KR20200037560A - Communication Method of Sensor Node in sparse-Coded Ambient Backscatter system and system thereof - Google Patents

Abstract

The present invention relates to a communication method of a sensor node in a sparse-coded ambient backscatter system and a system thereof. A communication method of a sensor node according to an embodiment of the present invention, which is a communication method of each sensor node in an ambient backscatter system including an access point and a plurality of sensor nodes, comprises the steps of: storing energy by energy-harvesting wireless signals transmitted by the access point; generating M-order data in the case of storing energy equal to or greater than a preset threshold value to switch to an active state; projecting the M-order data to a predefined mapping function to generate a symbol; spreading the symbol to generate a code word; and transmitting the code word by reflecting a carrier received from the access point, wherein the plurality of sensor nodes transmit the code word in a non-orthogonal multiple access (NOMA) manner. The present invention can be applied for supporting large scale connections of tags in a low power IoT network.

Description

Communication method of a sensor node and its system in a sparse code-based ambient backscatter system and system thereof

The present invention relates to a communication method of a sensor node in a sparse code-based ambient backscatter system and a system thereof, and more specifically, a large-scale connection in ambient energy backscatter communication (Ambient) based on wireless energy harvesting ( Communication method of sensor node in sparse code based ambient backscatter system that generates sparse code to support Massive Connectivity and transmits it in non-orthogonal multiple access (NOMA) It's about the system.

In the Internet of Things (IoT) environment, there are techniques for transmitting data of tags by using AmBC (Ambient Backscatter Communication) technology for TV signals, Wi-Fi signals, and the like. For example, in an existing AmBC environment, there is a duty-cycling operation in which a tag collects sufficient energy required for data transmission through energy harvesting and back-scatters and transmits the data. There are scheduling techniques that allocate time for energy harvesting and data transmission.

This resource allocation technique corresponds to orthogonal multiple access (OMA) in which multiple accesses are performed by dividing time and allows access to only one tag during one time slot to multiple access interference (MAI) Was removed.

Also, in order to utilize M-order modulation in a tag, a method of manufacturing a tag by connecting the impedance of a number corresponding to a modulation order to a microcontroller has been proposed.

However, the conventional AmBC technology mainly deals with the OMA environment, which is not suitable for supporting large-scale connectivity, and has a disadvantage in that the manufacturing cost of the tag increases because the load impedance increases the size of the tag. In addition, since it greatly depends on the duty cycling operation, in a wireless environment in which the efficiency of energy harvesting is low or in a network densification environment, there is a disadvantage that a transmission speed of a communication network is significantly reduced.

Prior art related to this is Korean Patent Publication No. 10-2018-0087917 (Invention name: backscatter communication method using variable power level and tag for the same).

An object of the present invention is to support large-scale connectivity in wireless energy harvesting-based ambient signal backscatter communication (Ambient Backscatter Communication: AmBC), through which the sparse can improve the energy harvesting efficiency and signal detection performance of the sensor node In a code-based ambient backscatter system, a sensor node communication method and a system thereof are provided.

Another object of the present invention is to reduce the overhead caused by scheduling and radio resource allocation in the ambient backscatter system to realize low latency communication and sparse code that can improve the performance of the duty cycling operation of the sensor node. It is to provide a communication method of a sensor node and a system in the based ambient backscatter system.

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

The communication method of a sensor node according to an embodiment of the present invention is in a communication method of each sensor node in an ambient backscatter system including an access point and a plurality of sensor nodes, and energy hobbing a radio signal transmitted from the access point. Accumulating energy by stinging, generating energy of M-order data when energy above a predetermined threshold is accumulated and switching to an active state, generating symbols by projecting the M-order data to a predefined mapping function, Generating a codeword by spreading the symbols, and transmitting the codeword by reflecting a carrier wave received from the access point, wherein the plurality of sensor nodes code in a non-orthogonal multiple access (NOMA) method It is characterized by transmitting a word.

Preferably, the symbol is generated by at least one of 1, 0, -1, and may be characterized in that it has an active time slot length.

Preferably, the codeword may be a sparse codeword having a length corresponding to the product of the number of time slots and the symbol period.

Preferably, the codeword can be transmitted to the access point via a dialic channel.

