JP2018033112A - Communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a transmission rate in transmission of a signal of a terrestrial digital broadcast by DRoF system.SOLUTION: A communication system includes: an optical transmitter for receiving a terrestrial digital broadcast signal, converting the signal, and transmitting a resultant signal; and an optical receiver for receiving the signal transmitted by the optical transmitter, converts the signal, and outputting a resultant signal. The optical transmitter includes a CP deletion processing unit for deleting a cyclic prefix from the terrestrial digital broadcast signal and transmitting a resultant signal. The optical receiver includes a CP re-addition processing unit for adding a cyclic prefix to the terrestrial digital broadcast signal transmitted by the optical transmitter.SELECTED DRAWING: Figure 1

Description

  The present invention relates to communication technology for terrestrial digital broadcast signals.

  DRoF (Digital Radio On Fiber) is a technique for A / D (Analog to Digital) conversion of a radio signal and transmitting the obtained digital signal through an optical digital network. In the FTTH (Fiber-To-The-Home) service, a technique of A / D converting a terrestrial digital broadcast signal in an RF (Radio Frequency) band and optically transmitting the obtained signal by the DRoF method is considered (for example, Non-patent document 1).

  Digital terrestrial broadcasting (DTT) in Japan, for example, as shown in Non-Patent Document 2, realizes transmission using an ISDB-T (Integrated Services Digital Broadcasting-Terrestrial) system. A feature of this method is that an OFDM (Orthogonal Frequency-Division Multiplexing) modulation method capable of frequency division multiplexing with a minimum frequency interval without inter-carrier interference is employed for effective use of the frequency band.

  In the DRoF method, A / D conversion is performed on an RF time axis signal, which is a radio signal, so that the signal transmission rate is increased by sampling and quantization processing. The transmission rate depends on the sampling frequency at the time of quantization and the number of quantization. Based on these facts, the transmission rate is reduced by reducing the sampling frequency and the number of quantizations (see Non-Patent Document 3).

A. Nirmalathas et al., “Digitized RF Transmission over Fiber”, Microw. Mag., Vol. 10, pp. 75-81, 2009. M. Takada and M. Saito, “Transmission systems for ISDB-T,” Proceedings of the IEEE, vol. 94, no. 1, pp. 251-256, 2006. Ryo Akira, Shinobu Namba, Masayuki Oishi, Hirohito Tanaka. I / Q data compression method for C-RAN base station entrance circuit using nonlinear quantization. IEICE Transactions C, 98 (8), 158-166 , 2015.

  Terrestrial digital broadcast signals (hereinafter referred to as “DTT signals”) are signals for 10 channels in a frequency band of 60 MHz. When performing A / D conversion on the DTT signal in a lump, assuming that the sampling frequency is 120 MHz and the quantization number is 15 bits, the transmission rate is 1.8 Gbps. This is a transmission rate of 10 times or more compared to the transmission rate 168.5 Mbps in the TS (Transport Stream) of the MPEG2 system. Therefore, in the DRoF method, the required speed for the network is significantly higher than when the TS is directly transmitted as a baseband signal. As a result, there is a possibility of lowering the economy. Therefore, when a DTT signal is transmitted by DRoF, a significant reduction in transmission rate is required. For example, it is necessary to reduce the sampling frequency and the number of quantization during A / D conversion and D / A conversion, which are one of the parameters for determining the transmission rate, and to compress data of the DTT signal on the time axis.

  In view of the above circumstances, an object of the present invention is to provide a technique for reducing a transmission rate in transmission of a terrestrial digital broadcast signal by the DRoF method.

  One aspect of the present invention is a communication including an optical transmitter that receives a terrestrial digital broadcast signal, converts the signal, and transmits the signal, and an optical receiver that receives the signal transmitted from the optical transmitter, converts the signal, and outputs the signal. The optical transmitter includes a CP deletion processing unit that deletes and transmits a cyclic prefix from the digital terrestrial broadcast signal, and the optical receiver transmits the terrestrial signal transmitted by the optical transmitter. A communication system including a CP re-addition processing unit for adding a cyclic prefix to a digital broadcast signal.

