Proposal for Low Rate DS-UWB (DS-UWB-LR)

1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [TG4a Proposal for Low Rate DS-UWB (DS-UWB-LR)] Date Submitted: [January 2004] Source: [Matt Welborn] Company [Freescale Semiconductor, Inc] Address [8133 Leesburg Pike, Vienna VA 22182] Voice:[703-269-3000], FAX: [], E-Mail:[matt.welborn @ freescale.com] Re: [Response to Call for Proposals] Abstract: [This document describes a proposal for the TG4a baseline draft standard.] Purpose: [Proposal Presentation for the IEEE802.15.4a 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. Welborn, Freescale

2. UWB for Low Rate Communications • UWB has great potential for low power communications • Low fading margin can provide same range for lower transmit power • Large (ultra-wide) bandwidth can provide fine time resolution provides potential for accurate ranging • Drawbacks due to regulations • Limited transmit power – how much is enough? • Operation at long ranges is highly dependent on NLOS path loss characteristics Welborn, Freescale

3. Proposal for TG4a Alternate PHY Layer Welborn, Freescale

4. Overview of DS-UWB-LR TG4a Proposal • Based on higher rate DS-UWB proposal under consideration in TG3a, but modified for low power and lower complexity • Variable-length code spreading with BPSK modulation of data • Chip rates are 1/3 the rates used in DS-UWB (so about 450 MHz) • Bandwidth is only ~500 MHz (instead of ~1500 M) • Lower complexity FEC convolutional code (constraint length k=4) • Data rates of 30 kbps to 10 Mbps • Use spreading codes of length 24 to 6144 • AWGN range of 15 to 75 meters (assuming n=3.5 PL at > 10m) • Support for precise ranging • Very straight forward solutions using RTT measurements with corrections for non-direct-path propagation effects • Flexible pulse shaping • Allows many pulse generation, antenna and receiver architectures • Supports requirements for coexistence & regulatory constraints • Will enable interoperation between higher rate DS-UWB devices and low rate, low complexity TG4a devices • Support wider range of asymmetric applications • Enables active coexistence and coordination Welborn, Freescale

5. Benefits of Low Rate DS-UWB • Bandwidth & operating frequency • Transmit power, ranging, complexity & performance • Pulse rate • Effects on efficiency & implementation • Data Rate • Interoperability & Coexistence Welborn, Freescale

6. Operating Frequency • Multiple operating channels with different center frequencies to provide FDM operation for different networks • Three piconet bands at 3536, 4056, and 4576 MHz • Different performance due to 20 Log10(Fc) term in path loss • Also uses CDM for sharing of each band by different piconets • Cost of generating the reference frequency depends on the specific frequency • DS-UWB is based on low cost, high quality 26 MHz crystals (widely used in cell phones) • Better frequency accuracy can relax other system constraints • Acquisition at longer range requires longer integration and therefore more accurate reference frequency • High accuracy clock can allow longer “sleep” time & better power management • Precise ranging using TOA methods requires high precision time measurements over relatively long intervals (RTT) to determine small differences in signal propagation times • Simplified and improved with good reference clock Welborn, Freescale

7. Signal Operating Bands for Low Rate UWB Relative PSD (dB) Possible Lower Rate Signaling Bands (500 MHz bandwidth) High rate DS-UWB Low Band with RRC Pulse Shape 0 -3 FCC Mask -20 3536 4056 4576 Frequency (MHz) 3100 5100 • Ultra-wideband ~500+ MHz bands for each piconet • Code-division and Frequency-division multiplexing • Multiple piconets in each band using different codes • Operation in close proximity, interference avoidance or coexistence • Three piconet bands at 3536, 4056, and 4576 MHz Welborn, Freescale

