Radio communication system and base station

A radio communication system includes a first base station, a second base station, a third base station, and a user equipment, wherein the radio communication system includes a determination unit that determines allocation of signal processing that is commonly performed by the first base station and the second base station and signal processing that is performed by the third base station, based on a predetermined reference value; a first signal processor that performs the signal processing allocated to the first base station in accordance with the allocation determined by the determination unit; a second signal processor that performs the signal processing allocated to the second base station in accordance with the allocation determined by the determination unit; and a third signal processor that performs the signal processing allocated to the third base station in accordance with the allocation determined by the determination unit.

TECHNICAL FIELD

An aspect of the present disclosure relates to a radio communication system and a base station.

BACKGROUND ART

In a radio communication system of Long Term Evolution (LTE) and LTE-Advanced (LTE-A), there is known a technology called a centralized radio access network (C-RAN) capable of accommodating a plurality of cells while suppressing a device cost so as to efficiently support an area such as a high-traffic hot spot.

The C-RAN is formed of one or a plurality of remote antenna units (RAUs) which are remote installation type base stations (slave station), and a baseband unit (BBU) that is a base station (master station) that concentrically controls the RAU. The BBU has a function of Layer1to Layer3which are provided to the base station. A digital baseband signal, which is generated in the BBU, is transmitted to the RAU, and is transmitted from a radio frequency (RF) function unit provided to the RAU.

A network line that connects the BBU and the RAU is called a front haul (FH), and a common public radio interface (CPRI) is used as the FH in the LTE.

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

In the current LTE, the functions of Layer 1 (physical layer: L1), Layer 2 (MAC, RLC, PDCP), and Layer 3 (RRC) are implemented on a BBU side. Accordingly, a band, which is necessary for the FH in the case of using 2×2 multiple input multiple output (MIMO), is approximately 16 times greater than a peak rate that is supported in the BBU. For example, as illustrated inFIG. 1, in a case where a system band is 20 MHz, and the BBU supports a radio communication (maximum: 150 Mbps) of 2×2 MIMO, a band necessary for the CPRI is approximately 2.5 Gbps. In addition, in this configuration, the band necessary for the CPRI increments in proportion to an increase in the number of antennas and the system band.

When 5G, which has been currently studied, is introduced, the band necessary for the FH significantly increases in accordance with an improvement in a peak rate. In the case of realizing a peak rate of 10 Gbps, the band necessary for the CPRI is several hundreds of Gbps or greater, and thus it is difficult to cope with a current CPRI standard (maximum: 24.33 Gbps).

Here, an examination has been conducted to reduce a transmission amount through the FH by realizing a part of the layers mounted in the BBU on an RAU side. Various variations have been studied with respect to function sharing between the BBU and RAU. As an example thereof, a plan in which the entirety of a plurality of kinds of processing of Layer 1 are implemented in RAU, and processing of Layer 2 or higher is implemented in the BBU, a plan in which a part of the processing of Layer 1 is implemented on the RAU side, the remaining processing of Layer 1 and the processing of Layer 2 or higher are implemented on the BBU side, and the like have been studied.

In addition, application of a network such as a passive optical network (PON) in which one optical fiber is shared by multiple nodes and Ethernet (registered trademark) to the FH has been studied (FIG. 2) to implement the FH that is cheaper than the CPRI. The networks are shared by the multiple nodes, and thus it is considered that a control of a transmission amount through the FH is necessary in correspondence with a variation of a signal quantity between the nodes.

In addition, it is assumed that processing capability of the RAU is relatively lower than that of the BBU. Accordingly, when simply reducing the transmission amount of the FH, a processing load of the RAU tends to increase. Accordingly, there is a need for a structure capable of appropriately changing the function sharing between the BBU and the RAU in correspondence with a situation in consideration of the processing load of the RAU, communication quality with a user equipment, and the like.

A disclosed technology has been made in consideration of the above-described situations, and an object thereof is to provide a technology capable of appropriately changing function sharing between a BBU and an RAU in a radio communication network according to a C-RAN.

Means for Solving the Problems

According to an aspect of the present disclosure, there is provided a radio communication system including a first base station, a second base station, a third base station that performs a communication with the first base station and the second base station, and a user equipment that performs a communication with the first base station and the second base station. The radio communication system includes a determination unit that determines allocation of signal processing that is commonly performed by the first base station and the second base station and signal processing that is performed by the third base station, based on a predetermined reference value; a first signal processor that performs the signal processing allocated to the first base station in accordance with the allocation that is determined by the determination unit; a second signal processor that performs the signal processing allocated to the second base station in accordance with the allocation that is determined by the determination unit; and a third signal processor that performs the signal processing allocated to the third base station in accordance with the allocation that is determined by the determination unit.

Effect of the Invention

According to an aspect of the present disclosure, a technology is provided that is capable of appropriately changing function sharing between a BBU and an RAU in a radio communication network according to a C-RAN.

MODES FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the invention is described by referring to the accompanying drawings. Note that, the following embodiment is illustrative only, and an embodiment to which the invention is applicable is not limited to the following embodiment. For example, in a radio communication system according to this embodiment, a system of a method in conformity to an LTE or 5G is assumed, but the invention is applicable to other methods without limitation to the LTE or 5G. Furthermore, in this specification and claims, “LTE” is used in wide meaning including not only a communication method corresponding to Release 8 or 9 of 3GPP but also a corresponding fifth generation communication method subsequently to Release 10, 11, 12, 13, or 14 of 3GPP.

FIG. 3is a view illustrating a system configuration example of the radio communication system according to the embodiment. As illustrated inFIG. 3, the radio communication system according to this embodiment includes a BBU1, an RAU2a,an RAU2b,and a user equipment UE. In the following description, in the case of not discriminating the RAU2aand the RAU2b,the RAU2aand the RAU2bwill be described as “RAU2”. InFIG. 3the RAU2aand the RAU2bare illustrated, but three or greater of RAUs2may be included.

The BBU1may be referred to as an aggregate base station, a master station, or a base station (enhanced Node B (eNB)) in a simple manner. The RAU2may be referred to as a satellite base station, a slave station, or a base station in a simple manner. The BBU1and the RAU2transmits and receives a predetermined signal through an FH.

In addition, the BBU1performs a control so that the RAU2aand the RAU2btransmits (cooperatively transmits) a DL signal to a user equipment UE in cooperation with each other. Similarly, the BBU1performs a control so that composition, selection, and the like of a UL signal, which is received from each of the RAU2aand the RAU2b,are performed to receive (cooperatively receive) the UL signal from the user equipment UE on the BBU1side in a cooperative manner.

<Function Sharing between BBU and RAU>

FIGS. 4A and 4Bare views illustrating a function sharing example between a BBU and an RAU.FIG. 4Aillustrates a function sharing example in a UL, andFIG. 4Billustrates a function sharing example in a DL. Boundaries “U1” to “U9” inFIG. 4Arepresent boundaries of a plurality of kinds of processing of UL which are respectively performed in the BBU1and the RAU2. For example, in the case of function sharing in the boundary “U6”, processing according to a function of Layer 2 or higher is performed on a BBU1side, and processing according to a function of Layer 1 is performed on an RAU2side. Furthermore, for example, in the case of function sharing at the boundary “U2”, among a plurality of kinds of processing according to the function of Layer 1, processing up to an FFT is performed on the RAU2side, and processing subsequent to resource demapping (resource element demapping) is performed on the BBU1side. The boundary “U1” corresponds to a configuration of connecting the BBU1and the RAU2by using a CPRI. Furthermore, in a case where a communication by an MIMO is not performed in the UL, signal detection processing is omitted.

