JPH08154269A - Mobile communication system - Google Patents

Abstract

PURPOSE: To realize a mobile communication system in which hand-over is secured even during high speed movement of a mobile station. CONSTITUTION: When a mobile station 31 detects deterioration in a level of a communication carrier in use with a radio base station 21 connecting to the station 31, the mobile station 31 detects a frequency of a communication carrier used by a surrounding radio base station 22 and sends a frequency of the detected communication carrier to a base station controller 1 via the radio base station 21 connected at present. The base station controller 1 retrieves the operating frequency table (set in an internal memory) based on the received frequency to decide a radio base station 22 being an object station of hand-over. Then the base station controller 1 requests hand-over to the radio base station 22 being an object station of hand-over. The base station controller 1 informs a radio base station being an object of hand-over to the mobile station 31 in response to a reply from the radio base station 22 being an object station of hand-over. The mobile station 31 enters hand-over processing with the radio base station 22 being an object station of hand-over base on the notice.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mobile communication system, and more specifically, as a mobile station moves, a radio base station connected to the mobile station is sequentially changed.
The present invention relates to a communication system that performs so-called handover processing.

[0002]

2. Description of the Related Art In recent years, the convenience of mobile communication has been recognized, and the demand for wireless communication services such as automobiles and mobile phones is increasing. As a result, personal mobile communication terminals are rapidly becoming widespread, and along with this, the effective use of frequency resources is becoming more important.

By the way, recently, as one of new mobile communication systems, a personal handyphone system (hereinafter referred to as PHS) has been attracting attention, and various studies have been made for practical use. In this PHS, transmission of information between a mobile station and a base station is performed using a communication carrier and a control carrier. The communication carrier is mainly used for voice communication, and the control carrier is used for transmitting broadcast information necessary for processing other than voice communication such as incoming call, calling, and handover.

In order to effectively use the frequency resources, the control carrier is assigned to only one channel at a maximum for several channels, which is extremely smaller than the number of channels of the communication carrier. A plurality of base stations existing in the same system intermittently transmit the above-mentioned notification information to the mobile stations within their own radio zones using control carriers. This notification information includes an identification code unique to each base station. Therefore, the mobile station can discriminately receive the broadcast information sent from the peripheral base stations, and can detect the wireless zone in which it is currently located based on the received broadcast information.

By the way, in the above PHS, when the mobile station tries to enter the radio zone of the new base station through the radio zone of the base station currently communicating, the call is switched to the communication carrier of the new base station. Therefore, it is necessary to perform processing for so-called handover processing. Conventionally, this handover process has been performed as follows.

That is, the mobile station constantly monitors the reception level and the reception voice quality of the communication carrier used with the currently connected base station, and the deterioration of the reception level and the reception voice quality. When it detects "," it detects that the currently connected base station is about to leave the wireless zone, and prepares for the handover process. Accordingly, the mobile station receives the broadcast information on the control carrier, which is intermittently transmitted from the neighboring base stations, by using the empty slot of the communication carrier currently used, and the handover candidate is determined from the received electric field strength. Determine the base station of. Then, the mobile station requests the base station control device for the handover processing via the connected base station. The base station control device that has received the request for the handover requests the handover candidate base station determined on the mobile station side for the handover, and waits for a response from the base station control device. As a result of the response, if the mobile station and the handover candidate base station can communicate with each other, the base station control device instructs the mobile station via the currently connected radio base station. The mobile station that has received the handover instruction transmits a synchronization packet to the wireless base station that is a candidate for handover using the control carrier. The radio base station that has received the synchronization packet also transmits the synchronization packet to the mobile station. Upon receiving this synchronization packet, the mobile station switches the communication channel to the communication channel of the new base station. As a result, the base stations that relay the communication of the mobile station are switched one after another according to the movement of the mobile station.

[0007]

As is well known, PHS is known.
Then, the zone covered by each radio base station has a radius of 100.
It is a small zone of about 200 m. Therefore, in PHS, the base station to be connected must be frequently changed as the mobile station moves.

