JP2015177211A - Digital radio receiver and digital radio communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a digital radio receiver capable of restraining change in a propagation path by reducing the amount of relative movement of a reception point relative to the earth.SOLUTION: A digital radio receiver 1000 comprises: a linear array antenna 10 arranged along the travelling direction of a mobile object; a switching unit 20 for sequentially switching an antenna which is made receivable; a Doppler shift estimating unit 306 for estimating the amount of Doppler shift on the basis of a signal received from an earth station via the antenna made receivable by the switching unit; an interpolation unit 304 for performing interpolation to a plurality of reception signals received from the earth station via the antenna made receivable by the switching unit; and a switching control unit 308 for controlling antenna switching by the switching unit so that the amount of Doppler shift of the interpolated signal will be minimum.

Description

  The present invention relates to a configuration of a receiving apparatus for a mobile unit that performs digital communication between a mobile station installed on a mobile unit that moves at high speed and a ground station installed on the ground.

  Mobile communication terminals such as smartphones are now a daily necessities, and the amount of communication is increasing even in buses, trains, and airplanes.

  In an environment where a large number of terminals exist and involve movement, it is more efficient for each terminal to communicate via a relay device installed in the moving body than to individually communicate with a base station outside the moving body. It is preferable also from a surface. Public wireless LAN (Local Area Network) services using this method have already been provided for buses and trains. However, due to the recent increase in the number of terminals and traffic volume, a shortage of entrance lines is becoming apparent.

  In the Shinkansen, LCX (Leaky Coaxial cable) is used for the entrance line, and research to improve performance (for example, see Non-Patent Document 1) has been conducted. However, there is a concern that the capacity will be insufficient. Considering the introduction of a new entrance line, multi-level modulation such as 256QAM and 1024QAM, massive MIMO, and use of high frequencies such as millimeter waves are assumed. However, conventional equalization based on a reference signal is fast. Since the performance is significantly degraded due to channel fluctuation, new countermeasures are required.

  By the way, conventionally, in order to reduce the Doppler shift that occurs with high-speed movement and reduce the fluctuation speed of fading, in addition to 1) selecting a low carrier frequency and 2) applying fading equalization technology, 3) A method of providing fading tolerance using an orthogonal frequency-division multiplexing (OFDM) method is known.

  However, in the method 1), frequency resources are limited, and it is not easy to secure a wide band at a low frequency. In the method 2), since a known signal necessary for equalization needs to be frequently transmitted, a portion contributing to information transmission in the transmission signal is reduced. In addition, it is necessary to perform calculations at high speed in order to follow fluctuations. Even in the method 3), the Doppler shift causes interference between subcarriers constituting the OFDM, resulting in performance degradation.

  Therefore, in the patent document, reception at a point relatively fixed with respect to the ground based on a plurality of reception signals received from the base station using a plurality of antennas arranged along the traveling direction of the moving body. A method for estimating a signal and estimating or demodulating a modulation parameter using this estimated value is shown.

  And in patent document 2, the method of minimizing the reception characteristic degradation of the virtual reception signal when the reception characteristic degradation occurs in the reception signals of some antennas, which is the drawback of the method according to Reference Document 1. It is shown.

  Furthermore, the adaptive array antenna control apparatus disclosed in Patent Document 3 has an array having a plurality of antenna elements for the purpose of suppressing interference generated in subcarriers due to the Doppler effect or the like when receiving signals transmitted by OFDM. Based on a digital signal output from the analog / digital conversion means that is output from the antenna means and receives an analog received signal after weighted synthesis as an input signal, adaptively controls weighting factors for a plurality of antenna elements. This apparatus performs an Fourier transform of a digital signal to extract a signal component for each of a plurality of subcarriers included in an analog reception signal, and a signal component for a predetermined subcarrier among the plurality of subcarriers And adaptive control means for adjusting the weighting coefficient so as to suppress.

JP 2002-152105 A JP 2002-345429 A JP 2004-214857 A

Ohashi, Akinori et al., Mitsubishi Electric Technical Review, pp.595, Nov. 2012.

  However, when trying to apply the methods of Patent Document 1 and Patent Document 2 to a wireless system that adopts an existing wireless standard, the existing wireless standard forms a frame composed of a plurality of symbols, and a propagation path in units of this frame. Therefore, there is a problem that it is difficult to equalize the propagation path. It is also necessary to detect the moving speed.

  In the method of Patent Document 3, it is necessary to adjust the weighting coefficient according to the situation each time, and the calculation load is heavy. In addition, since channel estimation and channel equalization are performed in units of frames, it is also a problem that channel equalization becomes difficult.

  The present invention has been made to solve the above-described problems, and is a digital radio reception capable of reducing the amount of movement of a reception point relative to the ground and suppressing a change in propagation path. An apparatus and a digital wireless communication system are provided.

