Cellular networks face two major types of interference: co-channel interference and adjacent channel interference. Co-channel interference occurs between cells using the same frequency, while adjacent channel interference is caused by signals leaking into nearby frequency bands from imperfect receiver filters. To reduce interference, cellular systems employ frequency reuse by allocating frequencies to distant cells, careful channel assignment to separate adjacent channels, and cell splitting to increase capacity by dividing cells. The frequency reuse factor and worst-case signal-to-interference ratio must be considered in the design to ensure sufficient voice quality.
Wireless communication systems are impacted by fading effects that cause fluctuations in signal strength. Fading occurs due to multipath propagation which results in multiple versions of the transmitted signal reaching the receiver at different times. This can cause either flat or frequency selective fading depending on the delay spread. Modulation techniques like BPSK can be used to combat fading. Simulation of a Rayleigh fading channel, which occurs when there is no dominant signal path, showed that it significantly impacts the bit error rate of a BPSK modulated signal. Future work could explore additional modulation techniques and integrating the model into a network simulator.
Introduction to basics of wireless networks such as
• Radio waves & wireless signal encoding techniques
• Wireless networking issues & constraints
• Wireless internetworking devices
This document provides an overview of GSM link budget calculations. It defines key terms used in link budgets such as effective radiated power, antenna gain, diversity gain, receiver sensitivity, path loss, and fade margin. It explains the objectives of calculating a link budget are to estimate maximum allowable path loss, compute required effective isotropically radiated power for a balanced link, estimate coverage design thresholds, and evaluate technology performance. It also provides examples of uplink and downlink link budget calculations for a GSM network and defines indoor, in-car, and outdoor coverage requirements.
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.
This document provides an overview of Global System for Mobile Communications (GSM) including its key objectives, services offered, network architecture and components, operations, signaling, and other aspects. The main points are:
GSM aims to provide improved spectrum efficiency, international roaming, low-cost devices, high-quality voice calls, and support for new data services. The core network consists of mobile stations, base station subsystems, network switching subsystems, and operation support subsystems. GSM uses TDMA/FDMA to allow multiple users to access the network simultaneously and efficiently. Signaling in GSM networks allows for call establishment, management, and control between different network elements.
4G refers to fourth-generation wireless which aims to provide faster data speeds and more capabilities than 3G. 4G LTE and 4G LTE Advanced are competing 4G standards. 4G LTE aims to provide speeds up to 10 times faster than 3G, while 4G LTE Advanced, standardized in 2011, is an enhancement that provides even higher speeds and more advanced technologies. The key difference is that 4G LTE Advanced supports newer technologies for higher performance compared to 4G LTE.
Spread spectrum communication uses wideband noise-like signals that are hard to detect, intercept, or jam. It spreads data over multiple frequencies. There are two main techniques: direct sequence spread spectrum multiplies a data signal by a pseudorandom code, and frequency hopping spread spectrum modulates a narrowband carrier that hops between frequencies. Spread spectrum provides benefits like resistance to interference and jamming, better signal quality, and inherent security. It finds applications in wireless networks, Bluetooth, and CDMA cellular systems.
Wireless communication systems are impacted by fading effects that cause fluctuations in signal strength. Fading occurs due to multipath propagation which results in multiple versions of the transmitted signal reaching the receiver at different times. This can cause either flat or frequency selective fading depending on the delay spread. Modulation techniques like BPSK can be used to combat fading. Simulation of a Rayleigh fading channel, which occurs when there is no dominant signal path, showed that it significantly impacts the bit error rate of a BPSK modulated signal. Future work could explore additional modulation techniques and integrating the model into a network simulator.
Introduction to basics of wireless networks such as
• Radio waves & wireless signal encoding techniques
• Wireless networking issues & constraints
• Wireless internetworking devices
This document provides an overview of GSM link budget calculations. It defines key terms used in link budgets such as effective radiated power, antenna gain, diversity gain, receiver sensitivity, path loss, and fade margin. It explains the objectives of calculating a link budget are to estimate maximum allowable path loss, compute required effective isotropically radiated power for a balanced link, estimate coverage design thresholds, and evaluate technology performance. It also provides examples of uplink and downlink link budget calculations for a GSM network and defines indoor, in-car, and outdoor coverage requirements.
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.
This document provides an overview of Global System for Mobile Communications (GSM) including its key objectives, services offered, network architecture and components, operations, signaling, and other aspects. The main points are:
GSM aims to provide improved spectrum efficiency, international roaming, low-cost devices, high-quality voice calls, and support for new data services. The core network consists of mobile stations, base station subsystems, network switching subsystems, and operation support subsystems. GSM uses TDMA/FDMA to allow multiple users to access the network simultaneously and efficiently. Signaling in GSM networks allows for call establishment, management, and control between different network elements.
4G refers to fourth-generation wireless which aims to provide faster data speeds and more capabilities than 3G. 4G LTE and 4G LTE Advanced are competing 4G standards. 4G LTE aims to provide speeds up to 10 times faster than 3G, while 4G LTE Advanced, standardized in 2011, is an enhancement that provides even higher speeds and more advanced technologies. The key difference is that 4G LTE Advanced supports newer technologies for higher performance compared to 4G LTE.
