Signal converter, wireless signal transmission system, and wireless signal reception system

A signal converter 100 provided on an optical cable connecting the baseband unit 300 and the radio units 420 and 430. The signal converter 100 has a function to return time domain signals output from the baseband unit 300, to frequency domain signals and generate as many time domain signals as the number of antennas by assigning weights onto the frequency domain signals, and a function to combine, by an array combining, a plurality of time domain signals to a single frequency domain signal, and output the single frequency domain signal to the baseband unit 300.

TECHNICAL FIELD

The present invention relates to a wireless signal transmission/reception system and a signal converter used in the system, and in particular to a wireless signal transmission/reception system with the adaptive array technology used in the main part thereof, and a signal converter used in the system.

BACKGROUND ART

It is known that, in order to cause a wireless base station not supporting the adaptive array to support the adaptive array, a replacement of the baseband unit is required.FIG. 3shows a structure of a conventional wireless base station that does not support the adaptive array.FIG. 4shows a structure of a conventional wireless base station that supports the adaptive array.

As shown inFIG. 3, a baseband unit300, which performs an omnidirectional communication, includes a MAC processing unit301, a signal modulation unit302, an inverse FFT (Fast Fourier Transfer) unit303, a CP (Cyclic Prefix) attaching unit304, a signal demodulation unit305, a FFT (Fast Fourier Transfer) unit306, and a CP removing unit307. The signal modulation unit302, inverse FFT unit303, and CP attaching unit304are functional units that function only when a signal is transmitted, and the signal demodulation unit305, FFT unit306, and CP removing unit307are functional units that function only when a signal is received. When the wireless base station shown inFIG. 3is caused to support the adaptive array, it is necessary to replace the baseband unit300.

FIG. 4is a functional structure diagram of the wireless base station in which the baseband unit300has been replaced with the baseband unit400, includes as many radio units as the number of antennas, and supports the adaptive array. The baseband unit400includes a MAC processing unit401, a signal modulation unit402, inverse FFT units404and406, CP attaching units405and407, a signal demodulation unit412, FFT units414and416, and CP removing units415and417.

As understood by comparingFIG. 3withFIG. 4, in order to support the adaptive array, as many inverse FFT units, CP attaching units, FFT units, and CP removing units as the number of antennas are required.

Patent Literature 1 discloses a wireless base station that can switch between the adaptive array and the omnidirectional communication.

CITATION LIST

Patent Literature

Patent Literature 1

Japanese Patent Application Publication No. 2008-48236

SUMMARY OF INVENTION

Technical Problem

Meanwhile, the replacement of the baseband unit is not welcome since it takes much loading cost. More specifically, the functional units such as the MAC processing unit, signal modulation unit, and signal demodulation unit in the baseband unit require a high-performance CPU to perform signal processing. Creating a baseband unit newly for this purpose takes much cost. Signals output from the signal modulation unit of the original baseband unit may be extracted for use of this purpose. However, this approach may not be available depending on the baseband unit (for example, if the baseband unit has been made by a different maker).

It is therefore an object of the present invention to provide a signal converter which enables a wireless base station not supporting the adaptive array to support the adaptive array without replacement of the baseband unit and without modification of the original baseband unit, and to provide a transmission/reception system including the signal converter.

Solution to Problem

In one aspect of the present invention, the above problems are solved by a signal converter connected with a plurality of radio units, the signal converter comprising: a first interface unit operable to receive input of a single time domain signal to be used for a wireless transmission; a first converting unit operable to transform the time domain signal received by the first interface unit to a frequency domain signal which is a signal constituted from frequency components; a generating unit operable to generate a plurality of different frequency domain signals by performing a weighting calculation onto the frequency domain signal; a second converting unit operable to transform the plurality of frequency domain signals generated by the generating unit to a plurality of time domain signals and output the time domain signals; and a second interface unit operable to output the plurality of time domain signals output from the second converting unit, one-to-one to different radio units.

