JP5069083B2 - User apparatus, base station apparatus, and MIMO transmission control method - Google Patents

Description

  The present invention relates to a user apparatus, a base station apparatus, and a MIMO transmission control method.

  The MIMO (Multiple Input Multiple Output) transmission method is a multi-antenna communication method that uses a plurality of antennas for communication to increase the speed and / or quality of a transmission signal.

  The MIMO transmission method includes a MIMO multiplexing method and a MIMO diversity method. The MIMO multiplexing method is a method of transmitting different signals in parallel from a plurality of antennas using the same radio resource (frequency and time). Since the number of signals that can be transmitted increases as the number of antennas increases, the MIMO multiplexing method is effective in increasing the throughput. The MIMO diversity method is a method of transmitting the same signal from a plurality of antennas by space-time (or space-frequency) coding. Since a transmission diversity effect is obtained, the MIMO diversity method is effective in increasing the data rate and coverage at the cell edge.

  FIG. 1 shows application examples of the MIMO multiplexing method and the MIMO diversity method. Utilizing the advantages as described above, the base station apparatus applies the MIMO multiplexing method to a user apparatus that is close to the base station apparatus and has a large received SINR (Signal-to-Interference and Noise power Ratio), and the data rate Can be increased. On the other hand, for users who are far from the base station apparatus and have a small received SINR, the base station apparatus can apply the MIMO diversity method to increase the data rate at the cell edge. Controlling the number of signal sequences transmitted in parallel with the same radio resource (also referred to as “number of transmission streams” or “rank”) in accordance with the channel state of the user apparatus is referred to as rank adaptation (non-patent document). 1).

  FIG. 2 shows a configuration example of rank adaptation. The base station apparatus controls channel encoding and data modulation based on information from the user apparatus such as CQI (Channel Quality Indicator) and also controls the number of transmission antennas. Thus, rank adaptation means not only switching between the MIMO multiplexing method and the MIMO diversity method, but also adaptively controlling the number of transmission streams or the rank widely.

  In addition, in the MIMO transmission method, a signal can be transmitted to a communication partner using a beam with a controlled directivity by duplicating a stream of a transmission signal and combining and transmitting the duplicated streams together with appropriate weights. . This is called a precoding scheme, and the weighting factor (weight) used is called a “precoding vector” or more generally a “precoding matrix” (Non-Patent Documents 2 and 3).

  FIG. 3 shows a configuration example of precoding. The two streams (transmission signals 1 and 2) are duplicated in two systems by the copy unit, multiplied by the precoding vector in each system, combined and transmitted. From the viewpoint of using a more appropriate precoding vector, closed loop precoding as shown in the figure is preferable. In this case, the precoding vector is adaptively controlled to be a more appropriate value based on the channel state (channel estimation value) measured by the user apparatus. In the precoding scheme, throughput can be increased by increasing directivity gain and reducing inter-stream interference.

In the precoding scheme, it is considered that both the base station apparatus and the user apparatus manage a set of predetermined precoding matrices as a codebook. In a precoding scheme based on a codebook, a user apparatus may feed back an optimal precoding matrix index (also called PMI: Precoding Matrix Indicator). Therefore, it is possible to reduce the feedback overhead as compared with the case where the user apparatus feeds back the channel estimation value.
RW Heath Jr. and A. Paulraj: "Switching Between Diversity and Multiplexing in MIMO Systems," IEEE Trans. Commun., Vol. 53, No. 6, pp. 962-968, Jun. 2005. Emre Telatar: "Capacity of Multi-Antenna Gaussian Channels," European Transactions on Telecommunications, Vol. 10, No. 6, pp.585-595, Nov / Dec 1999. DJ Love, RW Heath and T. Strohmer Jr .: "Grassmannian Beamforming for Multiple-Input Multiple-Output Wireless Systems," IEEE Trans. Inform. Theory, Vol. 49, No. 10, pp. 2735-2747, Oct. 2003 .

  When a base station apparatus performs rank adaptation in a MIMO transmission system using precoding, the following procedure is required.

  As illustrated in FIG. 4, the user apparatus receives signals transmitted from the respective antennas of the base station apparatus, and measures the downlink channel state. An example of CQI (Channel Quality Indicator) measured by the user apparatus at this time is shown in FIG. The user equipment measures the optimum PMI for each rank, and the user equipment determines the rank that can increase the data rate most according to the channel state and the optimum PMI (and CQI) at that rank. Feedback to the device. In the case of FIG. 5, the user apparatus measures the PMI (and CQI) of rank 1 to rank 4, and feeds back rank = 1, PMI = 2 (and CQI = 5) to the base station apparatus.

