KR102530452B1 - Multiantenna Backscatter Communication System and Method for estimating Forward Channel in the same - Google Patents

Abstract

A multi-antenna backscatter communication system and forward channel estimation method are disclosed.
In this device, a Hybrid Access Point (HAP) transmits a carrier signal through a plurality of antennas as an energy source for backscatter communication. A plurality of backscattering devices receive a carrier signal transmitted from the HAP, and when the received signal is reflected, modulates the received signal into a backscattered signal containing data and transmits it to the HAP. HAP selects only one antenna among a plurality of antennas based on channel power information for each antenna in a training step of performing channel estimation, transmits a training signal to a plurality of backscatter devices through the selected one antenna, and HAP has one When a reflection modulated signal is received from a specific backscatter device in response to a training signal transmitted through an antenna of HAP, a forward channel from the HAP to the backscatter device is estimated based on the antenna selected to transmit the training signal.

Description

Multiantenna Backscatter Communication System and Method for estimating Forward Channel in the same}

The present invention relates to a multi-antenna backscatter communication system and a forward channel estimation method.

Backscatter communication has recently emerged to reduce power consumption of small devices, which are key components of the Internet of Things (IoT). Such backscattered communication does not generate a carrier wave that consumes a lot of power, so ultra-low power or powerless communication is possible. For example, backscatter communication uses carrier signals such as TV, MF radio, LoRa (Long Range), and Wi-Fi that exist around us or a carrier signal transmitted from a designated RF source.

In this backscattering communication, a transmitter that transmits a carrier wave to a backscattering device and a reader that receives a reflection-modulated signal from the backscattering device simultaneously perform the roles of a transmitter and a reader in monostatic backscattering communication in the same location. A device that does this is called a Hybrid Access Point (HAP).

The HAP needs to estimate a backscatter channel from HAP-device-HAP for coherent demodulation or estimate a forward channel between HAP-device for transmit beamforming.

To this end, when the HAP-device forward channel and the device-HAP reverse channel are mutually reciprocal, a method of estimating the HAP-device forward channel from the backscatter channel estimate between the HAP-device-HAP in a multi-antenna HAP has been proposed.

However, these technologies transmit the same orthogonal training signal through multiple antennas regardless of channels.

An object of the present invention is to provide a multi-antenna backscatter communication system and a method for estimating a forward channel for improved channel estimation performance required for demodulation and transmission beamforming.

In order to achieve the objects of the present invention as described above and realize the characteristic effects of the present invention described later, the characteristic configuration of the present invention is as follows.

According to one aspect of the present invention, a backscatter communication system is provided, comprising:

A Hybrid Access Point (HAP) that transmits a carrier signal through a plurality of antennas as an energy source for backscatter communication, receives the carrier signal transmitted from the HAP, and includes data when the received signal is reflected. and a plurality of backscatter devices that modulate a backscattered signal and transmit the modulated backscattered signal to the HAP, wherein the HAP selects only one antenna from among the plurality of antennas based on channel power information for each antenna in a training step of performing channel estimation. and transmits a training signal to the plurality of backscatter devices through one selected antenna, and the HAP receives a reflection-modulated signal from a specific backscatter device in response to the training signal transmitted through the one antenna. , estimates the forward channel from the HAP to the backscatter device based on the antenna selected to transmit the training signal.

Here, the HAP is based on an order/ideal selection method in which the order of channel power of each antenna of the forward channel is known in advance, and the order of channel power is selected so that the index of the antenna does not have a duplicate value. The one antenna selection is performed.

In addition, the HAP selects the antenna having the highest power by allowing overlapping antenna indices in a state in which the antenna having the highest channel power among the channel powers of each antenna of the forward channel is known. The one antenna selection is performed according to an ideal) selection method.

In addition, the HAP randomly selects one antenna to transmit the first training signal, and then one antenna to transmit the training signal is based on the accumulation of received signals corresponding to the previously transmitted training signals It is selected according to the estimated channel power of each of the plurality of antennas.

In addition, the selection of the one antenna through which the HAP transmits the n-th (n is a natural number equal to or greater than 2) training signal results in the backscattered signal for the training signal transmitted by the HAP being the q-th (q<n) training signal. up to, the next received power for the mth antenna (where 1≤m≤M)

은 l번째 훈련 신호에 대한 상기 m번째 안테나에서의 수신 신호이다.is done according to, where

Is the received signal at the m-th antenna for the l-th training signal.

In addition, the HAP performs training signal transmission in a distributed manner applicable to the case of supporting the plurality of backscatter devices so as to secure a received signal and calculation time for antenna selection in advance to increase the value of q. do.

)는 다음의 관계식In addition, the one antenna (

) is the relational expression

It is selected according to, where M is the number of antennas, and N<M.

)는 다음의 관계식In addition, the one antenna (

) is the relational expression

It is selected according to, where M is the number of antennas, and N<M.

According to another aspect of the present invention, a forward channel estimation method is provided, which includes:

A method for estimating a forward channel in a backscatter communication system, wherein a hybrid access point (HAP) that transmits a carrier signal to a plurality of backscatter devices through a plurality of antennas in the backscatter communication system uses a preset antenna selection method and each antenna Generating a training signal based on channel power information, selecting a corresponding antenna based on the preset antenna selection method and the channel power information for each antenna, through the one antenna selected in the selecting step. transmitting the training signal generated in the generating step to the plurality of backscattering devices; receiving a reflection-modulated signal from the backscattering device in response to the training signal transmitted through the one antenna; and estimating the forward channel based on an antenna selected to transmit a training signal.

