JPH11113049A - Wireless communication system - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a wireless communication system capable of effectively using a frequency and providing high communication quality. SOLUTION: In this wireless communication system, all carriers f1 to fn are arranged without setting a guard band between adjacent carriers on a frequency axis. Further, in two types of time slots 41 and 42 alternately set on the time axis, a communication channel including m carriers discretely selected from n carriers is frequency division multiplexed. In addition, a symbol time slot including a guard interval and a time interval for executing the discrete Fourier transform is set for each unit symbol time.
The base station and the mobile station can accurately demodulate the reverse frame and the forward frame without inter-symbol interference by the guard interval.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wireless communication system, and more particularly, to a mobile communication system in which an entire service area is covered by a plurality of cells and a mobile station located in a certain cell is one of all communication channels. The present invention relates to a wireless communication system that communicates with a base station that forms the cell using one communication channel.

[0002]

2. Description of the Related Art Conventionally, a radio communication system of a so-called multi-cell configuration has a TAC system employing an analog system.
S (Total Access Communication System) and AMPS (Ad
vancedMobile Phone Service) and PDC (Personal Digital Cellrl)
ar), GSM (Grobal System for Mobilecommunication
s) and PHS (Personal Handy-phone System).

In these wireless communication systems, each service area is covered by cells formed by a plurality of base stations. A plurality of carriers that can be used for communication are allocated to a cell, which is an area where signals from each base station reach, and each mobile station located in this cell is assigned one of the carriers allocated by the base station. Communication is performed using a carrier as a communication channel. These wireless communication systems employ a frequency multiplexing method for such communication. That is, the plurality of carriers assigned to one cell are arranged on the frequency axis without overlapping each other and at predetermined intervals (guard bands). This guard band has been narrowing with recent technological advances,
It is determined so that each mobile station can select (separate) one carrier assigned to itself by a band-pass filter provided internally. Further, these wireless communication systems adopt a multi-cell configuration as described above, and carriers of the same frequency are repeatedly used between cells separated by a certain distance from each other, thereby achieving effective use of frequency resources.

[0004]

However, in a conventional multi-cell radio communication system, it is necessary to always take the above-mentioned guard band, and it is possible to allocate a carrier of the same frequency to a plurality of cells adjacent to each other. Therefore, there is a problem that the effective use of the frequency is not sufficiently achieved. Further, since the mobile station can use only one carrier for communication, there is a problem that the bit error rate is extremely deteriorated due to the effects of dynamic reflection and interference generated on the transmission path. By the way, the fact that a mobile station receives diversity from a signal from a plurality of base stations by selecting a signal having a better reception state or combining the plurality of signals is called site diversity. Is a technique used in so-called handoff. In order to realize site diversity when carriers of different frequencies are allocated between adjacent cells as in a conventional multi-cell configuration, each mobile station is provided with an internal PL.
The frequency of a local oscillator using L (Phase Locked Loop) must be changed as needed to search for a base station to be subjected to site diversity. For this reason, conversations are interrupted, and it is difficult to switch base stations (soft handoff) while maintaining communication quality.

[0005] Therefore, an object of the present invention is to provide a radio communication system which can effectively use a limited frequency and can provide high communication quality.

[0006]

Means for Solving the Problems and Effects of the Invention In order to achieve the above object, the present invention has the following aspects,
Further, each aspect has the following effects. First according to the present invention
In the aspect, the service area is covered by laying a plurality of cells formed by the base station, and communication between one mobile station located in a certain cell and the base station forming the cell is performed by the mobile station. A wireless communication system which is performed using one communication channel selected from all communication channels available in a service area, wherein a predetermined communication channel is used for all communication channels available in the service area. In the frequency band, n (n is a natural number of 2 or more) carriers having different frequencies from each other are allocated in advance, and the base station and the mobile station are discretely arranged on the frequency axis from the n carriers. Select m carriers (m is a natural number satisfying 2 ≦ m ≦ n) that are arranged and do not overlap with other communication channels, and are configured by the selected m carriers. And performing communication using a communication channel that.

[0007] According to the first aspect described above, m carriers in one communication channel are discretely arranged on the frequency axis, and thus have transmission path characteristics having low correlation with each other. By using such a communication channel, the effect of frequency diversity can be obtained,
The effects of reflection and interference in the transmission path are dispersed to m carriers, and the bit error rate can be improved as compared with the related art.