  One aspect of the present invention is the communication system described above, wherein the CP deletion processing unit includes an A / D conversion unit that performs analog / digital conversion on the N-channel multiplexed signal, and a signal after the A / D conversion. A channel separation unit that performs frequency separation for each channel, a plurality of CP detection units that detect the start position of the cyclic prefix for each channel, and a start position of the cyclic prefix in a plurality of channels based on the detected start position An interchannel symbol synchronizer that aligns the signals, a channel multiplexer that frequency-multiplexes the synchronized signals, and a symbol extractor that collectively deletes the cyclic prefixes of the multiplexed signals. The additional processing unit includes a symbol detection unit that detects a boundary between symbols with respect to the signal transmitted from the optical transmitter, and a detected symbol. Based on the position comprises a CP re adding section for adding produces a cyclic prefix, a D / A converter for digital / analog conversion on the signal cyclic prefix is added, the.

  One aspect of the present invention is the communication system described above, wherein the CP deletion processing unit converts the frequency band of the channel-separated signal into a channel separation unit that frequency-separates the N-channel multiplexed signal for each channel. A plurality of frequency converters, a plurality of A / D converters that perform analog / digital conversion on the frequency-converted signal, and a plurality of cyclic prefixes that detect the head position of the cyclic prefix for each A / D converted channel A CP detection unit, a plurality of symbol extraction units for deleting the cyclic prefix of the signal for each channel based on the head position of the cyclic prefix, and a multiplexing for multiplexing the signal with the cyclic prefix deleted for each channel The CP re-addition processing unit, and a separation unit that separates a signal from the multiplexed signal transmitted from the optical transmitter; A plurality of symbol detection units that detect the boundary between symbols, a plurality of CP re-addition units that generate and add a cyclic prefix based on the boundary between symbols, and a cyclic prefix are added to the separated signal A plurality of D / A converters for digital / analog conversion of the converted signals, a plurality of frequency converters for performing frequency conversion for each channel on the D / A converted signals, and a frequency conversion for each channel. A frequency multiplexing unit that frequency-multiplexes the signal.

  According to the present invention, the transmission rate can be reduced in the transmission of the terrestrial digital broadcast signal by the DRoF method.

It is a figure which shows the outline | summary of the communication system which transmits a DTT signal via an optical digital network by a DRoF system. It is a figure which shows an example of the transmission equipment of the terrestrial digital broadcasting station. It is a figure which shows the outline of the symbol and CP in mode3. It is a schematic block diagram which shows the structure of the communication system of the 1st Embodiment of this invention. 3 is a diagram illustrating a spectrum of a signal in each functional unit of the DRoF transmitter 10. FIG. 4 is a diagram illustrating a spectrum of a signal in each functional unit of the DRoF receiver 20. FIG. It is a figure which shows the outline | summary of the DTT signal before and behind CP deletion process in the DRoF transmitter. It is a figure which shows the outline | summary of the DTT signal before and behind CP re-addition processing in the DRoF receiver. It is a block diagram which shows the structure which concerns on the communication system of the 2nd Embodiment of this invention. 3 is a diagram illustrating a spectrum of a signal in each functional unit of the DRoF transmitter 10. FIG. An outline of CP and symbols of the main signal input to the inter-channel symbol synchronization unit 114 is shown. It is a figure which shows CP and a symbol output from the D / A conversion part 213. It is a figure which shows the spectrum of the signal output from the D / A conversion part 213. It is a block diagram which shows the structure which concerns on the communication system of the 3rd Embodiment of this invention. 3 is a diagram illustrating a spectrum of a signal in each functional unit of the DRoF transmitter 10. FIG. It is a figure which shows the outline | summary of the DTT signal before and behind CP re-addition processing in the DRoF receiver.

  FIG. 1 is a diagram showing an outline of a communication system that transmits a DTT signal via an optical digital network by the DRoF method. In FIG. 1, a terrestrial digital broadcasting station 90 transmits a DTT signal. As will be described later, an ISDB-T (Integrated Services Digital Broadcasting-Terrestrial) system is used for the DTT signal transmitted from the terrestrial digital broadcasting station 90. Further, OFDM (Orthogonal Frequency-Division Multiplexing) is adopted as a modulation method.

  In FIG. 1, the DTT signal transmitted from the terrestrial digital broadcasting station 90 is received by the DRoF transmitter 10 installed at the relay location and the viewing terminal 92 installed at the viewing terminal installation location. The DRoF transmitter 10 includes a digital terrestrial broadcast receiving antenna 11. The viewing terminal 92 includes a terrestrial digital broadcast receiving antenna 91. The viewing terminal 92 reproduces the terrestrial digital broadcast based on the DTT signal received via the terrestrial digital broadcast receiving antenna 91.

