KR100254515B1 - Symbol-by-symbol based multistage interference canceller on multipath channels - Google Patents

Abstract

PURPOSE: An apparatus for eliminating cascade adaptive interference in symbol unit is to eliminate the interference from a signal synthesized by a rake receiver in the symbol unit to remove a feedback structure due to re-spreading, thereby simplifying a structure of the apparatus. CONSTITUTION: A receiving portion(410) receives a baseband signal to estimate a transmitting symbol. A deciding portion(420) decides an estimated value of the receiving portion as an original transmitting symbol according to a size thereof. An adaptive filtering portion(430) receives the estimated value of the receiving portion and the symbol decided by the deciding portion, and adjusts a coefficient generated at a calculating process therein to output the same signal as a predetermined reference value. The receiving portion is comprised of a plurality of receiving units for receiving the baseband signal to estimate the transmitting symbol. The receiving unit is a rake receiver or a matching portion. The deciding portion is comprised of a plurality of deciding units for deciding the estimated value of the receiving portion as the original transmitting symbol according to the size thereof. The adaptive filtering portion is comprised of a plurality of adaptive filtering units for receiving the estimated value of the receiving portion and the symbol decided by the deciding portion to perform the adaptive filtering operation.

Description

Symbolic Multistage Adaptive Interference Canceller in Multipath Channels

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an adaptive interference canceller for canceling the interference of a combined signal in a multipath channel. In particular, the present invention relates to multiple access interference and symbols encountered by a base station in a system using DS / CDMA (Direct Sequence Code Division Multiple Access). The present invention relates to a symbol-based multistage adaptive interference canceller that removes interference between symbols.

In general, in a DS / CDMA system, multiple users communicate on the same channel using a pre-assigned spreading sequence, so that in case of reverse communication from a mobile station to a base station, Signals by the users at the location enter the base station at the same time, the size of the signal received from the base station is different depending on the location of the mobile station.

1 is a structural diagram of a receiver of a conventional multipath channel.

As shown in FIG. 1, a conventional multipath channel interference cancellation receiver includes a receiver 110 for receiving a baseband signal r (t) transmitted from a user's terminal and predicting a size of a transmission symbol; The determiner 120 determines the largest predicted value among the predicted values of the receiver 110 as a received symbol, demodulates the determined received symbol into an original transmitted symbol, and transmits the result to the outside.

The receiver 110 is composed of a plurality of receivers 110-1 to 110-k.

A plurality of receivers 110-1 to 110-k receive signals transmitted through different paths at the same time, and a rake receiver or matching device for adding and receiving the received signals is used.

The rake receiver is composed of a plurality of fingers (finger) that can detect the input signal for each path.

The determination unit 120 is composed of a plurality of determination units 120-1 to 120-k.

The receiver 110 and the determiner 120 are disposed in the base station, and receive a signal transmitted from the terminal to relay the signal to a place where the user of the terminal wants to transmit.

The operation of the receiver of the conventional multipath channel having the above structure will be described in detail as follows.

When k users transmit transmission symbols using their respective terminals, the k receivers 110-1 through 110-k located in the base station are each code division multiple access modulated baseband signals r (t). Are respectively received, and k receivers 110-1 through 110-k predict the magnitude of the original transmission symbol based on the received baseband signal r (t) to predict the predicted values y ₁ (i) to y _k. (i)) are transmitted to k determiners 120-1 through 120-k, respectively. The k determiners 120-1 through 120-k then receive the largest predicted value among the predicted values y ₁ (i) through y _k (i) of the _k receivers 110-1 through 110-k, respectively. After determining the symbol, the determined received symbols are respectively determined as original transmission symbols b ₁ (i) to b _k (i) and transmitted to the outside.

However, in order to remove edges in the conventional multipath channel receiver as described above, there has been a problem in that partial cross-correlation between signals of all paths of all users must be known and the magnitude of signals of all paths must be estimated.

2 shows a block diagram of a sequential interference cancellation receiver using conventional respreading.

