Base station, mobile station, wireless communications system, and wireless communications method

At a base station, a lookup table is prepared that for each index value among multiple different index values, associates repetition counts of different channels correlated with each other. The base station acquires reception information indicating a reception state of a wireless signal at a mobile station, determines a repetition count for each channel based on the reception information, and acquires from the lookup table, an index value corresponding to the respective repetition counts for the channels. The base station transmits to the mobile station, a wireless signal that includes the index value to notify the mobile station of the index value. The mobile station has a lookup table that for each index value among different index values, associates repetition counts of different channels correlated with each other and acquires the repetition counts of the channels from the lookup table, based on the index value from the base station.

FIELD

The embodiments discussed herein are related to a base station, a mobile station, a wireless communications system, and a wireless communications method.

BACKGROUND

In a conventional wireless network, control information is transmitted multiple times so as to receive the control information under an environment with a low signal-to-noise ratio (SNR). Additionally, a communications system exists that is called machine-to-machine (M2M) in which machines such as terminals communicate with each other or machine-type communication (MTC) in which a machine and a server on a network communicate with each other (see, for example, Published Japanese-Translation of PCT Application, Publication Nos. 2012-522427, 2013-524563, and 2013-520100).

For example, under an environment with a low signal-to-interference and noise power ratio (SINR), transmission power may be increased (power boost) or transmission may be repeated to expand coverage and maintain a communication link between a base station and a mobile station. If transmission is repeated, the base station notifies the mobile station of information necessary for signal reception such as a transmission repetition count.

However, a required transmission repetition count varies depending on the transmission power of the base station and also varies depending on physical channels, which have differing quality requirements. Therefore, the base station notifies the mobile station of information concerning a power offset amount for increasing the transmission power and information concerning the transmission repetition count for each of the physical channels, resulting in a problem of increased information that is to be notified.

SUMMARY

According to an aspect of an embodiment, a base station includes a transmitting circuit that transmits a first wireless signal to a mobile station by using different physical channels; a receiving circuit that receives a second wireless signal transmitted from the mobile station; an acquiring circuit that acquires reception information indicating a reception state of the first wireless signal at the mobile station, from the second wireless signal received by the receiving circuit; a determining circuit that based on the reception information acquired by the acquiring circuit, determines a repetition count of a third wireless signal repeatedly transmitted from the transmitting circuit; and a lookup table that has an index value associated with repetition counts of the different physical channels. The base station uses the receiving circuit to receive the second wireless signal that includes the reception information from the mobile station. The base station uses the acquiring circuit to acquire the reception information from the second wireless signal that includes the reception information. The base station uses the determining circuit to determine based on the reception information, the repetition count for each physical channel among the different physical channels. The base station acquires from the lookup table, the index value that corresponds to the repetition counts of the different physical channels. The base station uses the transmitting circuit to transmit a fourth wireless signal that includes the index value, to the mobile station and notify the mobile station of the index value.

DESCRIPTION OF EMBODIMENTS

Embodiments of a base station, a mobile station, a wireless communications system, and a wireless communications method according to the present invention will be described in detail with reference to the accompanying drawings. In the description of the embodiments hereinafter, identical components are given the same reference numeral and redundant description is omitted herein. Furthermore, the present invention is not limited by the following embodiments.

FIG. 1is a diagram of an example of a wireless communications system according to an embodiment. As depicted inFIG. 1, the wireless communications system includes a base station1and a mobile station2.

The base station1has a transmitting unit11, a receiving unit12, an acquiring unit13, a determining unit14, and a lookup table15. The transmitting unit11is a base-station transmitting unit; the receiving unit12is a base-station receiving unit, the acquiring unit13is a base-station acquiring unit; and the lookup table15is a base-station lookup table. The units11to14and the lookup table15of the base station1will be described in detail in a first example of a base station described later.

The mobile station2has a transmitting unit21, a receiving unit22, a generating unit23, an acquiring unit24, and a lookup table25. The transmitting unit21is a mobile-station transmitting unit; the receiving unit22is a mobile-station receiving unit; the acquiring unit24is a mobile-station acquiring unit; and the lookup table25is a mobile-station lookup table. The units21to24and the lookup table25of the mobile station2will be described in detail in a first example of a mobile station described later.

The base station1transmits a wireless reference signal to the mobile station2. The mobile station2receives the wireless reference signal, generates reception information indicating a reception state based on the wireless reference signal, and transmits a wireless signal including the reception information to the base station1. As a result, the base station1is notified of the reception information.

The base station1receives the wireless signal that includes the reception information, acquires the reception information from the wireless signal, and for each physical channel among multiple different physical channels, determines a repetition count for a repeatedly transmitted wireless signal, based on the reception information. The repetition counts of the different physical channels correlate with each other. Therefore, for each piece of reception information, the repetition counts of the different channels can be associated with one index value.

The base station1acquires from the lookup table15thereof, an index value that corresponds to the respective repetition counts of the physical channels and transmits a wireless signal including the index value to the mobile station2. As a result, the mobile station2is notified of the index value.