Spread spectrum communication uses wideband noise-like signals that are hard to detect, intercept, or jam. It spreads data over multiple frequencies. There are two main techniques: direct sequence spread spectrum multiplies a data signal by a pseudorandom code, and frequency hopping spread spectrum modulates a narrowband carrier that hops between frequencies. Spread spectrum provides benefits like resistance to interference and jamming, better signal quality, and inherent security. It finds applications in wireless networks, Bluetooth, and CDMA cellular systems.
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.
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 document discusses mobile radio propagation and propagation models. It begins by introducing how radio channels are random and time-varying. It then covers the free space propagation model and how received power decreases with distance. Reflection, diffraction, and scattering are described as the main propagation mechanisms. The two-ray ground reflection model is presented to model propagation over large distances. Diffraction is explained using the knife-edge diffraction model. Fresnel zones and diffraction gain are also defined.
What is GSM?
The Global System for Mobile communications is a digital cellular communications system. It was developed in order to create a common European mobile telephone standard but it has been rapidly accepted worldwide.
Formerly it was “Groupe Spéciale Mobile” (founded in 1982)
now: Global System for Mobile Communication.
Services:
Tele-services
Bearer or Data Services
Supplementary services
Applications:
Mobile telephony
GSM-R
Telemetry System
- Fleet management
- Automatic meter reading
- Toll Collection
- Remote control and fault reporting of DG sets
Value Added Services
Advantages:
Better Quality of speech
Data transmission is supported
New services offered due to ISDN compatibility
International Roaming possible
Large market
Crisper, cleaner quieter calls
disadvantages:
Dropped and missed calls
Less Efficiency
Security Issues
conclusion
The mobile telephony industry rapidly growing and that has become backbone for business success and efficiency and a part of modern lifestyles all over the world.
In this session I have tried to give and over view of the GSM system. I hope that I gave the general flavor of GSM and the philosophy behind its design.
The GSM is standard that insures interoperability without stifling competition and innovation among the suppliers to the benefit of the public both in terms of cost and service quality.
This document provides an overview of digital microwave communication principles and concepts. It begins with an introduction explaining that the course is intended to educate engineers on the basics of digital microwave communications. It then outlines the learning objectives, which include explaining the concepts, components, networking modes, propagation principles, anti-fading technologies, and design of microwave transmission links. The document also includes sections on the history and development of microwave communication, definitions of key terms, modulation techniques, frame structures, equipment types, and antenna technology.
Global System for Mobile (GSM) is a second generation cellular standard developed for voice services and data delivery using digital modulation. It has a network subsystem including components like the MSC, HLR, VLR, and AuC that handle call processing and subscriber information. The radio subsystem consists of BSCs controlling multiple BTSs to manage radio network access. GSM provides international roaming, high quality voice calls, and supports data services like SMS and fax in addition to voice.
Mobile satellite communication uses satellites to enable communication between mobile users. There are different types of satellite orbits used - geostationary, medium earth orbit, and low earth orbit. Each orbit has advantages and disadvantages for mobile communication. Mobile satellite services include maritime, land, aeronautical, personal, and broadcast. Signal propagation is impaired by effects like reflection, refraction, shadowing, and different types of noise. Thermal noise places a fundamental limit on communication performance.
This document discusses microwave communication and factors involved in microwave link design. It describes microwave communication as utilizing radio frequencies between 2-60 GHz for communication. Key factors in microwave link design include line-of-sight considerations, loss and attenuation calculations, fading predictions, and ensuring sufficient fade margin. Proper microwave link design is an iterative process that considers propagation losses, interference analysis, and ensuring quality and availability requirements are met.
This document provides an overview of 4G LTE technology. It discusses key LTE concepts such as OFDM and MIMO used in the downlink and uplink, as well as requirements for IMT-Advanced systems. It describes the 3GPP releases that specified LTE and LTE-Advanced standards and components of the LTE network architecture including the E-UTRAN, EPC, and interfaces between nodes. The document also provides explanations of OFDM, MIMO, SC-FDMA, and the LTE physical layer frame structure and resource grid. Special features introduced in LTE-Advanced like carrier aggregation and relaying are also summarized.
Cellular networks divide geographic areas into cells served by low-power base stations to reuse frequencies. Adjacent cells are assigned different frequencies to avoid interference. As capacity demands increase, networks employ techniques like frequency borrowing, cell splitting, cell sectoring, and microcells. Cellular standards like GSM use TDMA to allow multiple users per cell by dividing the air interface into time slots. CDMA spreads user data over a wide bandwidth using unique codes and allows soft handoff between cells. Third generation networks support high-speed data and multimedia services.
Cellular communication systems have evolved through multiple generations from analog 1G to digital 4G systems. A cellular network is divided into geographical areas called cells served by base transceiver stations. Cells are grouped into clusters where frequencies are reused to allow for more subscribers. When making a call, the cellular phone registers with the local base station which routes the call through switching centers to establish communication with the intended recipient. Modern cellular networks support additional services beyond voice like texting, internet access, and location tracking through technologies like GSM that employ protocols like TDMA for efficient frequency usage.
Orthogonal Frequency Division Multiplexing, OFDM uses a large number of narrow sub-carriers for multi-carrier transmission to overcome the effect of multi path fading problem. LTE uses OFDM for the downlink, from base station to terminal to transmit the data over many narrow band careers of 180 KHz each instead of spreading one signal over the complete 5MHz career bandwidth. OFDM meets the LTE requirement for spectrum flexibility and enables cost-efficient solutions for very wide carriers with high peak rates.
