KR102067050B1 - Communication Method of Access-Point in sparse-Coded Ambient Backscatter system and system thereof - Google Patents

Abstract

The present invention relates to a communication method of an access point in a sparse code-based ambient backscatter system and a system thereof which can obtain diversity gain. According to an embodiment of the present invention, the communication method of an access point in an ambient backscatter system including an access point and a plurality of sensor nodes comprises: a step of receiving a signal transmitted by a non-orthogonal multiple access (NOMA) method from the plurality of sensor nodes; a step of using channel reciprocity with compressed sensing to estimate a dyadic channel of the received signal; and a step of considering inter-symbol interference (ISI) with the estimated dyadic channel to repeatedly update information of a factor node and a variable node a set number of times, and detecting a codeword of the plurality of sensor nodes based on updated results.

Description

[Communication Method of Access-Point in sparse-Coded Ambient Backscatter system and system]

The present invention relates to a method and system for communication of an access point in a sparse code based ambient backscatter system, wherein sensor nodes are used as sparse codes in ambient energy backscatter communication (AMBC) based on wireless energy harvesting. The present invention relates to a communication method of an access point and a system in a sparse code based ambient backscatter system that detects a coded non-orthogonal multiple access (NOMA) signal.

In the Internet of Things environment, a technique of using a TV signal, a Wi-Fi signal, and the like to modulate data by backscattering the tag and to detect it at the receiving end has been proposed. For example, in a traditional Wi-Fi-based AmBC environment, a tag modulates data using M-ary Phase-Shift Keying, and a backscattered signal over a Diadix channel is detected by an ISI-damaged portion of a Wi-Fi access point. After filtering, signals in the remaining time domain were detected using a maximum ratio combining method.

Meanwhile, a time division multiple access (TDMA) scheme is used to transmit tags, and an environment in which multiple access interference (MAI) is minimized is assumed.

As described above, the conventional AmBC technology mainly deals with an Orthogonal Multiple Access (OMA) environment excluding ISI and MAI, and is not suitable for supporting large-scale connectivity. There is a disadvantage in that the loss in the received signal-to-noise ratio (SNR) is not reflected in the detection. In addition, since the signal scarcity is not utilized, the wireless energy harvesting efficiency is low, or the transmission speed is lowered in a high-density network environment.

Related prior arts include Korean Patent Publication No. 10-2018-0087917 (name of the invention: a backscatter communication method using a variable power level and a tag therefor).

An object of the present invention is to support large-scale connectivity in ambient energy backscatter communication (AMBC) based on wireless energy harvesting, and to obtain diversity gain by utilizing MAI and ISI for detection of backscatter signals at a receiving end. The present invention provides a method and system for communicating an access point in a sparse code-based ambient backscatter system.

Another object of the present invention is to implement a low complexity algorithm by using the inherent sparsity of the signal in the ambient backscatter system for repetitive decoding, and by designing a signal reception technique that shows robust characteristics in the Diadi channel environment, The present invention provides a method and system for communicating an access point in a sparse code-based ambient backscatter system that can greatly improve the quality of service of a communication network.

The problem to be solved by the present invention is not limited to the problem (s) mentioned above, and other object (s) not mentioned will be clearly understood by those skilled in the art from the following description.

In a communication method of an access point according to an embodiment of the present invention, the access point communication method in an ambient backscatter system including an access point and a plurality of sensor nodes, the non-orthogonal multiple from the plurality of sensor nodes Receiving a signal transmitted in an Access) method, estimating a diadic channel of the received signal using compressed sensing and channel interactivity, the interference between the estimated diadic channel and the symbol (ISI) Taking into consideration the repetition of the information about the factor node and the versatile node, and detecting codewords of the plurality of sensor nodes based on the updated result.

Preferably, the received signal may be a signal that has passed through a dialect forward channel and a dialect backward channel.

Preferably, the estimating of the diadic channel comprises: obtaining composite channel information using compressed sensing, and initial value of a first channel impulse response using channel interactivity based on the composite channel information. Estimating an impulse response of the remaining channels over time based on an initial value of the first channel impulse response, and estimating a diadic forward channel and a diadic backward channel using the estimated impulse responses of the channels. It includes a step.

과 다이애딕 백워드 채널

은 아래 수학식을 이용하여 추정할 수 있다.Advantageously, said diadic forward channel

And the Diary Dick Channel

Can be estimated using the following equation.

[Equation]

는 타임슬롯 k에서 전송한 신호, S_{k -1} 은 타임슬롯 (k-1)에서 전송한 신호,

,

는 퇴플리츠(Toeplitz) 행렬임.here,

Is the signal transmitted in timeslot k, S _{k -1} is the signal transmitted in timeslot (k-1),

,

Is the Toeplitz procession.

Preferably, the detecting of the codewords of the plurality of sensor nodes comprises: generating a factor factor graph and determining whether to reflect ISI information based on a channel impulse response obtained when the diadic channel is estimated. Determining, and calculating initial information by selectively reflecting the ISI information according to the determination result, determining whether the ISI exists based on the diadic factor graph, and selectively projecting codeword information according to the determination result. Updating information of a factor node, transmitting a first message including the updated information to a versatile node, determining whether there is an ISI based on the message, and selectively projecting the code according to the determination result Expand the word information to update the information of the versatile node, and receive a second message including the updated information. Transmitting to the factor node. Outputting a log likelihood ratio when the process of delivering the first message and the second message is repeated the number of times; detecting a codeword of each sensor node based on the log likelihood ratio; It includes.

Preferably, the calculating of the initial information may be performed based on a threshold time at which ISI occurs in the channel impulse response, and the signal within the threshold time reflects ISI information to calculate initial information.

Preferably, the step of transmitting the first message to the versatile node comprises: determining the presence or absence of ISI based on the number of '1's of each row in the diadic factor graph; If the factor node is calculated and transmits the first message to the verifiable node, if the ISI does not exist, calculating the factor node by projecting codeword information, and then transmitting the first message to the verifiable node; Can be.

Preferably, the transmitting of the second message to the factor node comprises: determining whether ISI is present based on the number of '1's of each row in the diadic factor graph, and the ISI is present. In the case of calculating a versatile node and transmitting a second message to the factor node, and if there is no ISI, calculating the verifiable node by expanding the projected codeword information and transmitting the second message to the factor node. It may include.

Preferably, the step of detecting the codeword of each sensor node, if the log likelihood ratio is positive, it can be decoded to '0', if it is negative it can be decoded to '1' to detect the codeword of each sensor node. .

An access point according to another embodiment of the present invention, a transceiver for receiving a signal transmitted in a non-orthogonal multiple access (NOMA) method from a plurality of sensor nodes, the reception using the compression sensing (Compressed Sensing) and channel interactivity A channel estimator for estimating a didic channel of the decoded signal, repeatedly updating information of a factor node and a versatile node in consideration of the estimated diadic channel and symbol interference (ISI), and updating the result; And a signal detector for detecting codewords of the plurality of sensor nodes.

