JP2006222560A - Call reception control apparatus, call reception control method, and wireless base station - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a call reception control technology whereby a base station can automatically set and automatically update a call reception threshold value to be used by the base station autonomously so that an optimum cell coverage and an optimum load margin can be obtained. <P>SOLUTION: A call reception control apparatus (30) for an uplink in a mobile communication system includes: a permissible interference amount calculation means (41) for calculating a permissible interference amount by each mobile station on the basis of a report value transmitted from each mobile station to the base station and a state of wireless resources in the base station; a storage/statistics arithmetic means (43) for storing a prescribed number of the permissible interference amounts by each mobile station and applying statistics processing to the permissible interference amounts to calculate the call reception threshold value; and an uplink call reception storage medium (60) for controlling the reception of calls from each mobile station on the basis of the call reception threshold value. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a call for determining whether or not a mobile station newly requesting connection to a base station can be accepted in a W-CDMA cellular system in which the same frequency band is shared between users using a code division multiple access method. In particular, the present invention relates to a call admission control technique in which a base station autonomously sets and automatically updates a call admission threshold, which is a criterion for determining whether or not to accept a call on an uplink.

  In the code division multiple access system, the same frequency band is shared by a plurality of communication waves by spreading the frequency with a spreading code (code sequence) that allows each communication wave to be detected and distinguished from each other. For example, in the uplink of a W-CDMA cellular system, each mobile station uses a different spreading code (channelization code) so that it can be distinguished on the receiving side even if one mobile station sets up multiple channels at the same time and performs communication. Is spread within the mobile station. Further, in order to be able to freely and repeatedly use a limited number of channelization codes in the system, different signals are added to the multiplexed signals using different spreading codes (scrambling codes) for each mobile station. Spread and transmit. For this reason, the base station on the uplink receiving side receives a large number of channels from a plurality of mobile stations simultaneously within the same frequency band, but can be discriminated under certain conditions.

  In order for a base station to detect, identify and correctly demodulate a number of channels from a plurality of mobile stations received simultaneously within the same frequency band for each communication, the communication quality of the demodulation target channel must be sufficient. . If the radio propagation environment is constant, the channel communication quality is determined by the ratio (SIR) of the received signal power of the channel to be demodulated and the interference noise power considering the processing gain. Interference noise power is the sum of the power of the delay wave of the demodulation target channel that has arrived at the receiver of the base station, the interference of other channels, and the thermal power of the receiver, but the despreading process to restore the spread channel Later, the processing gain is reduced to 1 / spread code code length per information bit. Since the channel to be demodulated also causes interference in the same way as described above, the mobile station sets the transmission power to a large value and increases the received signal power at the base station to obtain an unnecessarily high communication quality. Attempting to do so is not allowed. The base station controls the transmission power of the mobile station at high speed (high-speed transmission power control) so that communication is performed with the minimum transmission power necessary to obtain sufficient communication quality for the radio propagation environment.

  As the number of communications performed simultaneously within the same frequency band increases, the total received power level at the base station receiver increases. This is because the interference power noise increases as the number of channels increases, and the mobile station performing high-speed transmission power control increases the transmission power in an attempt to secure the required SIR of each channel, which further increases the interference power noise. This is to cause an increase. If the upper limit transmission power of the mobile station is sufficiently large, the number of simultaneous communication channels can be increased to near the limit capacity (pole capacity), but in reality there is an upper limit on the transmission power of the mobile station. For this reason, the transmission power reaches the upper limit first from a mobile station with a large propagation loss from the base station, and it is not possible to obtain sufficient communication quality, so the channel being communicated is forcibly disconnected or new communication is to be started. There arises a problem that the connection request of the mobile station does not reach the base station with sufficient communication quality. This is also referred to as cell breathing because it has the same effect as virtually reducing cell coverage. Even if the upper limit transmission power of the mobile station can be made infinite, it is impossible in principle to accommodate the number of simultaneous communication channels exceeding the pole capacity.

  Therefore, in order to protect the communication quality of the channel being communicated and the new connection request from the mobile station at the cell coverage end and prevent the cell coverage from being reduced, the amount of increase in the total received power level is designed in advance. It is necessary to control the number of communications performed simultaneously in the same frequency band so as not to greatly exceed (load margin). However, if the amount of increase in the total received power level exceeds the set value, if the channel of the mobile station in communication is forcibly disconnected, the convenience for the user is significantly impaired. For this reason, when the amount of increase in the total received power level approaches the load margin, reception of a call (channel setting) to a mobile station that has newly requested a connection is rejected. By doing this, it is possible to control the number of communications performed simultaneously so that the probability that the amount of increase in the total received power level exceeds the load margin is reduced while protecting the channel of the mobile station already communicating. At this time, the amount of increase in the total received power level at which the base station starts a call acceptance refusal state for a mobile station that has newly requested a connection is referred to as a call acceptance threshold. In general, the call acceptance threshold is set to a value that is several dB smaller than the load margin. The amount of increase in the total received power level is defined with reference to receiver thermal noise.

