JP5795723B2 - Radio transmission apparatus and transmission control method - Google Patents

Description

  The present invention relates to a radio transmission apparatus having a plurality of antennas and a transmission control method in the radio transmission apparatus.

  In recent years, various MIMO (Multiple Input Multiple Output) systems have begun to be adopted in wireless communication systems. In the MIMO scheme, an STBC (Space Time Block Coding) scheme that is resistant to propagation path fluctuations and a high throughput SM (Spatial Multiplexing) scheme are employed (for example, see Non-Patent Document 1). ).

3GPP TS 36.211 V8.7.0 “Physical Channels and Moduration”, MAY 2009

  In a wireless communication system employing the MIMO scheme, further improvement in reception characteristics is desired. In particular, in wireless communication using a wireless channel whose propagation path characteristics are unknown, it is desired to improve reception characteristics.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a wireless transmission device and a transmission control method that can improve reception characteristics.

In order to solve the above-described problems, the present invention has the following features. A feature of the present invention is a radio communication apparatus (radio base station eNB1) having a plurality of antenna elements (array antenna 108A, array antenna 108B, array antenna 108C, array antenna 108D), and a plurality of weights (transmissions) orthogonal to each other. A storage unit (storage unit 103) that stores a plurality of sets of weights selected from weight sets, and the wireless channel propagation path characteristics toward the wireless terminal are unknown. For each signal sequence (data stream) to be transmitted corresponding to each of a plurality of antenna elements (array antenna 208A, array antenna 208B) included in the Weighting is performed with different sets of weights. The signal sequence of the transmitted, wherein the antenna element combining the synthetic signal for each (combined data stream) transmission unit for transmitting a radio base station and (BB processing unit 106), and summarized in that comprises a.

  Such a wireless transmission device performs weighting with weights orthogonal to each other for each of a plurality of transmission target signal sequences. As a result, the wireless transmission apparatus combines the N weighted signal sequences to be transmitted for each of the M antenna elements, and transmits the resultant signal with high reception characteristics corresponding to the number of antenna elements. It can be performed.

The gist of the present invention is that the transmission unit cyclically selects the weight set used for the weighting from the plurality of weight sets .

A feature of the present invention is a transmission control method in a wireless transmission device having a plurality of antenna elements, in which the wireless transmission device has a plurality of weights each consisting of a set of weights selected from a plurality of weights orthogonal to each other. In the step of storing a plurality of sets and the propagation path characteristics of the radio channel toward the radio terminal are unknown, the radio terminal for each signal sequence to be transmitted corresponding to each of the plurality of antenna elements included in the radio terminal Weighting is performed with a set of weights different from the set of weights used for weighting at the previous transmission timing for, and the weighted transmission target signal sequence is combined for each antenna element of the radio base station And transmitting the composite signal.

  According to the present invention, reception characteristics can be improved.

1 is an overall schematic configuration diagram of a wireless communication system according to an embodiment of the present invention. It is a block diagram of the radio base station which concerns on embodiment of this invention. It is a figure which shows an example of the transmission weight vector which concerns on embodiment of this invention. It is a figure for demonstrating the process of the wireless base station which concerns on embodiment of this invention. It is a block diagram of the radio | wireless terminal which concerns on embodiment of this invention. It is a flowchart which shows the operation | movement of the wireless base station which concerns on embodiment of this invention.

  Next, an embodiment of the present invention will be described with reference to the drawings. Specifically, (1) the configuration of the radio communication system, (2) the operation of the radio base station, (3) the operation and effect, and (4) other embodiments will be described. In the description of the drawings in the following embodiments, the same or similar parts are denoted by the same or similar reference numerals.

(1) Configuration of Radio Communication System First, the configuration of the radio communication system according to the embodiment of the present invention will be described.

  FIG. 1 is an overall schematic configuration diagram of a wireless communication system 10 according to an embodiment of the present invention.

