JP2007235305A - Receiver, receiving method and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a receiver of simple circuitry in which inter-carrier interference can be lessened by receiving such a signal as the factor of reception characteristics aggravation, i.e. Doppler shaft, is minimized during high speed movement. <P>SOLUTION: Out of directivity antennas 11a-11d provided in a mobile, pointing range of antennas 11b, 11d in the advance right/left direction of the mobile is set narrower than the pointing range of antennas 11a, 11c in the advance front/back direction. Based on the receiving power value of each antenna obtained from a receiving power measuring section 14 and the moving speed of the mobile obtained from a moving speed detecting section 21, an antenna selecting section 15 selects such a signal of the antenna 11b or 11d as the Doppler shaft is minimized preferentially during high speed movement, and an OFDM demodulation section 23 demodulates a selected signal. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technique for receiving radio waves when moving at high speed.

  In recent years, techniques for receiving terrestrial digital broadcasts while moving at high speed, such as on-vehicle reception, have been actively studied. Digital terrestrial broadcasting employs OFDM (Orthogonal Frequency Division Multiplexing), which is one of multi-carrier transmission schemes, and performs transmission using a number of orthogonal carriers. The multicarrier scheme is generally known as a modulation scheme that has excellent resistance to frequency selective fading, which is a kind of mobile radio channel. Frequency selective fading has a problem of degrading channel quality in broadband wireless communication.

  Under a high-speed moving reception environment, when a radio wave modulated by the OFDM method is received, a Doppler shift, which is a frequency shift based on the Doppler effect, becomes an obstacle. Doppler shift is particularly likely to cause deterioration in reception characteristics when a multipath through which radio waves propagate through a plurality of paths has frequency selectivity. This is because if frequency fluctuations occur independently for each subcarrier, synchronization between subcarriers on the receiving side becomes difficult, orthogonality is lost, and intercarrier interference (ICI) occurs. Since the frequency shift caused by the Doppler shift is proportional to the speed of the moving body, inter-carrier interference becomes particularly noticeable during traveling at high speed. In order to suppress inter-carrier interference in a multipath environment, there is a method of estimating each path and equalizing its fluctuation component. Patent Document 1 (Japanese Patent Laid-Open No. 2003-87213) proposes a concept of providing a plurality of directional antennas with different directivity directions on a moving body and switching the directivity to improve characteristic degradation due to inter-carrier interference in a multipath environment. is doing.

  FIG. 3 shows a combination of the first and second embodiments described in Patent Document 1. In FIG. 3, the 360 ° range around the moving vehicle is divided into four sectors of 90 °, and directional antennas 31 a to 31 d are provided in each sector. The antennas 31a and 31c have directivity in the forward and backward direction of the vehicle, and the antennas 31b and 31d have directivity in the lateral direction of the vehicle. The radio receiving units (RV) 32 a to 32 d amplify radio signals received by the antennas 31 a to 31 d, convert the frequencies to baseband signals, and input the baseband signals to the antenna switching unit 33. The reception power measurement unit 34 measures reception power by measuring reception signal strength of each of the radio reception units 32a to 32d, for example, Received Signal Strength Indicator (RSSI). The antenna selection unit 35 selects an antenna that minimizes fading fluctuation (Doppler spread) based on the received power and moving speed detection unit 41 based on the velocity information of the moving object. The received signal of the selected antenna is input to the orthogonal demodulator 36 that constitutes the demodulator DEM. The orthogonal demodulator 36 performs orthogonal demodulation processing on the received signal. The demodulated signal is timing-synchronized by the GI removal unit 37 and is output after the guard period (GI) is removed. The variation average shift amount calculation unit 38 calculates the variation average shift amount Δθ per symbol of multipath fading by calculating the correlation between the known pilot signal and the received signal. The multiplier 39 multiplies the received signal by exp (−jΔθ) to compensate for multipath fading. The FFT operation unit 40 converts a time-axis signal into a frequency-axis signal (carrier signal). The frequency axis signal is subjected to error detection correction and decoding processing by an error detection and correction decoding unit (not shown).