  The DRoF transmitter 10 converts the received DTT signal into an optical signal and transmits it through the optical digital network (optical digital NW) 30. The optical signal transmitted by the DRoF transmitter 10 is received by the DRoF receiver 20 installed at the viewing terminal installation location. The optical signal received by the DRoF receiver 20 is converted into a DTT signal and output to the viewing terminal 21. The viewing terminal 21 reproduces the terrestrial digital broadcast based on the DTT signal generated by the DRoF receiver 20.

  Next, a transmission facility of the terrestrial digital broadcasting station 90 will be described. FIG. 2 is a diagram illustrating an example of a transmission facility of the terrestrial digital broadcasting station 90. Note that the transmission facility shown in FIG. 2 is a facility for transmitting an ISDB-T DTT signal, which is terrestrial digital broadcasting in Japan. The transmission facility of the terrestrial digital broadcasting station 90 includes a plurality of information source encoding units 31, a TS remultiplexing unit 32, and a transmission path encoding unit 33.

  The information source encoding unit 31 includes a video encoding unit 41, an audio encoding unit 42, a data encoding unit 43, and a multiplexing unit 44. The video encoding unit 41 compresses and encodes video data. For example, MPEG (Moving Picture Experts Group) 2 system is used for compression encoding of video data. The MPEG2 system is a technique in which motion compensation predictive coding, DCT (Discrete Cosine Transform) conversion, and variable length coding are combined. The audio encoding unit 42 compresses and encodes audio data. For compression encoding of audio data, for example, AAC (Advanced Audio Coding) is used. The data encoding unit 43 encodes data such as PSI (Program Specific Information). The multiplexing unit 44 multiplexes video data, audio data, and data into a TS (Transport Stream). The TS is composed of, for example, a TSP (TS Packet) in which 188-byte fixed-length packets are continuous.

  A plurality of information source encoding units 31 may be provided in the transmission facility of the terrestrial digital broadcasting station 90. A plurality of TSs (TS 1, TS 2, TS 3,...) Output from the information source encoding unit 31 are input to the TS remultiplexing unit 32. The TS remultiplexing unit 32 generates TS ′ by multiplexing a plurality of TSs (TS1, TS2, TS3,...) According to the MPEG2-System method. TS ′ is input to the transmission path encoding unit 33.

  The transmission path encoding unit 33 includes a signal processing unit 51, an IFFT (Inverse Discrete Fourier Transform) unit 52, a CP addition unit 53, and a D / A conversion unit 54.

  The signal processing unit 51 performs processing such as error correction coding, interleaving, carrier modulation, and OFDM frame processing. These processes are performed by layer-coding transmission lines in parallel for each segment and making them hierarchical. The IFFT unit 52 performs serial / parallel conversion on transmission data for each symbol, performs IFFT processing, and modulates with a plurality of subcarriers orthogonal to each other. CP adding section 53 adds a cyclic prefix (hereinafter referred to as “CP”) to the transmission signal. The D / A converter 54 converts the transmission signal into an analog signal and transmits it as a DTT signal.

  In this way, the ISDB-T system is adopted in terrestrial digital broadcasting in Japan. In the ISDB-T system, in order to support various broadcasting methods such as mobile reception and fixed reception, a plurality of modes 1 to 3 are prepared according to the number of multiplexed OFDM carriers. In the fixed reception, Mode 3 having 5617 carriers per channel is used. In Mode 3, the symbol length is 1008 μsec, and 1/8 of the symbol length is used as the CP.

  FIG. 3 is a diagram showing an outline of symbols and CPs in mode 3. CP1 is generated by copying 1/8 of the rear end of symbol 1, and is added to the head of symbol 1. Similarly, CP2 and CP3 are generated by copying the rear end 1/8 of symbol 2 and symbol 3, respectively, and added to the heads of symbol 2 and symbol 3, respectively.

<First Embodiment>
FIG. 4 is a schematic block diagram illustrating the configuration of the communication system according to the first embodiment of this invention. FIG. 5 is a diagram illustrating a spectrum of a signal in each functional unit of the DRoF transmitter 10. FIG. 6 is a diagram illustrating a spectrum of a signal in each functional unit of the DRoF receiver 20.