Preferably, the channel estimator obtains composite channel information using compression sensing, calculates an initial value of a first channel impulse response using channel interactivity based on the composite channel information, and initializes the first channel impulse response. The impulse response of the remaining channels over time may be estimated based on the value, and the diadic forward channel and the diadic backward channel may be estimated using the estimated impulse response of the channels.

Preferably, the signal detection unit generates a didic factor graph, determines whether ISI is present based on the diadic factor graph, and selectively codes codeword information according to the determination result to display information of the factor node. Update the information of the variable node by expanding the projected codeword information according to the presence or absence of the ISI, and output a log likelihood ratio when the information update of the factor node and the variable node is repeated the number of times. The codeword of each sensor node may be detected based on the log likelihood ratio.

According to another embodiment of the present invention, a sparse code-based ambient backscatter system accumulates energy by harvesting an ambient wireless signal and stores M-order data when energy above a predetermined threshold is accumulated and converted into an active state. A symbol is generated by projecting onto a predefined mapping function, a sparse codeword is generated by spreading the symbol, and a non-orthogonal multiple access (NOMA) scheme is performed by reflecting a carrier wave received from an access point. A plurality of sensor nodes to be transmitted, estimates a didic channel of a signal received from the plurality of sensor nodes using compression sensing and channel interactivity, and considers the estimated diacetic channel and the interference between symbols (ISI) Update the information of the node and the versatile node repeatedly for a predetermined number of times, based on the updated result And an access point for detecting codewords of the plurality of sensor nodes.

Since SC-AmBC according to the present invention enables NOMA, it can support large-scale connectivity, and enables effective reception signal detection using multipath diversity in time domain.

In addition, the sparse code of the present invention can be used to detect backscattered signals without discarding MAI and ISI, thereby obtaining diversity gain and reducing bit error rate.

Therefore, the present invention can be applied to a smart home built on the basis of Wi-Fi, and a low-power wireless device can be applied to a dense communication network and poor signal back scattering of poor signal reception, thereby contributing to improving service quality. In particular, the present invention may be closely utilized to support large-scale connection of tags in a low-power IoT network.

On the other hand, the effects of the present invention is not limited to the above-mentioned effects, various effects may be included within the scope apparent to those skilled in the art from the following description.

1 is a view for explaining a sparse code based ambient backscatter system (SC-AmBC) according to an embodiment of the present invention.
2 is a diagram illustrating duty cycling of a sparse code based ambient backscatter system according to an embodiment of the present invention.
3 is a view for explaining a signal transmitted and received in the SC-AmBC according to an embodiment of the present invention.
4 is a diagram illustrating a protocol structure of an SC-AmBC according to an embodiment of the present invention.
5 is a diagram for describing an operation of a sparse code based ambient backscatter system (SC-AmBC) according to an embodiment of the present invention.
6 is a diagram illustrating a method of transmitting data by a tag according to an embodiment of the present invention.
7 is a diagram for explaining a mapping function of SC-AmBC according to an embodiment of the present invention.
8 is a view for explaining a sensor node according to an embodiment of the present invention.
9 is a view for explaining the operation of the access point according to an embodiment of the present invention.
10 is a diagram illustrating a method for estimating a channel by an access point according to an embodiment of the present invention.
FIG. 11 is a diagram for describing a method of detecting a backscattered signal according to an embodiment of the present invention. FIG.
FIG. 12 is a diagram for describing a didic factor graph according to an embodiment of the present invention. FIG.
13 is a view for explaining the configuration of an access point according to an embodiment of the present invention.
14 is a graph comparing the M-ary modulation performance of the SC-AmBC method and the conventional TD-AmBC method of the present invention.
15 is a graph comparing the duty cycling operation performance of the SC-AmBC method and the conventional TD-AmBC method of the present invention.
FIG. 16 is a graph comparing performance of a didic channel of the SC-AmBC method and the conventional TD-AmBC method of the present invention.
17 is a graph comparing the performance according to the reflection coefficient of the SC-AmBC method and the conventional TD-AmBC method of the present invention.

As the present invention allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the written description. However, this is not intended to limit the present invention to specific embodiments, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention. In describing the drawings, similar reference numerals are used for similar elements.

Terms such as first, second, A, and B may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as the second component, and similarly, the second component may also be referred to as the first component. The term and / or includes a combination of a plurality of related items or any item of a plurality of related items.

When a component is referred to as being "connected" or "connected" to another component, it may be directly connected to or connected to that other component, but it may be understood that other components may be present in between. Should be. On the other hand, when a component is said to be "directly connected" or "directly connected" to another component, it should be understood that there is no other component in between.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the terms "comprise" or "have" are intended to indicate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, and one or more other features. It is to be understood that the present invention does not exclude the possibility of the presence or the addition of numbers, steps, operations, components, components, or a combination thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. Terms such as those defined in the commonly used dictionaries should be construed as having meanings consistent with the meanings in the context of the related art, and are not construed in ideal or excessively formal meanings unless expressly defined in this application. Do not.

Prior to the full description, the terms described in the specification will be described or defined.

Non-orthogonal multiple access (NOMA) is a technology that improves system performance and improves fairness of scheduling for devices by allowing multiple devices to use the same non-orthogonal time / frequency resources. to be.

In a NOMA system, an access point allocates the same time / frequency resource to multiple devices, and each device transmits signals in superposition. The access point restores a signal of each device that has successively canceled a signal of other devices from the received signal.

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

1 is a view for explaining a sparse code based ambient backscatter system (SC-AmBC) according to an embodiment of the present invention, Figure 2 is a sparse code based ambient backscatter system according to an embodiment of the present invention FIG. 3 is a diagram for describing duty cycling, and FIG. 3 is a diagram for explaining a signal transmitted and received at the SC-AmBC according to an embodiment of the present invention, and FIG. 4 is a diagram illustrating a protocol structure of the SC-AmBC according to an embodiment of the present invention. It is a figure for demonstrating.

Referring to FIG. 1, a sparse code-based ambient backscatter system (SC-AmBC) includes an access point (AP) 100, a terminal device 200, and a sensor node 300.

The access point 100 transmits an RF signal and supports connection of a wireless network of a peripheral device. For example, the access point 100 may broadcast and transmit a Wi-Fi wireless signal. The access point 100 may perform a process of supporting connection of a wireless network of the connected terminal device 200 by using the transmitted wireless signal.

The terminal device 200 receives a radio signal transmitted from the access point 100, and accordingly, if a channel is set according to a connection procedure with the access point 100, the terminal device 200 accesses a wireless network through the established channel to transmit and receive data. Means the user's device. The terminal device 200 may be configured to include a wireless Internet communication module, such as a Wi-Fi communication module, such as a typical mobile phone, smartphone, tablet PC, laptop, etc., the sensor node 300 is a tag In this case, it may be referred to as a kind of reader capable of tagging.

