Radio communication device and pilot arrangement method

Provided is a radio communication device capable of reducing the number of pilots while maintaining a channel estimation accuracy. The radio communication device includes: a unicast pilot generation unit (105) which generates a unicast pilot sequence and outputs it to an arrangement unit (106); and an arrangement unit (106) arranges unicast data, multicast data, a unicast pilot sequence, and a multicast pilot sequence at a position on the two-dimensional plane formed by a frequency axis and a time axis for output to an IFFT (Inverse Fast Fourier Transform) unit (107). Here, the arrangement unit (106) does not arrange pilots of the multicast pilot sequence at a time when the single frequency is different from the position where identical pilots are arranged between sectors among the respective pilots of the unicast pilot sequence in one sub frame.

TECHNICAL FIELD

The present invention relates to a radio communication apparatus and a pilot arrangement method.

BACKGROUND ART

In the field of mobile communication, a variety of information such as image and data in addition to speech becomes transmission targets in recent years. Accompanying this, the demand for reliable and high-speed transmission has increased. However, when high-speed transmission is carried out in mobile communications, the influence of delayed waves due to multipath cannot be ignored, and transmission performance deteriorates due to frequency selective fading.

As one of countermeasure techniques for frequency selective fading, multicarrier communication represented by OFDM (Orthogonal Frequency Division Multiplexing) communication becomes a focus of attention. In multicarrier communication, data is transmitted using a plurality of subcarriers where transmission speed is suppressed to an extent not to cause frequency selective fading. Particularly, in OFDM communication, the frequencies of a plurality of subcarriers where data is arranged are orthogonal to each other, so that it is possible to achieve the maximum frequency efficiency in multicarrier communication schemes and realize multicarrier communication in a relatively simple hardware configuration. Consequently, OFDM communication is attracted attention as a communication method to be employed in cellular scheme mobile communications, and is studied variously. In addition, in OFDM communication, to avoid ISI (Intersymbol Interference) the tail part of an OFDM symbol is attached to the beginning of that OFDM symbol as a cyclic prefix (CP). By this means, for the receiving side, it is possible to avoid ISI as long as the delay time of delay waves stays within the time length of CP (hereinafter “CP length”).

Further, studies have been recently conducted for multicast communication. Multicast communication is point-to-multipoint communication, unlike unicast communication, which is point-to-point communication. That is, in multicast communication, one radio communication base station apparatus (hereinafter abbreviated as “base station”) transmits the same data (i.e. multicast data) to a plurality of radio communication mobile stations (hereinafter abbreviated as “mobile station”) at the same time. By this multicast communication, in mobile communication systems, for example, delivery services of music data and video image data and broadcast services such as television broadcast are realized.

Further, in multicast communication, one base station transmits the same multicast data to a plurality of mobile stations at the same time as described above, and, when one cell is divided into a plurality of sectors, multicast data is the same in a plurality of sectors. Furthermore, when one cell is divided into a plurality of sectors, the same multicast data is transmitted for a plurality of sectors at the same time, and therefore, a mobile station near the cell boundary receives multicast data for a plurality of sectors in a mixed manner.

Here, in cases of using the OFDM scheme in multicast communication, when a mobile station near the sector boundary receives a plurality of identical OFDM symbols, which are transmitted to a plurality of sectors at the same time, within the CP length, the mobile station receives them in a state where these OFDM are combined and received power is amplified. This method of transmitting the same data using the same resources (i.e. the same time and the same frequency) via a plurality of paths is referred to as “SFN (Single Frequency Network) transmission.” In SFN transmission, a mobile station is able to receive data without inter-sector interference, so that it is possible to carry out high quality transmission with a lower error rate.

Further, to compensate channel fluctuation (phase fluctuation and amplitude fluctuation) of this combined signal by channel estimation, a channel estimation value of the combined signal is needed. That is, in multicast communication using the OFDM scheme, pilots used to find the channel estimation value need to be transmitted to a plurality of sectors at the same time, as in the case of multicast data. That is, the multicast pilot needs to be a common pilot between a plurality of sectors.

