KR101409022B1 - Apparatus for detecting spectrum in multiple antenna system - Google Patents

Abstract

A spectrum detection apparatus of a multi-antenna system includes a plurality of antennas; A plurality of energy detectors disposed in each of the plurality of antennas, the plurality of energy detectors obtaining a plurality of primary decision values from received signals passed through the plurality of antennas; And a detection decision unit for detecting presence or absence of a spectrum using the plurality of primary decision values. The above spectrum detection apparatus can efficiently detect the spectrum of the multi-antenna system and improve the reliability of the multi-antenna system.

A cognitive radio (CR), a spectrum, a spectrum detection, a threshold, an energy detector, a signal-to-noise ratio (SNR)

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a multi-

1 is an exemplary diagram showing a mobile communication system.

2 is a block diagram of a spectrum detection apparatus according to an embodiment of the present invention.

3 is a block diagram of an energy detector according to an embodiment of the present invention.

4 is a graph showing simulation results for one antenna system and multiple antenna system.

5 is a block diagram of a spectrum detection apparatus according to another embodiment of the present invention.

6 is a block diagram of an energy detector according to another embodiment of the present invention.

DESCRIPTION OF REFERENCE NUMERALS OF THE MAIN PARTS OF THE DRAWINGS

210-1, ..., 210-N: antenna

220-1, ..., 220-N: energy detector

230:

310: Bandpass filter

320: Squared

330: integrator

340: threshold value determiner

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to wireless communication and, more particularly, to a spectrum detection apparatus for a multi-antenna system.

Various types of wireless communication technologies that require more and more use in everyday life are rapidly evolving. In particular, services using radio such as mobile communication, WLAN, digital broadcasting, and satellite communication as well as RFID / USN (Radio Frequency Identification / Ubiquitous Sensor Network) and WiBro (Wireless Broadband) are rapidly increasing. The demand for frequency resources with limited resources is rapidly increasing due to the diversification and use of wireless communication services, which are rapidly developing.

Compared to the demand for continuous radio resources, the lack of remaining spectrum and inefficient use of spectrum currently in use. Therefore, a frequency sharing technique that can utilize the unused frequency resources efficiently is being developed. Here, the spectrum refers to available radio resources.

Frequency sharing technology can be widely applied to all fields of wireless service. Among them, a cognitive radio (CR) technology is emerging that can detect idle frequencies that are assigned frequencies but are not actually used, and can be efficiently used and shared. CR technology recognizes various information related to the surrounding wireless environment, and when it detects that the spectrum allocated for other purposes is in the idle state, the idle band is temporarily used by the secondary user while ensuring the priority of the main user of the spectrum Among them, a spectrum detection technique for finding an idle spectrum hole (Hole) is important. Where the primary user is a person who has a license to use the spectrum and the secondary user is someone who does not have a license to use the spectrum.

A multiple input multiple output antenna (MIMO) is a system that improves data transmission / reception efficiency by using multiple transmit antennas and multiple receive antennas. The MIMO technique has a spatial multiplexing technique and a spatial diversity technique. The spatial multiplexing technique can transmit high-speed data without increasing the bandwidth of the system by simultaneously transmitting different data. The spatial diversity technique can achieve the transmit diversity by transmitting the same data in multiple transmit antennas.

MIMO technology can be used for two purposes. First, it can be used for the purpose of increasing the diversity gain to reduce the performance degradation due to the channel fading environment. Secondly, it can be used to increase the data rate in the same frequency band. MIMO technology is advantageous in that it can send more data than single-input single-output (SISO) technology using one transmitting / receiving antenna without increasing frequency bandwidth. Next-generation wireless communication networks require high-speed data transmission speeds (more than 20 Mbps (bit per second)), but MIMO technology is essential to realize this with a limited bandwidth (10 to 20 MHz).

Spectrum detection techniques are rapidly degraded in the presence of channel effects or interference such as fading or shadowing. Therefore, if the spectrum of the main user actually exists but it is determined that the spectrum does not exist, the secondary user uses the spectrum of the main user, thereby interfering with the main user and interfering with the communication. Conversely, if the spectrum of the main user does not actually exist but the spectrum is judged to be present, the secondary user will not use the spectrum of the main user, so that the user will be distracted from the available spectrum, resulting in an inefficient operation. Furthermore, in the case of the MIMO system, there are a plurality of independent channels, and spectrum detection is not easy due to channel influences such as fading for each channel.

