JP4528930B2 - Multi-cell wireless communication system and communication method - Google Patents

Description

  The present invention relates to a multi-cell radio communication system, and particularly to a technique for performing good communication by preventing inter-channel interference even in a multi-cell environment when a modulation scheme having multi-path propagation characteristics is used.

  In recent years, digital terrestrial broadcasting has been started. Here, an OFDM (Orthogonal Frequency Division Multiplexing) modulation scheme that is resistant to signal degradation due to multipath propagation is employed. In addition, as the error correction code used in the baseband processing circuit, a concatenated code that performs further convolutional coding is adopted for the signal that has undergone Reed-Solomon coding, and at the same time, powerful error correction is achieved by using both frequency interleaving and time interleaving The ability is realized.

  As a result of such signal processing improvements that enhance the error correction effect, even when poor signal degradation due to multipath or the like occurs, the system can receive high-quality signals. In addition, a single frequency network is realized by such many devices. A single frequency network is used even in an interference region with a low DU ratio even when a plurality of base stations transmit a signal of the same channel at the same frequency and perform a broadcast service in a form that continuously covers an area. It is a system that can receive good TV images.

  Broadcasting services that make it easy to prepare a complex system on the base station side are unlikely to be a major obstacle, but such a method that relies on coding and interleaving in the baseband processing circuit not only complicates the communication device but also generates signals. Is accompanied by a large time delay, and is not suitable for high-speed communication.

For example, an ultrahigh-speed wireless access system using a millimeter wave band (a radio wave of 30 GHz band or higher) has recently been studied as high-speed communication. Such a millimeter wave band system has a large signal attenuation due to propagation due to its short wavelength. For this reason, when trying to construct a cellular communication form, one cell size must be very narrow, from several meters to several tens of meters.
In order to expand this, it is only necessary to continuously install base stations and access points to make multi-cells. However, since the cell size is very narrow, the conventional multi-cell method according to the cellular system found in current cellular phone systems has a problem in that signal processing becomes complicated because frequent handover is required during movement. .

  Even in a wireless access system using the microwave band, not limited to the millimeter wave band, for example, in road-to-vehicle communication in ITS communication, the size of one cell is usually relatively narrow and limited to a pico cell or street cell. Become. In addition, since high-speed mobile communication is required, a signal processing problem for handover during movement occurs as described above.

  In addition, even in an environment for constructing a wireless access system such as a wireless LAN that is now in widespread use, not only a high capacity is always required, but there is a case where it is desired to easily construct a wireless access system over a wider range. Even in such a case, the signal processing problems are the same in the conventional multi-cell technique.

Due to the problems described above, it is expected that the demand for a multi-cell radio communication system capable of good co-channel distribution / access even under an extremely low DU ratio environment without performing signal processing in handover is expected to increase.
For multi-celling, a plurality of access points that can transmit and receive the same radio frequency and radio channel are installed by distributing and combining signals from the base station or to the base station through coaxial lines or optical fibers. Then, when viewed from a wireless terminal that accesses the base station, a system can be realized in which the entire area covered by the plurality of access points can be substantially regarded as one wireless zone.

In order to provide multipath propagation resistance in such a system, an OFDM scheme or a scheme conforming thereto, for example, a CDMA scheme, a multicarrier CDMA scheme combining them, or the like is preferable.
However, in the conventional multi-cell radio communication system, there is a problem in that inter-channel interference occurs in the boundary area between adjacent cells covered by each access point, resulting in signal degradation. The problem of co-channel interference is that in a mobile communication environment using a microwave band, the propagation characteristics change from moment to moment, so that the degradation is smoothed, and these degradations are not necessarily improved by error correction codes. Although not a problem, when a higher frequency such as a millimeter wave band is used, the propagation characteristic becomes static, which sometimes causes a serious problem.

In the technical field to which the present invention belongs, there are the following three documents as known techniques.
First, Patent Document 1 relates to a method for receiving a code division multiple access signal in a multipath propagation environment and a mobile reception device such as a mobile phone and a laptop computer in a code division multiple access system.
According to this document, in order to minimize multiple access interference, when a terminal apparatus receives signals from a plurality of base stations or transmitters, the signal from each base station is unique to each base station. It encodes by. The terminal device includes a signal processing circuit in which a plurality of antenna elements and a plurality of channel estimators respectively corresponding to the base stations are incorporated, and a matrix calculator.

Japanese Patent Laid-Open No. 2003-218836

  Although such an approach can surely suppress interference, it does not realize the same channel access, and it is not an essential solution such that it cannot connect to an unspecified base station. In addition, the base station needs to be switched in the terminal device, which causes a problem similar to the signal processing problem of the handover.

Patent Document 2 discloses a method of transmitting data using a direct frequency division multiplexed signal including a symbol having a predetermined length and a guard time having a predetermined length arranged between the transmitting side and the receiving side. ing.
Patent Document 3 discloses an invention relating to a hierarchical modulation scheme and a transmission / reception apparatus using an orthogonal frequency division multiplexing digital modulation scheme. In this document, a method of generating an OFDM signal by cyclically switching the power and modulation scheme for transmission data of each layer for each transmission symbol is used.

JP-A-8-321820 Japanese Unexamined Patent Publication No. 7-321765

  In any of the above methods, a simple system can prevent flat fading and degradation of the received CN ratio over a wide signal band in situations such as co-channel two-wave interference with a low DU ratio in an adjacent cell boundary region such as OFDM. It is not a technology that can be prevented.

  The present invention was created in view of the above-mentioned problems of the prior art, and in a wireless communication system using a modulation scheme having anti-multipath propagation characteristics, prevents interference between the same channels even in a multi-cell environment, and is good The purpose of this is to perform secure communication.

In order to solve the above-described problems, the present invention provides the following configuration of a multi-cell radio communication system.
Here, the multi-cell radio communication system of the present invention uses a modulation scheme according to an OFDM modulation scheme having resistance to signal degradation due to multipath propagation, and includes a plurality of base stations and at least one radio terminal, Communication is performed bidirectionally between the base station and the wireless terminal or unidirectionally from the base station to the wireless terminal.
According to the first aspect of the present invention, all or some of the base stations in the system generate a modulation signal of the same channel addressed to a specific or all target wireless terminal, and the modulation signal , A pseudo multipath circuit that generates a pseudo multipath signal by artificially adding at least one of a delayed signal, phase rotation, and amplitude fluctuation equivalent to those generated in a multipath propagation environment, and transmission for transmitting the signal And at least a device.

