20CS2007 Computer Communication Networks

Professor à Karunya Institute of Technology and Sciences, Coimbatore, TN, India
14 Sep 2021

Contenu connexe


20CS2007 Computer Communication Networks

  1. 20CS2007 Computer Communication Networks Module 4 Wireless Wide Area Networks and LTE Technology Design Private and public leased networks. Video conferencing, television and radio broadcast transmissions. Wireless WAN, Cellular Networks, Mobile IP Management in Cellular Networks, Long-Term Evolution (LTE) Technology, Wireless Mesh Networks (WMNs) with LTE, Characterization of Wireless Channels. Dr.A.Kathirvel, Professor, DCSE, KITS
  2. Wireless Networks
  3. 3 Wireless networks  Access computing/communication services, on the move  Wireless WANs – Cellular Networks: GSM, GPRS, CDMA – Satellite Networks: Iridium  Wireless LANs – WiFi Networks: 802.11 – Personal Area Networks: Bluetooth  Wireless MANs – WiMaX Networks: 802.16 – Mesh Networks: Multi-hop WiFi – Adhoc Networks: useful when infrastructure not available
  4. 4 Limitations of the mobile environment  Limitations of the Wireless Network  limited communication bandwidth  frequent disconnections  heterogeneity of fragmented networks  Limitations Imposed by Mobility  route breakages  lack of mobility awareness by system/applications  Limitations of the Mobile Device  short battery lifetime  limited capacities
  5. Mobile communication  Wireless vs. mobile Examples   stationary computer   laptop in a hotel (portable)   wireless LAN in historic buildings   Personal Digital Assistant (PDA)  Integration of wireless into existing fixed networks: – Local area networks: IEEE 802.11, ETSI (HIPERLAN) – Wide area networks: Cellular 3G, IEEE 802.16 – Internet: Mobile IP extension
  6. 6 Wireless v/s Wired networks  Regulations of frequencies – Limited availability, coordination is required – useful frequencies are almost all occupied  Bandwidth and delays – Low transmission rates • few Kbits/s to some Mbit/s. – Higher delays • several hundred milliseconds – Higher loss rates • susceptible to interference, e.g., engines, lightning  Always shared medium – Lower security, simpler active attacking – radio interface accessible for everyone – secure access mechanisms important
  7. 384 Kbps 56 Kbps 54 Mbps 72 Mbps 5-11 Mbps 1-2 Mbps 802.11 Wireless Technology Landscape Bluetooth 802.11b 802.11{a,b} Turbo .11a Indoor 10 – 30m IS-95, GSM, CDMA WCDMA, CDMA2000 Outdoor 50 – 200m Mid range outdoor 200m – 4Km Long range outdoor 5Km – 20Km Long distance com. 20m – 50Km µwave p-to-p links .11 p-to-p link 2G 3G
  8. 8 Reference model Application Transport Network Data Link Physical Medium Data Link Physical Application Transport Network Data Link Physical Data Link Physical Network Network Radio
  9. 9 Effect of mobility on protocol stack  Application – new applications and adaptations – service location, multimedia  Transport – congestion and flow control – quality of service  Network – addressing and routing – device location, hand-over  Link – media access and security  Physical – transmission errors and interference
  10. 10 Perspectives  Network designers: Concerned with cost-effective design – Need to ensure that network resources are efficiently utilized and fairly allocated to different users.  Network users: Concerned with application services – Need guarantees that each message sent will be delivered without error within a certain amount of time.  Network providers: Concerned with system administration – Need mechanisms for security, management, fault-tolerance and accounting.
  11. RF Basics
  12. 12 Factors affecting wireless system design  Frequency allocations – What range to operate? May need licenses.  Multiple access mechanism – How do users share the medium without interfering?  Antennas and propagation – What distances? Possible channel errors introduced.  Signals encoding – How to improve the data rate?  Error correction – How to ensure that bandwidth is not wasted?
  13. 13 Frequencies for communication  VLF = Very Low Frequency UHF = Ultra High Frequency  LF = Low Frequency SHF = Super High Frequency  MF = Medium Frequency EHF = Extra High Frequency  HF = High Frequency UV = Ultraviolet Light  VHF = Very High Frequency  Frequency and wave length:  = c/f  wave length , speed of light c  3x108m/s, frequency f 1 Mm 300 Hz 10 km 30 kHz 100 m 3 MHz 1 m 300 MHz 10 mm 30 GHz 100 m 3 THz 1 m 300 THz visible light VLF LF MF HF VHF UHF SHF EHF infrared UV optical transmission coax cable twisted pair
  14. 14 Wireless frequency allocation  Radio frequencies range from 9KHz to 400GHZ (ITU)  Microwave frequency range – 1 GHz to 40 GHz – Directional beams possible – Suitable for point-to-point transmission – Used for satellite communications  Radio frequency range – 30 MHz to 1 GHz – Suitable for omnidirectional applications  Infrared frequency range – Roughly, 3x1011 to 2x1014 Hz – Useful in local point-to-point multipoint applications within confined areas
  15. 15 Frequencies for mobile communication  VHF-/UHF-ranges for mobile radio – simple, small antenna for cars – deterministic propagation characteristics, reliable connections  SHF and higher for directed radio links, satellite communication – small antenna, focusing – large bandwidth available  Wireless LANs use frequencies in UHF to SHF spectrum – some systems planned up to EHF – limitations due to absorption by water and oxygen molecules (resonance frequencies) • weather dependent fading, signal loss caused by heavy rainfall etc.
