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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. >>>>>>>>>>>>>>>>> <<<<<<<<<<<<<<<<<<
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. 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? >>>>>>>>>>>>>>>>>>> <<<<<<<<<<<<<<<<<<
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. Eldad Office +1 631 622 4134 Mobile +1 631 428 4052 Based in NY area -----Original Message----- 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 |