Mobile communications system and mobile communications method

ES 2 239 396 T3

DESCRIPTION

Mobile telecommunications system and procedure.

Technical field

The present invention relates to a mobile station apparatus and a base station apparatus for carrying out data transmission of a CDMA (Code Division Multiple Access) system and a communication method using these apparatuses. Background of the invention

It is being planned to use a CDMA system as a radio access system in a third generation mobile communication system. In general, in the CDMA system, a unique spreading code of each radio cell (radio base station) is used for a radio signal (direct link), which each radio base station transmits. Furthermore, a spreading code peculiar to each mobile station is used with respect to a radio signal (reverse link), which each mobile station transmits.

In the CDMA system an advantage is exploited in that the same frequency can be used between adjacent radio cells (hereinafter referred to as cell as required) and a soft handover system is adopted as a handover system, which is used when the mobile station moves between cells. The soft handoff system combines radio signals from the source mobile cell base station and the destination mobile cell base station.

To execute such handover, the mobile station has to perform a peripheral cell search to search for the base station of the destination mobile cell. Each base station always transmits one radio channel, which is called the pole channel. The pole channel is transmitted from each cell (base station) using an inherent spreading code.

Therefore, each station notifies the mobile station of the spreading code, which is used in the peripheral cells, of the auto-station as retransmitted information. On the other hand, the mobile station periodically detects a link quality (receive SIR (signal interference ratio) of the radio channel (peripheral cell pole channel) using the reported spreading code. Or the mobile station periodically detects receive Eb / I0 (ratio of the energy of a received signal per bit to interference, a heat control power spectrum density ratio). Next, the mobile station notifies the network side of the detection result. By performing the so-called peripheral cell search, the network can determine to which cell the mobile station is moving.

Fig. 1 is a view showing a general structure of a conventional mobile communication system, in particular the structure relating to handover. The mobile communication system mainly includes a mobile station, radio base stations and a control station.

A mobile station M mainly includes a radio reception and transmission section 11, a message decoder 12, a spreading code storage section 13, a reception quality detector section 14, a peripheral cell control section 15, and a message generator 16. The radio reception and transmission section 11 receives and transmits a radio signal between the mobile station M and the radio base station. The message decoder 12 decodes control information contained in the signal received by the radio reception and transmission section 11. The spreading code storage section 13 stores spreading codes of an object to be subjected to the designated peripheral cell search. from the network side, that is, the spreading codes used in the peripheral cells. The reception quality detecting section 14 detects the link quality of the signal received by the radio reception and transmission section 11. The peripheral cell search control section 15 sets the spreading codes stored in the data storage section. spreading code 13 to be used in the peripheral cells with respect to the reception quality detector section 14, sequentially. Then, the peripheral cell search control section 15 manages the reception quality detection cycle, and the number of detection times, and provides averaging processing to the detection result. Message generator 16 generates a message, including control information, for the network.

The base radio stations B mainly include a plurality of radio reception and transmission sections 17, a cable reception and transmission section 18, and a radio control section 19. The radio reception and transmission sections 17 receive and transmit the Radio signals between the mobile station and the radio base station. The cable reception and transmission section 18 receives and transmits control signals, that is, a mobile station control signal and a base station radio control signal between the control station and the radio base stations B via radio. The radio control section 19 controls the radio reception and transmission sections 17 according to a designation of the control station. A plurality of radio base stations Ba, Bb, and Bc thus structured are provided.

Control section C mainly includes station place storage section

20, a peripheral cell information generator

21, a cable reception and transmission section 22, a message decoder 23, a mobile address determination section 24, a handover control section 25, and a message generator 26. The location storage section Station 20 stores the inherent spreading code, which is used by the radio base station under the control of the auto-station. The peripheral cell information generator 21 generates peripheral cell information for each radio cell based on the station location information stored in the station location storage section 20. The cable reception and transmission section 22 receives and transmits control signals, which are received and transmitted from / to radio base stations Ba, Bb, and Bc. The message decoder 23 decodes control information from the mobile station. The mobile address determining section 24 determines a destination mobile cell of the mobile station based on a peripheral cell search result report of the mobile station and information from the station location storage section 20. The control section transfer 25 designates the execution of the transfer to mobile station M and radio stations2

ES 2 239 396 T3 nes base B when it is determined that the handover is necessary based on the information in the mobile address determination section 24. The message generator 26 generates a message including control information about the mobile station M and base radio stations B.

