KR100306168B1 - A symbol-level rake receiver of direct spread cdma mobile communication system and receiving method thereof - Google Patents

Abstract

The present invention relates to a radio signal receiver and a method of a direct spread code division multiple access demodulation type mobile communication system, and more particularly, to an adaptive receiver and a method for eliminating multiple access interference. The present invention converts the matched filter output in each user path into symbol units, and then converts the converted symbols into inputs of an adaptive filter corresponding to each path, and sums the outputs through the adaptive filter by channel estimation. After that, the summed result is outputted as the determination target information. Therefore, a new adaptive receiver structure can be proposed through the implementation of the present invention, which leads to a drastically improved receiver performance compared to the conventional adaptive receiver.

Description

Direct spreading code division multiple access demodulation system Wireless signal receiver and method therefor {A SYMBOL-LEVEL RAKE RECEIVER OF DIRECT SPREAD CDMA MOBILE COMMUNICATION SYSTEM AND RECEIVING METHOD THEREOF}

The present invention relates to a radio signal receiver and a method of a direct spread code division multiple access demodulation type mobile communication system, and more particularly, to an adaptive receiver and a method for eliminating multiple access interference.

As the amount of data required in a direct spread CDMA system increases, there is a demand for a receiver that dramatically increases the capacity of the system. In recent years, various adaptive receivers have been actively researched and proposed in order to satisfy these demands.

In the conventional receiver according to the prior art in the CDMA system, it is to ignore the signal of the other user in detecting the signal of the desired user, whereas the adaptive receiver as described above ignores the signal of the other user It is configured to use it, rather than to improve the performance of the system. In other words, the performance and capacity of the CDMA system is determined by the multiple access interference (MAI) component, unlike other systems, the conventional single-user receiver is to demodulate only the signal of the user who wants to ignore the other user's signal In order to solve this problem, there is no choice but to limit the total system capacity according to the interference of other users' signals.

However, recently, the proposed adaptive receivers have to increase the complexity of the system to be implemented in a real wireless environment, and has shown that the performance improvement is not excellent compared to the increase in the complexity. In order to solve the conventional receiver problem, there have been proposals of such an adaptive receiver and an interference canceller used therein, but an adaptive receiver having an appropriate performance that can solve the above problem has not been made.

1 is a diagram illustrating an internal configuration state of an adaptive receiver according to the prior art, and in particular, illustrates an internal configuration of a standard adaptive receiver on a chip-by-chip basis.

As a reference thereof, the configuration and operation of an adaptive receiver according to the related art will be described.

First, the receiver uses a signal passed through the chip matching filter 101 as a tap input vector of the adaptive filter 102. The signal passed through the chip matching filter 101 becomes an input signal of the channel estimator 103, which becomes a general operation of the conventional adaptive receiver. The estimated channel parameter values as the output of the channel estimator 103 are multiplied by the output of the adaptive filter 102 to effect channel compensation. The channel-compensated value is determined through the determination unit 104 to the corresponding value, thereby making a data output of the determination result. The determination data output from the determination unit 104 is compensated by the channel parameter estimated by the channel estimator 103 to become a reference response value of the adaptive algorithm 105, and this reference signal value Again the output of the adaptive filter 102 is subtracted to generate an error signal for tap coefficient correction. The corrected tap coefficients become new tap coefficients of the adaptive filter 102.

In the simulation performed prior to the proposal of the present invention, a rake receiver structure applied to the mobile communication terminal system is introduced to the adaptive receiver having the above-described configuration in consideration of the multipath, and the tap coefficients are converged. No training sequence was used. This shows the results as shown in Figure 5 attached.

As shown in FIG. 5, the chip-based adaptive receiver of the above configuration shows a slight performance improvement compared to the conventional matching filter scheme, but has a low signal-to-noise ratio similar to that of a real wireless environment. It shows that the performance improvement is insignificant compared to the increased complexity of the hardware to operate in the channel environment of.

