Method and apparatus for a deep-sleep mode in a digital cellular communication system

A method and apparatus is provided for extending the battery life of a cellular radiotelephone. A cellular radiotelephone is conditioned to operate in a pager-only mode wherein the radiotelephone may receive short messages from a base station while conserving battery life by cyclically adopting a deep-sleep state. The base station is notified by the radiotelephone before the radiotelephone enters the deep-sleep state that the radiotelephone is unable to receive messages. After a period of time, the radiotelephone wakes-up, re-establishes contact with the base station and notifies the base station that the radiotelephone is ready to receive messages. After receipt of any messages the radiotelephone repeats the process.

FIELD OF THE INVENTION 
The present invention relates generally to cellular radio communications 
and, more specifically, to a method and apparatus for maximizing the 
battery life of portable cellular radiotelephones used in digital cellular 
communication systems. 
BACKGROUND OF THE INVENTION 
Cellular communications systems are well-known. Analog cellular systems 
such as designated AMPS, ETACS, NET-450, and NET-900 have been deployed 
successfully throughout the world. More recently, digital cellular systems 
such as designated IS-54B in North America and the pan-European GSM system 
have been introduced. These systems, and others, are described, for 
example, in the book titled Cellular Radio Systems by Balston, et al., 
published by Artech House, Norwood, Mass., 1993. 
The IS-54B specification entitled Cellular System Dual-Mode Mobile Station 
Base Station Compatibility Standard (available from the Telecommunications 
Industry Association, 2001 Pennsylvania Avenue, N.W., Washington , D.C., 
20006) provides increased system capacity through digital time division 
multiple access (TDMA) while allowing compatibility with existing analog 
systems. Mobile stations designed to meet the IS-54B specification are 
able to function with both the new TDMA systems and the existing AMPS 
analog systems. Throughout this specification the terms mobile station, 
cellular telephone, cellular phone, mobile phone, and cellular 
radiotelephone are used interchangeably to refer to the same device. One 
drawback to the current specification is that the both the digital and 
analog systems make use of the existing AMPS analog control channels. 
Therefore TDMA capable mobile stations are constrained by the old analog 
protocols and are not able to fully utilize all the features possible with 
digital communications. 
Currently, cellular mobile radiotelephones are limited in stand-by battery 
life because they must continuously monitor the analog control channel for 
paging messages indicating an incoming call. Even with high capacity 
batteries, stand-by times in excess of about 24 hours are rare. This may 
be contrasted with paging receivers, or "beepers", which have battery 
lives of about 100-200 hours from a single AA battery achieved by cyclical 
operation. The need for longer battery life in cellular radiotelephones is 
therefore self-evident. 
A digital control channel (DCC) has recently been proposed to the 
Telecommunications Industry Association (TIA). The DCC specification is 
identified as PN 3011-1 and PN 3011-2 and is available from the TIA at the 
above address. When adopted, the DCC will become part of a new IS-54C 
specification. The specifications PN 3011-1 and PN 3011-2 are incorporated 
herein by reference in their entirety. 
One feature of the DCC is called short message service (SMS.) With SMS it 
will be possible to send alphanumeric messages to compatible mobile 
stations in a manner similar to that presently done with paging receivers. 
This feature opens the door for many new cellular phone options. 
Unlike voice communications in which a caller is waiting for a response 
from the called-party, alphanumeric messages do not require an immediate 
response and can be stored and subsequently delivered to the mobile 
station some period of time after origination. This allows the mobile 
phone to adopt what will hereinafter be referred to as a "pager-only mode" 
of operation. 
The pager-only mode of the mobile station will allow the user to receive 
SMS messages but not to receive incoming conversation type calls. The call 
origination capability remains thereby allowing the user to place calls 
without exiting the pager-only mode. The pager-only mode offers many 
advantages to the user not the least of which is the benefit of much 
longer battery life. The pager-only mode also functions as a 
do-not-disturb mode for business meetings, and allows the mobile station 
user to perform "call screening" of incoming calls. Unlike the known 
broadcast page receiver (i.e., "beeper") , the mobile phone is immediately 
available to place a call to the message originator. 
