JP5557941B1 - Wireless communication apparatus and wireless transmission system - Google Patents

Abstract

A radio communication apparatus and a radio transmission system capable of determining an optimum rank even when there is frequency selective fading in a radio transmission path capable of communication by a MIMO radio transmission system.
A signal-to-interference noise ratio (SINR) is calculated for each of a plurality of subcarriers of each transmission stream based on signals transmitted and received by a plurality of transmission streams, and a plurality of signals are calculated based on the SINR calculated for each subcarrier. The channel capacity is calculated for each subcarrier. A channel capacity index value obtained by summing or averaging the plurality of channel capacities calculated for the plurality of subcarriers on the frequency axis is calculated for each of the plurality of ranks of the wireless transmission path, and is calculated for each of the plurality of ranks. Based on the index value of the channel capacity, the rank used for the next data transmission in the wireless transmission path is determined.
[Selection] Figure 1

Description

  The present invention relates to a wireless communication apparatus and a wireless transmission system that can communicate via a wireless transmission path.

  2. Description of the Related Art Conventionally, a MIMO (Multi Input Multi Output) wireless transmission system that transmits and receives data with a plurality of antennas is known. This MIMO radio transmission system is adopted in the LTE (Long Term Evolution) communication standard defined by 3GPP (Third Generation Partnership Project), which is a standardization project for third generation (3G) mobile communication systems, and is also LTE- Adoption is also being studied in the Advanced communication standard. In a mobile communication system employing a MIMO wireless transmission scheme, a base station apparatus (eNode-B) that is one of the plurality of wireless communication apparatuses that perform data transmission and reception and a mobile station that is the other wireless communication apparatus (eNode-B) By transmitting and receiving data with a plurality of different transmission layers (transmission streams) using a plurality of antennas with a UE (user equipment), wireless transmission by the MIMO spatial multiplexing scheme or the MIMO diversity scheme can be performed. . The MIMO spatial multiplexing scheme is a scheme in which different signals are transmitted in parallel from a plurality of antennas using the same radio resource (frequency and time), and the MIMO diversity scheme is the same signal transmitted from a plurality of antennas in space-time (or , Space-frequency) transmission. In LTE / LTE-Advanced, precoding is applied on the transmission side in both the MIMO spatial multiplexing scheme and the MIMO diversity scheme, but an open-loop type (Open-Loop MIMO) that does not use feedback control from the reception side, There is a closed loop type (Closed-Loop MIMO) using feedback information from the receiving side (see Non-Patent Document 1, Non-Patent Document 2, and Non-Patent Document 3).

  In the MIMO radio transmission method, the rank (“number of transmission streams”, “number of transmission layers” or “number of transmission layers” or “number of transmission layers” is determined according to the channel state such as signal-to-interference plus noise power ratio (SINR) of the received signal. Rank adaptation control that adaptively controls “the number of spatial multiplexing” is applied (for example, see Non-Patent Documents 4 to 7). Here, a rank of 1 corresponds to the MIMO diversity scheme, and a rank of 2 or more corresponds to the MIMO spatial multiplexing scheme. In order to apply the rank adaptation control, the mobile station (UE) on the receiving side feeds back information (RI: Rank Indicator) on the rank determined in the mobile station to the base station (eNode-B) on the transmitting side. Thus, the base station performs dynamic rank control (see, for example, Non-Patent Documents 4 and 5).

  In Patent Document 1, a signal-to-interference and noise ratio (SINR) for each subcarrier of each transmission stream of MIMO is calculated, and an average channel capacity (Shannon capacity) for each of a plurality of ranks is calculated from an average SINR averaged between transmission streams. And a MIMO wireless transmission scheme that selects a rank to be used based on the calculation result is disclosed. In this MIMO wireless transmission system, for example, the control is performed to rank 1 in an environment where the average SINR is low, and the control is performed to rank 2 in an environment where the average SINR is high.

  However, in the conventional MIMO radio transmission system via a plurality of subcarriers disclosed in Patent Document 1 and the like, when the rank is switched according to SINR, the presence / absence of fading correlation between antennas, the modulation multi-level number, etc. The rank cannot be accurately switched under the influence, and the throughput in the wireless transmission path may be deteriorated.

  The present invention has been made in view of the above problems, and an object thereof is to improve the rank switching accuracy based on SINR in a wireless transmission path of a MIMO wireless transmission system via a plurality of subcarriers and suppress throughput degradation. A wireless communication device and a wireless transmission system that can be used.

A wireless transmission system according to the present invention is a wireless transmission system capable of transmitting and receiving data using a plurality of different transmission streams between a plurality of wireless communication devices, and a plurality of wireless transmission paths between the plurality of wireless communication devices. Means for calculating a signal-to-interference noise ratio (SINR) for each of a plurality of subcarriers of the transmission stream based on a signal transmitted / received in one or a plurality of transmission streams including a plurality of subcarriers, and for each of the plurality of subcarriers Based on the calculated signal-to-interference noise ratio (SINR), a means for calculating channel capacity for each of the plurality of subcarriers and a plurality of ranks of the wireless transmission path are calculated for each of the plurality of subcarriers. Means for calculating an index value of channel capacity obtained by adding or averaging a plurality of channel capacities on the frequency axis; and the plurality of ranks Based on the index value of the channel capacity calculated for respectively, and means for determining a rank to use for transmitting the next data in the radio transmission path.
In this wireless transmission system, the SINR and the channel capacity based on the SINR are calculated for each of the plurality of subcarriers, and the channel capacity calculated by adding or averaging the plurality of channel capacities calculated for each of the plurality of subcarriers on the frequency axis. Is calculated for each of a plurality of ranks. Based on the channel capacity index value calculated in this way, it is possible to accurately determine the average channel capacity over the plurality of subcarriers in each of the plurality of ranks in consideration of the presence or absence of fading correlation between antennas. Therefore, the rank used for the next data transmission can be accurately determined so as to suppress the deterioration of the throughput according to the SINR in the actual wireless transmission path. Therefore, it is possible to increase the rank switching accuracy based on the SINR in the radio transmission path of the MIMO radio transmission system via a plurality of subcarriers, and suppress the degradation of the throughput.

In the wireless transmission system, means for calculating a mutual information amount (MIB) per bit from the signal-to-interference noise ratio (SINR) for each of the plurality of subcarriers, and for each of the plurality of subcarriers, the 1 A means for calculating a mutual information amount (MI) per modulation symbol from a mutual information amount (MIB) per bit, and a mutual information amount per modulation symbol for the plurality of subcarriers for each of a plurality of modulation schemes The means for calculating the sum of (MI) and the sum of mutual information (MI) per modulation symbol calculated for each of the plurality of modulation schemes are compared with each other, and the sum of the mutual information (MI) is maximized. Means for selecting a modulation scheme, and for each of a plurality of ranks of the wireless transmission path, the calculated modulation scheme Means for calculating an index value of channel capacity obtained by adding or averaging mutual information (MI) per modulation symbol for each number of subcarriers on the frequency axis, and an index of the channel capacity calculated for each of the plurality of ranks Means for comparing the values with each other and determining a rank having a maximum index value of the channel capacity as a rank used for next data transmission in the wireless transmission path.
In this wireless transmission system, the channel capacity is calculated for each of a plurality of subcarriers based on the MIB, so that the modulation method (modulation multi-value number) used in the actual wireless transmission path and the bit level to the symbol level are changed. The channel capacity for each of the plurality of subcarriers used for determining the rank can be calculated in consideration of the influence of mapping. Therefore, the rank switching accuracy based on the SINR can be further increased.

In the wireless transmission system, the channel capacity for each of the plurality of subcarriers calculated based on the signal-to-interference noise ratio (SINR) may be a Shannon capacity.
In this wireless transmission system, the calculation process of the channel capacity for each subcarrier can be simplified by using the Shannon capacity that is easy to calculate.

