MIMO communication method, terminal, and base station apparatus for transmitting and receiving pilot signals to estimate a channel

Abstract

A MIMO communication method of performing MIMO communication between a base station having a plurality of antennas and each of a plurality of terminals covered by the base station using uplink data slots and downlink data slots that are alternately placed on a time axis. The method includes, in the base station, despreading a received signal that is transmitted from each of the plurality of terminals demodulating the transmission data transmitted from a respective terminal on the basis of the value of the estimated channel; decoding a received signal included in the uplink data slots, estimating a current channel between each of all antennas of the base station and the respective terminal; and comparing the stored value of the estimated channel with a value of the estimated current channel and updating the stored value of the estimated channel to the value of the estimated current channel.

Claims

1. A MIMO communication method of performing MIMO communication between a base station having a plurality of antennas and each of a plurality of terminals covered by the base station using uplink data slots and downlink data slots that are alternately placed on a time axis, comprising: in each of the plurality of terminals, setting pilot transmission headers to be used for transmission of a pilot signal at predetermined header intervals as headers of the uplink data slots; spreading the pilot signal in the pilot transmission headers using corresponding one of orthogonal codes that are assigned to the plurality of terminals and are orthogonal to one another and transmitting the spread pilot signal; spreading the pilot signal in the uplink data slots using a data orthogonal code that is different from the orthogonal code used in the pilot transmission headers, superimposing the spread pilot signal on transmission data, and transmitting the transmission data; in the base station, despreading a received signal that is transmitted from each of the plurality of terminals and is included in the pilot transmission headers using the orthogonal code assigned to a respective one of the terminals, estimating a channel between each of all antennas of the base station and the respective terminal, and storing a first value of the estimated channel; demodulating the transmission data transmitted from the respective terminal on a basis of the first value of the estimated channel; decoding a received signal included in the uplink data slots using the data orthogonal code assigned to the respective terminal and estimating a current channel between each of all antennas of the base station and the respective terminal; and comparing the stored first value of the estimated channel with a second value of the estimated current channel and updating the stored first value of the estimated channel to the second value of the estimated current channel when a difference between the values is larger than a third value set in advance.

2. The MIMO communication method according to claim 1, further comprising: in each of the plurality of terminals, adjusting an amplitude of the pilot signal; additively superimposing the amplitude-adjusted pilot signal on the transmission data in a time direction or a frequency direction; and transmitting a signal obtained from the superimposition; in the base station, receiving a signal transmitted from the respective terminal; and subtracting the amplitude-adjusted pilot signal from the received signal in the time direction or the frequency direction and performing demodulation for MIMO communication using a remaining signal.

3. The MIMO communication method according to claim 1, wherein the uplink data slot is separated into a plurality of data sections and the pilot signal is superimposed on at least one of the plurality of data sections.

4. The MIMO communication method according to claim 3, wherein the data sections are orthogonal frequency division multiplexing (OFDM) symbols.

5. The MIMO communication method according to claim 4, wherein a frequency component in the OFDM symbol is separated into a plurality of blocks and the pilot signal is superimposed on each of the plurality of blocks.

6. The MIMO communication method according to claim 1, wherein OFDM is used for data communication, wherein each of the plurality of terminals performs, in a frequency domain, the superimposition of the pilot signal on the transmission data in the uplink data slots before performing inverse fast Fourier transform (IFFT) of OFDM, and wherein the base station performs fast Fourier transform (FFT) on the received signal so as to convert the received signal into a frequency-domain signal and performs the subtraction, the demodulation, and the channel estimation in the frequency domain.

