JP2016181928A - Communication system, radio base station and radio terminal - Google Patents

Abstract

To improve reception characteristics of a control signal. In a communication system, a common pilot signal is transmitted to each of radio terminals (131, 132) at a first timing (t1) at frequencies (f1, f2) based on identification information of the own cell for each cell (121, 122). The The radio base station 111 transmits a common pilot signal at the first timing t1, and at a second timing t2 different from the first timing t1, the dedicated pilot signal to the radio terminal 131 of the own cell 121 and the radio of the own cell 121 are transmitted. The control signal to the terminal 131 is transmitted at different frequencies f1 to f3. The radio terminal 131 demodulates the control signal transmitted by the radio base station 111 based on the dedicated pilot signal transmitted by the radio base station 111. [Selection] Figure 1

Description

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

  LTE-A (LTE-Advanced), an extension of LTE (Long Term Evolution), which is one of mobile communication systems, in 3GPP (3rd Generation Partnership Project), which is one of the standardization organizations that formulate wireless communication system specifications Study work and specification work are being done. Although the specification of LTE-A basic functions has been completed, the introduction of new functions has been proposed and discussions have continued and the system has evolved with the aim of further improving performance and improving the ability to handle diversified system operation scenarios. I keep doing it. In the LTE-A specifications so far, wireless parameters for directly transmitting wireless parameters (position of the frequency domain where the data signal is arranged, modulation scheme, coding rate, etc.) directly related to wireless transmission of the transmitted data signal are transmitted. The control signal was transmitted in a time domain different from that of the data signal. In other words, the radio resource area used for transmitting the radio control signal and the radio resource area used for transmitting the data signal are time-multiplexed. In the latest discussion, in order to be able to increase the amount of radio resources available for transmission of radio control signals according to the situation, the radio control is also applied to the area used for data signal transmission. It is being considered to be able to place signals. However, if a part of the area for transmitting the data signal can be used for transmitting the radio control signal, the amount of radio resources that can be used for transmitting the data signal is reduced. Therefore, it is desirable to apply a high-efficiency transmission method to a radio control signal transmitted on a region used for data signal transmission and to minimize the amount of radio resources used. One way to achieve this is to apply a high-order modulation degree modulation method to a radio control signal, and it is known to apply a high-order modulation method to a downlink control signal arranged in the vicinity of a pilot signal. (For example, see Patent Document 1 below.) When receiving and demodulating a radio signal to which a high-order modulation scheme is applied in which information bits are mapped using not only phase components such as 16QAM and 64QAM but also amplitude components, the demodulation characteristics may be improved. is necessary. Usually, channel estimation information for demodulating data signals is obtained by interpolating channel estimation results for multiple pilot signals, and data signals are demodulated. However, the demodulation characteristics of signals placed near the pilot signals Get better.

International Publication No. 2007/052767

  However, when a transmission frequency shift of a common pilot signal is performed between radio cells, for example, LTE and LTE-A, a radio control signal to which a modulation scheme of a higher-order modulation degree is applied is arranged near the pilot signal. However, the reception characteristics of the control signal may be deteriorated due to interference from the common pilot signal of the adjacent cell, and the benefit of improving the demodulation characteristics by arranging the demodulation target signal in the vicinity of the pilot signal cannot be sufficiently received.

  In order to solve the above-described problems, an object of the present invention is to provide a communication system, a radio base station, and a radio terminal that can improve control signal reception characteristics.

  In order to solve the above-described problems and achieve the object, according to one aspect of the present invention, in a communication method of a communication system including a wireless terminal and a wireless base station, the wireless base station uses cell identification information as a cell identification information. A common pilot signal is transmitted to the wireless terminal at a frequency based on the first timing, and the wireless base station transmits an individual pilot signal and a control signal to the wireless terminal at a second timing different from the first timing. A communication system, a radio base station, and a radio that transmit simultaneously on different frequencies, and in which the radio terminal demodulates the control signal transmitted by the radio base station based on the dedicated pilot signal transmitted by the radio base station A terminal is proposed.

  According to an aspect of the present invention, the influence of interference from any common pilot signal from an adjacent radio base station can be reduced. In addition, by arranging the radio control signal in the vicinity of the pilot signal used for demodulation, it is possible to improve the reception characteristic of the radio control signal.

FIG. 1 is a diagram illustrating an example of a communication system according to an embodiment. FIG. 2 is a diagram illustrating an example of downlink radio resources. FIG. 3A is a diagram illustrating an example of a configuration of a communication unit of a radio base station. FIG. 3-2 is a diagram illustrating an example of a signal flow in the communication unit of the radio base station depicted in FIG. 3-1. FIG. 4A is a diagram illustrating an example of a configuration of a communication unit of a wireless terminal. FIG. 4-2 is a diagram illustrating an example of a signal flow in the communication unit of the wireless terminal depicted in FIG. 4-1. FIG. 5 is a flowchart showing an example of the operation of the arrangement selection unit of the radio base station. FIG. 6 is a diagram illustrating an example of the cell arrangement. FIG. 7-1 is a diagram (part 1) illustrating an example of a frequency shift of a common pilot signal. FIG. 7-2 is a diagram (part 2) illustrating an example of the frequency shift of the common pilot signal. FIG. 7-3 is a diagram (part 3) illustrating an example of the frequency shift of the common pilot signal. FIG. 7-4 is a diagram (part 4) illustrating an example of the frequency shift of the common pilot signal. FIG. 7-5 is a diagram (part 5) illustrating an example of the frequency shift of the common pilot signal. FIG. 7-6 is a diagram (part 6) illustrating an example of the frequency shift of the common pilot signal. FIG. 8 is a diagram illustrating an example of a hardware configuration of the radio base station. FIG. 9 is a diagram illustrating an example of a hardware configuration of the wireless terminal.

