May, 2005
Celestino A. Corral et al., FreescaleSlide 1
doc.: IEEE 802.15-05/290r0
Submission
Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)
Submission Title: [Ultra-Wideband Peak Power Limits]Date Submitted: [15 May, 2005]Source: [Celestino A. Corral, Shahriar Emami and Gregg Rasor] Company [Freescale Semiconductor, Inc.]
Address [6100 Broken Sound Pkwy., N.W., Suite 1, Boca Raton, Florida USA 33487]Voice:[561-544-4057], FAX: [ ]
Re: [Recent FCC Waiver]
Abstract: [This document provides analytical and theoretical comparison of MB-OFDM and DS-UWB under peak power limited applications.]
Purpose: [For discussion by IEEE 802.15 TG3a.]
Notice: This document has been prepared to assist the IEEE P802.15. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.
Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P802.15.
May, 2005
Celestino A. Corral et al., FreescaleSlide 2
doc.: IEEE 802.15-05/290r0
Submission
Ultra-WidebandPeak Power Limits
Celestino A. Corral, Shahriar Emami and Gregg Rasor
Freescale Semiconductor, Inc.6100 Broken Sound Parkway., N.W., Suite 1
Boca Raton, Florida USA
May 17, 2005
May, 2005
Celestino A. Corral et al., FreescaleSlide 3
doc.: IEEE 802.15-05/290r0
Submission
Motivation Goal: To provide a comparison between DS-UWB and
MB-OFDM for peak-limited applications under the recent FCC waiver.
Note: Recent FCC waiver is technology-neutral. Devices can be measured under “normal” operating conditions. These conditions can include hopping or gating.
Approach: Consider DS-UWB and MB-OFDM waveforms under average- and peak-power measurements. Emphasis is on peak-to-average power ratio of waveforms.
Additionally: Provide peak-power headroom levels for actual implementation considerations.
May, 2005
Celestino A. Corral et al., FreescaleSlide 4
doc.: IEEE 802.15-05/290r0
Submission
Average Power Measurements
Spectrum analyzers measure average value of the total signal power quantized within resolution bandwidth by making a fixed number of measurements and computing a corrected average figure of power density normalized to that bandwidth.
RadiatedWaveform
May, 2005
Celestino A. Corral et al., FreescaleSlide 5
doc.: IEEE 802.15-05/290r0
Submission
Average Power MeasurementsResolution bandwidth filter
Block Diagram of Typical Spectrum Analyzer
For FCC emission measurements, the resolution bandwidth is 1 MHz with 1 msec integration time for the RMS power and resulting EIRP. Resolution bandwidth is 50 MHz for peak power measurements.
May, 2005
Celestino A. Corral et al., FreescaleSlide 6
doc.: IEEE 802.15-05/290r0
Submission
Gated Signals
T
Gating allows greater power transmissions over narrower time intervals. This power can be used to improve SNR, SIR or range. Limit is now peak power.
gated signal
ungated signal
May, 2005
Celestino A. Corral et al., FreescaleSlide 7
doc.: IEEE 802.15-05/290r0
Submission
Peak Power Measurements
key determinant for peak-power levels
Minimize PAPR to achieve more headroom in peak power levels
Peak power measurements actually made with spectrum analyzer on “peak hold” capturing over a long time period (several minutes).
50 MHz 1 MHz
May, 2005
Celestino A. Corral et al., FreescaleSlide 8
doc.: IEEE 802.15-05/290r0
Submission
Direct-Sequence UWB Sinusoidal carrier, PAPR = 3
dB Data spread by chipping code Upconverted to desired freq. Shaped by RRC filter with =
0.3. Spectral BW = 1.5 GHz.
Waveform has 40% fractional bandwidth between 3.1 and 4.6 GHz and consequently good fading resilience.
0.26 ns
data
code 4.1 GHz adjust RRCFilter
May, 2005
Celestino A. Corral et al., FreescaleSlide 9
doc.: IEEE 802.15-05/290r0
Submission
What Spectrum Analyzer Measures
1 MHzFilter
50 MHzFilter
DS-UWB WaveformSignal over air has 5.5 dB PAPR
DS-UWB has 8.5 dB PAPR (ungated) in 50 MHz filter.
May, 2005
Celestino A. Corral et al., FreescaleSlide 10
doc.: IEEE 802.15-05/290r0
Submission
Worst-Case PAPR of MB-OFDM Subcarrier spacing is 4.125 MHz. In 50 MHz resolution bandwidth
this corresponds to 12 subcarriers.
Worst-case PAPR is 10log(12)=10.8 dB.
Above occurs even if MB-OFDM waveform is clipped to 9 dB PAPR.
If we consider that hopping contributes 5.8 dB additional PAPR for 3 hops, the total worst-case PAPR is 16.6 dB.
As a result, we have about 7.7 dB headroom for MB-OFDM.
50 MHz
May, 2005
Celestino A. Corral et al., FreescaleSlide 11
doc.: IEEE 802.15-05/290r0
Submission
How Often Does This Happen?
QPSKConstellation
270o
90o
180o 0o
May, 2005
Celestino A. Corral et al., FreescaleSlide 12
doc.: IEEE 802.15-05/290r0
Submission
Impact of Filtering OperationWorst-Case OFDM Symbol
12 SubcarriersFilter Impulse Response
(50 MHz)Output of Filter(Convolution)
The filter impulse response is very narrow relative to the OFDM waveform, so convolution results in OFDM symbol and PAPR is conserved.
pulse width Pulse width is about 8% of the length of OFDM symbol.
May, 2005
Celestino A. Corral et al., FreescaleSlide 13
doc.: IEEE 802.15-05/290r0
Submission
What Spectrum Analyzer Measures
1 MHzFilter
50 MHzFilter
Multi-Band OFDM WaveformSignal over air has 9 dB PAPR
On average, peak power is -11.1 dBm and PAPR is 15 dB. Worst-case PAPR is 16.6 dB and peak-power is -7.7 dBm.
May, 2005
Celestino A. Corral et al., FreescaleSlide 14
doc.: IEEE 802.15-05/290r0
Submission
Summary of Results
Parameter DS-UWB MB-OFDM
PAPR at transmit pin 3.0 dB 9.0 dB
PAPR over air after pulse shaping 5.5 dB 9.0 dB
PAPR at output of 50 MHz filter 8.5 dB 16.6 dB
Peak power in 50 MHz bandwidth -15.8 dBm -7.7 dBm
Thus, DS-UWB has 8.1 dB more headroom than MB-OFDM. This can be employed to overcome cable losses, antenna losses, etc. DS-UWB has a net 15.8 dB headroom for exploiting gating.
May, 2005
Celestino A. Corral et al., FreescaleSlide 15
doc.: IEEE 802.15-05/290r0
Submission
Conclusions DS-UWB is generated from a sinusoid having 3 dB peak-
to-average that grows to 5.5 dB over air after pulse shaping. The PAPR of DS-UWB in the 50 MHz filter is 8.5 dB (ungated). Hence, DS-UWB has 8.1 dB more headroom than MB-OFDM for overcoming cable, filter and antenna losses.
DS-UWB has 15.8 dB maximum headroom for transmission which can be exploited for gated signals. This corresponds to about 3% duty cycle.
Multi-band OFDM, even if clipped to 9 dB peak-to-average over the air can still result in up to 16.6 dB PAPR in a 50 MHz resolution bandwidth. The 16.6 dB level is due to 10.8 dB of signal PAPR for 12 subcarriers captured and 5.8 dB PAPR due to duty cycle of 3-hop sequence.
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