Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to wireless telephone systems and is useful, in particular, for
providing telephone communic~tion to a plurality of wireless h~n~,set~ over a predetermined
5 reception region, such as a high-rise offlce building, a factory or other business or industrial
premlses.
Digital cordless telephone h~ lsel~ using low power levels at RF frequencies have been employed
to exchange telephone signals with a wireless base station connected to a public switched
10 telephone network.
There exists a need to adapt such a system to a relatively restricted environment, for example to
an office building, or part of an offlce building, a factory or some other relatively restricted
commercial or industrial premises in order to provide wireless mobility for key employees of a
15 corporation operating on the premises.
In such an e"viro~ a difficulty arises in that the low tl~nsn iL power of the cordless h~n~set.~
and of the base station restricts the range of the base station. It has therefore previously been
necessary to employ a plurality of base stations at di~rere"~ locations distributed applopliately
20 around the reception region of the premises.
However, the use of the plurality of base stations gives rise to the problem of how to locate a
particular handset in the event of an incoming call for that handset, since it is not clear to where
the switchboard should direct the call.
Also, it is desirable for the handset to be mobile from the coverage zone of one of the base
stations into the overlapping covering zone of an a~jacçnt base station, however without some
kind of call hand-off control, it is difflcult to "pass" the call from one of the base stations to the
other in a seamless fashion.
The base stations can be designed to handle a plurality of simlllt~neous calls, for example by
adding ~ sc~iver cards to the base stations. When a number of base stations are required to be
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distributed around the reception region, each of the base stations will normally require numerous
transceiver cards so as to avoid call blocking issues, i.e. giving "busy" signals whenever an
u~ A~e~iledly large number of handset users congregate in the coverage zones of one of the base
stations instead of being more evenly distributed over the zones of all of the base stations.
Prior art wireless telephone systems have employed di~rerenl approaches to deal with these
issues.
Some of the prior art systems employ computer networks to keep track of individual handsets
10 or to carefully control the ability of a base station to service a call. Typically, mobility is provided
by a cellular radio-like approach, in which the computer system monitors the received signal
strengths ofthe off-air signals from any of the handsets at each base station, and, on the basis of
this i"rO, 1"~l ;on, clears ~h~ .le and alerts ~(ljacPnt base stations if the h~nd,set is moving towards
the coverage zone of an adjacent base stations. Such systems can provide ubiquitous roaming
15 and full incoming call capability, but are relative complicated and expensive.
Other prior art systems have ignored the disadvantages associated with the use of a plurality of
base stations, thus providing only a limited degree of mobility.
20 According to the present invention, there is provided a time division duplex wireless telephone
system which comprises a switchboard connected to a public switched telephone network, a base
station for RF modulation of outgoing telephone signals and demodulation of incoming telephone
signals, a plurality of RF repeaters connected to the base station and a plurality of telephone lines
connecting the switchboard to the base station.
In operation, the RF repeaters may be distributed over an area requiring coverage. These RF
repeaters int~ .e the off-air signals to/from mobile h~ndsets, to a signal conduit that relays the
off-air signals back to a central site at which the base station is located. Typically, the signal
circuit is a dedicated coaxial cable, although coaxial cable common to other services, or fiber
30 optic cable, may be used.
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At the central site, the base station demodulates/modulates communications with the h~n~set~
In such an application, the base station typically coll~ains multiple transceiver cards so as to
support a number of ~imlllt~neous users. The base station typically interfaces to the switchboard
by simple line card interfaces.
The use of the base station in this manner, instead of employing a plurality of base stations to
service the same number of h~ndsets as in the prior art, allows the predetermined reception
region, e.g. an office building, factory or other commercial or industrial premises, to be served
by fewer line cards and Ll~lsceivers than were previously required. (i.e. to obtain greater trunking
10 efficiencies in the RF system).
The RF repeaters can be designed to provide multiple call capability, thus emlll~ting the
functionality of a base station with many transceiver cards. Since the RF repeaters are
substantially less costly than the line cards, a considerable savings is achieved.
The RF repeaters may be connected to the base station through a coaxial cable or a fiber cable
as part of a combiner nc;~wolk preserving RF amplitude and phase h~lllla~ion. In these
circllm~t~nces, overlapping coverage zones of ~dj~cPnt RF repeaters form elements of a single
~ntP.nn~ pattern, sometimes referred to as a distributed ~ntçnn~ pattern, which can be "shaped"
20 in accordance with the area of which it is required to provide wireless mobility for the h~n(lsets
Within the predetermined reception region defined by this distributed ~ntenn~ pattern, the
h~ndset~ are afforded mobility, since call hand-off is not required within a single ~nt~nn~ pattern
(distributed or otherwise). For relatively small and medium sized commercial and industrial
premises, a single distributed antenna pattern can be arranged to serve the required number of
25 handsets over the reception region. Under these circllm~t~nces, location of any particular
h~n~et, for a call incoming from or outgoing to that h~ndset, does not present a problem, since
all of the h~n~set~ are within the reception region defined by the single distributed ~ntPnn~
pattern. Alternatively it may be convenient to define a very limited number of separate distributed
~nt~nn~ patterns, and to accept the consequences of such an arrangement.
