KR20070058271A - Apparatus and method for cancelling neighbor cell interference signal in a receiver of an orthogonal frequency division multiplexing access system - Google Patents

Abstract

A method for canceling neighbor cell interference signals in a receiver of an OFDMA(Orthogonal Frequency Division Multiplexing Access) system and a device therefor are provided to remarkably improve reception performance of a terminal in comparison with an existing receiver even in an area where signal interference with an inter-cell border region is serious, by using the receiver having an interference canceller. A controller measures CINR(Carrier to Interference Noise Ratio) values of interference signals of BSs(Base Stations)(1201), and selects interference signals to be cancelled(1203). The controller determines an interference signal having the highest CINR value(1205), and detects interference signals to be controlled by performing a decoding process(1207-1211). A transmission module regenerates interference signals(1213), and subtracts the regenerated interference signals(1215).

Description

FIELD OF THE INVENTION AND METHOD AND APPARATUS FOR CANCELING NECESSARY CELL INTERFERENCE SIGNALS IN THE RECEIVER OF OCTOOUS FREQUENCY SPLITTING MULTIPLE ACCESS SYSTEM {APPARATUS AND METHOD FOR CANCELLING

1 is a block diagram showing the configuration of a typical transmitter in an OFDMA system

2 is a block diagram showing the configuration of a typical receiver in an OFDMA system

3 is a diagram illustrating a structure of a frame transmitted and received in an IEEE 802.16 based OFDMA system

4 is a flowchart illustrating a process of decoding a downlink burst in a receiver of a typical OFDMA system.

5 is a block diagram illustrating an example of a configuration of a receiver for removing interference signals in an OFDMA system according to the present invention.

6 is a flowchart illustrating a method of canceling an interference signal according to an embodiment of the present invention.

7 illustrates a structure of a preamble pilot signal in an IEEE 802.16 based OFDMA system

8 is a diagram illustrating a sector structure when a mobile terminal is located in a cell overlap region formed by three base stations of an OFDM system.

9 illustrates a structure of a pilot signal in a PUSC substitution scheme

10 is a block diagram showing another configuration example of a receiver for removing an interference signal in an OFDMA system according to the present invention.

11 is a view showing the BER performance of the receiver with an interference signal cancellation apparatus according to the present invention

12 is a flowchart illustrating a method of canceling an interference signal according to another embodiment of the present invention.

13 is a flowchart illustrating a method of canceling an interference signal according to another embodiment of the present invention.

The present invention relates to a receiving method and apparatus in an orthogonal frequency division multiple access system, and more particularly, to an interference signal removing method and apparatus for efficiently canceling adjacent cell interference signals in a receiver of an OFDMA system.

In general, a wireless communication system using a multi-carrier transmission scheme was first applied to military radios in the late 1950s, and an OFDM scheme, a typical multi-carrier transmission scheme overlapping a plurality of orthogonal subcarriers, began to develop in the 1970s.

The OFDM method converts symbol strings serially input in parallel and modulates each of them through a plurality of subcarriers having mutual orthogonality. The OFDM method uses digital audio broadcasting (DAB). And digital transmission technologies such as digital television, wireless local area network (WLAN), and wireless asynchronous transfer mode (ATM).

The OFDM scheme is a system suitable for a wireless communication environment in which a linear signal component (LOS) is not guaranteed in a multipath, and is known to provide an efficient platform for high-speed data transmission by using the strong advantage in multipath fading. . In the OFDM scheme, all channels are divided into a plurality of orthogonal narrowband sub-channels and transmitted to efficiently overcome selective fading of frequencies.

In addition, the OFDM scheme inserts a cyclic prefix (CP) longer than the delay spread of the channel at the front of the symbol, thereby eliminating symbol interference (ISI), which is most suitable for high-speed data transmission. effective. Due to these advantages, IEEE 802.16 has been standardized. IEEE 802.16 supports not only a single carrier system, but also multiple carrier systems OFDM and OFDMA.

The Orthogonal Frequency Division Multiplexing Access (OFDMA) scheme divides a frequency domain into subchannels consisting of a plurality of subcarriers, divides a time domain into a plurality of time slots, and allocates subchannels for each user. And a multi-access method capable of accommodating a plurality of users with limited frequency resources by performing resource allocation considering both frequency domains.

1 is a block diagram showing the configuration of a typical transmitter in an OFDMA system.

