MIMO communication method, transmitting device, and receiving device

1. A Multiple Input Multiple Output (MIMO) communication method for performing communication between N (N is an integer greater than or equal to 2) mobile communication devices each having a transmit antenna and at least one base station device having N receive antennas by using a multi-user MIMO scheme, the MIMO communication method comprising:

dividing the N mobile communication devices into a plurality of sets, at least one of the sets including at least two mobile communication devices, and assigning a plurality of OVSF codes, from among a plurality of orthogonal OVSF codes that are spread to have an orthogonal relationship, to each set of mobile communication devices as a digital signal sequence to be transmitted by each of the mobile communication devices, wherein the plurality of OVSF codes assigned to each set of mobile communications includes at least a first order OVSF code and a pair of second order OVSF codes which share the single first order OVSF code as a root; and

arranging the digital signal sequences to be transmitted by the mobile communication devices in a frequency domain in which an inverse fast Fourier transform is performed, and performing coding, wherein each of an in-phase and quadrature portion of a transmit data stream is multiplied by the assigned codes at each mobile communication device prior to each mobile communication device performing the inverse fast Fourier transform, wherein the first order OVSF code and the pair of second order OVSF codes are multiplied with different portions of the transmit data stream in a multiplexed manner.

2. The MIMO communication method according to claim 1 , further comprising:

repeating, for an entire transmission range, a process for assigning one OVSF code having a length of 2 to the power of n per signal bit to each of frequencies, the number of which is equal to 2 to the power of n (n is an integer), on a frequency axis on which an inverse fast Fourier transform is performed.

3. The MIMO communication method according to claim 2 , further comprising:

as coding in a first stage for the digital signal sequences, performing coding with an OVSF code having a length 2 to the power of n,

as coding in a second stage, assigning an OVSF code having a length of 2 to the power of (n+1) per signal bit to frequencies, the number of which is equal to 2 to the power of (n+1), on the frequency axis on which an inverse fast Fourier transform is performed, and an amplitude thereof is multiplied by a coefficient greater than 1, and

adding signals coded in the second stage to signals coded in the first stage.

4. The MIMO communication method according to claim 3 , further comprising:

as a coding in a stage higher than the second stage, assigning one OVSF code having a length of 2 to the power of (n+2) per signal bit to frequencies, the number of which is equal to 2 to the power of (n+1), on the frequency axis on which an inverse fast Fourier transform is performed, and an amplitude thereof is multiplied by a coefficient greater than 1, and

adding signals coded in the respective stages.

5. The MIMO communication method according to claim 1 , further comprising:

individually assigning the N mobile communication devices an OVSF code sequence to be used, and adaptively setting communication speeds of the respective mobile communication devices.

6. The MIMO communication method according to claim 3 , wherein

the at least one base station device including the N receive antennas includes N receiving units to which the respective receive antennas are connected, and

each receiving unit:

despreads a received signal with an OVSF code of (2 to the power of n) to separate a signal spread by an OVSF code having a length of (2 to the power of n),

despreads the separated signal with an OVSF code of (2 to the power of (n+1)) to extract a signal spread by an OVSF code having a length of 2 to the power of (n+1), subtracts a signal obtained by multiplying the extraction result by a signal of a corresponding channel from the result obtained by separation, and

despreads the subtraction result using the OVSF code having a length of (2 to power of n), thereby extracting a spread signal.

7. The MIMO communication method according to claim 1 , wherein

the base station device performs reception using receive antennas, the number of which is larger than the number of mobile communication devices in the plurality of sets, and using receiving units connected to the receive antennas, and combines receive signals obtained by the respective receiving units by using maximum-ratio combining.

