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Pulse-Shaping and Modulation Techniques for Ultra-wide band (UWB) Communications

Pulse-Shaping and Modulation Techniques for Ultra-wide band (UWB) Communications . Simon Bikulcius Ruben Aguila Hien La. Agenda. Introduction to UWB Pulse Shaping concept. Gaussian Pulse Shaping Type of Gaussian shape Matched Filter. UWB Modulation Techniques. Spread spectrum

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Pulse-Shaping and Modulation Techniques for Ultra-wide band (UWB) Communications

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  1. Pulse-Shaping and Modulation Techniques for Ultra-wide band (UWB) Communications Simon Bikulcius Ruben Aguila Hien La UWB EE252 spring/2003

  2. Agenda • Introduction to UWB • Pulse Shaping concept Gaussian Pulse Shaping Type of Gaussian shape Matched Filter • UWB Modulation Techniques • Spread spectrum • Mono pulse modulation • Maximum access capacity • UWB Applications • Transceiver comparison • Typical applications for TM-UWB • Summary UWB EE252 spring/2003

  3. What is UWB ? Short pulse with large bandwidth Relative bandwidth Typical bandwidth allocation (narrow band) UWB Bandwidth usage ! For usefulness, must operate over already allocated Spectrum UWB EE252 spring/2003

  4. Concept Data in LNA Modulate MF Detector Data out Pulse shaping filter Matched Filter Pulse Generator Pulse Generation Simplified System; looking at pulse only Excluding Multi-path Reference : Ultra-Wideband Impulse Radar – An Overview of the Principles, Malek G.M. Hussian, IEEE Result of HP of Antennas Received (Equivalent to Gaussian shape) Transmit (example) UWB EE252 spring/2003

  5. Concept From a mathematical point of view, the treatment of a pulse can be deduced to a Gaussian Shape for understanding. However, there are other possible pulses which depend on filtering methods triplet c) b) A) hex-let doublet The idea : To have more bandwidth, N is minimized or increases Index of Breadth of band Reference: UWB EE252 spring/2003

  6. Concept Time Model of Gaussian Pulse N=16 Bipolar case , 2 time instants Reference: Principles of High-Resolution Radar Based on Nonsinusoidal Waves-Part 1: Singal Representation and Pulse Compression, Malek G. M. Hussian, IEEE UWB EE252 spring/2003

  7. Concept Pulse through an Ideal matched filter autocorrelation and PSD In the frequency domain Has the function of a Sinc Autocorrelation of binary transmission Sum of two arbitrary Autocorrelations N= length of binary sequence D = duty ratio m,n=pair of integer Reference: Principles of High-Resolution Radar Based on Nonsinusoidal Waves-Part 1: Singal Representation and Pulse Compression, Malek G. M. Hussian, IEEE UWB EE252 spring/2003

  8. Concept Filtering At the receiver Because the and a raised cosine can be used on the receiving end (Other possibility is a Correlator) Guard band factor commonly 0.35 Exchange for the Correction notation References: Ultawideband (UWB) Impulse Signal Detection And Processing Issues, Elizabeth C. Kisenwether, HRB Systems,Inc Circuits and Systems Faculty of Electrical Engineering Mekelweg 4, http://cas.et.tudelft.nl UWB EE252 spring/2003

  9. Power density (dB) 0 -0.2ns 0.2ns -10 -20 -30 T -40 -50 0 1 2 3 4 5 Fc Frequency (GHz) UWB Modulation Technique • UWB is a Spread Spectrum System • Basic Gaussian Monocycle waveform produces a “spread spectrum” BW • Center Frequency, Fc = 1/(T*3.14) • BW approx. equal to 1/T UWB EE252 spring/2003

  10. UWB Modulation Technique 0 -10 -20 -30 -40 -50 0 1 2 3 4 5 Frequency (GHz) • A UWB system uses a long sequence of pulses for communication. • A regular pulse train produces energy spikes (comb-lines) at regular intervals. • Pulse train carries no information and “comb-lines” interfere with conventional radios. Power density (dB) Pulse train Time Frequency Spectrum • Pulse-modulation scheme: one that communicates information and reduces the amplitude of the “comb-lines” . UWB EE252 spring/2003

  11. UWB Modulation Technique • Pulse Modulation (PAM) • “tall” and “short” mono-pulse waveforms correspond to “1” and “0”. • On-off keying (OOK) • The presence of a pulse is a “1” and the absence of a pulse is “0”. • Direct Sequence Modulation (DSC) • A sequence of binary pulses directly modulate high duty cycle mono-pulses. • Pulse Position modulation (PPM) • A “1” and a “0” is determined by a pico-second delay T1 or T2. • of a mono-pulse. This modulation scheme also makes use of “time-hopping” • The modulation technique of choice for a UWB “impulse radio” is the PPM • with time-hopping. It offers the following advantages: • - multiple access communication (i.e. many users) • - security “time-hopping” code • -low power frequency spectrum that appears like noise • Ref: M.Z. Win, R.A. Scholtz, L.W. Fullerton, “Time-hopping SSMA Techniques for Impulse Radio..” UWB EE252 spring/2003

  12. UWB Modulation Technique Power density (dB) 0 -10 -20 -30 -40 -50 0 1 2 3 4 5 Frequency Spectrum Frequency (GHz) Time T1 T2 • UWB Impulse systems use pulse position modulation (PPM) • The PPM modulates the position of a pulse about a nominal position. • A “1” and a “0” is determined by a pico-second delay T1 or T2 of a mono-pulse. • PPM “smooths-out” the spectrum making the transmitted look almost like noise. UWB EE252 spring/2003