Next, a handover operation of the conventional mobile communication system structured as before will be explained with reference to Fig. 2.

The spreading code that each radio base station uses as a reverse link is established in advance, and the information about the spreading code parameter is managed by the station location storage section of the control station.

The radio control section 19 of the radio base station Ba uses a predetermined spreading code Ca as a forward link, and the mobile station M uses a spreading code Cm peculiar to the mobile station as a reverse link.

The mobile station M is in a cell area a. The mobile station M receives from the radio base station Ba a peripheral cell spreading code indication offering a service from cell a, so that the spreading codes used in the peripheral cells are stored in the cell code storage section. widening 13 (ST1).

The peripheral cell search control section 15 sets a cell search execution cycle At on a timer T (ST2). Then, when the timer counts up (ST3), the spreading codes, which are used by the peripheral cells stored in the spreading code storage section 13, are set sequentially in the reception quality detector section 14. The reception quality detecting section 14 detects the reception quality of the peripheral cells of the radio base station Ba (ST4).

Then the peripheral cell search result refers to the network. The case where the peripheral cell search result referred to the network each time each peripheral cell search was executed was explained above. However, the result does not necessarily refer to the network each time.

The mobile address determining section 24 of the control station C first determines the mobile address based on the peripheral cell reception quality report of the mobile station M (ST5) to determine whether the cell has to be moved or not. If it is determined that the cell does not have to move (ST6), no control information is transmitted to the mobile station. For this reason, the reception quality of the peripheral cell is detected again (ST4).

If it is determined that the cell has to be moved as a result of the determination of the mobile direction (ST5), that is, the mobile station M is moving to a cell b from cell a, the following operation is executed. More specifically, the initiation of forward link transmission to mobile station M and of reverse link reception from mobile station M are designated for radio base station Bb offering a service from cell b. This operation is called soft transfer designation.

After that, mobile station M moves to cell b by soft handoff state (ST8). The control station then notifies the mobile station of the spreading code used in the peripheral cells of cell b.

Thus, in the case where the same frequency is used between adjacent cells, the handover is executed by performing the peripheral cell search in the mobile station and referring the result to the network.

The CDMA system can cover the entire service area using only a single frequency since the same frequency can be used between adjacent cells. However, in the CDMA system, there is a higher limitation since the number of users, which can be contained by using one frequency, is determined by the amount of interference.

On the other hand, to increase the number of users per cell, a plurality of frequencies should be used. In the service area to which the mobile communication system is applied, there are various areas including an extremely high traffic area, such as an urban area, to a low traffic area, such as a suburban area. The appropriate frequency is preferably used for an amount of traffic, which is required in each area. Therefore, in the service area, the transfer must be carried out after being able to freely establish the frequency to be used in each area.

However, the mobile communication system is predicated on the point where the same frequency is used in the entire service area. If the mobile communication system is used in the service area having a different frequency, a problem occurs that the handover cannot be performed successfully between the cells having a different frequency.

Documents EP 0 566 551 A2 describe that the mobile unit assists in making handover decisions by monitoring the signal strength of control channels transmitted by base stations in contiguous cells. In this document, three types of transfer are introduced. A first way, called internal handover, occurs when the network decides to keep the mobile station connected to its current base station, but to switch transmissions from the mobile station to another frequency. A second form of handover is handover from one mobile station to another base station without frequency change. A third type of handover that can be made is a frequency change when changing base stations.

WO 98/54916 discloses that a mobile station in a CDMA communication system is commanded to transmit a temporary message that is used to aid hard handover between frequencies.

Document EP 0 933 955 A1 provides a CPU in each base station that monitors the channel occupancy of each of a plurality of radio frequencies assigned to the base station. When the difference between the channel occupations of a plurality of radio frequencies assigned to a single base station turns out to be a predetermined state, the CPU switches the radio frequency as a candidate for use by a predetermined base station of the mobile stations that are present in the cell formed by the base station and put in the standby state at a radio frequency whose channel occupation is in the predetermined state.

ES 2 239 396 T3

WO 97/44983 provides forward link spatial diversity by transmitting the forward link signal twice from two different antennas spaced a sufficient distance to provide fading independence from the remote unit.

Description of the invention

The present invention has been made with the above-mentioned problem in mind. An object of the present invention is to provide a mobile communication system capable of successfully performing handover even in service areas each having a different frequency, and to provide a mobile communication method.

The above object can be achieved by changing the usage frequency in advance when determining a mobile address of a mobile station M on a network side (control station) and further determining whether or not the mobile station M leaves the line. same frequency area, and when mobile station M goes out of the same frequency area.

