KR100462022B1 - Apparatus and method for group-wise interference cancellation in a mobile communication system - Google Patents

Abstract

In the interference cancellation apparatus, a baseband signal input to a detector is input to a plurality of fingers, each finger detecting a multipath signal of each user, and estimating a channel of the baseband signal. Next, the maximum ratio combiner outputs the soft bit determination value through the signal and channel estimate despread and output from the finger. The signal regenerator regenerates the baseband signal through the hard bit determination value and the channel estimate obtained from the funger. The SIR meter measures the SIR through the soft bit decision value and the channel estimate obtained from the despreader. The signal selector compares the SIR measurement of each detector with the target SIR, and when the SIR measurement exceeds the target SIR, selects a reproduction signal output from the corresponding detector and groups the received signals. The subtractor subtracts the reproduced signals selected by groups from the signal selector from the baseband signal output from the buffer to remove interference.

Description

Apparatus and method for eliminating interference in mobile communication systems {APPARATUS AND METHOD FOR GROUP-WISE INTERFERENCE CANCELLATION IN A MOBILE COMMUNICATION SYSTEM}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for interference cancellation in a mobile communication system, and more particularly, to a method for canceling interference by groups for reducing multiple access interference in a code division multiple access (CDMA) system.

In the CDMA system, since signals transmitted in the same frequency band are mixed and received at each mobile station using a unique spreading code, the performance of the system is degraded by the multiple access interference generated during despreading of the received signal. Therefore, in order to increase the performance and capacity of the system, a subtractive interference cancellation method has been proposed, which removes an interference signal other than a magnetic signal from a received signal in which several user signals are mixed. Subtractive interference cancellation methods include a successive interference cancellation (SIC) scheme for removing interference signals one by one and a parallel interference cancellation (PIC) scheme for simultaneous cancellation. Serial interference cancellation improves the performance of the system, but it introduces time delays and is difficult to implement in a real system. Parallel interference cancellation has a problem in that performance is degraded in a multipath fading environment in which channel variation is severe. In order to compensate for the disadvantage of the subtracted interference cancellation method, a method of performing interference cancellation by grouping interference into groups has been proposed.

Methods for removing interference by group include a method of removing interference by grouping signals according to signal power, selecting a group from the larger signal power in order, weighting each group, and then removing interference at the same time. Then, the signals are grouped by fingers according to the power of the received signal to select from the group with the largest signal power, subtract the reproduced signal to perform interference cancellation, and then add them again at the next interference cancellation step. There is a way.

The interference cancellation method proposed in the prior art divides the group in consideration of the power of the transmission signal, the data rate during multiple transmission, or the strength and maximum ratio combiner output value of the received signal. However, in a multipath fading channel environment, even if a strong signal is transmitted, the signal power may be very weak at the time of reception, and this signal is involved in interference cancellation, resulting in performance degradation. Also, in the case of multi-data rate transmission, since the bit length is different for each signal, it is more reliable that the instantaneous bit energy is higher than the instantaneous power at the time of reception. There is a problem that is not.

In addition, in the conventional grouping method, the number of signals for each group for interference cancellation must be determined in advance, or the number of signals for each group is predetermined according to the transmission speed at the time of transmission. However, the optimum value of the number of signals per group cannot be known in advance, and even if the number of signals per group is determined in advance by the transmission rate at the time of transmission, it may not be accurate grouping in a multipath fading channel environment.

An object of the present invention is to provide an interference cancellation apparatus for performing interference cancellation for each group by grouping received signals in accordance with a required bit error rate of a mobile communication system.

1 is a block diagram of an interference cancellation apparatus according to a first embodiment of the present invention.

2 is a schematic block diagram of an interference cancellation apparatus according to a second embodiment of the present invention.

In order to solve this problem, the present invention measures the SIR of the received signal and groups it into an SIR measurement.