The primary advantage of OFDM over single-carrier schemes is its ability to cope with severe channel conditions. Channel equalization is simplified. The low symbol rate makes the use of a guard interval between symbols affordable, making it possible to eliminate inter symbol interference (ISI).
GSM. Global System for Mobile Communication.Student
This document provides an overview of Global System for Mobile Communication (GSM) technology. It discusses the history and evolution of GSM from 1G to future 5G networks. The key components of a GSM network are described, including the mobile equipment, subscriber identity module, base station system consisting of base transceiver stations and base station controllers, mobile switching center, home location register, visitor location register, and authentication center. Applications, advantages like worldwide connectivity, and disadvantages like limited range are highlighted. The presentation concludes with references and an acknowledgment.
This document summarizes the evolution of cellular networks from 1G to 4G. It describes the key technologies and standards for each generation including 1G analog networks, 2G digital networks with text messaging, 2.5G networks adding low-speed data, and 3G supporting broadband multimedia. It also discusses some of the technical challenges faced and different approaches taken in the US and Europe during this evolution.
The document discusses different channel assignment strategies for wireless networks, including fixed channel assignment where each cell is predetermined channels and dynamic channel assignment where channels are allocated on request based on factors like channel occupancy. It also describes a partially overlapping channel (FPOC) assignment strategy that aims to increase capacity while minimizing interference through intelligent channel allocation between neighboring nodes.
The document provides step-by-step instructions for using Atoll to design an LTE network using NSN parameter settings. It describes how to:
1) Create an LTE project in Atoll by importing default NSN parameter settings from an .mdb file.
2) Import necessary data like clutter, DTM, vector and antenna pattern data.
3) Define parameters like frequency bands, bearers, quality indicators, schedulers and equipment.
4) Perform coverage prediction studies like coverage by downlink best signal level and C/(I+N).
Frequency shift keying (FSK) is a digital modulation technique that encodes digital information by shifting the frequency of a carrier wave. There are different types of FSK including binary FSK, which uses two discrete frequencies to represent binary 1 and 0, and double frequency shift keying (DFSK), which uses four frequencies to transmit two independent data streams simultaneously. FSK modulation can be demodulated using either FM detector demodulators, which treat the FSK signal as an FM signal, or filter-type demodulators, which use optimal filters matched to the FSK signal parameters. The filters are used to detect the mark and space frequencies, and a decision circuit then determines which was transmitted.
The document provides an overview of LTE (Long Term Evolution) network architecture and transmission schemes. It describes the simplified LTE network elements including eNB, MME, S-GW and P-GW. It explains the downlink transmission scheme using OFDMA and reference signal structure. It also covers uplink transmission using SC-FDMA, control and data channels as well as frame structure in both FDD and TDD modes.
This document discusses radio propagation and propagation models. It begins with an introduction to radio and propagation mechanisms like free space propagation, refraction, diffraction, and scattering. It then discusses the objective of developing propagation models to predict signal strength at a receiver. The document outlines that propagation models are specialized based on scale, environment, and application. It covers large-scale path loss models and small-scale fading models. It discusses specific propagation mechanisms and models like free space, log-distance path loss, ground reflection, hilly terrain, indoor models, and statistical fading models.
Cellular systems use multiple low-power transmitters (base stations) rather than a single, high-power transmitter to increase capacity and coverage. Frequency reuse is used to allocate channels to nearby base stations to minimize interference. Handoff strategies are employed to transfer calls between base stations as users move. Interference and power control techniques aim to equalize signal power levels and improve capacity. Traffic engineering principles including Erlang formulas are applied to determine the optimal number of channels needed based on expected call volumes.
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 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.
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 document discusses mobile radio propagation and propagation models. It begins by introducing how radio channels are random and time-varying. It then covers the free space propagation model and how received power decreases with distance. Reflection, diffraction, and scattering are described as the main propagation mechanisms. The two-ray ground reflection model is presented to model propagation over large distances. Diffraction is explained using the knife-edge diffraction model. Fresnel zones and diffraction gain are also defined.
What is GSM?
The Global System for Mobile communications is a digital cellular communications system. It was developed in order to create a common European mobile telephone standard but it has been rapidly accepted worldwide.
Formerly it was “Groupe Spéciale Mobile” (founded in 1982)
now: Global System for Mobile Communication.
Services:
Tele-services
Bearer or Data Services
Supplementary services
Applications:
Mobile telephony
GSM-R
Telemetry System
- Fleet management
- Automatic meter reading
- Toll Collection
- Remote control and fault reporting of DG sets
Value Added Services
Advantages:
Better Quality of speech
Data transmission is supported
New services offered due to ISDN compatibility
International Roaming possible
Large market
Crisper, cleaner quieter calls
disadvantages:
Dropped and missed calls
Less Efficiency
Security Issues
conclusion
The mobile telephony industry rapidly growing and that has become backbone for business success and efficiency and a part of modern lifestyles all over the world.
In this session I have tried to give and over view of the GSM system. I hope that I gave the general flavor of GSM and the philosophy behind its design.