[0008] A second aspect of the present invention is characterized in that, in the first aspect, the base station and the mobile station perform communication using an orthogonal frequency division multiplex system.

As is well known, in the above-mentioned orthogonal frequency division multiplexing method, it is not necessary to provide a guard band between adjacent carriers on the frequency axis. Therefore, according to the above-described second aspect employing this scheme, carriers can be arranged on the frequency axis at a higher density than in a conventional wireless communication system employing the frequency division multiplexing scheme. Further, when the orthogonal frequency division multiplexing method is employed, each mobile station can collectively and accurately demodulate only signals transmitted from a base station forming a cell in which the mobile station is located by a Fourier transform process. Also, by controlling the transmission power in the communication between the base station and the mobile station, the mobile station can execute accurate demodulation processing even if the same communication channel is used between adjacent cells. As a result, the frequency can be effectively used, and a large number of carriers can be accommodated in the wireless communication system.

According to a third aspect of the present invention, in the second aspect, the base station notifies a signal transmission timing for each mobile station located in a cell formed by the base station. Transmit a signal to the base station according to the signal transmission timing notified from the base station forming the cell in which the mobile station is located, thereby correcting the deviation of the arrival timing of the signal transmitted from each mobile station to the base station. Features.

In a wireless communication system, the time required for a signal transmitted by a mobile device to reach a base station differs depending on the position of the mobile device in a cell. In addition, in order for the orthogonal frequency division multiplexing method to be adopted, and for each base station to execute the Fourier transform processing, the arrival timing of the signal from the mobile station needs to be uniform within a predetermined error. Therefore, in the third aspect, the base station notifies the timing of signal transmission for each mobile station located in the cell formed by the base station, and corrects the above-described deviation of the arrival timing of the signal. Thereby, the arrival timings of the above-described signals can be aligned within a predetermined error range.

According to a fourth aspect of the present invention, in the second or the third aspect, each of the base stations in the service area has a different communication channel as a communication channel used when transmitting the reference signal. Pre-assigned, each base station in the service area, for each mobile station in a cell formed by itself, periodically transmits a reference signal using a pre-assigned communication channel, the mobile station, On the basis of a reference signal transmitted from a base station, the base station itself specifies a base station with which communication is to be performed.

When a wireless communication system employs a plurality of cell configurations, it is necessary to change a base station with which communication is performed by moving a mobile station. Thus, in the fourth aspect, each base station periodically transmits a reference signal using a different frequency. In each mobile station, for example, even if it is located near the boundary between adjacent cells and can receive a plurality of reference signals, since the wireless communication system adopts the orthogonal frequency division multiplexing method, the received The reference signal can be demodulated collectively and accurately, and a base station to communicate with can be specified based on the reference signal (so-called handoff). Therefore, according to the present wireless communication system, unlike a conventional wireless communication system, there is no need to search for a base station to be communicated while switching the PLL at any time, so that soft handoff can be performed while maintaining high speed and communication quality. it can.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the configuration of a multi-cell adopted in a wireless communication system (hereinafter, referred to as "the present system") according to an embodiment of the present invention will be described with reference to FIG. In FIG. 1, the present system includes, as an example, cells mc1 to mc7 formed by base stations bs1 to bs7. These seven cells mc1 to mc7 are spread in a continuous plane so as not to overlap with each other,
This covers the service area of the system. A plurality of mobile units ms (only one station is shown) accommodated in this system can move freely in this service area,
It communicates with the base station bs (1-7) forming the cell mc (1-7) in which it is currently located, using one communication channel selected by the base station bs from all communication channels. I do.

Next, regarding the above-mentioned communication channel, FIG.
This will be described with reference to FIG. FIG. 2A shows a frequency allocation of a plurality of carriers that can be used in the present system. In the present system, orthogonal frequency division multiplexing is used for communication between the base station bs and the mobile station ms.
Two carriers f1 to f32 are allocated in advance. As will be described later, these carriers f1 to f32 are subjected to FFT in a time section 432 excluding the guard interval 431 in the symbol time slot 43 (see FIG. 4).
When the windows are provided, the windows have a relationship orthogonal to each other. In such an orthogonal frequency division multiplexing method, it is not necessary to provide a guard band between adjacent carriers on the frequency axis, as is well known. Therefore, as shown in FIG. 2A, the present system can accommodate a large number of carriers at a high density, as compared with the conventional system, whereby the frequency can be used effectively.

