4.2 concepts of diversity
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This document discusses concepts of diversity in wireless communication. It defines diversity as a technique to ensure the same information reaches the receiver through statistically independent channels to improve channel quality and reduce fading. It explains that diversity is most effective when transmission channels carry independently faded copies of signals, and discusses correlation coefficient as a measure of correlation between diversity branches. Finally, it classifies diversity techniques as microscopic for small-scale fading and macroscopic for large-scale fading.
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4.3 types of diversity
This document discusses different types of diversity techniques used in wireless communications to combat fading. It describes micro diversity techniques including spatial, temporal, frequency, angular, and polarization diversity which use multiple antenna elements separated in space, time, frequency, orientation, or polarization. It also discusses macro diversity which uses multiple base stations to reduce large scale fading over long distances. The key methods are explained along with their advantages and disadvantages.
2. wireless propagation models free space propagation
This document discusses wireless communication propagation mechanisms and propagation models. It explains that when a signal hits an obstacle, it can be reflected, diffracted, or scattered depending on the surface properties. Propagation models are used to predict the average received signal power and design wireless systems by characterizing radio wave propagation based on factors like frequency and distance. Small-scale fading models predict power fluctuations over short ranges, while large-scale models predict average power decreases over large distances between transmitter and receiver.
8. introduction to small scale fading
Small scale fading, also known as fading, describes the rapid fluctuations of signal amplitude and phase over short periods of time. It is caused by interference between multiple versions of a transmitted signal that take different paths to the receiver. This can result in changes to amplitude, phase, and time of arrival depending on factors like multipath propagation, Doppler shifts from mobile speed, movement of surrounding objects, and the signal bandwidth.
2.1 introduction to cellular architecture
Cellular systems allow mobile users to communicate wirelessly using a network of base stations and switches. A mobile station communicates with the nearest base station, which connects to a mobile switching center. The switching center routes calls between mobile stations and the public switched telephone network. Coverage areas are divided into cells served by individual base stations to allow frequency reuse that improves system capacity.
9. parameters of mobile multipath channels
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.
2.5 capacity calculations of fdma, tdma and cdma
The document discusses the capacity calculations of cellular systems using FDMA, TDMA, and CDMA. For FDMA systems, capacity is limited by co-channel interference and calculated based on channel bandwidth, frequency reuse factor, and signal-to-interference ratio. TDMA systems improve capacity over analog systems through techniques like timeslot allocation and adaptive channel assignment. CDMA systems can reuse the entire spectrum in all cells, and capacity is interference-limited rather than bandwidth-limited. Capacity is increased in CDMA through sectorization, monitoring voice activity, and controlling transmit power.
2.6 cellular concepts - frequency reusing, channel assignment
- Cellular networks address the problem of limited spectrum availability by using frequency reuse, where nearby base stations are assigned different channels to avoid interference. Cells are arranged in a hexagonal pattern and the same set of channels are reused in cells sufficiently far from each other.
- There are two main channel assignment strategies - fixed assignment, where each cell has a predetermined set of channels, and dynamic assignment, where channels are allocated on demand by a central controller considering interference levels. Dynamic assignment helps improve spectrum utilization but requires more complex coordination.
- Frequency reuse allows the available spectrum to be reused as needed across multiple cells as long as interference is kept at acceptable levels, increasing network capacity.
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This document provides an overview of signal processing techniques used in wireless systems, including diversity and equalization. It discusses various diversity techniques like spatial, temporal, frequency, angular, and polarization diversity as well as macro and micro diversity. It also explains different types of combining diversity including selection, maximal ratio combining, and equal gain combining. The document concludes with sections on linear equalizers such as zero forcing and MMSE, as well as nonlinear equalizers using algorithms like LMS and RLS.
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This document discusses different types of diversity techniques used in wireless communications to combat fading. It describes micro diversity techniques including spatial, temporal, frequency, angular, and polarization diversity which use multiple antenna elements separated in space, time, frequency, orientation, or polarization. It also discusses macro diversity which uses multiple base stations to reduce large scale fading over long distances. The key methods are explained along with their advantages and disadvantages.
