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: IEEE 802.15 TG3a MB-OFDM Interference Example Date Submitted: Tuesday, September 12, 2003 Source: John Barr and Tom D’Amico Company: Motorola Address: 1303 E. Algonquin Road, Schaumburg, IL 60196 USA Voice: 847.576.8706, FAX: 847-576-6758, E-Mail: john.barr@motorola.com Re: TG3a Minutes from July Plenary Meeting Abstract: MB-OFDM signals produce interference effects that are detrimental to some victim receivers operating in licensed spectrum that overlaps with UWB spectrum. Purpose: Prepared to summarize the MB-OFDM interference problems encountered by Motorola Labs analysis of potential problems with proposed UWB modulation techniques. 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 these viewgraphs becomes the property of IEEE and may be made publicly available by P802.15. John R. Barr (Motorola)

2. Frequency Hopping Characteristics • The MB-OFDM (wide bandwidth frequency hopping) signal appears as a periodic intermittent signal to a victim receiver operating on a fixed frequency. The signal: • Appears to be turned “on” during the dwell time of the frequency hopping signal when the victim receiver frequency is within the bandwidth of the MB-OFDM signal, and • Appears to be turned “off “when the MB-OFDM signal hops to other frequencies. John R. Barr (Motorola)

3. EIRP Measurement • The Effective Isotropic Radiated Power (EIRP) of the MB-OFDM signal during the dwell time exceeds the FCC limit. • Assuming non-overlapping hopping frequencies, the higher EIRP is given (approximately) by the following expression: PDwell= XPFCC where X = number of hopping frequencies PDwell = EIRP during the dwell time in watts PFCC = EIRP of FCC limit in watts • The EIRP when averaged over a time period that includes both the signal on interval (dwell time) and signal off interval (dwell times on other frequencies), the EIRP is within the FCC limit. • This is the result when measured with a 1 MHz resolution bandwidth as specified. John R. Barr (Motorola)

4. Interference Characteristics • Due to the short duration of the dwell time, narrowband receivers do not typically respond to the higher EIRP levels. • The interference level and effects would normally be equivalent to the average EIRP. • Wideband receivers typically do respond to the higher EIRP levels if the victim receiver bandwidth approaches the inverse of the dwell time. • The increased interference level is approximately proportional to the number of hopping frequencies, but with a reduced duty cycle. • For example, 3 hopping frequencies results in interference levels of 3X or 4.77 dB higher than the FCC limit, 7 hopping frequencies produces interference levels of 7X or 8.45 dB higher, etc. John R. Barr (Motorola)

5. FCC Power Measurements • Historically, the FCC has required power measurements to be performed over intervals of continuous transmission. • The intent of power measurement over intervals of continuous transmission is to prevent increased levels of interference as previously described. John R. Barr (Motorola)

6. Interference Conclusions • MB-OFDM (wide bandwidth frequency hopping) was not considered during the UWB Proceeding. • Deployment of such devices will result in higher levels of interference to some incumbents than was contemplated or intended under the First Report and Order. • The FCC urges “that IEEE perform technical analyses to ensure that any UWB standard it develops will not cause levels of interference beyond that already anticipated by the rules.” • See attached FCC response from Julius Knapp • Since • the current MB-OFDM proposal can be shown to cause higher levels of interference • recommend that the TG3a Task Group either: • select a proposal that does not cause higher levels of interference or • identify how to properly measure MB-OFDM proposals to prevent higher levels of interference and evaluate resulting performance. John R. Barr (Motorola)

7. FCC Response from Julius Knapp (11Sept03) Over the past few weeks several parties have met with the staff of the Federal Communications Commission Office of Engineering and Technology to discuss how the Commission’s rules for Ultrawideband devices might be applied for certain signal formats that are being considered by IEEE 802.15. OET believes it is premature to make any determination as to the appropriate measurement methods for particular signals because this matter is under active discussion in IEEE. In this regard, we have no immediate plans to respond to the XSI/Motorola request for a declaratory ruling. We urge that IEEE perform technical analyses to ensure that any UWB standard it develops will not cause levels of interference beyond that already anticipated by the rules. This information will be needed to support any necessary FCC rules interpretations or other appropriate action for the chosen standard. The FCC has had a long history of working cooperatively with the IEEE 802 committee in addressing any regulatory issues that may arise relative to standards. We recommend that IEEE proceed with its standards development process and that the committee address any questions to us at a later time when it has formed a specific proposal. John R. Barr (Motorola)