JP2008294588A - Optical wireless fused communication system, transmitter-receiver for optical wireless fused communication system and communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ROF system suppressing the influence of multi-path interference due to the delay waves of transmission signals transmitted accompanied by the same information from a plurality of local radio stations without lowering transmission efficiency. <P>SOLUTION: One of a radio base station 100 and a mobile station 200 is provided with a GI information providing part 220 for measuring propagation delay characteristics inside a communication area, determining the length of a guard interval (GI) on the basis of the propagation delay characteristics and providing the other of the radio base station and the mobile station with information relating to the length of the GI. The radio base station is provided with a first GI control part 116 for variably controlling the length of the GI to be inserted to a transmission symbol and a multicarrier modulation part 300 for executing multicarrier modulation using the GI to the transmission symbol to be transmitted. The mobile station is provided with: a second GI control part 216 for variably controlling the length of the GI to be removed from the transmission symbol; and a multicarrier demodulation part 350 for executing multicarrier demodulation using the GI to the transmission symbol received from the radio base station. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical wireless fusion communication (ROF: Radio Over Fiber) system, a transmission / reception apparatus and a communication method for the ROF system.

  An optical wireless fusion communication system is used in which communication is performed by intensity-modulating an optical signal with a radio signal on the transmission side and transmitting the optical signal to an optical fiber, and optical / electrical conversion on the reception side to reproduce the original radio signal. Yes.

  The ROF system can be used for various purposes because it can expand the communication area by using a low-loss and broadband optical fiber. As an application example of the ROF system, for example, a road-to-vehicle communication system described in Patent Document 1 below can be cited. In the road-to-vehicle communication system, by applying the ROF system to the communication between the road and the vehicle, a large amount of information can be communicated between the road and the vehicle at high speed.

  FIG. 1 is an explanatory diagram showing a system configuration of an ROF system, taking a road-vehicle communication system as an example. As shown in FIG. 1, the ROF system includes a radio base station 10, an optical fiber 14, a plurality of local radio stations 15 a to 15 d and a mobile station 20. The plurality of local radio stations 15 a to 15 d are connected to the radio base station 10 via the optical fiber 14.

  At the time of downlink transmission of the ROF system, the radio base station 10 modulates the intensity of the optical signal with the radio signal, transmits the optical signal to the optical fiber 14, and transmits it to the plurality of local radio stations 15a to 15d. The plurality of local radio stations 15 a to 15 d optically / electrically converts the transmitted optical signal to reproduce the radio signal, and transmits the radio signal to the receiving side such as the mobile station 20. Thus, a wide range of information communication services can be provided by bundling the communication areas of the local radio stations 15a to 15d into one communication area.

JP 2001-93084 A

  However, in the ROF system, the same information is transmitted at the same frequency from the plurality of local radio stations 15a to 15d in order to expand the communication area. For this reason, in the communication area of each local radio station 15a-15d, the influence of an interference wave may arise between the boundary with an adjacent communication area, and the communication area of the vicinity. This is because the same radio signal reaches the mobile station 20 with a relative delay as a plurality of arrival waves via propagation paths (multipaths) of different distances. As a result, a delayed wave with a relative delay acts as an interference wave, and the communication characteristics of the system are deteriorated.

  In order to avoid this problem, for example, a multi-carrier (MC) transmission method such as an orthogonal frequency division multiplexing (OFDM) method is effective. The MC transmission scheme uses a guard interval (GI) having a predetermined length, thereby making it possible to reduce the influence of delayed waves that reach the GI.

  On the other hand, in the MC transmission method using GI, transmission is performed by inserting the GI into the original information (transmission symbol) that is the purpose of transmission, and therefore the transmission efficiency is reduced by the amount of the inserted GI. Therefore, the length of the GI to be inserted is preferably as short as possible. Usually, the GI length is fixedly set so as to absorb a delay wave with the maximum delay time (maximum delay wave) after measuring a propagation delay characteristic in an assumed communication environment in advance.

  However, for example, in an ROF system applied to a road-to-vehicle communication system or the like, communication is performed between the radio base station 10 and the mobile station 20 in a communication area with various communication environments.

  FIG. 2 is an explanatory diagram schematically showing a relationship between a communication area and a signal propagation path in the ROF system. FIG. 2 shows a) a communication area with many buildings 30 around the local radio stations 15a to 15d, and b) a communication area with few buildings 30 around the local radio stations 15a to 15d and a signal propagation path. Each relationship is shown.

  As shown in FIG. 2a), in the communication area where there are many buildings 30 around the local radio stations 15a to 15d, the radio signals transmitted from the local radio stations 15a to 15d are easily reflected by the building 30. The mobile station 20 is reached via a relatively short propagation path 32. On the other hand, as shown in FIG. 2b), in the communication area where there are few buildings 30 around the local radio stations 15a to 15d, the radio signals transmitted from the local radio stations 15a to 15d are reflected by the building 30. It becomes difficult to reach the mobile station 20 via the relatively long propagation path 34.

  Therefore, since the signal propagation path varies depending on the communication environment in the communication area, the propagation delay state of the radio wave reaching the mobile station 20 also varies. In such a case, if the GI length is set so as to absorb the maximum delay wave in consideration of the propagation delay characteristics in all communication areas, the transmission efficiency is undesirably lowered.

