# Patent

## Title
Radio communication base station apparatus in multiple-carrier communication and radio communication method

## Abstract

A base station is provided to suppress a drop of receiving power and deterioration of receiving characteristics by cancellation between the same symbols in the case of application of a repetition technology to multiple-carrier communication. In this base station (100), a repetition unit (103) for reproducing (making repetition of) each data symbol input from a modulating unit (102) to make out a plurality of identical data symbols, and a phase rotating unit (106) for giving a phase rotation to a data symbol input from a multiplexing unit (105). This time the phase rotating unit (106) provides the identical symbols made out by the repetition with the phase rotation which has a phase rotating difference different from phase rotating differences among a plurality of identical symbols transmitted with the ones identical to a plurality of the identical symbols at time and a frequency identical to those of a plurality of the identical symbols in adjacent cells or adjacent sectors.

## Background
TECHNICAL FIELD
The present invention relates to a radio communication base station apparatus and radio communication method in multicarrier communication.
BACKGROUND ART
Recently, in radio communication, particularly, in mobile communication, various information such as images and data other than speech are transmission targets. It is anticipated that demands for higher-speed transmission will increase in the future, and a radio transmitting technique for realizing high transmission efficiency utilizing limited frequency resources more efficiently to perform high-speed transmission is demanded.
OFDM is one of radio transmitting techniques to meet these demands. OFDM is a multicarrier transmitting technique for transmitting data in parallel using a plurality of subcarriers, and is known to have features of realizing high frequency efficiency and reducing inter-symbol interference under multipath environment and be effective for improving transmission efficiency.
Further, OFDM provides the maximum frequency efficiency in multicarrier communication because the frequencies of a plurality of subcarriers in which data is arranged are orthogonal to each other, and enables multicarrier communication with a comparatively simple hardware configuration. For this reason, OFDM is focused upon as a communication method to be employed in cellular scheme mobile communication and various studies upon this communication are underway. Further, with OFDM, to prevent inter-symbol interference (ISI), the rear portion of an OFDM symbol is added to the head of the OFDM symbol as a cyclic prefix (CP). Consequently, the receiving end is able to prevent ISI as long as the delay time of the delay wave stays within the time length of the CP (hereinafter simply “CP length”).
Furthermore, with OFDM, quality varies significantly between subcarriers due to frequency selective fading resulting from multipath. In this case, given that a signal allocated to a subcarrier in a location which is a valley of fading has poor quality and makes demodulation difficult, it is necessary to improve quality such that demodulation is possible.
There is a repetition technique as a technique for improving quality in OFDM. The repetition technique is directed to performing transmission by generating a plurality of the same symbols by repeating (i.e. repetition) a certain symbol and allocating a plurality of the same symbols to a plurality of different subcarriers or different times, so that the receiving end is able to obtain diversity gain by performing maximum ratio combining of these same symbols (see, for example, Non-Patent Document 1).
On the other hand, transmission diversity techniques which are effective to reduce inter-cell interference include a technique of transmitting the same symbol at the same time, by the same frequency, from the radio communication base station apparatuses (hereinafter “base stations”) of a plurality of cells. As a result of such transmission, a radio communication mobile station apparatus (hereinafter “mobile station”) located near the cell edge receives mixed same symbols from a plurality of base stations. Consequently, in cases where OFDM is applied to this transmission diversity technique, in the mobile station located near the cell edge, inter-cell interference is not produced as long as a plurality of the same OFDM symbols transmitted from a plurality of base stations at the same time are received with a time lag within the range of the OP length, and these OFDM symbols are combined and received as OFDM symbols with amplified transmission power, so that it is possible to obtain diversity gain.
Non-Patent Document 1: “Performance Comparisons between OFCDM and OFDM in a Forward Link Broadband Channel,” Noriyuki MAEDA, Hiroyuki ATARASHI, Yoshihisa KISHIYAMA, Mamoru SAWAHASHI, The Institute of Electronics, Information and Communication Engineers, TECHNICAL REPORT OF ISICE, RCS2002-162, August 2002, pp. 95 to 100
DISCLOSURE OF INVENTION
Problems to be Solved by the Invention
A case will be described here where radio communication that combines the above techniques is performed in the mobile communication system shown in FIG. 1. That is, in this mobile communication system, the base station in cell A (BSA) and the base station in cell B (BSB) both transmit the same OFDM symbols (OFDM symbol A and OFDM symbol B) comprised of subcarriers of the same frequency, to a mobile station (MS) at the same time. OFDM symbol A and OFDM symbol B are each formed with subcarriers f1 to f4 as shown in FIG. 2. Further, in base station BSA and base station BSB, the same data symbols S1 and S1′ (S1′ is a data symbol which is generated by repeating S1 and which is the same as S1; the same applies below) are allocated to subcarriers f1 and f3, and the same data symbols S2 and S2′ are allocated to subcarriers f2 and f4.
In this case, as shown in FIG. 3, if S1 and S1′ in cell A and S1 and S1′ in cell B are each received in the mobile station with out of phase due to the influence of channel variation in the channels, given that S1s cancel each other and S1′s cancel each other, the received power of both S1 and S1′ decrease significantly and diversity gain resulting from combination of S1 and S1′ cannot be obtained, which results in degradation of received performances. Further, FIG. 3 shows a case where the phases of S1 and S1′ in cell B rotate 180 degrees in the channels.
It is therefore an object of the present invention to provide a base station and radio communication method that, in cases where the repetition technique is employed in multicarrier communication, make it possible to prevent reduction in received power resulting from cancellation between the same symbols and prevent degradation of received performances.
Means for Solving the Problem
The base station according to the present invention that transmits a multicarrier signal comprised of a plurality of subcarriers to a radio communication mobile station apparatus, includes: a repetition section that repeats a first symbol to generate a plurality of same first symbols; a phase rotation section that applies a phase rotation to the plurality of first symbols; and a transmitting section that transmits the multicarrier signal in which the plurality of first symbols given phase rotations are allocated to the plurality of subcarriers, and employs a configuration in which the phase rotation section makes a phase rotation difference produced between the plurality of first symbols different from a phase rotation difference produced between a plurality of second symbols which are the same as the plurality of first symbols and which are transmitted in adjacent cells or adjacent sectors at the same time, by the same frequency, as the plurality of first symbols.
ADVANTAGEOUS EFFECT OF THE INVENTION
The present invention makes it possible to prevent reduction in received power resulting from cancellation between the same symbols and prevent degradation of received performances in cases where the repetition technique is employed in multicarrier communication.



BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 shows cell arrangement of a two-cell model;
FIG. 2 shows a data symbol after repetition;
FIG. 3 shows a data symbol influenced by channel variation;
FIG. 4 is a block diagram showing a configuration of a base station according to an embodiment of the present invention;
FIG. 5 is a block diagram showing a configuration of a mobile station according to an embodiment of the present invention;
FIG. 6 illustrates phase rotation according to an embodiment of the present invention (cell A);
FIG. 7 illustrates phase rotation according to an embodiment of the present invention (cell B);
FIG. 3 illustrates phase rotation according to an embodiment of the present invention (cell A);
FIG. 9 illustrates phase rotation according to an embodiment of the present invention (cell B);
FIG. 10 shows a data symbol according to an embodiment of the present invention (cell A);
FIG. 11 shows a data symbol according to an embodiment of the present invention (cell B);
FIG. 12 shows a received symbol according to an embodiment of the present invention;
FIG. 13 shows a received symbol according to an embodiment of the present invention;
FIG. 14 shows a received symbol according to an embodiment of the present invention;
FIG. 15 shows a received symbol according to an embodiment of the present invention;
FIG. 16 shows cell arrangement according to an embodiment of the present invention (three-cell model);
FIG. 17 illustrates phase rotation according to an embodiment of the present invention (cell B);
FIG. 18 illustrates phase rotation according to an embodiment of the present invention (cell C);
FIG. 19 shows sector arrangement according to an embodiment of the present invention (three-sector model);
FIG. 20 is a block diagram showing a configuration of the base station according to an embodiment of the present invention (three-sector model);
FIG. 21 illustrates phase rotation according to an embodiment of the present invention (cell A); and
FIG. 22 illustrates phase rotation according to an embodiment of the present invention (cell B).



BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described in detail below with reference to the drawings.
With the present embodiment, the base station applies phase rotations to a plurality of the same symbols generated by repetition such that the phase rotation differences produced between a plurality of the same symbols are different from the phase rotation differences produced between a plurality of the same symbols transmitted in adjacent cells or adjacent sectors at the same time, by the same frequency as a plurality of the same symbols generated by repetition.
FIG. 4 shows a configuration of base station 100 according to the present embodiment. With the present embodiment, base station BSA and base station BSB shown in FIG. 1 both employ a configuration shown in FIG. 4.
In base station 100, encoding section 101 carries out encoding processing of inputted transmission data (bit sequence), and modulating section 102 generates a data symbol by carrying out modulation processing of the encoded transmission data by the modulation scheme such as QPSK and 16QAM.
Repetition section 103 generates a plurality of the same data symbols by repeating (i.e. repetition) each data symbol inputted from modulating section 102, and outputs a plurality of the same data symbols to S/P section (serial-to-parallel converting section) 104. In the following description, a plurality of the same data symbols will be referred to as the “unit of repetition.”
S/P section 104 converts, into parallel, the data symbol sequence inputted from repetition section 103 in a series, and outputs the data symbol sequence to multiplexing section 105. By means of this serial-to-parallel conversion, each data symbol is allocated to a plurality of subcarriers forming a multicarrier signal.
Multiplexing section 105 time-domain-multiplexes the data symbols and the pilot symbols by selecting and outputting a pilot symbol each time a predetermined number of data symbols (for example, one frame of data symbols) are inputted from S/P section 104.
Phase rotation section 106 applies phase rotations to the data symbols inputted from multiplexing section 105. The phase rotation will be described in detail later. The data symbols given phase rotations are outputted to IFFT (Inverse Fast Fourier Transform) section 107.
IFFT section 107 performs an IFFT of a plurality of subcarriers to which the pilot symbols or data symbols are allocated, to acquire an OFDM symbol which is a multicarrier signal.
CP adding section 108 provides a CP by adding the same signal as the rear portion of an OFDM symbol, to the head of the OFDM symbol.
Radio transmitting section 109 carries out transmission processing such as D/A conversion, amplification and up-conversion of the OFDM symbol after the CP is added, and transmits the result to the mobile station shown in FIG. 5 from antenna 110.
Next, FIG. 5 shows a configuration of mobile station 200 according to the present embodiment. Mobile station MS shown in FIG. 1 employs the configuration shown in FIG. 5.
In mobile station 200, the OFDM symbol received through antenna 201 is subjected to reception processing such as down-conversion and A/D conversion in radio receiving section 202, is removed the CP in CP removing section 203 and is inputted to FFT (Fast Fourier Transform) section 204.
FFT section 204 extracts the symbol allocated to each subcarrier by performing an FFT of the OFDM symbol, and outputs one OFDM symbol to channel compensating section 205.
Channel compensating section 205 calculates a channel estimation value of each subcarrier by performing channel estimation using the received pilot symbol, and compensates for the channel variation of the data symbols based on this channel estimation value. In this case, channel compensating section 205 calculates a channel compensation value taking into account the phase rotation applied in base station 100. One OFDM symbol of the data symbols after channel variation compensation is outputted in parallel, to P/S section 206.
P/S section 206 converts the data symbol sequences inputted in parallel from channel compensating section 205 into a series, and outputs the result to combining section 207.
Combining section 207 combines the data symbols in repetition units, that is, between the same data symbols generated by repetition in base station 100.
Further, the operations of channel compensating section 205 and combining section 207 will be described in detail.
The combined symbol is demodulated in demodulating section 208 and is decoded in decoding section 209. By this means, received data can be obtained.
Next, the phase rotation applied in phase rotation section 106 of base station 100 and the operations of channel compensating section 205 and combining section 207 of mobile station 200 will be described in detail.
First, a case will be described where there is one cell, cell B, adjacent to cell A, as shown in FIG. 1. In the following description, as described above, OFDM symbol A and OFDM symbol B are each formed with subcarriers f1 to f4. Further, in the base station in cell A (BSA) and the base station in cell B (BSB), the same data symbols S1 and S1′ are allocated to subcarriers f1 and f3, and the same data symbols S2 and S2′ are allocated to subcarriers f2 and f4. Then, base station BSA and base station BSB both transmit the same OFDM symbols (OFDM symbol A and OFDM symbol B) comprised of subcarriers of the same frequency to a mobile station (MS) at the same time. Further, although the following description focuses upon data symbol S1 and S1′, as to data symbols S2 and S2′, the present invention can be implemented in the same way.
As shown in FIG. 6, base station BSA applies phase rotations of phase rotation angles φA1 and φA3 to the same data symbols S1 and S1′. In this way, the phase rotation difference between S1 and S1′ in cell A is ΔφA=φA3−φA1.
On the other hand, as shown in FIG. 7, base station BSB applies phase rotations of phase rotation angles φB1 and φB3, to the same data symbols S1 and S1′. In this way, the phase rotation difference between S1 and S1′ in cell B is ΔφB=φB3−φB1.