The source data encoded by forward error correction (FEC) through the FEC encoder 101 in the transmitter 100 of FIG. 1 is passed through a symbol mapper 103 to QPSK / Modulation is performed according to a predetermined modulation method such as 16QAM / 64QAM. The modulated transmission signal is repeated according to a repetition number set by the base station through the repeater 105 and then transmitted to the subcarrier permutation part 107. The subcarrier substituent 107 mixes the transmission order of the transmission signals according to a predetermined substitution rule and allocates the subcarriers in the mixed order. In FIG. 1, the scrambler 109 multiplies the assigned subcarriers with a scrambling sequence for encryption, and the scrambled transmission signal is transmitted through an Inverse Fast Fourier Transform (IFFT) 111. The signal is converted into a signal in the time domain and transmitted to the wireless network through the antenna 113.

Meanwhile, a receiver of a mobile station (MS) receives a signal transmitted from a neighboring base station to a wireless network from a base station (BS) to which it is connected. That is, the receiver of the terminal receives a neighbor cell interference signal of the neighbor BS as well as the serving BS. For example, assuming only one interference signal, the reception signal y (k) of the terminal can be represented by Equation 1 by adding a noise signal n (k).

In Equation 1, h _S (k) is a frequency response of a channel corresponding to a k-th subchannel between a serving base station and a mobile terminal, and h _I (k) is an adjacent base station generating an interference signal. And a channel frequency response between the mobile station and the mobile station. Here, assuming that the power of the transmission signal x (m) of the base station is 1, and that x (m), h (k), and n (k) are independent of each other, the carrier signal versus interference of the reception channel and Carrier to Interference Noise Ratio (CINR) may be expressed as Equation 2 below.

2 is a block diagram illustrating a configuration of a general receiver in an OFDMA system.

The receiver 200 of FIG. 2 has a symmetrical configuration with the transmitter 100 of FIG. 1 and performs signal processing in the reverse direction of the transmitter structure. The signal received through the antenna 201 of the receiver 200 is converted into a signal in the frequency domain at the FFT 203.

The descrambler 205 descrambles the FFT-converted received signal, and the descrambled signal is transmitted to the channel estimator 207 and the channel compensator 209. The channel estimator 207 extracts only the pilot signal component from the descrambled signal to perform channel estimation, and the channel compensator 209 performs channel compensation of the data component using the estimated channel value. The subcarrier aligner 211 subcarrier ordering the channel compensated data signal to align the subcarrier order again in subchannel units. The aligned subchannel signals are then combined via a repetition combiner 213. A symbol demapper 215 calculates the LLR for the combined subchannel signals, and the FEC decoder 217 performs forward error correction on the received signal.

Meanwhile, the mean squared error (MSE) of the signal input to the symbol demapper 215 is expressed by Equation 3 below.

In addition, the relationship between MSE and CINR has a relationship of Equation 4 below with a product of a repetition coefficient R assuming an AWGN channel.

3 illustrates a structure of a frame transmitted and received in an IEEE 802.16 based OFDMA system, which illustrates a frame structure of an OFDMA system using a time division duplexing (TDD) scheme.

3 shows that the downlink (DL) section and the uplink (UL) section are separated in time. The first symbol of the downlink frame is a preamble 301. The receiver of the mobile terminal uses the preamble 301 to use synchronization acquisition, base station ID acquisition, channel estimation, and the like. Since the base station ID is used as a seed value of scrambling, subcarrier permutation, and the like, it is necessary to acquire the base station ID in order to decode the DL data burst.

After the preamble 301, a Frame Control Header (FCH) 302 is attached, and the FCH 302 includes information necessary for decoding the DL-MAP. In other words, the FCH 302 contains contents such as a DL-MAP length, a DL-MAP coding scheme, and the like. The DL-MAP includes information required for DL data burst decoding of this frame, that is, position and size information for each burst, MCS (Modulation and Coding Scheme) information of bursts, and the like. Therefore, in order to decode the DL data burst, signal processing procedures of steps 401 to 407 are required to acquire a base station ID, perform FCH decoding, and perform DL MAP decoding and DL burst decoding as shown in FIG. 4. Do.

However, in the OFDMA system having the above configuration, since the frequency reuse factor is assumed to be 1, the receiver of the mobile station located at the boundary of the cell receives an interference signal generated by receiving transmission signals of neighboring base stations. There is a problem that the reception performance is significantly lowered.

The present invention provides a method and apparatus for canceling adjacent cell interference signals at a receiver of an OFDMA system.

The present invention also provides a method and apparatus for removing neighbor cell interference signals using preamble estimates of OFDM symbols in a receiver of an OFDMA system.

The present invention also provides a method and apparatus for removing neighbor cell interference signals using CINR measurement error in a receiver of an OFDMA system.

The present invention also provides a method and apparatus for removing adjacent cell interference signals by checking whether an FCH error occurs in a receiver of an OFDMA system.

In addition, the present invention provides a method and apparatus for removing adjacent cell interference signal by checking the DL-MAP error in the receiver of the OFDMA system.

