U.S. patent application number 14/692204 was filed with the patent office on 2015-08-13 for method and apparatus for device-to-device communication.
The applicant listed for this patent is Google Technology Holdings LLC. Invention is credited to Ravi Kuchibhotla, Robert T. Love, Vijay Nangia, Ajit Nimbalker, Ravikiran Nory.
Application Number | 20150230284 14/692204 |
Document ID | / |
Family ID | 49885395 |
Filed Date | 2015-08-13 |
United States Patent
Application |
20150230284 |
Kind Code |
A1 |
Nimbalker; Ajit ; et
al. |
August 13, 2015 |
METHOD AND APPARATUS FOR DEVICE-TO-DEVICE COMMUNICATION
Abstract
A first user equipment (UE) wirelessly communicates with a
network element (e.g., an eNB) on a carrier (e.g., a cellular
uplink or downlink carrier) in accordance with its first capability
partitioning configuration. The first UE engages in direct wireless
communication on the carrier with a second UE in accordance its
second capability partitioning configuration.
Inventors: |
Nimbalker; Ajit; (Buffalo
Grove, IL) ; Kuchibhotla; Ravi; (Gurnee, IL) ;
Love; Robert T.; (Barrington, IL) ; Nangia;
Vijay; (Algonquin, IL) ; Nory; Ravikiran;
(Buffalo Grove, IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Google Technology Holdings LLC |
Mountain View |
CA |
US |
|
|
Family ID: |
49885395 |
Appl. No.: |
14/692204 |
Filed: |
April 21, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13727692 |
Dec 27, 2012 |
9042938 |
|
|
14692204 |
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Current U.S.
Class: |
455/450 |
Current CPC
Class: |
H04L 1/1835 20130101;
H04W 72/048 20130101; H04W 76/14 20180201; H04L 1/1822 20130101;
H04L 1/1874 20130101; H04L 1/1812 20130101; H04W 88/02
20130101 |
International
Class: |
H04W 76/02 20060101
H04W076/02 |
Claims
1. A method in a first user equipment, the method comprising:
wirelessly communicating with a network element on a carrier in
accordance with a first capability partitioning configuration of
the first user equipment; engaging in direct wireless communication
on the carrier with a second user equipment in accordance with a
second capability partitioning configuration of the first user
equipment.
2. The method of claim 1, wherein the first capability partitioning
configuration comprises a first buffer partitioning configuration,
and wherein the second capability partitioning configuration
comprises a second buffer partitioning configuration.
3. The method of claim 1, wherein the carrier is a first carrier,
the method further comprising acquiring information regarding at
least the second capability partitioning configuration from the
network element, via a second carrier.
4. The method of claim 2, wherein the second buffer partitioning
configuration comprises at least one of: a maximum number of HARQ
processes that the first user equipment will use for communicating
with the second user equipment; the size of a soft buffer that the
first user equipment will use for communicating with the second
user equipment a number of soft channel bits that the first user
equipment will use for communicating with the second user
equipment
5. The method of claim 2, wherein the first buffer partitioning
configuration comprises at least one of the following: the HARQ
processes that the first user equipment will use for communicating
with the network element, the size of a soft buffer that first user
equipment will use for communicating with the network element, and
the total number of soft channel bits that the first user equipment
will use to communicate with the network element.
6. The method of claim 1, wherein the carrier is a first carrier,
the method further comprising: transmitting information regarding a
capability configuration of the first user equipment to the network
element via the first carrier, receiving information regarding a
capability partitioning configuration of the second user equipment
from the network element via a second carrier; wherein the engaging
step comprises engaging in wireless communication directly with the
second user equipment on the first carrier in accordance with the
capability partitioning configuration of the second user equipment
and the capability partitioning configuration of the first user
equipment.
7. The method of claim 1, further comprising: receiving, from the
second user equipment, information regarding a category of the
second user equipment; wherein the engaging step comprises engaging
in wireless communication directly with the second user equipment
in accordance with the second user equipment's category.
8. A method in a first user equipment, the method comprising
wirelessly communicating with a network element on a carrier;
encoding a packet in accordance with a capability partitioning
configuration of a second user equipment; and wirelessly
transmitting the encoded packet on the carrier directly to the
second user equipment.
9. The method of claim 8, wherein the carrier is a first carrier,
the method further comprising: receiving information regarding the
capability partitioning configuration of the second user equipment
from the network element on a second carrier.
10. The method of claim 8, wherein the carrier is an uplink
carrier, the method further comprising: receiving information
regarding the capability partitioning configuration of the second
user equipment from the network element on a downlink carrier.
11. The method claim 8, wherein the encoding step further comprises
encoding the packet in accordance with the category of the second
user equipment.
12. The method of claim 8, wherein the capability partitioning
configuration of the second user equipment comprises a
configuration of the second user equipment's soft buffer.
13. The method of claim 12, wherein the second user equipment's
soft buffer configuration comprises a number of soft channel bits
used by the second user equipment for device to device
communication.
14. The method of claim 12, the method further comprising
partitioning the first user equipment's soft buffer for
simultaneous communication with the network element and the second
user equipment.
15. The method of claim 8, wherein the capability partitioning
configuration comprises a maximum number of HARQ processes that can
be used by the second user equipment for device to device
communication.
16. A method in a first user equipment, the method comprising
wirelessly communicating with a network element on a carrier;
wirelessly receiving a packet directly from a second user equipment
on the carrier; and decoding the packet in accordance with a
capability partitioning configuration of the second user
equipment.
17. The method of claim 16, wherein the carrier is a first carrier,
the method further comprising: receiving information regarding the
capability partitioning configuration of the second user equipment
from the network element on a second carrier.
18. The method claim 16, further comprising: wherein the decoding
step further comprises decoding the packet in accordance with the
category of the second user equipment.
19. The method of claim 16, wherein the carrier is an uplink
carrier, the method further comprising: receiving information
regarding the capability partitioning configuration of the second
user equipment from the network element on a downlink carrier.
20. The method of claim 16, wherein the capability partitioning
configuration of the second user equipment comprises a
configuration of the second user equipment's soft buffer.
21. The method of claim 20, wherein the second user equipment's
soft buffer configuration comprises a number of soft channel bits
used by the second user equipment for device to device
communication.
22. The method of claim 20, the method further comprising
partitioning the first user equipment's soft buffer for
simultaneous communication with the network element and the second
user equipment.
23. The method of claim 16, wherein the capability partitioning
configuration comprises a maximum number of HARQ processes that can
be used by the second user equipment for device to device
communication.
24. A first user equipment comprising: a transceiver; a memory
communicatively linked to the transceiver, the memory being
configured to store data representing a first capability
partitioning configuration of the first user equipment and a second
capability partitioning configuration of the first user equipment;
a processor communicatively linked to the memory and to the
transceiver, the processor being configured to retrieve the data
from the memory and, using the retrieved data, control the
transceiver to communicate with a network element according to the
first capability partitioning configuration and with a second user
equipment according to the second capability partitioning
configuration.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation of U.S. patent
application Ser. No. 13/727,692, filed Dec. 27, 2012, the
disclosure of which is incorporated herein by reference.
TECHNICAL FIELD
[0002] The disclosure relates to device-to-device communication in
a wireless network.
BACKGROUND
[0003] The demand for data capacity in wireless networks has
increased dramatically with the widespread use of smartphones and
tablet computers. In addition to traditional voice services,
consumers now expect to be able to use their wireless devices to
watch streaming video, often in a high-definition format, play
on-line games in real-time, and transfer large files. This has put
additional load on wireless networks and, in spite of advances in
cellular technology (e.g., the deployment of 4G networks, the use
of newer versions of the IEEE 802.11 family of standards), capacity
is still an issue that providers have to consider.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] FIG. 1 is an example of a communication system in which
various embodiments of the invention may be implemented.
[0005] FIG. 2 is a block diagram depicting certain aspects of a
network entity in accordance with an embodiment of the
invention.
[0006] FIG. 3 is a block diagram depicting aspects of a UE in an
embodiment of the invention.
[0007] FIG. 4A is a frame structure according to an embodiment of
the invention.
[0008] FIG. 4B is a resource block according to an embodiment of
the invention.
[0009] FIG. 5 is an uplink subframe according to an embodiment of
the invention.
[0010] FIG. 6 is a downlink subframe according to an embodiment of
the invention.
[0011] FIG. 7A is a carrier according to an embodiment of the
invention.
[0012] FIG. 7B is an aggregation of component carriers according to
an embodiment of the invention.
[0013] FIG. 8A is a wireless network according to an embodiment of
the invention.
[0014] FIG. 8B shows a frame, subframe, and special subframe
according to an embodiment of the invention.
[0015] FIGS. 9, 10, and 11 show a D2D communication scheme
according to an embodiment of the invention.
[0016] FIGS. 12, 13, 15, and 16 depict steps taken during D2D
communication according to various embodiments of the
invention.
[0017] FIG. 14 depicts HARQ buffering according to an embodiment of
the invention.
DESCRIPTION
[0018] Cellular networks such as LTE and UMTS have traditionally
operated on a model in which the network controls radio
communications. For example, assume that UE1 and UE2 operate in a
traditional cellular network, and that the network includes eNB1
and eNB2, with UE1 being connected to eNB1, and UE2 being connected
to eNB2. When UE1 transmits data that is intended for UE2, the data
travels from UE1 to eNB1, which relays the data to eNB2. The eNB2
then relays the message to UE2. Thus, it takes at least two hops
(UE1->eNB1) (eNB2->UE2) on the cellular network for data to
get from UE1 to UE2. There may also be further delay resulting from
additional hops being needed for routing. Such delays may occur
even if the two UEs are connected to the same eNB.
[0019] However, if the UEs are able to communicate directly with
one another using so-called Device-to Device (D2D) communication,
it would take only one hop (UE1->UE2) for data to get from UE1
to UE2.
[0020] In an embodiment of the invention, UEs communicate directly
with one another without passing through a network or other
intermediate entity. To carry out such D2D communication, the UEs
use resources (e.g., cellular spectrum) of the network. The UEs
may, however, maintain their usual connections to the network
(e.g., each UE may still be connected to an eNB of a cellular
network).
[0021] Benefits of D2D communication in a cellular network include
(1) increased cellular system throughput (e.g., D2D traffic uses
fewer resources to communicate same amount of data), and (2)
improved user experience (e.g., faster data transfer and reduced
latency).
[0022] In accordance with the foregoing, a method and apparatus for
device-to-device communication is provided. In an embodiment of the
invention, a first user equipment (UE) wirelessly communicates with
a network element (e.g., an eNB) on a carrier (e.g., a cellular
uplink or downlink carrier) in accordance with its first capability
partitioning configuration. The first UE engages in direct wireless
communication on the carrier with a second UE in accordance its
second capability partitioning configuration.
[0023] The first UE may also engage in direct wireless
communication with the second UE in accordance with the second UEs
capability partitioning configuration. Examples of such
communication include: transmitting/receiving encoded packets
to/from the second UE; and encoding/decoding such packets. The
first UE may also acquire information regarding a capability
partitioning configuration of the second UE from the network
element, via a second carrier.
[0024] In some embodiments, the UE's first and second capability
partitioning configurations are first and second buffer
partitioning configurations. Possible buffer configurations
include: a maximum number of HARQ processes that the first UE will
use for communicating with the second UE (or network element); the
size of a soft buffer that the first UE will use for communicating
with the second UE (or network element); and a number of soft
channel bits that the first UE will use for communicating with the
second UE (or network element).
