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LabVIEW 2013 Adaptive Filter Toolkit Help

Edition Date: June 2013

Part Number: 372357B-01

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The purpose of adaptive channel equalization is to compensate for signal distortion in a communication channel. Communication systems transmit a signal from one point to another across a communication channel, such as an electrical wire, a fiber-optic cable, or a wireless radio link. During the transmission process, the signal that contains information might become distorted. To compensate for this distortion, you can apply an adaptive filter to the communication channel. The adaptive filter works as an adaptive channel equalizer.

The following figure shows a diagram of an adaptive channel equalization system.

In the previous figure, s(n) is the signal that you transmit through the communication channel, and x(n) is the distorted output signal. To compensate for the signal distortion, the adaptive channel equalization system completes the following two modes:

1. Training mode—This mode helps you determine the appropriate coefficients of the adaptive filter. When you transmit the signal s(n) to the communication channel, you also apply a delayed version of the same signal to the adaptive filter. In the previous figure, z–Δ is a delay function and d(n) is the delayed signal. y(n) is the output signal from the adaptive filter and e(n) is the error signal between d(n) and y(n). The adaptive filter iteratively adjusts the coefficients to minimize e(n). After the power of e(n) converges, y(n) is almost identical to d(n), which means that you can use the resulting adaptive filter coefficients to compensate for the signal distortion.
2. Decision-directed mode—After you determine the appropriate coefficients of the adaptive filter, you can switch the adaptive channel equalization system to decision-directed mode. In this mode, the adaptive channel equalization system decodes the signal y(n) and produces a new signal , which is an estimation of the signal s(n) except for a delay of Δ taps.

Refer to the Adaptive Channel Equalization VI in the examples\Adaptive Filters\Applications\Adaptive Channel Equalization directory for an example that uses the LabVIEW Adaptive Filter Toolkit to compensate for signal distortion.