  A wireless communication system 10 illustrated in FIG. 1 is a TDD-LTE wireless communication system. The radio communication system 10 includes a radio base station eNB1 and a radio terminal UE2. In FIG. 1, a radio base station eNB1 constitutes an E-UTRAN (Evolved-UMTS Terrestrial Radio Access Network) together with another radio base station eNB (not shown). The radio terminal UE2 exists in the cell 3 that is a communicable area provided by the radio base station eNB1.

  Time division duplex is adopted for radio communication between the radio base station eNB1 and the radio terminal UE2, OFDMA (Orthogonal Frequency Division Multiplexing Access) for downlink radio communication, and SC for uplink radio communication. -Single carrier frequency division multiple access (FDMA) is adopted. Here, downlink means a direction from the radio base station eNB1 to the radio terminal UE2, and uplink means a direction from the radio terminal UE2 to the radio base station eNB1.

  The radio base station eNB1 allocates a resource block (RB: Resource Block) as a radio resource to the radio terminal UE2 in the cell 3.

  Resource blocks include a downlink resource block (downlink RB) used for downlink radio communication and an uplink resource block (uplink RB) used for uplink radio communication. A plurality of downlink resource blocks are arranged in the frequency direction. Similarly, a plurality of uplink resource blocks are arranged in the frequency direction.

  The downlink resource block is divided into a control information channel (PDCCH: Physical Downlink Control CHannel) for downlink control information transmission and a shared data channel (PDSCH: Physical Downlink Shared CHannel) for downlink user data transmission in the time direction. Composed.

  On the other hand, in the uplink resource block, a control information channel (PUCCH: Physical Uplink Control CHannel) for uplink control information transmission is configured at both ends of all frequency bands that can be used for uplink radio communication. A shared data channel (PUSCH: Physical Uplink Shared CHannel) for user data transmission is configured.

  When allocating resource blocks, frequency hopping in which the allocated frequency is changed according to a predetermined frequency hopping pattern is applicable.

(1.2) Configuration of Radio Base Station FIG. 2 is a configuration diagram of the radio base station eNB1. As shown in FIG. 2, the radio base station eNB1 is an adaptive array radio base station, and includes a control unit 102, a storage unit 103, an I / F unit 104, a base band (BB) processing unit 106, an RF (RF: Radio Frequency) transmission processing section 107, array antenna 108A, array antenna 108B, array antenna 108C, and array antenna 108D are included. Note that the radio base station eNB1 shown in FIG. 2 shows only the configuration related to transmission of radio signals.

  The control unit 102 is configured by a CPU, for example, and controls various functions provided in the radio base station eNB1. The memory | storage part 103 is comprised by memory, for example, and memorize | stores the various information used for control etc. in the radio base station eNB1. The I / F unit 104 can communicate with other radio base stations eNB via the X1 interface. The I / F unit 104 can communicate with an EPC (Evolved Packet Core), specifically, an MME (Mobility Management Entity) / S-GW (Serving Gateway) via the S1 interface.

  The BB processing unit 106 includes an encoding modulation unit 134, a MIMO (Multi Input MultiOutput) precoding processing unit 135, a weight weighting unit 136, an IFFT (Inverse Fast Fourier Transform) processing unit 138, and a CP (Cyclic Prefix) adding unit 140. .

  When the data for the radio terminal UE from the control unit 102 is input, the code modulation unit 134 performs coding and modulation on the data, and obtains transmission data that is a frequency domain signal. The encoding modulation unit 134 outputs the transmission data to the MIMO precoding processing unit 135.

  The MIMO precoding processing unit 135 performs predetermined MIMO precoding such as STBC scheme or SM scheme on the transmission data from the encoding modulation unit 134, thereby to transmit the transmission data in the radio terminal UE2 described later. Convert to the number of data streams corresponding to each of the antennas. Here, the number of antennas in the radio terminal UE2 is two. Therefore, MIMO precoding processing section 135 converts the transmission data into two data streams by performing MIMO precoding, and outputs the two data streams to weight weighting section 136. The plurality of data streams obtained by the MIMO precoding processing unit 135 may be the same data stream or different data streams.

  The weight weighting unit 136 sets an antenna weight (transmission weight) at the time of transmitting a downlink radio signal to the radio terminal UE2 for each of the array antennas 108A to 108D.