The mobile station2receives the wireless signal that includes the index value corresponding to the reception information reported by the mobile station2and acquires the index value from the wireless signal. The mobile station2, from the lookup table25thereof, acquires for each physical channel, the repetition count corresponding to the index value. As a result, the mobile station2can acquire the repetition counts of the different physical channels.

FIG. 2is a diagram of a functional configuration of a first example of the base station according to the embodiment.FIG. 3is a diagram of a flow of signals or data in the base station depicted inFIG. 2. As depicted inFIGS. 2 and 3, the base station1has the transmitting unit11, the receiving unit12, the acquiring unit13, the determining unit14, and the lookup table15.

The transmitting unit11is connected to the lookup table15and an antenna16. The transmitting unit11transmits from the antenna16to the mobile station2, wireless signals by using different physical channels. The transmitting unit11transmits the wireless reference signal from the antenna16to the mobile station2. The transmitting unit11transmits from the antenna16to the mobile station2, a wireless signal that includes an index value acquired from the lookup table15. As a result, the base station1notifies the mobile station2of the index value.

The receiving unit12is connected to an antenna17. The receiving unit12receives wireless signals transmitted from the mobile station2via the antenna17.

The acquiring unit13is connected to the receiving unit12. The acquiring unit13acquires from the wireless signal received by the receiving unit12, the reception information indicating a reception state of a wireless signal at the mobile station2. Based on the reception information acquired by the acquiring unit13, the determining unit14determines for the respective physical channels, the repetition counts for wireless signals repeatedly transmitted from the transmitting unit11.

In the lookup table15, different index values are respectively associated with the repetition counts of the different physical channels. From the lookup table15, index values are obtained that correspond to the repetition counts determined by the determining unit14for the different physical channels.

FIG. 4is a diagram of an example of a hardware configuration of the base station according to the embodiment. As depicted inFIG. 4, the base station1has a processor101, memory102, and an interface103. The processor101, the memory102, and the interface103may be connected to a bus104.

The processor101processes a program implementing a wireless communications method performed by a base station described later. The acquiring unit13and the determining unit14may be implemented in this way at the base station1depicted inFIG. 2. Examples of the processor101include a central processing unit (CPU), a digital signal processor (DSP), an application specific integrated circuit (ASIC), and a programmable logic device such as a field programmable gate array (FPGA).

The memory102retains the lookup table15. The memory102stores a boot program and the program implementing the wireless communications method performed by the base station described later. If the processor101is a programmable logic device, the memory102may store circuit information of the programmable logic device.

The lookup table15, various programs, or the circuit information may be stored in a non-volatile area of the memory102. The non-volatile area of the memory102may be implemented by, for example, read only memory (ROM) such as mask ROM, electrically erasable programmable read only memory (EEPROM), and flash memory.

In the memory102, a volatile area may be used as a work area of the processor101. The volatile area of the memory102may be implemented by, for example, random access memory (RAM) such as dynamic random access memory (DRAM) and static random access memory (SRAM).

The interface103manages the input and output of signals and data between the transmitting unit11and the receiving unit12. The interface103may manage the input and output of data from and to an application not depicted, for example. The receiving unit12and the transmitting unit11of the base station1depicted inFIG. 2may be implemented by a processor that processes wireless signals. The processor that processes wireless signals may be provided separately from the processor101.

The wireless communications method performed by a base station may be performed by the base station depicted inFIG. 2. In the description of this example, the wireless communications method performed by a base station is assumed to be performed by the base station1ofFIG. 2.

FIG. 5is a diagram of an example of the wireless communications method performed by the base station according to the embodiment. As depicted inFIG. 5, when the wireless communications method is started at the base station1, the base station1uses the receiving unit12to receive from the mobile station2, a wireless signal that includes reception information (step S1). The base station1uses the acquiring unit13to acquire the reception information from the wireless signal (step S2).

Subsequently, the base station1uses the determining unit14to determine for the respective physical channels and based on the reception information, repetition counts for repeated transmission of a wireless signal (step S3). The base station1acquires from the lookup table15, an index value corresponding to the repetition counts for the respective physical channels determined at step S3(step S4).

Subsequently, the base station1uses the transmitting unit11to transmit to the mobile station2, a wireless signal including the index value acquired at step S4(step S5). As a result, the base station1notifies the mobile station2of the index value. The base station1then terminates a sequence of the wireless communications method. The base station1subsequently performs communication through the physical channels with the mobile station2, at the repetition count for each physical channel corresponding to the index value in the notification to the mobile station2.

According to the wireless communications system depicted inFIG. 1, the base station1depicted inFIG. 2, or the wireless communications method depicted inFIG. 5, the base station1notifies the mobile station2of the index value corresponding to the repetition counts of the different physical channels. Therefore, as compared to when the base station1notifies the mobile station2of the repetition counts of the different channels for each physical channel, the amount of information transmitted from the base station1to the mobile station2is reduced. Thus, the base station1can efficiently notify the mobile station2of the information necessary for signal reception by the mobile station2.

FIG. 6is diagram of a functional configuration of a first example of the mobile station according to the embodiment.FIG. 7is a diagram of a flow of signals or data in the mobile station depicted inFIG. 6. As depicted inFIGS. 6 and 7, the mobile station2has the transmitting unit21, the receiving unit22, the generating unit23, the acquiring unit24, and the lookup table25.

