JPH08186861A - Radio channel allocation method in mobile communication system - Google Patents

Abstract

PURPOSE: To prevent deterioration in speech quality in a cellular mobile communication system and forced interruption to the utmost by providing a stage measuring a reception electric field strength of a mobile station receiving a call to decide a channel and a stage allocating a decided channel when the measured value of desired wave versus interference wave power ratio has a prescribed margin or over. CONSTITUTION: When a call is made by mobile stations MS1, MS2, base stations BS1, BS2 measure reception electric field strength from the mobile stations MS1, MS2. Then a channel corresponding to the measured reception electric field strength is decided and the base stations BS1, BS2 measure a desired wave versus interference wave power ratio (CIR) of an up link of the channel and the mobile stations MS1, MS2 measure the CIR of a down-link, and when they have a prescribed margin or over, the decided channel is allocated. When they do not have the prescribed margin, whether or not other channel is to be allocated is checked.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio allocation method in a mobile communication system.

[0002]

2. Description of the Related Art Generally, a cellular mobile communication system has a structure shown in FIG. That is, a predetermined service area is divided into a plurality of cells E1, E2, E3, ... And the like, and base stations BS1, BS2 ,. Wireless communication is performed between the mobile stations MS1, MS2 and MS3. Then, the signal transmitted from the mobile station, for example, the mobile station MS1 to the base station BS1 is transmitted to the other party via the exchange EX and the public telephone network CL.

In such a mobile communication system,
Frequency allocation methods for wireless communication are roughly divided into two types: fixed channel allocation methods and dynamic channel allocation methods. In the fixed channel allocation method, channels are allocated in advance in each base station (each cell) so as not to interfere, as shown in FIG. For example, cell 71 has channel f
_1, the cell 72 channel f _2, the channel f ₃ in the cell 73, the cell 74 channel f _2, the cell 75 assigns a channel f _3. On the other hand, in the dynamic channel allocation method, all channels are made available in each base station as shown in FIG. 9, and channels are allocated so that there is no interference for each communication. Therefore, the dynamic channel allocation method can more flexibly cope with the varying traffic.

In the dynamic channel allocation method, when a mobile station makes a call, a desired to interference power ratio (CIR (Carrier to Interference Ratio)) of the uplink channel and the downlink channel in the mobile station and the base station, respectively.
Is measured, and if both the uplink channel and the downlink channel satisfy the required threshold value, the channel is assigned. As described above, in the dynamic channel allocation method, CIR is detected when allocating a channel, but the state (used frequency) of the mobile station that is using the same channel in the surrounding cells is not checked, which causes interference to the mobile station in communication. there is a possibility.

Many algorithms have been proposed as dynamic channel allocation methods. In particular, an algorithm that determines a search start channel according to the received power intensity is known. For example, it is disclosed in Kataoka, Miyake, Fujino, “Autonomous distributed dynamic channel allocation method using base station reception level”, Technical Report RCS93-70. In this method, the search start channel is autonomously decentralized based on the mobile station reception level received by the base station, and the channels are searched in the order of increasing channel number from that channel, and the channels satisfying the required threshold are assigned. ing. Then, it adopts a reus partitioning structure capable of accommodating many calls and further reduces the number of channel searches.

[0006]

In the distributed dynamic channel allocation method in the micro cell system, it is difficult to avoid co-channel interference because the situation of surrounding cells is unknown. Then, the mobile station that receives the interference will switch the channel, but if there is no empty channel, the worst forced disconnection will occur. Even if there is a channel to be switched, if it takes time to find the channel, it leads to deterioration of the communication quality and increases the load on the base station.

The present invention has been made in view of the above circumstances, and provides a radio channel allocation method in a cellular mobile communication system capable of preventing deterioration of call quality and forced disconnection as much as possible. With the goal.

