MATLAB SIGNAL PROCESSING BLOCKSET 7 Guide de l'utilisateur télécharger pdf (Page 125)

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Delay and Latency

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Delay and Latency

There are two distinct types of delay that affect Simulink models:

•Computational delay

•Algorithmic delay

The following sections explain how you can configure Simulink to minimize

both varieties of delay and increase simulation performance.

Computational Delay

The computational delay of a block or subsystem is related to the number of

operations involved in executing that component. For example, an FFT block

operating on a 256-sample input requires Simulink to perform a certain

number of multiplications for each input frame. The actual amount of time that

these operations consume (as measured in a benchmark test, for example)

depends heavily on the performance of both the computer hardware and

underlying software layers, such as MATLAB and the operating system.

Computational delay for a particular model therefore typically varies from one

computer platform to another.

The simulation time represented on a model’s status bar (which can be

accessed via Simulink’s Digital Clock block) does not provide any information

about computational delay. For example, according to the Simulink timer, the

FFT mentioned above executes instantaneously, with no delay whatsoever. An

input to the FFT block at simulation time t=25.0 is processed and output at

time t=25.0, regardless of the number of operations performed by the FFT

algorithm. The Simulink timer reflects only algorithmic delay (described

below), not computational delay.

The next section discussed methods of reducing computational delay.

Reducing Computational Delay

There are a number of ways to reduce computational delay without actually

running the simulation on faster hardware. To begin with, you should

familiarize yourself with “Improving Simulation Performance and Accuracy” in

the Simulink documentation, which describes some basic strategies. The

section below supplements that information with several additional options for

improving performance.

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