The sensor node according to another embodiment of the present invention accumulates energy by energy harvesting a radio signal received through the transceiver in an inactive state and a transceiver for communication with an access point, and accumulates energy above a predetermined threshold. A state control unit switching to an active state, when switched to an active state, projects M-order data into a predefined mapping function to generate a symbol, spreads the symbol to generate a codeword, and the codeword to the access point It includes a modulator for reflecting and transmitting the carrier wave received from.

According to another embodiment of the present invention The sparse code-based ambient backscatter system accumulates energy by energy harvesting an access point that transmits a radio signal, and a radio signal that is transmitted from the access point, and when energy above a preset threshold is accumulated and is switched to an active state M-dimensional data is projected to a predefined mapping function to generate a symbol, the symbol is spread to generate a sparse codeword, and the sparse codeword is reflected by a carrier wave received from the access point, and NOMA (Non- orthogonal multiple access), but the wireless signal and the sparse codeword may be transmitted and received through a dialic channel.

Preferably, the access point receives the overlapped codewords transmitted by the NOMA method from the plurality of sensor nodes, and estimates the dialic channel based on the Dyadic Channel Estimation Algorithm. Codewords transmitted from the plurality of sensor nodes may be detected based on an Iterative Message Passing Algorithm that takes into account the inter-symbol interference (ISI) between the estimated diadic channel and the symbol.

SC-AmBC according to the present invention enables M-ary modulation of sensor nodes (tags), non-orthogonal multiple access (NOMA), and thus can support large-scale connectivity, and the scarcity of signals is reflected in the modulation method. It is advantageous both in terms of energy harvesting and information transmission of RF tags operated by cycling.

Accordingly, the present invention can be applied to a smart home that is built on Wi-Fi, and can be usefully applied to wireless devices, such as biosensors and wearable devices, which are very limited in size and battery capacity. In particular, it can be used closely to support large-scale connection of tags in a low-power IoT network.

Meanwhile, the effects of the present invention are not limited to the above-mentioned effects, and various effects may be included within a range obvious to a person skilled in the art from the following description.

1 is a diagram for describing a sparse code-based ambient backscatter system (SC-AmBC) according to an embodiment of the present invention.
2 is a diagram for explaining 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 view for explaining the protocol structure of the SC-AmBC according to an embodiment of the present invention.
5 is a view for explaining the operation of the sparse code-based ambient backscatter system (SC-AmBC) according to an embodiment of the present invention.
6 is a diagram for explaining a method of transmitting data by a tag according to an embodiment of the present invention.
7 is a view 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 for explaining a method for an access point to estimate a channel according to an embodiment of the present invention.
11 is a view for explaining a method for detecting a backscattering signal according to an embodiment of the present invention.
12 is a diagram for explaining a diametric factor graph according to an embodiment of the present invention.
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 M-ary modulation performance of the SC-AmBC method of the present invention and the conventional TD-AmBC method.
15 is a graph comparing the performance of the duty cycling operation of the SC-AmBC method of the present invention and the conventional TD-AmBC method.
16 is a graph comparing the performance of the SC-AmBC method of the present invention and the conventional TD-AmBC method in a diadic channel.
17 is a graph comparing the performance according to the reflection coefficient of the SC-AmBC method of the present invention and the conventional TD-AmBC method.

The present invention can be applied to various changes and can have various embodiments, and specific embodiments will be illustrated in the drawings and described in detail. However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention. In describing each drawing, similar reference numerals are used for similar components.

Terms such as first, second, A, and B can 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 other components. For example, the first component may be referred to as a second component without departing from the scope of the present invention, and similarly, the second component may be referred to as a first component. The term and / or includes a combination of a plurality of related described items or any one of a plurality of related described items.

When an element is said to be "connected" or "connected" to another component, it is understood that other components may be directly connected to or connected to the other component, but may exist in the middle. It 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 no other component exists in the middle.

The terms used in this application are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions, unless the context clearly indicates otherwise. In this application, the terms "include" or "have" are intended to indicate the presence of features, numbers, steps, actions, components, parts or combinations thereof described herein, one or more other features. It should be understood that the existence or addition possibilities of fields or numbers, steps, operations, components, parts or combinations thereof are not excluded in advance.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person skilled in the art to which the present invention pertains. Terms such as those defined in a commonly used dictionary should be interpreted as having meanings consistent with meanings in the context of related technologies, and should not be interpreted as ideal or excessively formal meanings unless explicitly defined in the present application. Does not.

