Reception device, radio communication terminal, radio base station, and reception method

A reception device 10 includes a channel estimator 130 configured to calculate channel estimation information for each of first to fourth known signals, the channel estimation information indicating estimation of a characteristic of a channel of the radio signal and an SNR estimator 150 configured to interpolate channel estimation information on an intersection by using the channel estimation information on each of the first known signal and the fourth known signal, the intersection being where a line joining the first known signal and the fourth known signal intersects with a line joining the second known signal and the third known signal, and to interpolate channel estimation information on the intersection by using the channel estimation information on each of the second known signal and the third known signal, and to calculate noise power of the radio signal on the basis of a difference between the interpolated two channel estimation information.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a U.S. National Phase Application of International Application No. PCT/JP2008/066783 filed Sep. 17, 2008, which claims priority to Japanese Patent Application No. 2007-255815 filed Sep. 28, 2007, the disclosures of which are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a reception device, a radio communication terminal, a radio base station, and a reception so method for receiving a radio signal including multiple known signals that are disposed in a scattered manner in the time direction and the frequency direction.

BACKGROUND ART

In radio communication systems, signal-to-noise ratio (SNR) has heretofore been widely used as a measure to indicate the receiving quality of a radio signal received by a reception device from a transmission device.

In a radio communication system, the amplitude and phase of a radio signal vary due to characteristics of a radio channel (e.g., frequency response characteristic) in addition to the influence of noise. For this reason, for accurate measurement of an SNR, it is important to remove the varied portion of the radio signal caused by the characteristics of the channel, and then calculate noise power.

In addition, the following technique has been proposed as an SNR measurement technique applicable to a multicarrier scheme using a number of sub carriers (see Patent Document 1).

The reception device described in Patent Document 1 receives a radio signal from a transmission device via a radio channel and estimates an SNR by using a first known signal and a second known signal included in the received radio signal. The first known signal and the second known signal here are signals whose signal pattern (e.g., an M sequence, a Walsh sequence, or the like) is known by the reception device. Moreover, the second known signal is disposed continuously after the first known signal in the time direction.

The reception device described in Patent Document 1 calculates the first known signal's channel estimation information indicating estimation of characteristics of the channel, and multiplies the second known signal by the calculated channel estimation information. The reception device then calculates noise power on the basis of the difference between the second known signal after the multiplication by the channel estimation information and the second known signal before the multiplication by the channel estimation information.Patent Document 1: Japanese Patent No. 3455773 ([Claim 1], FIG. 3)

DISCLOSURE OF THE INVENTION

Meanwhile, in a multicarrier scheme, multiple known signals are not always continuous with each other in the time direction and are disposed in a scattered manner in the time direction and the frequency direction in some case.

Thus, with the technique described in Patent Document 1, if the first known signal and the second known signal are disposed in a scattered manner in the time direction, the characteristics of the channel at the time of reception of the first known signal may possibly differ from the characteristics of the channel at the time of reception of the second known signal.

The technique described in Patent Document 1 assumes that the channel estimation information corresponding to the first known signal is equivalent to the channel estimation information corresponding to the second known signal. Thus, disposition of the first known signal and the second known signal in a scattered manner in the time direction undermines the above assumption, leading to a possibility of being unable to calculate noise power accurately.

The present invention has been made to solve the above problem and has an objective to provide a reception device, a radio communication terminal, a radio base station, and a reception method which allow accurate calculation of noise power and thus accurate estimation of an SNR even when multiple known, signals are disposed in a scattered manner in the time direction and the frequency direction.