As shown in FIG. 2, a sequential interference cancellation receiver using a conventional respread includes a buffer 210 temporarily storing a baseband signal r (t) transmitted from a user's terminal, and a buffer 210. A plurality of receivers 220-1 through 220-k for receiving the corresponding baseband signal outputted and predicting a transmission symbol, and a predicted value of the plurality of receivers 220-1 through 220-k as the original transmission symbols are '0'. Through the plurality of determination units 230-1 to 230-k determining a symbol of '1' or '1', and the plurality of determination units 230-1 to 230-k using a spreading code designated for each user in advance. Provides a control signal by arranging the symbols predicted through the plurality of respreaders 240-1 through 240-k and the plurality of receivers 220-1 through 220-k in order of magnitude. According to the control unit 250 and the control signal output from the control unit 250, the signals re-spread through the plurality of re-diffusion units 240-1 to 240-k A plurality of switching units 260-1 to 260-k for switching, a redistribution bus 270 that transfers the signals re-spread through the plurality of switching units 260-1 to 260-k, and a buffer 210. Delay unit 280 for delaying the baseband signal (r (t)) output from the delay, and through the delayed baseband signal (r (t)) and the re-spread bus 270 And a subtractor 290 for subtracting the respread signal.

A plurality of receivers 220-1 to 220-k are used for rake receivers and matching devices, respectively.

The plurality of respreaders 240-1 to 240-k respread the input signals using different codes for each user.

Referring to the operation of the conventional parallel interference canceller having the structure as described above in detail as follows.

The buffer 210 temporarily stores and outputs the baseband signal r (t) transmitted from the terminals of the users. Here, the baseband signal r (t) is a signal obtained by combining signals transmitted from terminals of various users.

The plurality of receivers 220-1 to 220-k receive corresponding baseband signals output from the buffer 210, predict the transmission symbols, and output the predicted symbols to the plurality of demodulators 230-1 to 230-k. The plurality of determination units 230-1 to 230-k respectively determine predicted values of the plurality of receivers 220-1 to 220-k as '0' or '1', which are transmission symbols, and control the determined reception symbols. Output to 250 and a plurality of re-diffusion units 240-1 to 240-k.

The plurality of respreading units 240-1 to 240-k respread the demodulated signals output from the plurality of determination units 230-1 to 230-k by using a predetermined code for each user. Output at (260-1 to 260-k).

For example, assuming that the demodulation signal output from the demodulator 230-1 is r1 and the spreading code predetermined in the respreader 240-1 is α, the respreader 240-1 is αr1. The respread signal is output to the switching unit 260-1. Further, assuming that the demodulation signal output from the demodulator 230-k is rk and the spreading code designated in advance in the respreader 240-k is β, the respreader 240-k is respread to be βrk. The signal is output to the switching unit 260-k.

The controller 250 arranges the signals predicted by the plurality of receivers 220-1 to 220-k in order of magnitude, and provides a control signal according to the size of the arranged signals to provide a plurality of switching units 260-. 1 to 260-k).

For example, if the signal output from the demodulator 230-1 is the largest, turn on the switching unit 260-1, and if the signal output from the demodulator 230-2 is the largest, the switching unit Turn on (260-2).

Then, in the following, r1 output signal of the receiver 220-1, r2 output signal of the receiver 220-, r3 output signal of the receiver 220-3 and output signal of the receiver 220-k Assume rk and also assume rk <--- <r3 <r2 <r1.

The controller 250 arranges the signals output from the plurality of receivers 220-1 to 220-k in the order of rk, ---, r3, r2, r1, and outputs r1, which is the largest signal, to the user1. After determining and outputting d1, a control signal is provided to turn on the switching unit 260-1.

