Mobile Communication and Mobile Computing

Prof. Dr. Alexander Schill

http://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 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

4

Building site

Architect

Enterprise A (main office)

Enterprise B

Construction supervisor

Gigabit Ethernet

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: Consumer Application

5

8:56PM

URL LOGIN

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

Service Login

Rent-A-Bike

Alexander Schill Login:

********** Password:

Mobile Multimedia

6

Product Data Client LAN-Access Maintenance

technician

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

Mobile Access

Local Resources, Test Protocols

Main office Caching

Traffic Telematics Systems

7

Internet

Content Provider

Main Office

Infrastructure

GSM

Radio/Infrared

Gigabit Ethernet

Point-to-Point Radio, Internet

Content Provider

DAB: Digital Audio Broadcasting

RDS/TMC: Radio Data System/ Traffic Message Channel

Mobile Communication: Development

8

2000 1995 1990

Mobile Phone Networks

Packet Networks

Circuit Switched Networks

Satellite Networks

Local Networks

2005

D (GSM900) C

Modacom

Mobitex

Tetra

Inmarsat

IR-LAN

IMT/ UMTS

IEEE 802.11 Bluetooth

Radio-LAN

Iridium/ Globalstar

E (GSM1800)

HSCSD

GPRS

Cordless Telephony

CT DECT

2010

4G

(LTE -

advanced,

WiMAX)

EDGE

LTE

2015

Used Acronyms

9

C: Analog “C” Network (1st Generation)

CT: Cordless Telephone

DECT: Digital Enhanced Cordless Telecommunications

GSM: Global System for Mobile Communications (2nd Generation)

GPRS: General Packet Radio Service

HSCSD: High Speed Downlink Packet Access (advanced)

High Speed Uplink Packet Access (advanced)

High Speed Circuit Switched Data

EDGE: Enhanced Data Rates for GSM Evolution

IMT: International Mobile Telecommunications

LTE: Long Term Evolution

TETRA: Terrestrial Trunked Radio (Multicast Communication System)

UMTS: Universal Mobile Telecommunications System (3rd Generation)

4G: 4th Generation Networks

WiMAX Worldwide Interoperability for Microwave Access

C:

CT:

DECT:

GSM:

GPRS:

HSDPA+:

HSUPA+:

HSCSD:

EDGE:

IMT:

LTE:

TETRA:

UMTS:

4G:

WiMAX:

Correspondent data rates

10 1 9 9 5 2 0 0 0 2 0 0 5 2 0 1 0

10 M b i t / s UMTS (pico cell)

1 0 k b i t / s GSM

HSCSD/ GPRS

EDGE

100 k b i t / s

1 M b i t / s

UMTS (macro cell)

Satellites

DECT

100 M b i t / s

300 M b i t / s

2 0 1 5

LTE (uplink) / HSDPA+

LTE (downlink)

WLAN

50 M b i t / s

200 M b i t / s

HSUPA+

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

HIPERLAN1

5176-5270

MHz

Bluetooth

2402-2480

HIPERLAN2

(~5200-5600)

WLAN

2412-2472

HomeRF...(approx.2400)

Circuit Switched Radio Mobile Phones Cordless Phones Wireless LANs

- 2,4 GHz and higher: often license free, nationally different

-> interesting for high data rates

(~17000)

HIPER-Link

1GHz 500Mhz

TFTS - Terrestrial Flight Telephone System

NMT – Nordic Mobile Telephone

IEEE 802.11a: 5,15-5,25; 5,25-5,35; 5,725-5,825

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-equatorial orbit

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 highways or train lines

for covering of 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. 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

15

Structure of a cellular network

• Major problems:

limited frequency resources

interference

• reuse of frequency channels in remote cells

• cluster of N cell types

• reuse distance

• where R – cell radius

16

22 jjiiN

,2,1,0, ji

RND 3

1

1

1

1

2

2 3

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 with R – cell radius; D – reuse distance with 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

f1

f2

f3

f4

f5

f6

s – secure distance

s

FDMA selects frequency

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 selects slot

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

24 t

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

915 200 kHz

935,2

960

25 MHz 45 MHz

25 MHz

uplink

downlink

CDMA (Code Division Multiple Access)

25

k1 k2 k3 k4 k5 k6

f1 CDMA

decoded

• 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

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

df

dP

f

df

dP

f

df

dP

f

df

dP

f

df

dP

f