KR101908064B1 - Apparatus and method for mitigating doppler shift in high-speed rail communication system - Google Patents

Apparatus and method for mitigating doppler shift in high-speed rail communication system Download PDF

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KR101908064B1
KR101908064B1 KR1020150185731A KR20150185731A KR101908064B1 KR 101908064 B1 KR101908064 B1 KR 101908064B1 KR 1020150185731 A KR1020150185731 A KR 1020150185731A KR 20150185731 A KR20150185731 A KR 20150185731A KR 101908064 B1 KR101908064 B1 KR 101908064B1
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antenna
doppler shift
rus
signal
railway
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KR20170076845A (en
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회빙
김준형
김일규
김태중
이훈
정희상
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한국전자통신연구원
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2655—Synchronisation arrangements
    • H04L27/2689—Link with other circuits, i.e. special connections between synchronisation arrangements and other circuits for achieving synchronisation
    • H04L27/2695—Link with other circuits, i.e. special connections between synchronisation arrangements and other circuits for achieving synchronisation with channel estimation, e.g. determination of delay spread, derivative or peak tracking
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/022—Site diversity; Macro-diversity
    • H04B7/024—Co-operative use of antennas of several sites, e.g. in co-ordinated multipoint or co-operative multiple-input multiple-output [MIMO] systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/08—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station
    • H04B7/0837—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station using pre-detection combining
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2655—Synchronisation arrangements
    • H04L27/2689—Link with other circuits, i.e. special connections between synchronisation arrangements and other circuits for achieving synchronisation
    • H04L27/2691—Link with other circuits, i.e. special connections between synchronisation arrangements and other circuits for achieving synchronisation involving interference determination or cancellation

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  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Mobile Radio Communication Systems (AREA)

Abstract

A receiving apparatus of a high-speed railway communication system receives through a forward link and a reverse link through a first antenna and a second antenna arranged opposite to each other with respect to the same transmission signal, and the first antenna and the second antenna And multiplies the received signal.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for mitigating a Doppler shift in a high-speed railway communication system,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for mitigating Doppler shift in a high-speed railway communication system.

Recently, a solution for providing stable railway communication service on high-speed rail (HSR) over 500 km / h is being promoted. Long term evolution (LTE) or LTE-A (advanced) systems using an orthogonal frequency division multiplexing (OFDM) scheme are mentioned as candidates. However, the LTE or LTE-A air interface is optimized for multipath fading, dense deployment of base stations, and terrestrial mobile communications where there are many terminals. In addition, the carrier frequency of the LTE or LTE-A system is sub 6 GHz, and the performance requirements of high-speed mobile are functional.

On the other hand, the scenario of HSR communication is completely different. From a channel environment perspective, trains often travel in suburban, rural areas, mountains, and tunnels with urban areas. There is always a line-of-sight (LoS) link in HSR communication. The mobility of the train is also increasing, and the passenger's QoS must be guaranteed. A millimeter wave (mmWave) license-exempt band can be employed for HSR communication to provide higher data rates and avoid interference with existing terrestrial cellular communication systems.

Since OFDM systems, such as LTE or LTE-A systems, are vulnerable to carrier frequency offset (CFO), Doppler shift is a major challenge.

In the downlink, the discrete Doppler shift appears as an offset from the base station carrier frequency f c, tx of the downlink signal transmitted to the terminal receiver. The terminal receiver derives the carrier frequency of the downlink signal transmitted from the downlink signal received by the frequency estimation method. The terminal receiver can not distinguish between the frequency shift due to the Doppler effect or the frequency offset in the base station transmitter. The terminal receiver only adapts to the shifted frequency.

