JP2002152105A - Transmitter/receiver for moving object to perform digital communication - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the deterioration of transmission characteristics on a phasing communication path to be fluctuated at extremely high speed. SOLUTION: A transmitter/receiver 1a for moving object to perform digital communication is provided with plural antennas 21-2K arrayed along with the advancing direction of a moving object, a received signal estimating part 14a for estimating a received signal at a spot P fixed relatively to the ground on the basis of plural received signals s21-s2K received from a base station through the plural antennas 21-2K, a modulation parameter estimating part 15 for estimating the modulation parameter of each of signals transmitted from the base station on the basis of the received signal estimated by the received signal estimating part 14a, and a demodulation part 16 for demodulating the received signal estimated by the received signal estimating part 14a on the basis of the modulation parameter estimated by the modulation parameter estimating part 15.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission / reception apparatus for a mobile object used when digital communication is performed between a mobile object moving at a high speed and a base station.

[0002]

2. Description of the Related Art Conventionally, an adaptive modulation method for selecting a modulation parameter according to fading of a received signal has been known.

[0003] FIG. 6 is a diagram showing "Otsuki, Sanbei, Morinaga:" Transmission characteristics of modulation multilevel variable adaptive modulation system ", IEICE Transactions, J78-B-II, 6, pp. 435-444,
The configuration of a conventional adaptive modulation type transmitting / receiving apparatus disclosed in "June 1995" is shown.

[0006] In FIG. 6, reference numerals 101 to 105 indicate constituent elements of a transmitting / receiving apparatus of a mobile body, and reference numeral 111.
Reference numerals 115 denote constituent elements of the transmission / reception device of the base station.

[0005] A transmitting / receiving apparatus of a mobile unit includes an instantaneous fading estimation unit 103 for estimating an instantaneous fading value received by the received signal based on the received signal at the mobile unit, and an appropriate modulation based on an output signal of the instantaneous fading estimating unit 103. A modulation parameter control unit 102 for determining parameters,
Modulation section 101 that modulates transmission data s101 in accordance with a modulation parameter determined by modulation parameter control section 102, and a modulation parameter estimation section that estimates a modulation parameter of a signal transmitted from a base station based on a received signal in a mobile unit. 105, and a demodulation unit 104 that demodulates a received signal at the mobile according to the modulation parameter estimated by the modulation parameter estimation unit 105.

[0006] The transmitting and receiving apparatus of the base station includes an instantaneous fading estimator 113 for estimating an instantaneous fading value received by the received signal based on the received signal at the base station, and an appropriate modulation based on an output signal of the instantaneous fading estimator 113. A modulation parameter control unit 112 for determining parameters,
A modulation section 111 that modulates transmission data s111 according to a modulation parameter determined by modulation parameter control section 112, and a modulation parameter estimation section that estimates a modulation parameter of a signal transmitted from a mobile based on a reception signal at a base station. 115, and a demodulation unit 114 that demodulates a received signal at the base station according to the modulation parameter estimated by the modulation parameter estimation unit 115.

Next, with reference to FIG. 7, the operation of the transmitting / receiving device of the mobile unit (FIG. 6) and the operation of the transmitting / receiving device of the base station (FIG. 6) will be described. The base station and the mobile unit perform time division duplex (TDD: TDD) in which transmission is performed alternately using the same frequency.
One-to-one communication is performed by an "im Division Duplex".

FIG. 7 shows the timing of communication between a mobile unit and a base station.

At the timing of "1" shown in FIG. 7, the end of the burst is transmitted from the mobile unit to the base station.

[0010] The base station receives the end of the burst transmitted from the mobile.

The instantaneous fading estimator 113 calculates
The amount of attenuation due to instantaneous fading of the received signal is estimated. This estimated value is input to modulation parameter control section 112, and modulation parameter control section 112 determines an appropriate modulation parameter. By the modulation unit 111,
Transmission data s111 is modulated according to the modulation parameter determined by modulation parameter control section 112. As a result, a modulated signal is generated.

The modulated signal generated by the modulator 111 is transmitted as a burst from the base station to the mobile unit in the section "2" shown in FIG.

[0013] The mobile receives the modulated signal transmitted from the base station as a burst.

