192620010 Mobile & Wireless Networking - Universiteit Twenteheijenkgj/mwn/slides/... ·...

Mobile and Wireless Networking 2013 / 2014

192620010

Mobile & Wireless Networking

Lecture 6: Cellular Systems (UMTS / LTE) (2/2)

& Other systems

[Reader, Part 5] [Optional: Schiller, Section 4.2, 4.3, 5, 6]

Geert Heijenk


2

Outline of Lecture 6

q  Cellular Systems (UMTS / LTE) (2/2) q  UMTS High Speed Downlink Packet Access (HSDPA) q  UMTS High Speed Uplink Packet Access (HSUPA) q  Long Term Evolution (LTE)

q  Other systems

q  DECT q  TETRA q  Satellite Systems


3

HSDPA (The downlink) Main improvements:

q  MAC-layer: from RNC to base station q  Improved radio: higher order modulation

initially 16-QAM, newer releases 64 QAM Techniques used:

q  Fast Adaptive Modulation & Coding q  Fast Channel-Dependent Scheduling q  Fast Hybrid ARQ

Result: q  increases throughput (→14.4 Mbps) q  reduces latency q  increases data capacity q  newer releases promise throughputs up to 86.4 Mbps

(with MIMO, 64-QAM, and multiple carriers (dual-cell)) Introduction:

q  2006 (in NL, max 28.8 Mbps (2012))


Fast Channel-Dependent Scheduling

Schedule a packet for transmission to a certain user when it has a “good” channel

•  Increases throughput •  May decrease fairness between users à trade-off

4


Example of Fast Channel-Dependent Scheduling

Proportional Fair Scheduling: Rm(n): achievable data rate of user m in the nth slot / subframe Tm(n): average data rate of user m in the the last tc slots / subframes base station will transmit to user m* in the nth slot / subframe: average data rate is updated after each slot / subframe:

5

m*(n) = arg maxm=1,2,...,M

Rm (n)Tm (n)

Tm (n+1) =(1! 1

tc)Tm (n)+ (

1tc)Rm (n) m =m*(n)

(1! 1tc)Tm (n) m "m*(n)

#

$

%%

&

%%


6

HSUPA (the enhanced uplink)

Main improvements: q  MAC-layer: from RNC to base station (as HSDPA)

l  no higher order modulation

Techniques used: q  Fast Channel-Dependent Scheduling q  Fast Hybrid ARQ

Result: q  increases throughput (→5.76 Mbps) q  reduces latency q  increases data capacity q  newer releases promise throughputs up to 23 Mbps

(with higher order modulation, and multiple carriers (dual-cell)) Introduction:

q  2008 (in NL, max 5.76 Mbps (2012))


7



q  Other systems



Long Term Evolution: Background

•  Evolution of 3G UMTS radio access technology •  Supporting (only) (IP) packet-based services •  Targets:

•  Increased data rates (ê100 Mbit/s, é50 Mbit/s) •  Increased capacity (3 – 4 x Rel. 6 (HSDPA)) •  Improved spectrum efficiency (x3) •  Reduced latency: <5 ms RTT, <100ms channel setup, •  Reduced cost •  Spectrum flexibility

8


LTE Characteristics

•  Flexible channel bandwidth: •  1.4, 3, 5, 10, 15, 20 MHz

•  Duplexing: •  FDD, TDD, and combined FDD/TDD (half duplex)

•  Downlink: •  OFDMA

•  Uplink: •  Single Carrier FDMA (OFDMA with extra Discrete Fourier Transform)

•  MIMO: •  up to 4x4 in downlink, or multi-user MIMO (down-/uplink)

•  Hybrid ARQ: •  multiple parallel stop-and-wait, with soft combining / incremental

redundancy •  Max Data Rates:

•  75 Mbit/s (uplink), 300 Mbit/s (downlink, with MIMO) •  New core network:

•  Evolved Packet Core (EPC) / Evolved Packet System (EPS)

9


LTE Resource Blocks

• Resource Blocks (RB) is the smallest resource unit that can be assigned to a mobile (2 at a time) • RB lasts 0.5 ms (6 or 7 OFDM symbols) • RB spans over a 180 kHz sub-channel (containing 12 15 kHz subcarriers) • Number of sub-channels depends on channel bandwidth

10

Source: Capozzi, Piro, Grieco, Boggia & Camarda: Downlink Packet Scheduling in LTE Cellular Networks In: IEEE Communications Surveys & Tutorials, Early Access Article, IEEE Xplore, 2012, pp. 1 - 8."


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Source: Capozzi, Piro, Grieco, Boggia & Camarda: Downlink Packet Scheduling in LTE Cellular Networks In: IEEE Communications Surveys & Tutorials, Early Access Article, IEEE Xplore, 2012, pp. 1 - 8."


