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Patent 1261981 Summary

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(12) Patent: (11) CA 1261981
(21) Application Number: 580344
(54) English Title: WIRELESS TELEPHONE SYSTEM
(54) French Title: SYSTEME TELEPHONIQUE SANS FIL
Status: Expired
Bibliographic Data
(52) Canadian Patent Classification (CPC):
  • 379/1
  • 325/3
(51) International Patent Classification (IPC):
  • H04J 13/00 (2011.01)
  • H04B 1/69 (2011.01)
  • H04B 5/00 (2006.01)
  • H04M 7/00 (2006.01)
  • H04B 1/69 (2006.01)
(72) Inventors :
  • CAREY, MICHAEL J. (United Kingdom)
  • ANDERSON, ADRIAN J. (United Kingdom)
(73) Owners :
  • MITEL CORPORATION (Canada)
(71) Applicants :
(74) Agent: AVENTUM IP LAW LLP
(74) Associate agent:
(45) Issued: 1989-09-26
(22) Filed Date: 1984-03-08
Availability of licence: N/A
(25) Language of filing: English

Patent Cooperation Treaty (PCT): No

(30) Application Priority Data:
Application No. Country/Territory Date
8502735 United Kingdom 1985-02-04

Abstracts

English Abstract






ABSTRACT

A wireless telephone communication system
for wireless, voice, data or voice and data
terminals comprising apparatus at a central location
for receiving one or a plurality of signals for
communication with selected ones of wireless
communication terminals, apparatus for converting the
signals to spread spectrum radio frequency signals,
a leaky transmission line located in a communication
region, apparatus for applying the spread spectrum
radio frequency signals to the transmission line for
electromagnetic radiation within the region, at least
one wireless communication terminal adapted to receive
a predetermined one of the spread spectrum radio
frequency signals and for demodulating it into an
intelligible signal.




Claims

Note: Claims are shown in the official language in which they were submitted.



The embodiments of the invention in which
an exclusive property or privilege is claimed are
defined as follows:


1. A telephone system comprising:
(a) a central switching system having a
plurality of line circuits,
(b) means for converting signals carried
by at least certain ones of said line circuits to
spread spectrum RF signals, each signal carried by
said certain line circuits having a different
spreading code,
(c) first means for wireless transmitting
said spread spectrum RF signals,
(d) one or a plurality of mobile telephone
sets, for receiving, decoding and reproducing said
signals carried by the line circuits and for wireless
transmitting to said central switching system spread
spectrum RF signals originating at said mobile sets,
each said latter signal being transmitted using a
spreading code different in each mobile set from other
mobile sets.


2. A telephone system as defined in claim
1 in which the spread sprectrum RF signals transmitted
by said first means are in a first frequency band
having one centre frequency, and in which the spread
spectrum RF signals transmitted by the mobile sets are
in a second frequency band having a different centre
frequency.


3. A telephone system as defined in claim
1 or 2 further including a supervisory channel
associated with the central switching system for
providing spread spectrum RF signals carrying digital
control data receivable by the mobile sets for
31





controlling the transmit and receive spreading and
despreading codes of the mobile sets which correspond
to the receive and transmit despreading and spreading
codes associated with respective ones of said line
circuit.

4. A telephone system as defined in claim
1 or 2 in which the means for wireless transmitting
and receiving are comprised of antennae.

5. A telephone system as defined in claim
1 or 2 in which the means for transmitting and
receiving associated with the mobile sets are
comprised of antannae, and the means for transmitting
and receiving associated with the central switching
system is comprised of one or more leaky cables
transmission line.
32





Description

Note: Descriptions are shown in the official language in which they were submitted.


