JP3813770B2 - Wireless transmission device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to, for example, a configuration of a radio apparatus, particularly a transmission apparatus, that is used in a base station for mobile radio communication and configured using an array antenna.
[0002]
[Prior art]
In a mobile communication base station that communicates with multiple mobile stations, multiple antennas are arranged in an array, and the amplitude and phase of the signal radiated from each antenna are optimally controlled for each mobile station. A method for improving communication quality by doing so is known.
[0003]
FIG. 3 shows a configuration example of a wireless transmission apparatus according to the prior art, wherein 18 is an antenna, 22 is a digital / analog converter, 23 is a transmitter that generates a signal in a radio frequency band, and 26 is an amplifier. These are provided with a plurality of the same ones, and the following description will be made assuming that there are N units. These N devices are connected to the transmission signal processing device 21. Of these, antennas are often installed at high places such as steel towers or rooftops of buildings, and other wireless devices are often placed inside buildings. During this time, they are connected by a coaxial cable 30.
[0004]
In this wireless transmission device, a plurality of transmission signals 20 directed to individual mobile stations are subjected to digital signal processing by a transmission signal processing device 21 and converted into N transmission signals corresponding to each antenna, respectively. The digital / analog converter 22 converts the signal into an analog baseband signal. These are further converted into high frequency signals by the transmitter 23, amplified by the power amplifier 26, and then transmitted from the antenna 18 via the coaxial cable 30.
[0005]
As a high-frequency signal transmission method, there is known a method in which this is once converted into an optical signal and transmitted via an optical fiber cable. FIG. 4 shows an example of a wireless transmission device configured by applying such optical fiber transmission. The radio frequency band high-frequency signal generated by the transmitter 23 is converted by the electrical / optical converter 25 into the form of an optical signal modulated by the high-frequency electrical signal. This optical signal is transmitted toward the antenna by the optical fiber cable 31 and is returned to the electric signal by the optical / electrical converter 11. This electric signal is amplified to a required power level by the amplifier 13 and transmitted from the antenna 18.
[0006]
[Problems to be solved by the invention]
In the transmission apparatus using the array antenna as shown in FIG. 3, the amplitude and phase of the signal transmitted from each antenna are controlled in accordance with the propagation conditions in order to optimize the transmission beam shape. It changes every moment. For this reason, the power transmitted from each antenna is not uniform, and the total transmission power may be concentrated on one antenna. Therefore, each of the N amplifiers needs to have an ability to cover the total transmission power. For this reason, the shape of these amplifier groups becomes extremely large, which is wasteful in terms of cost and power consumption.
[0007]
In addition, in order to connect the radio device and the antenna, a large amount of coaxial cable is connected from the height of the building where the antenna is installed to the inside of the building where the antenna is installed in order to connect the radio device and the antenna. Since it is necessary to install the base station, the construction cost of the base station is high, and the construction may be difficult depending on the conditions of the installation location.
In the transmission apparatus configured as shown in FIG. 4, an optical fiber is used instead of the coaxial cable. Since optical fibers are fine and lightweight, laying work is easier than when coaxial cables are used. However, the electrical / optical converter 25 and the optical / electrical converter 11 generate distortion in the process of conversion between optical / electrical when the amplitude level of the signal is high. For this reason, there is a limit to the dynamic range that can be transmitted, and as described above, it is difficult to apply to a transmission system in which the power level is not uniform and the total power may be concentrated on one antenna. Further, N high-power amplifiers are installed in high places, which may hinder the installation location.
[0008]
An object of the present invention is to provide a wireless transmission device that is small and easy to install, eliminating the difficulties in cable laying work and device installation as described above.
[0009]
[Means for Solving the Problems]
In the radio transmission apparatus according to the first aspect of the invention, the N-sequence transmission signals generated by the transmission signal processing apparatus are rearranged into signals having the same N amplitude levels through distribution and synthesis operations. Converted into an optical signal. These signals are transmitted toward the antenna through an optical fiber cable, returned to an electric signal again, amplified by an amplifier, returned to a transmission signal by a distribution / synthesis circuit, and fed to the antenna.
[0010]
In the wireless transmission device according to the first aspect of the invention, the optical / electrical conversion is performed on the signals having the same amplitude level, and the power level of the amplifier is also equalized. For this reason, there is an advantage that the dynamic range for optical / electrical conversion can be reduced and the maximum output of the amplifier can be reduced.