SUMMARY OF THE INVENTION 
In view of the foregoing background, it is therefore an object of the 
present invention to provide a method for increasing the battery life of a 
battery-powered cellular radiotelephone. 
It is also an object of the present invention to provide a pager-only mode 
for a cellular radiotelephone thereby allowing the user of a portable 
cellular radiotelephone to receive short messages broadcast to it from a 
cellular base station. 
These and other objects, advantages, and features of the present invention 
are provided by a method for saving battery power in a cellular radio 
communication system having a base station with a base station control 
signal and a mobile station conditioned to adopt a pager-only mode wherein 
the mobile station cyclically transmits a first signal to the base station 
indicating that the mobile station is unable to receive messages from the 
base station. After transmitting the first signal, the mobile station is 
further conditioned to deactivate selected circuits within itself for a 
predetermined period of time and then to automatically reactivate the 
selected circuits after the predetermined time period has elapsed and to 
transmit a second signal to the base station indicating that the mobile 
station is able to receive messages. 
In another embodiment, the first and second signals transmitted by the 
mobile station include power-down and power-up registration messages. 
In yet another embodiment, the mobile station is adapted to allow the user 
to set and reset the pager-only mode. 
A further embodiment of the invention comprises a cellular communications 
system having a mobile station conditioned to transmit a first signal to a 
base station to notify the base station when the mobile station is unable 
to receive messages. The mobile station includes a controller to 
deactivate selected circuits within the mobile station for a period of 
time and to automatically re-activate the selected circuits after the 
period of time has expired. The mobile station is further conditioned to 
transmit a second signal after the period of time has elapsed to notify 
the base station that the mobile station is ready to receive messages. The 
mobile station is conditioned to repeat this sequence of operations until 
it is set by the user into another mode. The controller is adapted to 
cause other selected circuits, not deactivated, to operated at reduced 
levels of power consupmption to further increase battery life. The 
predetermined period of time may be adjusted to even further increase 
battery life. 
In accordance with the present invention, a method for saving battery power 
in a cellular radio communication system having a base station with a base 
station control signal, by transmitting a first signal from a mobile 
station to the base station indicating that the mobile station is unable 
to receive messages from the base station, deactivating selected circuits 
within the mobile station for a predetermined period of time, 
automatically reactivating said selected circuits within the mobile 
station after said predetermined time period, transmitting a second signal 
from the mobile station to the base station indicating that the mobile 
station is able to receive messages. 
These and other features and advantages of the present invention will be 
readily apparent to one of ordinary skill in the art from the following 
written description when read in conjunction with the drawings in which 
like reference numerals refer to like elements.

DESCRIPTION OF THE INVENTION 
In the following description, for purposes of explanation and not 
limitation, specific details are set forth, such as particular circuits, 
circuit components, techniques, etc. in order to provide a thorough 
understanding of the invention. However it will be apparent to one of 
ordinary skill in the art that the present invention may be practiced in 
other embodiments that depart from these specific details. In other 
instances, detailed descriptions of well-known methods, devices, and 
circuits are omitted so as not to obscure the description of the present 
invention with unnecessary detail. 
System Operation 
Referring initially to FIG. 1, a typical cellular network 100 is 
illustrated showing the interconnection of two regional systems 101A and 
101B. The system components shown are exemplary and as is obvious to one 
of ordinary skill in the art not all cellular systems will be limited to, 
or inclusive of, these components; other arrangements are possible as 
well. Regional system 101A comprises, for example, a mobile telephone 
switching office (MTSO) 107 connected to a plurality of base stations 110 
each by communications link 113. Base station 110 provides the radio link 
114 to each mobile station 109. Landline telephone user 103 and data users 
102 are connected to the public telephone switched network (PSTN) 105 by 
communications link 115. The PSTN is, in turn, connected to the MTSO 107 
by communications link 116. MTSO 107 is also connected to a visiting/home 
location register (VLR/HLR) 106 and to message center 104. Interconnection 
between networks 101A and 101B are effected between MTSOs 107 via an IS-41 
communications link, in this case microwave link 108 using microwave 
antennas 108A and 108B, or alternately through the long-distance PSTN 
lines 117. As shown, communication connections may be established between 
landline telephone user 103 or data users 102 and mobile stations 109. 
