JP6609357B2 - Radio base station and user terminal - Google Patents

Description

  The present invention relates to a radio base station and a user terminal suitable for a future radio communication system.

  In UMTS (Universal Mobile Telecommunications System), also called W-CDMA (Wideband Code Division Multiple Access), code division multiple access (CDMA) is used as a radio access scheme. CDMA is an intra-cell non-orthogonal radio access scheme. For this reason, in UMTS, transmission power control (TPC) is performed in order to reduce multi-access interference (inter-user interference and intra-cell interference) associated with a near / far problem.

  Moreover, in the uplink of LTE (Long Term Evolution), single carrier frequency division multiple access (SC-FDMA) is used as a radio access method (for example, Non-Patent Document 1). SC-FDMA is an intra-cell orthogonal radio access scheme. Further, in LTE, link adaptation such as scheduling and adaptive modulation and coding (AMC) is performed every transmission time interval (TTI) having a length of 1 msec. For this reason, in LTE, it is not necessary to perform transmission power control for reducing the interference between users in a cell like W-CDMA.

  On the other hand, since LTE is based on one-cell frequency repetition, interference from neighboring cells (inter-cell interference) and propagation loss (path loss) between the user terminal and the radio base station increase. Therefore, in LTE, transmission power control is performed in consideration of inter-cell interference, propagation loss, and the like in order to satisfy required reception quality for uplink signals (for example, Non-Patent Document 1).

3GPP TS 36.213, V8.8.0 “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures”

  By the way, in a future radio communication system called FRA (Future Radio Access) or the like, as an uplink radio access system, non-orthogonal multiple access (NOMA: Non-Orthogonal Multiple Access) premised on interference cancellation on the receiving side. Access) is under consideration.

  In non-orthogonal multiple access, uplink signals from a plurality of user terminals having different channel conditions (for example, propagation loss, SINR (Signal to Interference plus Noise Ratio), SNR (Signal-Noise Ratio), etc.) are transmitted to the same radio resource. Superpose (non-orthogonal multiplexing) and transmitted with different transmission power. On the receiving side, an uplink signal from a desired user terminal is extracted by canceling an uplink signal of another user terminal.

  However, when non-orthogonal multiple access (NOMA) is used in the uplink, when the transmission power control for LTE targeting inter-cell interference reduction is performed on the uplink signals of a plurality of user terminals that are non-orthogonally multiplexed, There is a possibility that the gain of non-orthogonal multiplexing cannot be fully exhibited.

  The present invention has been made in view of the above points, and provides a radio base station and a user terminal capable of performing uplink signal transmission power control suitable for using non-orthogonal multiple access (NOMA) in the uplink The purpose is to do.

  The radio base station of the present invention includes a determination unit that determines whether or not non-orthogonal multiplexing is performed by superimposing uplink signals of a plurality of user terminals, and the uplink signal is non-orthogonal based on a determination result by the determination unit A first transmission power control method for differentiating a reception SINR (Signal to Interference plus Noise Ratio) of the uplink signal used when multiplexing, or a second transmission power control method used when the uplink signal is not non-orthogonal multiplexed Switching information for instructing switching to any one of the above, transmission power determination information used to determine the transmission power of the uplink signal, a transmission unit that transmits to the user terminal, the switching information and the transmission power determination information, A receiving unit that receives an uplink signal transmitted from the user terminal with a transmission power determined based on the transmission power, and the switching information includes the first transmission power control. If for instructing switching to the method, the transmission power determination information is characterized in that based on a predetermined threshold for the channel state between the user terminal and the radio base station.

  ADVANTAGE OF THE INVENTION According to this invention, the transmission power control of the uplink signal suitable when using non-orthogonal multiple access (NOMA) in an uplink can be performed.

It is explanatory drawing of an example of the link adaptation in an uplink. It is explanatory drawing of an example of the non-orthogonal multiple access (NOMA) in an uplink. It is explanatory drawing of the downlink control information used with the transmission power control method which concerns on a 1st aspect. It is a sequence diagram which shows the transmission power control method which concerns on a 1st aspect. It is a flowchart which shows the transmission power control method which concerns on a 1st aspect. It is explanatory drawing of the downlink control information used with the transmission power control method which concerns on a 2nd aspect. It is a sequence diagram which shows the transmission power control method which concerns on a 2nd aspect. It is a block diagram of the radio | wireless communications system which concerns on this Embodiment. It is a whole block diagram of the wireless base station which concerns on this Embodiment. It is a functional block diagram of the radio base station which concerns on this Embodiment. It is a whole block diagram of the user terminal which concerns on this Embodiment. It is a functional block diagram of the user terminal which concerns on this Embodiment.

  FIG. 1 is an explanatory diagram of an example of link adaptation in the uplink. As illustrated in FIG. 1, a radio communication system to which link adaptation is applied includes a radio base station (eNB: Macro eNodeB) that forms a cell and a user terminal (UE: User Equipment).

  In the wireless communication system shown in FIG. 1, a user terminal transmits a sounding reference signal (SRS) in the uplink (step S1). The radio base station uses the sounding reference signal to set the channel gain of the uplink (for example, SINR (Signal to Interference plus Noise Ratio), SNR (Signal-Noise Ratio), RSRQ (Reference Signal Received Quality), etc.) Is also measured (step S2).

  In addition, the radio base station performs user allocation (scheduling) for radio resources (for example, resource blocks (RB)) based on the measured channel state. Also, the radio base station determines a modulation scheme and a coding rate based on the measured channel state (adaptive modulation coding (AMC)).

  The radio base station uses a downlink control channel (PDCCH: Physical Downlink Control Channel, EPDCCH: Enhanced Physical Downlink Control Channel) to indicate radio resource allocation information (RB Assignment), modulation scheme and coding rate. Information (MCS Assignment), retransmission control information (HARQ related signals), and the like are transmitted (step S3).

  The user terminal transmits an uplink shared channel (PUSCH) using the radio resource indicated by the allocation information from the radio base station, the modulation scheme and the coding rate indicated by the modulation and coding scheme information (step S4).

