JP5496777B2 - base station - Google Patents

Description

  The present invention relates to a receiving apparatus and a base station.

  At present, communication systems using LTE (Long Term Evolution) based on OFDM (Orthogonal Frequency Division Multiplexing), WiMAX (Worldwide Interoperability for Microwave Access), and the like have appeared. In these communication systems, a low-power microcell base station is arranged between cells that cannot be covered by a high-power macrocell base station as a base station placement form.

  However, when a terminal is present at the edge of a cell of the macro cell base station, the terminal transmits a high level of power to the macro cell base station. Link performance (reception characteristics) deteriorates. For example, when a frequency deviation (Doppler shift) occurs in the OFDM signal output by the terminal due to the terminal moving at high speed (or the radio waves that are fixedly communicated are reflected by an object moving at high speed) The OFDM signal becomes an interference wave and degrades the reception characteristics of the macrocell base station. In particular, when the frequency of the desired wave subcarrier is subtracted from the frequency of the interference wave, and the remainder (offset frequency) obtained by dividing the calculation result by the frequency interval of the subcarrier is ½ times the subcarrier frequency interval. Then, the interference wave and the subcarrier are correlated and the reception characteristic is most deteriorated (for example, see FIG. 5A).

  Therefore, in order to solve such a problem, in Patent Document 1 below, a mobile station's moving speed, latitude, and longitude are calculated using a GPS satellite, and the mobile station is calculated based on the moving speed, latitude, and longitude. And the base station, the Doppler shift amount of the transmission wave from the mobile station is calculated from the angle, and the transmission wave of the mobile station is finely adjusted based on the calculation result. A mobile communication system for correcting the above is disclosed.

JP 2001-119333 A

  By the way, in the above prior art, by correcting the Doppler shift, it is possible to suppress the occurrence of interference waves due to the Doppler shift, but the cause of the interference waves is not only the Doppler shift but there are various causes. When an interference wave is generated due to a cause other than the Doppler shift, it is not possible to suppress the deterioration of reception characteristics due to the interference wave.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to suppress deterioration of reception characteristics due to interference waves.

  In order to achieve the above object, according to the present invention, as a first solving means relating to a receiving apparatus, a receiving apparatus that receives a radio signal based on a multicarrier communication scheme using a plurality of subcarriers, When there is an interference wave, the frequency of the desired wave subcarrier is subtracted from the frequency of the interference wave, and a remainder (offset frequency) obtained by dividing the calculation result by the frequency interval of the subcarrier is calculated. Based on the offset frequency A means for providing a communication means for changing the reception frequency setting is employed.

  In the present invention, as a second solving means related to the receiving apparatus, in the first solving means, the receiving apparatus receives a radio signal from a transmitting apparatus, wherein the communication means calculates the offset frequency, and A means for changing the reception frequency setting based on the offset frequency and transmitting an instruction to the transmission apparatus to change the transmission frequency based on the offset frequency is adopted.

  In the present invention, as a third solving means relating to the receiving device, in the first or second solving means, the communication means receives the reception signal when an error rate of a received signal exceeds a predetermined threshold value. A means for detecting an interference wave of a signal and calculating the offset frequency when an interference wave exists in the received signal is employed.

  In the present invention, as a fourth solving means relating to the receiving apparatus, a means is adopted in which the error rate is a FER (Frame Error Rate) in the third solving means.

  Further, in the present invention, as a first solving means related to a base station, a base station that receives a radio signal based on a multicarrier communication scheme using a plurality of subcarriers, and an interference wave exists in the received signal Then, the frequency of the desired wave subcarrier is subtracted from the frequency of the interference wave, a remainder (offset frequency) obtained by dividing the calculation result by the frequency interval of the subcarrier is calculated, and the reception frequency setting is changed based on the offset frequency. A means of providing communication means is adopted.

  In the present invention, as the second solving means related to the base station, in the first solving means, the base station receives a radio signal from a terminal, wherein the communication means calculates the offset frequency, and A means is adopted in which the reception frequency setting is changed based on the offset frequency, and an instruction is transmitted to the terminal to change the transmission frequency based on the offset frequency.

