PORTABLE RADIO TELEPHONE HAVING POWER SAVER

Abstract: A battery-powered portable radio telephone for use in a mobile telephone network receives signals from the network and judges from the received signal whether the radio telephone is inside or outside of the service area of the network. A battery saver is provided to periodically interrupt the battery power of the telephone when the latter is judged as being outside of the service area.

Description: The present invention relates to a portable radio communication unit for use in a mobile switched telecommunication network. Portable radio telephones are designed to work with the conventional cellular mobile telephone network in the same manner as automobile units are working with it. However, the current portable radio telephones are not provided with a battery saver, requiring a relatively large battery. It has been desired to provide a battery saver to minimize power consumption. US-A-4,086,537 discloses a TDM (time division multiplex) receiver in which the clock and framing components are detected from a received TDM signal and the power of the receiver is controlled in accordance with different sync states of the clock signal and the framing signal. No comparison is made between the strongest signal and a threshold corresponding to the signal level of the boundary of a service area. JP-A-52133/85 describes a mobile station which determines its location by searching the field intensity levels of signals of different time slots and by detecting the time slot having the highest signal level as corresponding to the cell in which it is located. The station is tuned to the detected time slot and power supplies are intermittently cut off to reduce power consumption. GB-A-1,111,006 relates to a receiver whose power consumption is reduced in the absence of a signal. JP-A-16732/85 relates to a technique for reducing power consumption of a mobile station. When the field technique intensity level of the station is low, it enters a standby state in which power supplies are periodically cut off. In both devices no search is made for detecting the strongest of signals from different cell sites and no comparison is made between it and a boundary indicating threshold. The present invention is based on the fact that the transmission power level of conventional portable radio telephones is typically 6 or 7 dB lower than that of the automobile telephone. The service area of the portable telephone is smaller than that of the automobile telephone and hence portable units can easily go beyond the boundary of the service area, wasting their battery power. It is therefore an object of the present invention to provide a battery-powered portable radio communication unit for use in a mobile switched telecommunication network, wherein the telephone is provided with a battery saver for periodically interrupting battery power when the portable unit is outside of the service area of the network. This object is solved with the features of the claims. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be described in further detail with reference to the accompanying drawings, in which: Fig. 1 is a schematic block diagram of a portable radio telephone according to the present invention; Fig. 2 is a flowchart describing the operation of the control unit of Fig. 1 according to a first embodiment of the invention; Fig. 3 is a flowchart describing the operation of the control circuit according to a second embodiment; Fig. 4 is a flowchart describing the operation of the control circuit according to a third embodiment; and Figs. 5 to 7 are timing diagrams associated respectively with the first, second and third embodiments. DETAILED DESCRIPTION A portable radio telephone set of the present invention shown in Fig. 1 is adapted for working to the conventional cellular mobile telephone system in the same manner as mobile units mounted on automotive vehicles. Therefore, the portable radio telephone of the invention is identical in construction to such mobile units with the exception that it includes a novel power saving circuit. Before describing the present invention, a description will be given to portions of the portable radio telephone set which are identical to the vehicle-mounted units. In Fig. 1, a speech signal from handset 10 is applied to a circuit 11 where it is limited both in frequency and amplitude and applied to a frequency modulator/power amplifier unit 12 to which control data from control unit 13 is also applied. The speech signal is frequency-division multiplexed with the data signal and modulated upon a carrier frequency which is supplied from a frequency synthesizer 14 which is in turn controlled by control unit 13. The carrier frequency is selected so as to tune to a channel having the strongest signal. The modulated carrier is supplied through a duplexer 15 to an antenna 16 for transmission to cell sites which are connected to a mobile telephone switching office. A radio frequency amplifier/mixer unit 17 is coupled to the duplexer 15 to receive a signal from the cell sites to demodulate it into an IF signal, which is amplified by IF amplifier 18. The amplified IF signal is applied to a limiter/discriminator unit 19 and thence to a