Note: Descriptions are shown in the official language in which they were submitted.
CA 02245801 2000-11-02
1
ROUTING CELLULAR TELEPHONE CALLS
The present invention relates to cellular telephone systems, and
particularly to the provision of a communication path between a mobile
telephone
and a cellular telephone call-switching system. A cellular telephone system
has a
system of "cells" which are geographical areas, each of which is associated
with a
radio base station. As the mobile unit moves from one cell to another, radio
contact is 'handed-over' from one radio base station to another.
As the usage of mobile telephones increases, the provision of acceptable
quality of service to subscribers becomes increasingly difficult as the demand
for
radio channels exceeds the availability of channels allocated to network
operators.
The allocation of radio frequency (r.f.) spectrum to different services is
carried out
by national governments which operate within the framework set by the WARC
(World Administrative Radio Conference). Furthermore, expansion of the
allocated
1 5 band" beyond a certain size would cause technical problems far the design
of _
mobile telephones. In particular, there would be the problem of providing
effective
broadband frequency synthesizers, r.f. amplifiers and antennas.
It is an aim of the present invention to overcome the aforementioned problem
by
providing'an additional communication path independent of the system of cells
of the
cellular telephone system. It is known to provide a mobile telephone which is
also capable
. of operation according to a cordless radio standard (e.g. OECT) to a nearby
radio base
station, or to a fixed (PSTN) line dedicated to the user or a specified group
of users.
Examples of the latter are to be found in IBM Technical Disclosure Vol 38 No 6
and
European patent Application EP0660628 (Nokia), both published in 1995.
However, such
systems require a separate user subscription on the fixed network, and an
associated
separate network identity (telephone number), requiring call diversion
arrangements to be
set up to allow the user to be contacted. The cordless examples also require
their own
allocation of radio frequency spectrum, and so they do not overcome the
fundamental
Problem of limited radio spectrum.
According to a first aspect of the invention, there is provided a cellular
telephone system
comprising a system of cells, each cell comprising a radio base station
between a mobile telephone and
a cellular telephone call-switching system, the communication path comprising
an interface means for
providing a comrtwnications connection between a mobile telephone and the
cellular telephone call-
switching system so as to by-pass the telephone's radio antenna.
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t
2
In another aspect, the invention comprises an interface apparatus for
providing a
communications connection between a mobile telephone and a cellular telephone
call-
switching system so as to by-pass the telephone's radio antenna, the apparatus
comprising a first connector for exchanging speech and data signals with a
cellular mobile
telephone, a second connector for connecting the apparatus to a transmission
line, and
means for exchanging said speech and data signals via the second connector.
In a further aspect, the invention comprises a telephone for a cellular
telephone
system including processing circuitry and an externally accessible connector,
the
connector being coupled to the processing circuitry to exchange baseband
speech and
1 O data signals therewith, and having radio frequency transceiver circuitry
for coupling to the
processing circuitry to exchange baseband speech and data signals therewith,
the
processing circuitry including means for detecting whether the externally
accessible
connector is in communication with a complementary connector, and switch means
under
the control of the processing circuitry to disconnect the processing circuitry
from the
1 5 transceiver circuitry when the externally accessible connector is so
connected wherein-the
first connector communicates with the mobile telephone by means of an
electrical
connection, further comprising a power supply connection for supplying
electrical power
to the mobile telephone through the electrical connection.
Preferably, such a telephone includes r.f. circuitry for transmitting and
receiving
20 speech and data signals, and a further externally accessible connector and
switching
means, wherein the switching means is responsive to a signal applied to the
further
connector to disable the r.f. circuitry.
In a further aspect, the invention comprises a method of connecting a mobile
telephone to the call-switching system of a cellular telephone system
comprising the step
25 of establishing an additional communication path, independent of the system
of cells of
the cellular telephone system, between the mobile telephone and a fixed part
of the
cellular telephone system, by putting the mobile telephone in communication
with an
interface means, the interface means being connected to the call-switching
system of the
cellular telephone system by a communications path.
30 The interface apparatus may provide a communications connection to the
mobile
telephone for baseband speech and control data signals. In this case, the
interface means
may comprise a modem for transmitting the speech and control data over longer
distances. The modem may include dialling means so that a switched network,
e.g. PSTN
(public switched telephone network) or ISDN (integrated services digital
network), may be
35 used for the communications path. Alternatively, the communications path
may comprise
a fixed point-to-point signal path. This could be a leased line, a permanent
ISDN
connection, a cable television (CATV) transmission line or a microwave link.
AMEMDED SHEEN
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Advantageously, the interface means is arranged for connecting a plurality
of mobile telephones to the cal! switching system and the bandwidth of the
' communications path is sufficient for a plurality of simultaneous calls.
