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US005541976A
United States Patent [19]
[11] Patent Number:
Ghisler
[45] Date of Patent:
[54]
COMMUNICATIONS SYSTEM FOR
INTEGRATING A PAGIN G SYSTEM WITH
CELLULAR RADIO TELEPHONES
Assignee: Telefonaktiebolaget LM Ericsson,
Stockholm, Sweden
0140351
5/ 1985
63-224422
9/1988
Japan ..................................... .. 379/57
2201866
9/1988
United Kingdom .
telephone system which incorporates an independent paging
capability with an existing mobile telephone by taking
advantage of call forwarding and redirecting features avail
[51]
Int. Cl.6 ..................................................... .. H04Q 7/22
[531
US. Cl. .............................. 1. 379/57; 379/59; 455/343
Field of Search ................................ .. 379/57, 58, 59;
455/383, 127, 343, 33.1
References Cited
U.S. PATENT DOCUMENTS
3,564,150
2/1971 Muller.
3,575,558
4/1971 Leyburn .
3,581,013
4/1971 Muller.
4,399,555
4,642,425
4,747,122
4,748,655
4,850,006
4,873,711
8/1983 MacDonald et a1. .
2/1987 Guinn, Jr. et a1. ...................... .. 379/57
5/1988 Bhagat et a1. .
5/1988 Thrower et al. .
7/1989 Sasaki et al. .
10/1989 Roberts et a1. .
4,906,989
3/1990 Kasugai ..
5,020,090
5/1991
5,040,204
8/1991 Sasaki et al.
5,054,052
10/1991
5,065,423
11/1991 Gaskill
5,097,500
.. .... . ..
Nonarni
.... . ..
able on the telephone switching network. When a mobile
telephone is set to an active or “on” mode, calls are directed
to that mobile telephone using the cellular paging channel
and conventional cellular paging procedures. However,
when the mobile telephone is set to a sleep mode and the
power is switched off, the mobile switching center auto
matically forwards calls to the mobile to an independent
paging system which transmits the call as a paging signal to
a small pager associated with the mobile telephone. When
the pager receives a page signal as a result of the forwarded
call, the pager transmits a low-power signal to the mobile
telephone which switches on the power of the mobile
3/1989 Focarile et a1. .
Morris
ABSTRACT
The present invention relates to a cellular mobile radio
Continuation of Ser. No. 159,116, Nov. 30, 1993, aban
doned, which is a continuation of Serv No. 686,600, Apr. 17,
1991, abandoned.
H610
-
[57]
Related US. Application Data
[63]
European Pat. O?‘. .
Primary Examiner—Curtis Kuntz
Assistant Examiner—G. J. Oehling
Attorney, Agent, or Firm—Burns, Doane, Swecker &
Mathis, L.L.P.
121] Appl. No.: 476,041
Jun. 7, 1995
[22] Filed:
Jul. 30, 1996
FOREIGN PATENT DOCUMENTS
[75] Inventor: Walter Ghisler, Upplands Vasby,
Sweden
5,541,976
..................... .. 455/11.1 X
. . . . . ..
379/58
379/57 X
. . . . . ..
telephone. A predetermined time after forwarding the call to
the paging system, the mobile switching center redirects the
forwarded calls using redirecting procedures to the mobile
telephone. By the time the call is redirected, the mobile
station has been activated and can now receive the call
directly Because the active pager consumes much less
power than the mobile telephone listening to a paging
channel of the cellular system, setting the mobile telephone
to the sleep mode results in considerably less battery drain.
When the mobile is set to a page mode, the pager functions
as a conventional paging device.
379/57
. 379/57
3 Claims, 5 Drawing Sheets
3/1992 Itoh ......................................... .. 379/62
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5,541,976
1
2
COMMUNICATIONS SYSTEM FOR
INTEGRATING A PAGING SYSTEM WITH
CELLULAR RADIO TELEPHONES
mobile telephone battery. As a result, large, bulky batteries
are required.
Although mobile telephones have a greater number and
variety of functions as compared to pagers, with respect to
This application is a continuation of application No.
the paging function, pagers require less battery power.
08/159,116, ?led Nov. 30, 1993 which was a continuation of
Attempts have been made to reduce the size and the weight
application No. 07/686,600, ?led Apr. 17, 1991 (both now
of mobile telephone batteries, in particular, the batteries of
abandoned).
hand held mobile telephones. Specialized techniques have
been developed in conjunction with these reduced batteries.
FIELD OF THE INVENTION
10
One method is discontinuous transmission (DTX) where the
sender draws current only when speech is actually transmit
ted. Another method is discontinuous reception (DTR)
The present invention is directed to cellular telephone and
where paging occurs at predetermined intervals known to
the mobile and the land system with the mobile receiver
paging systems. More particularly, the present invention is
directed to a mobile cellular telephone that incorporates
independent paging capabilities.
being turned off during inactive periods. Nonetheless, bat
tery size and weight in hand held mobile telephones are still
BACKGROUND OF THE INVENTION
Radio paging systems and mobile radio telephone sys
tems are well known and widely used. Upon receipt of a
page, radio paging systems provide a user with audio and/or
visual information from the paging party, but cannot trans
20
analog and digital voice channels but use analog control
channels. While the next generation of mobile telephones
will include purely digital mobiles communicating over
mit information back to the paging party. Recently, national
and international paging services have been implemented so
that individuals may receive a page throughout the United
a considerable problem.