  As described above, if a large load margin is set, the number of simultaneous communication channels increases. However, since the call acceptance threshold is set to be large, the increase in the total received power level at the base station receiver may also increase. is there. As a result, the guaranteed cell coverage is reduced. Conversely, if a small load margin is set, the number of simultaneous communication channels is reduced, but the call admission threshold is set to be larger accordingly, so that an increase in the total received power level at the base station receiver is suppressed to a small level. Therefore, the guaranteed cell coverage is expanded. That is, since the load margin and the guaranteeable cell coverage are in a trade-off relationship, it can be seen that the call acceptance threshold needs to be designed according to the service area.

  In a conventional macro cell (cell radius of 10 km or less) or micro cell (cell radius of 3 km or less) environment, the maximum transmittable power of the mobile station, antenna gain of both the mobile station and the base station, feed loss, base station reception sensitivity, required Cell design system that can take into account rough urban structure using electronic map when SIR, shadowing margin and fading margin, indoor intrusion loss, diversity gain, urban structure (propagation estimation formula) are given as conditions With the support of (computer), he designed the load margin and the guaranteed cell coverage. More specifically, a link budget (for example, see Non-Patent Document 1) is used to derive the relationship between the above-described cell design parameters, the load margin, and the maximum allowable propagation loss (cell radius), and the load margin. And was designing cell coverage.

  A design that determines cell coverage by determining the load margin is called “design under capacity limitations”, and conversely, design that determines the load margin by determining cell coverage is “designed under coverage limitations”. " In general, in a densely populated area in a metropolitan area where geographical communication traffic density is high and traffic is accommodated by building a service area with a large number of cells with a small cell radius. Design ". Conversely, when the service area is economically constructed with a small number of cells with a large cell radius and low geographical communication traffic density, such as in a depopulated area in rural areas, “design under coverage restrictions” Become. Actually, there are many places that require intermediate design between metropolitan areas and rural areas such as local cities and suburbs, and each base station is designed individually, or a design example in a typical urban structure A design example that is closest to the surrounding environment of the base station to be designed is selected, and an error from the actual surrounding environment is accepted, and a call acceptance threshold corresponding to that is applied. ing. In either case, decision making (cell system design) by radio network designers and verification work (cell system evaluation) by field experiments must be performed. This necessitates repeated redesigns, which is a cumbersome operation.

A technique has been proposed in which a base station determines whether or not to accept a new call while coping with the reduction and expansion of cell coverage according to the increase and decrease of the load in the cell (see, for example, Patent Document 1). When accepting a new call, the base station requests a new connection from the user to determine whether another call can be accepted without adversely affecting the QoS of the already established communication. Then, the value representing the gain of the transmission channel between the user and the base station and the newly added load are compared with the highest expected load (maximum allowable load). That is, if the channel gain exceeds the maximum allowable load and can be transmitted, and the new load is within the range of the maximum allowable load, the connection is permitted. In this document, the maximum allowable load value as a call admission threshold is determined and monitored by a radio resource manager (RRM) of a radio network controller (RNC) that controls a group of neighboring base stations.
"W-CDMA mobile communication system", pp. 187-202, supervised by Keiji Tachikawa, Maruzen Co., Ltd., June 2001 JP 2004-40756 A

  In a cell smaller than a macro cell or a micro cell, such as a street micro cell (cell radius of 1 km or less) or a pico cell (cell radius of 0.5 km or less), which is considered to be mainstream in the future, a load margin using a link budget, Designing cell coverage that can be guaranteed becomes more difficult. This is explained as follows.

  In macro and micro cells, antenna coverage is installed at high locations such as towers, rooftops of high-rise buildings, and summits to form wide-area cell coverage. Since the propagation distance to the cell edge is relatively long, the influence of individual buildings is statistically averaged for each direction as seen from the base station, so the cell edge is close to a hexagon that is smoothly continuous. Can be formed. For this reason, it was possible to accurately estimate the propagation loss at the cell edge using the propagation estimation formula defined for each rough city structure. That is, as described above, the cell design parameter and load margin using the link budget and the maximum allowable propagation loss (with the assistance of the cell design system considering the rough city structure using the electronic map) Cell radius) was derived, and it was possible to design a load margin and a guaranteed cell coverage.

  On the other hand, in a street micro cell or a pico cell, a cell coverage in a narrow area is formed by installing an antenna at a position lower than a building around a base station. Because the propagation distance to the cell edge is relatively short, it is easily affected by individual buildings and features for each direction seen from the base station, and cells with discontinuous and complicated shapes (amoeba) are formed at the cell edge. Will be. For this reason, it is difficult to accurately estimate the propagation loss at the cell edge using the propagation estimation formula defined for each rough city structure.

  In a cell design system that estimates propagation loss by the ray tracing method, it is possible to consider individual buildings and features when estimating propagation by allowing a large amount of calculation. However, since the electronic map cannot completely describe the real environment such as the detailed shape of the building, and the information of the electronic map does not have real-time characteristics that follow the real environment that changes over time, its estimation accuracy Is not enough. In addition, since the aspect varies greatly depending on the direction seen from the base station, a unique derivation of the relationship between the cell design parameters using the link budget and the load margin, the maximum allowable propagation loss (cell radius), and the load margin It becomes difficult to design a guaranteed cell coverage.

  Furthermore, the cell-reduction measures that expand the service area with street microcells and picocells are effective in overcoming propagation loss and increasing user throughput and system capacity. However, since the number of base stations increases significantly, cell systems There has been a problem that the design / evaluation work is greatly complicated.

