Paper presentation Ultra-Portable Devices

Paper presentation – Ultra-Portable Devices

Paper:

Presented by:

John F. M. Gerrits,1 Michiel H. L. Kouwenhoven, et al.

Principles and Limitations of Ultra-Wideband FM

Communications Systems. EURASIP Journal on

Applied Signal Processing 2005, Issue 3, pp. 382-396,

2005

Carl Bryant

2010-05-09 1Paper Presentation - Ultra Portable Devices

Outline

• Introduction

• Principles of UWB-FM

• UWB-FM receiver

• BER performance

• Conclusions

• Discussion

• Further reading

• Skipping sections analyzing interference & multipath performance (orig. paper is 15 pages)

2010-05-09 Paper Presentation - Ultra Portable Devices 2

Introduction

• UWB

– Short range, low-power communications

– -10dB BW > 20% or 500MHz

– Does not specify air interface or modulation scheme

– Started as impulse radio

• UWB-FM

– Intended for low to medium data rate

– Continous carrier

– Constant envelope

– Simple implementation


Principles of UWB-FM

• Analog implementation of spread spectrum

– Spreading gain equal to modulation index β ( )

– UWB if β >> 1

• FM signal expressed as a sum of sidebands

• BW ≈ 2(Δf + fm)


mf

f

n

mcn tnJAtV )sin()()(

Ampitude of bessel functions Jn(β)


• Proposed implementation

– Two layers of FM modulation

– Low frequency, FSK subcarrier modulated into UWB signal

– Subcarrier: Triangle wave, 0.5 < βSUB < 4

– Multiple subcarriers possible

– Subcarriers can have differing rates



• Figure shows -13dBm signal

– fSUB=1MHz

– β ≈ 600

• Spectral density lowered by a factor 10log10(β) = 28dB


UWB-FM receiver


UWB-FM receiver

• Delay line demodulator, τ = N/(4fc), N=1,3,5…

• Result is sine of original signal times a constant


))()(sin())(sin()(

))cos(sin()(

))(sin()(

2

ttttAtV

ttAtV

ttAtV

mcmcDEMOD

mc

mc

))sin(2

sin(2

1)(

...5,3,1,24

))()(cos(2

)(

2)2/)1((

,

2

,

tNA

tV

NNT

N

tttA

tV

m

c

N

LPDEMOD

c

mmcLPDEMOD

Low pass filtered:

UWB-FM receiver

• Demodulator sensitivity proportional to N

• Useful bandwidth of demodulator is 2fc/N

• Multipath introduces some distortion (see paper)– without equalization useful subcarrier range limited to one octave


)2

cos(2

)(2

,

c

FMDEMODf

fN

AtV

BER performance

• BER performance with AWGN

• Nonlinear function of input SNR

• Bandwidth of FSK subcarrier BSUB


BER performance

• Assume βSUB = 1, binary FSK, coherent detection, BRF = 1GHz

• Probability of error:


22

1 SUBb

SNRerfcP

BER performance

• Difference ~constant at higher data

rates


BER performance

• PTX=-11dBm


Conclusions

- Performance degraded by 10-15dB compared to NBFM

+ Rubust to multipath and interference

+ Multi-user


Discussion

+ Constant envelope (TX)

+ No RF oscillator in receiver

+ Interference

+ Wideband only at RF

+ Little RF receiver filtering?

- Lower inherent efficiency/bit

- FCC unlicenced UWB spectrum 3.1-10 GHz (-41.3dBm/MHz)

- Delay element non trivial?

- Requires UWB LNA (comes for free if inductorless)

2010-05-09 15Paper Presentation - Ultra Portable Devices

Further reading

• Yi Zhao, Yunzhi Dong, et al. A Short Range, Low Data Rate, 7.2 GHz-7.7 GHz FM-UWB Receiver Front-

End. IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 44, NO. 7, JULY 2009

• 802.15 proposal (may 2009): https://mentor.ieee.org/802.15/dcn/09/15-09-0276-00-0006-csem-fm-uwb-

proposal.pdf


http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=5109786&tag=1







https://mentor.ieee.org/802.15/dcn/09/15-09-0276-00-0006-csem-fm-uwb-proposal.pdf

















Paper presentation Ultra-Portable Devices

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