The invention described in claim 2 is provided with a pseudo multipath circuit having multipath propagation characteristics that are not correlated with each other or have sufficiently low correlation in the at least two base stations. In the cell area, completely different multipath signals are inputted from both base stations.
Note that the sufficiently low correlation means that the statistical properties of the fluctuation amount of the delay time τ, the phase θ, and the amplitude A occurring in the multipath propagation environment are independent or sufficiently different. If this is expressed by an equation with amplitude as an example, it can be expressed by E [(A ₁ -m _A1 ) (A ₂ -m _A2 )] = 0 or ≦ (predetermined threshold). Here, E [] is the ensemble average, and A ₁ and m _A1 are the amplitude of # 1 and the average value of the amplitudes.

The invention described in claim 3 is characterized in that radio waves having a short wavelength equal to or lower than the millimeter wave band are used for communication between the base station and the wireless terminal.

The present invention can also provide a communication method in the multi-cell radio communication system according to claim 4.
That is, a modulation scheme according to an OFDM modulation scheme that is resistant to signal degradation due to multipath propagation is used, and is composed of a plurality of base stations and at least one wireless terminal, and between the base station and the wireless terminal A communication method in a multi-cell wireless communication system that performs bidirectional communication or unidirectional communication from a base station to a wireless terminal, and all or some of the base stations are specified or all targeted from a transmission signal A modulated signal of the same channel addressed to the wireless terminal is generated, and at least one of a delayed signal, phase rotation, and amplitude fluctuation equivalent to those generated in a multipath propagation environment is added to the modulated signal in a pseudo manner A pseudo multipath signal is generated, and the pseudo multipath signal is transmitted.

  The invention according to claim 5 is characterized in that, in at least two or more base stations, a pseudo-signal having multipath propagation characteristics that are not correlated with each other or have sufficiently low correlation is added. A communication method in the system can be provided.

  The invention described in claim 6 provides a base station in the multi-cell radio communication system. That is, a base station used in the multi-cell radio communication system generates a modulation signal of the same channel addressed to a specific or all target radio terminals from a transmission signal, and multipath propagation for the modulation signal A pseudo multipath circuit that generates a pseudo multipath signal by pseudo-adding at least one of a delay signal, phase rotation, and amplitude fluctuation equivalent to those generated in an environment, and a transmission device that transmits the pseudo multipath signal And at least.

  The base station according to claim 7, wherein the pseudo multipath circuit has a multipath propagation characteristic that is not correlated with a multipath propagation characteristic of a pseudo multipath circuit of another base station or has a sufficiently low correlation. Features.

Further, the multi-cell radio communication system according to the present invention may have the following aspect in which the base station is configured differently from the above.
That is, the invention according to claim 8 uses at least one base station provided with a plurality of access points for transmitting and receiving signals, using a modulation system according to the OFDM modulation system having resistance to signal degradation due to multipath propagation. A multi-cell wireless communication system that includes a station and at least one wireless terminal, and performs bidirectional communication between the base station and the wireless terminal or in a unidirectional manner from the base station to the wireless terminal. .

  In the system, a base station generates a modulation signal of the same channel addressed to a specific or all target wireless terminals from a transmission signal, a distribution circuit that distributes the modulation signal to each access point, After passing through the distribution circuit, a pseudo multipath signal is generated by artificially adding at least one of a delay signal, phase rotation, and amplitude fluctuation equivalent to those generated in the multipath propagation environment to each modulated signal. It is characterized by comprising at least a pseudo multipath circuit, a transmission line for transmitting the pseudo multipath signal from the base station to each access point, and a transmission device for transmitting the pseudo multipath signal at the access point.

  Alternatively, in the case of uplink communication from the wireless terminal to the base station, the configuration of claim 9 can be adopted. That is, at least one base station provided with a plurality of access points for transmitting and receiving signals using a modulation scheme according to an OFDM modulation scheme having resistance to signal degradation due to multipath propagation, and at least one wireless terminal And a multi-cell wireless communication system that performs bidirectional communication between the base station and the wireless terminal or unidirectionally from the wireless terminal to the base station.

  In the system, a base station receives a modulated signal generated at the wireless terminal at each access point, a transmission line for transmitting the received signal from each access point to the base station, and for each received signal A pseudo multipath circuit that generates a pseudo multipath signal by artificially adding at least one of a delayed signal, phase rotation, and amplitude fluctuation equivalent to those generated in a multipath propagation environment, and each pseudo multipath signal And a demodulating device for demodulating the synthesized signal.

Here, the invention of claim 10 is provided after passing through the distribution circuit in claim 8, and provided in front of the synthesis circuit in claim 9, each of the plurality of pseudo multipath circuits are correlated with each other. Or a pseudo multipath circuit having multipath propagation characteristics with sufficiently low correlation.
Furthermore, the invention described in claim 11 provides a multi-cell radio communication system that uses radio waves of a short wavelength below the millimeter wave band for communication between a base station and a radio terminal.

  The invention described in claim 12 uses at least one base station provided with a plurality of access points for transmitting and receiving signals, using a modulation method according to an OFDM modulation method having resistance to signal degradation due to multipath propagation. A communication method in a multi-cell radio communication system that is configured with at least one radio terminal and performs communication in a bidirectional manner between the base station and the radio terminal or in a unidirectional manner from the base station to the radio terminal. is there.

  In the communication method described above, the base station generates a modulated signal of the same channel addressed to a specific or all target wireless terminals from the transmission signal, and distributes the modulated signal to each access point. In addition, at the access point transmitted via the transmission line, at least one of a delayed signal, phase rotation, and amplitude fluctuation equivalent to those generated in a multipath propagation environment is added to each modulation signal in a pseudo manner. A pseudo multipath signal is generated, and the pseudo multipath signal is transmitted from each access point connected to the base station via a transmission line.

