Wireless Communications Network Slides

Question: Describe about the Wireless Communications for Network Slides. Answer: 1 - What does an amplifier do and why is one needed in a radio system? Amplifier: An amplifier boosts the electric current. Amplifiers are commonly used in electronic circuits in order to enhance the amplitude of a signal waveform, without any change in the factors of the waveform such as frequency or wave shape. Below shown is the general symbol of the amplifier. Amplifiers are used in radio systems to provide the voltage amplification of a radio signal. Various type of amplifiers are used in radio systems. The block diagram of FM radio is shown below. Block diagram of FM Radio Audio frequency Amplifiers AF amplifiers are used for the amplification of signals in human hearing range i.e. 20Hz to 20 kHz. Low level signals are amplified by using the voltage amplifiers and for the tone correction equalization of signal levels. Power amplifier receives the amplified input from voltage amplifiers and provides required power for the loudspeakers. R.F. Amplifiers In Radio frequency amplifiers the tuned circuit governs the frequency of operation.. The bandwidth of the amplifier depends upon the use. It can be narrow or wide. These amplifiers have low input resistance. These amplifiers have a special feature of low noise performance that is why they are used in the earlier stages of receiver. Low noise FET transistors are commonly seen in these stages in order to keep the background noise produced by electronic devices at minimum level. I.F. Amplifiers These Frequency intensifiers are utilized as a part of radio framework. Prior to the data conveyed by the sign is isolated from the radio signal. Also, these are used to provide the voltage enhancement of a radio signal. The frequency on which these amplifiers work is lower than receiving radio signals and higher than the audio signal. It depends upon the equipment type. 2: What is the purpose of a mixer? Include a discussion of sidebands in your answer. A mixer is an electronic device that performs the process of frequency conversion by the multiplication of two signals. A mixer can be as simple as a diode or it can be complicated. It is an active or passive device that converts signals from one frequency to another. Normally, a mixer circuit has two inputs and the output can be the sum or difference of the input frequencies. Electronic devices such as diode, transistor and valve can be used as a mixer. Single Sideband mixers: These mixers play an important role as modulator and demodulator in high frequency signals. They control the phase in process of amplitude modulation and allow measuring the phase and amplitude of high frequency signals. SSB or I/Q modulators are helpful in separating and expelling the lower sideband (LSB)or upper sideband (USB) created during frequeny conversion, particularly when sidebands are close in frequency and attenuation of one of the sidebands can't be accomplished with filtering. Double Balanced Mixers: Double balanced mixers have properties dealing with frequencies, phase and amplitudes due to which they can be used to work as RF devices. These mixers play the multiple roles. They can be used as Current-Controlled Attenuator, frequency doublers, phase detector, amplitude modulator, product detector and balanced modulator (DSB). When using it as a phase detector, RF signal is applied to LO terminal and the other RF signal is connected to RF port. As a frequency doublers, RF signal is applied to both LO and RF ports. In order to use as a current controlled attenuator, RF signal is connected to LO Port and DC control current is applied to IF port. When used as a balanced modulator, RF signal is connected to LO port and modulating signal is connected at IF port. 3- Compare and contrast the multiplexing techniques CDMA and FDMA in the area of wireless networking? A multiplexer has multiple inputs and a single output. There are 3 different protocols to enable multiple signals to a single communication channel such as frequency division multiple access (FDMA), time division multiple access (TDMA) and code division multiple access (CDMA). . These protocols are used to maximize the bandwidth efficiency. FDMA Different signals are assigned different channels with frequency division multiple access. The channel is frequency. It is the basic technology for AMPS(Advanced mobile phone system). One channel can be assigned to single user at a time, with FDMA. It is used in total access communication system and fiber optic communication system as well. Every information system is assigned a different light frequency for transmission purposes. Every individual channel is wider in order to accommodate signal spectra. CDMA It is also a digital technique and known as spread spectrum. In this technology, different pseudorandom binary sequence is assigned to each user that modulates the carrier, spreading the spectrum of the waveform. It provides a unique code pattern to each user. Every user in a CDMA framework utilizes an alternate code for signal modulation. Picking the codes used to adjust the signal is vital in the execution of CDMA frameworks. The best result will achieve when there is great partition between the sign of a wanted client and the signals of different users. In the event that the signal matches the code of user then the relationship capacity will be high. There are two basic categories of CDMA i.e. synchronous and asynchronous CDMA. It is used in telephone systems in 800-MHz bands and in satellite systems for transportation purposes. The XOR circuit is used in CDMA to spread the digitized and compressed signal. Then, this signal can be shared with other users using different codes. References: Coates, E (2016). Learn about electronics- amplifiers. https://www.learnabout-electronics.org/Amplifiers/amplifiers10.php Koome, B. Single Sideband, SSB Modulation. Retrieved from https://www.radio-electronics.com/info/rf-technology-design/am-amplitude-modulation/single-sideband-ssb-modulation.php Poole, I. RF Mixer, Radio electronics (2011) https://www.radio-electronics.com/ Rohde, U. RF Circuit Design for Wireless Applications, retrieved from https://supportforums.cisco.com/document/93126/understanding-rf-fundamentals-and-radio-design-wireless-networks-slides-expert Rosu, I. RF Mixers. YO3DAC / VA3IUL ,retrieved from https://www.qsl.net/va3iul Spirito, P. Review of basic of power amplifiers for analog electronics. Power Devices and Circuits 2012. https://www.analog.com/library/analogDialogue/archives/43-09/EDCh%204%20rf%20if.pdf Spirito, P. RF/IF circuits. Power Devices and Circuits 2012.