JP2017200084A - Wireless communication system - Google Patents

Abstract

An object of the present invention is to implement cooperative transmission early in a wireless communication system while improving deterioration of reception performance due to frequency deviation. In a wireless communication system, pilot signals transmitted from base stations 1001 and 1002 are orthogonal to each other, and a mobile station 200 moves with each base station 1001 and 1002 from each pilot signal extracted by a pilot extraction unit. A frequency deviation estimator for estimating a frequency deviation with respect to the station 200, a pilot corrector for correcting each pilot signal based on the frequency deviation, and movement with each base station 1001, 1002 based on each corrected pilot signal Equalization for extracting transmission data of each of the base stations 1001 and 1002 from the received signal of the mobile station 200 based on the transmission path characteristics and the frequency deviation based on the transmission path characteristics estimation unit for estimating the transmission path characteristics with the station 200 A section. [Selection] Figure 1

Description

  The present invention relates to a wireless communication system that performs coordinated transmission.

  In recent years, standardization of LTE-Advanced has been advanced in 3GPP (Third Generation Partnership Project). LTE-Advanced is an extension of a next-generation mobile communication technique called LTE (Long Term Evolution). In LTE-Advanced, in order to achieve high requirements, carrier aggregation (CA) technology, multi-user multi-output (MIMO) technology, coordinated multi-point transmission / transmission (CoMP) reception) technology is under consideration.

  The CoMP technology improves user communication quality by performing diversity transmission to a cell edge user between a plurality of base stations. Alternatively, in the case of CoMP technology, when the communication quality of cell edge users is sufficient, it is possible to improve user throughput by performing spatial multiplexing transmission using MIMO technology between base stations.

  However, when cooperative transmission is performed between a plurality of base stations, a frequency deviation occurs due to an individual difference between clock transmitters between the base stations, so that the mobile station receives a composite signal of a plurality of signals having a frequency deviation. Become. Also, a frequency deviation occurs between the mobile station and the base station due to individual differences of the clock transmitter. Therefore, the mobile station needs to correct the frequency deviation between the base stations and the frequency deviation between the mobile station and the base station.

  As a conventional technique for estimating and correcting a frequency deviation, a technique disclosed in Patent Document 1 is known. According to the method of Patent Document 1, a mobile station receives a transmission signal of a base station A among base stations A and B that perform coordinated transmission, and the mobile station detects a frequency deviation from the base station A to detect a clock of the mobile station. Correct the transmitter. Thereafter, base station B receives the transmission signal from the mobile station, and base station B detects the frequency deviation from the mobile station and corrects the clock transmitter of base station B. Thereby, there is no frequency deviation between the base stations A and B and the mobile station.

JP 2014-135560 A

  However, in the method of Patent Document 1, it is necessary to estimate and correct the frequency deviation in both the mobile station and the base station B. Furthermore, it is necessary to perform coordinated transmission after the base station B receives the transmission signal from the mobile station. Therefore, there is a problem that it takes time until the cooperative transmission is performed.

  In view of the above-described problems, the present invention shortens the time until cooperative transmission is performed while improving deterioration in reception performance due to frequency deviation in the case of cooperative transmission between a plurality of base stations and mobile stations. For the purpose.

  A radio communication system according to the present invention is a radio communication system including a mobile station and a plurality of base stations that cooperatively transmit a transmission signal including a pilot signal and transmission data to the mobile station. The pilot signals are orthogonal to each other, and the mobile station extracts the pilot signal from each base station from the received signal of the mobile station, and each base station from each pilot signal extracted by the pilot extraction unit A frequency deviation estimator for estimating a frequency deviation between the mobile station, a pilot correction unit for correcting each pilot signal based on the frequency deviation estimated by the frequency deviation estimator, and each pilot signal corrected by the pilot correction unit Based on the channel characteristics estimation unit for estimating the channel characteristics between each base station and the mobile station, the channel characteristics estimated by the channel characteristics estimation unit, and the frequency Based on the frequency deviation estimated by the difference estimating section, and a equalizer from the received signal of the mobile station extracts the transmission data of each base station.

  According to the radio communication system of the present invention, the mobile station estimates the frequency deviation with each base station from the pilot signal received from each base station, and extracts the transmission data of each base station based on the frequency deviation. Coordinated transmission can be performed at an early stage while improving the degradation of reception performance due to deviation.

1 is a diagram showing a configuration of a radio communication system according to Embodiment 1. FIG. 3 is a diagram illustrating a configuration example of a wireless transmission device according to Embodiment 1. FIG. 3 is a diagram illustrating a configuration example of a radio reception apparatus according to Embodiment 1. FIG. It is a figure which shows the example of symbol arrangement | positioning in the transmission signal of a base station. It is a figure which shows the example of symbol arrangement | positioning in the transmission signal of a base station It is a figure which shows the example of symbol arrangement | positioning of the received signal of a mobile station. It is a figure which shows the example of symbol arrangement | positioning of the transmission data of each base station in the received signal of a mobile station. FIG. 3 is a diagram illustrating a configuration of an equalization unit and its periphery according to the first embodiment. 6 is a diagram illustrating a configuration example of a receiving apparatus according to Embodiment 2. FIG. It is a figure which shows the structure of the equalization part which concerns on Embodiment 2, and its periphery. 6 is a diagram showing a configuration of a radio communication system according to Embodiment 3. FIG. It is a figure which shows the hardware constitutions of a transmitter and a receiver. It is a figure which shows the hardware constitutions of a transmitter and a receiver.