The transmitting unit21is connected to the generating unit23and an antenna26. The transmitting unit21transmits wireless signals from the antenna26to the base station1. The transmitting unit21transmits from the antenna26to the base station1, a wireless signal including reception information generated by the generating unit23. As a result, the mobile station2notifies the base station1of the reception information indicating the reception state of the mobile station2.

The receiving unit22is connected to an antenna27. The receiving unit22receives via the antenna27, a wireless signal transmitted from the base station1by using the different physical channels. The receiving unit22receives a wireless reference signal via the antenna27from the base station1. The receiving unit22receives via the antenna27from the base station1, a wireless signal that includes the index value corresponding to the reception information in the notification from the receiving unit22.

The generating unit23is connected to the receiving unit22. The generating unit23generates based on the wireless reference signal received by the receiving unit22, the reception information indicating the reception state of the mobile station2. The acquiring unit24is connected to the receiving unit22. The acquiring unit24acquires the index value from the wireless signal received by the receiving unit22.

In the lookup table25, the repetition counts of the different physical channels are associated with different index values, respectively. From the lookup table25, the repetition counts corresponding to the index value acquired by the acquiring unit24are acquired for each physical channel.

Information of the repetition counts for each physical channel acquired from the lookup table25is sent from an output terminal28connected to the lookup table25, to a processing unit that executes a data process based on the information of the repetition counts for each physical channel in the mobile station2. For example, the information of the repetition counts for each physical channel may be sent from the output terminal28to the transmitting unit21or from a signal generating unit generating a wireless signal transmitted from the transmitting unit21.

The hardware configuration of the mobile station2is identical to the hardware configuration of the base station1depicted inFIG. 4. Therefore, the hardware configuration of the mobile station2is not depicted and will not be described. It is noted that in the configuration depicted inFIG. 4, the processor101processes a program implementing a wireless communications method performed by a mobile station described later. The generating unit23and the acquiring unit24may be implemented in this way in the mobile station2depicted inFIG. 6.

The lookup table25is retained in the memory102. The interface103manages the input and output of signals and data between the transmitting unit21and the receiving unit22. The transmitting unit21and the receiving unit22of the mobile station2depicted inFIG. 6may be implemented by a processor that processes wireless signals. The processor that processes wireless signals may be provided separately from the processor101.

The wireless communications method performed by a mobile station may be performed by the mobile station depicted inFIG. 6. In the description of this example, the wireless communications method performed by a mobile station is assumed to be performed by the mobile station2depicted inFIG. 6.

FIG. 8is a diagram of an example of the wireless communications method performed by the mobile station according to the embodiment. As depicted inFIG. 8, when the wireless communications method is started at the mobile station2, the mobile station2uses the receiving unit22to receive a wireless reference signal from the base station1(step S11). The base station1transmits the wireless reference signal before step S1in the wireless communications method depicted inFIG. 5.

Subsequently, the mobile station2uses the generating unit23to generate reception information indicating the reception state of the mobile station2, based on the received wireless reference signal (step S12). The mobile station2then uses the transmitting unit21to transmit the wireless signal including the reception information generated at step S12to the base station1(step S13). As a result, the mobile station2notifies the base station1of the reception state of the mobile station2.

Subsequently, the mobile station2uses the receiving unit22to receive from the base station1, a wireless signal that includes the index value corresponding to the reception information transmitted at step S13(step S14). The mobile station2uses the acquiring unit24to acquire the index value from the wireless signal (step S15).

Subsequently, for each physical channel, the mobile station2acquires from the lookup table25, repetition counts that correspond to the index value acquired at step S15(step S16). The mobile station2then terminates a sequence of the wireless communications method. The mobile station2subsequently performs communication through the channels with base station1by using the repetition counts of the respective physical channels, corresponding to the index value in the notification from the base station1.

According to the mobile station2depicted inFIG. 6or the wireless communications method depicted inFIG. 8, the mobile station2notified of an index value by the base station1can acquire from the lookup table25and for each physical channel, the repetition counts that correspond to the index value. This means that the base station1suffices to notify the mobile station2of an index value instead of giving notification of the repetition counts for each channel among the different channels. Therefore, as compared to when the base station1notifies the mobile station2of a repetition count for each channel, the amount of information transmitted from the base station1to the mobile station2is reduced. Thus, the base station1can efficiently notify the mobile station2of the information necessary for signal reception by the mobile station2.

An example of application to an MTC System will be described. Under an environment with a low SINR, for example, when a mobile station is present in the vicinity of a boundary with an adjacent cell, the SINR may become lower than the value required for communication between a base station and the mobile station. In such a case, as described above, for example, transmission power may be increased (power boost) or transmission may be repeated to expand coverage.

FIG. 9is a diagram of an example of maximum coupling loss between uplink and downlink. A table depicted inFIG. 9is introduced in 3GPP TR 36.888 V2.0.2, “Study on provision of low-cost MTC UEs based on LTE.” In this table, MCL (Maximum Coupling Loss) stands for a maximum coupling loss. FDD (Frequency Division Duplex) stands for a frequency division duplex mode. TDD (Time Division Duplex) stands for a time division duplex mode.