  In the present invention, as a third solving means relating to a base station, in the first or second solving means, the communication means is configured to receive the reception signal when an error rate of a received signal exceeds a predetermined threshold value. A means for detecting an interference wave of a signal and calculating the offset frequency when an interference wave exists in the received signal is employed.

  In the present invention, as the fourth solving means relating to the base station, a means is adopted in which the error rate is a FER (Frame Error Rate) in the third solving means.

  According to the present invention, when there is an interference wave in the received signal, the communication means subtracts the frequency of the desired wave subcarrier from the frequency of the interference wave, and divides the calculation result by the frequency interval of the subcarrier ( Offset frequency) is calculated, and the reception frequency setting is changed based on the offset frequency. In this way, by changing the reception frequency setting based on the offset frequency, it is possible to receive a signal that is uncorrelated with the interference wave. Therefore, by demodulating the signal, it is possible to suppress deterioration in reception characteristics due to the interference wave. it can.

It is a system configuration | structure figure which shows the radio | wireless communications system S provided with the microcell base station A which concerns on embodiment of this invention. It is a functional block diagram of the microcell base station A which concerns on embodiment of this invention. 3 is a functional block diagram of terminal C. FIG. It is a flowchart which shows operation | movement of the microcell base station A which concerns on embodiment of this invention. It is a figure which shows the change of a receiving frequency setting based on the offset frequency of the microcell base station A which concerns on embodiment of this invention.

Embodiments of the present invention will be described below with reference to the drawings.
The wireless communication system S is a communication system that employs an OFDM (Orthogonal Frequency Division Multiplexing) system or the like, and as shown in FIG. 1, the microcell base station A, the macrocell base station B, and the terminals C and D according to the present embodiment. It is composed of

The microcell base station A is a low-power base station that covers a gap between cells of the high-power macrocell base station B and other macrocell base stations (not shown), forms a cell CL1, and is located in the cell CL1. Communicate with terminal C to
The macrocell base station B is a high-power base station that forms a cell CL2 and communicates with a terminal D located in the cell CL2.

The terminal C is located in the cell CL1 of the microcell base station A, communicates with the microcell base station A, and performs voice communication or data communication.
The terminal D is located in the cell CL2 of the macro cell base station B, communicates with the macro cell base station B, and performs voice communication or data communication.

Next, the functional configuration of the microcell base station A will be described with reference to FIG.
The microcell base station A includes a receiving unit 1, a transmitting unit 2, and a control unit 3. The reception unit 1, the transmission unit 2, and the control unit 3 constitute communication means in the present embodiment.
The receiving unit 1 includes an antenna 1a, an amplifier 1b, a mixer 1c, a frequency adjusting unit 1d, an A / D converter 1e, and a demodulation processing unit 1f.

The antenna 1a outputs the received reception signal to the amplifier 1b.
The amplifier 1b amplifies the reception signal input from the antenna 1a and outputs it to the mixer 1c.
The mixer 1c mixes the received signal input from the amplifier 1b with the local signal input from the frequency adjusting unit 1d, thereby frequency-converting (down-converting) the received signal into an IF received signal having an IF frequency. The IF reception signal is output to the A / D converter 1e.

The frequency adjusting unit 1d generates a local signal for IF frequency conversion and outputs the local signal to the mixer 1c. The reference pulse oscillator 1d-1, the counter 1d-2, the phase comparator 1d-3, and the loop filter 1d-4 And a local signal oscillator 1d-5.
The reference pulse oscillator 1d-1 is composed of a crystal oscillator or a ceramic oscillator, generates a reference pulse signal based on the periodic vibration of the oscillator, and outputs the reference pulse signal to the phase comparator 1d-3.
The counter 1d-2 divides the local signal input from the local signal oscillator 1d-5 based on the frequency division ratio set in the register by the control unit 3, and the divided pulse signal is used as the phase comparator 1d-. 3 is output.

The phase comparator 1d-3 generates a phase difference pulse signal based on the phase difference between the reference pulse signal input from the reference pulse oscillator 1d-1 and the pulse signal input from the counter 1d-2. The phase difference pulse signal is output to the loop filter 1d-4.
The loop filter 1d-4 outputs a voltage signal obtained by integrating the phase difference pulse signal input from the phase comparator 1d-3 to the local signal oscillator 1d-5.
The local signal oscillator 1d-5 generates a local signal for IF frequency conversion having a frequency based on the voltage signal input from the loop filter 1d-4, and outputs the local signal to the mixer 1c.