  As shown in FIG. 4, the DRoF transmitter 10 includes a frequency conversion unit 101 and a CP deletion processing unit 102. The frequency conversion unit 101 converts a DTT signal of N (N is the number of channels) channels received via the terrestrial digital broadcast receiving antenna 11 from an RF signal to an IF signal. The CP deletion processing unit 102 converts the frequency-converted N-channel DTT signal from an analog signal to a digital signal. The CP deletion processing unit 102 deletes the CP from the digital signal DTT signal. The CP deletion processing unit 102 transmits the DTT signal from which the CP has been deleted to the DRoF receiver 20 via the optical digital network 30.

  The DRoF receiver 20 includes a CP re-addition processing unit 201 and a frequency conversion unit 202. The CP re-addition processing unit 201 re-adds the CP to the received DTT signal. The CP re-addition processing unit 201 converts the DTT signal with the CP re-added from a digital signal to an analog signal. The frequency conversion unit 202 converts the frequency of the DTT signal from the IF signal to the original RF signal and outputs it.

  The DTT signal at the time of reception by the terrestrial digital broadcast receiving antenna is an RF signal, which is in the frequency band shown in FIG. Therefore, the DTT signal in the frequency band shown in FIG. The frequency conversion unit 101 converts the frequency of the DTT signal into an IF signal in a frequency band as shown in FIG. The frequency-converted DTT signal is converted into a digital signal by the CP deletion processing unit 102, and the CP is deleted. In this way, the DRoF transmitter 10 transmits a signal from which the CP has been deleted.

  The DRoF receiver 20 receives a DTT signal from the optical digital network 30. The DTT signal at the time of reception does not include the CP, and is a signal in the frequency band shown in FIG. The CP re-addition processing unit 201 re-adds the CP to the received DTT signal. The CP re-addition processing unit 201 converts the DTT signal into an analog signal, and converts the frequency of the DTT signal into the original RF signal. The frequency band of the DTT signal after frequency conversion is as shown in FIG. This frequency band is the same as the input frequency band of the DRoF transmitter 10 shown in FIG.

  FIG. 7 is a diagram illustrating an outline of the DTT signal before and after the CP deletion process in the DRoF transmitter 10. In digital terrestrial broadcasting, as shown in FIG. 7A, CP1, CP2, CP3,... Are added to the heads of the symbols 1, 2, 3,. When an OFDM signal is transmitted wirelessly, CP1, CP2, CP3,... Are necessary in order to reduce the influence of signal deterioration due to delayed waves generated in a multipath environment.

  The CP deletion processing unit 102 of the DRoF transmitter 10 deletes the CP from the DTT signal. As a result, a signal as shown in FIG. 7B is generated. In the optical digital network 30, since there is no delay due to multipath, CP1, CP2, CP3,... Are not necessarily required. That is, even if communication is performed in a state where CP1, CP2, CP3,... Are deleted, the communication quality is hardly affected. On the other hand, by deleting the CP, the data amount is 8/9 compared to the DTT signal before the CP deletion processing. Therefore, the transmission rate of the optical signal from the DRoF transmitter 10 to the DRoF receiver 20 is reduced by 1/9.

  FIG. 8 is a diagram illustrating an outline of the DTT signal before and after the CP re-addition processing in the DRoF receiver 20. The DRoF receiver 20 receives the DTT signal from which CP1, CP2, CP3,... Are deleted as shown in FIG. The CP re-addition processing unit 201 adds the same CP1, CP2, CP3,... Originally added to the DTT signal to the DTT signal from which the CP has been deleted. Thereby, as shown in FIG. 8B, a signal similar to the DTT signal transmitted from the terrestrial digital broadcasting station 90 is generated.

  Such processing may be applied to signals having different CP lengths, such as Mode 1 to Mode 3 of ISDB-T. In that case, the expected transmission rate reduction amount varies depending on the CP length.

  As described above, in the first embodiment, the CP is deleted and the DTT signal is transmitted from the DRoF transmitter 10 to the DRoF receiver 20. As a result, when the DTT signal is digitized and transmitted via an optical digital network, the transmission rate in the optical transmission section can be reduced.

  With the DTT signal of ISDB-T Mode 3, the DRoF transmitter 10 deletes the CP, whereby the transmission rate of the wired transmission section can be reduced to 8/9. Further, the DRoF receiver 20 generates a CP with the same algorithm as the digital terrestrial broadcasting station 90 and adds it to the signal. Therefore, the DTT signal that has passed through the optical digital network 30 can be returned to the signal form defined in ISDB-T. Therefore, it is possible to view the video by using the existing receiving terminal as it is.

