PulseShaping and Modulation Techniques

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

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
4
Concept
Data in
LNA
Modulate
Detector
Data out
MF
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)
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
6
Concept
Time Model of Gaussian Pulse
N16
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
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,npair of integer
Reference Principles of High-Resolution Radar
Based on Nonsinusoidal Waves-Part 1 Singal
Representation and Pulse Compression, Malek G. M.
Hussian, IEEE
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
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UWB Modulation Technique

• UWB is a Spread Spectrum System
• Basic Gaussian Monocycle waveform produces a
  spread spectrum

BW

• Center Frequency, Fc 1/(T3.14)

• BW approx. equal to 1/T

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UWB Modulation Technique

• 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 .

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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

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UWB Modulation Technique

• 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.

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UWB Modulation Technique

• Pseudo-Random noise coding (PN-codes) are used
  for channelization.
• Time-hopping, shifting each pulses 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.

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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
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UWB Modulation Technique

• 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

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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
Rs10 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
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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)
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UWB versus Traditional Narrow Band Transceiver
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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.
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TM-UWB Receiver
Modulation is decoded as either early or
late in Time Modulation or as a Positive
or Negative pulse in Polarity Modulation
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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- BERlt10E-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..

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• Direct Sequence Phase Coded UWB (DSC-UWB)
• Less Popular
• Suitable mostly for Data Communications
• Information About FCCs UWB Regulation
• UWB Device is permitted as follows
• Frequency 3.1 GHz to 10.6 GHz.
• Mean Transmit power lt-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)

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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 UWBs applications have been implemented
• FCCs regulation for UWB has been established