  The base station apparatus transmits a signal based on the fed back rank and PMI (and CQI). Usually, a base station apparatus transmits a signal according to the rank fed back from the user apparatus. In the case of FIG. 5, the base station apparatus transmits signals with rank = 1 and PMI = 2.

  However, when the period in which the user apparatus feeds back the rank differs from the period in which the base station apparatus finally switches the rank, the base station apparatus may not follow the rank fed back from the user apparatus. In addition, since retransmission packets remain, even if feedback is given from the user apparatus so as to lower the rank, the base station apparatus may not follow the fed back rank. Furthermore, even if feedback is given from the user apparatus so as to increase the rank, the base station apparatus may not follow the fed back rank in relation to other user apparatuses. Thus, when the base station apparatus does not follow the rank fed back from the user apparatus, the PMI fed back from the user apparatus is different from the optimum PMI in the actual rank. For example, in the case of FIG. 5, when the base station apparatus selects rank = 2 even though the user apparatus feeds back rank = 1 and PMI = 2, PMI = 2 is not the optimum PMI for the user apparatus. Therefore, there arises a problem that the reception quality of the user apparatus is deteriorated.

  Further, the user apparatus needs to select an optimum PMI for each rank as shown in FIG. 5, and the number of processes increases as the number of ranks increases.

  In view of the above problems, an object of the present invention is to reduce processing of a user apparatus associated with rank adaptation in a MIMO transmission system using precoding.

In order to solve the above-described problem, a user apparatus according to the present invention provides:
A user apparatus that communicates with a base station apparatus that performs rank adaptation in a MIMO transmission system using precoding, wherein:
A PMI determination unit that determines a precoding matrix indicator (PMI) according to a channel state with a rank notified from the base station device; and a transmission unit that transmits the PMI to the base station device;
One of the features is to have

The base station apparatus according to the present invention is
A base station apparatus that performs rank adaptation in a MIMO transmission system using precoding, wherein:
A rank determining unit that determines a rank for communicating with the user device based on a rank requested from the user device; and a transmitting unit that transmits the determined rank as control information to the user device;
One of the features is to have

Also, the MIMO transmission method according to the present invention is:
A MIMO transmission control method between a base station apparatus and a user apparatus that performs rank adaptation in a MIMO transmission system using precoding, which includes:
The base station apparatus notifying the user apparatus of a rank;
The user apparatus determines a precoding matrix indicator (PMI) according to a channel state with a rank notified from the base station apparatus;
The user apparatus transmitting the PMI to the base station apparatus; and the base station apparatus multiplying a precoding matrix based on the PMI;
One of the features is to have

  According to the embodiment of the present invention, it is possible to reduce the processing of the user equipment associated with rank adaptation in the MIMO transmission system using precoding.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 6 shows a relationship between rank and reception quality and a general relationship between MCS (Modulation and Coding Scheme) and reception quality. When the reception quality is poor (for example, when the reception SINR is small), the rank number is set small in order to obtain transmission diversity. Therefore, the throughput is low. On the other hand, when the reception quality is good (for example, when the reception SINR is large), the rank number is set large in order to increase the throughput.

  Similarly, for the MCS, when the reception quality is poor (for example, when the CQI is small), a modulation scheme (for example, BPSK) for increasing the transmission reliability and a small channel coding rate are used. Also, when the reception quality is good (for example, when the CQI is large), a modulation scheme (for example, 16 QAM) and a large channel coding rate are used to improve transmission efficiency.

  The rank can be controlled up to the number of antennas, whereas the MCS can be finely controlled. Also, with regard to precoding, fine control can be performed similarly to MCS by setting fine PMI. Typically, MCS and precoding control can be performed more finely than rank control.

  In addition, when the base station apparatus controls the rank, the control is performed in consideration of the presence / absence of a retransmission packet and data to other user apparatuses. Therefore, the rank control is more complicated than the MCS and precoding control. Accordingly, rank control is preferably performed in a longer cycle than MCS and precoding control. In the following description, an embodiment for performing rank control with a long cycle and performing MCS and precoding control with a short cycle will be described.

  FIG. 7 shows a method of rank adaptation performed by a base station apparatus according to an embodiment of the present invention in a MIMO transmission system using precoding.

