Note: Descriptions are shown in the official language in which they were submitted.
130~
SIMULCAST BROADCASTING SYSTEM AND METHOD
Technical Field
This invention relates generally to simulcast radio cornmunications systems.
Background Art
Simulcast radio comrnunications systems are typically employed to provide
wide area one-way or two-way radio communications services. In such a system, a source
site typically originates (or forwards from another originating site) a signal to be generally
broadcast. This signal is routed from the source site to a plurality of remote sites. Each
remote site then simultaneously broadcasts the signal with other remote sites to facilitate
reception of the signal by receivers within the area covered by the system.
In this way, a receiver outside the operating range of one remote site may stillbe within the range of one or more other remote sites, thereby reasonably ensuring that the
receiver can receive the signal.
One particularly difficult problem with such simulcast systems involves
coordinating the various
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remote sites to ensure that the signals are in ~act
substantially simultaneously broadcast by ea~h. A
failure to accompllsh this will result in instances of
unacceptable reception coherence as potentially caused by
phas~ orfsets, deviation, distortion and the like.
Another problem arises when more than two signals
must be transmitted simultaneously; for example, a voice
signal and a data signal. Prior art methods of
processing such combined signals in a simulcast
environment have not always been ade~uately conducive to
supporting necessary levels of reception coherence.
Finally, even when initially properly adjusted
for proper reception coherence, the operating per~ormance
of a given simulcast system may vary in responce to a
number of changing operating and environmental factors.
No prior art systems provids for a means of allowing a
simulcast system to respond in any convenient or
efficaclous manner to such circumstances.
A need exists for a simulcast system that
provides for the substantially simultaneous broadcast of
a signal from a plurality of remote sites, particularly
where the signal to be broadcast itself $ncludes at least
two signals. A need further exists for a system that can
adapt one or mor~ of its operating parameters to
continually provide transmissions of acceptable reception
cohsrencQ even when other operating factors or
envlronmental conditlons change.
Summarv Or the Invention
These needs and others are substantially met
through provision of the improved simulcast broadcasting
system disclosed herein. The system includes generally a
source site for providing an original signal to be
broadcast, and a plurality o~ remote sites for
subs~antially simultaneously broadcasting the original
siynal from the source site.
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In one embodiment, the source site provides both
a first and a second signal (~uch as voice and data).
The source site provides thesle ~wo signals to the remote
sites discrete from one ano~her. Only a~ter reception
and appropriate processing at the remote site will the
two signals be combined to facilitate their broadcast.
In one embodiment, the appropriate processing
provided to the first and second signals a~ the remote
sites includes introduction of an appropriate time delay
to ensure that all of the remote sites broadcast
substantially the same signal with substantially the same
phase relationship.
In another embodiment, a monitoring device can be
provided to monitor broadcast signals from the remote
sites, and determine whether the broadcast signals
exhibit an acceptable reception coherence. One or more
broadcast system parameters can then be automatically
varied in response to this determinatlon as appropriate
to improve rsception coherence.
Brief De~cription of the Drawinqs
Fig. 1 comprise~ a block diagram depiction of
source site structure;
Flg. 2 comprises a block diagram depiction of
remote site strUcture:
Fig. 3 comprises a block diagram depiction of the
remote delay module of the remote site; and
Fig. 4 comprises a block diagram depiction of a
monitoring sitQ.
~est Mode for ~arry-ing out the Invention
The invention includes generally a source si~e
unit lSSU) (100) ~Fig. 1) and a remote site unit (RSU)
(200) (Fig. 2).
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Referring to Fig. 1, the SSU (100) includes
generally a microwave radio (101~ that raceives both
audio and data input. The microwave radio (101)
functions to transmit the two incoming signals in a known
multiplexed manner to the RSUs (200) ag described below
in more detail.
The SSU audio p~th (102) lncludes an audio source
input (103) (which may be on ~ite or o~, as may be
appropriate to the application or function) that pas~es
through a transmission block (104) conrigured in known
manner as a double sideband/reduced carrier, the output
o~ whlch transmitter (104) couples to a transmitter input
port of the microwave radio (101). In certain
applications, as in trunked communications, this input
(103) could alternatively receive high speed data, such
as control channel signalling.
Ths data path (105) includes a data source (106)
(which provides, for example, low cpeed data intended to
be ultimately coupled subaudibly with the audio
information). The data source (106) pa~ses through an
FSK modulator (107) to a single sideband configured
transmitter (108). The latter transmitter (108) sums to
a transmit port of the microwave radio (101).
For pUrpO8Q5 of explanation, the audio signal can
be a ~irst ~ignal, and the data signal can be a second
signal, with the ultimate intent being to provide a
signal to a subscriber unit, such as a mobile, portable
or ~ixed receiver, in a combined format. Upon reception,
the radio will render ~he voice information audible, and
30 will subaudibly process and act accordingly upon the data
information or in~tructions. It should be noted that in
this system, contrary to prior art technique, the rirs~
and sQcond ~ignals are not combined at the SSU (100).
Instead, they are transmitted separately and discrete
from one another, in a multiplexed manner, to the ~SUs
(20~).
