JP2000013298A - Radio communication system and radio communication equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radio communication system that uses information data for a radio relay system where an airship is resident in the stratosphere. SOLUTION: The radio communication system is a system where a flying body such as an airship resident in the stratosphere transmits a digital information signal with a radio wave at a high frequency band to ground and consists of a means 12 that extracts a channel assigned for broadcast with the frequency of the digital information signal by a tuning filter, a means 14 that converts the signal from the extraction means into a primary intermediate frequency, means 15-17 that limit a frequency band to the information signal converted into the primary intermediate frequency and down-convert the signal to a VHF frequency band, a means 18 that A/D convert the signal from the down-convert means, means 31-35 that convert digital data from the A/D converter means into an orthogonal multi-carrier signal, a means 36 that up-converts the orthogonal multi-carrier signal from the conversion means into a very weak radio wave, and a means 37 that transmits an output of the means that up-converts the orthogonal multi-carrier signal from the conversion means into a very weak radio wave.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio communication system and a synchronous multicarrier transmission apparatus, and more particularly to a radio communication system and a synchronous multicarrier transmission apparatus using information data of a radio relay system in which an airship stays in the stratosphere.

[0002]

2. Description of the Related Art Transmission of information having a relatively large amount of information, such as digital video signals, requires a wide frequency band according to the amount of information. Therefore, high-frequency carriers such as submillimeter waves and millimeter waves are used. It is common to transmit. Conventionally, for transmitting digital information, the Internet, which runs communication-type multimedia, has been used. A modem is connected to an ISDN (Integrated Services Digital Network) or analog telephone line to transmit digital information. ing. However, the data rate of the Internet is on the order of several tens of kilobits per second, and at most, only information on the order of still images can be transmitted. For transmission of information called multimedia, it is desirable to be able to transmit a moving image of 1 megabit to 6 megabits per second, and it is desired to construct an infrastructure therefor.

[0003] CATV by laying optical cables to each home
If optical fiber networking (fiber-to-the-form (FTTH)) that provides various other communication services functions, a bit rate sufficient to transmit moving images can be obtained, but construction of optical cable terminals The cost is extremely high, estimated at 30 trillion yen. This means 300 Japanese households
Assuming that there are 10,000 households, this is a calculation that costs 1 million yen per household. At present, implementing fiber-to-the-form (FTTH) is quite difficult. Also, xDS is used as a communication means for securing a transmission rate of several Mbps per second by means other than the optical cable.
There is L. This is a method that uses a twisted pair telephone line that is wired to the home, but in Japan, the characteristics of the telephone line vary greatly, and it is impossible to reliably compensate the signal of the required transmission rate to the home. It is difficult, and it is difficult to introduce and operate it in practice.

[0004] In this respect, attention is paid to flying objects such as airships and balloons staying in the stratosphere (altitudes of about 10 km to 50 km) where the weather conditions are relatively stable, and are used as stationary satellite relay stations in satellite communication systems. This is a wireless communication system that performs wireless communication by considering it as such (Yoshihiro Hase et al.,
Proposal of High Speed Wireless Access Network Using Stratospheric Wireless Platform ", IEICE Technical Report, SS
T97-54, RCS97-93 (1997-09)). In the wireless communication system using this flying object, the construction cost of the optical cable is expensive near the residential area of the individual, but the signal arrives at the window facing the flying object such as an airship, so the device that receives the radio wave from the airship Can be installed to bring a relatively large amount of information into the home. Further, in this wireless communication system, since the flying object such as an airship is hovering at an altitude of about 20 km, the altitude is lower than that of the geostationary satellite, and the transmission power from the terrestrial transmitting terminal is smaller than that of the geostationary satellite. It is also possible to construct a nationwide multimedia network by deploying a large number of wireless platforms in order to reduce the delay time. Conventionally, in a system in which a flying object staying in the stratosphere is regarded as a relay station and performs wireless communication, a signal having a high frequency stability received from a reference earth station by a reference frequency of a wireless platform (air station) is provided. There is also known a system capable of transmitting a signal having a frequency stability satisfying the requirements of the applied communication system to each user ground station such as a mobile station by reproducing from the communication system (Japanese Unexamined Patent Application Publication No. Hei.
No. 25,952).

