CHAPTER 4 CELLULAR WIRELESS NETWORKS These slides are

CHAPTER 4 CELLULAR WIRELESS NETWORKS These slides are made available to faculty in Power. Point form. Slides can be freely added, modified, and deleted to suit student needs. They represent substantial work on the part of the authors; therefore, we request the following. If these slides are used in a class setting or posted on an internal or external www site, please mention the source textbook and note our copyright of this material. All material copyright 2016 Cory Beard and William Stallings, All Rights Reserved Wireless Communication Networks and Systems 1 st edition Cory Beard, William Stallings © 2016 Pearson Higher Education, Inc. Cellular Wireless Networks 13 -1

CELLULAR NETWORKS • Revolutionary development in data communications and telecommunications • Foundation of mobile wireless – Telephones, smartphones, tablets, wireless Internet, wireless applications • Supports locations not easily served by wireless networks or WLANs • Four generations of standards – – 1 G: Analog 2 G: Still used to carry voice 3 G: First with sufficient speeds for data networking, packets only 4 G: Truly broadband mobile data up to 1 Gbps Cellular Wireless Networks 13 -2

CELLULAR NETWORK ORGANIZATION • Use multiple low-power transmitters (100 W or less) • Areas divided into cells – Each served by its own antenna – Served by base station consisting of transmitter, receiver, and control unit – Band of frequencies allocated – Cells set up such that antennas of all neighbors are equidistant (hexagonal pattern) Cellular Wireless Networks 13 -3

13. 1 CELLULAR GEOMETRIES Cellular Wireless Networks 13 -4

FREQUENCY REUSE • Adjacent cells assigned different frequencies to avoid interference or crosstalk • Objective is to reuse frequency in nearby cells – 10 to 50 frequencies assigned to each cell – Transmission power controlled to limit power at that frequency escaping to adjacent cells – The issue is to determine how many cells must intervene between two cells using the same frequency Cellular Wireless Networks 13 -5

13. 2 FREQUENCY REUSE PATTERNS Cellular Wireless Networks 13 -6

APPROACHES TO COPE WITH INCREASING CAPACITY • Adding new channels • 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 • Cell sectoring – cells are divided into a number of wedgeshaped sectors, each with their own set of channels • Network densification – more cells and frequency reuse – Microcells – antennas move to buildings, hills, and lamp posts – Femtocells – antennas to create small cells in buildings • Interference coordination – tighter control of interference so frequencies can be reused closer to other base stations – Inter-cell interference coordination (ICIC) – Coordinated multipoint transmission (Co. MP) Cellular Wireless Networks 13 -7

13. 3 CELL SPLITTING Cellular Wireless Networks 13 -8

CELLULAR SYSTEMS TERMS • Base Station (BS) – includes an antenna, a controller, and a number of receivers • Mobile telecommunications switching office (MTSO) – connects calls between mobile units • Two types of channels available between mobile unit and BS – Control channels – used to exchange information having to do with setting up and maintaining calls – Traffic channels – carry voice or data connection between users Cellular Wireless Networks 13 -9

13. 5 OVERVIEW OF CELLULAR SYSTEM Cellular Wireless Networks 13 -10

STEPS IN AN MTSO CONTROLLED CALL BETWEEN MOBILE USERS • • • Mobile unit initialization Mobile-originated call Paging Call accepted Ongoing call Handoff Cellular Wireless Networks 13 -11

13. 6 EXAMPLE OF MOBILE CELLULAR CALL Cellular Wireless Networks 13 -12

ADDITIONAL FUNCTIONS IN AN MTSO CONTROLLED CALL • • Call blocking Call termination Call drop Calls to/from fixed and remote mobile subscriber Cellular Wireless Networks 13 -13

MOBILE RADIO PROPAGATION EFFECTS • Signal strength – Must be strong enough between base station and mobile unit to maintain signal quality at the receiver – Must not be so strong as to create too much co-channel interference with channels in another cell using the same frequency band • Fading – Signal propagation effects may disrupt the signal and cause errors Cellular Wireless Networks 13 -14

HANDOFF PERFORMANCE METRICS • Cell blocking probability – probability of a new call being blocked • Call dropping probability – probability that a call is terminated due to a handoff • Call completion probability – probability that an admitted call is not dropped before it terminates • Probability of unsuccessful handoff – probability that a handoff is executed while the reception conditions are inadequate Cellular Wireless Networks 13 -15

