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Chapter 1
INTRODUCTION
Based on the slides of Dr. Andrea Goldsmith, Stanford University and Dr. Dharma P. Agrawal, University of Cincinnati
2
Course Objectives:
This course will cover the fundamental aspects of wireless networks, with emphasis on current and next-generation wireless networks. Various aspects of wireless networking will be covered including: fundamentals of cellular communication, mobile radio propagation, multiple access techniques, mobility support, channel allocation, Wireless PAN/LAN/MAN standards, mobile ad-hoc networks, wireless sensor networks, and routing in wireless and mobile networks. The goal of this course is to introduce the students to state-of-the-art wireless network protocols and architectures. We will introduce the students to wireless networking research and guide them to investigate novel ideas in the area via semester-long research projects. We will also look at industry trends and discuss some innovative ideas that have recently been developed. Some of the course material will be drawn from research papers, industry white papers and Internet RFCs.
3
Wireless History
Radio invented in the 1880s by Marconi
Many sophisticated military radio systems were developed during and after WW2
Cellular has enjoyed exponential growth since 1988, with almost 1 billion users worldwide today
Ignited the recent wireless revolution3G roll-out disappointing in Europe, nascent in USAsia way ahead of the rest of the world
Much hype in 1990s, great failures around 20001G Wireless LANs/Iridium/Metricom
Ancient Systems: Smoke Signals, Carrier Pigeons, …
4
Exciting Developments
Internet and laptop use exploding
2G/3G wireless LANs growing rapidly
Huge cell phone popularity worldwide
Emerging systems such as Bluetooth, UWB, Zigbee, and WiMAX opening new doors
Military and security wireless needs
Important interdisciplinary applications
5
Future Wireless Networks
Wireless Internet accessNth generation CellularWireless Ad Hoc NetworksSensor Networks Wireless EntertainmentSmart Homes/SpacesAutomated HighwaysAll this and more…
Ubiquitous Communication Among People and Devices
•Hard Delay Constraints•Hard Energy Constraints
6
Design Challenges
Wireless channels are a difficult and capacity-limited broadcast communications medium
Traffic patterns, user locations, and network conditions are constantly changing
Applications are heterogeneous with hard constraints that must be met by the network
Energy and delay constraints change design principles across all layers of the protocol stack
7
Evolution of Current Systems
Wireless systems today2G Cellular: ~30-70 Kbps.WLANs: ~10 Mbps.
Next Generation3G Cellular: ~300 Kbps.WLANs: ~70 Mbps.
Technology Enhancements Hardware: Better batteries. Better circuits/processors.Link: Antennas, modulation, coding, adaptivity, DSP, BW.Network: Dynamic resource allocation. Mobility support.Application: Soft and adaptive QoS.
“Current Systems on Steroids”
8
Future Generations
Rate
Mobility
2G
3G
4G802.11b WLAN
2G Cellular
Other Tradeoffs:Rate vs. CoverageRate vs. DelayRate vs. CostRate vs. Energy
Fundamental Design Breakthroughs Needed
9
Multimedia Requirements
Voice VideoData
Delay
Packet Loss
BER
Data Rate
Traffic
<100ms - <100ms
<1% 0 <1%
10-3 10-6 10-6
8-32 Kbps 1-100 Mbps 1-20 Mbps
Continuous Bursty Continuous
One-size-fits-all protocols and design do not work well
Wired networks use this approach, with poor results
10
Wireless Performance Gap
WIDE AREA CIRCUIT SWITCHING
User Bit-Rate (kbps)
14.4digitalcellular
28.8 modem
ISDN
ATM
9.6 modem
2.4 modem2.4 cellular
32 kbps PCS
9.6 cellular
wired- wireless bit-rate "gap"
1970 200019901980YEAR
LOCAL AREA PACKET SWITCHING
User Bit-Rate (kbps)
Ethernet
FDDI
ATM100 M Ethernet
Polling
Packet Radio
1st genWLAN
2nd genWLAN
wired- wirelessbit-rate "gap"
1970 200019901980.01
.1
1
10
100
1000
10,000
100,000
YEAR
.01
.1
1
10
100
1000
10,000
100,000
11
Quality-of-Service (QoS)
QoS refers to the requirements associated with a given application, typically rate and delay requirements.