8~

01 This application is a division of Canadian
02 application Serial No. 499,189 filed January 8, 1986.
03 This invention relates to a telephone
04 communication system utilizing wireless voice, data,
05 or voice and data terminals.
06 It is often difficult to provide telephone
07 service to personnel who are continuously moving, yet
08 must be quickly available at a telephone or data
09 terminal, e.g. warehouse stock takers, personnel
responsible for building maintenance or security, etc.
11 Paging recelvers have been used to summon such personnel
12 to call a number via the closest telephone set.
13 Sometimes such personnel are required to enter data into
14 a terminal for storage at a central computer. Yet wired
jacks for interfacing a telephone with a PABX or
16 terminal to a computer are often spaced at substantial
17 distances from each other in warehouses, for example.
1~3 Voice communication of such personnel has
19 been partly solved by the use of cordless (wireless)
telephones each operating at a different frequency
21 from the other. However such telephones have
22 exhibited substantial problems. There are usually a
23 limited number of channels available, limiting the
24 number of telephone/wireless receiver sets which can
be used in a given area. Often interference from
26 adjacent channels or other services is encountered.
27 Transmission or reception nulls are often encountered
28 when a cordless telephone is oriented in a particular
29 direction relative to the main transmitting and
receiving station. Such nulls are also caused by
31 shielding by steel and concrete of which the building
32 housing the system is built. The system lacks
33 privacy; since the common radio bands are used, the
34 signals can be readily intercepted.
In addition, the use of wireless presents
36 a range problem. Particularly for large areas, such
37 as when an entire building, a large warehouse, or
38 aircraft hangar, etc., is to be covered by the system,
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01 a high powered central transmitter could be used.
02 However the power of the transmitter cannot be greater
03 than a level prescribed by the regulatory agencies.
04 This places a limitation on the communication range.
05 In the event -that many low power transmitters are used
06 scattered around the building, the cost increases
07 substantially.
08 In the system described in U.S. patent
09 4,462,113 issued July 24, 1984, domestic A.C. power
lines are used as an antenna for a low power
11 transmitter. However in this case the null problem
12 still exists, and in addition there is a severe
13 bandwidth limitation to below approximately 150 or
14 200kHz. Further, transmission of signals via the A.C.
power lines is notoriously insecure, since such
16 signals are often carried by the power lines to
17 neighbouring offices and buildings.
18 Due to the inherent lack of security,
19 nulls and power/distance limitations, the use of a
mobile telephone handset has been limited to the home
21 environment, or to very special applications. Until
22 the present invention was made it had not yet been
23 found suitable -for commercial applications in which,
2~ for example, an entire multi-story building housing
many different companies, some possibly being
26 competitors with each other, could be served mobile
27 telephone and data services reliably from the same
28 PABX. Such prior art systems could not ensure
29 complete security of communications, sufficiently low
power radiation outside the confines of the building,
31 and absences of nulls or fade areas within structures.
32 Clearly for the above reasons portable
33 terminals could also not be used for reliable
34 transmission and reception of data to a central
computer.
36 The present invention provides a
37 communication system which can be connected to a PABX
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01 switching system, which solves the problems noted
02 above. In addition to the provision of secure mobile
03 (wireless) communications in a low power environment
04 with the substantial elimination of the null or fade
05 areas, it provides multi-channel wideband
06 communications which can reliably carry voice, data
07 and signalling (supervisory) signals.
08 According to the present invention leaky
09 transmission cables are used to radiate and to receive
communication signals within the communication
11 region. While at single frequencies such cables
12 exhibit nulls along the cables at regular intervals,
13 the communication signals which are carried and which
14 are received in the present invention are spread
spectrum.
16 The use of spread spectrum signals carried
17 by a leaky cable transmission system achieves several
18 highly desirable results. Firstly, nulls are
19 virtually undetectable or are eliminated due to the
spreading of the signals over a wide bandwidth.
21 Secondly, since pseudo-noise bandwidth spreading
22 (correlation) code is used for each channel, privacy
23 of communications is virtually assured as well as
24 immunity from interference between channels.
Since a leaky cable is used to distribute
26 the signal in the communication region, t~e
27 transmitter power and resulting effective radiated
28 power can be very low. Furthermore, the power which
29 is used is spread amongst the frequencies of a wide
bandwidth, further reducing the power used at any one
31 frequency. Thus the interference that may be caused
32 to other radio signals outside of the building is
33 virtually nil. Also the radiated power within the
34 building can be increased to a substantial degree in
comparison with a non-spread spectrum, single or
36 multi-point antenna transmitter to minimize the bit
37 error rate, yet the effective interference with
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01 external or other wirel~ss services remains virtually
02 nil, while the reliability of communication within the
03 builaing is increased.
04 The spread spectrum-leaky cable system
05 according to this invention can operate side-by-side
06 with other similar systems or with conventional AM or
07 FM wireless systems with substantially no or minimal
08 interference. The maximum interference which might be
09 apparent in such other systems would merely be an
increase in the background noise level.
11 The various handsets or wireless remote
12 terminals to be used in the present system are
13 preferred to be accessed by address code on a
14 supervisory channel, and to be controlled to
internally selec-t a pseudo-noise correlation code
16 which matches a predetermined channel transmit
17 pseudo-noise spreading code. This type of system
18 would benefit by the use of universal wireless
19 handsets or terminals. However in another type of
system each handset or terminal is channel fixed with
21 a predetermined pseudo-noise correlation code
22 circuit, and the head end terminal changes its
23 transmit pseudo-noise spreading code to suit that of
24 the selected handset.
In the reverse transmission direction
26 which uses a different RF centre ~requency the mobile
27 handset is either fixed with a transmit pseudo-noise
28 spreading code for encoding the transmitted signal, or
29 it can be caused to transmit on a channel selected by
the head end under control of the head end via signals
31 on the supervisory channel.
32 Leaky cable transmission systems have long
33 been used to communicate in tunnels and mines. One
34 such system is described in U.S. Patent 4,476,574
issued October 9, 1984. A large number of
36 publications is listed in that patent which will
37 provide background in~ormation to the reader on the
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01 use of leaky Eeeder communication systems both
02 subsurface and above the surface of the earth.
03 However those systems suffer from one or more of the
04 problems described above which restrict them from use
05 in a reliable co~mercial communication system. A text
06 which describes leaky feeder systems is LEAKY FEEDERS
07 AND S~BSURFACE RADIO COMMU~ICATIONS by P. Delogne, IEE
08 Electromagnetic Waves Series 14, 1982 Peter PeregrinuS
09 Ltd.
Spread spectrum systems have been used in
11 wireless systems in the past, as well as in certain
12 specialized wired systems. A wireless spread spectrum
13 system is described in U.S. patent 4,455,651 issued
14 June 19, 1984 and in U~S. patent 4,086,504 issued
April 25, 1978. However in both those cases the power
16 limitation problem and the null problem described
17 above did not present problems, since in the first
18 case directional antennas were used, and in the second
19 case high power could be used and the system was not
used in a communication system of -the present kind.
21 Furthermore, the locations of the various transmitting
22 stations used in the latter patent, which relates to a
23 seismic exploration system, can all be tested for
24 proper spectrum prior to use and the transmitters
moved in case a null is encountered. In addition, the
26 locations of the spread spectrum transceivers are all
27 fixed and preknown, since they are used for
28 triangulation purposes.
29 Spread spectrum systems have also been
