JP6523377B2 - User terminal, wireless base station, and wireless communication method - Google Patents

Description

  The present invention relates to a user terminal, a radio base station, and a radio communication method.

  A specification of Long Term Evolution (LTE) has been formulated for the purpose of speeding up and reducing the delay of Universal Mobile Telecommunications System (UMTS) (Non-Patent Document 1). In LTE, a communication system based on orthogonal frequency division multiple access (OFDMA) is used for downlink (downlink), and communication based on single carrier frequency division multiple access (SC-FDMA) for uplink (uplink). The method is used.

  Further, in LTE, Multiple Input Multiple Output (MIMO) transmission is adopted in which different information data sequences are transmitted in parallel from a plurality of transmission antennas using the same radio resource (frequency band, time slot). Since this MIMO transmission transmits a plurality of information data sequences on different routes using the same radio resource, high throughput and system capacity can be realized by space division multiplexing.

3GPP TR 25.913 "Requirements for Evolved UTRA and Evolved UTRAN"

  By the way, the throughput and the system capacity realized by the above-mentioned MIMO transmission depend on the number of information data sequences transmitted in parallel. Therefore, if the number of information data sequences to be transmitted in parallel is increased by, for example, increasing the number of antennas involved in transmission and reception, it is possible to increase throughput and system capacity. However, in this method, the system configuration is complicated as the number of antennas increases, so that the achievable throughput and system capacity are limited.

  The present invention has been made in view of the foregoing, and it is an object of the present invention to provide a user terminal, a radio base station, and a radio communication method of a new configuration that can increase throughput and system capacity.

A user terminal according to an embodiment applies a signal in which signals for each of a plurality of user terminals including the own terminal are multiplexed using different powers in a predetermined layer, and multiplexing using different powers in the predetermined layer is applied is information indicating that it has been, the control information for different power ratios of the predetermined layer, and a receiver for receiving a signal addressed to the own terminal from the signal received by front Symbol receiving unit, the control information And a signal processing unit for decoding based on the

  According to the present invention, it is possible to provide a user terminal, a radio base station, and a radio communication method of a new configuration that can increase throughput and system capacity.

It is a schematic diagram which shows the basic structural example of the radio | wireless communications system with which MIMO transmission was applied. It is a schematic diagram which shows the basic structural example of the radio | wireless communications system to which NOMA was applied. It is a schematic diagram which shows the structural example of the radio | wireless communications system with which opportunistic beam forming was applied. It is a graph which shows the relationship between the number of user terminals and an average throughput. It is a schematic diagram for demonstrating the radio | wireless communication system which concerns on a 1st aspect. It is a schematic diagram which shows the example of a radio | wireless resource structure of the downlink reference signal transmitted from a radio | wireless base station. It is a schematic diagram for demonstrating a mode that the downlink signal transmitted by non-orthogonal multiplexing was received by each user terminal. It is a schematic diagram which shows the example of the transmission system supported by the radio | wireless communication system of this Embodiment. It is a schematic diagram which shows the example of a radio | wireless resource structure of the reference signal for demodulation transmitted from a radio | wireless base station. It is a flowchart which shows the control flow by the side of a wireless base station in the radio | wireless communication system which concerns on a 1st aspect. It is a flowchart which shows the control flow by the side of a user terminal in the radio | wireless communication system which concerns on a 1st aspect. It is a flowchart which shows the control flow by the side of a wireless base station in the radio | wireless communication system which concerns on a 2nd aspect. It is a flowchart which shows the control flow by the side of a user terminal in the radio | wireless communication system which concerns on a 2nd aspect. It is a schematic diagram which shows the structural example of a radio | wireless communications system. It is a block diagram which shows the structural example of a wireless base station. It is a block diagram which shows the structural example of a user terminal. It is a block diagram which shows the structural example of the baseband signal processing part which a wireless base station and a user terminal have.

  FIG. 1 is a schematic view showing a basic configuration example of a wireless communication system to which MIMO (Multiple Input Multiple Output) transmission is applied. The wireless communication system illustrated in FIG. 1 includes a wireless base station eNB # 1 (eNB: eNodeB) having a plurality of transmission antennas. In the coverage area of the radio base station eNB # 1, a plurality of user terminals UE # 1 (UE: User Equipment) (here, user terminals UE # 1A, UE # 1B, UE # 1C) are present .

  In this radio communication system, different data sequences are transmitted in parallel from a plurality of antennas of the radio base station eNB # 1 to a plurality of user terminals UE # 1. That is, a plurality of information data sequences are transmitted using the same radio resource in different routes. As an aspect of MIMO transmission, single-user MIMO (SU-MIMO: Single User MIMO) transmission in which a plurality of information data sequences are transmitted in parallel to a single user terminal UE # 1 and a user terminal having a plurality of information data sequences different There is multi-user MIMO (MU-MIMO: Multiple User MIMO) transmission that transmits in parallel to UE # 1. FIG. 1 shows the case where multi-user MIMO transmission is applied.

  The throughput and system capacity of a wireless communication system to which MIMO transmission is applied depend on the number of information data sequences transmitted in parallel. That is, if the number of information data sequences transmitted in parallel is increased by increasing the number of antennas of the radio base station eNB # 1 and the user terminal UE # 1, the throughput and system capacity of the radio communication system can be increased. it can. However, increasing the number of information data sequences transmitted in parallel complicates the system configuration required for transmission and reception, and in the future, throughput will be different in an approach different from space division multiplexing (spatial dimension multiplexing) of the above-mentioned MIMO transmission. And system capacity needs to be increased.

  For example, by applying non-orthogonal access (also called non-orthogonal multiplexing, power division multiplexing, power dimension multiplexing, etc.) in which downlink transmission power (transmission power) is made different for each user terminal UE # 1, Throughput and system capacity can be further increased. Therefore, we examined NOMA (Non-Orthogonal Multiple Access), which is non-orthogonal access on the premise of interference cancellation on the receiving side.

  FIG. 2 is a schematic view showing a basic configuration example of a wireless communication system to which NOMA is applied. In FIG. 2, a cell formed by the radio base station eNB # 2 is illustrated. In the coverage area of the radio base station eNB # 2, a plurality of user terminals UE # 2 (here, user terminals UE # 2A, UE # 2B, UE # 2C) are arranged. In this radio communication system, downlink data signals are transmitted from the transmission antenna of the radio base station eNB # 2 to the plurality of user terminals UE # 2 with different transmission powers.

  In the wireless communication system shown in FIG. 2, for example, transmission is performed according to the reception SINR of the user terminal UE # 2, path loss (propagation loss, path loss) between the radio base station eNB # 2 and the user terminal UE # 2, etc. Power is controlled. Specifically, control is performed such that transmission power of user terminal UE # 2A having large reception SINR (small path loss) is allocated small and transmission power of user terminal UE # 2C having small reception SINR (large path loss) is allocated large. To be done.