It is hard to make a one-size-fits all network that supports requirements of different applications.
Wired networks often use this approach with poor results, and they have much higher data rates and better reliability than wireless.
QoS for all applications requires a cross-layer design approach.
Crosslayer Design
Application
Network
Access
Link
Hardware
Delay ConstraintsRate Constraints
Energy ConstraintsChannel-State
Adapt across design layersReduce uncertainty through scheduling
Provide robustness via diversity
13
Current Wireless Systems
Cellular Systems
Wireless LANs
Satellite Systems
Bluetooth
Ultrawideband radios
Zigbee radios
14
Fundamentals of Cellular Systems
Illustration of a cell with a mobile station and a base station
BS
MS
Cell
Hexagonal cell area used in most models
Ideal cell area (2-10 km radius)
Alternative shape of a cell
MS
15
FDMA (Frequency Division Multiple Access)
User 1
User 2
User n
…
Time
Frequency
16
FDMA Bandwidth Structure
1 2 3 … nFrequency
Total bandwidth
4
17
FDMA Channel Allocation
Frequency 1 User 1
Frequency 2 User 2
Frequency n User n
Base Station
… …
Mobile Stations
18
TDMA (Time Division Multiple Access)
Use
r 1
Use
r 2
Use
r n
…
Time
Frequency
19
TDMA Frame Structure
1 2 3 … nTime
Frame
4
20
TDMA Frame Illustration for Multiple Users
Time 1
Time 2
Time n……
Base Station
User 1
User 2
User n
…
Mobile Stations
21
CDMA (Code Division Multiple Access)
Use
r 1
Time
Frequency
Use
r 2
Use
r n
Code
...
22
Transmitted and Received Signals in a CDMA System
Information bits
Code at transmitting end
Transmitted signal
Received signal
Code at receiving end
Decoded signal at the receiver
23
Frequency Hopping
Frequency
f5
f4
f3
f2
f1
Frame Slot
Time
24
Cellular System Infrastructure
BS
Service area (Zone)
Early wireless system: Large zone
25
Cellular System: Small Zone
BS BS
BS BS BS
BS BS
Service area
Cellular Systems:Reuse channels to maximize capacity
Geographic region divided into cellsFrequencies/timeslots/codes reused at spatially-separated locations.Co-channel interference between same color cells.Base stations/MSCs coordinate handoff and control functionsShrinking cell size increases capacity, as well as networking burden
BASESTATION
MSC
27
Home phone
PSTN
MSC
BSC …
BS
…
…
MS
…
BS MS
BSC
BS MS
…
BS MS
BSC
BS MS
…
BS MS
BSC
BS MS
…
BS MS
MSC
MS, BS, BSC, MSC, and PSTN
28
Control and Traffic Channels
Base Station
Forward
(downlin
k) contro
l channel
Mobile Station
Reverse (
uplink) c
ontrol c
hannel
Forward
(downlin
k) traff
ic channel
Reverse (
uplink) tr
affic
channel
29
Steps for a Call Setup from MS to BS
BS MS
1. Need to establish path
2. Frequency/time slot/code assigned
(FDMA/TDMA/CDMA)
3. Control Information Acknowledgement
4. Start communication
30
Steps for a Call Setup from BS to MS
BS MS
2. Ready to establish a path
3. Use frequency/time slot/code
(FDMA/TDMA/CDMA)
4. Ready for communication
5. Start communication
1. Call for MS # pending
31
A Simplified Wireless Communication System Representation
Information to be transmitted (Voice/Data)
Coding Modulator Transmitter
Information received
(Voice/Data)
Decoding Demodulator Receiver
Antenna
AntennaCarrier
Carrier
32
Signaling
before, during, after connection/call
call setup and teardown (state)
call maintenance (state)
measurement, billing (state)
between:
end-user <-> network
end-user <-> end-user
network element <-> network element
signaling: exchange of messages among network entities to enable (provide service) to connection/call
33
Telephone network: circuit-switched voice trunks (data plane)
