Title of Invention


Abstract A method and apparatus for reducing power consumed by mobile, wireless units, such as personal communications systems or wireless PBX telephones, by reducing the frequency with which various circuits within the units are fully energized. During on-going voice communications between a base station and a wireless unit, the wireless unit reduces the frequency of its references to a control channel and may eliminate auch references altogether. In addition, while idle, the wireless units may not attempt to reference the control channel during all occurrences of the control channel, reducing both power consumption and the possibility of collisions with other wireless units in attempting to access the control channel.
This application is one of a group of applications filed on
even date herewith, specifically: "A Wireless Communications
System and Method Using a Reusable Control Channel", by Jackson
et al., Serial Number ; "A Multiple Orientation, Multiple
Antenna Apparatus", by Jackson, et al., Serial Number ; "A
System For Communicating Digital Information Between A Base Unit
and Plural Mobile Units", by Jackson, et al., Serial Number
A Wireless Communications System and Method Having
Dynamic Reallocation of Communications Frequencies", by Jackson,
et al. , Serial Number ; "A Method and Apparatus For
Reducing Power Consumption In Wireless, Mobile Communicating
Devices", by Hadar et al.,Serial Number ; "A Method and
Apparatus For Determining Symbol Timing In A Wireless
Communications System", by Hadar, et al. , Serial Number ;
"A Method and Apparatus For Using Duality To Remotely
Communicate", by Klein, et al. , Serial Number ; "A Method
and Apparatus For Confriguring Dispersed Components In A
Communications System", by Jackson, et al. , Serial Number
and, "A Multiple Use Wireless Communications System and Method",
by Jackson, et al. , Serial Number . Each of the
forelisted applications are herein incorporated by reference.
The present application is directed in general to systems
and methods for communicating in telephone systems and in

particular to systems and methods for using portable, wireless
telephones integrated with a land-based wired telephone eyatem.
The telephone industry has experienced tremendous growth in
the last few years, driven in part by the availability of
relatively inexpensive cellular telephone service. In such
service, telephone subscribers use portable, battery-powered,
hand-held telephone instruments to communicate via RF links with
a network of base stations which interface the signals on the RF
links into the land-based public telephone network. In such
systems, a cellular configuration is generally used in which a
particular base station uses certain frequencies to communicate
with portable telephones within its "cell" and adjacent base
stations use other f requencies _£© communicate with telephones
within their cells. If base stations are sufficiently distant
from each other, the same frequencies may be used in both cells
so long as neither the base station nor the telephones in one
cell generate signals of sufficient power to carry into the other
cell. In this way, a limited number of frequencies can be re-
used in a non-conflicting pattern which provides telephone
service throughout a particular geographic area. Of course, as a
telephone leaves from one cell to another, the telephone may have
to switch frequencies (or "hop" to a new channel) during the
middle of an on-going call to avoid broadcasting into a non-
adjacent cell which is using the same frequency for a different

The use of cellular telephone technology has permitted broad
geographic regions to be provided with the availability of many
portable telephones. As the popularity of portable telephones
has expanded, however, the frequencies (or "channels") have
become filled. Within the limited R? bandwidth available for all
the competing uses thereof, the solution to cellular overcrowding
does not necessarily lie in merely adding additional frequencies
or channels within each cell.
It has been proposed in the prior art to utilize smaller
cells and to reduce the power of the cellular equipment so that
frequencies may be reused in greater proximity to one another.
Such a solution is not entirely satisfactory, however, as with
much reduced power levels, the signal to noise ratios of the
communications may approach levels unacceptable in telephone
communications. Along these lines, -he prior art has proposed
making an office building, a portion of an office building or an
office complex a cell site or a small cellular system. Given the
crowding on the existing cellular systems, however, such proposed
systems are generally limited in the number of portable
telephones which they can accommodate.
In many office situations, the persons working in the
offices frequently are away from their assigned duty locations
for extended periods of time and may even roam throughout the
office as their business needs arise. Providing telephone
service to such roaming persons in the prior art often meant
using call-forwarding schemes or the like to automatically route

the call from one location to another. Such systems usually
required substantial user input to implement, a drawback in a
typical office environment:."""" Thus, it is desirable to utilize
portable or cellular technology for persons within an office. In
a typical office building, the addition of cellular telephones to
the already-present land-based system, such as a Private Business
Exchange (or "PBX1") provides some mobile communication but is
insufficient for effective communication. Generally, the
portable telephones are tied to a base unit which integrates the
RF communications of the cellular system with the public land-
based telephone system and not directly with the business
person's own PBX. Effectively, such a solution in an office
environment yields two independent telephone systems not well
tied into each other or coordinated in any way. Additionally,
the external structure of the building housing the office may
make impractical the transmission of typical cellular RF signals
to and from conventional base stations.
A solution to the desire to permit workers to roam within a
particular geographic space, such as an office building or a
portion of an office building, yet permit such workers to
continue to be reachable by the telephone system and to permit
the workers to utilize the advantages of the telephone system is
to integrate a wireless system with a PBX. With such an
integration, incoming calls to workers can be directed by the
wireless system to the worker wherever that person may be within
the operating range of the system. At: the same time, the roaming

worker will be able to readily place telephone calls both within
and without the office a(s readily as if sitting at his own desk
on the hard-wired system. The roaming worker would also have the
benefit of all of the features of the PBX (such as a personalized
repertory dialer, special access to restricted circuits, etc.) no
matter where the worker may be located within the office.
Desirably, a wireless-PBX system would include a portable
telephone unit which is easy to use, lightweight and has an
extended battery life. The latter two desires are somewhat at
odds with each other inasmuch as battery life often has a direct
relation to the size (and weight) of a battery. Accordingly, it
is often important in the design of portable units that they be
as power-efficient as possible.
Within prior art cellular systems it is known for a
particular base station to have associated therewith one or more
control channels and several or numerous voice channels. The
control channels are used to communicate with the control
portions of the portable units to coordinate the use of voice
frequencies and to perform an analog of typical central office
functions (e.g., dialing a number, ringing the portable unit,
etc.). When all of the voice channels within a base station are
being utilized, there may no longer be a need for a control
channel as there are no more control tasks to be performed until
one of the voice channels again becomes available. In such
systems, it is desirable to not waste the non-functioning voice
channel and an additional voice channel can be obtained to

enlarge system capabilities over conventional systems with no
additional hardware costs and no additional bandwidth being
occupied by the system.
Accordingly, it is an object of the present invention
to provide a novel system and method to integrate a wireless
telephone system into a private branch exchange or similar office
telephone system.
It is another object of the present invention to provide a
novel system and method to utilize every available channel of a
wireless system for voice (or data) messages.
It is yet another object of the present invention to provide
a novel system and method for reducing power consumption within a
portable unit without reducing capabilities of such a unit.
It is still another object of the present invention to
provide a novel system and method which can be installed in an
office environment without extensive wiring and/or substantial
It is a further object of the present invention to provide a
novel system and method of providing an integrated wireless-PBX
telephone capability using housings which can be readily mounted
on existing wall or ceiling surfaces of an office.
It is yet a further object of the present invention to
provide a novel system and method of: communicating in a wireless
system in which base^st:at^ions_jnay readily be added to the system
(or reset after a power outage) and brought on-line without
extensive programming.