The sensor node 300 is a batteryless device that does not have a separate power supply (battery). The sensor node 300 receives a radio signal from the access point 100 and collects energy harvesting, that is, a received radio signal. It refers to a device that can operate by charging a small amount of energy using. The sensor node 300 may be a micro device or a portable device that is difficult to supply power such as a tag, a micro sensor device, or an IoT device or a wearable device.

The sensor node 300 may absorb or reflect the radio signal transmitted from the access point 100, and may transmit information to the ambient backscatter communication technique using the received RF signal. That is, the sensor node 300 accumulates energy by harvesting an RF signal transmitted from an access point in an idle state due to a duty cycling operation, and accumulates energy, and when a sufficient amount of energy is collected, an active state Is converted to generate a codeword for backscattering. At this time, the sensor node 300 encodes M-ary data with a small number of symbols by applying a method of projecting a codeword to a mapping function. The generated codewords are sparse codewords due to the sparsity of the signals, and are robust to channel distortion and attenuation because data is encoded in a multidimensional signal space.

In addition, the sensor node 300 loads a codeword on a carrier received from the access point 100 and transmits the codeword. In this case, since the sensor nodes 300 transmit the codewords in the NOMA method, the codewords are overlapped with each other, and when the sensor nodes 300 pass through the diadic channel and reach the access point 100, they are greatly distorted due to intersymbol interference.

개의 타임 슬롯 중에

타임 슬롯 동안 활성화되므로, 듀티사이클(D)은

을 만족한다. 또한, 태그와 태그 사이의 데이터 전송은 비직교 방식으로 일어나므로 MAI가 발생하고, 코드워드에서

개의 심벌 사이에 심벌 간 간섭(Intersymbol Interference: ISI)이 존재한다. 만약,

을 만족한다면, 이러한 간섭들은 신호의 코드워드의 희박성(sparsity)을 이용한 메시지 전달 알고리즘(Message Passing Algorithm: MPA)로 완화시킬 수 있다. 이에, 액세스 포인트(100)는 MPA(Message Passing Algorithm)과 같은 낮은 복잡도 알고리즘을 이용하여 중첩된 코드워드로부터 각 센서노드(300)의 코드워드를 검출할 수 있다. Meanwhile, in the duty cycling of the system according to the present invention, as shown in FIG. 2, a cycle between tags and tags may overlap each other, and multiple access interference (MAI) may occur. ) Is generated. Specifically, the tag is full

Of time slots

Active during the time slot, the duty cycle (D)

To satisfy. In addition, since data transfer between tags occurs in a non-orthogonal manner, MAI occurs,

Intersymbol Interference (ISI) is present between the two symbols. if,

These interferences can be mitigated with a Message Passing Algorithm (MPA) using the sparsity of the codeword of the signal. Accordingly, the access point 100 may detect the codeword of each sensor node 300 from the overlapping codewords using a low complexity algorithm such as a message passing algorithm (MPA).

On the other hand, the codewords transmitted by the sensor nodes 300 are greatly distorted due to intersymbol interference when they pass through the diadic channel and reach the access point. In other words, since the diacdic channel is composed of a forward channel and a backward channel, since the signal is distorted twice by ISI, the signal received by the access point 100 is subject to considerable distortion.

는 임펄스 응답

으로 표현되는 포워드 채널을 통과하게 되므로, (b)와 같이 태그

(300)에서 수신한 신호는 ISI로 왜곡된다. 한편, 태그(300)에서 반사 계수(Reflection Coefficient)

으로 후방 산란되어 액세스 포인트(100)로 도달한 신호는 백워드 채널을 거치면서 다시한번 왜곡되므로, (c)와 같이 시간영역 수신 신호의 상당 부분이 왜곡되는 현상이 발생한다. The signal of the SC-AmBC will be described with reference to FIG. 3. Signal transmitted from the access point 100 as shown in Figure 3 (a)

Impulse response

Since it passes through the forward channel represented by, as shown in (b)

The signal received at 300 is distorted with ISI. Meanwhile, the reflection coefficient in the tag 300 is reflected.

Since the signal scattered back to the access point 100 is distorted once again through the backward channel, a large portion of the time-domain received signal is distorted as shown in (c).

In this way, since the diad channel consists of a forward channel and a backward channel, and the signal is distorted twice by the ISI, the signal received by the access point 100 is subjected to considerable distortion. Therefore, there is a need for a new channel estimation method that takes into account the distortion of signals in the time domain.

Accordingly, the access point 100 estimates channel information by using a D-CEA algorithm (D-CEA algorithm), and detects overlapping sparse codewords by applying a Dyadic MPA (D-MPA). Here, the D-CEA algorithm and the Diaddic MPA are algorithms for detecting the channel estimation and the codeword in consideration of the Diaddic channel model and the ISI, which will be described later. Diadyk channel model has different signal characteristics from Rayleigh fading channel used in the existing communication system, and has inherent characteristics of backscatter communication such as received signal distortion by ISI and dual channel attenuation. In addition, since most receiver structures for backscatter communication use a method of removing ISI using guard time or Cyclic Prefix, loss of SNR occurs in this process. If it is used in the iterative propagation algorithm in the time domain without removing the ISI, the loss of the SNR can be prevented, thereby greatly improving the reception signal detection performance.

개의 태그들은 이 신호를 활용하여 데이터를 변조하여 전송할 수 있다. 데이터 전송 단계에서 시간은

개의 타임 슬롯들로 분할되고, 각각의 타임 슬롯은

개의 샘플링 주기가 된다.On the other hand, the system configured as described above supports a non-orthogonal multiple access (NOMA) and thus has a protocol structure as shown in FIG. Referring to FIG. 4, the protocol structure includes a channel estimating step and a data transmission step. In the channel estimation step, a self-interference channel is estimated for self-interference cancellation, and a plurality of backscatter channels are estimated for NOMA. On the other hand, due to signal scarcity, the backscattering channels can be estimated with low complexity using a compressed sensing technology. If the access point 100 transmits a carrier signal for backscattering the tag 300 in the data transmission step,

The tags can use this signal to modulate and transmit the data. In the data transfer phase, the time is

Into time slots, each time slot being

Sampling periods.

Through the protocol of the above-described structure, the access point 100 can estimate the self-interference channel and the backscattering channel, and the sensor nodes 300 can transmit data simultaneously in multiple times, and are transmitted from the access point 100. The signal can be used for energy harvesting or as a carrier for backscattering.

Meanwhile, in FIG. 1, the sensor node 300 has been described, but for the convenience of description, the following description will be limited to tags.

5 is a diagram for describing an operation of a sparse code based ambient backscatter system (SC-AmBC) according to an embodiment of the present invention.

Referring to FIG. 5, when the access point broadcasts an RF signal (S510), the tag 1 and tag 2 accumulate energy by energy harvesting the RF signal received from the access point (S520).

Then, tag 1 and tag 2 is switched to the active state when the energy of the predetermined threshold or more is accumulated (S530), and generates a codeword for backscattering (S540). A detailed description of how a tag generates a codeword will be described later.

