Transcript Cellular networks

Computer Networks
Cellular Networks and
Cognitive Radio
Lin Gu
[email protected]
Computer Networking: A Top Down Approach 6th edition. Jim Kurose and Keith Ross.
Part of the slides are adapted from course companion materials.
Chapter 6 outline
6.1 Introduction
Wireless
6.2 Wireless links,
characteristics
 CDMA
6.3 IEEE 802.11 wireless
LANs (“Wi-Fi”)
6.4 Cellular Internet access
 architecture
 standards (e.g., GSM)
Mobility
6.5 Principles: addressing and
routing to mobile users
6.6 Mobile IP
6.7 Handling mobility in
cellular networks
6.8 Mobility and higher-layer
protocols
6.9 Summary
Wireless, Mobile Networks
6-2
Cellular Systems
Maxwell predicted the existence of radio waves (1864);
Hertz demonstrated radio waves (1886); Marconi
implemented wireless communications (1895); Bell Labs
developed the cellular concept (1957 & 1960) …
In the 1970’s, 1G cellular phone systems started to
operate
Advanced Mobile Phone Service (AMPS)
 US trials (1978); Deployment in Japan (1979) and
US (1983)
 800MHz, two 20MHz bands
Nordic Mobile Telephony (NMT)
 Sweden, Norway, Denmark, Finland (1981)
 450MHz & 900MHz (NMT900)
Total Access Communications System (TACS)
 Similar to AMPS, deployed in 1985
6-3
History of Wireless Communications
1G systems
Analog
 FDMA (Frequency Division Multiple Access)
 Designed for voice communication
 Almost extinct now
6-4
2G (voice) network architecture
Base station system (BSS)
MSC
BTS
G
BSC
Public
telephone
network
Gateway
MSC
Legend
Base transceiver station (BTS)
Base station controller (BSC)
Mobile Switching Center (MSC)
Mobile subscribers
Wireless, Mobile Networks
6-5
Cellular standards: brief survey
2G systems: voice channels
 IS-136 TDMA: combined FDMA/TDMA (north
America)
 GSM (global system for mobile communications):
combined FDMA/TDMA

most widely deployed
 IS-95 CDMA: code division multiple access
 IS-95A provides data communication up to 14.4kbps
GSM
Don’t drown in a bowl
of alphabet soup: use this
for reference only
6: Wireless and Mobile Networks
6-6
Cellular standards: brief survey
2.5 G systems: voice and data channels
 for those who can’t wait for 3G service: 2G extensions
 general packet radio service (GPRS)
 evolved from GSM
 data sent on multiple channels (if available)
 enhanced data rates for global evolution (EDGE)
 also evolved from GSM, using enhanced modulation
 data rates up to 384K
 CDMA-2000 (phase 1)
 data rates up to 144K
 evolved from IS-95
6: Wireless and Mobile Networks
6-7
3G (voice+data) network architecture
MSC
G
radio
network
controller
Gateway
MSC
G
SGSN
Key insight: new cellular data
network operates in parallel
(except at edge) with existing
cellular voice network
 voice network unchanged in core
 data network operates in parallel
Public
telephone
network
Public
Internet
GGSN
Serving GPRS Support Node (SGSN)
Gateway GPRS Support Node (GGSN)
Wireless, Mobile Networks
6-8
3G (voice+data) network architecture
MSC
G
radio
network
controller
Public
telephone
network
Gateway
MSC
G
SGSN
Public
Internet
GGSN
radio interface
(WCDMA, HSPA)
radio access network
Universal Terrestrial Radio
Access Network (UTRAN)
core network
General Packet Radio Service
(GPRS) Core Network
public
Internet
Wireless, Mobile Networks
6-9
Cellular standards: brief survey
3G systems: voice/data
 The 3G vision



Universal global
Multimedia (voice, data, video, …)
Data-centric architecture
 3G systems are mandated to provide
 144kbps at driving speeds
 384kbps for outside stationary use or walking speeds
 2Mbps for indoors
 Universal Mobile Telecommunications Service (UMTS)
 CDMA-2000
 TD-SCDMA (Standard led by China)
… But adoption is slower than expected…
6-10
Cellular standards: brief survey
4G systems: broadband voice/data
 No formal definition, but no doubt 4G systems
will appear and, very likely, dominate
 Expected:
 Much higher data rates: 1 Gbps or more (stationary),
100 Mbps (moving)
 Seamless roaming across heterogeneous networks
 Pre-4G or potential 4G standards
 LTE (Long Term Evolution), WiMAX, UMB, …
6-11
Components of cellular network architecture
MSC
connects cells to wired tel. net.
 manages call setup (more later!)
 handles mobility (more later!)

cell
covers geographical
region
 base station (BS)
analogous to 802.11 AP
 mobile users attach to
network through BS
 air-interface: physical
and link layer protocol
between mobile and BS

Mobile
Switching
Center
Public telephone
network
Mobile
Switching
Center
wired network
Wireless, Mobile Networks 6-12
Cellular networks: the first hop
Techniques for sharing mobileto-BS radio spectrum
TDMA, FDMA, CDMA
 combined FDMA/TDMA:
divide spectrum in frequency
channels, divide each channel
into time slots
 combined TDMA/CDMA:
CDMA in TDMA
frequency
bands
 3.5G and 4G wireless
systems optimize a
combination of frequency,
time and code multiplexing
time slots
6-13
CDMA
Code Devision Multiple Access
 All users share the same frequency band
 First deployed in Hong Kong in late 1994
 Verizon and Sprint use CDMA in U.S.
 Easy to migrate to 3G

Same modulation
 3G CDMA standards: CDMA2000, W-CDMA,
TD-SCDMA
6-14
GSM
Global system for mobile communications (originally,
Groupe Spécial Mobile)
 Dominant cellular standard
 It’s believed that 81% cell phone users are on GSM! 42% GSM
users are in Asia. AT&T and T-Mobile use GSM in U.S.
 Lowest cost to deploy
 Joint European effort began in 1982, focusing on
seamless roaming across Europe; service launched in
1991
 Based on FDM/TDM


900MHz, 1800MHz, 1900MHz bands
Quad-band “world phones”: support 850/900/1800/1900MHz
6-15
GSM – FDM/TDM technology
 200KHz frequency bands
 Each frequency band supports 8 TDM calls
 Base Station Controller (BSC)
 One BSC typically services 10s of BTSes; forms a BSS (Base
Station System)
 Allocate BTS channels to mobile subscribers
 Paging (locating the cell in which a mobile subscriber is resident)
 Handoff
 MSC (Mobile Switching Center)
 Authentication
 Accounting
 Call establishment/teardown/handoff
 Typically contains 5 BSCs, 200K subscribers
6-16
2G (voice) network architecture
Base station system (BSS)
MSC
BTS
G
BSC
Public
telephone
network
Gateway
MSC
Legend
Base transceiver station (BTS)
Base station controller (BSC)
Mobile Switching Center (MSC)
Mobile subscribers
6: Wireless and Mobile Networks
6-17
2.5G (voice+data) network architecture
MSC
BSC
G
Public
telephone
network
Gateway
MSC
G
SGSN
Key insight: new cellular data
network operates in parallel
(except at edge) with existing
cellular voice network
 voice network unchanged in core
 data network operates in parallel
Public
Internet
GGSN
Serving GPRS Support Node (SGSN)
Gateway GPRS Support Node (GGSN)
6: Wireless and Mobile Networks
6-18
GSM – 2.5G
Leave the core GSM network untouched; provide Internet
access at the edge of cellular systems
 Internet data service as an add-on functionality
 Introduce a separate network of Serving GPRS Support
Node (SGSN) nodes


At the BSC, IP-datagram-carrying FDM/TDM channels are
forwarded to SGSN
SGSN forwards the datagrams to and from Internet
 GPRS (General Packet Radio Service)
 Function in the radio network
 Allow GSM users to dynamically use multiple radio channels for
data communication at up to 115kbps
6-19
GSM – 2.5G or 2.75G
EDGE (Enhanced Data Rates for Global Evolution)
 Still 200 KHz bands and TDMA
 Enhance GSM/GPRS network to support up to
384kbps