Here, the operation of the antenna selection unit 35 (method for selecting an antenna) will be described in detail. To that end, the frequency characteristics of fading will be described first. The frequency characteristic of fading is expressed as Doppler spectrum (S (f)) as shown in FIG. 7A by the scattering ring model of James. Here, the average value is assumed to be received with equal power from all directions, and since the initial phase of each elementary wave is instantaneously different, the fading frequency or Doppler frequency (fd) is within a frequency range defined by dispersion ( −fd _{max to} fd _max ).

  Note that the fading frequency or Doppler shift frequency fd described above is such that the travel speed vector length of the moving body is V, the angle between the travel speed direction and the radio wave arrival direction is θ, the broadcast frequency is fc, and the radio wave propagation speed is C. Can be expressed by the following (formula 1).

f _d = (1 / C) · V · cos θ (Formula 1)
When an omnidirectional antenna is used, the signal is subjected to fluctuations having a Doppler spread (Δfd) as shown in FIG. Therefore, the maximum frequency fluctuation between carriers is 2 fd _max , and the evaluation of inter-carrier interference is this worst case. This scattering ring assumes that an incoming wave (elementary wave) with a time difference smaller than the time resolution of the receiver (that is, there is no path difference of the incoming path) is received from the 360 ° direction of the moving body and becomes a synthesized wave. When the reception point moves in such a case, Doppler fluctuations according to the arrival direction (θ) of the elementary wave occur (dynamic fading model).

  When a directional antenna, for example, a 90 ° directional antenna is used, the signal is subjected to fluctuations having a Doppler spread Δf as shown in FIG. 7B for each path within the directional range. FIG. 7B is a model showing suppression of the Doppler spread (Δf) due to directivity and the average Doppler frequency (fd) of the elementary wave arriving within the directivity range. In this manner, Doppler spread can be suppressed by using a directional antenna having an arbitrary directivity range.

As shown in FIG. 4, the Doppler spread of the directional antenna in the moving body front-rear direction (S1, S3) having a directivity range of 90 ° is changed to the Doppler spread of the directional antenna in the moving body traveling left-right direction (S2, S4). The antenna selection unit 35 in FIG. 3 preferentially selects the antenna in the forward or backward direction of the moving object.
JP 2003-87213 A

  In the above conventional example, a plurality of directional antennas having an equidirective range (for example, 90 degrees each) are used, and priority is given to the antennas in the forward and backward directions so that Doppler spread is minimized among these antennas. Is selected. However, the average Doppler shift of each carrier is larger than the Doppler shift of the advancing left and right antennas, so that the inter-carrier interference also increases and the reception performance deteriorates.

  The present invention is intended to solve the above-described conventional problems, and an object of the present invention is to provide a receiving apparatus that can receive radio waves with small Doppler shift and Doppler spread and reduce inter-carrier interference.

  In order to achieve the above object, an invention according to claim 1 of the present application is a high-speed mobile reception apparatus, which includes a plurality of directional antennas having directivities in different directivity ranges in different directions, and the plurality of directional antennas. A received power measurement unit that measures received power of the received signal received at the mobile station, a movement detection unit that detects a moving speed of the moving body, and the plurality of directivities based on outputs of the received power measurement unit and the movement detection unit. An antenna selection unit that selects a directional antenna that receives a radio wave having a minimum Doppler shift among the antennas, and a reception signal selected by the antenna selection unit is demodulated.

  According to claim 2 of the present application, in the high-speed mobile receiver according to claim 1, the mobile object is compared with the directivity range of the directional antenna in the direction in which the mobile object is not traveling and the opposite direction of the plurality of directional antennas. The directivity range of the traveling directional antenna is narrow.

  A third aspect of the present invention is the high-speed mobile receiver according to the second aspect, wherein the directivity range of each directional antenna is set so that the Doppler spread of the traveling left-right antenna is equal to or less than the Doppler spread of the traveling front-rear antenna. It is characterized by determining.

  According to a fourth aspect of the present invention, in the high-speed mobile reception device according to any one of the first to third aspects, a high gain directional antenna is used as a directional antenna in a moving left and right direction of the moving body among the plurality of directional antennas. It is characterized by using.

