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Claims  |
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We claim:
1. A method of processing radiotelephone calls in at least first and second
radiotelephone systems and a central office for providing telephone
service to radiotelephones located in a geographical area, said
geographical area divided into a plurality of cells, each cell assigned a
plurality of voice radio channels, at least one paging/access radio
channel and/or at least one access-only radio channel which differ from
those radio channels assigned to adjoining cells, aid first radiotelephone
system including a plurality of out trunks, a plurality of inter-office
trunks and a plurality of fixed site radio apparatus each located in a
different cell for communicating with said radiotelephones, and said
second radiotelephone system including a plurality of in trunks, a
plurality of out trunks, a plurality of inter-office trunks and a
plurality of fixed site radio apparatus each located in a different cell
for communicating with said radiotelephones, said method comprising the
steps of:
coupling out trunks of said first radiotelephone system to the central
office;
coupling in trunks and out trunks of said second radiotelephone system to
the central office;
coupling interoffice trunks of said first radiotelephone system to
inter-office trunks of said second radiotelephone system;
locating each fixed site radio apparatus of said second radiotelephone
system with the fixed site radio apparatus of said first radiotelephone
system in the same cell;
assigning for each cell at least one access-only radio channel and at least
one of the plurality of voice radio channels for the cell to the fixed
site radio apparatus of said first radiotelephone system located in the
cell, and at least one paging/access radio channel and at least one of the
plurality of voice radio channels for the cell to the fixed site radio
apparatus of said second radiotelephone system located in the cell; and
directing a predetermined percentage of telephone calls originated by
radiotelephones from said second radiotelephone system to said first
radiotelephone system.
2. The method according to claim 1, wherein new cells are added for
expanding the geographical area and where in said locating step further
includes the step of locating fixed site radio apparatus of said second
radiotelephone system in each new cell.
3. The method according to claim 1, wherein each originating radiotelephone
sends a dialed telephone number and said directing step further includes,
at said first radiotelephone system, the steps of:
receiving a request for a voice channel form an originating radiotelephone;
assigning a voice radio channel to said originating radiotelephone; and
terminating said originating radiotelephone to an available one of the out
trunks of said first radiotelephone system or inter-office trunks of said
first radiotelephone system.
4. The method according to claim 1, wherein said directing step further
includes the step of sending a directed retry message to said originating
radiotelephone.
5. The method according to claim 1, further including the steps of:
receiving a telephone number of a radiotelephone from one of said in
trunks; and
paging the radiotelephone having the received telephone number on the
paging/access channels of each cell.
6. The method according to claim 1, wherein said radiotelephones transmit a
page response message in response to receiving a paging message, and said
paging step includes the step of sending a paging message to the the
radiotelephone having the received telephone number, said method further
including the steps of:
receiving a page response message from said paged radiotelephone; and
sending a voice channel assignment message to said paged radiotelephone if
a page response message is received.
7. A method of processing radiotelephone calls in at least first and second
radiotelephone systems and a central office for providing telephone
service to radiotelephone s locate d in a geographical area, said
geographical area divided into a plurality of cells, each cell assigned a
plurality of voice radio channels, at least one paging/access radio
channel and/or at least one access-only radio channel which differ from
those radio channels assigned to adjoining cells, said first
radiotelephone system including a plurality of inter-office trunks and a
plurality of fixed site radio apparatus each located in a different cell
for communicating with said radiotelephones, and said second
radiotelephone system including a plurality of in trunks, a plurality of
out trunks, a plurality of inter-office trunks and a plurality of fixed
site radio apparatus each located in a different cell for communicating
with said radiotelephones, said method comprising the steps of:
coupling in trunks and out trunks of said second radiotelephone system to
the central office;
coupling inter-office trunks of said first radiotelephone system to
inter-office trunks of said second radiotelephone system;
locating each fixed site radio apparatus of said second radiotelephone
system with the fixed site radio apparatus of said first radiotelephone
system in the same cell;
assigning for each cell at least one access-only radio channel and at least
one of the plurality of voice radio channel for the cell to the fixed site
radio apparatus of said first radiotelephone system located in the cell,
and at least one the paging/access radio channel and at least one of the
plurality of voice radio channels for the cell to the fixed site radio
apparatus of said second radiotelephone system located in the cell; and
directing a predetermined percentage of telephone calls originated by
radiotelephone s from said second radiotelephone system to said first
radiotelephone system.
