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  1. 1. DILLA UNIVERSITY COLLEGE OF ENGINEERING & TECHNOLOGY School of Computing & Informatics M. Sc in Computer Science & Networking By Chapter-01 Dr. Ananda Kumar K S M.Tech, Ph.D Associate Professor, School of Comp & Info Email: anandgdk@du.edu.et COET, Dilla University 1 Course Number CN6117 Course Title Mobile Computing
  2. 2. Mobile Computing CHAPTER-01 1. Mobile Networking 2. Applications of wireless networks and mobile communications 3. Multiple Access Schemes COET, Dilla University 2
  3. 3. 1. Mobile Networking  Mobile networking refers to technology that can support voice and/or data network connectivity using wireless, via a radio transmission solution. The most familiar application of mobile networking is the mobile phone.  Over the last few decades, mobile radio communications have become ubiquitous throughout the world.  People have become accustomed to the technology through commercial mobile phones. COET, Dilla University 3
  4. 4. Cont..  The mobile network infrastructure that enables communications has become a normal part of urban environment in which people live.  There is also great number of other mobile radio applications essential in the modern world that are used in navigation, transportation, machine-to-machine communications (M2M), robotics, emergency and low enforcement services, broadcasting, space exploration, the military and so on. COET, Dilla University 4
  5. 5. Cont..  Each application was developed on the basis of specific needs and, in some aspects, the mobile radio networks for emergency services and commercial mobile services are different.  Nonetheless, the underlying principles in mobile communications, such as radio link design given performance constraints, separation of control and traffic channels, mobility support, principles of the channel allocation in the cell, radio network management and so on, have lots in common in many applications. COET, Dilla University 5
  6. 6. Cont..  Many people will be mobile – already one of the key characteristics of today’s society.  Think, for example, of an aircraft with 800 seats. Modern aircraft already offer limited network access to passengers, and aircraft of the next generation will offer easy Internet access.  In this scenario, a mobile network moving at high speed above ground with a wireless link will be the only means of transporting data to and from passengers.  Think of cars with Internet access and billions of embedded processors that have to communicate with, for instance, cameras, mobile phones, CD-players, headsets, keyboards, intelligent traffic signs and sensors.  This plethora of devices and applications show the great importance of mobile communications today. COET, Dilla University 6
  7. 7. Cont..  Before presenting more applications, the terms ‘mobile’ and ‘wireless’ as used throughout this course should be defined.  There are two different kinds of mobility: user mobility and device portability. COET, Dilla University 7
  8. 8. User mobility and Device portability User 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.  Examples for mechanisms supporting user mobility are simple call-forwarding solutions known from the telephone or computer desktops supporting roaming (i.e., the desktop looks the same no matter which computer a user uses to log into the network). Device portability • With device portability, the communication device moves (with or without a user). • Many mechanisms in the network and inside the device have to make sure that communication is still possible while the device is moving. • A typical example for systems supporting device portability is the mobile phone system, where the system itself hands the device from one radio transmitter (also called a base station) to the next if the signal becomes too weak COET, Dilla University 8
  9. 9. A communication device can thus exhibit one of the following characteristics:  Fixed and wired: This configuration describes the typical desktop computer in an office. The devices use fixed networks for performance reasons.  Mobile and wired: Many of today’s laptops fall into this category; users carry the laptop from one place to the next, reconnecting to the company’s network via the telephone network and a modem.  Fixed and wireless: This mode is used for installing networks, e.g., in historical buildings to avoid damage by installing wires, or at trade shows to ensure fast network setup.  Mobile and wireless: This is the most interesting case. No cable restricts the user, who can roam between different wireless networks. Most technologies discussed in this course deal with this type of device and the networks supporting them. Today’s most successful example for this category is GSM with more than 800 million users. COET, Dilla University 9