Another wireless transmission system according to the present invention is a wireless transmission system capable of transmitting and receiving data using a plurality of different transmission streams between a plurality of wireless communication devices, and a wireless transmission path between the plurality of wireless communication devices. The average signal-to-interference noise ratio (SINR) for each of the plurality of subcarriers used in the wireless transmission path between the plurality of transmission streams based on the signals transmitted and received in the plurality of transmission streams including the plurality of subcarriers in FIG. Means for calculating a value, means for calculating a mutual information amount (MIB) per bit from an average value of the signal to interference noise ratio (SINR) for each of the plurality of subcarriers, and for each of the plurality of subcarriers Means for calculating a mutual information amount (MI) per modulation symbol from the mutual information amount (MIB) per bit, and a plurality of modulation schemes, respectively. A means for calculating a sum of mutual information (MI) per modulation symbol for the plurality of subcarriers; and a mutual information (MI) per modulation symbol calculated for each of the plurality of modulation schemes. Means for comparing each other and selecting a modulation scheme that maximizes the sum of the mutual information (MI), and for each of a plurality of ranks of the wireless transmission path, the plurality calculated for the selected modulation scheme Means for calculating an index value of channel capacity obtained by summing or averaging mutual information (MI) per modulation symbol for each subcarrier on the frequency axis, and an index value of the channel capacity calculated for each of the plurality of ranks Are used for the next data transmission on the wireless transmission path. And means for determining the ranks, the.
In this wireless transmission system, an average SINR value is calculated for each of a plurality of subcarriers between a plurality of transmission streams, and a plurality of channel capacities calculated for each of the plurality of subcarriers are summed or averaged on the frequency axis. A capacity index value is calculated for each of a plurality of ranks. Based on the channel capacity index value calculated in this way, it is possible to accurately determine the average channel capacity over the plurality of subcarriers in each of the plurality of ranks in consideration of the presence or absence of fading correlation between antennas. Therefore, the rank used for the next data transmission can be accurately determined so as to suppress the deterioration of the throughput according to the SINR in the actual wireless transmission path. Therefore, it is possible to increase the rank switching accuracy based on the SINR in the radio transmission path of the MIMO radio transmission system via a plurality of subcarriers, and suppress the degradation of the throughput.
In addition, by calculating the channel capacity for each of a plurality of subcarriers based on the MIB, the influence of the modulation scheme (number of modulation levels) used in the actual wireless transmission path and the mapping from the bit level to the symbol level In consideration of the above, the channel capacity for each of a plurality of subcarriers used for determining the rank can be calculated. Therefore, the rank switching accuracy based on the SINR can be further increased.

In the wireless transmission system, the mutual information amount (MIB) per bit may be calculated with the reception processing method as an ideal.
In this wireless transmission system, the MIB calculation process can be simplified.

In the wireless transmission system, the mutual information amount (MIB) per bit may be calculated in consideration of a reception processing method that is actually used.
In this wireless transmission system, the channel capacity for each of the plurality of subcarriers can be calculated using an MIB that takes into account the reception processing method that is actually used, so that the rank switching accuracy based on the SINR can be further improved. .

In the wireless transmission system, the Shannon capacity may be a Shannon limit capacity calculated with an ideal reception processing method and without setting an upper limit based on a modulation method.
In this wireless transmission system, the Shannon capacity calculation process can be simplified.

In the wireless transmission system, the Shannon capacity may be calculated without setting an upper limit based on a modulation method in consideration of a reception processing method that is actually used.
In this wireless transmission system, the channel capacity for each of the plurality of subcarriers can be calculated using the Shannon capacity in consideration of the actually used reception processing method, so that the rank switching accuracy based on the SINR can be further improved. it can.

In the wireless transmission system, the Shannon capacity may be calculated in consideration of a reception processing method actually used and an upper limit based on a modulation method.
In this wireless transmission system, the channel capacity for each of the plurality of subcarriers can be calculated using the Shannon capacity that takes into account the reception processing method actually used and the upper limit of the modulation method, so that rank switching based on the SINR is performed. The accuracy can be further increased.

According to another aspect of the present invention, there is provided a wireless transmission system capable of transmitting and receiving data using a plurality of different transmission streams between a plurality of wireless communication devices, wherein the wireless transmission between the plurality of wireless communication devices is performed. Based on the means for calculating the channel capacity for each of the plurality of ranks of the path and the channel capacity for each of the plurality of ranks calculated for each of the plurality of past calculation timings, in the next data transmission timing on the wireless transmission path The channel capacity for each of the plurality of ranks may be predicted, and a rank used for next data transmission on the wireless transmission path may be determined based on the prediction result.
In this wireless transmission system, rank switching based on the SINR can be accurately performed while suppressing the influence of delay time from the rank determination timing to the data transmission timing to which the rank is applied.

Further, in the wireless transmission system, for each of the plurality of ranks at the next data transmission timing on the wireless transmission path, based on the channel capacity for each of the plurality of ranks calculated at each of the latest two previous calculation timings. Channel capacity may be linearly predicted.
In this wireless transmission system, it is possible to simplify the channel capacity prediction process for suppressing the influence of the delay time until the data transmission timing to which the rank is applied.

A wireless communication device according to the present invention is a wireless communication device on a data receiving side in a wireless transmission system capable of transmitting and receiving data using a plurality of different transmission streams between a plurality of wireless communication devices, and the plurality of wireless communication devices Means for calculating a signal-to-interference noise ratio (SINR) for each of a plurality of subcarriers of the transmission stream based on a signal transmitted and received by a single or a plurality of transmission streams including a plurality of subcarriers in a wireless transmission path between A means for calculating a channel capacity for each of the plurality of subcarriers based on the signal-to-interference and noise ratio (SINR) calculated for each of the plurality of subcarriers, and for each of a plurality of ranks of the radio transmission path, Calculates the channel capacity index value obtained by adding or averaging multiple channel capacities calculated for each subcarrier on the frequency axis. Means for determining, based on the channel capacity index value calculated for each of the plurality of ranks, means for determining a rank to be used for next data transmission in the wireless transmission path, and data transmission of the information on the determined rank Means for notifying the wireless communication device on the side.
In the wireless communication apparatus, means for calculating a mutual information amount (MIB) per bit from the signal-to-interference noise ratio (SINR) for each of the plurality of subcarriers, and for each of the plurality of subcarriers, the 1 A means for calculating a mutual information amount (MI) per modulation symbol from a mutual information amount (MIB) per bit, and a mutual information amount per modulation symbol for the plurality of subcarriers for each of a plurality of modulation schemes The means for calculating the sum of (MI) and the sum of mutual information (MI) per modulation symbol calculated for each of the plurality of modulation schemes are compared with each other, and the sum of the mutual information (MI) is maximized. Means for selecting a modulation scheme, and the plurality of calculated for the selected modulation scheme for each of a plurality of ranks of the wireless transmission path Means for calculating an index value of channel capacity obtained by adding or averaging mutual information (MI) per modulation symbol for each subcarrier on the frequency axis; and an index value of the channel capacity calculated for each of the plurality of ranks. Means for comparing each other and determining a rank having a maximum index value of the channel capacity as a rank used for next data transmission in the wireless transmission path.
Another wireless communication apparatus according to the present invention is a wireless communication apparatus on a data receiving side in a wireless transmission system capable of transmitting and receiving data by a plurality of different transmission streams between a plurality of wireless communication apparatuses, For each of a plurality of subcarriers used in the wireless transmission path between the plurality of transmission streams, based on signals transmitted and received by a plurality of transmission streams including a plurality of subcarriers in a wireless transmission path between the wireless communication devices Means for calculating an average value of signal-to-interference noise ratio (SINR), and calculating a mutual information amount (MIB) per bit from the average value of signal-to-interference noise ratio (SINR) for each of the plurality of subcarriers And a mutual information amount (MI) per modulation symbol from the mutual information amount (MIB) per bit for each of the plurality of subcarriers. Means for calculating a sum of mutual information (MI) per modulation symbol for each of the plurality of subcarriers for each of a plurality of modulation schemes, and the modulation calculated for each of the plurality of modulation schemes Means for comparing the sum of mutual information (MI) per symbol with each other and selecting a modulation scheme that maximizes the sum of the mutual information (MI), and for each of the plurality of ranks of the wireless transmission path, the selection Means for calculating an index value of channel capacity obtained by summing or averaging on the frequency axis the mutual information (MI) per modulation symbol for each of the plurality of subcarriers calculated for the plurality of subcarriers; The channel capacity index values calculated for the channel capacity are compared with each other, and the rank with the maximum channel capacity index value is And means for determining a rank to use for the next data transmission in the transmission path, and means for notifying information ranks the determined to the wireless communication device of the data transmission side.
Still another wireless communication device according to the present invention is a wireless communication device on the data receiving side in a wireless transmission system capable of transmitting and receiving data using a plurality of different transmission streams between a plurality of wireless communication devices, The wireless transmission based on the channel capacity for each of the plurality of ranks of the wireless transmission path between the wireless communication devices and the channel capacity for each of the plurality of ranks calculated at each of a plurality of past calculation timings. Means for predicting channel capacity for each of the plurality of ranks at the next data transmission timing on the path, and determining a rank to be used for next data transmission on the radio transmission path based on the prediction result; And means for notifying the data transmission-side wireless communication device of the rank information.

