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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] 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]
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----- 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. >>>>>>>>>>>>>>>>>
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 |