Radio communication apparatus and transmission power control method

A radio communication apparatus and transmission power control method are disclosed, which can maintain communication with handsets while avoiding an increase in radio interference to another radio communication system as much as possible when radio communication is performed with one or more handsets. The handset transmits a communication start request signal to a base unit. Upon verifying the reception of the communication start request, the base unit measures the RSSI level of the communication start request signal transmitted from the handset, determines a transmission power value based on a power control table that has been updated with the measured RSSI level, and controls the transmission power of a control signal transmitted to the handset.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is entitled to the benefit of Japanese Patent Applications No. 2013-010910 filed on Jan. 24, 2013, No. 2013-014208 filed on Jan. 29, 2013 and No. 2013-126583 filed on Jun. 17, 2013, the disclosures of which including the specifications, drawings and abstracts are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a radio communication apparatus and a transmission power control method applicable to a digital cordless telephone.

BACKGROUND ART

Cordless telephones having a cordless handset and enabling a conversation with a person at a distance from a base unit connected to a telephone line are widely used. With this widespread use, situations where a plurality of radio communication systems exist in the same area have arisen. If the base unit always transmits a radio signal with the maximum power in such situations, although communication is made possible between the base unit and the handset at a distance from one another, there arises a problem in that the radio used for the communication causes significant interference to other radio communication systems.

Given this, cordless telephones variably controlling the transmission power of the base unit have been developed. For example, Japanese Patent Application Laid-Open No. 2001-332987 (hereinafter, referred to as “PTL 1”) discloses a technique that sets the optimum transmission power by making a control such that the transmission power value of a radio communication apparatus is made the maximum value at the start of communication and the transmission power value is reduced by a predetermined amount each time transmission succeeds and increased by a predetermined amount when transmission fails, for example.

Japanese Patent Application Laid-Open No. 2002-345026 (hereinafter, referred to as “PTL 2”) discloses a technique that controls the transmission power of the base unit (connection apparatus) in accordance with whether or not a handset is linked to a charging cradle. That is, PTL 2 discloses the technique whereby communication is done with a low transmission power when the handset is linked to the charging cradle and communication is done with a high transmission power when the handset is removed from the charging cradle. By doing this, the technique of PTL 2 enables maintenance of communication between a handset and a connection apparatus even if an interfering signal is received in the process of the handset moving away from the connection apparatus.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

However, PTL 1 is the technique for controlling the power between the handset and the base unit to be low during a call (or during other data communication), and is not directed to power control of the control channel for synchronization and control signal transmission between the base unit and a handset except for during a call. Also, PTL 2 is an invention related to a control between one handset and a base unit, and cannot be practiced when a plurality of handsets exist. Additionally, the above-noted related art does not consider interference by a control channel signal with respect to another cordless telephone system.

FIG. 1shows how interference with respect to another nearby cordless telephone system occurs. As shown inFIG. 1, if there are a plurality of handsets (handsets A and B) registered to a base unit, and if the power on the control channel on which the base unit is transmitting is made maximum to enable reception at the distant handset B, there is a risk of great interference with respect to another nearby cordless telephone system.

PTL 2 describes a connection apparatus making the transmission power low when one handset having the same terminal number as the connection apparatus is linked to a charging cradle, but does not disclose anything about transmission power control of a control signal when a plurality of handsets having the same terminal number as the connection apparatus exist. For example, if the base unit reduces the transmission power of the control signal when a nearby handset is placed into a charging cradle, there is a risk that communication between a distant handset and the base unit will be cut off.

An object of the present invention is to provide a radio communication apparatus and transmission power control method that can maintain communication with all the handsets while avoiding an increase in radio interference to another radio communication system as much as possible when radio communication is performed with one or a plurality of handsets.

Solution to Problem

A radio communication apparatus according to an aspect of the present invention is a radio communication apparatus that performs radio communication with a handset, using a TDMA system, the apparatus including: a level measurement section that measures a reception level of a predetermined signal transmitted from the handset; and a transmission power control section that performs transmission power control so as to determine a transmission power value in accordance with a minimum value of the reception level and to transmit a control signal to the handset, using a control channel and the determined transmission power control value.

A radio communication apparatus according to an aspect of the present invention includes: a level measurement section that measures a reception level of a communication start request signal indicating a request to start communication or a communication end request signal indicating a request to end communication transmitted from one or more handsets; a storage section that stores the reception level for each of the handsets; and a transmission power control section that performs transmission power control so as to determine a transmission power value in accordance with a minimum value of the stored reception level and to transmit a control signal to the one or more handsets, using the determined transmission power control value.

A transmission power control method according to an aspect of the present invention is a transmission power control method of a radio communication apparatus that performs radio communication with a handset, using a TDMA system, the method including: measuring a reception level of a predetermined signal transmitted from the handset; and performing transmission power control so as to determine a transmission power value in accordance with a minimum value of the reception level and to transmit a control signal to the handset, using a control channel and the determined transmission power control value.

A radio communication method according to an aspect of the present invention includes: measuring a reception level of a communication start request signal indicating a request to start communication or a communication end request signal indicating a request to end communication transmitted from one or more handsets; storing the reception level for each of the handsets; and performing transmission power control so as to determine a transmission power value in accordance with a minimum value of the stored reception level and to transmit a control signal to the one or more handsets, using the determined transmission power control value.

Advantageous Effects of Invention

According to the present invention, it is possible to maintain communication with a plurality of handsets while the received signal level at the handsets is maintained to the extent sufficient to maintain communication, and an increase in radio interference to another radio communication system is avoided as much as possible during radio communication with one or a plurality of handsets.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be described in detail below with references made to the drawings. In the following, a digital cordless telephone conforming to the DECT (Digital Enhanced Cordless Telecommunication) standard is described as an example. DECT is a system that has been established as a standard by ETSI (European Telecommunications Standards Institute), which is a telecommunications standardization organization in Europe.

A digital cordless telephone includes one base unit (refer toFIG. 2), a plurality handsets2(refer toFIG. 3), and the same number of charging cradles3(refer toFIG. 3) as that of handsets2. Base unit1(radio communication apparatus) performs radio communication with each handsets2by the TDMA (time division multiple access) system.

FIG. 2is a block diagram showing the configuration of base unit1according to an embodiment of the present invention. As shown inFIG. 2, base unit1mainly includes telephone line interface101, signal processing section102, memory section103, radio section104, antenna105, display section106, operation section107, microphone108, and speaker109.