On the other hand, in unicast communication, in cases of dividing one cell into a plurality of sectors, different data (i.e. unicast data) is transmitted to a plurality of sectors. That is, unicast data is unique per sector. Consequently, in unicast communication, as for pilots used to find the channel estimation values, different pilots for unicast data (i.e. unicast pilots) need to be transmitted to a plurality of sectors similar to unicast data. That is, unicast pilots needs to be individual between a plurality of sectors.

Multicast communication adopts a scheme of transmitting information only to specific mobile stations subscribing to services including news groups, and, meanwhile, broadcast communication adopts a scheme of transmitting information to all mobile stations like current TV broadcasting or radio broadcasting. However, multicast communication and broadcast communication are similar in involving point-to-multipoint communication, and, a description using MBMS (Multimedia Broadcast/Multicast Service) which combines multicast communication and broadcast communication, may be given depending on documents. Further, a description may be given using broadcast communication instead of multicast communication, depending on documents.

Here, when one cell is divided into a plurality of sectors, to reduce interference between sectors, an orthogonal pilot channel sequence, which is orthogonal between sectors, is set as a unicast pilot sequence. For example, when one cell is formed with three sectors, that is, sectors1to3, as shown inFIG. 1, a sequence formed with all “1's” (the amount of phase rotation θ=0) is set for sector1, a sequence by multiplying the sequence of sector1and a sequence formed with 1, exp(j2p/3), and exp(j4p/3) . . . (the amount of phase rotation θ=2p/3) is set for sector2, and, a sequence by multiplying the sequence of sector1and a sequence formed with 1, exp(j4p/3), and exp(j2p/3) . . . (the amount of phase rotation θ=4p/3) is set for sector3. That is, as shown inFIG. 1, unicast pilot sequences of sector1to3, are orthogonal to each other based on one unit (orthogonal sequence unit) formed with three chips in the combination of 1, exp(j2p/3), and exp(j4p/3). Further, each unicast pilot sequence is formed with a plurality of identical orthogonal sequence units. For example, the unicast pilot sequence for sector1is a repetition of the orthogonal sequence unit “1, 1, 1,” the unicast pilot sequence for sector2is a repetition of the orthogonal sequence unit “1, exp(j2p/3), exp(j4p/3),” and the unicast pilot sequence for sector3is a repetition of the orthogonal sequence unit “1, exp(j4p/3), exp(j2p/3).”

Then, this unicast pilot arrangement method is studied as shown inFIG. 1(see Non-patent Document 1). InFIG. 1, for ease of description, a case is shown as one example where one OFDM symbol is formed with subcarriers f1to f25and where one sub-frame is formed with OFDM symbols #1to #7. The same applies to the drawings below. In the example shown inFIG. 1, the unicast pilot is arranged to subcarriers f1, f7, f13, f19and f25in OFDM symbol #1and subcarriers f4, f10, f16and f22in OFDM symbol #5in the sectors. That is, for example, the unicast pilot “1” of sector1, the unicast pilot “1” of sector2and the unicast pilot “1” of sector3are multiplexed on subcarrier f1in OFDM symbol #1on the channel. The unicast pilot “1” of sector1, the unicast pilot “exp(j2p/3)” of sector2and the unicast pilot “exp(j4p/3)” of sector3are multiplexed on subcarrier f4in OFDM symbol #5on the channel. The unicast pilot “1” of sector1, the unicast pilot “exp(j4p/3)” of sector2and the unicast pilot “exp(j2p/3)” of sector3are multiplexed on subcarrier f7in OFDM symbol #1on the channel. That is, unicast pilots of a plurality of sectors are multiplexed on the same frequency of the same time. By adopting this arrangement, it is possible to arrange unicast pilots in one sub-frame both in the frequency domain and the time domain all over.

