The document provides an overview of cellular mobile communications including:
1) The historical development from isolated mobile systems to modern cellular networks with handoff capabilities and connections to public networks.
2) The key components of a cellular system including mobile stations, base transceiver stations, base station controllers, and mobile switching centers.
3) How the cellular concept enables frequency reuse through the use of lower power transmissions in smaller coverage areas called cells, allowing the same frequencies to be reused in separated cells.
Cellular communication allows for wireless communication as users travel within a city or between cities. It works by dividing geographic areas into cells served by low-power base stations. Each user is assigned a temporary radio channel to communicate with the local base station. As the user moves between cells, the channel is handed off to the new base station. A cellular system consists of cells managed by base stations, a switching office to connect calls to the public network, and mobile subscriber units used by customers.
The cellular concept was developed to solve the problem of spectral congestion and increase user capacity without major technological changes. It involves replacing single, high power transmitters with many low power transmitters covering small areas. Neighboring cells are assigned different channel groups to minimize interference, and the same channels are reused at different locations. When designing cellular systems, providing good coverage and services in high density areas requires considering factors like geographical separation and shadowing effects that allow frequency reuse.
This presentation contains the basic of cellular system.
in which direction the cellular system works and how it changes the network from one bast station to another is simply explained.
how Hand-off occur between two base station is shown via figure to understand well.
the cell system in mobile network and the cell spliting, sectoring, microcell zone concept is also explained well.
Please take a look.
may be it is helpfull for you.
Thank you.
Wireless cellular networks divide geographic areas into cells served by base stations to allow for frequency reuse. As users travel between cells, their calls are handed off seamlessly. Cellular systems improve capacity by allocating unique frequency groups to each cell and reusing the same frequencies in cells sufficiently distant from each other. Larger networks connect multiple base stations and mobile switching centers to facilitate roaming and complete calls between mobile and fixed users.
The key characteristic of a cellular network is the ability to reuse frequencies to increase both coverage and capacity. Cellular networks divide geographic areas into smaller cells and assign different frequency groups to neighboring cells to minimize interference and allow for frequency reuse. This allows the same frequencies to be reused in different cells separated by a sufficient distance.
The document discusses cellular network architecture and interference. It describes how cellular networks divide geographic coverage areas into hexagonal cells serviced by low-power base stations to reuse frequencies and increase capacity. Interference between cells using the same frequency is a major limiting factor and can be reduced by increasing the distance between co-channel cells. The document also discusses types of interference like co-channel and adjacent channel interference and techniques to mitigate interference like increasing cluster size and implementing power control.
Interference occurs when signals from one wireless channel leak into another, degrading performance. Adjacent channel interference specifically refers to interference between neighboring frequency bands. It results from imperfect receiver filters allowing nearby frequencies to blend together. This causes distorted transmissions, dropped calls, and reduced throughput. Interference can be minimized by carefully assigning non-adjacent channels to different cells and using adequate filtering to separate signals.
Mobile computing allows for anytime, anywhere computing through portable devices that can access wireless networks. However, mobile computing faces several challenges compared to traditional distributed systems, including resource scarcity due to limitations of mobile devices, variable connectivity, bandwidth and interfaces, and increased security vulnerabilities. These issues must be addressed through systems that can adapt to varying resources and environmental conditions, handle intermittent connectivity and mobility across domains, and maintain scalability.
Cellular communication allows for wireless communication as users travel within a city or between cities. It works by dividing geographic areas into cells served by low-power base stations. Each user is assigned a temporary radio channel to communicate with the local base station. As the user moves between cells, the channel is handed off to the new base station. A cellular system consists of cells managed by base stations, a switching office to connect calls to the public network, and mobile subscriber units used by customers.
The cellular concept was developed to solve the problem of spectral congestion and increase user capacity without major technological changes. It involves replacing single, high power transmitters with many low power transmitters covering small areas. Neighboring cells are assigned different channel groups to minimize interference, and the same channels are reused at different locations. When designing cellular systems, providing good coverage and services in high density areas requires considering factors like geographical separation and shadowing effects that allow frequency reuse.
This presentation contains the basic of cellular system.
in which direction the cellular system works and how it changes the network from one bast station to another is simply explained.
how Hand-off occur between two base station is shown via figure to understand well.
the cell system in mobile network and the cell spliting, sectoring, microcell zone concept is also explained well.
Please take a look.
may be it is helpfull for you.
Thank you.
Wireless cellular networks divide geographic areas into cells served by base stations to allow for frequency reuse. As users travel between cells, their calls are handed off seamlessly. Cellular systems improve capacity by allocating unique frequency groups to each cell and reusing the same frequencies in cells sufficiently distant from each other. Larger networks connect multiple base stations and mobile switching centers to facilitate roaming and complete calls between mobile and fixed users.
The key characteristic of a cellular network is the ability to reuse frequencies to increase both coverage and capacity. Cellular networks divide geographic areas into smaller cells and assign different frequency groups to neighboring cells to minimize interference and allow for frequency reuse. This allows the same frequencies to be reused in different cells separated by a sufficient distance.
The document discusses cellular network architecture and interference. It describes how cellular networks divide geographic coverage areas into hexagonal cells serviced by low-power base stations to reuse frequencies and increase capacity. Interference between cells using the same frequency is a major limiting factor and can be reduced by increasing the distance between co-channel cells. The document also discusses types of interference like co-channel and adjacent channel interference and techniques to mitigate interference like increasing cluster size and implementing power control.
Interference occurs when signals from one wireless channel leak into another, degrading performance. Adjacent channel interference specifically refers to interference between neighboring frequency bands. It results from imperfect receiver filters allowing nearby frequencies to blend together. This causes distorted transmissions, dropped calls, and reduced throughput. Interference can be minimized by carefully assigning non-adjacent channels to different cells and using adequate filtering to separate signals.
Mobile computing allows for anytime, anywhere computing through portable devices that can access wireless networks. However, mobile computing faces several challenges compared to traditional distributed systems, including resource scarcity due to limitations of mobile devices, variable connectivity, bandwidth and interfaces, and increased security vulnerabilities. These issues must be addressed through systems that can adapt to varying resources and environmental conditions, handle intermittent connectivity and mobility across domains, and maintain scalability.
Intorduction to cellular communicationZaahir Salam
This document provides an introduction to cellular communications. It discusses how mobile networks use separate radio channels and pairs of frequencies for communication between mobile devices and cell sites. It also describes how early mobile systems used one powerful transmitter while modern cellular networks use many low-power transmitters and a cellular structure. Key aspects of cellular network design are also summarized such as cells, clusters, frequency reuse, and handovers.
GENERAL DESCRIPTION OF THE PROBLEM , CONCEPT OF FREQUENCY CHANNELS, CO-CHANNEL iNTERFERENCE REDUCTION FACTOR , DESIRED C/I FROM A NORMAL CASE IN A OMNI DIRECTIONAL ANTENNA SYSTEM , CELL SPLITTING , CONSIDERATION OF THE COMPONENTS OF CELLULAR SYSTEM.
The document outlines the key concepts and units covered in a course on wireless and cellular communications. Unit 1 discusses cellular system design fundamentals including frequency reuse, interference, and capacity. Unit 2 covers speech coding techniques and radio channel characterization. Unit 3 discusses modulation techniques, diversity techniques, and OFDM. Unit 4 introduces MAC protocols for wireless networks. Unit 5 introduces satellite communication systems. Reference books on wireless communication principles and standards are also listed.
The cellular concept was developed to solve the problem of spectral congestion. It uses multiple low-power transmitters to provide coverage over small areas called cells, reusing frequencies in neighboring cells. Each cell is served by a base station connected to a mobile switching center, which manages call routing and user location. As users move between cells, their connections are handed off in a process that must be seamless. Cell sizes and handover methods vary to efficiently support both high-speed and low-speed mobile users.