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

Non-orthogonal Multiple Access (NOMA) is a technology that increases the performance of the system and increases the fairness of scheduling for devices by allowing multiple devices to use the same time / frequency resource that is not orthogonal. to be.

In the NOMA system, an access point allocates the same time / frequency resource to multiple devices, and each device transmits signals superpositioned. The access point restores signals of each device by removing signals from other devices from the received signal (Successive Interference Cancellation).

Hereinafter, preferred 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, and FIG. 2 is a sparse code-based ambient backscatter system according to an embodiment of the present invention. 3 for explaining duty cycling, FIG. 3 is a diagram for explaining signals transmitted and received in SC-AmBC according to an embodiment of the present invention, and FIG. 4 is a protocol structure for SC-AmBC according to an embodiment of the present invention It is a figure for illustration.

Referring to FIG. 1, the 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, by broadcasting a Wi-Fi wireless signal. In addition, the access point 100 may perform a process of supporting the connection of the wireless network of the connected terminal device 200 using the transmitted wireless signal.

The terminal device 200 receives a radio signal transmitted from the access point 100, and accordingly, when a channel is established according to a connection procedure with the access point 100, the terminal device 200 connects to a wireless network through a set 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, for example, a Wi-Fi communication module, such as a typical mobile phone, smartphone, tablet PC, laptop, etc., and the sensor node 300 is a tag. In this case, it may be referred to as a kind of reader capable of tagging tags.

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

The sensor node 300 may absorb or reflect a radio signal transmitted from the access point 100, and may transmit information using an ambient backscatter communication method using the received RF signal. That is, the sensor node 300 accumulates energy by energy harvesting the RF signal transmitted from the access point in the idle state due to the duty cycling operation, and when a sufficient amount of energy is collected, the active state (Active State) Is converted to and generates a codeword for backscattering. At this time, the sensor node 300 applies a method of projecting a codeword as a mapping function to encode M-ary data with a small number of symbols. The codeword generated in this way is a sparse codeword due to the sparse nature of the signal, and has strong characteristics in channel distortion and attenuation because data is encoded in a multidimensional signal space.

In addition, the sensor node 300 transmits the code word on the carrier wave received from the access point 100. At this time, since the sensor nodes 300 transmit the codewords in a NOMA manner, the codewords are transmitted overlapping each other, and when they pass through the dialic channel and reach the access point 100, they are greatly distorted due to inter-symbol 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. On the other hand, in the duty cycling of the system according to the present invention, as shown in FIG. 2, cycles between tags and tags overlap each other, and multiple access interference (MAI) may occur, and transmitted symbols overlap with delay spread to intersymbol interference (ISI). ). Specifically, the tag is full

Out of time slots

Since it is active during the time slot, the duty cycle (D) is

Satisfies In addition, MAI occurs because data transmission between tags and tags occurs in a non-orthogonal manner.

Intersymbol Interference (ISI) exists between dog symbols. if,

If is satisfied, these interferences can be mitigated by a message passing algorithm (MPA) using sparseness of the codeword of the signal. Accordingly, the access point 100 may detect the codeword of each sensor node 300 from the overlapped codewords using a low complexity algorithm such as MPA (Message Passing Algorithm).

On the other hand, the codewords transmitted by the sensor nodes 300 are greatly distorted by inter-symbol interference when passing through the dialic channel and reaching the access point. That is, since the diadic channel is composed of a forward channel and a backward channel, the signal is distorted twice by the ISI, so that the signal received from the access point 100 receives significant 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 SC-AmBC signal will be described with reference to FIG. 3. Signal transmitted from the access point 100 as shown in Figure 3 (a)

The impulse response

As it passes through the forward channel represented by, it is tagged as (b).

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

As the signal scattered back and reaches the access point 100 is distorted once again through the backward channel, as shown in (c), a significant portion of the time domain received signal is distorted.

As such, since the diadic channel is composed of a forward channel and a backward channel, and the signal is distorted twice by the ISI, the signal received from the access point 100 is subject to considerable distortion. Therefore, a new channel estimation method considering signal distortion in the time domain is needed.