In the table depicted inFIG. 9, a UE (User Equipment, mobile station) has one transmission antenna and two reception antennas. Therefore, MCL (FDD, 2×2eNB) represents a maximum coupling loss when communication is performed in the frequency division duplex mode between an eNB (evolutional Node B, base station) having two transmission antennas and two reception antennas and a UE having one transmission antenna and two reception antennas. MCL (TDD, 8×8eNB) represents a maximum coupling loss when communication is performed in the time division duplex mode between an eNB having eight transmission antennas and eight reception antennas and a UE having one transmission antenna and two reception antennas.

As depicted inFIG. 9, the maximum coupling loss is different for each of the physical channels. For example, in the example depicted inFIG. 9, the maximum coupling loss in the case of the frequency division duplex mode is 147.2 dB in PUCCH(1a), 141.7 dB in PRACH, and 140.7 dB in PUSCH. The maximum coupling loss in the case of the frequency division duplex mode is 145.4 dB in PDSCH, 149.0 dB in PBCH, 149.3 dB in SCH, and 146.1 dB in PDCCH(1A).

As depicted inFIG. 9, the maximum coupling loss differs depending on the mode of duplex operation. For example, in the example depicted inFIG. 9, the maximum coupling loss in the case of the time division duplex mode is 149.4 dB in PUCCH(1a), 146.7 dB in PRACH, and 147.4 dB in PUSCH. The maximum coupling loss in the case of the time division duplex mode is 148.1 dB in PDSCH, 149.0 dB in PBCH, 149.3 dB in SCH, and 146.9 dB in PDCCH(1A). The maximum coupling loss MCL is calculated by expression (1), for example.
MCL=[actual transmission power]−([effective noise power]+[required value of SINR])

The PUCCH is a physical uplink control channel. The PRACH is a physical random access channel. The PUSCH is a physical uplink shared channel. The PDSCH is a physical downlink shared channel. The PBCH is a physical broadcast channel. The SCH is a synchronization channel. The PDCCH is a physical downlink control channel.

When the current SINR value is smaller than the minimum SINR value required for communication through a physical channel, a coverage expansion level is required that reduces the difference therebetween to zero. By suitably selecting a level of increase in transmission power and a transmission repetition count, a required coverage expansion level can be satisfied. If a UE is in a coverage hole, the required coverage expansion level is approximately 0 to 20 dB, for example.

The minimum SINR required for communication through each of the physical channels differs with consideration of different reception probabilities according to the purposes of the physical channels.

The coverage expansion level required for each of the physical channels is defined as a difference between the current SINR value and the minimum SINR value required for communication through the physical channel and is therefore different for each of the physical channels. The difference between the current SINR value and the minimum SINR value required for communication through a physical channel can be eliminated by increasing the transmission power and/or increasing the transmission repetition count for the physical channel. Therefore, the transmission repetition count for a physical channel varies depending on the transmission power for the physical channel. Thus, if a level of increase in transmission power for each physical channel is determined, the transmission repetition count satisfying the coverage expansion level required for the physical channel is determined for each physical channel. It is noted that the values of the maximum coupling loss are not limited to those depicted inFIG. 9.

FIG. 10is a diagram of an example of a relation between the repetition count and the power boost for the required coverage expansion level. In the example depicted inFIG. 10, for example, a physical channel PHYCH1has a required coverage expansion level of 10 dB and a gain of 10 dB may be achieved by repeating transmission 10 times. For example, a physical channel PHYCH2has a required coverage expansion level of 10 dB identical to the PHYCH1and a gain of 6 dB may be acquired by repeating transmission four times while a gain of 4 dB is achieved by power boost.

For example, a physical channel PHYCH3has a required coverage expansion level of 12 dB and a gain of 6 dB may be acquired by repeating transmission four times while a gain of 6 dB is achieved by power boost. It is noted that the values of the required coverage expansion level, the transmission repetition count, and the power boost are not limited to those depicted inFIG. 10.

The PHYCH1, the PHYCH2, and the PHYCH3may be, for example, a PDSCH, a PDCCH, a PHICH, or an EPDCCH. The PHICH is a physical hybrid-ARQ indicator channel. The EPDCCH is an enhanced physical downlink control channel.

FIG. 11is a diagram of a functional configuration of a second example of the base station according to the embodiment.FIG. 12is a diagram of a flow of signals or data in the base station depicted inFIG. 11. In this example, description will be taking as an example, a case where coverage is expanded for two physical channels, a PDCCH and a PDSCH, in an MTC system.

As depicted inFIGS. 11 and 12, a base station31has a radio frequency (RF) receiving unit32, a cyclic prefix (CP) removing unit33, and a fast Fourier transform (FFT) unit34. The base station31has a PUSCH signal demodulating unit35, a determining unit36, and a lookup table37. The base station31has a PDSCH signal generating unit38, a PDCCH signal generating unit39, a PBCH signal generating unit40, an inverse fast Fourier transform (IFFT) unit41, a CP adding unit42, and an RF transmitting unit43.