Similarly, boundaries “D1” to “D10” inFIG. 4Brepresent boundaries of a plurality of kinds of processing of the DL which are respectively performed in the BBU1and the RAU2. For example, in the case of function sharing at the boundary “D7”, processing according to the function of Layer 2 or higher is performed on the BBU1side, and processing according to the function of Layer 1 is performed on the RAU2side. In addition, for example, in the case of function sharing at the boundary “D2”, among the plurality of kinds of processing according to the function of Layer 1, processing up to resource element mapping is performed on the BBU1side, and OFDM signal generation is performed on the RAU2side. The boundary “D1” corresponds to a configuration of connecting the BBU1and the RAU2by using the CPRI. Furthermore, in a case where a communication by the MIMO is not performed in the DL, processing layer mapper and processing of precoding are not performed.

The BBU1, the RAU2a,and the RAU2baccording to this embodiment are capable of arbitrarily changing that the function sharing is to be made (signal processing is to be shared) at which boundary among boundaries “U1” to “U9” in an UL. Similarly, the BBU1, the RAU2a,and the RAU2baccording to this embodiment are capable of arbitrarily changing that the function sharing is to be made (signal processing is to be shared) at which boundary among boundaries “D1” to “D10” in a DL. Furthermore, the BBU1, the RAU2a,and the RAU2baccording to this embodiment may be configured to commonly change the function sharing in a unit of the RAU2aand the RAU2b(in other words, the same function sharing may be allowed to be made in the RAU2aand the RAU2b), or to commonly change the function sharing in a unit of the user equipment UE (in other words, the same function sharing may be allowed to be made with respect to the same user equipment UE). In addition, the function sharing may be changed independently in the UL and the DL.

(Switching of Function Sharing in UL)

FIG. 5is a sequence diagram illustrating an example of a procedure for switching function sharing in the UL.

In step S101, the BBU1or the RAU2determine sharing (determine function sharing) between signal processing performed by the BBU1and signal processing performed by the RAU2(signal processing that is commonly performed by the RAU2aand the RAU2b). In this embodiment, the boundaries (“U1” to “U9”) of the function sharing between the BBU1and the RAU2may be determined in the BBU1or the RAU2.

More specifically, the BBU1or the RAU2determines allocation of signal processing performed by the RAU2and signal processing performed by the BBU1on the basis of a predetermined reference value. For example, a table, in which a range of a predetermined reference value and the boundaries “U1” to “U9” in the UL are correlated one-to-one, is retained in the BBU1or the RAU2. The BBU1or the RAU2may determine allocation of the signal processing performed by the RAU2and the signal processing performed by the BBU1by comparing the table and the predetermined reference value with each other. In addition, a predetermined threshold value may be retained in the BBU1or the RAU2, and the BBU1or the RAU2may determine that the function sharing is to be made at which boundary among the boundaries “U1” to “U9” through determination of whether or not the predetermined reference value is equal to or greater than the predetermined threshold value. Acquisition (measurement) of the predetermined reference value may be performed by the BBU1or the RAU2. The BBU1or the RAU2may notify a counterpart (the RAU2or the BBU1) of an acquisition result (or measurement result) as necessary. A specific example of the predetermined reference value will be described later.

The BBU1or the RAU2notifies a counterpart (the RAU2or the BBU1) of the determination result of the function sharing. Furthermore, in a case where the RAU2makes a determination of the function sharing, the notification of the determination result of the function sharing is made between the RAU2aand the RAU2b.In addition, in a case where the RAU2makes a determination of the function sharing, the RAU2aand the RAU2bmay apply an identifier, which indicates that signal processing according to which function has been performed on the RAU2aside or on the RAU2bside, to header information of a UL signal that is transmitted in a procedure in step S113aand step S113bto be described later. According to this, the function sharing of the UL can be changed in a dynamic manner.

In step S111a,the RAU2areceives an UL signal that is transmitted from the user equipment UE. Similarly, in step S11b,the RAU2breceives an UL signal that is transmitted from the user equipment UE. Subsequently, the RAU2aperforms signal processing to be performed by the RAU2a(S112a), and transmits a signal after being subjected to the signal processing to the BBU1(S113a). Similarly, the RAU2bperforms signal processing to be performed by the RAU2b(S112b), and transmits a signal after being subjected to the signal processing to the BBU1(S113b).

In step S114, the BBU1performs signal processing to be performed by the BBU1(S114). Here, the BBU1performs cooperative reception by using the UL signal transmitted from the RAU2aand the UL signal transmitted from the RAU2b.A method of performing the cooperative reception may be any method. For example, the BBU1may select a UL signal from any one side among UL signals received from the RAU2aand UL signals received from the RAU2b,or may combine and receive the UL signals from the both sides. In addition, in the case of selecting a UL signal from any one side, the BBU1may measure reception quality (SNR, SINR, and the like) of the UL signals from the RAU2aand the RAU2bto select a UL signal in which reception quality of the UL signal is satisfactory.

Furthermore, the procedure in step S101to S114described above may be repetitively performed with a predetermined interval. According to this, for example, the function sharing of the UL can be switched in a dynamic manner on the basis of a variation in reception quality of the UL signal or a DL signal, a variation in a processing load of the RAU2, and the like.

(Switching of Function Sharing in DL)

FIG. 6is a sequence diagram illustrating an example of a procedure for switching function sharing in the DL. Furthermore, in this embodiment, the boundaries “D1” to “D10” of function sharing between the BBU1and the RAU2may be determined in the BBU1or the RAU2.

In step S201, the BBU1or the RAU2determines sharing (determines function sharing) between signal processing performed by the BBU1and signal processing performed by the RAU2(signal processing that is commonly performed by the RAU2aand RAU2b). In this embodiment, the boundaries (“D1” to “D10”) of the function sharing between the BBU1and the RAU2may be determined in the BBU1or the RAU2.

More specifically, the BBU1or the RAU2determines allocation of signal processing performed by the RAU2and signal processing performed by the BBU1on the basis of a predetermined reference value. For example, a table, in which a range of a predetermined reference value and the boundaries “D1” to “D10” in the DL are correlated one-to-one, is retained in the BBU1or the RAU2. The BBU1or the RAU2may determine allocation of the signal processing performed by the RAU2and the signal processing performed by the BBU1by comparing the table and the predetermined reference value with each other. In addition, a predetermined threshold value may be retained in the BBU1or the RAU2, and the BBU1or the RAU2may determine that the function sharing is to be made at which boundary among the boundaries “D1” to “D10” through determination of whether or not the predetermined reference value is equal to or greater than the predetermined threshold value. Acquisition (measurement) of the predetermined reference value may be performed by the BBU1or the RAU2. The BBU1or the RAU2may notify a counterpart (the RAU2or the BBU1) of an acquisition result (or measurement result) as necessary.

The BBU1or the RAU2notifies a counterpart (the RAU2or the BBU1) of the determination result of the function sharing. Furthermore, in a case where the RAU2determines the function sharing, the determination may be made by both of the RAU2aand the RAU2bor the determination may be made by any one of the RAU2aand the RAU2b,and a counterpart (the RAU2bor the RAU2a) may be notified of the determination result. In addition, in a case where the BBU1determines the function sharing, the BBU1may apply an identifier, which indicates that signal processing according to which function has been performed on the BBU1side, to header information of a DL signal that is transmitted in a procedure of step S211to be described later. According to this, the function sharing of the DL can be switched in a dynamic manner.

