KR20110080053A - System and spectrum sensor for cognitive radio - Google Patents

Abstract

PURPOSE: A system for CR(Cognitive Radio) communication and a spectrum sensor are provided to improve the sensing performance of the spectrum of a primary user. CONSTITUTION: A plurality of spectrum sensor(120) is dispersedly arranged in an installation space to independently receive a radio signal each other. The plurality of spectrum sensors creates information about whether a primary user appears with spectrum sensing. A collection center(110) is connected to the plurality of spectrum sensors through a network. The collection center collects the information from the plurality of spectrum sensors.

Description

SYSTEM AND SPECTRUM SENSOR FOR COGNITIVE RADIO}

The disclosed technology relates to a system and spectrum sensor for cognitive wireless communication.

Cognitive Radio is an advanced form of the SDR (Software Defined Radio) concept proposed to improve the efficiency of the use of frequency resources.It measures the radio environment and adjusts the operating parameters of the radio device to suit the measured radio environment. Wireless communication technology that operates by setting. Cognitive radio technology is a technology that can be used in many types of wireless devices, and related technologies are being developed. The IEEE 802.22 working group is applying standardization to a wireless regional area network (WRAN).

In an environment to which cognitive radio communication technology is applied, it is possible to sense, manage, and share spectrum resources. For example, in a cognitive wireless communication environment, the unused frequency spectrum of the primary user may be found so that the secondary user uses the corresponding spectrum section at a time when the primary user does not use it. At this time, spectrum sensing is a technique for finding an unused frequency spectrum section called spectral space and is a basic and essential technique for implementing a cognitive wireless communication system.

The technical problem to be achieved by the disclosed technology is to provide a system and spectrum sensor for cognitive radio communication.

In order to achieve the above technical problem, the first aspect of the disclosed technology is distributed in an installation space so as to receive radio signals independently of each other, and whether or not a primary user (PU) appears through spectrum sensing A plurality of spectrum sensors for generating information for determining; And a collection center connected to the network with the plurality of spectrum sensors, the collection center collecting the information from the plurality of spectrum sensors.

A second aspect of the disclosed technology to achieve the above technical problem is an information generation unit for generating information for determining whether a primary user (hereinafter, referred to as a PU) through the spectrum sensing; And a transmission unit for transmitting the information generated by the information generation unit to a collection center, distributed on an intelligent transport system (ITS) period structure, and capable of communicating with the collection center through an ITS network. A spectrum sensor for cognitive radio communication is provided.

A third aspect of the disclosed technology to achieve the above technical problem is a plurality of spectral sensors distributed in the installation space to receive radio signals independently of each other and generating information for determining whether the PU appears through the spectrum sensing An information collection unit for collecting the information from the communication network; And a determination unit that determines whether the PU occupies a radio spectrum based on the collected information.

Embodiments of the disclosed technique may have effects that include the following advantages. It should be understood, however, that the scope of the disclosed technology is not to be construed as limited thereby, since the embodiments of the disclosed technology are not meant to include all such embodiments.

According to the cognitive wireless communication system of the disclosed technology, it is possible to improve the sensing performance of the spectrum of the primary user, and the reliability of the sensing result is improved. In addition, according to one embodiment of the disclosed technology, when constructing a cognitive wireless communication system using the infrastructure of the intelligent transport system, it is possible to maintain a predetermined distance between the spectrum sensor, and to build the system at a low cost There is this.

According to another embodiment of the disclosed technology, whether the spectrum of the secondary user is available may be determined in consideration of the distance between the primary user and the secondary user. Therefore, there is an advantage that more efficient use of radio resources. In addition, according to another embodiment, it is possible to increase the energy consumption efficiency of the spectrum sensor.

1 is a diagram illustrating a system for cognitive wireless communication according to an embodiment of the disclosed technology.
FIG. 2 is a block diagram illustrating the spectrum sensor of FIG. 1.
3 is a graph showing a false alarm probability according to a threshold value.
4 is a block diagram illustrating the collection center of FIG. 1.
5 is a graph illustrating spectrum sensing performance of a cognitive wireless communication system according to a determination method in a number and collection apparatus of spectrum sensors.
6 is a graph illustrating sensing performance according to a distance between a PU and a spectrum sensor.
FIG. 7 is a diagram for describing an embodiment in which information that a spectral region of a PU may be used according to a distance between a PU and a SU is differently provided.