used ln wired systems. For example in U.S. patent
31 4,438,519 issued March 20, 1984, a spread spectrum
32 system is used connected to an A.C. power line, which
33 is not a leaky feeder transmission cable, but
34 constitutes an antenna. In that patent, however, it
is clear that the bandwidth o~ the power line is very
36 low, and the transmission region is limited to areas
37 which are not isolated by a transformer. ~Ience such
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01 systems are not useful for wide band multi-channel
02 voice and data communication system~.
03 A spread spec-trum signal is applied to
04 telephone lines in the invention described in U.S.
05 patent 4,475,208 issued October 2, 1984. In this
06 system data signals are converted to spread spectrum
07 and are transmitted simultaneously with voice over
08 already existing telephone lines which are not leaky
09 feeder transmission cables . The bandwidth of such
telephone lines is so low that the data signals are oE
11 very low bit rate. Clearly the system is not suitable
12 for use in multi-channel wide bandwidth transmission.
13 In addition, the system is unsuitable for use with
14 wireless handsets or terminals since the telephone
transmission lines cannot carry radio frequency
16 signals for any significant distance.
17 A general description of the history and
18 structure of spread spectrum systems will be found in
19 the publication SPREAD-SPECTRUM COMMU~ICATIO~S, edited
by Charles ~. Cook et al, published by the IEEE Press,
21 Institute of Electrical and Electronic Engineers, Inc.
22 Carriage of a plurality of spread spectrum
23 communication signals, each modulated by a different
24 pseudo-random spreading or correlation code, by a
leaky cable transmission system thus provides a new
~6 form of wireless mobile voice and data communication
27 system previously not thought possible, that is, a
28 reliable, private and low power communication system
29 using a large number oE noted telephone handsets that
can be carried within a predefined environment whic7n
31 can be used sharing the same bandwidth as other
32 commercial wireless services without interference
33 between the two kinds of systems. Such a system for
34 the first time is viable within a building structure,
i.e. steel and concrete, which previously would not
36 reliably support reliable wireless communication to
37 the required degree.
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01 Beca~lse of the broadband and multi-channel
02 capability of the present system, the various mobile
03 telephone sets can be provided with a full xange of
04 features normally made available only to wired telephone
05 sets by the PABX, such as local alphanumeric display,
06 conferencing, abbreviated dialing, etc., as well as
07 computer access, remote control oE various apparatus
08 such as automatic door locks, etc. Such features are
09 not now possible with the well known cordless
telephones. A 32 channel system of the type described
11 herein could give typically 200 users at a site mobile
12 telephone facility depending on traffic. Further, the
13 communication channel between the remote mobile unit and
14 a PABX which connects to a larger computer can provide
to the remote unit enormous computational power which
16 would otherwise not be available in a hand held computer
17 due to its size and cost limitations, and since a large
18 shared data base can be stored at the central computer.
19 A preferred embodiment of the invention is
a telephone system comprising a central switching system
21 having a plurality of line circuits, apparatus for
22 converting signals carried by at least certain ones of
23 the line circuits to spread spectrum RF signals, each
24 signal carried by the certain line circuits having a
different spreading code, first apparatus for wireless
26 transmitting the spread spectrum RF signals, and one or
27 a plurality of mobile telephone sets, for receiving,
28 decoding and reproducing the signals carried by the line
29 circuits and for wireless transmitting to the central
switching system spread spectrum RF signals originatlng
31 at the mobile sets, each of the latter signals being
32 transmitted using a spreading code different in each
33 mobile set from other mobile sets.
34 The invention also facilitates any of the
wireless communication terminals to initiate a
36 communication with the central location, such a
37 communication being capable of having as its final
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01 destination any telephone connectable to the central
02 location, including others of the wireless
03 communication terminals.
04 ~ better understanding oE the invention
05 will be obtained by reference to the detailed
06 description below of the preferred embodiment, with
07 reference to the following drawings:
08 Figure 1 is a general block diagram of a
09 system according to the present invention,
Figure lA illustrates a code arrangement
11 used in multiplexing the channels of the spectrum,
12 Figure 2 is a block diagram illustrating
13 the mobile handset according to the preferred
14 embodiment of the invention,
Figure 3 is a block diagram of the central
16 equipment according to the preferred embodiment of the
17 invention, and
18 Figure 4 is a block diagram of a preferred
19 form of transmit channel used in the system.
To briefly review the spread spectrum
21 concept, this technique causes the spectrum of the
22 transmitted signal of each channel to be spread over a
23 greater amount of bandwidth than would be the case if
24 time or frequency division multiplexing techniques
were used. Indeed, the signals of all of the channels
26 used are spread over the same band. This is achieved
27 by multiplying a generated data stream to be
28 transmitted by a sequence with the correct
29 auto~correlation and cross-correlation properties
(pseudo-random/noise code sequence). The resulting
31 output signal is then a sequence having a higher data
32 rate than that of the input data stream, whi~h when
33 used to modulate some foxm of amplitude, frequency or
34 phase shift keyed system, causes the spectrum to be
spread over a wide bandwidth. `-
36 At the receiver the incoming signal is
37 multiplied by the same pseudo-random/noise sequence
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01 and the spectrum becomes despread to its original
02 bandwidth. It is important to note that any
03 interfering signal is spread at the receiver rather
04 than despread. The signal is then filtered at the
05 receiver to the original bandwidth, leaving the
06 original signal intact but the interEering signal is
07 attenuated and thus its effect is diminished. This
08 occurs whether the interfering signal is a real signal
09 or is a hoLe (i.e. null~ in the spectrum generated by
some propagation effect. Thus a spread spectrum
11 system provides not only immunity against interfering
12 signals but also protection against holes in the
13 spectrum.
14 Because a large number of spread spectrum
sequences are generally known, it is possible to
16 choose a set for a system which would be very
17 dif~icult to decode by an intruder or eavesdropper.
18 The spread spectrum system therefore contains its own
19 intrinsic security. The interference to which the
system is immune may of course be other channels of
21 the system using the same spectrum. Spread spectrum
22 is therefore intrinsically a multiplexing system.
23 Different channels using the same bandwidth can be
24 immune to each other if they use different spreading
sequences for modulation and demodulation.
26 For example, for a pseudo random code
27 having length 255 bits, there are probably
28 approximately 40000 codes which are strongly
29 orthogonal, and thus are highly secure. It is
preferred in the present system to use a centre
31 frequency of between about 150 mHz to 1000 mHz,
32 although the invention is not limited to this band,
33 each channel being approximately 32k Hz wide, in which
34 the voice signals are digitized in a well known
manner. The spread channel is preferred to be 8 mHz
36 wide.
37 Turning now to Figure 1, the basic system
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01 according to the invention is illustrated. Within the
02 confines of a building periphery 1 a leaky cable 2 is
03 laid. The leaky cable can be coaxial cable with holes
04 in its shield, such as described in Canadian Patent
05 1,014,245 issued 3uly 19, 1977, or other types of
06 leaky transmission cables as described in the
07 aforenoted text by P. Delogne. The cable can be
0~ sinuously laid above the false ceiling over the entire
09 width and breadth of the building, can extend down the
centre of a narrow building, and can pass from .storey
11 to storey in a multi-storey building as well as extend
12 over the ceiling area of a building. The leaky cable
13 can be located within movable walls or within an
14 electromagnetically transparent floor. Clearly the
location of the cable is dependent on the region to be
16 covered and many variations are possible. The
17 important aspect of the placement of the cable is that
18 for a given minimum electromagnetic field strength,
