A method and apparatus for battery conservation in a radio pager

Abstract: In a radio pager for receiving a paging signal of a superframe structure comprising a recurrent series of frames each containing a series of burst signals containing a synchronization field, a frame number field and an address field, one of the frames in each superframe being assigned to the pager. The pager comprises a receiver and a synchronizer connected to the receiver for establishing synchronization to a bit sequence in the synchronization field. A short warm-up period and a short time-out period are established before each of the burst signals of the assigned frame of a first superframe are received and a long warm-up period and a long time-out period are established before the burst signals of the assigned frame of a second superframe are received. The receiver is activated at the start of the short warm-up period advanced from the start of each burst signal of the assigned frame and a determination is made on whether synchronization is established within the subsequent short time-out period. If synchronization is not established, the receiver is deactivated at the end of the short time-out period, and if established, the receiver is deactivated after the end of the short time-out period. A long warm-up period and a long time-out period are then established and the receiver is deactivated. The receiver is reactivated at the start of the long warm-up period advanced from the start of the assigned frame of a second superframe, and determination is made on whether synchronization is established within the long time-out period. If synchronization is established, the receiver is deactivated at the end of the long time-out period, and if established, the receiver is deactivated after the end of the long time-out period. The short warm-up and short time-out periods are established again for reception of successive burst signals .

Description: The present invention relates generally to radio pager power saving techniques and more particularly to the improvement of the power saving performance of radio pagers wherein the power supply to their receiver, or front end is interrupted at short intervals during reception of a user (assigned) frame and at long intervals each time the user frame has been received. In a radio paging system such as ERMES (European Radio Message System), paging signals are transmitted in a superframe format in which frames are transmitted in a recurrent series. Each paging user is assigned one of the frames. The frame contains a series of burst signals each having a sync field, a burst/frame number, an address field and an information field. The address field carries a plurality of user address numbers and the information field carries a corresponding number of messages. During the reception of the burst signals of a frame assigned to a particular pager, the pager's front end is repeatedly activated at intervals (typically 12 seconds) corresponding to the burst signals and deactivated for a long period (typically 60 minutes) when the assigned frame has been received. In order to allow the pager's synchronizer to resynchronize to a burst signal in the next user frame after the relatively long period of deactivation of its front end, the front end is activated at timing advanced from the start of the first burst signal of the next user frame so that it is warmed up sufficiently before the start of the first burst signal and the pager is then given a sufficient time-out period for resynchronization. The same values of these warm-up and time-out periods are used for repeatedly activating the pager during the reception of the user frame burst signals. Since the same warm-up and time-out periods are used for power-saving the pager during the reception of successive burst signals as in the case of the post-long-inactive period, the front end is activated too early and the time-out period of the synchronizer is too long. Therefore, the power saving performance of the prior art pager is not satisfactory. US-A-4 086 537 relates to a time division multiplex communication receiving apparatus. Noise and intensity of a TDM signal detected by the receiver are evaluated and its operation is classified into one of three receiving modes. According to these modes, a power saving operation is controlled. During mode 1, the receiver is full-time activated, during mode 2, it is periodically activated such that the period of activity exactly coincides with a period of a subframe and during mode 3, the receiver is periodically activated as in mode 2, but the period of activity is slightly longer than that of mode 2. The prolongation of the period of activity during mode 3 is intended to increase the chance of the receiver to resynchronize to the transmitter when a phase displacement is encountered. In contrast to the present application US-A-4 086 537 does not refer to a "warm-up period" and a "time-out period" of a radio pager. Furthermore, the advanced timing of the prolonged period of activity does not correspond to the warming-up of the receiver in preparation for a burst according to the present invention and the delayed timing of the