In the near future, dual mode mobile telephones will be
introduced into the U.S.A. according to the EIA/TIA Stan
dard 13-54 which are capable of communicating over both
digital voice channels only and using only digital control
25
channels, most of these digital mobiles will be hand held
telephones and will be used in the cities. It is likely that the
States or throughout Europe. Despite the advances in paging
mobile telephone base stations in rural areas will remain
technology, a signi?cant disadvantage of radio paging is that
analog for quite some time. In that situation, the radio
after an individual carrying a pager has learned that a paging
coverage for digital mobile stations will be less than it is for
party wishes to communicate, that individual must locate a
telephone communication system to contact the paging 30 pagers. Thus, it is desirable to take advantage of both
cellular and traditional paging services.
One disadvantage with cellular telephony is that a sub
Party
Radio paging systems typically include a radio transmitter
for transmitting a coded, radio frequency signal associated
with a party to be paged and a portable paging receiver. To
contact a party carrying a pager, a person dials a telephone
scriber’s location must be known to the cellular system.
35
number. The number is transferred by the Public Switching
Telephone Network (PSTN) to the radio transmitter. The
Subscriber location is achieved by registering each mobile
periodically. In contrast, paging systems do not require
individual pagers to register. Thus, paging services are
advantageous in situations where a subscriber desires to
keep his exact location secret but still wants to have the
transmitter transmits a page signal coded to all pagers in the
range of the transmitter. Because each mobile pager
option of being contacted.
responds to a different paging signal, only the pager having
Recently, it has become possible to subscribe to a cellular
a code corresponding to that transmitted is activated. The
service and to an independent paging system. Telephone
calls from the land-based telephone network are attempted
activated pager generates an audible tone or some other
signal to notify the designated party that he or she has been
initially with the mobile station over the cellular network. If
paged. That party typically responds by calling a speci?c
45 the subscriber does not answer, the call is diverted to a FM
telephone number to receive further instructions.
One advantage of paging systems is that they can serve
radio paging system.
A cellular pager is disclosed in U.S. Statutory Invention
Registration H610 to Focarile et al. In this system, a separate
relatively large geographic areas. Another advantage is that
a paging subscriber may be reached anywhere in the trans
paging system is used in conjunction with the cellular
telephone system. The paging system provides a backup for
mitter coverage area without knowing the location of that
subscriber. As described above, the major disadvantage of
cellular telephone calls intended for an associated cellular
telephone which has been deactivated because the subscriber
is, for example, temporarily away from his automobile.
paging systems is that a subscriber cannot immediately
communicate with the persons who initiated the call. In fact,
the subscriber cannot even acknowledge that he has received
the page.
Assigned the same number as the associated cellular tele
55
In contrast, mobile radio telephone systems allow ?exible,
two-way radio communications with a plurality of mobile
subscribers. Cellular telephones allow subscribers to be
phone, the pager provides an alert signal to the subscriber of
the cellular telephone indicating that a caller is trying to
reach the telephone’s assigned number. Later, the subscriber
may call an appropriate service number for the information
paged immediately over cellular paging frequencies (as long
when the subscriber returns to the automobile and activates
as the phone unit is “on”) via the wired telephone network.
The mobile telephone responds immediately to a page in
the cellular telephone.
Another system combining paging capabilities with a
order to capture a voice channel for the communication. In
cellular system is disclosed in U.S. Pat. No. 4,748,655 to
addition, subscribers may initiate calls themselves. Unfor
tunately, mobile telephones cannot be paged while the
mobile telephone is “011" or deactivated. To keep the mobile
telephone activated continuously in order to monitor a
cellular paging channel imposes a signi?cant drain on the
Thrower et al. In addition to conventional cellular compo
65
nents, the Thrower patent incorporates a pocket-sized, radio
telephone for short range, low-powered communication with
the cellular system over various “gateway” devices, e.g., a
mobile radio telephone set. These pocket-sized phones are
5,541,976
3
4
similar to cordless telephones which communicate with the
gateway devices using low-power transmitter/receiver units.
FIG. 1 shows a functional block diagram of a page phone
and associated land system according to the present inven
The portable telephone transmits its identi?cation number to
the gateway device which transmits the portable telephone’s
tion;
identi?cation number and location via the base station to the
mobile switching center of the cellular network. When the
subscriber is out of range of a gateway device or does not
have a gateway device, his portable telephone can operate as
a paging device from a separate paging station. However,
because of the portable telephone’s low power, the sub
scriber is unable to communicate back with the paging
station.