In this specification, “reception processing method is ideal” means that when calculating the signal-to-interference noise ratio (SINR) for each of the plurality of subcarriers when determining the channel capacity of the wireless transmission path, This means that the channel estimation of the wireless transmission path is ideal without considering a specific method such as ZF or MMSE described later as a reception processing method.
Further, in this specification, the “upper limit by the modulation scheme” means the number of bits of information amount per modulation symbol when modulated by a certain modulation scheme. For example, when the modulation method is QPSK, 16QAM, and 64QAM, the upper limit by the modulation method is 2 bits, 4 bits, and 6 bits, respectively.

  According to the present invention, there is an effect that it is possible to improve rank switching accuracy based on SINR in a radio transmission path of a MIMO radio transmission system via a plurality of subcarriers and suppress throughput degradation.

The functional block diagram which shows an example of schematic structure of the user apparatus as a radio | wireless communication apparatus of the receiving side in the downlink of the closed loop type MIMO wireless transmission system which concerns on embodiment of this invention. The functional block diagram which shows an example of schematic structure of the radio base station as a radio | wireless communication apparatus of the transmission side in the downlink in the downlink of the MIMO radio | wireless transmission system. Explanatory drawing which shows the model of the wireless transmission path between a user apparatus and a wireless base station. The graph which shows the result of having calculated the reception level corresponding to the element (transmission path response value) of a MIMO channel matrix in case the value of fading correlation (rho) is 0.0 for every subcarrier. The graph which shows the result of having calculated the reception level corresponding to the element (transmission path response value) of a MIMO channel matrix in case the value of fading correlation (rho) is 0.5 for every subcarrier. The graph which shows the result of having calculated the reception level corresponding to the element (transmission path response value) of a MIMO channel matrix in case the value of fading correlation (rho) is 0.9 for every subcarrier. The graph which shows the result of having calculated the reception level corresponding to the element (transmission path response value) of a MIMO channel matrix in case the value of fading correlation (rho) is 1.0 for every subcarrier. The graph which shows the relationship between the average SNR per receiving antenna in case the value of fading correlation (rho) is 0.0 at the time of using a ZF system for rank 2 signal detection, and an average channel capacity. The graph which shows the relationship between the average SNR per receiving antenna when the value of fading correlation (rho) is 0.5 at the time of using a ZF system for rank 2 signal detection, and an average channel capacity. The graph which shows the relationship between the average SNR per receiving antenna in case the value of fading correlation (rho) is 0.0 at the time of using the MMSE system for rank 2 signal detection, and an average channel capacity. The graph which shows the relationship between the average SNR per receiving antenna in case the value of fading correlation (rho) is 0.5 at the time of using the MMSE system for rank 2 signal detection, and an average channel capacity. The functional block diagram which shows the example of 1 structure of the channel capacity calculation / comparison part in the user apparatus which concerns on embodiment of this invention. 13 is a flowchart showing an example of a rank determination procedure using the channel capacity calculation / comparison unit of FIG. Explanatory drawing which shows the model of the wireless transmission path between the user apparatus for demonstrating the rank determination procedure using the channel capacity calculation / comparison part of FIG. The graph which shows an example of the relationship between MIB and SINR of each modulation system (QPSK, 16QAM, 64QAM). The graph which shows an example of the relationship between the mutual information amount [bit / symbol] per symbol and SINR calculated from MIB of FIG. The functional block diagram which shows the other structural example of the channel capacity calculation / comparison part in the user apparatus which concerns on embodiment of this invention. 18 is a flowchart showing an example of a rank determination procedure using the channel capacity calculation / comparison unit of FIG. The functional block diagram which shows the further another structural example of the channel capacity calculation / comparison part in the user apparatus which concerns on embodiment of this invention. 20 is a flowchart showing an example of a rank determination procedure using the channel capacity calculation / comparison unit of FIG. The functional block diagram which shows the further another structural example of the channel capacity calculation / comparison part in the user apparatus which concerns on embodiment of this invention. The flowchart which shows an example of the rank determination procedure using the channel capacity calculation / comparison part of FIG. FIG. 12 and FIG. 13 are graphs showing simulation results for calculating the relationship between the average SNR per receiving antenna and the average channel capacity when the rank is determined (signal detection method: ZF, fading correlation ρ value = 0). 0.0). FIG. 12 and FIG. 13 are graphs showing simulation results for calculating the relationship between the average SNR per receiving antenna and the average channel capacity when the rank is determined (signal detection method: ZF, fading correlation ρ value: 0). .5). FIG. 12 and FIG. 13 are graphs showing simulation results for calculating the relationship between the average SNR per receiving antenna and the average channel capacity when the rank is determined (signal detection method: MMSE, fading correlation ρ value: 0). .5). FIG. 12 and FIG. 13 are graphs showing simulation results for calculating the relationship between the average SNR per receiving antenna and the average channel capacity when the rank is determined (signal detection method: MMSE, fading correlation ρ value: 0). 0.0). The functional block diagram which shows the further another structural example of the channel capacity calculation / comparison part in the user apparatus which concerns on embodiment of this invention. The functional block diagram which shows the further another structural example of the channel capacity calculation / comparison part in the user apparatus which concerns on embodiment of this invention. The functional block diagram which shows the further another structural example of the channel capacity calculation / comparison part in the user apparatus which concerns on embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, an overall configuration of a MIMO wireless transmission system having a wireless communication apparatus to which the present invention can be applied will be described.
FIG. 1 is a functional block diagram illustrating an example of a schematic configuration of a user apparatus 10 as a reception-side radio communication apparatus in a downlink of a closed-loop type MIMO radio transmission system according to an embodiment of the present invention. FIG. 2 is a functional block diagram showing an example of a schematic configuration of the radio base station 20 as a radio communication device on the transmission side in the downlink in the downlink of the MIMO radio transmission system.

The MIMO wireless transmission system according to the present embodiment is based on control information (PMI: Precoding Matrix Indicator) that is an index of a candidate data table (codebook) of an optimum transmission antenna weight matrix fed back from the user apparatus 10 (transmission stream ( This is a closed-loop MIMO wireless transmission system that multiplies a transmission signal by a transmission antenna weight that is different for each transmission layer. Further, in the downlink of the wireless transmission system of the present embodiment, an orthogonal frequency division multiplexing (OFDM) that is a frequency multiplexing method using a plurality of subcarriers orthogonal to each other is used.
In the closed-loop MIMO radio transmission system (Closed-Loop MIMO) of this embodiment, downlink data communication is performed by switching 1,2-transmission layers (number of ranks: 1, 2) conforming to the LTE communication standard. However, the present invention is not limited to this configuration.

  In the example of FIG. 1, the user apparatus 10 includes two antennas 100, but the number of antennas 100 included in the user apparatus 10 is not limited to a specific number. For example, the user apparatus 10 may include more than two (for example, four) antennas 100. Further, the user apparatus 10 may be capable of switching the number of antennas used during actual MIMO communication.

Next, a schematic configuration and an outline of processing operation in the downlink of the user apparatus 10 will be described.
In FIG. 1, a user device 10 is a wireless communication device that can be used when a user uses various communication services, and is referred to as a “communication terminal” or a “terminal” or can be moved. Sometimes called a “station”, sometimes called a “radio”. The user device 10 may be a mobile communication terminal such as a mobile phone.

