KR20210092443A - Iterative interference cancellation receiver with MMSE filter for QAM-FBMC system - Google Patents

Abstract

Disclosed are a method and a system for receiving phased interference control using an MMSE filter in a QAM-FBMC system. According to the present invention, the method for receiving phased interference control using the MMSE filter in the QAM-FBMC system includes the steps of: detecting transmission symbols adjacent to the corresponding symbol to remove interference; and re-detecting the corresponding symbol again using a detected symbol component. The present invention provides a receiver capable of controlling residual interference without calculating a complex multi-tap matrix polynomial.

Description

Stepped interference control reception method and system using MMSE filter in QAM-FBMC system {Iterative interference cancellation receiver with MMSE filter for QAM-FBMC system}

The present invention relates to a method and system for receiving phased interference control using an MMSE filter in a QAM-FBMC system.

CP-OFDM, which has been used for a long time as a wireless communication system standard, has a simple modulation/demodulation method and a structure suitable for signal processing. However, CP-OFDM has the disadvantage of reducing the system frequency efficiency due to the high emission characteristics outside the frequency band due to the rectangular waveform pulse formation. In order to overcome these shortcomings, candidates for a new waveform to replace CP-OFDM have been discussed for a long time in next-generation wireless communication.

The biggest characteristic that a new waveform should have is that it should be well localized in the time and frequency axes, and it should have a high degree of freedom to respond through a flexible design in a complex channel environment such as an asynchronous environment. In order to satisfy this point, QAM-FBMC has been recently proposed and dealt with.

QAM-FBMC is a proposed technology that overcomes the shortcomings of the existing OQAM-FBMC. Basically, since it follows the structure of the FBMC, it is possible to satisfy various scenarios by applying filters per subcarrier to each of the subcarriers to improve frequency limiting characteristics and to enable flexible waveform design. The existing technology, OQAM-FBMC, uses OQAM modulation, which is greatly affected by interference in a complex channel environment because it achieves only orthogonality on the real axis. On the other hand, QAM-FBMC specifically designs the pulse shaping filter through global optimization of filter coefficients.

According to the Balian-Low theorem, since it is impossible to simultaneously satisfy the time and frequency localization and orthogonality of the system pulse shaping filter, QAM modulation is implemented in a form that achieves localization and relaxed orthogonality as much as possible by relaxing some orthogonality conditions when designing the filter. came to use The QAM-FBMC system through such a filter design guarantees a certain degree of orthogonality and high frequency limiting characteristics, but since the filter does not have perfect orthogonality, a performance limit exists due to the remaining interference components.

In this way, residual interference is basically present in the system through the non-orthogonal filter design, which causes a slight performance degradation in the bit error rate, and there have been studies to improve it through processing at the receiving end.

Prior literature [1]: Method and apparatus for controlling interference in QAM-FBMC system (US10,164,803 (2018.12.25)).

The existing technology constructs an equivalent transfer function for the entire transmission and reception of QAM-FBMC, performs spectral factorization, and through this, interference is reduced through precoding and decision feedback equalizer. A way to remove it is suggested. If the equivalent transfer function can be accurately configured, it can be applied regardless of the type of transmit/receive filter to remove residual interference and greatly alleviate performance degradation. However, the complexity of a process of frequency decomposing by constructing a system equivalent function is high, and computational complexity and system delay required when additionally necessary multi-tap filters are applied may be pointed out as disadvantages.

On the other hand, MMSE (minimum mean-squared) replaces the matched filter receiver used by all existing QAM-FBMC systems to minimize the interference in QAM-FBMC, a non-orthogonal system in which interference exists. -error) method using the receive filter has been proposed.

Prior literature [2]: A method and apparatus for designing a transmission/reception filter to minimize the inherent interference of a filter bank multi-carrier system (10-2019-0010724 (2019.01.28))

Prior literature [3]: H. Han, N. Kim and H. Park, "Design of QAM-FBMC Waveforms Considering MMSE Receiver," will be appeared in IEEE Communications Letters.(https://doi.org/10.1109/LCOMM .2019.2952375)

An object of the present invention is to provide a receiver capable of controlling residual interference without calculating a complex multi-tap matrix polynomial by stepwise canceling residual interference of a received signal using an MMSE filter.

