JPH11355209A - Light analog transmitter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light analog transmitter which does not deteriorate a carrier to noise ratio(CNR) of an intermediate frequency signal when a laser is directly modulated by a signal, which is the combines of an intermediate frequency signal and an unmodulated wave signal, and is transmitted to the transmitter from a transmission terminal station. SOLUTION: This device is a light analog transmitter which is equipped with a combining means 6 which combines an intermediate frequency signal modulated by information to be transmitted and an unmodulated wave signal being a sine wave, and a means 7 for subjecting the combined signal to electrical to optical conversion by direct modulation of a semiconductor laser diode with a resonance frequency fr and transmitting the result to an optical fiber 3. In this case, the condition that the frequency fIF of the intermediate frequency signal and the frequency fL0 of the unmodulated wave signal satisfy the conditions fL0 -fIF>=1 [GHz] and 2fIF<fL0 <(2/3).fr.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical analog transmission device for transmitting a high-frequency signal such as a radio signal using an optical fiber.

[0002]

2. Description of the Related Art With the development of mobile communication in recent years, there has been a demand for an expansion of a radio communication service area. In order to make effective use of radio frequency resources and to reduce the cost of radio base equipment, Each wireless zone (cell)
, And instead, a large number of wireless zones are arranged at high density. This is called picocellization of the wireless zone. To realize picocelling, a wireless communication base station configuration in which a transmitting device and a transmitting terminal are connected by an optical fiber has been considered.

That is, a radio base station includes a transmitting terminal station and a transmitting device. A plurality of transmitting devices per transmitting terminal station are provided, and each transmitting device reduces the output to reduce the cost. Each transmitting terminal transmits a transmission signal received from the transmitting terminal.

[0004] The transmitting apparatus is mainly composed of an antenna unit, and is arranged in each cell. The transmitting terminal station includes a modulator and a demodulator and a controller corresponding to a plurality of transmitting devices of each cell. Then, the wireless information signal is optically analog-transmitted via the optical fiber between the transmitting device and the transmitting terminal. With this configuration, the transmission device can be simplified and downsized, and a large number of cells can be provided by one wireless communication base station.

In the optical analog transmission, an electric / optical converter (E / O converter) is used to convert an electric signal (wireless information signal) to be transmitted into an optical signal. As the E / O conversion means, a means for modulating the output light of the semiconductor laser element with a radio information signal and outputting the modulated light is used as a method of directly modulating the semiconductor laser element or an external light modulation. Any of the modulation methods by the modulator is adopted.

Comparing the superiority of these two methods, direct modulation of the laser element is superior in consideration of the modulation distortion characteristics, device scale, device cost, and the like. But,
Technology trends show that the trend toward higher frequencies, such as the shift of the carrier frequency to the 2 [GHz] to 5 [GHz] band with the increase in the capacity of radio frequency signals, is becoming clearer.
A distributed feedback laser device (DFB-L
In D), the modulation frequency region where the modulation distortion is relatively small is
It is at most 2-3 [GHz] or less. Therefore, direct modulation of the laser element by the radio frequency signal is becoming difficult.

Therefore, as shown in, for example, Japanese Patent Application Laid-Open No. 6-164427, an intermediate frequency signal modulated by an information signal and a radio modulation wave signal which is a sine wave are superimposed and transmitted from a transmitting terminal to a transmitting apparatus. A method such as optical analog transmission has been proposed.

[0008] The transmission system proposed in this publication is a system in which a transmitting device performs frequency conversion of an intermediate frequency signal with a multiplied wave obtained by multiplying a received unmodulated wave signal to obtain a radio frequency signal. . However, the laser element to be used is intended to be used in a low frequency band portion having excellent modulation distortion characteristics, and is characterized by superimposing an unmodulated wave signal near a frequency of an intermediate frequency signal.

According to the embodiment described in the above publication, as shown in FIG. 12, a 300 [MHz] unmodulated wave signal is superimposed on a 200 [MHz] band intermediate frequency signal. . In the case of this method, in order to secure the noise characteristics of the radio frequency signal and improve the quality of the frequency stability, the transmitting apparatus side needs to perform CNR (Carrier-to-Carrier) of the received intermediate frequency signal and the unmodulated wave signal. Noise Ratio (carrier to noise ratio) must be high. That is, the noise level must be low.

However, in a frequency band near the unmodulated wave signal, RIN (Relative Intensity Noise: Relative Intensity Noise) increases. If placed near the band, CNR degradation will occur.

For example, FIG. 13 shows a result obtained by an experiment conducted by the inventors of the present invention. The intermediate frequency signal band is set to 500 [MHz],
In the case where the unmodulated wave signal band is set to 550 [MHz], as shown in FIG. 13, the RIN characteristic is remarkably increased according to the modulation degree of the unmodulated wave signal, especially when the modulation degree is 15% or more. You can see that it has deteriorated. Therefore, the communication quality of the radio frequency signal is greatly deteriorated.

[0012]

When an optical fiber is used to transmit a wireless modulation wave signal by light, an optical signal of the wireless modulation wave signal is obtained by directly modulating a laser element with the wireless modulation wave signal. However, due to the characteristics of the laser device, the usable frequency range is at most 2-3 [GH].
z].

However, in recent years, it has been required to use optical transmission in a frequency band higher than that, so that direct modulation of a laser element cannot be used. Therefore, a method has been proposed in which a transmitting apparatus performs frequency conversion of an intermediate frequency signal with a multiplied wave obtained by multiplying a received unmodulated wave signal to obtain a radio frequency signal.

However, in the case of the proposed method, when the intermediate frequency signal and the unmodulated wave signal are multiplexed, converted into an optical signal by direct modulation of a semiconductor laser, and sent to an optical fiber for transmission, an optical analog transmission is performed. When the frequency bands of the intermediate frequency signal and the unmodulated wave signal are close to each other, there is a problem that the CNR of each signal deteriorates due to an increase in RIN.

In particular, when the degree of modulation of the unmodulated wave signal increases, the increase in RIN is remarkable. Therefore, the radio frequency signal generated by converting the frequency of the intermediate frequency signal using the unmodulated wave signal has much noise and the transmission characteristics are deteriorated. Also, by transmitting a radio frequency signal containing a lot of noise, other radio frequency signals are affected by the noise, and other radio communication is interrupted. Therefore, it is required to solve such a problem.

Therefore, the object of the present invention is to:
When the laser is directly modulated and optical analog transmission is performed by combining the intermediate frequency signal and the unmodulated wave signal, the CNR of the intermediate frequency signal is not deteriorated even if the modulation degree of the unmodulated wave signal is increased. Another object of the present invention is to provide an optical analog transmission device capable of generating a radio frequency signal having excellent noise characteristics by transmitting an intermediate frequency signal and an unmodulated wave signal having excellent CNR to a transmission device.

[0017]

In order to achieve the above object, the present invention is configured as follows. That is, [1] The optical analog transmission apparatus according to the first present invention (first claim) combines an intermediate frequency signal modulated with information to be transmitted and an unmodulated wave signal that is a sine wave. Means for converting the multiplexed signal into electrical / optical signals by direct modulation of a semiconductor laser element having a resonance frequency fr and transmitting the converted signal to an optical fiber for downlink. Is fr, the frequency f _IF of the intermediate frequency signal and the frequency f _LO of the unmodulated wave signal are f _LO
−f _IF ≧ 1 [GHz] and 2f _IF <f _LO <(2/3) ·
It is characterized in that the configuration satisfies the condition of fr.

In this configuration, an intermediate frequency signal modulated with information and a non-modulated wave signal which is a sine wave are multiplexed by multiplexing means, and the multiplexed signal is combined with a signal having a resonance frequency fr.
The direct modulation of the semiconductor laser diode
The light is converted and transmitted to an optical fiber.

Assuming that the resonance frequency of the semiconductor laser diode used is fr, in the case of the optical analog transmission device of the present invention, the frequency f _IF of the intermediate frequency signal and the frequency f _{LO of the} unmodulated wave signal are f _LO −f _IF ≧ 1 [GHz] and 2f _IF <f _LO <(2/3)
・ Meet fr condition.