However, as described above, the conventional P
In HS, since each base station intermittently transmits the broadcast information using the control carrier, the broadcast information transmission cycle becomes relatively long. Moreover, the frame synchronization does not match between the base stations. Therefore, it takes a long time from when the mobile station detects the deterioration of the reception level of the currently used communication carrier and the deterioration of the reception voice quality until it receives the broadcast information from the neighboring base stations. As a result, the mobile station selects a handover candidate base station in the handover process.
I can't do it quickly. Therefore, conventional PHS
Cannot perform handover during high-speed movement (moving by car, train, etc.), and can be used only at a speed of about a pedestrian.

Therefore, it is an object of the present invention to provide a mobile communication system capable of performing a handover reliably even when moving at high speed.

[0010]

The invention according to claim 1 is
A system capable of mobile communication within a predetermined service area, which is provided in the service area and has a plurality of wireless base stations each having a unique zone for wireless communication, and a base that controls and controls each wireless base station The station control device and a plurality of mobile stations that freely move within the service area and can communicate via the radio base station corresponding to the zone in which they are currently located, each mobile station is a communication carrier currently in use. When the reception level of is deteriorated, the communication carrier frequency detecting means for detecting the frequency of the communication carrier currently being used by a wireless base station other than itself and the communication carrier frequency detected by the frequency detecting means are currently connected. Via a wireless base station in the communication base frequency control means for notifying the base station control device, the base station control device, each wireless base station in the system The currently used communication carrier frequency is used frequency storage means for storing each radio base station, and a frequency matching the communication carrier frequency notified from the communication carrier frequency relay means is searched from the used frequency storage means, Handover candidate determination means for determining a radio base station that is using a corresponding communication carrier frequency as a handover candidate radio base station, and request transmission means for transmitting a handover request to the radio base station determined as a handover candidate. Including each of the wireless base stations, in response to the handover request from the request transmitting means, to the base station control device, including a request response returning means for returning a request response indicating whether to permit the handover process, The base station control device, when the request response received from the request response returning means indicates permission of the handover process, The mobile station further includes a handover instruction transmitting unit that transmits, to the mobile station that has notified the frequency of the receiving carrier, an instruction indicating permission of handover via the radio base station connected to the mobile station. It is characterized by further including communication channel switching means for switching the communication channel to the given wireless base station.

According to a second aspect of the present invention, in the first aspect of the present invention, when each radio base station is not communicating with any mobile station, it transmits a communication carrier for determining a handover candidate to any of the idle channels. And means for doing so.

According to the invention of claim 3, in the invention of claim 1, each radio base station can simultaneously handle a plurality of sets of radio section frames each having a plurality of slots,
It further includes means for transmitting one channel as a communication carrier for determining a handover candidate when all slots on the same time axis are empty channels.

According to a fourth aspect of the present invention, in the first aspect of the invention, each mobile station gives priority to the communication carrier frequencies detected by the communication carrier detecting means in order from the one having the largest received electric field strength. The handover candidate determining means further includes a priority assigning means, and the handover candidate determining means searches the used frequency storage means in order from a communication carrier frequency having a high priority, and determines a handover candidate wireless base station.

[0014]

According to the first aspect of the invention, when the mobile station detects the deterioration of the reception level of the communication carrier being used with the currently connected radio base station, the mobile station is in communication with the surrounding radio base stations. The frequency of the carrier is detected, and the detected frequency value of the communication carrier is transmitted to the base station controller via the currently connected radio base station. The base station control device searches the used frequency storage means based on the received frequency value, and determines the wireless base station of the handover candidate. Then, the handover request is requested to the handover candidate radio base station.
In response to the request response from the handover candidate wireless base station, the base station control device notifies the mobile station of the handover candidate wireless base station. The mobile station enters the handover process with the handover candidate radio base station by this notification.