  Exemplary embodiments of a communication system, a radio base station, and a radio terminal according to the present invention will be described below in detail with reference to the accompanying drawings.

(Embodiment)
FIG. 1 is a diagram illustrating an example of a communication system according to an embodiment. As shown in FIG. 1, the communication system 100 includes radio base stations 111 and 112 and radio terminals 131 and 132. A cell 121 is a cell of the radio base station 111. A cell 122 is a cell of the radio base station 112.

  The wireless terminal 131 is located in the cell 121 and is connected to the wireless base station 111. However, the wireless terminal 131 is also located in the cell 122 and receives interference from a wireless signal transmitted from the wireless base station 112. The wireless terminal 132 is located in the cell 122 and is connected to the wireless base station 112.

  The radio base station 111 transmits a downlink radio signal to the radio terminal 131. The radio base station 112 transmits a downlink radio signal to the radio terminal 132. For example, OFDM (Orthogonal Frequency Division Multiplexing) can be used for the radio signals transmitted by the radio base stations 111 and 112.

  The signal arrangement 141 shows the signal arrangement of radio signals transmitted from the cell 121 by the radio base station 111. The signal arrangement 142 shows the signal arrangement of radio signals transmitted from the radio base station 112 in the cell 122. In the signal arrangements 141 and 142, “C” indicates a radio resource in which a downlink common pilot signal is arranged. “D” indicates a radio resource in which a downlink dedicated pilot signal is arranged. Further, a cross indicates a radio resource in which a downlink control signal is arranged.

  The common pilot signal and the dedicated pilot signal are symbols used for radio communication synchronization and channel equalization, for example, and are signals that the radio base stations 111 and 112 transmit to their own cells at a predetermined period. The common pilot signal is a pilot signal transmitted in common to each wireless terminal in the cell. The dedicated pilot signal is a pilot signal transmitted individually to each wireless terminal in the cell.

  In the communication system 100, a frequency shift is performed for each cell so that a common pilot signal to each wireless terminal of the own cell is transmitted at the first timing t1 by a frequency based on the identification information of the own cell. For example, it is assumed that the identification information of the radio base stations 111 and 112 is identification information # 1 and # 2, respectively. Further, it is assumed that the frequencies based on the identification information # 1 and # 2 are frequencies f1 and f2 (f1 ≠ f2), respectively.

  In this case, the radio base station 111 transmits a common pilot signal at the first timing t1 by using the frequency f1 based on the identification information # 1 of the own cell. On the other hand, the radio base station 112 transmits a common pilot signal using the frequency f2 based on the identification information # 2 of the own cell at the same first timing t1 as that of the radio base station 111.

  In addition, the radio base station 111, at a second timing t2 different from the first timing t1, the dedicated pilot signal to the radio terminal of the own cell (for example, the radio terminal 131), the control signal to the radio terminal of the own cell, Are transmitted simultaneously on different frequencies. Specifically, the radio base station 112 transmits the dedicated pilot signal to the radio terminal of the own cell using the frequencies f1 and f3. In addition, the radio base station 111 transmits a control signal to the radio terminal (for example, the radio terminal 132) of the own cell at the frequency f2.

  As described above, the radio base station 111 transmits a downlink control signal at the second timing t2 different from the first timing t1 at which the common pilot signal is transmitted in each cell. Thereby, even if a common pilot signal is transmitted at any frequency in an adjacent cell such as the cell 122, interference with the control signal of the own cell due to the common pilot signal of the adjacent cell can be suppressed. For this reason, the reception characteristic of the control signal in the wireless terminal 131 can be improved.

  The second timing t2 for transmitting the control signal to the wireless terminal 131 is also the timing for transmitting the dedicated pilot signal to the wireless terminal 131. As a result, the channel characteristics of the dedicated pilot signal received by the wireless terminal 131 and the control signal are close, and the demodulation accuracy of the control signal based on the channel estimation result of the dedicated pilot signal is improved. For this reason, the reception characteristic of the control signal in the wireless terminal 131 can be improved.

  In the example illustrated in FIG. 1, the case where the cells 121 and 122 are formed by the radio base stations 111 and 112 has been described. However, the cells 121 and 122 are cells (sectors) formed by one radio base station. Also good. Further, the communication system 100 may include three or more cells.

  In the example illustrated in FIG. 1, the case where the control signal is transmitted simultaneously with the dedicated pilot signal in the cell 121 has been described. However, the control signal may be transmitted simultaneously with the dedicated pilot signal in the cell 122. Thereby, the reception characteristic of the control signal in the wireless terminal 132 can also be improved.

  FIG. 2 is a diagram illustrating an example of downlink radio resources. A physical resource block 200 illustrated in FIG. 2 is, for example, one physical resource block (PRB) in the radio downlink section of the cell 121.

  The vertical axis direction of the physical resource block 200 indicates time resources in units of subframes having a length of 1 [ms]. One subframe includes 14 (or 12) OFDM symbols. The horizontal axis direction of the physical resource block 200 indicates frequency resources in units of 12 subcarriers.

