JP2002010314A - Mobile communication system and hand-over methode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide method to carry out hand-over accurately and smoothly between different frequency zones regarding to the mobile communications and hand-over method in CDMA communications system. SOLUTION: Including plural base station 1-1, 1-2, a control station 3 and a exchange station 4, etc., and mobile stations 2-1, 2-2 which communicate with the station 1-1, 1-2 by the CDMA system, the stations 2-1, 2-2 include a measuring part 24 for testing a communication quality required by the station 1-1, 1-2. The station 1-1, 1-2 include a receiving level of the mobile station in the self-radio zone, a distance from the base station and an administration table for the mobile station depending on the information of present location, require for measurement of communication quality for the other mobile station moving into a radio zone, and process hand-over depending on the information on the communication quality as a result of measurement and the on/off information status of the blank channel.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001] The present invention includes a control station, a base station, and a mobile station, and performs CDMA (code division) between the base station and the mobile station.
The present invention relates to a mobile communication system for performing communication according to the n Multiple Access method and a handover method for smoothly switching connection of a base station when the mobile station moves between base station zones in different frequency bands.

[0002]

2. Description of the Related Art FIG. 5 is an explanatory view of a mobile communication system, in which 51-1 and 51-2 are base stations, 52 is a mobile station, and 53 is a mobile station.
Indicates a control station, 54 indicates a mobile communication switching station, 55 indicates a fixed network switching station, and 56-1 and 56-2 indicate wireless zones. The plurality of base stations 51-1 and 51-2 are distributed and connected to the control station 53. A single or a plurality of control stations 53 are connected to the mobile communication exchange 54, and a fixed network exchange 55 to which a fixed telephone or the like is connected is connected to the mobile communication exchange 54.

While the mobile station 52 in the wireless zone 56-1 of the base station 51-1 is communicating with a fixed telephone or another mobile station via the base station 51-1, the adjacent base station 51-2
Is moved in the direction of the arrow to the wireless zone 56-2, a handover process for switching the channel with the base station 51-1 to the channel with the base station 51-2 is performed. For this handover process, various means such as a hard handover that causes an instantaneous interruption at the time of switching and a soft handover that switches so as not to cause an instantaneous interruption have been proposed.

[0004] For example, as the mobile station 52 moves, the reception level between the mobile station 52 and the base station 51-1 decreases,
Based on the information that the reception level has risen with the base station 51-2, the control station 53 determines that the base station whose reception level has risen is the destination, and determines the free channel of the destination base station 51-2. Is selected, a handover is requested to the mobile communication switching center 54, and the base station 51-1 instructs the mobile station 52 to perform a handover. Then, the mobile communication switching center 54
If the line connection between the base station 51-2 and the base station 51-2 is good,
Switching from the wireless channel between the base station 51-1 and the mobile station 52 to the wireless channel between the base station 51-2,
There is known a soft handover in which communication with the mobile station 52 is continued on the path of the mobile communication switching center 54, the control station 53, and the base station 51-2.

[0005] In a mobile communication system using the CDMA system, when each base station uses the same frequency,
The above-mentioned handover can be realized by switching the spreading code of the wireless channel. in this case,
Although the time required for the initial synchronization establishment accompanying the switching of the spreading code is required, synchronization can be established in a short time. Also known is a diversity handover system that enables soft handover by enabling communication with a plurality of base stations.

[0006]

In a mobile communication system using the CDMA system, when each base station uses the same frequency, it is possible to realize handover by switching spreading codes as described above. it can. However, when the radio frequencies of the base station at the source and the destination are different, for example, the base station 51-1 has the radio frequency f1, the base station 51-2 has the radio frequency f2, and the FDD (Frequency).
When the mobile station 52 is communicating with the base station 51-1 using the spreading code c1, the mobile station 52 switches to another radio frequency, for example, at a specific position in the compression mode and transmits broadcast information or the like by the Division Duplex method. Receiving, thereby, when the reception level from the base station 51-2 in the adjacent wireless zone becomes higher than the reception level from the base station 51-1,
It is determined that the mobile station 52 has moved from the wireless zone 56-1 to the adjacent wireless zone 56-2, and the execution of the handover is started.