The modulation parameter estimation section 105 estimates the modulation parameters of the signal transmitted from the base station. The demodulation unit 104 controls the modulation parameter estimation unit 10
The received signal at the mobile unit is demodulated according to the modulation parameter estimated by 5.

Next, at the timing "3" shown in FIG. 7, the end of the burst is transmitted from the base station to the mobile unit.

[0016] The mobile receives the end of the burst transmitted from the base station.

The instantaneous fading estimator 103 calculates
The amount of attenuation due to instantaneous fading of the received signal is estimated. This estimated value is input to the modulation parameter control unit 102, and the modulation parameter control unit 102 determines an appropriate modulation parameter. By the modulation unit 101,
Transmission data s101 is modulated according to the modulation parameter determined by the modulation parameter control unit. As a result, a modulated signal is generated.

The modulated signal generated by the modulator 101 is transmitted as a burst from the mobile unit to the base station in the section "4" shown in FIG.

Thereafter, the transmitting / receiving apparatus of the mobile unit and the transmitting / receiving apparatus of the base station repeat the above-described operations.

If the attenuation due to fading of the received signal due to the propagation path can be considered to be constant during the received burst, transmission is possible with the modulation parameters determined by the modulation parameter control unit. However, when the moving object moves at high speed and the fading fluctuation cannot be regarded as constant between bursts, a situation occurs in which the modulation parameters that can be transmitted at the head of the burst are not transmittable at the end of the burst. As a result, there is a problem that the transmission of the burst fails and a transmission error occurs.

[0021]

As described above, in the prior art, when the moving body moves at a high speed, the fading fluctuation becomes high, so that the modulation parameter control cannot follow the fading, and the transmission characteristics deteriorate. There were challenges.

The present invention has been made to solve the above-mentioned problem, and has as its object to improve the deterioration of transmission characteristics in a fading communication path that fluctuates at a very high speed.

[0023]

A transmitting / receiving apparatus according to the present invention comprises:
A transmitting and receiving device for a mobile body performing digital communication, wherein a plurality of antennas arranged along the traveling direction of the mobile body, and a plurality of received signals received from a base station via the plurality of antennas. A received signal estimating unit for estimating a received signal at a point fixed relative to the ground, and a signal transmitted from the base station based on the received signal estimated by the received signal estimating unit. A modulation parameter estimating unit for estimating the modulation parameter of, and a demodulation unit for demodulating the received signal estimated by the received signal estimating unit based on the modulation parameter estimated by the modulation parameter estimating unit. ,
Thereby, the above object is achieved.

[0024] The received signal estimating section may include a moving distance estimating section for estimating a moving distance of the moving object, and a predetermined number of received signals received from the base station via the plurality of antennas. And performing an interpolation operation to estimate a received signal at a point separated by the movement distance in a direction opposite to a traveling direction of the moving body from a head antenna of the plurality of antennas. Is also good.

[0025]

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1A and 1B show the arrangement of an antenna array (a plurality of antennas arranged in a straight line) provided on a moving body. FIG. 1A is a top view, and FIG.
(B) is a side view.

The K antennas 21 to 2K are provided on a housing 31 of the moving body. K antennas 21 to 2K
Are arranged on a straight line along the traveling direction of the moving body. The spacing between adjacent antennas is d (m). Therefore, the first antenna 21 (the leading antenna)
Assuming that the distance to the 2nd antenna 2K (the last antenna) is D, D = (K-1) d (m) holds.

S21 to s2K are the antenna 2
2 shows a received signal received from a base station via 1-2K. In addition, s21 and s2K may indicate transmission signals transmitted from the mobile via the antennas 21 and 2K, respectively, as described later.

FIG. 2A shows the configuration of a mobile transmitting / receiving apparatus 1a according to the present invention. The transmission / reception device 1a of the mobile body includes:
Typically, the housing 31 of the moving body (FIGS. 1A and 1B)
Is housed inside.

The transmitting / receiving device 1a of the mobile object includes an antenna 21
Received signals s21 to s21 received from the base station through .about.2K
Received signal estimating unit 14a that estimates a received signal at point P fixed relative to the ground based on s2K
including.