The document discusses the cellular concept and frequency reuse in cellular networks. It describes how:
1) The cellular concept addresses the shortcomings of early mobile networks by dividing coverage areas into cells and reusing frequencies through frequency planning, allowing for greater capacity.
2) Each cell is assigned a group of channels, and neighboring cells are assigned different groups to minimize interference. The size of the frequency reuse cluster and number of channels impacts capacity and interference.
3) Handoffs must be performed seamlessly as users move between cells to maintain calls. Different cellular systems use different handoff techniques, such as network-controlled or mobile-assisted handoffs.
cellular concepts in wireless communicationasadkhan1327
The document discusses the concept of frequency reuse in cellular networks. It explains that a limited radio spectrum is used to serve millions of subscribers by dividing the network coverage area into cells and reusing frequencies across spatially separated cells. Each cell is allocated a portion of the total available frequencies, and neighboring cells are assigned different frequencies to minimize interference. The frequency reuse factor is defined as the ratio of the minimum distance between co-channel cells to the cell radius. Larger frequency reuse factors provide better isolation between co-channel cells but reduce network capacity. The document also covers additional topics like different channel assignment strategies, handoff methods, interference calculation and optimization of frequency reuse networks.
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.
The cellular concept divides a large service area into smaller cells served by low-power base stations to improve capacity and spectrum reuse. Each base station is allocated a group of radio channels for its cell. Areas are divided into hexagonal cells served by a central base station to allow frequencies to be reused efficiently while minimizing interference between adjacent cells. Handoff allows calls to be transferred between base stations as users move between cells to maintain call quality.
The document discusses the cellular concept in wireless networks. Key points include:
- Cells have a hexagonal shape and neighboring cells reuse frequencies to avoid interference and increase capacity.
- Frequency reuse allows more simultaneous calls by allocating the same set of frequencies to different neighboring cells.
- Cell size is a tradeoff between interference and system capacity - smaller cells mean lower power needs but more cells and handoffs.
Channel planning is critical for wireless network deployment. Poor planning can lead to unreliable networks with low capacity and performance. Assigning appropriate radio channels to each base station while determining frequency reuse ratios and cell separation distances is an important but difficult process. Cellular systems do not always follow homogeneous path loss models. Control channels are vital and generally use more conservative frequency reuse than voice channels. Cell breathing occurs as CDMA cell sizes dynamically shrink and grow depending on the number of users in the cell. Near-far problem and reverse link power control are also important CDMA concepts.
Wireless cellular networks divide geographic areas into smaller sections called cells to improve capacity and coverage. Each cell uses a subset of available frequencies and is served by a base station. As users move between cells, their active connections are handed off between base stations through a process managed by the mobile switching center. Cell sizes and the frequency reuse plan must be optimized to balance capacity, coverage, and interference between cells using the same frequencies.
This document provides an overview of cellular networks. It discusses key concepts like cells, base stations, frequency reuse, and multiple access methods. It describes how location of mobile devices is managed through location updating and paging. It also covers handoff which allows active calls to continue seamlessly as users move between different cells.
This document discusses the evolution of mobile communication technologies from 1G to 5G. It provides details on each generation including key features and technologies. 1G introduced analog cellular networks while 2G brought digital networks and basic data. 3G enabled increased data speeds and multimedia. 4G further increased speeds and capabilities. 5G is focused on high speeds, capacity, and supporting wireless web applications. The document also covers cellular concepts like frequency reuse, cell splitting, and cell sectoring which help improve network capacity and efficiency.
Basic cellular system, cellular system, What is cellular system, Generations of cellular system, Features of cellular systems, Shape of cells, Types of Basic cellular systems, Types of cellular systems, Circuit-Switched Systems, Analog cellular system, Analog cellular system, Digital Systems , Packet-switched system, 1g, 2g, 3g, 4g, 5g, MGCGV, Shubham Mishra
The document discusses the growth of cellular networks worldwide and in Pakistan. It provides statistics on the rising number of mobile subscribers globally, with Asia Pacific projected to account for half of all subscribers by the end of the decade. It then describes key components of cellular networks including mobile phones, base stations, mobile switching centers, and the use of frequency reuse to increase network capacity by dividing coverage areas into cells and assigning different frequency groups to adjacent cells.
Cellular networks address the problems of spectral congestion and limited user capacity by replacing single high-power transmitters with many low-power transmitters. This allows for frequency reuse, where the same frequencies can be used in cells farther apart due to lower transmission powers. Key aspects of cellular networks include frequency reuse patterns, cell types and sizes, co-channel interference management through techniques like sectorization and microcell deployment, and balancing capacity gains from smaller cells and frequency reuse against infrastructure costs. Cellular networks provide major improvements in spectral efficiency and user capacity over traditional wireless networks.
Here are 8 assignment problems from the document:
1. Derive the C/I from a Normal case in an Omni directional Antenna system.
2. Explain two kinds of cell splitting techniques with neat sketches.
3. Explain the Concept of frequency Reuse channels and mention the two schemes of frequency reuse.
4. Explain how Co-channel interference in measured in real time mobile radio Trans receivers.
5. Derive the relation for received power in when the wave is propagating over water or flat open area between two fixed stations.
6. What are the different synthesis of sum pattern? Explain them briefly.
7. What are the advantages of Reuse
This document discusses handoff in mobile communication networks. It begins with defining handoff as the transition of signal transmission from one base station to an adjacent one as a user moves. It then discusses various handoff strategies such as prioritizing handoff calls over new calls, monitoring signal strength to avoid unnecessary handoffs, and reserving guard channels for handoff requests. The document also covers types of handoffs, how handoff is handled differently in 1G and 2G cellular systems, challenges like cell dragging, and concepts like umbrella cells to minimize handoffs for high-speed users.
This presentation provides an overview of the cellular concept and key related topics:
- Cells are small geographical service areas defined by a base station and radio channels. Multiple cells are grouped into clusters to fully utilize available frequencies through frequency reuse.
- Handoff is the process of transferring voice and control signals between cells as a mobile moves between cells during a call. Successful and infrequent handoffs are important.
- Interference is reduced through frequency reuse and strategies like cell splitting and sectoring. Cell splitting divides cells into smaller areas served by low-power base stations to increase channel reuse and capacity. Sectoring uses directional antennas to reduce interference from co-channel cells.
The document discusses the architecture and operation of wireless cellular networks. It covers topics like the cellular concept, frequency reuse, channel allocation strategies, capacity expansion techniques like cell splitting and sectoring, and mobility management functions. The key aspects are maximizing channel availability in an area through frequency planning and reuse, and techniques to increase network capacity as demand grows. Mobility management aims to provide continuous connectivity as users move between different areas of the network.
1) Cellular networks divide a region into smaller areas called cells to improve capacity and reuse frequencies. Each cell contains a base station that can communicate with user equipment within its coverage area.
2) Frequency reuse allows the same set of frequencies to be reused in different cells by ensuring sufficient distance between cells using the same frequencies. This increases overall network capacity.
3) Handoff allows calls to be transferred between base stations as users move between cells to maintain call quality. Various handoff strategies aim to minimize call drops during handoffs.
The document discusses key concepts in mobile communication systems, including:
1. Cellular networks segment coverage areas into cells using multiple carrier frequencies to allow frequency reuse, with different frequencies used in adjacent cells. As user density increases, cells can be split into smaller cells.
2. Frequency reuse is key to cellular systems, allowing the same frequency to be used in different cells as long as they are sufficiently separated. Proper frequency planning is needed to minimize co-channel interference between cells using the same frequency.
3. When a mobile user moves between cells, a handover transfers the call to the new cell to maintain coverage. Handover thresholds and strategies aim to balance call quality and burden on the network.