The switching unit 260-1 transmits the signal re-spreaded through the respreader 240-1 to the subtractor 290 through the respread bus 270, and the subtractor 290 transmits the delay unit 280. Delay the signal r '(t) subtracted by subtracting the signal re-spreaded by the respreader 240-1 from the baseband signal r (t) transmitted through the delay unit 280 again. do. Here, the delay unit 280 is a signal output from the buffer 210 through the receiver 220-1, the demodulator 230-1, the re-spreader 240-1 and the switching unit 260-1 Delay the baseband signal r (t) by the time it reaches up to adder 290.

Subsequently, r '(t) from which the signal of the user 1 having the largest signal is removed is input again to the plurality of receivers 220-1 to 220-k for the users 2 to k, and the size is estimated again. Repeat for the user of the signal.

This process is repeated for all users to obtain the final decision values d1 to dk.

However, the conventional sequential interference cancellation receiver as described above has to be rearranged in order of magnitude whenever the signal size changes, and it is difficult to accurately estimate the magnitude of the signal coming into each finger of the rake receiver in a fading environment. There was this. In addition, since it must be performed sequentially for each user, a high speed is required, and there is a problem of being complicated in proportion to the number of fingers of the rake receiver.

Figure 3 shows a block diagram of a two stage parallel interference canceller using conventional respreading.

As shown in FIG. 3, a two-stage parallel interference canceller using conventional respreading includes a buffer 310 and a buffer 310 that temporarily store a baseband signal r (t) transmitted from a user's terminal. Receiving the corresponding baseband signal outputted from the plurality of receivers 320-1 to 320-k and the predicted values of the plurality of receivers 320-1 to 320-k, respectively. Through a plurality of determination units 330-1 through 330-k and a plurality of determination units 330-1 through 330-k that determine the received symbols and determine and output the determined received symbols as original transmission symbols, respectively. After reading the determined symbols, re-spread the largest signal to the corresponding baseband signal, subtract the re-spread signal from the baseband signal r (t) output from the buffer 310, and remove it as a result of the subtraction. Interference estimation and removal unit 340 for outputting the baseband signal, and a plurality of judging unit (350-1) 350-k).

The plurality of receivers 320-1 to 320-k each use a rake receiver.

Referring to the operation of the conventional parallel interference canceller having the structure as described above in detail as follows.

The buffer 310 temporarily stores the code division multiple access modulated baseband signal r (t) for transmission symbols transmitted from k terminals, and then k receivers 320-1 to 320-k and interference estimation. And remover 340.

The k receivers 320-1 to 320-k respectively predict the magnitude of the original transmission symbol by the corresponding baseband signal in the baseband signal r (t) transmitted from the buffer 310 to obtain k prediction values. Output to the determination parts 330-1 to 330-k. Subsequently, the k decision units 330-1 to 330-k determine the received prediction symbol that is the largest predicted value among the corresponding prediction values output from the k determination units 330-1 to 330-k, respectively, and then determine the determined reception symbol. It determines the original transmission symbol and outputs it to the interference estimation and removal unit 340.

Then, the interference estimator and remover 340 reads the demodulated symbols through the k determiners 330-1 through 330-k, and then respreads them into corresponding baseband signals that are output to the outside as the largest signal. A signal obtained by respreading the demodulation symbol output from the step 330-1 is subtracted from the baseband signal r (t) output from the buffer 310. Subsequently, the subtracted baseband signals are inputted back into k receivers 320-1 to 320-k to repeat the above process.

The interference estimator and remover 340 sequentially performs the above process to determine all output signals of the k determiners 330-1 to 330-k.

Therefore, the conventional parallel interference canceller double modulates and demodulates the baseband signal as described above, thereby transmitting a more accurate transmission symbol to the outside.

However, since the conventional parallel interference canceller as described above needs to know spreading codes for all users, there is a problem in that partial cross-correlation between spreading codes of users must be obtained in order to estimate the amount of interference from other users. In addition, in a fading environment, it is difficult to accurately estimate the magnitude of a signal received by each finger of the rake receiver, and there is a problem that it is complicated in proportion to the number of fingers of the rake receiver.

