| 摘要 |
An improved digital bi-directional communications transceiver in which the upstream (24) and downstream (22) portions of the frequency spectrum are allocated different bandwidths and positioned at different locations on the frequency spectrum in response to transmission line conditions and impairments such as system provisioning, background noise, radio frequency interference (RFI), crosstalk and reflected signals. The movements of the upstream and downstream carrier frequencies are elastic in that they may be adjusted in near rear-time, involving methods for determining a signal quality parameter (SQP) of the received signal. The SQP is used to estimate the bit error rate (BER) of the received signal and also takes into account the total signal-to-interference ratio (SIR), where the interference includes, crosstalk, RFI and residual echo from the neighboring upstream (24) or downstream (22) channel. Because the carrier frequencies of the upstream (24) and downstream (22) channels are being dynamically allocated, it is necessary to implement a robust carrier acquisition, recovery and lock algorithm. The robust carrier algorithms allow carrier recovery of the transmitted upstream and downsteam signals independent of the particular modulation or symbol rates.
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