  According to a thirteenth aspect of the present invention, there is provided at least one base using a modulation scheme according to the OFDM modulation scheme having resistance to signal degradation due to multipath propagation, and having a plurality of access points for transmitting and receiving signals. Communication in a multi-cell wireless communication system that is configured with a station and at least one wireless terminal, and performs bidirectional communication between the base station and the wireless terminal or in a unidirectional manner from the wireless terminal to the base station A method of receiving a modulated signal of the same channel addressed to a specific or all target wireless terminals at each access point from a transmission signal generated at the wireless terminal, and receiving signals from each access point to a base station For each received signal, at least one of delayed signal, phase rotation, and amplitude fluctuation equivalent to those generated in a multipath propagation environment is transmitted. After generating a pseudo multipath signals similar to addition, to synthesize the pseudo multipath signal, and demodulating the combined signal.

  In this communication method, as described in claim 14, the plurality of pseudo multipath circuits may be pseudo multipath circuits having multipath propagation characteristics that are not correlated with each other or have sufficiently low correlation.

The invention according to claim 15 uses at least one base station provided with a plurality of access points for transmitting and receiving signals, using a modulation method according to an OFDM modulation method having resistance to signal degradation due to multipath propagation. A base station used in a multi-cell radio communication system, which is configured with at least one radio terminal and performs communication between the base station and the radio terminal bidirectionally or unidirectionally from the base station to the radio terminal I will provide a.
That is, the base station generates, from a transmission signal, a modulation device that generates a modulation signal of the same channel addressed to a specific or all target wireless terminals, a distribution circuit that distributes the modulation signal to each access point, and the distribution A pseudo multipath signal that generates a pseudo multipath signal by artificially adding at least one of a delayed signal, phase rotation, and amplitude fluctuation equivalent to that generated in a multipath propagation environment to each modulated signal after passing through the circuit A path circuit and at least a transmission device that transmits the pseudo multipath signal are provided.

The invention according to claim 16 uses at least one base station provided with a plurality of access points that control transmission and reception of signals using a modulation method according to an OFDM modulation method having resistance to signal degradation due to multipath propagation. A base station used in a multi-cell radio communication system that is configured with at least one radio terminal and performs communication between the base station and the radio terminal bidirectionally or unidirectionally from the radio terminal to the base station I will provide a.
Then, the base station receives a modulated signal generated at the wireless terminal at each access point, a transmission line for transmitting the received signal from each access point to the base station, and each received signal, A pseudo multipath circuit that generates a pseudo multipath signal by artificially adding at least one of delayed signal, phase rotation, and amplitude fluctuation equivalent to those generated in a multipath propagation environment, and each pseudo multipath signal is synthesized. And a demodulator that demodulates the synthesized signal.

  Also in the configuration of the fifteenth or sixteenth aspect, the plurality of pseudo multipath circuits may be pseudo multipath circuits having multipath propagation characteristics that are not correlated with each other or have sufficiently low correlation.

  The invention according to claim 18 is the multi-cell radio communication system according to any one of claims 1 to 3 and 8 to 11, wherein the transmitting device in the transmitting base station or radio terminal uses a local oscillation signal. The transmission signal is converted from the intermediate frequency band to the radio frequency band, and the local oscillation signal and the radio frequency band modulation signal are simultaneously transmitted by radio, while the receiving device in the receiving base station or the radio terminal transmits both the signals. The structure which performs the radio | wireless communication of the self-heterodyne system which converts into an intermediate frequency band by producing | generating a product component of is provided.

  According to a nineteenth aspect of the present invention, in the communication method in the multi-cell wireless communication system according to any one of the fourth, fifth, and twelfth to fourteenth aspects, the transmitting device in the transmitting base station or the wireless terminal has a local oscillation A signal is used to convert a transmission signal from an intermediate frequency band to a radio frequency band, and the local oscillation signal and the radio frequency band modulation signal are simultaneously transmitted wirelessly. The present invention provides a configuration for performing self-heterodyne wireless communication in which a product component of both signals is generated and converted to an intermediate frequency band.

According to a twentieth aspect of the present invention, in the configuration of the multi-cell radio communication system according to the eighth aspect of the invention, the first and the first having different wavelengths are formed together with the modulation device that generates the intermediate frequency band signal in the base station on the transmission side. The first optical signal is modulated with the intermediate frequency band signal into a carrier non-suppression single sideband (SSB) optical modulation signal or a double sideband (DSB) optical modulation signal. A modulator, and an optical mixer that mixes the optical modulation signal with the second optical signal, which is an unmodulated light source having a frequency separated from the optical modulation signal by a desired radio frequency band, and transmits the optical signal Prepare.
Further, the transmission line is an optical fiber transmission line for transmitting an optical signal transmitted from a base station, and the access point is not subjected to photoelectric conversion of the optical signal transmitted from the optical fiber transmission line. A transmission device that generates a modulated carrier and a radio modulated signal and radiates from an antenna is received, and the radio terminal receives an unmodulated carrier and a radio modulated signal transmitted from the access point, and a product product of these two signals By generating the intermediate frequency band, a configuration for taking out the intermediate frequency band conversion signal and demodulating the signal is provided.

The invention according to claim 21 is the communication method in the multi-cell radio communication system according to claim 12, wherein an optical fiber transmission line is used for the transmission line connecting the base station and the access point. In the base station, first and second optical signals having different wavelengths are generated by the first and second laser light sources, and the first optical signal is carrier-suppressed by the pseudo multipath signal. The second modulated light source is a non-modulated light source that modulates a single sideband (SSB) optical modulation signal or a double sideband (DSB) optical modulation signal and is separated from the optical modulation signal by a desired radio frequency band. An optical signal obtained by mixing the optical signal and the optical modulation signal is transmitted from the base station through an optical fiber transmission line. Of course, the second optical signal can be obtained by passing the output of the first laser light source through the optical frequency shifter and shifting the output by a desired radio frequency band.
Also, after receiving the optical signal transmitted from the optical fiber transmission line at the access point, photoelectric conversion is performed to generate an unmodulated carrier and a radio modulated signal, which is radiated from the access point antenna and transmitted from the remote antenna station. The unmodulated carrier and the radio modulated signal thus received are received by the radio terminal, and a product component of these two signals is generated to extract the intermediate frequency band conversion signal and demodulate the signal.