prolonged period does not correspond to the timing-out of the activity when the synchronizer fails to synchronize within a set time-out period according to the present invention. It is therefore an object of the present invention to improve the power saving performance of a radio pager by controlling the receiver warm-up period and the synchronizer time-out period according to the length of the preceding inactive period of the receiver. This object is achieved with the features of the claims. The present invention will be described in further detail with reference to the accompanying drawings, in which: Fig. 1 is a block diagram of a radio display pager embodying the present invention; Fig. 2 shows the structure of the paging signal used in the present invention and the power saving timing operation during successive frames of the signal; Fig. 3 shows the advanced timing and sync acquisition time-out period in relation to a burst signal; and Figs. 4 and 5 are flowcharts illustrating the operation of the controller of the pager according to the present invention. DETAILED DESCRIPTION In Fig. 1, there is shown a selective calling radio display pager incorporating the sync acquisition timing arrangement of the present invention for power savings purposes. The radio pager includes a power switching circuit 22 for periodically activating a front end 10 with energy supplied from a voltage source 23. When activated, the front end 10 provides frequency conversion of received radio-frequency paging signal to baseband frequency and supplies the baseband signal to a synchronizer 11. As illustrated in Fig. 2, the paging signal is in a superframe format. According to the ERMES standard, a superframe comprises a series of 60-second frames, numbered "01" through "59". Each frame contains a series of subframes, or burst signals. Typically, five burst signals are transmitted within a frame at 12-second intervals. Paging users are assigned one of the frames and a paging signal destined to a particular user is transmitted by one of the burst signals of the assigned user frame. A plurality of radio frequencies are allocated to the ERMES paging system and one of the frequencies is used for a particular transmission. Provision is therefore made in the system to notify a called user of which frequency to use for reception of a paging signal. If more than one paging signal is transmitted within the period of 60 seconds, more than one frequency is used. In this case, the controller 14 provides frequency control on the front end 10 through line 24. Since the frequency selection scheme is beyond the scope of the present invention, the description thereof is omitted for simplicity. Each of the burst signals in a frame contains a sync field 30 having a particular bit sequence to permit acquisition of bit synchronization and burst synchronization. The sync field 30 of each burst signal is followed by a burst/frame number field 31 containing the identification number of the burst signal and the identification number of the frame to which it belongs. An address field 32 contains a series of user address numbers, address field 32 being followed by an information field 33 containing a series of messages corresponding respectively to the address numbers in the address field 32. Front end 10 is activated at 12-second intervals corresponding to the burst signals in a user frame when a given superframe is being received and deactivated for an interval of 60 minutes until the same user frame appears during the next superframe. Synchronizer 11 provides acquisition of bit synchronization and burst synchronization each time the front end is energized, using the bit sequence contained in the sync field 30. When the pager is synchronized to the incoming bit stream, the signals contained in the fields 31 to 33 following the sync field are supplied to a conventional decoder 12. Decoder 12 compares the received frame number with a frame number assigned to the user and stored in an EEPROM (electrically erasable programmable read-only memory) 13. If they match, the decoder communicates this fact to a microprocessor-based controller 14 along with the received burst number. Decoder 12 proceeds to compare each of the address numbers contained in the address field 32 with the user's address stored in the EEPROM. If one of the received address number matches the user's address, the decoder supplies a corresponding message in the information field to the controller 14. Controller 14 stores the message in a random access memory 15 for later retrieval for display on a liquid crystal display unit 17 via a driver 16, and alerts the user by operating an annunciator 19 through driver 18. A counter 20 is provided for counting high-speed clock pulses from a clock source 21, and the operation of the counter 20 is controlled by the controller 14. As will be described in detail later, the controller 14 controls the power switching circuit 22 so that the front end is given a sufficient time to be powered up for synchronization and given a sufficient time-out period to acquire bit synchronization and burst synchronization. As shown in Fig. 3, the time period advanced from the