JP6105962B2 - Interference amount estimation apparatus, communication apparatus, and control method - Google Patents

Description

  The present invention relates to an interference amount estimation technique.

  In mobile communication, communication is usually performed by transmitting and receiving radio signals between a base station and a mobile terminal using a predetermined frequency band. Therefore, communication is possible when the mobile terminal can receive the radio wave transmitted by the base station and the base station can receive the radio wave transmitted by the mobile terminal. Here, radio waves are attenuated by the propagation distance and shielding objects, and considering that there is a physical or legal limit in the transmission power of signals from base stations and mobile terminals, the radiated signals can be received normally. There may be a geographical area where the received signal power drops to an inadequate power level. Similarly, there may be geographical areas where the radiated power is not normally received at the counterpart device.

  In conventional mobile communication using a frequency band having a relatively low center frequency, many base stations are installed so that such a geographical area becomes as narrow as possible. However, in recent years when demand for high-speed communication is increasing, it is necessary to use a frequency band with a high center frequency, and due to the attenuation characteristics and straightness of the radio waves, there are areas where surface coverage is difficult. Yes.

  However, for example, in a region where radio waves from the base station do not reach, even if the mobile terminal transmits radio waves, it does not reach the base station, that is, the transmission signal does not interfere with the base station. Similarly, in a region where radio waves from other mobile terminals do not reach, it is considered that the other mobile terminals do not interfere. In such a region, it can be considered that the frequency band and time resources that radio waves do not reach are not used (that is, “free”). Therefore, a mobile terminal existing in such a region directly transmits / receives a signal to / from another mobile terminal using at least one of a frequency band and a time resource used for communication with the base station. It is considered possible.

  In this way, direct communication between mobile terminals is performed using at least one of frequency resources and time resources that are vacant in some areas so as not to interfere with the base station and other mobile terminals. Thus, the frequency band can be effectively used.

W. A. Gardner, “Cyclostationarity in Communications and Signal Processing”, IEEE Press, New York, USA, 1993. M.M. Oner and F.M. Jondral, “Air interface recognition for software and radiology system exploration cy- posal system symptoms of the air interface for software radio systems.” 3, pp. 1947-951, September 2004

  When performing inter-terminal communication directly using at least one of a free frequency resource and a time resource, it is important to be able to estimate the amount of interference received from other communications and the amount of interference given to other communications. This is because when the mobile terminal transmits a signal and gives strong interference to other communications, the throughput of the entire system can be affected. Estimation of the amount of interference and the amount of interference can be achieved by the mobile terminal measuring the received signal strength. However, for example, when a large number of mobile terminals execute inter-terminal communication at various locations, interference increases and increases, so even a sufficiently low power signal (for example, a signal with a power below a noise level) can be obtained. Can affect communications. Therefore, there is a need for a technique for estimating how much interference is generated even with such low power interference.

  The present invention has been made in view of the above problems, and an object of the present invention is to make it possible to estimate the power even when the interference is sufficiently small.

In order to achieve the above object, a power estimation apparatus according to the present invention estimates at least any interference amount of interference provided from a received signal to another communication apparatus and interference received from another communication apparatus in the communication apparatus. An interference amount estimation device, for the received signal, calculates a feature amount based on a known signal or a feature amount based on autocorrelation over a predetermined number of samples while changing a time interval or frequency to be calculated, The power of the received signal is estimated from the calculation means for calculating the ratio between the peak value of the feature amount and the value other than the peak, and the ratio and the predetermined number of samples, and the interference amount is estimated from the power And estimating means.

  According to the present invention, even an interference signal with sufficiently small power can be estimated.