In order for the present invention to be implemented with existing mobile
telephone equipment, the interface means may provide a connection with the
r.f.
circuitry of a mobile telephone, for carrying r.f. speech and data signals.
Some
handheld telephones are already provided with an r.f. connector to enable them
to
be used with adaptors for vehicle-mounted operation.
Preferably, the communication path includes a transmission line and the
interface means comprises means for connecting the telephone's r.f. circuitry
to
the transmission line. More preferably, the communication path comprises a
point
to-point microwave link and transposer means for transposing the signals on
the
transmission fine to the operating band of the microwave link and transposing
signals received from the microwave link to the operating band of the mobile
'I5 telephone and applying them to the transmission line. Thus, the telephone
and a
BTS (base transceiver site) substitute, providing connection to the mobile
telephone call switching system, may both operate with substantially unchanged
software. In practice, only the BTS software would need to be changed and then
primarily only in respect of the control of its frequency synthesizers.
However,
even this change could be avoided if a transposer means were to be used at the
BTS. If the "BTS" is connected directly to the transmission line, the
transpaser
means can be dispensed with.
Advantageously, the interface means provides a communications
connection to the transmission sine from the r.f. circuitry of a plurality of
mobile
telephones.
Preferably, the interface means is provided with user input means to
enable the telephone or ISDN (Integrated Services Digital Network) number of a
BTS to be entered. In the simplest case, this could merely be a numerical key
pad.
However, the service provider may wish to keep the telephone or ISDN numbers
of
its BTSs secret. In this case, the interface means could be programmed with a
' table of encrypted numbers. The correct number could then be retrieved and
decrypted on the basis of a postcode or zip code entered by a user. A furl:her
option would be for the user to be instructed to call a central station using
his
mobile telephone. The cellular system can identify the location of the mobile
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1 . 1-
telephone in the cellular network and can then download the correct BTS
telephone
number or ISDN number to the mobile telephone. Connecting the mobile telephone
to the interface means for the first time would cause the mobile telephone to
transfer the downloaded number to the interface means.
In a multi-user embodiment, the interface apparatus may comprise one or
more further communications connectors for receiving baseband speech and data
signals from one or more further cellular mobile telephones, and a multiplexer
for
multiplexing signals from the first and further connectors, the modem being
arranged for transmitting the output of the multiplexer.
. Preferably, the interface apparatus includes control means and dialling
means, wherein the control means is responsive to cellular telephone data
signals
from the first connector (and further connectors, if provided) to cause the
dialling
means to output telephone or ISDN dialling signals via the second connector.
In most of the embodiments to be described below, a mechanical/electrical
plug and socket connection is used to provide the communications connection
between the telephone and interface unit, which may also provide a power
supply
to the telephone. However, connection may instead be provided by means of an
optical (e.g. infra-red) or ultrasonic beam, carrying either a, digital signal
(e.g.
according to the IrDA (Infra-red data access) standard, originally developed
for use
in connecting portable computers to printers etc), or an analogue signal.
Embodiments of the present invention will now be described, by way of
example, with reference to the accompanying drawings, in which:
Figure 1 is a block diagram of a mobile telephone according to the present
invention;
Figure 2 is a block diagram of an interface unit complementary to the
mobile telephone of Figure 1 , according to the present invention;
Figure 3 is a block diagram of the fixed elements of a cellular telephone
system according to the present invention;
Figure 4 is a block diagram of a call processing apparatus of a base
transceiver site according to the present invention;
Figure 5 illustrates the frame structure of the output from the interface
unit of Figure 2;
- AIV~F_t~lG~'~~ ~i-i~~ ~
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Figure 6 is a block diagram of another embodiment of a subscriber
installation according to the present invention;
' Figure 7 is a block diagram of one of the remote parts of the interface
system of Figure 6;
5 Figure 8 is a block diagram of a central part of the interface system ofi
Figure 6;
Figure 9 is a block diagram of another cellular telephone according to the
present invention; and
Figure 10 is a block diagram of an interface unit complementary to the
cellular telephone of Figure 9, according to the present invention.