A first aspect of the present invention is summarized as a reception device (reception device10) which receives a radio signal including a first known signal (first pilot signal P1), a second known signal (second pilot signal P2), a third known signal (third pilot signal P3), and a fourth known signal (fourth pilot signal P4) that are disposed in a scattered manner in a time direction and a frequency direction, the reception device comprising: an estimation information calculator (channel estimator130) configured to calculate channel estimation information (channel estimation values h^1(n) to h^4(n)) for each of the first known signal, the second known signal, the third known signal, and the fourth known signal, the channel estimation information indicating estimation of a characteristic of a channel of the radio signal; a first interpolation unit (first interpolation unit151) configured to interpolate channel estimation information on an intersection by using the channel estimation information (channel estimation values h^1(n) and h^4(n)) on each of the first known signal and the fourth known signal, the intersection being where a line joining the first known signal and the fourth known signal intersects with a line joining the second known signal and the third known signal; a second interpolation unit (second interpolation unit152) configured to interpolate channel estimation information on the intersection by using the channel estimation information (channel estimation values h^2(n) and h^3(n)) on each of the second known signal and the third known signal; and a noise power calculator (noise power calculator154) configured to calculate noise power of the radio signal on the basis of a difference between the channel estimation information (channel estimation value h^01-4(n)) interpolated by the first interpolation unit and the channel estimation information (channel estimation value h^02-3(n)) interpolated by the second interpolation unit.

With such feature, by utilizing the fact that the values of the channel characteristics of the intersection are equal to each other, the noise power can be calculated while removing a varied portion of the radio signal caused by the channel characteristic. Accordingly, it is possible to provide a reception device which allows accurate calculation of the noise power and thus accurate estimation of an SNR even when multiple known signals are disposed in a scattered manner in the time direction and the frequency direction.

A second aspect of the present invention is summarized as the reception device according to the first aspect, wherein, when a noise is excluded from the radio signal, the channel estimation information interpolated by the first interpolation unit coincides with the channel estimation information interpolated by the second interpolation unit.

A third aspect of the present invention is summarized as the reception device according to the first aspect, wherein, based on a least squares method, the estimation information calculator compares the first known signal, the second known signal, the third known signal, and the fourth known signal with predetermined reference signals, respectively, to thereby calculate the channel estimation information on each of the first known signal, the second known signal, the third known signal, and the fourth known signal.

A fourth aspect of the present invention is summarized as the reception device according to the first aspect, further comprising: a third interpolation unit (third interpolation unit153) configured to interpolate channel estimation information (channel estimation value h^0(n)) on the intersection by using the channel estimation information on each of the first known signal, the second known signal, the third known signal, and the fourth known signal; and a signal power calculator (signal power calculator155) configured to calculate signal power of the radio signal by using the channel estimation information interpolated by the third interpolation unit and the noise power calculated by the noise power calculator.

A fifth aspect of the present invention is summarized as the reception device according to the first aspect, further comprising an SNR calculator (SNR calculator156) configured to calculate a signal-to-noise ratio of the radio signal by using the signal power calculated by the signal power calculator and the noise power calculated by the noise power calculator.

A sixth aspect of the present invention is summarized as a radio communication terminal (radio communication terminal200) comprising the reception device according to any one of the first to fifth aspects.

A seventh aspect of the present invention is summarized as a radio base station (radio base station100) comprising the reception device according to any one of the first to fifth aspects.

A eighth aspect of the present invention is summarized as a reception method of receiving a radio signal including a first known signal, a second known signal, a third known signal, and a fourth known signal that are disposed in a scattered manner in a time direction and a frequency direction, the reception method comprising the steps of: calculating (step S104) channel estimation information for each of the first known signal, the second known signal, the third known signal, and the fourth known signal, the channel estimation information indicating estimation of a characteristic of a channel of the radio signal; interpolating (step S106) channel estimation information on an intersection by using the channel estimation information on each of the first known signal and the fourth known signal, the intersection being where a line joining the first known signal and the fourth known signal intersects with a line joining the second known signal and the third known signal; interpolating (step S106) channel estimation information on the intersection by using the channel estimation information on each of the second known signal and the third known signal; and calculating (step S109) noise power of the radio signal on the basis of a difference between the channel estimation information interpolated by using the channel estimation information on each of the first known signal and the fourth known signal and the channel estimation information interpolated by using the channel estimation information on each of the second known signal and the third known signal.