When the complete connection occurs within the boundaries 101A or 101B 
mobile station 109 is said to be in its "home" system. If a connection 
occurs across systems 101A and 101B mobile station 109 is said to be 
"roaming." The terms "home system" and "roaming" are well-known to one of 
ordinary skill in the art. 
As shown in FIG. 1 connections may occur between mobile stations 109 in the 
same system or mobile stations in different systems. Similarly, a 
communications connection may occur between a landline telephone user 103 
or data user 102 and a mobile station 109. It may further be stated that 
mobile station 109 may be a cellular radiotelephone, a radio modem, or a 
personal digital assistant (PDA.) 
The typical operation of the SMS procedure is described by the flowchart of 
FIG. 2A. In one instance, for example, a landline telephone user, or 
caller, 103 attempts to place a call through the PSTN 105 and the MTSO 107 
to mobile station 109 as indicated in block 201. If mobile station 109 
answers (i.e., responds to the page broadcast from one of the base 
stations 110) then the connection is made according to known methods as 
indicated by block 203. Alternatively, if mobile station 109 does not 
answer then the caller 103 is routed through the MTSO 107 to the message 
center 104 as indicated in block 204. 
There are several ways in which a message in block 206 may be received by 
the message center 104. The prompt in block 205 may, in one instance, be a 
human operator who answers the call and enters the message through a 
computer or console into message center 104. In another instance, the user 
103 is prompted as indicated in block 205 to enter the message via the 
telephone keypad in a manner similar to the known procedures used to leave 
a message to be transmitted to a broadcast paging receiver. In yet another 
instance, the user may directly transfer the message from a personal 
digital assistant, or a personal computer 102. In this case the prompt in 
block 205 is a computer tone similar to a fax machine's set-up signaling. 
Regardless of the method used, a brief alphanumeric message is stored in 
message center 104 for later transmission to mobile station 109. 
A description of how the stored message is forwarded to mobile station 109 
is shown by the flowchart of FIG. 2B. When the mobile station is first 
powered-on, or otherwise wishes to make contact with the system as will be 
described in more detail hereinafter, mobile station 109 performs a 
registration with the system according to Section 6.3.7 of Specification 
PN 3011-1 as indicated in block 209. Based on information contained within 
mobile station's registration signal, system 101A, for example, determines 
if mobile station 109 is in its home system 101A or if it is roaming in 
system 101B as indicated in block 210. If the mobile station is in home 
system 101A, the SMS message stored in the message center 104 is broadcast 
as indicated in block 214 to mobile station 109 via the DCC protocols to 
be described. If, alternately, mobile station 109 is roaming in, for 
example, system 101B a registration message is sent to mobile station's 
109 home system 101A via the IS-41 link 108 as indicated in block 212. 
Upon receipt of the registration message, the home system 101A message 
center 104 transfers the SMS message previously stored to roaming system 
101B via the IS-41 link 108 as indicated in block 213. If no SMS messages 
are stored an indication thereof is alternately communicated. Once 
received, the SMS messages are broadcast via base station 110 to mobile 
station 109 according to the DCC specification. 
Description of the DCC 
A complete and thorough description of the DCC is provided in 
specifications PN 3011-1 and PN 3011-2 previously incorporated by 
reference. In the following, a summary description of the DCC is provided 
as necessary to make clear the operation of the present invention. 