Figure 1 1 is a block diagram of another cellular telephone according to the
present invention;
Figure 12 is a block diagram of a remote part of an interface system for
use with the telephone of Figure 1 1;
Figure 13 is a block diagram of a subscriber installation for use with the
telephone of Figure 11 and interface system of Figures 12 and 14;
Figure 14 is a block diagram of the central part of the interface system of
the subscriber installation of Figure 13;
Figure 15 is a block diagram of a cellular telephone system which uses the
telephone of Figure 11;
Referring to Figure 1, a GSM (Global System for Mobile communication)
cellular telephone 1 comprises r.f. transceiver circuitry 2 coupled to an
antenna 3,
baseband signal processing and control circuitry 4, a rechargeable battery
pack 5,
a switch 6 and a socket 7. The processing and control circuitry 4 has a data
output terminal coupled to both the r.f, transceiver circuitry 2 and a first
contact
7a of the socket 7. A data input terminal 4b of the processing and control
circuitry 4 is coupled to the r.f. circuitry 2 and a second contact 7b of the
socket
7. A third contact 7c of the socket 7 is coupled to a control input of the
- processing and control circuitry 4. The battery pack 5 is connected to
fourth and
fifth contacts 7d, 7e of the socket 7, which are respectively for OV and + V
power
' supply tines, for powering the telephone 1 and recharging its batteries. The
+ V
terminal of the battery pack 5 is also connected to the processing and control
circuitry 4 and to an input terminal of the switch 6. The output terminal of
the
switch 6 is coupled to a -t- V input terminal of the r.f. circuitry 2. A
control
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6
terminal of the switch 6 is coupled to an output of the processing and control
circuitry 5.
Referring to Figure 2, an interface unit 1 1 comprises a control circuit 12, a
user input unit 13, including a keypad and a display, a V.24 9.6 kbit/s modem
14,
a power supply unit 15 and a plug 16. The plug 16 has five contacts 16a-16e
which correspond to contacts 7a-7e of the socket 7 of the cellular telephone
1.
The first contact 16a of the plug 16 is coupled to a data input terminal of
the
control circuit 12 and the second contact 16b of the plug 16 is coupled to a
data
output terminal of the control circuit 12. A bi-directional serial link 18 is
provided
between the control circuit 12 and the modem 14 for modem control and data
signals. The third contact 16c and fifth contact 16e of the plug 16 are
coupled to
the + V output of the power supply unit 15. The fourth contact 16d of the plug
16 is coupled to the interface unit's OV supply wiring. The user input unit 13
is
coupled to the control circuit 12 for the input of user commands and the
output of
1 5 display control signals from the control unit 12 to the user input unit
13. The + V
output of the power supply unit 15 is also coupled to + V input terminals 12a,
13a, 14a of the control circuit 12, the user input unit 13 and the modem 14.
The
modem 14 is coupled to a telephone line 17 and the power supply unit 15 is
arranged to receive power from a mains electricity supply 19.
Referring to Figure 3, a BTS (base transceiver site) of a GSM cellular
telephone system comprises a mast 22, supporting one or more antennas 23, and
a call processing 'apparatus 24. The call processing apparatus 24 is connected
to
the antenna 23, a telephone line 25 and, in the conventional manner, to a BSC
(base
station controller) 26. The BSC 26 is linked, also in the conventional manner,
to a MSC
(mobile switching centre) 27 which connects the GSM cellular telephone system
to the
PSTN.
Referring to Figure 4, the call processing apparatus 24 comprises a
controller 30, r.f. transceiver circuitry 31 coupled to the antenna or
antennas 23,
and a V.24 9.6 Kbit/s modem 32. The modem 32 is connected to the telephone
line 25. The operation of the cal! processing apparatus 24 is substantially
conventio~;al. There may be a plurality of telephone lines and associated
modems.
However, only one of each is shown in the interests of clarity.
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7
Referring to Figure 5, communication between the interface unit 11 and
the BTS 21 uses a TDM (time-division multiplex) scheme wherein one in eight
slots
is used for the BCCH (broadcast control channel) and the other slots are used
for a
TCH (traffic channel).
The departures from the conventional operation of a GSM BTS
will
become apparent from the following description of the operation
of the system
shown in Figures 1 to 5. As shown in Figure 1, the interface
unit 1 1 is located at a
subscriber's home or office. in order to make the interface
unit 1 1 ready for use, it
must be programmed with its own telephone number and the telephone
number of
the BTS 21. Typically, the BTS 21 will be nearby, in order
to minimise telephone
charges. However, if the local BTSs are all heavily used,
for example in a city
centre, the telephone number of a more lightly used BTS, for
instance one in a
rural area, could be programmed into the interface unit 11.
The entry of the
telephone number is effected using the user input unit 13.
Programming of
apparatus for automatic diafiing of telephone numbers is well-known
in the art.
Different BTSs, and therefore different telephone numbers,
could be used
according to the time of day, to make use of spare capacity
available at different
times at different BTSs.
While the subscriber is on the move, his mobile telephone
1 interacts with
the GSM network in the usual manner. However, when he arrives
at a location
having an interface unit 1 1, he connects the plug 16 of the
interface unit 11 to i:he
socket 7 on his telephone 1 by a cable (not shown). Assuming
that the interface
unit 11 is powered up, the voltage on the third contact 7c
of the socket 7 is
detected by the processing and control circuitry 4 which thereby
determines that
the telephone 1 has been connected to the interface unit 11.
