References

1. References • A. Goldsmith, Wireless Communications, Cambridge University Press, 2005. • D. Tse and D. Vaswanth, Fundamentals of Wireless Communications, Cambridge University Press, 2005. • T. Rappaport, Wireless Communications, Principles and Practice, 2nd Edition, Prentice Hall. • J. Fayyaz, Radio Design of Cellular Networks, Naghoos Press, 2011.

2. Contents Background and Preview Wireless Propagation Channel Multiple Access Methods Cellular Systems Diversity Issues Information Transmission Capacity Multiple Antenna Technologies Cooperative Communications

3. Wired Vs. Wireless Communications Each cable is a different channel One media (cable) shared by all Signal attenuation is low Highsignal attenuation No interference High interference noise; co-channel interference; adjacent channel interference

4. Why Wireless? • Advantages • Sometimes it is impractical to lay cables • User mobility • Cost • Limitations • Bandwidth • Fidelity • Power • Security

5. Wireless ≈ Waves • Electromagnetic radiation • Emitted by sinusoidal current running through a wire (transmitting antenna) • Creates propagating sinusoidal magnetic and electric fields according to Maxwell’s equations: • Fields induce current in receiving antenna.

6. Propagation Principle electric field propagation direction magnetic field

7. Propagation Mechanisms Line-of-Sight S D Non Line-of-Sight Scattering λ >> D Diffraction λ  D Reflection λ << D

8. Propagation in the “Real World” a wave can be absorbed penetrate reflect bend

9. The Cluttered World of Radio Waves hills girders rain hallways windows vehicles trees walls

10. ISM band 902 – 928 Mhz 2.4 – 2.4835 Ghz FM radio S/W radio TV TV AM radio cellular 5.725 – 5.785 Ghz VHF UHF SHF EHF LF MF HF  300MHz 30MHz 30GHz 300GHz 3GHz 3MHz 30kHz 300kHz  1mm 10cm 10m 1cm 1m 100m 10km 1km Electromagnetic Spectrum X rays Gamma rays visible UV infrared  1 MHz 1 GHz 1 kHz 1 THz 1 EHz 1 PHz Propagation characteristics are different in each frequency band.

11. Evaluating Frequencies • 50 MHz-250 MHz: Good for outdoor range, large antenna size, bending and penetrating. No foliage problems. “Sees” metallic building structures, doesn’t pass through windows or down corridors. • 450 MHz to 2 GHz: - Good compromise for cellular-type systems. Small antenna, but big enough for outdoor range. Minor foliage effects. OK for windows walls and corridors. • 5-20 GHz: Antenna too small for outdoor range. Foliage and rain effects. Indoor microcells, Point-to-point, and Satellites to ground stations.

12. Unlicensed Radio Spectrum(ISM: Industrial, Science, Medicine)  12cm 5cm 33cm 26 Mhz 83.5 Mhz 125 Mhz 902 Mhz 2.4 Ghz 5.725 Ghz 2.4835 Ghz 5.850 Ghz 928 Mhz 802.11a 802.11b Bluetooth Microwave oven cordless phones baby monitors WaveLan

13. Free-space Path-loss • Power of wireless transmission reduces with square of distance (due to surface area increase of sphere). • Reduction also depends on wavelength: • Long wave length (low frequency) has less loss • Short wave length (high frequency) has more loss

14. Path-loss Models • Path-Loss Exponent Depends on environment: L(d) = L(d0)(d/d0)n Free space n = 2 Urban area cellular n = 2.7 to 3.5 Shadowed urban cell n = 3 to 5 In building LOS n = 1.6 to 1.8 Obstructed in building n = 4 to 6 Obstructed in factories n = 2 to 3

15. Multi-path Propagation • Electromagnetic waves bounce off of conductive (metal) objects. • Reflected waves received along with direct wave.

16. Multi-Path Effect • Multi-path components are delayed depending on path length, causes delay spread. • Phase shift causes frequency dependent constructive / destructive interference.

17. Multi-transmitter Interference • Similar to multi-path • Two transmitting stations will constructively/destructively interfere with each other at the receiver. • Receiver will “hear” the sum of the two signals, which usually means garbage.

18. Modulation • Modulation allows the wave to carry information by adjusting its properties (Amplitude, Frequency, and Phase) in a time varying way. • Digital modulation using discrete “steps” so that information can be recovered well despite noise/interference. • 8VSB - US HDTV • BFSK - Mote Sensor Networks • QPSK - 2 Mbps 802.11 & CMDA(IS-95)

19. Symbol Rate & Bandwidth • Modulation allows transmission of one of several possible symbols (two or more). • Data stream is encoded by transmitting several symbols in succession. • Symbol rate ≈ Bandwidth • Symbol Rate or Baud Rate (symbols/sec) • Bit Rate or Throughput (bits/sec) • Spectrum Usage or Bandwidth (Hz) • Inter-symbol interference (ISI) occurs unless delay spread << symbol time.

20. Thermal Noise • Ever-present thermal noise in wireless medium. • Sums with any wireless transmission. • Potentially causes errors in reception (digital) or degradation of quality (analog). • Effectively limits transmission range when transmitting signal strength falls below a threshold.

