JPH10210002A - Mobile communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mobile communication system having a high frequency use efficiency overall by utilizing advantages suitable for multiple access of CDMA(code division multiple access) as well as an advantage that the frequency use rate is high during transmission of an OFDM(orthogonal frequency division multiplex) signal. SOLUTION: A common symbol synchronizing signal is transmitted from a master station to plural slave stations by the CDMA system, and each slave station decodes the reception signal by a CDMA decoder 14 and generates a symbol synchronizing signal or the like synchronized with the transmission symbol synchronizing signal by an OFDM synchronous circuit 15 and transmits an OFDM signal through an OFDM modulator 23 and a high frequency converter 24. Thus, synchronized OFDM signals are transmitted from plural slave stations, and they are kept orthogonal to mutual carriers. The control of access in multiple access and normal voice communication are performed by CDMA.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mobile communication system, and more particularly to an orthogonal frequency division multiplexing (OFDM).
The present invention relates to a mobile communication system for transmitting and receiving information by using a common band for a frequency division multiplex (CDMA) signal and a code division multiple access (CDMA) signal.

[0002]

2. Description of the Related Art In a mobile communication system, a frequency division multiple access (FDMA), a frequency division multiple access (FDMA),
Time division multiple access (TDMA)
cess) and CDMA are known. FDs in which each channel is multiplexed by being allocated to a different frequency band
The MA and the TDMA in which each channel to be multiplexed is distributed and multiplexed in different time domains have already been put to practical use.

Further, CDMA in which each channel uses the same frequency, modulates information of each channel by using an independent spreading code for each channel, and expands and multiplexes the band of each channel.
Are also being put to practical use. In this CDMA, spread spectrum communication signals of a plurality of channels separately spread by different spreading codes are multiplexed and transmitted in the same time band or frequency band, and each channel is identified and received by utilizing a difference in the spreading code. I do.

[0004] On the other hand, OFDM, which is known as one of the digital modulation systems, is a system in which multilevel modulated digital information is transmitted as an OFDM signal using a large number of carrier waves. As modulation schemes for digital television broadcasting, studies are being made in Japan and Europe. This OFDM uses a large number of carriers and provides a guard interval to obtain reception characteristics that are not easily affected by multipath distortion, but has not been applied to a public communication system.

[0005] Although communication using OFDM signals is performed using a large number of carriers, each carrier is arranged and transmitted and received orthogonally, so that a highly efficient modulation characteristic can be obtained. Here, “carriers are orthogonal” means that the spectrum of an adjacent carrier becomes zero at the frequency position of the carrier. The OFDM signal is generated using an inverse fast Fourier transform (IFFT) circuit, but when transmitted from one transmitter, the synchronization state between the carriers, for example, the symbol synchronization and the sample synchronization relationship are also single. In this case, the orthogonal relationship between the carriers is maintained in a good state.

[0006]

SUMMARY OF THE INVENTION However, the above OF
In communication using DM signals, a digitally modulated wave with a good frequency utilization rate can be generated, such as a rectangular spectrum distribution in the transmission band, but since a large number of carriers are used,
Control of each carrier in the communication field is complicated, and it is difficult to use the multiple access method in practical use.

On the other hand, the above-mentioned CDMA is a digital signal modulation system in which information symbols are spread at an extremely large chip rate and transmitted. Many transmission devices use a common band by a plurality of different spreading codes. Can be used for communication, so that many transmission devices with low operation rates can share a band and configure an efficient frequency use state.

[0008] However, in this CDMA, when the information signal to be transmitted is particularly infrequently used, such as a control signal or a voice signal of a transmission system, the frequency utilization rate can be increased as described above. In the case of continuous transmission, C is one of the spread spectrum communication systems.
In DMA, the frequency utilization efficiency is reduced.