Advantageous Effects of Invention

With the above-described structure, the signal converter transforms a single time domain signal to be used for a wireless transmission to a frequency domain signal and generates as many time domain signals as the number of radio units by assigning weights onto the frequency domain signal. Thus when the signal converter is connected to be able to receive an output of the baseband unit, the wireless base station can execute the adaptive array transmission. Furthermore, in this case, there is no need to replace or modify the baseband unit. Thus the above-described problems are all solved.

Also, in another aspect of the present invention, there is provided a signal converter comprising: a second interface unit operable to receive input of a plurality of time domain signals; a first converting unit operable to transform the plurality of time domain signals received by the second interface unit to a plurality of frequency domain signals which are signals constituted from frequency components; a combining unit operable to generate a single frequency domain signal by combining the plurality of transformed frequency domain signals; a second converting unit operable to transform the single frequency domain signal generated by the combining unit to a single time domain signal; and a first interface unit operable to output the single time domain signal.

With the above-described structure, even when a plurality of radio units receive time domain signals, it is possible to generate a single time domain signal by performing the array combining and output the single time domain signal to the original baseband unit. Thus, without replacement of the baseband unit, the adaptive array reception can be executed only with installation of the signal converter on a line connecting the baseband unit and the radio units.

DESCRIPTION OF EMBODIMENTS

The following describes a signal converter in one embodiment of the present invention with reference to the attached drawings.

Embodiment

Structure

FIG. 1is a structure diagram showing the system structure of the wireless base station.

The wireless base station includes a BBU (Base Band Unit)300, a signal converter100, a RRU (Remote Radio Unit)420, and a RRU421.

The baseband unit300and the radio unit420are the same as those that had originally been loaded in the wireless base station in the state not supporting the adaptive array, and the present invention is characterized by the signal converter100which is additionally provided on the communication path connecting the baseband unit300and the radio unit420.

The baseband unit300includes a MAC processing unit301, a signal modulation unit302, an inverse FFT unit303, a CP attaching unit304, a signal demodulation unit305, a FFT unit306, and a CP removing unit307.

The MAC processing unit301has a function to transform the data constituting a signal to be transmitted (substantial data or the like) to a packet signal, and output the packet signal to the signal modulation unit302, and a function to analyze a demodulation signal input from the signal demodulation unit305and output the signal after the analysis to an upper layer (not illustrated).

The signal modulation unit302has a function to modulate a signal input from the MAC processing unit301and output a frequency domain signal to the inverse FFT unit303.

The inverse FFT unit303has a function to transform the frequency domain signal input from the signal modulation unit302to a time domain signal by performing the inverse FFT onto the frequency domain signal, and output the time domain signal to the CP attaching unit304.

The CP attaching unit304has a function to attach a CP to the time domain signal input from the inverse FFT unit303and output the resultant signal to outside the baseband unit300. The CP (Cyclic Prefix) is used for the reception side to recognize the start and end of the substantial data contained in the time domain signal transmitted thereto, and attaching the CP means copying a predetermined number of bits from the end of the time domain signal to the start thereof. The CP may be called a guard interval as well.

The CP removing unit307has a function to remove the CP from the time domain signal input from outside of the baseband unit300, and output the time domain signal, from which the CP has been removed, to the FFT unit306.

The FFT unit306transforms the time domain signal input from the CP removing unit307, from which the CP has been removed, to a frequency domain signal by performing the FFT onto the time domain signal, and outputs the frequency domain signal to the signal demodulation unit305.

The signal demodulation unit305has a function to obtain a demodulated signal by demodulating the frequency domain signal input from the FFT unit306, and output the demodulated signal to the MAC processing unit301.

The signal converter100includes a CP removing unit101, a FFT unit102, a weight calculating unit103, an inverse FFT unit104, a CP attaching unit105, an inverse FFT unit106, a CP attaching unit107, a CP attaching unit111, an inverse FFT unit112, an array processing unit113, a FFT unit114, a CP removing unit115, a FFT unit116, and a CP removing unit117.

