Mobile Computing - Computer Networks

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Nov 24, 2013 (3 years and 6 months ago)

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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

8:56
PM

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

2
2
j
j
i
i
N







,
2
,
1
,
0
,

j
i
R
N
D


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

R
N
D


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 A
d
=1, Key A
k

= 010011 (set: „0“=
-
1, „1“= +1)


Transmit signal A
s

=A
d

*A
k

= (
-
1, +1,
-
1,
-
1, +1, +1)

Sender B


sends B
d

=0, Key B
k

= 110101 (set: „0“=
-
1, „1“= +1)


Transmit signal B
s

=B
d
*B
k

= (
-
1,
-
1, +1,
-
1, +1,
-
1)


Both signals overlay on the air


Faults are ignored here (noises etc.)


C = A
s
+ B
s

=(
-
2,0,0,
-
2,+2,0)


Receiver will listen to Sender A


uses Key A
k

bitwise (internal product)


A
e

= C * A
k

=2 +0+0 +2 +2+0 = 6


Result is greater than 0, so sent bit was „1“


likewise B


B
e

= C * B
k

=
-
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