Intorduction to cellular communicationZaahir Salam
This document provides an introduction to cellular communications. It discusses how mobile networks use separate radio channels and pairs of frequencies for communication between mobile devices and cell sites. It also describes how early mobile systems used one powerful transmitter while modern cellular networks use many low-power transmitters and a cellular structure. Key aspects of cellular network design are also summarized such as cells, clusters, frequency reuse, and handovers.
GENERAL DESCRIPTION OF THE PROBLEM , CONCEPT OF FREQUENCY CHANNELS, CO-CHANNEL iNTERFERENCE REDUCTION FACTOR , DESIRED C/I FROM A NORMAL CASE IN A OMNI DIRECTIONAL ANTENNA SYSTEM , CELL SPLITTING , CONSIDERATION OF THE COMPONENTS OF CELLULAR SYSTEM.
The document outlines the key concepts and units covered in a course on wireless and cellular communications. Unit 1 discusses cellular system design fundamentals including frequency reuse, interference, and capacity. Unit 2 covers speech coding techniques and radio channel characterization. Unit 3 discusses modulation techniques, diversity techniques, and OFDM. Unit 4 introduces MAC protocols for wireless networks. Unit 5 introduces satellite communication systems. Reference books on wireless communication principles and standards are also listed.
The cellular concept was developed to solve the problem of spectral congestion. It uses multiple low-power transmitters to provide coverage over small areas called cells, reusing frequencies in neighboring cells. Each cell is served by a base station connected to a mobile switching center, which manages call routing and user location. As users move between cells, their connections are handed off in a process that must be seamless. Cell sizes and handover methods vary to efficiently support both high-speed and low-speed mobile users.
The document discusses the cellular concept and frequency reuse in cellular networks. It describes how:
1) The cellular concept addresses the shortcomings of early mobile networks by dividing coverage areas into cells and reusing frequencies through frequency planning, allowing for greater capacity.
2) Each cell is assigned a group of channels, and neighboring cells are assigned different groups to minimize interference. The size of the frequency reuse cluster and number of channels impacts capacity and interference.
3) Handoffs must be performed seamlessly as users move between cells to maintain calls. Different cellular systems use different handoff techniques, such as network-controlled or mobile-assisted handoffs.
cellular concepts in wireless communicationasadkhan1327
The document discusses the concept of frequency reuse in cellular networks. It explains that a limited radio spectrum is used to serve millions of subscribers by dividing the network coverage area into cells and reusing frequencies across spatially separated cells. Each cell is allocated a portion of the total available frequencies, and neighboring cells are assigned different frequencies to minimize interference. The frequency reuse factor is defined as the ratio of the minimum distance between co-channel cells to the cell radius. Larger frequency reuse factors provide better isolation between co-channel cells but reduce network capacity. The document also covers additional topics like different channel assignment strategies, handoff methods, interference calculation and optimization of frequency reuse networks.
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.
The cellular concept divides a large service area into smaller cells served by low-power base stations to improve capacity and spectrum reuse. Each base station is allocated a group of radio channels for its cell. Areas are divided into hexagonal cells served by a central base station to allow frequencies to be reused efficiently while minimizing interference between adjacent cells. Handoff allows calls to be transferred between base stations as users move between cells to maintain call quality.
The document discusses the cellular concept in wireless networks. Key points include:
- Cells have a hexagonal shape and neighboring cells reuse frequencies to avoid interference and increase capacity.
- Frequency reuse allows more simultaneous calls by allocating the same set of frequencies to different neighboring cells.
- Cell size is a tradeoff between interference and system capacity - smaller cells mean lower power needs but more cells and handoffs.
Channel planning is critical for wireless network deployment. Poor planning can lead to unreliable networks with low capacity and performance. Assigning appropriate radio channels to each base station while determining frequency reuse ratios and cell separation distances is an important but difficult process. Cellular systems do not always follow homogeneous path loss models. Control channels are vital and generally use more conservative frequency reuse than voice channels. Cell breathing occurs as CDMA cell sizes dynamically shrink and grow depending on the number of users in the cell. Near-far problem and reverse link power control are also important CDMA concepts.
Wireless cellular networks divide geographic areas into smaller sections called cells to improve capacity and coverage. Each cell uses a subset of available frequencies and is served by a base station. As users move between cells, their active connections are handed off between base stations through a process managed by the mobile switching center. Cell sizes and the frequency reuse plan must be optimized to balance capacity, coverage, and interference between cells using the same frequencies.
This document provides an overview of cellular networks. It discusses key concepts like cells, base stations, frequency reuse, and multiple access methods. It describes how location of mobile devices is managed through location updating and paging. It also covers handoff which allows active calls to continue seamlessly as users move between different cells.
This document discusses the evolution of mobile communication technologies from 1G to 5G. It provides details on each generation including key features and technologies. 1G introduced analog cellular networks while 2G brought digital networks and basic data. 3G enabled increased data speeds and multimedia. 4G further increased speeds and capabilities. 5G is focused on high speeds, capacity, and supporting wireless web applications. The document also covers cellular concepts like frequency reuse, cell splitting, and cell sectoring which help improve network capacity and efficiency.
Basic cellular system, cellular system, What is cellular system, Generations of cellular system, Features of cellular systems, Shape of cells, Types of Basic cellular systems, Types of cellular systems, Circuit-Switched Systems, Analog cellular system, Analog cellular system, Digital Systems , Packet-switched system, 1g, 2g, 3g, 4g, 5g, MGCGV, Shubham Mishra
The document discusses the growth of cellular networks worldwide and in Pakistan. It provides statistics on the rising number of mobile subscribers globally, with Asia Pacific projected to account for half of all subscribers by the end of the decade. It then describes key components of cellular networks including mobile phones, base stations, mobile switching centers, and the use of frequency reuse to increase network capacity by dividing coverage areas into cells and assigning different frequency groups to adjacent cells.
Cellular networks address the problems of spectral congestion and limited user capacity by replacing single high-power transmitters with many low-power transmitters. This allows for frequency reuse, where the same frequencies can be used in cells farther apart due to lower transmission powers. Key aspects of cellular networks include frequency reuse patterns, cell types and sizes, co-channel interference management through techniques like sectorization and microcell deployment, and balancing capacity gains from smaller cells and frequency reuse against infrastructure costs. Cellular networks provide major improvements in spectral efficiency and user capacity over traditional wireless networks.
Here are 8 assignment problems from the document:
1. Derive the C/I from a Normal case in an Omni directional Antenna system.
2. Explain two kinds of cell splitting techniques with neat sketches.
3. Explain the Concept of frequency Reuse channels and mention the two schemes of frequency reuse.
4. Explain how Co-channel interference in measured in real time mobile radio Trans receivers.
5. Derive the relation for received power in when the wave is propagating over water or flat open area between two fixed stations.
6. What are the different synthesis of sum pattern? Explain them briefly.
7. What are the advantages of Reuse
This document discusses handoff in mobile communication networks. It begins with defining handoff as the transition of signal transmission from one base station to an adjacent one as a user moves. It then discusses various handoff strategies such as prioritizing handoff calls over new calls, monitoring signal strength to avoid unnecessary handoffs, and reserving guard channels for handoff requests. The document also covers types of handoffs, how handoff is handled differently in 1G and 2G cellular systems, challenges like cell dragging, and concepts like umbrella cells to minimize handoffs for high-speed users.
This presentation provides an overview of the cellular concept and key related topics:
- Cells are small geographical service areas defined by a base station and radio channels. Multiple cells are grouped into clusters to fully utilize available frequencies through frequency reuse.
- Handoff is the process of transferring voice and control signals between cells as a mobile moves between cells during a call. Successful and infrequent handoffs are important.