7. A terminal for performing MIMO communication with a base station apparatus having a plurality of antennas, the terminal comprising: a transmitter configured to transmit data to the base station apparatus using uplink data slots and transmit pilot transmission headers to the base station using time slots separate from the uplink data slots; and processing circuitry configured to set the pilot transmission headers to be used for transmission of a pilot signal at predetermined header intervals as headers of the uplink data slots, spread the pilot signal in one of the pilot transmission headers using corresponding one of orthogonal codes that are assigned to a plurality of terminals and are orthogonal to one another and transmit the spread pilot signal, wherein the pilot signals for all of the plurality of terminals are spread to overlap in time within a same time slot of the pilot transmission header, wherein the processing circuitry is configured to spread the pilot signal in one of the uplink data slots using a data orthogonal code that is different from the orthogonal code used in the pilot transmission headers, and multiplex the spread pilot signal on transmission data, and the transmitter is configured to transmit the transmission data in the one of the uplink data slots, wherein the transmission data for all of the plurality of terminals overlap in time within the one of the uplink data slots.

8. A base station apparatus for performing MIMO communication with a plurality of terminals covered by the base station apparatus comprising: a plurality of antennas; and processing circuitry configured to despread a signal that is received from each of the plurality of terminals via the plurality of antennas and is included in pilot transmission headers using an orthogonal code assigned to a respective one of the terminals, estimate a channel between each of all of the plurality of antennas of the base station and the respective terminal, store a first value of the estimated channel, process the signal received from each of the plurality of terminals, demodulate transmission data transmitted from the respective terminal on a basis of the first value of the estimated channel, decode a received signal included in the uplink data slots using a data orthogonal code assigned to the respective terminal and estimate a current channel between each of all of the plurality of antennas of the base station and the respective terminal, and compare the stored first value of the estimated channel with a second value of the estimated current channel and updates the stored first value of the estimated channel to the second value of the estimated current channel when a difference between the values is larger than a third value set in advance.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a diagram illustrating the time slot configuration of a signal stream transmitted/received from/by a base station in massive MIMO according to a first embodiment of the present disclosure.

(2) FIG. 2 is a diagram illustrating the configuration of a transmission unit in user equipment and the configurations of units for performing receiving processing and data processing in a base station according to the first embodiment.

(3) FIG. 3 is a diagram illustrating a first modification of the first embodiment.

(4) FIG. 4 is a diagram illustrating a second modification of the first embodiment.

(5) FIG. 5 is a diagram illustrating the configuration of a transmission unit in user equipment and the configurations of units for performing receiving processing and data processing in a base station according to a second embodiment of the present disclosure.

(6) FIG. 6 is a graph illustrating a result of characteristic simulation according to an embodiment of the present disclosure.

(7) FIGS. 7A and 7B are diagrams illustrating a situation in which the constellation of received signals rotated because of Doppler effect is recovered after a channel estimation update has been performed with a pilot superimposed on data.

(8) FIG. 8 is a graph illustrating a simulation result of the effect of an amplitude adjustment factor Pg according to an embodiment of the present disclosure.

(9) FIG. 9 is a diagram describing a known method of transmitting pilots from terminals for the purpose of channel estimation.

(10) FIG. 10 is a diagram illustrating an exemplary massive MIMO configuration.

DETAILED DESCRIPTION

(11) The first embodiment of the present disclosure will be described in detail below.

(12) FIG. 1 is a diagram illustrating the time slot configuration of a signal stream transmitted/received from/by a base station in massive MIMO according to an embodiment of the present disclosure.

(13) In this embodiment, a single base station covers Nv mobile terminals (UE#1 to UE#Nv). In the following description, a mobile terminal is merely referred to as a terminal. The distance between each terminal and a base station is measured in advance and a transmission time at the terminal is adjusted in accordance with the distance, so that signals transmitted from the terminals can be synchronized at a receiving point. This method is used for Long Term Evolution (LTE). In a signal stream, uplinks (ULs) and downlinks (DLs) are time-separated through time division duplex (TDD). The same frequency is used for the ULs and the same frequency is used for the DLs.

(14) A header is set so that it precedes each of the uplinks and the downlinks. There are two types of UL headers, a first UL header and a second UL header. The first UL header is a header dedicated to pilot transmission (pilot header). The pilot headers are not all UL headers and are dispersedly located at regular intervals in a stream. The second UL header is a general-purpose header used for the other purposes. All of DL headers are general-purpose headers.

