Mobile Communications

1
Mobile Communications

• Prof. Dr.-Ing. Rolf Kraemer
• Lehrstuhl für Systeme, BTU Cottbus
• Abteilungsleiter Drahtlose Systeme, IHP
• kraemer_at_ihp-microelectronics.com
• Tel [phone]

2
Overview of the lecture

• Introduction
• Use-cases, applications
• Definition of terms
• Challenges, history
• Wireless Transmission
• frequencies regulations
• signals, antennas, signal propagation
• multiplexing, modulation, spread spectrum,
  cellular system
• Media Access
• motivation, SDMA, FDMA, TDMA (fixed, Aloha, CSMA,
  DAMA, PRMA, MACA, collision avoidance, polling),
  CDMA

• Wireless LANs
• Basic Technology
• IEEE 802.11a/b/g,
• IEEE802.15.1/.3/.4
• Bluetooth

3
Institute Building
Summer 2001
4
IHP in a Nutshell

• (Re)founded 1992
• Re-establish region as high tech area
• Create high tech jobs
• Budget 20 Mio , National Research Lab
• Third Party Funding 13 Mio
• About 250 employees
• Since 1996 focus on wireless and broadband
  communication technologies
• System Design (50)
• RF Circuit Design (30)
• Technology
• Pilot Line (80)
• Process Research (20)
• Materials, Diagnosticsand Prototyping (10)
• Material Research (15)

5
IHP-Structure
6
IHP IC Prototyping and Production Services

• MPW-Shuttle runs (Multi Project Wafer)
• Have a low cost entry into your chip realization
• Starting with 2500/mm2 up to 7000/mm2
• Share cost with others
• Have regular tape outs and sample delivery
• 50 samples you get per run additional samples
  on mutual agreement
• Engineering Run
• Have you own run with your own mask set
• Get 6 wafers with your own designs
• Allow cost effective re-ordering of wafers
• Start the run whenever you wish

7
Cleanroom
8
Strategy
IHPs Technology Focus More than Moore
THz Electronics
Si Photonics
SoC
IHP

• Scaling Down
• E-Beam (Mix-Match)
• CMOS Cooperation
• LETI, IMEC and/or
• Companies

Source ITRS Roadmap
9
MPW Offering
C 5
C 11
C 14
C 12
C 13
C 19
C 18
C 10
C 16
C 15
C 7
C 8
C 17
C 9
C 6
10
CD Groups
mm-Wave Wireless-Transceivers (Scheytt)
Broadband Mixed- Signal (Gustat)
Ultra-Low-Power Wireless-Transceivers
(Fischer)
11
Projects

• mm-Wave Wireless 100 GHz and beyond
• Benchmarking (internal)
• Communication building blocks up to gt100 GHz
• Feasibility of communication building blocks in
  SiGe technologies
• Operating frequencies up to gt ½ fT, fmax
• TeraCom (Leibniz excellence project, started Jan.
  2008)
• Wireless frontend for THz communication 100
  Gbps_at_250 GHz
• Short range communication, WPAN, wireless data
  sync

Slow-wave transmission line
95 GHz frequency divider
115 GHz to 180 GHz VCO
94 to 180 GHz LNAs
12
Projects

• mm-Wave Radar
• KOKON (BMBF, ended Q2 / 2007)
• 77...81 GHz VCO, PA, Radar RX Frontend in SiGe
• Automotive Radar, Adaptive Cruise Control
• 24 GHz Radar (internal industry, Q2 / 2007
  transferred to spin-off)
• 24 GHz radar components, radar frontend
• Autmotive radar, ultra-low cost radar for
  security applications

77 GHz Mixer
77 81 GHz VCO w. PA, Layout Plot
79 GHz Radar Receiver Frontend
13
Projects

• Integrated Frequency Synthesizers
• SiMS, 3020 (ESA), SiSSi (DLR)
• 10 GHz, 19 GHz DSM fractional-N synthesizer PLLs
• Fully-integrated, radiation-hard
• Broadband satellite communication
• MxMobile (BMBF)
• Fully-integrated synthesizer in SiGe BiCMOS for
  0.7 4.4 GHz
• Multi-standard / multi-band basestations,
  software-defined radio (SDR)
• Easy-A, WIGWAM (BMBF)
• Fully-integrated 56 GHz Synthesizer
• Fully-integrated 48 GHz Synthesizer
• 60 GHz WPAN

Chip photo 19 GHz Synthesizer
Layout Plot 19 GHz Synthesizer
56 GHz Synthesizer
48 GHz Synthesizer
14
Projects

• Low-Power Wireless Frontends
• Pulsers II (EU FP6)
• 3 to 10 GHz Impulse Ultra-Wide-Band Frontend
  with localization
• Sensor networks, localization
• Homeplane (BMBF)
• 5 GHz WLAN Transceiver 802.11a/p
• WLAN, car-2-car communication
• GPS LNA (industry)
• Low-cost, low-noise GPS LNA
• GPS in cell phones
• MiMAX (EU FP7, started Jan. 2008)
• MIMO Frontend with analog combining
• High-performance low-power WLAN

UWB RX IC
UWB test board
15
Wireless Systems Roadmap (Source Fettweis)
16
Organisation of the department
Wireless Systems Prof. R. Kraemer
Main Projects HomePlaneOMEGA Galaxy MIMAX EASY-A
Terahertz
Main Projects Tandem WSAN4CIP RealFlex FeuerWhere
Matrix SMART Secure Sensornode
Main Projects Libraries for 0.25 mm and 130
nm Radiation hard designs Test Methodologies Proce
ssors DEDIS SATIS
17
Wireless Engine
Non Functional Requirements
Appl
Appl. Eng.
Prot. Eng.
Power Mang.
Test Eng.
TCP/IP
DLC
Management Plane
BB
RF
BB
DLC
Phy
Basic Communication Processing
18
Single-Chip Modem for embedded Applications