  In the physical resource block 200, a response signal (for example, ACK or NACK) for an uplink data signal and a downlink control signal are arranged in the first N OFDM symbols (first section SF1). The downlink control signal includes, for example, downlink data signal notification information and uplink data signal transmission instruction information.

  Further, for example, PDCCH (Physical Downlink Control Channel) is used as the downlink control signal. The PDCCH is a physical layer (Layer 1) level downlink control signal including information related to data signal transmission.

  Parameters related to data signal transmission are stored in a downlink control signal associated with the data signal, and transmitted to the wireless terminal using the same downlink subframe as the target data signal. Parameters related to data signal transmission include, for example, information on which part in the frequency domain the data signal for each wireless terminal is transmitted, the modulation scheme and coding rate applied to the data signal, and data transmission. This is a parameter of HARQ (Hybrid Automatic Repeat Request) concerned.

  Also, a common pilot signal is used for demodulating the downlink control signal and data signal. The position (subcarrier) on the frequency axis of the common pilot signal is frequency-shifted based on a value uniquely determined by the value of identification information (recognition number) of a cell in which the common pilot is transmitted. Thereby, it is possible to prevent a common pilot collision from occurring between adjacent cells. The cell identification information is, for example, PCI (Physical Cell ID).

  In the example shown in FIG. 2, N = 3, but N may be 1 or 2, for example. Further, the value of N may be a different value in each downlink subframe. The value of N is, for example, from the radio base station 111 to the radio terminal using a control signal such as PCFICH (Physical Control Format Channel) transmitted on the first OFDM symbol of each downlink subframe. 131 is notified.

  In the physical resource block 200, “C” indicates a resource element in which a common pilot signal is arranged. “D” indicates a resource element in which the dedicated pilot signal is arranged. “D” indicates a resource element in which a data signal such as PDSCH (Physical Downlink Shared Channel) is arranged.

  A downlink data signal such as PDSCH is arranged in a portion of the physical resource block 200 other than the head section SF1. The control information of the upper layer (for example, Layer 2 or Layer 3) level is stored in the data signal and transmitted. The downlink control signal in LTE uses QPSK or the like as a modulation scheme, and is transmitted from a transmission antenna of a radio base station using a transmission diversity scheme.

  An E-PDCCH (Enhanced-Physical Downlink Control Channel: extended physical downlink control channel) is a downlink control signal that is arranged and transmitted in a portion other than the head section SF1 of the physical resource block 200. Thereby, it is possible to expand the capacity of the radio resource in which the downlink control signal can be arranged. Moreover, it becomes possible to apply the interference control technique between cells not only to a data signal but to a downlink control signal.

  Further, a higher-order modulation scheme or a spatial multiplexing scheme can be applied to the E-PDCCH. High-order modulation schemes are, for example, QPSK (Quadrature Phase Shift Keying), 16QAM (Quadrature Amplitude Modulation), 64QAM, and 256QAM. The spatial multiplexing method is, for example, MIMO (Multiple Input Multiple Output). Thereby, since E-PDCCH can be transmitted with few radio | wireless resources, the reduction | decrease of the capacity | capacitance of the radio | wireless resource which can arrange | position a data signal can be suppressed.

  For demodulation of E-PDCCH, a dedicated pilot signal is used instead of a common pilot signal. For this reason, it is possible to calculate a different inter-antenna space matrix for each wireless terminal or for each E-PDCCH.

  Resource elements 211 to 214 marked with “x” indicate resource elements in which the E-PDCCH is arranged. As shown in resource elements 211 to 214, subframes SF2 and SF3 in which the E-PDCCH is arranged are time resources in which no common channel signal is arranged in each cell. Thereby, it is possible to avoid interference on the E-PDCCH by the common pilot from the adjacent cell regardless of the frequency resource of the common pilot of the adjacent cell due to the application of the frequency shift.

  Furthermore, subframes SF2 and SF3 in which E-PDCCH is arranged are time resources in which dedicated pilot signals are arranged in common in each cell. And subcarriers SC1 and SC2 in which E-PDCCH is arranged are frequency resources different from the frequency resources in which dedicated pilot signals are arranged in each cell.

  Thereby, the time resource of E-PDCCH becomes the same as the time resource of the dedicated pilot signal, and the channel estimation accuracy of E-PDCCH based on the dedicated pilot signal can be improved. For this reason, even if a higher-order modulation scheme such as 16QAM or 64QAM or a spatial multiplexing transmission scheme is applied to the E-PDCCH, the demodulation characteristics of the E-PDCCH can be improved.

  Also, the radio base station 111 transmits the dedicated pilot signal and a part of the control signal (for example, E-PDCCH) arranged at adjacent frequencies. Thereby, the channel estimation precision of E-PDCCH based on a dedicated pilot signal can be further improved.

  In each cell, no frequency shift is applied to the dedicated pilot signal. Therefore, by shifting the frequency resources of the E-PDCCH and the dedicated pilot signal in the own cell, it is possible to avoid interference with the E-PDCCH due to the dedicated pilot signal from the adjacent cell.

  Thus, the radio base station 111 arranges the E-PDCCH in the resource elements 211 to 214 that are not subject to interference due to the common pilot signal and the dedicated pilot signal from the adjacent cell. Thereby, the reception characteristic of the downlink control signal by E-PDCCH in the radio | wireless terminal 131 can be improved.

