JPH0761176B2 - Mobile communication channel allocation method - Google Patents

Description

The present invention relates to a mobile communication system using a cell system.

More specifically, it relates to channel allocation for wireless communication between a mobile unit and a fixed station.

(B) Conventional technology In the cell method, the service area is divided into units called cells, fixed stations are installed in each cell, and each cell communicates with mobile units in the cell, thereby causing co-channel interference, etc. The same channel is repeatedly used between cells that are separated by a distance that does not receive the signal.

Conventionally, as a channel allocation method to each of these cells (fixed stations), a fixed channel allocation method has been used in which the allocation of all channels to cells is constant and invariable with time. In each cell, among the allocated channels, the channels are allocated by the mobile unit's channel allocation request. Channel allocation to each cell is determined in advance according to the average call volume of each cell, etc., so if the call volume in each cell changes frequently over time, all assigned channels are used in a cell. However, even when the cell is in a shortage state, there are many vacant channels in other cells, and the frequency cannot be effectively used.

Also, considering the case where a mobile moves a cell during communication, co-channel interference will not occur and the same channel will not be allocated because the co-channel interference conditions differ in the target cell. The channel that has been used up to now cannot be used after the cell is moved and a new channel is used, so that the channel must be switched. When the channel is switched, a momentary interruption occurs due to the channel switching, and control processing such as search for a channel to be switched and transmission / reception of a switching signal is performed. Further, a channel may not be assigned in the cell of the moving destination and forced disconnection may occur during communication. The probability of this occurring is equal to the loss probability for calls originating in that cell to be assigned a new and different channel, as previously described. This is a problem because, from the viewpoint of service quality, forced disconnection during communication should be prioritized over call loss for live calls, so it must be better than the call loss rate.

(C) Problems to be solved by the invention In the future, it is necessary to effectively use a finite frequency as the demand for mobile communication is expected to increase. Therefore, the cell area is reduced and the frequency is repeatedly used at high density. Is essential. In that case, the mobile unit inevitably moves the cell during communication. Then, the call volume in each cell often changes with time, which causes a problem that the frequency is not used effectively as described in (a). In addition, as described in (a), there is a problem that the number of control processes such as forced disconnection during communication, instantaneous disconnection due to channel switching, search for a channel to be switched, transmission / reception of a switching signal, and the like increases as the cell moves. The present invention aims to solve these problems.

(D) Means for Solving the Problems In the present invention, once a channel is assigned to a certain mobile unit, the mobile unit can use the same channel as much as possible even if the cell is moved. I thought to try. Therefore, for this purpose, it should be noted that the cell movement of the mobile body first occurs due to the mobility of the mobile body. Then, I thought that it was important for channel allocation to incorporate and use movement information such as how the moving body was moving or how it was planned to move. Then, instead of allocating a channel to a mobile among the channels pre-allocated to each cell as seen in the fixed channel allocation method, the channel used by the mobile is continuously allocated even after the cell is moved. Therefore, we considered not to fix the channel allocation to each cell, but to give priority to the channel allocation request for continuous calls.

Figure 1 shows the algorithm. First, if the need for channel allocation arises, check whether it is due to the mobile moving cells during communication, and if so, allocate the channel in order to preferentially allocate the channel that has been used so far. Check if possible and assign if it is possible. If it cannot be assigned, a new channel is searched for as described below as in the case where a new call is made.

If allocatable channels are searched, if there is no call, a call is not accepted if the call occurs, so-called call loss occurs, and if the cell moves, the call is forcibly disconnected during communication.
If there is an allocatable channel, it is selected from among them according to the mobile information, and further, a channel in use in the cell closest to the cell is selected and allotted. The reason why the channel used in the closest cell is selected is to narrow the repetition interval of the same channel and to increase the frequency utilization efficiency of the entire service area.

(E) Action In the algorithm of FIG. 1, when the necessity of channel allocation occurs, if it is due to cell movement, if the channel that has been used up to now can be assigned, it will be assigned where it is assigned. It is not impossible to use the same channel as before without changing, as in the fixed channel allocation method. Moreover, by doing this before searching for a new channel, the use of the same channel will be prioritized. If the same channel can be used, processing such as instantaneous interruption due to channel switching, search for a channel to switch to, and transmission / reception of a switching signal are eliminated.

In addition, where mobile information is selected from among allocatable channels, it is the same as a mobile that is moving or is planning to move in the same way, and is in communication in a cell that is more than the minimum reuse interval of the same channel. By allocating channels, there can be a set of mobiles that use or plan to move in the same way using the same channels. Then, when a mobile unit moves forward to move a cell, a pair of mobile units also move forward to move a cell, and the cells located in each other come close to each other by the cell move and the same channel can be used. It will not disappear, and the intervals between cells that are assigned the same channel will become almost constant. As a result, the same channel can often be used even if the cell is moved,
In addition, since there is no channel to be allocated in the destination cell, forced disconnection is reduced. Furthermore, if the same channel interval is assigned so as to be the minimum, the channels are repeatedly used at a high density and the frequencies are effectively used, but this does not decrease much due to cell movement.

(F) Example A case will be described in which a service area such as an expressway has a one-dimensional cell structure and a moving body moves at a substantially constant speed.

Figure 2 shows the algorithm (MD method). The MD method is a method of allocating a channel used by a mobile unit moving in the same direction as that of a mobile unit originating a call as much as possible. In other words, the mobiles moving in the same way are assigned to form a set that uses the same channel. By doing so, as described in (e), when a certain moving body moves forward to move the cell, the paired moving bodies also move forward to move the cell, and eventually the same channel is used. It can be used and the probability of forced disconnection and channel switching is reduced. In addition, since the closest channel is set to be Dr + 1 (Dr is the minimum reuse interval of the same channel, 1 is the distance between 1 base stations) or more, the reuse interval of the same channel in the entire service area is also small. That is, the channels are repeatedly used with high density. One extra Dr + 1 is taken after considering the speed difference of the mobile unit and the position difference of the other mobile units forming a pair with the calling mobile unit in the cell.

FIG. 3 shows an example of allocation by the fixed method and the MD method.
In the fixed method, since only one channel is assigned to each cell, two or more communications cannot be performed in each cell, resulting in call loss or forced disconnection. On the other hand, in the MD method, since channels are not fixedly assigned to cells, up to three communications can be performed simultaneously in one cell, and in this case there is no call loss or forced disconnection. Furthermore, in the MD method, the number of channels required for allocation in consideration of the moving direction is two, and channels are allocated more efficiently and effectively than in the fixed method. Also, the probability of call loss and forced disconnection is small. In addition, the evaluation of the switching of the channel is performed by the C value (C value is
It is the number of times the channel is switched during communication divided by the number of cell movements during communication. However, the case of forced disconnection is also added. ). Then, it turns out to be 1,0, and the fixed method always changes, whereas the MD method does not change even once in this case.

(G) Effect of the Invention According to the present invention, even if a mobile object is often moved to a cell,
There are many cases where the same channel is used. Also, the same channel use interval can be kept small and almost constant, and the frequency can be effectively used. Then, it is possible to obtain an effect that forced disconnection during communication that occurs when a channel is not allocated in the cell of the moving destination, instantaneous interruption due to channel switching, control processing such as channel search and transmission / reception of switching signal, and the like are reduced.

[Brief description of drawings]

FIG. 1 is an algorithm of the present invention. FIG. 2 shows an example of the present invention, MD (Moving Direction).
Algorithm, D is the same channel reuse interval, Dr
Is the minimum reuse interval of the same channel, and 1 of Dr + 1 is 1
Indicates the distance between base stations. Figure 3 is an example of allocation of fixed method and MD method, hexagon is cell, a, b,
The c is a channel, and the subscript is, for example, a ₁₁ indicates that the a channel is allocated at the beginning at the time of 1, and Δ indicates call origination, ◯ indicates continuation, and × indicates call loss or forced disconnection. The C value in the table is the number of times the channel is switched during communication divided by the number of cell movements during communication (however, the case of forced disconnection is also added).

Claims (2)

[Claims] 1. A mobile unit which is divided into a plurality of cells in a communication area and is assigned a channel for wireless communication between a mobile unit and a fixed station in each cell when the channel assignment is determined and before the channel assignment is determined. A channel allocation method for mobile communication, characterized in that the same channel as that used for mobile communication in a cell separated by a distance not less than co-channel interference is selected based on the mobile information of . 2. A prioritized allocation of an already used channel so that the channel used in the cell before the movement can be continuously used even after the mobile moves to a cell having a different co-channel interference condition. The channel allocation method for mobile communication according to claim 1, wherein