Transmission Equipment

Abstract

To provide a transmission device capable of reducing influence of noise even in a case of weak reception strength.SOLUTION: Bandwidth of a pilot signal PL to be input to a mixer 14 is limited by a BPF (Band Pass Filter), a BPF 12A having a wider bandwidth and a BPF 12B having a narrower bandwidth are provided as the BPF, and they are switched by a switcher 171. Assuming that a pilot signal passed through the BPF 12A is PL1 and a pilot signal passed through the BPF 12B is PL2, either the PL1 or the PL2 is selected by the switcher 171 and becomes a pilot signal PL, then the pilot signal PL is used for generating a receiving side local signal LoR. Switching operation by the switcher 171 is performed according to received signal strength of an RF signal. Fading margin improves by the amount of change in the noise increase factor due to the switching.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a transmission device of an IF transmission system using a low noise slave synchronization system. [Background technology]

[0002] TTL (Transmitter to Transmitter Link) devices that use microwave radio waves are used as transmission devices for terrestrial digital broadcasting. Here, TTL devices (TTL lines) are used for communication between a master station transmitting station (playing studio) and a relay transmitting station (transmitting station), or between two different relay transmitting stations, forming a relay network.

[0003] The transmission method in this case is described in, for example, Non-Patent Document 1 and Patent Document 1. Here, there are two types: the TS-TTL method, which demodulates and regenerates the TS multiplexed signal from the received microwave and then transmits it again in the same way as the STL device, and the IF-TTL method, which converts the OFDM (orthogonal multiplexed signal) signal into an IF (Intermediate Frequency) signal without performing such demodulation and regeneration, and transmits it. The latter method is suitable for relay stations used only for relaying, as it has a simple and small device configuration because it does not perform demodulation or regeneration.

[0004] In such an IF transmission method, it is required that the receiving side local signal used when performing frequency conversion on the receiving side is synchronized with the transmitting side local signal used for frequency conversion on the transmitting side. Synchronization methods for this purpose are roughly classified into two types, (1) an independent synchronization method and (2) a dependent synchronization method, as described in, for example, Non-Patent Document 1. In the (1) independent synchronization method, a common external reference signal (e.g., a GNSS: Global Navigation Satellite System signal) that is independent of the transmitted signal and can be used for synchronization is used on the transmitting side and the receiving side. On the other hand, in the dependent synchronization method, a pilot signal synchronized with the transmitting side local signal used when performing frequency conversion on the transmitting side is superimposed on the OFDM signal (a signal corresponding to the data that should be transmitted originally: a main signal) in the transmission signal. On the receiving side, this pilot signal is extracted from the transmission signal, and the receiving side local signal is set to synchronize with this pilot signal. Therefore, in the (1) independent synchronization method, only an OFDM signal is transmitted, whereas in the dependent synchronization method, a pilot signal is multiplexed on the OFDM signal and transmitted. In this case, not only the pilot signal but also a service channel (SC) signal may be multiplexed at the same time. Specific configurations of transmission signals for each of these methods are described in, for example, Non-Patent Document 1.

[0005] 7 is a simplified diagram showing the configuration of a transmitter 80 and a receiver 90 constituting such a slave synchronization type transmission device 9. Here, only components directly related to the above operation are shown. In the transmitter 80, an IF signal (IF) is generated by synthesizing a pilot signal PL generated by a pilot signal oscillator 81 with an OFDM signal (OFDM: main signal) formed by modulating information to be transmitted in a synthesizer 82. In response to this, a local signal (transmitter local signal) LoT generated by a local oscillator (transmitter local oscillator) 83 is mixed in a mixer 84 for frequency conversion, and finally, an RF (Radio Frequency) signal (RF) is generated.

[0006] Fig. 8 shows a simplified frequency arrangement of this RF signal. This configuration is similar to that described in Non-Patent Document 1, and it is assumed here that an SC signal is not used. As shown in the figure, the pilot signal PL is multiplexed so as not to overlap with the OFDM signal, with F0 being the center frequency of the OFDM signal (OFDM) configured in a wide band, and so as to be F0+4 MHz.

[0007] In Fig. 7, the receiver 90 receives this RF signal, separates the pilot signal at RF by a separator 91, and passes it through a bandpass filter (BPF) 92 having a passband corresponding to the pilot signal PL in Fig. 8, thereby extracting it as the pilot signal PL to be used on the receiver 90 side. Meanwhile, a local oscillator (receiving side local oscillator) 93 for converting the RF signal to IF is provided, and the output of the local oscillator and the extracted pilot signal PL are mixed in a mixer 94 to generate a receiving side local signal LoR, which is mixed with the original RF signal by a mixer 95 to generate an IF signal (IF). Here, the strength of the RF signal input to the mixer 95 is adjusted by an AGC (Automatic Gain Control) 96.

