WO2013051112A1

WO2013051112A1 - Wireless system, base station, mobile terminal, and wireless communication method

Info

Publication number: WO2013051112A1
Application number: PCT/JP2011/072879
Authority: WO
Inventors: 義博河▲崎▼
Original assignee: 富士通株式会社
Priority date: 2011-10-04
Filing date: 2011-10-04
Publication date: 2013-04-11
Also published as: JP5626479B2; JPWO2013051112A1

Abstract

The present invention addresses the problem of finding a transmission power for a wireless signal which is to be properly transmitted by a terminal to a small cell in a mixed cell where a large cell and the small cell have the same physical cell ID. To resolve the problem, a large cell base station (102) allocates to a small cell base station (302) a combination of CSI RSs that is determined by selecting four CSI RSs from among eight CSI RSs provided in order to assess the wireless quality of a downlink to a UE (304). The large cell base station transmits a combination signal indicative of one combination in which four CSI RSs have been selected from among eight CSI RSs on the basis of the location of the UE. The small cell base station transmits the four CSI RSs allocated to itself. The UE finds a propagation loss for the downlink between itself and the small cell base station on the basis of a reception result from the receipt of the combination of the CSI RSs according to the combination signal, and finds a transmission power for an uplink wireless signal to be transmitted to the small cell base station (302).

Description

Wireless system, base station, mobile terminal, and wireless communication method

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

In recent years, there are wireless cell deployments in which one or more small wireless cells exist in a large wireless cell, which has already been realized in commercial systems. In a radio system based on LTE (Long Term Evolution) specifications formulated by 3GPP (Third Generation Partnership Project), one of the standardization organizations, a radio cell configuration as shown in FIG. 1 is currently being implemented. FIG. 1 is a diagram showing a configuration of a conventional mixed cell.

As shown in FIG. 1, a plurality of small cells 700 and 800 (pico cells) are provided in a large cell 600 (macro cell). In this example, it is assumed that the large cell base station 602 corresponding to the large cell 600 is communicating with the UE (User Equipment) 604, and the small cell base station 702 corresponding to the small cell 700 is communicating with the UE 704. . Further, it is assumed that a small cell base station 802 corresponding to the small cell 800 is communicating with the UE 804.

Different physical cell IDs are assigned to the large cell 600 and the

small cells

700 and 800, respectively. In addition, various parameters of the code sequence constituting the radio signal transmitted in the large cell 600 and the

small cells

700 and 800, the parameter of the scrambled signal calculated (multiplication processing, etc.) on the radio signal, etc. are associated with the physical cell ID. It is done. For example, the large cell base station 602, the small cell base station 702, and the small cell base station 802 transmit identifiable Data # 1, Data # 2, and Data # 3 to the UE 604, UE 704, and UE 804, respectively.

By associating the physical cell ID with the parameters of the radio signal in this way, the UE can not only distinguish between cells when the presence of a plurality of cells is confirmed, but also the influence of radio signal interference between cells. Can be relaxed. For example, when the UE 704 existing in the small cell 700 receives a radio signal from the small cell base station 702, the radio signal transmitted from the large cell base station 602 is also received at the same time, thereby causing radio signal interference. However, for each signal, the scramble signal associated with the physical cell ID of each cell is processed, so that the radio signal can be identified, and the influence of interference is alleviated to some extent.

By the way, the radio data signal transmitted to the UE is demodulated using a common pilot signal (CRS: Common Reference Signal) transmitted from the base station that transmits the radio data signal. The common pilot signal transmitted from the base station of each cell is not only different in code sequence parameters, but is offset in the transmission position on the frequency axis according to the value determined by the physical cell ID. The interference between them is small. For example, the large cell base station 602, the small cell base station 702, and the small cell base station 802 transmit identifiable CRS # 1, CRS # 2, and CRS # 3 to the entire area in each cell, respectively. UE 604, UE 704, and UE 804 each receive their CRS.

Also, the UE in each cell calculates and determines the transmission power when transmitting a radio signal on the radio uplink to the base station of each cell based on a predetermined formula. For the calculation, downlink propagation loss (path loss) calculated from the measurement result of the received power for the common pilot signal transmitted from each base station is used. That is, the transmission power of the radio signal in the uplink is the downlink propagation loss value, the value determined in advance by the modulation method and the signal bandwidth, the value broadcast from the base station, and the base station every time transmission is performed in the uplink. It is determined by a power correction value transmitted from the station for each terminal. In determining this transmission power, the proportion of downlink propagation loss is large. Therefore, the UE in each cell performs radio measurement on a common pilot signal transmitted from each base station to obtain a downlink propagation loss with the base station, and uses the obtained propagation loss to transmit power. Ask for.

Special table 2011-521562 gazette

However, the prior art does not consider appropriately obtaining transmission power in a mixed cell in which a large cell and a small cell have the same physical cell ID.