  In the example illustrated in FIG. 2, 24 resource elements 211 to 214 for E-PDCCH exist in the physical resource block 200. For example, when 16QAM is applied to the E-PDCCH, information bits after 96-bit encoding are mapped to 24 resource elements 211 to 214 and can be transmitted.

  In LTE, there are four types of PDCCH sizes, and the analysis results show that the smallest one is used most frequently. In this minimum PDCCH, 72-bit encoded information bits are transmitted, and it is possible to map one downlink control signal to which 16QAM is applied to 24 resource elements 211 to 214. .

  Further, the interval between the areas where the individual pilot signals are arranged may be about ½ of the coherent bandwidth. For example, in the physical resource block 200 shown in FIG. 2, the interval between the areas where the dedicated pilot signals are arranged is 3 subcarriers.

  FIG. 3A is a diagram illustrating an example of a configuration of a communication unit of a radio base station. FIG. 3-2 is a diagram illustrating an example of a signal flow in the communication unit of the radio base station depicted in FIG. 3-1. As illustrated in FIGS. 3A and 3B, the radio base station 111 includes an encoding unit 301, a modulation unit 302, an arrangement selection unit 303, an encoding unit 304, a modulation unit 305, and an encoding unit. A unit 306, a modulation unit 307, a frequency multiplexing unit 308, and a time multiplexing unit 309 are provided. The radio base station 111 includes a radio transmission unit 310, a transmission antenna 311, a reception antenna 312, a radio reception unit 313, a pilot signal processing unit 314, a demodulation unit 315, a decoding unit 316, and a control signal extraction. Part 317.

  The encoding unit 301 encodes the input data signal. Then, encoding section 301 transmits the encoded data signal to modulation section 302. The modulation unit 302 modulates the data signal output from the encoding unit 301. Modulation section 302 then transmits the modulated data signal to frequency multiplexing section 308.

  The arrangement selection unit 303 selects an area in which the input control signal is arranged (mapped). In addition, the arrangement selection unit 303 performs region selection based on the DL radio characteristic information output from the control signal extraction unit 317. Then, the arrangement selection unit 303 outputs the input control signal to the encoding units 304 and 306 based on the region selection result.

  Specifically, arrangement selection section 303 outputs a control signal arranged in the same time domain as the data signal to encoding section 304, and outputs a control signal arranged in a time domain different from the data signal to encoding section 306. . Further, the arrangement selection unit 303 sets a modulation scheme for the control signal by the modulation unit 307 based on the DL radio characteristic information. The operation of the arrangement selection unit 303 will be described later (see, for example, FIG. 5).

  Each of the encoding units 304 and 306 encodes the control signal output from the arrangement selection unit 303. Then, encoding sections 304 and 306 output the encoded control signals to modulation sections 305 and 307, respectively. Modulating sections 305 and 307 modulate the control signals output from encoding sections 304 and 306, respectively. Modulation sections 305 and 307 then output the modulated control signals to frequency multiplexing section 308 and time multiplexing section 309, respectively.

  The frequency multiplexing unit 308 frequency-multiplexes the data signal output from the modulation unit 302 and the control signal output from the modulation unit 305. Then, the frequency multiplexing unit 308 outputs the frequency multiplexed signal to the time multiplexing unit 309.

  The time multiplexing unit 309 time-multiplexes the signal output from the frequency multiplexing unit 308 and the control signal output from the modulation unit 307. Then, the time multiplexing unit 309 outputs the time multiplexed signal to the wireless transmission unit 310. The wireless transmission unit 310 wirelessly transmits the signal output from the time multiplexing unit 309 to each wireless terminal of the cell 121 via the transmission antenna 311.

  The wireless reception unit 313 receives a signal wirelessly transmitted from each wireless terminal of the cell 121 via the reception antenna 312. Radio receiving section 313 outputs the received signal to pilot signal processing section 314 and demodulation section 315.

  Pilot signal processing section 314 extracts a pilot signal included in the signal output from radio reception section 313, and outputs the extracted pilot signal to demodulation section 315. The demodulator 315 demodulates the signal output from the wireless receiver 313 based on the pilot signal output from the pilot signal processor 314. Demodulation section 315 then outputs the demodulated signal to decoding section 316.

  The decoding unit 316 decodes the signal output from the demodulation unit 315. Then, the decoding unit 316 outputs a data signal and a control signal included in the decoded signal. The control signal output from the decoding unit 316 is input to the control signal extraction unit 317.

  The control signal extraction unit 317 outputs the control signal output from the decoding unit 316. Further, the control signal extraction unit 317 extracts DL radio characteristic information included in the control signal output from the decoding unit 316. Then, the control signal extraction unit 317 outputs the extracted DL radio characteristic information to the arrangement selection unit 303.

  FIG. 4A is a diagram illustrating an example of a configuration of a communication unit of a wireless terminal. FIG. 4-2 is a diagram illustrating an example of a signal flow in the communication unit of the wireless terminal depicted in FIG. 4-1. As illustrated in FIGS. 4A and 4B, the wireless terminal 131 includes a reception antenna 401, a wireless reception unit 402, a pilot signal processing unit 403, a wireless characteristic measurement unit 404, a time separation unit 405, A control signal detection / demodulation / decoding unit 406 and a frequency separation unit 407 are provided. The wireless terminal 131 switches between a control signal detection / demodulation / decoding unit 408, a data signal demodulation / decoding unit 409, an encoding unit 410, a modulation unit 411, an encoding unit 412, and a modulation unit 413. Unit 414, wireless transmission unit 415, and transmission antenna 416.