In FIG. 1, a user apparatus 10 includes a plurality of antennas 100, a plurality of demultiplexers (DEMUXs) 101, a downlink control information demodulation unit 102, a spatial filter unit 103, and a log likelihood ratio (LLR: Logarithm of Likelihood). Ratio) generation section 104, error correction / decoding section 105, and parallel / serial (P / S) conversion section 106.
The received signal received by each antenna 100 is subjected to fast Fourier transform (FFT) processing after removing the guard interval (GI) and then input to the DEMUX 101.
The DEMUX 101 divides the received signal from each antenna 100 into received signals of a reference signal RS part, a data signal part, and a downlink control signal part.
Based on the downlink control signal output from the DEMUX 101, the downlink control information demodulator 102 is configured to use rank designation information (RI: Rank Indicator 9, MCS (Modulation and Coding Scheme) as transmission rank information used for downlink data transmission. ) And T-PMI (Transmit-Precoding Matrix Indicator).
The spatial filter unit 103 receives from the DEMUX 101 based on control information such as transmission rank information (RI) output from the downlink control information demodulation unit 102 and a spatial filter coefficient output from a spatial filter coefficient generation unit described later. Separation and / or synthesis of output signals. Also, the spatial filter unit 103 converts the data composed of a predetermined number of code words subjected to the above separation and / or synthesis into received data (user data) usable by the user according to the downlink rank (RI). Convert.
The LLR generation unit 104 generates a log-likelihood ratio (LLR) for each bit for decoding the data signal based on the signal output from the spatial filter unit 103.
The error correction / decoding unit 105 performs error correction processing and decoding processing on the data signal based on the LLR output from the LLR generation unit 104 and information on a predetermined error correction encoding method and modulation method.
The parallel / serial (P / S) conversion unit 106 converts a plurality of parallel data output from the error correction / decoding unit 105 and outputs a sequence of original transmission data.

In addition, the user apparatus 10 includes a channel estimation / noise power estimation unit 110, spatial filter coefficient generation units 111 (1) and 111 (2), and post-signal separation / synthesis SINR estimation units 112 (1) and 112 (2). A channel capacity calculation / comparison unit 113, a rank designation information (RI: rank indicator) generation unit 114, an uplink control information generation unit 115, and an uplink transmission unit 116. Here, the spatial filter coefficient generation unit 111 (1) and the post-signal separation / synthesis SINR estimation unit 112 (1) correspond to rank 1, and the spatial filter coefficient generation unit 111 (2) and the post-signal separation / synthesis SINR estimation unit 112 ( 2) corresponds to rank 2.
The channel estimation / noise power estimation unit 110 performs MIMO on the radio propagation path between each antenna 200 of the base station apparatus 20 and each antenna 100 of the user apparatus 10 based on the reference signal RS of each subcarrier output from the DEMUX 101. Channel response and noise power are estimated respectively. Here, since the reference signal RS is a signal specific to a cell, it is also called a cell-specific reference signal (CSRS).
The first spatial filter coefficient generation unit 111 (1) determines the rank in the radio transmission path between the user apparatus 10 and the radio base station 20 based on the estimation result of the MIMO channel response and the estimation result of the noise power. Spatial filter coefficients for 1 (the number of transmission streams is 1) are generated. Further, the first signal separation / combination SINR estimation unit 112 (1) estimates the SINR value for each subcarrier when the rank is 1, and outputs the estimated value.
On the other hand, the second spatial filter coefficient generation unit 111 (2) uses a radio channel between the user apparatus 10 and the radio base station 20 based on the estimation result of the MIMO channel response and the estimation result of the noise power. A spatial filter coefficient is generated when the rank is 2 (the number of transmission streams is 2). Further, second post-signal separation / combining SINR estimation section 112 (2) estimates the SINR value for each subcarrier when the rank is 2, and outputs the estimated value.
The channel capacity calculation / comparison unit 113 calculates the channel for each of ranks 1 and 2 based on the SINR value for each subcarrier output from the SINR estimation units 112 (2) and 112 (2) after signal separation / combination. Calculate capacity. Further, the channel capacity calculation / comparison unit 113 compares the channel capacities of ranks 1 and 2 with each other, and determines a rank used for the next downlink data transmission based on the comparison result. Specifically, the rank corresponding to the larger channel capacity among the two channel capacities corresponding to ranks 1 and 2 is determined as the rank used for the next downlink data transmission. The channel capacity calculation / comparison unit 113 will be described in detail later.
The rank designation information (RI) generation unit 114 generates RI (rank indicator) as rank information for notifying the determined base rank to the radio base station 20 side.
The uplink control information generation unit 115 generates control information including the RI generated by the rank designation information (RI) generation unit 114. In addition to the RI, the control information includes PMI (Precoding Matrix Indicator) indicating a precoding matrix suitable for downlink data transmission, and channel quality information measured based on the estimation result of the MIMO channel response. CQI (Channel Quality Indicator) may be included.
The uplink transmission unit 116 generates a transmission signal of a predetermined symbol including the control information generated by the uplink control information generation unit 115, and transmits the radio base station from the antenna 100 via the uplink control channel (PUCCH or PUSCH). Transmit to station 20.

Next, an outline configuration and processing operation in the downlink of the base station apparatus 20 will be described.
In FIG. 2, a radio base station 20 is a radio communication device that relays radio communication between the communication network side and the user terminal device 10, and is called a “base station device” or simply called a “base station”. There is also a case. Also, the radio base station 20 may be called “eNodeB (evolved Node B)” in the 3GPP and LTE specifications.

In FIG. 2, the radio base station 20 includes a plurality of antennas 200, an uplink receiving unit 201, a transmission stream number selecting unit 202, a first signal processing path switching unit 203, and serial-parallel (S / P) conversion. Unit 106, encoding / modulating unit 205 (1) when the rank is 1 (the number of transmission streams is 1), and a plurality of encoding / modulating units 205 (1) when the rank is 2 (the number of transmission streams is 2) 2), 205 (3), a second signal processing path switching unit 206, a precoder unit 207, an inverse fast Fourier transform (IFFT) unit 208, and a guard interval (GI) adding unit 209.
The uplink reception unit 201 receives control information (RI, CQI, PMI) from the user apparatus 10 via the uplink control channel (PUCCH), and sends it to the transmission stream number selection unit 202.
The transmission stream number selection unit 202 determines and controls various control parameters used in the downlink with the user apparatus 10 based on the control information (RI, CQI, PMI) received from the uplink reception unit 201. For example, the transmission stream number selection unit 202 is based on the RI received from the uplink reception unit 201 so that the number of transmission streams at the time of the next data transmission becomes the number of transmission streams specified by the RI. 203 and 206 are controlled.
Based on the control command from the transmission stream number selection unit 202, the signal processing path switching units 203 and 206 change the encoding and modulation signal processing paths so that data can be transmitted at a specified rank (number of transmission streams). Switch. For example, in the case of rank 1, the signal path is switched so that the data to be transmitted is processed by the encoding / modulation unit 205 (1) for rank 1. On the other hand, in the case of rank 2, the data to be transmitted is converted into parallel data by the serial / parallel (S / P) converter 106, and then encoded / modulators 205 (2) and 205 (3) for rank 2. The signal path is switched to process each.
Based on the precoding weight (precoding matrix) for controlling the phase and / or amplitude of the transmission signal set for each of the plurality of antennas 200, the precoder unit 207 encodes / modulates the unit 205 (1), or The transmission target data received from the encoding / modulation units 205 (2) and 205 (3) is precoded. That is, the precoder 207 multiplies transmission target data by a precoding weight based on the RI, and controls (shifts) the phase and amplitude, respectively. Thereafter, after adding by an adder (Σ) (not shown) for each transmission stream, the reference signal RS and the control signal are further multiplexed by a multiplexer (not shown), and a transmission signal is generated for each of the plurality of antennas 200.
A transmission signal generated for each of the plurality of antennas 200 is subjected to inverse Fourier transform by an inverse fast Fourier transform (IFFT) unit 208 and a guard interval (GI) adding unit 209 is added with a predetermined guard interval (GI). Transmitted from each of the two antennas 200.