  Furthermore, the configuration of the first embodiment can further use other transmission rate reduction methods such as a reduction in sampling frequency and a reduction in the number of quantizations. Therefore, a further improvement in the transmission rate reduction rate can be expected as compared with the case where only a technique such as a sampling frequency reduction or a quantization number reduction is used.

<Second Embodiment>
Next, a second embodiment of the present invention will be described. FIG. 9 is a block diagram showing a configuration according to the communication system of the second exemplary embodiment of the present invention. Note that the frequency conversion unit 101 and the frequency conversion unit 202 have the same configurations as those of the first embodiment, and thus description and illustration thereof are omitted. The DRoF transmitter 10 according to the second embodiment includes a CP deletion processing unit 102 a instead of the CP deletion processing unit 102. The DRoF receiver 20 according to the second embodiment includes a CP re-addition processing unit 201a instead of the CP re-addition processing unit 201.

  The CP deletion processing unit 102a synchronizes the CP timing of the N-channel DTT signal, and deletes the CP of the N-channel DTT signal in a batch. The CP re-addition processing unit 201a re-adds the CP to the N-channel DTT signal all at once. The CP deletion processing unit 102a includes an A / D conversion unit 111, a channel separation unit 112, a plurality of CP detection units 113 (113-1, 113-2, ..., 113-N), an inter-channel symbol synchronization unit 114, and channel multiplexing. Unit 115 and symbol extraction unit 116.

  The A / D converter 111 converts the N-channel DTT signal frequency-converted by the frequency converter 101 from an analog signal to a digital signal. The channel separation unit 112 separates the frequency of the digitized DTT signal for each channel. CP detectors 113-1, 113-2,..., 113-N obtain the CP head position information of the DTT signal of each channel.

  The inter-channel symbol synchronization unit 114 synchronizes the CP start position of each channel based on the CP start position information for each channel. The channel multiplexing unit 115 frequency multiplexes the DTT signal of each channel in which the CP start positions are aligned. The symbol extraction unit 116 collectively deletes the CP from the DTT signal of each channel in a state where the CP is aligned.

  The CP re-addition processing unit 201a includes a symbol detection unit 211, a CP re-addition unit 212, and a D / A conversion unit 213. The symbol detector 211 detects a boundary for each symbol from the received DTT signal, and detects symbol head position information. The CP re-adding unit 212 generates and adds CPs of DTT signals for N channels based on the symbol head position information. The D / A converter 213 converts the DTT signal from a digital signal to an analog signal.

  FIG. 10 is a diagram illustrating a spectrum of a signal in each functional unit of the DRoF transmitter 10. As shown in FIG. 10A, the A / D converter 111 receives an N-channel DTT signal converted into an IF signal, as shown in FIG. The A / D converter 111 converts the DTT signal from an analog signal to a digital signal.

  The DTT signal digitized by the A / D conversion unit 111 is input to the channel separation unit 112, and each channel (ch. # 1, ch. #) Is input as shown in FIGS. 2,..., Ch. # N) for each DTT signal. The frequency-separated DTT signal of each channel is branched into two and input to CP detectors 113-1 to 113-N and inter-channel symbol synchronizer 114, respectively.

  CP detectors 113-1 to 113-N acquire the head position information of the CP. As a method of acquiring the head position information of the CP, the signal in the CP section is a signal obtained by copying the last time-axis waveform of the symbol, so that detection using correlation can be performed. For example, a method of detecting a correlation coefficient between a signal obtained by performing delay processing on the source signal and the source signal and detecting the head position of the CP may be used. Information on the head position of the CP of each channel detected in this way is input to the inter-channel symbol synchronization section 114.

  FIG. 11 shows an outline of CPs and symbols of the main signal input to the inter-channel symbol synchronization unit 114. In FIG. 11, the horizontal axis indicates time. As shown in FIGS. 11A to 11C, the arrival times of the symbols of each channel vary, and the CP timing differs for each channel.

  The inter-channel symbol synchronization unit 114 aligns the CP start positions of each channel based on the input CP start position information for each channel. At this time, the inter-channel symbol synchronization section 114 aligns the CP start positions with reference to the channel that arrives first among the N-channel DTT signals. FIGS. 11D to 11F show the CP and symbols of the main signal after the CP start positions are aligned by the inter-channel symbol synchronization section 114.

  In this way, the DTT signal of each channel in which the CP start positions are aligned is sent to the channel multiplexer 115. The channel multiplexing unit 115 multiplexes the DTT signal of each channel. As shown in FIG. 10E, the signal output by the channel multiplexing unit 115 has a frequency arrangement in which N-channel DTT signals are frequency-multiplexed.

