ECEN5553 Telecom Systems Dr ECEN5553 Telecom Systems Dr. George Scheets Week #12 Read [24a] "The Troubled Past and Uncertain Future of Radio Interference" [24b] "Fantastic 4G" [25] "Riding the Data Tsunami in the Cloud" [26a] "Mobile's Millimeter Wave Makeover" [26b] "Telecom Experts Plot a Path to 5G" Exam #2: Results to date: Hi = 90, Lo = 74.5, Ave = 81.62, σ = 4.76 Term Paper: Due 4 November (Live Sites) Due 11 November (DL)

EM Waves and You Solids: Concrete Wood Glass: Similar Similar except 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/

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

Do Cell Phones Cause Brain Cancer? Studies in [21b] 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

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 energy Won't radiate well Need to shift all pulse's energy to higher frequency range

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

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

Binary FSK 1.5 -1.5 .00001 Two different frequencies are transmitted -1.5 .00001 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

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

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

4-Ary ASK 1.5 1 MHz -1.5 .000015 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

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

Unfiltered 802.11b Spectrum

Cosine & Cosine2 Cosine Cosine2

Cosine & Cosine*Sine Cosine Sine Cosine*Sine

RF Wireless Layer 1 Issues Message mapped onto carrier wave Binary: PSK 4-Ary: 4-PSK, a.k.a. QPSK M-Ary: QAM (combo of ASK & PSK) Hi frequency RF carrier Small antenna Less penetration Wireless is a Hostile Environment Compared to Guided Media (fiber, copper cable) Noisier & received power is very weak

Forward Error Correction XMTR Adds extra parity bits to the bit stream FEC codes allow trade-off of an increase in the bit rate for a reduced RCVR Message 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 Long Haul Fiber Optic Systems Compact Disk ...and other applications.

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.

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

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)

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)

Receiver FEC Decoder INPUT: Baseband Bits Traffic we want + parity bits OUTPUT: Baseband Bits Traffic bits Some may be in error

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

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)

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

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 time -1 T

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 -1 T

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 words 00, 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 = .81 P(One bit in error) = 2*.9*.1 = .18 P(Both bits in error) = .1*.1 = .01 Decoder takes 2 Code bits at a time & outputs 1 bit of Data If 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

SSD 2:1 FEC FEC Coder: Input = 1 bit. Source Modulator 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 app. bits code 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

Example) SSD 3 bit code words Transmit each bit thrice, P(Code Bit Error) = .1 Legal Transmitted code words; 000, 111 Possible received code words 000, 111 (appears legal, 0 or 3 bits in error) 001, 010, 100 (clearly illegal, 1 or 2 bits in error) 011, 101, 110 (clearly illegal, 1 or 2 bits in error) P(No bits in error) = .9*.9*.9 = .729 P(One bit in error) = 3*.92*.1 = .243 P(Two bits in error) = 3*.9*.12 = .027 P(Three bits in error) = .1*.1*.1 = .001 Decoder takes 3 bits at a time & outputs 1 bit. Majority Rules. 72.9% + 24.3% = 97.2% of time correct bit is output .1% + 2.7% = 2.8% of time incorrect bit is output Improved performance @ 3x the required bit rate

SSD 3:1 FEC Source Coder: Input = 1 bit. Source Channel Coder Output = Input + two parity bits. Source Channel Coder data bits R bps Symbol rate transmitted must triple compared to no FEC case, or 8-Ary signaling must be used. code bits 3R bps data bits code bits Source Decoder: Looks at blocks of 3 bits. Outputs 1 bit. Symbol Detector: Single sample Channel P(data bit error) = .028 P(code bit error) = .1 3:1 FEC offers superior performance than simpler no FEC code system.

Example) MFD No Coding Probability of a Bit Error will improve over that of Single Sample Detector to, say, P(Bit Error) = .02 No Coding: Transmit each Data Bit Once Legal Transmitted data‘words’; 0, 1 Possible received data words 0, 1 (legal or 1 bit in error, no way to tell) P(Data Bit OK) = .98 P(Data Bit in error) = .02

Matched Filter Detector & No coding: Block Diagram Source Channel Coder Symbol Detector: Matched Filter Channel P(Bit Error) = .02 Matched Filter shows reduced bit errors compared to SSD Improvement decreases as symbol rate increases

