JPH0411498A - Radio channel control system - Google Patents

Abstract

PURPOSE:To communicate with good quality while switching a base station by preventing the collision of signals generated while assigning the same channel at switching and shortening average time to complete switching while maintaining switch completion within constant time. CONSTITUTION:A assignable radio channel capable of assigning one or plural channels is respective flames at every base stations (a) 10 and (b) 10 newly is set. Then, when a moving station (a) 20 starts communication newly or assigns the plural channels newly for instance, the assignable radio channel can be set. Then, when the mobile station (a) 20 starts the communication newly or switches the channel during the communication, the base station (a) 10 assigns the radio channel newly and starts transmission when the assignable radio channel in the base station (a) 10 is present in the one or plural channels and a mobile station (a) 10 changes the designation of the radio channel are requires connection again when the radio channel is not assigned.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a wireless line #J control system of a small zone system (cellular system) mobile communication system.

(Conventional technology) As a next-generation mobile phone system, multiple base stations are placed within a service area, and multiple channels are provided for communication between base stations and mobile stations on the same frequency using time division multiplexing. Systems that repeatedly use channels spatially have been proposed.

The structure of the time division multiplex frame in this system is shown in Figure 2, with a part used for transmission from the base station to the mobile station (downlink) and a part used for transmission from the mobile station to the base station (uplink). These two parts are further divided into a plurality of time slots. Here, a set of one downlink time slot and one uplink time slot is called a channel.

The channel allocation method in this system is not a method of fixedly allocating a specific channel to each base station.If co-channel interference is not a problem between the base station and mobile station that are communicating, each base station has its own unique channel allocation method. This method allocates channels based on judgment.

A base station that is communicating with a mobile station transmits its own ID in the signal it sends, and a base station that is not communicating with a mobile station at all uses one channel in each frame to transmit its own ID.
Since the mobile station is transmitting D, the mobile station can measure the reception level of the signals of each base station in the vicinity.

When a mobile station starts a new communication or switches channels during communication, it measures the reception level of signals from surrounding base stations and selects the base station with the highest level as the base station to communicate with or switch to. At the same time, it monitors all downlink channels, selects a channel with a low level of interference, and notifies it to the base station to communicate with or switch to. Then, the communication destination or switching destination base station starts communication with the mobile station using one of the selected channels, if the base station has a low level of interference.

In the following explanation, the operation of allocating a new channel and starting transmission from the base station is the same whether starting a new communication or switching a channel during communication, so the explanation will be based on the case of channel switching.

(Problem to be Solved by the Invention) Since the mobile phone system described above does not systematically allocate channels to all base stations, multiple mobile stations simultaneously request different base stations to switch to the same channel. In this case, there is a possibility that signals from multiple base stations will collide.

As shown in FIG. 3, there are two base stations alo and bl.

Two mobile stations a20. When mobile station a20 issues a switching request to base station alo and mobile station b20 requests switching to the same channel at the same time to base station blo when base station b20 exists, base station alo and base station blo simultaneously use the same channel. If two mobile stations are close to each other, these signals may collide.

As described above, when a plurality of mobile stations switch channels at the same time, if the plurality of mobile stations are close to each other, there is a relatively high possibility that the same channel will be selected as the channel with the least co-channel interference.

Furthermore, as the density of base stations increases, the frequency of channel switching increases, so the probability that a plurality of mobile stations request switching at the same time also increases. Therefore, in a small zone type mobile communication system, if the density of base stations is increased to increase frequency usage efficiency, and channels are frequently switched while always selecting a better channel to maintain good communication quality, the same Signal collision due to simultaneous channel switching becomes a major problem.

As a countermeasure to this problem, a method may be considered in which when a collision occurs, the mobile station or base station retransmits data with a certain probability from the second time onwards. With this method, there is a possibility of repeated collisions and there is no guarantee that channel switching will be completed within a certain amount of time.
The quality of the original channel may deteriorate significantly and the switching may fail.

Another possibility is to make adjustments between base stations to avoid collisions before switching channels, but this method requires base stations to exchange information for channel switching. Become.

Furthermore, in order to solve these drawbacks, there is a method of switching channels only in a specific frame set for each base station, but with this method, the maximum time required to complete switching can be guaranteed, that is, it is constant. Although channel switching is completed within a certain amount of time, the disadvantage is that the average time required for channel switching becomes large.

Therefore, an object of the present invention is to prevent signal collisions without exchanging information for channel switching between base stations, and to switch channels in a short time while ensuring completion of channel switching within a certain time. The objective is to provide a wireless line control method that completes the following.

(Means for Solving the Problems) The radio channel control system of the present invention allows a plurality of base stations and a plurality of mobile stations to communicate in a plurality of frames consisting of a plurality of radio channels time-division multiplexed on the same frequency. A radio channel control method for a mobile communication system that communicates using a certain radio channel, in which one or more channels on each frame are set as assignable radio channels that can be newly assigned for each base station. When a mobile station starts a new communication or switches channels during communication, it specifies one or more wireless channels and requests connection to the target base station. If the base station has the assignable radio channel among the channels, the base station newly assigns that radio channel and starts transmission; if no radio channel is assigned, the mobile station specifies a radio channel. It is characterized by changing the connection and requesting connection again.

(Operation) According to the present invention, collisions during wireless channel switching can be avoided without exchanging information between base stations.

Furthermore, the average time required to complete switching is shortened while ensuring that switching of wireless channels is completed within at least a certain period of time.

(Example) Next, an example of the present invention will be described with reference to the drawings.

