JP2010206658A - Mobile station device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mobile station device capable of conducting direct communications among mobile stations without generating a drop in frequency-utilization efficiency and an interference in a radio system using an OFDM. <P>SOLUTION: The mobile station device includes a switching circuit for switching a mode for communication among base stations in conducting communication with a base station 1 and a mode for direct communications among mobile stations in conducting direct communication with the other mobile stations 2a to 2d without the base station 1. The communication is conducted by using an OFDM signal using a center carrier as a carrier hole in the mode for communications among the base stations, and the communication is conducted by using only the center carrier for the OFDM signal in the mode for direct communication among the mobile stations. Bits of each symbol are modulated by a second modulation system having an excellent error resistance with fewer BPSKs or the like than a first modulation system, which is carried out in the mode for communication among base stations, and a complex base band signal is generated in the mode for direct communication among mobile stations. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a mobile station apparatus that performs digital wireless communication with a base station, and in particular, a mobile station that performs digital wireless communication with a base station using an Orthogonal Frequency Division Multiplexing (OFDM). Relates to the device.

  As a radio system composed of a base station and a plurality of mobile stations, for example, there are an MCA (Multi-Channel Access) system, a digital mobile communication system for public works, and the like. In these wireless communication systems, a communication method called direct communication between mobile stations for performing communication between mobile stations without using a base station is defined as a standard. In direct communication between mobile stations, time division duplex (TDD) or TDD (Time Division Duplex) or a frequency channel different from normal communication (hereinafter referred to as inter-base station communication) that performs communication via a base station is individually assigned. Communication is performed by simplex (see, for example, Non-Patent Document 1).

  WiMAX (Worldwide Interoperability for Mobile Access), which employs a multiple access method called orthogonal frequency division multiple access (OFDMA), is defined as a mobile station and only a mobile station. The inter-station direct communication function does not exist as a specification. In order to realize direct communication between mobile stations in the WiMAX system, for example, a method of preparing another frequency channel for direct communication between mobile stations can be considered as in the above-described digital communication system for public works. When considering direct communication between mobile stations in the same frequency band as communication between base stations, a function as a TDD synchronization master similar to the base station is implemented in the mobile station, It is necessary to manage radio resources so that interference does not occur in the same system in cooperation with other mobile stations.

  Further, as another communication system using an orthogonal frequency division multiplexing (OFDM), wireless LAN (WiFi: Wireless Fidelity) is widely spread. WiFi is a wireless system that operates as a base station and communicates with an access point connected to a network and one or more mobile stations, and shares the same frequency channel with a plurality of mobile stations and the access point. It is the specification which communicates by the system called (Carrier Sense Multiple Access with Collation Aviation). Ad hoc mode is defined as a mode corresponding to direct communication between mobile stations, but one wireless channel has a specification that allows only one-to-one communication between two mobile stations. From the viewpoint, the efficiency is the same as when a dedicated frequency channel for direct communication between mobile stations is prepared.

  Also, in time division multiple access (TDMA), the frequency channel for communication between base stations and the frequency channel for direct communication between mobile stations are set to different frequencies (see, for example, Patent Document 1). ).

JP 2002-325281 A

Radio Industry Association Standard "Prefectural / Municipal Digital Mobile Communication System" ARIB STD-T79

  As described above, in the conventional wireless system composed of a base station and a plurality of mobile stations, in order to realize direct communication between mobile stations, a new frequency band for direct communication between mobile stations is prepared, It is necessary to perform radio resource management by mounting a function as a master of TDD synchronization according to the base station in the mobile station.

  However, when a new frequency band for direct communication between mobile stations is prepared, there is a problem that deterioration of frequency use efficiency is unavoidable, and the mobile station functions as a master of TDD synchronization according to the base station. However, there is a problem that the apparatus configuration in the mobile station becomes complicated and is not practical.

  The present invention has been made in view of such a situation, and in a radio system using OFDM, a mobile station capable of performing direct communication between mobile stations without causing a decrease in frequency use efficiency or causing interference. An object is to provide an apparatus.

  In order to solve the above problems, the present invention provides an inter-base station communication mode in which communication is performed with a base station, and direct communication between mobile stations in which direct communication is performed with another mobile station without going through the base station. Switching means for switching between modes, and when the communication mode between base stations is set by the switching means, communication is performed using an OFDM signal with the center carrier as a carrier hole, and direct switching between mobile stations is performed by the switching means. When the communication mode is set, communication is performed using only the center carrier of the OFDM signal.