The method of the present invention is a method of receiving an orthogonal frequency division multiple access system, the method comprising: scanning neighbor base stations that generate interference signals, and carrier to interference noise ratio (CINR) values of the interference signals received from the neighbor base stations; Estimating a value, determining a CINR value that is higher than a predetermined threshold among the estimated CINR values, regenerating an interference signal having the highest CINR value, and regenerating the reproduced interference from a received signal. Subtracting the signal.

The apparatus of the present invention is a mobile terminal of an orthogonal frequency division multiple access system, comprising: means for scanning adjacent base stations for generating interference signals, and a carrier to interference noise ratio (CINR) value of the interference signals received from the adjacent base stations; Means for estimating the highest CINR value greater than a predetermined threshold among the estimated CINR values, and regenerating an interference signal having the highest CINR value under control of the controller. And a transmitting module and means for subtracting the regenerated interfering signal from the received signal.

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

5 is a block diagram showing an example of a configuration of a receiver for removing an interference signal in an OFDMA system according to the present invention, the interference signal cancellation apparatus according to the present invention is connected to the output terminal of the receiving module to be described later to the interference And a transmitting module for regenerating the signal and subtracting means for subtracting the regenerated interference signal from the received signal. According to the present embodiment, in another embodiment to be described below, the transmission module may share a transmitter provided in the terminal or use a separate transmission module.

The receiver of FIG. 5 is a receiver to which a sequential interference cancellation method is applied to a received signal and removes the interference signal from the frequency axis after FFT processing, which is highly received in a region with high interference such as a cell boundary region. Configured to show success rate.

In the receiver structure of FIG. 5, the FFT 505, the descrambler 509, the channel estimator 510, the channel compensator 511, the subcarrier aligner 513, the combiner 515, the symbol mapper 519, and the FEC decoder After receiving an OFDM signal and performing an FFT process, the receiver performs channel compensation, performs symbol demapping according to a predetermined demodulation scheme, and configures a receiving module for performing forward error correction. Since the basic operation of each component of the receiving module is the same as that of the general receiver described with reference to FIG. 2, a detailed description thereof will be omitted.

In addition, in the receiver structure of FIG. 5, the FEC encoder 527, the symbol mapper 529, the iterator 523, the subcarrier substituent 535, and the scrambler 537 are again subjected to FEC encoding and predetermined modulation on a received signal that has undergone FEC decoding. A transmission module for generating an interference signal to be removed by configuring a transmission process that performs symbol mapping, symbol repetition, subcarrier substitution, and scrambling according to a scheme is configured. Since the basic operation of each component of the transmitting module is the same as that of the general transmitter described with reference to FIG. 1, a detailed description thereof will be omitted.

The above-described configuration of FIG. 5 removes the interference signal from the received signal by subtracting 507 the interference signal generated by the transmission module from the received signal on the frequency axis passing through the FFT 505 of the reception module. In this case, the transmitting module generates an interference signal by multiplying an output signal of the scrambler 537 by a channel estimation value. In addition, in FIG. 5, the controller 501 includes means for scanning the neighbor base station, measuring the CINR of the signal received from the neighbor base station, and controlling the overall apparatus of the transmitting module and the receiving module. 531 and 541 on / off control to remove the interference signal from the received signal. In addition, in FIG. 5, the slicer 521 connected between the two switches 517 and 531 is a component having both a symbol demapper 519 and a symbol mapper 529, and a combiner 515 and an iterator 533. Form a feedback path of the received signal to connect the.

That is, in the present invention, the feedback path of the reception module generating the interference signal may selectively use the signal path between the FEC decoder 523 and the FEC encoder 527 and the signal path between the combiner 515 and the repeater 533.

FIG. 6 is a flowchart illustrating a method for canceling an interference signal according to an embodiment of the present invention. The method of the present invention measures CINR of a serving base station signal and interference signals in step 601 and removes interference signals in step 603. The interfering signal is screened by a certain criterion. The criterion for selecting the interference signal is, for example, identifying neighboring base stations generating an interference signal from neighbor BS set information known to the terminal and exceeding a predetermined threshold value among the interference signals of the neighboring base stations. Interfering signals can be selected. In this specification, the term "interfering base station" is to be understood as having the same meaning as a neighboring base station generating an interference signal above the threshold. Thereafter, the receiver of the UE arranges the CINR values among the interference signals to be removed in ascending order in step 605, and decodes the interference signals to be removed by decoding the FCH, DL-MAP, and DL-burst in steps 607 to 611. Interference detection

In step 613, the transmission module of FIG. 5 generates an interference signal, and then, in step 615, the interference module generated in step 613 is removed from the signal of the frequency axis output from the FFT terminal of the reception module of FIG. 5. interference subtraction). Subsequently, in step 617, the receiver of FIG. 5 determines whether the interference signal removal is completed. If not, the receiver proceeds to step 607 and repeats the operation of generating the interference signal. When the interference signal removal is completed, the receiver proceeds to step 619. FCH decoding is performed, and DL-MAP decoding and DL burst decoding are performed in steps 621 and 623.

