----------------------------------------------- TrueTime 1.5 Example: Distributed Wireless Control System Directory: $DIR/examples/wireless-----------------------------------------------1. INTRODUCTIONThis example shows distributed control of a DC-servo usingcommunication over a wireless network. The example also shows how tosimulate power consumption and how to use the battery block. The modelcontains two computer nodes located 20 m apart, each represented by aTrueTime kernel block. A time-driven sensor/actuator node samples theprocess periodically and sends the samples over the network to thecontroller node. The control task in this node calculates the controlsignal and sends the result back to the sensor/actuator node, where itis actuated. The wireless communication link is at the same timesubject to a simple power control scheme. Power control tasks runningin both the sensor/actuator node and in the controller nodeperiodically send out ping messages to the other node to test thechannel transmission. If a reply is received, the channel is assumedto be good and the transmission power is lowered. If on the other handno reply is received, then the transmission power is considerablyincreased until it saturates or a reply is received again.2. COMPILING THE SIMULATION FILES2.1 Configuring the TrueTime Environment    Before starting Matlab, you must set the environment variable    TTKERNEL to point to the directory with the TrueTime kernel files:        Unix/Linux: > export TTKERNEL=$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. SIMULATIONSOpen 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.