In addition, Figures 2 and 3 above use respreading, so basically the number of fingers is equal to the number of multipaths. Therefore, since the respread bus for respreading forms a feedback structure from the output of the rake receiver back to the input of the rake receiver, it is difficult to control, and the size of the signal received by each finger of the rake receiver for respreading is difficult to control. Since all of them need to be estimated, a large amount of computation is required, and a canceller is added to each finger of the rake receiver, which causes a complexity in proportion to the number of fingers.

Accordingly, the present invention devised to solve the above-described problems, by eliminating the interference by the symbol unit by using the signal coupled by the rake receiver as the object of interference cancellation, eliminating the feedback structure due to re-spreading It is an object of the present invention to provide a multi-path channel-by-symbol multi-stage adaptive interference canceller that can be implemented in a very simple manner so that the complexity is independent of the number of internally configured reception functions (Fingers) of the rake receiver.

1 is a block diagram of a receiver of a conventional multipath channel.

2 is a block diagram of a sequential interference canceller using conventional respreading.

3 is a block diagram of a two stage parallel interference canceller using conventional respreading;

4 is a block diagram of an embodiment of a symbol unit multistage adaptive interference canceller of a multipath channel according to the present invention;

5 is a block diagram of an embodiment of the adaptive filter of FIG.

Explanation of symbols on the main parts of the drawings

410: receiving unit 420: determining unit

430: adaptive filtering unit 410-1 to 410-k: receiver

420-1 to 420-k: determiner 430-1 to 430-k: adaptive filter

In order to achieve the above object, a multi-stage adaptive edge eliminator of a multipath channel of the present invention includes: receiving means for receiving baseband signals received from terminals to predict transmission symbols; Judging means for judging the predicted value of the receiving means as an original transmission symbol according to the magnitude; And adaptive filtering means for receiving a predicted value of the receiving means and a symbol determined by the determining means, adjusting a coefficient generated in an internal calculation process and outputting a signal equal to a preset reference value.

Hereinafter, a preferred embodiment of the present invention will be described with reference to FIG. 4.

4 is a block diagram of an embodiment of a symbol unit multi-stage adaptive interference canceller of a multipath channel according to the present invention.

As shown in FIG. 4, the symbol-level multi-stage adaptive interference canceller of the multipath channel according to the present invention receives a baseband signal r (t) received from users' terminals and predicts a transmission symbol. And the determination unit 420 for determining the predicted value of the receiver 410 as an original transmission symbol according to the magnitude, and receiving the predicted value of the receiver 410 and the symbol determined through the determination unit 420 to perform adaptive filtering. An adaptive filtering unit 430 is provided.

The receiving unit 410 is composed of a plurality of receivers 410-1 to 410-k that receive baseband signals r (t) received from users' terminals and predict transmission symbols, respectively.

A plurality of receivers 410-1 to 410-k are each used with a rake receiver, matcher, and the like.

The determination unit 420 is composed of a plurality of determiners 420-1 to 420-k which respectively determine predicted values of the plurality of receivers 410-1 to 410-k according to their magnitudes as original transmission symbols.

The adaptive filtering unit 430 receives the predicted values of the plurality of receivers 410-1 to 410-k and the symbols determined through the plurality of determiners 420-1 to 420-k and performs adaptive filtering respectively. Adaptive filters 430-1 to 430-k.

The plurality of adaptive filters 430-1 to 430-k includes k decision symbols, which are determination values of the determiners 420-1 to 420-k for each user, and each adaptive filter 430-1 to 430-k. An adaptive filtering process is performed by receiving one predicted value and a total of k + 1 of the corresponding receivers 420-1 to 420-k. Here, the adaptive filter is a filter for adjusting the coefficient to output the input signal equal to the reference value, which is a well-known technique and used in the present invention as shown in FIG. 5.

The detailed operation of the symbol unit multi-stage adaptive interference canceller of the multipath channel of the present invention having the structure as described above will be described first after explaining the adaptive filter shown in FIG.

