JPWO2017073156A1 - Transmission equipment - Google Patents

Abstract

An object of the present invention is to achieve stable transmission by optimizing a bandwidth and a modulation method for a transmission cable. The transmission device of the present invention is a transmission device that transmits and receives video signals bidirectionally via a single transmission line, and the transmission side uses a calibration signal having a bandwidth that is at least the transmission bandwidth or more as the transmission line. The transmission side calculates the SN ratio for each frequency of the transmission line based on the received calibration signal, calculates the optimal transmission bandwidth that maximizes the transmission capacity based on the SN ratio, and the transmission side is the optimal The transmission bandwidth is divided into a plurality of divisions, and a modulation scheme that satisfies the required S / N ratio within the divided frequency band is selected.

Description

  The present invention relates to a transmission apparatus.

A television camera apparatus used for broadcasting generally has a camera head unit that converts an optical image into an electric signal, and a camera control unit (CCU: Camera Control Unit) that performs various shaping processes on the electric signal and controls the camera head unit. ). Here, video signals, audio signals, etc. generated by the camera head unit are transmitted as main line signals from the camera head unit to the camera control unit, while monitoring from the camera control unit to the camera head unit is performed by the camera head unit. Video signals, contact audio signals, etc. are transmitted.
In the following description, transmission from the camera head unit to the camera control unit is referred to as a downlink (Down Link: DL), and transmission from the camera control unit to the camera head unit is referred to as an uplink (Up Link: UL). To. When these DL and UL transmissions are transmitted using cables, a triax cable in which three coaxial cables for power supply, ground, and signal transmission are combined is often used.
Thus, with a triax cable, DL and UL transmission are transmitted using one cable for signal transmission.

  Conventionally, video signals, audio signals, etc. are converted into MPEG-2 (Moving Picture Experts Group 2) or H.264. Transmission using digital modulation schemes such as Orthogonal Frequency Division Multiplexing (OFDM), which is digitized by video encoding such as H.264, is used. Then, bi-directional transmission is performed by a frequency division multiplexing method in which modulated signals are generated for each of DL and UL, and these signals are multiplexed and transmitted at different frequencies. In the camera video transmission, generally, DL transmits a main line signal, and UL transmits a monitor signal. Therefore, DL requires a wider bandwidth. FIG. 3 shows the spectrum arrangement of bidirectional transmission by frequency division multiplexing. In FIG. 3, the DL spectrum is arranged at the low frequency and the UL spectrum is arranged at the high frequency. In this way, by dividing the frequency and transmitting, it is possible to perform bidirectional transmission with a single cable.

  As a prior art document, for example, in Patent Document 1, a reference BER (Bit Error Rate) and CNR (Carrier to Noise ratio) are ensured upon reception of the other transmitting / receiving device. An invention that can transmit with as little transmission power as possible is disclosed.

JP 2004-72666 A

FIG. 4 shows the frequency characteristics of a transmission cable that is generally used in the conventional technology described above. FIG. 4 shows the attenuation of the cable per unit meter. As can be seen, the attenuation increases as the frequency increases.
An example in the case of performing transmission using such a transmission cable will be described. FIG. 5 shows, for example, the reception spectrum observed at each receiving end when the cable length is 100 m. FIG. 5 also shows thermal noise mixed in by the receiving amplifier.
In this case, the level of the high-frequency spectrum, that is, the UL spectrum is slightly attenuated due to attenuation by the cable, but since the cable length is short and the attenuation is small, the signal-to-noise ratio (Signal to Noise ratio) Ratio) is also large. Therefore, transmission with a cable length of 100 m can be performed without any problem.
Next, FIG. 6 shows a reception spectrum when the cable length is 1 km. In this case, since the DL spectrum is less attenuated by the cable, the signal-to-noise ratio is high and transmission can be realized without any problem. However, the signal-to-noise ratio is greatly deteriorated at a high UL frequency, and correct transmission cannot be performed. In this way, when the cable length is long, transmission using the frequency division multiplexing method may cause a large difference between the DL transmission characteristic and the UL transmission characteristic.
Therefore, when transmission is performed by frequency division multiplexing, it is necessary to limit the cable length to be short so that the SN ratio of the high-frequency spectrum with high attenuation by the cable becomes an SN ratio (necessary SN ratio) that does not cause an error. There is.
An object of the present invention is to achieve stable transmission by optimizing a bandwidth and a modulation method for a transmission cable.