The DCC 420 comprises the logical channels shown in FIG. 4A which is 
adapted from FIG. 2-3 of Specification 3011-1. Uplink channel 414 
transmitted from mobile station 109 to base station 110 consists of the 
random access channel (RACH) 413. Downlink channel 415 transmitted from 
base station 110 to mobile station 109 consists of the broadcast control 
channel (BCCH) 416 and the short message, paging, and access control 
channel (SH) 407. 
In FIG. 4B is shown the frame structure of the Downlink DCC 415 as 
specified in specification PN 3011-1. To ensure compatibility with 
existing equipment, the DCC makes use of the present IS-54B TDMA frame 
structure. A TDMA frame 400 is defined as three contiguous time slots 401, 
402, and 403. As specified in IS-54B, mobile station 109 will receive 
signals broadcast from base station 110 on every specified third slot, for 
example, mobile station 109 may continuously monitor slot 1 401 and slot 4 
401A, slot 2 402 and slot 5 402A, or alternately slot 3 403 and slot 6 
403A. Therefore during each TDMA frame 400 the mobile station receiver 303 
(FIG. 3) to be described in more detail hereinafter need only be on 1/3 of 
the time. 
A DCC superframe 408 is defined as a number of sequential TDMA frames 400. 
In the example shown in FIG. 4B, the DCC superframe 408 comprises 
information transmitted sequentially on every third slot of an IS-54B 
frame. Within the DCC superframe 408 are contained different information 
slots. The FBCCH 404, EBCCH, 405 and the SBBCH 406 are broadcast control 
channels which transmit global information for all mobile stations. FBCCH 
404, EBCCH 405, and SBCCH 406 may extend over several slots as indicated 
by the dots in adjacent slots of the DCC superframe 408. The FBCCH 404, 
EBCCH 405, and the SBCCH 406 are described in more detail in Section 2.3.2 
of PN 3011-1. 
Slot 407 contains information directed at specific mobile stations 109 
comprising the paging control channel (PCH) 410, access control channel 
(ARCH) 411, and the short message service control channel (SMSCH) 412. 
Two DCC superframes 408 are arranged sequentially into a primary and 
secondary superframe which together are known as a hyperframe 409. SMS 
messages may be interleaved in the SH slot 407 across several 
hyperframes. 
Mobile Station Operation 
Normal monitoring of the DCC downlink 415 by mobile station 109 involves 
checking, for example, each SH slot 407 on the DCC superframe 408 as 
shown in FIG. 4B. In order to monitor each slot, the mobile station 
executes the sequence of operations shown by the flowchart of FIG. 5. 
Mobile station 109 first "powers-up" as indicated in block 501. Powering 
up may be effected by the user turning mobile station 109 on from being 
completely off, or it may be waking up from what is refered to as a "deep 
sleep state" as will be described in more detail hereinafter. After 
powering up, mobile station 109 scans, according to known methods, a 
predetermined set of DCC downlink channels 415 and locks its receiver to 
one of the DCCs 415 as indicated in block 502. Once locked to a DCC 415, 
mobile station 109 receives and decodes DCC hyperframe 409 as indicated in 
block 503. In the FBCCH slot 404 is contained information identifying the 
SH paging slot and the paging class mark, to be described in more 
detail hereinafter, to be used by mobile station 109. As indicated by 
block 504, mobile station 109 transmits via RACH 414 a "power-up" 
registration to the base station 110 and receives via the downlink DCC 415 
an acknowledgment back from base station 110. The acknowledgment may 
contain additional information instructing mobile station 109 to monitor 
another DCC 420 or to otherwise override the FBCCH information. Assuming 
that an acknowledgment and no instructions are received from base station 
110, mobile station 109 assumes in block 505 the paging class 
corresponding to the paging class mark in FBCCH slot 404 received in block 
503. Paging class marks are described in greater detail in section 4.5.5 
of specification PN 3011-1. 