Here, the step of selecting the one antenna includes determining whether transmission of a training signal is the first time, and if the transmission of the training signal is the first time, selecting a corresponding antenna according to the preset antenna selection method. or, if the transmission of the training signal is not the first time, a corresponding one antenna is selected according to the channel power information calculated using the reflection modulated signal corresponding to the transmission of the previous training signal and the preset antenna selection method. It includes a selection step.

In addition, the preset antenna selection method may be a sequential selection method in which overlapping is not allowed when selecting antennas in a state in which the order of higher channel powers of the forward channel is known in advance, or the order of higher channel powers of the forward channel is known in advance. A best selection method that allows overlapping when selecting antennas in a state in which there is a forward channel, or a sequential/accumulative selection method that does not allow overlapping when selecting antennas in a state where the order of higher channel powers of the forward channel is not known in advance, or This is a best/accumulative selection method that allows overlapping when selecting antennas in a state where the order of higher channel power is not known in advance.

In addition, in the case of the sequential/cumulative selection method and the best/accumulative selection method, the transmitting of the training signal may include each of the plurality of antennas based on accumulation of signals received corresponding to previously transmitted training signals. Estimating channel power, and selecting an antenna having the highest channel power among the estimated channel powers as the one antenna.

According to the present invention, channel estimation performance required for demodulation and transmit beamforming in a backscatter communication system can be improved.

In addition, by improving the forward channel estimation performance, the transmission beamforming performance is improved, and accordingly, the information transmission radius and the energy transmission radius of the monostatic backscatter communication are widened.

의 정규화된 MUSE를 나타낸 도면이다.1 is a schematic diagram of a multi-antenna backscatter communication system to which the present invention is applied.
2 is a detailed configuration diagram of a backscatter communication system according to an embodiment of the present invention.
3 is a diagram illustrating a data frame structure used in general backscatter communication.
4 is a schematic flowchart of a forward channel estimation method according to an embodiment of the present invention.
5 shows forward channel estimates for various channel adaptive training signals as a function of SNR.

It is a diagram showing the normalized MUSE of

Hereinafter, with reference to the accompanying drawings, embodiments of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein. And in order to clearly explain the present invention in the drawings, parts irrelevant to the description have been omitted, and similar reference numerals have been attached to similar parts throughout the specification.

Throughout the specification, when a certain component is said to "include", it means that it may further include other components without excluding other components unless otherwise stated. In addition, terms such as “… unit”, “… unit”, and “module” described in the specification mean a unit that processes at least one function or operation, which may be implemented as hardware or software or a combination of hardware and software. there is.

Throughout the specification, it should be understood that the term "and/or" describes only an association relationship for describing the related objects and indicates that three relationships may exist. For example, A and/or B may indicate three cases in which only A exists, both A and B exist, and only B exists. Also, throughout the specification, the character "/" generally indicates an "or" relationship between related objects.

Devices described in the present invention are composed of hardware including at least one processor, memory device, communication device, and the like, and a program to be executed in combination with the hardware is stored in a designated place. The hardware has the configuration and capability to implement the method of the present invention. The program includes instructions implementing the operating method of the present invention described with reference to the drawings, and implements the present invention in combination with hardware such as a processor and a memory device.

Hereinafter, a multi-antenna backscatter communication system according to an embodiment of the present invention will be described with reference to the drawings.

First, a general multi-antenna backscatter communication system will be described with reference to FIG. 1 .

Referring to FIG. 1, a backscatter communication system 10 includes a hybrid access point (HAP) 100 and a plurality of backscatter devices 200-1, 200-2, ..., 200-k (where k is a natural number greater than or equal to 1).

The HAP 100 operates as a power source for the backscatter devices 200-1, 200-2, ..., 200-k and at the same time detects the backscatter devices 200-1, 200-2, ..., 200-k. collect the data

The HAP 100 includes a plurality of antennas, for example, M (where M is a natural number greater than or equal to 1) antennas 110, and uses the M antennas 110 to transmit an active carrier signal to the backscatter device 200. -1, 200-2, …, 200-k).

In addition, the HAP 100 receives a backscattered signal transmitted after being backscattered modulated from one backscatter device 200-k at a specific time. Referring to FIG. 1, carrier signals transmitted from the HAP 100 to the backscatter devices 200-1, 200-2, ..., 200-k are indicated by solid lines, and the backscatter devices 200-1, 200 Backscattered signals transmitted from -2, ..., 200-k) to the HAP 100 are indicated by dotted lines.

In this way, when there are several backscatter devices 200-1, 200-2, ..., 200-k in the backscatter communication system 10, the HAP 100 provides each backscatter device 200-1, 200 Since the training signals for -2, ..., 200-k are transmitted to be orthogonal to each other on a time basis, a training signal transmission method for each backscattering device (200-1, 200-2, ..., 200-k) and The channel estimation method can be equally applied, using the HAP 100 and one backscattering device (eg, 200-1, hereinafter referred to as “200”) to transmit training signals for forward channel estimation and A channel estimation method is described.

First, the HAP 100 has N transmit/receive antennas, and a forward channel between the HAP 100 and the backscatter device 200 is as shown in Equation 1 below.

[Equation 1]

복소 행렬 집합을 나타낸다.here,

Represents a set of complex matrices.

