1. ECEN5533 Modern Commo Theory Dr. George Scheets Lesson #36 11 April 2016 n Read 7.1 – 7.2 n Problems: 6.4, 6.5, 9.8 n Corrected tests due Friday, 15 April

2. ECEN5533 Modern Commo Theory Dr. George Scheets Lesson #37 13 April 2016 n Read 7.3 n Problems: 6.9, 9.9 n Corrected tests due Friday, 15 April

3. ECEN5533 Modern Commo Theory Dr. George Scheets Lesson #38 15 April 2016 n Read 7.4 n Problems: 6.11, 6.13 n Corrected tests due Friday, 15 April

4. Performance n Uncoded BPSK n Hard coded Block or Convolutional BPSK n Soft coded Convolutional BPSK n Turbo Coded BPSK & LDPC Codes n All of these require an increase in the transmitted bit rate u Need more bandwidth, or u Go M-Ary Improved Performance

5. Low Density Parity Check Codes n Developed by Robert Gallagher, 1963 MIT Grad u Low Density → Few 1's in rows & columns of H u Impractical to implement then n Linear Block Codes u Huge block sizes u DVB-S2 (Video) Code 43,200 data bits & 21,600 parity bits n Offers comparable performance to Turbo Codes u Being used in some of the newest standards F 10 Gbps Ethernet over twisted pair F 802.11n & 802.11ac (optional) u Turbo Codes: Easy to Encode, Hard to Decode LDPC Codes: Hard to Encode, Easy to Decode

6. Spread Spectrum n Two Kinds u Direct Sequence u Frequency Hopping n Advantages u Interference Suppression u Low Probability of Exploitation u Multipath Effects are Reduced u Code Division Multiple Access n Uses u 3G Cell Phone Standards u Lower to mid speed WiFi

7. +1 time +1 +1 Traffic (9 Kbps) Spreading Signal 27 Kcps Transmitted (Baseband) Signal 27 Kcps +1 DSSS - Transmit Side

8. Wireless X 100 Kcps Zero Mean Square Pulses cos(2πf c t) BPSK output 100 Kcps 90% of power in 200 KHz BW centered at f c Hertz X cos(2πf c t) BPSK input 100 Kcps + noise + 2nd DSSS Signal 100 Kcps Zero Mean Square Pulses + filtered noise RCVR Front End RF Transmitter Low Pass Filter (Wide Band) Band Pass Filter (Wide Band)

9. Spread Spectrum Receiver X cos(2πf c t) BPSK input 100 Kcps + noise + 2nd DSSS Signal 100 Kcps Zero Mean Square Pulses + filtered noise + 2nd DSSS signal RCVR Front End Low Pass Filter (Wide Band) Band Pass Filter (Wide Band) X Despread Sequence Low Pass Filter (Narrow Band) 10 Kbps Message + noise + 2nd DSSS interference (noise like)

10. time +1 +1 Despreading Signal 27 Kcps Received (Baseband) Signal 27 Kcps +1 +1 time Recovered Traffic 9 Kbps DSSS-Receiver

11. DSSS Receiver n If the another source is transmitting... n...our receiver will have the wrong despread sequence... n...and the output will be garbage.

12. time+1 Received Signal #2 27 Kcps +1 time Recovered Garbage from 2nd signal +1 time +1 Despreading Signal 27 Kcps +1 DSSS-Receiver

13. DSSS Receiver n If the both sources are transmitting... n...and the signals are equal power at the receiver... n...the bit detector will be fed the sum of the two results.

14. Input to Matched Filter Detector (sum) +1 time Recovered Traffic 9 Kbps time Recovered Garbage from 2nd signal +1 +2+1 +1-2 time DSSS-Receiver +2

15. Receiver Matched Filter Detector Output Additional signals transmitting at the same time increase the apparent noise seen by our system. Message BER will increase. +1 time Input to Matched Filter Detector (sum) +2-2 time T Bit +2

16. FDM FDMA WDM frequency time Different channels use some of the bandwidth all of the time. 12345

17. TDM TDMA frequency time Different channels use all of the bandwidth some of the time. Predictable time assignments. 1 2 3 1 etc.

18. CDMA frequency time Different channels use all of the bandwidth all of the time. Channels use different codes. Other channels cause noise-like interference.

19. CDMA: 3D View code #1 code #2 code #3 frequency time

20. F-15 Eagle RCS ≈ Barn Door?

21. F-117 Nighthawk RCS ≈ Hummingbird = 0.025 m 2 ?

22. B-2 Spirit RCS ≈ 0.1 m 2 ?

23. Impulse Response Non-stealth vs Stealth Source: Cheville & Grischkowsky, "Time Domain THz Impulse Response Studies", Applied Physics Letters, October 1995

24. Impulse Response Looking Down from Top Left Source: Cheville & Grischkowsky, "Time Domain THz Impulse Response Studies", Applied Physics Letters, October 1995