  In the MIMO radio transmission system having the configuration shown in FIGS. 1 and 2, the rank at the time of data transmission is determined by the radio base station 20 based on the rank designation information (RI) fed back from the user apparatus 10 as described above. . For example, the selection is normally made such that rank = 1 when RI = 1 and rank = 2 when RI = 2. When rank = 1, single transmission beamforming is performed, and when rank ≧ 2, multibeam transmission spatial multiplexing is performed. As in the 3GPP specification, since the radio base station 20 side has the final right to determine the rank at the time of data transmission, the rank information RI of the user apparatus 10 is determined when the radio base station 20 side determines the rank. It is not always necessary to follow the value of.

  Next, a plurality of examples showing a more specific configuration example of the channel capacity calculation / comparison unit 113 in the user apparatus 10 having the above-described configuration according to the embodiment of the present invention will be described.

FIG. 3 is an explanatory diagram showing a model of a wireless transmission path between the user apparatus 10 and the wireless base station 20 configured as described above. In the model of FIG. 3, data communication between the user apparatus 10 and the radio base station 20 is performed using a plurality of subcarriers. Also, h ₁₁ (k), h ₁₂ (k), h ₂₁ (k) and h ₂₂ (k) in the figure are elements of the MIMO channel matrix represented by the following equation (1), and their values are “ Also called “transmission path response value”. K is an index (number) of a subcarrier.

Further, the fading correlation ρ _{ij, iq} (hereinafter abbreviated as “ρ” as appropriate) between the transmitting antennas in the wireless transmission path of FIG. 3 is expressed by the following equation (2). Here, i is the index (number) of the receiving antenna, and j and q are the index (number) of the transmitting antenna.

4 to 7 show MIMO channel matrix elements (transmission path response values) when the value of fading correlation ρ in the above equation (2) is 0.0, 0.5, 0.9, and 1.0, respectively. It is a graph which shows the result of having calculated the corresponding reception level [dB] for every subcarrier. 4 to 7, a 3GPP EVA (extended vehicle A) Shannon model is used, the number of transmitting antennas Nt = 2, the number of receiving antennas Nr = 2, and the receiving SNR = 0 [dB].
As shown in FIGS. 4 to 7, when the fading correlation between the transmitting antennas in the wireless transmission path increases (the value of ρ increases), the transmission path response values (h ₁₁ (k) and h ₁₂ (k), h ₂₁ (k) and h ₂₂ (k)) approach the same value. As a result, the characteristics of the spatial filter of the wireless transmission path deteriorate, signal separation between antennas becomes difficult, and channel capacity decreases.

  8 and 9 are graphs showing the relationship between the average SNR [dB] per receiving antenna and the average channel capacity [bps / Hz] when the value of the fading correlation ρ is 0.0 and 0.5, respectively. . 8 and 9, the 3GPP EVA (extended vehicle A) Shannon model is used, and there are three types of modulation schemes (QPSK (Quadrature Phase Shift Keying), 16QAM (Quadrature Amplitude Modulation), 64QAM). ) Adaptive control. Further, in rank 1 of the solid line in the figure, the calculation is performed for the case where SFBC (Space Frequency Block Coding) based on Maximum Ratio Combining (MRC) is used for decoding on the receiving side. In rank 2, calculation was performed for the case where spatial multiplexing by SDM (Space Division Multiplexing) was used, and the ZF (Zero Forcing) method was used for decoding on the receiving side as a signal detection method. The dotted lines in FIGS. 8 and 9 are Shannon limit capacities calculated for the ranks 1 and 2.

  In conventional rank switching according to SNR, the Shannon limit capacity curve (dotted line) in the case of rank 1 and the Shannon limit capacity curve (dotted line) in the case of rank 2 intersect (point A in the figure). A switching threshold value is set in the SNR of For example, in the example of ρ = 0 in FIG. 8, 6 [dB] is set as the switching threshold, and in the example of ρ = 0.5 in FIG. 9, 12 [dB] is set as the switching threshold.

  However, as indicated by the solid lines in FIGS. 8 and 9, the intersections of the channel capacity curves of ranks 1 and 2 in consideration of the actual reception processing method, modulation method, and fading correlation ρ are the conventional switching thresholds, that is, in the figure. Deviation from the intersection of the Shannon limit capacity curves shown by the dotted line. Specifically, in the case of FIG. 8, the point is shifted from the point A of SNR = 6 [dB] to the point B of 10 [dB], and in the case of FIG. 9, the point is 19 [dB] from the point A of SNR = 12 [dB]. Shift to point B. Therefore, when the rank switching control with the conventional switching threshold is applied, the throughput deteriorates in the range C of SNR = 7 to 10 [dB] in the case of FIG. 8, and the SNR = 12 to in the case of FIG. The throughput deteriorates in the range C of 19 [dB].

  10 and 11 are graphs showing the relationship between the average SNR [dB] per receiving antenna and the average channel capacity [bps / Hz] when the value of the fading correlation ρ is 0.0 and 0.5, respectively. . 10 and 11, the MMSE (Minimum Mean Square Error) method is used for decoding on the receiving side as the rank-2 signal detection method. Other conditions are the same as those in FIGS.

  10 and 11, the intersections (points B in the figure) of the channel capacity curves of ranks 1 and 2 in consideration of the actual reception processing method, modulation method, and fading correlation ρ are the conventional switching thresholds, that is, It deviates from the intersection (point A in the figure) of the Shannon limit capacity curve indicated by the dotted line in the figure. Specifically, in the case of FIG. 10, the point a of SNR = 6 [dB] is shifted to the point B of −10 [dB], and in the case of FIG. 11, the point of SNR = 12 [dB] is changed to 18 [dB]. It shifts to a point. For this reason, when the conventional rank switching control in which the switching threshold is set is applied, the throughput deteriorates in the range C of SNR = −10 to 6 [dB] in the case of FIG. 10, and the SNR = 12 in the case of FIG. Throughput is degraded in a range C of ˜18 [dB].

  Therefore, in this embodiment, for each of ranks 1 and 2, a signal-to-interference noise ratio (hereinafter referred to as “SINR”) [dB] in consideration of at least one of the actual reception processing method, modulation method, and fading correlation ρ. ] Is accurately calculated. Then, the channel capacities calculated for the ranks 1 and 2 are compared with each other, and the rank used for the next data transmission in the downlink is determined based on the comparison result. Hereinafter, calculation and comparison of channel capacity and determination of rank based on the comparison result in the wireless communication system according to the present embodiment will be described with a plurality of examples.

  FIG. 12 is a functional block diagram showing a configuration example of the channel capacity calculation / comparison unit 113 in the user apparatus 10 according to the embodiment of the present invention. FIG. 13 is a flowchart showing an example of a rank determination procedure using the channel capacity calculation / comparison unit 113 of FIG. FIG. 14 is an explanatory diagram showing a model of a radio transmission path between the user apparatus 10 and the radio base station 20 for explaining a rank determination procedure using the channel capacity calculation / comparison unit 113 of FIG. . In FIG. 14, K is the number of transmission streams, M is the number of transmission antennas, and L is the number of reception antennas.

  In this example, first, the MIMO channel response H (k) and noise power n of the radio propagation path between each antenna 200 of the base station apparatus 20 and each antenna 100 of the user apparatus 10 are estimated for each subcarrier (FIG. 13). S101). After the estimation, for each of ranks 1 and 2, spatial filter coefficients W (k) depending on the reception algorithm are generated for each subcarrier (118 in FIG. 12, S102 in FIG. 13), and SINRj ( k) is estimated for each subcarrier (119 in FIG. 12, S103 in FIG. 13).

  Next, using the estimated value of SINRj (k), the mutual information amount per bit (hereinafter referred to as “MIB”) after error correction coding considering the reception processing method for each of a plurality of subcarriers. Calculate (120 in FIG. 12, S104 in FIG. 13). For example, considering a ZF (Zero Forcing) method or an MMSE (Minimum Mean Square Error) method as a reception processing method, all of a plurality of modulation methods (QPSK, 16QAM, 64QAM) under the constraint condition of usable signal point arrangement MIB is calculated for Q (= 2, 4, 6).

