The document discusses various aspects of wireless channels including:
1) Large-scale path loss models like the free space and two-ray models for estimating mean signal strength over distance.
2) Small-scale fading parameters caused by multipath time delay and Doppler spread which can result in flat or frequency selective fading.
3) Characteristics of the mobile radio channel that introduce problems like fading and interference not seen in wired channels.
This document summarizes several indoor propagation models. It begins with introducing path loss factors like reflection, diffraction, and scattering. It then describes the ITU indoor path loss model, log-distance path loss model, and Ericsson multiple breakpoint model. The ITU model calculates path loss based on frequency, distance, and floor number. The log-distance model uses a path loss exponent to estimate loss over distance. The Ericsson model provides upper and lower loss bounds based on measurements in an office building.
The document discusses various propagation mechanisms that affect radio signals, including reflection, diffraction, scattering, and their effects on signal strength over distance. It also covers propagation models like free space path loss, two-ray ground reflection model, and log-distance path loss for estimating average received signal power at a given distance. Fresnel zones and knife-edge diffraction are explained as factors in signal propagation around obstructions. Log-normal shadowing is described as a statistical model to account for variations from the average path loss.
The document discusses OFDM (Orthogonal Frequency Division Multiplexing) for wireless communication. It introduces OFDM as a modulation technique that divides the available bandwidth into multiple orthogonal subcarriers. This allows for overlapping subchannels and improves spectral efficiency compared to conventional FDM. The document then covers OFDM system modeling, generation of subcarriers, fading effects, use of guard times and cyclic extensions to mitigate multipath interference, windowing techniques, and factors to consider when choosing OFDM system parameters.
Wireless communication systems are impacted by fading effects that cause fluctuations in signal strength. Fading occurs due to multipath propagation which results in multiple versions of the transmitted signal reaching the receiver at different times. This can cause either flat or frequency selective fading depending on the delay spread. Modulation techniques like BPSK can be used to combat fading. Simulation of a Rayleigh fading channel, which occurs when there is no dominant signal path, showed that it significantly impacts the bit error rate of a BPSK modulated signal. Future work could explore additional modulation techniques and integrating the model into a network simulator.
The document provides an overview of spread spectrum techniques, including:
- A brief history noting its invention in the 1940s and military applications since the 1950s.
- Three main types of spread spectrum are described: direct sequence, frequency hopping, and time hopping.
- Direct sequence spread spectrum is explained in more detail, showing how the information signal is modulated by a spreading sequence.
- Advantages of spread spectrum techniques include resistance to jamming, ability to handle multipath interference, privacy, and allowing multiple access through different spreading codes.
This document provides training materials on calculating wireless link budgets to determine the feasibility and optimal configuration of radio links. It defines key concepts like free space loss, link budget, antenna gain and Fresnel zone. An example link budget calculation is shown for a 5km link. It also introduces the Radio Mobile software tool, which can automatically simulate radio links and calculate the required Fresnel zone clearance by considering terrain profiles. The document concludes with an example of using Radio Mobile to analyze a potential link in Chuuk and poses questions about configuring the masts, transmit power and antennas.
This document summarizes a student project on OFDM transmitters and receivers. It includes an introduction to OFDM that describes its use of orthogonal subcarriers. It also compares single carrier modulation to multi-carrier modulation using OFDM. The document outlines the basic OFDM transmitter and receiver block diagrams. It discusses the constellation mapper, IFFT block, cyclic prefix, and design approaches for these blocks. Simulation results are presented comparing transmitted and received signals. BER performance is evaluated for different modulation schemes like QPSK and QAM. The document concludes that OFDM provides high bandwidth efficiency and overcomes interference through the IFFT and cyclic prefix.
1) The document discusses parameters used to characterize mobile multipath channels including power delay profile, mean excess delay, RMS delay spread, maximum excess delay, coherence bandwidth, Doppler spread, and coherence time.
2) These parameters are derived from the power delay profile and describe aspects of the channel such as time dispersion, frequency selectivity, and time variation due to Doppler shift.
3) Examples of typical values for different channel parameters are given for outdoor and indoor mobile radio channels.
This document summarizes several indoor propagation models. It begins with introducing path loss factors like reflection, diffraction, and scattering. It then describes the ITU indoor path loss model, log-distance path loss model, and Ericsson multiple breakpoint model. The ITU model calculates path loss based on frequency, distance, and floor number. The log-distance model uses a path loss exponent to estimate loss over distance. The Ericsson model provides upper and lower loss bounds based on measurements in an office building.
The document discusses various propagation mechanisms that affect radio signals, including reflection, diffraction, scattering, and their effects on signal strength over distance. It also covers propagation models like free space path loss, two-ray ground reflection model, and log-distance path loss for estimating average received signal power at a given distance. Fresnel zones and knife-edge diffraction are explained as factors in signal propagation around obstructions. Log-normal shadowing is described as a statistical model to account for variations from the average path loss.
The document discusses OFDM (Orthogonal Frequency Division Multiplexing) for wireless communication. It introduces OFDM as a modulation technique that divides the available bandwidth into multiple orthogonal subcarriers. This allows for overlapping subchannels and improves spectral efficiency compared to conventional FDM. The document then covers OFDM system modeling, generation of subcarriers, fading effects, use of guard times and cyclic extensions to mitigate multipath interference, windowing techniques, and factors to consider when choosing OFDM system parameters.
Wireless communication systems are impacted by fading effects that cause fluctuations in signal strength. Fading occurs due to multipath propagation which results in multiple versions of the transmitted signal reaching the receiver at different times. This can cause either flat or frequency selective fading depending on the delay spread. Modulation techniques like BPSK can be used to combat fading. Simulation of a Rayleigh fading channel, which occurs when there is no dominant signal path, showed that it significantly impacts the bit error rate of a BPSK modulated signal. Future work could explore additional modulation techniques and integrating the model into a network simulator.
The document provides an overview of spread spectrum techniques, including:
- A brief history noting its invention in the 1940s and military applications since the 1950s.
- Three main types of spread spectrum are described: direct sequence, frequency hopping, and time hopping.
- Direct sequence spread spectrum is explained in more detail, showing how the information signal is modulated by a spreading sequence.
- Advantages of spread spectrum techniques include resistance to jamming, ability to handle multipath interference, privacy, and allowing multiple access through different spreading codes.
This document provides training materials on calculating wireless link budgets to determine the feasibility and optimal configuration of radio links. It defines key concepts like free space loss, link budget, antenna gain and Fresnel zone. An example link budget calculation is shown for a 5km link. It also introduces the Radio Mobile software tool, which can automatically simulate radio links and calculate the required Fresnel zone clearance by considering terrain profiles. The document concludes with an example of using Radio Mobile to analyze a potential link in Chuuk and poses questions about configuring the masts, transmit power and antennas.
This document summarizes a student project on OFDM transmitters and receivers. It includes an introduction to OFDM that describes its use of orthogonal subcarriers. It also compares single carrier modulation to multi-carrier modulation using OFDM. The document outlines the basic OFDM transmitter and receiver block diagrams. It discusses the constellation mapper, IFFT block, cyclic prefix, and design approaches for these blocks. Simulation results are presented comparing transmitted and received signals. BER performance is evaluated for different modulation schemes like QPSK and QAM. The document concludes that OFDM provides high bandwidth efficiency and overcomes interference through the IFFT and cyclic prefix.
1) The document discusses parameters used to characterize mobile multipath channels including power delay profile, mean excess delay, RMS delay spread, maximum excess delay, coherence bandwidth, Doppler spread, and coherence time.
2) These parameters are derived from the power delay profile and describe aspects of the channel such as time dispersion, frequency selectivity, and time variation due to Doppler shift.
3) Examples of typical values for different channel parameters are given for outdoor and indoor mobile radio channels.
Diversity Techniques in Wireless CommunicationSahar Foroughi
This document discusses diversity techniques for wireless communication, including cooperative diversity. It begins by introducing wireless systems and the impairments they face like fading. It then covers various diversity techniques like space, frequency, and time diversity that provide multiple transmission paths to reduce fading. Cooperative diversity is described as allowing single-antenna devices to achieve MIMO-like benefits by sharing antennas. The document outlines cooperative transmission protocols and challenges at different network layers in implementing cooperation. In conclusion, diversity techniques improve performance by providing multiple signal replicas to overcome fading, while cooperation enables reliability and throughput gains with challenges to address across protocol layers.
