01 Introduction Principles

Department of Computer Science Institute for System Architecture, Chair for Computer Networks Mobile Communication and ...

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Department of Computer Science Institute for System Architecture, Chair for Computer Networks

Mobile Communication and Mobile Computing

Prof. Dr. Alexander Schill http://www.rn.inf.tu-dresden.de

Structure of the Lecture Part I: Mobile Communication -

Introduction and Principles GSM and Extensions UMTS LTE and beyond WLAN Satellite and Broadcast Systems

Part II: Mobile Computing

-

Mobile IP and TCP Location Based Services Context Awareness and Adaptation Service Based Architecture Mobile File Systems, Databases, Information Services Mobile Applications

Reference: - Jochen Schiller: Mobile Communications, Addison-Wesley

2

Introduction and Principles

3

Application Example: Civil Engineering, Field Service

Enterprise A (main office) Gigabit Ethernet

Large archives, Videoconferences

Drafts, urgent modification

Gigabit Ethernet

Fast Ethernet

Enterprise A (branch office)

Architect

Selected drafts, Videoconferences

UMTS, LTE

Enterprise B

Construction supervisor Material data, status data, dates

GSM, UMTS

Building site

4

Example: Consumer Application

8:56PM

http://www.bike-rental...

Rent-A-Bike Service Login

Login:

Alexander Schill

Password:

URL

**********

LOGIN

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Mobile Multimedia Local Resources, Test Protocols

Product Data Main office Caching

Maintenance technician Mobile Access

Client LAN-Access

Very different performances and costs: radio networks versus fixed networks Software-controlled, automatic adaptation to concrete system environments Example: Access to picture data / compressed picture data / graphics / text

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Traffic Telematics Systems Content Provider Main Office Content Provider Gigabit Ethernet Internet

GSM

Point-to-Point Radio, Internet

Radio/Infrared

DAB: Digital Audio Broadcasting RDS/TMC: Radio Data System/ Traffic Message Channel

Infrastructure

7

Mobile Communication: Development Mobile Phone Networks

E (GSM1800)

D (GSM900)

C

HSCSD

EDGE

GPRS

Packet Networks

Modacom

Circuit Switched Networks

Mobitex Tetra

Satellite Networks Cordless Telephony Local Networks

IMT/ UMTS

4G (LTE advanced, WiMAX)

Iridium/ Globalstar

Inmarsat

CT

LTE

DECT

Radio-LAN IR-LAN

1990

IEEE 802.11 Bluetooth

1995

2000

2005

2010

2015 8

Used Acronyms C: C: Analog “C” Network (1st Generation) CT: CT: Cordless Telephone DECT: Digital Enhanced Cordless Telecommunications DECT: GSM: Global System for Mobile Communications (2nd Generation) GSM: GPRS: General Packet Radio Service GPRS: HSDPA+: HSCSD:High Speed Downlink Packet Access (advanced) HSUPA+: High Speed Uplink Packet Access (advanced) HSCSD: High Speed Circuit Switched Data EDGE: Enhanced Data Rates for GSM Evolution EDGE: IMT: International Mobile Telecommunications IMT: LTE: Long Term Evolution LTE: TETRA: TETRA: Terrestrial Trunked Radio (Multicast Communication System) UMTS: Universal Mobile Telecommunications System (3rd Generation) UMTS: 4G:4G: 4th Generation Networks WiMAX: WiMAX Worldwide Interoperability for Microwave Access 9

Correspondent data rates LTE

300 Mbit/s

(downlink)

200 Mbit/s LTE (uplink) / HSDPA+

100 Mbit/s 50 Mbit/s

HSUPA+ 10 Mbit/s

UMTS (pico cell)

WLAN DECT

1 Mbit/s

EDGE HSCSD/ GPRS

100 kbit/s 10kbit/s

GSM

1995

UMTS (macro cell) Satellites

2000

2005

2010

2015

10

Frequency Assignment Circuit Switched Radio Mobile Phones Cordless Phones Wireless LANs TETRA