2. wireless propagation models free space propagation
This document discusses wireless communication propagation mechanisms and propagation models. It explains that when a signal hits an obstacle, it can be reflected, diffracted, or scattered depending on the surface properties. Propagation models are used to predict the average received signal power and design wireless systems by characterizing radio wave propagation based on factors like frequency and distance. Small-scale fading models predict power fluctuations over short ranges, while large-scale models predict average power decreases over large distances between transmitter and receiver.
8. introduction to small scale fading
Small scale fading, also known as fading, describes the rapid fluctuations of signal amplitude and phase over short periods of time. It is caused by interference between multiple versions of a transmitted signal that take different paths to the receiver. This can result in changes to amplitude, phase, and time of arrival depending on factors like multipath propagation, Doppler shifts from mobile speed, movement of surrounding objects, and the signal bandwidth.
2.1 introduction to cellular architecture
Cellular systems allow mobile users to communicate wirelessly using a network of base stations and switches. A mobile station communicates with the nearest base station, which connects to a mobile switching center. The switching center routes calls between mobile stations and the public switched telephone network. Coverage areas are divided into cells served by individual base stations to allow frequency reuse that improves system capacity.
9. parameters of mobile multipath channels
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.
2.5 capacity calculations of fdma, tdma and cdma
The document discusses the capacity calculations of cellular systems using FDMA, TDMA, and CDMA. For FDMA systems, capacity is limited by co-channel interference and calculated based on channel bandwidth, frequency reuse factor, and signal-to-interference ratio. TDMA systems improve capacity over analog systems through techniques like timeslot allocation and adaptive channel assignment. CDMA systems can reuse the entire spectrum in all cells, and capacity is interference-limited rather than bandwidth-limited. Capacity is increased in CDMA through sectorization, monitoring voice activity, and controlling transmit power.
2.6 cellular concepts - frequency reusing, channel assignment
- Cellular networks address the problem of limited spectrum availability by using frequency reuse, where nearby base stations are assigned different channels to avoid interference. Cells are arranged in a hexagonal pattern and the same set of channels are reused in cells sufficiently far from each other.
- There are two main channel assignment strategies - fixed assignment, where each cell has a predetermined set of channels, and dynamic assignment, where channels are allocated on demand by a central controller considering interference levels. Dynamic assignment helps improve spectrum utilization but requires more complex coordination.
- Frequency reuse allows the available spectrum to be reused as needed across multiple cells as long as interference is kept at acceptable levels, increasing network capacity.
Ec 2401 wireless communication unit 4
This document provides an overview of signal processing techniques used in wireless systems, including diversity and equalization. It discusses various diversity techniques like spatial, temporal, frequency, angular, and polarization diversity as well as macro and micro diversity. It also explains different types of combining diversity including selection, maximal ratio combining, and equal gain combining. The document concludes with sections on linear equalizers such as zero forcing and MMSE, as well as nonlinear equalizers using algorithms like LMS and RLS.
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The document describes the structure of a wireless communication link. It involves various processes between the transmitter and receiver including source coding, channel coding, modulation, upconversion to radio frequency, propagation over the wireless channel, downconversion to baseband, and decoding. Key components are the analog to digital converter and digital to analog converter, local oscillators, filters, amplifiers, modulators, demodulators, multiplexers, and decoders. The goal is to transmit digital data over an analog wireless channel reliably while accounting for noise and interference.
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Frequency Division Multiple Access (FDMA) is a multiple access technique that assigns individual frequency bands or channels to each user. FDMA avoids interference by ensuring each user is allocated a unique frequency band. While FDMA allows multiple users to access the channel simultaneously and has low inter-symbol interference, it requires tight RF filtering to minimize adjacent channel interference and duplexers, increasing costs. Non-linear effects from power amplifiers can also cause intermodulation frequencies, interfering with adjacent channels. The capacity of an FDMA system is calculated based on the total spectrum allocation, guard band allocation, and channel bandwidth.
Interferences
1) Frequency reuse in cellular networks results in co-channel interference from signals using the same frequency band but located in different cells.