[0007] In this case, after confirming that there is an empty channel in the wireless zone 56-2 of the base station 51-2, the mobile station 52 controls the synthesizer to change the radio frequency to f.
After switching from 1 to f2 and confirming the establishment of the initial synchronization, the spreading code is switched from c1 to c2, and a continuity test between the base station 51-2, the control station 53, and the mobile switching center 54 is performed. The handover is completed. Therefore, communication is interrupted during this time.

[0008] In order to improve such a problem, it has been proposed to use two systems of reception processing functions. For example, by providing two systems, a working-side despreading unit that receives the radio frequency f1 and the spreading code c1 and a protection-side despreading unit that receives the radio frequency f2 and the spreading code c2, the radio frequency switching is performed. And the spread code switching are performed in parallel to reduce the instantaneous interruption time of the handover in different frequency bands, or as disclosed in Japanese Patent Application Laid-Open No. 10-12312, the instantaneous Although a method for reducing the disconnection time has been proposed, it requires a relatively complicated procedure.

According to such handover means,
Even if the adjacent wireless zones in the moving process of the mobile station are partially overlapped with each other, it is possible to set the spare side reception processing function in advance to the radio frequency of the destination wireless zone and receive the desired data. Communication quality can be maintained.
However, the procedure of the frequency switching process is complicated and 2
There is a problem that the circuit size increases and the cost increases due to an increase in the circuit scale due to the provision of the system reception processing function.
An object of the present invention is to enable an optimal handover by adding a few functions.

[0010]

The mobile communication system according to the present invention will be described with reference to FIG. 1. Referring to FIG. 1, a plurality of distributed base stations 1-1 and 1-2 and base stations 1-1 and 1 are provided. -2 is connected between the control station 3 to which -2 is connected and the base stations 1-1 and 1-2.
A mobile communication system including mobile stations 2-1 and 2-2 performing communication according to the MA method, wherein mobile stations 2-1 and 2-2 are provided.
Has means for measuring the communication quality with the base station, the base stations 1-1 and 1-2 manage the distance between the serving mobile station or the position of the mobile station, Means for sending a communication quality measurement request to another mobile station in the vicinity of the destination of the mobile station with reference to the management means. Means for performing connection switching control of the mobile station to the destination base station based on the presence or absence of an idle channel of the base station and the measurement result of the communication quality of another mobile station near the destination of the mobile station. Things. In addition, the global positioning means (GPS) is provided to the mobile station.
ystem), and the current position by this means can be managed by the management means of the base station.

In the handover method of the present invention, communication is performed by a CDMA system between a plurality of distributed base stations 1-1 and 1-2, a control station 3 connecting the base stations, and a base station. A handover method in a mobile communication system including mobile stations 2-1 and 2-2, wherein the mobile station performs a handover with respect to another mobile station in the vicinity of the destination of the mobile station during a handover accompanying the movement of the mobile station. Requesting a measurement of the communication quality from the base station to which the mobile station has moved, and the measurement result of the communication quality and
The method includes a step of controlling connection switching of the mobile station to a destination base station based on the presence or absence of an idle channel of the base station. In this case, the management means of the base station can manage the reception level of the mobile station being located, or manage the current position information by the global positioning means (GPS) provided in the mobile station.