Power delay profile,delay spread and doppler spreadManish Srivastava
The document discusses power delay profiles and multipath propagation effects. It defines power delay profiles as giving the intensity of a signal through a multipath channel as a function of time delay between multipath arrivals. Multipath propagation can cause fading effects from signals combining constructively or destructively at the receiver. The time spread of arriving multipath signals is called the delay spread and determines whether a channel is flat or frequency-selective fading, while Doppler spread from receiver/transmitter motion causes time-varying fading.
This document provides an overview of GSM link budget calculations. It defines key terms used in link budgets such as effective radiated power, antenna gain, diversity gain, receiver sensitivity, path loss, and fade margin. It explains the objectives of calculating a link budget are to estimate maximum allowable path loss, compute required effective isotropically radiated power for a balanced link, estimate coverage design thresholds, and evaluate technology performance. It also provides examples of uplink and downlink link budget calculations for a GSM network and defines indoor, in-car, and outdoor coverage requirements.
This document discusses multiple-input multiple-output (MIMO) systems. It begins by outlining the motivations and aspirations for developing MIMO systems, including achieving high data rates near 1 gigabit/second while maintaining quality of service. It then provides an overview of MIMO system modeling and capacity studies. Key topics covered include diversity versus spatial multiplexing design criteria, example architectures, MIMO with orthogonal frequency-division multiplexing, and networking applications involving MAC protocols.
This document provides an overview of Orthogonal Frequency Division Multiplexing (OFDM), Orthogonal Frequency Division Multiple Access (OFDMA) and Scalable OFDMA (SOFDMA). It describes how OFDM divides available bandwidth into multiple orthogonal subcarriers to combat multipath interference in wireless channels. OFDMA further divides subcarriers to enable multiple access by multiple users. SOFDMA, defined in IEEE 802.16e, allows dynamic allocation of subcarriers for scalable bandwidth allocation to users.
Introduction To Wireless Fading ChannelsNitin Jain
The document summarizes key concepts related to wireless fading channels, including:
1. Multipath fading causes fluctuations in signal strength over small physical distances due to constructive and destructive interference from multiple signal paths.
2. Rayleigh fading occurs when there is no line-of-sight path between transmitter and receiver, resulting in fast, large fluctuations in signal strength over small physical distances.
3. Doppler spread and coherence time describe how quickly the wireless channel varies over time due to mobility, with fast fading occurring if the channel changes significantly within a symbol period.
This document summarizes the two-ray propagation model used in wireless communications. It assumes both a line-of-sight signal and a reflected signal propagate between the transmitter and receiver. The key parameters estimated are the electric field of each ray, the path difference between them, the phase difference, and time delay. Using geometry, the path difference is derived as approximately equal to 2 times the transmitter and receiver heights divided by the separation distance. The phase difference and time delay are then defined in terms of this path difference. Finally, the total electric field is written as the sum of the individual LOS and reflected signal fields.
This document discusses key concepts in telecommunications network planning and traffic engineering. It covers:
- Types of random processes used to model network usage patterns like call arrival rates and durations.
- How traffic engineering balances factors like grade of service, resources, blocking vs. delay systems based on traffic amounts.
- Key metrics like erlangs, traffic intensity, busy hour, traffic volume that are used to quantify network usage and demand.
- Concepts like grade of service, blocking probability, and how they measure network performance during busy periods.
The document provides an overview of MIMO (multiple-input multiple-output) systems in wireless communications. It discusses how MIMO can provide array gain, diversity gain, and multiplexing gain to improve spectral efficiency, coverage, and quality of service. It also describes how MIMO reduces co-channel interference. The document covers MIMO channel models and capacity results for different scenarios. It concludes by discussing how MIMO can be used to maximize diversity or throughput through different transmission techniques.
The document discusses small-scale fading and multipath propagation in wireless communications. It describes how multipath propagation leads to fading effects as multiple versions of the transmitted signal combine at the receiver. Channel sounding techniques are used to measure the power delay profile and characterize the time dispersion parameters of mobile radio channels, including mean excess delay, RMS delay spread, and maximum excess delay. Direct pulse systems, spread spectrum correlators, and frequency domain analysis are channel sounding methods discussed.
In this video, I will explain what is QAM modulation and what is 16QAM.
QAM Stands for Quadrature Amplitude Modulation. QAM is both an analog and a digital modulation method. But here, we are only talking about QAM as a digital modulation.
Quadrature means that two carrier waves are being used, one sine wave and one cosine wave. These two waves are out of phase with each other by 90°, this is called quadrature.
At the receiving end, the sine and cosine wave can be decoded independently, this means that by using both a sine wave and a cosine wave, the communication channel's capacity is doubled comparing to using only one sine or one cosine wave. That is why quadrature is such a popular technique for digital modulation.
QAM modulation is a combination of Amplitude Shift Keying and Phase Shift Keying, both carrier wave is modulated by changing both its amplitude and phase. As shown in this 8QAM waveform, the top is the sine wave carrier, for bit 000, the sin wave has a phase shift of 0°, and an amplitude of 2. While for bit 110, the phase shift is 180°, and the amplitude now is 1. So both phase and amplitude are changed.
In 16QAM, the input binary data is combined into groups of 4 bits called QUADBITS.
As shown in this picture, the I and I' bits are sent to the sine wave modulation path, and the Q and Q' bits are sent to the cosine wave path. Since the bits are split and sent in parallel, so the symbol rate has been reduced to a quarter of the input binary bit rate. If the input binary data rate is 100 Gbps, then the symbol rate is reduced to only 25 Gbaud/second. This is the reason why 16QAM is under hot research for 100Gbps fiber optic communication.
The I and Q bits control the carrier wave's phase shift, if the bit is 0, then the phase shift is 180°, if the bit is 1, then the phase shift is 0°.
The I' and Q' bits control the carrier wave's amplitude, if bit is 0, then the amplitude is 0.22 volt, if the bit is 1, then the amplitude is 0.821 volt.
So each pair of bits has 4 different outputs. Then they are added up at the linear summer. 4X4 is 16, so there is a total of 16 different combinations at the output, that is why this is called 16QAM.
This illustration shows an example of how the QUADBIT 0000 is modulated onto the carrier waves.
Here I and I' is 00, so the output is -0.22 Volt at the 2-to-4-level converter, when timed with the sine wave carrier, we get -0.22sin(2πfct), here fc is the carrier wave's frequency. QQ' is also 00, so the other carrier wave output is -0.22cos(2πfct).
Here is the proof that quadbit 0000 is modulated as a sine wave with an amplitude of 0.311volt and a phase shift of -135°. You can now pause for a moment to study the proof.
This list shows the 16QAM modulation output with different amplitude and phase change for all 16 quadbits. On the right side is the constellation diagram which shows the positions of these quadbits on a I-Q diagram.
You can visit FO4SALE.com f
This document provides an introduction and overview of orthogonal frequency division multiplexing (OFDM). It discusses the limitations of single-carrier transmission at high data rates due to inter-symbol interference (ISI) and the complexity of equalizers. OFDM is presented as a solution that divides the available bandwidth into multiple orthogonal subcarriers. The key concepts of OFDM covered include cyclic prefix, orthogonality of subcarriers, modulation and demodulation, and how the cyclic prefix mitigates ISI between symbols. Bit error rate simulation of an OFDM system is also demonstrated.
MIMO uses multiple antennas at both the transmitter and receiver to improve wireless communication performance. It takes advantage of multipath propagation by using spatial diversity or spatial multiplexing. With spatial diversity, the same information is transmitted from different antennas to improve reliability and coverage. With spatial multiplexing, different data streams are transmitted from different antennas to increase data rates. MIMO can significantly increase capacity, quality, and spectral efficiency compared to single-input systems. It is used in technologies like 3G, 4G, and will be important for 5G networks.
The document discusses different types of antennas used for satellite communication systems. It describes earth station antennas including axisymmetric dishes, offset dishes, and array antennas. It also describes satellite antennas including circular/elliptical beam antennas for global coverage, shaped/contoured beam antennas using feed arrays, and multibeam antennas. Key antenna specifications like radiation pattern, gain, directivity, polarization are also discussed. Common antenna types mentioned include horn antennas, reflector antennas, and array antennas.
The document provides information on the evolution of wireless networks from 1G to 3G. It discusses the key components and architecture of cellular systems including base stations, mobile switching centers and their connection to the public switched telephone network. It also compares the differences between wireless and wired networks, and describes some of the limitations of early wireless networking. Finally, it covers topics like traffic routing, circuit switching, packet switching and the X.25 protocol.