The description of the disclosed technique is merely an example for structural or functional explanation and the scope of the disclosed technology should not be construed as being limited by the embodiments described in the text. That is, the embodiments may be variously modified and may have various forms, and thus the scope of the disclosed technology should be understood to include equivalents capable of realizing the technical idea.

On the other hand, the meaning of the terms described in the present application should be understood as follows.

The terms " first ", " second ", and the like are used to distinguish one element from another and should not be limited by these terms. For example, the first component may be named a second component, and similarly, the second component may also be named a first component.

When a component is referred to as being "connected" to another component, it should be understood that there may be other components in between, although it may be directly connected to the other component. On the other hand, when an element is referred to as being "directly connected" to another element, it should be understood that there are no other elements in between. On the other hand, other expressions describing the relationship between the components, such as "between" and "immediately between" or "neighboring to" and "directly neighboring to", should be interpreted as well.

Singular expressions should be understood to include plural expressions unless the context clearly indicates otherwise, and terms such as "include" or "have" refer to features, numbers, steps, operations, components, parts, or parts thereof described. It is to be understood that the combination is intended to be present, but not to exclude in advance the possibility of the presence or addition of one or more other features or numbers, steps, operations, components, parts or combinations thereof.

Each step may occur differently from the stated order unless the context clearly dictates the specific order. That is, each step may occur in the same order as specified, may be performed substantially simultaneously, or may be performed in the reverse order.

All terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the disclosed technology belongs, unless otherwise defined. Terms defined in commonly used dictionaries should be interpreted to be consistent with meaning in the context of the relevant art and can not be construed as having ideal or overly formal meaning unless expressly defined in the present application.

1 is a diagram illustrating a system for cognitive wireless communication according to an embodiment of the disclosed technology. Referring to FIG. 1, the cognitive wireless communication system 100 collects sensing information for determining whether a primary user (PU) is present and a collection center 110. ) Includes a plurality of spectrum sensors 120 distributed in an installation space for collecting the sensing information.

The collection center 110 is connected to the plurality of spectrum sensors 120 through a wired or wireless network to collect the sensing information from the spectrum sensors 120. A cognitive radio communication system determines whether a PU appears, that is, whether the PU occupies its spectrum, based on the collected sensing information in order to efficiently use radio resources. In this case, the cognitive wireless communication system may determine whether the PU occupies its spectrum based on the spectrum sensing information collected from one sensor, but in the present invention, the plural wireless communication system may improve the spectrum sensing performance and the reliability of the sensing result. A plurality of sensing information is collected from the spectral sensors of, and based on this, it is determined whether the PU occupies its spectrum.

The spectrum sensor 120 receives the signal from the PU to perform the spectral sensing of the PU, and generates sensing information for determining whether the PU appears based on the spectrum sensing result. For efficient power consumption of the spectrum sensors 120, according to an embodiment, the spectrum sensors 120 may perform spectrum sensing when there is a spectrum sensing command of a secondary user (hereinafter, referred to as SU). . In one example, the spectrum sensing command of the SU may be transmitted to the spectrum sensor 120 directly from the SU. In another example, the collection center may receive the sensing command and issue a sensing command to the spectrum sensor 120.

The plurality of spectrum sensors 120 are distributed in a predetermined installation space while maintaining a separation distance more than a predetermined distance. The spectrum sensors 120 may lower the correlation between the spectrum sensors 120 by maintaining a separation distance greater than or equal to a predetermined distance from each other. In the case of cooperative sensing in which a plurality of spectrum sensors 120 are used as in the present embodiment, if the correlation between each spectrum sensor 120 is minimized and the signals received by each spectrum sensor 120 are maintained to be independent, The performance of the sensing can be improved.

In order to install the spectral sensors 120 to maintain a predetermined distance from each other, it is necessary to build a separate infrastructure, in which case, using an intelligent transport system (ITS) infrastructure, to build a new infrastructure Time, cost, etc. can be saved.

