* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download ppt
Survey
Document related concepts
Time-to-digital converter wikipedia , lookup
Opto-isolator wikipedia , lookup
Cellular repeater wikipedia , lookup
Battle of the Beams wikipedia , lookup
Analog-to-digital converter wikipedia , lookup
Telecommunication wikipedia , lookup
Serial digital interface wikipedia , lookup
Continuous-wave radar wikipedia , lookup
Valve RF amplifier wikipedia , lookup
UniPro protocol stack wikipedia , lookup
Active electronically scanned array wikipedia , lookup
Regenerative circuit wikipedia , lookup
Analog television wikipedia , lookup
Transcript
ECEN5553 Telecom Systems Dr. George Scheets Week #2 Read [3] "A Roadmap to 100G Ethernet at the Enterprise Data Center" Exam #1 Lecture 15, 21 September (Live) No later than 28 September (Remote DL) Outline 7 October 2015, Lecture 22 (Live) No later than 14 October (Remote DL) Outlines Received due 7 October (local) 14 October (remote) 0% Fiber Optic Cable 1 1/4 inch SC Physical Layer Ailments... Attenuation Signal power weakens with distance Distortion Pulse shapes change with distance Copper cabling High frequencies attenuate faster Pulses smear Fiber cabling Frequencies propagate at different speeds Dispersion (Pulses change shape) Generating a Square Wave... 5 Hz + 15 Hz + 25 Hz + 35 Hz 1.5 0 -1.5 0 1.0 cos2*pi*5t - (1/3)cos2*pi*15t + (1/5)cos2*pi*25t - (1/7)cos2*pi*35t) Effects of Dispersion... 5 Hz + 15 Hz + 25 Hz + 35 Hz 1.5 0 -1.5 0 1.0 cos2*pi*5t + (1/3)cos2*pi*15t + (1/5)cos2*pi*25t + (1/7)cos2*pi*35t) In this example the 15 and 35 Hz signals have suffered a phase shift (which can be caused as a result of different propagation speeds) with respect to the 5 and 25 Hz signals. The pulse shape changes significantly. Smearing (a.k.a. Inter-symbol Interference) 4.5 input output z k z2 k 0 4.5 0 0 20 40 60 80 k 100 120 140 127 Pulse energy is no longer confined to a T second time interval. Makes receiver symbol detector's life more difficult. Examples of Amplified Noise Radio Static (Thermal Noise) Analog TV "snow" 2 seconds of White Noise SNR = Average Signal Power = Infinity Average Noise Power 4.5 z2 x 0 k k 4.5 0 0 20 60 40 k Binary Signal Sequence = 0011010111 80 100 99 SNR = 100 4.5 z2 x 0 k k 4.5 0 0 20 40 60 80 k Signal a sequence +1 and -1 volt pulses For your info, SSD BER ≈ 0.0 100 99 SNR = 10 4.5 z2 x 0 k k 4.5 0 0 20 40 60 80 k Signal a sequence +1 and -1 volt pulses For your info, SSD P(BE) = 0.000783 = 1/1277 100 99 SNR = 1 4.5 z2 x 0 k k 4.5 0 0 20 60 40 80 k Signal a sequence +1 and -1 volt pulses For your info, SSD P(BE) = 0.1587 = 1/6.3 100 99 SNR = .1 8.5 z2 x 0 k k 8.5 0 0 20 60 40 80 k Signal a sequence +1 and -1 volt pulses For your info, SSD P(BE) = 0.3759 100 99 Single Sample Detector: SNR = 1 Threshold is placed midway between nominal Logic 1 and 0 values. 4.5 0 4.5 0 0 20 40 60 k 80 100 99 Detected sequence = 0011010111 at the receiver, but there were some near misses. Fall 2002 Final 'Average' based on 1 test chosen at random 126.00 out of 150 Analogous with "Single Sample" Detector 'Average' based on 10 tests chosen randomly 109.44 out of 150 Analogous with "Multiple Sample" Detector Average based on 10 samples tends to be more accurate than "Average" based on 1 sample Actual Midterm Average 106.85 out of 150 Matched Filter Detector: SNR = 1 Orange Bars are average voltage over that symbol interval. 4.5 0 4.5 0 0 20 40 60 k 80 100 99 Averages are less likely to be way off the mark. SSD P(BE) = 0.3759, MFD P(BE) = 0.000783 (10 samples/bit) Receiver Detection SNR tends to worsen with distance Digital Receiver Symbol Detectors Examine received symbol intervals (T sec.) Decide which of M symbols was transmitted Single Sample Detectors Sample each symbol once Compare sampled value to a threshold Matched Filter Detectors (Optimal) Sample each symbol multiple times & generate an average Compare the average value to a threshold Channel Capacity Bandwidth affects usable symbol rate Rapidly changing symbols need hi frequencies Baud rate too high? Distortion!! M-Ary allows increased bit rate SNR Each symbol can represent multiple bits Affects RCVR ability to tell symbols apart Bandwidth & SNR affect usable bit rate Channel Capacity (C) Bandwidth, Bit Rate, SNR, and BER related Channel Capacity defines relationship C = Maximum reliable bit rate C = W*Log2(1 + SNR) bps Bandwidth sets the maximum Baud rate If move too many Baud, symbols will smear. SNR sets the maximum number of different symbols (the "M" in M-ary) you can reliably tell apart. Channel Capacity (a.k.a. Shannon-Hartley Theorem) Claude Shannon Ralph Hartley Power Line Communications Transformers don't pass high frequency signals. Image Source Wikipedia Power Lines act as Antennas Source: http://www.doobybrain.com/2008/02/03/electromagnetic-fields-cause-fluorescent-bulbs-to-glow/ Home Power Line Networks Possible using home wiring Outside Step Down Transformer blocks further wired transmission Signal radiates off internal house wiring Netgear claims 500 Mbps Normalized Propagation Delay NPD = End-to-End Propagation Delay Average time to inject a Packet NPD > 1 1 or more packets can simultaneously be in transit If NPD = 5, 5 average sized packets can be physically on the line NPD < 1 Packet front end hits far side before back end transmitted Transmitter High Speed Low Speed Receiver Types of Traffic... Computer Data Bursty Highly sensitive to errors Not as time sensitive as voice or video Interactive Voice/Video Fixed Rate (if not compressed) *Not very sensitive to errors Fixed or Variable Rate (if compressed) *Sensitive to errors Time Sensitive IEEE Institute for Electrical & Electronics Engineers Largest Technical Organization in the World Promotes betterment of Electrical Engineering Journals & Magazines Conferences Standards IEEE 802.3 Ethernet Based on late 1970’s technology Covers OSI Layers 1 & 2 10 Mbps Line Speed Logical Bus Designed to move Computer Data The various 802.3 flavors dominate the wired LAN Serial Bit Stream: NRZ Coding Logic One Logic Zero 0 0 T volts +1 Called ‘Non Return to Zero’ because voltage never dwells on zero volts. 0 time -1 T Ethernet Uses Manchester Coding Logic One Logic Zero 0 0 volts +1 All symbols have a transition in the middle. 0 time -1 T Ethernet Uses Manchester Coding volts +1 0 time -1 T High Pass Filters Emphasize Change High Pass Filter Output +1 0 time -1 Rectify (Absolute Value) +1 0 T time -1 Result always has pulses T seconds apart. Useful for receiver synchronization. What is CSMA/CD? Polite One Conversation node active at a time No deliberate interruptions Collisions sometimes occur after a pause 802.3 Back-Off Algorithm choose random number 1st Collision 0, 1 2nd Collision 0, 1, 2, 3 3rd Collision 0, 1, ..., 6, 7 4th Collision 0, 1, ..., 14, 15 10th Collision 0, 1, ..., 1022, 1023 15th Collision 0, 1, ..., 1022, 1023 16th Collision Punt Wait (Random Number*.0000512) seconds