  13. Power density (dB) hopping 0 -10 -20 -30 -40 Time -50 Nominal pulse train New position after hopping 0 1 2 3 4 5 Frequency Spectrum Frequency (GHz) UWB Modulation Technique • Pseudo-Random noise coding (PN-codes) are used for channelization. • Time-hopping, shifting each pulse’s time position, in accordance with a code • channelizes the pulse train. • Only a receiver with the same PN-code template can decode the pulse transmission. • The Pseudo-Random noise coding makes the spectrum appear very-much like noise. UWB EE252 spring/2003

  14. UWB Modulation Technique A typical time hopping format with PPM is, • where, • - W(t) represents a narrow monocycle pulse waveform. • - Tf represents the time between pulses. • - (Cj)Tc represents the distinct pulse-shift pattern (time-hopping code). Tc • is a reference time shift. Each hopping code Cj provides an added time shift. • -d(k) represents the data sequence and is a binary (0 or 1) symbol stream. For “0”, no time-shift occurs. For “1”, a time-shift of delta occurs. A total of Ns mono- cycle-pulses are transmitted per symbol; thus, this is an over-sampled • modulation system. • A single symbol has a duration of Ts = Ns times Tf • The binary symbol rate, Rs, is equal to 1/Ts. Ref: RA Scholtz, “Multiple Access with Time-hopping Impulse Modulation” UWB EE252 spring/2003

  15. UWB Modulation Technique Multi-path signal Reflected pulse Direct pulse Direct pulse Reflected pulse building Receive Window (500 Pico-seconds) • The mono-pulse short duration waveform is immune to multi-path cancellation. • Rayleigh fading due to mult-path is a CW phenomenon. • A UWB Impulse system does not have a CW carrier. • The extra length traveled by a multi-path signal causes it to arrive outside the Receive • time window UWB EE252 spring/2003

  16. UWB Modulation Technique • A high density of simultaneous users can be achieved by using PN-codes for channelization. • In the receiver, a template of the PN-code is correlated with the in-coming received signal. • A UWB utilizing PN-codes (time-hopping) has excellent multiple-access performance. • The un-coded Bit-error probability is dependent on the number of active users and • the binary symbol rate, Rs. Log10(Perror) -2.3 Rs= 20 kbps -2.4 Condition: SNR = 9.8 dB -2.5 -2.6 Rs=10 kbps -2.7 -2.8 Rs= 5 kbps -2.9 -3.0 2000 4000 6000 8000 Number of active users 10000 Ref: RA Scholtz “Multiple access with time-hopping IM” UWB EE252 spring/2003

  17. UWB Modulation Technique • For the UWB system utilizing time-hopping, the Maximum Access Capacity • is dependent on additional power required to maintain the required SNR and BER. • The number of active users increases rapidly as the power increases from 0 to 10 dB, • No significant increase in number of users for any further increase in power. Total number of users 30000 BER = 0.001 20000 BER = 0.0001 BER = 0.00001 10000 Ref: Win, Scholtz, “Impulse Radio: How it works.” 0 0 10 20 30 40 Additional power, dB (compared to power for one user) UWB EE252 spring/2003

  18. UWB versus Traditional Narrow Band Transceiver UWB EE252 spring/2003

  19. TM UWB Transmitter Generated PN time coding And time modulation Pico second precision timer Implemented in an Integrated Circuit is a key technological component of the TM-UWB system. UWB EE252 spring/2003

  20. TM-UWB Receiver Modulation is decoded as either “early” or “late” in Time Modulation or as a Positive or Negative pulse in Polarity Modulation UWB EE252 spring/2003

  21. Typical Applications for Low Duty cycle UWB(TM-UWB) More popular • Full duplex 1.3 GHz Radio System: • * 250 uW output power • * Variable data rate 39kbps-156kbps • * 16Km in range • Simplex 2.0GHz Data Link: • * 50uW output power • * Data rate of 5Mbps- BER<10E-8 without FEC • * Range of 10m thru multiple walls inside an office building • Thru Wall Radar: • * Detect human presence and movement through wall • Radio Frequency Identification (RFID) • * Monitor the status of equipment in warehouses or in hospitals and transmit • sensor data to a central network along with location information. • And many more….. UWB EE252 spring/2003

  22. Direct Sequence Phase Coded UWB (DSC-UWB) • Less Popular • Suitable mostly for Data Communications • Information About FCC’s UWB Regulation • UWB Device is permitted as follows: • Frequency: 3.1 GHz to 10.6 GHz. • Mean Transmit power: <-41 dBm/MHz • equivalent to 500uV at three meters distance. • Peak/Mean power ratio: limited to less • than 20 dB. • Measurement procedures of 47CFR15.35(May 10/2000) UWB EE252 spring/2003

  23. Summary • From an analytical point of view the UWB can be viewed as a reception of Gaussian pulses • The Fourier transform of the autocorrelation shows a distribution of spaced spectra which is representative of the pulse period. Dithering or sequencing is need to reduce The spectra from interfering. • The filtering/matching of the pulse on the receiving end will need the • bandwidth approximately that of the Rise time of the pulse. • UWB Pulse position Modulation with time-hopping offers: • -multiple access communication for 25,000 users. • -channelized security codes • -noise-like wide frequency spectrum • -multi path immunity • -nearly “all-digital” with minimal RF microwave electronic • UWB transceiver can be simpler and resulted at lower cost • Many UWB’s applications have been implemented • FCC’s regulation for UWB has been established UWB EE252 spring/2003

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