  The present invention has been made in view of the above problems, and its purpose is to reduce the effects of multipath interference caused by delayed waves of transmission signals transmitted with the same information from a plurality of local radio stations, and to improve transmission efficiency. It is an object of the present invention to provide a new and improved ROF system, a transmission / reception apparatus for the ROF system, and a communication method that can be suppressed without being lowered.

  In order to solve the above problems, according to a first aspect of the present invention, communication is performed between a radio base station and a mobile station via a plurality of local radio stations connected to the radio base station by optical fibers. An optical wireless fusion communication system is provided. In this optical wireless fusion communication system, at least one of a radio base station and a mobile station measures a propagation delay characteristic in a communication area, and sets a guard interval for use in communication based on the propagation delay characteristic to a predetermined length. And a guard interval information providing unit that provides information on a predetermined length of the guard interval to either the radio base station or the mobile station. The radio base station also variably controls a first guard interval control unit that variably controls a guard interval to be inserted into a transmission symbol to a predetermined length, and multicarrier modulates a transmission symbol to be transmitted and changes the transmission symbol to a multicarrier modulated transmission symbol. A multi-carrier modulation section for inserting a controlled guard interval. On the other hand, the mobile station removes the guard interval that is variably controlled from the transmission symbol received from the radio base station, the second guard interval control unit that variably controls the guard interval to be removed from the transmission symbol to a predetermined length, A multicarrier demodulator that multicarrier demodulates the transmission symbol from which the guard interval is removed.

  According to this configuration, the propagation interval characteristic in the communication area is measured by the guard interval information providing unit provided in the radio base station or the mobile station, and the guard interval to be used for communication is determined based on the propagation delay characteristic. Determined by length. Here, the information regarding the predetermined length of the guard interval is shared between the radio base station and the mobile station. In the radio base station, the transmission symbol is subjected to multicarrier modulation, and a guard interval having a predetermined length is inserted into the transmission symbol subjected to multicarrier modulation and transmitted to the mobile station. In the mobile station, a guard interval having a predetermined length is removed from the received transmission symbol, and the transmission symbol from which the guard interval is removed is subjected to multicarrier demodulation.

  Thereby, according to the propagation delay characteristic in a communication area, the guard interval used by a multicarrier transmission system can be inserted or removed with respect to a transmission symbol by predetermined length. Therefore, it is possible to suppress the influence of multipath interference caused by delayed waves of transmission signals transmitted with the same information from a plurality of local radio stations without lowering the transmission efficiency. In addition, by variably controlling the guard interval length according to the propagation delay characteristics in the communication area, it is possible to ensure flexibility in system design such as local radio station placement design and to ensure system transmission efficiency. be able to.

  In order to solve the above problems, according to a second aspect of the present invention, communication is performed between a radio base station and a mobile station via a plurality of local radio stations connected to the radio base station by optical fibers. There is provided a transmission / reception device applied to a radio base station or a mobile station in an optical / radio fusion communication system. The transmitting / receiving apparatus measures a propagation delay characteristic in a communication area, determines a guard interval to be used for communication based on the propagation delay characteristic, to a predetermined length, and transmits information on the predetermined length of the guard interval to a communication partner. A guard interval information providing unit provided to the first, a first guard interval control unit that variably controls the guard interval to be inserted into the transmission symbol to a predetermined length, and a transmission in which the transmission symbol to be transmitted is multi-carrier modulated and multi-carrier modulated. A multi-carrier modulation unit that inserts a guard interval that is variably controlled into the symbol, a second guard interval control unit that variably controls the guard interval to be removed from the transmission symbol to a predetermined length, and variably controlled from the received transmission symbol. Remove the guard interval, remove the guard interval And a multi-carrier demodulator for multicarrier demodulation transmission symbol.

  According to this configuration, the guard interval information providing unit provided in the transmission / reception device of the radio base station or the mobile station measures the propagation delay characteristic in the communication area, and uses the guard interval for communication based on the propagation delay characteristic. Is determined to be a predetermined length. Here, the information regarding the predetermined length of the guard interval is shared between the radio base station and the mobile station. In either one of the radio base station and the mobile station, the transmission symbol is subjected to multicarrier modulation, and a guard interval having a predetermined length is inserted into the transmission symbol subjected to multicarrier modulation and transmitted. In the other transmitting / receiving apparatus of the radio base station and the mobile station, a guard interval having a predetermined length is removed from the received transmission symbol, and the transmission symbol from which the guard interval is removed is subjected to multicarrier demodulation. Thereby, according to the propagation delay characteristic in a communication area, the guard interval used by a multicarrier transmission system can be inserted or removed with respect to a transmission symbol by predetermined length. Therefore, it is possible to suppress the influence of multipath interference caused by delayed waves of transmission signals transmitted with the same information from a plurality of local radio stations without lowering the transmission efficiency.

  The guard interval information providing unit may measure the propagation delay characteristics in the communication area based on the reception status of impulses transmitted simultaneously from each of the plurality of local radio stations.

  According to such a configuration, the propagation delay characteristic in the communication area is measured based on the reception status of the impulses transmitted simultaneously from each of the plurality of local radio stations. Therefore, a predetermined guard interval used in the multicarrier transmission method is measured. The length can be determined appropriately.