Telephone line interface101is an interface for connecting a telephone line with signal processing section102, performs incoming call-receiving processing and call originating processing to connect to an outside telephone via a telephone line, and performs release and closing of the line.

Signal processing section102, based on a control program stored in memory section103, processes signals output from various sections and controls various sections. In particular, signal processing section102encodes digital voice data by the ADPCM (adaptive differential pulse code modulation) system, adds control data thereto, inserts it into a predetermined slot within a frame, performs modulation processing such as frequency modulation, and generates a baseband transmitted signal. Signal processing section102demodulates the received baseband signal, extracts control data and encoded voice data from a predetermined slot within the frame, decodes the encoded voice data by the ADPCM system, and generates digital voice data.

Memory section103stores predetermined information, such as a control program and IDs (identifications) of handsets. Of the information stored in memory section103, the parts that are related to the present invention will be described later.

Radio section104amplifies and performs radio processing such as up-conversion with respect to the baseband digital signal output from signal processing section102, and transmits a radio signal from antenna105. Radio section104also amplifies and performs radio processing such as down-conversion of a radio signal received at antenna105and outputs a baseband digital signal to signal processing section102.

Display section (LCD: liquid crystal display)106displays various information output from signal processing section102. Operation section107has various buttons, dials, and keys and converts operations based on a user's intention to electrical signals, and outputs the signals to signal processing section102.

Microphone108collects sounds from a user's voice, converts these to a voice signal, and outputs the signal to signal processing section102. Speaker109converts the voice signal output from signal processing section102to a voice and outputs the voice.

In this case, a feature of the present invention is that signal processing section102includes transmission power control section102a. Additionally, radio section104includes level measurement section104aand amplification section104b.

Transmission power control section102acalculates the transmission power based on the RSSI (received signal strength indicator) level of the received signal from each handset2measured by level measurement section104aand outputs a control signal indicating the calculation result to amplification section104b. The specific transmission power control method in transmission power control section102awill be described later.

Level measurement section104ameasures the RSSI level of the received signal from each handset2and outputs an RSSI signal indicating the measurement result to transmission power control section102a.

Amplification section104b, amplifies the power of the radio signal transmitted from antenna105, based on control by transmission power control section102a.

FIG. 3is a block diagram showing the configuration of handset2and charging cradle3according to an embodiment of the present invention. As shown inFIG. 3, handset2mainly includes signal processing section201, memory section202, radio section203, antenna204, display section205, operation section206, microphone207, speaker208, charging circuit211, secondary battery212, and voltage regulation circuit213. Handset2also has terminals T21and T22.

Signal processing section201of handset2, based on a control program stored in memory section202, processes signals output from various sections and controls various sections. Upon receiving a charging detection signal from charging circuit211, signal processing section201transmits to base unit1, via radio section203and antenna204, a notification signal for notification that handset2has been placed into charging cradle3(hereinafter referred to as the “placement notification signal”).

When the charging detection signal that has been output from charging circuit211stops, signal processing section201transmits to base unit1, via radio section203and antenna204, a notification signal for notification that handset2has been removed from charging cradle3(hereinafter referred to as the “removal notification signal”).

Memory section202stores predetermined information such as a control program.

Radio section203performs radio processing such as amplification and up-conversion of the baseband digital signal output from signal processing section201and transmits a radio signal from antenna204. Radio section203also performs radio processing such as amplification and down-conversion of the radio signal received at the antenna204and outputs a baseband digital signal to signal processing section201.

Display section205displays various information output from signal processing section201. Operation section206has various buttons, dials, and keys, and converts operations based on a user's intention to electrical signals, and outputs them to signal processing section201.

Microphone207collects sounds from a user's voice, converts these to a voice signal, and outputs the signal to signal processing section201. Speaker208converts the voice signal output from signal processing section201to a voice and outputs the voice.

Terminals T21and T22are for inputting a charging current by making contact with terminals T31and T32when handset2is placed into charging cradle3.

Charging circuit211receives, as input, a charging current supplied from charging cradle3and supplies the current to secondary battery212and voltage regulation circuit213. When handset2is placed into charging cradle3and a charging current from charging cradle3is detected, charging circuit211outputs a charging detection signal to signal processing section201. When handset2is removed from charging cradle3in which handset2had been placed and the charging current is no longer detected from charging cradle3, charging circuit211stops outputting the charging detection signal.

Secondary battery212accumulates the charging current from charging circuit211and discharges into voltage regulation circuit213.

Voltage regulation circuit213is a voltage-regulated source supplying a stabilized DC voltage to signal processing section201, and converts a DC voltage from charging circuit211or secondary battery212(for example, 2.5 V) to a lower voltage (for example, 1.8 V).

Charging cradle3mainly includes external power supply connector301and power supply circuit302, and also includes terminals T31and T32.

Terminals T31and T32are for supplying a charging current to handset2.

External power supply connector301connects to an external power supply and receives a DC current as input.

Power supply circuit302is a DC/DC converter that converts DC voltage from external power supply connector301(for example, 6.5 V) to an appropriate voltage (for example, 2.5 V) and supplies the voltage to charging circuit211of handset2.

Handset2is configured to enable easy placement into and removal from charging cradle3as shown inFIG. 4. When handset2is placed into charging cradle3, it is electrically connected to charging cradle3, and a charging current from charging cradle3is accumulated in secondary battery212. There are base units1configured to enable charging of handset2. In case of such base unit1, when being placed into the charging part of base unit1, handset2is electrically connected to the charging part of base unit1, and a charging current from base unit1is accumulated in secondary battery212.

Next, communication between a base unit and a handset in the standby state in the DECT system will be described usingFIG. 5AandFIG. 5B.

As shown inFIG. 5AandFIG. 5B, the DECT system adopts a TDMA/TDD (time division multiple access/time division duplex) system including 24 slots (12 slots for the uplink and 12 slots for the downlink) in one frame with a period of 10 ms. At least one slot is provided as a control channel slot, and the control channel and calling channels are both transmitted and received with a frame period of 10 ms.

The base unit determines a predetermined slot that is pre-determined as a control channel with respect to a handset for each frame (the 2nd slot inFIG. 5AandFIG. 5B), and transmits a control signal (beacon) on this channel.

