01 introduction principles
TRANSCRIPT
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
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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)
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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
• 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
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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
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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
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)
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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
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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)
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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)
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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
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df
dP
f
df
dP
f
df
dP
f
df
dP
f
df
dP
f