  In order to solve the above problems, according to a third aspect of the present invention, communication is performed between a radio base station and a mobile station via a plurality of local radio stations connected to the radio base station by optical fibers. Provided is a communication method applied to an optical wireless fusion communication system. This communication method measures a propagation delay characteristic in a communication area, determines a guard interval to be used for communication based on the propagation delay characteristic, to a predetermined length, and transmits information on the predetermined length of the guard interval to a communication partner. A guard interval information providing step to be provided, a first guard interval control step for variably controlling a guard interval inserted into a transmission symbol to a predetermined length, and a transmission symbol to be transmitted is subjected to multicarrier modulation and multicarrier modulation transmission A multi-carrier modulation step for inserting a guard interval that is variably controlled in the symbol, a second guard interval control step for variably controlling the guard interval to be removed from the transmission symbol to a predetermined length, and a variably controlled from the received transmission symbol. Remove the guard interval It includes multicarrier demodulation step of multicarrier demodulation transmission symbol obtained by removing the intervals, the.

  According to this method, the propagation delay characteristic in the communication area is measured, and a guard interval to be used for communication is determined to be a predetermined length based on the propagation delay characteristic. Here, the information regarding the predetermined length of the guard interval is shared between the radio base station and the mobile station. Then, the transmission symbol is subjected to multicarrier modulation, and a guard interval having a predetermined length is inserted into the transmission symbol subjected to multicarrier modulation and transmitted. On the other hand, a guard interval having a predetermined length is removed from the received transmission symbol, and the transmission symbol from which the guard interval is removed is subjected to multicarrier demodulation. Thereby, according to the propagation delay characteristic in a communication area, the guard interval used by a multicarrier transmission system can be inserted or removed with respect to a transmission symbol by predetermined length.

  Further, the guard interval information providing step includes a step of simultaneously transmitting an impulse from each of the plurality of local radio stations, and a step of measuring a propagation delay characteristic in the communication area based on a reception status of the plurality of impulses. It may be included.

  According to this method, since the propagation delay characteristic in the communication area is measured based on the reception status of the impulses transmitted simultaneously from each of the plurality of local radio stations, a predetermined guard interval used in the multicarrier transmission method is measured. The length can be determined appropriately.

  Advantageous Effects of Invention According to the present invention, an ROF system and an ROF system capable of suppressing the influence of multipath interference caused by delayed waves of transmission signals transmitted with the same information from a plurality of local radio stations without reducing transmission efficiency Can be provided.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the present specification and drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

Hereinafter, the configuration and operation method of the ROF system according to an embodiment of the present invention will be described with reference to FIGS. FIG. 3 is an explanatory diagram illustrating a configuration of a transmission / reception device on the radio base station side of the ROF system according to the present embodiment. FIG. 4 is an explanatory diagram showing a configuration of a mobile station transmission / reception device of the ROF system according to the present embodiment. FIG. 5 is an explanatory diagram showing configurations of the multicarrier modulation unit and the multicarrier demodulation unit of the ROF system according to the present embodiment.
FIG. 6 is an explanatory diagram showing an operation method of the ROF system according to the present embodiment. FIG. 7 is an explanatory view schematically showing a method for measuring propagation delay characteristics in the ROF system according to the present embodiment.

(Configuration of ROF system according to this embodiment)
First, the configuration of the ROF system according to the present embodiment will be described with reference to FIGS.

<Transmitting / receiving device of radio base station side 100, 150>
FIG. 3 shows the transmission / reception device of the radio base station 100 and the transmission / reception devices of the local radio stations 150a and 150b constituting the transmission / reception device on the radio base station side according to the present embodiment. 3 shows a case where the transmitting / receiving device of the radio base station 100 is connected to the transmitting / receiving devices of the two local radio stations 150a and 150b via the optical fiber 140, but there are three or more radio base stations 100. The same applies to the case where the local wireless station is connected.

  The transmission / reception apparatus of the radio base station 100 includes an impulse generator 102, a multicarrier modulation / demodulation unit 104 (hereinafter also referred to as “MC modulation / demodulation unit”), a baseband modulation / demodulation unit, and an intermediate frequency modulation / demodulation unit 106 (hereinafter referred to as “IF (Intermediate Frequency)”. ), A duplexer 108, an electrical / optical converter 110 (hereinafter also referred to as "E / O (Electrical / Optical transducer)"), and an optical / electrical converter 112 (hereinafter referred to as "E / O converter"). O / E (Optical / Electrical transducer) "), a multiplexer 114, and a guard interval control unit 116 (hereinafter also referred to as" GI control unit "). Next, each component which comprises the transmission / reception apparatus of the wireless base station 100 is demonstrated.

  The impulse generator 102 generates an impulse as a training signal prior to actual communication. MC modulation / demodulation section 104 MC modulates transmission data input from an upper layer of radio base station 100 and outputs the result to IF modulation / demodulation section 106, and MC-demodulates the reception signal input from IF modulation / demodulation section 106 to receive data To the upper layer. The IF modulation / demodulation unit 106 orthogonally modulates the transmission signal input from the MC modulation / demodulation unit 104, performs IF modulation to the IF band, outputs the result to the duplexer 108, and IF-demodulates the reception signal input from the multiplexer 114. To the MC modulation / demodulation unit 104.

