KR20070064933A - Method and apparatus for canceling neighbor cell interference signals in orthogonal frequency division multiple access - Google Patents

Abstract

A method and an apparatus for canceling an adjacent cell interference signal in an orthogonal frequency division multiple access are provided to improve performance of a hand-over by removing an interference signal. A method for canceling an adjacent cell interference signal in an orthogonal frequency division multiple access includes the steps of: detecting an interference signal from signals received from peripheral radio stations and serving radio stations; measuring strength of the interference signal detected and checking whether the strength of the interference signal is more than a predetermined threshold value; aligning the peripheral radio stations having the interference signal whose strength is more than the predetermined threshold value; selecting and detecting the interference signal in a sequence of the peripheral radio stations to be aligned; normalizing the detected interference signal by calculating an interference and noise dispersion for the interference signal; re-generating the interference signal by decoding the normalized interference signal; and reducing the re-generated interference signal from the received signals.

Description

METHOD AND APPARATUS FOR CANCELING NEIGHBOR CELL INTERFERENCE SIGNALS IN ORTHOGONAL FREQUENCY DIVISION MULTIPLE ACCESS}

1 is a view showing an example of a terminal located in an area where three base stations overlap in an OFDMA system;

2 is a block diagram of a transmitter in a typical OFDMA system,

3 is a block diagram of a receiver in a typical OFDMA system,

4 is a diagram illustrating an example of a frame structure of an OFDMA system using a time division duplexing (TDD) scheme;

5 is a flowchart illustrating a signal processing procedure for DL burst decoding of an OFDMA receiver;

6 is a block diagram of a receiver to which an iterative interference signal canceller is added to remove an interference signal in an OFDMA system according to the present invention;

7 is a block diagram illustrating a receiver in an OFDMA system according to an embodiment of the present invention;

8 is a constellation diagram according to input bits of QPSK, 16QAM, and 64QAM;

9 is a block diagram illustrating an apparatus for normalizing an input metric of a channel decoder in an OFDMA receiver having an iterative interference canceller according to a first embodiment of the present invention;

10 is a block diagram illustrating an apparatus for normalizing an input metric of a channel decoder in an OFDMA receiver having an iterative interference canceller according to a second embodiment of the present invention;

11 is a block diagram of a device for normalizing an input metric of a channel decoder in an OFDMA receiver having an iterative interference canceller according to a third embodiment of the present invention;

12 is a block diagram of an apparatus for normalizing an input metric of a channel decoder in an OFDMA receiver having an iterative interference canceller according to a fourth embodiment of the present invention;

FIG. 13 is a block diagram of an apparatus for normalizing an input metric of a channel decoder in an OFDMA receiver having an iterative interference canceller according to a fifth embodiment of the present invention;

14 is a block diagram of an apparatus for normalizing an input metric of a channel decoder in an OFDMA receiver having an iterative interference canceller according to a sixth embodiment of the present invention;

15 is a block diagram illustrating an apparatus for normalizing an input metric of a channel decoder 615 in an OFDMA receiver equipped with an interference canceller of a slicer method according to a seventh preferred embodiment of the present invention.

16 is a flowchart illustrating a method for normalizing a channel decoder input metric in a receiver having an interference signal canceller according to a channel decoding feedback method according to embodiments of the present invention;

17 is a flowchart illustrating a method for normalizing a channel decoder input metric in a receiver having an interference signal canceller according to a slicer method according to embodiments of the present invention;

The present invention relates to a method and apparatus for receiving data in a broadband wireless communication system, and more particularly, to a method and apparatus for canceling interference signal when receiving data in an orthogonal division multiple access communication 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. . That is, the OFDM divides all channels into narrowband subchannels having a plurality of orthogonalities and transmits them, thereby efficiently overcoming 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 inter-symbol interference (ISI). Most effective. Due to these advantages, IEEE802.16a has been standardized, and 802.16a supports Single Carrier System, OFDM, and OFDMA.

Here, the Orthogonal Frequency Division Multiplexing Access (OFDMA) divides a frequency domain into subchannels consisting of a plurality of subcarriers, divides the time domain into a plurality of time slots, and allocates subchannels for each user to allocate both time and frequency domains. It is a multiple access method that can accommodate a large number of users with limited frequency resources by performing resource allocation.

In the OFDMA system, subchannels composed of different subcarriers can be allocated to different users. Therefore, when an adaptive antenna system (AAS), which is a method for increasing system capacity based on the 802.16a standard, is applied to an adjacent subcarrier, A subchannel can be configured. By using this, multi-user diversity gains can be obtained by allocating the best channel to users experiencing different channel environments.

Currently, the WiBro system, an IEEE 802.16 based OFDMA system, supports two modes of frequency reuse factor 1 and 1/3. Since the frequency reuse coefficient 1 is much more advantageous in terms of cell capacity due to the higher frequency efficiency, the current OFDMA system is based on the frequency reuse coefficient 1. When the frequency reuse factor is 1, there is an excellent advantage in terms of frequency efficiency, but there is a disadvantage in that all used subcarriers overlap with the subcarriers of neighboring base stations and act as interference between each other. That is, since the same frequency is used between neighboring cells, signals transmitted by neighboring cells act as interference signals. A cell currently communicating with a terminal is called a serving cell, and an adjacent cell that causes major interference in the terminal is called an interference cell. If the terminal is located at the boundary between the serving cell and the interfering cell, since the signal output from the terminal is similar, only the signal encoded at a very low code rate can be normally transmitted and received. In particular, when the terminal is undergoing a time-varying fading channel, the average output may have a much larger interference signal than the serving cell signal, even if the signal of the serving cell is larger than the interference signal, which is the most robust encoding, QPSK, 1 /. Even with a code rate of 12, an error cannot be corrected.

Due to the interference signal of the neighboring base station, the terminal located near the cell boundary degrades the reception performance, and also degrades the handover performance, resulting in a phenomenon in which communication is lost.

1 is a diagram illustrating an example of a terminal located in an area where three base stations overlap in an OFDMA system. In order to overcome the interference signal problem at the cell boundary 101, 103, 105, and 107 as shown in FIG. 1, the IEEE802.16 standard transmits a base station transmission signal in a low modulation order such as QPSK. It modulates, applies low Forward Error Correction (FEC) Code Rate, and uses Repetition Coding up to 6 times. However, despite these efforts, the existing terminal receiver has a high outage probability near the cell boundary on the fading channel, and handover performance is also deteriorated. In order to fundamentally overcome this problem, the frequency reuse factor must be brought to 3, but in this case, the frequency efficiency is reduced to 1/3 compared to the frequency reuse factor 1, and the cell planning becomes complicated. It's a very reluctant way. For example, in the conventional CDMA mobile communication system, the frequency reuse factor is 1.

There are many ways to improve the receiver's reception performance. For example, a method of obtaining receive diversity by using two or more antennas in a receiver. This method has the advantage that the reception performance is improved by more than 3dB by using only two reception antennas, but in this case, the complexity of the receiver is greatly increased, and the degradation of performance due to the interference signal is not greatly improved. there is a problem. The most important part of the reception performance is the reception of DL-MAP. Since the DL-MAP is a signal that is broadcast to all terminals in the base station, it is difficult to improve the DL-MAP reception performance even if the smart antenna technology or the multiple input / output (MIMO) technology applied to the individual terminals is applied. there is a problem. In addition, the problem of poor reception performance near the cell boundary causes another big problem of poor handover performance.

As described above, the present invention provides a method for improving reception performance by removing interference signals in an orthogonal frequency multiple access system, and a receiver accordingly.

The present invention provides an interference signal cancellation method and a receiver according to the present invention, which improves the performance of handover by removing interference signals in an orthogonal frequency multiple access system.

The present invention provides an interference signal canceling method and a receiver according to the present invention for improving decoding performance even after canceling an interference signal in an orthogonal frequency multiple access system.

In the receiver of an Orthogonal Frequency Division Multiple Access (OFDMA) system according to the present invention, a method for receiving a signal transmitted from a serving base station detects an interference signal from neighboring base stations and signals received from the serving base station. And measuring the intensity of the detected interference signals and checking whether the detected interference signals are greater than a predetermined threshold value, aligning neighbor base stations satisfying the check, and interfering interference signals in order of the neighbor base stations to be aligned. Selecting and detecting, calculating and normalizing interference and noise variance of the detected interference signal, decoding and regenerating the normalized interference signal, and regenerating the regenerated interference signal in the received signal. Includes subtraction process.