The conceptual diagram which shows a radio | wireless communication network in case two mobile terminals are contained in a vacant frequency area | region. The conceptual diagram which shows a radio | wireless communication network in case only one mobile terminal is contained in a vacant frequency area | region. The conceptual diagram which shows a radio | wireless communication network when there is no vacant frequency area | region. The block diagram which shows the hardware structural example of an interference amount estimation apparatus. The block diagram which shows the function structural example of an interference amount estimation apparatus. The figure which shows the concept of correlation detection. The figure which shows the concept of the feature-value by periodic steadiness. The figure which shows the relationship between the ratio of the peak value of a feature-value at the time of using a preamble by simulation, and the non-peak value ratio, and the signal power. The figure which shows the relationship between the ratio of the peak value of a feature-value at the time of using cyclic prefix (CP) by simulation, and the ratio of the non-peak value, and the electric power of a signal.

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

(Configuration of wireless communication system)
FIG. 1 shows a wireless communication network including one or more base stations and mobile terminals. In a region where radio waves are not received at a predetermined power or higher and are in an idle frequency state, two mobile terminals are directly wireless. This shows a state where communication is performed. In FIG. 1, in a network 100 formed by a base station 101, a mobile terminal 111 and a mobile unit are in a region 110 where the base station 101 and a mobile terminal 102 communicating with the base station 101 are not received with a predetermined power or more. The terminal 112 is in direct communication. Hereinafter, a region such as the region 110 where a radio wave is not received at a predetermined power or higher between the mobile terminal and the base station 101 and the mobile terminal 102 is referred to as a “free frequency region”. Further, FIG. 1 shows a communication device that performs communication by a solid arrow, and shows that a signal does not reach with a power higher than a predetermined power between communication devices without an arrow.

  1 shows a case where two mobile terminals directly communicate with each other in a network including one or more base stations 101 and one mobile terminal 102, but the present invention is not limited to this. Any case may be used as long as the two mobile terminals perform direct communication using a predetermined frequency band used for communication between a plurality of other communication apparatuses.

  As shown in FIG. 1, when both the mobile terminal 111 on the transmission side and the mobile terminal 112 on the reception side exist in the free frequency region 110, the base station 101 and the mobile terminal can be moved regardless of how signals are transmitted and received. It is considered that the body terminal 102 does not interfere. Therefore, the mobile terminal 111 and the mobile terminal 112 can perform direct wireless communication by freely using time resources and frequency resources.

  However, for example, as shown in FIG. 2, when only the mobile terminal 111 exists in the vacant frequency region 110, the signal transmitted by the mobile terminal 112 is transmitted to other communication devices (base station 101 and mobile terminal 102). have a finger in the pie. Further, signals transmitted by other communication apparatuses (base station 101 and mobile terminal 102) interfere with mobile terminal 112. Similarly, as shown in FIG. 3, when both the mobile terminal 111 and the mobile terminal 112 are not included in the vacant frequency region, between the mobile terminal 111 and the mobile terminal 112 and other communication devices. Interference occurs. 2 and 3 both show that interference is caused by broken line arrows.

  Therefore, in the case of FIG. 2 and FIG. 3, in order to check whether communication between terminals is possible or to determine whether to give interference to other communication apparatuses, the mobile terminal 111 and the mobile terminal The body terminal 112 needs to constantly monitor the power of the interfering signal and the interfered signal. The “interference signal power” here includes not only the power of a pure signal but also the carrier-to-noise ratio (C / N) or signal-to-noise ratio (S / N) of the interference signal, The interference power further includes a carrier-to-interference ratio (C / I) or a signal-to-interference ratio (S / I). The amount of interference can be considered as the power of the received interference signal itself, and the amount of interference can be considered to be almost equal to the reception power of the interference signal.

  Here, when inter-terminal communication is performed between a large number of terminals, as a result of the accumulation of interference, for example, a large amount of interference may be given to the base station 101 or the mobile terminal 102. In addition, especially when using a high frequency band with high straightness, if radio waves are blocked by buildings etc. with other communication devices, the amount of interference and the amount of interference will be reduced by a small amount of movement. Both can be expected to increase significantly. On the other hand, for example, by setting the limits of the amount of interference and the amount of interference to be sufficiently low power below the noise level, it is possible to protect both the communication between terminals and the communication between other communication devices. Therefore, it is important to find a weak signal and estimate the power of the signal.

