This document provides an introduction and overview of mobile computing and related technologies. It begins with definitions of mobile computing and discusses characteristics like ubiquity, location awareness, and adaptation. It then covers applications of mobile computing like in vehicles, emergencies, and business. The document discusses generations of mobile communication technologies and different multiple access protocols like SDMA, TDMA, FDMA, and CDMA. It provides details on TDMA protocols including fixed TDM, Aloha, slotted Aloha, and CSMA.
Universal mobile telecommunication System (UMTS) is actually the third generation mobile, which uses WCDMA. The Dream was that 2G and 2.5G systems are incompatible around the world.
-Worldwide devices need to have multiple technologies inside of them, i.e. tri-band phones, dual-mode phones
To develop a single standard that would be accepted around the world.
-One device should be able to work anywhere.
Increased data rate.
- Maximum 2048Kbps
UMTS is developed by 3GPP (3 Generation Partnership Project) a joint venture of several organization
3G UMTS is a third-generation (3G): broadband, packet-based transmission of text, digitized voice, video, multimedia at data rates up to 2 Mbps
Also referred to as wideband code division multiple access(WCDMA)
Allows many more applications to be introduce to a worldwide
Also provide new services like alternative billing methods or calling plans.
The higher bandwidth also enables video conferencing or IPTV.
Once UMTS is fully available, computer and phone users can be constantly attached to the Internet wherever they travel and, as they roam, will have the same set of capabilities.
GPRS Architecture and its components are covered extensively.
The slides give a little information about gprs and also gets into deeper explanation of its architecture.
Universal mobile telecommunication System (UMTS) is actually the third generation mobile, which uses WCDMA. The Dream was that 2G and 2.5G systems are incompatible around the world.
-Worldwide devices need to have multiple technologies inside of them, i.e. tri-band phones, dual-mode phones
To develop a single standard that would be accepted around the world.
-One device should be able to work anywhere.
Increased data rate.
- Maximum 2048Kbps
UMTS is developed by 3GPP (3 Generation Partnership Project) a joint venture of several organization
3G UMTS is a third-generation (3G): broadband, packet-based transmission of text, digitized voice, video, multimedia at data rates up to 2 Mbps
Also referred to as wideband code division multiple access(WCDMA)
Allows many more applications to be introduce to a worldwide
Also provide new services like alternative billing methods or calling plans.
The higher bandwidth also enables video conferencing or IPTV.
Once UMTS is fully available, computer and phone users can be constantly attached to the Internet wherever they travel and, as they roam, will have the same set of capabilities.
GPRS Architecture and its components are covered extensively.
The slides give a little information about gprs and also gets into deeper explanation of its architecture.
IT6601 MOBILE COMPUTING UNITI
INTRODUCTION
Mobile Computing – Mobile Computing Vs wireless Networking – Mobile Computing Applications – Characteristics of Mobile computing – Structure of Mobile Computing Application. MAC Protocols – Wireless MAC Issues – Fixed Assignment Schemes – Random Assignment Schemes – Reservation Based Schemes.
In the seven-layer OSI model of computer networking, media access control (MAC) data communication protocol is a sublayer of the data link layer (layer 2). The MAC sublayer provides addressing and channel access control mechanisms that make it possible for several terminals or network nodes to communicate within a multiple access network that incorporates a shared medium, e.g. an Ethernet network. The hardware that implements the MAC is referred to as a media access controller.
The MAC sublayer acts as an interface between the logical link control (LLC) sublayer and the network's physical layer. The MAC layer emulates a full-duplex logical communication channel in a multi-point network. This channel may provide unicast, multicast or broadcast communication service.
LTE Basic Parameters, Data Rates, Duplexing & Accessing, Modulation, Coding & MIMO, Explanation of different nodes and Advantage & Disadvantages of different nodes.
Mobile Originated Call Process in Simple WordsAssim Mubder
Call Setup
Different procedures are necessary depending on the initiating and terminating party:
Mobile Originating Call MOC: Call setup, which are initiated by an MS
Mobile Terminating Call MTC: Call setup, where an MS is the called party
Mobile Mobile Call MMC: Call: setup between two mobile subscribers; MMC thus consists of the execution of a MOC and a MTC one after the other.
Mobile Internal Call MIC: a special case of MMC; both MSs are in the same MSC area, possibly even in the same cell.
Global system for mobile communication(GSM)Jay Nagar
~Introduction
~GSM Architecture
~GSM Entities
~SMS Service In GSM
~Call Routing In GSM
~PLMN Interfaces
~GSM Addresses and Identifiers
~Network aspects in GSM
~Handover
~Mobility Management
~GSM Frequency Allocation
~Authentication and Security In GSM
GSM-architecture-Location tracking and call setup- Mobility management- Handover-
Security-GSM SMS –International roaming for GSM- call recording functions-subscriber and
service data mgt –-Mobile Number portability -VoIP service for Mobile Networks – GPRS –
Architecture-GPRS procedures-attach and detach procedures-PDP context procedure-
combined RA/LA update procedures-Billing
IT6601 MOBILE COMPUTING UNITI
INTRODUCTION
Mobile Computing – Mobile Computing Vs wireless Networking – Mobile Computing Applications – Characteristics of Mobile computing – Structure of Mobile Computing Application. MAC Protocols – Wireless MAC Issues – Fixed Assignment Schemes – Random Assignment Schemes – Reservation Based Schemes.