On the uplink, the terminal transmitter uses the carrier frequency derived from the Doppler shifted base station carrier frequency. Therefore, in the case of the LTE system of the frequency division duplex (FDD) scheme, the uplink carrier frequency of the terminal transmitter is the sum of the Doppler shifted base station carrier frequencies fc , tx + fo, Doppler and the duplex offset f FDD . In the case of the time division duplex (TDD) system, the uplink carrier frequency of the terminal transmitter becomes the Doppler shifted base station carrier frequency fc , tx + fo, Doppler . As the uplink signal of the terminal transmitter also experiences the Doppler shift, the uplink signal arriving at the base station has a frequency offset twice that of the Doppler shift.

Since the Doppler shift in a HSR system is much higher than in a cellular network system, the frequency offset of twice the Doppler shift can exceed the estimated performance of the base station in the HSR scenario. Therefore, Doppler frequency shift compensation technology is very important when an OFDM system is considered for HSR communication. In particular, higher Doppler shifts can occur when the millimeter waveband is considered for transmission.

A suitable pilot-based channel estimation method in LTE or LTE-A systems may not be able to perform Doppler compensation for received and / or transmitted signals, since the Doppler shift can not be clearly measured from the pilot signal.

On the other hand, in order to increase the accuracy of the CFO estimation, it is possible to increase the estimation time or the number of samples for estimation, which leads to a high computational complexity and a considerable load of measurement.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an apparatus and method for reducing a Doppler shift in an OFDM-based high-speed railway communication system using a millimeter-wave band.

According to an embodiment of the present invention, a method for mitigating Doppler shift of a receiving apparatus in a high-speed railway communication system is provided. A method for mitigating Doppler shift comprises receiving on a forward link and a reverse link in a first antenna and a second antenna arranged opposite to each other for the same transmission signal, And multiplying the signal.

The transmission signal may include a downlink signal.

Wherein a plurality of RUs (radio units) are disposed along a railway, each of the plurality of RUs includes a third antenna and a fourth antenna provided so as to face each other in opposite directions, and the first antenna and the second antenna, And can be mounted on a moving body traveling on the upper side.

The transmission signal may include an uplink signal.

A plurality of RUs are arranged along a railway, each of the plurality of RUs includes two antennas installed so as to face each other in opposite directions, and the first antenna and the second antenna each comprise two adjacent RUs And an omnidirectional antenna may be mounted on a mobile body traveling on the railway.

The Doppler shift mitigation method may further include converting the signals received at the first antenna and the second antenna to an intermediate frequency signal before the multiplication.

The Doppler shift mitigation method may further include a step of high-pass-filtering the multiplied signal to remove noise.

According to another embodiment of the present invention, a Doppler shift mitigation apparatus in a high-speed railway communication system is provided. The Doppler shift mitigation apparatus includes a first antenna, a second antenna, and a multiplier. The first antenna and the second antenna are installed to face each other. The multiplier multiplies the signals received through the first and second antennas with respect to the same transmission signal and outputs the multiplied signals.

The Doppler shift mitigation apparatus may further include a first intermediate frequency (IF) converter and a second intermediate frequency (IF) converter for converting signals received through the first antenna and the second antenna into intermediate frequency signals and outputting the intermediate frequency signals to the multiplier .

The Doppler shift mitigation apparatus may further include a high-pass filter for eliminating noise by high-pass-filtering the multiplied signal.

The transmission signal is a downlink signal, and the first antenna and the second antenna may be mounted on a moving body traveling on a railroad.

A plurality of RUs (radio units) may be disposed along the railway, and each of the plurality of RUs may include two antennas installed so as to face each other in opposite directions.

The transmission signal is an uplink signal, and a plurality of RUs (radio units) are arranged along the railway, and the first antenna and the second antenna may be installed in two adjacent radio units (RUs).

Each of the plurality of RUs may include two antennas arranged opposite to each other.

At least one antenna may be mounted on the mobile body traveling on the railway.