  According to the mobile station apparatus of the present invention, in the inter-base station communication mode, communication is performed using the OFDM signal with the center carrier as a carrier hole, and in the inter-mobile station direct communication mode, only the center carrier of the OFDM signal is used. By configuring to perform communication, inter-base station communication and direct communication between mobile stations can be simultaneously accommodated within the system band of a wireless system using OFDM. It is possible to improve the utilization efficiency and to achieve an efficient direct communication between mobile stations that prevents the occurrence of interference.

It is a system configuration | structure figure which shows the example of a radio | wireless system structure by which embodiment of the mobile station apparatus which concerns on this invention is used. It is a figure which shows the example of the radio | wireless resource allocation method seen from the frequency time space of the communication between base stations in the radio | wireless system shown in FIG. 1, and the direct communication between mobile stations. It is a block diagram which shows the structure of the OFDM modulation / demodulation apparatus in the base station shown in FIG. It is a figure which shows the OFDM signal example which made the center carrier used for the communication between base stations in the radio | wireless system shown in FIG. 1 the carrier hole. FIG. 2 is a block diagram showing a configuration of an OFDM modulation / demodulation device in the mobile station shown in FIG. 1. 3 is a flowchart for explaining a communication mode switching operation of the OFDM modulation / demodulation apparatus in the mobile station shown in FIG. It is a figure which shows the OFDM signal example which made only the center carrier used for the direct communication between mobile stations in the radio | wireless system shown in FIG. 1 a subcarrier.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a system configuration diagram showing an example of a radio system configuration in which an embodiment of a mobile station apparatus according to the present invention is used. FIG. 2 is a diagram showing communication between base stations and direct communication between mobile stations in the radio system shown in FIG. It is a figure which shows the example of the radio | wireless resource allocation method seen from the frequency time space of communication.

  Referring to FIG. 1, the present embodiment is configured by at least one base station 1 and a plurality of mobile stations 2a to 2d, and communication between the mobile stations 2a to 2d is performed via the base station 1. There are two communication modes: “communication between stations” and “direct communication between mobile stations” in which communication is performed between the two mobile stations 2 a to 2 d without going through the base station 1. For example, in FIG. 1, the communication on the route indicated by the solid line arrow between the mobile station 2a and the mobile station 2b via the base station 1 is “inter-base station communication”, and the base station between the mobile station 2c and the mobile station 2d Communication along the path indicated by the solid line arrow not passing through the station 1 is “direct communication between mobile stations”.

  In such a wireless system, when “direct communication between mobile stations” and “communication between base stations” are performed at the same time, occurrence of interference is expected along a route indicated by a dotted arrow in FIG. Therefore, in the present invention, as a countermeasure against interference, communication between base stations is performed using an OFDM signal in which the center carrier is set to a carrier hole, and direct communication between mobile stations is performed using an OFDM signal using only the center carrier. . Note that OFDM is a multicarrier modulation scheme in which subcarriers are densely arranged on the frequency axis while maintaining the orthogonal relationship of a plurality of subcarriers. However, when communication is performed using subcarriers located in the center carrier, analog circuits and It is known that the influence of DC offset due to digital signal processing appears as noise. Accordingly, when multi-level modulation such as 16QAM (Quadrature Amplitude Modulation) or 64QAM is applied as the primary modulation, a countermeasure for reducing the DC offset is required. Therefore, in WiMAX, WiFi, etc., the center carrier is used as a carrier hole. Specifications are not used for communication.

  Referring to FIG. 2, the inter-base station communication of the present invention is a frequency above the center (shown in FIG. 2), assuming that the number of AMC users in the band AMC method, which is one of the radio resource allocation methods used for WiMAX, is two. This is very similar to the operation in which * A) is assigned to the communication for the mobile station 2a and the frequency below the center (* B shown in FIG. 2) is assigned to the communication for the mobile station 2b. Further, when TDD is used as a duplex method for inter-base station communication, downlink communication is performed in the TDL section shown in FIG. 2, and uplink communication is performed in the TUL section shown in FIG. In addition, direct communication between mobile stations is performed in a carrier hole (* C shown in FIG. 2) of communication between base stations. The duplex method may be TDD or simplex. By using such radio resource allocation, simultaneous communication is possible without interfering with each other in communication between base stations and direct communication between mobile stations.

