JPH02224424A - Channel assigning method considering movement information of mobile body - Google Patents

Abstract

PURPOSE:To efficiently use frequency, and simultaneously, to reduce the control processing of the retrieval of a channel or the transfer of a switching signal, etc., by considering the movement information of the mobile body, and simultaneously, giving priority to use the same channel to the mobile body even after the cell movement of the mobile body at the time of assigning the channel. CONSTITUTION:At first, when necessity to assign the channel arises, it is investigated whether it is owing to the cell movement of the mobile body during communication or not, and if so, it is investigated whether the channel having been used till then can be assigned or not in order to assign this channel preferentially, and if it can be assigned, it is assigned. If it can not be assigned, another channel is newly retrieved similarly to the case when a call is newly originated. In the case of no channel capable of being assigned after the retrieval, if the necessity of the assignment of the channel is owing to the generation of the call, it results in what is called call loss in which the call is not accepted, and if it is owing to the cell movement, it results in forced disconnection during the communication. It there are the channels capable of being assigned, the channel is selected from among them according to the movement information, and further, the channel being used in the cell nearest to the cell concerned is selected from among them and assigned.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial Application Field The present invention relates to a mobile communication system using a cell system.

More specifically, it relates to channel allocation for wireless communication between mobile units and fixed stations.

(b) Conventional technology In the cell system, the service area is divided into units called cells, a fixed station is installed in each cell, and each cell communicates with mobile objects within that cell.

The same channel is repeatedly used between cells that are separated by a distance that does not cause co-channel interference.

Conventionally, as a method for allocating channels to each of these cells (fixed stations), a fixed channel allocation method has been used in which all channels are allocated to cells without changing over time. In each cell, a channel is allocated among the allocated channels according to a channel allocation request from a mobile unit. Channel allocation to each cell is determined in advance based on the average traffic volume for each cell, so if the traffic volume in each cell changes frequently over time, all the allocated channels may be used in a certain cell. Even when there is a shortage of channels in other cells, there are often vacant channels in other cells, which has the disadvantage that frequencies are not used effectively.

Furthermore, when a mobile unit moves from one cell to another while communicating, the same channel will not be assigned to the adjacent cell it is moving to due to co-channel interference, so The channel that was previously used cannot be used after the cell is moved, and the channel must be switched to use a new, different channel. When a channel is switched, a momentary interruption occurs due to the channel switching, and control processing such as searching for a channel to be switched and transmitting/receiving a switching signal is performed. Furthermore, a channel may not be allocated in the destination cell and forced disconnection may occur during communication. The probability that this will happen is equal to the call drop rate for calls originating in that cell to be assigned a new, different channel, as stated earlier. This is a problem because, from the perspective of service quality, forced disconnection during communication should be given more weight than call loss in response to an incoming call, so it is necessary to make it better than the call loss rate.

(c) Problems that the invention aims to solve In the future, as demand for mobile communications is expected to increase, it will be necessary to make effective use of limited frequencies, and it will be necessary to reduce the cell area and use frequencies repeatedly at high density. It is essential to do so. In that case, the mobile object inevitably moves from cell to cell during communication. This causes the traffic volume in each cell to change frequently over time, resulting in the problem that frequencies are not used very effectively as described in (a). Furthermore, as described in (a), cell movement causes problems such as forced disconnection during communication, instantaneous interruption due to channel switching, and increased processing by the controller, such as searching for a channel to be switched and sending and receiving switching signals. The present invention aims to solve these problems.

(d) Means for Solving the Problems The present invention solves the above-mentioned problem by ensuring that once a channel is assigned to a mobile body, that mobile body can use the same channel as much as possible even if it moves from cell to cell. I thought of solving it. To this end, we first focus on the fact that cell migration of mobile bodies occurs because of the mobility of the mobile body. Then, we thought it would be important to incorporate and utilize movement information, such as how the mobile object is moving or how it plans to move, in channel assignment. Instead of assigning a channel to a mobile unit from among the channels previously assigned to each cell, as seen in the fixed channel allocation method, the channel used by the mobile unit is continuously assigned even after the mobile unit moves. Therefore, instead of fixing channel assignment to each cell, we considered giving priority to continuous channel assignment requests.

Figure 1 shows the algorithm. First, when it becomes necessary to allocate a channel, check whether this is due to the mobile unit moving from cell to cell during communication, and if so, make sure that the channel that has been used until now is allocated preferentially. Check if it is possible and allocate it if possible. If allocation is not possible, a new and different channel is searched as described below, in the same way as when a new call occurs.

A search is made for an allocatable channel, and if one is not found, the call will not be accepted if it is due to call generation, and the call will be forcibly disconnected during communication if it is due to cell movement.

If there are any channels that can be assigned, they are selected from them based on the movement information, and the channel that is in use in the cell closest to the cell is selected and assigned. Note that the reason why a channel used in a nearby cell is selected is to narrow the repetition interval of the same channel and increase frequency utilization efficiency in the entire service area.

(E) In the algorithm shown in Figure 1, when the need for channel allocation occurs and it is due to a cell movement, the channel that has been used up until now would be allocated if it was possible, but the channel would be cut due to the cell movement. It is no longer impossible to use the same channels as before without any change, as is the case with the fixed channel allocation method. Furthermore, by doing this before searching for a new channel, the use of the same channel will be prioritized. If the same channel is available,
This eliminates instantaneous interruptions caused by channel switching, processes such as searching for a channel to switch to, and transmitting and receiving switching signals.

In addition, when selecting channels based on movement information among allocatable channels, mobile units that are moving or planning to move in the same way, and that are communicating in a cell that is separated by at least the same channel minimum reuse interval, By assigning channels, there is a set of moving objects that use the same channel and move or plan to move in the same way. Then, when a mobile unit moves forward and moves from cell to cell, the mobile units in the pair also move forward and move from cell to cell, and the cells in each other's service area come close to each other due to cell movement and cannot use the same channel. This will no longer occur, and the intervals between cells that are assigned the same channel will become almost constant. This means that the same channel can often be used even if you move from cell to cell.
In addition, there are fewer cases of forced disconnection because there are no channels to allocate in the destination cell. Furthermore, if the same channel spacing is minimized, the channels will be used repeatedly at a high density and the frequency will be used effectively, but this will not decrease much due to cell movement.

(F) Example A case will be described in which a system in which the service area consists of a one-dimensional cell structure and mobile objects move at approximately the same speed, such as an expressway, will be described.

Figure 2 shows the algorithm (MD method). The MD method is a method of allocating a channel used by a mobile body moving in the same direction as possible to a mobile body that originates a call. In other words, the allocation is made so that groups of moving objects moving in the same direction use the same channel. If we do this, as mentioned in (e), when a certain moving object moves forward and moves from cell to cell, the moving object that becomes silk will also move forward and move from cell to cell, and in the end it will end up using the same channel. This reduces the probability of forced disconnection or channel switching. Also, if possible, Dr+1 (
Dr indicates the same channel minimum reuse interval, and 1 indicates the distance between one base station. ) Since the closest channel is allocated in the above manner, the same channel reuse interval in the entire service area becomes small, and the channel is repeatedly used at a high density. The reason for adding Dr+1 is to take into account the speed difference between the moving objects and the difference in position within the cell of the calling moving object and other moving objects forming a pair.

FIG. 3 shows an example of allocation using the fixed method and the MD method. In the fixed method, since only one channel is allocated to each cell, communication with two or more channels in each cell is impossible, 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 carried out simultaneously in one cell, and in this case, there is no call loss 9 forced disconnection. Furthermore, in the MD method, the number of channels required for allocation considering the direction of movement is 2.
This method allocates channels more efficiently and effectively than the fixed method. Also, I lost calls.

The probability of forced amputation is also low. In addition, the evaluation of channel switching is Cf, (Cfa is the number of times the channel switches during communication divided by the number of cell movements during communication.

However, this also applies in the case of forced disconnection. ). Then, 1
, 0, and the fixed method always changes every time, whereas the MD method does not change even once in this case. (G) Effects of the Invention According to the present invention, even if a mobile object often moves from cell to cell, it often uses the same channel.

Furthermore, the same channel use interval can be kept small and almost constant, allowing effective use of frequencies. In addition, the effect of reducing forced disconnection during communication that occurs when a channel is not allocated in the destination cell, instantaneous interruption due to channel switching, and control processing such as channel search and transmission/reception of switching signals can be reduced.

[Brief explanation of the drawing]

FIG. 1 is the algorithm of the present invention. FIG. 2 shows an MD (Moving D) which is an example of the present invention.
In this algorithm, D is the co-channel reuse interval, Dr is the co-channel minimum reuse interval, and 1 in Dr+1 indicates the distance between one base station. Figure 3 shows an example of allocation for the fixed method and MD method, where the hexagons are cells and a
, b, and c are channels; the subscript, for example, al, indicates that channel a is assigned first at time 1; Δ indicates call occurrence; and O indicates continuation. × indicates call loss or forced disconnection. The C value in the table is calculated by dividing the number of channel changes during communication by the number of cell changes during communication (however, the case of forced disconnection is also included).

Claims (2)

[Claims] (1) A channel allocation method incorporating movement information of a mobile body, characterized in that the movement information of the mobile body is incorporated when allocating a channel for wireless communication between the mobile body and a fixed station. (2) A channel allocation method incorporating movement information of a mobile body according to claim (1), wherein priority is given so that the mobile body can use the same channel even after moving from cell to cell.