[0008] Here, there are two types of (2) slave synchronization methods: (2-1) standard slave synchronization method and (2-2) low-noise slave synchronization method. On the transmitting side, phase noise is added to the OFDM signal relative to an ideal signal. When the phase noise added to the OFDM signal and the pilot signal is equivalent, the phase noise in the receiving local signal LoR synchronized with the pilot signal can be made to be in opposite phase to the phase noise in the OFDM signal. Therefore, the advantage of the slave synchronization method is that the phase noise in the IF after conversion (the output of the mixer 95 in FIG. 7) can be compressed using the receiving local signal LoR. In this respect, the low-noise slave synchronization method is superior to the standard slave synchronization method or even to the independent synchronization method.

[0009] However, this situation depends on the extraction band of the pilot signal on the receiving side (the transmission band of the BPF 92 in FIG. 7), and the above-mentioned effect cannot be obtained for phase noise outside this extraction band. Therefore, in the (2-2) low-noise slave synchronization method, the above-mentioned effect is particularly large when the extraction band is set sufficiently wide.

[0010] As described above, it is possible to reduce the effect of phase noise in the OFDM signal at the receiving side. However, there is another noise component, thermal noise. This thermal noise is random, and its power is proportional to the bandwidth. If the thermal noise per unit bandwidth at the receiving side is n0 [W / Hz], then the total power of the OFDM signal is P ofdm [W], the bandwidth of the OFDM signal is B [Hz], and the level of the pilot signal is P pl The C / N ratio (C / N) of the OFDM signal input to the mixer on the receiving side is expressed as [W] and the bandwidth of the pilot signal is b [Hz]. ofdm , C / N ratio of the receiving local signal (C / N) local are given by the following equations (1) and (2), respectively, and the overall C / N ratio (C / N) on the receiving side is total is given by the following equation (3).

[0011]

number

[0012] The denominator in equation (3) is (1+(C / N) ofdm / (C / N) local ) corresponds to the increase in thermal noise at the receiving end. Let the increase in dB be X, and X is given by the following equation (4).

[0013]

number

[0014] That is, by widening the bandwidth b of the pilot signal, the thermal noise becomes larger. This is the opposite relationship to the phase noise mentioned above. Furthermore, as described in the above-mentioned Non-Patent Document 1, in IF-TTL, in addition to the pilot signal, an SC (service channel) signal may also be multiplexed onto the OFDM signal. In this way, when multiple types of signals other than the OFDM signal (main signal) are multiplexed, it is possible to generalize the above and set the index corresponding to each type of component other than the OFDM signal as i, and the level of the corresponding component as P. i Then, the total power P and the OFDM power P ofdm The relationship between these is as shown in equation (5) below, and Y, which is expressed in dB like X, is as shown in equation (6). Here, each component identified by i includes the pilot signal and SC signal, and is generalized here to include other components as well.

[0015]

number

[0016] This Y is the degree of increase in thermal noise. The sum (X+Y) of the above X (equation (4)) and Y (equation (6)) is the noise increase coefficient z, which indicates the increase in noise on the receiving side, and is taken into consideration when designing a line by adding it to the thermal noise of the receiver. The specifications of the pilot signals and SC signals in the above three types of transmission methods are described in Non-Patent Document 1, and FIG. 9 is a table showing part of the contents. As described above, in the low noise slave synchronization method, the phase noise can be compressed by setting the extraction band of the pilot signal wide.

[0017] Also, as described in the Information and Communications Council's report on consultation No. 110, "Technical conditions for digital STL / TTL," also described in Non-Patent Document 1, when a target value for total noise (C / N) is set, the allocation of each noise component can be set accordingly. Figure 10 shows an example of this allocation when the total noise (C / N) is set to 37.6 dB. The local noise shown here is related to the compression of the phase noise, and the thermal noise is related to the noise increase factor.

[0018] In addition, such noise component allocation must be considered between the parent station transmitter and the final user's television receiver. This point is also described in Non-Patent Document 1, where the threshold C / N is defined as the C / N when fading occurs in the TTL section (received power decreases) and the C / N deteriorates, causing the broadcasting system to go down. In terms of system design, it is required to set this threshold C / N to an appropriate value based on appropriate grounds, and the noise components are allocated in this case as well. This threshold C / N is set based on a rational criterion, and for example, this criterion can be "when fading does not occur in the broadcasting area, the interference and multipath noise is smaller than the allocated value, and the C / N is 22 dB at the receiver located at the boundary of half the area of ​​the area." The table in FIG. 11 shows the allocation of noise (C / N) in this case when the target area is divided into four types according to their size. Here, the transmission line noise becomes the threshold C / N for TTL, and the value is 28 dB.