[0009] The present invention has been made in view of the above points,
An object of the present invention is to provide a mobile communication system with high overall frequency use efficiency by using both an advantage suitable for CDMA multiple access and an advantage that a frequency utilization rate is high during transmission of an OFDM signal.

[0010]

In order to achieve the above object, the present invention comprises a fixed master station and one or more slave stations which move within the wireless zone of the master station. In a mobile communication system in which a slave station communicates with a master station or a partner station via a master station and a network, the master station spreads at least a symbol synchronization signal for an orthogonal frequency division multiplexed signal using a spreading code common to all slave stations. And the base station transmits a control signal corresponding to the slave station by a spreading code assigned to each slave station for communication and wirelessly transmits the control signal. The slave station uses a spreading code assigned to each slave station transmitted from the master station. The spread signal is decoded, and at least one of the control information including at least the transmission rate of the information to be communicated and the voice signal to be communicated is spread by the spreading code assigned to the slave station and wirelessly transmitted to the master station. Multiple access with master station Is performed by a code division multiple access system, and is synchronized with a symbol synchronization signal for an orthogonal frequency division multiplex signal obtained by decoding a signal spread by a common spreading code transmitted from a master station and common to all slave stations, and The wireless communication with the master station is performed using a carrier wave designated by a control signal from the master station among a number of carrier waves constituting the orthogonal frequency division multiplexed signal.

In the present invention, multiple access which is the basis of mobile communication between a master station and a slave station is performed by a code division multiple access (CDMA) system, and a relatively high transmission rate is applied to a signal which is continuously transmitted. Orthogonal frequency division multiplexing (OFD)
M) It is configured to be performed by a signal. Where CDMA
Is an excellent accessibility method that performs communication while sharing a common broadband by a plurality of communication devices.
The present invention can make use of the features of both of these schemes, since they have excellent frequency use efficiency when transmitting continuously.

Further, the master station of the method of the present invention transmits a control signal indicating a carrier to be used for an orthogonal frequency division multiplex signal when transmission rate information in control information from a communicating slave station is equal to or greater than a predetermined value. When the transmission rate information is less than a predetermined value, the radio signal to be communicated in place of the control signal is spread by the spreading code assigned to each slave station and wirelessly transmitted. To perform communication by the CDMA system.

Here, when an OFDM signal is used by a large number of users as in the present invention, communication is performed by dividing and allocating a plurality of carriers to a plurality of communicators. In this case, a band-divided OFD transmitted by a plurality of users
If the M signals have a common synchronization relationship, orthogonality between the carriers is maintained, so there is no need to provide a guard band between the divided bands, and the high-efficiency transmission characteristics are maintained as they are. . Therefore, when the transmitting devices of a plurality of slave stations divide a common wide band into a comb-like shape and perform communication using OFDM signals, especially when the number of division points increases, the OFDM generated from the transmitting devices of the plurality of slave stations. The synchronizing relationship of the signals needs to be kept the same.

Therefore, according to the present invention, a common symbol synchronization signal is transmitted from a master station to a plurality of slave stations by a CDMA system, and the slave station transmits an OF signal according to the received symbol synchronization signal.
By transmitting a DM signal, synchronized OFDM signals are transmitted from a plurality of slave stations, and orthogonality is maintained with respect to each other's carrier waves. There is no need to set bands.

In the present invention, access control in multiple access and normal voice communication are performed by CDMA. However, when a terminal (slave station) requests communication by a continuous signal such as a video signal, the CDMA signal is transmitted. Specifies OFDM signal carriers to be used, sends OFDM signal synchronization information, and manages OFDM communication time. While receiving these signals, the slave station generates an OFDM signal wave in which orthogonality is maintained between the slave stations by the commanded signal, and transmits information.

The synchronization signal of the OFDM signal to be transmitted by the slave station is transmitted from the master station, but the slave station always receives it, and errors such as the synchronization period, the carrier number indicating the carrier to be used, and the like are always corrected. I do. In the present invention, CDMA transmits a signal by fully using a wide transmission band, and a slave station transmits an OFDM signal except for a part of the transmission band using a carrier having a carrier number designated by a master station.