The connection of
the battery 5 to the power supply 15 by way of the connections
7d/16d and
7e/16e also allows the battery to be recharged.
Once the processing and control circuitry 4 has determined
that the
telephone 1 has been connected to the interface unit 1 1,
it sends a control signal
to the switch 6, causing it to open, isolating the r.f. circuitry
2 from the battery
' pack 5 and the power supply 15 in the interface unit 11. The
processing and
control circuitry 4 also responds to the voltage on the third
contact 7c of the
socket 7 by selecting alternative control programs or constant
data to allow for
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delays in the signal path from the telephone 1 to the controller 30 which are
caused by the use of the PSTN and the modems 14, 32.
If the telephone 1 is switched off when it is connected to the interface
unit 1 1, it must register with the cellular telephone network. To do this,
the
processing and control circuitry 4 produces the conventional GSM registration
signal. The registration signal is not transmitted from the antenna 3 because
the
r.f. circuitry 2 is disabled. Instead, it is output to the interface unit 1 1
via the first
contacts 7a, 16a of the socket 7 and plug 16.
The control circuit 12 detects the registration signal and identifies it as
such. In response to the registration signal, the control circuit ] 2
instructs the
modem 14 to dial the telephone number of the BTS 21.
The controller 30 is notified by the modem 32 of the ring signal on the
telephone line 25 and sends an "answer" command to the modem 32. Before
proceeding further, the BTS 21 carries out a call screening process to check
that
the calling party is in fact an interface unit. This may be done conveniently
by a
"handshake" procedure involving the interface unit 11 transmitting either its
own
telephone number or some other identifying code to the BTS 21. The interface
unit 1 1 then relays the registration signal to the BTS 21 using the BCCH
slots.
The controller 30 responds to the registration signal in the conventional
manner
and the telephone 1 is then registered with the cellular telephone network.
After
registration signalling has been completed, the interface unit modem 14 sends
the
interface unit's telephone number to the BTS 21 where it is stored by the
controller. 30 together with the telephone's 1 network ID. After the interface
unit's telephone number has been received, the controller 30 sends an "on
hook"
command to the modem 32. The control circuit 12 receives a "no carrier" signal
from the modem 14 and returns an "on hook" command.
If the telephone 1 is switched on when is connected to the interface unit
1 1, it does not need to register. However, it~must perform a location update.
The
location update is carried out in a similar manner to registration. Similarly,
if the
telephone 1 is disconnected from the interface unit 11 while it is switched
on, it
Sv.
must perform a location update as soon as its r.f. circuitry 2 becomes active
again.
Location updating is a conventional aspect of GSM systems.
A colt from the telephone 1 wilt now be described.
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When the subscriber wishes to make a call, he enters the called
party's
telephone number into the telephone 1 in the normal manner
and then presses the
' SEND key. If the telephone is connected to the interface unit
11, the control
circuit 12 detects the call set-up signals from the telephone
1 (received over the
connection 7a, 16a) and causes the modem 14 to dial up the
BTS 21. The BTS's
controller 30 answers the call, as described above. Once the
connection betwBen
the interface unit 1 1 and the BTS 21 has been established,
the control circuit 12
relays the call set up signals to the BTS 21.
When the controller 30 receives the call set up signals from
the interface
unit 1 1, it gets a channel allocation for the call from the
BSC 26. The BSC 26 will
note that the telephone 1 has a dedicated channel and wilt
therefore allocate the
dedicated channel rather than proceed with the conventional
radio channel
allocation process. The request for a call to be set up is
passed to the MSC 27 via
the BSC 26. The MSC 27 then operates to establish a connection
between the
called party and the BTS 21, by way of the PSTN.
The controller 30 communicates the allocated channel to the
interface unit
1 1 . Although this is predetermined, it serves to indicate
that the call has been set
up. Using a dummy allocated signal is convenient because it
mimics the operation
of the system when the telephone 1 is mobile. Once the call
has been set up, the
control circuit 12 relays speech and control data from the
telephone 1 to the BTS
21 and vice versa.
When the call is complete, the controller 30 and the control
circuit 12
break the connection between the interface unit 11 and the
BTS 21.
A call to the telephone 1 will now be described.
When the telephone 1 is called, the MSC identifies the called
number as
relating to a telephone currently registered with the BTS
21, and routes the call to
the BTS 21 via the BSC 26. The BSC 26 first checks the ID
of the telephone 1
against its list of mobile units with dedicated channels.
The BSC 26 finds the
- telephone's ID in the list and modifies its operation accordingly.
Having found the
telephone's 1D on the list, the BSC 26 instructs the controller
30 to retrieve the
' interface unit's telephone number and causes the modem 32
to dial it.
