## What is Power Spectral Density & it’s benefits?

Updated on 23-Jun-2021 15:07:18
A composite signal is composed of several frequency components. Each frequency component corresponds to a signal. Such signals of different frequencies put togetherforms a composite signal. Different signal frequencies present in the signal respond differently to the channel noise conditions. Power spectral density specifies the power levels of the frequency components present in a signal. It is denoted as PSD inshort. The PSD specifies the power of various frequencies present in the signal and we can determine the range of power over which the signal frequencies are operating at. Essentially, the PSD profile is a plot of the power over ... Read More

## Signal-To-Noise Ratio Numerical Problems with Solutions

Updated on 23-Jun-2021 15:05:57
This article presents some of the numerical problems on SNR.Question 1At the transmitter, the signal power is 23 mW. The input SNR is 40 dB. The channel offers 3 dB attenuation to the signal and the output noise is thrice the input noise level. Determine the SNR at the output.Soln − $SNR_{i/p}=\frac{S_{i/p}}{N_{i/p}}$Calculation Of Output Power LevelAn attenuation of 3 dB equals halving the input transmission power. If the ratio of two quantities on the linear scale is 1/2, it translates to -3 dB on the dB scale which is indicated as attenuation. So, the output signal power is 23mW/2 =11.5 mW.Calculation ... Read More

## What is Signal to Noise Ratio?

Updated on 23-Jun-2021 14:52:33
The ‘Signal-to-Noise’ ratio or, SNR (in short), is a metric that describes the signal performance in the presence of wireless channel noise (interference). In the linear scale, the SNR is the ratio of the signal power to the noise power. The wireless channel is never noise-free.There always exist noise floors that the signal must combat to reach the receiver successfully. At the receiver, we, therefore, not only receive the transmitted signal. We have a noisy or, noise added version of the transmitted signal.Below is an example of SNRExpression for SNR$$SNR=\frac{Signal\:Power}{Noise\:Power}$$$$SNR(dB)=10log_{10}(\frac{Signal\:Power}{Noise\:Power})$$Key Properties of SNRSignal to Noise ratio in short is called ... Read More

## Path Loss - Solved Numerical Problems from Wireless Communications

Updated on 23-Jun-2021 14:46:59
Let us understand the significance of path loss by solving some numericals.Example 1 − Problem SolutionFor a microwave terrestrial-based line-of-sight communication operating at 10 GHz, what is the maximum faithful coverage distance that the signal could make before requiring a repeater? The following details are provided −Signal transmission power = 27.78 dBWTransmit antenna gain = 18 dBiReceive antenna gain = 20 dBiSignal transmission bandwidth = 4 MHz2- sided Noise power spectral density = 10-10 W/HzSolution − We are provided with the following data −ParameterValuePt30 dBW = 1000 WGt35 dBi = 3162.22Gr35 dBi = 3162.22f10 GHzB4 MHzN0/210-10 W/HzWe know that the channel ... Read More

## Path Loss Definition, Overview and Formula

Updated on 23-Jun-2021 14:45:48
Usually, the wireless channel is noisy. We can’t have a noise-free communication. We often use the AWGN (Additive White Gaussian Noise) model for interpretation of the channel noise. Noise is assumed to get added to the signal and at the receiver; we have a signal that carries both the data and the noise. It is important that signal level at the receiver is reasonably above the noise floor so that the detector can faithfully detect and decode the signal data.Apart from noise, losses in the atmosphere can also distort the transmitted signal. Some of the common losses taken into consideration ... Read More

## Wireless Channel Noise: Solved Problems on Noise Power

Updated on 23-Jun-2021 14:44:46
In this section, we will solve some problems on wireless channel noise based on the white noise model.Example Problem 1A white noise has a 2-sided power spectral density of 6 kW/MHz. It is passed through a low pass filter having a bandwidth of 1 kHz. Compute the output noise power.Solution −The 2-sided power spectral density is 6 kW/MHz. The power spectral density is usually represented in W/Hz.$$\frac{6kW}{MHz}=\frac{6000W}{1000000Hz}=\frac{0.006W}{Hz}=\frac{N_{0}}{2}$$The 2-sided power spectral density N0/2 is 0.006W/Hz. Therefore, N0 = 0.012W/Hz.The noise power is expressed as the product of the noise power spectral density and the noise bandwidth.$$N_{p}=N_{0}.BW$$$$N_{p}=\frac{0.012W}{Hz}.1kHz=12W$$The noise power of the given ... Read More

## Wireless Channel Noise – Definition, Models and Comparison

Updated on 23-Jun-2021 14:44:01
What is Wireless Channel Noise?It is not possible to have any wireless communication system/link with absolutely zero noise level. Noise is additive and hence at the receiver, we have the signal that contains both the transmitted data and noise. The most commonly used noise model is the Additive White Gaussian Noise (AWGN). The noise follows Gaussian distribution with zero mean.What are the effects of channel noise?The channel noise could distort the original user data signal.If the channel noise is too high, it will bring down the Signal-to-Noise Ratio (SNR) of the signal as a result of which the receiver might not be ... Read More

## Amplifier Gains – Solved Problems on Power & Voltage Ratios

Updated on 23-Jun-2021 14:43:00
Let us look at some numerical on amplifiers to get a better grip of the theoretical understanding.The ratio of output to input voltage of an amplifier is 20. Compute the voltage gain.Solution − The voltage ratio is given as 20. We need to convert this linear ratio into logarithmic ratio to arrive at the solution.$$Voltage\:gain(dB)=20log_{10}(20)\sim\:26dB$$The positive voltage gain indicates that the output power is greater than the input power.What does amplification in power by 3 dB indicate?Solution − Let the output power be ‘y’ and input power be ‘x’. Representing this as an equation, we have$$3dB=10log_{10}(\frac{y}{x})$$$$log_{10}(\frac{y}{x})=0.3dB\Rightarrow\:\frac{y}{x}=10^{0.3}\sim\:2$$Thus, the output power is twice the ... Read More

## Amplifier Gains – Functions, Problems & Solutions

Updated on 23-Jun-2021 14:41:51
Function of AmplifiersAmplifiers boost up or amplify weak signals. Repeaters are good examples of amplifying devices. They are present in few to several numbers at intermediate points between the transmitter and receiver, depending on the actual distance between the two. Periodic amplification at intermediate stations between the transmitter and receiver ensures that there is a desired level of signal-to-noise ratio (SNR) maintained with the signal to successfully complete the final mile of transmission.Understanding Amplifier GainsExample 1If in a two-amplifier system where the amplifiers are cascaded in series, the first amplifier provides a gain of 10 dB while the second amplifier ... Read More

## Solutions for Decibel Representation Problem Sets of Wireless Communications

Updated on 23-Jun-2021 14:40:25
Problem 1 on Power LevelFor a communication link, the received power level is measured as 5 dBm. What does this mean?Here, we have a positive ‘dBm’ and hence we can say that the received power level is greater than the reference power level which is 1 mW.$$5dBm=10log_{10}(\frac{P_{received}}{1mW})$$$$log_{10}(\frac{P_{received}}{1mW})=\frac{5}{10}=0.5$$$$(\frac{P_{received}}{1mW})=10^{0.5}=3.1622$$$$P_{received}=3.1622mW$$We can infer that the received power level is 3.1622 times greater than the reference power level. However, this doesn’t mean that the received power level is greater than the input or transmitted power level. In fact, the received power level can never be greater than the transmitter power. In practice, the received power ... Read More