JPH10257551A - Transmission station arranging method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the considerable degradation of reception quality at the time of mobile communication and to provide almost uniform quality inside a service area by arranging plural transmission stations in the almost equal distance from a concentrated area. SOLUTION: The same contents are simultaneously transmitted at the same frequency from transmission stations 1 and 2 for providing information through an orthogonal frequency division multiplex transmission system. Radio waves are received while moving mobile reception terminals 4 and 5 inside a service area 3 of the same frequency network as an area in which the radio waves from the transmission stations 1 and 2 can be received. The transmission stations 1 and 2 are installed so as to be positioned at the almost equal distance from the mobile reception terminal 4 for receiving the radio waves while moving through places in which buildings 6 such as high-rise buildings are irregularly constructed. The same frequency network service area 3 is composed of area 7 to be mainly served by the transmission station 1 and area 8 to be mainly served by the transmission station 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of arranging transmitting stations for transmitting and receiving radio waves in a single frequency network (SFN) environment using, for example, an orthogonal frequency division multiplexing (OFDM) transmission system.

[0002]

2. Description of the Related Art Terrestrial broadcasting systems and portable / car telephone systems have been started from analog transmission systems. Recently, the number of subscribers has increased sharply due to lower prices of mobile and mobile telephone terminals and drastic reductions in call charges, and frequency resources have become tight. Therefore, digitalization of mobile / mobile telephone systems has begun with the aim of effectively utilizing frequency resources.
In general, digital transmission is different from analog transmission, which is intended to reproduce faithful transmission waveforms and spectra.
Since it is easy to realize high transmission quality, high reliability, and high confidentiality using correction, and it is not necessary to reproduce a faithful transmission waveform or spectrum, narrowing and multiplexing are possible. Also,
It is suitable for future multimedia because it can handle voice, image, data, etc. in an integrated manner. This flow is called PDC
It has led to the spread of digital mobile phones such as mobile phones and PHSs.

[0003] On the other hand, the digitization of television broadcasting has been gradually advanced, and the digitization that began with satellite broadcasting is currently
It has spread to CATV. However, the digitalization of terrestrial television broadcasting, which has the largest number of users, has been carefully standardized in consideration of the burden on users, avoiding rapid market expansion, and digital broadcasting of terrestrial broadcasting will be promoted in 2010. It is a plan to be started.

[0004] In the field of mobile communication such as portable and car telephone systems, GMSK modulation and π / 4 shift differential QPSK are used.
Digital modulation such as modulation and access methods (transmission methods) such as TDMA and CDMA have been put to practical use. In mobile communication, the propagation environment is generally poor, so that the reception characteristics are improved by applying an adaptive automatic equalizer or diversity reception. In particular, when distortion due to multi-path propagation peculiar to mobile communication occurs, the reception characteristics are greatly deteriorated. Therefore, it may be necessary to improve the reception quality by further means in order to maintain the reception quality. However, the mobile / car phone system divides the communication range covered by one base station into several (km) zones to improve the frequency efficiency, so that multipath propagation distortion is not so large. Sufficient reception quality has been achieved by applying an automatic equalizer and diversity reception.

On the other hand, in a terrestrial broadcasting system, the range covered by one transmitting station is extremely large, several tens of kilometers (km). More than double. To compensate for such large multipath propagation distortion,
The effects of the adaptive automatic equalizer and the diversity receiving system are no longer effective, and it is important to adopt a more robust transmission system. Therefore, an orthogonal frequency division multiplexing (OFDM) transmission system capable of transmitting high-quality information even in a poor multipath propagation environment has been adopted as a transmission system for digital terrestrial television broadcasting. The OFDM signal has a guard period in which a part of a transmission symbol is copied, and this guard period absorbs multipath propagation distortion and does not cause intersymbol interference. In digital terrestrial television broadcasting, this O
Single frequency network (SF
N) is planned. SFN is a method in which the same program is broadcast simultaneously by a plurality of transmitting stations using the same frequency band, whereby the frequency band allocated to the broadcast can be significantly compressed, and the frequency is effectively used (frequency efficiency is improved). Is possible. In Europe, the Digital Audio Broadcasting System (DAB) was first commercialized, and the development of the Digital Television Broadcasting System (DVB) has been rushed.