There are 8 paging classes designated 1-8 which specify the frequency with 
which mobile station 109 listens to SH slot 407 for a SMS message as 
indicated in block 506. A first mobile station 109 assigned to paging 
class 1 monitors one SH slot 407 for each hyperframe 409, a second 
mobile station 109 assigned to paging class 2 monitors one SH slot 407 
for every other hyperframe 409, a third mobile station 109 assigned to 
paging class 3 monitors one SH slot 407 for every third hyperframe 409, 
and so on. In paging class 8, for example, mobile station 109 may only 
monitor a SH slot 407 every 2 minutes for SMS messages. This procedure 
allows the system operator to assign so called sleep-modes. This procedure 
is known and described in greater detail in specifications PN 3011-1 and 
PN 3011-2. 
Referring now to FIG. 3, a partial functional block diagram of a mobile 
station 109 is shown. During SH slot 407, power must be applied to 
receiver 303, demodulator 302, controller 304, timing generator 305, and 
the timebase/automatic frequency control (AFC) 306. The timebase 306 may 
be a temperature controlled crystal oscillator (TCXO). In between SH 
slots 407 however, all that is required to be activated is timing 
generator 305 and the timebase/AFC 306 to keep track of when the next 
SH slot 407 is to occur. However, if the next SH slot 407 is to be 
decoded correctly, as is obvious to one of ordinary skill in the art, the 
timing accuracy must be accurate to within a couple of symbol periods. 
This requires timing generator 305 and the timebase/AFC 306 to operate in 
a precise manner wherein power must also be applied to the controller 304 
to control operation of timing generator 305 and AFC 306. During the 
intervals between SH slots 407 timing generator 305 and controller 304 
may operate at a greatly reduced instruction rate and therefore have 
reduced current requirements. However, in order to maintain the timing 
accuracy required the timebase/AFC 306 must remain fully active between 
SH slots 407. The necessity of maintaining the timebase/AFC 306 fully 
active places a lower limit on the amount of current drawn from battery 
310 and hence limits the absolute battery life. 
Operation of the Page Only Mode 
When a user of mobile station 109 wishes to place calls but not to receive 
incoming calls the user may simply turn the phone off until such time as 
the user decides to place a call. By so doing the user may maximize the 
life of battery 310 since little or no current is drawn by the circuits 
shown in FIG. 3 when mobile station 109 is deactivated. However, if the 
mobile station 109 is deactivated mobile station 109 is not able to 
receive incoming SMS messages. 
If, alternately, the user of mobile station 109 wishes to place calls and 
to also receive SMS messages while at the same time maximizing battery 
life, the user of mobile station 109 may select to place the phone into 
what is refered to as the "pager-only mode." One method by which the user 
may place mobile station 109 into a pager-only mode is described in FIG. 
6A. It will be understood by those of ordinary skill in the art that there 
are many ways for the user to establish/select a pager-only function in a 
cellular telephone. The example given in FIGS. 6A and 6B are therefore 
exemplary only and are not meant to be limitative. First, as indicated in 
block 601, the mobile station 109 is be turned on in the normal manner. 
Then as shown in FIG. 6B ,the user then sequentially presses function key 
607, the `1` key 608, and finally the `5` key 609 on the keypad of mobile 
station 109 as indicated in blocks 602-603. Executing this sequence will 
toggle the mobile station into the pager-only mode. Repeating the sequence 
will reset the mobile station into the normal stand-by mode where mobile 
station 109 monitors the DCC according to its assigned paging class. 
Another method for placing mobile station 109 into a pager-only mode 
requires the user to enter a menu mode and, using the arrow keys 610 
commonly found on mobile stations, the user can sequence through the 
available options to select or deselect the pager-only mode. To confirm 
that mobile station 109 is in the pager-only mode a brief indication will 
be shown on display 606 of the mobile station 109 as indicated in block 
604. After a brief period, display 606 will go blank until such time as a 
SMS message is received. 
