JP2009171421A - Mimo radio communication system, transmitter, receiver, and mimo radio communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain improvement in communication efficiency when performing communication between a plurality of transmitters and one receiver in accordance with a MIMO radio communication scheme. <P>SOLUTION: In a MIMO radio communication system for performing communication between a plurality of transmitters (base stations A, B) and one receiver (mobile station) in accordance with a MIMO radio communication scheme, whether reception powers from the transmitters are strong or weak in the receiver is determined and from the transmitter of the strong reception power, transmission to the receiver is performed according to a spatial multiplexing scheme but from the transmitter of the weak reception power, transmission to the receiver is performed according to a transmission diversity scheme. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a MIMO (Multiple Input Multiple Output) wireless communication system, a transmitter, a receiver, and a MIMO wireless communication method.

Conventionally, for example, Non-Patent Document 1 proposes a method of using MIMO technology in cooperation between a plurality of base stations in order to improve communication quality of a mobile station located at a cell edge in a cellular system. In the prior art described in Non-Patent Document 1, when a mobile station is located at the overlapping portion of the cell edges of two base stations, both base stations use the space time coding (STC) method. Communicate with the mobile station. The STC method is one of wireless communication methods using MIMO technology (hereinafter referred to as a MIMO wireless communication method), and can reduce a required signal-to-noise power ratio. Besides the STC method, for example, a spatial multiplexing (SM) method is known as a MIMO wireless communication method. The SM method can improve the transmission speed.
Manabu Mikami, Teruya Fujii, “Examination of downlink transmission method in OFDM system using MIMO between multiple base stations”, 2007 IEICE Society Conference, pp.366

  However, in the conventional technique described in Non-Patent Document 1 described above, the mobile station can perform efficient communication when the received power from the two base stations is substantially equal, but otherwise, the communication efficiency. (Refer to FIG. 3 of Non-Patent Document 1).

  The present invention has been made in view of such circumstances, and an object thereof is to improve communication efficiency when communication is performed by a MIMO wireless communication method between a plurality of transmitters and one receiver. An object is to provide a MIMO wireless communication system, a transmitter, a receiver, and a MIMO wireless communication method.

  In order to solve the above problems, a MIMO wireless communication system according to the present invention is a MIMO wireless communication system in which a plurality of transmitters and one receiver communicate with each other by a MIMO wireless communication scheme. The strength of received power from each transmitter is determined, a transmitter with strong received power performs transmission to the receiver by a spatial multiplexing method, and a transmitter with weak received power transmits to the receiver by a transmit diversity method. Is transmitted.

  The transmitter according to the present invention includes a transmitter for a MIMO wireless communication scheme, a spatial multiplexing scheme transmission processing means, a transmission diversity scheme transmission processing means, a switch for switching between the spatial multiplexing scheme and the transmission diversity scheme, and a receiver. Switch control means for controlling the switch on the basis of the above information.

  In the transmitter according to the present invention, the switch control means determines the strength of received power from the own transmitter in the receiver based on information from the receiver, and if the received power is strong, the spatial multiplexing method is used. If the received power is weak, a transmission diversity method is selected.

The transmitter according to the present invention receives received power information from a receiver.
The transmitter according to the present invention is characterized by receiving position information from a receiver.
The transmitter according to the present invention is characterized by receiving designation of a MIMO wireless communication system from a receiver.

  A receiver according to the present invention is a MIMO wireless communication system receiver for switching a spatial multiplexing system and a transmission diversity system to a spatial multiplexing system reception processing means, a transmission diversity system reception processing means, and a transmitter. And an information transmitting means for transmitting the information.

In the receiver according to the present invention, the information transmitting means transmits information indicating received power from the transmitter to the transmitter.
In the receiver according to the present invention, the information transmitting means transmits position information of the receiver itself to the transmitter.

  In the receiver according to the present invention, the information transmitting means determines the strength of received power from the transmitter, and when the received power is strong, instructs the transmitter to perform a spatial multiplexing scheme, and when the received power is weak. Is characterized by instructing the transmitter on a transmission diversity scheme.

