We have drawn the decision directed
mode to run for the duration of the data portion of the time slot, it is up to the system designer what
to do with the two groups of data available.
One approach to decide when to engage in bidirectional equalization is to use the received signal
strength to help. Figure 6.6 shows a receiver operating under the conditions if the received signal
Pilot Pilot Pilot Data Data
Time Slot Time Slot
Train
Decision Directed
Decision Directed
Train
Train Train
Faded Envelope
FIGURE 6.6 Bidirectional equalization example.
strength falls below a certain threshold, the adaptive signal processing is halted and the data is stored
until the next time slot arrives. When the next pilot bits arrive the training sequence begins, however in
the opposite direction. This is shown below for two consecutive time slots using three pilot bit fields.
Once again the dashed lines are used to denote the signal processing performed in the reverse direction.
6.1.3 Maximal Likelihood Sequential Estimation (MLSE)
This next form of estimation moves away from the symbol-by-symbol-based detectors presented
above; here a sequence of transmitted bits are estimated. In order to proceed, we will assume the
received signal is represented as follows:
(6.
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