The GSM is standard that insures interoperability without stifling competition and innovation among the suppliers to the benefit of the public both in terms of cost and service quality.
This document provides an overview of digital microwave communication principles and concepts. It begins with an introduction explaining that the course is intended to educate engineers on the basics of digital microwave communications. It then outlines the learning objectives, which include explaining the concepts, components, networking modes, propagation principles, anti-fading technologies, and design of microwave transmission links. The document also includes sections on the history and development of microwave communication, definitions of key terms, modulation techniques, frame structures, equipment types, and antenna technology.
Global System for Mobile (GSM) is a second generation cellular standard developed for voice services and data delivery using digital modulation. It has a network subsystem including components like the MSC, HLR, VLR, and AuC that handle call processing and subscriber information. The radio subsystem consists of BSCs controlling multiple BTSs to manage radio network access. GSM provides international roaming, high quality voice calls, and supports data services like SMS and fax in addition to voice.
Mobile satellite communication uses satellites to enable communication between mobile users. There are different types of satellite orbits used - geostationary, medium earth orbit, and low earth orbit. Each orbit has advantages and disadvantages for mobile communication. Mobile satellite services include maritime, land, aeronautical, personal, and broadcast. Signal propagation is impaired by effects like reflection, refraction, shadowing, and different types of noise. Thermal noise places a fundamental limit on communication performance.
This document discusses microwave communication and factors involved in microwave link design. It describes microwave communication as utilizing radio frequencies between 2-60 GHz for communication. Key factors in microwave link design include line-of-sight considerations, loss and attenuation calculations, fading predictions, and ensuring sufficient fade margin. Proper microwave link design is an iterative process that considers propagation losses, interference analysis, and ensuring quality and availability requirements are met.
This document provides an overview of 4G LTE technology. It discusses key LTE concepts such as OFDM and MIMO used in the downlink and uplink, as well as requirements for IMT-Advanced systems. It describes the 3GPP releases that specified LTE and LTE-Advanced standards and components of the LTE network architecture including the E-UTRAN, EPC, and interfaces between nodes. The document also provides explanations of OFDM, MIMO, SC-FDMA, and the LTE physical layer frame structure and resource grid. Special features introduced in LTE-Advanced like carrier aggregation and relaying are also summarized.
Cellular networks divide geographic areas into cells served by low-power base stations to reuse frequencies. Adjacent cells are assigned different frequencies to avoid interference. As capacity demands increase, networks employ techniques like frequency borrowing, cell splitting, cell sectoring, and microcells. Cellular standards like GSM use TDMA to allow multiple users per cell by dividing the air interface into time slots. CDMA spreads user data over a wide bandwidth using unique codes and allows soft handoff between cells. Third generation networks support high-speed data and multimedia services.
Cellular communication systems have evolved through multiple generations from analog 1G to digital 4G systems. A cellular network is divided into geographical areas called cells served by base transceiver stations. Cells are grouped into clusters where frequencies are reused to allow for more subscribers. When making a call, the cellular phone registers with the local base station which routes the call through switching centers to establish communication with the intended recipient. Modern cellular networks support additional services beyond voice like texting, internet access, and location tracking through technologies like GSM that employ protocols like TDMA for efficient frequency usage.
Orthogonal Frequency Division Multiplexing, OFDM uses a large number of narrow sub-carriers for multi-carrier transmission to overcome the effect of multi path fading problem. LTE uses OFDM for the downlink, from base station to terminal to transmit the data over many narrow band careers of 180 KHz each instead of spreading one signal over the complete 5MHz career bandwidth. OFDM meets the LTE requirement for spectrum flexibility and enables cost-efficient solutions for very wide carriers with high peak rates.
The primary advantage of OFDM over single-carrier schemes is its ability to cope with severe channel conditions. Channel equalization is simplified. The low symbol rate makes the use of a guard interval between symbols affordable, making it possible to eliminate inter symbol interference (ISI).
GSM. Global System for Mobile Communication.Student
This document provides an overview of Global System for Mobile Communication (GSM) technology. It discusses the history and evolution of GSM from 1G to future 5G networks. The key components of a GSM network are described, including the mobile equipment, subscriber identity module, base station system consisting of base transceiver stations and base station controllers, mobile switching center, home location register, visitor location register, and authentication center. Applications, advantages like worldwide connectivity, and disadvantages like limited range are highlighted. The presentation concludes with references and an acknowledgment.
This document summarizes the evolution of cellular networks from 1G to 4G. It describes the key technologies and standards for each generation including 1G analog networks, 2G digital networks with text messaging, 2.5G networks adding low-speed data, and 3G supporting broadband multimedia. It also discusses some of the technical challenges faced and different approaches taken in the US and Europe during this evolution.
The document discusses different channel assignment strategies for wireless networks, including fixed channel assignment where each cell is predetermined channels and dynamic channel assignment where channels are allocated on request based on factors like channel occupancy. It also describes a partially overlapping channel (FPOC) assignment strategy that aims to increase capacity while minimizing interference through intelligent channel allocation between neighboring nodes.
The document provides step-by-step instructions for using Atoll to design an LTE network using NSN parameter settings. It describes how to:
1) Create an LTE project in Atoll by importing default NSN parameter settings from an .mdb file.
2) Import necessary data like clutter, DTM, vector and antenna pattern data.