10
The prior art attempts to integrate paging and cellular
communications systems are not always convenient to the
subscriber and e?icient in terms of battery consumption.
15
Focarile’s system requires a subscriber to carry an activated
paging device around as well as an activated mobile tele
20
page number. Once paged, the subscriber must activate his
mobile telephone, dial a message center, retrieve the mes
sage/number, and call back the paging party. Similarly, a
major drawback of the Thrower system is that it requires, in
addition to standard cellular components, cumbersome, por
table phone and gateway circuitry which are energy ine?i
according to the present invention; and
FIG. 5 illustrates the signaling format of paging signals
broadcast by the paging system according to the present
invention.
DETAILED DESCRIPTION OF THE
PREFERRED EMBODIMENTS
phone. This situation is burdensome and wastes consider
able battery power. Moreover, if only the paging device is
activated, the subscriber can only be reached by dialing his
FIG. 2 illustrates a more detailed functional block dia
gram of a low power, radio transmission system to imple
ment communications between pager and mobile according
to the present invention;
FIG. 3 shows a ?ow chart of the paging process according
to the present invention.
FIG. 4 shows a functional block diagram of the commu
nications unit and mode switch in the mobile telephone
Referring now to FIG. 1 the overall system operation of
a cellular page phone 20 will be described. The page phone
20 consists of two elements: a pager 21 and a mobile
25
telephone 30. In general, the pager 21 includes a radio
frequency receiver 22, preferably an FM receiver, for receiv
ing page communications transmitted by a conventional,
independent paging network 50. The pager 21 also includes
cient and relatively expensive.
a control unit 23, a beeper 24, a display 25, and a conven
tional, low-power FM transmitter 26. The mobile telephone
30 includes a communications unit 34, described in more
SUMMARY OF THE INVENTION
detail in conjunction with FIG. 3, which houses the com
munications circuitry found in standard mobile telephones.
A mode switch 32 is used to switch the mobile telephone
The present invention relates to a cellular mobile radio
telephone system which incorporates an independent paging
capability with an existing mobile telephone by taking
advantage of call forwarding features available on the tele
phone switching network. When a mobile telephone is set to
35
an active or “on” mode, calls are directed to that mobile
telephone using the cellular paging channel and conven
tional cellular paging procedures. However, when the
mobile telephone is set to a sleep mode and the power is
into one of four distinct modes: an on mode, a sleep mode,
a page mode, and an off mode. The communications unit 34
is powered by a battery unit 36.
The page phone includes an AC power receptacle 38
which recharges the battery 36 and provides power to the
mobile telephone 30 when the telephone is placed in the
receptacle. As such, the telephone 30 may be operated in the
switched oil, the mobile switching center automatically
“on” mode without a drain to the battery 36. The receptacle
forwards calls to the mobile to an independent paging
38 may be located, for example, in the subscriber’s auto
system which transmits the call as a paging signal to a small
mobile or at the subscriber’s desk. When the subscriber
pager associated with the mobile telephone. When the pager
moves away from his automobile or his desk and removes
receives a page signal as a result of the forwarded call, the
45 the telephone 30 from the power receptacle 38, that removal
pager transmits a low-power signal to the mobile telephone
is detected by a contact switch 39 located on the surface of
which switches on the power of the mobile telephone. A
the telephone 30 that interfaces with the power receptacle
predetermined time after forwarding the call to the paging
38. In that situation, the contact switch causes the mode
system, the mobile switching center redirects the forwarded
switch to change from the “on” mode to the “sleep" mode in
calls to the mobile telephone. By the time the call is 50 order to conserve the battery 36.
redirected, the mobile station has been activated and can
Calls initiated from the land-based system may be
now receive the call directly. Because the active pager
directed through a public switching telephone network
consumes much less power than the mobile telephone lis
(PSTN) 44 to a mobile switching center (MSC) 42 and
tening to a paging channel of the cellular system, setting the
?nally through a base station 40 associated with the page
mobile telephone to the sleep mode results in considerably
less battery drain. When the mobile is set to a page mode, the
pager functions as a conventional paging device. The pager
and mobile are separate physical units and may communi
cate using low power, radio transmission or acoustical
signals.
55
other mobile telephones may be communicated to the page
60
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will now be described in more
detail with reference to preferred embodiments of the inven
tion, given only by way of example, and illustrated in the
accompanying drawings, and in which:
phone 20. Alternatively, calls which have been initiated by
65
phone 20 from a corresponding base station 41 through the
mobile switching center 42 and the base station 40.
The pager 21 and the mobile telephone 30 is separated
into two distinct mechanical packages. In the preferred
embodiment, the pager 21 is physically separated from the
mobile telephone 30 and is housed in a wristwatch worn by
the subscriber. Since the pager 21 is separately housed, it
must also be provided with a small battery (not shown)
suitable for powering the wristwatch as well as the paging
circuitry. Although the subsequent description pertains to the
pager 21 communicating with the mobile telephone via FM
5,541,976
5
6
radio signals, it will be recognized by those skilled in the art
that the pager 21 and mobile telephone 30 may communicate
The additional FM radio communications circuitry for
signalling between the pager 21 and the mobile telephone 30
is well known and may include, for example, the conven
tional FM transmitter 26 and the FM receiver 37 pair
using acoustical signals or hardwired connections as well.
