In a radio communication system that includes a plurality of base stations for providing communication service to mobile users or fixed users distributed over a plurality of areas, the radio parameters of each base station are determined to enable the provision of high-quality communication service when constructing the radio communication system or when making additions of radio stations to the already existing radio communication system.
One representative example of the radio parameters of each base station is the tilt angle of an antenna having directivity within a vertical plane. Other examples include the height of an antenna above the ground and the transmission power of the pilot channel that is transmitted from an antenna. The determination of radio parameters is typically realized by using a radio network design tool. A radio network design tool finds the propagation loss from the antenna to a prescribed location based on information such as the position, altitude, buildings, and topology of the base station in which the antenna is installed for which radio parameters are to be determined; calculates the reception power when a signal transmitted from the antenna is received at a prescribed location based on the transmission power from the antenna, the direction of the directivity within the horizontal plane of the antenna, the beam pattern within the horizontal plane and vertical plane of the antenna, and the previously found propagation loss; or calculates the reception quality indicated by the S/N (signal-to-noise) ratio or SIR (signal-to-interference ratio). Locations at which the reception power or reception quality do not satisfy prescribed values are then defined as “deterioration points,” and the radio network design tool finds the deterioration rate, which is the proportion of all areas of the service area that is occupied by deterioration points.
In addition, the radio network design tool virtually generates mobile users, calculates the interference power caused by the generation of mobile users, and then, by determining whether the users can be accommodated, calculates the radio capacity that is defined by the number of users or the amount of traffic that can be accommodated. The radio network design tool can automatically find radio parameters for which the above-described deterioration rate is reduced or for which the radio capacity is increased.
Explanation next regards methods of automatically finding radio parameters implemented in the related art. The selection of an antenna that changes tilt angle, which is a representative radio parameter, and the determination of the angle of this antenna are realized as described hereinbelow.
“Antennas in which the deterioration rate of the coverage of one antenna is at least a prescribed value” are selected as antennas for which the tilt angle is to be decreased and the tilt angle of the selected antennas is set smaller. The alteration angle of the tilt angle when decreasing is assumed to be a fixed angle. In addition, “antennas in which the deterioration rate of the coverage of one antenna is no greater than a prescribed value” are selected as antennas for which the tilt angle is to be increased. The alteration angle of the tilt angle when increasing is assumed to be a fixed angle. The tilt angle for decreasing the deterioration rate of all areas is found by automatically repeating the above-described processes.
Other methods of altering the tilt angle relating to typical radio parameters indicate that “all algorithms can be used” in the “optimizing process” as in, for example, the wireless network optimizing method disclosed in JPA-2001-204069. More specifically, several methods exist, examples that can be offered including hereditary algorithms or typical optimizing algorithms in the field of set-optimizing that take as objective functions deterioration rate, coverage, and radio capacity. A radio communication system small in size in which the processing speed of the optimizing algorithm does not present problems would permit the use of a “round-robin algorithm” in which the set of all radio parameters is searched and tested.
For example, FIG. 10 shows the configuration of a conventional example of a radio parameter determination device that takes the deterioration rate as the objective function regarding the tilt angle of an antenna, which is a representative radio parameter. This example of the related art is composed of initial tilt angle input means 101 and all-area deterioration-rate-decreasing tilt angle determination means 102; wherein all-area deterioration-rate-decreasing tilt angle determination means 102 takes the initial tilt angle as the initial value, determines the tilt angle at which the deterioration rate of all areas is reduced, and supplies as output the tilt angle of all areas and the deterioration rate of all areas following the determination of tilt angle.