3) Define parameters like frequency bands, bearers, quality indicators, schedulers and equipment.
4) Perform coverage prediction studies like coverage by downlink best signal level and C/(I+N).
Frequency shift keying (FSK) is a digital modulation technique that encodes digital information by shifting the frequency of a carrier wave. There are different types of FSK including binary FSK, which uses two discrete frequencies to represent binary 1 and 0, and double frequency shift keying (DFSK), which uses four frequencies to transmit two independent data streams simultaneously. FSK modulation can be demodulated using either FM detector demodulators, which treat the FSK signal as an FM signal, or filter-type demodulators, which use optimal filters matched to the FSK signal parameters. The filters are used to detect the mark and space frequencies, and a decision circuit then determines which was transmitted.
The document provides an overview of LTE (Long Term Evolution) network architecture and transmission schemes. It describes the simplified LTE network elements including eNB, MME, S-GW and P-GW. It explains the downlink transmission scheme using OFDMA and reference signal structure. It also covers uplink transmission using SC-FDMA, control and data channels as well as frame structure in both FDD and TDD modes.
This document discusses radio propagation and propagation models. It begins with an introduction to radio and propagation mechanisms like free space propagation, refraction, diffraction, and scattering. It then discusses the objective of developing propagation models to predict signal strength at a receiver. The document outlines that propagation models are specialized based on scale, environment, and application. It covers large-scale path loss models and small-scale fading models. It discusses specific propagation mechanisms and models like free space, log-distance path loss, ground reflection, hilly terrain, indoor models, and statistical fading models.
Cellular systems use multiple low-power transmitters (base stations) rather than a single, high-power transmitter to increase capacity and coverage. Frequency reuse is used to allocate channels to nearby base stations to minimize interference. Handoff strategies are employed to transfer calls between base stations as users move. Interference and power control techniques aim to equalize signal power levels and improve capacity. Traffic engineering principles including Erlang formulas are applied to determine the optimal number of channels needed based on expected call volumes.
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 provides an introduction to cellular concepts. Key points include:
1) Cellular networks divide a service area into smaller sections called cells to allow for frequency reuse and serve more subscribers. Each cell has a base station with a limited number of radio channels.
2) The same set of radio frequencies can be reused in cells separated by a sufficient distance to avoid co-channel interference exceeding acceptable levels.
3) Factors like terrain, buildings, and mobility affect signal propagation and can cause fading, interference, and frequency shifts. Techniques like sectoring cells and using directional antennas help mitigate these issues and improve frequency reuse.
Frequencies management,Channel assignments,
Frequency reuse, System capacity and its improvement: Cell spliting and sectoring, Handoffs & its types, prioritizing handoff, Umbrella cell approach, Cell dragging, Roaming, Co channel and adjacent channel interference, Improving coverage- Repeaters for range extension and microcell zone concept, Examples
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.
1. Cellular networks reuse frequencies across cells to increase capacity. Neighboring cells are assigned different channel groups to reduce interference.
2. The size of the frequency reuse cluster, channel allocation strategies, and techniques like cell splitting, sectoring, and microcells can improve capacity.
3. Key factors that impact network performance are co-channel and adjacent channel interference, which frequency planning and antenna configurations aim to minimize.
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.
This document provides an overview of wireless communication and cellular systems. It discusses key concepts such as frequency reuse, cell footprint, handover, interference, and system capacity. It explains how cellular networks divide a service area into smaller cells served by low-power base stations to improve capacity. Neighboring cells are assigned different frequency groups to reduce interference. The same frequencies can be reused in cells far enough apart. Handover allows calls to be transferred between cells as users move. The document also covers channel assignment strategies and methods for expanding system capacity through cell splitting or reducing the frequency reuse factor.
1. The document discusses co-channel interference which occurs when the same frequency is reused in different cell locations. It describes how directional antennas and increasing the number of sectors can reduce this interference.
2. Methods to calculate the carrier-to-interference ratio in different scenarios are presented, including for omni-directional antennas with different frequency reuse patterns and for directional antenna systems.
3. Determining the co-channel interference area involves measuring signal levels with a mobile receiver and comparing to thresholds for carrier-to-interference and carrier-to-noise ratios.
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.
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.
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.
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.
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.
This document provides an overview of key cellular coverage concepts including cell splitting, channel grouping, carrier to interference ratios, tower distance to cell radius ratios, and cellular network architecture. It explains how these concepts are used to efficiently provide cellular coverage and maximize channel capacity.
Concepts of & cell sectoring and micro cellKundan Kumar
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.
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.
Cellular Concepts by Mian Shehzad Iqbal,
Earlier systems used single high power
transmitter. So no frequency reuse
• Cellular concept solve the problem of spectral
congestion and user capacity without any major
technological changes.
• Replaces single high power transmitter with
many low power transmitters.
• Each base station is allocated portion of
available channels.
• Distribution to neighbors so that minimize
interference.
Hexagonal shape is only logical shape.
Actual coverage of cell is known as
footprint and is determined by
measurements and prediction models.
Cell must be designed to serve the
weakest mobile at edge in footprint.
MSC plays major role by monitoring reuse
distance, cost function and other issues. • MSC
needs to collect real time data on channel
occupancy, traffic distribution and radio signal
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2. MAJOR LIMITING FACTOR for Cellular System performance
is the INTERFERENCE
Interferences can cause:
CROSS TALK
Missed and Blocked Calls.