According to the embodiment of the present invention, since the two antennas are provided so as to have the same moving speed and face each other in opposite directions, the residual Doppler shift can be reduced to 0 Hz with a 90% probability even if the moving speed changes with time, The pilot density can be reduced in the time domain. Even when there is a peak of residual Doppler shift, the influence of the peak residual Doppler shift is limited in data transmission and reception because the handover must be performed at the correct time of the peak residual Doppler.

Also, according to the embodiment of the present invention, since the carrier frequency after multiplying the received two downlink signals is doubled, the residual Doppler shift in the downlink can be reduced to half for uplink transmission.

Also, since the frequency offset is drastically reduced by the Doppler shift mitigation method according to the embodiment of the present invention, the frequency offset remaining in the automatic frequency control (AFC) having a relatively low calculation complexity can be compensated.

1 is a diagram illustrating an example of an HSR communication system according to an embodiment of the present invention.
2 is a diagram illustrating another example of the HSR communication system according to the embodiment of the present invention.
3 is a diagram showing the arrangement of DU and RU in the HSR communication system according to the embodiment of the present invention.
4 is a diagram showing the maximum Doppler shift.
5 is a diagram illustrating a Doppler shift mitigation apparatus according to an embodiment of the present invention.
6 is a flowchart illustrating a Doppler shift mitigation method according to an embodiment of the present invention.
FIG. 7 is a graph illustrating performance comparison of Doppler shift in the downlink according to an embodiment of the present invention.
8 is a graph illustrating performance comparison of Doppler shifts before uplink transmission according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

Throughout the specification and claims, when a section is referred to as "including " an element, it is understood that it does not exclude other elements, but may include other elements, unless specifically stated otherwise.

Now, an apparatus and method for mitigating Doppler shift in a high-speed railway communication system according to an embodiment of the present invention will be described in detail with reference to the drawings.

1 is a diagram illustrating an example of an HSR communication system according to an embodiment of the present invention.

Referring to FIG. 1, the HSR communication system includes a base station and a moving object (hereinafter referred to as "train") 200. Terminal equipment (not shown) is mounted on the train 200. A user terminal (not shown) is connected to the terminal device mounted on the train 200 by using a radio signal such as Wi-Fi.

The base station includes a plurality of radio units (RUs) 110 and 120 and a digital unit (DU) (not shown). Only the nth RU 110 and the (n + 1) th RU 120 are shown in FIG.

The RUs 110 and 120 are installed along the railway and are mounted on the respective RUs 110 and 120 such that the two directional antennas 112, 114, 122 and 124 are opposite to each other.

The terminal apparatus includes two directional antennas (210, 220). Two directional antennas 210 and 220 are mounted on the train 200. Assuming that the train 200 moves from left to right at a speed of v (t), the directional antennas 210 and 220 located on the train 200 are connected to each other via a different link between the front RU 120 and the rear RU 120, Lt; RTI ID = 0.0 > 110 < / RTI > The directional antenna 210 located at the front of the train 200 is referred to as a head antenna 210 and the directional antenna 220 located at the rear of the train 200 is referred to as a tail antenna 220 for convenience.

Thus, the purpose of using the directional antenna in the HSR communication system is to avoid interference, for example, interference from the RU 120 to the tail antenna 220 and interference from the RU 110 to the head antenna 210. [

In this HSR communication system, a handover occurs when the train 200 passes the RUs 110 and 120. For example, when the head antenna 210 passes the RU 120, the forward link is connected to the (n + 2) th RU (not shown) installed next to the RU 120 along the railway in the moving direction of the train 200 And when the tail antenna 220 passes through the RU 120, the reverse link handover to the RU 120 is performed.

2 is a diagram illustrating another example of the HSR communication system according to the embodiment of the present invention.

2, the terminal device of the HSR communication system may include one omni-directional antenna 230, and one omnidirectional antenna 230 may be connected to the train 200, Respectively.

As shown in FIG. 2, when one omnidirectional antenna 230 is mounted on the train 200, handover between the forward link and the reverse link occurs simultaneously.