Accordingly, the access point 100 estimates channel information by using a D-CEA algorithm (Dyadic Channel Estimation Algorithm), and detects overlapped sparse codewords by applying a D-MPA (D-MPA). Here, the D-CEA algorithm and the diadic MPA are algorithms for detecting channel estimation and codewords in consideration of the diadic channel model and ISI, and detailed description will be described later. The diadic channel model shows a different signal characteristic from the Rayleigh fading channel, which is mainly used in existing communication systems, and has unique characteristics of backscattered communication, such as distortion of a received signal by ISI and dual channel attenuation. In addition, since the receiving end structure for most of the backscatter communication mainly uses a method of removing ISI using guard time or a Cyclic Prefix, SNR loss occurs in this process. If the ISI is used in an iterative delivery algorithm in the time domain without removing the ISI, the loss of SNR can be prevented, and thus the performance of receiving signal detection can be greatly improved.

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. 4. Referring to FIG. 4, the protocol structure includes a channel estimation 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 the scarcity of the signal, the back scattering channels can be estimated with low complexity using compressed sensing technology. In the data transmission step, the access point 100 transmits a carrier signal for backscattering of the tag 300,

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

Divided into 4 time slots, each time slot

It becomes the sampling cycle of dogs.

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 simultaneously transmit data multiplexed and transmitted from the access point 100. It can be used for energy harvesting using signals or as a carrier for backscattering.

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

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

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

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

When step S540 is performed, tag 1 and tag 2 reflect and transmit the codewords received from the access point (S550), and the access point receives the overlapped codewords (S560). At this time, since the tag 1 and the tag 2 transmit the codewords in the NOMA method, the codewords are transmitted overlapping each other, and when they pass through the dialic channel and reach the access point, they are greatly distorted by inter-symbol interference.

The access point receiving the overlapped codewords by performing the step S560 estimates the dialic channel (S570), and detects the codewords of tags 1 and 2 using the estimated dialic channel (S580). At this time, the access point estimates the channel information using a D-CEA algorithm (Dyadic Channel Estimation Algorithm), and detects overlapped sparse codewords by applying a D-MPA (D-MPA). That is, the access point estimates the dialic channel of the signals received from the tags 1 and 2 using compression sensing and channel reciprocity, and considers the interference between the estimated dialic channel and the symbol (ISI) and is variable. The information of the node is updated repeatedly a predetermined number of times, and codewords of tags 1 and 2 are detected based on the updated results.

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

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

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

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

When the tag is switched to the active state, it generates log ₂ M bit data.

For example, if the number of tags N = 6 and M = 4, each tag generates data of log ₂ 4 bits (2 bits). 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], of tag 6 Data: As shown in [00], each tag can generate 2-bit data.

When step S640 is performed, the tag projects M-order data to a predefined mapping function to generate a symbol (S650). At this time, the tag can generate symbols of the active time slot K ₁ length with 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 it into a mapping function.

Here, projection may mean that the number of symbols for which data is encoded is reduced. For example, if there is no projection, when M = 4, 4 symbols are required as complex numbers 1, -1, j, -j, but if projection is applied, the symbols are real 1, 0,-as shown in Fig. 7 (b). Since only 3 of 1 are required, the complexity required to implement encoding and decoding of data can be greatly reduced.

In the conventional time-division-based AmBC (TD-AmBC) based on time division, the reflection coefficient is mainly used as the M-ary phase shift modulation (Phase-Shift Keying) method, as shown in FIG. 7 (a). (Reflection Coefficient). The signal modulation of TD-AmBC mainly uses a method of arranging signal points in the signal space so that symbols do not overlap each other using M-PSK. However, in SC-AmBC according to the present invention, since signal modulation overlaps and transmits symbols, only three types of symbols exist in the signal space. This codeword projection method can reduce the number of load impedance required for the tag 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. By doing so, the energy harvesting efficiency of the tag can also be improved. As described above, the modulation method of the present invention is a method of allowing overlapping between symbols and projecting them into three symbols, and such a modulation method can obtain an effect of improving energy harvesting efficiency and reduce the production cost of the tag.

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

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

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

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

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

When the mapping function is defined as described 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 a carrier (S670). That is, the tag can finally convert a symbol of an active time slot K ₁ length into a sparse codeword of KL length. Here, K is the number of time slots, L is an integer value indicating the symbol period of the tag, and the symbol transmitted by the tag during L repeatedly appears.

For example, if the sampling period of the carrier is 50 ns and the symbol period of the tag is 150 ns, L = 3 and the number of timeslots K = 4, the sparse codeword may be generated with a length of 12. At this time, the diagram factor graph may be represented by the following matrix consisting of KL = 12 rows and N = 6 columns.

Using this factor graph, a symbol of length 2 can be converted into a sparse codeword of length 12. Each column of the factor graph has a structure of (K ₁ XL) one.

