1. Summary of I2R’s proposals
July 2006
doc.: IEEE yy/xxxxr0
July 2006
Summary of I2R’s proposals
IEEE P Wireless RANs Date:
Authors:
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Ang Chee Wei, Institute for Infocomm Research
Ang Chee Wei, Institute for Infocomm Research

2. July 2006
doc.: IEEE 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

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

4. 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

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

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

7. 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

8. 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

9. 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

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

11. 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

12. Conventional TDD All CPEs are aligned with the farthest one. July 2006
doc.: IEEE 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

13. 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

14. 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

15. 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

16. 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

17. 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

18. Table 1: Format of an AdaptiveTDD IE
July 2006
Proposed Text Change
We propose to add a new section: “Section AdaptiveTDD IE” to the current MAC document. In particular, the new Section will be as follows.
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

19. 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

20. 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 , 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

21. July 2006
References
[1] IEEE Wireless RAN, Functional Requirements for the WRAN Standard, IEEE /0007r46, October 2005.
[2] Y.-C. Liang et al, System description and operation principles for IEEE WRANs, Document Number: _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