When a user selects the ON mode using the mode switch
32, the mobile telephone 30 operates in a conventional
manner within the cellular system. A call to the mobile
telephone 30 from the base station 40 will be initiated as a
page over the cellular control channel assigned to the base
station 40. Each mobile telephone is identi?ed by a number
of digits referred to as the mobile identi?cation number. In 1O
the ON mode, the mobile telephone 30 actively monitors the
control channel assigned to the base station 40 for page
illustrated in more detail in FIG. 2. The FM transmitter 26
includes an oscillator 200 connected to a modulator 204 and
a two tone generator 202. Similarly, the FM receiver 37
includes an oscillator 210 connected to a demodulator 214
and a two tone detector 212. Essentially, the oscillators 200
and 210 generate a frequency corresponding to the FM
carrier frequency. In the FM transmitter 26, the carrier and
two tone information signal are mixed and transmitted via an
signals containing its identi?cation number. Oncethe mobile
telephone 30 detects a page having its identi?cation number,
antenna. The FM receiver 37 receives the FM signal and
demodulates the carrier from the tone signal in the demodu
a voice channel is obtained so that the intended communi
15 lator 214. The two tone signal is detected by the detector 212
cation can take place. If the subscriber does not answer, the
which generates a power-on signal for activating the mobile
mobile switching center 42 may store the calling subscrib
telephone 30.
er’s number, usually referred to as the A-number, for sub
An alternative embodiment to PM signalling is the trans
sequent retrieval by the subscriber. A major disadvantage of
mission of one or more acoustical tones from the pager of
this type of cellular system is that even though the mobile
one or more acoustical tones from the pager 21 to the mobile
telephone 30 is only monitoring the control channel and no
station 30 when the pager 21 receives a page. The mobile 30
conversation is taking place, it drains the battery 36.
may include a conventional “key-?nder” receiver where an
audible tone or pair of tones from the pager 21 causes the
except for the FM receiver 37 and the pager 21 is activated.
key-?nder to generate an answer signal. In this case, the
Just before the mobile telephone 30 is deactivated, it sends 25 answer signal would be a power on signal.
a deactivation message to the mobile switching center 42.
In the sleep mode, the mobile telephone 30 is deactivated
The mobile switching center 42 registers this fact and
establishes a call forwarding procedure for calls placed to
the mobile telephone 30. Call forwarding is a well known
feature available on most, if not all, telephone networks.
Thus, whenever a caller dials the telephone number of a
mobile telephone in the sleep mode, the MSC 42 directs the
call through the PSTN 44 to the independent paging network
50. When the paging network 50 receives the forwarded call,
it transmits a paging signal to the pager 21 over the con
ventionally assigned paging frequencies. Wide area paging
35
A predetermined time after the call has been forwarded to
the pager 21, the MSC 42 is programmed to redirect the call
back to the mobile telephone 30. Thus, the call to the mobile
telephone 30 is forwarded initially to the pager 21 because
of the call forwarding feature activated in the sleep mode.
After a predetermined time, the MSC 42 terminates the call
to the paging system and reroutes the call back to the mobile
telephone 30 via the base station 40. By the time the call is
rerouted, the pager 21 has turned the power of the mobile
telephone 30 “on” so that it is prepared to receive the call
directly.
systems use telephone numbers to identify a paging sub
scriber. Paging subscribers may be treated exactly like any
By taking advantage of call forward capabilities available
over the existing telephone network, the present invention
activates a sleeping mobile telephone only when a call is
being placed to that mobile telephone. In this way, power is
drawn from the battery 36 only when an actual call is being
directed to the mobile telephone 30, when the subscriber
initiates a call, and when there is an on-going call. Moreover,
other telephone subscribers. Dialing the telephone number
assigned to the paging subscriber results in paging of that
subscriber. The details of how the Page redirection process
is performed in the telephone network is known to those
skilled in the art and therefore will not be described here. In
general, however, the telephone number of the mobile
station is translated in the MSC 42 to the telephone number 45 the subscriber does not have to be concerned with monitor
ing a pager or with returning a phone call after receiving a
identifying the pager, and this new number is used for
page.
forwarding the call to the paging system. The receiver 22 of
the pager 21 detects its paging identi?cation number. The
A subscriber may select the page mode if he does not want
paging control unit 23 generates a FM radio signal via the
to be interrupted but would, nonetheless, like to be informed
low power, FM transmitter 26. The frequencies over which
of incoming calls and return them at a later time. As in the
the FM signal is transmitted are different from cellular or
sleep mode, the mobile telephone 30 is deactivated and the
paging frequencies. Such frequencies may be, for example,
pager 21 is activated. The caller dials the page phone
in the frequency band assigned to amateur radio enthusiasts.
number, the call is forwarded to the paging system 50 and
Finally, the FM signal is received by the FM receiver 37
paging is performed. The pager 21 does not activate the
which activates the power to the mobile telephone 30.
