Freescale™ and the Freescale logo are trademarks of Freescale Semiconductor, Inc. All other product or service names are the property of their respective owners. © Freescale Semiconductor, Inc. 2005.
TM
The Promise of UWB for Personal CommunicationsMatthew WelbornFreescale Semiconductor, IncApril 12, 2006
TM Freescale™ and the Freescale logo are trademarks of Freescale Semiconductor, Inc. All other product or service names are the property of their respective owners. © Freescale Semiconductor, Inc. 2005.
Slide 1
Overview
• UWB characteristics & applications• Hurdles to UWB development
RegulatoryCoexistence
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Slide 2
Ultra-Wideband: Key Characteristics & Applications
• Large fractional bandwidth – lower fading relative to narrowband• Low transmit power spectral density - overlay• Large absolute bandwidth – due to PSD limitation
• Wireless personal area network applications Short range & high bandwidth - scaling to multi-Gbps data rates
• Ranging and imaging applications
PowerSpectralDensity
dBm/MHz900 MHzCordlessPhones
PCS
802.11a& RLAN
UWB
Frequency (GHz)1 2 3 4 5 6 7 8 9 10
−41 dBm/MHz
802.11b/g& BT
TM Freescale™ and the Freescale logo are trademarks of Freescale Semiconductor, Inc. All other product or service names are the property of their respective owners. © Freescale Semiconductor, Inc. 2005.
Slide 3
UWB: High Speed Personal Area Networks (PAN)
Bit Rate (Mb/s) vs. Range (m)
110
4000
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35Range (m)
Bit
Rat
e (M
bps)
DS-UWBSpace
802.11Space
11n
11g/a
TM Freescale™ and the Freescale logo are trademarks of Freescale Semiconductor, Inc. All other product or service names are the property of their respective owners. © Freescale Semiconductor, Inc. 2005.
Slide 4
Performance Implications
• Proper design to benefit from UWB advantagesWide signal bandwidth ( 2 x BW > raw Rate power efficient)Wide modulation bandwidth (to benefit from reduced fading)
• Effective system design is critical for low power and costKey UWB applications will require low power & low costEffective solution depends on much more than PHY waveformAlso requires effective MAC and transport to ensure efficient operation and provide quality of service for applications
-30 -25 -20 -15 -10 -5 0 5 100
0.2
0.4
Received Energy (dB)
1.3 GHz BW UWB Fading
NO deep fades!
00.02
0.040.060.080.1
4 MHz NB or MC fading
Deep fades
-30 -25 -20 -15 -10 -5 0 5 10
TM Freescale™ and the Freescale logo are trademarks of Freescale Semiconductor, Inc. All other product or service names are the property of their respective owners. © Freescale Semiconductor, Inc. 2005.
Slide 5
Initial UWB Application: Cable-FreeTM USB
• Use existing USB 2.0 and 1.1 protocols, but extended for wireless• Leverage the 700M+ existing USB devices
No new software, drivers, etc. for “plug and play” experienceWorks like a USB cable, but uses UWB for transmission
• Initial products announced – embedded products to follow
TM Freescale™ and the Freescale logo are trademarks of Freescale Semiconductor, Inc. All other product or service names are the property of their respective owners. © Freescale Semiconductor, Inc. 2005.
Slide 6
Regulatory Hurdles for UWB Products
• Regulation uncertainty in some regions of the worldOpposition to UWB technology has delayed regulatory proceedings and led to [excessively] conservative limits
• Regulatory regional differences Additional requirements lead to higher cost and riskCan have a significant impact on UWB performance – may compromise economic viability for some applications
• Performance differences for mobile devices in different regions may lead to future harmonization or “grey market”
Bluetooth and WLANLow power FM
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Slide 7
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993 4 5 6 7 8 10 11x 10• Most current approaches initially developed for 3.1 to 4.8 GHz
Technology and performance issues• Can scale to high band, but best case performance is reduced
Antenna and RF issuesDepending on bandwidth, ~6-8 dB performance differential up to ~3 dB
PSD(dBm/MHz)
Frequency
“Low Band” “High Band”
Same BW aslow band
2x BW oflow band
Performance Impact of Scaling to Other Bands
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Slide 8
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993 4 5 6 7 8 10 11x 10• European proposed rules
Low band now requires “mitigation” to -85 dBm/MHz to protect incumbent services (fixed wireless and future mobile – requirements TBD) Spectrum from 4.2 to 4.8 GHz may be available until 2010: ~5 dB worseHigh band only from 6 to 8.5 GHz: performance is ~4-6 dB worse
PSD(dBm/MHz)
Frequency
Low Band: mitigation or time limits High Band: 6 to 8.5 GHz
Performance Impact of Proposed Rules in Europe
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Slide 9
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993 4 5 6 7 8 10 11x 10
PSD(dBm/MHz)
Frequency
• Japanese proposed rules (Korea similar) Low band now requires “mitigation” to actively protect incumbentservices (satellite, FWA, mobile, broadcast – requirements TBD) Spectrum from 4.2 to 4.8 GHz may be available only until 2008High band only from 7.25 to 10.25 GHz: ~4-6 dB worse
Low Band: mitigation or time limits High Band: 7.25 to 10.25 GHz
Performance Impact of Proposed Rules in Asia
TM Freescale™ and the Freescale logo are trademarks of Freescale Semiconductor, Inc. All other product or service names are the property of their respective owners. © Freescale Semiconductor, Inc. 2005.