In the seven-layer OSI model of computer networking, media access control (MAC) data communication protocol is a sublayer of the data link layer (layer 2). The MAC sublayer provides addressing and channel access control mechanisms that make it possible for several terminals or network nodes to communicate within a multiple access network that incorporates a shared medium, e.g. an Ethernet network. The hardware that implements the MAC is referred to as a media access controller.
The MAC sublayer acts as an interface between the logical link control (LLC) sublayer and the network's physical layer. The MAC layer emulates a full-duplex logical communication channel in a multi-point network. This channel may provide unicast, multicast or broadcast communication service.
LTE Basic Parameters, Data Rates, Duplexing & Accessing, Modulation, Coding & MIMO, Explanation of different nodes and Advantage & Disadvantages of different nodes.
Mobile Originated Call Process in Simple WordsAssim Mubder
Call Setup
Different procedures are necessary depending on the initiating and terminating party:
Mobile Originating Call MOC: Call setup, which are initiated by an MS
Mobile Terminating Call MTC: Call setup, where an MS is the called party
Mobile Mobile Call MMC: Call: setup between two mobile subscribers; MMC thus consists of the execution of a MOC and a MTC one after the other.
Mobile Internal Call MIC: a special case of MMC; both MSs are in the same MSC area, possibly even in the same cell.
Global system for mobile communication(GSM)Jay Nagar
~Introduction
~GSM Architecture
~GSM Entities
~SMS Service In GSM
~Call Routing In GSM
~PLMN Interfaces
~GSM Addresses and Identifiers
~Network aspects in GSM
~Handover
~Mobility Management
~GSM Frequency Allocation
~Authentication and Security In GSM
GSM-architecture-Location tracking and call setup- Mobility management- Handover-
Security-GSM SMS –International roaming for GSM- call recording functions-subscriber and
service data mgt –-Mobile Number portability -VoIP service for Mobile Networks – GPRS –
Architecture-GPRS procedures-attach and detach procedures-PDP context procedure-
combined RA/LA update procedures-Billing
Introduction: Mobile Communications, Mobile Computing – Paradigm, Promises/Novel Applications and Impediments and Architecture; Mobile and Handheld Devices, Limitations of Mobile and Handheld Devices.
GSM – Services, System Architecture, Radio Interfaces, Protocols, Localization, Calling, Handover, Security, New Data Services, GPRS, CSHSD, DECT.
This ppt define the basic concepts of mobile computing. It is the first part of mobile computing.
It defines the following terms
Introduction to mobile computing
Generations of mobile computing
Cellular concepts
Signalling, modulation and Demodulation
Spread Spectrum
Frequency Reuse
Multiple access schemes
GSM
GPRS
CDMA
UNIT I INTRODUCTION
Introduction to Mobile Computing – Applications of Mobile Computing- Generations of Mobile Communication Technologies- Multiplexing – Spread spectrum -MAC Protocols – SDMA- TDMA- FDMA- CDMA
In this Presentation explained about the Unit 5 - 4G Networks and Beyond concepts for third year ECE students, which makes very clear to understand all the Generation networks and its features and applications. Hope it will be useful to all student community.
IT2255 Web Essentials - Unit II Web Designingpkaviya
HTML - Form Elements - Input types and Media elements - HTML 5 - CSS3 - Selectors, Box Model, Backgrounds and Borders, Text Effects, Animations, Multiple Column Layout, User Interface.
IT2255 Web Essentials - Unit I Website Basicspkaviya
Internet Overview – Fundamental computer network concepts – Web Protocols – URL – Domain Name – Web Browsers and Web Servers – Working principle of a Website – Creating a Website – Client-side and server-side scripting.
BT2252 - ETBT - UNIT 3 - Enzyme Immobilization.pdfpkaviya
Enzymes are catalysts that perform all vital biological reactions within an organism’s body. Their distinguishing characteristic is that they endure the reaction unchanged.
Therefore, they can be utilised repeatedly. However, soluble enzymes are limited by their separation from the product and substrate.
The majority of Enzymes in a living organism are either connected to the cell membrane or encapsulated within the cells.
This result led to the hypothesis that pure separated enzymes may work better when immobilised on a solid substrate.
The phrase immobilised enzyme refers to “catalytically active enzymes that are physically limited or localised in a specific region of space and can be used again and continuously.”
The benefit of immobilisation is that it promotes work-up product isolation. Listed below are some potential advantages and disadvantages of immobility.
Soluble Enzyme + Substrate———– Product (single time usage of enzyme)
Immobilized Enzyme + Substrate———Product (Repeated usage of enzyme)
A number of essential considerations must be made when immobilising an enzyme.
The enzyme’s biological activity should be maintained.
The enzyme ought to be more stable than its soluble equivalent.
The price of immobilisation shouldn’t be excessively high.
