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Hi Sungcheol, all Please see a comment below
regarding coverage extension. Eldad Office +1 631 622 4134 Mobile +1 631 428 4052 Based in NY area From: Chang, Sungcheol
[mailto:scchang@etri.re.kr] Hi Haiguang, Please seem my comments. Haiguang, when I reply your mail, your mail format is plain
text. Can you check your mail format? Best regards, Sungcheol Chang, Ph.D. Mobile Access Technology Research Team, ETRI 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? Sungcheol: I can’t agree easily that a
forwarding HR-MS, but its nature is a transparent mode relay like 16j relay, is
categorized into an HR-MS of peer-to-peer direct communication. If we call it
as a forwarding HR-MS, then 16 specification family has two names for one
transparent relay operation. One is a transparent mode relay and the other is a
forwarding HR-MS. So I think that an HR-MS having a modified function of
transparent mode relay is classified into a set of relay. It keeps consistency. Anh Tuan: Sungcheol and Eldad, I myself
do not agree to link HR-MS forwarding (when both HR-MSs are within coverage) to
a 16j transparent-relay mode. There are fundamental configurations/restrictions
applied to a transparent relay that a forwarding HR-MS may not need to follow,
such as handling of network entry of subordinate MSs, relative positions of
relay/access zones, no source/sink of data... I would rather implement HR-MS
forwarding through modifications to the existing DL/UL control signaling (like
A-MAP) of the current 16e/m specs. >>>>>>>>>>>>>>>>>
<<<<<<<<<<<<<<<<<<
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. Sungcheol: I understand what Eldad and
Haiguang worry about. My answers to the comments follows: - For backward compatibility.
Direct communication is defined on 16n specification between HR-MS and HR-BS.
HR-MS is attached to 16m BS as 16m MS. I don’t understand why you say about
backward compatibility. - For Licensed spectrum. I
partially agree with you. As you know, we are trying to adapt 16n system as a
candidate for Korea PPDR system. It’s hard to get frequency bandwidth
allocations for PPDR application from government agency. Furthermore, there is
no possibility to get additional frequency allocations for direct
communication. Under this consideration, it’s a only way that direct
communication is operated within PPDR frequency allocation. Direct
communication is an essential functionality of PPDR system. If 16n
specification allows only direct communication in a frequency band different
from infrastructure frequency band, 16n system is not applicable to Korea PPDR
system. It’s our motivation to propose that direct communication is within
infrastructure frequency band. I believe that when we developed 16n SRD
document I have presented several materials about this. - For authorization and
licensing. If a frequency band is allocated to PPDR application and 16n specification
is adapted, there is no issue on these. But it’s important that infrastructure
communication and direct communication work within a frequency bandwidth. - For interference and Femto.
I agree that Eldad and Haiguang point out about possibility of interference.
It’s why I propose the DC specific dedicated resource for direct communication.
In principle, DC specific dedicated resources and infrastructure resources are
mutually exclusive. We propose an interference avoidance approach (mutually
exclusive resource usages) to minimize interference each other. Also we
provided a material about this interference and please refer to
C80216n-11_0051r2. - For distributed scheduling.
I understand that centralized control mechanism is efficient. But it requires a
central controller like HR-BS. When we consider that HR-MSs are within or out
of the coverage, it’s hard to insist that centrally control mechanism is only a
solution for resource scheduling. I highlight Forwarding mode. In
my view, a forwarding MS is mapped to gateway which relay packets between two
interfaces, direct communication and infrastructure communication for PPDR
system. Two interfaces work independently and packets are relayed as gateway
function. It’s different from 16j or 16m relay operation which is based on
relay and access zones in single frame structure. This difference comes from
different applications, for example Smart Grid and PPDR. Under this
consideration, is it necessary to find a solution for two applications? I
believe that Forwarding mode is an extension of direct communication for PPDR
application and is a modification of transparent mode relay for Smart Grid
application. I could not find one solution applicable to two applications. I
don’t agree that a modification of transparent mode relay is a solution for
PPDR. Ming-Tuo: In case that two HR-MSs are
within coverage of a HR-BS/RS, what's the difference between: 1) a HR-MS relays data/control
message of another HR-MS to HR-BS/RS; 2) a HR-MS forwards
data/control message of another HR-MS to HR-BS/RS. Anh Tuan: Like Eldad, I prefer to use the
terms "BS conrolled peer to peer mode" and "BS cotrolled
forwarding mode". I also believe that we should avoid using the term
"transparent" and regarding "BS controlled forwarding mode"
as a modification of "16j transparent relay mode". We can support 16n
HR-MS forwarding without specifying relay/access zones. Sungcheol: The
relay/access zones are used for Tx and Rx separation of a station. Though we
need to consider these terminologies and their concepts, Tx and Rx separation
per HR-MS is necessary for peer-to-peer communication. Haiguang: Please correct me if I am wrong.
May I know that a specific PHY
and MAC has been defined for PPDR in Korea or other countries? In my view, the PPDR is just an
application. It just requires MAC and PHY to find a way to delivery the voice
data packet generated by PPDR application to the peer. I do not see the need of
a dedicated channel for the communication. Sungcheol: Haiguang,
You are right. I highlight that just delivering voice packets is meaningless to
PPDR usages. With HR-MS’s power emission limitation, it’s important that the
coverage of direct communication is extended at the basement environment. If
just delivering voice packets over the coverage is a purpose, I myself will
reuse relay station that we have already specifications about and I don’t find
any motivation to introduce wideband direct communication for this. As you
know, infrastructure communication are based on wideband transmissions of
preamble and SFH. For example, Femto cell coverage is known as hundred meters
and if Femto cell is deployed at the basement can you imagine its coverage of
HR-BS (like Femto cell) with limited power emission? Practical scenario of
fireman is that as fireman goes down from ground the need of direct
communication increases. In that scenario it’s important that HR-MS maintains
communicate with other HR-MSs in the basement. If we design direct
communication with wideband frequency resource usages, its coverage will be
smaller than one of Femto cell because there are several number of obstacles
between floors and walls between rooms in the basement. It’s related to fireman
survivability. That is a scenario of direct communication for PPDR application. Eldad: HR-MS forwarding is also
meant to and can solve the coverage hole issues as well and can do a much
better job of it than simply using narrowband signaling. Suppose we reduce the allocation
size to one third (1/3) of its minimum today. That buys you 5dB. A coverage
hole could easily be much deeper than 5dB in which case narrowband signaling
alone isn't sufficient. On the other hand, a link through another HR-MS acting
to forwarding MS can easily bridge the gap using low power transmission and therefore
creating low interference. >>>>>>>>>>>>>>>>>
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. Sungcheol: Please refer to the
third answer to Topic B. 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? Sungcheol: It’s kind of OFDMA packets, not
the CDMA code because of its complexity. Yes, I prefer smaller frequency domain
allocations for all the OFDMA packet of direct communication. It’s for coverage
extension. We consider smaller frequency domain allocation of dedicated
resources for direct communication. Packets for synchronization and contention
has the same frequency domain allocation (or may be smaller than). We are under
design. The result come from performance comparision. ________________________________ |