Department of Computer and IT Engineering University of Kurdistan Computer Networks II

1. Department of Computer and IT Engineering University of Kurdistan Computer Networks II Wireless Networks By: Dr. Alireza Abdollahpouri

2. Outline • Basic Concepts of Wireless Networks • Applications of Wireless Networks • Overview of Research Topics

3. Outline • Basic Concepts of Wireless Networks • Applications of Wireless Networks • Overview of Research Topics

4. Wireless Communications • There is no physical link in wireless networks. Signals are transmitted on a certain frequency, propagate in the space and are captured by the receiver tuned to the same frequency. • Wireless communication is normally broadcast communication, i.e., all nodes within the transmission range of a particular node can receive the transmitted packets. • Transmissions in a common neighborhood will interfere with each other. If the Signal-to-Interference-Noise-Ratio (SINR) in the receiver is large enough, a packet can be correctly decoded.

5. Wireless Communications

6. Electromagnetic wave

7. Electromagnetic Spectrum

8. Wireless Attracts Many Users I’ve Upgraded To Wireless

9. wireless hosts • laptop, PDA, IP phone • run applications • may be stationary (non-mobile) or mobile • wireless does not always mean mobility network infrastructure Elements of a Wireless Network

10. base station • typically connected to wired network • relay - responsible for sending packets between wired network and wireless host(s) in its “area” • e.g., cell towers, 802.11 access points network infrastructure Elements of a Wireless Network

11. network infrastructure Elements of a Wireless Network wireless link • typically used to connect mobile(s) to base station • also used as backbone link • multiple access protocol coordinates link access • various data rates, transmission distance

12. Mobility vs. Throughput

13. Wireless Propagation Channel(s) • Multipath propagation: signals reach the receiver via multiple paths. Outdoor indoor

14. Shadowing D C B A C D A B

15. Radio Propagation اثر بازتابي : (Reflection effect) اين اثر نيز به خاطر وجود موانع بزرگ (در مقايسه با طول موج سيگنال تابش شده) است. در اين حالت سيگنال تابش شده پس از برخورد به مانع بزرگ منعكس مي گردد. اما سيگنال منعكس شده داراي توان كمتري نسبت به سيگنال اصلي است. اثر پخشي : (Scattering effect) اگر اندازه مانع در حدود طول موج يا كمتر از طول موج سيگنال تابيده شده باشد، مانع مي تواند باعث پخش شدن موج تابيده شده شود. بنابراين موج تابيده شده به چند موج ضعيف تر شكسته مي شود. اثر شکست : (Refraction effect) اين اثر به دلیل ورود سیگنال از یک محیط به محیط دیگر به وجود می آید.

16. SNR 25 20 15 10 5 0 -5 Distance Distance Sensitivity in Wireless Networks 64QAM 16QAM QPSK

17. Adaptive Modulation and Coding Robustness Throughput AMC To provide a tradeoff between throughput and robustness

18. Antennas

19. Limitations of the Wireless Environment • Limitations of the Wireless Network • limited communication bandwidth • frequent disconnections • heterogeneity of fragmented networks • Limitations Imposed by Mobility • route breakages • lack of mobility awareness by system/applications • Limitations of the Mobile Device • short battery lifetime • limited capacities

20. Wireless Networks • Single-hop wireless networks: cellular network, wireless LAN. • Multi-hop wireless networks: mobile ad hoc network, wireless mesh network, wireless sensor network.

21. Wireless Mesh Networks (WMN) Mesh nodes

22. Wireless Mesh Networks (WMN)

23. Wireless Sensor Networks (WSN) Sensor nodes

24. Wireless Sensor Networks (WSN)

25. Wireless Multi-hop (Mesh vs. Sensor) Wireless Sensor Networks Wireless Mesh Networks • Bandwidth is generous (>1Mbps) • Some nodes mobile, some fixed • Normally not energy limited • Resources are not an issue • Most traffic is user-to-gateway • Bandwidth is limited (tens of kbps) • In most applications, fixed nodes • Energy efficiency is an issue • Resource constrained • Most traffic is user-to-gateway

26. Relaying Relaying for (a) Throughput enhancement, and (b) Coverage extension

27. Outline • Basic Concepts of Wireless Networks • Applications of Wireless Networks • Overview of Research Topics

28. Applications Broadband home networking. Community networking.

29. Applications - Biomedical

30. Habitat Monitoring on Great Duck Island • http://www.greatduckisland.net/ • Intel Research Laboratory at Berkeley initiated a collaboration with the College of the Atlantic in Bar Harbor and the University of California at Berkeley to deploy wireless sensor networks on Great Duck Island, Maine (in 2002) • Monitor the microclimates in and around nesting burrows used by the Leach's Storm Petrel • Goal : habitat monitoring kit for researchers worldwide

31. Applications - Habitat monitoring

32. FireBug • Wildfire Instrumentation System Using Networked Sensors • Allows predictive analysis of evolving fire behavior • Firebugs: GPS-enabled, wireless thermal sensor motes based on TinyOS that self-organize into networks for collecting real time data in wild fire environments • Software architecture: Several interacting layers (Sensors, Processing of sensor data, Command center) • A project by University of California, Berkeley CA.

33. Applications Metropolitan area networks Transportation systems

34. Applications Emergency Response Source: www.meshdynamics.com

35. Many Other Applications • Remote monitoring and control • Public transportation Internet access • Multimedia home networking Source: www.meshnetworks.com (now www.motorola.com).

36. Outline • Basic Concepts of Wireless Networks • Applications of Wireless Networks • Overview of Research Topics

37. Overview of Research Topics • Security • Network Management • Cross-layer design • Physical Layer • MAC Layer • Network Layer • Transport Layer • Application Layer

38. Advanced Physical Layer Techniques • Combination of different modulation and coding rates • Using OFDM and UWB for high speed transmission • Using Multi-antenna systems like: MIMO, Smart antenna • Software Antenna: Programmable RF bands, Channel access modes and channel modulation Multiple-antenna systems

39. PHY - Modulation • Existing modulations work well (OFDM, DSSS, FSK, etc.). • UWB may be an interesting alternative for short distances (480 Mbps up to 1.6 Gbps at distances up to a few meters) • Spread spectrum solutions are preferred as they tend to have better reliability in the face of • Fading (very important for mobile applications) • Interference (more of a factor than in any other wireless system)

40. Omnidirectional antenna Variable delay Signal to transmit Direction changed by the delays Radiation Pattern PHY – Smart Antennas • Background • Implemented as an array of omnidirectional antennas • By changing the phase, beamforming can be achieved • The result is a softwaresteered directional antenna

41. PHY-Smart Antennas Advantages • Low power transmissions • Battery not a big concern in many applications • Enables better spatial reuse and, hence, increased network capacity

42. PHY-Smart Antennas Advantages (cont.) • Punch-through links • Better delays • Less packet loss • Better data rates • Less power

43. PHY-Smart Antennas Advantages (cont.) • Better SNR • Better data rates • Better delays • Better error rates

44. PHY-Smart Antennas Disadvantages • Specialized hardware • Specialized MAC (difficult to design) • Difficult to track mobile users

45. GW GW GW PHY – Transmission Power Control Just right Too high Too low Transmission power can control network topology

46. PHY – Transmission Power Control (cont.) • Optimization Criteria • Network capacity • Delay • Error rates • Power consumption • The ideal solution will depend on • Network topology • Traffic load

47. Overview of Research Topics • Physical Layer • MAC Layer • Network Layer • Transport Layer • Application Layer • Security • Network Management • Cross-layer design

48. MAC: A Simple Classification Wireless MAC Centralized Distributed On Demand MACs, Polling Guaranteed or controlled access Random access Aloha, CSMA/CA SDMA, FDMA, TDMA

49. MAC – MultichannelWhat? • Channels can be implemented by: • TDMA (difficult due to lack of synchronization) • FDMA • CDMA (code assignment is an issue) • SDMA (with directional antennas) • Combinations of the above

50. Ch-1 3 2 2 1 1 Ch-1 Ch-1 2 Ch-2 1 3 4 3 4 Ch-1 Ch-2 Chain bandwidth = B User bandwidth = B/2 User bandwidth = B MAC – MultichannelWhy? • Increases network capacity B = bandwidth of a channel