Further, in the method of the present invention, the master station comprises: a first spreading code generator for generating a first spreading code common to all slave stations spread by the sample synchronization signal for the orthogonal frequency division multiplexing signal; A second spreading code generator for generating a second spreading code common to all slave stations spread by the synchronization signal, and a third spreading code generator for generating a third spreading code assigned to each slave station And a first multiplying unit for multiplying the first and second spreading codes
, A second multiplier that multiplies the first and third spreading codes, and a third multiplication that multiplies an output signal of the second multiplier by one of a control signal and a voice signal corresponding to a slave station. Vessel and the third
And an adder that adds the output signal of the multiplier and the output signal of the first multiplier to output a combined spreading code, and wirelessly transmits the combined spreading code.

Alternatively, instead of the third spreading code generator, the master station delays the second spreading code by a different time for each slave station and shifts the starting point of the spreading code to equivalently generate the third spreading code. May be provided.

In the present invention, before the slave station transmits the OFDM signal, communication conditions with the master station are set by the CDMA signal. The spreading code used by the master station is set by setting a common code for a specific OFDM device for a slave station having an OFDM function. A control signal to a slave station capable of transmitting and receiving an OFDM signal is performed by the above-described combined spreading code using a plurality of spreading codes called Gold codes. The first spreading code among the codes constituting the Gold code is a common spreading code for the entire OFDM transmitter, such as a synchronization signal, and transmits a sample synchronization signal for driving the IFFT. The second spreading code is used to transmit information about the IFFT symbol synchronization signal. The third spreading code is used for transmitting a control signal for an individual slave station or a voice signal in a CDMA system.

The slave station uses a plurality of OFDM signals such as a synchronization signal required for OFDM signal transmission using the first and second spreading codes.
The control signal addressed to the own terminal can be decoded by using information common to the function-equipped terminal and further using the third spreading code.

According to the present invention, CDMA spreads a signal over a relatively wide band by using a spreading code of a predetermined chip rate and transmits the signal. However, an OFDM signal transmits a signal using a minimum required band. The CDMA receivers in the master station and the slave station have excellent signal rejection capability of a spectrum that is concentrated like an OFDM signal. In addition, since CDMA spreads and transmits energy, the CDMA receiver is provided to the OFDM receiver in the slave station. The influence is relatively small, and it is possible to transmit and decode both signals using a common band when traffic is not congested.

[0022]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of a slave station which is a main part of the system of the present invention, FIG. 2 (A) is an overall schematic diagram of an example of the system of the present invention, and FIG. 1 shows an example of a frequency spectrum of a signal used in the system. First, the overall schematic configuration of the present invention will be described with reference to FIG. 2A. In the mobile communication system, a master station (master unit) 1 corresponding to a fixed radio base station and a slave station (child station) corresponding to a mobile station are used. g) consisting of 2 ₁ to 2 ₃ Tokyo. It should be noted that the number of slave stations is not limited to the illustrated three.

The master station 1 is connected directly to a public network (not shown) or by a wire through a control station. The master station 1 transmits and receives voice signals and control signals according to a standard CDMA system, and performs continuous transmission and reception. And a function of transmitting and receiving an orthogonal frequency division multiplexed signal (OFDM signal) for transmitting a typical signal. With the slave station 2 ₁ to 2 ₃ comprises a transmission and reception function according to the CDMA method, the amount of information such as video signals is large and has a function of transmitting and receiving OFDM signals transmitted continuous signal.

