Note: Descriptions are shown in the official language in which they were submitted.
3~
PAGER WATCH SYSTEM UTILI2ING TIME SLOT COMMUNICATION
BACKGROUN~ OF THE INVENTION
The invention relates to the field of paging
systems utilizing battery powered portable pagers.
Paging systems have used various methods for
reducing the power consumption of battery-operated por-
table pagers in order to miniaturize the pager unit.
One such approach involves supplying power to the re-
ceiver circuitry only during predetermined time slots
in which data relating to the particular pager unit is
broadcast. In the absence of accurate synchronization
between the transmitter and receiver, a long time slot
is required to insure that the pertinent data is received
and thus more power is consumed.
Apart from paging systems there are methods
by which a clock can be remotely reset by a transmitted
signal. Tohyama et al., U.S. Patent No. 4,358,836, for
example, shows a method for setting a watch from a trans-
mitted time announcement signal.
A combination of a pager utilizing time slot
transmission with a resettable watch is shown by Natori
et al., U.S. Patent No. 3,937,00~. The Natori system
shows a watch controlled by a countPr which is periodic-
ally reset by a transmitted signal. The use of an in-
ternal counter allows errors to accumulate since the
counter will have some amount of error, and the error
in each count will be added to ~he time indication.
Thus, the watch may stray from the correct time. This
straying requires the use of a large time slot to accom-
modate errors in the time when the pager~s receiver is
powered up.
~ i2~
SUMMARY OF THE INVENTION
The present invention is a method and appara-
tus for transmitting paging and time information from a
- 5 central station and receiving such information at a
remote electronic timepiece and pager unit during a
short kime slot assigned to the pager unit. In the
pager unit, an oscillator is coupled to a timer which
produces a time display. These functions are constantly
powered. The timer periodically causes power to be
supplied to the receiver and message decoding components,
during a short time slot in which the transmitted data
is to be received. The receiver detects and reconsti-
tutes the transmitted signal. The transmitted signal
is processed through a decoder which extracts paging
and time update data. If ~he paging data includes the
pager unit's ID number, the unit audibly and/or visually
indicates to the user that a page has been received.
The time update data extracted from the trans-
mitted signal is used to synchronize the timer in the
pager unit. The timer serves the dual function of pro-
viding an accurate time indication for the watch func-
tion as well as causing power to be supplied during the
time slot as described.
By transmitting time update information rather
than resetting an internal counter, the watch function
is accurately synchronized and will not stray. Because
the timer which is synchronized powers up the receiver
during the pager unit's assigned time slot in addition
to indicating the correct time, a very short time slot
can be used.
In the preferred embodiment, the unit corrects
its time slot alignment by comparing the transmitted
time slot position to its assigned time slot position.
If they do not match, this means the timer has caused
the receiver circuit to be powered at the wrong time,
so the timer is adjusted by the difference in time be-
tween the received time slot and its assigned tim~ slot.
The timer will thereafter cause the receiver circuit to
be powered up during its assigned time slot.
In the preferred embodiment, if a time slot
- 5 i6 not filled with data, an end of message signal in-
structs the pager unit to power down early, thereby
achieving an additional reduction in power consumption
beyond the reduction achieved by only powering the re-
ceiver circuit during short time slots. Because of its
low cost, compactness and thus possible widespread use,
the present invention could be used in a system where
the employer of the person to be paged (an office, hos~
pital, etc.~ is the subscriber, or in a broader system,
such as where each person with a pager watch is a sub
scriber and can be called by anyone.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a perspective view of a preferred
embodiment of the pager watch of the present invention.
Fig. 2A-2C is a time slot diagram of the pre-
ferred er~odiment of the time slot format of the present
nventlon.
Fig. 3A is a time slot block diagram of the
preferred embodimen-t of the transmitter station of the
present in~ention.
Fig. 3B is a block diagram of the preferred
embodiment of the timepiece and pager unit.