8. A mobile communication device used for a multi-user MIMO scheme in which N (N is an integer greater than or equal to 2) mobile communication devices divided into a plurality of sets are used, at least one of the sets including at least two mobile communication devices, and perform wireless communication with at least one base station device having N receive antennas, the mobile communication device comprising:

circuitry configured to

generate a digital signal sequence to be transmitted, using a plurality of OVSF codes, from among a plurality of orthogonal OVSF codes that are spread to have an orthogonal relationship, assigned to each of the sets, wherein the plurality of OVSF codes assigned to each set of mobile communications includes at least a first order OVSF code and a pair of second order OVSF codes which share the single first order OVSF code as a root;

assign the obtained orthogonal OVSF codes to each frequency on a frequency domain, perform an inverse fast Fourier transform, and generate an OFDM signal;

transmit, as a radio frequency signal, the generated OFDM signal through the transform; and

a transmit antenna connected to the circuitry,

wherein each of an in-phase and quadrature portion of a transmit data stream is multiplied by the assigned codes prior to performing the inverse fast Fourier transform, wherein the first order OVSF code and the pair of second order OVSF codes are multiplied with different portions of the transmitted data stream in a multiplexed manner.

9. The mobile communication device according to claim 8 , wherein

the circuitry repeats, for the entire transmission range, a process for assigning one OVSF code having a length of 2 to the power of n per signal bit to each of frequencies, the number of which is equal to 2 to the power of n (n is an integer), on a frequency axis on which an inverse fast Fourier transform is performed.

10. The mobile communication device according to claim 9 , wherein

the circuitry:

performs, as coding in a first stage, coding with an OVSF code having a length 2 to the power of n,

as coding in a second stage, assigns an OVSF code having a length of 2 to the power of (n+1) per signal bit to frequencies, the number of which is equal to 2 to the power of (n+1), on the frequency axis on which an inverse fast Fourier transform is performed, multiplies an amplitude thereof by a coefficient greater than 1, and

adds signals coded in the second stage to signals coded in the first stage.

11. The mobile communication device according to claim 10 , wherein the circuitry:

further, assigns as a coding in a stage higher than the second stage, one OVSF code having a length of 2 to the power of (n+2) per signal bit to frequencies, the number of which is equal to 2 to the power of (n+1), on the frequency axis on which an inverse fast Fourier transform is performed, and an amplitude thereof is multiplied by a coefficient greater than 1, and

adds signals coded in the respective stages.

12. The mobile communication device according to claim 11 , wherein

an OVSF code is used as an OVSF code, and an OVSF code included in a code sequence in the first stage is used for coding in a stage higher than the second stage.

13. A base station device used for a multi-user MIMO scheme comprising:

N receive antennas that receive signals transmitted from N (N is an integer greater than or equal to 2) mobile communication devices divided into a plurality of sets, at least one of the sets including at least two mobile communication devices, wherein

the signals received by the receive antennas include

a signal obtained by performing an inverse fast Fourier transform on a digital signal sequence using a plurality of OVSF codes, from among a plurality of orthogonal OVSF codes that are spread to have an orthogonal relationship, assigned to mobile communication devices in each of the plurality of sets into which the N mobile communication devices are divided, wherein the plurality of OVSF codes assigned to each set of mobile communications includes at least a first order OVSF code and a pair of second order OVSF codes which share the single first order OVSF code as a root,

wherein each of an in-phase and quadrature portion of a transmit data stream is multiplied by the assigned codes at each mobile communication device prior to each mobile communication device performing the inverse fast Fourier transform, wherein the first order OVSF code and the pair of second order OVSF codes are multiplied with different portions of the transmit data stream in a multiplexed manner.

14. The base station device according to claim 13 , further comprising:

N receiving units to which the receive antennas are individually connected, and each receiving unit:

despreads a received signal with an OVSF code of (2 to the power of n) to separate a signal spread by an OVSF code having a length of (2 to the power of n),

despreads the separated signal with an OVSF code of (2 to the power of (n+1)) to extract a signal spread by an OVSF code having a length of 2 to the power of (n+1), subtracts a signal obtained by multiplying the extraction result by a signal of a corresponding channel from the result obtained by separation, and

despreads the subtraction result using the OVSF code having a length of (2 to the power of n), thereby extracting a spread signal.

15. The base station device according to claim 13 , wherein

the base station device performs reception using:

the receive antennas, the number of which is larger than the number of mobile communication devices in the plurality of sets, and

receiving units connected to the receive antennas,

and the base station device combines receive signals obtained by the respective receiving units by using maximum-ratio combining.