In the electromagnetic spectrum, all omnidirectional waves in the frequencies 3KHz to 1GHz are called radio waves. They are widely used for communications since they are easy to generate, can travel long distances and can penetrate buildings. Radio waves have omnidirectional antennas, i.e. antennas that can send signals in all directions. The properties of radios waves vary according to their frequencies. However, radio waves at all frequencies are prone to interference from electrical equipments like motors etc. Low and Medium Frequency Radio Waves Low and medium frequency radio waves can pass through obstacles and have ground propagation. However, the ... Read More

The electromagnetic spectrum is the entire range of electromagnetic radiation according to the wavelength or frequencies. It has a range of frequencies from 1Hz to Hz. The waves in order of increasing frequencies are radio waves, microwaves, infrared rays, visible light, UV rays, X-rays and gamma rays.Among these range, the frequencies between Hz to Hz are used for communication. The following diagram shows the electromagnetic spectrum. The first figure gives the full range of frequency spectrum while the second figure elaborates that part of the spectrum which can be used for data communication − The ... Read More

In wireless transmission media, data is transmitted in the form of electromagnetic waves that do not require any physical conductors for transmission. The waves are broadcast through free space and any device who has permission to connect can receive them. The three ways in which unguided signals travel are − Ground Propagation: It is a method of propagation, in which radio waves travel through the lowest layers of the atmosphere along the earth’s surface, following the earth’s curvature. The frequency of these signals is low (≤ 2MHz), and the distance they travel is directly proportional to the power ... Read More

In passband transmission, the amplitude, phase or frequency of the carrier signal is regulated to transmit the bits. The incoming data stream is modulated onto a carrier and then transmitted over a band-pass channel. The types of passband transmission are illustrated as − Amplitude Shift Keying (ASK) In ASK, the amplitude of the signal is varied to represent the signal levels, while frequency and phase remains constant. In order to represent 0 and 1, two different amplitudes are used. Frequency Shift Keying (FSK) In FSK, the frequency of the signal is modulated to represent the signal levels, while ... Read More

In baseband transmission, the data bits are directly converted into signals. Generally a higher voltage level represents the bit 1, while a lower voltage level represents bit 0.The different encoding schemes are shown in the diagram. Among these, the first three are come in the category of polar encoding. In polar signaling, one logical state is represented by only one voltage state. In bipolar schemes, two voltage levels may be used to represent a logical state.NRZ (Non – Return to Zero)NRZ is an unipolar coding scheme. Here, a high voltage represents 1, while a low voltage represents 0. Non-return to ... Read More

Fiber optic communications and satellite communications are complementary to each other. Their properties are very different from one another and consequently their usage varies.Comparison between satellite communication and optical fiber communication can be done based upon the following areas −TerrainSatellite communication is best suited for rough terrains, poorly connected areas and places where it is difficult to lay wires.On the other hand, fibers are suited for urban areas with good infrastructures, where it is convenient to lay communication lines.BandwidthFiber optic promises extremely higher bandwidth with negligible electromagnetic interference. Satellites have lesser bandwidth and are prone to interferences.Data Rate and DelayThe ... Read More

Virtualization in operating system changes a normal operating system so that it can run different types of applications that may be handled on a single computer system by many users. The operating system may appear different to each user and each of them may believe they are interacting with the only operating system i.e. this does not interfere with user experience.Operating system virtualization can also be used to migrate a process from one instance of the operating system to another. However, all the processes in the system are isolated and there operations are strictly monitored so there are no discrepancies ... Read More

Mobile Computing deals with human computer interaction using mobile devices. It contains mobile hardware and software as well as mobile computing devices. A mobile computing infrastructure usually uses ad-hoc networks and communication protocols. This is considerably different than a traditional computing structure as it uses fixed topology and protocols.An image describing mobile computing architecture is as follows −As seen above, the mobile computing architecture contains various mobile devices such as mobile phones, mobile tablets, laptops etc. These devices are connected to the mobile network which is a part of the internet. All the data is linked to cloud computing data ... Read More

Real time systems are those systems that work within strict time constraints and provide a worst case time estimate for critical situations. Embedded systems provide a specific function in a much larger system. When there is an embedded component in a real time system, it is known as a real time embedded system.Types of Real Time Embedded SystemsThere are primarily two types of real time embedded systems i.e. hard and soft. An illustration to explain this further is −Hard Real Time Embedded SystemThis type of system makes sure that all critical processes are completed within the given time frame. This ... Read More

There are two modes of operation in the operating system to make sure it works correctly. These are user mode and kernel mode.They are explained as follows −User ModeThe system is in user mode when the operating system is running a user application such as handling a text editor. The transition from user mode to kernel mode occurs when the application requests the help of operating system or an interrupt or a system call occurs.The mode bit is set to 1 in the user mode. It is changed from 1 to 0 when switching from user mode to kernel mode.Kernel ... Read More