As shown inFIG. 5A, in the standby state a signal is not transmitted from the handset to the base unit. If an event such as the handset being placed into a charging cradle occurs, the handset transmits to the base unit a notification signal in a pre-determined predetermined slot (14th slot inFIG. 5A).

Next, communication between the base unit and a handset in the call-in-progress state in the DECT system is shown inFIG. 5B. In the call-in-progress state, the base unit transmits a control signal (beacon) in the same manner as in the standby state. The base unit and the handset each transmit a voice signal in each frame, in slots that have been specified by the base unit (5th and 17th in respective slots inFIG. 5B).

Base unit1in the present embodiment measures the RSSI level of a notification signal (such as the placement notification signal or the removal notification signal) transmitted from each handset2and controls the transmission power based on the measurement result.

Next, the information stored in memory section103of base unit1will be described usingFIG. 6. As shown inFIG. 6, for each handset2, memory section103of base unit1stores, in association with one another, the ID number (IDi) of the handset, the measured RSSI level (Pppi) of the notification signal (such as the placement notification signal or the removal notification signal), and the time (Tppi) of receiving the notification signal. In the following, the table shown inFIG. 6will be called the power control table.

Each time a notification signal is received by base unit1from each handset2, level measurement section104ameasures the RSSI level of the notification signal and outputs the measurement result to signal processing section102(transmission power control section102a).

Upon receiving a notification signal from any handset2, signal processing section102stores the ID of the handset2, the RSSI level, and the time of reception, in association with one another into memory section103.

Next, the transmission power control method when the base unit according to the present embodiment transmits a control signal on the control channel will be described.

At a predetermined timing, transmission power control section102acalculates the transmission power value, using a minimum value of RSSI level (Pppi) stored in memory section103. The timing of transmission power control section102aperforming transmission power control can be, for example, the timing at which the contents stored in memory section103shown inFIG. 6are updated.

Specifically, transmission power control section102areads each RSSI level (Pppi) stored in memory section103when the notification signal transmitted from each handset2is received and selects the minimum value from among the RSSI levels. The transmission power value of each handset2that allows for communication with base unit1is set to the same value. Base unit1may know the transmission power value of each handset2beforehand. Additionally, at the time of a registration operation, each handset2may notify base unit1of its transmission power value. The transmission power value of each handset2is stored beforehand into memory section103of base unit1when the product is manufactured.

In the present embodiment, the amplification of amplification section104bwhen a control signal is transmitted is controlled to suit the handset2for which the received signal level is the weakest. Specifically, from information stored in memory section103, base unit1reads out the RSSI level (minimum RSSI level) of handset2having the weakest received signal level and subtracts the minimum RSSI level (Pppi) from a known value of handset transmission power, so as to calculate the propagation path loss related to handset2having the weakest received signal level. In a cordless telephone in which base unit1and handset2transmit with the same transmission power, the propagation path loss up to handset2can be calculated using the transmission power of base unit1itself rather than the transmission power of handset2.

Transmission power control section102acalculates the transmission power value for transmission of a control signal by base unit1in accordance with a value that is the sum of the propagation path loss related to handset2with the weakest level and a received power reference value. The received power reference value is the received power value required to maintain communication between base unit1and handset2and to avoid an increase in communication interference, to which a margin is added. For example, in a case where the RSSI level (Pppi) of the signal received from one handset2falls below the received power reference value when it is recognized that all handsets2are placed in their charging cradles3, base unit1may stop the transmission power control and transmit the control signal with full power.

Transmission power control section102athen controls amplification section104bso that the signal is transmitted with the calculated transmission power value.

FIG. 7AandFIG. 7Bshow how the signal footprint is adjusted when the base unit transmits a control signal on a control channel in the present embodiment. Let us consider a case where the RSSI levels at the base unit of the notification signals transmitted by handsets with ID1, ID2, and ID3are taken to be, respectively, Ppp1, Ppp2, and Ppp3. In this case, if the RSSI levels of the notification signals of the handsets (ID1, ID2, and ID3) at the base unit are such that Ppp1>Ppp2>Ppp3, the base unit calculates the transmission power value using the minimum value Ppp3.

Doing this enables reception of a control signal transmitted from base unit1on a control channel at even a handset at a distance from the base unit1and having a large propagation path loss, with a received power value required for maintaining communication. Because the transmission power of base unit1is reduced, it is also possible to avoid an increase in radio interference to another radio communication system.

As described above, according to the present embodiment, in the case of radio communication with a plurality of handsets by the TDMA system, because the transmission power can be controlled so that the received signal level at a handset located far from the base unit is an amount that slightly exceeds a predetermined threshold enabling maintenance of communication. Thus, it is possible to maintain communication with all handsets, while avoiding an increase in radio interference to another radio communication system as much as possible.

Although the present embodiment has been described for the case of the RSSI levels of a received notification signal being stored in memory section103, this is not a restriction on the present invention, and another value such as a propagation path loss may be calculated and stored beforehand, for example.

Because the configurations of base unit1and handset2according to Embodiment 2 of the present invention are the same as those shown inFIG. 2toFIG. 4regarding Embodiment 1, the descriptions of the configurations of base unit1and handset2will make use of these drawings as appropriate.

In Embodiment 2 as well, as shown inFIG. 4, handset2is configured to enable the user to easily place handset2into and remove handset2from charging cradle3. When handset2is placed into charging cradle3, it is electrically connected to charging cradle3, and a charging current from charging cradle3is accumulated in secondary battery212. There are base units1configured to enable charging of handset2. In this case, when handset2is placed into the charging part of base unit1, it is electrically connected to base unit1, and a charging current from base unit1is accumulated in secondary battery212.

Because the power control table stored in memory section103of base unit1is the same as that shown inFIG. 6, the description of the power control table will be omitted. In addition, the descriptions of the measurement by the level measurement section104aof the RSSI level of the notification signal, the processing of the notification by signal processing section102, and storage into memory section103will be omitted because the measurement, processing and storage are the same as in the foregoing embodiment.

Similarly, the description of the transmission power control method when a control signal is transmitted on a control channel by the base unit according to the present embodiment will be omitted because the method is same as in the foregoing embodiment.