FIG. 5 is a block diagram of an embodiment of the adaptive filter of FIG. 4.

The adaptive filter comprises a total of k transmission symbols determined by the plurality of determiners 420-1 to 420-k and a predicted value of the receiver 410-1 among the plurality of receivers 410-1 to 410-k. Get k + 1 inputs. Here, description is made with k + 1 set to n for convenience of explanation.

As shown in FIG. 5, the adaptive filter of FIG. 4 includes a plurality of delay units 511 to 51n and a plurality of delay units 511 to 51n for delaying the plurality of input signals I1 to In, respectively. A multiplier 521 to 52n for multiplying the delayed signal with the coefficient transmitted from the coefficient adaptor 560, an adder 530 for adding a multiplier multiplied by the plurality of multipliers 521 to 52n, and an adder; A determiner 540 for determining the added value added at 530 as a transmission symbol according to the magnitude, a subtractor 550 for subtracting the added value of the adder 530 from the value determined through the determiner 510, A coefficient adaptation unit 560 for correcting the coefficient by using the subtracted value of the subtractor 550 as an error is provided.

The plurality of delay units 511 to 51n include a plurality of delay units ((511-1 to 511-m) to (51n-1 to 51n-m) for sequentially delaying the plurality of inputs I1 to In, respectively. It is provided.

The plurality of multipliers 521 to 52n receive signals delayed through the plurality of delay units (511-1 to 511-m) to (51n-1 to 51n-m) and coefficients transmitted from the coefficient adaptation unit 560. And a plurality of multipliers (521-1 to 521n-m) to (52n-1 to 52n-m), each of which is multiplied by. M is a natural number of 1 or more.

The coefficient adaptation unit 560 corrects the coefficient so that the error value is '0', and various adaptive filtering methods such as LMS and RLS may be used as the correction method.

Referring to the operation of the adaptive filter applied to the present invention having the structure as described above in detail as follows.

The plurality of delayers 511-1 to 511-m sequentially delay the input signal I1 and transmit the delayed signals to the plurality of multipliers 521-1 to 521-m. Subsequently, the multipliers 521-1 to 521-m multiply the coefficients transmitted from the coefficient adaptation unit 560 with the output signals of the plurality of delayers 511-1 to 511-m, respectively, and add the multiplied values. Output to (530).

Similarly, the plurality of delay units (512-1 to 512-m) to (51n-1 to 51n-m) perform the same process as described above with respect to the plurality of input signals I2 to In. Multiple multipliers ((521-1 to 521n-m) to (52n-1 to 52n-m)) also have multiple delayers ((512-1 to 512-m) to (51n-1 to 51n-m). The multiplier multiplies the output values of the multipliers by the coefficients transmitted from the adaptive coefficient unit 560 and outputs the multiplied value to the adder 530.

This process is commonly referred to as aftermath.

Subsequently, the subtractor 530 adds the multiplication values transferred from the plurality of multipliers 521 to 52n and outputs the result to the determiner 540. The determiner 540 determines the output of the filter process as a transmission symbol according to the size and outputs the result to the subtractor 550.

The subtractor 550 outputs an error obtained by subtracting the addition value of the adder 530 from the value determined by the determiner 510 to the coefficient adaptor 560. Subsequently, the coefficient adaptor 560 receives an error that is a subtracted value of the subtractor 550, and if the error is greater than '0', the coefficient adaptor 560 constantly increases each coefficient in consideration of the current error and the delayed error of the previous step. Or, if it is smaller than '0', the process of decreasing each coefficient is repeatedly performed.

This process is performed at the same time for each input, and when the error approaches '0', the coefficient is no longer adapted and the constant adjustment is completed by maintaining a constant value.

Next, the operation of the symbol-level multistage adaptive interference canceller of the multipath channel of FIG. 4 will be described in detail.