Therefore, the receiver performing the process of FIG. 6 controls the interference signals to be removed from the received signal and finally detects the signal of the serving base station.

Hereinafter, the derivation process of the present invention for removing the neighbor cell interference signal from the receiver of the OFDM system will be described in detail.

First, the following methods are required to efficiently remove an interference signal from a receiver of an OFDMA system.

1. Effective Channel Estimation

2. Effective CINR Estimation

3. Correct operation of interference canceling device

In addition, the most appropriate scheme should be selected using the characteristics of the frame structure and preamble structure of the OFDMA system.

In the OFDMA system, if the channel estimated value using the pilot signal with high interference is used in the interference signal canceller of the present invention (hereinafter referred to as "interference canceller"), as shown in Equation 1, Residual Interference signals will remain large and the performance of the interference canceller will be very poor. Therefore, channel estimation is a very important part. The present invention proposes an effective channel estimation scheme that can reduce the residual interference. In addition, the operation of the interference canceller in FIG. 6 compares CINR values of an interference base station, that is, a neighboring base station and a serving base station, to determine whether the operation is performed. The present invention proposes an effective CINR estimation scheme and an operation scheme of an interference canceller when a plurality of interfering base stations exist.

In addition, referring to FIG. 4 illustrating a data reception process in an IEEE 802.16 based OFDMA system, FCH decoding must be performed first for DL-MAP or DL-burst decoding. Therefore, when regenerating the DL-MAP interference signal or the DL-burst interference signal in the operation of the interference canceller, the FCH of the interference signal must be decoded first. However, since it is meaningless to regenerate DL-MAP of an interfering base station without determining whether or not the decoded FCH is a meaningful value, in the present invention, a method of determining whether an interference canceller is operated by not only the CINR value but also the FCH error Suggest.

FIG. 7 illustrates a pilot configuration structure of a preamble in an IEEE 802.16 based OFDMA system. In the IEEE 802.16 based OFDMA system, a preamble has a pilot configuration shown in FIG.

In FIG. 7, the pilot signals 71, 73, and 75 of the preamble are allocated only one pilot per three subcarriers SO, S1, and S2, and the remaining subcarrier positions are left blank. In addition, there are three sectors of sectors 0, 1, and 2. If the sectors are different, the pilot signals of the preamble do not overlap as shown in FIG. Therefore, when the sectors are different, the preamble may be regarded as having no influence of interference by neighboring base stations. 8 shows a sector structure when the terminal MS is located in an overlapping area of three base stations BS1, BS2, and BS3. As in the case of FIG. 8, since the base stations are installed such that overlapping regions have different sectors in general, the preamble is likely to have very little interference.

In addition, the permutation used after the preamble in the IEEE 802.16 based OFDMA system is to use a Partial Usage of Subchannels (PUSC) scheme.

9 is a diagram illustrating an arrangement of pilot signals in a PUSC replacement scheme. Since all base stations using the PUSC scheme always use pilot (parts shown by arrows) signals at the same position, the pilot signal having the structure of FIG. It can be predicted that interference will be very severe. Since the FCH and DL-MAP are located immediately after the preamble in time, the PUSC scheme must be used. In the DL-burst region other than the DL-MAP, a substitution of a scheme other than the PUSC scheme may be used, but the interference of the pilot signals is very severe since the substitution of the other scheme also transmits pilot signals to the same positions for each base station. On the other hand, since the preamble has different sectors in the overlapping region between cells and no overlap between the different sectors, the pilot signal of the preamble has little influence on interference.

However, since the preamble exists at a position different in time from the DL-burst region, a channel estimation value using the preamble may be significantly different from the actual channel value of the DL-burst region for a channel that changes rapidly in time. However, since the DL-MAP is immediately adjacent to the preamble in time, the influence on the channel's temporal change is not large, and the loss caused by the pilot's interference is much more serious than the loss caused by the temporal change. It is advantageous to extend the channel value estimated by the preamble on the time axis and use it as it is.

On the other hand, in the case of DL-burst, which is far from the preamble in time, it is necessary to use not only the preamble but also a pilot signal of a data region in which the DL-burst is located. In this case, when not only interference data but also a corresponding pilot signal are removed together when performing interference cancellation, a channel estimation error due to interference of the pilot signal can be reduced to some extent. That is, in the process of regenerating the interference signal, not only the data but also the pilot signal of the interfering base station may be regenerated to remove both the data and the pilot signal when the interference signal is removed.