filter/amplifier unit 20 where the speech signal is separated from the data signal and applied to the handset 10. The data signal is applied to the control unit 13. The output of IF amplifier 18 is also applied to a logarithmic amplifier 21 to generate a signal indicating the signal strength, or received signal strength indicator (RSSI) for coupling to control unit 13. Control unit 13 directs the frequency synthesizer 14 to scan available channels and examines their RSSI signals to determine the strongest one. As will be described, this channel selection is performed in the process of initialization and as often as is necessary to keep the portable unit to be constantly tuned to the best channel. A pushbutton dialing set 22 is connected to control unit 13 for entry of dialed digits for origination of calls. Battery 23 is connected through a manually operated power switch 24 and a battery saving switch 26 to various power drain units of the portable telephone through power line 27. Battery saving switch 26 is responsive to a battery saving (BS) enabling signal supplied from control unit 13 to cut off the power line 27 when battery saving is justified and responsive to the removal of the BS enabling signal to activate the power drain units whenever battery saving is not justified. Control unit 13 constantly receives power from battery 23 through power switch 24 as indicated by a broken-line 25 to prevent various control data from being lost during power saving periods. The RSSI signal from logarithmic amplifier 21 is also applied to a comparator 28 which compares it with a threshold voltage supplied from a voltage source 29. This threshold voltage represents the signal level at the boundary of the service area of a particular portable unit. When the portable telephone is within the service area, the RSSI signal of the best available channel is higher than the boundary threshold and comparator 28 generates a high voltage output. Conversely, when it is outside of the service area, the RSSI signal of the best available channel is lower than the threshold and comparator 28 generates a low voltage output. Control unit 13 responds to the comparator 28 output and generates a BS enabling signal in a manner as herein described with reference to Figs. 2 to 4. Referring to Fig. 2, program execution begins with an initialization step to perform channel selection subroutine 30 when the portable unit is energized. The channel selection subroutine starts with channel designation block 31 which directs the setting of a paging channel count PGCH equal to 1 so that the frequency synthesizer 14 is controlled to select a first one of available paging channels. Exit is to operations block 32 which directs the detecting of the RSSI value of the selected paging channel. Control proceeds to decision block 33 which detects a match between the PGCH count with a maximum count to determine whether the RSSI values of all the available paging channels have been detected. If the PGCH count is smaller than the maximum, exit is to operations block 34 which directs the incrementing of the PGCH count by 1. Blocks 32, 33 and 34 are repeatedly executed until the RSSI value of the last paging channel is detected, whereupon control proceeds to block 35 which directs the determination of a channel having the strongest RSSI value. Program execution advances to decision block 36 to check for the presence of a high voltage output from comparator 28 to determine that the portable unit is within the mobile telephone service area. If there is one, control goes to operations block 37 which directs the examining of the cell-site identification received on the selected channel and directs the registration of the cell-site identification into a memory. Exit from operations block 37 is to decision block 38 which checks for the reception of an incoming call, and if there is one, operations block 39 is executed by performing a call completion subroutine in which an access channel is selected for communicating necessary control data to the registered cell site to ring up the portable unit, and a voice channel is selected for establishing a talking connection. At the end of the incoming call, control returns to decision block 38. If the answer at block 38 is negative, control proceeds to decision block 40 which checks for the presence of a request for an outgoing call. Exit then is to operations block 41 which performs a call setup subroutine. In this subroutine, an access channel is selected to send dialed digits to the cell site and a voice channel is selected to establish a talking connection with the cell site. At the end of the outgoing call, control returns to decision block 38. If the answer at block 40 is negative, exit is to decision block 42 which checks for the presence of a high voltage output from the comparator 28. If there is one, exit is to block 38 to repeat the above process, and if there is none, control advances to operations block 43 which performs the channel selection subroutine identical to that performed by the subroutine 30 to seek a new paging channel having the strongest signal. Control proceeds to decision block 44 which checks for the presence of a high voltage output from the comparator 28. If there is