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EE 179: Introduction to Communications

EE 179: Introduction to Communications. Professor Andrea Goldsmith Stanford University USA. Outline. Course Info and background Course Syllabus Wireless History and Trends Wireless Vision for the Future Technical Challenges Current Wireless Systems Emerging Wireless Systems

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EE 179: Introduction to Communications

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  1. EE 179: Introduction to Communications Professor Andrea Goldsmith StanfordUniversity USA

  2. Outline • Course Info and background • Course Syllabus • Wireless History and Trends • Wireless Vision for the Future • Technical Challenges • Current Wireless Systems • Emerging Wireless Systems • Spectrum Regulation • Standardization

  3. Wireless (Pre-)History • ”Pre-historic” times: smoke signals, bonfires, lighthouses, torches • 1895: first radio transmission (Marconi, Isle of Wight, 18 mile distance) • 1915: Wireless voice transmission established between San Francisco and New York • 1945: Arthur C. Clarke(sci-fi writer) suggests geostationary satellites • 1946: Public mobile telephony introduced in 25 US cities • 1947: Invention of cellular concept (AT&T) • 1957: First deployed communication satellite (Sputnik, Soviet Union) • 1963: First deployed geostationary satellite (NASA) • 1971: First packet-based radio network (ALOHANET, Univ. of Hawaii) • 1983: First analog cellular system deployed (Chicago) • 1985: Unlicensed frequency bands first authorized for WLAN use • Ca. 1990: First digital cellular systems (”2G”) • 2000 - now: Standardization of 3rd generation mobile communication systems, WLANs, WPANs, sensor network radios,...

  4. Wireless History, cont’d First Mobile Radio Telephone 1924

  5. Pre-Cellular Wireless • One highly-elevated, high-powered antenna in a large service area • Small number of channels (few users) • Analog transmission, inefficient use of spectrum (no frequency reuse) • Very low capacity, power-inefficient

  6. BASE STATION Cellular Systems:Re-use channels to maximize capacity • Geographic regions are divided into cells • Frequencies/timeslots/codes reused at spatially separated locations. • NB: Co-channel interference (between same-color cells below). • Base stations/MTSOs (Mobile Telephone Switching Offices) coordinate handoff and control functions • Shrinking cell size increases capacity - but also networking burden.. MTSO

  7. BS BS BS MTSO MTSO Cellular Phone Networks San Francisco PSTN: Public Service Telephone Network Internet New York PSTN

  8. The Wireless Revolution • Cellular is the fastest growing sector of communication industry (exponential growth since 1982, with over 2 billion users worldwide today) • Modern-day “generations” of wireless (pre-cellular: 0G): • First Generation (1G - ex. NMT, ca. 1982 - ): Analog 25 or 30 KHz FM, voice only, mostly vehicular communications. • Second Generation (2G - ex. GSM, ca. 1993 - ): Narrowband TDMA and CDMA, voice and low bit-rate data, portable units. 2.5G - 2.75G: Enhancements to 2G network for increased data transmission capabilities (ex. GPRS + EDGE, ca. 2000 - ). • Third Generation (3G - UMTS/IMT-2000, ca. 2002 - ): Wideband TDMA and CDMA, voice and high bit-rate data, portable units • 4th Generation (4G/B3G, ca. 2010 - ?): ???... Heterogeneous network of several interacting systems/networks, not one dedicated network; diverse, advanced, adaptive air interfaces, protocols, and resource allocation mechanisms; multitude of services including high-capacity multimedia)

  9. Exciting Developments • Internet and laptop use exploding • Wireless LANs and PANs 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 • Sensor networks

  10. Future Wireless Networks (The Wireless Vision) Ubiquitous Communication Among People and Devices Wireless Internet access Nth generation Cellular Wireless Ad Hoc Networks Sensor Networks Wireless Entertainment Smart Homes/Spaces Automated Highways All this and more… • Hard Delay Constraints • Hard Energy Constraints

  11. Design Challenges • The wireless channel is a difficult and capacity-limited broadcast communications medium! • Traffic patterns, user locations, and network conditions are constantly changing... • Traffic is nonstationary, both in space and in time • Energy and delay constraints change design principles across all layers of the protocol stack (points towards cross-layer design)

  12. Evolution of Current Systems • Wireless systems today • 2G + 2.5G Cellular: ~30-70 Kb/s. • WLANs: ~10 Mb/s. • Next Generation • 2.75G + 3G Cellular: ~300 Kb/s. • WLANs: ~70 Mb/s. • Technology Enhancements • Hardware: Better batteries. Better circuits/processors. Co-optimization with transmission schemes. • Link: Antennas, modulation, coding, adaptivity, DSP, BW. • Network: Dynamic resource allocation. Mobility support.

  13. Global Satellite Suburban Urban In-Building Picocell Microcell Macrocell Basic Terminal PDA Terminal Audio/Visual Terminal 3G: ITU-developed, UMTS/IMT-2000

  14. 4G 3G 2G Future Generations Other Tradeoffs: Rate vs. Coverage Rate vs. Delay Rate vs. Cost Rate vs. Energy Rate 802.11b WLAN 2G Cellular Mobility Still: Fundamental Design Breakthroughs Needed

  15. Current Wireless Systems • Cellular Systems • Wireless LANs (802.11a/b/g, Wi-Fi) • Satellite Systems • Paging Systems • Bluetooth • Ultrawideband radios (UWB) • Zigbee/802.15.4 radios • WiMAX (802.16)

  16. Wireless Local Area Networks (WLANs) 1011 0101 01011011 Internet Access Point • WLANs connect “local” computers (~100 m range) • Breaks data into packets • Channel access is shared (random access) • Backbone Internet provides best-effort service • Poor performance in some app’s (e.g. video)

  17. In future all WLAN cards will have all 3 standards... Wireless LAN Standards (Wi-Fi) • 802.11b (Current Generation) • Standard for 2.4GHz ISM band (bw 80 MHz) • Frequency hopped spread spectrum • 1.6-10 Mbps, 500 ft range • 802.11a (Emerging Generation) • Standard for 5GHz NII band (bw 300 MHz) • OFDM with time division • 20-70 Mbps, variable range • Similar to HiperLAN in Europe • 802.11g (New Standard) • Standard in both 2.4 GHz and 5 GHz bands • OFDM (multicarrier modulation) • Speeds up to 54 Mbps

  18. Satellite Systems • Cover very large areas • Different orbit heights • GEOs (39000 Km) via MEOs to LEOs (2000 Km) • Trade-off between coverage, rate, and power budget! • Optimized for one-way transmission: • Radio (e.g. DAB) and movie (SatTV) broadcasting • Most two-way systems struggling or bankrupt... • (Too) expensive alternative to terrestrial systems • (But: a few ambitious systems on the horizon)

  19. Paging Systems (Personsøk) • Broad coverage for (very) short messaging • Message broadcast from all base stations • Simple terminals • Optimized for 1-way transmission • Answer-back is hard • Overtaken by cellular

  20. Bluetooth • “Cable replacement” RF technology (low cost) • Short range (10 m, extendable to 100 m) • 2.4 GHz ISM band (crowded!) • 1 Data (700 Kbps) + 3 voice channels • Widely supported by telecommunications, PC, and consumer electronics companies • Few applications beyond cable replacement! 8C32810.61-Cimini-7/98

  21. UltraWideband Radio (UWB) • Impulse radio: sends pulses of tens of picoseconds (10-12) to nanoseconds (10-9) - duty cycle of only a fraction of a percent • Uses a lot of bandwidth (order of GHz) • Low probability of detection by others + beneficial interference properties: low transmit power (density) spread over wide bandwidth • This also results in short range. • But : Excellent positioning (ranging) capability + potential of high data rates • Multipath highly resolvable: both good and bad • Can use e.g. OFDM or equalization to get around multipath problem.

  22. Why is UWB interesting? • Unique Location and Positioning properties • 1 cm accuracy possible • Low Power CMOS transmitters • 100 times lower than Bluetooth for same range/data rate • Very high data rates possible (although low spectral efficiency) - 500 Mbps at ~10 feet range under current regulations • 7.5 Ghz of “free spectrum” in the U.S. • FCC (Federal Communications Commission) recently legalized UWB for commercial use in the US • Spectrum allocation overlays existing users, but allowed power level is very low, to minimize interference • “Moore’s Law Radio” • Data rate scales with the shorter pulse widths made possible with ever faster CMOS circuits

  23. IEEE 802.15.4/ZigBee radios • Low-Rate WPAN (Wireless Personal Area Network) - for communications < 30 meters. • Data rates of 20, 40, 250 kbps • Star topology or peer-to-peer operation, up to 255 devices/nodes per network • Support for low-latency devices • CSMA-CA (carrier sense multiple access with collision avoidance) channel access • Very low power consumption: targets sensor networks (battery-driven nodes, lifetime maximization) • Frequency of operation in ISM bands

  24. WiMAX: Worldwide Interoperability for Microwave Access • Standards-based (PHY layer: IEEE 802.16 Wireless MAN family/ETSI HiperMAN) technology, enabling delivery of ”last mile” (outdoor) wireless broadband access, as an alternative to cable and DSL (MAN = Metropolitan Area Network). Several bands possible. • OFDM-based adaptive modulation, 256 subchannels. TDM(A)-based. Antenna diversity/MIMO capability. Advanced coding + HARQ. • Fixed, nomadic, portable, and mobile wireless broadband connectivity without the need for direct line-of-sight (LOS) to base station. • In a typical cell radius deployment of 3 to 10 kms, expected to deliver capacities of up to 40 Mbps per channel, for fixed and portable access. • Mobile network deployments are expected to provide up to 15 Mbps of capacity within a typical cell radius deployment of up to 3 kms. • WiMAX technology already has been incorporated in some notebook computers and PDAs. Potentially important part of 4G?

  25. Data rate 100 Mbit/sec UWB 802.11g 802.11a 802.11b 10 Mbit/sec 1 Mbit/sec 3G Bluetooth 100 kbits/sec ZigBee ZigBee 10 kbits/sec UWB 0 GHz 1GHz 2 GHz 3 GHz 4 GHz 5 GHz 6 GHz Frequencies occupied

  26. Range 10 km 3G 1 km 100 m 802.11b,g 802.11a Bluetooth 10 m ZigBee ZigBee UWB UWB 1 m 0 GHz 1GHz 2 GHz 3 GHz 4 GHz 5 GHz 6 GHz

  27. Power Dissipation 10 W 802.11a 802.11bg 3G 1 W 100 mW Bluetooth UWB ZigBee 10 mW ZigBee UWB 1 mW 0 GHz 1GHz 2 GHz 3 GHz 4 GHz 5 GHz 6 GHz

  28. Emerging Systems • Ad hoc wireless networks • Sensor networks • Distributed control networks

  29. Ad-Hoc Networks • Peer-to-peer communications. • No backbone infrastructure (no base stations). • I.e. “Truly wireless”! • Routing can be multihop. • Topology is dynamic in time; networks self-organize. • No centralized cooordination. • Fully connected, even with different link SINRs (signal-to-interference plus noise ratios)

  30. Design Issues • Ad-hoc networks provide a flexible network infrastructure for many emerging applications. • The capacity of such networks is however yet generally unknown (hot research topic). • Transmission, access, and routing strategies for ad-hoc networks are generally also still ad-hoc... • Cross-layer design critical and very challenging. • Energy constraints impose interesting design tradeoffs for communication and networking (nodes typically battery-driven).

  31. Nodes typically powered by nonrechargeable batteries. Data (sensor measurements) flow to one centralized location (sink node, data fusion center). Low per-node rates - but up to 100,000 nodes. Sensor data highly correlated in time and space. Nodes can cooperate in transmission, reception, compression, and signal processing. Sensor NetworksEnergy is the driving constraint

  32. Energy-Constrained Nodes • Each node can only send a finite number of bits. • Transmit energy minimized by maximizing bit time • Circuit energy consumption increases with bit time • Introduces a delay versus energy tradeoff for each bit! • Short-range networks must consider transmit, circuit, and processing energy - jointly. • Most sophisticated transmission techniques not necessarily most energy-efficient! • Sleep modes save energy - but complicate networking. • Changes everything about the network design: • Bit allocation must be optimized across all protocols. • Delay vs. throughput vs. node/network lifetime tradeoffs. • Optimization of node cooperation.

  33. Spectrum Regulation • Spectrum is a limited natural resource used by many. • The worldwide radio spectrum is controlled by ITU-R (International Telecommunications Union) • In Europe, by ETSI (European Telecommunications Standardization Institute). • In the US, by FCC (Federal Communications Commission; commercial) and OSM (Office of Spectral Management; defense). • In Norway, by Post- og teletilsynet (PT). • Spectrum can be auctioned, paid fixed price for, or “given away” (unlicensed bands). • Some spectrum typically set aside for universal use. Regulation, although necessary, can also stunt innovation, cause economic disasters, and delay system rollout... (cf. UMTS spectrum auctions in Europe)

  34. Standards • Interacting systems require standardization (compatibility, interoperability) • Typically: Companies want their own systems adopted as standard! • Alternatively: try for “de-facto” standards • Worldwide standards determined by ITU-T (International Telecommunications Union) • In Europe, by ETSI (European Telecommunications Standardization Institute) • In the US by TIA (Telecommunications Industry Association) • IEEE standards often adopted (also worldwide) • Process fraught with inefficiencies and interest conflicts... Standards for current systems are summarized in Appendix D in the textbook.

  35. Main Points • The wireless vision for the future encompasses many exciting systems and applications • Technical challenges transcend across all layers of the system design. • Cross-layer design is emerging as a key theme in wireless. • Existing and emerging systems provide excellent quality for certain applications, but poor interoperability. • Standards and spectral allocation heavily impact the evolution of wireless technology. • This course will however focus on basic technology issues related to and relevant for current and upcoming wireless systems.

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