  First, the base station apparatus determines the rank and notifies the user apparatus. At this time, the base station apparatus may refer to the rank (rank request information) fed back from the user apparatus. The user apparatus determines an optimum PMI with the rank notified from the base station apparatus, and feeds back to the base station apparatus. That is, even if the rank notified from the base station apparatus is not optimal for the user apparatus, it follows the rank notified from the base station apparatus. At this time, the user apparatus may determine a rank more suitable than the rank notified from the base station apparatus, and may feed back the rank request information to the base station apparatus.

  Thus, in one embodiment of the present invention, the base station apparatus determines the rank and notifies the user apparatus with a control signal such as an L1 / L2 control signal or an L3 control signal. A user apparatus determines PMI according to the rank notified from the base station apparatus. Therefore, regardless of whether or not the base station apparatus follows the rank fed back from the user apparatus, the user apparatus can feed back the optimum PMI (and CQI) at the rank notified from the base station apparatus.

  Further, the PMI (and CQI) measured by the user apparatus is simplified as shown in FIG. The user apparatus does not need to measure the PMI (and CQI) of all ranks, and may measure the PMI (and CQI) with the rank notified from the base station apparatus. As a result, it is possible to reduce the processing of the user device.

  Further, when the number of bits to be fed back differs depending on the rank (for example, when the number of bits of PMI and CQI differs between rank = 1 and rank = 2 in the multicode word), blind detection is performed in the uplink. And rank, PMI and CQI can be demodulated.

  Furthermore, when the user apparatus feeds back the rank, PMI and CQI to the base station apparatus, it becomes possible to encode these control information together. By such encoding, an encoding gain is obtained and the reception quality of control information is improved.

<Flowchart of MIMO transmission control method>
FIG. 9 shows a flowchart of a MIMO transmission control method according to an embodiment of the present invention.

  First, the base station apparatus determines a rank and notifies the user apparatus (S101). The user apparatus determines an optimum PMI according to the rank notified from the base station apparatus according to the channel state. Further, the user apparatus measures CQI representing the reception quality at the rank notified from the base station apparatus. PMI and CQI are fed back to the base station apparatus (S103). The base station apparatus determines the MCS according to the CQI and also determines the precoding matrix based on the PMI. The base station apparatus modulates and channel-codes user data with the determined MCS, multiplies the determined precoding matrix, and transmits the user data (S105). In addition, S101-S105 are repeated with the period which measures PMI and CQI.

  When the user apparatus determines that the data rate can be increased by changing the rank in consideration of the channel state, the user apparatus sets a rank (rank request information) more suitable than the rank notified from the base station apparatus. Feedback may be provided (S107). The base station apparatus determines the rank in consideration of the rank request information and notifies the user apparatus (S109). At this time, the base station apparatus may not follow the rank request information from the user apparatus. For example, the base station apparatus may receive rank request information from the user apparatus until a predetermined number of times, and average the results to determine the rank. The rank may be transmitted on the L1 / L2 control channel or may be transmitted on the L3 control channel. Thereafter, S101 to S105 are similarly repeated.

<Configuration of user device>
FIG. 10 shows a block diagram of the user apparatus 10 according to an embodiment of the present invention. The user apparatus 10 includes an RF reception unit 101, a reception timing estimation unit 103, an FFT (Fast Fourier Transform) unit 105, a channel estimation unit 107, a signal detection unit 109, a data channel decoding unit 111, and a control channel decoding Unit 113, CQI measurement unit 115, PMI determination unit 117, and rank request unit 119.

  The RF receiving unit 101 converts signals received from the respective antennas into baseband signals. The frame timing of the baseband signal is estimated by the reception timing estimation unit 103 and converted into the frequency domain by the FFT unit 105.

  The channel estimation unit 107 compensates for distortion of the signal from the antenna to be written, and outputs the result to the signal detection unit 109. The signal detection unit 109 separates and / or combines signals from the respective antennas, outputs user data to the data channel decoding unit 111, and outputs control information to the control channel decoding unit 113. The control information decoded by the control channel decoding unit 113 includes the rank notified from the base station apparatus.

  CQI measurement section 115 measures CQI based on the reception quality of the reference signal (pilot signal). At this time, the rank notified from the base station apparatus is used. That is, the CQI measurement unit 115 does not need to measure CQIs of all ranks.

  The PMI determination unit 117 determines the optimum PMI with the rank notified from the base station based on the reception quality of the reference signal (pilot signal). For example, the PMI determination unit 117 determines a precoding matrix suitable for downlink data transmission based on the reception quality of the reference signal, and selects a PMI indicating the precoding matrix from the codebook. Similarly, the PMI determination unit 117 need not determine PMIs for all ranks.

  The rank request unit 119 determines a rank that maximizes the data rate based on the reception quality of the reference signal (pilot signal), and generates this rank as rank request information.