Therefore, the present invention solves the problem of adopting a scheme that the existing adaptive receiver having the above-described configuration removes the MAI using only a single user signal, that is, there is a limit to the performance improvement of the receiver. The present invention aims to implement a new method of adaptive receiver.

In particular, in the present invention, to solve the above problem, an adaptive filter which uses other user's signals together in detecting a desired user's signal and receives an output symbol of a symbol unit matching filter as an input is provided. An adaptive receiving device is provided. This is due to the fact that the tap coefficient of the filter increases as the multipath increases, thereby achieving a drastic improvement in performance.

As a result, an object of the present invention is to solve the problem of the conventional adaptive receivers of the above-described configuration, that is, the signal-to-noise ratio similar to the wireless environment in a real system. An adaptive receiver and a method for solving the problem that the performance improvement of the receiver in the low channel environment is inevitable.

In order to achieve the above object, the present invention converts the matched filter output in each user path into symbol units, and then converts the converted symbols into inputs of an adaptive filter corresponding to each path, and outputs the outputs through the adaptive filter. The present invention proposes an adaptive radio signal receiving apparatus and method, characterized by outputting the summed result as the determination target information after summing and estimating the channel.

1 is an internal configuration diagram of a mobile communication system adaptive receiver according to the prior art.

2 is an internal configuration diagram of an adaptive receiver of a direct spread code division multiple access demodulation type mobile communication system according to a preferred embodiment of the present invention.

3 is a time relationship diagram of an asynchronous channel in an input signal of a direct spread code division multiple access demodulation type mobile communication system adaptive receiver proposed in the present invention.

4 is a diagram illustrating an internal configuration of a channel estimator configured in a direct spread code division multiple access demodulation type mobile communication system adaptive receiver according to a preferred embodiment of the present invention.

5 is a graph showing the results according to the preferred embodiment of the present invention.

6 is a graph showing another result according to a preferred embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. First of all, in adding reference numerals to the components of each drawing, it should be noted that the same reference numerals have the same reference numerals as much as possible even if displayed on different drawings. Also, in the following description, many specific details such as components of specific circuits are shown, which are provided to help a more general understanding of the present invention, and the present invention may be practiced without these specific details. It is self-evident to those of ordinary knowledge. In the following description of the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

First, the symbol-level adaptive receiver (SRMbol-level Rake MMSE receiver) proposed in the present invention operates under the assumption of an asynchronous reverse link, a multipath (frequency selective) fading channel, and an additive white Gaussian noise (AWGN) environment. do.

In addition, the operating state of the present invention is based on the premise that there are K users and L multipaths at the current cell boundary, and the user's spreading code is a Gold code having a length of 31. ) Is used.

2 is a view showing the overall configuration of an adaptive receiver according to a preferred embodiment of the present invention.

Referring to FIG. 2, first, a sum of user signals corresponding to K names passing through a predetermined channel is converted into a baseband signal and then input to a receiver according to the present invention. This input signal is disclosed as r (t). Based on the input signal r (t), the rake receiver of the adaptive receiver acquires timing of each path of all users and consists of LK chip matched filter banks. The demodulation process is performed as an input signal of 203. Output signals in chip units, which are output from the chip matching filter group 203, are again input to LK symbol matching filter groups 205. The symbol matching filter group 205 demodulates the input signal using a code sequence of each user. The output of the symbol matching filter group 205 is processed and output by the following equation.

here, Is sampled at the i th symbol time as the output of the symbol matching filter of the first path of the first user.

The first term of the right term in Equation 1 represents the i-th symbol of User 1 damaged by the channel, the second term represents self-interference due to another path of the magnetic signal, and the third term and the last term. The terms represent multiple access interference (MAI) and white Gaussian noise (AWGN), respectively. In Equation 1 Denotes a phase with a complex channel amplitude and a uniform distribution having a Rayleigh distribution at the time of the i symbol of the i th path of the n th user.

