KR102337137B1 - Communication device and method for cooperative communication and method for decoding at hybrid access point - Google Patents

Abstract

The present invention relates to a method for a second communication device to perform cooperative communication with a first communication device, which comprises the steps of: receiving an RF signal from at least one of a hybrid access point and a low power access point to collect energy; receiving a first signal including shared information, as information which the first communication device transmits to the hybrid access point through backscattering, from the first communication device; and transmitting the first signal to the hybrid access point by backscattering the first signal using an unmodulated carrier wave received from the low power access point. The transmitting step may include transmitting the first signal according to a time delay corresponding to the second communication device.

Description

A communication device performing cooperative communication, a method thereof, and a decoding method at a mixed access point

The present invention relates to a communication device for performing backscatter-based cooperative communication in a wireless power heterogeneous communication network, a method thereof, and a decoding method at a mixed access point, and more particularly, to a LoRa backscatter-based long-distance cooperative communication. The present invention relates to a communication device performing the same, a communication method using the same, and a signal decoding method.

(1) Sequential cooperative communication based on AB/BB backscatter

The wireless power heterogeneous communication network refers to a communication network that collects energy through RF signals distributed around devices and can transmit and receive signals using this.

In the conventional wireless power heterogeneous communication network, a hybrid access point (H-AP) sends a signal to a legacy receiver, and a carrier emitter (CE) continuously transmits an unmodulated carrier wave (Unmodulated Carrier). are sending In such a communication network structure, Internet of Things (IoT) devices collect necessary energy through energy harvesting, and through this, short-range (Ambient Backscatter: AB)-based or Long-distance (Bistatic Backscatter: BB)-based cooperative communication is performed.

Specifically, to implement power-free operation, devices perform dual-band energy harvesting from H-AP and CE to obtain energy required for transmission and reception, and perform AB-based information exchange and BB-based cooperative transmission through the collected energy. Information exchange through AB must satisfy the following two conditions. First, the strength of the surrounding RF signal to be used as a carrier must be sufficient. Second, devices to be paired for cooperation must satisfy the AB decoding condition. If the conditions are not met, the devices individually perform BB-based non-cooperative communication without an information exchange process. Prior to information exchange, an optimal pair is found through graph matching theory, and paired devices exchange information with each other through short-range AB and then sequentially transmit information to H-AP through long-range BB.

(2) Hardware offset-based collision resolution technique - Choir

The Choir technique is designed to implement a Low Power Wide Area Network (LPWAN) for sensor nodes in an urban area. Implementing a city-scale LPWAN has problems of signal collision due to high density and signal attenuation due to many obstacles. Sensors or base stations at both ends have limited hardware performance to solve these problems. Choir uses the Chirp signal structure of LPWAN radio to separate multiple transmissions that cause interference from a single antenna base station, and proposes a method to increase the service area through cooperation when the strength of each signal is small. The chirp signal is a signal whose frequency changes linearly with time, and the frequency increases with time and changes cyclically again when the upper limit of the bandwidth is reached.

First among the characteristics of the chirp signal, collisions can be resolved by using hardware frequency offsets unique to devices. For example, the same signal coming from two transmitters has a fine frequency offset according to each independent oscillator. Two signals can be distinguished by being located in different frequency bins through a simple inverse chirp and FFT process. However, in the case of the above method, since the values appearing in the bin are expressed as hardware offsets and information offsets, there is room for various interpretations in decoding. To solve this problem, Choir uses the fact that, unlike the data frequency, the hardware offset does not appear as an integer multiple of the Fourier bin. First, the user's hardware offset is estimated through the known preamble, and when the decimal point value of the bin is the same in the FFT of the data signal, the same user can be matched. Information can be successfully decoded using the data offset value remaining after user identification.

Second among the characteristics of the chirp signal, when the transmission power of an individual device is lower than the noise, the reception power can be enhanced through cooperation of several devices. To ensure that the signal is added constructively, the time is aligned using the beacon sent from the base station, and the unavoidable remaining time offset is included in the hardware offset due to the chirp signal structure, so the user can be identified in the same way as above.