  When such transmission power assignment is performed, the signals addressed to the user terminals UE # 2A and UE # 2B become sufficiently weak at the located position of the user terminal UE # 2C. Therefore, user terminal UE # 2C can decode the signal addressed to an own terminal by considering interference with the signal addressed to user terminal UE # 2A, UE # 2B small. On the other hand, at the location in which the user terminal UE # 2A is located, the signals addressed to the user terminal UE # 2B and UE # 2C are strong. Therefore, user terminal UE # 2A receives the signal addressed to user terminal UE # 2B and UE # 2C in addition to the signal addressed to an own terminal.

  In NOMA, the signal addressed to each user terminal UE # 2 is multiplexed in an identifiable manner. The user terminal UE # 2A decodes the signal addressed to the user terminal UE # 2B and UE # 2C by SIC (Successive Interference Cancellation), and then separates the signal addressed to the own terminal. Throughput and system capacity can be further increased by applying the NOMA and multiplexing (non-orthogonal multiplexing) signals addressed to a plurality of user terminals UE # 2 to the same radio resource (frequency band, time slot) with different transmission powers It is considered possible.

Here, the affinity between SIC used for NOMA and MIMO transmission is considered. For example, in the system configuration shown in FIG. 1, the channel matrix representing the channel state between the radio base station eNB # 1 and the user terminal UE # 1A is h ₁ = [100 99], the radio base station eNB # 1 and the user terminal Let h ₂ = [1 −1] be the channel matrix representing the channel condition with UE # 1 B. When precoding using precoder m ₂ = [1 −1] ^T , h ₁ · m ₂ = 1 <h ₂ · m ₂ = 2 holds, and therefore the received signal strength of user terminal UE # 1A is the user terminal It becomes smaller than the received signal strength of UE # 1B. On the other hand, when precoding using precoder m ₂ = [1 1] ^T , h ₁ · m ₂ = 199> h ₂ · m ₂ = 0, and therefore the received signal strength of user terminal UE # 1A is the user It becomes larger than the received signal strength of the terminal UE # 1B.

  As described above, in MIMO transmission, the signal strength received by the user terminal UE # 1 fluctuates according to the applied precoder, and thus the superiority or inferiority of the channel state can not be uniquely determined. Therefore, there is a possibility that the signal addressed to the other user terminal UE # 1 that causes interference can not be decoded and removed only by the control of the transmission power. That is, in the MIMO transmission, since the downlink communication channel can not be treated as a Degraded Broadcast Channel (BC), the superiority or inferiority of the channel state can not be uniquely determined, and the application of the above SIC is difficult.

  The above-mentioned problems can be solved by applying precoding by DPC (Dirty Paper Coding) (for example, THP (Tomlinson Harashima Precoding)). However, in that case, the system configuration is complicated. Moreover, since precoding by DPC is sensitive to the quality of channel state information (CSI: Channel State Information) to be fed back, there is a problem that communication quality is likely to be deteriorated due to the deterioration of channel estimation accuracy or feedback error. There is also.

  To solve these problems, the present inventors apply non-orthogonal multiplexing (NOMA) to a system configuration capable of treating the downlink communication channel as Degraded BC in MIMO transmission using a plurality of transmitting and receiving antennas, We thought that throughput and system capacity could be increased without complication. As a system configuration capable of treating the downlink communication channel as Degraded BC, for example, a system configuration to which opportunistic beamforming is applied can be considered. Opportunistic beamforming may be called random beamforming.

  FIG. 3 is a schematic view showing a configuration example of a wireless communication system to which opportunistic beamforming is applied. The wireless communication system illustrated in FIG. 3A includes a wireless base station eNB # 3 that generates transmission beams B1, B2, and B3 of a predetermined pattern or a random pattern. The plurality of transmission beams B1, B2, and B3 generated by the radio base station eNB # 3 are, for example, orthogonal to one another. However, since interference between transmission beams can be removed on the reception side by an IR (Interference Rejection Combining) receiver of a linear filter, etc., it is not necessary to make the beams completely orthogonal. In this opportunistic beamforming, as shown in FIG. 3B, transmission beams B1, B2, and B3 are generated using radio resources (frequency bands, time slots) of a predetermined pattern or a random pattern. . Note that in opportunistic beamforming, a plurality of transmission beams may be generated using a predetermined pattern of radio resources, so the number of transmission beams generated at any timing (time slot) may be one.

  A plurality of user terminals UE # 3 are arranged in the coverage areas of the transmission beams B1, B2, and B3, respectively. Each user terminal UE # 3 performs channel estimation based on the beam-specific downlink reference signal transmitted by each of the transmission beams B1, B2, and B3, and transmits the channel quality information (CQI: Channel Quality Indicator) to the radio base station eNB # 3. Feedback). The radio base station eNB # 3 performs downlink data transmission by selecting the user terminal UE # 3 with the highest CQI in each of the transmission beams B1, B2, and B3.

  FIG. 4 is a graph showing the relationship between the number of user terminals and the average throughput. In opportunistic beamforming (Opp.BF: Opportunistic BeamForming), as described above, the user terminal UE # 3 with the highest CQI is within the coverage area of each of the transmission beams B1, B2, and B3 generated in an arbitrary pattern. To perform downlink data transmission. When the number of user terminals UE # 3 in each coverage area increases, the existence probability of user terminals UE # 3 with good channel quality also increases. Therefore, as shown in FIG. 4, the above-mentioned MIMO transmission (Coherent BF: Coherent Beam Forming) It is possible to achieve high throughput comparable to

  In this opportunistic beamforming, for example, the communication channel can be treated as Degraded BC by removing interference between each of the transmission beams B1, B2, and B3 with a linear filter. Therefore, the affinity to SIC is high and interference can be appropriately removed even by applying non-orthogonal multiplexing. Therefore, in the present invention, non-orthogonal multiplexing is applied to this opportunistic beamforming. Hereinafter, each aspect of the present invention will be described.

(First aspect)
A first aspect of a wireless communication scheme in which non-orthogonal multiplexing (NOMA) is applied to opportunistic beam forming will be described. FIG. 5 is a schematic view for explaining the wireless communication system according to the first aspect.

  The wireless communication system illustrated in FIG. 5A includes a wireless base station eNB # 5 that generates N transmission beams Beam # 1 to Beam # N of a predetermined pattern or a random pattern. The N transmission beams Beam # 1 to Beam # N generated by the radio base station eNB # 5 are orthogonal to one another. In this wireless communication system, transmission beams Beam # 1 to Beam # N are generated using radio resources (frequency bands, time slots) of a predetermined pattern or a random pattern.

