Apparatus and method for communication

An eigen value expansion section 103 calculates eigen values and eigen vectors in a correlation matrix or covariance matrix of input signals. When the ratio between a maximum eigen value and other eigen values is equal to or lower than a threshold, an assignment method selection section 104 selects a code assignment method whereby systematic bits are transmitted with their respective eigen vectors. As a result, a communication apparatus 100 transmits a systematic bit X with the respective eigen vectors. On the other hand, when the ratio between a maximum eigen value and other eigen values is greater than the threshold, the assignment method selection section 104 selects a code assignment method whereby systematic bits are transmitted with only the eigen vector having the maximum eigen value. As a result, the communication apparatus 100 transmits the systematic bit X with only the eigen vector having the maximum eigen value. This makes it possible to obtain an effect of improving sufficient communication quality even when the difference between the maximum eigen value and other eigen values is large in a communication system which combines a turbo code and MIMO.

TECHNICAL FIELD

The present invention relates to a communication apparatus and communication method used in a communication system which combines a turbo code and MIMO (Multiple-Input Multiple-Output).

BACKGROUND ART

For a radio communication, an error correcting code is a technology indispensable for transmitting/receiving high-reliability information. A turbo code is becoming a focus of attention as a correcting code having a strong error correcting capacity in recent years.

A basic turbo coder is constructed of a parallel connection of a plurality of recursive systematic convolutional coders (RSC) through an interleaver as shown inFIG. 1and outputs a systematic bit (information bit) X and parity bits Y1, Y2.

Furthermore, MIMO (Multiple-Input Multiple-Output) is becoming a focus of attention in recent years as a system for effectively realizing high-speed transmission using a limited frequency band.

The MIMO is a system which uses an array antenna for both transmission and reception to simultaneously transmit/receive independent signals on the same band using a plurality of eigen vectors. Using this MIMO makes it possible to expand a transmission capacity without expanding the frequency band.

There is also an on-going study for improving communication quality by combining a turbo code and MIMO.

Here, when the ratio between systematic bits and parity bits transmitted is equal among eigen vectors, the amount of improvement in communication quality increases as the respective eigen values become more uniform and the effect of improvement in communication quality decreases as the difference between a maximum eigen value and other eigen values increases.

However, in a conventional communication system, magnitudes of eigen values are not taken into consideration and the ratio between systematic bits and parity bits of each eigen vector always remains constant, and therefore when a difference between a maximum eigen value and other eigen values is large, the effect of improvement in communication quality using a turbo code decreases.

Especially in a situation such as a base station of a cellular system in which an antenna on the transmitting side is set high for the purpose of covering a wide range, a maximum eigen value becomes a value by far larger than other eigen values, and therefore it seems necessary to add certain improvement.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a communication apparatus and communication method in a communication system that combines a turbo code and MIMO capable of obtaining sufficient effects of improvement in communication quality even when there is a large difference between a maximum eigen value and other eigen values.

This object can be attained by measuring a ratio between the maximum eigen value and other eigen values and controlling the type of coded data to be transmitted with the respective eigen vectors based on the measurement result.

BEST MODE FOR CARRYING OUT THE INVENTION

The present inventor has come up with the present invention noting that since an amount of improvement in communication quality of MIMO is proportional to the magnitude of an eigen value, when a maximum eigen value is much greater than other eigen values, transmitting systematic bits with only an eigen vector having the maximum eigen value makes it possible to obtain a coding gain and improve the amount of improvement in communication quality.

With reference now to the attached drawings, embodiments of the present invention will be explained in detail below. As shown in the communication system inFIG. 2, a case where data is transmitted/received between a communication apparatus10and a communication apparatus20each provided with an array antenna using two eigen vectors A, B (suppose the eigen vector of a maximum eigen value is “A”) will be explained. Also suppose that the communication apparatus of each embodiment encodes transmission data using the turbo coder shown inFIG. 1.

FIG. 3is a block diagram showing the configuration of a communication apparatus according to Embodiment 1 of the present invention. The communication apparatus100inFIG. 3is one of the communication apparatuses10,20shown inFIG. 2.

The communication apparatus100inFIG. 3is mainly constructed of antenna elements101-1to m, reception RF sections102-1to m, an eigen value expansion section103, an assignment method selection section104, a beam forming section105, demodulation sections106,107, an assignment method decision section108, a turbo decoding section109, a turbo coding section151, a code assignment section152, a repetition section153, modulation sections154,155and transmission RF sections156-1to m.

The plurality of antenna elements101-1to m constitute an adaptive array antenna, receive a signal sent from the other party of communication, output the signal to the corresponding reception RF sections102-1to m and transmit signals output from the corresponding transmission RF sections156-1to m to the other party of communication by radio.