An interference cancellation apparatus according to a first aspect of the present invention includes an interference cancellation stage for receiving a baseband signal to remove interference, and a final determination unit for receiving a signal output from the interference cancellation stage and performing hard bit determination. A first interference canceling unit is formed in the interference canceling stage, and the first interference canceling unit includes a plurality of first detectors, signal selectors, and subtractors connected in parallel. The signal selector compares the SIR measurements measured at the plurality of first detectors with a predetermined target SIR, and selects a reproduction signal reproduced in the first detector whose SIR measurements exceed the target SIR. The subtractor subtracts the baseband signal from the baseband signal and outputs the reproduced signal selected by the signal selector.

In this case, the first detector includes a plurality of first fingers, a first maximum ratio combiner, and an SIR meter. The first finger despreads a corresponding path signal among the received signals to determine a channel estimate and reproduces the received signal. The first maximum ratio combiner maximum ratio combines the inversely converted signals from the plurality of first fingers using the channel estimate, and the signal reproducer transmits the soft bit decision value obtained through the first maximum ratio combiner after determining the temporary hard bit. The received signal is reproduced through the same process as when. The SIR meter determines the SIR measurement of the received signal using the channel estimate and the signal output from the first maximum ratio combiner.

Preferably, the interference cancellation stage of the interference cancellation apparatus further includes at least one second interference cancellation unit connected in series to the first interference cancellation unit. The second interference canceller receives a signal output from an adjacent first or second interference canceller, and includes a plurality of first detectors, a signal selector, and a subtractor.

The final judging unit of the interference elimination apparatus preferably includes a plurality of second detectors connected in parallel while receiving signals output from the interference elimination stage. The second detector combines a plurality of second fingers despreading the signal output from the interference canceling stage and a signal maximum despread from the plurality of second fingers and outputs a second maximum ratio of outputting a soft bit determination value. A combiner, and a hard bit determiner for making a bit decision on the soft bit decision value and outputting a final hard bit decision value.

According to a second aspect of the present invention, an interference cancellation method is provided. According to this method, a baseband signal is first inputted to a plurality of detectors, and a signal inputted to each detector through channel estimates of a soft bit decision value determined at the maximum ratio combiner of each detector and a path-specific received signal obtained from the plurality of fingers. SIR is measured. Next, the SIR measured at each detector is compared with a predetermined target SIR to select a first reproduced signal that is reproduced and output at a detector whose measured SIR exceeds the target SIR. Then, the selected first reproduction signal is subtracted from the baseband signal.

In addition, according to the interference cancellation method according to the present invention, it is preferable that the following process is further performed. A baseband signal obtained by subtracting the selected first reproduction signal is input to the plurality of detectors, and the SIR of the signal input to each detector is measured. Next, the SIR measured at each detector is compared with the predetermined target SIR to select a second reproduction signal that is reproduced and output at a detector whose measured SIR exceeds the target SIR. Then, the selected second reproduction signal is subtracted from the baseband signal.

In the interference canceling apparatus according to the third aspect of the present invention, a plurality of interference canceling units respectively receiving the first received signal are connected in series. The interference canceling unit includes a plurality of detectors, signal selectors and subtractors connected in parallel. The signal selector compares the SIR measurements measured at the plurality of detectors with the target SIR, respectively, to select a reproduction signal reproduced at the detector whose SIR measurement exceeds the target SIR, and the subtractor selects the reproduction signal selected at the signal selector in the first received signal. Subtract the output. The detector despreads the second received signal for each path to determine a channel estimate, and uses the channel estimates of the inversely converted signals for each path from the plurality of fingers and the plurality of fingers that generate the reproduced signal by reproducing the second received signal, respectively. And a maximum ratio combiner for making a soft bit decision by combining the maximum ratio, and an SIR measuring device for determining an SIR measurement of the second received signal using the soft bit determination value and the channel estimate determined by the maximum ratio combiner.

In this case, the second received signal input to the plurality of detectors of the interference canceling unit is a signal output from a subtractor adjacent to the interference canceling unit, and the first received signal is input to the plurality of detectors of the first interference canceling unit of the interference removing unit. .

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

Now, a method and apparatus for canceling interference in a mobile communication system according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 is a block diagram of an interference cancellation apparatus according to a first embodiment of the present invention.

