Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)

February 2004

McCorkle, MotorolaSlide 1

doc.: IEEE 802.15-04/081r2

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: [Compromise for UWB Interoperability – PHY Overview]Date Submitted: [20 February, 2004]Source: [John McCorkle] Company [Motorola, Inc]Address [8133 Leesburg Pike]Voice:[703-269-3000], FAX: [703-249-3092], E-Mail:[[email protected]]

Re: [IEEE 802.15.3a Call For Intent to Present for Ad-Hoc Meeting]

Abstract: [This document provides an overview of a proposed Common Signaling Mode that would allow the inter-operation or MB-OFDM and DS-UWB devices.]

Purpose: [Promote further discussion and compromise activities to advance the development of the TG3a Higher rate PHY standard.]

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.

February 2004


doc.: IEEE 802.15-04/081r2

Submission

Talking with each other: Basic Requirements

• Each class of UWB devices (MB-OFDM or DS-UWB) needs a way to send messages to the other type– MB-OFDM DS-UWB – DS-UWB MB-OFDM

• Even better, design a common signaling mode that can be understood by either class of devices

• Goal: Minimize additional complexity for each type of device while enabling this extra form of communications– Use existing RF components & DSP blocks to transmit message to

“other-class” devices– Also need to support a low-complexity receiver– Lower rate mode could be acceptable if it can be used to provide

robust control functions

February 2004


doc.: IEEE 802.15-04/081r2

Submission

The CSM Waveform• One waveform that would be straightforward for either class of device is

a BPSK signal centered in the middle of the “low band” at ~ 4GHz

• Such a signal could be generated by both MB-OFDM and DS-UWB devices using existing RF and digital blocks

• MB-OFDM device contains a DAC nominally operating at 528 MHz– A 528 MHz BSPK (3 dB BW) signal is likely too wide for MB-OFDM band

filters– Instead, DAC can be driven at slightly lower clock rate to produce a BPSK

signal that will fit the MB-OFDM Tx filter– Result is a 500 MHz wide BPSK signal that a DS-UWB device could receive

& demodulate, as would an MB-OFDM receiver

• DS-UWB device contains a pulse generator– Use this to generate a 500 MHz BPSK signal at lower chip rate – This signal would fit MB-OFDM baseband Rx filter and could be

demodulated by both the MB-OFDM receiver and the DS-UWB receiver

February 2004


doc.: IEEE 802.15-04/081r2

Submission

CSM Waveform Makes All Connections

XMIT DS

REC DS

XMITMB-OFDM

RECMB-OFDM

February 2004


doc.: IEEE 802.15-04/081r2

Submission

MB-OFDM & DS-UWB Signal Spectrum with CSM Compromise Solution

4488396034323100 5100

DS-UWB Low BandPulse Shape (RRC)

MB-OFDM (3-band)Theoretical Spectrum

Proposed CommonSignaling Mode Band (500 MHz bandwidth)

FCC Mask

Frequency (MHz)

0-3

-20

RelativePSD (dB)

February 2004


doc.: IEEE 802.15-04/081r2

Submission

CSM Interoperability Signal Overview

• 500 MHz BPSK signal has similar characteristics to original pulsed-multiband signals

– Proposed by several companies in TG3a CFP

• Adopt MB-OFDM band 2 center frequency for common signaling band– Centered at 3960 MHz with approximately 500 MHz bandwidth– BPSK chip rate easily derived from carrier: chip rate = carrier frequency / 9– Frequency synthesis circuitry already present in MB-OFDM radio

• Does not suffer from Rayleigh fading (>500 MHz BW)• Uses different CSM piconet code for each piconet

– Each DEV can differentiate beacons of different piconets – Provides processing gain for robust performance: signal BW is much

greater than data rate

• Relatively long symbol intervals (55 ns) used to avoid/minimize ISI– Equalization still very simple in worse multipath channels

February 2004


doc.: IEEE 802.15-04/081r2

Submission

MB-OFDM Transceiver Recovery of the CSM Signal

• Proposed MB-OFDM transmitter architecture contains almost all required blocks for CSM signal generation

– Use real-valued (single) DAC clocked at 440 MHz (less than design speed)– Use length-24 ternary (-1/0/1) per-piconet spreading code

• This would be matched in DS-transmitter with a 3*24 = 72 length code– Result is BPSK signal with 520+ MHz bandwidth (at -10 dB points)– BPSK “chip” is a “pulse” of nine cycles of a sinusoid at 3960 MHz

DACScramblerConvolutional

EncoderPuncture

BitInterleaver

ConstellationMapping

IFFTInsert Pilots

Add CP & GI

Time Frequency Code

cos(2pfct)

Input Data(9.2 Mbps w/ FEC,18.3 Mbps un-coded)

(hold fixed at band 2 frequency 3960 MHz)

Only required if FEC is used for CSM

Not used for CSM

Apply length-24 (-1/0/1)piconet spreading code

XmtLPF

440 MHz DAC clock

Already present in MB-OFDM Transceiver Add piconet coder

February 2004


doc.: IEEE 802.15-04/081r2

Submission

528 MHz

PLL

/ 8 / 2

SSB

4224 MHz

264 MHz

SSB

Select

DesiredCenter

Frequency

SamplingClock

792 MHz

MB-OFDM Frequency Synthesis for CSM

• Clock for DAC based on existing MB-OFDM PLL– 440 MHz = Band #2 center frequency / 9

/ 9

DAC Clock440 MHz

Select

CarrierFrequency

Band 2 = 3960 MHz

Already present in MB-OFDM Transceiver

AddedDivider &Selector

February 2004


doc.: IEEE 802.15-04/081r2

Submission

Pre-SelectFilter

LNA

sin(2fct)

cos(2fct)