However, since the time overhead for pairing and information exchange between devices increases as the density of devices increases, the loss due to overhead becomes greater than the increase in throughput at some point. In addition, the collision resolution technique introduced in the prior art Chirp uses a hardware frequency offset of active LoRa communication, but it is difficult to apply backscatter-based passive communication because there is no hardware frequency offset. Therefore, there is a need for a new technique that can support the resolution of overhead problems according to sequential pairing and information exchange and efficient collision resolution of LoRa backscatter communication.

Republic of Korea Patent Publication No. 10-2018-0024371 (2018.03.08)

The present invention relates to a communication device and method for performing backscatter-based cooperative communication in a Wireless-Powered Heterogeneous Network (WPHetNet) according to the above-described problems and needs, and more particularly, LoRa An object of the present invention is to provide a communication device and method for performing long-distance cooperative communication based on backscattering.

In order to solve the above problem, a device that wants to transmit information performs one-way broadcasting through short-range peripheral backscattering to form a multiple pairing cluster with peripheral devices, and sets up a multiple pairing cluster with devices belonging to the cluster at an arbitrary time. An object of the present invention is to provide a communication device for transmitting information through long-distance backscattering by generating a delay and a communication method using the same.

In addition, it is intended to provide a decoding method at the mixed access point to optimize the throughput in consideration of the fairness of the information throughput of communication devices performing cooperative communication.

The method for performing cooperative communication according to the present invention for achieving the above object is a method in which a second communication device performs cooperative communication with a first communication device, the RF signal from at least one of a mixed access point and a low power access point collecting energy by receiving, by the first communication device, receiving a first signal including shared information, which is information to be transmitted to the mixed access point, from the first communication device, and from the low-power access point and transmitting the first signal to the mixed access point by backscattering the first signal using the received unmodulated carrier, wherein the transmitting includes the first signal according to a time delay corresponding to the second communication device. can be sent.

In addition, in the step of receiving the first signal according to the present invention for achieving the above object, the first communication device backscatters the RF signal transmitted from at least one of the mixed access point and the low power access point. The first signal that is a broadcast signal may be received from the first communication device.

In addition, the second communication device according to the present invention for achieving the above object transmits the first signal to the mixed access point through cooperative communication with the first communication device based on the distance from the first communication device. It can be included in a cluster consisting of devices for transmitting.

In addition, the backscattered signal according to the present invention for achieving the above object has a characteristic of a chirp signal, the time when the second communication device transmits the first signal is the first communication device It may be different from a time point at which the first signal is transmitted.

In addition, the time delay according to the present invention for achieving the above object is expressed as (BW/T _s )τ _{m ,} and the time delay has a value within the range _{of τ m} ∈[0, T _s / _γ] can Here, BW is the bandwidth of the first signal, T _s is the period of the first signal, τ _m is the time delay, _γ is the time delay index.

A communication device for performing cooperative communication according to the present invention for achieving the above object is a second communication device for performing cooperative communication with a first communication device, the RF signal from at least one of the mixed access point and the low-power access point An energy collecting unit for receiving and collecting energy, a receiving unit for receiving a first signal including shared information, which is information for the first communication device to transmit to the mixed access point, from the first communication device, and the low-power access point and a transmitter for transmitting the first signal to the mixed access point by backscattering the first signal using an unmodulated carrier wave received from can send

In addition, the receiving unit according to the present invention for achieving the above object is a signal that is broadcast as the first communication device backscatters the RF signal transmitted from at least one of the mixed access point and the low power access point. A first signal may be received from the first communication device.

In addition, the second communication device according to the present invention for achieving the above object transmits the first signal to the mixed access point through cooperative communication with the first communication device based on the distance from the first communication device. It is possible to perform cooperative communication, characterized in that it is included in a cluster consisting of devices for transmitting.

In addition, the backscattered signal according to the present invention for achieving the above object has a characteristic of a chirp signal, the time when the second communication device transmits the first signal is the first communication device It may be different from a time point at which the first signal is transmitted.

In addition, the decoding method at the mixed access point according to the present invention for achieving the above object is a method for the mixed access point to decode a signal received from a first communication device and a second communication device, the first communication device Receiving a first signal including sharing information to be shared with a peripheral communication device from the receiving device, receiving a second signal from the second communication device that is a backscattered signal of the first signal, the first signal and identifying the first communication device and the second communication device in consideration of a time delay between the second signals, and decoding the first signal and the second signal according to the identification result.

