WO2003003782A1 - Cdma mobile communication system and its call cut-off prevention method - Google Patents

Abstract

A CDMA mobile communication system in which when a mobile terminal (30) is in an environment to receive transmission signals from a number of base stations (20, 21, 22, ...) or sectors (α, β, Ϝ) more than necessary, for example, in a sector congestion region, a base station control apparatus (10) detects the state according to a pilot intensity report transmitted from the mobile terminal and causes the mobile terminal to perform hard handover to another carrier frequency corresponding to a sector of different arrangement or a base station of different arrangement, so that the mobile terminal can perform stable communication. A call cut-off prevention method is also disclosed.

Description

 Specification

C D MA mobile communication system and method for preventing call disconnection

 The present invention relates to a CDMA mobile communication system and a method for preventing a call disconnection thereof. In the same service area, multiple base stations that control wireless transmission and reception with mobile terminals are arranged so that each wireless area partially overlaps each other, and one carrier frequency is used for mobile terminals. The present invention relates to a CDMA mobile communication system capable of simultaneously connecting to a plurality of sectors in a plurality of base stations, and a method for preventing a call disconnection in an area where the sectors are concentrated. Background art:

 In a CDMA mobile communication system, a plurality of base stations (or sectors) operate at the same carrier frequency, and a mobile terminal receives one frequency, and each base station (or sector) receives a spreading code. Recognizes the signal from. In this system, one receiver (mobile terminal) can simultaneously receive signals from multiple base stations, so that handover without instantaneous interruption called soft handover is possible. .

On the other hand, in order to recognize a signal from a base station with a spreading code, a signal strength that is at least the minimum required signal-to-interference ratio (SIR) determined by the spreading factor is required. In an environment where signals from multiple base stations (or sectors) are received, when trying to receive signals from one base station (or sector), signals from other base stations (or sectors) may be lost. All signals become interference waves. As a result, more base stations (or sectors) In places where signals are received, there are cases where signals cannot be demodulated despite the strong electric field.

 Now, let's calculate an example of the ratio of the power of the pilot signal from a specific sector to the interference (SNR). Assuming that the mobile terminal can receive the transmission power of all sectors equally, and assuming that the ratio of the pilot signal power to the transmission power of a certain sector is 20%, the pilot of a certain sector received by the mobile terminal is When 7 sectors can be received, the pilot signal power to interference ratio = 0.2 / 7

 = 0. 0 2 8 5 7 1 4 2 8--15.5 dB

Becomes

 By the way, if only 4 sectors can be received,

 Pilot signal power to interference ratio = 0.2 / 4

 = 0. 0 5

 =-13.0 dB

And the difference is 2.5 dB.

 In an environment with fading, the signal strength from each base station (or sector) changes rapidly without correlation. Adding a base station (or sector) subject to Soft-Z softer handover requires a much longer processing time than fading. Also, as the number of base station sector signals that can be received by the mobile terminal increases, the signal-to-interference ratio from a certain base station (or sector) decreases, and the signal cannot be demodulated with a little fading. The chances are high.

In other words, including a base station (or sector) that is transmitting a signal that can be received strong enough to demodulate at a certain moment in the soft-Z softer handover means that the number of base stations (or sectors) that can be received increases. The more difficult it becomes. The mobile terminal performs stable communication in an environment where transmission signals from more base stations (or sectors) than necessary reach. This is the reason that the call in progress is disconnected.

 The present invention is directed to a base station control apparatus in a case where a mobile terminal is placed in an environment where transmission signals from an unnecessarily large number of base stations or sectors as described above reach, for example, in a densely populated sector area. By detecting the situation according to the pilot strength report transmitted from the terminal and making the mobile terminal perform a hard handover to another carrier frequency corresponding to a sector with a different configuration or a base station with a different configuration. It aims to provide a CDMA mobile communication system that enables mobile terminals to perform stable communication, and a method for preventing call disconnection. Disclosure of the invention:

 To achieve the above object, according to a first aspect of the present invention, each radio carrier corresponding to a plurality of carrier frequencies is divided into a plurality of sectors, and each radio carrier is divided into a plurality of sectors within the same service area. Are provided so as to partially overlap each other, and each base station is provided with a plurality of base stations for controlling wireless transmission / reception to / from a mobile terminal while transmitting a pilot signal in parallel. A plurality of sectors in each of the plurality of base stations and a mobile terminal can be connected simultaneously, and each of the base stations has a sector configuration different from each other for at least two different carrier frequencies. The mobile terminal connected to any of the base stations using the carrier frequency simultaneously performs handover from a number of sectors exceeding a predetermined threshold value. Upon receiving a pilot signal of a signal strength that can be targeted, a hard handover to another carrier frequency corresponding to another sector which is differently arranged for the mobile terminal is performed. A featured CDMA mobile communication system is provided.

According to the second aspect of the present invention, each radio carrier corresponding to a plurality of carrier frequencies is divided into a plurality of sectors, respectively, In a single service area, each radio area is arranged so as to partially overlap with each other, and comprises a plurality of base stations for controlling radio transmission and reception with a mobile terminal while transmitting a pilot signal in parallel with each other, In this case, a plurality of sectors in each of the plurality of base stations and a mobile terminal can be simultaneously connected using one carrier frequency, and each of the base stations is different from each other for at least two different carrier frequencies. The signal strength of the pilot signals from all the sectors in the handover received by the mobile terminal connected to any base station using a certain carrier frequency, and If the threshold falls below an arbitrarily set value within the range of the signal strength that can be exceeded, the location will be different for the mobile terminal. A CDMA mobile communication system is provided in which a handover to another carrier frequency corresponding to another sector is performed.

