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Decision Feedback Equalizer Stabilization in Adaptive Mode

IP.com Disclosure Number: IPCOM000049014D
Original Publication Date: 1982-Apr-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 2 page(s) / 39K

Publishing Venue

IBM

Related People

Godard, D: AUTHOR [+3]

Abstract

In modem synchronous data transmission systems, the sequence of bits to be transmitted is converted into a sequence of data symbols.

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Decision Feedback Equalizer Stabilization in Adaptive Mode

In modem synchronous data transmission systems, the sequence of bits to be transmitted is converted into a sequence of data symbols.

Each symbol may be defined through its quadrature components, and the various available symbols are preselected to be distributed over a predetermined constellation (see figure). The data symbols are transmitted using double sideband quadrature carrier modulation techniques. On the receiving side, the received signal has to be sampled, converted into its orthogonal components, demodulated and equalized, and submitted to a decoding or detecting operation for deriving the received data symbols therefrom. The conventional type of equalizers used in data receivers are the so-called decision feedback equalizers. One of the main drawbacks of decision feedback equalizers is that they are subject to error propagation, i.e., past decision errors tending to produce new wrong decisions so that long sequences of error are likely to occur. In that case, the error signal used for updating equalizer tap-gains and carrier phase is no more meaningful, which results rapidly in a complete loss of equalization.

This is an important problem when transmitting over switched network lines where the occurrence of each burst of noise would require new receiver synchronization.

This loss of equalization may be avoided by adopting the following approach: defining a neighborhood (e.g., a circular) regio...