  According to an aspect of the present invention, there is provided a digital wireless receiver for a mobile body that performs digital wireless communication, and a plurality of antennas arranged along a traveling direction of the mobile body, and reception is possible among the plurality of antennas. A switching unit for sequentially switching antennas, a Doppler shift estimation unit for estimating a Doppler shift amount based on a signal received from a ground station via an antenna that can be received by the switching unit, and a switching unit An interpolation unit that performs interpolation on a plurality of received signals received from a ground station via an antenna that can be received, and a unit that performs demodulation and decoding on the interpolated signal And a switching control unit for controlling switching of the antenna by the switching unit so that the Doppler shift amount in the interpolated signal is minimized. Equipped with a.

  Preferably, the moving body is a vehicle that moves on a track, and the plurality of antennas are arranged on an outer upper portion of the moving body along a traveling direction of the moving body.

  Preferably, for a frame constituting a signal of digital wireless communication, the switching control unit synchronizes with the frame period at the timing of switching from the rear end element that performs reception to the first element at the end of the frame period. Switch to.

  Preferably, the switching control unit switches the antenna with respect to a symbol included in a frame constituting a signal of digital wireless communication at a cycle timing that is an integer ratio of the symbol cycle.

  According to another aspect of the present invention, a digital wireless communication system for performing digital wireless communication, comprising a ground station that transmits a digital wireless signal and a mobile station that receives the digital wireless signal, From the ground station via a plurality of antennas arranged along the traveling direction of the mobile station, a switching unit for sequentially switching the antennas that can be received among the plurality of antennas, and an antenna that can be received by the switching unit Based on the received signal, a Doppler shift estimation unit for estimating a Doppler shift amount, and interpolating a plurality of received signals received from the ground station via an antenna that can be received by the switching unit. An interpolation unit to be executed, a reception processing means for performing demodulation and decoding on the interpolated signal, and a doppling in the interpolated signal As Shifuto amount is minimum, and a switching control unit for controlling the switching of the antenna by the switching unit.

  According to the digital wireless receiver and the digital wireless communication system of the present invention, the linear array antenna composed of a plurality of antennas arranged along the traveling direction of the moving body is used in the direction opposite to the movement of the moving body. By sequentially switching the antennas to be transmitted, it is possible to reduce the amount of movement of the reception point relative to the ground and suppress changes in the propagation path.

It is a functional block diagram for demonstrating the structure of the digital radio | wireless receiver 1000 of embodiment. It is a functional block diagram for demonstrating the structure of the digital radio | wireless communications system 2000 of embodiment. It is a conceptual diagram for demonstrating the process which switches the antenna made into a receiving state in the linear array antenna. In the linear array antenna 10, it is a conceptual diagram for demonstrating the change of a received waveform when switching the antenna made into a receiving state. It is a figure which shows the example of the antenna in the case of applying the digital radio receiving apparatus 1000 of this Embodiment to a MIMO system.

  Hereinafter, a radio communication system according to an embodiment of the present invention will be described with reference to the drawings. In the following embodiments, components and processing steps given the same reference numerals are the same or equivalent, and the description thereof will not be repeated unless necessary.

(Outline of wireless communication system)
FIG. 1 is a functional block diagram for explaining a configuration of a digital radio receiving apparatus 1000 according to the embodiment.

  As will be described later, it is assumed that digital wireless reception apparatus 1000 is installed in a mobile body and receives a signal transmitted from a ground station (for example, a base station).

  Referring to FIG. 1, a digital radio receiving apparatus 1000 includes a linear array antenna 10 aligned in one direction. The linear array antenna includes n antennas. When it is necessary to distinguish each antenna, antennas 10.1 to 10. It shall be described as n.

  The digital radio receiving apparatus 1000 further includes antennas 10. a reception signal switching unit 20 for sequentially selecting and switching antennas to be received from n and a digital signal processing unit 30 for performing signal processing on the signal from the reception signal switching unit 20 .

  The digital signal processing unit 30 includes antennas 10.1 to 10. n, A / D conversion units 302.1 to 302. for analog-digital conversion of the received signals. n and the A / D converters 302.1 to 302. An interpolation interpolation unit 304 is provided for generating a signal in which the influence of the Doppler shift is reduced by performing interpolation in the time axis direction on the signals sequentially given from n.

  The digital signal processing unit 30 further includes a Doppler shift amount estimation unit 306 that estimates a Doppler shift amount based on a signal from the array antenna 10 and a signal from the interpolation unit 304, and the estimated Doppler shift amount is minimal. The received signal switching control unit 308 that sets the switching speed of the array antenna, the demodulating unit 310 that performs demodulation processing on the signal interpolated by the interpolation unit 304, and the demodulated signal A decoding / error correction unit 312 for executing decoding and error correction processing is included.