According to the third aspect of the present invention, each radio area corresponding to a plurality of carrier frequencies is divided into a plurality of sectors, and each radio area partially overlaps in the same service area. A plurality of base stations arranged so as to control wireless transmission and reception to and from a mobile terminal while transmitting pilot signals in parallel, wherein the plurality of base stations are transmitted using one carrier frequency. , The plurality of sectors and the mobile terminal can be connected simultaneously, and each of the base stations has a different sector configuration from each other for at least two different carrier frequencies, and uses any one carrier frequency. Of the signal strength that the mobile terminal connected to the base station can simultaneously be subjected to handover from a number of sectors exceeding a predetermined threshold value. The signal strength of the pilot signal received by the mobile terminal from all sectors during the handover received by the mobile terminal is within the range of the signal strength that can be targeted for the handover. If the threshold value is arbitrarily set in step 2, the other sectors with different locations for the mobile terminal A CDMA mobile communication system is provided, in which a hard handover to another corresponding carrier frequency is performed.

According to the fourth aspect of the present invention, each radio carrier corresponding to a plurality of carrier frequencies is divided into a plurality of sectors, and each radio carrier partially overlaps in the same service area. And a plurality of base stations arranged in such a way as to transmit and receive a pilot signal in parallel while controlling radio transmission / reception with a mobile terminal, wherein the plurality of base stations are provided using one carrier frequency. A plurality of sectors and mobile terminals in each of the base stations are simultaneously connectable, and each of the base stations has a different sector configuration from each other for at least two different carrier frequencies; and Means for connecting to any base station using a certain carrier frequency, and means for measuring the signal-to-interference power ratio as the signal strength of the received pilot signal When the above measurement result is determined and it is detected that a new pilot signal of a predetermined strength or more is received, a handover addition request of the corresponding sector including the above measurement result is transmitted to the connected base station. Means for transmitting, to a connected base station, signal strength reports of pilot signals from all the sectors being handed over in accordance with a preset trigger, and further comprising: And controlling the plurality of base stations to control the connection of the mobile terminal, and receiving the handover addition request and the signal strength report of the gateway signal from the mobile terminal via the base station. In some cases, the mobile terminal may be simultaneously subjected to handover from a number of sectors exceeding a predetermined threshold, which is a condition for performing a predetermined hard handover. A pilot signal of signal strength is received, and the signal strength of the pilot signals from all sectors during handover received by the mobile terminal is within the range of the signal strength that can be excluded from the handover. It is determined whether one or both of the conditions are satisfied, or whether or not both are below a threshold value arbitrarily set in the case where the above conditions are satisfied. The present invention further provides a CDMA mobile communication system, comprising: a base station control device for performing a hard handover to another carrier frequency corresponding to another sector arranged differently with respect to the mobile terminal. .

 According to a fifth aspect of the present invention, in the CDMA mobile communication system according to any one of the first to fourth aspects, each base station having a different sector arrangement configuration for at least two different carrier frequencies. Instead of a station, it is provided with a plurality of base stations at different locations where at least one of at least two different carrier frequencies is allocated to each of the base stations, and hard-handed to the mobile terminal there. A mobile communication system is provided in which a hard handover to another carrier frequency corresponding to another base station having a different arrangement is performed when performing a mobile communication.

 According to a sixth aspect of the present invention, in the CDMA mobile communication system according to any one of the first to fourth aspects, each base station uses the same adaptive array antenna and has a different carrier frequency. A CDMA mobile communication system characterized in that each sector has a different sector arrangement configuration.

According to the seventh aspect of the present invention, each radio area corresponding to a plurality of carrier frequencies is divided into a plurality of sectors, and each of the radio areas communicates with a mobile terminal while transmitting a pilot signal in parallel. A plurality of base stations for controlling transmission / reception are arranged so that each radio area partially overlaps each other in the same service area, and a plurality of sectors in each of the plurality of base stations are arranged using one carrier frequency. A method for preventing a call disconnection in a crowded sector area in a CDMA mobile communication system in which a mobile terminal can be simultaneously connected, wherein at least two different carrier frequencies are allocated to the base stations at different locations. The power to be assigned to each sector is assigned to differently arranged sectors of the same base station. When the mobile terminal connected to any base station using the carrier frequency receives a pilot signal of signal strength that can be subjected to handover simultaneously from a number of sectors exceeding a predetermined threshold value, respectively. A method of performing a hard handover to another carrier frequency corresponding to another base station or sector differently arranged with respect to the mobile terminal. Is done.

 According to the eighth aspect of the present invention, each radio area corresponding to a plurality of carrier frequencies is divided into a plurality of sectors, and radio transmission / reception with a mobile terminal is performed while transmitting pilot signals in parallel with each other. A plurality of base stations for controlling the mobile stations are arranged so that each radio area partially overlaps each other within the same service area, and each of the plurality of sectors and the mobile terminal in the plurality of base stations is arranged using one carrier frequency. Is a method for preventing a call disconnection in a densely packed sector in a CDMA mobile communication system that can be connected simultaneously, wherein at least two different carrier frequencies are respectively transmitted to the base stations at different locations. The power to be allocated is allocated to sectors of the same base station that are different from each other, and is assigned to any base station using a certain carrier frequency. The signal strength of the pilot signals from all the sectors in the handover received by the mobile terminal during the handover has been set arbitrarily within the range of the signal strength that can be targeted for the handover. Performing a handover to another carrier frequency corresponding to another base station or sector that is differently arranged for the mobile terminal when the threshold value is dropped below the mobile terminal. A method for preventing a call disconnection is provided.

