Cellular Networks:
Architectural and Functional Overview,
Evolving Trends, and Clean Slate Design
Paradigms
Jatinder Pal Singh
Deutsche Telekom Labs,
Stanford University,
Oct., 2007
Agenda
 Basics & Technology Evolution
 Architecture and Functionality (GSM, 3G and
beyond)
 Cellular future goals (2010 and beyond)
 Emerging trends
 Alternative wireless access technologies
 Convergence
 Comparison with Internet and sample scenario
studies
 Economics of operation
 From a clean slate
Basics: Structure
Multiple Access
Downlink
Handoff
Uplink
Mobile Station
Base Station
Distributed transceivers
Fixed transceiver
Cells
Different
Frequencies or
Codes
Basics: Multiple Access Methods
Frequency
CMDA: Code
Division Multiple
Access
TDMA: Time
Division Multiple
Access
FDMA: Frequency
Division Multiple
Access
Codes
Time
Some More Basics
 Uplink & Downlink separated in
 Time: Time Division Duplex (TDD), or
 Frequency: Frequency Division Duplex (FDD)
 Information (voice, data) is digitized and bit
streams modulated onto carrier
 Modulation, data redundancy (coding),
transmission power, data retransmissions (ARQ)
adapted to varying wireless channel quality
 Spatial attenuation of signal
 Frequency or codes can be reused (frequency reuse)
Cellular Technology Evolution
 0G: Mobile radio telephones (PTT, MTS)
 1G: Analog
 2G/3G and beyond - digital:
GSM Family
cdmaOne/CDMA2000 Family
GSM
GPRS
2G
cdmaOne/IS-95
EDGE
HSCSD
3G
WCDMA (UMTS)
HSPA
CDMA2000 EV-DO
Agenda
 Basics & Technology Evolution
 Architecture and Functionality (GSM, 3G
and beyond)
 Cellular future goals (2010 and beyond)
 Emerging trends
 Alternative wireless access technologies
 Convergence
 Comparison with Internet and sample scenario
studies
 Economics of operation
 From a clean slate
Global System for Mobile
communications (GSM)
 900/1800 MHz band (US: 850/1900 MHz)
 For 900 MHz band
 Uplink: 890-915
 Downlink: 935-960
 25 MHz bandwidth - 124 carrier frequency
channels, spaced 200KHz apart
 Time Division Multiplexing for 8 full rate speech
channels per frequency channel.
 Circuit Switched Data with data rate of 9.6 kbps
 Handset transmission power limited to 2 W in
GSM850/900 and 1 W in GSM1800/1900.
Architecture
The Base Station Subsystem (BSS)
 Base Transceiver Station BTS - transceivers serve
different frequencies.
 Frequency hopping by handsets and transceivers
 Sectorization using directional antennas
 Base Station Controller (BSC) controls several
(tens to hundreds) of BTSs
 allocation of radio channels
 handovers between BTSs
 concentrator of traffic
 databases with information such as carrier frequencies,
frequency hopping lists, power reduction levels, etc.
for each cell site
Network Switching Subsystem (NSS)
 GSM circuit-switched core network manages
communication between mobile phones & PSTN
 Mobile Switching Center (MSC) : provides circuit
switched calling, mobility management, GSM
services for users
 Gateway MSC – interfaces with PSTN, determines
which visited MSC the subscriber being called is
currently located at
 Visited MSC - MSC where a customer is currently
located. The Visitor Location Register (VLR) associated
with this MSC has subscriber's data.
 Anchor MSC - MSC from which handover initiated.
 Target MSC - MSC toward which a handover should
take place.
GPRS core network
 Mobility management, session
management, and transport for IP services
 GPRS Tunneling Protocol, GTP (over UDP)
allows end users mobility with continued
Internet connectivity
 GPRS support nodes (GSN)
GGSN - Gateway GPRS Support Node
SGSN - Serving GPRS Support Node
GSM Support for Data Services:
GPRS
 User gets pair of uplink and downlink
frequencies.
 Multiple users share the same frequency channel
with time domain multiplexing.
