Appeal No. 2003-2027
Application No. 08/804,908
response during a defined time period with respect to the sign-on
message on a specific frequency. Assume that remote unit 30
wishes to sign on to the system. Remote unit 30 then responds
with a sign-on message. Head end unit 20 receives a sign-on
response in the expected time slot on the expected frequency. In
this case, the head end unit responds to the sign-on response and
performs tests requested in the response and subsequent messages
from the remote unit. See page 5 of Appellants' specification.
If head end unit 20 does not detect a sign-on response, there are
three possible reasons for lack of response. The first
possibility is that no response was sent. The second possibility
is the return path is not functioning properly. The third
possibility is noise or other carrier interference with the
transmission. Head end unit 20 distinguishes between these
possibilities by measuring the power in the return path frequency
band specified for the response. See page 5 of Appellants'
specification. If the peak level detected was sufficient to
interfere with communications, head end unit 20 sends an error
message in the forward direction indicating that the return path
had sufficient noise to interfere with communications thereon.
In the preferred embodiment of the present invention, the message
includes a spectral measurement of the entire return frequency
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