In the signal converter100, the time domain signal output from the baseband unit300is received by a first interface unit118, and then input into the CP removing unit101. Also, a time domain signal to which a CP has been attached by the CP attaching unit111is output from the first interface unit118to the baseband unit300. The first interface unit118is provided with two ports one of which is used for transmitting time domain signals on which the adaptive array process has not been performed, and the other is used for receiving such time domain signals.

Also, in the signal converter100, time domain signals output from the radio units420and421are received by a second interface unit119, and then input into the CP removing units115and117, respectively. Also, time domain signals to which CPs have been attached by the CP attaching units105and107are output from the second interface unit119to the radio units420and421, respectively. The second interface unit119is provided with two ports one of which is used for transmitting time domain signals on which the adaptive array process has not been performed, and the other is used for receiving such time domain signals.

The first interface unit118and the second interface unit119are ports conforming to the standard of the communication path to which the baseband unit300and radio units had originally been connected. For example, when the baseband unit300and radio units had been connected by an optical fiber cable conforming to the standard of OBSAI (Open Basestation Standard Initiative), the first interface unit118and the second interface unit119are ports conforming to the standard of OBSAI; and when the baseband unit300and radio units had been connected by an optical fiber cable conforming to the standard of CPRI (Common Public Radio Interface), the first interface unit118and the second interface unit119are ports conforming to the standard of CPRI.

The CP removing unit101has a function to remove the CP from the time domain signal input from the baseband unit300via the first interface unit118, and output the time domain signal, from which the CP has been removed, to the FFT unit102.

The FFT unit102transforms the time domain signal input from the CP removing unit101, from which the CP has been removed, to a frequency domain signal by performing the FFT onto the time domain signal, and outputs the frequency domain signal to the signal demodulation unit103.

The weight calculating unit103has a function to perform a weighting calculation by multiplying the weight signal calculated by the array processing unit113, and output as many frequency domain signals as the number of antennas. Note that the weighting calculation is already known, and detailed description thereof is omitted here. The weight calculating unit103outputs the frequency domain signal for the radio unit420to the inverse FFT unit104, and outputs the frequency domain signal for the radio unit421to the inverse FFT unit106.

The inverse FFT unit104has a function to transform the frequency domain signal input from the signal modulation unit103to a time domain signal by performing the inverse FFT onto the frequency domain signal, and output the time domain signal to the CP attaching unit105.

The CP attaching unit105has a function to attach a CP to the time domain signal input from the inverse FFT unit104and output the resultant signal to the radio unit420via the second interface unit119.

The inverse FFT unit106has a function to transform the frequency domain signal input from the signal modulation unit103to a time domain signal by performing the inverse FFT onto the frequency domain signal, and output the time domain signal to the CP attaching unit107.

The CP attaching unit107has a function to attach a CP to the time domain signal input from the inverse FFT unit104and output the resultant signal to the radio unit421via the second interface unit119.

The CP removing unit117has a function to remove the CP from the time domain signal input from the radio unit421via the second interface unit119, and output the time domain signal, from which the CP has been removed, to the FFT unit116.

The FFT unit116has a function to transform the time domain signal input from the CP removing unit117, from which the CP has been removed, to a frequency domain signal by performing the FFT onto the time domain signal, and output the frequency domain signal to the array processing unit113.

The CP removing unit115has a function to remove the CP from the time domain signal input from the radio unit420via the second interface unit119, and output the time domain signal, from which the CP has been removed, to the FFT unit114.

The FFT unit114has a function to transform the time domain signal input from the CP removing unit115, from which the CP has been removed, to a frequency domain signal by performing the FFT onto the time domain signal, and output the frequency domain signal to the array processing unit113.

The array processing unit113has a function to return a plurality of frequency domain signals input from the FFT units114and116by performing an array combining process onto the frequency domain signals and output a single frequency domain signal to the inverse FFT unit112. Also, the array processing unit113has a function to notify the weight calculating unit103of a weight signal that is to be multiplied during the outputting performed by the weight calculating unit103. Note that the array combining process is already known, thus detailed description thereof is omitted here.