  The symbol extraction unit 116 collectively deletes the CPs from the DTT signal in which the head positions of the CPs of each channel are aligned. As shown in FIGS. 11G to 11I, the symbol extraction unit 116 outputs an N-channel DTT signal from which the CP has been deleted.

  As described above, in the second embodiment, the CP deletion processing unit 102a synchronizes the start positions of the CPs of the N-channel DTT signals and deletes the CPs in a lump. The N-channel DTT signal from which the CP has been deleted is transmitted to the DRoF receiver 20 while maintaining symbol synchronization.

  The CP re-addition processing unit 201a of the DRoF receiver 20 branches the input signal into two. One signal is input to the CP re-addition unit 212. The other signal is input to the symbol detector 211. The symbol detection unit 211 detects a boundary for each symbol and notifies the CP re-addition unit 212 of the symbol head position information.

  The CP re-addition unit 212 generates a DTT signal CP for N channels based on the head position information and adds the CP to the signal. Since the symbol positions of the DTT signals of all channels are synchronized, CP generation and addition can be performed collectively on the signals multiplexed in N channels. Therefore, the CP re-addition unit 212 may perform CP addition in a lump.

  The signal to which the CP is added by the CP re-addition unit 212 is input to the D / A conversion unit 213. The D / A converter 213 converts the digital signal into an analog signal and outputs it.

  FIG. 12 is a diagram illustrating CPs and symbols output from the D / A conversion unit 213. As shown in FIGS. 12A to 12C, the D / A converter 213 outputs a DTT signal to which a CP is added in synchronization with N channels.

  FIG. 13 is a diagram illustrating a spectrum of a signal output from the D / A conversion unit 213. As shown in FIG. 13, the signal output from the CP re-addition processing unit 201a has the same frequency arrangement as the input signal (FIG. 10A) to the CP deletion processing unit 102a.

  As described above, in the second embodiment, the DRoF transmitter 10 deletes the CP of the DTT signal of each channel at once by synchronizing the position of the CP of the DTT signal.

<Third Embodiment>
Next, a third embodiment of the present invention will be described. FIG. 14 is a block diagram showing a configuration according to the communication system of the third exemplary embodiment of the present invention. Note that the frequency conversion unit 101 and the frequency conversion unit 202 have the same configurations as those of the first embodiment, and thus description and illustration thereof are omitted. The DRoF transmitter 10 according to the third embodiment includes a CP deletion processing unit 102b instead of the CP deletion processing unit 102. The DRoF receiver 20 according to the third embodiment includes a CP re-addition processing unit 201b instead of the CP re-addition processing unit 201.

  The CP deletion processing unit 102b deletes the CP of the DTT signal for each channel, and outputs the DTT signal of each channel by time division multiplexing. The CP re-addition processing unit 201b separates the time-division multiplexed DTT signal of each channel and re-adds the CP for each channel.

  The CP deletion processing unit 102b includes a channel separation unit 121, frequency conversion units 122-1 to 122-N, A / D conversion units 123-1 to 123-N, CP detection units 124-1 to 124-N, and a symbol extraction unit. 125-1 to 125-N and a multiplexing unit 126 are provided.

  The channel separation unit 121 performs frequency separation for each channel on the N-channel frequency multiplexed DTT signal. The frequency conversion units 122-1 to 122-N convert the frequency of the DTT signal into a predetermined frequency for each channel. The A / D converters 123-1 to 123-N convert the frequency-converted DTT signals from analog signals to digital signals for each channel. CP detectors 124-1 to 124-N obtain CP head position information for each channel. The symbol extraction units 125-1 to 125-N delete the CP of the DTT signal for each channel based on the CP head position information. The multiplexing unit 126 performs time division multiplexing on the DTT signal from which the CP has been deleted, and outputs a signal.

  The CP re-addition processing unit 201b includes a separation unit 221, symbol detection units 222-1 to 222-N, CP re-addition units 233-1 to 223-N, D / A conversion units 224-1 to 224-N, and frequency conversion. Units 225-1 to 225 -N and a frequency multiplexing unit 226.

  The separation unit 221 separates the time-division multiplexed signal in units of channels. The symbol detectors 222-1 to 222-N detect the boundary for each symbol for each channel. The CP re-addition units 223-1 to 223 -N generate and add CPs for each channel based on the symbol head position.

