Re: [STDS-802-16] [802.16n][DC] Discussion on Usages and Frame Structure for DC - CONSOLIDATED
Hi, Eldad, Sungcheol and all.
I have some comments on the "independent modes" in Topic B.
Please see my comments in line.
Regards.
Haiguang
-----Original Message-----
From: Zeira, Eldad [mailto:Eldad.Zeira@INTERDIGITAL.COM]
Sent: Tue 4/12/2011 5:14 AM
To: STDS-802-16@LISTSERV.IEEE.ORG
Subject: Re: [STDS-802-16] [802.16n][DC] Discussion on Usages and Frame Structure for DC - CONSOLIDATED
Hi Sungcheol, please see below (incl. some questions for clarification)
I think this was a good exchange of opinions.
Eldad
Office +1 631 622 4134
Mobile +1 631 428 4052
Based in NY area
From: Chang, Sungcheol [mailto:scchang@etri.re.kr]
Sent: Monday, April 11, 2011 5:23 AM
To: STDS-802-16@LISTSERV.IEEE.ORG
Subject: Re: [STDS-802-16] [802.16n][DC] Discussion on Usages and Frame Structure for DC - CONSOLIDATED
Hi DC RG participants and all,
Please see my comments in the consolidate text.
Note) Please see my second answer in Topic B.
I provide new mode categorization to cover all the previous discussions.
Best regards,
Sungcheol Chang, Ph.D.
Mobile Access Technology Research Team, ETRI
From: Zeira, Eldad [mailto:Eldad.Zeira@INTERDIGITAL.COM]
Sent: Monday, April 11, 2011 12:04 AM
To: STDS-802-16@LISTSERV.IEEE.ORG
Subject: Re: [STDS-802-16] [802.16n][DC] Discussion on Usages and Frame Structure for DC - CONSOLIDATED
Hi Anh Tuan, All
Thanks for the quick response, please see my comments below at the bottom of each topic.
(BTW Anh Tuan, you mentioned your comments in blue but it didn't come through the mail, perhaps because you have used plain text)
Eldad
Office +1 631 622 4134
Mobile +1 631 428 4052
Based in NY area
-----Original Message-----
From: Hoang Anh Tuan [mailto:athoang@I2R.A-STAR.EDU.SG]
Sent: Saturday, April 09, 2011 10:33 AM
To: STDS-802-16@LISTSERV.IEEE.ORG
Subject: Re: [STDS-802-16] [802.16n][DC] Discussion on Usages and Frame Structure for DC
Dear Sungcheol and all,
Please see my responses (blue) in the consolidated text (thanks Eldad for this useful compilation).
Best regards,
Anh Tuan
Regarding use cases:
<<<<<<<<<<<<<<<<<< Topic A
Sungcheol:
Agrees with 1) Infrastructure nodes are absent and 2) One HR-MS is associated with an infrastructure node and one or more other HR-MSs are out of coverage of an infrastructure node.
Does not agree with: The use case of both two HR-MS under an infrastructure node - 802.16n is for reliability enhancements, questions if this use case is for that.
Anh Tuan:
The direct link, in certain cases, provides higher rates etc.
Eldad:
I would agree with Anh Tuan. Stated differently, if 2 HR-MS are at the edge of the cell than their supportable data rate with the BS can be too low. For voice this isn't an issue as the voice data rate is similar to the data rate of the associated signaling for MS control. On the other hand if the mission requires e.g. video than these 2 HR-MS may not be able to maintain video link with the HR-BS - but can with each other. Then it is a reliability issue. I also agree that MS-MS communications under a BS is simpler than HR-MS forwarding.
Sungcheol:
If just communication is needed between two HR-MSs, then we can use multi-mode operation of HR-MS as relay function instead of defining new specification. My preference is the reuse and modification of existing specification. If one HR-MS changes its role as relay and the HR-MS relays or terminates packets with the other HR-MS, it's nature is direct communication. I don't object the motivation of communication between HR-MS under coverage, but updating existing 16 specifications has a priority to defining new specification. Is it impossible to achieve two HR-MS communication under BS coverage with HR-MS multi-mode operation as relay?
Anh Tuan:
From your reply, I think we have already agreed on two important points:
- There is no objection for direct/forwarding communications between HR-MSs under coverage (and one of the purposes is to enhance reliability at cell edge, as explained by Eldad).
- For 16n, reusing/updating of current 16e/m features should take priority over introducing totally new specifications.
With the above two agreeable points, we can proceed to evaluate different approaches and probably get more consensus. Let us remember that we are discussing the use cases here, and not the solutions. So we should first agree on the usefulness, then move on to discuss the solutions (e.g., frame structure).
Eldad:
That HR-MS direct and forwarding communications (with and without infrastructure) is required has been discussed extensively during the SRD phase which we have all agreed to. In the SRD it exists as a distinct requirement from HR-MS role change to e.g. HR-BS. This has also been discussed extensively. The reason for it appearing as a separate requirement is that, as we decided, when HR-MS changes its role to HR-RS it is an HR-RS with all the HR-RS functionality (although possibly with reduced capability). We didn't feel that a forwarding HR-MS, for example, need ALL the functionality of an HR-RS (although of course it needs some).
Having said that I agree with the principle that 16e/16n baselines should be reused as much as possible.
Sungcheol:
We need to clarify scope of e-mail discussion. Under 16n SRD document, we discuss the use case of direct communication between HR-MSs (not 16n use case). If a forwarding MS has a subset of HR-RS functions like 16j transparent-mode relay, is it classified into use case of direct communication? It seems that the forwarding MS should be classified into enhancement or modification of HR-RS because 16j specification describes already that kind of relay function. I'd like to differentiate direct communication with modification of HR-RS. In principle direct communication is a peer-to-peer communication. Using this peer-to-peer communication, a forwarding function can be an additional function on it (my view). If we want to add 16j-like transparent mode relaying function as a forwarding function, it should come from modification of relay specifications, 16j or 16m relay definitions. I think that two approaches are on different basis technologies: one is on peer-to-peer communication!
and the other is on relay function. How can we clarify this?
Eldad:
If we agree that 802.16 baseline should be reused as much as possible then it follows that HR-MS Forwarding re-uses e.g. 802.16m relay designs. That doesn't, in my opinion, mean that we make a forwarding HR-MS into an HR-RS, would you agree?
>>>>>>>>>>>>>>>>>
<<<<<<<<<<<<<<<<<< Topic B
Eldad:
* Modes for HR-MS direct communication
- Both HR-MSs are associated with an infrastructure node.
- Infrastructure nodes are absent.
* Modes for HR-MS local forwarding
- One HR-MS is associated with an infrastructure node and one or more other HR-MSs are out of coverage of an infrastructure node.
Anh Tuan:
1) We can have an HR-MS that is outside-of-coverage but can still be associated with an infrastructure node (through the help of a forwarding HR-MS). So for the 1st mode of HR-MS direct communications, When we say "Both HR-MSs are associated with an infrastructure node.", do we mean "association" or "coverage"?
2) For HR-MS forwarding to network (we should not use "HR-MS local forwarding" as 16n SRD uses "local forwarding" to refer to a different scenario), I would like to add the 3rd mode of "Both HR-MSs are within the coverage of an infrastructure node". This can be beneficial when HR-MSs are power-limited
Eldad (Answer):
- Agree with the terminology "forwarding to network"
- I agree to add to HR-MS Forwarding the case where both HR-MS are in coverage (point 2). Actually this is the same argument I used for MS-MS communications as a reliability enhancement.
- For MS-MS direct communications (point 1) I'm not so sure it is needed. HR-MS that are of coverage of the HR-BS will likely be at cell edge. They will have few neighbor HR-MS. They will have even fewer HR-MS they will need peer to peer connection to. Therefore I think this isn't an important case. Therefore I would disagree with this case.
Anh Tuan:
I am not quite clear about your last point, can you please elaborate?
Eldad:
I'll try. The difference between forwarding and peer to peer communications is that the former is non-specific, the latter is specific. HR-MS forwarding is mostly needed for an HR-MS that is in a coverage hole (indoors, basement, etc.). It will have very few other HR-MS within range, any of those could potentially help to forward its data. On the other hand if we assume that peers are spread through the cell then the chances that one of those would also be a peer (to directly communicate with) are smaller.
Sungcheol:
Refer to the third answer to Topic A.
Sungcheol:
I'd like to point out MS mobility. A HR-MS can be moved into under BS coverage because HR-MS can move freely. So if we define two modes depending on location it will give participants misunderstanding of this modes.
So I'd like to classify them into three modes:
1) Transparent mode (with/under BS control)
- Both HR-MSs are associated with HR-BS and HR-BS controls communication between HR-MSs including resource allocation. Its nature is on centralized control scheme.
- This category contains one use cases that we described in the previous discussion.
* When both HR-MSs are within the coverage of an infrastructure node
2) Forwarding mode (with/under BS control)
- One HR-MS within the coverage is associated with HR-BS and forwards data and control packets into the other MS. The other MS may be within the coverage or out of the coverage.
- This category contains two use cases that we described in the previous discussion.
* When both HR-MSs are within the coverage of an infrastructure node
* When only one HR-MS is within the coverage
3) Independent mode (without BS control)
- Communication between HR-MSs occurs independent of BS control. Resource allocation is done in distributed way. (But it still keeps minimum synchronization to infrastructure frame if possible)
- This category contains three use cases that we described in the previous discussion.
* When both HR-MSs are within the coverage of an infrastructure node
* When only one HR-MS is within the coverage
* When both HR-MSs are in absent of infrastructure node.
I thinks that all the proposals in previous discussion are covered by this categorization. And practically it's hard to switch resource control methods when a MS change its resource allocation algorithm according to detection of their radio environments. When we consider that HR-MS moves across the boundary of BS coverage freely, it's not proper that three modes are dependent on MS's location. With this mode definition we can develop more practical direct communication operation.
For forwarding mode, there are two implementations. One is an extension of transparent mode. The other is an extension of independent mode. I found that Anh Tuan and Eldad prefer the extension of transparent mode. But my preference is the extension of independent mode. If we accept two approaches we can step next. But if we select one of two approaches, we need selection procedure.
Eldad:
I would agree with modes 1 & 2 although I would like to rename "transparent mode" à "BS controlled peer to peer mode" and "forwarding mode" à " BS controlled forwarding mode".
I have serious concerns with mode 3 "independent mode" within coverage of BS. This type of uncontrolled operation would cause serious interference issues with legacy (non-HR) BS. As I see it, if an HR-MS is within coverage of an HR-BS, HR-RS or another HR-MS that is within coverage of one and can act as forwarding HR-MS, it must attach itself to it. This is required for the following reasons:
- Backward compatibility is an agreed SRD requirement.