The relationship between humans and enzymes has evolved over time. Even during historical times, where there was no concept of enzymes, ancient Egypt people produced beer and wine by enzymatic fermentation. After several thousand years, enzymatic studies have significantly progressed. Enzymes are proteins that accelerate many biochemical and chemical reactions. They are natural catalysts and are ubiquitous, in plants, animals, and microorganisms, where they catalyze processes that are vital to living organisms. The growing knowledge and technique improvement about protein extraction and purification lead to the production of many enzymes at an analytical grade purity for research and biotechnological applications. Enzymes are intimately involved in a wide variety of traditional food processes, such as cheese making, beer brewing, and wine industry. Recent advances in biotechnology, particularly in protein engineering, have provided the basis for the efficient development of enzymes with improved properties. This has led to establishment of novel, tailor-made enzymes for completely new applications, where enzymes were not previously used. The technology of immobilized enzymes is still going through a phase of evolution and maturation. Evolution is reflected in the ever-broadening range of applications of immobilized enzymes. Maturation is mirrored in the development of the theory of how immobilized enzymes function and how the technique of immobilization is related to their primary structure through the formation and configuration of their three dimensional structure. There still remains much room for the development of useful processes and materials based on this hard-won understanding.
Forklift Classes Overview by Intella PartsIntella Parts
Discover the different forklift classes and their specific applications. Learn how to choose the right forklift for your needs to ensure safety, efficiency, and compliance in your operations.
For more technical information, visit our website https://intellaparts.com
Hybrid optimization of pumped hydro system and solar- Engr. Abdul-Azeez.pdffxintegritypublishin
Advancements in technology unveil a myriad of electrical and electronic breakthroughs geared towards efficiently harnessing limited resources to meet human energy demands. The optimization of hybrid solar PV panels and pumped hydro energy supply systems plays a pivotal role in utilizing natural resources effectively. This initiative not only benefits humanity but also fosters environmental sustainability. The study investigated the design optimization of these hybrid systems, focusing on understanding solar radiation patterns, identifying geographical influences on solar radiation, formulating a mathematical model for system optimization, and determining the optimal configuration of PV panels and pumped hydro storage. Through a comparative analysis approach and eight weeks of data collection, the study addressed key research questions related to solar radiation patterns and optimal system design. The findings highlighted regions with heightened solar radiation levels, showcasing substantial potential for power generation and emphasizing the system's efficiency. Optimizing system design significantly boosted power generation, promoted renewable energy utilization, and enhanced energy storage capacity. The study underscored the benefits of optimizing hybrid solar PV panels and pumped hydro energy supply systems for sustainable energy usage. Optimizing the design of solar PV panels and pumped hydro energy supply systems as examined across diverse climatic conditions in a developing country, not only enhances power generation but also improves the integration of renewable energy sources and boosts energy storage capacities, particularly beneficial for less economically prosperous regions. Additionally, the study provides valuable insights for advancing energy research in economically viable areas. Recommendations included conducting site-specific assessments, utilizing advanced modeling tools, implementing regular maintenance protocols, and enhancing communication among system components.
Vaccine management system project report documentation..pdfKamal Acharya
The Division of Vaccine and Immunization is facing increasing difficulty monitoring vaccines and other commodities distribution once they have been distributed from the national stores. With the introduction of new vaccines, more challenges have been anticipated with this additions posing serious threat to the already over strained vaccine supply chain system in Kenya.
Cosmetic shop management system project report.pdfKamal Acharya
Buying new cosmetic products is difficult. It can even be scary for those who have sensitive skin and are prone to skin trouble. The information needed to alleviate this problem is on the back of each product, but it's thought to interpret those ingredient lists unless you have a background in chemistry.
Instead of buying and hoping for the best, we can use data science to help us predict which products may be good fits for us. It includes various function programs to do the above mentioned tasks.
Data file handling has been effectively used in the program.
The automated cosmetic shop management system should deal with the automation of general workflow and administration process of the shop. The main processes of the system focus on customer's request where the system is able to search the most appropriate products and deliver it to the customers. It should help the employees to quickly identify the list of cosmetic product that have reached the minimum quantity and also keep a track of expired date for each cosmetic product. It should help the employees to find the rack number in which the product is placed.It is also Faster and more efficient way.
Explore the innovative world of trenchless pipe repair with our comprehensive guide, "The Benefits and Techniques of Trenchless Pipe Repair." This document delves into the modern methods of repairing underground pipes without the need for extensive excavation, highlighting the numerous advantages and the latest techniques used in the industry.
Learn about the cost savings, reduced environmental impact, and minimal disruption associated with trenchless technology. Discover detailed explanations of popular techniques such as pipe bursting, cured-in-place pipe (CIPP) lining, and directional drilling. Understand how these methods can be applied to various types of infrastructure, from residential plumbing to large-scale municipal systems.
Ideal for homeowners, contractors, engineers, and anyone interested in modern plumbing solutions, this guide provides valuable insights into why trenchless pipe repair is becoming the preferred choice for pipe rehabilitation. Stay informed about the latest advancements and best practices in the field.
Sachpazis:Terzaghi Bearing Capacity Estimation in simple terms with Calculati...Dr.Costas Sachpazis
Terzaghi's soil bearing capacity theory, developed by Karl Terzaghi, is a fundamental principle in geotechnical engineering used to determine the bearing capacity of shallow foundations. This theory provides a method to calculate the ultimate bearing capacity of soil, which is the maximum load per unit area that the soil can support without undergoing shear failure. The Calculation HTML Code included.
Automobile Management System Project Report.pdfKamal Acharya
The proposed project is developed to manage the automobile in the automobile dealer company. The main module in this project is login, automobile management, customer management, sales, complaints and reports. The first module is the login. The automobile showroom owner should login to the project for usage. The username and password are verified and if it is correct, next form opens. If the username and password are not correct, it shows the error message.