  A MIMO wireless communication method according to the present invention is a MIMO wireless communication method in which a plurality of transmitters and one receiver communicate with each other by a MIMO wireless communication method, and received power from each transmitter in the receiver. A transmitter having a high reception power transmits to the receiver by a spatial multiplexing method, and a transmitter having a low reception power transmits to the receiver by a transmission diversity method. And

  According to the present invention, it is possible to improve communication efficiency when communication is performed between a plurality of transmitters and one receiver using the MIMO wireless communication method.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a conceptual diagram showing a configuration of a MIMO wireless communication system according to an embodiment of the present invention. In FIG. 1, the MIMO wireless communication system has base stations A and B and a mobile station. The base station A forms a cell 100A that is in a range where wireless communication with the mobile station is possible. The base station B forms a cell 100B that is in a range where radio communication with a mobile station is possible. The cells 100A and 100B have a cell overlap region 110 where the cell edges overlap. Base stations A and B simultaneously transmit signals to mobile stations in the cell overlap region 110 at the same frequency using the MIMO wireless communication method. The mobile station receives signals from both base stations A and B by the MIMO wireless communication system.

  FIG. 2 is a conceptual diagram for explaining the outline of the present invention. In FIG. 2, the cell overlap region 110 is divided into three regions α, β, and γ. The regions α, β, and γ are divided according to the received power from the base stations A and B in the mobile station. A method of dividing the regions α, β, and γ is shown in FIG. Area α is an area where the received power from base station A is strong and the received power from base station B is weak in the mobile station in the area. Area β is an area where both the received power from base station A and the received power from base station B are weak in the mobile station in the area. The area γ is an area where the received power from the base station A is weak and the received power from the base station B is strong in the mobile station in the area.

  When the mobile station is in the region β, the received power from the base station A and the received power from the base station B are substantially equal in the mobile station. For this reason, both base stations A and B transmit signals to the mobile station using the STC method. This reduces the required signal-to-noise power ratio and improves the communication quality.

  When the mobile station is in the area α or the area γ, the received power from the base stations A and B is different. For this reason, the base station with higher received power transmits a signal to the mobile station by the SM method, and the base station with lower received power transmits a signal to the mobile station by the STC method. As a result, the transmission speed is improved by transmitting a signal from the base station having a higher received power to the mobile station by the SM method, and thus, a large received power can be effectively utilized. On the other hand, the required signal-to-noise power ratio can be reduced by transmitting a signal from the base station with the weaker received power to the mobile station using the STC method, thus improving the communication quality by compensating for the weaker received power. Can be planned.

  As described above, when communication is performed between a plurality of base stations (transmitters) and one mobile station (receiver) using the MIMO wireless communication method, there is a difference in received power from each base station in the mobile station. By using the STC method and SM method separately, the frequency utilization efficiency can be improved and the communication efficiency can be improved.

  Hereinafter, the base station (transmitter) and the mobile station (receiver) according to the present embodiment will be described in detail.

  FIG. 4 is a block diagram showing a configuration of transmitter 1 provided in the base station shown in FIG. In FIG. 1, an error correction encoder 2 performs error correction encoding on input transmission data. The interleaver 3 interleaves the error correction encoded data. A modulator (Symbol Mapping) 4 maps the interleaved bit string to modulation symbols. Examples of the modulation scheme include QPSK (Quadrature Phase Shift Keying), 16QAM (16-positions Quadrature Amplitude Modulation), and 64QAM (64-positions Quadrature Amplitude Modulation). The modulation symbol data is input to the switch 5. The switch 5 switches the output destination of the input modulation symbol data to the serial-parallel converter (S / P) 6 or the STC encoder 7.

  The serial-parallel converter 6 converts the modulation symbol data into a parallel signal. The parallel signal of the modulation symbol data is input to the switch 8. The STC encoder 7 encodes the modulation symbol data by the STC method and outputs the STC encoded data as a parallel signal. The parallel signal of the STC encoded data is input to the switch 8.

  The switch 8 has an output port of the serial-parallel converter 6 and an output port of the STC encoder 7 connected to the input ports. The switch 8 switches whether an input signal from the serial-parallel converter 6 or an input signal from the STC encoder 7 is output.

  The switch controller 9 switches the switches 5 and 8 in synchronization. The switch controller 9 causes the switches 5 and 8 to select the serial-parallel converter 6 when operating the own transmitter in the SM system. On the other hand, the switch controller 9 causes the switches 5 and 8 to select the STC encoder 7 when operating the own transmitter in the STC method.

  OFDM (Orthogonal Frequency Division Multiplexing) modulators 10-1 and 10-2 and multiplexers 11-1 and 11-2 are provided corresponding to each of the two transmission antennas Tx1 and Tx2. Thus, two wireless transmission systems are configured.