55 mobile telephone 30 upon receiving a page. After a prede
termined time, the call is redirected to the mobile station 30
It may be necessary to distinguish the low power, FM
by the MSC 42, but the mobile station does not answer
radio signal between one pager and its associated mobile
because it is deactivated. As a result, the MSC 42 registers
telephone from a signal corresponding to another pager/
mobile pair, in order to prevent activation of another, nearby
mobile telephone. This distinction is achieved substantially,
for example, by assigning to different subscribers different
frequencies or different pairs of frequencies modulating an
FM carrier out of a number of prede?ned frequencies. Only
the page, i.e., the A-number of the calling subscriber for later
retrieval. Thus, the pager simply performs as a conventional
pager as described in the background of the invention. The
control unit 23 alerts the subscriber of a call audibly by
in rare situations will there be an occasional error in acti
telephone number of the caller on the display 25.
In the fourth mode, the mobile telephone 30 is “o?”. In
this mode both the mobile telephone 30 and the pager 21 are
vating a neighbor mobile station. Nonetheless, the drain on
that neighboring mobile’s battery occurs for only a short
time because no neighboring call will be received.
activating the beeper 24 and visibly by displaying the
65
turned off in order to minimize costs and eliminate any
5,541,976
7
8
interruption to the subscriber from incoming calls. Of
course, if there are incoming calls, the mobile switching
operates in accordance with the present invention is illus
trated. This particular example pertains to a mobile station
that can be used in a purely digital Time Division Multiple
Access (TDMA) communications system, i.e. one in which
digitized voice information is transmitted between base and
mobile stations and in which the control channels are digital
TDMA channels. Furthermore, the operation of the system
is explained in the context of full-rate transmissions, in
which each packet of digital information is interleaved over
two spaced time slots in a frame of data. It will be readily
center 42 may store any messages and/or numbers so that the
subscriber may deal with these calls at a later time.
It should be recognized that when a mobile station is in
the ON mode, that mobile station continually registers with
the MSC 42 to provide the MSC 42 with its current location.
This registration also takes place when the mobile is acti
vated by a signal from the pager 21 in the sleep mode.
However, when the mobile station is switched from the on 10
appreciated, however, that the invention is equally appli~
mode to any of the other modes (sleep, page or o?), it ?rst
cable to other types of cellular radio systems, such as those
signals to the MSC 42 that it is no longer “on”. Based on that
in which information is transmitted in an analog format or
deactivation signal, the M80 42 forwards calls directed to
transmitted digitally at a half rate.
the deactivated mobile to the paging network 50 for further
In the mobile station depicted in FIG. 4, a speech coder
processing depending on the actual mode.
15
101
converts the analog voice signal generated by a micro~
FIG. 3 illustrates the program ?ow followed in routing an
phone into a binary data stream. The data stream is divided
incoming call from a subscriber A, assumed only for pur
poses of description to be connected to the public switching
telephone network, to a cellular subscriber B. Obviously, the
incoming call could be initiated from another mobile tele
into data packets, according to the TDMA principle. A fast
associated control channel (FACCH) generator 102 gener
20
phone.
In step 70, subscriber A initiates a call to subscriber B
ates control and supervision signalling messages that are
transmitted from the mobile station to the land-based sys
tem. The FACCH message replaces a user frame (speech/
data) whenever it is to be transmitted. A slow associated
from the public switching network (PSTN). The public
control channel (SACCH) generator 103 provides signalling
switching telephone network 44 routes that incoming call to
the mobile switching center (MSC) 42 in step 72. In step 74,
the mobile switching center 42 determines the current mode
of the mobile telephone 30 of the subscriber B. If the “on”
mode has been selected in block 75, the mobile switching
messages that are transmitted over a continuous channel for
25
the exchange of information between the base station and
the mobile station and vice-versa. A ?xed number of bits,
e.g. twelve, is allocated to the SACCH for each time slot of
a message train. Channel coders 104 are respectively con
nected to the speech coder 101, FACCH generator 102, and
SACCH generator 103 for manipulating the incoming data
center 42 transmits a page to the mobile telephone 30 over
the cellular control channel of its associated base station in
step 80. In step 92, the mobile switching center 42 deter
mines whether or not the call has been answered by the
subscriber B. If the call has been answered, voice commu
in order to carry out error detection and correction. The
techniques used by the channel coders 104 are preferably
convolutional encoding, which protects important data bits
in the speech code, and cyclic redundancy check (CRC),
nications between subscriber A and subscriber B commence
wherein the perceptually signi?cant bits in the speech coder
as indicated in step 94. Otherwise, the fact of the call as well 35 frame, e.g. twelve bits, are used for computing a seven-bit
as a message (e.g., the caller’s telephone number) may be
stored in the memory of the mobile switching center 42 in
step 96 for later recall by the subscriber B.