When a customer search for a automobile, if the automobile is available, they will be taken to a page that shows the details of the automobile including automobile name, automobile ID, quantity, price etc. “Automobile Management System” is useful for maintaining automobiles, customers effectively and hence helps for establishing good relation between customer and automobile organization. It contains various customized modules for effectively maintaining automobiles and stock information accurately and safely.
When the automobile is sold to the customer, stock will be reduced automatically. When a new purchase is made, stock will be increased automatically. While selecting automobiles for sale, the proposed software will automatically check for total number of available stock of that particular item, if the total stock of that particular item is less than 5, software will notify the user to purchase the particular item.
Also when the user tries to sale items which are not in stock, the system will prompt the user that the stock is not enough. Customers of this system can search for a automobile; can purchase a automobile easily by selecting fast. On the other hand the stock of automobiles can be maintained perfectly by the automobile shop manager overcoming the drawbacks of existing system.
Student information management system project report ii.pdfKamal Acharya
Our project explains about the student management. This project mainly explains the various actions related to student details. This project shows some ease in adding, editing and deleting the student details. It also provides a less time consuming process for viewing, adding, editing and deleting the marks of the students.
Welcome to WIPAC Monthly the magazine brought to you by the LinkedIn Group Water Industry Process Automation & Control.
In this month's edition, along with this month's industry news to celebrate the 13 years since the group was created we have articles including
A case study of the used of Advanced Process Control at the Wastewater Treatment works at Lleida in Spain
A look back on an article on smart wastewater networks in order to see how the industry has measured up in the interim around the adoption of Digital Transformation in the Water Industry.
About
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
• Remote control: Parallel or serial interface.
• Compatible with MAFI CCR system.
• Compatible with IDM8000 CCR.
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
• Easy in configuration using DIP switches.
Technical Specifications
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
Key Features
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
• Remote control: Parallel or serial interface
• Compatible with MAFI CCR system
• Copatiable with IDM8000 CCR
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
Application
• Remote control: Parallel or serial interface.
• Compatible with MAFI CCR system.
• Compatible with IDM8000 CCR.
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
• Easy in configuration using DIP switches.
2. Unit I - Introduction
Introduction to Mobile Computing - Applications of
Mobile Computing - Generations of Mobile
Communication Technologies - MAC Protocols -
SDMA - TDMA - FDMA - CDMA
3. Introduction to Mobile Computing
• What is computing?
– The capability to automatically carry out certain processing related to service
invocations on a remote computer.
• What is the mobility?
– The capability to change location while communicating to invoke computing
service at some remote computers.
• Mobile Computing is an umbrella term used to describe technologies that enable
people to access network services anyplace, anytime, and anywhere.
• Advantage: Flexibility to the users.
4. Introduction to Mobile Computing
User Mobility Vs. Device Mobility
• User Mobility: Refers to a user who has access to the same or similar
telecommunication services at different places. (i.e.) the user can be mobile, and the
services will follow him or her.
• Device Mobility: The communication device moves. Many mechanisms in the
network and inside the device have to make sure that communication is still
possible while the device is moving.
5. Introduction to Mobile Computing
Mobile Computing Vs. Wireless Networking
• Mobile computing is based on wireless networking and helps to invoke computing
services on remote servers while on the move.
• So Wireless networking is an important and necessary ingredient of mobile
computing.
• Mobile computing also requires the applications themselves – their design and
development, the hardware at the client and server sides.
6. Introduction to Mobile Computing
Mobile Computing Vs. Wireless Networking
Mobile Computing Wireless Networking
The ability to compute while on
the move.
Basic communication
infrastructure which is necessary for
mobile computing.
It comes under the category of
computing.
It comes under the category of
networking.
Mobile computing is a part of
wireless networking.
Wireless networking is not a part of
mobile computing.
7. Introduction to Mobile Computing
Characteristics of Mobile Computing
• Ubiquity: The ability of a user to perform computation from anywhere and at
anytime. (Eg: Business Notifications)
• Location awareness: Many applications requires or value additions by location
based services. (Eg: Traffic Control Applications – GPS)
• Adaptation: Ability to adjust to bandwidth fluctuations without inconveniencing the
user. Fluctuations can arise due to a number of factors such as handoff, obstacles,
environmental noise, etc.
• Broadcast: Efficient delivery of data can be made simultaneously to hundreds of
mobile users. (Eg: Advertising information by a taxi service provider)
• Personalization: Services in a mobile environment can be easily personalized
according to a user‟s profile.
8. Introduction to Mobile Computing
Characteristics of Communication Devices
• Fixed and Wired: Desktop Computers
• Mobile and Wired: Laptops
• Fixed and Wireless: Cameras with network connectivity
• Mobile and Wireless: Mobile Phones
9. Applications of Mobile Computing
• Vehicles
• Emergencies
• Business
• Replacement of wired networks
• Infotainment and more
• Location dependent services
– Follow-on services
– Location aware services
– Privacy
– Information services
– Support services
• Mobile and Wireless devices
– Sensors
– Embedded controllers
– Pager
– Mobile phones
– Personal Digital Assistant (PDA)
– Pocket computer
– Notebook / laptop
10. Applications of Mobile Computing
• Vehicles
– Transmission of news, road condition, weather, music via DAB
– Personal communication using GSM
– Position via GPS
– Local ad-hoc network with vehicles close-by to prevent accidents, guidance
system, redundancy
– Vehicle data (e.g., from busses, high-speed trains) can be transmitted in advance
for maintenance
• Emergencies
– Early transmission of patient data to the hospital, current status, first diagnosis
– Replacement of a fixed infrastructure in case of earthquakes, hurricanes, fire etc.
