Channel selection system for mobile radio communication equipment

Abstract: A channel selection system for radio communication equipment which uses a control channel for interchanging control signals for connection and a plurality of data channels for interchanging data and emits an electromagnetic wave by using any one of the data channels after determining that it is idle by carrier sensing. The system rarely selects a data channel adjoining the control channel since the probability that such a data channel is registered as an idle channel is extremely low. The system, therefore, reduces the possibility of the equipment being unable to use the control channel due to the influence of power leaking from the data channel adjoining the control channel.

Description: The present invention relates to a channel selection system for mobile radio communication equipment of the type using a control channel for interchanging control signals for connection and a plurality of data channels for interchanging data and deciding whether or not to emit an electromagnetic wave after determining whether or not other equipment associated therewith are emitting electromanetic waves. A conventional channel selection system for the above-described type of communication equipment selects an idle data channel with no regard to whether or not that channel adjoins the control channel with respect to frequency. It is, therefore, quite likely that a data channel adjoining the control channel is used for communication. The use of such a data channel would not matter at all if a transmit station were located remote enough from a desired receive station to sense no carrier on the adjoining control channel. However, as the transmit station approaches the receive station, the probability that the transmit station senses the carrier on the control channel increases due to power which leaks from the adjoining data channel. Then, the transmit station would be unable to emit an electromagnetic wave over the control channel and, therefore, to connect itself to the receive station. In the specification of a European patent application, which was published under number EP-A-0 244872 on November 11 1987, there was proposed, for use in a radio communication network, a base station which was capable of monitoring the occurrence of interference on every transmission. On the occurrence of such interference the allocated speech wave was changed to another speech radio wave under the control of a line control. In the specification of United States patent number 4,672,657 which was published on June 9 1987,a multi-channel R.F. telephone system was proposed in which a channel status monitor developed a list of available communications channels and in which a common channel transceiver transmitted the list to the telephones. A channel to be used was selected from the list by the telephones by sequentially accessing the list a number of times. If a selected channel was unavailable, the telephone was able to update the list that it maintained independently. A feature of an embodiment to be described below is a channel selection system for mobile radio communication equipment which allows the equipment to emit an electromagnetic wave over a control channel by keeping it away from power leaking from a data channel adjoining the control channel. A channel selection system for radio communication equipment to be described is defined in Claim 1 and uses a control channel for interchanging control signals for connection and a plurality of data channels for interchanging data and emits an electromagnetic wave by using any one of the data channels after determining that the one data channel is idle by carrier sensing. When the one data channel is idle, another data channel is selected if the one channel adjoins the control channel with respect to frequency. A method of selecting a channel for radio communication equipment is defined in Claim 2 and will also be described. The following description and drawings disclose, by means of an example, the invention which is characterised in the appended claims, whose terms determine the extent of the protection conferred hereby. In the drawings:- Fig. 1 is a block diagram showing a specific construction of radio communication equipment to which the present invention is applicable; Fig. 2 is a flowchart showing a specific operation of a channel selection system embodying the present invention relating to the registration of idle channels in a storage; and Fig. 3 is a flowchart showing a specific operation for starting on a transmission. DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to Fig. 1 of the drawings, radio communication equipment to which the present invention is applicable is shown and generally designated by the reference numeral 10. As shown, the equipment 10 has a receiver 12 for receiving signals, a controller 14 implemented with a microcomputer, an operation board 16, a transmitter 18 for transmitting signals, an oscillator 20 using a synthesizer, a carrier sensing unit 22, and a storage 24 implemented as a RAM. A signal received by the receiver 12 is fed to the controller 14. Data entered on the operation board 16 is applied to the transmitter 18 by way of the controller 14. In response, the transmitter 18 transmits the input data. The frequencies which the transmitter 12 and receiver 18 can transmit and receive over the radio channels are determined by the reference frequency which is generated by the oscillator 20. The reference frequency is, in turn, determined by frequency data applied to the oscillator 20 from the controller 14. The equipment 10 detects a frequency available for transmission by sensing a carrier. Specifically, the carrier sensing unit 22 measures, for example, the IF (Intermediate Frequency) level of a received signal and, when the measured IF level is higher than a predetermined level, determines that a received electric field exists. Then, the carrier sensing unit 22 informs the controller 14 of such an occurrence. The controller 14 sequentially switches over the channel of the receiver 12 while in a waiting condition so as to sense a carrier on the individual channels. On detecting an idle channel usable for transmission, the controller 14 registers it in the storage 24. A specific sequence of steps for registering idle channels is shown in Fig. 2. As shown, whether or not a certain data channel f n adjoins a control channel f c is determined (step S1). If the answer of the step S1 is NO, the carrier on the channel f n is sensed to see if the channel f n is idle (step S2). If the data channel f n adjoins the control channel f c as determined in the step S1, whether or not any data channel has been registered in the storage 24 as an idle channel is determined (step S3). If the answer of the step S3 is NO, the step S2 is executed. When the channel f n is idle as determined in the step S2, it is registered in the storage 24 (step S4). Subsequently, the channel f n is updated (step S5) to examine the next channel. If the answer of the step S2 is NO, the channel f n is also updated (step S5) to check the next channel f n+1 . If the answer of the step S3 is YES, i. e. , if the channel f n adjoins the control channel f c and any channel has been registered as an idle channel, the channel f n is also updated (step S5). In the above procedure, it is only when no idle channels are available that the data channel adjoining the control channel is registered in the storage 24. Stated another way, the probability that the data channel adjoining the control channel is registered in the storage 24 as an idle channel is low. Fig. 3 is a flowchart representative of a specific procedure for the equipment 10 to start on a transmission. As shown, the controller 14 checks the storage 24 to see if, among the channels registered in the storage 24 as stated above, a channel f x intended for a transmission is idle by carrier sensing, whether it be the control channel or the data channel (step S11). If the answer of the step S11 is YES, the controller 14 starts on a transmitting operation (step S12). If the answer of the step S11 is NO, the controller 14 determines whether or not the channel f x is the control channel (step S13). If the answer of the step S13 is NO, the controller 14 selects another channel f x out of the storage 24 (step S14). If the answer of the step S13 is YES, the program returns to the step S11 to wait until it detects an idle channel. In summary, it will be seen that the present invention provides a channel selection system which rarely selects a data channel adjoining a control channel since the probability that such a data channel is registered as an idle channel is extremely low. The system, therefore, reduces the possibility of mobile radio communication equipment being unable to use the control channel due to the influence of power leaking from the particular data channel. Various modifications will become possible for those skilled in the art after receiving the teachings of the present disclosure without departing from the scope of the protection afforded by the appended claims.