개의 훈련 신호 벡터를 후방산란 디바이스(200)로 송신한다. 여기서, HAP(100)이 송신하는 n(1≤n≤N)번째 훈련 신호 벡터를

이라고 하면(여기서 일반성 상실 없이

로 가정함), HAP(100)이 송신한 훈련 신호를 후방산란 디바이스(200)가 반사 전력 비율

로 반사한 신호를 HAP(100)이 수신한다. 이 때, HAP(100)에서 수신되는 신호를 스케일링하여 나타내면 다음의 [수학식 2]와 같다. To estimate the forward channel vector in the backscatter communication system 10, the HAP 100

Ng training signal vectors are transmitted to the backscatter device 200. Here, the n (1≤n≤N)th training signal vector transmitted by the HAP 100

(without loss of generality here

), the backscattering device 200 reflects the power ratio of the training signal transmitted by the HAP 100

The HAP (100) receives the reflected signal. At this time, when the signal received from the HAP 100 is scaled and expressed, it is as shown in [Equation 2].

[Equation 2]

는 스케일링 후의 M개의 안테나(110)의 잡음 벡터로, 분산이

인 독립인 가우시안 잡음으로 구성되며, 여기서

는 송신 전력이고,

는 경로 손실이며,

는 HAP(100)에서의 배경 잡음 분산이다. here

Is the noise vector of the M antennas 110 after scaling, where the variance is

is composed of Gaussian noise that is independent, where

is the transmit power,

is the path loss,

is the background noise variance in the HAP 100.

When the signals received by the HAP 100 for N training signal vectors are expressed as matrices, the following [Equation 3] is obtained.

[Equation 3]

는 HAP-디바이스-HAP으로의 후방산란 채널이고,

는 훈련 신호 행렬이며,

은 잡음 행렬이다. here

is the backscatter channel to the HAP-device-HAP,

is the training signal matrix,

is the noise matrix.

개의 훈련 신호 송신 구간에 직교 훈련 신호 행렬

을 처음 N개의 송신 안테나로 송신한다. 이 때의 훈련 신호 행렬은 다음의 [수학식 4]와 같이 표현할 수 있다. In general backscatter communication,

An orthogonal training signal matrix in the training signal transmission interval

is transmitted through the first N transmit antennas. The training signal matrix at this time can be expressed as the following [Equation 4].

[Equation 4]

,

,

이다. 즉,

은

를 만족하는 임의의 직교 행렬이다.here

am. in other words,

silver

is any orthogonal matrix that satisfies

The received signal for the training signal according to the above-described [Equation 4] can be rewritten as the following [Equation 5].

[Equation 5]

은 [수학식 6]과 같이 나타낼 수 있다.where the backscatter channel

can be expressed as in [Equation 6].

[Equation 6]

을 LS(least square) 또는 LMMSE(linear minimum mean square error)와 같은 선형 추정 기법으로 추정한

을 얻고, 이로부터 순방향 채널 추정치

를 얻는다. In a general technique, the truncated backscattered channel in [Equation 5]

estimated by a linear estimation technique such as least square (LS) or linear minimum mean square error (LMMSE).

is obtained, from which the forward channel estimate

get

를 얻는 방법으로 순방향 채널

를 훈련 신호가 송신되는 안테나 그룹 에 해당하는 채널

와 훈련 신호가 송신되지 않는 안테나 그룹 에 해당하는 채널

로 나누어 추정한다. In this case, the forward channel estimate

How to get forward channel

Channel corresponding to the antenna group through which the training signal is transmitted

and a channel corresponding to an antenna group on which training signals are not transmitted.

estimated by dividing by

와

임을 알 수 있고, 따라서

와

로 나누어 채널 추정을 순차적으로 수행한다. According to the above explanation,

and

can be known, and therefore

and

Divided by , channel estimation is sequentially performed.

Therefore, the truncated backscatter channel of [Equation 6] can be expressed as [Equation 7].

[Equation 7]

이고

이다. here

ego

am.

를 만족하며, 이를 실수값으로 바꾸어 나타내면 다음의 [수학식 8]과 같다. Accordingly, the antenna group A through which the training signal is transmitted is

is satisfied, and when expressed by converting it to a real value, the following [Equation 8] is obtained.

[Equation 8]

과

는 실수 부분과 허수 부분을 각각 나타낸다. here,

class

represents the real part and the imaginary part, respectively.

Meanwhile, the antenna group (B) to which the training signal is not transmitted satisfies the following [Equation 9].

[Equation 9]

로부터,

의 추정치

와

의 추정치

를 얻을 수 있다. Backscattered channel estimate truncated according to [Equation 8] and [Equation 9] described above

from,

estimate of

and

estimate of

can be obtained.

는 [수학식 8]에 따라 다음의 [수학식 10]의 행렬의 최대 고유값(eigenvalue)에 해당하는 고유 벡터 (eigenvector)를 구해 얻을 수 있다. Specifically

can be obtained by obtaining an eigenvector corresponding to the maximum eigenvalue of the matrix of the following [Equation 10] according to [Equation 8].

[Equation 10]

는 [수학식 9]와 전술한 바와 같이 산출되는

를 이용하여 다음의 [수학식 11]과 같이 산출할 수 있다. Next, estimate

Is calculated as described above with [Equation 9]

It can be calculated as in the following [Equation 11] using

[Equation 11]

As such, in the general technique, if the number of training signals is , training signals are transmitted through the number of antennas 110 . Accordingly, the training signal was transmitted through all the antennas 110 in the rear surface.

Therefore, in a general technique, the same orthogonal training signal is transmitted through multiple antennas regardless of channels.

Meanwhile, in an embodiment of the present invention, referring to the following [Equation 12], the training signal has a form in which only one element of a vector having a length is not 0 and the rest are 0. At this time, the index to which a value other than 0 is transmitted is the selected antenna index.

