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POTS Connectivity

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POTS Connectivity

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  1. ECEN5553 Telecom SystemsDr. George ScheetsWeek 11Read [23a] "Fantastic 4G"[23b] "Inside the IT Challenges of Sports and Entertainment"[24a] "A Surge in Small Cells"[24b] "Spectrum Access Technologies"Exam #2 no later than 6 November (Remote DL) 1-1.5 pages off 2012 Exam #2 Covers Internet – Fiber, Readings [5] – [20]Term Paper 8 November (Local) 15 November (Remote DL)

  2. POTS Connectivity Copper Local Loop Copper Local Loop Fiber Optic Trunk CO CO Phone Phone 4 Wire 2 Wire ‘4 Wire’ 2 Wire 4 Wire Analog Digital 64 Kbps TDM Analog

  3. POTS Connectivity (ISDN)All-Digital Phone System V1.0 Copper Local Loop Copper Local Loop Fiber Optic Trunk CO CO Phone Phone 4 Wire 2 Wire ‘4 Wire’ 2 Wire 4 Wire Digital 64 Kbps

  4. Integrated Services Digital Network • Basic Rate Interface (BRI) • Aimed at typical home users, SOHO crowd • Provides 2 x 64 Kbps Bearer Channels... • Phone & Computer usage • ... & 16 Kbps signaling channel. • Looked good in early '90's • Compared to a 14.4 Kbps dial up modem • RBOC's deployed ISDN capable switches slowly.

  5. RIP ISDN • SBC was gearing up to push this in mid '90's.Then... • Internet use exploded • DSL came along • BRI = Too Little, Too Late • Voice calls will eventually be all-digital, but not as envisioned with ISDN • VoIP or VoMPLS

  6. ISDN • Primary Rate Interface (PRI) • Aimed at medium to large business • Provides 23 x 64 Kbps Bearer Channels... • ... & 64 Kbps signaling channel. • Has seen more success. • Reasonably common way to connect corporate PBX to PSTN

  7. Router Router All-Digital Phone System V2.0 LAN LAN ISP IP Phone IP Phone Digital, ?? Kbps

  8. All-Digital Phone System V3.0 Router Router ISP Cell Phone Cell Phone Digital, ?? Kbps

  9. EM Waves and You Solids: Concrete Wood Similar Effect. MHz GHz THz PHz EHz Glass: Similar except around visible light & infrared. Metal: Blocks everything. Gamma can punch thru thin sheets. source: http://hyperphysics.phy-astr.gsu.edu/

  10. Atmospheric Absorption source:http://www.phys.hawaii.edu/~anita/web/

  11. Do Cell Phones Cause Brain Cancer? • Studies in [23b] show mixed results • Some show increased chances • Some show decreased chances • World Health Organization says maybe • Laws of Physics & Frequencies Used Today • Localized "Heating" possible • 1 watt cell by ear? 1/2 watt hits head. • Oklahoma Mesonet, 2:50 pm, 31 October 2011 • 600 watts/meter2 solar radiation falling (hazy) • Top of Dr. Scheets' head ≈ 0.03 meters2 • 19.2 watts of solar radiation hit top

  12. Radio Transmission • Want a reasonable size antenna? • λ (= velocity/frequency) needs to be small • Signal needs high frequencies • Injecting pulses directly into antennas? • Won't work well • All pulses have a lot of low frequency energyWon't radiate well • Need to shift all pulse's energy to higher frequency range

  13. 1 MHz Sinusoid 1.5 1 vp 1 MHz 0 -1.5 .000005 0 Power Spectrum freq (Hertz) 1,000,000

  14. Binary ASK 1.5 1 MHz 0 -1.5 .00001 0 Two different Amplitudes are transmitted 10 cycles/.00001 seconds = 1 MHz 5 cycles/symbol 200 K symbols/second = 200 K bits/second

  15. Binary FSK 1.5 0 -1.5 .00001 0 Two different frequencies are transmitted Symbol #1) 5 cycles/.000005 seconds = 1 MHz Symbol #2) 10 cycles/.000005 seconds = 2 MHz 1.5 MHz Average (center) Frequency 2 symbols in .00001 seconds = 200 K symbols/second = 200 K bits/second

  16. Binary PSK 1.5 1 MHz 0 -1.5 .00001 0 Two different phases are transmitted 10 cycles/.00001 seconds = 1 MHz 5 cycles/symbol 200 K symbols/second = 200 K bits/second

  17. M-Ary Signaling • One of M possible signals transmitted each symbol interval • Tends to be used where bandwidth is tight & SNR decent at the receiver. • Each symbol can represent log2M bits • Example: In 16 FSK • one of 16 possible frequencies is transmitted every symbol interval • each symbol can represent 4 bits

  18. 4-Ary ASK 1.5 1 MHz 0 -1.5 .000015 0 4 different Amplitudes are transmitted (3 shown) 4th symbol might be 0 volts for 5 μ seconds 15 cycles/.000015 seconds = 1 MHz 5 cycles/symbol 200 K symbols/second = 400 K bits/second

  19. Quadrature Amplitude Modulation(form of M-Ary Modulation) 1.5 1 MHz 0 -1.5 .000015 0 Different amplitudes and phases are transmitted 15 cycles/.000015 seconds = 1 MHz 5 cycles/symbol 200 K symbols/second = Log2M*200 K bits/second

  20. Unfiltered 802.11b Signal

  21. Cosine & Cosine2 Cosine Cosine2

  22. Cosine & Cosine*Sine Cosine Sine Cosine*Sine

  23. RF Wireless Layer 1 Issues • Message mapped onto carrier wave • Binary: PSK • 4-Ary: 4-PSK, a.k.a. QPSK • M-Ary (M > 4): QAM (combo of ASK & PSK) • Hi frequency RF carrier frequency • Small antenna • Hi frequency RF carrier frequency • Less penetration

  24. Forward Error Correction • Adds extra parity bits to the bit stream • FEC codes allow designer to trade-off an increase in the bit rate for an reduced Bit Error Rate • Cranking up transmitted signal power can do the same • Distance between legal code words sets error correcting capability • FEC codes are used on... • Cell Phones • NASA Deep Space probes • Compact Disk • ...and other applications.

  25. Digital Communication System Source Data, Digitized audio or video. Outputs bits. Modulator Converts bits to a symbol suitable for channel. FEC Adds extra parity bits. Optional FEC Decoder Examines blocks of bits. If possible, corrects or detects bit errors. Outputs estimate of source bit stream. Symbol Detector Examines received symbol & outputs 1 (binary) or more (M-Ary) bits. Channel Attenuates, distorts, & adds noise to symbols.

  26. Modulator • Copper Cable • Electrical pulses frequently used • Fiber Cable • Electrical pulses converted to optical pulses • RF Systems • High frequency sinusoid symbols used • Carrier frequency impacts antenna size • Binary versus M-Ary • M-Ary packs more bits in the bandwidth • M-Ary more susceptible to decoding errors • M-Ary used when bandwidth is tight & SNR decent

  27. RF Modulator • May map 1 Mbps stream from the FEC coder to... • ... 1 M symbol/sec Binary ASK,PSK, or FSK signal • ... 500 K symbol/sec 4-Ary ASK,PSK (a.k.a. QPSK), or FSK signal • 2 bits per symbol • Would require less Bandwidth than Binary as BW proportional to symbol rate • ... other M-Ary signal (QAM)

  28. Receiver Symbol Detector • If Radio system • INPUT: attenuated, noisy & distorted Binary PSK, QPSK, or QAM • If copper cable • INPUT: attenuated, noisy & distorted square electrical pulses (Baseband) • If fiber • INPUT: attenuated, noisy, & distorted square optical pulses (Baseband) • OUTPUT: Baseband (square electrical pulses)

  29. Receiver • FEC Decoder • INPUT: Baseband BitsTraffic we want + parity bits • OUTPUT: Baseband BitsTraffic bits • Some may be in error

  30. FEC Examples • Single Sample Detector (SSD) • Samples each symbol once, compares result to threshold • Matched Filter Detector (MFD) • Samples each bit multiple times and computes an average, compares average to a threshold • MFD will have lower P(BE) than SSD • MFD P(BE) gets worse as bit rate increases • Averaging time becomes shorter • Number of independent samples gets smaller

  31. FEC Examples • In the limit, as bit interval T approaches zero seconds • # of independent samples approaches 1 • MFD P(BE) approaches SSD P(BE) • Suppose you have a system where • P(BE) = 0.1 for SSD for all bit rates • P(BE) = 0.02 for MFD at bit rate R (no FEC) • P(BE) = 0.03 for MFD at bit rate 2R (2:1 FEC) • P(BE) = 0.04 for MFD at bit rate 3R (3:1 FEC)

  32. Block Diagram:Single Sample Detector & no FEC Source Channel Coder • If symbol detector screws up 10% of the time, P(Bit Application Error) = 0.1 Data bits R bps Symbol Detector: Single Sample Channel P(Bit Error) = .1 R bps

  33. Example: Source Output • 500 Kbps Data Bit Stream • Layer 2 protocols and above • Voice, Computer Data, or Video T = .000002 seconds/bit 1/T = 500 K Data bps. volts +1 0 time -1 T

  34. Example: 2:1 FEC Coder Output • Might duplicate each application bit • for every 1 data bit input, two code bits (1 parity bit & the input application bit) are output T = .000001 seconds/bit 1/T = 1 M Code bps. volts +1 time 0 -1 T

  35. Example) SSD 2 bit code words • Suppose you now transmit each bit twice, and P(Code Bit Error) = .1 • Legal Transmitted code words; 00, 11 • Possible received code words00, 11 (appears legal, 0 or 2 bits decoded in error) 01, 10 (clearly illegal, 1 bit decoded in error)P(No bits in error) = .9*.9 = .81P(One bit in error) = 2*.9*.1 = .18P(Both bits in error) = .1*.1 = .01 • Decoder takes 2 Code bits at a time & outputs 1 bit of DataIf illegal code word received, it can guess 0 or 1.81% + 18%(1/2) = 90% of time the correct bit is output 1% + 18%(1/2) = 10% of time the incorrect bit is output • Same performance as No Coding @ twice the bit rate

  36. SSD 2:1 FEC FEC Coder: Input = 1 bit. Output = Input + Parity bit. Source Modulator data bits R bps Symbol rate transmitted must double compared to no FEC case, or 4-Ary signaling must be used. code bits 2R bps code bits app. bits FEC Decoder: Looks at blocks of 2 bits. Outputs 1 bit. Symbol Detector: Single sample Channel P(data bit error) = .1 P(code bit error) = .1

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