  The transmission device of the present invention is a transmission device that transmits and receives video signals bidirectionally via a single transmission line, and the transmission side uses a calibration signal having a bandwidth that is at least the transmission bandwidth or more as the transmission line. The transmission side calculates the SN ratio for each frequency of the transmission line based on the received calibration signal, calculates the optimal transmission bandwidth that maximizes the transmission capacity based on the SN ratio, and the transmission side is the optimal The transmission bandwidth is divided into a plurality of divisions, and a modulation scheme that satisfies the required S / N ratio within the divided frequency band is selected.

  The transmission apparatus according to the present invention is the above-described transmission apparatus, wherein the transmission side further divides the video signal in terms of time.

  Furthermore, the transmission apparatus of the present invention is the above-described transmission apparatus, wherein the transmission path is a triax cable.

  According to the present invention, stable transmission can be achieved by optimizing the bandwidth and modulation method for the transmission cable.

It is a block diagram of the transmission apparatus which concerns on one Example of this invention. It is a block diagram of the transmission apparatus which concerns on another one Example of this invention. It is a figure which shows the spectrum of DL and UL by a frequency division multiplexing system. It is a figure which shows the relationship between the frequency of a cable and the amount of attenuation. It is a figure which shows the example of a reception spectrum characteristic in case a cable length is 100 m. It is a figure which shows the example of a reception spectrum characteristic in case a cable length is 1000 m. It is a timing chart for demonstrating operation | movement of the transmission apparatus which concerns on one Example of this invention. It is a figure which shows the example of a characteristic of the transmission signal and reception signal of a broadband known signal. It is a block diagram for demonstrating the adaptive modulation control part of the transmission apparatus which concerns on one Example of this invention. It is a figure which shows the example of the relationship between bandwidth BW and channel capacity. It is a figure for demonstrating allocation of the modulation | alteration multi-value number which satisfy | fills the S / N ratio of the transmission apparatus which concerns on one Example of this invention, and required SN ratio.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
A first embodiment of the present invention will be described in detail with reference to FIG.
FIG. 1 is a block diagram of a transmission apparatus according to an embodiment of the present invention.
In FIG. 1, the transmission apparatus includes a camera head unit 110, a camera control unit 120, and a transmission cable 130.
The camera head unit 110 includes a known signal generation unit 111, an adaptive modulation transmission unit 112, a selection unit 113, a reception unit 114, an SN ratio determination unit 115, an adaptive modulation control unit 116, and a time division selection unit 117.
The camera control unit 120 includes a known signal generation unit 121, an adaptive modulation transmission unit 122, a selection unit 123, a reception unit 124, an SN ratio determination unit 125, an adaptive modulation control unit 126, and a time division selection unit 127.
The transmission cable 130 which is a transmission path may be a triax cable.

Next, calibration processing for selecting an optimal transmission method and transmission bandwidth according to the cable length will be described with reference to FIG.
FIG. 7 is a timing chart for explaining the operation of the transmission apparatus according to the embodiment of the present invention.
Selection of the optimal transmission method and transmission bandwidth according to the cable length is based on two processing steps.
In FIG. 7, the upper timing chart indicates the camera head unit, and the lower timing chart indicates the camera control unit. A square solid line indicates a transmission signal, and a dotted line indicates a reception signal.
Furthermore, although the time division division multiplexing system in which bi-directional transmission of DL and UL between the camera head unit and the camera control unit is divided in terms of time will be described, unidirectional transmission may be used.

First, the calibration process will be described.
In the calibration process, a calibration signal is generated from the known signal generator 111 provided in the camera head unit 110. The calibration signal generates a wideband signal covering from the lowest frequency to the highest frequency that can be used for cable transmission, and sends it to the selection unit 113. The selection unit 113 operates to select and output the known signal generation unit 111 during the calibration processing period, and operates to select and output the signal from the adaptive modulation transmission unit 112 during the data transmission processing period.
In the calibration processing period, a broadband known signal from the known signal generator 111 is output and sent to the time division selector 117.