Here, the above-mentioned MIB is error correction in consideration of the mapping from the bit level to the symbol level, which is calculated by fixing the modulation method to any one method under the condition that the error correction coding method is ideal. This is the capacity per bit after encoding. This MIB can be calculated by the following equation (3), for example.

Here, γ _n is the received SINR after equalization of the nth modulation symbol, M _ary (n) is the modulation multi-level number of the nth modulation symbol, and Q (n) is the number of bits per modulation symbol (“Q (n ) = Log _{2 Mary} (n)), s _rep (m) is a complex value of the modulation symbol m, and _{cm and q} are bit values of the q-th bit of the modulation symbol m (b = 0 or 1). ), Z is a complex Gaussian random number, and _EZ is an expected value calculation using a complex Gaussian random number.

In addition, you may calculate MIB of each modulation system (QPSK, 16QAM, 64QAM) using the following approximate formula (4)-(6) (refer nonpatent literature 8).

However, the function J (x) and its coefficients a1, b1, c1, a2, b2, c2, d2 in the above formulas (4) to (6) are as follows.

  FIG. 15 is a graph showing an example of the relationship between the MIB and SINR of each modulation scheme (QPSK, 16QAM, 64QAM) calculated using the approximate equations (4) to (6). FIG. 16 is a graph showing an example of the relationship between the mutual information amount (MI) [bit / symbol] per modulation symbol calculated from the MIB of FIG. 15 and SINR for each of a plurality of subcarriers. The mutual information amount (MI) per modulation symbol for each subcarrier in each modulation scheme in the figure corresponds to the channel capacity for each subcarrier.

Here, when the reception processing method is the ZF method, channel capacity C _{Q, Rank K} (k) for each subcarrier when transmitting with rank K (1 ≦ K ≦ min (M, L)), that is, for each subcarrier. The mutual information amount (MI) per modulation symbol in each of the plurality of modulation schemes can be calculated by the following equation (8) using the MIB (= I _Q ). Here, the same modulation scheme is used for all subcarriers. SINR _j (k) is the SINR of the jth filter output for subcarrier k, and wj (k) is a weighting coefficient matrix obtained by the following equations (10) to (13). P _K (k) in equation (10) is a matrix of transmission average power for subcarrier k in the case of rank K.

Next, as shown in the above equation (9), the channel capacity (mutual information amount (MI) per modulation symbol) for each subcarrier calculated for each of the plurality of modulation schemes for each rank K is added on the frequency axis. The channel total capacities (ΣC _{Q, Rank K} (k)) are compared with each other, and an optimum modulation scheme (value of Q _K ) that maximizes the channel total capacity is determined for each rank K. The capacity (C _{Q, Rank K} ) is obtained (120 in FIG. 12, S105 in FIG. 13).

Note that the maximum channel capacity (mutual information amount per modulation symbol (MI)) and total channel capacity for each subcarrier when SFBC (only applicable to two transmission antennas) is selected as rank 1 transmission is as follows. (14) and (15).

Next, for each of the plurality of ranks K (1 ≦ K ≦ min (M, L)), the channel capacity per subcarrier (per modulation symbol) calculated for the selected optimal modulation scheme (value of Q _K ) The total channel capacity is calculated as an index value obtained by adding the mutual information (MI)) on the frequency axis. Then, the channel total capacities calculated for the plurality of ranks K are compared with each other, and K having the maximum channel total capacity is set as the number of ranks (121, 122 in FIG. 12, S106 in FIG. 13).

The channel capacity C _RA when applying the rank adaptation for determining the rank by the above procedure is expressed by the following equation (16).

When the reception processing method is the MMSE method, the channel capacity C _{Q, Rank K} (k) for each subcarrier when transmitting with rank K (1 ≦ K ≦ min (M, L)) (mutual per modulation symbol) The amount of information (MI)) can be calculated by the following equation (17) using the MIB (= I _Q ), and the maximum value of the channel total capacity C _{Q, Rank K} is expressed by the following (18) It can be calculated by the formula. Other procedures are the same as those when the reception processing method is the ZF method.

In S106 of FIG. 13, the channel total capacity as an index value obtained by adding the channel capacity of each subcarrier in the selected optimal modulation scheme (Q _K value) on the frequency axis is compared for each rank. However, an average value of channel capacities obtained by averaging channel capacities for each subcarrier on the frequency axis may be compared as an index value.

  FIG. 17 is a functional block diagram showing another configuration example of the channel capacity calculation / comparison unit 113 in the user apparatus 10 according to the embodiment of the present invention. FIG. 18 is a flowchart showing an example of a rank determination procedure using the channel capacity calculation / comparison unit 113 of FIG. The functions 118 and 119 in FIG. 17 and the steps S201 to S203 in FIG. 18 are the same as those in FIGS.

In this example, for each rank 1 and 2, based on the channel estimation value (G _K (k)) for each subcarrier, for each subcarrier, the channel limit with the ideal reception processing method as shown in equation (19) Calculate the Shannon limit capacity, which is the capacity. Then, as shown in the equation (20), for each rank K, the total channel capacity is calculated as an index value obtained by adding the Shannon limit capacity for each subcarrier on the frequency axis (123 and 121 in FIG. 17, and FIG. 18). S204).

  Next, the channel total capacities calculated for the respective ranks K shown in the above equation (20) are compared with each other, and K that gives the maximum channel capacity is set as the number of ranks (122 in FIG. 17, S205 in FIG. 18).

  Note that, in S204 and 205 of FIG. 17, the total channel capacities as index values obtained by adding the Shannon limit capacities of the subcarriers for each rank K on the frequency axis are compared with each other. An average value of channel capacities obtained by averaging capacities on the frequency axis may be compared as an index value.

  FIG. 19 is a functional block diagram showing still another configuration example of the channel capacity calculation / comparison unit 113 in the user apparatus 10 according to the embodiment of the present invention. FIG. 20 is a flowchart showing an example of a rank determination procedure using the channel capacity calculation / comparison unit 113 of FIG. The functions 118 and 119 in FIG. 19 and the steps S301 to S303 in FIG. 20 are the same as those in FIGS.

In this example, for each rank 1 and 2, the channel capacity is calculated for each subcarrier with the Shannon capacity corrected in consideration of the reception processing method, based on the channel estimation value (G _K (k)) for each subcarrier. . Then, for each rank K, the channel total capacity is calculated as an index value obtained by adding the channel capacity for each subcarrier on the frequency axis (124 and 121 in FIG. 19 and S304 in FIG. 20).

Here, when the reception processing method is the ZF method, the channel capacity C _{Q, Rank K} (k) for each subcarrier when transmitting with rank K (1 ≦ K ≦ min (M, L)) is the Shannon capacity. Based on the following equation (21), it can be calculated. Here, the same modulation scheme is used for all subcarriers. SINR _j (k) is the SINR of the jth filter output for subcarrier k, and wj (k) is a weighting coefficient matrix obtained by the above-described equations (10) to (13).

  Then, as shown in the above equation (22), for each rank K, the total channel capacity obtained by adding the channel capacity for each subcarrier on the frequency axis is obtained (121 in FIG. 19 and S305 in FIG. 20).

Note that the channel capacity and the total channel capacity for each subcarrier when SFBC (applicable only to two transmission antennas) is selected as rank 1 transmission are expressed by the following equations (23) and (24).

When the reception processing method is the MMSE method, the channel capacity C _{Q, Rank K} (k) for each subcarrier when transmitting with rank K (1 ≦ K ≦ min (M, L)) is based on the Shannon capacity. (25)

  Then, as shown in the above equation (26), the total channel capacity obtained by adding the channel capacity for each subcarrier on the frequency axis for each rank K is obtained (121 in FIG. 19 and S305 in FIG. 20).

Note that the channel capacity and total channel capacity for each subcarrier when SFBC (only applicable to two transmission antennas) is selected as rank 1 transmission are as shown in the following equations (27) and (28).

  Next, the channel total capacities calculated for the respective ranks K are compared with each other, and K that provides the maximum channel capacity is set as the number of ranks (122 in FIG. 19 and S305 in FIG. 20).

