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192620010 Mobile & Wireless Networking Lecture 6: Cellular - - PowerPoint PPT Presentation
192620010 Mobile & Wireless Networking Lecture 6: Cellular - - PowerPoint PPT Presentation
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 Mobile and Wireless Networking 2013 / 2014 Outline of
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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))
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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
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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:
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m*(n) = arg max
m=1,2,...,M
Rm(n) Tm(n)
Tm(n +1) = (1! 1 tc )Tm(n)+(1 tc )Rm(n) m = m*(n) (1! 1 tc )Tm(n) m " m*(n) # $ % % & % %
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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))
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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
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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
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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)
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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
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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.
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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
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EPS user-plane protocols
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EPS control-plane protocols
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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
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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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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
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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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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
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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
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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
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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
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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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