  The wireless reception unit 402 receives a signal wirelessly transmitted from the wireless base station 111 via the reception antenna 401. Radio receiving section 402 then outputs the received signal to pilot signal processing section 403 and time separation section 405.

  Pilot signal processing section 403 extracts a pilot signal included in the signal output from radio reception section 402. Then, pilot signal processing section 403 outputs the extracted pilot signal to radio characteristic measuring section 404, control signal detection / demodulation / decoding section 406, control signal detection / demodulation / decoding section 408 and data signal demodulation / decoding section 409. .

  Radio characteristic measuring section 404 measures the downlink radio characteristics from radio base station 111 to radio terminal 131 based on the pilot signal output from pilot signal processing section 403. For example, SINR (Signal to Interference and Noise Ratio) can be used as the radio characteristics measured by the radio characteristic measurement unit 404. Radio characteristic measuring section 404 outputs DL radio characteristic information indicating the measured downlink radio characteristics to encoding section 410.

  The time separation unit 405 performs time separation on the signal output from the wireless reception unit 402. The time separation unit 405 outputs the time-separated signals to the control signal detection / demodulation / decoding unit 406 and the frequency separation unit 407, respectively. Specifically, the time separation unit 405 outputs, to the control signal detection / demodulation / decoding unit 406, a signal in which only the control signal is mapped among the time-separated signals. Also, the time separation unit 405 outputs a signal in which the data signal and the control signal are mapped among the time-separated signals to the frequency separation unit 407.

  Control signal detection / demodulation / decoding section 406 detects a control signal from the signal output from time separation section 405 based on the pilot signal output from pilot signal processing section 403, and demodulates and decodes the detected control signal. I do. Then, the control signal detection / demodulation / decoding unit 406 outputs the decoded control signal. The control signal output from the control signal detection / demodulation / decoding unit 406 is input to the data signal demodulation / decoding unit 409.

  The frequency separation unit 407 performs frequency separation on the signal output from the time separation unit 405. Then, the frequency separation unit 407 outputs the control signal obtained by the frequency separation to the control signal detection / demodulation / decoding unit 408. Further, the frequency separation unit 407 outputs a data signal obtained by the frequency separation to the data signal demodulation / decoding unit 409.

  The control signal detection / demodulation / decoding unit 408 detects the control signal output from the frequency separation unit 407 based on the pilot signal output from the pilot signal processing unit 403, and demodulates and decodes the detected control signal. . Then, the control signal detection / demodulation / decoding unit 408 outputs the decoded control signal. The control signal output from the control signal detection / demodulation / decoding unit 408 is input to the data signal demodulation / decoding unit 409.

  The data signal demodulation / decoding unit 409 demodulates and decodes the data signal output from the frequency separation unit 407. Specifically, data signal demodulation / decoding section 409 is based on the pilot signal output from pilot signal processing section 403 and the control signals output from control signal detection / demodulation / decoding sections 406 and 408. Demodulate and decode. Then, the data signal demodulation / decoding unit 409 outputs the decoded data signal.

  The encoding unit 410 encodes the input control signal. Also, encoding section 410 stores DL radio characteristic information output from radio characteristic measuring section 404 in the control signal to be encoded. Then, encoding section 410 outputs the encoded control signal to modulation section 411.

  The modulation unit 411 modulates the control signal output from the encoding unit 410. Modulation section 411 then outputs the modulated control signal to switching section 414. The encoding unit 412 encodes the input data signal. Then, the encoding unit 412 outputs the encoded data signal to the modulation unit 413. The modulation unit 413 modulates the data signal output from the encoding unit 412. Modulation section 413 then outputs the modulated data signal to switching section 414.

  The switching unit 414 outputs the control signal output from the modulation unit 411 and the data signal output from the modulation unit 413 to the wireless transmission unit 415 while switching. The wireless transmission unit 415 wirelessly transmits the signal output from the switching unit 414 to the wireless base station 111 via the transmission antenna 416.

  FIG. 5 is a flowchart showing an example of the operation of the arrangement selection unit of the radio base station. For example, the arrangement selection unit 303 of the radio base station 111 executes the following steps for the downlink to the radio terminal 131. First, the arrangement selection unit 303 acquires downlink radio characteristics of the radio terminal 131 (step S501). The downlink radio characteristics of the radio terminal 131 can be acquired by DL radio characteristic information included in a control signal received from the radio terminal 131, for example.

  Next, the arrangement selection unit 303 determines whether or not the wireless characteristic acquired in step S501 is greater than or equal to the first reference value (step S502). When the wireless characteristic is equal to or higher than the first reference value (step S502: Yes), the arrangement selecting unit 303 determines whether the wireless characteristic is equal to or higher than the second reference value (step S503). The second reference value is larger than the first reference value.

  In step S503, when the radio characteristics are equal to or higher than the second reference value (step S503: Yes), the arrangement selection unit 303 sets the modulation method of the control signal to 64QAM (step S504), and proceeds to step S506. When the wireless characteristic is less than the second reference value (step S503: No), the arrangement selection unit 303 sets the modulation scheme of the control signal to 16QAM (step S505).

  Next, the arrangement selection unit 303 maps the control signal to a specific part in the control signal resource (step S506), and ends a series of mapping operations. The specific part is a time during which the common pilot signal is not transmitted in each cell and the dedicated pilot signal of the own cell is transmitted, and is a radio resource having a frequency different from that of the dedicated pilot signal of the own cell. The specific part is, for example, the resource elements 211 to 214 shown in FIG.