beginning of a burst signal is represented as "X" and the time-out period subsequent thereto is represented as "Y". If bit and burst synchronization is not established by the end of the period Y for a given burst, the front end is deactivated as indicated by a dotted line 34. According to the present invention, these timing values X and Y are variable with the amount of time during which the front end is deactivated, and are represented as follows. X = A × T = {1/(c-a) - 1/c} × c × T Y = B × T = {1/c - 1/(c+b)} × c × T where, "a" and "b" are pager's clock rate errors in negative and positive directions, respectively, with respect to the transmitted clock rate "c", and A = {1/(c-a) - 1/c)×c and B = {1/c - 1/(c+b)}×c represent the negative and positive timing errors during the period of a second, and T is the interval at which the front end is activated. Since T is 12 seconds during a user frame and 3600 seconds between successive user frames, the timing values X and Y are variable with battery saving intervals. In Fig. 1, the integers A and B are stored in EEPROM 13. The operation of the controller 14 is illustrated in flow diagram form in Figs. 4 and 5. In Fig. 4, it is seen that when the pager's power switch is operated by the user the operation of the controller 14 starts with block 40. Initially, the front end is continuously activated to provide a search for the user frame. This is first done by synchronizer 11 to acquire bit and burst synchronization with a burst signal that occurs in any of the frames at the instant the pager is powered on. Subsequently, decoder 12 provides the controller 14 with a burst number and a frame number contained in the synchronized burst. Flow proceeds to block 41 where the controller 14 commands the counter 20 to start counting the clock. Controller 14 reads integers "A" and "B" from EEPROM 13 (block 42) and initializes a variable "i" and a flag "F" to zero (block 43). A test is made in block 44 to examine the frame number and the controller determines whether the current frame is the user frame or not. If the decision is negative, flow proceeds from block 44 to block 45 where the controller determines the initial turn-off period "Ti" seconds between the current burst signal and the beginning of the user frame. In block 46, a variable T is set equal to Ti seconds and timing variables X and Y are calculated by multiplying integers A and B with the variable T. Controller 14 controls the power switching circuit 22 to turn off the power supply to the front end 10 (block 47). Flow proceeds to block 48 to check the counter 20 to see if the count value "t" is equal to T - X. Since T = Ti and X = A x Ti, the count value t = T - X represents the advance timing that occurs before the beginning of the user frame by an amount proportional to the time interval from the current burst signal to the user frame. As illustrated in Fig. 2, the front end 10 will be reactivated at the timing advanced by a warm-up interval x 1 which is equal to A x Ti in a manner to be described below. If the decision at block 44 is affirmative, flow proceeds to block 49 to set the variable T equal to 12 seconds and calculate the X and Y timing variables by multiplying the integers A and B with T = 12 seconds. In block 50, the flag F is set to 1 and the variable "i" is set equal to the burst number detected in block 40. Flow proceeds from Fig. 4 to Fig. 5. If the current frame is not the user frame, flow proceeds from block 48 (Fig. 4) to block 51 (Fig. 5) where the controller operates the power switching circuit 22 to reactivate the front end 10 before time x 1 advanced from the beginning of the first burst signal of the user frame and restarts the counter 20. Controller 14 then checks to see if the counter 20 indicates that time X has lapsed (block 52). If this is the case, it is determined that the beginning of the first burst signal is detected, and flow proceeds to clear the counter 20 and restarts its count operation (block 53), increments the variable "i" by one (block 54), and determines, in block 55, whether synchronization is established by synchronizer 11 by sensing an output line 25 from the synchronizer. The synchronization test continues until the output of the counter 20 is equal to Y by repeatedly performing executions through blocks 55 and 70. If block 55 is first visited in the execution of the program, the synchronizer 11 is given a sufficient time-out period Y equal to B x Ti. This time-out period is indicated as y 1 in Fig. 2. If synchronization is established within the time-out period y 1 , flow proceeds from block 55 to block 56 to check to see if F = 1. If block 56 is first visited, F is not equal to 1 and flow proceeds from block 56 to block 57 to reset the timing variable T to 12 seconds and calculate the X and Y timing variables by multiplying the integers A and B with T = 12 seconds. In block 58, flag F is set equal to 1. If flag F is already set to 1, so that the decision in block 56 is affirmative, or first set to 1 in block 58, flow proceeds to block 59. Additionally, if the current frame is the user frame, flow proceeds from block 50 (Fig. 4) to block 59. In block 59, the controller 14 