 Packets have constant length corresponding to a
GSM time slot.
 Downlink uses FCFS packet scheduling
 Uplink
 Slotted ALOHA for reservation inquiries during
contention phase
 data transferred using dynamic TDMA with FCFS
scheduling.
 Upto 64 kbps (more for EDGE) downlink per user.
UMTS and 3G technologies
(WCDMA & HSPA)
 Universal Mobile Telecommunications System (UMTS) - WCDMA as
the underlying interface
 Supports up to 14 Mbps rates with HSDPA (typical present deployed
rates per user 384kbps)
 Frequency bands
 1885-2025 Mhz (uplink), 2110-2200 Mhz (downlink)
 US: 1710-1755 MHz and 2110-2155 MHz
 W-CDMA has 5 Mhz wide radio channels (CDMA2000 transmits on
one or several pairs of 1.25 Mhz radio channels).
 HSDPA allows networks based on UMTS to have higher data rates
(1.8. 3.6, 7.2, 14.4 Mbps via AMC, and HARQ, fast packet scheduling.
 UMTS air interface forms Generic Radio Access Network (GeRAN)
which can be connected to various backbone networks like the
Internet, ISDN, GSM or UMTS.
 Using PCMCIA or USB card, or cellular router customers are able to
access 3G broadband services
Agenda
 Basics & Technology Evolution
 Architecture and Functionality (GSM, 3G and
beyond)
 Cellular future goals (2010 and beyond)
 Emerging trends
 Alternative wireless access technologies
 Convergence
 Comparison with Internet and sample scenario
studies
 Economics of operation
 From a clean slate
In the decade beyond 2010
 Next Generation Mobile Networks (NGMN) Ltd. Consortium with partnership of major mobile
operators
 Recommendations without specific technology
prescriptions
 Target to establish performance targets,
recommendations and deployment scenarios for
future wide-area mobile broadband network
packet switched core
 The architecture intended to provide a smooth
migration of existing 2G/3G networks towards an
IP network that is cost competitive and has
broadband performance.
NGMN: Beyond 3G
 Video telephony and multimedia conferencing, IM, video
streaming – among high drivers for NGMN
 Essential System recommendations
 Seamless mobility across all bearers with service continuity
through a min of 120 km/h
 Peak uplink data rates 30-50 Mbps
 Peak > 100Mbps downlink
 Latency core < 10ms, RAN <10ms, <30ms e2e
 QoS based global roaming
 Broadcast, multicast, and unicast services to subscribers of all
environments
 Real time, conversational and streaming in PS across all required
bearers
 Cost per MB : as close to DSL as possible
NGMN Envisioned System
Architecture
Agenda
 Basics & Technology Evolution
 Architecture and Functionality (GSM, 3G and
beyond)
 Cellular future goals (2010 and beyond)
 Emerging trends
 Alternative wireless access technologies
 Convergence
 Comparison with Internet and sample scenario
studies
 Economics of operation
 From a clean slate
Alternative fixed wireless and MAN
standards
 WiMAX, the Worldwide Interoperability for
Microwave Access based on IEEE 802.16
standard
 Last-mile broadband access, backhaul for cellular
networks, interconnectivity for hotspots
 OFDMA used by 802.16e. MIMO support amongst
recent developments
 Licensed spectrum profiles: 2.3GHz, 2.5GHz and
3.5GHz. US mostly around 2.5 GHz, assigned
primarily to Sprint Nextel, Clearwire.
 Claims for delivery of 70 Mbps, and over 50
kilometers, not simultaneously true.