The output of the symbol matching filter 205 is an input signal of a hi-speed router. The fast router 207 serves to connect the matching filter unit and the adaptive filter unit of the adaptive receiver.

FIG. 3 is a diagram referred to in describing a sorting algorithm of the fast router, and illustrates a time relationship diagram of an asynchronous channel in an input signal of an adaptive receiver proposed in the present invention.

In FIG. 3, the reference line represents the reference symbol time of the receiver. Based on this reference symbol time, it can be seen that user 3 has the smallest delay, and then user 1 and 2 have the smallest delay. In FIG. 3, part a denotes the i th symbol of user1. The other user's symbols acting as multiple access interference on this symbol are i-1th symbol (part b) and i-th symbol (part c) because User 2 has a delay greater than User 1, and User 3's delay is Since it is smaller than user 1, it becomes i th symbol (d part) and i + 1 th symbol (e part). Through this process, all symbols that interfere with User 1 can be identified.

For reference, in the reference to the time relationship diagram of FIG. 3, multipath is not considered for convenience of description.

All symbols b, c, d, and e that interfere with the symbols of the first path of the first user selected by the fast router 207 become the tap input signal of the adaptive filter 209. Equation 2 shows a state in which the tap input signal of the adaptive filter 209 is expressed in a vector form.

(2K-1) x1vector u 1 (i):

here, Is disclosed in Equation 1 above, and the filter tap input vector Constituents are the corresponding symbols of the hatched portion shown in FIG.

The tap of the adaptive filter adopts the most common Least Mean Square (LMS) algorithm.

The output signal of the adaptive filter is a symbol of the first path of the first user from which the magnetic interference and multiple access interference have been largely eliminated by the LMS algorithm. At this time, the symbols of the respective paths of the user are coherent combined by the rake receiver structure to form a decision variable. This decision variable is output by a decision device 214 as a hard decision value or a soft decision value. The output of the soft decision value is applied in a system using channel coding such as a mobile communication system.

As a result, in a system in which a soft decision value is applied, the signal of the output value becomes an input signal of a decoder and undergoes a corresponding process.

On the other hand, the configuration of the adaptive receiver according to a preferred embodiment of the present invention shown in FIG. 2 shows a case that is applied to the hard decision method. The symbol thus determined is channel compensated by a channel estimator of the configuration shown in FIG. 4, which is used as a reference signal of the LMS algorithm. At this time, the tap coefficient of the filter is determined as an error signal for correcting the tap coefficient of the filter.

4 is a diagram illustrating an internal configuration of a channel estimator configured in an adaptive receiver according to an exemplary embodiment of the present invention. The operation of the channel estimator applied in the present invention will be described with reference to this.

As shown in FIG. 1, the channel estimator input of the conventional adaptive receiver becomes an input of an adaptive filter front end. However, in the present invention, the matching filter section and the adaptive filter section are configured to be input values of the estimator. The reason for using this structure in the present invention is to compensate for the fact that the tap coefficient of the filter diverges to 0 when channel estimation is performed using only the output signal of the adaptive filter. As a result, the channel estimator 403 compensates the output signal of the determination unit 214 by outputting the final channel estimation value through an internal operation. At this time, the internal operation and the estimator output value in the channel estimator are output by the following equation (3).

here Are inputs to the channel estimator, respectively, and output through the router and output through the adaptive filter. And a and b are arbitrary two weights.

In the simulation results according to the preferred embodiment of the present invention described with reference to FIG. 5 and FIG. 6, a and b in Equation 3 are results of states given as values 1 and 10, respectively.