On the other hand, by contrast with this unicast pilot arrangement method, a multicast pilot arrangement method is studied as shown inFIG. 2(see Non-patent Document 2). As shown in the above description, multicast pilots of a plurality of sectors are required to be arranged to the same frequency of the same time. In the example shown inFIG. 2, in each sector, the multicast pilot is arranged to subcarriers f4, f10, f16and f22in OFDM symbol #1and subcarriers f1, f7, f13, f19and f25in OFDM symbol #5. By adopting this arrangement, similar to a unicast pilot, it is possible to arrange multicast pilots in one sub-frame both in the frequency domain and in the time domain all over. Further, conventionally, to sufficiently acquire accuracy of channel estimation for multicast data in all frequencies, as shown inFIG. 2, the number of multicast pilots and the number of unicast pilots arranged in one sub-frame are the same.Non-patent Document 1: 3GPP TSG RAN WG1 Meeting #46, R1-062099, Tallinn, Estonia, Aug. 28-Sep. 1, 2006, NTT DoCoMo, Ericsson, Fujitsu, Intel Corporation, KDDI, Mitsubishi Electric, NEC, Panasonic, Qualcomm, Sharp, and Toshiba Corporation, “Orthogonal Reference Signal Structure for Sectored Beams in E-UTRA Downlink”Non-patent Document 2: 3GPP TSG RAN WG1 Meeting #44bis, R1-060779, Athens, Greece, 27-31 Mar. 2006, NTTDoCoMo, Mitsubishi Electric, NEC, Sharp, Toshiba Corporation, “Investigations on Pilot Channel Structure for MBMS in E-UTRA Downlink”

DISCLOSURE OF INVENTION

Problems to be Solved by the Invention

Now, communication resources that can be used in the mobile communication system are limited, and therefore the demand for high speed and large capacity of data transmission further increase today, and resources for data use are requested to be secured as much as possible in the limited resources. To secure as much resources for data use as possible, it is possible to reduce the number of pilots and assign the resources where the pilots have been assigned, to data. However, if the number of pilots is simply decreased, the accuracy of channel estimation is deteriorated.

It is therefore an object of the present invention to provide a radio communication apparatus and pilot arrangement method that maintains the accuracy of channel estimation and reduces the number of pilots.

Means for Solving the Problem

The radio communication apparatus of the present invention adopting the configuration including: an arrangement section that arranges first pilot sequences (i.e. unicast pilot sequences) that vary between a plurality of sectors or between a plurality of cells and second pilot sequences (i.e. multicast pilot sequences) that are shared between the plurality of sectors or between the plurality of cells, to positions on a two dimensional plane defined by a frequency domain and a time domain; and a transmission section that transmits the first pilot sequences and the second pilot sequences arranged on the two dimensional plane, wherein, in one sub-frame, the arrangement section does not arrange pilots of the second pilot sequences to different times of a same frequency as positions where same pilots in the first pilot sequences are arranged in a neighboring sector or in a neighboring cell.

Advantageous Effect of the Invention

According to the present invention, it is possible to maintain the accuracy of channel estimation and reduce the number of pilots.

BEST MODE FOR CARRYING OUT THE INVENTION

Now, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Although, in the following description, the OFDM scheme will be explained as a multicarrier communication scheme, the present invention is not limited to the OFDM scheme.

First,FIG. 3shows the mobile communication system according to the present embodiment. Here, a case will be shown as an example where one cell is divided into three sectors, that is, sectors1to3. Further, sectors1to3are neighboring each other. Base station10has three antennas for each sector, and transmits signals to each sector from each antenna.

Next,FIG. 4shows the configuration of base station10according to the present embodiment. Base station10has radio communication apparatuses100-1to100-3for sectors1to3, respectively. Further, base station10has multicast pilot generation section150that is common between radio communication apparatuses100-1to100-3, that is, common between sectors1to3. Multicast pilot generation section150generates a multicast pilot sequence, that is, a pilot sequence that is common between sectors1to3, and output the sequence to radio communication apparatuses100-1to100-3.