  The present invention uses a modulated signal of the same channel that does not cause a handover signal processing problem in a multi-cell wireless communication system. Further, while using a modulation method according to the OFDM modulation method having multipath propagation resistance, flat fading that occurs in a situation such as co-channel two-wave interference with a low DU ratio in an adjacent cell boundary region, and a wide signal band It is possible to prevent the deterioration of the received CN ratio.

The present invention can achieve the above effects by a simple means of providing a pseudo multipath circuit in a base station / access point.
In other words, even in an area where only signals from two base stations / access points interfere with each other, an environment equivalent to communication in a multipath multipath environment is created. While making up for the weaknesses of the OFDM modulation method, etc. against fading or flat fading, it realizes good communication utilizing its strong characteristics in the multi-wave multipath environment.
As a result, it is not necessary to use strong error correction coding such as a concatenated code, and a burden on the signal processing circuit and a processing delay are not generated.

  In addition, as disclosed in claims 18 and 19, the present applicant combines the self-heterodyne communication method disclosed in Patent Documents 4 to 8 and the present technology, and OFDM that is usually required to have extremely high frequency stability. Signals such as modulation schemes can be handled with a very low cost and simple configuration. In particular, this configuration is an important configuration at a high frequency of the millimeter wave band or higher.

  Furthermore, when trying to perform the same channel communication based on the OFDM modulation scheme or the like in the multi-cell environment as in the present invention, all remote base stations and access points must transmit signals of the same frequency. However, achieving this in a high frequency band such as the millimeter wave band is extremely difficult from the viewpoint of frequency stability, and the communication system itself is very expensive.

On the other hand, by applying the self-heterodyne method to the system of the present invention, as long as the same frequency can be obtained at a stage such as a microwave with a simple device configuration, the stability of the frequency even in the millimeter wave band, Accuracy can be ensured. Therefore, applying the self-heterodyne method to the present multi-cell wireless communication system has a synergistic effect.
Furthermore, by adopting the self-heterodyne method, there is an advantage that ultrahigh-speed mobile communication becomes easy. That is, adopting the self-heterodyne method in such a configuration can greatly reduce the Doppler effect in principle, and can realize stable communication.

JP 2001-53640 A JP 2002-9655 A JP 2003-179516 A JP 2003-264470 A JP 2003-298442 A

As disclosed in claims 20 and 21, a configuration in which the present applicant uses a self-heterodyne access point fused with the optical fiber link disclosed in Patent Document 9 is also suitable.
That is, by using the technology of Patent Document 9 as the principle of downlink signal generation at each access point, it is possible to reduce the cost of the access point and to stabilize communication, which are the features of the self-heterodyne method, and to generate the signal In addition, since a beat of light is used, a signal in a high frequency range such as a millimeter wave band can be easily generated.

JP 2004-80409 A

  Hereinafter, embodiments of the present invention will be described based on examples shown in the drawings. The embodiment is not limited to the following. The present invention is greatly characterized in that a pseudo multipath circuit is provided in a base station and an access point, but together with the first embodiment in which a pseudo multipath circuit unique to each base station is provided, a signal from one base station is received. A second embodiment for transmitting and communicating with a plurality of access points is provided. Further, a third embodiment in which the self-heterodyne method is adopted in the first embodiment or the second embodiment, and a fourth embodiment in which the optical / electrical fusion system is adopted in the second embodiment will be sequentially described. .

(First embodiment)
FIG. 1 is an overall configuration diagram of a radio communication system according to the first embodiment of the present invention. The present invention provides a multi-cell environment in which a plurality of base stations (10) are arranged adjacent to each other in a radio communication system using a high frequency band such as a millimeter wave band. In particular, co-channel communication that does not require handover between base stations is performed.

As a modulation method, an OFDM modulation method having resistance against signal degradation due to multipath propagation is used. This system is particularly used as a system having resistance to a multipath propagation environment in a unidirectional communication system (such as a broadcasting system called SFN) that has been put into practical use in recent years.
The OFDM modulation method eliminates interference by alternately arranging orthogonal carrier waves in addition to the FDM method of converting a high-speed data signal into a low-speed and narrow-band data signal and transmitting it in parallel on the frequency axis. . Since a plurality of carrier waves can be arranged closely without overlapping each other while partially overlapping, wideband transmission that efficiently uses a narrow frequency range is realized, and frequency use efficiency is increased.

The same channel signal is transmitted from each base station (10). At this time, the movable digital broadcast receiving terminal (11) is located in the adjacent area (12) of the two base stations as shown in the figure. There is.
The OFDM signal spectrum transmitted from the base station (10) is one in which a large number of subcarriers are densely orthogonal frequency multiplexed on the frequency axis as shown in FIG. The signal transmitted from the station (10) interferes. Even in an OFDM modulation system that is strong in a multipath propagation environment, such two-wave interference that arrives at the same delay time, especially those that do not involve fluctuations in temporal propagation characteristics, are not resistant, and signal strength reduction called flat fading Or, the reception CN ratio deteriorates.
For example, like the spectrum shown in FIG. 4, a large drop in the received CN ratio always occurs over a wide frequency range.

On the other hand, the OFDM modulation scheme is resistant to interference in a multi-wave multipath propagation environment assumed in a normal mobile communication environment as shown in FIG. Therefore, the present invention transmits a signal equivalent to a pseudo multipath propagation environment in a base station in advance, and a reception signal that can be regarded as multiwave interference in the receiving terminal (11) even if it is actually two-wave interference. Created a structure that would be
The configuration of the base station is shown in FIG.

That is, a digital broadcast transmission facility (13) is provided as a base station. Since the equipment (13) basically includes known elements conventionally used, although details are omitted, an OFDM modulation signal generator (14), an amplifier circuit (16), and an antenna for creating a signal are mainly used. (17).
In addition to this, in the present invention, a pseudo multipath circuit (15) is disposed after the OFDM modulation signal generator (14).

FIG. 6 shows the configuration of the pseudo multipath circuit. The pseudo multipath circuit (15) has a distribution circuit, a delay line, an amplitude control circuit, and a synthesis circuit as main components.
Then, the input signal is distributed to, for example, three lines by the distribution circuit (20), and a delay line (21a-c) is provided for each line to delay the signal. Further, amplitude control is performed by the variable attenuator (22), and these are again synthesized by the synthesis circuit (23) and output.