It is still a further object of the present invention to
provide a novel system and method for accurately and efficiently
communicating between plural wireless telephones and plural base
These and many other objects and advantages of the present
invention will be readily apparent to one skilled in the art to
which the invention pertains from a perusal of the claims, the
appended drawings, and the following detailed description of the
preferred embodiments.
Figure 1 is a simplified functional block diagram
illustrating an embodiment of the system of the present
Figure 2 is a timing diagram showing the relationship of
frames and slots which may be used within the communication
system of the present invention.
Figure 3 is a timing diagram showing the timing of control
and communications channels in a system of the prior art.
Figure 4 is a timing diagram shewing the timing of control
and communication channels and the timing of receive and
transmission portions of*a communication frame which may be used
in the present invention.
Figure 5 is a schematic view of t:he interior of a building
showing possible locations of persons and telephone base stations
positioned therein.

Figure 6 is a frequency assignment table illustrating the
use of carrier frequencies within an embodiment of the present
Figure 7 is a pictorial diagram of a base station housing
and plural antennas in one aspect of the present invention.
Figure 8 is a timing diagram showing a frame which may be
used in the communications portions between the base stations and
the portable telephones in the present invention.
Figure 9 is a diagram showing an exemplary chart of the
output of a correlator which may be used in the present
Figure 10 is a simplified functional block diagram
illustrating another embodiment of the system of the present
With reference to Figure lj,_a telephone system using the
present invention may include a switch 10 which is connected to
plural lines or trunks of a standard telephone network such as
the public telephone network in the United States. The switch 10
is also connected to plural land-based telephones 14 via wires or
similar non-propagating media. The switch 10 may also be
connected through a Base Station Interface Unit ("BSIU") 16 to
one or more base stations 18 through a base station connector 20.
Each base station 18 includes means for wireless communications
with plural portable telephones 22, as described further below.

In operation, Che switch performs as a standard telephone
switching unit such as a PBX, a PABX, key-system or the like and
functionally interconnects telephones 14 with the public
telephone network. Such a switch 10 could be a switching unit
such as the unit sold by Harris Corporation as the "Harris
20/20". Depending on the scope and complexity of the switch, it
may have many features available to assist the telephone user
with his calls including memory dialing, call forwarding, voice
mail answering and delivery, and the many other features common
on modern telephone switches.
One of the tasks accomplished by the switch is the mapping
of in-bound or intercom telephone calls to a desired telephone
instrument and the provj^exonr- of- "outside lines" to system
telephones upon request. If an in-bound call is bound for one of
the land-based telephones 14, the switch 10 conventionally rings
the desired telephone through a wire connection and establishes a
voice communicatipn path along the same or another wire
connection between the desired telephone 14 and the outside line
on which the call was received.
Calls received by the switch 10 destined for portable
telephones 22 are routed to the BSIU which sends the appropriate
control information to the base station currently controlling the
portable telephone 22 through methods described below. When a
call is to be connected between portable telephone 22 and another
telephone, the switch 10 operates to direct the voice circuit to
the BSIU 16, which in turn directs the voice circuit to a

selected base station 18, which in turn sends information
regarding the voice message on the voice circuit to the desired
portable telephone 22 via a wireless link 24.
As is well known, telephone voice circuits can be either
analog or digital. In one conventional system, the telephone
lines arriving from the telephone network may be analog lines.
Through conventional switch circuits, the switch 10 may route the
analog voice circuits arriving from the telephone network to the
land based telephones 14 in either analog or digital modes. If a
digital switch is being used, the switch 10 may first convert the
voice information arriving from the analog telephone network to a
series of digital bits and communicate those bits by conventional
means to the land-based telephones 14. Communications arriving
from a digital land-based telephone 14 destined for the telephone
network 12 may be transmitted from the telephone 14 to the switch
10, converted to an equivalent analog signal and impressed on the
lines from the telephone network 12.
The present invention is not limited to use with only analog
switches or only digital switches and the inventive concepts
disclosed herein may readily be implemented in association with
either analog or digital switches. Nor is the present invention
limited to use with a PBX or similar "stand-alone" equipment but
may be applied to any telephone system or sub-system in which it
is desired to integrate a wireless telephone with other
telephones, wireless or landbased. Thus, the switch 10 may
itself communicate with the "external" telephone network 12

through any conventional means, not limited to wired systems,
such as via microwave links. Thus, while the descriptions of a
preferred embodiment may describe a particular signal within a
switch 10 as being a digital signal or an analog signal, the
invention is not limited to systems having only such signals, the
description being merely illustrative and not limiting.
Analog telephone calls from the telephone network 12
destined for one of the portable telephones 22 may be converted
to a digital form within the switch 10 and are passed to the BSIU
16. At the BSIU, the digital information from the call may be
combined with similar digital information from other calls and
passed via the communication links 20 to the base station 18 then
handling the call. In turn, and in a method discussed below, the
base station 18 may communicate the digital information from the
telephone call to the desired portable telephone 22. Note that
as the present system is a telephone system, there exists a
return path for the telephone call which simply reverses the flow
described above to provide the digital form of the voice applied
at the portable telephone 22 through the base station 18 and the
BSIU 20 to the appropriate line from the telephone network 12.
If the telephone network line is an analog line, the digital form
of the return signal will be converted to the analog form for
impression on the telephone network line 12.
As is well known, evferT tHbugh a voice message may be thought
of as continuous, the digital form o[ such a message does not
need to be a continuous stream of digital bits. Rather, if the

digital equipment is sufficiently fast, clusters of digital bits
representing the voice signal may be transmitted together
followed by a period of time before another cluster of bits must
again be sent. If the series of clusters of digital bits arrives
within a certain latency period between clusters when the digital
signal is converted bacft to analog, a user listening to the
received analog signal cannot detect, the fact that the voice
message was transmitted in separate portions. The present
invention utilizes this fact to permit multiple portable
telephones to simultaneously time-share a single frequency or
channel between a base station 18 and a portable telephone 22.
With reference now to Figure 2, in a form of communication
known as Time-Division-Multiple-Access, plural portable
telephones may share a single frequency. As depicted in Figure 2,
a particular frequency (or carrier) may be divided into plural
slots, eight (8) in the system of Figure 2. With proper
coordination between a base station 19 and a portable telephone
22, the portable telephone may expect: to receive its digital
messages in slot 2, the slot repeatedly occurring as one of eight
slots. Thus, the portable telephone 22 receives the digital data
in the slot 2 as shown in Figure 2. Seven slots after the end of
the first slot 2, a second slot 2 arrives, again bearing digital
data for the specified portable telephone 22. Each slot can
deliver plural digital bits of data. So long as the slots repeat
with sufficient frequency, the portable telephone 22 will receive
the digital form of the voice message at a sufficient rate that