  10. 10. COET, Dilla University Elements of a wireless network network infrastructure 10
  11. 11. COET, Dilla University wireless hosts  laptop, smartphone  run applications  may be stationary (non- mobile) or mobile  wireless does not always mean mobility Elements of a wireless network network infrastructure 11
  12. 12. COET, Dilla University infrastructure mode  base station connects mobiles into wired network  handoff: mobile changes base station providing connection into wired network Elements of a wireless network network infrastructure 12
  13. 13. COET, Dilla University Characteristics of selected wireless links Indoor 10-30m Outdoor 50-200m Mid-range outdoor 200m – 4 Km Long-range outdoor 5Km – 20 Km .056 .384 1 4 5-11 54 2G: IS-95, CDMA, GSM 2.5G: UMTS/WCDMA, CDMA2000 802.15 802.11b 802.11a,g 3G: UMTS/WCDMA-HSPDA, CDMA2000-1xEVDO 4G: LTWE WIMAX 802.11a,g point-to-point 200 802.11n Data rate (Mbps) 13
  14. 14. COET, Dilla University infrastructure mode  base station connects mobiles into wired network  handoff: mobile changes base station providing connection into wired network Elements of a wireless network network infrastructure 14
  15. 15. COET, Dilla University ad hoc mode  no base stations  nodes can only transmit to other nodes within link coverage  nodes organize themselves into a network: route among themselves Elements of a wireless network 15
  16. 16. COET, Dilla University Wireless network taxonomy single hop multiple hops infrastructure (e.g.,APs) no infrastructure host connects to base station (WiFi, WiMAX, cellular) which connects to larger Internet no base station, no connection to larger Internet (Bluetooth, ad hoc nets) host may have to relay through several wireless nodes to connect to larger Internet: mesh net no base station, no connection to larger Internet. May have to relay to reach other a given wireless node MANET,VANET 16
  17. 17. 2. APPLICATIONS OF WIRELESS NETWORKS AND MOBILE COMMUNICATIONS a) Vehicles b) Emergencies c) Business d) Replacement of wired networks e) Infotainment and more f) Location dependent services g) Mobile and wireless devices COET, Dilla University 17
  18. 18. a. Vehicles  Today’s cars already comprise some, but tomorrow’s cars will comprise many wireless communication systems and mobility aware applications.  Music, news, road conditions, weather reports, and other broadcast information are received via digital audio broadcasting (DAB) with 1.5 Mbit/s.  For remote areas, satellite communication can be used, while the current position of the car is determined via the global positioning system (GPS). COET, Dilla University 18
  19. 19. b. Emergencies  Just imagine the possibilities of an ambulance with a high-quality wireless connection to a hospital.  Vital information about injured persons can be sent to the hospital from the scene of the accident.  All the necessary steps for this particular type of accident can be prepared and specialists can be consulted for an early diagnosis.  Wireless networks are the only means of communication in the case of natural disasters such as hurricanes or earthquakes. COET, Dilla University 19
  20. 20. c. Business  A travelling salesman today needs instant access to the company’s database: to ensure that files on his or her laptop reflect the current situation, to enable the company to keep track of all activities of their travelling employees, to keep databases consistent etc. With wireless access, the laptop can be turned into a true mobile office, but efficient and powerful synchronization mechanisms are needed to ensure data consistency.  Gas stations may offer WLAN hot spots as well as gas.  Trains already offer support for wireless connectivity. COET, Dilla University 20
  21. 21. d. Replacement of wired networks  In some cases, wireless networks can also be used to replace wired networks, e.g., remote sensors, for tradeshows, or in historic buildings.  Due to economic reasons, it is often impossible to wire remote sensors for weather forecasts, earthquake detection, or to provide environmental information. wireless connections, e.g., via satellite, can help in this situation.  Tradeshows need a highly dynamic infrastructure, but cabling takes a long time and frequently proves to be too inflexible.  Wireless access points in a corner of the room can represent a solution. COET, Dilla University 21