The plurality of receivers 410-1 to 410-k receive baseband signals r (t) transmitted from terminals of various users, predict the transmission symbols, and determine the plurality of determiners 420-1 to 420-k. Will output The plurality of determiners 420-1 to 420-k determine the transmission symbol according to the magnitudes of the predicted symbols of the plurality of receivers 410-1 to 410-k, and determine the determined values by the plurality of adaptive filter 430-1. 430-k).

Subsequently, the plurality of adaptive filters 430-1 through 430-k include a plurality of decision symbols which are output signals of the determiners 420-1 through 420-k for all users and the receivers 410-1 through 410 of each user. -k) receives the prediction symbol of the user to which he belongs.

As described with reference to FIG. 5, the plurality of adaptive filters 430-1 to 430-k perform an adaptive filtering process for each user at the same time, and then perform an interference cancellation function by outputting the adaptive filter.

The present invention described above is capable of various substitutions, modifications, and changes without departing from the spirit of the present invention for those skilled in the art to which the present invention pertains, and the above-described embodiments and accompanying It is not limited to the drawing.

As described above, the symbol-level multistage adaptive interference canceller of the multipath channel of the present invention removes the interference by the symbol unit by using the signal coupled by the rake receiver as the object of interference cancellation, thereby making it possible to obtain a rake in the existing system. Regardless of the structure of the receiver, it can be added to the system, and the complexity is irrelevant to the number of fingers of the rake receiver, which is very simple to implement. In addition, unlike the conventional method, it is very easy to control by eliminating the feedback structure, and since the amount of interference is estimated by using an adaptive algorithm, it does not require information on spreading codes of other users.

Claims (8)

Receiving means for receiving baseband signals received from the terminals to predict transmission symbols; Judging means for judging the predicted value of the receiving means as an original transmission symbol according to the magnitude; And Adaptive filtering means for receiving the predicted value of the receiving means and the symbol determined by the determining means, and adjusting the coefficient generated in the internal calculation process to output the same signal as the preset reference value. The symbol unit multi-stage adaptive interference canceller of the multipath channel comprising a. The method of claim 1, The receiving means, A plurality of receivers for receiving the baseband signals received from the terminals to predict the transmission symbol, respectively The symbol unit multi-stage adaptive interference canceller of the multipath channel comprising a. The method of claim 2, The plurality of receivers, A symbol unit multi-stage adaptive interference canceller of a multipath channel, wherein a rake receiver or a matcher is used, respectively. The method of claim 2, The determination means, A plurality of determination units that respectively determine predicted values of the plurality of receivers as original transmission symbols according to their sizes; The symbol unit multi-stage adaptive interference canceller of the multipath channel comprising a. The method of claim 4, wherein The adaptive filtering means, A plurality of adaptive filters for receiving the predicted values of the plurality of receivers and the symbols determined through the plurality of determination units to perform adaptive filtering respectively The symbol unit multi-stage adaptive interference canceller of the multipath channel comprising a. The method of claim 5, The plurality of adaptive filters, respectively A plurality of delay means for delaying each of the plurality of input signals; A plurality of multiplication means for multiplying the delayed signal through the plurality of delay means and the coefficient transmitted from the coefficient adaptation means; Addition means for adding multiplication values multiplied by the plurality of multiplication means; A judging unit for judging the addition value added by said adding means according to the magnitude | size as a transmission symbol; Subtraction means for subtracting an addition value of the addition means from the value determined by the determiner; And The coefficient adaptation means for correcting the coefficient by taking the subtracted value of the subtraction means as an error The symbol unit multi-stage adaptive interference canceller of the multipath channel comprising a. The method of claim 6, The plurality of delay means, respectively A plurality of delay units for sequentially delaying the plurality of input signals, respectively The symbol unit multi-stage adaptive interference canceller of the multipath channel comprising a. The method of claim 7, wherein The multiplication means, A plurality of multipliers for multiplying the delayed signal through the plurality of delay means and the coefficient transmitted from the coefficient adaptation means, respectively The symbol unit multi-stage adaptive interference canceller of the multipath channel comprising a.

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