the analog form of the message may be reconstructed accurately by
a digital-to-analog conversion at the portable telephone 22. The
length of time which may pass before consecutive slots must be
received to avoid a loss of data depends upon how many bits are
sent at one time and the frequencies of the sounds within the
voice message in a well known relationship. As noted previously,
a typical telephone message is two-way and thus, two slots are
needed for a telephone call, one for the passage of the digital
signal to the portable telephone 22 and the other for the passage
of the digital signal from the portable telephone 22.
Because one telephone call occupies only two slots of the
frame, the other slots are available for simultaneous usage by
other portable telephones 22. Generally, the base unit uses a
particular protocol to inform the portable telephones 22 which
slots are to be used for a particular telephone call and to
ensure that all of the communicating portable telephones are
synchronized (to avoid having two portable telephone transmitting
at exactly the same time which would usually destroy the signals
being transmitted by both.)
In prior art systems, typically, the first slots of a frame
are used for sending voice signals from the base station to the
various portable telephones then being controlled by it. For
example, and with reference to Figure 3, an 9 slot frame of the
prior art may use the first slot (CON) as a control slot (for
sending control messages from the base unit to the stations,
etc.), the next four slots for voice signals going from the base

station to the portable telephone (Ti, T2, T3, T4) and the last
four slots for voice signals going from the portable telephones
to the base station (Rl, R2, R3, R4).
In the system of the present invention, and as depicted in
Figure 4, the first slot of a frame (CON) may be used as a
control slot; however, in contrast to the prior art, the
remaining slots are divided into two half-slots with the base
station transmitting in the first half-slot and the base station
receiving (portable telephone sending) in the second half-slot of
each slot.
Compared with the prior art, the use of the present
invention is- particularly beneficial in reducing power
consumption by a portable telephone.. It is known in the prior
art to reduce the power supplied to the communication portions of
a portable telephone when the communication portions are not
expected to be needed. Thus, for example that in the prior art
system of Figure 3, a portable telephone could reduce the power
to its communication portions in all but three slots, i...e. , the
slots when it is scheduled to transmit, to receive and to
communicate within the control slot.. In one aspect of the
present invention, the communication portions of the portable
telephone are required to be fully energized only during one slot
(as explained below, the portable telephone of the present
invention may not need to monitor the communication channel (or
slot) while it is engaged in a telephone call. Thus, the
present invention reduces the relatively inefficient periods

during which power is being brought, up and reduced from the
communications circuits in addition to reducing the need to power
up such circuits at all during fewer slots per frame.
As is known in prior art systems, the control channel can be
used to establish timing for the frames of the communications
system and for communicating control information between the base
station and the portable telephones. For example during the
periods of the control channels, the; base station can transmit
data informing particular portable telephones which slots and
frequencies to use for their voice data or informing a particular
telephone how to react to certain user entries of the telephones
keypad. Also during the control slot, the system may provide a
period of time during which any portable telephone seeking a
voice circuit may transmit its request for such a circuit and/or
may transmit other administrative data or functional requests of
the base station or PBX.
With reference now to Figure 5, the ability of a system of
the present invention to provide continuous coverage of an area
may be illustrated on an outline of a typical floor of an office
space 50. Within the office space !50, a number of walls 52
divide the space into individual rooms 54 and corridors 56. Base
Stations BS 1 and BS 2 can be placed within the office space 50
to provide telephone coverage throughout. The number and
location of Base Stations depends upon the amount of telephone
traffic expected and the configuration of the space to be
covered. The space may be a portion of a single floor of a

building, multiple floors of a building, multiple buildings,
and/or external space associated with the buildings. When a user
desires to use his portable telephone within the space covered by
the system of the present invention, he may enter a set of
instructions onto his portable telephone. By a process discussed
below, the portable telephone selects a Base Station with which
to communicate and sends the user's request for a voice circuit
to the selected Base Station during one of the control slots
associated with that Bas,p-Stat±on. The Base Station determines
which slots and frequencies are available and returns a message
to the portable telephone identifying the slot and frequency to
be used by the portable telephone as a voice channel. Through
standard signallipg techniques, the portable telephone may then
transmit the subscriber number of the telephone to be dialed or
request some other function of the telephone system.
By way of example and with continued reference to Figure 5,
each of the Base Stations within the system may have associated
with it a frequency to be used for its control channel. When
the portable telephone seeks a voice circuit or other function
from the telephone system, the portable telephone may scan those
frequencies known to be assigned as control channels to determine
which control channel signal is received with the highest signal
strength, signal to noise ratio, and/or any other metric of
signal quality. The control channel signal with the best quality
having been selected, the portable telephone will then initiate
contact with the Base Station sending that signal via the control

channel. With respect to the office space of Figure 5, portable
telephones PT1 and PT3 may be expected to communicate with Base
Station 1, if that base station has an available channel, because
that base station is closejr than any other, otherwise portable
telephones PT1 and PT2 may be expected to communicate with Base
Station 2. Similarly, portable telephone PT4 may be expected
to communicate with (and obtain a voice channel from) communicate
with Base Station 2 for the same reasons. The base station with
which PT3 and PT5 would communicate cannot be readily determined
from the outline of the space of Figure 5. Note that portable
telephone PT5 is physically closer to Base Station 2 than to Base
Station 1; however, the direct path between the portable
telephone PT5 and Base Station 2 is through a wall. Depending
upon a myriad of factors, including the thickness and composition
of the wall and the size of the door opening to the corridor from
the room in which portable telephone PT5 is located, either Base
Stations 1 or Base Station 2 (if available) might be where
portable telephone PT5 lands.
Note that by the use of the selection scheme of the present
invention, the assignment of portable telephones to particular
base stations is dynamic and takes into account local variations
in the signals communicated between the portable telephone and
the base station.
In one embodiment of the present invention, incoming and
outgoing telephone calls can be handled with practically the same
processes at the portable telephone, the difference being only

that the incoming telephone calls are preceded by a "Ring"
signal. Upon the receipt of the "Ring" signal, the present
invention may use the same protocol in the portable telephone for
both incoming and outgoing calls.
During a telephone call at a particular portable telephone,
the user of the portable telephone may be moving about the
office. As the user moves, he will at some time move away from
the base station controlling the call. In the system of the
present invention, the portable telephone monitors the quality of
the communications between the portable telephone and the base
station and, upon the degradation of the signal below
predetermined criteria, reselects its base station and requests
that the call be moved to a new channel (or slot/frequency
combination, explained below) at the base station then having the
best communications with the portable telephone. For example,
and with reference again to Figure 5, a portable telephone at the
location designated PT1 within the space may be expected to
initially use the nearest base station BS1 (assuming that BS1 has
an available channel). If the user of the portable telephone
then moves during the call from PTl to PT4, the signal between
the portable telephone and its controlling base station (BS1 in
this example) may degrade sufficiently to cause the portable
telephone to seek a new communication path. At the position
designated PT4, the portable telephone may be expected to select
the nearest base station, now BS2, and obtain a voice channel
from the newly selected base station. Note that in the system of