That is, in 3GPP, introduction of a new mixed cell in which a large cell and a small cell have the same physical cell ID is being studied. In the new mixed cell, the common pilot signals transmitted from the large cell and the small cell not only have the same code sequence parameters, but also have the same time timing and position on the frequency axis to be transmitted.

Thus, in the new mixed cell, since the common pilot with the same content is transmitted at the same frequency at the same time, the UE receives the synthesized common pilot signal. On the other hand, since it is difficult for the UE to separate the received common pilot signal, it is difficult to obtain a downlink propagation loss with a specific base station.

The disclosed technology has been made in view of the above, and a radio system, a base station, a mobile terminal, and a mobile station capable of appropriately obtaining transmission power in a mixed cell in which a large cell and a small cell have the same physical cell ID, and An object is to realize a wireless communication method.

In one aspect, a wireless system disclosed in the present application includes a first base station corresponding to a first wireless cell, and a plurality of second base stations provided in the first wireless cell and smaller than the first wireless cell. A plurality of second base stations respectively corresponding to the two radio cells, and a mobile terminal. The first base station has N reference signals (N is smaller than M) among M reference signals (M is an integer of 2 or more) provided for evaluating downlink radio quality to the mobile terminal. An allocation unit that allocates a plurality of different combinations determined by selecting (integer) reference signals to the plurality of second base stations. In addition, the first base station includes a notification unit that transmits a combination signal indicating one combination in which the N reference signals are selected from the M reference signals based on the position of the mobile terminal. . Each of the second base stations has a signal transmission unit that transmits N reference signals allocated to the own base station among the M reference signals. The mobile terminal includes a reception unit that receives the combination signal transmitted by the notification unit and a reference signal of a combination corresponding to the combination signal. Further, the mobile terminal transmits an uplink with a second base station to which a combination of reference signals corresponding to the combination signal is assigned based on a reception result of the reference signal received by the reception unit. A transmission power calculation unit for obtaining power is included.

According to one aspect of the wireless system disclosed in the present application, transmission power can be appropriately obtained in a mixed cell in which a large cell and a small cell have the same physical cell ID.

FIG. 1 is a diagram showing a configuration of a conventional mixed cell. FIG. 2 is a diagram showing the configuration of the mixed cell of this embodiment. FIG. 3 is a diagram illustrating a configuration of the wireless system. FIG. 4 is a functional block diagram of the large cell base station. FIG. 5 is a diagram illustrating an example of assignment of CSI RS to each cell. FIG. 6 is a diagram showing an example of a combination table of CSI RS ports. FIG. 7 is a functional block diagram of the small cell base station. FIG. 8 is a diagram illustrating an example of a subframe for transmitting a CSI RS. FIG. 9 is a hardware configuration and functional block diagram of the mobile terminal. FIG. 10 is a flowchart showing processing of the wireless system.

Hereinafter, embodiments of a wireless system, a base station, a mobile terminal, and a wireless communication method disclosed in the present application will be described in detail based on the drawings. The disclosed technology is not limited by this embodiment.

FIG. 2 is a diagram showing the configuration of the mixed cell of this embodiment. As shown in FIG. 2, the mixed cell of this embodiment is provided with a plurality of small cells 200 and 300 (pico cells) in a large cell 100 (macro cell). The same physical cell ID is assigned to the large cell 100 and the

small cells

200 and 300. In this example, the large cell base station 102 corresponding to the large cell 100 and the small cell base station 202 corresponding to the small cell 200 are communicating with the UE 204, and the small cell base station 302 corresponding to the small cell 300 is communicating with the UE 304. Assume communication. For example, the large cell base station 102 and the small cell base station 202 transmit Data # 1 and CRS # 1 to the UE 204. The small cell base station 302 transmits Data # 3, DM RS (DeModulation Reference Signal), and CSI RS (Channel State Information Reference Signal) to the UE 304. The UE 204 is assumed to be a terminal developed and manufactured so as to conform to existing specifications in which different physical cell IDs are assigned to large cells and small cells. The UE 304 is assumed to be a terminal developed and manufactured so as to conform to a new specification in which the same physical cell ID is assigned to a large cell and a small cell.

In the mixed cell of this embodiment, the same physical cell ID is assigned to the large cell 100 and the

small cells

200 and 300. For this reason, the common pilot signals transmitted from the large cell base station 102 and the small

cell base stations

202 and 302 have not only the same code sequence parameters but also the time timing to be transmitted and the position on the frequency axis to be transmitted. Be the same.

The UE 204 transmits wireless data signals having the same content from the large cell base station 102 and the small cell base station 202. Radio data signals transmitted from the large cell base station 102 and the small cell base station 202 are received by the radio reception antenna of the UE 204 as a radio signal that is simply spatially synthesized. Similarly, the common pilot signal transmitted from the large cell base station 102 and the small cell base station 202 is received as a common pilot signal that is simply spatially combined by the radio reception antenna of the UE 204.