FIG. 4 is a diagram showing an example of the configuration of a mobile communication system.
In this figure, a to flo represent base stations, and a to b20 represent mobile stations. In this mobile communication system, the communication channels between the base station and mobile stations are time-divided on the same frequency as shown in Figure 2. It is multiplexed. Both the base station and mobile station can receive all channels with one receiver. In the present invention, different switching channels are set within the same frame for base stations that interfere with each other. In FIG. 4, base stations a to clo set different switching channels within the same frame, and alo and blo, blo and e
lo, and clo and fl.

It is assumed that the same switching channel is set within the same frame. Therefore blo, clo.

dlo and dlo, elo, flo and blo, dlo
, flo are set as different switching channels. FIG. 1 is a flow diagram of a base station that implements the radio channel control system of the present invention, and each base station decides to execute channel switching according to this flow. In this figure, n is the period of the switching channel set within each frame (in this example, n = 3>, i is the serial number of the frame, Mod (i, n) is the remainder kx ( x=a to f) are constants for determining the channel to be switched in each frame of the base station xlO, and in this embodiment, ka=kd=o, kb=ke=1, k
c=kf=2, j is an integer in the range where nJ+Mod (i, n)+kx exists as a channel number. The switching channel number set in this example is nj+Mod
(i, n) is expressed as 10kx, and is shifted in order for each frame. FIG. 5 shows a switching channel set for a certain base station. In this figure, 1.2.3. ... is the channel number, io, f
o +1. fo +2. . . . indicates the serial number of the frame, and the circle mark indicates the switching channel set in each frame.

Mobile station a was communicating with base station cfo via the third@th channel (hereinafter m1M channel is referred to as CHm).
When mobile station b20, which was communicating with base station alo using CH4 and base station CIO using CH4, attempts to switch channels to base station blo at the same time, if CH1 is not used in the surrounding area, the mobile station a20 is base station al
C) (1), and the mobile station b20 issues a request to the base station blo to switch to CHI.In Figure 1, the base station alo divides the serial number 10 of the next frame by n. If the remainder is 0, ka=o
Therefore, the number of channels that can be switched during the next frame 1° is 3,6.9...
On the other hand, since the base station blo has kb=1, the channel numbers that can be switched are 1.4, 7, . ...is... Therefore, the base station alo cannot allocate CHI, and the base station blO allocates CH1 from the time of signal transmission to the mobile station in the next frame Io and sends it to the mobile station b20.
Start communicating with. Mobile station a20, which was unable to switch channels, continues to issue switching requests to another CH2 to the same base station alO, and in frame 10+2, the channel numbers that base station alo can switch to are 2.5, 8, . ...so that frame io+
At step 2, base station alo allocates CH2 and starts communication with mobile station a20.

If the mobile station requests switching to another base station during communication, the base station that is communicating with the mobile station can receive the switching request signal, but at that point, it cannot switch to the new base station in the next frame. Since it is not known whether channel switching will be performed or not, even if a new channel is allocated, the original base station will transmit only once. For example, in frame 10, base station blo transmits to mobile station b20 using channel CHI, but base station clo also transmits to mobile station b20 using CH4. If the mobile station does not send a signal to the base station clo using the channel CH4 in that frame, the base station clo determines that the channel switching has been successful, ends the communication using CH4, and releases this channel.

In this embodiment, generally speaking, if the mobile station continues to issue switching requests to the same channel to the same base station X, then n(=3)
Since there is a frame in which the requested channel can be switched up to the frame number, switching is performed at that frame.

Next, an example is shown in which the mobile station specifies not one but multiple channels to switch to.
The mobile station b20 instructs the base station blo to switch to CH5, CH6, or CH7.
When requesting to switch to one of 7,
The channel numbers that base station alo can switch to in frame i0 are 3.6, 9, . ..., base station bl
The channel numbers that o can switch are 1, 4,
7. ... Therefore, the base station alo allocates CH6 to the mobile station a20, and the base station blo allocates CH7 to the mobile station b20. In this way, when a mobile station requests switching, the greater the number of channels that can be switched to, the higher the probability that they will be allocated at once, and the average time required to complete switching can be reduced. .

Note that although the above embodiments have only shown the case where channels are switched for different base stations, the same applies to the case where channels are switched within the same base station.

Further, in the above embodiments, the order of transmission within a frame is that the downlink is sent first and the uplink is sent later, but the present invention can be carried out in the same way even if this is reversed.

(Effects of the Invention) As described above, according to the present invention, it is possible to prevent signal collisions that occur by simultaneously allocating the same channel at the time of switching. Furthermore, it is possible to shorten the average time required to complete channel switching while ensuring that switching is completed within a certain amount of time. Therefore, communication can be continued with good quality even while switching base stations.

Furthermore, since there is no need for communication and control between base stations for channel switching, the system can be configured easily.

[Brief explanation of drawings]

Figure 1 is a flow diagram of a base station that implements the radio channel control system of the present invention, Figure 2 is a diagram showing communication channels time-division multiplexed on the same frequency, and Figure 3 is a diagram showing communication channels that are simultaneously transmitted from multiple base stations. FIG. 4 is a diagram showing an example of a configuration of a mobile communication system, and FIG. 5 is a diagram showing switching channels for each frame set at a certain base station. be. 10...Base station, 20...Mobile station.

Claims (1)

[Claims] In a radio channel control method for a mobile communication system in which a plurality of base stations and a plurality of mobile stations communicate using a certain radio channel in a plurality of frames consisting of a plurality of radio channels time-division multiplexed on the same frequency, One or more channels on each frame are set as assignable wireless channels for each base station, and when a mobile station starts new communication or switches channels during communication, When a connection is requested to a target base station by specifying one or more wireless channels, the base station transmits a request to the base station if there is a wireless channel that can be assigned to the base station among the one or more channels. The mobile station allocates a new wireless channel and starts transmission, and if the wireless channel is not allocated, the mobile station changes the wireless channel designation and requests connection again.