8. The method according to claim 7, wherein new cells are added for
expanding the geographical area, and wherein said locating step further
includes the step of locating fixed site radio apparatus of said second
radiotelephone system in each new cell.
9. The method according to claim 7, wherein each originating radiotelephone
sends a dialed telephone number and said directing step further includes,
at said first radiotelephone system, the steps of:
receiving a request for a voice channel form an originating radiotelephone;
assigning a voice radio channel to said originating radiotelephone; and
terminating said originating radiotelephone to an available one of the
inter-office trunks of said first radiotelephone system.
10. The method according to claim 7, wherein said directing step further
includes the step of sending a directed retry message to said originating
radiotelephone.
11. The method according to claim 7, further including the steps of:
receiving a telephone number of a radiotelephone from one of said in
trunks; and
paging the radiotelephone having the received telephone number on the
paging/access channels of each cell.
12. The method according to claim 7, wherein said radiotelephones transmit
a page response message in response to receiving a paging message, and
said paging step includes the step of sending a paging message to the the
radiotelephone having the received telephone number, said method further
including the steps of:
receiving a page response message from said paged radiotelephone; and
sending a voice channel assignment message to said paged radiotelephone if
a page response message is received.
13. A communications system coupled to a central office for processing
radiotelephone calls, comprising, in combination:
first and second radiotelephone systems for providing telephone service to
radiotelephones located in a geographical area, said geographical area
divided into a plurality of cells, each cell assigned a plurality of voice
radio channels, at least one paging/access radio channel and/or at least
one access-only radio channel which differ from those radio channels
assigned to adjoining cells;
said first radiotelephone system including:
a plurality of inter-office trunks; and
a plurality of fixed site radio apparatus each located in a different cell
for communicating with said radiotelephones, each fixed site radio
apparatus of said first radiotelephone system being assigned at least one
access-only radio channel and at least two of the plurality of voice radio
channels for the cell in which it is located;
said second radiotelephone system including;
a plurality of in trunks and a plurality of out trunks coupled to the
central office;
a plurality of inter-office trunks coupled to inter-office trunks of said
first radiotelephone system; and
a plurality of fixed site radio apparatus each located in a different cell
for communicating with said radiotelephones, each fixed site radio
apparatus of said second radiotelephone system being assigned at least one
paging/access radio channel and at least two of the plurality of voice
radio channels for the cell in which it is located, and each fixed site
radio apparatus of said first radiotelephone system being located with the
fixed site radio apparatus of said second radiotelephone system in the
same cell. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
The present invention generally relates to radiotelephone communication
systems and more specifically to a method and apparatus for
interconnecting two or more cellular radiotelephone systems covering the
same geographical area.
Mobile radiotelephone service has been in use for some time and
traditionally has been characterized by a central site transmitting by way
of high-power transmitters to a limited number of mobile or portable
radiotelephones in a large geographic area. To avoid repetition, the word
"mobile" will be used hereinafter to mean mobile and/or portable
radiotelephones. Mobile transmissions, due to their lower power
transmitters, were generally received in previous systems by a network of
satellite receivers remotely located from the central site for receiving
and relaying mobile transmissions to the central site for processing. In
previous systems only a limited number of radio channels were available,
thus limiting the number of radiotelephone conversations in an entire city
to the specific number of available channels.
Modern cellular radiotelephone systems have a comparatively large number of
radio channels available which, further, can be effectively multiplied by
reuse of the radio channels in a geographical area, such as the
metropolitan area of a large city like Chicago or New York, by dividing
the radio coverage area into smaller coverage areas called "cells" using
low power transmitters and coverage restricted receivers. Such cellular
systems are further described in U.S. Pat. Nos. 3,906,166 and 4,268,722.
The limited coverage area enables the radio channels used in one cell to
be reused in another cell geographically separated according to a
predetermined plan, such as a four cell pattern shown and described in
U.S. Pat. No. 4,128,740. In this four cell pattern, each cell is assigned
a subset of the available radio channels and reuse of the radio channels
is accomplished by repeating the pattern throughout a geographical area.