The BBU1performs signal processing to be performed by the BBU1with respect to a DL signal to be transmitted to the user equipment UE (S211), and transmits the DL signal after being subjected to the signal processing to the RAU2aand the RAU2b(S212a,S212b). Here, the BBU1performs a control so that the RAU2aand the RAU2btransmit (cooperatively transmit) the DL signal to the user equipment UE in cooperation with each other in a procedure of step S211. For example, the BBU1may be allowed to transmit a signal that is generated to both of the RAU2aand the RAU2b,or may be allowed to transmit the DL signal to any one of the RAU2aand the RAU2b.In a case where any one of the RAU2aand the RAU2bis selected, reception quality of the DL signal between the user equipment UE and the RAU2aand reception quality of the DL signal between the user equipment UE and the RAU2bmay be allowed to be fed back from the user equipment UE to the BBU1, and the BBU1may allowed to select the RAU2in which the reception quality is satisfactory. In addition, the BBU1may allow the user equipment UE to feed back a DL signal propagation state (for example, channel information and the like) between the user equipment UE and the RAU2aand the RAU2bto the BBU1, and the BBU1may be allowed to generate a DL signal to be transmitted to the RAU2aand a DL signal to be transmitted to the RAU2bon the basis of the propagation state that is fed back and may be allowed to transmit the DL signals which are generated to the RAU2aand the RAU2b,respectively.

Subsequently, the RAU2aand the RAU2brespectively perform signal processing to be performed by the RAU2aor the RAU2bon the basis of function sharing (S213a,S213b), and respectively transmit DL signals after being subjected to the signal processing to the user equipment UE (S214a,S214b).

Furthermore, the procedure of step S201to S214described above may be repetitively performed with a predetermined interval. According to this, for example, the function sharing of the DL can be changed in a dynamic manner on the basis of a variation in reception quality of the UL signal or the DL signal, a variation in a processing load of the RAU2, and the like.

(Example of Predetermined Reference Value)

For example, the predetermined reference value may be a value of a signal to interference plus noise power ratio (SINR) or a signal to noise ratio (SNR) of the UL signal received from the user equipment UE or the DL signal that is received by a user equipment UE. As a table in which a range of the SINR or the SNR and the boundaries in the UL or the DL are correlated with each other, for example, a table, in which correlation of (boundaries “U9”, “U8”, “U7”, “U6”, “U5”, “U4”, “U3”, “U2”, and “U1”) or (boundaries “D10”, “D9”, “D8”, “D7”, “D6”, “D5”, “D4”, “D3”, “D2”, and “D1”) is made in the order from a side in which the range of the SINR or the SNR is great, may be used. That is, as the SINR or the SNR becomes greater, the number of processing performed on the RAU2side may be set to increase. In addition, as another example, in a case where the SINR or the SNR is equal to or greater than a predetermined threshold value, the function sharing may be divided at a predetermined boundary in the UL or the DL (for example, the function sharing may be divided at “U6”, “D7”, and the like), and in a case where the SINR or the SNR is less than the predetermined threshold value, the function sharing may be divided at a predetermined boundary (for example, “U2”, “D2”, and the like) in the UL or the DL.

Acquisition (measurement) of the SINR or the SNR may be performed in the RAU2or the BBU1. In addition, in a case where the measurement is performed in the RAU2, a side, in which an SINR or an SNR which is measured in the RAU2aand an SINR or an SNR which is measured in the RAU2bis greater, may be selected and used. In addition, in a case where the function sharing is changed for each user equipment UE, the RAU2or the BBU1may acquire (measure) the SINR or the SNR for each user equipment UE on the basis of series of a reference signal or a resource position allocated to the user equipment UE. In this case, the RAU2may be notified of the series of the reference signal or the resource position allocated to the user equipment UE from the BBU1in advance. In addition, in the case of changing the function sharing for unit of the RAU2, for example, the changing of the function sharing per unit of the RAU2may be implemented by dividing scheduling time of a radio resource of the DL or UL for each user equipment UE.

In addition, the predetermined reference value may be a cyclic redundancy check (CRC) check success rate of the UL signal that is received from the user equipment UE or the DL signal that is received by the user equipment UE. The CRC check success rate represents a probability of determination as being correct in the CRC that is included in a radio signal transmitted with a predetermined physical channel. In a case where radio quality between the user equipment UE and the RAU2deteriorates, the CRC check success rate decreases.

As a table in which a range of the CRC check success rate and the boundaries in the UL or the DL are correlated with each other, for example, a table, in which correlation of (boundaries “U9”, “U8”, “U7”, “U6”, “U5”, “U4”, “U3”, “U2”, and “U1”) or (boundaries “D10”, “D9”, “D8”, “D7”, “D6”, “D5”, “D4”, “D3”, “D2”, and “D1”) is made in the order from a side in which a range of the CRC check success rate is high, may be used. That is, as the CRC check success rate is high, the number of processing performed on the RAU2side may be set to increase. In addition, as another example, in a case where the CRC check success rate is equal to or greater than a predetermined threshold value, the function sharing may be divided at a predetermined boundary in the UL or the DL (for example, the function sharing may be divided at “U6”, “D7”, and the like), and in a case where the CRC check success rate is less than the predetermine threshold value, the function sharing may be divided at a predetermined boundary (for example, “U2”, “D2”, and the like) in the UL or the DL.

Acquisition (measurement) of the CRC check success rate may be performed by the RAU2or the BBU1. In addition, in a case where the measurement is performed by the RAU2, a side, in which a CRC check success rate measured by the RAU2aand a CRC check success rate measured by the RAU2bis greater, may be selected and used. Furthermore, the CRC check is performed when performing decoding processing, and thus it is preferable that a device (BBU1or RAU2), which performs processing according to the decoding, performs acquisition of the CRC check success rate.

In addition, the predetermined reference value may be the number of retransmission times of the UL signal or the DL signal from the user equipment UE in a predetermined period (or an average value of the number of retransmission times in the predetermined period). For example, the number of retransmission times of the DL signal to the user equipment UE in a predetermined period may be counted as the number of notification times of NAK by a PUCCH or a PUSCH.

As a table in which a range of the number of retransmission times and the boundaries in the UL or the DL are correlated with each other, for example, a table, in which correlation of (boundaries “U9”, “U8”, “U7”, “U6”, “U5”, “U4”, “U3”, “U2”, and “U1”) or (boundaries “D10”, “D9”, “D8”, “D7”, “D6”, “D5”, “D4”, “D3”, “D2”, and “D1”) is made in the order from a side in which a range of the number of retransmission times is small, may be used. That is, as the number of retransmission times is small, processing performed on the RAU2side may be set to increase. In addition, as another example, in a case where the number of retransmission times is less than a predetermined threshold value, the function sharing may be divided at a predetermined boundary (for example, “U6”, “D7”, and the like) in the UL or the DL, and in a case where the number of retransmission times is equal to or greater than the predetermined threshold value, the function sharing may be divided at a predetermined boundary (for example, “U2”, “D2”, and the like) in the UL or the DL.

Acquisition (measurement) of the number of retransmission times may be performed in the RAU2or the BBU1. In addition, the measurement is performed by the RAU2, an average value of the number of measurement times in the RAU2aand the number of measurement times in the RAU2bmay be used, and a side, in which the number of measurement times is greater, may be selected and used. Furthermore, reception of the NAK is performed with a signal after being decoded, and thus it is preferable that the acquisition of the number of retransmission times is performed by a device (the BBU1, the RAU2a,or the RAU2b) that performs processing in accordance with decoding.

