Telecommunications – Wireless distribution system – Receiver for satellite broadcast
Reexamination Certificate
2000-01-04
2001-08-07
Vo, Nguyen T. (Department: 2682)
Telecommunications
Wireless distribution system
Receiver for satellite broadcast
C455S012100, C455S067700
Reexamination Certificate
active
06272313
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to satellite communication systems, and more particularly to a method and system for detecting signal lock between a satellite receiver and a satellite in a digital DBS system.
Generally, in modem digital satellite communication systems a ground-based transmitter transmits a forward-error-coded uplink signal to a satellite positioned in geosynchronous orbit. The satellite in turn relays the signal back to a ground-based receiver antenna in a separate location. Direct broadcast satellite (“DBS”) systems allow households to receive audio, data, and video directly from the DBS satellite. Each household subscribing to the system receives the broadcast signals through a receiver unit and a satellite dish receiver antenna.
The typical consumer DBS system consists of a satellite receiver antenna which includes an e.g. 18-inch parabolic dish and low noise block (“LNB”), and a receiver unit which may include an integrated receiver decoder module, or “IRD”. The receiver antenna is typically mounted outside the house, and cables are provided to link the LNB to the indoor IRD and associated equipment (e.g. video display).
Several factors can degrade received DBS signals. For example, the satellite receiver antenna can accumulate snow, ice, leaves, or other debris unseen by the user. Remote blockage may also develop, such as shadowing foliage (e.g. trees). This accumulation or other shadowing obstruction can degrade the received signal strength enough to interrupt IRD operation. Furthermore, due to the significant amount of forward error correction used, the DBS picture or data quality may not suffer any noticeable decrease although signal strength is continuously degrading. When signal strength falls below a certain minimum, the signal can be completely lost without warning.
Other sources of DBS signal degradation include antenna tracking errors in mobile installations, such as ships, trains, or automobiles, each of which require constant adjustments to the receiver antenna's orientation. As with fixed DBS systems, the signal degradation in a mobile DBS installation can result in complete loss of signal lock without warning.
Therefore, there is a need for an inexpensive and simple method and system for automatically detecting signal degradation and for warning the user when a DBS signal is degrading, to provide an incipient signal loss warning or reaction. There is a particular need for such a method and system which may be added to existing satellite receiving equipment without modification, e.g. as an “add-on” device.
SUMMARY OF THE INVENTION
The present invention provides an inexpensive and simple method and system to detect signal degradation and to warn the user that signal strength is degrading or has degraded below a given threshold. The present invention may be embodied in a system that processes a portion of the receive antenna/LNB output and splits this incoming RF signal. In a preferred embodiment, the signal is split into three components, one having the majority of the received power and the others having lesser power. The RF signal in one path (preferably one of the lesser-power paths) is passed through a filter that isolates a portion of the frequency spectrum corresponding at least predominantly to an intelligence carrying or “service” frequency signal, such as a portion of a satellite transponder signal of the DBS system. The RF signal in another path (preferably also lesser power) is passed through a second filter that isolates a portion of the frequency spectrum which contains only (or predominantly) “noise” signals.
The difference in power between the two filtered signal components is then detected. For example, the output of each filter is passed to a separate RF detector. Each RF detector converts the RF signal at its input to a DC voltage or some other output (e.g. a digital output) that is proportional to the input signal power. Scaling (e.g. amplification, attenuation, or digital manipulation) may be used to compensate for differences in absolute outputs of the one or more portions of the device. The difference between the two power levels is then detected. For example, in one embodiment a voltage corresponding to one of the RF signals (e.g. non-signal noise power) is passed through an inverter. This inverted signal is then summed with a DC signal corresponding to the other signal component (e.g. the service frequency signal power). In this way, a voltage is obtained which is proportional to the difference in the relative powers of the desired service signal and the noise signal (the “difference” value or voltage). Finally, the RF signal in the third path, preferably having the majority of received power, may be passed unaffected to a receiver (e.g. IRD) for normal processing.
The difference value or voltage can then be passed to a comparator (or several comparators) or the like for comparison to one or more predetermined thresholds. For instance, a difference voltage can be compared to a level corresponding to loss of signal lock. The difference voltage could also be compared to a level somewhat higher than the loss of signal lock level, relating to a degraded signal or incipient signal loss.
In another aspect of the invention, the system includes a user interface for alerting the user of an approaching loss of signal lock. The user interface may in part allow the user to activate an external device, or otherwise select a corrective measure from a menu of options to curtail signal loss.
The invention may be further embodied in a method that includes the steps of establishing a first threshold value (e.g. between the respective levels representative of the satellite signal and the noise), combining a value indicative of a noise frequency signal component with a value indicative of a service frequency signal component to obtain a difference signal value, comparing the difference signal value with a first threshold value, and issuing a command if the difference signal value is below the first threshold value. The command may indicate e.g. that signal lock has been lost. In another aspect of this method, the steps further include establishing at least a second threshold value greater than the first threshold value. The second threshold may be used e.g. to issue a warning that signal lock is degrading and may soon be lost.
The present invention thus provides a method and system for determining when a received signal has degraded, or has been lost, by detecting the relative levels of the desired (i.e. service frequency) to background (i.e. noise) signal components present in the signal. In certain embodiments, the method and system allows the user the opportunity to take steps to correct the degrading signal independent of the receiver. The method and system utilize a small number of simple electronic components and do not require a microprocessor (although one may be utilized), thereby allowing the unit to be more reliable and inexpensive. Furthermore, the method and system can warn the user of signal degradation and possible loss, allowing the user to take corrective measures before the signal is completely lost.
In preferred embodiments, the system may be implemented as an add-on accessory for use with a variety of receivers. In one preferred embodiment, the detection circuits may be housed in a module for insertion in-line between an LNB and an IRD. A bypass path or through line may be provided to conduct the majority of the received signal power directly from the LNB to the IRD. Because the invention operates to detect signal loss or degradation without requiring analysis of signal content or intelligence, the add-on device does not require complex tuners, decoders or error measurement circuits. The device may therefore in certain embodiments work independently of the IRD, other receiving components, or the signal format used for the satellite signal.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only,
Arsenault Robert G.
Loner Patrick J.
Crook John A.
Hughes Electronics Corporation
Sales Michael W.
Vo Nguyen T.
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