If the mobile telephone 30 has been switched to a sleep
mode in block 76, the mobile switching center 42 forwards
check.
A two burst interleaver 106 is connected to the channel
coders 104 associated with the speech coder 101 and the
FACCH generator 102, respectively. The interleaver 106 is
controlled by a microprocessor controller 130 so that, at
appropriate times, user information over a particular speech
channel is replaced with system supervision messages over
the FACCH. Data to be transmitted by the mobile station is
interleaved over two distinct time slots. A packet of 260 data
bits, which constitute one transmitting word, are divided into
two equal parts and are interleaved over two different time
slots. The effects of RAYLEIGH fading will be reduced in
this manner. The output of the two-burst interleaver 106 is
provided to the input of a modulo-two adder 107 so that the
calls to the paging system 50in step 82. The paging system
50 signals the pager 21 to activate the mobile telephone 30
in step 86. In step 88, the mobile switching center 42
redirects the incoming call back to page the mobile tele
phone 30 over the cellular control channel after a predeter
mined time. In step 92, it is determined whether or not the
call has been answered by the subscriber B. If the call is
answered, then the communication between subscriber A
and subscriber B is carried out in step 94. Otherwise, a
message is stored in the mobile switching center 42 in step
96 for later recall by the subscriber B.
When the mobile telephone 30 has been switched to the
page mode in block 77, the mobile switching center 42 sends
transmitted data is ciphered bit-by-bit by logical modulo
two-addition of a pseudo-random bit stream.
The output of the channel coder 104 associated with the
SACCH generator 103 is connected to a 22~burst interleaver
a page message to the pager 21 in step 82. In step 86, even
55 108. The 22-burst interleaver 108 interleaves data transmit
though the pager 21 is activated, any attempts to activate the
ted over the SACCH over 22 time slots each consisting of 12
switched oiT mobile station 30 are without effect. The
bits of information.
subscriber B is alerted of the page in step 88, and the
The mobile station further includes a Sync Word/DVCC
telephone number of the subscriber A may be displayed in
display 25 and stored in the mobile switching center 42 for
subsequent retrieval by the subscriber B in step 96 because
60
code) which are to be associated with a particular connec
the call is not answered.
In the “011" mode in block 78, any calls to the subscriber
B are stored at the mobile switching center 42 for subsequent
retrieval. Steps 82, 86, and 88 have no effect.
Referring now to FIG. 4, an embodiment of a mobile
station that can be utilized in a cellular telephone system that
generator 109 for providing the appropriate synchronization
word (Sync Word) and DVCC (digital veri?cation color
tion. The Sync Word is a 28 bit word used for time slot
synchronization and identi?cation. The DVCC is an 8-bit
code sent by the base station to the mobile station, and
65
vice-versa, for assuring that the proper channel is decoded.
A burst generator 110 generates message bursts for trans
mission by the mobile station. The burst generator 110 is
5,541,976
9
10
connected to the outputs of the modulo-two-adder 107, the
signal, thus generating an intermediate frequency. The inter
mediate frequency signal is then demodulated by an IF
demodulator 128, which restores the original 1r/4-DQPSK—
modulated information.
The restored information provided by the IF demodulator
128 is supplied to the equalizer 114. A symbol detector 115
converts the received symbol format of the digital data from
22-burst interleaver 108, the Sync Word/DVCC generator
109, an equalizer 114, and a control channel message
generator 132, to integrate the various pieces of information
from these respective units into a single message burst. For
example, according to the published U.S. standard EIA/TIA
IS-54, a message burst comprises data (260 bits), SACCH
(12 bits), Sync Word (28 bits), coded DVCC (12 bits), and
the equalizer 114 to a single-bit data stream. The symbol
detector 115 in turn produces three distinct output signals.
12 delimiter bits, combined for a total of 324 bits. Under the
control of the microprocessor 130, two different types of
message bursts are generated by the burst generator 110:
control channel message bursts from the control channel
message generator 132 and voice/traffic message bursts. The
Control channel messages are sent to a control message
detector 133 which supplies detected control channel infor
mation to the microprocessor controller 130. Any speech
data/FACCH data is supplied to a modulo-two adder 107 and
a two-burst deinterleaver 116. The speech data/FACCH data
control channel message uses a TDMA time slot reserved to
a control channel, where it replaces the SACCH as well as
the speech data normally generated in a voice/traffic burst.
15
is reconstructed by these components by assembling and
rearranging information from two time slots of the received
data. The symbol detector 115 supplies SACCH data to a
22-burst deinterleaver 117. The 22-burst deinterleaver 117
reassembles and rearranges the SACCH data, which is
spread over 22 consecutive frames.