In the Orthogonal Frequency Division Multiple Access (OFDMA) system according to the present invention, a receiver for receiving a signal transmitted from a serving base station measures a signal strength received from the serving base station and a signal strength received from a neighboring base station. When the difference in signal strength satisfies a predetermined threshold value, the interference signal received from the neighboring base station is regenerated, and a specific interference and noise signal is distributed among the signals received from the serving base station and the neighboring base station. A control unit for controlling the output of the control unit, an interference canceller for regenerating the interference signal under control of the control unit, an interference and noise estimating unit for outputting interference and noise dispersion information under control of the control unit, and the interference and noise adding unit; Based on the above information received from the government In the signal received from the qualified groups, the serving base station for normalizing the metric includes a subtractor for subtracting the regenerated interference signal.

DETAILED DESCRIPTION Hereinafter, detailed descriptions of preferred embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that the same components in the figures represent the same numerals wherever possible. Specific details are set forth in the following description, which is provided to aid a more general understanding of the invention. 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.

The present invention proposes a method and apparatus for removing interference signals to improve reception performance in a receiver of an OFDMA system. The interference signal cancellation method and apparatus proposed by the present invention can be applied to both a synchronous system and an asynchronous system. First, the OFDMA system will be described first for better understanding of the present invention, and then the method and apparatus according to the present invention will be described.

2 is a block diagram of a transmitter 200 in a typical OFDMA system.

Referring to FIG. 2, a channel encoder 201 such as a forward error correction (FEC) encoder first performs a sequence of code words on the transmission data d (n) including control information through channel encoding. Generate W (n). Thereafter, the symbol mapper 203 performs mapping using a predetermined modulation method, and outputs x (m) which is a QAM symbol such as quadrature phase shift keying (QPSK), quadrature amplitude modulation (16QAM), and 64QAM. The symbol repeater 205 is repeated according to a repetition number set by the base station for more robust communication. The symbol repeated signal s (l) in the symbol iterator 205 becomes the rearranged signal s (k) through the allocator 207. It includes not only the rearranged s (k) coded symbols but also pilot symbols for synchronization and channel estimation of the receiver. The scrambler 209 multiplies the s (k) by the scrambling sequence q (k) applied to each base station. The inverse fast Fourier transformer 211 converts the received signal q (k) s (k) into a signal X (i) in the time domain and transmits it through the antenna.

3 is a block diagram of a receiver 300 in a typical OFDMA system.

Referring to FIG. 3, the signal Y (i) received through the antenna is converted into a signal sequence y (k) in the frequency domain through the fast Fourier transformer 301. y (k) is descrambled by the descrambler 303 as q (k) ^* , which is a conjugate complex pair of the scrambling sequence q (k), and outputs data Z (k) in the frequency domain. The channel estimator 305 performs channel estimation using pilot subcarriers among the signal Z (k) in the frequency domain. The channel estimator 305 uses the pilot of the preamble and the pilot of the data region in the process of channel estimation. Thereafter, the extractor 307 extracts the estimated channel value and data according to the allocation information of the control information already known to the terminal or the allocation information given in the DL-MAP.

The extractor 307 rearranges data such as an allocation process according to the transmitter 200 standard. The data extracted by the extractor 307 is represented by P (l), which is a signal obtained by multiplying a channel response by a signal transmitted through each subcarrier. When the extractor 307 extracts P (l), the corresponding channel value c (l) is simultaneously extracted. The channel compensator 309 outputs a QAM symbol in which the final channel compensation is performed by Equation 1 below.

The QAM symbol, which is the compensated signal r (l) obtained by using Equation 1, is input to a repeating combiner 311, and 1, 2, 4, 6 repetition in the sign and modulation process in the repeating combiner 311. In this case, the repetition symbols are combined by the number of repetitions to obtain a combination result of x (m) and the channel response coefficient. The symbol demapper 313 receives the input and obtains an input metric Λ (n) corresponding to each bit necessary for channel decoding. However, the order of the iterator combiner 311 and the symbol demapper 313 may be changed. The configuration example of the present invention includes such a case.) A channel decoder 315 such as an FEC decoder outputs the decoded data d (n) using the input metric thus obtained.

FIG. 4 is a diagram illustrating an example of a frame structure of an OFDMA system using a time division duplexing (TDD) scheme.

Referring to FIG. 4, in the frame, the vertical axis 401 represents a frequency band of a subcarrier, and the horizontal axis 403 represents a time axis with an OFDMA symbol. As shown in the figure, it can be seen that a downlink (DL) 410 section and an uplink (UL) 430 section are separated in time. The first symbol of the downlink frame is a preamble 411. The terminal uses the preamble 411 to acquire synchronization, 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, the DL data bursts 419, 421, 423, 425, and 427 are decoded. In order to achieve this, it is necessary to acquire a base station identifier (BSID). The Preamble 411 is followed by a Frame Control Header (FCH) 413, which contains information necessary for decoding the DL-MAP 415. In other words, the FCH 413 contains contents such as a DL-MAP length, a coding scheme of the DL-MAP, and the like. The DL-MAP 415 contains information necessary for DL data burst decoding of this frame. That is, the location and size information of each burst, Modulation and Coding Scheme (MCS) information of bursts, etc. are included, and thus DL data bursts (417, 419, 421, 423). In order to decode 425, the signal is processed as shown in FIG. 5.

5 is a flowchart illustrating a signal processing procedure for DL burst decoding of an OFDMA receiver. As shown in FIG. 5, the receiver acquires a base station ID (Base Station: BS) based on the preamble (501), and decodes the FCH corresponding to the obtained base station ID (503). The corresponding DL MAP is decoded using the DL MAP decoding information present in the MAP. (505) The DL bursts are identified from the DL MAP and the DL bursts are decoded by identifying the positions of the DL bursts 417, 419, 421, 423, and 425. .

In order to remove an interference signal in such an OFDMA system, first, an interference signal is correctly estimated and detected, the detected interference signal is transformed into a transmission signal type, regenerated, and subtracted from the received signal. The process is necessary.

The most suitable to apply this interference cancellation scheme is the DL-MAP (415). Since the DL-MAP 415 comes from the same base station at all base stations, the interference between the base stations is the most severe, which is the biggest cause of the deterioration of handover performance. The key to the interference cancellation technique is to correctly detect the interference signal. The DL-MAP 415 is generally modulated by QPSK and repetition coding is applied, so that it is easy to detect the interference signal. In addition, since the DL-MAP 415 immediately follows the preamble signal 411 having less influence of the interference signal in time, the channel estimation of the interference signal using the preamble signal is also easy. have.

Then, in the following description, an interference signal cancellation technique that can effectively remove an interference signal to improve a reception performance of a receiver will be described. In addition, when the interference signal cancellation method applied to the present invention is first outlined, the signal received from the transmitter is received, and the interference signal of the received signal is detected and regenerated to remove the regenerated interference signal from the received signal. It is done.

Next, a structure of a receiver to which an interference signal cancellation method according to the present invention is applied and a signal processing procedure for interference signal removal will be described for each embodiment.

6 is a block diagram of a receiver in which an iterative interference signal canceller 620 is added to remove an interference signal in an OFDMA system according to the present invention. The receiver 600 according to the present invention is a structure that improves reception performance by generating an interference signal for a received signal by applying channel decoding and subtracting the interference signal from the received signal in a frequency domain. In the following description, a method of decoding up to a DL burst of an interference signal when generating an interference signal will be referred to as a channel decoding feedback method.

Referring to FIG. 6, the receiver 600 according to the present invention uses the control unit 610 for controlling the respective functional blocks to use the feedback of the channel decoding result and the interference signal for regenerating the interference signal using the feedback of the channel decoding result. Configured with a remover 620.

Since the receiver 600 according to the present invention has already described the reception process from the serving base station (serving cell), the interference signal canceler for regenerating the interference signal using the feedback of the control unit 610 and the channel decoding result in FIG. 620 will be described mainly.

