KR20200077079A - SC-FDE Transceiver System Robust Narrowband Interference and Low Pilot Overhead - Google Patents

Abstract

The present invention relates to an SC-FDE transmission/reception system for coping with a narrowband interference signal and reducing a pilot overhead. The system comprises: a receiver for receiving a pilot signal in a narrowband jammer environment; a transmitter for transmitting a pilot signal; a CP remover for removing a CP from the received pilot signal; an FFT; and a channel estimator. According to the present invention, even in the presence of a jammer, frequency domain channel estimation is possible without time domain channel estimation.

Description

SC-FDE Transceiver System Robust Narrowband Interference and Low Pilot Overhead for coping with narrowband interference signals and reducing pilot overhead

The present invention relates to an SC-FDE transmission/reception system for coping with narrowband interference signals and reducing pilot overhead, and to a new SC-FDE transmission/reception structure capable of coping with narrowband interference signals while reducing pilot overhead caused by pilots. It is about.

In order to transmit high-speed data in a multipath fading environment, channel equalization must be easily performed at a receiver. In addition to mobile communication, communication method design considering channel equalization is being made in military tactical communication and communication between UAV and ground stations.

Among various communication methods considering this point, OFDM (Orthogonal Frequency Division Multiplexing) and SC-FDE (Single Carrier Frequency Domain Equalization) are the most widely used communication methods.

OFDM is a method of compensating a channel with a simple equalization technique in the frequency domain by allowing cyclic convolution of a transmission signal and a channel impulse response. It is advantageous in that multi-user simultaneous access is possible by dividing frequencies.

Due to these advantages, OFDM is used as a broadband wireless communication system such as IEEE802.11 wireless LAN and LTE downlink transmission technology. However, due to the high peak-to-average ratio (PAPR), OFDM puts a lot of burden on the power amplifier and has a problem of low power efficiency. In addition, there is also a problem that ICI (Inter Channel Interference) occurs due to carrier frequency offset.

One of the ways to solve this problem is SC-FDE (Single Carrier Frequency Domain Equalization). SC-FDE has similar performance to OFDM, has a relatively small PAPR, and can perform frequency domain equalization in a multipath fading environment, thereby simplifying channel distortion compensation. Because cellular phones have high power efficiency, SC-FDE is used for LTE uplink. It is also applied to battery operated military tactical radios and military drone communications.

The conventional SC-FDE (Single Carrier Frequency Domain Equalization) structure has a disadvantage in that the performance of the receiver is deteriorated due to difficulty in estimating the time domain channel when a narrow band jammer is present. In addition, there is a problem in that the spectrum efficiency decreases as a pilot for channel estimation is transmitted for every SC-FDE.

Accordingly, in order to solve the above-mentioned problem, the present applicant can directly estimate the frequency domain channel without time domain channel estimation even in an environment where jammers exist, and each of the pilots is estimated through linear interpolation channel estimation using the estimated channel in the frequency domain. It is possible to find a channel characteristic in data blocks, so that the present invention can reduce the degradation of channel estimation performance in a mobile environment while reducing pilot overhead.

Korean Patent Publication No. 10-2015-0091370

An object of the present invention, by inserting a CP for the pilot, it is possible to directly estimate the frequency domain channel without the time domain channel estimation even in the presence of jammers, and pilot through linear interpolation channel estimation using the estimated channel in the frequency domain It is possible to find a channel characteristic in each data block in between, thereby reducing pilot overhead and reducing channel estimation performance degradation in a mobile environment.

)를 추출하고, 송신한 파일럿 신호로부터 주파수 영역 파일럿 신호(

)를 추출하는 FFT; 및 두 주파수 영역 파일럿 신호(

,

)로부터 선형보간을 통해 각각 주파수 영역 채널(

)을 추정하는 채널 추정기를 포함하는 것을 특징으로 한다.SC-FDE transmission and reception system for narrow-band interference signal response and pilot overhead reduction according to an embodiment of the present invention for achieving the above object, a receiver for receiving a pilot signal in a narrow-band jammer environment; A transmitter that transmits a pilot signal; A CP remover to remove CP from the received pilot signal; The frequency domain pilot signal (

), and the frequency domain pilot signal (

FFT to extract ); And two frequency domain pilot signals (

,

) Through linear interpolation to each frequency domain channel (

Characterized in that it comprises a channel estimator for estimating ).