The time division selection unit 117 selects and outputs the signal from the selection unit 113 during the DL transmission period. In the DL transmission period of the calibration period, a broadband known signal for calibration is transmitted to the transmission cable 130.
The broadband known signal is transmitted to the camera control unit 120 via the transmission cable 130. At this time, as shown in FIG. 4, when a long cable length is used, the amount of attenuation at a high frequency increases. FIG. 8 shows signal level characteristics of a transmission signal of the wideband known signal from the camera head unit 110 and a reception signal of the camera control unit 120. FIG. 8 is a diagram illustrating an example of characteristics of a transmission signal and a reception signal of a broadband known signal.

The time division selection unit 117 receives a known broadband signal via the transmission cable 130. At this timing, the camera control unit enters a reception period. The time division selection unit 117 receives the signal from the transmission cable 130 as the reception unit 114 and the SN ratio. It outputs to the determination part 115.
In the calibration period, a reception spectrum as shown in FIG. 8 is input to the SN ratio determination unit 115, and the SN ratio determination unit 115 measures the SN ratio for each frequency.

Next, two specific examples of the SN ratio calculation method will be described.
As a first specific example, the received signal level is observed for each frequency by frequency analysis processing such as Fast Fourier Transform (FFT), and the level difference from thermal noise is calculated for each frequency. The S / N ratio is measured.

  The second specific example performs frequency analysis processing such as FFT similarly to the first specific example, and calculates the frequency characteristic of the transmission cable 130 using the fact that the transmission signal is a known signal. There are various methods for calculating the frequency characteristic. For example, the received signal and the known signal are divided. Since it is wired transmission, it is assumed that there is no fluctuation in the transmission path, and the division result is filtered in the time direction to remove disturbance components due to thermal noise, and the frequency characteristics of the transmission cable 130 are as accurate as possible. To calculate. This method is called channel estimation processing in radio signal processing. Then, when the division result and the frequency characteristic of the cable subjected to the time filter are divided, the division result becomes “1” when no thermal noise is mixed. However, since the value of “1” shifts due to the mixing of thermal noise, the SN ratio can be measured by performing a plurality of calibration trials and calculating the variance of the division result.

  When the transmission of the DL known broadband known signal in FIG. 7 is completed, the transmission of the UL known broadband known signal is started. This is because transmission and reception are divided and transmitted in a time-sharing manner. Therefore, when the camera control unit 120 is in the transmission period (UL transmission), the wideband known from the known signal generation unit 121 is the same as the camera head unit 110. Output a signal. A signal from the known signal generator 121 is sent to the transmission cable 130 via the selector 123 and the time division selector 127.

The signal output from the transmission cable 130 is connected to the reception unit 114 and the SN ratio determination unit 115, and the SN ratio determination unit 115 calculates the SN ratio for each frequency by the same processing as the SN ratio determination unit 125 described above.
With the above processing, the SN ratio for each frequency of the transmission cable 130 is calculated by the camera head unit 110 and the camera control unit 120, respectively. Since both DL and UL pass through the same transmission cable 130, the above S / N ratio has the same value for DL and UL.
The output of the SN ratio determination unit 115 of the camera head unit 110 is input to the adaptive modulation control unit 116, and similarly, the output of the SN ratio determination unit 125 is input to the adaptive modulation control unit 126.

By the way, as described above, in one embodiment of the present invention, an OFDM system is used in which transmission is performed by dividing a transmission band into a plurality of subcarriers as a modulated signal.
Note that the modulation scheme may be a scheme in which transmission is performed by dividing a transmission band into a plurality of transmissions, similar to the OFDM scheme.

  Adaptive modulation control sections 116 and 126 control the number of modulation levels assigned to each subcarrier based on the S / N ratio for each frequency of transmission cable 130 so that the transmission capacity is maximized.

