Battery-saving method for a cordless telephone system.

0001The present invention relates to a battery-saving method for a cordless or wireless telephone system constituted by a base communication unit which is connected to a telephone line connection, and a portable communication unit which is connected to the base unit by a wireless communication link.

0002A prior art cordless telephone system usually comprises a base communication unit and a corresponding portable communication unit, and the portable unit performs battery saving (BS) operation at a specific period in order to enhance the service life of battery adapted to power the portable unit. This, however, brings about a drawback that a plurality of telephone lines cannot be used at a time unless the same number of cordless telephone systems as the telephone lines are installed. Another problem is that the total power saving performance attainable with the prior art system is limited because the battery saving operations of the independent portable units occur at the same period and at entirely different timings.

0003EP-A-0 171 071 describes a radio communication system comprising a portable unit carrying out a battery saving operation related to a scanning operation of a fixed unit. The portable unit is intermittently put in a waiting state thereof to active and inactive. The active and inactive durations, respectively are related to the channel scanning period.

0004GB-A-2 115 195 relates to a radio circuit of a portable apparatus having a battery saving feature wherein the operation of such radio circuit is controlled. In this system coded electrical signals are transmitted from a central control station to a plurality of radio receivers which are used for controlling a programmable timer within the receivers to control the battery saving operation. In particular, the control station changes the battery saving period depending on time.

0005EP-A-0 124 788 discloses a radio paging system and receivers therefor which reduces the power consumption of the paging receiver and changes the repetition period of the battery-saving pulses for paging receivers depending on the call traffic. Dependent on whether the number of calls exceeds a predetermined number, a paging receiver powered at a first repetition period is changed in response to a control code into a second repetition period and is changed back to the first repetition period in response to a preamble code. The duration of the battery-saving is changed in response to a signal sent from a central station.

0006It is therefore an object of the present invention to provide a battery-saving method for a cordless telephone system which, consisting of a base unit connected to a telephone system network and portable units each being connected to the base unit by a wireless communication link, achieves high power saving efficiency. This object is achieved by the features of the claims.

0007The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description taken with the accompanying drawings. <ul id="ul0001" list-style="none"><li>Fig. 1 is a block diagram showing a specific construction of a base unit of a cordless telephone system embodying the present invention;</li><li>Fig. 2 is a block diagram showing a specific construction of a portable unit of the system in accordance with the present invention;</li><li>Fig. 3 is a block diagram schematically showing the entire system of the present invention;</li><li>Figs. 4A to 4E are charts demonstrating exemplary BS operations which occur when the portable units in accordance with the present invention are powered one after another;</li><li>Figs. 5A to 5F are charts representative of exemplary changeover of the BS operations which occurs in response to the receipt of a call;</li><li>Figs. 6A to 6F are charts representative of exemplary changeover of the BS operations occurring when a call is originated within the system of the present invention;</li><li>Figs. 7A to 7F are charts representative of exemplary changeover of the BS operations occurring when a communication on the system of the present invention is terminated; and</li><li>Figs. 8A to 8F are charts useful for explaining a difference between the BS operation of a prior art cordless telephone system and a cordless telephone system of the present invention.</li></ul>

DESCRIPTION OF THE PREFERRED EMBODIMENT

0008Referring to Figs. 1 and 2, there are shown, respectively, a specific construction of a base communication unit and that of a portable communication unit which constitute a cordless telephone system of the present invention. In this particular embodiment, the system is assumed to be connected to five telephone connections.

0009As shown in Fig. 1, the base unit, generally 100, includes duplex radio transceivers 101 to 105 each being assigned to a respective one of the five telephone lines, a hybrid switch 106 for selectively connecting the transceivers 101 to 105 to the telephone lines, and a controller 107. The transceivers 101 to 105 include, respectively, transmit sections TR1 to TR5, receive sections RE1 to RE5, synthesizers SY1 to SY5, transmit antennas 118 to 122, and receive antennas 123 to 127. As shown in Fig. 2, the portable unit consists of a transmit section 201, a telephone section 202, a controller 203, a synthesizer 204, a receive section 205, a transmit antenna 206, and a receive antenna 207. The overall arrangement of the system of the present invention is shown in Fig. 3. In Fig. 3, there are shown five portable units, or telephone sets, TEL1 to TEL5 which are connected to the base unit 100 by wireless communication links at transmit frequencies f'₁ to f'₅ and receive frequencies f₁ to f₅, respectively.

0010Figs. 4A to 4E demonstrates BS operations occurring when the portable units TEL1 to TEL5 are powered one after another. First, when the portable unit TEL1 is powered in a condition wherein only the base unit 100 has been powered, the portable unit TEL1 sends a POWER-ON signal to the base unit 100. The base unit 100 responsive to the POWER-ON signal transmits a BS period designate signal to the portable unit TEL1 at a predetermined timing t₁₁ and, at the same time, registers the unit TEL1 in a storage which is built in the controller 107. In response to the BS period designate signal, the portable unit TEL1 enters into a BS operation at a particular period as designated by the input signal and on the lapse of a period of time ΔT since the timing t₁₁, i.e. at a timing t'₁₁. The procedure described so far is shown in Fig. 4A.

0011When the second portable unit, e.g., portable unit TEL2 is powered, it sends a POWER-ON signal to the base unit 100 in the same manner as the first portable unit TEL1. Then, the base unit 100 delivers BS period designate signals to the portable units TEL1 and TEL2 at timings t_1l and t_2l, respectively. At this instant, the controller 107 of the base unit 100 registers the portable units TEL1 and TEL2 in its storage in the order of powering. The portable unit TEL1 changes its BS period from the previous T to 2T receiving the BS period designate signal at a timing t'_1l. The portable unit TEL2, on the other hand, responds to the BS period designate signal by beginning a BS operation at the period of 2T on the lapse of a period of time ΔT since the timing t_2l, i. e. at a timing t'_2l. Such a procedure is shown in Fig. 4B.