  In this embodiment, in order to estimate the amount of interference, the correlation of the signal is used, and the power of the interference signal is estimated based on the correlation peak and the correlation values in other regions. Hereinafter, an interference amount estimation apparatus that estimates this interference amount will be described in detail.

(Hardware configuration of interference estimation device)
FIG. 4 is a block diagram illustrating a hardware configuration example of the interference amount estimation apparatus 400. As illustrated in FIG. 4, the interference amount estimation apparatus 400 includes, for example, a CPU 401, a ROM 402, a RAM 403, an external storage device 404, and a communication device 405. The interference amount estimation apparatus 400 is provided in a communication apparatus such as a mobile terminal.

  In the interference amount estimation apparatus 400, for example, the CPU 401 executes a program that realizes each function of the interference amount estimation apparatus 400 shown below, which is recorded in any of the ROM 402, the RAM 403, and the external storage device 404. Then, the interference amount estimation apparatus 400 acquires a reception signal through the communication apparatus 405, and estimates the power of the interference signal included in the reception signal. In addition, the interference amount estimation apparatus 400 may include a plurality of communication apparatuses 405 in order to monitor signals corresponding to, for example, uplink and downlink frequencies or a plurality of communication systems.

  The interference amount estimation apparatus 400 may include dedicated hardware that executes each function described below, or a part is executed by hardware and the other part is executed by a computer that operates the program. May be. Further, all the following functions may be executed by a computer and a program.

(Functional configuration and operation of interference estimation device)
FIG. 5 is a block diagram illustrating a functional configuration example of the interference amount estimation apparatus 400. The interference amount estimation apparatus 400 includes, for example, a radio signal acquisition unit 501, a feature amount calculation unit 502, and an interference amount estimation unit 503 as functions. The interference amount estimation apparatus 400 may further include a calculated feature amount switching unit 504. Hereinafter, the operation of the interference amount estimation apparatus 400 will be described together with the description of each functional block.

[Radio signal acquisition unit 501]
The wireless signal acquisition unit 501 receives and acquires a wireless signal via an antenna (not shown). Here, the “radio signal” includes a radio signal having a level equal to or lower than noise. Therefore, a waveform that can be acquired from an antenna over a predetermined period regardless of whether there is a significant signal from which data can be acquired by demodulation is referred to as a “radio signal”. In addition, although the radio signal acquired here shall be sampled, the signal before sampling may be sufficient.

[Feature amount calculation unit 502]
The feature amount calculation unit 502 calculates a feature amount for the wireless signal acquired by the wireless signal acquisition unit 501. For example, when a known signal (for example, preamble) is included in the interference amount estimation apparatus 400 in the radio signal, correlation detection is performed using the waveform of the known signal to calculate a feature amount. In this case, the radio signal acquisition unit 501 acquires a radio signal having a time length sufficiently longer than a known signal time length.

  FIG. 6 shows a conceptual diagram of correlation detection using a known signal. In the correlation detection, a predetermined time interval having the same time length as the known signal is extracted from the acquired wireless signal, and the correlation between the extracted wireless signal and the waveform of the known signal is calculated. The feature amount calculation unit 502 extracts radio signals while changing the time interval, and executes correlation detection for each. Then, the feature amount calculation unit 502 uses the magnitude of the correlation value (scalar value or square value) as the feature amount, and specifies the timing at which the peak of the feature amount appears.

  If the preamble has good autocorrelation characteristics, a correlation peak appears when the timing of the time interval for correlation calculation matches the timing of the preamble, and for time intervals where the timing does not match, The value is low. For example, as shown in FIG. 6, the correlation value is low in time interval 1 and time interval 3, but a sufficiently high peak is detected for time interval 2. Therefore, in the example of FIG. 6, the feature amount calculation unit 502 specifies the timing of the time interval 2 (for example, the start timing of the time interval) as the correlation peak timing.