[0006] However, it has been reported that the reception characteristic of a terminal that moves linearly between two adjacent transmitting stations greatly deteriorates in the SFN service in DAB in which the service is started in advance. This is thought to be due in part to the fact that terrestrial broadcasting systems have installed transmitting antennas at high positions in order to secure a large service area, and the antennas of multiple transmitting stations can be viewed directly from the receiving terminal. I have. In the case of mobile reception under such a radio wave propagation environment, a direct wave greatly shifted by Doppler arrives from a plurality of directions, and particularly when moving on a line connecting two transmitting stations, a periodic time dependent on the Doppler frequency is obtained. Since the fading in the axial direction occurs, the receiving characteristics are greatly deteriorated. To explain this qualitatively with a simple model,
It looks like this: Assuming that the radio frequency is fc (Hz) and the Doppler frequency is fd (Hz), the received signal y of the terminal moving near the midpoint on the line connecting the two transmitting stations
Y (t) = Acos {2π (fc + fd) t} + Aco
s {2π (fc−fd) t} = {2Acos (2πfd)
t)｝ cos (2πfct)

From the above equation, the signal received by the terminal is observed as if a signal wave {cos (2πfct)} having a constant amplitude was amplitude-modulated, and the amplitude of the signal periodically becomes zero (0). You can see that the moment is coming. From here, S
It can be explained that, in the FN service, the reception characteristics of a terminal that moves linearly between two adjacent transmitting stations greatly deteriorate.

[0008] Therefore, it is conceivable to perform some processing on the receiver itself as a measure taken to realize sufficient reception characteristics under such a poor radio wave propagation environment. However, since the terminal is always required to be portable, it is inevitable to reduce the size and reduce the power consumption, and it is not desirable to provide the terminal, that is, the receiver, with a means for improving reception characteristics. In addition, since the retransmission control method is not suitable for information providing services and telephone services that value real-time properties, it is common to apply robust error correction.However, error correction corresponding to poor reception characteristics is good. It is useless at the time of receiving characteristics, and it has been a problem in terms of economy and effective use of resources.

[0009]

As described above, a terrestrial broadcasting system that provides information in a single frequency network (SFN) environment employing an orthogonal frequency division multiplexing (OFDM) transmission system has a large service area. Since the transmitting antenna is installed at a high position to secure, when moving and receiving in a radio wave propagation environment where you can directly see the antennas of multiple transmitting stations, direct waves that are greatly Doppler shifted will come from multiple directions, In particular, when moving on a line connecting two transmitting stations, there is a problem that periodic deep fading in the direction of the time axis occurs depending on the Doppler frequency, and reception characteristics are extremely deteriorated.

A mobile radio terminal considering portability is:
Due to demands for miniaturization, low power consumption, low cost, etc., even a terrestrial broadcasting system receiver that is not pursued as portable as a telephone, it is not desirable to have a complicated signal processing function Was also a problem.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and has been made in consideration of a single frequency network (S).
It is an object of the present invention to provide a method of arranging a transmitting station that can prevent the reception quality from being extremely deteriorated during mobile reception even under an FN) environment and can obtain substantially uniform reception quality within a service area.

Another object of the present invention is to provide a method of arranging a transmitting station which can cope with downsizing, low power consumption, and low cost of a mobile receiving terminal by realizing such uniform receiving quality. .

[0013]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention according to the first aspect of the present invention is directed to a system for transmitting the same information from a plurality of transmitting stations at the same time and at the same frequency. The plurality of transmitting stations are arranged at a distance.

According to a second aspect of the present invention, in a system for transmitting the same information from a plurality of transmitting stations at the same time and at the same frequency, the plurality of transmitting stations are arranged at substantially the same distance from an area susceptible to near reflection. It is characterized by having done.