The interface unit 1 1 causes the modem 14 to answer the call
and once
the connection has been established, the controller 30 sends
a calf signal to the
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interface unit 1 1. The interface unit 11 recognises the cal! signal and
relays it to
the telephone 1 via the second pins 16b, 7b of the plug 16 and socket 7. The
telephone 1 then responds as if it were receiving the signal from the antenna
3 and
starts to ring.
5 The subscriber hears the telephone 1 ringing and presses the answer
button on the telephone 1. The telephone 1 and the controller 30 then exchange
signals via the interface unit 11 using the BCCH slots to set up the call. The
channel allocation is of course predetermined. Once the connection is
established
between the calling party and the telephone 1, the controller 12 relays speech
10 signals between the telephone 1 and the BTS 21, and vice versa, until the
call is
terminated.
It will be appreciated that the PSTN link 25 between the interface unit and
the BTS 21 may be replaced by an ISDN link (52, Figure 6?. ISDN links provide
much greater bandwidth than PSTN links. Consequently, a single ISDN link can
be
used to connect a plurality of mobile telephones to a BTS. Such a system wilt
now
be described, with reference to Figures 1, 3, 6, 7 and 8. For a proper
understanding of the following embodiment, the channel codec of the telephone
1
should be viewed as forming part of the r.f. circuitry 2 (Figure 11.
Referring to Figure 6, an interface system 40 comprises a central part 41
and eight remote parts 42a - 42h. The remote parts 42a - 42h are each
connected
to the central part 41 by respective transmission lines 43a - 43h.
Referring to Figure 7, a remote part 42a comprises a baseband data
transceiver 44, a power supply unit 45 connected to a mains electricity supply
19.
and a plug 46. The plug 46 has five contacts 46a-a which correspond to
contacts
7a-7e of the socket 7 of the cellular telephone 1 (Figure 1 ) and have similar
functions to the contacts 16a -16e in the socket of the interface unit 16
previously
described with reference to Figure 2. The first contact 46a of the plug 46 is
coupled to a data input terminal of the transceiver 44 and the second
contact~of
the plug 46 is coupled to a data output terminal of the transceiver 44. The
third
contact 46c and fifth contact 46e of the plug 46 are coupled to the + V output
of
the power supply unit 45. The fourth contact 46d of the plug 46 is coupled to
the
remote part's OV supply wiring. The + V output of power supply unit 45 is
also:
coupled to + V input terminal of the transceiver 44. The transceiver 44 is
also
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11
coupled to the transmission line 43a between the remote part 42a and the
central
part 41. Remote parts 42b - 42h have the same construction as remote part 42a.
' Referring to Figure 8, the central part 41 comprises a control circuit 47, a
user input unit 48, a 9-to-1 multiplexes 49 and a modem 50. The user input
unit
48 is coupled to the control circuit 47 and enables a user to program the
interfiace
system with the ISDN number of a BTS 21. The user input unit 48 includes a
display on which is displayed status information for the interface system.
The control circuit 47 is coupled to each of the transmission lines 43a
43h for communicating with telephones at the remote parts 42a - 42h, tVine
parallel data tines 51 connect the control unit 47 to the multiplexes 49. The
multiplexes 49 has its common terminal connected to the modem 50 which
provides a link to an ISDN line 52, providing connection to the BTS 21, in
place of
the PSTN link 25 shown in Figure 3. Control lines 53, 54 link the control
circuit
47 to the multiplexes 49 and the modem 50.
7 5 An ISDN2 fink fi.e. having two 64 kbitls "8" (bearer) channels and one
16kbit/s "D" (signalling) channel) is described here, and has adequate
capacity to
support eight remote parts 42a - 42h. An ISDN30 link (thirty B channels, one D
channel and a synchronisation channel, all of 64 kbit/s) could be used if
greater
capacity were required.
Of the nine data lines 51 between the control circuit 47 and the
multiplexes 49, eight correspond to respective remote parts 42a - 42h and the
ninth is used for ~BCCH signals. The two B channels of the ISDN2 link to the
f3TS
can carry a total of eight TCHs, the BCCH signals being carried in the D
channel.
The various channels are time-division multiplexed in the ISDN2 link.
In the embodiment depicted in Figure 8, the signal paths and multiplexes
49 of the central part 41 are bi-directional. However, it will be appreciated
that
separate paths and multtplexers may be used for signals from and to a BTS.
The operation of this embodiment will now be described with reference to
Figures 1, 3, 6, 7 and 8.