When the step S540 is performed, the tag 1 and the tag 2 reflects and transmits the codeword received from the access point (S550), and the access point receives the overlapped codewords (S560). In this case, since tag 1 and tag 2 transmit codewords in a NOMA manner, the codewords are superimposed on each other, and are greatly distorted due to intersymbol interference when passing through the diadic channel and reaching the access point.

The access point that receives the overlapped codewords by performing step S560 estimates a didic channel (S570), and detects the codewords of tag 1 and tag 2 using the estimated diadic channel (S580). In this case, the access point estimates channel information by using a D-CEA algorithm (D-CEA algorithm), and detects overlapping sparse codewords by applying a Ddi-MPA (D-MPA). That is, the access point estimates the didic channel of the signal received from the tag 1 and the tag 2 using compression sensing and channel interactivity, and considers the factor node and the variable by considering the estimated diacetic channel and symbol interference (ISI). The node information is updated repeatedly by a predetermined number of times, and codewords of tag 1 and tag 2 are detected based on the updated result.

6 is a diagram illustrating a method of transmitting data by a tag according to an embodiment of the present invention, and FIG. 7 is a diagram illustrating a mapping function of an SC-AmBC according to an embodiment of the present invention.

Referring to FIG. 6, the tag accumulates energy by harvesting an RF signal received from an access point in an inactive state (S610), and determines whether energy above a predetermined threshold is accumulated (S620).

As a result of the determination of step S620, when energy above the threshold is accumulated, the tag is switched to the active state (S630), and generates M-ary data (S640).

That is, the tag is switched to the active state when the received power is greater than the circuit power. For example, the tag is activated when the received power is 500nW> 400nW, and is deactivated when the received power is 300nW <400nW.

When the tag goes active, it generates log ₂ M bit data.

For example, if the number of tags N = 6 and M = 4, each tag generates log ₂ 4 bits (2 bits) of data. That is, data of tag 1: [01], data of tag 2: [11], data of tag 3: [00], data of tag 4: [10], data of tag 5: [11], tag 6. Data: As shown, each tag can generate 2-bit data.

When the step S640 is performed, the tag generates a symbol by projecting the M-order data to the predefined mapping function (S650). In this case, the tag may generate symbols having an active time slot K ₁ length using a mapping function. For example, when K ₁ = 2, the tag may convert M-ary data into a symbol having a length of 2 by projecting the mapping function.

Here, projection may mean reducing the number of symbols in which data is encoded. For example, if there is no projection, when M = 4, four symbols of complex 1, -1, j, and -j are required, but if projection is applied, the symbols are real 1, 0,-as shown in (b) of FIG. Only three of ones are needed, which greatly reduces the complexity required to implement encoding and decoding of data.

In the time-division-based AmBC (TD-AmBC) based on the conventional time division, the reflection coefficient as shown in (a) of FIG. 7 mainly uses M-ary phase-shift keying. Create a Reflection Coefficient. The signal modulation of the TD-AmBC uses a method of arranging signal points in a signal space so that symbols do not overlap each other using M-PSK. However, in the SC-AmBC according to the present invention, since signal modulation is transmitted by superimposing symbols, only three kinds of symbols exist in the signal space. This codeword projection method can reduce the number of load impedances required for the tag's modulator to two, and the zero symbol supplies a certain amount of energy to the tag's circuit, similar to the on-off keying method. As a result, the energy harvesting efficiency of the tag can be improved. As described above, the modulation method of the present invention is a method of allowing the overlap between symbols to project three symbols, and this modulation method can obtain an energy harvesting efficiency improvement effect and reduce a manufacturing cost of a tag.

For example, the mapping function may be defined as follows.

Data [00]-> symbol [1, 0]

Data [01]-> symbol [0, 1]

Data [11]-> symbol [-1, 0]

Data [10]-> symbol [0, -1]

When the mapping function is defined as above, each tag may generate symbols as shown in Table 1 below through the mapping function.

TABLE 1

When step S650 is performed, the tag spreads the symbol generated in step S250 to generate a sparse codeword (S660), and transmits the generated sparse codeword by reflecting the carrier (S670). That is, the tag may convert a symbol of an active time slot K ₁ length into a sparse codeword of KL length. Here, K denotes the number of time slots, L denotes an integer value indicating the symbol period of the tag, and symbols transmitted by the tag during L appear repeatedly.

For example, if the sampling period of the carrier is 50ns and the symbol period of the tag is 150ns, when L = 3 and the number of timeslotsK = 4, the sparse codeword may be generated with a length of 12. In this case, the diadytic factor graph may be represented by a matrix consisting of KL = 12 rows and N = 6 columns.

This factor graph can be used to convert a symbol of length 2 into a sparse codeword of length 12. Each column of the factor graph has a structure of (K ₁ XL) ones.

If K ₁ = 2, L = 3, the codeword is generated by substituting the first symbol for the first three 1s and the second symbol for the remaining three 1s in the factor graph.

That is, in order to generate the codeword of the symbol [0, 1] of the tag 1, '0' is inserted into the first three 1's of the determinant column 1, and '1' is inserted into the remaining three 1's. Then, the codeword of tag 1 may be generated as [0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 0]. In order to generate the codeword of the symbol [-1, 0] of the tag 2, '-1' is substituted for the first three 1s of the determinant column 2, and '0' is substituted for the remaining three 1s. Then, the codeword of tag 2 may be generated as [-1, -1, -1, 0, 0, 0, 0, 0, 0, 0, 0, 0]. In order to generate the codeword of the symbol [1, 0] of the tag 3, '1' is substituted for the first three 1s of the determinant column 3, and '0' is substituted for the remaining three 1s. Then, the codeword of tag 3 may be generated as [1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0]. In order to generate the codeword of the symbol [0, -1] of the tag 4, '0' is assigned to the first three 1's of the determinant four columns and '-1' to the remaining three 1's. Then, the codeword of tag 4 may be generated as [0, 0, 0, 0, 0, 0, -1, -1, -1, 0, 0, 0]. In order to generate the codeword of the symbol [-1, 0] of the tag 5, '-1' is substituted into the first three 1s of the determinant column 5, and '0' is substituted into the remaining three 1s. Then, the codeword of tag 5 may be generated as [0, 0, 0, -1, -1, -1, 0, 0, 0, 0, 0, 0]. In order to generate the codeword of the symbol [1, 0] of the tag 6, '1' is assigned to the first three 1's of the determinant column 6 and '0' to the remaining three 1's. Then, the codeword of tag 6 may be generated as [0, 0, 0, 0, 0, 0, 1, 1, 1, 0, 0, 0].

That is, codewords of respective tags as shown in Table 2 below may be generated.

TABLE 2

When the codeword of each tag is generated as shown in Table 2, each tag transmits the generated sparse codeword by reflecting the carrier in the NOMA method.

On the other hand, the tag performing the operation as described above can implement the NOMA using a sparse code, it can have improved connectivity compared to the conventional TD-AmBC. This sparse code is a method that uses the duty cycling structure of tags operating by wireless energy harvesting, and the sparsity of the signal enables the tag to implement M-ary modulation even with a small number of load impedances.