Next, the configuration of the OFDM modulation / demodulation apparatus 10 in the base station 1 will be described in detail with reference to FIG. 3 and FIG.
3 is a block diagram showing a configuration of the OFDM modulation / demodulation apparatus 10 in the base station 1 shown in FIG. 1, and FIG. 4 uses a center carrier used for inter-base station communication in the wireless system shown in FIG. 1 as a carrier hole. It is a figure which shows an OFDM signal example.

  Referring to FIG. 3, the OFDM modulation / demodulation apparatus 10 in the base station 1 includes a transmission unit including a modulation circuit 11, a distribution circuit 12, an IFFT circuit 13, and a quadrature modulation circuit 14, a quadrature detection circuit 15, an FFT circuit 16, and a coupling circuit. 17 and a demodulating circuit 18.

  When transmitting an information code, first, a modulation base 11 performs quadrature amplitude modulation such as 16QAM or 64QAM on the information code to be transmitted to generate a complex baseband signal. The complex baseband signal generated by the modulation circuit 11 is input to the distribution circuit 12.

  The distribution circuit 12 inputs zero as a subcarrier component corresponding to direct current, and inputs a complex baseband signal input to the other subcarrier components, thereby converting the input complex baseband signal to each of the components other than the center carrier. Distribute to subcarriers.

  The complex baseband signal distributed to each subcarrier other than the center carrier is subjected to inverse discrete Fourier transform in the IFFT circuit 13 and then orthogonally modulated in the orthogonal modulation circuit 14, so that N which is orthogonal on the frequency axis. An OFDM signal multiplexed by an orthogonal frequency division multiplexing modulation system composed of a number of subcarriers is generated. As shown in FIG. 4, the generated OFDM signal becomes an OFDM signal with the center carrier as a carrier hole. In the example shown in FIG. 4, the number of subcarriers corresponds to N = 7, the center carrier indicated by the dotted line is set to a carrier hole that is not used for data transmission, and the six subcarriers indicated by solid lines other than the center carrier are It will be used for data transmission.

  When the OFDM signal is received, the received OFDM signal is subjected to quadrature detection by the quadrature detection circuit 15 and then subjected to Fourier transform processing, which is the reverse processing of the IFFT circuit 13 of the transmission unit, in the FFT circuit 16. Restore the complex baseband signal.

  Next, the combining circuit 17 extracts and combines signals included in subcarriers other than the center carrier from the complex baseband signals of the subcarriers restored by the FFT circuit 16.

  Finally, the demodulating circuit 18 demodulates the complex baseband signal combined by the combining circuit 17 by a demodulation method corresponding to the modulation method in the modulation circuit 11, and the information code is reproduced.

Next, the configuration of the OFDM modulation / demodulation apparatus 20 in the mobile stations 2a to 2d will be described in detail with reference to FIG.
FIG. 5 is a block diagram showing a configuration of OFDM modulation / demodulation apparatus 20 in mobile stations 2a to 2d shown in FIG.

  Referring to FIG. 5, the OFDM modulation / demodulation apparatus 20 in the mobile stations 2a to 2d includes a transmission unit including a modulation circuit 21, a distribution circuit 22, an IFFT circuit 13, and an orthogonal modulation circuit 14, an orthogonal detection circuit 15, an FFT circuit 16, The receiving unit includes a coupling circuit 27 and a demodulating circuit 28, a changeover switch 29, a changeover circuit 30, an identification signal generation circuit 31, and an identification signal detection circuit 32. In addition, about the same structure as the OFDM modulation / demodulation apparatus 10 in the base station 1, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  The modulation circuit 21 modulates the information code with the same first modulation scheme as the modulation circuit 11 of the OFDM modulation / demodulation apparatus 10 in the base station 1 and the second bit with fewer bits per symbol than the first modulation scheme. And a function of modulating the information code by the modulation method. When the switching circuit 30 is set to the “inter-base station communication” mode by the switching circuit 30, the modulation circuit 21 is set to the “direct communication between mobile stations” mode by the switching circuit 30 in the first modulation scheme. First, a modulation baseband signal is generated by modulating information codes to be transmitted by the second modulation method. As the second modulation scheme, a modulation scheme in which transmission information per symbol is 2 bits or less is preferable. For example, a modulation scheme with excellent error resistance such as BPSK (Binary Phase Shift Keying) is preferable.