According to the present invention, it is possible to provide a reception device, a radio communication terminal, a radio base station, and a reception method which allow accurate calculation of noise power and thus accurate estimation of an SNR even when multiple known signals are disposed in a scattered manner in the time direction and the frequency direction.

BEST MODES FOR CARRYING OUT THE INVENTION

Next, embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, same or similar reference_signs denote same or similar elements and portions.

In the following, descriptions will be provided for (1) a schematic configuration of a radio communication system, (2) a configuration of a reception device, (3) operation of the reception device, (4) advantageous effects, and (5) other embodiments.

(1) SCHEMATIC CONFIGURATION OF RADIO COMMUNICATION SYSTEM

First, a schematic configuration of a radio communication system according to an embodiment will be described.FIG. 1is an overall schematic configuration diagram of the radio communication system1according to this embodiment.

As shown inFIG. 1, the radio communication system1includes a radio base station100and a radio communication terminal200. The radio communication system1employs what is called a multicarrier scheme in which a radio signal RS is formed of multiple subcarriers.

Specifically, the radio communication system1employs the orthogonal frequency division multiplexing (OFDM) scheme. That is, a radio signal RS is formed based on the OFDM.

An OFDM system is assumed to be used for wideband communication. The OFDM is characterized in that a time period given for each symbol is longer than a case of a single carrier scheme. This means that the longer time period works advantageously in a multipath environment but also increases, relatively, a time variation of the symbol in a channel. That is, in a broad frequency domain and a long time domain, both a frequency variation and a time variation occur due to the influence of frequency selectivity and Doppler frequency.

In this embodiment, the radio communication system1employs dynamic channel assignment (DCA) for dynamically assigning subcarriers in accordance with an SNR, and adaptive modulation for selecting the modulation scheme in accordance with an SNR. In the adaptive modulation, an appropriate modulation scheme is selected from multiple modulation schemes, such as BPSK to (Binary Phase Shift Keying) and 24QAM (Quadrature Amplitude Modulation). For this reason, the radio base station100and the radio communication terminal200measure the SNR periodically.

FIG. 2is a frame configuration diagram showing a configuration of a frame used for uplink communication or downlink communication in the radio communication system1, in other words, a configuration of an uplink subframe or a downlink subframe.

The radio communication terminal200has at least one cluster (which is a communication unit including a certain number of symbols in the time direction and in the frequency direction) assigned thereto in a subframe, and performs communication on a cluster basis. In a cluster, four or more known symbols (hereinafter, pilot signals) are disposed in a scattered manner in the time direction and the frequency direction. In this embodiment, four pilot signals P1to P4are disposed on the four corners of a cluster, respectively.

The radio base station100and the radio communication so terminal200calculate the channel estimation values indicating estimation of characteristics of a radio channel (e.g., frequency response characteristic), by using received pilot signals. The radio base station100and the radio communication terminal200then equalize data signals (data symbols) by using the calculated channel estimation values.

To be more specific, the radio base station100and the radio communication terminal200calculate the channel estimation values for the respective pilot signals by using the least squares (LS) method. For this reason, the channel estimation values each reflect not only the characteristics of the radio channel but also a noise component therein.

The radio base station100and the radio communication terminal200perform two-dimensional (frequency/time) interpolation (such as linear, quadratic or spline interpolation) by using the channel estimation values for the pilot signals to thereby estimate the channel estimation value for a data signal.

(2) CONFIGURATION OF RECEPTION DEVICE

Next, a configuration of a reception device10provided in the radio base station100and the radio communication terminal200will be described with reference toFIGS. 3 to 5. Note that in the following, points regarding the present invention will be mainly described.