8. Low Rate DS-UWB Pulse Rate • “Impulse radio” (IR) originally meant low pulse rate (10’s of M pulse/sec) using “time hopping” for multiple access and pulse position modulation (PPM) • More generally, IR is just pulse-based spread spectrum with data modulation • Many choices for modulation (BPSK, PPM, OOK, etc.) • One or more pulses per data symbol • Low rate DS-UWB uses a chip rate that is designed to meet minimum 500 MHz bandwidth for simple BSK modulation • Center frequency is always a multiple of 26 MHz • Chip rate is equal to center frequency divided by 9 (e.g. 4052 / 9 = 450.66MHz) • Spreading codes are based on 24-chip code • Longer spreading codes are derived from the basic code by further sreading with PN sequence (e.g. length 192 code is a length 24 code spread by a length 8 PN code) • Pulse rate does not fundamentally affect transmit power, signal bandwidth or system performance • Pulse rate does affect energy per pulse and therefore peak power (and voltage) Welborn, Freescale

9. Higher Pulse Rate = Lower Peak Power Higher peak power & voltage for same average power • Lower pulse rate requires higher “energy per pulse” and therefore higher peak power (and voltage) for same transmit power • Process technology can limit available peak voltage that can be achieved without an external power amplifier ___ • If pulse rate is 100x slower, then peak voltage is 100 = 10x higher Welborn, Freescale

10. Data Rate Considerations • Lowest PHY data rate does not necessarily mean lowest energy consumption • In fact, a fast radio can potentially be more energy efficient than a slow radio. Example: • Compare a 1 Mbps radio at 100 mW versus 10 kbps radio at 10 mW • 32 kB @ 10 kbps = 0.256 mW*seconds • 32 kB @ 1 Mbps = 0.0256 mW*seconds – 1/10 of the energy per bit! • Assumptions • Both radios achieve minimum range requirement for application • Minimum acquisition time is a function of SNR (range) not data rate • Requires fast wake-up and shut down of radio with aggressive power management • Relative energy usage depends on packet size • Fast radio advantage is higher for longer packets • Notice transmit power is a small fraction of the total power (<1%) • The largest power use is turning on the radio and processing signal Welborn, Freescale

11. Data Rate Considerations Lower radio power, but longer transmission time for data payload Power Preamble Time Higher peak power but shorter transmission time for same payload Power Preamble Time • Total energy use from battery is the “area” under the power vs. time curves shown above • Relative efficiency depends on power & duration (payload size) Welborn, Freescale

12. Low Rate DS-UWB Data Rates • LR-DS-UWB data rates are designed to support relatively high rate operation at relatively small duty cycle Welborn, Freescale

13. Link Budget Welborn, Freescale

14. Link Budget Notes • Assumptions • Chipping rate = 450.66 MHz • Includes 1.9 dB Tx power reduction for spectral ripple in certification testing • Assumes 3.8e-5 BEr to achieve 1% Per with 32 octet data packet Welborn, Freescale

15. Interoperability & Coexistence • All of the specific co-existing systems in the Slection Requirements are out-of-band to LR-DS-UWB • Robustness against in-band interference is provided by the UWB bandwidth of the LR-DS-UWB system (large processing gain) • Many types of other UWB systems and waveforms will share the UWB bands • Interoperability between TG4a & higher rate systems could enable improved coexistence • Interoperation with higher rate systems could increase the utility of the TG4a standard • Interoperability of low cost sensor/RFID devices with nearby UWB CE devices • Interoperability with DS-UWB could be quite simple if correct parameters are chose for TG4a • Common reference frequency, codes & operating bands Welborn, Freescale

16. Technical Feasibility • The Low rate DS-UWB solution for TG3a has a high level of manufacturability • Based on existing DS-UWB technology • Can be implemented in low-cost CMOS technology • Time to Market • Time to market is quite reasonable. Compliant PHY implementations could be available for integration in 2005. • Regulatory Impact • DS-UWB technology is know to be compliant with FCC UWB rules • Other regulatory administrations are using FCC rules as a basis for initial discussions • Many mechanisms exist to ensure compliance for other regions that adopt other regulations Welborn, Freescale

17. System Performance • System and SOP simulations are underway – results TBD Welborn, Freescale