  16. 16 Frequency regulations  Frequencies from 9KHz to 300 MHZ in high demand (especially VHF: 30-300MHZ)  Two unlicensed bands – Industrial, Science, and Medicine (ISM): 2.4 GHz – Unlicensed National Information Infrastructure (UNII): 5.2 GHz  Different agencies license and regulate – - US – - Europe – - India – - International co-ordination  Regional, national, and international issues  Procedures for military, emergency, air traffic control, etc
  17. 17 Wireless transmission  Wireless communication systems consist of: – Transmitters – Antennas: radiates electromagnetic energy into air – Receivers  In some cases, transmitters and receivers are on same device, called transceivers. Transmitter Receiver Antenna Antenna
  18. 18 Transmitters Amplifier Oscillator Mixer Filter Amplifier Antenna Transmitter Suppose you want to generate a signal that is sent at 900 MHz and the original source generates a signal at 300 MHz. •Amplifier - strengthens the initial signal •Oscillator - creates a carrier wave of 600 MHz •Mixer - combines signal with oscillator and produces 900 MHz (also does modulation, etc) •Filter - selects correct frequency •Amplifier - Strengthens the signal before sending it Source
  19. Antennas
  20. 20 Antennas  An antenna is an electrical conductor or system of conductors to send/receive RF signals – Transmission - radiates electromagnetic energy into space – Reception - collects electromagnetic energy from space  In two-way communication, the same antenna can be used for transmission and reception Omnidirectional Antenna (lower frequency) Directional Antenna (higher frequency)
  21. 21  Radiation and reception of electromagnetic waves, coupling of wires to space for radio transmission  Isotropic radiator: equal radiation in all directions (three dimensional) - only a theoretical reference antenna  Real antennas always have directive effects (vertically and/or horizontally)  Radiation pattern: measurement of radiation around an antenna Antennas: isotropic radiator z y x z y x ideal isotropic radiator
  22. 22 Antennas: simple dipoles  Real antennas are not isotropic radiators – dipoles with lengths /4 on car roofs or /2 (Hertzian dipole)  shape of antenna proportional to wavelength  Gain: maximum power in the direction of the main lobe compared to the power of an isotropic radiator (with the same average power) side view (xy-plane) x y side view (yz-plane) z y top view (xz-plane) x z simple dipole /4 /2
  23. 23 Antennas: directed and sectorized side view (xy-plane) x y side view (yz-plane) z y top view (xz-plane) x z top view, 3 sector x z top view, 6 sector x z  Often used for microwave connections or base stations for mobile phones (e.g., radio coverage of a valley) directed antenna sectorized antenna
  24. 24 Antenna models In Omni Mode:  Nodes receive signals with gain Go In Directional Mode:  Capable of beamforming in specified direction  Directional Gain Gd (Gd > Go)
  25. 25 Directional communication Received Power  (Transmit power) *(Tx Gain) * (Rx Gain) Directional gain is higher Directional antennas useful for:  Increase “range”, keeping transmit power constant  Reduce transmit power, keeping range comparable with omni mode
  26. 26 Comparison of omni and directional Issues Omni Directional Spatial Reuse Low High Connectivity Low High Interference Omni Directional Cost & Complexity Low High
  27. 27 Antennas: diversity  Grouping of 2 or more antennas – multi-element antenna arrays  Antenna diversity – switched diversity, selection diversity • receiver chooses antenna with largest output – diversity combining • combine output power to produce gain • cophasing needed to avoid cancellation + /4 /2 /4 ground plane /2 /2 + /2
  28. Signal Propagation and Modulation
  29. 29 Signals  physical representation of data  function of time and location  signal parameters: parameters representing the value of data  classification – continuous time/discrete time – continuous values/discrete values – analog signal = continuous time and continuous values – digital signal = discrete time and discrete values  signal parameters of periodic signals: period T, frequency f=1/T, amplitude A, phase shift  – sine wave as special periodic signal for a carrier: s(t) = At sin(2  ft t + t)
  30. 30 Signal propagation ranges distance sender transmission detection interference  Transmission range – communication possible – low error rate  Detection range – detection of the signal possible – no communication possible  Interference range – signal may not be detected – signal adds to the background noise
  31. 31 Attenuation: Propagation & Range
  32. 32 Attenuation  Strength of signal falls off with distance over transmission medium  Attenuation factors for unguided media: – Received signal must have sufficient strength so that circuitry in the receiver can interpret the signal – Signal must maintain a level sufficiently higher than noise to be received without error – Attenuation is greater at higher frequencies, causing distortion  Approach: amplifiers that strengthen higher frequencies
  33. 33 Signal propagation  Propagation in free space always like light (straight line)  Receiving power proportional to 1/d² (d = distance between sender and receiver)  Receiving power additionally influenced by – fading (frequency dependent) – shadowing – reflection at large obstacles – refraction depending on the density of a medium – scattering at small obstacles – diffraction at edges reflection scattering diffraction shadowing refraction