  In this way, in a wireless communication system that performs link adaptation, it is possible to follow instantaneous fading fluctuations by adaptive modulation coding (AMC), so high-speed transmission power control (for example, transmission power control in units of several milliseconds to several tens of milliseconds) ) Is not necessary. On the other hand, in order to satisfy the required reception quality for uplink signals, it is necessary to perform transmission power control in consideration of inter-cell interference and propagation loss.

  Therefore, in a radio communication system that performs link adaptation, an open signal (for example, the above-described uplink shared channel, an uplink control channel (PUCCH: Physical Uplink Control Channel), a reference signal (for example, the above-mentioned uplink loop control and closed loop control) are combined. , SRS), etc.). The open loop control is performed based on a parameter notified by the radio base station in a relatively long cycle and a propagation loss measured by the user terminal.

  On the other hand, the closed loop control is performed based on a TPC (Transmission Power Control) command that the radio base station notifies in a relatively short cycle. The TPC command is determined based on a channel state (for example, SINR, SNR, RSRQ, etc.) between the user terminal and the radio base station. Further, the TPC command may be a value determined based on the difference between the reception SINR averaged at the averaging time t in the radio base station and the target reception SINR.

  Thus, the transmission power control of the uplink signal combining the open loop control and the closed loop control is also referred to as fractional transmission power control (TPC). In fractional TPC, for example, the transmission power of the downlink shared channel (PUSCH) in subframe i is determined by Equation (1).

・・・式（１）
ここで、Ｐ_ＣＭＡＸは、ユーザ端末の最大送信電力である。また、Ｍ_{ＰＵＳＣＨ}は、送信帯域幅である。また、Ｐ_{Ｏ＿ＰＵＳＣＨ}は、伝搬ロスが０である場合の目標受信電力である。また、αは、フラクショナルＴＰＣの重み係数である。ＰＬは、ユーザ端末における伝搬ロスの測定値である。また、Δ_ＴＦは、ＭＣＳ（変調方式、符号化率）に応じたオフセットであり、０であってもよい。ｆ（ｉ）は、ＴＰＣコマンドによる補正値である。

... Formula (1)
Here, P _CMAX is the maximum transmission power of the user terminal. M _PUSCH is a transmission bandwidth. _{PO_PUSCH} is the target received power when the propagation loss is zero. Α is a weighting factor of fractional TPC. PL is a measured value of propagation loss at the user terminal. Δ _TF is an offset according to MCS (modulation scheme, coding rate), and may be zero. f (i) is a correction value by the TPC command.

  According to the fractional TPC, in the open loop control, the PL term is changed according to the propagation loss of the user terminal, and the target received power is set. Specifically, the target reception power of the user terminal at the cell edge is set to be small, and the target reception power of the user terminal at the cell center is set to be large. For this reason, according to the open loop control of said Formula (1), the interference between cells can be reduced. In addition, the parameter in said Formula (1) may be changed suitably.

  By the way, the use of non-orthogonal multiple access (NOMA) is being studied as an uplink radio access scheme. FIG. 2 is an explanatory diagram of an example of NOMA in the uplink. In FIG. 2A, the user terminal (UE) 1 is located in the central part (hereinafter referred to as cell central part) of the cell formed by the radio base station (eNB), and the end part (hereinafter referred to as cell edge part) of the cell. The case where the user terminal (UE) 2 is located is shown in FIG. In FIG. 2A, the propagation loss in the cell increases from the cell center toward the cell edge. For this reason, in the radio base station, the received SINR from the user terminal 2 is lower than the received SINR from the user terminal 1.

  In uplink NOMA, a plurality of user terminals having different channel states (for example, also called channel gains such as propagation loss, SINR, and SNR) are multiplexed on the same radio resource. For example, in FIG. 2A, user terminals 1 and 2 having different received SINRs at a radio base station are multiplexed on the same radio resource. The radio base station extracts a desired uplink signal by removing the interference signal from the received signal by SIC (Successive Interference Cancellation). Specifically, the radio base station decodes uplink signals from user terminals in descending order of reception SINR, and removes the decoded uplink signals.

・・・式（２）
ここで、ｘ_１、ｘ_２は、それぞれ、ユーザ端末１、２からの上り信号を示す。また、Ｐ_１、Ｐ_２は、ユーザ端末１、２からの上り信号の送信電力を示す。また、ｈ_１、ｈ_２は、それぞれ、ユーザ端末１、２と無線基地局との間のチャネル状態を示す。また、ｗは、所定の係数である。 For example, when the uplink signals of the user terminals 1 and 2 are non-orthogonal multiplexed in FIG.

... Formula (2)
Here, x ₁ and x ₂ indicate uplink signals from the user terminals 1 and 2, respectively. P ₁ and P ₂ indicate transmission power of uplink signals from the user terminals 1 and 2. Further, h ₁ and h ₂ indicate channel states between the user terminals 1 and 2 and the radio base station, respectively. W is a predetermined coefficient.

As illustrated in FIG. 2B, the radio base station decodes the uplink signal from the user terminal 1 having a high reception SINR, generates a replica of the uplink signal, and subtracts it from the reception signal y. Next, the radio base station decodes the user terminal 2 having a low received SINR based on the subtraction result of the uplink signal from the user terminal 1. In FIG. 2B, R ₁ and R ₂ indicate uplink transmission rates from the user terminals 1 and 2.

Thus, when NOMA is used as the uplink radio access scheme, the transmission power P ₁ and P ₂ of the user terminals 1 and 2 that are non-orthogonally multiplexed are appropriately controlled to control the throughput at the cell edge and the entire cell. It is desirable to maximize performance indicators such as throughput.

  However, when NOMA is used as an uplink radio access scheme, non-orthogonal multiplexing is performed when, for example, transmission power control using the above equation (1) is performed on uplink signals of a plurality of non-orthogonal multiplexed user terminals. There is a possibility that the system performance improvement by can not be fully demonstrated.