The RF receiving unit32is connected to an antenna44. The RF receiving unit32receives via the antenna44, a wireless signal transmitted from a mobile station. The RF receiving unit32is an example of a receiving unit.

The CP removing unit33is connected to the RF receiving unit32. The CP removing unit33removes a cyclic prefix from the wireless signal received by the RF receiving unit32. The FFT unit34performs fast Fourier transform for the signal from which the cyclic prefix is removed by the CP removing unit33. As a result, a time-domain signal is converted into a frequency-domain signal.

The PUSCH signal demodulating unit35demodulates a PUSCH signal converted into a frequency-domain signal by the FFT unit34. The PUSCH signal demodulating unit35demodulates the PUSCH signal and thereby, acquires an SINR value in a notification through the PUSCH signal from the mobile station. The SINR value is an example of reception information indicating the reception state of a mobile station. The PUSCH signal demodulating unit35is an example of an acquiring unit.

The determining unit36determines transmission repetition counts and power offset amounts for increasing the transmission power for the PDCCH and the PDSCH, based on the SINR value acquired by the PUSCH signal demodulating unit35. The determining unit36can determine the repetition counts and the power offset amounts for the physical channels with a known technique based on the SINR value reported from the mobile station.

From the lookup table37, an index value is acquired based on the respective repetition counts and power offset amounts for the PDCCH and the PDSCH determined by the determining unit36. The index value is common to the PDCCH and the PDSCH. The power offset amount is set for the PDCCH and the PDSCH, respectively.

The PDSCH signal generating unit38generates a PDSCH signal. The PDSCH signal generating unit38generates the PDSCH signal including the index value and the power offset amounts for the PDCCH and the PDSCH. The PDCCH signal generating unit39generates a PDCCH signal. The PBCH signal generating unit40generates a PBCH signal.

The IFFT unit41performs inverse fast Fourier transform for the PDSCH signal generated by the PDSCH signal generating unit38, the PDCCH signal generated by the PDCCH signal generating unit39, or the PBCH signal generated by the PBCH signal generating unit40. As a result, a frequency-domain signal is converted into a time-domain signal.

The CP adding unit42adds a cyclic prefix to the time-domain signal converted by the IFFT unit41. The RF transmitting unit43is connected to the CP adding unit42and an antenna45. The RF transmitting unit43transmits the wireless signal having the cyclic prefix added by the CP adding unit42, from the antenna45to the mobile station. The RF transmitting unit43is an example of a transmitting unit.

FIG. 13is a diagram of an example of a lookup table. As depicted inFIG. 13, the lookup table37has 16 records corresponding to 16 index values of 0, 1, 2, . . . , 15, for example. For each record, an SINR value corresponding to the SINR value in the notification from the mobile station is set along with respective repetition count reference values and repetition count correction values for the PDSCH and the PDCCH.

In the lookup table37, the SINR value corresponding to the SINR value in the notification from the mobile station is preset at the installation stage of the base station31. The SINR value corresponding to the SINR value in the notification from the mobile station is acquired from simulation, for example.

The repetition count reference value is the repetition count when the power offset amount is 0 dB. In the lookup table37, the repetition count reference values are preset at the installation stage of the base station31. The repetition count reference values are acquired from simulation, for example. From the repetition count reference values, a record to be used inFIG. 13is determined and an index value corresponding thereto can be acquired.

The repetition count correction value is a value for correcting the repetition count reference value according to the power offset amount. The repetition count correction value is acquired by, for example, multiplying the repetition count reference value by a correction coefficient derived from the power offset amount.

For example, in the example depicted inFIG. 13, when the index value is denoted by k, a record of an index value k has SINRkset as the SINR value corresponding to the SINR value reported by the mobile station. It is noted that k is an integer from 0 to 15. The record of the index value k has RLPDSCH,kas the repetition count reference value for the PDSCH and RLPDCCH,kas the repetition count reference value for the PDCCH.

The record of the index value k has a calculation expression expressed by, for example, expression (2) set as the repetition count correction value for the PDSCH. The record has a calculation expression expressed by, for example, expression (3) as the repetition count correction value for the PDCCH. It is noted that aPDSCHand aPDCCHare correction coefficients for the PDSCH and the PDCCH, respectively.
RLPDSCH,k×aPDSCH(2)
RLPDCCH,k×aPDCCH(3)

When the power offset amount for the PDSCH is denoted by POPDSCH, the correction coefficient aPDSCHfor the PDSCH is expressed by expression (4), for example. When the power offset amount for the PDCCH is denoted by POPDCCH, the correction coefficient aPDCCHfor the PDCCH is expressed by expression (5), for example.

POPDSCHmay take on values of 0 dB, 2 dB, 4 dB, and 6 dB, for example. POPDCCHmay take on values of 0 dB, 2 dB, 4 dB, and 6 dB, for example. The values that POPDSCHmay take and the values that POPDCCHmay take may differ.

For example, once the repetition counts and the power offset amounts for the physical channels are determined by the determining unit36, repetition count correction values can be obtained for the physical channels from the lookup table37depicted inFIG. 13by using the respective power offset amounts and repetition reference values.