[Equation 12]

= [0 … 010 … 0]^T

= [0 … 010 … 0] ^T

Referring to [Equation 12], the received signal according to [Equation 3] described above is rewritten as the following [Equation 13].

[Equation 13]

은 n번째 훈련 신호에 대한 번째 수신 안테나 신호이다. here

is the th receive antenna signal for the n th training signal.

의 채널 전력이 높은 순서를 미리 알고 있는 경우를 고려한다. 즉, HAP(100)이 m번째로 채널 전력이 큰 안테나 인덱스를 으로 표시하는 경우, HAP(100)은 다음의 [수학식 14]와 같이 안테나별 채널 전력이 높은 순서를 알고 있다. First, HAP 100 is a forward channel

Consider the case where the order of higher channel powers is known in advance. That is, when the HAP 100 indicates the m-th antenna index having the largest channel power as , the HAP 100 knows the order of the highest channel power for each antenna as shown in [Equation 14].

[Equation 14]

으로 할 수 있고, 이 경우, N개의 훈련 신호를 송신할 때 신호를 송신한 안테나 그룹 인덱스는

이고, 그에 따른 수신 신호는 다음의 [수학식 15]와 같다. 즉, 순차 선택 방법에서는 총 N개의 서로 다른 안테나로 훈련 신호가 전송되는 것이다.In this state, as a method of selecting an antenna for transmitting a training signal in the HAP 100, an order/ideal selection method that does not allow overlap, that is, an antenna index for the nth training signal

In this case, when N training signals are transmitted, the antenna group index that transmitted the signals is

, and the resulting received signal is as follows [Equation 15]. That is, in the sequential selection method, training signals are transmitted through a total of N different antennas.

[Equation 15]

와

를 구성하고, [수학식 15]의 수신 벡터의 열 순서를

에 해당하는 열이 위에 오도록 다음의 [수학식 16]과 같이 변환할 수 있다. thus,

and

, and the order of the columns of the received vector in [Equation 15]

It can be converted as shown in [Equation 16] so that the column corresponding to is at the top.

[Equation 16]

에 해당하므로 전술한 [수학식 10]과 [수학식 11]을 사용하면 훈련 신호를 송신하는 그룹의 안테나 인덱스

에 대응하는 채널 추정치

와 훈련 신호를 송신하지 않는 그룹의 안테나 인덱스 에 대응하는 채널 추정치

를 산출할 수 있다. The above [Equation 16] is

, so using [Equation 10] and [Equation 11] described above, the antenna index of the group transmitting the training signal

Channel estimate corresponding to

and a channel estimate corresponding to the antenna index n of the group not transmitting the training signal.

can be calculated.

을 적용할 수 있다. On the other hand, when the HAP 100 knows the order of the highest channel power for each antenna, that is, when [Equation 14] is known, the HAP 100 selects the antenna 110 for transmitting the training signal, The best/ideal selection method that allows overlap, i.e.

can be applied.

이다. 따라서, 이 경우 수신 신호에 대한 전술한 [수학식 13]은 가 된다. 이 경우, 수신 신호를 다음의 [수학식 17]과 같이 평균화하여 잡음을 줄일 수 있다.In this case, the antenna group transmitting the training signal is

am. Therefore, in this case, the above-described [Equation 13] for the received signal becomes In this case, noise can be reduced by averaging the received signal as shown in [Equation 17] below.

[Equation 17]

에 해당하는 수신 신호가 위에 오도록 다음의 [수학식 18]과 같이 순서를 바꿀 수 있다. The vector of [Equation 17] described above

The order can be changed as shown in [Equation 18] so that the received signal corresponding to is on top.

[Equation 18]

에 해당하므로 전술한 [수학식 10]과 [수학식 11]을 사용하면 훈련 신호를 송신하는 그룹의 안테나 인덱스

에 대응하는 채널 추정치

와 훈련 신호를 송신하지 않는 그룹의 안테나 인덱스 에 대응하는 채널 추정치

를 산출할 수 있다. The above [Equation 18] is

, so using [Equation 10] and [Equation 11] described above, the antenna index of the group transmitting the training signal

Channel estimate corresponding to

and a channel estimate corresponding to the antenna index n of the group not transmitting the training signal.

can be calculated.

의 채널 전력 정보를 모르고 있는 경우를 고려한다.Next, in another embodiment of the present invention, HAP 100 is a forward channel

Consider a case where the channel power information of is not known.

).In this case, the first training signal is transmitted using an arbitrary antenna (

).

Then, in order to select an antenna to transmit a training signal, the HAP 100 may estimate received power for each antenna using a currently available received signal (that is, a signal with n<2 in [Equation 13]).

In addition, in order to select an antenna to transmit the next training signal, the HAP 100 may estimate received power for each antenna using a currently available received signal (that is, a signal with n<3 in [Equation 13]). .

If this is generalized, in the criterion for the HAP 100 to select an antenna for transmitting the n th training signal, when there are backscattered signals for the training signal received by the HAP 100 up to the q th (q<n) training signal , the received power for antenna m can be estimated and selected as in [Equation 19] below.

[Equation 19]

으로 선택하고, 일 때 훈련 신호를 송신하는 안테나는 [수학식 19]를 활용하여 다음의 [수학식 20]과 같이 산출할 수 있다.In this case, in the embodiment of the present invention, an order/accumulation (Order/Acc) selection method that does not allow overlap can be applied, and in this case, the antenna transmitting the training signal is randomly

An antenna that is selected as , and transmits a training signal when , can be calculated as shown in [Equation 20] using [Equation 19].