According to the ninth aspect of the present invention, each wireless area corresponding to a plurality of carrier frequencies is divided into a plurality of sectors, and wireless transmission and reception with a mobile terminal are performed while transmitting pilot signals in parallel with each other. The base stations that control the radio are arranged so that each radio area partially overlaps each other within the same service area, and use one carrier frequency. A method for preventing call disconnection in a densely packed sector area in a CDMA mobile communication system in which a plurality of sectors and a mobile terminal in each of the plurality of base stations are simultaneously connectable, wherein at least two different carrier frequencies are used. The power to be assigned to each of the base stations at different locations, respectively, is assigned to the differently located sectors of the same base station, and the mobile terminal connected to any of the base stations is determined using a certain carrier frequency. Pilot signals of the signal strengths that can be simultaneously targeted for handover from the number of sectors exceeding the threshold value of the mobile terminal, and the pilot signals from all the sectors during the handover received by the mobile terminal are received. Arbitrarily set within the range of the signal strength that can be targeted by the handover. If the value is less than the value, the method includes a step of performing a handover to another carrier frequency corresponding to another base station or sector differently arranged with respect to the mobile terminal. A method for preventing call disconnection is provided.

According to a tenth aspect of the present invention, each radio carrier corresponding to a plurality of carrier frequencies is divided into a plurality of sectors, and radio transmission and reception with a mobile terminal are performed while transmitting pilot signals in parallel with each other. A plurality of base stations for controlling the radio are arranged so that each radio area partially overlaps each other within the same service area, and move with each of the plurality of sectors in the plurality of base stations using one carrier frequency. A method for preventing call disconnection in a densely populated sector in a CDMA mobile communication system in which terminals can be connected simultaneously, wherein at least two different carrier frequencies are transmitted to said base stations at different locations. The pilot signal received by the mobile terminal is assigned to each of the differently allocated sectors of the same base station. By measuring the signal-to-interference power ratio as the signal strength of the signal, if it is detected that a new pilot signal of a predetermined strength or more has been received, handover of the corresponding sector including the measurement result is performed. Along with sending an add request to the connected base station. The plurality of base stations transmit a signal strength report of a pilot signal from all sectors during handover to a connected base station according to a preset timing, and control the connection with the mobile terminal. In the base station control device that controls the handover, when the handover addition request and the signal strength report of the gateway signal from the mobile terminal via the base station are received, a preset hard hand The mobile terminal simultaneously receives, from the number of sectors exceeding a predetermined threshold value, a pilot signal having a signal strength that can be a target of handover, which is a condition for performing over, and The signal strength of the pilot signals received by the terminal from all the sectors during the handover is within the range of the signal strength that can be targeted for the handover. It is determined whether a value falls below an arbitrarily set threshold value, or one or both of the conditions are satisfied.If the condition is satisfied, a different arrangement for the mobile terminal is determined. A method for performing a handover to another base station or another carrier frequency corresponding to sector 2, comprising the steps of: Brief description of the drawings:

 FIG. 1 is an overall configuration diagram showing one embodiment of a CDMA mobile communication system,

 FIG. 2 is a schematic diagram of a sector configuration for explaining how the sector configuration differs depending on the frequency at a certain frequency.

 FIG. 3 is a schematic sector configuration diagram for explaining how the sector configuration differs depending on the frequency in the case of another frequency.

 FIG. 4 is a schematic sector configuration diagram for explaining a situation in which the base station arrangement itself is changed for each frequency, and

FIG. 5 is a block diagram showing one configuration example of the terminal in FIG. BEST MODE FOR CARRYING OUT THE INVENTION

 First, the outline of the present invention will be described. A CDMA mobile communication system corresponds to a plurality of carrier frequencies, each of which is divided into a plurality of sectors (for example, sector zones α,] 3, y shown in FIG. 2), and each of them is partially divided. Multiple base stations with overlapping wireless areas are operated in parallel so that they can be identified by spreading codes. In the present invention, different carrier frequencies are assigned to each base station (its radio area). Each carrier is assigned to a different sector of the same base station. In other words, when viewed from the mobile terminal side, the change in frequency may result in a different arrangement of communicable base stations, or a different arrangement of sectors even if the arrangement of base stations is the same. In this state, the mobile terminal connected to one of the base stations using a certain carrier frequency has a signal strength that can be simultaneously subjected to handover from a number of sectors exceeding a predetermined threshold. Or the signal strength of the pilot signals received by the mobile terminal from all sectors during the handover is set arbitrarily within the range of signal strengths that can be targeted for handover. If the force falls below the threshold or one of the two forces occurs, or both occur simultaneously (these conditions can be determined in advance), they will be different from each other. It is characterized in that a hard handover is performed to another carrier frequency corresponding to the base station or sector being used.