  Accordingly, the present invention provides a call admission control capable of automatically setting and updating a call admission threshold to be used by a base station in order to automate the design of a load margin and a guaranteeable cell coverage. The purpose is to provide technology.

  In addition, a call admission control technology that can autonomously update a call admission threshold adapted to a change in the environment, even in a fluid network form, without requiring a radio resource manager for controlling the base station group. The purpose is to provide.

  In order to realize this, the call reception threshold to be used by the base station is autonomously determined by using the report value from the mobile station while recognizing the actual surrounding environment. In such a configuration, a plurality of design examples in a conventional system, that is, a typical urban structure, are determined, a design example closest to the surrounding environment of the base station to be designed is selected, and a call acceptance threshold corresponding to the design example is selected. The system efficiency is better than when applying.

Specifically, according to a first aspect of the present invention, there is provided a call admission control device that controls uplink call admission in a mobile communication system. The call admission control device
(A) an allowable interference amount calculating means for calculating an allowable interference amount for each mobile station based on a report value transmitted from the mobile station to the base station and a state of radio resources in the base station;
(B) Accumulation / statistical calculation means for calculating a call admission threshold by accumulating a certain number of allowable interference amounts for each mobile station and performing statistical processing;
(C) comprising uplink call admission control means for controlling admission of a call from the mobile station based on the call admission threshold.

  According to such a call admission control device, the base station can automatically set and automatically update the call admission threshold while recognizing the actual surrounding environment.

  As a good configuration example, when a predetermined condition is satisfied, for example, the allowable interference amount for each mobile station is accumulated and statistical processing is performed only in a time zone in which the uplink interference amount at the base station is a constant value.

  Thereby, it is possible to set a call admission threshold representing the characteristics of the mobile station over the entire cell coverage.

  As another good configuration example, a correction value setting unit is provided that generates a correction value for correcting the call acceptance threshold when the deterioration rate of the communication quality of the uplink channel exceeds a certain ratio.

  The correction value setting means generates a correction value that sets, for example, a call acceptance threshold value smaller than the current value when the deterioration rate of the communication quality exceeds a certain rate.

  As a result, the call acceptance threshold can be automatically set to an optimum value that more closely matches the current situation.

  In a second aspect of the present invention, a radio base station in a mobile communication system is provided. The radio base station receives and monitors a report value transmitted from the mobile station, and monitors a state related to the uplink channel, and a report value acquired by the transmitter / receiver and a state related to the uplink channel And a call admission control device that controls call admission on the uplink. The call admission control device calculates the allowable interference amount for each mobile station based on the report value received by the transceiver and the state of the radio resource in the radio base station, and calculates the allowable interference amount for each mobile station. A fixed number of calls are accumulated and subjected to statistical processing to automatically set a call acceptance threshold and control call acceptance based on the call acceptance threshold.

In a third aspect of the present invention, a call admission control method in a mobile communication system is provided. The call admission control method is
(A) receiving a report value at a base station from a mobile station belonging to a cell;
(B) monitoring the state of radio resources in the base station;
(C) calculating an allowable interference amount for each mobile station based on the report value and the state of radio resources;
(D) accumulating a certain number of allowable interference amounts for each mobile station, calculating a call acceptance threshold by performing statistical calculation,
(E) controlling the acceptance of a call from the mobile station based on the call acceptance threshold.

  With the configuration and method described above, the base station can automatically set and automatically update the call acceptance threshold to be used. This makes it possible to automate the optimum design of the load margin and the guaranteed cell coverage.

  Work such as cell system design and cell system evaluation by the radio network designer can be reduced, and it is not necessary to repeat redesign as the base station is newly installed or the radio environment changes.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of a cellular mobile communication system 1 to which call admission control according to the present invention is applied. The mobile communication system 1 includes a radio base station 2 and a mobile station 3. The radio base station 2 may be fixed or mobile. A plurality of mobile stations 3 exist under the radio base station 2, and the radio base station 2 is simultaneously connected to the plurality of mobile stations 3 through a radio interface. In FIG. 1, only a single mobile station 3 is shown for convenience.

  The mobile station 3 includes, in the radio unit 70, a downlink channel receiving unit 71 that receives a signal from the radio base station 2 via a reception antenna, and an uplink channel that transmits a signal to the radio base station 2 via a transmission antenna. It has a transmission means 72. Further, the mobile station report value generation means 80 reports a report value indicating a communication state in the mobile station 3, for example, current transmission power, maximum transmittable power, or reception power of the common control channel from the radio base station 2. A value is generated and transmitted from the transmission antenna to the radio base station 2.

  The radio base station 2 includes a transceiver 10 having a radio function necessary for the mobile communication system 1 and a call admission control device 30 that performs admission control of a call from the mobile station.

  The transceiver 10 includes a downlink channel transmission unit 11, an uplink channel transmission unit 12, and a monitoring unit 20.

  The downlink channel transmission means 11 generates a radio signal of a downlink channel such as a control channel (common control channel, dedicated control channel) or a communication channel (common communication channel, dedicated communication channel), and transmits it from the transmission antenna.