  As a method of estimating the Doppler shift amount by the Doppler shift amount estimation unit 306, for example, the following can be considered.

  1) Observe the difference between the oscillation frequency generated locally by the digital radio receiving apparatus 1000 and the reception frequency of the received signal.

  2) In a multipath environment, reflected waves arrive from various directions such as forward and backward in the moving direction, and these are subjected to different fading, so that a band is observed with respect to the original transmission frequency. When the direction of arrival of the reflected wave is uniform, this power density function S (v) can be expressed as follows, where v is a frequency shift and fd is a Doppler frequency.

It can be expressed as Thus, the Doppler shift amount can be estimated from the frequency bandwidth of the received signal.

Bibliography http://en.wikipedia.org/wiki/Rayleigh_fading
In this method, it is possible to perform estimation that is not easily influenced by an error in the oscillation frequency generated locally.

  3) When the signal transmitted from the ground station includes a plurality of frequency components, as in the case of OFDM, for example, the influence of the Doppler shift differs depending on the frequency. Therefore, the frequency shift amount between the plurality of frequency components It is also possible to detect the Doppler shift by comparing.

  FIG. 2 is a functional block diagram for explaining the configuration of the digital wireless communication system 2000 according to the embodiment.

  In FIG. 2, a train moving on a track is taken as an example of the moving body.

  In this embodiment, paying attention to the one-dimensional movement of the train 2010, a multi-element antenna is installed and the elements to be received are sequentially switched to reduce the channel fluctuation. In this technique, a linear array antenna 10 in which a large number of antenna elements are arranged in a straight line along the traveling direction of a train as shown in FIG. 2 is used.

  A radio signal is transmitted from the ground station 200 to the train, and as described in FIG. i is switched by the received signal switching unit 20.

  The linear array antenna 10, the received signal switching unit 20, and the digital signal processing unit 30 function as an in-vehicle relay station.

  The received signal from the digital signal processing unit 30 is converted again into a wireless signal (for example, a wireless LAN signal) of a predetermined communication standard via the in-vehicle access point 40, and the terminals 300.1 to 300. sent to m.

  FIG. 3 is a conceptual diagram for explaining a process of switching the antenna to be received in the linear array antenna 10.

  As shown in FIG. 3, the receiving elements of the linear array antenna 10 are sequentially switched in reverse to the traveling direction according to the movement of the train 2010 between the times t1 to tm, and the entire length of the linear array antenna 10 is changed. In the movement within a certain range determined by the length L, the reception point is substantially fixed at the certain position P, so that the occurrence of channel fluctuation and Doppler shift is ideally eliminated. Even if the reception point is moved at such a high speed that it is difficult to ideally fix the reception point at the fixed position P, it is possible to reduce channel fluctuation and Doppler shift.

  Therefore, a greater effect can be expected as the carrier frequency increases and the movement speed increases.

  In the switching control of the reception signal switching control unit 308, the switching cycle and timing consider the sampling of the A / D converter, and the symbol cycle and FFT window position in the case of OFDM.

  In addition, the reception signal switching control unit 308 synchronizes with the frame period detected by a well-known method on the receiving side at the timing of switching from the rear end element that performs reception to the first element at the end of the frame period. Switch.

  That is, the total length of the linear array antenna is determined by the maximum speed assumed by the mobile body and the maximum frame length employed in the communication system.

  For example, if the frame length time is Tf (s) and the maximum velocity of the moving body is V (m / s), at least the total length L of the linear array antenna needs to be L = Tf × V or more. This is, for example, about 30 cm when V = 100 km / h and Tf = 10 ms.

  Then, as described above, the reception signal switching control unit 308 prevents an operation for switching from the last antenna in the moving direction to the first antenna in the frame. In addition, the antenna element switching timing is not the physical speed of the moving body, but the Doppler shift amount of the received signal in order to reduce the influence of the reflected wave of the radio wave from the structure on the moving body newly generated by switching. Is controlled to be minimum (or minimum).

  Then, in order to reduce deterioration in the A / D conversion process, antenna switching timing in a period that is an integer ratio of symbol periods is employed.

  FIG. 4 is a conceptual diagram for explaining changes in the received waveform when the antenna to be received is switched in the linear array antenna 10.

  The Doppler shift when the mobile station moves is caused by an increase in the number of waves that reach the mobile station per unit time as a result of an increase in the relative speed of the mobile station with respect to the radio wave.

  Consider a case where the array antenna 10 is moving toward the ground station 200 as shown in FIG. At this time, reception is performed by the antenna 10.1.

  On the other hand, at a certain point in time, as shown in FIG. 4B, when the antenna that is in the reception state is switched to the antenna 10.2, the antenna that receives the wave is effectively opposite to the moving direction of the moving body. It will move in the direction.