The document discusses RF transceivers, considering architectures like heterodyne receivers, direct conversion receivers, and digital IF receivers. It also discusses transmitter architectures like direct conversion and two-step transmitters. Characterization of RF transceivers includes tests for sensitivity, dynamic range, unwanted emissions, and modulation mask compliance. An example Philips GSM transceiver implementation is presented using a 1.3GHz VCO, 800MHz VLO, and fabricated using 13GHz BiCMOS technology.
This document discusses bandwidth utilization and multiplexing techniques. It begins by explaining that bandwidth is a precious commodity in communication and that bandwidth utilization aims to make wise use of available bandwidth. It then discusses various multiplexing techniques including frequency-division multiplexing (FDM), time-division multiplexing (TDM), and wavelength-division multiplexing (WDM). For each technique, it provides examples and applications. It also covers digital carrier systems like T1, T2, T3 and discusses the North American digital multiplexing hierarchy.
Mobile radio propagation models are derived using empirical and analytical methods to account for all known and unknown propagation factors. Signal strength must be strong enough for quality but not too strong to cause interference. Fading can disrupt signals and cause errors. Path loss models predict received signal level as a function of distance and are used to estimate signal-to-noise ratio. Path loss includes propagation, absorption, diffraction, and other losses. Large-scale models describe mean path loss over hundreds of meters while small-scale models characterize rapid fluctuations over small distances.
Diversity Techniques in Wireless CommunicationSahar Foroughi
This document discusses diversity techniques for wireless communication, including cooperative diversity. It begins by introducing wireless systems and the impairments they face like fading. It then covers various diversity techniques like space, frequency, and time diversity that provide multiple transmission paths to reduce fading. Cooperative diversity is described as allowing single-antenna devices to achieve MIMO-like benefits by sharing antennas. The document outlines cooperative transmission protocols and challenges at different network layers in implementing cooperation. In conclusion, diversity techniques improve performance by providing multiple signal replicas to overcome fading, while cooperation enables reliability and throughput gains with challenges to address across protocol layers.
Power delay profile,delay spread and doppler spreadManish Srivastava
The document discusses power delay profiles and multipath propagation effects. It defines power delay profiles as giving the intensity of a signal through a multipath channel as a function of time delay between multipath arrivals. Multipath propagation can cause fading effects from signals combining constructively or destructively at the receiver. The time spread of arriving multipath signals is called the delay spread and determines whether a channel is flat or frequency-selective fading, while Doppler spread from receiver/transmitter motion causes time-varying fading.
This document provides an overview of GSM link budget calculations. It defines key terms used in link budgets such as effective radiated power, antenna gain, diversity gain, receiver sensitivity, path loss, and fade margin. It explains the objectives of calculating a link budget are to estimate maximum allowable path loss, compute required effective isotropically radiated power for a balanced link, estimate coverage design thresholds, and evaluate technology performance. It also provides examples of uplink and downlink link budget calculations for a GSM network and defines indoor, in-car, and outdoor coverage requirements.
This document discusses multiple-input multiple-output (MIMO) systems. It begins by outlining the motivations and aspirations for developing MIMO systems, including achieving high data rates near 1 gigabit/second while maintaining quality of service. It then provides an overview of MIMO system modeling and capacity studies. Key topics covered include diversity versus spatial multiplexing design criteria, example architectures, MIMO with orthogonal frequency-division multiplexing, and networking applications involving MAC protocols.
This document provides an overview of Orthogonal Frequency Division Multiplexing (OFDM), Orthogonal Frequency Division Multiple Access (OFDMA) and Scalable OFDMA (SOFDMA). It describes how OFDM divides available bandwidth into multiple orthogonal subcarriers to combat multipath interference in wireless channels. OFDMA further divides subcarriers to enable multiple access by multiple users. SOFDMA, defined in IEEE 802.16e, allows dynamic allocation of subcarriers for scalable bandwidth allocation to users.
Introduction To Wireless Fading ChannelsNitin Jain
The document summarizes key concepts related to wireless fading channels, including:
1. Multipath fading causes fluctuations in signal strength over small physical distances due to constructive and destructive interference from multiple signal paths.
2. Rayleigh fading occurs when there is no line-of-sight path between transmitter and receiver, resulting in fast, large fluctuations in signal strength over small physical distances.
3. Doppler spread and coherence time describe how quickly the wireless channel varies over time due to mobility, with fast fading occurring if the channel changes significantly within a symbol period.
This document summarizes the two-ray propagation model used in wireless communications. It assumes both a line-of-sight signal and a reflected signal propagate between the transmitter and receiver. The key parameters estimated are the electric field of each ray, the path difference between them, the phase difference, and time delay. Using geometry, the path difference is derived as approximately equal to 2 times the transmitter and receiver heights divided by the separation distance. The phase difference and time delay are then defined in terms of this path difference. Finally, the total electric field is written as the sum of the individual LOS and reflected signal fields.
This document discusses key concepts in telecommunications network planning and traffic engineering. It covers:
- Types of random processes used to model network usage patterns like call arrival rates and durations.
- How traffic engineering balances factors like grade of service, resources, blocking vs. delay systems based on traffic amounts.
- Key metrics like erlangs, traffic intensity, busy hour, traffic volume that are used to quantify network usage and demand.
- Concepts like grade of service, blocking probability, and how they measure network performance during busy periods.
The document provides an overview of MIMO (multiple-input multiple-output) systems in wireless communications. It discusses how MIMO can provide array gain, diversity gain, and multiplexing gain to improve spectral efficiency, coverage, and quality of service. It also describes how MIMO reduces co-channel interference. The document covers MIMO channel models and capacity results for different scenarios. It concludes by discussing how MIMO can be used to maximize diversity or throughput through different transmission techniques.
The document discusses small-scale fading and multipath propagation in wireless communications. It describes how multipath propagation leads to fading effects as multiple versions of the transmitted signal combine at the receiver. Channel sounding techniques are used to measure the power delay profile and characterize the time dispersion parameters of mobile radio channels, including mean excess delay, RMS delay spread, and maximum excess delay. Direct pulse systems, spread spectrum correlators, and frequency domain analysis are channel sounding methods discussed.
In this video, I will explain what is QAM modulation and what is 16QAM.
QAM Stands for Quadrature Amplitude Modulation. QAM is both an analog and a digital modulation method. But here, we are only talking about QAM as a digital modulation.
Quadrature means that two carrier waves are being used, one sine wave and one cosine wave. These two waves are out of phase with each other by 90°, this is called quadrature.
At the receiving end, the sine and cosine wave can be decoded independently, this means that by using both a sine wave and a cosine wave, the communication channel's capacity is doubled comparing to using only one sine or one cosine wave. That is why quadrature is such a popular technique for digital modulation.
QAM modulation is a combination of Amplitude Shift Keying and Phase Shift Keying, both carrier wave is modulated by changing both its amplitude and phase. As shown in this 8QAM waveform, the top is the sine wave carrier, for bit 000, the sin wave has a phase shift of 0°, and an amplitude of 2. While for bit 110, the phase shift is 180°, and the amplitude now is 1. So both phase and amplitude are changed.
In 16QAM, the input binary data is combined into groups of 4 bits called QUADBITS.
As shown in this picture, the I and I' bits are sent to the sine wave modulation path, and the Q and Q' bits are sent to the cosine wave path. Since the bits are split and sent in parallel, so the symbol rate has been reduced to a quarter of the input binary bit rate. If the input binary data rate is 100 Gbps, then the symbol rate is reduced to only 25 Gbaud/second. This is the reason why 16QAM is under hot research for 100Gbps fiber optic communication.
The I and Q bits control the carrier wave's phase shift, if the bit is 0, then the phase shift is 180°, if the bit is 1, then the phase shift is 0°.
The I' and Q' bits control the carrier wave's amplitude, if bit is 0, then the amplitude is 0.22 volt, if the bit is 1, then the amplitude is 0.821 volt.
So each pair of bits has 4 different outputs. Then they are added up at the linear summer. 4X4 is 16, so there is a total of 16 different combinations at the output, that is why this is called 16QAM.
This illustration shows an example of how the QUADBIT 0000 is modulated onto the carrier waves.
Here I and I' is 00, so the output is -0.22 Volt at the 2-to-4-level converter, when timed with the sine wave carrier, we get -0.22sin(2πfct), here fc is the carrier wave's frequency. QQ' is also 00, so the other carrier wave output is -0.22cos(2πfct).
Here is the proof that quadbit 0000 is modulated as a sine wave with an amplitude of 0.311volt and a phase shift of -135°. You can now pause for a moment to study the proof.