Syn

chro

niza

tion

Rem

ove

CP

FFT

FEQ

Rem

ove

Pilo

ts

Vit

erbi

Dec

oder

De-

scra

mble

r

AGC

CarrierPhaseand

TimeTracking

De-

Inte

rlea

ver

I

Q

LPF

LPF

VGA

VGA

ADC

ADC

OutputData

Already present in MB-OFDM Transceiver

MB-OFDM Transceiver Recovery of the CSM Signal• Data processing speed is much lower due to reduced data rates (10x slower)• No Equalization needed (symbol interval is 55ns, almost no ISI, hence 60ns CP)• Proposed MB-OFDM receiver already contains the needed blocks

– MB-OFDM receiver contains both time-domain and frequency-domain processing– Time domain processing of BPSK signal is straight-forward

• MB-OFDM already contains correlator blocks used for synchronization functions – Frequency domain processing possible using FFT engine for fast correlation

• MB-OFDM receiver uses I&Q sampling with 4-5 bits resolution, could be under-clocked at 440 MHz

• Could implement RAKE / Channel-matched-filter

Low-complexity BPSK demodulator can useMB-OFDM DSP blocks

BPSK demodulationAnd FEC decoding

February 2004


doc.: IEEE 802.15-04/081r2

Submission

Simplified DS CSM Signal Generator

• Proposed DS-UWB transmit architecture contains all required blocks for CSM generation– Use length-24 ternary (-1/0/+1) per-piconet spreading code– Chipping rate of 440 MHz requires dividing chipping rate by 3– Result is same CSM BPSK signal with 520+ MHz bandwidth

LPFScrambler

ConvolutionalEncoder

PunctureBit

Interleaver

Input

Only required if FEC is used for CSP Apply length-72 (-1/0/1)

Piconet spreading code

Data(9.2 Mbps w/ FEC,18.3 Mbps un-coded) 3960 MHz)

February 2004


doc.: IEEE 802.15-04/081r2

Submission

Would the CSM mode need to use Forward Error Correction?

• Based on link budget analysis, an un-coded CSM mode (18 Mbps) would have less margin at 10 m than the 110 Mbps MB-OFDM

• But we want the CSM to be more robust, not less…• FEC could be added to improve robustness, however there is no

code that is common to both MB-OFDM & DS-UWB proposals• MB-OFDM uses punctured codes based on a rate 1/3 k=7 code

• DS-UWB uses punctured codes based on a rate 1/2 k=7 code

• Adding FEC to the CSM could result in as much as 5 dB coding gain• Would require a common code that both receivers can decode

• Pick one of the codes from the two proposals, or

• Choose a different code with relatively low complexity

• Following slides show link budgets for a few sample FEC choices

February 2004


doc.: IEEE 802.15-04/081r2

Submission

Link Budgets for CSM with Several Possible FEC Modes

CSM Uncoded

CSM rate 5/8 k=7 Conv Code

CSM rate 1/2 k=7 Conv code

CSM rate 1/2 k=6 Conv code

CSM r=1/2 Reed-Muller block code

MB-OFDM 110 Mbps

FEC Rate 1.0 0.6 0.5 0.5 0.5 0.3Data Rate 18.3 11.5 9.2 9.2 9.2 110.0Theoretical Tx Power -14.8 -14.8 -14.8 -14.8 -14.8 -10.3Transmit Power (dBm) -16.7 -16.7 -16.7 -16.7 -16.7 -10.8Total Path Loss (dB) 64.2 64.2 64.2 64.2 64.2 64.2Received Power -80.9 -80.9 -80.9 -80.9 -80.9 -75.0Noise Power per Bit -101.4 -103.4 -104.4 -104.4 -104.4 -93.6Noise Figure 6.6 6.6 6.6 6.6 6.6 6.6Total Noise Power -94.8 -96.8 -97.8 -97.8 -97.8 -87.0Error Code Gain 0.0 4.9 5.1 4.6 2.5 5.6Required Eb/No 9.6 4.7 4.5 5.0 7.1 4.0Implementation Loss 2.5 2.5 2.5 2.5 2.5 2.5Link Margin at 10 m 1.7 8.7 9.8 9.3 7.2 5.5Sensitivity -82.7 -89.6 -90.8 -90.3 -88.2 -80.5

February 2004


doc.: IEEE 802.15-04/081r2

Submission

FEC Conclusions

• Based on complexity versus performance trade-off analysis for convolutional and block codes to provide ~10 Mbps for CSP

• CSP must provide a more robust link than data modes (110+ Mbps)

• Requiring either MB-OFDM or DS-UWB receiver to implement additional decoder for a different convolutional code would increase complexity

• Further analysis is underway, no definitive recommendation at this time

February 2004


doc.: IEEE 802.15-04/081r2

Submission

Conclusions• GOAL: A CSM that allows interoperability between DS-UWB and MB-

OFDM devices– The efficiency is FAR better than allowing the devices to collide.

• A Common Signaling Mode is described that meets that goal– Minimum useful data rate for 15.3 MAC-based interoperability is ~10 Mbps– Achieves desired data rates and robust performance– Prevents coexistence problems for two different UWB PHYs– Provides interoperability in a shared piconet environment

• The creation of a common signaling mode (CSM) is simple to add– Essentially ZERO cost for both DS and MB-OFDM– MB-OFDM requires addition of a divide-by-9

• Multiple options for receive using either time or frequency domain DSP blocks in MB-OFDM radio

• Using existing MB-OFDM band 2 center frequency and bandwidth– DS requires more change, but is feasible

• changing clocks,• adding mode to support 1/3 rd chipping rate

Documents

Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)