UE 204 uses a common pilot signal that is simply spatially synthesized and received in order to demodulate the received wireless data signal that is simply spatially synthesized. When receiving the radio data signal, the UE 204 receives signals simultaneously transmitted from the large cell base station 102 and the small cell base station 202, so that the received signal power increases and the probability of successful reception increases. Alternatively, compared to the case where transmission is performed only from a single base station (for example, the large cell base station 102), the coding rate applied to the wireless data signal is reduced, and the wireless data signal is transmitted from the base station to the UE 204 at a higher data rate. Can be sent to.

The large cell 100 and the small cell 200 have the same physical cell ID, the same wireless data signal is simultaneously transmitted at the same frequency, and the same scrambled signal is processed. Thereby, although UE204 is transmitted from the large cell base station 102 and the small cell base station 202, it should just process as if the signal from a single base station is received. Therefore, the UE 204 can transmit and receive data not only in the mixed cell shown in FIG. 1 but also in the mixed cell shown in FIG.

In the mixed cell shown in FIG. 2, when the large cell base station 102 and the small

cell base stations

202 and 302 transmit radio data signals having the same content in all radio resources, the merit that the UE 204 can enjoy increases. On the other hand, there is a demerit that the number of UEs that can simultaneously transmit and receive wireless data is constant regardless of the number of small cells. In order to solve this disadvantage, 3GPP is studying to enable data transmission / reception only with a single small cell (for example, the small cell 300) like the UE 304.

The radio data signal transmitted to the UE 304 is transmitted only from the small cell 300, and the pilot signal used for demodulating this radio data signal is not a common pilot signal but an individual pilot signal. The dedicated pilot signals can be transmitted not only from the large cell 100 and the small cell 200 at the same time, but also from only one cell. When the radio data signal is transmitted only from the small cell 300 to the UE 304, the dedicated pilot signal for the UE 304 is transmitted only from the small cell 300. When a radio data signal is transmitted from the small cell 300 to the UE 304, the radio data signal is transmitted to other terminals simultaneously from other small cells within the same large cell 100 and located at some distance from the small cell 300. It is possible to send. In this way, the number of terminals that can simultaneously transmit and receive data can be increased.

2, the UE 204 receives the radio data signal only from the small cell 300 and the common control signal from the large cell 100 at the same time from the large cell 100 and the small cell 200. Since the physical cell IDs of the large cell 100 and the

small cells

200 and 300 are the same, the UE 204 and the UE 304 operate as if receiving a radio data signal from the large cell 100.

By the way, when the UE 304 that performs radio communication only with the small cell 300 transmits a radio signal in the uplink, the radio signal transmitted from the UE 304 may be transmitted with a transmission power that can reach the small cell base station 302 sufficiently. preferable. On the other hand, even if the radio signal transmitted from the UE 304 does not reach the large cell base station 102 with sufficient reception power, the transmission power value is set so that the radio signal reaches the large cell base station 102 with sufficiently low power. It is preferable to set.

The reason for this is that it interferes with signals transmitted by other UEs communicating with the large cell base station 102 and communicates with familiar base stations to reduce the transmission power value and reduce power consumption. It is to be able to reduce. In order to realize such transmission, the transmission power of the radio signal in the uplink is determined based on the downlink propagation loss between the small cell base station 302 and the UE 304 where the radio data signal is transmitted. It is possible to do.

In the mixed cell shown in FIG. 2, since the same content of the common pilot is transmitted at the same frequency at the same time, the UE 304 receives the synthesized common pilot signal and cannot separate the signal. It is difficult to obtain a propagation loss between. While the common pilot signal is always transmitted, the dedicated pilot signal transmitted to a certain UE is transmitted only when the radio data signal is transmitted to the UE on the downlink. Therefore, when data is not transmitted on the UE in the downlink, there is no transmission of a dedicated pilot signal for the UE. Therefore, it is not preferable to obtain the propagation loss based on the radio measurement for the dedicated pilot signal transmitted on the downlink.

On the other hand, LTE Advanced, whose specifications have been established by 3GPP, introduced a new reference signal (CSI RS: Channel State Information Reference Signal) for measuring radio channel quality information for the purpose of measuring downlink radio quality. ing. Therefore, it is conceivable to calculate the downlink propagation loss used when calculating the uplink transmission power from the result of radio measurement for the CSI RS.

However, in the mixed cell shown in FIG. 2, since the large cell and the small cell have the same physical cell ID, it is difficult for the UE to identify the CSI RS transmitted from a specific cell. A maximum of 8 CSI RSs can be used per cell, but if 8 CSI RSs having the same contents are transmitted from the large cell 100 and the

small cells

200 and 300, the large cell 100 and the

small cells

200 and 300 or the small cell are transmitted. CSI RS interference may occur between 200 and 300.