(2.1) Functional Block Configuration of Reception Device

FIG. 3is a functional block configuration diagram of the reception device10. As shown inFIG. 3, the reception device10includes a serial-parallel conversion unit (hereinafter, an S/P unit)110, a Fourier transformer120, a channel estimator130, an equalizer140, an SNR estimator150, a parallel-serial conversion unit (hereinafter, a P/S unit)160, and a demodulator170.

The S/P unit110receives received signals via an antenna, an RF unit and the like whose illustrations are omitted here. The S/P unit110performs serial-parallel conversion on the received signals. The parallel signals to be outputted from the S/P unit110correspond to subcarriers, for example.

The Fourier transformer120performs FFT or DFT on the received signals after the serial-parallel conversion to thereby transform the received signals in the time domain to signals in the frequency domain.

The channel estimator130receives the received signal subjected to the frequency domain transform. The channel estimator130calculates channel estimation values by using the LS method. Specifically, the channel estimator130stores therein reference signals which are a signal sequence equivalent to pilot signals, and calculates channel estimation values through a comparison between the pilot signals and the reference signals.

In this embodiment, for each cluster, the channel estimator130calculates channel estimation values h^1(n) to h^4(n) (n: cluster number) for the pilot signal P1, the pilot signal P2, the pilot signal P3, and the pilot signal P4, respectively. The channel estimation values h^1(n) to h^4(n) indicate estimation of the characteristics of the channel of the radio signal RS.

The equalizer140receives the received signals subjected to the frequency domain transform. The equalizer140performs channel equalization on the received signals by using the channel estimation values calculated by the channel estimator130. Specifically, the equalizer140corrects phase distortion and amplitude distortion in the radio signal RS generated through the channel, and reproduces the signal sequence transmitted at the transmitting side.

The P/S unit160performs parallel-serial conversion on the received signals after the correction. The demodulator170demodulates the output signals from the P/S unit160into the signal sequence transmitted at the transmitting side.

The SNR estimator150receives the channel estimation values calculated by the channel estimator130. The SNR estimator150estimates the SNR of the radio signal RS (received signal) by using the channel estimation values.

(2.2) Functional Block Configuration of SNR Estimator

Next, a functional block configuration of the SNR estimator150will be described.FIG. 4is a functional block configuration diagram of the SNR estimator150.

As shown inFIG. 4, the SNR estimator150includes a first interpolation unit151, a second interpolation unit152, a third interpolation unit153, a noise power calculator154, a signal power calculator155, and an SNR calculator156.

The first interpolation unit151performs first linear interpolation by using the channel estimation values h^1(n) and h^4(n) respectively for the pilot signal P1and the pilot signal P4to thereby acquire a channel estimation value h^01-4(n) for an intersection C (seeFIG. 5) where a line joining the pilot signal P1and the pilot signal P4intersects with a line joining the pilot signal P2and the pilot signal P3.

The second interpolation unit152performs first linear interpolation by using the channel estimation values h^2(n) and h^3(n) respectively for the pilot signal P2and the pilot signal P3to thereby acquire a channel estimation value h^02-3(n) for the intersection C.

The third interpolation unit153performs first linear interpolation by using the channel estimation values h^1(n) to h^4(n) respectively for the pilot signal P1, the pilot signal P2, the pilot signal P3, and the pilot signal P4to thereby acquire a channel estimation value h^0(n) for the intersection C.

The noise power calculator154calculates noise power P^n of the radio signal RS on the basis of the difference between the channel estimation value h^01-4(n) interpolated by the first interpolation unit151and the channel estimation value h^02-3(n) interpolated by the second interpolation unit152.

The signal power calculator155calculates the signal power of the radio signal RS by using the channel estimation value h^0(n) interpolated by the third interpolation unit153and the noise power P^n calculated by the noise power calculator154.

Specifically, the signal power calculator155uses the channel estimation value h^0(n) to estimate a value of “signal power+quasi noise power” (the quasi noise power is acquired by multiplying the noise power by a constant), and calculates the signal power on the basis of the difference between the noise power P^n and the value of “signal power+quasi, noise power.”