  The distribution circuit 22 inputs zero as a subcarrier component corresponding to direct current, and inputs a complex baseband signal input to the other subcarrier component, thereby converting the input complex baseband signal to each of the components other than the center carrier. The function of executing the first distribution method for distributing to subcarriers, and the complex baseband signal is input only to the subcarrier component corresponding to direct current, and zero is input to the other subcarrier components. And a function of executing a second distribution method of distributing the complex baseband signal only to the center carrier. When the distribution circuit 22 is set to the “inter-base station communication” mode by the switching circuit 30, the distribution circuit 22 is set to the “direct communication between mobile stations” mode by the switching circuit 30 in the first distribution method. Distributes the complex baseband signal respectively input by the second distribution method to each subcarrier component.

  The combining circuit 27 has a function of extracting and combining from a complex baseband signal of each subcarrier restored by the FFT circuit 16 by a first extraction method for extracting a signal included in subcarriers other than the center carrier, And a second extraction method for extracting a signal included only in the carrier. When the switching circuit 30 is set to the “inter-base station communication” mode, the coupling circuit 27 is set to the “direct communication between mobile stations” mode by the switching circuit 30 in the first extraction method. First, a signal included in each subcarrier is extracted by the second extraction method.

  The demodulation circuit 28 has a function of demodulating the complex baseband signal by the first demodulation method corresponding to the first modulation method in the modulation circuit 21 and a second demodulation method corresponding to the second modulation method in the modulation circuit 21. And a function of demodulating a complex baseband signal. When the switching circuit 30 is set to the “inter-base station communication” mode, the demodulation circuit 28 is set to the “direct communication between mobile stations” mode by the switching circuit 30 in the first demodulation method. First, the complex baseband signal is demodulated by the second demodulation method.

  The changeover switch 29 is a switch for switching between “communication between base stations” and “direct communication between mobile stations”, and is operated by an operator.

  When switching to “communication between base stations” is operated by the switch 29, the switching circuit 30 connects the modulation circuit 21, the distribution circuit 22, the coupling circuit 27, the demodulation circuit 28, and the identification signal generation circuit 31 to “between base stations”. When the mode is set to “communication” and switching to “direct communication between mobile stations” is operated by the switch 29 or a detection signal is input from the identification signal detection circuit 32, the modulation circuit 21, the distribution circuit 22, The coupling circuit 27, the demodulation circuit 28, and the identification signal generation circuit 31 are set to the “direct communication between mobile stations” mode.

  When the switching circuit 30 sets the “direct communication between mobile stations” mode, the identification signal generation circuit 31 sends an identification signal indicating “direct communication between mobile stations” to the orthogonal modulation circuit before transmitting the information code. 14 for output. The identification signal input to the quadrature modulation circuit 14 is quadrature modulated and transmitted.

  The identification signal detection circuit 32 receives the OFDM signal, detects the identification signal from the signal orthogonally detected by the orthogonal detection circuit 15, and outputs the detection signal to the switching circuit 30 when the identification signal is detected.

Next, the transmission / reception operation of the OFDM modulation / demodulation apparatus 20 in the mobile stations 2a to 2d will be described in detail with reference to FIG. 6 and FIG.
6 is a flowchart for explaining the communication mode switching operation of the OFDM modulation / demodulation apparatus 20 in the mobile stations 2a to 2d shown in FIG. 1, and FIG. 7 is used for direct communication between mobile stations in the wireless system shown in FIG. It is a figure which shows the OFDM signal example which used only the center carrier used as a subcarrier.

  First, the communication mode switching operation in the OFDM modem 20 will be described. Referring to FIG. 6, switching circuit 30 sets modulation circuit 21, distribution circuit 22, coupling circuit 27, demodulation circuit 28, and identification signal generation circuit 31 to the “inter-base station communication” mode as an initial setting (step A1).

