Communication system and apparatus

A communication device (16) comprises first and second transceivers and apparatus for determining when the communication device (16) is in an on-site area (11) and when the communication device (16) is in an off-site area. The first transceiver transmits and receives signals on a first communication medium (17), when the communication device (16) is in a first area (11); whereas, second transceiver transmits and receives signals on a second communication medium (28), when the communication device (16) is in a second area.

TECHNICAL FIELD 
This invention relates generally to communication systems, and more 
particularly to a local area communication system for reducing channel 
congestion. 
BACKGROUND 
Generally, local area communication systems, commonly referred to as 
on-site systems, operate as low power communication systems that 
facilitate communication within a building or other small geographic area 
(site). By employing low power transmitters, on-site transceivers enjoy a 
longer battery life, and may be made physically smaller and lighter than 
their high power transceiver counterparts. However, on-site systems may be 
subject to problems such as radio-frequency (RF) channel overcrowding. 
Thus, the present invention solves this problem by providing a 
communication system whereby different communication media may be used for 
communication within and without the on-site environment. 
SUMMARY OF THE INVENTION 
Briefly, according to the invention, a communication device comprises first 
and second transceiver means and means for determining when the 
communication device is operating in an on-site area and when the 
communication device is operating in an off-site area. The first 
transceiver means transmits and receives signals on a first communication 
medium, when the communication device is operating in the on-site area; 
whereas, second transceiver means transmits and receives signals on a 
second communication medium, when the communication device is operating in 
the off-site area.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1, an on-site/off-site communication system 10 comprises 
an on-site area 11 (e.g., a building) with a plurality of rooms (or areas) 
12, and an off-site area (i.e., the area outside the on-site area). Each 
room 12 contains a stationary infrared (IR) transceiver 14 for 
communicating with other transceivers that enter the room 12. In other 
embodiments, the transceiver 14 could communicate on other communication 
media, such as ultrasonic waves. Preferably, a wired communication link 19 
(comprising several individual lines) connects each room to an on-site 
network controller 18 that operates on two different frequencies or 
services and that includes an antenna 20 for re-transmission of signals 
received from an IR transceiver 14, or for re-transmission of any off-site 
radio-frequency signals that it receives through its antenna 20. A 
portable communication unit (or transceiver) 16 includes transceivers that 
can communicate on two different communication media (IR and RF, in this 
example). When it is within the on-site network, the portable 
communication unit 16 can communicate with the IR transceiver 14 (that is 
located in the room in which the portable communication unit is in) 
through an IR medium 17. Alternatively, the portable unit 16 may 
communicate with other communication units (e.g., a mobile radio 30) on 
the RF medium. 
The network controller 18 communicates with off-site network(s) by the 
antenna 20. A repeater 24, with an antenna 26, represents a possible 
plurality of repeaters for communication among communication units in the 
on-site system and portable and mobile units in the off-site system (or 
among units within the off-site system). The repeater 24 may be either a 
conventional repeater or a "smart" repeater. A smart repeater is capable 
of storing and replaying messages to a user, and may also be capable of 
keeping track of the locations of its users (e.g., by a registration 
and/or polling procedure). The repeater 24 may be coupled to the on-site 
network controller 18 by wire 25 (or radio). A public or private telephone 
company network 22 could be also coupled (by wire 23, for example) to the 
on-site network controller 18 for facilitating communication among the 
on-site and off-site units and telephones in the telephone company network 
22. 
The transceiver 14 may repeat the IR signals from the portable 16 to other 
transceivers 16 within the on-site network (through the wired network 19). 
The transceiver 14 can also repeat the IR signals received from the 
portable 16 to portable or mobile units outside the on-site network. 
Preferred methods of repeating IR signals of a portable 16 use either 
specialized mobile radio (SMR) services within a trunked or a conventional 
communication system. According to a preferred embodiment, a trunked 
communication system 32 includes a plurality of antennas 34 for 
communication with units within the system 32. For example, a mobile unit 
30 could transmit a signal 36 to the portable 16 through the trunked 
system 32. The trunked system 32 would locate an available channel and 
communicate with the portable 16 (if within range) or with the repeater 26 
for retransmission. When the repeater 24 receives an outbound signalling 
word (OSW) directed to the portable 16, it decodes the trunking protocol 
in the OSW and looks up the portable 16 in a table to determine whether 
the portable 16 is within the on-site area 11. The portable 16 may also 
communicate with telephones within the telephone company network 22 
(through the wired network 19 and the on-site network controller 18). 
