GB2300541A

GB2300541A - Control channel selection in a cordless telephone system

Info

Publication number: GB2300541A
Application number: GB9605511A
Authority: GB
Inventors: Noriaki Nagashima; Yoshinori Kuroki; Kazuyuki Tate; Akihiro Sawada
Original assignee: Hitachi Ltd; NEC Corp; Nippon Telegraph and Telephone Corp; Oki Electric Industry Co Ltd
Current assignee: Hitachi Ltd; NEC Corp; Nippon Telegraph and Telephone Corp; Oki Electric Industry Co Ltd
Priority date: 1995-03-17
Filing date: 1996-03-15
Publication date: 1996-11-06
Anticipated expiration: 2016-03-15
Also published as: CN1083229C; GB9605511D0; SG47094A1; AU712162B2; GB2300541A8; JPH08256373A; GB2300541B; CN1137215A; HK1011479A1; AU4810596A

Abstract

A base station of a cordless telephone system or personal handy phone system (PHS) monitors time slots on control channels and transmits control information on a time slot of a channel that it determines to be free. This is then used as the selected control channel of that base station. The monitoring and selecting procedure is necessarily carried out when the base station is switched on and preferably at predetermined intervals or when a call set up fails. The procedure may alternatively be carried out at a cordless telephone handset.

Description

1 0.

2300541 1 RADIO CONTROL SIGNAL'TRANSMISSION ME2ROD FOR A PERSONAL DIGITAL RADIO COHMUNICATION SYSTEM 1(0 20) BACKGROUND OF THE INVENTION

1. Field of the Invention:

The present invention relates to a radio control signal transmission method of personal digital radio communication system composed of a mobile station and base station wire-connected to electronic communication circuit equipment. 2. Description of the Related Art:

In the case of second-generation cordless telephone systems (Personal Handy phone Systems), which constitute one example of the practical application of digital radio technology in Japan, the first edition of PHS specifications RCRSTD-28 (December 20, 1993) does not stipulate a carrier sense capability for recognizIng an available channel (frequency and time slot).

Based on the rules and regulations of the FCC (Federal Communications Commission), it is standard practice in the United States for US PCS (Personal Communications Services) to employ carrier sense for recognizing an available channel (frequency or time slot) even at the start of transmission on a control channel, to monitor in advance the channel status, i.e., the control frequency or time slot, intended for 1 l(D 20) 23 2 - use, confirm that the frequency is not being used, and then transmit on the control channel.

In control channel transmission for personal use, such as in the Personal Handy phone System (PHS) for home- or office-use in Japan, carrier sense as practiced by the US PCS is not employed. Rather, a control channel of a base station is individually set for each base station at the time of installation, and as a result, adjacent base stations are asynchronous, control frequencies coincide, oyerlapping of slot timing occurs between base stations, and radio interference is produced. Consequently, at the time of installation, the setting of control frequency is presently carried out while checking for the presence of radio interference. Although the installation time for a personal-use base station can be shortened by employing carrier sensing before transmitting on a control channel, as is required in the US, control channels rarely become unusable as long as the arrangement of base stations in the vicinity does not change, and carrier sensing therefore need not be employed before every transmission on a control channel.

SUMARY OF THE INVENTION

The object of the present invention is to provide a radio control signal transmission method other than PO is carrier sensing for tdducing the occurrence of inter- ference in control channels in a personal digital radio communication system, and a personal digital radio communication system using such a method.

Another object of the present invention is to provide a radio control signal transmission method for a digital radio communication system that limits moni toring of control channels to a low level, and a personal digital radio communication system using such a method.

The personal digital radio communication system according to the present invention includes steps for monitoring in advance the status of all channels, i.e., available frequencies and time slots for control use, and selecting from among the monitored channels an unused channel when transmitting on a control channel between a base station and a mobile station; and a step for using the selected unused channel and transmitting on the control channel.

With the present invention, control-use frequencies of adjacent personal base stations need not be identified when installing a personal base station to avoid radio interference, and a personal base station can be freely established without the necessity of selecting frequencies differing from those of adjacent personal base stations. Moreover, the invention allows 4 a reduction of the time and expense required for installing a base station.

According to an embodiment of the present invention, monitoring of the control channel status, i.e., frequency and time slot, may be performed in response to a request when power supply to the base station is turned ONf when a call cannot be accepted, or with each passage of a fixed time interval; and at the very least, is performed when power supply to the base station is turned ON; and the control channel selected through channel status monitoring in response to the request is used until the next monitoring of channel status.

In this way, by monitoring control channels when power is turned ON, when a call is not accepted, and at fixed time intervals, monitoring of control channels can be kept to a minimum while still obtaining the same level of performance as when monitoring control channels at all times.

According to another embodiment of the present invention, transmission on a channel is initiated upon confirmation that the frequency and time slot are available, and if through monitoring of the channel status, a frequency and time slot intended for control use are found to be in use by another station and therefore unavailable, the channel status of a different control channel is similarly monitored, availability confirmed, and radio transmission initiated.