3 is a diagram showing the arrangement of DU and RU in the HSR communication system according to the embodiment of the present invention.

Referring to FIG. 3, DU is connected to a plurality of RUs. For example, the ith DU (DUi) is connected to k RUs (RU (m + 1) to RU (m + k) RU (n + 1) to RU (n + p)]. As described above, a plurality of RUs RU (m + 1) to RU (m + k), RU (n + 1) to RU (n + p)) can be installed along the railway.

The Doppler shift mitigation method according to an embodiment of the present invention can be implemented in both the downlink and uplink in the case of FIG. 1 and in the uplink in the case of FIG.

A channel model for explaining a Doppler shift mitigation method according to an embodiment of the present invention will be described.

To illustrate the Doppler shift mitigation method according to an embodiment of the present invention, a tapped delay line (TDL) channel model for multi-path multi-tap is used. The TDL channel sound pulse response is given by Equation (1).

Figure 112015126731550-pat00001

Here, A r represents the received signal size, M represents the number of paths, and P m represents the average power of the m-th tap.

Figure 112015126731550-pat00002
Represents the delay time of the m-th tap, T m (t) represents the time-varying m- th tap weight.

The m-th tap weight T m (t) for Wide-Sense Stationary Uncorrelated Scattering (WSSUS) can be given as:

Figure 112015126731550-pat00003

Here, N 0 represents the number of scatter,

Figure 112015126731550-pat00004
Represents a complex Gaussian random variable.
Figure 112015126731550-pat00005
Represents the maximum Doppler shift,
Figure 112015126731550-pat00006
Represents an angle of arrival uniformly distributed at [0, 2π].

From equations (1) and (2), the factor associated with the Doppler shift is the multiplier term in the channel response pulse response.

Next, a Doppler shift mitigation method according to an embodiment of the present invention will be described.

The Doppler shift mitigation method according to an embodiment of the present invention is suitable for a channel environment in which a dominant path exists, such as a tunnel or a rural environment. In most cases, the channel characteristics of the tunnel environment is the maximum Doppler shift rather than the Doppler spread. Since the tunnel environment is space-limited, a dominant path is formed. In other words, the channel in the tunnel can be regarded as a one-tap channel with the maximum Doppler shift. In this case, the TDL channel impulse response can be simplified as shown in Equation (3).

Figure 112015126731550-pat00007

Here, M = 1 corresponds to a single tap channel,

Figure 112015126731550-pat00008
The item is removed.

In the embodiment of the present invention, since the Doppler shift element is focused on, other elements can be excluded and Equation (3) can be simplified as shown in Equation (4).

Figure 112015126731550-pat00009

here,

Figure 112015126731550-pat00010
Is expressed by Equation (5).

Figure 112015126731550-pat00011

In the HSR communication system shown in Figs. 1 and 2, if the Doppler shift of the forward link is defined as fd.fwd and the Doppler shift of the reverse link is defined as fd.bwd , the channels of the forward link and the reverse link are Can be expressed by Equations (6) and (7).

Figure 112015126731550-pat00012

Figure 112015126731550-pat00013

4 is a diagram showing the maximum Doppler shift.

As shown in Fig. 4, the maximum Doppler shift is given by Equation (8).

Figure 112015126731550-pat00014

Where v is the moving speed, c is the speed of light, and fc is the carrier frequency. And θ is the Angle of Arrival (AoA). θ = 0 indicates that the moving direction is opposite to the propagation direction, θ = 90 indicates that the moving direction is perpendicular to the propagation direction, and θ = 180 indicates that the moving direction is the same as the propagation direction.

The Doppler shift has a positive value when the movement direction is opposite to the propagation direction and a negative value when the movement direction is the same direction as the propagation direction.