When the telephone 1 is first connected to, for example, remote part ~42a
of the interface system 40, it must register with the cellular telephone
network or
perform a location update. To do this, the processing and control circuitry 4
produces the conventional GSM registration or location update signal. The
signal
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12
is not transmitted from the antenna 3 because the r.f. circuitry is disabled"
However, it is output to the remote part 42a via the first contact 7a of the
socket:
7.
The signal is then relayed by the data transceiver 44 along the
transmission line 43a to the central part 41 of the interface system. The
control
circuit 47 detects the signal and identifies it as a registration or location
update
signal as the case may be. In response to the signal, the control circuit 47
first:
determines whether the interface system is already connected to the BTS 21. If
a~
. connection already exists, the control circuit 47 passes the signal through
to the
multiplexer 49. When the multiplexer 49 selects the appropriate input line 51,
the
signal is supplied to the modem which transmits it to the BTS 21 via the ISDN2
link 52.
However, if the control circuit 47 determines that an ISDN connection
needs to be established, it instructs the modem 50 to dial the ISDN number of
the
BTS 21. At the BTS 21, the controller 30 is notified by the modem 32 of the
call
on the ISDN line 25 and sends an "answer" command to the modem 32. The
central part 41 of the interface system then relays the registration or
location
update signal to the BTS 21 using the ISDN2 D channel. The controller 30
responds to the registration or location update signal in the conventional
manner
and the telephone is then registered, if necessary, with the cellular
telephone
network. After registration or location update signalling has been completed,
the
control circuit 47 sends the interface system's ISDN number and the channel
for
the remote part 42a to the BTS 21 where they are stored by the controller 30
together with the telephone's 1 network ID. An indication of the interface
system
40, the channel for the remote part 42a and the telephone's 1 network ID are
passed on to the BSC 26. The connection 52 between the interface system 40
and the BTS 21 will then be broken if it is no longer required.
Since the telephone 1 is not operating in the conventional manner and, in
effect, has a dedicated channel allocated to it, the BSC 26 must recognise
when
the telephone 1 is being called and depart from the conventional channel
allocation
process.
A call from a telephone 1 at, for example, remote part 42a will now be
described.
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13
When the subscriber wishes to make a call, he enters the called party's
telephone number into the telephone 1 in the normal manner and then presses
the
SEND key. If the telephone 1 is connected to one of the remote parts e.g. 42a,
the call set-up signals are sent by way of the connections 7a, 46a and the
remote
part 42a to the central part 41 where they are detected by the control circuit
.47.
if the interface system is already connected to the BTS 21, the call set-up
signals
are immediately applied to the multiplexer 49 ready for transmission in the
appropriate TDM slot.
However, if a connection needs to be established, the control circuit 47
1 O causes the modem 50 to dial up the BTS 21. The BTS's controller 30 answers
'the
call, as described above. Once the connection between the interface system and
the BTS 21 has been established, the control circuit 47 relays the call set up
signals to the BTS 21 using the D channel.
When the controller 30 receives the call set up signals from the interface
system, the BSC 26 allocates a channel for the call. However, the BSC 26 will
note that the telephone 1 has a dedicated channel and will therefore allocate
'the
dedicated channel rather than proceed with the conventional radio channel
allocation process. The request for a call to be set up to is passed on to the
MSC
27 from the BSC 26. The MSC 27 then operates to establish a connection
between the called party and the BTS 21, by way of the PSTN.
The controller 30 communicates the allocated channel to the interface
system. Although this is predetermined, it serves to indicate that the call
has been
set up. Using a dummy allocated signal is convenient because it mimics vthe
operation of the system when the telephone 1 is mobile. Once the call has been
set up, the control circuit 47 relays speech and control data from the
telephone 1
to the BTS 21 and vice versa, using the allocated TCH for speech data and the
D
channel for control signals.
After the call is complete and either party has hung up, the controller 30
and the control circuit 47 release the ISDN channel between the interface
system
40 and the BTS 21. If the channel was the only one in use, the ISDN connection
between the interface system 40 and BTS 21 can also be released. There may be
a delay before such release occurs, to allow for the possibility that the user
intends
to make a further calf as soon as the first clears down.
CA 02245801 1998-08-07
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14
A call to the telephone '! will now be described.
When the telephone 1 is called, the MSC identifies the called number as
relating to a telephone currentty registered with the BTS 21, and routes the
call to
the BTS 21 via the BSC 2fi. The BSC 26 first checks the ID of the telephone 1
against its list of mobile units with dedicated channels. The BSC 26 finds the
telephone's tD in the list and modifies its operation accordingly. Having
found the
telephone's ID on the list, the BSC 26 instructs the controller 30 to retrieve
the
ISDN number of the interface system 40. If the ISDN link is not already open,
it:
next causes the modem 32 to dial it, and the interface system 40 then causes
the
modem 14 to answer the calf. Once the ISDN link is open, or if it is already
open,
the controller 30 is informed. of the ISDN link channel allocated to the
telephone 1
by the BSC 26. This indicates which TDM slot must be used for the called
telephone.