8 is a view for explaining a sensor node according to an embodiment of the present invention.

Referring to FIG. 8, the sensor node 300 according to an embodiment of the present invention includes a transceiver 310, a state controller 320, and a modulator 330.

The transceiver 310 is a component for receiving a radio signal from an AP or a terminal device and transmitting data encoded using whether a carrier is reflected.

The state controller 320 accumulates energy by energy harvesting the RF signal received through the transceiver in the deactivated state, and switches to the activated state when energy above a predetermined threshold is accumulated. The state controller 320 may be switched to an active state when the received power is greater than the circuit power. For example, the tag is activated when the received power is 500nW> 400nW, and is deactivated when the received power is 300nW <400nW.

The modulator 330 projects the M-order data into a predefined mapping function to generate a symbol, and spreads the symbol to generate a codeword. In this case, the generated codeword may be encoded information. Then, the transceiver 310 transmits a codeword by reflecting the received carrier.

The modulator 330 includes an M-order data generator 332, a symbol generator 334, and a codeword generator 336.

The M-order data generator 332 generates log ₂ M-bit data when the tag is switched to the activated state. The generated log ₂ M bit data may be M-order data.

The symbol generator 334 generates a symbol by projecting the M-order data generated by the M-order data generator 332 to a predefined mapping function. In this case, the symbol generator 334 generates symbols having a length of K ₁ as a mapping function. For example, when K ₁ = 2, the symbol generator 334 projects the M-ary data into a mapping function and converts the M-ary data into a symbol having a length of 2.

The codeword generator 336 spreads the symbols generated by the symbol generator 334 to generate a sparse codeword. For example, the codeword generator 336 may convert a symbol having a length of K ₁ into a sparse codeword having a length of KL.

9 is a view for explaining the operation of the access point according to an embodiment of the present invention.

Referring to FIG. 9, the access point transmits an RF signal (S910) and receives a signal from at least one tag (S920). In this case, the access point transmits a signal through a forward channel, receives a signal through a backward channel, and a signal received from a tag may be a superimposed codeword transmitted in a NOMA method.

When the step S920 is performed, the access point estimates a didic channel of the received signal by using compression sensing and channel interoperability (S930), and detects a codeword transmitted from each tag by using the estimated diadic channel. (S940). At this time, the access point uses a Dyadic Channel Estimation Algorithm (D-CEA) that effectively estimates a Dyadic channel and utilizes intersymbol interference (ISI) for signal detection. It is possible to estimate the didic channel. The access point also uses an iterative message passing algorithm (MPA) to successfully detect non-orthogonal multiple access (NOMA) signals encoded by sparse codes. Can detect a codeword.

A detailed description of how an access point estimates a didic channel will be described with reference to FIG. 10, and a detailed description of a method of detecting a codeword will be described with reference to FIG. 11.

10 is a diagram illustrating a method for estimating a channel by an access point according to an embodiment of the present invention.

Referring to FIG. 10, the access point transmits an RF signal (S1010) and receives a modulated signal from at least one tag (S1020). In this case, the access point transmits an RF signal through a forward channel and receives a modulated signal through a backward channel.

는 임펄스 응답

으로 표현되는 포워드 채널을 통과하게 되므로, 태그

에서 포착된 신호는 ISI로 왜곡된다. 한편, 태그에서 반사 계수(Reflection Coefficient)

으로 후방 산란되어 액세스 포인트로 도달한 신호는 백워드 채널을 거치면서 다시한번 왜곡되므로, 시간영역 수신 신호의 상당 부분이 왜곡되는 현상이 발생한다. Specifically, the signal transmitted from the access point

Impulse response

Pass through the forward channel represented by

The signal captured at is distorted by ISI. On the other hand, the reflection coefficient in the tag

Since the signal scattered back to the access point is distorted once again through the backward channel, a large portion of the time-domain received signal is distorted.

를 만족하고, 액세스 포인트의 자가간섭은 제거가 가능하다. 이에, 액세스 포인트가 타임슬롯

에서 수신한 신호(t_k)는 아래 수학식 1과 같이 표현할 수 있다. In addition, since the signal sent by the access point passes back through the tag back to the access point, channel reciprocity is established.

, Self-interference of the access point can be eliminated. Thus, the access point is timeslot

The received signal t _k can be expressed by Equation 1 below.

[Equation 1]

는 잡음,

,

는 각각 다이애딕 포워드 채널, 다이애딕 백워드 채널로 정의된다.

,

는 퇴플리츠(Toeplitz) 행렬로, 아래 수학식 2와 같이 표현된다.here,

Is noise,

,

Are respectively defined as a diadic forward channel and a diadic backward channel.

,

Is a Toeplitz matrix, which is represented by Equation 2 below.

[Equation 2]

,

는 각각 크기가

인 퇴플리츠 포워드 시프트 행렬, 퇴플리츠 백워드 시프트 행렬을 나타낸다. here,

,

Each has a size

A phosphorous forward shift matrix and a Hungaryplet forward shift matrix are shown.

인 벡터

으로 표현될 수 있다. When the access point receives a signal as shown in Equation 1, the access point acquires composite channel information by using compressed sensing (S1030). In this case, the composite channel information means a composite forward-backward channel and has a length.

Phosphorus vector

It can be expressed as.

를 만족한다. 따라서, 액세스 포인트는 채널 상호성을 이용한 아래 수학식 3을 이용하여 첫번째 채널 임펄스 응답의 초기값(f_n(1))을 획득할 수 있다. When step S1030 is performed, the access point obtains an initial value of a first channel impulse response using channel interactivity (S1040). In other words, since the signal transmitted by the access point passes back through the tag to the access point, channel reciprocity is established.

Satisfies. Accordingly, the access point may obtain an initial value f _n (1) of the first channel impulse response by using Equation 3 below using channel interactivity.

[Equation 3]

)을 추정한다(S1050).When step S1040 is performed, the access point uses the following equation 4 to impulse response of the remaining channels (

) Is estimated (S1050).

[Equation 4]

Herein, l 'and i' are integer values representing a time (for example, a sampling time of 50ns is represented by an integer of 1 and a sampling time of 150ns is represented by an integer of 3), and h _n (l ') represents a random channel representing time. It can mean one complex value.

Equation 4 represents the impulse response of the composite channel when channel interactivity is established, that is, when h _n = f _n * f _n . If h _n is given, the equation to be solved to obtain f _n can be represented by Equation 4.

For example, when the maximum length of the forward channel L _n + = 3, the length of the composite channel h _n is 2L _n + -1 = 5, and each component of the vector h _n is f _n (1), f _n (2), f _n (3) can be expressed. That is, h _n (1) = f _n (1) f _n (1), h _n (2) = f _n (1) f _n (2) + f _n (2) f _n (1), h _n ( 3) = f _n (1) f _n (3) + f _n (2) f _n (2) + f _n (3) f _n (1), h _n (4) = f _n (2) f _n ( 3) + f _n (3) f _n (2), h _n (1) = f _n (3) f _n (3) and the like.

