WO2013001650A1

WO2013001650A1 - Wireless communication system, mobile station, base station, and wireless communication method

Info

Publication number: WO2013001650A1
Application number: PCT/JP2011/065105
Authority: WO
Inventors: 田中　良紀
Original assignee: 富士通株式会社
Priority date: 2011-06-30
Filing date: 2011-06-30
Publication date: 2013-01-03
Also published as: JP5605509B2; JPWO2013001650A1

Abstract

The present invention reduces a sensitivity-inhibiting effect produced by received signal processing of a mobile station. The wireless communication system has a mobile station (10) and a base station (20). The mobile station (10) detects the sensitivity-inhibiting effect produced by received signal processing on the basis of the received signal level of another frequency that is different from the frequency that the mobile station uses for communication, and transmits control information (13) indicating a request for a frequency change in accordance with the detection conditions of the sensitivity-inhibiting effect. The base station (20) receives control information (13) from the mobile station (10), and changes, on the basis of the control information (13), the assigned frequency that the mobile station (10) uses for communication.

Description

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

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

Currently, wireless communication systems such as mobile phone systems and wireless LANs (Local Area Networks) are widely used. In addition, active discussions are ongoing on next-generation wireless communication technology in order to further increase the speed and bandwidth of wireless communication.

For example, 3GPP (3rd Generation Partnership Project), one of the international standardization organizations, uses W-CDMA (Wideband-CDMA), which employs code division multiple access (CDMA), or orthogonal frequency division multiple access ( Communication systems such as LTE (Long Term Evolution) using OFDMA: Orthogonal Frequency Division Multiple Multiple Access have been proposed. In 3GPP, a communication method called LTE-A (LTE--Advanced), which is an extension of LTE, is discussed.

Many wireless communication systems employ a cellular system in which a plurality of base stations are installed in a service area to form a plurality of cells. In addition to a macro cell that covers a wide area, a wireless communication system may include a pico cell or a femto cell having a cell radius smaller than that of the macro cell (ie, transmission power of the base station is small). A radio access network including a plurality of types of cells having different cell radii may be referred to as a heterogeneous network. A pico cell or a femto cell may be formed such that all or part of the area overlaps with the macro cell.

When the cellular system can use the first carrier frequency adjacent to the carrier frequency of the other cellular system and the second carrier frequency not adjacent to the other carrier system, the second carrier is transmitted to the mobile station having a large interference with the other cellular system. A method of using a frequency has been proposed. In addition, a system has been proposed in which a plurality of arbitration stations belonging to different service sets mutually mediate interference between service sets by transmitting and receiving beacons on a common channel in a predetermined frequency band. In addition, the signal strength of each usable radio channel (candidate channel) is measured to calculate the influence level of interference from other channels, and communication is selected as the radio channel that uses the candidate channel with the minimum influence level of interference. A device has been proposed.

Japanese Patent Laid-Open No. 11-341555 JP 2006-254398 A JP 2008-78698 A

In order to reduce interference between cells, a base station of a certain cell (for example, a macro cell) and a base station of another cell (for example, a pico cell or a femto cell in which the macro cell and the area overlap) use different frequencies. Can be considered. However, in the mobile station, even if the desired frequency used for communication by the mobile station is different from the frequency of other cells, if the received signal level from other cells is high, a sensitivity suppression effect may occur. .

Here, the sensitivity suppression effect is that a small desired signal is buried in noise or quantization noise in the analog receiver when the reception level of other cell signals with a frequency different from that of the desired signal is very high. This is a phenomenon in which reception characteristics deteriorate. For example, consider a case where the reception level of a macro cell signal having a desired frequency is relatively very small and the reception level of a femto cell signal having a frequency close to the desired frequency is relatively very high. In such a case, a signal of another frequency close to a desired frequency cannot be completely removed by the reception filter, and a reception signal (femtocell signal) having a large level from another cell passes through the reception filter. As a result, the detection accuracy of a received signal (macrocell signal) having a desired frequency is lowered, and a sensitivity suppression effect may occur.

In a wireless communication system, the reception quality such as SINR (Signal-to-Interference-and-Noise-Ration) may decrease due to the sensitivity suppression effect, so it is desirable to reduce this. However, the conventional technique has a problem that the sensitivity suppression effect cannot be reduced.

The present invention has been made in view of these points, and an object of the present invention is to provide a radio communication system, a mobile station, a base station, and a radio communication method that can reduce the sensitivity suppression effect that occurs in received signal processing. To do.

A wireless communication system having a mobile station and a base station is provided. The mobile station detects the sensitivity suppression effect generated in the received signal processing based on the received signal level of the other frequency different from the frequency used by the mobile station, and requests to change the frequency according to the detection status of the sensitivity suppression effect. The control information indicating is transmitted. The base station receives control information from the mobile station, and changes allocation of frequencies used by the mobile station for communication based on the received control information.

Also provided is a wireless communication method performed by a system including a mobile station and a base station. In the wireless communication method, the sensitivity suppression effect generated in the received signal processing of the mobile station is detected based on the received signal level of another frequency different from the frequency used by the mobile station for communication. Control information indicating a frequency change request is transmitted from the mobile station to the base station according to the detection state of the sensitivity suppression effect. Based on the control information, allocation of frequencies used by the mobile station for communication is changed.

It is possible to reduce the sensitivity suppression effect generated in the received signal processing of the mobile station.
These and other objects, features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings which illustrate preferred embodiments by way of example of the present invention.

It is a figure which shows the radio | wireless communications system of 1st Embodiment. It is a figure which shows the radio | wireless communications system of 2nd Embodiment. It is a figure which shows the example of a carrier aggregation. It is a block diagram which shows the mobile station of 2nd Embodiment. It is a block diagram which shows the base station of 2nd Embodiment. It is a figure which shows the example of the generation condition of a sensitivity suppression effect. It is a figure which shows the example of the periphery cell table which a base station has. It is a figure which shows the example of the message from a mobile station to a base station. It is a flowchart which shows a 1st mobile station process. It is a flowchart which shows a 2nd mobile station process. It is a flowchart which shows a 3rd mobile station process. It is a flowchart which shows a base station process. It is a figure which shows the 1st example of a shift of the pass band of a filter. It is a figure which shows the 2nd example of a shift of the pass band of a filter. It is a figure which shows the 3rd example of a shift of the pass band of a filter. It is a figure which shows the 4th example of a shift of the pass band of a filter.