As shown in FIG. 1, the interference cancellation apparatus according to the first embodiment of the present invention includes an interference cancellation unit 10 and a final determination unit 20. In general, a digital signal transmitted from a mobile station is received through a receiver antenna (not shown in FIG. 1) and converted into an intermediate frequency (IF) signal through a carrier demodulator and an analog / digital converter. The intermediate frequency (IF) signal is converted into a baseband signal and stored in a buffer through a root shaping filter (not shown) which is the same as the root pulse shaping filter used by each mobile station. An interference cancellation apparatus according to an embodiment of the present invention receives a baseband signal stored in a buffer (not shown) and removes interference.

The interference cancellation unit 10 performs interference cancellation for each baseband signal for each group, and includes a plurality of detectors 100, a signal selector 200, and a subtractor 300 connected in parallel. The plurality of detectors 100 receive each baseband signal provided from a buffer, and include a plurality of fingers 110, a maximum ratio combiner (MRC) 120 and an SIR meter (connected in parallel). 130). A plurality of fingers 110 in each detector 100 receives a baseband signal to detect a plurality of multipath signals, and includes a despreader 112 and a signal regenerator 114.

The despreader 112 generates the same PN code as the PN code used for the transmitted signal by using the input baseband signal, and despreads the baseband signal through the generated PN code to generate a multipath signal of each user. Detect. The despreader 112 estimates the channel through estimation of amplitude, phase, and power values, which are channel parameters. The signal regenerator 114 hard-determines the value obtained by the maximum ratio combiner 120, spreads the same as when transmitting the signal, and then uses the channel estimate obtained by the despreader 112 to obtain the received signal. Play it.

The maximum ratio combiner 120 combines signals that are despread and output from the plurality of fingers 110 in a maximum ratio combining manner using channel estimates, and makes soft bit determinations on them. The SIR measurer 130 calculates an SIR by measuring signal power, interference, and noise power by using a soft bit determination value obtained from the maximum ratio combiner 120 and channel estimates output from the plurality of fingers 110.

The signal selector 200 compares the target SIR determined by the bit error rate (BER) required in the mobile communication system with the SIR measured by the SIR measuring devices 130 inside the plurality of detectors, and compares the results with each other. Accordingly, the internal switch is turned on / off to select signals output from the plurality of detectors 100. That is, the signal selector 200 selects the signals reproduced by the detector 100 whose measured SIR exceeds the target SIR as a group. The subtractor 300 removes the interference by subtracting the signal selected by the signal selector 200 from the baseband signal output from the buffer.

The final determination unit 20 includes a plurality of detectors 400, and the plurality of detectors 400 receive the signal from which the interference is removed from the interference removal unit 10. Each detector 400 includes a plurality of fingers 410, a maximum ratio combiner 420, and a hard bit determiner 430 connected in parallel. The plurality of fingers 410 includes a despreader 412, similarly to the finger 110, to detect a plurality of multipath signals and to perform channel estimation. The maximum ratio combiner 420 combines the signals despread and output from the plurality of fingers 410 with the maximum ratio and outputs a soft bit determination value. The hard bit determiner 430 makes a hard bit decision on the soft bit decision value, determining the bit as 1 if it is negative or finally determining the bit as -1 if it is negative.

Hereinafter, the interference cancellation method in the interference cancellation apparatus will be described in detail.

First, the baseband signal output from the buffer is input to each detector 100 of the interference cancellation device, and the baseband signal input to the detector 100 is input to the plurality of fingers 110. Each finger 110 despreads the baseband signal through the despreader 112 to detect the multipath signal of each user, and estimates the channel of the baseband signal. Next, the maximum ratio combiner 120 performs soft bit determination using the signal and the channel estimate despread and output from the finger 110.

The hard bit determination value is input to the signal regenerator 114, and the signal regenerator 114 reproduces the baseband signal through the soft bit determination value and the channel estimate obtained by the despreader 112. The soft bit determination value and the channel estimate obtained by the despreader 112 are input to the SIR meter 130, and the SIR meter 130 measures the signal power and the interference and noise power to obtain the SIR.