2) Under normal conditions, co-channel signals do not interfere due to being located outside the cell boundary. However, troposcattering and transmission power issues can cause co-channel interference.
3) Measuring the carrier-to-interference ratio and carrier-to-noise ratio can help quantify co-channel interference levels. Frequency reuse increases spectrum efficiency but also co-channel interference, so reduction techniques are important.
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The document describes the structure of a wireless communication link. It involves various processes between the transmitter and receiver including source coding, channel coding, modulation, upconversion to radio frequency, propagation over the wireless channel, downconversion to baseband, and decoding. Key components are the analog to digital converter and digital to analog converter, local oscillators, filters, amplifiers, modulators, demodulators, multiplexers, and decoders. The goal is to transmit digital data over an analog wireless channel reliably while accounting for noise and interference.
2.2 frequency division multiple access
Frequency Division Multiple Access (FDMA) is a multiple access technique that assigns individual frequency bands or channels to each user. FDMA avoids interference by ensuring each user is allocated a unique frequency band. While FDMA allows multiple users to access the channel simultaneously and has low inter-symbol interference, it requires tight RF filtering to minimize adjacent channel interference and duplexers, increasing costs. Non-linear effects from power amplifiers can also cause intermodulation frequencies, interfering with adjacent channels. The capacity of an FDMA system is calculated based on the total spectrum allocation, guard band allocation, and channel bandwidth.
Interferences
1) Frequency reuse in cellular networks results in co-channel interference from signals using the same frequency band but located in different cells.
2) Under normal conditions, co-channel signals do not interfere due to being located outside the cell boundary. However, troposcattering and transmission power issues can cause co-channel interference.
3) Measuring the carrier-to-interference ratio and carrier-to-noise ratio can help quantify co-channel interference levels. Frequency reuse increases spectrum efficiency but also co-channel interference, so reduction techniques are important.
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The process of communication and Basic Block Diagram of Communication system is presented in this PPT.
The various Blocks like Information Source, Transmitter, Communication Channel, Noise, Receiver and Destination Blocks are discussed in detail
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This presentation discusses two types of interference that can impede communication: external interference which comes from outside sources, and internal interference which comes from within. It then explains two basic channels of interference - co-channel interference which occurs when multiple cells use the same frequency, and adjacent channel interference which results from nearby frequencies leaking into the pass band and can be minimized through filtering and channel assignment.
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Small-scale fading in wireless channels is caused by multipath propagation. There are three main effects: rapid signal strength changes over small distances/times, random Doppler shifts from multipath signals, and time dispersion of echoes. Multipath results from reflection, diffraction and scattering off surroundings. Several methods measure multipath structure including direct RF pulse systems, spread spectrum sliding correlators, and frequency domain channel sounding using vector network analyzers. These techniques help determine power delay profiles and understand time-varying multipath effects.
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This document discusses different techniques for achieving diversity in wireless communications and combining received signals:
1. Selection diversity techniques select the strongest signal from multiple antennas, either based on received signal strength (RSSI) or bit error rate (BER). Combining diversity techniques combine all received signals.
2. Combining diversity techniques include maximal ratio combining (MRC), which weights signals by amplitude, and equal gain combining (EGC), which weights all signals equally after phase correction. MRC achieves better performance than EGC when signals are highly faded.
3. The document compares the advantages and disadvantages of different selection criteria and combining techniques. It also describes switched and feedback selection diversity approaches.
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This document summarizes several statistical distributions used to model fading in wireless communication channels: Rician, Rayleigh, and lognormal distributions. It describes the Rayleigh distribution as modeling channels without a line-of-sight component, where the received signal envelope follows a Rayleigh distribution. The Rician distribution models channels with a dominant line-of-sight component, reducing to a Rayleigh distribution when the line-of-sight component fades. It also briefly discusses the Okumura and Hata propagation path loss models used for cellular system design.
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The document discusses concepts related to cellular network sectoring and microcells. It explains that cells can have square or hexagonal shapes, with hexagons providing equidistant antennas. Frequency reuse allows the same frequencies to be used in different cells by controlling base station power to limit interference. Common frequency reuse patterns include reuse factors of 1, 3, 7, etc. Capacity can be increased through methods like frequency borrowing, cell splitting, cell sectoring, and microcells which use smaller cell sizes.