  Specifically, in FIG. 2A, in the transmission power control of the above formula (1), the transmission power of the user terminal 2 at the cell edge is increased and the transmission power of the user terminal 1 at the cell center is decreased. However, the transmission power control (1) is mainly to reduce interference with other cells. In NOMA, since multiple users are multiplexed in the same cell, the difference in received SINR of uplink signals from user terminals 1 and 2 in the radio base station based on the channel gain of the multiple users, rather than reducing interference with other cells. It is desired to control the uplink transmission power so as to increase. For this reason, when the transmission power control of the above formula (1) is performed, there is a possibility that the system performance improvement by non-orthogonal multiplexing cannot be sufficiently exhibited.

  Therefore, the present inventors differ between a transmission power control method when uplink signals of a plurality of user terminals are non-orthogonal multiplexed and a transmission power control method when uplink signals of the plurality of user terminals are not non-orthogonal multiplexed. In this way, when the uplink signals of a plurality of user terminals are non-orthogonal-multiplexed on the same radio resource, the idea of preventing the non-orthogonal multiplexing gain from being sufficiently exerted is obtained.

  In the transmission power control method according to the first aspect of the present invention, the radio base station determines whether or not the uplink signals of a plurality of user terminals are non-orthogonal multiplexed, and the uplink signal is non-orthogonal multiplexed based on the determination result. Switching information instructing switching to either the first transmission power control method used in the case of the transmission or the second transmission power control method used in the case where the uplink signal is not non-orthogonal multiplexed, and the transmission power of the uplink signal Transmission power determination information used for the determination is generated and transmitted to the user terminal. The user terminal determines the transmission power of the uplink signal based on the switching information and the transmission power determination information, and transmits the uplink signal with the determined transmission power.

  According to the transmission power control method according to the first aspect of the present invention, the user terminal switches application of the first transmission power control method or the second transmission power control method based on switching information from the radio base station. When the uplink signals of the user terminals are non-orthogonal multiplexed, it is possible to prevent the gain of non-orthogonal multiplexing from being sufficiently exhibited.

  Further, the present inventors do not calculate the transmission power of the uplink signal by the user terminal itself, but the radio base station determines the transmission power of the uplink signal and notifies the user terminal, thereby allowing a plurality of users. In the case of uplink signal non-orthogonal multiplexing from a terminal, the idea of preventing the non-orthogonal multiplexing gain from being insufficiently obtained was obtained.

  In the transmission power control method according to the second aspect of the present invention, the radio base station determines the transmission power of the uplink signal and transmits transmission power allocation information indicating the determined transmission power to the user terminal. The user terminal transmits the uplink signal with the transmission power indicated by the transmission power allocation information.

  According to the transmission power control method according to the second aspect of the present invention, when the uplink signal from the user terminal is non-orthogonal multiplexed, the transmission power of the uplink signal so that the radio base station can exhibit the gain of non-orthogonal multiplexing. Since this is determined and notified to the user terminal, it is possible to prevent the gain of non-orthogonal multiplexing from being sufficiently exhibited.

Hereinafter, the transmission power control method according to the first and second aspects of the present invention will be described in detail.
(First aspect)
With reference to FIGS. 3-5, the transmission power control method which concerns on a 1st aspect is demonstrated. In the transmission power control method according to the first aspect, the radio base station determines whether or not non-orthogonal multiplexing is performed on uplink signals from a plurality of user terminals. In addition, the radio base station, based on the determination result, the first transmission power control method when the uplink signal is non-orthogonal multiplexed (hereinafter referred to as NOMA power control method) or the uplink signal when the uplink signal is not non-orthogonal multiplexed Switching information for instructing switching to a second transmission power control method (hereinafter referred to as an OMA power control method) and transmission power determination information used for determining the uplink signal are transmitted to the user terminal.

  Here, when the switching information instructs to switch to the NOMA power control method, the transmission power determination information is predetermined for the channel state (for example, SINR, SNR, RSRP, etc.) between the user terminal and the radio base station. It may be a threshold value. On the other hand, when the switching information instructs switching to the OMA power control method, the transmission power determination information may be a TPC command.

  Further, the switching information may be transmitted using a downlink control channel, or may be transmitted using higher layer signaling such as RRC signaling. The transmission power determination information is transmitted using a downlink control channel. Hereinafter, a case where switching information and transmission power determination information are transmitted using a downlink control channel will be described as an example.

  FIG. 3A is an example of downlink control information (DCI) transmitted using the downlink control channel. As shown in FIG. 3A, in the transmission power control method using the above equation (1), DCI (eg, DCI formats 0, 3, 4) includes a TPC command. For example, in FIG. 3A, increase / decrease in the transmission power of the uplink signal is instructed in four stages by a 2-bit TPC command.

  FIG. 3B is an example of DCI used in the transmission power control method according to the first aspect. As shown in FIG. 3B, in the transmission power control method according to the first aspect, DCI includes the above-described switching information and transmission power determination information. As shown in FIG. 3B, the switching information is composed of 1 bit, and “0” or “1” indicates switching to the NOMA power control method or the OMA power control method. For example, “0” instructs switching to the OMA power control method, and “1” instructs switching to the NOMA power control method.

  Whether “0” and “1” instruct switching of the NOMA power control method or the OMA power control method may be defined by a switching rule (described later), and is not limited to the above. Further, the number of bits of the switching information may not be 1 bit.

  In FIG. 3B, when the switching information instructs switching to the OMA power control method, the transmission power determination information may be a TPC command (see FIG. 3A). On the other hand, when the switching information indicates the NOMA power control method, the transmission power determination information is a predetermined threshold for a channel state (for example, SINR, SNR, RSRP, etc.) between the user terminal and the radio base station. Also good.

  FIG. 4 is a sequence diagram showing a transmission power control method according to the first aspect. In FIG. 4, the switching information is transmitted using the downlink control channel (PDCCH, EPDCCH), but may be transmitted using higher layer signaling such as RRC signaling.

