This invention relates to a personal digital cellular telecommunication system (PDC) using a code division multiple access (CDMA) system and, in particular, to a call control method for use in mobile communication to fix a radio zone upon call origination at a mobile terminal irrespective of a communication traffic and to a system therefor.
In a conventional mobile/hand-held cellular telecommunication system, a plurality of service areas (PDC/cell, PHS [personal handyphone system]/microcell) are continuously formed to enable connection of a communication line upon continuous movement of a mobile terminal. In each radio service area (may be referred to as a radio zone), a single radio base station (cell base station) accommodated in a mobile communication control station via a wired or a wireless line or channel (WILL system) is arranged. The mobile terminal moves between the radio zones from one to another. In a CDMA system for example, the radio base station notifies information such as an identifier assigned to the station and an available radio channel by continuously transmitting the information via a radio channel called a pilot channel.
Moving in the radio zone of each radio base station, the mobile terminal at first receives the pilot channel and also receives and collects the information of peripheral radio base stations. Upon call origination, the mobile terminal originates a call to a particular radio base station having a strongest reception field strength (RSSI (Reception Signal Strength Indicator)) among the information of the radio base stations collected as mentioned above, and starts communication therewith. Each radio base station can use a plurality of radio channels and determines a radio channel to be used with reference to a radio wave propagation state between the station and the mobile terminal to communicate therewith.
If the radio wave propagation state of a current radio channel being used is deteriorated during communication, i.e., upon occurrence of decrease in reception field strength (RSSI) or deterioration in quality data (QI (Quality Indicator)) representative of presence/absence of word errors, the current radio channel is switched into another radio channel. Specifically, a mobile assisted handover procedure is executed to switch the current radio channel being involved in communication into another radio channel so that no line interruption occurs. Proposal is also made of a method (diversity handover) in which a same signal is transmitted from a plurality of radio base stations to a mobile terminal and the mobile terminal selects a particular reception signal among a plurality of reception signals (see Masuhito AKEBI et al xe2x80x9cHandover Control Schemes Using Micro-Diversity Techniques for Microcellular Communications Systemsxe2x80x9d, Technical Report of IEICE, RCS 93-86, 1994).
In a CDMA mobile communication system, diversity handover may be called soft handover. In the CDMA, mobile communication system of an IS-95 standard, transmission is carried out under closed/open loop control for fixing transmission power of the pilot channel. In addition, a particular mobile terminal controls connection of a radio base station upon soft handover by the use of a peripheral zone set including the information of the pilot channels of the peripheral radio zones and an active set of a combination of the radio base stations simultaneously connected to the mobile terminal.
As conventional mobile communication systems of the type, xe2x80x9cCDMA Radio Transmission System and Transmission Power Control Device and Transmission Power Controlling Measuring Device Used in the Systemxe2x80x9d is disclosed in Japanese Unexamined Patent Publication (JP-A) No. H10-56421 and xe2x80x9cMobile Communication Systemxe2x80x9d is disclosed in Japanese Patent No. 2739850.
If the control is carried out to fix the transmission power of the pilot channel in the conventional systems described above, variation in communication/control traffic in and out of each radio zone causes the fluctuation in reception quality of the pilot channel at the mobile terminal. This results in variation in area of the radio zone. In other words, it is required to provide a control method for fixing the area of the radio zone upon call origination at the mobile terminal irrespective of the communication/control traffic.
If the mobile terminal transmits an access request (or a connection request) to a particular radio base station for multiple access on the basis of the above-mentioned peripheral radio zone set, the particular radio base station as a requested station determines allowance/rejection of the multiple access request, taking into account the communication traffic at the station and the communication quality, and notifies the result of determination to the mobile terminal. However, production of such control signal also constitutes a factor of deterioration of the communication quality. In the above-mentioned call control method, a mobile terminal during soft handover and a mobile terminal originating a new call are similarly dealt with. This increase a call loss ratio.
Systems disclosed as conventional systems in the above-mentioned publications have similar problems.
It is an object of this invention to provide a call control method in mobile communication and a system therefor, which are capable of starting stable communication.
It is another object of this invention to provide a call control method in mobile communication and a system therefor, which are capable of fixing a call origination allowable area irrespective of a downlink communication traffic.
It is still another object of this invention to provide a call control method in mobile communication and a system therefor, in which a mobile terminal can produce a multiple access request in correspondence to a propagation loss.