The use of time division duplex technology provides substantial cost savings as compared to
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frequency division duplex systems.
Further features, objects and advantages of the invention will be more readily apparent from the
following description thereof taken in conjunction with the acco~l,pa"yhlg drawings in which:-
Figure 1 shows a diagl ~" " "~ illustration of an embodiment of the present invention employing
a distributed ~ntenn~ array;
Figure 2 shows a diagram, taken vertically through a multi-story building, of an adaptation of the
10 distributed ~ntenn~ array of Figure 1; and
Figure 3 is a diagrammatic illustration of a telephone system providing communications in
di~l en~ ways to di~erell~ reception regions.
15 Figure 1 of the accompanying drawings illustrates a wireless telephone system connected to a
public switched telephone network, which, for convenience of illustration, is shown as a box
labelled by reference numeral 10.
The public switched telephone network 10 is connected through a switchboard 12 to a base
20 station 14. The switchboard 12 possesses the full functionality of a public switchboard in the
present embodiment of the invention but may alternatively have the more limited capability of a
key-set switchboard.
The base station 14 modulates outgoing telephone signals at RF frequencies for bro~dc~ting as
25 off-air signals, and demodulates incoming RF signals to provide two-way voice/data telephony.
In order to extend the coverage zone of the base station 14, the output of the base station 14 is
connected by a dediç~ted coaxial cable 15 to a plurality of RF repeaters 16, with power and
timing signals as may be necessary being inserted at RF repeater 16A.
Such an arrangement has the advantage that, instead of being restricted to a relatively small
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coverage zone, as would be the case if the output ofthe base station 14 were tr~n.~mitte~ through
a single base station ~nt~nn~, the off-air signals can be exchanged with h~n(l~ets 18 throughout
the coverage zones of the plurality of RF repeaters 16. These coverage areas can be arranged
to overlap and can be distributed so as to provide a combined reception and tran~mi~ion region
adapted to the extent of, for ~ , a collllllelc;~l or industrial premises such as the multi-story
office building diagr~mm~tic~lly represented in Figure 2 of the drawings.
As shown in Figure 2, RF repeaters 17 are provided at alternate stories of a building indicated
generally by lt;;re~ ce numeral 20 and are connected through a base station 15 and a switchboard
11 to the public switched telephone network 10. Powering and timing signals are inserted onto
the signal conduit by RF repeater 17B.
It will be observed that the building 20 is also equipped with a microcell extender 17A which is
located on the exterior of the building 20 to provide coverage, for example, in a car park, loading
dock or other adjacent area.
Figure 3 diagl~nllllaLically illustrates in greater detail, and with some variations, a wireless
telephone system employing the present invention.
As can be seen from Figure 3, the ~wiLchl~oard, which is indicated generally by reference numeral
12, comprises trunks 22, switches 24 and a plurality of line cards 26. The line cards 26 are
respectively associated with telephone lines 28, 30 and 32.
The telephone lines 28 connect the switchboard 12 to a base station 14A, in which the lines 28
are connected to respective base station components 34, the outputs of which are, in turn,
connected to a combiner 36, which combines the higher frequency output signals of the base
station 14A onto a leaky coaxial cable indicated generally by reference numeral 40.
Figure 3 also shows, as a second alternative a~ p,~ , the base station 14, which is connected
to the switchboard 12 by the telephone lines 30. In this case, the telephone lines 30 are
connected to respective base station components 34A, the outputs of which are connected by a
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combiner 36 and dedicated coaxial cable 15 to a plurality of RF repeaters 16A and 16B for
communicating with the h~ndsets 18. The RF repeaters 16B are distributed over an offlce or
factory area or other commercial or industrial premises, as discussed above, in order to provide
a distributed antenna array covering a predet~rmined reception region.
The above-described components, 16, 16A and 17, 17B are m~nllf~ctl~red and sold by Nexus
Engineering Corp., of Burnaby, B.C., Canada, as parts nos. CT-A2 and CT-B2, respectively.
As a third alternative, Figure 3 also shows the telephone lines 37 from the switchboard 12 as
10 being connected to a public base station 50, the output of which can be connected through a
signal conduit 52 to a leaky coaxial cable (not shown) similar to the coaxial cable 40, and through
a signal conduit 54 to an array of RF repeaters or microcell extenders (not shown).
As will be apparent to those skilled in the art, various modifications may be made to the above
15 described appal~Lus within the scope of the appended claims.
