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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.