It is yet another object of this invention to provide a call control method in mobile communication and a system therefor, in which a radio base station can control whether or not the station acts as a multiple access destination depending upon the communication traffic of the station without carrying out useless call control.
It is a further object of this invention to provide a call control method in mobile communication and a system therefor, which is capable of assuring, in case where a call setup request is produced by a mobile terminal when a communication traffic at a radio base station exceeds a threshold level, a communication capacity for a requested call to decrease a call loss ratio by suppressing the possibility that the radio base station acts as a multiple access destination.
According to this invention, there is provided a call control method in mobile communication in which communication is carried out through a radio channel between a mobile terminal and each of a plurality of radio base stations accommodated in a mobile communication control station and each radio base station at first carries out notification of information through a pilot channel to the mobile terminal moving into a radio zone thereof, wherein:
each of the radio base stations carries out:
a step of storing pilot channel transmission power level information into the pilot channel to be transmitted; and
a step of carrying out transmission by the pilot channel;
the mobile terminal carrying out:
a step of receiving the pilot channel from each of the radio base stations;
a step of calculating a difference between a reception field strength of the pilot channel of each of the radio base stations and the transmission power level information received;
a step of detecting from the difference a particular radio base station of a minimum propagation loss; and
a step of originating a call to the particular radio base station of a minimum propagation loss thus detected.
According to this invention, there is provided a call control method in mobile communication in which communication is carried out through a radio channel between a mobile terminal and each of a plurality of radio base stations accommodated in a mobile communication control station and each radio base station at first carries out notification of information through a pilot channel to the mobile terminal moving into a radio zone thereof, wherein:
each of the radio base stations carries out:
a step of judging whether or not a downlink communication traffic is great or small;
a step of making the pilot channel to be transmitted store transmission power level information having a value greater than a pilot channel transmission power level actually transmitted in case where the communication traffic is small or making the pilot channel to be transmitted store the transmission power level information having a value smaller than the pilot channel transmission power level actually transmitted in case where the downlink communication traffic is great; and
a step of carrying out transmission by the pilot channel;
the mobile terminal carrying out:
a step of receiving the pilot channel from each of the radio base stations;
a step of calculating a difference between a reception field strength of the pilot channel of each of the radio base stations and the transmission power level information received;
a step of detecting from the difference a particular radio base station of a minimum propagation loss; and
a step of originating a call to the particular radio base station of a minimum propagation loss thus detected.
According to this invention, there is provided a call control method in mobile communication in which communication is carried out through a radio channel between a mobile terminal and each of a plurality of radio base stations accommodated in a mobile communication control station and each radio base station at first carries out notification of information through a pilot channel to the mobile terminal moving into a radio zone thereof, wherein:
each of the radio base stations carries out:
a step of storing pilot channel transmission power level information into the pilot channel to be transmitted; and
a step of carrying out transmission by the pilot channel;
the mobile terminal carrying out:
a step of receiving the pilot channel from each of the radio base stations upon execution of soft handover when approaching its radio zone;
a step of calculating a difference between a reception field strength of the pilot channel and the transmission power level information; and
a step of determining a particular radio base station for multiple access with reference to the difference.
According to this invention, there is provided a call control method in mobile communication in which communication is carried out through a radio channel between a mobile terminal and each of a plurality of radio base stations accommodated in a mobile communication control station and each radio base station at first carries out notification of information through a pilot channel to the mobile terminal moving into a radio zone thereof, wherein:
each of the radio base stations carries out:
a step of judging whether or not a downlink communication traffic is great or small;
a step of identifying the case where the downlink communication traffic exceeds a predetermined threshold level in the judging step;
a step of setting transmission power level information to a value greater than a transmission power level transmitted by the station in case where the threshold level is exceeded in the identifying step;
a step of storing the pilot channel transmission power level information into the pilot channel to be transmitted; and
a step of transmitting the pilot channel;
the mobile terminal carrying out:
a step of receiving the pilot channel from each of the radio base stations upon execution of soft handover when approaching its radio zone;
a step of calculating a difference between a reception field strength of the pilot channel and the transmission power level information; and
a step of determining a particular radio base station for multiple access with reference to the difference.