  22. 22. e. Infotainment and more  Static information might be loaded via CD- ROM, DVD, or even at home via the Internet. But wireless networks can provide up-to-date information at any appropriate location.  The travel guide might tell you something about the history of a building (knowing via GPS, contact to a local base station, or triangulation where you are) downloading information about a concert in the building at the same evening via a local wireless network.  Another growing field of wireless network applications lies in entertainment and games to enable, e.g., ad-hoc gaming networks as soon as people meet to play together. COET, Dilla University 22
  23. 23. f. Location dependent services Several services that might depend on the actual location can be distinguished: • Follow-on services • Location aware services • Privacy • Information services • Support services COET, Dilla University 23
  24. 24. g. Mobile and wireless devices The following list gives some examples of mobile and wireless devices graded by increasing performance (CPU, memory, display, input devices etc.). Sensor Embedded controllers Pager Mobile phones Personal digital assistant Pocket computer Notebook/laptop COET, Dilla University 24
  25. 25. 3. TYPES OF MOBILE NETWORK BY MULTIPLE-ACCESS SCHEME  Mobile radio networks can be distinguished by operation modes, services and applications and multiple-access schemes.  A major influence on the development of commercial radio communication systems is the scarcity of radio spectrum available for utilization.  An apparent objective is to assign the maximum number of users to an available radio frequency segment.  This objective is achieved by using various multiple-access schemes. COET, Dilla University 25
  26. 26. Cont.. Here, we list the four most common technologies: a) 1) Frequency division multiple access (FDMA) b) 2) Time-division multiple access (TDMA) c) 3) Code division multiple access (CDMA) d) 4) space division multiple access (SDMA). COET, Dilla University 26
  27. 27. Multiple Access • Access coordination may be carried out in different domains: – frequency domain – time domain – code domain – space domain. • Four main multiple access technologies are used by the wireless networks: – frequency division multiple access (FDMA) – time division multiple access (TDMA) – code division multiple access (CDMA) – space division multiple access (SDMA). COET, Dilla University 27
  28. 28. A. Frequency Division Multiple Access  FDMA is certainly the most conventional method of multiple access and was the first technique to be employed in modern wireless application.  The channel bandwidth is a function of the services to be provided and of the available technology and is identified by its center frequency, known as a carrier. COET, Dilla University 28
  29. 29. Frequency Division Multiple Access (FDMA) User 1 User 2 User n … Time Frequency • Separate (unique) carrier frequency per user • All 1G (first-generation) systems use FDMA 29 COET, Dilla University
  30. 30. Basic Structure of a FDMA System - 1 BS and n MSs - fi’ and fi – for MS #i MS #1 MS #2 MS #n BS f1’ f2’ fn’ f1 f2 fn … … … Reverse channels (Uplink) Forward channels (Downlink) 30 COET, Dilla University
  31. 31. FDMA Channel Structure 1 2 3 … n Frequency Total bandwidth W = N * Wc (for reverse channels or for forward channels) Guard Band Wg 4 Frequency Protecting bandwidth … f1’ f2’ fn’ … f1 f2 fn Reverse channels Forward channels Subband Wc 31 COET, Dilla University
  32. 32. b. Time Division Multiple Access  TDMA is another widely known multiple- access technique and succeeded FDMA in modern wireless applications.  In TDMA, the entire bandwidth is made available to all signals but on a time-sharing basis.  Transmission then occurs within a time interval known as a (time) slot. COET, Dilla University 32
  33. 33. Time Division Multiple Access (TDMA) User 1 User 2 User n … Time Frequency • Separate (unique) time slot per user • The same carrier (frequency) split into time slots • Each frequency efficiently utilized by multiple users • Most of 2G systems use TDMA 33 COET, Dilla University
  34. 34. Basic Structure of TDMA MS #1 MS #2 MS #n BS … … Reverse channels (Uplink) Forward channels (Downlink) t Frequency f ’ #1 … #1 … Frame Slot … #1 … #1 Frame … t Frequency f Frame Frame … t #2 … #2 … … t #n … #n … … #2 … #2 … t … #n … #n … t Slot 34 COET, Dilla University
  35. 35. TDMA Frame Structure … Time Frequency #1 #2 #n #1 #2 #n … … #1 #2 #n Frame Frame Frame Head Data Guard time Time slot Notice Guard time between Time slots - Minimize interference due to propagation delays 35 COET, Dilla University