(15) In this embodiment, a pilot signal of “1” is used. Pilot orthogonal codes Pcode#1 to Pcode#Nv are assigned to a plurality of pieces of user equipment. Each piece of user equipment spreads the pilot signal of “1” using the assigned orthogonal code and transmits the spread pilot signal using a pilot header. The “spread” means that exclusive OR processing is performed with a pilot signal and an orthogonal code.

(16) The base station BS receives pilots from all pieces of user equipment at the same time, and can distinguish among these pieces of user equipment by performing despreading using the orthogonal codes. The “despread” means that exclusive OR processing is performed with a received signal and the orthogonal code and then addition processing is performed over an overall code length. This process is equivalent to the inner product of vectors.

(17) By using the pilot orthogonal code for the pilot signal received from the piece of user equipment, a channel H0 between each of all antennas of the base station BS and the piece of user equipment can be estimated.

(18) Subsequently, each piece of user equipment transmits data using a UL data slot. At that time, a pilot is spread with one of data orthogonal codes Dcode#1 to Dcode#Nv that are different from the orthogonal code for the pilot described above. A result of the spreading is multiplied by an amplitude adjustment factor Pg and is then multiplexed (superimposed) on data. That is, the piece of user equipment transmits data Tx_data obtained from the following equation (1) as data for a user equipment number jv.
Tx_data=data+Pg.Math.Dcode#jv.Math.Pilot (1)

(19) The addition of the first term and the second term on the right side of equation (1) is performed for each bit. That is, the length of the data orthogonal code Dcode is in agreement with the total data length. As is apparent from equation (1), while a pilot signal is spread with an orthogonal code, data is merely superimposed.

(20) The base station BS receives a signal Rx_data represented by the following equation (2).

(21) $\begin{matrix} \begin{matrix} Rx_data = H 0 r .Math. Tx \\ = H 0 r .Math. (data + Pg .Math. Dcode # jv .Math. Pilot) \end{matrix} & (2) \end{matrix}$

(22) In this equation, H0r represents a channel. The channel H0r may be changed from the initial channel H0 obtained from the pilot header.

(23) The base station performs despreading on the received signal Rx_data using the data orthogonal code assigned to the piece of user equipment so as to obtain a channel-related receiving signal. This process is represented by the following equation (3).
Channel-related receiving signal=Rx_data(x)Dcode#jv.sup.T=H0r.Math.(data+Pg.Math.Dcode#jv.Math.Pilot)(x)Dcode#jv.sup.T (3)

(24) In this equation, an index T represents transposition and (x) represents a vector inner product operation (despreading). In equation (3), since data is random and its autocorrelation is low, the inner product of the data and the long-period code Dcode is substantially zero. Consequently, when the length of the data orthogonal code Dcode is LN, equation (3) becomes the following equation.
Channel-related receiving signal=H0r.Math.Pg.Math.LN.Math.Pilot (4)

(25) From equation (4), the channel H0r is obtained by Channel-related receiving signal/(Pg.Math.LN.Math.Pilot).

(26) Demodulated data is obtained from the following equation.
(Rx_data/H0r)−Σ.sub.jvPg.Math.Dcode#jv (5)
In equation (5), the second term of (Σ.sub.jvPg.Math.Dcode#jv) is known and its value is prepared in advance.

(27) As is apparent from the following equation (6), the demodulated data can be obtained by multiplying equation (5) by H0*. This multiplication is performed for correlation.
{(data+Pg.Math.Dcode#jv.Math.Pilot)−Σ.sub.jvPg.Math.Dcode#jv}×H0* (6)
where “*” of H0* represents a complex conjugate transpose.

(28) Next, operations will be described.

(29) When a piece of user equipment is placed under the control of a base station (is present in a corresponding cell) and is powered on, a registration request is issued and initial setting is performed. At that time, the base station assigns two types of orthogonal codes, the pilot orthogonal code and the data orthogonal code, to this piece of user equipment.