An efficient spectral detection technique is needed in MIMO systems.

SUMMARY OF THE INVENTION The present invention is directed to an apparatus for detecting a spectrum in a multi-antenna system.

According to an aspect of the present invention, a spectrum detection apparatus includes a plurality of antennas; A plurality of energy detectors disposed in each of the plurality of antennas, the plurality of energy detectors obtaining a plurality of primary decision values from received signals passed through the plurality of antennas; And a detection decision unit for determining presence / absence of a spectrum using the plurality of primary decision values.

According to another aspect of the present invention, a spectrum detection apparatus includes a first antenna; A second antenna; A first energy detector receiving a first reception signal having passed through the first antenna and measuring the energy of the first reception signal and outputting a first determination value; A second energy detector for receiving a second reception signal having passed through the second antenna and measuring the energy of the second reception signal and outputting a second decision value; And a detection decision unit receiving the first decision value and the second decision value and judging presence or absence of a spectrum received by the first antenna and the second antenna.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Like reference numerals designate like elements throughout the specification.

1 is an exemplary diagram showing a mobile communication system.

Referring to FIG. 1, a mobile communication system includes a base station (BS) 110 and a plurality of UEs (UEs) 120. The mobile communication system is widely deployed to provide various communication services such as voice, packet data, and the like.

A base station 110 generally refers to a fixed station that communicates with a terminal 120 and may be referred to in other terms such as a node-B, a base transceiver system (BTS), an access point, Can be called.

The terminal 120 may be fixed or mobile and may be referred to by other terms such as a mobile station (MS), a user terminal (UT), a subscribers station (SS), a wireless device,

The base station 110 communicates with a plurality of terminals 120 and the plurality of terminals 120 includes a main user 120-1 and a secondary user 120-2, The secondary user 120-2 is a person who communicates with the base station 120 at the frequency of the corresponding band and the secondary user 120-2 temporarily communicates the frequency of the idle band when the main user 120-1 does not communicate at the frequency of the corresponding band He is the one who does. At this time, the base station 110 and the terminal 120 have a multi-antenna structure, and the spectrum detection apparatus of the multi-antenna system may be the base station 110 or the terminal 120.

2 is a block diagram of a spectrum detection apparatus according to an embodiment of the present invention.

2, the spectrum detecting apparatus 200 includes an antenna 210-1, ..., 210-N, energy detectors 220-1, ..., 220-N, and a detection determining unit 230, .

The antennas 210-1, ..., 210-N receive an external signal. Here, the external signal includes a mobile communication signal, a digital communication signal, and a satellite communication signal.

The energy detectors 220-1 to 220-N are respectively disposed in the antennas 210-1 to 210-N, and the antennas 210-1 to 210- The presence or absence of the spectrum is first detected from the received signal. Suppose that the output of each energy detector 220-1, ..., 220-N is H ⁱ ₀ or H ⁱ ₁ ( ₁ ? _I ? N), the superscript of H is the energy detectors 220-1,. .., 220-N), and the subscript "0" represents a case where the spectrum of the corresponding band does not exist, and the subscript "1" represents a case where the spectrum of the corresponding band exists. That is, the output of the i H ⁱ energy detector is a non-detection H ⁱ ₀ when the spectrum of the band does not exist, and the detection H ⁱ ₁ in the case of the spectrum of the band exists.

The detection determination unit 230 determines the presence or absence of a spectrum using the primary result values (H ¹ , H ² , ..., H ^N ) obtained from the energy detectors 220-1, Secondarily. That is, the detection determination unit 230 performs the secondary detection determination by combining the detection information (H ⁱ ₀ or H ⁱ ₁ ) obtained from the energy detectors 220-1 to 220-N. Hereinafter, H ^f ₀ denotes the case where the spectrum of the corresponding band does not exist, and H ^f ₁ denotes the case where the spectrum of the corresponding band exists. At this time, various algorithms can be employed for secondary detection.

In one embodiment, the number of detected H ⁱ ₁ (or non-detected H ⁱ ₀ ) among the N primary results may be compared with a reference value K (1? K? N) to make a secondary detection decision. For example, if the number of H ⁱ ₁ among the first-order result values is equal to or greater than the reference value K, the secondary detection determines that the spectrum of the corresponding band exists (H ^f ₁ ). Or if the number of H ⁱ ₀ among the primary result values is equal to or greater than K reference values, the secondary detection determines that the spectrum of the corresponding band does not exist (H ^f ₀ ).

At this time, the reference value K can be changed according to the required reliability. If you want high reliability, increase K value. If low reliability is required, decrease K value. The term reliability refers to a low detection probability and a false alarm probability. The higher the reliability, the higher the detection probability by increasing the value of K, and the lower the probability of non-detection to be. Here, the Miss detection probability refers to a probability that a spectrum is present but does not exist in the corresponding frequency band. False alarm probability refers to the probability that a spectrum is present even if there is no spectrum in the frequency band.

In another embodiment, the total number of undetected H ⁱ _{0 and} the total number of detected H ⁱ ₁ among the N primary results are compared and the secondary detection can be performed to the larger number. For example, if there are eight energy detectors in total, the total number of undetected H ⁱ ₀ is 5, and the total number of detected H ⁱ ₁ is 3, then the spectrum of the corresponding band (H ^f ₀ ) .

Table 1 shows an example of determining the presence or absence of spectrum (H ^f ₀ or H ^f ₁ ).

The first energy detector The second energy detector The third energy detector The detection determination unit

H ¹ ₀
H ² _O H ³ ₀ H ^f ₀ H ³ ₁ H ^f ₀
H ² 1 H ₀ ³ H ^f ₀ H ³ ₁ H ^f ₁

H ¹ ₁
H ² _O H ³ ₀ H ^f ₀ H ³ 1 H ^f ₁
H ² ₁ H ³ ₀ H ^f ₁ H ³ ₁ H ^f ₁

Considering table 1, the first output of the energy detector is H ¹ ₀ and the second output of the energy detector is H ² _0, and the third output of the energy detector in the case of H ³ _1, the number of non-detection H ₀ detected detection decision output of so many more number of H ₁ is a H ^f _0.

3 is a block diagram of an energy detector according to an embodiment of the present invention.

3, the energy detector 300 includes a band pass filter 310, a squarer 320, an integrator 330, and a threshold device 340. [ Here, the energy detector 300 corresponds to each of the energy detectors 220-1, .., 220-N of FIG.

The band-pass filter 310 outputs a signal belonging to a certain frequency band among the reception signals. That is, a center frequency belonging to a certain frequency band is selected to determine the bandwidth.

Squarer 320 squares the frequency band signal.

The integrator 330 integrates the squared frequency band signal of the squarer by the observation time and outputs the reception energy E _n . For example, the observation time can be from 0 to T.

The threshold value determiner 340 compares the received energy E _n output from the integrator 330 with a threshold value E _c to determine whether a spectrum exists. That is, the reception energy (E _n) is the threshold value (E _C) is smaller than is not the spectrum in the band of presence (H _0), opposed to the reception energy (E _n) is the threshold value (E _C) is greater than has There is spectrum in that band. (H ₁ )

For each energy detector disposed in each of the multiple antennas, the threshold may be set equal. Alternatively, the threshold value may be set not to be the same for each energy detector. If the threshold values are set not to be the same, the threshold value can be set using the additional information received from each antenna. If the channel state is not good according to the channel information estimated using the pilot signal, the received data and the estimated information of the control channel signal as the additional information received from each antenna, the spectrum detection probability can be increased by lowering the threshold, The probability of spectrum detection can be increased by increasing the threshold value. Alternatively, an ACK (Acknowledgment) / NACK (Non-Acknowledgment) signal used in the error detection technique can be used as the additional information. If the ACK signal is received and the channel state is good, the probability of spectrum detection can be increased by raising the threshold. On the contrary, when the NACK signal is received, if the channel state is bad, the spectrum detection probability can be increased by lowering the threshold value. Here, the ACK signal is a signal indicating that transmission has been correctly received, and the NACK signal is a signal indicating that transmission has not been correctly received. And may use the channel quality indicator (CQI) information received as the additional information. According to the CQI information, when the channel state is not good, the spectrum detection probability can be increased by lowering the threshold value. If the channel state is good, the spectrum detection probability can be increased by increasing the threshold value.

4 is a graph showing simulation results for one antenna system and multiple antenna system. In case of using Rayleigh channel with 10dB SNR and 15dB SNR and using one antenna with fixed threshold and 3 detection antennas with fixed threshold, ) And a false alarm probability. At this time, the condition of the Rayleigh channel is applied while the terminal moves at 3 km / h.

Referring to FIG. 4, it can be seen that the SNR of 15 dB is lower than that of SNR of 10 dB, and the detection probability and the false alarm probability are lower than that of SNR of 10 dB. . According to the proposed method, the probability of correct detection in multiple antennas with high SNR is increased.