  A plurality of user terminals UE # 5 are arranged in the coverage areas of the transmission beams Beam # 1 to Beam # N, respectively. The radio base station eNB # 5 is a downlink reference signal (CSI-RS (Channel State Information Reference Signal), DM-RS (CSI-RS) specific to each of the transmission beams Beam # 1 to Beam # N for a plurality of user terminals UE # 5. Send DeModulation Reference Signal) etc.). FIG. 6 is a schematic diagram showing an example of the radio resource configuration of the downlink reference signal transmitted from the radio base station, and shows the case where four transmission beams Beam # 1 to Beam # 4 are generated simultaneously. As shown in FIG. 6, the downlink reference signal specific to each transmission beam is multiplexed, for example, in a PDSCH (Physical Downlink Shared Channel) region of each resource block (RB). As a method of multiplexing reference signals addressed to a plurality of user terminals UE # 5 in each transmission beam, a method of multiplexing reference signals suitable for conventional non-orthogonal access multiplexing may be applied.

  Each user terminal UE # 5 performs channel estimation based on the beam-specific downlink reference signal transmitted by each of the transmission beams Beam # 1 to Beam # N, and transmits channel quality information (CQI) to the radio base station eNB # 5. give feedback. The radio base station eNB # 5 determines a set of multiple user terminals UE # 5 to be non-orthogonally multiplexed to each of the transmission beams Beam # 1 to Beam # N based on the fed back CQI. In addition, the information fed back from each user terminal UE # 5 is not limited to channel quality information (CQI). At least, channel state information (CSI) indicating a channel state may be fed back.

A set of user terminals UE # 5 to be non-orthogonally multiplexed is determined based on an arbitrary scheduling metric such that an index value for user terminal selection such as a sum rate is maximized. For example, in an arbitrary frequency block b, since the interference of all users i satisfying h _{i, b} / N _{i, b} <h _{k, b} / N _{k, b} can be eliminated by the SIC of user k, the throughput of user k R ^(sic) (k) is represented by the following formula (1).

When scheduling is performed to maximize the worst user throughput (minimum throughput), a plurality of user terminals UE non-orthogonally multiplexed are solved by solving the optimal power allocation problem represented by the following equations (2) and (3) You can decide the set of # 5. K indicates the total number of user terminals, B indicates the total number of transmission beams, and P indicates the total value of transmission power.

  When a set of a plurality of user terminals UE # 5 to be non-orthogonally multiplexed into transmission beams Beam # 1 to Beam # N is determined, the radio base station eNB # 5 transmits each of the transmission beams Beam # 1 to Beam # N. Then, the downlink signal addressed to the corresponding user terminal UE # 5 is non-orthogonally multiplexed by superposition coding. That is, the signals addressed to a plurality of user terminals UE # 5 are multiplexed in the same radio resource (frequency band, time slot) while changing the transmission power. Further, information on other user terminals # 5 necessary for interference removal by SIC is notified to each user terminal # 5.

  As shown to FIG. 5B, the downlink signal corresponding to the set of several user terminal UE # 5 of each transmission beam Beam # 1-Beam # N is non-orthogonally multiplexed by the one part frequency band f1. For example, in FIG. 5B, downlink signals addressed to user terminals UE # 5A, UE # 5B, and UE # 5C are non-orthogonally multiplexed in frequency band f1 of transmission beam Beam # 1. Further, downlink signals addressed to user terminals UE # 5H, UE # 5I, and UE # 5J are non-orthogonally multiplexed in frequency band f1 of transmission beam Beam # N.

  In the frequency band f2 of each of the transmission beams Beam # 1 to Beam # N, another signal (downlink signal or uplink signal) is multiplexed. Thus, FIG. 5B shows a radio resource configuration (orthogonal / non-orthogonal hybrid multiple access) combining orthogonal multiplexing by frequency bands f1 and f2 and non-orthogonal multiplexing, but non-orthogonal multiplexing in all frequency bands Only may be applied.

  In each of the transmission beams Beam # 1 to Beam # N, the transmission power of the signal to be non-orthogonally multiplexed is determined based on the feedback CQI (or CSI). For example, as shown in FIG. 5B, the radio base station eNB # 5 minimizes the transmission power of the user terminal UE # 5A having the largest received SINR (the smallest path loss) in the transmission beam Beam # 1, and the received SINR is the largest. The transmission power of the small (largest path loss) user terminal UE # 5C is maximized. Also, the radio base station eNB # 5 minimizes the transmission power of the user terminal UE # 5H with the largest received SINR (the smallest path loss) in the transmission beam Beam # N, and the smallest received SINR (the largest path loss). ) The transmission power of the user terminal UE # 5J is maximized.

  FIG. 7 is a schematic diagram for explaining how downlink signals transmitted by non-orthogonal multiplexing are received by each user terminal. In FIG. 7, the reception SINR of the user terminal UE # 7B is smaller than the reception SINR of the user terminal UE # 7A. Alternatively, the path loss between the radio base station eNB # 7 and the user terminal UE # 7B is larger than the path loss between the radio base station eNB # 7 and the user terminal UE # 7A. Therefore, the radio base station eNB # 7 sets the transmission power of the user terminal UE # 7A having a large reception SINR (small path loss) smaller than the transmission power of the user terminal UE # 7B having a small reception SINR (large path loss) doing.

  At the location where the user terminal UE # 7B is located, the signal addressed to the user terminal UE # 7A is sufficiently weak. Therefore, user terminal UE # 7B can decode the signal addressed to an own terminal, without receiving interference by the signal addressed to user terminal UE # 7A. On the other hand, at the located position of the user terminal UE # 7A, the signal addressed to the user terminal UE # 7B is strong. Therefore, user terminal UE # 7A receives the signal addressed to user terminal UE # 7B in addition to the signal addressed to the own terminal.

  Signals directed to user terminals UE # 7A and UE # 7B are multiplexed in such a manner that they can be identified. Therefore, the user terminal UE # 7A removes the signal addressed to the user terminal UE # 7B by SIC and separates the signal addressed to the own terminal. As a result, the user terminal UE # 7A can decode the signal addressed to the own terminal. The same applies to the user terminals UE # 7C and UE # 7D. That is, user terminal UE # 7D deems that the interference due to the signal addressed to user terminal UE # 7C is small, and decodes the signal addressed to itself. On the other hand, user terminal UE # 7C removes the signal addressed to user terminal UE # 7D by SIC, separates the signal addressed to the own terminal, and decodes it.

  The above-described SIC is applied to signal removal addressed to the user terminal UE in which the state of the transmission path is worse (the received SINR is smaller or the path loss is larger) than the own terminal. The signal addressed to the user terminal UE whose transmission path status is worse than that of the own terminal is transmitted with higher power than the signal addressed to the own terminal, so that the own terminal can correctly decode. Therefore, such interference due to the signal for the user terminal UE is appropriately removed by the SIC. On the other hand, since the signal addressed to the user terminal UE in which the state of the transmission path is better than the own terminal is transmitted with lower power than the signal addressed to the own terminal, the interference can be ignored.

In the wireless communication system of this aspect configured as described above, the transmission signal vector x is represented by the following equation (4). B indicates the total number of transmission beams, m _b indicates the beam vector (precoder) of the b-th transmission beam, and P _{b, u} indicates the transmission to the u-th user terminal that is superposition coded on the b-th transmission beam Power (transmission power) is shown, and s _{b, u} is a signal to the u-th user terminal which is superimposed and encoded on the b-th transmission beam.