(30) Each piece of user equipment spreads a pilot signal in a slot for a pilot header using an assigned pilot orthogonal code and transmits the spread pilot signal. At the time of data transmission, each piece of user equipment multiplexes (superimposes) a data pilot on data and transmits the data.

(31) The base station first receives the pilot header and estimates the channel H0 between each of all antennas of the base station and the piece of user equipment using the pilot orthogonal code assigned to the piece of user equipment. The channel H0 is stored in the base station. Subsequently, the base station receives from the piece of user equipment data on which a data pilot has been superimposed.

(32) FIG. 2 is a diagram illustrating the configuration of a transmission unit in user equipment 200 and the configurations of units for performing receiving processing and data processing in a base station 100. This drawing illustrates a case where an Orthogonal Frequency Division Multiplexing (OFDM) system is used.

(33) In a certain piece of terminal 200 (UE#jv), transmission data Data#jv is subjected to inverse fast Fourier transform in an inverse fast Fourier transformer (IFFT) 220 and is converted into a time-domain transmission signals (a1, a2, . . . and, aNf). Subsequently, to the obtained time-domain transmission signals (a1, a2, . . . and, aNf) output from the IFFT 220, a result of the product of an amplitude adjustment factor Pg and a pilot (a pilot of “1” in this example) 235 spread using an orthogonal code Dcode#jv is added for each bit (230). A resultant signal is subjected to high-frequency processing and is transmitted via an antenna. The description of known processing operations such as the addition of a cyclic prefix, digital-to-analog (D/A) conversion, high-frequency conversion, and amplification is omitted.

(34) The base station 100 receives signals from a plurality of pieces of user equipment 200 at a time via a plurality of antennas under the effect of the channel H0r. The description of known configurations of a Radio Frequency (RF) unit, a quadrature modulation unit, and an analog-to-digital conversion unit will be omitted.

(35) A pilot header processor 170 in the base station 100 receives a pilot header and performs despreading of the received signal using a pilot orthogonal code assigned to a corresponding piece of user equipment, thereby distinguishing the piece of user equipment from the other pieces of user equipment and estimating the channel H0 between each of all antennas of the base station and the piece of user equipment. The channel H0 is stored in a storage unit 139 in the base station 100.

(36) As described previously, the channel H0r indicates that it may be changed from the channel H0 at the time of reception of a pilot header. Subsequently, a data processor 130 performs data decoding processing and channel estimation processing for each piece of user equipment. In the drawing, an index “TTL” is an abbreviation for total and represents the combination of all pieces of user equipment.

(37) In data decoding processing that corresponds to equations (5) and (6) and is illustrated in the upper portion of the block of the base station 100 in FIG. 2, first, the data orthogonal code component of all pieces of user equipment is subtracted from the received signal. The data orthogonal code component of all pieces of user equipment is obtained by multiplying the amplitude adjustment factor Pg.

(38) Subsequently, in order to correlate a result of the subtraction and the complex conjugate transpose H0* of the channel matrix H0 stored in the storage unit 139, the subtraction result is subjected to multiplication. As a result, received signals are separated on a terminal-by-terminal basis in accordance with the characteristic of MIMO communication. Subsequently, a fast Fourier transformer (FFT) 135 performs an FFT operation on the obtained signal, so that original transmission data can be acquired (decoded).

(39) In channel estimation processing illustrated in the lower portion of the data processor 130 in the base station 100 in FIG. 2, each of signals received from all pieces of user equipment is despread using the code Dcode#jv of a corresponding one of these pieces of user equipment. Using the above-described equations (3) and (4), the channel H0r is estimated. Subsequently, a comparator 137 compares the obtained channel H0r with the channel H0 stored in the storage unit 139. When the difference between the estimated values of the channels H0r and H0 is equal to or larger than a certain value, the channel H0 stored in the storage unit 139 is updated to the channel H0r. The estimation of the channel H0, which is performed by the pilot header processor 170 using a pilot header, may be performed at the time of the above-described initial setting and the restart of communication. During communication, the update of a channel estimation value is performed using a pilot superimposed on a data slot. The channel estimation performed with a pilot header is not performed or a result of the channel estimation is eliminated after performance of the channel estimation.

(40) Next, exemplary specific numerical values of main parameters will be described. Both time lengths of a massive MIMO uplink slot and a massive MIMO downlink slot under consideration are 500 μS. The time length of a header has not been set yet. Accordingly, an LTE time standard is employed. The reason for this is that the fifth generation (5G) system will be probably compliant with the fourth generation (4G) system. In this case, the TDD-LTE standard of 1 slot=500 μS can be employed. Since seven OFDM symbols are transmitted, a time length of a single OFDM symbol becomes approximately 70 μS. When this time length is used for a header, approximately 32 nS is obtained per OFDM bin (FFT symbol). Accordingly, in a case where one bit is assigned to one bin, a pilot orthogonal code having the length of 2048 bits can be prepared. This means that 2048 pieces of user equipment can be distinguished. Massive MIMO under consideration estimates the number of pieces of user equipment covered by a single base station at 10 to 20. Accordingly, this code numerical value is sufficiently large.

(41) The data length of a data orthogonal code is 2048×7 since seven OFDM symbols are included in a single slot. An orthogonal code having this length can be used. Some methods of using the orthogonal code can be proposed, and will be described below as first and second modifications.

(42) In the first modification in FIG. 3, an exemplary case where seven OFDM symbols are included in an uplink data slot UL-data and a pilot is superimposed on only one symbol is illustrated. The other OFDM symbols are used only for data transmission. In the exemplary case in FIG. 3, although a pilot is superimposed on a first OFDM symbol OFDM#1, a pilot may be superimposed on another symbol. Alternatively, pilots may be superimposed on a plurality of OFDM symbols. The length of a single slot is 500 μS. Accordingly, when it can be assumed that there is no channel variation in this period, a system can be simplified. Thus, an uplink data slot can be separated into a plurality of data sections and a pilot can be superimposed on at least one data section.

(43) The second modification illustrated in FIG. 4 differs from the exemplary case illustrated in FIG. 3 in that an OFDM frequency component is separated into a plurality of blocks (four blocks in the drawing) and pilots are superimposed on these blocks. The same orthogonal code is assigned to these blocks. In an exemplary case in FIG. 4, an orthogonal code having the length of 512 is assigned to each block. Under the assumption that frequency fading occurs, channel estimation can be performed for each block when there is a frequency characteristic. Thus, a pilot can be superimposed on each of a plurality of blocks into which a frequency component in an OFDM symbol is separated.

(44) In the embodiment in FIG. 1, exemplary pilot superimposition processing in a time domain is illustrated. When OFDM is employed, frequency domain processing can be performed. In this case, since a channel is obtained for each OFDM subcarrier, more detailed frequency characteristic can be covered.

(45) A second embodiment in which frequency domain processing is performed will be described with reference to FIG. 5. This exemplary case is substantially the same as the exemplary case illustrated in FIG. 1 in which time domain processing is performed. The difference between them is that, in a piece of user equipment, the superimposition of a pilot is performed in a frequency domain before inverse fast Fourier transform (IFFT) is performed and then the conversion into a time-domain signal is performed by the IFFT 220. In a base station, first, the FET 135 converts a received signal into a frequency-domain signal. Subsequently, in a frequency domain, the subtraction of a pilot, correlation processing, data demodulation, and channel estimation are performed.

(46) FIG. 6 is a graph illustrating a result of characteristic simulation according to an embodiment of the present disclosure. In this example, the number of pieces of user equipment is 3, the number of antennas of a base station is 100, the type of modulation is quadraphase shift keying (QPSK), and an FET size is 512. An amplitude adjustment factor Pg is set to 1.0, and the description of this value will be described later. Since a high speed is not required in uplink transmission from user equipment, it is considered that QPSK is generally used. FIG. 6 illustrates the effect of channel estimation performed with a pilot superimposed on data. A horizontal axis represents a deviation from a channel estimated with a pilot header which is caused by Doppler effect, and a vertical axis represents the change in bit error rate (BER) with the deviation. The term of “w/o correction” indicates that there is no channel update. When a channel error exceeds 30%, BER markedly increases. This indicates that the massive MIMO channel diagonalization is inadequate. A case in which update is performed with a pilot superimposed on data is represented by the term of “w/ correction” in the drawing. In spite of the fact that a channel error increases, the BER is maintained at a low constant value. The reason why an error-free result is not obtained is that the interference of other pieces of user equipment cannot be completely eliminated even if correlation processing is performed.

(47) FIGS. 7A and 7B are diagrams illustrating a situation in which the constellation of received signals rotated because of Doppler effect is recovered after a channel estimation update has been performed with a pilot superimposed on data. FIG. 7A illustrates the constellation when a channel error is 100%. Referring to the drawing, the constellation is rotated. FIG. 7B illustrates the constellation when the update is performed. As is apparent from the drawing, the constellation is recovered.

(48) FIG. 8 illustrates a simulation result of the effect of the amplitude adjustment factor Pg. This simulation is performed under the same conditions as those described with reference to FIG. 6. The amplitude adjustment factor Pg serves as an index for determining when to separate a pilot from data. When the value of this factor is small, a pilot value becomes inaccurate because of the interference of data. When the value of this factor is large, transmission power increases. Referring to this drawing, a constant BER value is obtained when Pg>0.3. Since a pilot in data is obtained by despreading a data orthogonal code, the pilot is multiplied by a factor of the data orthogonal code. In this example, since a code having the length of 512 is used, the pilot is multiplied by 512. As is apparent from this drawing, the interference of data markedly decreases after Pg exceeds a certain value.

(49) The present disclosure can also be applied to a communication system other than the massive MIMO communication system in which channel estimation is required. For example, in the case of a pilot signal to be used in MIMO performed in CDMA, by performing code spreading of a channel estimation signal, data, and a pilot and multiplexing them, the effect of the present disclosure can be obtained.

(50) According to an embodiment of the present disclosure, by preparing headers for pilot transmission and headers for the other purposes in uplink and placing the pilot headers at regular intervals, the load of pilot transmission can be reduced. Furthermore, by multiplexing data and a pilot signal and embedding the pilot signal in data, a base station can perform channel estimation at the time of data reception and can always obtain the latest channel information.

(51) The separation among a plurality of pieces of user equipment is performed with orthogonal codes. Consequently, signals from terminals in close vicinity of one another can be separated. Furthermore, since signals from the other cells can be separated, pilot contamination can be solved. In the present disclosure, since a long-period orthogonal code can be used, a code shortage does not occur.

(52) According to the present disclosure, the following method and the following apparatuses are provided. (1) A MIMO communication method of performing MIMO communication between a base station having a plurality of antennas and each of a plurality of terminals covered by the base station using uplink data slots and downlink data slots that are alternately placed on a time axis, comprising:

(53) in each of the plurality of terminals,

(54) setting pilot transmission headers to be used for transmission of a pilot signal at predetermined header intervals as headers of the uplink data slots;

(55) spreading the pilot signal in the pilot transmission headers using corresponding one of orthogonal codes that are assigned to the plurality of terminals and are orthogonal to one another and transmitting the spread pilot signal;

(56) spreading the pilot signal in the uplink data slots using a data orthogonal code that is different from the orthogonal code used in the pilot transmission headers, superimposing the spread pilot signal on transmission data, and transmitting the transmission data;

(57) in the base station,

(58) despreading a received signal that is transmitted from each of the plurality of terminals and is included in the pilot transmission headers using the orthogonal code assigned to the terminal, estimating a channel between each of all antennas of the base station and the terminal, and storing a value of the estimated channel;

(59) demodulating the transmission data transmitted from the terminal on the basis of the value of the estimated channel;

(60) decoding a received signal included in the uplink data slots using the data orthogonal code assigned to the terminal and estimating a current channel between each of all antennas of the base station and the terminal; and

(61) comparing the stored value of the estimated channel with a value of the estimated current channel and updating the stored value of the estimated channel to the value of the estimated current channel when a difference between them is larger than a value set in advance. (2) The MIMO communication method according to (1), comprising:

(62) in each of the plurality of terminals,

(63) adjusting an amplitude of the pilot signal;

(64) additively superimposing the amplitude-adjusted pilot signal on the transmission data in a time direction or a frequency direction;

(65) transmitting a signal obtained from the superimposition;

(66) in the base station,

(67) receiving a signal transmitted from the terminal; and

(68) subtracting the amplitude-adjusted pilot signal from the received signal in the time direction or the frequency direction and performing demodulation for MIMO communication using a remaining signal. (3) The MIMO communication method according to (1), wherein the uplink data slot is separated into a plurality of data sections and the pilot signal is superimposed on at least one of the plurality of data sections. (4) The MIMO communication method according to (3), wherein the data sections are orthogonal frequency division multiplexing (OFDM) symbols. (5) The MIMO communication method according to (4), wherein a frequency component in the OFDM symbol is separated into a plurality of blocks and the pilot signal is superimposed on each of the blocks. (6) The MIMO communication method according to (1),

(69) wherein OFDM is used for data communication,

(70) wherein each of the plurality of terminals performs, in a frequency domain, the superimposition of the pilot signal on the transmission data in the uplink data slots before performing inverse fast Fourier transform (IFFT) of OFDM, and

(71) wherein the base station performs fast Fourier transform (FFT) on the received signal so as to convert the received signal into a frequency-domain signal and performs the subtraction, the demodulation, and the channel estimation in the frequency domain. (7) A terminal for performing MIMO communication with a base station apparatus having a plurality of antennas, the terminal comprising:

(72) a transmission unit configured to transmit data to the base station apparatus using uplink data slots, and

(73) wherein the transmission unit sets pilot transmission headers to be used for transmission of a pilot signal at predetermined header intervals as headers of the uplink data slots,

(74) wherein the transmission unit spreads the pilot signal in the pilot transmission headers using corresponding one of orthogonal codes that are assigned to a plurality of terminals and are orthogonal to one another and transmits the spread pilot signal, and

(75) wherein the transmission unit spreads the pilot signal in the uplink data slots using a data orthogonal code that is different from the orthogonal code used in the pilot transmission headers, superimposes the spread pilot signal on transmission data, and transmits the transmission data. (8) A base station apparatus for performing MIMO communication with a plurality of terminals covered by the base station apparatus comprising:

(76) a pilot transmission header processing unit configured to despread a signal that is received from each of the plurality of terminals via a plurality of antennas and is included in pilot transmission headers using an orthogonal code assigned to the terminal, estimate a channel between each of all of the plurality of antennas of the base station and the terminal, and store a value of the estimated channel; and

(77) a data processing unit configured to process the signal received from each of the plurality of terminals, and

(78) wherein the data processing unit demodulates transmission data transmitted from the terminal on the basis of the value of the estimated channel,

(79) wherein the data processing unit decodes a received signal included in the uplink data slots using a data orthogonal code assigned to the terminal and estimates a current channel between each of all of the plurality of antennas of the base station and the terminal, and

(80) wherein the data processing unit compares the stored value of the estimated channel with a value of the estimated current channel and updates the stored value of the estimated channel to the value of the estimated current channel when a difference between the values is larger than a value set in advance.

(81) Although the preferred embodiments of the present disclosure have been described above, various modifications and various changes other than those described above can be made. That is, it is obvious to those skilled in the art that various changes, various combinations, other embodiments can be made in consideration of design or another factor insofar as they are within the scope of the present disclosure as claimed or the equivalents thereof.

REFERENCE SIGNS LIST

(82) 100: base station

(83) 130: data processor

(84) 135: FFT

(85) 137: comparator

(86) 200: user equipment (terminal)

(87) 220: IFFT

MIMO communication method, terminal, and base station apparatus for transmitting and receiving pilot signals to estimate a channel

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Abstract

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Description