In addition, the method for decoding a mixed access point according to the present invention for achieving the above object is based on at least one of an information processing amount of the first communication device and an energy amount corresponding to the first communication device, the first communication The method may further include determining, by the device, a transmission time point, which is a time point at which information is to be transmitted, and a timeslot indicating a length of time for transmitting information, and transmitting the determined transmission time point and the timeslot to the first communication device. have.

In addition, the timeslot according to the present invention for achieving the above object is at least one included in a cluster consisting of a device for transmitting the first signal to the mixed access point through cooperative communication with the first communication device. Among the above communication devices, it may be within the time required for energy harvesting of the communication device that requires the most energy.

According to the embodiments of the present invention, energy efficiency can be increased compared to the prior art through the use of a low-power communication technique, the effect of increasing the service area can be confirmed through cooperative communication based on LoRa backscattering, and the issue of equity between nodes It has a mitigating effect.

In addition, according to embodiments of the present invention, it is possible to reduce the time overhead for pairing and information exchange between devices as the density of devices used for conventional cooperative communication increases, and effective collision resolution through time delay offset (Collision Resolution: CR) can be achieved.

In addition, according to the embodiments of the present invention, when applied to smart homes and smart factories, which have become issues recently, there is an effect that more efficient operation and management are possible. There is an effect that can be used and can be applied in a wide area wireless communication network environment.

1A and 1B are diagrams of a cooperative communication system of a wireless power heterogeneous communication network including a communication device for performing cooperative communication according to the present invention.
1c is a block diagram illustrating a communication device for performing cooperative communication in the present invention.
2 is a flowchart illustrating a method for performing cooperative communication in the present invention.
3 is a time structure diagram of a wireless power heterogeneous communication network system including a communication device performing cooperative communication in the present invention.
4 is a diagram illustrating a time-frequency domain structure of a chirp signal.
5 is a diagram illustrating digital information encoded according to a frequency shift of a chirp signal.
6A and 6B are diagrams illustrating a collision resolution technique in which the concept of a frequency offset is applied to a chirp signal.
7A and 7B are diagrams illustrating an effect of increasing a service area according to cooperative communication of a chirp signal.
8 is a diagram illustrating an arbitrary time delay applied during LoRa backscattering in the present invention.
9 is a view showing an observation window at a mixed access point when a time delay is applied in the present invention.
10 is a diagram illustrating the removal of interference between signals before decoding in the present invention.
11 is a flowchart illustrating a decoding method at a mixed access point in the present invention.
12 is a diagram illustrating a process of decoding a signal received from a plurality of communication devices according to a synchronous detection method according to the present invention.

Since the present invention can have various changes and can have various embodiments, specific embodiments will be described in detail with reference to the drawings. However, this is not intended to limit the present invention to specific embodiments, and it should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention. In describing each figure, like reference numerals have been used for like elements.

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

When a component is referred to as being “connected” or “connected” to another component, it may be directly connected or connected to the other component, but it should be understood that other components may exist in between. something to do. On the other hand, when it is said that a certain element is "directly connected" or "directly connected" to another element, it should be understood that the other element does not exist in the middle.

The terms used in the present application are only used to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In the present application, terms such as “comprise” or “have” are intended to designate that a feature, number, step, operation, component, part, or combination thereof described in the specification exists, but one or more other features It should be understood that this does not preclude the existence or addition of numbers, steps, operations, components, parts, or combinations thereof.

Unless defined otherwise, all terms used herein, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the related art, and should not be interpreted in an ideal or excessively formal meaning unless explicitly defined in the present application. does not

Throughout the specification and claims, when a part includes a certain element, it means that other elements may be further included, rather than excluding other elements, unless otherwise stated.

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

1A and 1B are diagrams of a cooperative communication system of a wireless power heterogeneous communication network including a communication device for performing cooperative communication according to the present invention, and FIG. 1C is a diagram illustrating a communication device for performing cooperative communication according to the present invention. It is a block diagram, and FIG. 2 is a flowchart illustrating a method for performing cooperative communication according to the present invention.

1A and 1B, a cooperative communication system of a wireless power heterogeneous communication network including a communication device for performing cooperative communication according to the present invention is a hybrid access point (H-AP), a low power access point (CE), and a plurality of communications It may be configured to include a device.