In addition, the predetermined reference value may be a channel estimation error of the UL signal that is received from the user equipment UE or the DL signal that is received by the user equipment UE. The channel estimation error represents an index indicating that a variation (dispersion) occurs to a certain extent between an average value of results obtained by performing channel estimation by using a plurality of reference signals included in the UL signal that is received from the user equipment UE or the DL signal which the user equipment UE receives, and a result obtained by performing channel estimation of each of the reference signals. In a case where radio quality between the user equipment UE and the RAU2deteriorates, the channel estimation error increases.

As a table in which a range of the channel estimation error and the boundaries in the UL or the DL are correlated with each other, for example, a table, in which correlation of (boundaries “U9”, “U8”, “U7”, “U6”, “U5”, “U4”, “U3”, “U2”, and “U1”) or (boundaries “D10”, “D9”, “D8”, “D7”, “D6”, “D5”, “D4”, “D3”, “D2”, and “D1”) is made in the order from a side in which a range of the channel estimation error is small, may be used. That is, as the range of the channel estimation error is small, processing performed on the RAU2side may be set to increase. In addition, as another example, in a case where the channel estimation error is less than a predetermined threshold value, the function sharing may be divided at a predetermined boundary (for example, “U6”, “D7”, and the like) in the UL or the DL, and in a case where the channel estimation error is equal to or greater than the predetermined threshold value, the function sharing may be divided at a predetermined boundary (for example, “U2”, “D2”, and the like) in the UL or the DL.

In addition, the predetermined reference value may be the magnitude of a processing load of the RAU2(a processor utilization rate, a memory utilization rate, the amount of data between the BBU1and the RAU2, and the like). With regard to the magnitude of the processing load of the RAU2, a processing load of the RAU2, which is the greatest between a processing load of the RAU2aand a processing load of the RAU2b,may be used. As a table in which a range of the magnitude of the processing load of the RAU2and the boundaries in the UL or the DL are correlated with each other, for example, a table, in which correlation of (boundaries “U1”, “U2”, “U3”, “U4”, “U5”, “U6”, “U7”, “U8”, and “U9”) or (boundaries “D1”, “D2”, “D3”, “D4”, “D5”, “D6”, “D7”, “D8”, “D9”, and “D10”) is made in the order from a side in which a range of the processing load of the RAU2is great, may be used. That is, as the processing load of the RAU2is great, processing of Layer1, which is performed on the RAU2side, is set to decrease. In addition, as another example, in a case where the magnitude of the processing load of the RAU2is less than a predetermined threshold value, the function sharing may be divided at a predetermined boundary (for example, “U6”, “D7”, and the like) in the UL or the DL, and in a case where the magnitude of the processing load is equal to or greater than the predetermined threshold value, the function sharing may be divided at a predetermined boundary (for example, “U2”, “D2”, and the like) in the UL or the DL.

The processing load of the RAU2may be measured by the RAU2aand/or the RAU2b,or may be estimated by the BBU1on the basis of the amount of data transmitted to the RAU2aand/or the RAU2bfrom the BBU1, the amount of data that is scheduled by the BBU1with respect to the RAU2aand/or the RAU2b,and the like.

In addition, the predetermined reference value may relate to whether or not at least one of the number of antennas provided to the RAU2aand the number of antennas provided to the RAU2bis equal to or greater than the number of antennas provided to the user equipment UE. For example, in a case where at least one of the number of antennas provided to the RAU2aand the number of antennas provided to the RAU2bis equal to or greater than the number of antennas provided to the user equipment UE, reception of the UL signal by using the MIMO is possible even in the RAU2, and thus the function sharing may be made at a predetermined boundary (for example, “U6” and the like in the UL. In contrast, in a case where the number of antennas provided to each of the RAU2aand the RAU2bis smaller than the number of antennas provided to the user equipment UE, it is determined that it is necessary to perform reception of the UL signal by using the MIMO on the BBU1side, and the function sharing may be made at a predetermined boundary (for example, “U2” and the like).

Note that the number of the antennas included in the user equipment UE may be reported from the user equipment UE to the BBU1by a higher layer, etc.

(Operation Example of a Process of Switching Function Sharing in UL)

FIGS. 7A and 7Bare views illustrating an operation example of function sharing changing processing in the UL.FIGS. 7A and 7Billustrate an operation example in the case of using the SINR as the predetermined reference value. Note that, inFIGS. 7A and 7B, a part of various kinds of signal processing of Layer 1 as illustrated inFIG. 4Ais not illustrated, and boundaries “U2”, “U4”, and “U6” illustrated inFIGS. 7A and 7Brespectively correspond to the boundaries “U2”, “U4”, and “U6” illustrated inFIG. 4(a). Note that the boundaries illustrated inFIGS. 7A and 7Bare examples, and it is not intended to limit the boundaries. For example, the boundary “U2” inFIGS. 7A and 7Bmay be the boundary “U3”, and the boundary “U4” inFIGS. 7A and 7Bmay be the boundary “U5”. In addition, although not illustrated inFIGS. 7A and 7B, the function sharing may be changed at any one of boundaries “U1”, and “U7” to “U9”.

In addition, description is made on the assumption that the BBU1has a function of measuring the SINR of the UL signal that is received from the user equipment UE, and determination of the function sharing is made on the BBU1side on the basis of the SINR measured in the BBU1.

As illustrated inFIG. 7A, in a case where the SINR of the UL signal received from the user equipment UE is equal to or greater than a predetermined threshold value, that is, reception quality of the UL signal is satisfactory, the BBU1determines that the entirety of a plurality of kinds of signal processing in accordance with Layer1are performed on the RAU2aside and on RAU2bside (determines that function sharing is made at the region “U6”). Subsequently, the BBU1notifies the RAU2aand the RAU2bof the determination result.

The RAU2aand the RAU2bperform the entirety of the plurality of kinds of signal processing in accordance with Layer1on the basis of the determination result that is transmitted in the notification, and transmit a UL signal that is decoded to the BBU1through the FH. The BBU1selects any one UL signal among UL signals which are received from the RAU2aand the RAU2band are decoded, and performs signal processing subsequent to Layer2with respect to the UL signal that is selected.

On the other hand, as illustrated inFIG. 7B, in a case where the SINR of the UL signal received from the user equipment UE is less than a predetermined threshold value, that is, in a case where reception quality of the UL signal is not satisfactory, the BBU1determines that among the plurality of kinds of signal processing according to Layer1, processing up to FFT processing is performed on the RAU2aside and the RAU2bside, and the subsequent signal processing is performed on the BBU1side (determines that function sharing is made at the region “U2”). Then, the BBU1notifies the RAU2aand the RAU2bof the determination result.

The RAU2aand the RAU2bperform signal processing up to the FFT processing among the plurality of kinds of signal processing according to Layer1on the basis of the determination result that is transmitted in the notification, and transmits the UL signal after the FFT processing to the BBU1through the FH. The BBU1performs cooperative reception (for example, minimum mean squared error (MMSE) composition, composition by maximum likelihood detection (MLD), and the like) with respect to the UL signals which are received from the RAU2aand the RAU2band are subjected to the FFT processing, and performs signal processing subsequent to Layer2.

Furthermore, in the above-described operation example, in a case where function sharing is changed for each user equipment UE, the BBU1may notify the RAU2aand the RAU2bof a determination result for each user equipment UE and information (for example, a radio resource position in a frequency direction, and the like) for identification of the user equipment UE in correlation with each other so that the RAU2aand the RAU2bcan recognize that which radio resource is scheduled to which a user equipment UE on the RAU2aside and the RAU2bside.

