OFDM Parameters And Preambles September 2006 doc.: IEEE 802.22-yy/xxxxr0 December 2006 OFDM Parameters And Preambles IEEE P802.22 Wireless RANs Date: 2006-12-06 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. > Monisha Ghosh, Philips Carlos Cordeiro, Philips

OFDM Parameters Concerns about latest proposal: December 2006 OFDM Parameters Concerns about latest proposal: Too few preamble symbols will lead to performance degradation. Allows acquisition and synchronization ONLY on the Superframe short preamble, i.e once every 160ms Robust downlink acquisition, synchronization (frequency offset and timing), and channel estimation are crucial for robust performance. Relying solely on distributed pilots for channel estimation is problematic for the following reasons: In a packet data system, OFDM symbols will need to be buffered while channel estimation is performed. Note that in DVB-T one does not need to do this since it is streaming video. Granularity of packets can be too large (e.g 7 OFDM symbols) for short data bursts, leading to excessive overhead. Monisha Ghosh, Philips

Proposal For Downlink Parameters December 2006 Proposal For Downlink Parameters SUPERFRAME PREAMBLE: One OFDM symbol of 4 repetitions of short training, followed by TWO OFDM symbols of long training. This will allow robust acquisition, frequency offset estimation and one-shot channel estimation because the long preamble will have a training symbol on every frequency. Negligible additional overhead: one OFDM symbol (about 0.3 ms) every 160 ms. Will allow robust decoding of the SCH. FRAME PREAMBLE: Mandatory: One OFDM symbol for channel estimation, with training symbol on every 2nd frequency. Optional: additional OFDM symbol for acquisition, similar to short training in SF. The channel estimation OFDM symbol could be omitted for the first frame only. Frames 5 and 10 should have a frame preamble of 2 OFDM symbols. PILOT DENSITY: Can be lower than 240/OFDM symbol as in the current proposal, since the combination of superframe and frame preambles will be adequate for channel tracking. Monisha Ghosh, Philips

Preamble Sequences Need 3 kinds of preamble sequences: December 2006 Preamble Sequences Need 3 kinds of preamble sequences: Superframe/frame short: Training symbol on every 4th frequency. Superframe long: Training symbol on every frequency. Frame long: Training symbol on every 2nd frequency. 802.16e does not provide these different kinds of sequences. Moreover 802.16e parameters (no of used tones, frequency of symbols etc.) are different. Cannot use 802.16e preamble sequences directly. We have a simple method (not the one in the current draft) of generating low PAPR (less than 5 dB) preamble sequences for 4-times oversampled sequences for each of the above. Monisha Ghosh, Philips

PAPR Of Random QPSK Data December 2006 PAPR Of Random QPSK Data PAPR < 5 dB for the preamble sequences will be adequate. Monisha Ghosh, Philips

Recommendations Preambles: Pilot density: December 2006 Recommendations Preambles: Increase the Superframe preamble from 2 to 3 OFDM symbols. Frame preamble is 1 OFDM symbol, except on Frame #1 which will have no frame preamble and Frames # 5 and 10, where 2 OFDM symbols will be used. The above changes will have negligible impact on overhead, but improve robustness and ease of implementation considerably. Pilot density: Reduced from 240 per symbol to 192 per symbol. Monisha Ghosh, Philips