)를 제거하는 것을 특징으로 한다.CP remover removes CP from the pilot signal from the receiver, but the length of CP from the received signal in the pilot signal (

It is characterized by removing.

)를 추출하고, 상기 송신기가 송신한 파일럿 신호로부터 주파수 영역 파일럿 신호(

)를 추출하는 것을 특징으로 한다.The FFT is a frequency-domain pilot signal (

), and the frequency domain pilot signal (

It characterized in that the extraction.

)가 기 설정된 값을 초과하는 경우, 주파수에 협대역 재머가 존재하는 것으로 판단하는 재머 감지기를 더 포함하는 것을 특징으로 한다.Frequency domain pilot signal extracted by FFT (

If) exceeds a predetermined value, it is characterized in that it further comprises a jammer detector for determining that a narrow-band jammer is present in the frequency.

According to the present invention, by estimating each frequency domain channel through linear interpolation from the frequency domain pilot signal extracted by removing the CP, it is possible to estimate the frequency domain channel directly without time domain channel estimation even in an environment where jammers exist. Using the estimated channel, channel characteristics in each data block between pilots can be found through linear interpolation channel estimation, thereby reducing pilot overhead and reducing channel estimation performance degradation in a mobile environment.

The following drawings attached in this specification are intended to illustrate preferred embodiments of the present invention, and serve to further understand the technical idea of the present invention together with the detailed description of the invention described below, and thus the present invention is described in such drawings. It is not limited to interpretation.
1 is a view showing a conventional SC-FDE transmission structure and reception process.
FIG. 2 is a diagram illustrating the structure of an SC-FDE transmission/reception system for coping with narrowband interference signals and reducing pilot overhead according to an embodiment of the present invention.
3 is a block diagram showing an SC-FDE transmission and reception system for narrowband interference signal response and pilot overhead reduction according to an embodiment of the present invention.
4 is a block diagram showing a jammer detector of an SC-FDE transmission/reception system for coping with narrowband interference signals and reducing pilot overhead according to an embodiment of the present invention.
5 is a block diagram showing a simulation environment of an SC-FDE transmission/reception system for coping with narrowband interference signals and reducing pilot overhead according to an embodiment of the present invention.
FIG. 6 is a diagram illustrating an estimated channel when an ideal channel and a narrow band jammer exist in the frequency domain based on the environment shown in FIG. 5.
FIG. 7 is a diagram showing channel estimation values at each frequency when three data blocks exist between two pilots.
FIG. 8 is a diagram showing bit error ratio (BER) performance according to the presence or absence of a narrow band jammer and the number M of data blocks in a fading environment when the moving speed is 100 [km/h].

Hereinafter, the present invention will be described in detail with reference to the contents described in the accompanying drawings. However, the present invention is not limited or limited by the exemplary embodiments. The same reference numerals in each drawing denote members that perform substantially the same function.

The objects and effects of the present invention may be naturally understood or more apparent by the following description, and the objects and effects of the present invention are not limited only by the following description. In addition, in the description of the present invention, when it is determined that the detailed description of the known technology related to the present invention may unnecessarily obscure the subject matter of the present invention, the detailed description will be omitted.

1 is a view showing a conventional SC-FDE transmission structure and reception process. As shown in FIG. 1, one SC-FDE block is composed of CP (Cyclic Prefix), pilot, and data. SC-FDE is a single carrier transmission structure, and unlike OFDM, there is no IFFT (Inverse Fast Fourier Transform) process in the transmitter.

이며 데이터의 마지막

개 심볼이다. 파일럿과 데이터의 길이는 각각

,

이다. 파일럿과 데이터 길이의 합은 N(

) 이다.