According to this invention, there is provided a call control method in mobile communication in which communication is carried out through a radio channel between a mobile terminal and each of a plurality of radio base stations accommodated in a mobile communication control station and each radio base station at first carries out notification of information through a pilot channel to the mobile terminal moving into a radio zone thereof, wherein:
each of the radio base stations carries out:
a step of judging whether or not a downlink communication traffic is great or small;
a step of making the pilot channel store first transmission power level information having a value greater and smaller than a pilot channel transmission power level actually transmitted in case where the downlink communication traffic is decreased and increased in the judging step, respectively;
a step of making the pilot channel store second transmission power level information having a value greater than the transmission power level transmitted by the station in case where the downlink communication traffic is increased to exceed a predetermined threshold level and a call setup request is received from the mobile terminal; and
a step of transmitting the pilot channel;
the mobile terminal carrying out:
a step of receiving the pilot channel from each of the radio base stations;
a step of calculating a difference between the reception field strength of the pilot channel of each of the radio base stations and the first transmission power level information received;
a step of detecting from the difference a first particular radio base station of a minimum propagation loss;
a step of originating a call to the particular radio base station of a minimum propagation loss thus detected;
a step of calculating a difference between the reception field strength of the pilot channel and the second transmission power level information upon execution of soft handover; and
a step of determining a second particular radio base station for multiple access with reference to the difference.
According to this invention, there is provided a mobile communication system in which communication is carried out through a radio channel between a mobile terminal and each of a plurality of radio base stations accommodated in a mobile communication control station and each radio base station at first carries out notification of information through a pilot channel to the mobile terminal moving into a radio zone thereof, wherein:
each of the radio base stations makes the pilot channel to be transmitted store pilot channel transmission power level information and transmits the pilot channel;
the mobile terminal receiving the pilot channel from each of the radio base stations, detecting a particular radio base station of a minimum propagation loss given by the difference between a reception field strength of the pilot channel and the transmission power level information received, and originating a call thereto.
Each of the radio base stations comprises:
storing means for storing the pilot channel transmission power level information into the pilot channel to be transmitted; and
transmitting means for transmitting on the pilot channel the transmission power level information stored by the storing means;
the mobile terminal comprising:
receiving means for receiving the pilot channel from each of the radio base stations;
difference generating means for calculating a difference between the reception field strength of the pilot channel of each of the radio base stations that is received by the receiving means and the transmission power level information received;
detecting means for detecting a particular radio base station of a minimum propagation loss given by the difference calculated by the difference generating means; and
call originating means for originating a call to the particular radio base station of a minimum propagation loss that is detected by the detecting means.
According to this invention, there is provided a mobile communication system in which communication is carried out through a radio channel between a mobile terminal and each of a plurality of radio base stations accommodated in a mobile communication control station and each radio base station at first carries out notification of information through a pilot channel to the mobile terminal moving into a radio zone thereof, wherein:
each of the radio base stations makes the pilot channel to be transmitted store transmission power level information having a value greater than a pilot channel transmission power level actually transmitted in case where a downlink communication traffic is small and transmits the pilot channel or makes the pilot channel to be transmitted store the transmission power level information having a value smaller than the pilot channel transmission power level actually transmitted in case where the downlink communication traffic is great and transmits the pilot channel;
the mobile station calculating a difference between a reception field strength of the pilot channel received from each of the radio base stations and the transmission power level information received, and originating a call to a particular base station of a minimum propagation loss detected from the difference.
Each of the radio base stations comprises:
judging means for judging whether the downlink communication traffic is great or small;
storing means for making the pilot channel to be transmitted store the transmission power level information having a value greater than the pilot channel transmission power level actually transmitted in case where the communication traffic is small in the judgement by the judging means or making the pilot channel to be transmitted store the transmission power level information having a value smaller than the pilot channel transmission power level actually transmitted in case where the downlink communication traffic is great; and
transmitting means for transmitting on the pilot channel the transmission power level information stored by the storing means;
the mobile terminal comprising:
receiving means for receiving the pilot channel from each of the radio base stations;
difference generating means for calculating a difference between the reception field strength of the pilot channel of each of the radio base stations that is received by the receiving means and the transmission power level information received;
detecting means for detecting a particular radio base station of a minimum propagation loss given by the difference calculated by the difference generating means; and
call originating means for originating a call to the particular base station of a minimum propagation loss that is detected by the detecting means.