The receiver 600 includes an interference signal canceller 620 for regenerating an interference signal received in addition to a general reception block, and a subtractor 602 for subtracting a signal regenerated from the interference signal canceller 620 from a signal of a base station currently being received. And a switching unit 604 for switching the subtraction, and a control unit 610 for controlling the use of a signal regenerated from the interference signal canceller 630 and the respective functional blocks. In the present invention, regenerating an interference signal means generating the same signal as that of the transmitter of the interference signal.

Looking at the receiver 600 in detail, the control unit 610 first detects the interference signal using the neighbor base station ID causing the interference in order to detect the interference signal. Here, the interference signal is detected by a CINR meter (not shown). The control unit 610 measures the interference signal of the neighbor base stations from the CINR measuring unit and the interference signal canceller 620 and the switching unit 604 at the control unit 610 in the neighbor base stations when the predetermined condition is satisfied. When the interference signal exceeds a predetermined threshold, the controller 610 receives the interference signal of the base station. The method for detecting an interference signal that becomes the interference signal is performed in the same manner as the OFDMA receiver as described with reference to FIG. 3. That is, the received signal is detected through the descrambler 603, the extractor 607, the channel compensator 609, the iterator combiner 611, the symbol demapper 613, and the channel decoder 615. Although the receiver 600 uses CINR to detect an interference signal, the receiver 600 may detect the interference signal by measuring the strength of a received signal, that is, the strength of a pilot signal. In this case, the controller 610 should have a pilot strength meter (not shown).

The interference signal canceller 620 regenerates the interference signal transmitted through the channel by using the interference signal detected from the receiver. Regenerating the interference signal means generating the same as the transmission signal.

The order of regenerating the interference signal follows the scheme generated in the OFDMA transmitter as shown in FIG. Accordingly, the interference signal canceller 620 includes a channel encoder 617, a symbol mapper 619, a symbol repeater 621, an allocator 623, a scrambler 625, and a multiplier 627. That is, the method for generating the interference signal is subjected to channel encoding, symbol mapping, repetition coding, allocating, and scrambling.

The multiplier 627 multiplies the generated interference signal by the channel estimation result of the channel estimator 605. Then, the interference signal received through the channel can be obtained. When the regenerated interference signal is finally subtracted from the received signal, a clean signal from which the interference signal has been removed can be obtained. The receiver 600 of the present invention may detect its own signal by using the serving cell base station ID again using the received signal from which the interference signal has been removed. The controller 610 controls the flow of these signals. That is, when detecting or regenerating an interference signal, the base station ID of the interference signal is provided to the scrambler 625, the descrambler 603, the extractor 607, and the allocator 623. The belonging base station ID is provided to the blocks.

7 is a block diagram illustrating a receiver 700 in an OFDMA system according to an embodiment of the present invention. Although FIG. 6 has an advantage of detecting a more accurate interference signal through channel encoding, the channel encoder 617 has a larger time delay and complexity than the other blocks, and thus, it is time to remove the interference signal. Latency and complexity are greatly increased. Therefore, the performance of FIG. 7 is slightly lower than that of FIG. 6, but the method can greatly reduce the latency and complexity. Note that in the following description, the same reference numerals are used for the same apparatus as the apparatus described above.

Referring to FIG. 7, the receiver 700 includes an interference signal canceller 720 for regenerating interference signals other than a general reception block, and a base station currently receiving a signal regenerated from the interference signal canceller 720. A subtractor 703 for subtracting the signal of the signal, a switching unit 705 for switching the subtraction or not, and a control unit 710 for controlling the use of the interference signal regenerated from the interference signal canceller 720 and the respective functional blocks. ) Is configured.

Unlike the channel decoding feedback method, the interference signal canceller 720 of the receiver 700 does not include a channel encoder 617, and is assigned a slicer 721, a symbol mapper 722, an iterator 723, and an assignment. Group 725, scrambler 727, and multiplier 729. The slicer 721 performs a series of processes, such as symbol mapping, using the signal output from the symbol demapper 613.

Accordingly, the interference signal canceller 720 does not perform LLR (Log Likelyhood Ratio) calculation and channel encoding by regenerating the interference signal using the received signal. That is, a method of regenerating an interference signal using a symbol demapped signal. In a communication system, a low effective code rate is achieved by using a combination of channel coding and repetitive coding for reliable delivery of important information such as control information. This method is a technique of regenerating an interference signal using only symbol combining corresponding to a repetition code.

This method has a disadvantage in that the CINR gain is lost due to no channel decoding, but it has the advantage of greatly reducing the complexity and the latency. In the following description, this method will be referred to as a slicer method.

Among them, the method using the channel decoding feedback has a high complexity, but shows better performance when the interference signal is removed. The repetitive interference signal removing apparatus and method has a large amount of interference signal when the signal transmitted by the interference cell and the serving cell are located at the same position in a time-frequency space, or when the code rate is low in a low modulation order. Even if the interference signal is decoded using the well-decoded phenomenon, the interference signal is removed, and only when the strong modulation encoding with low modulation order and low code rate is applied, a good effect can be obtained. In general, since the modulation modulation and low code rate robust modulation coding is applied to the FCH 413 and the DL-MAP 415 in FIG. 4, it is advantageous to remove the interference signal.

In the FCH 413 and DL-MAP 415 of FIG. 4, convolutional codes and convolutional turbo codes are applied to QPSK and 1/2, respectively, and 8 or 6 repetitions are performed. Has an effective code rate of 12. 6 shows an iterative interference signal cancellation apparatus using such a channel decoder.

Hereinafter, the interference cancellation technique using the channel decoding feedback method among the interference cancellation techniques described above will be described.

In FIG. 6, the received signal passing through the fast Fourier transformer 601 may be modeled as in Equation 2 below.

The <Equation 2> s _o (k) is the signal from pre-scrambling of the serving cell, c _o (k) is a channel that s _o (k) through. s _o (k) means a signal received from a cell having a segment ID of 0, and the serving sector of the serving cell does not lose its generality even if the segment ID is assumed to be 0. In the present invention, a cell having a segment ID of 0 is assumed to be a serving cell, and s _o (k) is assumed to be a signal in a frequency domain before scrambling transmitted by the serving cell. Equation (2) is modeled by dividing a signal received from a receiver into a signal of a serving cell, an interference cancelable signal, and a noise and interference signal that cannot be canceled, and have two interference cancelable signals. .

S ₁ (k) is an interference signal coming from a cell having a segment ID of 1, and S ₂ (k) is a signal received from an interfering cell having a segment ID of 2. And c ₁ (k) and c ₂ (k) are channels through which respective interference signals are inputted to the receiver.

Here, the interference signal received from the cell with segment ID 1 is c ₁ (k) q ₁ (k) s ₁ (k), and the interference signal received from the cell with sector ID 2 is c ₂ (k) q ₂ ( k) s ₂ (k).

Therefore, in the present invention, c ₁ (k) q ₁ (k) s ₁ (k) and c ₂ (k) q ₂ (k) s ₂ (k) become interference signals to be removed. n (k) is noise, and I (k) is the sum of interference signals that are not included in the interference cancellation target or that interference cancellation is impossible.

In general, the reference included in the interference target among the interference signals received by the receiver may be the size of the carrier-to-interference noise ratio (CINR) of each interference signal, which is actually removable as described above. The interfering signal generally has a preamble ID distinct from the serving cell and is limited to interfering signals having a CINR above a threshold. Although a preferred embodiment of the present invention describes a method of removing an interference signal by measuring the size of a CINR, the interference signal may be removed based on the strength of a signal received from a serving cell and a neighboring cell in addition to the CINR. However, in the embodiments of the present invention described below, a method of performing interference cancellation using CINR will be described.

This is because, when an interference cancellation is attempted for an interference signal whose CINR is less than or equal to a threshold, it is impossible to correctly reproduce the interference signal, which is a factor of performance deterioration. In the present invention, c ₁ (k) q ₁ (k) s ₁ (k) and c ₂ (k) q ₂ (k) s ₂ (k) as the interference cancellation target, first, c ₁ (k) q Assume that ₁ (k) s ₁ (k) is removed, and c is the order in which c ₂ (k) q ₂ (k) s ₂ (k) is removed.