the present invention, the portable telephone need not switch
base stations merely because the user moves his location and
another base station becomes closer and/or more direct. Rather,
to avoid unnecessary hopping from one channel to another, the
portable telephone of the present invention may continue to stay
with its present base station so long as the quality of the voice
communication remains acceptable.
The portable telephone may evaluate any characteristic of
the communications channel between the portable telephone and the
base station. It has been found efficient in the present
invention to use the voice quality estimate typically provided by
a vocoder in the transmission circuit: as an estimate of signal
quality. The use of this estimate for control of hopping is
particularly efficient because most vocoder circuits already
develop the estimate as part of their volume control operation
and thus this use avoids the need for another circuit or
processing function.
In the standby mode (no on-gong voice communications), the
portable telephone may estimate signal quality based on the
quality of the control channel from the base station. If the
signal quality degrades to a predetermined criteria, the portable
telephone may switch to the control channel of another base
station. This technique, sometimes called soft roaming, may
prevent a transient effect which can occur when a call is
initiated or received by a portable telephone just before the
signal quality in fact degrades to below the level needed for

seeking a hop. In such a situation on a newly established call,
the portable telephone may not have obtained sufficient useful
call quality data on the communications channel to accurately
initiate a base station/frequency-slot switch. By using this
technique during stand-by modes, the system of the present
invention attempts to increase the probability that the portable
telephone will use the best base station nearby.
By remaining in a given voice channel so long as the channel
has acceptable communications, the portable unit typically does
not need to monitor the control channel during a telephone call.
Because the assigned slot occurs at a known repetition rate,
during a voice communication the portable unit may deenergize its
communication circuits except during the slot in which it is
communicating. Upon the end of a slot, the portable unit can
deenergize its communications circuits and set a timer to
reenergize such circuits immediately before the next occurrence
of the assigned slot. In the time periods between the slots, the
portable telephone continues to convert any digital voice data
received from the forward channel (the channel from the base
station to the portable telephone) from digital to analog form
for application to the telephone's speaker (or earpiece) and to
accumulate digital information corresponding to any audio inputs
(or user keypad entries) received during the time period between
slots. When the next slot occurs, the portable telephone
receives the next packet of forward channel voice data and
transmits the next packet of voice data input from the user

during the inter-slot periods. So long as the clocking circuits
within the portable telephone remain sufficiently synchronized to
the clocking circuits of the base stations, the portable
telephone will be fully able to jump directly from one slot to
the same slot in the next frame by use of timing circuits and
without need to consult with the control channel.
With reference now to Figure 6, in a system of the present
invention, a slot or channel may be considered to be a particular
slot/frequency combination. In a system having eights slots per
frame, there are eight channels or communication opportunities
available per frame, each "opportunity" including a forward
communication and a reverse (from the portable telephone to the
base unit) communication. Within a slot, the forward and reverse
communications are carried out at the same carrier frequency.
Thus, each base station has eight slots under its control. Each
of the slots is independent of the other slots within a frame and
each slot may be at. any-,of--fehe—channel frequencies used within
the system. Thus, for example for base station 2 in the system
of Figure 6, slot 1 (generally the control channel, but see
below) may be the control channel operating a particular
frequency, f6. ^t the time of the example of the system of
Figure 6, base station B also had three voice communications on-
going, one portable telephone using frequency fl3 on slot 3,
another using frequency f2 on slot 6 and still another using
frequency f3 on slot 7. Each of the slots starts a predetermined
time after the start of the frame. Thus, when a portable

telephone is instructed by the base station to "use slot 6,
frequency f2", the portable unit knows that it will receive
forward voice data on frequency f2 the predetermined period of
time associated with slot 6 after the beginning of each frame and
that it is to send its reverse data on frequency f2 during the
appropriate time within slot 6.
In the system of the present invention, any of the assigned
frequencies may be used in any slot at any base station.
Accordingly, there are no assignments of frequencies or sets of
frequencies to particular base stations. This feature of the
present invention provides considerable ease in installing the
system, a replacement base station or a new base station. In
addition, this feature of the present invention provides
considerable flexibility of the system to respond to highly
mobile users and shifting service demands through the geography
of a given system.
In operation, a base station scans the channels assigned to
the system to determine available slot/frequency combinations.
By tuning to each of the assigned frequencies during its non-used
slots, the base station can determine which slot/frequency
combinations are not being used within its range and can assign
one of those available slot/frequency combinations when a new
voice channel is requested by a portable telephone.
Significantly, the available slot/frequency combination data is
done by each base station on a local basis. Because of the
limited range of the base stations and the portable telephones,

the fact that a particular slot/frequency combination is being
used within the system does not necessarily mean that it cannot
be used elsewhere in the system. For example, with reference to
the system of Figure 6, base station A can assign one of the
portable telephones being controlled by it to use slot 5 and
frequency f9 and the same slot and frequency can be used in a
relatively remote base station area such as in base station N of
the system of Figure 6. As long as the base stations and their
controlled portable telephones are sufficiently remote,
frequency/slot combinations can be used and reused multiple times
throughout the system of £h~e^present invention, providing
substantial capability for a system to handle many simultaneous
telephone calls.
Generally, the system of the present invention may use the
monitoring of the system during unused slots to determine whether
a slot/frequency combination is available to it. If the base
station cannot detect the on-going use of a particular
slot/frequency, that slot/frequency may be considered "available"
despite the fact that a relatively remote portable telephone and
base station are using the same slot/frequency combination. In
such a system, it is possible that even though a particular base
station is sufficiently remote from a particular use of a
slot/frequency.combination that it believes the combination to be
available, the portable telephone being controlled by that base
station may receive interference from the "remote" use of the
same slot/frequency combination. However, because, as noted

previously, the portable telephone is monitoring the quality of
the voice signal being communicated during its assigned slot,
such interference if it occurred would cause the portable
telephone to initiate a hop to another frequency/slot combination
at the same or another base station.
In yet another aspect of the present invention, the capacity
of the system to carry telephone calls may be improved by the use
of disappearing control channels at each of the base stations.
When all of the non-control channels are being used for on-going
telephone calls, the base station is free to assign its control
channel as a voice channel. As noted earlier, once a telephone
call is established on one of the slots, the portable telephone
with that call has no further need t_o use the control channel of
the base station. If all of the "normal" voice channels are
filled and only the control channel remains at a base station,
once the base station assigns that channel as a voice channel,
there simply is no need for a control channel at that base
station so long as all the channels remain occupied with voice
communications. Any portable telephones desiring a new voice
channel within the geographic area serviced by a base station
which has given up its control channel will automatically not
detect the base station as being available and will select
another base station with which to communicate on its control
As mentioned previously, power reduction is an important
consideration in the design of the portable telephones. In