In one aspect, the step-by-step interference control reception method using the MMSE filter in the QAM-FBMC system proposed by the present invention includes the steps of detecting transmission symbols adjacent to the corresponding symbol in order to remove the interference, and using the detected symbol component again. and re-detecting the symbol.

The step of detecting the transmission symbols adjacent to the corresponding symbol in order to remove the interference includes selectively performing pre-cancellation, performing the detection of the corresponding symbol, and a hard decision symbol of the corresponding symbol. symbol), and performing removal of the corresponding symbol.

The step of detecting the transmission symbols adjacent to the corresponding symbol in order to remove the interference includes performing detection for each symbol on the transmission symbols adjacent to the corresponding symbol, calculating a hard decision symbol of each symbol, and removing each symbol. Repeat the steps to perform

In the step of detecting the transmission symbols adjacent to the corresponding symbol in order to cancel the interference, the interference signal from the preceding symbol is removed based on the prior detection information on the preceding symbol. In other words, the interference signal from the preceding symbol is removed based on the previously determined preceding symbol information.

Re-detecting the corresponding symbol using the detected symbol component includes removing all interference components other than the corresponding symbol and re-detecting the corresponding symbol.

In another aspect, in the QAM-FBMC system proposed in the present invention, the staged interference control receiving apparatus using the MMSE filter detects the transmission symbols adjacent to the corresponding symbol in order to remove the interference using the MMSE filter, and the detected symbol and a detector for re-detecting the corresponding symbol again using the component.

According to embodiments of the present invention, unnecessary complexity can be minimized by configuring to restrictively remove major interference components of QAM-FBMC using a reception filter designed according to the MMSE condition. In addition, since inter-symbol interference (ISI) from an adjacent symbol is removed through block signal processing in a target time period without using a received signal for an adjacent symbol, interference without additional computational complexity and system delay can be removed.

1 is a diagram illustrating a QAM-FBMC transmission structure based on extended FFT according to an embodiment of the present invention.
FIG. 2 is a flowchart illustrating a method for receiving step-by-step interference control using an MMSE filter in a QAM-FBMC system according to an embodiment of the present invention.
3 is a simulation result according to an embodiment of the present invention according to an embodiment of the present invention.

The present invention proposes a receiver capable of controlling residual interference without calculating a complex multi-tap matrix polynomial by stepwise canceling residual interference of a received signal using an MMSE filter. The proposed technique minimizes unnecessary complexity by using a receive filter designed according to the MMSE condition to restrictively remove major interference components of QAM-FBMC. In addition, since inter-symbol interference (ISI) is removed through block signal processing in a target time interval without using a received signal for an adjacent symbol, interference without additional computational complexity and system delay was allowed to be removed.

From the computer simulation results, it can be confirmed that the residual interference is greatly reduced through the receiver using the proposed interference cancellation method, and as a result, the bit error rate performance is improved.

According to an embodiment of the present invention, a method of repeatedly updating and calculating the MMSE filter is used to remove residual interference of QAM-FBMC. In addition, for interference cancellation, an order determination and block processing method for removing major interference components in stages are used. Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a diagram illustrating a QAM-FBMC transmission structure based on extended FFT according to an embodiment of the present invention.

First, in order to explain the present invention, it is necessary to model the interference system of QAM-FBMC by a matrix expression. The stacked vector expression of the QAM-FBMC system below was borrowed from the previous literature [3].

For the stacked matrix representation of the transmitted signal, the parameters are defined as follows.

: 부반송파 수

: number of subcarriers

: 오버샘플링 계수(Oversampling factor)

: Oversampling factor

For the stacked vector expression of the transmission signal considering the overlap-and-sum structure, the parameters are defined as follows.

:

길이를 갖는 전송된 신호

:

transmitted signal with length

의

을 벡터로 만든 것이다. this is the transmit signal

of

is made into a vector.

: 쌓인 데이터 벡터(

)

: Stacked data vector (

)

:

번째 시간 구간의

번째 부반송파에 해당하는 데이터 심볼

을 원소로 가지는

벡터

:

of the second time interval

data symbol corresponding to the second subcarrier

having as an element

vector

: 쌓인 필터링 행렬

: stacked filtering matrix

길이 구간에서 앞

샘플만큼을 더 고려한다. corresponding to a symbol

front in length section

Consider more samples.