[0019] When the threshold C / N is set in this way, the margin for this becomes an issue, and in line design, the difference between the C / N of thermal noise in a steady state and this threshold C / N is defined as the fading margin corresponding to this margin. The C / N of thermal noise used here ((C / N) NF ) is the level of the received electric field P in [dBm], Boltzmann's constant k [J / K], temperature T [K], noise figure w, and the noise increase factor z are given by the following equation (7).

[0020]

number

[0021] That is, when calculating the fading margin, it is not the local noise (phase noise) but the thermal noise that is the problem. Or, in a situation where fading occurs, the thermal noise, not the phase noise, becomes dominant. In this case, according to equation (7), in addition to the original thermal noise component (log component), the noise increase factor z is added in the low noise slave synchronization method, so the amount (C / N) NF becomes smaller, and the fading margin decreases.

[0022] Moreover, the calculation of the fading margin as described above is premised on the assumption that the electric field strength of the entire carrier wave is uniformly attenuated when the reception strength is low. However, in reality, there are cases where the electric field strength drops only in a specific frequency band (frequency selective fading). When this frequency selective fading occurs in the range of the OFDM signal having a wide band in FIG. 8, only partial subcarrier attenuation occurs, and if this effect is compensated for by other subcarriers, the substantial deterioration of the reception characteristics due to this is small. However, when such frequency selective fading occurs in a pilot signal having a narrower band than this, the pilot signal cannot be recognized normally on the receiver side, so that the IF signal cannot be generated properly even if no abnormality occurs in the band of the OFDM signal. Such a problem does not occur in the independent synchronization method that does not use a pilot signal.

[0023] For this reason, the independent synchronization method is preferable in situations where fading is likely to occur (where the received electric field strength is likely to decrease).Also, the independent synchronization method does not use a pilot signal, so problems caused by the pilot signal do not occur, and is therefore preferable in environments where problems caused by the pilot signal do occur. [Prior art documents] [Non-patent literature]

[0024] [Non-Patent Document 1] ARIB STD-B22 Digital STL / TTL transmission method for terrestrial digital broadcasting [Patent documents]

[0025] [Patent Document 1] International Publication WO2018 / 159411 DISCLOSURE OF THEINVENTION [Problem to be solved by the invention]

[0026] In the low noise slave synchronization system, while the objective of compressing the phase noise was achieved, the fading margin was reduced due to the noise rise factor z. The noise rise factor z becomes large when the bandwidth b of the pilot signal is wide, as shown by X (equation (4)). On the other hand, the original objective of the low noise slave synchronization system is to compress the phase noise by widening the bandwidth b, and narrowing the bandwidth b makes it difficult to compress the phase noise. In other words, in the conventional low noise slave synchronization system, there is a trade-off between reducing the thermal noise and compressing the phase noise, and for this reason, it was difficult to reduce the overall effect of noise, especially under conditions where the receiving electric field is weakened (where fading occurs).

[0027] For this reason, there has been a demand for a transmission device that reduces the effects of noise even when the receiving strength is low.

[0028] The present invention has been made in view of the above circumstances, and has an object to solve the above problems. [Means for solving the problem]

[0029] The transmission device of the present invention is a transmission device that uses an IF transmission system, in which a transmission signal having a configuration in which a pilot signal is multiplexed on a main signal is emitted from a transmitter to a receiver, and the receiver operates in a low noise slave synchronization system that compresses phase noise in the transmission signal by using the pilot signal extracted from the transmission signal when performing frequency conversion of the received transmission signal, and when the reception strength of the transmission signal is high, the receiver compresses the phase noise. doA first operation of performing the frequency conversion in the low noise slave synchronization method is performed, and when the reception strength is low, The above The effect of phase noise suppression This is a lower noise slave synchronization method. A second operation of performing the frequency conversion in a different manner is performed. In the transmission device of the present invention, the receiver may extract the pilot signal from the received transmission signal using a bandpass filter that transmits the pilot signal, and in the first operation, a first bandpass filter may be used as the bandpass filter, and in the second operation, a second bandpass filter having a narrower transmission band than the first bandpass filter may be used as the bandpass filter. In the transmission device of the present invention, a transmitting side local signal used when generating the transmission signal by frequency conversion in the transmitter is generated so as to be synchronized with an external reference signal, and the receiver, in the second operation, may perform an operation of an independent synchronization method in which the frequency conversion is performed using a receiving side local signal synchronized with the transmitting side local signal by being generated using an external reference signal that is common to the external reference signal used in the transmitter. In the transmission device of the present invention, the receiver may switch from the first operation to the second operation when the receiving strength becomes lower from a high state based on a threshold, and may switch from the second operation to the first operation when the receiving strength becomes higher from a low state based on the threshold and it is recognized that the change in the receiving state of the transmission signal at the receiver is small for a certain period of time. A transmission device of the present invention is a transmission device that uses an IF transmission method, in which a transmission signal having a configuration in which a pilot signal is multiplexed onto a main signal is emitted from a transmitter to a receiver, and when the receiver performs frequency conversion of the received transmission signal, operates with a low noise slave synchronization method in which phase noise in the transmission signal is compressed using the pilot signal extracted from the transmission signal, in which the transmitter emits the transmission signal in which a first pilot signal and a second pilot signal having different frequencies are multiplexed onto the main signal as the pilot signals, and the receiver extracts the first pilot signal and the second pilot signal from the transmission signal, generates a first receiving side local signal from the first pilot signal and a second receiving side local signal from the second pilot signal, and performs the frequency conversion using a mixed local signal obtained by mixing the first receiving side local signal and the second receiving side local signal. Effect of the Invention

[0030] According to the present invention, a transmission device can be obtained in which the influence of noise is reduced even when the reception strength is low. [Brief description of the drawings]

[0031] [Figure 1] FIG. 2 is a diagram illustrating a configuration of a receiver in a transmission device according to a first embodiment of the present invention. [Diagram 2] 4A to 4C are diagrams illustrating noise conditions before and after a switching operation in a transmission device according to a first embodiment of the present invention. [Diagram 3] FIG. 11 is a diagram illustrating configurations of a transmitter and a receiver in a transmission device according to a second embodiment of the present invention. [Figure 4] 5 is a flowchart showing an example of the operation of a receiver in the transmission device according to the first and second embodiments of the present invention. [Diagram 5] 13 is an example of a frequency arrangement of a transmission signal used in a transmission device according to a third embodiment of the present invention. [Figure 6] FIG. 11 is a diagram illustrating configurations of a transmitter and a receiver in a transmission device according to a third embodiment of the present invention. [Figure 7] FIG. 1 is a diagram illustrating an example of a configuration of a transmitter and a receiver in a conventional transmission device that operates in a slave synchronization system. [Figure 8] 2 is an example of a frequency arrangement of a transmission signal used in a conventional transmission device that operates in a slave synchronization system. [Figure 9] 1 is a table showing specifications of pilot signals and service channel (SC) signals in the independent synchronization method, the standard slave synchronization method, and the low noise slave synchronization method described in Non-Patent Document 1. [Figure 10] This is an example of the distribution of each noise component when a target value for total noise (C / N) is set, as described in the Information and Communications Council's report on consultation No. 110, "Technical conditions for STL / TTL in digital systems." [Figure 11] This is an example of the distribution of noise components when four types of areas are set.

[0032] Next, a transmission device according to an embodiment of the present invention will be specifically described. This transmission device operates in accordance with the IF-TTL method and the low noise slave synchronization method. For this reason, in this transmission device, as described above, a pilot signal is added to the OFDM signal (main signal), which is the original signal to be transmitted, and used as a transmission signal (RF signal). This pilot signal is used to generate a receiving-side local signal that is used when frequency-converting (down-converting) the received RF signal to an IF signal. As a result, frequency conversion is performed so that the phase noise and the phase noise in the OFDM signal cancel each other out.

[0033] However, as mentioned above, there is a trade-off between reducing thermal noise and suppressing phase noise, so in the past it was difficult to reduce the effects of noise overall. In contrast, in the present invention, the effects of noise are reduced overall by reducing them particularly when the reception strength is low, using the configuration described below. In each of the embodiments described below, the purpose of such operations is the same, but the operations or configurations performed to achieve this purpose are different.

[0034] (First embodiment) The transmission device 1 according to the first embodiment always operates in a slave synchronization system, and two types of bands of pilot signals used on the receiving side are set. FIG. 1 is a diagram showing the configuration of a receiver 10 in this transmission device 1. The transmitter used here is the same as the transmitter 80 in the conventional transmission device 9 shown in FIG. 7, and therefore its description is omitted. Therefore, the frequency arrangement of the transmission signal (RF signal) used here is also the same as that shown in FIG. 8.

[0035] In the receiver 10, the separator 11, the local oscillator (receiving side local oscillator) 13, the mixers 14 and 15, and the AGC 16 are similar to the separator 91, the local oscillator (receiving side local oscillator) 93, the mixers 94 and 95, and the AGC 96 in the receiver 90. Here, like the receiver 90, the band of the pilot signal PL input to the mixer 14 is limited by a BPF (band pass filter), but for this purpose, a BPF 12A with a wide bandwidth and a BPF 12B with a narrow bandwidth are provided, which are switched by a switch 171. If the pilot signal that has passed through the BPF 12A is PL1 and the pilot signal that has passed through the BPF 12B is PL2, either PL1 or PL2 is selected by the switch 171 to become the pilot signal PL, and this pilot signal PL is used to generate the receiving side local signal LoR. The switching operation in the switch 171 is performed according to the reception strength of the RF signal. The detector 182 detects a part of the RF signal branched off by the separator 181, and the switching control unit 172 detects the reception electric field P in Here, the wide-bandwidth BPF 12A corresponds to a standard low-noise slave synchronization method, and PL1 is equal to PL in FIG. 7. Here, when the received electric field reaches a certain value (switching threshold P SW ), the switching control unit 172 switches the switch 171 so as to select BPF 12B(PL2) from BPF 12A(PL1).

[0036] An example of this switching operation will be described below when the threshold C / N is 28 dB as shown in Fig. 11. According to equation (4), the noise increase coefficient is determined according to the bandwidth (BPF bandwidth) b of the pilot signal, and is set to 4.5 dB when BPF 12A with a wide bandwidth is used, and 0 dB when BPF 12B with a narrow bandwidth is used. That is, according to equation (7), by switching from the normal state using BPF 12A to BPF 12B, the thermal noise C / N of the local signal in receiver 10 ((C / N) Lo ) is improved by 4.5 dB. in However, when this switching is performed, the receiving electric field P SW Then, from equation (7), the following equation (8) is established.

[0037]

number

[0038] In this case, T is 298K (25℃), B=6MHz, w=4, and (C / N) when using BPF12A or BPF12B Lo If is 35 dB, P SW is -71.5dBm. in This P SW If you do not want to switch (C / N) Lo The receiving electric field P at which the threshold C / N (=28dB) is reached in is -74.1dB, while when switching is performed, in is -78.6 dB. In other words, this difference of 4.5 dB is the increase in the fading margin. Figure 2 shows this situation (left: before switching, right: after switching) in schematic form. In other words, the fading margin improves by the amount of the change in the noise rise factor due to switching.

[0039] In other words, by using such a receiver 10 and switching the bandwidth of the pilot signal according to the level of the received electric field, the received electric field P inIn high-noise conditions, a low-noise slave synchronization method is used, while the receiving electric field P in In a situation where the fading margin is low, the influence of thermal noise, which is dominant in this situation, can be reduced by switching the BPF, thereby maintaining a high fading margin.

[0040] (Second embodiment) In the transmission device 2 according to the second embodiment, the reception electric field P in and the switching threshold P SW The bandwidth of the BPF is changed according to the magnitude relationship of the , and the method (low noise dependent synchronization method, independent synchronization method) is switched according to these magnitude relationships. This configuration is preferable when the fading situation makes it easy for problems caused by pilot signals to occur on the receiving side.

[0041] 3 is a diagram showing the configurations of a transmitter 20 and a receiver 30 in a transmission device 2. Unlike the case of the transmission device 1, the configuration of the transmitter 20 is different from that of the transmitter 80 in the conventional transmission device 9, and so the configurations of the transmitter 20 and the receiver 30 are shown here. The pilot signal oscillator 21, the combiner 22, and the mixer 24 in this transmitter 20 are similar to the pilot signal oscillator 81, the combiner 82, and the mixer 84 in the transmitter 80, respectively. Therefore, the RF signal and the IF signal used here are also configured by multiplexing a pilot signal PL onto an OFDM signal (OFDM) as in the case shown in FIG.

[0042] However, the local oscillator (transmission side local oscillator) 231 used to convert the IF signal to an RF signal is set to synchronize with an external reference signal (e.g., a GNSS signal) used in a normal independent synchronization method, and for this purpose, an external reference signal acquisition unit 232 for acquiring this external signal is provided. Therefore, the transmission side local signal LoT2 used here is synchronized with the external reference signal. This allows the transmission device 2 to operate as a slave synchronization method (low noise slave synchronization method) and also as a separate synchronization method.

[0043] In the receiver 30 of FIG. 3, the separator 31, the BPF 32, the mixers 34 and 35, and the AGC 36 are the same as the separator 91, the BPF 92, the mixers 94 and 95, and the AGC 96 in the receiver 90. The BPF 32 has a wide transmission band corresponding to the low noise slave synchronization method. The first local oscillator 33 used here is the same as the local oscillator (receiving side local oscillator) 93 in the receiver 90. Therefore, the pilot signal is separated from the RF signal received by the receiver 30 by the separator 31 and passed through the BPF 32, whereby the pilot signal PL used on the receiver 30 side is extracted, and the first receiving side local signal LoR1 is generated using this pilot signal PL. This first receiving side local signal LoR1 is equal to the receiving side local signal LoR in FIG. 7. Therefore, an IF signal (OFDM signal) can be obtained by the low noise slave synchronization method using this first receiving side local signal LoR1.

[0044] Meanwhile, in this receiver 30, a second local oscillator 371 is also provided in addition to the first local oscillator 33. The second local oscillator 371 corresponds to the local oscillator (transmission side local oscillator) 231 on the transmitter 20 side, and is set to synchronize with an external reference signal common to the external reference signal used on the transmitter 20 side, and therefore an external reference signal acquisition unit 372 for acquiring this external signal is provided. Since the second reception side local signal LoR2 generated by the second local oscillator 371 is synchronized with the local signal LoT2 on the transmitter 20 side via the external reference signal, it is not necessary to use a pilot signal in this case. The operation of generating the second reception side local signal LoR2 in this way and performing frequency conversion using this as the reception side local signal LoR is similar to the normal independent synchronization method.

[0045] For this reason, this receiver 30 switches between two types of operation: a normal low-noise slave synchronization system operation and a normal independent synchronization system operation. For this switching operation, a switch 381 is provided that selects either LoR1 or LoR2 to set it as LoR. This switching operation in the switch 381 is performed by a detector 392 detecting a part of the signal that is branched off by a separator 391 from the pilot signal that has passed through the BPF 32 and been generated, and a switching control unit 382 detecting the reception electric field P in That is, the switching control unit 382 controls the reception electric field P in When is large (P in ≧P SW ), select LoR1 and receive signal strength P in When is small (P in <P SW ), the receiver 30 operates to select LoR2. in When the receiving electric field P in When the influence of thermal noise becomes large because the signal is small, the system operates in a detached synchronization mode without using a pilot signal.

[0046] This operation is due to the receiving electric field P in This is particularly preferable when frequency selective fading is likely to occur when θ is small, and problems due to the pilot signal, such as the loss of the pilot signal, are likely to occur.

[0047] The operation of the switching control unit 172 (switch 171) in the receiver 10 and the switching control unit 382 (switch 381) in the receiver 30 is performed in accordance with the reception electric field P in For this reason, both of the receivers 10 and 30 described above perform the normal low-noise slave synchronization system operation (first operation) when the reception strength is high, and perform another system operation (second operation) different from the normal low-noise slave synchronization system and having a smaller phase noise compression effect than the normal low-noise slave synchronization system when the reception strength is low. The switching between the first operation and the second operation is performed according to the reception electric field P in Size (P SWHowever, in a situation where fading occurs, the received electric field P in Since the received electric field P often fluctuates drastically in a short period of time, in and P SW If the switching is performed based only on the simple magnitude relationship with the first operation, the switching may be inappropriate. For this reason, if the reception strength drops from the normal (high) state when the reception strength is in the first operation, it is preferable to switch quickly to the second state, but if the reception strength increases from this state, it is preferable not to switch to the first state immediately, but to switch to the first state when it is recognized that the reception state is good for a certain period of time.

[0048] 4 is a flowchart showing an example of the operation of the switching control unit 172 (switching control unit 382). Here, for the above operation, the detector 182 (detector 392) detects the received electric field P in In addition to recognizing the time rate of change of the control voltage in the AGC16 (AGC36), α is used. The absolute value of α corresponds to the intensity of fluctuations in the reception conditions.

[0049] Here, the state in which the receiver operates in the normal low noise standard synchronization method (first operation) is defined as a standard setting (a state in which the switch 171 is connected to the PL1 (BPF 12A) side in the receiver 10, and a state in which the switch 381 is connected to the LoR1 side in the receiver 30), and the state in which the receiver operates in the second operation is defined as a non-standard setting (a state in which the switch 171 is connected to the PL2 (BPF 12B) side in the receiver 10, and a state in which the switch 381 is connected to the LoR2 side in the receiver 30). Below, the operation of the switch control unit 172 in the receiver 10 will be described, but the operation of the switch control unit 382 in the receiver 30 is similar.

[0050] In FIG. 4, first, the switching control unit 172 sets the switch 171 to the PL1 (BPF 12A) side as an initial state (standard setting (S1)). Next, the switching control unit 172 detects the reception electric field P in Recognizing that, in <PSW If so (S2: Yes), the switch 171 is switched to the PL2 (BPF12B) side (non-standard setting (S3)). This determination (S2) can be performed, for example, at a short constant interval. in ≧P SW If so, the reception is deemed to be good and the standard state is maintained.