Claims: Radio communication apparatus (10) which uses a control channel for interchanging control signals for establishing a connection, and a plurality of data channels for interchanging data, and which transmits a signal on one of the data channels after determining that the one data channel is free, including a first channel selector (14) for selecting a first free channel from a plurality of communication channels, a controller (14) for checking if the frequency of the first free channel adjoins that of the control channel, characterised in that there is provided a second channel selector (14) for selecting, when the controller (14) decides that the frequency of the first free channel adjoins that of the control channel, a second free channel from the plurality of communication channels which does not adjoin the control channel, and a transmitter (18) for communicating with another party over the second free channel. A method of selecting a channel for radio communication employing a control channel in interchanging control signals for establishing a connection, and a plurality of data channels for interchanging data, and in which it is decided whether or not to transmit a signal after determining whether or not a channel is free, including the steps of registering in a store the control channel and the data channels which are free while the apparatus is in a waiting condition, selecting one of the registered channels for transmission, determining whether or not the frequency of the selected channel adjoins that of the control channel, and should the selected channel be free and not adjoin the control channel transmitting on the selected channel, and should the selected channel not be free, or should the selected channel adjoin the control channel, updating the channel to one that is free and does not adjoin the control channel.

Inventors: KAGE KOUSOU C O NEC CORPORATIO, KAGE, KOUZOU, C/O NEC CORPORATION
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1990
Main classification: H04Q7
IPC codes: H04W48