Further, the following equation (5) holds. P _{b ′} indicates the transmission power of the b-th transmission beam, and P indicates the sum of transmission powers of all the transmission beams.

Further, the reception signal vector y _{b, u} of the u-th user terminal which is superposition-coded on the b-th transmission beam is expressed by the following equation (6). H _{b, u} denotes the channel matrix of the u-th user terminal superimposed and encoded in the b-th transmit beam, and w _{b, u} denotes the u-th user terminal superimposed and encoded in the b-th transmit beam Indicates a noise interference vector.

Interference between transmit beams can be suppressed by receive linear filtering instead of SIC. Taking this into consideration, the received signal vector y _{̃b, u} after filtering of the u-th user terminal that has been convolutionally encoded into the b-th transmission beam is expressed by the following equation (7). v ^H _{b, u} denotes a reception filter vector of the u-th user terminal which is superposition coded on the b-th transmission beam.

The following equation (8) is an equivalent channel expression of the above equation (7). w _{b b, u} denote power noise to the u-th user terminal which is superposition coded on the b-th transmission beam. g _{b, u} is represented by the following formula (9).

 It can be understood from the above equation (8) that the downlink communication channel can be regarded as Degraded BC. Therefore, in the wireless communication system of this aspect, interference in each transmission beam can be appropriately suppressed by the reception SIC.

  In the radio communication system according to the present embodiment, as described above, NOMA is applied to MU-MIMO transmission, but other transmission systems are also supported. FIG. 8 is a schematic view showing an example of a transmission scheme supported by the wireless communication scheme of this embodiment. FIG. 8A shows an example of SU-MIMO transmission, and FIG. 8B shows an example of transmit diversity. Peak rates can be increased by having the wireless communication system support the SU-MIMO transmission of FIG. 8A. In addition, in an application environment where the precoding gain is small, the transmission diversity in FIG. 8B is effective.

  FIG. 9 is a schematic view showing an example of a radio resource configuration of a demodulation reference signal (DM-RS) transmitted from the radio base station. 9A to 9D, the horizontal axis represents radio resources (time, frequency), and the vertical axis represents transmission power. As shown to FIG. 9A, when NOMA is applied to the transmission beam by one transmission antenna, the signal addressed to each user terminal UE # 9 is transmitted by different power in the same radio | wireless resource. In this case, for example, a DM-RS common to each user terminal UE # 9 can be used as a reference signal for demodulation. Further, as shown in FIG. 9B, in SU-MIMO transmission using transmission beams by a plurality of transmission antennas (here, two transmission antennas TX1 and TX2), a plurality (two) addressed to user terminal UE # 9A Information data sequences (layers) are multiplexed to the same radio resource. In this case, for example, DM-RSs orthogonal to one another can be used as reference signals for demodulation.

  On the other hand, as shown in FIG. 9C, when NOMA is applied to SU-MIMO transmission using transmission beams from a plurality of transmission antennas (here, two transmission antennas TX1 and TX2), each user terminal UE # A plurality of (two) information data sequences (layers) addressed to 9 are multiplexed to the same radio resource. Here, the signal addressed to the user terminal UE # 9 is transmitted with different powers. In this case, as the reference signal for demodulation, for example, DM-RSs that are common to user terminals in the same layer and are orthogonal between layers can be used.

  Furthermore, as shown in FIG. 9D, when NOMA is applied to MU-MIMO transmission using transmission beams by a plurality of transmission antennas (here, two transmission antennas TX1 and TX2), each user terminal UE # Signals addressed to 9 are multiplexed to the same radio resource. In the same transmission beam, signals addressed to each user terminal # 9 are transmitted at different powers. In this case, as the reference signal for demodulation, for example, DM-RSs that are common to the user terminals UE # 9 in the same transmission beam and are orthogonal between the transmission beams can be used. As described above, when the common DM-RS configuration is applied between user terminals, the ratio of transmission power for each user terminal is notified. In addition, although the case where common DM-RS structure was applied between user terminals was shown here, it is good also as a structure which transmits separate DM-RS for every user terminal.

  The control flow of the wireless communication system of this aspect will be described. FIG. 10 is a flow chart showing a control flow on the radio base station side. The radio base station eNB first determines a beam vector (precoder) of a transmission beam used for data transmission (step ST11). For example, when using two transmit antennas, two orthogonal beam vectors are randomly generated. Then, a downlink reference signal specific to each transmission beam is transmitted to the user terminal UE using the transmission beam precoded with each beam vector (step ST12).

  Next, the radio base station eNB requests all user terminals UE to feed back CQI based on the downlink reference signal transmitted by each transmission beam (step ST13). For example, the radio base station eNB instructs the user terminal UE to feed back only the CQI (corresponding to SINR). In this case, overhead associated with feedback can be reduced. However, the information to be fed back is not limited to CQI. At least CSI indicating a channel state may be fed back. In addition, in this feedback, the interference from another cell (another radio base station eNB) is considered.

  When CQI is fed back from the user terminal UE, the radio base station eNB performs scheduling of each transmission beam based on the fed back CQI, and determines the user terminal UE to perform non-orthogonal multiplexing (step ST14). That is, the radio base station eNB selects a user terminal UE to be subjected to frequency scheduling, and determines a user terminal UE to be subjected to non-orthogonal multiplexing. The determination of the user terminal UE to be subjected to non-orthogonal multiplexing is performed, for example, based on the above-described scheduling metric.

  Thereafter, the radio base station eNB generates a transmission signal based on the scheduling information and the information of the user terminal to be non-orthogonally multiplexed, and non-orthogonally multiplexes each transmission beam and transmits (S15). In addition, the radio base station eNB notifies each user terminal UE of information of another user terminal UE to be non-orthogonally multiplexed in the same transmission beam (step ST16). This notification is performed, for example, using higher layer signaling (such as RRC signaling), signaling based on control information of PDCCH, or the like.

  FIG. 11 is a flowchart showing the control flow on the user terminal side. The user terminal UE receives the downlink reference signal transmitted by each transmission beam (step ST21), calculates CQI, and feeds it back to the radio base station eNB (step ST22). The information to be fed back may be CSI indicating a channel state.

  Thereafter, the user terminal UE receives the transmission signal transmitted from the radio base station eNB together with the control information (step ST23), and the information directed to the own terminal and another user to be non-orthogonally multiplexed in the same transmission beam as the own terminal The information addressed to the terminal UE is acquired (step ST24). Also, the user terminal UE estimates CSI information of its own terminal by channel estimation (step ST25). The user terminal UE estimates CSI information of the other user terminal UE based on the notified reference signal of the other user terminal UE (step ST25).