The A / D converter 1e digitally converts the IF reception signal input from the mixer 1c and outputs the digital IF reception signal to the demodulation processing unit 1f as a digital IF reception signal.
The demodulation processing unit 1f performs demodulation processing based on the OFDM method such as Fourier transform processing, digital demodulation processing, and parallel-serial conversion processing on the digital IF reception signal input from the A / D converter 1e and the SC-FDM method. It outputs to the control part 3 as a band received signal. The demodulation processing unit 1 f detects an interference wave included in the digital IF reception signal during the Fourier transform process, and notifies the control unit 3 of the frequency of the interference wave. Further, the demodulation processing unit 1 f detects a FER (Frame Error Rate) of the received signal based on the digital IF received signal, and notifies the control unit 3 of the FER.

The transmission unit 2 includes a transmission circuit unit 2a and an antenna 2b.
The transmission circuit unit 2a modulates the baseband transmission signal input from the control unit 3 and outputs it to the antenna 2b as a transmission signal.
The antenna 2b transmits the transmission signal input from the transmission circuit unit 2a to the outside.
The control unit 3 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), an interface circuit for inputting / outputting signals to / from each unit, and the like, which are stored in the ROM. The overall operation of the microcell base station A is controlled based on the control program and the received signal received by the receiving unit 1. The control program stored in the ROM includes a base station interference suppression program, and the control unit 3 suppresses deterioration of reception characteristics due to interference waves based on the base station interference suppression program.

Next, the functional configuration of the terminal C will be described with reference to FIG.
The terminal C includes a receiving unit 11, a transmitting unit 12, and a control unit 13.
The receiving unit 11 includes an antenna 11a and a receiving circuit unit 11b.
The antenna 11a outputs the received reception signal to the reception circuit unit 11b.
The receiving circuit unit 11b demodulates the received signal under the control of the control unit 13, and outputs the demodulated signal to the control unit 13 as a baseband received signal.

The transmission unit 12 includes a modulation processing unit 12a, a D / A converter 12b, a mixer 12c, a frequency adjustment unit 12d, an amplifier 12e, and an antenna 12f.
The modulation processing unit 12a performs modulation processing based on the OFDM system such as serial-parallel conversion processing, digital modulation processing, and inverse Fourier transform processing on the baseband transmission signal input from the control unit 13, and SC-FDM system, and performs digital IF It is output to the D / A converter 12b as a transmission signal.

The D / A converter 12b converts the digital IF transmission signal input from the mixer 12c into an analog signal and outputs the analog IF transmission signal to the mixer 12c.
The mixer 12c mixes the IF transmission signal input from the D / A converter 12b and the local signal input from the frequency adjustment unit 1d, thereby converting the IF transmission signal to an RF frequency transmission signal (up-conversion). And the transmission signal is output to the amplifier 12e.

The frequency adjusting unit 12d generates a local signal for RF frequency conversion and outputs the local signal to the mixer 12c. The frequency adjusting unit 12d outputs a reference pulse oscillator 12d-1, a counter 12d-2, a phase comparator 12d-3, and a loop filter 12d-4. And a local signal oscillator 12d-5.
The reference pulse oscillator 12d-1 is composed of a crystal resonator or a ceramic resonator, generates a reference pulse signal based on the periodic vibration of the resonator, and outputs the reference pulse signal to the phase comparator 12d-3.
The counter 12d-2 divides the local signal input from the local signal oscillator 12d-5 based on the division ratio set in the register by the control unit 3, and the divided pulse signal is used as the phase comparator 12d-. 3 is output.

The phase comparator 12d-3 generates a phase difference pulse signal based on the phase difference between the reference pulse signal input from the reference pulse oscillator 12d-1 and the pulse signal input from the counter 12d-2. The phase difference pulse signal is output to the loop filter 12d-4.
The loop filter 12d-4 outputs a voltage signal obtained by integrating the phase difference pulse signal input from the phase comparator 12d-3 to the local signal oscillator 12d-5.
The local signal oscillator 12d-5 generates an RF frequency conversion local signal having a frequency based on the voltage signal input from the loop filter 12d-4, and outputs the local signal to the mixer 12c.