The inverse FFT unit112has a function to transform the frequency domain signal input from the array processing unit113to a time domain signal by performing the inverse FFT onto the frequency domain signal, and output the time domain signal to the CP attaching unit111.

The CP attaching unit111has a function to attach a CP to the time domain signal input from the inverse FFT unit112and output the resultant signal to the baseband unit300via the first interface unit118.

The radio unit420has a function to convert the time domain signal, which is input from the signal converter100and to which a CP has been attached by the CP attaching unit105, to an analog signal and transmit the analog signal via the antenna430wirelessly. Also, the radio unit420has a function to transform the time domain signal, which is received wirelessly via the antenna430, to a digital signal and output the digital signal to the signal converter100.

The radio unit421has a function to convert the time domain signal, which is input from the signal converter100and to which a CP has been attached by the CP attaching unit107, to an analog signal and transmit the analog signal via the antenna431wirelessly. Also, the radio unit421has a function to transform the time domain signal, which is received wirelessly via the antenna431, to a digital signal and output the digital signal to the signal converter100.

Note that it is necessary to add radio units and antennas as needed to the base station, in addition to those that had been provided originally in the base station.

FIG. 2shows an actual use form of the wireless base station described above, namely an arrangement example of the constituent elements.

The antennas430and431are, for example, installed in the rooftop of the building, and the radio units420and421are installed together with the antennas, respectively. From the radio unit420, two optical fiber cables for transmission and reception are extended to the signal converter100in an operator room200. From the radio unit421, two optical fiber cables for transmission and reception are extended to the signal converter100in the operator room200. The signal converter100is connected with the baseband unit300by the two optical fiber cables.

Note that the operator room200may be present in the building in which the radio units420and421are placed.

As described so far, according to the embodiment of the present invention, it is possible to cause a wireless base station not supporting the adaptive array to support the adaptive array, only by additionally providing a signal converter between the baseband unit and the radio units connected by optical fiber cables and preparing antennas and radio units as needed.

In the baseband unit, preparing the functional units: the MAC processing unit; signal modulation unit; and signal demodulation unit take more cost than preparing the functional units: the CP removing unit101; FFT unit102; CP attaching unit111; and inverse FFT unit112.

The signal converter is not provided with the MAC processing unit, signal modulation unit, or signal demodulation unit. Accordingly, it requires less cost for the present invention to cause a wireless base station not supporting the adaptive array to support the adaptive array, than realizing it by replacing the baseband unit.

In the above embodiment, a method for implementing the present invention has been described. However, embodiments of the present invention is not limited to this. The following describes various modifications other than the above embodiment that are included in the concept of the present invention.

(1) In the above embodiment, two antennas (antennas430and431) are used. However, the number of antennas is not limited to two, but a plurality of, for example, four antennas may be used. In that case, the signal converter needs to be provided with as many inverse FFT units, CP attaching units, FFT units, and CP removing units as the number of antennas, and the weighting calculation and the array combining calculation need to be performed in correspondence with the number of antennas. Also, in that case, the second interface unit119needs to be provided with four ports for transmission and four ports for reception.
(2) In the above embodiment, in the state of not supporting the adaptive array, the wireless base station has one antenna, and the baseband unit300has a structure of one-input, one-output.

However, when the wireless base station is a WiMAX base station, the base station is provided with two antennas and the baseband unit has a structure of two inputs and two outputs because the WiMAX base station supports MIMO.

Accordingly, in that case, in the signal converter, the first interface unit118has a port structure of two inputs and two outputs in correspondence with the number of inputs and outputs of the baseband unit.

(2) In the above embodiment, the time domain signal may only need to contain information of the time domain, and may be a modulation signal containing time domain information.

INDUSTRIAL APPLICABILITY

The signal converter of the present invention is useful as a device that enables a wireless base station not supporting the adaptive array to support the adaptive array without replacement of the baseband unit.

REFERENCE SIGNS LIST