Next, the procedure for determining the transmission power at the start of communication will be described usingFIG. 8. InFIG. 8, at step401(hereinafter, “step” will be indicated by prefixing the abbreviation ST to the step numbers), a communication start button on handset2is pressed, for example, to start communication with base unit1. At ST402, handset2transmits a communication start request to base unit1.

At ST403, base unit1verifies reception of the communication start request transmitted from handset2, and permits the start of communication with handset2. At ST404, base unit1transmits a communication start request acknowledgment to handset2.

At ST405, base unit1measures the RSSI level of the communication start request signal and updates the power control table with the measured RSSI level. Base unit1also, based on the updated power control table, determines a transmission power value for transmitting a control signal to suit the handset having the weakest received signal level, as described above. The transmission power value stored in memory section103is updated with the determined transmission power value, the amplification of amplification section104bis controlled by that transmission power value, and transmission power control is started.

At ST406, base unit1and handset2communicate with each other. At ST407, handset2notifies base unit1of the end of communication. At ST408, base unit1transmits a communication end acknowledgment to handset2.

In this manner, base unit1measures the RSSI level of the communication start request signal transmitted from handset2and, based on the power control table that has been updated with the measured RSSI level, determines the transmission power value and performs transmission power control. In the case of performing radio communication with one or a plurality of handsets, this transmission power control enables maintenance of communication with handsets while avoiding an increase in radio interference to another radio communication system as much as possible.

Next, the operation of handset2shown inFIG. 8will be described usingFIG. 9. InFIG. 9, at ST421, handset2judges whether or not there has been an instruction to start communication by, for example, pressing a communication start button. If there has been a communication start instruction (YES at ST421), the flow goes to ST422, and if there has not been a communication start instruction (NO at ST421), the flow returns to ST421.

At ST422, handset2requests base unit1to start communication. At ST423, handset2judges whether or not a communication start request acknowledgment (communication start permission) has been acquired from base unit1. If handset2has acquired permission (YES at ST423), the flow goes to ST424, and if it has not acquired permission (NO at ST423), the flow returns to ST422.

At ST424, handset2communicates with base unit1. At ST425, handset2judges whether or not communication is to end. If handset2is to end communication (YES at ST425), the flow ends, and if handset2is not to end communication (NO at ST425), the flow returns to ST425.

Next, the operation of base unit1shown inFIG. 8will be described usingFIG. 10. InFIG. 10, at ST441, base unit1judges whether or not there is a communication start request from handset2. If there is a communication start request (YES at ST441), the flow goes to ST442, and if there is no communication start request (NO at ST441), the flow returns to ST441.

At ST442, base unit1measures the RSSI level of the communication start request signal transmitted from handset2. At ST443, base unit1updates the RSSI level in the power control table of the handset2currently communicating.

At ST444, base unit1determines the transmission power value. At ST445, base unit1updates the initial value of the transmission power value and starts transmission power control.

At ST446, base unit1communicates with handset2. At ST447, base unit1judges whether communication is to be ended. If base unit1is to end communication (YES at ST447), the flow ends, and if base unit1is not to end communication (NO at ST447), the flow returns to ST447.

In this manner, according to Embodiment 2, base unit1measures the RSSI level of the communication start request signal transmitted from handset2and, based on the minimum RSSI level in the power control table that has been updated with the measured RSSI level, determines the transmission power value and controls the transmission power. In the case of performing radio communication with one or a plurality of handsets, this transmission power control enables maintenance of communication with handsets while avoiding an increase in radio interference to another radio communication system as much as possible.

Although the present embodiment has been described for the case of a call initiated by handset2, it can be applied also to the case of a call initiated by base unit1. In this case, a communication start request is transmitted from base unit1to handset2, and the RSSI level of the acknowledgment signal for the communication start request signal transmitted by handset2is measured.

In addition, although in the present embodiment the description has been provided for the case in which the transmission power value is determined based on the communication start request signal transmitted from handset2at the start of communication, in the present invention the transmission power value may be determined at the end of communication. The transmission power determining procedure of this case is shown inFIG. 11, in which parts that are in common with ones shown inFIG. 8have been assigned the same reference signs.

The differences inFIG. 11fromFIG. 8are as follows. Specifically, at ST411, base unit1measures the RSSI level of a communication end notification signal notified to base unit1by handset2, and updates the power control table. Base unit1also determines the transmission power value based on the updated power control table, updates the transmission power value stored in memory section103, and starts transmission power control. The determination of the transmission power may be made after transmission of the communication end acknowledgment at ST408.

Determining the transmission power at the end of communication enables the start of the next communication with the appropriate transmission power because the positional relationship between base unit1and handset2at the end of communication is likely to be the same as the positional relationship therebetween at the start of the next communication.

Because the configurations of base unit1and handset2according to Embodiment 3 of the present invention are the same as those shown inFIG. 2toFIG. 4regarding Embodiment 1, the descriptions of the configurations of base unit1and handset2will make use of these drawings as appropriate.

The procedure for determining the transmission power at the start of handset registration in Embodiment 3 of the present invention will be described usingFIG. 12. In this case, handset registration refers to processing to register an unregistered handset to the base unit.

InFIG. 12, at ST501, handset2transmits a handset registration start request to base unit1. At ST502, base unit1verifies acknowledgment of the handset registration start request transmitted from handset2, and permits registration of handset2.

At ST503, base unit1transmits a handset registration start request acknowledgment to handset2. At ST504, base unit1measures the RSSI level of the handset registration start request signal and updates the power control table with the measured RSSI level. In this embodiment as well, base unit1determines the transmission power value for transmitting the control signal to suit the handset having the weakest signal level. Base unit1then updates the transmission power value stored in memory section103with the determined transmission power value, and starts transmission power control.

At ST505, handset2notifies base unit1of handset registration information. At ST506, base unit1transmits to handset2an acknowledgment for the handset registration information. At ST507, base unit1notifies handset2of base unit registration information.

At ST508, handset2transmits to base unit1an acknowledgment for the base unit registration information. At ST509, handset2stores the base unit registration information into memory section202and, at ST510while base unit1stores the handset registration information into memory section103.

At ST511, handset2notifies base unit1of the completion of handset registration. At ST512, base unit1transmits to handset2an acknowledgment for the handset registration completion.