Hereinafter, the present embodiment will be described with reference to the drawings.
[First Embodiment]
FIG. 1 is a diagram illustrating a wireless communication system according to the first embodiment. The wireless communication system according to the first embodiment includes a mobile station 10 and a base station 20 that perform wireless communication. The mobile station 10 may communicate directly with the base station 20 or may communicate with the base station 20 via a relay station.

The mobile station 10 includes a detection unit 11 and a transmission unit 12.
The detection unit 11 detects the sensitivity suppression effect generated in the reception signal processing based on the reception signal level (for example, reception power) of another frequency different from the frequency used by the mobile station 10 for communication. The detection unit 11 may determine whether the sensitivity suppression effect is large from the received signal level of the frequency # 1 used for communication and the received signal level of the frequency # 2 not used for communication. For example, when the difference or ratio of the received signal level of frequency # 2 with respect to the received signal level of frequency # 1 exceeds the threshold, the detection unit 11 determines that the sensitivity suppression effect is large. Alternatively, the detection unit 11 determines that the sensitivity suppression effect is large when the received signal level of the frequency # 2 exceeds the threshold value.

Note that the mobile station 10 measures received signal levels of frequencies # 1 and # 2, for example. For the measurement of the reception signal level, a signal after passing through a reception filter used for reception signal processing such as a band pass filter (BPF: BandBPass Filter) may be used. The detection of the sensitivity suppression effect may be realized using a memory that stores a program such as a RAM (Random Access Memory) and a processor that executes a program such as a CPU (Central Processing Unit). Further, it may be realized using an electronic circuit such as ASIC (Application Specific Integrated Circuit) or FPGA (Field Programmable Gate Array).

The transmission unit 12 transmits, to the base station 20, control information 13 indicating a request for changing the frequency used by the mobile station 10 for communication in accordance with the detection status of the sensitivity suppression effect by the detection unit 11. For example, the transmission unit 12 transmits the control information 13 when it is determined that the sensitivity suppression effect is large. Alternatively, the transmission unit 12 determines that the sensitivity suppression effect is large, and the sensitivity suppression effect cannot be sufficiently reduced by changing the pass band of the reception filter (for example, shifting the pass band). When it is determined, the control information 13 is transmitted.

Whether or not the sensitivity suppression effect can be sufficiently reduced can be determined in consideration of the filter characteristics of the reception filter. For example, when the frequency # 1 cannot be excluded from the passband while the frequency # 1 is included in the passband of the reception filter because the difference between the frequency # 1 and the frequency # 2 is less than a predetermined width, It is determined that the sensitivity suppression effect cannot be reduced by the change. On the other hand, when it is determined that the sensitivity suppression effect can be sufficiently reduced by changing the pass band, the mobile station 10 does not transmit the control information 13 to the base station 20 and the frequency # 2 is excluded from the pass band. The pass band of the reception filter may be changed.

The base station 20 includes a receiving unit 21 and a control unit 22.
The receiving unit 21 receives control information 13 indicating a frequency change request from the mobile station 10.
When the receiving unit 21 receives the control information 13, the control unit 22 changes the allocation of frequencies used by the mobile station 10 for communication based on the control information 13. For example, the control unit 22 changes the frequency used by the mobile station 10 for communication to a frequency separated from the frequency # 2 (frequency not used for communication) causing the sensitivity suppression effect by a predetermined width or more. The control unit 22 may notify the mobile station 10 of the changed frequency. The frequency allocation change may be realized using a memory that stores a program such as a RAM and a processor that executes a program such as a CPU. Moreover, you may implement | achieve using electronic circuits, such as ASIC and FPGA.

Here, the base station 20 may acquire cell information indicating the frequency used by each peripheral base station for communication from the peripheral base station. In that case, the control unit 22 can refer to the cell information, specify the frequency at which the mobile station 10 can receive the signal of the neighboring base station, and determine the changed frequency so as to avoid the specified frequency. . In addition, the mobile station 10 may transmit the control information 13 by including information on a frequency whose reception signal level is high and which is desired to be excluded from the pass band of the reception filter. In that case, the control unit 22 can determine the changed frequency so as to avoid the excluded frequency indicated by the control information 13. Further, the mobile station 10 may calculate a frequency candidate after the change, and may transmit the frequency candidate information included in the control information 13. In that case, the control unit 22 can select the changed frequency from the frequency candidates indicated by the control information 13.

According to the wireless communication system of the first embodiment, the sensitivity suppression effect generated in the received signal processing of the mobile station 10 is detected based on the received signal level of another frequency different from the frequency used by the mobile station 10 for communication. . Control information 13 indicating a frequency change request is transmitted from the mobile station 10 to the base station 20 according to the detection state of the sensitivity suppression effect. Based on the control information 13, the allocation of frequencies used by the mobile station 10 for communication is changed. Thereby, the sensitivity suppression effect produced by the received signal processing of the mobile station 10 can be reduced, and the reception quality of the mobile station 10 can be improved.

For example, in a heterogeneous network including a plurality of types of cells having different cell radii, the mobile station has a higher level than the signal (desired signal) to be extracted if another base station is present near the connected base station. A signal that does not need to be extracted (unnecessary signal) may be received at a frequency that the local station does not use for communication. On the other hand, the mobile station may not be able to completely remove a signal having a frequency that is not used for communication and that is close to the frequency used for communication by the reception filter. As a result, the received signal after passing through the reception filter contains an unnecessary signal with a level greater than the desired signal, and the level of the desired signal is relatively suppressed through subsequent automatic gain control, thermal noise application, quantization processing, etc. Therefore, the detection accuracy of the desired signal may be lowered.

In contrast, when the mobile station 10 requests the base station 20 to change the frequency according to the detection state of the sensitivity suppression effect, it becomes easy for the mobile station 10 to remove unnecessary signals with the reception filter. However, the mobile station 10 does not need to request the base station 20 to change the frequency when the unnecessary signal can be removed by changing the pass band of the reception filter.

