JP2626161B2 - Wireless line control method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a radio channel control method for a small zone (cellular) mobile communication system.

(Prior Art) As a next-generation mobile phone system, a plurality of base stations are arranged in a service area, and a plurality of channels for communication between the base station and the mobile station are provided on the same frequency by time division multiplexing. A system that repeatedly uses a channel spatially has been proposed.

As shown in FIG. 2, the configuration of the time division multiplex frame of this system is a part used for transmission (downlink) from the base station to the mobile station and a part used for transmission (uplink) from the mobile station to the base station. The 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. Unless co-channel interference is a problem between the communicating base station and mobile station, each base station has its own Is a method of allocating a channel according to the judgment of.

The base station that is communicating with the mobile station transmits its own ID in the transmitted signal, and the base station that does not communicate with the mobile station at all uses one channel in each frame.
Is transmitted, the mobile station can measure the transmission level of the signal of each base station existing in the vicinity.

When newly starting communication or switching channels during communication, the mobile station measures the reception level of signals from peripheral base stations and selects the highest level base station as the communication destination or switching destination base station. At the same time, all downlink channels are observed, and a channel having a low interference level is selected and notified to a communication destination or a switching destination base station.
If the base station at the communication destination or the switching destination has a low interference level even at the base station among the selected channels, communication with the mobile station is started using one of the selected channels.

In the following description, the operation of allocating a new channel and starting transmission from the base station is the same for both starting a new communication and switching a channel during communication.

(Problems to be Solved by the Invention) Since the above-mentioned mobile phone system does not systematically allocate channels to the entire base station, a plurality of mobile stations simultaneously request different base stations to switch to the same channel at the same time. In such a case, collision of signals from a plurality of base stations may occur. Two base stations as shown in FIG.
When two mobile stations a20 and b20 exist near the middle of a10 and b10, the mobile station a20 becomes the base station a10 and the mobile station b20 becomes the base station b10.
When the base station a10 and the base station b10 transmit signals using the same channel at the same time and simultaneously issue a switching request to the same channel, these signals collide because the two mobile stations are close to each other. Sometimes.

When a plurality of mobile stations switch channels at the same time as described above, there is a relatively high possibility that the same channel is selected as a channel having the same channel interference least when the plurality of mobile stations are close to each other. Further, as the density of the base stations increases, the frequency of channel switching increases, so that the probability that a plurality of mobile stations request switching at the same time increases.
Therefore, in a small-zone mobile communication system,
Increase the density of base stations in order to increase the efficiency of spectrum utilization,
When frequently switching channels while always selecting a better channel in order to maintain good communication quality, signal collision due to simultaneous switching to the same channel becomes a serious problem.

As a countermeasure, a method is conceivable in which when a collision occurs, a mobile station or a base station retransmits at a certain probability from the second time. With this method, there is no guarantee that the channel switch will be completed within a certain time since there is a possibility of repeated collisions,
The quality of the original channel may be significantly degraded and switching may fail.

In addition, in order to avoid collisions, a method of switching channels after performing adjustment so that collisions do not occur between base stations may be considered, but this method requires information exchange for channel switching between base stations. .

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 in this method, the maximum value of the time until the switching is completed can be guaranteed, that is, a fixed value. Although the channel switching is completed within the time, there is a disadvantage that the average value of the time required for the channel switching becomes large.

Accordingly, an object of the present invention is to prevent signal collision 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. To provide a wireless channel control method that completes the above.

(Means for Solving the Problems) The radio channel control method according to the present invention is a radio channel control method comprising: a plurality of base stations and a plurality of mobile stations in a plurality of frames formed by a plurality of radio channels time-division multiplexed on the same frequency; What is claimed is: 1. A radio channel control method for a mobile communication system in which communication is performed using a certain radio channel, wherein one or a plurality of channels on each frame of each base station are mutually transmitted in the same frame by base stations that interfere with each other. Set as an allocatable radio channel that can be newly assigned,
When a mobile station newly starts communication or switches channels during communication, when one or more radio channels are designated and a connection is requested to a target base station, the base station transmits the one or more radio channels. If the assignable wireless channel in the base station is included in the channel, the base station newly assigns the wireless channel and starts transmission. If the wireless channel is not assigned, the mobile station changes the designation of the wireless channel. Request connection again.

(Operation) According to the present invention, collision at the time of wireless channel switching is avoided without exchanging information between base stations. Also, the average time to complete the switching is shortened while ensuring that the switching of the wireless channel is completed at least within a certain time.

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

FIG. 4 is a diagram showing a configuration example of a mobile communication system. In the figure, a to f10 represent base stations, and a to b20 represent mobile stations. In this mobile communication system, a communication channel between a base station and a mobile station is time-division multiplexed on the same frequency as shown in FIG. Both the base station and the mobile station can receive all channels with one receiver. In the present invention, different switching channels are set in the same frame for base stations that interfere with each other. In FIG. 4, base stations a to c10 set different switching channels in the same frame, and a10 and b10, b10 and e10, and c10
And f10 each set the same switching channel in the same frame. Therefore b10, c10, d10 and d10, e1
For 0, f10 and b10, d10 and f10, respectively, different switching channels are set. FIG. 1 is a flow chart of a base station for realizing the radio channel control method of the present invention. According to this flow, each base station determines execution of channel switching. In the figure, n is the cycle of the switching channel set in each frame (in this embodiment, n =
3), i is the serial number of the frame, Mod (i, n) is the remainder of dividing i by n, and kx (x = a to f) is for determining the channel to execute switching in each frame of the base station x10. In this embodiment, ka = kd = 0, kb = ke = 1, and kc =
kf = 2, j is an integer in a range where nj + Mod (i, n) + kx exists as a channel number. The switching channel number set in this embodiment is represented by nj + Mod (i, n) + kx, and is shifted in order for each frame. The switching channel set for a certain base station is shown in FIG.
FIG. In this figure, 1,2,3, ... are channel numbers,
_{i 0, i 0 + 1,} i 0 + 2, ... is a frame serial number, ○ marks represent the set switching channels at each frame.

The mobile station a20 that has been communicating with the base station c10 using the third channel (hereinafter, the m-th channel is referred to as CHm) is moving to the base station a10, and has been communicating with the base station c10 using CH4. If the station b20 attempts to switch channels to the base station b10 at the same time and the CH1 is not used in the vicinity, the mobile station a20 issues a request to the base station a10 to switch to CH1, and the mobile station b20 returns to the base station b10. A request to switch to CH1 is issued to b10. In FIG. 1, assuming that the remainder obtained by dividing the serial number i ₀ of the next frame by n is 0,
Since ka = 0, the numbers of the channels that can be switched during the next frame i ₀ are 3, 6, 9,. On the other hand, since kb = 1 in base station b10, the channel numbers that can be switched are 1, 4, 7,.... Therefore base station a10
Can not be assigned to CH1, base station b10 starts communication with a mobile station b20 from the time signal transmission to the mobile station assigns a CH1 in the next frame i _0. The mobile station a20 that could not switch the channel transmits another CH to the same base station a10.
Continuing issues a switching request to 2, since the frame i ₀ +2 channel number can be the base station a10 switches in that 2,5,8, ... become a base station in the frame i ₀ +2
a10 allocates CH2 and starts communication with the mobile station a20.

When the mobile station requests switching to another base station during communication, the base station communicating with the mobile station can receive the switching request signal, but at that time, the base station communicates with the new base station in the next frame. Since it is not known whether or not channel switching will be performed, even if a new channel is allocated, the original base station will transmit once and only once. For example, the frame i base station b10 in ₀ channel to the mobile station b20 CH1
, But base station c10 also uses mobile station b2 using CH4.
Send to 0. And in that frame from the mobile station to the base station c
If no signal is sent to channel 10 using channel CH4, base station c
10 judges that the channel switching has been successful, ends the communication by CH4, and releases this channel.

In this embodiment, if the mobile station generally keeps requesting the same base station x to switch to the same channel, n (=
3) Since there is a frame in which the channel requested by the frame can be switched, the switching is performed there.

Next, an example in which the mobile station specifies a plurality of switching destination channels instead of one switching channel will be described. Mobile station A20 becomes base station a10
CH5, CH6, switching of the one CH7, when the mobile station b20 has each request to switch to either the base station b10 CH5, CH6, CH7 of, that base station a10 switches in frame i ₀ Available channel numbers are 3,6,9,…, base station
The channel numbers that can be switched by b10 are 1, 4, 7,
, The base station a10 sends CH6 to the mobile station a20 and the base station b
10 assigns CH7 to the mobile station b20. As described above, when the mobile station requests switching, the greater the number of channels that can be switched, the higher the probability that the mobile station will be assigned at one time, and the average value of the time required to complete the switching can be reduced.

In the above embodiment, only the case where the channel is switched to a different base station is shown, but the same applies to the case where the channel is switched within the same base station. Further, in the above embodiment, the transmission order in the frame is down-stream first and up-stream rear, but the present invention can be similarly performed even if the order is reversed.

(Effects of the Invention) As described above, according to the present invention, it is possible to prevent collision of signals generated by allocating the same channel at the time of switching. In addition, the average time required to complete the channel switching can be reduced while ensuring the completion of the switching within a predetermined time. Therefore, communication can be continued with good quality while switching base stations.

Further, since there is no need to perform communication and control between base stations for channel switching, a system can be easily configured.

[Brief description of the drawings]

FIG. 1 is a flowchart of a base station for realizing the radio channel control method of the present invention, FIG. 2 is a diagram showing a communication channel time-division multiplexed on the same frequency, and FIG. FIG. 4 is a diagram illustrating an example of a configuration in which a mobile communication system is configured to collide with signals by allocating the same channel. FIG. 5 is a diagram illustrating a switching channel for each frame set by a certain base station. is there. 10 ... base station, 20 ... mobile station.

Claims (1)

(57) [Claims] 1. A radio communication system 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 composed of a plurality of radio channels time-division multiplexed on the same frequency. In the line control method, one or more channels on each frame are assigned to each base station as assignable radio channels that can be newly assigned so that base stations that interfere with each other are different from each other in the same frame. When a mobile station starts a new communication or switches channels during communication and requests connection to a target base station by specifying one or more radio channels, the base station sets the one Or, if the assignable wireless channel in the base station is among a plurality of channels, the base station newly assigns the wireless channel. Start the signal, the mobile station if assigned radio channel radio network controller and wherein the requesting connection again by changing the designation of the radio channels.