  Uplink channel transmission means 12 receives a radio signal via a receiving antenna, and receives a radio signal of an uplink channel such as a control channel (common control channel, dedicated control channel) or a communication channel (common communication channel, dedicated communication channel). To process. The report value generated and transmitted by the mobile station 3 is also received by the uplink receiving means 12 via the receiving antenna.

  The monitoring unit 20 monitors the overall wireless communication status including monitoring of the report value from the mobile station 3. The detailed configuration and function of the monitoring unit 20 will be described later with reference to FIG.

  The call admission control device 30 includes an analysis unit 50, a call admission threshold setting update unit 40, and an uplink call admission control unit 60. The analysis unit 50 analyzes necessary information among the information collected by the monitoring unit 20 of the transceiver 10. The detailed configuration and function of the analysis unit 50 will also be described later with reference to FIG.

  The call acceptance threshold setting update unit 40 automatically sets and updates a call acceptance threshold that is a criterion for call acceptance based on monitoring information including a report value from the mobile station 3 and an analysis result of the analysis unit 50. More specifically, the allowable interference amount calculation means 41 obtains the maximum (allowable) interference amount of each mobile station based on the report value from the mobile station and the analysis result of the monitoring information. On the other hand, the correction value setting means 42 generates a correction value for correcting the call admission threshold based on the actual deterioration rate such as SIR and block error rate obtained by the monitoring means 20 and the service type of the mobile station. .

  The accumulation / statistical calculation means 43 samples all or a part of the allowable interference amount calculated for each mobile station and performs statistical processing, and if correction is necessary, the correction value generated by the correction value setting means 42 is used. By applying, a call admission threshold that is uniformly applied to mobile stations distributed in the cell is calculated. The calculated call acceptance threshold is the output of the call acceptance threshold setting update unit 40.

  The uplink call admission control means 60 determines whether or not to implement call admission control from the call admission threshold set by the call admission threshold setting update unit 40 and the amount of uplink interference. If it is determined that the call admission control is to be performed, the uplink channel receiving means 12 stops the call acceptance of the mobile station newly requesting connection, and the downlink channel means 11 is stopping the call acceptance on the broadcast channel. Posts information indicating that it is.

  FIG. 2 is a detailed block diagram of the radio base station 2. In the example of FIG. 2, the radio base station 2 is connected to the mobile communication network through a radio control device (not shown), but adopts a base station configuration that autonomously configures the network without requiring the radio control device. Also good.

  In the transceiver 10, the radio resource monitoring means 21, the uplink channel monitoring means 22, the mobile station report value monitoring means 23, and the communication quality monitoring means 24 constitute a monitoring means 20 (see FIG. 1).

  The communication quality monitoring means 24 is connected to the uplink channel receiving means 12 and monitors the communication quality of the currently connected mobile station, such as SIR and block error rate. When the deterioration rate of the communication quality exceeds a certain ratio, the correction value setting unit 42 of the call reception threshold setting update unit 40 is instructed to correct the call reception threshold.

  The mobile station report monitoring means 23 is connected to the uplink channel receiving means 12 to monitor the report value from the mobile station 3 and sends the mobile station report value to the allowable interference amount calculation means 41 of the call admission threshold setting update unit 40. Provide information. Specific examples of the mobile station report value information will be described in each embodiment described later.

  The uplink channel monitoring unit 22 is connected to the uplink channel receiving unit 12 to monitor the uplink channel, and provides the uplink channel type and the received power value to the analysis unit 50 of the call admission control device 30.

  The radio resource monitoring unit 21 is connected to the uplink channel receiving unit 12 and the downlink channel transmitting unit 11 to monitor radio resources, and transmits the common control channel as radio resource monitoring information to the analyzing unit 50 of the call admission control device 30. Provides power and uplink interference.

  On the other hand, in the call admission control device 30, the common control channel transmission power analysis means 51, the uplink interference amount analysis means 52, the uplink channel reception power analysis means 53, the uplink channel type analysis means 54, and the mobile station specification storage means 55 Thus, the analysis means 50 (see FIG. 1) is configured. The mobile station specification storage means 55 stores the correspondence relationship between the uplink channel type and the maximum transmittable power of the mobile station.

  The common control channel transmission power from the radio resource monitoring unit 21 is supplied to the common control channel transmission power analysis unit 51, and the uplink interference amount is supplied to the uplink interference amount analysis unit 52.

  The uplink channel received power acquired by the uplink channel monitoring means 22 is supplied to the uplink channel received power analyzing means 53, and the uplink channel type information is supplied to the uplink channel type analyzing means 54. The uplink channel type identification means 54 determines the uplink channel type based on the correspondence between the uplink channel type supplied from the mobile station specification storage means 55 and the maximum transmittable power of the mobile station, and the maximum transmission of the mobile station. Replace with possible power.

  The analysis results of these analysis units 51 to 54 are input to the allowable interference amount calculation unit 41 of the call acceptance threshold setting update unit 40. The allowable interference amount calculation means 41 calculates the allowable interference amount for each mobile station based on the mobile station report value and the analysis result.

  The accumulation / statistical calculation means 43 of the call acceptance threshold setting update unit 40 accumulates a certain number of samples of the allowable interference amount supplied from the allowable interference amount calculation means 41. Then, according to the setting information designated by the setting means 35, the cumulative probability distribution of the sample is calculated, and if there is a correction, the call acceptance threshold is calculated in consideration of the correction value. The calculation result is output to the uplink reception control means 60.