Here, a mechanism for adding a certain sector to a handover by a mobile terminal will be described. The mobile terminal in communication is always searching for a pilot signal (Pi1οt), but a pilot signal that could not be received with sufficient power until now rises to a sufficient level (signal strength). And the determined signal-to-interference power ratio (called T-ADD in the IS-95 system): Normally, the ratio of the energy per pilot chip to the energy of the interference wave is “E c / lo ”to set in the range from 1 1 1 to 16 dB Above), a request to add the sector of the base station (BTS) transmitting the pilot signal to the handover (HZO) is sent to the base station currently communicating. The base station that has received the handover addition request notifies the base station controller (BSC) of the message. After receiving the message, the base station controller determines whether handover addition is possible, and if possible, prepares the handover destination base station for handover addition. A handover addition permission is transmitted to the mobile terminal via the handover source base station. Note that even if the pilot signal strength of a certain sector exceeds T-ADD, it is not always added to the handover due to system limitations. In this way, the pilot signal strength exceeds T-ADD and the sector added to the handover is called the active set, and even though the pilot signal strength exceeds T-ADD. Sectors not added to the handover are called candy set. Any sectors that have not been added to this handover will be sources of interference for the sectors that have been added to the handover.

 Conversely, when a mobile terminal deletes a sector from handover, even if the signal strength (ratio of signal power to interference wave power) of the pilot signal from the sector falls below T_ADD, it does not exceed T_ADD. The sector is not deleted from the handover unless it falls below the set T—DROP (eg, about 3 dB lower). When the pilot signal strength falls below T-DROP, the mobile terminal transmits a handover deletion request to the base station controller via the base station. Even if the mobile terminal sends a handover deletion request, the sector remains added to the handover until the handover deletion permission is sent, and when the handover deletion permission is received from the base station controller. To stop receiving the sector.

Therefore, the "handover" in the pilot signal from each sector "The signal strength that can be considered for the target" means that if the relevant sector has not yet been added to the handover, whether it is actually added or not, T-ADD is exceeded. Signal strength, if the relevant sector has already been involved in handover, maintain that state. Signal strength above T-DROP.

 In the system of the present invention, when the mobile terminal attempts to add a certain sector to the soft / soft handover, the base station control device, even if the sector is added, is subject to handover at that time. If the number of possible sectors (the total number of sectors) is less than the threshold, normal handover addition processing is performed. If the addition causes the number of sectors to exceed the threshold, or if the pilot power-to-interference ratio of all base stations (sectors) is lower than the threshold, or If these methods occur at the same time, the mobile terminal is instructed to perform a hard handover to another frequency with a different sector arrangement. It should be noted that the case in which the hard handover is performed can be set in advance in the base station controller. In this way, by handing over a mobile terminal in a strong interference area where signals from multiple sectors are received at one time to another frequency, the mobile terminal is called abnormal disconnection of the call. You can prevent things from happening.

 Next, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

 FIG. 1 is an overall configuration diagram showing one embodiment of a CDMA mobile communication system of the present invention. In FIG. 1, the CDMA mobile communication system of this example includes a base station controller 10, a plurality of base stations A 20, B 21, C 22, and mobile terminals (hereinafter abbreviated as terminals) 30. And only the part related to the present invention is shown. Note that a plurality of terminals 30 can be provided.

The base station controller 10 has data storage, processing, and communication functions. It is connected to the base station A 20, the base station B 21, and the base station C 22, and controls the base station and the terminal 30 via the base station. The base station control device 10 is also connected to an exchange (not shown) of a mobile communication network, and controls communication between the terminal 30 and other terminals connected to the communication network.

 The base station controller 10 manages all handover control of the terminal 30 and recognizes the number of sectors to be handed over for each terminal 30. Also, as a condition of hard handover, it is said that the terminal 30 receives, from a number of sectors exceeding a predetermined threshold value, a pilot signal having a signal strength capable of being subjected to handover simultaneously at the same time. The first condition is that the signal strength of pilot signals from all sectors during handover received by terminal 30 is arbitrarily within the range of signal strengths that can be targeted for handover. The system decides which one of the second condition that falls below the set threshold value and the third condition that the first condition and the second condition are satisfied at the same time is adopted. It can be set in advance by the operator.

 Each of the base station A 20, the base station B 21, and the base station C 22 establishes a radio link with the terminal 30 by a plurality of carrier frequencies (for example, two frequencies of F 1 and F 2) and It is operated in a plurality of sectors α, β, γ. The carrier frequency (hereinafter abbreviated as frequency) transmitted from each sector to the terminal 30 is multiplexed with a pilot signal in addition to a communication data signal, and subjected to modulation, spreading processing, and the like. Also, it demodulates and decodes the radio signal from the terminal 30. Each of the base stations A 20 to C 22 and the base station controller 10 are connected by wired transmission lines t 1 to t 3, whereby each base station is connected to the terminal 30 and the base station. Relays communication data, control data, etc. with the controller 10.

The terminal 30 is wirelessly connected to each of the base station A 20, the base station B 21, and the base station C 22, and in addition to communication of voice, data, and the like, controls connection of a wireless line (outgoing / incoming call). , Handover, etc.). Also the end Terminal 30 has the function of measuring the power intensity (signal-to-interference ratio) of the pilot signal from each base station (sector).

 FIG. 5 is a block diagram showing a configuration example of the terminal 30, and shows only a part related to the present invention. In FIG. 5, terminal 30 converts a radio wave from a base station received via an antenna into a baseband signal at a receiving section of radio section 31. The baseband signal output from the receiving unit is input to demodulation unit 32. The demodulation unit 32 has a plurality of demodulators called fingers (Finger), and each demodulator demodulates data at an independent sample timing. One of the demodulators is called a searcher (Fingerl in Fig. 5), which despreads a pilot (Pi1ot) signal at various timings, Searching for the presence of a pilot signal.