The cooperative communication system is a carrier that transmits relatively low power compared to a hybrid access point (H-AP) and a hybrid access point (H-AP) indicating a hybrid access point such as a base station that transmits high power Assume a network model in which a plurality of communication devices perform uplink wireless communication to a hybrid access point (H-AP) in an environment in which low-power access points (CEs) representing emitters are mixed. are doing

Specifically, a plurality of communication devices (Device) have a low-power access point (CE) as an origin and a density λ within a disk range A with a radius R according to a stochastic geometry that can realistically model a cellular network. It is assumed that distribution is a single Poisson point process under N conditions with parameters.

The hybrid access point (H-AP) may continuously transmit an RF signal that is a modulated signal, and the low-power access point (CE) may continuously transmit an unmodulated carrier wave.

A plurality of communication devices (Device) can perform cooperative communication by collecting energy by receiving a signal from a neighboring mixed access point (H-AP) or low power access point (CE) without a separate power source.

As shown in the figure, a plurality of communication devices exist in the service area of the low-power access point CE existing in the service area of the hybrid access point H-AP.

A communication device (Device i) that wants to send information to a mixed access point (H-AP) among a plurality of communication devices (Device) receives from at least one of a mixed access point (H-AP) and a low-power access point (CE). By backscattering the RF signal, it forms a multiple-pairing cluster with surrounding communication devices through unidirectional broadcasting instead of information exchange, and receives unmodulation from the low-power access point (CE) with the help of communication devices in the cluster. By using a carrier wave to backscatter a signal containing information, it can be transmitted to the H-AP.

At this time, when the backscattering operation for information transmission to the mixed access point (H-AP) is performed, the transmission is performed according to an arbitrary time delay corresponding to each communication device, thereby solving the signal overhead problem between communication devices configured with high density. can

Hereinafter, a method in which the second communication device (Device m) of a plurality of communication devices (Device) performs cooperative communication with the first communication device (Device i) will be described in detail with reference to FIG. 2 . For reference, it is assumed that cooperative communication is performed in a communication system in which the hybrid access point (H-AP) and the low power access point (CE) are mixed as described above.

First, the channel estimator (not shown) of the second communication device (Device m) may perform the step of measuring channel information between the device and the access point by transmitting a pilot signal together with the first communication device (Device i). .

Thereafter, the energy collection unit (refer to m10 of FIG. 1c ) of the second communication device (Device m) receives an RF signal from at least one of the hybrid access point (H-AP) and the low-power access point (CE) to collect energy. It can be (S110).

Energy collection may be achieved through an unmodulated carrier wave received from a low-power access point (CE), which will be described later, as well as an RF signal received from the hybrid access point (H-AP). Therefore, since the second communication device (Device m) can receive both types of signals from the hybrid access point (H-AP) and the low-power access point (CE), it collects energy through the dual band energy collection technology. Communication efficiency can be improved.

Then, the receiving unit of the second communication device (Device m) (refer to m20 in FIG. 1c) of the first communication device (Device i) transmits the information for the first communication device (Device i) to the hybrid access point (H-AP) through backscattering, which is shared information. The included first signal may be received from the first communication device (Device i) (S120).

The first signal is a signal including shared information, which is information that the first communication device (Device i) wants to send to the H-AP, and transmits the RF signal received from the H-AP as a carrier wave. It can be transmitted to the second communication device (Device m) by broadcasting by the first communication device (Device i).

In other words, in the step S120, the receiver backscatters the RF signal transmitted from at least one of the hybrid access point (H-AP) and the low-power access point (CE) by the first communication device (Device i). The first signal, which is a signal to be cast, may be received from the first communication device (Device i). In this case, the first signal may be broadcast to the second communication device (Device m) only when the strength of the RF signal to be used as the carrier is sufficiently large based on the threshold.

On the other hand, the second communication device (Device m) is to be included in the cluster (Cluster) consisting of devices for transmitting the first signal to the mixed access point (H-AP) through cooperative communication with the first communication device (Device i). can

That is, after the broadcasting of the first signal is performed, communication devices satisfying a predetermined criterion among the communication devices adjacent to the first communication device (Device i) may gather to form a cluster, and the communication devices included in the cluster They may be determined as devices for cooperatively communicating with the first communication device (Device i) to transmit the first signal to the H-AP. Such a cluster may be configured to include a second communication device (Device m).