19 the entire working area of the building which defines
the communication region should be enveloped by the
21 field strength leaked from the cable which is above
22 the minimum level.
23 It will be seen that since the field
24 strength drops off by between the square and the cube
of the distance from the cable, the effective radiated
26 power outside the building periphery will be low or
27 virtually nil.
28 As central equipment, feeding the cable at
29 one end is a transmitter 3, and receiving signals from
the other end of the cable is a receiver 4. The input
31 to the transmitter 3 is connected to a PABX S and the
32 output of receiver 4 is connected to the PABX 5. Also
33 connected to the PAB~ are trunks 6 and local telephone
34 sets 7. Of course the PABX can be divided by number
code so that groups of local telephone sets 7 can be
36 associated with one business or division while other
37 groups can be associated with another business or
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01 division, if desired.
02 One or a plurality o~ remote wireless
03 mobile telephone sets 8 are located within the
04 building. These telephone sets will be referred to
05 herein henceforth as mobile sets and can include data
06 originating and receiving terminals as well as, or in
07 place of voice handsets. Mobile sets 8 preferably are
08 bat-tery operated, can be carried by a user, can be
09 located on a desk, hung on a wall, etc. They are not
connected by wire to the telephone system PABX.
11 Depending on the characteristics of the
12 leaky cable 2, its length, etc., repeaters 9 may be
13 required to be connected at regular intervals in
14 series with the leaky cable. I'hese repeaters are
preferably wideband, such as CATV television
16 repeaters.
17 The PABX S is primarily a normal PABX
18 which operates to interconnect local telephone sets
19 with each other or with trunks 6. In order to
communicate with the mobile sets 8, one o~ the
21 telephone sets 7 dials an appropriate extension number
22 designating a mobile set. The PABX, instead o~
23 connecting the telephone set to one of the other sets
24 7, simply chooses a line terminal 10 which corresponds
to the mobile sets 8, connected to a predetermined
26 junctor. The selected line terminal connects to the
27 input of transmitter 3. In one embodiment ringing
28 current is applied to the line terminal in the normal
29 manner. ~he transmitter 3 converts the ringing
current to a predetermined digital code, interleaves
31 it with other digital codes on a supervisory channel,
32 converts the resul-ting signal to a spread spectrum
33 supervisory channel signal and applies the resulting
34 signal to the leaky cable 2.
The line terminal however designates which
36 mobile set is to be selected, since it corresponds to
37 the dialed number. Once the line terminal has been
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01 selected the transmitter prefixes the digital code
02 with an identifier code which is unique to the mobile
03 set. However it should be noted that rather than
04 using line terminals, junctors of the PABX can be
05 used. Also, instead of applying ringing current to
06 the terminal it can apply a ringing enable signal to a
07 ringing terminal associated with the line terminal.
08 The signal radiates from the leaky cable
09 into the communication region within the building
periphery 1, an~ is received by all o~ the sets 8.
11 All of the mobile sets continuously decode the
12 signalling signals, and as soon as the identifier
13 prefix which iden-tifies the designated set has been
14 received, that the identified set converts the
remaining code which calls for it to ring. Ringing is
16 effected in the mobile set by keying an internal
17 "warble" or other signal to alert the user in a well
18 known manner.
19 The user upon hearing the ringing signal,
switches his mobile set on, the equivalent of going
21 off hook. That mobile set then generates an off-hook
22 supervisory code which is converted to a spread
23 spectrum R.F. signal in the signalling channel, and is
24 transmitted via its own small local antenna to the
leaky cahle 2. Preferably the signal is sent within a
26 time slot designated by the synchronization and
27 control signals sent on the aforenoted supervisory
28 channel. Polling and response of the mobile sets in
29 sequence is preferred to be used in the supervisory
channel.
31 The spread spectrum off-hook code is
32 received by the leaky cable, and is carried to the
33 input of receiver 4. Receiver 4 demodulates,
34 despreads and decodes this signal and applies the
off-hook supervisory signal to the line input port 11
36 of PABX 5 associated with terminal 11 (or to the
37 associated junctor).
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01 It should be noted that while two
02 unidirectional ports 10 and ll have been indicated,
03 the transmitter and receiver can equally be connected
04 to separate inputs of a hybrid which is connected to a
05 bidirectional line or junctor.
06 The PABX 5, receiving the off hook
07 supervisory signal as if it were from a telephone set,
08 completes the connection between the calling party and
09 mobile set via the transmitter 3 and receiver 4 as i-f
10 it were to be connected to another telephone 7. The
11 transmitter 3 and receiver 4 are associated with fixed
12 voice channel transmit and receive pseudo-random
13 spreading codes. When this occurs control apparatus
14 associated with transmitter 3 and receiver 4 transmits
15 on the supervisory channel a data signal addressed to
16 the now off-hook mobile set 8 which designates the
17 transmit and receive pseudo-random codes for the
18 two-way voice channel to be used for voice
19 communication to match those of the transmitter and
20 receiver. The mobile set adopts the codes and thus
21 can transmit and receive on the designated channel.
22 Voice communication between the telephone set 7 and
23 mobile set 8 now proceeds on the specified channel,
24 while using the dedicated supervisory channel Eor
25 supervisory signals.
26 When either of the sets goes on hook at
27 the conclusion of the communication, the supervisory
2~ signal associated with that function is carried by the
2g supervisory channel as described earlier during the
30 set up of a call. The voice connection is then taken
31 down in a manner analogous to setting up all
32 supervisory and voice or data communication thus can
33 proceed in this manner.
34
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01 According to the preferred embodiment in
02 the present divisional patent application, any means
03 for wlreless transmitting the spread spectrum RF
04 signals can be used, such as an antenna. In
05 accordance with another embodiment, which is described
06 above, the transmitting and receiving apparatus
07 associated with a central switching system is
08 comprised of one or more leaky cable transmission
09 lines.
Figure lA illustrates the preferred form
11 of channel assignments. Dedicated pseudo-random codes
12 designate the .supervisory channel in each direction,
13 while a plurality of pseudo-random codes (e.g. up to
14
16
17
18
19
21
22
23
24
26
27
28
29
31
32
33
34
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01 approximately 40,000) can be used to designate the
02 transmit and receive channels. All channels use
03 essentially the same frequency band, though different
04 bands are used in -the centre to mobile and mobile to
05 centre directions. None will be found to interfere
06 with each other or with other wireless services using
07 the same frequencies, except for random bit errors
08 which will increase with traffic. In a typical system
09 only about 32 two-way channels will be required
although there is clearly capacity for many more,
11 given the number of codes available.
12 In a similar manner calls can be made from
13 any mobile set 8. All mobile sets 8 continuously
14 receive and transmit information on the supervisory
channel. Thus if a mobile set 8 goes off-hook this
16 information is transmitted by the supervisory channel
17 to receiver 4 where it is demodulated, despread and
18 decoded before passing to PAB~ 5. On receiving the
19 off-hook signal PABX 5 allocates a voice channel as
described above, transmits dial tone to the mobile set
21 8, receives signalling information from mobile set 8
22 and sets up the call in the usual manner. The mobile
23 sets 8 are clearly not limited to voice
24 communications; they can be combination voice and data
sets, or restricted to being data terminals. In this
26 respect one of the trunks 6 of PABX 5 can be connected
27 to a computer for receiving data from and transmitting
28 data to a mobile data set 8. Alternatively a computer
29 can be connected directly to the main bus of PABX 5
for communication with the mobile sets. In this
31 manner the mobile set 8 can be used as a remote
32 terminal to a central computer. Low speed data
33 communication can be effected with the mobile set 8
34 via the supervisory channel, or high speed via a
dedicated data channel, or via a voice channel shared
36 with and carrying data.
37 Block diagrams of the mobile set and
38 - 14 -