According to such a pseudo multipath circuit (15), a pseudo multipath similar to the multipath propagation environment shown on the output side is obtained from the input signal shown on the input side of FIG. 6 by a plurality of delay lines and amplitude control circuits. A path signal can be generated.
Here, it can be expected that the distribution circuit performs more distribution and gives different delay paths to each of them, but the effect is expected to be improved, but the configuration becomes complicated, and therefore, it is possible to appropriately set with three or more branches. .
As for amplitude control, a fixed value attenuator may be used, but a variable type is preferable as described above. For example, as a voltage control type amplitude modulator, a signal that varies with time in a Rayleigh distribution is used as a control signal. Furthermore, it is possible to generate a signal wave that approximates the multipath propagation environment.

It is desirable that the pseudo multipath propagation characteristics by the pseudo multipath circuit (15) used in each base station (10) have no correlation with each other or have a sufficiently low correlation. This is because even in the case of a pseudo-multipath signal, interference with these two waves having high correlation causes interference with deep signal fading similar to that in FIG. It is.
Therefore, it is desirable to provide pseudo-multipath propagation characteristics having no correlation, particularly between adjacent base stations. For that purpose, the characteristic values of the delay line and the amplitude control circuit in the pseudo multipath circuit (15) may be changed, and either or both values may be made unique. Since the problem of two-wave interference does not occur unless the base stations are close to each other, a pseudo multipath circuit may be configured by several patterns and distributed.

  In addition, when the pseudo multipath propagation environment is configured as described above, the reception level for each wave is lowered and the BER (bit error rate) is deteriorated. This is the same as the normal multipath propagation environment. Since the OFDM modulation method used in the present invention is highly resistant to such a failure, it does not hinder communication. Rather, since the serious problem such as flat fading due to two-wave interference can be avoided, the present invention works effectively.

  As described above, in the first embodiment, the digital broadcasting system has been described. However, the present invention is not limited to the unidirectional downlink communication from the base station to the wireless terminal, and may be used in a bidirectional wireless communication system capable of upstream communication. . For example, it can be used for a wireless LAN system.

(Second embodiment)
FIG. 7 shows a configuration diagram according to the second embodiment of the present invention. The wireless communication system includes a base station (30) and a plurality of access points (32) connected by a transmission line (31). The transmission line (31) is a coaxial line or an optical fiber line. In the configuration of FIG. 7, the transmission line (31) is provided with an upstream line (33) and a downstream line (34), respectively, so that bidirectional transmission / reception is possible. Good.

  Since a radio communication system that forms a multi-cell environment with a base station (30) and a plurality of access points (32) is known and the configuration of the base station (30) is also known, the general configuration is simplified and described. To do. The base station (30) includes an access control device (35) for performing transmission / reception signal control and an OFDM signal modulation device (36) for transmission, and an OFDM signal demodulation device (37) for reception. Normally, the downlink is distributed from the modulation device (36) by the distribution circuit (38) and transmitted to the access point via the transmission line, and the uplink is connected from the access point to the base station via the transmission line and synthesized by the synthesis circuit (39). Input to demodulator (37).

In the present invention, first, in the downlink, after passing through the distribution circuit (38) from the modulation device (36), it passes through a plurality of newly provided pseudo multipath circuits (40) to become pseudo multipath signals. This is transmitted to each access point (32) and transmitted. The pseudo multipath circuit (40) has the same configuration as shown in FIG.
Thereby, similar to the first embodiment, even when the mobile terminal (42) is located in the boundary area (41) between the access points, good communication can be performed.

Here, a problem similar to that of the down link occurs on the up link. That is, when signals are received by two adjacent access points from the mobile terminal (42) in the boundary area (41) and combined by the combining circuit, two-wave interference occurs.
Therefore, in the present invention, a pseudo multipath circuit (43) is also provided in the uplink, and a multipath signal equivalent to the multipath propagation environment is generated from the input signal from each access point, and this is combined with the synthesis circuit (39). Synthesize with
As a result, the combined signal becomes a signal regarded as multi-wave interference and can be demodulated well by the OFDM signal demodulator (37).

Even in this embodiment, when there is a correlation between the characteristics given by the pseudo multipath circuit of the adjacent access point, the effect cannot be expected, and the characteristics of the multipath propagation environment which is not correlated or sufficiently low in correlation can be given. desirable.
In FIG. 7, each pseudo multipath circuit (40) (43) is provided in the base station (30), but these may be provided in the access point (32). Furthermore, a pseudo multipath circuit that can be shared by the uplink (33) and the downlink (34) may be provided.

(Third embodiment)
In the third embodiment of the present invention, the self-heterodyne method proposed by the present applicant is used for the radio frequency transmission / reception apparatus of the base station or access point in the first or second embodiment.
An explanatory diagram of the self-heterodyne system is shown in FIG. For example, when provided at the access point in FIG. 7, the pseudo multipath signal (IF band modulation signal) input from the transmission line (31) is the mixer (52) to which the local oscillation signal obtained from the local oscillator (51) is input. Is input.

In the mixer (52), the IF band modulation signal and the local oscillation signal are multiplied, and an unnecessary wave component is removed from the output by the bandpass filter (53). As a result, a radio frequency (RF) band modulation signal is obtained. After a part of the power of the local oscillation signal used in the frequency conversion is added to this, the signal is amplified by the amplifier (54) to be transmitted to the transmitting antenna (55). ).
With this configuration, a signal in which a local oscillation signal component (57) having a coherent phase noise characteristic is combined with the RF band modulation signal (56) as in the spectrum in the figure is transmitted.

  On the other hand, the radio terminal is provided with a receiving antenna (58), an amplifier (59), a bandpass filter (60), and a mixer (61), and a local oscillation signal component superimposed on the RF band modulation signal (56) ( By generating the product component of (unmodulated carrier) (57), it is possible to down-convert it into a desired IF band modulated signal.