This list shows the 16QAM modulation output with different amplitude and phase change for all 16 quadbits. On the right side is the constellation diagram which shows the positions of these quadbits on a I-Q diagram.
You can visit FO4SALE.com f
This document provides an introduction and overview of orthogonal frequency division multiplexing (OFDM). It discusses the limitations of single-carrier transmission at high data rates due to inter-symbol interference (ISI) and the complexity of equalizers. OFDM is presented as a solution that divides the available bandwidth into multiple orthogonal subcarriers. The key concepts of OFDM covered include cyclic prefix, orthogonality of subcarriers, modulation and demodulation, and how the cyclic prefix mitigates ISI between symbols. Bit error rate simulation of an OFDM system is also demonstrated.
MIMO uses multiple antennas at both the transmitter and receiver to improve wireless communication performance. It takes advantage of multipath propagation by using spatial diversity or spatial multiplexing. With spatial diversity, the same information is transmitted from different antennas to improve reliability and coverage. With spatial multiplexing, different data streams are transmitted from different antennas to increase data rates. MIMO can significantly increase capacity, quality, and spectral efficiency compared to single-input systems. It is used in technologies like 3G, 4G, and will be important for 5G networks.
The document discusses different types of antennas used for satellite communication systems. It describes earth station antennas including axisymmetric dishes, offset dishes, and array antennas. It also describes satellite antennas including circular/elliptical beam antennas for global coverage, shaped/contoured beam antennas using feed arrays, and multibeam antennas. Key antenna specifications like radiation pattern, gain, directivity, polarization are also discussed. Common antenna types mentioned include horn antennas, reflector antennas, and array antennas.
The document provides information on the evolution of wireless networks from 1G to 3G. It discusses the key components and architecture of cellular systems including base stations, mobile switching centers and their connection to the public switched telephone network. It also compares the differences between wireless and wired networks, and describes some of the limitations of early wireless networking. Finally, it covers topics like traffic routing, circuit switching, packet switching and the X.25 protocol.
The document discusses RF transceivers, considering architectures like heterodyne receivers, direct conversion receivers, and digital IF receivers. It also discusses transmitter architectures like direct conversion and two-step transmitters. Characterization of RF transceivers includes tests for sensitivity, dynamic range, unwanted emissions, and modulation mask compliance. An example Philips GSM transceiver implementation is presented using a 1.3GHz VCO, 800MHz VLO, and fabricated using 13GHz BiCMOS technology.
This document discusses bandwidth utilization and multiplexing techniques. It begins by explaining that bandwidth is a precious commodity in communication and that bandwidth utilization aims to make wise use of available bandwidth. It then discusses various multiplexing techniques including frequency-division multiplexing (FDM), time-division multiplexing (TDM), and wavelength-division multiplexing (WDM). For each technique, it provides examples and applications. It also covers digital carrier systems like T1, T2, T3 and discusses the North American digital multiplexing hierarchy.
Mobile radio propagation models are derived using empirical and analytical methods to account for all known and unknown propagation factors. Signal strength must be strong enough for quality but not too strong to cause interference. Fading can disrupt signals and cause errors. Path loss models predict received signal level as a function of distance and are used to estimate signal-to-noise ratio. Path loss includes propagation, absorption, diffraction, and other losses. Large-scale models describe mean path loss over hundreds of meters while small-scale models characterize rapid fluctuations over small distances.
Path loss models are used to predict average signal strength over distance in wireless channels. The log distance path loss model predicts that signal strength decreases logarithmically with distance. The log normal shadowing model adds randomness to account for variations at each distance due to obstructions. Large-scale effects like reflection can be modeled using the two-ray model, which predicts signal strength falls off as distance squared under certain antenna height conditions. Small-scale effects cause rapid fluctuations and are modeled separately.
This document discusses mobile radio propagation and propagation models. It begins by introducing how radio channels are random and time-varying. It then covers the free space propagation model and how received power decreases with distance. Reflection, diffraction, and scattering are described as the main propagation mechanisms. The two-ray ground reflection model is presented to model propagation over large distances. Diffraction is explained using the knife-edge diffraction model. Fresnel zones and diffraction gain are also defined.
This document discusses various propagation models used in wireless communications. It begins by introducing the free space propagation model and 2-ray ground reflection model. It then describes the key propagation mechanisms of reflection, diffraction, and scattering. Reflection from smooth surfaces and conductors is explained. Fresnel zone geometry and knife edge diffraction models are used to analyze diffraction. Buildings can help diffraction by providing some gain, with the amount of diffracted energy dependent on factors like height and frequency. Propagation effects must be considered for accurate wireless system design and performance prediction.
Wireless channels in wireless communicationPreciousMposa1
The document discusses various wireless channel characteristics including large scale path loss models, small scale fading parameters, and multipath effects. It describes free space path loss and the two-ray ground reflection model for large scale path loss. For small scale fading, it discusses parameters such as coherence bandwidth and Doppler spread/coherence time that characterize multipath time delay spread and Doppler spread fading. It also summarizes multipath delay spread which occurs when a signal takes multiple paths causing interference from delayed components.
1. Radio propagation involves mechanisms like reflection, diffraction, scattering that affect the strength of the radio signal over distance.
2. Reflection occurs when the radio wave impinges on objects larger than the wavelength like buildings, walls. Diffraction allows signals to propagate beyond obstacles. Scattering occurs from objects smaller than the wavelength.
3. Propagation models like free space and two-ray ground reflection are used to predict signal strength over large distances. Factors like Fresnel zones and knife-edge diffraction also impact signal propagation around obstacles.
This document provides information about microwave communication systems. It defines microwave communication as a high radio frequency link designed to provide signal connection between two points. It operates in the 2-60 GHz band and can be analog or digital. Short, medium, and long haul systems exist based on distance and frequency used. The document discusses advantages like increased gain and reliability, as well as disadvantages like limitations in circuit design at high frequencies. It provides formulas for analyzing microwave links, including free space loss, antenna gain, system gain, and more. Worked examples of link calculations are also included.
Lecture on mobile radio environme, nt.pptNanaAgyeman13
The document discusses reasons why wireless signals are difficult to send and receive. It explains that radio channels are random due to multipath propagation from reflections, diffractions, and scattering caused by buildings, foliage and terrain. This creates interference between signals, shadowing effects, and small-scale fading. Additional challenges include interference between users and service providers. Accurately characterizing wireless channels requires statistical analysis and field measurements due to their unpredictable nature.
The document discusses path loss and radio wave propagation in wireless communications. It describes how the strength of radio signals falls off with distance due to path loss. The linear path loss and Friis free space equation are introduced to model the statistical decrease in signal strength over distance. Key concepts covered include line-of-sight propagation, reflection, diffraction, scattering, path loss exponents, cell radius prediction based on minimum received power, and the tradeoff between frequency reuse ratio and co-channel interference.
This document discusses point to point microwave transmission. It describes the basic modules of microwave radio terminals including digital modems, RF units, and passive parabolic antennas. It also covers microwave radio configurations, applications, advantages, planning aspects like network architecture, frequency bands, and propagation effects. Key factors in microwave link engineering like link budgets, reliability predictions, and interference analysis are summarized.
This document discusses small scale fading in mobile radio propagation systems. It begins by introducing radio wave propagation and the factors that influence it, such as buildings, foliage, and motion. It then discusses small-scale fading models which characterize rapid fluctuations over short distances or times. Large scale propagation models are also introduced. The document goes on to discuss specific topics relating to small-scale fading like Doppler shift, multipath propagation, and modeling the mobile radio channel using the impulse response.
Here are the steps to solve this example question:
A) Express the transmitter power in dBm:
- Transmitter power (Pt) = 50 W
- To convert to dBm we use: P(dBm) = 10log10(P/1mW)
- 50 W = 50,000 mW
- P(dBm) = 10log10(50,000/1) = 10log10(50,000) = 50 dBm
Therefore, the transmitter power in dBm is 50 dBm.
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The document discusses mobile radio propagation models. It begins by describing the free space propagation model, which predicts received signal strength between a transmitter and receiver with line of sight. It then discusses how distance, transmitted power, antenna gains, wavelength and losses impact received power based on Friis transmission equation. Later it introduces the ground reflection model, knife edge diffraction model and scattering model to account for common propagation mechanisms. It concludes by discussing how path loss models like log-distance and log-normal shadowing can be used for link budget design and outdoor propagation modeling.