Further, with the present invention, ΔφA≠ΔφB. That is, with the present invention, the phase rotation difference ΔφA between the data symbols S1 and S1′ in cell A and the phase rotation difference ΔφB between the data symbols S1 and S1′ in cell B, adjacent to cell A, are different.
For example, as shown in FIG. 8 and FIG. 9, ΔφA=0 degree assuming that φA1=0 degree and φA3=0 degree, and ΔφB=180 degrees assuming that φB1=0 degree and φB3=180 degrees. In this way, S1 and S1′ included in OFDM symbol A transmitted from base station BSA in cell A are as shown in FIG. 10, and S1 and S1′ included in OFDM symbol B transmitted from base station BSB in cell B are as shown in FIG. 11. OFDM symbol A and OFDM symbol B including S1 and S1′, to which such phase rotations are applied, are received by mobile station MS.
FIG. 12 shows the received symbol in mobile station MS. Data symbols received by means of subcarriers f1 and f4 are data symbols R1 to R4. R1 and R3 received by means of subcarriers f1 and f3 to which S1 and S1′ are allocated, will be focused upon and described. Further, in the following description, the channel variation in subcarrier f1 in cell A is hA1, the channel variation in subcarrier f3 in cell A is hA3, the channel variation in subcarrier f1 in cell B is hB1 and the channel variation in subcarrier f3 in cell B is hB3. Furthermore, assuming that the frequency interval between subcarriers f1 and f3 is narrow and these subcarriers stay in the coherent bandwidth, frequency performances in the channels are uniform between subcarriers f1 and f3, so that hA1=hA3 and hB1=hB3. Still further, assuming that subcarriers f1 and f3 stay in the coherent bandwidth, ΔφA applied in base station BSA and ΔφB applied in base station BSB are maintained as is until ΔφA and ΔφB reach to mobile station MS.
Three cases of (1) hA1=hA3=90 degrees and hB1=hB3=180 degrees, (2) hA1=hA3=90 degrees and hB1=hB3=270 degrees, and (3) hA1=hA3=45 degrees and hB1=hB3=90 degrees, will be assumed and described below.
(1) Case of hA1=hA3=90 degrees and hB1=hB3=180 degrees (FIG. 13A to H)
Given that hA1=90 degrees and hB1=180 degrees, the phase of S1 in cell A (FIG. 10) rotates 90 degrees in the channel and the phase of S1 in cell B (FIG. 11) rotates 180 degrees in the channel. In this way, S1 in cell A and S1 in cell B are combined in channels, so that received symbol R1 is as shown in FIG. 13A.
Given that hA3=90 degrees and hB3=180 degrees, the phase of S1′ in cell A (FIG. 10) rotates 90 degrees in the channel and the phase of S1′ in cell B (FIG. 11) rotates 180 degrees in the channel. In this way, S1′ in cell A and S1′ in cell B are combined in the channels, so that received symbol R3 is as shown in FIG. 13B.
On the other hand, channel estimation values resulting from channel estimation in channel compensating section 205 are hA1=hA3=90 degrees and hB1=hB3=180 degrees as shown in FIG. 13C and FIG. 13D.
According to φB3=180 degrees, channel compensating section 205 carries out processing to reverse the phase of hB3 in FIG. 13D 180 degrees as shown in FIG. 13E. This processing makes hB3=0 degree.
Next, channel compensating section 205 finds combined channel estimation value h1 in subcarrier f1 by combining hA1 and hB1 as shown in FIG. 13F, to find the channel estimation value for R1 obtained by combining S1 in cell A and S1 in cell B. In this way, h1=135 degrees. In the same way, channel compensating section 205 finds combined channel estimation value h3 in subcarrier f3 by combining hA3 and hB3 after the phase is reversed, as shown in FIG. 13G, to find the channel estimation value for R3 obtained by combining S1′ in cell A and S1′ in cell B. In this way, h3=45 degrees.
Next, as shown in FIG. 13H, channel compensating section 205 compensates for the channel variation in R1 based on h1 and compensates for the channel variation in R3 based on h3. That is, channel compensating section 205 carries out processing to reverse the phase of R1 135 degrees and the phase of R3 45 degrees.
Then, as shown in FIG. 13H, combining section 207 combines R1 and R3 after compensation for channel variation and acquires the combined symbol R1+R3.
In this way, ΔφA=0 degree and ΔφB=180 degrees, so that it is possible to prevent S1 and S1′ in cell A and S1 and S1′ in cell B from being received by mobile station MS with out of phase.
(2) Case of hA1=hA3=90 degrees and hB1=hB3=270 degrees (FIG. 14A to H)
Given that hA1=90 degrees and hB1=270 degrees, the phase of S1 in cell A (FIG. 10) rotates 90 degrees in the channel, and the phase of S1 in cell B (FIG. 11) rotates 270 degrees in the channel. In this way, S1 in cell A and S1 in cell B are combined in the channels, so that received symbol R1 is zero as shown in FIG. 14A.
Further, given that hA3=90 degrees and hB3=270 degrees, the phase of S1′ in cell A (FIG. 10) rotates 90 degrees in the channel, and the phase of S1′ in Cell B (FIG. 11) rotates 270 degrees in the channel. In this way, S1′ in cell A and S1′ in cell B are combined in the channels, so that received symbol R3 is as shown in FIG. 14B.
On the other hand, channel estimation values resulting from channel estimation in channel compensating section 205 are hA1=hA3=90 degrees and hB1=hB3=270 degrees as shown in FIGS. 14C and D.
According to φB3=180 degrees, channel compensating section 205 carries out processing to reverse the phase of hB3 in FIG. 14D 180 degrees as shown in FIG. 14E. This processing makes hB3=90 degrees.
Next, channel compensating section 205 finds combined channel estimation value h1 in subcarrier f1 by combining hA1 and hB1 as shown in FIG. 14F, to find the channel estimation value for R1 obtained by combining S1 in cell A and S1 in cell B. In this way, h1=zero. In the same way, channel compensating section 205 finds combined channel estimation value h3 in subcarrier f3 by combining hA3 and hB3 after the phase is reversed, as shown in FIG. 14G, to find the channel estimation value for R3 obtained by combining S1′ in cell A and S1′ in cell B. In this way, h3=90 degrees.
