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PRIOR ART
Significant strides have been made in two-way mobile radio communications
systems in recent years to meet the rapidly increasing demand. Typically
such a system includes a base station and a plurality of mobile stations
organized to provide radio communications services. Such a system is
usually allocated with one frequency for inbound signals from the mobile
station to the base station and another frequency for the outbound signal
from the base station to the mobile stations. Until recently, most of the
mobile radio communications need was met by a mobile radio communications
systems designed to handle only voice signals.
However, with the emergence of the mobile digital data terminals, in more
recent years, it was found possible to combine the mobile voice terminals
with the mobile digital data terminal in a mobile station to provide voice
as well as digital data communications capabilities. The digital data
terminals met the need for the transmission and reception of written
messages. This provided significant flexibility in mobile radio
communications services in that it eliminated the need for a person to be
present to receive incoming messages and freed him to tend to other tasks.
This is especially found useful in the police two-way radio communications
systems. For a detailed description of a mobile station that provides both
the voice and digital data capabilities as described, one may refer to the
U.S. Pat. No. 3,906,445 assigned to the present assignee.
However, prior art voice/data shared two-way mobile radio system is capable
of operating only in a simplex mode, as far as the applicants are aware.
Also, it has been found that the demand placed on the channel capacity of
the system was compounded when digital data signal transmission was added.
This was in addition to the fact that, as it were, already the
communications handling capability of the system was often taxed to the
limit to handle voice communications. So when the data terminals were
added to the mobile stations, the capability of the channel was further
taxed and throughput capacity of the system was taxed to the limit.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved mobile
radio digital and voice shared communications system.
It is another object of the present invention to provide a full duplex
voice/data shared radio communications system.
It is still another object of the present invention to increase throughput
capacity of mobile radio communications system.
It is yet another object of the present invention to increase the
reliability of the mobile radio communications system.
It is still another object of the present invention to combine two-way
mobile radio voice systems with digital systems with minimum amount of
changes so that they operate as a single integrated system.
It is yet further object of the present invention to provide improved
data/voice shared two-way radio communications systems wherein the message
integrety is maintained.
It is still another object of the present invention to provide a two-way
mobile radio system wherein human fatigue involved in the use of the
system is minimized.
It is yet another object of the present invention to provide a two-way
radio communications system wherein the data communications and voice
communications is provided in a duplex mode without interfering with each
other.
The foregoing and other objects of the invention are obtained by providing
a control circuitry in the base station of the communications system that
permits or inhibits transmission of digital data and voice signals
selectively in a way that enables the system to operate in a full duplex
mode of operation.
According to a feature of the present invention there is provided a
circuitry which inhibits transmission of inbound digital data from the
mobile to the base station while an inbound voice signal is being
transmitted from a mobile station to the base.
According to another feature of the present invention, there is provided a
control circuitry that inhibits outbound digital data transmission when an
outbound voice signal is being transmitted from the base station to a
mobile station or vice versa. In this instance the circuitry still permits
inbound transmission of voice or digital signal from the mobile station to
the base station.
The foregoing and other objects and features of the present invention will
be made clearer from the foregoing detailed description of an illustrative
embodiment of the present invention in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a basic system block diagram of the two-way mobile radio
voice/data shared system of the present invention.
FIG. 2 shows a detailed functional logic block diagram of the control
circuitry in the base station that enables the system to operate in a full
duplex mode.
DETAILED DESCRIPTION
As shown in FIG. 1 a mobile radio communications system includes a
plurality of mobile stations (11, 12) each of which may include a mobile
radio transceiver for transmitting and receiving RF digital data and voice
terminals coupled to the tranceiver. The system includes a base station 21
for transmitting and receiving voice or digital data to and from the
mobile stations. The base station 21 is coupled, via suitable paths 22, to
a communications processor 23 that includes a control network commonly
known as a radio control chassis 25. The chassis 25 is interposed between
the base station and the dispatcher's voice 27 and digital data 29
consoles. Different paths 24a, 24b, 24c, 24d are used to couple the
dispatcher's console 27 for voice transmission, reception, takeover or
override control and dispatching function as well known. The digital data
console may be in the form of CRT or teletypewriter or the like. The
communications processor 23 is usually coupled, via a suitable
conventional link 31, as illustrated in FIG. 1, to a data base 30 for
providing data sought by mobiles and dispatchers.