- : .

.

9~
01 central equipment constitutiny the transmitter and
02 receiver are shown in Figures 2 and 3. The mobile set
03 will be described first, with reference to Figure 2.
04 An analog telephone set 15 to which a
05 handset or handset with display 16 is connected and,
06 if desired, a keypad ]7 has an intexnal hybrid with an
07 output line connected to an analog-to-digital PCM
08 encoder 18. Preferably the encoder is an adaptive
09 differential encoder of toll quality, e.g. it will
encode a signal which is output at 32 Xb/sec.
11 The output of encoder 18 i5 connected to
12 the input of modulator 19, which both spread spectrum
13 ana RF modules the incoming signal. The output of
14 modulator 19 is connected to the input of a combiner
21 which is connected through a transmit filter 22 and
16 directional coupler 22A to an antenna 23.
17 The filter preferably is 8 megahertz wide,
18 having a Q between 20 and 100. It can for example be
19 a printed strip line controlled by varacter diodes
such as is often found in the tuner of a TV set.
21 The antenna 23 is similarly connected
22 through a directional coupler 23A to the input of the
23 receive filter 24 (which is similar to filter 22)
24 which is connected to the input of a splitter 25. One
output of splitter 25 is connected to demodulator 27
26 which both spread spectrum and RF demodulates the
27 signal. The output of demodulator 27 is connected to
28 the input of digital-to-analog PCM decoder 28, the
29 output of which is connected to the input line to
tele~hone 15.
31 A data interface circuit 29 is also
32 connected to telephone set 15, which con~ains data
33 encoding and signalling circuitry as well as
34 associated buffers. Considering only the signalling
aspect for the moment, off-hook, on-hook, etc. and
36 other signalling signals as are norm lly generated in
37 a telephone set are applied via interface circuit 24
38 - 15 -


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01 to a synchronization and control circuit 30. The
02 synchroniza-tion and control circuit contains a master
03 clock for the mobile set, and controls the filters 22
04 and 24. The clock signal used in the synchronization
05 and control circuit is obtained from the incoming
06 signal received via antenna 23.
07 A spread spectrum and RF modulator 31 has
08 its input connected to synchronization and control
09 circuit 30, and its output connected to another input
of combiner 21. The output of RF modulator 38 is
11 connected to another input of combiner 21.
12 A second output of splitter 25 is
13 connected to an input of demodulator 34, which has its
14 output connected to synchronization and control
circuit 30.
16 A voltage controlled oscillator circuit 35
17 is connected to the synchronization and control
18 circuit 30, and has outputs connected to modulators
19 19, 31 and 38 and demodulators 27, 34 and 41.
Synchroniza-tion and control circuit 30
21 also has outputs connected to modulators 19, 31 and 38
22 and demodulators 27, 34 and 41.
23 In operation, according to the preferred
24 embodiment of the invention the pseudo-random codes
designating the transmit and receive supervisory
26 channels are Fixed by means of code plugs or other
27 similar code designating means, fixed in modulator 31
28 and demodulator 34. A supervisory signal having a
29 spreading code correlatable by the correlation code in
demodulator 34 is received from the leaky cable
31 transmission line 2 (Figure 1) by antenna 23. The
32 signal passes through directional coupler 22A/ is
33 filtered in filter 24, passes through splitter 25 and
34 into demodulators 27 and 34. However since
demodulator 27 will not recognize the encoded signal,
36 it outputs only a low level random noise signal.
37 However since spread spectrum modulator 34 does
38 - 16 -




~, :

~l~6~

01 recognize the supervisory channel codet it decodes the
02 signal and applies it to synchronization and control
03 circuit 30. Synchronization and control circuit 30
0~ recognizes a data header designating the local mobile
05 set and further recognizes the demodulated code as
06 meaning that ringing should start. It applies a
07 signal to telephone controller 15, which begins
08 ringing. If the local mobile set data header was not
09 recognized, the ringing function would not be enabled.
It should be noted that on the supervisory
11 channel the code which is received can designate any
12 supervisory function or indeed can carry low speed
13 data communication signals. In this respect it is
14 preferred that the signal carried on this channel
should contain four 8 bit words in sequence: the
16 first 8 bits designating the station number of the
17 mobile set, and second 8 bits designating what
18 function should be performed, the third 8 bits should
19 contain bits to enable error detection and correction,
and the four-th group of 8 bits should contain a
21 synchronization pattern.
22 With the local telephone set going
23 off-hook, telephone controller 15 applies an off-hook
24 signal to synchronization and control circuit 30.
Synchronization and control circuit 30 in turn
26 generates a code sequence containing the local station
27 address identi~ier, a supervisory code designating
28 "off hook", error correction bits and a
29 synchronization pattern and applies it to modulator
31. Modulator 31 modulates the ~ignal using the fixed
31 supervisory channel code and also RF modulates the
32 signal applied to it before applying it to an input of
33 combiner 21. The output signal of combiner 21 is
34 applied through filter 22 and directional coupler 22A
to antenna 23 from which it is transmi-tted to leaky
36 cable transmission line 2.
37 A supervisory signal is also received from
38 - 17 -



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01 the central equipment in the same manner as noted
02 above which desi~nates which channel or channels the
03 incoming and outgoing analog and/or data signals from
04 and to the mobile set are to be transmitted. This
05 channel designating signal is received by the
06 synchronization and control circuit 30 over the
07 supervisory channel. The synchronization and control
08 circuit 30 upon receiving the channel designating
09 signals applies signals to modulator 19 and
demodulator 27 which control the pseudo-random
11 spreading and correlating codes respectively. Once
12 these codes have been established in the modulator and
13 demodulator, subsequent signals will be transmitted on
14 a spread spectrum channel designated by the modulation
pseudo-random spreading code and received by the
16 mobile set on a spread spectrum channel designated by
17 the designated correlation.
18 For transmission of analog or analog and
19 data signals from the local handset, such signals pass
from handset 16 (and/or keypad 17) into telephone 15
21 in the usual manner, are split into unidirectional
22 signals, e.g. in a hybrid, and the outgoing signals
23 are applied to PCM encoder 18. The resulting digital
24 output signals are applied to spread spectrum
modulator 19, are modulated using the channel
26 spreading code established therein as described above,
27 and are applied to RF modulator 20. Under control of
28 the synchronization and control circuit 30 modulator
29 20 modulates the signal, and the resulting RF
modulated spread spectrum signal is applied via
31 multiplexer 21 through filter 22 to antenna 23 ~or
32 transmission to the leaky cable transmission line.
33 A signal received from leaky cable
3~ transmission line 2 by antenna 23 is applied through
directional coupler 22A, filter 24, and splitter 25 to
36 demodulators 27 and 3~ which are controlled by
37 synchronization and control circuit 30. The resulting
38 - 18 -




-
" ' ' . ': ,:

38~

01 demodulated and despread signal from demodulator 27 is
02 applied to PCM decoder 28. The resulting analog
03 output signal is applied to the incoming signal line
04 of telephone 15 Erom where it is applied to handset
05 16. However since demodulator 34 will not recognize
06 the pseudo random code used it will not apply any
07 input to synchronization and control circuit 30.
08 In the above manner all of the supervisory
09 functions of the mobile set can be received and
transmitted, the analog signal receive and transmit
11 channels established and the analog and low speed data
12 transmitted and received.
13 It is preferred that when no radio
14 frequency signals are being received, decoder 28
should be switched into a silence mode. A silence
16 code genera-tor 36 is connected to the output of
17 demodulator 27. When the silence code generator 36
18 detects silence code at the output of demodulator 27,
19 it applies a signal to decoder 28 which causes it to
remain stable in a known state, whereby no analog
21 output signal is generated.
22 Similarly, a silence detector 37 is
23 connected to the outgoing signal line of telephone set
2~ 15 for detecting silence. The output of silence
detector 37 is applied to synchronization and control
26 circuit 30,which reduces or shuts off modulator 19 for
27 that interval. This results in a reduced error rate of
28 signals received by the central system and reproduced
29 in the mobile set. The silence code detector 28 and
silence detector 37 should be very fas~ acting so as
31 to prevent the clipping of the start of words.
32 Silence detectors have been used in TASI (time
33 assignment speech interpolation) transmission systems.
34 In order to transmit and receive high
speed data, data interface circuit 29 interfaces via
36 telephone 15 to the display in the display and handset
37 16 and to the keypad 17, or to an external port (not
38 - 19 -

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01 shown) which may receive data from a local data
02 collection machine or the like. The high speed data
03 is applied through data interface 29 to modulator 38
04 of construction similar to that of modulator 19. The
05 output of modulator 38 is connected to an input of
06 combiner 21.
07 An output of splltter 25 is connected to
08 an input of demodulator 41, which has its output
09 connected to the incoming data port of data interface
29.
11 For reception and transmission of data,
12 modulator 38 and demodulator 41 operate similarly to
13 modulator 19 and demodulator 27 respectively. The
14 modulator 38 and demodulator 41 are controlled upon
receipt of a signal in the synchronization and control
16 channel designating that data is to be received or
17 transmitted, in a manner similar to that described
18 earlier. Channels are designated by the allocation of
19 pseudo-random codes as described earlier. The data
can be transmitted using simple packets at 90.2
21 Kilobits per second, ~or example, the packets
22 containing data signals and error correction codes.
23 Turning now to Figure 3, the transmitter
24 and receiver and PABX interface at the central
equipment are illustrated. The elements in the
26 transmitter and receiver referred to with respect to
27 ~igure 1 will become evident by the description below
2~ and have not been segregated, for the purpose of
29 clarity of explanation.
A PABX 5 includes a plurality of interface
31 circuits 42, one of which is shown. ~ach inter~ace
32 circuit can be similar to a well known PABX line
33 circuit except that it has an additional communication
34 link with the main bus of the PABX for receiving
synchronization pulses for transmission to the mobile
36 se~.
37 ~ When a telephone set 7 wishes to
38 - 20 -


:

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01 communicate with a mobile se~, Eor example, a
02 subscriber will dial digits designative of the
03 particular mobile set to be contacted. The PABX, in
04 the normal manner, can select a line terminal or port
05 which is unique to that mobile set. However use of
06 the system in this manner would require as many line
07 circuits or terminations as there are mobile sets. It
08 is preEerred, instead, to have the PABX select a
09 particular junctor with a PABX interface connected
thereto, with the mobile set to be selected designated
11 by address or ground point. Use of the system in this
12 preferred manner will require only as many interface
13 circuits as the traffic requires, clearly a
14 considerably fewer number of interfaces, circuits and
channels than the number of mobile sets.
16 With the interface selected and either a
17 line termination enabled or a data code received from
18 the PABX which designates the mobile set to be rung, a
l9 sync and control circuit 43 receives both the
supervisory signal and designation of the mobile set
21 to be contacted from the PABX via the PABX interface.
22 The sync and control circuit 43 formulates a data
23 packet comprised of the station number, supervisory
24 signal, error correction and synchronization pattern
bits and transmits it to a modulator 44. Modulator 44
26 has a dedicated pseudo-random spreading code fixed to
27 the supervisory channel. The modulator 44 spread
28 spectrum and RF modulates the supervisory signal
29 (which in this case contains a supervisory sequence
which indicates that a particular mobile set should be
31 rung). The modulated output signal therefrom is
32 applied to multiplexer 46 from which it is passed to 8
33 megahertz filter 47, which is similar to filter 22.
34 The output signal of filter 47 is applied to one end
of leaky transmission cable 2. The signal passes
36 along transmission cable 2, radiating as described
37 earlier. The radiated signal is received by mobile
38 - 21 -



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~6~38~: `
01 set 8 in the manner described above.
02 A signal received from the mobile set 8
03 passes through 8 megahertz filter 48 (which is similar
04 to filter 47) and splitter 49 and demodulator 51.
05 Since the supervisory signal is on a fixed channel,
06 the pseudo-random correlation code for demodulator 51
07 is fixed, and the received signal is demodulated
08 resulting in a data signal applied to sync and control
09 circuit 43 which constitutes the return supervisory
signal (e.g. an off hook indication) from mobile set
11 8. Sync and control circuit 43 applies this signal to
12 PABX interface 42 which applies it in recognizable
13 form to PABX 5.
14 Sync and control circuit 43 also has
outputs connected to modulators 44, 53 and 59 and
16 demodulators 51, 56 and 62 for applying a
17 synchroniDation and control signals thereto.
18 Since a particular junctor, and thus PABX
19 interface 42 was selected by the PABX for the
forthcoming com~unication, the particular outgoing and
21 incoming channels are thereby designated, and a mark
22 signal related to the particular channels is applied
23 to sync and control circuit 43. Sync and control
24 circuit 43 contains a table of psuedo-random codes
corresponding to the selected spread spectrum
26 modulator and demodulator, and another table of mobile
27 set station numbers corresponding to the mark signal
28 (which identifies the called mobile station uniquely-
29 A supervisory signal is formulated in sync and control
circuit 43, which is sent to the selected mobile set 8
31 identified by station number, advising it ~hat spread
32 spectrum channel to tune itself to.
33 The supervisory signal can send to the
34 mobile set one of two kinds of signals- a signal
advising the mobile set to establish its rsceive and
36 transmit spread spectrum modulator and demodulator
37 pseudo-random codes to codes stored in a table in each
38 mobile set, i.e. identifying the codes by number.
39 - 22 -