SOURCES OF INTERFERENCE?
Another mobile in the same cell (if distance & frequency are
close)
A call in progress in neighboring cell (if frequency is close).
Other base stations operating in the same frequency band
(from co-channel cells)
Non-cellular systems leaking energy into cellular frequency
band
4. CO-CHANNEL INTERFERENCE
Frequency Reuse Given coverage area cells using the same set of
frequencies co-channel cell !!!
Interference between these cells is called
CO-CHANNEL INTERFERENCE.
However, co-channel interference cannot be overcome just by increasing the
carrier power of a transmitter.
Because increase in carrier transmit power increases the
interference.
How to Reduce co-channel interference?
Co-channel cells must be physically separated by a minimum distance to provide
sufficient isolation.
6. Co-Channel Interference
(Base Mobile) : DOWNLINK
(Mobile Base) : UPLINK
UPLINK All mobiles (in 6 cells + central cell)
assigned to the same frequency channel
DOWNLINK All base stations (in 6 cells and
central cell) have the same frequency channel.
Note: if we allocate channels to a cell, part of the
channels are used for “downlink”; the rest are for
“uplink”.
7. Co-Channel Interference
(Base Mobile ): DOWNLINK CASE
From the base stations of co-channel cells: interference
received by the mobile in the center cell.
Desired signal is from the base to mobile in the center cell
itself.
Alarge is the area of the hexagonal cells of the large one.
Asmall is the area of each cell.
Alarge/Asmall A number of cells in this each repetitious
pattern (3N).
8. Co-Channel Interference
Intracell Interference: interferences from other mobile
terminals in the same cell.
– Duplex systems
– Background white noise
Intercell interference: interferences from other cells.
– More evident in the downlink than uplink for reception
– Can be reduced by using different set of frequencies
Design considerations:
– Frequency reuse
– Interference
– System capacity
9. Co-Channel Interference
For simplicity, we consider only the average channel quality as a
function of the distance dependent path loss.
Signal-to-Co-channel interference ratio, (S/I), at the desired
mobile receiver which monitors the forward channel is defined
by
S is the desired signal power from desired base station
Ii is interference power caused by the i-th interfering
co-channel cell’s base station.
NI is the number of co-channel interfering cells
(NI = Cluster size –1)
S
I
=
S
∑
i=1
N I
Ii
10. Co-Channel Interference
The desired signal power S from desired base station
is proportional to r -, where r is the distance between the
mobile and the serving base station. is the path loss
component.
Likewise, from power viewpoint, the received interference,
Ii, between the ith interferer (base station) and the mobile
is proportional to (Di)-.
Assume the transmits powers from all base stations are equal,
then we have
S
I
=
r− κ
∑
i=1
N I
Di− κ
11. Co-Channel Interference
Consider only the first tier of interfering cells,
if all interfering base stations are equidistant from the
desired base station and if this distance is equal to
the distance D between cell centers,
then the above equation can be simplified to:
(i.e., r=R and assume Di=D and use q=D/R):
S
I
=
r− κ
∑
i=1
N I
Di− κ
=
R− κ
NI D− κ
=
( D/R)κ
NI
=
qκ
NI
12. Co-Channel Interference
Thus Frequency reuse ratio, q
e.g., NI = 6
Example: for =4, S/I > 18dB (the larger, the
better),
q > (6101.8)1/4 = 4.41. (dB=10Logx)
The cluster size N should be (from eq.
q=sqrt(3N) N = q2/3 > 6.79 7.
i.e.,A 7-cell reuse pattern is needed for an S/I
ratio of 18dB. Based on q=D/R, we can select D
by choosing the cell radius R.
q=[ N I (
S
I
)]
1/κ
q=[ 6(
S
I
)]
1/κ
13. Remember -- co-channel
reuse ratio (Frequency
Reuse Factor) q --
q=[ N I (
S
I
)]
1/κ
q=sqrt(3N)
q=D/R
NI = Cluster size –1
N =i2+ij+j2
14. Co-Channel Interference
An S/I of 18 dB is the measured value for
the accepted voice quality from the
present day cellular mobile receivers.
Sufficient voice quality is provided when
S/I is greater than or equal to 18dB.
15. Example:
Co-Channel Interference
If S/I = 15 dB required for satisfactory
performance for forward channel
performance of a cellular system.
a) What is the Frequency Reuse Factor q
(assume K=4)?
b) Can we use K=3?
Assume 6 co-channels all of them (same distance
from the mobile), I.e. N=7
16. Example:
Co-Channel Interference
a) NI =6 => cluster size N= 7, and when =4
The co-channel reuse ratio is
q=D/R=sqrt(3N)=4.583
S
I
=
qκ
NI
=
1
6
(4.583)4
= 75.3
Or 18.66 dB greater than the minimum required level
ACCEPT IT!!!
b) N= 7 and =3
S
I
=
qκ
NI
=
1
6
(4.583)3
= 16.04
Or 12.05 dB less than the minimum required level
REJECT IT!!!
17. Example:
co-Channel Interference
S
I
=
qκ
NI
=
1
11
(6)3
= 19.6
Or 15.56 dB N=12 can be used for minimum
requirement, but it decreases the capacity (we already
gave an example: when cluster size is smaller, the
capacity is larger).