[0025] In some embodiments, the first UE transmits information
regarding one or more of its capability configurations to the
network element via the first carrier, receives information
regarding a capability partitioning configuration of the second UE
from the network element (or the second UE) via a second carrier.
The first UE engages in wireless communication directly with the
second UE on the first carrier in accordance with the capability
partitioning configuration of the second UE and the capability
partitioning configuration of the first UE.
[0026] In an embodiment, the first UE can have multiple soft buffer
configurations, such as a first soft buffer configuration for
communicating with the network entity and a second soft buffer
configuration for communicating with the second UE, possibly
simultaneously.
[0027] In an embodiment, the first or second UE's soft buffer
configuration is one or more of (1) the maximum number of HARQ
processes that the UE will use for receiving packets (the number of
buffer partitions needed); (2) the size of a soft buffer that the
UE will use for receiving packets; and (3) the number of soft
channel bits that the UE will use for receiving packets.
[0028] An embodiment of the invention is a UE that includes a
transceiver; a memory, and a processor. The memory is
communicatively linked to the transceiver and is configured to
store data representing a first capability partitioning
configuration of the UE and a second capability partitioning
configuration of the UE. The processor is communicatively linked to
the memory and to the transceiver, and is configured to retrieve
the data from the memory and, using the retrieved data, control the
transceiver to communicate with a network element according to the
first capability partitioning configuration and with a another UE
according to the second capability partitioning configuration.
[0029] The UE further includes a memory communicatively linked to
the transceiver. The memory is configured to store data
representing the identified resources. The UE further includes a
processor communicatively linked to the memory and to the
transceiver. The processor is configured to retrieve the data from
the memory and, using the retrieved data, control the transceiver
to engage in direct wireless communication with the second UE using
the identified resources of the first carrier.
[0030] Referring to FIG. 1, an example of a wireless communication
network in which embodiments of the invention may be used will now
be described. The network 100 is configured to use one or more
Radio Access Technologies (RATs), examples of which include an
E-UTRA, IEEE 802.11, and IEEE 802.16. The network 100 includes a
first cell C1 and a second cell C2. Possible implementations of C1
and C2 include a cellular network macrocell, a femtocell, a
picocell, and a wireless access point. First cell C1 is managed by
a first network entity NE1 and second cell C2 is managed by a
second network NE2. Possible implementations of a network entity
include an E-UTRA base station, an eNB, a transmission point, a
Remote Radio Head, an HeNB, an 802.11 AP, and an IEEE 802.16 base
station.
[0031] Also shown in FIG. 1 are User Equipments (UE) UE1, UE2, and
UE3. Possible implementations of a UE include a mobile phone, a
tablet computer, a laptop, and an M2M (Machine-to-Machine) device.
Each of NE1 and NE2 transmits signals to and receives signals from
one or more of the UEs.
[0032] Communication between a network entity and a UE typically
occurs when the UE is located within the network entity's coverage
area. For example, NE1 would typically communicate with UE1 and
UE2, and NE2 would typically communicate with UE3. In certain
circumstances, each network entity may transmit signals to and
receive signals from UEs that are connected to other network
entities. For example, NE1 may be able to communicate with UE3 if
UE3 is close to NE1's coverage area.
[0033] The cells, network entities, and UEs of FIG. 1 are only
representative, and are intended to facilitate description. In
fact, the network 100 may have many cells and network entities and
be in communication with many UEs.
[0034] In some embodiments of the invention, C1 or C2 are
controlled by a single network entity, or by multiple network
entities that coordinate with one another, e.g., when Carrier
Aggregation (CA) or Coordinated Multipoint communication (COMP) is
being used. Furthermore, one or more of C1 and C2 may be a virtual
cell. A virtual cell is a cell that is created as a result of
multiple network entities cooperating. A UE generally does not
perceive any distinction between a virtual cell and a non-virtual
cell.
[0035] In an embodiment of the invention, each UE (FIG. 1) is a
wireless communication device capable of sending and receiving data
via the network entities NE1 and NE2 to and from other elements of
the network 100. Each UE is also capable of communicating with the
other UEs over the network 100 via one or more of the network
entities NE1 and NE2. Additionally, one or both of the UEs is
capable of engaging in D2D communication.
[0036] In various embodiments, each UE of FIG. 1 is capable of
transmitting user data and control information to one or more of
the network entities on an UL carrier, and receiving data and
control signals from one or more of the network entities on a DL
carrier. As used herein, "control information" includes data that
UEs and various elements of the network 100 use for facilitating
information, but that is not intended to be accessed by a user or
by user applications. "User data" as herein refers to data that is
intended to be accessed by a user and user applications.
[0037] In an embodiment of the invention, the UL carrier is made up
of a first set of RF frequencies, while the DL carrier is made up
of a second set of RF frequencies. In some embodiments, the
frequencies of the UL carrier do not overlap with the frequencies
of the DL carrier. The UL and DL carriers may be part of spectrum
licensed for use by a regulatory body, such as the Federal
Communication Commission (FCC). The UL and DL carriers may also be
assigned for un-licensed use by the regulatory body.
[0038] In one embodiment, at least one of the UL carrier and the DL
carrier is made up of a single block of contiguous frequencies. In
another embodiment, at least one of the UL carrier and the DL
carrier is made up of multiple, non-overlapping blocks of
contiguous frequencies.
[0039] Referring still to FIG. 1, the network 100 also includes a
backhaul system (not shown). The backhaul system includes wired and
wireless infrastructure elements, such a fiber optic lines, that
carry signals around various parts of the network 100, including
among the network entities. The network 100 also includes a core
106 that controls the operation of the network 100 using various
resources, including billing systems, home location registers, and
internet gateways. Several core resources are depicted in FIG. 1.
In an LTE implementation, resources of the core 106 communicate
with network entities over E-UTRA and with other networks. Examples
of core resources are depicted in FIG. 1.
[0040] FIG. 2 illustrates a configuration of a network entity (from
FIG. 1) in accordance with an embodiment of the invention. The
network entity includes a controller/processor 210, a memory 220, a
database interface 230, a transceiver 240, input/output (I/O)
device interface 250, a network interface 260, and one more
antennas, represented by antenna 221. Each of these elements is
communicatively linked to one another via one or more data pathways
270. Examples of data pathways include wires, including wires whose
dimensions are measured in microns, and wireless connections.
[0041] During operation of the network entity, the transceiver 240
receives data from the controller/processor 210 and transmits RF
signals representing the data via the antenna 221. Similarly, the
transceiver 240 receives RF signals via the antenna 221 converts
the signals into the appropriately formatted data, and provides the
data to the controller/processor 210. The controller/processor 210
retrieves instructions from the memory 220 and, based on those
instructions, provides outgoing data to, or receives incoming data
from the transceiver 240. If needed, the controller/processor can
retrieve, from a database via the database interface 230, data that
facilitates its operation.
[0042] Referring still to FIG. 2, the controller/processor 210 can
transmit data to other network entities of the network 100 (FIG. 1)
via the network interface 260, which is coupled to the backhaul
network. The controller/processor 210 can also receive data from
and send data to an external device, such as an external drive, via
the input/output interface 250.
[0043] The controller/processor 210 may be any programmable
processor. The controller/processor 210 may be implemented, for
example, as a general-purpose or a special purpose computer, a
programmed microprocessor or microprocessor, peripheral integrated
circuit elements, an application-specific integrated circuit or
other integrated circuits, hardware/electronic logic circuits, such
as a discrete element circuit, a programmable logic device, such as
a programmable logic array, field programmable gate-array, or the
like.
[0044] The memory 220 may be implemented in a variety of ways,
including as volatile and nonvolatile data storage, electrical,
magnetic optical memories, random access memory (RAM), cache, hard
drive, or other type of memory. Data is stored in the memory 220 or
in a separate database. The database interface 230 is used by the
controller/processor 210 to access the database. The database
contains any formatting data to connect UE to the network 100 (FIG.
1). The transceiver 240 creates a data connection with the UE.
[0045] The I/O device interface 250 may be connected to one or more
input devices that may include a keyboard, mouse, pen-operated
touch screen or monitor, voice-recognition device, or any other
device that accepts input. The I/O device interface 250 may also be
connected to one or more output devices, such as a monitor,
printer, disk drive, speakers, or any other device provided to
output data. The I/O device interface 250 may receive a data task
or connection criteria from a network administrator.
[0046] The network connection interface 260 may be connected to a
communication device, modem, network interface card, a transceiver,
or any other device capable of transmitting and receiving signals
from the network 100. The network connection interface 260 may be
used to connect a client device to the network.
[0047] According to an embodiment of the invention, the antenna 221
is one of a set of geographically collocated or proximal physical
antenna elements linked to the one or more data paths 270, each
having one or more transmitters and one or more receivers. The
number of transmitters that the network entity has is related, to
the number of transmit antennas that the network entity has. The
network entity may use the multiple antennas to support MIMO
communication.
[0048] FIG. 3 illustrates a block diagram of a UE (such as one or
more of the UEs depicted in FIG. 1) according to an embodiment of
the invention. The UE includes a transceiver 302, which is capable
of sending and receiving data over the network 100. The transceiver
is linked to one or more antennas 303 that may be configured like
the one or more antennas of the network entity of FIG. 2. The UE
may support MIMO.
[0049] The UE also includes a processor 304 that executes stored
programs, as well as a volatile memory 306, and a non-volatile
memory 308. The volatile memory 306 and the non-volatile memory 308
are used by the processor 304. The UE includes a user input
interface 310 that may comprise elements such as a keypad, display,
touch screen, and the like. The UE also includes a display screen
and an audio interface 312 that may comprise elements such as a
microphone, earphone, and speaker. The UE also includes a component
interface 314 to which additional elements may be attached, for
example, a universal serial bus (USB) interface. Finally, the UE
includes a power supply 316.
[0050] During operation, the transceiver 302 receives data from the
processor 304 and transmits RF signals representing the data via
the antenna 303. Similarly, the transceiver 302 receives RF signals
via the antenna 303, converts the signals into the appropriately
formatted data, and provides the data to the processor 304. The
processor 304 retrieves instructions from the non-volatile memory
308 and, based on those instructions, provides outgoing data to, or
receives incoming data from the transceiver 302. If needed, the
processor 304 can write to, or read from the volatile memory 306,
particularly for caching data and instructions that the processor
304 requires in order for it to perform its functions.
[0051] The user interface 310 includes a display screen, such as a
touch-sensitive display, that displays, to the user, the output of
various application programs. The user interface 310 additionally
includes on-screen buttons that the user can press in order to
cause the UE to respond. The content shown on the user interface
310 is generally provided to the user interface at the direction of
the processor 304. Similarly, information received through the user
interface 310 is provided to the processor, which may then cause
the UE to react.
[0052] Referring again to FIG. 1, the general mode of communication
of the network 100 according to an embodiment of the invention will
now be described. The network entities and the UEs generally
communicate with one another via physical UL channels of the UL
carrier and via physical DL channels of the DL carrier. In an LTE
embodiment, the modulation scheme used for communication between
the network entities and the UEs differs depending on whether the
signals are being sent in the UL direction (travelling from a UE to
a network entity) or in the DL direction (travelling from a network
entity to a UE). The modulation scheme used in the DL direction is
a multiple-access version of OFDM called Orthogonal
Frequency-Division Multiple Access (OFDMA). In the UL direction,
Single Carrier Frequency Division Multiple Access (SC-FDMA) or
DFT-SOFDM is typically used. In an LTE implementation, the
bandwidth of the UL or DL carrier varies depending upon whether
carrier aggregation is being used (e.g., up to 20 MHz without CA,
or up to 100 MHz with CA). In FDD operation, the frequencies in the
bandwidth of the UL carrier and the frequencies in the bandwidth of
the DL carrier do not overlap.
[0053] Referring to FIG. 4A, an LTE frame structure used for
carrying data between the UEs and the network entities on both UL
carriers and DL carriers according to an embodiment of the
invention will now be described. In LTE FDD operation, both uplink
and downlink Radio frames are each 10 milliseconds (10 ms) long,
and are divided into ten subframes, each of 1 ms duration. Each
subframe is divided into two slots of 0.5 ms each. Each slot
contains a number of OFDM symbols, and each OFDM symbol may have a
Cyclic Prefix (CP). The duration of a CP varies according to the
format chosen, but is about 4.7 microseconds in the example of FIG.
4A, with the entire symbol being about 71 microseconds. In the
context of time-frequency, the subframe is divided into units of
RBs, as shown in FIG. 4B. When a normal CP is used, each RB 402 is
12 subcarriers by 7 symbols (one slot). Each RB (when a normal CP
is used), in turn, is composed of 84 REs 404, each of which is 1
subcarrier by 1 symbol. However, RBs and REs may be other sizes in
other embodiments. Thus, the terms RE and RB may includes
time-frequency resources of any size. In LTE, an RB or an RB pair
is the typical unit to which resource allocations may be assigned
for uplink and downlink communications.
[0054] Referring to FIG. 5, a UL subframe structure used to carry
data from UEs to the network entities over an UL carrier according
to an LTE embodiment of the invention will now be described. The
horizontal scale of FIG. 6 represents frequency, while the vertical
scale represents time. In LTE, a UE typically transmits data to a
network entity on a Physical Uplink Shared Channel (PUSCH), and
typically transmits control information to a network entity on a
physical uplink control channel (PUCCH). The PUSCH generally
carries user data such as video data (e.g., streaming video) or
audio data (e.g., voice calls) from the UEs to the network
entities. A UE may also transmit control information on the PUSCH,
such as HARQ feedback, CSI reports. Additionally, a UE can transmit
a scheduling request (SR) on the PUCCH. A UE may also transmit a
sounding reference signal (SRS), which is not part of any
particular channel.
[0055] To request uplink resources from a network entity in an
embodiment of the invention, a UE transmits a scheduling request to
a network entity. Referring to FIG. 6, if the network entity grants
the request, it responds by sending a scheduling grant to the UE. A
scheduling grant is part of the downlink control information (DCI).
The network entity transmits the DCI on a downlink control channel
(e.g., a physical downlink control channel (PDCCH)). The scheduling
grant provides the UE with parameters that the UE uses to transmit
data on the PUSCH. These parameters include a data modulation and
coding scheme, the transport block size, a resource allocation
(e.g., resource blocks and position within the transmission
bandwidth configuration), hopping parameters, power control
information, and other control information.
[0056] In an embodiment of the invention, there are different PUCCH
formats, but regardless of format a PUCCH generally carries control
information from the UEs to the network entities. PUCCH resource
blocks are typically located at the edges of the UL carrier, while
the RBs in between may be used for PUSCH resource assignment. In
various embodiments of the invention described herein, a network
entity can configure a PUCCH to carry data from UE to UE in D2D
communication. The portion of the PUCCH used for D2D will be
referred to as PUCCH-D2D.
[0057] The control information transmitted by a UE on the PUCCH
includes HARQ feedback, SR, and CSI reports. The UE sends HARQ
feedback in order to ACK or NACK data that the UE receives from a
network entity. An SR is used by the UE to request UL resources
from the network 100, including from one or more network entities.
CSI reports are used by a UE to report, to a network entity,
information regarding the DL transmission channel as seen from the
point of view of the UE.
[0058] Each CSI report sent by a UE may include one or more of a
CQI, a PMI, PTI, and an RI. The UE uses the CQI to indicate the
highest MCS that, if used, would result in DL transmissions having
a BLER of no more than 10%. The UE uses the PMI to indicate, to the
network entity, which precoder matrix should be used for DL
transmissions. The RI is used by the UE to recommend the
transmission rank (number of transmission layers) that should
preferably be used for DL transmission to the UE. The PTI
distinguishes slow fading environments from fast fading
environments.
[0059] According to an embodiment of the invention, the UE
transmits control information on RB pairs configured for PUCCH-D2D.
The PUCCH-D2D RBs do not have to be contiguous. Each RB of a pair
may, for example, be located on opposite ends of the frequency
range of the transmission bandwidth.
[0060] A UE may transmit an UL DM-RS and/or SRS during
communication with the network. The UL DM-RS is used by a network
entity for channel estimation to enable coherent demodulation of
the PUSCH and/or PUCCH. The SRS is used by the network entity for
channel state estimation to support uplink channel-dependent
scheduling and link adaptation.
[0061] Referring to FIG. 6, a time-frequency diagram of a DL
subframe used for carrying data from one or more network entities
to a UE on a DL carrier will now be described. The horizontal scale
of FIG. 6 represents frequency, while the vertical scale represents
time. The horizontal scale is divided into multiple blocks of
frequency, or OFDM subcarriers ("subcarriers") that may be
allocated for transmission. The vertical scale of FIG. 6 is divided
into multiple blocks of time, or OFDM symbols ("symbols") that may
be allocated for transmission. The subframe is divided into
time-frequency resource blocks (RBs). Each RB is twelve subcarriers
by seven symbols typically for normal CP. The subframe is a total
of 1 ms long and is divided into two time slots of 0.5 ms each. In
turn, each RB can be divided into multiple resource elements (REs).
Each RE is one subcarrier by one symbol.
[0062] The DL subframe includes several types of reference signals.
The references signals are transmitted by the network entity to the
UE to enable the UE to perform various functions. One such
reference signal is Channel State Information Reference Signal
(CSI-RS), which is used by the UE to determine channel-state
information (CSI). The UE reports CSI to the network entity. The
CSI-RS is not necessarily transmitted in all subframes.
[0063] Referring again to FIG. 6, other reference signals on the UL
subframe include a Demodulation Reference Signal (DM-RS) with the
REs being referred to as DM-RS REs. Typically, reference signals
corresponding to antenna ports 7 and 8 are multiplexed using Code
Division Multiplexing (CDM) or other scheme and are mapped to the
same REs in time and frequency domain. The subframe can also
include other reference signals such as cell-specific reference
signal (CRS), positioning reference signal (PRS), primary
synchronization signal (PSS) and secondary synchronization signal
(SSS) that are distributed in the control regions and/or user data
regions of the sub-frame.
[0064] The network entity provides the CSI-RS configuration to the
UE via RRC signaling. The RRC layer in the UE provides the CSI-RS
configuration information to the physical layer in the UE (e.g.,
"higher layer signaling").
[0065] Referring to FIG. 7A, the structure of an uplink carrier
will now be described. The UL carrier 700 has a channel bandwidth
732 that spans a range of frequencies from a first edge 716 to a
second edge 720. The carrier 700 also has a range of frequencies
that make up a transmission bandwidth configuration 734. The
transmission bandwidth configuration starts at a first edge 722 and
ends at a second edge 724. Between the first edge 716 of the
channel bandwidth and the first edge 722 of the transmission
bandwidth configuration is a first spectral emissions region 708.
Between the second edge 720 of the channel bandwidth and the second
edge 724 of the transmission bandwidth configuration is a second
spectral emissions region 710.
[0066] Referring still to FIG. 7A the channel bandwidth 732 is the
RF bandwidth supporting a single RF carrier with the transmission
bandwidth configured in the uplink or downlink of a cell. The
channel bandwidth is typically measured in MHz and is usually used
as a reference for transmitter and receiver RF requirements. The
transmission bandwidth configuration 734 is the highest
transmission bandwidth permitted (e.g., according to industry
standards, or government regulation) for uplink or downlink in a
given channel bandwidth. In some cases (e.g., when the carrier is
an E-UTRA/LTE carrier), transmission bandwidth configuration is
measured in Resource Block units.
[0067] Referring to FIG. 7B, an aggregated carrier 750 is shown.
The carrier 750 has an aggregated channel bandwidth 780 and an
aggregated transmission bandwidth configuration 782. The aggregated
carrier 750 is made up of three component carriers 752, 754, and
756. As shown in FIG. 7B, the same elements described in
conjunction with FIG. 7A are present in the carrier 750.
Specifically, there are RBs 760 defined in the spectral emission
regions outside of the transmission bandwidth configuration of each
of the three component carriers but within the channel bandwidths
of each of the three carriers.
[0068] Referring still to FIG. 7B, the aggregated channel bandwidth
780 is the RF bandwidth in which a UE can transmit and/or receive
multiple contiguously aggregated carriers. The aggregated
transmission bandwidth configuration 782 is the highest
transmission bandwidth permitted (e.g., according to industry
standards, or government regulation) for uplink or downlink in a
given aggregated channel bandwidth. In some cases (e.g., when the
carrier is an E-UTRA/LTE carrier), transmission bandwidth
configuration is measured in Resource Block units.
Using HARQ
[0069] The structure of a soft buffer in the manner in which UEs
use the soft buffer in an embodiment of the invention will now be
described with reference to FIGS. 3 and 14. Referring to FIG. 3,
the transceiver 302 receives the signal via a carrier (e.g., a UL
carrier, a DL carrier, or a D2D carrier). The transceiver 302
passes the signal to the processor 304 which, in this example, is a
baseband processor. One or more of the transceiver 302 and
processor 304 includes a signal processing element 1400, which is
shown in FIG. 14.
[0070] The signal processing element 1400 may be implemented in
hardware, software, or a combination of the two. The signal
processing element 1400 is organized into functional blocks. These
blocks are depicted in FIG. 14, and their functions will now be
described. The signal is received by the transceiver 302 (FIG. 3),
which demodulates the signal and generates the received
Log-likelihood ratios (LLRs) for a given TB. The HARQ combining
element 1408 combines the received LLRs with stored LLRs for the TB
from a previous transmission. The combined LLRs are decoded by the
processor 304 at block 1410 and may be passed to another process
(e.g., sent to higher layers for further processing). If the TB is
not successfully decoded, then the combined LLRs for that TB are
stored in a partition 314 of a soft buffer 1412.
[0071] If a TB is not successfully decoded at block 1410, the UE
may transmit the HARQ feedback on its uplink. The soft buffer 1412
holds the combined LLR for a TB until the UE makes another attempt
to decode the TB.
[0072] The transmitting entity (not shown in FIG. 14), upon
receiving the HARQ feedback indicating the UE has not successfully
received the TB, attempts to retransmit the TB. The retransmitted
TB is put through the same functional blocks as before, but when
the UE attempts to decode the retransmitted TB at block 1410, the
UE retrieves the LLRs for the TB from its memory 1414, and uses the
HARQ combining element 1408 to combine the received LLRs and the
stored LLRs for the TB in a process known as "soft combining." The
combined LLRs are provided to the decoder 1410, which decodes the
TB and provides the successfully decoded TB to higher layers for
further processing.
[0073] The soft buffer 1412 may also be referred to as a HARQ
memory or HARQ buffer. Since there are multiple HARQ processes, a
HARQ process index or HARQ identity (typically signaled using an
explicit field within DCI format associated with the TB (e.g. for
downlink), or implicitly determined via subframe number, system
frame number, etc (e.g. for uplink)) is made available for the HARQ
combining element 1418 to correctly perform the combining
operation. For the uplink transmission, the implicit HARQ process
index is used by the UE to correctly determine the coded bits for
uplink transmissions.
[0074] If UE is configured with a transmission mode with a maximum
of one TB per HARQ process (or one TB per TTI), the soft buffer of
the UE may be divided into eight partitions 1414 as shown in FIG.
14. If the UE is configured with transmissions modes with a maximum
of two TBs per HARQ process (or two TBs per TTI), each of the eight
partitions 1414 may be further divided into a first partition 1414A
and a second partition 1414B or the soft buffer of the UE may be
divided into sixteen partitions.
[0075] In an LTE embodiment of the invention, a UE's soft buffer
configuration is determined at least in part by its category.
Referring to Table 1, for example, a UE of Category-3 is expected
to offer 1,237,248 soft channel locations, wherein each soft
channel location can store a Log-likelihood ratio (LLR).
[0076] For FDD, for a given component carrier, a UE has eight HARQ
processes in DL. Based on the transmission mode, the UE is capable
of receiving one or two transport blocks (corresponding to a HARQ
process) within a TTI. Thus, a UE may determine the amount of
storage per received transport block based on the total number of
soft channel bits, the maximum number of HARQ processes, the
transmission mode, etc. Similarly, NE1 may encode and transmit only
those coded bits that it knows the UE is capable of processing
and/or storing.
[0077] In some scenarios, if the UE has insufficient amount of
storage for a given transport block, and a decoding failure occurs,
the UE may choose to store some LLRs and discard some other LLRs.
In other scenarios, if no storage is available or no storage is
deemed necessary for a transport block, if a decoding failure
occurs, the UE may discard all LLRs corresponding to the transport
block. Such scenarios typically occur where the network entity
transmits a quantity of coded bits that exceed the storage capacity
of the UE. Typical examples include: (1) when carrier aggregation
is being used (e.g., a UE is supporting two or more carriers, and 8
HARQ processes per carrier), and (2) When TDD is being used (e.g.,
UE supporting up to HARQ processes per carrier). For FDD, and for
uplink, for a given component carrier, a UE has eight HARQ
processes when the UE is not configured in UL-MIMO transmission
mode (16 when the UE is configured in UL-MIMO transmission mode).
For TDD, the number of HARQ processes for the uplink is determined
based on the TDD UL/DL configuration.
[0078] With reference to Table 1, the soft buffer dimensioning for
UE Category 3 in LTE Rel-8/9 is defined assuming Limited Buffer
Rate Matching (LBRM). With LBRM, for a subset of large TB sizes,
the UE is allowed to provision a per TB soft buffer size that is
smaller than the maximum required soft buffer size to achieve
mother code rate of 1/3. For example, a standard-compliant LTE
Category 3 UE operating with 2 spatial layers should support a
largest TB size of 75376. For this TB size, given 1237248 total
soft channel bits (i.e., soft buffer size corresponding to these
bits), the UE can only provision 77328 soft channel bits per each
of the two possible TBs within a TTI. This amounts to an effective
mother code rate (ECR) or minimum achievable code rate of around
0.97 for that TB size. The effective mother code rate may be
defined as the number of information bits divided by the number of
encoded bits that can be stored in the soft buffer
[0079] It is to be noted that the effective mother code rate may be
different from the code rate employed by the FEC encoder (e.g.
turbo code), as the two are defined from different perspectives. It
is possible to have a turbo code (FEC encoder) code rate of 1/3,
wherein the code is shortened or some of the output parity bits are
punctured (due to soft buffer storage limitations) to lead to an
effective mother code rate larger than 1/3. For example, if 50% of
the output parity bits are punctured, then the ECR is approximately
2/3 whereas the turbo code rate is 1/3. For TB sizes less than
25456 approximately, the ECR is the same as mother code rate of
1/3, which means that LBRM need not be employed.
[0080] In an LTE embodiment of the invention, the number of soft
channel bits for encoding a TB is determined as follows:
N IR = N soft K C K MIMO min ( M DL _ HARQ , M limit )
##EQU00001##
[0081] where N.sub.soft is the total number of soft channel bits,
K.sub.MIMO is equal to 2 if the UE is configured to receive PDSCH
transmissions based on spatial multiplexing with rank greater than
1 such as transmission modes 3, 4 or 8, 1 otherwise, MDL_HARQ is
the maximum number of DL HARQ processes (i.e., HARQ processes in
the downlink direction), and Mlimit is a constant equal to 8, KC is
a value (from 1, 2 or 5) dependent on the UE category and UE
capability with regard to support of a number of spatial layers for
the component carrier on which the transport block is transmitted.
If a UE signals a Rel-10 UE category (one of 6, 7, 8) it also
signals a corresponding second category (one of 4, 5) for
backward-compatibility (e.g. to allow a Rel-10 Category6 UE operate
in a Rel-8/9 network). The value of Nsoft used for encoding a TB is
based on the signaled UE category, maximum number of layers
supported by the UE on the particular component carrier, etc. On
the UE side, the number of soft channel bits that UE offers for
storing a TB on a carrier may be given by the same formula above,
but replacing Nsoft with Nsoft/Ncell, where Ncell is the number of
configured components carriers for the UE.
[0082] When the UE transmits a transport block on the uplink to a
network entity, LBRM is typically not applied because the network
entity has adequate memory resources. Therefore, for uplink
transmission, the number of encoded bits for a transport block is
given by the turbo code mother code rate with the LBRM being
transparent. This implies that the rate-matching procedure on the
downlink direction (with LBRM) and the same in uplink direction
(i.e. w/o LBRM) is not symmetric.
D2D Communication
[0083] In an embodiment of the invention, UEs engage in D2D
communication using resources of either the UL or the DL carriers.
The UEs may also engage in D2D communication using resources of
other carriers that are not used by the UEs to communicate with the
network entities.
[0084] The UEs may, in an embodiment of the invention, engage in
D2D communication with one another on a frame structure that uses
time-frequency resources of either the UL carrier or the DL
carrier. In some embodiments the structure of the frame is based on
a TDD frame. The D2D frames/subframes can be completely distinct
from the frames/subframes that are used for communication between
the network elements and the UEs.
[0085] In various embodiments of the invention, UEs transmit data
to one another over channels defined similar to PUSCH when the UEs
are engaged in D2D communication, such as D2D-SCH (D2D-Shared
Channel) or PUCCH-D2D. The PUCCH-D2D may be seen as another
instantiation of a configured D2D-shared channel.
[0086] The RBs of an RB pair assigned for a D2D link may be next to
one another in the subframe or may be separated in frequency. In
some cases, when the UEs are engaged in D2D communication, the UEs
transmit data to one another over a separate physical channel that
is defined specifically for D2D communication (e.g., D2D-SCH).
[0087] The RBs of an RB pair assigned for a D2D-SCH may be next to
one another in the subframe or may be separated in frequency. The
RBs of an RB pair assigned for a D2D-SCH may be next to RBs of an
RB-pair assigned for PUSCH. RBs assigned for PUSCH and RBs assigned
for D2D-SCH may share the same UL carrier. D2D links carrying user
data and control information between UEs can occur over D2D-SCH or
similarly defined links. The configuration for the D2D links may be
similar to PUSCH, PDSCH or PUCCH. The PDSCH may be appropriate
since one UE is transmitting to another, similar to the network
transmitting to a UE in regular cellular communications.
Determining Whether D2D Communication is to be Used
[0088] In accordance with an embodiment of the invention, UEs enter
D2D mode based on a decision making process. This decision making
process may be carried out by one or more of the UEs, and/or by a
network entity. A UE or network entity can make this determination
when the UE is in idle mode, in which the UE is generally not
communicating with the network 100, except for sending or receiving
location information, paging signals, and emergency signals. The UE
or network entity can also make this determination when the UE is
in a connected mode, in which the network 100 has obtained
information about the specific UE, and maintains that
information.
[0089] Once it has been decided that the UEs are to start
communicating with one another in D2D mode, either one or more of
the UEs requests permission to begin D2D communication from the
network entity, or the network entity orders, without receiving a
request, one or more of the UEs to enter D2D mode. In an embodiment
of the invention, the decision is made by, at least in part, by the
core 106. It is to be understood, however, that the decision of
whether or not the UEs can enter D2D communication (e.g., a command
to do so) is communicated to the UEs from the network entity, even
if the resources of the core 106 take part in the decision
making.
[0090] According to an embodiment of the invention, the
determination as to whether or not UEs should communicate using D2D
is made based on one or more of a variety of factors, including the
proximity of the UEs to one another, the strength of reference
signals that one of the UEs receives from the other UE, the
strength of the signals that the network entity receives from one
or more of the UEs, the detection of a user input.
[0091] In one embodiment, the UE or network entity makes the D2D
determination based on the strength of a public safety network
signal (e.g., a public safety UE reference signal) that a UE and/or
network entity detects. As a result of the detected strength, it
may be decided that the UEs will reduce their maximum transmit
power, or that they will refrain from D2D communication entirely.
For example, if the public safety network signal is weak, then the
UEs or network entity may decide to refrain from D2D communication.
If the public safety network signal is strong, then the UEs or
network entity may decide to proceed with D2D communication.
However, in an emergency (e.g., a UE dials 911) a UE may be
permitted to transmit critical information, such as its location,
in D2D mode. In such a case, the UE would be able to use a limited,
designated set of resources (subframes and/or resource blocks) to
communicate.
[0092] In an embodiment of the invention, a network entity
determines whether to set up a D2D connection between UEs based on
the ability of each UE to engage in D2D communication, and based on
the ability of each UE to engage simultaneously in both D2D and
regular cellular communication. The network entity may, prior to
making this determination, establish a connection with one or more
of the UEs. In such case, the D2D communication may occur on the
same carrier that the network entity used for connecting to the
UEs.
[0093] Referring to FIG. 1, the network entities and the UEs may
request and receive information from the core 106 to assist in
making the D2D determination. A network entity can determine the
proximity between the UEs by requesting location information from
the core (which may maintain a record of the location of the UEs
and/or subscription information) or using GPS location reports from
the UEs. The network entity can determine the strength of signals
that, for example, UE2 receives from UE1 by obtaining a report from
UE2 describing the strength of reference signals transmitted by
UE1. The UEs can also determine their proximity to one another
using the DM-RS configuration of the other UE sent out by network
entity. The DM-RS serve as reference signals that are used by the
UE in conjunction with a threshold to determine their proximity to
one another.
[0094] In some circumstances, UEs may be operating in different
cells, yet be close enough and have a strong enough signal between
them to communicate D2D. For example, in FIG. 1, UE2 and UE3 may be
able to communicate using D2D even though UE1 is in C1 and UE3 is
in C2. In such a case, the network entity of C1 may need to
communicate with the network entity of C2 via the backhaul network
to coordinate the set of up such D2D communication.
REFERENCE SIGNALS FOR DISCOVERY
[0095] According to an embodiment of the invention, UEs having D2D
capability can transmit reference signals to allow other
D2D-capable UEs to discover them. There are many types of signals
that a UE can use as a reference signal for the purpose of D2D
discovery. In an embodiment of the invention, a UE implements a D2D
discovery reference signal by transmitting a zero power PUSCH or
PDSCH, in which only the embedded DM-RS has a non-zero power level.
Alternatively, the UE uses SRS, SR, HARQ feedback information as
reference signals. Alternatively, the UE may transmit a beacon
signal specifically defined for D2D discovery. The beacon signal
specifically defined for D2D discovery may be mapped to the same RE
locations in time-frequency that the UE would have used for
transmitting UL DM-RS or SRS to the network entity.
[0096] The reference signal may also include substantive data. For
example, a UE can use an SR or HARQ feedback information as a
reference signal. An SR and HARQ feedback each have a one-bit
field, which the UE can use to indicate information about itself,
such as its receiver type capabilities, power control information,
mobility information (e.g., is the device stationary), or
information about its preferred/desired D2D operating mode to be
used for communication.
[0097] In one embodiment of the invention, the network entity
over-provisions an existing channel in order to provide resource
blocks for use by the UEs to transmit a reference signal. In this
embodiment, a UE transmits a reference signal on resource blocks
that are on or near the edge of the transmission bandwidth
configuration of a carrier. The transmission bandwidth
configuration contains resources blocks that the network entity has
configured for use for typical UE to network communication. Not all
of the resource blocks within the transmission bandwidth
configuration are necessarily used during a given time. Examples
are shown in FIGS. 7A and 7B.
[0098] In another embodiment of the invention, the network entity
defines additional resource blocks on which UEs can transmit a
reference signal. These additionally-defined resource blocks are
within the channel bandwidth of the carrier, but are outside of the
transmission bandwidth configuration. These resource blocks are on
frequencies near the boundary of the spectral emissions mask. In
some cases, transmissions on these frequencies are of lower energy
than those frequencies that are within the channel bandwidth.
Examples are shown in FIGS. 7A and 7B.
[0099] There are many ways that the UEs may use a reference signal
to determine whether D2D communication is feasible. In one
embodiment, a UE varies the power level of the reference signal
using a ramping scheme. For example, referring to FIG. 8A, UE1
transmits a reference signal. UE1 varies increases the energy of
the reference signal over successive, adjacent symbols/subframes.
UE2 receives the reference signal, and measures the energy per
symbol or per subframe of the reference signal. UE2 then determines
whether the energy it detects in the reference signal reaches at
least a predetermined level (e.g., predetermined according to a
communication standard used by UE1 and UE2). UE2 then makes the D2D
feasibility determination based on the reference signal energy
detected. If the reference signal energy detected by UE2 does not
reach the predetermined level, then UE2 does not initiate D2D
communication. If the detected energy level does reach the
threshold, UE2 initiates D2D communication. Alternatively, UE2
reports, to the network entity, the highest reference signal power
level that UE2 can receive, and the network entity determines
whether D2D communication should occur, and orders one or both of
the UEs to engage in D2D communication.
[0100] In another embodiment, reference signals may be transmitted
at a predetermined power level. The predetermined power level may
be lower than the maximum power level allowed for D2D. The
predetermined power level may be a power level known to all UEs in
a cell and may be determined based on a signal received from a
network entity associated with the cell. For example, the network
entity broadcasts the allowed reference signal power level for D2D
communication for all UEs served in that cell. This effectively
allows the network entity to control the range of D2D communication
between UEs attached to that serving cell.
[0101] In another embodiment, UEs in a serving cell communicating
with the network entity using a particular RAT, can report
measurements or other information relevant to another RAT to the
network entity, and the network entity can use this information
determine the proximity of the UEs. For example, the UEs may report
the service set identifiers (SSIDs) or other Medium Access Control
IDs (MAC IDs) of the wireless access points that are `visible` to
them (for example signal strength or other related measurement such
as RSRP or RSRQ or RSSI exceeds a threshold) to the network entity,
and if the base station determines that two UEs can see the same
access point (i.e., two UEs report same SSID or MAC ID), it can
then configure the devices to turn on their D2D reference signals.
More generally, UEs may report the small cell identifiers of the
small cells that are `visible` to them to the network entity, and
if the base station determines that two UEs can see the same small
cell, it can then configure the devices to turn on their D2D
reference signals.
Frame/Subframe Format
[0102] According to an embodiment of the invention, UE1 and UE2
communicate with one another using the frame format shown in FIG.
8B. The subframes are time-multiplexed, with UE1 and UE2
transmitting on different subframes. An exception is during a
special subframe, during which a first set of symbols of the
subframe is reserved for UE1 to transmit; a second set of symbols
is a guard interval during which neither UE transmits to the other;
and a third set of symbols is reserved for the other UE to
transmit. In some embodiments, one or more of the subframes are
reserved for use by one or more of the UEs to listen for downlink
data from a network entity.
[0103] In an embodiment of the invention, the UE1 and UE2 (FIG. 1)
communicate with one another using the general frame structure of
FIG. 8B. As shown, the frame 800 includes regular subframes #0, #2,
#3, #4, #5, #7, #8, and #9. Each of the regular subframes will be
used for D2D, or for communicating with the network entity.
Subframes #1 and #6, which are labeled with reference numbers 801
and 803, are special subframes. A special subframe provides a
transition, in which a UE1 (but not UE2) transmits during a first
set of symbols 802, the second set of symbols 804 are used as a
guard interval, in which neither the UE1 nor UE2 transmits using
those resources, and a third set of symbols 806, in which UE2 (but
not UE1) transmits.
[0104] In an embodiment of the invention, the UEs can switch their
order of transmission in another special subframe 803, in which UE2
(but not the UE1) transmits during a first set of symbols 808, the
second set of symbols 810 are used as a guard interval, in which
neither the UE1 nor UE2 transmits using those resources, and a
third set of symbols 812, in which UE1 (but not UE2) transmits.
This scheme will be described in more detail with the examples that
follow. The placement of the special subframes in FIG. 8B is meant
for illustration purposes only, and the examples below may have
them placed differently.
[0105] Reference will now be made to FIGS. 9, 10, and 11 in order
to describe how D2D communication occurs in different embodiments
of the invention. It to be understood that special subframes may be
implemented using the structure of the special subframes 801 and
803 of FIG. 8B. It is also to be understood that some embodiments,
the entire special subframe is a guard interval, while in other
embodiments, the guard interval lasts for only a single symbol.
[0106] Referring to FIG. 9, it will be assumed that UE1 is sending
a file to UE2, and UE1 has been allocated three subframes for every
one subframe allocated to UE 1. Further, it will be assumed that
the data being transferred is organized into blocks of data, such
as transport blocks, packets, bursts, or the like. In subframes
900, 910, 920, and 930, UE1 transmits the first block 912 to UE2.
UE1 and UE2 switch transmitter and receiver roles during the
special subframe of slot 940. In subframe 950, UE2 transmits to UE1
(e.g. data and/or control information, such as an ACK). Again, UE1
and UE2 switch roles during special subframe 960. UE1 transmits a
second block 914 to UE2 during subframes 970, 980, and 990.
[0107] Referring to FIG. 10, another embodiment is shown. In this
embodiment, UE1 and UE2 communicate on time-duplexed slots. In
slots 1000, 1010, 1020, and 1030, UE1 transmits block 1012 to UE2.
In slot 1040, there is a special subframe, configured as the
subframes 801 and 803 shown in FIG. 8B. UE1 and UE2 switch
transmitter and receiver roles during the special subframe of slot
1040. UE1 then transmits a second block 1014 to UE2 during slots
1050, 1060, 1010, and 1080. In a slot 1090, which includes a
special subframe, UE1 and UE2 switch roles, with UE2 becoming the
transmitter, and UE1 becoming the receiver.
[0108] Referring to FIG. 11, another embodiment is shown. In this
embodiment, a subframe is set aside to allow UE1 and UE2 to receive
signals (such as paging messages) from the network entity NE1. In
the illustrated example, UE2 transmits on subframes 1110, 1120; UE1
transmits on subframes 1140 (which includes a one symbol gap at the
beginning), 1150, 1160, 1170, and 1180; and UE2 transmits on
subframe 1190, which includes a one symbol gap at the beginning. On
subframe 1100, both UE1 and UE2 listen for signals from NE1. UE1
and UE2 may listen to NE1 on a regular basis, such as during each
subframe following the transition subframe.
Network-Initiated D2D Communication
[0109] Referring again to FIG. 8A, in an embodiment of the
invention, the network entity initiates D2D communication by
allocating the appropriate time-frequency resources to the UEs,
which the UEs can use to communicate with one another, signaling
information about the allocated resources to the UEs, and ordering
the UEs to communicate directly with one another using the
allocated resources. One or both of the UEs may be in idle mode at
the time the D2D communication is initiated, but are already
camped, so that they are known to network entity.
[0110] The time-frequency resources allocated to the UEs may be a
subset of the UL resources, or may be a subset of the DL resources.
For example, the network entity may allocate one or more resource
blocks of a UL subframe or a DL subframe. These allocated resource
blocks may occur periodically, such as every frame, subframe, or
slot. Using these allocated RBs, UE1 and UE2 create a data stream,
which, for example, is structured as a series of time-multiplexed
subframes or slots, in which each subframe or slot uses one RB of
the UL carrier or the DL carrier. The RBs of the UL or DL carriers
that the UEs use may be on any subcarrier of the UL or DL carrier.
In certain embodiments, however, the RBs used by the UEs are taken
from the UL carrier. These RBs are selected from the PUCCH of the
UL carrier and are thus located at the highest and lowest frequency
subcarriers of the UL carrier.
[0111] Referring still to FIG. 8A, the carrier from which a
resource is allocated for UE1 and UE2 D2D is a first carrier. The
carrier that UE1 or UE2 uses to communicate with the network entity
is a second carrier. Furthermore, the UE1 and UE2 may communicate
in D2D mode using a third carrier that does not overlap with either
the first or second carriers.
[0112] Referring to FIG. 12, an example of how D2D communication is
initiated by the network 100 will now be described. As noted in the
figure, the UL carrier is designated as the first carrier, while
the DL carrier is designated as the second carrier. At step 1200,
UE1 establishes communication with NE1. This step may have been
performed long before the remaining steps (e.g., via RACH). At step
1201, NE1 determines, based on one or more of the criteria set
forth above, whether D2D communication between UE1 and UE2 is
needed or desirable.
[0113] If NE1 determines that D2D is needed or desirable, then, at
step 1202, NE1 orders UE1 to turn on its reference signal. If UE2
is connected to NE1, then, at step 1204, NE1 requests information
from UE2 regarding the link quality of the reference signal as
measured by UE2.
[0114] If it happened that UE2 was not connected to NE1, then NE1
could request, via the backhaul system and core 106, that UE2
connect with NE1. The core 106 may enable this by paging UE2 via
another network element, such as NE2. In response to the page, UE2
would then initiate a connection to NE1.
[0115] At step 1206, UE2 determines the link quality and reports
the link quality (e.g., RSRP, RSRQ, RSSI, CSI) to NE1. At step
1208, NE1 determines whether certain D2D criteria are met, such as
whether (a) UE1 and UE2 are within a predetermined distance of one
another, (b) the quality of the reference signal received by UE2
from UE1 is above a predetermined level, and (c) allowing UE1 and
UE2 would not adversely impact public safety communications.
[0116] If NE1 makes positive determinations regarding these
factors, then the process continues at step 1210, at which NE1
allocates resources for D2D (e.g., allocates PUCCH resource
blocks). If NE1 makes negative determinations about any of these
factors, then NE1 does not initiate D2D mode for the UEs.
[0117] At steps 1211A and 1211B, NE1 transmits a command to UE1 and
UE2. The command orders the UEs to communicate with one another
using D2D, and identifies to them the RBs that they should use. NE1
may transmit the command to the UEs on, for example, the PDSCH or
the PDCCH/EPDCCH. At step 1212, the UEs may engage in a handshaking
procedure via the resources allocated by NE1. At step 1214, the UEs
communicate with each other in D2D mode. It should be noted steps
1210 and step 1211A (or 1211B) may be performed as a single step.
It should also be noted that the UEs may, in various embodiments,
communicate on the UL carrier, DL carrier, or a third, separate
carrier.
Device-Initiated D2D Communication
[0118] In a device-initiated scheme, one or more of the UEs
transmits a request to network. The request includes the identity
of another UE with which the requesting UE wishes to communicate.
If the network grants the request, the network responds by
allocating the appropriate resources and configuring the UEs to use
those resources.
[0119] For example, assume that users of UE1 and UE2 are aware of
one another (e.g., they are next to each other, have discovered
each other using a "finding friends" application such as Google
Latitude.TM. or near field communication (NFC)). The user of UE1
decides to transfer a file to the user of UE2. If both UEs are not
already on the network, UE1 should be able to request that UE2 be
connected to UE1's network or to a common network. UE1 and UE2 can
then operate on the same band/carrier, and be allocated resources
from the network on which they are operating as described
above.
[0120] In an embodiment of the invention, if the UEs are in idle
mode then UE1 may enter a connected mode by connecting to NE1 and
indicating "D2D interest" to NE1. UE1 may provide information about
UE2 to NE1. Such information may include the IMEI of UE2, or
handle-like information such as UE2's userid@network_name.d2d, or
the like. The network entity passes this information on to the core
106 (e.g., to a billing server) (FIG. 1). One or more of the
control elements checks the subscription information for both of
the UEs to determine whether the data plans for the UEs include D2D
capability. The core then provides a success or failure indication
to NE1.
[0121] NE1 may obtain updated mobility measurements for each UE,
and provide updated mobility measurements to the UEs, thereby
allowing NE1 to control measurements and mobility.
[0122] In one implementation of the device initiated D2D, UE1 (in
idle mode) determines that it can carry out D2D communication with
UE2, using spectrum in a particular frequency band. UE1 then
connects to a network entity operating in that frequency band and
downloads, from the network 100, information that can be used for
D2D communication, such as reference signal power, reference signal
identifying information, maximum power allowed for D2D
communication and other power control parameters, and the subframes
that the network 100 allows UE1 to use for D2D communication. UE1
then initiates D2D (e.g., by starting to transmit a reference
signal). UE2 performs similar steps and also initiates D2D. The UEs
can release their connection to the network (i.e., move back to
idle mode) after downloading the D2D information, and continue to
communicate in a D2D mode, even though they are in idle mode with
respect to the network 100. For this implementation, the network
100 may also indicate a "validity duration" associated with the
information related to D2D transmission. Alternately, a predefined
validity period may be assumed the UEs, and if the duration of the
D2D session exceeds the validity period, the UEs may need to
re-connect to the network to check if the D2D information is still
valid or if they have to download new values.
[0123] The handover of a UE from NE1 to another may be delayed
until after the D2D session between the UEs is complete.
[0124] According to an embodiment of the invention, UE1, upon
determining that D2D may be used, autonomously initiates D2D
communication in a set of uplink RBs in a frequency band containing
the uplink carrier. The UE1 can determine the set of uplink RBs
based on signaling received from NE1. NE1 can refrain from
scheduling regular UE transmission (i.e., UE to network entity
transmission) in those RBs. If NE1 does this, the UEs in D2D mode
may be able to communicate with maximum power possible for D2D
communication. This is useful for example, when the UE is used in a
public safety scenario. For example, if the public safety UE
determines that it is out of coverage from an LTE network for
infrastructure based communication, it can autonomously fall back
to D2D mode over a set of potentially pre-determined uplink
RBs.
[0125] Referring to FIG. 13, an example of device initiated D2D
communication will now be described. At step 1300, a user interacts
with the user interface of UE1 to indicate the user's desire to
engage in D2D communication. At step 1302, UE1 transmits, via a
first carrier or UL carrier, a request to NE1 for D2D communication
with UE2. At step 1304, NE1 determines whether UE2 is connected. If
it is not, then NE1 requests, to the core 106, that UE2 be
connected to NE1. If UE2 is already connected, or becomes connected
in response to the request from NE1, then NE1 allocates resources
(e.g., RBs from the UL carrier or the DL carrier) for use by the
UEs for the D2D communication. At steps 1306A and 1306B, NE1
transmits, via a second carrier or DL carrier, information
identifying the allocated resources to the UEs. At step 1308, the
UEs can carry out a handshaking procedure using the allocated
resources, and using a D2D subframe structure. At step 1310, the
UEs communicate with one another using the D2D subframes.
UE Capabilities and Capability Partitioning
[0126] According to an embodiment of the invention, each UE has a
set of one or more capabilities, i.e., a capability configuration.
A capability configuration may include one or more of: [0127] (1)
the data rate (e.g., the maximum data rate) that a UE supports;
[0128] (2) how many transmit and/or receive antennas the UE has;
[0129] (3) the types of transmission schemes supported by the UE
(Tables 3 and 4 show examples of transmission schemes); [0130] (4)
the soft buffer configuration of the UE; [0131] (5) the UE's MIMO
capability (e.g., supported number of layers per band, support of
UL MIMO); [0132] (6) the UE's the carrier aggregation capability
[0133] (7) the UE's battery life; [0134] (8) the maximum number of
transport block bits rate per TTI supported by the UE [0135] (9)
the UE's processing capability (e.g., the number of processors a UE
has, the number of simultaneous processes it can execute at one
time).
[0136] Each UE may, in an embodiment of the invention, divide its
capabilities. Each divided set of capabilities will be referred to
as a capability partitioning configuration.
[0137] As noted, one of the capabilities that a UE can partition is
its soft buffer configuration. A UE's soft buffer configuration is
one or more of (1) the maximum number of HARQ processes that the UE
will use for receiving packets (the number of buffer partitions
needed); (2) the size of a soft buffer that the UE will use for
receiving packets; and (3) the number of soft channel bits that the
UE will use for receiving packets. Thus, a first set of one or more
of these characteristics would constitute a first soft buffer
configuration, and a second set would constitute a second soft
buffer configuration.
[0138] For example, given a first UE and a second UE, a first
buffer partitioning configuration may include at least one of: (1)
a maximum number of HARQ processes that the first UE will use for
receiving from the network entity; (2) the size of a soft buffer
that the first UE will use for receiving from the network entity,
and (3) a number of soft channel bits that the first UE will use
for receiving from the network entity.
[0139] The second buffer partitioning configuration comprises at
least one of: 1) a maximum number of HARQ processes that the first
UE will use for receiving from the second UE; 2) the size of a soft
buffer that the first UE will use for receiving from the second UE,
and 3) a number of soft channel bits that the first UE will use for
receiving from the second UE.
[0140] An example of a UE dividing its capabilities into capability
partitioning configurations will now be provided. If a UE has two
processors and two antennas, it could divide these capabilities
into a first capability partitioning configuration, which
constitutes one processor and one antenna, and a second capability
partitioning configuration, which constitutes one processor and one
antenna.
[0141] In an embodiment of the invention, a UE uses different
capability partitioning configurations for communicating with
different devices. For example, a UE might communicate with a
network entity using a first capability partitioning configuration
of 1 processor, 4 soft buffer partitions, and in transmission mode
1. The UE might also communicate with another UE in D2D mode using
a second capability partitioning configuration of 1 processor, 2
soft buffer partitions, and in D2D transmission mode. This example
also illustrates a UE changing its soft buffer configuration. The
first soft buffer configuration would include 4 soft buffer
partitions and the second soft buffer configuration would include 2
soft buffer partitions.
[0142] In some embodiments, the UE communicates with two other
devices, such as another UE and a network entity, simultaneously
using both a first and a second capability partitioning
configuration. In other embodiments, the UE switches from using one
capability partitioning configuration to another depending on the
device with which the UE is communicating, and do so in a
time-multiplexed manner.
[0143] Any of the capability configurations of a UE, including
those made up of one or more of the capabilities noted above, may
be divided into multiple capability partitioning
configurations.
[0144] Referring to FIG. 1, for example, UE1 may change its
capability partitioning configuration (e.g., lower its data rate,
alter number of soft buffer partitions, etc.) so that its
configuration is compatible with that of UE2 so at to allow UE1 and
UE2 to communicate with one another, while also supporting
communication between UE1 and the network entity. UE2 may also
change its capability partitioning configuration so that the
capability partitioning configuration of UE1 and the configuration
of UE2 are compatible.
[0145] For example, if UE1 can transmit up to 100 megabits per
second, and UE2 can receive up to only 50 megabits per seconds,
then UE1 may change its capability configuration so that it only
transmits up to 50 megabits per second.
[0146] An example of different LTE UE categories/capabilities that
UEs may have in an embodiment of the invention is shown in Table 1
(for the downlink) and Table 2 (for the uplink).
Downlink Physical Layer Parameter Values Set by the Field
Ue-Category
TABLE-US-00001 [0147] TABLE 1 Maximum Maximum number of number of
Maximum DL-SCH bits of a number of transport DL-SCH Total supported
block bits transport number layers for received block re- of soft
spatial UE within a TTI ceived with- channel multiplexing Category
(Note) in a TTI bits in DL Category 1 10296 10296 250368 1 Category
2 51024 51024 1237248 2 Category 3 102048 75376 1237248 2 Category
4 150752 75376 1827072 2 Category 5 299552 149776 3667200 4
Category 6 301504 149776 (4 3654144 2 or 4 layers) 75376 (2 layers)
Category 7 301504 149776 (4 3654144 2 or 4 layers) 75376 (2 layers)
Category 8 2998560 299856 35982720 8
Uplink Physical Layer Parameter Values Set by the Field
Ue-Category
TABLE-US-00002 [0148] TABLE 2 Maximum number of Maximum number of
UL-SCH transport bits of an Sup- block bits UL-SCH transport port
for UE transmitted block transmitted 64QAM Category within a TTI
within a TTI in UL Category 1 5160 5160 No Category 2 25456 25456
No Category 3 51024 51024 No Category 4 51024 51024 No Category 5
75376 75376 Yes Category 6 51024 51024 No Category 7 102048 51024
No Category 8 1497760 149776 Yes
PDCCH/EPDCCH and PDSCH Configured by C-RNTI
TABLE-US-00003 [0149] TABLE 3 Transmission scheme of Transmission
DCI PDSCH corresponding to mode format Search Space PDCCH Mode 1
DCI Common and Single-antenna port, port format 1A UE specific by
C-RNTI DCI UE specific Single-antenna port, port format 1 by C-RNTI
0 Mode 2 DCI Common and Transmit diversity format 1A UE specific by
C-RNTI DCI UE specific Transmit diversity format 1 by C-RNTI Mode 3
DCI Common and Transmit diversity format 1A UE specific by C-RNTI
DCI UE specific Large delay CDD or format 2A by C-RNTI Transmit
diversity Mode 4 DCI Common and Transmit diversity format 1A UE
specific by C-RNTI DCI UE specific Closed-loop spatial format 2 by
C-RNTI multiplexing or Transmit diversity Mode 5 DCI Common and
Transmit diversity format 1A UE specific by C-RNTI DCI UE specific
Multi-user MIMO format 1D by C-RNTI Mode 6 DCI Common and Transmit
diversity format 1A UE specific by C-RNTI DCI UE specific
Closed-loop spatial format 1B by C-RNTI multiplexing using a single
transmission layer Mode 7 DCI Common and If the number of PBCH
format 1A UE specific antenna ports is one, by C-RNTI
Single-antenna port, port 0 is used, otherwise Transmit diversity
DCI UE specific Single-antenna port, port format 1 by C-RNTI 5 Mode
8 DCI Common and If the number of PBCH format 1A UE specific
antenna ports is one, by C-RNTI Single-antenna port, port 0 is
used, otherwise Transmit diversity DCI UE specific Dual layer
transmission, format 2B by C-RNTI port 7 and 8 or single- antenna
port, port 7 or 8 Mode 9 DCI Common and Non-MBSFN subframe: If
format 1A UE specific the number of PBCH by C-RNTI antenna ports is
one, Single-antenna port, port 0 is used otherwise Transmit
diversity MBSFN subframe: Single- antenna port, port 7 DCI UE
specific Up to 8 layer format 2C by C-RNTI transmission, ports 7-14
or single-antenna port, port 7 or 8 Mode 10 DCI Common and
Non-MBSFN subframe: If Format 1A UE specific the number of PBCH by
C-RNTI antenna ports is one, Single-antenna port, port 0 is used
otherwise Transmit diversity MBSFN subframe: Single- antenna port,
port 7 DCI UE specific Up to 8 layer format 2C by C-RNTI
transmission, ports 7-14
[0150] The content of Tables 1 and 2 can generally be found in
"LTE; Evolved Universal Terrestrial Radio Access (E-UTRA); User
Equipment (UE) radio access capabilities (3GPP TS 36.306 version
10.0.0 Release 10)" (by 3rd Generation Partnership Project (3GPP)
in January 2011), Tables 4.1-1 and 4.1-2.
[0151] The content of Table 3 can generally be found in "Technical
Specification Group Radio Access Network; Evolved Universal
Terrestrial Radio Access (E-UTRA); Physical layer procedures"
(Release 11), (3rd Generation Partnership Project (3GPP), September
2012) Tables 7.1-5 and 7.1-6. Table 3 shows the transmissions modes
used for the downlink. A UE is configured in one of the
transmission modes by the network entity. A UE in a given
transmission mode monitors the downlink control channels for
downlink control information (DCI) format corresponding to the
transmission mode and receives PDSCH based on the corresponding
transmission scheme (e.g., single antenna port, transmit diversity,
open loop spatial multiplexing, closed loop spatial multiplexing,
beam formed transmission (single antenna port, port 7), etc).
Signaling Capabilities and Categories
[0152] According to an LTE embodiment, a UE informs a network
entity of its Release, category, and additional capabilities. This
allows the network entity to properly configure its communication
with the UE. A UE may discard (or disregard) any received
message/signal that does not conform to its
release/category/capabilities. A UE of a particular category offers
the characteristics/capabilities (in the downlink and uplink) as
shown in Tables 1 and 2.
[0153] During their D2D handshake process, UEs may establish a
master-slave relationship. The UE having the best capability (e.g.,
the UE supports larger data rate, longer battery life, etc.) will
generally be the master. For instance, if the two UEs participating
in a D2D belong to distinct categories, then the UE with the larger
category may be the master device. For example if a Category 3 and
a Category 7 device participate in D2D, then the Category 7 may be
the master device. The master UE will dictate the resources that
are expected from the slave UE for the D2D communication. The slave
UE may respond with a message indicating that it cannot provide
such resources. If this occurs, the master UE may need to lower its
expectations of the slave UE. For example, the slave UE may need to
use at least some of its soft buffer partitions to communicate with
the network entity.
Capability Exchange Example
[0154] Referring to FIG. 15, an example of how UEs exchange
capability information for the purpose of D2D communication will
now be described. In the example, the following assumptions will be
made. UE1 uses RBs from the UL carrier to transmit subframes to UE2
over a D2D carrier, using a structure such as that shown in FIG.
8B. UE1 in this example is a Category 4 UE and UE2 is a Category 2
UE. As shown in Tables 1 and 2, Category 4 UEs have DL/UL rates of
150 Mbps/50 Mbps, and Category 2 UEs have DL/UL rates of 50 Mbps/25
Mbps. Thus, the UE1-to-UE2 link has a maximum data rate of 50 Mbps
(UE2-rx), and UE2-to-UE1 has a maximum data rate of 25 Mbps
(UE2-tx). This asymmetry is in spite of the fact that both UEs have
the capability to decode 50 Mbps.
[0155] It is also assumed that the network entity has already
granted UE1 authorization to engage in D2D communication with UE2,
and that UE1 is aware of UE2 (UE2 may likewise be aware of UE1).
These assumptions are made for the purpose of illustration
only.
[0156] At step 1500, UE1 establishes communication with NE1. At
step 1501, NE1 allocates RBs and/or subframes that the UEs may use
to communicate with one another in D2D mode. These RBs may be RBs
of the DL carrier or RBs of the UL carrier. At step 1510, UE1
determines a first set of the allocated RBs and/or subframes that
the UEs will use to communicate with one another. At step 1520, UE1
receives information from NE1 regarding UE2's capabilities (e.g.,
UE2's category). Alternatively, at step 1520', UE2 transmits its
capability information to UE1 via the D2D carrier.
[0157] UE1 and UE2 then may initiate a handshake process with one
another at step 1530, in which they establish a master-slave
relationship, agreeing that UE1 is the master. At step 1540, UE1
determines the appropriate configuration for the UEs to enter for
communication, including what resources (e.g. capability) the UEs
should allocated for D2D communication. These include the data
rate, coding scheme, and HARQ buffer configuration. In this
example, UE1 determines that the UE2 should devote three soft
buffer partitions 1416 (in FIG. 14) for receiving transport blocks
from UE1. The UE2 may then, for example, use the remaining five
soft buffer partitions 1418 for communication with NE1. At step
1550, UE1 may inform the UE2 of the resources expected or the UE1
may configure the required resources of UE2 for the D2D
communication. At step 1560, UE1 and UE2 communicate in D2D mode
using the RBs/subframes allocated by NE1 in a D2D carrier, and
using the internal resources that UE1 determined should be used. At
step 1560, UE1 and UE2 engage in a D2D communication.
[0158] A modified version of the procedure of FIG. 15 is depicted
in FIG. 16. In the procedure of FIG. 16, the user of UE1 initiates
the D2D communication at step 1600. At step 1602, there are three
alternatives depicted. NE1 may inform UE1 of UE2's capability, UE1
may receive capability information directly from UE2, or UE1 and
UE2 may exchange capability information with one another. The
remaining steps are similar to those of FIG. 15.
[0159] To further illustrate capability and category exchange
during D2D communication according to an embodiment, assume that
UE1 and UE2 engage in D2D communication and that UE1 is aware of
the release/capability/category of UE2. UE1 will then configure the
D2D link such that UE2 can properly transmit encoded messages to,
and receive encoded transmissions from UE1. If the UEs are
different categories, UE1 may choose its soft buffer configuration
based on UE2's category. The higher category UE may be configured
as the master in the D2D connection.
[0160] In another embodiment of the invention, a UE may directly
signal its category to another UE when the UEs are engaged in D2D
communication. Furthermore, a network entity or the master device
may configure (a) the soft buffer allocation for D2D reception in
the first UE and/or the HARQ buffer allocation for D2D reception in
the second UE, b) the maximum number of HARQ processes for D2D
transmission from the first UE to the second UE and/or the maximum
number of HARQ processes configured for D2D transmission from the
second UE to the first UE. Additionally, the network entity may
configure one or more of the following restrictions:
[01] Transmission mode restriction [02] Modulation restriction
(limited to QPSK/16-QAM) [03] Bandwidth restriction (e.g. if UE1
and UE2 are operating on different BWs, UE1 is regular UE and UE2
is MTC device with a smaller Rx BW).
[0161] The network entity may signal a default configuration for
the D2D communication. The signaling of the default configuration
may be a cell-specific signaling or UE-specific signaling the
default configuration for the direct communication may include:
transmission mode for direct transmission, transmission scheme for
direct transmission, demodulation RS configuration, component
carrier(s) for direct communication etc. The network entity may
override/re-configure some or all default configuration parameters
when direct communication with another UE is enabled. The
configuration may be valid for the session or used by the UE for
direct communication with the other UE for certain predefined time
duration. The configuration information may be reset to the default
configuration within the predefined time duration on receiving a
specific signaling from the network entity, transition to RRC idle
mode, handover etc.
Control Channel Over-Provisioning
[0162] Referring to FIG. 7A, an example of how RBs are allocated
for use by reference signals according to an embodiment of the
invention will now be described. This example will focus on those
RBs near the first edge 722 of the transmission bandwidth
configuration. However, the same RB allocation scheme may also be
applied to those RBs near the second edge 724.
[0163] It will be assumed for this example that, without any RBs
being reserved for D2D, the network entity would ordinarily
allocate RB0 and RB1 to UEs for transmission on the PUCCH. To
facilitate D2D communication, however, the network entity instead
allocates RB1 and RB2 for the PUCCH and reserves RB0 for D2D
reference signaling. The network entity NE1 would, in the D2D case,
provide information (e.g., via higher layer signaling, such as RRC
signaling) to the UEs regarding the signal configuration of the
reference signal. However, the network entity allocating in
resources does not necessarily have to provide the signal
configuration information. A second network entity, such as NE2,
could do so.
[0164] In this example, the reference signal's signal configuration
is that RB1 and RB2 are to be used for the PUCCH, and that RB0 is
to be used by the UEs to transmit reference signals. This RB
allocation scheme allows UEs that do not have D2D capability to use
the PUCCH as they always have, but using RB1 and RB2, while the
D2D-capable UEs are able to use RB0 for reference signaling in
addition to using the PUCCH. Also, in many cases, the transmission
power used for D2D communication is expected to be small and using
the edge RBs for D2D helps in reducing interference outside the
channel bandwidth.
[0165] One way in which the network entity can notify a first UE
about the signal configuration of a second UE's reference signal is
by transmitting information regarding the modified PUCCH RB
allocations to the first UE. Such information can be in the form of
a modified nRB-CQI value.
[0166] In an LTE embodiment, for example, nRB-CQI (or
N.sub.RB.sup.(2)) may denote the bandwidth in terms of resource
blocks that are available for use by PUCCH formats 2/2a/2b
transmission in each slot in a subframe. PUCCH formats 2/2a/2b may
be used for transmitting periodic CSI reports. An LTE UE could use
the nRB-CQI value to determine the PUCCH resources it will use for
transmitting HARQ-ACK using PUCCH format 1/1a/1b. More
specifically, the LTE UE would not transmit HARQ-ACK using PUCCH
format 1/1a/1b in the edge RBs identified by nRB-CQI value.
[0167] To allow D2D communication on the edge RBs of a transmission
bandwidth configuration, the signal configuration information sent
by the network entity can indicate an additional RB offset (e.g.
D2D-RB-offset) using which D2D capable UEs can determine the edge
RBs used for D2D communication. For example, if RBs of a
transmission bandwidth configuration are numbered RB0, RB1, RB2,
RB3, RB4 . . . with RB0 being closest to the transmission bandwidth
edge, the network entity can signal a D2D-RB-offset value 2 and
nRB-CQI value of 5. UEs that are not configured for D2D
communication (and UEs that are not capable of D2D communication)
do not transmit HARQ-ACK in the first 5 RBs starting from the edge
of the transmission bandwidth configuration (i.e., RB0 to RB4). UEs
that are configured for D2D communication use the first 2RBs (i.e.,
RB0 and RB1) for D2D communication. The other RBs (i.e., RB2, RB3,
RB4) can be used for PUCCH formats 2/2a/2b transmission by all the
UEs. As seen from the example, over-provisioning the PUCCH resource
value (i.e., signaling a larger value of n_RB_CQI than that needed
to support PUCCH format 2/2a/2b transmissions) allows the network
100 to support D2D communication in a manner that is transparent to
UEs that are not capable of supporting D2D communication. Such
transparent operation may improve overall network efficiency, since
UEs that supports D2D communication can share a carrier with UEs
that do not support D2D communication.
[0168] In another example, it will be assumed that the carrier 700
is using a channel (e.g., channel 13) that is adjacent to a public
safety channel (e.g., channel 14), and that the network entity is
not permitted to use RB0, RB1 and RB2. Under these circumstances,
the network entity allocates RB4 and RB5 for use by the UEs for
PUCCH and allocates RB3 for D2D reference signaling.
[0169] In another embodiment of the invention, the network entity
defines an RB within one or more of the first spectral emissions
region 708 and the second spectral emissions region 710 (RBs 730
and 718). These regions ordinarily would not be used for data or
control signaling due to limits on the power of signals in those
regions (imposed by, for example, law or industry agreement) for
avoiding interference to adjacent channels. However, because
reference signals for D2D discovery purposes do not necessarily
have to be as strong as regular control signals, the UEs may use
those RBs for D2D reference signals. The interference caused by the
D2D reference signals is expected to be quite small as long as the
transmit power of the signals is kept a sufficiently low level.
[0170] In another embodiment of the invention, the techniques
described in conjunction with FIG. 7A can be applied to an
aggregated carrier 750 (FIG. 7B). Edge RBs 0 of the three component
carriers 752, 754, and 756 of carrier 750 is used for D2D reference
signaling, and RBs 1 and 2 is used for the PUCCH. As noted in
conjunction with FIG. 7A, one or more RBs 760 may be defined within
the spectral emissions mask for use by the UEs for D2D reference
signaling.
[0171] In another embodiment a specific PUCCH resource index is
defined to indicate which portion of the normal (e.g., Rel-8 LTE)
control channels available for a given PUCCH are instead reserved
for D2D reference signaling channels. Note the other normal control
channels supported by a given PUCCH may be HARQ-ACK channels, SRS
channels, SR channels, and Channel state information channels which
include rank information and precoding feedback and channel quality
feedback channels. This index could be signaled (broadcast) by
higher layer signaling using a Radio Resource Control (RRC) message
sent as part of a system information block. The PUCCH resource
index or which of the D2D reference signaling channels to use for a
UE to perform D2D reference signaling on could be determined by a
field in a broadcast scheduling grant. Such a broadcast scheduling
grant might also indicate which unscheduled/unassigned resource
blocks in a subframe are available for random access or D2D data
transmission. Such a broadcast scheduling grant may also be
referred to as a contention grant. A hashing function based on user
ID (e.g. such as IMSI, radio network terminal indicator) and/or
subframe, slot, or radio frame index could also determine which D2D
reference signaling channel to use for transmitting a given D2D
reference signal. If PUCCH resources for D2D reference signaling
are only to be used in specific subframes or slots in a radio frame
or in specific radio frames then a subframe, slot, and/or radio
frame indicator is also signaled regarding D2D reference signaling
resources. The PUCCH resource index can be identified using a
.DELTA..sub.Shift.sup.PUCCH value, a n.sub.PUCCH.sup.(2) value or a
n.sub.PUCCH.sup.(2). The PUCCH resource index can also be
identified using a "Scheduling Request (SR) resource" value or a
combination of the SR resource value and one or more of the values
described above, all of which can be signaled by the network
entity. The candidate set of radio resources used for D2D reference
signaling may be considered common resources where one or more UEs
may transmit on the resources simultaneously.
[0172] In some embodiments, configuration information regarding the
reference signals can be received by a UE, from a network entity,
in a DL carrier within a downlink operating band of a frequency
division duplex (FDD) mode operating band. Reference signals (from
another UE) can be received by the UE in a UL carrier within an
uplink operating band of the FDD mode operating band. While the
reference signals are received in the UL carrier of the FDD mode
operating band, other data related to D2D transmission (e.g.
application data of the other UE formatted for physical layer
transmission) can be received in a separate carrier. The separate
carrier may in a different operating band. Alternately, the other
data may be received in the UL carrier within the uplink operating
band of the FDD mode operating band. In some cases, the reference
signal may be transmitted by the UE in a separate carrier.
[0173] After receiving a reference signal from another UE (UE2),
the UE (UE1) can determine the link quality between UE1 and UE2 by
measuring the reference signal and using the configuration
information related to the reference signal. To determine the link
quality, the UE may measure Reference Signal Received Power (RSRP),
Reference Signal Received Quality (RSRQ), or Received Signal
Strength Indicator (RSSI), or a Channel State Information (CSI).
The UE can report the measured link quality to the network entity
from which it has received the reference signal configuration
information. In some cases, the UE may report the measured link
quality to a different network entity. For example the UE may
receive reference signal configuration information from a first
transmission point but later report link quality (of a D2D link
between UE and UE2) to another transmission point.
[0174] Generally UE reception of reference signal and UE reporting
of link quality to the network entity occur in different subframes.
For cases where the UE receives reference signals in a UL carrier
of a FDD mode operating band, the UE is only expected to receive
the reference signals in only those subframes where it is not
scheduled to transmit on the same UL carrier.
[0175] Configuration information related to reference signals can
include information identifying the subframes in which the UE is
expected to receive reference signals, information identifying the
resource elements in a subframe in which the UE is expected to
receive reference signals, RB index of the RBs on which the UE can
receive the reference signals, RB offset (e.g. D2D-RB-offset) of
the RBs on which the UE can receive the reference signals,
information identifying a reference signal sequence index or a
reference signal cyclic shift of a reference signal associated with
the reference signal.
[0176] In some embodiments, the UE may receive information
regarding a maximum transmission power limit for communication on
the carrier on which the UE has to transmit reference signals
and/or other D2D data. In some implementations, the maximum
transmission power limit can be a configured maximum UE output
power PCMAX,c where c is the carrier index) for the carrier on
which the UE transmits reference signal and/or D2D data. The UE may
also receive information related to Maximum Power Reduction (MPR)
associated with D2D reference signal or other D2D data
transmission. When the UE receives information related to MPR
values, it can reduce its configured maximum UE output power for
D2D transmission based on the MPR value. The UE can adjust the
power of its reference signal and/or D2D transmissions such that
power of those transmissions does not exceed the configured maximum
UE output power for D2D transmissions.
[0177] The UE may receive configuration information related to
reference signals from via broadcast signaling from a network
entity while the UE is in idle mode. In LTE, when the UE is in idle
mode, the UE performs procedures related to RRC_IDLE state. In LTE,
The broadcast signaling can be included is a Master Information
Block (MIB) or a System information Block (SIB).
[0178] There are many uses to which the D2D communication
embodiments described herein may be put. For example, a user having
a smartphone could engage in D2D communication with a D2D-capable
kiosk to download movies.
[0179] The terms, descriptions and figures used herein are set
forth by way of illustration only and are not meant as
limitations.
[0180] For example, in the present disclosure, when two or more
components are "electrically coupled," they are linked such that
electrical signals from one component will reach the other
component, even though there may be intermediate components through
which such signals may pass.
[0181] In another example, interactions between UE1, UE2 and/or NE1
are often described as occurring in a particular order. However,
any suitable communication sequence may be used.
LIST OF ACRONYMS
[0182] BS Base Station [0183] CA Carrier Aggregation [0184] CCE
Control Channel Element [0185] CoMP Coordinated Multi-Point [0186]
CP Cyclical Prefix [0187] CQI Channel Quality Indicator [0188] CRC
Cyclic Redundancy Check [0189] C-RNTI Cell RNTI [0190] CRS Common
Reference Signal [0191] CSI Channel State Information [0192] CSI-RS
Channel State Information Reference Signal [0193] CSS Common Search
Space [0194] D2D Device to Device [0195] D2D-SCH D2D Shared Channel
[0196] DCI Downlink Control Information [0197] DL Downlink [0198]
DL-SCH Downlink Shared Channel [0199] DM-RS Demodulation Reference
Signal [0200] DFT-SOFDM Discrete Fourier Transform Spread OFDM
[0201] eNB Evolved Node B [0202] EPBCH Enhanced Physical Broadcast
Channel [0203] EPDCCH Enhanced Physical Downlink Control Channel
[0204] EPRE Energy Per Resource Element [0205] E-UTRA Evolved UTRA
[0206] FDD Frequency Division Duplex [0207] FFT Fast Fourier
Transform [0208] GPS Global Positioning System [0209] HARQ Hybrid
Automatic Repeat Request [0210] IMEI International Mobile station
Equipment Identity [0211] LBRM Limited Buffer Rate Matching [0212]
LTE Long-Term Evolution [0213] MAC Media Access Control [0214]
MBSFN Multicast-Broadcast Single Frequency Network [0215] MCS
Modulation and Coding Scheme [0216] MIB Master Information Block
[0217] MIMO Multiple-Input Multiple-Output [0218] MU-MIMO
Multi-User MIMO [0219] NFC Near Field Communication [0220] OFDMA
Orthogonal Frequency Division Multiple Access [0221] P/S-SCH
Primary/Secondary Synchronization Channel [0222] PBCH Primary
Broadcast Control Channel [0223] PCID Physical Cell Identifier
[0224] PDCCH Physical Downlink Control Channel [0225] PDCP Packet
Data Convergence Protocol [0226] PDSCH Physical Downlink Shared
Channel [0227] PHICH Physical Hybrid ARQ Channel [0228] PMI
Precoding Matrix Indicators [0229] PRB Physical Resource Block
[0230] P-RNTI Paging RNTI [0231] PRS Positioning Reference Signal
[0232] PSS Primary Synchronization Signal [0233] PTI Precoder Type
Indication [0234] PUCCH Physical Uplink Control Channel [0235]
PUSCH Physical Uplink Shared Channel [0236] QAM Quadrature
Amplitude Modulation [0237] QPSK Quadrature Phase Shift-Keying
[0238] RACH Random Access Channel [0239] RAT Radio Access
Technology [0240] RB Resource Block [0241] RE Resource Element
[0242] REG Resource Element Group [0243] RF Radio Frequency [0244]
RI Rank Indicator [0245] RNC Radio Network Controller [0246] RNTI
Radio Network Temporary Identifier [0247] RRC Radio Resource
Control [0248] RRH Remote Radio Head [0249] RS Reference Symbol
[0250] RSRP Reference Signal Received Power [0251] RSRQ Reference
Signal Received Quality [0252] RSSI Received Signal Strength
Indicator [0253] SC-FDMA Single-Carrier Frequency Division Multiple
Access [0254] SFN System Frame Number [0255] SIB System Information
Block [0256] SI-RNTI System Information RNTI [0257] SPS
Semi-Persistent Scheduling [0258] SR Scheduling Request [0259]
S-RNTI Serving RNC RNTI [0260] SRS Sounding Reference Signal [0261]
SSID Service Set Identifier [0262] SSS Secondary Synchronization
Signal [0263] TDD Time Division Duplex [0264] tm Transmission Mode
[0265] TP Transmission Point [0266] TTI Transmission Time Interval
[0267] UE User Equipment [0268] UERS UE-specific Reference Symbol
[0269] UL Uplink [0270] UL-SCH Uplink Shared Channel [0271] UMTS
Universal Mobile Telecommunications System
* * * * *