ここで、ケーブル伝送では図８に示すように周波数毎のＳＮ比が大きく異なるため、サブキャリア毎のＳＮ比も異なり、また、ケーブルであるため無線伝送と異なり、帯域幅ＢＷの制限もない。
このことから、有線伝送に対してシャノンの通信路容量定理を適用すると、（式２）として表される。

Next, selection of an adaptive modulation scheme and an optimum frequency bandwidth in a wired transmission environment will be described.
According to the general Shannon channel capacity theorem, the channel capacity depends on the SN ratio and the bandwidth BW, and is expressed by (Equation 1).

Here, in the cable transmission, the SN ratio for each frequency is greatly different as shown in FIG. 8, so that the SN ratio for each subcarrier is also different, and since the cable is a cable, there is no restriction on the bandwidth BW unlike the wireless transmission.
From this, applying Shannon's channel capacity theorem to wired transmission is expressed as (Equation 2).

Next, (Expression 2) and (Expression 3) will be described.
In (Expression 2), assuming that the variable of the subcarrier is ω, the start frequency of the transmission band is ωst, and the end frequency is ωen, the bandwidth BW is BW = ωen−ωst.
As for the variable α, the channel capacity indicated by Shannon's channel capacity theorem shown in (Equation 1) is a theoretical limit value, and the actual transmission capacity considering device implementation is lower than that. Therefore, the variable α is provided to indicate the amount of deterioration of the transmission capacity in the actual system, and α <1.

Further, the symbol [X, L] is a clip function for limiting X = L when X is larger than L. As the S / N ratio increases, a · log ₂ {1 + SNR (ω, BW)} also increases, but this value is also limited by the system noise included in the device when considering an actual system. Is done.
Specifically, since when considering system noise included in the device when performing multi-level modulation, for example, 4096QAM (Quadrature Amplitude Modulation) degree becomes transmittable limit in this case is 4096 = 2 ^12, It is limited by L = 12.
The above is the description regarding (Formula 2).

Next, SNR (ω, BW) included in (Expression 2) will be described using (Expression 3).
SNR (ω, BW) is expressed as a function of subcarrier ω and bandwidth BW. The signal-to-noise ratio is obtained by multiplying the transmission power P by the characteristic L (ω) of the transmission cable 130 to obtain the signal power that reaches the receiving unit 124. At this time, the transmission cable characteristic L (ω) varies depending on the transmission distance, for example, as shown in FIG.
Further, the noise component is dominated by thermal noise applied by the low noise power amplifier provided at the first stage of the receiving unit 124, and N ₀ (BW) = kT · BW.
Here, k is the Boltzmann constant, T is the absolute temperature, and BW is the bandwidth.

Next, the operation of the adaptive modulation control unit that optimally controls the modulation scheme using (Equation 1) and (Equation 2) will be described with reference to FIG.
FIG. 9 is a block diagram for explaining an adaptive modulation control unit of a transmission apparatus according to an embodiment of the present invention.
The adaptive modulation control units 116 and 126 include an SN ratio correction unit 901, a BW variable unit 902, an optimum bandwidth calculation unit 903, an SN ratio correction unit 904, and an SNR versus modulation multilevel number calculation unit 905.
The adaptive modulation control units 116 and 126 calculate (Equation 2) and (Equation 3) while varying the bandwidth BW with respect to the S / N ratio obtained by the S / N ratio determination units 115 and 125, thereby obtaining the bandwidth. The relationship of width BW to transmission capacity C is obtained.

FIG. 10 illustrates an example of the relationship between the bandwidth BW and the transmission capacity C at a transmission distance of 1 to 3 km.
FIG. 10 shows that when the cable length is assumed to be 1.5 km, for example, the maximum bit rate of about 640 Mbps can be realized when the bandwidth BW is about 80 MHz.
The calculation of the optimum bandwidth is performed by the SN ratio correction unit 901, the BW variable unit 902, and the optimum bandwidth calculation unit 903 in FIG. 9, and specific processing will be described.

