UWB Interoperability Compromise: PHY Overview Proposal

1. 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:[john@xtremespectrum.com] 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. McCorkle, Motorola

2. 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 McCorkle, Motorola

3. 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 McCorkle, Motorola

4. CSM Waveform Makes All Connections XMIT DS REC DS XMIT MB-OFDM REC MB-OFDM McCorkle, Motorola

5. MB-OFDM & DS-UWB Signal Spectrum with CSM Compromise Solution Proposed Common Signaling Mode Band (500 MHz bandwidth) Relative PSD (dB) 0 -3 DS-UWB Low Band Pulse Shape (RRC) -20 3432 3960 4488 Frequency (MHz) 3100 5100 FCC Mask MB-OFDM (3-band) Theoretical Spectrum McCorkle, Motorola

6. 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 McCorkle, Motorola

7. 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 440 MHz DAC clock Not used for CSM IFFT Input Constellation Convolutional Bit Xmt LPF DAC Puncture Insert Pilots Scrambler Data (9.2 Mbps w/ FEC, 18.3 Mbps un-coded) Mapping Encoder Interleaver Add CP & GI p Only required if FEC is used for CSM cos ( 2 f t ) c Apply length-24 (-1/0/1) Already present in MB-OFDM Transceiver piconet spreading code Time Frequency Code (hold fixed at band 2 frequency 3960 MHz) Add piconet coder McCorkle, Motorola

8. / 9 MB-OFDM Frequency Synthesis for CSM Select Already present in MB-OFDM Transceiver • Clock for DAC based on existing MB-OFDM PLL • 440 MHz = Band #2 center frequency / 9 DAC Clock 440 MHz Added Divider & Selector Carrier Frequency Band 2 = 3960 MHz McCorkle, Motorola

9. 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 use MB-OFDM DSP blocks BPSK demodulation And FEC decoding Already present in MB-OFDM Transceiver McCorkle, Motorola

10. 3960 MHz) 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 LPF Input Convolutional Bit Puncture Scrambler Data (9.2 Mbps w/ FEC, 18.3 Mbps un-coded) Encoder Interleaver Only required if FEC is used for CSP Apply length-72 (-1/0/1) Piconet spreading code McCorkle, Motorola

11. 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 McCorkle, Motorola

12. Link Budgets for CSM with Several Possible FEC Modes McCorkle, Motorola

13. 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 McCorkle, Motorola

14. 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 McCorkle, Motorola