Page 28 - DCAP608_REAL TIME SYSTEMS

Unit 2: Introduction to Real-time Applications

falls at the base station. The base station monitors this and as soon as the RSS falls below a certain Notes
threshold value, it hands-off the details of the on-going call of the mobile to the base station of
the cell to which the mobile has moved. The hand-off must be completed within a sufficiently
small predefined time interval so that the user does not feel any temporary disruption of service
during the hand-off. Typically call hand-off is required to be achieved within a few milliseconds.
2.4.6 Aerospace

A few important uses of real-time systems in aerospace applications are: avionics, flight
simulation, airline cabin management systems, satellite tracking systems, and computer on-
board an aircraft.

Example: Computer On-board an Aircraft
In many modern aircrafts, the pilot can select an “auto pilot” option. As soon as the pilot
switches to the “auto pilot” mode, an on-board computer takes over all controls of the aircraft
including navigation, take-off, and landing of the aircraft. In the “auto pilot” mode, the computer
periodically samples velocity and acceleration of the aircraft. From the sampled data, the on-
board computer computes X, Y, and Z co-ordinates of the current aircraft position and compares
them with the pre-specified track data. Before the next sample values are obtained, it computes
the deviation from the specified track values and takes any corrective actions that may be
necessary. In this case, the sampling of the various parameters, and their processing need to be
completed within a few micro seconds.

Internet and Multimedia Applications

Important use of real-time systems in multimedia and Internet applications include: video
conferencing and multimedia multicast, Internet routers and switches.

Example: Video Conferencing
In a video conferencing application, video and audio signals are generated by cameras and
microphones respectively. The data are sampled at a certain pre-specified frame rate. These are
then compressed and sent as packets to the receiver over a network. At the receiver-end, packets
are ordered, decompressed, and then played. The time constraint at the receiver-end is that the
receiver must process and play the received frames at a predetermined constant rate. Thus if
thirty frames are to be shown every minute, once a frame play-out is complete, the next frame
must be played within two seconds.

2.4.7 Consumer Electronics

Consumer electronics area abounds numerous applications of real-time systems. A few sample
applications of real-time systems in consumer electronics are: set-top boxes, audio equipment,
Internet telephony, microwave ovens, intelligent washing machines, home security systems,
air conditioning and refrigeration, toys, and cell phones.

Example: Cell Phones
Cell phones are possibly the fastest growing segment of consumer electronics. A cell phone at
any point of time carries out a number of tasks simultaneously. These include: converting input
voice to digital signals by deploying digital signal processing (DSP) techniques, converting
electrical signals generated by the microphone to output voice signals, and sampling incoming

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