The BW variable unit 902 varies the bandwidth BW from a narrow bandwidth to a wide bandwidth and inputs it to the SN ratio correction unit 901 in order to calculate the optimum bandwidth BW as shown in FIG.
In addition, the SN ratio calculated by the SN ratio determination units 115 and 125 is input to the SN ratio correction unit 901. Since the S / N ratio is proportional to the reciprocal of the bandwidth BW, if the bandwidth of the known broadband signal is BW ₀ when calculated in the calibration period, the SNR ′ (ω, BW) corrected by the S / N ratio correction unit 901 is (Expression 4)

The corrected SNR ′ (ω, BW) is input to the optimum bandwidth calculation unit 903, and the optimum bandwidth calculation unit 903 substitutes SNR ′ (ω, BW) into (Equation 2). Perform the calculation. By performing this process while changing the BW by the BW variable unit 902, the characteristics of the transmission capacity C (BW) shown in FIG. 10 are obtained, and the bandwidth BW that is the maximum value is set as the optimum bandwidth BW _opt. Calculated.

FIG. 10 is a diagram illustrating an example of the relationship between the bandwidth BW and the channel capacity.
The optimum bandwidth BW _opt from the optimum bandwidth calculation unit 903 in FIG. 9 is input to the SN ratio correction unit 904, and the SN ratio calculated by the SN ratio determination units 115 and 125 is input to the other input of the SN ratio correction unit 904. Is entered. As shown in (Equation 5), the SN ratio correction unit 904 calculates the SNR ′ (ω, BW _opt ) of the correction SN ratio corresponding to the optimum bandwidth BW _opt .

  The SN ratio from the SN ratio correction unit 904 is input to the SNR vs. modulation multilevel number calculation unit 905 in FIG. As shown in FIG. 11, the SNR vs. modulation multilevel number calculation unit 905 assigns a modulation multilevel number that satisfies the required SN ratio in each subcarrier to the corrected SN ratio. FIG. 11 is a diagram for explaining the assignment of the modulation multilevel number satisfying the SN ratio and the required SN ratio of the transmission apparatus according to an embodiment of the present invention.

The above processing is performed during the calibration period, and then the data transmission period starts.
The setting of the modulation multilevel number calculated for each subcarrier is input to the adaptive modulation transmission sections 112 and 122 in FIG. 1, and mapping is performed on the DL transmission data and the UL transmission data according to the modulation multilevel number, respectively. . Thereafter, an OFDM modulation signal is generated using processing such as inverse Fourier transform. A known technique is used to generate the OFDM modulated signal.

Further, the assignment of the modulation multi-value number for each subcarrier and the optimum transmission bandwidth BW _opt are notified in advance when the receiving unit 124 demodulates the modulation signal. Such information may be transmitted by being superimposed on the modulated signal, but may be notified to the receiving side using another frequency, and the notification method is not particularly limited.

In the data transmission period, the selection unit 113 in FIG. 1 selects and outputs a signal from the adaptive modulation transmission unit 112. In the DL period, the time division selection unit 117 selects and outputs a signal from the selection unit 113.
The DL signal from the time division selection unit 117 is input to the time division selection unit 127 via the transmission cable 130. In the DL period, the time division selection unit 127 selects and outputs the signal of the transmission cable 130 to the reception unit 124.

This DL transmission is shown as a BW _opt bandwidth modulated signal in the data transmission period DL of FIG.
The receiving unit 124 performs demodulation processing based on the modulation multi-level number for each subcarrier assigned on the transmission side, and outputs a demodulation result signal as DL reception data. This OFDM demodulation and error correction decoding use well-known techniques.

Similarly, in UL transmission, a modulation signal is generated by the adaptive modulation transmission unit 122, and the selection unit 123 selects and outputs a signal from the adaptive modulation transmission unit 122 in the data transmission period. In the UL period, the time division selection unit 127 selects and outputs a signal from the selection unit 123.
The UL signal from the time division selection unit 127 is input to the time division selection unit 117 via the transmission cable 130. In the UL period, the time division selection unit 117 selects and outputs the signal of the transmission cable 130 to the reception unit 114.
This UL transmission is shown as a BW _opt bandwidth modulated signal in the data transmission period DL of FIG.
Similarly to the receiving unit 124, the receiving unit 114 performs demodulation processing on the signal from the time division selection unit 117, and outputs a demodulation result signal as UL reception data.