FIG. 2B shows one communication channel used for communication in the present system. FIG.
In FIG. 2B, the communication channel is the communication channel 3 shown in FIG.
It is composed of four carriers that are discretely arranged on the frequency axis from the two carriers f1 to f32 and do not overlap with other communication channels. Such 4
Since the carriers have low correlations in the transmission path characteristics, if the communication is performed using the four carriers, the effect of the frequency diversity can be obtained, and the bit error rate is improved as compared with the conventional system. it can. In the present embodiment, as is clear from the above, eight communication channels can be obtained. For example, the communication channel 1 shown in FIG. 2C has four discretely selected carriers f.
1, f9, f17 and f25 are allocated, and thereafter, the communication channels 2 to 8 are allocated frequencies as shown in FIG.

Next, the forward link fl and the reverse link rl used in the present system will be described with reference to FIG. As shown in FIG. 3, for example, the base station bs1 forming the cell mc1 is the mobile station ms in the cell mc1.
1 to transmit a forward frame 51 (see FIG. 5) to the forward link fl1. Also, the mobile station ms1 transmits a reverse frame 52 (see FIG. 5) to the reverse link rl1 in order to communicate with the base station bs1.
Is sent. Further, the present system employs time division duplex as shown in FIG. 4, and time slots 41 and 42 for the forward link and the reverse link are alternately set on the time axis. In these two types of time slots, each of the above-described communication channels including a plurality of carriers is subjected to orthogonal frequency division multiplexing, and the plurality of carriers are modulated by the forward frame 51 or the reverse frame 52 illustrated in FIG. One forward frame 51 or reverse frame 52 obtained by modulating a plurality of carriers in this way is transmitted using one forward link or reverse link time slot 41 and 42. Further, these two types of time slots 41
And, a symbol time slot 43 (for example, refer to a portion with a dot in FIG. 4) is set for each predetermined unit symbol time. The time slot 43 of this symbol is a guard interval 431
And a time interval 432 for executing a Fourier transform process
And

Next, the forward frame 51 and the reverse frame 52 used in the present system will be described with reference to FIG. In FIG. 5, the forward frame 51
Is a preamble indicating the head position of the frame, etc., address information of the mobile station ms that is the transmission destination of the forward frame 51, first control information used for correcting the synchronization of the time slot 43 described later, and transmission described later. Fields 511, 512, and 51 for setting second control information and transmission data used for power correction control
3, 514 and 515. The reverse frame 52 includes a preamble indicating the head position of the frame and the like, address information of the base station bs to which the reverse frame 52 is transmitted, and fields 521, 522, and 523 for setting transmission data 523. The forward and reverse frames 51 and 52 are a set of symbol time slots 43, as is clear from FIG.

In this system employing the arrangement of communication channels shown in FIG. 2, base stations bs (1 to 7) use one communication channel in forward link time slot 41 to internally generate a forward link. The frame 51 is transmitted to the mobile station ms in the cells mc (1 to 7) formed by itself. On the other hand, the mobile station ms uses the same communication channel in the reverse link time slot 42 to generate a reverse frame 52 internally generated.
To the base stations bs (1 to 7) forming the cells mc (1 to 7) in which they are located.

Hereinafter, the base station bs1 and the mobile station m shown in FIG.
Taking the communication with s1 as an example, the communication procedure in this system will be described. For the sake of simplicity, it is assumed that the state of communication between the base station bs1 and the mobile station ms1 is good and that there is no need for handoff. First, a detailed block configuration of the base station bs1 and the mobile station ms1 will be described with reference to FIG. 6, the base station bs1 includes a frame configuration device 611, a carrier designation device 612, a modulation device 613, a transmission / reception device 614,
A synchronization control device 615, a time division control device 616, a demodulation device 617, a slot processing device 618, and a frame disassembly device 619 are provided. The other base stations bs2 to bs7 shown in FIG. 1 have the same configuration. In FIG. 6, mobile device ms1 includes transmitting / receiving device 621, demodulation device 622, frame disassembly device 623, handoff control device 624, frame configuration device 625, carrier designation device 626, modulation device 627, A timing control device 628. In addition, the other mobile device ms shown in FIG.
2 to ms8 have the same configuration.

First, the operation of the base station bs1 that multiplexes the forward frames 51 for the mobile stations ms1 to ms8 and sends the multiplexed frames to the forward link fl will be described. In FIG. 6, the frame configuration device 611 of the base station bs1 includes:
Transmission data dfl1 to dfl8 to be transmitted are input. The transmission data dfl1 to dfl8 are input when all of the communication channels 1 to 8 are used. Also, assuming that transmission data dfl1 among these transmission data is transmitted to mobile station ms1,
It is further assumed that communication channel 1 has already been assigned to mobile station ms1. Transmission data dfl1 to dfl8
Are assigned communication channels 1 to 8 that do not overlap with each other, and are input to the frame configuration device 611. The frame configuration device 611 receives the input transmission data d
The serial-parallel conversion is performed on fl1 to dfl8. Here, the degree of parallelism corresponds to the number of carriers constituting one communication channel. The frame configuration device 611 performs, for example, error correction coding on the parallelized transmission data dfl1, then performs the preamble, the address information of the mobile device ms1 to which the transmission data is to be transmitted, and the slot processing device 618 described below. The input first control information and second control information for the mobile station ms1 are added to the transmission data dfl1 after the error correction coding. Thereby, the information corresponding to the fields 511 to 515 shown in FIG. 5 is set, and the parallelized forward frame 51 is configured. The frame configuration device 611 transmits the other transmission data dfl2 to df
The forward frame 51 is similarly configured for 18.

Here, the slot processing device 618 monitors the phase information of the time slot 43 for each communication channel on the reverse link rl, and based on the phase information, determines the reference timing (the immediately preceding forward time) at the base station bs1. The reception time of the time slot 43 with respect to the frame 51 transmission timing) is calculated. If the calculated reception time is equal to or longer than the guard interval 431, the slot processing device 618 generates first control information indicating the time lag and outputs the first control information to the frame configuration device 611. Further, the slot processing device 618 monitors the signal strength of each time slot 43, generates second control information indicating a deviation of the signal strength from a predetermined threshold regarding the signal strength, and generates a frame configuration. Device 6
11 is output.

The carrier designating device 612 includes a memory table as shown in FIG.
communication channels 1 to 1 assigned to fl1 to dfl8
A plurality of carriers f1 to f32 constituting the modulation device 8
13 is output. The modulation device 613 receives a plurality of carriers input from the carrier designation device 612 and inputs a plurality of carriers input from the frame configuration device 611 to include a guard interval 431 (see FIG. 4) for each predetermined unit symbol time. Modulation is performed in the frame 51. In this modulation, for example, carriers f1, f9, f17 and f25 constituting the communication channel 1 are modulated by a forward frame 51 to be transmitted to the mobile station ms1. The modulator 613 further orthogonally multiplexes the carriers f1 to f32 modulated in the respective forward frames 51 and outputs the carrier f1 to the transmitter / receiver 614.

Here, the time of the guard interval 431 corresponds to the movement of the base station bs (1 to 7) and the cell mc (1 to 7) formed by the base station bs (1 to 7) which is assumed to be located farthest from the base station bs. The transmission delay time is determined in consideration of the propagation delay time with the device ms. In the present embodiment, the time interval of the guard interval 431 is a fixed value in consideration of simplification of the description. Also, in the time interval of the guard interval 431, the FFT window for the discrete (or high-speed) Fourier transform by the mobile device ms is not applied, and the discrete (or high-speed) Fourier transform following the guard interval 431 is executed. Window is applied only to the time section 432 for this purpose.

The transmission / reception device 614 includes a synchronization control device 615
After amplifying the orthogonal frequency multiplexed signal input from the modulator 613 according to the timing control by the time division controller 616, the time slot 41 of the forward link
(See FIG. 4). Here, the synchronization control device 615
Controls the timing so that each of the symbol time slots 43 transmitted from the transmitting / receiving devices 614 of the base stations bs1 to bs8 installed in the present system is synchronized with the internal clock. The synchronization control device 615 performs timing control according to time information transmitted from, for example, a GPS (Global Positioning System). Further, the time division control device 616 controls the transmission timing to the forward link time slot 41 and the reception timing to the reverse link time slot.

This frequency multiplex signal is received by all the mobile stations ms in the cell mc. Hereinafter, the operation of the mobile device ms1 will be described from the viewpoint of clarifying the description. In FIG. 6, the transmitting / receiving device 621 of the mobile device ms1
Receives the frequency multiplexed signal input from the forward link fl in accordance with the timing control performed by the timing control device 628. At this time, the timing control device 628 adjusts the reception timing to the predetermined time section of the forward link time slot 41 so that the burst orthogonal frequency multiplexed signal can be received. Further, the timing control device 628
The time slot 43 of the symbol included in the frequency multiplexed signal is synchronized with the internal clock. In particular, with respect to the synchronization of the symbol time slots 43, the synchronization may deviate as time elapses. Therefore, the phase information of a predetermined number of received time slots 43 is referred to, and the synchronization is reliably performed. Controlled to be established. The phase information of the time slot 43 is input from the demodulation device 622.

The demodulation device 622 applies four carriers f1, f9, f constituting the communication channel 1 to the time slot 43 of the symbol whose synchronization has been established as described above.
17 and f25, a discrete Fourier transform process is performed by applying an FFT window for each time interval 432 excluding the guard interval 431, and the time slots 43 of the four carriers are collectively demodulated. Phase information, signal strength information, and the like regarding 43 are extracted. As described above, when the communication channel 1 has already been allocated, the carriers f1,
Since the discrete Fourier transform process only needs to be performed on f9, f17, and f25, the amount of calculation is reduced.

However, in order to execute soft handoff, it is necessary to collectively demodulate carriers of a predetermined number of communication channels to search for a base station to be subjected to handoff control, or to simultaneously execute a plurality of communication channels. When so-called multi-rate transmission is used, a relatively high-speed algorithm such as a fast Fourier transform is used in the demodulation device 622, and a time interval 432 excluding the guard interval 431 is used for all carriers.
Are demodulated collectively.

The demodulation result of the demodulation device 622 is output to the frame decomposing device 623, and the phase information extracted at the same time is also output to the timing control device 628.
The signal strength information is output to the handoff control device 624. Based on the phase information extracted by the demodulation device 622, the timing control device 628 described above controls the carriers f1, f9, and f received from the forward link 41.
The time slots 43 of the symbols 17 and f25 are synchronized with the internal clock. Thus, the mobile station ms1
Performs open loop control using the transmission / reception device 621, the demodulation device 622, and the timing control device 628 during reception processing from the forward link 41, and reliably establishes synchronization of the symbol time slot 43. Note that a description of the processing of the handoff control device 624 will be given later, and will not be repeated here.

The frame disassembly device 623 includes the demodulation device 62
After the forward frame 51 is reproduced and parallel-serial-converted based on the demodulation result input from 2, the forward frame 51 is decomposed to extract and receive the transmission data dfl1. Further, the first and second control information 513 and 514 extracted by this decomposition are output to the timing control device 628 and the transmission / reception device 621.

Thus, the transmission data dfl1 from the base station bs is transmitted to the mobile station ms1. In response to the transmission data dfl1, the mobile station ms1 transmits the base station bs1.
Is generated and input to the frame configuration device 625. The frame configuration device 625 uses the same communication channel 1 as in the case of the forward link 41. The frame configuration device 625 performs the serial / parallel conversion and the error correction coding on the transmission data d as in the case of the base station bs1.
After the execution of rl1, the above preamble and the address information of the base station bs1 to which the transmission data is to be transmitted are added to the transmission data drl1 after the error correction coding. Thereby, information corresponding to the fields 521 to 523 shown in FIG. 5 is set, and the parallelized reverse frame 5 is set.
2 are configured. The process of configuring the reverse frame is similarly executed in other mobile devices ms (2 to 8).

The carrier specifying device 626 includes a memory table as shown in FIG.
Output the four carriers that constitute the communication channel 1 used for communication. The modulator 627 performs the same processing as the modulator 613 included in the base station bs1, and outputs a modulated signal. The transmission / reception device 621 transmits the modulated signal input from the modulation device 627 to the communication channel 1 of the reverse link rl according to the timing control performed by the timing control device 628. At this time, the timing control unit 628 controls the transmission timing of the modulated signal to the reverse link 42 so as to correct the time lag indicated by the first control information received via the immediately preceding forward link 41. Since the first control information is created for each mobile station ms, the control amount of the time lag of the transmission timing differs for each mobile station ms. Further, the modulated signal is transmitted and received by the transmitting / receiving device 62 based on the difference in signal strength indicated by the second control signal.
The signal is amplified or attenuated at 1 and transmitted. The modulated signal transmitted to the communication channel 1 of the reverse link 42 in this way is superimposed on the signal transmitted from another mobile station ms, and reaches the base station bs1.

The transmission / reception device 614 of the base station bs1 receives the superimposed signal from the reverse link 42 according to the timing control of the time division control device 616 and amplifies it. In the modulated signal (carrier modulated by the reverse frame) included in the superimposed signal, symbol synchronization is not completely established for each communication channel. However, the mobile station ms having a time lag longer than the guard interval is the first mobile station.
Since the time lag is corrected based on the control information described above, all the modulation signals included in the above-described superimposed signal are synchronized with accuracy within the guard interval. The demodulation device 617 outputs the FF having a predetermined time section after the time of (2 × Tdb) + (time of hardware processing) has elapsed from the transmission of the immediately preceding forward frame 51.
A fast Fourier transform process is performed with a T window. At this time, the demodulation device 622 sets, for each carrier of all communication channels, the time slot 43 of the symbol.
Are demodulated collectively, and each time slot 4
3, phase information and signal strength information are extracted.

Here, the timing at which the fast Fourier transform processing is executed in the base station bs1 will be described.
In this system, the propagation delay time of the forward frame 51 and the like transmitted from the base station bs forming the cell mc differs depending on the position of the mobile station ms in the cell mc1. That is, as shown in FIG.
It is assumed that s1 and ms2 are located in the cell mc1, and the mobile station ms2 is the mobile station ms located farthest from the base station bs1 in the cell mc1.
It is assumed that the mobile station ms2 receives the symbol transmitted at the reference timing in the base station bs1 after the propagation delay time Tdb. This propagation delay time Tdb is equal to the cell mc1
Is the largest among the propagation delay times when all the mobile stations ms located within receive the symbols transmitted at the same timing. This symbol is the base station bs1 and the mobile station ms
In order to make one round trip between the two, a propagation delay time (2 × Tdb) is required as shown in FIG. In addition, since the hardware processing in the mobile station ms2 is added during this one round trip, the timing at which the fast Fourier transform processing is executed in the base station bs1 is (2 × Tdb) + ( Hardware processing time). Further, guard interval 431
Is determined such that intersymbol interference does not occur in the fast Fourier transform processing executed at such timing.

The demodulation device 617 applies the FFT window at the above-described timing and executes the fast Fourier transform processing. Even if the modulated signals included in the superimposed signal are not symbol-synchronized with each other, Symbol (part except guard interval 431)
Is guaranteed not to temporally overlap (inter-symbol interference) with all the symbols to be demodulated this time (excluding the guard interval 431). This allows
As shown in FIG. 8A, the modulated signal included in the superimposed signal has the orthogonality of the orthogonal frequency multiplexing method maintained while its spectrum overlaps each other on the frequency axis.
Accurate demodulation can be performed. However, if the demodulation device 61
7, when the FFT window is applied to all the unit symbols, the immediately preceding symbol may interfere with the symbol to be demodulated this time. In this case, FIG.
As shown in (b), the orthogonality of the spectrum is lost and accurate demodulation is not performed.

As described above, in the present system, the orthogonal frequency division multiplexing method is adopted, and the mobile station ms can execute the discrete Fourier transform or the like to accurately transmit the forward frame 51 addressed to itself transmitted from the base station bs. Can receive. Further, the cell mc defines the limit of the propagation distance of the signal transmitted from the base station bs forming the cell mc. Also,
In the present system, the base station bs transmits the second control information 514
Can be used to control the transmission power of the mobile station ms. Therefore, by appropriately controlling the transmission power, even if the cells mc adjacent to each other use the same carrier,
The communication of the mobile station ms located in each cell mc does not hinder. For example, the mobile station ms located in the cell mc1 shown in FIG. 1 and the mobile station ms located in the cell mc5 can communicate using the same communication channel. Therefore, by executing the above-described appropriate transmission power, the present system can use the frequency more effectively than the conventional system in which cells adjacent to each other must use different carriers.

Next, the site diversity in a multi-cell like the present system will be described. In this case, the timing at which the fast Fourier transform processing is executed in the base station bs1 is different from the above-described case, and is as follows.

Here, FIG. 9 (a) shows a configuration of a multi-cell adopted in the present system as in FIG. 1, and a reference cell mc1 formed by the base station bs1 and a cell adjacent to the cell mc1. Six adjacent cells mc2 to mc7 are shown. Base stations bs2 to bs7 are installed in adjacent cells mc2 to mc7. Forward frame 51 transmitted from these seven base stations bs1 to bs7
Are mutually established by the time information by GPS as described above. FIG. 9B shows reception timings of signals from the base stations bs1 and bs2 in the mobile station ms1 when performing site diversity. In FIG. 9B, the mobile station bs1 has a signal from the base station bs1 installed in the reference cell mc1 located up to that point blocked by shadowing, and the base station bs5 installed in the adjacent cell mc5. To perform site diversity.

As described above, in order to execute the site diversity, not only the propagation delay time Ta of the signal from the base station bs1 as a reference but also the propagation delay time Tb of the signal from the adjacent base station bs5 is taken into consideration. I have to enter. Therefore, in this case, the base stations bs1 and bs5, etc. must execute the fast Fourier transform processing immediately after the time of (2 × Tb) + (hardware processing time) elapses after the immediately preceding signal transmission. Further, the guard interval 431 (see FIG. 4) is determined so that intersymbol interference does not occur in the fast Fourier transform processing executed at such timing.

Hereinafter, a communication procedure for performing site diversity in the present system will be described with reference to FIG. 10 which is a sequence chart showing the procedure. All the base stations bs1 to bs7 basically communicate with the mobile station ms1 based on the arrangement of communication channels as shown in FIG. However, the base stations bs1 to bs7 periodically transmit a reference signal (referred to as a time section t1), which is a signal for each mobile station ms to perform site diversity, using different communication channels. Now, FIG. 9 (a)
As shown in (1), the communication channel 1 is allocated to the base station bs1. Hereinafter, it is similarly assumed that communication channels 2 to 7 are allocated to base stations bs2 to bs7.
Note that other communication channels than these are not used in a time section for transmitting the reference signal. The assignment of the communication channel for such a reference signal is also stored in advance in a memory (not shown) inside the mobile station ms accommodated in the present system.

The mobile station ms1 synchronizes the plurality of received reference signals with the internal clock, and then receives the reference signals in the same procedure as when the forward frame 51 is received. At this time, the signal strength information of each reference signal extracted by the demodulation device 622 is:
It is input to the handoff control device 624. The handoff control device 624 selects a reference signal having the strongest signal strength from the input signal strength information of each reference signal, determines whether to perform soft handoff based on this selection, and performs soft handoff. If it is determined that it should be, the base station bs as the target is specified and notified to the frame configuration device 625. Frame construction device 6
25 sets the address information of the reverse frame 52 based on this notification as described above.

Next, in the time section t2, each of the base stations bs1 to bs7 performs the normal communication by transmitting the forward frame 51. At this time, the mobile station ms that performs handoff control collectively demodulates the signal from the forward link 41 while executing the above-described fast Fourier transform processing and the synchronization establishment processing of the symbol time slot 43. At this time, the handoff control device 624 searches for a free communication channel where communication is not currently being performed by comparing a predetermined threshold value with the received signal strength of each communication channel, and searches for one free communication channel. Select a communication channel. Next, in the time section t3, the mobile station ms creates transmission data drll for requesting allocation of the selected free communication channel, and installs the transmission data drll in the cell ms currently located using the communication channel. The reverse frame 52 is transmitted to the base station bs. In response to the reverse frame, the base station bs, which is the target of soft handoff, executes the above-described fast Fourier transform process and, upon receiving the above-mentioned request for allocating a free communication channel, installs itself. It is determined whether the communication channel allocated to the mobile station ms already located in the cell mc and the requested free communication channel conflict with each other. At this time, at the same time, the slot processing device 618 detects a time lag and a signal strength of a time slot of a reverse frame transmitted by the mobile station ms that performs soft handoff control.