According to this invention, there is provided a mobile communication system in which communication is carried out through a radio channel between a mobile terminal and each of a plurality of radio base stations accommodated in a mobile communication control station and each radio base station at first carries out notification of information through a pilot channel to the mobile terminal moving into a radio zone thereof, wherein:
each of the radio base stations makes the pilot channel to be transmitted store pilot channel transmission power level information and transmits the pilot channel;
the mobile terminal receiving the pilot channel from each of the radio base stations upon execution of soft handover when approaching its radio zone, and carrying out multiple access with reference to the difference between a reception field strength of the pilot channel and the transmission power level information.
Each of the radio base stations comprises:
storing means for storing the pilot channel transmission power level information into the pilot channel to be transmitted; and
transmitting means for transmitting on the pilot channel the transmission power level information stored by the storing means;
the mobile terminal comprising:
receiving means for receiving the pilot channel from each of the radio base stations upon execution of soft handover when approaching its radio zone;
difference generating means for calculating a difference between a reception field strength of the pilot channel received by the receiving means and the transmission power level information; and
determining means for determining a particular base station for multiple access with reference to the difference generated by the difference generating means.
According to this invention, there is provided a mobile communication system in which communication is carried out through a radio channel between a mobile terminal and each of a plurality of radio base stations accommodated in a mobile communication control station and each radio base station at first carries out notification of information through a pilot channel to the mobile terminal moving into a radio zone thereof, wherein:
each of the radio base stations makes the pilot channel to be transmitted store transmission power level information having a value greater than a transmission power level transmitted by the station in case where the downlink communication traffic exceeds a predetermined threshold level and transmits the pilot channel;
the mobile terminal carrying out multiple access with reference to the difference between the reception field strength of the pilot channel received from each of the radio base stations and the transmission power level information upon execution of soft handover when approaching its radio zone.
Each of the radio base stations comprises:
judging means for judging whether the downlink communication traffic is great or small;
identifying means for identifying the case where the downlink communication traffic exceeds a predetermined threshold level in the judgement by the judging means;
generating means for generating the transmission power level information having a value greater than the transmission power level transmitted by the station in case where the threshold level is exceeded in the identification by the identifying means;
storing means for making the pilot channel store the transmission power level information generated by the generating means; and
transmitting means for transmitting on the pilot channel the transmission power level information stored by the storing means;
the mobile terminal comprising:
receiving means for receiving the pilot channel from each of the radio base stations upon execution of soft handover when approaching its radio zone;
difference generating means for calculating a difference between a reception field strength of the pilot channel received by the receiving means and the transmission power level information; and
determining means for determining a particular base station for multiple access with reference to the difference generated by the difference generating means.
According to this invention, there is provided a mobile communication system in which communication is carried out through a radio channel between a mobile terminal and each of a plurality of radio base stations accommodated in a mobile communication control station and each radio base station at first carries out notification of information through a pilot channel to the mobile terminal moving into a radio zone thereof, wherein:
each of the radio base stations makes the pilot channel store first transmission power level information having a value greater and smaller than a pilot channel transmission power level being transmitted in case where the communication traffic is decreased and increased, respectively, and makes the pilot channel to be transmitted store second pilot channel transmission power level information having a value greater than the actual transmission power level transmitted by the station in case where the downlink communication traffic is increased to exceed a predetermined threshold level and a call setup request is received from the mobile terminal;
the mobile terminal originating a call to a first particular radio base station of a minimum propagation loss detected from a difference between a reception field strength of the pilot channel received from each of the radio base stations and the first transmission power level information received, and determining, upon execution of soft handover, a second particular radio base station for multiple access with reference to the difference between the reception field strength of the pilot channel and the second transmission power level information.
Each of the radio base stations comprises:
judging means for judging whether the downlink communication traffic is great or small;
first storing means for making the pilot channel store first transmission power level information having a value greater and smaller than the pilot channel transmission power level actually transmitted in case where the downlink communication traffic is decreased and increased in the judgement in the judging means, respectively;
second storing means for making the pilot channel to be transmitted store second pilot channel transmission power level information having a value greater than the actual transmission power level being transmitted by the station in case where the downlink communication traffic is increased to exceed a predetermined threshold level and a call setup request is received from the mobile terminal; and
transmitting means for transmitting the pilot channel in which the first or the second transmission power level information is stored by the first or the second storing means;
the mobile terminal comprising:
receiving means for receiving the pilot channel from each of the radio base stations;
first difference generating means for calculating the difference between the reception field strength of the pilot channel of each of the radio base stations that is received by the receiving means and the first transmission power level information received;
detecting means for detecting the particular radio base station of a minimum propagation loss with reference to the difference calculated by the first difference generating means;
call originating means for originating a call to the particular radio base station of a minimum propagation loss that is detected by the detecting means;
second difference generating means for calculating, upon execution of soft handover, the difference between the reception field strength of the pilot channel and the second transmission power level information; and
determining means for determining the particular radio base station for multiple access with reference to the difference generated by the first or the second difference generating means.