- Licensed spectrum is owned by operators who always require to maintain tight control of it. This is the only way in which they can guarantee service.
- In some regulatory environments mobile units aren't allowed to transmit unless authorized by a fixed controller (e.g. TVWS)
- In normal cellular operation an MS always tries to attach itself to the best BS it can find which as we know leads to optimal operation. The recent introduction of closed groups for Femto cells is known to create interference problems, not all of them have been solved by 802.16m. Now imagine same issues but with many more interference sources
All of the above tells me that independent mode within coverage of a BS cannot be the only mode for 802.16n. It can perhaps be allowed in specific spectrum. Whether or not it is worth developing as a secondary mode is a matter we should discuss.
Because of the above, forwarding mode under BS cannot be an extension of independent mode.
[ Haiguang Wang :]
First of all, I agreed with Eldad that serious interference may be caused in the
"independent mode" within coverage of BS. And also, in licensed band, such behavior
usually is not allowed by spectrum owner.
Second, distributed scheduling may cause significant overhead due to long symbol
duration. In my view, it is quite complex to define a distributed scheduling
mechanism under the current 802.16 framework. Significant PHY change may be required.
>>>>>>>>>>>>>>>>>
Regarding frame structure:
<<<<<<<<<<<<<<<<<< Topic C
Question-1) Are 2 HR-MS in the same cell allowed to transmit on the same resources (assuming that they are far enough)?
Anh Tuan:
This resource reuse should be encouraged, as long as mechanisms are provided to mitigate interference among HR-MS direct/forwarding transmissions. For such interference-mitigating mechanisms to work, we need neighbor discovery schemes to determine the distances between pairs of nodes.
Sungcheol:
I think we don't allow that. If it is guaranteed that two HR-MSs are far enough, two HR-MSs may transmit on the same resources. However, how can it be guaranteed? Interference mitigation has been a challenging research topic. But I don't agree that 16n specification adapts interference management approaches because its complexity. (Do we consider direct communication among HR-MSs in the same cell? I am negative)
Anh Tuan:
For the spatial reuse of resource allocated to HR-MS direct transmissions, I am open to the possibility. However, as mentioned in previous email, I share Sungcheol's concern of interference mitigation. In fact, Eldad has also previously discussed this interference concern. To me, even without reusing allocated resource, controlling interference between HR-MSs direct communications and legacy transmissions (between HR-BS and HR-MS) is tough enough. Having said that, I do not see how reserving a fixed resource for HR-MS direct transmissions would better minimize interference, compared to the approach when BS allocates resource dynamically, but without two transmissions sharing (re-using) the same logical resource units.
Eldad
I think that allowing the HR-BS to allocate MS-MS resources dynamically, in combination with good HR-MS discovery and spatial separation, should allow the HR-BS to determine the correct resources. We do not specify that the HR-BS must share resources but on the other hand we do not prevent it from doing so. In my opinion, MS-MS connections that aren't allowed to share resources will not be very efficient.
Question-2): Is the HR-BS allowed to re-use the same resources for its own DL transmissions or the UL transmissions of one of its HR-MS (assuming that the HR-MS is close enough to the HR-BS)?
Anh Tuan:
Similar to answer to question 1 with the note that interference mitigation will depend on whether HR-MS direct/forwarding transmissions are scheduled in DL or UL area of each frame.
Sungcheol:
Generally I think that resource used for infrastructure communication is exclusive to resource for direct communication. From this agreement, we can extend resource usages if its algorithm is simple. Exclusive resource allocation guarantees that interference each other may be controlled easily.
Eldad:
I think the answer is very similar to question-1. While the specific interference mechanism depends if transmission takes place in UL or DL or both, good interference control mechanisms as indicated above should solve both.
Question-3): Are these resources fixed for all cells?
Anh Tuan:
I believe that HR-MS direct communications and forwarding to network are opportunistic in nature. Therefore, resources should be dynamically allocated across space (cells), time/frequency (frames).
Sungcheol:
We need fixed resources of direct communications for all cells if HR-MS may be at several radio environment cases including under infrastructure node, in absent of infrastructure not, and in the middle of infra-structure nodes. It is recommended that this fixed resource shall be as small as possible because the resource is not be used by infrastructure node for interference avoidance.
Eldad:
I would support Anh Tuan.
Sungcheol:
We need to separate DC specific resources into two. One is for the usage case of direct communication that two HR-BSs are under the coverage of infrastructure node. Dynamic resource allocation can be acceptable for this use case only. The other is for two usage cases that 1) one HR-MS under infrastructure node coverage and the other HR-MS in absent of infrastructure node 2) two HR-MSs in absent of infrastructure node. When we consider HR-MS in absent of HR-BS, dynamic resources allocation information is carried on the fixed resource of direct communication. It's why I propose two-step resource allocation.
Anh Tuan:
I would like to promote the following general approach for allocating resource dynamically to HR-MS direct/forwarding transmissions:
- When both HR-MSs are within the coverage of an infrastructure node, say HR-BS, HR-BS can dynamically schedule resource using A-MAP and/or other DL control messages.
- When only one HR-MS is within the coverage, the resource can still be scheduled by HR-BS through A-MAP and control messages, and the inside-of-coverage HR-MS shall relay the scheduling information to the out-of-coverage HR-MS.
- When there is no infrastructure node, one HR-MS shall be elected as network coordinator to fulfill the scheduling tasks of an infrastructure node.
The above approach, I believe, preserves the basic resource-allocating principles of 16e/m.
Eldad:
I also would like to partition the use cases for resource allocations but I think that both HR-MS under HR-BS is similar to forwarding HR-MS (only one under HR-BS). The case of no HR-BS is different.
Because of that, I tend to agree with Anh Tuan that resource allocation for HR-MS forwarding and HR-MS DC under HR-BS is dynamic (e.g. using A-MAP although we can decide that later). For no infrastructure case I agree that one of the HR-MS takes control.
I'm not sure yet what is the nature of an coordinator. It looks to me very similar to an HR-BS.
Sungcheol:
My approach is a distributed way. If we find a distributed solution of coordination among the HR-MS, there is no coordinator similar to an HR-BS. As you know, 802.11 terminals are synchronized in a distributed approach. We can make the modification of the distributed synchronization algorithm.
Eldad: I wouldn't want to use 802.11 as a model.
Question-4): Can they change over time?
Anh Tuan:
Similar to answer to question-3.
Sungcheol:
It depends on design. The fixed resource of direct communication is static and limits resources for infrastructure communications. To solve this problem, the fixed resource is reserved at minimum and additional resource information can broadcast on the fixed resource. Its additional resource may be quasi-static and cell specific if possible. How about two step resource of direct communication?
Eldad:
I would support Anh Tuan. I'm not sure what a two-step resource allocation means but does it lengthens latency?
Sungcheol:
No. It does not length latency. Control information including resource allocation shall be carried on common dedicated resource. It's all. Common or dynamic resource can be used for carrying data packets among HR-MSs because the HR-MSs have exchanged resource allocation information each other using control packets on the common dedicated resource..
Eldad:
Thanks, Sungcheol, now I think I understand you. It seems we all agree to dynamic resource allocation. So if, for example, we use A-MAP to carry the assignment, then the only question that remains is that whether A-MAP location, length etc. are A) fixed for all cells and for all times or B) can vary cell to cell and time to time and are SOMEHOW signaled (broadcast or unicast) to HR-MS. Is that correct?
Sungcheol:
Generally yes. In my approach, common resource is a fixed resource independent of cells while dynamic resources can be allocated cell by cell. We need more discussion about the form of control information.
But, Please refer to my second answer to Topic B at first.
>>>>>>>>>>>>>>>>>>>
<<<<<<<<<<<<<<<<<< Topic D
Sungcheol:
For frame structure of direct communication, we need discuss types of DC specific resources, TDM and FDM separations. TDM means that its bandwidth of DC specific resources is wideband. FDM means that narrowband resources can be reserved for DC specific resources. I prefer that the DC resources shall be allocated as narrowband because of its coverage enhancement. So I have a preference to FDM for DC specific resource separation. Is there any reason that DC specific resource shall be FDM in 16n specification based on 16m specification? (I understand that TDM is a way of DC specific resource allocation for 16e specification because diversity zone and AMC zone are exclusive in time domain)
Anh Tuan:
Regarding TDM vs FDM, current approach in 16m is based on FDM (within each subframe). So FDM to me is a natural approach. However, I propose that we stick to the 16m subframe boundaries when doing resource allocation for HR-MS direct comm/forwarding. Do we have a strong reason/motivation for allocating a narrow band resource spanning several subframes for a HR-MS direct transmissions?
Eldad:
- If you meant FDM per sub-frame I would agree with you, we go FDM. Otherwise it's usually called TDM/FDM.
- If you accept the premise that resources are allocated by the BS then we don't have to decide here whether it's broadband or narrowband.
- 802.16m already has a long-TTI mechanism for added robustness. I'm not sure we need another one.
Sungcheol:
We need to separate discussions into two like my answer to Question-3). For the use case that two HR-BSs are under the coverage of infrastructure node, we need to follows 16m or 16e frame structure as similar as possible. For the other use case, we need to define DC specific frame structure because HR-MSs in absent of HR-BS are not aware of infrastructure frame structure.
Anh Tuan:
I just want to clarify:
-When at least one HR-MS is within the coverage, the frame configuration (and resource allocation) can be forwarded to the other HR-MS.
-In absent of HR-BS, a network coordinator can be elected to distribute a common understanding of frame configuration among a cluster of HR-MSs.
Eldad:
Please see my comments for previous question.
Regarding narrowband operation for 802.16n, I have indicated above that 802.16m already has long-TTI operation. The combination of long TTI with the narrowest allocation allowed today under 802.16m should provide sufficient coverage. I don't see any reason to design new waveforms, pilot placement, etc. to accommodate even narrower bandwidth.
Sungcheol:
There are two reasons that usage of DC specific resource is different from one of infrastructure frame.
1) Two additional channels are introduced for synchronization and initial packet transmission. For synchronization channel, I don't believe that its resource unit is similar to one for traffic transmission. For contention channel, An initial packet is designed as small as possible. When we put large number of contention slots, we reduce contention probability.
2) Coverage limitation. My preference is extending signal coverage for direct communication. When we decide to use the same resource unit, it means that the coverage of direct communication is limited because MS-to-MS channel characteristics are different to BS-to-MS channel ones. But we are now developing resource unit for direct communication with performance evaluation. Currently I don't propose the size of resource unit.
Eldad:
Please let me understand - for 1): The channels for synchronization and initial packet transmission - are they new waveforms? If I understand correctly you prefer smaller frequency domain allocations for random access? Is this for the CDMA code or for the OFDM packet?
________________________________
From: Sungcheol Chang [mailto:scchang@ETRI.RE.KR]
Sent: Sat 4/9/2011 3:35 PM
To: STDS-802-16@LISTSERV.IEEE.ORG
Subject: Re: [STDS-802-16] [802.16n][DC] Discussion on Usages and Frame Structure for DC
Dear Eldad, Anh Tuan, and all
Thanks for your effort to collecting all the opinions.
I add my inline opinion per discussion for consistency.
Best regards,
Sungcheol Chang, Ph.D.
Mobile Access Technology Research Team, ETRI
From: Zeira, Eldad [mailto:Eldad.Zeira@INTERDIGITAL.COM]
Sent: Saturday, April 09, 2011 6:06 AM
To: STDS-802-16@LISTSERV.IEEE.ORG
Subject: Re: [STDS-802-16] [802.16n][DC] Discussion on Usages and Frame Structure for DC
Dear Sungcheol, Anh Tuan, all
To try expedite the discussion I have collected all the opinions I saw so far (including mine). I think it reflects very well the differences between the approaches and will allow us all to form a more informed opinion.
Warning: very long email, but easier to read than multiple threads.
Hope you find it useful.
(I suggest we use HTML as email format, some folks use simple text which doesn't preserve formatting and makes it difficult to read. HTML is platform independent)
Cheers - happy weekend -
Eldad
Regarding use cases:
<<<<<<<<<<<<<<<<<< Topic A
Sungcheol:
Agrees with 1) Infrastructure nodes are absent and 2) One HR-MS is associated with an infrastructure node and one or more other HR-MSs are out of coverage of an infrastructure node.
Does not agree with: The use case of both two HR-MS under an infrastructure node - 802.16n is for reliability enhancements, questions if this use case is for that.
Anh Tuan:
The direct link, in certain cases, provides higher rates etc.
Eldad:
I would agree with Anh Tuan. Stated differently, if 2 HR-MS are at the edge of the cell than their supportable data rate with the BS can be too low. For voice this isn't an issue as the voice data rate is similar to the data rate of the associated signaling for MS control. On the other hand if the mission requires e.g. video than these 2 HR-MS may not be able to maintain video link with the HR-BS - but can with each other. Then it is a reliability issue. I also agree that MS-MS communications under a BS is simpler than HR-MS forwarding.
Sungcheol:
If just communication is needed between two HR-MSs, then we can use multi-mode operation of HR-MS as relay function instead of defining new specification. My preference is the reuse and modification of existing specification. If one HR-MS changes its role as relay and the HR-MS relays or terminates packets with the other HR-MS, it's nature is direct communication. I don't object the motivation of communication between HR-MS under coverage, but updating existing 16 specifications has a priority to defining new specification. Is it impossible to achieve two HR-MS communication under BS coverage with HR-MS multi-mode operation as relay?
>>>>>>>>>>>>>>>>>
<<<<<<<<<<<<<<<<<< Topic B
Eldad:
* Modes for HR-MS direct communication
- Both HR-MSs are associated with an infrastructure node.
- Infrastructure nodes are absent.
* Modes for HR-MS local forwarding
- One HR-MS is associated with an infrastructure node and one or more other HR-MSs are out of coverage of an infrastructure node.
Anh Tuan:
1) We can have an HR-MS that is outside-of-coverage but can still be associated with an infrastructure node (through the help of a forwarding HR-MS). So for the 1st mode of HR-MS direct communications, When we say "Both HR-MSs are associated with an infrastructure node.", do we mean "association" or "coverage"?
2) For HR-MS forwarding to network (we should not use "HR-MS local forwarding" as 16n SRD uses "local forwarding" to refer to a different scenario), I would like to add the 3rd mode of "Both HR-MSs are within the coverage of an infrastructure node". This can be beneficial when HR-MSs are power-limited
Eldad (Answer):
- Agree with the terminology "forwarding to network"
- I agree to add to HR-MS Forwarding the case where both HR-MS are in coverage (point 2). Actually this is the same argument I used for MS-MS communications as a reliability enhancement.
- For MS-MS direct communications (point 1) I'm not so sure it is needed. HR-MS that are of coverage of the HR-BS will likely be at cell edge. They will have few neighbor HR-MS. They will have even fewer HR-MS they will need peer to peer connection to. Therefore I think this isn't an important case. Therefore I would disagree with this case.
>>>>>>>>>>>>>>>>>
Regarding frame structure:
<<<<<<<<<<<<<<<<<< Topic C
Question-1) Are 2 HR-MS in the same cell allowed to transmit on the same resources (assuming that they are far enough)?
Anh Tuan:
This resource reuse should be encouraged, as long as mechanisms are provided to mitigate interference among HR-MS direct/forwarding transmissions. For such interference-mitigating mechanisms to work, we need neighbor discovery schemes to determine the distances between pairs of nodes.
Sungcheol:
I think we don't allow that. If it is guaranteed that two HR-MSs are far enough, two HR-MSs may transmit on the same resources. However, how can it be guaranteed? Interference mitigation has been a challenging research topic. But I don't agree that 16n specification adapts interference management approaches because its complexity. (Do we consider direct communication among HR-MSs in the same cell? I am negative)
Anh Tuan:
For the spatial reuse of resource allocated to HR-MS direct transmissions, I am open to the possibility. However, as mentioned in previous email, I share Sungcheol's concern of interference mitigation. In fact, Eldad has also previously discussed this interference concern. To me, even without reusing allocated resource, controlling interference between HR-MSs direct communications and legacy transmissions (between HR-BS and HR-MS) is tough enough. Having said that, I do not see how reserving a fixed resource for HR-MS direct transmissions would better minimize interference, compared to the approach when BS allocates resource dynamically, but without two transmissions sharing (re-using) the same logical resource units.
Eldad
I think that allowing the HR-BS to allocate MS-MS resources dynamically, in combination with good HR-MS discovery and spatial separation, should allow the HR-BS to determine the correct resources. We do not specify that the HR-BS must share resources but on the other hand we do not prevent it from doing so. In my opinion, MS-MS connections that aren't allowed to share resources will not be very efficient.
Question-2): Is the HR-BS allowed to re-use the same resources for its own DL transmissions or the UL transmissions of one of its HR-MS (assuming that the HR-MS is close enough to the HR-BS)?
Anh Tuan:
Similar to answer to question 1 with the note that interference mitigation will depend on whether HR-MS direct/forwarding transmissions are scheduled in DL or UL area of each frame.
Sungcheol:
Generally I think that resource used for infrastructure communication is exclusive to resource for direct communication. From this agreement, we can extend resource usages if its algorithm is simple. Exclusive resource allocation guarantees that interference each other may be controlled easily.
Eldad:
I think the answer is very similar to question-1. While the specific interference mechanism depends if transmission takes place in UL or DL or both, good interference control mechanisms as indicated above should solve both.
Question-3): Are these resources fixed for all cells?
Anh Tuan:
I believe that HR-MS direct communications and forwarding to network are opportunistic in nature. Therefore, resources should be dynamically allocated across space (cells), time/frequency (frames).
Sungcheol:
We need fixed resources of direct communications for all cells if HR-MS may be at several radio environment cases including under infrastructure node, in absent of infrastructure not, and in the middle of infra-structure nodes. It is recommended that this fixed resource shall be as small as possible because the resource is not be used by infrastructure node for interference avoidance.
Eldad:
I would support Anh Tuan.
Sungcheol:
We need to separate DC specific resources into two. One is for the usage case of direct communication that two HR-BSs are under the coverage of infrastructure node. Dynamic resource allocation can be acceptable for this use case only. The other is for two usage cases that 1) one HR-MS under infrastructure node coverage and the other HR-MS in absent of infrastructure node 2) two HR-MSs in absent of infrastructure node. When we consider HR-MS in absent of HR-BS, dynamic resources allocation information is carried on the fixed resource of direct communication. It's why I propose two-step resource allocation.
Question-4): Can they change over time?
Anh Tuan:
Similar to answer to question-3.
Sungcheol:
It depends on design. The fixed resource of direct communication is static and limits resources for infrastructure communications. To solve this problem, the fixed resource is reserved at minimum and additional resource information can broadcast on the fixed resource. Its additional resource may be quasi-static and cell specific if possible. How about two step resource of direct communication?
Eldad:
I would support Anh Tuan. I'm not sure what a two-step resource allocation means but does it lengthens latency?
Sungcheol:
No. It does not length latency. Control information including resource allocation shall be carried on common dedicated resource. It's all. Common or dynamic resource can be used for carrying data packets among HR-MSs because the HR-MSs have exchanged resource allocation information each other using control packets on the common dedicated resource..
>>>>>>>>>>>>>>>>>>>
<<<<<<<<<<<<<<<<<< Topic D
Sungcheol:
For frame structure of direct communication, we need discuss types of DC specific resources, TDM and FDM separations. TDM means that its bandwidth of DC specific resources is wideband. FDM means that narrowband resources can be reserved for DC specific resources. I prefer that the DC resources shall be allocated as narrowband because of its coverage enhancement. So I have a preference to FDM for DC specific resource separation. Is there any reason that DC specific resource shall be FDM in 16n specification based on 16m specification? (I understand that TDM is a way of DC specific resource allocation for 16e specification because diversity zone and AMC zone are exclusive in time domain)
Anh Tuan:
Regarding TDM vs FDM, current approach in 16m is based on FDM (within each subframe). So FDM to me is a natural approach. However, I propose that we stick to the 16m subframe boundaries when doing resource allocation for HR-MS direct comm/forwarding. Do we have a strong reason/motivation for allocating a narrow band resource spanning several subframes for a HR-MS direct transmissions?
Eldad:
- If you meant FDM per sub-frame I would agree with you, we go FDM. Otherwise it's usually called TDM/FDM.
- If you accept the premise that resources are allocated by the BS then we don't have to decide here whether it's broadband or narrowband.
- 802.16m already has a long-TTI mechanism for added robustness. I'm not sure we need another one.
Sungcheol:
We need to separate discussions into two like my answer to Question-3). For the use case that two HR-BSs are under the coverage of infrastructure node, we need to follows 16m or 16e frame structure as similar as possible. For the other use case, we need to define DC specific frame structure because HR-MSs in absent of HR-BS are not aware of infrastructure frame structure.
Eldad
Office +1 631 622 4134
Mobile +1 631 428 4052
Based in NY area
-----Original Message-----
From: Hoang Anh Tuan [mailto:athoang@I2R.A-STAR.EDU.SG]
Sent: Friday, April 08, 2011 1:00 PM
To: STDS-802-16@LISTSERV.IEEE.ORG
Subject: Re: [STDS-802-16] [802.16n][DC] Discussion on Usages and Frame Structure for DC
Hi Sungcheol and all,
REGARDING USE CASES:
I support the allowance of HR-MS direct communications and forwarding when both HR-MSs are within coverage of an infrastructure node. The reasons are:
- Enhancing reliability/robustness: the direct link between a pair of HR-MSs basically provides us with an alternative path. This path, when chosen properly (e.g., based on distance, channel quality), allows communications to happen at higher rate and/or lower probability of error, and/or lower transmit power. All these contribute to the higher reliability/robustness of an HR network. To me, it can even be argued that this mode of communications (when both HR-MSs are within coverage) is more reliability-relevant than the mode of coverage extension (when one HR-MS is outside of coverage). Coverage extension is like enhancing the capability of a network, rather than reliability/robustness. Of course, one can argue it in an opposite way, but I think all three coverage scenarios should be supported.
- Acceptable complexity: I believe that if someone provides a reasonable design to support HR-MS direct communication or forwarding under the two scenarios of no infrastructure node or only one HR-MS is within coverage, then a simpler design can always be derived to support the scenario when both HR-MSs are within coverage. In other words, if you have some mechanism to support a rather complicated use case, why don't you just simplify that to also support an easier use case? Take note that this simpler use case does provide reliability benefits.
REGARDING FRAME STRUCTURE:
For the spatial reuse of resource allocated to HR-MS direct transmissions, I am open to the possibility. However, as mentioned in previous email, I share Sungcheol's concern of interference mitigation. In fact, Eldad has also previously discussed this interference concern. To me, even without reusing allocated resource, controlling interference between HR-MSs direct communications and legacy transmissions (between HR-BS and HR-MS) is tough enough. Having said that, I do not see how reserving a fixed resource for HR-MS direct transmissions would better minimize interference, compared to the approach when BS allocates resource dynamically, but without two transmissions sharing (re-using) the same logical resource units.
Regarding TDM vs FDM, current approach in 16m is based on FDM (within each subframe). So FDM to me is a natural approach. However, I propose that we stick to the 16m subframe boundaries when doing resource allocation for HR-MS direct comm/forwarding. Do we have a strong reason/motivation for allocating a narrow band resource spanning several subframes for a HR-MS direct transmissions?
Best regards,
Anh Tuan
________________________________
From: Chang, Sungcheol [mailto:scchang@etri.re.kr]
Sent: Fri 4/8/2011 8:55 PM
To: STDS-802-16@LISTSERV.IEEE.ORG
Subject: Re: [STDS-802-16] [802.16n][DC] Discussion on Usages and Frame Structure for DC
Dear Eldad and all,
REGARDING USE CASES:
From the 16n SRD document, we can consider three usage scenarios.
I can agree two use cases: 1) Infrastructure nodes are absent and 2) One HR-MS is associated with an infrastructure node and one or more other HR-MSs are out of coverage of an infrastructure node.
But, we need more discussion about both HR-MSs under an infrastructure node.
For the use case of both two HR-MS under an infrastructure node,
What is the motivation that 16n specification includes this use case?
As you knows, 16n specification is for reliability enhancement.
Is this usage case related to reliability enhancement?
I thank that the major gain of this use case is that resource usage efficiency increases using higher modulation scheme with good channel quality.
Can you tell me the motivation of this usage case?
REGARDING FRAME STRCUTRE:
I respond Eldad's questions as the follwings:
1) I think we don't allow that. If it is guaranteed that two HR-MSs are far enough, two HR-MSs may transmit on the same resources. However, how can it be guaranteed? Interference mitigation has been a challenging research topic. But I don't agree that 16n specification adapts interference management approaches because its complexity. (Do we consider direct communication among HR-MSs in the same cell? I am negative)
2) Generally I think that resource used for infrastructure communication is exclusive to resource for direct communication. From this agreement, we can extend resource usages if its algorithm is simple. Exclusive resource allocation guarantees that interference each other may be controlled easily.
3) We need fixed resources of direct communications for all cells if HR-MS may be at several radio environment cases including under infrastructure node, in absent of infrastructure not, and in the middle of infra-structure nodes. It is recommended that this fixed resource shall be as small as possible because the resource is not be used by infrastructure node for interference avoidance.
4) It depends on design. The fixed resource of direct communication is static and limits resources for infrastructure communications. To solve this problem, the fixed resource is reserved at minimum and additional resource information can broadcast on the fixed resource. Its additional resource may be quasi-static and cell specific if possible. How about two step resource of direct communication?
For frame structure of direct communication, we need discuss types of DC specific resources, TDM and FDM separations. TDM means that its bandwidth of DC specific resources is wideband. FDM means that narrowband resources can be reserved for DC specific resources. I prefer that the DC resources shall be allocated as narrowband because of its coverage enhancement. So I have a preference to FDM for DC specific resource separation. Is there any reason that DC specific resource shall be FDM in 16n specification based on 16m specification? (I understand that TDM is a way of DC specific resource allocation for 16e specification because diversity zone and AMC zone are exclusive in time domain)
We need to speed up e-mail discussion for usage and frame structure of direct communication.
I look forward to 16n participants' reply emails.
Best regards,
Sungcheol Chang, Ph.D.
Mobile Access Technology Research Team, ETRI
From: Zeira, Eldad [mailto:Eldad.Zeira@INTERDIGITAL.COM]
Sent: Wednesday, April 06, 2011 9:43 PM
To: STDS-802-16@LISTSERV.IEEE.ORG
Subject: Re: [STDS-802-16] [802.16n][DC] Discussion on Usages and Frame Structure for DC
Hi All
Thanks, Sungcheol and Haiguang,
In order to keep same thread I'm commenting on both Sungcheol's email and Haiguang comment. Let's try to keep the number of threads to a minimum;
Regarding use cases:
I like Haiguang's proposal to separate the overview along SRD lines. To clarify what I think is the intent, I would like to modify that text (see below).
I also support Haiguang's statement that as the SRD doesn't discuss services then all scenarios should support all services.
Other than some minor editorials, the reasons for the suggested changes are as follows:
- AWD text shouldn't discuss usage which is up to implementation. We can discuss modes.
- I have used the term "infrastructure node" to refer to HR-BS or HR-RS.
- I have replaced "HR-MSs does not associate to HR-BS " with "Infrastructure nodes are absent". The latter is from the SRD, the former implies that HR-BS is present but the HR-MS ignore it which is not in the SRD.
The cleaned, revised text is therefore:
* Modes for HR-MS direct communication
- Both HR-MSs are associated with an infrastructure node.
- Infrastructure nodes are absent.
* Modes for HR-MS local forwarding
- One HR-MS is associated with an infrastructure node and one or more other HR-MSs are out of coverage of an infrastructure node.
Regarding frame structure:
One of the alternatives discussed by Sungcheol is a "DC specific frame structure including dedicated resource usage (Zone)"
I would like to ask the Sungcheol and the rest of the forum what is the meaning of this alternative, specifically:
1) Are 2 HR-MS in the same cell allowed to transmit on the same resources (assuming that they are far enough)?
2) Is the HR-BS allowed to re-use the same resources for its own DL transmissions or the UL transmissions of one of its HR-MS (assuming that the HR-MS is close enough to the HR-BS)?
3) Are these resources fixed for all cells?
4) Can they change over time?
Thanks and Best Regards,
Eldad
Office +1 631 622 4134
Mobile +1 631 428 4052
Based in NY area
-----Original Message-----
From: Wang Haiguang [mailto:hwang@I2R.A-STAR.EDU.SG]
Sent: Wednesday, April 06, 2011 5:55 AM
To: STDS-802-16@LISTSERV.IEEE.ORG
Subject: Re: [STDS-802-16] [802.16n][DC] Discussion on Usages and Frame Structure for DC
Hi, Sungcheol and all.
According the SRD, the system requirements for
direct communication (6.1.3.1) and HR-MS forwarding
(6.1.3.2) are defined in two separate sub-sections.
I think that we should define two separate sets of usages
for the direct communication and local forwarding as follows:
* Usages [EZ] Modes for HR-MS direct communication
- [EZ] Both HR-MSs are associated with an HR-BS infrastructure node.
- HR-MSs does not associate to HR-BS.[EZ] Infrastructure nodes are absent.
* Usages [EZ] Modes for HR-MS local forwarding
- One HR-MSs [EZ]is associated [EZ] with HR-BS infrastructure node and another one [EZ] one or more other HR-MSs are out of the coverage of HR-BS infrastructure nodes.
The direct communication and local forwarding should
be designed to support various applications, including
both data, video and voice since the SRD does not
make any constraint on the supported application.
Regards.
Haiguang
-----Original Message-----
From: Sungcheol Chang [mailto:scchang@etri.re.kr]
Sent: Wed 4/6/2011 8:48 AM
To: STDS-802-16@LISTSERV.IEEE.ORG
Subject: [STDS-802-16] [802.16n][DC] Discussion on Usages and Frame Structure for DC
Dear 16n participants,
This is a kick-off mail for e-mail discussion on Usages and Frame Structure for direct communication
I suggest discussion guidelines as the followings:
- The subject of all the e-mails begins with the tag "[STDS-802-16] [802.16n][DC]" because DC RG has one e-mail discussion group now.
- Reply mails are expected to be within 24 hours because participants have different time zones.
- Any participants can add technical discussion issues for DC usage scenarios ad DC frame structure only.
[STDS-802-16] [802.16n][DC][Usage] Discussion on Usage Scenarios
There are three scenarios of direct communication (Let's focus on two HR-MSs at first)
1) Two HR-MSs under HR-BS coverage
2) One HR-MS under HR-BS coverage and The other HR-MS out of HR-BS coverage. (HR-MS forwarding)
3) Two HR-MSs in absent of HR-BS
[STDS-802-16] [802.16n][DC][Frame] Discussion on Frame Structure
Two cases of frame structure for direct communication
1) 16 frame structure including infrastructure frame structure and relay frame structure.
2) DC specific frame structure including dedicated resource usage (Zone)
Two cases of DC resource separation within 16 frame structure
1) TDM separation (Wideband approach)
2) FDM separation (Narrowband approach)
Note) Base on this kick-off e-mail, 16n participants concerning direct communication are encouraged to join this e-mail discussion actively.
Note) If participants want, participants can trigger e-mail discussion on other topic freely. Please use the other tag! (DC RG is not authorized to manage e-mail discussion among participants from 16n TG)
Best regards,
Sungcheol Chang