FIG. 10 is a block diagram illustrating another configuration of a receiver for removing an interference signal in an OFDMA system according to the present invention. The interference signal removing device according to the present embodiment is connected to an output terminal of a receiving module to be described below in a feedback structure. A transmission module for regenerating an interference signal, preamble extraction means for extracting a preamble located on an input path of the reception module, pilot insertion means for inserting a pilot symbol located on an output path of the transmission module; And subtracting means for subtracting the regenerated interference signal from the received signal to remove the interference signal using the channel estimation value of the preamble. That is, the interference canceller of FIG. 10 differs from the interference canceller of FIG. 5 in regenerating and removing not only data but also pilot signals in a data region, and using the channel estimation value of the preamble to remove interference signals. In addition, the controller 1001 of FIG. 10 controls the pilot signal of the preamble and the pilot signal of the data area to be used together for channel estimation when all interference signals are removed.

In the receiver structure of FIG. 10, the FFT 1005, the descrambler 1009, the channel estimator 1013, the channel compensator 1015, the subcarrier aligner 1017, the combiner 1019, the symbol mapper 1023, and the FEC decoder 1027 configures a receiving module that performs OFDM compensation after receiving an OFDM signal, performs channel compensation, performs symbol demapping according to a predetermined demodulation scheme, and performs forward error correction. Basic operation of each component of the receiving module is the same as that of the receiver described with reference to FIG. 5.

Also, in the receiver structure of FIG. 10, the FEC encoder 1031, the symbol mapper 1033, the iterator 1037, the subcarrier substituent 1039, and the scrambler 1043 are again subjected to FEC encoding and predetermined modulation on a received signal that has undergone FEC decoding. The transmission module performs symbol transmission, symbol repetition, subcarrier substitution, and scrambling according to a scheme, thereby configuring a transmission module in the receiver 1000 that regenerates an interference signal to be removed. Basic operation of each component of the transmission module is the same as that of the transmitter described with reference to FIG. 5.

10, the preamble extractor 1011 located on the input path of the receiving module extracts the preamble from the output signal of the FFT 1005, and the channel estimator 1013 performs channel estimation on the extracted preamble. The output is performed to the channel compensator 1015 of the receiving module and the multiplier 1045 connected to the transmitting module. In addition, the pilot inserter 1041 located on the output path of the transmitting module inserts a pilot symbol into the output signal of the subcarrier substituent 1039, and the subtractor 1007 subtracts the regenerated interference signal from the received signal.

The above-described configuration of FIG. 10 removes the interference signal from the received signal by subtracting 1007 the interference signal regenerated by the transmitting module from the received signal on the frequency axis passing through the FFT 1005 of the receiving module. Here, the transmitting module generates an interference signal by multiplying the output signal of the scrambler 1043 by the channel estimation value of the preamble. In addition, in FIG. 10, the controller 1001 includes means for scanning a neighbor base station, measuring a CINR of a signal received from the neighbor base station, and controlling the overall apparatus of the transmitting module and the receiving module. 1029, 1035, and 1047 are controlled on / off to remove the interference signal using the channel estimation value of the preamble from the received signal.

Also, in FIG. 10, the slicer 1025 connected between the two switches 1021 and 1035 is a component having both a symbol demapper 1023 and a symbol mapper 1033. The combiner 1019 and the repeater 1037 are shown in FIG. Form a feedback path of the received signal to connect the. That is, in the present invention, the feedback path of the receiving module generating the interference signal may selectively use the signal path between the FEC decoder 1027 and the FEC encoder 1031 and the signal path between the combiner 1019 and the repeater 1037.

In accordance with the present invention, channel estimation used for removing interference signals of FCH and DL-MAP is performed in the following manner.

1. Interference signal detection: All channel estimates for the interference signal use the values estimated from the preamble.

2. Regeneration of Interference Signals: In regeneration of interfering FCH and interfering DL-MAP data, the interfering PUSC pilot signal is regenerated together with the data.

3. Interference signal canceller: When removing the interference signal, remove the interference PUSC pilot signal together with the interference FCH and the interference DL-MAP data.

4. Detection of serving base station signal: When detecting the FCH and DL-MAP data of the serving base station after all interference signals are removed, the preamble for channel estimation and the PUSC pilot signal from which the interference signal is removed are used together.

FIG. 11 is a diagram illustrating a bit error rate (BER) performance of a receiver having an interference signal according to the present invention. Referring to FIG. 11, the performance of the interference canceller using only a severe interference PUSC pilot signal is an interference signal. Compared to the conventional receiver which does not remove the signal, it shows superior performance, but shows very low performance compared to the method using the pilot signal of the preamble without the influence of the interference signal. In addition, it can be seen that the performance of the interference canceller using the pilot signal of the preamble shows only the difference between the performance of the receiver and the residual interference caused by the small channel estimation error in the environment without interference.

