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Chapter 4: Problem 40

Describe Rayleigh fading in approximately 4 lines and without using a diagram.

Short Answer

Expert verified
Rayleigh fading describes random variation in signal amplitude due to multiple scattered paths arriving at different times, typically in environments with many obstacles and no direct line-of-sight.

Step by step solution

01

- Definition

Rayleigh fading describes the phenomenon where the amplitude of a signal passing through a communication channel varies randomly.
02

- Cause

It occurs due to the superposition of multiple scattered signal paths arriving at the receiver at different times.
03

- Conditions

Rayleigh fading usually happens in environments where there are many obstacles causing scattering, like urban areas.
04

- Assumption

The assumption is that there is no line-of-sight path between the transmitter and receiver.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Signal Amplitude Variation
When discussing Rayleigh fading, the term 'signal amplitude variation' refers to the changes in the strength of a received signal. This is not a smooth, predictable change but rather a random fluctuation. These variations are due to the environment through which the signal travels. Imagine the signal is like water waves hitting a beach; sometimes the waves are strong, sometimes weak.
In the context of communication, these fluctuations can cause issues like signal dropouts or reduced clarity. Understanding this variation is crucial for designing robust communication systems.
Scattered Signal Paths
Rayleigh fading occurs primarily due to scattered signal paths. When a signal is transmitted, it doesn't always take a single, straight path to the receiver. Instead, it bounces off various objects, like buildings, trees, or even vehicles. Each of these reflections creates a new path, and all these paths combine before they reach the receiver.
This superposition of multiple paths can cause the signal to either strengthen or weaken, depending on how these paths align. This scattering effect is essential to consider when analyzing or predicting Rayleigh fading.
Urban Communication Environments
Urban areas are prime examples of where Rayleigh fading is commonly observed. These environments are filled with obstacles like tall buildings, signs, and other structures that cause signal scattering.
In cities, signals often have to navigate around numerous objects. This frequent scattering creates multiple paths for the signals, making Rayleigh fading a common issue. Engineers must take these environments into account to improve communication reliability and ensure seamless connectivity.
No Line-of-Sight Path
One of the key assumptions in Rayleigh fading is the absence of a direct line-of-sight path between the transmitter and receiver. Without a clear line of sight, the signal primarily reaches the receiver through indirect paths caused by scattering.
This scenario is common in dense urban environments where buildings and other structures obstruct direct signal paths. The lack of a line-of-sight path emphasizes the importance of considering Rayleigh fading in designing urban communication networks, as it significantly impacts signal strength and quality.

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Most popular questions from this chapter

An antenna with an efficiency of \(50 \%\) has an antenna gain of \(12 \mathrm{dBi}\) and radiates \(100 \mathrm{~W}\). What is the EIRP in watts?

A communication system operating at \(2.5 \mathrm{GHz}\) includes a transmit antenna with an antenna gain of \(12 \mathrm{dBi}\) and a receive antenna with an effective aperture area of \(20 \mathrm{~cm}^{2}\). The distance between the two antennas is \(100 \mathrm{~m}\). (a) What is the antenna gain of the receive antenna? (b) If the input to the transmit antenna is \(1 \mathrm{~W}\), what is the power density at the receive antenna if the power falls off as \(1 / d^{2},\) where \(d\) is the distance from the transmit antenna? (c) Thus what is the power delivered at the output of the receive antenna?

The output stage of an RF front end consists of an amplifier followed by a filter and then an antenna. The amplifier has a gain of \(27 \mathrm{~dB},\) the filter has a loss of \(1.9 \mathrm{~dB},\) and of the power input to the antenna, \(45 \%\) is lost as heat due to resistive losses. If the power input to the amplifier is \(30 \mathrm{dBm},\) calculate the following: (a) What is the power input to the amplifier? (b) Express the loss of the antenna in decibels. (c) What is the total gain of the RF front end (amplifier + filter)? (d) What is the total power radiated by the antenna in \(\mathrm{dBm}\) ? (e) What is the total power radiated by the antenna in milliwatts?

A transmitter and receiver operate at \(10 \mathrm{GHz}\), are at the same level, and are \(4 \mathrm{~km}\) apart. The signal must diffract over a building that is half way between the antennas and is \(20 \mathrm{~m}\) higher than the line between the antennas. What is the attenuation (in \(\mathrm{dB}\) ) due to diffraction?

A transmitter has an antenna with an antenna gain of \(20 \mathrm{dBi},\) the resistive losses of the antenna are \(50 \%\), and the power input to the antenna is \(100 \mathrm{~mW}\). What is the EIRP in watts?
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