 In the IS-95 system, the same signal is transmitted with the same spreading code in all sectors in all base stations. However, the transmission timing is different for each sector (called PN offset). In addition, each base station transmits the transmission timing of its own pilot and the transmission timing of an adjacent cell as broadcast information, and the base station received at a certain timing determines which base station The terminal can know from which sector of the sector.

 Each of the fingers (Finger-n) of the demodulation unit 32 has a function to measure the current reception level and the level of the desired signal after despreading. The ratio and the signal-to-interference ratio of the desired signal can be calculated. The control unit 34 generates a pilot signal strength report from the information, outputs the pilot signal strength report to the multiplexing unit (MUX) of the modulation unit 33, and modulates it together with communication data. To the connected base station.

Here, the pilot signal strength report transmitted by the terminal 30 will be described in more detail. Messages containing pilot signal strength information include: And PS MM (P ilot S trength Me asurement M esssage), there are two forces ^s of the PMR (P ower M easurement R eport M essage).

 The P SMM is a so-called “handover-one-addition request” that is voluntarily transmitted from the terminal. This PSMM is transmitted when a pilot signal from a sector other than the base station (sector) that is currently handing over exceeds the value of T-ADD specified in advance. Also, a PSMM is transmitted when the pilot signal strength from the sector in the handover falls below T_DROP. IS-95 systems can report pilot signal strength from up to 15 sectors, and the 15 pilot signal strengths are those currently added to the handover (active Not only sets but also those that exceed T-ADD but are not added to the handover (candy set) are reported.

 On the other hand, in the “Power Control 1 Parameter Message” transmitted from the base station to the terminal, the PMR is set for periodic PMR transmission. These settings are used as a trigger when settings such as sending are performed. Further, the PMR is also transmitted when the terminal receives "PilotMeasuemementRequestOrder" transmitted from the base station. Only those that are currently added to the handover are reported for PMRs, and up to 6 pilot signal strength reports can be made for IS-95 systems.

On the other hand, as described above, each of the base station A 20, the base station B 21, and the base station C 22 operates with a plurality of frequencies and a plurality of sectors. Each sector has a different sector configuration (the direction in which the sector faces terminal 30, that is, the arrangement is different). Figures 2 and 3 show sectors (sector zones) by frequency. It is a schematic sector block diagram for demonstrating a mode that a structure differs. FIG. 2 shows the arrangement of sectors in each base station at frequency F1, and FIG. 3 shows the arrangement of sectors at frequency F2.

 In each base station, a sector is formed for each frequency with physically different antennas pointing in different directions. Alternatively, by using an adaptive antenna or the like, it is also possible to use a same antenna and to have a different sector configuration for each frequency. The adaptive array antenna arranges a plurality of antenna elements in an array, and adaptively controls weighting factors (weights) for signal processing of received and transmitted signals of each antenna element, thereby obtaining an antenna gain (weight) in a specific direction. Directionality) can be increased or decreased. In both figures, the size of each sector is smaller than the actual size for easy viewing. In practice, the sector marked with an arrow toward the terminal in the center of the figure is large enough to cover the location of the terminal.

 In FIG. 2, each of base stations (BTS) A 20, B 21, C 22, and D 23 has three sectors α, β, and γ using a certain frequency F 1. Where terminal 30 is present, two sectors of base station A 20) 3, Ύ> one sector / 3 of base station B 21, two sectors α, γ of base station C 22 Thus, it is possible to mainly receive radio waves from seven sectors α and γ of two sectors of base station D 23.

 On the other hand, in FIG. 3, each of the base stations (BTS) A 20, B 21, C 22, and D 23 uses another frequency F 2, and is different from the arrangement of FIG. It has sectors α, β, and γ. In the place where the terminal 30 is located, one sector γ of the base station Α 20, two sectors α and β of the base station Β 21, base station C 22 Radio waves from five sectors, one sector γ of the base station D 23 and one sector α of the base station D 23.

Next, the operation of the CDM mobile communication system of the present invention will be described with reference to FIG. The terminal 30 communicating with the frequency F1 via the base station A20 and the base station B21 communicates with the base stations A20 and B21 (each sector) together with other base stations (of the respective sectors) while communicating. The pilot signal from each sector) is searched and the signal strength (signal power to interference wave power ratio) is measured. When approaching the base station C22, the signal strength of the pilot signal from the base station C22 that is not in a handover determines the threshold (T—ADD) for adding to the handover base station. If it exceeds (S l), the terminal 30 sends a pilot strength report (PSMM) to the base station controller 10 via the base station A 20 and base station B 21 that are currently communicating. Do (S2).

 The terminal 30 also searches (signal strength measurement) for a pilot signal from another base station (each sector) during handover, and performs a pilot signal from a certain base station (sector). When the signal strength of the signal falls below the threshold (T—DROP) for removal from the handover group, the terminal 30 sends a signal to the base station controller 10 via the communicating base station. And conduct a pilot strength report (PSMM).