  According to a fifth aspect of the present invention, in the high-speed mobile reception device according to any one of the first to fourth aspects, the received power of each of the directional antennas in the traveling left and right directions of the moving body among the plurality of directional antennas is set power. In the following case, the received power of the directional antennas in the left-right direction is combined, and the combined antenna is selected.

  The invention according to claim 6 of the present application selects the directional antenna that minimizes the Doppler shift among the directional antennas in which the received power exceeds the set power value in the high-speed mobile receiver according to any one of claims 1 to 5. It is characterized by this.

  The invention according to claim 7 of the present application selects the directional antenna that minimizes the Doppler shift from among the directional antennas in which the received power exceeds the set power value in the high-speed mobile receiver according to any one of claims 1 to 6. It is characterized by this.

  The invention of claim 8 of the present application is a high-speed mobile reception method, comprising: selecting one received signal from a plurality of directional received signals having different directivity ranges in different directions; and performing demodulation. In this selection process, selection is made so that the Doppler shift is minimized based on the received power of each received signal and the moving speed of the moving body.

  The invention of claim 9 of the present application is a program, characterized in that a signal processing procedure for executing the receiving method of claim 8 is described.

  According to the invention of claim 1, which achieves the above object, a signal having a minimum Doppler shift is received from received signals of a plurality of directional antennas having directivities in different directivity ranges in different directions based on received power and moving speed. There is provided a receiving apparatus capable of reducing the influence of inter-carrier interference by selecting and demodulating a selected received signal.

  Further, according to the invention of claim 2, which achieves the above object, the direction of the directional antenna in the moving left and right direction of the moving object is compared with the direction range of the directional antenna in the moving direction of the moving object among the plurality of directional antennas. By setting a narrow range, it is possible to receive a radio wave that minimizes the Doppler shift, and to reduce the influence of inter-carrier interference.

  Further, according to the invention of claim 3, which achieves the above object, by determining the directivity range of the directional antenna so that the Doppler spread of the traveling left-right antenna of the moving body is equal to or less than the Doppler spread of the traveling front-rear antenna, The Doppler shift of the received radio wave can be minimized and at the same time the Doppler spread can be suppressed to reduce the influence of inter-carrier interference.

  According to the invention of claim 4, which achieves the above object, a directional antenna having a higher gain than a directional antenna in the front-rear direction is used as a directional antenna in the left-right direction of the moving body among a plurality of directional antennas. By using it, it is possible to improve the shortage of received power in the case of a weak electric field of radio waves coming from the traveling left and right directions.

  According to the invention of claim 5 which achieves the above object, when the received power of each of the traveling directional antennas of the moving body among the plurality of directional antennas is less than or equal to the set power, the lateral directional antennas By combining the received power, it is possible to improve the shortage of received power in the case of a weak electric field of radio waves coming from the traveling left and right directions.

  According to the invention of claim 6, which achieves the above object, the influence of inter-carrier interference is reduced by selecting a directional antenna having a minimum Doppler shift among directional antennas whose received power exceeds a set power value. can do.

  According to the invention of claim 7, which achieves the above object, the mobile object synthesizes the reception signals of the directional antennas when moving at a low speed below the set speed, thereby providing an environment in which the radio wave arrival direction is not biased (low speed movement). ), The received power can be improved.

  According to the invention of claim 8, which achieves the above object, a signal having a minimum Doppler shift based on received power and moving speed from received signals of a plurality of directional antennas having different directivity ranges in different directions. And a high-speed mobile reception method that can reduce the influence of inter-carrier interference by demodulating the selected received signal.

  According to the invention of claim 9 which achieves the above object, a program describing a signal processing procedure for executing a receiving method is realized.

  In the embodiment of the present invention, a plurality of directional antennas having directivities of different directivity ranges in different directions, a received power measuring unit that measures received power of received signals received by the plurality of directional antennas, A radio wave is received so that both the Doppler shift and the Doppler spread of the plurality of directional antennas are reduced based on the output of the movement detection unit that detects the moving speed of the moving body, and the received power measurement unit and the movement detection unit. An antenna selection unit that selects a directional antenna and a demodulation unit that demodulates a reception signal selected by the antenna selection unit. With this configuration, it is possible to receive radio waves with small Doppler shift and Doppler spread that occur during high-speed movement, which is effective in reducing inter-carrier interference.