  34. 34  Signal can take many different paths between sender and receiver due to reflection, scattering, diffraction  Time dispersion: signal is dispersed over time   interference with “neighbor” symbols, Inter Symbol Interference (ISI)  The signal reaches a receiver directly and phase shifted   distorted signal depending on the phases of the different parts Multipath propagation signal at sender signal at receiver LOS pulses multipath pulses
  35. 35 Effects of mobility  Channel characteristics change over time and location – signal paths change – different delay variations of different signal parts – different phases of signal parts   quick changes in the power received (short term fading)  Additional changes in – distance to sender – obstacles further away   slow changes in the average power received (long term fading) short term fading long term fading t power
  36. 36 Propagation modes Earth Earth Earth a) Ground Wave Propagation b) Sky Wave Propagation c) Line-of-Sight Propagation Transmission Antenna Receiving Antenna Signal Signal Ionosphere Signal
  37. Chapter 16 Wireless WANs: Cellular Telephone and Satellite Networks and Satellite Networks 16.1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
  38. 16 16- -1 1 CELLULAR TELEPHONY CELLULAR TELEPHONY Cellular Cellular telephony telephony is is designed designed to to provide provide p y p y g g p p communications communications between between two two moving moving units, units, called called mobile mobile stations stations (MSs), (MSs), or or between between one one mobile mobile unit unit and and ( ), ( ), one one stationary stationary unit, unit, often often called called a a land land unit unit. . Topics discussed in this section Topics discussed in this section Frequency-Reuse Principle Transmitting Topics discussed in this section: Topics discussed in this section: Transmitting Receiving Roaming g First Generation Second Generation 16.2 Third Generation
  39. Figure 16.1 Cellular system 16.3
  40. Figure 16.2 Frequency reuse patterns 16.4
  41. N t AMPS is an analog cellular phone Note AMPS is an analog cellular phone system using FDMA. 16.5
  42. Figure 16.3 Cellular bands for AMPS 16.6
  43. Figure 16.4 AMPS reverse communication band 16.7
  44. Figure 16.5 Second-generation cellular phone systems 16.8
  45. Figure 16.6 D-AMPS 16.9
  46. Note D-AMPS, or IS-136, is a digital cellular h t i TDMA d FDMA phone system using TDMA and FDMA. 16.10
  47. Figure 16.7 GSM bands 16.11
  48. Figure 16.8 GSM 16.12
  49. Figure 16.9 Multiframe components 16.13
  50. Note GSM is a digital cellular phone system Note GS s a d g ta ce u a p o e syste using TDMA and FDMA. 16.14
  51. Figure 16.10 IS-95 forward transmission 16.15
  52. Figure 16.11 IS-95 reverse transmission 16.16
  53. Note IS-95 is a digital cellular phone system i CDMA/DSSS d FDMA using CDMA/DSSS and FDMA. 16.17
  54. Note The main goal of third-generation ll l t l h i t id cellular telephony is to provide universal personal communication. 16.18
  55. Figure 16.12 IMT-2000 radio interfaces 16.19
  56. 16 16- -2 2 SATELLITE NETWORKS SATELLITE NETWORKS A A satellite satellite network network is is a a combination combination of of nodes, nodes, some some of of A A satellite satellite network network is is a a combination combination of of nodes, nodes, some some of of which which are are satellites, satellites, that that provides provides communication communication from from one one point point on on the the Earth Earth to to another another. . A A node node in in the the one one point point on on the the Earth Earth to to another another. . A A node node in in the the network network can can be be a a satellite, satellite, an an Earth Earth station, station, or or an an end end- - user user terminal terminal or or telephone telephone. . user user terminal terminal or or telephone telephone. . Topics discussed in this section: Topics discussed in this section: Orbits Footprint Th C i f S lli Three Categories of Satellites GEO Satellites MEO Satellites 16.20 MEO Satellites LEO Satellites
  57. Figure 16.13 Satellite orbits 16.21
  58. Example 16.1 What is the period of the Moon, according to Kepler’s law? Here C is a constant approximately equal to 1/100. The period is in seconds and the distance in kilometers period is in seconds and the distance in kilometers. 16.22
  59. Example 16.1 (continued) Solution The Moon is located approximately 384,000 km above the Earth. The radius of the Earth is 6378 km. Applying the formula, we get. 16.23
  60. Example 16.2 According to Kepler’s law, what is the period of a satellite that is located at an orbit approximately 35,786 km above the Earth? Solution Solution Applying the formula, we get 16.24
  61. Example 16.2 (continued) This means that a satellite located at 35,786 km has a period of 24 h, which is the same as the rotation period of the Earth. A satellite like this is said to be stationary to the h h bi ill i ll d Earth. The orbit, as we will see, is called a geosynchronous orbit. 16.25
  62. Figure 16.14 Satellite categories 16.26
  63. Figure 16.15 Satellite orbit altitudes 16.27
  64. Table 16.1 Satellite frequency bands 16.28