one, control recognizes that the portable unit is still located within the service area and returns to block 38. If the answer is negative in decision blocks 36 and 44, control recognizes that the portable unit is outside of the service area and advances to operations block 45 which directs the introduction of a delay time Td by measuring the amount of time elapsed from the instant the portable unit has crossed the boundary of the service area. Control goes to decision block 46 which checkes for the presence of a high voltage output from the comparator 28. If there is one, control recognizes that the portable unit is returned to the service area and proceeds to block 38. If the answer in block 46 is negative, control recognizes that the portable unit is still outside of the service area and proceeds to operations block 47 which directs the application of a BS enabling signal to the battery saving switch 26. The purpose of the introduction of delay time Td and the threshold decision by execution of blocks 45 and 46 is to discriminate the actual leaving of the portable unit from the service area against false indication of this fact which might occur as a result of short-term variations of signal level. Exit then is to decision block 48 which directs the introduction of a time interval T1 following the execution of block 47 and at the end of time interval T1 control proceeds to block 49 which disables the battery saving by removing the BS enabling signal from the switch 26. Control goes to operations block 50 which directs the execution of the channel selection subroutine and proceeds to decision block 51 to check for the presence of a high voltage output from the comparator 28. If there is none, control recognizes that the portable unit is still outside of the service area and executes blocks 47 through 51 again. If the answer in block 51 is affirmative, control recognizes that the portable unit has reentered the service area and goes to operations block 37 to update the cell site identification. The time taken to execute blocks 50 and 51 corresponds to an interval T2 during which battery saving is disabled. According to the first embodiment of the invention, the power drain circuits are periodically deactivated as long as the portable unit is outside of the service area and activated continuously when it is within the service area as illustrated in Fig. 5. Fig. 3 is a flowchart describing a program according to a second embodiment of the present invention. The second embodiment is a modification of the first embodiment, the difference being the inclusion of a battery saving subroutine 60 between blocks 37 and 38. The battery saving subroutine 60 includes an operations block 61 which directs the application of a BS disabling signal to switch 26, a decision block 62 which introduces a time interval T3 following the disablement of battery saving. Upon termination of T3, control proceeds to operations block 63 which directs the removing of the BS disabling signal from the switch 26. The time interval T3 is shorter than interval T1. Control then executes blocks 38, 40, 42 through 44 and returns to block 61 within an interval T4 to repeat the above process. Thus, the power drain units are repeatedly activated for internal T3 and repeatedly de-activated for interval T4 as long as the portable unit is within the service area while awaiting reception of an incoming call or origination of a call as shown in Fig. 6. While the time interval T4 may vary depending on whether blocks 43 and 44 are executed or not, it remains constant if the signal level remains at a level higher than the boundary threshold. The battery saving subroutine 60 is also performed when the answer in decision block 46 is affirmative. Fig. 4 is a flowchart describing a program according to a third embodiment of the present invention. The third embodiment is a modification of the second embodiment, the difference being the inclusion of a transition subroutine 70 prior to the execution of block 47. The purpose of transition subroutine 70 is to prevent short-term signal level reductions from giving a false indication that the portable unit is leaving the service area in a manner similar to blocks 45 and 46 of Fig. 2. Transition subroutine 70 begins with operations block 71 which directs the disabling of battery saving. Exit then is to decision block 72 which introduces a time interval T5 and then to operations block 73 which directs the enabling of the battery saving. The channel selection subroutine is executed in block 74, followed by a decision block 75 which checks to see if the RSSI value of the channel selected in block 74 is higher than the boundary threshold. If the level reduction is a transitory event, the answer will be affirmative in block 75 and control returns to block 61. If the level reduction is continued, the answer will be negative and control proceeds to decision block 76 to check to see if a transition interval T6 is elapsed. If T6 is not elapsed, control executes blocks 71 to 76 again. The power drain units are thus periodically deactivated during the transistion period T6. Upon the termination of the interval T6, control exits to block 47 to effect battery saving at intervals T1 (see Fig. 7).