another aspect of the present invention,power is reduced when a
portable telephone is in a "stand-by" mode. In this mode, the
portable telephone is energized but voice communications are not
occurring, principally-while—awaiting a new telephone call or for
the user to place his next telephone call. In the stand-by mode,
a portable telephone in accordance with one aspect of the present
invention does not monitor every frame of the communications but
rather monitors every Nth frame and upon completion of the
monitoring, reducing power to the communications circuits and
setting a timer to re-power the communication circuits after the
passage of N-l frames. The series of N frames is called a
"superframe". In this way, communication power consumption is
reduced substantially, yet the telephone remains available to
"answer" calls and to readily place calls upon user request.
In one known problem in the prior art in communications
between plural remote devices and a base station, all or many of
the remote devices attempt to communicate with the base station's
control channel at approximately the same time, colliding with
each other's messages and permitting few or none to successfully
communicate with the base unit. Recall that in a system of the
present invention, the portable units attempt to communicate with
the base station by transmitting during a particular time period
during and timed from the beginning of the control channel slot.
If more than one portable telephone attempts to transmit
simultaneously, neither may be successful. The problems
associated with collisions on the control channel can be

particularly troublesome immediately after system turn on or
reset when all of the portable telephones may attempt to reestablish
contact with the base stations. To reduce the
collision on the control channel, a portable telephone of the
present invention uses a number assigned to it to determine in
which frame of a superframe to attempt to contact the base
station's control channel. The number assigned to the portable
telephone may be programmed into one of its memories or may be
input by way of DIP switches which can be read by the
microprocessor within the telephone or any similar semi-permanent
(or permanent) method. In the system of the present invention,
the base station indicates in the control channel the position of
each frame within the superframe. For example, if a superframe
consists of 32 frames in a particular system, the control channel
communication would include an indication that the successive
frames numbered from 1 to 32. Portable telephones may divide the
assigned number by a modulus number, usually the number of frames
in a superframe, and attempt to access the control channel during
the frame having the number equal to the modulus remainder. For
example if a portable telephone has been assigned the number 179
in a system having 32 frames per superframe, that portable would
attempt to communicate with a base unit during the 19th frame of
the superframe (i.e., 179 modulus 32 leaves a remainder of 19).
Note that there is no need for each portable telephone to have a
unique number so long as the numbers are assigned in a fashion

which spreads the attempted accesses to the control channel over
the entirety of the superframe.
In the event that collisions occur on the control channel
even with the advantages of the present invention, a fallback
contention scheme can be used such as the scheme used in "slotted
aloha" systems in which each colliding portable telephone waits a
random period of time before attempting to access the control
channel in the expectation that the randomness of the period will
eliminate or reduce further collisions.
It is well known in telecommunications systems that
electromagnetic signals transmitted from one device often do not
travel directly to a receiver but follow various paths bouncing
from one object or surface to another until received. Multipath
is a particularly significant problem inside a building where a
signal will bounce off walls, penetrate through walls and bounce
off other surfaces until received. During the bouncing and at
the receiving antenna, the various multipath signals combine and
interfere with each other so that the received signal is usually
plural copies of the original signal arriving at different phases
with various cancellations within the waveform. To reduce the
effects of multipath, it is known in the prior art to use plural
antennas at the receiver to provide both spatial and frequency
diversity. In many such systems, the receiver contains logic
circuits which select the antenna having the best signal,
accepting the signal from that antenna and rejecting the other
signals. In other antenna diversity systems in the prior art,

the receiver's circuitry attempts to combine the signals
appearing at the diverse antennas. Usually in the prior art, the
latter systems have provided better reception but at a cost of
increased complexity and circuitry.
The problems associated with multipath are often exacerbated
in a portable system in which power levels are generally low (to
conserve power and permit frequency reuse) and in which the
portable telephone is not fixed in space. It is a frequent
occurrence that the user readjusts the position of the portable
telephone during a conversation, each time realigning the antenna
with respect to the base station (generally internal to the
telephone or fixed externally in orientation to the telephone).
In addition, the user is often moving which will cause coriolis
effects in the transmitted signal. Thus, it is particularly
useful in portable systems to use a diversity of antennas at both
the base station and the portable telephone.
In another aspect of the present invention, the system of
the preset invention uses "duality" to improve signal reception.
With reference to Figure 7, each base station 70 may include
plural antennas 72 associated therewith. During each slot in
which the base station is communicating with a portable
telephone, the portable telephone first communicates with the
base station. During the preamble portion of the communication
from the portable telephone to the base station, the portable
telephone includes within the preamble a predetermined bit
pattern which the base unit uses to test the reception on each of

its antennas (four in the system of Figure 7). The base station
then uses the best antenna to receive the rest of the
communication from the portable telephone. During the same slot,
the base station has an opportunity to communicate forward data
to the portable station and will use the same antenna to transmit
such data as it just used to receive data from the portable unit.
Because the base station transmit portion of the communication to
the portable telephone immediately follows the receipt of a
communication from the portable telephone and an evaluation of
the best antenna to be used, it is unlikely that the portable
station has changed its position such that the previously
selected antenna is no longer the best one to be used between the
base station and the telephone.
The base station can use the same antenna evaluation and
selection for each of its slots during'a frame. Thus, it" is
; entirely possible that the base station would select a different
antenna to be used for each successive slot.
It has been found by the present inventors that during
antenna selection, the antennas may be switched while still
measuring their signal quality. The delays inherent in the
switching chain and the delays in th^ measurement of the received
RF signal, permit testing to continue for some period of time
after an antenna has been commanded t.o be switched out of the
communication. The advantage of such a technique is the ability
to test more signal data without having to dedicate more of the
preamble to antenna diversity functions.