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

That is, in order to generate codewords of symbols [0, 1] of tag 1, '0' is assigned to the first 3 1's in the determinant column 1, and '1' is assigned to the remaining 3 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 codewords for the symbols [-1, 0] of tag 2, '-1' is assigned to the first 3 1s of the determinant column 2, and '0' is assigned to the other 3 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 codewords for the symbols [1, 0] of tag 3, '1' is assigned to the first 3 1s of the determinant column 3, and '0' is assigned to the remaining 3 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 codewords of symbols [0, -1] of tag 4, '0' is assigned to the first 3 1's of the determinant column 4, and '-1' is assigned to the remaining 3 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 codewords for the symbols [-1, 0] of tag 5, '-1' is assigned to the first 3 1s of the determinant column 5, and '0' is assigned to the remaining 3 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 codewords for the symbols [1, 0] of tag 6, '1' is assigned to the first 3 1's of the determinant 6 column, and '0' is assigned to the remaining 3 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, a codeword of each tag 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 wave in the NOMA method.

On the other hand, since the tag performing the operation as described above can implement NOMA using a sparse code, it can have improved connectivity compared to the existing TD-AmBC. This sparse code is a method in which the duty cycling structure of tags operating by radio energy harvesting is used in reverse, and the scarcity of the signal can enable the M-ary modulation method to be implemented with only 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 transmitter / receiver 310 is a configuration for receiving a radio signal from an AP or a terminal device and transmitting coded data using whether or not the carrier is reflected.

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

The modulator 330 projects M-order data to a predefined mapping function to generate a symbol, and spreads the symbol to generate a codeword. At this time, the generated codeword may be coded information. Then, the transmission / reception unit 310 reflects the received carrier wave and transmits a codeword.

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

The M-th data generation unit 332 generates log ₂ M bit data when the tag is switched to the active state. At this time, the generated log ₂ M bit data may be M-order data.

The symbol generator 334 projects the M-th data generated by the M-th data generator 332 to a predefined mapping function to generate symbols. At this time, the symbol generator 334 generates K ₁ length symbols with a mapping function. For example, when K ₁ = 2, the symbol generator 334 projects M-ary data into a mapping function to convert it into a symbol of length 2.

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

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

9, the access point transmits an RF signal (S910), and receives signals from at least one tag (S920). At this time, the access point transmits a signal through a forward channel, receives a signal through a backward channel, and the signal received from the tag may be an overlapped codeword transmitted in a NOMA method.

When step S920 is performed, the access point estimates the dialic channel of the received signal using compression sensing and channel reciprocity (S930), and detects the codeword transmitted from each tag using the estimated dialic channel. (S940). At this time, the access point uses a Dyadic Channel Estimation Algorithm (D-CEA) to effectively estimate the Dyadic channel and utilize Intersymbol Interference (ISI) for signal detection. To estimate the diametric channel. In addition, the access point tags each tag using an Iterative Message Passing Algorithm (MPA) for successfully detecting non-orthogonal multiple access (NOMA) signals encoded by sparse codes. The codeword of can be detected.

10 for a detailed description of a method for an access point to estimate a diametric channel, and FIG. 11 for a detailed description of a method for detecting a codeword.

10 is a diagram for explaining a method for an access point to estimate a channel 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). At this time, 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

The impulse response

Since it passes through the forward channel represented by

The signal captured at is distorted by ISI. Meanwhile, the reflection coefficient in the tag

As the signal that has been scattered back and reaches the access point is distorted once again through the backward channel, a significant 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 through the tag and goes back to the access point, channel reciprocity is established.

And self-interference of the access point can be removed. Thus, the access point is timeslot

The signal t _k received at can be expressed as 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 the noise,

,

Is defined as a diadic forward channel and a diadic backward channel, respectively.

,

Is a Toeplitz matrix and is expressed as Equation 2 below.

[Equation 2]

,

는 각각 크기가

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

,

Each size

Int Fleats Forward Shift Matrix, and Twenty Fleats Backward Shift Matrix.

인 벡터

으로 표현될 수 있다. When a signal such as Equation 1 is received, the access point obtains composite channel information using compressed sensing (S1030). Here, the composite channel information refers to a composite forward-backward channel, and the length

Phosphorus vector

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 acquires an initial value of the first channel impulse response using channel reciprocity (S1040). That is, since the signal transmitted by the access point passes through the tag and returns to the access point again, channel reciprocity is established.