  The parallel signal output from the switch 8 is distributed to each wireless transmission system and input to the corresponding OFDM modulators 10-1 and 10-2. The OFDM modulators 10-1 and 10-2 modulate an input signal by an orthogonal frequency division multiplexing method. Multiplexers 11-1 and 11-2 time-multiplex a predetermined pilot signal with respect to the orthogonal frequency division multiplexed signal. This multiplexed signal is transmitted from the transmission antennas Tx1 and Tx2.

  When this transmitter operates in the SM system, the modulation symbol data is converted into a parallel signal by the serial-parallel converter 6 and transmitted using two wireless transmission systems. This doubles the wireless transmission rate. On the other hand, when this transmitter operates in the STC scheme, the modulation symbol data is STC encoded by the STC encoder 7 and the STC encoded data is transmitted using two radio transmission systems. As a result, the required signal-to-noise power ratio can be reduced while the wireless transmission speed remains unchanged.

  Based on the information received from the mobile station (receiver), the switch controller 9 determines whether to operate the own transmitter in the SM system or the STC system. Hereinafter, an example of information received from a mobile station (receiver) will be described.

[When receiving information indicating received power from a mobile station (receiver)]
The mobile station has a function of measuring received power and notifies the base station of received power information (for example, received signal strength indicator (RSSI)) indicating received power from the base station. The switch controller 9 compares the received power information received from the mobile station with a reference value, and determines the strength of the received power from the own base station. As a result, when the received power from the own base station is strong, the own transmitter is operated in the SM system. On the other hand, when the received power from the own base station is weak, the own transmitter is operated by the STC method.

[When receiving location information from a mobile station (receiver)]
The mobile station has a positioning function such as GPS (Global Positioning System), acquires position information (for example, latitude and longitude) indicating the position of the mobile station, and notifies the base station of the position information. The switch controller 9 has a map around the base station, and calculates a radio wave environment value such as a path loss of a radio wave propagation path from the mobile station to the base station on the map based on position information received from the mobile station. . The switch controller 9 estimates the received power from the base station in the mobile station based on the radio wave environment value. The switch controller 9 compares the estimated received power with a reference value, and determines the strength of the received power from the own base station. As a result, when the received power from the own base station is strong, the own transmitter is operated in the SM system. On the other hand, when the received power from the own base station is weak, the own transmitter is operated by the STC method.

[When receiving specification of MIMO wireless communication system from mobile station (receiver)]
The mobile station has a reception power measurement function and measures the reception power from each base station. The mobile station compares each measured received power with a reference value and determines the strength of the received power from each base station. As a result, the SM scheme is designated for base stations with high received power, and the STC scheme is designated for base stations with low received power. The switch controller 9 operates the own transmitter by the MIMO wireless communication method designated by the mobile station.

  FIG. 5 is a block diagram showing a configuration of the receiver 30 provided in the mobile station shown in FIG. In FIG. 5, the receiver 30 has three receiving antennas Rx1, Rx2, and Rx3. The required number of receiving antennas at the receiver is the quotient obtained by dividing the number of transmitters transmitting by the STC method by 2 (when STC is performed with two transmitting antennas as a set), and transmitted by the SM method. This is the sum of the total number of transmitting antennas of the transmitting transmitter. Therefore, as in the present embodiment, when communicating with two transmitters each using two transmission antennas using the STC method and the SM method, the receiver 30 needs to include three reception antennas. is there.

  Separators 20-1 to 20-3 and OFDM demodulators 21-1 to 3 are provided corresponding to each of the three receiving antennas Rx1 to Rx1. Thus, three radio reception systems are configured. Received signals received by the receiving antennas Rx1 to Rx1 are input to the separators 20-1 to 20-3. Separators 20-1 to 20-3 separate the time-multiplexed pilot signal from the received signal. The separated pilot signal is input to the reception power meter 22. The OFDM demodulators 21-1 to 21-3 perform demodulation in the orthogonal frequency division multiplexing system on the received signal after the pilot signal separation. This OFDM demodulated signal is input to a maximum likelihood estimation (MLD) unit 23.

  The reception power meter 22 calculates reception power from each base station based on the pilot signal separated from the reception signal. The receiver 30 transmits information indicating received power from the base station to the base station.