A cellular system typically utilizes a pair of radio frequencies for each
radio channel in each cell. Each cell is assigned at least one
paging/access channel and several voice channels The paging/access channel
is dedicated to controlling the operation of the mobiles by means of data
messages transmitted to and received from the mobiles. Control functions
performed include paging selected mobiles, receiving requests for service
from mobiles, instructing mobiles to tune to a voice channel where a
conversation may take place, identifying the particular system to the
mobiles, and enabling mobile registration by which process the mobiles
identify themselves to the system. The data message and radio channel
specifications for U.S. cellular radiotelephone systems are set forth in
Electronic lndustries Association (EIA) lnterim Standard IS-3 implemented
in accordance with 47 CFR 22 and the Report and Orders pertaining to
Federal Communications Commission Docket 79-318. Copies of EIA Interim
Standard IS-3 may be obtained from the Engineering Department of the
Electronic Industries Association at 2001 Eye Street, N.W., Washington,
D.C. U.S.A. 20006.
A cellular system can grow by adding more voice channels to existing cells,
subdividing existing cells into smaller cells and adding new cells until
the call switching capacity of the cellular system control terminal is
consumed, or until the traffic density limit inherent in the particular
frequency re-use pattern is reached. At that point, additional switching
capacity is required for further growth, or a different frequency re-use
pattern must be adopted. When the original equipment manufacturer for the
system is unable to supply switching equipment with higher capacity or a
frequency re-use pattern with a higher inherent density, the only recourse
is to incorporate equipment from a different manufacturer or to curtail
further growth. Since signalling protocols between cells and the cellular
system control terminal are proprietary to each equipment manufacturer,
growth by interconnection of different manufacturers' control terminal
equipment and cell equipment is not possible. Accordingly, there is a need
for an improved method and apparatus for interconnecting two or more
cellular system covering the same geographical area in order to
accommodate cellular system growth, or to allow graceful transition to
equipment supplied by a different manufacturer which may offer more useful
performance or other characteristics.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide an improved
method and apparatus for interconnecting cellular systems covering the
same geographical area in order to accommodate cellular system growth.
It is a further object of the present invention to provide an improved
method and apparatus for sharing the radiotelephone traffic load between
interconnected cellular systems covering the same geographical area.
Briefly described, the present invention encompasses an improved method of
processing radiotelephone calls in at least first and second
radiotelephone systems coupled to a central office for providing telephone
service to radiotelephones located in the same geographical area. The
geographical area is divided into a plurality of cells each assigned a
plurality of voice radio channels, at least one paging/access radio
channel and/or at least one access-only radio channel which differ from
those radio channels assigned to adjoining cells. The first radiotelephone
system including a plurality of inter-office trunks and fixed site radio
apparatus for communicating with said radiotelephones, and the second
radiotelephone system including a plurality of in trunks, out trunks,
inter-office trunks and fixed site radio apparatus for communicating with
said radiotelephones. The novel method comprises the steps of: coupling in
trunks and out trunks of said second radiotelephone system to the central
office; coupling the said first radiotelephone system to the said second
radiotelephone system by means of inter-office trunks using standard
channel-associated supervisory signalling and standard multi-frequency
address signalling or other equivalent signalling methods accommodated by
both said radio telephone systems; locating fixed site radio apparatus of
said second radiotelephone system with fixed site radio apparatus of said
first radiotelephone system in each cell; assigning the access-only radio
channels and at least two of the plurality of the voice radio channels to
the fixed site radio apparatus of said first radiotelephone system located
therein, and the paging/access radio channels and at least two of the
plurality of the voice radio channels to the fixed site radio apparatus of
said second radiotelephone system located therein to each cell; arranging
the information contained in the data messages transmitted by the fixed
site radio apparatus of the said first and second radiotelephone systems
on the access-only and the paging/access radio channels, respectively, so
that mobile stations in the idle state always monitor the paging/access
radio channels controlled by the said second radiotelephone systems;
processing all land-originated calls to mobile stations through said
second radiotelephone system, transmitting all pages on the paging/access
radio channels controlled by said second radiotelephone system; receiving
all page responses from mobile stations via the paging/access radio
channels and processing those responses in said second radiotelephone
system; receiving all mobile-originated calls via the paging/access
channels controlled by the said second radiotelephone system; and
redirecting a dynamically selectable percentage of telephone calls
originated by radiotelephones from said second radiotelephone system to
said first radiotelephone system by Way of the access-only radio channels.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of two interconnected cellular radiotelephone
systems covering substantially the same geographical area.