HANDOFF PERFORMANCE METRICS • Handoff blocking probability – probability that a handoff cannot be successfully completed • Handoff probability – probability that a handoff occurs before call termination • Rate of handoff – number of handoffs per unit time • Interruption duration – duration of time during a handoff in which a mobile is not connected to either base station • Handoff delay – distance the mobile moves from the point at which the handoff should occur to the point at which it does occur Cellular Wireless Networks 13 -16

HANDOFF STRATEGIES USED TO DETERMINE INSTANT OF HANDOFF • • Relative signal strength with threshold Relative signal strength with hysteresis and threshold • Prediction techniques Cellular Wireless Networks 13 -17

13. 7 HANDOFF BETWEEN TWO CELLS Cellular Wireless Networks 13 -18

POWER CONTROL • Reasons to include dynamic power control in a cellular system – Received power must be sufficiently above the background noise for effective communication – Desirable to minimize power in the transmitted signal from the mobile • Reduce co-channel interference, alleviate health concerns, save battery power – In SS systems using CDMA, it’s necessary to equalize the received power level from all mobile units at the BS Cellular Wireless Networks 13 -19

TYPES OF POWER CONTROL • Open-loop power control – Depends solely on mobile unit – No feedback from BS – Not as accurate as closed-loop, but can react quicker to fluctuations in signal strength • Closed-loop power control – Adjusts signal strength in reverse channel based on metric of performance – BS makes power adjustment decision and communicates to mobile on control channel Cellular Wireless Networks 13 -20

TRAFFIC ENGINEERING • Ideally, available channels would equal number of subscribers active at one time • In practice, not feasible to have capacity handle all possible load • For N simultaneous user capacity and L subscribers – L < N – nonblocking system – L > N – blocking system Cellular Wireless Networks 13 -21

13. 8 EXAMPLE DISTRIBUTION OF TRAFFIC IN A CELL WITH CAPACITY 10 Cellular Wireless Networks 13 -22

BLOCKING SYSTEM PERFORMANCE QUESTIONS • Probability that call request is blocked? • What capacity is needed to achieve a certain upper bound on probability of blocking? • What is the average delay? • What capacity is needed to achieve a certain average delay? Cellular Wireless Networks 13 -23

TRAFFIC INTENSITY • Load presented to a system: • λ = mean rate of calls attempted per unit time • h = mean holding time per successful call • A = average number of calls arriving during average holding period, for normalized λ Cellular Wireless Networks 13 -24

FACTORS THAT DETERMINE THE NATURE OF THE TRAFFIC MODEL • Manner in which blocked calls are handled – Lost calls delayed (LCD) – blocked calls put in a queue awaiting a free channel – Blocked calls rejected and dropped • Lost calls cleared (LCC) – user waits before another attempt • Lost calls held (LCH) – user repeatedly attempts calling • Number of traffic sources – Whether number of users is assumed to be finite or infinite Cellular Wireless Networks 13 -25

FIRST-GENERATION ANALOG • Advanced Mobile Phone Service (AMPS) – In North America, two 25 -MHz bands allocated to AMPS • One for transmission from base to mobile unit • One for transmission from mobile unit to base – Each band split in two to encourage competition – Frequency reuse exploited Cellular Wireless Networks 13 -26

AMPS OPERATION • Subscriber initiates call by keying in phone number and presses send key • MTSO verifies number and authorizes user • MTSO issues message to user’s cell phone indicating send and receive traffic channels • MTSO sends ringing signal to called party • Party answers; MTSO establishes circuit and initiates billing information • Either party hangs up; MTSO releases circuit, frees channels, completes billing Cellular Wireless Networks 13 -27

DIFFERENCES BETWEEN FIRST AND SECOND GENERATION SYSTEMS • Digital traffic channels – first-generation systems are almost purely analog; second-generation systems are digital – Using FDMA/TDMA or CDMA • Encryption – all second generation systems provide encryption to prevent eavesdropping • Error detection and correction – second-generation digital traffic allows for detection and correction, giving clear voice reception • Channel access – second-generation systems allow channels to be dynamically shared by a number of users Cellular Wireless Networks 13 -28

GLOBAL SYSTEM FOR MOBILE COMMUNICATIONS (GSM) • FDMA/TDMA approach • Developed to provide a common second-generation technology for Europe – Over 6. 9 billion subscriber units by the end of 2013 • Mobile station communicates across the Um interface (air interface) with base station transceiver in the same cell as mobile unit • Mobile equipment (ME) – physical terminal, such as a telephone or PCS – ME includes radio transceiver, digital signal processors and subscriber identity module (SIM) • GSM subscriber units are generic until SIM is inserted – SIMs roam, not necessarily the subscriber devices Cellular Wireless Networks 13 -29