In addition, in the configuration of FIG. 10, the controller 1001 may control to provide an interference signal by using a CINR measurement error, an FCH error, or a DL-MAP error as in the embodiments of FIGS. 12 and 13 to be described later.

Hereinafter, the features of the present invention for controlling the interference canceller using the measurement error of the CINR, the FCH error or the DL-MAP error will be described in detail.

The parameter that determines whether or not the interference canceller should operate on the received frame is an estimated CINR value. The basic operation of the interference canceller according to the present invention compares the CINR value of the serving base station and the CINR value of the interfering base station, and operates the interference canceller when a difference between the two values exceeds a predetermined threshold. Therefore, the accuracy of the estimated CINR value is very important. Estimation of the CINR value uses the pilot signal of the preamble or the pilot signal of the data region. Like the channel estimation method, since the pilot signal of the data region has a large influence due to interference, the CINR value is estimated using the pilot signal of the data region. The result is not as good as the estimation result of the CINR value using the pilot signal of the preamble. Therefore, the CINR value for the interference canceller operation is advantageously using a pilot signal of the preamble.

Meanwhile, in the embodiment of FIG. 6, when there are two or more interfering base stations that generate an interfering signal having a threshold value or higher, interference cancellation is performed in the order of increasing CINR values of the interfering base stations. That is, the receiver sequentially removes the interference signal having a relatively large value. In this process, the CINR values of the serving base station and the remaining interference base station are different from the CINR values before the interference occurs. For example, the following situation may occur:

The CINR values of Interference 1 (I ₁ ), Interference 2 (I ₂ ), and Interference 3 (I ₃ ) are measured, and the threshold of the interference cancellation operation is set to '0', and the measurement result of the initial CINR value is described above. In Equation 5, interference 1, interference 2, and interference 3 are all subject to interference cancellation. Since the CINR value of interference 1 is the largest, it is the first removal target. In the embodiment of FIG. 6, after the interference 1 is removed, the interference 2 and 3 are sequentially removed.

However, once the effect of interference 1 is removed, the effects of interference 2 and 3 may differ from the first.

For example, after the removal of the first interference 1, the CINR value is measured again as shown in Equation 6, and the interference 3 is no longer subjected to interference cancellation. The reason for this may be that interference 2 and 3 have different effects on the preamble and the pilot signal in the data area, depending on whether interference 1 is removed, which may cause errors in estimation of CINR values. Because.

In order to solve the above problem, when removing the interference signal, the interference preamble and the pilot signal of the data area are subtracted together from the received signal, and the CINR values of the remaining interference base station and the serving base station are measured again to determine the interference cancellation target again. It would be desirable to. In this method, since the interference signal removal target is selected again each time the interference cancellation is performed, only the interference signal having the largest CINR value among the interference target interference signals is selected and removed.

12 is a flowchart illustrating a method for canceling an interference signal according to another embodiment of the present invention, which shows a process of selecting and removing only an interference signal having a largest CINR value among interference signals.

The difference between the embodiment of FIG. 12 and the embodiment of FIG. 6 is that when the interference signal is removed, the pilot signals of the preamble and the data region are also removed, and the CINR value is measured again based on the received signal from which the interference signal is removed. After selecting them, only the interference signal having the largest CINR value among the interference signals to be removed is removed. The operation of removing the interference signal having the largest CINR value is repeated until the interference signal to be removed no longer exists.

For the above operation, in step 1201 of FIG. 12, the controller 1001 measures CINR values of signals of an interfering base station, and selects an interfering signal to be removed from the interfering signals by a predetermined criterion in step 1203. The criterion for selecting the interference signal is, for example, identifying neighboring base stations generating an interference signal from neighbor BS set information known to the terminal and exceeding a predetermined threshold value among the interference signals of the neighboring base stations. Interfering signals can be selected.

When the removal target interference signals are determined in step 1203, the controller 1001 determines an interference signal having the highest CINR value among the removal target interference signals in step 1205, and the FCH, DL-MAP, and DL in steps 1207 through 1211. Perform decoding on the burst to detect interference signals to be controlled. Thereafter, the received signal passing through the receiving module of FIG. 10 is transmitted to the transmitting module through a feedback path, and in step 1213, the transmitting module not only regenerates the interference signal, but also pilot symbols inserted through the pilot inserter 1041. Regenerate the pilot signals of the interference preamble and the data region by using.