Claims: A battery-powered mobile station for use in a mobile telephone network covering a service area which is divided into a plurality of cells each having a cell site, comprising receive means (14, 17, 18) for receiving signals from the cell sites and battery saving means (13, 26), characterized by means (21) for generating strength indicating signals indicating respectively the strengths of the received signals and in that the battery saving means (13) detects a strongest signal from said received signals in accordance with said strength indicating signals, compares the detected strongest signal with a threshold corresponding to the signal strength at the boundary of said service area and periodically interrupts power supplies (23) to the power consuming portions of the mobile station when said strongest signal is lower than said threshold. A battery-powered mobile station as claimed in claim 1, characterized in that said battery saving means (13) generates a first output indicating that the mobile station is outside of the service area when the strongest signal is lower than said threshold, or a second output indicating that said mobile station is inside of said service area when said strongest signal is higher than said threshold, and introduces a time interval in response to said first output of a first occurrence and repeats the comparison between the strongest signal and said threshold upon termination of said time interval to generate said first output of a second occurrence when said strongest signal is still lower than said threshold, and periodically interrupts said power supplies in response to the second occurrence of said first output. A battery-powered mobile station as claimed in claim 1, characterized in that said battery saving means is responsive to said second output for periodically interrupting said power supplies when said mobile station is in a standby mode. A battery-powered mobile station as claimed in claim 3, characterized in that the intervals at which said power supplies are periodically interrupted in response to said second output are smaller than the intervals at which the power supplies are periodically interrupted in response to said first output. A battery-powered mobile station as claimed in claim 3, characterized in that said battery saving means periodically interrupts said power supplies during a prescribed time duration in response to a transition from said second output to said first output, and in that the intervals at which said power supplies are periodically interrupted during said prescribed time duration are smaller than the intervals at which said power supplies are periodically interrupted in response to said second output. A method for saving the battery power of a mobile station for use in a mobile telephone network covering a service area which is divided into cells having cell sites from which the mobile station is constantly receiving signals and wherein power supplies to power consuming portions of the station are periodically interrupted for battery saving purposes, characterized by the steps of: a) generating signals indicating respective strengths of the received signals and selecting the strongest signal from said received signals in accordance with said strength indicating signals; b) determining whether said selected strongest signal is higher or lower than a threshold corresponding to a signal strength at the boundary of said service area; c) if said strongest signal is determined as being lower than said threshold, interrupting power supplies to power consuming portions of said mobile station during a prescribed duration and then repeating the steps (a) and (b); and d) if said strongest signal is determined as being higher than said threshold, repeating the steps (a) and (b). A method as claimed in claim 6, further characterized by the steps of introducing a time interval between the steps (b) and (c) and repeating the step (b) at the end of said introduced time interval prior to the step (c). A method as claimed in claim 6 or 7, characterized in that the step (d) comprises the step of interrupting said power supplies for a second prescribed duration if said strongest signal is determined as being higher than said threshold prior to repeating the steps (a) and (b). A method as claimed in claim 8, characterized in that said second prescribed duration is smaller than the first-mentioned prescribed duration. A method as claimed in claim 6, 7, 8 or 9, characterized in that the step (c) comprises: (1) interrupting said power supplies for a third prescribed duration smaller than said second prescribed duration; and (2) repeating the steps (a), (b) and (c) for a predetermined duration prior to the interruption of the power supplies for the prescribed duration of step (c).

Inventors: BABANO, SOTOAKI C/O NEC CORPORATION, KASAI, YOSHIHIKO C/O NEC CORPORATION
Applicants: NEC CORPORATION
Application year: 1987
Main classification: H04B1
IPC codes: H04B7, H04B1, H04M1, H04Q7