:

을

번째 칼럼 벡터(column vector)로 가진

행렬

:

second

with the second column vector

procession

:

(

)을

번째 엘리먼트(element)로 가진

벡터

:

(

)second

with the second element

vector

For a time-domain convolutional channel matrix, parameters are defined as follows.

:

사이즈

:

size

의

번째 칼럼(column)

of

the second column

Time-domain slicer

For the stacked vector representation of the received signal, the parameters are defined as follows.

번째 수신 신호

는 다음과 같이 나타낼 수 있다.passed through the channel

second received signal

can be expressed as

: AWGN 벡터

: AWGN Vector

를 거친

번째 수신 심볼

는 다음과 같이 나타낼 수 있다. Receive Combine Filter

went through

second received symbol

can be expressed as

,

,

:

심볼들에 대한 수신 결합 필터

:

Receive Combine Filter for Symbols

번째 수신 신호로부터,

번째 송신 심볼에 대해서만 MMSE 조건을 고려하고 있다. 본 발명을 위해서는

번째 수신 신호로부터 인접한 다른 송신 심볼을 검출하여 단계적 간섭 제어에 활용해야 하므로, 해당 조건을

번째 심볼에 대하여 수정하여 적용한다. In the case of the prior literature [3] in the design of the receive combining filter considering the MMSE condition

From the second received signal,

The MMSE condition is considered only for the th transmission symbol. For the present invention

Since it is necessary to detect other adjacent transmission symbols from the first received signal and use them for step-by-step interference control, the corresponding condition

Modify and apply the second symbol.

번째 수신 신호로부터,

번째 송신 심볼을 검출하기 위한 MMSE 수신 결합 필터 조건은 다음과 같다.

From the second received signal,

The MMSE receive combining filter condition for detecting the th transmit symbol is as follows.

:

번째 심볼을 추출할 수 있도록 하는 샘플링 행렬

:

Sampling matrix that allows the th symbol to be extracted

의

번째 심볼에 대한 칼럼들을 추출하도록 하는 것이다. in other words,

of

It is to extract the columns for the th symbol.

The MMSE receive combining filter according to the corresponding condition can be expressed as follows.

번째 심볼만이 유효한 전송 심볼이며, 인접한

(

) 번째 심볼들은

번째 심볼을 검출하는데 온전한 간섭으로 작용하며 이는

번째 심볼보다 더 작은 간섭 파워를 가진다. 따라서, SIC의 순서를 고려하여 신호의 크기 순서대로 단계적 간섭 제거를 수행할 경우, 정작 원하는

번째 심볼은 간섭 제거에 의한 이득을 받을 수 없다.In the stepwise interference cancellation algorithm through the MMSE reception filter of QAM-FBMC according to an embodiment of the present invention, a process similar to the stepwise interference cancellation process of MMSE-SIC is basically performed. However, unlike the general SIC process, in the case of QAM-FBMC, the signal power is the largest.

Only the th symbol is a valid transmit symbol, and

(

)th symbols are

It acts as a complete interference in detecting the second symbol, which is

It has a smaller interference power than the th symbol. Therefore, when performing step-by-step interference cancellation in the order of the signal magnitudes considering the order of SIC

The th symbol cannot receive a gain due to interference cancellation.

(

) 번째 심볼들을 검출한 후, 해당 검출된 심볼 성분을 이용하여 마지막으로 다시 목표

번째 심볼을 재검출 하는 방식을 사용한다. Therefore, in the present invention, adjacent through SIC

(

) th symbols, and finally re-target using the detected symbol component

The method of re-detecting the second symbol is used.

If necessary, an additional gain can be considered by using inter-subcarrier step interference cancellation. However, since the complexity is usually too high and the effect is insignificant, in the present invention, a block operation is performed without SIC within the subcarriers within each symbol, and the operation speed and complexity was greatly reduced.

First, each parameter is as follows.