In this manner, base unit1measures the RSSI level of the handset registration start request signal transmitted from handset2, determines the transmission power value based on the power control table updated with the measured RSSI level, and performs transmission power control. In the case of performing radio communication with one or a plurality of handsets, this transmission power control enables maintenance of communication with handsets while avoiding an increase in radio interference to another radio communication system as much as possible.

Next, the operation of handset2shown inFIG. 12will be described usingFIG. 13. It is assumed that handset2is not registered to base unit1and does not operate even when the power is turn ON, and handset2waits for the register button to be pressed at the starting point inFIG. 13.

InFIG. 13, at ST521, handset2judges whether or not handset registration is to be started. If handset2is to start handset registration (YES at ST521), the flow goes to ST522, and if handset2is not to start handset registration (NO at ST521), the flow returns to ST521.

At ST522, handset2requests base unit1to start registering handset. At ST523, handset2judges whether or not the handset registration start request has been completed. If it has been completed (YES at ST523), the flow goes to ST524, and if it has not been completed (NO at ST523), the flow returns to ST522.

At ST524, handset2notifies base unit1of handset registration information. At ST525, handset2judges whether or not verification was possible of the notification of acknowledgment of the handset registration information from base unit1. If verification has been made (YES at ST525), the flow goes to ST526, and if verification has not been made (NO at ST525), the flow returns to ST524. The sequence of ST524and ST525may be reversed.

At ST526, handset2judges whether or not the handset registration has been completed. If it has been completed (YES at ST526), the flow ends, and if it has not been completed (NO at ST526), the flow returns to ST526.

Next, the operation of base unit1shown inFIG. 12will be described usingFIG. 14. It is assumed that the transmission power value of base unit1is set to the initial value at the starting point inFIG. 14. If no handsets are registered, the initial value of the transmission power value may be set to the full power (maximum transmission power value) of base unit1or to the minimum transmission power value. In the case in which another handset has already been registered, the initial value of the transmission power value may be set to the full power of base unit1or an already-determined transmission power value.

InFIG. 14, at ST541, base unit1judges whether there is a handset registration start request from handset2. If there is a request (YES at ST541), the flow goes to ST542, and if there is no request (NO at ST541), the flow returns to ST541.

At ST542, base unit1authenticates handset2that transmitted the handset registration start request and judges whether or not to accept the handset registration start request. If it is to be accepted (YES at ST542), the flow goes to ST543, and if it is not to be accepted (NO at ST542), the flow returns to ST542. At ST543, base unit1sends a handset registration acceptance notification to handset2.

At ST544, base unit1measures the RSSI level of the handset registration start request signal transmitted from handset2. At ST545, base unit1updates the RSSI level in the power control table of handset2that is communicating.

At ST546, base unit1determines the transmission power value. At ST547, base unit1updates the initial value of the transmission power value and starts transmission power control.

At ST548, base unit1judges whether or not handset registration information has been acquired. If it has been acquired (YES at ST548), the flow goes to ST549, and if it has not been acquired (NO at ST548), the flow returns to ST548.

At ST549, base unit1notifies handset2of acknowledgment of the handset registration information or base unit registration information. The sequence of ST548and ST549may be reversed.

At ST550, base unit1judges whether or not the handset registration has been completed. If it has been completed (YES at ST550), the flow ends, and if it has not been completed (NO at ST550), the flow returns to ST550.

In this manner, according to Embodiment 3, base unit1measures the RSSI level of the handset registration start request signal transmitted from handset2and, based on the minimum RSSI level in the power control table that has been updated with the measured RSSI level, determines the transmission power value and performs transmission power control. In the case of performing radio communication with one or a plurality of handsets, this transmission power control enables maintenance of communication with handsets while avoiding an increase in radio interference to another radio communication system as much as possible.

Also, although in the present embodiment the description has been provided for the case in which the transmission power value is determined based on the handset registration start request signal transmitted from handset2at the start of handset registration, in the present invention, the transmission power value may be determined at the end of handset registration. The transmission power determining procedure in this case is shown inFIG. 15, in which parts that are in common with ones shown inFIG. 12have been assigned the same reference signs.

The differences inFIG. 15fromFIG. 12are as follows. Specifically, at ST520, base unit1measures the RSSI level of a handset registration completion notification signal notified to base unit1by handset2, and updates the power control table. In this case as well, base unit1also determines the transmission power value for transmitting the control signal to suit the handset with the weakest received signal level. Base unit1then updates the transmission power value stored in memory section103with this determined transmission power value, and starts transmission power control. The determination of the transmission power value may be made after transmission of the handset registration completion acknowledgment at ST512.

Base unit1may determine the transmission power value during the handset registration. The procedure for determining the transmission power in this case is shown inFIG. 16. InFIG. 16, parts that are in common with ones shown inFIG. 12have been assigned the same reference signs.

The differences inFIG. 16fromFIG. 12are as follows. Specifically, at ST530, base unit1measures the RSSI level of a handset registration information notification signal notified to base unit1by handset2, and updates the power control table. In this case as well, base unit1also determines the transmission power value for transmitting the control signal to suit the handset with the weakest received signal level, based on the updated power control table, updates the transmission power value stored in memory section103, and starts transmission power control.

Because the configurations of base unit1and handset2according to Embodiment 4 of the present invention are the same as those shown inFIG. 2toFIG. 4regarding Embodiment 1, the descriptions of the configurations of base unit1and handset2will make use of these drawings as appropriate.

The procedure for determining the transmission power at the start of position registration in Embodiment 4 of the present invention will be described usingFIG. 17. In this case, position registration refers to processing of re-connecting to the base unit a handset registered to the base unit when the power for the handset has been set to on or when the handset returns from being out-of-range.

InFIG. 17, at ST601, handset2starts searching for a base unit and detects base unit1.

At ST602, handset2transmits a position registration request to base unit1. At ST603, base unit1verifies acknowledgment of the position registration request transmitted from handset2and permits registration of the position of handset2.

At ST604, base unit1transmits a position registration request acknowledgment to handset2. At ST605, base unit1measures the RSSI level of the position registration request signal and updates the power control table. In this case as well, base unit1also determines the transmission power value for transmitting the control signal to suit the handset with the weakest received signal level based on the updated power control table, updates the transmission power value stored in memory section103, and starts transmission power control.

At ST606, handset2notifies base unit1of position registration completion. At ST607, base unit1transmits to handset2an acknowledgment of the position registration completion.