In addition, the simulation is performed in the above-described environment, and in particular, in the case of multipath, the channel gain is equalized to 1 to receive signal-to-noise according to the number of multipaths. This was done so that the rain did not change. In addition, the simulation experiment sets the tap coefficient for the user signal desired to be detected as the initial condition of the adaptive filter to 1 and the signals of the users acting as other interferences to 0, so that the initial state has the existing matched filter structure. Make the same output as the receiver. Through this, the adaptive receiver according to the present invention does not need a training sequence, thereby having the same effect as a blind adaptive receiver.

The graph result of the state shown in FIG. 5 shows a matched filter receiver (MF), an adaptive receiver (MMSE) according to the prior art of the arrangement shown in FIG. 1, and the present invention of the arrangement shown in FIG. The adaptive receivers (SRMs) show the performance seen in the channel environment of the received signal-to-noise ratio corresponding to 5dB, 7dB, and 10dB. In the simulation of the results shown in FIG. 5, the chip rate transmitted is 3.968 Mcps, the speed of the moving body is fixed at 50 km / h, and the number of users is 20 at the current cell radius. In the multipath channel environment, the energy ratio of the dual path is 0, -9.5 dB, and the triple path is 0, -10, -13 dB, respectively.

On the other hand, comparing each receiver in a 20dB AWGN environment similar to the actual level required in a system that does not use channel codes, the MMSE receivers perform 1.7, 4.3, and 6.9dB, respectively, compared to matched filter receivers in each multipath. You can see the benefits. On the contrary, it can be seen from the above result that the SRM receiver according to the preferred embodiment of the present invention has gains of 7.0, 14.5, and 17.0 dB.

FIG. 6 is a graph showing how a matched filter receiver, an MMSE receiver, and an SRM receiver perform according to the number of users of a system. In this case, the gold code having a code length of 31 is used, so the maximum acceptable user number is 33. As shown in the graph of FIG. 6, it can be seen that the difference in performance gain is not severe as there are many users and few users. That is, although the system load is higher than the processing gain, the performance gain of the conventional matched filter receiver of the SRM receiver is maintained.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined not only by the scope of the following claims, but also by the equivalents of the claims.

The present invention as described above has an advantage of implementing a radio signal receiving apparatus having a more improved performance and at the same time efficiently eliminates multiple access interference.

Claims (20)