  Specifically, the weight weighting unit 136 reads a transmission weight vector stored in the storage unit 103. The storage unit 103 stores a plurality of transmission weight vectors that are orthogonal to each other.

FIG. 3 is a diagram illustrating an example of a transmission weight vector. Transmission weight vector W _TX1 , transmission weight vector W _TX2 , transmission weight vector W _TX3 , and transmission weight vector W _TX4 shown in FIG. 3 are orthogonal to each other. Here, the transmission weight vectors being orthogonal means that the sum of the cross correlations of the two transmission weight vectors becomes zero. Transmission weight vector W _TX1 , transmission weight vector W _TX2 , transmission weight vector W _TX3 , and transmission weight vector W _TX4 are each composed of four components. Each of the four components corresponds to four array antennas 108A to 108D.

The weight weighting unit 136 selects two transmission weight vectors from the read transmission weight vectors. Here, the weight weighting unit 136 cyclically selects two transmission weight vectors every time transmission is performed (every time the downlink resource block timing assigned to the radio terminal UE2 arrives). Here, the weight weighting unit 136 transmits the transmission weight vector W _TX1 and the transmission weight vector W _TX2 , the transmission weight vector W _TX2 and the transmission weight vector W _TX3 , the transmission weight vector W _TX3 and the transmission weight vector W _TX4 , and the transmission weight vector W _TX4. And the transmission weight vector W _TX1 in this order.

  Further, the weight weighting unit 136 performs weighting processing and combining processing on two data streams every time two transmission weight vectors are selected.

Specifically, at the first transmission timing, the weight weighting unit 136 determines the component of the Kth array antenna 108 in each of the two selected transmission weight vectors W _TX1 and W _TX2 as W _TX1 (k). , W _TX2 (k), and two data streams X1, X2, the combined signal W (k) to be transmitted from the Kth array antenna 108 is obtained by the following equation 1.

・・・（式1）

... (Formula 1)

In the second transmission timing, weight weighting section 136, in each of the transmission of the two selected weight vector W _TX2 and transmit weight vector W _TX3, the components of the K-th array antenna _{108 W TX2 (k), W} TX3 ( k), and the two data streams are X1 and X2, the combined signal W (k) to be transmitted from the Kth array antenna 108 is obtained by the following Expression 2.

・・・（式2）

... (Formula 2)

At the third transmission timing, the weight weighting unit 136 determines the components of the Kth array antenna 108 in each of the two selected transmission weight vectors W _TX3 and W _TX4 as W _TX3 (k), W _TX4 ( k), and the two data streams are X1 and X2, the combined signal W (k) to be transmitted from the Kth array antenna 108 is obtained by the following Expression 3.

・・・（式3）

... (Formula 3)

At the fourth transmission timing, the weight weighting unit 136 determines the components of the Kth array antenna 108 in each of the two selected transmission weight vectors W _TX4 and W _TX1 as W _TX4 (k), W _TX1 ( k), and the two data streams are X1 and X2, the combined signal W (k) to be transmitted from the Kth array antenna 108 is obtained by the following equation (4).

・・・（式4）

... (Formula 4)

At the fifth transmission timing, the weight weighting unit 136 uses the components W _TX1 (k) and W _TX2 (of the Kth array antenna 108 in the two transmission weight vectors W _TX1 and transmission weight vector W _TX2 selected again. k) A combined data stream W (k), which is a combined signal to be transmitted from the Kth array antenna 108, is obtained by Equation 1 using two data streams X1 and X2.

  The weight weighting unit 136 outputs the combined data stream to be transmitted from each of the array antennas 108A to 108D to the IFFT processing unit 138.

  The IFFT processing unit 138 performs inverse fast Fourier transform on the combined data stream to be transmitted from each of the array antennas 108A to 108D, and performs a base for each of the array antennas 108A to 108D. Get the band signal. CP adding section 140 adds a CP to the input baseband signal for each of array antenna 108A to array antenna 108D. CP adding section 140 outputs a baseband signal for each of array antennas 108A to 108D to which a CP has been added to RF transmission processing section 107.