In this manner, base unit1measures the RSSI level of the position registration request signal transmitted from handset2and, based on the power control table updated with the measured RSSI level, determines the transmission power value and performs transmission power control. In the case of performing radio communication with one or a plurality of handsets, this enables maintenance of communication with handsets while avoiding an increase in radio interference to another radio communication system as much as possible.

Next, the operation of handset2shown inFIG. 17will be described usingFIG. 18. InFIG. 18, at ST621, handset2starts searching for base unit1and judges whether or not base unit1has been detected. If it has been detected (YES at ST621), the flow goes to ST622, and if it has not been detected (NO at ST621), the flow returns to ST621.

At ST622, handset2transmits a position registration request to base unit1. At ST623, handset2judges whether or not the position registration request to base unit1has been completed. If it has been completed (YES at ST623), the flow goes to ST624, and if it has not been completed (NO at ST623), the flow returns to S623.

At ST624, handset2judges whether or not the position registration has been completed. If it has been completed (YES at ST624), the flow ends, and if it has not been completed (NO at ST624), the flow returns to ST624.

Next, the operation of base unit1shown inFIG. 17will be described usingFIG. 19. It is assumed that the transmission power value of base unit1is set to the initial value at the starting point inFIG. 19. The initial value of the transmission power value may be set to a transmission power value determined in processing performed before the position registration, such as at handset registration or when communicating. In the case in which the target handset is out of the coverage area of base unit1or has its power switched off, so that the target handset is not in the coverage area of base unit1, the initial value of the transmission power value may be set to the full power of base unit1.

InFIG. 19, at ST641, base unit1judges whether or not there is a position registration request from handset2. If there is a position registration request (YES at ST641), the flow goes to ST642, and if there is no position registration request (NO at ST641), the flow returns to ST641.

At ST642, base unit1authenticates handset2that transmitted the position registration request and judges whether or not to accept the position registration request. If it is to be accepted (YES at ST642), the flow goes to ST643, and if it is not to be accepted (NO at ST642), the flow returns to ST641.

At ST643, base unit1measures the RSSI level of the position registration request signal transmitted from handset2. At ST644, base unit1updates the RSSI level in the power control table of handset2that is communicating.

At ST645, base unit1determines the transmission power value. At ST646, base unit1updates the initial value of the transmission power value and starts transmission power control.

At ST647, base unit1judges whether or not the position registration has been completed. If it has been completed (YES at ST647), the flow ends, and if it has not been completed (NO at ST647), the flow returns to ST647.

In this manner, according to Embodiment 4, base unit1measures the RSSI level of the position registration request transmitted from handset2, and, based on the minimum RSSI level in the power control table that has been updated with the measured RSSI level, determines the transmission power value and performs transmission power control. In the case of performing radio communication with one or a plurality of handsets, this enables maintenance of communication with handsets while avoiding an increase in radio interference to another radio communication system as much as possible.

Also, although, in the present embodiment, the description has been provided for the case in which the transmission power value is determined based on the position registration request signal transmitted from handset2at the start of position registration, the present invention may determine the transmission power value at the end of the position registration. The procedure for determining the transmission power in this case is shown inFIG. 20. InFIG. 20, parts that are the same as ones shown inFIG. 17have been assigned the same reference signs.

The differences inFIG. 20fromFIG. 17are as follows. Specifically, at ST610, base unit1measures the RSSI level of a position registration completion notification signal notified to base unit1by handset2, and updates the power control table with the measured RSSI level. Base unit1determines the transmission power value for transmitting the control signal to suit the handset having the weakest received signal level based on the updated power control table, updates the transmission power value stored in memory section103, and starts transmission power control. The determination of the transmission power value may be made after transmission of the position registration completion notification at ST607.

Because the configurations of base unit1and handset2according to Embodiment 5 of the present invention are the same as those shown inFIG. 2toFIG. 4regarding Embodiment 1, the descriptions of the configurations of base unit1and handset2will make use of these drawings as appropriate.

The procedure for determining the transmission power at the time of placement into the charging cradle in Embodiment 5 of the present invention will be described usingFIG. 21. InFIG. 21, at ST701, handset2detects that it has been placed into charging cradle3. At ST702, handset2transmits to base unit1a placement notification indicating placement into charging cradle3.

At ST703, base unit1measures the RSSI level of the placement notification signal transmitted from handset2and updates the power control table with the measured RSSI level. Base unit1determines the transmission power value for transmitting the control signal to suit the handset having the weakest received signal level, based on the updated power control table, updates the transmission power value stored in memory section103, and starts transmission power control.

At ST704, base unit1transmits a placement notification acknowledgment to handset2.

In this manner, base unit1measures the RSSI level of the placement notification signal transmitted from handset2, and based on the power control table updated with the measured RSSI level, determines the transmission power value and performs transmission power control. In the case of performing radio communication with one or a plurality of handsets, this enables maintenance of communication with handsets while avoiding an increase in radio interference to another radio communication system as much as possible.

Next, the operation of handset2shown inFIG. 21will be described usingFIG. 22. InFIG. 22, at ST721, handset2judges whether or not handset2has been placed into charging cradle3. If it has been placed (YES at ST721), the flow goes to ST722, and if it has not been placed (NO at ST721), the flow returns to ST721.

At ST722, handset2transmits a placement notification signal to base unit1. At ST723, handset2judges whether or not the placement notification has been completed. If it has been completed (YES at ST723), the flow ends, and if it has not been completed (NO at ST723), the flow returns to ST723.

Next, the operation of base unit1shown inFIG. 21will be described usingFIG. 23. InFIG. 23, at ST741, base unit1judges whether or not the placement notification signal has been received from handset2. If it has been received (YES at ST741), the flow goes to ST742, and if it has not been received (NO at ST741), the flow returns to ST741.

At ST742, base unit1measures the RSSI level of the placement notification signal transmitted from handset2. At ST743, base unit1updates the RSSI level in the power control table of handset2that is communicating.

At ST744, base unit1determines the transmission power value. At ST745, base unit1updates the initial value of the transmission power value and starts transmission power control, and then the flow ends.

In this manner, according to Embodiment 5, base unit1measures the RSSI level of the placement notification signal transmitted from handset2, determines the transmission power value based on the minimum RSSI level in the power control table updated with the measured RSSI level, and performs transmission power control. In the case of performing radio communication with one or a plurality of handsets, this enables maintenance of communication with handsets while avoiding an increase in radio interference to another radio communication system as much as possible.