The transmission of a burst, which is equivalent to one
time slot, is synchronized with the transmission of other time
slots, which together make up a frame of information. For
example, under the U.S. standard, a frame comprises three
full-rate time slots. The transmission of each burst is
adjusted according to timing control provided by the equal
The two-burst deinterleaver 116 provides the speech
izer 114. Due to time dispersion, an adaptive equalization
data/FACCH data to two channel decoders 118. The convo
method is provided in order to improve signal quality. For
further information regarding adaptive equalization tech
lutionally encoded data is decoded using the reverse of the
niques, reference is made to U.S. patent application Ser. No.
315,561, ?led Feb. 27, 1989, and assigned to the same
assignee. Brie?y, the base station functions as the master and
the mobile station is the slave with respect to frame timing.
The equalizer 114 detects the timing of an incoming bit
stream from the base station and synchronizes the burst
generator 110. The equalizer 114 is also operable for check
ing the Sync Word and DVCC for identi?cation purposes.
The burst generator 110 is coupled to the frame counter
111 and the equalizer 114. The frame counter 111 updates a
ciphering code utilized by the mobile station for each
25
accordingly. A speech decoder 119 processes the received
speech data from the channel decoder 118 in accordance
with a speech decoder algorithm (e.g. VSELP), and gener
ates the received speech signal. The analog signal is ?nally
enhanced by a ?ltering technique. Messages on the fast
35
112 is provided for generating the ciphering code utilized by
the mobile station. A pseudo random algorithm is preferably
The output of the 22-burst deinterleaver 117 is provided
to a separate channel decoder 118. Messages on the slow
associated control channel are detected by a SACCH detec
utilized. The ciphering unit 112 is controlled by a key 113
which is unique for each subscriber. The ciphering unit 112
consists of a sequencer which updates the ciphering code.
The burst produced by the burst generator 110, is for—
tor 121, and that information is transferred to the micropro
cessor controller 130.
warded to an RF modulator 122. The RF modulator 122 is
45
1t/4-DQPSK method (1:14 shifted, Differentially encoded
Quadrature Phase Shift Keying). The use of this technique
implies that the information is differentially encoded, i.e.,
The microprocessor controller 130 controls the mobile
station activity and the base station communication, and also
handles the terminal keyboard input and display output 131.
Decisions by the microprocessor controller 130 are made in
accordance with received messages and measurements that
are made. The keyboard and display unit 131 enable infor
mation to be exchanged between the user and the base
station. The mode selection switch 134 is used to select one
2-bit symbols are transmitted as four possible changes in
phase; ‘fit/4 and i 3rt/4. The transmitter carrier frequency
supplied to the RF modulator 122 is generated by a trans
mitting frequency synthesizer 124 in accordance with the
selected transmitting channel. Before the modulated carrier
is transmitted by an antenna, the carrier is ampli?ed by a
of the four modes of operation of the mobile telephone.
The paging format followed by the pager 21 will now be
described in conjunction with FIG. 5. For a more detailed
power ampli?er 123 and passes a time switch 135. The RF 55
power emission level of the ampli?er is selected on com
mand by a microprocessor controller 130.
A receiver carrier frequency signal is generated in accor
dance with the selected receiving channel by a receiving
paging operation description, please refer to “The Book of
the CCIR Radiopaging Code No. 1,” published by the Radio
Standards Paging Group. A page transmission from the
paging network 50 includes a preamble followed by batches
of complete code words, each batch of code words starting
with a synchronization word. The preamble assists the pager
frequency synthesizer 125. Incoming radio frequency sig—
21 in obtaining bit, word, and batch synchronization. The
preamble is typically a pattern of bit reversals, e.g., 1010,
nals are received by a receiver 126. The signal strengths over
the cellular frequencies are measured by a signal level meter
129. Signal strength values are sent to the microprocessor
controller 130. An RF demodulator 127, which receives the
receiver carrier frequency signal from the receiving fre
quency synthesizer 125 and the radio frequency signal from
the receiver 126, demodulates the radio frequency carrier
associated control channel are detected by a FACCH detec
tor 120, and the information is transferred to the micropro
cessor controller 130.
transmitted frame, e.g. once every 20 ms. A ciphering unit
operable for modulating a carrier frequency according to the
above-mentioned coding principle. The received cyclic
redundancy check (CRC) bits are checked to determine if
any error has occurred. The FACCH channel decoder fur
thermore detects the distinction between the speech channel
and any FACCH information, and directs the decoders
repeated for a period of at least the number of bits making
up the duration of a batch plus a code word. The preamble
gives the pager 21 an opportunity to save battery power
65
because the receiver 22 can be turned on for a few milli
seconds and then turned off again for about one second if no
preamble is detected.
5,541,976
11
12
Code words are structured in batches which include a
The second alternative solution to call delay is to use a
synchronization code word followed by eight frames, each
voice synthesis device to inform the calling subscriber to
hang up and call again in a predetermined number of
seconds (e.g., 50 seconds) needed to page the subscriber,
when the number of page requests in the paging system is
greater than apredetermined value. This solution avoids
occupying the channel connection while a subscriber waits
frame containing two code words. The frames are numbered
0—7, and the page population is divided into eight groups.