Referring now to FIG. 7, the operation of mobile station 109 in the 
pager-only mode is described. Once mobile station 109 has entered the 
pager-only mode as indicated in block 701 all circuits non-essential to 
the operation of the mobile station 109 while in the pager-only mode are 
de-activated as will be described. This is refered to as the "deep-sleep" 
state. Referring back to FIG. 3, in the deep sleep state analog decode 
301, demodulator 302, receiver 303, analog encode 307, modulator 308, and 
transmitter 309, are deactivated. Time base/AFC 306 is kept running, but 
at a significantly reduced level since its accuracy can be allowed to 
drift substantially. Timing generator 305 must also be kept activated but 
at an extremely low level of activity only sufficient to count the number 
of oscillations generated by the timebase/AFC 306. In this state, the 
current requirements of mobile station 109 are extremely low and hence the 
current drain from the battery 310 is greatly reduced. 
After a predetermined period of time (e.g., 10 minutes), or equivalently a 
predetermined number of oscillations, timing generator 305 alerts 
controller 304 to "wake-up" and reactivate the receiver 303, the 
demodulator 302, and to increase the activity and hence the accuracy of 
the timebase/AFC 306. It is obvious to one of ordinary skill in the art 
that the predetermined period of time may be adjusted either by the user 
or at the time of manufacture. Controller 304 and the timing generator 305 
also increase their activity level sufficient to perform the functions 
necessary to monitor the DCC 415. This sequence of operations is termed 
"waking-up" as indicated in block 702. Again similar to FIG. 5, the mobile 
station begins to scan the DCC 415 and locks its receiver 303 to one of 
the DCC superframes 408 as indicated in block 703. As indicated in block 
704, mobile station 109 transmits via the RACH 413 a power-up registration 
message to base station 110 to alert, via MTSO 107, message center 104 
that mobile station 109 is active and prepared to receive SMS messages. 
Mobile station 109 begins to monitor the SH slot, pursuant to it's 
paging class as previously described, for SMS messages as indicated in 
block 705. If, as shown in block 706, it is indicated via the SH 407 
that there are no SMS messages waiting to be transmitted from base station 
110 and received by mobile station 109, mobile station 109 transmits via 
the RACH 413 a power off, or power-down, registration as indicated in 
block 707. Power-up, or power-on, and power-off, or power-down 
registration messages are transmitted from mobile station 109 to base 
station 110 over the uplink DCC 414, or RACH 413, as described in greater 
detail in specification PN 3011-1. The message format is identical except 
for the bit field which indicates whether the registration message is a 
power-up, or power-down registration. Once the transmission is complete, 
the mobile station 109 automatically re-enters the deep-sleep state and 
de-activates all non-essential circuits as previously described and 
indicated in block 708. Mobile station 109 remains in the deep-sleep state 
until again a predetermined time period has elapsed (i.e., 10 minutes) at 
which time the cycle is repeated. This continues until the user resets the 
pager-only mode as described above. 
If, alternatively, at block 706 the mobile station receives an SMS message 
from base station 110, it assumes the paging class set by the FBCCH 404 
and continuously monitors the DCC 415 until the complete SMS message is 
received as indicated in block 711. The SMS message is transmitted from 
base station 110 to mobile station 109 over sequential occurrences of the 
SH 407 according to known DCC protocols. As the message is received it 
is stored electronically within mobile station 109 for subsequent 
retrieval by the user. In block 712 mobile station 109 alerts the user via 
a visual, audible, or mechanical (e.g. vibration) that a SMS message has 
been received. At this point the user may elect to read the SMS message. 
After issuing the alert, and regardless of whether or not the user has 
reviewed the messages, the mobile station re-enters the sleep-mode via 
block 707 as previously described. 