• Main Components
• 5 GHz Analog Frontend (Superhet., 810 MHz IF)
• A/D and D/A Converters (7 Instances)
• OFDM Baseband Processor with Synchronisation and
  Channel Estimation
• MAC-Processor (MIPS-4kE) with Hardware-Accelerator
  
• PCMCIA (CardBus) Interface plus 2x UART and 1x
  I2C-Bus Interface
• Cache-Memory for MIPS und Data Buffers (44 kByte
  in total)
• Built-in Self-Test (BIST) with various specific
  test-modi
• EMI protection n-well Ring, GND-Ring,Buried
  Layer inside AFE

• Main Parameters
• Chip-Area ca. 90 mm2
• No. of Pins 240
• Power dissipation 2W (simulated)
• Clock frequency 80 MHz

19
Video Supply in Trains, Busses, Aircraft

• Combination of two Radios needed to achieve 100
  coverage
• High rate (60 GHz) system and secondary system
  (UWB, 802.11x) for video supply
• Data Shower 60 GHz only required for downlink
• Water-filling The secondary system covers only
  the gaps left by the 60 GHz
• Secondary system can also be used as
  feedback/control/management channel

20
PHY Parameters
RF band before and after first down-conversion
21
Architecture of Basisbandprocessors, Status
22
Constellation Diagram of 60 GHz OFDM Link
- OFDM, 16 QAM, - r 3/4, 720 Mbit/s -
TX-Power lt 0 dBm - Distance ca. 10 cm Use of
commercial Signal Generator and Vector Signal
Analyzer H/W in the loop approach with software
synchronizer BB-receiver
23
Enhanced Demonstrator at France Telecom
World first UWB at 60 GHz demonstration Hybrid
mode supported
Up to 200 Mb/s (3m) transmission speed
24
Distributed Control
Speech Input
CharacteristicsEach component is
self-supporting Communication as a result of
function calls by other modules AdvantagesSimple
modular scalabilityIdentical communication
structureLocal Intelligence DisadvantagesPotent
ially higher cost
Headset
Step counter
Distributed Control
Distributed Middleware
Display
MP3 Player
Pulse meter
25
Example of a body area system
Distributed Middleware
26
BAN Node Architecture
Serial

UART
I- SPRAM
DMA
IRQ
CPU
EJTAG
AMBA AHB
APB
EC
GPIO
Bridge
Bridge
GPIO
Protocol Processor
Memory Controller
Flash
D- SPRAM
SRAM
AES
Transceiver
iRAM
Antenna
27
TCP_2 Processor (WI, MBE)
Chip Photo of TCP_2 area 54
mm² transistors 4,300,000 memory 62
kByte SRAM speed 33 MHz (CardBus
clock) package LQFP-256 / 244 pins used

• Block Diagram of TCP_2 Implementation
• - power control via sleep mode possible

28
HW Accelerators Dual2 Crypto Chip

• Dual Crypto Support
• Secret Key Cryptography Advanced Encryption
  Standard (128 bit)
• Public Key Cryptography Elliptic Curve
  Cryptography (233 bit)
• Dual Interface
• PCCard
• Cardbus
• Characteristics

29
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30
Introduction and History
31
Mobile communication

• Two aspects of mobility
• user mobility
• users communicate (wireless) anytime, anywhere,
  with anyone
• device portability
• devices can be connected anytime, anywhere to the
  network
• Wireless vs. mobile Examples
• no no stationary computer
• no yes notebook in a hotel (more and more
  wireless access)
• yes no wireless LANs in historic buildings
• yes yes Personal Digital Assistant (PDA),
  Smartphone
• The demand for mobile communication creates the
  need for integration of wireless networks into
  existing fixed networks
• local area networks standardization of IEEE
  802.11, ETSI (HIPERLAN)
• Internet Mobile IP extension of the internet
  protocol IP
• wide area networks e.g., internetworking of GSM
  and ISDN

32
Applications I

• Vehicles (car-2-X)
• transmission of news, road condition, weather,
  music via DAB
• personal communication using GSM
• position via GPS
• local ad-hoc network with vehicles close-by to
  prevent accidents, guidance system, redundancy
• vehicle data (e.g., from busses, high-speed
  trains) can be transmitted in advance for
  maintenance
• Emergencies
• early transmission of patient data to the
  hospital, current status, first diagnosis
• replacement of a fixed infrastructure in case of
  earthquakes, hurricanes, fire etc.
• crisis, war, ...

33
Typical application road traffic
34
Location dependent services

• Location aware services
• what services, e.g., printer, fax, phone, server
  etc. exist in the local environment
• Follow-on services
• automatic call-forwarding, transmission of the
  actual workspace to the current location
• Information services
• push e.g., current special offers in the
  supermarket
• pull e.g., where is the Black Forrest Cherry
  Cake?
• Support services
• Caches, intermediate results, state information
  etc. follow the mobile device through the fixed
  network
• Privacy
• who should gain knowledge about the location

35
Wireless networks in comparison to fixed networks

• Higher loss-rates due to interference
• emissions of, e.g., engines, lightning
• Restrictive regulations of frequencies
• frequencies have to be coordinated, useful
  frequencies are almost all occupied
• Low transmission rates
• local some Mbit/s, regional currently, e.g., 53
  kbit/s with GSM/GPRS
• Higher delays, higher jitter
• connection setup time with GSM in the second
  range, several hundred milliseconds for other
  wireless systems
• Lower security, simpler active attacking
• radio interface accessible for everyone, base
  station can be simulated, thus attracting calls
  from mobile phones
• Always shared medium
• secure access mechanisms important

36
Early history of wireless communication

• Many people in history used light for
  communication
• heliographs, flags (semaphore), ...
• 150 BC smoke signals for communication(Polybius,
  Greece)
• 1794, optical telegraph, Claude Chappe
• Here electromagnetic waves areof special
  importance
• 1831 Faraday demonstrates electromagnetic
  induction
• J. Maxwell (1831 - 79) theory of electromagnetic
  Fields, wave equations (1864)
• H. Hertz (1857 - 94) demonstrateswith an
  experiment the wave characterof electrical
  transmission through space(1888, in Karlsruhe,
  Germany, at thelocation of todays University of
  Karlsruhe)

37
History of wireless communication I

• 1896 Guglielmo Marconi
• first demonstration of wirelesstelegraphy
  (digital!)
• long wave transmission, hightransmission power
  necessary (gt 200 kW)
• 1907 Commercial transatlantic connections
• huge base stations(30100m high antennas)
• 1915 Wireless voice transmission New York - San
  Francisco
• 1920 Discovery of short waves by Marconi
• reflection at the ionosphere
• smaller sender and receiver, possible due to the
  invention of the vacuum tube (1906, Lee DeForest
  and Robert von Lieben)
• 1926 Train-phone on the line Hamburg Berlin
• wires parallel to the railroad track

38
History of wireless communication II

• 1928 many TV broadcast trials (across Atlantic,
  color TV, TV news)
• 1933 Frequency modulation (E. H. Armstrong)
• 1958 A-Netz in Germany
• analog, 160 MHz, connection setup only from the
  mobile station, no handover, 80 coverage, 1971
  11000 customers
• 1972 B-Netz in Germany
• analog, 160 MHz, connection setup from the fixed
  network too (but location of the mobile station
  has to be known)
• available also in A, NL and LUX, 1979 13000
  customer in D
• 1979 NMT at 450 MHz (Scandinavian countries)
• 1982 Start of GSM-specification
• goal pan-European digital mobile phone system
  with roaming
• 1983 Start of the American AMPS (Advanced Mobile
  Phone System, analog)
• 1984 CT-1 standard (Europe) for cordless
  telephones

39
History of wireless communication III

• 1986 C-Netz in Germany
• analog voice transmission, 450 MHz, hand-over
  possible, digital signaling, automatic location
  of mobile device
• Was in use until 2000, services FAX, modem,
  X.25, e-mail, 98 coverage
• 1991 Specification of DECT
• Digital European Cordless Telephone (today
  Digital Enhanced Cordless Telecommunications)
• 1880 1900 MHz, 100 500 m range, 120 duplex
  channels, 1.2 Mbit/s data transmission, voice
  encryption, authentication, up to several 10000
  user/km2, used in more than 50 countries
• 1992 Start of GSM
• in D as D1 and D2, fully digital, 900 MHz, 124
  channels
• automatic location, hand-over, cellular
• roaming in Europe - now worldwide in more than
  200 countries
• services data with 9.6 kbit/s, FAX, voice, ...

40
History of wireless communication IV

• 1994 E-Netz in Germany
• GSM with 1800 MHz, smaller cells
• As Eplus in D (1997 98 coverage of the
  population)
• 1996 HiperLAN (High Performance Radio Local Area
  Network)
• ETSI, standardization of type 1 5.15 - 5.30 GHz,
  23.5 Mbit/s
• recommendations for type 2 and 3 (both 5 GHz)
  and 4 (17 GHz) as wireless ATM-networks (up to
  155 Mbit/s)
• 1997 Wireless LAN - IEEE802.11
• IEEE standard, 2.4 - 2.5 GHz and infrared, 2
  Mbit/s
• already many (proprietary) products available in
  the beginning
• 1998 Specification of GSM successors
• for UMTS (Universal Mobile Telecommunication
  System) as European proposals for IMT-2000
• Iridium
• 66 satellites (6 spare), 1.6 GHz to the mobile
  phone

41
History of wireless communication V

• 1999 Standardization of additional wireless LANs
• IEEE standard 802.11b, 2.4 - 2.5 GHz, 11 Mbit/s
• Bluetooth for piconets, 2.4 Ghz, lt 1 Mbit/s
• Decision about IMT-2000
• Several members of a family UMTS, cdma2000,
  DECT,
• Start of WAP (Wireless Application Protocol) and
  i-mode
• First step towards a unified Internet/mobile
  communicaiton system
• Access to many services via the mobile phone
• 2000 GSM with higher data rates
• HSCSD offers up to 57.6 kbit/s
• First GPRS trials with up to 50 kbit/s (packet
  oriented!)
• UMTS auctions/beauty contests
• Hype followed by disillusionment (100 B DM payed
  in Germany for 6 licenses!)
• 2001 Start of 3G systems
• Cdma2000 in Korea, UMTS tests in Europe, Foma
  (almost UMTS) in Japan

42
Wireless systems Overview of the development
wireless LAN
cordlessphones
cellular phones
satellites
1980CT0
1981 NMT 450
1982 Inmarsat-A
1983 AMPS
1984CT1
1986 NMT 900
1987CT1
1988 Inmarsat-C
1989 CT 2
1991 DECT
1991 D-AMPS
1991 CDMA
199x proprietary
1992 GSM
1992 Inmarsat-B Inmarsat-M
1993 PDC
1997 IEEE 802.11
1994DCS 1800
1998 Iridium
1999 802.11b, Bluetooth
2000 IEEE 802.11a
2000GPRS
analogue
2001 IMT-2000
digital
200? Fourth Generation (Internet based)
4G fourth generation when and how?
43
Mobile phone subscribers worldwide
44
Development of mobile telecommunication systems
CT0/1
FDMA
AMPS
CT2
NMT
IMT-FT DECT
IS-136 TDMA D-AMPS
EDGE
IMT-SC IS-136HS UWC-136
TDMA
GSM
GPRS
PDC
IMT-DS UTRA FDD / W-CDMA
IMT-TC UTRA TDD / TD-CDMA
CDMA
IMT-TC TD-SCDMA
IS-95 cdmaOne
IMT-MC cdma2000 1X EV-DO
cdma2000 1X
1X EV-DV (3X)
1G
2G
3G
2.5G
45
Areas of research in mobile communication

• Wireless Communication
• transmission quality (bandwidth, error rate,
  delay)
• modulation, coding, interference
• media access, regulations
• ...
• Mobility
• location dependent services
• location transparency
• quality of service support (delay, jitter,
  security)
• ...
• Portability
• power consumption
• limited computing power, sizes of display, ...
• Usability
• ...

46
Development of Mobile Access Speed

• Source VTC-2007, Fettweis

47
Simple reference model used here
Application
Application
Transport
Transport
Network
Network
Data Link
Data Link
Data Link
Data Link
Physical
Physical
Physical
Physical
Medium
Radio
48
Influence of mobile communication to the layer
model

• service location
• new applications, multimedia
• adaptive applications
• congestion and flow control
• quality of service
• addressing, routing, device location
• hand-over
• authentication
• media access
• multiplexing
• media access control
• encryption
• modulation
• interference
• attenuation
• frequency

• Application layer
• Transport layer
• Network layer
• Data link layer
• Physical layer

49
Physical Layer Issues
50
Frequencies for communication
coax cable
twisted pair
optical transmission
1 Mm 300 Hz
10 km 30 kHz
100 m 3 MHz
1 m 300 MHz
10 mm 30 GHz
100 ?m 3 THz
1 ?m 300 THz
visible light
VLF
LF
MF
HF
VHF
UHF
SHF
EHF
infrared
UV

• VLF Very Low Frequency UHF Ultra High
  Frequency
• LF Low Frequency SHF Super High Frequency
• MF Medium Frequency EHF Extra High
  Frequency
• HF High Frequency UV Ultraviolet Light
• VHF Very High Frequency
• Frequency and wave length
• ? c/f
• wave length ?, speed of light c ? 3 x 108 m/s,
  frequency f

51
Signals I

• physical representation of data
• function of time and location
• signal parameters parameters representing the
  value of data
• classification
• continuous time/discrete time
• continuous values/discrete values
• analog signal continuous time and continuous
  values
• digital signal discrete time and discrete
  values
• signal parameters of periodic signals period T,
  frequency f 1/T, amplitude A, phase shift ?
• sine wave as special periodic signal for a
  carrier s(t) At sin(2 ? ft t ?t)

52
Fourier representation of periodic signals
1
1
0
0
t
t
ideal periodic signal
real composition (based on harmonics)
53
Signals II

• Different representations of signals
• amplitude (amplitude domain)
• frequency spectrum (frequency domain)
• phase state diagram (amplitude M and phase ? in
  polar coordinates)
• Composed signals transferred into frequency
  domain using Fourier transformation
• Digital signals need
• infinite frequencies for perfect transmission
• modulation with a carrier frequency for
  transmission (analog signal!)

54
Antennas isotropic radiator

• Radiation and reception of electromagnetic waves,
  coupling of wires to space for radio transmission
• Isotropic radiator equal radiation in all
  directions (three dimensional) - only a
  theoretical reference antenna
• Real antennas always have directive effects
  (vertically and/or horizontally)
• Radiation pattern measurement of radiation
  around an antenna
• Is used as reference for measuring of antennas
  (EIRP Equivalent Isotropic Radiated Power)

z
z
y
ideal isotropic radiator
y
x
x
55
Antennas simple dipoles

• Real antennas are not isotropic radiators but,
  e.g., dipoles with lengths ?/4 on car roofs or
  ?/2 as Hertzian dipole? shape of antenna
  proportional to wavelength
• Example Radiation pattern of a simple Hertzian
  dipole
• Gain maximum power in the direction of the main
  lobe compared to the power of an isotropic
  radiator (with the same average power)
• Gain measure in dBi ( 10log10P1/P2)

Metallic Surface
56
Antennas directed and sectorized

• Often used for microwave connections or base
  stations for mobile phones (e.g., radio coverage
  of a valley)

y
y
z
directed antenna
x
z
x
side view (xy-plane)
side view (yz-plane)
top view (xz-plane)
z
z
sectorized antenna
x
x
top view, 3 sector
top view, 6 sector
57
(passive) Antennas diversity

• Grouping of 2 or more antennas
• multi-element antenna arrays
• Antenna diversity
• switched diversity, selection diversity
• receiver chooses antenna with largest output
• diversity combining
• combine output power to produce gain
• co-phasing needed to avoid cancellation

?/2
?/2
?/4
?/2
?/4
?/2


ground plane
58
Signal propagation ranges

• Transmission range
• communication possible
• low error rate
• Detection range
• detection of the signal possible
• no communication possible
• Interference range
• signal may not be detected
• signal adds to the background noise

sender
transmission
distance
detection
interference
59
Signal propagation

• Propagation in free space always like light
  (straight line)
• Receiving power proportional to 1/d² (d
  distance between sender and receiver)
• Receiving power additionally influenced by
• fading (frequency dependent H2O resonance at 2.5
  GHz O2 Resonance at 60 GHz)
• shadowing
• reflection at large obstacles
• refraction depending on the density of a medium
• scattering at small obstacles
• diffraction at edges

refraction
reflection
scattering
diffraction
shadowing
60
Real world example
61
Friis free-space equation in logarithmic form

• Prcvd(d) PtxGtGrPL in dB
• path loss in free space
• PL 10log10(4pdf/c)2 20log10(f)
  20log10(d) -20log10(c/4p)
• D Distance between Sender and Receiver
• f Frequency
• c Speed of light (300000km/s)
• First Fresnel Zone considerations for antenna
  highs and reference distance

d0
62
Multipath propagation

• Signal can take many different paths between
  sender and receiver due to reflection,
  scattering, diffraction
• Time dispersion signal is dispersed over time
  (delay spread)
• ? interference with neighbor symbols, Inter
  Symbol Interference (ISI)
• The signal reaches a receiver directly and phase
  shifted ? distorted signal depending on the
  phases of the different parts

multipath pulses
LOS pulses
signal at sender
signal at receiver
63
Multiplexing

• Multiplexing in 4 dimensions
• space (si)
• time (t)
• frequency (f)
• code (c)
• Goal multiple use of a shared medium
• Important guard spaces needed!

SM
64
Frequency multiplex

• Separation of the whole spectrum into smaller
  frequency bands
• A channel gets a certain band of the spectrum for
  the whole time
• Advantages
• no dynamic coordination necessary
• works also for analog signals
• Disadvantages
• waste of bandwidth if the traffic is
  distributed unevenly
• inflexible
• guard spaces

k2
k3
k4
k5
k6
k1
c
f
t
65
Time multiplex

• A channel gets the whole spectrum for a certain
  amount of time
• Advantages
• only one carrier in themedium at any time
• throughput high even for many users
• Disadvantages
• precise synchronization necessary

k2
k3
k4
k5
k6
k1
c
f
t
66
Time and frequency multiplex

• Combination of both methods
• A channel gets a certain frequency band for a
  certain amount of time
• Example GSM
• Advantages
• better protection against tapping
• protection against frequency selective
  interference
• higher data rates as compared tocode multiplex
• but precise coordinationrequired

k2
k3
k4
k5
k6
k1
c
f
t
67
Code multiplex
k2
k3
k4
k5
k6
k1

• Each channel has a unique code
• All channels use the same spectrum at the same
  time
• Advantages
• bandwidth efficient
• no coordination and synchronization necessary
• good protection against interference and tapping
• Disadvantages
• lower user data rates
• more complex signal regeneration
• Implemented using spread spectrum technology

c
f
t
68
Modulation

• Digital modulation
• digital data is translated into an analog signal
  (baseband)
• ASK, FSK, PSK - main focus in this chapter
• differences in spectral efficiency, power
  efficiency, robustness
• Analog modulation
• shifts center frequency of baseband signal up to
  the radio carrier
• Motivation
• smaller antennas (e.g., ?/4)
• Frequency Multiplexing
• medium characteristics
• Basic schemes
• Amplitude Modulation (AM)
• Frequency Modulation (FM)
• Phase Modulation (PM)

69
Modulation and demodulation
analog baseband signal
digital data
digital modulation
analog modulation
radio transmitter
101101001
radio carrier
analog baseband signal
digital data
analog demodulation
Synchronization/digital Demodulation/decision
radio receiver
101101001
radio carrier
70
Digital modulation

• Modulation of digital signals known as Shift
  Keying
• Amplitude Shift Keying (ASK)
• very simple
• low bandwidth requirements
• very susceptible to interference
• Frequency Shift Keying (FSK)
• needs larger bandwidth
• Phase Shift Keying (PSK)
• more complex
• robust against interference

71
Advanced Phase Shift Keying

• BPSK (Binary Phase Shift Keying)
• bit value 0 sine wave
• bit value 1 inverted sine wave
• very simple PSK
• low spectral efficiency
• robust, used e.g. in satellite systems
• QPSK (Quadrature Phase Shift Keying)
• 2 bits coded as one symbol
• symbol determines shift of sine wave
• needs less bandwidth compared to BPSK
• more complex
• Often also transmission of relative, not absolute
  phase shift DQPSK - Differential QPSK (IS-136,
  PHS)

72
Quadrature Amplitude Modulation

• Quadrature Amplitude Modulation (QAM) combines
  amplitude and phase modulation
• it is possible to code n bits using one symbol
• 2n discrete levels, n 2 identical to QPSK
• bit error rate increases with n, but less errors
  compared to comparable PSK schemes
• Example 16-QAM (4 bits 1 symbol)
• Symbols 0011 and 0001 have the same
  phase, but different amplitude. 0000 and
  1000 have different phase, but same
  amplitude.
• Used in several high speed systems

Q
0010
0001
0011
0000
I
1000
73
Hierarchical Modulation

• DVB-T modulates two separate data streams onto a
  single DVB-T stream
• High Priority (HP) embedded within a Low Priority
  (LP) stream
• Multi carrier system, about 2000 or 8000 carriers
  (OFDM)
• QPSK, 16 QAM, 64QAM
• Example 64QAM
• good reception resolve the entire 64QAM
  constellation
• poor reception, mobile reception resolve only
  QPSK portion
• 6 bit per QAM symbol, 2 most significant
  determine QPSK
• HP service coded in QPSK (2 bit), LP uses
  remaining 4 bit

Q
10
I
00
000010
010101
74
Multi Carrier Modulation (MCM)

• With Multi Carrier Modulation (MCM) the data
  stream is spilt into several concurrent
  communication streams using different frequencies
  
• Example of MCM are ADSL and OFDM where each
  frequency is further modulated using BPSK or QAM
• For IEEE802.11a/g and Hiperlan-2, LTE OFDM is
  used
• OFDM uses orthogonal frequencies to avoid inter
  carrier interference
• It uses long symbols to reduce ISI and to avoid
  complex equalization
• The initial symbol rate n can be divided onto m
  carriers such that the symbol rate/carrier is
  n/m.
• The distance between symbols (in the time domain)
  becomes larger and thus the ISI smaller.

75
MCM model for transmission
Ts T N(2(k-1)/Rb)
Rb ? bit rate (bps)
FFT
76
Fourier transform of a single puls
F
T/2
FT
-T/2
rect(T) si(T) sin(T)/T
77
OFDM model for transmission (contd)
Modulation factor
Constant phase
Fourier Transform
How do we select an appropiate value for ?f ?
78
OFDM model for transmission (contd)
?f 0.8/T
f T
We find ICI (Inter-Carrier-Interference)
?f 1.2/T
f T
79
OFDM model for transmission (contd)
?f 1/T
f T
No ICI We have orthogonality between the
different subcarriers
80
Components of a real OFDM system
Transmitter
Channel Coding
Modulation Interleaving
FFT
D/A
RF- Transmission
Receiver
Channel Decoding
Demodulation Deinterleaving
IFFT
A/D
RF- Reception
Synchronizer
Channel Estimator
81
Required Signal/Noise at the Receiver

• During transmission and reception noise will be
  added to the signal
• Thermal noise (Bolzmann noise)
• Receiver Noise (Noise Figure)
• Transmitter Noise caused by non linearities
• etc.
• The effect for the received signal is that in the
  constellation diagram the not a signal point but
  a cloud of points around the expected point are
  received.
• Due to these noise and distortion impacts the
  signal/noise (S/N) ratio to receive a signal
  correctly is at least around gt6 dB.
• The S/N is dependant on the modulation and the
  transmission type
• For 64 QAM the S/N is at least 4 dB higher than
  for 16 QAM etc.

82
5 GHz Analog-Transceiver Blocks
83
Spread spectrum technology

• Problem of radio transmission frequency
  dependent fading can wipe out narrow band signals
  for duration of the interference
• Solution spread the narrow band signal into a
  broad band signal using a special code
• Side effects
• coexistence of several signals without dynamic
  coordination
• tap-proof
• Alternatives Direct Sequence, Frequency Hopping

signal
interference
spread signal
power
power
spread interference
detection at receiver
f
f
84
Effects of spreading and interference
dP/df
dP/df
user signal broadband interference narrowband
interference
i)
ii)
f
f
sender
dP/df
dP/df
dP/df
iii)
iv)
v)
f
f
f
receiver
85
Spreading and frequency selective fading
narrowband channels
narrow bandsignal
spread spectrum channels
By spreading the effect of the fading channel is
equally distributed to all users! How can we
avoid interference of the chips?
86
DSSS (Direct Sequence Spread Spectrum) I

• XOR of the signal with pseudo-random number
  (chipping sequence)
• many chips per bit (e.g., 128, best known 11)
  result in higher bandwidth of the signal
• Advantages
• reduces frequency selective fading
• in cellular networks
• base stations can use the same frequency range
• several base stations can detect and recover the
  signal
• soft handover
• Disadvantages
• precise power control necessary
• Precise synchronization necessary(multi
  correlators can take advantagefrom multi-path
  propagation (Rake-receiver)

Spreading Factor s tb/tc
tb
user data
0
1
XOR
tc
chipping sequence
0
1
1
0
1
0
1
0
1
0
0
1
1
1

resulting signal
0
1
1
0
0
1
0
1
1
0
1
0
0
1
tb bit period tc chip period
87
DSSS (Direct Sequence Spread Spectrum) II
spread spectrum signal
transmit signal
user data
X
modulator
chipping sequence
radio carrier
transmitter
correlator
lowpass filtered signal
sampled sums
products
received signal
data
demodulator
X
integrator
decision
radio carrier
chipping sequence
receiver
88
Example Barker Code
89
FHSS (Frequency Hopping Spread Spectrum) I

• Discrete changes of carrier frequency
• sequence of frequency changes determined via
  pseudo random number sequence
• Two versions
• Fast Hopping several frequencies per user bit
• Slow Hopping several user bits per frequency
• Advantages
• frequency selective fading and interference
  limited to short period
• simple implementation
• uses only small portion of spectrum at any time
• Disadvantages
• not as robust as DSSS
• simpler to detect

90
FHSS (Frequency Hopping Spread Spectrum) II
tb
user data
0
1
0
1
1
t
f
td
f3
slow Hopping tblttd (3 bits/hop)
f2
f1
t
td
f
f3
fast Hopping tbgttd (3 hops/bit)
f2
f1
t
tb bit period td dwell time
91
FHSS (Frequency Hopping Spread Spectrum) III
spread transmit signal
narrowband signal
user data
Digital modulator
Analog modulator
transmitter
hopping sequence
frequency synthesizer
narrowband signal
received signal
data
Digital demodulator
Analog demodulator
hopping sequence
frequency synthesizer
receiver
92
Example Bluetooth Frequency Hopping

• Bluetooth uses a slow frequency hopping scheme
• The frequency is changed every slot (625 ms) so
  approximately 1600 hops/s
• For multi-slot packets the frequency is changed
  with the next packet
• The hopping sequence is determined by the master
  (derived from the bluetooth MAC address)
• During inquiry and paging the the master MAC and
  timing offset is exchanged with the slaves
• The slot are enumerated from 0 to 2 27 1
• The master uses always the even slot
• The slot size is 1, 3 or 5

93
Master / Slave Communication
B
D
Ma
SCO
A
E
C
ACL
f(k)
f(k2)
f(k4)
f(k6)
f(k8)
f(k10)
f(k14)
f(k12)
f(k16)
f(k20)
f(k18)
f(k22)
f(k24)
A
B
C
D
E
t
SCO 1
SCO 2
SCO 1
SCO 2
SCO 1
ACL
ACL
ACL
ACL
94
UWB-System

• Definition A signal is considered to be Ultra
  Wide Band if the Bandwidth of the signal is at
  least 25 of the carrier frequency
• Special definition of FCC For the UWB-Bands it
  is sufficient if the channel bandwidth is 500 MHz
  in the spectrum between 3.1 and 10.6 GHz
• Currently most systems use narrow band or wide
  band channels
• UWB spread the signal power over a very broad
  band and interferes therefore minimally with
  existing narrowband/wideband systems
• Spreading makes the system more stable against
  fading channel influences
• More bandwidth allow more data-rate
• More bandwidth allows more accurate location
  determination

95
UWB Spectrum

• FCC ruling permits UWB spectrum overlay

Bluetooth, 802.11b Cordless Phones Microwave Ovens
802.11a
Emitted Signal Power
PCS
Part 15 Limit
-41 dBm/MHz
UWB Spectrum
1.6
1.9
2.4
3.1
5
10.6
Frequency (Ghz)

• FCC ruling issued 2/14/2002 after 4 years of
  study public debate
• FCC believes current ruling is conservative

96
Theoretical Data Rates over Range
UWB shows significant throughput potential at
short range
97
What is Ultra Wideband?

• Radio technology that modulates impulse based
  waveforms instead of continuous carrier waves

98
Information Modulation
Pulse length 200 ps Energy concentrated in 2
6 GHz band Voltage swing 100 mV Power 10 µW

• Pulse Position Modulation (PPM)
• Pulse Amplitude Modulation (PAM)
• On-Off Keying (OOK)
• Bi-Phase Modulation (BPSK)

99
Related Standards

• IEEE 802.15 Wireless Personal Area Network
  (WPAN)
• IEEE 802.15.1 Bluetooth, 1 Mbps
• IEEE 802.15.3 WPAN/high rate, 50 Mbps
• IEEE 802.15.3a WPAN/Higher rate, 500 Mbps, UWB
• IEEE 802.15.3c WPAN Ultra High Data Rates 2 - 10
  Gb/s
• IEEE 802.15.4 WPAN/low-rate, low-power, mW
  level, 200 kbps
• IEEE 802.15.4a WPAN/low-rate, low-power,
  distance measurement UWB

100
Cell structure

• Implements space division multiplex base station
  covers a certain transmission area (cell)
• Mobile stations communicate only via the base
  station
• Advantages of cell structures
• higher capacity, higher number of users
• less transmission power needed
• more robust, decentralized
• base station deals with interference,
  transmission area etc. locally
• Problems
• fixed network needed for the base stations
• handover (changing from one cell to another)
  necessary
• interference with other cells
• Cell sizes from some 100 m in cities to, e.g., 35
  km on the country side (GSM) - even less for
  higher frequencies

101
Frequency planning I

• Frequency reuse only with a certain distance
  between the base stations
• Standard model using 7 frequencies
• Fixed frequency assignment
• certain frequencies are assigned to a certain
  cell
• problem different traffic load in different
  cells
• Dynamic frequency assignment
• base station chooses frequencies depending on the
  frequencies already used in neighbor cells
• more capacity in cells with more traffic
• assignment can also be based on interference
  measurements

102
Frequency planning II
f3
f7
f2
f5
f2
f4
f6
f5
3 cell cluster
f1
f4
f3
f7
f1
f2
f3
f6
f2
f5
7 cell cluster
3 cell cluster with 3 sector antennas
103
Cell breathing

• CDM systems cell size depends on current load
• Additional traffic appears as noise to other
  users
• If the noise level is too high users drop out of
  cells

104
Mobile CommunicationsChapter 3 Media Access

• Motivation
• SDMA, FDMA, TDMA
• Aloha
• Reservation schemes

• Collision avoidance, MACA
• Polling
• CDMA
• SAMA
• Comparison

105
Motivation

• Can we apply media access methods from fixed
  networks?
• Example CSMA/CD
• Carrier Sense Multiple Access with Collision
  Detection
• send as soon as the medium is free, listen into
  the medium if a collision occurs (original method
  in IEEE 802.3)
• Problems in wireless networks
• signal strength decreases proportional to (at
  least) the square of the distance
• the sender would apply CS and CD, but the
  collisions happen at the receiver
• it might be the case that a sender cannot hear
  the collision, i.e., CD does not work
• furthermore, CS might not work if, e.g., a
  terminal is hidden

106
Motivation - hidden and exposed terminals

• Hidden terminals
• A sends to B, C cannot receive A
• C wants to send to B, C senses a free medium
  (CS fails)
• collision at B, A cannot receive the collision
  (CD fails)
• A is hidden for C
• Exposed terminals
• B sends to A, C wants to send to another terminal
  (not A or B)
• C has to wait, CS signals a medium in use
• but A is outside the radio range of C, therefore
  waiting is not necessary
• C is exposed to B

B
A
C
107
Motivation - near and far terminals

• Terminals A and B send, C receives
• signal strength decreases (at least) proportional
  to the square of the distance
• the signal of terminal B therefore drowns out As
  signal
• C cannot receive A
• If C for example was an arbiter for sending
  rights, terminal B would drown out terminal A
  already on the physical layer
• Also severe problem for CDMA-networks - precise
  power control needed!

A
B
C
108
Access methods SDMA/FDMA/TDMA

• SDMA (Space Division Multiple Access)
• segment space into sectors, use directed antennas
  
• cell structure
• MIMO, Beam steering
• FDMA (Frequency Division Multiple Access)
• assign a certain frequency to a transmission
  channel between a sender and a receiver
• permanent (e.g., radio broadcast), slow hopping
  (e.g., GSM, Bluetooth), or fast hopping (FHSS,
  Frequency Hopping Spread Spectrum)
• TDMA (Time Division Multiple Access)
• assign the fixed sending frequency to a
  transmission channel between a sender and a
  receiver for a certain amount of time
• CDMA (Code Division Multiple Access)
• Different orthogonal codes are used for
  independent communication
• The multiplexing schemes presented in chapter 2
  are now used to control medium access!

109
Duplexing

• The duplex mode describes how the two
  communication directions are handled.
• Common examples are
• TDD Time division duplex
• FDD Frequency division duplex

110
FDD/FDMA - general scheme, example GSM
f
960 MHz
124
200 kHz
1
935.2 MHz
20 MHz
915 MHz
124
1
890.2 MHz
t
fu 890 MHz i0.2 MHz fd fu 45 MHz
FDD (frequency division duplex)
111
TDD/TDMA - general scheme, example DECT
417 µs
1
2
3
11
12
1
2
3
11
12
t
downlink
uplink
10ms
112
Aloha/slotted aloha

• Mechanism
• random, distributed (no central arbiter),
  time-multiplex
• Slotted Aloha additionally uses time-slots,
  sending must always start at slot boundaries
• Aloha
• Slotted Aloha

collision
sender A
sender B
sender C
t
collision
sender A
sender B
sender C
t
113
Aloha performance
114
Slotted Aloha performance
115
MACA - collision avoidance

• MACA (Multiple Access with Collision Avoidance)
  uses short signaling packets for collision
  avoidance
• RTS (request to send) a sender request the right
  to send from a receiver with a short RTS packet
  before it sends a data packet
• CTS (clear to send) the receiver grants the
  right to send as soon as it is ready to receive
• Signaling packets contain
• sender address
• receiver address
• packet size
• Variants of this method can be found in
  IEEE802.11 as DFWMAC (Distributed Foundation
  Wireless MAC)

116
MACA examples

• MACA avoids the problem of hidden terminals
• A and C want to send to B
• A sends RTS first
• C waits after receiving CTS from B
• MACA avoids the problem of exposed terminals
• B wants to send to A, C to another terminal
• now C does not have to wait for it cannot
  receive CTS from A

RTS
CTS
CTS
B
RTS
RTS
CTS
B
117
Mobile Communications Chapter 4 Wireless LANs

• Characteristics
• IEEE 802.11
• PHY
• MAC
• Roaming
• .11a, b, g, h, i

118
Characteristics of Wireless LANs

• Advantages
• Very flexible within the reception area
• Ad-hoc networks without previous planning
  possible
• (almost) no wiring difficulties (e.g. historic
  buildings, firewalls)
• More robust against disasters like, e.g.,
  earthquakes, fire - or users pulling a plug...
• Disadvantages
• Typically very low bandwidth compared to wired
  networks (1 - 10 Mbit/s)
• Many proprietary solutions, especially for higher
  bit-rates, standards take their time (e.g. IEEE
  802.11)
• Products have to follow many national
  restrictions if working wireless, it takes a vary
  long time to establish global solutions like,
  e.g., IMT-2000

119
Design Goals for Wireless LANs

• Global, seamless operation
• Low power for battery use
• No special permissions or licenses needed to use
  the LAN
• Robust transmission technology
• Simplified spontaneous cooperation at meetings
• Easy to use for everyone, simple management
• Protection of investment in wired networks
• Security (no one should be able to read my data),
  privacy (no one should be able to collect user
  profiles), safety (low radiation)
• Transparency concerning applications and higher
  layer protocols, but also location awareness if
  necessary

120
Comparison Infrared vs. Radio Transmission

• Infrared
• Uses IR diodes, diffuse light, multiple
  reflections (walls, furniture etc.)
• Advantages
• Simple, cheap, available in many mobile devices
• No licenses needed
• Simple shielding possible
• Disadvantages
• Interference by sunlight, heat sources etc.
• Many things shield or absorb IR light
• Low bandwidth
• Example
• IrDA (Infrared Data Association) interface
  available everywhere

• Radio
• Typically using the license free ISM band at 2.4
  GHz (5.2 GHz, 17 GHz, 60 GHz)
• Advantages
• Experience from wireless WAN and mobile phones
  can be used
• Coverage of larger areas possible (radio can
  penetrate walls, furniture etc.)
• Disadvantages
• Very limited license free frequency bands
• Shielding more difficult, interference with other
  electrical devices
• Example
• WaveLAN, HIPERLAN, Bluetooth

121
Comparison Infrastructure vs. Ad-hoc Networks
infrastructure network
AP Access Point
AP
AP
wired network
AP
ad-hoc network
122
802.11 - Architecture of an Infrastructure Network
802.11 LAN

• Station (STA)
• Terminal with access mechanisms to the wireless
  medium and radio contact to the access point
• Basic Service Set (BSS)
• Group of stations using the same radio frequency
• Access Point
• Station integrated into the wireless LAN and the
  distribution system
• Portal
• Bridge to other (wired) networks
• Distribution System
• Interconnection network to form one logical
  network (EES Extended Service Set) based on
  several BSS

802.x LAN
STA1
BSS1
Access Point
Access Point
ESS
BSS2
STA2
STA3
802.11 LAN
123
IEEE Standard 802.11
fixed terminal
mobile terminal
infrastructure network
application
application
access point
TCP
TCP
IP
IP
LLC
LLC
LLC
802.11 MAC
802.3 MAC
802.3 MAC
802.11 MAC
802.11 PHY
802.3 PHY
802.3 PHY
802.11 PHY
124
802.11 - Layers and Functions

• PLCP Physical Layer Convergence Protocol
• Clear channel assessment signal (carrier sense)
• PMD Physical Medium Dependent
• Modulation, coding
• PHY Management
• Channel selection, MIB
• Station Management
• Coordination of all management functions

• MAC
• Access mechanisms, fragmentation, encryption
• MAC Management
• Synchronization, roaming, MIB, power management

Station Management
LLC
DLC
MAC
MAC Management
PLCP
PHY Management
PHY
PMD
125
802.11 - MAC Layer I Distributed Foundation
Wireless MAC (DFWMAC)

• Traffic services
• Asynchronous Data Service (mandatory)
• Exchange of data packets based on best-effort
• Support of broadcast and multicast
• Time-Bounded Service (optional)
• Implemented using PCF (Point Coordination
  Function)
• Access methods
• DFWMAC-DCF CSMA/CA (mandatory)
• Collision avoidance via randomized back-off
  mechanism
• Minimum distance between consecutive packets
• ACK packet for acknowledgements (not for
  broadcasts)
• DFWMAC-DCF w/ RTS/CTS (optional)
• Avoids hidden terminal problem
• DFWMAC- PCF (optional)
• Access point polls terminals according to a list

126
802.11 - MAC Layer II

• Priorities
• Defined through different inter frame spaces
• No guaranteed, hard priorities
• SIFS (Short Inter Frame Spacing)
• Highest priority, for ACK, CTS, polling response
• PIFS (PCF IFS)
• Medium priority, for time-bounded service using
  PCF
• DIFS (DCF, Distributed Coordination Function IFS)
• Lowest priority, for asynchronous data service

DIFS
DIFS
PIFS
SIFS
medium busy
next frame
contention
t
direct access if medium is free ? DIFS
127
802.11 - CSMA/CA Access Method I
contention window (randomized back-offmechanism)
DIFS
DIFS
medium busy
next frame
t
direct access if medium is free ? DIFS
slot time

• Station ready to send starts sensing the medium
  (Carrier Sense based on CCA, Clear Channel
  Assessment)
• If the medium is free for the duration of an
  Inter-Frame Space (IFS), the station can start
  sending (IFS depends on service type)
• If the medium is busy, the station has to wait
  for a free IFS, then the station must
  additionally wait a random back-off time
  (collision avoidance, multiple of slot-time)
• If another station occupies the medium