  The setting unit 35 sets a processing target and conditions for generating the cumulative probability distribution of the allowable interference amount. Details of the setting information will be described later in each embodiment. Examples of the setting information include the service type of the mobile station that is the target of the cumulative probability distribution, the input threshold that restricts the input of the allowable interference amount, and the deterioration of the communication quality. It includes a permissible deterioration rate that controls the rate of occurrence of an increase in interference amount that can be caused, a predetermined reduction value that is used to determine a call acceptance threshold from a statistical calculation result of the permissible interference amount, and the like.

FIG. 3 is a schematic diagram for explaining a call admission control method according to the first embodiment of the present invention. In the cell coverage of the radio base station (BS) 2, i-th mobile station 3j _{i of} mobile station type (service type) #j and i′-th mobile station 3k _{i ′ of} mobile station type #k are shown. Has been. Maximum transmittable power value is determined for each mobile station type, # j in Tx _{MS_Maxpow_j} [dBm], it is set to # k in Tx _{MS_Maxpow_k} [dBm]. The current transmission power value of the mobile station is Tx _{MS_pow_j_i} [dBm] in the i-th mobile station 3j _{i of #j} , and Tx _{MS_pow_j_i ′} [dBm] in the _i'- th mobile station 3k _{i of #k.} ing.

  The transmission power of the mobile station 3 is controlled at a high speed by the base station 2 so as to be a minimum value necessary for obtaining a sufficient communication quality with respect to the radio propagation environment, and varies with the passage of time. The mobile station 3 measures its own transmission power value and periodically reports it to the base station 2 together with the maximum transmittable power. A control channel may be used for transmission of the report value, or it may be encoded and transmitted as control information in the communication channel.

The base station 2 measures the relative value I _BS [dB] of the amount of uplink interference from the receiver thermal noise power N as one of the radio resource states in the radio resource monitoring means 21. Using the uplink interference amount I _BS and the report value from each mobile station 3, the allowable interference amount calculation means 41 calculates the maximum uplink interference amount (allowable interference amount) that can be allowed for each mobile station. That is, for the i-th mobile station 3j _i of the mobile station type #j, the allowable interference amount I _{BS_allow_j_i} [dB] shown in the equation (1) is set for the _i′- th mobile station 3k _{i ′} of the mobile station type #k. Calculates the allowable interference amount I _{BS — allow_k — i ′} [dB] shown in Equation (2). The allowable interference amount takes a value of 0 or more.

実際には、動局のサービス種別は、＃ｊと＃ｋの２種類に限定されるわけではない。また、セルカバレッジ内には多数の移動局３が存在するため、報告値を送信してくる移動局３の数に応じて、許容干渉量の標本数も増加する。

Actually, service types of mobile stations are not limited to two types, #j and #k. In addition, since there are many mobile stations 3 in the cell coverage, the number of samples of the allowable interference amount increases according to the number of mobile stations 3 that transmit the report value.

  As shown in FIG. 4A, the cumulative / statistical calculation means 43 of the base station 2 statistically analyzes the sample for the mobile station type to be considered designated in advance by the setting means 35 from the obtained whole samples. An arithmetic processing is performed to calculate a cumulative probability distribution graph shown in FIG. However, the entire specimen is regularly updated to the latest status.

In the cumulative probability distribution graph of FIG. 4B, the horizontal axis represents the allowable interference amount, and the vertical axis represents the ratio of the samples having the allowable interference amount equal to or less than the value on the horizontal axis. Therefore, when a certain amount of uplink interference is assumed on the horizontal axis of the cumulative probability distribution graph, the corresponding vertical axis represents the ratio of mobile stations that cannot tolerate the amount of uplink interference even if transmission is performed with the maximum transmittable power. This means the ratio of mobile stations whose communication quality and connection quality deteriorate even when transmitted. In other words, the value on the horizontal axis corresponding to the rate of increase in the amount of interference that causes deterioration in communication quality in the mobile station 3 existing in the cell coverage (allowable deterioration rate) should be set in the base station 2 The upper limit value lm _BS [dB] of the allowable interference amount. The maximum allowable interference amount (call acceptance threshold) must be set so that the allowable deterioration rate is less than a certain value. By replacing the upper limit value lm _BS of the allowable interference amount with a load margin and setting a positive value (default reduction value) smaller than the upper limit value of the allowable interference amount by a predetermined number dB, the call admission threshold Thr _CAC [dB] Can be determined automatically.

When this is seen in FIG. 4A, the result of subtracting the predetermined reduction value from the upper limit value lm _BS of the allowable interference amount determined from the statistical calculation processing result and the specified allowable deterioration rate becomes the call acceptance threshold value Thr _CAC. .

  Thus, in the first embodiment, the mobile station 3 transmits a set of the current transmission power and the maximum transmittable power to the base station 2 as a report value. The base station 2 calculates the allowable interference amount for each mobile station 3 from the report value from the mobile station 3 and the radio resource state (uplink interference amount) in the base station 2, accumulates a certain amount of samples, and performs statistical calculation. Processing is performed to calculate a call acceptance threshold.