DESCRIPTION OF TH~ PREFERRED EMBODIMENT
Figure 1 illustrates a pager watch according
to the invention. The watch face shows a number of
indicator lights 7 which can be assigned to predefined
messages, such as "call home," "call the office," etc.
The digital display 8 may show a phone number to be
called. In addition, the display 9 indicates a time
and any other functions of a normal wristwatch.
The preferred embodiment of the invention is
best understood with reference to a specific transmission
data format, although a number of data formats could be
used. Figure 2 shows a preferred time slot frame format
for a transmitted signal. A time frame (Fig. 2A) indi-
- 5 cated by bidirectional arrow 10 is composed of 100 time
slots such as the one indicated at 12. In the preferred
embodiment, the length of the time frame is 10 minutes,
with each time slot thus being 6 seconds long. The
time frame is reinitiated every 10 minutes. The first,
or "0", time slot, indicated at 14, contains time update
information. The remaining time slots, numbered 1-99,
contain paging information in the format shown in ex-
panded time slot 12.
Time slot 12 is composed of up to 125 identi-
cal message channels (Fig. 2B) such as the one repre-
sented at 16 plus an initial time slot address channel,
represented at 18. The time slot address is a digital
representation of one of the numbers 0 through 99, de-
pending on which time slot is represented. Each message
channel is 40 milliseconds in length, except the time
slot address channel, which is 1 second long.
Message channel 16 is shown in expanded form
in Fig. 2C. A first portion 20 of message channel 16
contains synchronization bits. A second portion 22
contains the identification number for a particular
timepiece-pager unit. A third portion 2~ contains func-
tion data indicating the type of message to be indi-
cated on the face of the timepiece-pager unit. Alter-
nately, the function data could indicate that the nex-t
message channel contains a phone numbex to be displayed,
rathex than an identification number. A last portion
26 of the message channel contains error correction
data.
Figure 3A is a block diagram of a transmitting
system at a central paging site. The transmission of
the paging information in the present invention could
be achieved in a variety of manners, such as by using
traditional low-power transmissions, by using FM or ~M
sideband channels or by using the TV vertical blanking
intexval. As shown in Figure 3A, a series of incoming
phone lines 28 provide paging data to a telephone line
concentrator 30. Concentrator 30 buffers the relatively
slow data coming from a caller in the form of Dual-Tone
Multifrequency (DTMF) signals. The system can be totally
automatic, with no operators or dispatchers. Calls can
be prompted by computer voice messages which ask for
the caller's subscriber identification number (the user's
office, hospital, etc., if applicable), the page ID
number of the person to be paged, a predetermined message
function number (to indicate "call office," etc.), and
an optional phone number. The information is then given
to a computer 32, which numerically sorts the messages
by ID number and packs them into their assigned time
slots. Blocks of data are evaluated and error correc-
tion data is added to each block by computer 32. Compu-
ter 32 is connected to a master clock 34, and when the
master clock reference time reaches a particular time
slot, the block o~ data for such time slot is broadcast
by a transmitter 36 after being encoded for an appropri-
ate modulation scheme, such as frequency shift keying.
In the preferred embodiment, transmitter 36 is an FM
transmitter and the block of data is used to modulate a
subcarrier channel of the FM broadcast band.
If a particular time slot is not filled with
data, computer 32 will append an end of message code
after the last unit of data in the time slot which will
instruct the individual pager units to power down early.
The computer can also perform other functions, such as
preparing billing data for pager subscribers.
Figure 3B shows a block diagram of the pre-
ferred embodiment of a timepiece and pager unit. A
wrist loop antenna 38 picks up the transmitted signal
and is connected to a receiver 40. Receiver 40 is tuned
to the transmission frequency by an oscillator 42.
Oscillator 42 is also connected to a timer 44. Timer
3~
44 provides a time signal to a watch face time display
46. Oscillator 42, timer 44, and watch face time dis-
play 46 are constantly powered by a battery 48 (as are
the displays discussed later). The receiver and decoding
components of the pager unit, which are to the right of
dotted line 49, are only supplied power when timer 44
provides an enable signal to a switch 50. The timer is
programmed to send such an enable signal only during a
time slot assigned to the pager unit. The pager unit
may, for example, be assigned to time slot 12 shown in
Fig. 2.