[0012]

FIG. 1 is an explanatory diagram of an embodiment of the present invention. 1-1 and 1-2 are base stations, 2-1 and 2-2 are mobile stations, 3 is a control station, Is an exchange, 11 is a wireless transmission / reception unit, 12 is a transmission / reception processing unit, 13 is a control unit, 14 is a management table constituting management means, 15 is an interface unit,
Reference numeral 21 denotes a wireless transmission / reception unit, reference numeral 22 denotes a transmission / reception processing unit, reference numeral 23 denotes a control unit, and reference numeral 24 denotes a measurement unit constituting a communication quality measurement unit. The exchange 4 corresponds to a mobile communication exchange and a fixed network exchange. A plurality of control stations 3 are connected, and a plurality of base stations are connected to each control station to constitute a mobile communication system. .

The base stations 1-1 and 1-2 have the same configuration, and include a radio transmitting / receiving unit 11 including radio frequency transmitting / receiving means and CDMA modulation / demodulation means such as spread coding and despread decoding. A transmission / reception processing unit 12 for performing transmission / reception processing corresponding to a mobile station, a control unit 13 for controlling each unit, a management table 14 for managing a reception level, current position information, and the like corresponding to a mobile station in its own wireless zone. It has a configuration including an interface unit 15 for connecting to the control station 3 of the station.

The mobile stations 2-1 and 2-2 also have the same configuration, and include a radio transmission / reception unit 21 including radio frequency transmission / reception means and CDMA modulation / demodulation means such as spread coding and despread decoding. A transmission / reception processing unit 22 for performing transmission / reception processing of various data such as voices and images; a control unit 23 including a microprocessor or the like for controlling each unit;
Signal-to-interference power ratio (SIR; Signal Interference R)
atio), bit error rate (BER; Bit Error Rate)
), Etc., and a measuring unit 24 for measuring the communication quality.

The function of the measuring section 24 is to control transmission power (T
For PC (Transmit Power Control), the signal-to-interference power ratio SIR and the bit error rate BER are measured, and this function can be used. Also, the reception level measurement is necessary for performing handover,
The measurement unit 24 can use the function of measuring the reception level. That is, the measuring unit 24 can have an independent function, but other measuring functions can be used. A global positioning system (GPS; G
lobal Positioning System). This GPS can be easily mounted on a mobile phone.

When the mobile station moves from its own wireless zone to the adjacent line zone, the base stations 1-1 and 1-2 make an inquiry to the destination base station about the reception quality near the destination of the mobile station. Do. The base station having received the request for the reception quality refers to the management table 14 and requests the other mobile stations existing near the mobile station moving to the own radio zone to perform the reception quality measurement. In this case, the mobile station moving to the own wireless zone is in the vicinity of the wireless zone, and the mobile station located in the vicinity is determined by the reception level of the management table 14 according to the reception level.
Alternatively, it can be identified by the distance from the base station or by the current position by GPS. Therefore, it is possible to request the reception quality measurement by designating the mobile stations located around the own radio zone.

The mobile station that has received the reception quality measurement request measures the reception level by the measurement unit 24, the reception quality based on the signal-to-interference power ratio SIR, etc., and transmits information on the measurement result to the base station. The base station that has received the reception quality information transmits the reception quality request to the base station that has transmitted the reception quality request. In this case, information on the presence or absence of an empty channel is also transmitted. Accordingly, the base station determines the state of the base station to which the mobile station has moved, and
Can request a handover. Also, by transmitting the communication quality information of the movement destination to the moving mobile station, it is possible to set the initial transmission power at the time of starting to move to the adjacent wireless zone, switch the radio frequency and continue the communication. That is, by performing the handover after confirming the state of the destination of the mobile station, it is possible to perform the handover with a reduced instantaneous interruption time even between wireless zones having different wireless frequency bands.

FIG. 2 is a flowchart of the first embodiment of the present invention. For example, the mobile station 2-1 in the radio zone of the base station 1-1 in FIG. When moving toward the wireless zone, the mobile station 2
-1 has shifted to the adjacent wireless zone (A
1). When the adjacent radio zones have different radio frequencies, that is, when the radio frequencies of the base stations 1-1 and 1-2 are different,
The mobile station 2-1 measures the reception level between the mobile station 2-1 and the base station 1-1 which is currently communicating, and uses the vacant time zone of a fixed period during the communication to use the frequency band of the wireless zone of the base station 1-1. And measures the reception level in this adjacent wireless zone. Base station 1-1 communicating each measurement result
Report to. Therefore, it can be determined whether or not the mobile station 2-1 has moved between wireless zones.

When it is determined that the mobile station 2-1 has shifted to the adjacent wireless zone, it is determined whether there is an empty channel in the wireless zone to which the mobile station 2-1 has shifted (A2). That is, as described above, the base station 1-1 issues a handover request to the control station 3, and the control station 3 inquires of the base station 1-2 whether there is an available channel. If there is no vacant channel, communication cannot be continued, so the forced termination is set (A9).

If there is an available channel, the mobile station in communication in the destination wireless zone is requested to measure the communication quality (A3). In the above case, the base station 1-1 to the base station 1-
2 is requested to measure the communication quality near the transfer destination of the mobile station 2-1. Based on this request, the base station 1-2 requests the measurement of the communication quality by designating the mobile station 2-2 with reference to the management table 14, for example. The mobile station 2-2 sends the measurement result of the reception level and the signal-to-interference power ratio SIR to the base station 1-2 by the measurement unit. The base station 1-2 transfers the information on the communication quality measurement result to the base station 1-1 via the control station 3. The base station 1-1 notifies the mobile station 2-1 of the communication quality measurement result information of the destination wireless zone (A
4).

Then, a handover is executed (A
5). That is, the base station 1-1 sends the base station 1 to the control station 3.
-2 requests handover of the mobile station 2-1 and the control station 3 requests handover to the exchange 4 to establish a connection between the exchange 4, the control station 3 and the base station 1-2. A test is performed (A6). If the continuity test is good, the mobile station 2
-1 and a communication connection for continuing communication via the path between the base station 1-2 (A7), and the handover is completed. If the continuity test result is bad, it is determined whether or not there is another free channel (A8). If there is no free channel, the call is forcibly terminated (A9). If there is another free channel, the processing from step (A3) is executed again.

The moving mobile station 2-1 switches to the radio frequency of the destination radio zone and sets the initial transmission power based on the communication quality measurement result information of the destination radio zone. Thereafter, the mobile station 2 is controlled by the transmission power control TPC based on the signal-to-interference power ratio SIR with the base station 1-2.
-1 will be controlled.

FIG. 3 is a flowchart of the second embodiment of the present invention, in which steps (B1), (B2), (B
5) to (B9) correspond to steps (A1) and (A1) in FIG.
2), (A5) to (A9), and a duplicate description is omitted. In the present embodiment, in step (B3), a request for measurement of communication quality is issued to a plurality of mobile stations in a call in a wireless zone near the transfer destination of the mobile station, and the process proceeds to the next step (B4). In this case, each communication quality measurement result information is averaged. In this case, the averaging process is performed in the base station 1-2 which has transmitted the communication quality measurement request to the mobile station. Then, the average value information of the communication quality measurement result is transferred to the base station 1-1. In this case, a more reliable handover can be performed than when a handover is performed based on the measurement result of communication quality by a single mobile station.

FIG. 4 is a flow chart of the third embodiment of the present invention, in which steps (C1), (C2), (C
5) to (C9) correspond to steps (A1) and (A1) in FIG.
2), (A5) to (A9) and step (B) in FIG.
1), (B2), and (B5) to (B9) are the same as those described above, and thus redundant description will be omitted. In this embodiment, in step (C3), a mobile station that is in a call in the destination wireless zone of the mobile station and that is located at substantially the same distance between the mobile station and the base station of the destination wireless zone. Requests the station to measure communication quality.

In this case, the distance information can be based on the fact that the reception level from the base station decreases with distance. Alternatively, it can be obtained based on the transmission / reception time of radio waves. In addition, the above-described position information by GPS can be used. In this case, the position information is not affected by fading in the case of the reception level or the like, so that it is possible to accurately measure the communication quality corresponding to the position.

Also in this case, by transmitting a communication quality measurement request to a plurality of mobile stations from the base station in the destination wireless zone, a plurality of pieces of communication quality measurement result information are collected and averaged by the base station. The average value of the communication quality is notified to the base station and the moving mobile station of the communication quality measurement request (C
4). Therefore, it is possible to confirm the communication quality at the destination to which the mobile terminal moves from now on, so that stable handover is possible not only when the radio frequency is the same but also when the radio frequency is different.

The present invention is not limited to the above-described embodiments, but can be variously added and changed, and the communication quality can be various error rates in the maximum likelihood decoding process.
It is also possible to include a multipath fading state and the like. Further, a function of processing position information of a mobile station equipped with GPS at a base station can be provided.

[0028]

As described above, the present invention provides the CDM
Mobile stations 2-1 and 2- in the A-type mobile communication system
When the mobile station 2 moves between wireless zones, the mobile station measures and reports the communication quality of the destination wireless zone to other mobile stations existing in the wireless zone. It is possible to accurately determine whether or not the handover is possible, reduce the occurrence of forced disconnection and the like during handover between wireless zones having different radio frequencies, and reduce the instantaneous interruption time, enabling smooth handover. There are advantages that can be.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an embodiment of the present invention.

FIG. 2 is a flowchart according to the first embodiment of the present invention.

FIG. 3 is a flowchart according to a second embodiment of the present invention.

FIG. 4 is a flowchart according to a third embodiment of the present invention.

FIG. 5 is an explanatory diagram of a mobile communication system.

[Explanation of symbols]

 1-1, 1-2 Base station 2-1, 2-2 Mobile station 3 Control station 4 Switching station 11 Wireless transmission / reception unit 12 Transmission / reception processing unit 13 Control unit 14 Management table 15 Interface unit 21 Wireless transmission / reception unit 22 Transmission / reception processing unit 23 Control unit 24 Measurement unit

Claims (5)

[Claims] 1. A mobile communication system including a plurality of base stations distributed and arranged, a control station connecting the base stations, and a mobile station communicating with the base station by a CDMA method. The mobile station has a communication quality measurement unit with the base station, the base station manages a distance to a serving mobile station or a position of the mobile station, and the management unit Means for sending a communication quality measurement request to another mobile station in the vicinity of the movement destination of the mobile station by referring to the means, wherein the control station is a base station to which the mobile station moves during handover Means for controlling connection switching of the mobile station to a destination base station based on the presence or absence of a free channel of the mobile station and a measurement result of communication quality of another mobile station near the destination of the mobile station. A mobile communication system characterized by the above-mentioned. 2. The mobile station has global positioning means,
The mobile communication system according to claim 1, wherein the base station includes a management unit that manages a current position of the mobile station by a global positioning unit. 3. A hand in a mobile communication system including a plurality of distributed base stations, a control station connected to the base stations, and a mobile station communicating with the base station by a CDMA method. In the over method, at the time of handover accompanying the movement of the mobile station, requesting the other mobile stations in the vicinity of the destination of the mobile station to measure the communication quality from the base station of the destination of the mobile station, A handover method, comprising a step of controlling connection switching of the mobile station to a destination base station based on the communication quality measurement result and the presence or absence of an idle channel of the base station. 4. The base station manages the reception level of a serving mobile station, and at the time of handover, the reception level of another mobile station having the same reception level as that of a moving mobile station.
4. The handover method according to claim 3, further comprising transmitting a communication quality measurement request. 5. The mobile station comprises global positioning means,
The position information by the global positioning means is managed by the management means of the base station, and at the time of handover, the communication quality of the other mobile stations whose position information matches or approximates the position information of the moving mobile station. 4. The handover method according to claim 3, comprising transmitting a measurement request.