  65. Figure 16.16 Satellites in geostationary orbit 16.29
  66. Figure 16.17 Orbits for global positioning system (GPS) satellites 16.30
  67. Figure 16.18 Trilateration 16.31
  68. Figure 16.19 LEO satellite system 16.32
  69. Figure 16.20 Iridium constellation 16.33
  70. Note The Iridium system has 66 satellites in i LEO bit h t six LEO orbits, each at an altitude of 750 km. 16.34
  71. Note Iridium is designed to provide direct worldwide voice and data communication using handheld terminals a service similar to handheld terminals, a service similar to cellular telephony but on a global scale. 16.35
  72. Figure 16.20 Teledesic 16.36
  73. N t Teledesic has 288 satellites in 12 LEO Note Teledesic has 288 satellites in 12 LEO orbits, each at an altitude of 1350 km. 16.37
  74. Mobile IP Management in Cellular Network
  75. 2 Motivation: the changing wireless environment • Explosion in wireless services – Some connectivity everywhere – Overlapping, heterogeneous networks • Small, portable devices • A choice of network connectivity on one device – Sometimes built-in – Sometimes a portable “bridge” between choices
  76. 3 Opportunity for connectivity • New environment gives us opportunity – Continuous connectivity for a mobile host – Seamless movement between networks • Examples – Move from office to elsewhere in building – Move outside building, across campus, to cafe • Why maintain connectivity? – Avoid restarting applications/networks – Avoid losing “distributed state”
  77. 4 Different approaches • The traditional approach: support in the network – Intelligence (and expense) is in the network – End-points are cheap (handsets) – Allows for supporting infrastructure – Requires agreements/trust amongst multiple vendors – Examples: • A link/physical level (many wireless networks) • At routing level (Columbia, VIP) – Doesn’t work when switching between technologies and often not between vendors – In Internet would require modifying lots of routers
  78. 5 Different approaches, continued • The Internet approach: end-to-end – Intelligence (and expense) is in the end-points – Network is cheap (relatively) and as fast as possible – Implies self-support for many activities – Less work/trust required amongst multiple vendors • End-to-end support at transport/naming/application levels – May be ideal in future, but requires extensive changes – Not currently backwards compatible – TRIAD may be interesting approach
  79. 6 Different approaches, continued • Use end-to-end support at routing level – Makes problem transparent at layers above and below – Current Internet standard: Mobile IP (RFC 2002) application transport routing link physical Modify all applications? Modify TCP, UDP, etc.? Modify IP end-points? Modify all device drivers? How dies this work across network technologies? TCP/IP network stack:
  80. 7 IP address problem • Internet hosts/interfaces are identified by IP address – Domain name service translates host name to IP address – IP address identifies host/interface and locates its network – Mixes naming and location • Moving to another network requires different network address – But this would change the host’s identity – How can we still reach that host?
  81. 8 Routing for mobile hosts CH MH Home network MH CH MH = mobile host CH = correspondent host Home network Foreign network Foreign network How to direct packets to moving hosts transparently?
  82. 9 Domains versus interfaces • Switching domains & switching interfaces are the same problem at the routing level Network interfaces: Administrative domains: Mobile host ether radio 171.64.14.X 42.13.0.X 171.64.X.X 128.32.X.X
  83. 10 Mobile IP (RFC 2002) • Leaves Internet routing fabric unchanged • Does not assume “base stations” exist everywhere • Simple • Correspondent hosts don’t need to know about mobility • Works both for changing domains and network interfaces
  84. 11 Basic Mobile IP – to mobile hosts MH = mobile host CH = correspondent host HA = home agent FA = foreign agent (We’ll see later that FA is not necessary or even desirable) •MH registers new “care-of address” (FA) with HA •HA tunnels packets to FA •FA decapsulates packets and delivers them to MH HA CH Home network Foreign network FA MH
  85. 12 Packet addressing Source address = address of CH Destination address = home IP address of MH Payload Source address = address of HA Destination address = care-of address of MH Source address = address of CH Destination address = home IP address of MH Original payload Packet from CH to MH Home agent intercepts above packet and tunnels it
  86. 13 When mobile host moves again HA CH Home network Foreign network #1 FA #1 MH Foreign network #2 FA #2 MH •MH registers new address (FA #2) with HA & FA #1 •HA tunnels packets to FA #2, which delivers them to MH •Packets in flight can be forwarded from FA #1 to FA #2
  87. 14 Basic Mobile IP - from mobile hosts HA CH Home network Foreign network FA MH Mobile hosts also send packets •Mobile host uses its home IP address as source address -Lower latency -Still transparent to correspondent host -No obvious need to encapsulate packet to CH •This is called a “triangle route”