In a typical application where the aforedescribed mobile radio
communications is used by law enforcement agencies such as police
departments: a police officer travelling in a car equipped with the mobile
station may request certain data from the computer data base. This, he
does by keying in an inquiry at the mobile data terminal requesting an
information to the data base. The inquiry is appropriately modulated, by a
carrier frequency, f.sub.1, received, demodulated and sent to the control
processor and thence to the dispatcher console and to the data base. The
response to the querry is transmitted back to the mobile station carried
by the outbound carrier, f.sub.2, and the answer is displayed on the
display means. Voice communications between a voice terminal and
dispatcher takes place in a similar manner between the dispatcher and
mobile stations.
There are certain problems associated with prior art mobile two-way radio
voice/data shared communications systems. Although they are not apparent,
they are very real and they impose on the mobile radio communications
system severe constraints, especially on their throughput capacities. This
is largely due to the fact that the mobile radio systems of the
aforementioned type must operate within a particular frequency allocated
for it by regulatary agencies such as, the Federal Communications
Commission and that, heretofore, the systems have been designed to operate
on simplex mode.
This can be appreciated by the fact that inbound channel carrier frequency,
f.sub.1, and an outbound channel carrier frequency, f.sub.2, are used by
all of the mobile stations associated with and serviced by the base
station. Typically in the actual environment, more often than not, more
than one mobile station tries to transmit voice or data signals to the
base station at a given instant, while at the same instant, the dispatcher
may demand the channel, f.sub.2, to transmit data or voice. Inasmuch as
the same frequency channel frequencies (f.sub.1, f.sub.2) are used by all
of the inbound and outbound data and voice signals, unless control is
exercised the signal channels will be a garbled mixture of signals and
cause failure of the system to provide effective communication. Various
queing techniques are used to overcome or sequence demands for the channel
that take place simultaneously. However, this does not handle nor is
concerned with the task of increasing the throughput.
The kind of duplex communication needed for in the two-way mobile
voice/data shared systems to operate in a full duplex mode will now be
highlighted by specific situations that the systems encounter in operation
in handling signal transmission.
A situation is this: Suppose an inbound voice message is coming in from a
mobile station to the base station. While the voice is coming,
transmission of any other voice or digital data message from any other
inbound mobile terminals to the base station must be inhibited. At the
same time, however, the system must be capable of transmitting outbound
digital data or voice messages.
Another situation is this: Suppose an inbound digital data is coming in
from a mobile. When this happens, the system must be able to inhibit
transmission of any other digital data or voice from any of the mobile
stations to the base station. However, in this instance, voice override
should be provided so that the dispatcher can handle emergency and other
situations. This feature is incidentally required by the governmental
agencies. In this instance also, outbound digital data as well as voice
transmission must be permited while inbound data is coming in.
Still another situation is when outbound voice is being transmitted from a
base station to a mobile station. In this case, the system must be capable
of transmitting the voice signals to all of the mobile stations, as
generally provided. In addition, the system must be capable of inhibiting
the transmission of digital data from the base station to the mobile
stations when the voice signal is being transmitted from the base to the
mobile stations. This is so because the same frequency is used for both
the transmission of digital data as well as voice from the base to the
mobile stations. Also while the voice signal is going out, the system must
also permit transmission of digital data from any of the mobile stations
to the base station.
Still another situation is where outbound digital data is being sent out
from the base station to a mobile station. The system must be capable of
inhibiting transmission of voice as the outbound digital data are being
transmitted to a mobile station. However, a voice override feature must be
also provided as in the preceding situation. In this situation, while
digital data is being sent out, the system must also permit any of the
mobile stations to transmit voice or data messages to the base station and
enable the base station to receive them.
A conventional two-way mobile radio communications system is not capable of
providing all of the communications tasks set forth above. Restated, no
conventional voice/data shared two-way mobile radio communications system
is capable of rendering two-way mobile voice/data shared communications
services in a full duplex mode as described in the four situations
described above as far as the present inventors are aware.
FIG. 2 illustrates an inventive control circuitry of the present invention
that enables the two-way radio communication systems to operate in a full
duplex mode to provide the aforementioned communications tasks. Before the
operation of the control circuitry is described, functions of certain
functional block elements, especially those added to the existing
conventional systems, of the control circuitry will be described.