[Equation 20]

=이고,

은 순차/누적(Order/Acc) 안테나 선택 방법을 통해 q 번째 훈련 신호까지 훈련 신호를 송신한 안테나 그룹을 나타낸다. here

= and

denotes an antenna group that has transmitted training signals up to the q th training signal through an order/accumulation (Order/Acc) antenna selection method.

을 설정할 수 있으며, 이는 중복을 허용하지 않으므로 전술한 [수학식 13]으로부터 순차 선택(Order/ideal) 방법에서의 프로세스를 적용함으로써,

에 대응하는 채널 추정치

와 훈련 신호를 송신하지 않는 그룹의 안테나 인덱스 에 대응하는 채널 추정치

를 산출할 수 있다.In this case, the antenna group that transmitted the training signal during N training signal transmission times

can be set, which does not allow duplication, so by applying the process in the order / ideal method from [Equation 13] described above,

Channel estimate corresponding to

and a channel estimate corresponding to the antenna index n of the group not transmitting the training signal.

can be calculated.

의 채널 전력 정보를 모르고 있는 경우, 중복을 허용한 최선/누적(Best/Acc) 안테나 선택 방법이 적용될 수 있다.On the other hand, HAP (100) is the forward channel

If the channel power information of is not known, the best/accumulation (Best/Acc) antenna selection method allowing overlapping may be applied.

으로 선택하고 일 때 훈련 신호를 송신하는 안테나를 선택하는 방법은 전술한 [수학식 19]를 활용하여 다음의 [수학식 21]과 같이 얻을 수 있다.In this case, the antenna transmitting the training signal when

A method for selecting an antenna for transmitting a training signal when , and when , can be obtained as shown in [Equation 21] using the above-described [Equation 19].

[Equation 21]

, n=1,2,..,N 값이 동일한 값을 갖는 경우가 많다. here,

, n = 1,2,.., N values often have the same value.

를 훈련 신호를 송신한 안테나 그룹

으로 선택하고, 해당 안테나로 송신된 훈련 신호에 대한 수신 신호만을 평균화한 다음의 [수학식 22]를 사용한다. As can be seen from [Equation 19], it can be seen that the more received signals of the training signals are used, the more accurate the received power estimation for each antenna is. Therefore, in the best/cumulative antenna selection method, the last selected antenna

The antenna group that transmitted the training signal to

is selected, and the following [Equation 22] is used after averaging only the received signal for the training signal transmitted through the corresponding antenna.

[Equation 22]

이다.here,

am.

에 해당하는 수신 신호가 위에 오도록 다음의 [수학식 23]과 같이 순서를 바꿀 수 있다.Accordingly, the vector of [Equation 22]

The order can be changed as shown in [Equation 23] so that the received signal corresponding to is on top.

[Equation 23]

에 해당하므로 전술한 [수학식 10]과 [수학식 11]을 사용하면 훈련 신호를 송신하는 그룹의 안테나 인덱스

에 대응하는 채널 추정치

와 훈련 신호를 송신하지 않는 그룹의 안테나 인덱스 에 대응하는 채널 추정치

를 산출할 수 있다. The above [Equation 23] is

, so using [Equation 10] and [Equation 11] described above, the antenna index of the group transmitting the training signal

Channel estimate corresponding to

and a channel estimate corresponding to the antenna index n of the group not transmitting the training signal.

can be calculated.

Hereinafter, a backscatter communication system according to an embodiment of the present invention based on the above description will be described.

2 is a detailed configuration diagram of a backscatter communication system according to an embodiment of the present invention.

As shown in FIG. 2, a backscatter communication system 10 according to an embodiment of the present invention includes a hybrid access point (HAP) 100 and a plurality of backscatter devices (BD1 (200-1), BD2 (200-1) 2), ..., BDK (200-k)) (where k is a natural number greater than or equal to 1).

The HAP 100 operates as a power source for the backscatter devices 200-1, 200-2, ..., 200-k and at the same time detects the backscatter devices 200-1, 200-2, ..., 200-k. collect the data

The HAP 100 includes a plurality of antennas, for example, M (where M is a natural number greater than or equal to 2) antennas 110, and uses the M antennas 110 to transmit an active carrier signal to the backscattering device 200. -1, 200-2, …, 200-k).

In addition, the HAP 100 receives backscattered signals transmitted after being backscattered modulated at times assigned to the backscatter devices 200-1, 200-2, ..., 200-k, respectively. Referring to FIG. 1, carrier signals transmitted from the HAP 100 to the backscatter devices 200-1, 200-2, ..., 200-k are indicated by solid lines, and the backscatter devices 200-1, 200 Backscattered signals transmitted from -2, ..., 200-k) to the HAP 100 are indicated by dotted lines.

Specifically, the HAP 100 includes a decoupler 120, a training signal generator 130, a carrier transmitter 140, a demodulator 150, a channel estimation unit 160, and a control unit 170. do.

The decoupler 120 transmits training signals or carrier waves to the backscatter devices 200-1, 200-2, ..., 200-k through a plurality of antennas 110, and also transmits one backscatter device at a specific time. A backscattered signal transmitted after being backscattered modulated is received from (200-k). This decoupler 120 is capable of full-duplex operation enabling simultaneous transmission and reception of signals through the antenna 110 .

The training signal generating unit 130 generates a training signal for channel estimation of the backscatter communication system 10 using the power information for each channel in the channel estimating unit 160 . The training signal generating unit 130 according to an embodiment of the present invention uses the power information for each channel in the channel estimating unit 160 to perform training so that only one of the M antennas 110 can transmit a training signal. signal can be generated. Specifically, using the power information for each channel in the channel estimator 160, an order/ideal selection method that does not allow overlap, a best/ideal selection method that allows overlap, and an overlap that allows overlap It is possible to generate a training signal in a form corresponding to any one of an antenna selection method among an order/accumulation (Order/Acc) selection method that does not apply and a best/accumulation (Best/Acc) selection method that allows overlap.