Thus, by using the IR medium 17 while on-site, the portable 16 avoids 
possible radio frequency channel congestion problems. In addition the use 
of the on-site communication network enables the system controller 18 to 
keep track of the location of the portable 16. 
Referring to FIG. 2, the flow chart 50 illustrates one preferred mode of 
operation of a system in accordance with the invention. First, a portable 
16 operating on an RF communication medium enters the on-site area 12. 
Preferably, the network controller 18 "knows" that the portable 16 is in 
the on-site area 11 upon receipt of a registration code that is 
transmitted by the transceiver. It is also possible to operate the network 
controller 18 so that it periodically polls the on-site area 11 to 
determine which communication units are within that area 11. Upon 
recognizing that it is in the on-site area 12, the portable 16 lowers its 
RF power output and reconfigures its operating frequencies (52) to operate 
within a different communication medium (e.g. IR), while inside the 
on-site area 11. The network controller then updates (54) the repeater 24, 
so that the repeater 24 "knows" that the portable 16 is on-site. Next, the 
system may enter an idle mode (56) when there are no off-site SMR calls 
sent to the portable 16. On the other hand, when off-site SMR calls are 
sent to the portable 16, the network controller 18 locates (60) the 
portable 16 and the network controller 18 sends (62) a message to the 
portable 16 instructing it to respond to the off-site call. Upon receiving 
the message, the portable 16 may change its frequencies and power level to 
respond to the off-site call. To reduce congestion of the IR channels, the 
portable 16 may respond to off-site calls on an RF channel when the 
portable 16 is within range of the communication unit initiating the 
signal. 
In the event that the portable 16 is within the range of the off-site SMR, 
it communicates (68) on the frequencies of the SMR and at high transmitter 
power. If the portable 16 is not within the range of the off-site SMR, the 
portable 16 returns to on-site frequencies and low-power operation so that 
it can communicate with the SMR through the on-site network controller 18 
and the repeater 24. 
Referring to FIG. 3, a block diagram of a network controller 18 in 
accordance with the present invention is shown. The network controller 18 
may communicate voice information with any portable 16 operating within 
the on-site system via the microphone 71, which routes the voice to a 
modulator 72, which may be any suitable modulator, such as, for example, a 
frequency synthesized modulator of conventional design. The modulated 
signal is applied to a filter 73, which appropriately band-limits the 
modulated signal before application to a power amplifier 74. The power 
amplifier 74 is coupled to an antenna 75 via an antenna switch 76, which 
is controlled (via line 77) by a controller 78. The controller 78 
comprises the heart of the network controller 18 and controls the various 
elements of the network controller including the power amplifier 74, and a 
receiver 80 (via control lines 79 and 81 respectively). Preferably, the 
controller 78 comprises an MC68HC11, manufactured by Motorola, Inc., or 
its functional equivalent. 
The receiver 80 receives radio frequency signals from the antenna 75 via 
the antenna switch 76, and provides demodulated audio to a speaker 82 for 
reception by an operator of the network controller 18. Optionally, the 
network controller 18 may communicate data information by coupling a data 
source 83 to the modulator 72, and a data display (or printer) 84 to the 
receiver 80, and to the controller 78. 
In addition to voice and data communication, the network controller 18 is 
responsible for tracking each transceiver operating within the low power 
or on-site system. Tracking is achieved by storing each transceiver's 
identification code and a location code that each portable 16 
automatically transmits to the network controller 18 whenever a 
transceiver roams from one area to another within the on-site system. In 
this way, the location of each individual operating a portable 16 within 
the on-site system may be displayed to a network supervisor via the 
display 84. Moreover, the network supervisor may inquire as to the status 
or location of any particular subscriber by entering requests and commands 
via the keypad 85. In certain situations, it may be desirable to monitor 
whether particular individuals operating transceivers within the on-site 
system execute prearranged security routes throughout the on-site system. 
Accordingly, whenever a new location code is received by the network 
controller 18 for such an individual, the controller 78 starts an internal 
timer. Should this timer expire before the individual reaches the next 
prearranged area, or the individual enters a different area, an alarm 87 
may be activated and assistance or security personnel dispatched to the 
location indicated on the display 84. The controller 78 is also coupled to 
the on-site area 11 containing the network of IR transceivers 14 (shown in 
greater detail in FIG. 1). When the portable 16 is in the on-site area 11, 
the network controller communicates with the portable 16 via the IR 
transceiver 14 in the room in which the portable 16 is at. 