Details of the wireless system of the present embodiment for solving such problems will be described below. FIG. 3 is a diagram illustrating a configuration of the wireless system. As shown in FIG. 3, the radio system 50 according to the present embodiment includes a large cell base station 102 corresponding to the large cell 100 and a small cell corresponding to the small cell 300 provided in the large cell 100 and smaller than the large cell 100. A base station 302, a UE 304, and the like.

First, the configuration of a large cell base station will be described with reference to FIG. As illustrated in FIG. 3, the large cell base station 102 includes a radio unit 106, a baseband processing unit 108, an electrical / optical conversion unit 110, and an antenna 112.

The radio unit 106 receives a radio signal transmitted from, for example, the UE 204 via the antenna 112 and outputs the radio signal to the baseband processing unit 108. The wireless unit 106 is realized by an analog circuit, for example. The baseband processing unit 108 converts an RF (Radio Frequency) signal received by the radio unit 106 into a baseband signal, and converts the converted signal into a digital signal by an A (Analog) / D (Digital) converter. To do. The baseband processing unit 108 performs various processes such as a demodulation process and an error correction process on the converted digital signal. The baseband processing unit 108 is realized by, for example, a CPU (Central Processing Unit) or a DSP (Digital Signal Processor).

The electrical / optical conversion unit 110 converts the electrical signal processed by the baseband processing unit 108 into an optical signal, and transmits the converted optical signal to the small cell base station 302 via the optical cable 320.

The small cell base station 302 includes a radio unit 306, a baseband processing unit 308, an electrical / optical conversion unit 310, and an antenna 312. The radio unit 306 receives a radio signal transmitted from, for example, the UE 304 via the antenna 312 and outputs the radio signal to the baseband processing unit 308. The wireless unit 306 is realized by an analog circuit, for example.

The baseband processing unit 308 converts the RF signal received by the wireless unit 306 into a baseband signal, and converts the converted signal into a digital signal by an A / D converter. The baseband processing unit 308 performs various processes such as a demodulation process and an error correction process on the converted digital signal. The baseband processing unit 308 is realized by a CPU or a DSP, for example. The electrical / optical conversion unit 310 converts the electrical signal processed by the baseband processing unit 308 into an optical signal, and transmits the converted optical signal to the large cell base station 102 via the optical cable 320. That is, an optical signal is transmitted and received between the electrical / optical conversion unit 110 and the electrical / optical conversion unit 310.

FIG. 4 is a functional block diagram of the large cell base station. As illustrated in FIG. 4, the large cell base station 102 includes a signal transmission / reception unit 122, an allocation unit 124, a combination table 126, and a notification unit 128.

The signal transmission / reception unit 122 transmits / receives a signal to / from the UE 204, for example. For example, the signal transmission / reception unit 122 transmits a common pilot signal (CRS) or a reference signal (for example, 8 CSI RSs) provided for evaluating downlink radio quality to the UE to the UE.

Here, in 3GPP LTE Advanced physical layer (Layer 1) specifications (TS36.201, TS36.211, TS36.212, TS36.213), a logical antenna that transmits pilot signals and reference signals used in the radio section The port number is fixed. For example, there are four common pilot signals (for a maximum of four transmission antennas), and the four common pilot signals are transmitted from

antenna ports

0, 1, 2, 3 respectively. There are a maximum of 8 CSI RSs, which are transmitted from

antenna ports

15, 16, 17, 18, 19, 20, 21, and 22, respectively. The number of CSI RSs transmitted from one radio base station does not exceed the number of actual physical transmission antennas of that base station.

Here, an example of how a maximum of 8 CSI RSs are allocated to each small cell in this embodiment will be described. FIG. 5 is a diagram illustrating an example of assignment of CSI RS to each cell. In this example, it is assumed that there are four

small cells

200, 300, 400, and 500 in one large cell 100 as shown in FIG. Four CSI RSs are allocated to each small cell. For example, four CSI RSs assigned to the small cell 200 are transmitted from the logical antenna ports # 15, # 16, # 19, and # 20 of the base station of the small cell 200, respectively. These four logical antenna ports are usually mapped to four physical transmission antennas and transmitted from the actual physical antennas. If the small cell 200 has 8 physical antennas, the 4 logical antenna ports are mapped to 8 physical transmit antennas.

The CSI RS is transmitted to the small cells 300, 400, and 500 that are some distance away from the small cell 200 from a combination of antenna ports including a part of the antenna ports used for CSI RS transmission in the small cell 200. For example, CSI RS is transmitted from small cell 400 using antenna ports # 15, # 16, # 17, and # 18. A combination of four CSI RSs out of a maximum of eight CSI RSs is tabulated in a combination table 126, for example.