  Thereafter, the user terminal UE removes interference between transmission beams using linear filters such as MMSE and IRC (step ST26). For example, in a configuration using two receive antennas, an IRC receiver or an MMSE receiver with a linear filter is used to remove interference between the transmit beams. Next, the interference due to the signal for another user terminal non-orthogonally multiplexed in the same transmission beam is eliminated by SIC (step ST27). Here, SIC is applied to signal removal addressed to the user terminal UE in which the state of the transmission path is worse (the received SINR is smaller or the path loss is larger) than the own terminal. The signal addressed to the user terminal UE whose transmission path status is worse than that of the own terminal is transmitted with higher power than the signal addressed to the own terminal, so that the own terminal can correctly decode. Therefore, such interference due to the signal for the user terminal UE is appropriately removed by the SIC. On the other hand, since the signal addressed to the user terminal UE whose transmission path is better than the own terminal (the reception SINR is large or the path loss is smaller) is transmitted with lower power than the signal addressed to the own terminal, interference can be ignored. After removing the interference due to the signal for another user terminal UE, the user data for the own terminal is demodulated (step ST28).

  As described above, in the wireless communication system according to this aspect, non-orthogonal multiplexing is applied to opportunistic beamforming capable of achieving system characteristics equivalent to MIMO transmission, so that throughput and system capacity can be further enhanced.

(Second aspect)
In this aspect, a second aspect of a wireless communication system in which non-orthogonal multiplexing (NOMA) is applied to opportunistic beam forming will be described. Note that many parts of this aspect are common to the first aspect. Therefore, in this aspect, differences are mainly described.

  The wireless communication system according to this aspect uses a first stage that feeds back coarse channel state information and a second stage that feeds back accurate channel state information. FIG. 12 is a flow chart showing a control flow on the radio base station side. The radio base station eNB first determines a beam vector (precoder) of a transmission beam used for data transmission (step ST31). Then, a downlink reference signal specific to each transmission beam is transmitted to the user terminal UE using the transmission beam precoded with each beam vector (step ST32).

  Next, the radio base station eNB requests all user terminals UE to feed back coarse CSI (Coarse CSI) based on the downlink reference signal transmitted by each transmission beam (step ST33). That is, the radio base station eNB feeds back CSI obtained by quantizing the channel estimation result with a small number of bits to the user terminal UE. As coarse CSI, for example, CQI (corresponding to SINR) can be used. The coarse CSI fed back is quantized with a small number of bits, so overhead can be reduced. In addition, in this feedback, the interference from another cell (another radio base station eNB) is considered.

  After that, the radio base station eNB selects a plurality of user terminals UE to which CSI with high accuracy is to be fed back (step ST34). This selection is made based on the coarse CSI fed back from the user terminal UE. Specifically, a plurality of user terminals UE that can be targets of non-orthogonal multiplexing in each transmission beam are selected. In the step of requesting coarse CSI feedback (step ST33) and the step of selecting a plurality of user terminals UE to which accurate CSI is fed back (step ST34), the first stage of the wireless communication scheme according to this aspect (wireless Base station side is configured.

  When the first stage is finished, the radio base station eNB uses the user terminal UE selected in the above step to feed back a high-precision CSI (Fine CSI) based on the downlink reference signal transmitted by each transmission beam. Request (step ST35). That is, the radio base station eNB feeds back the CSI quantized by the number of bits larger than the coarse CSI to the user terminal UE. For example, SINR quantized with many bits can be used as CSI with high accuracy.

  Next, the radio base station eNB performs scheduling of each transmission beam based on the highly accurate CSI that is fed back, and determines a user terminal UE to perform non-orthogonal multiplexing (step ST36). That is, the radio base station eNB selects a user terminal UE to be subjected to frequency scheduling based on high accuracy CSI, and determines a user terminal UE to be subjected to non-orthogonal multiplexing. The determination of the user terminal UE to be subjected to non-orthogonal multiplexing is performed, for example, based on the above-described scheduling metric. Here, since scheduling is performed based on high-precision CSI to determine non-orthogonal multiplexing user terminals UE, communication quality can be sufficiently improved. In the step of requesting CSI feedback with high accuracy (step ST35) and the step of performing scheduling to determine non-orthogonal multiplexing user terminals UE (step ST36), the second stage of the wireless communication scheme according to this aspect The radio base station side is configured.

  After that, the radio base station eNB generates a transmission signal based on the scheduling information and the information of the user terminal to be non-orthogonally multiplexed, and non-orthogonally multiplexes each transmission beam and transmits it (step ST37). Also, the radio base station eNB notifies each user terminal UE of information of another user terminal UE to be non-orthogonally multiplexed in the same transmission beam (step ST38). This notification is performed, for example, using higher layer signaling (such as RRC signaling), signaling based on control information of PDCCH, or the like. For example, it is performed using signaling by higher layer signaling (RRC) or control information of PDCCH.

  FIG. 13 is a flowchart showing the control flow on the user terminal side. The user terminal UE receives the downlink reference signal transmitted by each transmission beam (step ST41), calculates coarse CSI, and feeds it back to the radio base station eNB (step ST42). That is, the user terminal UE feeds back CSI obtained by quantizing the channel estimation result with a small number of bits to the radio base station eNB. By this step (step ST42), the first stage (user terminal side) of the wireless communication system according to this aspect is configured.

  After that, when there is a request for feedback of CSI with high accuracy from the radio base station eNB, the user terminal UE feeds back CSI with high accuracy to the radio base station eNB (step ST43). That is, the user terminal UE feeds back the CSI quantized by the number of bits larger than the coarse CSI to the radio base station eNB. The second stage (user terminal side) of the wireless communication system according to this aspect is configured by this step (step ST43).

  Thereafter, the user terminal UE receives the transmission signal transmitted from the radio base station eNB together with the control information (step ST44), and the information directed to the own terminal and another user to be non-orthogonally multiplexed in the same transmission beam as the own terminal The information addressed to the terminal UE is acquired (step ST45). Also, the user terminal UE estimates CSI information of its own terminal by channel estimation (step ST46). The user terminal UE estimates CSI information of the other user terminal UE based on the notified reference signal of the other user terminal UE (step ST46).

  Thereafter, the user terminal UE removes interference between transmission beams using linear filters such as MMSE and IRC (step ST47). For example, in a configuration using two receive antennas, an IRC receiver is used to eliminate interference between the transmit beams. Next, the interference due to the signal for another user terminal non-orthogonally multiplexed in the same transmission beam is eliminated by SIC (step ST48). Here, SIC is applied to signal removal addressed to the user terminal UE in which the state of the transmission path is worse (the received SINR is smaller or the path loss is larger) than the own terminal. The signal addressed to the user terminal UE whose transmission path status is worse than that of the own terminal is transmitted with higher power than the signal addressed to the own terminal, so that the own terminal can correctly decode. Therefore, such interference due to the signal for the user terminal UE is appropriately removed by the SIC. On the other hand, since the signal addressed to the user terminal UE whose transmission path is better than the own terminal (the reception SINR is large or the path loss is smaller) is transmitted with lower power than the signal addressed to the own terminal, interference can be ignored. After removing the interference due to the signal for another user terminal UE, the user data for the own terminal is demodulated (step ST49).