The received signal estimating section 14a includes a moving distance estimating section 13 for estimating the moving distance of the moving object, and antennas 21 to 2
By performing a predetermined interpolation operation on the received signals s21 to s2K from K, a received signal at a point P separated from the head antenna 21 by a distance x ′ in a direction opposite to the traveling direction of the moving object is estimated. And an interpolation operation unit 14. Here, the distance x ', the mobile from the reference time t ₀ is equal to the distance x moved. Point P is shown in FIG. 1A.

The distance x that the moving body has moved since the reference time t ₀
Is represented, for example, by (Equation 1).

[0033]

(Equation 1)

Here, v indicates the speed at which the moving object moves, and t indicates the time elapsed from the reference time t ₀ .

The moving distance estimating unit 13 receives the signal s13 indicating the speed v at which the moving body moves, performs the operation shown in (Equation 1), and converts the signal indicating the distance x into the interpolation calculating unit 1.
4 is output.

Thus, regardless of the movement of the moving body,
By estimating the received signal at the point P fixed relative to the ground, it is possible to obtain a received signal in which fading fluctuation is compensated.

The transmitting / receiving apparatus 1a of the mobile terminal includes an instantaneous fading estimating section 10 for estimating propagation characteristics of a propagation path due to fading of a received signal based on an output from the interpolation calculating section 14, and an instantaneous fading estimating section 10a. A modulation parameter control section 11 for selecting a modulation parameter having a maximum transmission rate that can be transmitted under the propagation characteristics estimated by the above, and outputting a control signal indicating the selected modulation parameter to the modulation section 12; And a modulating unit 12 that modulates the transmission data s11 according to the control signal output from the controller to generate a modulated signal.

The transmission / reception apparatus 1a of the mobile terminal includes a modulation parameter estimating section 15 for estimating a modulation parameter of a signal transmitted from the base station based on an output from the interpolation section 14.
And a demodulation unit 1 that demodulates the output from the interpolation operation unit 14 based on the modulation parameter estimated by the modulation parameter estimation unit 15 to generate demodulated data s12.
And 6.

The switching unit 17 supplies the modulated signal generated by the modulation unit 12 to the antenna 21 or the antenna 2K.
Switch to supply. The switching unit 18 controls the antenna 2 during the reception period for receiving the signal transmitted from the base station.
1 and the interpolation calculation unit 14, and the antenna 21 and the modulation unit 12 are connected during a transmission period for transmitting a signal to the base station. The switching unit 19 connects the antenna 2K and the interpolation unit 14 during a reception period for receiving a signal transmitted from the base station, and connects the antenna 2K and the modulation unit 12 during a transmission period for transmitting a signal to the base station. I do.

FIG. 2 (b) shows a configuration of the transmitting / receiving device 1b of the base station according to the present invention.

The transmission / reception apparatus 1b of the base station performs estimation by an instantaneous fading estimator 41 and an instantaneous fading estimator 41 for estimating propagation characteristics of a propagation path due to fading received by the received signal based on the received signal s16 at the base station. A modulation parameter of the maximum transmission rate that can be transmitted under the selected propagation characteristics, and a modulation parameter control unit 42 that outputs a control signal indicating the selected parameter to the modulation unit 43; A modulation unit 43 that generates a modulation signal by modulating the transmission data s14 according to the output control signal.

The transmission / reception apparatus 1b of the base station estimates the modulation parameter of the signal transmitted from the mobile station based on the received signal s16 at the base station.
4 and a demodulation unit 45 that demodulates the received signal s16 based on the modulation parameter estimated by the modulation parameter estimation unit 44 to generate demodulated data s15.

The switching unit 46 connects an antenna (not shown) of the base station to the modulation unit 43 during a transmission period for transmitting a signal to the mobile unit, and connects the base station during a reception period for receiving a signal transmitted from the mobile unit. A station antenna (not shown) is connected to a modulation parameter estimator 44, a demodulator 45, and an instantaneous fading estimator 41.