As an embodiment, a cluster may be formed based on the distance between the first communication device Device i and the first communication device Device i among adjacent communication devices, for example, the first communication device Device i and the threshold A cluster may be configured including communication devices located within a distance within a value.

In another embodiment, a cluster may be formed based on the number of communication devices adjacent to the first communication device (Device i) and the amount of transmission power of the first communication device (Device i), for example, the first communication device (Device i) A cluster may be configured including communication devices satisfying the mapping table based on a mapping table to which the number of communication devices to which the first signal can reach according to the amount of transmit power of .

In this way, the communication devices constituting the cluster transmit signals including the same information to the H-AP, thereby enhancing reception power at the H-AP and increasing the throughput.

In the cooperative communication system, the low-power access point (CE) can continuously transmit an unmodulated carrier wave, and all communication devices in the cluster, including the first communication device (Device i), receive unmodulation from the low-power access point (CE). A carrier wave can be used.

Thereafter, the transmitter (refer to m30 of FIG. 1C ) of the second communication device (Device m) may transmit the first signal to the hybrid access point (H-AP) by backscattering it using the unmodulated carrier (S130). .

At this time, the signal backscattered using the unmodulated carrier wave, that is, the LoRa-backscattered signal has the characteristics of a chirp signal, and the second communication device (Device m) is the corresponding device (the second communication device (Device m) )), the first signal may be transmitted according to a time delay corresponding to the ).

As shown in FIG. 4 , the chirp signal is a signal whose frequency is linearly changed with time, and the frequency increases with time, and when the upper limit of the bandwidth is reached, the frequency changes cyclically again. In this case, as shown in FIG. 5 , digital information included in the chirp signal may be encoded according to a frequency shift.

On the other hand, Choir, which is a collision resolution technique using the structure of a chirp signal, may have the following two characteristics. First, it is possible to resolve the collision between signals by using the unique hardware frequency offset of communication devices configured with high density. For example, as shown in FIG. 6A , the same signal transmitted from two transmitters has a fine frequency offset according to each independent oscillator, and the two signals are placed in different frequency bins through frequency conversion such as FFT. can be divided into However, since the value shown in the bin is expressed together with the hardware offset and data, there is room for various interpretations in the decoding process. In order to solve this problem, it is possible to use the fact that the hardware offset does not appear as an integer multiple of the Fourier bin, unlike the data frequency. That is, as shown in FIG. 6B, when the hardware offset is estimated through the preamble and the decimal point values of the bins in the FFT of the data frequency match, the same device can be identified. Data can be successfully decoded using the value of the data offset remaining after device identification. Second, when the transmit power of individual devices is lower than noise, power can be strengthened through cooperative communication of multiple devices. That is, as shown in FIG. 7A, if the intensity of the signal transmitted by individual devices is less than the intensity of noise, it cannot be transmitted to the base station. As shown in FIG. 7B, a signal to be transmitted through cooperative communication between the individual devices. It is possible to increase the service area by making the strength of the noise higher than that of the noise.

However, unlike the prior art in which an active LoRa communication technique for identifying different devices using a hardware offset of the transmitter itself is performed, in the present invention, a carrier wave is reflected and transmitted to the H-AP There is no hardware offset as a passive LoRa communication technique is performed. Accordingly, by applying an arbitrary time delay for each communication device to the first signal to be transmitted through backscattering to generate a frequency offset, the same function as the hardware offset can be applied.

Due to the time delay as described above, a time point at which the first communication device (Device i) transmits the first signal is different from a time point at which the second communication device (Device m) transmits the first signal, and the first signal is It can be sequentially transmitted to the hybrid access point (H-AP).

This is to minimize the signal collision that occurs when the communication devices constituting the cluster simultaneously transmit the same signal to the mixed access point (H-AP). it was to be sent.

_{According to an embodiment, the time delay may be expressed as (BW/T s} )τ _m due to the characteristic of the chirp signal whose frequency varies with time, as shown in FIG. 8 , and the maximum of the time delay If the value is T _s / _γ , the time delay may have a value within the range _{of τ m} ∈[0, T _s / _γ]. Here, BW is a frequency bandwidth of the first signal, T _s is a period of the first signal, τ _m is a time delay, and _γ is a time delay index. _{For reference, when time delay τ m} and τ _M are respectively applied to the second communication device (Device m) and another communication device (Device M) among the communication devices in the cluster, the window observed at the mixed access point (H-AP) The size of (T _s + τ _max ) can be expressed as shown in FIG. 9 .