FIG. 5shows the configuration of each radio communication apparatus. In the present embodiment, radio communication apparatuses100-1to100-3shown inFIG. 4each adopt the configuration shown inFIG. 5.

In radio communication apparatus100, encoding section101encodes unicast data, and outputs the unicast data to modulation section102.

Modulation section102modulates the unicast data after encoding, and outputs the modulated data to arrangement section106.

Encoding section103encodes multicast data, and outputs the multicast data to modulation section104.

Modulation section104modulates the multicast data after encoding, and outputs the modulated data to arrangement section106.

Unicast pilot generation section105generates a unicast pilot sequence, that is, generates a pilot sequence varying between sector1, sector2and sector3, and outputs the sequence to arrangement section106. For example, when radio communication apparatus100is radio communication apparatus100-1for sector1, unicast pilot generation section105generates a unicast pilot sequence formed with unicast pilots “1, 1, 1, . . . .” Further, when radio communication apparatus100is radio communication apparatus100-2for sector2, unicast pilot generation section105generates a unicast pilot sequence formed with unicast pilots “1, exp(j2p/3), exp(j4p/3), . . . .” Further, when radio communication apparatus100is radio communication apparatus100-3for sector3, unicast pilot generation section105generates a unicast pilot sequence formed with unicast pilots “1, exp(j4p/3), exp(j2p/3), . . . .”

Further, arrangement section106receives a multicast pilot sequence as input from multicast pilot generation section150(FIG. 4).

Arrangement section106arranges the unicast data, the multicast data, the unicast pilot sequence, and the multicast pilot sequence to the positions on a two-dimensional plane defined by the frequency domain and the time domain, and outputs them to IFFT (Inverse Fast Fourier Transform) section107. The frequency domain corresponds to a plurality of subcarriers forming one OFDM symbol, and the time domain corresponds to a plurality of OFDM symbols transmitted in order. That is, arrangement section106arranges the unicast data, the multicast data, the unicast pilot sequence, and the multicast pilot sequence to a plurality of subcarriers in a plurality of OFDM symbols. Arrangement processing in arrangement section106will be described later in detail.

IFFT section107performs an IFFT over a plurality of subcarriers where the unicast data, the multicast data, the unicast pilot sequence, and the multicast pilot sequence are arranged and converts them to a time domain signal, to generate an OFDM symbol of a multicarrier signal.

CP attachment section108attaches the same signal as the tail part of an OFDM symbol, to the beginning of that OFDM symbol to provide a CP.

Radio transmitting section109performs transmission processing including D/A conversion, amplification and up-conversion, on the OFDM symbol with an attachment of a CP, and transmits the OFDM symbol after transmission processing from antenna110to mobile station200(FIG. 6). That is, transmitting section109transmits the unicast data, the multicast data, the unicast pilot sequence, and the multicast pilot sequence arranged on a two-dimensional plane defined by the frequency domain and the time domain.

Next, mobile station200according to the present embodiment will be explained.FIG. 6shows the configuration of mobile station200according to the present embodiment.

In mobile station200, radio receiving section202receives an OFDM symbol via antenna201and performs receiving processing including down-conversion and A/D conversion on the received OFDM symbol and outputs it to CP removal section203.

CP removal section203removes the CP attached to the OFDM symbol from the OFDM symbol after receiving processing, and outputs the OFDM symbol without a CP to FFT (Fast Fourier Transform) section204.

FFT section204performs an FFT on the OFDM symbol inputted from CP removal section203, to convert it to the frequency domain signal, and acquires unicast data, multicast data, unicast pilots or multicast pilots, and outputs them in the number of subcarriers in parallel to P/S section205.

P/S section205converts the unicast data, the multicast data, the unicast pilots or the multicast pilots inputted in parallel from FFT section204to serial, and outputs it to separation section206.