According to a third aspect of the present invention, in a system for transmitting the same information at the same time from a plurality of transmitting stations at the same frequency, one transmitting station is arranged on a substantially straight line passing through a non-dense area. It is characterized by.

According to a fourth aspect of the present invention, in a system for transmitting the same information from a plurality of transmitting stations at the same time and at the same frequency, one transmitting station is provided on a substantially straight line passing through an area which is not affected by nearby reflection. It is characterized by being arranged.

In the transmitting station arranging method according to the present invention, the transmitting stations are arranged so that they can be received in a Rayleigh fading environment, so that substantially uniform reception quality can be provided. Further, in the transmitting station arranging method according to the present invention, the transmitting stations are arranged so that the mobile receiving terminal can receive a direct wave from the transmitting station, so that it is possible to provide good reception quality, Since the transmitting stations are arranged so that the plurality of transmitting stations and the receiving terminal do not form a straight line, it is possible to eliminate the adverse effect on the reception quality and, as a result, improve the reception quality.

[0018]

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

FIG. 1 is a conceptual diagram showing a transmitting station arrangement method according to one embodiment of the present invention.

As shown in FIG. 1, the transmitting station 1 and the transmitting station 2 which provide information by the orthogonal frequency division multiplexing (OFDM) transmission method transmit the same contents at the same frequency at the same time. A mobile reception terminal 4 is located in an SFN (same frequency network) service area 3 which is an area where radio waves from the transmission station 1 and the transmission station 2 can be received.
The mobile receiving terminal 5 receives the radio wave while moving. The mobile receiving terminal 4 is located near the intermediate point between the transmitting station 1 and the transmitting station 2, and buildings 6 such as high-rise buildings are crowded around the mobile receiving terminal 4. The transmitting station 1 is positioned so as to be located at substantially the same distance from the mobile receiving terminal 4 that receives while moving in a place where a building 6 such as a high-rise building is crowded.
And the transmitting station 2 are installed, and an SFN service area 3 is constituted by an area 7 mainly served by the transmitting station 1 and an area 8 mainly served by the transmitting station 2.

In this case, the mobile radio terminal in consideration of portability is required to have a small size, low power consumption, low cost, and the like, and it is not desirable to have a complicated signal processing function. It can be said that it is more desirable to reduce the extremely poor reception characteristics of. The Rayleigh fading environment, which is well known in mobile communication, has no fixed and large Doppler shift because the transmitting station is not visible, and has almost constant reception characteristics regardless of the positional relationship between the receiving terminal and the transmitting station. Considering that it will be used to solve the above problems. Therefore, the mobile receiving terminal 4 is made to be able to receive in a Rayleigh fading environment caused by the building 6 that has been erected. That is, in FIG. 1, it is desirable that the mobile receiving terminal 4 cannot see the transmitting station 1 and the transmitting station 2 directly. Also, the mobile receiving terminal 5 in FIG.
Is located near the transmitting station 2, but in this case, the transmitting station 1 and the transmitting station 2 may be directly viewed.

FIG. 2 shows the transmitting station 1 as viewed from the mobile receiving terminal 4.
FIG. 9 is a diagram showing the results of a simulation study of the reception characteristics (bit error rate characteristics) when the transmission station 2 can directly view and the reception characteristics (bit error rate characteristics) when the transmission station 2 cannot directly see. The horizontal axis in the figure is the distance from the intermediate point between the transmitting station 1 and the transmitting station 2 (either in the direction of the transmitting station 1 or in the direction of the transmitting station 2).
And the vertical axis shows the bit error rate. As shown in the figure, the reception characteristic 9 in an environment (line-of-sight propagation) where the transmission station 1 and the transmission station 2 can be directly viewed from the mobile reception terminal 4 near the midway point between the transmission station 1 and the transmission station 2
It can be seen from FIG. 3 that the transmission station 1 and the transmission station 2 are more deteriorated than the reception characteristic 10 in an environment (Rayleigh fading propagation) where they cannot be directly viewed. From the above results, if the mobile receiving terminal 4 receiving the SFN service is near the midpoint between the transmitting station 1 and the transmitting station 2, the transmitting station 1 and the transmitting station 2 are arranged so that they can be received in a Rayleigh fading environment. It is desirable to do. Also, from the figure, when the mobile receiving terminal 4 approaches one of the transmitting stations, that is, in the case of the mobile receiving terminal 5 in FIG. 1, the mobile receiving terminal 5 clearly transmits from the transmitting station 1 or the transmitting station 2, or An environment where both base stations can look directly is desirable. Since the present invention aims to provide the mobile receiving terminal 4 and the mobile receiving terminal 5 with substantially constant reception characteristics, the transmitting station 1 and the transmitting station 1 are set so that the periphery of the mobile receiving terminal 4 is in a Rayleigh fading environment. The arrangement of the station 2 is very effective.

FIG. 3 is a diagram for explaining another embodiment of the present invention.

In the figure, four transmitting stations 11, 12, 1
The SFN service according to 3, 14 is provided. The four transmitting stations 11, 12, 13, and 14 are installed mainly at the hillside 15 and are installed so that the transmitting stations cannot be seen through each other. If the four transmitting stations can be seen from each other, a service area is provided on a line connecting them. It does not exist. The transmitting stations are arranged so that the town A16 is located at the center of the four transmitting stations 11, 12, 13, and 14, and the town B17 is located in the middle between the transmitting stations 11 and 12. Transmitting stations 11, 13, 14
Since is located near the hill, multipath propagation is a concern. However, due to the advantages of the OFDM transmission system, its effect can be completely ignored. In the center of the town A16, there is a building 18 such as a skyscraper, in which a mobile receiving terminal 19 is located. From the mobile receiving terminal 19, all the transmitting stations are not in line-of-sight and receive in a Rayleigh fading environment, and almost uniform reception quality can be obtained. Town A
Since the transmitting station 13 can be seen from the mobile receiving terminal 20 located outside the area 16, good receiving quality can be obtained.
The mobile receiving terminal 20 is also in a position where the transmitting station 12 can be seen, but is not positioned on a line connecting the two transmitting stations (not arranged in a straight line), so that there is no influence on the reception quality. Similarly, the town B17 has a building 21 such as a skyscraper in the center thereof, and all the transmitting stations cannot be seen from the mobile receiving terminal 22 therein. In particular, the transmitting station 11 and the transmitting station 12
Is in an environment in which is not visible, the mobile receiving terminal 22 receives in a Rayleigh fading environment, and almost uniform reception quality is obtained. Since the mobile receiving terminal 23 located outside the town B17 is close to the transmitting station 12, good receiving quality can be expected. When an SFN service area is constructed by two or more transmitting stations as described above, the transmitting stations are arranged in consideration of an area where buildings such as towns are dense.

FIG. 4 shows the reception quality (bit error rate characteristic) of the mobile terminal station 20 in FIG. The horizontal axis represents the distance from the intermediate point between the two transmitting stations 12 and 13, the vertical axis represents the bit error rate, θ represents a straight line connecting the mobile terminal station 20 and the transmitting station 12, and the mobile terminal station The angle between the straight line connecting the transmission station 20 and the transmission station 13 is shown. θ = 0 °, that is, the bit error rate when the mobile terminal station 20 is aligned with the transmitting station 12 and the transmitting station 13 is 2
4, θ = 75 °, that is, the mobile terminal station 20 and the transmitting station 12
And a straight line connecting the mobile terminal station 20 and the transmitting station 13 forms an angle of 75 °, the bit error rate is 2
Indicated at 5. From the figure, two transmitting stations 12 and 1
Even if 3 can be seen, it can be seen that the reception quality becomes uniform if there is no mobile receiving terminal on the line connecting them.

As described above, according to the arrangement method of the transmitting stations as shown in FIGS. 1 and 3, more uniform reception quality can be obtained as compared with the case where the arrangement method shown in the present invention is not used. I understand.

The present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the technical concept of the present invention.

For example, in the above embodiment, the mobile terminals 4, 5, 19, 20, 22, and 23 and the transmitting stations 1, 2, 1
Although the buildings 6, 18, and 21 such as high-rise buildings have been described as examples of shields between 1, 12, 13, and 14 as long as they block radio waves, they can be used even if they are not buildings. is there.

When it is difficult to dispose an arrangement that cannot be seen in FIG. 3, the same effect can be obtained by adjusting the transmission power or employing a transmission directional antenna instead of the arrangement shown in FIG. it can.

[0030]

As described in detail above, according to the present invention,
For example, even in an urban area where buildings under a single frequency network (SFN) environment where the same information is transmitted at the same time from a plurality of transmitting stations using the orthogonal frequency division multiplexing (OFDM) transmission method at the same time are used. In addition, it is possible to prevent the reception characteristics from being extremely deteriorated and to make the reception characteristics uniform within the same service area.

Further, according to the present invention, a single frequency network (SFN) environment in which the same information is transmitted at the same time from a plurality of transmitting stations at the same time by using, for example, an orthogonal frequency division multiplexing (OFDM) transmission method. Even in an area where a certain building is not densely packed, excellent reception characteristics can be maintained, extreme deterioration of reception characteristics can be prevented, and reception characteristics within the same service area can be made uniform.

Equalizing the reception characteristics has the merit that the user can receive the service regardless of the location, and also facilitates the design of the entire system, for example, the design of specific reception characteristic improvement measures and error correction. Therefore, since it is not necessary to provide a receiving terminal with a measure for improving reception characteristics that have been extremely deteriorated, it is not necessary to provide an extra signal processing function, and the mobile receiving terminal can be reduced in size and power consumption, and cost can be reduced. Can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view showing a transmitting station arrangement method according to an embodiment of the present invention.

FIG. 2 is a diagram showing a simulation result of reception characteristics (bit error rate characteristics) in the case of FIG.

FIG. 3 is a schematic perspective view illustrating a transmitting station arrangement method according to another embodiment of the present invention.

FIG. 4 is a diagram showing a simulation result of a reception characteristic (bit error rate characteristic) in the case of FIG. 3;

[Explanation of symbols]

 Reference Signs List 1 transmitting station A 2 transmitting station B 3 SFN service area 4 mobile receiving terminal A 5 mobile receiving terminal B 6 building such as high-rise building 7 main service area of transmitting station A 8 main service area of transmitting station B 9 at the time of line of sight propagation 10 bit error rate characteristics at the time of Rayleigh fading propagation 11 transmitting station C 12 transmitting station D 13 transmitting station E 14 transmitting station F 15 mountain 16 town A 17 town B 18 high-rise building or other building 19 mobile receiving terminal C Reference Signs List 20 mobile receiving terminal D 21 building such as high-rise building 22 mobile receiving terminal E 23 mobile receiving terminal F 24 bit error rate characteristic A 25 bit error rate characteristic B

Claims (4)

[Claims] 1. A transmitting station arrangement method in a system for transmitting the same information from a plurality of transmitting stations at the same time and at the same frequency, wherein the plurality of transmitting stations are arranged at substantially the same distance from a dense area. 2. A system for transmitting the same information from a plurality of transmitting stations at the same time and at the same frequency, wherein the plurality of transmitting stations are arranged at substantially the same distance from an area susceptible to near reflection. Station placement method. 3. A system for transmitting the same information at the same time from a plurality of transmitting stations at the same time, wherein one transmitting station is arranged on a substantially straight line passing through a non-dense area. Method. 4. A system for transmitting the same information from a plurality of transmitting stations at the same time and at the same frequency, wherein one transmitting station is arranged on a substantially straight line passing through an area unaffected by nearby reflection. Transmission station placement method.