13. 9 OVERALL GSM ARCHITECTURE Cellular Wireless Networks 13 -30

BASE STATION SUBSYSTEM (BSS) • BSS consists of base station controller and one or more base transceiver stations (BTS) • Each BTS defines a single cell – Includes radio antenna, radio transceiver and a link to a base station controller (BSC) • BSC reserves radio frequencies, manages handoff of mobile unit from one cell to another within BSS, and controls paging Cellular Wireless Networks 13 -31

NETWORK SUBSYSTEM (NS) • NS provides link between cellular network and public switched telecommunications networks – Controls handoffs between cells in different BSSs – Authenticates users and validates accounts – Enables worldwide roaming of mobile users • Central element of NS is the mobile switching center (MSC) Cellular Wireless Networks 13 -32

MOBILE SWITCHING CENTER (MSC) DATABASES • Home location register (HLR) database – stores information about each subscriber that belongs to it • Visitor location register (VLR) database – maintains information about subscribers currently physically in the region • Authentication center database (Au. C) – used for authentication activities, holds encryption keys • Equipment identity register database (EIR) – keeps track of the type of equipment that exists at the mobile station Cellular Wireless Networks 13 -33

GSM RADIO LINK • • Combination of FDMA and TDMA 200 k. Hz carriers Each with a data rate of 270. 833 kbps 8 users share each carrier Cellular Wireless Networks 13 -34

GENERALIZED PACKET RADIO SERVICE (GPRS) • Phase 2 of GSM • Provides a datagram switching capability to GSM – Instead of sending data traffic over a voice connection which requires setup, sending data, and teardown – GPRS allows users to open a persistent data connection – Also has a new system architecture for data traffic – 21. 4 kbps from a 22. 8 kbps gross data rate – Can combine up to 8 GSM connections • Overall throughputs up to 171. 2 kbps Cellular Wireless Networks 13 -35

ENHANCED DATA RATES FOR GSM EVOLUTION (EDGE) • The next generation of GSM – Not yet 3 G, so called “ 2. G” by some • Three-fold increase in data rate – Up to 3 bits/symbol for 8 -PSK from 1 bit/symbol for GMSK for GSM. – Max data rates per channel up to 22. 8 × 3 = 68. 4 kbps per channel – Using all eight channels in a 200 k. Hz carrier, gross data transmission rates up to 547. 2 kbps became possible • Actual throughput up to 513. 6 kbps. • A later release of EDGE (3 GPP Release 7) increased downlink data rates over 750 kbps and uplink data rates over 600 kbps Cellular Wireless Networks 13 -36

ADVANTAGES OF CDMA FOR CELLULAR SYSTEMS • Frequency diversity – frequency-dependent transmission impairments have less effect on signal • Multipath resistance – chipping codes used for CDMA exhibit low cross correlation and low autocorrelation • Privacy – privacy is inherent since spread spectrum is obtained by use of noise-like signals • Graceful degradation – system only gradually degrades as more users access the system Cellular Wireless Networks 13 -37

DRAWBACKS OF CDMA CELLULAR • Self-jamming – arriving transmissions from multiple users not aligned on chip boundaries unless users are perfectly synchronized • Near-far problem – signals closer to the receiver are received with less attenuation than signals farther away Cellular Wireless Networks 13 -38

MOBILE WIRELESS CDMA DESIGN CONSIDERATIONS • RAKE receiver – when multiple versions of a signal arrive more than one chip interval apart, RAKE receiver attempts to recover signals from multiple paths and combine them – See Chapter 9 • Soft Handoff – mobile station temporarily connected to more than one base station simultaneously – Requires that the mobile acquire a new cell before it relinquishes the old – More complex than hard handoff used in FDMA and TDMA schemes Cellular Wireless Networks 13 -39

IS-95 FORWARD LINK • Most widely used CDMA cellular standard is IS-95, used mainly in North America • Forward link channels – Pilot (channel 0) - allows the mobile unit to acquire timing information, provides phase reference and provides means for signal strength comparison – Synchronization (channel 32) - used by mobile station to obtain identification information about cellular system – Paging (channels 1 to 7) - contain messages for one or more mobile stations – Traffic (channels 8 to 31 and 33 to 63) – the forward channel supports 55 traffic channels • 9600 or 14, 400 bps Cellular Wireless Networks 13 -40