Is satisfied. Accordingly, the access point can obtain an initial value (f _n (1)) of the first channel impulse response using Equation 3 below using channel reciprocity.

[Equation 3]

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

) Is estimated (S1050).

[Equation 4]

Here, l 'and i' are integer values representing time (eg, sampling time 50 ns is represented by integer 1, sampling time 150 ns is expressed by integer 3), and h _n (l ') is a random channel representing time. It can mean a complex value.

Equation 4 shows the impulse response of the composite channel when channel reciprocity 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 expressed as Equation 4.

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

After performing step S1050, the access point determines whether impulse responses for all channels over time have been estimated (S1060).

,

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

, 다이애딕 백워드 채널

을 산출할 수 있다. If the impulse response of all channels is estimated as a result of the determination in step S1060, the access point uses the estimated impulse response to perform a diadic channel.

,

It is estimated (S1070). That is, the access point uses the Equation 5 below to perform the Diadic Forward Channel.

, Diadick Backward Channel

Can be calculated.

[Equation 5]

If, as a result of the determination in step S1060, the impulse responses of all channels are not estimated, the access point estimates the impulse responses of the next channel (S1080, S1050), and performs step S1060.

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

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

Specifically, the access point generates a dialect factor graph (S1111), and determines whether to consider the ISI condition (S1112). Here, the ISI condition means whether interference should be considered when detecting a backscattered signal at a specific time. For example, when ISI occurs within 50 ns due to channel delay time when passing through a channel, the signal sampled at 50 ns occurs when ISI detects a signal at an access point. Since the signal sampled at 100ns, 150ns, .., etc. is not affected by ISI in excess of 50ns, a low-complexity decoding technique without interference may be used.

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

When it is necessary to consider the ISI condition as a result of the determination in step S1112, the access point reflects ISI information (S1113), calculates initial information (S1114), and, if it is not necessary to consider the ISI condition, does not reflect the ISI information and receives the initial information. Calculate. That is, if the ISI condition needs to be considered, the access point reflects ISI information when calculating the codeword initial information, or otherwise calculates the initial information in the same way as the existing MPA.

The initial information means information calculated in the first step before iterating in the message delivery algorithm, and can be obtained by multiplying the overlapped codeword by a channel and obtaining a difference from a signal received from the access point. The initial information has a negative value, and the larger the value (the 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, 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 ISI is excluded, 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 calculation of the initial information, and the channel h ₂ is weighted and added to finally become a codeword (h ₁ xB ₁ + h ₂ xB ₂ ). Here, h ₂ xB ₂ may be defined as a weighted sum to be different from h ₁ xB ₁ used in the conventional MPA. When the initial information is calculated by adding the sum of the weights, ISI is considered, and the distortion of the signal can be effectively corrected.

When the initial information is calculated through the execution of step S1110, it is determined whether the message transmission process has been repeated the maximum number of repetitions (S1120).

As a result of the determination in step S1120, if the maximum number of repetitions is not repeated, the access point updates a message to be transmitted from a factor node (FN) to a variable node (VN) (FN update step) (S1130). .

Specifically, the access point determines the presence or absence of ISI based on the number of '1' of each row in the dialect factor graph (S1131).

If the ISI exists as a result of the determination in step S1131, the access point calculates a factor node (S1132) and transmits 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 described above, when the tag uses the M-ary modulation method, the access point selectively projects codeword information according to the ISI condition to reduce decoding complexity and transmits the calculated information to the variable node.

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

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

However, the symbol period of the tag is L, which is an integer multiple of the carrier signal, and among these, since the received signal is changed by the ISI for a period of ~ L, it is necessary to introduce a diamond factor graph to correct this.

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

If the forward factor graph and the backward factor graph with K = 4, L = 3, and N = 6 are expressed in a matrix, 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, a diamond factor graph ~ G * as shown in Table 4 below may be generated.

[Table 4]

Looking at the matrix representing the diagram of the diagram of Table 4, the 4 rows contain 5 1s, and the 8 rows contain 3 1s. Accordingly, the access point can determine the presence or absence of ISI by using the number of 1s of each row in the diagram of the diametric factor. That is, the access point may determine whether the number of 1s is different for each row by determining whether ISI exists.