  In step S502, when the wireless characteristic is less than the first reference value (step S502: No), the arrangement selection unit 303 sets the modulation method of the control signal to QPSK (step S507). Next, the arrangement selection unit 303 determines whether or not the mapping process of other control signals whose radio characteristics are equal to or higher than the first reference value has been completed (step S508), and other control signals equal to or higher than the first reference value. The process waits until all the mapping processes are completed (step S508: No loop).

  In step S508, when all other control signal mapping processes equal to or greater than the first reference value are completed (step S508: Yes), the arrangement selection unit 303 determines whether or not there is a space in a specific part in the control signal resource. (Step S509). If there is a vacancy in the specific part (step S509: Yes), the arrangement selection unit 303 proceeds to step S506.

  In step S509, when there is no space in the specific part (step S509: No), the arrangement selection unit 303 maps the control signal to a part other than the specific part in the control signal resource (step S510), and a series of mapping operations Exit. The part other than the specific part is, for example, a radio resource at a time when the common pilot signal is transmitted in each cell, or a radio resource at a time when the common pilot signal is not transmitted in each cell and the individual pilot signal of the own cell is not transmitted. It is.

  Through the above steps, the arrangement selection unit 303 can set the modulation scheme by the modulation unit 307 for the control signal based on the DL radio characteristic information. Further, the arrangement selection unit 303 preferentially maps a control signal to which higher order 64QAM or 16QAM is applied as compared with QPSK to a specific part, and deteriorates reception characteristics of the control signal to which a higher order modulation scheme is applied. Can be suppressed.

  As described above, the radio base station 111 transmits a control signal using a modulation scheme according to radio characteristics between the radio base station 111 and the radio terminal 131. Then, the radio base station 111 transmits the control signal using the higher order (multilevel) modulation scheme with higher priority by using the radio resource at the same time as the individual pilot signal in the second timing at which the common pilot is not transmitted. As a result, it is possible to improve the resource usage efficiency by using a higher-order modulation scheme for the control signal for the radio terminal 131 having good radio characteristics, and to suppress the deterioration of the reception characteristic of the control signal.

  FIG. 6 is a diagram illustrating an example of the cell arrangement. A communication system 600 shown in FIG. 6 includes radio base stations 610, 620, 630, and 640. The radio base station 610 forms cells 611 to 613 of identification information # 1 to # 3, respectively. The radio base station 620 forms cells 621 to 623 for identification information # 4 to # 6, respectively. The radio base station 630 forms cells 631 to 633 of identification information # 1 to # 3, respectively. The radio base station 640 forms cells 641 to 643 of identification information # 4 to # 6, respectively.

  FIGS. 7-1 to 7-6 are diagrams illustrating an example of the frequency shift of the common pilot signal. Physical resource blocks 701 to 706 shown in FIGS. 7-1 to 7-6 indicate physical resource blocks in the downlink of the cells whose identification information is # 1 to # 6, respectively. For example, the physical resource block 701 is a physical resource block in the cells 611 and 631 illustrated in FIG. A physical resource block 702 indicates a physical resource block in the cells 612 and 632 illustrated in FIG.

  “C” in the physical resource blocks 701 to 706 indicates a radio resource in which the common pilot signal is arranged. Also, illustration of the arrangement of signals other than the common pilot signals in the physical resource blocks 701 to 706 is omitted.

  As shown in the physical resource blocks 701 to 706, in each cell (cells 611 to 613, 621 to 623, 631 to 633, 641 to 643) of the communication system 600, a common pilot signal is transmitted using the same time resource. In each cell of communication system 600, a common pilot signal is transmitted using frequency resources based on identification information of the own cell.

  For example, in the communication system 600, each frequency resource is associated with a remainder when a cell ID (identification information) is divided by six. Each cell of the communication system 600 transmits a common pilot signal using a frequency resource corresponding to the remainder when the cell ID of the own cell is divided by 6.

  Thus, by performing frequency shift of the common pilot signal in each cell of the communication system 600, interference of the common pilot signal between adjacent cells can be suppressed. For example, although the cells 611 and 621 are adjacent to each other, the common pilot signals are transmitted at different frequencies based on the identification information # 1 and # 4, respectively, so that interference can be suppressed.

  The radio base station 111 described above can be applied to, for example, at least one of the radio base stations 610, 620, 630, and 640 of the communication system 600 shown in FIG. The above-described wireless terminal 131 can be applied to, for example, a wireless terminal located in at least one of the cells of the communication system 600 illustrated in FIG.

  Further, the radio base station 111 and the radio terminal 131 can be applied to each cell of a communication system in which a small cell (for example, a femto cell) exists in a large cell (for example, a macro cell). In such a communication system, when a wireless terminal in a large cell is forcibly connected to a small cell in order to release the traffic load of the large cell to the small cell, a pilot signal transmitted from the large cell by the wireless terminal is transmitted. The influence of interference received from is increased. Further, in such a communication system, the cell arrangement becomes complicated, so that it becomes difficult to control the inter-cell interference of pilot signals. On the other hand, by applying the radio base station 111 and the radio terminal 131, it is possible to suppress the influence of interference received from the pilot signal.