  Hereinafter, each embodiment of the invention will be described in detail with reference to the drawings.

(Embodiment 1)
FIG. 1 shows a configuration of an OFDM receiving apparatus according to Embodiment 1 of the present invention. In FIG. 1, four directional antennas are used in front, rear, left, and right with respect to the traveling direction of the moving body. The 360 degree range of the moving automobile is divided into four sectors as indicated by S1 to S4, and directional antennas 11a to 11d are provided in each sector. Sector S1 is directed in the forward direction of the vehicle, sector S3 is directed in the backward direction of the vehicle, and the remaining two sectors S2 and S4 are directed in the lateral direction of the vehicle. Here, the directivity range of the sectors S2 and S4 in the left and right direction of the vehicle travel is set narrower than the directivity range of the sectors S1 and S3 in the front and rear direction of the vehicle travel. Specifically, the directivity ranges of the directional antennas 11a to 11d are set so that the Doppler spread of the antennas (11b, 11d) in the lateral direction of travel is equal to or less than the Doppler spread of the antennas (11a, 11c) in the forward / backward direction. S1-S4) are determined. The radio receivers 12a to 12d amplify the received radio signals supplied from the antennas 11a to 11d and convert them to IF (Intermediate Frequency) signals, respectively, and supply those received signals to the antenna switching unit 13 as outputs. To do. The received power measuring unit 14 measures the received signal strength of the received signals supplied from the wireless receiving units 12a to 12d, and supplies the received power of those received signals to the antenna selecting unit 15 as an output. The moving speed detection unit 21 detects the moving speed of the moving vehicle, such as a moving body, from a speed meter or a navigation system, and supplies the moving speed of the moving body to the antenna selection unit 15 as an output. The antenna selection unit 15 selects an antenna based on the reception power and the movement speed of the reception signal of each antenna supplied from the reception power measurement unit 14 and the movement speed detection unit 21, and outputs the selected antenna information as an antenna switching unit. 13 is supplied. The antenna switching unit 13 inputs the antenna switching selected by the antenna selection unit 15 and the received signal of the switched antenna to the OFDM demodulation unit 23.

  The OFDM demodulator 23 includes an orthogonal demodulator 16, a GI remover 17, and an FFT unit 20. The orthogonal demodulator 16 performs orthogonal demodulation processing on the received signal of the antenna supplied from the antenna switching unit 13, and supplies the orthogonal demodulated signal as an output to a GI (guard interval) removal unit 17. The GI removal unit 17 removes the guard interval from the reception signal received from the quadrature demodulation unit 16 and supplies the reception signal from which the guard interval has been removed to the FFT unit 20 as an output. The FFT unit 20 converts the time-axis signal supplied from the GI removal unit 17 into a frequency-axis signal (carrier signal) by FFT (Fast Fourier Transform: FFT) processing, and outputs the signal to the equalization unit 22 as a demodulated signal. The equalization unit 22 calculates transmission path characteristics of an SP (Scattered Pilot) carrier, which is a known pilot signal defined in the digital terrestrial broadcasting standard, with respect to the frequency-axis demodulated signal, performs interpolation, and performs data interpolation. Generate carrier channel characteristics. Then, the equalizing unit 22 generates an equalized signal by dividing the frequency axis signal by the transmission path characteristic. The error correction unit 25 performs error correction of the equalized signal, the decoding unit 26 decodes the video and audio signals, and the display unit 27 displays and outputs the video and audio signals. Note that not only FFT processing but also other orthogonal transformation processing such as discrete cosine transformation, discrete wavelet transformation, etc. can be adopted as the processing of the FFT unit 20.