In another aspect of the present invention, the antenna
selection system may select the two best antennas for a given
slot, using the best antenna for transmission to the portable
telephone later in the slot and evaluating the two best antenna
for attenuation setting evaluation. If the signals received at
the two best antennas exceed a predetermined figure of merit, an
antenna can be added to the signal path during the next frame.
On the contrary, if the two best signals are weaker than a
predetermined figure of merit, the attenuation may be removed in
the next frame. In this way, the dynamic range of the reception
may be enhanced as the attenuation is selectively added or
removed based on the strength of the two signals. The use of the
signals from two antennas is not meant to be limiting to the
invention and more signals may be used if desired, at an
'increased processing burden. Similarly, the figure of merit may"
be related to the strength of the two signals, individually or
combined in a desired manner, or to any other characteristic of
the received signals.
With continued reference to Figure 7, a base station of the
present invention may be housed in a housing 76 of any suitable

configuration, and desirably of a configuration which blends
well into typical office decor. The base station 70 may include
plural independently attached antennas 74 which can be pivotally
moved from a position nestled along the side of the housing 76
(as seen with respect to the antenna 72a) or perpendicular
thereto (as seen with respect to the antenna 72). The antenna 72

may be attached to the housing through any conventional means
which permits rotation about a pivot 74 while maintaining
electrical contact between the antenna and the circuits within
the housing 76. Optionally, the antenna may be attached to the
housing by other conventional means which permits individual
alignment such as by a ball and socket arrangement (not shown)
which would permit rotation about more than a single axis.
Indeed, physical attachment of the antennas to the housing is not
necessary so long as an electrical path is maintained between the
antennas and the base station communication circuits.
In operation, the antennas 72 of the base station 70 may be
aligned in any manner which increases the ability of the base
station 70 to communicate with the portable telephones. For
example, in a system of the present embodiment, the base station
and the portable telephones may be designed to use vertical
polarization. If the base station is mounted on a ceiling, all
of the antennas 72 may be swung down to the vertical to provide
an orientation which matches the ssystem design. If the base
station is affixed to a vertical wall, the bottom set of antennas
may be left alongside the housing 76 while the two top antennas
may be swung out 'l80 degrees to a vertically-upward position.
Similarly, the antennas may be placed independently in any
position relative to the housing 76 which increases signal
throughput to a portable telephone to adjust for anomalous RF
propagation conditions in the geographic area near the base
station 70.

One means for implementing the signalling between a portable
telephone and a base station of the present invention is
illustrated in the timing diagram of Figure 8, which depicts the
functional composition of one-half a slot of the present
invention. The time slot may include plural bits of information,
240 bits are used in one embodiment of the present invention.
The first portion of the slot comprises a preamble, which may
include sufficient synchronization bits to permit the receiver to
acquire the signal before the data is received. Following the
preamble may be a "unique word", .i.e.., a predetermined set of
bits which are always found at the same location in a slot. By
use of a unique word at a known position within the slot, the
receiver is able to synchronize its frame clock to that of the
transmitter. Following the unique word may occur plural "data"
bits. The data bits, depending upon the type of message'arid the "
on-going activity at the transmitter, may include digital voice
data, control data, command data, or the like (generally referred
to herein as "application" data). Finally, some type of checksum
or CRC may be included to assist the receiver in ascertaining
that it has received the message correctly. Generally, any type
of known validation scheme may be used within the communications,
including checksums, check bits, folding checksums, error
correction bits, etc., realizing that there is a tradeoff between
the number of bits dedicated to message validity versus the data
throughput of the system.

During the preamble of the message from the portable
telephones to the base units, the four antenna selection fields
are included. Note that because the antenna selection bits
occupy a portion of the message which is conventionally used for
recovering symbol timing, symbol recovery by the base station may
be degraded unless other measures are undertaken. One such
measure could be to increase the size of the preamble relative to
the data portion of the message or to increase the overall length
of the message. Both these options entail a reduction in the
data bandwidth of the___system_T. In one aspect of the present
invention, neither bandwidth reducing measure is taken but a
novel method of recovering the symbol timing is used. With
reference to Figure 8, in one aspect of the present invention,
the symbol timing can be obtained from the output of a correlator
through which the signal is applied. In general, the received "
signal may be sampled to provide plural samples for each symbol;'^
In one embodiment of the present invention, each symbol of the
input signal is sampled ten times at the output of the
correlator. The magnitude of the correlator output at any one
time corresponds to probability t:hat the center of the received
symbol is at that time. For each ith sample within the symbol,
the total of the samples is obtained and compared to the total of
all the other samples, with the greatest total indicating the
sample most likely to correspond with the center of the symbol.
In other words, the receiver may calculate the following

where K equals the number of samples per symbol, and TOTAL equals
the total number of samples per slot (all the symbols). Note
that this aspect of the_ present invention uses the entire slot to
determine symbol timing and then uses that determination to
extract each of the symbols. To implement this aspect of the
invention, the incoming message may be stored in dynamic memory
while the symbol timing is being extracted; however, the symbol
timing determination may begin upon initial receipt of the
message and need not await receipt of the entire slot.
Once the symbol timing has been obtained the receiver of the
present invention may use a "moving window" correlator to find
the unique word. There is~~no need in the present inventionrfor" a
threshold correlator. Thus, the correlator examines finite ""'
portions of the incoming signal having a length of an entire slot
to determine where the unique word is most likely to be. Once
the correlator has determined the most likely location, the
processor of the receiver may make a bit for bit inspection to
the recovered slot to determine whether each bit of the assumed
unique word is present in the incoming message. If the unique
word is found, the receiver may then set up all of its framing
around the unique word, as it is predetermined where the unique
word appears within a frame.

Once Che unique word has been successfully acquired, the
unique word in subsequet frames may be used to measure the drift
between the transmitter and receiver and to adjust the receiver
for that drift. The acquisition cf the unique word in subsequent
frames does not need to examine the entire frame, however, as a
small window around the expected time for the unique word to
appear will usually suffice and reduce the processing burden on
the receiver.
To assist the base stations in maintaining synchronization
with each other so that they can correctly examine slot/frequency
combinations, a system of the present invention may include a
common clock pulse which is sent periodically to all the base
stations. The clock pulse may be derived from any relatively
stable source such as from typical.switch-used in association
with the base stations. For example, in a Pulse Coded Modulation
("PCM") system such as is often used in digital telephony
applications, one of the PCM slots between the base station and
the switch may be periodically programmed to carry a
synchronization (or reset) pulse which is received by all base
stations and used to synchronize its clock and the communication
frames derived therefrom.
The use of a single stable clock helps assure data alignment
and reduces the hardware costs as the base stations may not need
an expensive oscillator if provided with an accurate clock from
the switch. Still further, the portable telephones may use a
relatively inexpensive, and relatively less accurate, on-board

reference clock in the present invention by frequency correcting
the reference clock using the received RF carrier from the base
station (which, in turn, is locked onto the accurate clock, such
as the PCM clock, from the switch).
In another aspect of the present invention, a system may
include a protocol in which the remote unit, upon the initiation
of the user, may invoke a bit-error-rate ("BER") test of the
communications between the remote unit and a base station. This
BER test may include the transmission by the remote unit, the
base station or both of pseudo-random sequences. Both the base
unit nd the remote may use the receipt of such sequences to
determine the BER and (in the case of the base station) may
report the BER to the remote unit: for display to the user. The
displayed BER information is very useful to...system inst.4Ue.rs.to. .-.
determine and/or verify system coverage and performance."" This *"
aspect of the present invention is not limited to BER
measurements and a system of the present invention may send
signals and take signal measurements of any predetermined
characteristic of the RF signal, such as signal strength.
In still another aspect of the present invention, messages
between the base stations and the portable telephones may include
a system identifier which has beer, programmed into the portable
telephones. The system identifier may then be placed in the
messages, for example in the preamble. Portable telephones and
base stations may then examine the system identifier and if it
does not match the system identifier associated with the receiver