[0020] That is, this configuration is configured to employ at the transmitting end station, the transmitting end station, the intermediate frequency signal f _IF and the RF signal is a signal of an intermediate frequency band modulated with information to be transmitted (the frequency f _MW ) is converted into an optical signal after being multiplexed with a sine unmodulated wave signal f _LO used for frequency up-conversion, and sent to an optical fiber. A signal to be transmitted is converted into an optical signal by controlling a current of the semiconductor laser element according to the combined signal by using a semiconductor laser element for the optical signal conversion.

Since the semiconductor laser device generally has better modulation distortion characteristics and RIN characteristics as it goes to the lower side of the frequency band, the intermediate frequency signal in the frequency band of f _IF including the information signal is more than f _LO. Place on the low frequency side. Since f _LO is a sine-wave unmodulated wave signal, distortion is tolerant.

[0022] Figure 3, in the semiconductor laser element, showing the RIN characteristic of f _IF band for the frequency f _LO of the continuous wave signal. f _IF is 1 [GHz] and the modulation degree of f _LO is 40
[%] Is 1.2 [GHz], 2 [GHz], 3 [GHz]
], 3.5 [GHz], 4 [GHz]. RIN when the unmodulated wave signal f _LO is not superimposed is −152.
[DB / Hz]. RIN values, affected by the spectral component of f _LO, a large deterioration as the frequency band close to f _LO.

Then, the _{distance is} improved as the _distance from fLO is increased. As shown in FIG. 3, f _LO −f _IF ≧ 1 [GH
z], the RIN value asymptotically approaches the value when f _LO is not superimposed and stabilizes.

FIG. 4 shows f _{LO at} f _IF = 120 [MHz].
Is shown for RIN. The modulation degree of f _LO was set to 40 [%] as in FIG. RI when f _LO is not superimposed
N was -164.0 [dB / Hz].

From FIG. 4, f _LO is close to f _IF and 1 [GHz].
(That is, f _LO −f _IF <1
[GHz], the RIN value is -160 [dB / Hz] or more, and the RIN value is greatly deteriorated. However, f _LO −f _IF ≧
When f _LO = 2 [GHz], which is 1 [GHz], the RIN value is -162 [dB / Hz], which indicates that the deterioration is suppressed.

Therefore, the arrangement of f _LO −f _IF ≧ 1 [GHz] can improve the RIN characteristic. Also,
Semiconductor laser devices usually have non-linear electrical / optical conversion characteristics, and when the laser device is directly modulated, f _LO ± f _IF
Intermodulation distortion of f _LO and f _IF appears at the frequency of, which causes an increase in noise. Therefore, considering f _LO ± f _IF , f
_The placement of the _LO with respect to _fIF is important. When the frequency f _LO −f _IF of the low-frequency distortion overlaps the frequency band of f _IF , as described above, the RIN characteristic of the surrounding band deteriorates.

Therefore, by setting f _LO > 2f _IF , f _LO
-F _IF > f _IF to avoid the influence of RIN characteristic deterioration. Further, a semiconductor laser device has a resonance frequency fr at which the degree of modulation is extremely high at a specific frequency.

This is because the time delay with respect to the bias current due to the lifetime of carriers and photons of the semiconductor laser element coincides with the modulation period, and the modulation degree of the laser element is added to be extremely large. When modulation is applied to fr, the characteristics of the laser element become unstable, and RIN increases over the entire frequency range. Therefore, it is necessary to arrange f _LO so that the frequency f _LO + f _IF of the high-frequency side distortion is smaller than fr. And 2f _IF
From the condition of <f _LO and f _LO + f _IF <fr, this f _LO is
f _LO <(2/3) · fr.

[2] The optical analog transmission apparatus according to the second aspect of the present invention (second claim) is the optical analog transmission apparatus according to the above [1], wherein the intermediate frequency signal and the unmodulated wave signal are converted. A multiplexing unit for multiplexing, and a unit for performing electrical / optical conversion of the multiplexed signal by direct modulation of a semiconductor laser element (for example, a semiconductor laser diode) having a resonance frequency fr and transmitting the multiplexed signal to an optical fiber. An optical analog transmission device, wherein the frequency band f _IF of the intermediate frequency signal is f _IF
<1 [GHz] and the frequency band f of the unmodulated wave signal
It is characterized in that _LO is 2 [GHz] <f _LO .

As a semiconductor laser element, that is, a semiconductor laser diode, a distributed feedback semiconductor laser element (DFB-LD) or a Fabry-Perot semiconductor laser element (FP-LD) is used. In particular, DFB
-LD has a small modulation distortion for suppressing the dynamic range of a multi-channel signal, and is suitable for analog transmission. However, also in the DFB-LD, the modulation distortion characteristic is small,
The frequency band where the amount of noise is low is usually 1 GHz or less.

If the frequency f _IF of the intermediate frequency signal, which is an information signal, is arranged in the range of f _IF > 1 [GHz], the dynamic range is suppressed due to deterioration of modulation distortion characteristics and increase in noise. It is desired to arrange at f _IF <1 [GHz].

F _IF = 1 [GHz] in FIG. 3, which is an unmodulated wave signal frequency-RIN characteristic diagram in a relatively low frequency band.
] In FIG. 4 showing the RIN value and the unmodulated wave signal frequency-RIN characteristic in a relatively high frequency band.
_As can be seen from the RIN value in the case of _IF = 120 [MHz], the non-modulated wave signal frequency f _IF = 120 [MHz] has approximately 10 [dB / Hz] more excellent RIN characteristics.

From the above, the frequency arrangement of the intermediate frequency signal f _IF and the unmodulated wave signal f _LO is _defined as f _IF <1 [GHz], f _LO > 2
When [GHz] is set, the transmission characteristics can be maintained well without being affected by the RIN characteristics and the modulation distortion.

[3] An optical analog transmission apparatus according to a third aspect of the present invention (third claim) is the optical analog transmission apparatus according to the above [1] or [2].
The optical / analog transmission device according to item 1, further comprising: an optical / electrical conversion unit that receives an optical signal transmitted through the optical fiber; and a unit that separates the received signal into the intermediate frequency signal and the unmodulated wave signal. It is characterized by comprising means for obtaining a radio frequency signal by converting the frequency of the intermediate frequency signal using the separated unmodulated wave signal, and means for transmitting the obtained radio frequency signal.

This configuration is a configuration of the receiving device when the transmitting device is arranged at a position distant from the terminal device. In this configuration, the optical signal transmitted from the terminal device via the optical fiber is used. Is converted into an electric signal by the optical / electrical conversion means,
The electric signal is separated into an intermediate frequency signal and an unmodulated wave signal.
Then, the frequency of the intermediate frequency signal is converted using the separated unmodulated wave signal, converted into a radio frequency signal, and transmitted in the air.

On the transmitting terminal side, a sine-wave unmodulated wave signal fLO used for frequency up-conversion to an intermediate frequency signal fIF and a radio frequency signal (frequency fMW), which is an intermediate frequency band signal modulated with information to be transmitted. Are multiplexed, converted into an optical signal, and sent to an optical fiber. The optical signal conversion is performed by using a semiconductor laser device and controlling the current of the semiconductor laser device in accordance with the combined signal.

As the semiconductor laser device, a distributed feedback semiconductor laser device (DFB-LD) or a Fabry-Perot semiconductor laser device (FP-LD) is used. The modulation band fc of these laser elements is usually fc = 3 [GHz] in the DFB-LD and fc in the FP-LD.
= 1 to 2 [GHz], and the modulation efficiency becomes worse in the frequency band higher than that. Therefore, except for a special high-frequency laser element, the frequency band of the unmodulated wave signal that can be superimposed is limited to about 3 to 5 GHz.

The intermediate frequency signal used in the system of the present invention is
Since the frequency f _IF is about f _IF <1 [GHz],
The terminal device converts an optical signal by modulating and controlling the semiconductor laser element with a signal obtained by multiplexing the intermediate frequency signal and the unmodulated wave signal, and transmits the optical signal to the transmitting device. After converting the signal into an electric signal, it is separated into a signal before multiplexing and returned to an intermediate frequency signal and an unmodulated wave signal. The frequency of the intermediate frequency signal is converted using the separated unmodulated wave signal, and the radio frequency signal is Therefore, the terminal device does not need to use a special high-frequency laser element,
The cost of the system can be reduced without lowering the performance.