- Interference is reduced through frequency reuse and strategies like cell splitting and sectoring. Cell splitting divides cells into smaller areas served by low-power base stations to increase channel reuse and capacity. Sectoring uses directional antennas to reduce interference from co-channel cells.
The document discusses the architecture and operation of wireless cellular networks. It covers topics like the cellular concept, frequency reuse, channel allocation strategies, capacity expansion techniques like cell splitting and sectoring, and mobility management functions. The key aspects are maximizing channel availability in an area through frequency planning and reuse, and techniques to increase network capacity as demand grows. Mobility management aims to provide continuous connectivity as users move between different areas of the network.
1) Cellular networks divide a region into smaller areas called cells to improve capacity and reuse frequencies. Each cell contains a base station that can communicate with user equipment within its coverage area.
2) Frequency reuse allows the same set of frequencies to be reused in different cells by ensuring sufficient distance between cells using the same frequencies. This increases overall network capacity.
3) Handoff allows calls to be transferred between base stations as users move between cells to maintain call quality. Various handoff strategies aim to minimize call drops during handoffs.
The document discusses key concepts in mobile communication systems, including:
1. Cellular networks segment coverage areas into cells using multiple carrier frequencies to allow frequency reuse, with different frequencies used in adjacent cells. As user density increases, cells can be split into smaller cells.
2. Frequency reuse is key to cellular systems, allowing the same frequency to be used in different cells as long as they are sufficiently separated. Proper frequency planning is needed to minimize co-channel interference between cells using the same frequency.
3. When a mobile user moves between cells, a handover transfers the call to the new cell to maintain coverage. Handover thresholds and strategies aim to balance call quality and burden on the network.
This document discusses key concepts in cellular systems including frequency reuse, interference management, and capacity improvement techniques. The main points are:
1. Cells reuse radio frequencies to allow large numbers of users by allocating different frequency groups to neighboring cells. This reduces interference within tolerable limits.
2. Interference is managed through techniques like frequency planning, channel assignment strategies, and power control. The balance of interference and capacity is important.
3. System capacity can be improved through cell splitting, sectoring cells with directional antennas, using different cell sizes, and coverage zone techniques. Managing interference is crucial to improving cellular network capacity.
The document provides an overview of fundamental concepts in cellular engineering. It discusses the goals of cellular systems to have high capacity and large coverage area through efficient use of limited spectrum. Key concepts explained include frequency reuse, where the same radio channels are reused in different cells to serve more users; channel assignment strategies like fixed and dynamic allocation; and techniques to enhance capacity like cell splitting, sectoring, and microcell zones. The handoff process is also summarized, which allows seamless transfer of calls between base stations as users move between cells.
03. Chapter- Three Elements of Cellular Radio System Design1.pdfsamiulsuman
The document summarizes key elements of cellular radio system design including low power transmitters, frequency reuse, co-channel interference reduction, handoff mechanisms, and cell splitting. It discusses how frequency reuse allows the same channels to be used in different cells to increase capacity but can cause co-channel interference. Handoff mechanisms allow calls to be transferred between cells as users move. Cell splitting involves installing new base stations to reduce interference and increase capacity in busy areas.
The key characteristic of a cellular network is the ability to reuse frequencies to increase both coverage and capacity. Cellular networks divide geographic areas into smaller cell sites served by lower-power base stations. Neighboring cells are assigned different groups of channels to minimize interference. This frequency reuse allows the same frequencies to be used in multiple cells across an area.
This document discusses principles of cellular communication systems. It describes how cellular systems overcome limitations of conventional systems by dividing geographic areas into small cells served by low-power base stations, and reusing frequencies in different cells. This allows for higher capacity within limited spectrum. Key aspects covered include cell structure, frequency reuse patterns, cluster size and its impact on capacity, methods for locating co-channel cells, and factors like interference that influence network design.
Cellular networks divide a large geographic service area into smaller cellular regions or "cells" to improve spectrum efficiency and increase user capacity. Each cell uses a subset of available radio frequency channels and base stations operate at low power, reducing interference between cells using the same channel. By reusing the same set of frequencies in cells separated by a minimum distance, the available spectrum can be reused throughout the system. The ratio of the distance between co-channel cells to the cell radius is known as the frequency reuse ratio or factor.
The document discusses key concepts in cellular network design including:
1) The cellular concept divides a large service area into smaller cells served by low-power base stations to improve capacity compared to single transmitter systems.
2) Frequency reuse planning involves assigning different channel groups to neighboring cells to minimize interference while maximizing frequency reuse.
3) Handoff strategies are used to transfer calls between cells as users move, and guard channels and queuing can help reduce dropped calls.
4) Techniques like cell splitting, sectoring, and smaller cell zones can help improve coverage and capacity in congested areas without requiring additional spectrum.
The document discusses key concepts in cellular network design including:
- Frequency reuse which allows the same channels to be reused in different cells by assigning different channel groups to adjacent cells to minimize interference.
- Channel assignment strategies including fixed assignment where channels are permanently assigned to cells and dynamic assignment where channels are allocated on demand considering interference.
- Handoff strategies to transfer calls between cells as users move, prioritizing ongoing calls through guard channels and queuing handoff requests.
- Interference, particularly co-channel interference between cells using the same channels, which is the major limiting factor in capacity and requires sufficient separation between co-channel cells. Signal-to-interference ratio characterizes this interference.
In the early years of mobile radio systems, a large coverage was achieved by using a single high-powered transmitter with the antenna mounted on tall tower. Although a large coverage could be attained by this approach, it does not allow the reuse of the same radio frequencies due to interference. The cellular concept was invented in solving the spectral congestion and user capacity. Cellular telephony is a system-level concept, which replaces a single high power transmitter with a large number of low-power transmitters for communication between any two devices over a large geographic area.
2_cellular_network of mobile computing explainedbipik48002
The document discusses cellular network concepts and architecture. It introduces key terminology like base station, mobile switching center, mobile station, voice channels and control channels. It describes how a cellular call is initiated and maintained, including handoffs between cells. It discusses cellular design considerations like frequency reuse, co-channel interference, cell shape and size. Handoff strategies including mobile assisted handoff are covered. The document also provides an overview of the GSM cellular standard.
The document discusses key concepts in cellular network design including:
- Frequency reuse which involves dividing a service area into cells and assigning different channel groups to adjacent cells to allow channels to be reused.
- Channel assignment strategies including fixed assignment where channels are permanently assigned to cells and dynamic assignment where channels are allocated on demand.
- Handoff strategies for transferring calls between cells as users move, including techniques like guard channels and queuing handoff requests.
- Interference, which is the major limiting factor for capacity, including co-channel interference between cells using the same frequencies and adjacent channel interference from nearby frequencies.
M & WC unit 1.pptx very good condition and success20EC040
The document discusses various handoff strategies used in cellular networks. It explains that handoff is required when a mobile moves between base stations to transfer an ongoing call to a new channel and base station. It describes different types of handoff like hard handoff in TDMA networks and soft handoff in CDMA networks. It also discusses factors like minimizing unnecessary handoffs, ensuring successful handoffs, and making handoffs imperceptible to users.
Cellular concepts and system design fundamentalsKamal Sharma
The document discusses the cellular concept which aims to increase capacity by replacing single high-power transmitters with multiple low-power transmitters, each covering a small cell. Key aspects covered include:
- Cells are allocated different channel groups to minimize interference between nearby base stations.
- A cellular system reuses the same set of channels in different cells through frequency planning and by assigning different channel groups to neighboring cells.
- Hexagonal cell shapes help maximize coverage while minimizing gaps and support efficient frequency reuse patterns.
- Techniques like cell splitting, sectoring, and microcells help increase capacity by reducing cell sizes and reusing frequencies.