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The document discusses advanced transceiver schemes including spread spectrum systems, code division multiple access (CDMA), orthogonal frequency division multiplexing (OFDM), and wireless network standards. It provides details on direct sequence spread spectrum, frequency hopping spread spectrum, CDMA principles and power control, OFDM principles and implementation, and 2G and 3G wireless network standards including GSM.
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This document provides an overview of equalization and diversity techniques used in mobile communication systems. It discusses how equalization is used to compensate for intersymbol interference caused by multipath fading. Linear equalizers aim to minimize mean square error, while nonlinear equalizers also use decision feedback. Common equalizer structures include transversal filters adapted using algorithms like LMS or RLS. Diversity techniques like spatial or frequency diversity compensate for fading by combining signals from multiple antennas or frequency bands. Channel coding adds redundancy to improve link performance in the presence of errors.
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This document discusses various wireless propagation channels including free space propagation, reflection, scattering, and diffraction. It covers reflection propagation mechanisms such as reflection from dielectrics and conductors. Reflection coefficients and Snell's law are explained. Models for reflection, including the two-ray ground reflection model, are provided. Diffraction models like knife-edge diffraction and multiple knife-edge diffraction using methods like Bollington's method are summarized. Scattering models including Kirchoff's theory and perturbation theory are covered. Common fading models for mobile radio like Rayleigh, Rician, and Doppler shift models are described. Finally, different types of wireless channels including time-selective, frequency-selective, general, and WSSUS channels are classified
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The wireless channel has several characteristics that make it more unpredictable than wired channels, including multipath effects, shadow fading, Doppler shift, and delay spread. Multipath occurs as signals bounce off environmental objects, resulting in multiple copies of the signal arriving at different times. The delay spread is the time difference between the first and last arriving signals. Key channel parameters include coherence bandwidth, which is the range of frequencies over which the channel remains flat, and coherence time, which is the time over which the channel impulse response is correlated. Frequency-selective fading occurs if the signal bandwidth exceeds the coherence bandwidth, causing intersymbol interference, while flat fading results when the delay spread is less than the symbol duration. Doppler shift causes time-varying
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1) WCDMA uses a RAKE receiver for equalization to improve signal-to-noise ratio by combining multipath components.
2) Wi-Fi uses an adaptive equalizer to mitigate channel impairments caused by scatterers.
3) WiMAX employs a least mean-square equalizer for channel estimation and uses equalization to address Doppler effects on the channel impulse and frequency responses.
Mobile Radio Propagations
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.
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The document discusses various topics related to mobile and wireless communication including:
1) Cell capacity and reuse, defining how capacity increases as the cluster size decreases but interference also increases.
2) Traffic theory, defining concepts like arrival rate, holding time, load, and blocked calls. Formulas for blocking probability and Erlang B & C are provided.
3) Channel assignment strategies including fixed and dynamic assignment and how their impact on performance.
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This document discusses wireless communication channels and diversity techniques. It describes how wireless channels experience both large-scale and small-scale fading, unlike wired channels. Small-scale fading is caused by multipath interference and results in rapid channel variations. Diversity combines multiple independent copies of the signal to improve link performance over fading channels. It can be achieved through techniques like antenna, site, frequency, time, polarization and angle diversity. The capacity of wireless channels is fundamentally limited by information theory based on available channel resources.
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The wireless channel, diversity and capacity of wireless channels
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Compare and contrast transmit and receive diversity. Describe how each diversity type lead to an
improvement in system performance.