Next, as shown in FIG. 14H, channel compensating section 205 compensates for the channel variation in R1 based on h1 and compensates for the channel variation in R3 based on h3. In this case, given that R1 is zero, channel compensating section 205 carries out only processing to reverse the phase of R3 90 degrees.
Then, as shown in FIG. 14H, combining section 207 combines R1 and R3 after compensation for channel variation and acquires the combined symbol R1+R3. Given that R1 is zero, R3 can be obtained as the combined symbol.
In this way, ΔφA=0 degree and ΔφB=180 degrees, so that it is possible to prevent S1 and S1′ in cell A and S1 and S1′ in cell B from being received by mobile station MS with out of phase, as in case of above (1).
(3) Case of hA1=hA3=45 degrees and hB1=hB3=90 degrees (FIG. 15A to H)
Given that hA1=45 degrees and hB1=90 degrees, the phase of S1 in cell A (FIG. 10) rotates 45 degrees in the channel and the phase of S1 in cell B (FIG. 11) rotates 90 degrees in the channel. In this way, S1 in cell A and S1 in cell B are combined in channels, so that received symbol R1 is as shown in FIG. 15A.
Given that hA3=45 degrees and hB3=90 degrees, the phase of S1′ in cell A (FIG. 10) rotates 45 degrees in the channel and the phase of S1′ in cell B (FIG. 11) rotates 90 degrees in the channel. In this way, S1′ in cell A and S1′ in cell B are combined in channels, so that received symbol R3 is as shown in FIG. 15B.
On the other hand, channel estimation values resulting from channel estimation in channel compensating section 205 are hA1=hA3=45 degrees and hB1=hB3=90 degrees as shown in FIG. 15C and FIG. 15D.
According to φB3=180 degrees, channel compensating section 205 carries out processing to reverse the phase of hB3 in FIG. 15D 180 degrees as shown in FIG. 15E. This processing makes hB3=270 degrees.
Next, channel compensating section 205 finds combined channel estimation value h1 in subcarrier f1 by combining hA1 and hB1 as shown in FIG. 15F, to find the channel estimation value for R1 obtained by combining S1 in cell A and S1 in cell B. In this way, h1=67.5 degrees. In the same way, channel compensating section 205 finds combined channel estimation value h3 in subcarrier f3 by combining hA3 and hB3 after the phase is reversed, as shown in FIG. 15G, to find the channel estimation value for R3 obtained by combining S1′ in cell A and S1′ in cell B. In this way, h3=337.5 degrees.
Next, as shown in FIG. 15H, channel compensating section 205 compensates for the channel variation in R1 based on h1 and compensates for the channel variation in R3 based on h3. That is, channel compensating section 205 carries out processing to reverse the phase of R1 66.5 degrees and the phase of R3 337.5 degrees.
Then, as shown in FIG. 15H, combining section 207 combines R1 and R3 after compensation for the channel variation and acquires the combined symbol R1+R3.
In this way, ΔφA=0 degree and ΔφB=180 degrees, so that it is possible to prevent S1 and S1′ in cell A and S1 and S1′ in cell B from being received by mobile station MS with out of phase, as in cases of above (1) and (2).
As is clear from the above description, ΔφA≠ΔφB, so that, even when S1 and S1′ are influenced by the phase variation in the channels, it is possible to prevent the received power of both R1 and R3 from decreasing to zero in the mobile station and prevent R1 and R3 from being lost, and obtain diversity gain resulting from combination of S1 and S1′, and, consequently, prevent degradation of received performances.
It is preferable to maximize the phase rotation differences between adjacent cells to minimize degradation of received performances due to cancellation between S1s and between S1′s.
For example, in the two-cell model shown in FIG. 1, it is preferable to make the difference between the phase rotation difference ΔφA in cell A and the phase rotation difference ΔφB in cell B 180 degrees, as described above.
Further, in the three-cell model shown in FIG. 16 it is preferable to make the differences between the phase rotation difference ΔφA in cell A, the phase rotation difference ΔφB in cell B, and the phase rotation difference ΔφC in cell C, all 120 degrees. Consequently, for example, in cases where the phase rotation (ΔφA=0 degree assuming that φA1=0 degree and φA3=0 degree) as shown in FIG. 8 is applied in cell A, it is preferable that ΔφB=120 degrees assuming that φB1=0 degree and φB3=120 degrees in cell B as shown in FIG. 17 and ΔφC=240 degrees assuming that φC1=0 degree and φC3=240 degrees in cell C as shown in FIG. 18.
In this way, with the present embodiment, base stations in cells adjacent to each other make the phase rotation difference between S1 and S1′ a value matching the number of adjacent cells. For example, in the two-cell model shown in FIG. 1, there is one cell, B cell, adjacent to cell A and, in the three-cell model shown in FIG. 16, there are two cells adjacent to one cell, so that each base station applies phase rotations φ1 and φ3 that produce the phase rotation difference Δφ according to equation (1), to S1 and S1′. For example, in the two-cell model, by changing n in equation (1) to n=0 or 1, base station BSA applies phase rotations φA1 and φA3 that produce a phase rotation difference ΔφA in case of n=0, to S1 and S1′ and base station BSB applies phase rotations φB1 and φB3 that produce a phase rotation difference ΔφB in case of n=1, to S1 and S1′. Further, in the three-cell model, by changing n in equation (1) to n=0, 1 or 2, base station BSA applies phase rotations φA1 and φA3 that produce a phase rotation difference ΔφA in case of n=0, to S1 and S1′, base station BSB applies phase rotations φB1 and φB3 that produce a phase rotation difference ΔφB in case of n=1, to S1 and S1′ and base station BSC applies phase rotations φC1 and φC3 that produce a phase rotation difference ΔφC in case of n=2, to S1 and S1′.

Phase rotation difference=n×(360 degrees/(number of adjacent cells+1), where n is an integer  (Equation 1)

Further, although a case has been described with the above description where the present invention is implemented between adjacent cells, the present invention can be implemented as described above even between adjacent sectors in the same cell. For example, in the three-sector model shown in FIG. 19, the present invention can be implemented as in the three-cell model shown in FIG. 16. That is, assuming that cell A is sector A, cell B is sector B and cell C is sector C in the above description, the present invention can be implemented as described above. However, in cases where the present invention is implemented between adjacent sectors, base station BS shown in FIG. 19 makes the phase rotation difference between S1 and S1′ a value matching the number of sectors in one cell. That is, base station BS applies phase rotations φ1 and φ3 that produce the phase rotation difference Δφ according to equation (2), to S1 and S1′ in each sector. To be more specific, in the three-sector model shown in FIG. 19, given that the number of sectors in one cell is “3,” by changing n in equation (2) to n=0, 1 or 2, phase rotations φA1 and φA3 that produce a phase rotation difference ΔφA in case of n=0, are applied to S1 and S1′ in sector A, phase rotations φB1 and φB3 that produce a phase rotation difference ΔφB in case of n=1, are applied to S1 and S1′ in sector B and phase rotations φC1 and φC3 that produce a phase rotation difference ΔφC in case of n=2, are applied to S1 and S1′ in sector C. By so doing, it is possible to minimize degradation of received performances due to cancellation between S1s and between S1′s by maximizing the phase rotation differences between adjacent sectors.

Phase rotation difference=n×(360 degrees/number of sectors in one cell), where n is an integer  (Equation 2)

Further, FIG. 20 shows the configuration of base station BS of FIG. 19 as base station 300. Base station 300 has sector A apparatus 100-A, sector B apparatus 100-B and sector C apparatus 100-C that each have the same configuration. Sector A apparatus 100-A, sector B apparatus 100-B and sector C apparatus 100-C each have the same configuration as base station 100 shown in FIG. 4 and receive as input the same transmission data.
An embodiment of the present invention has been described above.
Further, the phase rotation may be applied in the base station to S1 and S1′ by multiplying S1 and S1′ by e(jθ). For example, in a case where the phase rotation difference in cell A is ΔφA=0, the phase rotation difference in cell B is ΔφB=e(jπ), and the difference between ΔφA and ΔφB is e(jπ) (that is, 180 degrees), e(jπ/4) is multiplied upon S1 and S1′ in cell A as shown in FIG. 21 and e(j3π/4) is multiplied upon S1 and e(j7π/4) is multiplied upon S1′ in cell B as shown in FIG. 22. Further, the phase rotation applied using this multiplication may be performed by multiplying cell-specific or sector-specific scrambling sequences comprised of e(jθ) sequence. Furthermore, in cases where the cell-specific or sector-specific scrambling sequences comprised of e(jθ) sequence are determined in advance and cannot be changed, the scrambling sequences may be multiplied by changing the arrangement of data symbols according to the scrambling sequence so as to produce the desired phase rotation difference. Still further, in cases where the scrambling sequence has been multiplied upon S1 and S1′, the phase rotation may be applied by further multiplying e(jθ) upon S1 and S1′.
The degree of phase rotation applied to each data symbol may be known in advance between the base station and the mobile station or may be reported from the base station to the mobile station. For example, the degree of phase rotation may be reported as control information each time the OFDM symbol is transmitted.
Further, although a case has been described with the above description as an example where two same data symbols can be acquired assuming that the repetition factor (RF) in repetition section 103 is RF=2, the present invention is not limited to RF=2 and may be applied to the case where RF is three or more.
Furthermore, although a case has been described with the above description where the present invention is applied to downlink, the present invention can be applied to uplink. It is possible to apply the present invention to uplink by, for example, providing a plurality of transmitting apparatuses in a mobile station, carrying out the same processing in a plurality of transmitting apparatuses as in base stations 100 and 300 and carrying out the same processing in the base station as in above mobile station 200.
Further, although a case has been described with the above description where the channel estimation value in cell A is found from the pilot in cell A, the channel estimation value in cell B is found from the pilot in cell B, and then the combined channel estimation value is found by combining these channel estimation values, the combined channel estimation value may be found by the following method. That is, the base station may apply the phase rotation with the same angle as the data symbol to the pilot in cell A and the pilot in cell B and transmit these pilots to the mobile station at the same time, by the same frequency, and the mobile station may find the combined channel estimation value directly from the combined received pilot in the channel.
Further, although a case has been described with the above description where the present invention is implemented for symbols arranged on the frequency axis (i.e. frequency domain), the present invention can be also implemented as described above for symbols arranged on the time axis (i.e. time domain).
Although OFDM has been described with the above description as an example of multicarrier communication, the present invention can be implemented in multicarrier communication other than OFDM.
Further, the base station, mobile station and subcarrier may be referred to as “Node B,” “UE” and “tone,” respectively. Furthermore, a CP may be referred to as “guard interval (GI).”
Also, although cases have been described with the above embodiments as examples where the present invention is configured by hardware, the present invention can also be realized by software.
Each function block employed in the description of the above embodiment may typically be implemented as an LSI constituted by an integrated circuit. These may be individual chips or partially or totally contained on a single chip. “LSI” is adopted here but this may also be referred to as “IC,” “system LSI,” “super LSI,” or “ultra LSI” depending on differing extents of integration.
Further, the method of circuit integration is not limited to LSI's, and implementation using dedicated circuitry or general purpose processors is also possible. After LSI manufacture, utilization of a programmable FPGA (Field Programmable Gate Array) or a reconfigurable processor where connections and settings of circuit cells within an LSI can be reconfigured is also possible.
Further, if integrated circuit technology comes out to replace LSI's as a result of the advancement of semiconductor technology or a derivative other technology, it is naturally also possible to carry out function block integration using this technology. Application of biotechnology is also possible.
The disclosure of Japanese Patent Application No. 2006-128258, filed on May 2, 2006, including the specification, drawings and abstract, is incorporated herein by reference in its entirety.
INDUSTRIAL APPLICABILITY
The present invention is applicable to, for example, a mobile communication system.

## Claims

1. A radio communication base station apparatus that transmits a multicarrier signal comprised of a plurality of subcarriers to a radio communication mobile station apparatus, the radio communication base station apparatus comprising:
a repetition section that repeats a first symbol to generate a plurality of same first symbols;
a phase rotation section that applies a phase rotation to the plurality of first symbols; and
a transmitting section that transmits the multicarrier signal in which the plurality of first symbols given phase rotations are allocated to the plurality of subcarriers, wherein
the phase rotation section makes a phase rotation difference between the plurality of first symbols different from a phase rotation difference between a plurality of second symbols which are the same as the plurality of first symbols and which are transmitted in a different cell or a different sector at the same time, by the same frequency, as the plurality of first symbols.

2. The radio communication base station apparatus according to claim 1, wherein the phase rotation section applies the phase rotation that produces a phase rotation difference matching a number of different cells or different sectors.

3. The radio communication base station apparatus according to claim 1, wherein the phase rotation section applies the phase rotation that produces a phase rotation difference represented by n×(360 degrees/(number of different cells+1)) or a phase rotation difference represented by n×(360 degrees/number of sectors in one cell), where n is an integer.

4. The radio communication base station apparatus according to claim 1, wherein the phase rotation section makes the phase rotation difference between the plurality of first symbols different from a phase rotation difference between the plurality of second symbols by multiplying the plurality of first symbols by a scrambling code that applies phase rotation that produces a phase rotation difference different from the phase rotation difference between the plurality of second symbols, to the plurality of first symbols.

5. A radio communication method used in a radio communication system where same symbols are transmitted at the same time, by the same frequency between a plurality of cells or between a plurality of sectors, the radio communication method comprising making a phase rotation difference between of the same symbols in a first cell or a first sector different from a phase rotation difference between the same symbols in a second cell, different from the first cell, or a second sector, different from the first sector.