This document discusses cellular network fundamentals including channel assignment strategies, handoff strategies, and practical handoff considerations. It describes fixed and dynamic channel assignment and explains that handoffs are given higher priority than new calls to reduce dropped calls. The document outlines factors that influence handoff decisions and dwell times, and describes different types of handoffs including hard and soft handoffs.
Cellular networks allow for mobile communication by dividing geographic areas into multiple "cells" served by base stations. This allows for frequency reuse which increases system capacity. Cellular networks have evolved through multiple generations with improvements in data transmission capabilities and bandwidth. Key aspects of cellular networks include frequency division duplexing, time division duplexing, and multiple access techniques like frequency division multiple access, time division multiple access, and code division multiple access which allow for sharing of bandwidth among users.
The cellular concept solves spectral congestion issues by reusing radio channels in different hexagonal cells. Hexagonal cells provide full coverage with minimal cells and equal distance between cell centers. Each cell is assigned a group of channels to limit interference between neighboring cells using frequency planning. The capacity of the system increases with the number of times the frequency plan can be reused across different cell clusters.
2.6 cellular concepts - frequency reusing, channel assignmentJAIGANESH SEKAR
- 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.
SYBSC(CS)_WCIOT_Sem-II-Unit 1 Overview of wireless communication.pdfshubhangisonawane6
The document provides an overview of the key components and technologies involved in wireless communication and cellular networks. It discusses the basic concepts of cellular telephony including frequency reuse, handoff strategies, and types of interference. It also provides block diagrams of the main components in a mobile handset, including the digital baseband chipset for communication processing, radio chipset for transmitting and receiving signals, and auxiliary components for additional connectivity standards.
Wireless communication involves transferring information over a distance without wires. It includes technologies like cellular phones, WiFi, Bluetooth, and wireless networking. The Wireless Application Protocol (WAP) was developed to allow access to internet content on wireless devices like mobile phones. It uses protocols like WML and WMLScript to adapt webpages to smaller screens. Common types of wireless communication technologies include WiFi, Bluetooth, infrared, radio frequency, and PC Cards/PCMCIA.
This document provides an overview of sonar technology. It discusses the history of sonar from its early developments in the late 19th/early 20th century to its modern applications. Key developments include Fessenden's early experiments in 1914, the creation of ASDIC by the British during WWI, and the transfer of technology between Britain and the US during WWII. The document also examines how sonar works using sound waves, and describes different sonar systems like active/passive sonar and side-scan/multi-beam sonar used for tasks like submarine detection, fishing, and seafloor mapping.
This document provides an overview of satellite communication systems. It discusses the need for satellites due to the curvature of the Earth, the different regions of space including low-Earth orbit (LEO), medium-Earth orbit (MEO), and geostationary orbit (GEO). It describes the basic components of a satellite system including satellites, ground stations, uplinks and downlinks. It also covers communication characteristics, advantages and disadvantages of satellite systems, and provides a historical overview of important milestones in satellite communication technology.
This document provides an overview of radio and satellite communication technologies. It discusses key topics such as radio propagation, signal characteristics, signal propagation ranges, antenna technology, the basics of how satellites work, different types of satellite orbits including GEO, LEO and MEO, factors that affect satellite communication, how satellites are used, and methods of capacity allocation like FDMA and TDMA. The document contains detailed information on these concepts through definitions, diagrams, and examples. It aims to educate the reader on the fundamentals of radio and satellite communication systems.
Satellite communications systems involve satellites orbiting Earth that relay signals between ground stations. The document discusses several key topics:
1. The types of satellites include communication, weather, navigation, military and scientific satellites. Different orbits are used including geostationary and polar orbits.
2. Satellite subsystems include power, communication, antenna and control subsystems. Earth stations have antenna, transmit, receive and power subsystems.
3. Satellites can route signals via transponders and techniques like frequency reuse increase channel capacity. Handovers allow signals to transfer between satellites or ground stations.
4. Applications include remote sensing, weather monitoring, global communications, navigation and space exploration. Satellite technology has many important
Satellite communication uses satellites in orbit around Earth to relay radio signals between Earth stations. There are three main types of satellite orbits - low Earth orbit (LEO), medium Earth orbit (MEO), and geosynchronous Earth orbit (GEO). Satellites have a payload that includes antennas and transponders to receive and transmit signals, and a bus that provides structure, power, and control. Common applications of satellite communication include satellite television broadcasting, internet access, telephony, and providing connectivity to remote areas.
A communication satellite receives radio signals from earth stations, amplifies them, and redirects them back to earth. It acts as a radio relay in space, allowing signals to be transmitted over greater distances than would be possible with terrestrial communication methods alone. A satellite's transponder receives uplink signals, amplifies them using a low-noise amplifier, down converts the frequency, filters it, amplifies it again using a power amplifier, and retransmits it back to earth on the downlink frequency. This allows the satellite to receive and redirect communications between various earth stations.
Radar uses radio waves to detect objects at a distance by transmitting pulses and measuring their reflection. It was developed for military use in World War 2 to locate ships and planes. There are two main types - pulse radar which measures distance using transit time of pulses, and continuous wave radar which relies on the Doppler effect. Radar has many applications including weather forecasting, air traffic control, and speed detection guns.
The document discusses the components and basic principles of radar. It explains that radar works by transmitting short bursts of radio signals and measuring the time it takes for those signals to reflect off objects and return. It identifies the three major components of radar as the scanner, transceiver, and indicator. The scanner rotates and transmits the radio signals, while the transceiver contains the transmitter and receiver. The indicator displays the objects detected by radar to help with navigation and collision avoidance. Basic radar components include a power supply, modulator, transmitter, and antenna system.
Radar uses radio waves to detect objects and determine their range, altitude, direction or speed. It works by transmitting pulses of radio waves which bounce off objects and return a portion of energy to the receiving antenna. Radar was developed in the 1930s-1940s and has two main types - pulse radar which uses pulse transmission and continuous wave radar which uses continuous transmission. Key components of radar systems include the transmitter, antenna, receiver and display. Factors like signal reception, bandwidth, power and beam width affect radar performance.
The document discusses the basic principles and components of pulse transmission and continuous wave radar systems. It describes how pulse radar determines range using pulse width, pulse repetition frequency, and time of return signals. Key components of pulse radar systems are identified as the synchronizer, transmitter, antenna, duplexer, receiver and display unit. Continuous wave radar relies on Doppler frequency shifts from moving targets and uses separate transmit and receive antennas. Modulation techniques for radar waves include amplitude, frequency, pulse-amplitude and pulse-frequency modulation. Factors that affect radar performance such as signal reception, bandwidth, power, beamwidth and signal-to-noise ratio are also covered.
This document provides an overview of mobile communication and cellular technologies. It begins with learning objectives which are to refresh basics of cellular technologies, understand functioning in a cellular environment, and explain technical aspects of cellular telecommunications. The document then outlines the course agenda which will cover topics like access methods, multiple access techniques, mobile services, evolution of cellular communication standards like GSM and CDMA, cellular networks, and wireless data technologies. It dives into concepts like electromagnetic waves, frequency division multiple access, time division multiple access, duplexing, cellular architecture with frequency reuse, and elements of mobile communication systems.
Arduino is an open-source hardware and software platform for building electronics projects. It provides a simple environment for writing code to control sensors, actuators and other inputs/outputs. The Arduino platform includes affordable microcontroller boards, and a development environment that uses a simplified version of C/C++ to write code. This allows projects to sense and control the physical world through inputs like light, motion and temperature, and outputs like motors, lights and displays.
The document provides an overview of Arduino, describing it as an open-source physical computing platform consisting of a programmable integrated circuit board and integrated development environment. It can be used for physical computing projects, interactive installations, and rapid prototyping. The document outlines what Arduino can do, including interacting with sensors to detect inputs and actuators to produce outputs. It explains how to get started with Arduino by obtaining a board, learning the programming language based on C/C++, and uploading simple programs to control outputs like LEDs. A pushbutton example circuit is demonstrated.
