Ultra Wide Band (UWB) 系統介紹
顏楠源 助理教授 南台科技大學資工系
蘇賜麟 教授 成功大學電機系
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UWB Definition
• Common Definitions
– UWB: Fractional BW = (f
H- f
L)/f
C> 25% or total BW > 1.5 GHz.
– Narrowband: (f
H- f
L)/f
C< 1%.
• FCC Definition of UWB
– Fractional bandwidth (measured at the -10dB points),
(f
H- f
L)/f
C> 20% or total BW > 500 MHz.
FCC regulations regarding UWB
• In February of 2002, the FCC amended their Part 15 rules (concerning unlicensed radio devices) to include the
operation of UWB devices without a license.
• Defined 3 types of UWB devices – Imaging Systems.
– Communications and Measurement Systems.
– Vehicular Radar.
• Below 960 MHz, all types must meet FCC §15.209 limits.
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FCC Mask for Communications
• Indoor
– Must show that they will not operate when taken outside (ex: require AC power).
• Handheld (outdoor)
– Operate in a peer-to-peer
mode without location
restriction.
Transmitted Power
• The FCC ruling allows UWB communication devices to
operate at low power (an EIRP of -41.3 dBm/MHz) in an
unlicensed spectrum from 3.1 to 10.6 GHz.
• 7.5 GHz equivalent bandwidth : 550 microWatts EIRP (-2.5 dBm)
• Allow 3 dB margin to the limit
• NET Transmitted Power = -5.5 dBm
• True Low Power Radio!
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Impulse Radio UWB
Continuous Sine Waves
¾ Carrier System
¾ Phase, Frequency, Amplitude
¾ PSK, FSK, ASK, Hybrids
Impulse Radio
¾ Carrierless System
¾ Pulse with width 0.2ns ~ 1.5ns
¾ PPM + THSS or DSSS
Impulse Radio UWB (Transmission)
UWB RCV UWB
XMIT
1 ns (time)
1 foot (space) free space
A Gaussian function
1
stderivation of a Gaussian function
2
ndderivation of a Gaussian function
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Impulse Radio Modulation
• Pulse position modulation (PPM) – Binary/M-ary
• Bipolar Signaling (BPSK)
• Pulse Amplitude Modulation (PAM)
• On/Off Keying (OOK)
• Orthogonal pulse shapes – Hermite Polynomials
• Combinations of the above
Impulse Radio UWB Techniques (1)
¾ Time-Modulated (Hopping) UWB (TM(H)-UWB) ：
— low duty cycle (Impulse radio)
— data modulation by pulse position (time dithering) or signal polarity
— multiaccess channelization by time coding (Time- Hopping, TH)
— for precise location, tracking, radar sensing
(through wall), data communications
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PPM + THSS
Tf
Ts : data symbol time Tc
pulse wtr(t) Str(t)
t
¾ transmitting 0
¾ transmitting 1
Tf
Ts Tc
δ δ δ
δ
( ) ∑∑
−( )
=
−
−
−
−
=
i Ns
j
i c
j f
s tr
tr
t w t iT jT c T d
S
1
0
δ
Str(t)
t
c f
c h f
s
f s
f s s
p
h
T T
e i T N T
N
T T
e i T N T
N
N C
⋅
=
⋅
≥
⋅
=
⋅
=
=
=
=
3 .,
.
symbol data
per pulses of
number :
4 ,
. .
4
period code
3
, ] 2 0 0 1 [ codeword
THSS Multiple Access
∑
= 31
)
(
( )
k
k
tr
t
S
t
User1 : C(1)=[1 0 0 2] d1=0 User2 : C(2)=[0 1 2 0] d2=1 User3 : C(3)=[2 2 1 1] d3=0
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Impulse Radio UWB Techniques (2)
¾ Direction-Sequence Phase Coded UWB (DS-UWB) ：
— high duty cycle
— data modulation by pulse polarity
— multiaccess channelization by PN coding (DS)
— suitable mostly for data-communication
applications
Impulse Radio Correlation Receiver
• The received signal is correlated with the expected received pulse (may differ from the transmitted pulse due to distortion by the antennas and channel).