Brief description of the drawings

Figure 1 is a block diagram representing a general structure of a conventional mobile communication system.

Figure 2 is a sequential view of the conventional mobile communication system.

Fig. 3 is a block diagram showing a general structure of a mobile communication system according to an embodiment of the present invention.

Figure 4 is a sequential view of the mobile communication system according to an embodiment of the present invention.

And Fig. 5 is a view explaining a mobile communication method of the present invention. Best Mode of Carrying Out the Invention

In the mobile communication system according to the embodiment of the present invention, the structure is used to change a first frequency to a second frequency in a mobile station apparatus to execute data reception and transmission of a CDMA system when a radio cell search from a first radio cell communicating at the first frequency to a second radio cell communicating at the second frequency different from said first frequency.

In the mobile communication system according to the embodiment of the present invention, the structure is used to change a first frequency to a second frequency in a mobile station apparatus to perform data reception and transmission of a CDMA system before carrying out a movement of the cell from a first radio cell communicating at the first frequency to a second radio cell communicating at the second frequency different from the first frequency.

In the mobile communication method according to the embodiment of the present invention, the structure is used to change a first frequency to a second frequency in a mobile station apparatus to execute data reception and transmission of a CDMA system before carrying out a movement of the cell from a first radio cell communicating at the first frequency to a second radio cell communicating at the second frequency different from the first frequency.

According to the above structure, even in a case where the frequency of use differs for each region of the service area, a handover can be executed between cells using a different frequency.

Furthermore, in the embodiment of the present invention, the structure is used in which the frequency change is carried out when a radio cell of a destination mobile is the first radio cell that contacts the second radio cell. Furthermore, in the embodiment of the present invention, the structure in which it is determined whether or not the mobile station apparatus leaves the frequency area when a radio cell of a destination mobile is a first radio cell is used to establish the first frequency that contacts a second radio cell to establish the second frequency. According to the previous structure, the frequency change is carried out when the cell of the destination mobile is a border cell between the first and second cell radio. As a result, the first frequency can be safely changed in advance of the second frequency set by the second radio cell, and handover between cells having a different frequency can be stably performed.

In the mobile communication method according to the embodiment of the present invention, The structure is used to change a first frequency to a second frequency different from the first frequency in a mobile station apparatus to execute data reception and transmission of a CDMA system when it is determined in a frequency area where communications are performed at the first frequency if the mobile station apparatus goes out of said frequency area and when the mobile station apparatus goes out of the frequency area or not. As a result, handover between cells having a different frequency can be stably performed.

Note that the present invention includes a communication terminal apparatus used in the mobile communication system such as a mobile station apparatus and a base station apparatus.

An embodiment of the present invention will now be described with reference to the accompanying drawings.

According to the present invention, even in a case where the frequency of use differs in each region of the service area, it is determined whether a mobile station moves in an area where the same frequency can be used or in an area where it cannot be used. it can use the same frequency on one network side (control station), and the frequency is switched by the mobile station in advance. This can provide a mobile communication system, which can perform a handoff between cells that have a different frequency of use.

Fig. 3 is a block diagram showing a general structure of the mobile communication system according to an embodiment of the present invention. The mobile communication system includes a mobile station M, radio base stations Ba, Bb, Bc, and a control station C.

In the mobile station M, a radio reception and transmission section 101 receives and transmits radio signals from / to the base radio stations. A message decoder 102 decodes control information included in the signals received by the radio reception and transmission section 101. A spreading code storage section 103 stores spreading codes of an object to be searched for the peripheral cell of4.

ES 2 239 396 T3 signed from the network side, that is, the spreading codes used in the peripheral cells.

A frequency change section 104 changes a frequency to be put into the radio reception and transmission section 101 by a designation of the control station C. A reception quality detector section 105 detects a link quality (reception level) of the signal received by the radio reception and transmission section 101. A peripheral cell search control section 106 sets the spreading codes stored in the spreading code storage section 103 to be used in the peripheral cells with respect to the reception quality detector section 105, sequentially. Then, the peripheral cell search control section 106 manages the reception quality detection cycle, and the number of detection times, and provides averaging processing to the detection result. A message generator 107 generates a message including control information for the network.

In each of the radio base stations Ba, Bb, and Bc, radio reception and transmission sections 108 receive and transmit radio signals between the radio base stations and the mobile station M. A cable reception and transmission section 109 receives and transmits control signals, that is, a mobile station control signal and a base station radio control signal between the control station C and the radio base stations by radio. A radio control section 110 controls the radio reception and transmission sections 108 according to a designation of the control station C. Note that the radio reception and transmission sections 108 of the radio base stations may set a different frequency, respectively. In this embodiment, the frequencies f1 and f2 are used in the radio base stations Ba and Bb, and only the frequency f1 is used in the radio base station Bc.

In the control station C, a station location storage section 111 stores an inherent spreading code, which is used by the radio base station under the control of the auto-station. A peripheral cell information generator 112 generates peripheral cell information for each cell based on the station location information stored in the station location storage section.

111. A cable reception and transmission section 113 receives and transmits control signals, which are received and transmitted from / to radio base stations.

A message decoder 114 decodes control information of the mobile station M. A mobile address determining section 115 determines a destination mobile cell of the mobile station M based on a peripheral cell search result report of the mobile station. M and station place storage section information 111. A determination section 116 for an outer zone of the same frequency determines whether or not the mobile station M leaves the same frequency area based on mobile destination cell information from the mobile address determining section 115 and information of the station place storage section 111.

When it is determined that a handover is needed based on information from the mobile address determining section 115, a handover control section 117 designates the execution of the handover to the mobile station M and the radio base stations. When it is determined that a frequency change is needed based on information from the determination section 116 for an outer zone of the same frequency (a case where the mobile station M goes out of the same frequency area), the section transfer control 117 designates the next execution. More specifically, the handover control section 117 designates the execution of the frequency change (hard handover in the cell) to the mobile station M and the radio base stations. A message generator 118 generates a message including control information about the mobile station M and the radio base stations.

Next, a case where the handover is actually executed in the mobile communication system of the above structure will be explained. Fig. 4 is a sequential view showing an operation of the mobile communication system according to an embodiment of the present invention. Fig. 5 is a view showing the relationship between a mobile path of the mobile station M and the cell (radio base station) according to an embodiment of the present invention. Next, a case will be explained in which a mobile station M2 uses frequency f2 (first frequency) in a high traffic area shown in Figure 5, and changes the frequency to frequency f1 (second frequency) when passing to the zone of low traffic during communications.

The spreading code that each radio base station uses as a forward link is established in advance. The parameter information is managed by the station location storage section 111 of the control station. Then, the peripheral cell information generator 112 generates peripheral cell information for each cell based on the station location information stored in the station location information storage section 111.

The radio control section 110 of the radio base station Ba uses a predetermined spreading code Ca as a direct code. The mobile station M uses a spreading code Cm peculiar to the mobile station as a reverse link.

Between the mobile station M and the control station C, the message, such as control information generated by the message generator 107 of the mobile section M, is sent to the radio reception and transmission section 108 of the base stations B from the radio reception and transmission section 101 of the mobile station M, and is further sent to the cable reception and transmission section 113 of the control station C by the cable reception and transmission section 109. The message is then decoded by message decoder 114 of control station C.

On the other hand, the message, such as control information generated by the message generator 118 of the mobile control station C, is sent to the cable reception and transmission section 109 of the base stations B of the reception section. and cable transmission 113 from the control station C, and is further sent to the radio reception and transmission section 101 of the mobile station M by the radio reception and transmission section 108. The message is then decoded by the message decoder 102 of the mobile station M, and sent to the code storage section of ensan5.

ES 2 239 396 T3 chamiento 103 and the frequency change section 104.

The mobile station M is in the area of ​​cell a, which is a first radio cell in which two frequencies f1 and f2, including the first frequency f2, are set by the radio reception and transmission section 108. The mobile station M receives a peripheral cell spreading code indication from radio base station Ba offering a service from cell a. As a result, the spreading codes used in the peripheral cells are stored in the spreading code storage section 103 (ST11).

The peripheral cell search control section 106 sets a cell search execution cycle At on a timer T (ST12). Then, when the timer counts up (ST13), the spreading codes, which are used by the peripheral cells stored in the spreading code storage section 103, are sequentially set in the reception quality detector section 105. The reception quality detecting section 105 detects the reception quality such as a reception level of the peripheral cells of the radio base station Ba (ST14).

Next, the peripheral cell search result is referred to the network. The case explained above in which the peripheral cell search result referred to the network each time each peripheral cell search was executed. However, the result does not necessarily refer to the network each time.

The mobile address determining section 115 determines the mobile address of the mobile station M based on the peripheral cell search result report of the mobile station M (ST15). As an example of the determination methods, the mobile address determining section 115 selects the highest reception quality from the reception quality levels L1, L2, ..., Ln sent from the respective cells Z1, Z2, ... Zn included in the peripheral cell reception quality report of the mobile station M, and determines the highest reception quality selected as the mobile address. In other words, if the reception quality level Lk of the cell Zk is the highest, it is determined that the destination mobile cell is Zk.

Furthermore, the mobile direction determining section 115 determines whether or not the movement of the cell is necessary. As an example of the determination methods, the mobile station M compares a level difference between the reception quality levels L0 and Lk, which have been sent from cell Z0 during communications, with a threshold value ALT for the determination of the cell movement. If the result of the comparison is dL0Lkz »LT, it is determined that cell movement is necessary. If the result of the comparison is DL0-LkD <LT, it is determined that cell movement is not necessary.

If it is determined that the cell movement is not necessary (ST16), the determining section 116 for an outer zone of the same frequency determines whether the destination mobile cell Zk, which has been determined by the mobile direction determining section 115, is a limit of the area where the frequency f2 is used. This determination is executed based on information when establishing the frequency used in each cell, thereby determining whether or not the cell leaves the same frequency area, which is the area where the frequency f2 can be used (ST17, ST18) . Furthermore, it is determined whether or not the frequency change is needed in the control station C based on the result of the above determination.

The determination of whether or not the cell leaves the same frequency area is carried out when the radio cell search is executed in a cell c, which is the second radio cell in which only the frequency f1 is set, from cell a, which is the first radio cell, or cell b. Furthermore, the above determination can be made before the movement of the cell from the first cell to or cell b to the second radio cell c.

Furthermore, the above determination can be made based on the designation of the mobile address determination section 115 when the radio cell of the destination mobile is the first radio cell that contacts the second radio cell. In this case, since the frequency f2 can be safely changed to the frequency f1 set by the second radio cell in advance, the handover between cells having a different frequency can be stably executed. In other words, peripheral cell reception quality refers to the process where mobile station M moves from cell a to cell b in Figure 5. As a result, the network can recognize that mobile station M is moving to cell b, which is the area boundary cell (in the same frequency area) using f2.

Next, if it is determined that the frequency change is needed, the control station C designates the reception and transmission using the frequency f1 for the radio base station Ba. Then, the control station C designates the change of frequency to the mobile station M (cell a of figure 5). The mobile station M changes the frequency based on the designation (ST19).

Since the frequency is f1 at the time mobile station M arrives at cell b of FIG. 5, mobile station M executes the peripheral cell search using frequency f1. This can detect a mobile designation cell c. As a result, the network (control station C) can designate the soft handoff from cell b to cell c based on the peripheral cell reception quality report from mobile station M by handoff control section 117. Therefore, the above designation results in the soft handoff state in the mobile station M (ST20).

Then, the mobile address determining section 115 of the control station C determines whether or not the cell movement is necessary based on the peripheral cell reception quality report from the mobile station M. Cell movement is necessary, that is, mobile station M is moving to cell c from cell b, control station C designates what follows. More specifically, the control station C designates the beginning of the forward link transmission to the mobile station M and the beginning of the reverse link reception of the mobile station M with respect to the radio base station Bc offering a cell service c. Furthermore, the control station C designates the beginning of the reception of the forward link from the radio base station Bb with respect to the mobile station M. Afterwards, the control station C notifies the mobile station M

ES 2 239 396 T3 of the spreading code used in the peripheral cells of cell c after mobile station M moves to cell c.

Thus, before the mobile station M reaches the limit of the area (in the same frequency area) where the same frequency can be used, the network detects that the mobile station is moving to the outer zone of the same frequency. Then, the control station C designates the frequency change to the mobile station M in advance. As a result, the handover can be successfully executed even between the cells using a different frequency in a state in which the reception frequency in the peripheral cell search, which the mobile station executes for handover, is limited to one.

Thus, according to the present invention, it is determined on the network side whether the mobile station is moving in the area where the same frequency can be used or the area where the same frequency cannot be used. Then, the frequency of use is changed in advance at the mobile station. As a result, even in a case where the frequency used differs in each region of the service area, handover can be successfully performed between cells using a different frequency.

Industrial applicability

The present invention can be suitably used in a digital radio communication system using CDMA. Therefore, even in a case where the frequency used differs in each region of the service area, a handover can be successfully performed.