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CSCD 433/533 Cellular Networks Winter 2019 Lecture 9 Cellular Networks

CSCD 433/533 Cellular Networks Winter 2019 Lecture 9 Cellular Networks. Topics. Cellular Networks Demand for Cell Phones History Cell Phone Operation Cell Phone Network Components Cell phone example Privacy and Health Future. 2. Ubiquitous Mobile Network Services.

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CSCD 433/533 Cellular Networks Winter 2019 Lecture 9 Cellular Networks

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  1. CSCD 433/533Cellular Networks Winter 2019 Lecture 9 Cellular Networks

  2. Topics Cellular Networks Demand for Cell Phones History Cell Phone Operation Cell Phone Network Components Cell phone example Privacy and Health Future 2

  3. Ubiquitous Mobile Network Services • Global Mobile Data Traffic • 7.2 exabytes/month in 2016 (63% growth) • 18 fold growth in the past five years • 7 fold growth by 2021 (49 exabytes/month) one quintillion (1018) bytes, or one billion gigabytes. 3 Source: Cisco Visual Networking Index, 2017: Global Mobile Data Traffic Forecast Update, 2016–2021 White Paper CS590 (Peng) 3

  4. Ubiquitous Mobile Network Services • Smartphones: primary Internet access points • By 2021, 98% traffic and 75% connections from “smart” devices • 4G: 75% traffic and 53% connections • 5G: 1.5% traffic and 0.2% connections CS590 (Peng) 4

  5. History Cellular networks have been around a long time They have been around since late 70's Debuted in 1979, as analog systems, 1G networks Then, digital systems, 1990's, 2G networks Finally, with higher data rates, 3G networks Still being deployed .. now, 4G and 5G Many standards and technologies defined along the way in evolving cellular networks

  6. 1G Cellular Networks Mobile phones began to spread 1980s with introduction of "cellular" phones Cellular networks with multiple base stations located relatively close to each other Had protocols for automated "handover" between two cells when phone moved between cells At this time, analog transmission was only option Mobile phones were larger than current ones, and at first, all were designed for permanent installation in vehicles … 007 had a cell phone in his car

  7. 1G Cellular Networks Soon, some early phones were converted for use as "transportable" phones size of a briefcase Motorola introduced first truly portable, hand held phone These systems later became known as first generation (1G) mobile phone However, this first attempt at wireless was not without limitations ...

  8. Problems of 1G Systems FDMA based sharing of all spectrum Inefficient use of bandwidth Purely Analog voice Channels Sensitive to interference from co-channel cells Impossible to add redundancy error correction Impossible to encrypt Impossible to add additional channels Analog FDMA technology Could not handle growing demand in cost-efficient mannet Devices were huge, clunky

  9. 2G Cellular Networks Global System for Mobile Communications (GSM)‏ - 1990's Most popular standard for mobile phones worldwide Its promoter, GSM Association, estimates that 80% of global mobile market uses standard GSM is used by over 3 billion people across more than 212 countries and territories 2G still dominates world cellular market today

  10. Cell Phone Dominance 2G Dominance According to GSMA Intelligence, 2G technology still accounts for 58.5 per cent of the world’s 7.11 billion mobile connections, Compared to 32.5 per cent for 3G and 9 per cent for 4G The Analyst House expects 2G technology to maintain global market dominance until the beginning of 2019 From Mobile World Live – June 2015 http://www.mobileworldlive.com/featured-content/top-three/operators-vendors-forecast-long-life-2g/

  11. 3G Systems 3G networks enable network operators to offer users a wider range of more advanced services while achieving greater network capacity through improved spectral efficiency Services include wide-area wireless voice telephony, video calls, and broadband wireless data Additional features also include data transmission capabilities, speeds up to 14.4 Mbit/s on the downlink and 5.8 Mbit/s on the uplink Basically, greatly increased speed of 2G networks Greater emphasis on data!

  12. 3G based on CDMA Recall ... TDMA – Time Division Multiplexing and FDMA – Frequency Division Multiplexing Turns out, both these are not so efficient when large numbers of mobile users want channels Used in previous versions cellular networks Code division multiple access (CDMA) Channel access method for simultaneously allowing communication by multiple calls over single communication channel This allows several users to share a bandwidth of frequencies .. did an example in class !!!