  In S304 and 305 in FIG. 20 described above, the total channel capacities as index values obtained by adding the Shannon capacities of the subcarriers for each rank K on the frequency axis are compared with each other. An average value of channel capacities averaged on the frequency axis may be compared as an index value.

  FIG. 21 is a functional block diagram showing still another configuration example of the channel capacity calculation / comparison unit 113 in the user apparatus 10 according to the embodiment of the present invention. FIG. 22 is a flowchart showing an example of a rank determination procedure using the channel capacity calculation / comparison unit 113 of FIG. The functions 118 and 119 in FIG. 21 and the steps S401 to S403 in FIG. 22 are the same as those in FIGS.

In this example, when the reception processing method is the ZF method, as shown in the following equation (29), the subcarriers for each rank 1 and 2 are based on the SINR estimation value (SINR _j (k)) for each subcarrier. Every time, the channel capacity C _{Q, Rank K} (k) is calculated by correcting the Shannon capacity in consideration of the reception processing system and the modulation system. Then, the channel capacity obtained by the equation (29) and the upper limit (Qmax) of the transmission rate by the modulation method are compared for each subcarrier so as not to exceed the upper limit, and as an index value as shown in the following equation (30) Are calculated (125 and 121 in FIG. 21 and S404 in FIG. 22).

Note that the channel capacity and total channel capacity for each subcarrier when SFBC (applicable only to two transmission antennas) is selected as rank 1 transmission are expressed by the following equations (31) and (32), respectively.

  Next, the channel total capacities for each rank are compared with each other, and K that provides the maximum capacity is set as the number of ranks (122 in FIG. 21, S406 in FIG. 22).

  FIG. 23 and FIG. 24 calculate the relationship between the average SNR [dB] per receiving antenna and the average channel capacity [bps / Hz] when the rank is determined by the procedure of FIG. 12 and FIG. 13 in the present embodiment. It is a graph which shows the result of having performed simulation. FIG. 23 shows the result when the value of the fading correlation ρ is 0.0, and FIG. 24 shows the result when the value of the fading correlation ρ is 0.5. In this simulation, a Shannon model of 3GPP EVA (extended vehicle A) was used, and adaptive control was performed using three types of modulation schemes (QPSK, 16QAM, and 64QAM). In rank 1, calculation was performed for the case where SFBC based on maximum ratio combining (MRC) was used for decoding on the receiving side. In rank 2, calculation was performed for the case where spatial multiplexing by SDM was used and the ZF method was used as a signal detection method in decoding on the receiving side.

As a result of the fading correlation ρ value of 0.0 in FIG. 23, there was no degradation in throughput even in the range C of SINR = 6 to 10 where degradation in throughput was observed in the conventional rank determination procedure.
Further, in the result of the fading correlation ρ value of 0.5 in FIG. 24, there was no degradation in throughput even in the range C of SINR = 12 to 19 in which significant degradation in throughput was observed in the conventional rank determination procedure. A dotted line D in FIG. 24 represents a change in average channel capacity when the rank is switched by the conventional rank determination procedure.

  FIG. 25 and FIG. 26 calculate the relationship between the average SNR [dB] per reception antenna and the average channel capacity [bps / Hz] when the rank is determined by the procedure of FIG. 12 and FIG. 13 in the present embodiment. It is a graph which shows the result of having performed simulation. FIG. 25 shows the result when the value of the fading correlation ρ is 0.0, and FIG. 26 shows the result when the value of the fading correlation ρ is 0.5. In this simulation, the MMSE method is used in decoding on the receiving side as a signal detection method in the case of rank 2. Other conditions are the same as those in FIGS.

As a result of the fading correlation ρ value of 0.0 in FIG. 25, there was no degradation in throughput even in the range C of SINR = −10 to 8 where degradation in throughput was observed in the conventional rank determination procedure.
In addition, in the result of the fading correlation ρ value of 0.5 in FIG. 26, there was no deterioration in throughput even in the range C of SINR = 12 to 20 in which large deterioration in throughput was observed in the conventional rank determination procedure.
The dotted line D in FIGS. 25 and 26 represents the change in average channel capacity when the rank is switched in the conventional rank determination procedure.

  FIG. 27 is a functional block diagram showing still another configuration example of the channel capacity calculation / comparison unit 113 in the user apparatus 10 according to the embodiment of the present invention. In the channel capacity calculation / comparison examples shown in FIGS. 12 to 16, the channel capacity calculation based on the MIB is performed in consideration of the reception processing method. However, the reception processing method is considered as shown in FIG. In other words, the channel capacity may be calculated based on the MIB with the reception processing system as an ideal.

  FIG. 28 is a functional block diagram showing still another configuration example of the channel capacity calculation / comparison unit 113 in the user apparatus 10 according to the embodiment of the present invention. In the example of the channel capacity calculation / comparison shown in FIGS. 12 to 16, the channel capacity for each subcarrier is calculated based on the MIB and then summed or averaged on the frequency axis. After calculating the average SINR value among a plurality of transmission streams, the channel capacity based on MIB may be calculated using the average SINR value. In the example of FIG. 28, the channel capacity is calculated based on the MIB without considering the reception processing method, that is, with the reception processing method ideal.

  FIG. 29 is a functional block diagram showing still another configuration example of the channel capacity calculation / comparison unit 113 in the user apparatus 10 according to the embodiment of the present invention. In the example of FIG. 29, similarly to FIG. 28, after calculating the average value of SINR among a plurality of transmission streams, the channel capacity based on MIB may be calculated using the average value of SINR. In the example of FIG. 29, unlike the example of FIG. 28, the channel capacity based on the MIB is calculated in consideration of the reception processing method.

  In the rank determination based on the channel capacity calculation / comparison shown in FIGS. 12 to 29, the channel capacity index value (total value or average) for each of a plurality of ranks calculated at each of a plurality of past calculation timings. The channel capacity index value for each of a plurality of ranks at the next data transmission timing is predicted based on the value), and the rank used for the next data transmission may be determined based on the prediction result. In this case, rank switching based on SINR can be accurately performed while suppressing the influence of delay time from the rank determination timing to the data transmission timing to which the rank is actually applied.

For example, as shown in the following formulas (33) and (34), based on channel capacity index values (total value or average value) for ranks 1 and 2 calculated at the most recent two previous calculation timings, respectively. Thus, the channel capacity index values for ranks 1 and 2 at the next data transmission timing may be linearly predicted.

  Note that the processing steps and the components of the wireless communication system and the wireless communication device described in this specification can be implemented by various means. For example, these steps and components may be implemented in hardware, firmware, software, or a combination thereof.

  For hardware implementation, means such as a processing unit used to realize the above steps and components in an entity (for example, various wireless communication devices, Node B, terminal, hard disk drive device, or optical disk drive device) One or more application specific ICs (ASICs), digital signal processors (DSPs), digital signal processing units (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors , A controller, a microcontroller, a microprocessor, an electronic device, other electronic units designed to perform the functions described herein, a computer, or a combination thereof.

  Also, for firmware and / or software implementation, means such as processing units used to implement the above components may be programs (eg, procedures, functions, modules, instructions) that perform the functions described herein. , Etc.). In general, any computer / processor readable medium that specifically embodies firmware and / or software code is means such as a processing unit used to implement the steps and components described herein. May be used to implement For example, the firmware and / or software code may be stored in a memory, for example, in a control device, and executed by a computer or processor. The memory may be implemented inside the computer or processor, or may be implemented outside the processor. The firmware and / or software code may be, for example, random access memory (RAM), read only memory (ROM), nonvolatile random access memory (NVRAM), programmable read only memory (PROM), electrically erasable PROM (EEPROM) ), FLASH memory, floppy disk, compact disk (CD), digital versatile disk (DVD), magnetic or optical data storage, etc. Good. The code may be executed by one or more computers or processors, and may cause the computers or processors to perform the functional aspects described herein.

  Also, descriptions of embodiments disclosed herein are provided to enable any person skilled in the art to make or use the present disclosure. Various modifications to the present disclosure will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other variations without departing from the spirit or scope of the disclosure. The present disclosure is therefore not limited to the examples and designs described herein, but should be accorded the widest scope consistent with the principles and novel features disclosed herein.

