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Lab 4

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**List The LOS Wireless Transmission impairments ?**

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**Briefly Discuss the error compensation mechanisms ?**

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**What is the difference between diffraction and scattering ?**

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**In ………………, Signals above 30 MHz are transmitted and not reflected by ionosphere**

a. Line Of Sight propagation b. Sky wave propagation c. Ground wave propagation d. b and c

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**…………is based on the fact that individual channels experience independent fading events.**

a. Reflection b. Diffraction c. Scattering d. Diversity e. Refraction

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**……………… is the unwanted coupling between signal paths.**

a. Thermal noise b. Impulse noise c. Intermodulation noise d. Crosstalk

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**……….. is a measure of the directionality of an antenna.**

a. Effective area b. carrier frequency c. Antenna gain d. speed of light ( 3 x108 m/s)

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**A high SNR means a. a high quality signal b**

A high SNR means a. a high quality signal b. low number of required intermediate repeaters c. high noise power d. a and b

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Shannon's result is that the maximum channel capacity but practically only much lower rates achieved as a. Shannon assumes thermal noise only b. Attenuation distortion or delay distortion not accounted for c. Lack of repeaters d. Shannon assumed low bandwidth e. a and b

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**State true or false for the following statements and correct the false:**

Omnidirectional antennas Radiates power equally in all directions ( ) Refraction occurs at the edge of an impenetrable body that is large compared to the wavelength of the radio wave. ( )

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What’s the parity bit? A parity bit appended to an array of binary digits to make the sum of all the binary digits, including the parity bit, always odd (odd parity) or always even (even parity).

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What is the CRC? The CRC is an error detecting code in which the code is the remainder resulting from dividing the bits to be checked by a predetermined binary number.

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**Why would you expect aCRC to detect more errors than a parity bit?**

The CRC has more bits and therefore provides more redundancy. That is, it provides more information that can be used to detect errors.

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**List three different ways in which the CRC algorithm can be described.**

Modulo 2 arithmetic, polynomials, and digital logic.

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**State true or false for the following statements and correct the false:**

a. CRCis an error detection process used in wireless transmission (false) Correction:FEC b. Cyclic Codeisdesignedto correct single bit errors Correction:Hamming Code c. Cyclic CodeCan be encoded and decoded usinglinear feedback shift registers (LFSRs) (True) d. CRCTakes fixed-length input (k) and producesfixed-length check code (n-k)but CyclicCodeaccepts arbitrary length input for fixed-length check code (false) Correction:Cyclic-CRC e. Forward error correction (FEC) encoder maps each k-bit block into an n-bit block codeword (true)

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