  The duplexer 108 duplicates the number of transmission signals corresponding to the number of local radio stations connected to the radio base station 100 from the transmission signal input from the IF modulation / demodulation unit 106. The E / O unit 110 performs electrical / optical conversion on the transmission signal (electrical signal) input from the duplexer 108 and transmits it as an optical signal to the local radio stations 150 a and 150 b via the optical fiber 140. The O / E unit 112 optically / electrically converts the optical signal transmitted from the local radio stations 150a and 150b via the optical fiber 140, and outputs the optical signal to the multiplexer 114 as an electric signal. The multiplexer 114 combines the reception signals input from the plurality of O / E units 112 and outputs the combined signals to the IF modulation / demodulation unit 106.

  The GI control unit 116 of the radio base station 100 uses the GI inserted into the transmission symbol to be transmitted and / or the received transmission symbol according to the predetermined length of the GI determined based on the propagation delay characteristic in the communication area. The length of the GI to be removed is variably controlled. In addition, the GI control unit 116 stores information on a predetermined length of the GI provided from the mobile station 200 over a communication period, as will be described later, in order to variably control the GI length.

  On the other hand, the transmission / reception apparatuses of local radio stations 150a and 150b include an O / E device 152, an E / O device 154, a radio frequency conversion unit 156 (hereinafter also referred to as “RF (Radio Frequency) conversion unit”), and The antenna unit 158 is configured for each. Next, each component which comprises the transmission / reception apparatus of the local radio stations 150a and 150b is demonstrated.

  The O / E device 152 optically / electrically converts the optical signal transmitted from the radio base station 100 via the optical fiber 140 and outputs the optical signal to the RF conversion unit 156 as an electrical signal. The E / O device 154 performs electrical / optical conversion on the electrical signal input from the RF conversion unit 156 and outputs the electrical signal as an optical signal to the radio base station 100 via the optical fiber 140. The RF conversion unit 156 up-converts and amplifies the electric signal input from the O / E unit 152 to the RF band, outputs the amplified signal to the antenna unit 158, and down-converts the received signal input from the antenna unit 158 to perform E / E. Output to the O device 154. The antenna unit 158 transmits the transmission signal input from the RF conversion unit 156 to the mobile station 200, and outputs the reception signal received from the mobile station 200 to the RF conversion unit 156.

<Transmitting / receiving device of mobile station 200>
FIG. 4 shows a transmitting / receiving device of the mobile station 200 according to the present embodiment.

  The transmission / reception device of the mobile station 200 includes a control unit 202, an MC modulation unit 204 and an MC demodulation unit 206 (or a baseband modulation unit and a baseband demodulation unit), an IF modulation unit 208 and an IF demodulation unit 210, an RF conversion unit 212, an antenna. The unit 214 and the GI control unit 216 are configured. Furthermore, the transmission / reception apparatus of the mobile station 200 includes a GI information providing unit 220 including a switch 222, a delay characteristic measurement unit 224, and a GI length determination unit 226. Next, each component which comprises the transmission / reception apparatus of the mobile station 200 is demonstrated.

  The control unit 202 outputs transmission data input from the upper layer of the mobile station 200 to the MC modulation unit 204 and outputs reception data input from the MC demodulation unit 206 to the upper layer. MC modulating section 204 and MC demodulating section 206 perform MC modulation on transmission data input from control section 202 as a transmission signal and output to IF modulating section 208, and MC demodulate the received signal input from IF demodulating section 210. And output to the control unit 202 as received data.

  IF modulation section 208 and IF demodulation section 210 perform quadrature modulation on the transmission signal input from MC modulation section 204, perform IF modulation on the IF band, output to RF conversion section 212, and receive signal input from RF conversion section 212 Is demodulated and output to the MC demodulator 206. The RF conversion unit 212 up-converts the transmission signal input from the IF modulation unit 208 to the RF band and outputs it to the antenna unit 214, and down-converts the reception signal input from the antenna unit 214 to the IF demodulation unit 210. Output. The antenna unit 214 transmits the transmission signal input from the RF conversion unit 212 to the local radio stations 150a and 150b, and outputs the reception signal received from the local radio stations 150a and 150b to the RF conversion unit 212.

  Similar to GI control unit 116 of radio base station 100, GI control unit 216 of mobile station 200 transmits transmission symbols according to a predetermined length of GI determined based on propagation delay characteristics in the communication area. GI and / or GI length to be removed from received transmission symbols are variably controlled.

  Further, the GI information providing unit 220 measures the propagation delay characteristics in the communication area, determines a predetermined length of the GI to be used for communication in the MC transmission scheme, and transmits information on the predetermined length of the GI to the radio base station. Provide to station 100. Next, each component constituting the GI information providing unit 220 will be described.

  The switching unit 222 outputs the reception signal input from the IF demodulation unit 210 to the MC demodulation unit 206 during normal processing of the reception signal, while receiving the reception signal input from the IF demodulation unit 210 during measurement of the propagation delay characteristic. The signal is output to the delay characteristic measurement unit 224. The delay characteristic measurement unit 224 measures the propagation delay characteristic in the communication area based on the received signal input from the switch 222, and outputs the measurement result to the GI length determination unit 226.

  The GI length determination unit 226 determines a predetermined length of the GI to be used for MC transmission communication based on the measurement result input from the delay characteristic measurement unit 224, and provides information regarding the predetermined length of the GI. Output to the control unit 202. Information on the predetermined length of the GI is transmitted to the radio base station 100 via the control unit 202. Information about the predetermined length of the GI is output to the GI control unit 216. Thereby, the information regarding the predetermined length of GI can be shared between the radio base station 100 and the mobile station 200.