  Next, in the “inter-base station communication” mode, the switching circuit 30 monitors the switching to “direct communication between mobile stations” by the operation of the changeover switch 29 (step A2), and also detects from the identification signal detection circuit 32. When the signal input is monitored (step A3) and the switching to the "direct communication between mobile stations" is operated by the changeover switch 29 or the detection signal is input from the identification signal detection circuit 32, the modulation circuit 21 The distribution circuit 22, the coupling circuit 27, the demodulation circuit 28, and the identification signal generation circuit 31 are set to the “direct communication between mobile stations” mode (step A4).

  Next, in the “direct communication between mobile stations” mode, the switching circuit 30 monitors switching to “communication between base stations” by the operation of the changeover switch 29 (step A5) and “direct communication between mobile stations”. The end is monitored (step A6), and the changeover switch 29 is operated to switch to “inter-base station communication” or “when the inter-mobile station direct communication ends, the process returns to step A1 and the modulation circuit 21, distribution The circuit 22, the coupling circuit 27, the demodulation circuit 28, and the identification signal generation circuit 31 are set to the “inter-base station communication” mode.

  In the transmission operation in the “inter-base station communication” mode, the information code to be transmitted is modulated by the modulation circuit 21 using the first modulation method, that is, the same modulation method as the modulation circuit 11 of the OFDM modem 10 in the base station 1 Generate a complex baseband signal. The complex baseband signal generated by the modulation circuit 11 is input to the distribution circuit 22, and the distribution circuit 22 uses the same distribution method as the distribution circuit 12 of the OFDM modulation / demodulation apparatus 10 in the base station 1. The input complex baseband signal is distributed to each subcarrier other than the center carrier.

  The complex baseband signal distributed to each subcarrier other than the center carrier is subjected to inverse discrete Fourier transform in the IFFT circuit 13 and then orthogonally modulated in the orthogonal modulation circuit 14, so that N which is orthogonal on the frequency axis. An OFDM signal multiplexed by an orthogonal frequency division multiplexing modulation system composed of a number of subcarriers is generated.

  When the OFDM signal is received, the reception operation in the “inter-base station communication” mode is performed by performing orthogonal detection on the received OFDM signal by the orthogonal detection circuit 15 and then inversely performing the IFFT circuit 13 of the transmission unit in the FFT circuit 16. A complex baseband signal of each subcarrier is restored by performing a Fourier transform process.

  Next, in the combining circuit 27, a first extraction method for extracting signals included in subcarriers other than the center carrier from the complex baseband signals of the subcarriers restored by the FFT circuit 16, that is, OFDM in the base station 1 The same extraction method as that of the combining circuit 17 of the modem 10 is extracted and combined.

  Finally, the demodulation circuit 28 demodulates the complex baseband signal combined by the combining circuit 17 by the first demodulation method, that is, by the same demodulation method as the demodulation circuit 18 of the OFDM modulation / demodulation apparatus 10 in the base station 1, and the information code Is played.

  In the “direct communication between mobile stations” mode, the modulation circuit 21 uses the modulation circuit 21 to convert the information code to the second modulation method, that is, a modulation method that is excellent in error resistance such as BPSK with fewer bits per symbol than the first modulation method. To generate a complex baseband signal. The complex baseband signal generated by the modulation circuit 11 is input to the distribution circuit 22, and the distribution circuit 22 inputs the complex baseband signal only to the second distribution method, that is, the subcarrier component corresponding to direct current, and the others. By inputting zero to the subcarrier component, the input complex baseband signal is distributed only to the center carrier.

  The complex baseband signal distributed only to the center carrier is subjected to inverse discrete Fourier transform by the IFFT circuit 13 and then orthogonally modulated by the orthogonal modulation circuit 14, so that N subcarriers having an orthogonal relationship on the frequency axis are obtained. An OFDM signal multiplexed by the orthogonal frequency division multiplex modulation scheme is generated.

  As shown in FIG. 7, the generated OFDM signal is an OFDM signal that uses only the center carrier for data transmission. In the example shown in FIG. 7, the number of subcarriers corresponds to N = 7, and only the center carrier indicated by a solid line is used for data transmission, and six subcarriers indicated by dotted lines other than the center carrier are used for data transmission. Will not be.