Referring to FIG. 2, there is shown a continuous tone codes squelch system
detector 51, hereinafter referred to also as CTCSS detector. The function
of the CTCSS detector is to detect inbound voice transmission from a
mobile station equipped with a CTCSS line encoder. A CTCSS encoder is a
generally known circuitry which generates a signal in a subaudible region
indicating that a voice signal is about to be transmitted and is present
during the entire voice transmission. For a more detailed description of
such a CTCSS encoder, one may refer to Electrical Industries Association
Specification RS 220. Typically, aforementioned conventional CTCSS squelch
detector takes about 130 milliseconds to detect the presence of CTCSS code
from the time it is presented to the base station first.
As it is generally known, carrier squelch detector 53 is provided in a
carrier squelch control circuitry 54 to detect the presence of RF carrier
and ususally the detector is provided in the receiver itself. Its function
is similar to that of CTCSS squelch detector except to handle carrier.
Data operated squelch circuit 55 detects the presence of digital data
messages in the incoming signal coming from a mobile station equipped wth
a data squelch encoder. Its typical detect time is 30 milliseconds and one
may refer to a more detailed description of a data operated squelch
circuit in U.S. Pat. No. 3,939,431 assigned to the present assignee.
Inhibit tone encoder 57 is an encoding circuitry which generates an
encoded signal to tell the mobile stations that there is an inbound data
or voice signal and tell the mobiles stations not to send in any other
data message. The tone inhibit signal as indicated by an inhibit tone
detector provided in each of the digital data terminals disables the
digital data terminals in the mobile stations so that they do not send out
digital data while the mobile station is receiving the inhibit tone. This
inhibit tone encoder is actuated to generate the inhibit code when inbound
voice or inbound digital data is detected.
Voice CTCSS line encoder 59 is used to generate a signal to tell mobile
stations that there is an inbound voice present from a mobile station to
the base station. With the voice CTCSS encoder actuated, an inbound voice
signal is rebroadcast and heard by all of the mobile stations. So the base
station acts as a repeater to repeat and broadcast the incoming inbound
voice message to all of the mobile stations.
The rest of the functional blocks of the control circuitry at a base shown
in FIG. 2 is a well-known conventional type and will not be described
separately. But their functions will be evident from the following
description.
Now the operation of the control circuitry of the present invention
provided in the data base station will be provided. The operation will be
described in the context of the four situations described hereinabove in
handling the communications tasks.
First, suppose there is an inbound voice signal from a mobile station to
the base station. The voice signal comes into the receiver 65 and is sent
to the dispatcher via audio path 56 and line driver 96 and communications
processor 23 under the control of the CTCSS squelch detector 51 and
inbound activity encoder 58 in a conventional manner. The voice CTCSS code
is also detected by the CTCSS squelch detector 51. In turn, the CTCSS
squelch detector provides an output which actuates inhibit tone encoder 57
via an OR gate 67 and the normal repeater push-to-talk 72 via a
conventional squelch gate 69 and OR gate 71. The normal repeater 72 in
turn causes voice CTCSS encoder 59 to be enabled via an OR gate 73. With
squelch gate 59 activated, the inbound voice signal is transmitted through
the path 56, a switch 70 provided in the squelch gate 69, and thence to
audio circuits 75 and thence to transmitter 77, as generally known.
With the voice CTCSS encoder and inhibit tone encoder 57 activated in the
aforementioned manner, the transmitter sends out an inhibit tone signal
and voice CTCSS signal and rebroadcasts the inbound voice signal to the
mobile stations via squelch gate 69 and audio circuits 75 and transmitter
77. In this manner the base station functions as an audio repeater and
thereby broadcasts the incoming voice signal from a mobile station to all
of the mobile stations. While this is taking place, the voice CTCSS and
inhibit tone signals are sent from the base station to the other mobiles
and the mobiles to inhibit all other mobile stations from transmitting
voice or data. Also, digital data signal can be transmitted from the base
station via a line driver 78 and transmit voice/data audio circuit 75 from
the dispatcher's console 29 (FIG. 1). The system will interrupt the
re-transmission of the incoming voice signal, as done in a conventional
system, when the voice override feature is required.