  The RF transmission processing unit 107 includes a mixer and a power amplifier (not shown). The RF transmission processing unit 107 converts (up-converts) the baseband signal for each of the array antennas 108A to 108D to which the CP is added into a downlink radio signal in the radio frequency band. Further, the RF transmission processing unit 107 amplifies the downlink radio signal in the radio frequency band, and the amplified radio frequency band downlink radio signal (the downlink radio signal in the amplified radio frequency band for each of the array antennas 108A to 108D). Signal). Here, the amplification factor is set so that the transmission power of each of the array antennas 108A to 108D is substantially the same.

  Next, the RF transmission processing unit 107 transmits each of the amplified downlink radio signals in the radio frequency band for each of the array antennas 108A to 108D via the corresponding array antenna 108A to array antenna 108D.

FIG. 4 is a diagram for explaining processing from MIMO precoding processing to transmission of a composite signal. As illustrated in FIG. 4, the radio base station eNB1 converts transmission data into two data streams S1 and S2 by a MIMO precoding process. Next, the radio base station eNB1 weights the data stream S1 using the transmission weight vector _WTX1 , and weights the data stream S2 using the transmission weight vector _WTX2 .

Then, the radio base station eNB1, for each array antenna 108A to the array antenna 108D, a data stream S1, weighted by transmission weight vector W _TX1, combines the data streams S2, weighted by the transmission weight vector W _TX2, each The combined data stream is transmitted via the corresponding array antenna 108A to array antenna 108D.

(1.3) Configuration of Radio Terminal FIG. 5 is a configuration diagram of the radio terminal UE2. As illustrated in FIG. 5, the radio terminal UE2 includes a control unit 202, a storage unit 203, a radio frequency (RF) reception processing unit 205, a baseband (BB) processing unit 206, an array antenna 208A, and an array antenna 208B.

  The control unit 202 is configured by a CPU, for example, and controls various functions provided in the radio terminal UE2. The storage unit 203 is configured by a memory, for example, and stores various types of information used for control and the like in the radio terminal UE2.

  The RF reception processing unit 205 receives a downlink radio signal in the radio frequency band from the radio base station eNB1 via the array antenna 208A and the array antenna 208B.

  The RF reception processing unit 205 includes a low noise amplifier (LNA) and a mixer (not shown). The RF reception processing unit 205 amplifies the received downlink radio signal in the radio frequency band, and converts (down-converts) it into a baseband signal. Further, the RF reception processing unit 205 outputs the baseband signal to the BB processing unit 206.

  The BB processing unit 206 includes a CP removal unit 222, an FFT processing unit 224, a channel equalization unit 228, and a demodulation / decoding unit 232.

  CP removing section 222 removes the CP from the input baseband signal. The FFT processing unit 224 performs fast Fourier transform on the baseband signal from which the CP is removed, and obtains a frequency domain signal.

  The channel equalization unit 228 performs channel equalization processing on the frequency domain signal corresponding to the frequency band of the downlink resource block allocated to the radio terminal UE2 among the frequency domain signals from the FFT processing unit 224. . The demodulation and decoding unit 232 performs demodulation and decoding processing on the signal that has been subjected to channel equalization processing. Thereby, the data transmitted by the radio base station eNB1 is obtained. Data is output to the control unit 202.

(2) Operation of Radio Base Station FIG. 6 is a flowchart showing the operation of the radio base station eNB1.

  In step S101, the radio base station eNB1 determines whether or not the signal transmission timing for the radio terminal UE2 has arrived.

  When the transmission timing has arrived, in step S102, the radio base station eNB1 cyclically selects two transmission weight vectors.

  In step S103, the radio base station eNB1 weights and combines the data streams for each array antenna 108 to obtain a combined signal.

  In step S104, the radio base station eNB1 transmits the combined signal via the corresponding array antenna 108.