은 수신기에서의 FFT(Fast Fourier Transform) 크기이다. 수신기에서는 파일럿을 이용하여 먼저 시간영역 채널추정을 수행한다. 추정된 시간영역 채널의 임펄스 응답은 주파수 영역 채널 추정 및 등화에 사용한다. 채널을 통과하여 수신된 수신신호를

이라고 하고 채널의 임펄스 응답을

, 송신 파일럿 신호를

이라고 하면 다음의 [수학식 1]과 같이 쓸 수 있다.At this time, the length of CP

Is the last of the data

Dog symbol. The length of the pilot and data is

,

to be. The sum of pilot and data length is N(

) to be.

Is the FFT (Fast Fourier Transform) size at the receiver. The receiver first performs time-domain channel estimation using a pilot. The estimated time domain channel impulse response is used for frequency domain channel estimation and equalization. The received signal received through the channel

And the impulse response of the channel

Transmit pilot signal

Can be written as [Equation 1] below.

[Equation 1]

는 채널 임펄스 응답 벡터이며

,

는 채널 임펄스 응답의 길이를 의미한다.

는 가우시안 잡음을 나타내고

는 송신 파일럿 벡터로

이다. 주파수 영역 등화를 위해서는 주파수 영역 채널이 필요하나 이를 위해 먼저 시간영역 채널 추정을 수행한다. 시간영역 채널의 FFT를 통해 주파수 영역 채널을 찾을 수 있다. 시간영역 채널 추정은 최소자승 기법을 통해 수행한다. here,

Is the channel impulse response vector

,

Denotes the length of the channel impulse response.

Denotes Gaussian noise

Is the transmit pilot vector

to be. A frequency domain channel is required for frequency domain equalization, but time domain channel estimation is first performed for this purpose. The frequency domain channel can be found through the FFT of the time domain channel. Time-domain channel estimation is performed using the least squares technique.

[Equation 2]

이고

이다. 추청한 시간영역 채널

의 N 포인트 FFT를 통해 주파수 영역 채널

를 얻는다. 채널을 보상하는 등화는 낮은 SNR(Signal to Noise Ratio) 영역에서 성능을 향상하기 위해 MMSE(Minimum Mean Square Error) 등화를 수행한다. 등화 수식은 다음과 같다.In [Equation 2]

ego

to be. Time domain channel

Frequency domain channel through N point FFT

Get The channel-compensated equalization performs MMSE (Minimum Mean Square Error) equalization to improve performance in a low signal to noise ratio (SNR) region. The equalization formula is as follows.

은 잡음의 분산,

는 주파수 영역 수신신호이다. 등화가 수행된

는 IFFT를 통해 시간영역 신호로 변환된다. here,

Dispersion of noise,

Is a frequency domain received signal. Equalized

Is converted to a time domain signal through IFFT.

The conventional method described above in the narrowband jamming environment has the following problems.

During a military operation, the frequency being used for communication can be exposed to the enemy, and the enemy can launch a radio attack, or jammer attack, on that frequency for malicious purposes.

When the SC-FDE communication is subjected to jammer attack, the time domain channel estimation cannot be performed properly due to the low signal to interference plus noise ratio (SINR) of the time domain signal, and accordingly, equalization cannot be performed properly, making communication difficult. .

In addition, in a universal SC-FDE transmission structure, pilots are inserted for every SC-FDE block for channel estimation in a mobile environment, and thus there is a big problem in pilot overhead. The pilot overhead is expressed by the following [Equation 3].

[Equation 3]

pilot overhead

If long pilots are used, channel estimation performance will improve, but pilot overhead will increase. Since the pilot overhead reduces the SC-FDE transmission spectrum efficiency, a method for reducing the pilot overhead and improving channel estimation performance is required.

Therefore, in one embodiment of the present invention described below, the pilot overhead is reduced by occasionally transmitting a pilot instead of transmitting it in every SC-FDE block, and by transmitting multiple SC-FDE data blocks between the pilot and the pilot transmission. We propose a new SC-FDE structure and suggest a channel estimation method according to the receiver.

