1. Some Solutions on Comments Submitted by Soo-Young Chang
Month Year
doc.: IEEE yy/xxxxr0
November 2007
Some Solutions on Comments Submitted by Soo-Young Chang
IEEE P Wireless RANs Date:
Authors:
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Soo-Young Chang, Huawei Technologies
John Doe, Some Company

2. Month Year
doc.: IEEE yy/xxxxr0
November 2007
Abstract
The author submitted comments for the second round TG1 letter ballot which was closed on Nov. 8, 2007.
In this document, solutions for some of comments are proposed.
Soo-Young Chang, Huawei Technologies
John Doe, Some Company

3. COMMENT #400 (3) 5.5 Page 13 line 29 November 2007
Soo-Young Chang, Huawei Technologies

4. November 2007
COMMENT #400 (3)
Reserved bits in a synch burst can be used to judge if a protecting device is in the initialization stage or not.
It helps fast recognition of this stage by other protecting devices when they enter the network without waiting for 10 seconds since every synch burst carries this information.
Soo-Young Chang, Huawei Technologies

5. November 2007
SUGGESTED REMEDY
Two reserved bits of a synch burst are set to '00' if this protecting device is in the initialization stage. Otherwise, they are set to other values which can be reserved for future use.
Only one fourth of information of these two bits is utilized for this purpose. It means the rest of three fourth of information still can be used for future use.
Soo-Young Chang, Huawei Technologies

6. COMMENT #402 (5) 6.2.1.2 Page 19 line 51 November 2007
Soo-Young Chang, Huawei Technologies

7. Month Year
doc.: IEEE yy/xxxxr0
November 2007
COMMENT #402 (5)
If PD-DATA.request primitive is issued and the PHY fails to transmit a beacon frame, in the next superframe, no signal can be transmitted. It means that during this superframe, the WRAN can not detect any beacon signals and may judge that there is no incumbent device operated.
It may result that the WRAN judges there is no 22.1 beaconing devices in the channel.
Soo-Young Chang, Huawei Technologies
John Doe, Some Company

8. Month Year
doc.: IEEE yy/xxxxr0
November 2007
SUGGESTED REMEDY
After the PPD monitors the first slot of the superframe,
Method 1
If no signal (or a synch burst or a synch word) is detected, it sends its own beacon frame right after this slot.
Method 2
If no signal (or a synch burst or a synch word) is detected in this first slot, for the remaining part of the superframe (from the third slot), the PHY of the PPD sends synch bursts continuously with proper index information and all zeros for the beacon logical channel.
In the second slot, switching from Rx to Tx will be done.
Soo-Young Chang, Huawei Technologies
John Doe, Some Company

9. COMMENT #407 (10) 6.7.2.1 Page 33 line 4 November 2007
Soo-Young Chang, Huawei Technologies

10. November 2007
COMMENT #407 (10)
For error control coding of the index field of the synch burst, a (15, 7) linear block code is used in the current draft. However, index information needs only 5 bits. More efficient code can be applied.
Total code length for the index can be up to 17 bits if two reserved bits are considered. However, to minimize the modification of current design, code length of the index can be less than 17 bits.
Soo-Young Chang, Huawei Technologies

11. November 2007
SUGGESTED REMEDY
A (16, 5) Hadamad code is a possible candidate for more efficient coding. This code has Hamming distance of 8 while (15, 7) linear code has this distance of 5.
(15, 7) linear code: detection of 4 errors, correction of 2 errors
(16.5) Hadamad code: detection of 7 errors, correction of 3 errors.
Other codes can be considered for better performance.
Soo-Young Chang, Huawei Technologies

12. November 2007
COMMENTS #413 AND 414 (16 AND 17)
7.4.3
Page 64 line 5 and page 65 line 47
Soo-Young Chang, Huawei Technologies

13. November 2007
COMMENT #413 (16)
If two or more SPDs send the same RTS codeword and they will be allowed to send their beacon frames, these beacon frames will be collided.
Also in the event that an SPD's RTS (request-to-send-a-beacon-frame) was denied, the re-try procedure will be initiated. For this re-try procedure, if each SPD has different back-off value from those of other SPDs, in the next round of re-try, it can send its beacon frame successfully without another collision.
Therefore a scheme to determine back-off values needs to be devised such that each SPD has a different value.
Soo-Young Chang, Huawei Technologies

14. November 2007
SUGGESTED REMEDY (1)
A scheme by which a different back-off value can be assigned to each SPD to avoid this collision is needed. In the document, _Proposal_on_Perfect_Backoff_Scheme, three schemes are being proposed. With these schemes each SPD keeps its own back-off value.
This value can be used for the following cases: (1) when it tries to be a new PPD in the initialization stage specified in 7.4.5, (2) when it tried to be a new PPD for the case that both the PPD and NPD quit their transmission without notice simultaneously, (3) for re-try procedure, and (4) all other cases that needs random back-off numbers.
Soo-Young Chang, Huawei Technologies

15. November 2007
SUGGESTED REMEDY (2)
Among these schemes, the most efficient and simplest scheme is that a unique number for back-off is assigned to each SPD which corresponds to the subchannel number in the TV channel.
Each SPD has a back-off value, l, corresponding to its subchannel number in the subchannel map. If this SPD covers multiple subchannels, it selects the smallest subchannel number. By using this rule each SPD can have its own back-off value.
Soo-Young Chang, Huawei Technologies

16. November 2007
COMMENT #414 (17)
During the initialization stage, each protecting device can not be synchronized with other protecting devices if there is no PPD. 
Therefore if each protecting device searches the channel for a period of (5 + m) superframe periods, it has a chance to collide with other protecting device because no frame synch is achieved.
Soo-Young Chang, Huawei Technologies

17. Synchronized with the PPD
November 2007
SUGGESTED REMEDY (1)
Case 1: A PPD already existed before a device enters
(5+m) rule applied: no collision
Device
start-up
5 +a
beacon
Device A
Device
start-up
5 +a +1
beacon
Device B
Synchronized with the PPD
Soo-Young Chang, Huawei Technologies

18. SUGGESTED REMEDY (2) Case 2: No PPD exists when a device enters
November 2007
SUGGESTED REMEDY (2)
Case 2: No PPD exists when a device enters
(5+m) rule applied: collision possible
Device
start-up
5 +a + 1
beacon
Device A
Device
start-up
5 +a
beacon
Device B
(5+2m) rule applied: no collision
Device
start-up
5 +a + 2
beacon
Device A
Device
start-up
5 +a
beacon
Device B
Soo-Young Chang, Huawei Technologies

19. November 2007
SUGGESTED REMEDY (3)
Change '5 + m' to '5 + 2m'  to avoid possible collisions with other protecting devices and to guarantee its successful transmission to be a new PPD when there is no PPD.
Here m is
the subchannel number in the TV channel for the first retry or
any random number from a set suggested in the current draft for the next retries.
Soo-Young Chang, Huawei Technologies

20. COMMENT #418 (21) 7.4.7.1 Page 71 line 31 November 2007
Soo-Young Chang, Huawei Technologies

21. November 2007
COMMENT #418 (21)
It is required for SPDs to notify the PPD of their activeness by sending its information periodically. Currently periodic transmission of beacon frames is considered. However, it is not necessary to send whole beacon frames to notify that they are still active.
In the PPD, one timer is needed for each SPD. Too many timers are required in the PPD to keep track SPDs to check whether each SPD is active or not. To resolve this problem, we need new schemes.
For an SPD to provide a heartbeat frame, it should be guaranteed that every a fixed number of superframes an SPD should send RTS and this RTS should be accepted. But this decision on this acceptance is made by the PPD. It means that it can not be guaranteed that an SPD can send its beacon frame periodically.
Soo-Young Chang, Huawei Technologies

22. November 2007
SUGGESTED REMEDY (1)
Right after an SPD or the NPD sends its beacon frame, the PPD mandatorily sends a beacon frame. It means that right after a beacon frame of an SPD or the NPD, RTS codewords sent in the receive period and ACK or NACK sent in the ANP period are meaningless (i.e., it does not carry any information) because any RTS codewords will be disregarded and a NACK will be sent for the PPD to send its beacon frame in the following superframe.
The Rx and ANP period after a beacon frame from an SPD or the NPD can be used for the notification of an SPD’s activeness.
Soo-Young Chang, Huawei Technologies

23. SUGGESTED REMEDY (2) November 2007
The basic concept is to transmit the subchannel information of an SPD or the NPD for the PPD to be informed periodically in the Rx/ANP period.
One possible way is transmitting its subchannel number periodically using a simple binary number. For example, consider 30 subchannels in a channel. In Rx/ANP period, 30 bits are used to deliver 30 subchannel information. ‘1’ means a subchannel occupied while ‘0’ means a vacant subchannel.
Another way is that one of RTS codewords is transmitted in one of Rx and ANP periods. In the Rx period, 15 codewords are assigned for the first 15 subchannels while in the ANP period, 15 codewords are assigned for the second 15 subchannels.
Every a fixed number of superframes or if it receives a beacon frame with the NPD indication subfield set to ’10”, each SPD or the NPD notifies its activeness by sending the subchannel number or RTS codeword corresponding to its subchannel number.
If the frequency band occupied by a microphone exists in two adjacent subchannels, these two subchannels should be reported at the same time. For this case, only information on lower subchannel can be delivered for this scheme.
Soo-Young Chang, Huawei Technologies

24. mth PPD’s superframe after Superframe n The SPD sends its RTS codeword
November 2007
SUGGESTED REMEDY (2)
Proposed scheme
If it receives a beacon frame with the NPD indication subfield set to ’10’, each SPD or the NPD notifies its activeness by sending the RTS codeword corresponding to its subchannel number in the next mth PPD’s superframe where m is the subchannel number of the SPD or the NPD.
mth PPD’s superframe after Superframe n
Superframe n
PPD frame with
NPD indication 10
Rx/ANP
PPD frame
Rx/ANP
The SPD sends its RTS codeword
To make sure that this codeword is received by the PPD, this procedure can be repeated once again.
Soo-Young Chang, Huawei Technologies

25. COMMENT #419 (22) 7.4.7.3.1 Page 72 line 1 November 2007
Soo-Young Chang, Huawei Technologies

26. November 2007
COMMENT #419 (22)
An MLME-START-BEACON.request primitive was issued with this subfield set to 00 to the MLME of the PPD to ask SPDs to volunteer to become a new NPD. Whenever the information for MPDU is changed, an MLME-START-BEACON.request primitive should be issued by the NHL. Therefore once an SPD has been selected as the NPD by the PPD, the NHL of the PPD will issue one more of this primitive with NPD indication subfield set to 01 in superframe n+2.
Soo-Young Chang, Huawei Technologies

27. November 2007
SUGGESTED REMEDY
The NHL’s decision on selection of an SPD as a new NPD can be notified by using an MLME-START-BEACON.request primitive with NPD indication subfield set to 01. After then if the selected SPD responded to this primitive by sending an NPD codeword, the PPD recognizes that this SPD becomes a new NPD and the MLME of all protecting devices can set their NPDAddress parameter to the address of the selected SPD.
Soo-Young Chang, Huawei Technologies

28. COMMENT #421 (24) 7.4.7.3.4 Page 73 line 1 November 2007
Soo-Young Chang, Huawei Technologies

29. November 2007
COMMENT #421 (24)
When the PPD quits and the NPD does not promote itself as a new PPD for any reason (e.g., the NHL of the NPD may then decide not to promote the device to PPD.), there is no PPD unless an SPD promotes to the PPD. It can be a serious problem for the system because any SPD does not promote if there is the NPD.
Soo-Young Chang, Huawei Technologies

30. SUGGESTED REMEDY This can be solved by applying the following:
November 2007
SUGGESTED REMEDY
This can be solved by applying the following:
An SPD should promote itself as the PPD if it does not hear the PPD for macMaxMissedBeaconsSPD2 (for example, 2*macMaxMissedBeaconsSPD) superframes while it hears the NPD.
In this procedure, macMaxMissedBeaconsSPD2 is greater than any macMaxMissedBeaconsNPD.
Soo-Young Chang, Huawei Technologies

31. COMMENT #422 (25) 7.4.8.1 Page 73 line 48 November 2007
Soo-Young Chang, Huawei Technologies

32. November 2007
COMMENT #422 (25)
If either the NPD or an SPD promotes itself to a new PPD, eventually every SPD should interrupt the PPD to send a beacon frame, ensuring that the PPD has the most current information.
If every SPD tries to interrupt the new PPD after it is detected, there may be a lot of collisions.
Soo-Young Chang, Huawei Technologies

33. November 2007
SUGGESTED REMEDY
The SPD should pick a random number and only try to interrupt the new PPD after that number of superframe time. This would avoid multiple collisions right after a new PPD takes over the control. A scheme to interrupt the PPD by SPDs should be provided such that less collisions or no collision can be achieved.
One possible way is that each SPD waits for a period of a fixed number of PPD’s superframes corresponding to its subchannel number and tries to interrupt the PPD to send its beacon frame. If an SPD fails, it tries to do it again with a random number from a set {0, 1, 2, .. , 15} for this number until it sends its beacon frame.
First new PPD’s superframe
mth new PPD’s superframe
PPD frame
Rx/ANP
PPD frame
Rx/ANP
The SPD sends its RTS codeword
whose subchannel number is m.
Soo-Young Chang, Huawei Technologies

34. November 2007
CONCLUSIONS
In the document, some solution proposals for the comments submitted by the author are addressed.
Comments 3, 5, 10, 16, 17, 21, 22, 24, and 25
Soo-Young Chang, Huawei Technologies

35. November 2007
References
Comments for the second TG1 letter ballot submitted by Soo-Young Chang, Nov. 8, 2007
Soo-Young Chang, Huawei Technologies