In operation 1215, the controller 1011 controls the switch 1047 to apply the regenerated interference signal and the interference preamble and the pilot signal of the data area to the subtractor 1007 to receive the output from the FFT stage of the receiving module of FIG. 10. The interference signal generated in step 1213 is removed from the signal. Thereafter, the controller 1001 of FIG. 10 proceeds to step 1201 and repeats the subsequent operation until all interference signals to be removed are removed. If all interference signals are removed, the controller 1001 proceeds to step 1217 to determine the FCH received from the serving base station. The decoding is performed, and in steps 1219 and 1221, decoding of the DL-MAP and decoding of the DL burst received from the serving base station are performed.

Accordingly, the receiver performing the process of FIG. 12 controls the interference signals to be removed from the received signal and finally detects the signal of the serving base station.

Meanwhile, in the above-described embodiment of FIG. 12, the detection of the FCH of the interfering base station should be the first priority when detecting the interfering signal. As shown in the field configuration of the FCH of Table 1, the FCH has used subchannel bitmap information, a repetition coding rate of the DL-MAP, and a channel code of the DL-MAP. This is because a coding indication and DL-MAP length information are included.

That is, in order to detect the DL-MAP of the interfering base station, the successful detection of the FCH of the interfering base station must be premised. If the FCH of the interfering base station is detected incorrectly, only interference cancellation for FCH should be performed, and interference cancellation for DL-MAP or DL-burst should not be performed. In general, the CRC bit is used to determine whether an error occurs. However, since the FCH does not include the CRC bit, it is difficult to make an accurate judgment. However, some features of the FCH can be used to determine the accuracy of the FCH. The FCH is encoded with a tail biting convolutional code, so that the initial state value and the final state value must be the same at the time of Viterbi decoding. In addition, if the FCH field value is checked after decoding, it can be checked whether the reserved bit shown in Table 1 is set to '0'. The FCH error is determined using the features of the FCH.

On the other hand, unlike the FCH, since the 32-bit CRC is included in the DL-MAP, the error of the DL-MAP can be detected by checking the CRC bit. Therefore, if the CRC of the DL-MAP is good by checking the CRC of the DL-MAP, the interference cancellation for the DL-MAP and the DL-burst is performed, and if the DL-MAP CRC is bad, the DL- It may be desirable to perform only interference cancellation for MAP and not interference cancellation for DL-burst.

In general, when an error of the FCH or DL-MAP is confirmed, it may be considered that interference should not be removed from the errored FCH or DL-MAP. However, if it is determined that an FCH or DL-MAP error occurs, only one of several bits constituting the FCH or DL-MAP is considered to be an overall error. Therefore, when the number of bit errors among the total bits is small enough, performing the interference cancellation guarantees better performance than the case where the interference cancellation is not performed. Therefore, in selecting the interference cancellation target, interference cancellation is performed only when the CINR value of the interfering base station exceeds a certain threshold value, i.e., the total number of bit errors is expected to be small enough even if a CRC error of FCH or DL-MAP occurs. It is desirable to. Since the threshold value depends on the channel state, channel coding scheme, code rate, etc. of the interference signal to be removed, it is necessary to use a threshold value suitable for the interference cancellation point.

13 is a flowchart illustrating a method for canceling an interference signal according to another embodiment of the present invention, which shows another operation of the interference canceller considering the CINR measurement error, the FCH error, and the DL-MAP error.

The difference between the embodiment of FIG. 12 and the embodiment of FIG. 13 is to determine whether the interference base station removes the DL-MAP and the DL-burst after checking whether the FCH and the DL-MAP are in error. That is, in case of an FCH error, only interference cancellation for FCH is performed, and in case of a DL-MAP error, interference cancellation for DL-MAP is performed.

For the above operation, in step 1301 of FIG. 13, the controller 1001 measures CINR values of signals of an interfering base station, and selects an interference signal to be removed from the interference signals by a predetermined criterion in step 1303. Here, the criterion for selecting the interference signal is the same as in the embodiment of FIG. 12. When the removal target interference signals are determined in step 1303, the controller 1001 determines an interference signal having the highest CINR value among the removal target interference signals in step 1305, and performs decoding on the FCH in step 1307. Detect interfering signals. Thereafter, the controller 1001 checks the channel coding scheme and the reserved bit of the FCH in step 1309 to check whether there is an error, and in step 1311, decodes the DL-MAP to detect an interference signal to be controlled. Detect.

In addition, in step 1313, the controller 1001 checks the CRC bit of the DL-MAP to determine whether there is an error, and in step 1315, detects an interference signal to be controlled by decoding the DL-burst in step 1315. After that, the process proceeds to step 1317. On the other hand, if the FCH error occurs in step 1309, the controller 1001 skips the interference signal detection operation for the DL-MAP and DL-burst, and proceeds directly to step 1317. In addition, when a DL-MAP error occurs in step 1313, the controller 1001 skips the interference signal detection operation for the DL-burst and proceeds directly to step 1317.

