Patent Application
20120178361
The present invention relates to a fading signal forming device, a channel signal transmission device and a fading signal forming method.
In recent years, radio cellular systems typified by mobile phone sets or the like have diversified service modes and are required to transmit not only speech data but also large-volume data such as still images and moving images by a high speed. As one such technology of realizing high-speed, large-volume transmission, MIMO (Multiple Input Multiple Output), which is a space division multiplexing scheme, is becoming a focus of attention and various research and development efforts and operation tests or the like are under way.
LTE (Long Term Evolution), which is a next-generation cellular system, assumes a service having a downlink peak rate on 100 Mbps and has determined to adopt MIMO technology for realizing this service.
MIMO transmission requires both a base station and a terminal to be provided with a plurality of antennas (multiple antennas). This transmission performance using MIMO technology depends on not only multi-antenna characteristics mounted on the terminal but also a relative environment between multiple antennas and a propagation environment surrounding the multiple antennas. Therefore, to satisfy quality requirements or the like for MIMO transmission, it is necessary to define a performance evaluation method and required performance for multiple antennas including the propagation environment.
Evaluating the performance of multiple antennas mounted on the terminal requires an OTA (Over The Air) evaluation using a spatial channel emulator that simulates a multipath environment, and 3GPP (3rd Generation Partnership Project) has currently started studies on this MIMO OTA.
Examples of MIMO OTA evaluation systems proposed until today include one disclosed in Non-Patent Literature 1. The MIMO OTA evaluation system disclosed in Non-Patent Literature 1 is configured of a fading simulator (FS) and an antenna for simulating local scatterers, and the system according to Non-Patent Literature 1 discloses a MIMO-based fading simulator that has eight output ports and performs signal processing for simulating an arbitrary multipath channel from the output ports, and eight antennas for simulating local scatterers connected to the respective output ports of the fading simulator. Therefore, in the MIMO OTA evaluation system in Non-Patent Literature 1, the fading simulator has eight independent channels, and can thereby generate eight independent fading waves weighted by eight spatially arranged antennas. In this way, the MIMO OTA evaluation system can construct a variety of space-times in a simulated fashion.
In a MIMO OTA evaluation system constructed of a fading simulator and antennas for simulating local scatterers, re-creating (generating) a more complicated simulative space-time requires that the number of antennas for local scatterers be increased and different fading waves be outputted from the respective antennas.
However, the MIMO OTA evaluation system described in Non-Patent Literature 1 needs to provide as many channels of the fading simulator as antennas for local scatterers, and therefore when the number of antennas increases, the number of channels increases in proportion thereto. Therefore, in the above-described MIMO OTA evaluation system, narrowing the antenna interval, increasing the number of antennas and densely arranging antennas in order to construct a more precise space-time would involve concern that the fading simulator might have an extremely complicated configuration, resulting in a high-cost evaluation system. On the other hand, widening the antenna interval and arranging a reduced number of antennas to reduce the cost would cause space-time densities to be reduced and cause the evaluation resolution of the MIMO OTA evaluation system itself to deteriorate.
It is an object of the present invention to provide a fading signal forming device, a channel signal transmission device and a fading signal forming method capable of constructing a complicated space-time with a simple structure.
A fading signal forming device according to the present invention includes a fading signal forming section that receives a channel signal transmitted from a main antenna from a fading simulator as input and forms a plurality of fading signals transmitted from different sub-antennas based on the channel signal and a phase rotation section provided in the fading forming section, that adds a phase corresponding to a relative position relationship between the main antenna and the sub-antenna into the channel signal and outputs the channel signal as the fading signal.
A channel signal transmission device according to the present invention includes the above-described fading signal forming device, the main antenna and the sub-antennas, wherein the main antenna and the sub-antennas are provided with a vertical polarized antenna or horizontal polarized antenna and vertical polarized antenna respectively.