The SIR measurement value measured by the SIR meter 130 of each detector 100 and the reproduction signal of the signal regenerator 114 are input to the signal selector 200 in the interference cancellation device. The signal selector 200 compares the SIR measurement and the target SIR of each detector 100 and selects a reproduction signal output from the corresponding detector 100 when the SIR measurement exceeds the target SIR, and the SIR measurement does not exceed the target SIR. If not, the reproduction signal of the detector 100 is not selected. In this way, the signal selector 200 groups the reproduction signals of the plurality of detectors 100. The subtractor 300 removes the interference by subtracting the reproduction signal selected for each group in the signal selector 200 from the baseband signal output from the buffer.

Next, the residual signal from which the interference is removed in the interference canceling unit 10 is input to the plurality of detectors 400 in the final determination unit 20, respectively. The maximum ratio combiner 420 in the detector 400 combines the despread signal in the detector 400 with the maximum ratio to output a soft bit decision value, and the hard bit determiner 430 is final for the soft bit decision value. The hard bit is judged and finally determined as a value of 1 or -1 and output.

In the first embodiment of the present invention, interference is removed using one interference canceller 10, but in actual application, a plurality of interference cancellers 10 are used to sequentially remove interference for each group. Hereinafter, this embodiment will be described in detail with reference to FIG. 2.

2 is a schematic block diagram of an interference cancellation apparatus according to a second embodiment of the present invention.

As shown in FIG. 2, the interference canceling apparatus according to the second embodiment of the present invention has the same structure as the first embodiment of the present invention except for the plurality of interference canceling units 10a, 10b,. Have

In detail, the plurality of interference canceling units 10a, 10b, ..., 10n are connected in series, and each has the same structure as the interference canceling unit 10 in the first embodiment. The plurality of interference cancellers 10a, 10b, ..., 10n form one interference canceller. The interference canceling unit 10a receives the baseband signal from the buffer and removes the interference in the same manner as the interference canceling unit 10 in the first embodiment. Next, the plurality of detectors 100 of the interference canceling unit 10b receive a residual signal from which the interference is removed from the interference canceling unit 10a instead of the baseband signal. Then, the plurality of detectors 100 of the interference canceling unit 10b undergo the same process as described above to reproduce the residual signal and measure the SIR. The signal selector 200 of the interference canceller 10b groups and selects a reproduction signal of the residual signal using the measured SIR, and the subtractor 300 of the interference canceller 10b selects the reproduced signal selected from the baseband signal. Subtract the output. Similarly, the interference canceling units 10c, ..., and 10n respectively receive and output interference by subtracting from the subtracting unit 300 of the interference canceling units 10b, ..., 10m to the baseband signal. .

The baseband signal from which the interference has been removed by the last interference canceling unit 10n is input to the final determining unit 20, and a hard bit is determined to have a value of 1 or -1 and finally output.

Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

As described above, according to the present invention, given the required bit error rate of the system in any environment, the system itself can be grouped by the received signal according to the system itself according to the required bit error rate, the performance of the system compared to the conventional method for removing interference by group Overdose can be improved.

Claims (9)