[0025] Here, in this embodiment, the slave stations 2 ₁ -
2 ₃ multiple access with the other terminal of the public network which is interposed master station 1 according to is performed by CDMA system, but the CDMA signal (e.g., spread spectrum communication signal) occupies a wide band as shown by I in FIG. 3 cage, and by the carrier wave of the slave station 2 ₁ to 2 ₃ is the carrier number specified from the master station 1, FIG. 3
As shown by II, O is obtained by using a part of the CDMA signal band.
Transmit the FDM signal. Since FIG. 3 shows a signal at the receiver input of the master station 1, the CDMA signal is shown in a plurality of layers.

Further, in this embodiment, a plurality of slave stations 2 ₁ to 2 ₃ master station 1 is residing in the reception-enabled wireless zones
Relative to supply a common synchronization signal by the CDMA system, the slave station 2 ₁ to 2 ₃ to transmit an OFDM signal synchronized with the synchronizing signal by receiving the synchronization signal. The OFDM signal is
Digital data sampled based on the sample synchronization signal is input to an IFFT circuit having a predetermined window function together with the sample synchronization signal and the symbol synchronization signal,
Generated by the circuit.

The slave stations 2 _{1 to} 2 ₃ transmit the OFDM signal divided into bands. Since the OFDM signals are transmitted based on the common synchronization signal, the orthogonality of the carrier waves of the OFDM signals is maintained. That is, for transmitting the OFDM signal is the slave station 2 ₁ to 2 ₃ on the basis of a common synchronization signal, the frequency spectrum of each carrier which constitutes their OFDM signal as shown in FIG. 4, each carrier frequency is regularly And the phases are the same as well as the frequency of the window time, whereby the orthogonality of each carrier is maintained, and the frequency spectrum of the k-th carrier is shifted by the symbol synchronization signal frequency to the next (k +1), the signal level becomes zero (no interference) at the (k-1) th carrier point. This allows
There is no need to provide a guard band between the divided bands, and the highly efficient transmission characteristics of OFDM are maintained.

The synchronizing signal includes a sample synchronizing signal for driving an IFFT circuit for generating an OFDM signal and a symbol period including an IFFT window period (effective symbol period) and a guard interval, as described later. There is a symbol synchronization signal to be determined, but it includes at least the symbol synchronization signal. If the symbol synchronization signal is shifted,
This is because the carrier of the FDM signal disappears. Note that the guard interval is a section for removing multipath distortion, and
It is added to the FT-calculated data.

Here, in FIG. 2B, the frequency f1
Band ~f2 the OFDM signal transmitting and receiving bands allocated to the slave station 2 _3, an OFDM signal transmission and reception band band frequencies f3~f4 is assigned to the slave station 2 _2, frequency f5~f6
The band is OFDM signal transmission and reception band assigned to the slave station 2 _1. Each OFDM signal transmission / reception band includes one or two or more carriers of the OFDM signal. Although each OFDM signal transmission / reception band is illustrated in FIG. 2B as a similar bandwidth here, different bandwidths may be used. In response to a request from the slave station, the master station 1 allocates a bandwidth according to the amount of information to be communicated with the free band.

Next, a description will be given of each configuration of the slave station 2 ₁ to 2 _3. The slave station 2 ₁ to 2 _3, respectively identical configuration, as shown in the block diagram of FIG. 1, an antenna 10, an intermediate frequency (IF) converter 11, the synchronization detector 12, the spreading code generator 13, CDMA decoder 14 , An OFDM synchronization circuit 15 and an OFDM decoder 16, a receiving unit A, a spreading code generator 20, a CDMA modulator 21, an OFDM modulator 23,
The transmission unit B includes a high-frequency converter 24 and an antenna 25.

The synchronization detector 12 detects a synchronization signal for a CDMA signal. Spreading code generators 13 and 20 each generate a spreading code assigned in advance to each slave station. C
The DMA decoder 14 is composed of, for example, a multiplier,
Here, OFDM synchronization information, slave station control signals, and audio signals are output. The OFDM synchronization circuit 15 generates a sample synchronization signal and a symbol synchronization signal. OFDM decoder 1
6 decodes the carrier in the OFDM signal of the band specified by the master station 1. The CDMA modulator 21 outputs a CDMA signal. The OFDM modulator 23 generates an OFDM signal in the band specified by the master station 1.