According to the second aspect of the present invention, each radio base station transmits a communication carrier for determining a handover candidate to any of the idle channels when it is not communicating with any mobile station. As a result, the mobile station can reliably detect surrounding wireless base stations.

According to the third aspect of the present invention, the radio base station capable of simultaneously handling a plurality of sets of radio section frames having a plurality of slots has one channel for determining a handover candidate when all slots on the same time axis are empty channels. To be transmitted as a communication carrier. As a result, the mobile station can reliably detect surrounding wireless base stations.

In the invention according to claim 4, the mobile station gives priority to the communication carrier having the highest electric field strength, and notifies the base station control device together with the detected frequency. The base station control device searches the used frequency storage means in order from the communication carrier frequency having the highest priority, and determines the handover candidate radio base station.

[0018]

1 is a block diagram showing the configuration of a mobile communication system according to an embodiment of the present invention. In the mobile communication system, a plurality of base station control devices, a plurality of radio base stations (CS), and a plurality of mobile stations (P
S) and exist. In addition, in FIG. 1, for simplification of description, one base station control device 1 and two radio base stations 2 are provided.
1, 22 and two mobile stations 31, 33 are shown. The base station control device 1 controls and controls a plurality of radio base stations, and performs a predetermined exchange work between the corresponding radio base stations and public telephone lines. In addition, a plurality of radio base stations 21 and 22 are installed at predetermined intervals in the area covered by the communication system. When the mobile communication system is, for example, PHS, each radio base station has a radius of 100-
It covers a small zone of about 200 m. Each mobile station 3
1 and 32 communicate with other mobile stations (not shown) or home telephones via a radio base station, a base station controller and a public telephone line. As the mobile station moves, the wireless base stations connected to the mobile station are sequentially switched by the handover process.

FIG. 2 shows the frame structure of the wireless section of the wireless base station in the mobile communication system of FIG. As shown in FIG. 2, one frame of the wireless section has a length of 5 msec and is divided into eight slots. The first 4 slots are allocated to the transmission section from the radio base station to the mobile station, and the latter 4 slots are allocated to the transmission section from the mobile station to the radio base station. That is, a frame structure using time division multiplexing-time division duplex (abbreviated as TDMA-TDD) is adopted for communication between the mobile station and the radio base station. Also, 1
One radio base station can handle four sets of TDMA-TDD frames at the same time, and employs a multicarrier system in which the carrier frequency can be arbitrarily set within a prescribed range for each slot. Therefore, one radio base station has a capacity of 16 lines. Then, of the 16 lines, one is a control channel using a control carrier,
The rest is a communication channel using a communication carrier.

FIG. 3 is a diagram showing a frame structure of a radio section of one mobile station. In FIG. 3, 2 out of 8 slots
Slots are used for communication from the radio base station to the mobile station and from the mobile station to the radio base station. The unused 6 slots are used as a carrier detection section for detecting a communication carrier used by a peripheral wireless base station to which the mobile station is not connected, as described later.

FIG. 4 is a diagram showing details of the carrier detection section shown in FIG. In the carrier detection section in FIG. 4, a period T1 in which a communication carrier frequency is set in a frequency synthesizer (not shown) provided inside the mobile station, and the tuning frequency is waited for to stabilize, Periods T2 for measuring the electric field strength appear alternately. In each period T1, the communication carrier frequencies defined as usable in the system are sequentially set in the frequency synthesizer. Therefore, the mobile station will search all the communication carriers existing in the system.

FIG. 5 is a diagram showing a CS table set in an internal memory (not shown) of the base station controller 1. In this CS table, the base station control device 1 controls
The identification numbers of the wireless base stations located in the periphery of each of all the controlled wireless base stations are registered.
For example, wireless base stations with identification numbers CS2, CS3, CS4, and CS7 exist around the wireless base station assigned with the identification number CS1.