According to this operation, in a case where reception quality of the UL signal received from the user equipment UE is satisfactory, the entirety of the plurality of kinds of signal processing of Layer 1 are performed on the RAU2side, and thus it is possible to secure reception performance of the UL signal while reducing the transmission amount through the FH. Furthermore, since the transmission amount through the FH is reduced, it is possible to suppress occurrence of transmission delay. On the other hand, in a case where reception quality of the UL signal received from the user equipment UE is not satisfactory, the cooperative reception is performed on the BBU1side, and thus it is possible to secure reception performance of the UL signal.

(Operation Example of a Process of Switching Function Sharing IN DL)

FIGS. 8A and 8Bare views illustrating an operation example of a process of switching the function sharing in the DL.FIGS. 8A and 8Billustrate an operation example in the case of using a processing load of the RAU2as a predetermined reference value. Note that, inFIGS. 8A and 8B, a part of the plurality of kinds of signal processing of Layer 1, which are illustrated inFIG. 4B, is omitted. Boundaries “D2”, “D4”, and “D7” illustrated inFIGS. 8A and 8Brespectively correspond to the boundaries “D2”, “D4”, and “D7” illustrated inFIG. 4B. The boundaries illustrated inFIGS. 8A and 8Bare illustrative only, and there is no limitation to the boundaries. For example, the boundary “D2” inFIGS. 8A and 8Bmay be the boundary “D3”, and the boundary “D4” inFIGS. 8A and 8Bmay be the boundary “D6” or “D7”. In addition, although not illustrated inFIGS. 8A and 8B, the function sharing may be changed at any one of the boundaries “D1”, and “D8” to “D10”.

In the example ofFIGS. 8A and 8B, description is made on the assumption that the RAU2a(or the RAU2b) measures a processing load thereof and notifies the BBU1of the processing load, and the function sharing is determined on the BBU1side.

As illustrated inFIG. 8A, in a case where the processing load of the RAU2a(or the RAU2b) is less than a predetermined threshold value, the BBU1determines that the entirety of the plurality of signal processing according to Layer 1 are performed on the RAU2aside and the RAU2bside (determines that function sharing is made at the region “D7”. Furthermore, BBU1transmits a DL signal that is subjected to the signal processing according to Layer 2 to the RAU2aand the RAU2bthrough the FH on the basis of the determination result. In addition, when transmitting the DL signal to the RAU2aand the RAU2b,the BBU1may perform the transmission by applying a predetermined header to the DL signal, and by applying an identifier, which indicates that signal processing up to Layer 2 has been performed, to the header. In the case ofFIG. 8A, in the RAU2aand the RAU2b,the entirety of the plurality of kinds of signal processing according to Layer 1 are performed.

Furthermore, in the case ofFIG. 8A, the BBU1may be configured to transmit the DL signal, which is subjected to the signal processing according to Layer 2, to any one of the RAU2aand the RAU2b.According to this, it is possible to further reduce the amount of signals through the FH.

On the other hand, as illustrated inFIG. 8B, in a case where the processing load of the RAU2(or RAU2b) is equal to or greater than a predetermined threshold value, the BBU1determines that among the plurality of kinds of signal processing according to Layer 1, processing up to resource element mapping is performed on the BBU1side (determines that function sharing is made at the region “D2”). In addition, the BBU1transmits the DL signal, which is subjected to the signal processing up to the resource element mapping, to the RAU2aand the RAU2bthrough the FH on the basis of the determination result. Furthermore, the BBU1may perform another precoding processing with respect to the DL signal to be transmitted to the RAU2aand the DL signal to be transmitted to the RAU2bon the basis of a propagation state (channel information and the like) of the DL signal between the RAU2aand the RAU2b,and the user equipment UE.

When transmitting the DL signal to the RAU2aand the RAU2b,the BBU1may perform the transmission by applying a predetermined header to the DL signal, and by applying an identifier, which indicates that signal processing up to the resource element mapping has been performed, to the header. In the case ofFIG. 8B, in the RAU2aand the RAU2b,signal processing in accordance with OFDM signal generation is performed.

According to this operation, when the processing load of the RAU2is tight, more kinds of signal processing are set to be performed on the BBU1side, and thus it is possible to reduce the processing load of the RAU2. In addition, in a case where the processing load of the RAU2is low, more kinds of signal processing are set to be performed on the RAU2side, and thus it is possible to reduce the transmission amount through the FH. In addition, since the transmission amount through the FH is reduced, it is possible to suppress occurrence of transmission delay.

(Supplementary Item with Respect to Procedure)

When function sharing is changed, the BBU1or the RAU2may stop scheduling of the DL and the UL for a predetermined period of time. According to this, it is possible to avoid a possibility that the function sharing is changed during transmission of the DL signal or the UL signal, and thus a signal is damaged.

Functional configuration examples of the BBU1and the RAU2are described, which are for implementing the operation of the above-described embodiment.

FIG. 9is a view illustrating a functional configuration example of the BBU according to this embodiment. As illustrated inFIG. 9, the BBU1includes an inter-RAU signal transmission unit101, an inter-RAU signal reception unit102, a higher layer processing unit103, and a function sharing determination unit104. Furthermore,FIG. 9illustrates only function units, which particularly related to this embodiment, of the BBU1, and the BBU1also has a function (not illustrated) of performing at least an operation in conformity to LTE (including 5G). In addition, the functional configuration illustrated inFIG. 9is illustrative only. Function classification or the name of the function units may be arbitrary as long as the operation according to this embodiment can be executed.

The inter-RAU signal transmission unit101has a function of performing signal processing with respect to a DL signal received from the higher layer processing unit103on the basis of function sharing as a notification from the function sharing determination unit104or the RAU2to generate a signal, and of transmitting the signal that is generated to the RAU2through the FH. The inter-RAU signal reception unit102has a function of performing signal processing with respect to an UL signal received from the RAU2through the FH on the basis of the function sharing as a notification from the function sharing determination unit104or the RAU2, and of transmitting the resultant signal to the higher layer processing unit103.

In addition, the inter-RAU signal transmission unit101transmits the signal, which is subjected to the signal processing, to any one of a plurality of the RAUs2or the plurality of RAUs2(performs cooperative transmission). In addition, the inter-RAU signal reception unit102performs signal processing by using one signal or a plurality of signals among a plurality of signals which are subjected to the signal processing in the plurality of RAUs2(performs cooperative reception). In addition, the inter-RAU signal transmission unit101and the inter-RAU signal reception unit102include a function as an interface of a predetermined protocol that is used in the FH.

The higher layer processing unit103includes a function of performing signal processing on and above Layer2, and a function of transmitting, to a core network, etc., a signal to which the signal processing up to Layer 2 or the signal processing above Layer 2 is applied.

The function sharing determination unit104includes a function of determining allocation of signal processing that is performed by the RAU2and signal processing that is performed by the BBU1on the basis of a predetermined reference value.