  13. 3G Networks CDMA2000 represents a family of International approved 3G standards Deliver increased network capacity to meet growing demand for wireless services and high-speed data services Includes other sophisticated modulation techniques MIMO antenna technologies CDMA2000 1X was the world's first 3G technology commercially deployed (October 2000)‏

  14. 4G LTE • Developed in 2010 • Faster & more reliable • Speed up to 100 Mbps • High performance • Smart Phones era • Lower cost

  15. What is 4G/LTE? • LTE stands for “Long Term Evolution” • Fourth-generation (4G) cellular technology from 3GPP • Deployed worldwide • 4G LTE: First global standard • Increased speed • IP-based network (All circuits are gone) • New air interface: OFDMA (Orthogonal Frequency-Division Multiple Access), MIMO (multiple antennas) • Also includes duplexing, timing, carrier spacing, coding... • New service paradigm (e.g., VoLTE) CS590 (Peng) 16

  16. 5G • Next major phase of mobile telecommunication & wireless system • 10 times more capacity than others • Expected speed up to 1 Gbps • More faster & reliable than 4G • Lower cost than previous generations

  17. Comparison Between 3,4,5 G

  18. Comparing 4G and 5G

  19. Comparing 1G to 5G Speeds

  20. Present vs Future Networks

  21. Cells are Heart of Cell Networks

  22. How Cellular Networks Operate Each mobile device uses separate, temporary radio channel to talk to cell site Cell site talks to many mobiles at once, using one channel per mobile Channels use pair of frequencies for communication One frequency for transmitting One frequency to receive calls from the users

  23. Definitions A cell site or cell tower Cellular telephone site where antennae and electronic communications equipment are placed usually on a radio mast, tower or other high place, to create a cell (or adjacent cells) in a cellular network. Used interchangeably in our slides with base station

  24. How Cellular Networks Operate PSTN = Public Switched Telephone Network

  25. Cell Concept In old days … one main transmitter for large geographic area, like a TV broadcast system Cellular concept helped increase power of mobile telephone networks Instead of using one powerful transmitter, many low-power transmitters were placed thru coverage area So, by dividing metropolitan region into one hundred different areas, each with low-power transmitter … Could increase from 12 conversations, using one powerful transmitter to 1,200 conversations using 100 low-power transmitters

  26. 3 Core Principles 1. Small cells tessellate overall coverage area 2. Users handoff as they move from one cell to another 3. Frequency reuse

  27. Tessellation Is defined as: Tessellation is a design that uses repeating interlocking shapes without overlapping or gaps There are only three regular polygons that tessellate any given region.

  28. Tessellation (Cont’d) Three regular polygons that always tessellate: Equilateral triangle Square Regular Hexagon Triangles Squares Hexagons

  29. Circular Coverage Areas Original cellular system was developed assuming base station antennas are omnidirectional, i.e., they transmit in all directions equally. Users located some distance to base station receive weak signals. Result: base station has circular coverage area. Weak signal Strong signal

  30. Circles Don’t Tessellate Thus, ideally base stations have identical, circular coverage areas. Problem: Circles do not tessellate. The most circular of the regular polygons that tessellate is the hexagon. Thus, early researchers started using hexagons to represent coverage area of a base station, i.e., a cell.

  31. Thus the Name Cellular With hexagonal coverage area, a cellular network is drawn as: Since the network resembles cells from a honeycomb, the name cellular was used to describe the resulting mobile telephone network. Base Station

  32. Shape of Cells Square Width d cell has four neighbors at distance d and four at distance d = Better if all adjacent antennas equidistant Simplifies choosing and switching to new antenna Hexagon became preferred shape Provides equidistant antennas Radius defined as radius of circle Distance from center to vertex equals length of side Distance between centers of cells radius R is R Not always precise hexagons Topographical limitations Local signal propagation conditions Location of antennas

  33. Cellular Geometries

  34. Cellular Interference But, some communication issues with the cellular concept Interference problems from mobile units using same channel in adjacent cells Cells had to be skipped before same channel could be reused