21. Thermal Noise Calculation • Noise power depends on channel bandwidth: Noise Power = -174dBm/Hz + 10log(BW in Hz) • So for 802.11 • BW = 25 MHz for 802.11b or 802.11a channel • Thus noise power is about -100 dBm • -100 dBm = 10-10mW

22. Physical Channel Properties Review • Received signal power depends on: • Transmit power • Loss over distance (falls off by dn) • Shadowing (e.g. absorption by walls) • Multi-path (e.g. bouncing off of metal objects) • Noise power depends on: • Thermal noise • Environmental noise (e.g. microwave ovens) • Channel Quality • Related to Signal to Noise Ratio

23. Current Wireless Technologies • Cellular Telephony (GSM, CDMA2000) • Fixed Wireless Access (WiMax) • Wireless Local Area Networks • Local Networks (Bluetooth, UWB) • Satellite Communications

24. Cellular Telephony (1)

25. Cellular Telephony (2)

26. Cellular Telephony (3) • Data is bursty, whereas voice is continuous. • 3G widens the data pipe • 384Kbps to few Mbps • Standard based of WCDMA • Packet-based switching for both voice and data • New generations • HSDPA, HSPA+, LTE • WiMAx added to 3G • 4G systems start to come up • Mostly based on OFDM

27. Fixed Wireless Networks (WiMax) • Provide broadband wireless access to homes/offices in a few Km range. • A potential replacement of ADSL • Provide high speed Internet and VOD

28. Wireless Local Area Networks (1) • WLANs connect local computers (100m to a few Km range) • Breaks data into packets • Channel is shared (random access) • Backbone internet provides best-effort service • Poor performance in some applications (e.g. video)

29. Wireless Local Area Networks (2) • 802.11b (oldest) • Standard for 2.4GHz ISM band (80MHz BW) • Frequency hopped spread spectrum • 1.6-10Mbps, few hundred meter range • 802.11a (old) • Standard for 5.7GHz NII band (300MHz BW) • OFDM with time division • 20-70Mbps, variable range • 802.11g (newer) • Standard for 2.4GHz and 5.7GHz bands • OFDM • Up to 54Mbps, few hundred meter range • 802.11n (current) • Up to 140Mbps • Uses smart antenna technology

30. Ultra Wide-Band • Also known as “Impulse Radio”. • Use very high bandwidth to decrease power level. • Hard synchronization • No license problem, but seems to interfere with GPS • Now mainly targeted to small distance applications. (home networks to replace Bluetooth) • Smaller delay and longer range than Bluetooth • Emerging as competitor for 802.11

31. Satellite Communications • Cover very large areas. • Different orbit heights • GEO (36000 Km), MEO and LEO (<2000 Km) • Optimized for one-way transmission • Radio (DAB) and TV (DVB-S) broadcast • Two-way systems • Expensive alternative to terrestrial systems

32. Evolution of Current Technologies • Link: Modulation, Coding, Adaptivity, Smart Antennas • Network: Dynamic resource allocation, Mobility support • Hardware: Better batteries, Circuits/Processors • Applications: Soft and adaptive QoS (main issue in real-time multi-media services)

33. Moving toward Real Multimedia

34. Design Challenges • Wireless channels are capacity-limited broadcast communication medium. • Two main problems in wireless media: • Fading • Interference • Traffic patterns, user locations, and network conditions are constantly changing. • Energy and delay constraints change design principles across all layers of the protocol stack.

35. Emerging Systems • Ad-hoc Wireless Networks • Wireless Sensor Networks • Distributed Control Networks • Cooperative Networks • Cognitive Radio Networks

36. Ad-hoc Wireless Networks (1)

37. Ad-hoc Wireless Networks (2) • Peer-to-peer communications • No backbone infrastructure • Multi-hop routing • Dynamic topology • Fully connected with different link SNRs

38. Ad-hoc Wireless Networks (3) • Ad-hoc Wireless Networks provide a flexible network infrastructure for any emerging application. • The capacity of such a network is generally unknown. • Transmission, access, and routing strategies are generally ad-hoc • Energy constraints impose interesting design tradeoffs for communication and networking.

39. Wireless Sensor Networks (1) 40

40. Wireless Sensor Networks (2) • Energy is the driving constraint. • Nodes powered by non-rechargeable batteries. • Data flows to central location. • Low per-node rates but up to 100000 nodes. • Data highly correlated in transmission. • Nodes can cooperate in transmission, reception, compression, and signal processing.

41. Wireless Sensor Networks (3) (Energy-constrained nodes) • Short-range networks must consider transmit, circuit, and processing energy. • Sleep modes save energy but complicate networking. • Changes everything about the network design: • Optimization of bit allocation across all protocols • Delay vs. throughput vs. node/network lifetime tradeoffs • Optimization of nodes cooperation • Efficient MAC layer communication and Scheduling

42. Distributed Control (1) • Packet loss and/or delay impacts controller performance. • Controller design should be robust to network faults. • Joint application and communication network delay. • Interesting ideas in packet-based communication and file transfer.

43. Distributed Control (2) • There is no methodology to incorporate random delays or packet losses into control system design. • The best rate/delay tradeoff for a communication system in distributed control can not be determined. • Current autonomous vehicle platoon controllers are not string stable with any communication delay. • What are the best routing technologies?

44. Cooperative Networks (1)

45. Cooperative Networks (2) • Increase coverage area • Reduce number of “blind spots” • Reduce transmit power per node • Increase in transceiver complexity • More complex synchronization problems • More interference to be handled properly • Higher end-to-end delays • Additional delay to be handled in real-time applications

46. Cognitive Radio (1) • Available spectrum looks scarce. • Measurements show the allocated spectrum is vastly underutilized.

47. Cognitive Radio (2)

48. Cognitive Radio (3) • Sense, learn, and exploit the environment • One “simple” option: • Use “un-used” spectrum • Agile Radios • Give priority to ”primary” users • But not receiving a signal in wireless environment does not mean that no signal is actually transmitted at that frequency! • Even in simplest form is very challenging. • Many ideas such as: • Game Theory • Near-Noise Level Signal detection • BW transactions • Trust theories (how to identify users with “bad” intensions?)

49. Summary • The wireless vision encompasses many exciting systems and applications. • Technical challenges go across all layers of the system design. • Wireless systems today still have limited performance and interoperability.