[0051] When the non-standard settings are selected (S3), the switching control unit 172 subsequently determines whether or not to change this state (whether or not to return to the standard settings). To this end, the switching control unit 172 starts monitoring the time rate of change α of the control voltage in the AGC 16 (S4). Next, the switching control unit 172 determines whether the absolute value of α (|α|) is greater than or equal to a certain threshold value α0 during a predetermined period (X seconds) (S5). Here, if |α|≦α0 at all times during this period (S5: No), it is considered that the change in the reception state during this period is small, so the next step is to switch back to the standard settings. in and P SW The magnitude relationship between P in ≧P SW If so (S6: No), it is considered that there was no sudden change in the reception state and the reception state was stable and good for X seconds, so the switching control unit 172 returns the switch 171 to the standard setting again (S7), thereby returning to the initial state (S1).

[0052] If |α|>α0 during X seconds (S5: Yes), the reception state during this period is recognized as unstable, and it is not preferable to immediately return to the standard setting. Therefore, the switching control unit 172 again determines whether |α| is larger than α0 during the next X seconds (S8). Here, if |α|≦α0 during this period (S8: No), it is considered that the reception state has gradually recovered, and the switching control unit 172 returns the switch 171 to the standard setting again (S7), as in the above case.

[0053] If |α|>α0 in the next X seconds (S8: Yes), the switching control unit 172 constantly switches to P in≧P SW It is determined whether or not the in ≧P SW If so (S9: Yes), P in Since it is considered that the high state of P has been maintained for a long period of time, the switching control unit 172 returns the switch 171 to the standard setting again (S7), regardless of the value of α. in <P SW If there is a case where this is the case (S9: No), the magnitude relationship between |α| and α0 for X seconds is judged again (S8), and the above operation is repeated.

[0054] According to the above operation, if the reception state deteriorates (S2: Yes), the setting is immediately switched to the non-standard setting (S3), whereas the setting is switched from the non-standard setting to the standard setting only when a good reception state continues for a certain period (X seconds, Y seconds) (S5: No, S8: No, S9: Yes). This allows the transmission devices 1 and 2 to operate stably even in conditions where fading is likely to occur. Note that the flowchart in Fig. 4 is an example of such an operation, and the criteria for determining whether the reception state was good for a certain period can be set appropriately.

[0055] (Third embodiment) The transmission device 3 according to the third embodiment always operates in a low noise slave synchronization system, and does not switch signals according to the situation, as in the transmission device 1 (receiving device 10) and the transmission device 2 (receiving device 30). In this transmission device 3, two types of pilot signals are simultaneously added to the OFDM signal in the transmitter 40. FIG. 5 shows the frequency arrangement of the RF signal in this case in correspondence with FIG. 8. Here, one pilot signal (first pilot signal PLA) is the same as the pilot signal PL in FIG. 8, and its center frequency is F0+4 MHz. In contrast, the other pilot signal (second pilot signal PLB) is set to a position symmetrical to the first pilot signal PLA in FIG. 5, and its center frequency is F0-4 MHz.

[0056] 6 is a diagram showing the configuration of this transmission device 3 (transmitter 40, receiver 50). The local oscillator (transmission side local oscillator) 43 and mixer 44 in the transmitter 40 are similar to the local oscillator (transmission side local oscillator) 83 and mixer 84 in the transmitter 80, and they also generate an RF signal from an IF signal.

[0057] However, in this transmitter 40, a first pilot signal oscillator 41A for oscillating a first pilot signal PLA and a second pilot signal oscillator 41B for oscillating a second pilot signal PLB are used simultaneously, and the first pilot signal PLA and the second pilot signal PLB are multiplexed into an OFDM signal by a combiner 42 to generate a signal with a frequency arrangement corresponding to that shown in Fig. 5, which is then converted into an RF signal. A common phase noise is superimposed on the first pilot signal PLA and the second pilot signal PLB. For this reason, the phase noise can be compressed on the receiving side by using these signals in the operation of the low noise slave synchronization method.

[0058] Receiver 50 receives this RF signal and recognizes the first pilot signal PLA and the second pilot signal PLB from this RF signal. For this purpose, BPF 52A having a band corresponding to the first pilot signal PLA in Fig. 5 and BPF 52B having a band corresponding to the second pilot signal PLB are provided, and the RF signal is split by separator 51 into the respective systems to which these are provided. BPF 52A, which passes first pilot signal PLA, is the same as BPF 92 in Fig. 7. The transmission bandwidths of BPFs 52A and 52B are set to be sufficiently wide in accordance with the low noise slave synchronization method.

[0059] 7, the receiver 50 generates a first receiver local signal LoRA using the first pilot signal PLA, first local oscillator 53A, and mixer 54A, and generates a second receiver local signal LoRB using the second pilot signal PLB, second local oscillator 53B, and mixer 54B. The first local oscillator 53A and second local oscillator 53B are independent.

[0060] The mixer 55 and the AGC 56 in the receiver 50 are similar to the mixer 95 and the AGC 96 in Fig. 7. However, here, the receiver local signal LoR used to convert the RF signal into an IF signal in the mixer 55 is a mixed local signal LoRM generated by combining the first receiver local signal LoRA and the second receiver local signal LoRB in a combiner 57.