The document discusses Arduino, an open-source hardware and software system for building electronics projects. It describes Arduino boards, which use AVR microcontrollers and can be programmed with a simplified version of C/C++. Arduino makes microcontrollers easy to use through an open development environment and standardized hardware/software components. A variety of Arduino boards and shields are available to add functionality like Ethernet, Bluetooth, and more. Alternative platforms like BascomAVR are also presented.
The document discusses the history and development of microprocessors and microcontrollers. It defines a microprocessor as a CPU integrated onto a single chip that serves as the central component of modern computers. Microcontrollers are similar but integrated with additional components like memory and I/O ports to control embedded systems. The first microprocessor was conceived in 1969 at Intel to power programmable calculators, and the first device was delivered in 1971. Microcontrollers were first created in 1971 and commercialized in 1974 to integrate all components needed to control a device. Modern microprocessors and microcontrollers now power many electronic devices from appliances to vehicles to cell phones.
Microprocessors and microcontrollers are both integrated circuits that contain a processor, memory, and input/output peripherals on a single chip. Microprocessors are general purpose CPUs used to build computer systems, while microcontrollers are self-contained systems that control embedded devices. Microcontrollers contain additional components like timers and analog-to-digital converters that make them suitable for real-time control applications in devices and appliances. Common applications of microcontrollers include industrial control systems, home appliances, automotive engine control systems, and consumer electronics. Microprocessors are used to build more complex computer systems for applications like desktop PCs, servers, communication equipment, and industrial instrumentation.
The document provides an overview of the 8051 microcontroller, including its features, applications, evolution, and architecture. Specifically, it discusses the 8051's 4K bytes of ROM, 128 bytes of RAM, four 8-bit I/O ports, two 16-bit timers, serial interface, and 64K external memory spaces. It also describes the 8051's registers, memory mapping, ports, timers/counters, and interrupt system. The document traces the evolution of microcontrollers from the Motorola 6801 in 1976 to modern 32-bit ARM and Intel processors.
The document provides an overview of the 8051 microcontroller, including its features, applications, evolution, and architecture. Specifically, it discusses the 8051's 4K bytes of ROM, 128 bytes of RAM, four 8-bit I/O ports, two 16-bit timers, serial interface, and 64K external memory spaces. It also describes the 8051's registers, memory mapping, ports, timers/counters, and interrupt system. The document traces the evolution of microcontrollers from the Motorola 6801 in 1976 to modern 32-bit ARM and Intel processors used in devices like mobile phones.
Introduction- e - waste – definition - sources of e-waste– hazardous substances in e-waste - effects of e-waste on environment and human health- need for e-waste management– e-waste handling rules - waste minimization techniques for managing e-waste – recycling of e-waste - disposal treatment methods of e- waste – mechanism of extraction of precious metal from leaching solution-global Scenario of E-waste – E-waste in India- case studies.
Optimizing Gradle Builds - Gradle DPE Tour Berlin 2024Sinan KOZAK
Sinan from the Delivery Hero mobile infrastructure engineering team shares a deep dive into performance acceleration with Gradle build cache optimizations. Sinan shares their journey into solving complex build-cache problems that affect Gradle builds. By understanding the challenges and solutions found in our journey, we aim to demonstrate the possibilities for faster builds. The case study reveals how overlapping outputs and cache misconfigurations led to significant increases in build times, especially as the project scaled up with numerous modules using Paparazzi tests. The journey from diagnosing to defeating cache issues offers invaluable lessons on maintaining cache integrity without sacrificing functionality.
CHINA’S GEO-ECONOMIC OUTREACH IN CENTRAL ASIAN COUNTRIES AND FUTURE PROSPECTjpsjournal1
The rivalry between prominent international actors for dominance over Central Asia's hydrocarbon
reserves and the ancient silk trade route, along with China's diplomatic endeavours in the area, has been
referred to as the "New Great Game." This research centres on the power struggle, considering
geopolitical, geostrategic, and geoeconomic variables. Topics including trade, political hegemony, oil
politics, and conventional and nontraditional security are all explored and explained by the researcher.
Using Mackinder's Heartland, Spykman Rimland, and Hegemonic Stability theories, examines China's role
in Central Asia. This study adheres to the empirical epistemological method and has taken care of
objectivity. This study analyze primary and secondary research documents critically to elaborate role of
china’s geo economic outreach in central Asian countries and its future prospect. China is thriving in trade,
pipeline politics, and winning states, according to this study, thanks to important instruments like the
Shanghai Cooperation Organisation and the Belt and Road Economic Initiative. According to this study,
China is seeing significant success in commerce, pipeline politics, and gaining influence on other
governments. This success may be attributed to the effective utilisation of key tools such as the Shanghai
Cooperation Organisation and the Belt and Road Economic Initiative.
KuberTENes Birthday Bash Guadalajara - K8sGPT first impressionsVictor Morales
K8sGPT is a tool that analyzes and diagnoses Kubernetes clusters. This presentation was used to share the requirements and dependencies to deploy K8sGPT in a local environment.
Embedded machine learning-based road conditions and driving behavior monitoringIJECEIAES
Car accident rates have increased in recent years, resulting in losses in human lives, properties, and other financial costs. An embedded machine learning-based system is developed to address this critical issue. The system can monitor road conditions, detect driving patterns, and identify aggressive driving behaviors. The system is based on neural networks trained on a comprehensive dataset of driving events, driving styles, and road conditions. The system effectively detects potential risks and helps mitigate the frequency and impact of accidents. The primary goal is to ensure the safety of drivers and vehicles. Collecting data involved gathering information on three key road events: normal street and normal drive, speed bumps, circular yellow speed bumps, and three aggressive driving actions: sudden start, sudden stop, and sudden entry. The gathered data is processed and analyzed using a machine learning system designed for limited power and memory devices. The developed system resulted in 91.9% accuracy, 93.6% precision, and 92% recall. The achieved inference time on an Arduino Nano 33 BLE Sense with a 32-bit CPU running at 64 MHz is 34 ms and requires 2.6 kB peak RAM and 139.9 kB program flash memory, making it suitable for resource-constrained embedded systems.
A review on techniques and modelling methodologies used for checking electrom...nooriasukmaningtyas
The proper function of the integrated circuit (IC) in an inhibiting electromagnetic environment has always been a serious concern throughout the decades of revolution in the world of electronics, from disjunct devices to today’s integrated circuit technology, where billions of transistors are combined on a single chip. The automotive industry and smart vehicles in particular, are confronting design issues such as being prone to electromagnetic interference (EMI). Electronic control devices calculate incorrect outputs because of EMI and sensors give misleading values which can prove fatal in case of automotives. In this paper, the authors have non exhaustively tried to review research work concerned with the investigation of EMI in ICs and prediction of this EMI using various modelling methodologies and measurement setups.
Advanced control scheme of doubly fed induction generator for wind turbine us...IJECEIAES
This paper describes a speed control device for generating electrical energy on an electricity network based on the doubly fed induction generator (DFIG) used for wind power conversion systems. At first, a double-fed induction generator model was constructed. A control law is formulated to govern the flow of energy between the stator of a DFIG and the energy network using three types of controllers: proportional integral (PI), sliding mode controller (SMC) and second order sliding mode controller (SOSMC). Their different results in terms of power reference tracking, reaction to unexpected speed fluctuations, sensitivity to perturbations, and resilience against machine parameter alterations are compared. MATLAB/Simulink was used to conduct the simulations for the preceding study. Multiple simulations have shown very satisfying results, and the investigations demonstrate the efficacy and power-enhancing capabilities of the suggested control system.