We need a larger N (thus q is larger). Use eq. N
=i2+ij+j2, for i=j=2 next possible value is
N=12.
q=D/R=sqrt(3N) =6 and =3
18. Worst Case Co-Channel Interference
i.e., mobile terminal is located at the cell boundary where it receives
the weakest signal from its own cell but is subjected to strong
interference from all all the interfering cells.
We need to modify our assumption, (we assumed Di=D).
The S/I ratio can be expressed as
R
D-R
D-R
D+R
D+R
D
D
S
I
=
r−κ
∑
i=1
N I
Di− κ
=
R−κ
2(D− R)− κ
+ 2D− κ
+ 2(D+R)−κ
S
I
=
1
2(q− 1)− 4
+ 2q−κ
+ 2(q+1)− 4
Used D/R=q and =4.
Where q=4.6 for
normal seven cell reuse pattern.
19. Example: Worst Case
Cochannel Interference (2)
A cellular system that requires an S/I
ratio of 18dB. (a) if cluster size is 7, what
is the worst-case S/I? (b) Is a frequency
reuse factor of 7 acceptable in terms of
co-channel interference? If not, what
would be a better choice of frequency
reuse ratio?
Solution
(a) N=7 q = . If a path loss component of =4, the worst-
case signal-to-interference ratio is S/I = 54.3 or 17.3 dB.
(b) The value of S/I is below the acceptable level of 18dB.
We need to decrease I by increasing N =9. The S/I is
95.66 or 19.8dB.
√
3N= 4.6
20. Example: Worst Case
Cochannel Interference
For a conservative estimate if we use
the shortest distance (=D-R) then
S
I
=
1
6(q− 1)− 4
=
1
6(3.6)− 4
= 28
Or 14.47 dB.
REMARK: In real situations, because of imperfect cell site locations
and the rolling nature of the terrain configuration, the S/I
ratio is often less than 17.3 dB. It could be 14dB or lower which
can occur in heavy traffic.
Thus, the cellular system should be designed around the S/I ratio
of the worst case.
21. Example: Worst Case
Co-Channel Interference
REMARK:
If we consider the worst case for a 7-cell reuse pattern
We conclude that a co-channel interference reduction factor of
q=4.6 is not enough in an omnidirectional cell system.
In an omnidirectional cell system N=9 (q=5.2) or N=12 (q=6.0)
the cell reuse pattern would be a better choice.
These cell reuse patterns would provide the S/I ratio of 19.78 dB
and 22.54 dB, respectively.
22. 2. ADJACENT CHANNEL INTERFERENCE
Interference resulting from signals which are adjacent
in frequency to the desired signal is called
ADJACENT CHANNEL INTERFERENCE.
WHY?
From imperfect receiver filters (which allow nearby frequencies) to leak
into the pass-band.
NEAR FAR EFFECT:
Adjacent channel user is transmitting in very close range to a
subscriber’s receiver, while the receiver attempts to receive a base
station on the desired channel.
Near far effect also occurs, when a mobile close to a base station
transmits on a channel close to one being used by a weak mobile.
Base station may have difficulty in discriminating the desired mobile
user from the “bleedover” caused by the close adjacent channel mobile.
23. ADJACENT CHANNEL INTERFERENCE
How to reduce?
• Careful filtering
• Channel assignment no channel assignment which are all adjacent in
frequency.
• Keeping frequency separation between each channel in a given cell as
large as possible.
e.g., in AMPS System there are 395 voice channels which
are divided into 21 subsets each with 19 channels.
• In each subset, the closest adjacent channel is 21 channels away.
• 7-cell reuse -> each cell uses 3 subsets of channels.
• 3 subsets are assigned such that every channel in the cell is assured of
being separated from every other channel by at least 7 channel spacings.
24. ADJACENT CHANNEL INTERFERENCE
How to reduce?
• Careful filtering
• Channel assignment no channel assignment which are all adjacent in
frequency.
• Keeping frequency separation between each channel in a given cell as
large as possible.
e.g., in AMPS System there are 395 voice channels which
are divided into 21 subsets each with 19 channels.
• In each subset, the closest adjacent channel is 21 channels away.
• 7-cell reuse -> each cell uses 3 subsets of channels.
• 3 subsets are assigned such that every channel in the cell is assured of
being separated from every other channel by at least 7 channel spacings.
25. Cell Splitting
A method to increase the capacity of a cellular system
by dividing one cell into more smaller cells.
Cell splitting reduces the call blocking probability
because the number of channels is increased. But it
increases the handoff rate, i.e., more frequent
crossing of borders between the cells.
We have the formula in calculating path loss:
Pr(dBW) = P0(dBW) - 10 log10(d/d0)
where d0 is the distance from the reference point to
the transmitter, and P0 is the power received at the
reference point.
26. Cell Splitting brings stronger Pr
Let Pt1 and Pt2 be the transmit power of
the large cell BS and medium cell BS,
respectively.
From dB viewpoint, The received power
at the edge of large cell is
Pr1 = P0 - 10 log10(R/d0)
From non-dB viewpoint, The received
power at the edge of large cell, Pr1
is proportional to
Pt1 (R)- .