34
Telephone network: data and control planes
35
SS7: telephone signaling network
Note: redundancy in SS7 elements
36
Signaling System 7: telephone network signaling
out-of-band signaling: telephony signaling carried over separate network from telephone calls (data)
allows for signaling between any switches (not just directly-connected )
allows for signaling during call (not just before/after)
allows for higher-than-voice-data-rate signaling
security: in-band tone signaling helps phone phreaks; out of band signaling more secure
SS7 network: packet-switched
calls circuit-switched
lots of redundancy (for reliability) in signaling network links, elements
37
Signaling System 7: telephone network
signaling between telephone network elements:
signaling switching point (SSP):
attach directly to end user
endpoints of SS7 network
signaling control point (SCP):“services” go heree.g., database functions
signaling transfer point (STP):packet-switches of SS7 networksend/receive/route signaling messages
38
Example: signaling a POTS call
1. caller goes offhook, dials callee. SSP A decides to route call via SSP B. Assigns idle trunk A-B
A B
W
X
Y
2. SSP A formulates Initial Address Message (IAM), forwards to STP W
3. STP W forwards IAM to STP X
4. STP X forwards IAM SSP B
39
Example: signaling a POTS call5. B determines it serves callee,
creates address completion message (ACM[A,B,trunk]), rings callee phone, sends ringing sound on trunk to A
A B
W
XY
Z7. SSP A receives ACM, connects subscriber line to allocated A-B trunk (caller hears ringing)
6. ACM routed to Z to Y to A
40
Example: signaling a POTS call8. Callee goes off hook,
B creates, sends answer message to A (ANM[A,B,trunk])
A B
W
XY
Z
10. SSP A receives ANM, checks caller is connected in both directions to trunk. Call is connected!
9. ANM routed to A
41
Example: signaling a 800 ca11
A B
WM
1. Caller dials 800 number, A recognizes 800 number, formulates translation query, send to STP W
800 number: logical phone numbertranslation to physical phone number needed, e.g., 1-800-CALL_ATT translates to 162-962-1943
2. STP W forwards request to M
3. M performs lookup, sends reply to A
A
Y
42
Example: signaling a 800 call
A B
W
X
MZ
1. A begins signaling to set up call to number associated with 800 number
800 number: logical phone number
translation to physical phone number needed
A
43
3G Cellular Design: Voice and DataData is bursty, whereas voice is continuous
Typically require different access and routing strategies
3G “widens the data pipe”:384 Kbps.Standard based on wideband CDMAPacket-based switching for both voice and data
3G cellular struggling in Europe and Asia
Evolution of existing systems (2.5G,2.6798G):GSM+EDGEIS-95(CDMA)+HDR100 Kbps may be enough
What is beyond 3G? The trillion dollar question
44
Third Generation Cellular Systems and Services
IMT-2000 (International Mobile Telecommunications-2000):
- Fulfill one's dream of anywhere, anytime communications a reality.
Key Features of IMT-2000 include:
- High degree of commonality of design worldwide;
- Compatibility of services within IMT-2000 and with the fixed networks;
- High quality;
- Small terminal for worldwide use;
- Worldwide roaming capability;
- Capability for multimedia applications, and a wide range of services and terminals.
45
Third Generation Cellular Systems and Services
Important Component of IMT-2000 is ability to provide high bearer rate capabilities:
- 2 Mbps for fixed environment;- 384 Kbps for indoor/outdoor and pedestrian environments;- 144 kbps for vehicular environment.
Standardization Work:- Release 1999 specifications- In processing
Scheduled Service:- Started in October 2001 in Japan (W-CDMA)
46
Subscriber Growth
3G Subscribers
2G Digital only Subscribers
1G Analogue only Subscribers
Sub
scri
bers
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
Year
47
Wireless Local Area Networks (WLANs)
WLANs connect “local” computers (100m range)
Breaks data into packets
Channel access is shared (random access)
Backbone Internet provides best-effort service
Poor performance in some apps (e.g. video)
01011011
InternetAccessPoint
0101 1011
48
Wireless LAN Standards
802.11b (Current Generation)Standard for 2.4GHz ISM band (80 MHz)Frequency hopped spread spectrum1.6-10 Mbps, 500 ft range
802.11a (Emerging Generation)Standard for 5GHz NII band (300 MHz)OFDM with time division20-70 Mbps, variable rangeSimilar to HiperLAN in Europe
802.11g (New Standard)Standard in 2.4 GHz and 5 GHz bandsOFDM Speeds up to 54 Mbps
In 200?,all WLAN cards will have all 3 standards
49
Satellite Systems
Cover very large areas
Different orbit heightsGEOs (39000 Km) versus LEOs (2000 Km)
Optimized for one-way transmissionRadio (XM, DAB) and movie (SatTV) broadcasting
Most two-way systems struggling or bankruptExpensive alternative to terrestrial system
8C32810.61-Cimini-7/98
Bluetooth
Cable replacement RF technology (low cost)
Short range (10m, extendable to 100m)
2.4 GHz band (crowded)
1 Data (700 Kbps) and 3 voice channels
Widely supported by telecommunications, PC, and consumer electronics companies
Few applications beyond cable replacement
51
Ultrawideband Radio (UWB)
UWB is an impulse radio: sends pulses of tens of picoseconds(10-12) to nanoseconds (10-9)
Duty cycle of only a fraction of a percent
A carrier is not necessarily needed
Uses a lot of bandwidth (GHz)
Low probability of detection
Excellent ranging capability
Multipath highly resolvable: good and badCan use OFDM to get around multipath problem.
52
IEEE 802.15.4 / ZigBee Radios
Low-Rate Low-Cost WPAN
Data rates of 20, 40, 250 kbps
Star clusters or peer-to-peer operation
Support for low latency devices
CSMA-CA channel access
Very low power consumption
Frequency of operation in ISM bands
Focus is primarily on radio and access techniques
53
Data rate
10 kbits/sec
100 kbits/sec1 Mbit/sec
10 Mbit/sec
100 Mbit/sec
0 GHz 2 GHz1GHz 3 GHz 5 GHz4 GHz 6 GHz
802.11a
UWBZigBee
Bluetooth
ZigBee
802.11b
802.11g
3G
UWB
54
Range
1 m
10 m
100 m
1 km
10 km
0 GHz 2 GHz1GHz 3 GHz 5 GHz4 GHz 6 GHz
802.11a
UWB
ZigBee BluetoothZigBee
802.11b,g
3G
UWB
55
Power Dissipation
1 mW
10 mW
100 mW
1 W
10 W
0 GHz 2 GHz1GHz 3 GHz 5 GHz4 GHz 6 GHz
802.11a
UWB
UWBZigBee
Bluetooth
ZigBee
802.11bg3G
56
Emerging Systems
Ad hoc wireless networks
Sensor networks
Distributed control networks
57
Ad-Hoc Networks
Peer-to-peer communications.No backbone infrastructure.Routing can be multihop.
Topology is dynamic.
Fully connected with different link SIRs
58
Design Issues
Ad-hoc networks provide a flexible network infrastructure for many emerging applications.
The capacity of such networks is generally unknown.
Transmission, access, and routing strategies for ad-hoc networks are generally ad-hoc.
Crosslayer design critical and very challenging.
Energy constraints impose interesting design tradeoffs for communication and networking.
59
Sensor NetworksEnergy is the driving constraint
Nodes powered by nonrechargeable batteriesData flows to centralized location.Low per-node rates but up to 100,000 nodes.Data highly correlated in time and space.Nodes can cooperate in transmission, reception, compression, and signal processing.
60
Spectrum Regulation
Spectral Allocation in US controlled by FCC (commercial) or OSM (defense)
FCC auctions spectral blocks for set
applications.
Some spectrum set aside for universal use
Worldwide spectrum controlled by ITU-RRegulation can stunt innovation, cause economic
disasters, and delay system rollout
61
62
Standards
Interacting systems require standardization
Companies want their systems adopted as standard
Alternatively try for de-facto standards
Standards determined by TIA/CTIA in US
IEEE standards often adopted
Process fraught with inefficiencies and conflicts
Worldwide standards determined by ITU-TIn Europe, ETSI is equivalent of IEEE
Protocols are standardized by IETF as RFCs