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
5
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
6
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
12
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
*
**
13
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
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
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
20
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“
27
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