FIG. 2 is a block diagram of the equipment which would be employed in a
conventional center illuminated sector cellular system.
FIG. 3 is a block diagram of the control terminal in FIG. 2.
FIG. 4 is a block diagram of the base sites in FIG. 2.
FIG. 5 shows a flow diagram executed by a mobile for scanning the
paging/access channels in the cellular systems in FIG. 1.
FIGS. 6A and 6B show a flow diagram executed by a mobile for a page
response and a flow diagram executed by a mobile for an, origination
access, respectively, in the cellular systems in FIG. 1.
FIGS. 7A and 7B show a flow diagram executed by the M-system base site
controllers in FIG. 1 for processing calls.
FIGS. 8A and 8B show a flow diagram executed by the M-system control
terminal in FIG. 1 for processing calls.
FIG. 9 shows a flow diagram executed by the M-system control terminal in
FIG. 1 for disconnecting a call.
FIG. 10 shows a flow diagram executed by the M-system control terminal in
FIG. 1 for terminating a call.
FIG. 11 shows a flow diagram executed by the X-system control terminal in
FIG. 1 for processing calls.
FIG. 12 shows a flow diagram executed by the X-system control terminal in
FIG. 1 for disconnecting a call.
FIG. 13 shows a flow diagram executed by the X-system control terminal in
FIG. 1 for terminating a call.
FIG. 14 shows a diagram of the overhead message train.
FIG. 15 shows a diagram of a portion of the mobile memory.
FIG. 16 shows a diagram of the directed re-try message.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
In FIG. 1, there is illustrated two interconnected cellular systems 101 and
102, each covering the same geographical area, such as the metropolitan
area of a large city. Cellular system 102, referred to as X-system, is an
existing cellular system which, for purposes of discussion, shall be
assumed to be lacking in additional switching capacity for further growth.
X-system 102 may be any conventional cellular system currently
commercially available from a number of different manufacturers. X-system
102 includes control terminal 120 and illustrative base sites 121-124 in
cells 401-404, respectively, for providing telephone service to mobiles
131 in its geographical area. X-system 102 may grow by adding more voice
channels to existing cells 401-404, subdividing existing cells 401-404
into smaller cells, and/or adding new cells until the switching capacity
of its control terminal is consumed. Further growth is then possible only
by adding additional switching capacity, which currently may be
implemented only by replacing the existing control terminal of the
X-system 102 with a control terminal having greater switching capacity at
substantial costs in terms of money and cellular service interruptions.
However, by utilizing the present invention, switching capacity may be
added to X-system 102 by interconnecting it with another cellular system,
such as M-system 101 in FIG. 1. Interconnecting systems 101 and 102
increases available switching capacity, while at the same time, existing
control terminal 120 and base sites 121-124 continue to be used, the new
M-system can be phased in gradually, and mobile service is not affected
and need not be interrupted.
Referring to FIG. 1, M-system 101 includes control terminal 420 and
illustrative base sites 411-415 in cells 401-405, respectively, for
providing telephone service to radiotelephones in the same geographical
area covered by X-system 102. Control terminal 420 of M-system 101 may be
located (e.g., colocated on the same or different floors of a building or
colocated in adjacent buildings) with control terminal 120 of X-system 102
and interconnected by conventional inter-office trunks 150 using standard
channel-associated supervisory signalling and standard multi-frequency
address signalling or other equivalent signalling methods accommodated by
both systems 101 and 102. Out trunks 159, if used, (conventional telephone
trunks) of X-system control terminal 120 are connected to central office
110, and all in trunks of X-system control terminal 120 are disconnected
and not used. Out trunks 155 and in trunks 157 of M-system control
terminal 420 are connected to central office 110. As a result, all land
originations are routed by central office 110 only to M-system control
terminal 420.