Slide 10
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993 4 5 6 7 8 10 11x 10
PSD(dBm/MHz)
Frequency
Mitigation? TBD Only common band 7.25 to 8.5 GHz
• What about a “harmonized” band?Some products will need a common band for worldwide deployment“Permanent bands” for UWB are targeted above 6 GHz – some applications will require no UWB use below 6 GHzCommon band is then 7.25 to 8.5 GHz: ~10 dB loss relative to low band!
Performance of a Long Term “Common” Band
TM Freescale™ and the Freescale logo are trademarks of Freescale Semiconductor, Inc. All other product or service names are the property of their respective owners. © Freescale Semiconductor, Inc. 2005.
Slide 11
Coexistence for UWB
• Success for commercial deployment of UWB will depend on robust application performance
• Multiple UWB waveforms will be deployed in productsAdditional waveforms and “flavors” under development> High rate WPAN> Low rate “sensor networks”> Cable replacement
Proliferation of UWB devices will result in “UWB-on-UWB” coexistence situations
• No easy answers and little attention to problem at present
TM Freescale™ and the Freescale logo are trademarks of Freescale Semiconductor, Inc. All other product or service names are the property of their respective owners. © Freescale Semiconductor, Inc. 2005.
Slide 12
Conclusions
• Great potential for key applicationsMuch interesting work remains to develop low cost, low power implementations ant to optimize performance
• Challenges remain Viable regulations worldwide Coexistence strategies
TM Freescale™ and the Freescale logo are trademarks of Freescale Semiconductor, Inc. All other product or service names are the property of their respective owners. © Freescale Semiconductor, Inc. 2005.
Slide 13
TM Freescale™ and the Freescale logo are trademarks of Freescale Semiconductor, Inc. All other product or service names are the property of their respective owners. © Freescale Semiconductor, Inc. 2005.
Slide 14
• Backup Slides
TM Freescale™ and the Freescale logo are trademarks of Freescale Semiconductor, Inc. All other product or service names are the property of their respective owners. © Freescale Semiconductor, Inc. 2005.
Slide 15
Scaling UWB Technology to Longer Range
• Wideband UWB enables efficient scalability to low rates at long range Optimized for low power applications (cell phones, portables, etc.)Architectures can be designed to provide low complexity
> IEEE 802.15.4a developing waveforms that allow scalable complexity> Minimize RF and analog processing to reduce complexity
• No fundamental communications advantage over narrowband at low rates But… ranging capabilities are also desirable at longer ranges
• Precision ranging used to compute relative location information• Fine time resolution enables precision ranging between radios
Time resolution is inversely proportional to bandwidthExample: 1 GHz BW can provide about 1 ns time resolutionRange measurements are based on propagation delay measurementsRequires knowledge of channel to compensate for multipath delays
UWB Longer Range
with Precision Location
Ultra-low Costand
Complexity
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Slide 16
Time
Single random 16-pulse burst (about 32 ns)
PPM Slot 1 PPM Slot 2 PPM Slot 1 PPM Slot 2
Symbol (k) Symbol (k+1)
Two PPM-BPSK symbols (about 1 usec)
A Novel Hybrid Waveform for 802.15 TG4a
• TG4a has developed a BPSK + 2-PPM waveform that uses phase and position modulation of pulse bursts
Enables the use of both coherent and non-coherent receivers > Very low complexity possible with non-coherent architectures
Enables wide trade-off between performance and complexity
TM Freescale™ and the Freescale logo are trademarks of Freescale Semiconductor, Inc. All other product or service names are the property of their respective owners. © Freescale Semiconductor, Inc. 2005.
Slide 17
Systematic Codes for Flexible Decoding
• TG4a is also using a concatenated code for flexible decodingConcatenation of Reed Solomon and Convolutional codesAllows non-coherent receiver to decode only RS block codeA flexible trade-off between decode complexity and performance
SystematicConvolutional
EncoderR=1/2 k=3
SystematicEncoder
RS(63,55,8)R=0.87
2-PPM + BPSKModulator1 or 2 bits
Per symbolSign (parity) bit
Non-coherentreceiver uses only this code
Non-coherentreceiver sees
only this bitSystematic (position) bit
Input Data Bits Encoded Bits for
Transmission
TM Freescale™ and the Freescale logo are trademarks of Freescale Semiconductor, Inc. All other product or service names are the property of their respective owners. © Freescale Semiconductor, Inc. 2005.