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~2~1~8 IL
01 Alternatively the sync and control circuit can
02 transmit the actual pseudo-random codes to the
03 selected mobile ~et 8 to enable it to set its
04 modulator and demodulator to the designated spread
05 spectrum channels. In this manner, in a 200 mobile
06 set system, typically 32 junctors and thus 32 P~BX
07 interfaces can be used, rather than 200 interfaces
08 would be required if each line circuit were separately
09 interEaced. However the present invention
contemplates the use of individual line circuits for
11 each two-way channel if economics dictate.
12 Since a particular ~unctor, and thus a
13 particular PABX interface circuit 42 has been selected
14 by the PABX in the normal manner to carry the
communication, the outgoing and incoming channels are
16 also fixed as noted above. The output signal from the
17 PABX interface circuit is applied to analog digital
18 PCM encoder 52. The resulting encoded output signal
19 is applied to the input of modulator 53 which has a
dedicated pseudo-random code related to that
21 particular channel. The RF modulated output signal is
22 applied to an input of combiner 46, from which it
23 passes through filter 47 and is applied to the leaky
24 cable 2. Since the spread spectrum modulation codes
in modulator 53 and modulator 44 are different, there
26 will be no interference between the two signals. The
27 signal applied to leaky cable 2 is radiated for
28 reception by mobile sets 8 as described earlier.
29 A received signal from the leaky cable 2
transmitted by mobile set 8 passes through filter 48
31 and combiner 49, is demodulated and despread in
32 demodulator 56, and the resulting signal is passed to
33 analog PCM decoder 57. The resulting output signal is
34 applied to PABX interface 42 for application to the
junctor of PABX 5. Since the spread spectrum
36 pseudo-random spreading code at the mobile set for
37 signals transmitted thereat under control of sync and
38 - 23 -



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01 control circuit 43, were desiyna~ed by the selection
02 of a particular junctor and PABX interface circuit 42
03 by normal operation of the PABX, which is identical to
04 that pseudo-random code in spread spectrum demodulator
05 56, the signal received from mobile set 8 is properly
06 decoded in demodulator 56, but is rejected by
07 demodulator 51.
08 The PABX interface can also interface to
09 high speed data junctors, or to a data bus in the PABX
which designates by code which mobile set is to be
11 communicated with. Either by junctor se]ection
12 as described above or by decoded selection from the
13 PABX data bus, the high speed data signal is applied
14 to outgoing data interface circuit 58. The output
signal is applied to modulator 59, in a manner
16 analogous to that described earlier. The RF modulated
17 signal is applied to an input of combiner 46, passes
18 through filter 47 and is applied to the leaky cable 2.
19 Received high speed data signals from
mobile set 8 are received by leaky cable 2 and pass
21 through filter 48, splitter 49 and are applied to
22 demodulator 62. The resulting data output signal
23 after spread spectrum and RF demodulation is applied
24 to data interface circuit 63, from which the data
signal is applied to the junctor or data bus of the
26 PABX through PABX interface circuit 42. The data
27 channel selection at the mobile set 8 is established
28 as the incoming and outgoing data channels in a manner
29 analogous to that described above for the ougoing and
incoming analog channel.
31 It is preferred that a silence detector
32 and a silence code detector should be used in each of
33 the incoming and outgoing analog channels of the
34 central equipment (not shown) which are similar to
those described with reference to Figure 2 and are
36 similarly connected. The silence and silence code
37 detectors should be very fast acting. Since the error
38 - 24 -



~' , - .- .: :

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`

~l~6~

01 rates of the signals which are received are dependent
02 on the total number of channels sharing the same
03 bandwidth, it is highly desirable -to switch the RF or
04 IF signals of~ or to extremely low level during silent
05 periods. Fox a given error rate, the use of silence
06 detectors will increase the number oE channels which
07 can share the same bandwidth at the same time.
08 Synchroni~ation will not be lost since the supervisory
09 channel will alwaysbe operating and carries
s~nchronization signals. Thus the receivers at the
11 mobile sets and at the central equipment can always
12 regain synchronization if it is lost.
13 When communication has been set up the
14 mobile sets thus each will have two receive addresses,
one which is a polling address which is used on the
16 synchronization channel and the other which is the
17 pseudo-random code, i.e. the correlation code that it
18 is instructed to use via the supervisory channel. It
19 will use two transmit addresses, one which designates
it and allows it to be recognized in the superVisorY
21 receive channel at the central equipment and one a
22 pseudo-random code which matches the analog or digital
23 receive channel code at the central equipment. Thus
24 the instruction to use a particular correlation code
is similar to the designation to the mobile set to use
26 a particular junctor, and is directly analogous to the
27 junctor selected at the PABX. It can additionally
28 have separate high speed data channel receive and
29 transmit spreading and correlation code addresses.
The pulse code modulation scheme which is
31 used is preferred to be adaptive differential PCM, a
32 full description of which can be obtained in the draft
33 recommendation G721 of CCITT. According to this
34 specification PCM is transcoded from 64 Kilobits per
second to 32 Rilobits per second. It is also
36 preferred that the pseudo noise code sequence used in
37 the spread spectrum modulator should be 255 bits,
38 - 25 -




.

01 although it is expected that other sequence lengths
02 could be used. It is also preferred that the RF
03 modulation should be phase shift keyed, and can be
04 minimum shift keyed, bandwidth phase shift keyed, QPSK
05 or staggered phase shift keyed. It is also preferred
06 that the data channels should transmit at 90.2
07 kilobi-ts per second.
08 It should be noted that only one sync and
09 supervisory channel modulator and demodulator 44 and
51 need be used for the entire system while the PABX
11 interface and decoders, modulators and demodulators
12 are duplicated for each channel. Of course apparatus
13 used for the data, or Eor the analog channels need not
14 be used if one or the other kind of communication is
not to be provided for a particular junctor or for
16 communication to the mobile sets in general.
17 Referring now to Figure 4, the modulation
18 portion of the transmitter is shown. An incoming PCM
19 or data signal from encoder 52, for example, is
carried on line 64 to a data circuit 65, in which the
21 incoming signal is synchronized and speed adjusted.
22 The outgoing signal from data circuit 65 is applied to
23 an exclusive OR gate 66. A sequence generator 67
24 generates a pseudo-random code which is specific to
the channel to be transmitted and applies its output
26 to another input of exclusive OR gate 66. One
27 complete pseudo-random code, of preferred length 255
28 bits, is Exclusively ORed with each data bit. The
29 resulting P~ sequence of exclusive OR gate 66 is
applied to an input of data modulator 68. The data
31 circuit 65, sequence generator 67 and exclusive OR
32 gate 66 provides the spread spectrum modulation.
33 An intermediate frequency (IF) oscillator
34 69 generates a signal which is applied to data
modulator 68, where it modulates the signal, resulting
36 in a IF signal on line 70. The IF signal is applied
37 to a summer 71, along with the IF signals of other
38 - 26 -