The pager 21 is allocated to one of the eight frames
according to the three least signi?cant bits of its 21 bit
identi?cation code. For example, if the least three signi?cant
bits equal 000, that pager is allocated to the frame 0 and it
only examines address code words in that frame. Therefore,
each pager’s address code words must be transmitted only in
for the call request to be connected as well as avoids asking
the called subscriber to ring back and pay for the call.
the allocated frame. This frame structure within a batch
o?’ers another means of battery saving within the pager
because the receiver need only be turned on to monitor the
synchronization code word and its particular frame. Accord
ingly, the energy requirements are reduced considerably
when compared to that required for constant reception.
Message code words for any receiver may be transmitted in
any frame that directly follows the associated address code
word. A message may consist of any number of code words
15
From the foregoing description of the speci?c embodi
ment, others can, by applying current knowledge, readily
modify and/or adapt for various applications such speci?c
embodiments without departing from the general nature of
the invention, and, therefore, such adaptations and modi?
20
the meaning and usage of equivalents of the disclosed
embodiments. It is to be understood that the terminology
employed herein is for the purpose of description and not of
limitation.
cations should and are intended to be comprehended within
transmitted consecutively and may span one or more
batches.
What is claimed is:
Code words contain 32 bits which are transmitted with the
1. A cellular communication system, where mobile tele
most signi?cant bits ?rst. The structure of a code word is
phones
communicate with a network switching center via a
illustrated in FIG. 5. Bit 1 is ?ag bit of an address code word
corresponding base station, and used in conjunction with a
and is always a zero. This distinguishes it from a message
25
paging system, comprising:
code word. Bits 2—19 are address bits corresponding to the
18 most signi?cant bits of a 21 bit identi?cation number
a plurality of mobile radio telephones, each mobile tele
assigned to the pager. Bits 20 and 21 are two function bits
phone operating in one of multiple modes; and
which are used to select the required address from the four
a plurality of pagers, each pager transmitting and receiv
assigned to the pager. Hence the total number of addresses
ing only radio signals and being associated with but
is 223 (over eight million). Bits 22 to 31 are parity check bits,
separate from one of said plurality of mobile tele
and the ?nal bit 32 is chosen to give even parity.
phones, wherein each of said pagers comprises:
a receiver for receiving page signals and an identi?ca
tion number speci?c for the pager;
When using the above-described paging system with a
mobile in the sleep mode, the delay through the paging
system may be longer than the time a calling subscriber may
be expected to wait. This delay also affects telephone
35
control means connected to said receiver for generating
an activation signal when said mobile telephone is in
network operators that may not want to tie up resources
a ?rst mode; and
a transmitter connected to said control means for gen
waiting for the call to be connected during which they do not
receiver compensation. Two alternatives are described
erating a radio signal having a frequency different
from the radio frequencies sent between said base
station and the mobile station, modulated by a low
below which provide solutions to these problems.
First, the paging system may monitor the total number of
page requests. If this number exceeds a certain limit, one or
frequency signal which is speci?c for the pager,
several groups of mobiles may be ordered out of the sleep
mode to monitor the cellular paging channels in the con
ventional manner. In this way, the number of page requests 45
demanded of the paging system is reduced at the cost of
increased battery drain on mobiles that have been activated
for paging purposes. When the number of page requests has
wherein the radio signal includes an address of the
mobile telephone associated with the pager, wherein
each of said mobile telephones has a receiver includ
ing demodulating means for demodulating, in cor
decreased below another predetermined limit, those mobile
groups initially ordered to monitor the cellular paging chan
nels are ordered back into the sleep mode so that paging via
the conventional paging system is restored. Battery drain is
50
respondence with the modulation of said radio signal
transmitted from the pager, said radio signal from
said transmitter in the associated pager for generat
ing an activating signal in order to provide power to
the mobile telephone;
wherein said paging system comprises:
distributed evenly between the mobile groups by alternating
which group is ordered to monitor the cellular paging
channels. For example, the order to monitor the cellular 55
paging channel may be implemented as a group paging
message to reach some fraction (e.g., one-eighth), of the
paging population as speci?ed by a group identi?cation
number in addition to the individual paging and identi?ca
tion number assigned to each pager. In paging systems 60
means for monitoring a total number of page requests;
means for comparing said total number of page
requests with a predetermined limit; and
means for ordering at least one mobile telephone to
switch from said ?rst mode to a second mode when
said total number of page requests exceeds said
predetermined limit.
following the (POCSAC) standard described above, this
2. The system according to claim 1, wherein said ?rst
mode is a sleep mode.
group identi?cation number may be transmitted in the frame
associated with the pagers in question. The order to return a
mobile telephone monitors cellular paging signals transmit
3. The system according to claim 1, wherein said ordered
group of mobiles to the sleep mode via the cellular system
is accomplished by sending on the cellular paging channels
a page to a virtual mobile with the appropriate group
identi?cation number.
ted on a control channel associated with said corresponding
65
base station.
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