After performing step S1050, the access point determines whether an impulse response for all channels over time is estimated (S1060).

,

를 추정한다(S1070). 즉, 액세스 포인트는 아래 수학식 5를 이용하여 다이애딕 포워드 채널

, 다이애딕 백워드 채널

을 산출할 수 있다. If it is determined in step S1060 that the impulse responses of all the channels have been estimated, the access point uses the estimated impulse response to the diadic channel.

,

It is estimated (S1070). That is, the access point uses the following equation (5) to be a diadic forward channel

, Diadick Backward Channel

Can be calculated.

[Equation 5]

If it is determined in step S1060 that the impulse response of all channels is not estimated, the access point estimates the impulse response of the next channel (S1080, S1050) and performs step S1060.

FIG. 11 is a diagram for describing a method of detecting a backscattering signal according to an embodiment of the present invention, and FIG. 12 is a diagram for explaining a diadytic factor graph according to an embodiment of the present invention.

Referring to FIG. 11, the access point performs an initialization step based on a diadi channel (S1110). At this time, the access point calculates initial information.

In detail, the access point generates a factor factor graph (S1111), and determines whether to consider the ISI condition (S1112). Here, the ISI condition means whether interference should be considered when detecting the backscattered signal at a specific time. For example, if the ISI occurs within 50ns due to the channel delay time through the channel, the signal sampled at 50ns when the signal is detected at the access point must use signal detection considering interference because ISI occurs. Since signals sampled at 100 ns, 150 ns, ..., etc. are not affected by ISI in excess of 50 ns, a low complexity decoding technique without considering interference may be used.

As such, the ISI condition is a condition for determining whether the sampled backscattered signal is distorted by the ISI. The ISI condition may be determined by using channel impulse response information obtained at channel estimation. For example, based on the threshold time at which ISI occurs in the channel impulse response, it may be determined that a signal within the threshold time should consider the ISI condition.

If the determination result of step S1112 is to consider the ISI condition, the access point reflects the ISI information (S1113), calculates the initial information (S1114), and if it is not necessary to consider the ISI condition, the initial information is not reflected without the ISI information. Calculate That is, when the ISI condition needs to be considered, the access point reflects the ISI information when calculating the codeword initial information. Otherwise, the access point calculates the initial information in the same manner as the existing MPA.

The initial information refers to information calculated in the first step before iteration in the message transfer algorithm. The initial information may be obtained by multiplying a superimposed codeword by a channel and obtaining a difference from a signal received from an access point. The initial information has a negative value, and as the value increases, the larger (closer to 0), the higher the probability of the corresponding codeword in the MPA.

For example, received signal y = 1, composite channel (except ISI) h ₁ = 0.6, codeword (except ISI) B ₁ = 1, composite channel (ISI component) h ₂ = -0.4, codeword (ISI component) When B ₂ = -1, the initial information can be calculated using the following equation.

First, when ISI is included, initial information may be calculated using Equation 6 below.

[Equation 6]

Next, when the ISI is excluded, the initial information may be calculated using Equation 7 below.

[Equation 7]

If ISI is included, the ISI component, i.e., B _2, is required for the initial information calculation, which is added with the channel h ₂ weighted and finally becomes a codeword (h ₁ xB ₁ + h ₂ xB ₂ ). Here, h ₂ xB ₂ may be defined as a weighted sum so as to be different from h ₁ xB ₁ used in the conventional MPA. When the initial information is calculated by adding the weighted sums, ISI may be considered to effectively correct distortion of the signal.

When the initial information is calculated by performing step S1110, it is determined whether the message delivery process is repeated by the maximum number of repetitions (S1120).

As a result of the determination in step S1120, if it has not been repeated as many times as the maximum number of repetitions, the access point updates a message to be delivered from a factor node (FN) to a variable node (VN) (FN Update Step) (S1130). .

In more detail, the access point determines the presence or absence of ISI based on the number of '1's in each row in the dyad factor graph (S1131).

If the ISI is present as a result of the determination in step S1131, the access point calculates a factor node (S1132) and delivers a message to the scalable node (S1133).

If the ISI does not exist as a result of the determination in step S1131, the access point projects codeword information (S1034) and calculates a factor node (S1032).

As such, when the tag uses the M-ary modulation scheme, the access point selectively projects the codeword information according to the ISI condition and transmits the calculated information to the variable node in order to reduce decoding complexity.

Meanwhile, the factor graph is a graph representing a relationship between the data and the codeword when encoding and decoding the data, and may be expressed as a factor node and a variable node. Here, the factor node may indicate a resource (eg, a time slot) used to deliver data, and the variable node may indicate a subject (eg, a tag) that sends data.

The factor graph can be expressed as a binary matrix with only 0 and 1, and if the factor node k and the variable node n are connected to each other and expressed as a matrix, the kth row nth column is given as 1, and the physical The meaning is that the nth tag sends a symbol to the kth timeslot.

However, since the symbol period of the tag becomes L, which is an integer multiple of the carrier signal, and the received signal is deteriorated by the ISI during the period of ~ L, the diadytic factor graph needs to be introduced to correct this.

The diadytic factor graph cycles through the forward factor graph ~ G + by ~ L and obtains a backward factor graph ~ G- where all rows except K x ~ L satisfy 0, then forward factor graph ~ G + and It may be a graph obtained by calculating the backward factor graph ~ G- with exclusive OR. This diadytic factor graph may be the same as FIG. 12.

When a forward factor graph and a backward factor graph having K = 4, L = 3, and N = 6 are expressed as matrices, they may be as shown in Table 3 below.

TABLE 3

When an exclusive OR operation is performed on the matrixes of the forward factor graph and the backward factor graph of Table 3, the diacetic factor graph ~ G * as shown in Table 4 below may be generated.

TABLE 4

If we look at the matrix representing the didic factor graph in Table 4, the four rows contain five 1s, and the remaining eight rows contain only three threes. Accordingly, the access point may determine the presence or absence of ISI by using the number of 1s in each row in the dyad factor graph. That is, the access point may determine whether or not the ISI exists by determining that the number of 1s is changed for each row.

In the case of Table 4, when the number of 1 is 5, it can be determined that ISI exists, and when the number of 1 is 3, it can be determined that there is no ISI.

If there is an ISI, there will be five 1s in the row of the diacetic factor graph, so that the factor node must receive a message from five variable nodes. A message is a variable that is updated repeatedly as you run an algorithm, associated with a probability value that infers what the data sent by the tags is.

If the data to be sent by the tag is M-ary, the message may be represented by a real vector having a length M.

For example, if ISI is present and M = 4, then the message sent from factor node k to variable node n is 'I _nk (1) I _nk (2) I _nk (3) I _nk (4)'. I can express it.