11. Applications of Mobile Computing
UMTS, WLAN,
DAB, DVB, GSM,
cdma2000, TETRA, ...
Personal Travel Assistant,
PDA, Laptop,
GSM, UMTS, WLAN,
Bluetooth, ...
13. Applications of Mobile Computing
• Business
– Direct access to customer files stored in a central location
– Consistent databases for all agents
– Mobile office
• Replacement of wired networks
– Remote sensors, e.g., weather, earth activities (Due to economic reasons)
– Flexibility for trade shows
– LANs in historic buildings
• Infotainment and more
– Outdoor Internet access
– Intelligent travel guide with up-to-date location dependent information
– Ad-hoc networks for multi user games
14. Applications of Mobile Computing
• Location dependent services
– Follow-on services
• Automatic call-forwarding, transmission of the actual workspace to the current
location
– Location aware services
• What services, e.g., printer, fax, phone, server etc. exist in the local environment
– Privacy
• Who should gain knowledge about the location
– Information services
• “push”: e.g., current special offers in the supermarket
• “pull”: e.g., where is the Black Forrest Cherry Cake?
– Support services
• Caches, intermediate results, state information etc. „follow“ the mobile device
through the fixed network
15. Applications of Mobile Computing
• Mobile and Wireless Devices
– Sensor
– Embedded controllers
– Pager
– Mobile phones
performance
Pager
• Receive only
• Tiny displays
• Simple text messages
Mobile Phones
• Voice, data
• Simple graphical displays
PDA
• Graphical displays
• Character recognition
• Simplified WWW
Packet PC
• Tiny keyboard
• Simple versions of standard
applications
Laptop/Notebook
• Fully functional
• Standard applications
Sensors,
embedded
controllers
• Mobile and Wireless Devices
– Personal Digital Assistant
– Pocket computer
– Notebook/Laptop
16. Mobile Computing - Advantages & Disadvantages
• Advantages
– Location Flexibility
– Device Portability
– User Mobility
– Saves Time
– Enhanced Productivity
– Entertainment
• Disadvantages
– Less range and bandwidth
– Less secure
– Less power storage
– More Interference
– Limited user interfaces
– Loss of data
– High risk to health
17. Generations of Mobile Communication Technologies
• 1979 NMT (Nordic Mobile Telephone) at 450MHz (Scandinavian countries)
• 1982 Start of GSM-specification
– Goal: pan-European digital mobile phone system with roaming
• 1983 Start of the American AMPS (Advanced Mobile Phone System, analog)
• 1984 CT-1 standard (Europe) for cordless telephones
• 1986 C-Netz in Germany
– Analog voice transmission, 450MHz, hand-over possible, digital signaling,
automatic location of mobile device
– It was in use until 2000, services: FAX, modem, X.25, e-mail, 98% coverage
18. Generations of Mobile Communication Technologies
• 1991 Specification of DECT
– Digital European Cordless Telephone (today: Digital Enhanced Cordless
Telecommunications)
– Spectrum 1880-1900MHz, ~100-500m range, 120 duplex channels, 1.2Mbit/s
data transmission, voice encryption, authentication, support up to several 10000
user/km2, used in more than 110 countries
• 1992 Start of GSM
– 900MHz, 124 full duplex channels
– Full international roaming, automatic location services, authentication, encryption
on wireless link, efficient interoperation with ISDN systems, high audio quality.
– Services: data with 9.6kbit/s, SMS, FAX, Voice.
19. Generations of Mobile Communication Technologies
• 1994 E-Netz in Germany
– GSM with 1800MHz, smaller cells
• 1996 HiperLAN (High Performance Radio Local Area Network)
– Type 1: 5.2GHz, 23.5Mbit/s
– Type 2 and 3 (both 5GHz) and Type 4 (17GHz)
• 1997 Wireless LAN - IEEE802.11
– IEEE standard, 2.4 GHz and infrared, 2Mbit/s
• 1998 Specification of GSM successors
– For UMTS (Universal Mobile Telecommunication System) as European
proposals for IMT-2000
• 1998 Iridium
– 66 satellites (+6 spare), 1.6GHz to the mobile phone
20. Generations of Mobile Communication Technologies
• 1999 Standardization of additional wireless LANs
– IEEE standard 802.11b, 2.4GHz, 11Mbit/s
– Bluetooth for piconets, 2.4GHz, <1Mbit/s
• Decision about IMT-2000
– Several “members” of a “family”: UMTS, CDMA2000, DECT.
– Start of WAP (Wireless Application Protocol) and i-mode
– First step towards a unified Internet/mobile communication system
– Access to many services via the mobile phone
• 2000 GSM with higher data rates
– HSCSD, GPRS, UMTS
• 2001 Start of 3G systems
– CDMA2000 in Korea, UMTS tests in Europe, FOMA (almost UMTS) in Japan
22. MAC Protocols
• The MAC protocol is a sub-layer of the data link layer protocol and it directly invokes
the physical layer protocol.
• A channel-access scheme is also based on a multiple access protocol and control
mechanism, also known as media access control (MAC).
• This protocol deals with issues such as addressing, assigning multiplex channels to
different users, and avoiding collisions.
23. Responsibility & Objective of MAC Protocol
• Responsibility: Enforce discipline in the access of a shared channel when multiple
nodes contend to access that channel.
• Objective: Maximization of the utilization of the channel and minimization of average
latency of transmission.
24. Properties Required of MAC Protocols
• The design of a MAC protocol depends upon the specific environment in which it is
intended to operate and the specific characteristics of the application for which it is
being designed.
• A good MAC protocol needs to possess the following features:
– It should implement some rules that help to enforce discipline when multiple
nodes contend for a shared channel.
– It should help maximize the utilization of the channel.
– Channel allocation needs to be fair. No node should be discriminated against at
any time and made to wait for an unduly long time for transmission.
– It should be capable of supporting several types of traffic having different
maximum and average bit rates.
– It should be robust in the face of equipment failures and changing network
conditions.
25. Wireless MAC Protocols: Some Issues
• It is difficult to implement a collision detection scheme in a wireless environment,
since collisions are hard to be detected.
• In infrastructure-less networks, the issue of hidden and exposed terminals & near and
far terminals make a MAC protocol extremely inefficient.
26. Hidden and Exposed Terminals
Hidden terminals
• A sends to B, C cannot hear A
• C wants to send to B, C senses a “free” medium (Carrier Sense fails)
• Collision at B, A cannot receive the collision (Collision Detection fails)
• C is “hidden” from A
Exposed terminals
• B sends to A, C wants to send to another terminal (not A or B)
• C senses the carrier and detects that the carrier is busy
• C postponed its transmission until it detects the medium become idle
• But A is outside radio range of C, waiting is not necessary (unnecessary delay)
• C is “exposed” to B
27. Near and Far Terminals
Terminals A and B send, C receives
• Signal strength decreases proportional to the square of the distance
• B‟s signal drowns out A‟s signal
• C cannot receive A
• If C was an arbiter, B would drown out A
• Near/far effect is a severe problem for CDMA networks
• Precise power control needed to receive all senders with the same strength at a receiver.
28. Space Division Multiple Access (SDMA)
• Used for allocating a separate space to users in wireless
networks.
• Application involves assigning an optimal base station to a
mobile phone user.
• The mobile phone may receive several base stations with
different quality.
• A MAC algorithm should decide which base station is best,
taking into account which frequencies (FDM), time slots
(TDM), or code (CDM) are still available.
• SDMA is never used in isolation.
• Always works in combination with one or more other
schemes.
• SDMA algorithm is formed by cells and sectors.
• Single users are separated in space by individual beams.
29. Time Division Multiple Access (TDMA)
• Flexible scheme, which comprises all technologies that allocate certain time slots for
communication.
• Now tuning into a certain frequency is not necessary (i.e.) the receiver can stay at the
same frequency the whole time.
• Synchronization between sender and receiver has to be achieved in the time domain.
• This can be done by using a fixed pattern similar to FDMA technique, (i.e.) allocating
a certain time slot for a channel, or by using a dynamic allocation scheme
30. Time Division Multiple Access (TDMA)
1. Fixed TDM
• Simplest algorithm for using TDM is allocating time slots for channels in fixed
pattern.
• Assign the fixed sending frequency to a transmission channel between a sender and
a receiver for a certain amount of time.
• If synchronization is assured, each mobile station knows its turn and no interference
will happen.
• Fixed access patterns fit perfectly well for connections with a fixed bandwidth.
• This patterns guarantee a fixed delay - one can transmit.
• TDMA schemes with fixed access patterns are used in IS-54, IS-136, GSM, DECT.
31. Time Division Multiple Access (TDMA)
1. Fixed TDM
• Used to implement multiple access and a duplex
channel between a base station and mobile station.
• Assigning different slots for uplink and downlink
using the same frequency is called Time Division
Duplex (TDD).
• The base station uses one out of 12 slots for the
downlink, whereas the mobile station uses one out
of 12 different slots for the uplink.
• A lot of bandwidth is wasted, if the station has no
data to transmit.
32. Time Division Multiple Access (TDMA)
2. Classical Aloha
• Neither coordinates medium access nor does it resolve contention on the MAC layer.
• Instead, each station can access the medium at any time.
• Random access scheme, without a central arbiter controlling access and without
coordination among the stations.
• If two or more stations access the medium at the same time, a collision occurs and the
transmitted data is destroyed.
• Resolving this problem is left to higher layers (e.g., retransmission of data).
• It works fine for a light load and does not require any complicated access
mechanisms.
• Data packet arrival follows a Poisson distribution, maximum throughput is achieved
for an 18 percent load.
34. Time Division Multiple Access (TDMA)
3. Slotted Aloha
• All senders have to be synchronized, transmission can only start at the beginning
of a time slot.
• Still, access is not coordinated.
• Introduction of slots raises the throughput from 18 percent to 36 percent,
(i.e.) slotting doubles the throughput.
• Aloha systems work perfectly well under a light load.
• But they cannot give any hard transmission guarantees, such as maximum delay
before accessing the medium, or minimum throughput.
• New mobile communication systems like UMTS have to rely on slotted Aloha for
medium access in certain situations.
35. Time Division Multiple Access (TDMA)
4. Carrier Sense Multiple Access (CSMA)
• CSMA - One improvement to the basic Aloha is sensing the carrier before
accessing the medium.
• Sensing the carrier and accessing the medium only if the carrier is idle decreases
the probability of a collision.
