Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1997-08-08
2001-03-06
Eisenzopf, Reinhard J. (Department: 2745)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S515000, C455S522000, C370S462000
Reexamination Certificate
active
06198924
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a frequency channel selection method for a radio communication system and, more particularly, to a frequency channel selection method for a radio communication system in which a plurality of radio stations communicate with each other.
2. Description of the Prior Art
In a conventional radio communication system such as a car or cellular telephone system, the service area is covered by a plurality of basic stations, and the same frequency channel (to be simply referred to as a channel hereinafter) is repeatedly used between basic stations which cause no radio interference, thereby realizing the effective use of frequencies. Such a system is called a cellular system. In the cellular system, when a given basic station and a given movable station start to communicate with each other, the basic station measures the carrier to co-channel interference ratio (to be referred to as a C/I hereinafter) of each of unused channels to select a channel that has a lower interference wave power and a C/I higher than a predetermined C/I. In general, a desired carrier power (C) is obtained by measuring the reception power of a control channel ensured independently of a communication channel, and an interference wave power (I) is obtained by measuring the reception power of the communication channel to be selected, as in the channel assigning method disclosed in Japanese Unexamined Patent Publication No. 3-174827.
In a radio packet communication system like the one disclosed in Draft Standard IEEE802. 11, P802. 11D2.0, Wireless LAN Medium Access Control and Physical Layer Specifications, one radio link is shared by one basic station and a plurality of movable stations which are connected to a wire network. Channels are permanently assigned to the respective basic stations on the basis of propagation environments and predicted communication traffics. The user of a given movable station manually sets a channel to be used on the radio link to which the given station belongs. Alternatively, a channel is set on the basis of a control signal which is constantly or periodically transmitted from a basic station. Since the output of each basic station is fixed, the coverage of the service area is also fixed.
As described above, in the conventional radio communication system, to select a channel, a control channel other than a communication channel is required, or a control signal must be periodically transmitted. For this reason, frequencies cannot be effectively used.
In addition, as described above, in the conventional radio packet communication system, channels are permanently assigned to the respective basic stations. For this reason, when a plurality of basic stations are to be installed, channel assignment design must be performed in advance to assign specific channels to specific basic stations. Such assignment of channels cannot be automatically performed. Furthermore, since the output of each basic station cannot be automatically changed depending on communication states, communication is sometimes performed on a transmission power that is higher than required, resulting in an increase in interference wave power in other radio stations.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the above situation in the prior art, and has as its object to provide a channel selection method for a radio communication system, in which when a channel is to be dynamically selected, control signals need not be constantly or periodically transmitted, and radio channels can be effectively used.
According to the present invention, each radio station dynamically selects a channel to be used in accordance with the radio environment set for each station and the form of a radio link to be established. Each station does not use control signals which are constantly or periodically transmitted, but transmits a control signal only when each station determines that transmission of the signal is required.
In order to achieve the above object, according to the first aspect of the present invention, there is provided a channel selection method for a radio communication system constituted by a plurality of radio stations, comprising causing each radio station to transmit a control signal only when required, but causing each radio station not to constantly transmit a control signal.
According to the second aspect of the present invention, the channel selection method according to the first aspect is characterized by comprising, when each radio station is to perform packet communication to irregularly and discontinuously perform communication, causing each radio station to transmit a control signal as a control packet by using a communication channel.
According to the third aspect of the present invention, the channel selection method according to the second aspect is characterized by comprising causing a radio station which is to perform communication to check a state of a communication channel, select a channel determined as a channel that is not being used any other radio station when a new radio link is to be established, and select a channel determined as a channel that is being used by some other radio station when the radio station is to be connected to an existing radio link.
According to the fourth aspect of the present invention, the channel selection method according to the second and third aspects is characterized by comprising when a radio station which is to perform communication checks states of communication channels, causing the radio station to determine the use states of the channels by receiving packets transmitted from other radio stations by using the respective channels.
According to the fifth aspect of the present invention, the channel selection method according to the second, third, and fourth aspects is characterized by comprising, when a radio station which is to perform communication checks a state of a communication channel, causing the radio station to transmit the control packet and determine the use state of the channel on the basis of a response to the control packet from some other station.
According to the sixth aspect of the present invention, the channel selection method according to the fifth aspect is characterized by comprising causing a radio station which has received the control packet transmitted from the radio station which is to perform communication to transmit a response control packet.
According to the seventh aspect of the present invention, the channel selection method according to the fifth aspect is characterized by comprising causing a radio station which has received the control packet transmitted from the radio station which is to perform communication to transmit no response control packet upon reception of a response control packet from some other radio station.
According to the eighth aspect of the present invention, the channel selection method according to the fifth aspect is characterized by comprising causing only a specific one of radio stations which have received the control packet transmitted from the radio station which is to perform communication to transmit a response control packet.
According to the ninth aspect of the present invention, the channel selection method according to the third aspect is characterized by comprising causing a radio station which is to perform communication to check states of communication channels in a predetermined order common to all radio stations, select a channel if the channel can be selected, and check a next channel if the channel cannot be selected.
According to the 10th aspect of the present invention, the channel selection method according to the third aspect is characterized by comprising causing a radio station which is to perform communication to normally check states of communication channels in a predetermined order common to all radio stations, check the states of the communication channels in a reverse order to the predetermined order when an independent network is to be constructed, select a chann
Ishii Kenichi
Osawa Tomoki
Eisenzopf Reinhard J.
Kincaid Lester G.
McGuireWoods LLP
NEC Corporation
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