The spreading code generator 13 and the CDMA decoder 14 in the slave station may be configured as shown in the block diagram of FIG. In the figure, the spreading code generator 31 is C
At the timing based on the DMA synchronization signal, a first spreading code common to all slave stations is generated. The spreading code generator 32 generates a second spreading code unique to each slave station. Multiplier 33
Is the first spreading code from the spreading code generator 31 and the received C
The signal is multiplied by a DMA signal to output OFDM synchronization information. The multiplier 34 multiplies the output signal of the multiplier 33 by the second spreading code from the spreading code generator 32 and outputs a slave station control signal and a voice signal.

Next, the configuration of the main part of the master station 1 will be described. FIG. 6 shows a block diagram of a main part of one embodiment of the master station 1. The master station 1 has a modulation section and a decoding section for an OFDM signal, and generates a first spreading code in synchronization with a sample synchronization signal as shown in FIG.
A first spreading code generator 41 for generating a first spreading code spread by the sample synchronization signal, and a second spreading code in synchronization with the symbol synchronization signal (in other words,
A second spread code generator 42 for generating a second spread code spread by the symbol synchronization signal) and a second spread code generator 42 for generating a different third spread code corresponding to the other terminal in synchronization with the CDMA synchronization signal. 3 spreading code generators 43 and the first and second spreading code generators 43.
, A second multiplier 45 for multiplying the first and third spreading codes, and a multiplier 4 for multiplying the first and third spreading codes.
5 is multiplied by a control input signal (such as a carrier number or other power control information) or a voice signal, and a combined spread code (Gold And a adder 47 for outputting a code.

Here, the first and second spreading code generators 4
The first and second spreading codes output by 1 and 42 are common spreading codes to all slave stations, respectively. When the CDMA decoding circuit of the slave station has the configuration shown in FIG.
The spread code of 1 has the same value as the output spread code of the multiplier 44, and the spread code of the spread code generator 32 has the same value as the output spread code of the third spread code generator 43.

Next, the operation of the embodiment of the present invention described with reference to FIGS. 1 to 6 will be described. After being line connection by known methods with the counterpart terminal connected to the public network via a base station 1 and any one of the slave stations of the slave station 2 ₁ to 2 ₃ shown in FIG. 2, The slave station transmits control data (information for identifying whether only a voice signal or a video signal is to be transmitted, information on its own address and transmission amount information, etc.) about information to be communicated via the terminal 19 shown in FIG. The modulated signal is supplied to a CDMA modulator 21, where the modulated wave obtained by modulating the spread code from the spread code generator 20 is converted into a CDMA signal by a high-frequency converter 24 and wirelessly transmitted from the antenna 25 to the master station 1. I do.

After the master station 1 receives and decodes the CDMA signal by a receiving / decoding section (not shown), the spreading code of the slave station is determined based on the address unique to the slave station in the control data as shown in FIG.
Is set in the spreading code generator 43 shown in (1), and the set spreading code is generated in synchronization with a CDMA synchronization signal and supplied to the multiplier 45 so that the first spreading code from the spreading code generator 41 is Perform a multiplication modulo 2.
The output signal of the multiplier 45 is supplied to a multiplier 46, where a multiplication modulo 2 is performed on the audio signal or the control input signal.

Here, the master station 1 communicates only with the CDMA signal when communicating only the audio signal between the slave station and the partner terminal. In this case, the multiplier 46 supplies the multiplier 46 with the audio signal from the partner terminal. Is input and the output signal of the multiplier 45 is multiplied modulo 2. However, when a request for communication by a continuous signal such as a video signal is issued from a slave station, the master station 1 transmits and receives a request for communication using an OFDM signal.
Of a large number of carriers constituting the FDM signal, a carrier number not used for communication and a carrier number indicating a number of carriers according to the amount of transmission information, and power control information and multi-level QAM are transmitted. A control input signal composed of multi-valued values is supplied to a multiplier 46 to execute multiplication modulo 2 with the output signal of the multiplier 45.

