ECEN5553 Telecom Systems Dr. George Scheets Week #12 Read [27] "Fantastic 4G" [28] "Mobiles Millimeter Wave Makeover" [29] "Emerging Technologies and Research Challenges for 5G Wireless Networks"" Term Paper 6 November (Live) 81, B > 70, C > 61

Cosine & Cosine 2 Cosine Cosine 2

Cosine & Cosine*Sine Cosine Sine Cosine*Sine

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

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

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

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

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

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

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

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

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

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

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

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

Example) SSD 2 bit code words n Suppose you now transmit each bit twice, and P(Code Bit Error) =.1 u Legal Transmitted code words; 00, 11 u 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 u 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 u Same performance as No twice the bit rate

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

Example) SSD 3 bit code words n Transmit each bit thrice, P(Code Bit Error) =.1 u Legal Transmitted code words; 000, 111 u 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*.9 2 *.1 =.243 P(Two bits in error) = 3*.9*.1 2 =.027 P(Three bits in error) =.1*.1*.1 =.001 u Decoder takes 3 bits at a time & outputs 1 bit. Majority Rules. 72.9% % = 97.2% of time correct bit is output.1% + 2.7% = 2.8% of time incorrect bit is output u Improved 3x the required bit rate

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

Example) MFD No Coding n Probability of a Bit Error will improve over that of Single Sample Detector to, say, P(Bit Error) =.02 n No Coding: Transmit each Data Bit Once u Legal Transmitted data‘words’; 0, 1 u 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 Channel Coder Symbol Detector: Matched Filter P(Bit Error) =.02 n Matched Filter shows reduced bit errors compared to SSD u Improvement decreases as symbol rate increases

Example) MFD 2 bit code words n Suppose you transmit each bit twice, smaller bit width will cause P(Code Bit Error) to increase to, say 0.03 u Legal Transmitted code words; 00, 11 u 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 u Decoder takes 2 code bits at a time and outputs 1 data bit If illegal code word received, it can guess 0 or % %(1/2) = 97% of time correct bit output.09% %(1/2) = 3% of time the incorrect bit is output u FEC makes it worse: 3% data bit error vs 2% No Coding

Typical FEC Performance SNR P(BE) Coded Plot changes as type of symbol, type of detector, and type of FEC coder change. 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.

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

Example) MFD 3 bit code words n Transmit each bit thrice, P(Bit Error) again increases to, say 0.04, due to further increase in the bit rate. u Legal Transmitted code words; 000, 111 u 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 = P(One code bit in error) = 3*.96 2 *.04 = P(Two code bits in error) = 3*.96*.04 2 = P(Three code bits in error) =.04*.04*.04 = u Decoder takes 3 bits at a time & outputs 1 bit. Majority Rules % % = % of time correct bit is output.0064% % = % of time incorrect bit is output u FEC makes Data BER better (.5% vs thrice the bit rate

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

Typical FEC Performance Received SNR P(BE) Coded Uncoded 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. Different FEC codes will have different curves!

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

Arecibo Radio Telescope (305 m) Direct TV Antenna (1/2 m)

Omni-Directional Antenna Array source: Belkin Wireless Pre-N Router F5D Steerable beams.

Two Omni Array Example 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.) λ/2 Directivity Strength

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

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

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

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

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

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

Bit Error Rate Unsatisfactory? System designer has several options: n Use FEC codes n Increase received signal power u Crank up transmitter power out u Use directional antennas n Use more effective modulation technique n Slow down the transmitted symbol rate n Use less noisy receiver electronics

Voyager II Deep Space Probe n Used all of previous techniques on downlink: u 2:1 FEC Coding (different code than in previous examples) u Increasingly sophisticated earth receive antennas u Binary PSK signaling u Reduced bit rates u Cryogenically cooled receiver electronics n Flight history u Launch, August 1977 u Jupiter fly-by, July 1979, Message bit rate: Kbps u Saturn fly-by, August 1981, Message bit rate: 44 Kbps u Uranus fly-by, January 1986, Message bit rate: 29.9 Kbps u Neptune fly-by, August 1989, Message bit rate: 21.6 Kbps u Now well past Pluto. NASA is still in contact.

Pre-Cellular Mobile Telephony source: Telecommunications by Warren Hioki, 1st Edition

0 th Generation Mobile Phones Source:

Cellular Telephone System source: Telecommunications by Warren Hioki, 1st Edition ISP

Cellular Telephony Advantages: n n Frequency Reuse n n Reduced Transmitter Power Out n n Reduced Multipath Problems n n Reduced brain damage? n n Subdividing Cells increases System Capacity n n More Reliable due to cell overlap

Cellular Telephony Disadvantages: n More complex n More installation hassles n BS to MTSO link (Backhaul) & switching requirements can get out of hand

1987 Mobile Phone source: September 1987 Electronic Design Magazine

One Big Cell 30 Channels could support 30 users

Seven Smaller Cells Set #3 10 Channels Set #1 10 Channels Set #2 10 Channels Can Support 70 Users with same Channel set.

Mobile Traffic Source: "The Great Spectrum Famine", IEEE Spectrum Magazine, October 2010.

London, 1995

Hidden Cell Towers sources: businessweek.com mobilitydigest.com