  As described above, in the wireless communication method according to this aspect, coarse CSI is fed back in the first stage, and after selecting a plurality of user terminals UE that can be targets for non-orthogonal multiplexing, high precision CSI is calculated in the second stage. Since feedback and scheduling are performed to determine user terminals to be subjected to non-orthogonal multiplexing, overhead associated with feedback can be suppressed while maintaining high communication quality.

(Example of configuration of wireless communication system)
The details of the radio communication system according to the present embodiment will be described below. FIG. 14 is a schematic view showing a configuration example of a wireless communication system according to the present embodiment. The wireless communication system illustrated in FIG. 14 is a system including, for example, an LTE system or an LTE-A (LTE-Advanced) system. This wireless communication system may be called IMT-Advanced or may be called 4G.

  As shown in FIG. 14, the wireless communication system 1 includes a wireless base station 10 (10A, 10B) and a plurality of user terminals 20 (20A, 20B) communicating with the wireless base station 10. The radio base station 10 is connected to the higher station apparatus 30, and the higher station apparatus 30 is connected to the core network 40. Each user terminal 20 can communicate with the radio base station 10 in the cells C1 and C2. The user terminal 20 may be a mobile terminal or a fixed terminal. The upper station apparatus 30 includes, for example, an access gateway apparatus, a radio network controller (RNC), a mobility management entity (MME), and the like, but is not limited thereto.

  In the radio communication system 1, as the radio access scheme, OFDMA (Orthogonal Frequency Division Multiple Access) is applied to the downlink, and SC-FDMA (Single Carrier-Frequency Division Multiple Access) is applied to the uplink. OFDMA is a multicarrier transmission scheme in which a frequency band is divided into a plurality of narrow frequency bands (subcarriers) and data is mapped to each subcarrier to perform communication. SC-FDMA is a single carrier transmission scheme that divides the system band into bands consisting of one or continuous resource blocks for each terminal, and a plurality of terminals use different bands to reduce interference between the terminals. .

  Here, communication channels used in the wireless communication system 1 shown in FIG. 14 will be described. The downlink communication channel has a PDSCH (Physical Downlink Shared Channel) shared by each user terminal 20 and a downlink L1 / L2 control channel (PDCCH, PCFICH, PHICH, enhanced PDCCH). User data and higher control information are transmitted by PDSCH. Scheduling information etc. of PDSCH and PUSCH are transmitted by PDCCH (Physical Downlink Control Channel). The number of OFDM symbols used for PDCCH is transmitted by PCFICH (Physical Control Format Indicator Channel). The HARQ ACK / NACK for the PUSCH is transmitted by the PHICH (Physical Hybrid-ARQ Indicator Channel).

  The uplink communication channel has a PUSCH (Physical Uplink Shared Channel) as an uplink data channel shared by each user terminal 20, and a PUCCH (Physical Uplink Control Channel) which is an uplink control channel. User data and higher control information are transmitted by this PUSCH. Also, downlink channel quality information (CQI: Channel Quality Indicator), ACK / NACK and the like are transmitted by the PUCCH.

  FIG. 15 is a block diagram showing an example of configuration of a radio base station according to the present embodiment. The wireless base station 10 includes a plurality of transmit / receive antennas 101 for opportunistic beamforming, an amplifier unit 102, a transmit / receive unit 103, a baseband signal processing unit 104, a call processing unit 105, and a transmission path interface 106. Is equipped.

  User data transmitted from the radio base station 10 to the user terminal 20 in downlink is input from the higher station apparatus 30 to the baseband signal processing unit 104 via the transmission path interface 106.

  The baseband signal processing unit 104 performs RLC layer transmission processing such as processing of the PDCP layer, division / combination of user data, transmission processing of RLC (Radio Link Control) retransmission control, and MAC (for the input user data). Medium Access Control Retransmission control, for example, HARQ transmission processing, scheduling, transmission format selection, channel coding, inverse fast Fourier transform (IFFT) processing, precoding processing, and transfer to each transmission / reception unit 103 Do. Also, transmission processing such as channel coding and IFFT processing is performed on downlink control information, and the transmission processing is performed to each transmission / reception unit 103.

  Also, the baseband signal processing unit 104 notifies the user terminal 20 of control information for communication in the serving cell by means of a broadcast channel. The information for communication in the serving cell includes, for example, uplink or downlink system bandwidth and the like.

  Each transmission / reception unit 103 converts the baseband signal output from the baseband signal processing unit 104 for each antenna into a radio frequency band. The amplifier unit 102 amplifies the frequency converted radio frequency signal and transmits it from the transmitting and receiving antenna 101.

  On the other hand, data transmitted from the user terminal 20 to the radio base station 10 by uplink is received by each transmitting and receiving antenna 101 and input to the amplifier unit 102. The amplifier unit 102 amplifies the radio frequency signal input from each transmitting and receiving antenna 101 and sends the amplified signal to each transmitting and receiving unit 103. The amplified radio frequency signal is converted into a baseband signal by each transmission / reception unit 103, and is input to the baseband signal processing unit 104.

  The baseband signal processing unit 104 performs Fast Fourier Transform (FFT) processing, Inverse Discrete Fourier Transform (IDFT) processing, and error on user data included in the input baseband signal. It performs correction decoding, reception processing of MAC retransmission control, reception processing of the RLC layer, and PDCP layer, and transfers it to the higher station apparatus 30 via the transmission path interface 106. The call processing unit 105 performs call processing such as setting and release of a communication channel, status management of the radio base station 10, management of radio resources, and the like.

  FIG. 16 is a block diagram showing a configuration example of a user terminal according to the present embodiment. The user terminal 20 includes a plurality of transmission / reception antennas 201, an amplifier unit 202, a transmission / reception unit 203, a baseband signal processing unit 204, and an application unit 205.

  Downlink data is received by the plurality of transmission / reception antennas 201 and input to the amplifier unit 202. The amplifier unit 202 amplifies the radio frequency signal input from each transmitting and receiving antenna 201 and sends it to each transmitting and receiving unit 203. The amplified radio frequency signal is converted to a baseband signal by each transmission / reception unit 203, and is input to the baseband signal processing unit 204. The baseband signal processing unit 204 performs reception processing of FFT processing, error correction decoding, retransmission control, and the like on the input baseband signal. User data included in downlink data is transferred to the application unit 205. The application unit 205 performs processing on a layer higher than the physical layer and the MAC layer. Also, broadcast information included in downlink data is also transferred to the application unit 205.

  On the other hand, uplink user data is input from the application unit 205 to the baseband signal processing unit 204. The baseband signal processing unit 204 performs retransmission control (H-ARQ (Hybrid ARQ)) transmission processing, channel coding, precoding, discrete Fourier transform (DFT) processing on input user data. , IFFT processing, etc., and transfer to each transmission / reception unit 203. Each transmission / reception unit 203 converts the baseband signal output from the baseband signal processing unit 204 into a radio frequency band. Thereafter, the amplifier unit 202 amplifies the frequency converted radio frequency signal and transmits it from the transmitting / receiving antenna 201.