<Multi-carrier modulation section 300 and multi-carrier demodulation section 350>
FIG. 5 shows an MC modulation unit 300 and an MC demodulation unit 350 according to this embodiment. The MC modulation unit 300 corresponds to a part of the MC modulation / demodulation unit 104 of the radio base station 100 and / or the MC modulation unit 204 of the mobile station 200, and the MC demodulation unit 350 corresponds to the MC modulation / demodulation unit 104 of the radio base station 100. And / or the MC demodulation unit 206 of the mobile station 200.

  The MC modulation section 300 includes a serial / parallel conversion section 302 (hereinafter also referred to as “S / P (Serial / Parallel) conversion section”), mapping sections 304-1 to 304-n, and a fast inverse Fourier transform section 306 ( Hereinafter, it is also referred to as an “IFFT (Invert Fast Fourier Transformer) unit”) and a GI insertion unit 308. Next, each component constituting the MC modulation unit 300 will be described.

  The S / P conversion unit 302 performs S / P conversion on the input transmission data and outputs it as n symbols to each of the mapping units 304-1 to 304-n. Mapping sections 304-1 to 304-n map each symbol input from S / P conversion section 302 to each signal point. The IFFT unit 306 performs fast inverse Fourier transform on n symbols mapped to each signal point, and collectively maps the frequency domain mapped data generated by the mapping units 304-1 to 304-n into the time domain. Convert. The GI insertion unit 308 inserts the GI into the mapped data converted into the time domain, and outputs it to the IF modulation / demodulation unit.

  The MC demodulator 350 includes a parallel / serial converter 352 (hereinafter also referred to as “P / S (Parallel / Serial) converter”), a demapping unit 354-1 to 354 -n, and a fast Fourier transform unit 356 ( Hereinafter, it is also referred to as an “FFT (Fast Fourier Transformer) unit”) and a GI removal unit 358. Next, each component constituting the MC demodulation unit 350 will be described.

  The GI removal unit 358 removes the GI from the reception signal input from the IF demodulation unit and outputs the GI to the FFT unit 356. The FFT unit 356 performs Fourier transform on the received signal, collectively converts the received signal into the frequency domain, and outputs n symbols mapped to each signal point to the demapping units 354-1 to 354-n. The demapping units 354-1 to 354-n demap the symbols input from the FFT unit 356 and output them to the P / S unit 352. The P / S unit 352 P / S converts the received signals input from the demapping units 354-1 to 354-n, generates a serial signal, and outputs it as received data.

  The GI control unit is connected to each of the MC modulation unit 300 and the MC demodulation unit 350. The GI control unit connected to the MC modulation unit 300 and the MC demodulation unit 350 shares information regarding a predetermined length of the GI. The GI control unit of the MC modulation unit 300 controls the length of the GI inserted into the transmission symbol of the transmission signal with respect to the GI insertion unit 308, while the GI control unit of the MC demodulation unit 350 includes the GI removal unit 358. In contrast, the length of the GI to be removed from the transmission symbol of the received signal is controlled.

(Operation of ROF system according to this embodiment)
Next, the operation of the ROF system according to the present embodiment will be described with reference to FIGS.

  First, the data transmission operation in the radio base station 100 will be described.

  When transmitting data from the radio base station 100, the ROF system first determines a predetermined length of GI used in the MC transmission scheme. Several methods are conceivable as a method for determining the GI length. Hereinafter, a method for determining the GI length based on the impulse transmitted from the radio base station 100 will be described. FIG. 7 schematically shows a method for measuring the propagation delay characteristic in the communication area when the GI length is determined by this method.

  When determining the GI length, the radio base station 100 or the mobile station 200 notifies the communication partner that the radio base station 100 or the mobile station 200 shifts to the delay characteristic measurement mode. In the following description, it is assumed that the mobile station 200 notifies the radio base station 100 of the mode change prior to actually performing data communication after reaching the communication area.

  When the mobile station 200 is notified of the mode change, the radio base station 100 generates an impulse as a training signal by the impulse generator 102 (S102). The generated impulse 300 is transmitted to the plurality of local radio stations 150a to 150d via the optical fiber 140, and transmitted from the plurality of local radio stations 150a to 150d substantially simultaneously (at time t0).

  The mobile station 200 receives impulses transmitted simultaneously from the plurality of local radio stations 150a to 150d at different times as shown in FIG. 7, for example (S104). An example of the impulse reception status (delay profile) is shown in the upper left part of FIG. 7. In this example, in the mobile station 200, impulses 400 a to 400 d from local radio stations 150 a to 150 d are t 1 to t 4. Received at each time.

  The received impulses 400a to 400d are processed by the delay characteristic measuring unit 224 as follows. The delay characteristic measuring unit 224 detects only impulses that are equal to or higher than a predetermined reception sensitivity level or a reception power level that is a threshold value based on the reception sensitivity level among the received impulses 400a to 400d. The delay characteristic measuring unit 224 measures the maximum delay time as a difference between the reception time of the first impulse and the reception time of the last impulse among impulses received and detected after shifting to the delay characteristic measurement mode, and determines the GI length. The data is output to the unit 226 (S106).