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

If ISI is present, there will be 5 1s in the row of the diametric factor graph, and as a result, the factor node must receive a message from 5 variable nodes. The message is a variable that is repeatedly updated while operating the algorithm, and is associated with a probability value that infers what data the tags send.

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

For example, if ISI exists and M = 4, the message sent from the factor node k to the 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 the ISI does not exist, there are three 1s in the diametric factor graph, and the size of the message is determined according to the M value. At this time, if the value of M is large, the size of the message increases, and there may be a disadvantage that the calculation amount increases in the algorithm. Accordingly, 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, the signal is not distorted, so using the property of a predefined mapping function, M-ary data can be compressed into a number of symbols smaller than M. Through this process, the complexity of the decoding process is reduced and computation is performed. 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 projection is' ~ I with a size of 3 after projection. _nk (1) ~ I _nk (2) ~ I _nk (3) '.

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

Specifically, the access point determines the presence or absence of ISI based on the number of '1' of each row in the dialect factor graph (S1141).

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

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

As described above, the access point calculates a variable node by calculating a variable node when it needs to consider ISI, and transmits a message including update information to a factor node, or expands the projected information if it is not necessary to consider ISI. The updated information is transmitted back to the factor node.

The method for the access point to project-extend the codeword information has an advantage of lowering the complexity for codeword detection even if the tag uses the M-ary modulation method.

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

The access point can effectively detect data transmitted by tags even in a wireless environment in which ISI exists by using a log likelihood ratio.

The log likelihood ratio is a value representing each bit probability and has a real value. When there is M-ary data, the size of the log likelihood ratio is log ₂ M, and the output log likelihood ratio is used when decoding data. If the log likelihood ratio is positive, data is decoded to 0, and data is decoded to negative 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], and the log likelihood ratio of tag 3: [1.3 -0.9], The access point can detect the decryption data of tag 1 [10], the decryption data of tag 2 [00], and the decryption data of tag 3 [01], 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, the 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 transmitter / receiver 110 transmits a radio signal and receives a signal transmitted in a non-orthogonal multiple access (NOMA) method from a plurality of sensor nodes.

The channel estimator 120 estimates a diacic channel of the received signal using compressed sensing and channel reciprocity. That is, the channel estimator 120 obtains composite channel information using compression sensing and calculates an initial value of the first channel impulse response using channel reciprocity 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 perform a diametric forward channel and a diadic backward. Estimate the channel.

The signal detection unit 130 repeatedly updates the information of the factor node and the variable node a predetermined number of times in consideration of the interference between the diadic channel and the symbol (ISI) estimated by the channel estimation unit 120, and the updated result Based on this, codewords of a plurality of sensor nodes are detected. That is, the signal detection unit 130 generates a diametric factor graph, determines the presence or absence of ISI based on the diametric factor graph, and selectively updates code node information by projecting codeword information according to the determination result Then, the information of the variable node is updated by expanding the projected codeword information according to the presence or absence of the ISI. Then, when the information update of the factor node and the variable node is repeated a predetermined number of times, the signal detection unit 130 outputs a log likelihood ratio and detects a codeword of each sensor node based on the log likelihood ratio.

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

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

Referring to FIG. 14, in the case of SC-AmBC, wireless energy harvesting efficiency shows a slight decrease compared to TD-AmBC when M = 2,8, but when M = 4, symbol mapping improves energy harvesting efficiency. It has no difference in performance. On the other hand, the bit error rate (Bit Error Rate) can be confirmed that the case of SC-AmBC is significantly better than that of TD-AmBC, because the backscattered signal spreads in the time domain through NOMA to obtain diversity gain. to be. In this way, SC-AmBC can successfully implement M-ary modulation while simplifying the hardware of the tag.

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

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.15, the duty cycle in the TD-AmBC method is

Is given, and the number of tags

When increases, the duty cycle decreases, and the time that the tag can use for data transmission is scaled down. On the other hand, in the SC-AmBC method of the present invention, since the scaling phenomenon of duty cycling can be reversely converted to the scarcity of the signal, the number of tags that can be connected to the access point is the Overloading Factor,

Scaled by,

Greatly increases. Moreover, since the sparse codeword can provide diversity gain in a diametric channel structure, it has the advantage of supporting large-scale connectivity and reducing bit error rate compared to the existing technique.

16 is a graph comparing the performance of the SC-AmBC method of the present invention and the conventional TD-AmBC method of the diadic channel, and FIG. 17 is a reflection coefficient of the SC-AmBC method and the conventional TD-AmBC method of the present invention. It is a graph comparing the performances.