  Next, the feature amount calculation unit 502 calculates a ratio between the peak value of the feature amount and the average value of values other than the peak. Explaining using the example of FIG. 6, the ratio between the peak value of the correlation value at the timing of the correlation peak and the average value of the correlation value in the period other than the peak is calculated. Here, the average value of the correlation value in the period other than the peak is the sum of the correlation values in the period other than the peak, which is obtained by subtracting 1 from the number of time intervals in which the correlation value is calculated (the time when the peak is obtained). Divided by the number excluding the interval).

が、サイクリックプリフィックスの周期をＴ_cpとするときに、α＝Ｍ／Ｔ_cp及びｆ＝Ｎ／Ｔ_cpにおいて、相関ピークを有する。ここで、ＭとＮは整数である。なお、この関数で表される特徴を周期定常性の特徴と言う（非特許文献１参照）。 On the other hand, the feature amount calculation unit 502 calculates a feature amount based on the autocorrelation of a wireless signal for a wireless signal that does not include a known signal. This utilizes the fact that a characteristic occurs in a waveform in the modulation signal, unlike noise. For example, a signal using a cyclic prefix (guard interval) such as an OFDM signal has a peak at a frequency corresponding to the reciprocal of the cyclic prefix period. That is, when the radio signal is x (t) and the complex conjugate is indicated by the superscript *, the function

But the period of the cyclic prefix when the T _cp, at α = M / T _cp and f = N / T _cp, has a correlation peak. Here, M and N are integers. The feature represented by this function is referred to as a periodic steadiness feature (see Non-Patent Document 1).

  Here, the concept of the magnitude of the calculation result when α is varied with respect to one f is shown in FIG. The feature of the periodic stationarity is that a peak is generated only for a signal without generating a peak for noise by calculating a signal having a sufficiently long time length. Therefore, a peak occurs at a specific frequency as shown in FIG. 7 by performing the above calculation for a sufficiently long radio signal. In the above description, a signal having a cyclic prefix has been described. However, even a signal other than this has a characteristic of periodic steadiness, and therefore, a similar method can be applied (Non-Patent Document 2). reference).

  Subsequently, the feature amount calculation unit 502 calculates a ratio between the peak value of the feature amount and the average value of values other than the peak from the value calculated as in the above equation. That is, the ratio of the magnitude (scalar value or square value) of the calculated value for the frequency at which the peak appears (peak frequency) and the average value of the calculated values for the other frequencies is calculated. .

  As shown in FIG. 7, a signal having a cyclic prefix has a peak not only at the frequency obtained by the reciprocal of the cyclic prefix period, but also at an integer multiple of the frequency. For this reason, the magnitudes of the calculated values at these frequencies may be added and the average value may be treated as the peak value. Also, the ratio between the peak value and the other value can be calculated by dividing the sum of the calculated values at a predetermined number of peak frequencies by the sum of the calculated values at frequencies other than the same number of peaks. Good. Note that the ratio value can be stabilized by calculating the ratio using a plurality of peak values in this way.

  Note that the peak of the periodic steadiness feature is determined by the cyclic prefix period, that is, the position where the peak determined by the communication system signal specifications appears. Therefore, the feature value calculation unit 502 determines the average value of the peak (the feature value at the frequency position where the peak should appear) and the value of the feature value other than the peak, regardless of whether or not the peak actually appears. The ratio may be calculated. Also, in the case of correlation detection using a known signal waveform, if the time during which the known signal waveform is to be received is determined by the specifications of the signal of the communication system, the feature amount calculation unit 502 performs the correlation at that time. A ratio between the value and the average value of the correlation values at other times may be calculated.

  The feature amount calculation unit 502 transfers the ratio between the peak value of the feature amount and the value other than the peak calculated as described above to the interference amount estimation unit 503.