Then , another pilot signal is added to each of the N signals rearranged through the distributing and combining operations. An amplitude phase adjuster is provided on the input side of the amplifier, and means for detecting the pilot signal previously applied is provided on the output side of the amplifier. The amplitude phase adjuster is controlled so that the detected pilot signal has a predetermined amplitude and phase.
[0011]
Since the pilot signal is controlled to be constant, an effect that it is possible to correct the phase and amplitude of the deviation generated in the electrical / optical conversion and the course of the amplification and the process of optical transmission.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The embodiment of the present invention defined in claim 1 Symbol placement will be described with reference to FIG.
The wireless transmission device mainly includes a device installed indoors, a device installed at a high place such as on a steel tower or a rooftop of a building, and an optical fiber cable 31 connecting them. The apparatus mainly installed indoors is a transmission signal processing device 21 in which N sets of digital / analog converters 22 and transmitters 23 are connected, a distribution synthesizer 32a for performing a distribution synthesis operation on the transmitter output, and a transmitter output. The synthesizer 24 for adding pilot signals and the electrical / optical converter 25 are composed of N sets, an oscillator 33 for generating pilot signals, and a distributor 34a for distributing pilot signals. The device installed at a high place includes an optical / electrical converter 11, an amplitude phase adjuster 12, an amplifier 13, a directional coupler 14, a filter 15 for removing a pilot signal, a filter 16 for extracting a pilot signal, and an amplitude phase comparator. The apparatus includes N sets of devices equivalent to 17 sets, a distribution / combination circuit 32 b, a distributor 34 b, and N antennas 18.
[0013]
A plurality of signals 20 to be transmitted are converted into N series digital signals corresponding to individual antennas by a transmission signal processing device 21. These are converted into analog signals having a required amplitude and phase by the digital / analog converter 22 and become high-frequency signals modulated by the transmitter 23. These are rearranged into N signals having a uniform amplitude by the distribution synthesizer 32a. The functions of the distribution synthesizer 32a will be described later. Note that an operation corresponding to the operation in the distributor / synthesizer 32a may be previously performed in the state of a digital signal in the transmission signal processing device 21. In that case, the distribution synthesizer 32a is unnecessary.
[0014]
A pilot signal generated by the oscillator 33 is added to each of the reorganized N signals, converted into an optical signal modulated by a high frequency signal by the electrical / optical converter 25, and an antenna is installed by the optical fiber cable 31. It is transmitted toward the designated high place.
The optical signal is converted back to an electrical signal by the optical / electrical converter 11 and amplified to a required power level by the power amplifier 13 via the amplitude / phase adjuster 12. A part of the output of the power amplifier 13 is extracted by the directional coupler 14 and the pilot signal is extracted by the filter 16. This pilot signal is compared with the output of the oscillator 33 distributed by the distributors 34a and 34b, and the amplitude and phase adjuster 12 is controlled so that both coincide with each other or keep a constant offset. The pilot signal is removed from the main output of the power amplifier 13 by the filter 15. The N signals obtained in this way are again converted to N transmission signals corresponding to the output of the transmitter 23 by the distribution synthesizer 32b and transmitted from the antenna 18.
[0015]
Next, the distribution synthesizer 32a will be described with reference to FIGS. 2a and 2b.
For the operation of such a circuit, see, for example, Egami, Kawai: “Multi-terminal power combining type multi-beam transmission system”, IEICE Journal, Vol. J69-BNo.2, PP.206-212 (February 1986 Issue). FIG. 2a shows a configuration example in which each of the input and output is 4 ports, and 41 to 44 are 90 ° hybrid circuits. The 90 ° hybrid circuit has the property that when a signal is input from one port, it is distributed with equal power to two of the other three ports and with a phase difference of 90 ° from each other, and is not output to the remaining one port. Have. Therefore, when a signal is input to the port 61 in FIG. 2a, it is distributed to two ports other than the port 62 by the 90 ° hybrid circuit 41, and further distributed by the 90 ° hybrid circuits 43 and 44 to the ports 71 to 74 with uniform power. Is output. The signals input to the ports 62 to 63 are also distributed in the same manner and output to the ports 71 to 74. When independent signals are simultaneously input to the ports 61 to 63, these are superposed, but in any case, the power output to the ports 71 to 74 is uniform.