10 User equipment 20 Wireless base station 100 Antenna 101 DEMUX
102 downlink control signal demodulation unit 103 spatial filter unit 104 LLR generation unit 105 error correction / decoding unit 106 parallel serial (P / S) conversion unit 110 channel estimation / noise power estimation unit 111 (1), 111 (2) spatial filter Coefficient generation unit 112 (1), 112 (2) SINR estimation unit after signal separation and synthesis 113 Channel capacity calculation / comparison unit 114 RI generation unit 115 Uplink control signal generation unit 116 Uplink transmission unit 200 Antenna 201 Uplink reception unit 202 Transmission stream number selection unit 203, 206 Signal processing path switching unit 204 Serial parallel (S / P) conversion unit 205 (1) Encoding / modulation unit (for rank 1)
205 (2), 205 (3) Encoding / modulating section (for rank 2)
207 Precoder unit 208 Inverse Fast Fourier Transform (IFFT) unit 209 Guard interval (GI) adding unit

JP 2012-105271 A

3GPP TS36.211 V10.1.0, "Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation (Release 10)," March 2011. 3GPP TS36.212 V10.1.0, "Evolved Universal Terrestrial Radio Access (E-UTRA); Multiplexing and channel coding (Release 10)," March 2011. 3GPP TS36.213 V10.1.0, "Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures (Release 10)," March 2011. H. Taoka, S. Nagata, K Takeda, Y. Kakishima, X. She, and K. Kusume, "MIMO and CoMP in LTE-Advanced," NTT DoCoMo Technical Journal (English Edition), vol.12, no.2 , pp.20-28, Sept. 2010. Taoka et al., "MIMO and inter-cell cooperative transmission / reception technology in LTE-Advanced" NTT DOCOMO Technical Journal, Vol. 18, No.2, pp.22-30, July. 2010. 3GPP TS36.211 V10.5.0, June 2012. Hara et al., "Basic Principles of Multi-Antenna", 2010 UEC, BT-1-1, March 2010. IEEE 802.16 BWAWorking Group, IEEE 802.16m-08 / 004r2, July 2008.

Claims (6)

A wireless transmission system capable of transmitting and receiving data using a plurality of different transmission streams between a plurality of wireless communication devices,
Means for calculating a signal-to-interference noise ratio (SINR) for each of a plurality of subcarriers of the transmission stream, based on signals transmitted and received in one or a plurality of transmission streams in a wireless transmission path between the plurality of wireless communication apparatuses; ,
Before SL each of a plurality of sub-carriers, means for calculating mutual information per bit (MIB) from the signal to interference noise ratio (SINR),
Means for calculating a mutual information amount (MI) per modulation symbol from the mutual information amount (MIB) per bit for each of the plurality of subcarriers;
Means for calculating a sum of mutual information (MI) per modulation symbol in the plurality of subcarriers for each of a plurality of modulation schemes;
Means for comparing the sum of mutual information (MI) per modulation symbol calculated for each of the plurality of modulation schemes, and selecting a modulation scheme that maximizes the sum of the mutual information (MI);
For each of a plurality of ranks of the wireless transmission path, a channel capacity obtained by adding or averaging on a frequency axis the mutual information (MI) per modulation symbol for each of the plurality of subcarriers calculated for the selected modulation scheme. Means for calculating an index value;
Means for comparing the channel capacity index values calculated for each of the plurality of ranks, and determining a rank that maximizes the channel capacity index value as a rank used for next data transmission in the wireless transmission path; ,
A wireless transmission system comprising: A wireless transmission system capable of transmitting and receiving data using a plurality of different transmission streams between a plurality of wireless communication devices,
Signal-to-interference noise for each of a plurality of subcarriers used in the wireless transmission path between the plurality of transmission streams based on signals transmitted and received in a plurality of transmission streams in a wireless transmission path between the plurality of wireless communication apparatuses Means for calculating an average value of the ratio (SINR);
Means for calculating a mutual information amount (MIB) per bit from an average value of the signal-to-interference noise ratio (SINR) for each of the plurality of subcarriers;
Means for calculating a mutual information amount (MI) per modulation symbol from the mutual information amount (MIB) per bit for each of the plurality of subcarriers;
Means for calculating a sum of mutual information (MI) per modulation symbol in the plurality of subcarriers for each of a plurality of modulation schemes;
Means for comparing the sum of mutual information (MI) per modulation symbol calculated for each of the plurality of modulation schemes, and selecting a modulation scheme that maximizes the sum of the mutual information (MI);
For each of a plurality of ranks of the wireless transmission path, a channel capacity obtained by adding or averaging on a frequency axis the mutual information (MI) per modulation symbol for each of the plurality of subcarriers calculated for the selected modulation scheme. Means for calculating an index value;
Means for comparing the channel capacity index values calculated for each of the plurality of ranks, and determining a rank that maximizes the channel capacity index value as a rank used for next data transmission in the wireless transmission path; ,
A wireless transmission system comprising: The wireless transmission system according to claim 1 or 2 ,
The wireless information transmission system according to claim 1, wherein the mutual information amount (MIB) per bit is calculated with an ideal reception processing method. The wireless transmission system according to claim 1 or 2 ,
The wireless transmission system according to claim 1, wherein the mutual information (MIB) per bit is calculated in consideration of a reception processing method that is actually used. A wireless communication device on a data receiving side in a wireless transmission system capable of transmitting and receiving data by a plurality of different transmission streams between a plurality of wireless communication devices,
Means for calculating a signal-to-interference noise ratio (SINR) for each of a plurality of subcarriers of each transmission stream based on signals transmitted and received in a plurality of transmission streams in a wireless transmission path between the plurality of wireless communication devices ;
Before SL each of a plurality of sub-carriers, means for calculating mutual information per bit (MIB) from the signal to interference noise ratio (SINR),
Means for calculating a mutual information amount (MI) per modulation symbol from the mutual information amount (MIB) per bit for each of the plurality of subcarriers;
Means for calculating a sum of mutual information (MI) per modulation symbol in the plurality of subcarriers for each of a plurality of modulation schemes;
Means for comparing the sum of mutual information (MI) per modulation symbol calculated for each of the plurality of modulation schemes, and selecting a modulation scheme that maximizes the sum of the mutual information (MI);
For each of a plurality of ranks of the wireless transmission path, a channel capacity obtained by adding or averaging on a frequency axis the mutual information (MI) per modulation symbol for each of the plurality of subcarriers calculated for the selected modulation scheme. Means for calculating an index value;
Means for comparing the channel capacity index values calculated for each of the plurality of ranks, and determining a rank that maximizes the channel capacity index value as a rank used for next data transmission in the wireless transmission path; ,
A wireless communication apparatus comprising: A wireless communication device on a data receiving side in a wireless transmission system capable of transmitting and receiving data by a plurality of different transmission streams between a plurality of wireless communication devices,
Signal-to-interference noise for each of a plurality of subcarriers used in the wireless transmission path between the plurality of transmission streams based on signals transmitted and received in a plurality of transmission streams in a wireless transmission path between the plurality of wireless communication apparatuses Means for calculating an average value of the ratio (SINR);
Means for calculating a mutual information amount (MIB) per bit from an average value of the signal-to-interference noise ratio (SINR) for each of the plurality of subcarriers;
Means for calculating a mutual information amount (MI) per modulation symbol from the mutual information amount (MIB) per bit for each of the plurality of subcarriers;
Means for calculating a sum of mutual information (MI) per modulation symbol in the plurality of subcarriers for each of a plurality of modulation schemes;
Means for comparing the sum of mutual information (MI) per modulation symbol calculated for each of the plurality of modulation schemes, and selecting a modulation scheme that maximizes the sum of the mutual information (MI);
For each of a plurality of ranks of the wireless transmission path, a channel capacity obtained by adding or averaging on a frequency axis the mutual information (MI) per modulation symbol for each of the plurality of subcarriers calculated for the selected modulation scheme. Means for calculating an index value;
Means for comparing the channel capacity index values calculated for each of the plurality of ranks, and determining a rank that maximizes the channel capacity index value as a rank used for next data transmission in the wireless transmission path; ,
Means for notifying information of the determined rank to the wireless communication device on the data transmission side;
A wireless communication apparatus comprising:

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