In addition, according to the example of the information sent from the mobile station to the base station, the configuration for sending information from the mobile station to the base station is changed as follows.
[When sending location information from a mobile station]
The mobile station has a positioning function such as GPS, acquires position information indicating the position of the mobile station, and notifies the base station of the position information.
[When specifying a MIMO wireless communication system from a mobile station]
The mobile station has a reception power measurement function and measures the reception power from each base station. The mobile station compares each measured received power with a reference value and determines the strength of the received power from each base station. As a result, the SM scheme is designated for base stations with high received power, and the STC scheme is designated for base stations with low received power.

  Maximum likelihood estimator 23 performs STC and SM reception processing on the OFDM demodulated signal. A demodulator (Symbol Demapping) 25 performs symbol demapping on the output signal of the maximum likelihood estimator 23 to obtain a soft decision value. The deinterleaver 26 deinterleaves the soft decision value. The error correction decoder 27 performs error correction decoding on the deinterleaved signal.

Here, the processing performed by the maximum likelihood estimator 23 will be described. FIG. 6 is a conceptual diagram for explaining the principle of the MIMO wireless communication system according to the present embodiment. In FIG. 6, the base station A uses two transmission antennas Tx1 and Tx2 and performs a transmission operation using the STC method. The base station B uses the two transmission antennas Tx3 and Tx4 and performs a transmission operation using the SM method. The mobile station uses three receiving antennas Rx1, Rx2, and Rx3 to perform reception operation using the STC method and the SM method. h _nm indicates the frequency response of the channel between the transmitting antenna Txn (n is 1, 2, 3, 4) and the receiving antenna Rxm (m is 1, 2, 3).

FIG. 7 shows transmission signals from the transmission antennas Tx1 and Tx2 of the base station A and transmission signals from the transmission antennas Tx3 and Tx4 of the base station B at each time t and t + 1. Note that * represents a complex conjugate. In this case, signals r1 _{, t} , r2 _{, t} , r3 _{, t} , r1 _{, t + 1} , r2 _{, t + 1} , r3 _{, t} received by the receiving antennas Rx1, Rx2, and Rx3 of the mobile station. ₊₁ is expressed by the equations (1) and (2).

The maximum likelihood estimator 23 creates a reference symbol replica for the received signals r ₁ , r ₂ , r ₃ and demodulates each symbol by maximum likelihood estimation (MLD).

  According to the embodiment described above, frequency communication efficiency can be improved when communication is performed between a plurality of base stations (transmitters) and one mobile station (receiver) using the MIMO wireless communication scheme. For example, when the received power from the base station A is small and the received power from the base station B is large, the weakness of the received power in the mobile station can be compensated by transmitting from the base station A by the STC method, A large received power can be effectively utilized from the base station B by transmitting in the SM system.

  In the above-described embodiment, the STC method and the SM method are exemplified as the MIMO wireless communication method, but other methods can also be used. For example, the STC scheme is an example of a transmission diversity scheme, and another transmission diversity scheme may be used instead of the STC scheme.

  FIG. 8 is a block diagram showing a configuration of a MIMO wireless communication system according to another embodiment of the present invention. In FIG. 8, a server 30 is provided. The base stations A and B and the server 30 are connected by a communication line. The base station A transmits the information received from the mobile station to the server 30. The server 30 determines the MIMO wireless communication method used in the base station B based on the information, and instructs the base station B to use the MIMO wireless communication method. Hereinafter, an example of information received from a mobile station will be described. Note that the MIMO wireless communication system used by the base station A in its own station is determined in the same manner as in the above-described embodiment.

[When receiving information indicating received power from a mobile station]
Base station A receives received power information indicating received power from the base station from the mobile station. The base station A notifies the server 30 of the received power information. The server 30 estimates the received power from the base station B in the mobile station based on the received power information. For example, the received power is estimated assuming that the received powers of the base stations A and B are inversely proportional. The server 30 compares the estimated received power with a reference value, and determines the strength of the received power from the base station B. As a result, when the received power from the base station B is strong, the SM system is instructed to the base station B. On the other hand, when the received power from the base station B is weak, the STC system is instructed to the base station B.

[When receiving location information from a mobile station]
Base station A receives location information of the mobile station from the mobile station. The base station A notifies the server 30 of the position information. The server 30 has a map around the base station B, and calculates a radio wave environment value such as a path loss of a radio wave propagation path from the mobile station to the base station B on the map based on the position information received from the mobile station. Server 30 estimates the received power from base station B in the mobile station based on the radio wave environment value. The server 30 compares the estimated received power with a reference value, and determines the strength of the received power from the base station B. As a result, when the received power from the base station B is strong, the SM system is instructed to the base station B. On the other hand, when the received power from the base station B is weak, the STC system is instructed to the base station B.