checks the output of the decoder 12 to determine whether there is the pager address in the address field of the paging signal. If there is no matching address number in a burst signal, flow proceeds from block 59 to block 60 to turn off the front end power. If the answer is affirmative in block 59, on the other hand, flow proceeds to block 67 where the controller 14 activates the annunciator 19 to alert the user and stores the corresponding message into RAM 15. Then, a test made in block 68 to determine whether the end-of-burst timing is reached. If so, flow proceeds from block 68 to block 60 to turn off the front end power. Following the execution of block 60, the variable "i" is checked to see if it is equal to "5" (block 61). If the address search is not performed on five burst signals, flow proceeds from block 60 to block 61 to determine whether the counter 20 indicates that a time period T - X has elapsed from the restart timing of counter 20 in block 53. If the period T - X has elapsed, flow exits block 62 and returns to block 51 to repeat the process to make a further address search in another burst signal of the same user frame. This is done by reactivating the front end and restarting counter 20 (block 51), restarting it again after elapse of time X (blocks 52, 53), incrementing the variable "i" by one and looping blocks 55 and 70 for a synchronization test using the timing values X and Y of block 57. During this process, the X and Y values are updated to the values of block 57, so that the front end 10 is reactivated at timing advanced by period x 2 and synchronizer 11 is given a time-out period y 2 as shown in Fig. 2. If the address search has been performed on all burst signals of the user frame, the decision in block 61 is affirmative and flow proceeds to block 63 to check to see if the counter 20 indicates the end of the user frame. If so, flow advances to block 64 to restart the counter 20 and proceeds to block 65 where the controller 14 resets the variable T to 3600 seconds and updates the timing variables X and Y accordingly. In block 66, controller 14 now resets the flag F and variable "i" to zero and proceeds to block 62 to check to see if the time period T - X has elapsed. If so, flow returns to block 51 to repeat the process for making a further address search in the next superframe. During this process, the X and Y values are updated to the values of block 65, so that the front end 10 is reactivated at timing advanced by period x 3 and synchronizer 11 is given a time-out period y 3 as shown in Fig. 2. It will be appreciated from the foregoing that the time-out period Y is first set to y 1 corresponding to Ti, then to y 2 corresponding to the 12-second turn-off interval during a user frame, and then to y 3 which corresponds to the 3600-second interval between successive superframes. When the receiver enters the second superframe, the time-out period is again changed to y 2 as illustrated in Fig. 2. If the initially synchronized burst signal is in the user frame when the pager is manually powered on, the X and Y timing variables are set equal to x 2 and y 2 , respectively. As long as the pager is powered on, the timing variables X and Y are varied between x 2 , y 2 and x 3 , y 3 . If synchronization is not established within the time-out period Y of any of the values y 1 , y 2 and y 3 , flow proceeds from block 70 to block 71 where the controller 14 turns off the front end 10, and proceeds to block 72 to check for F = 1. If flag F is 0, it is determined that the time-out period Y has still been set either to y 1 or y 3 , and flow proceeds to block 73 to reset the variable T to 12 seconds and update the X and Y timing variables accordingly, and proceeds to block 74 to set the flag F to 1. Exit then is to block 75 to check to see if variable "i" is equal to or greater than 2, or not. If variable "i" is 1, flow proceeds from block 75 to block 62 to check for the turn-on timing T - X in order for the front end 10 to be turned on again in block 51 at the instant advanced by x 2 . If variable "i" is equal to or greater than 2, flow proceeds from block 75 to block 76 where the controller 14 multiplies the integers A and B by variable "i", and updates the timing variables X and Y accordingly. Therefore, if sync acquisition has failed twice for successive burst signals, the integers A and B and hence the timing advance variable X and the time-out period Y are scaled up by a factor corresponding to the number of times the sync acquisition has repeatedly failed. If F = 1 is detected in block 72, it is determined that the time-out period Y has already been reset to y 2 , and flow proceeds to block 75 by skipping blocks 73 and 74. A further test in block 77 determines whether the variable "i" is equal to a predetermined number "k". If sync acquisition has failed "k" times in succession, it is determined that sync acquisition cannot be achieved even though it is repeated further. In this case, the decision in block 77 is affirmative and flow returns to the starting point of the program to restart the program execution over again. If variable "i" is smaller than "k", flow proceeds from block 77 to block 62.

