IEEE P802.22 Wireless RANs Date: 2006-01-18 Month Year doc.: IEEE 802.22-yy/xxxxr0 January 2006 System Level Ranging IEEE P802.22 Wireless RANs Date: 2006-01-18 Authors: Notice: This document has been prepared to assist IEEE 802.22. 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 grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.22. Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures http://standards.ieee.org/guides/bylaws/sb-bylaws.pdf including the statement "IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance with both mandatory and optional portions of the standard." Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chair Carl R. Stevenson as early as possible, in written or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE 802.22 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at patcom@iee.org. > Jeff Zhuang, Motorola John Doe, Some Company

Month Year doc.: IEEE 802.22-yy/xxxxr0 January 2006 Abstract Ranging is a critical PHY element. It provides timing advance information for the CPE and a means of requesting initial access or bandwidth resources, among other things. The accuracy of the timing advance is important since errors must be absorbed in the cyclic extension along with the channel delay spread. Detection of bandwidth requests is important for minimizing latency and effectively allocating resources. This contribution proposes evaluation criteria for ranging and inquires whether improvements can be made over existing techniques. Jeff Zhuang, Motorola John Doe, Some Company

Goal Understand the system-level functional requirement for ranging January 2006 Goal Understand the system-level functional requirement for ranging Understand the performance of ranging in relevance to other system parameters Discuss the possible improvement under 802.22 deployment scenarios Jeff Zhuang, Motorola

January 2006 Background (1) All wireless networks need to allow unsolicited access, with CPEs requesting initial registration, resource allocation, timing/power adjustment, and so on. “Random access” transmission fulfills critical system functionalities: Initial Access: Enter the system for the first time or re-enter after loss of sync Bandwidth Request: Ask for resource allocation for uplink data Handover Access: Register with another sector (unnecessary for .22) Maintenance functions: Maintain periodic timing/power adjustment, etc. Jeff Zhuang, Motorola

January 2006 Background (2) A “good” random access scheme directly impacts user experience Reliable: high success rate/low collision rate Efficient: low overhead 3G CDMA: Sequence-based single carrier transmission IEEE802.16 (OFDM systems): Binary PN sequence on 144 dispersed subcarriers Jeff Zhuang, Motorola

Evaluation Criteria (1) January 2006 Evaluation Criteria (1) Detection and estimation performance are most relevant Detection performance Success rate: average ranging requests that can be successfully detected Miss rate: average ranging requests that are present but not detected Collision rate: average ranging requests that share the same code False alarm: average number of false detections Considerations: Number of users will vary in any given frame (traffic dependent) Number of ranging opportunities allocated (available codes × physical resources) Received signal power (CPE Tx power likely power controlled) Jeff Zhuang, Motorola

Evaluation Criteria (2) January 2006 Evaluation Criteria (2) Estimation performance Timing offset accuracy (for initial ranging) Considerations Cyclic extension: the longer the CE, the more inaccuracy can be tolerated (but lower efficiency) Number of ranging subcarriers (ratio to FFT size) Tradeoff: the more ranging subcarriers, the better is the resolution, but most likely with less received signal power per subcarrier Ranging subcarrier distribution: Dispersed across the whole band: zero stuffing results in unpredictable false peaks Contiguous (sub-band): no false peaks but loss in resolution (multiple proximate rays can collapse to one) Jeff Zhuang, Motorola

Possible areas for improvement over 802.16e January 2006 Possible areas for improvement over 802.16e Design a flexible and adjustable scheme after anticipating future traffic’s impact on ranging Initial ranging will not be as frequent as in mobile deployment More simultaneous ranging with heavy VoIP usage Allocate more ranging subcarriers (particularly for FFT size > 2K) Better timing offset estimation accuracy (power constraint is not that serious) Increase the maximum round-trip delay (RTD) allowed for larger cell size 35 km = 233 µs, 100 km = 667 µs Use contiguous (rather than dispersed) subcarriers Better timing offset estimation Better detection performance Consider codes with better cross-correlation and low PAPR Have observed significant performance degradation when two or more codes are occupied (no collision, but interfering with each other) Jeff Zhuang, Motorola

January 2006 References IEEE C802.16e-04/143r1, Ranging Improvement for 802.16e OFDMA PHY, 7 July 04, Xiangyang (Jeff) Zhuang, Kevin Baum, Vijay Nangia, Mark Cudak Jeff Zhuang, Motorola