The output signal of the multiplier 46 is obtained by combining the first and second spread codes output from the spread code generators 41 and 42 in synchronization with the OFDM signal sample synchronization signal and OFDM signal symbol synchronization signal, respectively. Multiplier 44 for multiplication
Is added in an adder 47 to generate a combined spread code, which is converted into a CDMA signal in a high frequency band by a transmitting unit (not shown) and wirelessly transmitted to a slave station. The sample synchronization signal and the symbol synchronization signal input to the spread code generators 41 and 42 are always input even when performing communication by CDMA, so that the master station 1 always uses the sample synchronization signal common to all slave stations. Signal and symbol synchronization signal are CDMA
It is transmitted by a signal.

The slave station receives the CDMA signal by the antenna 10 shown in FIG. 1, converts the CDMA signal into an IF signal by the IF converter 11, and synchronizes with the synchronizing signal in the CDMA signal detected by the synchronizing detector 12 to generate a spread code. The generator 13 generates a spread code and supplies the spread code to the CDMA decoder 14. Here, reception C
A spread code having the same value as the combined spread code used for the DMA signal is decoded only by a predetermined slave station generated from the spread code generator 13, and a decoded output is output to a terminal 17.

When communication is performed using OFDM signals,
Control information such as a carrier number output from the CDMA decoder 14 is supplied to the OFDM decoder 16 and the OFDM modulator 23, respectively, and the carrier in the OFDM signal to be decoded is
Each carrier in the OFDM signal to be modulated is set. Also, the OFDM output from the CDMA decoder 14 is
The synchronization signal for use is supplied to an OFDM synchronization circuit 15 to generate a sample synchronization signal and a symbol synchronization signal, and supply them to an OFDM decoder 16 and an OFDM modulator 23.

After setting the above communication conditions, the slave station inputs the audio information to be communicated by the own station to the CDMA modulator 21 via the terminal 19, or outputs a continuous signal such as a video signal to the terminal 22. Is supplied to the OFDM modulator 23 via the. Both or one of the CDMA signal obtained by the CDMA modulator 21 and / or the OFDM signal obtained by the OFDM modulator 23 is supplied to the high frequency converter 24, where it is converted into a high frequency band and transmitted to the master station 1. . Thereafter, the transmission information from the partner terminal passes through the master station 1 and is received by the receiver A of the slave station.
, And the decoded signal is output to terminals 17 and 18.

As described above, according to this embodiment, C
DMA and OFDM are modulation schemes whose properties are completely different in terms of frequency.
A continuous signal with a relatively high transmission rate by DM
Since transmission can be performed within the transmission band of the MA, communication can be performed by selecting one that can use the frequency more effectively.
Also, in the case of OFDM transmission, since a large number of slave stations can transmit using synchronized carriers, orthogonality is maintained for each carrier, and there is no need to provide a guard band for each individual transmission frequency, and the frequency is effectively used. Can be used.

The circuit section of the master station 1 for generating the combined spread code may have the configuration shown in the block diagram of FIG. 6, the same components as those of FIG. 6 are denoted by the same reference numerals, and the description thereof will be omitted. In FIG. 7, the symbol synchronization signal and the CD
In synchronization with the MA synchronization signal, the spreading code generator 48
And outputs the same to the multiplier 44, while delaying the code start point by the delay circuit 49 and supplying it to the multiplier 45 as a third spreading code. Here, the amount of delay by the delay circuit 49 is set to a value unique to the slave station based on the address unique to the slave station in the control data obtained by receiving and decoding the received CDMA signal.