:

번째 수신 신호

:

second received signal

:

번째 검파 신호

:

second detection signal

:

의 경판정 심볼(hard decision symbol) 계산

:

Calculation of the hard decision symbol of

: QAM-변조 및 복원(demodulator and regeneration)

: QAM-modulator and regeneration

:

에서

번째 심볼에 해당하는 칼럼만을 추출한 것으로,

의

번째 칼럼

:

at

By extracting only the column corresponding to the th symbol,

of

second column

:

에서

번째 심볼에 대한 칼럼을 모두 제거하거나 0으로 채워 널링(Nulling)한 행렬. 여기서, 널링은 칼럼을 모두 제거하거나　0으로 채우는 것을 의미한다.

:

at

A matrix in which all columns for the th symbol are removed or filled with zeros. Here, nulling means removing all columns or filling them with zeros.

2 is a flowchart illustrating a method for receiving step-by-step interference control using an MMSE filter in a QAM-FBMC system according to an embodiment of the present invention.

The specific process will be described below as a pseudo-algorithm.

The step-by-step interference control reception method using the MMSE filter in the proposed system includes the steps of detecting transmission symbols adjacent to the corresponding symbol in order to remove interference (210) and re-detecting the corresponding symbol using the detected symbol component (220). ) is included.

The specific process will be described below as a pseudo-algorithm.

In step 210, transmission symbols adjacent to the corresponding symbol are detected in order to cancel the interference. More specifically, in step 211, pre-cancellation is selectively performed.

의 선행 심볼에 대한 검출 정보를 바탕으로 사전 심볼로부터의 간섭 신호를 제거한다. 다시 말해, 사전에 판정 완료된 선행 심볼 정보에 기초하여 선행 심볼로부터의 간섭 신호를 제거한다.

The interference signal from the preceding symbol is removed based on the detection information on the preceding symbol of . In other words, the interference signal from the preceding symbol is removed based on the previously determined preceding symbol information.

If the detection result for the previous symbol is unreliable, this process may be omitted.

에 대해 검출을 수행한다. in step 212

detection is performed on

의 경판정 심볼(hard decision symbol)을 계산한다. in step 213

Compute the hard decision symbol of

에 대해 제거를 수행한다. In step 214

perform removal on

에 대해서 단계(212) 내지 단계(214)을 반복한다. in step 215

Repeat steps 212 to 214 for

At this time, the following are calculated in order.

에 대해서도 신호 파워가 큰 순서대로 해당 과정을 반복한다.If the pre-removal operation of step 211 is not performed,

For , the process is repeated in the order of increasing signal power.

의 인접 심볼을 제외하면 간섭의 파워의 크기가 크지 않으므로,

에 대해서만 SIC 를 수행할 수 있다. For QAM-FBMC with well designed pulse shaping filter

Since the magnitude of the power of interference is not large, excluding the adjacent symbols of

SIC can be performed only for

A corresponding symbol is re-detected again using the symbol component detected in step 220 .

을 제외한 나머지 간섭 성분을 모두 제거한다. in step 221

All other interference components are removed except for .

에 대해 다시 검출을 수행한다. in step 222

detection is performed again.

:

행렬 연산 시,

에서

번째 심볼에 해당하는 칼럼을 널링하여 계산한 것이다.

:

In matrix operation,

at

It is calculated by nulling the column corresponding to the th symbol.

를 통해 QAM 복조를 수행한다. in step 223

QAM demodulation is performed through

3 is a simulation result according to an embodiment of the present invention.

The parameters of the simulation according to an embodiment of the present invention are as follows:

= 64, 64-QAM이고,

= 64, 64-QAM,

Extended Pedestrian A

Applied filter G30/G50 [3]

에 대해 단계적 간섭 제거를 시행하였다. As previously described, the pre-cancellation in step 210 is applied, and in step 250

Step-by-step interference cancellation was performed.

3 is a BER performance result according to an embodiment of the present invention. As a result of computer simulation, it was confirmed that residual interference was greatly reduced through the receiver using the proposed interference cancellation method, and as a result, improved bit error rate performance was exhibited.