A fading signal forming method according to the present invention is a fading signal forming method for receiving a channel signal transmitted from a main antenna and forming a plurality of fading signals transmitted from different sub-antennas based on the channel signal, including a step of forming a duplication signal for duplicating the channel signal, and a fading signal forming step of adding a phase corresponding to a relative position relationship between the main antenna and the sub-antenna into the duplication signal and outputting the duplication signal as the fading signal.
The present invention can provide a fading signal forming device, a channel signal transmission device and a fading signal forming method capable of constructing a precise space-time with a simple structure.
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the embodiments, the same components will be assigned the same reference numerals and overlapping descriptions thereof will be omitted.
[MIMO OTA Evaluation System 10]
Fading simulator 100 receives a predetermined MIMO transmission signal as input, generates a spatio-temporal channel signal and outputs the signal to fading signal forming device 200. The spatio-temporal channel signal is generated by producing an arbitrary delay wave in an input signal and multiplying each delay wave produced by a MIMO channel matrix made up, for example, of 4×4 elements. The channel signal is subjected to such signal processing inside a MIMO-based fading simulator and then outputted from a plurality of output terminals.
Fading signal forming device 200 receives a channel signal group as input. Fading signal forming device 200 then duplicates a channel signal, adjusts each of the plurality of duplication signals and thereby forms a plurality of fading signals expressing spatial expansion. The channel signal and the plurality of fading signals are outputted from different antenna ports. To be more specific, the channel signal is outputted from a main antenna port connected to a main antenna, and the fading signals adjusted by phase-rotating the channel signal by different amounts of rotation are outputted from sub-antenna ports connected to sub-antennas.
Antenna device 300 is connected to each antenna port of fading signal forming device 200 and has antenna groups which are actually spatially arranged. Antenna device 300 then transmits the channel signals and fading signals received from fading signal forming device 200, from antennas that form a space.
[Configuration of Fading Signal Forming Device 200]
Control section 210 generates signal adjustment control signals and outputs the control signals to signal forming base unit 220.
Signal forming base unit 220 receives the channel signal as input, duplicates the channel signal, adjusts each duplication signal and thereby forms a fading signal having spatial expansion. Signal forming base units 220-1 to 4 are subject to the four channel signals outputted front fading simulator 100 respectively.
Signal forming base unit 220 has distribution section 221 and signal adjustment section 222 as shown in
Distribution section 221 forms a plurality of duplication signals from the inputted channel signal, and outputs the channel signal and the plurality of duplication signals to signal adjustment section 222.
Signal adjustment section 222 in Embodiment 1 has phase adjustment sections 231-1 and 2. Signal adjustment section 222 adjusts the duplication signal received from distribution section 221 based on the signal adjustment control signal received from control section 210 and thereby forms a spatial fading signal. To be more specific, antennas connected to phase adjustment sections 231-1 and 2 are arranged spatially on the right and left sides of a reference antenna to which a signal not passing through the phase adjustment section is inputted. Signal adjustment section 222 then gives predetermined amount of phase rotation at phase adjustment sections 231-1 and 2, and thereby forms two fading signals of different amounts of Doppler shift. The amount of phase rotation given by phase adjustment sections 231-1 and 2 corresponds to a difference from the original signal having an amount of Doppler shift corresponding to the antenna arrangement.
For example, phase adjustment section 231-1 gives phase rotation by ej(w+Δw)t and phase adjustment section 231-2 provides phase rotation by ej(w−Δw)t. This causes two fading signals equally phase-rotated before and after the phase of the channel signal as a reference to be formed.
The fading signals formed in signal adjustment section 222 are outputted from sub-antenna ports connected to the sub-antennas to antenna device 300, and the channel signal is outputted from a main antenna port connected to the main antenna to antenna device 300. Here, a case has been described where there are two phase adjustment sections 222 and two sub-antenna ports, but there are no restrictions other than that the number of antennas needs to be an odd number, and in cases where there are three or more antennas, the device may also be constructed with similar means.