may ignore the message entirely. Thus, two totally separate
systems may exist side-by-side to each other covering portions of
the same geographic areas. Similarly, the portable telephones
may be programmed to operate on more than one installed system
and would thereby be free to roam from one system to another.
Depending upon traffic and security considerations, persons may
be provided with portable telephones which \4ried in their
abilities to be accessed fj|jbm various geographic areas by
changing the system identifications which are authorized for
particular portable telephones.
Similarly, the portable telephones of the present invention
may be used on multiple wireless systems without requiring the
user to initiate any action other than to energize his remote
unit. (The administrator of each system providing access to the
portable telephone must configure the system to accept the
portable telephone.) This feature is particularly useful in
installations in which different systems operate in different
locations within the same (or nearby) business campus. In such
an installation, the user may travel Erom one area of the
location to another, in which a wholly different wireless system
has been installed, and still have full use of his portable
telephone, including the personal features associated with that
user. On the other hand, if two adjacent systems do not wish to
authorize the users of one system to use the other, the wireless
system of the present invention automatically ignores
unauthorized portable telephones and the portable telephones do

not attempt to use the base stations and communications channels
being used by the "foreign" system.
The system of the present invention may also be used
simultaneously as a pager system and a telephone system. In this
aspect, the portable telephones may receive an alphanumeric
message for their displays and the ringer can be energized to
alert the user of the message. When used as a pager, the mobile
station does not complete a telephone call to the user at the
portable telephone but merely uses the existing communication
system to forward the pager message. The remote units used in a
combination pager/telephone wireless system may be the same for
all users, or optionally, some of the units used exclusively for
paging may be reduced-cost units lacking the voice communications
With reference again to Figure 1, installation of the
system of the present invention may be made relatively easy by
its architecture. For example, the switch may be a digital
switch having associated therewith a BSIU 16 capable of
communicating with the base stations 18 through a communication
means 20. The communication means 20 may be as simple as two
sets of twisted wires, two of the wires being used for
transmission of data to the base station 16 and two of the wires
being used for transmission of data to the BSIU 16. The
transmission of data on the four wires can be made using a
protocol known as E-l to handle the plural digital messages which
may be simultaneously occurring on each pair of wires. In

addition, the four wires could also carry power and ground
references to the base stations so that integration of the base
station into a buildings electrical wiring is not necessary.
In operation, a base station 18 can be mounted on any
convenient surface, such as a wall or ceiling, and four wires
carried between the base station 18 and the BSIU 16. By use of a
generalized power-up Programmable Read Only Memory ("PROM")
„-...- . . " ■:'~~tf ....:_ . .;
"associated with the base station 18, the base station 18 may boot
itself using the PROM upon the application of power from the
communication means 20 or from the available electrical wiring.
Once the base station 18 has booted, it may then send a message
to the BSIU requesting a download of the system unique data and
configuration. Because the base station 18 does not have
frequencies assigned and operates primarily on an evaluation of
signal strength rather than telephone location, no extensive
programming of the base station is generally necessary. _This
lack of programming necessity makes installation of the system
easier and provides for automatic resumption of service after a
power failure or surge.
In still"another embodiment of the present invention as
depicted in Figure 10 (using common reference numerals as used in
Figure 1 for common elements), a switch 10 used in the present
invention need not be a digital switch as described above but may
be a conventional analog switch which interconnects the public
telephone network 12 to the system. In such a system, a Base
Station Interface Apparatus ("BSIA") 90 may be used to interface

between the digital wireless system and a conventional analog
switch 10. The BSIA provides the wireless system (the base
stations 18 and portable telephones 22) with all of the functions
of the BSIU described with respect to Figure 1. Additionally,
the BSIA of the alternative system of Figure 10, converts all of
the digital: communications to and from the portable telephones to
conventionajl analog communications and may convert function
requests from the portable telephones 22 into standard switch
(e.g., PBX) protocols and signalling. Alternatively, the BSIA 90
may cause some of the functions to be implemented directly by the
portable telephones by appropriately programming the portable
telephones 22 (as explained below) t:o take specific, PBX-related
actions in response to specified user inputs.
With continued reference to Figure 10, the BSIA may be
configured and controlled through a standard personal computer 91
or similar computing device which may be removably attached to
the BSIA 90 when desired. The personal computer could be
connected, for example, when the system administrator wanted to
make configuration changes, initiate tests or gather data
regarding the system's performance. Software within the personal
computer 91 would typically include software for: System
Configuration, Uploading, Analysis of Performance Statistics and
Alarms, and Downloading of New Programs to the BSIA and base
stations. New or updated programming for the base stations may
readily and conveniently be implemented by downloading such
programs into the BSIA for communication to the base stations (or

through the BSIU in systems such as in Figure 1). Thus,
reprogramming of new and improved features does not require
removal or access to the base stations, resulting in significant
savings for personnel in maintaining installed systems.
The BSIA (or the BSIU) may also include the capability for
the portable telephone user to execute macro commands by simple,
brief keying actions. In the macro capability, the BSIA may
provide signals necessary for the protocol to the switch to be
readily implemented by a single keystroke on the portable
telephone. For example, if a certain function in the switch
required the successive transmission of the DTMF signals for the
numbers 1, 2 and 3, a single function key on the portable
telephone could be used to signal c:he BSIA that the exemplary
function was desired. The BSIA, in turn, would cause the DTMF
signals for the numbers 1, 2 and 3 to be successively transmitted
to the switch. The switch receives the DTMF signals, understands
that the requested function is desired and performs the actions
conventionally necessary to perform the requested function. A
set of macros may be programmed into the BSIA, some of which are
portable telephone dependent, so that the same key on different
telephones may cause different signals to be sent to the switch.
Still further, differing sets of macros may be developed for
different types of switches to accommodate the differences in the
switch protocols and the appropriate set downloaded into the BSIA
during installation.