Next, the operation of the transmitting / receiving apparatus 1a (FIG. 2 (a)) of the mobile unit and the operation of the transmitting / receiving apparatus 1b (FIG. 2 (b)) of the base station will be described with reference to FIG. The base station and the mobile perform digital communication. For example, a base station and a mobile unit perform time division duplex (TDD) in which transmission is performed alternately using the same frequency.
plex) to perform one-to-one communication.

FIG. 3 shows the timing of communication between the mobile unit and the base station, and the positions of the antennas 21 and 2K relative to the ground (relative positions with respect to the ground).

At the timing "1" shown in FIG. 3, a signal (pilot tone signal) for measuring the propagation characteristics of the propagation path is transmitted from the mobile unit to the base station using the antenna 21. Here, the bold line corresponding to the timing of “1” shown in FIG. 3 indicates the position of the antenna 21 used for transmitting the pilot tone signal with respect to the ground (relative position with respect to the ground).

[0047] The base station receives the pilot tone signal transmitted from the mobile unit. The propagation characteristic of the propagation path is estimated based on the received signal. Such estimation of the propagation characteristic of the propagation path is performed by the instantaneous fading estimator 41. A modulation parameter satisfying a predetermined condition is selected under the estimated propagation characteristics. For example, the predetermined condition is that transmission is possible so as to satisfy required transmission quality, and that the transmission speed is maximum. Such modulation parameter selection is performed by the modulation parameter control unit 42. By modulating the transmission data s14 according to the selected modulation parameter, a modulated signal is generated. The generation of such a modulation signal is performed by the modulation unit 43.

The modulated signal generated by the modulator 43 is transmitted from the base station to the mobile unit in the section "2" shown in FIG.

The mobile receives the modulated signal transmitted from the base station using antennas 21 to 2K.

The received signal s21 from the antennas 21 to 2K
Based on に お け る s2K, the received signal at point P fixed relative to the ground is estimated. Such estimation of the received signal is performed by the received signal estimating unit 14a. Here, the bold line corresponding to the section “2” shown in FIG. 3 indicates the position of the point P with respect to the ground (relative position with respect to the ground).

More specifically, the estimation of the received signal at the point P is based on the distance x traveled by the moving object from the reference time t ₀ , based on the received signal s from the antennas 21 to 2K.
This is performed by performing a predetermined interpolation operation on 21 to s2K.

The distance x is obtained by the moving distance estimating unit 13 according to the above (Equation 1). Here, (Equation 1)
The reference time t _{0 which} is the reference of the elapsed time t in FIG.
(I.e., the time when the pilot tone signal is transmitted from the mobile unit to the base station).

The received signal s21 from the antennas 21 to 2K
The predetermined interpolation operation for .about.s2K is performed by the interpolation operation unit 14.

The predetermined interpolation operation performed by the interpolation operation unit 14 is expressed by (Equation 2).

[0055]

(Equation 2)

Here, r _k (t) is the received signal 2 (k + 1) from the antenna 2 (k + 1) at the elapsed time t.
Is shown. r (t) is the distance x ′ from the head antenna 21 in the direction opposite to the traveling direction of the moving object at the elapsed time t.
A received signal at a point P separated by (= x) is shown. The received signal r (t) is output from the interpolation unit 14 as a calculation result of the interpolation unit 14.

Note that f represents a function representing an interpolation operation.
As f, a function representing an arbitrary interpolation operation can be used. For example, a function f shown in (Equation 3) or a function f shown in (Equation 4) may be used as the function f representing the interpolation operation.

[0058]

(Equation 3)

[0059]

(Equation 4)

Here, (Equation 3) shows an example of the function f in the case of performing the primary interpolation, and (Equation 4) shows an example of the function f in the case of performing the interpolation with higher precision than the linear interpolation. Show.

The point P shown in FIG. 1A moves in a direction opposite to the moving direction of the moving body by a distance equal to the moving distance of the moving body. Therefore, this point P does not move relative to the ground regardless of the movement of the moving body. For this reason, the received signal obtained according to the interpolation operation shown in (Equation 2) is obtained while the interpolation operation is being performed.
This can be regarded as a received signal received with the moving object stopped. From this, it can be considered that the fading fluctuation received by the signal transmitted from the base station to the mobile unit in the section “2” shown in FIG. 3 is constant. As a result, the modulation parameter selected in the base station at the timing of “1” shown in FIG. 3 is “2” shown in FIG.
, The required transmission quality can be satisfied.