  The D / A converters 224-1 to 224 -N convert the DTT signal of each channel from a digital signal to an analog signal. The frequency converters 225-1 to 225 -N convert the frequency of the DTT signal of each channel into a frequency for each channel. The frequency multiplexing unit 226 performs frequency multiplexing of the DTT signal of each channel.

  FIG. 15 is a diagram illustrating a spectrum of a signal in each functional unit of the DRoF transmitter 10. As shown in FIG. 15A, the signal input to the A / D trunk 111 has a different frequency for each channel (ch # 1, ch # 2,... Ch # N). The channel separation unit 121 performs frequency separation for each channel on the analog DTT signal multiplexed in N channels. In the channel separation unit 121, as shown in FIGS. 15B to 15D, the DTT signal for each channel is separated.

  The channel-separated DTT signals are input to frequency converters 122-1 to 122-N, respectively. The frequency converters 122-1 to 122 -N convert the DTT signal for each channel in the frequency band as shown in FIGS. 15B to 15 D into FIGS. 15E to 15 G. Frequency conversion to a signal of the same predetermined frequency band as shown. The frequency-converted DTT signal is input to the A / D conversion units 123-1 to 123-N and digitized.

  The digitized DTT signal is branched into two, one is input to the symbol extraction units 125-1 to 125-N, and the other is input to the CP detection units 124-1 to 124-N. The CP detection units 124-1 to 124-N acquire the head position information of the CP. As a method for acquiring the head position information of the CP, since the signal in the CP section is a signal obtained by copying the last time-axis waveform of the symbol, detection using correlation can be performed. For example, a method of detecting a correlation coefficient between a signal obtained by performing delay processing on the source signal and the source signal and detecting the head position of the CP may be used.

  The detected CP head position information is notified to the symbol extraction units 125-1 to 125-N. The symbol extraction units 125-1 to 125-N delete the CP of the DTT signal based on the CP start position information and extract the symbol.

  Symbols individually extracted for each channel are input to multiplexing section 126. The multiplexing unit 126 multiplexes the DTT signal of each channel using a multiplexing technique such as time division multiplexing. The multiplexed DTT signals for N channels are transmitted to the DRoF receiver 20 via the optical digital network 30.

  FIG. 16 is a diagram illustrating an outline of the DTT signal before and after the CP re-addition process in the DRoF receiver 20. In the CP re-addition processing unit 201b of the DRoF receiver 20, the DTT signal of each channel that is time-division multiplexed is input to the separation unit 221. This signal is separated by the separation unit 221 into DTT signals for each channel as shown in FIGS. 16 (A) to 16 (C).

  The separated DTT signals of each channel are branched into two, one is input to the CP re-adding units 223-1 to 223 -N, and the other is input to the symbol detection units 222-1 to 222 -N. The symbol detectors 222-1 to 222-N detect the boundary for each symbol, and transmit the symbol head position information to the CP re-adders 223-1 to 223-N.

  The CP re-adding units 223-1 to 223 -N generate and add a CP of the DTT signal for each channel based on the transmitted head position information of the symbols. The signal to which the CP is added is input to the D / A converters 224-1 to 224 -N and converted from a digital signal to an analog signal. Output signals of the D / A converters 224-1 to 224-N are input to the frequency converters 225-1 to 225-N.

  In the frequency converters 225-1 to 225 -N, the frequency of the DTT signal of each channel is converted for each channel as shown in FIGS. 16D to 16F. Then, the output signals of the frequency conversion units 225-1 to 225-N are input to the frequency multiplexing unit 226.

  The frequency multiplexing unit 226 outputs a signal having a frequency arrangement as shown in FIG. 16G by frequency multiplexing the signals of the respective channels. For this reason, the signal output from the CP re-addition processing unit 201b has the same frequency arrangement as the input signal (FIG. 15A) to the CP deletion processing unit 102b.

  As described above, in the third embodiment, when the CP is deleted and the DTT signal is transmitted, the CP of the DTT signal is deleted for each channel. Also, the DTT signal of each channel from which the CP has been deleted can be multiplexed (eg, time division multiplexed) and transmitted from the DRoF transmitter 10 to the DRoF receiver 20.