International Conference on NLP, Artificial Intelligence, Machine Learning an...gerogepatton
International Conference on NLP, Artificial Intelligence, Machine Learning and Applications (NLAIM 2024) offers a premier global platform for exchanging insights and findings in the theory, methodology, and applications of NLP, Artificial Intelligence, Machine Learning, and their applications. The conference seeks substantial contributions across all key domains of NLP, Artificial Intelligence, Machine Learning, and their practical applications, aiming to foster both theoretical advancements and real-world implementations. With a focus on facilitating collaboration between researchers and practitioners from academia and industry, the conference serves as a nexus for sharing the latest developments in the field.
Literature Review Basics and Understanding Reference Management.pptxDr Ramhari Poudyal
Three-day training on academic research focuses on analytical tools at United Technical College, supported by the University Grant Commission, Nepal. 24-26 May 2024
2. Section Overview
• Historical Development
• Cellular System Components
• Cellular Concept & Frequency Reuse
• Co-Channel Interference
• Cell Sectoring & Beam Tilting
• Channel Assignment Techniques
• Cell Splitting
• Handoff and Handoff Types
• Power Control, open loop and closed loop
• System Channels & Typical Call
3. Historical Development
• Started with isolated wireless service
areas
– Stand alone areas
– No connection to public telephones
• Added communication among service
areas belonging to same system
• Cellular Concepts developed
– Interconnection
– Connection to Public Telephony
– Handoff for uninterrupted service
5. • First generation cellular mobile
communications: (1980 )
– Technology: FDMA and Analog Technology.
– Systems: AMPS(USA), NMT-900(Sweden),
HCMTS(Japan)
– Shortages: Low capacity, poor Security, Low
quality, voice only (no data)
– Advantages: enough for the time
Historical Development
6. Historical Development …
• Second generation, 2G : (1992)
– Technology: TDMA, TDMA hybrid FDMA
– Systems: DAMPS(USA, IS-54), GSM
– Advantages: Higher Capacity, good Security, good
speech quality
– Technology: CDMA (Qualcomm)
– Systems: CDMA(IS-95)
– Advantages: Good Security, Higher & Soft Capacity,
Speech Activity, Multipath Diversity Rx., good speech
quality
– Shortages: Mainly Voice Service & low data rate
Services
7. Historical Development …
• 2.5 Generation, 2.5 G: (1996-2000)
– GPRS in Europe: Higher data rate (up ~ 150
kbps), Packet Switched Data, compatible
with GSM
– IS-95 B in US: Higher Data rate (up to ~114
kbps), Packet or Switched Data, compatible
with IS-95
8. Historical Development …
• The third generation 3G: (2001-2005)
– Support Multimedia Service, especially Internet
Service, 144kb/s(Outdoor and higher velocity ),
384kb/s(from Outdoor to indoor, lower velocity),
2Mb/s(indoor)
– Better Speech Quality and other services
– New Technologies like Tx Diversity, Turbo coding,
Multiuser Detection and Interference Cancellation,
Beam forming and Smart Antennas
9. System Components
• Mobile Stations
– Transceiver
– Antenna
– Control circuitry
– Moves at pedestrian or vehicle speeds
• Base Transceiver Station (BTS)
– Several transmitters and receivers
– Tower that supports several transmitting and receiving antennas
• Base Station Controller (BSC)
– Control one or more BTS
– Bridge between all mobile users of the BTSs and a Mobile switching
center
• Mobile Switching Center (MSC)
– Connects MSs to the PSTN (public-switched telephone network)
– Coordinates activities of all BSCs
– Controls all billing and system maintenance functions
– Several MSCs in large cities
11. Cellular Concept
• Idea: replace high power transmitter
with several lower power transmitters to
create small “cells”
• Multiple cells cover a geographic area
• Each cell assigned a set of frequencies
• Neighboring cells assigned different
group of frequencies to reduce adjacent-
cell interference
12. Cellular Concept…
Enables spatial frequency reuse
Increase capacity by increasing number of
transmitters and decreasing transmit power
Enables fixed bandwidth to serve arbitrarily
large number of subscribers
Users within a cell communicate with the
cell BS
As users move between cells, calls go
through “hand-off” when switching to new
cell BS
13. Cellular Concept…
• Large-radius cells for large coverage area
with small number of users
• Evolve into small-radius cells when number
of users increase using cell-splitting
• Main ideas of cellular systems
– Small coverage areas (cells)
– Frequency reuse
– Handoff
– Cell splitting to increase capacity
14. Why are Cells Required?
• Original mobile voice networks used
transmitter with large power to cover
very large area
• Capacity severely limited by available
bandwidth
• Spectrum limited, so could not increase
capacity by adding new channels
• Cellular concept was born
– Ushered in modern communication systems
15. Frequency Reuse
• Design cells to be non-overlapping and cover
entire region
• Cells depicted as hexagons
– Conceptual design allowing easy analysis of system
– Close to circular shape achieved by omnidirectional
antennas
• “Footprint”: actual radio coverage of a cell
– Determined from field measurements or propagation
prediction models
– Amorphous in nature
– Use hexagon to approximate shape
16. Frequency Reuse…
• Due to Co-channel Interference (CCI),
cannot use same frequency in adjacent cell
• Cells that use same frequencies must be
separated by distances large enough to keep
interference levels low
• Frequencies assigned to different cells using
frequency reuse plan
• Adjacent cells assigned different
frequencies to avoid interference or
crosstalk
17. Frequency Reuse…
• Objective is to reuse frequency in nearby
cells
• 10 to 50 frequencies assigned to each cell
• Transmission power controlled to limit power at
that frequency escaping to adjacent cells
• The issue is to determine how many cells must
intervene between two cells using the same
frequency
18. Frequency Reuse…
• Cells with same letter use the same set of
frequency channels
• Using hexagonal cells, BS located at center of
cell
• MS at edge of cell receives weak signal from
BS, i.e., low Carrier to Interference ratio (C/I)
A
F
E
D
B
G C
A
F
E
D
B
G C
A
F
E
D
B
G C
19. Frequency Reuse…
• Suppose system has S total channels & k
channels per cell (k < S)
• Channels divided among N cells into disjoint
groups, S = kN, N cells which use all S channels
called “cluster” (N = cluster size, typically 4, 7, 12)
• Clusters replicated in system
• Typically cluster size N = i2
+ ij + j2
– N=7 i=2, j=1
– N=3 i=1, j=1
Move i cells in any direction
Turn 60o
CCW
Move j cells in this direction
23. Co-Channel Interference
• Cells using the same frequency cause
interference to each other
• Called co-channel interference (CCI)
• CCI increases as the cluster size N
decreases
• Important factor for signal quality is the
Carrier to Interference Ratio C/I
• Most interference comes from the first tier
of co-channel cells
25. ∑=
= IK
k
kI
C
I
C
1
C/I is calculated as:
The maximum number of K in the first tier is 6 and knowing that
γγ
α −−
=∝ RRC
∑=
−
−
= IK
k
kD
R
I
C
1
γ
γ
γγ
α −−
=∝ DDI
Wanted signal
Interfering signal
The above equation becomes:
Co-Channel Interference…
KI = # of interfering cells
26. ( )
11
1 1
II
KK
k
k
kk
C
I D q
R
γ
γ
−
−
==
= =
÷
∑∑
Rearranging:
and
R
D
q k
k =
The qk is the co-channel interference reduction factor with kth
co-channel interfering cell.