Convergence
 Heterogeneous access technologies
 Multi-mode access devices
 Dual mode phones (WiFi, 2.5/3G), UMA
 Heterogeneous Services
 Cellular Internet access and Internet based
voice/video access
 Challenges
 Time variant heterogeneous network characteristics
 Heterogeneous applications with different utilities
 System design and networking challenges
Agenda
 Basics & Technology Evolution
 Architecture and Functionality (GSM, 3G and
beyond)
 Cellular future goals (2010 and beyond)
 Emerging trends
 Alternative wireless access technologies
 Convergence
 Comparison with Internet and sample
scenario studies
 Economics of operation
 From a clean slate
Cellular Networks and Internet
Cellular Networks
Incipient
Service
Voice
Circuit Switched Analog
Technology
Circuit Switched Digital
Internet
Data
Packet
Switched
C.S. Voice + P.S. Data
Evolution
New Services
Mobility
Support
Controlled
Operator initiated
or partnered
Good
Semi-Organic
Third party/
independent (largely)
Poor
Cellular Networks and Internet
Cellular Networks
QoS at edges
Data rates for
supporting
broadband
services
Cost per MB
of data
Good Support
(voice vs. data)
Insufficient as of
present
Higher
Internet
Mostly absent
Relatively high
Lower
Internet : Sample scenario –
Residential Broadband access
Internet
DSLAM
BRAS
Home WiFi Router
QoS: Wireless hop (802.11e?), PPPoE, IP QoS (Diffserv)
and translation mechanisms
Mobility Options: MIP - high-barrier, delay performance,
incremental patch rather than clean solution?
Cellular Scenario
Better QoS, scheduling
Better Mobility within the cellular network
Integrated voice/data Authentication
Downside is excessive edge network delays,
costs of network deployment.
Agenda
 Basics & Technology Evolution
 Architecture and Functionality (GSM, 3G and
beyond)
 Cellular future goals (2010 and beyond)
 Emerging trends
 Alternative wireless access technologies
 Convergence
 Comparison with Internet and sample scenario
studies
 Economics of operation
 From a clean slate
The Economics
 3G spectrum licensing and migration cost
 Telecom equipment vendors – economics
of operation, meeting bids vs. system
upgrades for technical innovation
 Stiff competition for fixed and mobile
segments of operators, drive towards
services.
 Interesting and sometimes conflicting
dynamics for both fixed and mobile
operators.
Agenda
 Basics & Technology Evolution
 Architecture and Functionality (GSM, 3G and
beyond)
 Cellular future goals (2010 and beyond)
 Emerging trends
 Alternative wireless access technologies
 Convergence
 Comparison with Internet and sample scenario
studies
 Economics of operation
 From a clean slate
From a Clean Slate
 Greater intelligence at edges of networks, eventually leading to just
network elements of different sizes and capabilities
 Functional homogeneity in network elements in terms of
storage/caching, processing, networking capability. Such network
element should likely
 be multi-homed connected with heterogeneous technologies (including
p2p, delay tolerant),
 have intelligence for resource allocation, QoS
 have interaction capability with other network elements (including user
devices),
 support mobility, handoffs
 have ability to recognize needs of existing and new applications (HDTV,
phone, streaming video)
 be plug and play
 Interfacing of applications/services (QoS specs) with underlying
serving networks for fast and easy deployment.
 Heterogeneity in access technologies amongst user carried devices
honored and accepted by the network elements.
Options for operators
 Sharing the spectrum/infrastructure costs?
 New service models to forestall cost of
upgrades
 Good opportunity for fixed and mobile
carriers to take initiative.
Deutsche Telekom Laboratories:
Related Research Efforts
 Broadband Access Sharing (Extended HotSpots)
 Commercial grade routers with virtualization, user traceability, limited
QoS support.
 Limited trail in Berlin; Pilot for extensive evaluation launched and
technology on company product roadmap for 2008.
 Distributed Authentication framework for a Global WiFi network
(Mobicom’07, extended abstract)
 Heterogeneous Network access
 Optimal Control theoretic approach for rate allocation (WiOpt’07)
 Convex optimization framework for media-aware rate allocation for HD
video sequences (ACM Multimedia’07, best student paper award)
 Markov Decision Process based flow assignment over heterogeneous
networks (IEEE WoWMoM’07, top 15 papers)
 Peer to Peer Media Streaming
 Large scale dynamics of a commercial P2P streaming session and realworld testing of commercial P2P streaming solutions.
 Gossip based P2P streaming protocol (Journal on Advances in
Multimedia’07)
Email:
jatinder@stanford.edu
Publications and other information:
http://www.stanford.edu/~jatinder