  36. 36. c. Code Division Multiple Access  CDMA is a nonconventional multiple-access technique that immediately found wide application in modern wireless systems.  In CDMA, the entire bandwidth is made available simultaneously to all signals.  In theory, very little dynamic coordination is required, as opposed to FDMA and TDMA in which frequency and time management have a direct impact on performance.  To accomplish CDMA systems, spread-spectrum techniques are used.  In CDMA, signals are discriminated by means of code sequences or signature sequences.  Each pair of transmitter-receivers is allotted one code sequence with which a communication is established. COET, Dilla University 36
  37. 37. Code Division Multiple Access (CDMA) • Separate (unique) code per user • Code sequences are orthogonal => different users can use same frequency simultaneously (see Fig above) • Some 2G systems use CDMA / Most of 3G systems use CDMA User 1 Time Frequency User 2 User n Code . . . 37 COET, Dilla University
  38. 38. Structure of a CDMA System (with FDD) Notes: 1) FDD (frequency division duplexing) since f for all forward channels, and f’ for all reverse channels 2) Ci = i-the code 3) Ci’ x Cj’ = 0, i.e., Ci’ and Cj’ are orthogonal codes on f’ Ci x Cj = 0, i.e., Ci and Cj are orthogonal codes on f MS #1 MS #2 MS #n BS C1’ C2’ Cn’ C1 C2 Cn … … … Reverse channels (Uplink) Forward channels (Downlink) Frequency f ’ Frequency f 38 COET, Dilla University
  39. 39. d. Space Division Multiple Access  SDMA is a nonconventional multiple-access technique that finds application in modern wireless systems mainly in combination with other multiple-access techniques.  In SDMA, the entire bandwidth is made available simultaneously to all signals.  Signals are discriminated spatially, and the communication trajectory constitutes the physical channels.  The implementation of an SDMA architecture is based strongly on antennas technology coupled with advanced digital signal processing.  The antenna beams must be electronically and adaptively directed to the user so that.  The location alone is enough to discriminate the user. COET, Dilla University 39
  40. 40. Space Division Multiple Access (SDMA) The concept of SDMA Beam n Beam 1 Beam 2 Beam 3 Beam i s(f,t,c) s(f,t,c) s(f,t,c) s(f,t,c) s(f,t,c) Space divided into spatially separate sectors Omni-directional transmission COET, Dilla University 40
  41. 41. Transmission in SDMA The basic structure of a SDMA system MS1 MS2 MS3 BS Beam 1 Beam 2 Beam 3  Noise and interference for each MS and BS is minimized  Enhance the quality of communication link and increase overall system capacity  Intra-cell channel reuse can be easily exploited COET, Dilla University 41
  42. 42. Multiple Access Techniques in use Multiple Access Technique Advanced Mobile Phone System (AMPS) FDMA/FDD Global System for Mobile (GSM) TDMA/FDD US Digital Cellular (USDC) TDMA/FDD Digital European Cordless Telephone (DECT) FDMA/TDD US Narrowband Spread Spectrum (IS-95) CDMA/FDD Cellular System 42 COET, Dilla University
  43. 43. Comparison of Various Multiple Division Techniques 43 Technique FDMA TDMA CDMA SDMA Concept Divide the frequency band into disjoint sub-bands Divide the time into non-overlapping time slots Spread the signal with orthogonal codes Divide the space in to sectors Active terminals All terminals active on their specified frequencies Terminals are active in their specified slot on same frequency All terminals active on same frequency Number of terminals per beam depends on FDMA/ TDMA/CDMA Signal separation Filtering in frequency Synchronization in time Code separation Spatial separation using smart antennas Handoff Hard handoff Hard handoff Soft handoff Hard and soft handoffs Advantages Simple and robust Flexible Flexible Very simple, increases system capacity Disadvantages Inflexible, available frequencies are fixed, requires guard bands Requires guard space, synchronization problem Complex receivers, requires power control to avoid near-far problem Inflexible, requires network monitoring to avoid intra cell handoffs Current applications Radio, TV and analog cellular GSM and PDC 2.5G and 3G Satellite systems, LTE COET, Dilla University
  44. 44. References Reference Text Books: • J. Schiller, Mobile Communications, Addison Wesley, 2003. • Alexander Kukushkin, Introduction to Mobile Network engineering GSM,3G-WCDMA, LTE and the Road to 5G, Wiley COET, Dilla University 44
  45. 45. THANK YOU COET, Dilla University 45