Communications & Networks Introduction

Transcription

1 Communications & Networks Introduction Alexander Nelson February 19th, 2018 University of Arkansas - Department of Computer Science and Computer Engineering

2 Networking Number of Connected Devices 1

3 How can 50B devices all be connected? 1

4 Wireless Networking Categories LPWAN Low Power Wide Area Network WWAN - Wireless Wide Area Network WPAN Wireless Personal Area Network WLAN Wireless Local Area Network 2

5 WWANs

6 Wireless Networking Categories 1 1 Smart Cities Technologies Ivan Nunes Da Silva and Rogerio Andrade ISBN

7 WWAN Wireless Wide Area Network WWAN Set of technologies that provide wireless access to geographically distant sources Includes: Cellular Technologies 2G 3G LTE LTE-M IEEE WiMAX LPWAN Technologies LoRA SigFox Ingenu Mesh Networking? 4

8 Cellular Communications Cellular Network Communication network where last link is wireless Distributed over land areas cells 2 By Andrew pmk - SVG version of Frequency reuse.fig by Mozzerati, CC BY-SA 2.5, 5 2

9 Cellular Communications Advantages: More capacity than a single large transmitter, same frequency used for multiple links in different cells Cell towers are closer Mobile devices use less power than with single transmitter Larger coverage area than a single terrestrial transmitter additional cell towers can be added indefinitely 6

10 Cellular Communications Range is inversely proportional to frequency CDMA2000 Network 7

11 WiMAX WiMAX Worldwide Interoperability for Microwave Access Microwave meaning 300MHz-300GHz frequencies Meant to provide last-mile broadband over wireless Originally 30-40Mbps Upgraded to 1Gbps in

12 WiMAX WiMAX Worldwide Interoperability for Microwave Access Microwave meaning 300MHz-300GHz frequencies Meant to provide last-mile broadband over wireless Originally 30-40Mbps Upgraded to 1Gbps in 2011 Most WiMAX deployments are winding down 9

13 LPWAN Communications LPWAN Low Power Wide Area Network Designed for long range communications at low bit rates Data Rates 0.3kbps-50kbps 10

14 LPWAN Communications LPWAN Low Power Wide Area Network Designed for long range communications at low bit rates Data Rates 0.3kbps-50kbps Intended for sensor-type deployments at long range Power IoT/Smart-City type applications 11

15 LPWAN Communications 12

16 Mesh Networks WANETs Wireless Ad hoc Networks MANETs Mobile Ad hoc Networks ad hoc latin, literally for this Does not rely on static infrastructure MANETs allow for nodes to move freely geographically 13

17 Mesh Networks Mesh Networks as WWAN? Communications technologies similar to cellular networks Can provide WAN access to small devices through sink nodes 14

18 Wireless Network Challenges

19 Wireless Communication Given a certain amount of RF frequency spectrum, how to optimize communication? Metrics: Throughput Total network bits-per-second Latency Average time form packet creation to reception Fairness Do devices receive equal share of resource (airtime)? 15

20 Multiple Access Techniques If multiple wireless clients exist, how to divide resources? Multiple Access Methods Techniques for dividing resources CSMA Carrier Sense Multiple Access TDMA Time Division Multiple Access FDMA Frequency Division Multiple Access CDMA Code Division Multiple Access SDMA Space Division Multiple Access 16

21 Carrier-Sense Multiple Access CSMA Carrier Sense Multiple Access Nodes check to see if anyone is communicating If channel is empty, they may start 17

22 Hidden Node Problem Not detecting communication does not mean channel is clear 18

23 CSMA/CA CSMA/CA CSMA with Collision Avoidance 1. Carrier Sense Listen for other transmission 2. Random Backoff If channel is busy, backoff for random amount of time 3. Request to Send/Clear to Send (RTS/CTS) Access Control Signals 4. Transmission Send entire packet to Access Point (AP) 5. Acknowledgment AP sends acknowledgment if packet is received 6. Exponential Backoff If no ACK, assume collision and backoff 19

24 CSMA Advantages Low latency if channel is not busy No need for centralized control Disadvantages Busy channel causes many collisions low throughput & high energy waste 20

25 TDMA TDMA Time Division Multiple Access 3 3 By Mozzerati at English Wikipedia - 13:13, 2004 Sep 5 (UTC), CC BY-SA 3.0, 21

26 TDMA Advantages Nodes only need to listen during frame save power Guaranteed no collision Disadvantages Lower Throughput A node may not need to use their frame 22

27 FDMA FDMA Frequency Division Multiple Access Divide available frequency into channels Nodes communicate on their own channel Wi-Fi FDMA 5MHz channel width 22MHz spectrum spread 23

28 CDMA CDMA Code Division Multiple Access Use orthogonal psuedorandom codes to allow additive communication on same spectrum Four mutually orthogonal codes 24

29 CDMA Example 25

30 CDMA Advantages Multiple nodes may communicate at the same time Flexible length of codes dynamic allocation Disadvantages Reduced throughput per device per frame That is, takes n times as long to transmit a single bit, where n is length of the code Subject to Near-Far problem 26

31 Near Far Problem Problem with SNR for geographically disparate nodes Near node Noise may be similar to magnitude of far node signal 27

32 Phase Shift Keying Phase Shift Keying PSK Code division multiple access Codes are multiplexed by phase rather than time 28