1. Field of the Invention
This invention relates to digital receivers generally and, more particularly, to signal acquisition detection methods for digital carrier systems or the like.
2. Description of the Prior Art
Digital carrier systems require a fast method to reliably report when a received digital signal is removed and reapplied.
Prior art techniques relied on framing bits embedded in the digital signal matching a predetermined pattern to establish if the digital signal was present or not. Because the framing bits are relatively infrequent compared to the data rate (for a DS1 signal, the data rate is about 1.544 Mbits/second and the framing rate is 8000 bits/second), a relatively long sequence of valid framing bits must be received before a valid signal is indicated.
In an effort to speed up acquisition detection, Bellcore has specified a series of tests that must be satisfied before loss/acquisition of signal status changes. See Bellcore standard TR-TSY-000009 DS1, section 4.1 (Loss of Signal). Implementation of the standard is not specified.
Thus, it is desirable to provide a reliable method of detecting when a valid digital signal is applied to a receiver.
It is additionally desirable to provide an apparatus which reliably implements a reliable digital signal validity detection method.