| Communications Toolbox | |
A symbol-spaced linear equalizer consists of a tapped delay line that stores samples from the input signal. Once per symbol period, the equalizer outputs a weighted sum of the values in the delay line and updates the weights to prepare for the next symbol period. This class of equalizer is called "symbol-spaced" because the sample rates of the input and output are equal.
Below is a schematic of a symbol-spaced linear equalizer with N weights, where the symbol period is T.
The algorithms for the Weight Setting and Error Calculation blocks in the schematic are determined by the adaptive algorithm chosen from the list in Equalizer Features of the Toolbox. The new set of weights depends on these quantities:
The current set of weights
The input signal
The output signal
For adaptive algorithms other than CMA, a reference signal, d, whose characteristics depend on the operation mode of the equalizer
The table below briefly describes the nature of the reference signal for each of the two operation modes.
| Operation Mode of Equalizer | Reference Signal |
|---|---|
| Training mode | Preset known transmitted sequence |
| Decision-directed mode | Detected version of the output signal, denoted by yd in the schematic |
In typical applications, the equalizer begins in training mode to gather information about the channel, and later switches to decision-directed mode.
The error calculation operation produces a signal given by the expression below, where R is a constant related to the signal constellation.
| | Overview of Adaptive Equalizer Classes | Fractionally Spaced Equalizers | |
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