Further, the terminal 30 measures the signal strength for the pilot signal from each base station (sector) during the handover, as needed, according to the content specified by the message from the base station. The pilot strength report (PMR) is sent to the base station 10 via the communicating base station (S2) _c. The setting for this PMR report is made at the elapse of a predetermined cycle time (periodical). Reports), when the frame error on the wireless link exceeds a predetermined threshold, and when there is a report request from the base station.

Upon receiving these pilot strength reports (PSMM and PMR) from the terminal 30, the base station controller 10 analyzes the type and content of the pilot strength reports, and a new The number of base stations (sectors) that have been requested to be added to the handover or deleted from the handover are detected, and the PMR provides a pilot signal for each base station (sector) during the handover. Detect the power to interference wave power ratio. In the base station controller 10, conditions for performing the characteristic hard handover in the present invention are set in advance by a system administrator. The first condition is that the sum of the number of sectors during a handover (active set) and the number of sectors during an additional request for a handover (candy set) is a predetermined threshold (for example, Any number between 3 and 7: hereinafter referred to as the sector number threshold). The second condition is that in all sectors during handover, the signal strength of the pilot signal (signal power to interference power ratio), an arbitrary threshold value equal to or higher than T-DROP (for example, T-DROP to T-ADD) Any level between +2 dB: below the intensity threshold). The third condition is when the first condition and the second condition are simultaneously satisfied. Of the above three conditions, the actual conditions under which the hard handover is performed are set in advance. In this setting, when there are a plurality of terminals 30, any one of the three conditions can be arbitrarily set for each terminal. When the ratio of pilot signal power to interference wave power in all sectors during handover falls below T-DROP, all sectors are subject to deletion from handover and hard handover becomes necessary. This is the same as in the past.

 Furthermore, the base station controller 10 registers, for each terminal 30, information on all the sectors currently in handover and all the sectors requesting the handover addition.

 The base station controller 10 compares the analysis result of the above-mentioned pilot strength report with the set and registered hard handover condition and the number of sectors during the current handover and requesting addition, and the terminal 30 It is determined whether or not to make a hard handover to another frequency.

If the first condition above (when the total number of sectors during the handover and during the addition request exceeds the sector number threshold) is set as the condition of the handover, the pilot strength is set. Report (PS MM) Add the number of sectors requested to add a handover to the number of sectors that are already being handed over and requesting an addition before the report, and compare the total number with the sector count threshold. If the total number does not exceed the number-of-sectors threshold, the reported sector is added to the handover at the terminal 30 (active set) and an addition request is made (candidate set). If the total number exceeds the sector number threshold, the terminal 30 is caused to perform a hard handover to another available frequency. If the above second condition (when the pilot signal strengths of all sectors during the handover do not exceed the strength threshold) is set as the hard handover condition, the pilot strength is set. The pilot signal strength of each sector during handover reported in the report (PMR) is compared with the strength threshold. If the pilot signal strength of any one of the sectors exceeds the strength threshold, hard handover for terminal 30 is not performed. If the pilot signal strength does not exceed the power threshold in all sectors, the terminal 30 is hard handed over to another available frequency.

 When the third condition (the first condition and the second condition) is set as the condition of the hard handover, the judgment result based on the first condition and the judgment result based on the second condition are set. If the result indicates that a hard handover bar is required, the terminal 30 is caused to perform a hard handover to another available frequency.

When the base station controller 10 determines that it is necessary to perform a handover to the terminal 30 as a result of the determination under the above-described various conditions, the base station controller 10 sets a signal to each base station communicating with the terminal 30. (S 3). _(Of course, at this frequency F 2, the above-mentioned condition of hard handover is satisfied.) After that, the base station controller 10 sends a hardware request to the terminal 30 via the base station A 20 and the base station B 21. A signal for handover control is transmitted (S4).

 The terminal 30 that has received the handover control signal performs control to move to the frequency F2 and resumes communication at the frequency F2. As a result, abnormal disconnection of a call that is likely to occur if the frequency remains at F1 can be prevented.

 Next, another embodiment of the CDMA mobile communication system of the present invention will be described with reference to FIG.

 In this embodiment, instead of changing the sector configuration in each base station, as shown in FIG. 4, the arrangement itself of each base station is changed for each frequency, thereby achieving the same effect as in the previous embodiment. The effect can be obtained.

In FIG. 4, each of base stations (BTS) A 20, B 21, C 22, and D 23 has three sectors α, β, and γ using frequency F 1. The base station (BTS) Ε 24, F 25, G 26, and 7 27 each have three sectors α, β, and γ using the frequency F 2. When the terminal 30 uses the frequency F2, the base station Ε 24, sector _y , the base station F25, sector 3), the base station G26, sector J3, and the base station H27, sector γ Can be connected.

Industrial applicability:

 As is apparent from the above description, according to the present invention, the electric field of the transmission wave from each base station is strong in a mobile terminal located in a place (sector dense area) where signals from a plurality of base stations can be received. Nevertheless, when the transmission waves from each base station become interference waves with each other and stable downlink signals cannot be received, the base station arrangement configuration or another carrier having a different sector arrangement configuration within the same base station may be used. Since the hard handover is performed on the rear frequency, abnormal disconnection during communication can be prevented, and a CDMA mobile communication system capable of performing stable communication can be provided.