LTE Network Architecture: Evolved Packet System

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UE: User Equipment eNodeB: evolved Node B MME: Mobility Management Entity HSS: Home Subscriber Server SGW: Serving GateWay PGW: Packet data network GateWay


EPS user-plane protocols

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EPS control-plane protocols

14


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q  Other systems



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Digital Enhanced Cordless Telecommunication (DECT)

q  DECT (Digital European Cordless Telephone) standardized by ETSI for cordless telephones, renamed for international marketing reasons into „Digital Enhanced Cordless Telecommunication“

q  standard describes air interface between base-station and mobile phone

q  Characteristics q  frequency: 1880-1990 MHz q  channels: 120 full duplex q  duplex mechanism: TDD (Time Division Duplex) with 10 ms frame

length q  multiplexing scheme: FDMA with 10 carrier frequencies,

TDMA with 2x 12 slots q  modulation: digital, Gaußian Minimum Shift Key (GMSK) q  power: 10 mW average (max. 250 mW) q  range: approx. 50 m in buildings, 300 m open space


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DECT Dynamic Channel Allocation

q  periodically (< 30s) measure RSSI on all frequency/timeslot combinations

q  keep list of combinations with least RSSI for setting up new channels

q  listen to channels with high RSSI to see what is strongest base-station


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q  Other systems



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Trunked Radio Systems

q  many different radio carriers q  assign single carrier for a short period to one user/group of

users q  police, ambulance, rescue teams, taxi service, fleet

management q  interfaces to public networks, voice and data services q  very reliable, fast call setup, local operation


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TETRA - Terrestrial Trunked Radio

q  ETSI standard q  formerly: Trans European Trunked Radio q  offers Voice+Data and Packet Data Optimized service q  point-to-point and point-to-multipoint q  ad-hoc and infrastructure networks q  several frequencies: 380-400 MHz, 410-430 MHz q  FDD, DQPSK q  group call, broadcast, discrete listening q  Netherlands: C2000 project


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q  Other systems



22

Satellite Basics

q  elliptical or circular orbits q  complete rotation time depends on distance satellite-earth q  inclination: angle between orbit and equator q  elevation: angle between satellite and horizon q  LOS (Line of Sight) to the satellite necessary for connection

è high elevation needed, less absorption due to e.g. buildings q  Uplink: connection base station - satellite q  Downlink: connection satellite - base station q  typically separated frequencies for uplink and downlink

q  transponder used for sending/receiving and shifting of frequencies q  transparent transponder: only shift of frequencies q  regenerative transponder: additionally signal regeneration


23

Four different types of satellite orbits can be identified depending on the shape and diameter of the orbit:

q  GEO: geostationary orbit, ca. 36000 km above earth surface

q  LEO (Low Earth Orbit): ca. 500 - 1500 km q  MEO (Medium Earth Orbit) or ICO (Intermediate Circular

Orbit): ca. 6000 - 20000 km q  HEO (Highly Elliptical Orbit) elliptical orbits

Orbits I


24

Orbits II

earth

km 35768

10000

1000

LEO (Globalstar,

Irdium)

HEO

inner and outer Van Allen belts

MEO (ICO)

GEO (Inmarsat)

Van-Allen-Belts: ionized particles 2000 - 6000 km and 15000 - 30000 km above earth surface


25

Geostationary satellites

q  Orbit 35,786 km distance to earth surface, orbit in equatorial plane (inclination 0°)

è  complete rotation exactly one day, satellite is synchronous to earth rotation

q  fix antenna positions, no adjusting necessary q  satellites typically have a large footprint (up to 34% of earth

surface!), therefore difficult to reuse frequencies q  bad elevations in areas with latitude above 60° due to fixed position

above the equator q  high transmit power needed q  high latency due to long distance (ca. 275 ms)

è not useful for global coverage for small mobile phones and data

transmission, typically used for radio and TV transmission


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LEO systems

Orbit ca. 500 - 1500 km above earth surface q  visibility of a satellite ca. 10 - 40 minutes q  global radio coverage possible q  latency comparable with terrestrial long distance

connections, ca. 5 - 10 ms q  smaller footprints, better frequency reuse q  but now handover necessary from one satellite to another q  many satellites necessary for global coverage q  more complex systems due to moving satellites Examples: q  Iridium (start 1998, 66 satellites, FDMA/TDMA-based,

uses inter-satellite links) q  Bankruptcy in 1999, deal with US DoD (free use, saving from “deorbiting”)

q  Globalstar (start 1999, 48 satellites, CDMA-based, no inter-satellite links è no service when no gateway station in view) q  Bankruptcy in 2002, assets sold to new company.


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MEO systems

q  Orbit ca. 5000 - 12000 km above earth surface q  comparison with LEO systems:

q  slower moving satellites q  less satellites needed q  simpler system design q  for many connections no hand-over needed q  higher latency, ca. 70 - 80 ms q  higher sending power needed q  special antennas for small footprints needed

Example: q  GPS (Global Positioning System)

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