NMT TETRA

380-400 453-457 450-470

LTE 800

500Mhz

CT2

CT1+ GSM900

CT1+

790-862 864-868 885-887 890-915 930-932

GSM900

935-960

1GHz

410-430 463-467 (nationally different) TFTS (Pager, aircraft phones)

1670-1675

GSM1800

TFTS

GSM1800

1710-1785 1800-1805 1805-1880

DECT

UMTS

1880-1900

(1885-2025 2110-2200)

WLAN IEEE 802.11b/g/n Bluetooth

LTE 2600 WIMAX

IEEE 802.11a: 5,15-5,25; 5,25-5,35; 5,725-5,825 HIPERLAN1 HIPERLAN2 HIPER-Link MHz

2400-2483 2402-2480 2412-2472 HomeRF...(approx.2400)

2500-2690

3500

TFTS - Terrestrial Flight Telephone System NMT – Nordic Mobile Telephone

5176-5270

(~5200-5600)

(~17000)

- 2,4 GHz and higher: often license free, nationally different -> interesting for high data rates 11

Principles of Mobile Communication Based on electro-magnetic radio transmission

radio transmission orbital (satellite)

terrestrial point-to-point

Broadcast radio cellular

equatorial orbit

non-equatorial orbit

non-cellular

Principles: – Propagation and reception of electro-magnetic waves – Modulation and multiplex methods; focusing on cellular networks

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Cellular networks • well known from mobile networks (GSM, UMTS) • base station (BS) covers at least one cell; a combination of multiple cells is also called a cellular structure • provides different kinds of handovers between the cells • higher capacity and better coverage than non-cellular networks • bidirectional* antennas instead of omni-directional** can better serve the selected sectors

along highways or train lines

for covering of larger areas

*

**

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Cellular networks: handover (1)

A procedure inside a cellular network, which controls the switching process between the cells and end devices Reasons for handovers are:

 leaving the transmission range of a cell  overloading or breakdown of the used cell  loss of connection quality

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Cellular networks: handover (2) Handover classes  Intra-cell: switch-over inside the cell onto other frequency or other timeslot  Inter-cell: switch-over to a neighboring cell  Inter-system: switch-over between different technologies (e.g. GSM and UMTS); roaming

Handover types  Hard handover: active connection gets disconnected before the connection to a new cell is established  Soft handover: active connection gets disconnected after the connection to a new cell is established

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Structure of a cellular network

1 4

2 1

3 1

4 3

2 1

• Major problems:  limited frequency resources  interference • reuse of frequency channels in remote cells • cluster of N cell types

N  i2  i  j  j2 i, j  0,1,2, • reuse distance

D  3N  R • where R – cell radius 16

D/R Ratios versus Reuse Patterns

R

D

3N  R

D/R-Ratio

Cluster size, N

3,46

4

4,6

7

6

12

7,55

19

3

3

Cluster of N cells with R – cell radius; D – reuse distance with the use of sectorized antennas 17

Frequency Distribution: Examples

D/R=3 with N=3 • Frequency distribution according to IEEE 802.11b/g/n D/R=4.6 with N=7 • Frequency distribution according to IEEE 802.11a 18

Multiplex Methods: Principles Multiplex  Concurrent usage of the medium without interference  4 multiplex methods:  Space  Time  Frequency  Code

Medium Access  controls user access to medium  implemented by combining and exploiting multiplex methods 19

SDMA (Space Division Multiple Access) Communication channel relates to definite regional area or physical infrastructure Space Multiplex for instance in the Analog Phone Systems (for each participant one line), for Broadcasting Stations, and in Cellular Networks Problem: secure distance (interferences) between transmitting stations is required (using one frequency), and by pure Space Multiplex each communication channel would require an own transmitting station Therefore space Multiplex is only reasonable in combination with other multiplex methods