Because the configurations of base unit1and handset2according to Embodiment 6 of the present invention are the same as those shown inFIG. 2toFIG. 4regarding Embodiment 1, the descriptions of the configurations of base unit1and handset2will make use of these drawings as appropriate.

The procedure for determining the transmission power at the start of intermittent operation in Embodiment 6 of the present invention will be described usingFIG. 24. InFIG. 24, parts that are the same as ones shown inFIG. 8are assigned the same reference signs, and differences fromFIG. 8will be described.

InFIG. 24, at ST801, handset2maintains synchronization with a period of 10 ms and shifts to intermittent operation with a period of 640 ms.

At ST802, handset2notifies base unit1of shifting to intermittent operation. At ST803, base unit1measures the RSSI level of the intermittent operation shifting signal notified to base unit1by handset2, and updates the power control table with the measured RSSI level. Base unit1determines the transmission power value for transmitting the control signal to suit the handset having the weakest received signal level, based on the updated power control table, updates the transmission power value stored in memory section103, and starts transmission power control. In this case, the determination of the transmission power value may be made after transmission of the position registration completion acknowledgement at ST607.

At ST804, base unit1transmits to handset2an intermittent operation shifting acknowledgment.

Next, the operation of handset2shown inFIG. 24will be described usingFIG. 25. InFIG. 25, at ST821, handset2judges whether or not communication is to start with base unit1. If communication is to start (YES at ST821), the flow goes to ST822, and if communication is not to start (NO at ST821), the flow returns to ST821.

At ST822, handset2judges whether or not communication with base unit1is to end. If communication is to end (YES at ST822), the flow goes to ST823, and if communication is not to end (NO at ST822), the flow returns to ST822.

At ST823, handset2maintains synchronization with base unit1with a period of 10 ms. At ST824, handset2judges whether or not a predetermined time has elapsed. If the predetermined time has elapsed (YES at ST824), the flow goes to ST825, and if the predetermined time has not elapsed (NO at ST824), the flow returns to ST824.

At ST825, handset2notifies base unit1of shifting to intermittent operation with a period of 640 ms. At ST826, handset2judges whether or not the intermittent operation shifting notification has been completed. If it has been completed (YES at ST826), the flow ends, and if it has not been completed (NO at ST826), the flow returns to ST825.

In this manner, base unit1measures the RSSI level of the intermittent operation shifting notification signal transmitted from handset2, determines the transmission power value based on the power control table updated with the measured RSSI level, and performs transmission power control. In the case of performing radio communication with one or a plurality of handsets, this enables maintenance of communication with handsets while avoiding an increase in radio interference to another radio communication system as much as possible.

Next, the operation of base unit1shown inFIG. 24will be described usingFIG. 26. InFIG. 26, at ST841, base unit1judges whether or not base unit1is in communication with handset2. If base unit1is in communication (YES at ST841), the flow goes to ST842, and if base unit1is not in communication (NO at ST841), the flow returns to ST841.

At ST842, base unit1judges whether or not communication with handset2has ended. If communication has ended (YES at ST842), the flow goes to ST843, and if communication has not ended (NO at ST842), the flow returns to ST842.

At ST843, base unit1judges whether or not the intermittent operation shifting notification signal has been received handset2. If it has been received (YES at ST843), the flow goes to ST844, and if it has not be received (NO at ST843), the flow returns to ST843.

At ST844, base unit1measures the RSSI level of the intermittent operation shifting notification signal transmitted from handset2. At ST845, base unit1updates the RSSI level of handset2in the power control table that is communicating.

At ST846, base unit1determines the transmission power value. At ST847, base unit1updates the initial value of the transmission power value, starts transmission power control, and ends the procedure for determining the transmission power at the base unit side at the start of intermittent operation.

In this manner, according to Embodiment 6, base unit1measures the RSSI level of the intermittent operation shifting notification signal transmitted from handset2, determines the transmission power value based on the minimum RSSI level in the power control table updated by the measured RSSI level, and performs transmission power control. In the case of performing radio communication with one or a plurality of handsets, this enables maintenance of communication with handsets while avoiding an increase in radio interference to another radio communication system as much as possible.

Although in the above-described embodiments the description has been for the case in which the RSSI level of a received signal is stored in memory section103, this is not a restriction on the present invention, and another value, such as a propagation path loss may be calculated and stored beforehand.

Next, an embodiment for the case in which the conditions for shifting to the state of performing transmission power control and the conditions for canceling transmission power control are made different will be described. Because transmission power control of the control signal in the case of a plurality of handsets existing is done in accordance with a handset at a distant position, the possibility of the control signal not reaching the handset at the distant position is made small, and communication with all handsets is maintained while avoiding an increase in radio interference to another radio communication system as much as possible.

Upon receiving a removal notification signal from any handset2, signal processing section102of base unit1removes the values of the RSSI level (Pppi) and the placement notification signal receiving time (Tppi) from the list in memory section103regarding handset2. As an example,FIG. 27shows a situation where a removal notification signal has been received from handset2having the ID number of ID3and the values of the RSSI level (Pppi) and the placement notification signal receiving time (Tppi) regarding that handset2have been removed.

When a removal notification signal is received from any handset2as noted above, and the RSSI level (Pppi) of memory section103is deleted, transmission power control section102acancels the transmission power control and controls amplification section104bso that a radio signal is always transmitted with the maximum power.

When an RSSI level (Pppi) other than the minimum value in memory section103is deleted, transmission power control section102acan select, instead of immediately canceling the transmission power control, either maintaining or canceling of transmission power control in accordance with the RSSI level of a voice signal subsequently transmitted from handset2. That is, if a removal notification signal is transmitted from handset2that has an RSSI level (Pppi) other than the minimum level, transmission power control section102amaintains transmission power control at that point.

After that, when a signal (signal carrying voice data related to a call or other notification signal) is transmitted from that handset2, transmission power control section102aof base unit1compares the RSSI level of the signal at that time with a received power reference value. If the RSSI level of the voice signal or the like from that handset2(handset2having an RSSI level other than the minimum value at the time the removal notification signal was transmitted) decreases to no greater than a predetermined received power reference value, transmission power control section102acancels transmission power control, but maintains transmission power control if the level exceeds the received power reference value.