0012When the third, fourth and fifth portable units TEL are powered one after another, they enter into BS operations individually through the above procedure, as shown in Figs. 4C to 4E. In the condition shown in Fig. 4E, the controller 107 of the base unit 100 has registered the portable units TEL1, TEL2, TEL3, TEL4 and TEL5 in this order in its storage, and those portable units are performing BS operations in the same order and in synchronism with a signal which is generated within the base unit 100.

0013What occurs in response to an incoming call under the condition of Fig. 4E will be described with reference to Figs. 5A to 5F. Assuming that a call is received at a timing t_c between timings t₂₁ and t₃₁, then the base unit 100 connects a particular telephone line connection over which the call has been received to the transceiver 103 and, by using the transmit section TR3, delivers a call receipt signal to the portable unit TEL3 at the timing t₃₁. Receiving the call receipt signal at a timing t''₃₁, the portable unit TEL3 interrupts its BS operation and, instead, performs a connecting operation. Meanwhile, the base unit 100 sends BS period designate signals to the other portable units TEL4, TEL5, TEL1 and TEL2 at timings t₄₁, t₅₁, t₁₂ and t₂₂, respectively. Receiving the BS period designate signals at, respectively, timings t''₄₁, t''₅₁, t''₁₂ and t''₂₂, the portable units TEL4, TEL5, TEL1 and TEL2 change their BS period to 4T as designated. Thereafter, the portable units TEL1, TEL2, TEL4 and TEL5 repeat their BS operations in that order. In short, in response to an incoming call, the base station 100 connects the busy telephone line to one of the portable units TEL which becomes BS-OFF (i.e. receive section ON) first after the time of receipt of the call and, at the same time, sequentially changes the BS periods of the other portable units TEL, starting from the unit TEL which becomes BS-OFF next. This causes the units TEL other than the one which has been connected to the telephone line to perform BS operations at equal intervals according to the order which is registered in the storage of the controller 107.

0014Figs. 6A to 6F show how the BS operations are effected when a call is originated in the system under the condition of Fig. 4E. Assuming that a call is placed on the portable unit TEL5 at a timing t_H, then the unit TEL5 immediately stops its BS operation and enters into a connecting operation. The base station 100 sends a BS period designate signal to the portable unit TEL1, which is to become BS-OFF after the unit TEL5, at a timing t₁₂ just before the BS-OFF timing of the unit TEL1. Subsequently, the base station 100 transmits BS period designate signals to the portable units TEL2, TEL3 and TEL4 in this order and at timings t₂₂, t₃₂ and t₄₂, respectively. Receiving those signals at, respectively, timings t''₁₂, t''₂₂, t''₃₂ and t''₄₂, the portable units TEL1, TEL2, TEL3 and TEL4 change their BS period to 4T as designated. As a result, the portable units TEL other than the one which has performed the connecting operation are caused to enter into BS operations at equal intervals according to the order which is stored in the controller 107 of the base unit 100, as has been the case with the receipt of a call.

0015Referring to Figs. 7A to 7F, there is shown a change in the BS operations which occurs when a communication is terminated. Assume that the portable unit TEL4 which is in communication has its hook switch turned on at a timing t_S to terminate the communication. Sensing the termination of the communication, the base unit 100 sends a BS period designate signal to the portable unit TEL5, which is to become BS-OFF after the portable unit TEL4, at a timing t₅₁ just before the BS-OFF timing of the unit TEL5. Subsequently, the base unit 100 sequentially delivers BS period designate signals to the portable units TEL1, TEL2, TEL3 and TEL4 in this order and at timings t₁₂, t₂₂, t₃₂ and t₄₂, respectively. In response, the portable units TEL5, TEL1, TEL2 and TEL3 change their BS periods to 5T as designated, at individual timings of t''₅₁, t''₁₂, t''₂₂ and t''₃₂ at which they receive the BS period designate signals. The portable unit TEL4 receives the BS period designate signal at a timing t'''₄₂ and starts on a 5T BS operation at a timing t'₄₂. Consequently, the portable units TEL1 to TEL5 sequentially enter into BS operations based on the particular order which is registered in the storage of the controller 107 of the base unit 100.

0016While the above description has concentrated on the changes in BS operations which are caused by the receipt of a call, the origination of a call, and the termination of a call each using a single telephone line, it will be understood that even when two more telephone lines are used simultaneously, the portable units TEL surely perform BS operations through the same procedure in a registered order and at a period which is produced by multiplying the unit period T of the internally generated signal of the base unit 100 by the number of currently usable circuits.

0017Figs. 8A to 8F show a difference between the cordless telephone system of the present invention and a prior art cordless telephone system. Specifically, Fig. 8A is representative of a prior art system in which a portable unit TEL performs a BS operation at a period of T, while Figs. 8B to 8F are representative of the system of the present invention in which the portable units TEL1 to TEL5 sequentially perform BS operations at a period of 5T each. It will be seen that the system of the present invention achieves fives times greater power saving effect than the prior art system and, yet, the period of time necessary for connection in the event of receipt of a call remains the same despite the longer BS period.

0018In summary, it will be seen that in accordance with the present invention the BS period of idle portable communication units TEL are changed at adequate timings based on the number of telephone lines used, so that the units TEL sequentially perform intermittent receipt at equal intervals of T. Therefore, a BS period which is a product of the period T and the number of telephone lines used suffices, whereby the power consumed by each portable unit TEL is reduced.