Base sites 411-414 of M-system 101 in FIG. 1 are located With or adjacent
to corresponding existing base sites 121-124 of X-system 102. That is, for
example, base site 411 of M-system 101 may be colocated with base site 121
of X-system 102 for covering cell 401. New cells may be added by means of
additional base sites, such as base site 415, which are connected only to
M-system control terminal 420. A previously explained, each cell is
assigned at least one paging/access channel and several voice channels. In
U.S. cellular systems, twenty-one channels have been reserved for
paging/access channels. For the interconnected systems 101 and 102 in FIG.
1, nine paging/access channels may be assigned to base sites 121-124 of
X-system 102 and nine paging/access channels may be assigned to base sites
411-415 of M-system 101 (having three paging/access channels unused) where
a nine cell pattern of channel reuse is adopted (see U.S. Pat. No.
4,128,740 for an explanation of re-use of channels in cellular systems).
Mobiles identify the paging/access channels (see FIG. 5) by reading the
overhead message train (see FIG. 14) received from the strongest of the
twenty-one channels.
In the interconnected systems 101 and 102 in FIG. 1, the assignment of
paging/access channels is further characterized in that, according to the
present invention, the nine channels assigned to base sites 121-124 of
X-system 102 are access-only channels, and the nine channels assigned to
to base sites 411-415 of M-system 101 are paging/access channels. As a
result, all mobile originations are made to base sites 411-415 of M-system
101. M-system 101 process all mobile originations and transfers a
percentage of the mobile originations to X-system 102 by sending a
directed retry message to the originating mobile. The percentage of calls
transferred by M-system 101 to X-system 102 can be preselected to provide
X-system 102 with a desired traffic load or may be dynamically varied
depending on parameters selected by the system operator and the actual
traffic load of both systems 101 and 102. Upon receipt of the directed
retry message, the originating mobile scans and selects one of the nine
access-only channels of base sites 121-124. As a result of this unique
operating mode of systems 101 and 102, all incoming traffic from central
office 110 is processed by M-system 101 and the outgoing traffic from
mobiles is split between them M-system 101 and X-system 102.
The operation of interconnected systems 101 and 102 can be summarized by
the following process steps which take place during mobile turn on, land
originations and mobile originations. When the mobile is first turned on,
all twenty-one paging/access channels are scanned and the strongest is
selected. The overhead message train (see FIG. 14) transmitted on the
selected paging/access channel is read and used to obtain the channel
numbers of the paging channels, which will be the paging/access channels
of base sites 411-415. The mobile then scans the paging channels, selects
the strongest paging channel and reads the overhead message thereon. The
overhead message on the strongest paging channel is used to obtain the
channel numbers of the access channels, which again will be the
paging/access channels of base sites 411-415. Thus, for paging and access
purposes, mobiles will always use the paging/access channels of base sites
411-415 in M-system 101. The foregoing process is described in more detail
hereinbelow with respect to FIGS. 5 and 6.
For land originations, an incoming call is routed via in trunks by central
office 110 to M-system control terminal 420. The dialed digits of the
incoming call are received and translated by M-system control terminal.
The translated mobile number corresponding to the dialed digits is
validated in the subscriber data base and the mobile is paged in all
cells. If the mobile receives the page, it responds on a paging/access
channel of one of the base sites 411-415. The foregoing process is
described in more detail hereinbelow with respect to FIGS. 8-10.
Mobile originations may result in a land termination or a mobile
termination. For mobile originations, a mobile selects a paging/access
channel of M-system base sites 411-415. According to the present
invention, M-system base sites 411-415 transfer a dynamically selected
percentage of the mobile originations to X-system 102 as shown in FIG. 7.
If the mobile origination is not transferred, M-system control terminal
420 may then process the mobile origination as shown is FIGS. 8-10. If the
mobile origination is transferred to X-system 102, X-system control
terminal 120 may then process the mobile origination as shown is FIGS.
11-13.