Actually, the final signal to be obtained by interference cancellation from the received signal of Equation 2 is expressed by Equation 3 below.

That is, the interference signal i ₁ (k) = c ₁ (k) q ₁ (k) s ₁ (k), i ₂ (k) = c ₂ (k) q ₂ in Equation 2 through interference cancellation. will remove (k) s ₂ (k).

First, the OFDMA receiver 600 according to the present invention assumes S ₁ (k) as a signal to be decoded and proceeds with the operation of a general receiver. The channel estimator 605 then estimates c ₁ (k), regenerates i ₁ (k) through the decoding process and symbol mapping, and subtracts i ₁ (k) from y (k) via a subtractor 604. By subtracting, the interference signal from the cell having the sector ID of 1 is removed from y (k).

Then, i ₂ (k) is regenerated from the signal from which i ₁ (k) has been removed to remove the interference signal from the cell having sector ID 2, thereby removing the interference signal. The ideal form of the final signal obtained through this process is shown in Equation 4 below.

However, since i ₁ (k) and i ₂ (k) cannot be completely reproduced, the final signal is obtained as shown in Equation 5 below.

는 i₁(k)의 근사치이며,

는 i₂(k)의 근사치 이다.After this interference cancellation process, the interference cancellation receiver decodes the data transmitted from the serving cell through a final decoding process. In Equation 5 above

Is an approximation of i ₁ (k),

Is an approximation of i ₂ (k).

The receiver of the OFDM and OFDMA systems generates an input metric of the channel decoder 615 while passing the symbol demapper 613 from the channel compensated signal. The generation of such a metric requires proper normalization so that the channel decoder 615 shows optimal performance. The data p (l) in the frequency domain can be expressed as in Equation 6 below.

P (l) is data passed through the channel of s (l) and can be viewed as data after descrambling and extracting the frequency domain of the data actually received. That is, p (l) is multiplied by the channel response c (l) and appears as a sum of noise signals. Where n _xl and n _yl are the noise of the channel containing the interfering signal. C (l) s (l) may be represented by a complex number A ₁ + jB ₁ . In this case, s (l) may be obtained as shown in Equation 7 below.

Equation 7 represents mapping from information bits to QAM symbols. m bits generate one QAM symbol. In the case of IEEE 802.16, m has values of 2, 4, and 6, which correspond to QPSK, 16QAM, and 64QAM, respectively. 8 is a constellation diagram according to input bits of QPSK, 16QAM, and 64QAM. In Figure 8 it can be seen the relationship of the output symbol for each information bit.

In a communication system using QAM modulation, for channel decoding, a metric reflecting the reliability of each bit constituting the codeword is obtained using the received QAM symbol p (l) and the channel response c (l). In general, this confidence can be expressed as a loglikelihood ratio. The Log Likelihood Ratio (LLR) for u _{l, i,} which is a bit constituting the received QAM symbol p (l), is expressed by Equation 8 below.

은 간섭 및 잡음 신호의 분산이며, 간섭 및 잡음 추정부(902)에 의해 생성되어 LLR 정규화기(904)로 출력된다. 따라서 LLR 정규화기(904)는 채널 디코더(615)의 입력으로 사용될 적절한 LLR 값의 계산을 위해

값 혹은 그에 상응하는 가공된 값이 필요하게 된다. 상기 LLR의 계산에서 정규화에 해당하는

을 제외한 L(-u_l,i)는 다양한 방법으로 계산이 가능하다. 예를 들어, [Y . Xu, H.-J. Su, E.Geraniotis, "Polot symbol assisted QAM with interleaved filtering and turbo decoding over Rayleigh flat-fading channel," in Proc. MICOM ' 99, pp.86-91]의 논문에 기재된 듀얼 최소 메트릭(Dual minmum metric)법을 사용하여, 매우 간단한 선형 계산만으로 LLR 값의 근사치를 얻을 수 있다.In Equation 8 above

Is the variance of the interference and noise signals, and is generated by the interference and noise estimator 902 and output to the LLR normalizer 904. Thus, the LLR normalizer 904 can calculate the appropriate LLR value to be used as the input of the channel decoder 615.

The value or the corresponding milled value is required. Corresponding to normalization in the calculation of the LLR

L (-u _{l, i} ) can be calculated in various ways. For example, [Y. Xu, H.-J. Su, E. Geraniotis, "Polot symbol assisted QAM with interleaved filtering and turbo decoding over Rayleigh flat-fading channel," in Proc. Using the dual minmum metric method described in MICOM '99, pp. 86-91, an approximation of the LLR value can be obtained with very simple linear calculation.

에 해당하는 정규화를 행해야 최적의 채널 복호 성능을 얻을 수 있으며, 하드웨어 복잡도를 최소화 할 수 있다. 이러한 정규화를 위하여, 채널 디코더(615)에서 복호될 신호에 대한 간섭 및 잡음 분산

값 혹은 그에 상응하는 정규화 파라미터가 필요하며, 이러한 파라미터를 이용하여 정규화를 수행함으로써 간섭 신호 제거기(620)를 구비한 수신기를 구현할 시 효율을 높일 수 있다.

에 해당하는 정규화는 상기 설명한 L(-u_l,i)의 계산 혹은 듀얼 최소 메트릭 법 혹은 디맵핑을 수행한 후에 출력된 비트 메트릭에 적용될 수 있다. 혹은 L(-u_l,i)의 계산 혹은 듀얼 최소 메트릭 법 혹은 디매핑을 수행하기 전에 정규화를 적용하는 것도 가능하다. 본 발명은 추출(Deallocation)이후 수행해야하는 모든 과정 중에서

혹은 그에 상응하는 정보를 이용하여 가능한 모든 정규화 방법을 포함한다.Decoding is performed in the channel decoder 615 using the LLR thus obtained. In order to prevent performance deterioration at the time of performing the fixed point operation,

Normalization is performed to obtain optimal channel decoding performance and to minimize hardware complexity. For this normalization, interference and noise variance for the signal to be decoded in the channel decoder 615

A value or a normalization parameter corresponding thereto is required, and the normalization may be performed using these parameters to increase efficiency when implementing a receiver having an interference signal canceller 620.

The normalization corresponding to may be applied to the bit metric output after performing the above-described calculation of L (−u _{l, i} ) or the dual minimum metric method or demapping. It is also possible to apply normalization before performing the calculation of L (-u _{l, i} ) or the dual least metric method or demapping. The present invention out of all the processes that must be performed after the extraction (Deallocation)

Or include all possible normalization methods using the corresponding information.

The OFDMA receivers equipped with the interference cancellers 620 and 720 described with reference to FIGS. 6 and 7 greatly improve the reception performance of the terminal in the case where the interference between cells is severe. When the interference cancellation technique using the channel decoding feedback method described in FIG. 6 is implemented in the terminal, and the general automatic gain control loop is operated, the automatic gain control loop is a sum of the magnitude of the magnetic signal and the magnitude of the interference signal. Will adjust the gain.

In this case, when the interference signals are sufficiently smaller than the magnetic signal, in the decoding process of the first interference signal, normalization of the channel decoding input is not appropriate, and there may be a performance degradation in the decoding process of the first interference signal. The reason for this is that in channel decoding performing fixed-point arithmetic, the optimal performance of the input metric requires proper normalization. The magnitude of the first interfering signal is automatically adjusted by the gain control loop and the channel compensator 609 and the iterative combiner. This is because a case in which the general operation range is exceeded by the interworking process of the 611 and the symbol demapub 613 may occur.

The automatic gain control loop performs an operation so that the representation range of the values processed inside the receiver is appropriately within the representation range provided by the hardware while the receiver is processing the signal. However, if it is sufficiently smaller than the magnetic signal of the interfering signals, the automatic gain adjustment loop will suit the magnetic signal. Therefore, the interfering signal is represented by a much smaller value, and if only channel compensation and symbol demapping are performed, the value of the input metric of the channel decoder 615 is represented by a value much smaller than an appropriate representation range. At this time, performance deterioration is caused during channel decoding.

For example, an input metric of the channel decoder 615 may represent 127 to -127, and it is assumed that the channel decoder 615 exhibits sufficient performance only when the average of the metric is about 32. However, when the interference signal is actually a much smaller value than the magnetic signal, and the input average becomes 5, only a much smaller range is expressed even though the actual expression range is 127 to -127. Performance degradation also occurs in actual channel decoding.

In this case, the reliability of the feedback value will be lowered, and error propagation may occur even in the interference cancellation process, which may lead to performance degradation of the overall interference cancellation technique. That is, when the signal to remove the interference is not properly decoded, a large difference between the original interference signal and the estimated interference signal causes a lot of errors even when the magnetic signal is decoded.

In the actual implementation, however, interference cancellation is not performed when the size of the interference signal is sufficiently smaller than that of the magnetic signal, so this case is not a problem.

In particular, when the size of the interference signal is larger than the magnetic signal received from the serving cell, it may cause greater performance degradation. The reason is that even if normal channel decoding is performed on the interference signal to be decoded first, the magnitude of the magnetic signal remaining after the interference cancellation is too small, so that the input of the channel decoder 615 generated by the symbol demapper 613 is generated. The value of the metric becomes a small value out of an appropriate size, which may cause performance deterioration.

Accordingly, embodiments of the present invention will be described in the OFDMA receiver equipped with the interference canceller 620, a method and apparatus for preventing performance degradation during channel decoding by the implementation of a fixed point operation during the interference cancellation process. In other words, the performance of the channel decoder 615 does not occur when the receiver implements two or more iterative channel decoding processes. To this end, embodiments of performing input metric normalization of the channel decoder 615 using interference and noise variance corresponding to a signal to be decoded at the time of decoding each channel will be described below.

FIG. 9 is a block diagram of a device for normalizing an input metric of a channel decoder 615 in an OFDMA receiver 900 equipped with an iterative interference canceller 620 according to a first embodiment of the present invention. That is, FIG. 9 relates to normalization of the channel decoder 615 input metric in the OFDMA receiver 900 for canceling the interference signal using the channel decoding feedback method. First, the normalization process will be described, and the components of FIG. 9 will be described.

As described above, the present invention removes the interference signal by sequentially removing the interference signals i ₁ (k) and i ₂ (k) from Equation (1).

이며, 상기 간섭 및 잡음에 대한 분산은 하기 <수학식 9>와 같다.In order to remove the interference, the receiver 900 decodes the signal s ₁ (k) of the interfering cell having the segment ID of 1 to obtain d _i1 (n), and thus, c ₁ (k) through the channel estimator 605. ) Is estimated by passing the symbol demapper 613 with a signal obtained by multiplying y (k) by q (k) and c ₁ (k) ^* (conjugate complex number of c ₁ (k)). Get the input metric. At this time, the signals obtained by subtracting i ₁ (k) from y (k) are defined as interference and noise signals to define interference and noise variance values. In this case, in decoding of d ₁ (n), interference and noise are

The dispersion for the interference and noise is expressed by Equation 9 below.

을 반영시킨다. 채널 디코더(615)에서 채널 디코딩을 수행한 후, 신호 i₁(k)를 재생성하여 y(k)로부터 i₁(k)를 제거하는 것이 가능하다. 간섭 제거를 수행한 후의 신호 즉, 감산기(602)를 통과한 신호는 하기 <수학식 10>과 같다.In Equation 9, V [.] Is a function that reflects variance. In performing the decoding of d ₁ (n), the normalization of the input metric of the channel decoder 615 is performed.

To reflect. After performing a channel decoding in a channel decoder 615, the re-create the signal i ₁ (k) and it is possible to eliminate the ₁ i (k) from y (k). The signal after performing the interference cancellation, that is, the signal passing through the subtractor 602 is expressed by Equation 10 below.

의 분산으로서, 하기 <수학식 11>과 같다.Subsequently, decoding and interference cancellation are performed on d _i2 (n), which is a signal transmitted from an interference cell having a sector ID of 2. In performing interference cancellation for i ₂ (k), the values of interference and noise variance used are the interference signals for i ₂ (k) in the remaining signal.

As a dispersion, it is represented by the following formula (11).

를 이용한다. The decoding process for the i ₂ (k) signal is performed in the same manner as the decoding of i ₁ (k). In the decoding process, Equation 11

Use

If decoding of the i ₂ (k) signal is successful, d ₂ (n) can be obtained, and i ₂ (k) can be effectively obtained. However, in this decoding process, the noise contributing to the normalization of the metric can be approximated as shown in Equation 12 under the assumption that the decoding and interference elimination of d ₁ (n) is perfectly performed.

대신

을 사용하는 것도 가능하다. 정상적으로 간섭 제거가 이루어지는 상황에서는

이 0 에 가깝게 되고,

이

에 거의 유사한 값이 될 것이기 때문이다. 본 발명에서는

와

을 사용하는 경우를 모두 포함한다.In the decoding process of i ₂ (k)

instead

It is also possible to use. In situations where interference is normally removed

Is closer to zero,

this

Because it will be almost the same value. In the present invention

Wow

This includes all cases of using.

After the interference cancellation is performed on the interference signals i ₁ (k) and i ₂ (k), the last remaining signal is represented by Equation 13 below.

Then, from Equation 13, d _o (k), which is a signal transmitted from the serving cell, is decoded. In this case, when normalizing the input metric of the channel decoder 615, the interference and noise for s ₀ (k) may be expressed as Equation 14 below.

In addition, the variance of Equation 14 is equal to Equation 15 below.

Under the assumption that the interference cancellation is almost complete, Equation 16 holds.

혹은

을 사용하는 것이 가능하다. 이는 간섭 제거가 잘 이루어졌을 경우,

및

의 값이 충분히 작은 값이 되어

는

의 근사값으로 사용하여도 무방하기 때문이다. 본 발명에서는

혹은

및 이에 해당하는 값의 가공된 값을 이용하여, 정규화에 이용하는 과정을 포함한다.In addition, even in the final normalization process of the magnetic signal,

or

It is possible to use This means that if the interference is removed well,

And

Is a small enough value

Is

This is because it may be used as an approximation of. In the present invention

or

And using the processed value of the corresponding value, for normalization.

및

는 각 간섭 제거의 단계에서 간섭이 제거된 신호, y'(k)에서 추출된 파일럿 부반송파를 이용하여 계산한다. 이는 다양한 방법으로 계산 가능하다. The interference and noise dispersion of Equation 9, Equation 11, Equation 12, Equation 15, and Equation 16 are based on a preamble or data region in the IEEE 802.16e OFDMA system. The pilot subcarrier can be used to calculate in various ways. First, the interference and noise variance given in Equations 11 and 15 above.

And

Is calculated using a signal from which interference is removed at each interference cancellation step, and pilot subcarriers extracted from y '(k). This can be calculated in various ways.

및

는 프리앰블의 파일럿을 이용하여, 추정할 수 있다. 프리앰블에서는 세그먼트 ID별로 서로 겹치지 않는 파일럿 만을 사용하기 때문에, <수학식 12> 및 <수학식 16>에서 주어지는

및

을 다음과 같은 방법으로 계산할 수 있다.Approximate values of interference and noise variance given by Equations 12 and 16

And

Can be estimated using the pilot of the preamble. Since the preamble uses only pilots that do not overlap each other for each segment ID, the equations given by Equations 12 and 16

And

Can be calculated in the following way.

In general, in the OFDMA system of IEEE 802.16e, the variances as shown in Equation 17 can be calculated through power measurement using the point that pilots used when the segment IDs of the preambles are different do not overlap.

는 상기 <수학식 17>에서 주어진 바와 같이 서빙 셀의 신호 s₀(k)에 대한 수신 전력의 추정치이다. 이는 프리앰블의 파일럿 부반송파를 이용하여 추정할 수 있다. 단, 실제 추정치에는 세그먼트 ID 0을 같이 사용하는 간섭 신호의 전력이 더해질 수 있으나, 셀 계획이 잘 되었다면 이 값을 무시할 정도로 작은 값일 것이다. 상기 <수학식 17>에서

및

는 식에서 주어지는바와 같이 간섭 셀의 신호 s₁(k) 및 s₂(k)에 대한 수신 전력의 추정치이다. 실제 추정치에는 세그먼트 ID가 일치하는 다른 셀의 신호 전력의 값이 더해질 수 있다. 상기 <수학식 9>, <수학식 12>, <수학식 16>에서 주어지는 상기 간섭 및 잡음 분산의 값은 상기 <수학식 17>에서 주어진 값들을 이용하여, 하기 <수학식 18>과 같이 나타낼 수 있다.Using the variances calculated by Equation 17, it is possible to calculate the interference and noise variances given by Equations 12 and 16, which were required in the interference cancellation process. From above

Is an estimate of the received power for the signal s ₀ (k) of the serving cell as given by Equation 17 above. This can be estimated using the pilot subcarriers of the preamble. However, the actual estimate may be added to the power of the interference signal using the segment ID 0, but if the cell planning is good, the value may be small enough to ignore this value. In Equation 17 above

And

Is an estimate of the received power for the signals s ₁ (k) and s ₂ (k) of the interfering cells, as given in the equation. The actual estimate may be added with the value of the signal power of another cell with the matching segment ID. The interference and noise variance values given in Equations 9, 12, and 16 are represented by Equation 18 using the values given in Equation 17. Can be.

의 선형 조합으로 나타낼 수 있다.The noise and variance listed as in Equation 18 are the variance values calculated in Equation 17.

It can be represented by a linear combination of.

를 사용한다. 또한 LLR 정규화기(904)에서는 간섭 제거의 각 단계에서 채널 디코더(615) 입력 메트릭의 정규화를 위하여 필요한 간섭 및 잡음 분산 값으로

을 사용할 수도 있다. 단, 전자를 사용하는 경우에는 간섭 및 잡음 분산을 계산하는 데에 있어, 간섭이 제거된 신호, y'(k)를 이용하여, 잡음 분산을 반복적으로 계산을 해야 한다. 상술한 바와 같이

을 사용하는 경우는 상기 <수학식 18>과 같이 미리 계산된 간섭 및 잡음 분산을 이용할 수 있다. 이는 프리앰블에서 이미

이 계산되며,

는 단지

의 선형 조합으로 표현이 가능하기 때문이다. 이때는 간섭 및 잡음 분산의 계산에 있어, 프리앰블의 y(k)만을 이용하는 것으로 충분하다.In order to normalize the channel decoder input metric while the receiver proceeds with the interference cancellation, the LLR normalizer 904 at each stage of the interference cancellation

Use The LLR normalizer 904 also uses the interference and noise variance values required for normalization of the channel decoder 615 input metrics at each stage of interference cancellation.

You can also use However, in the case of using the former, in calculating the interference and noise variance, it is necessary to repeatedly calculate the noise variance using the signal from which the interference is removed, y '(k). As mentioned above

In the case of using, the interference and noise variance calculated in advance as in Equation 18 may be used. This is already in the preamble

Is calculated,

Just

Because it can be expressed as a linear combination of. In this case, it is sufficient to use only y (k) of the preamble in the calculation of interference and noise variance.

9, which was mentioned above, illustrates one of the normalization methods of the channel decoder 625 input metric for the receiver 900 equipped with the interference canceller 620.

를 사용하는 경우이다.또한, 상기 도 9에서는 심볼 디맵퍼(613)로부터 출력되는 LLR 값을 간섭 및 잡음 분산의 역인

을 곱하거나, 이에 상응하는 동작을 취함으로써, 채널 디코더(615)의 입력 메트릭 정규화를 수행한다. 즉, 상기 도 9에서는 상기 <수학식 8>에서와 같이 심볼 디맵퍼(613)에서 L(-u_i,j)를 먼저 계산하고, 그 후에

을 곱하는 동작을 수행한다. 간섭 및 잡음 분산은 y(k)로부터 구해지며, 미리 구해진 간섭 및 잡음 분산

로부터, 반복적인 간섭 신호 제거에 이용되는 간섭 및 잡음 분산의 값

을 계산해 낸다. 이 동작은 간섭 및 잡음 분산 추정기(902)에서 행해지며, 제어부(910)에서는 간섭 및 잡음 분산 추정기(902)로 간섭 제거의 각 단계에 맞게

중 어느 것을 출력할 것인지에 대한 정보(IC Info.)를 제공한다.9 illustrates interference and noise dispersion in the process of removing the interference signal.

In addition, in FIG. 9, the LLR value output from the symbol demapper 613 is the inverse of the interference and noise variance.

By multiplying or taking a corresponding action, the input metric normalization of the channel decoder 615 is performed. That is, in FIG. 9, L (-u _{i, j} ) is first calculated by the symbol demapper 613 as shown in Equation 8, and then

Multiply by. The interference and noise variance is obtained from y (k), and the previously obtained interference and noise variance

Value of the interference and noise variance used for repetitive interference signal cancellation

Calculate This operation is performed by the interference and noise variance estimator 902, and the control unit 910 uses the interference and noise variance estimator 902 for each step of interference cancellation.

Provides information (IC Info.) On which to output.

을 전달할 경우에는, 상기 LLR 정규화기(904)는 상기

의 역수를 심볼 디매핑된 신호 L(-u_l,i)에 곱하고,

을 전달할 경우에는 상기 LLR 정규화기(902)는 상기

에 상기 심볼 디매핑된 신호 L(-u_l,i)를 곱한 신호를 채널 디코더(615)로 출력한다.The interference and noise variance estimator 902 provides the normalizer 904 with an interference and noise variance value corresponding to the information received from the controller 910 or corresponding information (meaning processed information). That is, an interference and noise variance estimator 902 is sent to the LLR normalizer 904.

In case of passing the LLR normalizer 904

Multiply the inverse of by the symbol demapped signal L (-u _{l, i} ),

When passing the LLR normalizer 902 is the

A signal obtained by multiplying the symbol de-mapped signal L (−u _{l, i} ) by the channel decoder 615 is output.

FIG. 10 is a block diagram of an apparatus for normalizing an input metric of a channel decoder in an OFDMA receiver 1000 equipped with an iterative interference canceller 620 according to a second embodiment of the present invention.

을 미리 곱하여 정규화를 실현한다.In FIG. 10 according to the second embodiment of the present invention, the operation similar to that of FIG. 9 is performed, except that the normalization of the channel decoder 615 input metric is performed at another position. That is, in FIG. 10, the output of the channel compensator 609 is normalized in advance by the normalizer 1004, so that the input of the channel decoder 615 operates in an appropriate region. That is, in FIG. 10, the input of the repeater coupler 611 is used.

Multiply in advance to realize normalization.

FIG. 11 is a block diagram of an apparatus for normalizing an input metric of a channel decoder 615 in an OFDMA receiver 1100 having an iterative interference canceller 620 according to a third embodiment of the present invention.

In FIG. 11, normalization of the metric is made at the output of the extractor 607.

Other configurations are the same as the above embodiments and will be omitted.

을 이용한다는 점이 다르다. 이 경우에는 잡음 및 간섭 분산을 추정함에 있어, 반복적으로 얻어지는 y'(k)의 값을 이용해야 한다. 실제

을 계산함에 있어 y'(k)로부터 추출된 파일럿 부반송파를 이용한다. 상기 도 12에서는 심볼 디맵퍼(613)의 출력에 정규화를 적용하였다.FIG. 12 is a block diagram of an apparatus for normalizing an input metric of a channel decoder 615 in an OFDMA receiver 1200 equipped with an iterative interference canceller 620 according to a fourth embodiment of the present invention. In the fourth embodiment of the present invention, the same operation as in FIG. 9 is performed, but with interference and noise dispersion.

The difference is that it uses. In this case, in estimating noise and interference variance, the value of y '(k) obtained repeatedly should be used. real

In calculating, we use the pilot subcarriers extracted from y '(k). In FIG. 12, normalization is applied to the output of the symbol demapper 613.

을 이용한다. 상기 도 13에서 수신기(1300)는 간섭 및 잡음 분산을 추정함에 있어, y'(k)를 이용하여, 반복적으로 계산되어야 한다.

를 계산함에 있어 y'(k)로부터 추출된 파일럿 부반송파를 이용한다. 이렇게 구해진 간섭 및 잡음 분산을 이용하여, 채널 보상기(609)의 출력 에 간섭 및 잡음 분산의 역을 곱하는 정규화를 적용함으로써, 채널 디코더(615)입력의 정규화를 실현한다.FIG. 13 is a block diagram of an apparatus for normalizing an input metric of a channel decoder 615 in an OFDMA receiver 1300 having an iterative interference canceller 620 according to a fifth exemplary embodiment of the present invention. In the fifth embodiment, as in the embodiment of FIG.

Use In FIG. 13, the receiver 1300 needs to be repeatedly calculated using y '(k) in estimating interference and noise variance.

In calculating, we use the pilot subcarriers extracted from y '(k). Using the obtained interference and noise variance, the normalization of the input of the channel decoder 615 is realized by applying a normalization by multiplying the inverse of the interference and noise variance to the output of the channel compensator 609.

14 is a block diagram of an apparatus for normalizing an input metric of a channel decoder in an OFDMA receiver 1400 having an iterative interference canceller 620 according to a sixth preferred embodiment of the present invention.

In FIG. 14, the interference and noise estimator 1402 obtains interference and noise information in the same manner as in FIG. 13, and normalizes the output of the symbol extractor 613 through the symbol normalizer 1404. Other configurations are the same as the above embodiments and will be omitted.

FIG. 15 is a block diagram of an apparatus for normalizing an input metric of a channel decoder 615 in an OFDMA receiver 1400 equipped with an interference canceller 720 of a slicer method according to a seventh preferred embodiment of the present invention.

를 사용하며, 심볼 디맵퍼(613)의 출력을 정규화하는 것으로 되어있으나, 상술한 채널 복호 피드백 방법의 실시 예인 제1 내지 제6실시 예들과 같이 정규화기를 사용하여 채널 디코더(615)의 입력 메트릭을 정규화 할 수 있음은 당업자라면, 당연할 것이다.15 is an example of an input metric normalization method of a channel decoder in an interference cancellation receiver using a slicer method. Here, slicing means hard decision. In this method, normalization is performed only when decoding the last magnetic signal without performing normalization when performing interference cancellation. 15 illustrates the metric normalization for the channel decoder 615.

Although the output of the symbol demapper 613 is normalized, the input metric of the channel decoder 615 is determined using a normalizer as in the first to sixth embodiments of the channel decoding feedback method described above. It will be obvious to those skilled in the art that this can be normalized.

16 is a flowchart illustrating a method for normalizing an input metric of a channel decoder 615 in a receiver having an interference signal canceller 620 according to a channel decoding feedback method according to embodiments of the present invention. The flowchart illustrates that the removal of the interference signal to which the low code rate is applied to the control information to which the low code rate is applied in the interference cancellation.

Referring to FIG. 16, in order to remove an interference signal, the receiver first scans an ID of a neighbor BS that is causing interference in step 1601 and measures a CINR value corresponding to the BS ID. . Here, the CINR measurement value uses a CINR measurement device that is provided in advance. Then, in step 1603, the receiver compares the measured CINR values of the neighboring base stations with the CINR values of the serving BS to which the current terminal belongs, and then measures the interference of the neighboring base stations, and then compares the CINRs of the serving base station and the neighboring base stations. do. Here, the comparison method may include a method of checking whether a difference between two CINRs is greater than a predetermined threshold value. In step 1605, the receiver selects and lists neighboring base stations whose comparison result satisfies a predetermined condition. For example, there may be an enumeration method in which an interference signal is arranged in order of increasing magnitude but no further decoding is performed after decoding of the own signal.

Then, in step 1607, the receiver selects the base station having the largest CINR to remove the interference signal received from the interference base station signal having the strongest interference among the selected base stations. That is, in step 1605, the sequence of base station signals to be decoded is listed, and in step 1607, the interfering base station signals to be decoded are determined in the listed order.

 The reason why the interference signal is removed from the base station signal is that the interference signal is easier to detect than the weak signal is detected, the interference cancellation performance is increased. In step 1607, when the interference signal is selected to the signal of the base station, the interference signal and noise variance of the base station is calculated in step 1609, and in step 1611 normalization of the interference signal of the base station. The interference signal normalization in operation 1611 may be applied to an output of the symbol demapper 613, an output of the channel compensator 609, and an output of the extractor 607. After normalization of the interference signal, the receiver decodes the signal of the corresponding base station in step 1613. In step 1613, the decoding of the OFDMA frame is started. Step 1613 includes all steps that must be completed before full interference cancellation starts, such as reception of a preamble.

In operation 1615, the receiver regenerates the decoded interference signal by using an interference signal canceller. In step 1615, the interference signal is regenerated through a process of channel encoding, modulation, subchannel repetition, allocation, and the like based on the decoded data in step 1613.

Then, in step 1617, the receiver subtracts the interference signal generated from the reception signal of the serving base station by the subtractor 602 to perform the interference signal removal process. Here, the reconstruction and removal of the interference signal regenerates and removes a signal after channel decoding as in the channel decoding feedback method.

In step 1617, the receiver which removes the strongest interference signal checks whether the interference signal removal is completed. The method of checking whether the interference signal removal is completed in step 1619 is when there is no base station satisfying a predetermined condition in step 1619. Accordingly, if the interference signal removal is not completed, the process proceeds to step 1607 to remove the interference signal of the base station next to the removed interference signal, followed by the base station transmitting the interference and noise signal removed in step 1617. In step 1609, the base station having a high strength is selected, the interference signal and noise variance of the selected base station are calculated, and in step 1611, the process of normalizing the interference signal is repeated.

On the other hand, if the removal of the interference signals of the currently serving base station is completed as a result of the check in step 1619, the receiver proceeds to step 1621 to calculate the interference and noise variance of the serving base station signal. In step 1623, after normalizing the serving base station signal, in step 1625, the signal of the serving base station serving the receiver is decoded.

17 is a flowchart illustrating a method for normalizing a channel decoder 615 input metric in a receiver having an interference signal canceller 720 according to a slicer method according to embodiments of the present invention.

Referring to FIG. 17, in order to remove an interference signal, the receiver first scans an ID of a neighbor BS that is causing interference in step 1701 and measures a CINR value corresponding to the BS ID. . Here, the CINR measurement value uses a CINR measurement device that is provided in advance. Then, in step 1703, the receiver compares the measured CINR values of the neighboring base stations with the CINR values of the serving base station (Serving BS), and then compares the CINRs of the serving base station and the neighboring base station. do. Here, the comparison method may include a method of checking whether a difference between two CINRs is greater than a predetermined threshold value. In step 1705, the receiver selects neighboring base stations whose comparison result satisfies a predetermined condition. The base station satisfying the predetermined condition indicates neighboring base stations with severe interference.

Then, in step 1707, the receiver selects the base station having the largest CINR to remove the interference signal received from the interference base station signal having the strongest interference among the selected base stations. That is, in step 1705, the order of the base station signals to be decoded are listed, and in step 1707, the interfering base station signals to be decoded are determined in the order of the decoding.

The reason why the interference signal is removed from the base station signal is that the interference signal is easier to detect than the weak signal is detected, the interference cancellation performance is increased. In step 1707, when the interference signal of the base station is selected, the signal of the base station is sliced (hard decision). In operation 1711, the signal of the corresponding base station is regenerated by the interference signal canceller 720. In step 1711, the interference signal is regenerated through the process of symbol mapping, subchannel repetition, and allocation after the slicing in step 1709.

Thereafter, in step 1713, the receiver subtracts the interference signal generated from the received signal of the serving base station by the subtractor 703 to perform the interference signal removal process. Here, the regeneration and removal of the interference signal regenerates and removes a signal before channel decoding as in the slicer method.

In step 1713, the receiver which removes the strongest interference signal checks whether the interference signal removal is completed. The method of checking whether the interference signal removal is completed in step 1715 is when there is no base station satisfying a predetermined condition in step 1715. Accordingly, if the interference signal removal is not completed, the process proceeds to step 1707 to remove the interference signal of the base station next to the removed interference signal, followed by the base station transmitting the interference and noise signals subtracted in step 1713. In step 1709, select the base station to transmit the signal, and slicing the signal of the next strong base station, regenerating the interference signal in step 1711, and subtracts the interference signal in step 1713.

On the other hand, if the removal of the interference signals of the currently serving base station is completed as a result of the check in step 1715, the receiver proceeds to step 1717 to calculate the interference and noise variance of the serving base station signal. In operation 1719, after normalizing the serving base station signal, in step 1721, the signal of the serving base station serving the receiver is decoded.

That is, FIG. 17 performs a process similar to that of FIG. 16, but since the slicer method is used instead of the channel decoding feedback method in the processing of the interference signal, metric normalization of the interference signal is not required.

As described above, according to the present invention, in an interference cancellation receiver using a channel decoding feedback method in a receiver of an OFDMA system, two or more iterative channel decoding processes are implemented in the interference cancellation process. By performing normalization of the input metric of the channel decoder using interference and noise variance corresponding to the signal, degradation of performance in the channel decoder can be minimized.

Claims (25)

In the method of receiving a signal transmitted from a serving base station in a receiver of an Orthogonal Frequency Division Multiple Access (OFDMA) system, Detecting an interference signal from signals received from neighboring base stations and the serving base station; Measuring the intensity of the detected interference signals and checking whether the detected interference signals are greater than a predetermined threshold value; Aligning neighboring base stations satisfying the test; Selecting and detecting an interference signal in order of neighbor base stations to be aligned; Calculating and normalizing interference and noise variance of the detected interference signal; Decoding and regenerating the normalized interference signal; And subtracting the regenerated interference signal from the received signal. According to claim 1, The process of detecting the interference signal, And measuring a carrier to noise interference ratio (CINR) of the signals received from the neighbor base stations and the serving base station. Way. According to claim 1, The process of detecting the interference signal, And measuring strength of pilot signals received from the neighbor base stations and the serving base station. The method of claim 1, wherein the sorting of the list of neighbor base stations satisfying the condition is as follows. The method of removing neighbor cell interference signals in an orthogonal frequency multiple access system, characterized in that it comprises the step of identifying by using the identifier (ID) of the neighbor base stations. The method of claim 1, wherein the selecting and detecting the interference signal in the order of the order of the neighboring base stations is performed. Sorting the list of neighboring base stations in order of the strength of the interference signal of the neighboring base stations; Receiving and descrambling the neighbor base station signal having the greatest intensity of the interference signal among the aligned neighbor base stations; Extracting the descrambled signal; Performing channel compensation on the extracted signal; Repeatedly combining the channel compensated signal; And symbol demapping the repeated combined signal. The method of claim 5, wherein decoding and regenerating the normalized interference signal comprises: Detecting and encoding the decoded interference signal; Symbol mapping the encoded signal; Repeating the symbol-mapped signal a predetermined number of times; Allocating a subcarrier to the repeated signal; And performing scrambling on the signal to which the subcarrier has been allocated. The method of claim 1, wherein the decoding and regenerating of the normalized interference signal comprises: And normalizing an input metric of a channel decoder using interference and noise variance corresponding to the signal to be decoded. According to claim 1, Removing all the interference signals, normalizing the input metric of the channel decoder by using the interference and noise variance of the signal received from the serving base station. Way. In the method of receiving a signal transmitted from a serving base station in a receiver of an Orthogonal Frequency Division Multiple Access (OFDMA) system, Detecting an interference signal from signals received from neighboring base stations and the serving base station; Measuring the intensity of the detected interference signals and checking whether the detected interference signals are greater than a predetermined threshold value; Sorting a list of neighboring base stations satisfying the condition; Selecting and detecting an interference signal in order of the aligned neighbor base stations; Slicing and regenerating the normalized interference signal; And subtracting the regenerated interference signal from the received signal. The method of claim 9, Detecting the interference signal from the signals received from the neighbor base stations and the serving base station, A method of canceling adjacent cell interference signals in an orthogonal frequency multiple access system, comprising measuring a carrier to noise interference ratio (CINR) of signals received from neighboring base stations and the serving base station. . The method of claim 9, Detecting the interference signal from the signals received from the neighbor base stations and the serving base station, And measuring strength of pilot signals received from the neighbor base stations and the serving base station. The method of claim 9, wherein the sorting of the list of neighbor base stations satisfying the condition is as follows. The method of removing neighbor cell interference signals in an orthogonal frequency multiple access system, characterized in that it comprises the step of identifying by using the identifier (ID) of the neighbor base stations. The method of claim 9, wherein the selecting and detecting the interference signal in the order of the order of the neighboring base stations is performed. Sorting the list of neighboring base stations in order of the strength of the interference signal of the neighboring base stations; Receiving and descrambling the neighbor base station signal having the greatest intensity of the interference signal among the aligned neighbor base stations; Extracting the descrambled signal; Performing channel compensation on the extracted signal; Repeatedly combining the channel compensated signal; And symbol demapping the repeated combined signal. The method of claim 13, wherein regenerating the normalized interference signal comprises: Detecting and slicing the symbol-mapped signal; Symbol mapping the sliced signal; Repeating the symbol-mapped signal a predetermined number of times; Allocating a subcarrier to the repeated signal; And performing scrambling on the signal to which the subcarrier has been allocated. The method of claim 9, Removing all the interference signals, normalizing the input metric of the channel decoder by using the interference and noise variance of the signal received from the serving base station. Way. A receiver for receiving a signal transmitted from a serving base station in an orthogonal frequency division multiple access (OFDMA) system, By measuring the signal strength received from the serving base station and the signal strength received from the neighboring base station and regenerating the interference signal received from the neighboring base station when the difference in the signal strength satisfies a predetermined threshold value; A control unit controlling an output of a distribution of a specific interference and noise signal among signals received from a serving base station and the neighboring base station; An interference canceller for regenerating the interference signal under control of the controller; An interference and noise estimator for outputting interference and noise variance information under control of the controller; A normalizer for normalizing an input metric based on the information received from the interference and noise estimator; And a subtractor for subtracting the regenerated interference signal from the signal received from the serving base station. The method of claim 16, wherein the signal strength, Adjacent cell interference signal canceling device in an orthogonal frequency multiple access system, characterized in that the carrier to interference noise ratio (CINR). The method of claim 16, wherein the signal strength, Adjacent cell interference signal cancellation apparatus in orthogonal frequency multiple access system, characterized in that the pilot signal strength. The method of claim 16, The control unit, And determining the order in which the interference signals are to be canceled in the largest order of the interference signals. The method of claim 16, The interference canceller, A channel encoder for encoding an interference signal decoded at a channel decoder of the receiver; A symbol mapper for mapping the encoded interference signal; A repeater for repeating the mapped interference signal a predetermined number of times; An allocator for allocating subcarriers to the repeated interference signal; A scrambler that scrambles an interference signal to which the subcarrier is allocated; And a multiplier for multiplying the scrambled interference signal with a signal estimated by a channel estimator of the receiver. A receiver for receiving a signal transmitted from a serving base station in an orthogonal frequency division multiple access (OFDMA) system, By measuring the signal strength received from the serving base station and the signal strength received from the neighboring base station and regenerating the interference signal received from the neighboring base station when the difference in the signal strength satisfies a predetermined threshold value; A control unit controlling an output of a distribution of a specific interference and noise signal among signals received from a serving base station and the neighboring base station; An interference canceller for regenerating the interference signal under control of the controller; An interference and noise estimator for outputting interference and noise variance information of the received signal from which the interference signal is removed under control of the controller; A normalizer for normalizing an input metric based on the information received from the interference and noise estimator; And a subtractor for subtracting the regenerated interference signal from the signal received from the serving base station. The method of claim 21, wherein the signal strength, Adjacent cell interference signal canceling device in an orthogonal frequency multiple access system, characterized in that the carrier to interference noise ratio (CINR). The method of claim 21, wherein the signal strength, Adjacent cell interference signal cancellation apparatus in orthogonal frequency multiple access system, characterized in that the pilot signal strength. The method of claim 21, The control unit, And determining the order in which the interference signals are to be canceled in the largest order of the interference signals. The method of claim 21, The interference canceller, A slicer for hard determining a signal demapped by a symbol demapper of the receiver; A symbol mapper for mapping the sliced interference signal; A repeater for repeating the mapped interference signal a predetermined number of times; An allocator for allocating subcarriers to the repeated interference signal; A scrambler that scrambles an interference signal to which the subcarrier is allocated; And a multiplier for multiplying the scrambled interference signal with a signal estimated by a channel estimator of the receiver.

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