27. Co-Channel Interference…
• As N decreases the number of frequency
channels per cell increases but C/I
decreases
• C/I is improved by different methods
– Sectored antennas: reduces KI
– Beam tilting: Reduces power to co-channel
cells
– Channel assignment: minimizes activation of
co-channel frequencies, which reduces KI
28. CCI Reduction: Cell Sectoring
• Shown 120 sectored
antennas
• Channel per cell are
divided among 3 sectors
• CCI decreased. Sector 0
gets interference from
sectors 4, 5 and 6 only
• 60 degrees sectored also
possible
29. CCI Reduction: Beam Tilting
By tilting down the antenna beam, the power
outside the cell, causing CCI reduces
30. Channel Assignment
• Fixed Channel Assignment
– Cell allocated predetermined set of channels
– Any call within the cell must use one of the
unused channels assigned to cell
– If all channels used, call is blocked
• Channel Borrowing
– If all channels are used in a cell has, it can,
temporarily, borrow from neighboring cells
– MSC supervises borrowing
– Should not cause high CCI to other cell
31. Channel Assignment …
Dynamic Channel Assignment
• Channels not permanently assigned to cells
• BSC requests channel from MSC when call made
• MSC allocates channel to call based on algorithm that takes
into account
– Probability of future blocking within cell
– Frequency of use of candidate channel
– Reuse distance of channel
• MSC assigns channel that will not interfere with existing calls
• Reduces probability of blocking &Increases channel
utilization
32. Cell splitting
• If higher capacity is needed in a spot, we need to go,
locally, to smaller cluster size N
• Each cell can be split into multiple “microcells” with own
BS
• Rescaling system to smaller cell size
• Transmit power of BS reduced to obtain smaller
coverage area than original BS
• Enables more spatial reuse → greater system capacity
• Cell splitting preserves original frequency reuse plan
• Cell splitting causes increased handoff
• Can use “umbrella” cells where fast-moving mobiles
covered by original cell and slower mobiles covered by
microcells
33. Cell Splitting Example
F D
B
G C
F
E
D
G
C
F
E
D
B E
B
G
C
D
E
F
G
B
C
A
F D
B
G C
F
E
D
G
C
F
E
D
B E
B
G
C
A
35. Handoff
• Mobiles may move out of coverage area of a cell and into
coverage area of a different cell during a call
• MSC must identify new BS to handle call
– MSC must seamlessly transfer control of call to new BS
– MSC must assign call new forward and reverse channels within
the channels of new BS
• Some important performance metrics in handoff:
– Seamless – user should not know handoff occurring
– Minimum unnecessary Handoff due to short time fading
– Low probability of blocking new calls in the new cell
– Handoff to a good SNR channel so that an admitted call is not
dropped
36. Handoff ...
• Handoff Main Steps
1. Initiation: either mobile or network identifies need for handoff and
begins the process
2. Resource reservation: required resources necessary to support
handoff are allocated
3. Execution: actual handoff takes place and mobile uses new
resources
4. Completion: unneeded resources are freed
• Important handoff parameter:
– SNRold to initiate handoff based on minimum acceptable quality
– SNRnew of the target channel (SNRnew > SNRold )
– D = SNRnew - SNRold dB
1. If D too small, unnecessary handoffs occur
2. If D too large, may be insufficient time to complete handoff before SNRold
becomes too weak and signal is lost
38. Handoff ...
• Intersystem handoff
– Handoff may be to a cell in a different system
– Requires compatibility of different MSCs
– Roaming requirements important
• Some systems prioritize handoff over new calls
– Dropped calls more annoying than blocked calls
– Guard channel
Some voice channels reserved for handoff
Reduces total carried traffic
Can use dynamic channel assignment to increase efficiency
– Queuing handoff requests
Effectiveness depends on the time interval between when handoff
initiated and when the call will be dropped due to low signal strength
39. Handoff Strategies
• BS typically averages signal strength over moving window of
time to remove rapid fluctuations due to multipath fading
• Handoff will occur using different metrics
– Relative SNR strength
When SNR at new BS higher than SNR at current BS
– Relative SNR strength with threshold
When SNR at current BS is below a threshold and SNR at new BS is
higher than at current BS
– Relative SNR strength with hysteresis
When SNR at new BS is stronger than at current BS by a threshold
– Relative SNR strength with hysteresis and threshold
SNR at current BS below a threshold and at new BS stronger than at
current BS by a threshold
40. Mobile Assisted Handoff (MAHO)
• Mobile stations measure received SNR
from surrounding BSs
– Inform current BS of measurements
– Handoff initiated when SNR from other BS
exceeds SNR from current BS by a certain
level or for a certain period of time
• Handoff much quicker using MAHO
41. Handoff Problems
• High-speed mobiles require frequent handoffs
– Burdens MSC
– Can use “umbrella cells” to minimize handoff
– Pedestrian users covered in small cells
– High-speed users covered in large umbrella cell
– Minimizes handoffs for high-speed users while ensuring capacity for
pedestrian users
• Cell dragging
– If a user has a good LOS path to BS, SNR might be large even when
user has left the cell
– Causes interference and traffic management problems (user in new
cell but managed by old BS)
• Handoff times
– 1st
generation analog systems: 10 s
– 2nd
generation digital systems: 1-2 s (using MAHO)
42. Types of Handoff
• Hard handoff (Break before Make)
– Whenever mobile enters new cell, must be assigned new channel for
communication
– E.g., FDMA, TDMA
• Soft handoff (Make before Break)
– Mobile can use channels from two or BS simultaneously
– Mobile adds new channel from the target BS(s)
– Signal from multiple BSs are combined (Macro diversity)
– Mobile concurrently transmitting to and receiving from multiple BSs
– BS with low SNR is dropped
– Used mainly with CDMA (IS-95, CDMA2000 & WCDMA)
43. Power Control
• If MS is near the BS or in LOS situation, power
to/from the MS can be reduced
– Helps Reduce CCI
– Save battery power
– Alleviate health concerns
• Coarse power control is adequate
– Implemented through Open Loop Power Control
• In CDMA systems all MS use same frequency
• Fine power control is crucial to mitigate the
near-far effect
– Both Open & Closed Loop Power Control
44. Open-Loop Power Control
• MS measures power on forward link
• If power is high, mobile unit reduces its
uplink power and vice versa
• Power measurements averages the
Rayleigh fading
– Depends on distance and shadowing only
• No feedback from BS
• Not as accurate as closed-loop power
control
45. Closed-Loop Power Control
• Performed on top of the Open Loop Power
Control
• BS measures the uplink power from MS
• BS transmits power control commands on
the forward link
• MS steps its power up or down
accordingly
• In IS-95, the power control rate is 800 Hz
46. Cellular System Channels
• Control channels
– Forward and Reverse
– Setting up and maintaining calls
– Exchange commands an/or messages
between MS and BS or MSC (as needed)
• Traffic channels
– Carry voice and/or data traffic
47. Typical call
• Mobile unit initialization
– Scan and select strongest set up control channel
– Automatically selected BS antenna of cell
• Usually but not always nearest (propagation
environment)
– Handshake to identify user and register location
– Scan repeated to allow for movement
• Change of cell
– Mobile unit monitors for pages (see below)
• Mobile originated call
– Check set up channel is free
• Monitor forward channel (from BS) and wait for idle
– Send number on pre-selected channel
48. Typical call…
• Paging
– MSC attempts to connect to mobile unit
– Paging message sent to BSs depending on called
mobile number
– Paging signal transmitted on set up channel
• Call accepted
– Mobile unit recognizes number on set up channel
– Responds to BS which sends response to MSC
– MSC sets up circuit between calling and called
BSs
– MSC selects available traffic channel within cells
and notifies BSs
– BSs notify mobile unit of channel
49. Typical call…
• Ongoing call
– Voice/data exchanged through respective BSs
and MSC
• Handoff
– Mobile unit moves out of range of cell into
range of another cell
– Traffic channel changes to one assigned to
new BS
• Without interruption of service to user
50. Summary
• Cellular Concept
• Frequency Reuse
• Co-Channel Interference
• Channel Assignment and Cell Splitting
• Handoff Issues and Handoff Types
• Power Control
• Typical Call Scenario