  FIG. 17 is a block diagram showing a configuration example of a baseband signal processing unit included in the radio base station and the user terminal according to the present embodiment. Although only a part of the configuration is shown in FIG. 17, the radio base station 10 and the user terminal 20 are equipped with the necessary components without a shortage.

  As shown in FIG. 17, the radio base station 10 includes a beam generation unit 301, a downlink control information generation unit 302, a downlink control information coding / modulation unit 303, a downlink transmission data generation unit 304, and a downlink transmission data coding / modulation unit. A downlink reference signal generation unit 306, a downlink channel multiplexing unit 307, and a scheduling unit 308 are provided.

  The beam generation unit 301 generates a plurality of transmission beams orthogonal to each other using radio resources (frequency bands, time slots) of a predetermined pattern or a random pattern.

  The downlink control information generation unit 302 generates downlink control information (DCI) specific to user terminals (UE-specific) transmitted by PDCCH. The downlink control information specific to the user terminal includes a DL assignment (DL assignment) that is PDSCH allocation information, a UL grant (UL grant) that is PUSCH allocation information, and the like. When the first aspect is applied, the downlink control information includes control information that requests each user terminal 20 to feedback CQI (or CSI). Also, when the second aspect is applied, this downlink control information includes control information that requests coarse CSI feedback to each user terminal 20, and control information that requires accurate CSI feedback. Be

  The downlink control information generated by the downlink control information generation unit 302 is input to the downlink control information coding / modulation unit 303 as the downlink control information transmitted on the PDCCH together with the common control information common to the user terminals. The downlink control information coding / modulation unit 303 performs channel coding and modulation on the input downlink control information. The modulated downlink control information is output to the downlink channel multiplexing unit 307.

  The downlink transmission data generation unit 304 generates downlink user data for each user terminal 20. The downlink user data generated by the downlink transmission data generation unit 304 is input to the downlink transmission data coding / modulation unit 305 as downlink transmission data to be transmitted on the PDSCH, together with higher control information. The downlink transmission data encoding / modulation unit 305 channel encodes and modulates downlink transmission data for each user terminal 20. The modulated downlink transmission data is output to the downlink channel multiplexing unit 307.

  The downlink reference signal generation unit 306 generates downlink reference signals (CRS (Cell-specific Reference Signal, CSI-RS, DM-RS, etc.)). The generated downlink reference signal is output to the downlink channel multiplexing unit 307. Note that, for example, CSI-RS or the like specific to each transmission beam is used to measure CQI (or CSI).

  The downlink channel multiplexing unit 307 combines the downlink control information, the downlink reference signal, and the downlink transmission data (including higher control information) to generate a downlink signal (transmission signal). Specifically, downlink channel multiplexing section 307 performs non-orthogonal multiplexing for each transmission beam of downlink signals for a plurality of user terminals 20 determined in scheduling section 308 according to the scheduling information notified from scheduling section 308. Do. The downlink signal generated by the downlink channel multiplexing unit 307 is transferred to the transmission / reception unit 103 through inverse fast Fourier transform processing, precoding processing, and the like.

  Scheduling section 308 is a radio resource for downlink transmission data and downlink control information based on instruction information from higher station apparatus 30 and CSI from each user terminal 20 (CQI (Channel Quality Indicator), RI (Rank Indicator), etc.). Generate scheduling information that instructs assignment of Also, the scheduling unit 308 determines, based on the feedback CQI (or CSI), a plurality of user terminals UE to be non-orthogonally multiplexed for each transmission beam. For example, when the first aspect is applied, the scheduling unit 308 schedules each transmission beam based on the CQI (or CSI) fed back from the user terminal 20, and determines the user terminal 20 to be non-orthogonally multiplexed. Do. On the other hand, when the second aspect is applied, the scheduling unit 308 selects a plurality of user terminals 20 to which CSI with high accuracy is to be fed back based on the coarse CSI fed back. Also, the scheduling unit 308 performs scheduling of each transmission beam based on the highly accurate CSI fed back, and determines the user terminal 20 to be non-orthogonally multiplexed.

  In the radio base station 10, a beam generation unit 301 determines a beam vector (precoder) of a transmission beam used for data transmission. The downlink reference signal (for example, CSI-RS) specific to the transmission beam generated by the downlink reference signal generation unit 306 is transmitted to the user terminal 20 by the transmission beam corresponding to each beam vector. When the first aspect is applied, control information requesting feedback of CQI (or CSI) is generated by downlink control information generation section 302 and transmitted to all user terminals 20. When the second aspect is applied, control information that requests coarse CSI feedback is generated by the downlink control information generation unit 302 and transmitted to all user terminals 20.

  In the case where the first aspect is applied, when CQI (or CSI) is fed back from each user terminal 20, scheduling section 308 performs scheduling of each transmission beam based on the feedback CQI, and performs non-orthogonal multiplexing. The user terminal 20 to be determined is determined. Also, the downlink channel multiplexing unit 307 non-orthogonally multiplexes downlink signals for each of the plurality of user terminals 20 determined by the scheduling unit 308 according to the scheduling information notified from the scheduling unit 308. Also, the radio base station 10 notifies each user terminal 20 of information on another user terminal 20 that is non-orthogonally multiplexed in the same transmission beam.

  On the other hand, when the second aspect is applied, the scheduling unit 308 selects a plurality of user terminals 20 to which CSI with high accuracy is to be fed back based on the coarse CSI fed back. Also, control information that requests CSI feedback with high accuracy is generated by the downlink control information generation unit 302 and transmitted to the selected user terminal 20. Thereafter, the scheduling unit 308 performs scheduling of each transmission beam based on the highly accurate CSI fed back, and determines the user terminal 20 to be non-orthogonally multiplexed. Also, the downlink channel multiplexing unit 307 non-orthogonally multiplexes downlink signals for each of the plurality of user terminals 20 determined by the scheduling unit 308 according to the scheduling information notified from the scheduling unit 308. Also, the radio base station 10 notifies each user terminal 20 of information on another user terminal 20 that is non-orthogonally multiplexed in the same transmission beam.

  As shown in FIG. 17, the user terminal 20 includes a downlink control information receiving unit 401, a channel estimating unit 402, a feedback unit 403, an interference removing unit 404, and a downlink transmission data receiving unit 405.

  The downlink signal transmitted from the radio base station 10 is received by the transmission / reception antenna 201, removed from the cyclic prefix, subjected to fast Fourier transform processing, and the like, and transferred to the baseband signal processing unit 204. The downlink signal is separated into downlink control information, downlink transmission data (including higher-order control information), and downlink reference signal by the baseband signal processing unit 204. The downlink control information is input to the downlink control information reception unit 401, the downlink transmission data is input to the downlink transmission data reception unit 405, and the downlink reference signal is input to the channel estimation unit 402.

