Appeal No. 96-3366
Application 08/292,700
Appellants’ Invention
The error correcting capability of a digital communication system maintains audio quality (i.e.,
reduces noise) even at distances which would otherwise give an indication to a user of increasing
distance from the transmitter. As such, breakdown of audio quality sufficient to indicate a fringe
condition does not occur until the user is close to the out-of-range distance, at which point corrective
actions may not be able to be taken without at least a temporary loss of communications.
Analog communication systems offer no such protection against noise in received signals.
Because the amount of noise in a received message is directly proportional to the distance between the
transmitter and receiver, the amount of background noise in received audio is used to judge the strength
of the received signal, and consequently, where users are relative to the outer limits of a given
transmitter’s coverage area. Thus, users can take corrective action to stay within the coverage area.
The present invention provides for the indication of coverage area limits within digital
communication systems. With respect to Figure 4, error correction information, preferably in the form
of bit-error rates (BER)(402) and/or received signal strength information (RSSI)(403), is provided. A
threshold comparison and range determination function (405) uses the BER and/or RSSI to determine
the distance between the transmitter and the receiver. A simulated analog RF channel noise generator
(407) generates noise proportional to the range indication, which noise is added (410) to recovered
speech signals during silent or near-silent periods of speech, as determined by a speech analyzer (409).
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