~6~8,~,

01 data modulators, illustrated by line 71A. The output
02 signal o~ summer 71 is applied to a mixer 72, to which
03 is applied an RF carrier signal generated in a carrier
04 generator 73. The carrier signal is mixed with the
05 sum IF signal and the resulting RF modulated output
06 signal of mixer 72 is applied to an 8 megahert~ filter
07 74. The output ~ilter of signal 74 is applied to
08 leaky transmission line 2.
09 It is preferred that the data modulator
should modulate the IF signal with the output of
11 E~clusive OR gate ~6 using phase shift modulation.
12 It will be noted that in the circuit of
13 Figure 4 the modulated signals have been summed prior
14 to RF modulation in mixer 72. The summer 71 is of
course equivalent to combiner 46. The IF signals can
16 be summed prior to RF modulation as shown in Figure 4,
17 or the RF signals can be summed following RF
18 modulation as shown in Figure 3.
19 The receive channel is similar to Figure 4
in that the mixer outputs to a splitter the IF signal
21 in a well known manner and the resulting signal is
22 applied to a data demodulator. The demodulator
23 multiplies the incoming signal by an IF signal
24 modulated by the same pseudo-random code used in the
transmitter. The output of the demodulator is then
26 low~pass filtered to recover the data.
27 While the circuit of Figure 4 can be used
28 in the transmit and receive channels of the central
29 equipment shown in Figure 3, the major different
between that circuit and the circuit used in mobile
31 set 8 is that the sequence generator can generate a
32 selected code sequence in the latter. As noted
33 earlier the sequence is established either by a look
3~ up table in the mobile set which is designated by the
supervisory signal received from the central equipment
36 or b~ reception of the actual sequence to be used. Of
37 course the receive channel is directly analogous to
38 - 27 -




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~1 the transmit ehannel.
02 Returning to the supervisory channel,
03 during idle intervals i-t is preferred that the cen-tral
04 equipment should transmit a 32 bit supervisory polling
05 message to each mobile set in sequence and to wait for
06 a response in the following 32 bit message. In case
07 erroneous messages are received, it is preferred that
08 a reques-t for a repetition should be transmitted in
09 the next supervisory sequence designated for the
particular mobile set or the particular ~unctor
11 channel time period. In the analog and data channels
12 either repe-tition or error correction, or ignoring
13 packets which have been designated as erroneous can be
14 implemented. Since the supervisory channel operates
by polling, transmission collisions are avoided.
16 Each of the elements described above can
17 be implemented in dedicated logic to provide the
18 func-tions described, or can be grouped and implemented
19 in microprocessor-memory combinations operated using
firmware written using the algorithms described
21 herein.
22 Since radiation from a leaky transmission
23 cable is used, extremely low powers can be used, e.g.
24 ten milliwatts per channel. Clearly the power used in
the mobile sets~ typically operated by battery, is
26 greatly economized.
27 Since spread spectrum is used in
28 combination with the leaky cables, nulls which are
29 usually encountered using leaky feeder systems, and
signal dropout regions often encountered using fixed
31 antenna radiators are substantially avoided. Since
32 there is a fast drop off of signal level with distance
33 from the leaky cable radiator, the judicious placement
34 of leaky cable in the ceiling or other peripheral
region of the building will establish detectable power
36 levels throughout the building, but virtually
37 undetectable RF signals outside of the environs of the
38 - 2~ -




-

~Z6~

01 building. Thus the system is highly localized,
02 minimizing any interference with any other kinds of
03 systems.
04 Further, because the system is spread
05 spectrum, it is inherently private, which is highly
06 unusual in a wireless telephone system. It is
07 economical of spectrum space, since substantially the
08 same bandwidth is used for all channels. With the
09 very low level of power which is used, and each
channel being spread over a wide bandwidth, the actual
11 transmitted signal appears to be little more than very
12 low level noise to conventional wireless systems. Yet
13 because there are such a great number of pseudo random
14 codes which can be used, the possibility of
interference between channels, or of intercep-tion
16 outside of the present system is rendered almost nil.
17 The system can be used for conventional
18 analog voice communication, as noted earlier, or in
19 addition or in alternative the mobile set can be a
hand held computer terminal. However since each
21 mobile set can transmit on either a designated or
22 centrally controlled secure channel, the mobile set
23 can also be used for remote control of apparatus such
24 as automatic doors, various building services, etc.
with high security. For example it can control
26 robots, domestic appliances, etc. The mobile set is
27 thus a highly versatile unit used in conjunction with
28 the system described above.
29 It should also be noted that while the
modulators and demodulators at the central equipment
31 have fi~ed pseudo random codes and those at the mobile
32 sets have codes which are variable, in an alternative
33 system the codes at the mobile sets can be fixed, and
34 the codes at the central equipment can be varied to
select a channel corresponding to -the designated
36 mobile set. However in this case the number of
37 variable pseudo-random codes which are used will
38 - 29 -



,: ~



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~;26~

01 correspond to t~ice the number of mobile sets (two
02 one-way channels to each mobile set), plus two for
03 supervisory while in the case in which the mobile sets
04 change their correlation codes, the number of
05 correlation codes used will correspond to twice the
06 number of junctors or toial channels expected to be
07 used for communication (plus two for supervisory), a
08 far fewer number.
09 Further, the central apparatus described
herein could usefully be employed to operate with one
11 or a group of distributed antennae, rather than, or in
12 addition to, the leaky cable. Such a structure would
13 find great utility in buildings or outdoor areas in
14 which it is not feasible to wire telephone system
connected by wires, or to deploy a leaky cable.
16 A person understanding this invention may
17 now conceive of various alternative structures using
18 the principles described herein. All are considered
19 to be within the scope of t~e invention as defined in
the claims appended hereto.




21




,

Representative Drawing

Sorry, the representative drawing for patent document number 1261981 was not found.

Administrative Status

For a clearer understanding of the status of the application/patent presented on this page, the site Disclaimer , as well as the definitions for Patent , Administrative Status , Maintenance Fee  and Payment History  should be consulted.

Administrative Status

Title Date
Forecasted Issue Date 1989-09-26
(22) Filed 1984-03-08
(45) Issued 1989-09-26
Expired 2006-09-26

Abandonment History

There is no abandonment history.

Payment History

Fee Type Anniversary Year Due Date Amount Paid Paid Date
Application Fee $0.00 1988-10-17
Registration of a document - section 124 $50.00 1998-02-16
Registration of a document - section 124 $50.00 2001-05-04
Owners on Record

Note: Records showing the ownership history in alphabetical order.

Current Owners on Record
MITEL CORPORATION
Past Owners on Record
ANDERSON, ADRIAN J.
CAREY, MICHAEL J.
MITEL TELECOM LIMITED
Past Owners that do not appear in the "Owners on Record" listing will appear in other documentation within the application.
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Document
Description 
Date
(yyyy-mm-dd) 
Number of pages   Size of Image (KB) 
Drawings 1993-09-14 3 90
Claims 1993-09-14 2 64
Abstract 1993-09-14 1 20
Cover Page 1993-09-14 1 24
Description 1993-09-14 31 1,518
Fees 1992-09-09 1 36
Fees 1991-11-08 1 41