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.