Preferably, such a telephone includes r.f. circuitry for transmitting and
receiving speech and data signals, a further externally accessible connector
and
switching means, wherein the switching means is responsive to a signal applied
te~
the further connector to disable the r.f. circuitry.
Once the connection has been established, the controller 30 sends a.
dummy channel allocation signal to the interface system. The interface unit 11
recognises the dummy channel allocation signal and relays it to the telephone
1 via
the transmission line 43a. The telephone 1 then responds as if it were
receiving
the signal from ttie antenna 3 and starts to ring.
The subscriber hears the telephone 1 ringing and presses the answer'
button on the telephone 1. The telephone 1 and the controller 30 then exchange
signals via the interface system to set up the call. Once the connection is
established between the calling party and the telephone 1, the controller 47
relays
speech signals between the telephone 1 and the BTS 21, and vice versa, in the
allocated TCH until the call is terminated.
it will be appreciated that the dial-up connections, described above, could
be replaced by leased lines from another operator or dedicated fines owned by
the
cellular network operator, providing a permanent connection between the
interface
unit or system and a BTS.
CA 02245801 1998-08-07
VSO 97/3fc442 PCT/G~97/00559
Instead of the efectrical/mechanical plug-and-socket connections 7/16 and
7/46 illustrated in Figures 1, 2, and 7, the connection between the mobile
telephone and the interface unit may be by means of an ultrasonic or optical
(e.g.
infra-red) link, as will now be described with reference to Figures 9 and 1 d,
in
5 which components having equivalent features to those in Figures 1 and 2 are
given
the same reference numerals.
Referring to Figure 9, the cellular telephone 1 a is similar to that already
described with reference to Figure 1, except that the socket 7 is replaced by
an
ultrasound or optical antenna (sensor/transmitter) 96, connected by means of a
1 ~ suitable transceiver 97 to the process and control circuitry 4 and R.f.
circuitry 2.
Referring to Figure 1 O, the interface unit 1 1 a is similar to that described
with reference to Figure 2, except that the plug 16 is replaced by an
ultrasound or
optical antenna (sensor/transmitter) 98, complementary to the antenna 96 in
the
telephone 1 a, and connected by means of a suitable transceiver 99 to the
control
15 circuit 12.
The transceivers 97, 99 convert baseband signals (either conventional
analogue signals, or digitised signals such as would normally be transmitted
from /
received by the antenna 3) received from the control units 4, 12 respectively
into
signals suitable for transmission by the antennas 96, 98 respectively. These
signals may simply be a modulation of the optical or ultrasonic carrier, or
they may
be converted by the transceivers 97,99 to a digital format such as the IrDA
protocol previously referred to. These signals are then transmitted by the
antennas
96, 98. Signals received by the antennas 96,98 are reconverted to baseband
analogue or digital signals, by the respective transceivers 97,99, for further
processing and onward transmission by the control units 4, 12 respectively.
The operation of this system is largely similar to that of Figures 1 and 2.
However, as there is no electrical correction between the mobile telephone 1 a
and
the interface unit 1 1 a, there can be no external power supply to the
telephone 1 a,
and therefore no equivalent to the electrical power connections 7c/16c;
7d/16d;
7e/16e. This has two further consequences. Firstly, the battery 5 cannot be
- recharged by means of the interface unit 11 a (separate battery charging
arrangements being necessary). As shown in Figure 9 the battery is delivering
power to the various components 4, 97, etc. Moreover, detection of the
presence
CA 02245801 1998-08-07
WO 97/36442 PCT/GB97/00559
16
of a connection cannot be done by detecting the presence of a voltage as is
done
in the embodiment of Figure 1 (connection 7c). Instead, the control apparatus
4 is
arranged to respond to the presence of a signal on the input 4b, (received by
the
antenna 96) to control the switch 6. Alternatively, the switch may be
controlled)
manually.
The arrangement of Figure 7 may be adapted for use by an optical or'
ultrasonic connection in a similar manner to the adaptations to Figure 2
illustrated
in Figure 1 O.
In the foregoing embodiments, a "land line" is used to connect the
interface unit or system to the BTS. A further embodiment will now be
described,
with reference to Figures 1 1, 12, 13, 14, and 15 which uses a wireless link
between an interface system and a BTS.