The reception RF sections102-1to m carry out radio processing such as amplification and down-conversion on the signals received by the corresponding antenna elements101-1to m and output baseband signals to the eigen value expansion section103and beam forming section105.

The eigen value expansion section103calculates eigen values and eigen vectors of a correlation matrix or covariance matrix of input signals based on the signals output from the reception RF sections102-1to m and outputs the eigen values to the assignment method selection section104and the eigen vectors to the beam forming section105.

The assignment method selection section104calculates the ratio between the maximum eigen value and other eigen values, compares this ratio with a preset threshold, selects a code assignment method based on the decision result and outputs a command indicating the selected code assignment method (hereinafter referred to as “assignment method indication command”) to the code assignment section152and modulation section154. The processing of the assignment method selection section104will be explained more specifically later.

The beam forming section105combines the signals output from the reception RF sections102-1to m using the eigen vectors output from the eigen value expansion section103and outputs the combined signal to the demodulation sections106,107. Furthermore, the beam forming section105divides signals output from the modulation sections154,155into m portions corresponding in number to the antenna elements, carries out complex multiplication processing on each signal using eigen vectors and outputs these signals to the transmission RF sections156-1to m.

The demodulation section106demodulates the signal which is output from the beam forming section105and received with the eigen vector A, outputs a control signal to the assignment method decision section108and outputs the coded data to the turbo decoding section109. Furthermore, the demodulation section107demodulates the signal which is output from the beam forming section105and received with the eigen vector B and outputs the coded data to the turbo decoding section109.

The assignment method decision section108decides the code assignment method of the other party of communication based on the assignment method indication command included in the output signal of the demodulation section106and outputs the decision result to the turbo decoding section109.

The turbo decoding section109carries out turbo decoding processing on the coded data output from the demodulation sections106,107based on the decision result of the assignment method decision section108and extracts the received data.

The turbo coding section151carries out turbo coding processing on the transmission data and outputs coded data made up of a systematic bit X and parity bits Y1, Y2to the code assignment section152.

The code assignment section152outputs the coded data output from the turbo coding section151to the modulation section154or modulation section155based on the assignment method indication command from the assignment method selection section104and outputs a control signal to the repetition section153. Details of the processing by the code assignment section152will be described in detail later.

The repetition section153carries out repetition processing on coded data (parity bit Y2) output from the turbo coding section151and outputs the coded data after repetition processing to the modulation section155according to the control signal from the code assignment section152.

The modulation section154modulates data to be transmitted with the eigen vector A, which is the coded data output from the code assignment section152and an assignment method indication command from the assignment method selection section104and outputs the modulated signal to the beam forming section105.

The modulation section155modulates data to be transmitted with the eigen vector B, which is the coded data output from the code assignment section152or the repetition section153and outputs the modulated signal to the beam forming section105.

The transmission RF sections156-1to m carry out radio processing such as amplification and up-conversion on the signal output from the beam forming section105and output the processed signals to the corresponding antenna elements101-1to m.

Next, details of the processing by the assignment method selection section104and code assignment section152will be explained usingFIG. 4AandFIG. 4B.FIG. 4AandFIG. 4Billustrate data transmitted with the respective eigen vectors of this embodiment.FIG. 4Ashows coded data transmitted with the eigen vectors when the ratio between a maximum eigen value and other eigen values is equal to or lower than a threshold, whileFIG. 4Bshows coded data transmitted with the eigen vectors when the ratio between a maximum eigen value and other eigen values is greater than the threshold.

When the ratio between a maximum eigen value and other eigen values is equal to or lower than the threshold, the assignment method selection section104selects a code assignment method of transmitting systematic bits with the respective eigen vectors and outputs a command “0” which indicates this selection result.

When code assignment section152receives the assignment method indication command “0” from the assignment method selection section104, it outputs a systematic bit X and a parity bit Y1to the modulation section154and outputs the systematic bit X and parity bit Y2to the modulation section155, and controls the repetition section153so as to stop outputting coded data.

As a result, the communication apparatus100transmits the systematic bit X with the respective eigen vectors A, B as shown inFIG. 4A.

On the other hand, when the ratio between the maximum eigen value and other eigen values is greater than the threshold, the assignment method selection section104selects a code assignment method of transmitting systematic bits with only an eigen vector having a maximum eigen value and outputs a command “1” indicating this selection result.

When the code assignment section152receives the assignment method indication command “1” from the assignment method selection section104, it outputs the systematic bit X and parity bit Y1to the modulation section154and controls the repetition section153so as to output coded data to the modulation section155.