[4] The fourth aspect of the present invention (fourth aspect) is the optical analog transmission apparatus according to the above [1] or [2].
The optical / analog transmission apparatus according to item 1, further comprising: an optical / electrical conversion unit that receives the optical signal transmitted through the optical fiber, converts the optical signal into an electric signal, and outputs the electric signal. Separating means for separating the intermediate frequency signal and the unmodulated wave signal, multiplying means for multiplying the unmodulated wave signal among these separated signals, and using the multiplied unmodulated wave signal, A means for frequency-converting the obtained intermediate frequency signal to obtain a radio frequency signal; and a means for transmitting the obtained radio frequency signal.

The present system having such a configuration converts an optical signal transmitted from the transmitting terminal via the optical fiber into an electric signal, and then separates the signal into an intermediate frequency signal and an unmodulated wave signal. Then, the separated unmodulated wave signal is multiplied by a multiplying means, and the frequency of the intermediate frequency signal is converted using the multiplied unmodulated wave signal to obtain a radio frequency signal. Then, the obtained radio frequency signal is transmitted to the air.

On the transmitting terminal station side, an unmodulated sine wave signal f used for up-conversion to an intermediate frequency signal fIF and a radio frequency signal (frequency f _MW ) which is an intermediate frequency band signal modulated with information to be transmitted. _After combining with the _LO, it is converted into an optical signal and sent to an optical fiber. The optical signal conversion is performed by using a semiconductor laser device and controlling the current of the semiconductor laser device in accordance with the combined signal.

As the semiconductor laser device, a distributed feedback semiconductor laser device (DFB-LD) or a Fabry-Perot semiconductor laser device (FP-LD) is used. The modulation band fc of these laser elements is usually fc = 3 [GHz] in the DFB-LD and fc in the FP-LD.
= 1 to 2 [GHz], and the modulation efficiency becomes worse in the frequency band higher than that. Therefore, except for a special high-frequency laser element, the frequency band of the unmodulated wave signal that can be superimposed is limited to about 3 to 5 GHz.

The intermediate frequency signal used in the system of the present invention is
Since the frequency f _IF is about f _IF <1 [GHz],
The frequency f _MW of the radio frequency signal which is f _IF + f _LO is originally limited to 4 to 6 [GHz].

However, by adopting a configuration in which the multiplier is provided, the unmodulated wave signal used for the frequency conversion is multiplied by n, so that the frequency f _MW of the radio frequency signal is f _MW
= F _IF + nf _LO (where n is a positive integer), so that a radio frequency signal in a high frequency band is generated without being limited to the modulation band of the laser element in the electric / optical converter 7. It is possible to do.

[5] An optical analog transmission apparatus according to a fifth aspect of the present invention (fifth claim) is the optical analog transmission apparatus according to the above-mentioned [3], wherein the optical analog transmission apparatus receives a radio signal and receives a radio frequency signal. A receiving unit that obtains an electric signal of the same, and using the unmodulated wave signal obtained by the separation unit, frequency-converts an electric signal of a radio frequency obtained by the receiving unit, and a receiving system that obtains an intermediate frequency signal. Frequency conversion means, to convert the intermediate frequency signal obtained by the frequency conversion means of the receiving system into an optical signal,
Means for transmitting to an upstream optical fiber.

This system not only uses radio transmission,
It also enables wireless reception. In the configuration of the wireless transmission system, after converting an optical signal into an electric signal, the obtained intermediate frequency signal for downlink (for transmission) is frequency-converted into a wireless frequency signal for downlink. The unmodulated wave signal of the above is also used in the receiving system to convert the frequency of the upstream (receiving) radio frequency signal,
An intermediate frequency signal for reception is obtained, converted into an optical signal, and optically transmitted to the terminal device.

Thus, a system capable of transmitting and receiving can be constructed. [6] An optical analog transmission device according to a sixth aspect of the present invention (the sixth claim) is the optical analog transmission device according to the item [4], which receives a radio signal and converts it into an electric signal of a radio frequency. Receiving means, a multiplying means for subjecting the unmodulated wave signal obtained by the separating means to a desired multiplication, and outputting the multiplied unmodulated wave signal obtained by the multiplying means. Frequency conversion means for converting the obtained radio frequency electric signal to obtain an intermediate frequency signal, and converting the intermediate frequency signal obtained by the reception system frequency conversion means into an optical signal, Means for transmitting to an optical fiber.

This system is not limited to radio transmission,
It also enables wireless reception. In the configuration of the wireless transmission system, after converting an optical signal into an electric signal, the obtained intermediate frequency signal for downlink (for transmission) is frequency-converted into a wireless frequency signal for downlink. The unmodulated wave signal multiplied by is also used in the receiving system to convert the frequency of an uplink (receiving) radio frequency signal to obtain an intermediate frequency signal for reception, and convert this to an optical signal to convert the signal into an optical signal. Optical transmission to the side.

Thus, a system capable of transmitting and receiving in a high radio frequency band can be constructed. According to the present invention, even if the degree of modulation of the unmodulated wave signal is increased, the C
There is no deterioration in NR, and a superior CNR unmodulated wave signal can be obtained on the transmitting device side. In the transmitting device, since the radio frequency signal received from the antenna may be weak, the signal for frequency conversion in the multiplier has a high CNR.
However, it is possible to provide an unmodulated wave signal from the transmitting terminal as such a signal for frequency conversion. In addition, when the unmodulated wave signal is multiplied as a signal for frequency conversion, the CNR of the received unmodulated wave signal is high, so that the noise characteristics are not significantly degraded during frequency conversion.

As described above, according to the various configurations of the present invention, the RIN of the intermediate frequency signal band is obtained by combining the unmodulated wave signals.
Value can be suppressed, so that the CNR degradation of the intermediate frequency signal band can be reduced and the RI of the intermediate frequency signal band can be reduced.
It is possible to increase the degree of modulation of the unmodulated wave signal without deteriorating N, to increase the CNR characteristic of the unmodulated wave signal received by the transmitting device, and to suppress additional noise during frequency conversion. Thus, it is possible to obtain a high quality radio frequency signal. Then, the CNR of the intermediate frequency signal and the unmodulated wave signal
If the deterioration of the characteristics can be suppressed, it is possible to extend the distance of the optical fiber transmission. For example, when the optical analog transmission of the present invention is applied to a wireless communication base station, the communication service area that can be covered by one transmitting terminal station is expanded. It becomes possible.

[0051]

Embodiments of the present invention will be described below in detail with reference to the drawings. (First Embodiment) FIG. 1 shows a first embodiment of the present invention.
In FIG. 1, 1 is a transmitting terminal, 6 is an adder, 7 is an electric /
An optical (E / O) converter, 20 is a driver amplifier, 22 is a current source, and 24 is a semiconductor laser device.

The adder 6 combines the intermediate frequency signal 51 and the unmodulated wave signal 52 to obtain a radio information signal 53, and the E / O converter 7 generates the radio information signal 53.
Is converted into an optical signal.
0, a current source 22, an inductance 21, a resistor 23, and a laser element 24. The inductance 21 is for applying a bias for the output signal of the driver amplifier 20 to the output of the current source 22, and the resistor 23 is for outputting the output of the driver amplifier 20 to which the bias has been applied to the semiconductor laser element 24 as a modulation signal. Is the input resistance to be added. The terminal device 1 includes these components.

In the optical transmitter having such a configuration, the transmitting terminal 1 converts the radio information signal 53 obtained by multiplexing the intermediate frequency signal 51 and the unmodulated wave signal 52 by the adder 6 into an E / O signal. Input to the converter 7.

Let the frequency of the intermediate frequency signal 51 be f _IF and the frequency of the unmodulated wave signal 52 be f _LO . In the E / O converter 7, after the wireless information signal 53 is amplified by the driver amplifier 20, a bias current from the current source 22 is added to the wireless information signal 53 to directly modulate the semiconductor laser device 24. The semiconductor laser element 24 emits a laser beam modulated in accordance with the wireless information signal 53 and sends out the laser beam to the optical fiber 2 as a transmission path. The semiconductor laser element 24 used here is a DFB laser diode for analog transmission.