Note that the LTE technical specification (TS36.101) states that if the reception power of an unnecessary signal at a frequency 15 to 60 MHz away from the frequency of the desired signal is −44 dBm or less, the throughput is lower than when no unnecessary signal is present. Is required to be kept within 5%. However, the received power from the base station at the mobile station 5 m away from the base station having a transmission power of 20 dBm is −32 dBm, which exceeds the above-mentioned reference value of −44 dBm. For this reason, even if the mobile station complies with the LTE specification, the reception quality of the desired signal may be greatly reduced due to the sensitivity suppression effect near the pico cell or the femto cell.

In the second embodiment described below, an example of a wireless communication system assuming LTE-A is given. However, the wireless communication method described in the first embodiment can of course be applied to a wireless communication system employing a communication method other than LTE-A.

[Second Embodiment]
FIG. 2 is a diagram illustrating a wireless communication system according to the second embodiment. The wireless communication system according to the second embodiment includes a mobile station 100 and

base stations

200 and 200a.

The mobile station 100 is a wireless terminal device that connects to the

base stations

200 and 200a to perform wireless communication. The mobile station 100 may be a mobile phone or a mobile information terminal.
The

base stations

200 and 200a are communication devices having a wireless interface and a wired interface.

Base stations

200 and 200a each form a cell. The area of the cell of the base station 200a overlaps with at least a part of the cell of the base station 200. The cell of the base station 200 may be a macro cell, and the cell of the base station 200a may be a femto cell. The

base stations

200 and 200a are connected to a wired network 30 (for example, a core network).

Here, the

base stations

200 and 200a communicate with the mobile station 100 via a wireless interface. A relay station may be interposed between the

base stations

200 and 200a and the mobile station 100. However, in the second embodiment, a case where the mobile station 100 connects to the base station 200 is considered. The base station 200 and the base station 200a use frequency bands that do not overlap each other for wireless communication. The base station 200 can perform wireless communication using a plurality of frequency bands called component carriers (CC: Component Carrier). The

base stations

200 and 200a can communicate with each other via the wired network 30.

FIG. 3 is a diagram illustrating an example of carrier aggregation. The base station 200 can aggregate two or more CCs among a plurality of CCs set in advance and use them for communication with the mobile station 100. CC aggregation is sometimes referred to as carrier aggregation.

For example, five CCs (CC # 1 to # 5) are provided at continuous or discontinuous frequencies. CCs # 1 to # 5 may be a set of bands belonging to the same frequency band (for example, 800 MHz band, 2.5 GHz band, 3.5 GHz band, etc.), or may belong to a plurality of different frequency bands. It may be a set. When adopting time division duplex (TDD: Time Division Duplex), a band for downlink (DL) and uplink (UL: Uplink) is secured for each CC. When employing frequency division duplex (FDD), a frequency band for DL and a frequency band for UL are secured for each CC.

The base station 200 transmits a radio frame for each CC, and controls allocation of radio frame resources (for example, radio resources subdivided by a time axis and a frequency axis). The base station 200 can use a bandwidth wider than the bandwidth of one CC for communication with the mobile station 100 by allocating radio resources of two or more CCs to the mobile station 100 in parallel. In addition, the bandwidth of each CC can be set to 5 MHz, 10 MHz, 15 MHz, 20 MHz, etc., for example. The bandwidths of the plurality of CCs may not be the same.

FIG. 4 is a block diagram illustrating a mobile station according to the second embodiment. The mobile station 100 includes an antenna 111, a duplexer 112,

oscillators

113, 125 and 145, radio frequency (RF) filters 121 and 149,

mixers

122, 126, 146 and 148, and an intermediate frequency (IF) filter 123. 147, automatic gain controller (AGC: Auto Gain Controller) 124, 128, baseband (BB) filters 127, 144, analog-to-digital converter (ADC: 129), demodulator 130, RRC ( A radio resource control unit 131, a measurement unit 132, a control unit 133, a multiplexing unit 141, a modulation unit 142, and a digital-to-analog converter (DAC) 143 are included.

The antenna 111 outputs a radio frequency reception signal to the duplexer 112. The radio frequency transmission signal acquired from the duplexer 112 is transmitted. Note that the mobile station 100 may include a plurality of antennas, and may separate the transmitting antenna and the receiving antenna.

The duplexer 112 isolates the transmission signal and the reception signal by using a filter or the like, so that the antenna 111 can be used as an antenna for both transmission and reception. The duplexer 112 is sometimes called an antenna duplexer. The duplexer 112 outputs a radio frequency reception signal acquired from the antenna 111 to the RF filter 121. The radio frequency transmission signal acquired from the RF filter 149 is output to the antenna 111.

The oscillator 113 generates a reference signal used for signal conversion (down-conversion and up-conversion) between a radio frequency and an intermediate frequency lower than the radio frequency. The oscillator 113 supplies the generated reference signal to the

mixers

122 and 148.

The RF filter 121 is a band pass filter that acquires a radio frequency reception signal from the duplexer 112 and passes only a signal in a predetermined frequency band. The pass band of the RF filter 121 is set to a desired frequency band (800 MHz band, 2.5 GHz band, 3.5 GHz band, etc.) wider than the pass band of the IF filter 123 and the BB filter 127 in the subsequent stage.

The mixer 122 superimposes the reference signal generated by the oscillator 113 on the radio frequency reception signal that has passed through the RF filter 121, and down-converts the radio frequency reception signal into an intermediate frequency reception signal. Then, the intermediate frequency reception signal is output to the IF filter 123.

The IF filter 123 is a band pass filter that acquires an intermediate frequency received signal from the mixer 122 and passes only a signal in a frequency band according to an instruction from the control unit 133. For example, the IF filter 123 fixes the passband bandwidth and shifts the passband according to an instruction from the control unit 133. The pass band of the IF filter 123 is wider than the pass band of the BB filter 127 at the subsequent stage, and includes a desired CC frequency and its peripheral frequencies.