2 is a diagram illustrating the structure of an SC-FDE transmission/reception system for coping with narrowband interference signals and reducing pilot overhead according to an embodiment of the present invention.

As shown in FIG. 2, the structure according to an embodiment of the present invention transmits a pilot every predetermined time, and a CP (Cyclic Prefix) corresponding to a pilot enables a frequency domain channel estimation without time domain channel estimation even when there is jammer. ).

라고 하고 CP의 길이는

라고 한다. 이로 인해 데이터 블록 뿐만아니라 채널 추정에서도 FFT를 통한 주파수 영역 채널 추정을 가능하게 한다. 데이터 블록은 길이

의 CP와 길이

의 데이터로 이루어진다.At this time, the length of the pilot

And the length of CP

It is said. This enables frequency domain channel estimation through FFT in channel estimation as well as data blocks. Data block length

CP and Length

It is made of data.

Since the pilot is not included in the data block, the pilot transmission rate of the structure according to an embodiment of the present invention is much lower than that of the existing structure. However, if the pilot is occasionally transmitted, there may be a problem in accurately estimating the time-varying channel in the mobile environment.

Therefore, in an embodiment of the present invention, this problem is solved by a linear interpolation method, channel estimation is performed in each pilot, and a channel between the pilot and the pilot is estimated using a linear interpolation method. Since the linear interpolation method is not a perfect interpolation method, the estimation performance may deteriorate in a high-speed wireless environment, but the simulation results confirm that there is no deterioration in channel estimation performance even at a movement speed of 100 km/h or more.

)를 추출하고, 송신한 파일럿 신호로부터 주파수 영역 파일럿 신호(

)를 추출하는 FFT(400), 및 두 주파수 영역 파일럿 신호(

,

)로부터 선형보간을 통해 각각 주파수 영역 채널(

)을 추정하는 채널 추정기(500)를 포함하여 구성된다.Referring to FIG. 3, the SC-FDE transmission/reception system (S) for coping with narrowband interference signals and reducing pilot overhead according to an embodiment of the present invention includes a receiver 100 for receiving a pilot signal in a narrowband jammer environment , A transmitter 200 for transmitting a pilot signal, a CP remover 300 for removing CP from the received pilot signal, and a frequency domain pilot signal (

), and the frequency domain pilot signal (

FFT 400 to extract ), and two frequency domain pilot signals (

,

) Through linear interpolation to each frequency domain channel (

It comprises a channel estimator 500 for estimating ).

은 협대역 재머를 나타낸다.Specifically, the signal received by the receiver 100 in a narrowband jammer environment can be expressed as [Equation 4], where

Represents narrowband jammer.

[Equation 4]

)를 제거한다.CP remover 300 removes the CP from the pilot signal from the receiver 100, CP and the length of the CP from the pilot signal including the pilot (

).

)를 추출하고, 송신기(200)가 송신한 파일럿 신호로부터 주파수 영역 파일럿 신호(

)를 추출한다.The FFT 400 is a frequency domain pilot signal (

), and the frequency domain pilot signal (from the pilot signal transmitted by the transmitter 200)

).

At this time, the extracted frequency domain pilot signals can be expressed as in the following equation.

,

)로부터 선형보간을 통해 각각 주파수 영역 채널을 추정하며, 주파수 영역 채널 추정값(

)은 아래의 수학식과 같이 표현할 수 있다.And, the channel estimator 500 is a two frequency domain pilot signal (

,

) To estimate each frequency domain channel through linear interpolation, and estimate the frequency domain channel (

) Can be expressed as the following equation.

Specifically, the channel estimator 500 estimates a channel using linear interpolation to estimate a channel in a data block between pilots, and it is assumed that a radio channel between two pilots changes linearly with time.

It is assumed that there are M data blocks between the two pilots, and that the front pilot of the data is called the 0th block and the rear pilot is called the M+1th block.

) 데이터 블록의

번째 주파수 영역 채널 특성을

라고 표현한다. 첫 번째 파일럿과 두 번째 파일럿에서 의 채널 추정 값은 각각

와

라고 표현한다. m번째 데이터 블록의 채널은 다음과 같이 선형보간법으로 구하면 아래의 [수학식 5]와 같이 도출된다.mth (

) Of data blocks

Frequency domain channel characteristics

It is expressed as The channel estimates for the first pilot and the second pilot are

Wow

It is expressed as When the channel of the m-th data block is obtained by linear interpolation as follows, it is derived as shown in [Equation 5] below.

[Equation 5]

At this time, the pilot overhead is equal to [Equation 6].

[Equation 6]

pilot overhead

According to one embodiment of the present invention as described above, it is possible to reduce the pilot overhead to 1/M than the conventional SC-FDE structure.

In addition, the SC-FDE transmission/reception system (S) for coping with narrowband interference signals and reducing pilot overhead according to an embodiment of the present invention further includes a jammer detector 600 for detecting the existence of a narrowband jammer. It is composed.

)가 기 설정된 값을 초과하는 경우, 주파수에 협대역 재머가 존재하는 것으로 판단한다.4, the jammer detector 600 is a frequency domain pilot signal extracted by the FFT 400 (

) Exceeds a preset value, it is determined that a narrowband jammer exists in the frequency.

)이 기 설정된 값을 초과하는 경우, 주파수에 협대역 재머가 존재하는 것으로 판단한다.In addition, the jammer detector 600 estimates the frequency domain channel estimated by the channel estimator 500 (

) Exceeds a preset value, it is determined that a narrowband jammer exists in the frequency.

에서 큰 값이 관찰될 것이기 때문이다. 이 경우 해당

도 큰 값이 나타나게 된다.When a narrow-band jammer exists at a specific frequency, a channel estimation value greater than a preset value is observed at that frequency.

Because a large value will be observed. In this case

Also, a large value appears.

At this time, if the received signal is divided into the estimated channel to perform equalization, the signal of the frequency where the jammer is present is naturally reduced in size.

In general, knowing the frequency where the jammer is located, it is best to make the position 0, but the structure according to an embodiment of the present invention has a nulling effect that naturally makes it 0 during the equalization process.

Accordingly, according to the structure of the SC-FDE transmission/reception system for coping with narrowband interference signals and reducing pilot overhead according to an embodiment of the present invention, the effect of jammer is reduced in the process of equalization without the need to estimate the frequency of the jammer, Therefore, there is no need to separately estimate the existence of jammers.

Meanwhile, FIG. 5 is a block diagram showing a simulation environment of an SC-FDE transmission/reception system for coping with narrowband interference signals and reducing pilot overhead according to an embodiment of the present invention.

First, the transmitter generates binary data and performs forward error correction (FEC) encoding for error correction.

Subsequently, interleaving is performed to rearrange the order of data in a certain unit to prevent a cluster error that is likely to occur in a wireless channel environment.

Subsequently, CP and pilot are inserted and transmitted to perform QPSK modulation, to prevent interference between blocks, and to perform frequency domain equalization.

At this time, the transmitted signal is received through the channel. If a narrow-band jammer exists, the transmitted signal is received by adding a narrow-band jammer.

Subsequently, in order to perform frequency domain channel estimation and equalization, the receiver FFTs two pilots of the received signal to obtain a frequency domain channel.

Then, channel equalization is performed. Accordingly, IFFT is performed on the channel-compensated signal, and data is restored by sequentially performing soft decision, deinterleaving, and FEC decoding.

[Table 1]

=32), 파일럿 길이 및 FFT 크기는 512

이다. 채널코드는 코드율이 1/2인 LDPC(Low-density Parity-check) 코드를 사용하였다. 협대역 재머가 존재하는 환경을 위해 1개의 협대역 재머를 고려하였으며 JSR(Jammer to Signal Ratio)은 0 dB로 고정하였다.[Table 1] above shows detailed parameters used in the simulation. Where CP length is symbol (

=32), pilot length and FFT size is 512

to be. LDPC (Low-density Parity-check) code with a code rate of 1/2 was used as the channel code. For the environment where a narrowband jammer exists, one narrowband jammer was considered and the jammer to signal ratio (JSR) was fixed at 0 dB.