Claims

The scope of the claims 1. Each radio carrier corresponding to a plurality of carrier frequencies is divided into a plurality of sectors, and each radio area is arranged so as to partially overlap each other in the same service area, and each radio area is arranged in parallel. It has multiple base stations that control wireless transmission and reception with mobile terminals while transmitting pilot signals.  A plurality of sectors in each of the plurality of base stations and a mobile terminal can be simultaneously connected using one carrier frequency,  Each of the base stations has a different sector configuration from each other for at least two different carrier frequencies,  When the mobile terminal connected to any base station using a certain carrier frequency receives pilot signals of signal strengths that can be simultaneously targeted for handover from a number of sectors exceeding a predetermined threshold value, A hard handover to another carrier frequency corresponding to another sector arranged differently with respect to the mobile terminal is performed. A CDMA mobile communication system characterized by the above feature.  2. Each radio carrier corresponding to a plurality of carrier frequencies is divided into a plurality of sectors, and each radio area is arranged so as to partially overlap each other in the same service area, and each radio area is arranged in parallel. A plurality of base stations that control wireless transmission and reception with mobile terminals while transmitting pilot signals.  A plurality of sectors in each of the plurality of base stations and a mobile terminal can be simultaneously connected using one carrier frequency,  Each of the base stations has a different sector configuration from each other for at least two different carrier frequencies, A packet from all sectors during handover received by the mobile terminal connected to any base station using a certain carrier frequency. If the signal strength of the pilot signal falls below a threshold value arbitrarily set within the range of signal strengths that can be targeted for handover, other sectors that are allocated differently to the mobile terminal concerned A hard handover to another carrier frequency corresponding to A CDMA mobile communication system characterized by the above feature.  3. Each radio carrier corresponding to a plurality of carrier frequencies is divided into a plurality of sectors, and each radio carrier is arranged so as to partially overlap each other in the same service area, and each radio carrier is arranged in parallel. A plurality of base stations that control wireless transmission and reception with mobile terminals while transmitting pilot signals.  A plurality of sectors in each of the plurality of base stations and a mobile terminal can be simultaneously connected using one carrier frequency,  Each of the base stations has a different sector configuration from each other for at least two different carrier frequencies,  The mobile terminal connected to one of the base stations using a certain carrier frequency receives, from a number of sectors exceeding a predetermined threshold value, a pilot signal of a signal strength that can be simultaneously subjected to handover, respectively. And, the signal strength of the pilot signals received by the mobile terminal from all the sectors during the handover is arbitrarily set within the range of the signal strength that can be the target of the handover. A CDMA mobile communication system characterized by performing a hard handover to another carrier frequency corresponding to another sector 2 arranged differently with respect to the mobile terminal when a threshold value is dropped below the threshold value. 4. Each radio carrier corresponding to a plurality of carrier frequencies is divided into a plurality of sectors, and each radio carrier is arranged so as to partially overlap each other in the same service area, and each radio carrier is arranged in parallel. It has multiple base stations that control wireless transmission and reception with mobile terminals while transmitting pilot signals. A plurality of sectors in each of the plurality of base stations and a mobile terminal can be simultaneously connected using one carrier frequency,  Each of the base stations has a different sector configuration from each other for at least two different carrier frequencies,  Further, the mobile terminal connects to any one of the base stations using a certain carrier frequency, and a unit for measuring a signal-to-interference-wave power ratio as a signal strength of a received pilot signal. Means for judging the measurement result and transmitting, to the connected base station, a handover addition request for the sector including the measurement result upon detecting that a new pilot signal having a predetermined strength or more is received. Means for transmitting signal strength reports of pilot signals from all sectors during handover to a connected base station in accordance with a preset timing,  Furthermore, while controlling the plurality of base stations to control the connection with the mobile terminal, the signal strength of the handover addition request and the gateway signal from the mobile terminal via the base station When the report is received, the mobile terminal is not subject to handover simultaneously from a number of sectors exceeding a predetermined threshold, which is a condition for performing a predetermined hard handover. Receiving the pilot signal of the obtained signal strength, and the signal strength of the pilot signals from all the sectors in the handover received by the mobile terminal is within the range of the signal strength that is not applicable to the handover. It is determined whether or not one or both of the conditions are satisfied below the threshold value arbitrarily set in, and if the above conditions are satisfied, , It said mobile terminal c to another Kiyaria frequencies corresponding to other sectors has a different arrangement relative to the - C D M A mobile communication system comprising: a base station controller to de handover. 5. Instead of each said base station having a different arrangement of sectors for at least two different carrier frequencies, at least two different A plurality of base stations to which only any one of the carrier frequencies is allocated, and which are located at different locations from each other. 2. The CDMA mobile communication system according to claim 1, wherein a hard handover to another carrier frequency corresponding to another base station having a different carrier frequency is performed.  6. Instead of each base station having a different sector arrangement for at least two different carrier frequencies, any one of at least two different carrier frequencies may be assigned. A plurality of base stations located at different locations from each other, and when performing a handover to the mobile terminal, a plurality of base stations corresponding to other base stations having different locations are provided. 3. The CDMA mobile communication system according to claim 2, wherein handover is performed. 7. Instead of each of the base stations having different sector arrangements for at least two different carrier frequencies, only one of at least two different carrier frequencies is assigned to each. A plurality of base stations located at different locations from each other, and when performing a handover to the mobile terminal, a hard handover to another carrier frequency corresponding to another base station having a different location is provided. 4. The CDMA mobile communication system according to claim 3, wherein over is performed. 