5 is a block diagram of a spectrum detection apparatus according to another embodiment of the present invention.

5, the spectrum detecting apparatus 500 includes antennas 210-1 to 210-N, energy detectors 520-1 to 520-N, and a detection determining unit 530, .

The antennas 210-1, ..., 210-N receive an external signal. The energy detectors 520-1 to 520-N receive the reception energy E ₁ , ..., E-N from the reception signals that have passed through the antennas 210-1 to 210- _n ). Detection determining unit 530 by using the N reception energy _{(E 1, ..., E n} ) and determines the presence or absence of spectrum secondarily.

N reception energy detected in decision 530 There are various methods to determine the presence or absence of the spectrum can be used by using the _{(E 1, ..., E n} ). For example, the average value E _avg of the N received energies E ₁ , ..., E _n is calculated, and the average value is compared with the average threshold E _c of the detection determining unit 530 It is judged whether or not it exists. That is, if the average value E _avg is smaller than the average threshold value E ' _c , it is determined that the spectrum of the corresponding band does not exist (H ^f ₀ ). If the average value E _avg is smaller than the average threshold value E ` <sub>c</sub> ), it is judged that the spectrum of the corresponding band exists (H <sup>f</sup> <sub>1</sub> ). As another example, to obtain the standard deviation (σ) and average value (E <sub>avg)</sub> of N received energy <sub>(E 1, ..., E n</sub> ), except for the received energy exceeds the standard deviation value based on the average value. That is, if La E <sub>avg</sub> ± σ one Q output of the energy detector with the received energy in the range (Q≤N), comparing the average value of Q of the received energy to the average threshold value (E` _c) of the sensing determiner 530 Thereby determining whether or not the spectrum exists. In other words, the average value is above a certain threshold (E` <sub>c)</sub> is smaller than that determined by the spectrum of the band does not exist (H <sup>f</sup> <sub>0),</sub> and that the mean value is greater than the predetermined threshold value (E` _c) the band (H ^f ₁ ).

6 is a block diagram of an energy detector according to another embodiment of the present invention.

Referring to FIG. 6, the energy detector 600 includes a bandpass filter 310, a squarer 320, and an integrator 330. Here, the energy detector 600 corresponds to each of the energy detectors 520-1 to 520-N in FIG.

The bandpass filter 310 outputs a signal belonging to a certain frequency band, the squarer 320 squares the frequency band signal, and the integrator 330 observes the squared frequency band signal of the squarer And outputs the reception energy E _N.

All of the functions described above may be performed by a processor such as a microprocessor, a controller, a microcontroller, an application specific integrated circuit (ASIC), etc. according to software or program code or the like coded to perform the function. The design, development and implementation of the above code will be apparent to those skilled in the art based on the description of the present invention.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the invention. You will understand. Therefore, it is intended that the present invention covers all embodiments falling within the scope of the following claims, rather than being limited to the above-described embodiments.

As described above, according to the present invention, spectrum can be efficiently detected in a multi-antenna system, and reliability of a multi-antenna system can be improved. This will be the basis for secondary users (license-free users) to reliably use the spectrum of the primary user (licensed user).

Claims (7)

1. A spectrum detector for a multi-antenna system, N antennas; An energy detector for receiving N received signals having passed through the N antennas, measuring energy of each of the N received signals and outputting N first presence / absence information; And And a detection decision unit for determining presence or absence of a secondary spectrum based on the number of detection (H1) or the number of undetected (H0) among the presence or absence of N primary spectrums. The method according to claim 1, The energy detector is comprised of N energy detectors, A band-pass filter for outputting a constant frequency band signal among the received signals; A squarer for squaring the frequency band signal; An integrator for integrating a frequency band signal obtained by squaring the squared signal by an observation time and outputting reception energy EN; And And a threshold determiner for comparing the received energy (EN) with a threshold value (Ec) and outputting detection (H1) or non-detection (H0) as a corresponding decision value. The method according to claim 1, Wherein the detection determination unit compares at least one of the number of the detection (H1) and the number of the non-detection (H0) with a reference value to determine the presence or absence of the secondary spectrum, Wherein the reference value is changeable according to a required reliability. The method according to claim 1, Wherein the detection determination unit compares an average value of the energy of the N received signals with a reference value to determine whether the secondary spectrum exists, Wherein the reference value is changeable according to a required reliability. delete delete delete

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