The hardware configuration of the base station31is the same as the hardware configuration of the base station1depicted inFIG. 4. Therefore, the hardware configuration of the base station31is not depicted and redundant description is omitted. It is noted that in the configuration depicted inFIG. 4, the processor101processes the program that implements the wireless communications method performed by the base station31. The units33to36,38to42excluding the RF receiving unit32and the RF transmitting unit43may be implemented in this way at the base station31depicted inFIG. 11.

The lookup table37is retained in the memory102. The interface103manages the input and output of signals and data between the RF transmitting unit43and the RF receiving unit32. The RF transmitting unit43and the RF receiving unit32of the base station31depicted inFIG. 11may be implemented by a processor that processes wireless signals. The processor that processes wireless signals may be provided separately from the processor101.

The wireless communications method performed by the base station31is identical to the method depicted inFIG. 5, for example. Therefore, redundant description of the method is omitted. It is noted that in the method depicted inFIG. 5, the reception information is the SINR value. At step S3, the base station31uses the determining unit36to determine the repetition counts and the power offset amounts. At step S5, the base station31uses the RF transmitting unit43to transmit the wireless signal including the index value and the power offset amounts to the mobile station.

According to the base station31depicted inFIG. 11, the base station31notifies the mobile station of an index value common to the repetition counts of the different physical channels. Therefore, as compared to when the base station31notifies the mobile station of the repetition counts for each physical channel among the different channels, the amount of information sent from the base station31to the mobile station is reduced. Thus, the base station31can efficiently notify the mobile station of the information necessary for signal reception by the mobile station.

According to the base station31depicted inFIG. 11, the base station31notifies the mobile station of the power offset amount for each channel. This enables the mobile station to obtain the repetition counts of the respective physical channels, based on the index value common to the different physical channels and the power offset amount for each physical channel.

According to the base station31depicted inFIG. 11, the repetition count can be corrected according to the power offset amount based on a calculation expression set in the lookup table37. Additionally, the index value can be easily acquired by finding the index value for which the repetition count correction values obtained by using the lookup table37matches the repetition counts determined based on the SINR value in the notification from the mobile station. Moreover, in the lookup table37, since the SINR value and the repetition count reference value are acquired by, for example, simulation, the lookup table37can be easily created.

FIG. 14is a diagram of a functional configuration of a second example of the mobile station according to the embodiment.FIG. 15is a diagram of a flow of signals or data in the base station depicted inFIG. 14. In this example, description will be taken as an example, a case where coverage is expanded for two physical channels, a PDCCH and a PDSCH, in an MTC system.

As depicted inFIGS. 14 and 15, the mobile station51has an RF receiving unit52, a CP removing unit53, and an FFT unit54. The mobile station51has a PDSCH signal demodulating unit55, a PDCCH signal demodulating unit56, a reference signal demodulating unit57, a PBCH signal demodulating unit58, a lookup table59, and a SINR calculating unit60. The mobile station51has an RF transmitting unit61, a CP adding unit62, an IFFT unit63, a PRACH signal generating unit64, a PUSCH signal generating unit65, and a user data buffer66.

The RF receiving unit52is connected to an antenna67. The RF receiving unit52receives via the antenna67, a wireless signal transmitted from a base station. The RF receiving unit52is an example of a receiving unit.

The CP removing unit53is connected to the RF receiving unit52. The CP removing unit53removes a cyclic prefix from the wireless signal received by the RF receiving unit52. The FFT unit54performs fast Fourier transform for the signal from which the cyclic prefix is removed by the CP removing unit53. As a result, a time-domain signal is converted into a frequency-domain signal.

The PDSCH signal demodulating unit55demodulates a PDSCH signal converted into a frequency-domain signal by the FFT unit54. The PDSCH signal demodulating unit55demodulates the PUSCH signal and thereby, acquires an index value and a power offset amount in a notification through a PDSCH signal from the base station. The PDSCH signal demodulating unit55is an example of an acquiring unit.

The PDCCH signal demodulating unit56demodulates a PDCCH signal converted into a frequency-domain signal by the FFT unit54. The reference signal demodulating unit57demodulates a reference signal converted into a frequency-domain signal by the FFT unit54. The PBCH signal demodulating unit58demodulates a PBCH signal converted into a frequency-domain signal by the FFT unit54.

From the lookup table59, the repetition count for the PDSCH corresponding to the power offset amount for the PDSCH is acquired based on the index value and the power offset amount for the PDSCH acquired by the PDSCH signal demodulating unit55. Additionally, from the lookup table59, the repetition count for the PDSCH corresponding to the power offset amount for the PDSCH is acquired based on the index value and the power offset amount for the PDSCH acquired by the PDSCH signal demodulating unit55. The lookup table59may be the same table as the lookup table37depicted inFIG. 13.

The information of the repetition counts of the respective physical channels acquired from the lookup table59and the respective power offset amounts of the physical channels is sent from an output terminal69connected to the lookup table59, to a processing unit that executes a data process based on this information at the mobile station51.

For example, the information of the repetition count and the power offset amount for the PDSCH is sent to the PDSCH signal demodulating unit55. The PDSCH signal demodulating unit55demodulates the PDSCH signal based on the information of the repetition count and the power offset amount for the PDSCH. The information of the repetition count and the power offset amount for the PDCCH is sent to the PDCCH signal demodulating unit56. The PDCCH signal demodulating unit56demodulates the PDCCH signal based on the information of the repetition count and the power offset amount for the PDCCH.

As is the case with the PDSCH and the PDCCH, the information of the respective repetition counts and power offset amounts is acquired for the PRACH and the PUSCH. For example, the information of the repetition count and the power offset amount for the PRACH is sent to the PRACH signal generating unit64. The PRACH signal generating unit64generates the PRACH signal based on the information of the repetition count and the power offset amount for the PRACH. The information of the repetition count and the power offset amount for the PUSCH is sent to the PUSCH signal generating unit65. The PUSCH signal generating unit65generates the PUSCH signal based on the information of the repetition count and the power offset amount for the PUSCH.

The SINR calculating unit60calculates an SINR value based on the reception intensity of the reference signal demodulated by the reference signal demodulating unit57. The SINR calculating unit60can calculate the SINR value by a known technique based on the reception intensity of the reference signal. The SINR value is an example of the reception information indicating the reception state of the mobile station51. The SINR calculating unit60is an example of a generating unit.

The user data buffer66temporarily retains the SINR value acquired by the SINR calculating unit60. The PUSCH signal generating unit65generates a PUSCH signal including the SINR value stored in the user data buffer66. The PRACH signal generating unit64generates a PRACH signal.

The IFFT unit63performs inverse fast Fourier transform for the PRACH signal generated by the PRACH signal generating unit64or the PUSCH signal generated by the PUSCH signal generating unit65. As a result, a frequency-domain signal is converted into a time-domain signal.

The CP adding unit62adds a cyclic prefix to the time-domain signal converted by the IFFT unit63. The RF transmitting unit61is connected to the CP adding unit62and an antenna68. The RF transmitting unit61transmits from the antenna68to the base station, the wireless signal having the cyclic prefix added by the CP adding unit62. The RF transmitting unit61is an example of a transmitting unit.

The hardware configuration of the mobile station51is identical to the hardware configuration of the base station1depicted inFIG. 4. Therefore, the hardware configuration of the mobile station51is not depicted and redundant description is omitted. It is noted that in the configuration depicted inFIG. 4, the processor101processes the program implementing the wireless communications method performed by the mobile station51. The units53to58,60,62to65except the RF receiving unit52and the RF transmitting unit61may be implemented in this way in the mobile station51depicted inFIG. 14.

The lookup table59is retained in the memory102. The user data buffer66may be implemented by the memory102. The interface103manages input and output of signals and data between the RF transmitting unit61and the RF receiving unit52. The RF transmitting unit61and the RF receiving unit52of the mobile station51depicted inFIG. 14may be implemented by a processor processing a wireless signal. The processor processing a wireless signal may be provided separately from the processor101.

The wireless communications method performed by the mobile station51is identical to the method depicted inFIG. 8, for example. Therefore, redundant description of the method is omitted. It is noted that in the method depicted inFIG. 8, the wireless reference signal is the reference signal and that the reception information is the SINR value. At step S14, the mobile station51receives the wireless signal including the index value and the power offset amounts of the respective channels.

According to the mobile station51depicted inFIG. 14, when notified of the index value from the base station, the mobile station51can acquire for the respective physical channels from the lookup table59, the repetition counts corresponding to the index value. This means that the base station can notify the mobile station51of the index value instead of giving notification of the repetition counts for each physical channel among the different physical channels. Therefore, as compared to when the base station notifies the mobile station51of repetition counts for each physical channel, the amount of information sent from the base station to the mobile station51is reduced. As a result, the base station can efficiently notify the mobile station51of the information necessary for signal reception by the mobile station51.

According to the mobile station51depicted inFIG. 14, the base station notifies the mobile station51of the respective power offset amounts for the physical channels. This enables the mobile station51to obtain the respective repetition counts of the physical channels based on the index value common to the different physical channels and the respective power offset amounts of the physical channels.

According to the mobile station51depicted inFIG. 14, the repetition count can be corrected according to the power offset amount, based on a calculation expression set in the lookup table59for each index value. Additionally, since the repetition count reference value in the lookup table59is acquired by, for example, simulation, the lookup table59can be easily created.

FIG. 16is a diagram of an example of a wireless connection process sequence in a wireless communications system according to the embodiment. As depicted inFIG. 16, it is assumed that the wireless communications system includes a base station, a mobile station A, and a mobile station B. The mobile station A and the mobile station B may have required coverage expansion levels different from each other. For example, the coverage expansion level required for the mobile station A may be 15 dB and the coverage expansion level required for the mobile station B may be 20 dB.

When the wireless connection process is started, first, the base station transmits synchronization signals to the mobile station A and the mobile station B (step S21). Subsequently, the base station uses the PBCH signals to transmit system information, SIB (system information block), to the mobile station A and the mobile station B. At this point in time, the base station does not know the coverage expansion levels required for the mobile station A or the mobile station B and therefore, transmits the PBCH signals at the maximum repetition count (step S22).

Subsequently, the mobile station A and the mobile station B transmit the PRACH signals to the base station at the maximum repetition count (step S23). Subsequently, the base station transmits cell-specific reference signals (CRSs) to the mobile station A and the mobile station B (step S24). The mobile station A and the mobile station B receive the reference signals and then calculate the SINR values to roughly determine the coverage expansion levels (step S25). The base station transmits the PDCCH signals to the mobile station A and the mobile station B at the maximum repetition count (step S26).

Subsequently, the mobile station A and the mobile station B transmit the PUSCH signals including the SINR values to the base station at the maximum repetition count to feed back the SINR values to the base station (step S27). The base station receives the PUSCH signals including the SINR values and then determines the repetition counts and the power offset amounts for channels, for example, the PDCCH and the PDSCH, based on the SINR values (step S28).

Subsequently, the base station acquires from the lookup table, an index value common to the channels and power offset values for the respective channels. The base station transmits the PDSCH signals including the index value to the mobile station A and the mobile station B to notify the mobile station A and the mobile station B of the index value (step S29). The base station transmits the PDSCH signals including the power offset amounts of the respective channels to the mobile station A and the mobile station B to notify the mobile station A and the mobile station B of the respective power offset amounts of the channels (step S30).

The mobile station A and the mobile station B acquire the respective repetition counts of the channels from the lookup tables, based on the index value and the power offset amounts. Subsequently, communication links are maintained between the base station and the mobile stations A, B based on the repetition counts of the respective channels and the power offset amounts of the respective channels.

A reduction in the amount of information sent from the base station to the mobile station will be described.FIG. 17is a diagram of an example of a sequence of notification of an index value common to channels.FIG. 18is an example of a sequence of notification of respective repetition counts for the channels. In the examples depicted inFIG. 17andFIG. 18, it is assumed that physical channels PHYCH1, PHYCH2, PHYCH3, and PHYCH4exist.

As depicted inFIG. 17, in the case of notification of an index value common to the channels, a base station transmits a PDSCH signal including the index value to a mobile station (step S41). The base station transmits a PDSCH signal including a power offset amount for the PHYCH1to the mobile station (step S42). The base station transmits a PDSCH signal including a power offset amount for the PHYCH2to the mobile station (step S43). The base station transmits a PDSCH signal including a power offset amount for the PHYCH3to the mobile station (step S44). The base station transmits a PDSCH signal including a power offset amount for the PHYCH4to the mobile station (step S45).

On the other hand, as depicted inFIG. 18, in the case of notification of the respective repetition counts for the channels, the base station transmits a PDSCH signal including the repetition count for the PHYCH1to the mobile station (step S51). The base station transmits a PDSCH signal including the repetition count for the PHYCH2to the mobile station (step S52). The base station transmits a PDSCH signal including the repetition count for the PHYCH3to the mobile station (step S53). The base station transmits a PDSCH signal including the repetition count for the PHYCH4to the mobile station (step S54).

Additionally, the base station transmits a PDSCH signal including a power offset amount for the PHYCH1to the mobile station (step S55). The base station transmits a PDSCH signal including a power offset amount for the PHYCH2to the mobile station (step S56). The base station transmits a PDSCH signal including a power offset amount for the PHYCH3to the mobile station (step S57). The base station transmits a PDSCH signal including a power offset amount for the PHYCH4to the mobile station (step S58).

In the examples depicted inFIG. 17andFIG. 18, for example, the power offset amount is assumed to be any of four values of 0 dB, 2 dB, 4 dB, 6 dB and the repetition count is assumed to be any of 1, 2, . . . , 15, and 16. The index value is assumed to be any of 0, 1, . . . , 14, and 15. In this case, the base station requires an information amount of two bits for notifying the mobile station of a power offset amount. The base station requires an information amount of four bits for notifying the mobile station of a repetition count. The base station requires an information amount of four bits for notifying the mobile station of an index value.

Therefore, in the case of notification of the index value depicted inFIG. 17, since four bits are required for the notification of the index value and eight bits are required for the notification of the power offset amounts of the four channels, a total of 12 bits are required. In contrast, in the case of notification of the repetition counts for the respective channels depicted inFIG. 18, since 16 bits are required for notification of the repetition counts of the four channels and eight bits are required for the notification of the power offset amounts of the four channels, a total of 24 bits are required.

Therefore, the notification of the index value reduces the number of bits required for notification by half as compared to the case of notification of the repetition counts for each channel. If the number of channels further increases, the number of bits required for notification of the index value does not change while the number of required bits increases in the case of notification of the repetition counts for each channel and therefore, the sufficient number of bits required for notification of the index value is equal to or less than a half of the number of bits required for notification of the repetition counts for each channel. As described above, the notification of the index value can reduce the number of bits required for notification as compared to the case of notification of the repetition counts for each channel.

Although a terminal that wirelessly communicates with a base station is a mobile station in the examples described above, the terminal may be fixed at a certain position without moving.

The base station, the mobile station, the wireless communications system, and the wireless communications method provide an effect that a base station can efficiently notify a mobile station of information necessary for signal reception.