In addition, a personal digital communication system according to the present invention includes a base station wired to electronic communication circuit equipment and a mobiie station, the base station being equipped with a radio device that, when transmitting on a control channel between the base station and mobile station, monitors in advance the channel status of available frequencies and tipe slots for control use, confirms the availability of this frequency and time slot for control use, and initiates transmission on the control channel.

According to an embodiment of the present invention, the radio device includes:

a power-ON detector that detects if the power supply is ON in the mobile station or the base station In which the radio device is provided, and sends out a request for generating a monitor command; optionally includes:

a call-not-accepted detector that counts the number of times calls cannot be accepted, and sends out a request to generate a monitor command when the count value exceeds a set value; and a timer that sends out a request to generate a monitor command upon each passage of a fixed time interval; and further includes:

a channel status monitor that, when transmitting on a control channel between the base station and mobile station, monitors in advance the channel status of all available control-use'frequencies and time slots, and selects an available channel from among the monitored channels; and a control channel status monitor command section that activates the channel s.tatus monitor in response to a request to generate a monitor command from the power-ON detector, call-not-accepted detector, and timer.

The above and other objects, features, and advantages of the present invention will become apparent from the following description with references to the accompanying drawings which illustrate examples of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows the configuration of one embodiment of the personal digital radio communication system of the present invention.

Fig. 2 shows the configuration of the base station of Fig. 1.

Fig. 3 is a flow chart illustrating a command to monitor control channels.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to Fig. 1, the personal digital radio communication system of the present embodiment is made up of mobile stations PS1-PS3 and base stations BS1-BS3 wire-connected to an independent communication network or public communication network NW. Area 1, Area 2, and Area 3 are the radio-wave ranges of base station BS1, base station BS2, and base spation BS3, respectively.

Referring to Fig. 2, base stations BS1-BS3 are each constructed of: a radio section 1, a power-ON detector 5 that detects powering-up of that base station and sends out a request to generate a monitor command; a call-not-accepted detector 6 that counts the number of times calls cannot be accepted and sends out a request to generate a monitor command when the count value exceeds a set value; a fixed-time timer 7 that sends out a request to generate a monitor command upon each passage of a fixed time interval; a channel status monitor 2 that, when transmitting on a control (for communication) channel to a mobile station, monitors in advance the channel status of all available control (for communication) frequencies and time slots, selects an unused channel from among the monitored channels, and transmits by way of radio section 1; a control is channel status monitor command section 3 that activates channel status monitor 2 in response to a request to generate a monitor command from power-ON detector 5, call-not-accepted detector 6, and fixed time timer 7; and a communication-use channel status monitor command section 4 that activates channel status monitor 2.

A Frame Error Rate (FER) measurement method may be employed as a method of retrieving available control channels in channel status monitor 2. In other words, available control frequencies and time slots are monitored in advance; the number of errors in the monitor data is stored; of the stored data, the best frequency and time slot having the fewest number of errors are calculated and fixed, and that time slot is used in transmitting from radio section 1.

Monitoring of frequency and time slot, and transmission on a control channel through selection of an available frequency and slot at a base station are carried out through intermittent action upon power-ON detection, upon call-not-accepted detection, and at fixed times, thereby reducing load upon the CPU.

This intermittent action can be illustrated as follows: First, if based on prior interference conditions, monitoring is essential after turning power ON following installation of the base station. This monitoring, which is activated by powering up the base 11) 9 - station following installation, enables avoidance of interference with control channels of adjacent base stations at this time.

If power to an already installed base station should for some reason be interrupted or the installation state of other base stations in the vicinity be subsequently altered, avoidance of control channel interference can again be effected by again activating channel status monitor 2 when a call fails to be accepted. Further, monitoring of control channels can be carried out at fixed time inervals such as once every day or once a week without monitoring every call.

Normally, if a base station is capable of avoiding control channel interference as described hereinabove, simply turning power ON after installation obviates frequent monitoring such as at set times or when a call cannot be accepted. However, because a base station lacking the capability to avoid control channel interference as in the present invention might possibly be established, channel status monitor 2 must be activated after installation based on a set standard of operation time. In this way, the number of times of monitoring of control channels can be limited, and monitor circuits can be simplified by not monitoring outside these time limits.

The operation of this embodiment will next be is 210 - explained with reference to Fig. 3.

Power-ON detector 5 detects that the power supply to the device has been turned ON, and sends a request to generate a monitor command to control channel status monitor command section 3.

Call-not-accepted detector 6 turns ON in Step 11 and resets incoming-call number N to "0" in Step 12. In Step 13, detector 6 judges if a call can be accepted, and if not accepted, increments the count number in Step 14. In Step 15, detector 6 judges whether the count value has exceeded the prescribed value N1 or not, again counts the number of accepted calls N if the count value has reached N1, and sends a request to generate a monitor command to control channel status monitor command section 3 when the count value exceeds the prescribed value N1.