<A. Embodiment 1>
FIG. 1 shows the configuration of a radio communication system according to Embodiment 1 of the present invention. As shown in FIG. 1, the radio communication system according to Embodiment 1 of the present invention includes a mobile station 200 and Nb base stations 100 _{1 to} 100 _Nb that perform coordinated transmission to the mobile station 200. Composed. The base stations 100 _{1 to} 100 _Nb perform diversity transmission or spatial multiplexing transmission.

FIG. 2 illustrates a configuration example of a wireless transmission device (hereinafter simply referred to as “transmission device”) included in each of the base stations 100 _{1 to} 100 _Nb . FIG. 3 illustrates a configuration example of a wireless reception device (hereinafter also simply referred to as “reception device”) included in the mobile station 200.

In the present embodiment, a case where data is transmitted from _Nb base stations 100 ₁ to 100 Nb including the transmission device 10 illustrated in FIG. 1 to the mobile station 200 including the reception device 20A illustrated in FIG. The operation will be described. Further, as shown in FIGS. 1 and 2, the number of transmission antennas of the transmission device 10 is Nt, and the number of reception antennas of the reception device 20A is Nr.

As illustrated in FIG. 2, the transmission device 10 includes an error correction encoding unit 1, a mapping unit 2, time frequency conversion units 3 _{1 to} 3 _Nt , pilot insertion units 4 ₁ to 4 _Nt , and frequency time conversion units 5 _{1 to} 5. _Nt , guard interval insertion units 6 _{1 to} 6 _Nt , and transmission antennas 7 _{1 to} 7 _Nt .

The transmission apparatus 10 has Nt transmission antennas, and a set of a time frequency conversion unit 3, a pilot insertion unit 4, a frequency time conversion unit 5, and a guard interval insertion unit 6 is provided corresponding to the Nt transmission antennas. Nt. In the following description, when it is necessary to distinguish each of the _Nt transmission antennas, a subscript is added like the transmission antenna 7 ₁ or the transmission antenna 7 _Nt , and in other cases, the transmission antenna is simply used. 7 is called. The time frequency conversion unit, pilot insertion unit, frequency time conversion unit, and guard interval insertion unit are handled in the same manner as the transmission antenna.

  The error correction encoding unit 1 performs error correction encoding processing on transmission data. The mapping unit 2 maps the transmission data that has been subjected to error correction coding processing to symbols. The time frequency conversion unit 3 converts the mapped transmission data from the time domain to the frequency domain. The pilot insertion unit 4 creates a transmission signal by inserting a pilot signal into frequency domain transmission data. The frequency time conversion unit 5 converts the transmission signal in the frequency domain into which the pilot signal is inserted into the time domain. The guard interval insertion unit 6 adds a guard interval to the time domain transmission signal. The transmission antenna 7 transmits a transmission signal in which a guard interval is inserted. That is, the transmission signal from the transmission antenna 7 to the mobile station 200 includes a pilot signal, transmission data, and a guard interval.

As shown in FIG. 3, the receiving device 20A includes an error correction decoding unit 21, a demapping unit 22A, a frequency time conversion unit 23, an equalization unit 28A, a channel characteristic estimation unit 29, a pilot correction unit 30, a frequency deviation estimation. Unit 31, pilot extraction units 24 _{1 to} 24 _Nr , time frequency conversion units 25 _{1 to} 25 _Nr , guard interval removal units 26 _{1 to} 26 _Nr , and reception antennas 27 _{1 to} 27 _Nr .

The receiving apparatus 20A has Nr reception antennas, and has Nr sets of pilot extraction units 24, time frequency conversion units 25, and guard interval removal units 26 corresponding to the Nr reception antennas. . In the following description, when it is necessary to distinguish each of the Nr reception antennas, the reception antennas 27 ₁ or the reception antennas 27 _Nr as shown in FIG. In other cases, it is simply referred to as a receiving antenna 27. The pilot extraction unit, the time frequency conversion unit, and the guard interval removal unit are handled in the same manner as the reception antenna.

The receiving antenna 27 receives signals transmitted from the base stations 100 _{1 to} 100 _Nb . The guard interval removing unit 26 removes the guard interval from the signal received by the receiving antenna 27. The time frequency conversion unit 25 converts the received signal from which the guard interval is removed from the time domain to the frequency domain. The pilot extraction unit 24 extracts a pilot signal arranged at each of the base stations 100 _{1 to} 100 _Nb from the reception signal converted into the frequency domain. The frequency deviation estimation unit 31 estimates the frequency deviation between the base stations 100 _{1 to} 100 _Nb and the mobile station 200 using the pilot signal extracted by the pilot extraction unit 24. The pilot correction unit 30 performs correction to remove the frequency deviation from the pilot signals of the base stations 100 _{1 to} 100 _Nb based on the frequency deviation estimated by the frequency deviation estimation unit 31.