[0016]
As shown in FIG. 2b, two sets of such distribution synthesizers are prepared, and in a system in which equivalent amplifiers 51 to 54 are sandwiched between them, the signal inputted from the port 61 is phase-shifted to the amplifiers 51 to 54. It is known that they are input with different but equal power, amplified respectively, and are aggregated only in the port 81 by the output-side synthesizer and do not appear in the ports 82 to 84. It is also known that a larger number of input / output ports are configured by combining more 90 ° hybrid circuits.
[0017]
In the embodiment shown in FIG. 1, the signal level is equalized by passing the output of the transmitter 23 through the distribution synthesizer 32a. Therefore, the peak power handled by the amplifier 13 is reduced, and the maximum output power that the amplifier 13 should have can be reduced to 1 / N. In addition, since the signal amplitude input to the electrical / optical converter 25 is also made uniform, the peak level of the signal is lowered, and it is less susceptible to distortion. Therefore, transmission is possible even if the dynamic range of the transmission system is narrow.
[0018]
Further, since a pilot signal is inserted and detected and fed back at the output of the amplifier, a phase and amplitude shift occurring in the process of electrical / optical conversion and amplification and optical transmission is corrected. For this reason, a stable operation is possible despite the long path from the distribution synthesizer 32a to the distribution synthesizer 32b.
[0019]
【The invention's effect】
As described above, according to the present invention, connection from a high place such as a rooftop to the inside of a building can be performed by an optical fiber cable, so that the construction is simplified and the influence of distortion due to optical / electrical conversion is reduced. It can be kept low. In addition, since the maximum output power required for the amplifier can be reduced, the apparatus can be reduced in size. Further, since the fluctuation of the phase difference and the attenuation amount from the transmitter to the amplifier output is suppressed, there is an effect that a stable operation becomes possible.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of the invention.
FIG. 2A is a block diagram showing a configuration example of a distribution / synthesis circuit, and FIG. 2B is a block diagram showing an amplifier using the distribution / synthesis circuit.
FIG. 3 is a block diagram showing a conventional wireless transmission device.
FIG. 4 is a block diagram showing a wireless transmission device using optical fiber transmission according to the prior art.
[Explanation of symbols]
11 Optical / Electric Converter 12 Amplitude Phase Adjuster 13, 26 Amplifier 14 Directional Coupler 15, 16 Filter 17 Amplitude Phase Comparator 18 Antenna 21 Transmitted Signal Processing Device 22 Digital / Analog Converter 23 Transmitter 24 Synthesizer 25 Electricity / Optical converter 30 Coaxial cable 31 Optical fiber cables 32a and 32b Distributor / synthesizer 33 Pilot signal oscillators 34a and 34b Distributors 41, 42, 43 and 44 90 ° hybrid circuit

Claims (1)

N antennas arranged in an array,
A transmission signal processing device that optimally controls the amplitude and phase of each transmission signal directed to an individual mobile station, respectively, for the mobile station;
N transmitters that respectively generate N signals from the transmission signal processing device into radio frequency band signals;
A first distribution synthesizer composed of a plurality of 90 ° hybrids and reorganizing the transmission signals of the N transmitters into N transmission signals each having a uniform amplitude;
N synthesizers that respectively add the pilot signal from the pilot signal oscillator to the reorganized N transmission signals of the first combiner / distributor;
N electrical / optical converters that convert the output signals of the N combiners into optical signals;
N optical fiber cables for transmitting optical signals from the N electrical / optical converters;
N optical / electrical converters for converting optical signals transmitted by the N optical fiber cables into electrical signals, respectively;
N amplifiers for amplifying each electrical signal from the N optical / electrical converters;
N filters for detecting pilot signals from the outputs of the N amplifiers;
N amplitude phase comparators for comparing the amplitude and phase of the pilot signal from the N filters and the pilot signal from the pilot signal oscillator, respectively.
N amplitude phase adjusters for adjusting the input electric signals of the corresponding amplifiers so that both amplitudes and phases to be compared coincide with each other or maintain a constant offset by the outputs of the N amplitude phase comparators. When,
A signal composed of a plurality of 90 ° hybrids and amplified by the N amplifiers is distributed and synthesized in reverse to the distribution and synthesis of the first distribution and synthesizer, and returned to the transmission signal from the transmission signal processing device. And a second combiner / distributor that feeds power to a corresponding antenna.

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