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1. WIRELESS CHANNELS
Dr. S. Mary Praveena
Associate Professor
ECE DEPARTMENT
SRI RAMAKRISHNA INSTITUTE OF TECHNOLOGY
COIMBATORE-10
E-mail: marypraveena.ece@srit.org
1
10/1/2021
2. WIRELESS CHANNELS
Large scale path loss – Path loss models: Free
Space and Two-Ray models -Link Budget design –
Small scale fading- Parameters of mobile
multipath channels – Time dispersion parameters-
Coherence bandwidth – Doppler spread &
Coherence time, Fading due to Multipath time
delay spread – flat fading – frequency selective
fading – Fading due to Doppler spread – fast
fading – slow fading.
Dr.S.Mary Praveena,ASP/ECE 2
10/1/2021
4. 4
Problems Unique to Wireless (not wired) systems:
• Paths can vary from simple line-of-sight to
ones that are severely obstructed by buildings,
mountains, and foliage.
• Radio channels are extremely random and
difficult to analyze.
• Interference from other service providers
• out-of-band non-linear Tx emissions
Dr.S.Mary Praveena,ASP/ECE
10/1/2021
5. 5
Interference from other users (same
network)
– CCI due to frequency reuse
– ACI due to Tx/Rx design limitations & large
# users sharing finite BW
Shadowing
– Obstructions to line-of-sight paths cause
areas of weak received signal strength
Dr.S.Mary Praveena,ASP/ECE
10/1/2021
6. 6
Fading
– When no clear line-of-sight path exists, signals
are received that are reflections off obstructions
and diffractions around obstructions
– Multipath signals can be received that interfere
with each other
– Fixed Wireless Channel → random &
unpredictable
must be characterized in a statistical fashion
field measurements often needed to characterize radio
channel performance
Dr.S.Mary Praveena,ASP/ECE
10/1/2021
7. 7
** The Mobile Radio Channel (MRC) has
unique problems that limit performance **
– A mobile Rx in motion influences rates of
fading the faster a mobile moves, the more
quickly characteristics change
Dr.S.Mary Praveena,ASP/ECE
10/1/2021
8. Dr.S.Mary Praveena,ASP/ECE 8
•Electromagnetic wave propagation
•reflection
•diffraction
•scattering
•Urban areas
•No direct line-of-sight
•high-rise buildings causes severe diffraction loss
•multipath fading due to different paths of varying lengths
•Large-scale propagation models predict the mean signal strength for an
arbitrary T-R separation distance.
•Small-scale (fading) models characterize the rapid fluctuations of the
received signal strength over very short travel distance or short time
duration.
Introduction to Radio Wave Propagation
10/1/2021
9. Radio Propagation Models
• As the mobile moves over small distances, the
instantaneous received signal will fluctuate rapidly
giving rise to small-scale fading
• The reason is that the signal is the sum of many
contributors coming from different directions and
since the phases of these signals are random, the sum
behave like a noise (Rayleigh fading).
• In small scale fading, the received signal power may
change as much as 3 or 4 orders of magnitude (30dB or
40dB), when the receiver is only moved a fraction of
the wavelength.
Dr.S.Mary Praveena,ASP/ECE 9
10/1/2021
10. Radio Propagation Models
• As the mobile moves away from the transmitter
over larger distances, the local average received
signal will gradually decrease. This is called large-
scale path loss.
• l Typically the local average received power is computed by
averaging signal measurements over a measurement track of
5 to 40 (For PCS, this means 1m-10m track)
• The models that predict the mean signal strength
for an arbitrary-receiver transmitter (T-R)
separation distance are called large-scale
propagation models
• l Useful for estimating the coverage area of transmitters
Dr.S.Mary Praveena,ASP/ECE 10
10/1/2021
11. Path Loss Models
• Free Space Propagation Model
• Two Ray Model
Dr.S.Mary Praveena,ASP/ECE 11
10/1/2021
12. Free-Space Propagation Model
• Used to predict the received signal strength when
transmitter and receiver have clear, unobstructed LOS
path between them.
• The received power decays as a function of T-R
separation distance raised to some power.
• Path Loss: Signal attenuation as a positive quantity
measured in dB and defined as the difference (in dB)
between the effective transmitter power and received
power.
Dr.S.Mary Praveena,ASP/ECE 12
10/1/2021
14. Free Space Propagation Model
• The free space propagation model is used to predict
received signal strength when the transmitter and receiver
have a clear line-of-sight path between them.
– satellite communication
– microwave line-of-sight radio link
• Friis free space equation
: transmitted power : T-R separation distance
: received power : system loss
: transmitter antenna gain : wave length in meters
: receiver antenna gain
L
d
G
G
P
d
P r
t
t
r 2
2
2
)
4
(
)
(
=
t
P
)
(d
Pr
t
G
r
G
d
L
Dr.S.Mary Praveena,ASP/ECE 14
10/1/2021
15. • The gain of the antenna
: effective aperture is related to the physical size of the
antenna
• The wave length is related to the carrier frequency by
: carrier frequency in Hertz
: carrier frequency in radians
: speed of light (meters/s)
• The losses are usually due to transmission line
attenuation, filter losses, and antenna losses in the
communication system. A value of L=1 indicates no loss in the
system hardware.
2
4
e
A
G =
e
A
c
c
f
c
2
=
=
f
c
c
)
1
(
L
Dr.S.Mary Praveena,ASP/ECE 15
10/1/2021
16. • Isotropic radiator is an ideal antenna which radiates power with
unit gain.
• Effective isotropic radiated power (EIRP) is defined as
and represents the maximum radiated power available from
transmitter in the direction of maximum antenna gain as
compared to an isotropic radiator.
• Path loss for the free space model with antenna gains
• When antenna gains are excluded
• The Friis free space model is only a valid predictor for for
values of d which is in the far-field (Fraunhofer region) of the
transmission antenna.
t
tG
P
EIRP =
−
=
= 2
2
2
)
4
(
log
10
log
10
)
(
d
G
G
P
P
dB
PL r
t
r
t
−
=
= 2
2
2
)
4
(
log
10
log
10
)
(
d
P
P
dB
PL
r
t
r
P
Dr.S.Mary Praveena,ASP/ECE 16
10/1/2021
17. • The far-field region of a transmitting antenna is defined as the
region beyond the far-field distance
where D is the largest physical linear dimension of the antenna.
• To be in the far-filed region the following equations must be
satisfied
and
• Furthermore the following equation does not hold for d=0.
• Use close-in distance and a known received power at
that point
or
2
2D
d f =
D
d f
f
d
L
d
G
G
P
d
P r
t
t
r 2
2
2
)
4
(
)
(
=
0
d )
( 0
d
Pr
2
0
0 )
(
)
(
=
d
d
d
P
d
P r
r
f
d
d
d
0
+
=
d
d
d
P
d
P r
r
0
0
log
20
W
001
.
0
)
(
log
10
dBm
)
( f
d
d
d
0
Dr.S.Mary Praveena,ASP/ECE 17
10/1/2021
18. • Expressing the received power in dBm and dBW
l Pr(d) (dBm) = 10 log [Pr(d0)/0.001W] + 20log(d0/d)
where d >= d0 >= df and Pr(d0) is in units of watts.
l Pr(d) (dBW) = 10 log [Pr(d0)/1W] + 20log(d0/d)
where d >= d0 >= df and Pr(d0) is in units of watts.
• Reference distance d0 for practical systems:
l For frequencies in the range 1-2 GHz
• 1 m in indoor environments
• 100m-1km in outdoor environments
Dr.S.Mary Praveena,ASP/ECE 18
10/1/2021
19. Example Problems
A transmitter produces 50W of power.
A) Express the transmit power in dBm
B) Express the transmit power in dBW
C) If d0 is 100m and the received power at that
distance is 0.0035mW, then find the received power
level at a distance of 10km.
L Assume that the transmit and receive antennas have
unity gains.
Dr.S.Mary Praveena,ASP/ECE 19
10/1/2021
21. Solution
c) Pr(d) = Pr(d0)(d0/d)2
Substitute the values into the equation:
lPr(10km) = Pr(100m)(100m/10km)2
Pr(10km) = 0.0035mW(10-4)
Pr(10km) = 3.5x10-10W
Pr(10km) [dBm] = 10log(3.5x10-10W/1mW)
= 10log(3.5x10-7)
= -64.5dBm
Dr.S.Mary Praveena,ASP/ECE 21
10/1/2021
22. The Three Basic Propagation Mechanisms
• Basic propagation mechanisms
– reflection
– diffraction
– scattering
• Reflection occurs when a propagating electromagnetic
wave impinges upon an object which has very large
dimensions when compared to the wavelength, e.g.,
buildings, walls.