Referring to FIG. 4, a block diagram of a portable 16 in accordance with 
the present invention is shown. Operationally, speech energy impressed 
upon a microphone 102 is applied to a modulator 104, which may be any 
suitable modulator, such as, for example, a frequency synthesized 
modulator of conventional design. The modulated signal is applied to a 
filter 106, which appropriately band-limits the modulated signal before 
application to a power amplifier 108. The power amplifier 108 is coupled 
to an antenna 110 via an antenna switch 112, which is controlled (via line 
114) by a controller 116. The controller 116 comprises the heart of the 
portable 16 and controls the various elements of the transceiver including 
the power amplifier 108, and a receiver 120 (via control lines 118 and 121 
respectively). Preferably, the controller comprises an MC68HC11, 
manufactured by Motorola, Inc., or its functional equivalent. 
The receiver 120 receives radio frequency signals from the antenna 110 
through the antenna switch 112, and provides demodulated audio to a 
speaker 122 for reception by an operator of the portable 16. Optionally, 
the portable 16 may communicate data information by coupling a data source 
124 (controlled by the controller 116) to the modulator 104, and a data 
display (or printer) 126 to the receiver 120 and the controller 116. 
The portable 16 also includes a secondary or control receiver, such as an 
IR receiver (128), which forwards information (via line 130) to the 
controller 116. According to the invention, this information is decoded by 
the controller 116 and is used to determine when the portable 16 is 
operating in a low power or on-site system or in a higher power off-site 
system. After making the system/site determination, the controller 116 may 
adjust the output power of the power amplifier 108 via the control line 
118. Optionally, other operational parameters of the portable 16 may be 
adjusted. For example, the identification codes used by the portable 16 in 
the on-site and off-site systems may change; the communication frequencies 
used may vary from system to system; and, receiver parameters may be 
altered to allow the portable 16 to more efficiently operate within both 
the on-site and off-site systems. In addition, the IR transmitter 129 and 
receiver 128 can be used to communicate with an IR transceiver 14 when the 
portable 16 is in the on-site area 11, to reduce congestion of the RF 
channels used in the system 10. Alternately, the IR receiver 128 may be 
replaced with an ultra-sonic transducer, an RF receiver, electromagnetic 
detector, radiation detector, or functional equivalents thereof. However, 
IR transmission is preferred by the present invention since information 
transmitted via IR will not interfere with existing RF systems, and 
because IR radiation (i.e., the transmission illumination) is limited to 
the room (or area) in which it is generated. The reason for this latter 
limitation arises from the fact that the depth of penetration of an 
electromagnetic signal is inversely proportional to the square root of the 
transmission frequency. Therefore, optical signals cannot pass through 
most objects (i.e., walls or other obstructions), while radio frequency 
signals can. 
Referring to FIG. 5, a flow diagram illustrating the steps executed by the 
network controller 18 in accordance with the present invention is shown. 
The routine begins with decision 340, which determines whether a status 
request has been received from the network supervisor. If so, the 
requested status is displayed (via display 84) in step 342 for the network 
supervisor. If, however, decision 340 determines that a status request was 
not received, the routine proceeds to decision 344, determines whether a 
transceiver has transmitted its ID and a new location code. An affirmative 
determination by decision 344 causes the ID code and the location code to 
be displayed (on the display 84) in step 346. Following this, decision 348 
determines whether the received ID code corresponds to an individual that 
must follow a predetermined route while operating within the on-site 
system. A negative determination of decision 348 or decision 344 returns 
control via reference letter A. Assuming, however, that the individual 
associated with the received transceiver ID must follow a prearranged 
route, the routine proceeds to decision 350, which determines whether the 
individual properly progressed to the correct area within the allotted 
time. Failure to progress from area to area within the time allowed, or 
entering any area other than authorized results in a negative response 
from decision 350 and an alarm is activated in step 352. Conversely, if 
the individual has properly entered the correct area within the time 
allowed, a timer within the controller 78 is reset in step 354, which 
starts the timing interval for the individual to travel to the next area 
according to the prearranged route.