[0005]

As an application of a wireless communication system in which the above-mentioned flying object staying in the stratosphere is regarded as a relay station, multipoint small area broadcasting in a point-to-multipoint format is considered. Since this wireless communication system uses submillimeter waves and millimeter waves as described above,
The propagation environment is almost limited to the line-of-sight area. Therefore, in consideration of use inside a home or office, wired transmission using a coaxial cable to a receiver, which is normally received by a parabolic antenna (beam antenna) installed outdoors, can be considered. However, in this method, a cable wiring operation to the receivers is required for each of the plurality of receivers, which is very complicated.

Therefore, it is conceivable to provide wireless indoor service, but there are the following problems in realizing it. 1) The operating frequency of the stratospheric wireless platform is 30
GHz range is planned. For this reason, even if the frequency is amplified and re-wired indoors as it is, reception cannot be performed unless it is in a perfect line-of-sight area. 2) When re-wireless, transmission power is limited due to restrictions in radio regulations, and in consideration of the technical level of the RF device of the receiver, conversion to a lower frequency is required when re-wireless. It is. 3) The indoor environment is a propagation environment in which the reception level difference between the direct wave and the delayed wave having a relatively short time is small (the D / U ratio is small), and the reception wave from the stratospheric wireless platform is simply transmitted to the lower frequency carrier. Even if the conversion is performed, there is a possibility that a sufficient bit error rate (BER) cannot be secured. The present invention has been made in view of the above points, and an object of the present invention is to provide a wireless communication system that can effectively use a frequency.

[0007]

In order to achieve the above object, the invention of claim 1 transmits a digital information signal to the ground by radio in a high frequency band transmitted from a flying object such as an airship staying in the stratosphere. A wireless communication system, comprising: receiving a desired reception data band from a high frequency band digital information signal from the flying object; converting the received high frequency band digital information signal into a VHF band orthogonal multicarrier frequency; The signal converted to the multicarrier frequency is retransmitted as a transmission radio signal. The invention according to claim 2 is a wireless communication system for wirelessly transmitting a digital information signal to the ground in a high frequency band from a flying object such as an airship staying in the stratosphere by the orthogonal multicarrier modulation method, wherein the wireless communication system transmits the digital information signal from the flying object. A desired reception data band is received from the high frequency band digital information signal, the received high frequency band digital information signal is converted to a VHF band carrier frequency, and the VHF band orthogonal multicarrier signal is re-transmitted as a transmission radio signal. Send it. According to a third aspect of the present invention, in the wireless communication system according to the first or second aspect, the transmission wireless signal is retransmitted as a weak radio wave. According to a fourth aspect of the present invention, in the wireless communication system according to the first or second aspect,
In the transmission radio signal, information data is arranged in an effective symbol period, and is modulated by a plurality of multicarrier modulation signals provided with a guard interval period, and retransmitted.

According to a fifth aspect of the present invention, there is provided a wireless communication apparatus for wirelessly transmitting a digital information signal to the ground in a high frequency band from a flying object such as an airship staying in the stratosphere. Means for extracting the assigned channel with a tuning filter, means for converting a signal from the extracting means to a first intermediate frequency, and band limiting the information signal converted to the first intermediate frequency, Means for down-converting to a VHF frequency band, and A / D
Means for converting the digital data from the means for A / D conversion into orthogonal multi-carrier signals; means for up-converting the orthogonal multi-carrier signals from the converting means into weak radio waves; Means for transmitting the output of the means for up-converting to radio waves.

According to a sixth aspect of the present invention, there is provided a wireless communication apparatus for wirelessly transmitting a digital information signal to the ground in a high frequency band from a flying object such as an airship staying in the stratosphere by orthogonal multicarrier modulation. Means for extracting a channel allocated for broadcasting from the frequency of the signal with a tuning filter, means for converting the signal from the extracting means to an intermediate frequency, and band limiting the information signal converted to the intermediate frequency Means, means for up-converting the orthogonal multicarrier signal from the means for band limiting to a weak radio wave, and means for retransmitting the output of the means for up-converting the signal to the weak radio wave.

[0010]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing one embodiment of a wireless communication system (synchronous multicarrier transmitting apparatus) according to the present invention. In this embodiment, similar to the above-described stratospheric wireless platform, wireless communication between an airship and a ground station equipped with a server connected to a large-capacity ATM (asynchronous transfer mode) network suspended in the stratosphere at an altitude of about 20 km is used. Holds. This wireless communication system is intended to realize the advanced multimedia society, which is to be realized by optical cables, using a wireless system. Since free space is used as a transmission path, transmission distortion is small, and compared to geostationary satellites. Since the airship stays in the low altitude, it has features that the delay time is small, the transmission power is small, and the cost for realizing the airship is lower than that of FTTH or the like.

In this embodiment, the operating frequencies are sub-millimeter wave and millimeter wave bands, and a center frequency of 30 GHz and a frequency band of about 800 MHz are secured. As a modulation method, a single carrier such as QPSK or DQPSK has been proposed. The synchronous multicarrier transmitting apparatus shown in FIG. 1 tunes a desired signal from a received signal from an airship and tunes the signals to the first intermediate frequency and the second intermediate frequency. A / D converter 18 for converting to digital signal, synchronous reproduction circuit 3
1. Multi-frequency oscillator 3 for generating a multi-carrier signal
2, a control circuit 33, an adder 34, a D / A converter 35 for converting a digital signal into an analog signal, and a frequency converter 36 for converting an analog signal into a weak radio wave.

Next, a synchronous multi-carrier weak modulation system used in the wireless communication system of the present embodiment will be described. In frequency division using multicarriers, a symbol period is provided and the same period is set in order to maintain orthogonality between the multicarriers. That is, in generating a multicarrier signal in which a large number of carriers to be frequency division multiplexed are dispersed and modulated by one information signal, a symbol period in which a digital data sequence indicating information signal content to be a modulated signal is arranged is defined by each multipath. The same is assumed for the carrier signal. Further, in consideration of providing different broadcasting services of several channels in a broadcasting channel allocated to a band of 100 MHz, there are the following two methods of frequency division. As shown in FIG. 3, the first frequency division method is a method of dividing the entire transmittable frequency band into arbitrary divided frequency bands 21 to 27. Here, seven divisions are taken as an example, but the number of divisions is determined according to the system to which the system is applied, and is not limited to this.

As shown in FIG. 4A, in the second frequency division method, a plurality of carriers are arranged at predetermined frequency intervals (for example, 100 kHz intervals) in the entire transmittable frequency band. As shown in FIG. 4 (b), transmission of a plurality of carriers every other plurality (FIG.
In the example of (b), nine are used, and they are dispersed and modulated with digital data and multiplexed and transmitted. In the second frequency division method, the total number of carriers transmitted in all frequency bands is, for example, p × q (where p ≦ q) in which all used frequency bands are arranged at predetermined frequency intervals.
q) Of the q carriers, a total of p sets of carrier groups different from each other consisting of q carriers are obtained, so that each set of carrier groups is multiplexed as one multicarrier signal. In other words, when the number of repetition frequencies is r and the transmission cell number is s, s, r + s, 2r +
..,..., nr + s, a multicarrier signal composed of carriers having numbers such as nr + s is allocated to the cell having the transmission cell number s.

Compared to the first frequency division method shown in FIG. 3, the second frequency division multiplexing method shown in FIG. 4 is more advantageous for frequency-selective fading since it transmits over a wide frequency band. is there. That is, in the first frequency division method shown in FIG. 3, the predetermined carrier frequency is canceled out by the influence of the anti-phase multipath, and when there is a sharp level drop, the level of the carrier adjacent in frequency is also greatly attenuated. Likely to be. If some of the carriers to be decoded are damaged, the lost data can be restored by the error correction method. However, if many carriers are damaged at the same time, the error correction method Restoration is difficult. In this sense, the second frequency division method according to FIG. 4 has the effect of frequency interleaving and is advantageous for frequency selective multipath fading.

Next, an embodiment of the synchronous multicarrier transmitting apparatus according to the present invention will be described with reference to the block diagrams of FIGS. The system of the present invention is a radio communication system for wirelessly transmitting a digital information signal to the ground in a high frequency band from a flying object such as an airship staying in the stratosphere in a push-type broadcast from a frequency of 30 GHz and a band of about 800 MHz of the digital information signal. Means for extracting a channel (band 100 MHz) allocated for use by a tuning filter, means 13 and 14 for converting the extracted signal to a primary intermediate frequency of about 1.5 GHz, Means 15 to 17 for down-converting the converted information signal to a VHF frequency band having a center frequency of 51 MHz by BPF, means for A / D converting the down-converted signal, and A / D converted digital Means 31 to 35 for converting data into orthogonal multicarrier signals; More constructed orthogonal multicarrier signal to the weak radio wave of about a center frequency 270MHz and means 36 for up-converting.

In FIG. 1, a center frequency 30 GHz and a bandwidth 10 received by a parabolic antenna (beam antenna) 11 are shown.
The 0 MHz information signal is obtained by extracting a channel signal required by the tuning filter 12,
M (double balanced modulator) 14
The frequency is converted to a first intermediate frequency having a center frequency of 5 GHz. Next, after removing unnecessary spurious and image signals by a BPF (Band Pass Filter) 15, the local frequency oscillator 16 and a DBM (Double Balanced Modulator) 17 remove the 51 MHz signal.
Is double-converted to a second intermediate frequency having a center frequency. 51M double converted
A signal having a center frequency of 100 MHz and a band of 100 MHz is A
The data is converted into digital data by the / D converter 18.
Then, the digital data is supplied to an interface circuit 3 constituting the multi-carrier modulation circuit 30 shown in FIG.
1, multi-frequency oscillator 32, control circuit 33, adder 34,
The signal is converted into a weak multicarrier signal by the D / A converter 35 and the frequency converter 36.

Next, the multi-carrier modulation circuit 30 shown in FIG.
Will be described. In FIG. 2, after an amount of data that is serially input to an interface circuit 31 in a multicarrier modulation circuit 30 and can be transmitted in each symbol period and is converted into an m-bit × n-column parallel signal, An m-bit signal is input as a control signal to each oscillator in the multi-frequency oscillator 32 including n oscillators arranged in parallel. Control circuit 33
Controls which oscillation output of the multi-frequency oscillator 32 is to be generated in accordance with the input signal content. For example, assuming that a quadrature multicarrier signal to be transmitted is a signal modulated by 16QAM, the control circuit 33 determines a multi-frequency oscillator 32 based on 4-bit input subscriber system data.
Determine which of the 16 oscillators to operate. Thus, the multi-frequency oscillator 32 outputs 1
It is extracted as a modulator output signal equivalent to the 6QAM signal.

As described above, the number of carriers (here, n carriers) transmitted from the multi-frequency oscillator 32 has information on the type of oscillation signal required in the multi-level state. , A modulated wave modulated by an m-bit input signal by a predetermined modulation method is dispersed and output by n modulated orthogonal multicarriers. The same symbol period of each carrier is modulated with the same data, and the frequency interval of each carrier is set to be an integral multiple of the symbol synchronization frequency.

The n modulated carriers extracted from the multi-frequency oscillator 32 are frequency-division multiplexed by an adder 34 into one multiplexed signal (orthogonal multi-carrier signal). Is converted into an analog signal by digital-to-analog conversion. Furthermore, the signal
The power is supplied to the weak power frequency converter 36 and the frequency is converted to a VHF band of 270 MHz. Then, the weak radio wave is radiated from the antenna 37 into the air and indoors. When each symbol period of data for modulating each carrier of the multicarrier signal is composed of an effective symbol period in which data is arranged and a guard interval period arranged before the effective symbol period, the guard interval period has a longer time. Since the interference of the channel interference wave can be reduced, the same content can be broadcasted from different airships, and SFN (single frequency broadcast) in which a service area is continuously secured is also possible. Further, the multicarrier signal can be applied by any of the frequency division methods shown in FIGS.

Another embodiment of the radio communication system (synchronous multi-carrier transmission device) according to the present invention will be described below. As a present embodiment, there is a wireless communication system in which a digital information signal is wirelessly modulated from a flying object such as an airship staying in the stratosphere to a ground in a high frequency band by orthogonal multi-carrier modulation. In this system, a local frequency oscillator 16, a DBM (double balanced modulator) 17, and an A / D converter 18 shown in FIG.
Is not necessary, and the weak power frequency converter 36 shown in FIG.
Is not required. Therefore, the output of the BPF 15 is directly supplied to the weak power frequency converter 36. With this configuration, the weak multi-carrier modulation signal in the VHF band having the center frequency of 270 MHz is converted into the weak power frequency converter 36.
Can be obtained as output. According to the present invention, it is possible to convert a multicarrier modulation signal from a millimeter wave band to a VHF band at low cost.

[0021]

As described above, according to the present invention,
Millimeter-wave band information data transmitted from flying objects such as airships is frequency-converted to the VHF band, converted to multicarrier, and retransmitted as weak radio waves, so that it can be stably used even under indoor multipath environments. Data can be demodulated. Further, according to the present invention, since a multicarrier is used as a modulation method of a retransmission signal, a communication speed can be kept low, transmission and reception can be switched by time division, and a signal speed on a terminal side can be changed. Since it is not faster than necessary, it can be set without increasing the burden on the hardware.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of a wireless communication system (synchronous multicarrier transmission device) according to the present invention.

FIG. 2 is a block diagram of one embodiment of a wireless communication system (multi-carrier modulation device) according to the present invention.

FIG. 3 is a diagram illustrating a method of dividing a frequency for each frequency band.

FIG. 4 is a diagram illustrating a method of dividing a frequency by using frequencies at predetermined frequency intervals.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Parabolic antenna (beam antenna) 12 Tunable filter 13, 16 Local frequency oscillator 14, 17 DBM (double balanced modulator) 15 BPF 18 A / D converter 21-27 Divided frequency band 30 Multicarrier modulator 31 Interface circuit 32 Multi Frequency oscillator 33 control circuit 34 adder 35 D / A converter 36 weak power frequency converter 37 antenna

Claims (6)

[Claims] 1. A radio communication system for wirelessly transmitting a digital information signal to the ground in a high frequency band from a flying object such as an airship staying in the stratosphere, wherein the high frequency band digital information signal is transmitted from the flying object. Receiving the desired reception data band, converting the received high-frequency band digital information signal into a quadrature multi-carrier frequency in the VHF band, and retransmitting the signal converted into the multi-carrier frequency as a transmission radio signal. A wireless communication system, comprising: 2. A wireless communication system for wirelessly transmitting a digital information signal to the ground in a high frequency band from a flying object such as an airship staying in the stratosphere by orthogonal multi-carrier modulation. A desired reception data band is received from the frequency band digital information signal, and the received high frequency band digital information signal is converted to VH.
A radio communication system wherein the frequency is converted to an F-band carrier frequency, and the orthogonal multi-carrier signal in the VHF band is retransmitted as a transmission radio signal. 3. The radio communication system according to claim 1, wherein the retransmitted radio signal is retransmitted as a weak radio wave. 4. The radio communication system according to claim 1, wherein the retransmission radio signal includes a plurality of multicarrier modulated signals in which information data is arranged in an effective symbol period and a guard interval period is provided. A wireless communication system characterized in that the signal is modulated and transmitted. 5. A radio communication apparatus for radio transmitting a digital information signal to the ground in a high frequency band from a flying object such as an airship staying in the stratosphere, comprising: a channel allocated for broadcasting from the frequency of the digital information signal. Means for extracting a signal from the extracting means, a means for converting the signal from the means for extracting to a first intermediate frequency, and a band limitation of the information signal converted to the first intermediate frequency to down-convert to a VHF frequency band. Means for A / D converting a signal from the means for down-converting; means for converting digital data from the means for A / D conversion into an orthogonal multi-carrier signal; Means for up-converting the orthogonal multicarrier signal into a weak radio wave; and Retransmitting means. 6. A radio communication apparatus for transmitting a digital information signal from an airplane such as an airship staying in the stratosphere to the ground in a high frequency band by radio using a quadrature multicarrier modulation method, comprising: Means for extracting a channel assigned for use by a tuning filter; means for converting a signal from the extracting means to an intermediate frequency; means for band-limiting the information signal converted to the intermediate frequency; A wireless communication apparatus comprising: means for up-converting a quadrature multicarrier signal from a limiting means to a weak radio wave; and means for retransmitting an output of the means for up-converting the orthogonal multi-carrier signal to a weak radio wave.