  According to the above configuration, the access point can perform frequency conversion to, for example, the millimeter wave band by the self-heterodyne method, and transmit it to the wireless terminal. Further, by exchanging the transmission side and the reception side in FIG. 8, a self-heterodyne communication system can be constructed for the uplink. These are described in detail in the above-mentioned Patent Documents 4 to 8.

  Here, when the self-heterodyne method is used, signal interference occurs in the boundary region with respect to the unmodulated carrier component. Therefore, it is preferable to use oscillators having different frequencies between adjacent access points for the local oscillation signal (57). . Alternatively, an oscillator in which the frequency is hopped or frequency spread by phase modulation or the like can be used.

Patent Document 10 discloses a multi-cell technology using a self-heterodyne method by the applicant. The self-heterodyne method is suitable for communication in a high frequency band such as a millimeter wave band because it is not necessary for all base stations to transmit the exact same frequency as described in the patent document.
However, since co-channel interference still occurs in the intermediate frequency band or the like, the configuration using the pseudo multipath circuit according to the present application has a very high effect.

International Patent Publication Number WO 2004/077697

(Fourth embodiment)
A fourth embodiment to which the technical contents disclosed in Patent Document 9 by the applicant of the present application are applied is shown in the second embodiment. FIG. 9 is a block diagram of this system. In the present invention, the base station (60) and the access point (61) are configured as described below, and an optical fiber line is used for the transmission line (62).
In the configuration of the base station (60), components similar to those in the second embodiment are denoted by the same reference numerals, and description of functions is omitted.

First, the same elements as those disclosed in Patent Document 9 will be described. In the downstream direction, the first and second laser light sources (63) (64) are arranged immediately after the pseudo multipath circuit (40) of the base station (60), and the optical external modulation provided for each access point. The signal is modulated by the device (65).
That is, a laser light source (63) that oscillates in a single mode at an oscillation frequency f01, and a laser light source that oscillates at an oscillation frequency f02 corresponding to a radio frequency fRF having a desired interval from the oscillation frequency f01 of the laser light source (63). (64), an external optical modulator (65), and an optical coupler (66).

  The output of the laser light source (63) is input to the carrier non-suppression optical single sideband (optical SSB) modulator (65). The modulator (65) receives the pseudo multipath signal from the pseudo multipath circuit (40) as a modulation signal. As a result, signal light (f01 + fIF) in which the optical carrier is SSB modulated on the optical frequency axis as shown in FIG. 11A is obtained.

  In this embodiment, the carrier residual optical SSB signal is obtained by inputting the intermediate frequency band signal to the carrier non-suppression optical single sideband (optical SSB) modulator (65). The same effect can be obtained by using a carrier non-suppressing optical double sideband (optical DSB) modulator as the detector (65) to obtain the carrier residual optical DSB signal. Also, as a method of obtaining the carrier residual optical DSB signal, it is possible to directly modulate the light source with the intermediate frequency band signal, instead of providing a modulator outside the light source as shown in FIG.

The signal light (f01 + fIF) and the output light of the laser light source (64) that oscillates in a single mode at an oscillation frequency f02 different from the oscillation frequency f01 are input to the optical coupler (66) and mixed.
The output of the optical mixer (66) is transmitted to the access point (61) by the optical fiber transmission line (62). In the optical signal spectrum received at the access point (61) at this time, as shown in FIG. 11B, the interval between the oscillation frequency f01 and the oscillation frequency f02 corresponds to the desired RF frequency fRF. ing. A laser light source that oscillates at a single mode at an oscillation frequency f02 branches the output of a laser light source (63) that oscillates at a single mode at an oscillation frequency f01, and passes it through an optical frequency shifter to obtain a desired RF frequency. It is of course possible to obtain a light source whose frequency is shifted by fRF and substitute it.

  As shown in FIG. 10, in the access point (61), the received signal light is detected by the photoelectric conversion element (70), an unmodulated carrier and a radio modulated signal are generated, then amplified by an amplifier, and then amplified by an antenna (71). Radiates into space.

By the way, in the configuration of the present invention, the optical phase external modulator controlled by the control circuit (66) before the laser light source (63) is input to the carrier residual optical SSB modulator or DSB modulator (65) or An optical frequency shifter (67) is provided to spread or shift the radio frequency.
This is a configuration for avoiding interference in the radio frequency band, and was newly developed in the configuration of the present application. The control circuit (66) provides a spreading code that can sufficiently suppress interference between adjacent access points, or performs control so that the frequency is completely divided.

  The signal radiated from the antenna (71) of the access point (61) is received by the antenna of the wireless terminal. By the self-heterodyne method, the unmodulated carrier and the wireless modulation signal component received by the wireless terminal are amplified by an amplifier, and then unnecessary components are removed by a bandpass filter. Thereafter, the unmodulated carrier and the radio modulated signal component are detected by a square detector, and a product product of these two components is generated to reproduce the IF band signal.

For uplink, the wireless terminal transmits an RF band signal in accordance with the above-described self-heterodyne method, receives it at the reception antenna (72) of the access point (61) in FIG. 10, and receives the frequency in the IF band at the receiver (73). Convert. Further, the electro-optical conversion element (74) performs optical conversion and sends it out through the upstream optical fiber line (62).
On the upstream side of the base station (60), the photoelectric conversion element (75) is disposed immediately before each pseudo multipath circuit (43) and restored to an electrical signal, and then the pseudo multipath described in the second embodiment. To the circuit.

  In this embodiment, separate optical fiber lines are shown for upstream and downstream, but it is also possible to configure a network with the same optical fiber line by applying, for example, a wavelength multiplexing technique.

It is a block diagram of 1st Example of this invention. It is a block diagram of the base station of 1st Example of this invention. It is explanatory drawing of the signal spectrum of an OFDM modulation system. It is explanatory drawing of the signal spectrum at the time of two-wave interference. It is explanatory drawing of the signal spectrum at the time of multiwave interference. It is a block diagram of the pseudo multipath circuit by this invention. It is a block diagram of 2nd Example of this invention. It is explanatory drawing of the self heterodyne system based on 3rd Example of this invention. It is a block diagram of 4th Example of this invention. It is a block diagram of the access point of 4th Example of this invention. It is explanatory drawing explaining the frequency conversion of 4th Example of this invention.