As shown in FIG. 3 , the carrier wave transmitter 140 transfers the training signal generated by the training signal generator 130 to an antenna connected through the decoupler 120 in the training phase 21 of the data frame. 110) to the backscattering devices 200-1, 200-2, ..., 200-k, and in the data phase 22, the antenna 110 connected through the decoupler 120 The carrier wave is transmitted to the backscattering devices 200-1, 200-2, ..., 200-k. Here, allocation of training signals to the backscatter devices 200-1, 200-2, ..., 200-k in the training step 21 may be performed in a clustered or distributed manner. Here, the distributed method may be applied to transmission of a training signal when multiple devices are supported so that a received signal and calculation time for antenna selection can be secured in advance.

In addition, when transmitting the training signal generated by the training signal generator 130, the carrier transmitter 140 transmits the training signal according to the selection method used when the training signal generator 130 generates the training signal. An antenna 110 may be selected. Specifically, the carrier transmitter 140 selects an order/ideal selection method that does not allow overlapping, a best/ideal selection method that allows overlapping, and an order/accumulation (Order/Acc) selection method that does not allow overlapping. The antenna 110 to transmit the training signal may be selected according to the selection method used in the training signal generation unit 130 from among best/accumulation (Best/Acc) selection methods allowing overlapping.

The demodulator 150 demodulates the signal received through the decoupler 120 . Since such demodulation is already well known, a detailed description thereof will be omitted.

The channel estimator 160 calculates power information for each channel of the backscatter communication system 10 using the signal demodulated by the demodulator 150 and performs channel estimation based thereon. Such channel estimation may be performed after all N training signals are transmitted. In particular, the channel estimator 160 transmits a training signal from one of the M antennas 110 in the carrier transmitter 140 in the training step 21, and then transmits the training signal to one backscatter device 200-k. ), channel power information is calculated using the received and demodulated signal, and forward channel estimation is performed accordingly. The channel estimator 160 may perform forward channel estimation according to the selection method used when the training signal generator 130 generates the training signal. Specifically, the channel estimator 160 uses an order/ideal selection method that does not allow overlap, a best/ideal selection method that allows overlap, and an order/accumulation (Order/Acc) method that does not allow overlap. Forward channel estimation may be performed according to a selection method used in the training signal generator 130 among selection methods and a best/accumulation (Best/Acc) selection method allowing overlapping.

The controller 170 controls the overall operation of the backscatter communication system 10 by controlling the training signal generator 130, the carrier transmitter 140, the demodulator 150, and the channel estimator 160. In particular, the controller 170 includes a policy flag 171 indicating an antenna selection method to be performed in the backscatter communication system 10 . That is, the policy flag 171, as described above, is an order/ideal selection method that does not allow overlap, a best/ideal selection method that allows overlap, and an order/accumulation method that does not allow overlap. /Acc) and a best/accumulative (Best/Acc) selection method allowing overlapping, a value or an identifier indicating one antenna selection method is stored. Here, the policy flag 171 may be directly or indirectly set by a user or operator as one selection method among the above-described four antenna selection methods, or may be additionally modified after being set.

Therefore, the training signal generator 130, the carrier transmitter 140, and the channel estimator 160 check the antenna selection method through the policy flag 171 in the control unit 170, and according to the checked antenna selection method, It can generate training signals, select antennas, and also perform forward channel estimation using the received signals.

Meanwhile, in the above, it has been described that the policy flag 171 is placed in the control unit 170 to freely set four antenna selection methods and generate a training signal according to the set selection method to perform forward channel estimation. However, the present invention It is not limited to this only, and can be designed to operate fixedly with one selection method selected from four selection methods. For example, the backscatter communication system 10 according to an embodiment of the present invention can be designed to operate only in an order/ideal selection method that does not allow overlapping.

Next, a forward channel estimation method according to an embodiment of the present invention will be described.

4 is a schematic flowchart of a forward channel estimation method according to an embodiment of the present invention. The forward channel estimation method according to FIG. 4 may be performed by the HAP 100 of the backscatter communication system 10 described with reference to FIGS. 2 and 3 .

Referring to FIG. 4 , first, the HAP 100 checks an antenna selection method to be performed in the backscatter communication system 10 and channel power information for each antenna (S100). For example, an antenna selection method to be performed in the backscatter communication system 10 may be confirmed through the policy flag 171 .

Next, a training signal is generated according to the confirmed antenna selection method and channel power information for each antenna (S110).

Then, it is determined whether transmission of a training signal for a specific backscatter device 200-k is the first time (S120).

If the training signal is transmitted for the first time, the training signal generated in step S110 is sent to the backscattering devices 200-1, 200-2, ..., 200-k) is transmitted (S130).

However, if the transmission of the training signal is not the first time, the training generated in step S110 is performed through the antenna 110 selected according to the channel power information for each antenna calculated according to the previous transmission of the training signal and the confirmed antenna selection method. The signal is transmitted to the backscatter devices 200-1, 200-2, ..., 200-k (S140).

The training signal transmitted for the specific backscattering device 200-k is reflected-modulated with a fixed reflection coefficient by the backscattering device 200-k and transmitted to the HAP 100 again.

Accordingly, the HAP 100 receives the reflection-modulated signal from the backscatter device 200-k (S150).

