Ultra-Wideband Part II David Yee. Overview a.k.a. impulse radio because it sends pulses of tens of...
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Transcript of Ultra-Wideband Part II David Yee. Overview a.k.a. impulse radio because it sends pulses of tens of...
Ultra-WidebandPart II
David Yee
Overview a.k.a. impulse radio because it sends pulses of
tens of picoseconds(10-12) to nanoseconds (10-9)
Duty cycle of only a fraction of a percent
Uses a lot of bandwidth (GHz)
Fourier time scaling property
Capacity increases linearly with bandwidth but logarithmically with power
Shannon
a
Fa
atf1
02 1log
BN
PBC
Overview aka impulse radio because it sends pulses of
tens of picoseconds(10-12) to nanoseconds (10-9)
Duty cycle of only a fraction of a precent
Uses a lot of bandwidth (GHz)
Fourier time scaling property
Low probability of detection because it looks like noise to an unintended listener
a
Fa
atf1
Overview (con’t) Low Probability of Detection because it looks like
noise to an unintended listener
Multipath cancellation is not a problem because the direct path gets processed before the multipath signals arrive. (so no need for a rake receiver, though some source suggest it)
There is no need for a carrier frequency, but there can be one, most likely to get out of range of GPS (1.6GHz) which is sensitive to noise
Types of Pulses Gaussian pulse
Gaussian monocycle(first derivative)
Gaussian doublet(second derivative)
Pulse Modulations Pulse Amplitude
Modulation (PAM)
On-Off Keying (OOK)
Bi-Phase Modulation (BPSK)
Pulse Modulations (con’t) Pulse Position Modulation (PPM)
Time Hopping
Problem possibility of severe collisions with
multiple users
Solution add pseudorandom time shifts to the
pulse train
This will also adds a layer of security, since the receiver must know the shift schedule
PPM with Time Hopping
• w(t) – system’s waveform (monocycle)
• Tf – pulse repetition time or frame time
• cf – time hopping sequence
• Tc – delay of the hopping code
• – delay of bit 1 from bit 0• d – data symbol
• Ns – number of monocycles per symbol
j
kNjc
kjf
k
sdTcjTtwts )()( )(
]/[)()(
Comparison:Example Bluetooth
Radio Uses FSK Needs VCO and
PLL Modulation for
carrier Demodulation
can possibly be several steps (super-heterodyne)
Filter to get rid of images
Comparison:Example UWB Radio
Low system complexity
Can apply pulse directly to antenna
After received signal is amplified, it’s DSP (match filter/correlator then decision)
Receiver Model
Receiver Model (con’t)
Received signal Aks(k) – attenuated signal from user k n(t) – white Gaussian noise – time asynchronism between receiver and
transmitter
Correlation template v(t) is the difference between two pulses shifted by One of the pulses is for the transmitted bit 0 and the
other for bit 1
Nu
kk
kk tntsAtr
1
)( )()()(
)()()( twtwtv
Decision Rule
Output:
If result was negative, 1 was transmitted If result was positive, 0 was transmitted
1
0
)1()(
1
1
)()(Ns
j
Tj
jTc
kjfbit
f
f
dtTcjTtvtr
Performance Energy per bit to noise ratio
Bit Error Rate also dependent on peak power
BTk
TP
N
E
e
durationpeakb
0
1101 10/
SNRMPN
P
u
Performance (con’t) Has great throughput over short distances Range is also effected by output power,
which the FCCis limiting
1 kilometer with high gainantenna
10-20 metersnormally