The second situation is where digital data is being transmitted from a data
terminal of a mobile station to the base station. The inbound data is
received by the receiver 65 and its presence is detected by the data
operated squelch circuitry 55. Circuitry 55 in turn actuates the inhibit
tone encoder 57 to generate inhibit tone signal and the normal
push-to-talk or repeater 72 via gate 71 to transmit the incoming digital
signal to the transmitter 77 of the base station. Thus, incoming data
signal is transmitted back to the mobile stations. Persons at the mobile
stations will detect the presence of rebroadcast digital data signal, in
the form of a hushing noise, although they will not be able to decipher
the data signal content. This enables the persons in the mobile stations
to realize that a mobile station is transmitting a digital message to the
base station and alert them not to interfere. So they will not interrupt
the inbound data transmission taking place unless an emergency situation
exists. When an emergency exists, a person at a mobile station can cut in
and override data signals. This is a well-known repeater operation of the
system so that the dispatcher can interrupt and send out voice signals to
mobile stations. Note that the digital data is retransmitted without the
addition of the voice CTCSS signal. This allows the circuitry in the
mobile radio to be arranged so that the user can hear the presence of the
rebroadcast digital data only when he pulls out or unhooks his microphone
and tries to transmit a voice signal. When he does this, he hears a
hushing sound signifying to him that an inbound digital data from a base
station is being rebroadcast by the base station.
The third situation is where an outbound voice signal goes out from a base
station to a mobile station. The voice signal comes from the dispatcher's
voice console 27 via radio control chassis 25. The voice signal actuates a
conventional voice push-to-talk circuit 82 and circuit 82 in turn actuates
voice CTCSS line encoder 59 to enable voice terminals in the mobile
stations. The voice signal from the base station is transmitted via a
voice/data normal audio circuit 75 and transmitter 77. The dispatcher's
voice is then heard by all of the people at mobile stations. While the
foregoing is taking place, the mobile stations can still send an inbound
data or voice from any one of the mobile stations. Transmission of data
from the base to the mobile is inhibited however by the radio control
chassis function shown in FIG. 1.
The fourth situation is when an outbound digital data is sent out to a
digital data terminal from the dispatcher's console 29 or data base 30
circuit. The presence of outbound data is detected by the data
push-to-talk circuit 80. The digital data signal is permitted to go out
via the transmit voice/data normal audio circuits 75 and the transmitter
77. The voice/data communications processor 23 is designed so that a
dispatcher can interrupt and send out a voice signal via the line driver
78 and transmit voice/data audio circuit 75 and transmitter 77. This
interrupts data transmission and the voice CTCSS encoder 59 sends a signal
to all mobiles signifying that there is now a voice message present. When
the dispatcher terminates his voice transmission, then the data
transmission is resumed. This is a built-in transmission arrangement that
gives voice preference over data transmission in a data/voice shared
two-way radio communication system wherein the channel frequency is
basically allocated to serve primarily for voice transmission. While the
digital data is going out, incoming voice as well as incoming digital
signal is permitted to come in via receiver 65 and line driver 96 and
thence to voice/data processor and thence to the dispatcher's console or
data base.
As described hereinabove, a data operated squelch detector 55 and CTCSS
squelch 51 detector, voice CTCSS encoder 59 and inhibit tone encoder 57
are used in an advantageous manner in the control circuitry of the base
station to enable a two-way mobile voice/data shared two-way radio
communications system to operate in a full duplexed mode as described
hereinabove which has not been possible heretofore.
In addition, the present invention provides the following advances to the
art. Thus, for example, the throughput of the system is significantly
increased by permitting the system to operate so that, while an inbound
data coming in, a voice signal can go out and vice versa. This increases
the throughput capacity of the system. There is no prior art two-way
system which is capable of combining data and voice transmission in this
manner.
The increase in the throughput capacity is also obtained by the fact that
the data operated squelch circuit in the control circuitry is faster than
CTCSS squelch decoder. The data operated squelch circuit of the
aforedescribed U.S. Pat. No. 3,939,431 is found to require 30 milliseconds
detection time as opposed to 120 millisecond detect time required by the
conventional CTCSS squelch detector 51. When projected over many number of
mobile stations of a system utilizing an allocated channel of limited
bandwidth, savings in time taken for setting up communication paths is
very significant. This in turn increases throughput of the system very
significantly.
While the present invention is described in the context of an embodiment
thereof hereinabove, other changes and modifications may be by persons of
ordinary skill without departing from the spirit and scope of the present
invention.
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