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SDMA: Example k1

k2

k3

k4

k5

k6

f1

s SDMA selects cell

s – secure distance 21

FDMA (Frequency Division Multiple Access) • frequencies are permanently assigned to transmission channels (known from broadcast radio)

k1

k2

k3

k4

k5

k6

f k6 k5

f1 f2 f3

s

FDMA selects frequency

f4 f5 f6

k4 k3 k2 k1

t

s – secure distance 22

TDMA (Time Division Multiple Access) • transmission medium is slot-assigned to channels for certain time, is often used in LANs • Synchronization (timing, static or dynamic) between transmitting and receiving stations is required

k1

k2

TDMA selects slot

k3

k4

k5

f1

k6

f

k1

k2

k3

k4

k5

k6

k1

t 23

Combination: FDMA and TDMA, (e.g. in GSM) • GSM uses combination of FDMA and TDMA for better use of narrow resources • the used bandwidth for each carrier is 200 kHz => approx. 124 * 8 = 992 channels f in MHz TS0 TS1 TS2 TS3 TS4 TS5 TS6 TS7 TS0

960

downlink

TS0 TS1 TS2 TS3 TS4 TS5 TS6 TS7 TS0 25 MHz 935,2

TS0 TS1 TS2 TS3 TS4 TS5 TS6 TS7 TS0

915

TS0 TS1 TS2 TS3 TS4 TS5 TS6 TS7 TS0

200 kHz

uplink

TS0 TS1 TS2 TS3 TS4 TS5 TS6 TS7 TS0

890,2

TS0 TS1 TS2 TS3 TS4 TS5 TS6 TS7 TS0

25 MHz 45 MHz t

24

CDMA (Code Division Multiple Access) k1

CDMA decoded

k2

k3

k4

k5

k6

f1

• definite Codes are assigned to transmission channels, these can be on the same Frequency for the same Time • uses cost-efficient VLSI components • high security level using spread spectrum techniques • but: exact synchronization is required, code of transmitting station must be known to receiving station, complex receivers for signal separation are required; noise should not be very high 25

CDMA illustrated by example • The principle of CDMA can be illustrated by the example of some party: • communication partners stand close to each other, each transmission station (Sender) is only so loud that it does not interfere to neighbored groups • transmission stations (Senders) use certain Codes (for instance, just different languages) • receiving station (Listener) tunes to a specific language (Code) in order to decode the content • if other receiving station (Listener) cannot understand this language (Code), then it can recognize the data (as a kind of background noise), but it cannot do anything with them • if two communication partners would like to have some secure communication line, then they should simply use a secret language (Code)

Potential Problems:  security distance is sometimes too small: interferences (i.e. Polish und Russian) 26

CDMA example technically Sender A • Sends Ad =1, Key Ak = 010011 (set: „0“= -1, „1“= +1) • Transmit signal As =Ad *Ak = (-1, +1, -1, -1, +1, +1) Sender B • sends Bd =0, Key Bk = 110101 (set: „0“= -1, „1“= +1) • Transmit signal Bs =Bd *Bk = (-1, -1, +1, -1, +1, -1) Both signals overlay on the air • Faults are ignored here (noises etc.) • C = As+ Bs =(-2,0,0,-2,+2,0) Receiver will listen to Sender A • uses Key Ak bitwise (internal product)  Ae = C * Ak =2 +0+0 +2 +2+0 = 6  Result is greater than 0, so sent bit was „1“ • likewise B  Be = C * Bk =-2 +0 +0 -2 -2 +0 = -6, i.e. „0“

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Spread Spectrum Techniques dP df

dP df

f

dP df

f

dP df

f

dP df

f

• Signal is spread by the Sender before the transmission • Small-bandwidth faults are spread by de-spreading in receiving station; especially important for CDMA (highly sensitive to faults) • band-pass deletes redundant frequency parts • dP/df value corresponds to called Power Density, Energy is constant (in the Figure: the filled areas) Objective: • Increase of robustness against small-bandwidth faults • Protection against unauthorized receivers: power density of spread-spectrum signals can be lower than that of background noise 28

f