• Diffraction occurs when the radio path between the
transmitter and receiver is obstructed by a surface that
has sharp edges.
• Scattering occurs when the medium through which the
wave travels consists of objects with dimensions that are
small compared to the wavelength.
Dr.S.Mary Praveena,ASP/ECE 22
10/1/2021
23. 23
Ground Reflection (2-Ray) Model
– Good for systems that use tall towers (over 50 m
tall)
– Good for line-of-sight microcell systems in urban
environments
Dr.S.Mary Praveena,ASP/ECE
10/1/2021
24. 24
• ETOT is the electric field that results from a
combination of a direct line-of-sight path and a
ground reflected path
is the amplitude of the electric field at distance d
ωc = 2πfc where fc is the carrier frequency of the signal
Notice at different distances d the wave is at a different
phase because of the form similar to
Dr.S.Mary Praveena,ASP/ECE
10/1/2021
25. 25
• For the direct path let d = d’ ; for the reflected path
d = d” then
for large T−R separation : θi goes to 0 (angle of
incidence to the ground of the reflected wave) and
Γ = −1
• Phase difference can occur depending on the phase
difference between direct and reflected E fields
• The phase difference is θ∆ due to Path difference ,
∆ = d”− d’, between
Dr.S.Mary Praveena,ASP/ECE
10/1/2021
26. 26
Using method of images (fig below) , the path difference can be expressed as:-
• From two triangles with sides d and (ht + hr) or (ht – hr)
Dr.S.Mary Praveena,ASP/ECE
10/1/2021
27. Dr.S.Mary Praveena,ASP/ECE 27
• Using taylor series the expression can be simplified as:-
• Now as P.D is known , Phase difference and time delay
can be evaluated as:-
• If d is large than path difference become negligible and
amplitude ELOS & Eg are virtually identical and differ only in
phase,.i.e
&
10/1/2021
30. Dr.S.Mary Praveena,ASP/ECE 30
or
As E-field is function of “sin” it decays in oscillatory fashion with
local maxima being 6dB greater than free space and local minima
reaching to-∞ dB.
10/1/2021
31. 31
note that the magnitude is with respect to a
reference of E0=1 at d0=100 meters, so near 100
meters the signal can be stronger than E0=1
– the second ray adds in energy that would have
been lost otherwise
for large distances it can be shown that
Dr.S.Mary Praveena,ASP/ECE
10/1/2021
34. 34
• The smoothed line is the average signal
strength. The actual is the more jagged line.
• Actual received signal strength can vary by
more than 20 dB over a few centimeters.
• The average signal strength decays with
distance from the transmitter, and depends on
terrain and obstructions.
Dr.S.Mary Praveena,ASP/ECE
10/1/2021
35. Two main channel design issues
Communication engineers are generally concerned
with two main radio channel issues:
Link Budged Design
• Link budget design determines fundamental quantities such as transmit
power requirements, coverage areas, and battery life
• It is determined by the amount of received power that may be expected
at a particular distance or location from a transmitter
Time dispersion
• It arises because of multi-path propagation where replicas of the
transmitted signal reach the receiver with different propagation delays
due to the propagation mechanisms that are described earlier.
• Time dispersion nature of the channel determines the maximum data
rate that may be transmitted without using equalization.
Dr.S.Mary Praveena,ASP/ECE 35
10/1/2021
36. Link Budget Design Using Path Loss Models
Radio propagation models can be derived
• By use of empirical methods: collect measurement,
fit curves.
• By use of analytical methods
• Model the propagation mechanisms mathematically and
derive equations for path loss
Long distance path loss model
• Empirical and analytical models show that
received signal power decreases logarithmically
with distance for both indoor and outdoor
channels
Dr.S.Mary Praveena,ASP/ECE 36
10/1/2021
37. Long distance path loss model
• The average large-scale
path loss for an arbitrary T-
R separation is expressed as
a function of distance by
using a path loss exponent
n:
• The value of n depends on
the propagation
environment: for free space
it is 2; when obstructions are
present it has a larger value.
PL(d) denotes the average large -scale path loss
at a distance d (denoted in dB)
PL(dB)= PL(d0 ) + 10n log( ) (eqn-A)
PL(d) (
d
)n
0
d0
d
Dr.S.Mary Praveena,ASP/ECE 37
d
10/1/2021
38. Path Loss Exponent for Different
Environments
Environment Path Loss Exponent, n
Free space 2
Urban area cellular radio 2.7 to 3.5
Shadowed urban cellular radio 3 to 5
In building line-of-sight 1.6 to 1.8
Obstructed in building 4 to 6
Obstructed in factories 2 to 3
Dr.S.Mary Praveena,ASP/ECE 38
10/1/2021
39. Selection of free space reference distance
• In large coverage cellular systems
1km reference distances are commonly used
• In microcellular systems
Much smaller distances are used: such as 100m
or 1m.
• The reference distance should always be in
the far-field of the antenna so that near-field
effects do not alter the reference path loss.
Dr.S.Mary Praveena,ASP/ECE 39
10/1/2021
40. Log-normal Shadowing
• (Equation A) does not consider the fact the
surrounding environment may be vastly
different at two locations having the same
T-R separation
• This leads to measurements that are different
than the predicted values obtained using the
above equation.
• Measurements show that for any value d, the
path loss PL(d) in dBm at a particular location
is random and distributed normally.
Dr.S.Mary Praveena,ASP/ECE 40
10/1/2021
41. PL(d ) denotes the average large-scale path loss (in dB) at a distance d.
X is a zero-mean Gaussian (normal) distributed random variable (in dB)
with standard deviation (also in dB).
PL(d0 ) is usually computed assuming free space propagation model between
transmitter and d0 (or by measurement).
Equation B takes into account the shadowing affects due to
cluttering on the propagation path. It is used as the propagation model for
log-normal shadowing environments.
Log-normal Shadowing- Path Loss
PL(d)[dB] = PL(d0 ) +10nlog(
d
) + X
Then adding this random factor:
PL(d)[dB] = PL(d) + X
d
0
Equation B
Dr.S.Mary Praveena,ASP/ECE 41
10/1/2021
42. Log-normal Shadowing- Received Power
• The received power in log-normal shadowing
environment is given by the following formula
(derivable from Equation B)
l The antenna gains are included in PL(d).
Pr (d)[dBm] = Pt [dBm]− PL(d0 )[dB]+10nlog(
d
) + X [dB]
Pr (d)[dBm] = Pt [dBm]− PL(d)[dB]
0
d
Dr.S.Mary Praveena,ASP/ECE 42
10/1/2021
43. Log-normal Shadowing, n and
• The log-normal shadowing model indicates
the received power at a distance d is normally
distributed with a distance dependent mean
and with a standard deviation of
• In practice the values of n and are
computed from measured data using linear
regression so that the difference between the
measured data and estimated path losses are
minimized in a mean square error sense.
Dr.S.Mary Praveena,ASP/ECE 43
10/1/2021
44. Example of determining n and
• Assume Pr(d0) = 0dBm and
d0 is 100m
• Assume the receiver power
Pr is measured at distances
100m, 500m, 1000m, and
3000m,
• The table gives the measured
values of received power
Distance from
Transmitter
Received Power
100m 0dBm
500m -5dBm
1000m -11dBm
3000m -16dBm
Dr.S.Mary Praveena,ASP/ECE 44
10/1/2021
45. 45
Log-Normal Shadowing
PL (d) = PL (do ) + 10 n log (d / do ) + Xσ
– describes how the path loss at any specific location may vary
from the average value
• has a the large-scale path loss component we have already seen
plus a random amount Xσ.
Dr.S.Mary Praveena,ASP/ECE
10/1/2021
46. 46
• Xσ : zero mean Gaussian random variable, a “bell
curve”
• σ is the standard deviation that provides the second
parameter for the distribution takes into account
received signal strength variations due to
shadowing
Dr.S.Mary Praveena,ASP/ECE
10/1/2021
47. Small Scale Fading
• Describes rapid fluctuations of the amplitude,
phase of multipath delays of a radio signal
over short period of time or travel distance
• Caused by interference between two or more
versions of the transmitted signal which arrive
at the receiver at slightly different times.
• These waves are called multipath waves and
combine at the receiver antenna to give a
resultant signal which can vary widely in
amplitude and phase.