FIG. 6 is a diagram showing a used frequency table set in an internal memory (not shown) of the base station controller 1. In this used frequency table, the communication carrier frequencies currently in use are registered for all of the wireless base stations that are integrated and controlled by the base station control device 1. For example, the radio base station assigned with the identification number CS1 is currently using the communication carriers of the frequencies f0, f1 and f2.

In the above configuration, the mobile station 31
Is currently communicating via the wireless base station 21, and is about to leave the unique wireless zone covered by this wireless base station 21. Then, the mobile station 31 selects the mobile station 32 as a handover candidate. Further, it is assumed that the radio base station 22 is in use of the masked slots of FIG. 2 and is in communication with the mobile station 32 using the second slot of the set C.

FIG. 7 is a flowchart showing the operation of the mobile station 31 which is about to leave the wireless zone of the wireless base station 21. FIG. 8 is a flowchart showing the operation of the wireless base station 21 to which the mobile station 31 is connected. FIG. 9 is a flowchart showing the operation of the handover candidate radio base station 22. FIG. 10 is a flowchart showing the operation of the base station control device 1 related to the handover processing.
Hereinafter, the operation of the mobile communication system shown in FIG. 1 will be described with reference to FIGS. 7 to 10.

The communication carrier frequency of the slot used in each radio base station is notified to the base station controller 1 in advance at the start of use of the slot and registered in the use frequency table shown in FIG. For example, as shown in FIG. 9, the mobile station 32 notifies the base station control device 1 of the unregistered used frequency when the use of the communication carrier is started (step S30).
1). As shown in FIG. 10, the base station control device 1 receives the notification of the used frequency from the mobile station (step S40).
1) The used frequencies are organized for each mobile station and registered in the used frequency table of FIG. 6 (step S402).

Further, each mobile station which is communicating through the radio base station constantly measures the reception level and the reception voice quality of the communication carrier in parallel with the communication. For example, the wireless base station 21
When the mobile station 31 communicating with the mobile station 31 tries to leave the radio zone of the radio base station 21, as shown in FIG. 7, the reception level deterioration and the reception voice quality deterioration of the currently used communication carrier are detected. (Step S101). Next, the mobile station 31 detects the unused 6 slots shown in FIG. 3 as a carrier detection section (step S102). After that, the mobile station 31 uses the carrier detection section detected in step S102 to detect the communication carrier used by the neighboring wireless base stations.

That is, the mobile station 31 sets one of the frequencies defined in advance as a communication carrier usable in this system in a frequency synthesizer (not shown) provided therein (step S103). . Next, the mobile station 31 waits for the tuning frequency of the frequency synthesizer to stabilize (step S104), and when stable, measures the electric field strength of the received radio wave at that time (S1).
05). After the measurement, the mobile station 31 stores the frequency of the received communication carrier and the received electric field strength in an internal memory (not shown) (step S106). afterwards,
The mobile station 31 sets a new communication carrier frequency in the frequency synthesizer and performs a new communication carrier detection operation. The operations of steps S103 to S106 are repeated until the carrier detection period ends, as shown in FIG. 4 (step S107). As a result, the reception states of all communication carriers existing in the system are detected.

Next, the mobile station 31 sets the currently used communication carrier frequency in the frequency synthesizer (step S108). As a result, the mobile station 31
Communication via the wireless base station 21 is restarted. Next, the mobile station 31 prioritizes some of the detected communication carriers, whose electric field strength exceeds a certain value, in descending order of the received electric field strength, and determines these detection frequencies. The data is notified to the connected wireless base station 21 (step S109).

As shown in FIG. 8, when the radio base station 21 receives the detection frequency data from the mobile station 31 (step S201), it outputs the detection frequency data to the base station controller 1 (step S202). .