  FIG. 8 is a diagram illustrating an example of a hardware configuration of the radio base station. The above-described radio base station 111 can be realized by, for example, the communication apparatus 800 illustrated in FIG. The communication device 800 includes a CPU 801, a memory 802, a user interface 803, a wired communication interface 804, and a wireless communication interface 805. The CPU 801, the memory 802, the user interface 803, the wired communication interface 804, and the wireless communication interface 805 are connected by a bus 809.

  A CPU 801 (Central Processing Unit) controls the entire communication apparatus 800. The communication apparatus 800 may include a plurality of CPUs 801. The memory 802 includes, for example, a main memory and an auxiliary memory. The main memory is, for example, a RAM (Random Access Memory). The main memory is used as a work area for the CPU 801. The auxiliary memory is, for example, a nonvolatile memory such as a magnetic disk, an optical disk, or a flash memory. Various programs for operating the communication device 800 are stored in the auxiliary memory. The program stored in the auxiliary memory is loaded into the main memory and executed by the CPU 801.

  The user interface 803 includes, for example, an input device that receives an operation input from the user, an output device that outputs information to the user, and the like. The input device can be realized by a key (for example, a keyboard) or a remote controller, for example. The output device can be realized by, for example, a display or a speaker. Further, an input device and an output device may be realized by a touch panel or the like. The user interface 803 is controlled by the CPU 801.

  The wired communication interface 804 is a communication interface that communicates with the outside of the communication device 800 (for example, a backbone network such as a mobile communication network) by wire. The wired communication interface 804 is controlled by the CPU 801. The wireless communication interface 805 is a communication interface that performs communication with the outside of the communication device 800 (for example, the wireless terminal 131) wirelessly. The wireless communication interface 805 is controlled by the CPU 801.

  The wireless transmission unit 310, the transmission antenna 311, the reception antenna 312 and the wireless reception unit 313 illustrated in FIGS. 3-1 and 3-2 can be realized by the wireless communication interface 805, for example. The other processing units illustrated in FIGS. 3A and 3B can be realized by the CPU 801, for example.

  FIG. 9 is a diagram illustrating an example of a hardware configuration of the wireless terminal. The above-described wireless terminal 131 can be realized by, for example, the communication device 900 illustrated in FIG. The communication device 900 includes a CPU 901, a memory 902, a user interface 903, and a wireless communication interface 904. The CPU 901, the memory 902, the user interface 903, and the wireless communication interface 904 are connected by a bus 909.

  The CPU 901, the memory 902, the user interface 903, and the wireless communication interface 904 are the same as the CPU 801, the memory 802, the user interface 803, and the wireless communication interface 805 shown in FIG. However, the wireless communication interface 904 is a communication interface that performs communication with the outside of the communication apparatus 900 (for example, the wireless base station 111) by wireless, for example.

  The reception antenna 401, the wireless reception unit 402, the wireless transmission unit 415, and the transmission antenna 416 illustrated in FIGS. 4-1 and 4-2 can be realized by the wireless communication interface 904, for example. Each of the other processing units illustrated in FIGS. 4A and 4B can be realized by the CPU 901, for example.

  As described above, according to the communication system, the radio base station, and the radio terminal, the common pilot is frequency-shifted between the cells, and the downlink control signal is transmitted at the time when the common pilot is not transmitted and the individual pilot is transmitted. can do. As a result, interference can be suppressed, channel estimation accuracy can be improved, and control signal reception characteristics can be improved.

  Therefore, for example, even when a higher-order modulation scheme or a spatial multiplexing transmission scheme is applied to transmission of a downlink control signal, it is possible to suppress deterioration of reception characteristics of the downlink control signal. For this reason, it is possible to improve the use efficiency of the radio resource of the downlink control signal while suppressing the deterioration of the reception characteristic of the downlink control signal.

  In addition, since channel estimation accuracy can be increased without reducing the interval between dedicated pilot signals, it is possible to suppress a reduction in radio resources in which data signals can be allocated.

  Further, the channel estimation accuracy can be increased without increasing the transmission power of the dedicated pilot signal. As a result, even when the transmission power when transmitting a radio symbol is constant in the time domain, the channel estimation accuracy can be increased without reducing the transmission power of the data signal transmitted on the same radio symbol. Can do. For this reason, it is possible to suppress the deterioration of the reception characteristics of the data signal.

  The following additional notes are disclosed with respect to the embodiment described above.

(Supplementary note 1) In a communication system in which a common pilot signal to each wireless terminal of the own cell is transmitted at a first timing by a frequency based on identification information of the own cell for each cell.
The common pilot signal is transmitted at the first timing, and an individual pilot signal to the radio terminal of the own cell and a control signal to the radio terminal of the own cell are transmitted at a second timing different from the first timing. Radio base stations transmitting simultaneously on different frequencies;
A radio terminal that demodulates the control signal transmitted by the radio base station based on an individual pilot signal transmitted by the radio base station;
A communication system comprising:

(Supplementary note 2) The communication system according to supplementary note 1, wherein the radio base station transmits the dedicated pilot signal and the control signal using adjacent frequencies.

(Supplementary note 3) The communication system according to supplementary note 1, wherein the second timing is a timing at which the common pilot signal is not transmitted in each cell.

(Supplementary note 4) The communication system according to supplementary note 1, wherein the radio base station transmits the dedicated pilot signal and a part of the control signal using adjacent frequencies.

(Supplementary Note 5) The radio base station transmits a data signal to the radio terminal of the own cell and transmits the control signal including a parameter related to transmission of the data signal,
5. The communication system according to claim 1, wherein the wireless terminal receives a data signal transmitted by the wireless base station based on a demodulation result of the control signal.

(Supplementary note 6) The communication system according to any one of supplementary notes 1 to 5, wherein the radio base station transmits the control signal by spatial multiplexing transmission.

(Supplementary note 7) The radio base station transmits the control signal using a modulation scheme according to radio characteristics with the radio base station, and the control signal using a higher-order modulation scheme is preferentially used. The communication system according to any one of appendices 1 to 6, wherein transmission is performed using a radio resource simultaneously with the dedicated pilot signal in the second timing.

(Supplementary Note 8) The radio base station transmits the control signal modulated by any one of QPSK (Quadrature Phase Shift Keying), 16QAM (Quadrature Amplitude Modulation), 64QAM, and 256QAM. The communication system according to any one of appendices 1 to 7, characterized in that:

(Supplementary note 9) In a radio base station of a communication system in which a common pilot signal to each radio terminal of the own cell is transmitted at a first timing by a frequency based on identification information of the own cell for each cell,
Transmitting the common pilot signal at the first timing;
Transmitting a dedicated pilot signal to the radio terminal of the own cell and a control signal to the radio terminal of the own cell at different timings at a second timing different from the first timing;
A wireless base station characterized by that.

(Additional remark 10) In the radio | wireless terminal of the communication system by which the common pilot signal to each radio | wireless terminal of an own cell is transmitted at the 1st timing with the frequency based on the identification information of an own cell for every cell,
Receiving the common pilot signal transmitted at the first timing by the radio base station of the own cell;
Receiving a dedicated pilot signal to the own terminal and a control signal to the own terminal, which are simultaneously transmitted by the radio base station at different frequencies at a second timing different from the first timing;
Demodulating the received control signal based on the received dedicated pilot signal;
A wireless terminal characterized by that.

(Additional remark 11) In the communication method of the communication system in which the common pilot signal to each radio | wireless terminal of an own cell is transmitted at the 1st timing with the frequency based on the identification information of an own cell for every cell,
A radio base station transmits the common pilot signal at the first timing,
The radio base station transmits a dedicated pilot signal to the radio terminal of the own cell and a control signal to the radio terminal of the own cell at different timings at a second timing different from the first timing,
The radio terminal of the own cell demodulates the control signal transmitted by the radio base station based on the dedicated pilot signal transmitted by the radio base station.
A communication method characterized by the above.

100, 600 Communication system 111, 112, 610, 620, 630, 640 Wireless base station 121, 122, 611-613, 621-623, 631-633, 641-643 Cell 131, 132 Wireless terminal 141, 142 Signal arrangement 200 , 701 to 706 Physical resource block 211 to 214 Resource element 301, 304, 306, 410, 412 Encoding unit 302, 305, 307, 411, 413 Modulation unit 303 Arrangement selection unit 308 Frequency multiplexing unit 309 Time multiplexing unit 310, 415 Radio transmitting unit 311, 416 Transmitting antenna 312, 401 Receiving antenna 313, 402 Radio receiving unit 314, 403 Pilot signal processing unit 315 Demodulating unit 316 Decoding unit 317 Control signal extracting unit 404 Radio characteristic measuring unit 405 Time separating unit 06,408 control signal detection / demodulation / decoding unit 407 frequency separation unit 409 data signal demodulator / decoder 414 switching unit 800, 900 communication device 801 and 901 CPU
802, 902 Memory 803, 903 User interface 804 Wired communication interface 805, 904 Wireless communication interface 809, 909 Bus

Claims (7)

In a communication system composed of wireless terminals and wireless base stations,
A common pilot signal is transmitted to the radio terminal at a frequency based on the cell identification information and at the first timing, and the individual pilot signal and the control signal are made different to the radio terminal at a second timing different from the first timing. A radio base station transmitting at the same time in frequency,
A radio terminal that demodulates the control signal transmitted by the radio base station based on the dedicated pilot signal transmitted by the radio base station;
A communication system comprising:   The communication system according to claim 1, wherein the radio base station transmits the dedicated pilot signal and the control signal using adjacent frequencies.   The communication system according to claim 1, wherein the radio base station transmits the dedicated pilot signal and a part of the control signal by using adjacent frequencies. The radio base station transmits a data signal to the radio terminal and transmits the control signal including parameters relating to the transmission of the data signal,
The communication system according to any one of claims 1 to 3, wherein the wireless terminal receives a data signal transmitted by the wireless base station based on a demodulation result of the control signal.   The radio base station transmits the control signal using a modulation scheme according to radio characteristics with the radio terminal, and the control signal using a higher-order modulation scheme is preferentially used in the second timing. The communication system according to any one of claims 1 to 4, wherein transmission is performed using radio resources simultaneously with the dedicated pilot signal. In the radio base station
Transmitting a common pilot signal to the wireless terminal at a frequency based on the identification information of the cell and at the first timing;
A communication interface that simultaneously transmits an individual pilot signal and a control signal at different frequencies to the wireless terminal at a second timing different from the first timing;
A wireless base station characterized by that. In the wireless terminal
Receiving a common pilot signal transmitted at a first timing at a frequency based on cell identification information from a radio base station;
Receiving a dedicated pilot signal and a control signal transmitted from the radio base station at a second timing different from the first timing and simultaneously at different frequencies;
Demodulating the received control signal based on the received dedicated pilot signal;
A wireless terminal characterized by that.

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