The amplifier 12e amplifies the transmission signal input from the mixer 12c and outputs it to the antenna 12f.
The antenna 12f transmits the transmission signal input from the amplifier 12e to the outside.
The control unit 13 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), an interface circuit for inputting / outputting signals to / from each unit, and the like, which are stored in the ROM. The overall operation of the terminal C is controlled based on the control program and the received signal received by the receiving unit 11. The control program stored in the ROM includes a terminal interference suppression program, and the control unit 13 reduces the reception characteristics of the microcell base station A due to interference waves based on the terminal interference suppression program. Suppress.

Next, the operation of the microcell base station A according to this embodiment configured as described above will be described with reference to FIG.
First, when the receiving unit 1 receives the received signal from the terminal C, the control unit 3 of the microcell base station A causes the demodulation processing unit 1f to detect the FER of the received signal and receives it based on the notification from the demodulation processing unit 1f. It is determined whether or not the FER of the signal exceeds a predetermined threshold value (step S1).
If it is determined “NO” in step S1, that is, if the FER does not exceed the predetermined threshold value, the control unit 3 waits for the next reception signal in step S1. When it is determined “YES” in step S1, that is, when the FER exceeds a predetermined threshold value, the control unit 3 causes the demodulation processing unit 1f to detect an interference wave and notifies the demodulation processing unit 1f. Based on the above, it is determined whether or not an interference wave exists (step S2).

If it is determined “NO” in step S2, that is, if there is no interference wave in the received signal, the control unit 3 transmits an instruction to perform handover to the terminal C (step S3). When it is determined “YES” in step S2, that is, when there is an interference wave in the received signal, the control unit 3 subtracts the frequency (center frequency) of the desired wave subcarrier from the frequency of the interference wave, The remainder (offset frequency) obtained by dividing the calculation result by the subcarrier frequency interval is calculated (step S4).
That is, the offset frequency Δf_a is calculated based on the following equation (1).
Offset frequency Δf_a = | interference wave frequency f_a−desired wave subcarrier interference wave frequency f_c | mod subcarrier frequency interval fs (1)

  For example, as shown in FIG. 5A, when the subcarrier frequency interval is 15 kHz, the value obtained by subtracting the frequency of the desired wave subcarrier from the frequency of the interference wave in step S4 is divided by 15 kHz, and the remainder 7.5 kHz is the offset frequency. In addition, when the offset frequency (7.5 kHz) is ½ times the subcarrier frequency interval (15 kHz), the reception characteristics are most deteriorated.

  Returning to FIG. 4, after step S4, the control unit 3 changes the reception frequency setting of the reception unit 1 based on the offset frequency (step S5). For example, when the offset frequency is 7.5 kHz as shown in FIG. 5A, the subcarrier reception frequency setting is shifted by 7.5 Hz as shown in FIG. 5B, that is, the subcarrier reception frequency. Increase the setting by 7.5 kHz. The control unit 3 changes the reception frequency setting by changing the register setting of the counter 1d-2.

  Returning to FIG. 4, after step S5, the control unit 3 causes the transmission unit 2 to transmit an instruction to the terminal C so as to change the transmission frequency based on the offset frequency (step S6). When the reception unit 11 receives the instruction from the microcell base station A, the control unit 13 of the terminal C changes the transmission frequency of the transmission unit 12 based on the offset frequency. For example, when the offset frequency is 7.5 kHz as shown in FIG. 5A, the subcarrier transmission frequency is shifted by 7.5 Hz, that is, the subcarrier transmission frequency is 7 as shown in FIG. Increase the frequency by 5 kHz. The control unit 13 changes the transmission frequency by changing the register setting of the counter 12d-2.

  Returning to FIG. 4, after step S <b> 6, the control unit 3 determines whether or not the FER of the subsequent reception signal exceeds a predetermined threshold based on the notification from the demodulation processing unit 1 f (step S <b> 7). If it is determined as “YES” in step S7, that is, if the FER of the received signal exceeds a predetermined threshold value, the control unit 3 determines that the received signal does not improve and is directed to the terminal C in step S3. To send an instruction to perform handover. If it is determined as “NO” in step S7, that is, if the FER of the received signal does not exceed the predetermined threshold, the control unit 3 maintains the communication state with the terminal C as it is (step S8). ).