Referring now to FIG. 2, there is illustrated a block diagram of cellular
system 101 and 102 in FIG. 1. Such cellular systems 101 and 102 are
further described in U.S. Pat. Nos. 3,906,166 and 4,268,722 each assigned
to the assignee of the present invention and incorporated herein by
reference and in an experimental cellular radiotelephone system
application filed under FCC Docket No. 18262 With the Federal
Communications Commission by Motorola and American Radio-Telephone
Service, Inc., in Feb. 1977. Such cellular systems provide telephone
coverage to mobiles located throughout a large geographical area, such as
the metropolitan area of one or more large cities. Mobiles may be cellular
radiotelephones of the type described in U.S. Pat. Nos. 4,486,624,
3,962,553 and 3,906,166 each assigned to the assignee of the present
invention and incorporated herein by reference, and in Motorola
instruction manual number 68P81039E25, published by Motorola Service
Publications, Schaumburg, Ill., in 1979. Mobiles are commercially
available in the U.S. from a number of cellular radiotelephone suppliers.
Although FIG. 2 shows three center-illuminated sector cells, it is obvious
that a person skilled in the art may be able to apply the essence of the
present invention to other types of cellular configurations such as, for
example, omnidirectional-illuminated or corner-illuminated cellular
configurations.
As illustrated in FIG. 2, the geographical area is subdivided into
illustrative cells 401-403 which are illuminated with radio frequency
energy from base sites 411-413. Each base site 411-413 is coupled by data
and voice lines to a radiotelephone control terminal 420 which may be
similar to the terminals described in aforementioned U.S. Pat. Nos.
3,906,166 and 4,268,722. These data and voice lines may be provided by
dedicated wire lines, pulse code modulated carrier lines, microwave radio
channels, or other suitable communication links. Control terminal 420 is,
in turn, coupled to the existing telephone network via a conventional
telephone central office 110 for completing telephone calls between
mobiles and landline telephones. Control terminal 420 may include its own
subscriber data base Which includes subscriber identification and billing
information or may also be coupled by data lines to a remote subscriber
data base 430.
A functional block diagram of a typical control terminal 420 is shown in
FIG. 3. This control terminal may be an EMX 100 available from Motorola,
Inc. or any other suitable commercially available equivalent. Basically,
the control terminal consists of a central processor (CCP) 602, a switch
control unit and switch 604, group multiplexer unit 606, voice group units
608-610, tone signalling unit 612, maintenance and status unit 614, data
acquisition subsystem 616, communications interface 618, modems 620,
real-time clock 622, cell data base 624 and subscriber data base 626. Cell
data base 624 includes data identifying border cells, adjacent cells and
lists of paging/access channels for directed retrys. Subscriber data base
626 includes data identifying valid subscriber identification numbers and
other subscriber related information. Communications over the data lines
to each BSC, cellular system and remote subscriber data base may be
accomplished via conventional modems 620 using any conventional
communications protocol such as Advanced Data Communications Control
Procedures (ADCCp).
The interconnection between control terminal 420 and the base sites 401-403
is further shown in FIG. 4. The interconnection may be on a line per
channel basis or a pulse-code-modulation (PCM) group basis. Either type of
interconnection is well known in the art. A separate data line, such as,
for example, a standard telephone line or other communications link
capable of carrying high-spaced data, is extended between the control
terminal 420 and each base site 401-403.
Referring to FIG. 4, each of the base site 411-413 includes a base site
controller (BSC) 950, a scanning receiver 910, a signalling transceiver
912 for operating on at least one duplex paging/access channel, a
plurality of voice channel transceivers 901-908 for operating on
corresponding duplex voice channels, receiving antennas 930, transmitter
combiner 920, and transmitter antenna 922. Voice channel transceivers
901-908 may be located substantially at the center of each of the
corresponding cells 401-403. The transmitters of signalling transceiver
912 and voice channel transceivers 901-908 may be combined by conventional
combiner 920 onto one omni-directional antenna 922, while the signalling
receiver 912 and receivers of voice channel transceivers 901-908 and
scanning transceiver 910 may be selectively intercoupled to two or more
directional or omni-directional antennas 930. Alternatively, in other
conventional embodiments, each transmitter of signalling transceiver 912
and voice channel transceivers 901-908 may also be coupled to two or more
directional antennas.