8. Instead of each base station having a different arrangement of sectors for at least two different carrier frequencies, any one of at least two different carrier frequencies is respectively assigned. A plurality of base stations located at different locations from each other, and when performing a handover to the mobile terminal, a hard handover to another carrier frequency corresponding to another base station having a different location is provided. over- 5. The CDMA mobile communication system according to claim 4, wherein:  9. The CDMA mobile communication system according to claim 1, wherein each of the base stations has a different sector arrangement configuration for each different carrier frequency using the same adaptive array antenna. 10. The CDMA mobile communication system according to claim 2, wherein each of the base stations has a different sector arrangement for each different carrier frequency using the same adaptive array antenna. 11. The CDMA mobile communication system according to claim 3, wherein each of the base stations has a different sector arrangement configuration for each of different carrier frequencies using the same adaptive array antenna. system. 12. The CDMA mobile communication system according to claim 4, wherein each of the base stations has a different sector arrangement configuration for each different carrier frequency by using the same adaptive array antenna. 1 3. Each radio area corresponding to a plurality of carrier frequencies is divided into a plurality of sectors, and a plurality of base stations that control radio transmission and reception with mobile terminals while transmitting pilot signals in parallel In the same service area, each radio area is arranged so as to partially overlap each other, so that a plurality of sectors in each of the plurality of base stations and a mobile terminal can be simultaneously connected using one carrier frequency. A method for preventing a call disconnection in a densely populated sector in a CDMA mobile communication system.  Assigning at least two different carrier frequencies to each of the base stations at different locations, or to different sectors of the same base station; The mobile terminal connected to one of the base stations using a certain carrier frequency receives, from a number of sectors exceeding a predetermined threshold, a pilot signal having a signal strength that can be simultaneously subjected to a handover, respectively. Then A call disconnection prevention method, comprising: performing a hard handover to another carrier frequency corresponding to another base station or sector differently arranged for the mobile terminal.  14 4. Each radio carrier corresponding to a plurality of carrier frequencies is divided into a plurality of sectors, and a plurality of base stations that control radio transmission and reception with a mobile terminal while transmitting pilot signals in parallel are used for the same service. In the area, each radio area is arranged so as to partially overlap each other, and a plurality of sectors in each of the plurality of base stations and a mobile terminal can be simultaneously connected using one carrier frequency. A method for preventing call disconnection in a densely populated sector in a CDMA mobile communication system,  Assigning at least two different carrier frequencies to each of the base stations at different locations, or to different sectors of the same base station;  The signal strength of the pilot signals from all the sectors in the handover received by the mobile terminal connected to any base station using a certain carrier frequency can be targeted for handover. If the threshold falls below an arbitrarily set value within the range, a hard handover to another carrier frequency corresponding to another base station or sector differently arranged for the mobile terminal is performed, A call disconnection prevention method comprising the steps of: 15 5. Each radio carrier corresponding to a plurality of carrier frequencies is divided into a plurality of sectors, and a plurality of base stations controlling radio transmission / reception with a mobile terminal while transmitting a pilot signal in parallel with each other are provided. In the same service area, each radio area is arranged so as to partially overlap each other, and a plurality of sectors in each of the plurality of base stations and a mobile terminal can be simultaneously connected using one carrier frequency. A method for preventing call disconnection in densely populated sectors in CDMA mobile communication systems hand,  Assigning at least two different carrier frequencies to each of the base stations at different locations, or to different sectors of the same base station;  The mobile terminal connected to any base station using a certain carrier frequency receives pilot signals of signal strengths that can be simultaneously handed over from a number of sectors exceeding a predetermined threshold value, and If the signal strength of pilot signals from all sectors during handover received by the mobile terminal falls below a threshold arbitrarily set within the range of signal strengths that can be targeted for the handover. Performing a hard handover to another carrier frequency corresponding to another base station or sector that is differently arranged with respect to the mobile terminal. 16. Each radio carrier corresponding to a plurality of carrier frequencies is divided into a plurality of sectors, and a plurality of base stations that control radio transmission and reception with a mobile terminal while transmitting pilot signals in parallel are the same. In the service area, each radio area is arranged so as to partially overlap with each other, so that a plurality of sectors in each of the plurality of base stations and a mobile terminal can be simultaneously connected using one carrier frequency. A method for preventing a call disconnection in a densely populated sector in a CDMA mobile communication system.  Assigning at least two different carrier frequencies to each of the base stations at different locations, or to different sectors of the same base station; In the mobile terminal, by measuring the signal-to-interference power ratio as the signal strength of the received pilot signal, when it is detected that a pilot signal having a predetermined strength or more is newly received, A handover addition request of the corresponding sector including the measurement result is transmitted to the connected base station. And transmitting a signal strength report of a pilot signal from all the sectors during handover to the connected base station in accordance with a preset timing, and controlling the connection with the mobile terminal. In a base station control device that controls a base station, when the handover addition request and the signal strength report of the pilot signal from the mobile terminal via the base station are received, a hardware set in advance is set. The mobile terminal receives, from the number of sectors exceeding a predetermined threshold, a pilot signal of a signal strength that can be simultaneously subjected to handover, which is a condition for performing handover, and The signal strength of the pilot signals received by the terminal from all the sectors in the handover bar may be subject to the handover. It is determined whether a value falls below a threshold value arbitrarily set within the range of, or whether one or both of the conditions are satisfied.If the condition is satisfied, the mobile terminal is Perform a hard handover to another base station or another carrier frequency corresponding to sector 2 A call disconnection prevention method comprising the steps of: