Summary of I2R’s proposals July 2006 doc.: IEEE 802.22-yy/xxxxr0 July 2006 Summary of I2R’s proposals IEEE P802.22 Wireless RANs Date: 2006-07-13 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. > Ang Chee Wei, Institute for Infocomm Research Ang Chee Wei, Institute for Infocomm Research

July 2006 doc.: IEEE 802.22-yy/xxxxr0 July 2006 Abstract This presentation summarizes and discusses comments raised on I2R’s MAC proposals on “On-demand EOBS” and “Adaptive TDD” Ang Chee Wei, Institute for Infocomm Research Ang Chee Wei, Institute for Infocomm Research

July 2006 On-Demand EOBS Ang Chee Wei, Institute for Infocomm Research

Summary of On-Demand EOBS proposal July 2006 Summary of On-Demand EOBS proposal We propose a scheme to enable on-demand activation of EOBS so as to minimize signaling overhead incurred by periodic out-of-band broadcasting in the candidate channels A special tone is transmitted by the affected CPE (a CPE that identified the occurrence of the hidden incumbent event) to signal the BS into activating EOBS The BS picks up this tone during in-band or out-of-band sensing EOBS broadcasting in the candidate channels is turned off after the BS made decision in response to the hidden incumbent report Ang Chee Wei, Institute for Infocomm Research

Operation at CPE (unused channels are available) July 2006 Operation at CPE (unused channels are available) Ang Chee Wei, Institute for Infocomm Research

Operation at BS (unused channels are available) July 2006 Operation at BS (unused channels are available) Ang Chee Wei, Institute for Infocomm Research

If unused channel is unavailable July 2006 If unused channel is unavailable The affected CPE transmits the tone in-band for some duration (in excess of 2 seconds), so that the BS can detect this tone during its in-band sensing The CPE then switches itself off The BS can either shutdown service or reduce coverage range Ang Chee Wei, Institute for Infocomm Research

July 2006 Discussions Why not just transmit the special tone in-band in all cases? If unused channels are available, transmitting the special tone out-of-band will not disrupt ongoing WRAN communications, and of course will not cause interference to the incumbent users Do we need to maintain a second channel? Maintaining a second channel is akin to running the WRAN in channel aggregation mode. If a WRAN is to operate in channel aggregation mode the hidden incumbent report can be easily sent in the other operating channels If a WRAN operates only in one channel, then there is no need to maintain a second channel. The WRAN will switch to another channel upon detection of an incumbent Ang Chee Wei, Institute for Infocomm Research

Discussions The occurrence of a TV hidden incumbent is rare July 2006 Discussions The occurrence of a TV hidden incumbent is rare This is the reason why we propose to make EOBS out-of-band broadcasting on-demand Wireless microphone transmission might not cause a nearby CPE to lose synchronization with the BS, because the BW is small compared to a full TV channel Wireless microphone BW of 200kHz will affect about 60 subcarriers. And this may affect many subchannels if distributed subcarrier allocation is used. This can affect part of the frame preamble and DS/US MAPs and may eventually affect synchronization Ang Chee Wei, Institute for Infocomm Research

July 2006 Adaptive TDD Ang Chee Wei, Institute for Infocomm Research

Summary of Adaptive TDD proposal July 2006 Summary of Adaptive TDD proposal Adaptive TDD allows the gap between DS and US transmissions to be CPE-dependant. Specifically, nearby CPEs are scheduled to start uplink transmission earlier than far-away CPEs. The OFDMA symbol boundaries of all CPEs are kept synchronized at BS. Adaptive TDD can achieve significant gain, in terms of the average uplink capacity. Very simple addition to the current MAC specifications is required to support Adaptive TDD. Ang Chee Wei, Institute for Infocomm Research

Conventional TDD All CPEs are aligned with the farthest one. July 2006 doc.: IEEE 802.22-yy/xxxxr0 July 2006 Conventional TDD PREAMBLE UL-MAP DL-MAP FCH Burst 1 Burst 2 Burst 3 Burst 4 Burst 5 Burst 6 Ranging/BW Request Frame n Frame n+1 Frame n-1 Frequency Time DS Subframe US Subframe TTG All CPEs are aligned with the farthest one. Ang Chee Wei, Institute for Infocomm Research Ang Chee Wei, Institute for Infocomm Research

Frame Structure with Adaptive TDD July 2006 Frame Structure with Adaptive TDD PREAMBLE UL-MAP DL-MAP FCH Burst 1 Burst 2 Burst 3 Burst 4 Burst 5 Burst 6 Burst 7 Ranging/BW Request Burst 8 Frame n Frame n+1 Frame n-1 Frequency Time DS Subframe US Subframe TTG1,2 Burst 1,2 TTG 3,4, 5, 6, 7, 8 Ang Chee Wei, Institute for Infocomm Research

Gain in Average Uplink Throughput July 2006 Gain in Average Uplink Throughput Cell radius = 30km; nearby CPEs within 5km; 2K FFT, nearby CPEs use 64QAM, ¾ code rate; faraway CPEs use QPSK, ½ code rate Ang Chee Wei, Institute for Infocomm Research

Adaptive TDD Uplink Allocation July 2006 Adaptive TDD Uplink Allocation OFDMA Symbols Logical Subchannels Early Start Time Allocation Start Time Ang Chee Wei, Institute for Infocomm Research

US MAP IE for AdaptiveTDD Bursts July 2006 Syntax Size Notes US-MAP_IE() { CID 16 bits UIUC 4 bits = 15 AdpativeTDD_IE() 24 bits Padding Nibble = 0x04 } Using an US Extended UIUC, called AdaptiveTDD IE, to specify an Adaptive TDD burst. To specify each AdaptiveTDD burst we need 48 bits, the same as that for a normal uplink TDD burst. Ang Chee Wei, Institute for Infocomm Research

AdaptiveTDD_IE (Extended UIUC) July 2006 AdaptiveTDD_IE (Extended UIUC) Syntax Size Notes AdaptiveTDD_IE() { Extended UIUC 4 bits 0x0F (Set to 15 to specifies Adaptive TDD transmission) Length 0x02 (in bytes) UIUC From 6 to 12 (this specifies the profile of the Adaptive TDD burst) Early Start Time = n 2 bits n = 0 => not employing Adaptive TDD n > 0 => Adaptive TDD is employed, starts n 0FDMA symbols earlier than what specified in the US-MAP. Duration} 10 bits In number of MAC slots Ang Chee Wei, Institute for Infocomm Research

Table 1: Format of an AdaptiveTDD IE July 2006 Proposed Text Change We propose to add a new section: “Section 6.8.4.1.2.3 AdaptiveTDD IE” to the current MAC document. In particular, the new Section will be as follows. 6.8.4.1.2.3 AdaptiveTDD IE Each AdaptiveTDD IE is 3 byte long and is specified as in Table 1. The important fields of this extended IE are: Extended UIUC: this 4 bit field is set to 0x0F to indicate an AdaptiveTDD IE. Length: length of data field = 2 bytes. UIUC: this 4 bit field specifies the burst profile of the corresponding AdaptiveTDD IE. Early Start Time: this is a 2-bit field that specifies how early this AdaptiveTDD IE should start, with respect to the global Allocation Start Time specified in the US MAP. Duration: The duration of the AdaptiveTDD IE in OFDMA slots. Syntax Size Notes AdaptiveTDD_IE() {   Extended UIUC 4 bits 0x0F Length 0x02 (in bytes) UIUC From 6 to 12 Early Start Time = n 2 bits n = 0 => not employing Adaptive TDD n > 0 => Adaptive TDD is employed, starts n 0FDMA symbols earlier than what specified in the US-MAP. Duration} 10 bits In number of MAC slots Table 1: Format of an AdaptiveTDD IE Each AdaptiveTDD IE allocation shall be restricted within its early US portion, i.e., between its Early Start Time and the Allocation Start Time. Each AdaptiveTDD IE allocation shall start at the unused MAC slot that has the lowest subchannel index followed by the lowest symbol index (i.e., subchannel index has higher priority than symbol index). Each AdaptiveTDD IE allocation shall advance in the time domain and shall not overlap with the previous AdaptiveTDD allocations. If the end of the Early US Portion has been reach, the allocation shall continue at the next subchannel at the first symbol, specified by its Early Start Time. Ang Chee Wei, Institute for Infocomm Research

July 2006 Q&A (1) Gerald proposed to use the 2-dimensional allocation approach for all US bursts to support Adaptive TDD. Motivations are: To support Adaptive TDD in an elegant way. To facilitate the use of US burst preambles. I2R’s responses: We agree that the 2-D US allocation will support Adaptive TDD but that will require a redesign of the US mapping. There are certain issues of 2-D allocation that must be considered: Significant extra signaling is required. Need 3 extra bytes per US burst. Higher scheduling complexity at BS. It is much harder to fit all “rectangular” US data regions into a US subframe. There will be unused gaps, which reduce efficiency. For each US burst, when the first symbol is used for preamble, the burst should be as long as possible (in the time domain) to improve efficiency. This is achieved with 1-D allocation. Ang Chee Wei, Institute for Infocomm Research

July 2006 Q&A (2) Gerald questioned the use of pilots for channel estimation in early OFDMA symbols gained by Adaptive TDD, especially when the burst is short. Gerald also stated that for short burst, using preamble is better to acquire channel state information. I2R’s responses: Using the method proposed by Li et al, as long as the number of pilots is greater than the number of time domain taps of the channel responses, we will be able to estimate the time domain channel responses, then convert them to the frequency domain (in all subcarriers). Y. Li et al, Channel estimation for OFDM systems with transmitter diversity in mobile wireless channels, IEEE JSAC, vol.17, No.3, pp.461-471, March 1999. For short US bursts, using preamble is not efficient. For example, if a short burst occupies 3 symbols, then 1/3 of the bandwidth is used for preamble. Ang Chee Wei, Institute for Infocomm Research

July 2006 References [1] IEEE 802.22 Wireless RAN, Functional Requirements for the 802.22 WRAN Standard, IEEE 802.22-05/0007r46, October 2005. [2] Y.-C. Liang et al, System description and operation principles for IEEE 802.22 WRANs, Document Number: 22-05-0093-00-0000_I2R_PHY_Proposal.doc, November 2005, Vancouver, Canada. [3] “IEEE P802.22TM/D0.1 – Draft Standard for Wireless Regional Area Networks Part 22: Cognitive Wireless RAN Medium Access Control (MAC) and Physical Layer (PHY) specifications”, May 2006. Ang Chee Wei, Institute for Infocomm Research