The received power at the edge of
R/2 cell (small cell), Pr2 is
proportional to
Pt2 (R/2)- .
With the equal received power, we have
Pt1 (R)- = Pt2 (R/2)- , i.e., Pt1/Pt2= 2
R
R/2
27. Example – Cell Splitting
Suppose each BS is allocated 60 channels regardless of the
cell size.
Find the number of channels contained in a 3x3 km2 area
without cell splitting, (assume cell size R= 1km),
and with cell splitting, R/2 = 0.5km.
The number of cells for R=1km.
1. Each large cell can cover 3.14km2, for 9 km2
approximately need 9/3.14 => 3 cells. However, N
=i2+ij+j2. A better approximation is 4 cells. So the
number of channels is 4x60=240.
2. With small cells, the number of cells (to cover 9 km2 )
is approximately 9 /(3.14x(1/0.5)2 )= 4 (last case) x4 =
16. Then the number of channels is 16x60=960.
28. Cell Sectoring
(Directional Antennas)
Omni-directional antennas allow transmission of radio
signals with equal power strength in all directions.
Reality is an antenna covers an area of 60 degrees or 120
degrees DIRECTIONAL ANTENNAS!!!!
Cells served by these antennas are called SECTORED
CELLS !!!
Many sectored antennas are mounted a BS tower located
at the center of the cell and an adequate number of
antennas is placed to cover the entire 360 degrees of the
cell.
.
30. Cell Sectoring
(Directional Antennas)
Advantages of Cell Sectoring:
Coverage of smaller area by each antenna and hence
lower power is required in transmitting radio signals.
Helps to decrease interference between co-channels.
Increase frequency reuse since each sector can reuse the
same set of frequency channels as in the parent cell.
Note that a quad-sector architecture (90) has higher
capacity for 90% area coverage than a tri-sector (120)
cell.
31. Co-Channel Interference Reduction with the
Use of Directional Antennas (Cell Sectoring)
The basic form of antennas are omnidirectional.
Directional antennas can increase the system
capacity.
If we sectorize the cell with
120o in each sector, the S/I
becomes
The capacity increase is 3.
(
S
I
)omni=
R− α
∑
i=1
N I
Di− α
=
qα
6
1
2
3
3
1
2
(
S
I
)120=
qα
2
Note: now 1,2,3 can use the same
channels since each antenna only
covers its own sector (no leak to
other sectors), i.e. NI= 2 instead of 6
now!
32. Fixed Channel Assignment (FCA)
Each cell is allocated a predetermined set of
voice channels.
The BS is the entity that allocates channels to
the requests. If all channels are used in one
cell, it may borrow a channel from its
neighbors through MSC.
Fast allocation, but may result high call
blocking probabilities.
33. Dynamic Channel Assignment (DCA)
Voice channels are not allocated to each
cell permanently.
When a request is received at the BS, this
BS request a channel from MSC.
DCA can reduce the call blocking
probability, but it needs real-time data
collection and signaling transmission
between BS and MSC.
34. Call Admission Control
CAC is used to avoid congestions over the radio
links and to ensure the QoS requirements of
ongoing services.
Quality of service (QoS)
– Packet-level factors
– Packet loss rate, packet delay, packet delay
variation, and throughput rate.
Grade of service (GoS)
– Call-level factors
– New call blocking probability, handoff call
dropping probability, connection forced
termination probability.
35. CAC Procedure
Determine the amount of available channels, i.e., the number of
channels for accepting new and handoff requests.
When the N-th request arrives, i.e., there are (N-1) ongoing
services.
If there are enough resources to admit the N-th request, then
the new request is admitted.
Otherwise, it will be denied.
In order to maintain the continuity of a handoff call, handoff
calls are given higher priority than the new call requests.
The prioritized call admission is implemented by reserving
channels for handoff calls. This method is referred to as guard
channels.
– Fixed reservation and dynamic reservation.
36. The average number of mobiles requesting service in unit time
(average call arrival rate):
The average length of time a mobile requires service (the
average holding time): T
The offered traffic load: a = T
– e.g., in a cell with 100 mobiles, on an average, if 30 requests
are generated during an hour, with average holding time
T=360 seconds, then the arrival rate =30/3600
requests/sec.
A servicing channel that is kept busy for 1 hour is quantitatively
defined as 1 Erlang.
Hence, the offered traffic load (a) by Erlang is then
a=
30 Calls
3600 Sec
⋅
360 Sec
call
= 3 Erlangs
Cell Capacity
37. Call Blocking
How likely a new user can get a connection established
successfully? Admission control of new calls.
It is measured by the probability of call blocking, which
is a quality of service (QoS) factor, a.k.a., (GoS) factor.
Assume we have a total number of S channels in a radio
cell.
If the number of active users during any period of time
is S, then the call blocking probability is 1.
If and only if the number of ongoing calls is less than S,
the probability of call blocking will be less than 1.
38. Summary
The advantage of cellular communications
– Capacity extension by frequency reuse
– Cell cluster and cochannel cells
– Number of cells in a cluster
– Frequency reuse ratio
Cochannel interference
– Impact of cluster size
– Worst-case cochannel interference
Traffic load and call blocking probability
– Average delay
– Probability of queuing delay
Cell splitting and sectoring
Fixed channel allocation and dynamic channel allocation