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Referring now to Fig. 2, an example RSU (200)
will be described. The RSU (200) includes a repeater
structure comprised of two microwave radios (201 and
202). Signals received by the first microwave radio
(201) ar~ sub6equently repeated and transmitted by the
se~ond microwave radio (202), ~or instance to another
RSU. Similarly, signal~ received fro~ down stream RSUs
can be received by the second microwave radio (202) and
transmittQd to the ssu via the flrst microwave radio
10 (201). Again, these radios (201 and 202) function in a
known manner to recoive and transmlt multiplexed signals,
including the first and second signals provided by the
SSU (100).
The RSU (200) also includes a combiner (203) as
woll understood in the art. The combiner provides a high
frequency received information line (204) and a high
frequency transmit in~ormation line (205). A single
sideband conrigured receiver (20~) couples to the receive
line (204) and ~unctions to receive the data information
as transmitted by the SSU (100). A double
~ideband/reduced carrier configurated receiver (207) also
couples to the receive line (204) and functions to
receive the audio information a~ separately transmitted
by the SSU (100).
The output of both receivers (206 and 207) is
provided to a remote delay modul~ (RDM) (203), the
con~iguration and operation o~ which will be described in
more detail below. The output (209) of the remote delay
module includes recovered audio infor~ation and recovered
data information, appropriately processed, delayed, and
combined. This combined signal can then be provided to
appropriate transmitter equipment to allow a general
broadcast of the informat~on in a known manner.
The RSU (200) al~o includes a single sideband
configured transceiver (210) that couples to both high
frequency lines o~ the combiner (203) and communicates
with a processor unit (211) that provides appropriate
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control instructi~n~ to the RDM (208) as also described
in more detail below.
Referring now to Fig. 3, the RDM (208) includes a
data path (301) and an audio path (302). The data path
(301) couples to the output of the single sideband
receiver (206) through a 600 ohm input unit (303),
~ollowing which the signal i~ appropriately clipped and
squared (304~ in a known manner. The data signal is then
passed through an appropriate delay unit (305). The
delay unit (305) introduces a time delay in any
appropriate known manner to accomplish a prede~ermined
delay o~ propagation of the data signal to the
transmitter of the RSU (200). (The purpose of this delay
i8 to ensure that all RSUs (200) transmit a given ~ource
signal as provided by the SSu (lOo) at substantially the
same time. Therefore, the delay at any particular RSU
(200) will llkely be unique to that RSU.) The delayed
data signal then pas~es through an appropriate FSK
deaoder (306) and subaudible data splatter filter (307)
to a digital attenuator unit (308). Following
appropriate att~nuation as required to provide necessary
equalization, the data signal is provided to a summing
unit (309), the operation of which will be disclosed in
more detail below.
The audio path (302) connects to the output of
the double sideband/reduced carrier receiver (207)
through an appropriate 600 ohm input (310). The audio
signal is then passed through an appropriate anti-alias
filter (311) to a delay unit (312), the function and
purpose of which is the same as that described above for
the data path delay unit (305).
Following introduction of the appropriate delay,
th~ audio signal passes through an appropriate splatter
filter (313) and digital attenuator (314) to provide th~
necessary equalization, following which the signal passes
through a highpass filter (315) to the summing unit
(309).
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The summing unit (309) functions to sum the delayed and properly
processed data s;gnals with the delayed and properly processed audio signals to
thereby provide a distinct composite signal. This dist;nct composite signal thenpasses through an appropriate 600 ohm output unit (316) for subsequent
processing (209) as referenced above. (In a trunked system, as noted earlier theaudio path (302) may receive high speed data instead of voice information. To
accommodate such an embodiment, the inputs to the summing unit (309) can be
controlled by a number of logic gates (317, 318, and 319) that res~ond to an
appropriate control signal (320). So configured, the summing unit (309) will
receive either both high pass filtered audio information and low speed data, or
high speed data only that has not been high pass filtered.)
It should be noted that the signal processing, such as equalization
and introduction of delay, occur at the RSU (200) as versus the SSU (lO0). Also,it should be noted that, at the RSU (200), the first and second signals are
individually and separately provided with the appropriate delay and other signalcompensation factors prior to their combination.
In Fig. 3, it can also be seen that the delay units (305 and 312) and
the digital attenuators (308 and 314) can be controlled by the processor (211)
referenced above. The processor (211) in turn can receive data information
and/or instructions from the SSU (lO0) through the microwave radio link. As a
result, instructions regarding the appropriate delay and attenuation can be
formulated at the SSU (lOO)and transmitted to the various RSUs (~00), and
implemented without human intervention.
With reference to Fig. 4, a monitoring site (400) in accordance with
the invention can be seen as depicted generally by the numeral 400. A typical
monitoring site includes a signal processing unit (401) that could include, for
example, a number of directional antennas
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(4023. Each ant~nna ~402~ could be dixected to a
particular RS~ (200). The signal processing unit (401)
utilizes that information to develop information
regarding reception coherence ~or signals broadcast by
the RSUs (2003. A processor (403) can be provided that
takes the reception coherence information developed by
the signal processing unit (401) and compares it against
an appropriate threshold or other criteria. Information
regarding the comparisons developed by the processor
(403) can be transmitted via an appropriate radio (404)
or other link to the SSU (lO0) or other control location.
Based upon information developed by the monitoring Sit2
(400) regarding reception coherence, the delay and/or
attenuation parameters for a given RSU (200) can be
selectively varied to accommodate changing operating or
environmental conditions.