Then, the forward channel is estimated based on the antenna that transmitted the training signal, that is, the antenna selected in step S130 or S140 (S160).

Hereinafter, a method of estimating a channel corresponding to the above four antenna selection methods will be described.

In an embodiment of the present invention, when a training signal is transmitted from one of the M antennas 110 and a reflection-modulated signal for the transmitted training signal is received, forward channel estimation is performed using the received signal. It is based on performing

의 채널 전력이 높은 순서를 미리 알고 있다. First, the case of an order/ideal selection method that does not allow duplication will be described. In this scheme, HAP 100 is a forward channel

The order of higher channel power of is known in advance.

In the step S110, since the index of the antenna through which the non-zero training signal is transmitted is n (1≤n≤N, N≤M), the training signal corresponding to the n index can be transmitted using [Equation 12] ], a training signal may be generated.

이고 훈련 신호를 송신하지 않는 그룹의 안테나 인덱스가 가 되도록 안테나가 선택된다. 이 때, 안테나의 선택은 중복이 허용되지 않는다. In the step S120, the antenna index of the group transmitting the training signal is

, and an antenna is selected such that the antenna index of a group not transmitting a training signal is . At this time, overlapping antenna selection is not allowed.

In step S130, channel estimation is performed using Equation 15, Equation 16, Equation 10, and Equation 11 described above.

Next, the case of the best/ideal selection method allowing duplication will be described.

의 채널 전력이 높은 순서를 미리 알고 있다. In this scheme, HAP 100 is a forward channel

The order of higher channel power of is known in advance.

이므로 이에 해당되는 훈련 신호만이 송신될 수 있도록 훈련 신호가 생성될 수 있다.In step S110, the index of the antenna through which the non-zero training signal is transmitted has the highest channel power.

Therefore, a training signal can be generated so that only the corresponding training signal can be transmitted.

이고 훈련 신호를 송신하지 않는 그룹의 안테나 인덱스가 가 되도록 안테나가 선택된다. 이 때, 안테나의 선택은 중복이 허용된다. In the step S120, the antenna index of the group transmitting the training signal is

, and an antenna is selected such that the antenna index of a group not transmitting a training signal is . At this time, overlapping antenna selection is allowed.

In step S130, channel estimation is performed using Equation 17, Equation 18, Equation 10, and Equation 11 described above.

Next, the case of a sequential/accumulative (Order/Acc) selection method that does not allow duplication will be described.

의 채널 전력이 높은 순서를 모른다.In this scheme, HAP 100 is a forward channel

I don't know the order in which the channel power of is higher.

In the step S110, a training signal may be generated as shown in [Equation 12] so that the training signal can be transmitted only from one antenna.

In step S120, an arbitrary antenna is selected when the first training signal is transmitted.

However, if the second or more training signals are transmitted, an antenna having the highest channel power estimated using received signals available up to now is selected. At this time, overlapping antenna selection is not allowed. Specifically, the antenna calculated through [Equation 19] and [Equation 20] described above may be selected.

과 훈련 신호를 송신하지 않는 그룹 를 사용하여 전술한 [수학식 15], [수학식 16], [수학식 10], [수학식 11] 등을 통해 채널 추정이 수행된다.In the step S130, the antenna group that transmitted the training signal

Channel estimation is performed using [Equation 15], [Equation 16], [Equation 10], [Equation 11], etc.

Next, the case of the best/accumulation (Best/Acc) antenna selection method allowing overlap will be described.

의 채널 전력이 높은 순서를 모른다.In this scheme, HAP 100 is a forward channel

I don't know the order in which the channel power of is higher.

In the step S110, a training signal may be generated as shown in [Equation 12] so that the training signal can be transmitted only from one antenna.

In step S120, an arbitrary antenna is selected when the first training signal is transmitted.

However, when the second or more training signals are transmitted, an antenna having the highest channel power estimated using received signals available up to now is selected. At this time, overlapping antenna selection is allowed. Specifically, the antenna calculated through [Equation 19] and [Equation 21] described above may be selected.

과 훈련 신호를 송신하지 않는 그룹 를 사용하여 전술한 [수학식 22], [수학식 23], [수학식 10], [수학식 11] 등을 통해 채널 추정이 수행된다.In the step S130, the antenna group that transmitted the training signal

Channel estimation is performed using [Equation 22], [Equation 23], [Equation 10], [Equation 11], etc.

의 정규화된 MUSE(mean unsigned square error)를 나타낸 도면이다.Meanwhile, FIG. 5 shows forward channel estimates for various channel adaptive training signals as a function of SNR.

It is a diagram showing the normalized mean unsigned square error (MUSE) of .

를 갖는 경향이 있어서, 그들이 더 많은 훈련 신호를 결합함으로써 Order 방식을 능가할 수 있다.Referring to FIG. 5, the performance of the channel adaptive design according to an embodiment of the present invention is shown, (a) is a graph when M = 8, N = 2, ρ = 0.8 (ρ is a correlation coefficient), ( b) is a graph when M = 16, N = 8, and ρ = 0. In (a) and (b) of FIG. 5 , the performance of the Orth/LS scheme for the prior art and the OSPC/LM scheme for the statistical design having the same power constraints as the channel adaptive design are compared. Although the OSPC/LM scheme outperforms the other schemes in the very low SNR region, even with real channel power estimation, most channel adaptive designs outperform the OSPC/LM scheme and the Orth/LS scheme as the SNR increases. . Also, the smaller N is, the larger the gain is observed. Although the Order/Ideal method and the Best/Ideal method perform similarly when N = 2 using two training signals for forward channel estimation, the Order/Acc method using two training signals is shown in FIG. 5(a). outperforms the Best/Acc method using just one of them. When N is increased to 8 in (b) of FIG. 5, the Best method is larger in [Equation 22].