The optical signal 61 oscillated by the semiconductor laser element 24 is input to the optical fiber 2 and transmitted. The resonance frequency of the semiconductor laser device 24 is represented by fr. In above configuration, as shown in FIG. 2, f _IF
Comprising a frequency arrangement of the intermediate frequency signal 51 and f _LO becomes the frequency of the modulated signal 52 of _{frequency, f LO -f IF ≧ 1 [} GHz
].

Since the semiconductor laser element 24 generally has better modulation distortion characteristics and RIN characteristics as it goes to the lower side of the frequency band, the intermediate frequency signal in the frequency band of f _IF including the information signal is compared with f _LO . Is also placed on the low frequency side. Since f _LO is a sine-wave unmodulated wave signal, distortion is tolerant.

[0057] Figure 3, in the semiconductor laser device 24 of the electric / optical converter within 7 shows the RIN characteristic of f _IF band for the frequency f _LO of the continuous wave signal 52. f _IF is 1 [GHz], 1.2 [GHz frequency in the modulation of f _LO 40 [%]
], 2 [GHz], 3 [GHz], 3.5 [GHz], 4 [GHz]
]. The RIN when the unmodulated wave signal f _LO was not superimposed was −152 [dB / Hz]. RIN values, affected by the spectral component of f _LO, a large deterioration as the frequency band close to f _LO.

Then, as the _distance from fLO is increased, it is improved. As shown in FIG. 3, f _LO −f _IF ≧ 1 [GH
z], the RIN value asymptotically approaches the value when f _LO is not superimposed and stabilizes.

FIG. 4 shows f _{LO at} f _IF = 120 [MHz].
Shows the RIN value for. The modulation degree of f _LO was set to 40 [%] as in FIG. f when f _LO is not superimposed
The IN value was -164.0 [dB / Hz].

From FIG. 4, f _LO is close to f _IF and 1 [GHz]
] (That is, f _LO −f _IF <
1 [GHz]), the RIN value is -160 [dB / Hz] or more, which is greatly deteriorated. However, f _LO −f
In f _LO = 2 is _{IF ≧ 1 [GHz] [GHz} ], RIN
The value is -162 [dB / Hz], which indicates that the deterioration is suppressed.

From the above, f _LO −f _IF ≧ 1 [GHz]
With this arrangement, the effect of improving the RIN characteristics can be achieved.
The semiconductor laser element 24 usually has a non-linear E / O conversion characteristic, and when the laser element is directly modulated, f _LO ± f
The _IF frequency, intermodulation distortion f _LO and f _IF appear, becomes a cause of noise increasing. Therefore, considering f _LO ± f _IF ,
The arrangement of f _LO with respect to f _IF is important. When the frequency f _LO −f _IF of the low-frequency distortion overlaps the frequency band of f _IF , as described above, the RIN characteristic of the surrounding band deteriorates.

Therefore, by setting f _LO > 2f _IF , f _LO
Create a relationship between the _LO -f _IF> f _IF, to avoid the influence of RIN degradation. Further, the semiconductor laser element 24 has a resonance frequency fr at which the degree of modulation is extremely high at a specific frequency.
Exists.

This is because the time delay with respect to the bias current due to the lifetime of the carriers and photons of the laser element coincides with the modulation period, and the modulation degree of the laser element is added to become extremely large. When this fr is modulated,
The characteristics of the laser element become unstable, and RIN increases over the entire frequency range.

Therefore, the frequency f _LO + f of the high-frequency distortion is obtained.
_It is necessary to arrange f _LO so that _IF is smaller than fr. And 2f _IF <f _LO and f _LO
From the condition of + f _IF <fr, this f _LO becomes f _LO <(2 /
3) · fr That is, f _IF satisfying these conditions
The frequency arrangement of (intermediate frequency signal 51) and f _LO (unmodulated wave signal 52) is as shown in FIG.

As the semiconductor laser element 24, that is, a semiconductor laser diode, a distributed feedback semiconductor laser element (DFB-LD) or a Fabry-Perot semiconductor laser element (FP-LD) is used. In particular, DFB
-LD has a small modulation distortion for suppressing the dynamic range of a multi-channel signal, and is suitable for analog transmission. However, also in the DFB-LD, the modulation distortion characteristic is small,
The frequency band where the amount of noise is low is usually 1 GHz or less.

[0066] The intermediate frequency signal 51 is the frequency f _IF is an information signal, placing in the range of f _IF> 1 [GHz], the degradation of the distortion characteristics, from the increase of noise, the dynamic range will be suppressed , F _IF <1 [GHz].

F _IF = 1 [GHz] in FIG. 3, which is a diagram of the unmodulated wave signal frequency-RIN characteristic in a relatively low frequency band.
] In FIG. 4, which is a diagram of the frequency-RIN characteristic of the unmodulated wave signal in a relatively high frequency band.
_As can be seen from the RIN value when _IF = 120 [MHz], the unmodulated wave signal frequency f _IF = 120 [MHz] is
It can be seen that the RIN characteristic is excellent about 10 [dB / Hz].

From the above, the frequency arrangement of the intermediate frequency signal f _IF (intermediate frequency signal 51) and the unmodulated wave signal f _LO (unmodulated wave signal 52) is changed as shown in FIG. 6 to f _IF <1 [GHz]. ,
If f _LO > 2 [GHz], good transmission characteristics can be maintained without being affected by RIN characteristics and modulation distortion.

(Second Embodiment) FIG. 7 shows a second embodiment of the present invention. In the second embodiment, the first embodiment of the present invention is applied to a base station device for wireless communication.

As shown in FIG. 7, a transmitting terminal 1 and a transmitting device 2 are connected by an optical fiber 3. Although only one is shown in FIG.
Are provided, and each transmitting device 2 is connected by an optical fiber 3. The transmitting devices 2 are arranged at distant positions, respectively, and the range where radio waves reach each becomes a wireless zone (cell), and becomes a service area where radio waves can be exchanged with communication terminals in the cell.

The transmitting terminal station 1 comprises a radio signal modulator 4, a local oscillator 5, an adder 6, an electric / optical converter (E / O converter) 7.
And the transmitting device 2 is an optical / electrical converter (O / E
Converter) 8, separator 9, band-pass filters 10, 1
1, 13, multiplier 12, power amplifier 14, antenna 1
And 5.

Among them, the radio signal modulator 4 is for modulating transmission data into an intermediate frequency signal 51 for radio signals, and the local oscillator 5 is an oscillator for oscillating an unmodulated wave signal 52 of a predetermined frequency. It is.

The adder 6 combines the intermediate frequency signal 51 and the unmodulated wave signal 52 and outputs the combined signal as a radio information signal 53. The E / O converter 7 is obtained by combining the signals. This is for converting the wireless information signal 53 into an optical signal and outputting it. The E / O converter 7 incorporates a semiconductor laser element as a light source, and has a function of outputting a light signal modulated by a wireless information signal by controlling the current of the semiconductor laser element in accordance with the wireless information signal 53. .

The optical fiber 3 is an optical transmission line connecting the E / O converter 7 of the terminal device 1 and the O / E converter 8 of the transmitting device 2. The O / E converter 8 receives the optical signal 61 transmitted through the optical fiber 3 and converts it into an electric signal. The separator 9 converts the electric signal output from the O / E converter 8 into two. And one of the branches is divided into bandpass filters 10.
And the other is supplied to the band-pass filter 11.

The band-pass filter 10 is a filter for extracting the intermediate frequency signal and a filter including _fIF in the transmission band, and the band-pass filter 11 is a filter for extracting the unmodulated wave signal and has the transmission frequency band f. _This is a filter that includes _LO .

The multiplier 12 multiplies the output signals of the two band-pass filters 10 and 11 and outputs the result. The band-pass filter 13 extracts a required radio frequency signal from the output of the multiplier 12. The power amplifier 14 amplifies the radio frequency signal output from the band-pass filter 13 and outputs the amplified signal, and the antenna 15 radiates the amplified signal as radio waves to the air. is there.

In the system having such a configuration, the transmitting terminal 1 transmits the intermediate frequency signal 5 from the radio signal modulator 4.
1, the unmodulated wave signal 52 from the local oscillator 5 is added to the adder 6
The wireless information signal 53 obtained by multiplexing is input to the E / O converter 7.