FIG. 6 is a diagram illustrating an example of a combination table of CSI RS ports. As shown in FIG. 6, the combination table 126 includes Configuration No. 150 and CSI RS Ports 160. Configuration No. 150 and CSI RS Ports 160 are associated one-to-one. In this example, since the combination table 126 is four combinations of eight CSI RSs, there are 70 combinations in total by ₈ C ₄ . Configuration No. 150 are assigned 70 numbers from # 0 to # 69. Also, Configuration No. is included in CSI RS Ports 160. Different combinations of CSI RSs are set according to 150 numbers.

For example, Configuration No. When 150 is “# 0”, “# 15, # 16, # 17, # 18” is associated with CSI RS Ports 160. For example, Configuration No. When 150 is “# 1”, “# 19, # 20, # 21, # 22” is associated with CSI RS Ports 160.

Note that eight CSI RSs are assigned to the large cell 100. When the number of transmission antennas of the large cell base station 102 is 4, for example, from four CSI RSs transmitted from # 15, # 16, # 17, and # 18, and from # 19, # 20, # 21, and # 22 It is transmitted in a time different from the four CSI RSs to be transmitted, that is, time multiplexed in different radio subframes. In this case, two logical antenna ports used for CSI RS transmission are mapped to one physical transmission antenna by time multiplexing.

Returning to the description of FIG. 4, the assigning unit 124 has N (N is an integer of 2 or more, for example, 4) smaller than M among M (M is an integer of 3 or more, for example, 8) CSI RSs. A plurality of different combinations determined by selecting the CSI RS are allocated to the small cell base stations of the

small cells

200, 300, 400, and 500, respectively. For example, the assigning unit 124 assigns Configuration No. to the small cell 300. CSI RS Ports 160 of “# 17, # 18, # 19, # 20” in which 150 is “# 4” is assigned. In addition, for example, the assigning unit 124 includes a configuration number “No. CSI RS Ports 160 of “# 19, # 20, # 21, # 22” in which 150 is “# 1” is assigned.

Based on the UE location, the notification unit 128 may select N (N is an integer of 2 or more, for example, 4) smaller than M out of M (M is an integer of 3 or more, for example, 8) CSI RSs. A combination signal indicating one combination for which the RS is selected is transmitted. For example, when the notification unit 128 determines that a certain UE belongs to the area of the small cell 300, the notification unit 128 receives the Configuration No. assigned to the small cell 300 to the UE. 150 “# 4” is notified. More specifically, the UE reports the results of receiving and measuring 8 CSI RSs to the large cell base station 102. Based on the reported reception results of the eight CSI RSs, the notification unit 128 indicates which small cell of the

small cells

200, 300, 400, 500 the UE belongs to, that is, in the vicinity of which small cell. Or whether it is not near any small cell. Then, the notification unit 128 sends a combined signal to the UE based on the determination result, that is, the corresponding Configuration No. 150 is transmitted. In addition, the notification unit 128 includes a configuration number, a control signal including information for performing modulation / demodulation of data when the UE receives data. 150 can be notified to the UE. In addition, the notification unit 128 includes a configuration No. along with a control signal including information used for data transmission when the UE transmits data. 150 can be notified to the UE.

Next, the small cell base station will be described. FIG. 7 is a functional block diagram of the small cell base station. In FIG. 7, as an example, the small cell base station 302 is described as an example, but other small cell base stations can have the same configuration. As illustrated in FIG. 7, the small cell base station 302 includes a signal transmission / reception unit 322, an assignment determination unit 324, and a combination table 326. The combination table 326 is the same as that shown in FIG.

The signal transmission / reception unit 322 transmits / receives a signal to / from the UE 304, for example. For example, the signal transmission / reception unit 322 transmits N (for example, four) CSI RSs allocated to the base station among M (for example, eight) CSI RSs. Here, the radio subframe in which the large cell base station 102 transmits the CSI RS and the radio subframe in which the small cell base station 302 transmits the CSI RS can be time-multiplexed and transmitted. In addition, the signal transmission / reception unit 322 may transmit N CSI RSs assigned to the base station by code multiplexing, frequency multiplexing, or time multiplexing.

FIG. 8 is a diagram illustrating an example of a subframe for transmitting a CSI RS. FIG. 8 shows a group of radio subframes including a CSI RS radio subframe transmitted from the large cell base station 102 and a CSI RS radio subframe transmitted from the small cell base station 302. FIG. 8 shows a radio subframe group transmitted along a time series from the left side to the right side of the page. As shown in FIG. 8, the CSI RS radio subframe 170 transmitted from the large cell base station 102 and the CSI RS radio subframe 180 transmitted from the small cell base station 302 are transmitted at different times. Is multiplexed. As a result, the UE 304 can identify the CSI RS radio subframe 170 transmitted from the large cell base station 102 and the CSI RS radio subframe 180 transmitted from the small cell base station 302.

Returning to the description of FIG. 7, the assignment determination unit 324 receives the configuration number transmitted from the large cell base station 102. Based on 150, it is determined which CSI RS is allocated to the base station. For example, the assignment determination unit 324 receives a configuration number from the large cell base station 102. When “4” is transmitted as 150, the combination table 326 is referred to. Then, assignment determination section 324 determines that the CSI RS port “# 17, # 18, # 19, # 20” is assigned to the own base station. The signal transmission / reception unit 322 transmits the CSI RS from the CSI RS port of “# 17, # 18, # 19, # 20” according to the determination result of the allocation determination unit 324.

Next, details of the UE (mobile terminal) will be described. FIG. 9 is a hardware configuration and functional block diagram of the mobile terminal. In FIG. 9, the UE 304 is described as an example as an example, but other UEs can have the same configuration.

The UE 304 includes a reception antenna 341, a radio demodulation unit 342, a decoding processing unit 344, a reference signal measurement unit 346, user data 348, a control signal generation unit 350, a transmission power calculation unit 352, a channel coding unit 354, a radio modulation unit 356, and A transmission antenna 358 is included.

The radio demodulation unit 342 performs demodulation processing on the modulated radio signal received via the reception antenna 341. Radio demodulation section 342 outputs the demodulated signal to decoding processing section 344 and reference signal measurement section 346. The decoding processing unit 344 performs a decoding process on the signal received from the radio demodulation unit 342. For example, the decoding processing unit 344 performs decoding of an encoded signal received from the radio demodulation unit 342, decoding of compressed data, and the like. Decoding processor 344 outputs the decoded data to user data 348 and control signal generator 350.

User data 348 is a memory that stores various data registered in the UE 304, and a signal output from the decoding processing unit 344 is stored in the user data 348. The control signal generator 350 selects the number of CSI RSs from the information output from the decoding processor 344 and the number of CSI RSs (M: 8 for example) and the number of CSI RSs from the M CSI RSs. The number (N: for example, 4 pieces) of information indicating whether to do is output to the reference signal measurement unit 346. In addition, the control signal generation unit 350 obtains CSI RS Ports information, that is, information corresponding to CSI RS Ports 160 indicating one combination of CSI RSs from the signal output from the decoding processing unit 344, as a reference signal measurement unit. To 346.

The reference signal measurement unit 346 measures a reference signal (CSI RS or CRS) included in the signal received from the radio demodulation unit 342. That is, UE304 has the mode which measures CSI RS, and the mode which measures CRS, and measures a reference signal based on the signal which instruct | indicates in which mode it measures.

The reference signal measurement unit 346 measures the CSI RS based on the combination information of one of M, N, and CSI RS output from the control signal generation unit 350 in the mode of measuring the CSI RS. .

For example, when the reference signal measurement unit 346 is instructed to perform characteristic evaluation on M (e.g., 8) CSI RSs, the reference signal measurement unit 346 performs characteristic evaluation for each CSI RS and wirelessly modulates the evaluation result. The data is transmitted to the large cell base station 102 via the unit 356. The large cell base station 102 determines, based on the evaluation result, whether the UE 304 is close to which small cell or is not close to any small cell. For example, if there is little difference in quality between CSI RSs, it can be determined that the UE 304 is not close to any small cell, and wireless data transmission can be performed only from the large cell base station 102 to the UE 304.

On the other hand, for example, when the quality of CSI RSs # 17, # 18, # 19, and # 20 is good, it can be determined that UE 304 is in or near small cell 300, and transmission of a radio data signal to UE 304 It can be done only from the station 302. When the large cell base station 102 transmits the radio data signal to the UE 304 only from the small cell 300, the large cell base station 102 sends a configuration No. to the UE 304. 150 # 4 is notified. In other words, the large cell base station 102 is configured with the configuration no. Based on the wireless measurement result (reception power) for the combination of CSI RSs indicated by # 4 of 150, an instruction is given to determine the downlink propagation loss used when determining the uplink transmission power.

When receiving this instruction, the reference signal measurement unit 346 measures the received power of the CSI RS at the CSI RS port of the combination assigned to the small cell base station 302. Then, the reference signal measurement unit 346 obtains a downlink propagation loss value based on the difference between the measured received power and the transmission power when the small cell base station 302 transmits the CSI RS.

In addition, Configuration No. The measurement for four CSI RSs belonging to 150 # 4 is for determining the downlink propagation loss when determining the uplink transmission power. The UE 304 periodically performs measurement for eight CSI RSs and reports to the base station. As a result, even when the UE 304 moves and approaches another small cell, the base station that transmits and receives the radio data signal can be switched.

The transmission power calculation unit 352 calculates the transmission power of the radio signal transmitted from the UE 304. For example, the transmission power calculation unit 352 receives a downlink propagation loss value, a value determined in advance by a modulation scheme or a signal bandwidth, a value broadcast from the base station, and every time transmission is performed from the base station to the UE. Based on a correction value or the like of the transmitted power, the transmission power of the radio signal is calculated. Here, the transmission power calculation unit 352 calculates the transmission power of the radio signal using the downlink propagation loss value obtained by the reference signal measurement unit 346.

The channel coding unit 354 performs transmission path coding (channel coding) processing on various data stored in the user data 348 and the signal output from the control signal generation unit 350. For example, the channel coding unit 354 performs error correction processing by adding a code that can be corrected on the receiving side even if an error occurs on the transmitting side. Further, the channel coding unit 354 performs an interleaving process for rearranging data so that it can be reproduced even if data is lost for a long time such as burst noise.

Radio modulation section 356 performs modulation processing on the signal output from channel coding section 354. Radio modulation section 356 transmits the modulated signal from transmission antenna 358 using the transmission power calculated by transmission power calculation section 352.

Next, the processing flow of the wireless system 50 will be described. FIG. 10 is a flowchart showing processing of the wireless system. As shown in FIG. 10, first, the large cell base station 102 instructs whether to use CRS or CSI RS for the calculation of the downlink propagation loss (DL Path Loss) (step S101). For example, the large cell base station 102 transmits an instruction signal indicating use of CRS or an instruction signal indicating use of CSI RS.

Subsequently, the large cell base station 102 determines whether or not to use CSI RS (step S102). When it is determined not to use the CSI RS (No in step S102), that is, when it is instructed to obtain the downlink propagation loss using the CRS, the UE 304 obtains the downlink propagation loss based on the measurement result for the CRS. (Step S103).

On the other hand, if the large cell base station 102 determines that the CSI RS is used (step S102, Yes), the large cell base station 102 notifies the value of M (for example, 8), that is, the total number of CSI RSs (step S104). Subsequently, the UE 304 performs measurement on M CSI RSs and reports the measurement result to the large cell base station 102 (step S105). This is a report for the large cell base station 102 to determine the location information of the UE 304.

Subsequently, the large cell base station 102 notifies N (for example, 4) values, that is, a number indicating how many CSI RSs are selected from among the M CSI RSs (step S106). Subsequently, the large cell base station 102 notifies the combination of CSI RS antenna ports (Antenna Port Combination) (step S107). The combination of CSI RS antenna port is shown in Configuration No. of the combination table. Information corresponding to 150. Based on the received power of M CSI RSs reported from the UE 304, the large cell base station 102 determines whether the UE 304 is located near which small cell base station, or near any small cell base station. Determine if it does not exist. If the large cell base station 102 determines that the UE 304 exists near any small cell base station, the CSI RS antenna port assigned to the small cell base station where the UE 304 exists nearby. Is notified to the UE 304.

Subsequently, the UE 304 performs measurement for the designated N CSI RSs, and obtains a downlink propagation loss (DL Path Loss) (step S108). For example, the UE 304 obtains a downlink propagation loss value based on the difference between the received power measured for N CSI RSs and the transmission power when the small cell base station 302 transmits the CSI RS. The UE 304 obtains uplink transmission power using the downlink propagation loss obtained in this way.

Subsequently, the UE 304 performs measurement on M CSI RSs and reports the measurement result to the large cell base station 102 (step S109). This is a report for the large cell base station 102 to determine the location information of the UE 304, and periodically to determine whether the small cell in which the UE 304 is nearby has changed as the UE 304 moves. It is a report to be performed.

Subsequently, the large cell base station 102 determines whether or not to notify a new CSI RS antenna port combination (Antenna Port Combination) (step S110). When the large cell base station 102 determines to notify the new CSI RS antenna port combination (Yes in step S110), the large cell base station 102 returns to step S107 and continues the processing. This is to notify a new CSI RS antenna port combination when, for example, a small cell in the vicinity of the UE 304 changes as the UE 304 moves.

On the other hand, when it is determined that the new CSI RS antenna port combination is not notified (step S110, No), the large cell base station 102 determines whether or not to notify a new value of N (step S111). .

When the large cell base station 102 determines to notify the new value of N (step S111, Yes), the large cell base station 102 returns to step S106 and notifies the value of N. On the other hand, when the large cell base station 102 determines not to notify the new value of N (step S111, No), the process returns to step S108 and continues processing. In other words, in this case, the new CSI RS antenna port combination is not notified, and the new N value is not notified, and the downlink propagation loss is obtained with the same CSI RS antenna port combination as the current situation. is there.

As described above, according to the wireless system 50 of the present embodiment, transmission power can be appropriately obtained in a mixed cell in which a large cell and a small cell have the same physical cell ID. That is, the large cell base station 102 is determined by selecting N (N is an integer of 2 or more smaller than M) CSI RSs from among M (M is an integer of 3 or more) CSI RSs. Are assigned to a plurality of small cell base stations. The small cell base station 302 transmits N reference signals allocated to the own base station among the M reference signals. And the large cell base station 102 transmits the combination signal which shows 1 combination which selected N CSI RS out of M CSI RS based on the position of UE304. The UE 304 receives a combination reference signal corresponding to the combination signal transmitted from the large cell base station 102, and obtains uplink transmission power with the small cell base station 302 based on the reception result. According to this, even if a large cell and a small cell are mixed cells having the same physical cell ID, each small cell transmits a different combination of CSI RSs, and the UE is transmitted from a small cell near its own device. The downlink propagation loss can be obtained based on the reception result of the combined CSI RS. As a result, it is possible to appropriately obtain the transmission power of the uplink with the small cell near the own device.

50 wireless system 100 large cell 102 large cell base station 122 signal transmission / reception unit 124

allocation unit

126, 326 combination table 128

notification unit

200, 300, 400, 500

small cell

202, 302 small cell base station 304 UE
322 Signal transmission / reception unit 324 Allocation determination unit 342 Radio demodulation unit 346 Reference signal measurement unit 352 Transmission power calculation unit 356 Radio modulation unit

Claims

A first base station corresponding to the first radio cell, and a plurality of second radio cells provided in the first radio cell and respectively corresponding to a plurality of second radio cells smaller than the first radio cell A wireless system comprising a base station and a mobile terminal,
The first base station is
N (N is an integer smaller than M) reference signals are selected from M (M is an integer equal to or greater than 2) reference signals provided for evaluating downlink radio quality to the mobile terminal. An allocating unit that allocates a plurality of different combinations determined by each to the plurality of second base stations;
A notification unit for transmitting a combination signal indicating one combination of the N reference signals selected from the M reference signals based on the position of the mobile terminal;
Each of the second base stations has
A signal transmission unit for transmitting N reference signals allocated to the base station among the M reference signals;
The mobile terminal
A receiving unit that receives the combination signal transmitted by the notification unit, and a reference signal of a combination corresponding to the combination signal;
A transmission power calculation unit that obtains uplink transmission power with the second base station to which a combination of reference signals corresponding to the combination signal is assigned based on a reception result of the reference signal received by the reception unit When,
A wireless system characterized by comprising:
The mobile terminal
A report unit for reporting a reception result of the M reference signals to the first base station;
The notification unit of the first base station determines which cell of the plurality of second radio cells the mobile terminal belongs to based on the reception result of the M reference signals reported by the report unit The wireless system according to claim 1, wherein the combination signal is transmitted based on a determination result.
The radio system according to claim 1, wherein the notification unit notifies the mobile terminal of the combination signal together with a control signal including information for the mobile terminal to perform data modulation / demodulation.
The signal transmission unit of the second base station is
2. The radio according to claim 1, wherein N reference signals allocated to a base station among the M reference signals are transmitted by code multiplexing, frequency multiplexing, or time multiplexing with each other. system.
Selecting N (N is an integer smaller than M) reference signals from M (M is an integer of 2 or more) reference signals provided for evaluating downlink radio quality to the mobile terminal A plurality of different combinations determined by the allocation unit assigned to a plurality of small base stations respectively provided in the own radio cell and corresponding to a plurality of small radio cells smaller than the own radio cell;
1 indicates a combination in which the N reference signals are selected from the M reference signals based on the position of the mobile terminal, and 1 of the reference signals is based on a result of receiving the reference signal at the mobile terminal. A notification unit that transmits a combination signal used when obtaining uplink transmission power with a small base station to which a combination of
A base station characterized by comprising:
Among M reference signals (M is an integer equal to or greater than 2) transmitted from the first base station corresponding to the first radio cell and provided for evaluating the downlink radio quality to the mobile terminal A combination signal indicating one combination of N (N is an integer smaller than M) reference signals selected, and a plurality of second radios provided in the first radio cell and smaller than the first radio cell A reference signal of a combination corresponding to the combination signal is received from a second base station assigned to transmit a combination reference signal corresponding to the combination signal among a plurality of second base stations corresponding to each cell. A receiving unit to
A transmission power calculation unit for obtaining uplink transmission power with a second base station to which a combination of reference signals corresponding to the combination signal is assigned based on a reception result of the reference signal received by the reception unit; ,
A mobile terminal comprising:
A first base station corresponding to the first radio cell, and a plurality of second radio cells provided in the first radio cell and respectively corresponding to a plurality of second radio cells smaller than the first radio cell The first base station of a wireless system comprising a base station and a mobile terminal,
N (N is an integer smaller than M) reference signals are selected from M (M is an integer equal to or greater than 2) reference signals provided for evaluating downlink radio quality to the mobile terminal. A plurality of different combinations determined by each of the plurality of second base stations,
Transmitting a combination signal indicating one combination in which the N reference signals are selected from the M reference signals based on the position of the mobile terminal;
Each of the second base stations
Transmitting N reference signals allocated to the base station among the M reference signals,
The mobile terminal is
Receiving a combination signal transmitted by the first base station, and a reference signal of a combination corresponding to the combination signal;
Radio communication characterized in that, based on a reception result of the received reference signal, uplink transmission power is obtained with a second base station to which a combination of reference signals corresponding to the combination signal is assigned. Method.