  As illustrated in FIG. 4, the radio base station notifies the user terminal of a transmission power control rule that is a rule for performing transmission power control and a transmission power control parameter that is a parameter used for transmission power control ( Step S101). For example, the transmission power control rule and the transmission power control parameter are notified to the user terminal by higher layer signaling such as RRC signaling.

  Specifically, the transmission power control rule includes a switching rule between the NOMA power control method and the OMA power control method, a determination rule between a channel state and a predetermined threshold in the NOMA power control method, and the like. For example, the switching rule instructs switching to the OMA power control method when the switching information is “0”, and instructs switching to the NOMA power control method when the switching information is “1”. Is specified. In addition, in the NOMA power control method, the determination rule is that the transmission power P1 is applied when the channel state is better than a predetermined threshold, and the transmission power P2 is applied when the channel state is worse than the predetermined threshold. Is specified. Note that the transmission power control rule is not limited to the above-described rule.

The transmission power control parameters include the maximum transmission power P _CMAX , the target reception power P _{O_PUSCH} , the weight coefficient α, and the like in the above equation (1) as parameters used in the OMA power control method. The transmission power control parameters include the above-described transmission powers P1, P2 and the like as parameters used in the NOMA power control method.

  The user terminal stores the notified transmission power control rule and transmission power control parameter in the storage unit (step S102). The user terminal transmits an uplink channel state measurement reference signal (for example, SRS) (step S103).

  The radio base station measures the channel state (for example, SINR, SNR, RSRP, etc.) based on the measurement reference signal from the user terminal, and non-orthogonally multiplexes uplink signals of a plurality of user terminals based on the measurement result Is determined (step S104).

  When uplink signals of a plurality of user terminals are non-orthogonal-multiplexed, the radio base station generates switching information instructing switching to the NOMA power control method and transmission power determination information indicating a predetermined threshold Th for the channel state To do. In addition, the radio base station determines a combination (user set, UE set) of a plurality of user terminals that are non-orthogonally multiplexed. On the other hand, when the uplink signals of a plurality of user terminals are not non-orthogonal multiplexed, the radio base station generates switching information for instructing switching to the OMA power control method and a TPC command as transmission power determination information.

  The radio base station transmits DCI including the generated switching information and transmission power determination information to the user terminal using the downlink control channel (step S105). The user terminal switches between the NOMA power control method and the OMA power control method based on the switching information, and sets the uplink signal transmission power based on the transmission power determination information (step S106).

  FIG. 5 is a flowchart showing the detailed operation of the user terminal in step S106. As shown in FIG. 5, the user terminal determines whether to switch to the NOMA power control method based on the switching information (see step S105 in FIG. 4) and the switching rule (see step S101 in FIG. 4). (No) is determined (step S201). For example, according to the switching rule, the user terminal determines to switch to the NOMA power control method when the switching information is “1”, and switches to the OMA power control method when the switching information is “0”. May be determined.

  When switching to the OMA power control method (step S201; NO), the user terminal sets the uplink signal transmission power based on the TPC command (step S105 in FIG. 5) as transmission power determination information (step S202). . For example, the user terminal may set the transmission power of the uplink signal by substituting the correction value by the TPC command into f (i) of the above formula (1).

  On the other hand, when switching to the NOMA power control method (step S201; YES), using downlink measurement reference signals (for example, CRS: Cell-specific Reference Signal, CSI-RS: Channel State Information-Reference Signal), A channel state (for example, SINR, SNR, RSRQ, etc.) between the user terminal and the radio base station is measured (step S203).

  The user terminal sets the transmission power of the uplink signal based on the comparison result between the measured channel state and the predetermined threshold Th indicated by the transmission power determination information. Specifically, the user terminal determines whether or not the measured channel state is higher than a predetermined threshold Th (step S204). Note that the determination in step S204 is merely an example, and different determinations may be made according to the determination rule (step S101 in FIG. 5).

  When the channel state is better than the predetermined threshold Th (step S204; YES), the user terminal sets transmission power P1 (step S205). In this case, since the user terminal is estimated to be located in the center of the cell, transmission power P1 smaller than transmission power P2 described later is used.

  On the other hand, when the channel state is equal to or less than the predetermined threshold Th (step S204; NO), the user terminal sets a transmission power P2 larger than the transmission power P1 (step S206). In this case, since the user terminal is estimated to be located at the cell edge, transmission power P2 larger than transmission power P1 is used.

  As described in steps S203 to S204, when switching to the NOMA power control method (step S201; YES), the user terminal, based on the comparison result between the channel state between the radio base station and a predetermined threshold, Sets uplink signal transmission power. In addition, although transmission power P1 and P2 shall be notified using higher layer signaling, such as RRC signaling, as a transmission power control parameter in step S101 of FIG. 4, it is not restricted to this. The transmission powers P1 and P2 may be notified from the radio base station to the user terminal using the downlink control channel. Further, the uplink signal transmission powers P1 and P2 may be set so that the reception SINRs in the radio base station are sufficiently different.

  As described above, in step S106 of FIG. 4, the user terminal determines the transmission power of the uplink signal. The user terminal transmits an uplink signal with the determined transmission power (step S107). The uplink signal may include an uplink shared channel (PUSCH), an uplink control channel (PUCCH), a reference signal (for example, SRS), and the like.

  According to the transmission power control method according to the first aspect, the user terminal switches application of the NOMA power control method or the OMA power control method based on the switching information from the radio base station. When the uplink signal is non-orthogonal multiplexed, it is possible to prevent the system performance improvement due to non-orthogonal multiplexing from being sufficiently exhibited.

(Modification 1)
In the transmission power control method according to the first aspect, when uplink signals of a plurality of user terminals are not non-orthogonal multiplexed, transmission using transmission power correction information (for example, correction value f (i) in the above equation (1)) is used. Power control is performed. In the transmission power control method according to the first modification, the transmission power correction information is used not only when uplink signals of a plurality of user terminals are not non-orthogonal multiplexed but also when uplink signals of a plurality of user terminals are non-orthogonal multiplexed. The transmission power control that was performed is performed.

  Here, the transmission power correction information is information for correcting the transmission power of the uplink signal, and is, for example, the correction value f (i) by the TPC command in the above equation (1). This transmission power correction information varies depending on whether or not uplink signals of a plurality of user terminals are non-orthogonal multiplexed.

  Specifically, when non-orthogonal multiplexing of uplink signals of a plurality of user terminals is performed, the radio base station transmits an extended TPC command as transmission power determination information to each of the plurality of non-orthogonal multiplexed user terminals. To be notified. The user terminal may set a correction value f (i) different from the case where the uplink signals of a plurality of user terminals are not non-orthogonal-multiplexed for the correction value f (i) based on the extended TPC command. Good.

(Modification 2)
In the transmission power control method according to the first aspect, when the uplink signals of a plurality of user terminals are non-orthogonal multiplexed, transmission power control is performed based on the comparison result between the channel state and a predetermined threshold. In the transmission power control method according to Modification 2, not only when uplink signals of a plurality of user terminals are not non-orthogonal multiplexed, but also when uplink signals of a plurality of user terminals are non-orthogonal multiplexed, the channel state and the predetermined threshold value Transmission power control based on the comparison result is performed.

  In the transmission power method according to the second modification, the set values of the transmission powers P1 and P2 notified as transmission power control parameters may differ depending on whether or not the uplink signals of a plurality of user terminals are non-orthogonal multiplexed. Good. Also, the predetermined threshold for the channel state may be different depending on whether or not the uplink signals of a plurality of user terminals are non-orthogonal multiplexed. Further, the above switching information may not be notified. However, the radio base station notifies whether or not the uplink signals of a plurality of user terminals are non-orthogonal multiplexed.

(Second aspect)
With reference to FIGS. 6-7, the transmission power control method which concerns on a 2nd aspect is demonstrated. In the transmission power control method according to the second aspect, the radio base station determines whether or not the uplink signals of a plurality of user terminals are non-orthogonal-multiplexed, and determines the transmission power of the uplink signal based on the determination result . Further, the radio base station transmits transmission power allocation information indicating the determined transmission power to the user terminal. The user terminal transmits the uplink signal with the transmission power indicated by the transmission power allocation information.

  Thus, in the transmission power control method according to the second aspect, the radio base station determines the transmission power of the uplink signal both when the uplink signal is non-orthogonal multiplexed and when the uplink signal is not non-orthogonal multiplexed. To the user terminal. In particular, the radio base station is determined based on the determination result of whether or not uplink signals are non-orthogonal multiplexed so that system performance improvement by non-orthogonal multiplexing can be exhibited. For this reason, when uplink signals from a plurality of user terminals are non-orthogonal multiplexed, it is possible to prevent the system performance improvement due to non-orthogonal multiplexing from being sufficiently exhibited.

  FIG. 6A is an example of DCI used in a transmission power control method such as LTE, as in FIG. 3A. Since FIG. 6A is the same as FIG. 3A, description thereof is omitted. FIG. 6B is an example of DCI used in the transmission power control method according to the second aspect.

  As illustrated in FIG. 6B, in the transmission power control method according to the second aspect, DCI includes the above-described transmission power allocation information. For example, in FIG. 6B, the transmission power control information includes m (m ≧ 1) bits.

  FIG. 7 is a sequence diagram showing a transmission power control method according to the second aspect. As illustrated in FIG. 7, the user terminal transmits an uplink channel state measurement reference signal (for example, SRS) (step S301).

  The radio base station measures the channel state (for example, SINR, SNR, RSRP, etc.) based on the measurement reference signal from the user terminal, and non-orthogonally multiplexes uplink signals of a plurality of user terminals based on the measurement result And the transmission power of the uplink signal is determined (step S302).

  When uplink signals from a plurality of user terminals are non-orthogonal multiplexed, the radio base station determines a combination (user set, UE set) of the plurality of user terminals, and system performance improvement by non-orthogonal multiplexing is maximized. Thus, the transmission power of the uplink signal of the plurality of user terminals is determined.

  On the other hand, when the uplink signals from a plurality of user terminals are not non-orthogonal-multiplexed, the radio base station determines the uplink signals of the user terminals based on channel states (for example, SINR, SNR, RSRP, etc.) with the user terminals. Determine the transmission power.

  The radio base station transmits transmission power allocation information indicating the determined transmission power to the user terminal using the downlink control channel (step S303). The user terminal sets the transmission power indicated by the transmission power allocation information as the transmission power of the uplink signal (step S304). The user terminal transmits an uplink signal with the set transmission power (step S305).

  According to the transmission power control method according to the second aspect described above, when the uplink signal from the user terminal is non-orthogonal multiplexed, transmission of the uplink signal is performed so that the radio base station can improve the system performance by non-orthogonal multiplexing. Since the power is determined and notified to the user terminal, it is possible to prevent the system performance improvement due to non-orthogonal multiplexing from being sufficiently exhibited. In addition, the radio base station determines the transmission power of the uplink signal itself and notifies the user terminal thereof, thereby increasing the overhead. However, the transmission power of the uplink signal can be controlled more adaptively.

(Configuration of wireless communication system)
Hereinafter, the configuration of the wireless communication system according to the present embodiment will be described. In this radio communication system, the transmission power control method according to the first and second aspects described above is applied.

  FIG. 8 is a schematic diagram of the radio communication system according to the present embodiment. As shown in FIG. 8, the radio communication system 1 includes a radio base station 10 (10A, 10B) and a plurality of user terminals 20 (20A, 20B). The radio base station 10 is connected to the upper station apparatus 30, and the upper 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.

  In the radio communication system 1, the radio base station 10 may be an eNodeB (eNB) that forms a (macro) cell, a transmission point, an RRH (Remote Radio Head) that forms a (small) cell, or an eNodeB (eNB ), Femto base station, pico base station, transmission point, etc. Further, the user terminal 20 may be a mobile terminal or a fixed terminal. The upper station device 30 includes, for example, an access gateway device, a radio network controller (RNC), a mobility management entity (MME), and the like, but is not limited thereto.

  In the radio communication system 1, non-orthogonal multiple access (NOMA) can be used as an uplink radio access scheme. In NOMA, uplink signals from a plurality of user terminals 20 having different channel states (SINR, SNR, propagation loss, etc.) are multiplexed on the same radio resource. Note that orthogonal multiple access such as SC-FDMA can be used as an uplink radio access scheme.

  In the radio communication system 1, non-orthogonal multiple access (NOMA) may be used as a downlink radio access method, or orthogonal multiple access such as OFDMA (Orthogonal Frequency Division Multiple Access) may be used.

  Further, in the radio communication system 1, as downlink communication channels, a downlink shared channel (PDSCH) shared by each user terminal 20, a downlink control channel (PDCCH), an extended downlink control channel (EPDCCH), PCFICH, PHICH, A broadcast channel (PBCH) or the like is used. Downlink data (including user data and higher layer control information) is transmitted by the PDSCH. Downlink control information (DCI) is transmitted by PDCCH and EPDCCH.

  Further, in the wireless communication system 1, as uplink communication channels, an uplink shared channel (PUSCH) shared by each user terminal 20 shared by each user terminal 20, a physical uplink control channel (PUCCH, EPDCCH), random An access channel (PRACH) or the like is used. Uplink data (including user data and higher layer control information) is transmitted by the PUSCH. Also, downlink channel state information (described later), delivery confirmation information (ACK / NACK), and the like are transmitted by PUCCH or PUSCH.

  In the radio communication system 1, a cell-specific reference signal (CRS), a channel state measurement reference signal (CSI-RS), or the like is used as a downlink reference signal. Also, a sounding reference signal (SRS) or the like is used as an uplink reference signal.

  The configuration of the radio base station according to the present embodiment will be described with reference to FIGS.

  FIG. 9 is an overall configuration diagram of the radio base station according to the present embodiment. As shown in FIG. 9, the radio base station 10 includes a transmission / reception antenna (antenna port) 101, an amplifier unit 102, a transmission / reception unit 103 (transmission unit, reception unit), a baseband signal processing unit 104, and a call processing unit. 105 and a transmission path interface 106. A plurality of transmission / reception antennas 101 may be provided.

  For the uplink data, the radio frequency signal received by the transmission / reception antenna 101 is amplified by the amplifier unit 102. The amplified radio frequency signal is frequency converted into a baseband signal in the transmission / reception unit 103. The baseband signal is subjected to predetermined processing (error correction, composite, etc.) by the baseband signal processing unit 104 and then transferred to the upper station apparatus 30 via the transmission path interface 106.

  Downlink data 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 retransmission control (HARQ (Hybrid Automatic Repeat Request)) processing, scheduling, transmission format selection, channel coding, and the like, and transfers the result to the transmission / reception unit 103. In the transmission / reception unit 103, the baseband signal output from the baseband signal processing unit 104 is frequency-converted into a radio frequency signal. The frequency-converted signal is then amplified by the amplifier unit 102 and transmitted from the transmission / reception antenna 101.

  The call processing unit 105 transmits and receives call processing control signals, and manages the state of the radio base station 10 and allocates resources. Note that the processing in the layer 1 processing unit 1041 and the MAC processing unit 1042 may be controlled by the call processing unit 105.

  With reference to FIG. 10, the functional configuration of the baseband processing unit of the radio base station according to the present embodiment will be described. FIG. 10 is a functional block diagram of the baseband signal processing unit 104 of the radio base station 10. As illustrated in FIG. 10, the baseband signal processing unit 104 includes a layer 1 processing unit 1041, a MAC (Medium Access Control) processing unit 1042, an RLC processing unit 1043, a measurement unit 1044, a determination unit 1045, Unit 1046.

  The layer 1 processing unit 1041 mainly performs processing related to the physical layer. In the layer 1 processing unit 1041, for example, processing such as channel decoding, discrete Fourier transform (DFT), demapping, Fourier transform (FFT), data demodulation, and the like is performed on the uplink signal received by the transmission / reception unit 103. Is called. Also, processing such as channel coding, data modulation, mapping, and inverse Fourier transform (IFFT) is performed on the downlink signal transmitted by the transmission / reception unit 103.

  The MAC processing unit 1042 performs processing such as retransmission control (HARQ) in the MAC layer for uplink signals, scheduling for uplink / downlink, selection of PUSCH / PDSCH transmission format, selection of PUSCH / PDSCH resource blocks, and the like.

  The RLC processing unit 1043 performs packet division, packet combination, retransmission control in the RLC layer, and the like on packets received on the uplink / packets transmitted on the downlink.

  The measurement unit 1044 measures the channel state (for example, SINR, SNR, RSRP, etc.) based on the measurement reference signal (for example, SRS). The measurement unit 1044 estimates channel state information (CSI) based on the channel state measurement result. The CSI may include a channel quality identifier (CQI), a rank identifier (RI), and a precoding matrix identifier (PMI).

  The determination unit 1045 determines whether or not the uplink signals of the plurality of user terminals 20 are non-orthogonal multiplexed. Specifically, the determination unit 1045 determines whether or not the uplink signals of the plurality of user terminals 20 are to be non-orthogonal multiplexed based on the channel state measurement result by the measurement unit 1044. In the case of non-orthogonal multiplexing, the determination unit 1045 may determine a combination (user set, UE set) of a plurality of user terminals 20 to be non-orthogonal multiplexed and output the combination to the generation unit 1046.

  The generation unit 1046 generates transmission power control information for controlling the transmission power of the uplink signal based on the determination result by the determination unit 1045. The transmission power control information may include switching information and / or transmission power determination information (first mode, modified examples 1 and 2), or may include transmission power allocation information (second mode).

  Specifically, in the first mode, generation unit 1046 may generate switching information and transmission power determination information based on the determination result by determination unit 1045. As described above, the switching information is a NOMA power control method (first transmission power control method) used when uplink signals are non-orthogonal-multiplexed, or OMA used when uplink signals are not non-orthogonally multiplexed. An instruction to switch (apply) one of the power control methods (second transmission power control method) is given.

  Further, the transmission power determination information is used for determining the transmission power of the uplink signal in the user terminal 20. When the switching information instructs to switch to the NOMA power control method, the transmission power determination information may be a predetermined threshold for the channel state between the user terminal 20 and the radio base station 10. Further, when the switching information instructs switching to the OMA power control method, the transmission power determination information may be a TPC command.

  In addition, the generation unit 1046 outputs the generated switching information and transmission power determination information to the layer 1 processing unit 1041. The switching information may be mapped to the downlink control channel (PDCCH, EPDCCH) in the layer 1 processing unit 1041, or may be mapped to the downlink shared channel (PDSCH) as higher layer control information such as RRC signaling. Good. Also, the transmission power determination information is mapped to the downlink control channel (PDCCH, EPDCCH) in the layer 1 processing unit 1041.

In addition, the generation unit 1046 includes transmission power control rules (such as the switching rule and determination rule described above) and transmission power control parameters (maximum transmission power P _CMAX , target reception power P _{O_PUSCH} , weighting factor α, equation (1) above). Transmission power P1, P2, etc. selected by the user terminal 20 may be generated based on a comparison result between the channel state and a predetermined threshold. The transmission power control rule and the transmission power control parameter may be mapped to the downlink shared channel (PDSCH) as higher layer control information such as RRC signaling in the layer 1 processing unit 1041.

  In the second mode, generation section 1046 determines (assigns) the transmission power of the uplink signal based on the determination result by determination section 1045, and transmission power allocation information indicating the determined (allocated) transmission power. Is generated. When the uplink signals from the plurality of user terminals 20 are not non-orthogonal multiplexed, the generation unit 1046 may determine the uplink signal transmission power based on the channel state with the user terminals 20. On the other hand, when non-orthogonal multiplexing is performed on the uplink signals of the plurality of user terminals 20, the generation unit 1046 determines a combination (user set, UE set) of the plurality of user terminals 20, and the plurality of user terminals 20 are non-orthogonal. The uplink signal transmission power may be determined so that multiple gains can be obtained.

  The generation unit 1046 outputs the generated transmission power allocation information to the layer 1 processing unit 1041. The transmission power allocation information is mapped to the downlink control channels (PDCCH, EPDCCH) in the layer 1 processing unit 1041.

  The configuration of the user terminal according to the present embodiment will be described with reference to FIGS.

  FIG. 11 is an overall configuration diagram of the user terminal 20 according to the present embodiment. As illustrated in FIG. 11, the user terminal 20 includes a transmission / reception antenna (antenna port) 201, an amplifier unit 202, a transmission / reception unit 203 (transmission unit, reception unit), a baseband signal processing unit 204, and a call processing unit 205. And an application unit 206. A plurality of transmission / reception antennas 201 may be provided.

  Uplink data is input from the application unit 206 to the baseband signal processing unit 204. The baseband signal processing unit 204 performs retransmission control (HARQ) processing, scheduling, transmission format selection, channel coding, transmission power setting, and the like, and transfers the result to the transmission / reception unit 203. The transmission / reception unit 203 frequency-converts the baseband signal output from the baseband signal processing unit 204 into a radio frequency signal. The frequency-converted signal is then amplified by the amplifier unit 202 and transmitted from the transmission / reception antenna 201.

  For downlink data, a radio frequency signal received by the transmission / reception antenna 201 is amplified by the amplifier unit 202. The amplified radio frequency signal is frequency-converted into a baseband signal by the transmission / reception unit 203. The baseband signal is subjected to predetermined processing (error correction, composite, etc.) by the baseband signal processing unit 204 and then transferred to the call processing unit 205 and the application unit 206. The call processing unit 205 manages communication with the radio base station 10, and the application unit 206 performs processing related to a layer higher than the physical layer and the MAC layer.

  With reference to FIG. 12, the functional configuration of the baseband processing unit of the user terminal according to the present embodiment will be described. FIG. 12 is a functional block diagram of the baseband signal processing unit 204 of the user terminal 20. The baseband signal processing unit 204 includes a layer 1 processing unit 2041, a MAC processing unit 2042, an RLC processing unit 2043, an acquisition unit 2044, a control method setting unit 2045, and a transmission power determination unit 2046.

  The layer 1 processing unit 2041 mainly performs processing related to the physical layer. In the layer 1 processing unit 2041, for example, processing such as channel decoding, discrete Fourier transform (DFT), demapping, Fourier transform (FFT), and data demodulation is performed on the downlink signal. Also, processing such as channel coding, data modulation, mapping, and inverse Fourier transform (IFFT) is performed on the uplink signal.

  The MAC processing unit 2042 performs retransmission control (HARQ) at the MAC layer for downlink signals, analysis of scheduling information for downlink (specification of PDSCH transmission format, identification of PDSCH resource block), and the like. Also, the MAC processing unit 2042 performs MAC retransmission control on uplink signals, analysis of uplink scheduling information (processing such as specifying a PUSCH transmission format, specifying a PUSCH resource block), and the like.

  The RLC processing unit 2043 performs packet division, packet combination, retransmission control in the RLC layer, and the like on packets received on the uplink and packets transmitted on the downlink received from the application unit 206.

  The acquisition unit 2044 acquires transmission power control information received from the radio base station 10. As described above, the transmission power control information may include both or one of the switching information and the transmission power determination information (first mode, modified examples 1 and 2), or may include transmission power allocation information. (Second embodiment). The acquisition unit 2044 may acquire the transmission power control rule and the transmission power control parameter described above.

  The control method setting unit 2045 sets (switches) the NOMA power control method or the OMA power control method based on the switching information input from the acquisition unit 2044. For example, the control method setting unit 2045 may set the OMA power control method when the switching information is “0”, and may set the NOMA power control method when the switching information is “1”. Note that whether “0” or “1” indicates an OMA power control method or a NOMA power control method may be defined by a switching rule notified from the radio base station 10.

  The transmission power determination unit 2046 determines the transmission power of the uplink signal and instructs the layer 1 processing unit 2041 to transmit the uplink signal with the determined transmission power.

  In the first aspect, when the transmission power determination unit 2046 is switched to the NOMA power control method, the transmission power determination unit 2046 is based on a comparison result between a channel state (for example, SINR, SNR, RSRP) and a predetermined threshold indicated by the transmission power determination information. Thus, the transmission power of the uplink signal may be determined. For example, the transmission power determination unit 2046 determines the transmission power P1 when the channel state is better (larger) than the predetermined threshold, and when the channel state is worse (smaller) than the predetermined threshold than the transmission power P1. A large transmission power P2 is determined. As described above, the transmission powers P1 and P2 may be notified in advance as transmission power control parameters.

  Further, in the first aspect, transmission power determination section 2046 determines the transmission power of the uplink signal based on the TPC command notified as the transmission power determination information when switched to (applied to) the OMA power control method. May be.

  In the first modification, the transmission power determination unit 2046 is based on transmission power correction information (for example, the correction value f (i) in the above equation (1)) that differs depending on whether or not the uplink signal is non-orthogonal multiplexed. Determine the transmission power of the uplink signal. In this case, the acquisition unit 2044 may receive an extended TPC command as transmission power control information from the radio base station. Also in the second modification, the transmission power determination unit 2046 determines the transmission power of the uplink signal based on the comparison result between the channel state and a predetermined threshold indicated by the transmission power determination information. In the first and second modification examples, the control method setting unit 2045 may be omitted, and the above switching information may not be notified to the user terminal 20. However, the radio base station 10 notifies whether or not the uplink signals of the plurality of user terminals 20 are non-orthogonal multiplexed.

  In the second mode, the transmission power determination unit 2046 determines the transmission power indicated by the transmission power allocation information notified from the radio base station 10. In the second aspect, the above-described control method setting unit 2045 may be omitted.

  As described above, according to radio communication system 1 according to the present embodiment, it is possible to perform uplink signal transmission power control suitable for using non-orthogonal multiple access (NOMA) in the uplink.

  Specifically, in the radio communication system 1, the user terminal 20 switches application of the NOMA power control method or the OMA power control method based on the switching information from the radio base station 10. When uplink signals are non-orthogonal multiplexed, it is possible to prevent the system performance improvement due to non-orthogonal multiplexing from being sufficiently exhibited (first mode).

  Also, in the radio communication system 1, when the uplink signal from the user terminal 20 is non-orthogonal multiplexed, the radio base station 10 determines the transmission power of the uplink signal so that the system performance can be improved by non-orthogonal multiplexing. Since it notifies to the user terminal 20, it can prevent that the gain of non-orthogonal multiplexing cannot fully be exhibited (2nd aspect).

  Although the present invention has been described in detail using the above-described embodiments, it is obvious to those skilled in the art that the present invention is not limited to the embodiments described in this specification. The present invention can be implemented as modified and changed modes without departing from the spirit and scope of the present invention defined by the description of the scope of claims. Therefore, the description of the present specification is for illustrative purposes and does not have any limiting meaning to the present invention.

DESCRIPTION OF SYMBOLS 1 ... Wireless communication system 10 ... Wireless base station 20 ... User terminal 30 ... Host station apparatus 40 ... Core network 101 ... Transmission / reception antenna 102 ... Amplifier part 103 ... Transmission / reception part 104 ... Baseband signal processing part 105 ... Call processing part 106 ... Transmission Route interface 201 ... Transmission / reception antenna 202 ... Amplifier 203 ... Transmission / reception unit 204 ... Baseband signal processing unit 205 ... Call processing unit 206 ... Application unit 1041 ... Layer 1 processing unit 1042 ... MAC processing unit 1043 ... RLC processing unit 1044 ... Measurement unit 1045 ... determination unit 1046 ... generation unit 2041 ... layer 1 processing unit 2042 ... MAC processing unit 2043 ... RLC processing unit 2044 ... acquisition unit 2045 ... control method setting unit 2046 ... transmission power determination unit

Claims (2)

A determination unit that determines whether or not non-orthogonal multiplexing is performed by superimposing uplink signals of a plurality of user terminals; and
A first transmission power control method for changing a reception SINR (Signal to Interference plus Noise Ratio) of the uplink signal used when the uplink signal is non-orthogonal-multiplexed based on a determination result by the determination unit, or the uplink Switching information for instructing switching to any one of the second transmission power control methods used when the signals are not non-orthogonal multiplexed, and transmission power determination information used for determining the transmission power of the uplink signal, to the user terminal A transmission unit for transmission;
A receiving unit that receives an uplink signal transmitted from the user terminal with transmission power determined based on the switching information and the transmission power determination information;
When the switching information instructs switching to the first transmission power control method, the transmission power determination information is based on a predetermined threshold for a channel state between the user terminal and a radio base station, Wireless base station. In a non-orthogonal multiplexing in which uplink signals of a plurality of user terminals are superimposed, a first transmission power control method in which a reception SINR (Signal to Interference plus Noise Ratio) of the uplink signal is different, or when the uplink signals are not non-orthogonal multiplexed A receiving unit that receives, from the radio base station, switching information for instructing switching to any of the second transmission power control methods used;
A determination unit that determines transmission power of the uplink signal based on the switching information;
A transmitter that transmits the uplink signal to the radio base station with the determined transmission power, and
When the switching information instructs switching to the first transmission power control method, the determination unit, based on a comparison result between a channel state between the user terminal and the radio base station and a predetermined threshold, A user terminal that determines the transmission power.

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