It is assumed that the frequency band of the intermediate frequency signal 51 is f _IF and the frequency band of the unmodulated wave signal 52 is f _LO . E / O converter 7
In, the laser is directly modulated by the wireless information signal 53 to obtain an optical signal 61, which is transmitted to the transmitting device 2 via the optical fiber 3.

On the transmitting device 2 side, the optical signal 61 transmitted through the optical fiber 3 is received by the O / E converter 8, converted into an electric signal, and then split into two by the separator 9. By separating one through a band-pass filter 10 including f _{IF in} the transmission band for the intermediate frequency signal and the other through a band pass filter 11 including f _{LO in} the transmission band for the unmodulated wave signal, To the intermediate frequency signal 51 and the unmodulated wave signal 52.

Then, these restored intermediate frequency signals 5
1 and the unmodulated wave signal 52 are input to the multiplier 12 and multiplied. Then, by passing the output of the multiplier 12 through the band-pass filter 13, the required radio frequency signal 54
The extracted radio frequency signal 54 is amplified via the power amplifier 14, then radiated as radio waves into the air through the antenna 15, and transmitted to the terminal in the cell.

With the above-described configuration and operation, as in the first embodiment, the intermediate frequency signal 51 in the frequency band f _IF and the unmodulated wave signal 52 in the frequency band f _LO are arranged in the following manner. f _LO −f _IF ≧ 1 [GHz], 2f _IF <f _LO <(2
/ 3) · fr or f _IF <1 [GHz], f _LO >
2 [GHz].

As described above, the first embodiment can be applied to a radio communication base station apparatus. The above is
A description has been given of the second embodiment of the present invention in which the first embodiment is applied to a base station device for wireless communication. Next, by changing the carrier of the radio frequency signal without replacing the hardware of the transmission device, a transmission device of the same specification
A third embodiment will be described as an embodiment in which the system can be used between adjacent cells and the cost of the system can be reduced.

(Third Embodiment) FIG. 8 shows a third embodiment of the present invention. The configuration of the transmitting terminal station 1 is the same as in the first and second embodiments, and the same reference numerals in the transmitting device 2 denote the same components as those in the transmitting device 2 of the first and second embodiments.

The transmitting device 2 in this embodiment includes an optical / electrical converter (O / E converter) 8, a separator 9, a multiplier 12, a bandpass filter 13, a power amplifier 14, and an antenna 1
5, low-pass filter 16, high-pass filter 17
It is composed of

In this system, the transmitting end station 1 combines the intermediate frequency signal 51 from the radio signal modulator 4 with the unmodulated wave signal 52 from the local oscillator 5 by the adder 6 to obtain a radio signal. The information signal 53 is input to the E / O converter 7, and the semiconductor laser element of the E / O converter 7 is directly modulated by the wireless information signal 53 to obtain an optical signal 61, which is transmitted to the optical fiber 3. The mechanism for transmission to the transmission device 2 via the communication interface is the same as in the first and second embodiments.

Among the components of the transmitting device 2, the O / E converter 8 receives the optical signal 61 from the terminal device 1 transmitted through the optical fiber 3, and converts it into an electric signal.
The separator 9 separates the electric signal output from the O / E converter 8 into two, and branches one of the two into a low-pass filter 16.
And the other to the high-pass filter 17.

The low-pass filter 16 is a filter for an intermediate frequency signal including f _IF in a transmission band, and the low-pass filter 17 is a filter for an unmodulated wave signal including f _LO in a transmission band.

The multiplier 12 is connected to these two filters 1
6 and 17 are output. The band-pass filter 13 is a filter for extracting a required radio frequency signal from the output of the multiplier 12, and the power amplifier 14 is a filter for extracting the required radio-frequency signal. And 13 amplifies and outputs the radio frequency signal output from 13
The antenna 15 emits the amplified signal into the air as a radio wave.

In this system having such a configuration, on the transmitting device 2 side, the optical signal 61 transmitted via the optical fiber 3 is received by the O / E converter 8 and converted into an electric signal. , And a low-pass filter 1 for an intermediate frequency signal including f _IF in a transmission band.
6, and the other is restored to the original intermediate frequency signal 51 and unmodulated wave signal 52 by passing through the high-pass filter 17 for the unmodulated wave signal including f _LO in the transmission band.

Then, these restored intermediate frequency signals 5
1 and the unmodulated wave signal 52 are input to the multiplier 12 and multiplied. Then, by passing the output of the multiplier 12 through the band-pass filter 13, the required radio frequency signal 54
The amplified radio frequency signal 54 is amplified via the power amplifier 14, then radiated into the air as radio waves through the antenna 15, and transmitted to the terminals in the cell.

As described above, in the present system shown in the third embodiment, the two outputs of the built-in separator 9 are input to the low-pass filter 16 and the high-pass filter 17 on the transmitting apparatus 2 side, and the intermediate frequency signal is output. 51 and the unmodulated wave signal 52 are extracted. That is, instead of using the band-pass filters 10 and 11, the low-pass filter 16 and the high-pass filter 17 are used, and the intermediate frequency signal 51 is used.
And the unmodulated wave signal 52 is extracted.

By adopting such a configuration so that the transmission band of the band-pass filter 13 for extracting the radio frequency signal at the subsequent stage can be given a margin, the low-pass filter 16 and the high-pass filter 17 become band-pass filters. Since the transmission frequency band is wider than in the above, the flexibility of frequency selection is increased, and the carrier of the radio frequency signal 54 can be changed without replacing other hardware of the transmission device.

In a configuration in which the original unmodulated wave signal and the intermediate frequency signal are extracted by a band-pass filter from the signal obtained by combining the unmodulated wave signal and the intermediate frequency signal, it usually depends on the CNR value of the signal to be processed. Then, a bandpass filter having a large Q is used. That is, in the conventional transmission device, if the CNR value of the reception signal 55 obtained from the terminal device 1 via the optical fiber 3 and photoelectrically converted by the O / E converter 8 seems to deteriorate, the bandpass Filters 10 and 11 are Q
Must be used, and the range of wavelength selection of the radio frequency signal is reduced.

However, according to the system of the present invention, even if the unmodulated wave signal 52 is superimposed on the transmitting terminal station 1, the deterioration of the RIN value of the intermediate frequency signal 51 band can be suppressed. Accordingly, the modulation degree of the unmodulated wave signal 52 can be increased without deteriorating the RIN value of the intermediate frequency signal 51 band.
, The separation of the intermediate frequency signal and the unmodulated wave signal becomes possible. Therefore, the flexibility of the radio frequency signal 54 can be increased, and a radio communication base station with a wide applicable range can be provided.

Next, an embodiment in which the frequency of the radio frequency signal can be raised even if the intermediate frequency signal and the unmodulated wave signal are not high will be described as a fourth embodiment. (Fourth Embodiment) FIG. 9 shows a fourth embodiment of the present invention. The configuration of the transmitting terminal station 1 is the same as in the first and second embodiments, and the same reference numerals are given to the same components in the transmitting apparatus 2 as well.

The transmitting apparatus 2 in this embodiment includes an optical / electrical converter (O / E converter) 8, a separator 9, a multiplier 12, a band-pass filter 13, a power amplifier 14, and an antenna 1
5, low-pass filter 16, high-pass filter 1
7, a multiplier 18 and a band-pass filter 19.

In this system, the transmitting end station 1 combines the intermediate frequency signal 51 from the radio signal modulator 4 with the unmodulated wave signal 52 from the local oscillator 5 by the adder 6 to obtain a radio signal. The information signal 53 is input to the E / O converter 7, and the semiconductor laser element of the E / O converter 7 is directly modulated by the wireless information signal 53 to obtain an optical signal 61, which is transmitted to the optical fiber 3. The mechanism for transmission to the transmission device 2 via the communication interface is the same as in the first and second embodiments.

Among the components of the transmitting device 2, the O / E converter 8 receives the optical signal 61 from the terminal device 1 transmitted through the optical fiber 3, and converts it into an electric signal.
The separator 9 separates the electric signal output from the O / E converter 8 into two, and branches one of the two into a low-pass filter 16.
And the other to the high-pass filter 17.

The low-pass filter 16 is a filter for an intermediate frequency signal including f _IF in a transmission band, and the low-pass filter 17 is a filter for an unmodulated wave signal including f _LO in a transmission band. The multiplier 18 is a filter that multiplies the filtered output of the low-pass filter 17 by n and outputs the same, and the band-pass filter 19 is a filter that extracts a predetermined frequency band component from the output multiplied by n. Note that the above n is a positive integer.

The multiplier 12 is provided with these two filters 1
The bandpass filter 13 is a filter for extracting a required radio frequency signal from the output of the multiplier 12, and the power amplifier 14 is a filter for extracting a required radio frequency signal from the output of the multiplier 12. And 13 amplifies and outputs the radio frequency signal output from 13
The antenna 15 emits the amplified signal into the air as a radio wave.

In this system having such a configuration, on the transmission device 2 side, the optical signal 61 transmitted via the optical fiber 3 is received by the O / E converter 8 and converted into an electric signal. , And a low-pass filter 1 for an intermediate frequency signal including f _IF in a transmission band.
6, and the other is restored to the original intermediate frequency signal 51 and unmodulated wave signal 52 by passing through the high-pass filter 17 for the unmodulated wave signal including f _LO in the transmission band.

Of the intermediate frequency signal 51 and the unmodulated wave signal 52 thus obtained, the unmodulated wave signal 52 is a multiplier 18
Then, by passing through the band-pass filter 19, a desired multiplied unmodulated wave signal 58 is obtained,
This is input to the multiplier 12 and used for frequency conversion.

The multiplier 12 multiplies the intermediate frequency signal 51 from the low-pass filter 16 by the unmodulated wave signal 58 and transmits the obtained signal output through the band-pass filter 13 so that a required radio-frequency signal is obtained. Extract. Then, the radio frequency signal output from the band pass filter 13 is power-amplified by the power amplifier 14 and then radiated into the air as a radio wave from the antenna 15.

In this embodiment, the configuration of the third embodiment is
Further, a frequency multiplier 18 and a band-pass filter 19 are provided. The filtered output of the low-pass filter 17 is multiplied by n, and a predetermined frequency band component is extracted from the n-multiplied output by the band-pass filter 19, thereby performing frequency conversion. To obtain a desired multiplied unmodulated wave signal 58 used in the above. This is a difference from the third embodiment.

The laser light source used in the electric / optical converter 7 of the transmitting terminal 1 is a distributed feedback semiconductor laser device (D
FB-LD) or Fabry-Perot type semiconductor laser device (FP-LD).

The modulation band f of these laser elements
c is usually fc = 3 [GHz] in DFB-LD and FP-
In the LD, fc = 1 to 2 [GHz], and the modulation efficiency becomes worse in a frequency band higher than fc. Therefore, except for the special high-frequency laser element, the superimposed unmodulated wave signal 5
The frequency band 2 is limited to about 3 to 5 [GHz].

Since the frequency f _IF of the intermediate frequency signal used in the system of the present invention is f _IF <1 [GHz], f _IF +
The frequency f _MW of the radio frequency signal 54 which is f _LO is originally limited to 4 to 6 [GHz].

However, by adopting the configuration of FIG. 8 provided with the multiplier, the unmodulated wave signal 58 used for frequency conversion becomes a desired multiplied signal. Therefore, the frequency f _MW of the radio frequency signal 54 becomes f _MW = F _IF + nf _LO , so that it is possible to generate a radio frequency signal 54 in a higher frequency band without being limited by the modulation band of the laser element in the electric / optical converter 7. Becomes

However, when the unmodulated wave signal 52 is multiplied by n, noise is inevitably added, so that the quality of the radio frequency signal 54 usually deteriorates. However, according to the present invention, the degree of modulation of the unmodulated wave signal 52 can be increased without deteriorating the RIN value of the intermediate frequency signal 51 band, so that the CNR characteristics of both signals 51 and 52 can be kept good. .

Therefore, the present invention provides a system in which the quality of the radio frequency signal 54 is not significantly deteriorated even when the multiplier 18 is used. In each of the embodiments described above, only transmission is mainly described. In an actual system, a system that enables transmission and reception is indispensable. Therefore, such a system will be described as a fifth embodiment.

(Fifth Embodiment) FIGS. 10 and 11 show a fifth embodiment of the present invention. The main configuration is the same as that of the second embodiment, and the same components are denoted by the same reference numerals. Further, as in the second embodiment, the present invention is applied to a base station device for wireless communication.

In FIG. 10, in order to enable two-way communication, the terminal station 1 is a transmitting / receiving terminal station 1A including a receiving function, and the transmitting device 2 connected to the terminal station has only a transmitting function. Transmitter / receiver 2A with receiving function
It has become.

The transmitting / receiving terminal 1A and the transmitting / receiving device 2A are connected by optical fibers 3a and 3b. Although only one is shown in the figure, a configuration in which a plurality of transmission / reception devices 2A are provided for one transmission / reception terminal station 1A can be naturally adopted. When there are a plurality of transmission / reception devices 2A, the transmission / reception devices 2A are arranged at distant positions, and the reach of each radio wave is each wireless zone (cell), and is a service area where radio waves can be exchanged with communication terminals in the cell.

Of the optical fibers 3a and 3b, the former is for the down line (for the transmission line), and the latter is for the up line (for the receiving line). The transmitting / receiving terminal 1A includes a wireless signal modulator 4, a local oscillator 5, an adder 6, and an electric / optical converter (E / O converter) 7 for downlink (for transmission), and for uplink (for reception). An optical / electrical converter (O / E converter) 8-2 and a demodulator 27 are provided.

The transmission / reception device 2A includes an electric / optical converter (E / O converter) 7-2, an optical / electric converter (O / E converter) 8-1, a separator 9, and a band-pass filter 10-. 1,
10-2, 11, 13-1, 13-2, multiplier 12-
1, 12-2, a power amplifier 14, an antenna 15, a circulator (or duplexer) 25, and a low noise amplifier 26.

Among them, the radio signal modulator 4 modulates transmission data into an intermediate frequency signal 51 for radio signals, and the local oscillator 5 generates an unmodulated wave signal 52 of a predetermined frequency. It is.

The adder 6 multiplexes the intermediate frequency signal 51 and the unmodulated wave signal 52 and outputs the multiplexed signal as a radio information signal 53. The E / O converter 7-1 obtains the multiplexed signal. The wireless information signal 53 is converted into an optical signal 61 and output. The E / O converter 7-1 incorporates a semiconductor laser element as a light source, and controls the current of the semiconductor laser element in correspondence with the wireless information signal 53, thereby
It has a function of outputting as an optical signal modulated by a wireless information signal. The E / O converter 7-1 is connected to the optical fiber 3a, and its optical signal output is output to the optical fiber 3a.

The O / E converter 8-2 is connected to the optical fiber 3
b, and converts the optical signal 3 transmitted from the transmitting / receiving device 2A transmitted through the optical fiber 3b into an electric signal and outputs the electric signal. In addition, the demodulator 27 uses this O /
It is for receiving the electric signal converted by the E converter 8-2 and demodulating the original wireless information signal.

The O / E converter 8-1, which is a component of the transmission / reception apparatus 2A, converts the optical signal 61 transmitted through the optical fiber 3a into an electric signal.
Converts the electric signal output from the O / E converter 8-1 into 2
And one of the branches is divided into a band-pass filter 10-
1 and the other to the band-pass filter 11.

The band-pass filter 10-1 is a filter for extracting an intermediate frequency signal and a filter including _{fIF in} a transmission band, and the band-pass filter 11 is a filter for extracting an unmodulated wave signal and has a transmission band. It is a filter including f _LO .

The multiplier 12 multiplies the output signals of the two band-pass filters 10-1 and 11 and outputs the product. The band-pass filter 13 outputs a required radio frequency signal from the output of the multiplier 12. The power amplifier 14 is a filter for extraction.
The antenna 15 receives the amplified signal via a circulator (or a duplexer) 25, radiates the amplified signal to the air as a radio wave, and also radiates the radio frequency signal output from the air. The low-frequency amplifier 26 is for capturing a radio wave generated by the low-noise amplifier 26 through the circulator 25.

The circulator 25 is a device for guiding a radio frequency signal to be transmitted to the antenna 15 and for switching a path for guiding a received radio frequency signal 56 captured by the antenna 15 to the low noise amplifier 26.