Dr.S.Mary Praveena,ASP/ECE 47
10/1/2021
48. Small Scale Multipath Propagation
Effects of multipath
• Rapid changes in the signal strength
• Random frequency modulation due to varying Doppler shifts
on different multiples signals
• Time dispersion (echoes) caused by multipath propagation
delays
Multipath occurs because of
• Reflections
• Scattering
Dr.S.Mary Praveena,ASP/ECE 48
10/1/2021
49. Multipath
• At a receiver point Radio waves generated from the
same transmitted signal may come from different directions
l with different propagation delays
l with (possibly) different amplitudes (random)
l with (possibly) different phases (random)
l with different angles of arrival (random).
• These multipath components combine vectorially at the
receiver antenna and cause the total signal
• to fade
• to distort
Dr.S.Mary Praveena,ASP/ECE 49
10/1/2021
51. Factors Influencing Small Scale Fading
Multipath propagation
• Presence of reflecting objects and scatterers cause
multiple versions of the signal to arrive at the receiver
• With different amplitudes and time delays
• Causes the total signal at receiver to fade or distort
Speed of mobile
• Cause Doppler shift at each multipath
component
• Causes random frequency modulation
Speed of surrounding objects
• Causes time-varying Doppler shift on the
multipath components
Dr.S.Mary Praveena,ASP/ECE 51
10/1/2021
52. Factors Influencing Small Scale Fading
Transmission bandwidth of the channel
• The transmitted radio signal bandwidth and
bandwidth of the multipath channel affect the
received signal properties:
• If amplitude fluctuates or not
• If the signal is distorted or not
Dr.S.Mary Praveena,ASP/ECE 52
10/1/2021
53. Doppler Effect
“When a transmitter or receiver is moving, the
frequency of the received signal changes, i.e. İt is
different than the frequency of transmission. This is
called Doppler Effect.”
• The change in frequency is called Doppler Shift.
• It depends on
• The relative velocity of the receiver with respect to
transmitter
• The frequency (or wavelength) of transmission
• The direction of traveling with respect to the direction of
the arriving signal.
Dr.S.Mary Praveena,ASP/ECE 53
10/1/2021
54. Doppler Shift – Transmitter is moving
The frequency of the signal
that is received in front of
the transmitter will be bigger
The frequency of the
signal that is received
behind the transmitter will
be smaller
Dr.S.Mary Praveena,ASP/ECE 54
10/1/2021
55. Doppler Shift –Receiver is moving
v
A mobile receiver is traveling from point X to point
Y
X Y
l
d
S
=
v
cos
2 t
1
f =
d
Dr.S.Mary Praveena,ASP/ECE 55
10/1/2021
56. Doppler Shift
• The Doppler shift is positive
If the mobile is moving toward the direction of arrival
of the wave.
• The Doppler shift is negative
If the mobile is moving away from the direction of
arrival of the wave.
Dr.S.Mary Praveena,ASP/ECE 56
10/1/2021
57. Impulse Response Model of a Multipath
Channel
• The wireless channel characteristics can be
expressed by impulse response function
• The channel is time varying channel when the
receiver is moving.
• Lets assume first that time variation due strictly to
the receiver motion (t = d/v)
• Since at any distance d = vt, the received power
will ve combination of different incoming signals,
the channel charactesitics or the impulse
response funcion depends on the distance d
between trandmitter and receiver
Dr.S.Mary Praveena,ASP/ECE 57
10/1/2021
58. Impulse Response Model of a Multipath
Channel
d = vt
v
d
• A receiver is moving along the ground at some constant velocity v.
• The multipath components that are received at the receiver will have
different propagation delays depending on d: distance between transmitter
and receiver.
• Hence the channel impulse response depends on d.
Lets x(t) represents the transmitter signal
y(d,t) represents the received signal at position d.
h(d,t) represents the channel impulse response which is dependent on d
(hence time-varying d=vt).
Dr.S.Mary Praveena,ASP/ECE 58
10/1/2021
60. Impulse Response Model of a Multipath
Channel
• The channel is linear time-varying channel, where the channel
characteristics changes with distance (hence time, t = d/v)
y(d , t) = x(t) h(d , t) = x(t )h(d , t −t )dt
−
• For a causal system, h(d,t) = 0 for t 0; hence
t
y(d , t) = x(t )h(d , t −t )dt
−
Wireless Multipath Channel
h(d,t)
x(t) y(t)
Dr.S.Mary Praveena,ASP/ECE 60
10/1/2021
61. Impulse Response Model
t
y(vt, t) = x(t )h(vt, t −t )dt
−
t
y(t) = x(t )h(vt, t −t )dt = x(t) h(vt, t) = x(t) h(d , t)
−
• We assume v is constant over short time.
x(t): transmitted waveform
y(t): received waveform
h(t,t): impulse response of the channel. Depends on d (and therefore t=d/v)
and also to the multiple delay for the channel for a fixed value of t.
t is the multipath delay of the channel for a fixed value of t.
y(t) = x(t )h(t,t )dt = x(t) h(t,t )
−
assume v is constant over time
d = vt
Dr.S.Mary Praveena,ASP/ECE 61
10/1/2021
62. Impulse Response Model
h(t,t ) = Re
j t
b
c
h (t,t )e
y(t) = x(t) h(t,t )
y(t) = Re r(t)e jct
r(t) = c(t)
1
h (t,t )
2
b
1
h (t,t )
2
b
x(t)
x(t) = Re
c(t)e jct
y(t)
c(t) r(t)
Bandpass Channel Impulse Response
Model
Baseband Equivalent Channel Impulse Response Model
Dr.S.Mary Praveena,ASP/ECE 62
10/1/2021
63. Impulse Response Model
2
x(t) = Re
c(t)e
y(t) = Re
r(t)e j2fct
c = 2fc
j 2fct
r(t) = c(t) hb (t,t )
1
• c(t) is the complex envelope representation of the transmitted
signal r(t) is the complex envelope representation of the
received signal
• hb(t,t) is the complex baseband impulse response
Dr.S.Mary Praveena,ASP/ECE 63
10/1/2021
64. • For small-scale fading, the power delay profile of the channel is found by
taking the spatial average of over a local area (small-scale area).
• If p(t) has a time duration much smaller than the impulse response of the
multipath channel, the received power delay profile in a local area is given
by:
Power Delay Profile
2
h (t;t )
b
2
P(t ) k hb (t;t )
• Gain k relates the transmitter power in the probing pulse p(t) to the
total received power in a multipath delay profile.
The bar represents the average over the local area of
2
h (t;t )
b
Dr.S.Mary Praveena,ASP/ECE 64
10/1/2021
65. Small-Scale Multipath Measurements
Several Methods
• Direct RF Pulse System
• Spread Spectrum Sliding Correlator Channel
Sounding
• Frequency Domain Channel Sounding
These techniques are also called channel
sounding techniques
Dr.S.Mary Praveena,ASP/ECE 65
10/1/2021
66. Direct RF Pulse Sys
Txtem
Pulse Generator
BPF Detector
Digital
Oscilloscope
RF Link
fc
Rx
Dr.S.Mary Praveena,ASP/ECE 66
10/1/2021
67. Parameters of Mobile Multipath Channels
• Time Dispersion Parameters
l Grossly quantifies the multipath channel
l Determined from Power Delay Profile
l Parameters include
§ Mean Access Delay
§ RMS Delay Spread
§ Excess Delay Spread (X dB)
• Coherence Bandwidth
• Doppler Spread and Coherence Time
Dr.S.Mary Praveena,ASP/ECE 67
10/1/2021
68. Measuring PDPs
l Power Delay Profiles
l Are measured by channel sounding techniques
l Plots of relative received power as a function of
excess delay
l They are found by averaging intantenous power
delay measurements over a local area
§ Local area: no greater than 6m outdoor
§ Local area: no greater than 2m indoor
§ Samples taken at /4 meters approximately
§ For 450MHz – 6 GHz frequency range.
Dr.S.Mary Praveena,ASP/ECE 68
10/1/2021
69. Timer Dispersion Parameters
Determined from a power delay profile.
Mean excess delay(
t ):
= t 2
− (
t )2
P(tk )
k
k
k
k
=
=
2
k
k
2
k
k k P(t )(t
a
a t )
2 2
t 2
t
Rms delay spread (t)
P(tk )
k
a t P(t k )(t k )
k
k k
=
t = 2
k
k
a
2
Dr.S.Mary Praveena,ASP/ECE 69
k
10/1/2021
70. Timer Dispersion Parameters
• Maximum Excess Delay (X dB):
Defined as the time delay value after which the
multipath energy falls to X dB below the maximum
multipath energy (not necessarily belonging to the first
arriving component).