The SNR calculator156calculates the SNR of the radio signal RS by using the signal power calculated by the signal power calculator155and the noise power P^n calculated by the noise power calculator154. In other words, the SNR calculator156calculates the ratio of the signal power to the noise power P^n as the SNR.

(2.3) Processing of Calculating Channel Estimation Value

Next, processing of calculating channel estimation values performed by the channel estimator130will be described by usingFIG. 5.

The channel estimator130calculates the channel estimation values h^1(n) to h^4(n) for the respective pilot signals P1to P4shown inFIG. 5. Here, the channel estimation values h^1(n) to h^4(n) acquired by the LS method reflect not only the characteristics of a channel but also a noise therein.

When the pilot signal P1is “r1(n)” and the transmitted signal (i.e., the reference signal) is “s1(n),” the channel estimation value h^1(n) corresponding to the pilot signal P1is calculated from a formula (1).

In addition, a formula (2) holds when the channel characteristics corresponding to the pilot signal P1are “h1(n)” and the noise corresponding to the pilot signal P1is “n1(n).”
[Formula 2]
r1(n)=h1(n)s1(n)+n1(n)  (2)

As shown in the formula (2), each received signal received by the reception device10is assumed to be a signal which is transmitted at the transmitting side and subjected to channel variations, and to which a noise is added thereafter.

A formula (3) is obtained by substituting the formula (2) into the formula (1).

Similarly, when the pilot signal P2is “r2(n),” the transmitted signal (i.e., the reference signal) is “s2(n),” the channel characteristics corresponding to the pilot signal P2are “h2(n)” and the noise corresponding to the pilot signal P2is “n2(n),” the channel estimation value h^2(n) corresponding to the pilot signal P2is expressed by a formula (4).

Moreover, when the pilot signal P3is “r3(n),” the transmitted signal (i.e., the reference signal) is “s3(n),” the channel characteristics corresponding to the pilot signal P3are “h3(n)” and the noise corresponding to the pilot signal P3is “n3(n)” the channel estimation value h^3(n) corresponding to the pilot signal P3is expressed by a formula (5).

Furthermore, when the pilot signal P4is “r4(n)” the transmitted signal (i.e., the reference signal) is “s4(n),” the channel characteristics corresponding to the pilot signal P4are “h4(n)” and the noise corresponding to the pilot signal P4is “n4(n)” the channel estimation value h^4(n) corresponding to the pilot signal P4is expressed by a formula (6).

(2.4) Processing of Calculating SNR

Processing of calculating an SNR performed by the SNR estimator150will be described by usingFIG. 5again.

The SNR estimator150performs estimation of the SNR of the intersection C where the lines each joining the corresponding two pilot signals intersect with each other (i.e., where a data signal so D1is located in the example inFIG. 3)

First, as shown in a formula (7), the SNR estimator150calculates the channel estimation value h^0(n) for the intersection C by using the channel estimation values h^1(n) to h^4(n) for the respective pilot signals P1to P4. The channel estimation value h^0(n) is used for estimation of the value of “signal power+quasi noise power.”

A formula (8) is obtained by substituting the formulae (3) to (6) into the formula (7).

Next, as shown in a formula (9), the SNR estimator150calculates the channel estimation value h^01-4(n) for the center portion by performing first linear interpolation using the channel estimation values h^1(n) and h^4(n) for the respective pilot signals P1and P4located diagonally to each other in the cluster (n).

Likewise, as shown in a formula (10), the SNR estimator150calculates the channel estimation value h^02-3(n) for the center portion by performing first linear interpolation using the channel estimation values h^2(n) and h^3(n) for the respective pilot signals P2and P3located diagonally to each other in the cluster (n).