[Interference amount estimation unit 503]
The interference amount estimation unit 503 estimates the interference amount based on the ratio between the peak value of the feature amount acquired from the feature amount calculation unit 502 and the value other than the peak. Specifically, the relationship between the value indicating the power of the signal such as the carrier-to-noise ratio (C / N) and the ratio of the above-described feature amount obtained in that case is obtained in advance by computer simulation or the like. The signal power is estimated according to the result. FIG. 8 and FIG. 9 respectively show the carrier-to-noise ratio of the signal and the ratio between the peak value and the non-peak value of the feature amount when the preamble (known signal) is used and when the cyclic prefix is used. It is the result of the simulation which calculated | required the relationship. It should be noted that the simulation result varies depending on the number of samples used for calculating the feature amount. 8 and 9, the value on the vertical axis is obtained by using the square value of the correlation value with a known signal and the value calculated by the above formula as the feature amount, or by using a scalar value as the feature amount. It depends on whether the size is used. That is, when the scalar value is used, the value on the vertical axis is halved as compared with the case where the square value is used.

  For example, when the feature amount ratio is obtained using the preamble, the interference amount estimation unit 503 calculates the carrier-to-noise ratio of the interference signal included in the wireless signal with reference to the relationship of FIG. For example, when the feature amount ratio is 10 dB, it can be estimated that the radio signal includes a signal having a carrier-to-noise ratio of −16 dB. Therefore, in this case, the interference amount estimation unit 503 can obtain an interference amount estimation result of −16 dB in the carrier-to-noise ratio.

  Similarly, the interference amount estimation unit 503 calculates the carrier-to-noise ratio of the interference signal included in the radio signal with reference to the relationship in FIG. To do. For example, when the feature amount ratio is 5 dB, it can be estimated that the radio signal includes a signal having a carrier-to-noise ratio of −6 dB. Accordingly, in this case, the interference amount estimation unit 503 can obtain an interference amount estimation result of −6 dB in the carrier-to-noise ratio.

  In the description here, the method of estimating the interference amount has been described using the graphs of FIGS. 8 and 9, but actually, the interference amount estimation unit 503 may store this relationship as a table. Good. In this case, since the feature amount ratio is calculated only for some carrier-to-noise ratios in the simulation, the feature amount ratio values included in the table are considered to be discrete. In this case, the interference amount estimation unit 503 may obtain the interference amount with respect to the feature amount ratio obtained from the received signal by interpolation from the value included in the table, or the closest feature amount ratio value included in the table. It is good also as interference amount with respect to. Thus, the structure which calculates | requires interference amount with reference to the table using a table can obtain easily the interference amount with respect to ratio of a feature-value.

[Calculated feature amount switching unit 504]
The calculated feature amount switching unit 504 switches the feature amount to be calculated by the feature amount calculating unit 502 depending on the case. Note that the calculated feature amount switching unit 504 may be included in the feature amount calculating unit 502, or may not be provided when all feature amounts that can always be calculated are calculated.

  For example, in the configuration as shown in FIG. 2 or FIG. 3, the base station 101 transmits a signal including a known signal, and the mobile terminal 102 transmits a signal not including a known signal. At this time, when the mobile terminal 112 transmits and receives a signal at the timing and frequency at which the base station 101 transmits a signal, the mobile terminal 112 does not interfere with the base station 101, but does not interfere with the base station 101. Yes. The mobile terminal 102 does not transmit a signal at the timing and frequency at which the base station 101 transmits a signal while the base station 101 transmits the signal. In this case, the mobile terminal 112 only needs to consider the signal from the base station 101 as the interfered. Therefore, in such a case, the calculated feature amount switching unit 504 of the interference amount estimation apparatus 400 included in the mobile terminal 112 obtains a known signal from the feature amount calculation unit 502 when obtaining the interference amount of interference. Based on this, the feature amount is calculated.

  On the other hand, in such a case, when the mobile terminal 112 transmits a signal at the timing and frequency at which the base station 101 transmits a signal, the signal can interfere with the mobile terminal 102. Therefore, when obtaining interference, the feature amount calculation unit 502 of the interference amount estimation apparatus 400 included in the mobile terminal 112 is caused to calculate, for example, a feature amount based on the periodic continuity as described above. Note that the interference amount estimation apparatus 400 included in the mobile terminal 112 estimates that the interference amount of the interference gives the same amount of interference as the interference amount received from the mobile terminal 102 by the mobile terminal 112. Thereby, the amount of interference can be easily estimated.

  Here, when estimating the amount of interference, for example, the feature amount based on the periodic steadiness is calculated, and when estimating the interfered, the feature amount based on a known signal is calculated. Depends on the communication method used. That is, in a wireless communication system that does not use any known signal such as a preamble, a feature value based on, for example, periodic stationarity may be calculated for both interference and interference. When interference can be given to the base station 101, a feature amount based on a known signal may be calculated for estimating the amount of interference.

  As described above, the calculated feature amount switching unit 504 calculates an appropriate feature amount depending on the case. Accordingly, since all the feature quantities that can be calculated are not always calculated, useless processing can be omitted and the processing amount can be reduced.

  As described above, the interference amount estimation apparatus 400 calculates the ratio between the peak value and the non-peak value of the feature amount for the received radio signal, and detects a signal having an intensity equal to or lower than the noise level based on the ratio. It becomes possible to do. This makes it possible to estimate the amount of interference and the amount of interference in detail. For example, the mobile terminal 111 and the mobile terminal 112 have both the estimated interference amount and interference amount of interference to be less than a predetermined value. If it is, it can be determined that it exists in the free frequency region. Therefore, the mobile terminal 111 and the mobile terminal 112 can perform inter-terminal communication at an appropriate timing and position.

Claims (11)

In a communication device, an interference amount estimation device that estimates an interference amount of interference given from a received signal to another communication device and interference received from another communication device,
With respect to the received signal, a feature amount based on a known signal or a feature amount based on autocorrelation is calculated over a predetermined number of samples while changing a time interval or a frequency to be calculated, and a peak value of the feature amount is calculated. A calculation means for calculating a ratio with a value other than the peak;
Estimating means for estimating the power of the received signal from the ratio and the predetermined number of samples , and estimating the amount of interference from the power ;
An interference amount estimation apparatus characterized by comprising: The estimation means estimates the amount of interference corresponding to the ratio and the predetermined number of samples using a table indicating a relationship between the ratio and the predetermined number of samples and the power of the received signal .
The interference amount estimation apparatus according to claim 1, wherein: The estimating means estimates an interference amount for the received signal as an interference amount for the given interference;
The interference amount estimation apparatus according to claim 1 or 2, wherein The feature amount based on the known signal is a correlation value between the known signal and the received signal.
The interference amount estimation apparatus according to any one of claims 1 to 3, wherein The received signal includes a cyclic prefix;
The feature quantity based on the autocorrelation is a periodic stationary feature quantity based on the cyclic prefix.
The interference amount estimation apparatus according to claim 1, wherein: The calculating means calculates the peak value of the feature value as a sum of the value of the feature value at a frequency obtained by reciprocal of the cyclic prefix period and an integer multiple of the frequency.
The interference amount estimation apparatus according to claim 5. The calculation means calculates a feature amount based on the autocorrelation when estimating an interference amount of the interference.
The interference amount estimation apparatus according to any one of claims 1 to 6, wherein The calculating means calculates a feature amount based on the known signal when estimating the interference amount of the interfered;
The interference amount estimation apparatus according to claim 1, wherein: The interference amount estimation apparatus according to any one of claims 1 to 8,
A communication device. When the interference amount estimated by the interference amount estimation device is less than a predetermined value, it further includes a determination unit that determines that the interference amount is not present and is present in a region that is not affected.
The communication apparatus according to claim 9. In the communication apparatus, an interference amount estimation method in an interference amount estimation apparatus that estimates at least one interference amount of interference given from a received signal to another communication apparatus and interference received from another communication apparatus,
A calculation means calculates a feature amount based on a known signal or a feature amount based on autocorrelation for the received signal over a predetermined number of samples while changing a time interval or a frequency to be calculated, and A calculation step of calculating a ratio between a peak value and a non-peak value;
An estimation unit estimates the power of the received signal from the ratio and the predetermined number of samples , and estimates the amount of interference from the power ;
An interference amount estimation method characterized by comprising:

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