Sometimes known as 2.75G
 8-PSK modulation

3 bits/symbol  3 times data rate
 Shorter range
 More sensitive to noise/interference
6-20
GSM – 3G
UMTS – Universal Mobile Telecommunications Service
Voice and data communication at higher rates
Keeps the existing GSM 2.5G network architecture
 Defined by 3GPP (3G Partnership Project)
 Uses CDMA in TDMA slots
 CDMA scheme defined by Direct Sequence Wideband CDMA
(DS-WCDMA)
 Requires a new cellular wireless-access network operating in
parallel with the BSS network
 In such a network, FDMA, TDMA, CDMA are all used
 Data service: High Speed Downlink/Uplink Packet
Access (HSDPA/HSUPA)

Data rate up to 14 Mbps
6-21
3G
3GSM/UMTS, CDMA 2000, TD-SCDMA
Globally, 18% subscribers on 3G, 82% on 2G, 0.01% on 1G
 TD-SCDMA (Time Division Synchronous CDMA)

Home brew standard in China
 3GSM (UMTS)
 Market leader
 CDMA 2000
 Don’t need additional spectrum
 Had an advantageous start, but is behind 3GSM now
 Even Verizon Wireless had decided to adopt LTE (a GSM-style
technology)
 The 3G networks in China
 China Mobile: TD-SCDMA
 China Unicom: 3GSM (UMTS)
 China Telecom: CDMA 2000
6-22
Cellular standards: brief survey
3G systems: voice/data
 Universal Mobile Telecommunications Service (UMTS)
 data service: High Speed Uplink/Downlink packet
Access (HSDPA/HSUPA): 3 Mbps
 CDMA-2000: CDMA in TDMA slots
 data service: 1xEvolution Data Optimized (1xEVDO)
up to 14 Mbps
….. more (and more interesting) cellular topics due to mobility (stay
tuned for details)
6: Wireless and Mobile Networks
6-23
GPRS or CDMA?
Up to 14.4kbps
Up to 64kbps
2G
2G+ (2.5G)
2G++ (2.75G?)
3G
North
America
IS-95A
IS-95B
IS-95C
CDMA2000
Europe
GSM
TDMA
GSM+
GPRS,HSCSD
GSM++
EDGE
WCDMA
Up to 115kbps
Up to 384kbps
Up to 14 Mbps
6-24
Other cellular services
 SMS – Short Message Service
 Text message service in cellular networks
 160 byte messages over signaling channel
 Multimedia message service, video services
 May use IP data path
 Mobile service breakdown
 Mobile services generated $800 billion revenue in
2007
 Voice: 81%
 SMS: 9.5%
 All other non-voice services: 9.5%
6-25
Cognitive Radio
Window of Opportunity
 Bandwidth is expensive and good
frequencies are taken
 Time scale of the spectrum
occupancy varies from msecs to
hours
Frequency (Hz)
 Unlicensed bands – biggest
innovations in spectrum efficiency
 Recent measurements by the FCC in
the US show 70% of the allocated
spectrum is not utilized
Time (min)
http://www.ntia.doc.gov/osmhome/allochrt.pdf
Radio Spectrum Use
 Measured signal strength in the air
 The length of duration also matters – how long a specific
frequency band is used
Spectrum usage in (0, 2.5) GHz
-40
Cell
Signal Strength (dB)
-45
-50
PCS
TV bands
-55
-60
-65
-70
-75
-80
-85
-90
0
0.5
1
1.5
Frequency (Hz)
2
2.5
x 10
9
Spectrum Sharing
 Existing techniques for spectrum sharing:
 Unlicensed bands (WiFi 802.11 a/b/g)
 Underlay licensed bands (UWB)
 Opportunistic sharing
 Recycling (exploit the SINR margin of legacy systems)
 Spatial Multiplexing and Beamforming
 Drawbacks of existing techniques:
 No knowledge or sense of spectrum availability
• Limited adaptability to spectral environment

Fixed parameters: BW, Fc, packet lengths,
synchronization, coding, protocols, …
 New radio design philosophy: all parameters are
adaptive