Through the above processing, it is possible to realize bidirectional data transmission at a higher bit rate than before by optimizing the bandwidth and the modulation method for each subcarrier according to the characteristics of the transmission cable used. Become.
In the above description, the ratio between the DL period and the UL period is not specified, but the DL / UL time ratio varies depending on the required system requirements. For example, if the transmission rate ratio of the UL transmission for transmitting the monitoring signal to the DL transmission for transmitting the main line signal is 2: 1, the DL / UL time ratio is also set to 2: 1. good.

  In the frequency division multiplexing system described in the above prior art, the DL transmission characteristic and the UL transmission characteristic are greatly different depending on the cable length. However, in the time division multiplexing system according to the embodiment of the present invention, the transmission characteristics are the same. Therefore, stable transmission can be realized.

Next, a second embodiment of the present invention will be described with reference to FIG.
FIG. 2 is a block diagram of a transmission apparatus according to another embodiment of the present invention.
In FIG. 2, the transmission apparatus includes a camera head unit 210, a camera control unit 220, and a transmission cable 130.
In the second embodiment, the SN ratio determination units 115 and 125 in the first embodiment shown in FIG. 1 are omitted, and the SNR (ω) signal to the adaptive modulation control units 116 and 126 can be input from the outside. Other configurations are the same as those of the first embodiment.

In the first embodiment, the optimum transmission can be adaptively handled according to the transmission cable by performing the calibration process. On the other hand, the second embodiment aims to provide a transmission apparatus suitable when the characteristics of the transmission cable 130 can be grasped in advance.
Since the characteristics of the transmission cable 130 can be grasped, the SNR (ω) is also a known characteristic, and this SNR (ω) is input to the adaptive modulation control units 116 and 126.

The adaptive modulation control units 116 and 126 perform adaptive modulation suitable for the transmission cable characteristics based on the SNR (ω) input from the outside as in the first embodiment. The difference is that the calibration process can be omitted.
The adaptive modulation control units 116 and 126 may calculate the optimum bandwidth BW _opt and the modulation multi-level number by off-line calculation.

The off-line processing may be a computer connected to the network, or may be configured to notify the off-line calculation result to the adaptive modulation transmission units 112 and 122 via an electronic file.
According to the second embodiment described above, there is an advantage that the load on the apparatus can be reduced by calculating the processing of the adaptive modulation control units 116 and 126 having a large number of arithmetic processes by an external computer.

  A transmission apparatus according to an embodiment of the present invention is to achieve stable transmission by optimizing a bandwidth and a modulation method for a transmission cable.

  Although one embodiment of the present invention has been described in detail above, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. This application claims the benefit of priority based on Japanese Patent Application No. 2015-214349 filed on October 30, 2015, the entire disclosure of which is incorporated herein by reference.

  By optimizing the bandwidth and modulation method in accordance with the characteristics of the transmission cable, it can be applied to applications in which stable transmission is performed.

  110, 210: camera head unit, 111, 121: known signal generation unit, 112, 122: adaptive modulation transmission unit, 113, 123: selection unit, 114, 124: reception unit, 115, 125: SN ratio determination unit, 116 , 126: adaptive modulation control unit, 117, 127: time division selection unit, 120, 220: camera control unit, 130: transmission cable, 901: SN ratio correction unit, 902: BW variable unit, 903: optimal bandwidth calculation unit 904: SN ratio correction unit, 905: SNR vs. modulation multilevel number calculation unit.

Claims (3)

A transmission device that transmits and receives a video signal in both directions via a single transmission line,
The transmission side sends a calibration signal having a bandwidth at least equal to or greater than the transmission bandwidth to the transmission line,
The receiving side calculates an SN ratio for each frequency of the transmission path based on the received calibration signal, and calculates an optimum transmission bandwidth that maximizes the transmission capacity based on the SN ratio,
The transmission apparatus divides the optimum transmission bandwidth into a plurality of parts and selects a modulation method that satisfies a required SN ratio within the divided frequency band. The transmission device according to claim 1,
A data transmission apparatus characterized in that the transmission side further divides the video signal in terms of time. The transmission device according to claim 1 or 2, wherein
The transmission apparatus, wherein the transmission path is a triax cable.

Images