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