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用于网络控制系统仿真

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 TrueTime 1.5
 Example: Distributed Wireless Control System
 Directory: $DIR/examples/wireless
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1. INTRODUCTION

This example shows distributed control of a DC-servo using
communication over a wireless network. The example also shows how to
simulate power consumption and how to use the battery block. The model
contains two computer nodes located 20 m apart, each represented by a
TrueTime kernel block. A time-driven sensor/actuator node samples the
process periodically and sends the samples over the network to the
controller node. The control task in this node calculates the control
signal and sends the result back to the sensor/actuator node, where it
is actuated. The wireless communication link is at the same time
subject to a simple power control scheme. Power control tasks running
in both the sensor/actuator node and in the controller node
periodically send out ping messages to the other node to test the
channel transmission. If a reply is received, the channel is assumed
to be good and the transmission power is lowered. If on the other hand
no reply is received, then the transmission power is considerably
increased until it saturates or a reply is received again.

2. COMPILING THE SIMULATION FILES

2.1 Configuring the TrueTime Environment

    Before starting Matlab, you must set the environment variable
    TTKERNEL to point to the directory with the TrueTime kernel files:

        Unix/Linux: > export TTKERNEL=$DIR/kernel
        Windows:  Control Panel / System / Advanced / Environment Variables

    Then add the following lines to your MATLAB startup script. This
    will set up all necessary paths to the TrueTime kernel files.

        addpath(getenv('TTKERNEL'))
        init_truetime;

2.2 Compilation

    As described in the reference manual it is possible to write a
    TrueTime simulation (i.e. the code functions for the tasks and the
    initialization commands) either as m-files or as C++ functions. For
    this example only the m-file approach is provided.
   
    Since the TrueTime archive contains pre-compiled files, no 
    compilation is required to run TrueTime in the Matlab version. 
    However, if needed, the files may be re-compiled by issuing the 
    command make_truetime from the command prompt.


3. SIMULATIONS

Open the model wireless.mdl to run the simulation. 

 - Run a first simulation without modifying anything. Look at the plots
   showing the battery levels in the two nodes. Note that the power control
   scheme is not activated until ~2 seconds have elapsed. Also note how the 
   measured values at some times deviate more than usual from the reference
   values. This deviation is caused by the fact that it is possible to lose
   several consecutive sensor value readings when using the simple power 
   control that is implemented in the nodes.

 - Switch off the power control scheme in the controller node. This is done
   by commenting out the creation of the task power_controller_task in 
   controller_init. Run the simulation again and now note that the power drain
   is constant in the controller node. This causes the battery to run out
   of energy, and the control is lost. Experiment with different network
   parameters and protocols. You can also configure the energy consumption and
   the CPU scaling in the kernel block with ttSetKernelParameter and
   experiment with different Dynamic Voltage Scaling techniques.