(3) Operation / Effect As described above, according to the present embodiment, the radio base station eNB1 includes the plurality of array antennas 108A, the array antenna 108B, the array antenna 108C, and the array antenna 108D. For each of the two data streams corresponding to the number of array antennas 208A and 208B of UE2, weighting is performed with vectors of transmission weights orthogonal to each other. Further, the radio base station eNB1 transmits a combined data stream obtained by combining the data stream weighted by the transmission weight vector for each of the array antennas 108A to 108D.

  Accordingly, the radio base station eNB1 combines the plurality of data streams weighted by the transmission weight vector for each of the plurality of array antennas, and transmits the combined data streams according to the number of array antennas. Transmission with high characteristics can be performed.

  In particular, when the channel characteristics of the radio channel from the radio base station eNB1 to the radio terminal UE2 are unknown, the two data streams are weighted with mutually orthogonal transmission weight vectors, so that the channel The data streams are prevented from being mixed.

  Also, the radio base station eNB1 cyclically selects a transmission weight vector. Thereby, the directivity patterns of the array antenna 108A to the array antenna 108D can be periodically changed, and the reception possibility in the moving radio terminal UE2 can be improved.

  In the radio base station eNB1, the transmission powers of the array antennas 108A to 108D are substantially the same. For this reason, effective radiated power (EIRP: Equivalent Isotropic Radiated Power) can be increased regardless of the composite data stream.

(4) Other Embodiments As described above, the present invention has been described according to the embodiment. However, it should not be understood that the description and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

  In the above-described embodiment, the case where radio communication by MIMO is performed between the radio base station eNB1 and the radio terminal UE2 has been described. However, the present invention can be similarly applied even when wireless communication by MIMO is performed between other wireless communication devices.

  In the above-described embodiments, the TDD-LTE radio communication system has been described. However, radio communication employing up / down asymmetric communication in which the frequency band of the uplink radio signal allocated to the radio terminal is different from the frequency band of the downlink radio signal. The present invention can be similarly applied to any system.

  Thus, it should be understood that the present invention includes various embodiments and the like not described herein. Therefore, the present invention is limited only by the invention specifying matters in the scope of claims reasonable from this disclosure.

  eNB1 ... radio base station, UE2 ... radio terminal, 3 ... cell, 10 ... radio communication system, 102 ... control unit, 103 ... storage unit, 104 ... I / F unit, 106 ... BB processing unit, 107 ... RF transmission processing unit 108A, 108B, 108C, 108D ... array antenna, 132 ... demodulation and decoding unit, 134 ... coding modulation unit, 135 ... MIMO precoding processing unit, 136 ... weight weighting unit, 138 ... IFFT processing unit, 140 ... CP addition unit , 202 ... control unit, 203 ... storage unit, 205 ... RF reception processing unit, 222 ... CP removal unit, 224 ... FFT processing unit, 228 ... channel equalization unit, 232 ... demodulation decoding unit

Claims (3)

A wireless transmission device having a plurality of antenna elements,
A storage unit for storing a plurality of sets of weights each consisting of a set of weights selected from a plurality of weights orthogonal to each other;
When propagation path characteristics of a radio channel directed to a radio terminal are unknown , weighting is performed at the previous transmission timing for the radio terminal for each signal sequence to be transmitted corresponding to each of a plurality of antenna elements included in the radio terminal. A transmission unit that performs weighting with a set of weights different from the set of weights used, and transmits a combined signal in which the weighted signal sequence to be transmitted is combined for each antenna element of the radio base station; A wireless transmission device comprising:   The radio transmission apparatus according to claim 1, wherein the transmission unit cyclically selects the set of weights used for the weighting from the plurality of sets of weights. A transmission control method in a wireless transmission device having a plurality of antenna elements,
The wireless transmission device stores a plurality of sets of weights each consisting of a set of weights selected from a plurality of weights orthogonal to each other;
When propagation path characteristics of a radio channel directed to a radio terminal are unknown , weighting is performed at the previous transmission timing for the radio terminal for each signal sequence to be transmitted corresponding to each of a plurality of antenna elements included in the radio terminal. Weighting with a set of weights different from the set of weights used, and transmitting a combined signal obtained by combining the weighted signal sequence to be transmitted for each antenna element of the wireless transmission device; Including a transmission control method.

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