FIG. 6 is a diagram illustrating an estimated channel when an ideal channel and a narrow band jammer are present in the frequency domain based on the environment illustrated in FIG. 5.

The blue dotted line represents the estimated channel and the red solid line represents the ideal channel. It can be seen that the ideal channel and the estimated channel are almost identical, including the jammer position and size.

FIG. 7 shows a channel estimation value at each frequency when M=3 is an estimated channel, that is, when three data blocks exist between two pilots. For convenience, among the 512 FFT points, only a frequency range in which a narrow band jammer is present is shown.

Through linear interpolation, it can be confirmed that the channel of the data block is estimated by equally dividing the data using the channel estimates of the two pilots.

8 shows a bit error ratio (BER) performance according to the presence or absence of a narrow band jammer and the number M of data blocks in a fading environment when the moving speed is 100 [km/h]. The performance of the existing SC-FDE structure is also shown when a narrow band jammer is present.

이다.The fading channel model is a 7-path Rayleigh model, and the power for each multipath is [0.73, 0.031, 0.034, 0.051, 0.061, 0.042, 0.051], and the multipath delay is [0, 1.6, 3.2, 4.8, 6.4, 8.0, 9.6]

to be.

According to the simulation results, it can be seen that the performance of the existing SC-FDE structure is significantly reduced when a narrow band jammer is present. However, the proposed SC-FDE structure shows a significant improvement in performance over the existing structure when a narrow-band jammer is present. The performance is about 2 dB lower than when the narrow-band jammer does not exist, but the existing structure shows relatively good performance considering that it can hardly communicate.

The simulation results show that the proposed SC-FDE structure not only enables communication even in the presence of narrow-band jammers, but also reduces pilot overhead, thereby improving both communication reliability and frequency efficiency.

As described above, according to an embodiment of the present invention, frequency channel estimation is performed without time-domain channel estimation and linear interpolation is used to show better performance than existing structures in an environment in which narrow-band jammers or interference signals exist and pilot It was also confirmed that the overhead can be reduced compared to the conventional method. Therefore, the proposed SC-FDE structure can be applied to safety-critical systems such as military communication systems and unmanned aerial vehicles.

Although the present invention has been described in detail through exemplary embodiments above, those skilled in the art to which the present invention pertains understand that various modifications are possible within the limits of the embodiments described above without departing from the scope of the present invention. will be. Therefore, the scope of rights of the present invention should not be limited to the described embodiments, but should be determined by any modified or modified form derived from the claims and equivalent concepts as well as the claims described below.

S: SC-FDE transmission/reception system for coping with narrowband interference signals and reducing pilot overhead
100: receiver
200: transmitter
300: CP eliminator
400: FFT
500: channel estimator
600: jammer detector

Claims (4)

A receiver for receiving a pilot signal in a narrowband jammer environment;
A transmitter that transmits a pilot signal;
A CP remover to remove CP from the received pilot signal;
The frequency domain pilot signal (

), and the frequency domain pilot signal (

FFT to extract ); And
Two frequency domain pilot signals (

,

) Through linear interpolation to each frequency domain channel (

Channel estimator to estimate)
SC-FDE transmission and reception system for narrow-band interference signal response and reduction of pilot overhead, characterized in that it comprises. According to claim 1,
The CP eliminator,
CP is removed from the pilot signal from the receiver,
The length of the pilot in the pilot signal (

) To CP length (

SC-FDE transmission and reception system for narrow-band interference signal reduction and pilot overhead reduction, characterized by removing. According to claim 1,
The FFT,
The frequency domain pilot signal (

), and the frequency domain pilot signal (

SC-FDE transmission and reception system for narrow-band interference signal response and pilot overhead reduction, characterized in that the extraction. According to claim 1,
The frequency domain pilot signal extracted by the FFT (

If exceeds the preset value, a jammer detector that determines that a narrow-band jammer exists in the frequency
SC-FDE transmission and reception system for narrow-band interference signal response and reduction of pilot overhead, characterized in that it further comprises.

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