In the adaptive receiving device of the mobile communication system, A symbol matching filter that converts the matching filter output in each user path in symbol units, An adaptive filter that removes and outputs multiple interferences, A path selector configured to use the converted symbol as an input of an adaptive filter corresponding to each path; And a determination unit for outputting the channel through the adaptive filter by channel estimation and summing, and outputting the summed result as a determination target value. The method of claim 1, wherein the determination unit, A channel estimator for making an appropriate channel estimate as an input signal and an output signal of the adaptive filter and compensating for the determination target value through the estimated channel value; And a summation unit for adding the outputs of the adaptive filter. In the wireless signal adaptive reception method of a mobile communication system, Converting the matched filter output in each user path into symbol units; A second process of using the transformed symbol as an input of an adaptive filter corresponding to each path, and summing channel sums of outputs through the adaptive filter; And a third step of outputting the summed result as a determination target value. The method of claim 3, wherein the third process, A channel estimation process of estimating an appropriate channel as an input signal and an output signal of the adaptive filter and compensating for the determination target value through an estimated channel value; And summing the outputs of the adaptive filters. In the wireless signal receiving apparatus of the direct spread code division multiple access demodulation method mobile communication system, A chip matching filter unit which acquires a corresponding path timing of each user and demodulates and outputs a received signal; A symbol matching filter unit for demodulating the output signal in symbol units as a corresponding code sequence of each user, and outputting the demodulated signal; A user path selector configured to select a path of each user by referring to whether the signal demodulated in the symbol unit is delayed according to a reference symbol time; And an adaptive filter unit which receives a corresponding signal of each selected path as an input, removes multiple interferences as a predetermined adaptive algorithm, and outputs a determination target value. The method of claim 5, And a channel estimating unit configured to estimate an appropriate channel as an input signal and an output signal of the adaptive filter unit, and to compensate for the determination target value through the estimated channel value. The method of claim 6, wherein the channel estimator, And outputting the channel estimation operation and the channel estimation value through Equation 4 below. - ; Output signal of the path selector - ; Output signal of adaptive filter unit a, b; Any two weights The method of claim 5, wherein the adaptive filter unit, A device characterized by eliminating multiple magnetic interference and multiple access interference through a Least Mean Squre (LMS) algorithm. The method of claim 5, wherein the chip matching filter unit, And a chip matching filter group consisting of K users and L multipaths within a current cell radius. 6. The apparatus of claim 5, wherein the symbol matching filter unit demodulates the symbol unit using symbol (5) and outputs the demodulated data. 6. - ; Output of the symbol matching filter of the first user's first path, sampled at the i symbol time. The first term of the right term; The i th symbol of user 1 damaged by the channel. -Second term of right term; Self-interference due to different paths of magnetic signal. -Third and last term; Multiple access interference (MAI) and white Gaussian noise (AWGN), respectively. - ; Phase with complex channel amplitude and uniform distribution with a Rayleigh distribution at the i th symbol time of the i th path of the n th user. The method of claim 5, wherein the user path selector, A selection unit for selecting a symbol affecting a specific user, including a buffer having a predetermined size, through the spirit algorithm; And an alignment unit to align the selected symbols to be an input vector of the adaptive filter unit. The method of claim 5 or 11, wherein the user path selection unit, The apparatus characterized in that for outputting the determination target value after removing the multiple interference through the equation (6). (2K-1) x1vector u 1 (i): ; Filter tab input vector. In the wireless signal reception method of the direct spread code division multiple access demodulation method, A first process of demodulating and outputting a received signal by acquiring a corresponding path timing of each user; A second process of demodulating the output signal in symbol units as a corresponding code sequence of each user; A third process of selecting a path of each user by referring to whether the signal demodulated in the symbol unit is delayed according to a reference symbol time; And a fourth process of receiving a corresponding signal of each selected path as an input and removing a multiple interference as a predetermined adaptive algorithm and outputting a determination target value. The method of claim 13, And a channel estimation process for estimating an appropriate channel as a determination target value from which the multiple interferences are removed and the corresponding signal of each of the selected paths, and compensating for the determination target value through the estimated channel value. How to. The method of claim 14, wherein the channel estimation process, A channel estimation operation and a channel estimation value are output through Equation 7 below. - ; Output signal of the path selector - ; Output signal of adaptive filter unit a, b; Any two weights The method of claim 13, wherein the fourth process, A method of eliminating multiple magnetic interference and multiple access interference through a Least Mean Squre (LMS) algorithm. The method of claim 13, wherein the first process comprises: A method of demodulating and outputting a received signal by acquiring a corresponding path timing of each user through chip matching filtering consisting of K users and L multipaths within a current cell radius. The method of claim 13, wherein the second process, Demodulating by a symbol unit through the equation (8) and outputs. - ; Output of the symbol matching filter of the first user's first path, sampled at the i symbol time. The first term of the right term; The i th symbol of user 1 damaged by the channel. The second term of the right term; Self-interference due to different paths of magnetic signal. -Third and last term; Multiple access interference (MAI) and white Gaussian noise (AWGN), respectively. - ; Phase with complex channel amplitude and uniform distribution with a Rayleigh distribution at the i th symbol time of the i th path of the n th user. The method of claim 13, wherein the path selection process of each user in the third process, A selection process of selecting a symbol affecting a specific user through a predetermined size of buffer through the spirit algorithm; And sorting the symbols selected in the selection process as predetermined input vectors. 20. The method of claim 13 or 19, wherein the path selection process of each user, The method characterized in that for outputting the determination target value after removing the multiple interference through the equation (9). (2K-1) x1vector u 1 (i): ; Filter tab input vector.