For reference, FIGS. 8 and 9 are diagrams illustrating an arbitrary time delay applied during LoRa backscattering according to the present invention.

As the first signals including the same information are sequentially transmitted as described above, the H-AP decodes the plurality of first signals transmitted with an arbitrary time delay to identify the communication device.

Specifically, the frequency offset to be implemented in the present invention consists only of the sum of the time delay and the data offset. A plurality of first signals transmitted with an arbitrary time delay are detected at the H-AP receiving the frequency offset. and a coherent detection method can be used to decode the data. In this case, prior to detection, it is possible to solve the inter-signal interference (ISI) problem. For example, as shown in FIG. 10 , since a signal corresponding to interference appears overlappingly in the FFT bins of two consecutive signals, the interference can be resolved by observing and removing it. For reference, FIG. 10 is a diagram illustrating the removal of interference between signals before decoding in the present invention.

A decoding method at a hybrid access point (H-AP) to be implemented in the present invention is shown in FIG. 11 . For reference, FIG. 11 is a flowchart illustrating a method of decoding a mixed access point in the present invention.

First, the hybrid access point (H-AP) may receive a first signal including sharing information for sharing with a neighboring communication device from the first communication device (Device i) (S210)

The first signal is a signal including shared information, which is information that the first communication device (Device i) wants to send to the H-AP, and is a communication device located in the vicinity, for example, the second communication device (Device). m) may include shared information to share with.

Thereafter, the mixed access point (H-AP) may receive a second signal, which is a signal in which the first signal is backscattered, from the second communication device (Device m) (S220).

The second signal is a signal broadcast by the first communication device (Device i) using the unmodulated carrier wave transmitted from the low-power access point (CE) by the second communication device (Device m). Accordingly, as a signal transmitted to the H-AP, the first communication device (Device i) may include shared information to be shared.

Thereafter, the hybrid access point H-AP may identify the first communication device Device i and the second communication device Device m in consideration of the time delay between the first signal and the second signal.

Thereafter, the hybrid access point (H-AP) may decode the first signal and the second signal according to the identification result.

On the other hand, before performing the decoding process as described above, it is preferable that the H-AP schedule the timing for each communication device to transmit information in advance.

In an embodiment, the hybrid access point (H-AP) is a transmission time point at which the first communication device transmits information based on at least one of an information processing amount of the first communication device and an energy amount corresponding to the first communication device A timeslot indicating a time point and a length of time for transmitting information may be determined. Thereafter, the determined transmission time and timeslot may be transmitted to the first communication device. Also, in the case of the second communication device, the mixed access point (H-AP) may transmit the transmission time and timeslot determined to correspond to the second communication device to the second communication device as described above.

Accordingly, the hybrid access point (H-AP) is capable of estimating the time delay between communication devices based on the information on the transmission time and timeslot in the process of identifying the first signal and the second signal when decoding is performed. will become

For reference, the timeslot in this embodiment is a cluster including the first communication device (Device i), that is, a device for transmitting the first signal to the mixed access point through cooperative communication with the first communication device (Device i) Among the at least one or more communication devices included in the cluster consisting of This is also the case for the timeslot of the second communication device (Device m).

Hereinafter, a decoding process at the H-AP will be described in more detail with reference to FIG. 12 . For reference, FIG. 12 is a diagram illustrating a process of decoding a signal received from a plurality of communication devices according to a synchronous detection method according to the present invention.

와 채널

을 추정한다. 이후, 공유정보를 포함하는 각각의 제1 신호들이 C^-1 및 FFT 과정을 거쳐 서로 다른 주파수 bin에 자리하게 된다. 이후, FFT bin의 소수점 값을 Preamble과 비교해 각 통신기기를 식별한 후, 시간지연 벡터 및 채널의 추정 값을 이용하여 신호를 재구성하고 최대 우도(ML) 복호를 수행한다. 이를 수식으로 표현하면