In addition, the inter-RAU signal transmission unit101is classified into a PDCP processing unit1011as a processing unit that performs signal processing of the DL of Layer 2, an RLC processing unit1012, a MAC processing unit1013, a channel coding unit1014as a processing unit that performs signal processing of the DL of Layer 1, a modulation unit1015, a layer mapping unit1016, a precoding unit1017, a resource mapping unit1018, and an OFDM signal generation unit1019. In addition, the inter-RAU signal transmission unit101includes an output unit1010. The PDCP processing unit1011performs various kinds of processing in accordance with a PDCP sub-layer. The RLC processing unit1012performs various kinds of processing in accordance with the RLC sub-layer. The MAC processing unit1013performs various kinds of processing in accordance with a MAC sub-layer. The channel coding unit1014performs processing such as application of CRC, code block division, and rate matching with respect to the DL signal received from the higher layer processing unit103. The modulation unit1015modulates a bit stream by using a predetermined modulation method. The layer mapping unit1016maps a modulation symbol to respective layers. The precoding unit1017performs precoding processing with respect to the modulation symbol of the respective layers to map the modulation symbol of the respective layers to respective antenna ports. The resource mapping unit1018maps the modulation symbol, which is transmitted from the respective antenna ports, to a predetermined resource element. The OFDM signal generation unit1019performs IFFT processing with respect to a signal of a frequency region that is mapped to a resource element to generate an OFDM signal. The output unit1010extracts a signal, which is generated by any one of the higher layer processing unit103, the PDCP processing unit1011, the RLC processing unit1012, the MAC processing unit1013, the channel coding unit1014, the modulation unit1015, the layer mapping unit1016, the precoding unit1017, the resource mapping unit1018, and the OFDM signal generation unit1019, on the basis of the function sharing as a notification from the function sharing determination unit104or the RAU2, and transmits the signal to the RAU2.

In addition, the inter-RAU signal reception unit102is classified into an FFT processing unit1021as a processing unit that performs signal processing of the UL of Layer 1, a resource demapping unit1022, a signal detection unit1023, a demodulation unit1024, a decoding unit1025, a MAC processing unit1026as a processing unit that performs signal processing of the UL of Layer 2, an RLC processing unit1027, and a PDCP processing unit1028. In addition, the inter-RAU signal reception unit102includes an input unit1020. The FFT processing unit1021performs removal of CP and FFT processing with respect to an UL signal that is received. The resource demapping unit1022extracts a modulation symbol, which is scheduled to respective pieces of a user equipment UE, from a modulation symbol that is subjected to the FFT processing. The signal detection unit1023separates a spatial multiplex modulation symbol for each layer. Furthermore, for example, the signal detection unit1023may perform signal detection by using MLD, and the like. The demodulation unit1024demodulates a bit stream from the modulation symbol that is detected. The decoding unit1025performs processing of decoding the bit stream that is demodulated. The MAC processing unit1026performs various kinds of processing in accordance with a MAC sub-layer. The RLC processing unit1027performs various kinds of processing in accordance with an RLC sub-layer. The PDCP processing unit1028performs various kinds of processing in accordance with a PDCP sub-layer. The input unit1020transmits the UL signal, which is received from the RAU2, to any one of the FFT processing unit1021, the resource demapping unit1022, the signal detection unit1023, the demodulation unit1024, the decoding unit1025, the MAC processing unit1026, the RLC processing unit1027, the PDCP processing unit1028, and the higher layer processing unit103on the basis of the function sharing as a notification from the function sharing determination unit104or the RAU2.

FIG. 10is a view illustrating a functional configuration example of the RAU in accordance with this embodiment. As illustrated inFIG. 10, the RAU2includes an inter-UE signal transmission unit201, an inter-UE signal reception unit202, an inter-BBU signal reception unit203, an inter-BBU signal transmission unit204, and a function sharing determination unit205. Furthermore,FIG. 10illustrates only function units, which particularly related to this embodiment, of the RAU2, and the RAU2also has a function (not illustrated) of performing at least an operation in conformity to LTE (including 5G). In addition, the functional configuration illustrated inFIG. 10is illustrative only. Function classification or the name of the function units may be arbitrary as long as the operation according to this embodiment can be executed.

The inter-UE signal transmission unit201includes a function of performing signal processing with respect to a DL signal received from the inter-BBU signal reception unit203on the basis of function sharing as a notification from the function sharing determination unit205or the BBU1to generate a signal, and of transmitting the signal that is generated to the user equipment UE. The inter-UE signal reception unit202includes a function of performing signal processing with respect to an UL signal received from the user equipment UE on the basis of the function sharing as a notification from the function sharing determination unit205or the BBU1, and of transmitting the signal to the inter-BBU signal transmission unit204.

The inter-BBU signal reception unit203and the inter-BBU signal transmission unit204include a function of transmitting and receiving a signal to and from the BBU1, and a function as an interface of a predetermined protocol that is used in the FH.

The function sharing determination unit205includes a function of determining allocation of signal processing that is performed by the RAU2and signal processing that is performed by the BBU1on the basis of a predetermined reference value.

In addition, the inter-UE signal transmission unit201is classified into a PDCP processing unit2011as a processing unit that performs signal processing of the DL of Layer 2, an RLC processing unit2012, a MAC processing unit2013, a channel coding unit2014as a processing unit that performs signal processing of the DL of Layer 1, a modulation unit2015, a layer mapping unit2016, a precoding unit2017, a resource mapping unit2018, and OFDM signal generation unit2019. In addition, the inter-UE signal transmission unit201includes an input unit2010. The PDCP processing unit2011, the RLC processing unit2012, the MAC processing unit2013, the channel coding unit2014, the modulation unit2015, the layer mapping unit2016, the precoding unit2017, the resource mapping unit2018, and the OFDM signal generation unit2019are respectively the same as the PDCP processing unit1011, the RLC processing unit1012, the MAC processing unit1013, the channel coding unit1014, the modulation unit1015, the layer mapping unit1016, the precoding unit1017, the resource mapping unit1018, and the OFDM signal generation unit1019of the BBU1, and thus description thereof will be omitted. The input unit2010transmits a DL signal received from the inter-BBU signal reception unit203to any one of the PDCP processing unit2011, the RLC processing unit2012, the MAC processing unit2013, the channel coding unit2014, the modulation unit2015, the layer mapping unit2016, the precoding unit2017, the resource mapping unit2018, and the OFDM signal generation unit2019on the basis of function sharing as a notification from the function sharing determination unit205or the BBU1.

In addition, the inter-UE signal reception unit202is classified into an FFT processing unit2021as a processing unit that performs signal processing of the UL of Layer 1, a resource demapping unit2022, a signal detection unit2023, a demodulation unit2024, a decoding unit2025, a MAC processing unit2026as a processing unit that performs signal processing of the UL of Layer 2, an RLC processing unit2027, and a PDCP processing unit2028. In addition, the inter-UE signal reception unit202includes an output unit2020. The FFT processing unit2021, the resource demapping unit2022, the signal detection unit2023, the demodulation unit2024, the decoding unit2025, the MAC processing unit2026, the RLC processing unit2027, and the PDCP processing unit2028are respectively the same as the FFT processing unit1021, the resource demapping unit1022, the signal detection unit1023, the demodulation unit1024, and the decoding unit1025, the MAC processing unit1026, the RLC processing unit1027, and the PDCP processing unit1028of the BBU1, and, thus, the description is omitted. The output unit2020extracts a signal, which is generated by any one of the FFT processing unit2021, the resource demapping unit2022, the signal detection unit2023, the demodulation unit2024, the decoding unit2025, the MAC processing unit2026, the RLC processing unit2027, and the PDCP processing unit2028, on the basis of the function sharing as a notification from the function sharing determination unit205or the BBU1, and transmits the signal to the inter-BBU signal transmission unit204.

The entirety of the above-described functional configuration of the BBU1and the RAU2may be implemented by a hardware circuit (for example, one or a plurality of IC chips). In addition, a part of the functional configuration may be configured as a hardware circuit, and the other portions may be implemented by a CPU and a program.

