TRANSMISSION DEVICE, MIMO COMMUNICATION SYSTEM, AND TRANSMISSION DIVERSITY METHOD
Provided are a transmission device and a transmission diversity method, which can suppress degradation of a transmission diversity performance even under the circumstances having a space correlation, in the case of performing a transmission diversity MIMO communication. The transmission device comprises an orthogonal conversion unit ( 201 ) for multiplexing an M-number of source symbols by an orthogonal conversion, to form an N-number of transmission symbols, and a beam forming unit ( 204 ) for changing the transmission symbols of the N-number one by one into beams by using the beam forming parameters of the N-number, thereby to transmit the transmission symbol beams timely sequentially one by one from a plurality of antennas. As a result, the beam forming unit ( 204 ) can form the transmission beam, from which the correlation between the individual transmission code channels is eliminated and from which the inter-code interference is eliminated, and the orthogonal conversion unit ( 201 ) can improve the diversity synthesis number of the source symbols.
1 . A transmitting apparatus used in a multiple-input multiple-output communication system, the apparatus comprising:
an orthogonal transforming section that forms N transmission symbols by multiplexing M original-symbols through orthogonal transformation, M and N being natural numbers; and
a beam forming section that changes the N transmission symbols into beams one symbol by one symbol using N beam forming parameters and transmit the transmission symbols changed into the beams in a time sequence one symbol by one symbol from a plurality of antennas.
2 . The transmitting apparatus according to claim 1 , further comprising a power distributing section that distributes power to the N transmission symbols using N power distribution coefficients matching with the N beam forming parameters.
3 . A multiple-input multiple-output communication system comprising a transmitting apparatus and a receiving apparatus for carrying out multiple-input multiple-output communication between the transmitting apparatus and the receiving apparatus, wherein:
the transmitting apparatus comprises:
an orthogonal transforming section that multiplexes M original-symbols through orthogonal transformation and forms N transmission symbols, M and N being natural numbers; and
a beam forming section that changes the N transmission symbols into beams one symbol by one symbol using N beam forming parameters and transmits the transmission symbols changed into the beams in a time sequence one symbol by one symbol from a plurality of antennas; and
the receiving apparatus comprises a parameter determining section that determines the N beam forming parameters based on secondary statistic characteristics of a channel and feeds back the determined N beam forming parameters to the transmitting apparatus through a feedback channel.
4 . The multiple-input multiple-output communication system according to claim 3 , wherein:
the transmitting apparatus further comprises a power distributing section that distributes power to the N transmission symbols using N power distribution coefficients matching with the N beam forming parameters; and
the receiving apparatus further determines the N power distribution coefficients at the parameter determining section and feeds back the determined N power distribution coefficients to the transmitting apparatus through a feedback channel.
5 . The multiple-input multiple-output communication system according to claim 3 , wherein:
the receiving apparatus further comprises a channel estimation section that estimates a channel characteristic matrix; and
the parameter determining section finds a transmission correlation matrix based on the channel characteristic matrix, obtains a plurality of eigen vectors and a plurality of eigen values matching with the plurality of eigen vectors by carrying out eigen value decomposition of the transmission correlation matrix, selects N eigen vectors matching with maximum N eigen values of the plurality of eigen values from among the plurality of eigen vectors and determines the N eigen vectors as the N beam forming parameters.
6 . The multiple-input multiple-output communication system according to claim 4 , wherein the parameter determining section determines coefficients having the same value as the N power distribution coefficients.
7 . The multiple-input multiple-output communication system according to claim 4 , wherein the parameter determining section determines the N power distribution coefficients P i (i=1 to N) as P i =(μ−Nσ n 2 /P total λ i ) + using the N eigen values {λ 1 , λ 2 , . . . , λ 3 } according to a water pouring method, where P total is a total transmission power limit value, μ is such a constant that the total transmission power limit value P total is set to a predetermined value, σ n 2 is a noise variance and the function (x) + is a function that takes x when x is zero or greater and that takes zero when x is less than zero.
8 . The multiple-input multiple-output communication system according to claim 5 , wherein the parameter determining section determines the N power distribution coefficients such that the magnitude of the N power distribution coefficients are proportional to the eigen values.
9 . The multiple-input multiple-output communication system according to claim 3 , wherein the parameter determining section determines the N beam forming parameters at predetermined time intervals.
10 . The multiple-input multiple-output communication system according to claim 9 , wherein the parameter determining section makes shorter a time interval for determining the N beam forming parameters when a time variation of a channel is fast compared to when the time variation of the channel is slow.
11 . A transmission diversity method in a multiple-input multiple-output communication system comprising:
forming N transmission symbols by multiplexing M original-symbols through orthogonal transformation, M and N being natural numbers; and
changing the N transmission symbols into beams one symbol by one symbol using N beam forming parameters and transmitting the transmission symbols changed into the beams in a time sequence one symbol by one symbol from a plurality of antennas.
12 . The transmission diversity method according to claim 11 , further comprising:
at the receiving apparatus that receives the transmission symbols, determining the N beam forming parameters based on a secondary statistic characteristic of a channel; and
at the receiving apparatus, feeding back the determined N beam forming parameters to the transmitting side through a feedback channel.