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
McCorkle, MotorolaSlide 2
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
McCorkle, MotorolaSlide 3
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
McCorkle, MotorolaSlide 4
doc.: IEEE 802.15-04/081r2
Submission
CSM Waveform Makes All Connections
XMIT DS
REC DS
XMITMB-OFDM
RECMB-OFDM
February 2004
McCorkle, MotorolaSlide 5
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
McCorkle, MotorolaSlide 6
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
McCorkle, MotorolaSlide 7
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
McCorkle, MotorolaSlide 8
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
McCorkle, MotorolaSlide 9
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
McCorkle, MotorolaSlide 10
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
McCorkle, MotorolaSlide 11
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
McCorkle, MotorolaSlide 12
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
McCorkle, MotorolaSlide 13
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
McCorkle, MotorolaSlide 14
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