The received signal compensated for the fading fluctuation obtained by the interpolation calculator 14 is input to a modulation parameter estimator 15, which estimates the modulation parameters of the signal transmitted from the base station. . The demodulation unit 16 demodulates the received signal in which the fading fluctuation obtained by the interpolation calculation unit 14 has been compensated according to the estimated modulation parameter signal. As a result, demodulated data s12 is generated.

Next, at timing "3" shown in FIG. 3, a signal (pilot tone signal) for measuring the propagation characteristics of the propagation path is transmitted from the base station to the mobile unit.

The mobile receives the pilot tone signal transmitted from the base station using antennas 21 to 2K.

The received signal s21 from the antennas 21 to 2K
Based on に s2K, a received signal received from the base station via the antenna 2K in the section “4” shown in FIG. 3 is estimated. Such estimation of the received signal is performed by the interpolation calculation unit 14. Here, as shown in FIG.
The bold line corresponding to the section of 4 ″ indicates the position of the antenna 2K with respect to the ground (the position relative to the ground).

More specifically, the interpolation operation unit 14
Estimates the received signal in the interval from D-vT to D from the antenna 21. Here, T indicates the length of the section "4" shown in FIG.

The received signal estimated by the interpolation calculator 14 is input to the instantaneous fading estimator 10. As shown in FIG. 3 by the instantaneous fading estimator 10.
The propagation characteristic of the propagation path in the section of 4 ″ is estimated,
The worst value is output to modulation parameter control section 11.
The modulation parameter control unit 11 selects the modulation parameter having the highest transmission rate among the modulation parameters satisfying the required transmission quality. Modulation section 12 modulates transmission data s11 according to the selected modulation parameter. As a result, a modulated signal is generated. Modulation unit 1
2 produces the modulated signal shown in FIG.
In the section 4 ", the signal is transmitted from the mobile unit to the base station using the antenna 2K.

The base station receives a signal transmitted from a mobile. The received signal s16 is output from the modulation parameter estimator 44.
, And the modulation parameter estimating unit 44 estimates the modulation parameter of the signal transmitted from the mobile unit. The demodulation unit 45 demodulates the received signal s16 according to the modulation parameter estimated by the modulation parameter estimation unit 44. As a result, demodulated data s15 is generated.

After "5" shown in FIG.
The operation from "1" to "4" is repeated.

FIG. 4 shows a result obtained by computer simulation of a burst error rate characteristic when digital data transmission is performed by the transmission / reception apparatus 1a according to the present invention.

In FIG. 4, the vertical axis represents the burst error rate, and the horizontal axis represents the normalized maximum Doppler frequency normalized by the burst length. In FIG. Shows the packet error rate characteristics when the conventional adaptive modulation scheme is used.
p. Indicates a packet error rate characteristic according to the present invention.

In FIG. 4, Δ, ○, □ and ●
Are the average carrier signal power to noise power ratio (CN
R: Carrier-to-noise power
ratio) is 10 dB, 20 dB, 30 dB and 4
9 shows a packet error rate characteristic in the case of 0 dB. here,
The number of the plurality of antennas arranged along the traveling direction of the moving object is 2, the interval between adjacent antennas is 0.1 wavelength, and the primary interpolation shown in (Equation 3) is used as the interpolation operation. The modulation method is QPSK, 16QAM, 64QA
It is assumed that a modulation scheme that satisfies the required bit error rate of 10 ^-3 is selected from five modulation schemes of M, 256 QAM, and 1024 QAM.

As shown in FIG. 4, in the conventional adaptive modulation system, when the normalized maximum Doppler frequency exceeds 0.01, the packet error rate sharply increases beyond 10 ^-3 . On the other hand, according to the present invention, a packet error rate of 10 ⁻³ or less can be achieved up to a normalized maximum Doppler frequency of about 0.1. From this fact, it can be seen that the adaptive modulation can be applied when the moving body moves about ten times as fast as the moving speed of the moving body.

FIG. 5 shows the throughput characteristic with respect to the normalized maximum Doppler frequency.