As shown in FIG. 10, when the base station control device 1 receives the data of the detected frequency from the radio base station 21 (step S403), the used frequency that matches the detected frequency is on the used frequency table of FIG. In order from the highest priority, and the radio base station that is using the communication carrier of the matching frequency is determined as the handover candidate radio base station (step S40).
4). Here, since the communication carrier used between the mobile station 32 and the radio base station 22 is already registered in the used frequency table, and the mobile station 31 is also notified as the detected frequency, the above step S404. The wireless base station 22 is determined as a handover candidate by performing the search for. However, there may be other radio base stations communicating in the system using the same frequency. In this case, the other wireless base station may be selected as a handover candidate. Therefore, the base station controller 1 refers to the CS table in FIG. 5 to screen out the other wireless base stations and narrow down only the wireless base stations 22 existing around the wireless base station 21 as handover candidates. Next, the base station controller 1
A handover request is issued to the wireless base station determined as the handover candidate, that is, the wireless base station 22 that is using the searched communication carrier frequency (step S40).
5).

As shown in FIG. 9, when the handover candidate radio base station 22 receives a handover request from the base station controller 1 (step S302), it notifies the base station controller 1 of a response to the request (step S302). S30
3). That is, the radio base station 22 is newly added to the mobile station 31.
When there is an empty slot for communication with the base station controller 1, the base station controller 1 is notified of a response indicating that handover is possible, and when there is no such empty slot, a response indicating that handover is not possible is transmitted. Notice.

By the way, when the respective radio base stations controlled and controlled by the base station control device 1 operate asynchronously with each other,
The synchronization between the mobile station 31 and the radio base station 22 is not guaranteed.
Therefore, it is necessary to establish synchronization with the synchronization packet. Therefore, when handover is possible, the radio base station 22 transmits a synchronization packet to the mobile station 31 in order to establish synchronization (step S305). After that, the radio base station 22 waits for reception of the synchronization packet from the mobile station 31 (step S306).

As shown in FIG. 10, the base station control device 1 judges whether the content of the response from the radio base station 22 which has notified the handover request indicates whether handover is possible or not (step S406). ). If the response content indicates that handover is possible, the base station controller 1 transmits a handover instruction message to the radio base station 21 (step S407). On the other hand, if the response content indicates that handover is not possible, the base station control device 1 returns to the operation of step S404, searches the used frequency table of FIG. 6 for a frequency that matches the detected frequency having the next priority, and A radio base station using the frequency is determined as the next handover candidate, and a handover request is issued to the determined radio base station.

As shown in FIG. 8, when the radio base station 21 receives a handover instruction message from the base station controller 1 (step S203), it transmits it to the mobile station 31 (step S204).

As shown in FIG. 7, when the mobile station 31 receives a handover instruction from the radio base station 21 (step S110), it waits for reception of a synchronization packet from the radio base station 22 that is a candidate for handover (step S11).
1). Upon receiving the synchronization packet, the mobile station 31 returns the synchronization packet to the radio base station 22 (step S
112), switching to a voice call and completing the handover processing (step S113).

As shown in FIG. 9, when the radio base station 22 receives the return of the synchronization packet from the mobile station 31 (step S305), since the synchronization is established, it switches to the voice call and completes the handover processing (step S305). Step S30
7).

Each radio base station outputs at least one channel as a communication carrier without a connection destination when all channels on the same time axis of the communication carrier are free channels. In the example of FIG. 2, all the channels on the same time axis are empty channels in the third slot portion, and the radio base station connects one channel of the third slot of the sets A to D. Output as a communication carrier with no destination. This allows the mobile station to reliably detect the communication carrier.

[0039]

According to the first aspect of the present invention, the frequency value of the communication carrier that is constantly transmitted is determined without using the broadcast information of the control carrier that is intermittently transmitted from the wireless base station as in the conventional case. Since the mobile station detects and the base station controller determines the wireless base station of the handover candidate based on the detection result, the handover time can be greatly shortened and the handover during high-speed movement is possible. Becomes

According to the invention of claim 2, when each radio base station is not communicating with any mobile station, it transmits the communication carrier for determining the handover candidate to any of the free channels. The mobile station can reliably detect surrounding wireless base stations.