Solution
Diversity refers to a technique for improving the transmission of a signal, by receiving and
processing multiple versions of the same transmitted signal. The multiple versions can be the
result of signals following different propagation paths, being transmitted at different times or
frequencies. In Transmit diversity, Spatial diversity is introduced into the signal by transmitting
through multiple antennas. The antennas are spaced far enough so that the signals emanating
from them can be assumed to undergo independent fading. In addition to diversity gain, antenna
gain can also be incorporated through channel state feedback. TD can improve the receiver
performance in the presence of flat fading. It reduces impact of fading by offering mutliple
copies of the digitally modulated waveform at the receiver, where the chance that all copies are
simultaneously in a fade is very small. In receiver diversity, the use of diversity at receiver
needs combining the outputs of statistically independent fading channels, in accordance with a
criterion that leads to improved receiver performance. Several techniques have been studied for
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Certainly! Let's break down the discussion on data communication into several parts. For a comprehensive understanding, we'll cover the basics, protocols, networking, security, and emerging trends. Each part will provide a more in-depth exploration of the topic.
### Part 1: Basics of Data Communication
Data communication is the process of exchanging information between two or more devices through a transmission medium such as cables, optical fibers, or wireless channels. It involves the use of protocols and technologies to ensure the reliable and efficient transfer of data.
#### 1.1 Components of Data Communication
Data communication systems consist of several key components, including:
- **Sender/Transmitter:** Initiates the communication by converting data into a signal.
- **Receiver:** Accepts the signal and converts it back into usable data.
- **Transmission Medium:** The physical path through which data travels (e.g., cables, airwaves).
- **Protocol:** A set of rules governing the exchange of data between devices.
#### 1.2 Types of Data Transmission
- **Analog vs. Digital:** Understanding the fundamental difference between analog and digital signals.
- **Simplex, Half-Duplex, and Full-Duplex:** Exploring the various modes of data transmission.
#### 1.3 Modulation and Multiplexing
- **Modulation:** The process of encoding digital information onto analog signals.
- **Multiplexing:** Techniques for combining multiple signals into a single transmission medium.
### Part 2: Data Communication Protocols
Data communication relies on standardized protocols to facilitate seamless interaction between devices. These protocols dictate the rules for data formatting, error checking, and synchronization.
#### 2.1 TCP/IP Protocol Suite
- **Transmission Control Protocol (TCP) and Internet Protocol (IP):** Fundamental protocols of the internet.
- **UDP (User Datagram Protocol):** A connectionless protocol for faster data transmission.
#### 2.2 OSI Model
- **Open Systems Interconnection model:** A conceptual framework for understanding network interactions divided into seven layers.
#### 2.3 Wireless Communication Protocols
- **Wi-Fi, Bluetooth, and NFC:** Popular wireless communication protocols.
### Part 3: Networking in Data Communication
Networking is a crucial aspect of data communication, encompassing the design, implementation, and management of interconnected systems.
#### 3.1 Types of Networks
- **LANs (Local Area Networks) and WANs (Wide Area Networks):** Differences and use cases.
- **MANs (Metropolitan Area Networks) and PANs (Personal Area Networks):** Exploring network scales.
#### 3.2 Network Topologies
- **Star, Bus, Ring, Mesh, and Hybrid Topologies:** Understanding how devices are interconnected.
#### 3.3 Network Devices
- **Routers, Switches, Hubs, and Modems:** Roles and functionalities in a network.
### Part 4: Security in Data Communication
As data communication becomes more prevalent, ensuring the security and
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- 5. Diversity - Principle • The principle of diversity is to ensure that the same information reaches the receiver on a statistically independent channels.
- 6. Diversity • This is a technique implemented to improve the channel quality and performance. • This is achieved by placing the Tx signals in a statistically independent channels. • This reduces the over all fading of the received signals at the receiver side. • This technique mainly addresses the fading problems.
- 7. Correlation Coefficient • Diversity is most efficient when the different transmission channels carry independently faded copies of the same signals. • The correlation coefficient characterises the correlation between signals on different diversity branches . • Correlation can be done on different parameters such as complex part of the signal, phase relations etc, • Most important one is correlation between the signal envelopes.
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- 9. • The correlation coefficient is given by: • Where x and y are the envelope of the signals. • The signals are said to be “effectively” decorrelated if , ρ is between a certain threshold value (typically 0.5 or 0.7)
- 10. Types of Diversity • How to obtain the diversity in the signals ? • Diversity are classified based on the fading methods. •Small scale fading • Microscopic diversity techniques are used. •Large scale fading • Macroscopic diversity techniques are used.