In FIG. 5, the horizontal axis represents the normalized maximum Doppler frequency, and the vertical axis represents the throughput characteristics.

In FIG. 5, □ indicates the throughput according to the conventional method, and ● indicates the throughput characteristic according to the present invention. 10dB, 20d as signal-to-noise power ratio (CNR)
B, 30 dB, and 40 dB are shown.

From FIG. 5, it is seen that in the conventional method, the throughput decreases greatly as the maximum normalized Doppler frequency increases from 0.01. On the other hand, according to the present invention, there is no decrease in throughput until the normalized maximum Doppler frequency is about 0.1.

As described above, according to the present invention, it is possible to compensate for a burst error and a decrease in throughput characteristics due to the movement of a moving object. Also, by increasing the number of antennas or performing a more advanced interpolation configuration, it is possible to compensate for the propagation characteristics of the propagation path even when moving at a higher speed.

[0079]

As described above, according to the present invention, a received signal at a point fixed relative to the ground is estimated, and a signal transmitted from the base station based on the estimated received signal is obtained. Are estimated. This allows efficient transmission using the modulation parameter selected in the base station during the period when the mobile station receives the signal transmitted from the base station. As described above, according to the present invention, there is an effect that it is possible to compensate for the deterioration of the transmission characteristics of the adaptive modulation scheme when the moving body moves at high speed.

When the signal transmitted from the mobile unit is received by the base station, the interpolating operation unit estimates the fading fluctuation in this period, so that the optimum modulation in the mobile unit in this period is performed. The parameters can be determined.

[Brief description of the drawings]

FIG. 1A is a top view illustrating an arrangement of antenna arrays provided on a moving body, and FIG. 1B is a side view illustrating an arrangement of antenna arrays provided on the moving body.

FIG. 2 (a) is a mobile transmitting / receiving apparatus 1a according to the present invention.
And (b) is a block diagram showing a configuration of a transmission / reception device 1b of the base station according to the present invention.

FIG. 3 shows timing of communication between a mobile unit and a base station;
It is a figure which shows the ground position (relative position with respect to the earth) of antenna 21, 2K.

FIG. 4 is a diagram illustrating a relationship between a normalized Doppler frequency and a packet error rate characteristic.

FIG. 5 is a diagram illustrating a relationship between a normalized Doppler frequency and a throughput characteristic.

FIG. 6 is a block diagram showing a configuration of a conventional adaptive modulation type transmission / reception apparatus.

FIG. 7 is a timing chart showing operation timings of a conventional adaptive modulation type transmitting / receiving apparatus.

[Explanation of symbols]

 1a Transmitter / receiver of mobile body 1b Transmitter / receiver of base station 10 Instantaneous fading estimation unit 11 Modulation parameter control unit 12 Modulation unit 13 Moving distance estimation unit 14 Interpolation operation unit 14a Received signal estimation unit 15 Modulation parameter estimation unit 16 Demodulation unit 17, 18, 19 switching unit 41 instantaneous fading estimation unit 42 modulation parameter control unit 43 modulation unit 44 modulation parameter estimation unit 45 demodulation unit 46 switching unit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04L 27/00 Z

Claims (2)

[Claims] 1. A transmission / reception apparatus for a mobile unit performing digital communication, comprising: a plurality of antennas arranged along a traveling direction of the mobile unit; and a plurality of antennas received from a base station via the plurality of antennas. A received signal estimating unit that estimates a received signal at a point fixed relative to the ground based on a plurality of received signals; and the base station based on the received signal estimated by the received signal estimating unit. And a demodulation unit that demodulates the received signal estimated by the received signal estimation unit based on the modulation parameter estimated by the modulation parameter estimation unit. A transmission / reception device comprising: 2. The received signal estimating unit, comprising: a moving distance estimating unit for estimating a moving distance of the moving body; and a predetermined signal for the plurality of received signals received from the base station via the plurality of antennas. And an interpolation operation unit that estimates a received signal at a point separated by the moving distance in a direction opposite to a traveling direction of the moving object from a head antenna of the plurality of antennas by performing the interpolation operation of the plurality of antennas. The transmission / reception device according to claim 1.