In another aspect of the present invention, the portable
telephone may include a display which can be programmed from the
switch (through the base station) to customize features for the
various telephones within a system. After the system has been
installed and energized, message may be sent from the switch to
the telephone to provide certain features within the telephone
and may control the appearance of the display on the telephone.
For example, the display of the telephone can be made to resemble
the keypad and switches of'a conventional land-based telephone.
By specifying the functions available to the telephone user, the
switch may make the switches of one telephone operate wholly
different functions than the switches at other telephones and may
cause the telephone displays to show different images indicative
of the functions programmed. For example, in a telephone display
which had five virtual switches thereon, the top switch on one
telephone could be used for a "hold" feature and on a different
telephone could be used for a "transfer" feature. Accordingly,
the display on the first telephone could be commanded to display
"hold" within or near the image of the switch on the telephone's
display while the second telephone could be commanded to display
"transfer" at the same location on the display. Changes to the
display and features of the various portable telephones used in
the system can be readily made centrally using the switch and the
command structure of the present invention. In addition, if the
portable telephone user is required to provide a user-related
code, each telephone could change its appearance and functions

responsively to the user code and the same telephone would have
different features depending upon the security level or service
level of the user.
The display may use both the familiar alphanumeric messages
of present cellular telephones and icons, i.e., graphical images
which suggest and represent certain states and actions such as
"e-mail waiting", battery strength, speaker volume level, line
status, etc.
An embodiment of the present invention may also be
configured to utilize one or more user interface characteristics
described below to make the remote units easier to use. For
example, an embodiment of the present invention may include a
user protocol in which the user may either dial the digits of
telephone number to be dialed and then press an action key (such
as a "CALL" key) or may first press the action key followed by
the digits of the telephone numbei to be dialed. The first
method resembles the user protocol currently common in cellular
telephone systems and the second method resembles the protocol
commonly used in present cordless telephones. In the present
invention, the user may be provided with the option of using
either protocol.
In another useful protocol which may be used in the present
invention, the user may press an action key twice to redial the
last telephone number dialed. For example, the user may press a
"CALL" key twice, the first time obtaining dial tone and the
second time redialing the previously dialed number. The use of a

single key assists the user by not requiring search on the
keypad for different keys to indicate Call and Redial functions.
In still another useful protocol, incoming telephone calls
may be redirected on an ad hoc basis by the user of a remote
unit. In this protocol, upon the receipt of telephone call at
the remote unit, the remote unit may indicate the incoming call.
by a standard method such as by ringing or vibrating. ;
Optionally, the remote unit may display the telephone number or1
extension of the calling party. The user may respond to the :
incoming call by either: pressing a "Call" key to answer the
call; pressing a "Clear" key to mute the ringing and leave the
call unanswered; or, pressing an "End""key to have the call
automatically redirected to another unit such as another
telephone, a message recording system, or a voice mail system.
In yet another protocol feature which may be used in the
present invention, the keyboard of a remote unit may be
electronically locked so that only a limited number of keys my be
used. For example, a user may input a predetermined key sequence
to lock the telephone from all use (except the unlocking
functions) or to lock the telephone to a restricted state. In
the restricted state, the user may be permitted to use three
keys, an "Unlock" key which restores full functions, a "Power"
key to turn the remote unit off, and a "Call" key to answer
incoming telephone calls. With the remote unit in the restricted
state, the remote unit may be freely carried about without
concerns for inadvertent or unauthorized depressions of the keys.

While preferred embodiments of the present invention have
been described, it is to be understood that the embodiments
described are illustrative only and the scope of the invention is
to be defined solely by the appended claims when accorded a full
range of equivalence, many variations and modifications naturally
occurring to those of skill in the art from a perusal hereof.

1. A telephone system in which plural base stations
communicate with plural remote units using RF links and in which
said base units provide telephone system coverage over a
predetermined geographic area, said base stations comprising RF
communication means for communicating with said remote units over
a predetermined set of RF frequencies, a method of communicating
comprising the steps of:
(a) monitoring at each base station each of the
predetermined set of RF frequencies to determine which
frequencies are in use by remote units within the communications
range of said base station;
(b) using one of the frequencies determined not to be in
use when a need to establish a new communication with one of said
remote units when requested by said remote unit.
2• A telephone system as claimed in Claim 1 wherein said
communications between said base units and said remote units on
said set of predetermined frequencies utilizes a time series of
repeating frames, each frame comprising plural slots and wherein
each slot at a particular base station may be communicated using
a different frequency from the other slots within a frame.
3. A telephone system as claimed in Claim 2 wherein said
base units determine available slot/frequency combinations within
said predetermined set of frequencies and wherein one of said
available slot/frequency combinations is dynamically assigned to
a remote station desiring to communicate application data.

4. A telephone system as claimed in Claim 3 wherein the
available slot/frequency combinations are determined to be
available at a particular bass station when said particular base
station detects that no communications are occurring within said
slot/frequency combination.
5. A telephone system as clajtmed in any one of Claims 1
to 4 including means within each of said remote units to evaluate
the quality of the signal being commiinicated between said remote
unit and a particular b*se station and means for requesting the
assignment of a new slot/frequency combination when the evaluated
quality fails to meet predetermined criteria.
6. A telephone system as claimed in Claims 3, 4 or 5
including means within each of said base stations to evaluate
the quality of the signal being communicated between one of said
remote units and said b?se station and means for changing the
assignment of the slot/frequency combination when the evaluated
quality fails to meet predetermined criteria.
7. A telephone system as claimed in any one of Claims 3
to 6 wherein each of said b?se stations monitors each possible
slot/frequency combination within said system.
8. A telephone system as claimed in any one of Claims 3
to 7 wherein each of said base stations may assign any of the
possible slot/frequency combinations to any of the communications
between said base station and one of said remote units*
9. A communications system comprising :
a telephonic switch for interconnecting telephone

plural portable telephones for wirelessly communicating
voice signals to plural b^se stations, said b^se stations
transforming said voice sign?ls received from said portable
telephones to second voice signals and providing control signals
and display information to said portable telephones;
ah interface device for communicating said second voice
signals between said switch ?n& said base stations;
plural paging units for wirelessly receiving said control
signaljs and operating a user notification device located thereon
upon receipt of control signals indicating paging from one of
said base stations;
said paging units use the same protocol for communicating
with said base units as is used by said portable telephones,
whereby a single set of base stations and interconnecting
wiring may simultaneously operate both a telephone system and
a paging system.
10. A communication system as claimed in Claim 9 wherein
said portable telephones may be used as paging units.
11. A communication system as claimed in Claim 10
wherein said portable telephones display at least some of
said display information while being used as a paging unit.

12. A telephone system substantially as herein described
with reference to the accompanying drawings.
13. A communication system substantially as herein
described with reference to the accompanying drawings.

A method and apparatus for reducing power consumed by
mobile, wireless units, such as personal communications systems
or wireless PBX telephones, by reducing the frequency with which
various circuits within the units are fully energized. During
on-going voice communications between a base station and a
wireless unit, the wireless unit reduces the frequency of its
references to a control channel and may eliminate auch references
altogether. In addition, while idle, the wireless units may not
attempt to reference the control channel during all occurrences
of the control channel, reducing both power consumption and the
possibility of collisions with other wireless units in attempting
to access the control channel.






1345-cal-1997-description (complete).pdf


1345-cal-1997-form 1.pdf

1345-cal-1997-form 2.pdf

1345-cal-1997-form 3.pdf

1345-cal-1997-form 5.pdf



1345-cal-1997-translated copy of priority document.pdf

Patent Number 191986
Indian Patent Application Number 1345/CAL/1997
PG Journal Number 30/2009
Publication Date 24-Jul-2009
Grant Date 25-Jun-2004
Date of Filing 16-Jul-1997
# Inventor's Name Inventor's Address
PCT International Classification Number G 10C 3/06
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA