Mobile Communication andMobile Computing

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

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

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 Internet Protocols- Web-based Mobile Applications- Mobile Platforms and Middleware- Context Awareness and Adaptation

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

2

Introduction and Principles

3

Application Example: Civil Engineering, Field Service

4

Building site

Architect

Enterprise A(main office)

Enterprise B

Construction supervisor

GigabitEthernet

UMTS, LTE GSM, UMTS

Selected drafts,Videoconferences

Material data,status data,dates

Large archives,Videoconferences

Drafts,urgent modification

Enterprise A(branch office)

Gigabit Ethernet Fast Ethernet

Example: End-User Application

5

Mobile Multimedia

6

Product Data ClientLAN-AccessMaintenance

technician

Very different performances and costs: radio networks versus fixed networks

Software-controlled, automatic adaptation to concrete system environmentsExample: Access to picture data / compressed

picture data / graphics / text

Mobile Access

Local Resources,Test Protocols

Main officeCaching

Traffic Telematics Systems

7

Internet

Content ProviderMain Office

Infrastructure

GSM

Radio/Infrared

GigabitEthernet

Point-to-Point Radio,Internet

Content Provider

DAB: Digital Audio Broadcasting

TMC: Traffic Message Channel

Mobile Communication: Development

8

200019951990

Mobile Phone Networks

Packet Networks

CircuitSwitchedNetworks

Satellite Networks

Local Networks

2005

D (GSM900)C

Modacom

MobitexTetra

Inmarsat

IR-LAN

3G/UMTS

IEEE 802.11Bluetooth

Radio-LAN

Iridium/Globalstar

E (GSM1800)

HSCSD

GPRS

Cordless Telephony

CT DECT

2010

5G(beyondLTE)

EDGE

4G/LTEadvanced

2015 2020

802.11n, acWiMAX

Used Acronyms

9

C: Analog “C” Network (1st Generation)CT: Cordless TelephoneDECT: Digital Enhanced Cordless TelecommunicationsGSM: Global System for Mobile Communications (2nd Generation)GPRS: General Packet Radio ServiceHSCSD:High Speed Downlink Packet Access (advanced)

High Speed Uplink Packet Access (advanced)High Speed Circuit Switched Data

EDGE: Enhanced Data Rates for GSM EvolutionLTE: Long Term EvolutionTETRA: Terrestrial Trunked Radio (Multicast Communication System)UMTS: Universal Mobile Telecommunications System (3rd Generation)4G: 4th Generation NetworksWiMAX Worldwide Interoperability for Microwave Access

C:CT:

DECT: GSM:

GPRS:HSDPA+:HSUPA+:

HSCSD:EDGE:

LTE:TETRA:UMTS:

4G: WiMAX:

Correspondent data rates

101995 2000 2005 2010

10Mbit/s UMTS(pico cell)

10kbit/s GSM

HSCSD/GPRS

EDGE

100kbit/s

1 Mbit/s

UMTS(macro cell)

Satellites

DECT

100 Mbit/s

300Mbit/s

2015

LTE (uplink) / HSDPA+

LTE (downlink)

WLAN

50Mbit/s

200 Mbit/s

HSUPA+

2020

1Gbit/s

5G

Frequency Assignment

11

TETRA

380-400

410-430

NMT

453-457

463-467

CT2

864-868

CT1+

885-887 890-915

GSM900 CT1+

930-932

GSM900

935-960

TFTS (Pager, aircraft phones) GSM1800

1670-1675 1710-1785 1800-1805

TFTS

1805-1880

GSM1800 DECT

1880-1900 (1885-2025

2110-2200)

TETRA

450-470

(nationally different)

UMTS

IEEE 802.11b/g/n

2400-2483 5176-5270

MHz

Bluetooth

2402-2480

Future 5G

Beyond 5 GHz up to 100 GHz

WLAN

2412-2472

Circuit Switched Radio Mobile Phones Cordless Phones Wireless LANs

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

1GHz500Mhz

TFTS - Terrestrial Flight Telephone System

NMT – Nordic Mobile Telephone

IEEE 802.11a/n

790-862

LTE 800

2500-2690

LTE 2600 WIMAX

3500

Principles of Mobile Communication

12

Based on electro-magnetic radio transmission

radio transmission

terrestrial orbital (satellite)

point-to-point Broadcast radio equatorial orbit

non-equatorialorbit

cellular non-cellular

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

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

13

along highwaysor train lines

for coveringof larger areas

* **

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

Cellular networks: handover (1)

14

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. UMTS and LTE); 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

15

Structure of a cellular network

• Major problems:§ limited frequency

resources§ interference

• Therefore: reuse of frequency channels in remote cells

• Recommended reuse distance D:

where:N is the number of different cell types, andR is the cell radius

16

RND ⋅= 3

1

1

1

1

2

23

3

4

4

D/R Ratios versus Reuse Patterns

17

R

D/R-­Ratio Cluster  size,    N

3,46 4

4,6 7

6 12

7,55 19

3 3

RND ⋅= 3

Cluster of N cells withR – cell radius; D – reuse distancewith the use of sectorized antennas

Frequency Distribution: Examples

18

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

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

20

SDMA: Example

21

k1 k2

s

s – secure distance

k3 k4 k5 k6

SDMA selects cell

f1

FDMA (Frequency Division Multiple Access)

• frequencies are permanently assigned to transmission channels (known from broadcast radio)

22

k1 k2 k3 k4 k5 k6

f1f2f3

f4f5f6

s – secure distance

s

FDMA selectsfrequency

t

f

k1

k2

k3

k4

k5

k6

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

23

k1 k2 k3 k4 k5 k6

f1

t

f

k1 k2 k3 k4 k5 k6 k1

TDMA selectsslot

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

24t

f in MHz

TS0 TS1 TS2 TS3 TS4 TS5 TS6 TS7 TS0

TS0 TS1 TS2 TS3 TS4 TS5 TS6 TS7 TS0

TS0 TS1 TS2 TS3 TS4 TS5 TS6 TS7 TS0

TS0 TS1 TS2 TS3 TS4 TS5 TS6 TS7 TS0

TS0 TS1 TS2 TS3 TS4 TS5 TS6 TS7 TS0

TS0 TS1 TS2 TS3 TS4 TS5 TS6 TS7 TS0

890,2

915200 kHz

935,2

960

25 MHz 45 MHz

25 MHz

uplink

downlink

CDMA (Code Division Multiple Access)

25

k1 k2 k3 k4 k5 k6

f1CDMA

decoded

• definite Codes are assigned to transmission channels, these can be on the same Frequency for the same Time

• Implemented efficiently in hardware• 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

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“

27

Spread Spectrum Techniques

• 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

dfdP

f

dfdP

f

dfdP

f

dfdP

f

dfdP

f