1. Enhancement of RTS and ACK Design for the IEEE 802.22.1 Standard
September 2006
doc.: IEEE /0128r1
Jan 2007
Enhancement of RTS and ACK Design for the IEEE Standard
IEEE P Wireless RANs Date:
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
Jan 2007
Abstract
We propose an enhanced RTS and ACK design for the IEEE Enhanced Detection of Part 74 Devices standard.
Ed Callaway, Motorola

3. Background IEEE 802.22.1 Standard
September 2006
doc.: IEEE /0128r1
Jan 2007
Background
IEEE Standard
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 for signalling the presence of low-power licensed devices that 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
Jan 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
Jan 2007
Baseline Receive Period and RTS burst
A 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 burs
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
Jan 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. PPD shall transmit a NACK and continue
September 2006
doc.: IEEE /0128r1
Jan 2007
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. Problems When a collision happens, PPD sometime can’t
September 2006
doc.: IEEE /0128r1
Jan 2007
Problems
When a collision happens, PPD sometime can’t
distinguish different SPDs effectively ;
A waste of the superframe and may more interference to the protected devices .
Ed Callaway, Motorola

9. Discussion with Motorola
Jan 2007
Discussion with Motorola
Question:
How does the PPD distinguish different SPDs which means how does the PPD sense a collision happens?
Answer:The PPD will not know about the collision .

10. Proposed Method Analysis:
Jan 2007
Proposed Method
Analysis:
In order to distinguish different SPDs effectively when a collision happens, we suggest use the RTS code enough. If the element number of RTS collection is n and the element number of PNs collection is n, then the probability that PPD can’t distinguish two different SPDs is 1/(n*m).
In order to use next superframe, when a collision happens, PPD need send a ACK including the ‘ID’.

11. It is assumed that PN sequences is following
September 2006
doc.: IEEE /0128r1
Jan 2007
Proposed Method
It is assumed that PN sequences is following
Index
PN Values 1 2 3 4 5 6 7 8
Ed Callaway, Motorola

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

13. Proposed Method Comparison Table Jan 2007 September 2006
doc.: IEEE /0128r1
Jan 2007
Proposed Method
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

14. Proposed Method Comparison Table Jan 2007 September 2006
doc.: IEEE /0128r1
Jan 2007
Proposed Method
Comparison Table
SPD Identifier
PN Values
RTS Values 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
Ed Callaway, Motorola

15. Proposed Method Perform Process:
Jan 2007
Proposed Method
Perform Process:
SPD wants to send beacon next superframe and send RTS in present superframe Rx Period. Before sends RTS, it should select a RTS and a PN from the  orthogonal circular RTS collection and PN collection, then sends the RTS;
If PPD receives several RTSs from SPDs, PPD should select one of them to send data next superframe, and sends corresponding ACK including a SPD Identifier corresponding to the selected PN and RTS; If PPD doesn’t receive a RTS, then sends NACK;
After receiving 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 next superframe; otherwise, it doesn’t send and before next RTS it should backoff a random time ,then continue the process

16. Jan 2007
Proposed Method
In order to support this function, we need 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 binary aequence of ID 3, the sequence
in ACK is 1
NACK format is shown following 1

17. Map between SPD and SPD Identifier
Jan 2007
Proposed Method
Map between SPD and SPD Identifier …
SPD Identifier
ACK structure
(Bits: 0,1,2…5) 1
000001 2
000010 3
000011 4
000100 5
000101 6
000110 7
000111 8
001000 9
001001 10
001010 11
001011 12
001100 13
001101 14
001110 15
001111 16
010000 17
010001 18
010010 19
010011 20
010100 21
010101 22
010110 23
010111 24
011000 25
011001 26
011010 27
011011 28
011100 29
011101 30
011110 31
011111 32
100000 …

18. Alternative Proposed Method
Jan 2007
Alternative Proposed Method
Updated RTS design (orthogonal circular)
RTS Index
RTS Values 1 2 3 … XX

19. Alternative Proposed Method
Jan 2007
Alternative Proposed Method
Map between RTS identifiers and ANP bits
RTS Identifier
ACK structure
(Bits: 0,1,2…5) 1
000001 2
000010 3
000011 4
000100 5
000101 6
000110 7
000111 8
001000 9
001001 10
001010 11
001011 12
001100 13
001101 14
001110 15
001111 16
010000 17
010001 18
010010 19
010011 20
010100 21
010101 22
010110 23
010111 24
011000 25
011001 26
011010 27
011011 28
011100 29
011101 30
011110 31
011111 32
100000 …

20. Jan 2007
Simulation

21. Summary Enhancement for RTS code and ACK Transmission is proposed;
Jan 2007
Summary
Enhancement for RTS code and ACK Transmission is proposed;
This method can help PPD distinguish different SPDs effectively;
This method can help utilize superframe more effectively;
This method is very simple .