  In the example shown in FIG. 7, the impulse 400d received from the local radio station 150d is equal to or lower than the received power level Th (corresponding to a so-called noise power level) serving as a threshold for the delay characteristic measuring unit. For this reason, the delay characteristic measurement unit 224 excludes the impulse 400d received from the local radio station 150d, and determines the maximum delay time (as a difference between the reception time t1 of the first impulse 400a and the reception time t3 of the last impulse 400c). = T3-t1) is measured.

  The GI length determination unit 226 determines a predetermined length of the GI used in the MC transmission scheme by comparing the measured maximum delay time with the current setting value of the GI length (S108). The GI length determination unit 226 determines the current setting value as a predetermined length of GI if the current setting value is equal to or greater than the maximum delay time. On the other hand, if the current setting value of the GI length is less than the maximum delay time, a delay wave with a delay time greater than or equal to the current setting value exists in the communication area, so the current setting value is changed to be greater than or equal to the maximum delay time. Then, the changed set value is determined as a predetermined length of GI.

  Note that the set value of the GI length is equal to or less than the maximum symbol length of the original transmission symbol (for example, OFDM symbol). Is determined to be about 25% or less.

  The set value of the GI length is output to the control unit 202 by the GI length determination unit 226, transmitted to the radio base station 100 (S110), and stored in the GI control unit 116 of the radio base station 100 (S112). The set value of the GI length is also output to the GI control unit 216 by the GI length determination unit 226. Thereby, the information regarding the predetermined length of GI can be shared between the radio base station 100 and the mobile station 200.

  Here, the case where the GI length is determined by the radio station measuring the delay characteristic has been described, but the delay characteristic is measured by the radio station measuring the delay characteristic, and the GI is measured by the radio station serving as the communication partner. The predetermined length may be determined. In this case, a function configuration unit that determines a predetermined length of the GI is provided in a radio station that is a communication partner, and the function configuration unit is based on a measurement result received from a radio station that measures delay characteristics. A predetermined length of GI is determined.

  When receiving information related to a predetermined length of GI, the radio base station 100 performs MC modulation processing (S122) by the MC modulation / demodulation unit 104. Next, details of the MC modulation processing by the MC modulation / demodulation unit 104 (corresponding to the MC modulation unit 300 shown in FIG. 5) will be described.

  In the MC modulation processing, the MC modulation unit 300 performs S / P conversion on transmission data input from an upper layer by the S / P conversion unit 302, and each of the mapping units 304-1 to 304-n as n symbols. Output to. Here, when binary phase shift keying (BPSK) is adopted as a modulation method, each symbol includes 1-bit information, and 16 quadrature amplitude modulation (16QAM) is obtained. ), Each symbol includes 4-bit information. As described above, the amount of information of each symbol varies depending on the modulation method, but in this embodiment, the modulation method is not limited.

  When the transmission data is S / P converted, MC modulation section 300 maps each symbol input from S / P conversion section 302 to each signal point by mapping sections 304-1 to 304-n.

  After mapping each symbol, MC modulation section 300 performs fast inverse Fourier transform on n symbols mapped to each signal point by IFFT section 306, and generates frequencies generated by mapping sections 304-1 to 304-n. Convert the mapped data of the area to the time domain at once.

  When the symbol is subjected to fast inverse Fourier transform, MC modulation section 300 copies the latter half of the signal converted into the time domain by GI insertion section 308 and inserts it at the beginning of the IFFT output waveform. Here, the length of the GI inserted by the GI insertion unit 308 is determined based on the information on the predetermined length of the GI determined and provided in the delay characteristic measurement mode. The control unit variably controls. When the GI is inserted, the transmission signal in which the GI is inserted is output to the IF modulation / demodulation unit 106. Thereby, the modulation processing by the MC modulation unit 300 (MC modulation / demodulation unit 104) ends.

  When the MC modulation process is completed, the radio base station 100 performs the following process (S124). The radio base station 100 performs orthogonal modulation on the transmission signal input from the MC modulation / demodulation unit 104 by the IF modulation / demodulation unit 106, IF-modulates it to an IF band, and outputs the result to the duplexer 108. When the transmission signal is IF-modulated, the radio base station 100 corresponds to the number of local radio stations 150 a to 150 d connected to the radio base station 100 from the transmission signal input from the IF modulator / demodulator 106 by the duplexer 108. Duplicate the number of transmitted signals. When the transmission signal is duplicated, the radio base station 100 performs electrical / optical conversion of the transmission signal (electric signal) input from the duplexer 108 by the E / O device 110.

  The radio base station 100 and the local radio stations 150a to 150d perform the following process (S126). The radio base station 100 transmits the transmission signal as an optical signal to the local radio stations 150a to 150d via the optical fiber 140. On the other hand, the local radio stations 150a to 150d optical / electrically convert the optical signal transmitted from the radio base station 100 via the optical fiber 140 by the O / E unit 152, and output the optical signal to the RF converter 156 as an electric signal. To do.

  When the electrical signal is output, the local radio stations 150a to 150d perform the following process (S128). The local radio stations 150 a to 150 d are up-converted and amplified to an RF band by the RF conversion unit 156 and output the electric signal to the antenna unit 158. When the electrical signal is output, the local radio stations 150 a to 150 d transmit the input transmission signal to the mobile station 200 through the antenna unit 158. Thereby, the same information is transmitted from the plurality of local radio stations 150a to 150d at the same frequency.