  35. Frequency Reuse Because only a small number of radio channel frequencies were available for mobile systems Engineers had to find a way to reuse radio channels to carry more than one conversation at a time ... Frequency Reuse Concept of frequency reuse is based on assigning to each cell a group of radio channels used within a small geographic area Cells are assigned a group of channels different in configuration from neighboring cells

  36. Cell Resuse Cells with same number have the same set of frequencies Here, because the number of available frequencies is 7, the frequency reuse factor is 1/7 Each cell is using 1/7 of available cellular channels

  37. Cells Are at Different Frequencies

  38. Cell Design E D F E A D F C G A B C G E B D F A C G B • Cells grouped into a cluster of seven • Letters indicate frequency use • For each frequency, a buffer of two cells is used before reuse • To add more users, smaller cells (microcells) are used

  39. Approaches to Increase Capacity • Adding/reassigning channels - some channels are not used • Frequency borrowing – frequencies are taken from adjacent cells by congested cells • Cell splitting – cells in areas of high usage can be split into smaller cells • Microcells – antennas move to buildings, hills, and lamp posts

  40. Cellular Network Components Cellular communications system have four major components that work together to provide mobile service Public switched telephone network (PSTN)‏ Mobile telephone switching office (MTSO)‏ Cell site with antenna system Mobile subscriber unit (MSU) or‏ Person with Cell phone

  41. Components MTSOMobile telephone switching office Central office for mobile switching Houses mobile switching center (MSC), field monitoring, and relay stations for switching calls from cell sites to wireline central offices (PSTN)‏ Mobile subscriber unit (MSU) consists of control unit and transceiver that transmits and receives radio transmissions to and from a cell site ... cell phones and other devices

  42. MSC • connects cells to wide area net • manages call setup • handles mobility cell • Covers geographical region • Base station (BS) Like 802.11 AP • Mobile users attach to network through BS • Air-interface: physical and link layer protocol between mobile and BS Mobile Switching Center PSTN Public telephone network, and Internet Mobile Switching Center wired network Cellular network architecture MTSC

  43. More Definitions for GSM and Other Mobile Networks Home network Network of cellular providers you subscribe to ( Sprint, Verizon)‏ Home Location Register (HLR) Database in home network containing permanent cell phone #, profile information (services, preferences, billing), information about current location Visited Network Network in which mobile currently resides Visitor Location Register (VLR) Database with entry for each user currently in network

  44. So how does it all work? When you first power up the phone ... It listens for an SID System Identification Code (SID) - a unique 5-digit number assigned to each carrier by FCC on control channel Control channel has special frequency that phone and base station use to talk to one another about things like call set-up and channel changing If phone can't find any control channels to listen to, it knows it is out of range and displays a "no service" message

  45. So how does it all work? 2. When it receives SID, phone compares it to SID programmed into phone Phone knows that cell it is communicating with is part of its home system. Along with SID, phone also transmits registration request, and MTSO (Mobile Telephone Switching Office) keeps track of your phone's location in a database -- 3. MTSO knows which cell you are in when it wants to ring your phone. MTSO gets call, and it tries to find you --- looks in its database to see which cell you are in MTSO picks a frequency pair that your phone will use in that cell to take call

  46. Mobility in Cellular Networks How do you handle roaming behavior in cellular networks? Think about, seamless handoff when you go between cell towers ... in a car or, I have service in Spokane, travel to New York City ... still have service Two issues: 1. How do you “hand off” the call between cells? 2. How is a “call routed” to me when I am not in my original local network?

  47. Handoff of Call Since adjacent areas do not use same radio channels, Call must either be dropped or transferred from one radio channel to another when a user crosses the line between adjacent cells Because dropping the call is unacceptable, the process of handoff was created

  48. Handoff of Call During a call, two parties are on one voice channel When mobile unit moves out of coverage area of a given cell site, reception becomes weak ... like with 802.11 AP's At this point, cell site in use requests a handoff System switches call to stronger-frequency channel in new site without interrupting call or alerting user Call continues as long as user is talking, and user does not notice the handoff ( if lucky!!)‏

  49. Handoff of Cell Phone Call Really? More blah, blah, blah Hello Bill, Blah, blah blah

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