In FIG. 8 is shown the power savings advantage afforded by the present 
invention. Note that power savings refers equivalently to the reduction of 
electrical current drawn from battery 310. Referring to FIG. 8 the 
relative current consumption of the mobile station 109, a measure of power 
consumption and hence relative battery life, is displayed on the ordinate 
axis 810. Time is displayed on the abscissa 811. Read in conjunction with 
the flowchart of FIG. 7 the significance of the graph of FIG. 8 will be 
described. After "waking-up" in block 702, mobile station 109 begins to 
scan control channels as indicated in section 802 of the graph. During 
channel scan, a moderate amount of current is required as indicated by 
I.sub.scan 807 on the ordinate. Once the receiver 303 locks on to a 
control channel 415 as indicated in block 703, the mobile station 109 
transmits a power-up registration as indicated in block 704. During the 
transmission phase 803 mobile station 109 draws the greatest amount of 
current from battery 310 as indicated by I.sub.transmit 806. After 
transmitting the power-up registration, mobile station 109 periodically 
scans in section 804 the SH 407 to see if any SMS messages as indicated 
in block 705 are present. Due to the periodic monitoring of the SH 407 
the current requirements I.sub.receive 808 are lower than when the 
receiver 303 continuously scans the control channels as in section 802. 
After reception of, if any, the SMS messages mobile station 109 transmits 
a power-down registration as in block 707. Again since mobile station 109 
is transmitting in section 805, the power requirements I.sub.transmit 806 
are high. After transmitting the power-off registration, the mobile 
station enters its deep-sleep state as in block 708. During this interval 
801 only the minimal essential circuits are energized and power and 
current consumption I.sub.idle 809 is greatly reduced. Mobile station 109 
remains in this state for a predetermined duration T.sub.idle and then the 
process repeats at block 702. For this cyclical operation, the average 
current consumption can be calculated as follows: 
##EQU1## 
Using Equation 1, the average current drawn from battery 310, 
I.sub.average, of the present invention can be compared to the average 
current drawn from battery 310 while continuously monitoring the DCC 415 
as is done presently. For typical mobile stations, the average current 
drawn from battery 310 while continuously monitoring the DCC 415 has been 
found to be approximately 15 milliamperes. With a 500 milliampere-hour 
battery this gives a stand-by time of approximately 33 hours. 
Typical values for the variables in equation 1 are given below in Table 1: 
TABLE 1 
______________________________________ 
Current Power Consumption 
Time Time 
Operation 
Variable (milliamperes) 
Variable 
(seconds) 
______________________________________ 
Transmit 
I.sub.transmit 
600 T.sub.transmit 
100 ms 
DCC Scan 
I.sub.scan 
200 T.sub.scan 
2 s 
Receive I.sub.receive 
15 T.sub.receive 
5 s 
SMS 
Sleep I.sub.sleep 
3 T.sub.sleep 
600 s 
______________________________________ 
Applying these values to Equation 1 yields an average current, 
I.sub.average, of 3.95 milliamperes. Therefore a mobile station 
incorporating the present invention equipped with the same 500 
milliampere-hour battery provides a battery life of approximately 128 
hours. This is a significant improvement over the prior-art and represents 
a distinct advantage to the user of a digital radiotelephone who wishes to 
make, but at times not to receive, calls and to utilize the SMS feature 
available under the DCC 415. As is obvious to one of ordinary skill in the 
art, significantly longer battery lives will be available by increasing 
the idle time above the 10 minutes used in the above example. 
The user enjoys the benefit of longer battery life until such time as the 
user takes affirmative action to exit the pager-only mode, for example, by 
repeating the steps shown in FIG. 6A. Of course, a phone call may be made 
at any time during which the pager-only mode is temporarily suspended for 
the length of the call. 
While the present invention has been described with respect to a particular 
digital cellular communications system, those skilled in the art will 
recognize that the present invention is also applicable to other 
communications systems and that therefore the present invention is not 
limited to the specific embodiments described and illustrated herein. 
Different embodiments and adaptations besides those shown and described as 
well as many variations, modifications and equivalent arrangements will 
now be reasonably suggested by the foregoing specification and drawings 
without departing from the substance or scope of the invention. While the 
present invention has been described herein in detail in relation to its 
preferred embodiments, it is to be understood that this disclosure is only 
illustrative and exemplary of the present invention and is merely for the 
purposes of providing a full and enabling disclosure of the invention. 
Accordingly, it is intended that the invention be limited only by the 
spirit and scope of the claims appended hereto.