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

Understand PSD issues in UWB signals, mechanisms to reduce PSD, application of linear feedback shift registers, and phase reversion to minimize PSD in UWB communication systems.

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

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  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 cellular, air navigation and landing systems Shaomin Mo, Panasonic -- PINTL

  4. Emission Levels for GSM & TDMA in the Cellular Receiver Bands Source: “Ultra-Wideband Radio – The New Part 15”, Microwave Journal, February 2003 Shaomin Mo, Panasonic -- PINTL

  5. Containing PSD is an Important Part in UWB System Design • Repeat pulse trains may generate strong line spectra and high PSD • Traditional scramblers are not sufficient to contain PSD • PSD suppression leads to • Prevention of interference to existing systems • Potential increase in rate, Tx power (distance) Shaomin Mo, Panasonic -- PINTL

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

  7. PSD of Repeat Pulse Train • Ps is determined by w(t) and Tc • Ps 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

  8. 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

  9. 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

  10. Simplified Form of PSD Shaomin Mo, Panasonic -- PINTL

  11. Relationship between Continuous and Discrete Components Shaomin Mo, Panasonic -- PINTL

  12. Relationship between Continuous and Discrete Components • Because total PSD is constant A(f) = B(f) Max(Sc(f)) = Max(Sd(f)) Shaomin Mo, Panasonic -- PINTL

  13. 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. • Continuous PSD is lower than that of discrete PSD on the same frequency components Shaomin Mo, Panasonic -- PINTL

  14. PSD with Different p Has Same Envelop but Different Level PSD of single pulse P = 0.25 peak = 9 Line spectra P = 0.5 P = 1.0 peak = 15 peak = 3 Shaomin Mo, Panasonic -- PINTL

  15. Objective of Design • Contain PSD • Reduce or eliminate discrete component of PSD  reduce PSD across whole spectrum • Make Shaomin Mo, Panasonic -- PINTL

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

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

  18. 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

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

  20. 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

  21. Model of Repeat Pulse Train of Multi-band • Signal model Shaomin Mo, Panasonic -- PINTL

  22. Model of Repeat Pulse Train (cont.) • {wm} is a set of waveforms on sub-bands • Probability function of an, same on all sub-bands Shaomin Mo, Panasonic -- PINTL

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

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

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

  26. w1 w4 w3 w2 w8 w7 w6 w5 To Make {wm} Evenly Distributed – Rotationally Wm is waveform on sub-band m, 1  m  M Shaomin Mo, Panasonic -- PINTL

  27. To Make {wm} Evenly Distributed – Randomly • Another way to make {wm} evenly distributed is to randomly and evenly choose wmso that Shaomin Mo, Panasonic -- PINTL

  28. To Make {an} Evenly Distributed • A random sequence {bn} is generated with • cn = an ^ bn. It can be proved that • {cn} is used as the new data for transmission. Shaomin Mo, Panasonic -- PINTL

  29. PSD of BPSK Data with p=1 & rotationally Line spectra peak = 21 Waveforms in multi-band Original data, p = 1 PS of waveforms Result data peak = 4 Shaomin Mo, Panasonic -- PINTL

  30. PSD of BPSK Data with p=0.25 & rotationally Line spectra peak = 17 Waveforms in multi-band Original data, p = 0.25 PS of waveforms Result data peak = 4 Shaomin Mo, Panasonic -- PINTL

  31. PSD of BPSK Data with p=0.4 & rotationally Line spectra peak = 9 Waveforms in multi-band Original data, p = 0.4 PS of waveforms Result data peak = 4 Shaomin Mo, Panasonic -- PINTL

  32. PSD of BPSK Data with p=1 & randomly Line spectra peak = 22 Waveforms in multi-band Original data, p = 1 PS of waveforms Result data peak = 5 Shaomin Mo, Panasonic -- PINTL

  33. PSD of BPSK Data with p=0.25 & randomly Line spectra peak = 15 Waveforms in multi-band Original data, p = 0.25 PS of waveforms Result data peak = 5 Shaomin Mo, Panasonic -- PINTL

  34. PSD of BPSK Data with p=0.4 & randomly Line spectra peak = 10 Waveforms in multi-band Original data, p = 0.4 PS of waveforms Result data peak = 5 Shaomin Mo, Panasonic -- PINTL

  35. PSD of QPSK Data with p=1 & rotationally Line spectra peak = 19 Waveforms in multi-band Original data, p = 1 PS of waveforms Result data peak = 4 Shaomin Mo, Panasonic -- PINTL

  36. PSD of QPSK Data with p=0.25 & rotationally Line spectra peak = 12 Waveforms in multi-band Original data, p = 0.25 PS of waveforms Result data peak = 4 Shaomin Mo, Panasonic -- PINTL

  37. PSD of QPSK Data with p=0.4 & rotationally Line spectra peak = 7 Waveforms in multi-band Original data, p = 0.4 PS of waveforms Result data peak = 4 Shaomin Mo, Panasonic -- PINTL

  38. PSD of QPSK Data with p=1 & randomly Line spectra peak = 18 Waveforms in multi-band Original data, p = 1 PS of waveforms Result data peak = 5 Shaomin Mo, Panasonic -- PINTL

  39. PSD of QPSK Data with p=0.25 & randomly Line spectra peak = 13 Waveforms in multi-band Original data, p = 0.25 PS of waveforms Result data peak = 4 Shaomin Mo, Panasonic -- PINTL

  40. PSD of QPSK Data with p=0.4 & randomly Line spectra peak = 7 Waveforms in multi-band Original data, p = 0.4 PS of waveforms Result data peak = 5 Shaomin Mo, Panasonic -- PINTL

  41. 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

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

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

  44. 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

  45. 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

  46. 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

  47. 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

  48. 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

  49. Scramble Symbols Shaomin Mo, Panasonic -- PINTL

  50. 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

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