On the other hand, if there is no ISI, there are three 1's in the diadic factor graph, and the size of the message is determined according to the M value. At this time, if the M value is large, the size of the message may be increased, and thus an amount of calculation may increase in an algorithm. Thus, a method called 'projection' is needed to reduce the size of the message vector to a value smaller than M.

If there is no ISI, since the signal is not distorted, the property of the predefined mapping function can be used to compress the M-ary data into fewer symbols than M, thereby reducing the complexity of the decoding process and It has the advantage of speeding up.

For example, when M = 4, the message 'I _nk (1) I _nk (2) I _nk (3) I _nk (4)' with a size of 4 before the projection is '~ I' _nk (1) ~ I _nk (2) ~ I _nk (3) '.

When step S1130 is performed, the access point updates the versatile node based on the received message (VN Update Step) (S1140).

In more detail, the access point determines the presence or absence of ISI based on the number of '1's of each row in the diadytic factor graph (S1141).

If the ISI is present in the determination result of step S1141, the access point calculates a variable node (S1142) and transmits a message to the factor node (S1143).

If the ISI does not exist as a result of the determination of step S1141, the access point expands the projected codeword information (S1144) and calculates a variable node (S1142).

In this way, the access point calculates a versatile node by calculating a versatile node when the ISI needs to be considered, and calculates a scalable node by expanding the projected information when the ISI does not need to be considered. Pass the updated information back to the factor node.

The method of projecting-extending the codeword information by the access point has an advantage of reducing the complexity for codeword detection even if the tag uses the M-ary modulation scheme.

The above-described message delivery process is repeated as many times as the maximum number of repetitions, and if this is satisfied, the access point outputs a log likelihood ratio (S1150).

The access point may use the log likelihood ratio to effectively detect data transmitted by tags even in a wireless environment in which ISI exists.

The log likelihood ratio is a value representing each bit probability and has a real value. When there is M-ary data, the log likelihood ratio becomes log ₂ M, and the output log likelihood ratio is used to decode the data. If the log likelihood ratio is positive, the data is decoded to 0, and if it is negative, the data is decoded to 1.

For example, when M = 4, the log likelihood ratio of tag 1: [-2.6 0.5], the log likelihood ratio of tag 2: [1.2 0.3], the log likelihood ratio of tag 3: [1.3 -0.9], The access point may detect the decoded data [10] of the tag 1, the decoded data [00] of the tag 2, and the decoded data [01] of the tag 3, respectively.

13 is a view for explaining the configuration of an access point according to an embodiment of the present invention.

Referring to FIG. 13, an access point 100 according to an embodiment of the present invention includes a transceiver 110, a channel estimator 120, and a signal detector 130.

The transceiver 110 transmits a radio signal and receives a signal transmitted from a plurality of sensor nodes in a non-orthogonal multiple access (NOMA) scheme.

The channel estimator 120 estimates a dyad channel of the received signal by using compressed sensing and channel interactivity. That is, the channel estimator 120 obtains composite channel information by using compression sensing, and calculates an initial value of a first channel impulse response using channel interactivity based on the composite channel information. Thereafter, the channel estimator 120 estimates the impulse response of the remaining channels over time based on the initial value of the first channel impulse response, and uses the estimated impulse response of the channels to be used for the diadic forward channel and the diadic backward. Estimate the channel.

The signal detector 130 repeatedly updates the information of the factor node and the variable node by a predetermined number of times in consideration of the diacetic channel and the ISI estimated by the channel estimator 120, and then updates the information on the updated result. Based on the detection, the codewords of the plurality of sensor nodes are detected. That is, the signal detection unit 130 generates a didic factor graph, determines whether ISI is present based on the diadic factor graph, and selectively updates codeword information according to the determination result to update the information of the factor node. Then, the projected codeword information is extended according to the presence or absence of the ISI, and the information of the versatile node is updated. Thereafter, the signal detector 130 outputs a log likelihood ratio when information update of the factor node and the variable node is repeated a predetermined number of times, and detects a codeword of each sensor node based on the log likelihood ratio.

Hereinafter, the performance of a sparse code-based AmBC system according to the present invention will be described.

14 is a graph comparing the M-ary modulation performance of the SC-AmBC method and the conventional TD-AmBC method of the present invention.

Referring to FIG. 14, the wireless energy harvesting efficiency is slightly lower than that of the TD-AmBC when M = 2 and 8 in the case of SC-AmBC, but when M = 4, symbol mapping improves the energy harvesting efficiency. It has no difference in performance. On the other hand, the bit error rate is much better for the SC-AmBC than for the TD-AmBC because the backscattered signal spreads in the time domain through NOMA to obtain diversity gain. to be. As such, SC-AmBC can simplify the hardware of the tag and successfully implement M-ary modulation.

15 is a graph comparing the duty cycling operation performance of the SC-AmBC method and the conventional TD-AmBC method of the present invention.

로 주어지며, 태그의 개수

가 증가하면 듀티사이클이 작아져서 태그가 데이터 전송에 사용할 수 있는 시간이 스케일링 다운되는 문제가 발생한다. 반면에 본 발명의 SC-AmBC 방식에서는 듀티사이클링의 스케일링 현상을 역으로 신호의 희소성으로 변환할 수 있으므로, 액세스 포인트와 연결될 수 있는 태그의 개수는 Overloading Factor,

만큼 스케일링되어,

로 크게 늘어난다. 더욱이 스파스 코드워드는 다이애딕 채널 구조에서 다이버시티 이득을 제공 가능하므로, 기존 기법과 비교하면 대규모 연결성을 지원함과 동시에 비트 오류율까지 감소시키는 장점이 있다.Referring to Figure 15, the duty cycle in the TD-AmBC scheme is

Given by the number of tags

If increases, the duty cycle becomes smaller, causing a problem that the time the tag can use for data transmission is scaled down. On the other hand, in the SC-AmBC scheme of the present invention, since the scaling phenomenon of the duty cycle can be converted into the sparsity of the signal, the number of tags that can be connected to the access point is overloading factor,

Scaled by

Greatly increases. Moreover, since sparse codewords can provide diversity gain in a diadic channel structure, the sparse codeword supports large-scale connectivity and reduces bit error rates compared to the conventional scheme.

16 is a graph comparing the performance of the SC-AmBC scheme of the present invention and the conventional TD-AmBC dialect channel, Figure 17 is a reflection coefficient of the SC-AmBC scheme and the conventional TD-AmBC scheme of the present invention This is a graph comparing performance.

Referring to FIG. 16, the wireless energy harvesting probability tends to improve as the number of multipaths increases. On the other hand, the bit error rate of the conventional MPA and TD-AmBC schemes, the performance is degraded as the multipath is large, because the ISI is distorting the received signal. Since the D-MPA technique of the present invention reflects the characteristics of the Diadix channel, the D-MPA technique may have a bit error rate smaller than that of the conventional MPA technique, which is not reflected. There is an improvement effect. As such, when the D-MPA and the D-CEA of the present invention are used, the distortion phenomenon is corrected, and thus the signal detection performance is improved as the multipath becomes larger. Therefore, it can be said that the SC-AmBC of the present invention shows better performance in the diadic channel.