In the circuit section for generating the combined spreading code of the master station 1 shown in FIGS.
1. The circuit portion including the spreading code generator 42 (48) and the multiplier 44 is replaced with a single spreading code generator 51 as shown in FIG.
Can be configured. In this case, the sample clock is removed by one cycle at the symbol synchronization start position indicated by 52 in FIG. As a result, a spread code similar to the spread code obtained by multiplying the first and second spread codes synchronized with the sample synchronization signal and the symbol synchronization signal is obtained from the spread code generator 51.

The present invention is not limited to the examples shown in FIGS. 6 to 8, but includes, for example, setting another information bit at the symbol clock position, inverting the phase of the sample clock for each symbol frequency, and the like. An information embedding method can also be used. Further, the mobile communication system of the present invention can be applied to a system in which a master station broadcasts to a plurality of slave stations. The slave station may be a slave unit used indoors, and the present invention is applicable to mobile communication systems in general.

[0046]

As described above, according to the present invention,
Multiple access is performed by CDMA, and the transmission rate is relatively high.
Since communication is performed using signals, an excellent mobile communication system that makes use of the merits of both can be constructed by selecting an appropriate method according to information to be transmitted.

Further, according to the present invention, CDMA having excellent accessibility in which a master station performs communication while sharing a common wide band.
, A common synchronization signal is transmitted to a plurality of slave stations, and the slave stations transmit an OFDM signal synchronized with the received synchronization signal. Therefore, orthogonality is maintained with respect to each other's carrier. There is no need to provide a guard band for each transmission band, and OFDM is not required within the frequency band used by the CDMA signal.
Since the communication can be performed by setting the frequency band of the signal, the frequency can be effectively used.

Further, according to the present invention, CDMA and OFD
A slave station (mobile station) capable of transmitting and receiving both signals of M can use a common circuit from the high-frequency conversion section and the intermediate frequency conversion section. A circuit can be expected to be miniaturized by making it a large scale integrated circuit (LSI), and a plurality of information having different purposes can be individually decoded by a plurality of multiplication functions of the CDMA, so that it can be realized without increasing the hardware burden so much.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of a slave station which is a main part of the system of the present invention.

FIG. 2A is an overall schematic configuration diagram of an example of the method of the present invention,
(B) is a diagram showing an example of a frequency spectrum of a signal used in the method of the present invention.

FIG. 3 is a diagram showing an example of a frequency spectrum of a CDMA signal and an OFDM signal used in the method of the present invention.

FIG. 4 is a diagram illustrating an example of a frequency spectrum of each carrier constituting an OFDM signal.

FIG. 5 is a block diagram illustrating an example of a CDMA decoding circuit unit of a slave station.

FIG. 6 is a block diagram of an embodiment of a part of a master station forming another main part of the system of the present invention.

FIG. 7 is a block diagram of another embodiment of a part of a master station forming another main part of the system of the present invention.

FIG. 8 is a diagram showing another example of generating a spreading code in a master station.

[Explanation of symbols]

Reference Signs List 1 master station 2 _{1 to} 2 ₃ slave station 11 intermediate frequency (IF) converter 12 synchronization detector 13, 20, 31, 32, 41, 42, 48, 51 spreading code generator 14 CDMA decoder 15 OFDM synchronization circuit 16 OFDM decoder 17 CDMA decoded signal output terminal 18 OFDM decoded signal output terminal 19 CDMA transmission signal input terminal 21 CDMA modulator 22 OFDM transmission signal input terminal 23 OFDM modulator 24 High frequency converter 33, 34, 44 to 46 Multiplier 47 Addition Device 49 delay circuit A receiving unit B transmitting unit

Claims (7)