Next, in the time section t4, the base station bs to be handed off, when this free communication channel can be allocated to the mobile station ms,
Transmission data dfl for allocating the communication channel
If the slot processing device 618 determines that it is necessary to correct the time lag or the power, the forward frame 5 including the first and second control information described above is generated.
1 is generated and transmitted.

As described above, in the present system, the orthogonal frequency division multiplexing system is adopted, and the mobile station ms can execute the fast Fourier transform process and collectively demodulate the signal received from the base station bs. It is not necessary to change the frequency of the PLL from time to time as in the case of handoff in. As a result, the present system can perform base station switching (soft handoff) while maintaining communication quality.

In the above-described embodiment, the number of carriers is set to 32 and the number of communication channels is set to 8 from the viewpoint of concrete description. However, the present invention is not limited to this number. The number of carriers may be n (n is a natural number of 2 or more), and the number of carriers constituting one communication channel may be m (m is a natural number satisfying 2 ≦ m ≦ n).

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a cell employed in a wireless communication system according to an embodiment of the present invention.

FIG. 2 is a diagram showing the above-mentioned communication channel employed in the present system.

FIG. 3 is a diagram showing a forward link and a reverse link employed in the present system.

FIG. 4 is a diagram showing time division duplex employed in the present system.

FIG. 5 is a diagram showing formats of a forward frame and a reverse frame employed in the present system.

FIG. 6 is a diagram showing a detailed block configuration of a base station bs1 and a mobile device ms1 accommodated in the present system.

FIG. 7 is a diagram for describing timing at which fast Fourier transform processing is executed in the base station bs1.

FIG. 8 is a diagram for explaining orthogonality of signals communicated in the present system.

FIG. 9 is a diagram for explaining the timing at which the base station bs1 executes the fast Fourier transform processing in the multi-cell configuration adopted in the present system.

FIG. 10 is a diagram showing a sequence when executing site diversity in the present system.

[Explanation of symbols]

 bs base station 611 frame configuration device 612 carrier designation device 613 modulation device 614 transmission / reception device 615 synchronization control device 616 time division control device 617 demodulation device 618 slot control device 618 frame decomposition device ms moving Machine 621 transmission / reception device 622 demodulation device 623 frame disassembly device 624 handoff control device 625 frame configuration device 626 carrier designation device 627 modulation device 628 timing control device

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yuji Igata 1006 Kazuma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (4)

[Claims] A service area is covered by laying a plurality of cells formed by a base station, and communication between one mobile station located in a certain cell and a base station forming the cell is performed by: A wireless communication system that is performed using one communication channel selected from all communication channels available in the service area, and for all communication channels available in the service area, In the predetermined frequency band, n (n is a natural number of 2 or more) carriers having different frequencies are assigned in advance, and the base station and the mobile station select a frequency axis from the n carriers. M (m is 2 ≦ m ≦) discretely arranged above and not overlapping with other communication channels
A wireless communication system, wherein a carrier of (a natural number satisfying n) is selected, and communication is performed using a communication channel including the selected m carriers. 2. The wireless communication system according to claim 1, wherein the base station and the mobile device perform communication using an orthogonal frequency division multiplexing system. 3. The base station notifies a timing of signal transmission for each mobile station located in a cell formed by the base station, and each mobile station is notified by a base station forming a cell in which the base station is located. 3. A signal according to claim 2, wherein a signal is transmitted to the base station in accordance with the signal transmission timing, whereby a difference in arrival timing of a signal transmitted from each mobile station to the base station is corrected. Wireless communication system. 4. Each base station in the service area includes:
Different communication channels are respectively allocated in advance as communication channels to be used when transmitting the reference signal, and each base station in the service area transmits to the mobile station in a cell formed by itself in advance. The mobile station periodically transmits a reference signal using the allocated communication channel, and based on the reference signal transmitted from the base station, specifies that the base station should perform communication with itself. The wireless communication system according to claim 2, wherein the wireless communication system is a wireless communication system.