  FIG. 5 is a schematic diagram for explaining a call admission control method according to the second embodiment of the present invention. In the second embodiment, the report value from the mobile station 3 is replaced with the set of the maximum transmittable power value and the current transmit power value, and the difference value between the maximum transmittable power value and the current transmit power value [(maximum transmittable power Value) − (current transmission power value)], which is the same as in the first embodiment.

The difference value of the i-th mobile station 3j _i of the mobile station type #j is expressed as Tx _{MS_margin_j_i} [dB] in the equation (3), and the difference value of the _i′- th mobile station 3k _{i ′} of the mobile station type #k is expressed as the equation If Tx _{MS_margin_k_i ′} [dB] in (4), the maximum uplink interference amount (allowable interference amount) that can be allowed for each mobile station is calculated using the uplink interference amount and the report value (difference value) from the mobile station 3, For the i-th mobile station 3j _i of the mobile station type #j, I _{BS_allow_j_i} [dB] (see Equation (5)), and for the _i′- th mobile station 3k _{i ′} of the mobile station type #k, I _{BS_allow_k_i ′} [dB]. (See Equation (6)).

得られた許容干渉量の標本全体から呼受付閾値を決定する過程は、図４（ａ）および図４（ｂ）を参照して説明した内容と同様である。このようにすることで、移動局３から基地局２へ送信される報告値の情報量を第１実施形態よりも低減しつつ、セルカバレッジ全体にわたって適正な呼受付閾値Thr_CAC［ｄＢ］を、適応的に自動決定することができる。

The process of determining the call acceptance threshold from the entire sample of the obtained allowable interference amount is the same as that described with reference to FIGS. 4 (a) and 4 (b). By doing in this way, while reducing the information amount of the report value transmitted from the mobile station 3 to the base station 2 as compared with the first embodiment, an appropriate call admission threshold Thr _CAC [dB] over the entire cell coverage is set. It can be automatically determined adaptively.

6 and 7 are schematic diagrams for explaining the call admission control method according to the third embodiment of the present invention. In the third embodiment, the radio base station (BS) 2 transmits a common control channel toward the cell coverage, and the mobile station 3 belonging to the cell measures the reception power of the common control channel and the result value To the base station 2 Rx _{BS_pow_CPICH_j_i} [dBm] is the received power value of the common control channel in the i-th mobile station 3j _i of the mobile station type #j, and the _i′- th mobile station 3k _{i ′ of the} mobile station type #k. The reception power value of the common control channel at Rx _{BS_pow_CPICH_k_i ′} [dBm] and the transmission power value of the common control channel transmitted by the base station 2 are Tx _{BS_pow_CPICH} [dBm].

The received power value at the base station (BS) 2 of the uplink channel such as the control channel or communication channel used for transmission of the report value by the mobile station 3 is set as Rx _{MS_pow_j_i} for the i-th mobile station 3j _i of the mobile station type #j. [ _DBm ], Rx _{MS_pow_k_i ′} [dBm] for the _i′- th mobile station 3k _{i ′} of the mobile station type #k. Further, the uplink channel type is Ch _{MS_j_i} for the i-th mobile station 3j _i of the mobile station type #j and Ch _{MS_k_i ′} for the _i′- th mobile station 3k _{i ′} of the mobile station type #k.

For example, the base station 2 refers to the conversion table 55a set in advance in the mobile station specification storage means 55 and reads the uplink channel type in each mobile station as the maximum transmittable power of the mobile station. In the example of FIG. 6, from the uplink channel type Ch _{MS_j_i,} the maximum transmittable power Tx _{MS_Maxpower_j} of type [dBm] is led, from the uplink channel type Ch _{MS_k_i ',} corresponding the maximum transmittable power Tx _{MS_Maxpower_k} [dBm] Gashirube It is burned.

In this case, Tx _{MS_margin_j_i} [dB] the difference value in the i-th mobile station 3j _i of the mobile station type #j (Equation (7)), the difference in the i 'th mobile station 3k _i' of the mobile station type #k If the value is Tx _{MS_margin_k_i ′} [dB] (see equation (8)), the maximum uplink interference amount (allowable interference amount) that can be allowed for each mobile station is the i-th mobile station 3j _i of the mobile station type #j. Is _{calculated as} I _{BS_allow_j_i} [dB] (see equation (9)), and _i′- th mobile station 3k _{i ′} of mobile station type #k is _{calculated as} I _{BS_allow_k_i ′} [dB] (see equation (10)). Can do.

このように第３実施形態では、移動局３からの報告値として、基地局２から送信された共通制御チャネルの移動局３での受信電力を採用する。移動局種別ごとの最大送信可能電力は、図７（ａ）に示すように、変換テーブル５５ａを用いて、チャネル種別から読み替えられる。読み替えられた最大送信可能電力と移動局からの報告値、および基地局２における共通制御チャネルの送信電力、基地局２における受信電力とから、各移動局における差分値が求まる。求められた差分値と基地局２でモニタされた上り干渉量とから、移動局３ごとの許容干渉量が計算される。

Thus, in the third embodiment, the received power at the mobile station 3 of the common control channel transmitted from the base station 2 is adopted as the report value from the mobile station 3. As shown in FIG. 7A, the maximum transmittable power for each mobile station type is read from the channel type using the conversion table 55a. The difference value in each mobile station is obtained from the retransmitted maximum transmittable power, the reported value from the mobile station, the transmission power of the common control channel in the base station 2, and the received power in the base station 2. An allowable interference amount for each mobile station 3 is calculated from the obtained difference value and the uplink interference amount monitored by the base station 2.