Separation section206separates the data and the pilots, and outputs the unicast data and the multicast data to compensation section209and outputs the unicast pilots and the multicast pilots to pilot selection section207.

Pilot selection section207selects the pilot depending on a type of data where channel estimation is performed. When the unicast data is outputted from separation section206to compensation section209, pilot selection section207selects the unicast pilot and outputs it to channel estimation section208, and, when the multicast data is outputted from separation section206to compensation section209, pilot selection section207selects the multicast pilot and outputs it to channel estimation section208.

Channel estimation section208calculates a channel estimation value using the pilot selected in pilot selection section207, and outputs the channel estimation value to compensation section209.

Compensation section209compensates channel fluctuation of the unicast data or the multicast data using the channel estimation value calculated in channel estimation value208, and outputs the compensated data to demodulation section210. Compensation section209compensates the channel fluctuation of each data by multiplying the data by the complex conjugate of the channel estimation value.

Demodulation section210demodulates each data inputted from compensation section209, and outputs each demodulated data to decoding section211.

Decoding section211decodes each data after demodulation. In this way, received data is acquired.

Next, the arrangement processing in arrangement section106of radio communication apparatus100will be explained in detail with a number of arrangement examples.

In cases where unicast pilot sequences are set as individual orthogonal pilot sequences between sectors and arranged as described above as shown inFIG. 1, as shown inFIG. 7, the first chip (i.e. head chip) in one orthogonal sequence unit is all “1” in sectors1to3, the unicast pilot “1” of sector1, the unicast pilot “1”of sector2and the unicast pilot “1” of sector3are multiplexed on the channel for subcarrier f1in OFDM symbol #1, subcarrier f10in OFDM symbol #5, and subcarrier f19in OFDM symbol #1. That is, when base station10(FIGS. 3 and 4) transmits unicast pilot sequences to sectors, in some of the unicast pilot sequences, the same pilots are transmitted at the same time from a plurality of antennas. In other words, on a two-dimensional plane defined by the frequency domain and the time domain, there are positions where the same pilots are arranged between a plurality of sectors in the pilots in the unicast pilot sequences. Then, the same pilots in unicast pilot sequences transmitted to a plurality of sectors at the same time are also available as multicast pilots.

Then, in the present embodiment, as shown in the following pilot arrangement examples 1 to 8, in one sub-frame, arrangement section106(FIG. 5) of radio communication apparatus100regards the same pilots between sectors1to3in the pilots of unicast pilot sequences, as multicast pilots, and, does not arrange the pilots of multicast pilot sequences to different times of the same frequency as the positions where the same pilots are arranged. In cases where multicast data is outputted from separation section206to compensation section209, pilot selection section207(FIG. 6) of mobile station200further selects a pilot that can be used as a multicast pilot in unicast pilot sequences, and outputs the selected pilot to channel estimation section208.

In this way, it is possible to maintain the accuracy of channel estimation of both unicast data and multicast data, and reduce the number of multicast pilots. Then, it is possible to arrange data to the positions where the reduced multicast pilots have been arranged, so that resources for data use can increase.

Hereinafter, pilot arrangement examples 1 to 5 in arrangement section106(FIG. 5) will be explained in cases where one cell is divided into three sectors, that is, sectors1to3.

In this way, it is possible to arrange pilots that can be used for channel estimation of multicast data at equal intervals (i.e. predetermined periods) in the frequency domain and reduce the number of multicast pilots in one sub-frame. Consequently, it is possible to maintain the accuracy of channel estimation for multicast data in the frequency domain, and to reduce the number of multicast pilots and increase resources for data use.

In this way, it is possible to arrange pilots that can be used for channel estimation of multicast data at equal intervals (i.e. predetermined periods) in the time domain, in addition to the frequency domain. That is, according to this arrangement example, it is possible to arrange pilots that can be used for channel estimation of multicast data at equal intervals (i.e. predetermined periods) both in the frequency domain and in the time domain, and reduce the number of multicast pilots in one sub-frame. Consequently, compared to arrangement example 1, this arrangement example improves the accuracy of channel estimation for multicast data in the time domain. This arrangement example is especially suitable for use in a case where a mobile station in a cell moves at high speed.

