Mobile communication system and distributed broadcast information control method in mobile communication system

Abstract: A mobile communication system can implement broadcasting control that generates broadcast information autonomously in a distributed manner, thereby obviating the need for an RNC (Radio Network Controller). Each base station (#1-#N) has an IP address and a base station multicast address. Each base station sends its own system information to all base stations using the multicast address. Each base station generates its broadcast information from its own system information and the system information received from other base stations. Thus, it can generate the broadcast information autonomously in a distributed manner without using the RNC.

Description: The present invention relates to a mobile communication system and a distributed broadcast information control method in the mobile communication system, which are characterized by the broadcast information control in the mobile communication system that offers communication services from a base station to a mobile station via a radio channel. In a mobile communication system, a base station periodically transmits various types of broadcast information such as regulation information and available channel information of each area to mobile stations via a broadcasting channel. Receiving such broadcast information, the mobile station can learn the current conditions of the mobile communication system. Fig. 1 shows the contents of a broadcast information message defined in a PDC (Personal Digital Cellular) system, as an example of the broadcast information. In the broadcasting control in the conventional mobile communication system, an RNC (Radio Network Controller), a higher level control office of the base station that controls multiple base stations, prepares the broadcast information and transmits it to the base stations in a point-to-point manner. Accordingly, the conventional system has a problem in that the load concentrated on the RNC increases with the number of the base stations controlled by the RNC. US-A-5724665 discloses a communication system in which each base station scans for control signals and evaluates the signal strength level of the signals to locate close by stations. The signals are ordered in order of decreasing signal strength above a threshold level. EP-A-0700173 discloses a mobile radio communication system in which each base station outputs a base station signal to the loop transmission line of the system including receiving level information indicating the receiving level of the received radio waves transmitted from a mobile station. It is therefore an object of the present invention to implement broadcasting control capable of obviating the need of the RNC by preparing the broadcast information autonomously in a distributed manner by interconnecting the base stations two-dimensionally to enable them to exchange information directly. According to a first aspect of the present invention, there is provided a base station that offers radio communication services in a service area, said base station being characterized by comprising: receiving means for receiving information about broadcast information sent from another base station, the broadcast information including information for controlling coverage of its own broadcast information; broadcast information generating means for generating broadcast information about a broadcasting area of said base station, based upon said received information about the broadcast information; judging means for judging whether a condition indicated by the controlling information is met or not, based upon said received information about the broadcast information; and transferring means for, when a result of the judgment meets the condition, transferring said received information about broadcast information to base stations other than said other base station which is a source of the information about broadcast information. The information for controlling the coverage of the information may include a hopping number field value. The information for controlling the coverage of the broadcast information may include latitude and longitude information of a source base station and its desired reception coverage value. According to a second aspect of the present invention, there is provided a method for controlling broadcast information in a base station that offers radio communication services in a service area, said method being characterized by comprising the steps of: receiving information about broadcast information sent from another base station, the broadcast information including information for controlling coverage of its own broadcast information; generating broadcast information about a broadcasting area of said base station, based upon said received information about the broadcast information; judging whether a condition indicated by the controlling information is met or not, based upon said received information about the broadcast information; and when a result of the judgment meets the condition, transferring said received information about broadcast information to base stations other than said other base station which is a source of the information about broadcast information. The information for controlling the coverage of the information may include a hopping number field value. The information for controlling the coverage of the information may include latitude and longitude information of a source base station and its desired reception coverage value. The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings. Fig. 1 is a table showing the relationship of Figs. 1A and 1B; Fig. 1A is a block table showing an example of the contents of a broadcast information message; Fig. 1B is a block table showing an example of the contents of a broadcast information message; Fig. 2 is a diagram illustrating an embodiment 1 of the mobile communication system in accordance with the present invention; Fig. 3 is a diagram illustrating an embodiment 2 of the mobile communication system in accordance with the present invention; Fig. 4A is a diagram illustrating a multicast packet format in the embodiment 2; Fig. 4B is a flowchart illustrating the operation when each base station in the embodiment 2 receives a multicast packet; Fig. 5 is a diagram illustrating an embodiment 3 of the mobile communication system in accordance with the present invention; Fig. 6A is a diagram