Fixed-time timer 7 sends a request to generate a monitor command to control channel status monitor command section 3 upon each passage of a set fixed time.

These requests to generate a monitor command to control channel status monitor command settion 3 cause control channel status monitor command section 3 to activate channel status monitor 2, whereby channel status monitor 2 checks the current channel status at the base station site from radio device 1 and selects a 11 - in is control channel.

Although power-ON detector 5, call-not-accepted detector 6, and fixedtime timer are all shown in the figures, only the provision of power-ON detector 5 is essential, and the other two components may be omitted.

In the foregoing explanation, a radio device that monitors the channel status, confirms that a channel is available, and initiates transmission on a control channel is provided in a base station, but such a radio device may also be provided on the mobile station side.

A case will be next be considered in which base station BS2 is newly established in the vicinity of base station BS1, which is transmitting on a control channel. If the frequency and time slot of the control channel transmitted from base station BS2 at this time coincides with that of base station BS1, collision between the control channels will occur where the radio-wave ranges of base stations BS1 and BS2 overlap, and as a consequence, mobile stations PS1 or PS2 in the region of overlap will be unable to recognize control information and therefore become inoperable.

Such a situation has conventionally been avoided by investigating control channels in the vicinity and setting control channels which will not coincide when establishing a base station (in this instance, base station BS2). However, if power is not supplied to base 12 - station BS1 when base station BS2 is being established in the vicinity of base station BS1, potential interference cannot be determined at the time of installing base station BS2, and each user must be aware that interference may occur immediately after power is subsequently supplied to base station BS1.

In contrast, in the present system, available control channels are checked before base station BS2 transmits on a control channels, and as a result, the above-described problem of interference between control channels will not occur even when the radio-wave ranges overlap as shown in Fig. 1.

While a preferred embodiment of the present invention has been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the scope of the following claims.

is iro

Claims

1. A radio control signal transmission method of a personal digital radio communication system comprising a base station wired to electronic communication circuit equipment and a mobile station, comprising: at the time of transmission on a control channel between said base station and said mobile station, a step for monitoring in advance channel status of all usable control frequencies and time slots and selecting an unused channel from among the monitored channels; and and a step for using the selected unused channel and transmitting a control channel.

2. A method according to claim 1 wherein monitoring of channel status of said control frequency and time slot is performed in response to, at least, a request when power supply to said base station is turned ONt and optionally, a request when a call cannot be accepted or with each passage of a fixed time interval; and a control channel selected through channel status monitoring in response to said request is used until the next monitoring of channel status.

3. A method according to claim 1 wherein transmission on said channel is initiated upon confirmation that a frequency and time slot are available, and if through monitoring of channel status, a frequency and time slot intended for control use are found to be in use by another station and therefore unavailable, channel status of a different control channel is similarly monitored, availability confirmed, and radio transmission initiated.

4. A personal digital radio communication system including a mobile station and a base station wireconnected to electronic communication circuit equipment, said base station being provided with a radio device that, at the time of transmission on a control channel between said base station and said mobile station, monitors in advance channel status of usable control frequencies and time slots, confirms availability of monitored control frequencies and time slots, and initiates transmission on a control channel.

5. A personal digital radio communication system including a mobile station and a base station wireconnected to electronic communication circuit equipment, said mobile station being provided with a radio device that, at the time of transmission on a control channel between said base station and said mobile station, monitors in advance channel status of usable 1C9 - is - control frequencies and time slots, confirms availabil ity of monitored control frequencies and time slots, and initiates transmission on a control channel.

6. A personal digital radio communication system according to claim 4 or claim 5 wherein said radio device comprises: a power-ON detector that detects if power supply is ON in said mobile station or said base station in which said radio device is provided, and sends out a request for generating a monitor command; said radio device optionally includes: a call-not-accepted detector that counts the number of times calls cannot be accepted, and sends out a request to generate a monitor command when the count value exceeds a set value; and a timer that sends out a request to generate a monitor command upon each passage of a fixed time interval; said radio device further includes: a channel status monitor that, at the time of transmission on a control channel between said base station and said mobile station, monitors in advance the channel status of all available control-use frequencies and time slots, and selects an available channel from among the monitored channels; and is a control channel status monitor command section that activates said channel status monitor in response to a request to generate a monitor command from said power-ON detector, said call-not-accepted detector, and said timer.

7. A cordless telephone station for use in a personal digital radio communication system which includes a mobile station and a base station wire-connected to electronic communication circuit equipment, comprising a radio device which, at the time of transmission on a. control channel between the base station and the mobile station, monitors in advance channel status of usable control frequencies and time slots, confirms availability of monitored control frequencies and time slots, and initiates transmission on a control channel.

8. A method radio communication substantially as herein described with reference to the drawings.

9. A personal digital radio communication system substantially as herein described with reference to the drawings.

10. A cordless telephone station substantially as herein described with reference to the drawings.