Cognitive Radio Technology
What is a Cognitive Radio?
 Cognitive radio requirements
 co-exists with legacy wireless systems
 uses their spectrum resources
 does not interfere with them
 Cognitive radio properties
 RF technology that "listens" to huge swaths of
spectrum
 Knowledge of primary users’ spectrum usage as a
function of location and time
 Share the available resources (time, frequency, space)
 Intelligently determine parameters based on the
spectral environment
Cognitive Radio Functions
Physical Layer
Sensing Radio
•
•
•
Wideband Antenna
•
High speed A/D &
•
D/A, moderate
•
resolution
Simultaneous Tx & Rx
OFDM transmission
Spectrum monitoring
Dynamic frequency
selection, modulation,
power control
PA
D/A
IFFT
LNA
A/D
FFT
RF/Analog Frontend
MAE/
POWER CTRL
CHANNEL
SEL/EST
ADAPTIVE
LOADING
INTERFERENCE
MEAS/CANCEL
Digital Baseband
MAC Layer
•
Optimize transmission
parameters
•
Adapt rates through
feedback
•
Negotiate or
opportunistically use
resources
TIME, FREQ,
SPACE SEL
LEARN
ENVIRONMENT
QoS vs.
RATE
FEEDBACK
TO CRs
MAC Layer
Appendix
LTE – Long Term Evolution
The 3GPP Long Term Evolution (LTE)
 3GPP Long Term Evolution - the next
generation of wireless cellular technology
beyond 3G
 Initiative taken by the 3rd Generation
Partnership Project in 2004
 Introduced in Release 8 of 3GPP
 Mobile systems likely to be deployed by
2010
3GPP Release/Freeze Timeline
WCDMA
HSDPA
HSUPA
HSPA+
MMS
IMS
MBMS
FBI
MSC
Split
Rel 99 Rel 4
LTE
I-WLAN
Rel 5
Rel 6
Rel 7
Rel 8
1999 2000 2001 2002 2003 2004 2005 2006 2007 2008
Introduction
LTE is the latest standard in the mobile
network technology tree that previously realized
the GSM/EDGE and UMTS/HSxPA network
technologies

Evolve from currently leading 3G technology
 LTE is the next step toward ‘4G’ mobile
systems, offering a smooth evolutionary path to
higher speeds and lower latency
Introduction
 Designed to meet carrier needs for high-speed data and
media transport as well as high-capacity voice support for
the next decade.
 Enables operators to offer high performance, massmarket mobile broadband services – high bit-rates, high
system throughput (uplink and downlink), low latency.
 Designed to be simple to deploy and operate, through
flexible technology that can be deployed in a wide variety of
frequency bands.
 Offers scalable bandwidths, from less than 5MHz up to
20MHz, together with support for both FDD (Frequency
Division Duplex) paired and TDD (Time Division Duplex)
unpaired spectrum.
LTE–SAE will interoperate with GSM, WCDMA/HSPA, TDSCDMA and CDMA.
LTE performance requirements
Data Rates:
Instantaneous
downlink peak data rate of 100Mbit/s in a
20MHz downlink spectrum (i.e. 5 bit/s/Hz)
Instantaneous uplink peak data rate of 50Mbit/s in a 20MHz
uplink spectrum (i.e. 2.5 bit/s/Hz)
Cell range
5
km - optimal size
30km sizes with reasonable performance
up to 100 km cell sizes supported with acceptable performance
Cell capacity
up
to 200 active users per cell (5 MHz)
Evolution of 3GPP Radio Rates
Peak Network Data Rates
100000
kbits/sec
10000
1000
UL
DL
100
10
1
GPRS
EDGE
WCDMA
HSPA
Technology
HSPA+
LTE
LTE performance requirements
Mobility
Optimized
speed
for low mobility(0-15km/h) but supports high
Improved spectrum efficiency
Scalable
bandwidth of 20MHz, 15MHz, 10MHz, 5MHz
and <5MHz
Co-existence with legacy standards
users
can transparently start a call or data transfer in
an area using an LTE standard, and, when there is no
coverage, continue the operation using GSM/GPRS or WCDMA-based UMTS
3G Evolution
 Radio Side
 Improvements in spectral efficiency, user throughput,
latency
 Simplification of the radio network
 Efficient support of packet based services
 Network Side (SAE – System Architecture
Evolution)