  Next, the data reception operation in the mobile station 200 will be described.

  The mobile station 200 first performs the following process (S130). The mobile station 200 receives reception signals from the local radio stations 150 a to 150 d by the antenna unit 214 and outputs them to the RF conversion unit 212. When the reception signal is output, the mobile station 200 down-converts the input reception signal by the RF conversion unit 212 and outputs it to the IF demodulation unit 210. When the reception signal is output, IF demodulation section 210 performs IF demodulation on the input reception signal and outputs it to MC demodulation section 206.

  When the received signal is output, the mobile station 200 performs MC demodulation processing (S132) by the MC demodulation unit 202. Next, details of the MC demodulation processing by the MC demodulation unit 202 (corresponding to the MC demodulation unit 350 shown in FIG. 5) will be described.

  In the MC demodulation process, the MC demodulation unit 350 removes the GI from the reception signal input from the IF demodulation unit 210 by the GI removal unit 358 and outputs the GI to the FFT unit 356. Here, the length of the GI removed from the received signal is variably controlled by the GI control unit 216 (second guard interval control unit) based on the predetermined length of the GI determined in the delay characteristic measurement mode. The

  In the present embodiment, since a variable length GI is inserted into a transmission symbol in accordance with the propagation delay characteristics in the communication area, the influence of a delayed wave reaching the GI is reduced. Note that since the variable-length GI is used, the length of the transmission symbol varies depending on the GI length. However, since information on the predetermined length of GI is shared between the radio base station 100 and the mobile station 200 over the communication period, the length of the GI removed from the transmission symbol can be variably controlled. . Thereby, a demodulation sample can be appropriately acquired according to the length of the transmission symbol.

  When the received signal from which the GI has been removed is output, the MC demodulation unit 350 performs fast Fourier transform on the received signal by the FFT unit 356, collectively converts the received signal into the frequency domain, and converts n symbols mapped to each signal point. Output to the demapping units 354-1 to 354-n. When the symbols are output, the MC demodulation unit 350 demaps the input symbols by the demapping units 354-1 to 354-n and outputs the demapped symbols to the P / S unit 352. When the demapped symbol is output, the MC demodulation unit 350 performs P / S conversion on the input reception signal by the P / S unit 352, generates a serial format signal, and outputs the serial signal to the control unit 202 as reception data. To do.

  The transmission / reception apparatus and communication method of the optical wireless fusion system according to this embodiment have been described above. According to the transmission / reception apparatus and communication method according to the present embodiment, the propagation interval characteristic in the communication area is measured by the guard interval information providing unit provided in the radio base station 100 or the mobile station 200, and based on the propagation delay characteristic. A guard interval for use in communication is determined to be a predetermined length. Here, information regarding a predetermined length of the guard interval is shared between the radio base station 100 and the mobile station 200. In radio base station 100, the transmission symbol is subjected to multicarrier modulation, a guard interval having a predetermined length is inserted into the transmission symbol subjected to multicarrier modulation, and transmitted to mobile station 200. In the mobile station 200, a guard interval having a predetermined length is removed from the received transmission symbol, and the transmission symbol from which the guard interval is removed is subjected to multicarrier demodulation.

  Thereby, according to the propagation delay characteristic in a communication area, the guard interval used by a multicarrier transmission system can be inserted or removed with respect to a transmission symbol by predetermined length. Therefore, it is possible to suppress the influence of multipath interference due to the delayed wave of the transmission signal transmitted from the plurality of local radio stations 150a to 150d with the same information without reducing the transmission efficiency. Further, by variably controlling the guard interval length according to the propagation delay characteristics in the communication area, flexibility in system design such as station placement design of the local radio stations 150a to 150d is ensured, and the transmission efficiency of the system Can be secured.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, this invention is not limited to the example which concerns. It is obvious for those skilled in the art that various changes or modifications can be conceived within the scope of the technical idea described in the claims. It is understood that it belongs to.

  For example, in the description of the above embodiment, the case where the mobile station 200 includes the GI information providing unit 220 has been described. However, the embodiment of the present invention is not limited to such a case, and when the same GI information providing unit is provided in the radio base station 100, or the same GI is applied to both the radio base station 100 and the mobile station 200. The same applies to the case where an information providing unit is provided.

  In the description of the above embodiment, the case where the MC transmission method is used for the baseband modulation / demodulation processing has been described. However, the embodiment of the present invention is not limited to such a case, and other transmission methods may be used. Further, the IF band frequency and the RF band frequency can also be applied to the ROF system using any frequency band within the allowable range of the devices constituting each functional component. For this reason, the embodiment of the present invention can be suitably applied to various ROF systems when it is desired to improve communication characteristics.

  In the description of the above embodiment, the method of determining the GI length by receiving the impulse transmitted from the radio base station 100 by the mobile station 200 and measuring the propagation delay characteristic in the communication area has been described. However, as a method for determining the GI length, for example, information related to channel estimation using adaptive equalization may be used. That is, in channel estimation using adaptive equalization, equalization is performed by adaptively adjusting the weight for each delay line using a tapped delay. Therefore, the maximum delay time can be estimated based on the weight information of each delay line.

  In the description of the above embodiment, when determining the GI length, the case where the mobile station 200 performs the operation for measuring the propagation delay characteristic before reaching the communication area and actually performing data communication has been described. However, the operation for measuring the propagation delay characteristic may be performed, for example, in the middle of a communication process or between a plurality of communication processes, instead of being performed prior to actual data communication.

  In the description of the above embodiment, the case where the ROF system is applied to a road-vehicle communication system has been described. However, the embodiment of the present invention is not limited to such a case. In addition to the road-to-vehicle communication system, the ROF system under the influence of multipath interference caused by delayed waves arriving from a plurality of local radio stations is also applicable. The same can be applied.

It is explanatory drawing which shows the system configuration | structure of a ROF system taking a road-vehicle communication system as an example. It is explanatory drawing which shows typically the relationship between the communication area and signal propagation path | route in a ROF system. It is explanatory drawing which shows the structure of the transmission / reception apparatus by the side of the wireless base station of the ROF system which concerns on this embodiment. It is explanatory drawing which shows the structure of the transmitter / receiver of the mobile station of the ROF system which concerns on this embodiment. It is explanatory drawing which shows the structure of the multicarrier modulation part and multicarrier demodulation part of the ROF system which concerns on this embodiment. It is explanatory drawing which shows the operation | movement method of the ROF system which concerns on this embodiment. It is explanatory drawing which shows typically the measuring method of the propagation delay characteristic in the ROF system which concerns on this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Radio base station 102 Impulse generator 104 MC modulation / demodulation part 106 IF modulation / demodulation part 108 Demultiplexer 110, 154 E / O unit 112, 152 O / E unit 114 Multiplexer 116, 216 GI control unit 140 Optical fiber 150 Local Radio station 156, 212 RF conversion unit 158, 214 Antenna unit 200 Mobile station 202 Control unit 204 MC modulation unit 206 MC demodulation unit 208 IF modulation unit 210 IF demodulation unit 220 GI information provision unit 222 Switch 224 Delay characteristic measurement unit 226 GI Long decision section

Claims (5)

In an optical wireless fusion communication system that performs communication between the radio base station and a mobile station via a plurality of local radio stations connected to the radio base station by optical fiber,
At least one of the radio base station and the mobile station measures a propagation delay characteristic in a communication area, determines a guard interval to be used for communication based on the propagation delay characteristic to a predetermined length, A guard interval information providing unit that provides information on a predetermined length of the guard interval to the other of the radio base station and the mobile station;
The radio base station is
A first guard interval control unit that variably controls a guard interval to be inserted into a transmission symbol to the predetermined length;
A multi-carrier modulation unit that multi-carrier modulates transmission symbols to be transmitted and inserts the variable-controlled guard interval into the multi-carrier modulated transmission symbols;
With
The mobile station
A second guard interval controller that variably controls the guard interval to be removed from the transmission symbol to the predetermined length;
A multi-carrier demodulator that removes the variable-controlled guard interval from the transmission symbol received from the radio base station and multi-carrier demodulates the transmission symbol from which the guard interval has been removed;
An optical wireless fusion communication system comprising: Applied to the radio base station or the mobile station in an optical wireless fusion communication system that performs communication between the radio base station and the mobile station via a plurality of local radio stations connected to the radio base station by optical fiber In the transmission / reception device
The propagation delay characteristic in the communication area is measured, a guard interval to be used for communication is determined to be a predetermined length based on the propagation delay characteristic, and information on the predetermined length of the guard interval is provided to the communication partner A guard interval information provider,
A first guard interval control unit that variably controls a guard interval to be inserted into a transmission symbol to the predetermined length;
A multi-carrier modulation unit that multi-carrier modulates transmission symbols to be transmitted and inserts the variable-controlled guard interval into the multi-carrier modulated transmission symbols;
A second guard interval controller that variably controls the guard interval to be removed from the transmission symbol to the predetermined length;
A multi-carrier demodulator that removes the variable-controlled guard interval from the received transmission symbol and multi-carrier demodulates the transmission symbol from which the guard interval has been removed;
A transmission / reception apparatus comprising:   The said guard interval information provision part measures the propagation delay characteristic in the said communication area based on the reception condition of the impulse transmitted simultaneously from each of these local radio stations, The Claim 2 characterized by the above-mentioned. The transmitter / receiver described. In a communication method applied to an optical wireless fusion communication system that performs communication between a radio base station and a mobile station via a plurality of local radio stations connected to the radio base station by optical fiber,
The propagation delay characteristic in the communication area is measured, a guard interval to be used for communication is determined to be a predetermined length based on the propagation delay characteristic, and information on the predetermined length of the guard interval is provided to the communication partner Guard interval information providing step;
A first guard interval control step for variably controlling a guard interval to be inserted into a transmission symbol to the predetermined length;
A multi-carrier modulation step of multi-carrier modulating a transmission symbol to be transmitted and inserting the variable-controlled guard interval into the multi-carrier modulated transmission symbol;
A second guard interval control step for variably controlling the guard interval to be removed from the transmission symbol to the predetermined length;
A multi-carrier demodulation step of removing the variable-controlled guard interval from the received transmission symbol and multi-carrier demodulating the transmission symbol from which the guard interval has been removed;
A communication method comprising:   The guard interval information providing step includes a step of simultaneously transmitting an impulse from each of the plurality of local radio stations, a step of measuring a propagation delay characteristic in the communication area based on a reception status of the plurality of impulses, The communication method according to claim 4, further comprising:

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