1. Enhancement of RTS and ACK Design for the IEEE 802.22.1 Standard
September 2006
doc.: IEEE /0128r1
January 2007
Enhancement of RTS and ACK Design for the IEEE Standard
IEEE P Wireless RANs Date:
Authors
Name
Company
Address
Phone
Linjun Lv
Huawei Technologies
Shenzhen, China
Zhou Wu
Mingwei Jie
Zhixue Shi
Soo-Young Chang
Davis, CA, U.S.
Jianwei Zhang
Shanghai, China
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Ed Callaway, Motorola

2. September 2006
doc.: IEEE /0128r1
January 2007
Abstract
We propose an enhanced RTS and ACK design for the IEEE Enhanced Detection of Part 74 Devices standard.
Ed Callaway, Motorola

3. September 2006
doc.: IEEE /0128r1
January 2007
Background
IEEE Standard is under development to enhance harmful interference protection for low-power licensed as secondary devices operating in TV Broadcast Bands (under Title 47 of the Code of Federal Regulations (CFR) in the USA and equivalent devices in other regulatory domains).
Target technologies considered for signalling the presence of low-power licensed devices are different from the sensing and cognitive radio technologies that are being considered elsewhere in
Motorola’s proposal has been selected as baseline in Sept meeting.
Ed Callaway, Motorola

4. Baseline Superframe Format
September 2006
doc.: IEEE /0128r1
January 2007
Baseline Superframe Format
BURSTS
Sync N
N-1 1
BEACON PSDU …
ANP
Frame period
BEACON
Rx period
Ed Callaway, Motorola

5. Baseline Receive Period and RTS Burst
September 2006
doc.: IEEE /0128r1
January 2007
Baseline Receive Period and RTS Burst
An SPD may send an RTS burst in the receive period, in order to send its beacon.
If the SPD receives an ACK from the PPD during the ANP, the SPD shall transmit its beacon frame during the following superframe.
If the SPD received a NACK during the ANP, it shall not transmit a beacon frame, and
Bits: 0-3
4-15
RTS codeword
Sync
SHR
PHY payload
Format of the RTS burst
Bits: 0 1 2 3 4 5 6 7 8 9 10 11
Format of the RTS codeword field
Ed Callaway, Motorola

6. September 2006
doc.: IEEE /0128r1
January 2007
Baseline ANP Burst
The ANP burst is used by the PPD to indicate whether or not it has received a request to transmit (i.e., an RTS burst) from an SPD in the receive period immediately preceding the ANP. If it has received a request, the PPD shall transmit an ACK. Note that the received request must be error-free in order to transmit an ACK. Otherwise, it shall transmit a NACK.
Bits: 0 1 2 3
ACK
NACK
Transmission
Ed Callaway, Motorola

7. When RTS Bursts Collided
September 2006
doc.: IEEE /0128r1
January 2007
When RTS Bursts Collided
PPD shall transmit a NACK and continue.
SPD shall use a random backoff time before requesting to send another RTS burst and continue.
Ed Callaway, Motorola

8. September 2006
doc.: IEEE /0128r1
January 2007
Problems to Be Solved
When a collision happens, PPD usually can not distinguish different SPDs effectively ;
It may cause waste of the superframes and more interference to the protected devices .
Ed Callaway, Motorola

9. Proposed Method (1) Analysis:
January 2007
Proposed Method (1)
Analysis:
In order to distinguish different SPDs effectively when a collision happens, we suggest use the RTS code enough. If the number of elements of RTS collection is n and the number of elements of PN collection is n, then the probability that PPD cannot distinguish two different SPDs is 1/(n*m).
In order to use next superframe, when a collision happens, the PPD needs to send an ACK including the ‘ID’.

10. It is assumed that PN sequences are as following:
September 2006
doc.: IEEE /0128r1
January 2007
Proposed Method (2)
It is assumed that PN sequences are as following:
Index
PN Value 1 2 3 4 5 6 7 8
Ed Callaway, Motorola

11. Our selected RTS (orthogonal circular)
September 2006
doc.: IEEE /0128r1
January 2007
Proposed Method (3)
Our selected RTS (orthogonal circular)
Index
RTS Values 1 2 3 4
Ed Callaway, Motorola

12. Proposed Method (4) Comparison Table January 2007 September 2006
doc.: IEEE /0128r1
January 2007
Proposed Method (4)
Comparison Table
SPD Identifier
PN Values
RTS Values 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Ed Callaway, Motorola

13. Comparison Table (cont’d)
September 2006
doc.: IEEE /0128r1
January 2007
Proposed Method (5)
Comparison Table (cont’d)
SPD Identifier
PN Values
RTS Values 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
Ed Callaway, Motorola

14. Proposed Method (6) Perform the following Procedure:
January 2007
Proposed Method (6)
Perform the following Procedure:
SPD wants to send beacon in next superframe and send RTS in present superframe Rx Period. Before it sends RTS, it should select an RTS and a PN from the  orthogonal circular RTS collection and PN collection. After then it sends the RTS;
If PPD receives several RTSs from SPDs, PPD should select one of them to send data in next superframe, and sends corresponding ACK including an SPD Identifier corresponding to the selected PN and RTS; if PPD does not receive an RTS, then it sends NACK;
After receiving an ACK, SPD should decode it and collate its PN and RTS which it has sent before. Then if the PN and the RTS are equal to the ACK in the comparison table, it can send data in next superframe; otherwise, it does not send and before next RTS it should back off a random time. Then it continues the process.

15. Proposed Method (7) January 2007
In order to support this procedure, we need to change the format of ACK.
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
high
low
For the binary sequence of the SPD Identifier, high bit is corresponding to
the same high bit. For example, for a binary sequence of ID 3, the sequence
in ACK is 1
NACK format is shown following 1

16. Summary Enhancement for RTS code and ACK transmission is proposed;
January 2007
Summary
Enhancement for RTS code and ACK transmission is proposed;
This method can help PPD to distinguish different SPDs effectively;
This method can help to utilize superframe more effectively;
This method is very simple to implement.