• It is also called excess delay spread.
Dr.S.Mary Praveena,ASP/ECE 70
10/1/2021
72. Noise Threshold
l The values of time dispersion parameters also
depend on the noise threshold (the level of
power below which the signal is considered as
noise).
l If noise threshold is set too low, then the noise
will be processed as multipath and thus
causing the parameters to be higher.
Dr.S.Mary Praveena,ASP/ECE 72
10/1/2021
73. Coherence Bandwidth (BC)
• Range of frequencies over which the channel can be
considered flat (i.e. channel passes all spectral
components with equal gain and linear phase).
§ It is a definition that depends on RMS Delay Spread.
• Two sinusoids with frequency separation greater than
Bc are affected quite differently by the channel.
f1
Receiver
f2
Multipath
Channel
Frequency Separation: |f1-f2|
Dr.S.Mary Praveena,ASP/ECE 73
10/1/2021
74. Coherence Bandwidth
Frequency correlation between two sinusoids: 0 <= Cr1, r2 <= 1.
50
1
BC =
• If we define Coherence Bandwidth (BC) as the range of frequencies over
which the frequency correlation is above 0.9, then
• If we define Coherence Bandwidth as the range of frequencies over
which the frequency correlation is above 0.5, then
5
1
BC =
is rms delay spread.
This is called 50% coherence bandwidth.
Dr.S.Mary Praveena,ASP/ECE 74
10/1/2021
75. Coherence Bandwidth
Example:
• For a multipath channel, is given as 1.37s.
• The 50% coherence bandwidth is given as: 1/5 = 146kHz.
• This means that, for a good transmission from a transmitter to a
receiver, the range of transmission frequency (channel bandwidth)
should not exceed 146kHz, so that all frequencies in this band
experience the same channel characteristics.
• Equalizers are needed in order to use transmission frequencies that
are separated larger than this value.
• This coherence bandwidth is enough for an AMPS channel (30kHz
band needed for a channel), but is not enough for a GSM channel
(200kHz needed per channel).
Dr.S.Mary Praveena,ASP/ECE 75
10/1/2021
76. Coherence Time
• Delay spread and Coherence bandwidth
describe the time dispersive nature of the
channel in a local area.
• They don’t offer information about the time varying nature of
the channel caused by relative motion of transmitter and
receiver.
• Doppler Spread and Coherence time are
parameters which describe the time varying
nature of the channel in a small-scale region.
Dr.S.Mary Praveena,ASP/ECE 76
10/1/2021
77. Doppler Spread
• Measure of spectral broadening caused by
motion
• We know how to compute Doppler shift: fd
• Doppler spread, BD, is defined as the
maximum Doppler shift: fm = v/
• If the baseband signal bandwidth is much
greater than BD then effect of Doppler spread
is negligible at the receiver.
Dr.S.Mary Praveena,ASP/ECE 77
10/1/2021
78. • Coherence time is the time duration over which the channel impulse
response is essentially invariant.
• If the symbol period of the baseband signal (reciprocal of the baseband
signal bandwidth) is greater the coherence time, than the signal will
distort, since channel will change during the transmission of the signal .
Coherence Time
fm
C
T 1
Coherence time (TC) is defined
as:
TS
TC
t=t2 - t1
t1 t2
f1
f2
Dr.S.Mary Praveena,ASP/ECE 78
10/1/2021
79. Coherence Time
• Coherence time is also defined as:
m
16f 2
TC
f
m
0.423
=
9
• Coherence time definition implies that two signals arriving with a
time separation greater than TC are affected differently by the
channel.
Dr.S.Mary Praveena,ASP/ECE 79
10/1/2021
80. Types of Small-scale Fading
Small-scale Fading
(Based on Multipath Tİme Delay Spread)
Flat Fading
1. BW Signal < BW of Channel
2. Delay Spread < Symbol
Period
Frequency Selective
Fading
1. BW Signal > Bw of Channel
2. Delay Spread > Symbol
Period
Small-scale Fading
(Based on Doppler Spread)
Fast
Fading
1. High Doppler Spread
2. Coherence Time < Symbol Period
3. Channel variations faster than
baseband signal variations
Slow
Fading
1. Low Doppler Spread
2. Coherence Time > Symbol Period
3. Channel variations smaller than
baseband signal variations
Dr.S.Mary Praveena,ASP/ECE 80
10/1/2021
81. Flat Fading
• Occurs when the amplitude of the received
signal changes with time
• For example according to Rayleigh Distribution
• Occurs when symbol period of the
transmitted signal is much larger than the
Delay Spread of the channel
• Bandwidth of the applied signal is narrow.
• May cause deep fades.
• Increase the transmit power to combat this situation.
Dr.S.Mary Praveena,ASP/ECE 81
10/1/2021
82. s(t)
Flat Fading
h(t,t) r(t)
0 TS 0 t 0 TS+t
t TS
Occurs when:
BS << BC
and TS >> t
BC: Coherence bandwidth
BS: Signal bandwidth
TS: Symbol period
t: Delay Spread
Dr.S.Mary Praveena,ASP/ECE 82
10/1/2021
83. Frequency Selective Fading
• Occurs when channel multipath delay spread
is greater than the symbol period.
• Symbols face time dispersion
• Channel induces Intersymbol Interference (ISI)
• Bandwidth of the signal s(t) is wider than the
channel impulse response.
Dr.S.Mary Praveena,ASP/ECE 83
10/1/2021
84. Frequency Selective Fading
h(t,t)
s(t) r(t)
0 TS 0 t 0 TS TS+t
t TS
Causes distortion of the received baseband signal
Causes Inter-Symbol Interference (ISI)
Occurs when:
BS > BC
and TS < t
As a rule of thumb: TS < t
Dr.S.Mary Praveena,ASP/ECE 84
10/1/2021
85. Fast Fading
• Due to Doppler Spread
• Rate of change of the channel characteristics is larger
than the Rate of change of the transmitted signal
• The channel changes during a symbol period.
• The channel changes because of receiver motion.
• Coherence time of the channel is smaller than the
symbol period of the transmitter signal
Occurs when:
BS < BD
and TS > TC
BS: Bandwidth of the
signal BD: Doppler Spread
TS: Symbol Period
TC: Coherence Bandwidth
Dr.S.Mary Praveena,ASP/ECE 85
10/1/2021
86. Slow Fading
• Due to Doppler Spread
• Rate of change of the channel characteristics is
much smaller than the Rate of change of the
transmitted signal
Occurs when:
BS >> BD
and TS << TC
BS: Bandwidth of the
signal BD: Doppler Spread
TS: Symbol Period
TC: Coherence Bandwidth
Dr.S.Mary Praveena,ASP/ECE 86
10/1/2021
87. Different Types of Fading
TS
TC
TS
Transmitted Symbol Period
With Respect To SYMBOL PERIOD
Symbol Period of
Transmitting
Signal
t
Flat Slow
Fading
Flat Fast
Fading
Frequency
Selective Slow
Fading
Frequency
Selective Fast
Fading
Dr.S.Mary Praveena,ASP/ECE 87
10/1/2021
88. Different Types of Fading
Transmitted Baseband Signal Bandwidth
With Respect To BASEBAND SIGNAL BANDWIDTH
BS
BD
Flat Fast
Fading
Frequency
Selective Slow
Fading
Frequency
Selective Fast
Fading
BS
Transmitted
Baseband
Signal
Bandwidth
Flat Slow
Fading
BC
Dr.S.Mary Praveena,ASP/ECE 88
10/1/2021
89. Fading Distributions
• Describes how the received signal amplitude
changes with time.
• Remember that the received signal is combination of multiple
signals arriving from different directions, phases and
amplitudes.
• With the received signal we mean the baseband signal,
namely the envelope of the received signal (i.e. r(t)).
• Its is a statistical characterization of the
multipath fading.
• Two distributions
• Rayleigh Fading
• Ricean Fading
Dr.S.Mary Praveena,ASP/ECE 89
10/1/2021
90. Rayleigh and Ricean
Distributions
l Describes the received signal envelope
distribution for channels, where all the
components are non-LOS:
l i.e. there is no line-of–sight (LOS) component.
l Describes the received signal envelope
distribution for channels where one of the
multipath components is LOS component.
l i.e. there is one LOS component.
Dr.S.Mary Praveena,ASP/ECE 90
10/1/2021