Explanation of symbols

30 base station 31 transmission line 32 access point 33 uplink 34 downlink 35 access control device 36 OFDM signal modulation device 37 OFDM signal demodulation device 38 distribution circuit 39 synthesis circuit 40 pseudo multipath circuit 41 boundary region 42 wireless terminal 43 pseudo multipath circuit

Claims (21)

It uses a modulation scheme according to the OFDM modulation scheme that is resistant to signal degradation due to multipath propagation, and is composed of a plurality of base stations and at least one wireless terminal, and bidirectional between the base station and the wireless terminal Or in a multi-cell wireless communication system that performs unidirectional communication from a base station to a wireless terminal,
All or some of the base stations
A modulation device that generates a modulation signal of the same channel addressed to a specific or all target wireless terminal from a transmission signal; and
A pseudo multipath circuit that generates a pseudo multipath signal by pseudo-adding at least one of a delayed signal, phase rotation, and amplitude fluctuation equivalent to those generated in a multipath propagation environment to the modulated signal;
A multi-cell radio communication system comprising: at least a transmission device that transmits the signal. In the at least two or more base stations,
The multi-cell radio communication system according to claim 1, further comprising a pseudo multipath circuit having multipath propagation characteristics that are not correlated with each other or have sufficiently low correlation. The multi-cell wireless communication system according to claim 1 or 2, wherein a radio wave having a short wavelength equal to or lower than a millimeter wave band is used for communication between the base station and the wireless terminal. It uses a modulation scheme according to the OFDM modulation scheme that is resistant to signal degradation due to multipath propagation, and is composed of a plurality of base stations and at least one wireless terminal, and bidirectional between the base station and the wireless terminal Or a communication method in a multi-cell wireless communication system that performs unidirectional communication from a base station to a wireless terminal,
All or some of the base stations
Generate a modulated signal of the same channel addressed to a specific or all target wireless terminal from the transmission signal,
A pseudo multipath signal is generated by artificially adding at least one of a delayed signal, phase rotation, and amplitude fluctuation equivalent to those generated in a multipath propagation environment to the modulated signal, and the pseudo multipath signal is generated. A communication method in a multi-cell radio communication system, characterized by comprising: In the at least two or more base stations,
5. The communication method in the multi-cell radio communication system according to claim 4, wherein pseudo signals having multi-path propagation characteristics that are not correlated with each other or have sufficiently low correlation are added. It uses a modulation scheme according to the OFDM modulation scheme that is resistant to signal degradation due to multipath propagation, and is composed of a plurality of base stations and at least one wireless terminal, and bidirectional between the base station and the wireless terminal Or a base station used in a multi-cell radio communication system that performs unidirectional communication from a base station to a radio terminal, the base station,
A modulation device that generates a modulation signal of the same channel addressed to a specific or all target wireless terminal from a transmission signal; and
A pseudo multipath circuit that generates a pseudo multipath signal by pseudo-adding at least one of a delayed signal, phase rotation, and amplitude fluctuation equivalent to those generated in a multipath propagation environment to the modulated signal;
A base station of a multi-cell radio communication system, comprising: at least a transmission device that transmits the pseudo multipath signal. The pseudo multipath circuit is
The base station of the multi-cell radio communication system according to claim 6, wherein the base station has a multi-path propagation characteristic that has no correlation with a multi-path propagation characteristic of a pseudo multi-path circuit of another base station or a sufficiently low correlation. At least one base station provided with a plurality of access points for transmitting and receiving signals using a modulation scheme according to an OFDM modulation scheme that is resistant to signal degradation due to multipath propagation, and at least one wireless terminal In a multi-cell wireless communication system configured to perform communication in a bidirectional manner between the base station and the wireless terminal or from the base station to the wireless terminal, the base station includes:
A modulation device that generates a modulation signal of the same channel addressed to a specific or all target wireless terminal from a transmission signal; and
A distribution circuit for distributing the modulated signal to each access point;
After passing through the distribution circuit, a pseudo multipath signal is generated by artificially adding at least one of a delay signal, phase rotation, and amplitude fluctuation equivalent to those generated in the multipath propagation environment to each modulated signal. A pseudo multipath circuit;
A transmission line for transmitting the pseudo multipath signal from the base station to each access point;
A multi-cell radio communication system comprising at least a transmission device that transmits the pseudo multipath signal at an access point. At least one base station provided with a plurality of access points for transmitting and receiving signals using a modulation scheme according to an OFDM modulation scheme that is resistant to signal degradation due to multipath propagation, and at least one wireless terminal In a multi-cell wireless communication system configured to perform communication in a bidirectional manner between the base station and the wireless terminal or in a unidirectional manner from the wireless terminal to the base station, the base station includes:
A receiving device for receiving the modulated signal generated at the wireless terminal at each access point;
A transmission line for transmitting a received signal from each access point to the base station;
For each received signal, a pseudo multipath circuit that generates a pseudo multipath signal by pseudo-adding at least one of a delayed signal, phase rotation, and amplitude fluctuation equivalent to those generated in a multipath propagation environment;
A synthesis circuit that synthesizes each pseudo multipath signal;
A multi-cell radio communication system, comprising: at least a demodulator that demodulates the synthesized signal. The plurality of pseudo multipath circuits are:
The multi-cell radio communication system according to claim 8 or 9, wherein the multi-cell radio communication system has multi-path propagation characteristics that are not correlated with each other or have sufficiently low correlation. The multi-cell radio communication system according to any one of claims 8 to 10, wherein a radio wave having a short wavelength equal to or less than a millimeter wave band is used for communication between the base station and the radio terminal. At least one base station provided with a plurality of access points for transmitting and receiving signals using a modulation scheme according to an OFDM modulation scheme that is resistant to signal degradation due to multipath propagation, and at least one wireless terminal A communication method in a multi-cell radio communication system configured to communicate in a bidirectional manner between the base station and the radio terminal or in a unidirectional manner from the base station to the radio terminal,
Generate a modulated signal of the same channel addressed to a specific or all target wireless terminal from the transmission signal,
After distributing the modulated signal to each access point,
At the base station or at the access point transmitted via the transmission line,
For each modulated signal, a pseudo multipath signal is generated by artificially adding at least one of a delayed signal, phase rotation, and amplitude fluctuation equivalent to those generated in a multipath propagation environment,