Multicast pilots are unnecessary to perform channel estimation for dedicated channels per sector. Then, this arrangement example differs from pilot arrangement example 2 (FIG. 9) in that multicast pilots are arranged to areas apart from the areas where dedicated control channels including SCCHs (Shared Control Channels) for each sector of sector1, sector2and sector3, are arranged in one sub-frame.FIG. 10shows the area defined by subcarriers f1to f25(frequency domain) and OFDM symbols #1and #2(time domain), as the area where SCCHs are arranged. That is, in this arrangement example, as shown inFIG. 10, multicast pilots are arranged to an area apart from the area defined by subcarriers f1to f25and OFDM symbols #1and #2, that is, subcarriers f7, f13and f25in OFDM symbol #3and subcarriers f4, f16and f22in OFDM symbol #6.

In this way, compared to arrangement example 2, this arrangement example improves the accuracy of channel estimation for multicast channels arranged to areas apart from the areas where dedicated channels (e.g. SCCHs) for each sector are arranged in one sub-frame.

A multicast pilot is only necessary to perform channel estimation for channels shared between sectors. Then, this arrangement example differs from pilot arrangement example 2 (FIG. 9) in that, in one sub-frame, multicast pilots are arranged to areas where shared channels including PCHs (Paging Channels) and BCHs (Broadcast Channels) between sectors1to3are arranged.FIG. 11shows the area defined by subcarriers f1to f13(frequency domain) and OFDM symbols #3to #7(time domain), as the area where PCHs or BCHs are arranged. That is, in this arrangement example, as shown inFIG. 11, multicast pilots are arranged to the area defined by subcarriers f1to f13and OFDM symbols #3to #7, that is, subcarriers f7and f13in OFDM symbol #3and subcarrier f4in OFDM symbol #6.

In this way, compared to arrangement example 2, this arrangement example improves the accuracy of channel estimation of shared channels including PCHs and BCHs between sectors.

This arrangement example differs from pilot arrangement example 3 (FIG. 10) in that, in one sub-frame, in a case where shared channels including PCHs and BCHs between sectors1to3are arranged to the area where dedicated control channels including SCCHs and PDCCHs (i.e. Physical downlink control channels) for each sector of sector1, sector2and sector3, are arranged, to improve the accuracy of channel estimation for the shared channels, multicast pilots are arranged to the area. To be more specific, in this arrangement example, as shown inFIG. 12, in a case where SCCHs are arranged to the area defined by subcarriers f1to f25(frequency domain) and OFDM symbols #1and #2(time domain) and where paging indicators are arranged to subcarriers f2, f8, f14and f20in OFDM symbol #1, multicast pilots are arranged to subcarriers f4, f16and f22in OFDM symbol #1and subcarriers f7, f13and f25in OFDM symbol #2.

Next,FIG. 13shows an arrangement example where one cell is divided into six sectors, that is, sectors1to6.

As shown inFIG. 13, sector1neighbors sectors2and6, sector2neighbors sectors1and3, sector3neighbors sectors2and4, sector4neighbors sectors3and5, sector5neighbors sectors4and6, and sector6neighbors sectors1and5. In this case, base station10has six antennas for each sector and transmits signals to each sector from each antenna. That is, base station10for six sectors has six radio communication apparatuses100shown inFIG. 5for sectors1to6.

Further, in a case where one cell is divided into six sectors, that is, sectors1to6, the orthogonal pilot sequences as shown inFIG. 14are set as unicast pilot sequences for sectors. By this means, the unicast pilot sequences of sectors1to6are orthogonal to each other in six-chip units (an orthogonal sequence unit) as shown inFIG. 14. Then, in cases of dividing one cell into six sectors, that is, sectors1to6, unicast pilot generation section105of radio communication apparatuses100(FIG. 5) generates unicast pilot sequences shown inFIG. 14and outputs them to arrangement section106.

