Home Computer Science Real-Time and Distributed Real-Time Systems: Theory and Applications

TrueTime Wireless Network Nodes

Figure 5.23 shows a TrueTime Wireless Network block, with supported protocols listed in a scroll-down.

The significance of the different parameters listed in the block are defined as follows:

FIGURE 5.22

TrueTime Kernel block.

FIGURE 5.23

A TrueTime Wireless Network node.

Network Number—Starts from 1 and defines the Network block number. Wired and wireless network nodes cannot share the same number.

Number of nodes—Defines the number of nodes in the network.

Date rate—Defines the transmission speed.

Frame size—Denotes the minimum frame size in terms of bits. A message shorter than this will be padded.

Transmit power—Defines the strength of the radio signal.

Receiving threshold—Threshold value of signal above which the medium will be tagged busy.

Pathloss exponent—This is modeled as path loss = (1/Da). This option allows choice of the parameter a based on the medium.

ACK timeout—The timeout value for receiving acknowledgment.

Retry limit—The number of times a node attempts retransmission.

Error coding threshold—The limiting value of block error for successful message reconstruction.

Detailed documentation of the TrueTime library blocks with examples may be found in Cervin et al. [4]. A TrueTime Battery block is optional and can be used in a simulation to test an energy model of communication, for example, in scenarios involving wireless sensor networks.

SIMULATION EXERCISES

• 5.1. Develop a real-time windows target to generate a sine wave y(t) = 2 sin 31.4t and hence derive a second sine wave from it having the same amplitude and frequency and a phase lag of 2n/5. Direct the outputs on a scope to generate a real-time output of both the sine waves.
• 5.2. Extend the Moore machine of Figure 5.12b to develop the xPC Target simulation module for the event scheduler and the full simulation of the earth-orbiter-rover communication scenario assuming that the distance between the Earth and the moon is 400,000 km and the orbiter rotates at an orbit that is 100 km from the surface of the moon.
• 5.3. For Exercise 5.2, if the earth station becomes the master clock, how do the simulation modules change? Develop the corresponding FSMs and the xPC Targets.
• 5.4. Translate the simulations of Exercises 5.2 and 5.3 to appropriate TrueTime models. In each case neglect, the transmission energy aspect and concentrate on the delay.
• 5.5. Wireless sensor nodes are placed radially outward from the center in a circular field such that the circular distance between two sensor nodes remains constant. Simulate a suitable traffic for the sensor network where the data from the nodes at the periphery are sent radially inward through nodes in the successive inner layers using TrueTime. Test the energy consumed using a TrueTime Battery node corresponding to the traffic model you developed.