The AGC 124 performs automatic gain control on the intermediate frequency received signal that has passed through the IF filter 123, and outputs the received signal after level adjustment to the mixer 126. For example, the AGC 124 decreases the gain when the received signal is strong and increases the gain when the received signal is weak so that the received signal level fluctuates in an appropriate range with respect to the average level.

The oscillator 125 generates a reference signal used for signal conversion (down conversion) from an intermediate frequency to a baseband frequency lower than the intermediate frequency. The frequency of the reference signal is instructed from the control unit 133 according to the CC used by the mobile station 100 for communication. The oscillator 125 supplies the generated reference signal to the mixer 126.

The mixer 126 superimposes the reference signal generated by the oscillator 125 on the intermediate frequency reception signal that has passed through the AGC 124, and down-converts the intermediate frequency reception signal into an analog baseband signal. Then, the analog baseband signal is output to the BB filter 127.

The BB filter 127 is a band-pass filter that acquires an analog baseband signal from the mixer 126 and passes a signal in a desired CC frequency band. However, the BB filter 127 may not completely remove a signal having a frequency close to a desired CC frequency band. Further, when the received signal passes through the AGC 124, the mixer 126, and the BB filter 127, element thermal noise may be applied to the received signal.

The AGC 128 performs automatic gain control on the analog baseband signal that has passed through the BB filter 127, and outputs the level-adjusted signal to the ADC 129.
The ADC 129 converts the analog baseband signal into a digital baseband signal and outputs the digital baseband signal to the demodulation unit 130. In analog-digital conversion, quantization distortion may occur in quantization in which the received signal level is represented by discrete values.

The demodulator 130 digitally demodulates the digital baseband signal acquired from the ADC 129. The received signal is subjected to multilevel modulation such as QPSK (Quadrature Phase Keying) and 16QAM (Quadrature Amplitude Modulation).

The RRC processing unit 131 performs RRC layer protocol processing on the demodulated received signal, and extracts the RRC control information transmitted by the base station 200. Then, at least a part of the extracted RRC control information is output to the control unit 133. The extracted RRC control information includes control information indicating a change in CC used by the mobile station 100.

The measuring unit 132 measures the received signal level (for example, received power) of the desired signal and the unnecessary signal based on the analog baseband signal before passing through the BB filter 127 and input to the AGC 128. For example, the measurement unit 132 measures the reception signal level of a specific frequency of CC used by the mobile station 100 for communication or the average or maximum of reception signal levels of a plurality of frequencies as the reception signal level of the desired signal. Further, the reception signal level of each frequency outside the CC frequency band is measured as the reception signal level of the unnecessary signal. Then, the measurement unit 132 notifies the control unit 133 of the measurement result of the received signal level. Note that the received signal level may be measured using an analog baseband signal before passing through the BB filter 127.

Based on the RRC control information acquired from the RRC processing unit 131 and the measurement result of the received signal level notified from the measuring unit 132, the control unit 133 detects the sensitivity suppression effect generated in the reception signal processing and reduces the sensitivity suppression effect. Control. The sensitivity suppression effect may occur, for example, when an unnecessary signal having a large level passes through the IF filter 123, the gain of the AGC 124 is suppressed, and element thermal noise is applied to the received signal. Moreover, it may occur due to the influence of quantization distortion generated in the ADC 129.

For example, the control unit 133 determines whether there is a possibility that a large sensitivity suppression effect may occur based on the desired signal and the received signal level of the unnecessary signal measured by the measurement unit 132. Further, it is determined whether or not the sensitivity suppression effect can be sufficiently reduced by shifting the pass band of the IF filter 123 from the frequency at which the unnecessary signal has a large level and the filter characteristics of the IF filter 123. When it is determined that the sensitivity suppression effect cannot be sufficiently reduced, the control unit 133 generates RRC control information indicating a request for changing the CC used for communication, and outputs the RRC control information to the multiplexing unit 141. Further, the control unit 133 controls the pass band of the IF filter 123 so that a desired signal passes and an unnecessary signal having a large level does not pass as much as possible from the CC used for communication and the filter characteristics of the IF filter 123. Further, the control unit 133 controls the oscillation frequency of the oscillator 125.

Here, the control unit 133 includes, for example, a processor 134 and a memory 135 in order to detect the sensitivity suppression effect and perform control to reduce the sensitivity suppression effect. The processor 134 executes a program and may be a CPU. The memory 135 stores a program at least temporarily, and may be a volatile storage medium such as a RAM. The processor 134 may read a program from a nonvolatile storage medium such as a ROM (Read Only Memory) or a flash memory and store the program in the memory 135. However, the control unit 133 can be realized using an electronic circuit such as an ASIC or FPGA.

The multiplexing unit 141 multiplexes the user data that has been subjected to error correction coding and the control information generated by the control unit 133 (mapped to radio resources), and outputs the multiplexed data to the modulation unit 142.
The modulation unit 142 acquires a digital baseband signal including user data and control information from the multiplexing unit 141, and performs digital modulation such as QPSK or 16QAM. Then, the modulation unit 142 outputs the modulated digital baseband signal to the DAC 143.

The DAC 143 converts the digital baseband signal into an analog baseband signal and outputs the analog baseband signal to the BB filter 144.
The BB filter 144 is a band pass filter that acquires an analog baseband signal from the DAC 143 and passes a signal in a CC frequency band used for communication.

The oscillator 145 generates a reference signal used for signal conversion (up-conversion) from a baseband frequency to an intermediate frequency, and supplies the generated reference signal to the mixer 146.
The mixer 146 superimposes the reference signal generated by the oscillator 145 on the analog baseband signal that has passed through the BB filter 144 and upconverts the signal to an intermediate frequency transmission signal. Then, the intermediate frequency transmission signal is output to IF filter 147.

The IF filter 147 is a band-pass filter that acquires an intermediate-frequency transmission signal from the mixer 146 and passes a signal in the CC frequency band used for communication.
The mixer 148 superimposes the reference signal generated by the oscillator 113 on the intermediate frequency transmission signal that has passed through the IF filter 147 and up-converts the signal to a radio frequency transmission signal. Then, a radio frequency transmission signal is output to the RF filter 149.

The RF filter 149 is a band-pass filter that acquires a radio frequency transmission signal from the mixer 148 and passes only a signal in a desired frequency band to the duplexer 112.
The control unit 133 is an example of the detection unit 11 described above. Multiplexer 141, modulator 142, DAC 143, BB filter 144, oscillator 145, mixer 146, IF filter 147, mixer 148, and RF filter 149 are examples of transmitter 12 described above.

FIG. 5 is a block diagram illustrating a base station according to the second embodiment. The base station 200 includes

antennas

211 and 238, a radio reception unit 212, a fast Fourier transform (FFT) unit 213, a demodulation unit 214, a decoding unit 215, a MAC (Medium Access Control) / RLC (Radio Link Control) process. Unit 216, wired interface 221, RRC processing unit 222, table storage unit 223, control unit 224, packet generation unit 231, scheduler 232, encoding unit 233, modulation unit 234, multiplexing unit 235, inverse fast Fourier transform (IFFT: Inverse Fast Fourier Transform) unit 236 and wireless transmission unit 237.

The antenna 211 receives a radio signal from the mobile station 100 and outputs it to the radio reception unit 212.
The radio reception unit 212 acquires a radio frequency reception signal from the antenna 211, down-converts the radio frequency to the baseband frequency, and outputs the reception signal converted into the digital baseband signal to the FFT unit 213. The wireless reception unit 212 includes circuits such as a band pass filter, an oscillator, a mixer, and an ADC for wireless signal processing.

The FFT unit 213 acquires a reception signal from the radio reception unit 212, converts a time component into a frequency component by FFT, and outputs the converted reception signal to the demodulation unit 214. However, the base station 200 may perform conversion from a time component to a frequency component by a method other than FFT.

The demodulator 214 digitally demodulates the received signal acquired from the FFT unit 213. The received signal is subjected to multilevel modulation such as QPSK or 16QAM.
The decoding unit 215 acquires the demodulated reception signal from the demodulation unit 214, performs error correction decoding, and outputs the decoded reception signal to the MAC / RLC processing unit 216. The received signal is error-correction-encoded, for example, by a convolutional code, a convolutional turbo code, a low density parity check (LDPC) code, or the like.

The MAC / RLC processing unit 216 acquires the received signal decoded from the decoding unit 215, and performs protocol processing of the MAC layer and the RLC layer. The user data extracted from the received signal is output to the wired interface 221, for example.

The wired interface 221 is an interface that is connected to the wired network 30 and performs packet communication. The wired interface 221 transfers user data transmitted from the mobile station 100 to the wired network 30, receives user data addressed to the mobile station 100 from the wired network 30, and outputs the user data to the packet generator 231. Also, the wired interface 221 acquires control information indicating the frequency band used for communication by the base station 200 a from the base station 200 a via the wired network 30 and outputs the control information to the control unit 224.

The RRC processing unit 222 performs RRC layer protocol processing on the demodulated received signal, extracts the RRC control information transmitted by the mobile station 100, and outputs the RRC control information to the control unit 224. The extracted RRC control information includes control information indicating a CC change request.

The table storage unit 223 is a volatile storage medium such as a RAM or a non-volatile storage medium such as a flash memory. The table storage unit 223 stores the peripheral cell table. The neighboring cell table includes information on frequency bands used by the base station 200a.

The control unit 224 performs control to reduce the sensitivity suppression effect of the mobile station 100 based on the RRC control information acquired from the RRC processing unit 222 and the peripheral cell table stored in the table storage unit 223. For example, when receiving the RRC control information indicating the CC change request from the mobile station 100, the control unit 224 changes the CC assignment to the mobile station 100 so that the sensitivity suppression effect is reduced. Then, the control unit 224 notifies the CC change to the scheduler 232, generates RRC control information indicating the CC change, and outputs the RRC control information to the packet generation unit 231.

Here, the control unit 224 includes, for example, a processor 225 and a memory 226 for control to reduce the sensitivity suppression effect. The processor 225 executes a program and may be a CPU. The memory 226 stores the program at least temporarily, and may be a volatile storage medium such as a RAM. The processor 225 may read a program from a nonvolatile storage medium such as a ROM or a flash memory and store the program in the memory 226. Further, the table storage unit 223 and the memory 226 may be the same storage device. However, the control unit 224 can also be realized using an electronic circuit such as an ASIC or FPGA.

The packet generation unit 231 converts the user data acquired from the wired interface 221 and the RRC control information acquired from the control unit 224 into a wireless section packet format.
The scheduler 232 acquires user data and RRC control information from the packet generation unit 231, performs scheduling according to the CC allocation status notified from the control unit 224, and sequentially outputs the user data and RRC control information to the encoding unit 233.

The encoding unit 233 acquires a transmission signal including user data and RRC control information from the scheduler 232, performs error correction encoding, and outputs the transmission signal to the modulation unit 234. For example, a convolutional code, a convolutional turbo code, an LDPC code, or the like is used as the error correction code.

The modulation unit 234 acquires the transmission signal encoded from the encoding unit 233, performs digital modulation such as QPSK or 16QAM, and outputs the modulated transmission signal to the multiplexing unit 235.
The multiplexing unit 235 obtains a transmission signal including user data and RRC control information from the modulation unit 234, multiplexes it with a control signal of a physical layer and a predetermined pilot signal (mapped to a radio resource), and converts the transmission signal into an IFFT To the unit 236.

The IFFT unit 236 acquires the transmission signal from the multiplexing unit 235, converts the frequency component into a time component by IFFT, and outputs the transmission signal to the wireless transmission unit 237. However, the base station 200 may perform conversion from a frequency component to a time component by a method other than IFFT.

The wireless transmission unit 237 acquires a digital baseband signal as a transmission signal from the wireless transmission unit 237, performs up-conversion from a baseband frequency to a radio frequency, and outputs a radio frequency transmission signal to the antenna 238. The wireless transmission unit 237 includes circuits such as a band pass filter, an oscillator, a mixer, and a DAC for wireless signal processing.

The antenna 238 outputs the transmission signal acquired from the wireless transmission unit 237. However, the base station 200 may not separate the transmitting antenna and the receiving antenna.
The wireless reception unit 212, the FFT unit 213, the demodulation unit 214, the decoding unit 215, the MAC / RLC processing unit 216, and the RRC processing unit 222 are examples of the above-described reception unit 21. The control unit 224 is an example of the control unit 22 described above. The base station 200a can also be implemented using the same hardware as the base station 200.

FIG. 6 is a diagram illustrating an example of a situation where the sensitivity suppression effect occurs. A pass band as shown in FIG. 6 is set in the IF filter 123. The pass band of the IF filter 123 can be shifted. At the boundary between the passband and other frequencies, there is an attenuation region where the attenuation of the received signal level changes. If an unnecessary signal having a large level exists in at least one of the pass band and the attenuation band, a sensitivity suppression effect may occur. In the example of FIG. 6, in addition to the desired signal, an unnecessary signal having a level greater than that of the desired signal exists in the pass band of the IF filter 123. For example, the desired signal is a signal (desired CC signal) received by the mobile station 100 from the base station 200, and the unnecessary signal is a signal transmitted by the base station 200a.

FIG. 7 is a diagram illustrating an example of a neighboring cell table included in the base station. The peripheral cell table 227 is stored in the table storage unit 223. The control unit 224 updates the neighboring cell table 227 based on the control information received from the base station 200a.

The peripheral cell table 227 includes cell ID and frequency list items. The cell ID is identification information for identifying neighboring cells of the base station 200. The frequency list includes one or more frequency bands used in the base station (peripheral base station) of the peripheral cell indicated by the cell ID. The frequency band may be expressed using a center frequency and a bandwidth, or may be expressed using a lower limit frequency and an upper limit frequency. In addition, when identification information is given in advance to a frequency band that can be used in a wireless communication system, the identification information (for example, CC ID) may be used.

FIG. 8 is a diagram illustrating an example of a message from the mobile station to the base station. A message as shown in FIG. 8 is transmitted from the mobile station 100 to the base station 200 as RRC control information indicating a CC change request. Here, the mobile station 100 can use any of the following three methods as a method for requesting the base station 200 to change the CC.

(A) In the first method, the mobile station 100 simply notifies the base station 200 that the CC should be changed. In this method, the mobile station 100 transmits RRC control information including its own identification information (mobile station ID) and a message type indicating a CC change request.

(B) In the second method, the mobile station 100 notifies the base station 200 of a frequency to be excluded from the pass band and the attenuation band of the IF filter 123 because an unnecessary signal having a large level is detected. In this method, the mobile station 100 transmits RRC control information including a list of excluded frequencies in addition to the mobile station ID and the message type.

(C) In the third method, the mobile station 100 notifies the base station 200 of frequency candidates that the local station preferably uses for communication in order to reduce the sensitivity suppression effect. In this method, the mobile station 100 transmits RCC control information including a list of frequency candidates in addition to the mobile station ID and the message type. The range of frequency candidates may be expressed using a lower limit frequency or an upper limit frequency, may be expressed using a center frequency and a bandwidth, or may be expressed using a CC ID.

FIG. 9 is a flowchart showing the first mobile station processing. The mobile station processing in FIG. 9 corresponds to a case where a CC change request is made by the first method described above. The process shown in FIG. 9 is executed continuously (for example, periodically) by the mobile station 100.

(Step S11) The measuring unit 132 acquires an analog baseband signal after passing through the IF filter 123 and the BB filter 127. However, the measurement unit 132 may acquire an analog baseband signal before passing through the BB filter 127.

(Step S12) The measuring unit 132 measures the received signal level of the desired signal and the received signal level of the unnecessary signal remaining after the filter from the acquired analog baseband signal. As the former, for example, the average or maximum of the reception signal level of a specific frequency belonging to the CC used for communication or the reception signal level of a plurality of frequencies belonging to the CC is measured. As the latter, for example, the received signal level of each frequency not belonging to the CC used for communication is measured.

(Step S13) The control unit 133 determines whether there is an unnecessary signal whose level is higher than the desired signal and whose difference or ratio with the desired signal exceeds the threshold value. If it exists, it is determined that a large sensitivity suppression effect is generated, and the process proceeds to step S14. On the other hand, if it does not exist, it is determined that a large sensitivity suppression effect does not occur, and the process ends. Note that the control unit 133 may determine that a large sensitivity suppression effect occurs when the reception signal level of the unnecessary signal exceeds the threshold value.

(Step S14) The control unit 133 determines the pass band from the filter characteristics of the IF filter 123 (including the pass band and the width of the attenuation band) and the frequency at which there is an unnecessary signal whose difference or ratio exceeds the threshold. It is determined whether or not the unnecessary signal can be excluded by shifting. If it can be excluded, the process proceeds to step S17. If it cannot be excluded, the process proceeds to step S15.

For example, the control unit 133 confirms whether or not the frequency where the detected unnecessary signal exists is included between the lower limit frequency and the upper limit frequency used for communication, and determines that it is not excluded. This can occur when the mobile station 100 uses more than one CC. Further, the control unit 133 calculates the distance (frequency difference between edges) between the frequency band of the CC used for communication and the frequency where the detected unnecessary signal exists, and cannot be excluded when the distance is less than a predetermined threshold. Judge. The distance threshold is set in advance in consideration of the filter characteristics of the IF filter 123.

(Step S15) The control unit 133 generates RRC control information (corresponding to the message (A) in FIG. 8) indicating a CC change request. The RRC control information is converted into a radio signal and transmitted from the antenna 111 to the base station 200.

(Step S16) The RRC processing unit 131 extracts RRC control information indicating a CC change instruction from the received signal from the base station 200. The control unit 133 instructs the oscillator 125 to change the oscillation frequency and changes the CC to be received. Note that the frequency band of each CC used by the base station 200 is described in broadcast information transmitted by the base station 200, for example.

(Step S17) The control unit 133 sets the pass band of the IF filter 123 so that the frequency band of the CC used for communication is included in the pass band and the attenuation band, and the frequency where the detected unnecessary signal exists is not included. Shift. For example, the control unit 133 determines the shift direction from the current pass band and the CC frequency band used for communication so that the distance between the pass band and the frequency where the detected unnecessary signal is present is equal to or greater than the threshold. Determine the shift amount.

FIG. 10 is a flowchart showing the second mobile station process. The mobile station processing of FIG. 10 corresponds to a case where a CC change request is made by the second method described above. The process shown in FIG. 10 is executed continuously (for example, periodically) by the mobile station 100.

Since the processes of steps S21 to S24, S27, and S28 are the same as those of steps S11 to S14, S16, and S17, the description thereof is omitted.
(Step S <b> 25) The control unit 133 lists the frequencies at which there are unnecessary signals whose difference or ratio from the desired signal exceeds the threshold as exclusion frequencies.

(Step S26) The control unit 133 indicates a CC change request and generates RRC control information (corresponding to the message (B) in FIG. 8) including an excluded frequency list. The RRC control information is converted into a radio signal and transmitted from the antenna 111 to the base station 200.

FIG. 11 is a flowchart showing the third mobile station process. The mobile station processing in FIG. 11 corresponds to a case where a CC change request is made by the third method described above. The process shown in FIG. 11 is executed continuously (for example, periodically) by the mobile station 100.

Since the processes of steps S31 to S34, S37, and S38 are the same as those of steps S11 to S14, S16, and S17, the description thereof is omitted.
(Step S <b> 35) The control unit 133 calculates frequency candidates for reducing the sensitivity suppression effect from the filter characteristics of the IF filter 123 and the frequency at which there is an unnecessary signal whose difference or ratio between the desired signal exceeds the threshold. . For example, the control unit 133 calculates a frequency range in which the distance from the frequency at which the detected unnecessary signal exists is equal to or greater than a threshold value.

(Step S36) The control unit 133 indicates a CC change request and generates RRC control information (corresponding to the message (C) in FIG. 8) including the frequency candidate list. The RRC control information is converted into a radio signal and transmitted from the antenna 111 to the base station 200.

FIG. 12 is a flowchart showing the base station processing.
(Step S41) The RRC processing unit 222 extracts RRC control information indicating a CC change request from the received signal from the mobile station 100.

(Step S42) The control unit 224 determines whether the extracted RRC control information specifies a frequency candidate (for example, corresponds to the format of the message (C) in FIG. 8). If a frequency candidate is designated, the process proceeds to step S44. If no frequency candidate is designated, the process proceeds to step S43.

(Step S43) The control unit 224 determines whether the extracted RRC control information specifies an excluded frequency (for example, corresponds to the format of the message (B) in FIG. 8). If an excluded frequency is designated, the process proceeds to step S45. If neither a frequency candidate nor an excluded frequency is designated, the process proceeds to step S46.

(Step S44) The control unit 224 selects the CC within the designated frequency candidate as the CC after change. When two or more CCs are used (when carrier aggregation is performed), the CCs are selected so that the two or more CCs do not straddle the frequency where the unnecessary signal exists. Then, the process proceeds to step S48.

(Step S45) The control unit 224 adjusts the pass band of the IF filter 123 to select the changed CC so that the specified excluded frequency can be excluded from the pass band and the attenuation band. For example, the control unit 224 calculates a frequency range in which the distance from the excluded frequency is equal to or greater than a threshold, and selects a CC within the calculated range. In addition, when performing carrier aggregation, CC is selected so that two or more CC may not straddle the frequency in which an unnecessary signal exists. Then, the process proceeds to step S48.

(Step S46) The control unit 224 searches the neighboring cell table 227 stored in the table storage unit 223, and confirms the frequency band used by the neighboring base station.
(Step S47) The control unit 224 selects the changed CC so that the frequency band of the neighboring base station can be excluded from the pass band and the attenuation band by adjusting the pass band of the IF filter 123. For example, the control unit 224 selects a CC by calculating a frequency range in which the distance from the frequency band of the surrounding base station is equal to or greater than a threshold value. In addition, when performing carrier aggregation, CC is selected so that two or more CC may not straddle the frequency band of a periphery base station.

(Step S48) The control unit 224 generates RRC control information that includes information on one or more selected CCs (for example, CC IDs) and indicates a CC change instruction. The RRC control information is converted into a radio signal and transmitted from the antenna 238 to the mobile station 100.

FIG. 13 is a diagram illustrating a first shift example of the passband of the filter. In the example of FIG. 13, an unnecessary signal having a high level (for example, a transmission signal from the base station 200a) is included in the passband of the IF filter 123. In this state, a large sensitivity suppression effect can occur. However, the desired signal received from the base station 200 is more than the threshold value away from the unnecessary signal on the frequency axis.

Therefore, the mobile station 100 does not request the base station 200 to change the CC, so that the frequency of the desired signal is included in the pass band and the frequency of the unnecessary signal is excluded from the pass band and the attenuation band. Shift the passband. In the example of FIG. 13, the mobile station 100 shifts the passband so that the edge of the attenuation region and the edge of the unnecessary signal are adjacent to each other so that the shift amount is minimized. In the state after the shift, the sensitivity suppression effect is sufficiently suppressed.

FIG. 14 is a diagram illustrating a second shift example of the passband of the filter. In the example of FIG. 14, an unnecessary signal with a high level (for example, a transmission signal of the base station 200 a) is included in the attenuation region of the IF filter 123. Even in this state, a large sensitivity suppression effect can occur. However, the desired signal received from the base station 200 is more than the threshold value away from the unnecessary signal on the frequency axis.

Therefore, the mobile station 100 does not request the base station 200 to change the CC, so that the frequency of the desired signal is included in the pass band and the frequency of the unnecessary signal is excluded from the pass band and the attenuation band. Shift the passband. In the example of FIG. 14, the mobile station 100 shifts the passband so that the edge of the attenuation region and the edge of the unnecessary signal are adjacent to each other so that the shift amount is minimized. In the state after the shift, the sensitivity suppression effect is sufficiently suppressed.

FIG. 15 is a diagram illustrating a third shift example of the passband of the filter. In the example of FIG. 15, the pass band of the IF filter 123 includes an unnecessary signal having a high level (for example, a transmission signal of the base station 200a). In this state, a large sensitivity suppression effect can occur. Further, the desired signal received from the base station 200 is not separated from the unnecessary signal by more than a threshold on the frequency axis. For this reason, the pass band of the IF filter 123 cannot be shifted so that the frequency of the desired signal is included in the pass band and the frequency of the unnecessary signal is excluded from the pass band and the attenuation band.