• Simple design, less RF hardware than narrowband receivers.
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Characteristics of
Impulse Radio UWB (1)
¾ Since the BW ranges from near dc to GHz, this impulse radio signal undergoes distortions in the propagation process.
¾ It has the best chance of penetrating materials that tend to be more opaque at higher frequencies.
¾ Multipath is resolvable down to the order of a nsec or less(a foot or less)
→ reduce fading effects (low fading margin and low
transmission power) in indoor environments.
Characteristics of
Impulse Radio -UWB (2)
¾ Resolvable multipaths → RAKE receiver
¾ Path overlap＜ half of the pulse length
→ positive contribution
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Impulse Radio UWB Potential Applications
¾ Advanced Radar Sensing
— through wall radar capability of detection, ranging, motion sensing
— effective vehicular anti-collision radar
— ground penetrating radar
¾ Precision Location and Tracking
— PLT(Position, Location, Tracking) systems.
¾ Communications
— especially for high quality, fully mobile short-range
indoor radio systems
UWB and IEEE 802.15.3a
¾ IEEE 802.15, of which we are concerned with, is responsible for Wireless Personal Area Network (WPAN) standards.
¾ TG3a was created to investigate physical layer alternatives for high data rate WPAN systems
The efforts of IEEE 802.15 are divided up into four main areas
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IEEE 802.15.3a Technical Requirements and Selection Criteria (1)
Parameter Value
Data Rates(PHY – SAP ) 110 Mbps, 200 Mbps and 480 Mbps(optional)
Range 10m, 4m and below
Power Consumption 100mW and 250mW Power management
modes
Capabilities such as power save, wake up etc
Co-located piconets 4 Interference
susceptibility
Robust to IEEE systems, PER < 8% for a 1024 byte packet length
IEEE 802.15.3a Technical Requirements and Selection Criteria (2)
Parameter Value Co-
existence capability
Reduced interference to IEEE systems, interfering average power at least 6dB below the minimum sensitivity level of non-802.15.3a device
Cost Similar to Bluetooth Location
awareness
Location information to be propagated to a suitable management entity
Scalability Backwards compatibility with 802.15, adaptable to various regulatory regions (such as the US, European countries, or Japan).
Signal
Acquisition
<20µs for acquisition from the beginning of the preamble to the beginning of the Header
Antenna practicality
Size and from factor consistent with original device
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Multi-band UWB
¾ The short duration of the pulses of impulse radio presents several technical challenges :
— The short duration makes them more susceptible to timing jitter.
— Increasing the pulse repetition frequency (PRF) would make the system more vulnerable to ISI.
¾ A more recent approach to UWB is a multi-band system where the UWB frequency band from 3.1 – 10.6 GHz is divided into several smaller bands. Each of these bands has a bandwidth greater than 500MHz, to comply with the FCC definition of UWB. Several
companies like Femto Devices, Focus Enhancements, General Atomics, Intel, Staccato Communications, Texas Instruments,
Time Domain, Mitsubishi, Matsushita, Philips, Samsung and Wisair support this approach.
Multi-band Spectrum Allocation
¾ At the recent March 2003 meeting of the IEEE 802.15.3a group, the majority of the proposals presented involved a multi-band UWB
system.
Time Domain’s Multiband Spectrum Allocation
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Signal Design
3.79 ns chip time
2 1 0 1 2
0 0.5 1
Rectified Cosine Pulse Shape
Time (ns)
Amplitude (volts)
Rectified cosine envelope
2 1.5 1 0.5 0 0.5 1 1.5 2
0.1 0 0.1
Band 0 Sinewave Carrier
Time (ns)
Amplitude (Volts)
2 1 0 1 2
0.2 0 0.2
Band 0 Chip Waveform
Time (ns)
Amplitude (Volts
x
3 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4 70
65 60 55 50 45 40
Band 0 Frequency Spectrum Shape
Frequency (GHz)
PSD (dBm/MHz)
Multi-band UWB Concept
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Multi-band Characteristics
¾ Flexibility
— Multiple bands of information may be managed
— Multi-band allows efficient filling of available spectrum
¾ Scalable performance
— Multi-band can efficiently support high and low data.