  Note that the server 30 may determine whether or not the mobile station is in the cell overlap area based on the received power from the base station A in the mobile station. When the mobile station is not in the cell overlap area, that is, when communication is possible only from the base station A and communication is not possible from the base station B, the server 30 does not transmit the base station B to the mobile station. To instruct.

  As yet another embodiment, the base station B may be provided with the function of the server 30 described above. In this case, the base stations A and B are connected by a communication line, and the information that the base station A has sent to the server 30 is sent to the base station B. Based on the information received from the base station A, the base station B determines the MIMO wireless communication method used by the base station.

  In these other embodiments, the relationship between the base station A and the base station B may be reversed.

As mentioned above, although embodiment of this invention was explained in full detail with reference to drawings, the specific structure is not restricted to this embodiment, The design change etc. of the range which does not deviate from the summary of this invention are included.
For example, although two transmitters are used in the above-described embodiment, three or more transmitters may be used.

It is a conceptual diagram which shows the structure of the MIMO radio | wireless communications system which concerns on one Embodiment of this invention. It is a conceptual diagram for demonstrating the outline | summary of this invention. It is a graph which shows the division | segmentation method of area | region (alpha), (beta), (gamma) based on this invention. It is a block diagram which shows the structure of the transmitter 1 with which the base station shown in FIG. 1 is equipped. It is a block diagram which shows the structure of the receiver 30 with which the mobile station shown in FIG. 1 is equipped. It is a conceptual diagram for demonstrating the principle of the MIMO radio | wireless communication system which concerns on this embodiment. It is a graph which shows the transmission signal from each transmission antenna in each time. It is a block diagram which shows the structure of the MIMO radio | wireless communications system which concerns on other embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Transmitter, 5,8 ... Switch, 6 ... Serial-parallel converter (spatial multiplexing transmission processing means), 7 ... STC encoder (transmission diversity transmission processing means), 9 ... Switch controller, 23 ... Maximum likelihood estimator (transmission diversity type reception processing means, spatial multiplexing type reception processing means), 30 ... receiver, Rx1, Rx2, Rx3 ... reception antenna, Tx1, Tx2 ... transmission antenna

Claims (11)

In a MIMO wireless communication system that communicates between a plurality of transmitters and one receiver using the MIMO wireless communication system,
The receiver determines the strength of received power from each transmitter in the receiver, performs transmission to the receiver by a spatial multiplexing method from a transmitter with strong received power, and transmits diversity from a transmitter with low received power. To send to the receiver,
A MIMO wireless communication system characterized by the above. In MIMO wireless communication system transmitters,
A spatial multiplexing transmission processing means;
A transmission diversity transmission processing means;
A switch for switching between the spatial multiplexing method and the transmission diversity method;
Switch control means for controlling the switch based on information from a receiver;
A transmitter characterized by comprising:   The switch control means determines the strength of received power from the own transmitter in the receiver based on information from the receiver, selects the spatial multiplexing method when the received power is strong, and the received power is weak The transmitter according to claim 2, wherein a transmission diversity scheme is selected for the transmitter.   4. The transmitter according to claim 3, wherein received power information is received from the receiver.   4. The transmitter according to claim 3, wherein the transmitter receives position information from the receiver.   The transmitter according to claim 2, wherein the transmitter receives a designation of a MIMO wireless communication system from the receiver. In a MIMO wireless communication system receiver,
Spatial multiplexing reception processing means;
A reception diversity reception processing means;
Information transmitting means for sending information for switching between a spatial multiplexing scheme and a transmission diversity scheme to the transmitter;
A receiver comprising:   The receiver according to claim 7, wherein the information transmission unit transmits information indicating received power from the transmitter to the transmitter.   The receiver according to claim 7, wherein the information transmitting unit transmits position information of the receiver itself to the transmitter.   The information transmission means determines the strength of received power from the transmitter, and when the received power is strong, instructs the transmitter to perform a spatial multiplexing scheme, and when the received power is weak, transmits to the transmitter a transmission diversity scheme. The receiver according to claim 7, wherein: A MIMO wireless communication method for communicating with a MIMO wireless communication method between a plurality of transmitters and one receiver,
Determining the strength of received power from each transmitter in the receiver;
From the transmitter with strong received power, perform transmission to the receiver by spatial multiplexing,
Transmitting from the transmitter with weak reception power to the receiver by transmission diversity method,
A MIMO wireless communication method characterized by the above.

Images