[0061] Since such a mixed local signal LoRM has the same phase noise as an OFDM signal superimposed thereon, the mixer 55 can compress this phase noise in the same manner as the receiver 90 in Fig. 7. That is, the operation in this case also becomes the low noise slave synchronization method. In this case, even if either the first pilot signal PLA or the second pilot signal PLB is lost due to frequency selective fading when the RF signal is transmitted from the transmitter 40 side to the receiver 50 side, the mixed local signal LoRM in Fig. 6 can be obtained, and the operation of the low noise slave synchronization method becomes possible. Particularly, in this case, unlike the transmission devices 1 and 2 described above, no switching operation is required on the receiver 50 side.

[0062] The present invention has been described above based on an embodiment. This embodiment is merely an example, and it will be understood by those skilled in the art that various modifications are possible in the combination of the respective components, and that such modifications are also within the scope of the present invention. [Explanation of symbols]

[0063] 1, 2, 3, 9 Transmission equipment 10, 30, 50, 90 Receiver 11, 31, 91, 181, 391 separator 12A BPF (Bandpass Filter: 1st Bandpass Filter) 12B BPF (Bandpass Filter: Second Bandpass Filter) 13, 93 Local oscillator (receiver local oscillator) 14, 15, 24, 34, 35, 44, 54A, 54B, 55, 84, 94, 95 Mixer 16, 36, 56, 96 AGC 20, 40, 80 Transmitter 21, 81 Pilot signal oscillator 22, 42, 57, 82 synthesizer 32, 52A, 52B, 92 BPF (Bandpass Filter) 33, 53A First local oscillator 41A First pilot signal oscillator 41B Second pilot signal oscillator 43, 83, 231 local oscillator (transmitter local oscillator) 53B, 371 Second local oscillator 171, 381 Switch 172, 382 Switching control section 182, 392 detector 232, 372 External reference signal acquisition unit LoR Receiver local signal LoR1 First receiver local signal LoR2 Second receiver local signal LoRM Mixed Local Signal LoT, LoT2 Transmitter local signal PL Pilot signal PLA 1st pilot signal PLB Second Pilot Signal

Claims

1. A transmission device that operates using a low noise slave synchronization method in which an IF transmission method is used, a transmission signal having a configuration in which a pilot signal is multiplexed on a main signal is emitted from a transmitter to a receiver, and when the receiver performs frequency conversion of the received transmission signal, the receiver compresses phase noise in the transmission signal by using the pilot signal extracted from the transmission signal, The receiver includes: performing a first operation of performing the frequency conversion using the low noise slave synchronization method for compressing the phase noise when the reception strength of the transmission signal is high; performing a second operation of performing the frequency conversion by another method in which the effect of suppressing the phase noise is lower than that of the low noise slave synchronization method when the reception strength is low; A transmission device comprising:

2. The receiver extracts the pilot signal from the received transmission signal using a bandpass filter that transmits the pilot signal; In the first operation, a first band-pass filter is used as the band-pass filter; 2. The transmission device according to claim 1, wherein in the second operation, a second bandpass filter having a narrower transmission band than the first bandpass filter is used as the bandpass filter.

3. a transmitter local signal used in generating the transmission signal by frequency conversion in the transmitter is generated so as to be synchronized with an external reference signal; 2. The transmission device according to claim 1, wherein in the second operation, the receiver performs an operation of an independent synchronization method in which the frequency conversion is performed using a receiving-side local signal that is synchronized with the transmitting-side local signal by generating the receiving-side local signal using the external reference signal that is common to the external reference signal used in the transmitter.

4. The receiver includes: switching from the first operation to the second operation when the reception strength becomes lower than a threshold value; switching from the second operation to the first operation when it is determined that the reception strength becomes high from a low state based on the threshold and the change in the reception state of the transmission signal in the receiver is small for a certain period of time; 4. The transmission device according to claim 1, wherein the first and second inputs are connected to the first and second inputs.

5. A transmission device that operates using a low noise slave synchronization method in which an IF transmission method is used, a transmission signal having a configuration in which a pilot signal is multiplexed on a main signal is emitted from a transmitter to a receiver, and when the receiver performs frequency conversion of the received transmission signal, the receiver compresses phase noise in the transmission signal by using the pilot signal extracted from the transmission signal, the transmitter emits the transmission signal in which a first pilot signal and a second pilot signal having different frequencies are multiplexed onto the main signal as the pilot signals; a first receiving side local signal from the first pilot signal and a second receiving side local signal from the second pilot signal, and a mixed local signal obtained by mixing the first receiving side local signal and the second receiving side local signal is used to perform the frequency conversion.

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