FIG. 11is a view illustrating a hardware configuration example of the BBU according to this embodiment.FIG. 11illustrates a configuration that is closer to a mounting example in comparison toFIG. 9. As illustrated inFIG. 11, the BBU1includes an inter-RAU IF301as an interface for connection to the RAU2, a BB processing module302that performs dedicated line connection system signal processing, a device control module303that performs processing of a higher layer and the like, and a communication IF304as an interface for connection to a core network and the like.

The inter-RAU IF301has a function of connecting physical lines of the FH that connects the BBU1and the RAU2to each other, and a function of terminating a protocol that is used in the FH. For example, the inter-RAU IF301includes parts of the inter-RAU signal transmission unit101and the inter-RAU signal reception unit102which are illustrated inFIG. 9.

The BB processing module302performs processing of converting an IP packet and a signal that is transmitted and received to and from the RAU2. A DSP312is a processor that performs signal processing in the BB processing module302. A memory322is used as a work area of the DSP312. For example, the BB processing module302includes parts of the inter-RAU signal transmission unit101and the inter-RAU signal reception unit102which are illustrated inFIG. 9, a part of the higher layer processing unit103, and a part of the function sharing determination unit104.

The device control module303performs protocol processing of an IP layer, operation and maintenance processing (OAM), and the like. A processor313is a processor that performs processing that is performed by the device control module303. The memory323is used as a work area of the processor313. Examples of an auxiliary storage device333include an HDD, and the like, and the auxiliary storage device333stores various kinds of setting information for an operation of the base station eNB, and the like. For example, the device control module303includes parts of the higher layer processing unit103and the function sharing determination unit104which are illustrated inFIG. 9.

FIG. 12is a view illustrating a hardware configuration example of the RAU according to this embodiment.FIG. 12illustrates a configuration that is closer to a mounting example in comparison toFIG. 10. As illustrated inFIG. 12, the RAU2includes a radio frequency (RF) module401that performs processing related to a radio signal, a base band (BB) processing module402that performs dedicated line connection system signal processing, and an inter-BBU IF403as an interface for connection to the BBU1.

The RF module401performs digital-to-analog (D/A) conversion, orthogonal modulation, frequency conversion, power amplification, and the like with respect to a digital baseband signal received from the BB processing module402to generate a radio signal to be transmitted from an antenna. In addition, the RF module401performs frequency conversion, analog-to-digital (A/D) conversion, orthogonal demodulation, and the like with respect to a radio signal that is received to generate a digital baseband signal, and transmits the signal to the BB processing module402. The RF module401includes an RF function. For example, the RF module401includes parts of the inter-UE signal transmission unit201and the inter-UE signal reception unit202which are illustrated inFIG. 10.

The BB processing module402performs processing of converting a signal that is transmitted and received to and from the BBU1through the inter-BBU IF403, and the digital baseband signal from each other. A digital signal processor (DSP)412is a processor that performs signal processing in the BB processing module402. The memory422is used as a work area of the DSP412. For example, the BB processing module402includes parts of the inter-UE signal transmission unit201and the inter-UE signal reception unit202, and the function sharing determination unit205which are illustrated inFIG. 10.

The inter-BBU IF403has a function of connecting physical lines of the FH that connects the BBU1and the RAU2to each other, and a function of terminating a protocol that is used in the FH. For example, the inter-BBU IF403includes the inter-BBU signal reception unit203and the inter-BBU signal transmission unit204which are illustrated inFIG. 10.

As described above, according to an embodiment, there is provided a radio communication system including a first base station, a second base station, a third base station that performs a communication with the first base station and the second base station, and a user equipment that performs a communication with the first base station and the second base station, the radio communication system including a determination unit that determines allocation of signal processing that is commonly performed by the first base station and the second base station and signal processing that is performed by the third base station, based on a predetermined reference value; a first signal processor that performs the signal processing allocated to the first base station in accordance with the allocation that is determined by the determination unit; a second signal processor that performs the signal processing allocated to the second base station in accordance with the allocation that is determined by the determination unit; and a third signal processor that performs the signal processing allocated to the third base station in accordance with the allocation that is determined by the determination unit. According to the radio communication system, there is provided a technology capable of appropriately changing function sharing between the BBU1and the RAU2in a radio communication network by a C-RAN.

The predetermined reference value may be a CRC check success rate, an SINR, or an SNR of an uplink signal that is transmitted from the user equipment or a downlink signal that is received by the user equipment, the number of retransmission times of the uplink signal or the downlink signal, or a channel estimation error, and wherein the determination unit may determine the allocation of the signal processing that is commonly performed by the first base station and the second base station and the signal processing that is performed by the third base station based on the CRC check success rate, the SINR, or the SNR of the uplink signal that is transmitted from the user equipment or the downlink signal that is received by the user equipment, the number of retransmission times of the uplink signal or the downlink signal, or the channel estimation error. According to this, it is possible to appropriately change function sharing between the BBU1and the RAU2by using the CRC check success rate, the SINR, or the SNR of the uplink signal or the downlink signal, the number of retransmission times of the uplink signal or the downlink signal, or the channel estimation error.

The predetermined reference value may be a processing load on the first base station, a processing load on the second base station, or a processing load on the third base station, and wherein the determination unit may determine the allocation of the signal processing that is commonly performed by the first base station and the second base station and the signal processing that is performed by the third base station on based on the processing load on the first base station, the processing load on the second base station, or the processing load on the third base station. According to this, it is possible to appropriately change the function sharing between the BBU1and the RAU2on the basis of the processing load of the RAU2. In addition, it is possible to reduce the processing load of the RAU2.

The predetermined reference value may be information indicating whether at least one of the number of antennas of the first base station and the number of antennas of the second base station is greater than or equal to the number of antennas of the user equipment, and wherein the determination unit may determine the allocation of the signal processing that is commonly performed by the first base station and the second base station and the signal processing that is performed by the third base station based on whether at least one of the number of antennas of the first base station and the number of antennas of the second base station is greater than or equal to the number of antennas of the user equipment. According to this, it is possible to appropriately change the function sharing between the BBU1and the RAU2on the basis of the number of antennas provided to the user equipment UE and the number of antennas provided to the RAU2.

The determination unit may determine that entire layer1signal processing of the uplink signal is performed by the first signal processor of the first base station and the second signal processor of the second base, upon determining that the CRC check success rate, the SINR, or the SNR of the uplink signal that is transmitted from the user equipment or the downlink signal that is received by the user equipment is greater than or equal to a predetermined threshold value, upon determining that the number of retransmission times of the uplink signal that is transmitted from the user equipment or the downlink signal that is received by the user equipment is less than a predetermined threshold value, or upon determining that the channel estimation error of the uplink signal that is transmitted from the user equipment or the downlink signal that is received by the user equipment is less than a predetermined threshold value, and wherein the third signal processor may perform layer 2 signal processing using one of a signal that is processed by the first signal processor and a signal that is processed by the second signal processor. According to this, it is possible to determine whether or not to perform cooperative reception in the BBU1while reducing a transmission amount through the FH.

The determination unit may determine that a part of the layer 1 signal processing of the uplink signal is performed by the first signal processor of the first base station and the second signal processor of the second base station and a remaining part of the layer 1 signal processing is performed by the third signal processor of the third base station upon determining that the CRC check success rate, the SINR, or the SNR of the uplink signal that is transmitted from the user equipment or the downlink signal that is received by the user equipment is less than a predetermined threshold value, upon determining that the number of retransmission times of the uplink signal that is transmitted from the user equipment or the downlink signal that is received by the user equipment is greater than or equal to a predetermined threshold value, or upon determining that the channel estimation error of the uplink signal that is transmitted from the user equipment or the downlink signal that is received by the user equipment is greater than or equal to a predetermined threshold value, and wherein the third signal processor may perform a remaining part of the layer 1 signal processing and layer 2 signal processing by using both of a signal that is processed by the first signal processor and a signal that is processed by the second signal processor. According to this, it is possible to determine whether or not to perform cooperative reception in the BBU1while reducing a transmission amount through the FH.