와 같으며, 제2 통신기기(Device m)를 기준으로 나타내었다. 여기서, h_m은 제2 통신기기(Device m)와 혼합 접속지점(H-AP) 간의 상향링크 채널을, f_c는 저전력 접속지점(CE)에서 송신되는 무변조 반송파의 중심 주파수를, d는 제1 신호의 정보를, y는 혼합 접속지점에서 수신한 신호를, C는 시간에 따라 주파수가 변하는 처프(chirp) 신호 구조를 만드는 변수를 ∀m은 클러스터 내 모든 통신기기에 해당함을 의미한다. 이후, 각 통신기기간 Majority Vote를 수행하여 최종 정보를 결정한다.Referring to FIG. 12, when a plurality of identical signals are transmitted to the H-AP, first, a Preamble for each of the first signals received from a plurality of communication devices at the H-AP time delay vector via

and channel

to estimate Thereafter, each of the first signals including the shared information is placed in different frequency bins through ^{C -1 and FFT processes.} Thereafter, after each communication device is identified by comparing the decimal point value of the FFT bin with the preamble, the signal is reconstructed using the time delay vector and the estimated value of the channel, and maximum likelihood (ML) decoding is performed. Expressing this as a formula

and is shown based on the second communication device (Device m). Here, h _m is the uplink channel between the second communication device (Device m) and the hybrid access point (H-AP), f _c is the center frequency of the unmodulated carrier transmitted from the low-power access point (CE), and d is The information of the first signal, y means the signal received at the mixed access point, C is a variable that creates a chirp signal structure whose frequency changes with time, and ∀m means that it corresponds to all communication devices in the cluster. Thereafter, the final information is determined by performing a majority vote between each communication device.

Meanwhile, the time structure (see FIG. 3 ) in the cooperative communication process of the present invention may be optimized in consideration of the fairness of the throughput of each communication device. To this end, the common throughput maximization problem can be defined as follows.

는 최적화 변수인 시간 벡터를,

는 통신기기의 처리량,

은 통신기기의 에너지 수집량을, t_E는 에너지 하베스팅 시간을, P^(T) _AB는 주변 후방산란(Ambient Backscatter)의 송신 전력을_, P^(R) _AB는 주변 후방산란(Ambient Backscatter)의 수신 전력을, P_LoRa ^(T)는 로라(LoRa) 후방산란의 송신 전력을, t_kB는 통신기기 k의 브로드캐스팅 시간, t_iT는 통신기기 i의 송신 시간, P_Ri는 통신기기 i가 수집한 총 에너지량, η_i는 통신기기 i의 에너지 수집 효율을 의미한다.here,

is the optimization variable, the time vector,

is the throughput of the communication device,

is the amount of energy collected by the communication device, t _E is the energy harvesting time, P ^(T) _AB is the transmit power of the ambient backscatter, _and P ^(R) _AB is the reception of the ambient backscatter power, P _LoRa ^(T) is the transmission power of the LoRa backscatter, t _kB is the broadcasting time of the communication device k, t _iT is the transmission time _{of the communication device i, P Ri} is the total amount of energy collected by the communication device i , η _i means the energy collection efficiency of the communication device i.

In this case, the given time constraint and energy constraint must be satisfied. The energy harvesting time (t _E ) was set as the upper limit of the harvesting time of the device requiring the most energy among the N communication devices. In addition, throughput was calculated as the prototype data rate of ambient backscatter communication and Sum-SNR by Non/Coherent Combining of LoRa signals. The defined convex optimization problem can be solved by transforming it into an Iterative Feasibility Check problem.

Accordingly, according to the embodiments of the present invention, energy efficiency can be increased compared to the prior art through the use of a low-power communication technique, and the effect of increasing the service area can be confirmed through cooperative communication based on LoRa backscattering, and the issue of equity between nodes can be alleviated.

In addition, according to embodiments of the present invention, it is possible to reduce the time overhead for pairing and information exchange between devices as the density of devices used for conventional cooperative communication increases, and effective collision resolution through time delay offset (Collision Resolution: CR) can be achieved.

In addition, according to the embodiments of the present invention, when applied to smart homes and smart factories, which have become issues recently, there is an effect that more efficient operation and management are possible. There is an effect that can be used and can be applied in a wide area wireless communication network environment.

The above description is merely illustrative of the technical idea of the present invention, and various modifications and variations may be made by those of ordinary skill in the art to which the present invention pertains without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical spirit of the present invention, but to explain, and the scope of the technical spirit of the present invention is not limited by these embodiments. The protection scope of the present invention should be construed by the following claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present invention.