The process of determining the call acceptance threshold from the entire sample of the obtained allowable interference amount is the same as that described in FIGS. 4 (a) and 4 (b). That is, the cumulative probability distribution shown in FIG. 7B is obtained by sample accumulation and statistical calculation, and the upper limit of the allowable interference amount in the cell is determined from the cumulative probability distribution and the given allowable deterioration rate. A value lower than the value by a predetermined reduction value is set as a call acceptance threshold Thr _CAC . In this way, the mobile station 3 reports the received power value of the common control channel to the base station 2 so that the call admission threshold Thr _CAC can be automatically determined.

8 and 9 are schematic views for explaining a call admission control method according to the fourth embodiment of the present invention. In the fourth embodiment, a sample of the allowable interference amount necessary for obtaining the cumulative probability distribution graph is collected only during a time period in which the uplink interference amount in the base station 2 is equal to or less than a certain value. That is, as shown in FIG. 9A, in order to control the input to the accumulation / statistical calculation means 43, a predetermined input threshold Ilow _BS [dB] is introduced. Other than this, the configuration is the same as that of the third embodiment shown in FIGS. As shown in FIG. 8, the mobile station 3 transmits the received power of the common control channel to the base station 2 as a report value, and the base station 2 uses the conversion table 55a to determine from the channel type for each mobile station type. Read the maximum transmittable power.

When the amount of uplink interference in the base station 2 is large, communication quality and connection quality are deteriorated for the mobile station 3 located at the cell coverage edge, and a control channel and a communication channel may not be established with the base station 2. Therefore, the result of the statistical calculation processing for generating the graph of the cumulative probability distribution of the allowable interference amount represents the characteristics of only the mobile station 3 located in the vicinity of the base station 2 and represents the mobile station 3 at the cell coverage end. There is no possibility. When the call acceptance threshold is calculated in such a situation, a value larger than an appropriate value may be calculated. Furthermore, there is a possibility that the mobile station 3 at the cell coverage end falls into a vicious circle that degrades communication quality and connection quality. In order to avoid this, an input threshold is introduced, and when the relative value of the uplink interference amount from the receiver thermal noise power is smaller than the input threshold, that is, only the sample of the allowable interference amount when I _BS <I low _BS is satisfied. By calculating the call acceptance threshold, it is possible to always obtain a calculation result representing the characteristics of the mobile station in the entire cell coverage.

The process of obtaining a cumulative probability distribution from a good sample group and determining the call acceptance threshold Thr _CAC therefrom is the same as in the first to third embodiments, as shown in FIG. 9B.

  In the fourth embodiment, the received power of the common control channel is used as the report value from the mobile station 3 as in the third embodiment, and the conversion from the channel type to the maximum transmission power is performed by the conversion table 55a. However, the configuration of the fourth embodiment in which statistical calculation is performed using only samples that satisfy a certain condition by performing input control to the statistical calculation processing is similarly applied to the first and second embodiments. Is possible.

  10 and 11 are schematic diagrams for explaining the call admission control method according to the fifth embodiment of the present invention. In the fifth embodiment, the communication quality of the uplink channel (communication channel, control channel) of the mobile station 3 in communication monitored by the base station 2 is accumulated, and the communication quality deterioration rate is a constant rate (communication quality deterioration threshold value). ), The call acceptance threshold value of the base station 2 is corrected to be smaller than the current value. The other configuration is the same as that of the fourth embodiment. That is, as shown in FIG. 10, the mobile station 3 reports the received power of the common control channel to the base station 2 as a report value, and the base station 3 uses the conversion table 55a to determine the maximum transmittable power from the channel type. The allowable interference amount is calculated for each mobile station 3 from the difference value in each mobile station 3 and the uplink interference amount in the base station 2. Further, as shown in FIGS. 11A and 11B, a cumulative probability distribution is obtained from a sample set of allowable interference amounts when a predetermined condition is satisfied by input control.

  The increase in the deterioration rate of communication quality exceeding a predetermined ratio is due to the fact that the current transmission power value of a certain percentage of mobile stations has reached the maximum transmittable power value. This is because the call reception threshold is too large so that the amount of uplink interference is so large that actual cell coverage cannot be guaranteed, or the mobile station 3 moves farther from the base station 2 than originally assumed. It shows that. Therefore, in such a case, the call acceptance threshold can be reset to a more appropriate value by correcting the call acceptance threshold of the base station 2 to be smaller than the current value.

  In order to realize this, as shown in FIG. 11A, the communication quality monitoring means 24 of the transceiver 10 of the base station 2 measures the deterioration rate of the connected mobile station from the SIR, the block error rate, and the like. When the deterioration rate exceeds a certain rate, the correction value setting means 42 of the call admission control device 30 is instructed to correct the call admission threshold. The correction value setting means 42 applies the current call acceptance threshold from the actually measured communication quality degradation rate, the preset communication quality degradation rate threshold, and the target mobile station type (service type). A correction value is generated. The accumulation / statistical calculation means 43 applies an appropriate correction to the call acceptance threshold value using the correction value.