As shown in FIG. 1, when the head antenna 210 and the tail antenna 220 are located on the same train 200, the traveling speeds of the forward link and the reverse link are the same, but the forward link and the reverse link are opposite to each other I have. Therefore, the relationship between the Doppler component of the forward link f d. Fwd and the Doppler component of the reverse link f d.bwd can be expressed as shown in Equation (9).

Figure 112015126731550-pat00015

Based on Equation (9), when the same OFDM symbol s (t) is transmitted on the forward link and the reverse link via the RUs 110 and 120, the Doppler shift of the HSR communication system is determined from the head and tail antennas 210 and 220 Can be removed by multiplying the received signal. At this time, the RUs 110 and 120 may be connected to the same DU and may be connected to different DUs.

In the downlink of FIG. 1, the signal y head (t) received at the head antenna at the radio frequency of fc can be expressed as Equation 10 and the signal y tail (t) received at the head antenna at the radio frequency of fc Can be expressed by Equation (11).

Figure 112015126731550-pat00016

Figure 112015126731550-pat00017

In Equation (10) and Equation (11), n head (t) and n tail (t) represent AWGN (additive white Gaussian noise) in the head antenna 210 and the tail antenna 220, respectively.

The OFDM symbol S (t) is given by Equation (12).

Figure 112015126731550-pat00018

Where s (t) is the baseband OFDM symbol.

The multiplication of the two received signals y head (t) and y tail (t) yields Equation (13).

Figure 112018048397600-pat00029

In Equation 13, the first term is the desired signal to be processed later, the second and third terms are the interference to the desired signal, and the fourth term is the AWGN in the head antenna 210 and the tail antenna 220.

In Equation 13, since the interference term has a radio frequency of fc and the desired signal term has a frequency of 2fc, the interference item can be eliminated by using a high-pass filter (HPF).

FIG. 5 is a diagram illustrating a Doppler shift mitigation apparatus according to an embodiment of the present invention, and FIG. 6 is a flowchart illustrating a Doppler shift mitigation method according to an embodiment of the present invention.

5, the Doppler shift mitigation apparatus 500 may include intermediate frequency (IF) converters 510 and 520, a multiplier 530, and an HPF 540. The Doppler shift mitigation apparatus 500 may further include two antennas 550 and 560. The Doppler shift mitigation apparatus 500 may be implemented in the RUs 110 and 120 of the base station and may be implemented in a terminal apparatus mounted on the train 200. [

And receives signals through the two antennas 550 and 560, respectively (S610).

When a very high carrier frequency, such as a millimeter wave, is used for transmission, the oscillation frequency of a 2fc oscillator must be used to demodulate the received signal in equation (13), and the hardware cost may increase accordingly.

Therefore, according to the embodiment of the present invention, before the two signals [y 1 (t), y 2 (t)] received at antennas 550 and 560 are multiplied, two received signals y 1 2 (t)] is used.

IF converter (510,520) converts the signal [y 1 (t), y 2 (t)] received at each antenna (550, 560) to an intermediate frequency signal (S620). The IF converters 510 and 520 can convert a very high carrier frequency to a relatively low frequency and lower the hardware cost of the receiver. Therefore, the IF converters 510 and 520 can be selectively used when using very high carrier frequencies such as millimeter waves.

The multiplier 530 multiplies the intermediate frequency signals converted by the IF converters 510 and 520, respectively (S630).

The HPF 540 filters the multiplied signal by the multiplier 530 to remove noise. As described above, the noise term of Equation 13 is removed by the HPF 540 (S640).

Thereafter, the signal Y (t) from which the noise has been removed can be further processed to obtain data as a received signal.

According to an embodiment of the invention, after the two signals by the multiplier 530 multiplies, Doppler shift Δf d of the wanted signal is relaxed as shown in equation (14).

Figure 112018048397600-pat00030

Such a Doppler shift mitigation method can be similarly applied to the uplink.

As shown in FIG. 5, two antennas 550 and 560 are required to implement the Doppler shift mitigation method according to the embodiment of the present invention.