  The downlink control information receiving unit 401 demodulates the downlink control information and outputs the downlink control information to the channel estimation unit 402, the feedback unit 403, the interference removal unit 404, and the like. When the first aspect is applied, channel estimation section 402 performs channel estimation based on a transmission beam specific downlink reference signal (such as CSI-RS) when a CQI (or CSI) feedback request is received by downlink control information. To measure CQI (or CSI). The CQI (or CSI) obtained by channel estimation is fed back to the radio base station 10 through the feedback unit 403.

  On the other hand, when the second aspect is applied, channel estimation section 402 performs channel estimation based on the downlink reference signal specific to the transmission beam when receiving a coarse CSI feedback request according to the downlink control information, and measures coarse CSI. Do. Further, when the channel estimation unit 402 receives a CSI feedback request with high accuracy based on downlink control information, the channel estimation unit 402 performs channel estimation based on a downlink reference signal specific to a transmission beam, and measures CSI with high accuracy. The coarse CSI and accurate CSI obtained by channel estimation are fed back to the radio base station 10 through the feedback unit 403.

  The interference removal unit 404 removes interference between transmission beams using a linear filter. Further, the interference removal unit 404 removes interference due to signals addressed to other user terminals 20 from the downlink signals addressed to a plurality of user terminals 20 non-orthogonally multiplexed for each transmission beam. Specifically, based on the information of the own terminal and other user terminals 20 notified by higher-order control information etc., the non-orthogonally multiplexed downlink signal addressed to the other user terminal 20 is removed to address the own terminal. Separate the downlink signal. The downlink transmission data reception unit 405 demodulates the downlink transmission data based on the separated downlink signal addressed to the own terminal.

  In the user terminal 20, when the downlink control information receiving unit 401 receives a CQI (or CSI) feedback request when the first aspect is applied, the channel estimation unit 402 performs downlink reference transmitted in each transmission beam. Calculate CQI (or CSI) based on the signal. The calculated CQI (or CSI) is fed back to the radio base station 10 through the feedback unit 403.

  On the other hand, when downlink control information receiving section 401 receives a feedback request of coarse CSI when the second aspect is applied, channel estimation section 402 performs coarse CSI based on the downlink reference signal transmitted by each transmission beam. calculate. The calculated coarse CSI is fed back to the radio base station 10 through the feedback unit 403. Also, when the downlink control information receiving unit 401 receives a highly accurate CSI feedback request, the channel estimation unit 402 calculates the highly accurate CSI based on the downlink reference signal transmitted by each transmission beam. The calculated CSI with high accuracy is fed back to the radio base station 10 through the feedback unit 403.

  The user terminal 20 acquires, for example, the information addressed to the own terminal and the information addressed to the other user terminal 20 based on the higher-level control information. Specifically, the user terminal 20 acquires information indicating interference between transmission beams and information on other user terminals 20 to be non-orthogonally multiplexed. Based on this information, the interference removal unit 404 removes interference between transmission beams using a linear filter such as MMSE, IRC, etc., and causes interference due to signals for other user terminals non-orthogonally multiplexed in the same transmission beam. Remove with SIC. SIC is applied to signal removal for the user terminal UE addressed to the user terminal UE in which the state of the transmission path is worse (the received SINR is smaller or the path loss is larger) than the own terminal. After removing the interference due to the signal to the other user terminal UE, the downlink transmission data reception unit 405 demodulates the downlink transmission data to the own terminal.

  As described above, according to the wireless communication system 1 according to the present embodiment, non-orthogonal multiplexing is applied to opportunistic beamforming that can realize system characteristics equivalent to MIMO transmission, so throughput and system capacity can be reduced. It can be further enhanced.

  The present invention can be embodied as modifications and alterations without departing from the spirit and scope of the invention. That is, the description in the present specification is for the purpose of illustration only, and does not limit the present invention.

1 wireless communication system 10 wireless base station 20 user terminal 30 upper station apparatus 40 core network 101 transmit / receive antenna 102 amplifier unit 103 transmit / receive unit 104 baseband signal processing unit 105 call processing unit 106 transmission path interface 201 transmit / receive antenna 202 amplifier unit 203 transmit / receive unit 204 baseband signal processing unit 205 application unit 301 beam generation unit 302 downlink control information generation unit 303 downlink control information encoding / modulation unit 304 downlink transmission data generation unit 305 downlink transmission data encoding / modulation unit 306 downlink reference signal generation unit 307 Downlink channel multiplexing unit 308 scheduling unit 401 downlink control information reception unit 402 channel estimation unit 403 feedback unit 404 interference removal unit 405 downlink transmission data reception unit

Claims (7)

A signal in which signals for each of a plurality of user terminals including the own terminal are multiplexed using different powers in a predetermined layer, and information indicating that multiplexing using different powers is applied in the predetermined layer, A receiver for receiving control information on different power ratios in the predetermined layer;
User terminal, characterized in that it comprises a signal addressed to the own terminal from the received signal, and a signal processing unit for decoding on the basis of the control information by the pre-Symbol receiver. The user terminal according to claim 1, wherein the signal for each of the plurality of user terminals includes a cell-specific reference signal (CRS) in common. In certain layer, a signal for each of the plurality of user terminals including the own terminal, a multiplexed signal using a different power, a signal containing common cell-specific reference signals (CRS), the predetermined layer A receiver for receiving control information indicating that multiplexing using different powers has been applied in
User terminal, characterized in that it comprises a signal addressed to the own terminal from the received signal, and a signal processing unit for decoding on the basis of the control information by the pre-Symbol receiver. In the layer, and a multiplexing unit for multiplexing using a signal for each of a plurality of user terminals, different power,
A generation unit configured to generate, for each layer, control information on the ratio of the different powers, which is information indicating that multiplexing using the different powers is applied;
The transmitted multiplexed with signals, the radio base station, characterized in that it comprises a transmitting section that transmits the control information. In the layer, the signal for each of the plurality of user terminals are multiplexed using different power, wherein the transmission signal comprises common cell-specific reference signals (CRS), a multiplexing unit,
A generation unit that generates control information for each layer indicating that multiplexing using different powers is applied;
The transmitted multiplexed with signals, the radio base station, characterized in that it comprises a transmitting section that transmits the control information. In certain layer, comprising: receiving a multiplexed signal of the signal for each of the plurality of user terminals including own terminal, using a different power,
Receiving information indicating that multiplexing with different powers has been applied in the predetermined layer, the control information regarding the ratio of the different powers in the predetermined layer;
The signal addressed to the own terminal from the signal received by the step of receiving a pre-SL signal, characterized in that it and a step of decoding on the basis of the control information, the wireless communication method of a user terminal. In certain layer, a signal for each of the plurality of user terminals including the own terminal, a multiplexed signal using a different power, comprising: receiving a signal including common cell-specific reference signals (CRS) ,
Receiving control information indicating that multiplexing with different powers has been applied in the predetermined layer;
The signal addressed to the own terminal from the signal received by the step of receiving a pre-SL signal, characterized in that it and a step of decoding on the basis of the control information, the wireless communication method of a user terminal.

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