The channel estimation values h^01-4(n) and h^02-3(n) are used for estimation of the noise power P^n. Specifically, the difference between the channel estimation values h^01-4(n) and h^02-3(n) represents the noise component of the intersection C.

Next, as shown in a formula (11), in order to estimate the signal power, the SNR estimator150calculates the ensemble mean of the squared absolute values of the channel estimation values h^0(n) for the intersection C of all the clusters assigned to the so user (the radio communication terminal200).

Here, <•> represents the ensemble mean regarding all the clusters assigned to the user. Note that the formula (11) assumes (h1(n)+h4(n))/2=(h2(n)+h3(n))/2=h0(n).

P^n in the formula (11) corresponds to the quasi noise power.

The SNR of the intersection C to be estimated by the SNR estimator150is the ratio of the power of the signal component in the received signal to the power of the noise component in the received signal. Specifically, when the channel characteristics of the intersection C are “h0(n),” the transmitted signal (i.e., the reference signal) of the intersection C is “s0(n),” and the noise of the intersection C is “n0(n)” the signal component is h0(n) s0(n) and the noise component is n0(n)

The ensemble mean of the squared absolute values of the SNRs of the intersection C of all the clusters assigned to the user (the radio communication terminal200) is expressed by a formula (13).

Next, as shown in a formula (14), in order to estimate the noise power P^n, the SNR estimator150calculates the ensemble mean of the squared absolute values of the differences between the channel estimation values for the intersection C that are expressed by the formulae (9) and (10).

Here, the channel characteristics of the intersection C can be regarded as equal between the channel estimation values h^03-4(n) and h^02-3(n), whereby a formula (15) holds. Note that the formula (15) assumes (h1(n)+h4(n))/2=(h2(n)+h3(n))/2 h0(n), as in the case of the formula (11).

Accordingly, the formula (14) is expressed by a formula (16) below.

Consequently, as shown in a formula (17), the SNR is estimated by using the “formula (11)−formula (16)/4” as the signal power and the formula (16) as the noise power P^n.

The SNR estimator150can therefore estimate the SNR from the formula (17).

(3) OPERATION OF RECEPTION DEVICE

Next, operation of the reception device10will be described by using the flowchart shown inFIG. 6.

In Step S101, the S/P unit110performs serial-parallel conversion on received signals having been amplified and down-converted by the antenna and the RF unit.

In Step S102, the received signals in the time domain are transformed to signals in the frequency domain by FFT or DFT.

In Step S103, the processing for each cluster assigned to the radio communication terminal200starts.

In Step S104, the channel estimator130calculates channel estimation values h^1(n) to h^4(n) in accordance with the formulae (3) to (6), respectively.

In Step S105, the third interpolation unit153calculates a channel estimation value h^0(n) for an intersection C in accordance with the formulae (7) and (8) using the channel estimation values h^1(n) to h^4(n).

In Step S106, the first interpolation unit151calculates a channel estimation value h^01-4(n) in accordance with the formula (9). In addition, the second interpolation unit152calculates a channel estimation value h^02-3(n) in accordance with the formula (10).

In Step S107, if it is judged that the processing from Steps S104to S106is completed for all the clusters assigned to the radio communication terminal200, the process flow proceeds to Step S108. On the other hand, if the processing from Steps S104to S106has not been completed for all the clusters assigned to the radio communication terminal200, the process flow returns to Step S103and the processing for the next cluster starts.

In Step S108, the signal power calculator155calculates a value of “signal power quasi noise power” in accordance with the formula (11).

In Step S109, the noise power calculator154calculates a noise power P^n in accordance with the formula (16).

In Step S110, the SNR calculator156calculates an SNR in accordance with the formula (17).

According to this embodiment, the noise power P^n is calculated by utilizing the fact that the values of the channel characteristics of the intersection C are equal to each other. That is to say, when a noise is excluded from the radio signal RS, the channel estimation value h^01-4(n) interpolated by the first interpolation unit151coincides with the channel estimation value h^02-3(n) interpolated by the second interpolation unit152.