Improvement in latency, capacity, throughput
Simplification of the core network
Emphasis on IP traffic and IP-based services
Simplified support and handover to non-3GPP access
technologies
LTE Technology
• Multiple access scheme
 Downlink: OFDMA (Orthogonal Frequency Division Multiple Access)
 Uplink: SC-FDMA (Single Carrier FDMA)
Adaptive modulation and coding
 DL modulations: QPSK, 16QAM, and 64QAM
 UL modulations: QPSK and 16QAM
•
• Bandwidth scalability for efficient operation in differently sized
allocated spectrum bands
Duplexing - Principles
FDD (Frequency Division Duplexing ) Uses One
Frequency for the DownLink, and a Second Frequency
for the UpLink.
TDD (time Division Duplexing) Uses the same frequency
for the Downlink and the Uplink.
Note: duplexing and multiple access are different
concepts
System Architecture Evolution(SAE)
System Architecture Evolution (a.k.a. SAE) is the core network
architecture of 3GPP's future LTE wireless communication standard.
SAE is the evolution of the GPRS Core Network, with some
differences.
The main principles and objectives of the LTE-SAE architecture
include :
A common anchor point and gateway (GW) node for all access
technologies
IP-based protocols on all interfaces;
Simplified network architecture
All services are via Packet Switched domain
LTE Architecture
MME/UPE
MME/UPE
S1
E-UTRAN
X2
eNB
eNB
X2
Evolved
Packet
EPC
Core
X2
eNB
MME/UPE = Mobility Management Entity/User Plane Entity
eNB = eNodeB
LTE Architecture
MME (Mobility Management Entity):
-Manages and stores the UE control plane context, generates
temporary ID, provides UE authentication, authorization, mobility
management
UPE (User Plane Entity):
-Manages and stores UE context, ciphering, mobility anchor, packet
routing and forwarding, initiation of paging
3GPP anchor:
-Mobility anchor between 2G/3G and LTE
SAE anchor:
-Mobility anchor between 3GPP and non 3GPP
3GPP Packet Core architecture
(SAE simplified)
IP networks
PCRF
HSS
S6
S7
SGi
IASA ”EVOLVED PACKET CORE”
SAE
Anchor
S4
S3
SGSN
Gb
2G
GERAN
Iu
S5b
3GPP
Anchor
S2
S5a
MME/
UPE
S1
3G
LTE
UTRAN
LTE RAN
MME = Mobility Management Entity
UPE = User Plane Entity
IASA = Inter-Access System Anchor
Non-3GPP
[Source:Technical Overview of 3GPP Long Term Evolution (LTE) Hyung G. Myung]
LTE Architecture
Conclusions
LTE is a highly optimized, spectrally efficient, mobile OFDMA
solution built for mobility, and it allows operators to offer advanced
services and higher performance for new and wider bandwidths.
LTE is based on a flattened IP-based network architecture that
improves network latency, and is designed to interoperate on and
ensure service continuity with existing 3GPP networks.
LTE leverages the benefits of existing 3G technologies and enhances
them further with additional antenna techniques such as higher-order
MIMO.
LTE vs WiMAX
 Both are 4G technologies designed to move data rather than voice and
both are IP networks based on OFDM technology.
WiMax is based on a IEEE standard (802.16), and like other popular
IEEE effort, it’s an open standard that was debated by a large community
of engineers before getting ratified. The level of openness means WiMax
equipment is standard and therefore cheaper to buy.
As for speeds, LTE will be faster than the current generation of WiMax,
but 802.16m that should be ratified in 2009 is fairly similar in speeds.
However, LTE will take time to roll out. WiMax is out now, and more
networks should be available later this year.
The crucial difference is that WiMAX requires a new network to be
built but LTE runs on an evolution of the existing GSM
infrastructure.This means that LTE may have a crucial incumbent
advantage.