  The CQI measured by the CQI measurement unit 115, the PMI determined by the PMI determination unit 117, and the rank determined by the rank request unit 119 are transmitted as control information from the transmission unit to the base station apparatus.

<Configuration of base station device>
In FIG. 11, the block diagram of the base station apparatus 20 which concerns on one Example of this invention is shown. The base station apparatus 20 includes a rank determination unit 201, an L1 / L2 control channel generation unit 203, an L3 control channel generation unit, a user channel generation unit 207, a precoding matrix (precoding vector) multiplication unit 209, and a multiplex Part 211.

  The rank determination unit 201 receives rank request information from the user device and determines a rank used for communication with the user device. The rank determination unit 201 may determine a rank every time a rank is received from a user apparatus, or may determine a rank by averaging a predetermined number of rank information. The rank may be determined when the same rank request information is received more than a predetermined number of times. The rank may be transmitted on the L1 / L2 control channel or may be transmitted on the L3 control channel.

  When the rank is transmitted through the L1 / L2 control channel, the L1 / L2 control channel generation unit 203 generates other L1 / L2 control information and rank as L1 / L2 control information. When the rank is transmitted on the L3 control channel, the L3 control channel generation unit 205 generates other L3 control information and rank as L3 control information. The L3 control information is multiplied by a precoding vector multiplying unit 209 by the precoding vector determined by the PMI received from the user apparatus together with the user data.

  The rank, other control information, and user data are multiplexed by the multiplexing unit 211 on radio resources determined by scheduling, and transmitted from the transmission unit to the user apparatus.

  As described above, according to the embodiment of the present invention, it is possible to reduce the processing of the user apparatus associated with rank adaptation in the MIMO transmission system using precoding. The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above-described embodiments, and various modifications and applications can be made within the scope of the claims. For example, the present invention is applicable to LTE (Long Term Evolution), which is a successor of W-CDMA (Wideband Code Division Multiple Access) and HSDPA (High Speed Downlink Packet Access), and further uses precoding and rank adaptation. It can also be applied to other MIMO systems.

The figure which shows the example of application of a MIMO multiplexing method and a MIMO diversity method Diagram showing rank adaptation in MIMO transmission Diagram showing MIMO transmission using precoding The figure which shows the rank adaptation in MIMO transmission using precoding The figure which shows an example of the reception quality measured by a user apparatus, when performing rank adaptation in MIMO transmission using precoding The figure which shows the relationship between reception quality and the number of ranks, and the relationship between reception quality and MCS The figure which shows the rank adaptation in the MIMO transmission using the precoding based on one Example of this invention The figure which shows an example of the reception quality measured with a user apparatus according to one Example of this invention The flowchart which shows the MIMO transmission control method based on one Example of this invention The block diagram of the user apparatus which concerns on one Example of this invention. The block diagram of the base station apparatus which concerns on one Example of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 User apparatus 101 RF receiving part 103 Reception timing estimation part 105 FFT part 107 Channel estimation part 109 Signal detection part 111 Data channel decoding part 113 Control channel decoding part 115 CQI measurement part 117 PMI determination part 119 Rank request part 20 Base station apparatus 201 Rank determination unit 203 L1 / L2 control channel generation unit 205 L3 control channel generation unit 207 User channel generation unit 209 Precoding matrix multiplication unit

Claims (4)

A user apparatus that communicates with a base station apparatus that performs rank adaptation in a MIMO transmission system using precoding, wherein:
A PMI determination unit that determines a precoding matrix indicator (PMI) according to a channel state with a rank notified from the base station device; and a transmission unit that transmits the PMI to the base station device;
A user device. A rank requesting unit that requests a rank more suitable than the rank notified from the base station apparatus according to a channel state;
The user apparatus according to claim 1, further comprising: A base station apparatus that performs rank adaptation in a MIMO transmission system using precoding, wherein:
A rank determining unit that determines a rank for communicating with the user device based on a rank requested from the user device; and a transmitting unit that transmits the determined rank as control information to the user device;
A base station apparatus. A MIMO transmission control method between a base station apparatus and a user apparatus that performs rank adaptation in a MIMO transmission system using precoding, which includes:
The base station apparatus notifying the user apparatus of a rank;
The user apparatus determines a precoding matrix indicator (PMI) according to a channel state with a rank notified from the base station apparatus;
The user apparatus transmitting the PMI to the base station apparatus; and the base station apparatus multiplying a precoding matrix based on the PMI;
A MIMO transmission control method comprising:

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