CA1316985C - Simulcast broadcasting system and method - Google Patents

Abstract

IMPROVED SIMULCAST BROADCASTING SYSTEM AND METHOD

Abstract of the Disclosure A simulcast broadcast system wherein two signals (103 an 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.

Description

.~ `^i " 131`-69 SIMULCAST BROADC~TING SYSTEM AND METHOD

Technical Field This invention relates generally to simulcast radio communications systems.

Backgrolmd Art Simulcast radio communications systems alle typically employed ~o provide wide area one-way or hvo-way radio communic~tions services. In such a system, a source site ~pically originates (or forwards ~om another originating site) a signal to be generally broadcast. This signal is routed from the source site to a pluralit~ 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 recei~e the signal.

One particularly difficult problem with such simulcast systems involves coordinating the various I

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remotQ ~ites to ensure that the sign21s are in fact substantially simultaneou~ly broadcast by each. A
failur~ to acco~pllsh thi~ will result in instanc~s of unacceptable reception coherence as potentially caused by phase of~s~ts, daviation, distortion and th~ like.
Anoth~r problem arises when more than two signals must be transmitted simultaneously: for example, a voice signal and a data signal. Prior ~rt methods of procesRing such combined ~ignals in a simulcast ~ environment have not alway~ heen aclequately conduciv~ to supporting necessary levels of reception coherence.
Finally, even when initially properly adjusted ~or proper reception coherence, the operating performance of a given si~ulcast system may vary in response to a - 15 number of changing operating and environmental factors.
No prior art 8ystems provide ~or a ~eans of allowlng a simulca~t system to respond in any convenient or e~icacious manner to such circumstances.
A need exists ~or a ~imulca6t system that provides for the ~ub~tantially simultaneous broadcast of a ~ignal fro~ a plurality of re~ote site~, particularly where th~ signal to b~ broadca~t itself includes at least :; two signals. A need further Qxlsts for a system that can adapt on~ or more o~ it operating param~ter~ to continually provid~ tran~missions o~ acceptable reception coher~nc0 ev~n when other operating ~actors or nviron~ental conditions ch~nge.

S ~ arX o~ th~ I _cntion : 3~
Thes~ n~eds and others are substan~ially met through provision of ~he improved simulcast broadcasting system disclosed h~rein. The system includes generally a source ~it~ ~or providing an original ~ignal ~o be broadcast, and a plurality of remote sites for substan~ially simultaneou~ly broadcasting the original signal from the source ~lte.

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In one e~bodimen~, the source site provides both a ~irst and ~ second signal (such as volce and data).
The source ~ite provides these two signals to the remote sites discrete from one another. Only a~ter recep~ion and appropriate processing at the remote Rite will the ~wo signals be combin~d to ~acilit~te their broadcast.
In one embodiment, the appropriate proce~sing provided to the first and ~econd signals at the remote sites includes introduction of an appropriate time delay to ensure that all of the remote ~ites broadcast substantially the sam~ signal with ub~tant$ally the same phase relakion~hip.
In another embodiment, a ~onitoring device can be provided to monitor broadcAst signal~ from the remote sites, and det~rmine wheth~r th2 broadcast ~ignals ~xhibit an acceptable reception coherence. One or more broadcas~ system parameters can then be automatlcally varied in re~pon~ to this determination as appropriate to improve r~ception coherence.

~rief~ D ~criPtion of th~ Drawinqa Fig. 1 co~pris~ a ~lock diagram d~piction of source s~te ~tructur~:
:~ ~ FigO 2 co~pri~s a block diagram depiction of remote sit~ ~tructure;
Fig. 3 co~prise a block diagram depiction of the re~ote de}ay module of tha remote site; and ~ Fig. 4 comprises a:block diagram depiction of a : monitoring site.
:` 30 est Mode ~or Carryinq out the Invention ~he inventlon includes generally a sourc~ site unit (SSU~ (100) (Fig. 1) and a remote site unit (RSU) (200) (Fig. 21.
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. Referrlng to Flg. 1, the SSU (100~ include gQnerally ~ ~icrowave radio (lol) that receive~ both audio and data input. The microwave radio ~101) functions to transmit the two lnco~ing ~ignals in a known ~ultiplexed ~anner to the RSUs (200) as descrihed below in mor~ d~tail.
The SSU audio p~th ~102) include~ an audio source input (103) ~which ~ay b2 on ~it or o~f, as may be appropriate to the application or functlon) that passe~
through a tran mi~sion bloc~ (104) con~igured ln known manner as a double sidehand/reducecl carrier, the output o~ which tran~mitter (104) couples to a transmitter input port of the microwav2 radio (lol). In certain application~, as in trunked co~unications, ~hi~ input (103) could alternatively rec~ive high speed data, æuch as control channel signalling.
The data path (105) includes a data source (106) (which provides, ~or examp}e, low speed data intended to :~ be ultimately coupled subaudibly with the audio in~ormation). The data ~ource (106) passes through an FS~ ~odulator (107) to a single sideband configured I trans~itter (~08). Th~ la~er transmit~er (}08) sums to : a transmit port of thQ microwave radio 1101).
For purpo~e~ Or ~xplanation, the audio signal can be a fir~t 3ignal, and the data sign~l can be a second ~ignal, with th~ ultimat~ intent being to provide a ~ignal to a subscriber unit, such a8 a mohile, portable or fixed rece~ver, in ~ combined ~ormat. Upon reception, : th~ radio will r~nder the voice information audible, and 30 will subaudlbly proce~s and act accordingly upon ~he data information or instruction~. It should ba noted t~at in thiB yste~, contrary to prior art technique, the first and second ~lgnal~ are not combined at the S5U (loo).
Instead, ~h~y are transmitted separately and discrete : 35 from one another, in a ~ultiplexed ~anner, to the RSUs (200).
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R@ferring now to Fig. 2, an example RS~ (200) will be de~cribed. The RSU t200) includes a repeater structure comprised o~ two mierowave radio~ (201 and 202). Signal~ r~c~ived by th~ ~irst microwave radio 5 (201) are ~ubsequ~ntly repeated and transmitted by the second microwave radio (202), ~ox instancP to another ~SU. Slmllarly, ~lgnal~ received ~rom down 8 ream RSUs can be received by the ~econd microwave radio (202) and transmitted to the SSU via the first microwaYe radio (201). ~g~in, the~ radio~ ~201 and 202) function in a : known manner to r~c~iv~ and tran~lt ~ultipl~xed signals, including th~ rirst and sscond signals pro~ided by the SSU (100~.
ThQ RSU (200) al~o includes a combinor (203) as well under~tood in th~ ~rt. ~h~ combiner provides a high ~requency received in~ormation line t204) and a hlgh ~requ~ncy trans~it ln~ormation line ~205). A single ~ideband con~igured receiver (206) couples to the receive line (204) and ~unctlons to receive the data information a~ tran~mitted by thè SSU (100). A double ~ideband~reduced carri~r configurated receiver (207) also couple~ to th~ receive line (204) and ~unctions to : receive th~ audio information ~5 ~eparately transmitted by ~he SSU ~100).
The output o~ both r~ceivexs (206 and 207~ is provided to a re~ota delay modul~ (RDMI (208~, the con~igur~tion and operation o~ which will be described in mor~ d*tail below. ~he output (209) o~ the remote delay . : module ~n~}ude~ recovared audio in~ormation and recovered data i~formation, appropriately processed, delayed, and co~bined. Thi~ combined signal can then be pro~ided to apprspriate transmit~er equipment to allow a gen~ral broadca~t o~ the in~ormation in a known manner.
The RSU t200~ also includes a single ~ideband configured ~ransceiv~r ~210) that couples to bo~h high ~: frequency lines of the co~biner (203) and communicates with ~ proc~ssor unit (211) that provi~es appropriate .