As a result, the communication apparatus100transmits the systematic bit X with only the eigen vector A having a maximum eigen value and transmits the parity bit Y2repeated with the eigen vector B as shown inFIG. 4B. Using repetition with eigen vectors having small eigen values can improve signal quality and make the quality of different beams uniform.

Thus, by transmitting systematic bits with the respective eigen vectors when the respective eigen values are uniform and transmitting systematic bits with only the eigen vector having the maximum eigen value when the maximum eigen value is much greater than the other eigen values, it is possible to obtain a maximum effect by combining a turbo code and MIMO through improvement of communication quality.

In both cases ofFIG. 4AandFIG. 4B, the communication apparatus100transmits an assignment method indication command with the eigen vector A having the maximum eigen value. This can reduce decision errors when the receiving side decides the assignment method and improve stability of the system.

In the cases ofFIG. 4AandFIG. 4B, a signal transmitted from the other party of communication with the eigen vector A having the maximum eigen value is demodulated by the demodulation section106, and therefore the assignment method decision section108extracts an assignment method indication command from the output signal of the demodulation section106, decides the content (“0” or “1”) and can thereby know the code assignment method of the other party of communication.

FIG. 5is a block diagram showing the configuration of a communication apparatus according to Embodiment 2 of the present invention and the communication apparatus200inFIG. 5is one of the communication apparatuses10,20shown inFIG. 2.

In the communication apparatus200shown inFIG. 5, components common to those of the communication apparatus100shown inFIG. 3are assigned the same reference numerals as those inFIG. 3and explanations thereof will be omitted. The communication apparatus200inFIG. 5adopts the configuration of the communication apparatus100inFIG. 3with a puncturing section201added. Furthermore, in the communication apparatus inFIG. 5, a code assignment section202carries out processing different from the code assignment section152inFIG. 3.

A turbo coding section151outputs a systematic bit X to the code assignment section202and outputs parity bits Y1, Y2to the puncturing section201.

The puncturing section201punctures the parity bits Y1, Y2and outputs the remaining parity bits Y1, Y2to the code assignment section202and outputs the punctured parity bits Y1′, Y2′ to a repetition section153.

The repetition section153carries out repetition processing on the coded data (parity bits Y1′, Y2′) output from the puncturing section201and outputs the coded data after the repetition processing according to a control signal from the code assignment section202to a modulation section155.

Based on an assignment method indication command from an assignment method selection section104, the code assignment section202outputs the coded data output from the turbo coding section151and puncturing section201to the modulation section154or modulation section155and outputs a control signal to the repetition section153.

More specifically, when the code assignment section202receives an assignment method indication command “0” from the assignment method selection section104, it outputs the systematic bit X and parity bits Y1, Y2to the modulation sections154,155respectively and controls the repetition section153so as to stop outputting coded data.

As a result, as shown inFIG. 6A, the communication apparatus100transmits the systematic bit X and parity bits Y1, Y2with eigen vectors A, B. Therefore, it is possible to complete signals transmitted from the respective eigen vectors as one coding unit.

On the other hand, when the code assignment section202receives an assignment method indication command “1” from the assignment method selection section104, it outputs the systematic bit X and parity bits Y1, Y2to the modulation section154and controls the repetition section153so as to output the coded data to the modulation section155.

As a result, as shown inFIG. 6B, the communication apparatus100transmits the systematic bit X, parity bits Y1, Y2with the eigen vector A and transmits the parity bits Y1′, Y2′ punctured with the eigen vector B and repeated. Therefore, it is possible to complete a signal transmitted from the eigen vector A having the maximum eigen value as one coding unit and assign an auxiliary role when decoding to the coded data transmitted from the eigen vector B having a value other than the maximum eigen value.

As in the case of Embodiment 1, in any one ofFIG. 6A,FIG. 6B, the communication apparatus200transmits the assignment method indication command from the eigen vector A having the maximum eigen value.

Furthermore, the above described embodiments have explained the case with two eigen vectors, but the present invention places no limit on the number of eigen vectors. Furthermore, the configuration of the turbo coder in the present invention is not limited to the one illustrated inFIG. 1.

As described above, according to the present invention, the communication system which combines a turbo code and MIMO controls the type of coded data to be transmitted with the respective eigen vectors based on the ratio between the maximum eigen value and other eigen values, and can thereby obtain a maximum effect of combining the turbo code and MIMO in realizing improvement of communication quality.

This application is based on the Japanese Patent Application No. 2003-040217 filed on Feb. 18, 2003, entire content of which is expressly incorporated by reference herein.

INDUSTRIAL APPLICABILITY

The present invention is suitable for use in a communication apparatus in a communication system which combines a turbo code and MIMO.