  As described above, in the microcell base station A according to the present embodiment, the demodulation processing unit 1f detects the interference wave from the digital IF reception signal, and the control unit 3 calculates the frequency of the desired wave subcarrier from the frequency of the interference wave. Then, the remainder (offset frequency) obtained by dividing the calculation result by the frequency interval of the subcarrier is calculated, and the reception frequency setting of the receiving unit 1 is changed based on the offset frequency. As a result, by changing the reception frequency setting based on the offset frequency, for example, a frequency deviation (Doppler shift) occurs in the transmission signal due to the high-speed movement of the terminal D, resulting in an interference wave for the microcell base station A. However, since it is possible to receive a signal that is uncorrelated with the interference wave, it is possible to suppress degradation of reception characteristics due to the interference wave by demodulating the signal. Further, in the microcell base station A, since the calculation process is only the calculation of the offset frequency, the process is simple and the development cost can be suppressed.

As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment, For example, the following modifications can be considered.
(1) In the embodiment of the present invention, the reception frequency setting is increased by the offset frequency, but the present invention is not limited to this. The reception frequency setting may be lowered by the value obtained by subtracting the offset frequency from the subcarrier frequency interval.

(2) In the embodiment of the present invention, the error rate of the received signal is determined based on FER, but the present invention is not limited to this.
For example, the error rate of the received signal may be determined based on BER (Bit Error Rate), and step S2 may be executed when the BER exceeds a predetermined threshold.

(3) In the embodiment of the present invention, the present invention is applied to a base station that communicates by the OFDM method, but the present invention is not limited to this.
For example, in a wireless communication system in which downlink communication is OFDMA (Orthogonal Frequency Division Multiple Access) and uplink communication is SC-FDMA (Single Carrier Frequency Division Multiple Access), when a base station and a terminal function as a receiving device. The present invention may be applied.

DESCRIPTION OF SYMBOLS S ... Wireless communication system, A ... Micro cell base station, B ... Macro cell base station, C, D ... Terminal, CL1, CL2 ... Cell, 1 ... Reception part, 1a ... Antenna, 1b ... Amplifier, 1c ... Mixer, 1d ... Frequency adjustment unit, 1d-1 ... reference frequency oscillator, 1d-2 ... counter, 1d-3 ... phase comparator, 1d-4 ... loop filter, 1d-5 ... local signal oscillator, 1e ... A / D converter, 1f ... Demodulation processing unit, 2 ... transmission unit, 2a ... transmission circuit unit, 2b ... antenna, 3 ... control unit, 11 ... reception unit, 11a ... antenna, 11b ... reception circuit unit, 12 ... transmission unit,
12a ... Modulation processing unit, 12b ... D / A converter, 12c ... Mixer, 12d ... Frequency adjustment unit, 12d-1 ... Reference frequency oscillator, 12d-2 ... Counter, 12d-3 ... Phase comparator, 12d-4 ... Loop Filter, 12d-5 ... Local signal oscillator, 12e ... Amplifier, 12f ... Antenna, 13 ... Control part

Claims (3)

A base station that receives a radio signal from a terminal based on a multicarrier communication scheme using a plurality of subcarriers,
When an error rate of the received signal exceeds a predetermined threshold, an interference wave of the received signal is detected. When an interference wave exists in the received signal, the frequency of the desired wave subcarrier is determined from the frequency of the interference signal. Communication means for subtracting the frequency, calculating a remainder (offset frequency) obtained by dividing the calculation result by the frequency interval of the subcarrier, and changing the reception frequency setting based on the offset frequency ;
A base station , comprising: a control unit that performs handover to the terminal when an error rate of a received signal after changing the reception frequency setting exceeds the predetermined threshold value . The base station according to claim 1, wherein the communication unit transmits an instruction to the terminal to change a transmission frequency based on the offset frequency . The base station according to claim 1 , wherein the error rate is a FER (Frame Error Rate) .

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