FIG. 1 illustrates a state in which the spectral sensors 120 are distributed and disposed on an ITS period structure, according to an exemplary embodiment. In this case, the collecting device 110 may also be installed on the ITS infrastructure, and collect sensing information from the spectrum sensor 120 using the ITS network. ITS is an intelligent transportation system that combines electronic, information, communication, and control technologies with traffic systems.It is based on traffic information collected by installing devices that can detect traffic information such as vehicle characteristics and speed on the road. This includes technologies that enable the analysis and management of traffic conditions. ITS main structures, devices that collect or provide traffic information, can be connected to each other via wired and wireless ITS networks. The ITS period structure may include, for example, traffic lights, CCTV, roadside roadside equipment, and the like. The ITS network may be constructed with fiber optic cables, which are assumed to be perfect channels without errors and attenuation.

FIG. 1 illustrates an example in which spectral sensors 120 are installed on traffic lights among the ITS period structures. When the traffic lights are located at an intersection, the spectrum sensor is only one of the plurality of traffic lights at the intersection. The cognitive radio communication system 100 can be efficiently constructed by installing the 120.

FIG. 2 is a block diagram illustrating the spectrum sensor of FIG. 1. Referring to FIG. 2, the spectrum sensor 120 includes a receiver 210, an information generator 220, and a transmitter 230. The receiver 210 receives a radio signal from a PU. The information generator 220 generates sensing information for determining whether a PU appears on the basis of a wireless signal received by the receiver 210. The transmitter 230 transmits the sensing information generated by the information generator 220 to the collection center 110.

The sensing information generated by the information generator 210 may include, for example, the strength of the signal received from the PU by the spectrum sensor 120 or whether the strength of the signal is greater than a preset threshold. In the latter case, for example, the sensing information may include '1' when the received signal is greater than a threshold value and '0' when it is less than the threshold value. In this case, '1' may also mean that the spectral interval of the PU is being used (or detected as being used), and on the contrary, '0' means that the spectral interval of the PU is not being used (or not used). Detected). The sensing information determined by each of the spectrum sensors 120 as to whether a PU uses a spectral section is referred to as LD (Local Decision).

For example, the threshold value may be determined based on experimental data or calculated as a value having a desired probability by a system designer or the like according to a probability theory. In this embodiment, for example, the threshold value is determined according to a constant false alarm rate (CFAR) algorithm. The method of calculating the constant false alarm rate is as follows.

셀의 경우와 점유하고 있지 않은

셀의 경우, n=1, 2, …, N 번째 센서로 수신된 신호

는 각각 하기의 수학식 1 및 수학식 2와 같이 나타낼 수 있다.PU is occupying frequency spectrum

Not occupied by the cell

For cells, n = 1, 2,... , The signal received by the Nth sensor

Can be represented by Equations 1 and 2, respectively.

는 컨벌루션 (Convolution) 연산을 나타낸다. 그리고 n(k)는 평균이 0 이고 분산이

인 부가 백색 가우시안 잡음 (AWGN: Additive White Gaussian Noise)를 나타낸다. 수신 무선 채널을 가우시안 채널로 가정하면

셀과

셀의 확률 밀도 함수 (PDF : Probability Density Function)는 각각 하기의 수학식 3 및 수학식 4와 같이 표현할 수 있다.Where h (k) is the shock response of the wireless channel, s (k) is the transmission signal transmitted from the PU,

Denotes a convolution operation. And n (k) has mean 0 and variance

Phosphorus addition represents Additive White Gaussian Noise (AWGN). Assume the receiving wireless channel is a Gaussian channel

Cell and

Probability Density Function (PDF) of the cell may be expressed as Equation 3 and Equation 4 below.

는 PU 신호의 평균값이다. 각 스펙트럼 센서(120)로 수신된 PU 송신 신호를 기초로 LD가 결정된 후, 이 결과들은 수집 센터(110)에 전달되어 PU의 스펙트럼 점유 여부를 판단(Global Decision: 이하, GD)하는데 사용된다. 수집 센터(110)에서 GD에 사용되는 신호는 수학식 5와 같이 나타낼 수 있다.here

Is the average value of the PU signal. After the LD is determined based on the PU transmission signal received by each spectrum sensor 120, these results are transmitted to the collection center 110 and used to determine whether the PU occupies the spectrum (Global Decision: hereinafter, GD). The signal used for the GD in the collection center 110 may be represented as shown in Equation 5.