The low-noise amplifier 26 is an amplifier having the ability to amplify the received radio frequency signal 56 with low noise. The band-pass filter 13-2 passes the output of the low-noise amplifier 26 in a required transmission band, and This is a filter for extracting a component of a required transmission band.
2-2 is for multiplying the output of the band-pass filter 13-2 by the unmodulated wave signal 52 output by the band-pass filter 11.

The band-pass filter 10-2 is a filter that passes the output of the multiplier 12-2 in a required transmission band and extracts a component of the required transmission band as a radio information signal 57. The O-converter 7-2 outputs the wireless information signal 57 obtained by the band-pass filter 10-2.
Is converted into an optical signal and output. E / O
The converter 7-2 incorporates a semiconductor laser element as a light source,
By controlling the current of the semiconductor laser device in accordance with the wireless information signal 57, the semiconductor laser device has a function of outputting an optical signal modulated by the wireless information signal. The E / O converter 7
The optical signal output by -2 is output to the optical fiber 3b.

In the system having such a configuration, the transmitting terminal 1 transmits the intermediate frequency signal 5 from the radio signal modulator 4.
1, the unmodulated wave signal 52 from the local oscillator 5 is added to the adder 6
The wireless information signal 53 obtained by multiplexing is input to the E / O converter 7-1.

It is assumed that the frequency band of the intermediate frequency signal 51 is f _IF and the frequency band of the unmodulated wave signal 52 is f _LO . E / O converter 7
In -1, the laser element is directly modulated by the wireless information signal 53 to obtain an optical signal 61, which is transmitted to the transmitting / receiving device 2A via the optical fiber 3a.

On the transmission device 2A side, the optical signal 61 transmitted through the optical fiber 3a is received by the O / E converter 8-1, converted into an electric signal, and then converted into an electric signal.
, And one is passed through a band-pass filter 10 including an _IF signal in a transmission band for an intermediate frequency signal, and the other is passed through a band-pass filter 11 including f _{LO in} a transmission band for an unmodulated wave signal. Thus, the original intermediate frequency signal 51 and the unmodulated wave signal 52 are restored.

Then, these restored intermediate frequency signals 5
1 and the unmodulated wave signal 52 are input to the multiplier 12 and multiplied. Then, by passing the output of the multiplier 12 through a band-pass filter 13-1, a required radio frequency signal 54 is extracted. The extracted radio frequency signal 54 is amplified through the power amplifier 14, and then the circulator 25 Through the antenna 15 to radiate into the air as radio waves and transmit them to the terminals in the cell.

On the other hand, a radio wave transmitted from a terminal in the cell is received by the antenna 15 and is transmitted to the circulator 25.
After that, the signal is input to the low-noise amplifier 14 and amplified, and a band-pass filter 13-2 extracts a required band component. Then, the signal of the extracted component is multiplied by the unmodulated wave signal 52 from the band-pass filter 11 in the multiplier 12-2, and then the band-pass filter 10-
2 extracts a predetermined band component, and this is extracted by the E / O converter 7.
After being converted into an optical signal at -2, it is transmitted to the optical fiber 3b as an upstream optical signal and transmitted to the terminal station 1A.

The feature of this embodiment is that the unmodulated wave signal 52 is extracted from the two outputs of the separator 9 in the transmitting / receiving device 2A by using the band pass filter 11, and the extracted unmodulated wave signal 52 is extracted. Is a multiplier 1 on the transmission system side
2-1 and the multiplier 12-2 on the receiving system side. And in the transmission system,
The extracted unmodulated wave signal 52 is multiplied by the intermediate frequency signal 51 by the multiplier 12-1 to obtain the intermediate frequency signal 5
Used to upconvert one frequency, and
In the receiving system, the radio frequency signal 5 is output by the multiplier 12-2.
6 is used for frequency down-conversion by multiplication using the unmodulated wave signal 52.

That is, the intermediate frequency signal 51 and the unmodulated wave signal 52 are extracted from the two outputs of the separator 9 in the transmission / reception apparatus 2A using the band pass filters 10-1 and 11. Then, the extracted unmodulated wave signal 52 is separated and input to the multipliers 12-1 and 12-2.

In the multiplier 12-1, the intermediate frequency signal 51 transmitted from the transmitting / receiving terminal 1A as described above.
Is up-converted using the unmodulated wave signal 52 to obtain a radio frequency signal 54, which is wirelessly transmitted via the power amplifier 14 and the antenna 15.

The multiplier 12-2 performs frequency down-conversion by multiplying the radio frequency signal 56 by using the unmodulated wave signal 52. That is, the radio frequency signal 56 transmitted by radio is received by the antenna 15, input to the low noise amplifier 26 by the circulator or duplexer 25, and a desired band is extracted by the band-pass filter 13-2. The frequency component of the extracted band component of the radio frequency signal 56 is down-converted by the multiplier 12-2 using the unmodulated wave signal 52, and the image and the like are removed by the band-pass filter 10-2. The desired intermediate frequency signal 57 is obtained by extracting a desired band. The upstream intermediate frequency signal 57 is supplied to the E / O converter 7
The signal is converted into an optical signal 62 at -2 and transmitted to the transmitting terminal 1 via the optical fiber 3.

In the transmitting terminal station 1, the optical / electrical converter 8-2 receives the optical signal 62 transmitted from the transmitting device 2 side.
Input to demodulator 27 to extract information. As described above, the present invention uses a band-pass filter to convert a non-modulated wave signal from a combined signal of the radio transmission intermediate frequency signal 51 and the non-modulated wave signal transmitted from the terminal device in the transmitting / receiving device 2A. And the extracted unmodulated wave signal 52
Is used for frequency up-conversion in the transmission system and frequency down-conversion for the received signal in the reception system.

Therefore, the frequency of the upstream signal from the transmitting / receiving device 2A to the transmitting / receiving terminal 1A can be down-converted without requiring a component such as a local oscillator in the transmitting / receiving device 2A. Therefore, the components in the receiving system can be simplified accordingly. Further, since the reception signal in the radio frequency band captured by the antenna is down-converted, the signal is input to the E / O converter 7-2, converted into an optical signal, and transmitted to the terminal equipment. The frequency band required for the I / O converter 7-2 can also be kept low,
Since the frequency band of the signal handled by the specification for the laser element, driver amplifier, and the like incorporated in the converter 7-2 is reduced, the frequency band is relaxed and a low-cost one can be used.

As described above, the size of the transmitting / receiving device 2A can be reduced and simplified, and the transmitting / receiving device 2A with reduced cost can be provided. FIG. 11 shows another configuration example of the transmission / reception device 2A. This FIG.
In the example shown in (1), the configuration of the transmitting and receiving apparatus 2A when the multiplied unmodulated wave signal 58 is used for frequency conversion is shown.

This example has a configuration in which a multiplier 18 and a band-pass filter 19 are serially inserted after the band-pass filter 11 in the transmission system.
In A, the unmodulated wave signal 52 extracted by the band-pass filter 11 is multiplied by the multiplier 18 to obtain a desired and multiplied unmodulated wave signal 58 by the band-pass filter 19, and the desired multiplied signal is obtained. The unmodulated wave signal 58 is used for frequency up-conversion in a transmission system and frequency down-conversion in a reception system.

The desired multiplied unmodulated wave signal 58 is
The other configuration is the same as that of FIG. 10 except that it is input to the multipliers 12-1 and 12-2 and used for up-conversion or down-conversion, and thus detailed description is omitted.

The circuit configuration is increased by the addition of the multiplier and the band-pass filter. However, even in this case, the frequency band required for the E / O converter 7-2 in the receiving system is similar to the embodiment of FIG. Can be kept low, and E / O
Since the frequency band of the signal handled by the specification for the laser element, the driver amplifier, and the like built in the converter 7-2 is reduced, the frequency band is relaxed and a low-cost one can be used.

According to the present embodiment, even if the degree of modulation of the unmodulated wave signal 52 is increased, the CNR of the intermediate frequency signal 51 does not deteriorate, and the transmitting apparatus 2 obtains an excellent unmodulated wave signal 52 of the CNR. be able to. In the transmitting apparatus 2, since the radio frequency signal 56 received from the antenna 15 may be weak, a high CNR is required for the signal for frequency conversion in the multiplier 12-1. It becomes possible to provide the unmodulated wave signal 52 from the transmitting terminal station 1 as a signal. In addition, when the unmodulated wave signal is multiplied as a signal for frequency conversion, the CNR of the received unmodulated wave signal is high, so that the noise characteristics are not significantly degraded during frequency conversion.