Thereafter, the received signal passing through the receiving module of FIG. 10 is transmitted to the transmitting module through a feedback path, and in step 1317, the transmitting module not only regenerates the interference signal but also interferes using the pilot symbol inserted through the pilot inserter 1041. Regenerate pilot signals in the preamble and data area. In operation 1319, the controller 1011 controls the switch 1047 to apply the regenerated interference signal and the interference preamble and the pilot signal of the data area to the subtractor 1007 to receive the output from the FFT stage of the receiving module of FIG. 10. The interference signal generated in step 1313 is removed from the signal.

Thereafter, the controller 1001 of FIG. 10 proceeds to step 1301 and repeats the subsequent operation until all interference signals to be removed are removed. When all interference signals are removed, the controller 1001 proceeds to step 1321 to determine the FCH received from the serving base station. The decoding is performed, and in steps 1323 and 1325, decoding of the DL-MAP and decoding of the DL burst received from the serving base station are performed.

Accordingly, the receiver performing the process of FIG. 13 controls the interference signals to be removed from the received signal and finally detects the signal of the serving base station.

As described above, according to the present invention, a receiver having an interference canceller can be used to significantly improve the reception performance of a terminal in a region where signal interference is severe, such as an intercell boundary region.

Claims (12)

In the reception method of an orthogonal frequency division multiple access system, Scanning adjacent base stations for generating interference signals; Estimating a carrier to interference noise ratio (CINR) value of the interference signals received from the neighbor base stations; Determining a CINR value that is higher than a predetermined threshold among the estimated CINR values; Regenerating an interference signal having the highest CINR value; Subtracting the regenerated interfering signal from a received signal. The method of claim 1, Each of the processes further comprises performing until all interference signals exceeding the threshold value are removed, the interference signal cancellation method in a receiver of an orthogonal frequency division multiple access system. The method according to claim 1 or 2, And decoding the signal received from the serving base station when the interference signal exceeding the threshold value is removed. The method of claim 1, Checking whether an FCH (Frame Control Header) error is detected with respect to the interference signal having the highest CINR value; The receiver of the orthogonal frequency division multiple access system further comprises the step of omitting the decoding of the downlink map (DL-MAP) and downlink burst (DL-burst) of the interference signal when the FCH error is confirmed. How to remove interfering signals from The method according to claim 1 or 4, Checking whether there is an error in a downlink map (DL-MAP) for the interference signal having the highest CINR value; If the error of the DL-MAP is confirmed, the method for removing the interference signal in the receiver of the orthogonal frequency division multiple access system, characterized in that further comprising the step of omitting the decoding of the DL-burst of the interference signal. The method of claim 1, And the channel estimate value for the interference signal is a channel estimate value for the preamble of the received signal. The method of claim 1, Orthogonal frequency characterized in that when the FCH and DL-MAP data of the serving base station is detected after all the interference signals are removed, the preamble for channel estimation and the PUSC (Partial Usage of Subchannels) pilot signal from which the interference signal is removed are used together. A method for canceling interference signals in a receiver of a divided multiple access system. In a mobile terminal of an orthogonal frequency division multiple access system, Means for scanning adjacent base stations generating interference signals, means for estimating a carrier to interference noise ratio (CINR) value of the interference signals received from the neighbor base stations, and greater than a predetermined threshold value of the estimated CINR values. And a controller having means for determining the highest CINR value; A transmitting module for regenerating an interference signal having the highest CINR value under the control of the controller; And means for subtracting the regenerated interfering signal from a received signal. The method of claim 8, And the controller is further configured to repeat the subtracting operation of the reproduced interference signal until all interference signals exceeding the threshold value are removed. The method according to claim 8 or 9, And the controller controls to decode the signal received from the serving base station when the interference signal exceeding the threshold is removed. The method of claim 8, The controller checks whether an FCH (Frame Control Header) error is detected with respect to the interference signal having the highest CINR value, and when the FCH error is confirmed, the controller controls a receiving module to determine a downlink map (DL-MAP) of the interference signal. The apparatus for canceling interference signal of a mobile terminal, characterized in that it is further configured to omit the decoding of the downlink burst (DL-burst). The method according to claim 8 or 11, wherein The controller checks the downlink map (DL-MAP) error for the interference signal having the highest CINR value and controls the receiving module to determine the downlink burst of the interference signal when the error of the DL-MAP is confirmed. The apparatus for canceling interference signal of a mobile terminal, characterized in that it is further configured to omit decoding of (DL-burst).

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