Introduction to Cellular Networking and Rethinking Mobile Architectures

Introduction to Cellular Networking and Rethinking Mobile Architectures Jatinder Pal Singh EE 392I, Lecture-3 April 13th, 2010

Agenda • Basics & Technology Evolution • Architecture and Functionality (GSM, 3G and beyond) • Cellular future goals • 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 StationDistributed transceivers Base StationFixed transceiver CellsDifferent 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 (e.g. MTS) • 1G: Analog • 2G/3G/4G .. - digital: GSM/3GPP Family cdmaOne/CDMA2000 Family GSM cdmaOne/IS-95 GPRS 2G EDGE UMTS, WCDMA CDMA2000 EV-DO 3G HSPA 4G LTE

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. • 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) • This GSM core network manages communication amongst mobile devices & with PSTN • Mobile Switching Center (MSC) : routing of calls and GSM services for users, mobility management, handovers, • Gateway MSC – interfaces with PSTN, determines the visited MSC at which the subscriber being called is currently located • 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. • Home Location Register (HLR): database with all mobile phone subscriber details

GPRS core network • Mobility management, session management, and transport for IP services • GPRS Tunneling Protocol, GTP allows end users mobility with continued Internet connectivity by transporting user’s data between users’ current SGSN and GGSN • 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) – commonly uses WCDMA as the underlying interface • Theoretically supports up to 14 Mbps rates with HSDPA • WCDMA 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 on downlink(1.8. 3.6, 7.2, 14.0 Mbps via AMC, and HARQ, fast packet scheduling.

Next Generation Mobile Networks • 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

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, Internet Services • 802.16d Fixed WiMAX, 802.16e - Mobile WiMAX. • Licensed spectrum profiles: 2.3GHz, 2.5GHz and 3.5GHz. US mostly around 2.5 GHz, assigned primarily to Sprint Nextel, Clearwire.

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

Circuit Switched Analog Circuit Switched Digital C.S. Voice + P.S. Data Cellular Networks and Internet Internet Cellular Networks Incipient Service Data Voice Packet Switched Technology Semi-Organic Evolution Controlled Operator initiated or partnered Third party/ independent (largely) New Services Mobility Support Good Poor

Cellular Networks and Internet Internet Cellular Networks QoS at edges Good Support (voice vs. data) Mostly absent Data rates for supporting broadband services Insufficient as of present Relatively high Lower Cost per MB of data Higher

Internet : Sample scenario – Residential Broadband access Internet BRAS DSLAM 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.

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.

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.

Introduction to Cellular Networking and Rethinking Mobile Architectures