A plurality of first detectors receiving baseband signals and connected in parallel, the signal to interference ratio (SIR) measurements measured at each of the plurality of first detectors are compared with a predetermined target SIR to determine the target SIR. A first interference canceller including a signal selector for selecting a reproduced signal reproduced by the first detector that surpasses, and a subtractor for subtracting and outputting a reproduced signal selected by the signal selector from the baseband signal; Receiving interference elimination stage, and Final determination unit for receiving a signal output from the interference cancellation stage to determine the hard bit Including; Each of the first detector, A plurality of first fingers despreading corresponding path signals among the received signals to determine channel estimates respectively, and reproducing the received signals to generate the reproduced signals; A first maximum ratio combiner for maximum ratio combining the inversely converted signals from the plurality of first fingers using the channel estimate, and A SIR meter that determines the SIR measurement of the received signal using the signal output from the first maximum ratio combiner and the channel estimate Apparatus for removing interference in a mobile communication system comprising a. The method of claim 1, The interference cancellation stage further includes at least one second interference cancellation unit connected in series to the first interference cancellation unit, The at least one second interference canceling unit receives a signal output from the adjacent first or second interference removing stage as the received signal, and the plurality of first detectors, the signal selector, and the subtractor connected in parallel. Apparatus for removing interference in a mobile communication system, each including. The method according to claim 1 or 2, The plurality of first fingers may include a despreader for despreading a corresponding path signal among the received signals to determine a channel estimate, and the reproduction using the soft bit determination value determined by the first maximum ratio combiner and the channel estimate. Each includes a player for generating a signal, The first maximum ratio combiner outputs the soft bit determination value by combining the inversely converted signals from the plurality of first fingers by using the channel estimate. The SIR meter determines the SIR measurement using the soft bit decision value and the channel estimate. Interference Cancellation Device in Mobile Communication System. The method according to claim 1 or 2, The final determining unit includes a plurality of second detectors connected in parallel to receive a signal output from the interference cancellation stage, Each second detector, A plurality of second fingers despreading the signal output from the interference cancellation stage; A second maximum ratio combiner for outputting a soft bit determination value by combining a maximum ratio of signals despread and output from the plurality of second fingers; and A hard bit determiner for making a bit decision on the soft bit decision value and outputting a hard bit decision value Apparatus for removing interference in a mobile communication system comprising a. The method according to claim 1 or 2, And the target SIR is determined by a bit error rate required in the mobile communication system. Receives a received signal and determines a channel estimate of the received signal for each corresponding path, and combines a plurality of fingers inversely converting the received signal and a maximum ratio of the received signals for each path that are despread and output from the plurality of fingers What is claimed is: 1. A method of canceling interference in a mobile communication system comprising at least one interference canceling unit having a plurality of detectors including a maximum ratio combiner for making a bit determination in parallel, A baseband signal is inputted to the plurality of detectors and the input of the signal inputted to each detector through a channel bit estimate of the received signal for each path obtained from the plurality of fingers and the soft bit decision value determined at the maximum non-combiner of each detector. Measuring SIR, Comparing the SIR measured by each detector with a predetermined target SIR, selecting a first reproduced signal reproduced and outputted by a detector whose measured SIR exceeds the target SIR, and Subtracting the selected first reproduction signal from the baseband signal Interference cancellation method in a mobile communication system comprising a. The method of claim 6, A baseband signal obtained by subtracting the selected first reproduction signal is input to the plurality of detectors, and the SIR of the signals input to each of the detectors is measured; Comparing a SIR measured at each detector with a predetermined target SIR, selecting a second reproduced signal that is reproduced and output at a detector whose measured SIR exceeds the target SIR, and Subtracting the selected second playback signal from the baseband signal The interference cancellation method in a mobile communication system further comprising. The method of claim 6, And the target SIR is determined by a bit error rate required in the mobile communication system. A plurality of detectors connected in parallel, A signal selector for comparing a signal to interference ratio (SIR) measurement measured at the plurality of detectors with a target SIR to select a reproduced signal reproduced at a detector where the SIR measurement exceeds the target SIR, and A subtractor for subtracting and outputting a reproduction signal selected by the signal selector from a first received signal; A plurality of interference cancellers each including are connected in series, Each detector, A plurality of fingers despreading a second received signal input to a detector for each path to determine a channel estimate, and reproducing the second received signal to generate the reproduced signal, respectively; A maximum ratio combiner configured to perform a maximum ratio combining of the inversely converted signals for each path in the plurality of fingers by using the channel estimate, and A SIR measurer that determines the SIR measurement of the second received signal using the soft bit decision value determined by the maximum ratio combiner and the channel estimate Including; The second received signal input to the plurality of detectors of the interference cancellation unit is a signal output from a subtractor of an adjacent interference cancellation unit, and the first reception signal is provided to the plurality of detectors of the first interference cancellation unit of the interference cancellation unit. Apparatus for eliminating interference in an inputted mobile communication system.