Pilot signal transmission method and radio communication apparatus

Abstract

In a radio communication system, transmission of CAZAC sequences as the pilot signal sequences by using code division multiplexing as at least one of user multiplexing schemes, is done by dividing a system band as a frequency band usable in the system into frequency blocks B1 and B2 having bandwidths W1 and W2, generating the pilot signals of the frequency blocks B1 and B2 with a single carrier, using the pilot signal sequences having sequence lengths L1 and L2 corresponding to frequency blocks B1 and B2 respectively; and, transmitting the generated pilot signals as the pilot signals corresponding individual users, with multicarriers using an arbitrary number of frequency blocks among the plural frequency blocks.

Claims

1. A base station comprising: a receiver configured to receive, from a user equipment, a first reference signal including a first sequence having a first sequence length corresponding to a first bandwidth assigned for a first single carrier data transmission and a second reference signal including a second sequence having a second sequence length corresponding to a second bandwidth assigned for a second single carrier data transmission; and a demodulator configured to demodulate a data signal of the first single carrier data transmission by using the received first reference signal and a data signal of the second single carrier data transmission by using the received second reference signal.

2. The base station in accordance with claim 1, wherein the receiver receives data signals using three or more bandwidths including the first bandwidth and the second bandwidth.

3. The base station in accordance with claim 1, wherein, the receiver receives data signals using a multi-carrier transmission of a first single carrier data transmission of the first bandwidth and a second single carrier data transmission of the second bandwidth.

4. The base station in accordance with claim 1 wherein, the first bandwidth equals the second bandwidth.

5. The base station in accordance with claim 1 wherein, the first bandwidth is different from the second bandwidth.

6. The base station in accordance with claim 1 wherein, at least one of the first sequence and the second sequence is a CAZAC sequence or a cyclic shifted CAZAC sequence.

7. A communication method by a base station comprising: receiving, from a user equipment, a first reference signal including a first sequence having a first sequence length corresponding to a first bandwidth assigned for a first single carrier data transmission and a second reference signal including a second sequence having a second sequence length corresponding to a second bandwidth assigned for a second single carrier data transmission, by a receiver implemented in the base station; and demodulating, by a demodulator implemented in the base station, a data signal of the first single carrier data transmission by using the received first reference signal and a data signal of the second single carrier data transmission by using the received second reference signal.

8. The communication method in accordance with claim 7, wherein receiving data signals using three or more bandwidths including the first bandwidth and the second bandwidth.

9. The communication method in accordance with claim 7, wherein, receiving data signals using a multi-carrier transmission of a first single carrier transmission of the first bandwidth and a second single carrier transmission of the second bandwidth.

10. The communication method in accordance with claim 7, wherein, the first bandwidth equals the second bandwidth.

11. The communication method in accordance with claim 7, the first bandwidth is different from the second bandwidth.

12. The communication method in accordance with claim 7, wherein, at least one of the first sequence and the second sequence is a CAZAC sequence or a cyclic shifted CAZAC sequence.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a diagram showing a configuration of a transmitter based on a single carrier transmission scheme shown in literature 1.

(2) FIG. 2 is a diagram showing the manner in which cyclic prefix addition in the cyclic prefix adder shown in FIG. 1 is performed.

(3) FIG. 3 is a diagram showing a configuration of a typical receiver that corresponds to the transmitter shown in FIG. 1.

(4) FIG. 4 is a diagram showing a configurational example of a conventional mobile radio system.

(5) FIG. 5 is a diagram showing one example of frequency blocks used by users and pilot signal sequences used by individual users in the mobile radio system shown in FIG. 4.

(6) FIG. 6 is a diagram showing another configurational example of a conventional mobile radio system.

(7) FIG. 7 is a diagram showing one example of frequency blocks used by users and pilot signal sequences used by individual users in the CL of the mobile radio system shown in FIG. 6.

(8) FIG. 8 is a diagram showing the first embodiment mode of a mobile radio system in which a radio communication apparatus of the present invention is used.

(9) FIG. 9 is a diagram showing bands through which individual users transmit pilot signals and CAZAC sequences used thereupon in the mobile radio system shown in FIG. 8.

(10) FIG. 10 is a diagram showing one configurational example of a pilot signal transmitter according to the first embodiment mode of a radio communication apparatus of the present invention.

(11) FIG. 11 is a diagram showing one configurational example of a pilot signal receiver that corresponds to the pilot signal transmitter shown in FIG. 10.

(12) FIG. 12 is a diagram showing one configurational example of the channel estimators shown in FIG. 11.