, 변조 차수

, 코드워드 관련 변수

에 따라 TD-AmBC 기법보다 훨씬 높은 전송속도를 가질 수 있고, 또한 성능을 더욱 탄력적으로 조절할 수 있음을 확인할 수 있다. In addition, since the SC-AmBC technique utilizes the signal sparsity at the receiving end, the reflection coefficient in the tag as shown in FIG.

Modulation order

, Codeword related variables

As a result, it can be seen that the transmission rate can be much higher than that of the TD-AmBC scheme and the performance can be more flexibly adjusted.

In the conventional TD-AmBC, since signal sparsity is not used, it has low connectivity and, as a result, low transmission rate. However, in the SC-AmBC of the present invention, since the sparsity of the signal is used for backscattering, it is possible to support large-scale connectivity, so that the graph moves in the Y-axis direction and shows improved connectivity. This connectivity can be adjusted with reflection coefficients, modulation orders, and codeword-related variables. Overall, SC-AmBC can tune these system parameters more flexibly to control backscattering performance.

As such, sparse code does not discard MAI and ISI, but rather utilizes it to support large-scale connectivity and to reduce bit error rate as compared to the existing scheme.

So far I looked at the center of the preferred embodiment for the present invention. Those skilled in the art will appreciate that the present invention can be implemented in a modified form without departing from the essential features of the present invention. Therefore, the disclosed embodiments should be considered in descriptive sense only and not for purposes of limitation. The scope of the present invention is shown in the claims rather than the foregoing description, and all differences within the scope will be construed as being included in the present invention.

100: access point
110, 310: transceiver
120: channel estimation unit
130: signal detector
200: terminal device
300: sensor node
320: status control
330: modulator

Claims (13)

A communication method of an access point in an ambient backscatter system including an access point and a plurality of sensor nodes,
Receiving a signal transmitted in a non-orthogonal multiple access (NOMA) scheme from the plurality of sensor nodes;
Obtaining composite channel information using compressed sensing, and estimating a diadic channel of the received signal using channel interactivity based on the composite channel information; And
It is determined whether there is inter-symbol interference (ISI) in consideration of the estimated diadic channel, and the information of the factor node and the variable node is repeatedly updated according to the determination result, and based on the updated result, Detecting codewords of the plurality of sensor nodes
Communication method of the access point comprising a. The method of claim 1,
And wherein the received signal is a signal passing through a dialect forward channel and a dialect backward channel. The method of claim 1,
The estimating the diadic channel may include:
Calculating an initial value of a first channel impulse response using channel interactivity based on the composite channel information;
Estimating the impulse response of the remaining channels over time based on the initial value of the first channel impulse response;
Estimating a dialect forward channel and a dialect backward channel using the estimated impulse responses of the channels. The method of claim 3,
The diadic forward channel

And the Diary Dick Channel

Is estimated using the following equation.
[Equation]

here,

Is the signal transmitted in timeslot k, S _{k -1} is the signal transmitted in timeslot (k-1),

,

Is the Toeplitz procession. The method of claim 1,
Detecting codewords of the plurality of sensor nodes,
Generating a factor factor graph;
Determining whether to reflect ISI information based on a channel impulse response obtained when the diadic channel is estimated, and calculating initial information by selectively reflecting ISI information according to the determination result;
It is determined whether the ISI exists based on the diadic factor graph, and optionally, codeword information is updated according to the determination result to update the information of the factor node, and the first node including the updated information is a versatile node. Transmitting to;
Based on the message, it is determined whether the ISI exists, and optionally, the projected codeword information is expanded to update the information of the versatile node according to the determination result, and the second message including the updated information is received as the factor. Transmitting to the node;
Outputting a log likelihood ratio when the process of delivering the first message and the second message is repeated the number of times; And
Detecting a codeword of each sensor node based on the log likelihood ratio. The method of claim 5,
Computing the initial information,
And based on a threshold time at which ISI occurs in the channel impulse response, a signal within the threshold time reflects ISI information to calculate initial information. The method of claim 5,
The transmitting of the first message to the versatile node may include:
Determining the presence or absence of ISI based on the number of '1's of each row in the diadytic factor graph;
If the ISI is present, the factor node is calculated and the first message is transmitted to the variable node. If the ISI is not present, codeword information is projected to calculate the factor node, and then the first message is calculated. And transmitting to the access point. The method of claim 5,
Sending the second message to the factor node,
Determining the presence or absence of ISI based on the number of '1's of each row in the diadytic factor graph;
If the ISI is present, the variable node is calculated and the second message is transmitted to the factor node. If the ISI is not present, the projected codeword information is expanded to calculate the variable node. Transmitting to the factor node. The method of claim 5,
Detecting the codeword of each sensor node,
If the log likelihood ratio is positive, it is decoded as '0', and if it is negative, it is decoded as '-1' to detect the codeword of each sensor node. A transceiver for receiving a signal transmitted from a plurality of sensor nodes in a non-orthogonal multiple access (NOMA) scheme;
A channel estimating unit for acquiring composite channel information by using compressed sensing and estimating a diadic channel of the received signal by using channel interactivity based on the composite channel information; And
It is determined whether there is inter-symbol interference (ISI) in consideration of the estimated diadic channel, and the information of the factor node and the variable node is repeatedly updated according to the determination result, and based on the updated result, A signal detector for detecting codewords of the plurality of sensor nodes
Access point comprising a. The method of claim 10,
The channel estimator,
Calculate an initial value of a first channel impulse response using channel interactivity based on the composite channel information, estimate an impulse response of remaining channels over time based on the initial value of the first channel impulse response, And using the impulse response to estimate the diadic forward channel and the diadic backward channel. The method of claim 10,
The signal detector,
Generates a die factor factor graph, determines whether there is an ISI based on the die factor factor graph, selectively updates codeword information by projecting codeword information according to the determination result, and updates the information of the factor node according to the presence of the ISI. Expands the projected codeword information to update the information of the variable node, and outputs a log likelihood ratio when the information on the factor node and the variable node is repeated the number of times and outputs a log likelihood ratio based on the log likelihood ratio. And detecting the codeword of the sensor node. Energy is collected by energy harvesting the surrounding radio signals, and when energy above a predetermined threshold is accumulated and converted into an active state, the M-order data is projected to a predefined mapping function to generate a symbol, and the symbol is spread to spread the spar. A plurality of sensor nodes generating a sparse codeword and transmitting the sparse codeword by reflecting a carrier wave received from an access point in a non-orthogonal multiple access (NOMA) scheme; And
Estimation of a diad channel of a signal received from the plurality of sensor nodes using compression sensing and channel interactivity, and information of a factor node and a variable node is considered in consideration of the estimated diacetic channel and symbol interference (ISI). An access point repeatedly updating a predetermined number of times and detecting codewords of the plurality of sensor nodes based on the updated result
Sparse code based ambient backscatter system comprising a.

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