13. 10 IS-95 CHANNEL STRUCTURE Cellular Wireless Networks 13 -41

ITU’S INITIAL VIEW OF THIRDGENERATION CAPABILITIES • The ITU’s International Mobile Telecommunications for the year 2000 (IMT-2000) initiative • Voice quality comparable to the public switched telephone network • 144 kbps data rate available to users in high-speed motor vehicles over large areas • 384 kbps available to pedestrians standing or moving slowly over small areas • Support for 2. 048 Mbps for office use – Much higher rates were developed Cellular Wireless Networks 13 -42

ITU’S INITIAL VIEW OF THIRDGENERATION CAPABILITIES • Symmetrical / asymmetrical data transmission rates • Support for both packet switched and circuit switched data services • An adaptive interface to the Internet to reflect efficiently the common asymmetry between inbound and outbound traffic • More efficient use of the available spectrum in general • Support for a wide variety of mobile equipment • Flexibility to allow the introduction of new services and technologies Cellular Wireless Networks 13 -43

ALTERNATIVE INTERFACES • Five alternatives for smooth evolution from 1 G and 2 G systems • Two most prevalent – Wideband CDMA (WCDMA) – CDMA 2000 • Both based on CDMA • Similar to but incompatible with each other Cellular Wireless Networks 13 -44

13. 11 IMT-2000 TERRESTRIAL RADIO INTERFACES Cellular Wireless Networks 13 -45

CDMA DESIGN CONSIDERATIONS • Bandwidth – limit channel usage to 5 MHz • Chip rate – depends on desired data rate, need for error control, and bandwidth limitations; 3 Mcps or more is reasonable • Multirate – advantage is that the system can flexibly support multiple simultaneous applications from a given user and can efficiently use available capacity by only providing the capacity required for each service Cellular Wireless Networks 13 -46

WCDMA AND UMTS • WCDMA is part of a group of standards from – IMT-2000 – Universal Mobile Telephone System (UMTS) – Third-Generation Partnership Project (3 GPP) industry organization • 3 GPP originally released GSM – Issued Release 99 in 1999 for WCDMA and UMTS – Subsequent releases were “Release 4” and onwards – Many higher layer network functions of GSM were carried over to WCDMA Cellular Wireless Networks 13 -47

WCDMA AND UMTS • 144 kbps to 2 Mbps, depending on mobility • High Speed Downlink Packet Access (HSDPA) – Release 5 – 1. 8 to 14. 4 Mbps downlink – Adaptive modulation and coding, hybrid ARQ, and fast scheduling • High Speed Uplink Packet Access (HSUPA) – Release 6 – Uplink rates up to 5. 76 Mbps • High Speed Packet Access Plus (HSPA+) – Release 7 and successively improved in releases through Release 11 – Maximum data rates increased from 21 Mbps up to 336 Mbps – 64 QAM, 2× 2 and 4× 4 MIMO, and dual or multi-carrier combinations • 3 GPP Release 8 onwards introduced Long Term Evolution (LTE) – Pathway to 4 G, Chapter 14 Cellular Wireless Networks 13 -48

13. 13 EVOLUTION OF CELLULAR WIRELESS SYSTEMS Cellular Wireless Networks 13 -49

CDMA 2000 AND EV-DO • CDMA 2000 first introduced 1 x. RTT (Radio Transmission Technology) – 1 times the 1. 2288 Mcps spreading rate of a 1. 25 MHz IS-95 CDMA channel – Not 3 G, so considered by some as “ 2. 5 G” • Evolution-Data Only (1×EV-DO) – Also 1×EV-DV (data/voice) which never succeeded – 1×EV-DO Release 0 • 2. 4 Mbps uplink, 153 kbps downlink • Only using 1. 25 MHz of 5 MHz required of CDMA – 1×EV-DO Release A • 3. 1 Mbps downlink, 1. 8 Mbps uplink, Qo. S – 1×EV-DO Release B • 5 MHz bandwidth, 14. 7 Mpbs uplink, 5. 4 Mbps downlink • EV-DO uses only IP, but Vo. IP can be used for voice Cellular Wireless Networks 13 -50

13. 14 CDMA 2000 1 XEV-DO CONFIGURATION ELEMENTS Cellular Wireless Networks 13 -51