The transmission path characteristic estimation unit 29 estimates transmission path characteristics between the base stations 100 _{1 to} 100 _Nb and the mobile station 200 using the corrected pilot signal. The equalization unit 28A receives transmission symbol data of each of the base stations 100 _{1 to} 100 _Nb using the transmission path characteristics obtained by the transmission path characteristic estimation unit 29 and the frequency deviation obtained by the frequency deviation estimation unit 31. Extract from signal. The frequency time conversion unit 23 converts the transmission symbol data of each of the base stations 100 _{1 to} 100 _Nb extracted by the equalization unit 28A from the frequency domain to the time domain. The demapping unit 22A performs demapping processing on the transmission symbol data of each of the base stations 100 _{1 to} 100 _Nb converted into the time domain, generates a soft decision value in bit units, and each of the base stations 100 _{1 to} 100 _Nb transmission symbol data is converted into bit data. The error correction decoding unit 21 decodes transmission data of each of the base stations 100 _{1 to} 100 _Nb by performing an error correction decoding process on the bit data obtained by the demapping process.

  The overall configuration of the transmission device 10 and the reception device 20A has been described above. Next, specific configurations and operations of components that perform characteristic processing in the transmission device 10 and the reception device 20A will be described in detail. In the following description, for ease of explanation, it is assumed that the number of base stations Nb for cooperative transmission is 2, the number of transmission antennas Nt of the base station is 1, and the number of reception antennas Nr of the mobile station is 2. However, the present invention is not limited to this combination of the number of base stations, the number of base station transmitting antennas, and the number of mobile station receiving antennas.

The pilot insertion unit 4 creates a transmission signal by inserting a pilot signal into the transmission data converted into the frequency domain by the time-frequency conversion unit 3. 4 shows a symbol arrangement examples in the transmission signal of the base station 100 _1, FIG. 5 shows a symbol arrangement examples in the transmission signal of the base station 100 _2. 4 and 5, the row direction of the symbol arrangement expressed in a matrix form indicates time, and the column direction indicates frequency. 4, black circles pilot signal added by the base station 100 _1, × indicates a null, respectively, the data signal of the base station 100 ₁ is inserted into the blank column. 5, white circles pilot signal added by the base station 100 _2, × indicates a null, respectively, the data signal of the base station 100 ₂ is inserted into the blank column. As shown in FIGS. 4 and 5, to a position where the pilot signal is inserted in the transmission signal of the base station 100 _1, nulls are inserted in the transmission signal of the base station 100 _2. Conversely, the position at which a pilot signal in the transmission signal of the base station 100 ₂ is inserted, a null is inserted in the transmission signal of the base station 100 _1. Thus, the pilot signal and the pilot signal of the base station 100 ₂ of the base station 100 _1, are orthogonal to each other. Therefore, these two pilot signals do not interfere with each other and can be extracted independently from the received signal of the mobile station 200.

FIG. 6 shows an example of symbol arrangement of received signals of mobile station 200 when the transmission signals shown in FIGS. 4 and 5 are transmitted from base stations 100 ₁ and 100 ₂ . In FIG. 6, the row direction of the symbol arrangement expressed in a matrix form indicates time, and the column direction indicates frequency. The black circle represents a pilot signal added with the base station 100 _1, a white circle indicates a pilot signal added with the base station 100 _2. The blank column is multiplexed with the data signal of the base station 100 ₁ of the data signal and the base station 100 _2. Further, (x, y, z) attached to a black circle or a white circle indicates that x is a base station index, y is a time index, and z is a frequency index. For example, it is shown that the black dot coordinate is attached as (1,1,1), the pilot signal from the base station 100 _1, the time and frequency are both 1.

Pilot extraction sections 24 ₁ and 24 ₂ extract the pilot signals of base station 100 ₁ and base station 100 ₂ from the received signals. As shown in FIG. 6, since both pilot signals are orthogonal to each other, the pilot extraction units 24 ₁ and 24 ₂ can extract them without interfering with each other. Specifically, extracts as a pilot signal signals the base station 100 ₁ of the position of black circle in FIG. 6, is extracted as a pilot signal of the base station 100 ₂ signal of the position of the white circle in FIG.

The frequency deviation estimation unit 31 uses the pilot signals of the base stations 100 ₁ and 100 ₂ extracted by the pilot extraction units 24 ₁ and 24 ₂ , and the frequency deviation between the base station 100 ₁ and the mobile station 200 and the base station estimating a frequency deviation between the station 100 ₂ and the mobile station 200. A method for estimating the frequency deviation will be described below, but this is merely an example, and the present invention is not limited to this.

Pilot extracting unit ₂₄ 1, 24 extracted pilot signal of the base station 100 _{1 2 {p 1} = p 1,1,1} , p 1,1,2, ... and _{p 1,4,4,} base station 100 the _second pilot signal _{{p 2} = p 2,1,1,} p 2,1,2, ... and _{p 2,4,4.} As shown in FIG. 6, _{x in px, y, z} is a base station index, y is a time index of pilot position, and z is a frequency index of pilot position. The base station 100 ₁ of the correlation value _{c 1} of the pilot signal _{{p 1},} the correlation value _{c 2} of the pilot signal of the base station 100 _{2 {p 2}} are respectively obtained from the following equation.

Here, p ^* represents a complex conjugate of the complex number p. Phase theta _1, and the phase theta ₂ of the correlation values c ₂ of the correlation values c ₁ can be calculated from the following formulas.

θ ₁ is a value related to the frequency deviation between the base station 100 ₁ and the mobile station 200, and θ ₂ is a value related to the frequency deviation between the base station 100 ₂ and the mobile station 200. The frequency deviation estimation unit 31 outputs the phases θ ₁ and θ ₂ obtained by the above formulas to the pilot correction unit 30 and the equalization unit 28A.

The pilot correction unit 30 corrects the frequency deviation of the pilot signal using the phases θ ₁ and θ ₂ obtained by the frequency deviation estimation unit 31. Specifically, pilot correction unit 30, the first base station 100 ₁ of the pilot signal _{{p 1}} and base station 100 ₂ pilot signal _{{p 2}} frequency deviation correction value for correcting the _{{B y}} or less Obtained from the equation

Here, B _{y, a} (a = 1, 2) is a frequency deviation correction value for the pilot signal of the base station 100 _a at the position where the time index is y. As can be seen from the equations (5) and (6), there is no frequency deviation correction value for the pilot signal of y = 1. This is because the frequency deviation correction is a process for correcting the phase change amount in the time direction, and since y = 1 is the reference position of the phase change amount, the pilot signal of y = 1 does not need the frequency deviation correction. is there. Also, B _{y, a} (a = 1, 2) does not depend on the frequency index z. This is because the frequency deviation correction is a process for correcting the phase change amount in the time direction and does not depend on the frequency.

In addition, (y−1) of the exponent part on the right side of the expressions (5) and (6) represents the distance in the time direction from the reference y = 1. Phases θ ₁ and θ ₂ are phase differences between pilot signals adjacent in the time direction. As shown in FIG. 6, the number of symbols in the time direction between pilot signals adjacent in the time direction is two. Further, as shown in FIG. 7, the number of symbols from y = 1 as a reference of data whose time index is y as a correction target is (y−1) × 2. Therefore, when correcting data with a time index of y, the amount of phase change is (y−1) times the phases θ ₁ and θ ₂ . For the above reason, the phases θ ₁ and θ ₂ are multiplied by (y−1) in the exponent part on the right side of the equations (5) and (6).

Pilot correcting unit 30 corrects the following formula base station 100 ₁ of the pilot signal _{{p 1}} and base station 100 ₂ pilot signal _{{p 2}} using the correction value _{{B y}.}

Equations (7) and (8) are for y = 1, and equations (9) and (10) are for y ≧ 2. Here, Q _{a, x, y} (a = 1, 2) represents the pilot signal at the corrected pilot position (x, y, z).

The transmission path characteristic estimator 29 is based on the corrected pilot signals Q _{a, x, y} (a = 1,2) corrected by the pilot corrector 30 between the base stations 100 ₁ , 100 ₂ and the mobile station 200. The transmission path characteristic is calculated as a transmission path characteristic value.

The equalization unit 28A uses the transmission path characteristic value obtained by the transmission path characteristic estimation unit 29 and the phases θ ₁ and θ ₂ obtained by the frequency deviation estimation unit 31 to determine the base stations 100 ₁ and 100 from the received signal. ₂ transmission data is extracted.

FIG. 7 shows an example of symbol arrangement of transmission data of the base stations 100 ₁ and 100 ₂ in the received signal of the mobile station 200. In FIG. 7, (m, n) represents a data position, m represents a data time index, and n represents a data frequency index. Here, the received data {D _mn } for the position (m, n) and the transmission path characteristic estimated value {H _mn } for the position (m, n) can be expressed by the following equations.

Here, D _{m, n, r} (r = 1, 2) represents received data at the receiving antenna 27 _r , and H _{m, n, a, b} (a = 1, 2, b = 1, 2) represents the base. A transmission path characteristic value between the station 100 _a and the receiving antenna 27 _b of the mobile station 200 is represented.

FIG. 8 is a diagram illustrating the configuration of the equalization unit 28A and its periphery. As shown in FIG. 8, the equalization unit 28 </ b> A includes a pseudo transmission line creation unit 281 and a transmission data extraction unit 282. The pseudo transmission path creation unit 281 uses the transmission path characteristic value {H _mn } which is the output of the transmission path characteristic estimation unit 29 and the phases θ ₁ and θ ₂ which are the outputs of the frequency deviation estimation unit 31 to transmit the transmission path. A pseudo transmission line characteristic value is generated by adding a frequency deviation to the characteristic value. That is, since the transmission path characteristic value is created from the corrected pilot signal, it does not include a frequency deviation. Therefore, the pseudo transmission path creation unit 281 generates a pseudo transmission path characteristic value by adding a frequency deviation to the transmission path characteristic value.

The transmission data extraction unit 282 extracts the transmission data of the base stations 100 ₁ and 100 ₂ from the reception signal that is the output of the time frequency conversion unit 25 using the pseudo transmission path obtained by the pseudo transmission path creation unit 281.

The pseudo transmission line creation unit 281 calculates the frequency deviation giving value {K _m } from the phases θ ₁ and θ ₂ by the following formula.

Furthermore, the pseudo transmission path creation unit 281 generates a pseudo transmission path characteristic value {V _mn } by the following formula.

Since the pseudo transmission line characteristic value {V _mn } is a transmission line characteristic including a frequency deviation, it can be regarded as a pseudo transmission line. Therefore, the transmission data extraction unit 282 at the subsequent stage can extract transmission data by a general equalization method without being aware of the frequency deviation.

The transmission data extraction unit 282 extracts the transmission data of the base stations 100 ₁ and 100 ₂ using the reception data {D _mn } and the pseudo transmission line characteristic value {V _mn }. Although there are various methods for extracting transmission data, an MMSE (Minimum Mean Square Error) equalization method will be described here as an example. Further, in the case of diversity transmission data to be cooperative transmission with the base station 100 ₁ and the base station 100 ₂ is the same for each case of the data to be coordinated transmission are different spatial multiplexing transmission with the base station 100 ₁ and the base station 100 ₂ explain.

For diversity transmission movement, by combining the transmission path between the base station 100 ₁ and the mobile station 200, and a transmission path between the base station 100 ₂ and the mobile station 200, as if from one base station Consider transmission to station 200. Specifically, the transmission data extraction unit 282, pseudo transmission channel characteristic value of the base station 100 ₁ and the _{{V mn},} synthesized artificial transmission channel characteristic values of the base station 100 _{2 {V mn}} by the following equation.

Here, V _{m, n, b} (b = 1, 2) is the pseudo transmission path value V _{m, n, b, 1} between the base station 100 ₁ and the receiving antenna 27 _b of the mobile station 200 _, and the base artificial transmission channel value _{V m} between the stations 100 ₂ and the receiving antenna 27 _b of the mobile station 200 _is a combined value of _n, and _{b, 2.} Based on this combined value, base station transmission data {W _mn } for position (m, n) is extracted from the following equation.

Here, V ^H _mn is a Hermitian transposed matrix of the matrix V _mn , and N represents noise power generated at the receiving antenna 27 of the mobile station 200. For N, a process for estimating noise power may be separately performed and the estimated value may be used, or a fixed value may be used. Here, a fixed value is used for simplification of description.

Since in diversity transmission is transmission data of the base station 100 ₁ and the base station 100 ₂ is the same, as the formula (20), transmission data to be extracted is one.

Then, the base station 100 ₁ and the base station 100 ₂ for performing spatial multiplexing transmission will be described extraction of the transmission data in the transmission data extraction unit 282. The transmission data extraction unit 282 extracts the transmission data {W _mn } of the base stations 100 ₁ and 100 ₂ with respect to the position (m, n) by the following expression.

Here, I is a 2 × 2 unit matrix, and W _{m, n, a} (a = 1, 2) represents an estimated value for transmission data of the base station a at the position (m, n).

Thus, the radio communication system according to the present embodiment includes mobile station 200 and a plurality of base stations 100 ₁ and 100 ₂ that cooperatively transmit a transmission signal including a pilot signal and transmission data to mobile station 200. Prepare. The pilot signals transmitted from the base stations 100 ₁ and 100 ₂ are orthogonal to each other. The mobile station 200 extracts each pilot signal from each base station from the received signal of the mobile station 200 and each pilot signal extracted by the pilot extraction units 24 _{1 to} 24 _Nr and the pilot extraction units 24 _{1 to} 24 _Nr. Correction is performed by the frequency deviation estimation unit 31 that estimates the frequency deviation between the base stations 100 ₁ and 100 ₂ and the mobile station 200, the pilot correction unit 30 that corrects each pilot signal based on the frequency deviation, and the pilot correction unit 30. Based on each pilot signal, the channel characteristic estimation unit 29 for estimating the channel characteristic between each of the base stations 100 ₁ , 100 ₂ and the mobile station 200, the movement based on the channel characteristic and the frequency deviation And equalizers 28A and 28B for extracting transmission data of the base stations 100 ₁ and 100 ₂ from the received signal of the station 200. Since the base stations 100 ₁ and 100 ₂ are arranged so that the pilot signals are orthogonal to each other, the mobile station 200 can extract the pilot signals of the base station 100 ₁ and the base station 100 ₂ without interfering with each other. . Furthermore, since the mobile station 200 can estimate the frequency deviation of each of the base stations 100 ₁ and 100 ₂ from the extracted pilot signal, the transmission data of the base station 100 ₁ and the base station 100 ₂ is corrected for the frequency deviation. It can be extracted in the state. Further, since the frequency deviation is corrected only by the mobile station 200, the frequency deviation can be corrected in a short time.

In addition, the equalization unit 28A of the wireless communication system uses a pseudo transmission line characteristic and a pseudo transmission line creation unit 281 that creates a pseudo transmission line characteristic including the frequency deviation by correcting the transmission line characteristic based on the frequency deviation. And a transmission data extraction unit 282 that extracts transmission data of the base stations 1001 and 1002 from the reception signal of the mobile station 200. Therefore, the transmission data extraction unit 282, the transmission data of the base station 100 ₁ and the base station 100 _2, can be extracted in a state of correcting the frequency deviation. Further, since the frequency deviation is corrected only by the mobile station 200, the frequency deviation can be corrected in a short time.

<B. Second Embodiment>
FIG. 9 is a diagram illustrating a configuration example of a radio reception device (hereinafter simply referred to as “reception device 20B”) included in the mobile station 200 in the radio communication system according to the second embodiment. The receiving device 20B is the same as the receiving device 20A of the first embodiment except that the equalizing unit 28A is replaced with the equalizing unit 28B and the demapping unit 22A is replaced with the demapping unit 22B. Is the same as that of the receiving device 20A.

FIG. 10 is a diagram showing a configuration of the equalization unit 28B and its surroundings. As shown in FIG. 10, the equalization unit 28 </ b> B includes a transmission data extraction unit 283 and a frequency deviation correction unit 284. The transmission data extraction unit 283 uses the transmission path characteristic estimation value estimated by the transmission path characteristic estimation unit 29, and receives the base station 100 _{1 to} 100 _Nb from the reception signal converted into the frequency domain by the time frequency conversion unit 25. Extract transmission data. The frequency deviation correction unit 284 performs correction to remove the frequency deviation of the transmission data extracted by the transmission data extraction unit 283 using the frequency deviation estimated by the frequency deviation estimation unit 31.

  In the following, for simplicity of explanation, the number of base stations Nb for coordinated transmission is assumed to be 2, the number of transmission antennas Nt of the base station is 1, and the number of reception antennas Nr of the mobile station is 2 as in the first embodiment. However, the present invention is not limited to this combination of the number of base stations, the number of base station transmitting antennas, and the number of mobile station receiving antennas.

Regardless of whether the coordinated transmission method of the base station is diversity transmission or spatial multiplexing transmission, the transmission data extraction unit 283 uses the following formula to transmit the transmission data {W _mn } of the base stations 100 ₁ and 100 ₂ in either case. To extract.

Expression (23) is an expression in which {V _mn } is replaced with {H _mn } in Expression (21) of Embodiment 1. W _{m, n, 1} represents an estimated value of transmission data of the base station 100 ₁ , and W _{m, n, 2} represents an estimated value of transmission data of the base station 100 ₂ . In the case of diversity transmission, the transmission data of the base station 100 ₁ and the base station 100 ₂ are the same, but the transmission data of the base station 100 ₁ and the base station 100 ₂ are calculated individually in equation (23). This is because both of the correction amounts are different in the frequency deviation correction unit 284 in the subsequent stage.

The frequency deviation correction unit 284 calculates a frequency deviation correction value {J _m } from the phases θ ₁ and θ ₂ calculated by the frequency deviation estimation unit 31 using the following formula.

In equations (25) and (26), J _{m, a} (a = 1, 2) represents the frequency deviation correction value for the transmission data of the base station 100 _{a at} the time index m, and e represents the natural logarithm. Represent. As can be seen from the equations (25) and (26), there is no frequency deviation correction value when m = 1. This is because the frequency deviation correction is a process for correcting the phase change amount in the time direction, and m = 1 is set as the reference position of the phase change amount. Further, the frequency deviation correction value J _{m, a} (a = 1, 2) does not depend on the frequency index n. This is because the frequency deviation correction is a process for correcting the phase change amount in the time direction and does not depend on the frequency.

Further, (m−1) of the exponent part on the right side of the expressions (25) and (26) represents the distance in the time direction from the reference m = 1. The phases θ ₁ and θ ₂ are phase differences between pilot signals adjacent in the time direction, and the distance in the time direction between pilot signals adjacent in the time direction is two symbols as shown in FIG. In addition, the transmission data of the time index m to be corrected has a distance in the time direction from the transmission data of m = 1 as a reference is the number of symbols (m−1) × 2. Therefore, the phase change amount of the data of the time index m is (m−1) times the phases θ ₁ and θ ₂ . For the above reason, in the exponent part on the right side of the above equation, the phases θ ₁ and θ ₂ are multiplied by (m−1).

Next, the frequency deviation correction unit 284 uses the frequency deviation correction value J _{m, a} (a = 1, 2) to transmit the transmission data {W of the base stations 100 ₁ and 100 ₂ obtained by the transmission data extraction unit 283. _mn } is corrected to remove the frequency deviation. The corrected transmission data {R _mn } = R _{m, n, 1} and R _{m, n, 2} are obtained by the following formulas when m = 1.

Further, the corrected transmission data {R _mn } = R _{m, n, 1} , R _{m, n, 2} is obtained by the following equation when m ≧ 2.

Here, R _{m, n, a} (a = 1, 2) represents an estimated value of data transmitted from the base station 100 _{a at the} position (m, n).

Next, the operation of the demapping unit 22B will be described. The demapping unit 22B performs demapping processing on the transmission data of each of the base stations 100 ₁ and 100 ₂ converted into the time domain by the frequency time conversion unit 23, and the soft decision value {L _ia } = L _{i, a, 1} and _{Li, a, s} are generated. Here, i is the time index of the data symbol transmitted from the base station, a is the base station index, and s is the number of bits per symbol. The demapping unit 22B outputs the soft decision value {L _ia } to the error correction decoding unit 21 as it is when the coordinated transmission between the base stations 100 ₁ and 100 ₂ is spatial multiplexing transmission. The operation of the demapping unit 22B so far is the same as that of the demapping unit 22A of the first embodiment.

However, when the coordinated transmission between the base stations 100 ₁ and 100 ₂ is diversity transmission, the demapping unit 22B performs a soft decision on the transmission data symbols of the base stations 100 ₁ and 100 _{2 at} the same time and the same bit position. The value is synthesized by the following formula. In the case of diversity transmission, the equalization unit 28A of the first embodiment extracts the transmission data of the base stations 100 ₁ and 100 ₂ as the same value, whereas the equalization unit 28B of the second embodiment This is because the transmission data of the base stations 100 ₁ and 100 ₂ are individually extracted.

In equation (31), G _{i, j} represents the soft decision composite value of the j-th bit (j = 1 to s) in the data symbol at time i.

  According to the radio communication system of the second embodiment, similar to the radio communication system of the first embodiment, the cooperative transmission data of the base stations 1001 and 1002 is extracted by removing the frequency deviation by the operation of only the mobile station 200. Therefore, cooperative transmission can be performed at an early stage. In addition to the effects common to the first embodiment, the wireless communication system according to the second embodiment has the following effects.

That is, in the receiving apparatus 20A of the first embodiment, the equalizing unit 28A performs correction for removing the frequency deviation on the pseudo transmission line characteristic value, so that the number of pseudo transmission line characteristic values, that is, (number of base stations Nb ) × (number of base station transmitting antennas Nt) × (number of mobile station receiving antennas Nr) is required to be complex multiplied. On the other hand, according to the receiving apparatus 20B of the second embodiment, the equalizing unit 28B uses the transmission path characteristics that do not include the frequency deviation to each base station 100 ₁ that includes the frequency deviation from the received signal of the mobile station 200. , 100 ₂ for transmitting data {W _mn }, and correction for removing frequency deviation from transmission data {W _mn } using the phases θ ₁ and θ ₂ calculated by the frequency deviation estimating unit 31. And a frequency deviation correction unit 284 for performing That is, the equalizing unit 28B performs correction for removing the frequency deviation from the transmission data after extracting the transmission data of each of the base stations 100 ₁ and 100 ₂ , so that the number of complex multiplications is calculated as the number of transmission data, that is, (base station (Number Nb) × (number of base station transmitting antennas Nt).

In addition, when each base station 100 ₁ , 100 ₂ performs diversity transmission as a coordinated transmission to the mobile station 200, the reception sensitivity at the mobile station 200 is improved, which is suitable for transmission of data that requires band-guaranteed transmission. Yes.

In addition, when each base station 100 ₁ , 100 ₂ performs spatial multiplexing transmission as a coordinated transmission to the mobile station 200, the throughput is improved, which is suitable for data transmission that requires best effort transmission.

<C. Embodiment 3>
In the first and second embodiments, diversity transmission and spatial multiplexing transmission are given as examples of coordinated transmission of base stations. The third embodiment is characterized in that the base stations are divided into two base station groups, one performing diversity transmission and the other performing spatial multiplexing transmission.

FIG. 11 is a diagram illustrating a configuration of a wireless communication system according to the third embodiment. Wireless communication system according to the third embodiment is performed with the mobile station 200, and base station ₁₀₁ 1 to 101 _K of K stations performing diversity transmission to the mobile station 200, the spatial multiplexing transmission to the mobile station 200 L Station base stations 102 _{1 to} 102 _L. Hereinafter, the base station ₁₀₁ 1 to 101 _K the base station group A of K stations performing diversity transmission, called a base station group B and the base station ₁₀₂ 1 to 102 _L of L station perform spatial multiplexing transmission.

  Diversity transmission is a transmission method characterized by improved reception sensitivity. On the other hand, spatial multiplexing is a transmission method characterized by an improvement in throughput. Therefore, for example, data that requires band-guaranteed transmission, such as control data that requires high reception quality at a low transmission rate, is diversity-transmitted using the base station group A. On the other hand, for example, data that requires best effort transmission, such as user data that requires a high transmission rate with minimum reception quality, is spatially multiplexed using the base station group B. This enables efficient data transmission.

  For the reception processing of the mobile station 200, the receiving device 20A of the first embodiment may be used, or the receiving device 20B of the second embodiment may be used. In the following description, a case will be described in which receiving apparatus 20B of Embodiment 2 is used for the reception process of mobile station 200.

For both transmission data of base station group A and base station group B, guard interval removal unit 26, time frequency conversion unit 25, pilot extraction unit 24, frequency deviation estimation unit 31, pilot correction unit 30 of reception device 20B, The transmission path characteristic estimation unit 29 and the equalization unit 28B perform the same processing as in the second embodiment. In the demapping unit 22B, soft decision values of the transmission data of the base station group A and the base station group B are generated. At this time, the soft decision values of the base stations 101 _f (1 ≦ f ≦ K) belonging to the base station group A are assigned to {T _if } = T _{i, f, 1} ,..., T _{i, f, s1} , base station group A The soft decision value of the base station 101 _g (1 ≦ g ≦ L) to which it belongs is assumed to be {U _ig } = U _{i, g, 1} ,..., U _{i, g, s2} . Here, i is the time index of the data symbol, s1 is the number of bits per symbol in the base station group A, and s2 is the number of bits per symbol in the base station group B.

The demapping unit 22B combines the soft decision values for the soft decision values {T _if } of the base station group A that performs diversity transmission using the following equation.

In Expression (32), R _{i, j} is a soft decision value at the j-th bit (1 ≦ j ≦ s1) of the time index i.

On the other hand, the demapping unit 22B does not synthesize the soft decision value {T _if } of the base station group B for spatial multiplexing transmission and outputs it as it is.

  Thus, in the wireless communication system according to Embodiment 3, the plurality of base stations that perform cooperative transmission to mobile station 200 include base station group A that performs diversity transmission as cooperative transmission, and a base that performs spatial multiplexing transmission as cooperative transmission. And station group B. Therefore, the base station group A can be used for data that requires bandwidth guaranteed transmission, and the base station group B can be used for data that requires best effort transmission. Thereby, it becomes possible to transmit data efficiently.

<D. Hardware configuration>
In the wireless communication system described above, the error correction coding unit 1, the mapping unit 2, the time frequency conversion unit 3, the pilot insertion unit 4, the frequency time conversion unit 5, and the guard interval insertion unit 6 of the transmission apparatus 10 are illustrated in FIG. The processing circuit 381 shown in FIG. Further, the error correction decoding unit 21, the demapping unit 22A, the frequency time conversion unit 23, the pilot extraction unit 24, the time frequency conversion unit 25, the guard interval removal unit 26, the frequency deviation estimation unit 31, the transmission path characteristics of the reception device 20A. The estimation unit 29, pilot correction unit 30, and equalization unit 28A are also realized by the processing circuit 381 shown in FIG. Further, the demapping unit 22B and the equalizing unit 28B of the receiving device 20B are also realized by the processing circuit 381 shown in FIG.

  That is, the processing circuit 381 includes an error correction coding unit 1, a mapping unit 2, a time frequency conversion unit 3, a pilot insertion unit 4, a frequency time conversion unit 5, a guard interval insertion unit 6, an error correction decoding unit 21, and a demapping. Unit 22A, frequency time conversion unit 23, pilot extraction unit 24, time frequency conversion unit 25, guard interval removal unit 26, frequency deviation estimation unit 31, transmission path characteristic estimation unit 29, pilot correction unit 30, equalization unit 28A, A mapping unit 22B and an equalization unit 28B are provided.

  Dedicated hardware may be applied to the processing circuit 381, or a processor that executes a program stored in the memory may be applied. The processor is, for example, a central processing unit, a processing unit, an arithmetic unit, a microprocessor, a microcomputer, a digital signal processor, or the like.

  When the processing circuit 381 is dedicated hardware, the processing circuit 381 corresponds to, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC, an FPGA, or a combination thereof. . Each function of each unit such as the equalizing unit 28A may be realized by a plurality of processing circuits 381, or the function of each unit may be realized by a single processing circuit.

  When the processing circuit 381 is a processor, the functions of the equalization unit 28A and the like are realized by a combination of software and the like (software, firmware or software and firmware). Software or the like is described as a program and stored in a memory. As illustrated in FIG. 13, the processor 382 applied to the processing circuit 381 realizes the functions of the respective units by reading and executing the program stored in the memory 383. Here, the memory 383 is a nonvolatile memory such as RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Electrically Programmable Read Only Memory), or EEPROM (Electrically Erasable Programmable Read Only Memory). Alternatively, at least one of a volatile semiconductor memory, an HDD (Hard Disk Drive), a magnetic disk, a flexible disk, an optical disk, a compact disk, a mini disk, a DVD (Digital Versatile Disk), and its drive device is included.

  It should be noted that the present invention can be freely combined with each other within the scope of the invention, and each embodiment can be appropriately modified or omitted.

DESCRIPTION OF SYMBOLS 1 Error correction encoding part, 2 Mapping part, 3,25 Time frequency conversion part, 4 Pilot insertion part, 5,23 Frequency time conversion part, 6 Guard interval insertion part, 7 Transmission antenna, 10 Transmission apparatus, 20A, 20B Reception Apparatus, 21 error correction decoding unit, 22A, 22B demapping unit, 24 pilot extraction unit, 26 guard interval removal unit, 27 reception antenna, 28A, 28B equalization unit, 29 transmission path characteristic estimation unit, 30 pilot correction unit, 31 frequency deviation estimation unit, 100 _{1 to} 100 _Nb , 101 _{1 to} 101 _K , 102 _{1 to} 102 _L base station, 200 mobile station, 281 pseudo transmission path generation unit, 282, 283 transmission data extraction unit, 284 frequency deviation correction unit , 381 processing circuit, 382 processor, 383 memory.

Claims (6)

A mobile station,
A plurality of base stations that cooperatively transmit transmission signals including pilot signals and transmission data to the mobile station, and
The pilot signals transmitted from each of the base stations are orthogonal to each other,
The mobile station
A pilot extractor for extracting a pilot signal from each of the base stations from the received signal of the mobile station;
A frequency deviation estimation unit that estimates a frequency deviation between each base station and the mobile station from each pilot signal extracted by the pilot extraction unit;
A pilot correction unit that corrects each pilot signal based on the frequency deviation estimated by the frequency deviation estimation unit;
Based on each pilot signal corrected by the pilot correction unit, a channel characteristic estimation unit that estimates a channel characteristic between each base station and the mobile station,
An equalization unit that extracts transmission data of each base station from a reception signal of the mobile station based on the transmission path characteristic estimated by the transmission path characteristic estimation unit and the frequency deviation estimated by the frequency deviation estimation unit; Comprising
Wireless communication system. The equalization unit
A pseudo transmission line creation unit that creates a pseudo transmission line characteristic including the frequency deviation by correcting the transmission line characteristic by the frequency deviation estimated by the frequency deviation estimation unit;
A transmission data extraction unit that extracts transmission data of each of the base stations from a reception signal of the mobile station using the pseudo transmission line characteristics,
The wireless communication system according to claim 1. The equalization unit
A transmission data extraction unit that extracts transmission data of each base station from a reception signal of the mobile station using the transmission path characteristics;
A frequency deviation correction unit that corrects the transmission data based on the frequency deviation estimated by the frequency deviation estimation unit,
The wireless communication system according to claim 1. The plurality of base stations perform diversity transmission as the cooperative transmission.
The radio | wireless communications system of any one of Claim 1 to 3. The plurality of base stations perform spatial multiplexing transmission as the cooperative transmission.
The radio | wireless communications system of any one of Claim 1 to 3. The plurality of base stations include a base station group that performs diversity transmission as the coordinated transmission and a base station group that performs spatial multiplexing transmission as the coordinated transmission,
The radio | wireless communications system of any one of Claim 1 to 3.

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