[0008]

A radio channel allocating method in a cellular mobile communication system according to the present invention divides a predetermined service area into a plurality of cells, installs base stations in these cells, respectively. In a cellular mobile communication system in which a plurality of wireless channels held by the service area are selectively allocated to the mobile station for wireless communication between the mobile station and the mobile station in the service area Measuring the received electric field strength from the station and determining a channel corresponding to the measured received electric field strength based on the allocation channel correspondence table;
Measuring a desired wave-to-interference wave power ratio in the determined channel and allocating the determined channel when the measured value has a margin of a predetermined value or more.

[0009]

According to the radio channel allocation method of the present invention having such a configuration, the received electric field strength from the mobile station making the call is measured, and the channel corresponding to the measured received electric field strength is the allocated channel. The desired channel-to-interference wave power ratio in the determined channel is measured based on the correspondence table, and when the measured value has a margin of a predetermined value or more, the determined channel is assigned. This makes it possible to prevent deterioration of call quality and forced disconnection as much as possible.

[0010]

FIG. 1 shows an allocation procedure of a first embodiment of a wireless channel allocation method in a cellular mobile communication system according to the present invention. In the cellular mobile communication system in which the radio channel allocation method of this embodiment is used, the base station measures the received electric field strength from the mobile station, and the correspondence between the predetermined received electric field strength and the channel is common to all cells. According to the correspondence table shown in FIG. 3, all cells 3 are provided for mobile stations having the same received field strength x [dB] as shown in FIG.
It is assumed that the same channel F1 is assigned to 1, 32 and 33.

Returning to FIG. 1 again, the allocation procedure of this embodiment will be described. First, when the mobile station makes a call, the base station measures the electric field strength received from the mobile station (see step F11). The channel corresponding to this measured received field strength is then determined (see step F12) and the CIR of the uplink on this determined channel is determined.
The (desired wave to interference wave power ratio) is measured by the base station and the downlink CIR is measured by the mobile station (see step F13). If each has a margin of a predetermined value or more, the call quality Since the deterioration and the forced disconnection can be prevented as much as possible, the channel determined above is assigned (step F
14 and F15), if it does not have a margin of a predetermined value or more, it is checked whether or not another channel can be assigned (see step F16), and if it is possible, that channel is assigned (see step F17). If not possible, the call is lost (see step F18).

Next, it will be explained that when the CIR has a margin of a predetermined value or more, it is possible to prevent deterioration of call quality and forced disconnection as much as possible.

Now, in a certain service area, channel c
Consider a case where n pairs of base stations and mobile stations communicate with each other by using, and each of these n pairs of wireless communication lines is further configured by two lines, an uplink and a downlink. The CIR of the radio communication line uplink and downlink of mobile station j are Γ ^{u, c} _{j, n−1} and Γ, respectively.
^{Let d, c} _{j, n-1} . Here, n-1 is the number of other stations using the same channel as the interference source.
It is assumed that the call quality of all n pairs of wireless communication lines is equal to or higher than a certain level, that is, equal to or higher than a predetermined threshold value γ.

Γ ^{u, c} _{j, n-1} > γ: j = 1, ... n Γ ^{d, c} _{j, n-1} > γ: j = 1, ... n (1) New in such a state Consider the case where a large call occurs. The base station and the mobile station that originated the call measure the CIRs of the uplink and downlink of channel c, and if they are above a certain threshold value ε · γ, channel c can be assigned to a new call. Become. Here, ε is ε> 1 and is called a call admission margin.

Consider how the uplink and downlink CIR for each line is represented. It is assumed that the base station i is talking to the mobile station i in the same cell. Then, the gain (attenuation ratio of transmission power) of the line between the base station i and the mobile station j is represented by X _ij . Instantaneous fluctuations in the received electric field strength such as Rayley-fading are removed by diversity and the like, and the gains of the uplink and downlink are equal. At this time, the gain between the n pairs of mobile stations and the base station using the channel c is represented by the following gain matrix.