  88. 15 Problems with Foreign Agents • Assumption of support from foreign networks – A foreign agent exists in all networks you visit? – The foreign agent is robust and up and running? – The foreign agent is trustworthy? • Correctness in security-conscious networks – We’ll see that “triangle route” has problems – MH under its own control can eliminate this problem • Other undesirable features – Some performance improvements are harder with FAs • We want end-to-end solution that allows flexibility
  89. 16 Solution HA CH Home network Foreign network MH •Mobile host is responsible for itself -(With help from infrastructure in its home network) -Mobile host decapsulates packets -Mobile host sends its own packets -“Co-located” FA on MH MH must acquire its own IP address in foreign network This address is its new “care-of” address Mobile IP spec allows for this option
  90. 17 Obtaining a foreign IP address • Can we expect to obtain an IP address? – DHCP becoming more common – Dynamic IP address binding like some dial-up services – Your friend can reserve an IP address for you – Various other tricks – More support for dynamic IP address binding in IPv6 • This assumes less than getting others to run a FA
  91. 18 Design implications • New issues: the mobile host now has two roles: – Home role – Local role - More complex mobile host - Loss of in-flight packets? (This can happen anyway.) + Can visit networks without a foreign agent + Can join local multicast groups, etc. + More control over packet routing = more flexibility
  92. 19 Problems with ingress filtering HA CH Home network Foreign network MH •Mobile host uses its home IP address as source address •Security-conscious boundary routers will drop this packet
  93. 20 Solution: bi-directional tunnel HA CH Home network Foreign network MH •Provide choice of “safe” route through home agent both ways •This is the slowest but most conservative option At the other extreme…
  94. 21 Problem: performance • Example: short-lived communication – When accessing a web server, why pay for mobility? – Do without location-transparency – Unlikely to move during transfer; can reload page – Works when CH keeps no state about MH
  95. 22 Solution: yet more flexibility HA CH Home network Foreign network MH •Use current care-of address and send packet directly -This is regular IP! •More generally: -MH should have flexibility to adapt to circumstances -A range of options: from slow-but-safe to regular IP -Should be an end-to-end packet delivery decision (no FA)
  96. 23 Routing options • Allow MH to choose from among all routing options • Options: – Encapsulate packet or not? – Use home address or care-of address as source address? – Tunnel packet through home agent or send directly? • Choice determined by: – Performance – Desire for transparent mobility – Mobile-awareness of correspondent host – Security concerns of networks traversed • Equivalent choices for CH sending packets to MH
  97. 24 Mobile IP issues on local network • Host visiting local network with foreign agent – No real presence on local network • Host visiting local network with its own IP address – Has a role on local network – Reverse name lookups through special name? – Or do you change the DNS entry? – Its IP address / HW address gets into local hosts’ ARP caches – Which IP address should go into cache? – How do you update caches if host moves again?
  98. 25 Local ARP cache problem • ARP caches store (IP address, HW address) pairs • MH host visits foreign network • Wants to talk directly back and forth to local hosts – If it wants to maintain connectivity with them after moving • Use home IP address • Other hosts address MH by HW address on local link • But if MH moves again, ARP cache entries are wrong – If it doesn’t care • Use local IP address • If MH moves, ARP cache is wrong, but nobody cares
  99. 26 Multiple Network Interfaces – Why? • Want to probe hosts through all active interfaces – Example: register with HA through new interface before switching to it – Helps with smooth handoff between types of networks • Want transparent mobility for more than one interface • Example: – One application users cheap/slow interface while another uses expensive/fast interface – Move to new network(s) or lose contact with one network – Don’t want to restart either application
  100. 27 Why is this hard? • System support missing in at least two areas • Need “next hop” info for more than one interface – Need to be able to send packets beyond local subnet for more than one interface – Current support only uses gateway info for one interface • Mobile IP doesn’t separate traffic flows to different interfaces – (This isn’t the Mobile IP “simultaneous binding” feature) – Current HA won’t keep different bindings for more than one interface per host based on traffic flow
  101. 28 Solution for next hop • Backwards-compatible extension to routing table – Add “next-hop” info for more than one interface – Take advantage of “metric” field for priority of interface – This maintains backwards compatible default route Destination Gateway Netmask Flags Metric Iface a.b.0.0 U 0 eth0 c.d.0.0 U 0 st0 U 0 lo a.b.0.1 UG 1 eth0 c.d.0.1 UG 100 st0
  102. 29 Solution for Mobile IP • Extend home agent • Mobile host registers flow-to-interface bindings Home Agent Mobile Host Correspondent Host flow 1 flow 2 flow 1 + flow 2 CoA1 CoA2
  103. 30 Flexible connectivity management • Need to manage this extra flexibility through adaptivity – Monitor availability of various interfaces – System detects & configures interfaces automatically – Applications can express interest in types of service – System (or application) can choose best interface – System feedback necessary: system notifies application of changes as conditions warrant
  104. 31 Connectivity management, continued • Must address protocol interaction when connecting – Is DHCP available? – Is this a frequently visited network? (probe for gateways) • If so, can use pre-determined address – Must the host use a foreign agent here? • If it’s broken, how do we find what’s wrong & fix it? – Cable loose? – Battery in radio dead? – Home agent dead? • Strong need for “no-futz” computing on mobile hosts
  105. Long Term Evolution (LTE) Technology
  106. Overview (1 of 2) Pg 2 |
  107. IMT-2000 Submission Plan [of Mar 2016] Pg 3 |
  108. Introduction • Spectrum is a finite and scarce but non- exhaustible natural resource which is a vital input for wireless services • Rapid development of wireless technology has ensured that there is an increasing range of valuable uses of the spectrum • With competing users, uses and growth of wireless services, the demand for spectrum has tremendously increased. 4
  109. Introduction • The trend of modern communications is towards mobility, with increasingly higher data rates/ speeds, for which wireless is the only option • The requirements of captive applications are also growing. • All these have resulted in greater demands/ pressure on the already scarce RF spectrum resource 5
  110. Introduction • Shortage of spectrum will be setback to innovations, competition, businesses and consumers. • Making spectrum available at a time when convergence is causing rapid and unpredictable change poses a severe challenge. • Advances in technology create the potential for systems to use spectrum more efficiently and to be much more tolerant of interference than in the past. The Second meeting of SATRC Working Group on Spectrum 12-13 December 2011 Colombo, Sri Lanka 6
  111. Introduction • With the availability of higher data speeds, the user requirements are also continually increasing wrt: – different services and applications, – expecting a dynamic, continuing stream of new capabilities that are ubiquitous and available across a range of devices using a single subscription and a single identity. • Requirement for new radio access technologies to satisfy the anticipated demands for higher bandwidth services is increasing. • IMT and IMT-Advanced technologies are the answers to these requirements 7
  112. IMT and IMT-Advanced Technologies • LTE, LTE Advanced and Wireless MAN- Advanced, are designed to enable high speed Internet/Broadband at anytime, anywhere. • These systems facilitate higher bandwidth, higher data rate and support higher level of user-level customization. • As per ITU for IMT-Advanced technologies, the targeted peak data rates are up to 100 Mbit/s for high mobility and up to 1 Gbit/s for low mobility scenario. Scalable bandwidths up to at least 40 MHz should be provided 8
  113. IMT-Advanced Technologies-Key Features • High degree of commonality of functionality worldwide while retaining the flexibility to support a wide range of services and applications in a cost efficient manner; • compatibility of services within IMT and with fixed networks; • capability of interworking with other radio access systems; • high quality mobile services; • User equipment suitable for worldwide use; • User-friendly applications, services and equipment; • Worldwide roaming capability; 9
  114. LTE and LTE-Advanced Technologies 10
  115. LTE and LTE-Advanced Technologies • LTE and Wimax technologies are available since 2009/2006. • Current versions are called ‘LTE-Advanced’ and WirelessMAN Advanced respectively. • Qualifies IMT-advanced technologies make use of same key technologies: – Orthogonal Frequency Division Multiplex (OFDMA) – Multiple Input Multiple Output (MIMO) and – System Architecture Evolution (SAE) 11
  116. Multiple Input Multiple Output (MIMO) • Uses multiple transmitter and receiver antennas, which allow independent channels to be created in space. • Various Approaches for MIMO: – Space diversity:- to improve the communication reliability by decreasing the sensitivity to fading by picking up multiple copies of the same signal at different locations in space. – Beamforming:- antenna elements are used to adjust the strength of the transmitted and received signals, based on their direction for focusing of energy. – Spatial Multiplexing:- Increased capacity, reliability, coverage, reduction in power requirement by introducing additional spatial channels that are exploited by using space- time coding 12
  117. Orthogonal Frequency Division Multiple Access (OFDMA) • Based on the idea of dividing a given high-bit-rate data stream into several parallel lower bit-rate streams and modulating each stream on separate carrier – often called sub-carriers or tones. • Multi-carrier modulation scheme minimize inter-symbol interference (ISI) by making the symbol time large enough so that the channel-induced delays are an insignificant (<10%) fraction of the symbol duration. • OFDM is a spectrally efficient version of multi-carrier modulation where the sub-carriers are selected such that they are all orthogonal to one another over the symbol duration, thereby avoiding the need to have non overlapping sub-carrier channels to eliminate inter-carrier interference . • Guard intervals are used between OFDM symbols. By making the guard intervals larger than the expected multi-path delay spread, ISI can be completely eliminated 13
  118. Long Term Evolution(LTE): Speed • Capabilities:- – Scalable bandwidth up to 20 MHz, covering 1.4, 3, 5, 10, 15, and 20 MHz – Up/Downlink peak data rates up to 86.4/326 Mbps with 20 MHz bandwidth – Operation in both TDD and FDD modes – Reduced latency, up to 10 ms round-trip times between user equipment and the base station, and upto less than 100 ms transition times from inactive to active 14
  119. Long Term Evolution(LTE): Specifications and Speed 15 Parameter Details Peak downlink speed with 64QAM in Mbps 100 (SISO), 172 (2x2 MIMO), 326 (4x4 MIMO) Peak uplink speeds(Mbps) 50 (QPSK), 57 (16QAM), 86 (64QAM) Data type All packet switched data (voice and data). No circuit switched. Channel bandwidth (MHz) 1.4, 3, 5, 10, 15, 20 Duplex schemes FDD and TDD Mobility 0 - 15 km/h (optimised), 15 - 120 km/h (high performance) Latency Idle to active less than 100ms Small packets ~10 ms Spectral efficiency Downlink: 3 - 4 times Rel 6 HSDPA Uplink: 2 -3 x Rel 6 HSUPA Access schemes OFDMA (Downlink) SC-FDMA (Uplink) Modulation types supported QPSK, 16QAM, 64QAM (Uplink and downlink) LTE specification
  120. Long Term Evolution(LTE)-Advanced: Key Features • Features:- – Compatibility of services – Enhanced peak data rates to support advanced services and applications (100 Mbit/s for high and 1 Gbit/s for low mobility). – Spectrum efficiency: 3 times greater than LTE. – Peak spectrum efficiency: downlink – 30 bps/Hz; uplink – 6.75 bps/Hz. – Spectrum use: the ability to support scalable bandwidth use and spectrum aggregation where non-contiguous spectrum needs to be used. 16
  121. Technologies(2G, IMT, IMT-Advanced) in SATRC countries 17 • Based on the data available, the bands being operated in SATRC Countries are: • 450, 700, 800, 900, 1800, 1900 MHz; 2.1, 2.3, 2.5, 3.3-3.6GHz for various mobile services i.e. 2G,3G,BWA services, with various block sizes offered to the mobile operators. • Spectrum Allocation methodologies varies from Command& Control to auction.
  122. 18 Spectrum Bands Identified for various wireless telecom services (INDIA) Band Technology 450MHz 2G & 3G 700 MHz Digital Mobile TV 800 MHz 2G & 3G 900MHz 2G 1800MHz 2G 1900MHz 2G & 3G 2010-2025 MHz BWA 2.1 GHz 3G 2.3 GHz BWA 2.5 GHz BWA 3.3 GHz BWA 3.4GHz BWA 2.4-2.4835, 5.15-5.35 & 5.725-5.875 GHz are unlicensed spectrum bands
  123. Challenges posed by technologies like LTE in spectrum management 19 • Identification of common spectrum bands – Common to SATRC Countries for Ubiquitous roaming – identify the availability of large chunk of spectrum in the identified bands • Spectrum management planning, allocation, allotment and regulations of frequency bands – to determine the use or uses that would best serve the public and government interest – to tackle the transmissions interference unless the user frequencies are sufficiently separated in terms of frequency, geography or time – co-ordination with neighbouring countries, to mitigate the extent of harmful interference – need to strike a balance between reducing the extent of harmful interference, through careful planning, and enabling new and potentially valuable new services to enter the market
  124. Challenges posed by technologies like LTE in spectrum management 20 • Frequency assignment and licensing – Traditional methods poses many challenges in terms of time, technological progress and the delivery of services, thus causing inefficient utilization of this precious resource. – to assign spectrum to those who value it the most and are able to utilize rationally and efficiently
  125. Challenges posed by technologies like LTE in spectrum management 21 • Responsive to change – to devise procedures to ration current and future demand for radio spectrum between competing commercial and public service users – it would require a detailed knowledge of supply and demand trends, technology developments, and the relative value to society of alternative services – accumulation and assimilation of sufficient information to make a correct assignment of spectrum to optimise use over time
  126. 22 Wireless Mesh Networks with LTE
  127. 23 Wireless routers Gateways Printers, servers Mobile clients Stationary clients Intra-mesh wireless links Stationary client access Mobile client access Internet access links Node Types Link Types Overview
  128. 24 Gateways • Multiple interfaces (wired & wireless) • Mobility – Stationary (e.g. rooftop) – most common case – Mobile (e.g., airplane, busses/subway) • Serve as (multi-hop) “access points” to user nodes • Relatively few are needed, (can be expensive) GW
  129. 25 Wireless Routers  At least one wireless interface.  Mobility  Stationary (e.g. rooftop)  Mobile (e.g., airplane, busses/subway).  Provide coverage (acts as a mini- cell-tower).  Do not originate/terminate data flows  Many needed for wide areas, hence, cost can be an issue.
  130. 26 Users • Typically one interface. • Mobility – Stationary – Mobile • Connected to the mesh network through wireless routers (or directly to gateways) • The only sources/destinations for data traffic flows in the network.
