Simulcast broadcasting system and method

A simulcast broadcast system wherein two signals (103 and 106) intended for simultaneous broadcast are transmitted from a source site (100) to remote sites (200) discrete from one another. At the remote sites, the two signals are separately processed, including the introduction of appropriate delay (305 and 312), prior to combining them for broadcast in conjunction with other remote sites. One or more monitoring sites (400) can also be provided to monitor reception coherence within the system and to provide operating measurement information to allow automatic control of various simulcast system parameters, including delay.

TECHNICAL FIELD 
This invention relates generally to simulcast radio communications systems. 
BACKGROUND ART 
Simulcast radio communications 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 
still be 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 remote sites to ensure that the signals are in 
fact substantially simultaneously broadcast by each. A failure to 
accomplish this will result in instances of unacceptable reception 
coherence as potentially caused by phase offsets, 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 adequately conducive to supporting necessary levels 
of reception coherence. 
Finally, even when initially properly adjusted for proper reception 
coherence, the operating performance of a given simulcast system may vary 
in response to a number of changing operating and environmental factors. 
No prior art systems provide for a means of allowing a simulcast system to 
respond in any convenient or efficacious 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 includes at least two 
signals. A need further exists for a system that can adapt one or more of 
its operating parameters to continually provide transmissions of 
acceptable reception coherence even when other operating factors or 
environmental conditions change. 
SUMMARY OF 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 of remote sites for substantially 
simultaneously broadcasting the original signal from the source site. 
In one embodiment, the source site provides both a first and a second 
signal (such as voice and data). The source site provides these two 
signals to the remote sites discrete from one another. Only after 
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 at 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 
One or more exhibit an acceptable reception coherence. One or more 
broadcast system parameters can then be automatically varied in response 
to this determination as appropriate to improve reception coherence.

BEST MODE FOR CARRYING OUT THE INVENTION 
The invention includes generally a source site unit (SSU) (100) (FIG. 1) 
and a remote site unit (RSU) (200) (FIG. 2). 
Referring to FIG. 1, the SSU (100) includes generally a microwave radio 
(101) that receives both audio and data input. The microwave radio (101) 
functions to transmit the two separate incoming signals in a known 
multiplexed manner to the RSUs (200) as described below in more detail. 
The SSU audio path (102) includes an audio source input (103) (which may be 
on site or off, as may be appropriate to the application or function) that 
passes through a transmission block (104) configured in known manner as a 
double sideband/reduced carrier, the output of which 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. 
The data path (105) includes a data source (106) (which provides, for 
example, low speed data intended to be ultimately coupled subaudibly with 
the audio information). The data source (106) passes 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 purposes of explanation, the audio signal can be a first signal, 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 fixed 
receiver, in a combined format. Upon reception, the radio will render the 
voice information audible, and will subaudibly process and act accordingly 
upon the data information or instructions. It should be noted that in this 
system, contrary to prior art technique, the first and second signals are 
not combined at the SSU (100). Instead, they are transmitted separately 
and discrete from one another, from any site, to the RSUs (200). 
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) are 
subsequently repeated and transmitted by the second microwave radio (202), 
for instance to another RSU. Similarly, signals received from down stream 
RSUs can be received by the second microwave radio (202) and transmitted 
to the SSU via the first microwave radio (201). Again, these radios (201 
and 202) function in a known manner to receive and transmit multiplexed 
signals, including the first and second signals provided by the SSU (100). 
The RSU (200) also includes a combiner (203) as well understood in the art. 
The combiner provides a high frequency received information line (204) and 
a high frequency transmit information line (205). A single sideband 
configured receiver (206) couples to the receive line (204) and functions 
to receive the data information as transmitted by the SSU (100). A double 
sideband/reduced carrier configurated receiver (207) also couples to the 
receive line (204) and functions to receive the audio information as 
separately transmitted by the SSU (100). 
The output of both receivers (206 and 207) is provided to a remote delay 
module (RDM) (208), the configuration and operation of which will be 
described in more detail below. The output (209) of the remote delay 
module includes recovered audio information 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 information in a known manner. 
The RSU (200) also includes a single sideband configured transceiver (210) 
that couples to both high frequency lines of the combiner (203) and 
communicates with a processor unit (211) that provides appropriate control 
instructions 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), following 
which the signal is 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 predetermined delay of propagation of the 
data signal to the transmitter of the RSU (200). (The purpose of this 
delay is to ensure that all RSUs (200) transmit a given source signal as 
provided by the SSU (100) at substantially the same time. Therefore, the 
delay at any particular RSU (200) will likely be unique to that RSU.) The 
delayed data signal then passes through an appropriate FSK decoder (306) 
and subaudible data splatter filter (307) to a digital attenuator unit 
(308). Following appropriate attenuation 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, the audio signal passes 
through an appropriate splatter filter (313) and digital attenuator (314) 
to provide the necessary equalization, following which the signal passes 
through a highpass filter (315) to the summing unit (309). 
The summing unit (309) functions to sum the delayed and properly processed 
data signals with the delayed and properly processed audio signals to 
thereby provide a composite signal. This composite signal then passes 
through an appropriate 600 ohm output unit (316) for subsequent processing 
(209) as referenced above. (In a trunked system, as noted earlier the 
audio 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 
respond 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 (100). 
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 signal compensation 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 (100) through the microwave radio link. 
As a result, instructions regarding the appropriate delay and attenuation 
can be formulated at the SSU (100) and transmitted to the various RSUs 
(200), 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 (402). Each antenna 
(402) could be directed to a particular RSU (200). The signal processing 
unit (401) utilizes that information to develop information regarding 
reception coherence for signals broadcast by the RSUs (200). 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 (100) or other control 
location. Based upon information developed by the monitoring site (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.