Therefore, the mobile station 100 requests the base station 200 to change the CC. The base station 200 changes the CC used for communication so that the desired signal is separated from the unnecessary signal by a threshold value or more on the frequency axis. When the CC is changed, the mobile station 100 shifts the pass band of the IF filter 123 so that the frequency of the desired signal is included in the pass band and the frequency of the unnecessary signal is excluded from the pass band and the attenuation band. In the example of FIG. 15, the mobile station 100 shifts the passband so that the edge of the attenuation band and the edge of the unnecessary signal are adjacent to each other so that the shift amount is minimized. In the state after the shift, the sensitivity suppression effect is sufficiently suppressed.

FIG. 16 is a diagram illustrating a fourth shift example of the passband of the filter. In the example of FIG. 16, the pass band of the IF filter 123 includes an unnecessary signal having a high level (for example, a transmission signal of the base station 200a). In this state, a large sensitivity suppression effect can occur. Further, two CCs used for communication sandwich an unnecessary signal on the frequency axis. For this reason, the pass band of the IF filter 123 cannot be shifted so that the frequency of the desired signal is included in the pass band and the frequency of the unnecessary signal is excluded from the pass band and the attenuation band.

Therefore, the mobile station 100 requests the base station 200 to change the CC. The base station 200 changes the CC used for communication so that the two CCs do not sandwich the unnecessary signal on the frequency axis and the desired signal is separated from the unnecessary signal by a threshold value or more. When the CC is changed, the mobile station 100 shifts the pass band of the IF filter 123 so that the frequency of the desired signal is included in the pass band and the frequency of the unnecessary signal is excluded from the pass band and the attenuation band. In the example of FIG. 16, the mobile station 100 shifts the passband so that the edge of the attenuation band and the edge of the unnecessary signal are adjacent to each other so that the shift amount is minimized. In the state after the shift, the sensitivity suppression effect is sufficiently suppressed.

The wireless communication system according to the second embodiment measures the received signal level of unnecessary signals to detect the sensitivity suppression effect, and determines whether the sensitivity suppression effect can be reduced by shifting the pass band of the IF filter 123. When it is determined that it is difficult to reduce the sensitivity suppression effect only by shifting the passband, the mobile station 100 requests the base station 200 to change the CC used for communication. For this reason, the sensitivity suppression effect produced by the received signal processing of the mobile station 100 can be efficiently reduced, and the reception quality of the mobile station 100 can be improved.

Also, the mobile station 100 can select any one of the three methods as the CC change request method. According to the first method, the mobile station 100 only needs to request a CC change, and the load on the mobile station 100 is reduced. According to the second method, the base station 200 can easily identify the actual frequency causing the sensitivity suppression effect, and can select the changed CC more appropriately. According to the third method, frequency candidates can be calculated in consideration of the actual filter characteristics of the mobile station 100, so that the changed CC can be selected more appropriately.

The above merely shows the principle of the present invention. In addition, many modifications and variations will be apparent to practitioners skilled in this art and the present invention is not limited to the exact configuration and application shown and described above, and all corresponding modifications and equivalents may be And the equivalents thereof are considered to be within the scope of the invention.

DESCRIPTION OF SYMBOLS 10 Mobile station 11 Detection part 12 Transmission part 13 Control information 20 Base station 21 Reception part 22 Control part

Claims

Control that detects the sensitivity suppression effect generated in the received signal processing based on the received signal level of the other frequency different from the frequency used for communication by the own station, and indicates a frequency change request according to the detection status of the sensitivity suppression effect A mobile station transmitting information;
Receiving the control information from the mobile station, and based on the received control information, a base station that changes the allocation of frequencies used by the mobile station for communication;
A wireless communication system.
The radio according to claim 1, wherein the mobile station determines whether to transmit the control information based on a detection status of the sensitivity suppression effect and a filter characteristic of a reception filter used for the reception signal processing. Communications system.
The wireless communication system according to claim 2, wherein when the mobile station determines not to transmit the control information, the mobile station changes a pass band of the reception filter so that the sensitivity suppression effect is reduced.
The base station obtains cell information indicating a frequency used for communication by the other base station from another base station, and refers to the cell information to determine a frequency used by the mobile station after the allocation change for communication. The wireless communication system according to claim 1.
The mobile station calculates an excluded frequency to be removed from the pass band of the reception filter based on the detection state of the sensitivity suppression effect, and transmits the control information including the excluded frequency information,
The radio communication system according to claim 1, wherein the base station determines a frequency used for communication by the mobile station after the allocation change based on the excluded frequency.
The mobile station calculates a frequency candidate after the change based on the detection state of the sensitivity suppression effect, and transmits the control information including the frequency candidate information,
The radio communication system according to claim 1, wherein the base station determines a frequency used for communication by the mobile station after the allocation change based on the frequency candidate.
The mobile station measures the received signal level of the frequency used by the local station for communication and the received signal level of the other frequency from the received signal after passing through the receiving filter, and suppresses the sensitivity based on the measurement result. The wireless communication system according to claim 1, wherein an effect is detected.
Based on the received signal level of the other frequency different from the frequency used by the own station for communication, a detection unit that detects the sensitivity suppression effect generated in the received signal processing;
In accordance with the detection status of the sensitivity suppression effect, a transmitting unit that transmits control information indicating a frequency change request used by the own station for communication to a base station that controls frequency allocation;
A mobile station.
A receiving unit that receives control information indicating a frequency change request transmitted from a mobile station according to a detection status of a sensitivity suppression effect generated in reception signal processing of the mobile station;
Based on the received control information, a control unit that changes allocation of frequencies used by the mobile station for communication;
Base station with
A wireless communication method performed by a system including a mobile station and a base station,
Based on the received signal level of the other frequency different from the frequency used by the mobile station for communication, the sensitivity suppression effect generated in the received signal processing of the mobile station is detected,
In accordance with the detection status of the sensitivity suppression effect, control information indicating a frequency change request is transmitted from the mobile station to the base station,
Based on the control information, changing the frequency allocation used by the mobile station for communication,
Wireless communication method.