When the two antennas 550 and 560 are positioned on the train 200 as the head antenna 210 and the tail antenna 220 as shown in FIG. 1, the Doppler shift mitigation method according to the embodiment of the present invention includes a downlink and uplink It can be applied to all.

However, as shown in FIG. 2, when only one omnidirectional antenna 230 is located on the train 200, the Doppler shift mitigation method according to the embodiment of the present invention can be applied only to the uplink. In this case, the two signals received by the different RUs 110 and 120 are multiplied to relax the Doppler shift. For this purpose, the RUs 110 and 120 may be connected to each other via the X2 interface.

Hereinafter, performance of the Doppler shift mitigation method according to the embodiment of the present invention will be described.

FIG. 7 is a graph illustrating performance comparison of Doppler shift in the downlink according to an embodiment of the present invention.

As shown in FIG. 1, when the head antenna 210 and the tail antenna 220 are located on the train 200, the parameters are set as shown in Table 1 for the performance comparison of the Doppler shift in the downlink. Table 1 is an example of a typical parameter setting for a train in a tunnel environment. When the head antenna 210 passes the RU, the position of the head antenna 210 is calculated as 0m.

Parameter Setup Frequency 32 GHz Antenna Configuration 1 Head Ant. + 1 Tail Ant. / Single Ant. Antenna Height 6.5 m for RU, 3 m for terminal equipment (TE) Antenna Setup Directional Ant. / Omni-directional Ant. Length of Train 200 m Distance between adjacent RUs 1 km Speed 100 m / s (360 km / h)

As described above, the head antenna 210 performs handover to the next RU at a position of 0 and 1000 m. As soon as handover is performed, the Doppler spread of the head antenna 210 is regarded as the maximum Doppler shift. This is because the tunnel is a space-limited environment and all the reflection paths with relatively high power reach the receiver with a very small time difference that can not be distinguished by the receiver.

Thus, in a tunnel, the channel is considered as a one-tap channel with the maximum Doppler shift. When the train 200 approaches the RU, the Doppler shift sharply decreases until the head antenna 210 hands over to the next RU. However, the duration of the Doppler shift is very short, for example, about 50 m. A similar situation also occurs in the tail antenna 220, but the handover of the tail antenna 220 occurs 200 meters behind the head antenna 210 due to the length of the train 200. [

In Fig. 7, the maximum Doppler shifts of the forward link and the reverse link are 10.667 kHz and -10.667 kHz, respectively, which are very large values to be processed at the receiver.

However, when a Doppler shift mitigation method according to an embodiment of the present invention is used, two Doppler shift peaks appear within 1 Km corresponding to the distance between adjacent RUs, and the remaining Doppler shifts are mitigated to 0 Hz in the other intervals. At this time, since the interval of each peak is about 50 m, the two peak intervals become about 100 m.

That is, when the Doppler shift mitigation method according to the embodiment of the present invention is used, it can be seen that the residual Doppler shift is relaxed to 0 Hz in the 900 m section excluding two peak sections of 1 km.

FIG. 8 is a graph illustrating a comparison of performance of a Doppler shift before uplink transmission according to an embodiment of the present invention, and shows a residual Doppler shift derived from a downlink to which a Doppler shift mitigation method is applied before uplink transmission.

In the case where the Doppler shift mitigation method according to the embodiment of the present invention is not used, the maximum Doppler shifts of the forward link and the reverse link for the uplink signal processed by the base station are 2 x 0.667 kHz and -2 x 10.667 kHz, respectively .

In the case of the downlink, if the Doppler shift mitigation method according to the embodiment of the present invention is used, the residual Doppler shift appears as shown in FIG.

The uplink transmission is performed at a carrier frequency that is Doppler shifted in the downlink, and the uplink transmission also experiences a Doppler shift. 8, since the carrier frequency after the two downlink signals are multiplied according to the Doppler shift mitigation method according to the embodiment of the present invention applied to the downlink is doubled, The peak of the residual Doppler shift is reduced to half (= 0.5 x 10.667 kHz) for uplink transmission.