The signal supplied to receiver 40 is recon-
stituted as a digital signal. The reconstituted digital
signal is then supplied to a decoder 52 which converts
it into its original digital format. The digital infor-
mation is then processed through an error correction
circuit 54 and any detected errors are corrected. The
corrected data is then applied simultaneously to an
identification number detector module 56 and to a func-
tion decoder 58. Module 56 determines whether the cor-
rect time slot position has been received and then exa-
mines each pager unit ID number received to determine
whether it matches the ID number assigned to the receiv-
ing pager unit.
In the event -the received time slot address
does not match the pager unit's assigned time slot posi-
tion, module 56 calculates the time until the correct
time slot by subtracting the received time slot position
from the pager unit's assigned time slot position and
sends a correction signal to timer 44 causing the timer
to open switch 50, thereby removing power from the re-
ceiver and message decoding components, until such cor-
rect time slot.
Function decoder 58 is only enabled by module
56 in the event there is a ma-tch between a received ID
number and the pager unit's ID number. If there is a
~time slot match and an ID number match for the
3~ f
appearing in the first channel of the time slot, time
slot position 18 in Figure 2. In the preferred embodi-
ment, this first message channel would be one second
5 long, and the time slot position would appear either at
the end of the time slot address channel or be repeated
throughout. Thus, the timepiece and pager unit can
drift by up to approximately one second every 10 minutes
or approximately 144 seconds a day and still be suffi-
10 ciently synchronized to receive paging information be-
cause the time is corrected with the time data update
every 10 minutes.
If the pager unit determines that it has turned
on during the wrong time slo-t, it will calculate the
15 difference between the time slot position detected and
its assigned time slot position. The pager unit will
then power down and later power up again during the
correc-t time slot.
In theory a pager unit only needs to power up
20 long enough to receive its paging information, so that
a time frame could be divided into a larger number of
small time slots, each representing a single pager unit,
instead of larger time slots to which are assigned a
block of pager units. However, current cost-effective
25 consumer electronics technology cannot maintain the
degree of timer accuracy needed to achieve such a precise
alignment.
As described above, each pager unit also powers
up during the initial time slot in order to receive
30 time update information. To achieve additional power
savings, a pager unit might only power up during this 7initial time slot in the event it has strayed from its
assigned time slot, while using the time at which it
receives the time slot position to provide minor correc-
35 tions to the timer.
If there is a low volume of paging messages,
such that a time slot is not completely filled with
data, the message cha~nel after the last message
f
channel containing data would contain a power down mes-
sage. This ~ould instruct the individual pagers to
turn of power for the remaining time of the time slot
- 5 since there is no additional information in the remain-
ing time of the time slot. Thus, if an end of message
signal appears af-ter four seconds into the six second
time slot, an additional power savings of one-third is
realized.
Upon recognition of i-ts ID number an indivi-
dual timepiece and pager unit would emit a sound to
alert the user that a page has been received. Function
data would then follow and could contain instructions
to illuminate an assigned marker for a predefined mes-
sage such as "call home" or "call the office," etc., or
could indicate that the next message channel contains a
phone number which is to be displayed on the face of
the timepiece and pager unit.
Additional features can be added to the pre-
sent invention to enhance its capabilities or reduce
the power consumption. For instance, individual pager
units can be programmed to shut off during off hours
such as after midnight and before seven in the morning.
In another variation, if an individual subscriber did
not want to have a delay of lO minutes before receiving
a paging message, that paging unit could be assigned to
two time slot positions so that at most there would be
a 5 minute delay before receiving a page message.
~s will be understood by those familiar with
the art, the present invention may be embodied in other
specific forms without departing from the spirit or
essential characteristics thereof. Accordingly, disclo-
sure of the preferred embodiment of the present inven-
tion is intended to be illustrative, but not limiting,
of the scope of the invention, which is set forth in
the following claims.