This makes it possible to calculate the noise power P^n while removing a varied portion of the radio signal RS caused by the channel characteristics. It is therefore possible to provide a reception device10which is capable of calculating noise power P^n accurately even when multiple pilot signals are disposed in a scattered manner in the time direction and the frequency is direction.

According to this embodiment, based on the LS method, the reception device10compares the pilot signal P1, the pilot signal P2, the pilot signal P3, and the pilot signal P4with the predetermined reference signals to thereby calculate the channel estimation values for the pilot signal P1, the pilot signal P2, the pilot signal P3, and the pilot signal P4.

In this case, the calculated channel estimation values reflect both the characteristics of the channel and the influence of noise; however, as described above, the noise power P^n can be calculated while removing the varied portion of the radio signal RS caused by the characteristics of the channel.

Accordingly, it is possible to calculate the noise power P^n accurately even in a case of using channel estimation values calculated based on an algorithm requiring a small amount of calculation, such as the LS method. In other words, this embodiment makes it possible to reduce the processing load on the reception device10as compared with a case of using a complicated algorithm.

If allowed, the calculation of the channel estimation values should preferably be simpler because the calculation amount may be significantly large if sophisticated channel estimation and channel equalization were to be performed especially in a wide band system, such as the OFDM.

According to this embodiment, the reception device10interpolates the channel estimation value for the intersection C, and calculates the signal power of the radio signal RS by using the interpolated channel estimation value h^0(n) and the calculated noise power P^n. Calculating the signal power by using the accurately calculated noise power P^n makes it possible to calculate the signal power more accurately.

According to this embodiment, the reception device10calculates the SNR of the radio signal RS by using the signal power and noise power P^n thus calculated. Since the signal power and noise power P^n are calculated accurately as described above, the SNR can be calculated more accurately. Thus, using the SNR calculated by the reception device10, dynamic channel assignment and adaptive modulation can be achieved more efficiently.

(5) OTHER EMBODIMENTS

As described above, the present invention has been described by using the embodiment. However, it should not be understood that the description and drawings which constitute part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples, and operation techniques will be easily found by those skilled in the art.

In the foregoing embodiment, the four pilot signals P1to P4are disposed on the four corners of the cluster (n), respectively. However, the present invention is not limited to such case where the pilot signals P1to P4are disposed on the four corners of the cluster (n). As shown inFIG. 7, the pilot signals P1to P4may be disposed at any positions in the cluster (n). In short, one line joining two of the pilot signals P1to P4only has to intersect with the other line joining the other two pilot signals.

Further, the number of pilot signals in the cluster (n) is not limited to four, and may be five or more. Also, there may be only one cluster to be assigned to the radio communication terminal200.

In the foregoing embodiment, the radio communication system1performing radio communication based on the OFDM is described. However, the radio communication system1may perform radio communication based on other multicarrier schemes than the OFDM.

In the foregoing embodiment, the noise power P^n calculated by the noise power calculator154is used for calculation of the SNR. However, the use of the noise power P^n calculated by the noise power calculator154is not limited to the calculation of the SNR, and may be used for adaptive array control, antenna calibration, and the like.

In the foregoing embodiment, the channel estimation values h^01-4and h^02-3are calculated through first linear interpolation. However, other interpolation methods than first linear interpolation may be employed.

As described above, it is to be understood that the present invention includes various embodiments which are not described herein. Accordingly, the present invention should be determined only by the matters to define the invention in the scope of claims regarded as appropriate based on this disclosure.

INDUSTRIAL APPLICABILITY

As has been described above, a reception device, a radio communication terminal, a radio base station, and a reception method according to the present invention allow accurate calculation of noise power and thus accurate estimation of an SNR even when multiple known signals are disposed in a scattered manner in the time direction and the frequency direction, and hence are useful in radio communication, such as mobile communication.