illustrating a multicast packet format in the embodiment 3; Fig. 6B is a flowchart illustrating the operation when each base station in the embodiment 3 receives a multicast packet; Fig. 7 is a diagram illustrating an embodiment 4 of the mobile communication system in accordance with the present invention; Fig. 8A is a diagram showing a structure of a broadcast information acquisition request packet format; Fig. 8B is a diagram showing another structure of a broadcast information acquisition request packet format; Fig. 8C is a diagram showing a structure of a broadcast information acquisition response packet format; and Fig. 9 is a block diagram showing a configuration of a base station used in the embodiments 1-4 of the mobile communication system in accordance with the present invention. Embodiments of the invention will now be described with reference to the accompanying drawings. In the following embodiments, a base station is assumed to have a configuration as shown in Fig. 9 as a component constituting the embodiments in accordance with the present invention. Specifically, the base station comprises a transmitting section 1 for transmitting necessary information to a mobile station; a receiving section 2 for receiving a signal transmitted from the mobile station; an information exchanging section 3 for exchanging information about broadcast information with other base stations via an IP (Internet Protocol) network 6; a broadcast information generating section 4 for preparing broadcast information about the broadcasting area the base station belongs to from the information about the broadcast information the information exchanging section 3 collects from the other base stations; and a control section 5 for controlling the transmitting section 1, the receiving section 2, the information exchanging section 3 and the broadcast information generating section 4. The information exchanging section 3, broadcast information generating section 4 and control section 5 can be constructed by a computer system. The computer system implements the functions of the information exchanging section 3, broadcast information generating section 4 and control section 5 by comprising a CPU, a ROM (and a hard disk drive) for storing programs to execute the present invention, a RAM for providing the CPU with a work area, and an interface for accessing the IP network 6, and by executing the programs stored in the ROM (and a hard disk drive) by the CPU. The operations of the following embodiments are executed under the control of the control section 5. On the other hand, the mobile station comprises in its internal memory a program storing area for storing programs to execute data processing that will be described below, and a temporarily storing area of data, and has its internal CPU execute the programs. (EMBODIMENT 1) Fig. 2 is a block diagram showing an embodiment 1 that implements the broadcast information control in accordance with the present invention in the IP network. In the present embodiment 1, each base station (#1-#N) has an IP address and a base station multicast address as follows. Node IP address Multicast address base station #1 xxx.xxx.0.0 xxx.xxx.1.0 base station #2 xxx.xxx.0.1 xxx.xxx.1.0 : : : base station #N xxx.xxx.0.N xxx.xxx.1.0 Each base station sends its own system information to all the base stations using the multicast address. Each base station generates its broadcast information from the system information of the other base stations and its own system information. (EMBODIMENT 2) Fig. 3 is a block diagram showing an embodiment 2 that implements the broadcast information control in accordance with the present invention in the IP network. In the present embodiment 2, each base station has an IP address and a base station multicast address as in the foregoing embodiment 1. Each base station sends its own system information using the multicast address. In this case, the transmission packet includes a hopping number field, in which a hopping number field value is set at the transmission to control the coverage of the packet. Fig. 4A shows a format of the multicast packet, and Fig. 4B shows the operating flow at the time when the base station receives the multicast packet. The operation is carried out by the data processing unit in each base station. More specifically, receiving the packet, each base station detects the hopping number field value of the received multicast packet at step S1. When the value is greater than one, it captures the information at step S2, reduces the hopping number field value by one, and transfers it to other base stations. On the other hand, when the hopping number field value of the received packet is one at step S1, although the base station captures the information at step S3, it does not transfer it to other base stations. To produce the broadcast information, since it is enough for only the base stations close to each other to exchange information, such control is very effective in terms of reducing the traffic of the network. Each base station generates the broadcast information from its own system information and the system information of other base stations received. (EMBODIMENT 3) Fig. 5 is a block diagram showing an embodiment 3 that implements the broadcast information control in accordance with the present invention in the IP network. In the present embodiment 3, each base station has an IP address and a base station multicast address as in the foregoing embodiment 1. Each base station sends its own system information using the multicast address. In this case, the transmission packet includes latitude and longitude information about a source base station, so that the coverage of the packet is controlled by a desired packet reception coverage value (Ddesire) that is set at the transmission. Fig. 6A shows a format of the multicast packet, and Fig. 6B shows the operating flow at the time when the base station receives the multicast packet. The operation is carried out by the data processing unit in each base station. More specifically, receiving the packet, each base station calculates the distance D between the base station and the source base station from its own latitude and longitude and from the latitude and longitude information about the source base station in the received multicast packet at step S11. At the next step S12, the data processing unit compares the distance D with the desired packet reception coverage value Ddesire. If D ≦ Ddesire, it captures the information in the packet at step S13, and transfers it to other base stations at step S14. In contrast, if D > Ddesire at step S12, it discards the packet at step S15 without transferring it. To produce the broadcast information, since it is enough for only the base stations close to each other to some extent to exchange information, such control is very effective for reducing the traffic of the network. Each base station generates the broadcast information from its own system information and the system information of other base stations received. (EMBODIMENT 4) Fig. 7 is a block diagram showing an embodiment 4 of the broadcast information control in accordance with the present invention. In the present embodiment 4, a mobile station MS carries out control using the broadcast information of neighboring base stations when it wishes to move to a particular destination with continuing its communication. Here, a description is made assuming that the broadcasting area consists of a single cell. First, the mobile station MS transmits a broadcast information acquisition request packet using the base station multicast address. In this case, the packet coverage control based on the hopping number or the latitude and longitude information as described in the embodiment 2 or 3 is applicable to the broadcast information acquisition request packet. Figs. 8(a) and 8(b) each illustrate a format of the broadcast information acquisition request packet when the control is applied. Receiving the broadcast information acquisition request packet, the base station transmits its own broadcast information to the mobile station MS using the format of the broadcast information acquisition response packet. Here, the broadcast information acquisition response packet includes the latitude and longitude information of the base station that transmits the packet. Thus, the mobile station MS can move to the destination cell with always selecting cells having available channels in accordance with the received broadcast information about individual stations. According to the present invention, the base stations are two-dimensionally connected to each other, so that the base stations can directly exchange information, and generate broadcast information autonomously in a distributed manner. Thus, the broadcasting control without requiring the RNC can be implemented. The present invention has been described in detail with respect to preferred embodiments, and it will now be apparent from the foregoing to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and it is the intention, therefore, in the appended claims to cover all such changes and modifications as fall within the scope of the claims.

Claims: A base station that offers radio communication services in a service area, said base station being characterized by comprising: receiving means (2) for receiving information about broadcast information sent from another base station, the broadcast information including information for controlling coverage of its own broadcast information; broadcast information generating means (4) for generating broadcast information about a broadcasting area of said base station, based upon said received information about the broadcast information; judging means for judging whether a condition indicated by the controlling information is met or not, based upon said received information about the broadcast information; and transferring means for, when a result of the judgment meets the condition, transferring said received information about broadcast information to base stations other than said other base station which is a source of the information about broadcast information. The base station as claimed in claim 1, wherein the information for controlling the coverage of the broadcast information includes a hopping number field value. The base station as claimed in claim 1, wherein the information for controlling the coverage of the broadcast information includes latitude and longitude information of a source base station and its desired reception coverage value. The base station as claimed in any one of claims 1 to 3, further comprising: means for sending information about broadcast information about the source and including information for controlling coverage of its own broadcast information, to another base station using a multicast address. A method for controlling broadcast information in a base station that offers radio communication services in a service area, said method being characterized by comprising the steps of: receiving information about broadcast information sent from another base station, the broadcast information including information for controlling coverage of its own broadcast information; generating broadcast information about a broadcasting area of said base station, based upon said received information about the broadcast information (S11); judging whether a condition indicated by the controlling information is met or not, based upon said received information about the broadcast information (S12); and when a result of the judgment meets the condition, transferring said received information about broadcast information to base stations other than said other base station which is a source of the information about broadcast information. The method for controlling broadcast information as claimed in claim 5, wherein the information for controlling the coverage of the broadcast information includes a hopping number field value. The method for controlling broadcast information as claimed in claim 5, wherein the information for controlling the coverage of the broadcast information includes latitude and longitude information of a source base station and its desired reception coverage value. A mobile communication system including multiple base stations of any one of claims 1 to 3 that are interconnected two-dimensionally and offer radio communication services in individual service areas. The mobile communication system as claimed in claim 8, including a mobile station comprising means for acquiring broadcast information about an area other than a broadcasting area the mobile station is visiting, from a base station in the broadcasting area the mobile station is visiting.

Inventors: IKEDA TAKEHIRO, OKAJIMA ICHIRO, UMEDA NARUMI, IKEDA, TAKEHIRO, OKAJIMA, ICHIRO, UMEDA, NARUMI
Applicants: NTT DOCOMO INC, NTT DOCOMO, INC.
Application year: 2001
Main classification: H04Q7
IPC codes: H04W80, H04W92, H04W4