Next, the operation of handset2according to the present embodiment will be described using the flow shown inFIG. 28.

When the user is to place handset2in the usable state, the power of handset2is first turned on and handset2is placed into charging cradle3(ST901).

When handset2is placed into charging cradle3(YES at ST901), handset2transmits a placement notification signal to base unit1, and goes into the idle state (ST902, ST903).

After that, consider the case in which the user removes handset2from charging cradle3, for example, to use handset2for a call (YES at ST904). In this case, handset2transmits a removal notification signal to base unit1(ST905). The flow then returns to ST901.

Next, the operation of the base unit according to the present embodiment will be described using the flow shown inFIG. 29.

With the default being that base unit1does not perform transmission power control and operates at full power, base unit1transmits a radio signal at all times with the maximum power (ST911).

After that, base unit1monitors whether or not a placement notification signal is received from handset2(ST912). Upon receiving the placement notification signal from handset2(YES at ST912), base unit1measures the RSSI and updates the information in memory section103(ST913, ST914). Specifically, as shown inFIG. 6, the RSSI level of a notification signal such as the placement notification signal transmitted from handset2and the time of reception of the signal are stored in association with the ID number of handset2into memory section103.

At ST915, base unit1checks to see whether or not the RSSI levels of the placement notification signals (or other notification signal) and the reception times of the signals regarding all handsets2registered in memory section103are present. Base unit1repeats the processing of ST911to ST914until the RSSI levels of the signals from all handsets2and the reception times of the signals are present (NO at ST915).

When placement notification signals are received from all handsets2and the RSSI levels and the reception times of signals from all handsets2are present in memory section103(YES at ST915), base unit1performs transmission power control (ST916).

After that, upon receiving a removal notification signal from any handset2(YES at ST917), base unit1deletes information regarding that handset2(RSSI level and reception time) from memory section103(ST918), cancels transmission power control, and goes into full-power operation (returns to ST911).

In the above example, base unit1performs transmission power control only in the case in which all handsets2are placed in charging cradles3or the charging part of base unit1and transmits the control signal with full power in the case in which any handset2is removed, so that even if a certain handset2is moved to a distance away from charging cradle3, there is little possibility of losing synchronization with the handset2.

Next, the operation of a base unit according to another embodiment of the present invention will be described using the flow shown inFIG. 30.

Base unit1operates with full power and transmits a radio signal at all times with the maximum power without performing transmission power control at the default setting (ST921).

After that, base unit1monitors whether or not a placement notification signal is received from handset2(ST912). Upon receiving the placement notification signal from handset2(YES at ST922), base unit1measures the RSSI and updates the information in memory section103(ST923, ST924). Specifically, as shown inFIG. 6, the RSSI level of a notification signal such as the placement notification signal transmitted from handset2and the time of reception of the signal are stored in association with the ID number of handset2into memory section103.

At ST925, base unit1checks to see whether or not the RSSI levels of the placement notification signals (or other notification signal) and the reception times of the signals regarding all handsets2registered in memory section103are present. Base unit1repeats the processing of ST921to ST924until the RSSI signal levels of all handsets2and the reception times of the signals are present (NO at ST925). ST925is processing to check placement of all handsets to judge whether or not all handsets2have been placed into charging cradles3.

When placement notification signals are received from all handsets2and the RSSI levels and the reception times of the signals from all handsets2are present in memory section103(YES at ST925), transmission power control is performed (ST926). If the RSSI levels and the reception times of the signals regarding all handsets2are not present (NO at ST925), full-power operation is maintained (and the flow returns to ST921).

After that, upon receiving a removal notification signal from any handset2(YES at ST927), base unit1checks whether or not the RSSI level of handset2that had given notification by a removal notification signal is the minimum value stored in memory section103(ST928). If the RSSI level of the handset2that had given notification by a removal notification signal is the minimum value (YES at ST928), base unit1deletes information (RSSI level and reception time) of that handset2from memory section103(ST929). Base unit1then cancels transmission power control and operates at full power (returns to ST921). ST928is processing to judge the reception level in order to cancel transmission power control in accordance with the reception level for the case in which one handset has been removed from a charging cradle.

At ST928, in the case in which the RSSI level of the handset that had given notification by the removal notification signal was not the minimum value (NO at ST928), base unit1measures the RSSI of a signal (voice signal or the like) subsequently transmitted from that handset2and checks whether or not the RSSI level of that handset2is no greater than a received power reference value (ST930). If the RSSI level of that handset2is no greater than the received power reference value (YES at ST930), base unit1measures the RSSI of a signal from that handset2and updates information in memory section103(ST931). Having done this, base unit1cancels transmission power control and operates at full power (returns to ST921).

If, however, the RSSI level of that handset2was greater than the received power reference value (NO at ST930), base unit1monitors whether or not a placement notification signal has been received from handset2(ST932). If a placement notification signal has not been received from handset2(NO at ST932), base unit1repeats the processing of ST928, ST930, and ST932, while continuing the transmission power control.

If a placement notification signal is received from that handset2(YES at ST931) before the RSSI level of the received signal of that handset2becomes the minimum value or is no greater than the received power reference value (NO at ST928and NO at ST932), base unit1measures the RSSI of that placement notification signal and updates information in memory section103(ST923, ST924). When doing this, if the RSSI levels and reception times for signals regarding all handsets2are not present (NO at ST925), base unit1cancels transmission power control and operates at full power (returns to ST921).

As described above, according to the present embodiment, even when one handset is removed from a charging cradle, transmission power control is cancelled in accordance with the reception level of a signal transmitted from that handset. Thus, even if that handset moves away from the base unit, it is possible to allow the handset to receive a control signal at a stronger level, thereby maintaining communication with the handset.

According to the present embodiment, transmission power control is cancelled when a handset having the minimum received signal level is removed from the charging cradle or when the received signal level of a handset removed from a charging cradle is no greater than a received power reference level value of the received signal level. This enables maintenance of communication with all handsets, while avoiding an increase in radio interference to another radio communication system as much as possible.

Although in the present embodiment the description has been provided with regard to the case in which the RSSI level of a received control signal is stored in memory section103, this is not a restriction on the present invention, and another value, such as a propagation path loss may be calculated and stored beforehand, for example.

REFERENCE SIGNS LIST