• Here hidden terminals cannot be detected, so, if a hidden terminal transmits at the
same time as another sender, a collision might occur at the receiver.
• This basic scheme is still used in most wireless LANs.
• Non-persistent CSMA - Stations sense the carrier and start sending immediately
if the medium is idle. If the medium is busy, the station pauses a random amount of
time before sensing the medium again and repeating this pattern.
36. Time Division Multiple Access (TDMA)
4. Carrier Sense Multiple Access (CSMA)
• In p-persistent CSMA systems nodes also sense the medium, but only transmit
with a probability of p, with the station deferring to the next slot with the
probability 1-p, i.e., access is slotted in addition.
• In 1-persistent CSMA systems, all stations wishing to transmit access the medium
at the same time, as soon as it becomes idle. This will cause many collisions if
many stations wish to send and block each other. To create some fairness for
stations waiting for a longer time, back-off algorithms can be introduced , which
are sensitive to waiting time as this is done for standard Ethernet.
37. Time Division Multiple Access (TDMA)
4. Carrier Sense Multiple Access (CSMA)
• CSMA with Collision Avoidance (CSMA/CA) is used in wireless LANs
following the standard IEEE 802.11. Here sensing the carrier is combined with a
back-off scheme in case of a busy medium to achieve some fairness among
competing stations.
• Elimination yield - non-preemptive multiple access (EY-NMPA) used in the
HIPERLAN 1 specification. Here several phases of sensing the medium and
accessing the medium for contention resolution are interleaved before one
“winner” can finally access the medium for data transmission. Here, priority
schemes can be included to assure preference of certain stations with more
important data.
38. Time Division Multiple Access (TDMA)
5. Demand Assigned Multiple Access (DAMA)
• Reservation mechanisms and combinations with some (fixed) TDM patterns.
• It typically have a reservation period followed by a transmission period.
• During the reservation period, stations can reserve future slots in the transmission
period.
• Collisions may occur during the reservation period, the transmission period can
then be accessed without collision.
• These schemes cause a higher delay under a light load (first the reservation has to
take place), but allow higher throughput due to less collisions.
• It is also called reservation Aloha, a scheme typical for satellite systems.
39. Time Division Multiple Access (TDMA)
5. Demand Assigned Multiple Access (DAMA)
• DAMA has two modes. During a contention phase following the slotted Aloha
scheme, all stations can try to reserve future slots.
• Collisions during the reservation phase do not destroy data transmission, but only
the short requests for data transmission.
• If successful, a time slot in the future is reserved, and no other station is allowed to
transmit during this slot.
• To maintain the fixed TDM pattern of reservation and transmission, the stations
have to be synchronized from time to time.
• DAMA is an explicit reservation scheme. Each transmission slot has to be
reserved explicitly.
41. Time Division Multiple Access (TDMA)
6. Packet Reservation Multiple Access (PRMA)
• An Implicit reservation scheme.
• A certain number of slots form a frame, frames are repeated in time.
• A base station, which could be a satellite, now broadcasts the status of each slot to all
mobile stations.
• All stations receiving this vector will then know which slot is occupied and which slot
is currently free.
42. Time Division Multiple Access (TDMA)
6. Packet Reservation Multiple Access (PRMA)
• The base station broadcasts the reservation status „ACDABA-F‟ to all stations, here
A to F.
• This means that slots one to six and eight are occupied, but slot seven is free in the
following transmission.
• Stations compete for empty slots using slotted aloha.
• Once station reserves a slot successfully, slot is assigned to this station in all
following frames as long as the station has data to send.
• Competition for a slot starts again once slot was empty in last frame.
43. Time Division Multiple Access (TDMA)
7. Reservation TDMA
• In a fixed TDM scheme N mini-slots followed by N*k data-slots form a frame that is
repeated.
• Every station has its own mini-slot and can use it to reserve up to k data-slots.
• This guarantees each station a certain bandwidth and a fixed delay.
• Other stations can send data in unused data-slots according to a round-robin sending
scheme (best-effort traffic)
44. Time Division Multiple Access (TDMA)
8. Multiple Access Collision Avoidance (MACA)
• MACA uses short signaling packets for collision avoidance
– RTS (request to send): A sender uses RTS packet to request right to send before it
sends a data packet
– CTS (clear to send): The receiver grants the right to send as soon as it is ready to
receive
• Signaling packets contain
– sender address
– receiver address
– packet size
• Variants of this method can be found in IEEE802.11 as DFWMAC (Distributed
Foundation Wireless MAC)
45. Time Division Multiple Access (TDMA)
8. Multiple Access Collision Avoidance
• MACA avoids the problem of hidden
terminals
– A and C want to send to B
– A sends RTS first
– C waits after receiving CTS from B
• MACA avoids the problem of exposed
terminals
– B wants to send to A, C to another
terminal
– Now C does not have to wait for it
cannot receive CTS from A
46. Time Division Multiple Access (TDMA)
8. Multiple Access Collision Avoidance (MACA)
• The sender is idle until a user requests the transmission of a data packet.
• The sender then issues an RTS and waits for the right to send.
• If the receiver gets an RTS and is in an idle state, it sends back a CTS and waits for
data.
• The sender receives the CTS and sends the data.
• Otherwise, the sender would send an RTS again after a time-out (e.g., the RTS could
be lost or collided).
• After transmission of the data, the sender waits for a positive acknowledgement to
return into an idle state.
• The receiver sends back a positive acknowledgement if the received data was
correct.
47. Time Division Multiple Access (TDMA)
8. Multiple Access Collision Avoidance (MACA)
• If not, or if the waiting time for data is too long, the receiver returns into idle state.
• If the sender does not receive any acknowledgement or a negative
acknowledgement, it sends an RTS and again waits for the right to send.
• Alternatively, a receiver could indicate that it is currently busy via a separate
RxBusy.
48. Time Division Multiple Access (TDMA)
9. Polling
• Where one station is to be heard by all others, polling scheme can be applied.
• Strictly centralized scheme - one master station and several slave station.
• The master can poll slaves: using round robin, randomly, according to reservation, etc.
• The master could also establish a list of stations wishing to transmit during contention
phase.
• After this phase, the station polls each station polls each station on the list.
• Schemes are used in Bluetooth wireless LAN.
49. Time Division Multiple Access (TDMA)
10. Inhabit Sense Multiple Access (ISMA)
• Current state of the medium is signaled via a “busy tone”.
• The base station signals on the downlink (base station to terminals) if the medium is
free or not.
• Terminals must not send if the medium is busy.
• Terminals can access the medium as soon as the busy tone stops.
• The base station signals collisions and successful transmissions via the busy tone and
acknowledgements, respectively.
• Mechanism used, e.g., for CDPD (USA, integrated into AMPS) – Digital Sense
Multiple Access
50. Frequency Division Multiple Access (FDMA)
• The available bandwidth is divided into many narrower frequency bands called channels.
• Frequency Division Duplex (FDD) - For full duplex communication to take place, each
user is allocated with
– Forward link – Communicating from MS to BS.
– Reverse link – Communication from BS to MS.
• Thus, each user making a call is allocated two unique frequency bands (channels) for
transmitting and receiving signals during the call.
• When the user is underway, no other user would be allocated the same frequency band to
make a call.
• Unused transmission time in a frequency band that occurs when the allocated caller pauses
between transmissions, or when no user is allocated a band, goes idle and is wasted.
• FDMA does not achieve high channel utilization.
51. Frequency Division Multiple Access (FDMA)
• All uplinks use the band between 890.2 and 915 MHz, all downlinks use 935.2 to 960
MHz.
• According to FDMA, the base station allocates a certain frequency for up- and
downlink to establish a duplex channel with a mobile phone.
• Up- and downlink have a fixed relation. If the uplink frequency is fu = 890 MHz +
n*0.2 MHz, the downlink frequency is fd = fu + 45 MHz, (i.e.) fd = 935 MHz + n*0.2
MHz for a certain channel n.
• Permanent (e.g., radio broadcast), slow hopping (e.g., GSM), fast hopping (FHSS,
Frequency Hopping Spread Spectrum)
52. Code Division Multiple Access (CDMA)
• Multiple users are allotted different codes that consists of sequences of 0 and 1 to access
the same channel.
• In CDMA, multiple users use the same frequency at the same time and no time
scheduling is applied.
• The bandwidth of this medium is much larger than the space that would be allocated to
each packet transmission during FDMA and the signals can be distinguished from each
other by means of a special coding schemes that is used.
• This is done with the help of a frequency spreading code known as the m-bit pseudo-
noise (PN) code sequence.
• Using m bits, 2^m-1 different codes can be obtained.
• From these codes, each user will use only one code.
• A code for a user should be orthogonal to the codes assigned to other nodes.
53. Code Division Multiple Access (CDMA)
Justify that a Barker code has good autocorrelation.
• A code for a certain user should have a good autocorrelation and should be orthogonal
to other codes.
• The Barker code (+1, –1, +1, +1, –1, +1, +1, +1, –1, –1, –1), for example, has a good
autocorrelation, (i.e.) the inner product with itself is large, the result is 11.
54. Code Division Multiple Access (CDMA)
• All terminals send on same frequency at the same time using entire bandwidth of
transmission channel.
• Each sender has a unique random number, sender XORs the signal with this random
number.
• The receiver can “tune” into this signal if it knows the pseudo random number.
Advantages:
• All terminals can use the same frequency, no planning needed.
• Huge code space compared to frequency space.
• Interference is not coded.
• Forward error correction and encryption can be easily integrated.
Disadvantages:
• Higher complexity of a receiver.
• All signals should have the same strength at a receiver.
55. Code Division Multiple Access (CDMA)
• Sender A
– sends Ad = 1, key Ak = 010011 (assign: “0”= -1, “1”= +1)
– sending signal As = Ad * Ak = (-1, +1, -1, -1, +1, +1)
• Sender B
– sends Bd = 0, key Bk = 110101 (assign: “0”= -1, “1”= +1)
– sending signal Bs = Bd * Bk = (-1, -1, +1, -1, +1, -1)
• Both signals superimpose in space
– interference neglected (noise etc.)
– As + Bs = (-2, 0, 0, -2, +2, 0)
• Receiver wants to receive signal from sender A
– apply key Ak bitwise (inner product)
• Ae = (-2, 0, 0, -2, +2, 0) · Ak = 2 + 0 + 0 + 2 + 2 + 0 = 6
• result greater than 0, therefore, original bit was “1”
– receiving B
• Be = (-2, 0, 0, -2, +2, 0) · Bk = -2 + 0 + 0 - 2 - 2 + 0 = -6, i.e. “0”