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control instructions to the RDM (?08) a~ also described in more detail below.
Referring now to ~ig. 3, the RDM (208) includes a data path (301) and an audlo path (302). The data pa h (301) couples to ~he ou~put of the ~ingle ldeband receiver t206) through a 600 ohm input unit (303), following which th~ ignal is appropriately clipp~d and squared ~3G4) in a known ~anner. Th~ data signal is then passed through an appropriat~ delay unit (305). The delay un~t (305) introduces a time delay in any approprlate known ~anner to accomplish a predeter~ined ~elay of propagation o~ the da~a ~iynal to th~
transmitter o~ the RSU t200). (The purpose o~ th~s delay is to Qn~ur~ that all RSU~ (200) transmit a given source signal as providQd by th~ SSU ~100) at 3ubstantlally the sama tl~e. Thero~ore, the delay at any particul~lr RSU
(200) will likely be unique to that RSU.) The d~layed data slgnal th0n pas~e3 through an appropriate FSK
decod~r ~306) and subaudible da~a splatter filter (307) ~o a digi~al att~nua~or uni~ (30a). Following appropriat~ attenuation as re~uired to provlde necessary equalization, th~ data signal is provided to a sum~ing :, unit (309j, tha operation of ~hich will b~ disclosed in ~ora datall b~low.
: 25 Th~ aua$o path (302) connects to the output of the do~ le ~ideband/reduced carrier receiver (207~
: through an appropriat~ 600 oh~ input (310). The audio signal i8 then passed through an appropriate anti-alias ' ~iltsr ~311) to a d~lay unit (312), the function and :~ 30 purpo~e of which i~ th~ ame as that described abovs for thQ data path delay unit (~305).
ol~owin~ introduction of the appropriato delay, the audio ~ignal passes through an appropriate ~platter ~ilt~r (313) and digi~al attenuator (314) ~o provide ~he nece~sary equalization, following which the signal passes : through ~ highpas~ ~ilter (3153 to the summing unit (309).

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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 distinc~ composite signal. This distinct composite signal thenS passes 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 respond to an appropriate control signal (320). So configured, the surnming 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 RSIJ (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) ; I referenced above. The processor (211) in turn can receive data information and/or instructions from the SSU (1003 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 (200), and implemented without human intelvention.

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; ~ With reference to Fig. 4, a monitoring site (4ûO) in accordance with the invention can be seen as depicted generally by the numeral 400. A typical `~ ~ 30 ~ monitoring site ~includes a signal processing unit (401) that could include, for example, a number of directional antennas ~:
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~402). Each antenna (402) could be directed to a particular RSU (200). The signal proce~sing unit (401) utili~es that infor~ation to develop information regarding reception coherance for ~ignals broadcast by the RSU~ t200~. A processor (403~ can be provided that takes the reception coherence information developed by the signal processing unlt (401) and compares it against an appropriate threshold or other criteria. Information regarding the co~parisons developed by the processor 10 ~403~ can be tran~itted via an appropriate radio (404) or other link to the S5U (100) or other con~rol location.
Basad upon information developed by ~he monitoring site : (400) regard~ng reception coher~nce, tAe delay and/or attenuation parame~ers for a given RSU (200) can be selectively varied to accommodate changing operating or environmental conditions.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a simulcast broadcast system wherein a broadcast signal is broadcast substantially simultaneously from at least two sites, an improved simulcast broadcasting method comprising the steps of:

a) monitoring, at least from time to time, said broadcast signal;

b) determining whether said broadcast signal has acceptable reception coherence;

c) automatically varying at least one broadcast system parameter to improve said reception coherence.