[Claims] 1. A fixed master station and one or more slave stations which move within a wireless zone of the master station, wherein the slave station is connected to the master station or the master station and a network via a network. In the mobile communication system for communicating with the partner terminal, the master station always spreads the symbol synchronization signal for at least the orthogonal frequency division multiplexing signal by a common spreading code for all slave stations, and always transmits the symbol synchronization signal. The control signal corresponding to the slave station is spread by the assigned spreading code and wirelessly transmitted, and the slave station decodes the signal spread by the spreading code assigned to each slave station and transmitted from the master station, and performs communication. Multiple access with the master station is performed by spreading at least one of the control information including at least the transmission rate of the information to be transmitted and the voice signal to be communicated by spreading the spreading code assigned to the slave station and wirelessly transmitting to the master station. Code division many Performed by the connection method, synchronized with the symbol synchronization signal for the orthogonal frequency division multiplexed signal obtained by decoding a signal spread from the common station and spread by the common spreading code for all slave stations, and A mobile communication system, wherein wireless communication is performed with the master station using a carrier wave indicated by the control signal from the master station among a plurality of carrier waves constituting an orthogonal frequency division multiplexed signal. 2. The slave station transmits a control signal indicating a carrier to be used for the orthogonal frequency division multiplex signal when transmission rate information in the control information from the slave station for communication is equal to or more than a predetermined value. When the transmission rate information is less than the predetermined value, a voice signal to be communicated in place of the control signal is spread with a spreading code assigned to each slave station. 2. The mobile communication system according to claim 1, wherein the mobile communication system performs wireless communication and performs communication by a code division multiple access system. 3. The first spread code generator for generating a first spread code common to all slave stations spread by the orthogonal frequency division multiplexed signal sample synchronization signal, and the symbol synchronization signal. A second spreading code generator for generating a second spreading code common to all slave stations spread by the above, and a third spreading code generator for generating a third spreading code assigned to each slave station A first multiplier for multiplying the first and second spreading codes, a second multiplier for multiplying the first and third spreading codes, and an output signal of the second multiplier. A third multiplier for multiplying one of the control signal and the audio signal corresponding to the slave station, and adding an output signal of the third multiplier and an output signal of the first multiplier to generate a combined spreading code. 2. An adder for outputting the combined spread code, wherein the combined spread code is wirelessly transmitted. Mobile communication method. 4. The master station comprises: a first spreading code generator for generating a first spreading code common to all slave stations spread by the orthogonal frequency division multiplexing signal sample synchronization signal; and the symbol synchronization signal. A second spreading code generator for generating a second spreading code common to all the slave stations spread by the above, and shifting the starting point of the spreading code by delaying the second spreading code by a different time for each slave station. A delay circuit that generates a third spreading code equivalently, a first multiplier that multiplies the first and second spreading codes, and a second multiplier that multiplies the first and third spreading codes. A multiplier, a third multiplier that multiplies the output signal of the second multiplier by one of the control signal and the audio signal corresponding to the slave station, and an output signal of the third multiplier and the first signal. An adder for adding the output signal of the multiplier and outputting a combined spreading code; The mobile communication system according to claim 1, wherein the code is transmitted wirelessly. 5. A fourth spreading code generator for generating a fourth spreading code common to all slave stations, spread by a signal obtained by inserting the symbol synchronization signal into the orthogonal frequency division multiplexing signal sample synchronization signal. 5. The mobile communication system according to claim 3, wherein the first and second spreading code generators and the first multiplier are provided in place of the first and second spreading code generators. 6. The slave station multiplies a fifth spreading code synchronized with the code division multiple access signal synchronization signal by a code division multiple access signal from the master station to convert at least the symbol synchronization signal. First decoding means for decoding;
And a second decoding means for multiplying the signal output from the decoding means by the third spreading code for each slave station to decode the voice signal or the control signal corresponding to the slave station. The mobile communication system according to claim 3. 7. The orthogonal frequency division multiplexing signal transmitted / received between the master station and the slave station is arranged in a frequency band of the code division multiple access signal transmitted / received between the master station and the slave station. The mobile communication system according to any one of claims 1 to 4, wherein: