Study or Work Item Proposal
Support for D2D Unicast Communications
Study Item/Work Item
Submitted For
TSDSI-SG1-SI5-V1.0.0-20150807
Supporter Name
Prakhar Nashine
Suresh Kalyanasundaram
Email ID
prakhar.v_nashine@nsn.com
suresh.kalyanasundaram@nsn.com
Information/Discussion
Supporters:
Description <Provide the Description in the below box.>
This contribution is submitted in support of the SG1-WG1 Study Item on D2D Communications (Study of
Unicast, Relays and V2X). This contribution considers the requirements for mode selection, resource allocation,
Power control and CSI feedback mechanisms and the required signaling mechanisms to enable D2D Unicast
communications.
1. Resource Allocation : Resource sharing/reuse between the D2D and Cellular transmissions (and among
the various D2D pairs) in a cell provides improved spectral efficiency and system throughput.
1) Requirements for resource reuse/sharing among D2D transmissions and Cellular transmissions may
be considered. The D2D pairs can reuse the uplink resource of the Cellular UEs. Mode 1 type
Resource allocation scheme may be considered where the eNodeB provides the resources to the D2D
transmitter for D2D communication.
2) Measurement of a suitable metric, i.e., maximization of the system’s sum utility (an appropriate
function of UE Throughputs of D2D and Cellular UEs taken together, e.g., using the logarithm of
user’s throughput as its utility) may be considered to decide on co-scheduling D2D and Cellular UEs
or multiple D2D transmissions on the same resource blocks.
3) Signaling mechanisms may have to be defined to get the cross channel gains in the system. Since it
would be impractical to know the cross channel gains of each and every link in the system,
requirements may be considered to include cross channel gains from the top and bottom N
interferers for any given D2D receiver UE.
2. Mode Selection : D2D communications can happen in two ways: 1) Direct Mode where D2D devices
transmit data on UL resources. The receiver D2D device is capable of decoding data on UL resources
(similar to an eNB). 2) Cellular Mode where the D2D devices transmit data via cellular. This is a twohop communication, where the UE transmits to the eNB using uplink resources that is followed by data
transmission from eNB to the receiver UE using downlink resources. Direct mode has the advantage of
better spectral efficiency and reduced interference if UEs are in close proximity. Cellular mode may give
better spectral efficiency and require lower transmit power if D2D receiver is far away from the
transmitter, when compared to the eNodeB. In addition, the amount of resources that the UEs can get in
direct and cellular mode will also influence which is the best mode, at a given time instance.
1) Requirements/Mechanism/Algorithms may have be considered for D2D mode selection for a given
source and destination pair of UEs, i.e., whether the communication should happen in D2D direct
mode or cellular mode every TTI. Suitable metric/mechanism to be used (SINR, Spectral Efficiency,
Resource utilization in both modes, interference impact, etc.) may have to be considered.
2) Signaling mechanism may have to be considered to convey the mode to the D2D transmit or receive
UEs.
3) Requirements for CSI feedback mechanism needs to be considered for the direct mode of D2D
communication.
3. Power Control : D2D power control in 3GPP considers either maximum allowed power or open loop
power control mechanism for D2D communications. To avoid large power transitions from one subframe to the next, use of maximum power for D2D transmissions are not preferred. The open loop
transmit power equation is a consequence of using only broadcast mode of transmission in 3GPP Rel.
12. Primary aim of the open loop power control is to control the interference to cellular transmissions.
D2D unicast communication provides opportunity for frequency re-use and use of a single-hop (instead
of an uplink and downlink hop) communication by using the proximity between transmitter and receiver
UEs. Resource reuse however increases interference levels and introduces large variations in
interference in a fast time scale.
1) Requirements may therefore be considered for a suitable power control algorithm for unicast D2D
communication in order to maintain sufficient quality on the transmitter to receiver link, while at the
same time not creating too much interference to victim receiver of the ongoing D2D links as well as
other cellular communications.
2) The proposed power control algorithm should consider the interference generated by the D2D
transmission to its neighbors and appropriately adapts the transmit power of the D2D user.
3) Requirements may be considered to provide for the D2D receivers to transmit sounding referece
signals at constant power. The D2D transmitter can then perform an open loop power control
estimate, based on received signal power from intended and victim receivers.
4) Requirements may also be considered for a closed loop power control mechanism where the
feedback can be provided both from the serving cell eNodeB and the receiver D2D UE. Provision of
two power control loops for unicast D2D Transmissions may be considered:, a) An outer power
control loop between serving cell and D2D transmitter done on a slow time scale and b) An inner
power control loop between D2D transmitter and receiver, where the feedback from the receiver
D2D UE is received on a fast time scale.
5) Signaling mechanisms may also have to be defined to get the cross channel gains in the system.
Since it would be impractical to know the cross channel gains of each and every link in the system,
requirements may be considered to include cross channel gains from the top and bottom N
interferers.
4. CSI Feedback Mechanism : Unicast D2D communications require a CSI feedback design that’s
different from what exists today, i.e., there is a need to capture the UE-UE interference impact. There
could be D2D receivers being interfered by other D2D transmissions or other UL transmissions.
1) Requirements may be considered to provide for a multiple CSI approach that captures the impact of
UE-UE interference. Each CSI feedback may corresponds to different hypothesis in terms of which
interferers are assumed to be co-scheduled.
2) Provisions may be made for interfering UEs (D2D transmitters) to transmit a reference signal
(similar to SRS) to allow victim UEs to estimate the channel/interference from the aggressor UEs.
Victim UEs can be informed of the SRS configuration of the aggressor UEs in advance. Victim UEs
then send the following information to the eNodeB:
A) Identity of the top N aggressor UEs, and the CSI corresponding to each of these aggressor
UEs acting as an interferer individually.
B) Identity of bottom N aggressor UEs, and the CSI corresponding to each of these aggressor
UEs acting as an interferer individually.
Figures 1 and 2 below illustrate the signal flow diagram for the proposed CSI feedback mechanism.
Victim UE
Aggressor UE Aggressor UE
Aggressor UE
eNB
SRS configuration
CSI configuration, including SRS
configuration of aggressor UEs
SRS
Channel
estimation
Multiple CSI feedback
corresponding to top and bottom
interferers and at least CSI
corresponding to bottom
interferers
Figure 1 : Signal flow for CSI feedback design to account for UE-UE interference (same cell scenario)
Victim UE
Aggressor UE Aggressor UE
Aggressor UE
eNB eNB eNB
SRS configuration
SRS
configuration
CSI configuration, including SRS
configuration of aggressor UEs
Channel
estimation
Multiple CSI feedback
corresponding to top and bottom
interferers and at least CSI
corresponding to bottom
interferers
Figure 2 : Signal flow for CSI feedback design to account for UE-UE interference (adjacent cell
scenario)
3) Using the multiple CSIs corresponding to top N aggressors and bottom N aggressors will allow the
eNodeB scheduler to determine
- Which UEs should not be scheduled together
- Which UEs can be scheduled together
- And when the latter happens, what the beamformer, transmit power and MCS should be
Summary <Provide the Summary in the below box.>
This contribution considers the requirements for mode selection, resource allocation, Power control and CSI
feedback mechanisms and the required signaling mechanisms to enable D2D Unicast communications.
Impact <Provide the Impact of SWIP in TSDSI in the below box.>
References <Provide the References in the below box.>
1. NIP15 - D2D Communication: Study of Unicast, Relays and V2X
2. D2D_nip_scope_consolidated_v5.docx (TSDSI Vision and Way forward in D2D Communication)
Instructions:
1. Title: The title shall be very specific and indicate the item clearly
2. Study Item/Work Item: Mention the name of the Study Item or Work Item related to this proposal. The list of
Study Items and Work Items are available at TSDSI website.
3. The e-mail ids shall be the official email ids with organization domains or ids used while registering as a
member with TSDSI.
4. If the contribution is supported by any other members of TSDSI, provide the organization name and contact
names for each of them.
5. The contribution may have references to any other contributions, standards, specifications, etc
6. The Proposal shall provide details of the problem addressed and solution proposed. It shall include detailed
analysis, simulation results and any other supporting data.
7. One form shall be related to only one SG/WG/SI/WI.
8. Log is used to track changes made to the proposal based on discussions in the group.
Where to send:
Please fill in all the details and mail the form and send to pavan@tsdsi.org. You will get an acknowledgement
along with a SWIP Number allocated to the request.