Example) MFD 2 bit code words Suppose you transmit each bit twice, smaller bit width will cause P(Code Bit Error) to increase to, say 0.03 Legal Transmitted code words; 00, 11 Possible received code words 00, 11 (appears legal, 0 or 2 bits in error) 01, 10 (clearly illegal, 1 bit in error) P(No code bits in error) = .97*.97 = .9409 P(One code bit in error) = 2*.97*.03 = .0582 P(Both code bits in error) = .03*.03 = .0009 Decoder takes 2 code bits at a time and outputs 1 data bit If illegal code word received, it can guess 0 or 1. 94.09% + 5.82%(1/2) = 97% of time correct bit output .09% + 5.82%(1/2) = 3% of time the incorrect bit is output FEC makes it worse: 3% data bit error vs 2% No Coding

Typical FEC Performance Coded Plot changes as type of symbol, type of detector, and type of FEC coder change. P(BE) Uncoded Plot changes as type of symbol, and type of detector change. Last example is operating here. There generally always is a cross-over point. The max possible P(BE) = 1/2. SNR

MFD 2:1 FEC 2R code bps Source Coder: Input = 1 bit. Source Output = Input + Parity bit. Source Channel Coder R data bps R app. bps 2R code bps Source Decoder: Looks at blocks of 2 bits. Outputs 1 bit. Symbol Detector: Matched Filter Channel P(data bit error) = .03 P(code bit error) = .03

Example) MFD 3 bit code words Transmit each bit thrice, P(Bit Error) again increases to, say 0.04, due to further increase in the bit rate. Legal Transmitted code words; 000, 111 Possible received code words 000, 111 (appears legal, 0 or 3 bits in error) 001, 010, 100 (clearly illegal, 1 or 2 code bits in error) 011, 101, 110 (clearly illegal, 1 or 2 code bits in error) P(No code bits in error) = .96*.96*.96 = .884736 P(One code bit in error) = 3*.962*.04 = .110592 P(Two code bits in error) = 3*.96*.042 = .004608 P(Three code bits in error) = .04*.04*.04 = .000064 Decoder takes 3 bits at a time & outputs 1 bit. Majority Rules. 88.4736% + 11.0592% = 99.5328% of time correct bit is output .0064% + .4608% = 0.4672% of time incorrect bit is output FEC makes Data BER better (.5% vs 2%) @ thrice the bit rate

MFD 3:1 FEC 3R code bps Source Coder: Input = 1 bit. Source Output = Input + two parity bits. Source Channel Coder R application bps R app. bps 3R code bps Source Decoder: Looks at blocks of 3 bits. Outputs 1 bit. Symbol Detector: Matched Filter Channel P(app. bit error) = .005 P(code bit error) = .04

Typical FEC Performance FEC allows target P(BE) to be reached with lower received SNR, but a higher bit rate must be transmitted. Used a lot in power limited environments. P(BE) Coded Uncoded Different FEC codes will have different curves! Received SNR

Very Large Array Parabolics Directional antennas. Larger size → narrower beam. Narrower beam → energy more focused (XMTR) Narrower beam → better at picking up weak signal (RCVR) image source: Wikipedia

FAST Radio Telescope (500 m) Direct TV Antenna (1/2 m)

Omni-Directional Antenna Array Belkin Wireless Pre-N Router F5D8230-4 Steerable beams. source: http://www.pcmag.com/article2/0,1759,1822020,00.asp

Two Omni Array Example λ/2 fc = 300 MHz λ = 1 meter Same signal fed to both antennas. Beam shoots out both sides at 90 degree angle. (Far side not shown.) Directivity Strength

Two Omni Array Example λ/2 fc = 300 MHz λ = 1 meter Signal to right antenna delayed by 333.3 picosecond ( = 10% wavelength) with respect to right antenna. Directivity Strength

Two Omni Array Example λ/2 fc = 300 MHz λ = 1 meter Signal to left antenna delayed by 333.3 picosecond ( = 10% wavelength) with respect to right antenna. Directivity Strength

Two Omni Array Example λ/2 fc = 300 MHz λ = 1 meter Signal to left antenna delayed by 833.3 picosecond ( = 25% wavelength) with respect to right antenna. Directivity Strength

Two Omni Array Example λ/2 fc = 300 MHz λ = 1 meter Signal to left antenna delayed by 1 2/3 nanosecond ( = 50% wavelength) with respect to right antenna. Directivity Strength

I/O LAN Antenna Combinations SISO Common Today SIMO, MISO, & MIMO Starting to see use on wireless LAN's & MAN's SIMO & MISO Can help cancel effects of multi-path MIMO Can provide spatial diversity Increases amount of usable RF bandwidth

Satcom & Flat Panel Antenna Arrays USS Lake Champlain: Aegis Guided Missile Cruiser image source: wikipedia