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

1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [System Design Issues for Low Rate UWB ] Date Submitted: [November 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 number of important design considerations for TG4a] Purpose: [Preliminary 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. Issues for Low Power & Cost TG4a UWB • Bandwidth • Transmit power • Ranging & complexity • Performance • Pulse rate • Effects on efficiency & implementation • Data Rate • Interoperability & Coexistence Welborn, Freescale

4. UWB Signal Bandwidth • Transmit power spectrum density is limited to -41.3 dBm/MHz (in the US) – power depends on bandwidth • Transmit power will vary from -14 dBm (500 MHz BW) to -10 dBm or more (1300 <Hz or more BW) • In general, time resolution is inversely proportional to signal bandwidth • Hardware complexity can also depend on signal bandwidth • Highly dependant on implementation, analog vs. digital, sample rates, etc. Welborn, Freescale

5. UWB Signal Bandwidth • One of the primary advantages of UWB is the potential to significantly reduce multipath fading • Narrowband radios can suffer significant multipath fades (15-20 dB or more) • UWB signals often fade only a few dB • However, this 10-15 dB potential advantage in transmit power may not matter unless radio power is very low • Tx power for UWB (~ -10 dBm = 0.1 mW) is a very small fraction of radio power consumption • Narrowband Tx power of ~5 dBm is only 3 mW – still a small fraction of total radio power consumption Welborn, Freescale

6. UWB Pulse Rate • “Impulse radio” 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 • Direct sequence UWB (DS-UWB) is simply high rate pulsed UWB with multiple pulses per symbol & BPSK • 1300-2600 M pulses/second • Low pulse rate means higher power per pulse and therefore higher peak power (and voltage) Welborn, Freescale

7. Data Rate Considerations • Lowest PHY data rate does not necessarily mean lowest energy consumption • In fact, a fast radio can be more efficient than a slow radio • Example: • Compare: 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! • Notice, transmit power is a small fraction of the total power budget • Assumes that 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 Welborn, Freescale

8. Operating Frequency • Multiple operating channels with different center frequencies will have different performance • Path loss includes 20 Log10(Fc) term • Complexity of generating the reference frequency depends on the specific frequency • Acquisition at longer range requires longer integration and therefore more accurate reference frequency • Example: low cost, high quality crystals are available at 26 MHz (widely used in cell phones) Welborn, Freescale