  131. 27 User – Wireless Router Links • Wired – Bus (PCI, PCMCIA, USB) – Ethernet, Firewire, etc. • Wireless – 802.11x – Bluetooth – Proprietary • Point-to-Point or Point-to- Multipoint • If properly designed is not a bottleneck. • If different from router-to- router links we’ll call them access links
  132. 28 Router to Router Links • Wireless – 802.11x – Proprietary • Usually multipoint to multipoint – Sometimes a collection of point to point • Often the bottleneck • If different from router-to- user links we’ll call them backbone links
  133. 29 Gateway to Internet Links • Wired – Ethernet, TV Cable, Power Lines • Wireless – 802.16 – Proprietary • Point to Point or Point-to- Multipoint • We’ll call them backhaul links • If properly designed, not the bottleneck
  134. 30 How it Works • User-Internet Data Flows – In most applications the main data flows • User-User Data Flows – In most applications a small percentage of data flows
  135. 31 Taxonomy Wireless Networking Multi-hop Infrastructure-less (ad-hoc) Infrastructure-based (Hybrid) Infrastructure-less (MANET) Single Hop Cellular Networks Wireless Sensor Networks Wireless Mesh Networks Car-to-car Networks (VANETs) Infrastructure-based (hub&spoke) 802.11 802.16 Bluetooth 802.11
  136. 32 Mesh vs. Ad-Hoc Networks • Multihop • Nodes are wireless, possibly mobile • May rely on infrastructure • Most traffic is user-to- user Ad-Hoc Networks Wireless Mesh Networks  Multihop  Nodes are wireless, some mobile, some fixed  It relies on infrastructure  Most traffic is user-to- gateway
  137. 33 Mesh vs. Sensor Networks  Bandwidth is limited (tens of kbps)  In most applications, fixed nodes  Energy efficiency is an issue  Resource constrained  Most traffic is user-to-gateway Wireless Sensor Networks Wireless Mesh Networks  Bandwidth is generous (>1Mbps)  Some nodes mobile, some fixed  Normally not energy limited  Resources are not an issue  Most traffic is user-to-gateway
  138. 34 Applications
  139. 35 Broadband Internet Access
  140. 36 Extend WLAN Coverage Source: Source:
  141. 37 Mobile Internet Access Law enforcement Intelligent transportation • Direct competition with G2.5 and G3 cellular systems. Source: (now
  142. 38 Emergency Response Source:
  143. 39 Layer 2 Connectivity • The entire wireless mesh cloud becomes one (giant) Ethernet switch • Simple, fast installation – Short-term events (e.g., conferences, conventions, shows) – Where wires are not desired (e.g., hotels, airports) – Where wires are impossible (e.g., historic buildings) Internet
  144. 40 Military Communications Source:
  145. 41 Community Networks Source:  Grass-roots broadband Internet Access  Several neighbors may share their broadband connections with many other neighbors  Not run by ISPs  Possibly in the disadvantage of the ISPs
  146. 42 Many Other Applications • Remote monitoring and control • Public transportation Internet access • Multimedia home networking Source: (now
  147. 43 Broadband Internet Access Cable DSL WMAN (802.16) Cellular (2.5-3G) WMN Bandwidth Very Good Very Good Limited Good Upfront Investments Very High High High Low Total Investments Very High High High Moderate Market Coverage Good Good Good Modest
  148. 44 WLAN Coverage Source: 802.11 WMN Wiring Costs Low High Number of APs As needed Twice as many Cost of APs High Low Bandwidth Good Very Good
  149. 45 Mobile Internet Access Cellular 2.5 – 3G WMN Upfront Investments Low High Geolocation Limited Good Bandwidth Good Limited Upgrade Cost Low High Source: (now
  150. 46 Emergency Response Cellular 2.5 – 3G WMN Source: Walkie Talkie Availability Reasonable Good Good Bandwidth Good Limited Poor Geolocation Poor Limited Poor
  151. 47 Layer 2 Connectivity Ethernet WMN Total Cost Low Moderate Mobile Users 802.11 needed Good Bandwidth Good Very Good Speed/Ease of Deployment Fast/Easy Slow/Difficult
  152. 48 Military Communications WMNs Source: Existing System(s) Coverage Very Good Good Good Poor Bandwidth Voice Support Good Very Good Covertness Poor Better Power efficiency Good Reasonable
  154. Characterization of Wireless Channels • Path loss models: Free Space and Two-Ray models • Link Budget design • Parameters of mobile multipath channels • Time dispersion parameters • Coherence bandwidth • Doppler spread & Coherence time • Small Scale fading • Fading effects due to multipath time delay spread • Fading effects due to doppler spread
  155. Introduction • Wireless communication – broadcasting and reception of signals by an appropriate receiver through wireless medium (air)
  156. Characteristics of wireless channels • Path loss • Fading • Interference • Doppler shift
  157. Path Loss • Ratio of power of the transmitted signal to the power of same signal received by reciever. • Dependent on radio frequency used and nature of terrain • Path loss models – Free space & Two ray • Free space – no attenuation of signals, only direct path • Two ray – direct path & Reflected path
  158. Fading • Fluctuations in signal strength when received at the receiver. • Types – (1) Fast/small scale fading (2) slow/large scale fading. • Fast fading – rapid fluctuations in amplitude, phase or multipath delays. • Slow fading – objects partially absorb the transmissions • Counter measure – Diversity & Adaptive modulation
  159. Interference • Types : (1) ACI (2) CCI (3) ISI Interference Counter measure ACI Guard band CCI Usage of directional antennas, dynamic channel allocation ISI Adaptive equalization
  160. Doppler shift • Change in frequency when transmitter and receiver are mobile in nature. • Higher frequency – when both move towards • Lower frequency – when both move away