The Promise of UWB for Personal Communications

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


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


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


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


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


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


Slide 7

-70

-65

-60

-55

-50

-45

-40

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


Slide 8

-70

-65

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-45

-40

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


Slide 9

-70

-65

-60

-55

-50

-45

-40

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


Slide 10

-70

-65

-60

-55

-50

-45

-40

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


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


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


Slide 13


Slide 14

• Backup Slides


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


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


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


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


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


Slide 20

UWB Performance in Multipath Fading Environments

6 8 10-25

-20

-15

-10

-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


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

-20 -15 -10 -5 0 510-2

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


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


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

The Promise of UWB for Personal Communications

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