(13) FIG. 13 is a diagram showing an example of a time-domain signal obtained from the IDFT portion shown in FIG. 12.

(14) FIG. 14 is a diagram showing the second embodiment mode of a mobile radio system in which a radio communication apparatus of the present invention is used.

(15) FIG. 15 is a diagram showing bands through which individual users transmit pilot signals and CAZAC sequences used thereupon in the mobile radio system shown in FIG. 14.

BEST MODE FOR CARRYING OUT THE INVENTION

(16) Next, the embodiment modes of the present invention will be described with reference to the drawings.

The First Embodiment Mode

(17) FIG. 8 is a diagram showing the first embodiment mode of a mobile radio system in which a radio communication apparatus of the present invention is used.

(18) As shown in FIG. 8, in this mode, in BS101 as a base station and a plurality of mobile stations MS102-105 for performing communications with BS101 in CL100 as a service area formed by BS101 are provided. Here, BS101 and MS102-105 are the radio communication apparatus of the present invention.

(19) FIG. 9 is a diagram showing bands through which individual users transmit pilot signals and CAZAC sequences used thereupon in the mobile radio system shown in FIG. 8.

(20) As shown in FIG. 9, the system band as the frequency band that is usable in the system is divided into frequency blocks B1 and B2. It is also assumed that every user uses a different band to transmit the data signal or control signal with a single carrier. In this case, all the users use identical CAZAC sequences having a sequence length of L1 or L2 corresponding to the frequency block bandwidth W1=W or W2=2.

(21) Accordingly, MS102 performs simultaneous multi-carrier transmission by using two frequency blocks B1 and B2 corresponding to CAZAC sequence lengths L1=I and L1=2 L. MS103 and MS104 perform single carrier transmission using bandwidth W1 corresponding to CAZAC sequence length L1=L. MS105 performs single carrier transmission using bandwidth W2 corresponding to CAZAC sequence length L2=2 L. Here, the users that perform transmission through the same band use identical CAZAC sequences that are cyclically shifted by a phase unique to each user.

(22) In this way, by unifying the bandwidth of the frequency blocks of pilot signals or by unifying CAZAC sequence length to be used, it is possible to make the users having pilot signals of different transmission bands orthogonal to each other.

(23) FIG. 10 is a diagram showing one configurational example of a pilot signal transmitter according to the first embodiment mode of a radio communication apparatus of the present invention.

(24) As shown in FIG. 10, this configuration is composed of a plurality of DFT portions 601-1 to 601-n, a plurality of subcarrier mapping portions 602-1 to 602-n, IFFT portion 603, cyclic prefix adder 604 and cyclic shifter 605.

(25) The pilot signal transmitter shown in FIG. 10 operates as follows.

(26) First, CAZAC sequences having sequence lengths corresponding to the bandwidth of frequency blocks are inserted to DFT portions 601-1 to 601-n, whereby they are transformed into frequency-domain pilot signals. Here, the number of points of DFT portions 601-1 to 601-n,
N.sub.Tx.sub._.sub.p.sub._.sub.1˜N.sub.Tx.sub._.sub.p.sub._.sub.n  [Math 12]
correspond to the sequence lengths corresponding to bandwidths of respective carriers. Here, n(n=1 to N) is the number of carries to be transmitted simultaneously.

(27) Then, the frequency-transformed pilot signals are inserted to subcarrier mapping portions 602-1 to 602-n, whereby they are subcarrier mapped. After sub-carrier mapping, the sub-carrier mapped frequency-domain pilot signals

(28) are supplied to IFFT portion 603, where they are subjected to FFT at points
N.sub.FFT.sub._.sub.p  [Math 13]
so as to be transformed into time-domain pilot signals.

(29) Thereafter, in cyclic shifter 605, a cyclic shift unique to the user is performed and a cyclic prefix is added in cyclic prefix adder 604.

(30) The thus generated pilot signals are time multiplexed over the data signal generated by the same process as in the conventional example.

(31) The process described heretofore is the process on the transmitter side in the pilot signal transmission method of the present invention.

(32) FIG. 11 a diagram showing one configurational example of a pilot signal receiver that corresponds to the pilot signal transmitter shown in FIG. 10. Here, the receiver of the data has the same configuration as the conventional one, hence only the receiver of the pilot signal after the pilot signal has been separated from the data signal by a multiplexer will be shown in FIG. 11.

(33) The pilot signal receiver shown in FIG. 11 includes cyclic prefix remover 701, FFT portion 702, a plurality of subcarrier demapping portions 703-1 to 703-n and a plurality of channel estimators 704-1 to 704-n.

(34) The pilot signal receiver shown in FIG. 11 operates as follows.

(35) First, the cyclic prefix is removed from the received signal in cyclic prefix remover 701. Then,

(36) the resultant signal is subjected to FFT at
N.sub.FFT.sub._.sub.p  [Math 14]
points, by FFT portion 702 to be transformed into the received signal in the frequency domain. Thereafter, the signal is demapped to subcarriers used by the individual user by subcarrier demapping portions 703-1 to 703-n. After subcarrier demapping, the subcarrier-demapped frequency signals are inserted into channel estimators 704-1 to 704-n.

(37) FIG. 12 is a diagram showing one configurational example of channel estimators 704-1 to 704-n shown in FIG. 11.

(38) As shown in FIG. 12, channel estimators 704-1 to 704-n shown in FIG. 11 each include pilot multiplier 801, pilot signal generator 802, IDFT portion 803, channel filter 804 and DFT portion 805.

(39) In pilot multiplier 801, the subcarrier demapped, frequency-domain received signal is multiplied with the complex conjugate of the pilot signal in frequency-domain representation, generated by pilot signal generator 802. Pilot signal generator 802 may be a memory that memorizes the pilot signal in frequency representation or a circuit that calculates based on a generation formula.

(40) Then, the multiplied signal is processed

(41) by IDFT portion 803 where it is subjected to IDFT at points
N.sub.Tx.sub._.sub.p.sub._.sub.n  [Math 15]
that corresponds to the bandwidth of the frequency block, so as to be transformed into the time-domain signal.

(42) FIG. 13 is a diagram showing an example of a time-domain signal obtained from IDFT portion 803 shown in FIG. 12.

(43) As shown in FIG. 13, the signal which the impulse responses to the channels for different users shifted with respect to time, by performing cyclic shifts unique to users in cyclic shifter 605 shown in FIG. 10.

(44) The thus obtained impulse responses to the channels are passed through channel filter 804, so that the impulse response to the channel corresponding to each user is obtained. The obtained impulse response of each user

(45) is processed through DFT portion 805 so that it is subjected to DFT at points
N.sub.Tx.sub._.sub.p.sub._.sub.n,  [Math 16]
so as to be transformed into the channel estimate in the frequency domain, which provides frequency response to the channel used for frequency equalization.

(46) The above-described process is the process on the receiver side in the pilot signal transmission method of the present invention.

(47) The first embodiment mode of the present invention was described by taking a case in which CAZAC sequences are transmitted as the pilot signal sequences while code division multiplexing is used as the user multiplexing method. In this case, the system band is divided into frequency blocks, and pilot signals are generated on a single carrier using the sequences that are obtained by cyclically shifting an identical pilot signal sequence having a sequence length corresponding to the bandwidth of each frequency block, and the pilot signals corresponding to each user are constructed so as to be transmitted with n multicarriers using arbitrary n frequency blocks of the frequency blocks. Accordingly, since CAZAC sequences of the same sequence length can be used for different users in the same band, it is possible to make the user pilot signals orthogonal to each other.

The Second Embodiment

(48) FIG. 14 is a diagram showing the second embodiment mode of a mobile radio system in which a radio communication apparatus of the present invention is used.

(49) As shown in FIG. 14, in this mode, in BS101 and BS301 as base stations and a plurality of mobile stations MS102-105 and MS302-305 for performing communications with BS101 and BS301 respectively in CL100 and CL300 as service areas formed respectively by BS101 and BS301 are provided. Here, BS101, 301, MS102-105 and 302-305 are the radio communication apparatus of the present invention.

(50) FIG. 15 is a diagram showing bands through which individual users transmit pilot signals and CAZAC sequences used thereupon in the mobile radio system shown in FIG. 14. Here, similarly to the conventional configuration, it is assumed that data signal or control signal is transmitted with a single carrier using frequency blocks having continuous frequencies.

(51) In the first embodiment mode, the bands through which individual users transmit their pilot signals by single carriers, are unified. In the second embodiment mode, the bands through which pilot signals are transmitted by single carriers are unified, inclusive of the users in another cell.

(52) Accordingly, referring to FIG. 15, MS102 of CL100 performs multi-carrier transmission by simultaneously transmitting three carriers (bandwidth W1=W2=W3=W) corresponding to CAZAC sequence lengths L1=L2=L3=L. MS103 and MS104 perform single carrier transmission using bandwidth W1 corresponding to CAZAC sequence length L1=L. MS105 performs multi-carrier transmission by simultaneously transmitting two carriers (bandwidth W2=W3=W) corresponding to CAZAC sequence lengths L2=L3=L.

(53) On the other hand, MS302 of CL300 performs multi-carrier transmission by simultaneously transmitting two carriers (bandwidth W1=W2=W) corresponding to CAZAC sequence lengths L1=L2=L. MS303 performs single carrier transmission using bandwidth W1 corresponding to CAZAC sequence length L1=L. MS304 and MS305 perform single carrier transmission using bandwidth W3 corresponding to CAZAC sequence length L3=L.

(54) As the sequences used for the pilot signals, in the same band inside the cell, the sequences that are obtained by cyclically shifting an identical CAZAC sequence by the phases unique to the users are used while in the same band of a different cell, a different CAZAC sequence is used. Since CAZAC sequences have the properties that only when sequences have the same length, there exist sequences that produce a low cross-correlation function, it is possible to unify the bandwidth of the frequency block of pilot signals in the same band of all the cells. That is, when the sequence lengths of CAZAC sequences are unified, it is possible to reduce inter-cell interference.

(55) The pilot signal transmitter and receiver of the second embodiment mode have the same configurations as those in FIGS. 10 to 12 described in the first embodiment mode, description will be omitted.

(56) In the second embodiment mode of the present invention, the same band of neighboring cells for neighboring service areas are divided into the same frequency blocks. The users of the different cells that transmit pilot signals through a divided frequency block, use different CAZAC sequences among the CAZAC sequences having a sequence length corresponding to the bandwidth of the frequency block to generate pilot signals with a single carrier. The pilot signal corresponding to each user is transmitted with n multicarriers using arbitrary n frequency blocks among the frequency blocks. Accordingly, in the same band of the users in the cell and different cell, CAZAC sequences having the same sequence length can be used. As a result, it is possible to make the pilot signals inside the cell orthogonal to each other and reduce inter-cell interference.

(57) Though the second embodiment mode was described taking a case where the same CAZAC sequence is used inside the cell for the different bands in the cell, the same effect can also be expected if different CAZAC sequences are used.

(58) Further, though the second embodiment mode of the present invention was described taking a case where there are two service cells for service areas, it goes without saying that the same effect can also be expected in a case where there are three or more service cells.

(59) Also, though the second embodiment mode was described taking a case where the neighboring service cells have the same system band, even when the system bands of the neighboring service cells are different from each other, the same effect can also be expected if the same band is divided into frequency blocks in the same manner.

(60) Also, though the embodiment mode of the present invention was explained taking a case where frequency blocks have different bandwidths (W1#W2), the same effect can be obtained when the bandwidths of frequency blocks are equal to each other (W1=W2).

(61) Also, though the embodiment mode of the present invention was described taking a case where the system band is divided into three frequency blocks, the same effect can also be expected when there are two or more frequency blocks.

(62) Also, though the embodiment mode of the present invention was described taking a case where the frequency blocks through which pilot signals are transmitted is constituted of bandwidth W and its integer multiples, the same effect can also be expected when frequency blocks not having the integer multiple of bandwidth W are included.

(63) Also, though the embodiment mode of the present invention was described taking a case where the pilot signal of each user is transmitted with multicarriers using frequency blocks whose frequencies are continuous, the same effect can also be expected when the pilot signal is transmitted with multicarriers using frequency blocks whose frequencies are discontinuous.

(64) Also, in the above description, BS101, 301 and MS102-105 and 302-305 were described as radio communication apparatus including the above-described pilot signal transmitter and pilot signal receiver to transmit signals.

(65) Further, the above first and second embodiment modes were described taking examples in which CAZAC sequences are used as the pilot signal sequences. A pilot signal sequence may be used, which at least has either the first property that the self-correlation value when the phase difference is other than zero, is equal to or lower than a predetermined threshold relative to the peak self-correlation value when the phase difference is zero, or the second property that the cross-correlation value between the sequences that are equal in sequence length is smaller than the cross-correlation value between the sequences that are different in sequence length. In this case, when the data signal to be demodulated has a low operational point (Eb/N0=0 to 5 dB) such as QPSK for example, if the threshold for the self-correlation value when the phase difference is other than zero is −20 dB (10%) relative to the self-correlation peak when the phase difference is zero, no degradation in characteristics will occur. However, when the data signal to be demodulated has a high operational point such as 16QAM and 64QAM, the threshold of the self-correlation value needs to be set at a further lower level.