은 LD 결과이며, GD는 예를 들어, AND 방식을 따를 경우,

의 값이 N인 경우, OR 방식을 따를 경우

의 값이 1 이상인 경우, Majority 방식을 따를 경우

의 값이 보다 큰 경우 PU가 스펙트럼을 점유하고 있다고 판단한다. here

Is the LD result, and GD follows, for example, the AND method,

If the value of N is N, the OR method is followed.

If the value of is greater than or equal to 1, the majority method is followed.

Has a value of If greater, it is determined that the PU occupies the spectrum.

셀과

셀에서의

의 PDF는 각각 수학식 6 및 수학식 7과 같이 나타낼 수 있다.

Cell and

In the cell

PDF may be expressed as Equation 6 and Equation 7, respectively.

와

은 각각

의 평균과 분산이다. here

Wow

Respectively

Is the mean and the variance.

When the PU is using the frequency spectrum, the probability of detecting the PU may be calculated as shown in Equation 8.

는 임계 값을 나타낸다. 수학식 8에서

로 치환하면, 수학식 9와 같이 나타낼 수 있다.here

Represents a threshold value. In equation (8)

If replaced with, it can be expressed as in Equation (9).

Where Q (·) represents the Q function.

Therefore, when the PU does not use the frequency, False Alarm Probability may be calculated as shown in Equation 10.

로 치환하면, 수학식 11과 같이 나타낼 수 있다. In equation (10)

If substituted with, it can be expressed as in Equation (11).

The system designer may calculate a threshold value having a desired false alarm probability by using the equation (10) or (11).

3 is a graph showing a false alarm probability according to a threshold value. The graph of FIG. 3 illustrates the false alarm probability of Equation 10 or 11 according to the change of the threshold value, and a system designer may determine a threshold having a desired false alarm probability using the graph of FIG. 3.

4 is a block diagram illustrating the collection center of FIG. 1. Referring to FIG. 4, the collection center 110 includes an information collecting unit 410 and a determining unit 420.

The information collector 410 collects sensing information for determining whether a PU appears from each spectrum sensor 120.

The determination unit 420 determines whether the PU occupies the radio spectrum based on the collected sensing information. For example, the determination unit 420 adds all of the '1' or '0' values included in the sensing information, and when the addition result is a majority of the number of the spectrum sensors 120 that collected the entire sensing information, the PU itself. It can be judged that it occupies the spectrum of. This method is called Majority method. As another example, an AND method or an OR method may be used. When the sensing information of all spectrums is '1', the PU determines that the PU occupies its spectrum. 1 ', the PU determines that it occupies its spectrum.

5 is a graph illustrating spectrum sensing performance of a cognitive wireless communication system according to a determination method in a number and collection apparatus of spectrum sensors. Here, the false alarm probability is set to 5%. In the case of the OR method, since it is determined that the PU does not occupy the spectrum only when all the sensing information is '0', it can be confirmed that the spectrum sensing performance is improved as the number of the spectrum sensors 120 increases. In contrast, the AND method determines that the PU occupies the spectrum only when all the sensing information is '1', so that the spectrum sensing performance decreases as the number of the spectrum sensors 120 increases. In the case of the majority method, when the signal-to-noise ratio (SNR) is about 3 dB or less, the sensing performance decreases as the number of the spectrum sensors 120 increases, but when the number of the spectrum sensors 120 increases, the sensing increases. Improves performance.

Meanwhile, referring to the graph of FIG. 5, when the number of the spectral sensors 120 reaches a predetermined level or more, the sensing performance is different depending on the determination method of the collection center 110, but the number of the spectral sensors 120 differs from the number of the spectral sensors 120. You can see almost irrelevant. As can be seen in the graph of FIG. 5, since the number of the spectrum sensors 120 is more than a predetermined level, it is almost irrelevant to the sensing performance, the collection center 110 according to an embodiment includes a plurality of spectrum sensors 120 installed. Among them, only a predetermined number of spectrum sensors 120 may be selected and used. In particular, when the collection center 110 selects and uses the spectrum sensors 120 having excellent reception channel quality, the sensing performance may be improved.

In order to select a spectrum sensor, the spectrum sensor 120 may generate sensor selection information and provide the generated sensor selection information to the collection center 110. The sensor selection information may include, for example, information on reception channel quality of the corresponding spectrum sensor 120. Information on reception channel quality may be, for example, received signal strength indication (RSSI). The signal to noise ratio (SNR), the signal to interference and noise ratio (SINR) of the received signal may be included. The SNR may be obtained by a method in which the spectrum sensor 120 receives the pilot signal or training sequence information periodically used by the PU to calculate the SNR of the received signal.

The collection center 110 that receives the sensor selection information together with the sensing information selects a predetermined number of spectrum sensors among the plurality of spectrum sensors 120 based on the sensor selection information. According to an embodiment, the collection center 110 may select the spectral sensors by the predetermined number in order of receiving channel quality (eg, SNR) being excellent. The collection center 110 determines whether the PU occupies the spectrum based only on sensing information collected from the selected spectrum sensors.

Referring back to FIG. 4, the collection center 110 provides a provider 430 which provides the SU with information on whether the spectral region of the PU can be used according to a result of determining whether the PU occupies its spectrum. It may further include.

According to one embodiment, when the collection center 110 determines that the PU is occupying the spectrum, all of the SUs in the cell provide information that the spectral region of the PU is not available, and the PU is not occupying the spectrum. If it is determined, information that the spectral region of the PU can be used can be provided to all SUs in the cell.

According to another embodiment, in order to improve the spectrum usage efficiency, the collection center 110 individually considers the sensing information collected from each spectrum sensor 120 to select the spectral region of the PU according to the position in the corresponding cell of the SU. You can also provide different information about the availability. For example, the collection center 110 may provide information to the SU located at a distance far enough from the PU in consideration of the distance between the PU and the SU, even if the PU occupies the spectrum even though the PU may occupy the spectrum. .

6 is a graph illustrating sensing performance according to a distance between a PU and a spectrum sensor. In this case, the false alarm probability is set to 5% and the signal-to-noise ratio is 0 dB. Referring to the graph of FIG. 6, as the distance from the PU to the spectrum sensor 120 increases, the energy of the received signal received from the PU decreases, so that the probability of the spectrum sensor 120 sensing the spectrum of the PU decreases. have. Therefore, even if the SU is in the cell where the PU exists, using the spectral region of the PU does not matter if the distance from the PU is sufficiently long.

FIG. 7 is a diagram for describing an embodiment in which information that a spectral region of a PU may be used according to a distance between a PU and a SU is differently provided. For example, a predetermined total cell area 710 for determining whether a PU occupies the spectrum by one collection center 110 may be divided into a plurality of small cell areas 720. In the case of FIG. 7, it is assumed that there are 19 small cell regions 720 and the radius of the small cell is 1 km. For example, the collection center 110 may include a first cell region 720a, a second cell region 720b, a third cell region 720c, and a fourth cell region (close to the position of the PU by an OR method). When sensing information indicating that the spectrum has been sensed is collected from the spectrum sensors positioned at 720d, it is determined that the PU occupies the spectrum for the entire cell region 710. However, if the distance of the SU is sufficiently far from the PU, the spectral region of the PU may be used. For example, the collection center 110 may use the small cell regions 720a, 720b, 720c, and 720d in which the spectrum is sensed. The SU located in the 15 small cells of may provide information that the spectral region of the PU can be used. In another example, the collection center 110 estimates the position of the PU based on the information of the small cell regions 720a, 720b, 720c, and 720d from which the spectrum is sensed, and estimates a predetermined threshold distance (for example, from the estimated position of the PU). For example, it is possible to provide the SU located in the small cell regions 720e, 720f, 720g, 720h, 720i, and 720j separated by more than 4km) to use the spectral region of the PU. The location of the PU may be estimated to be located at the midpoint 740 of the small cell regions 720a, 720b, 720c, 720d from which the spectrum is sensed, for example.

The spectral sensor 120 may, for example, identify the spectral sensor 120 or the small cell regions 720 in which the spectral sensor 120 is located to provide the sensing information. A spectrum sensor identifier (or a small cell identifier) may be added and provided. As another example, each sensing information may be identified using a Transmitter Identity (TxID) or an orthogonal code. Examples of orthogonal codes include PN codes, Gold codes, Walsh codes, and Ternary codes. Also, in this case, information about the sensor identifier or the code used is identified in the collection center 110 in which the spectral sensor 120 or the small cell region 720 in which the spectral sensor 120 is located is provided with each sensing information. Do it.

While the system and apparatus disclosed herein have been described with reference to the embodiments shown in the drawings for purposes of clarity of understanding, they are illustrative only and various modifications and equivalent embodiments can be made by those skilled in the art. I will understand that. Accordingly, the true scope of protection of the disclosed technology should be determined by the appended claims.

Claims (18)

A plurality of spectral sensors disposed in an installation space so as to receive wireless signals independently of each other, and generating information for determining whether a primary user (PU) is present through spectrum sensing; And
And a collection center networked with the plurality of spectrum sensors and collecting the information from the plurality of spectrum sensors. The method of claim 1,
Each of the spectral sensors is installed and distributed on an Intelligent Transport System (ITS) period structure,
And the network comprises an ITS network connecting between the ITS period structures. The method of claim 1, wherein the collection center,
And determine whether the PU is occupied by spectrum based on information for determining whether the PU collected from the plurality of spectrum sensors is present. The method of claim 3, wherein the collection center,
A system for cognitive radio communication that determines whether the PU is occupied by integrating information for determining whether the PU collected from the plurality of spectrum sensors is present in an AND, OR, or Majority method. The method of claim 1, wherein each of the spectrum sensors,
Receiving unit for receiving a radio signal from the PU;
An information generator configured to generate information for determining whether a PU including at least one of the strength of the received wireless signal and the strength of the wireless signal is greater than a preset threshold value; And
And a transmitter for transmitting the information generated by the information generator to the collection center. The method of claim 1, wherein the collection center,
An information collecting unit collecting information for determining whether the PU appears from each spectrum sensor; And
And a determination unit to determine whether the PU occupies a radio spectrum based on the collected information. The method of claim 2,
The ITS period structure includes a traffic light,
And when the traffic light is at an intersection, the spectrum sensor is installed only at any one of a plurality of traffic lights at the intersection. The method of claim 1,
The spectrum sensor generates information for sensor selection and provides it to the collection center,
The collection center selects a predetermined number of spectrum sensors among the plurality of spectrum sensors based on the sensor selection information, and based only on information for determining whether the PU collected from the selected spectrum sensors is present. The system for cognitive radio communication to determine whether the PU occupies the spectrum. According to claim 8, The sensor selection information,
A system for cognitive radio communication comprising information about received channel quality of a corresponding spectrum sensor. The method of claim 9, wherein the collection center,
And a spectral sensor is selected by the predetermined number in the order of excellent reception channel quality. The method of claim 9, wherein the information on the reception channel quality,
Information about at least one of Received Signal Strength Indication (RSSI), Signal to Noise Ratio (SNR) of the received signal, and Signal to Interference plus Noise Ratio (SINR). A system for cognitive wireless communication comprising. The method of claim 1, wherein the plurality of spectrum sensors.
A system for cognitive radio communication that performs spectrum sensing when a secondary user (hereinafter referred to as SU) has a spectrum sensing command. The method of claim 1, wherein the collection center,
And identify spectrum sensors that provide information for determining whether the PU is present, and to estimate an area in which the PU is located. The method of claim 3, wherein the collection center,
And provide information to the SU on whether the spectral region of the PU can be used based on whether the PU occupies the spectrum. The method of claim 14, wherein the collection center,
And identifying spectral sensors that provide information for determining whether the PU appears, and otherwise provide information that the spectral region of the PU can be used. The method of claim 14, wherein the collection center,
And provide information that the spectral region of the PU can be used for the SU that is separated from the PU by a distance greater than or equal to a preset threshold even when the PU determines that the PU occupies the spectrum. An information generation unit generating information for determining whether a primary user (PU) is present through spectrum sensing; And
A transmitter for transmitting the information generated by the information generator to a collection center,
Intelligent Transport System (hereinafter referred to as ITS) Spectrum sensors for distributed cognitive radio communication (Cognitive Radio) distributed over the structure, the communication center and the ITS network. An information collector for collecting the information through a communication network from a plurality of spectrum sensors distributed in an installation space so as to receive radio signals independently of each other and generating information for determining whether a PU appears through spectrum sensing. ; And
And a determination unit that determines whether the PU occupies a radio spectrum based on the collected information.

Images