Referring to Figure 11, a cellular telephone 61, generally conventional in
construction, comprises a battery pack 62, signal processing and control
circuitry
63 and r.f. circuitry 64. However, the telephone 61 further comprises a
connector
65 having three simple contacts 65a, 65b, 65c, a coaxial socket 65d, and an
r.f.
switching circuit 66. The first contact 65a of the connector 65 is coupled to
a
control input of the processing and control circuitry 63. The second and third
contacts 65b, 65c are connected respectively to the negative and positive
terminals of the battery pack 62. The r.f. switching circuit 66 is arranged to
connect the r.f. circuitry 64 to either an antenna 67 or the coaxial socket
65d in
dependence on a control signal from the processing and control circuitry 63,
The
first contact 65a of the connector 65 is connected to a control input of the
processing and control circuitry 62. When the processing and control circuitry
63
detects a voltage on the first contact 65a of the connector 65, it sends a
control
signal to the r.f. switching circuit 66 to connect the r.f. circuitry 64 to
the coaxial
socket 65d rather than the antenna 67. The connections 65b/73b and 65c/73c
allow the battery 5 to be recharged from the power supply unit 72.
Referring to Figure 12, a remote part 71 of an interface system comprises
a mains power supply unit 72 connected to a mains electricity supply 19, and a
connector 73 adapted to cooperate with the connector 65 of the telephone 61.
The first and third contacts 73a, 73c of the connector 73 are connected to the
+ V output of the power supply unit 72 and the second contact 73b of the
connector 73 is connected to the OV output of the power supply unit 72. The
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17
connector 73 includes a coaxial plug 74. A transmission line 75 extends
through
the remote part 71 and is coupled to the coaxial plug 74 by a tap 76 and a
branch
77 of the transmission line 75.
Referring to Figure 13, a plurality of interface system remote parts 7'I a
71 c are spaced along a transmission line 75, such as a coaxial cable. A
central
part 79 of the interface system is connected to one end of the transmission
line
75. A terminating impedance 78 is connected to the other end of the
transmission
line 75.
Referring to Figure 14, the central part 79 of the interface system
comprises a frequency transposer 80 for transposing signals from the
transmission
line 75 to a microwave band and transposing microwave signals to the band for
which the telephone 61 is adapted, a microwave power amplifier 81 for
amplifying
microwave signals from the transposer 80, a microwave pre-amplifier 82 for
amplifying received microwave signals before they are applied to the
transposer 80
and a duplexer 83 coupled to the output of the power amplifier 81, the input
of the
pre-amplifier 82 and a waveguide to a dish antenna 84.
Referring to Figure 15, the dish antenna 84 is mounted on a building 85,
for example an office block, and is aligned with another dish antenna 86 at a
BTS
87. The transmission line 75 extends substantially throughout the building 85.
The BTS 87 includes a UHF antenna 88 for conventional GSM communication and
a call processing apparatus 87a. The call processing apparatus 87a is Linked
to a
BSC 90 which is in turn finked to a MSC 92, providing connection to the PSTN.
Since the interface system merely transposes the band in which the
telephone 61 operates, the BTS 87 can be in fact two BTSs, one operating in a
conventional UHF GSM band using the UHF antenna 88, and the other operating in
a microwave band, using the dish antenna 86.
In the foregoing embodiments, an interface unit or system provides
communication to a conventional BTS site which has antennas for communicaning
with mobile equipment in its cell. However, the "BTS", with which the
interface
unit or system communicates, rnay be arranged solely for communication vvith
interface units or systems according to the present invention. Thus, in the
case of
a large office complex for example, it may be desirable to have the "BTS" at
the
complex and avoid the need for the telephone, ISDN, teased line or microwave
link.
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18
Adapters are known for allowing handheld mobile telephones to be used in
a vehicle-mounted installation. These systems often provide a microphone and a
loudspeaker to allow hands-free operation of the telephone. It will be
appreciated
that such an arrangement could be employed with the present invention.
Alternatively, the interface unit or remote part of the interface system could
be
provided with a handset to replace the microphone and loudspeaker of the
mobile
telephone when it is docked with the interface unit or remote part of an
interface
system according to the present invention. If the user does not need to use
the
microphone and the loudspeaker of the mobile telephone itself, it can be
plugged
directly into an interface unit or a remote part of an interface system
without the
need for a connecting cable.
GSM terminology has been used in the foregoing description. However,
the present invention is not limited to the GSM system and is applicable also
to
other systems, including DAMPS (digital advanced mobile phone system),
DCS1800 (digital communications system 1800MHz), PCS1900 (personal
communication system 1900MHz), Japanese PDC (personal digital cellular), US IS-
96 CDMA, UMTS (universal mobile telephone system) and FPLMTS (future public
land mobile telephone system). Additionally, the present invention can be
applied
to DECT (digital European cordless telephone) CT2 and Japanese Personal
Handyphone systems interacting with fixed intelligent systems. The present
invention is further applicable to analogue cellular telephone systems.
