Data Whitening in Base-band to Reduce PSD of UWB Signals

1. Data Whitening in Base-band to Reduce PSD of UWB Signals Shaomin Mo Panasonic Information and Networking Technologies Laboratories Shaomin Mo, Panasonic -- PINTL

2. Overview • Power Spectra Density (PSD) issue in UWB • Analysis of PSD of UWB signals • Mechanisms to reduce PSD • Phase reversion to reduce PSD • Architecture of using Linear Feedback Shift Register • Phase reversion for SYNC • Conclusion Shaomin Mo, Panasonic -- PINTL

3. PSD is an Important Issue in UWB Communication Systems • FCC limited authorization of UWB technology, Feb 14, 2002 • Use in restrict spectrum at restrict power • Do not interfere with other wireless systems • Other agencies still have some reservations about whether UWB will interfere with other wireless systems such as air navigation and landing systems Shaomin Mo, Panasonic -- PINTL

4. Reducing PSD is an Important Part in UWB System Design • TX power should be limited by peak in spectrum • Repeat pulse trains may generate strong line spectra and high PSD • Traditional scramblers are not sufficient to reduce PSD • PSD suppression results in • Prevention of interference to existing systems • Potential increased rate, Tx power (distance) Shaomin Mo, Panasonic -- PINTL

5. Model of Repeat Pulse Train • Signal model • Probability function of an Shaomin Mo, Panasonic -- PINTL

6. PSD of Repeat Pulse Train • Es is determined by w(t) and Tc • Es is not affected by Pr{an} • Total PSD is determined by w(t) and Tc • Total PSD is not affected by Pr{an} Shaomin Mo, Panasonic -- PINTL

7. PSD of Repeat Pulse Train W(f) PSD of repeat pulse trains consists of • Sc(f) – continuous component • Sd(f) – discrete component Tc p Shaomin Mo, Panasonic -- PINTL

8. Parameters that Determine PSD • W(f) – pulse shape & Tx power • Tc – clock period or pulse rate • p – probability in distribution function • Does not affect total PSD • Changes distribution of PSD between continuous and discrete components Shaomin Mo, Panasonic -- PINTL

9. Relationship between Continuous and Discrete Components • P = 0 or 1 Sc(f) = 0 and Sd(f) = max All PSD goes to the discrete component; • P = 0.5 Sc(f) = max and Sd(f) = 0 All PSD goes to the continuous component • Because total PSD is constant Max(Sc(f)) = Max(Sd(f)) Shaomin Mo, Panasonic -- PINTL

10. Relationship between Continuous and Discrete Components • Total continuous PSD equals total discrete PSD • The continuous distributes on all frequencies • The discrete distributes on those discrete frequencies separated by 1/Tc. • Peak value of continuous PSD is lower than that of discrete PSD Shaomin Mo, Panasonic -- PINTL

11. Objective of Design • Reduce or eliminate discrete component of PSD Shaomin Mo, Panasonic -- PINTL

12. PSD with Different p PSD of single pulse P = 0.25 peak = 9 Line spectra P = 0.5 P = 1.0 peak = 17 peak = 3 Shaomin Mo, Panasonic -- PINTL

13. TDMA Systems • Traditional communication systems require randomness inside a frame for timing recovery, equalization, etc. Shaomin Mo, Panasonic -- PINTL

14. New Requirements to UWB Communication Systems • Traditional: randomness in X direction • UWB: randomness in both X & Y directions Shaomin Mo, Panasonic -- PINTL

15. PSD Analysis: if data is not evenly distributed in Y direction, line spectra appear Waveform of single pulse Waveform of data • Phase Original stream: line spectra & peak = 17 PS of single pulse PSD of data Shaomin Mo, Panasonic -- PINTL

16. Propose 1: Phase Reversion to Reduce PSD • A random sequence {bn} is generated with • cn = an ^ bn. It can be shown that • {cn} is used as the new data for transmission. Shaomin Mo, Panasonic -- PINTL

17. Using proposed scheme, line spectra is eliminated and PSD is reduced Waveform of single pulse Waveform of data Proposed 1: PSD of cn, Line spectra gone peak reduced to 8 PS of single pulse PSD of data Shaomin Mo, Panasonic -- PINTL

18. Major Challenge in Implementing Phase Reversion • Simple way to generate random sequence • Easy way to synchronize random number generators in both transmitters and receivers Shaomin Mo, Panasonic -- PINTL

19. Propose 2: Architecture of LFSR • LFSR stands for Linear Feedback Shift Registers • Easy implementation • Very suitable for semiconductor implementation Shaomin Mo, Panasonic -- PINTL

20. LFSR is loaded with a RN per frame & updated per pulse Shaomin Mo, Panasonic -- PINTL

21. Synchronization of LFSR • Initial system channel access • Random vectors are generated in advance & stored in an array • Transmitters & receivers keep same array • Index to a vector in the array is put in data to transmit • Initial traffic channel access • Sequence number can be used Shaomin Mo, Panasonic -- PINTL

22. Proposed LFSR implementation Phase controlled by RNs as reference of low bound 15-bit LFSR vs. Idea Low Bound • LFSR is too short • Strong line spectra exist Shaomin Mo, Panasonic -- PINTL

23. Proposed LFSR implementation Phase controlled by RNs as reference of low bound 28-bit LFSR vs. Idea Low Bound • LFSR is long enough • Line spectra is suppressed • Very close to reference Shaomin Mo, Panasonic -- PINTL

24. Propose 3: Phase Reversion on SYNC Three mechanisms can be used: • Phase reversion on the whole SYNC • SYNC is divided into symbols & phase reversion on symbols • Phase reversion & scrambling on symbols Shaomin Mo, Panasonic -- PINTL

25. Phase Reversion on SYNC/symbols can eliminate line spectra but not ripples in PSD Waveform of symbols One cycle of symbols PSD without phase reversion PSD with phase reversion Propose 3: line spectra gone Original: strong line spectra Shaomin Mo, Panasonic -- PINTL

26. Scramble Symbols Shaomin Mo, Panasonic -- PINTL

27. Phase Reversion & Scrambling on SYNC/symbols can smooth ripples & eliminate line: snap shot at 10, 50 200 runs Proposed 3: PSD of symbol-based phase reversion & scrambling Very close to reference Phase controlled by RNs as reference of low bound Shaomin Mo, Panasonic -- PINTL

28. Conclusion • Phase reversion can effectively reduce PSD • Phase reversion can be applied to PAM, PPM, Time-Hopping to reduce PSD • LFSR is an easy way to generate RNs with good performance • Scrambling can enhance performance by smoothing ripples in PSD with extra processing & can be extended beyond SYNC Shaomin Mo, Panasonic -- PINTL

29. Thank you Shaomin Mo, Panasonic -- PINTL