You may make it implement | achieve CP deletion process parts 102, 102a, and 102b in embodiment mentioned above with a computer. Further, the CP re-addition processing units 201, 201a, and 201b in the above-described embodiment may be realized by a computer. In that case, a program for realizing this function may be recorded on a computer-readable recording medium, and the program recorded on this recording medium may be read into a computer system and executed. Here, the “computer system” includes an OS and hardware such as peripheral devices. The “computer-readable recording medium” refers to a storage device such as a flexible medium, a magneto-optical disk, a portable medium such as a ROM and a CD-ROM, and a hard disk incorporated in a computer system. Furthermore, the “computer-readable recording medium” dynamically holds a program for a short time like a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line. In this case, a volatile memory inside a computer system serving as a server or a client in that case may be included and a program held for a certain period of time. Further, the program may be a program for realizing a part of the above-described functions, and may be a program capable of realizing the functions described above in combination with a program already recorded in a computer system. You may implement | achieve using programmable logic devices, such as FPGA (Field Programmable Gate Array).
The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes designs and the like that do not depart from the gist of the present invention.

DESCRIPTION OF SYMBOLS 90 ... Terrestrial digital broadcasting station, 10 ... DRoF transmitter, 11 ... Antenna for terrestrial digital broadcast reception, 20 ... DRoF receiver, 21 ... Viewing terminal, 30 ... Optical digital network, 101 ... Frequency conversion part, 102: CP deletion process , 111: A / D converter, 112... Channel separation unit, 113-1 to 113 -N, CP detection unit, 114: inter-channel symbol synchronization unit, 115 ... channel multiplexing unit, 116 ... symbol extraction unit, 211 ... Symbol detection unit, 212... CP re-addition unit, 213... D / A conversion unit, 121... Channel separation unit, 122... Frequency conversion unit, 123-1 to 123 -N ... A / D conversion unit, 124-1 to 124 -N ... CP detection unit, 125-1 to 125-N ... symbol extraction unit, 126 ... multiplexing unit, 221 ... separation unit, 222- ˜222-N, symbol detection unit, 223-1 to 223-N, CP re-addition unit, 224-1 to 224-N, D / A conversion unit, 225-1 to 225-N, frequency conversion unit, 226,. Frequency multiplexing unit

Claims (3)

A communication system comprising: an optical transmitter that receives a digital terrestrial broadcast signal, converts the signal, and transmits the signal; and an optical receiver that receives the signal transmitted from the optical transmitter, converts the signal, and outputs the signal.
The optical transmitter includes a CP deletion processing unit that deletes and transmits a cyclic prefix from the terrestrial digital broadcast signal,
The optical receiver includes a CP re-addition processing unit that adds a cyclic prefix to the terrestrial digital broadcast signal transmitted by the optical transmitter. The CP deletion processing unit
An A / D converter for analog / digital conversion of N-channel multiplexed signals;
A channel separation unit for frequency-separating the signal after A / D conversion for each channel;
A plurality of CP detectors for detecting the head position of the cyclic prefix for each channel;
An inter-channel symbol synchronization unit that aligns the head positions of the cyclic prefixes in a plurality of channels based on the detected head positions;
A channel multiplexer for frequency multiplexing the synchronized signal;
A symbol extraction unit that collectively deletes the cyclic prefix of the multiplexed signal,
The CP re-addition processing unit
A symbol detector for detecting a boundary between symbols for a signal transmitted from the optical transmitter;
A CP re-addition unit for generating and adding a cyclic prefix based on the detected symbol position;
A D / A converter for digital / analog conversion of a signal with a cyclic prefix;
The communication system according to claim 1, comprising: The CP deletion processing unit
A channel separation unit for frequency-separating N-channel multiplexed signals for each channel;
A plurality of frequency converters for converting the frequency band of the channel-separated signal;
A plurality of A / D converters for analog / digital conversion of the frequency-converted signal;
A plurality of CP detectors for detecting the head position of the cyclic prefix for each A / D converted channel;
A plurality of symbol extraction units for deleting the cyclic prefix of the signal for each channel based on the head position of the cyclic prefix;
A multiplexing unit that multiplexes the signal with the cyclic prefix removed for each channel, and
The CP re-addition processing unit
A separation unit for separating a signal from the multiplexed signal transmitted from the optical transmitter;
A plurality of symbol detectors for detecting a boundary between symbols for the separated signal;
A plurality of CP re-addition units for generating and adding a cyclic prefix based on the boundary between symbols;
A plurality of D / A converters for digital / analog conversion of a signal to which a cyclic prefix is added;
A plurality of frequency conversion units that perform frequency conversion for each channel on the D / A converted signal;
A frequency multiplexing unit that frequency-multiplexes the frequency-converted signal of each channel;
The communication system according to claim 1, comprising:

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