  In the reception operation in the “direct communication between mobile stations” mode, when the OFDM signal is received, the received OFDM signal is orthogonally detected by the orthogonal detection circuit 15, and then the FFT circuit 16 reverses the IFFT circuit 13 of the transmission unit. The complex baseband signal of each subcarrier is restored by performing the Fourier transform process, which is the process of (1).

  Next, in the combining circuit 27, a second extraction method, that is, a signal included only in the center carrier is extracted from the complex baseband signal of each subcarrier restored by the FFT circuit 16.

  Finally, in the demodulation circuit 28, the complex baseband signal combined by the combining circuit 17 is demodulated by the second demodulation method, that is, the demodulation method corresponding to the second modulation method in the modulation circuit 21, and the information code is reproduced. The

According to the above embodiment, the mobile stations 2a to 2d communicate with the base station 1 in the “inter-base station communication” mode and the other mobile stations 2a to 2d without going through the base station 1. In the “inter-base station communication” mode, communication is performed using an OFDM signal with a center carrier as a carrier hole, and “mobile station” In the “direct communication” mode, communication is performed using only the center carrier of the OFDM signal. With this configuration, it becomes possible to simultaneously accommodate inter-base station communication and direct inter-mobile station communication within the system band of a wireless system using OFDM, thereby improving frequency utilization efficiency without adopting a complicated device configuration. As a result, it is possible to perform efficient direct communication between mobile stations while preventing the occurrence of interference.
Further, the mobile stations 2a to 2d modulate the information code to be transmitted with the same first modulation scheme as that of the base station 1, and the number of bits per symbol of the transmitted information code is smaller than that of the first modulation scheme. A modulation circuit 21 having a function of modulating with a second modulation scheme (for example, a modulation scheme such as BPSK with transmission information per symbol of 2 bits or less) is provided, and the modulation circuit 21 is in the “inter-base station communication” mode. The information code to be transmitted is modulated by the first modulation method, and in the “direct communication between mobile stations” mode, the information code to be transmitted is modulated by the first modulation method. With this configuration, even if “direct communication between mobile stations” is performed using a center carrier that is known to have an effect of DC offset appearing as noise, it is possible to establish good communication. .
In addition, when the “direct communication between mobile stations” mode is set by the switching circuit 30, the mobile stations 2a to 2d output an identification signal indicating “direct communication between mobile stations” prior to transmission of the information code. An identification signal generation circuit 31 that transmits the signal as an OFDM signal, and an identification signal detection circuit 32 that detects the identification signal from the received OFDM signal and outputs the detection signal to the switching circuit 30 when the identification signal is detected. The provided switching circuit 30 switches to the “direct communication between mobile stations” mode when a detection signal is input from the identification signal detection circuit 32. With this configuration, there is an effect that the receiving side can automatically switch from the “communication between base stations” mode to the “direct communication between mobile stations” mode.

  Note that the present invention is not limited to the above-described embodiments, and it is obvious that the embodiments can be appropriately changed within the scope of the technical idea of the present invention. In addition, the number, position, shape, and the like of the constituent members are not limited to the above-described embodiment, and can be set to a number, position, shape, and the like that are suitable for implementing the present invention. In addition, in each figure, the same 1 component is attached | subjected to the same 1 component.

DESCRIPTION OF SYMBOLS 1 Base station 2a-2d Mobile station 10 OFDM modulation / demodulation apparatus 11 Modulation circuit 12 Distribution circuit 13 IFFT circuit 14 Orthogonal modulation circuit 15 Orthogonal detection circuit 16 FFT circuit 17 Combination circuit 18 Demodulation circuit 20 OFDM modulation / demodulation apparatus 21 Modulation circuit 22 Distribution circuit 27 Combination Circuit 28 Demodulation circuit 29 Changeover switch 30 Changeover circuit 31 Identification signal generation circuit 32 Identification signal detection circuit

Claims (1)

A mobile station device that performs digital radio communication with a base station and performs modulation / demodulation of an information code,
A switching means for switching between a communication mode between base stations that communicates with the base station and a direct communication mode between mobile stations that communicates directly with other mobile stations without going through the base station,
When the communication mode between the base stations is set by the switching means, communication is performed using an OFDM signal with a center carrier as a carrier hole,
A mobile station apparatus that performs communication using only the center carrier of the OFDM signal when the direct communication mode between mobile stations is set by the switching means.

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