In the present invention, a directional antenna in which both the Doppler shift and the Doppler spread are reduced is selected so that inter-carrier interference can be reduced. Here, a trade-off occurs between the error floor due to inter-carrier interference and the S / N characteristic due to noise. Further, the inter-carrier interference is proportional to the moving speed (V) as shown in (Expression 1). That is, when the moving speed is increased, the Doppler shift fd _max is increased as shown in FIG. 6A and the Doppler spectrum is expanded to increase inter-carrier interference. However, when the moving speed is decreased, the Doppler shift fd _max is increased as shown in FIG. As shown, the Doppler shift fd _max is reduced, the Doppler spectrum is also narrowed, and the inter-carrier interference is reduced.

Next, details of the operation of the antenna selector 15 will be described. In the first embodiment of the present invention, a received power of S / N (or C / N) or higher that satisfies a required BER (BER, a scale used as a reception characteristic) at a speed higher than a preset moving speed is satisfied. If there are a plurality of antennas that exceed the antenna, the antenna that minimizes the Doppler shift is selected. Here, the received power is defined as a threshold received power (P _TH ) of the system.

The Doppler shift of the antenna having directivity in the forward direction and the backward direction is large as shown in FIG. 4A, and the Doppler shift of the antenna in the lateral direction is small as shown in FIG. Therefore, when there are a plurality of antennas that exceed the received power that satisfies the required BER at a predetermined moving speed or higher (in the case of high-speed movement), the left and right antennas are preferentially selected. That is, carrier interference or reception characteristics are calculated in advance from the maximum Doppler frequency obtained from the moving speed, a moving speed that becomes a threshold is determined, and the received power measuring unit 14 receives the received power of each of the antennas 11a to 11d above the threshold moving speed. The antenna selecting unit 15 compares the received power of each antenna with a preset threshold received power _PTH, and selects an antenna whose received power is larger than the threshold received power _{PTH as an} antenna to be selected (candidate antenna). To do. Further, the antenna selection unit 15 has a plurality of candidate antennas, and the received power of the antennas in the front-rear direction (S1, S3) and the left-right direction (S2, S4) (front-rear direction group and left-right direction group) is received by threshold reception. If it is greater than the power P _TH, the antenna 11b or 11d in the left / right direction set is always the final selection target antenna. When there is one set of candidate antennas, for example, when the two antennas 11b and 11d in the traveling right direction S2 and the traveling left direction S4 are selected, the antenna having the larger reception power is selected as the antenna to be finally selected. And

  As described above, during high-speed movement in which inter-carrier interference occurs, a carrier wave is reduced while maintaining a large reception power by selecting a directional antenna having a large reception power and a small Doppler shift and Doppler spread. be able to.

  Since the Doppler shift can be minimized, the fluctuation average shift amount calculation unit and the fading fluctuation correction unit are not necessary as described in the conventional example (Patent Document 1), and the Doppler fluctuation can be corrected with a simple equalization circuit. The circuit configuration of the receiving device is simplified.

  In addition, since a directional antenna having a narrow directivity range in the horizontal direction with respect to the traveling direction is used, the amount of radio waves that can be received is small and the received power may be small. For this reason, it is conceivable to use a high-gain antenna as a lateral directional antenna with a narrow directivity range compared to the front and rear antennas.

(Embodiment 2)
FIG. 2 shows a configuration of an OFDM receiving apparatus according to Embodiment 2 of the present invention. The difference from the first embodiment is that a combining unit 24 for combining the outputs of the radio receiving units 12b and 12d is provided, and the antenna selecting unit 15a selects each receiving antenna or combining antenna in consideration of the moving speed. The point is that the antenna switching unit 13a selects and outputs a reception signal or a combined signal from the antenna selected by the antenna selection unit 15a.

  Since a directional antenna having a narrow directivity range in the left-right direction with respect to the traveling direction is used, the amount of radio waves that can be received is small and the received power may be small. For this reason, it is conceivable to use a highly advantageous antenna as a directional antenna in the horizontal direction with a narrow directional range. However, if the reception outputs of the horizontal antennas 11b and 11d are not more than the threshold reception power, the antennas 11b and 11d are used. The antenna selection unit 15a selects the synthesized signal and demodulates the selected received signal.