Claims: A radio pager comprising a receiver (10) for receiving a paging signal when activated, a synchronizer (11) for synchronizing to a bit sequence contained in each burst signal of said paging signal, and power saving controller (14, 20-22) for periodically activating said receiver (10) at first intervals when the arrival of a burst signal after a short period of inactivity is expected and at second intervals longer than the first intervals when the arrival of a burst signal after a long period of inactivity is expected, wherein said power saving controller initiates the activation of the receiver (10) at power-on timing advanced from the start timing of each burst signal by a warm-up period and terminating the activation at power-off timing elapsed from said start timing by a time-out period if the synchronizer (11) fails to establish synchronism within the time-out period, characterized in that the warm-up and time-out periods (x 3 , y 3 ) of the receiver (10) when the receiver is expecting the arrival of a burst signal after a long period of inactivity are respectively longer than the warm-up and time-out periods (x 2 , y 2 ) of the receiver (10) when expecting the arrival of a burst signal after a short period of inactivity. A radio pager as claimed in claim 1, characterized in that said power saving controller (14, 20-22) comprises means (14) for increasing the length of the warm-up period (x 2 ) and the length of the time-out period (y 2 ) during the reception of said first burst signal when said synchronizer (11) repeatedly fails to establish synchronization. A radio pager as claimed in claim 1 or 2 characterized in that said power saving controller (14, 20-22) further comprises means (14) for counting the number of burst signals to which said synchronizer (11) fails to establish synchronization and multiplying the length of each of said warm-up period (x 2 ) and the time-out period (y 2 ) during the reception of said first burst signal by a factor corresponding to said counted number. A radio pager as claimed in claim 1, 2 or 3, characterized in that said power saving controller (14, 20-22) further comprises means (14) for counting the number of burst signals to which said synchronizer (11) fails to establish synchronization and initializing said pager so that the pager restarts operation if said counted number exceeds a predetermined value. A radio pager as claimed in any of the preceding claims, wherein said paging signal is in a superframe structure comprising a recurrent series of frames each containing a plurality of burst signals, each burst signal comprising a synchronization field, one of the frames of each superframe being assigned to the pager, and wherein said synchronizer (11) is arranged to establish synchronization to a bit sequence contained in said synchronization field, characterized in that said power saving control means (14, 20-22) comprises: means for activating the receiver at the start of the shorter warm-up period (x 2 ) preceding a burst signal of the assigned frame of a given superframe and determining whether synchronization is established by the synchronizer (11) within said shorter time-out period (y 2 ), means for deactivating said receiver at the end of said shorter time-out period (y 2 ) if synchronization is not established within said shorter time-out period (y 2 ) and deactivating said receiver after the end of said shorter time-out period (y 2 ) if synchronization is established within said shorter time-out period (y 2 ); means for activating said receiver at the start of the longer warm-up period (x 3 ) preceding an initial burst signal of the assigned frame of a superframe immediately following said given superframe, and determining whether synchronization is established by the synchronizer (11) within said longer time-out period (y 3 ); and means for deactivating said receiver at the end of the longer time-out period (y 3 ) if synchronization is not established within said longer time-out period (y 3 ), and deactivating said receiver after the end of the longer time-out period (y 3 ) if synchronization is established within said longer time-out period (y 3 ). A radio pager as claimed in claim 5, characterized in that said power saving control means further comprises: means for activating the receiver when the pager is initially turned on for detecting a burst signal and a frame which is assigned to the pager and determining a time interval (T i ) between the time of detection of the burst signal and the time of detection of the assigned frame; means for establishing an initial warm-up period and an initial time-out period in accordance with the determined time interval (T i ) and deactivating the receiver; means for activating the receiver at the start of the initial warm-up period preceding the start of the assigned frame and determining whether synchronization is established by the synchronizer within the initial time-out period; and means for deactivating said receiver at the end of the initial time-out period if synchronization is not established within the initial time-out period, and deactivating said receiver after the end of said initial time-out period if synchronization is established within the initial time-out period. A method for power-saving in a radio pager which comprises a receiver (10) arranged to be activated for receiving a paging signal, a synchronizer (11) for synchronizing to a bit sequence contained in each burst signal of said paging signal, and power saving controller (14, 20-22) for periodically activating said receiver (10) at first intervals when the arrival of a burst signal after a short period of inactivity is expected and at second intervals longer than the first intervals when the arrival of a burst signal after a long period of inactivity is expected, wherein said power saving controller initiates the activation of the receiver (10) at power-on timing advanced from the start timing of each burst signal by a warm-up period and terminating the activation at power-off timing elapsed from said start timing by a time-out period if the synchronizer (11) fails to establish synchronism within the time-out period, characterized in that, when the receiver is expecting the arrival of a burst signal after a long period of inactivity, the warm-up and time-out periods (x 3 , y 3 ) of the receiver (10) are respectively set at values which are respectively longer than the warm-up and time-out periods (x 2 , y 2 ) of the receiver (10) when the receiver is expecting the arrival of a burst signal after a short period of inactivity. A method as claimed in claim 7, characterized in that the length of the warm-up period (x 2 ) and the length of the time-out period (y 2 ) are increased during the reception of said first burst signal when said synchronizer (11) repeatedly fails to establish synchronization. A method as claimed in claim 7 or 8, characterized in that the number of burst signals to which said synchronizer (11) fails to establish synchronization is counted and in that the length of each of said warm-up period (x 2 ) and the time-out period (y 2 ) during the reception of said first burst signal are multiplied by a factor corresponding to the counted number of burst signals. A method as claimed in claim 7, 8 or 9, characterized in that the number of burst signals to which said synchronizer (11) fails to establish synchronization is counted and said pager is initialized when the counted number of burst signals exceeds a predetermined value so that the pager restarts operation. A method as claimed in any of the preceding claims, wherein said paging signal is in a superframe structure comprising a recurrent series of frames each containing a plurality of burst signals, each burst signal comprising a synchronization field, one of the frames of each superframe being assigned to the pager, and wherein the synchronizer (11) is arranged to establish synchronization to a bit sequence contained in said synchronization field, further characterized by the steps of: a) activating the receiver at the start of the shorter warm-up period (x 2 ) preceding a burst signal of the assigned frame of a given superframe and determining whether synchronization is established by the synchronizer within said shorter time-out period (y 2 ); b) if synchronization is determined by step (a) to be not established, deactivating said receiver at the end of said shorter time-out period (y 2 ), and if synchronization is determined by step (a) to be established, deactivating said receiver after the end of said shorter time-out period (y 2 ); c) activating said receiver at the start of the longer warm-up period (x 3 ) preceding an initial burst signal of the assigned frame of a superframe immediately following said given superframe, and determining whether synchronization is established by the synchronizer within said longer time-out period (y 3 ); and d) if synchronization is determined by step (c) to be not established, deactivating said receiver at the end of the longer time-out period (y 3 ), and if synchronization is determined by step (c) to be established, deactivating said receiver after the end of the longer time-out period (y 3 ). A method as claimed in claim 11, further characterized by the steps of: e) activating the receiver when the pager is initially turned on for detecting a burst signal and a frame which is assigned to the pager and determining a time interval (T i ) between the time of detection of the burst signal and the time of detection of the assigned frame; f) establishing an initial warm-up period and an initial time-out period in accordance with the determined time interval (T i ) and deactivating the receiver; g) activating the receiver at the start of the initial warm-up period preceding the start of the assigned frame and determining whether synchronization is established by the synchronizer within said initial time-out period; and h) if synchronization is determined by step (g) to be not established, deactivating said receiver at the end of the initial time-out period, and if synchronization is determined by step (g) to be established, deactivating said receiver after the end of said initial time-out period.

Inventors: AOSHIMA TAKASHI, AOSHIMA, TAKASHI, Aoshima, Takashi, c/o NEC Corporation
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1995
Main classification: H04B1
IPC codes: H04B7, H04B1, H04W52, H04W88