The device described above may be implemented as a hardware component, a software component, and/or a combination of the hardware component and the software component. For example, devices and components described in the embodiments may include, for example, a processor, a controller, an arithmetic logic unit (ALU), a digital signal processor, a microcomputer, a field programmable array (FPA), It may be implemented using one or more general purpose or special purpose computers, such as a programmable logic unit (PLU), microprocessor, or any other device capable of executing and responding to instructions. The processing device may execute an operating system (OS) and one or more software applications running on the operating system. The processing device may also access, store, manipulate, process, and generate data in response to execution of the software. For convenience of understanding, although one processing device is sometimes described as being used, one of ordinary skill in the art will recognize that the processing device includes a plurality of processing elements and/or a plurality of types of processing elements. It can be seen that can include For example, the processing device may include a plurality of processors or one processor and one controller. Other processing configurations are also possible, such as parallel processors.

The software may comprise a computer program, code, instructions, or a combination of one or more thereof, which configures a processing device to operate as desired or is independently or collectively processed You can command the device. The software and/or data may be any kind of machine, component, physical device, virtual equipment, computer storage medium or device, to be interpreted by or to provide instructions or data to the processing device. may be embodied in The software may be distributed over networked computer systems, and stored or executed in a distributed manner. Software and data may be stored in one or more computer-readable recording media.

The method according to the embodiment may be implemented in the form of program instructions that can be executed through various computer means and recorded in a computer-readable medium. The computer-readable medium may include program instructions, data files, data structures, etc. alone or in combination. The program instructions recorded on the medium may be specially designed and configured for the embodiment, or may be known and available to those skilled in the art of computer software. Examples of the computer-readable recording medium include magnetic media such as hard disks, floppy disks and magnetic tapes, optical media such as CD-ROMs and DVDs, and magnetic such as floppy disks. - includes magneto-optical media, and hardware devices specially configured to store and carry out program instructions, such as ROM, RAM, flash memory, and the like. Examples of program instructions include not only machine language codes such as those generated by a compiler, but also high-level language codes that can be executed by a computer using an interpreter or the like.

As described above, although the embodiments have been described with reference to the limited embodiments and drawings, various modifications and variations are possible by those skilled in the art from the above description. For example, the described techniques are performed in a different order than the described method, and/or the described components of the system, structure, apparatus, circuit, etc. are combined or combined in a different form than the described method, or other components Or substituted or substituted by equivalents may achieve an appropriate result.

Therefore, other implementations, other embodiments, and equivalents to the claims are also within the scope of the following claims.

Claims (10)

detecting transmission symbols adjacent to the corresponding symbol to cancel the interference; and
Re-detecting the corresponding symbol again using the detected symbol component
A stepwise interference control reception method comprising a. According to claim 1,
The step of detecting transmission symbols adjacent to the corresponding symbol in order to remove the interference comprises:
selectively performing pre-cancellation;
performing detection on the corresponding symbol;
calculating a hard decision symbol of the corresponding symbol; and
Steps to perform removal on that symbol
A stepwise interference control reception method comprising a. 3. The method of claim 2,
Repeating the steps of performing detection for each symbol, calculating a hard decision symbol of each symbol, and removing each symbol for transmission symbols adjacent to the corresponding symbol
Stepped interference control reception method. 3. The method of claim 2,
A method of removing an interference signal from a preceding symbol based on prior detection information on the preceding symbol.
Stepped interference control reception method. According to claim 1,
The step of re-detecting the corresponding symbol again using the detected symbol component,
removing all remaining interference components except for the corresponding symbol; and
Step of re-detecting for the corresponding symbol
A stepwise interference control reception method comprising a. A detection unit that detects transmission symbols adjacent to a corresponding symbol in order to remove interference using the MMSE filter, and re-detects the corresponding symbol using the detected symbol component
A staged interference control receiving device comprising a. 7. The method of claim 6,
the detection unit,
It selectively performs pre-cancellation, detects the corresponding symbol, calculates a hard decision symbol of the corresponding symbol, and performs cancellation on the corresponding symbol.
Staged interference control receiver. 8. The method of claim 7,
Repeating the steps of performing detection for each symbol, calculating a hard decision symbol of each symbol, and removing each symbol for transmission symbols adjacent to the corresponding symbol
Staged interference control receiver. 8. The method of claim 7,
A method of removing an interference signal from a preceding symbol based on prior detection information on the preceding symbol.
Staged interference control receiver. 7. The method of claim 6,
the detection unit,
It re-detects the corresponding symbol using the detected symbol component, removes all interference components except for the corresponding symbol, and re-detects the corresponding symbol.
Staged interference control receiver.

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