Referring to FIG. 16, the probability of harvesting wireless energy tends to improve as the number of multipaths increases. On the other hand, in the case of the existing MPA and TD-AmBC techniques, the bit error rate deteriorates as the multipath increases, because the ISI distorts the received signal. Since the D-MPA technique of the present invention reflects the characteristics of the diadic channel, it can have a smaller bit error rate than the existing MPA technique that does not reflect it, and has great performance compared to the existing TD-AmBC technique. It has an improvement effect. When the D-MPA and D-CEA of the present invention are used as described above, since the distortion phenomenon is corrected, the signal detection performance is improved as the multipath increases. 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 signal scarcity for detection at the receiving end, the reflection coefficient at the tag as shown in FIG.

, Modulation order

, Codeword related variables

As a result, it can be seen that it can have a much higher transmission rate than the TD-AmBC technique, and also can more flexibly adjust the performance.

In the conventional TD-AmBC, since signal scarcity was not used, it has low connectivity, and as a result, has a low transmission rate. However, in the SC-AmBC of the present invention, since the scarcity of such a signal is used for backscattering, it is possible to support large-scale connectivity, so it can be seen that the overall graph moves in the Y-axis direction to show improved connectivity. This connectivity can be adjusted by parameters related to reflection coefficient, modulation order, and codeword. Overall, it can be seen that SC-AmBC can tune these system variables more flexibly to adjust backscatter performance.

As described above, sparse code does not discard MAI and ISI, but rather utilizes it, and it has the advantage of reducing bit error rate while supporting large-scale connectivity compared to existing techniques.

So far, the present invention has been focused on the preferred embodiments. Those skilled in the art to which the present invention pertains will understand that the present invention can be implemented in a modified form without departing from the essential characteristics of the present invention. Therefore, the disclosed embodiments should be considered in terms of explanation, not limitation. The scope of the present invention is shown in the claims rather than the foregoing description, and all differences within the equivalent range should be interpreted as being included in the present invention.

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

Claims (7)

In the method of communication of each sensor node in the ambient backscatter system comprising an access point and a plurality of sensor nodes,
Accumulating energy by energy harvesting the radio signal transmitted from the access point;
Generating energy of M-order data when energy above a predetermined threshold is accumulated and converted to an active state;
Generating a symbol by projecting the M-th order data into a predefined mapping function;
Generating codewords by spreading the symbols; And
And reflecting and transmitting the codeword received from the access point,
The plurality of sensor nodes is a NOMA (Non-orthogonal Multiple Access) communication method of the sensor node, characterized in that for transmitting the codeword. According to claim 1,
The symbol is generated by at least one of 1, 0, -1, and has an active time slot length, the communication method of the sensor node. According to claim 1,
The codeword is a sparse codeword having a length corresponding to a product of a number of time slots and a symbol period. According to claim 1,
The codeword is transmitted to the access point via a dialic channel. A transmitting and receiving unit for communication with the access point;
A state control unit for energy harvesting the radio signal received through the transmission / reception unit in an inactive state to accumulate energy, and accumulating energy above a preset threshold to switch to an active state; And
When it is switched to the active state, M-order data is projected to a predefined mapping function to generate a symbol, spread the symbol to generate a codeword, and reflects the carrier wave received from the access point and transmits it A sensor node including a modulator. An access point transmitting a radio signal;
Energy harvesting the radio signal transmitted from the access point to accumulate energy, and when energy above a predetermined threshold is accumulated and converted into an active state, M-order data is projected to a predefined mapping function to generate a symbol, and Generating a sparse codeword by spreading the symbol, and includes a plurality of sensor nodes that transmit the sparse codeword by receiving a carrier wave received from the access point in a non-orthogonal multiple access (NOMA) method,
The wireless signal and the sparse codeword are transmitted and received through a dialic channel. A sparse code based ambient backscatter system. The method of claim 6,
The access point,
Receiving overlapped codewords transmitted in a NOMA manner from the plurality of sensor nodes,
Based on the Dyadic Channel Estimation Algorithm, the DADIC channel is estimated, and based on the Iterative Message Passing Algorithm in consideration of the estimated DID channel and symbol-to-symbol interference (ISI). Sparse code based ambient backscatter system, characterized in that for detecting the codeword transmitted from a plurality of sensor nodes.

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