  Further, in the receiving apparatus according to Embodiments 1 and 2, when the moving speed of the moving vehicle is a low speed that causes almost no inter-carrier interference, the outputs of all antennas are combined regardless of the received power. This improves the shortage of received power in the case of weak electrolysis.

  Also, the object of the present invention can be realized by describing the reception method in Embodiments 1 and 2 in a program memory as a program and performing a real-time demodulation process using a CPU.

  Further, at least a part of the receiving device may have a configuration realized by using at least one integrated circuit such as an IC, LSI, FPGA, DSP, or reconfigurable processor. In other words, any part constituting the device or a combination thereof may be integrated into an integrated circuit, and any number or type of integrated circuits may be used to realize a receiving device or receiving circuit. The reception processing may be performed using a reception program in the circuit.

  The receiving apparatus, the receiving method, and the program according to the present invention can be applied particularly to an in-vehicle receiving apparatus for terrestrial digital broadcasting, a wireless receiver, and the like.

The figure which shows the structure of the high-speed mobile receiver in Embodiment 1 of this invention. The figure which shows the structure of the high-speed mobile receiver in Embodiment 2 of this invention. Configuration diagram of a conventional receiving apparatus (Patent Document 1) Illustration of Doppler spread of directional antenna Explanatory drawing of Doppler spread of a directional antenna in Embodiments 1 and 2 of the present invention Diagram explaining the relationship between travel speed and Doppler spread Illustration of Doppler spectrum with and without directivity

Explanation of symbols

11a to 11d Antennas 12a to 12d Wireless reception unit 13 Antenna switching unit 14 Received power measurement unit 15 Antenna selection unit 16 Direct demodulation unit 17 GI removal unit 20 FFT unit 21 Movement speed detection unit 22 Equalization unit 23 OFDM demodulation unit 24 Synthesis unit 25 Error Correction Unit 26 Decoding Unit 27 Display Unit 31a to 31d Antenna 32a to 32d Wireless Reception Unit 33 Antenna Switching Unit 34 Received Power Measurement Unit 35 Antenna Selection Unit 36 Direct Demodulation Unit 37 GI Removal Unit 38 Fluctuation Average Shift Amount Calculation Unit 39 Multiplication 40 FFT unit 41 Moving speed detection unit

Claims (9)

A receiving device mounted on a mobile body,
A plurality of directional antennas having directivities of at least two different directivity ranges in different directions;
A received power measuring unit that measures received power of received signals received by the plurality of directional antennas;
A moving speed detector for detecting a moving speed of the moving body;
An antenna selection unit that selects a directional antenna that receives a radio wave having a minimum Doppler shift among the plurality of directional antennas based on outputs of the received power measurement unit and the moving speed detection unit;
And a demodulator that demodulates a received signal received by the antenna selected by the antenna selector. The receiving device according to claim 1, wherein a directivity range of the directional antenna in the traveling left and right direction of the mobile body is narrower than a directivity range of the directional antenna in the forward and backward direction of the mobile body among the plurality of directional antennas. The receiving device according to claim 2, wherein the directivity range of each directional antenna is determined so that the Doppler spread of the traveling left-right antenna is equal to or less than the Doppler spread of the traveling front-rear antenna. The directional antenna having a higher gain than a directional antenna in a traveling front-rear direction is used as a traveling directional antenna of a moving body among a plurality of directional antennas. Receiver device. The received power of the directional antennas in the left and right direction is combined and the combined signal is selected when the received power of each of the directional antennas in the moving left and right directions of the moving body is equal to or lower than a set power. Item 5. The receiving device according to any one of Items 1 to 4. The receiving apparatus according to any one of claims 1 to 5, wherein a directional antenna that minimizes a Doppler shift is selected from among directional antennas having received power exceeding a set power value. The receiving apparatus according to any one of 1 to 6, wherein the receiving signals of the directional antennas are combined when the moving body is equal to or lower than the set speed. Selecting and demodulating one received signal from directional received signals having at least two or more different directivity ranges in a plurality of different directions;
In the reception signal selection process, a reception method is selected so that the Doppler shift is minimized based on the reception power of each reception signal and the moving speed of the moving body. A program for executing a signal processing procedure for executing the receiving method according to claim 8.

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