Therefore, if the Doppler shift mitigation method according to the embodiment of the present invention is applied to both the downlink and the uplink, the total residual Doppler shift in the base station is calculated by subtracting the residual Doppler shift induced in the downlink from the residual Doppler shift . That is, the total residual Doppler shift at the base station is ± 0.5 × 10.667 kHz with a probability of 0 Hz, 18% (90% × 10% + 90% × 10%) with a probability of 81% (90% × 90% It is expected to have a probability of ± 1.5 (= 0.5 + 1) × 10.667 kHz with a probability of 10% (10% × 10%).

The embodiments of the present invention are not limited to the above-described apparatuses and / or methods, but may be implemented by a program for realizing functions corresponding to the configuration of the embodiment of the present invention or a recording medium on which the program is recorded. The embodiments can be easily implemented by those skilled in the art from the description of the embodiments described above.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, It belongs to the scope of right.

Claims (15)

A method for mitigating Doppler shift of a receiving apparatus in a high-speed railway communication system,
Receiving on the forward link and the reverse link on a first antenna and a second antenna, respectively, arranged opposite to each other for the same transmission signal, and
Multiplying the signal received by the first antenna with the signal received by the second antenna
Wherein the Doppler shift is performed by the Doppler shift method. The method of claim 1,
Wherein the transmission signal includes a downlink signal. 3. The method of claim 2,
A plurality of RUs (radio units) are arranged along the railway,
Wherein each of the plurality of RUs includes a third antenna and a fourth antenna provided so as to face each other in opposite directions,
Wherein the first antenna and the second antenna are mounted on a moving body traveling on the railroad. The method of claim 1,
Wherein the transmission signal includes an uplink signal. 5. The method of claim 4,
A plurality of RUs (radio units) are arranged along the railway,
Each of the plurality of RUs includes two antennas provided so as to face each other in opposite directions,
Wherein the first antenna and the second antenna are respectively installed in two adjacent radio units (RUs), and an omnidirectional antenna is mounted on a mobile body traveling on the railroad. The method of claim 1,
Converting the signals received at the first antenna and the second antenna to an intermediate frequency signal before the multiplication,
Further comprising: a Doppler shift mitigation method. The method of claim 1,
Removing the noise by high-pass-filtering the multiplied signal
Further comprising: a Doppler shift mitigation method. A Doppler shift mitigation apparatus in a high-speed railway communication system,
A first antenna and a second antenna provided so as to face each other in opposite directions, and
A multiplier for multiplying the signals received through the first and second antennas with respect to the same transmission signal,
And a Doppler shift amount. 9. The method of claim 8,
An intermediate frequency (IF) converter for converting signals received through the first antenna and the second antenna into intermediate frequency signals and outputting the intermediate frequency signals to the multiplier,
Further comprising: a Doppler shift mitigating device. 9. The method of claim 8,
A high-pass filter for eliminating noise by high-pass-filtering the multiplied signal;
Further comprising: a Doppler shift mitigating device. 9. The method of claim 8,
The transmission signal is a downlink signal,
Wherein the first antenna and the second antenna are mounted on a moving body traveling on a railroad. 12. The method of claim 11,
A plurality of RUs (radio units) are arranged along the railway,
Wherein each of the plurality of RUs includes two antennas provided so as to face each other in opposite directions. 9. The method of claim 8,
The transmission signal is an uplink signal,
A plurality of RUs (radio units) are arranged along the railway,
Wherein the first antenna and the second antenna are installed in two adjacent radio units (RUs). The method of claim 13,
Wherein each of the plurality of RUs includes two antennas provided so as to face each other in opposite directions. The method of claim 13,
Wherein at least one antenna is mounted on a moving body traveling on the railroad.
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