Slide 18
Scaling UWB Technology to Higher Data Rates
• Wideband UWB provides efficient scalability to 1+ GbpsCritical for “cable replacement” applications Streaming or file transfer applications: display, memory, media, etc.Goal is lowest power consumption and highest possible data rates in order to minimize session times for file transfers
• Scaling requires wide bandwidth combined with power efficient modulationIn narrowband systems, scaling to higher rates is done by increasing spectral efficiency (more bits/sec/Hz)
• Such approaches are less effective for UWB systems Higher order modulation reduces power efficiency, increases complexityMIMO approaches will require excessive complexity & cost
• Increased bandwidth is the best optionEven more so for devices using higher operating frequencies
UWB Higher DataRates and
Performance
Ultra-low Costand
Complexity
TM Freescale™ and the Freescale logo are trademarks of Freescale Semiconductor, Inc. All other product or service names are the property of their respective owners. © Freescale Semiconductor, Inc. 2005.
Slide 19
How a Fast Radio Saves Power forMobile Devices
Radio “ON”Power `
Radio “Sleep”Power
Radio “OFF”
Radio turned on and off during transfer of datato/from mobile device memory to minimize energy use
Time
PSleep
POn
• The UWB radio is turned on & off to transfer packets of data“On” time is a function of data rateRadio sleeps during data transfer to/from handset memory
• Total energy consumed from battery is the “area” under the curve• New provisions for gated UWB systems create even greater advantage for high rates• UWB approaches that do not scale will only provide limited benefits
TM Freescale™ and the Freescale logo are trademarks of Freescale Semiconductor, Inc. All other product or service names are the property of their respective owners. © Freescale Semiconductor, Inc. 2005.
Slide 20
UWB Performance in Multipath Fading Environments
6 8 10-25
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-5
0
5
10
Frequency (GHz)
Fadi
ng (d
B)
0 2 4
Frequency response of a typical indoor UWB channel
• UWB signal bandwidth leads to different operating regimes• UWB modulation bandwidth induces different fading statistics
Single carrier wideband UWB modulation results in frequency-selective fading with relatively low power fluctuation (variance)Multi-carrier UWB modulation creates a bank of parallel narrowband channels that experience flat fading with a Rayleigh distribution (deep fades)
• Different choices affect energy capture mechanisms & ISI compensation• These fundamental differences affect both complexity & flexibility
TM Freescale™ and the Freescale logo are trademarks of Freescale Semiconductor, Inc. All other product or service names are the property of their respective owners. © Freescale Semiconductor, Inc. 2005.
Slide 21
Modulation Bandwidth Determines Fading Statistics
• True UWB takes full advantage of natural channel physics
• Narrowband modulation suffers heavy fading
• Large coherent relative BW enables radios with no fading
This is a first for wirelessEnables better performance with less complex FEC
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10-1
100
X (dB)
Pr (R
ecei
ved
Ener
gy <
x)
4 MHz B
W
75 M
Hz B
W
1.4
GH
z B
WThe
oretic
al Ray
leigh
True UWB
Narrowband Modulation UWB
25%
25% of Narrow Band Channels are Faded by 6 dB or more
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Slide 22
Impact of Narrowband Fadingon Forward Error Correction Performance
K=7, Rate 3/4 Convolutional Code in Rayleigh Fading and AWGN
0 2 4 6 8 10 12 1410-6
10-5
10-4
10-3
10-2
10-1
100
Eb/No [db]B
ER
AWGN K=4RAY K=4
K=4, Rate 3/4 Convolutional Code in Rayleigh Fading and AWGN
8+ dB
True UWB takes full advantage of natural channel physics and does not suffer the performance degradation of narrowband modulation from Rayleigh-distributed fading
10-6
10-5
10-4
10-3
10-2
10-1
100
0 2 4 6 8 10 12 1410
Eb/No [db]
BER
AWGN K=7RAY K=7
6 dB
TM Freescale™ and the Freescale logo are trademarks of Freescale Semiconductor, Inc. All other product or service names are the property of their respective owners. © Freescale Semiconductor, Inc. 2005.
Slide 23
Scalability to Varying Multipath Conditions
• Multipath delay spread varies with range and propagation environment, but…• Compensating for multipath effects is the largest driver of receiver complexity
Collection of time-dispersed signal energy (using either FFT or rake processing)Forward error correction decoding & equalization
• Efficient processing for multipath conditions is critical for battery operated devices Support operation in severe channel conditions, but also…Provide ability to use less processing (& battery power) in less severe environments
• Effective waveform and receiver design allows efficient scaling of processing requirements with changes in multipath conditions and data rate
Scale processing with data rata, signal bandwidth, delay spread, SNR, etc
2 4 6 8 10 12 14 16 18 200
5
10
15
20
25
30
CM-3 (NLOS)CM-2 (NLOS)
CM-1 (LOS)
CM-4 (NLOS)RMS Delay Spread
Range (m)
Curves proportional to (Range)-1/2