, so they can outperform the Order scheme by combining more training signals.

The embodiments of the present invention described above are not implemented only through devices and methods, and may be implemented through programs that realize functions corresponding to the configuration of the embodiments of the present invention or a recording medium on which the programs are recorded.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concept of the present invention defined in the following claims are also included in the scope of the present invention. that fall within the scope of the right.

Claims (12)

A hybrid access point (HAP) that transmits a carrier signal through a plurality of antennas as an energy source for backscatter communication, and
A plurality of backscattering devices for receiving a carrier signal transmitted from the HAP, modulating the received signal into a backscattered signal containing data when the received signal is reflected, and transmitting the modulated backscattered signal to the HAP.
Including,
The HAP selects only one antenna among the plurality of antennas based on a preset antenna selection method and channel power information for each antenna in the training step of performing channel estimation, and transmits a training signal to the plurality of rear antennas through the selected antenna. transmit to the scattering device;
When the HAP receives a reflection-modulated signal from a specific backscatter device in response to the training signal transmitted through the one antenna, the HAP transmits the training signal to the backscatter device based on the antenna selected to transmit the training signal. estimate the forward channel;
The preset antenna selection method,
A sequential selection method that does not allow overlapping when selecting antennas in a state in which the order of high channel power of the forward channel is known in advance, or a sequential selection method that allows overlapping when selecting antennas in a state in which the order of high channel power of the forward channel is known in advance A best selection method, or a sequential/accumulative selection method that does not allow overlapping when selecting antennas in a state in which the order of the highest channel power of the forward channel is not known in advance, or a method in which the order of the highest channel power of the forward channel is not known in advance A best/accumulative selection method that allows overlap when selecting an antenna in the state,
Backscatter communication system. According to claim 1,
In a state in which the HAP knows in advance the order in which the channel power of each antenna of the forward channel is high,
Selecting the one antenna is performed according to an order / ideal selection method in which channel power is selected in order of increasing channel power so that the index of the antenna does not have a redundant value.
Backscatter communication system. According to claim 1,
In a state in which the HAP knows an antenna having the highest channel power among channel powers for each antenna of the forward channel,
Selecting the one antenna is performed according to a best / ideal selection method for selecting an antenna having the highest power by allowing overlapping antenna indices.
Backscatter communication system. According to claim 1,
The HAP randomly selects one antenna to transmit the first training signal, and then one antenna to transmit the training signal is estimated based on the accumulation of received signals corresponding to previously transmitted training signals Selected according to the channel power of each of the plurality of antennas,
Backscatter communication system. According to claim 4,
The selection of the one antenna through which the HAP transmits the n-th (n is a natural number equal to or greater than 2) training signal is such that the backscattered signal for the training signal transmitted by the HAP is up to the q-th (q<n) training signal. When, the next received power for the mth antenna (1≤m≤M)

is made according to
here

Is the received signal at the m-th antenna for the l-th training signal,
Backscatter communication system. According to claim 5,
The HAP transmits a training signal in a distributed manner applicable when supporting the plurality of backscatter devices so as to secure a reception signal and calculation time for antenna selection in advance to increase the value of q,
Backscatter communication system. According to claim 6,
The one antenna (

) is the relational expression

is selected according to
Where M is the number of antennas, N < M,
Backscatter communication system. According to claim 6,
The one antenna (

) is the relational expression

is selected according to
Where M is the number of antennas, N < M,
Backscatter communication system. A method for estimating a forward channel in a backscatter communication system, comprising:
Generating, by a hybrid access point (HAP) transmitting a carrier signal to a plurality of backscatter devices through a plurality of antennas in the backscatter communication system, a training signal based on a preset antenna selection method and channel power information for each antenna;
Selecting a corresponding antenna based on the preset antenna selection method and the channel power information for each antenna;
transmitting the training signal generated in the generating step to the plurality of backscattering devices through one antenna selected in the selecting step;
Receiving a reflection-modulated signal from the backscatter device in response to the training signal transmitted through the one antenna; and
estimating the forward channel based on an antenna selected to transmit the training signal;
Including,
The preset antenna selection method,
A sequential selection method that does not allow overlapping when selecting antennas in a state in which the order of high channel power of the forward channel is known in advance, or a sequential selection method that allows overlapping when selecting antennas in a state in which the order of high channel power of the forward channel is known in advance A best selection method, or a sequential/accumulative selection method that does not allow overlapping when selecting antennas in a state in which the order of the highest channel power of the forward channel is not known in advance, or a method in which the order of the highest channel power of the forward channel is not known in advance A best/accumulative selection method that allows overlapping when selecting an antenna in the state,
Forward channel estimation method. According to claim 9,
The step of selecting the one antenna,
determining whether transmission of a training signal is the first time; and
When the training signal is transmitted for the first time, a corresponding antenna is selected according to the preset antenna selection method, or
selecting a corresponding antenna according to channel power information calculated using a reflection modulated signal corresponding to a previous transmission of a training signal and the preset antenna selection method when the transmission of the training signal is not the first time;
Including, forward channel estimation method. delete According to claim 9,
In the case of the sequential/cumulative selection method and the best/cumulative selection method, the transmitting of the training signal comprises:
Estimating channel power of each of the plurality of antennas based on the accumulation of received signals corresponding to previously transmitted training signals; and
Selecting an antenna having the highest channel power among estimated channel powers as the one antenna
Including, forward channel estimation method.

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