[0016]

[Equation 1] By normalizing the row vector or column vector in the diagonal elements of the gain matrix X _n can be defined each as follows both downlink gain matrix X ^D _n, and the uplink gain matrix X ^U _n.

[0017]

[Equation 2] The component X of these uplink gain matrices X ^U _n
^U _ij (= 1 (i = j) or X _ij / X _ii (i + j) and the component X ^D _ij (= 1 (i) of the downlink gain matrix X ^D _n.
= J) or X _ij / X _jj (i ≠ j), the downlink CIR of the uplink CIR is expressed as follows.

[0018]

(Equation 3) Here, P ^m _i and P ^b _i are transmission powers of the mobile station i and the base station i, respectively.

As described above, the situation where the n pairs of mobile stations and the base station are talking can be described by using the uplink and downlink gain matrices. Now consider the situation where a new n + 1th call occurs between mobile station n + 1 and base station n + 1. This situation is obtained by adding one row and column vector to each matrix and is given by (n + 1) × (n
+1) uplink and downlink gain matrices

[0020]

[Equation 4] Described by. Where C ^D _{n + 1} , R ^D _{n + 1} , C ^U
_{n + 1} and R ^U _{n + 1} are vectors defined as follows, respectively.

[0021]

(Equation 5) Using these matrix elements, the uplink and downlink CIR for a new call and the CIR after a new call for an n pair of existing communication lines occurs is expressed as:

[0022]

(Equation 6) Here, if the transmission power from all mobile stations and the transmission power from all base stations are constant, P ^m _i = P ^m _j , P
^{Since b} _i = P ^b _j , equations (5), (6), (13)-
(16)

[0023]

(Equation 7) Becomes Further, when the radio wave propagation loss between the mobile station using the channel c and the base station is equal, X _ii = X _jj (i, j = 1, ... N + 1), so that ^ru _i = r ^D _i , C ^U _i = c ^D _i (23). Also, since the CIR of equation (17) is larger than the threshold value γ,

[0024]

(Equation 8) Also, from the equation (23), the CIR of equation (25) is larger than ε · γ.

[0025]

[Equation 9] Becomes Therefore, the CIR of equation (22) is calculated by equations (24) and (2
From 5)

[0026]

[Equation 10] Therefore, by allocating a new channel, it is possible to derive the lower limit of the CIR due to the interference with the mobile station that is communicating earlier. The same applies to Γ ^{D, c} _{i, n} .

Thus, by providing a margin larger than the amount of CIR deterioration at the time of channel allocation, when the same channel is used in the place where the radio wave propagation loss is equal,
Forced disconnection due to interference is reduced. Further, since the maximum deterioration value due to the interference wave is known in this way, system design is facilitated.

Now, the CIR when the mobile station i is assigned the channel c is Γ ^{u, c} _{i, n} = Γ ^{d, c} _{i, n} = a · γ (a >
ε), the number of mobile stations in the position having the same gain as that of the mobile station i in each cell within the line holding time of the mobile station i, and the number of mobile stations to which the same channel c as that of the mobile station i is assigned is h. Suppose there is. At this time, the CIR of the mobile station i (Γ ^{u, c}
_{i, n + h} ). After the mobile station i is assigned the channel c, when the same channel c is used for one line in another cell, the CIR of the mobile station i is

[0029]

[Equation 11] Becomes This is 1 / γ on the right side of equation (26)
(A · γ). Considering the case where the number of mobile stations using the channel c increases one line at a time and increases to h lines in this way, the CIR at this time is

[0030]

(Equation 12) Becomes Therefore, since a sufficient condition for the mobile station i not to be disconnected during a call is Γ ^{u, c} _{i, n + h} > γ, a > ε / (ε−h) (29). However, a > ε> h.

As described above, when mobile stations using the same channel talk at the position of the same gain, in order to prevent a mobile station from being forcibly disconnected during the hold time, the mobile station is assigned to that mobile station. It is understood that the CIR should be set to aγ or more by using a that satisfies the expression (16).

By the way, when a = ε and h = 1, the equation (1
From 6), a = ε ≧ 2, which corresponds to a margin of approximately 3 dB.

As described above, according to the present embodiment, it is possible to suppress the interference to the mobile station that is using the same channel in the surrounding cells to a certain value or less, which simplifies the system design and reduces the channel. The number of switching operations is reduced, and the control load on the base station is reduced. Then, when allocating channels, by adding an allocation margin for the maximum deterioration due to interference, it is possible to reduce the forced disconnection rate of mobile stations, which is more important in terms of service.

In the above example, the measured CIR
If there is no margin greater than the predetermined value, it will be checked whether or not another channel can be allocated. This will be described with reference to FIG. FIG. 2 is a flowchart showing the procedure of the second embodiment of the allocation method of the present invention.

In the communication system in which the allocation method of this embodiment is used, the channels that can be used are 1 to m channels.

When a call originates from the mobile station (step F2
1), the base station first measures the electric field intensity received from the mobile station. The base station prepares a table showing the channels to be assigned to each received electric field strength from the mobile station. In the table, the larger the received electric field strength, the smaller the channel number, and the smaller the received electric field strength, the larger the channel number. Then, it is assumed that a call originates from the mobile station and the channel corresponding to the received electric field strength measured by the base station is the k channel (see step F22).

When the k channel is not in use in the cell, the base station and the mobile station measure the CIR of the search start channel k channel determined according to the received electric field strength and check whether the allocated CIR is satisfied. It is checked, and if it is satisfied, it is assigned (see steps F23 and F24). k
When the channel is in use or does not satisfy the assigned CIR, the channel k is next selected in the order of (k-1) channel, (k + 1) channel, (k-2) channel, (k + 2) channel, and so on. Searches are alternately performed as the center (see steps F25 to F33). At this time, the CIR of both the uplink channel measured by the base station and the downlink CIR measured by the mobile station is first allocated to the mobile station. If there is no channel that satisfies the assigned CIR after searching all the channels, the call is lost (see step F34). Also, after the channels have been allocated, when the required CIR is not satisfied due to the co-channel interference from surrounding cells and the channels have to be switched, the calls are sequentially made again from the search start channel determined from the received electric field strength. The channel is searched in the same manner as that searched for, and the channel that first satisfies the required CIR is reassigned to the mobile station. At this time, even though all channels have been searched, the required CI
When there is no channel that satisfies R, forced disconnection is performed.

FIG. 4 shows an example in which a cell is virtually divided into small cells according to the value of the received electric field strength, and an example of a search start channel corresponding to each received electric field strength is shown in the table of FIG.
In FIG. 4, the area of the portion where the received electric field strength is larger than a [dB] is equal to the area of the portion where it is larger than b [dB] and smaller than a [dB]. In this way, the areas divided by the lines showing the respective received electric field strengths are all equal in area. Then, as shown in FIG. 5, when the total number of channels usable in the system is 60, the number of channels allocated to each small cell portion is set to 12 channels.

As described above, according to the present embodiment, even if a channel cannot be assigned according to the correspondence relationship between the radio wave propagation loss and the channel in the frequency allocation to the mobile station, the relationship between the radio wave propagation loss and the channel. As a result, since the allocation can be performed closer to each other, the Leus partitioning structure does not collapse much, and deterioration due to co-channel interference can be suppressed.

Next, the third method of channel allocation according to the present invention will be described.
An example will be described. In the channel allocation method of this embodiment, in the correspondence table of the received electric field strength and the channel prepared in the base station, the number of channels to be allocated when the received electric field strength is small is to be allocated when the received electric field strength is large. Try to be more than the number.
For example, considering that the point where the received electric field strength is large is close to the base station, the frequency reuse distance is short, and conversely, the point where the received electric field strength is small is far from the base station, and the frequency reuse distance is long. The number of channels that should be assigned to mobile stations located at points with receivable field strength that can be repeatedly used in adjacent cells should be assigned to mobile stations located at points that have receivable field strength that can reuse frequencies in one cell away. The number should be about one half of the number of channels. In this way, a larger number of channels are assigned as the distance from the base station increases. The channel allocation method is the same as in the case of the second embodiment. With such allocation, the correspondence table of the received electric field strength and the channel is more faithfully allocated. In FIG. 6, the frequency reuse distance is 1 in the portion where the received electric field strength is larger than a [dB] in FIG.
The frequency reuse distance of the portion larger than b [dB] and smaller than a [dB] is 2, and the reuse distance of the portion larger than c [dB] and smaller than b [dB] is 3, larger than c [dB]. ] The reuse distance of the smaller part is 4, d [d
B] An example of the reception electric field strength and the search start channel when the reuse distance of the smaller portion is 5 is shown.

Further, in the above embodiment, after the channel allocation is performed for the outgoing call, the channels are re-allocated according to the received electric field strength at a certain time interval even if there is no co-channel interference. You may make it close to the correspondence table of radio wave propagation loss and channel.

In the above embodiment, the transmission power control may be performed on the mobile station, the base station, or the mobile station and the base station after allocating the channel.

Further, the correspondence table of the relationship between the received electric field strength and the channel may be adaptively updated according to the situation of the call volume in each cell. For example,
When the base station measures the received electric field strength distribution within a certain time and detects that the call starts to concentrate in the center of the cell, it responds to the large received electric field strength in the relationship table between the received electric field strength and the channel. Increase the number of channels
It is also possible to adaptively reduce the number of channels corresponding to the place where the received electric field strength is small.

As described above, according to the third embodiment, since the number of channels is assigned based on the frequency reuse distance, it is possible to effectively utilize the channels.

[0045]

According to the present invention, it is possible to prevent deterioration of call quality and forced disconnection as much as possible.

[Brief description of drawings]

FIG. 1 is a flowchart showing an allocation procedure of a first embodiment of a channel allocation method according to the present invention.

FIG. 2 is a flowchart showing a channel allocation procedure according to the second embodiment of the present invention.

FIG. 3 is an explanatory diagram for explaining allocating the same channel to mobile stations having the same received electric field strength.

FIG. 4 is a schematic diagram showing a Leus partitioning structure in which a cell is virtually divided according to a received electric field strength.

FIG. 5 is a diagram showing a correspondence between a received electric field strength and a search start channel.

FIG. 6 is a diagram showing a correspondence between a received electric field strength and a search start channel.

FIG. 7 is a schematic configuration diagram of a cellular mobile communication system.

FIG. 8 is a schematic diagram illustrating a fixed channel allocation method.

FIG. 9 is a diagram illustrating a dynamic channel allocation method.

[Explanation of symbols]

 BS1, BS2 Base station MS1, MS2 Mobile station E1, E2 Cell EX Mobile switching center CL Wired line

Claims (2)

[Claims] 1. A predetermined service area is divided into a plurality of cells, a base station is installed in each of these cells, and radio communication is performed between these base stations and mobile stations in the service area. In a cellular mobile communication system in which a plurality of radio channels set for the service area are selectively assigned to the mobile station, the received electric field strength from the mobile station that made the call is measured, and the measured reception is measured. The step of determining a channel corresponding to the electric field strength based on the allocation channel correspondence table, and measuring the desired wave to interference wave power ratio in the determined channel, when this measured value has a margin of a predetermined value or more, Allocating the determined channel, and a method of allocating radio in a mobile communication system. 2. The radio according to claim 1, wherein the number of channels that can be assigned to the mobile station having the high received electric field strength is smaller than the number of channels that can be assigned to the mobile station having the low received electric field strength. Allocation method.