Then, in a case individual orthogonal pilot sequences varying between sectors are set up as unicast pilot sequences and arranged as shown inFIG. 14, similar to the case of dividing one cell into three sectors, the first chip (i.e. head chip) in one orthogonal sequence unit is all “1” in sectors1to6, and all the unicast pilots “1” are multiplexed on the channel at subcarriers f1and f19in OFDM symbol #1. That is, similar to the case of dividing one cell into three sectors, when base station10(FIG. 13) transmits unicast pilot sequences to sectors, in some of the unicast pilot sequences, the same pilots are transmitted at the same time from a plurality of antennas. Then, as described above, the same pilots in unicast pilot sequences transmitted from a plurality of antennas at the same time are also available as multicast pilots.

Hereinafter, pilot arrangement examples 6 to 8 in arrangement section106(FIG. 5) will be explained in cases where one cell is divided into six sectors, that is, sectors1to6.

By this means, only if one cell is divided into six sectors, it is possible to reduce the number of multicast pilots in one sub-frame and arrange pilots that can be used for channel estimation of multicast data at equal intervals (i.e. predetermined periods) both in the frequency domain and in the time domain.

In the case where one cell is divided into six sectors, that is, sectors1to6, as shown inFIG. 13, there are sector boundaries between sector1and2(i.e. sector boundary1), between sector2and3(i.e. sector boundary2), between sector3and4(i.e. sector boundary3), between sector4and5(i.e. sector boundary4), between sector5and6(i.e. sector boundary5) and between sector6and1(i.e. sector boundary6). That is, mobile station200(FIG. 6) located in the sector boundary receives multicast data of two sectors in a mixed manner. That is, as shown inFIG. 16, available pilots as multicast pilots in unicast pilot sequences can be classified into the available pilots as multicast pilots at all sector boundaries of sector boundaries1to6, the available pilots as multicast pilots at sector boundaries3and6, and the available pilots as multicast pilots at sector boundaries1,2,4and5.

Then, this arrangement example adopts the pilot arrangement showing inFIG. 17. This arrangement example differs from arrangement example6(FIG. 15) in that a multicast pilot is not arranged to subcarrier f10in OFDM symbol #6. By this means, it is possible to reduce the number of multicast pilots further.

In cases where pilots are arranged as such, in mobile station200located in sector boundary1,2,4or5, as shown inFIG. 18, unicast pilots arranged to subcarriers f1and f19in OFDM symbol #1and subcarrier f10in OFDM symbol #5can be also used as multicast pilots. Further, in mobile station200located in sector boundary3or6, as shown inFIG. 19, unicast pilots arranged to subcarriers f1, f7, f13, f19and f25in OFDM symbol #1can be also used as multicast pilots.

In arrangement example 7, the number of unicast pilots also available as multicast pilots varies depending on which sector boundary mobile station200is located in. To be more specific, the number of unicast pilots is three (FIG. 18) in mobile station200located in sector boundary1,2,4or5, and, meanwhile, the number of unicast pilots is five (FIG. 19) in mobile station200located in sector boundary3or6.

However, to maintain the accuracy of channel estimation for multicast data regardless of which cell boundary mobile station200is located in, the number of unicast pilots also available as multicast pilots is preferably the same regardless of which cell boundary mobile station200is located in.

In cases where these unicast pilots are arranged, in mobile station200located in sector boundary1or4, as shown inFIG. 24, unicast pilots arranged to subcarriers f1and f13in OFDM symbol #1, subcarriers f3and f15in OFDM symbol #4and subcarriers f1, f9and f17in OFDM symbol #7can be also used as multicast pilots. Further, in mobile station200located in sector boundary2or5, as shown inFIG. 25, unicast pilots arranged to subcarriers f1and f13in OFDM symbol #1, subcarriers f3, f11, and f19in OFDM symbol #4and subcarriers f1and f13in OFDM symbol #7can be also used as multicast pilots. Further, in mobile station200located in sector boundary3or6, as shown inFIG. 26, unicast pilots arranged to subcarriers f1, f9, and f7in OFDM symbol #1, subcarriers f3and f15in OFDM symbol #4and subcarriers f1and f13in OFDM symbol #7can be also used as multicast pilots. That is, regardless of which sector boundary mobile station200is located in, the number of available unicast pilots as multicast pilot is seven.

In this way, according to this arrangement example, regardless of which sector boundary mobile station200is located in, it is possible to equalize the number of available unicast pilots as multicast pilots.

This arrangement example differs from arrangement example3(FIG. 10) in that multicast pilots are arranged to areas apart from the areas where dedicated control channels (e.g. SCCHs and PDCCHs) for each sector of sector1, sector2and sector3are arranged, in one sub-frame, and, meanwhile, unicast pilots are arranged to the areas where dedicated control channels for each sector of sector1, sector2and sector3are arranged. To be more specific, in this arrangement example, as shown inFIG. 27, in the area defined by subcarriers f1to f25and OFDM symbols #3to #12, a multicast pilot is not arranged to subcarriers f1and f19in OFDM symbol #3.

According to this arrangement example, it is possible to arrange pilots that can be used for channel estimation of multicast data at equal intervals (i.e. predetermined periods) in the frequency domain and reduce the number of multicast pilots in one sub-frame.

An embodiment of the present invention has been explained.

Although cases have been explained above as one example where one cell is divided into three sectors or six sectors, the present invention is not limited to this, and the present invention can also be implemented in cases of any number of sectors.

Further, although cases have been explained with the present embodiment above where the present invention is implemented between sectors, the present invention may be also implemented between cells. In cases where the present invention is implemented between cells, the present invention adopts a configuration adding multicast pilot generating section150to each configuration shown inFIG. 5of the base station assigned to a cell.

Further, by reading “multicast” used in the above description as “broadcast,” the present invention may be implemented in a mobile communication system where broadcast data and unicast data are multiplexed. Further, by reading “multicast” used in the above description as “MBMS,” the present invention may be implemented in a mobile communication system where MBMS data and unicast data are multiplexed.

Further, the present invention may also be implemented using shared channels between a plurality of sectors, other than multicast channels including PCHs and BCHs.

Further, the sub-frame used in the above description may also be another transmission time unit, for example, a time slot or a frame. Furthermore, the sub-frame may also be a unit of the time period for a constant fading fluctuation, that is, a unit of coherence time, calculated from the highest speed of a mobile station assumed in mobile communication systems.

Further, a pilot used in the above description may also be referred to as a “reference signal.” Further, a multicast pilot may also referred to as a “MBSFN reference signal (Multicast/Broadcast Single Frequency Network Reference signal).”

Further, a unicast pilot sequence used in the above description may be a different pilot sequence for each mobile station, and, a different pilot sequence for each sector, that is, a pilot sequence that are common between a plurality of mobile stations located in one sector. Further, a different pilot sequence for each mobile station may be referred to as a “UE-specific reference signal,” and a different pilot sequence for each sector may be referred to as a “cell-specific reference signal.”

Further, a multicast channel may be referred to as a “SFN channel.”

Further, a CP used in the above description may be referred to as a “GI (Guard Interval).” Further, a subcarrier may be referred to as “tone.” Further, a base station may be referred to as “Node-B,” and a mobile station may be referred to as “UE.”

Moreover, although with the above embodiment a case has been described where the present invention is configured by hardware, the present invention may be implemented by software.

Each function block employed in the description of the aforementioned 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 an 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.

The disclosure of Japanese Patent Application No. 2006-259633, filed on Sep. 25, 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, mobile communication systems.