  Thus, in the fifth embodiment, call admission control with higher reliability can be performed by appropriately correcting the call admission threshold according to the change in the deterioration rate of the communication quality.

  Needless to say, the correction of the call acceptance threshold of the fifth embodiment is applicable not only to the fourth embodiment but also to the first to third embodiments.

  As described above, according to the call admission control apparatus and method of the present invention, the call admission threshold can be automatically set and automatically updated in the base station, and the system efficiency can be greatly improved.

It is a schematic block diagram of the radio base station and mobile station which comprise the mobile communication system which concerns on one Embodiment of this invention. It is a detailed block diagram of a radio base station according to a radio base station according to an embodiment of the present invention. It is the schematic for demonstrating the call admission control method which concerns on 1st Embodiment of this invention. FIG. 6 is a diagram for explaining a method of automatically calculating and updating a call acceptance threshold from a sample group of allowable interference amounts for each mobile station by statistical calculation processing in the first embodiment. It is the schematic for demonstrating the call admission control method which concerns on 2nd Embodiment of this invention. It is the schematic for demonstrating the call admission control method which concerns on 3rd Embodiment of this invention. It is a figure for demonstrating the method to calculate and update a call acceptance threshold value automatically in 3rd Embodiment. It is the schematic for demonstrating the call admission control method which concerns on 4th Embodiment of this invention. It is a figure for demonstrating the method to calculate and update a call acceptance threshold value automatically in 4th Embodiment. It is the schematic for demonstrating the call admission control method which concerns on 5th Embodiment of this invention. It is a figure for demonstrating the method to calculate and update a call acceptance threshold value automatically in 5th Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Mobile communication system 2 Radio base station 3, 3j _i , 3k _{i ′} Mobile station 10 Transceiver 11 Uplink channel transmission means 12 Downlink channel reception means 20 Monitoring means 21 Radio resource monitoring means 22 Uplink channel monitoring means 23 Mobile station Report value monitoring means 24 Communication quality monitoring means 30 Call admission control device 35 Setting means 40 Call admission threshold setting update unit 41 Allowable interference amount calculation means 42 Correction value setting means 43 Accumulation / statistical calculation means 50 Analysis means 55a Conversion table 60 Uplink Call admission control means

Claims (10)

A call admission control device for an uplink in a mobile communication system,
An allowable interference amount calculating means for calculating an allowable interference amount for each mobile station based on a report value transmitted from the mobile station to the base station and a state of radio resources in the base station;
Accumulation / statistical calculation means for calculating a call admission threshold by accumulating a certain number of allowable interference amounts for each mobile station and performing statistical processing;
A call admission control device comprising uplink call admission control means for controlling admission of a call from the mobile station based on the call admission threshold.   2. The accumulation / statistical calculation means includes an input control means, accumulates an allowable interference amount when a predetermined condition is satisfied, and calculates a call acceptance threshold value by performing statistical processing. The call admission control device described in 1. The state of the radio resource is the amount of uplink interference in the base station,
3. The call admission control according to claim 2, wherein the input control unit permits accumulation of an allowable interference amount for each mobile station only during a time period in which the uplink interference amount is a certain value or less. apparatus.   2. The correction value setting means for generating a correction value for correcting the call admission threshold when a deterioration rate of communication quality of an uplink channel exceeds a certain ratio. Call admission control device.   The correction value setting means generates a correction value that sets the call admission threshold to be smaller than the current value when the deterioration rate of the communication quality exceeds a certain ratio. The call admission control device described.   The accumulation / statistical calculation means obtains a cumulative probability distribution by statistically processing an allowable interference amount of the fixed number of mobile stations, and obtains the call admission threshold from the cumulative probability distribution. The call admission control device according to 1. A transceiver that receives and monitors a report value transmitted from a mobile station and monitors a state related to an uplink channel;
A radio base station comprising a call admission control device that controls admission of a call on an uplink based on a report value acquired by the transceiver and a state relating to an uplink channel,
The call admission control device calculates a permissible interference amount for each mobile station based on a report value received by the transceiver and a state of radio resources in the radio base station, and permissible interference for each mobile station. A radio base station characterized in that a predetermined number of amounts are accumulated and statistical processing is performed to automatically set a call acceptance threshold and control call acceptance based on the call acceptance threshold. Receiving a report value at a base station from a mobile station belonging to a cell;
Monitoring the state of radio resources at the base station;
Calculating an allowable interference amount for each mobile station based on the report value and the state of radio resources;
Storing a certain number of allowable interference amounts for each mobile station, calculating a call acceptance threshold by performing statistical calculation,
A call admission control method including a step of controlling admission of a call from the mobile station based on the call admission threshold. As the state of the radio resource, monitor the amount of uplink interference in the base station,
9. The call admission control method according to claim 8, wherein an allowable interference amount for each mobile station is accumulated only during a time period in which the uplink interference amount is a certain value or less. Monitoring the communication quality of the uplink channel;
9. The call admission control method according to claim 8, further comprising the step of setting the call admission threshold smaller than a current value when the deterioration rate of the communication quality exceeds a certain ratio.

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