Multiantenna communication device and coefficient update method

1. A multiantenna communication device that forms a directional beam by adding an antenna weight to respective signals of a plurality of antenna elements, the multiantenna communication device comprising:

a processor that executes performing distortion compensation on a transmission signal by using a distortion compensation coefficient;

a plurality of power amplifiers that are provided corresponding to the antenna elements, and that amplify the transmission signal subjected to the distortion compensation by the processor;

a multiplexer that multiplexes signals output from the power amplifiers to feed back; and

an analog/digital (A/D) converter that A/D converts a multiplex feedback signal that is obtained by the multiplexer, wherein

the processor executes:

generating demultiplex signals as many as number of the antenna elements by demultiplexing the transmission signal;

adding a weight same as an antenna weight per antenna element to each of the generated demultiplex signals;

generating a multiplex signal by multiplexing the demultiplex signals to which the weight is added; and

updating the distortion compensation coefficient by using the multiplex feedback signal A/D converted by the A/D converter and the multiplex signal.

2. The multiantenna communication device according to claim 1 , wherein the performing the distortion compensation includes:

generating, based on the multiplex signal, an address of a lookup table that stores the distortion compensation coefficient; and

subjecting the transmission signal to distortion compensation by using a distortion compensation coefficient stored at the generated address.

3. The multiantenna communication device according to claim 1 , further comprising

a level adjusting unit that adjusts a level of the multiplex feedback signal that is obtained by the multiplexer, wherein

the processor further executes detecting an amplitude of the multiplex signal and the multiplex feedback signal, and

the level adjusting unit adjusts a level of the multiplex feedback signal according to a maximum amplitude detected by the processor.

4. The multiantenna communication device according to claim 1 , wherein

the multiplexer multiplexes signals output from part of power amplifiers out of the power amplifiers to feed back, and

the updating includes:

generating a partial multiplex signal by multiplexing part of the multiplex signals to which the weight is added; and

updating the distortion compensation coefficient by using the partial multiplex signal and a partial multiplex feedback signal that is obtained by the multiplexer.

5. The multiantenna communication device according to claim 1 , wherein the updating further includes adding pseudo distortion corresponding to a variation of characteristics of the power amplifiers, to each of the demultiplex signals to which the weight is added.

6. The multiantenna communication device according to claim 5 , wherein the processor further executes:

generating an amplifier model that indicates a characteristic of the power amplifiers; and

calculating the pseudo distortion based on the generated amplifier model.

7. The multiantenna communication device according to claim 6 , wherein the generating the amplifier model includes:

controlling the antenna weight to cause a signal output from individual power amplifiers to be fed back; and

generating, by using the signal fed back, an amplifier model of a power amplifier that has output the signal.

8. The multiantenna communication device according to claim 6 , wherein the generating the amplifier model includes:

controlling a power source voltage of the power amplifiers to cause a signal output from individual power amplifiers to be fed back; and

generating, by using the signal fed back, an amplifier model of a power amplifier that has output the signal.

9. The multiantenna communication device according to claim 6 , wherein the generating the amplifier model includes:

controlling a switch arranged between the power amplifiers and the multiplexer to cause a signal output from individual power amplifiers to be fed back; and

generating, by using the signal fed back, an amplifier model of a power amplifier that has output the signal.

10. The multiantenna communication device according to claim 5 , wherein the updating further includes adding additional pseudo distortion corresponding to a variation of characteristic of an analog path between the power amplifiers and the multiplexer, to each of the demultiplex signals to which the pseudo distortion is added.

11. The multiantenna communication device according to claim 1 , further comprising

an amplitude control unit that controls an amplitude by applying a tap coefficient to a signal output from the power amplifiers, wherein

the multiplexer multiplexes signals, an amplitude of which is controlled by the amplitude control unit, to feed back.

12. A coefficient update method performed by a multiantenna communication device that forms a directional beam by adding an antenna weight to respective signals of a plurality of antenna elements, the coefficient update method comprising:

generating demultiplex signals as many as number of the antenna elements by demultiplexing a transmission signal;

adding a weight same as an antenna weight per antenna element to each of the generated demultiplex signals;

generating a multiplex signal by multiplexing the demultiplex signals to which the weight is added;

performing distortion compensation on the transmission signal by using a distortion compensation coefficient;

amplifying the transmission signal subjected to the distortion compensation with a plurality of power amplifiers that are provided corresponding to the antenna elements;

multiplexing signals output from the power amplifiers to feed back;

A/D converting a multiplex feedback signal that is obtained by the multiplexing; and

updating the distortion compensation coefficient by using the multiplex feedback signal A/D converted and the multiplex signal.