According to the third aspect of the present invention, each radio base station sets 1 when all slots on the same time axis are empty channels.
Since the channel is transmitted as the communication carrier for determining the handover candidate, the mobile station can reliably detect the surrounding wireless base stations.

According to the fourth aspect of the present invention, the base station control device searches the used frequency storage means in order from the frequency of the communication carrier having a high received electric field strength in the mobile station, and determines the handover candidate radio base station. Therefore, the radio base station having the best reception state can be determined as the handover candidate.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a mobile communication system according to an embodiment of the present invention.

FIG. 2 is a diagram showing a frame structure of a wireless section of a wireless base station in the mobile communication system of FIG.

FIG. 3 is a diagram showing a frame configuration of a wireless section of one mobile station in the mobile communication system of FIG.

FIG. 4 is a diagram showing details of a carrier detection section shown in FIG.

FIG. 5 shows C set in the internal memory of the base station controller 1.
It is a figure which shows S table.

FIG. 6 is a diagram showing a used frequency table set in an internal memory of the base station control device 1.

FIG. 7 is a flowchart showing an operation of the mobile station 31 trying to leave the wireless zone of the wireless base station 21.

FIG. 8 is a flowchart showing an operation of the wireless base station 21 to which the mobile station 31 is connected.

FIG. 9 is a flowchart showing an operation of a wireless base station 22 which is a handover candidate.

FIG. 10 is a flowchart showing an operation of the base station control device 1 related to a handover process.

[Explanation of symbols]

 1 ... Base station control device 21, 22 ... Radio base station 31, 32 ... Mobile station

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuhiro Andou 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (4)

[Claims] 1. A system capable of mobile communication within a predetermined service area, comprising a plurality of radio base stations provided in the service area, each radio base station having a unique zone in which radio communication is possible, A base station control device for controlling and controlling a station, and a plurality of mobile stations that freely move within the service area and can communicate via the radio base station corresponding to the zone in which the station is currently located, The mobile station, when the reception level of the currently used communication carrier deteriorates, communication carrier frequency detection means for detecting the frequency of the currently used communication carrier in the wireless base stations other than itself, and the frequency detection. Communication carrier frequency notifying means for notifying the base station control device of the communication carrier frequency detected by the means, via the radio base station currently connected. The base station control device includes a used frequency storage unit that stores the communication carrier frequency currently used by each of the wireless base stations in the system for each wireless base station, and is notified from the communication carrier frequency relay unit. A handover candidate determining unit that searches a frequency that matches a communication carrier frequency from the used frequency storage unit and determines a wireless base station that is using the corresponding communication carrier frequency as a handover candidate wireless base station; Request transmitting means for transmitting a handover request to the radio base station determined as a handover candidate, wherein each radio base station responds to the handover request from the request transmitting means to the base station control device. On the other hand, the request response returning means for returning a request response indicating whether to permit the handover process is included, The base station control device, when the request response received from the request response returning means indicates the permission of the handover process, issues an instruction indicating the permission of the handover to the mobile station that has notified the frequency of the communication carrier. The mobile station further includes handover instruction transmitting means for transmitting via the connected radio base station, and the mobile station further includes communication channel switching means for switching a communication channel to the radio base station that has given permission for the handover. Communications system. 2. The radio base station according to claim 1, further comprising means for transmitting a communication carrier for determining a handover candidate to any of the idle channels when not communicating with any of the mobile stations. Mobile communication system. 3. Each of the radio base stations can simultaneously handle a plurality of sets of radio section frames each having a plurality of slots, and when all slots on the same time axis are empty channels, one channel is used for handover candidate determination. The mobile communication system according to claim 1, further comprising means for transmitting as a communication carrier. 4. Each of the mobile stations further includes priority assigning means for assigning priority to communication carrier frequencies detected by the communication carrier detecting means in descending order of received electric field strength. The mobile communication system according to claim 1, wherein the deciding means searches the used frequency storage means in order from a communication carrier frequency having a higher priority to decide a radio base station as a handover candidate.