According to an embodiment, there is provided a base station that is used as a third base station in a radio communication system including a first base station, a second base station, the third base station that performs a communication with the first base station and the second base station, and a user equipment that performs a communication with the first base station and the second base station, the base station including a determination unit that determines allocation of signal processing that is commonly performed by the first base station and the second base station and signal processing that is performed by the base station on the basis of a predetermined reference value; and a signal processor that performs the signal processing allocated to the base station in accordance with the allocation that is determined in the determination unit. According to this base station, there is provided a technology capable of appropriately changing the function sharing between the BBU1and the RAU2in the radio communication network by the C-RAN.

According to an embodiment, there is provided a base station that is used as a first base station in a radio communication system including the first base station, a second base station, a third base station that performs a communication with the first base station and the second base station, and a user equipment that performs a communication with the first base station and the second base station, the base station including a determination unit that determines allocation of signal processing that is commonly performed by the base station and the second base station and signal processing that is performed by the third base station based on a predetermined reference value; and a signal processor that performs the signal processing allocated to the base station in accordance with the allocation that is determined in the determination unit. According to this base station, there is provided a technology capable of appropriately changing the function sharing between the BBU1and the RAU2in the radio communication network by the C-RAN.

Hereinbefore, the configuration of the respective devices (the BBU1and the RAU2) described in the embodiment of the invention may be a configuration that is implemented when a program is executed by a processor (CPU) in the device including the CPU and a memory, or a configuration that is implemented by hardware such as a hardware circuit including a logic of the processing described in this embodiment. In addition, the program or the hardware may coexist.

Hereinbefore, description has been given of the embodiment of the invention. However, the invention is not limited to the embodiment, and it should be understood by those skilled in the art that various modification examples, variation examples, alternative examples, substitution examples, and the like can be made. Description has been made by using a specific numerical example for comprehension of the invention, but numerical values are illustrative only, and arbitrary appropriate values may be used unless otherwise stated. The classification of the items in the above description is not essential in the invention, and details described in two or more items may be used in combination as necessary. In addition, details described in any item may be applied to details described in a different item (as long as inconsistency does not occur). It cannot be said that the boundary of the function units in the functional block diagram or the processing units correspond to a boundary of physical components. Operations of a plurality of function units may be performed physically with one component, or an operation of one function unit may be performed physically with a plurality of components. In the sequences and the flowcharts described in the embodiment, the order thereof may be changed as long as inconsistency does not occur. The BBU1and the RAU2have been described by using functional block diagrams for convenience of processing description, but the devices may be implemented by hardware, software, or a combination thereof. Software that operations by the processor provided to the BBU1in accordance with the embodiment of the invention, and software that operates by the processor provided to the RAU2in accordance with the embodiment of the invention may be respectively stored in a random access memory (RAM), a flash memory, a read only memory (ROM), an EPROM, an EEPROM, a register, a hard disk drive (HDD), a removable disk, a CD-ROM, a database, a server, or other appropriate storage media.

The first base station and the second base station in this embodiment are examples of the RAU2. The third base station is an example of the BBU1. The function sharing determination unit104or the function sharing determination unit205is an example of the determination unit. The inter-UE signal transmission unit201or the inter-UE signal reception unit202is an example of the first signal processing unit and the second signal processing unit. The inter-RAU signal transmission unit101or the inter-RAU signal reception unit102is an example of the third signal processing unit.

Reporting of information is not limited to the aspects/embodiments described in this specification, and may be performed by another method. For example, reporting of information may be implemented by physical layer signaling (e.g., DCI (Downlink Control Information)), UCI (Uplink Control Information)), higher layer signaling (e.g., RRC signaling, MAC signaling, broadcast information (MIB (Master Information Block), SIB (System Information Block)), other signals or a combination thereof. Furthermore, the RRC message may be referred to as RRC signaling. Furthermore, the RRC message may be, for example, an RRC connection setup (RRC Connection Setup) message, an RRC connection reconfiguration (RRC Connection Reconfiguration) message, and so forth.

The decision or determination may be performed by a value (0 or 1) represented by one bit; may be performed by a Boolean value (Boolean: true or false); or by numerical value comparison (e.g., a comparison with a predetermined value).

Note that the terms described in this specification and/or terms required for understanding the specification may be replaced with terms having the same or similar meanings. For example, a channel and/or a symbol may be a signal (signal). Furthermore, a signal may be a message.

The each aspect/embodiment described in the specification may be used alone; may be used in combination; or may be used by switching depending on execution. Furthermore, reporting of predetermined information (e.g., reporting of “being X”) is not limited to the method of explicitly performing, and may be performed implicitly (e.g., not perform reporting of the predetermined information).

The terms “determine (determining)” and “decide (determining)” may encompass a wide variety of operations. The “determine” and “decide” may include, for example, “determine” and “decide” what is calculated (calculating), computed (computing), processed (processing), derived (deriving), investigated (investigating), looked up (looking up) (e.g., looked up in tables, databases, or other data structures), ascertained (ascertaining). Furthermore, the “determine” and “decide” may include deeming that “determination” and “decision” are made on reception (receiving) (e.g., receiving information), transmission (transmitting) (e.g., transmitting information), input (input), output (output), and access (accessing) (e.g., accessing data in a memory). Furthermore, the “determine” and “decide” may include deeming that “determination” and “decision” are made on what is resolved (resolving), selected (selecting), chosen (choosing), established (establishing), and compared (comparing). Namely, the “determine” and “decide” may include deeming that some operation is “determined” or “decided.”

The phrase “based on” used in this specification does not imply “based only on” unless explicitly stated otherwise. In other words, the phrase “based on” implies both “based only on” and “based at least on.”

Furthermore, the order of the processing procedures, sequences, and so forth of the aspects/embodiments described in the specification may be re-arranged, provided that they do not contradict. For example, for the methods described in the specification, the elements of various steps are presented in an exemplary order, and are not limited to the specific order presented.

The input/output information, etc., may be stored in a specific location (e.g., a memory), or managed in a management table. The input/output information, etc., may be overwritten, updated, or additionally written. The output information, etc., may be deleted. The input information, etc., may be transmitted to another device.

Reporting of predetermined information (e.g., reporting of “being X”) is not limited to the method of explicitly performing, and may be implicitly performed (e.g., reporting of the predetermined information is not performed).

The information signals, etc. described in the specification may be represented by using any of a variety of different techniques. For example, the data, indication, command, information, signal, bit, symbol, chip, etc. may be represented by a voltage, an electric current, an electromagnetic wave, a magnetic field or magnetic particles, a light field or photons, or any combination thereof.

The present application is based upon and claims the benefit of priority of Japanese Patent Application No. 2016-048748 filed on Mar. 11, 2016 and the entire contents of Japanese Patent Application No. 2016-048748 are incorporated herein by reference.

LIST OF REFERENCE SYMBOLS

eNB Base station

101Inter-RAU signal transmission unit

102Inter-RAU signal reception unit

103Higher layer processing unit

104Function sharing determination unit

201Inter-UE signal transmission unit

202Inter-UE signal reception unit

203Inter-BBU signal reception unit

204Inter-BBU signal transmission unit

205Function sharing determination unit

301Inter-RAU IF

302BB processing module

303Device control module

304Communication IF

402BB processing module

403Inter-BBU IF