Antennas 930 in FIG. 4 may be implemented with six 60.degree. sector
antennas. Each sector antenna 930 primarily covers a portion of a cell as
shown in dashed lines in FIG. 2 and typically has a coverage area that
overlaps the coverage area of adjacent sector antennas. Since the
paging/access channel generally requires an omni-directional receiving
pattern, the signals received by the six sector antennas 930 may be
combined in signalling transceiver 912 by means of a maximal ratio
predetection diversity combiner, as illustrated and described in U.S. Pat.
Nos. 4,369,520 and 4,519,096 each assigned to the assignee of the present
invention and incorporated herein by reference. Furthermore, signalling
transceiver 912 may provide coverage of a portion of a cell by selectively
combining the signals received by two or more of the sector antennas 930.
The sector antennas 930 and associated receiving apparatus may be of the
type shown and described in U.S. Pat. Nos. 4,101,836, 4,317,229 and
4,549,311 each assigned to the assignee of the present invention and
incorporated herein by reference.
The base site equipment in FIG. 4 and its operation is described in further
detail in U.S. Pat. No. 4,485,486; in the instant assignee's copending
Pat. application Ser. No. 829,872, filed Feb. 18, 1986, entitled "Method
and Apparatus for Signal Strength Measurement and Antenna Selection in
Cellular Radiotelephone Systems", invented by Barry J. Menich et al.; in
the instant assignees copending patent application Ser. No. 925,427, filed
Oct. 31, 1986, entitled "Networked Cellular Radiotelephone Systems" and
invented by Michael Burke et al.; and in the instant assignees copending
patent application Ser. No. 37,268, filed Apr. 10, 1987, entitled
"Registration of Radiotelephones in Networked Cellular Radiotelephone
Systems" and invented by James M. Williams; all incorporated herein by
reference. Furthermore, the base site equipment illustrated in FIG. 4 is
commercially available from Motorola, Inc. and employs transceivers of the
type described in Motorola Instruction Manual No. 68P81060E30, published
by Motorola Service Publications, 1301 East Algonquin Road, Schaumburg,
Ill. in 1982.
Referring to FIG. 5, there is illustrated a flow diagram executed by
mobiles for scanning and selecting paging/access channels during
initialization and for receiving or initiating calls in cellular systems
101 and 102. The process in FIG. 5 is entered at START block 201 when the
mobile is turned on. At block 202, the mobile scans a predesignated group
of twenty-one dedicated control channels, which in systems 101 and 102
Will be the paging/access channels of base sites 411-415. The mobile
selects and tunes to the selected strongest paging/access channel and
reads the overhead message train (OMT) thereon. The overhead words inform
the mobile how the system is configured and how the mobile is to use the
system. Referring to FIG. 14, the OMT 1300 is transmitted on paging/access
channels throughout the cellular system service area, nominally once each
second, and include s a system parameter message SID, RECH and REGR 1301
plus, optionally, several other messages of Which the registration ID
message REGID 1302 and the re gistration increment message REGINCR 1303
are relevant to the mobile registration process. The mobile registration
process is described in more detail in my copending patent application
Ser. No. 37,268 , entitled "Registration of Radiotelephones in Networked
Cellular Radiotelephone Systems", filed on April 10, 1987 and assigned to
the instant assignee.
The purpose of registration is to permit calls to a mobile to be
automatically delivered, even though the mobile may be moving from place
to place through the cellular system. Registration may be enabled or
disabled individually for each class of mobile, e.g. home or roam, by
means of control bits REGH and REGR in the system parameter overhead
message 1301 in FIG. 14. Message 1301 also contains the identification of
the serving cellular system (SID) by means of which the mobile determines
whether it is a "home" or a "roam" mobile. Each mobile contains, in its
internal memory 1400 shown in FIG. 15, an entry 1420 indicating its home
cellular system (SIDH) and entries 1420-1423 indicating the four cellular
systems (SID1-SID4) in which it most recently registered successfully,
along with a value for each cellular system (NXTREG) used to determine
when it is scheduled to re-r | | |