The mobile communication system employs a code division multiple access system.
In the call control method in mobile communication and the system therefor according to this invention, the mobile terminal selects the radio base station of a minimum propagation loss represented by the difference between the transmission power level information from the radio base station and the reception field strength upon actual reception of the pilot channel, and originates a call thereto. As a result, it is possible to start stable communication.
In the call control method in mobile communication and the system therefor according to this invention, each radio base station transmits the pilot channel with the transmission power level information having a greater (smaller) value stored therein in case where the downlink communication traffic as measured at the station is small (great). The mobile terminal selects the radio base station of a minimum propagation loss represented by the difference between the transmission power level information from the radio base station and the reception field strength upon actual reception of the pilot channel, and originates a call thereto.
As a result, a call origination allowable area (service area) can be fixed irrespective of the downlink communication traffic. In other words, it is possible to eliminate useless call control processing and to prevent enlargement of the radio zone in case where the downlink communication traffic at a particular radio base station becomes smaller than a reference traffic and the signal quality of the pilot channel is relatively improved.
It is also possible to prevent contraction of the radio zone in case where the downlink communication traffic becomes greater than the reference traffic at the particular radio base station and the signal quality of the pilot channel is relatively deteriorated.
In the call control method in mobile communication and the system therefor according to this invention, the mobile terminal selects the radio base station of a minimum propagation loss represented by the difference between the transmission power level information from the radio base station and the reception field strength upon actual reception of the pilot channel, and produces a multiple access request. As a result, the mobile terminal can produce the multiple access request in correspondence to the propagation loss.
In the call control method in mobile communication and the system therefor according to this invention, the mobile terminal selects the radio base station of a minimum propagation loss represented by the difference between the transmission power level information having a value greater than the transmission power level and the reception field strength upon actual reception of the pilot channel in case where the communication traffic of the radio base station measured at the radio base station is greater than the threshold level, and produces a multiple access request thereto.
As a result, the radio base station controls whether or not it will be included in multiple access destinations depending upon the communication traffic without causing useless call control processing. Thus, it is possible to control the communication traffic in the station.
In the call control method in mobile communication and the system therefor according to this invention, the pilot channel with the first transmission power level information having a greater (smaller) value stored therein is transmitted in case where the communication traffic at the radio base station is small (great). Furthermore, in case where the communication traffic of the station is greater than a specific value and the call setup request is received from the mobile terminal, the pilot channel with the second transmission power level information having a greater value stored therein is transmitted. The mobile terminal selects the radio base station of a minimum propagation loss represented by the difference between the first transmission power level information and the reception field strength upon actual reception of the pilot channel, and originates a call thereto. Furthermore, the mobile terminal selects the radio base station of a minimum propagation loss represented by the difference between the second transmission power level information and the reception field strength upon actual reception of the pilot channel, and produces a multiple access request thereto.
Specifically, the radio base station controls whether or not it is included in multiple access destinations depending upon the communication traffic while the call origination allowable area is fixed without depending upon the downlink communication traffic, and controls the communication traffic at the station to impart the communication capacity which has been used for multiple access to the mobile terminal producing the call setup request.
As a result, it is possible to eliminate useless call control processing and to prevent enlargement of the radio zone in case where the downlink communication traffic at a particular radio base station becomes smaller than a reference traffic and the signal quality of the pilot channel is relatively improved. It is also possible to prevent contraction of the radio zone in case where the downlink communication traffic becomes greater than the reference traffic at the particular radio base station and the signal quality of the pilot channel is relatively deteriorated.
Thus, the radio base station controls whether or not it acts as the multiple access destination depending upon the communication traffic at the station without causing useless call control processing. In case where the communication traffic exceeds the threshold level and the call setup request is produced, the possibility of acting as the multiple access destination is decreased to assure the communication capacity for the requested call and to reduce the call loss ratio.