— Can scale with backward compatibility with new spectrum availability
— E.g., with 16 bands:
BPSK: 1bit/band/33.33ns (30MHz) frame = 480 Mbps QPSK: 2bits/band/33.33ns (30MHz) frame = 960 Mbps
¾ Peaceful co-existence
— dynamically manage bands to avoid interference
— Accelerate worldwide regulatory acceptance with flexible spectral use
TI Physical Layer Proposal
for IEEE 802.15.3a (March 2003)
Company Texas Instruments Spectrum Allocation:
# of bands
3 (additional bands can be added in the future)
Bandwidths 503.25 MHz
Frequency ranges 3.168 GHz – 4.752 GHz Modulation Scheme TFI-OFDM, QPSK
Coexistence method null band for WLAN (~5 GHz) Multiple access method not available
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TI Physical Layer Proposal
for IEEE 802.15.3a (March 2003)
Company Texas Instruments
# of simultaneous piconets
not available
Error correction codes Convolutional code
Code rates 11/32 @ 110 Mbps, 5/8 @ 200 Mbps, 3/4 @ 480 Mbps
Link margin 5.5 dB @ 10 m @ 110 Mbps, 10.2 dB @ 4 m @ 200 Mbps, 12.2 dB @ 2 m @ 480 Mbps Symbol period 312.5 ns OFDM symbol
Multipath mitigation method
1-tap (robust to 60.6 ns delay spread)
Intel Physical Layer Proposal for IEEE 802.15.3a (March 2003)
Company Intel
Spectrum Allocation:
# of bands
7 (+ optional 6 bands for future use)
Bandwidths 550 MHz
Frequency ranges 3.6 GHz – 6.9 GHz, (7.45 GHz – 10.2 GHz optional)
Modulation Scheme M-ary Bi-orthogonal Keying, QPSK Coexistence method null band for WLAN (~5 GHz)
Multiple access method DS/FH CDMA, optional FDMA
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Intel Physical Layer Proposal for IEEE 802.15.3a (March 2003)
Company Intel
# of simultaneous piconets
not available
Error correction codes Convolutional code, Reed-Soloman code
Code rates 6/32 @ 110 Mbps, 5/16 @ 200 Mbps, 3/4 @ 480 Mbps
Link margin 6.3 dB @ 10 m @ 108 Mbps, 8.0 dB @ 4 m @ 288 Mbps, 4.0 dB @ 4 m @ 577 Mbps
Symbol period 3 ns
Multipath mitigation method
frequency interleaving of MBOK chips;
time frequency codes; feed forward filter
XtremeSpectrum Physical Layer Proposal for IEEE 802.15.3a (March 2003)
Company XtremeSpectrum
Spectrum Allocation:
# of bands
2
Bandwidths 1.368 GHz, 2.736 GHz Frequency ranges 3.1 GHz – 5.15 GHz,
5.825 GHz – 10.6 GHz Modulation Scheme BPSK, QPSK
Coexistence method null band for WLAN (~5 GHz) Multiple access method Avoidance
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XtremeSpectrum Physical Layer Proposal for IEEE 802.15.3a (March 2003)
Company XtremeSpectrum
# of simultaneous piconets
Ternary CDMA
Error correction codes Convolutional code, Reed-Soloman code Code rates 1/2 @ 110 Mbps, RS(255,223) @ 200
Mbps,
RS(255,223) @ 480 Mbps Link margin 9.9 dB @ 10 m @ 110 Mbps,
13.2 dB @ 4 m @ 200 Mbps, 3.4 dB @ 2 m @ 600 Mbps
Symbol period 731 ps (Low band), 365.5 ps (High band) Multipath mitigation
method
Decision feedback equalizer
