift register 17 are operated by a two symbol unit clock, which consists of one adder, divider and register. That is, the adder adds the value input to the two-symbol clock and the output value of the register operated by the two-symbol clock divided by 1/2 to output the channel phase distortion prediction value.

4 is an operation timing diagram of the channel predictor according to the present invention, in which the frame start signal is " active high " In other words, taking the pilot pattern for antenna 2 as an example, "A, -A, -A, A" is repeated, which is called a symbol pattern group, and at the end of one frame, the first two patterns of the symbol pattern group At the start of the next frame, the rest does not continue, and the pilot pattern always starts again. In this timing diagram, it is assumed that the operation is performed at the falling edge.

5 is a graph showing the results of a computer simulation performed to compare the performance of the channel prediction method according to the present invention and the conventional channel prediction method. The horizontal axis of the graph represents the moving body speed, and the vertical axis is the noise energy spectral density (Eb / No) versus the bit energy required for the bit error rate to be 0.01. The graph 31 represented by (31) in the figure is a performance under the assumption that the receiver accurately predicts the distortion phase of the channel, which is independent of the moving velocity environment. In addition, graphs "33" and "34" represented by (■) and (▲) are the channel prediction performance results by the general method. In contrast, it can be seen that the channel prediction performance graph 32 using the method of the present invention expressed by (x) obtains a target bit error rate (preferably 0.01) as a small value of Eb / No.

The present invention described above is not limited to the above-described embodiments and the accompanying drawings, and various substitutions, modifications, and changes can be made in the art without departing from the technical spirit of the present invention. It will be apparent to those of ordinary knowledge.

According to the present invention made as described above, in space-time diversity demodulation, by reducing the incomplete orthogonal noise according to the antenna pattern, and by reducing the channel prediction delay, according to the delay error of the system, such as the extraction delay of the power control command bit Efficient channel prediction regardless of radio channel conditions such as fading rate by adopting a structure that improves performance deterioration and returns a part of summed and accumulated output values (preferably 0 to 1/2). Has the effect of enabling. In addition, when the correlation value of the antenna pattern is obtained, it is possible to save the power of the receiver by using the symbol unit instead of the chip unit.

Claims (5)

A channel predictor in a space-time diversity reception system, Means for generating a frame start signal; I channel processing means and Q channel processing means corresponding to each antenna, Each channel processing means, First integrating means for integrating an input signal in accordance with a chip unit clock; Means for generating a pilot pattern in synchronization with a symbol unit clock according to the control of the frame start signal generating means; Means for receiving the output of the first integration means as a symbol unit clock and mixing the generated pilot pattern; Second integrating means for integrating the output of the mixing means according to a symbol unit clock; And Adding and accumulating means for adding an output of the second integrating means with a cumulative previous value and outputting a phase distortion prediction value for each channel; And a channel predictor for a space-time diversity receiver. The method of claim 1, The addition and accumulation means, A channel predictor for a space-time diversity receiver, wherein the channel predictor operates in synchronization with a two-symbol unit clock. The method according to claim 1 or 2, The addition and accumulation means, And a portion of the output (preferably 0 to 1/2) is accumulated and added to the output of the second integrating means. A channel prediction method applied to a space-time diversity reception system, Integrating a signal input in synchronization with a chip unit clock for each of an I channel and a Q channel corresponding to each antenna; A second step of synchronizing a pilot pattern corresponding to each channel of each antenna to a symbol unit clock at a frame start time; A third step of mixing the value integrated in the first step and the pilot pattern generated in the second step in synchronization with the symbol unit clock; A fourth step of integrating the mixed signal of the third step in synchronization with the symbol unit clock; And A fifth step of adding the integrated signal of the fourth step in synchronization with a previously accumulated value and a two symbol unit clock to output a channel phase distortion prediction value; Channel prediction method comprising a. The method of claim 4, wherein The fifth step, And a part of the output (preferably 0 to 1/2) is accumulated and added to the integral value of the fourth step.