[0141]

As described in detail above, the present invention relates to an optical analog transmission apparatus for wireless communication for combining an intermediate frequency signal and an unmodulated wave signal and optically transmitting the signal from a transmitting terminal to a transmitting apparatus. This has the following effects.

The frequency band f _LO of the unmodulated wave signal to be multiplexed and the frequency band f _IF of the intermediate frequency signal are _defined as f _LO −f _IF ≧ 1 [GHz]
And 2f _IF <f _LO <(2/3) · fr (laser resonance frequency). In f _IF, it is possible to suppress deterioration of the RIN characteristics due to the multiplexing of f _LO, can provide good CNR characteristics in the transmitting apparatus side, thereby improving the communication quality of the optical signal to be transmitted. Also, if you meet the above conditions,
Even if the degree of modulation of the unmodulated wave signal is increased, the deterioration of the RIN characteristic can be suppressed.

If the degree of modulation of an unmodulated wave signal can be increased, f
_LO can be provided. Since f _LO is used in the multiplier as a local oscillation signal for frequency conversion, the amount of noise added to the multiplier output is reduced, and a radio frequency signal with a low noise component can be obtained.

If the CNR characteristic of f _LO is excellent,
Q extraction filter f _LO can be reduced, the transmission can be f _LO
Will be expanded. That is, the frequency range of the radio frequency signal handled by the transmitting device is widened, and a radio communication base station with a wide applicable range can be provided.

Also, since the unmodulated wave signal f _LO transmitted from the transmitting terminal station can be taken out by the excellent CNR on the transmitting device side, the amount of added noise can be suppressed and the frequency up-conversion and down-conversion of the radio frequency signal can be performed. . If the deterioration of the CNR characteristics of the intermediate frequency signal and the unmodulated wave signal is small, the optical transmission distance between the transmitting terminal station and the transmitting device can be made longer. That is, the installation range of the transmission device connected to one transmission terminal station can be expanded, the number of transmission devices that can be connected can be increased, and the wireless communication service area can be efficiently expanded.

In addition to RIN, another factor that degrades CNR characteristics is modulation distortion. The frequency band in which the modulation distortion characteristic of the laser is excellent is a band lower than 1 [GHz]. Therefore, by setting f _IF <1 [GHz] and 2 [GHz] <f _LO , it is possible to provide a transmission system that suppresses CNR deterioration against modulation distortion as well as RIN.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram showing a frequency arrangement of f _IF and f _LO in the first embodiment of the present invention.

FIG. 3 is a diagram showing RIN characteristics with respect to the frequency of f _LO at f _IF = 1 [GHz].

FIG. 4 is a diagram showing RIN characteristics with respect to the frequency of f _LO at f _IF = 120 [MHz].

FIG. 5 is a diagram showing a frequency arrangement of f _IF and f _LO in the first embodiment of the present invention.

FIG. 6 is a diagram showing a frequency arrangement of f _IF and f _LO in the first embodiment of the present invention.

FIG. 7 is a configuration diagram showing a second embodiment of the present invention.

FIG. 8 is a configuration diagram showing a third embodiment of the present invention.

FIG. 9 is a configuration diagram showing a fourth embodiment of the present invention.

FIG. 10 is a configuration diagram showing a fifth embodiment of the present invention.

FIG. 11 is a configuration diagram showing a fifth embodiment of the present invention.

FIG. 12 is a diagram showing a conventional frequency arrangement.

FIG. 13 is a diagram showing RIN characteristics with respect to a modulation degree of an unmodulated wave signal in a conventional frequency arrangement.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Transmission terminal station 1A ... Transmission / reception terminal station 2 ... Transmission apparatus 2A ... Transmission / reception apparatus 3, 3a, 3b ... Optical fiber 4 ... Modulator 5 ... Local oscillator 6 ... Adder 7, 7-1, 7-2 ... Electric / Optical converter (E / O converter) 8, 8-1, 8-2: Optical / electrical converter (O / E converter) 9: Separator 10, 10-1: Band-pass filter for intermediate frequency signal 10-2, 13-1, 13-2: Band-pass filter 11: Band-pass filter for unmodulated wave signal 12: Multiplier 13: Band-pass filter for radio frequency signal 14: Power amplifier 15: Antenna 16: Intermediate frequency Signal low-pass filter 17 Unmodulated wave signal high-pass filter 18 Multiplier 19 Multiplied unmodulated wave signal band-pass filter 20 Driver amplifier 21 DC current adding coil 22 Current source 23 Load resistance 24 Semiconductor laser device 25 circulator (or duplexer) 26 low-noise amplifier 27 demodulator 51 intermediate frequency signal 52 unmodulated wave signal 53 radio information signal 54 radio frequency signal 55 reception signal 56 radio frequency signal to be received 57: Uplink intermediate frequency signal 58: Multiplied unmodulated wave signal 61: Optical signal 62: Uplink optical signal

──────────────────────────────────────────────────続 き Continued on front page (51) Int.Cl. ⁶ Identification code FI H04B 10/06

Claims (6)

[Claims] 1. A means for multiplexing an intermediate frequency signal modulated with information to be transmitted and an unmodulated wave signal which is a sine wave, and combining the multiplexed signal with a semiconductor laser device having a resonance frequency fr. Means for performing electrical / optical conversion by direct modulation and transmitting the converted signal to a downstream optical fiber, and when the resonance frequency of the laser element is fr, the frequency f _{IF of the} intermediate frequency signal and the unmodulated wave signal Frequency f
_LO is f _LO −f _IF ≧ 1 [GHz] and 2f _IF <f _LO <(2/3)
An optical analog transmission device characterized in that the configuration satisfies the condition of fr. 2. An optical analog transmission apparatus according to claim 1, wherein: a multiplexing means for multiplexing the intermediate frequency signal and the unmodulated wave signal; and a semiconductor laser device having a resonance frequency fr of the multiplexed signal. Means for performing electrical / optical conversion by direct modulation of the intermediate frequency signal and transmitting the converted signal to an optical fiber, and converting the frequency band f _IF of the intermediate frequency signal to f _IF <1 [GH
z] and the frequency band f _LO of the unmodulated wave signal is 2 [GH
z] <f _LO . 3. The optical analog transmission device according to claim 1, wherein: an optical / electrical conversion unit for receiving an optical signal transmitted through the optical fiber; Means for separating a signal and the unmodulated wave signal, means for obtaining a radio frequency signal by converting the frequency of the intermediate frequency signal using the separated unmodulated wave signal, and converting the obtained radio frequency signal Transmitting means for transmitting the analog signal. 4. An optical / electrical transmission device according to claim 1, wherein said optical fiber transmission device receives an optical signal transmitted through said optical fiber, converts the optical signal into an electric signal, and outputs the electric signal. Separating means for separating the intermediate frequency signal and the non-modulated wave signal from the converted and output electric signal; and It is characterized by comprising means for frequency-converting the separated intermediate frequency signal using a multiplied unmodulated wave signal to obtain a radio frequency signal, and means for transmitting the obtained radio frequency signal. Optical analog transmission device. 5. The optical analog transmission apparatus according to claim 3, wherein: a receiving unit that receives a radio signal to obtain an electric signal of a radio frequency; and the unmodulated wave signal obtained by the separation unit. Frequency conversion means for converting an electric signal of a radio frequency obtained by the reception means to obtain an intermediate frequency signal, and an intermediate frequency signal obtained by the frequency conversion means for the reception system to an optical signal. Means for transmitting the signal to an upstream optical fiber. 6. An optical analog transmission apparatus according to claim 4, wherein: a receiving means for receiving a radio signal to obtain an electric signal of a radio frequency; and desirably multiplying said unmodulated wave signal obtained by said separating means. Using a multiplied unmodulated wave signal obtained by the multiplying means, and converting a radio-frequency electric signal obtained by the receiving means into a frequency to obtain an intermediate frequency signal. An optical analog transmission device, comprising: frequency conversion means; and means for converting an intermediate frequency signal obtained by the frequency conversion means of the reception system into an optical signal and transmitting the optical signal to an upstream optical fiber.