  As a result, when the antenna is sequentially switched in the direction opposite to the moving direction of the moving body in this way, the average for a certain period of time is equivalent to receiving at a fixed position regardless of the movement of the moving body. State.

  However, since the antenna switching in the array antenna 10 is discontinuous at regular intervals as described above, the interpolation interpolating unit 304 interpolates such discontinuity with respect to the time axis to continuously detect the antenna. Generate a signal equivalent to moving.

  In such a calculation, a signal at a virtual fixed position may be estimated by estimating the moving speed of the moving body as in Patent Document 1 (Japanese Patent Laid-Open No. 2002-152105). .

  Many systems currently employ MIMO (multiple-input and multiple-output) technology.

  FIG. 5 is a diagram illustrating an example of an antenna when the digital radio receiving apparatus 1000 according to the present embodiment is applied to such a MIMO scheme.

  FIG. 5 is a view of the train 2010 as viewed from above.

  As shown in FIG. 5, if the linear array antennas 10 are provided in two rows with respect to the traveling direction and the antennas in each row are sequentially switched in the same manner as described above, the receiving side supports MIMO. Can be received.

  As described above, according to the digital radio receiving apparatus and the digital radio communication system of the present embodiment, the mobile station uses a linear array antenna including a plurality of antennas arranged along the traveling direction of the mobile object. By sequentially switching the antennas used in the direction opposite to the movement of the body, it is possible to reduce the amount of movement of the reception point relative to the ground and suppress the change of the propagation path.

  Therefore, when the antenna element interval and the moving speed are optimal, it can be equivalent to receiving at a point fixed relative to the ground, and the moving speed is substantially equal in other cases. Therefore, equalization of the propagation path functions effectively by reducing the fluctuation speed of fading caused by movement. This enables efficient transmission and facilitates coexistence with conventional equipment.

  Embodiment disclosed this time is an illustration of the structure for implementing this invention concretely, Comprising: The technical scope of this invention is not restrict | limited. The technical scope of the present invention is shown not by the description of the embodiment but by the scope of the claims, and includes modifications within the wording and equivalent meanings of the scope of the claims. Is intended.

  10 Linear array antenna, 10.1-10. n antenna element, 20 received signal switching unit, 30 digital signal processing unit, 200 ground station, 302.1 to 302. n A / D conversion unit, 304 interpolation unit, 306 Doppler shift amount estimation unit, 308 received signal switching unit, 310 demodulation unit, 312 decoding / error correction unit, 40 in-vehicle access point, 300.1 to 300. m terminal, 1000 digital wireless receiver, 2000 digital wireless communication system, 2010 train.

Claims (5)

A receiving device for a mobile body that performs digital wireless communication,
A plurality of antennas arranged along the traveling direction of the moving body;
A switching unit for sequentially switching antennas that can be received among the plurality of antennas;
A Doppler shift estimation unit for estimating a Doppler shift amount based on a signal received from a ground station via an antenna enabled to be received by the switching unit;
An interpolation unit that performs interpolation on a plurality of received signals received from the ground station via an antenna that can be received by the switching unit;
Reception processing means for performing demodulation and decoding on the interpolated signal;
A digital radio receiving apparatus comprising: a switching control unit that controls switching of an antenna by the switching unit so that a Doppler shift amount in the interpolated signal is minimized. The moving body is a vehicle that moves on a track,
The digital radio reception apparatus according to claim 1, wherein the plurality of antennas are arranged on an outer upper portion of the moving body along a traveling direction of the moving body.   For the frames constituting the digital wireless communication signal, the switching control unit synchronizes with the frame period at the timing of switching from the rear end element that performs reception to the first element at the end of the frame period. The digital wireless receiver according to claim 1, wherein switching is performed.   4. The switching control unit according to claim 1, wherein the switching controller switches the antenna at a cycle timing that is an integer ratio of a symbol cycle with respect to a symbol included in a frame constituting the digital wireless communication signal. The digital wireless receiver described. A digital wireless communication system for performing digital wireless communication,
A ground station that transmits digital radio signals;
A mobile station for receiving the digital radio signal, the mobile station,
A plurality of antennas arranged along the traveling direction of the mobile station;
A switching unit for sequentially switching antennas that can be received among the plurality of antennas;
A Doppler shift estimation unit for estimating a Doppler shift amount based on a signal received from a ground station via an antenna enabled to be received by the switching unit;
An interpolation unit that performs interpolation on a plurality of received signals received from the ground station via an antenna that can be received by the switching unit;
Reception processing means for performing demodulation and decoding on the interpolated signal;
And a switching control unit that controls switching of the antenna by the switching unit so that a Doppler shift amount in the interpolated signal is minimized.