[Configuration of Antenna Device 300]
Each antenna group 310 has antennas 311-1 to 3. Antennas 311-1 and 3 are connected to phase adjustment sections 231-1 and 2 respectively via antenna ports. That is, antenna 311-2 is a main antenna that transmits a channel signal and is arranged in the center of each group, and antennas 311-1 and 3 are sub-antennas that transmit a fading signal.
All antennas 311 provided for antenna device 300 are arranged on the same circumference. Furthermore, in each antenna group 310, antennas 311-1 to 3 are arranged in order of antennas 311-1, 2 and 3 in one direction (clockwise or counterclockwise).
A terminal of multi-antenna (receiving antenna) to be evaluated is arranged in the center of the circle on which above antennas 311 are disposed.
[Operation of Fading Signal Forming Device 200]
Operation of fading signal forming device 200 configured as shown above will be described.
The channel signal generated by fading simulator 100 and simulating an arbitrary multipath propagation is inputted to fading signal forming device 200.
In fading signal forming device 200, signal forming base units 220-1 to 4 each receive a channel, signal as input, duplicate the channel signal, adjust each duplication signal and thereby form a plurality of fading signals.
To be more specific, phase adjustment sections 231-1 and 2 provided in signal forming base unit 220 phase-rotate the duplication signal by different amounts of rotation and thereby form two fading signals.
The fading signals and channel signals formed in this way are outputted from different antenna ports.
When a fading simulator is connected to each antenna, the same number of attenuators, delay lines and phase shifters as the number of antennas×attenuator for the number of delays such as Σ(i: number of antennas)Σ(n: number of delays)Ainejwint+Δtin are required, but adopting such a configuration only requires a configuration with the same number of attenuators, delay lines and phase shifters as attenuator for the number of delays such as Σ(i: number of sub-antennes)[(Σ(n: number of delays)Ainejwnt+Δtn)ewcosθit] and the same number of phase shifters as the number of sub-antennas. As a result, it is possible to construct a precise space-time with a relatively simple circuit structure.
Amplitude adjustment sections 232-1 to 3 adjust the amplitudes of their respective fading signals and channel signal. This makes it possible to change the space-time center of gravity having an incoming wave distribution that forms a certain group such as a Gaussian distribution or Laplacian distribution.
In a channel signal transmission device made up of fading signal forming device 200 and antenna device 300 of the present embodiment, each antenna 311 is constructed of a horizontal polarization antenna and a vertical polarization antenna.
By doing so, it is possible to generate a space-time taking into account XPR (cross polarization ratio) generated in a cellular environment, and realize MIMO OTA evaluation system 10 close to an actual environment.
Antenna position adjustment apparatus 410 adjusts a setup position (that is, spatial coordinates) of antenna 311 without changing a setup posture of antenna 311 (that is, three-dimensional coordinate system using a reference point in antenna 311 in a set up condition as the origin).
To be more specific, as shown in
Antenna position adjustment apparatus 410 adjusts the amount of rotation of a motor (not shown), power of the motor is transmitted to the central axis of the circular frame, and the circular frame thereby rotates. This causes the positions of antennas 311-1 and 3 with respect to antenna 311-2 to change. That is, antenna position adjustment apparatus 410 controls the rotation of the circular frame, and can thereby realize a plurality of antenna arrangement patterns.
Furthermore, since antennas 311-1 to 3 are axially attached to the circular frame, it is possible to always keep the postures of antennas 311-1 to 3 constant, based on the same principle as that of gondolas of a Ferris wheel which are always oriented in the vertical direction.
This makes it possible to perform MIMO OTA evaluation in a plurality of antenna arrangement patterns without increasing the number of antennas 311.
The disclosure of Japanese Patent Application No. 2009-221249, filed on Sep. 25, 2009, including the specification, drawings and abstract is incorporated herein by reference in its entirety.
The fading signal forming device, channel signal transmission device and fading signal forming method according to the present invention are useful as those capable of constructing a complicated space-time with a simple structure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-221249 | Sep 2009 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2010/005739 | 9/22/2010 | WO | 00 | 3/20/2012 |