A pseudo-multipath signal is transmitted from each access point connected to a base station via a transmission line. At least one base station provided with a plurality of access points for transmitting and receiving signals using a modulation scheme according to an OFDM modulation scheme that is resistant to signal degradation due to multipath propagation, and at least one wireless terminal A communication method in a multi-cell wireless communication system configured to communicate in a bidirectional manner between the base station and the wireless terminal or in a unidirectional manner from the wireless terminal to the base station,
Receiving at each access point the modulated signal generated at the wireless terminal;
Transmit the received signal from each access point to the base station,
For each received signal, a pseudo multipath signal is generated by artificially adding at least one of a delayed signal, phase rotation, and amplitude fluctuation equivalent to those generated in a multipath propagation environment.
Synthesize each pseudo multipath signal,
A communication method in a multi-cell wireless communication system, wherein the synthesized signal is demodulated. The plurality of pseudo multipath circuits are:
The communication method in the multi-cell wireless communication system according to claim 12 or 13, wherein the pseudo-multipath circuit has multipath propagation characteristics that are not correlated with each other or have sufficiently low correlation. At least one base station provided with a plurality of access points for transmitting and receiving signals using a modulation scheme according to an OFDM modulation scheme that is resistant to signal degradation due to multipath propagation, and at least one wireless terminal A base station configured to be used in a multi-cell radio communication system configured to communicate bidirectionally between the base station and the wireless terminal or unidirectionally from the base station to the wireless terminal, the base station comprising:
A modulation device that generates a modulation signal of the same channel addressed to a specific or all target wireless terminal from a transmission signal; and
A distribution circuit for distributing the modulated signal to each access point;
After passing through the distribution circuit, a pseudo multipath signal is generated by artificially adding at least one of a delay signal, phase rotation, and amplitude fluctuation equivalent to those generated in the multipath propagation environment to each modulated signal. A pseudo multipath circuit;
A base station of a multi-cell radio communication system, comprising: at least a transmission device that transmits the pseudo multipath signal. At least one base station provided with a plurality of access points for transmitting and receiving signals using a modulation scheme according to an OFDM modulation scheme that is resistant to signal degradation due to multipath propagation, and at least one wireless terminal A base station configured to be used in a multi-cell radio communication system configured to communicate in a bidirectional manner between the base station and the radio terminal or in a unidirectional direction from the radio terminal to the base station, the base station comprising:
A receiving device for receiving the modulated signal generated at the wireless terminal at each access point;
A transmission line for transmitting a received signal from each access point to the base station;
For each received signal, a pseudo multipath circuit that generates a pseudo multipath signal by pseudo-adding at least one of a delayed signal, phase rotation, and amplitude fluctuation equivalent to those generated in a multipath propagation environment;
A synthesis circuit that synthesizes each pseudo multipath signal;
A base station of a multi-cell radio communication system, comprising: at least a demodulator that demodulates the combined signal. The plurality of pseudo multipath circuits are:
The base station of the multi-cell radio communication system according to claim 15 or 16, wherein the base station is a pseudo multipath circuit having multipath propagation characteristics that are not correlated with each other or have sufficiently low correlation. In the multi-cell radio communication system,
A transmitting apparatus in a transmitting base station or wireless terminal converts a transmission signal from an intermediate frequency band to a radio frequency band using a local oscillation signal, and wirelessly transmits the local oscillation signal and the radio frequency band modulation signal simultaneously. on the other hand,
The receiving device in a receiving base station or a wireless terminal performs self-heterodyne wireless communication in which a product component of both signals is generated and converted to an intermediate frequency band. A multi-cell radio communication system according to claim 1. In the communication method in the multi-cell radio communication system,
A transmitting apparatus in a transmitting base station or wireless terminal converts a transmission signal from an intermediate frequency band to a radio frequency band using a local oscillation signal, and wirelessly transmits the local oscillation signal and the radio frequency band modulation signal simultaneously. on the other hand,
15. A receiving device in a receiving base station or a wireless terminal performs self-heterodyne wireless communication to convert to an intermediate frequency band by generating a product component of both signals. A communication method in the multi-cell wireless communication system according to claim 1. In the multi-cell radio communication system,
To the transmitting base station,
The first and second laser light sources having different wavelengths are provided together with the modulation device for generating an intermediate frequency band signal, and the first optical signal is carrier-suppressed single sideband by the intermediate frequency band signal. A modulator that modulates an (SSB) optical modulation signal or a double sideband (DSB) optical modulation signal;
An optical mixer that mixes the optical modulation signal with the second optical signal, which is an unmodulated light source having a frequency separated from the optical modulation signal by a desired radio frequency band, and transmits the optical signal.
The transmission line is an optical fiber transmission line for transmitting an optical signal transmitted from a base station,
The access point includes a transmission device that photoelectrically converts an optical signal transmitted from the optical fiber transmission line to generate an unmodulated carrier and a radio modulated signal, and radiates from an antenna.
The radio terminal receives an unmodulated carrier and a radio modulation signal transmitted from the access point, generates a product component of these two signals, extracts an intermediate frequency band conversion signal, and demodulates the signal. The multi-cell radio communication system according to claim 8, A communication method in the multi-cell radio communication system, comprising:
Using an optical fiber transmission line in the transmission line connecting the base station and the access point,
In the base station,
First and second laser light sources generate first and second optical signals of different wavelengths;
Modulating the first optical signal with the pseudo multipath signal into a carrier-suppressed single sideband (SSB) optical modulation signal or a double sideband (DSB) optical modulation signal;
An optical signal obtained by mixing the second optical signal and the optical modulation signal, which is an unmodulated light source separated by a desired radio frequency band with respect to the optical modulation signal, is transmitted from a base station through an optical fiber transmission line. ,
After receiving the optical signal transmitted from the optical fiber transmission path at the access point, photoelectrically converts to generate an unmodulated carrier and a radio modulated signal, and radiates from the antenna of the access point,
A radio terminal receives an unmodulated carrier and a radio modulation signal transmitted from a remote antenna station, generates a product component of these two signals, extracts an intermediate frequency band conversion signal, and demodulates the signal. The communication method in the multi-cell wireless communication system according to claim 12.

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