H-AP: mixed access point
CE: low-power access point
Device i: first communication device
Device m: second communication device
m10: energy collection unit
m20 : receiver
m30 : transmitter

Claims (12)

In the method for the second communication device to perform cooperative communication with the first communication device,
collecting energy by receiving an RF signal from at least one of the mixed access point and the low power access point;
Receiving, by the first communication device, a first signal including shared information, which is information to be transmitted to the mixed access point, from the first communication device; And
and transmitting the first signal to the mixed access point by backscattering the first signal using an unmodulated carrier wave received from the low-power access point,
In the transmitting step, the first signal is transmitted according to a time delay corresponding to the second communication device,
The backscattered signal has a characteristic of a chirp signal,
A time point at which the second communication device transmits the first signal is different from a time point at which the first communication device transmits the first signal,
The time delay due to the characteristic of the chirp signal is applied to generate a frequency offset, and the frequency offset is derived in consideration of the bandwidth of the first signal, the period of the first signal, the time delay and the time delay index. A method for performing cooperative communication, which is characterized.
According to claim 1,
Receiving the first signal comprises:
characterized in that the first communication device receives the first signal, which is a signal broadcast as the first communication device backscatters the RF signal transmitted from at least one of the mixed access point and the low-power access point, from the first communication device How to conduct cooperative communication.
3. The method of claim 2,
The second communication device is
Perform cooperative communication, characterized in that it is included in a cluster consisting of devices for transmitting the shared information to the mixed access point through cooperative communication with the first communication device based on the distance from the first communication device Way.
delete According to claim 1,
A frequency offset generated by applying the time delay due to the characteristics of the chirped signal is expressed as (BW/T _s )τ _{m ,} and the time delay is a value within the range _{of τ m} ∈[0, T _s / _{γ ].} Method for performing cooperative communication, characterized in that having.
Here, BW is the bandwidth of the first signal, T _s is the period of the first signal, τ _m is the time delay, _γ is the time delay index.
In the second communication device for performing cooperative communication with the first communication device,
an energy collecting unit for receiving an RF signal from at least one of the mixed access point and the low power access point to collect energy;
a receiving unit for receiving a first signal including shared information, which is information for the first communication device to transmit to the mixed access point, from the first communication device;
and
a transmitter for transmitting the first signal to the mixed access point by backscattering the first signal using an unmodulated carrier wave received from the low-power access point;
The transmitter transmits the first signal according to a time delay corresponding to the second communication device,
The backscattered signal has a characteristic of a chirp signal,
A time point at which the second communication device transmits the first signal is different from a time point at which the first communication device transmits the first signal,
The time delay due to the characteristic of the chirp signal is applied to generate a frequency offset, and the frequency offset is derived in consideration of the bandwidth of the first signal, the period of the first signal, the time delay and the time delay index. A communication device that performs cooperative communication, characterized in that it.
7. The method of claim 6,
the receiving unit
Cooperation, characterized in that the first communication device receives the first signal from the first communication device, which is a signal broadcast as the first communication device backscatters an RF signal transmitted from at least one of the mixed access point and the low-power access point. A communication device that performs communication.
8. The method of claim 7,
The second communication device is
Perform cooperative communication, characterized in that it is included in a cluster consisting of devices for transmitting the shared information to the mixed access point through cooperative communication with the first communication device based on the distance from the first communication device communication device.
delete A method for a mixed access point to decode a signal received from a first communication device and a second communication device,
receiving, from the first communication device, a first signal including sharing information for sharing with neighboring communication devices;
receiving a second signal that is a backscattered signal of the first signal from the second communication device;
identifying the first communication device and the second communication device in consideration of a time delay between the first signal and the second signal; and
Decoding the first signal and the second signal according to the identification result
including,
Based on at least one of the amount of information processing of the first communication device and the amount of energy corresponding to the first communication device, indicating a transmission time, which is a time point at which the first communication device transmits information, and a length of time for transmitting information determining a timeslot; and
and transmitting the determined transmission time point and the timeslot to the first communication device.
delete 11. The method of claim 10,
The timeslot is
An energy harvest of a communication device that requires the most energy among at least one or more communication devices included in a cluster including devices for transmitting the first signal to the mixed access point through cooperative communication with the first communication device A decryption method at a mixed access point, characterized in that it is within the time required for decoding.

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