U.S. patent application number 14/669823 was filed with the patent office on 2015-11-12 for demodulation reference signal (dmrs) sequence design for device-to-device (d2d) discovery.
The applicant listed for this patent is INTEL IP CORPORATION. Invention is credited to DEBDEEP CHATTERJEE, HUANING NIU, GANG XIONG.
Application Number | 20150326362 14/669823 |
Document ID | / |
Family ID | 54368764 |
Filed Date | 2015-11-12 |
United States Patent
Application |
20150326362 |
Kind Code |
A1 |
XIONG; GANG ; et
al. |
November 12, 2015 |
DEMODULATION REFERENCE SIGNAL (DMRS) SEQUENCE DESIGN FOR
DEVICE-TO-DEVICE (D2D) DISCOVERY
Abstract
Technology for performing device-to-device (D2D) discovery is
disclosed. A user equipment (UE) can identify a D2D discovery
resource that is M subframes in a time domain, wherein M is a
positive integer greater than one. The UE can generate K
demodulation reference signal (DMRS) sequences to be transmitted
from the UE for each subframe in the D2D discovery resource,
wherein K is a positive integer greater than two. The UE can apply
a predetermined orthogonal cover code (OCC) to each DMRS sequence.
The predetermined OCC can be selected based on a value of M and a
value of K. The UE can transmit the K DMRS sequences for each of
the M subframes of the D2D discovery resource.
Inventors: |
XIONG; GANG; (Beaverton,
OR) ; CHATTERJEE; DEBDEEP; (Mountain View, CA)
; NIU; HUANING; (Milpitas, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
INTEL IP CORPORATION |
Santa Clara |
CA |
US |
|
|
Family ID: |
54368764 |
Appl. No.: |
14/669823 |
Filed: |
March 26, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61990643 |
May 8, 2014 |
|
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Current U.S.
Class: |
370/336 |
Current CPC
Class: |
H04W 4/70 20180201; H04W
76/10 20180201; H04L 5/0051 20130101; H04W 72/00 20130101; H04L
5/0048 20130101; H04W 8/005 20130101; H04W 76/14 20180201; H04L
5/0016 20130101; H04W 72/0446 20130101 |
International
Class: |
H04L 5/00 20060101
H04L005/00; H04W 76/02 20060101 H04W076/02; H04W 72/04 20060101
H04W072/04; H04W 8/00 20060101 H04W008/00 |
Claims
1. A user equipment (UE) operable to perform device-to-device (D2D)
discovery, the UE comprising one or more processors configured to:
identify a D2D discovery resource of a single subframe; generate K
demodulation reference signal (DMRS) sequences to be transmitted
from the UE using the D2D discovery resource, wherein K is a
positive integer greater than two; apply an orthogonal cover code
(OCC) to each DMRS sequence, wherein the OCC is randomly selected
from a pool of OCCs, wherein the OCCs in the pool are predefined
based on a value of K; and transmit the K DMRS sequences using the
D2D discovery resource of the single subframe.
2. The UE of claim 1, wherein the one or more processors are
further configured to transmit the K DMRS sequences in a D2D
discovery message using a physical uplink shared channel
(PUSCH).
3. The UE of claim 1, wherein the one or more processors are
further configured to randomly select the D2D discovery resource
from a D2D discovery resource pool, wherein the D2D discovery
resource pool is allocated by an evolved node B (eNB) and indicated
to the UE via a system information block (SIB).
4. The UE of claim 1, wherein the one or more processors are
further configured to receive an indication of the D2D discovery
resource from an evolved node B (eNB) via radio resource control
(RRC) signaling.
5. The UE of claim 1, wherein the one or more processors are
further configured to transmit the K DMRS sequences using the
single subframe of the D2D discovery resource.
6. The UE of claim 1, wherein the UE is configured to perform Type
1 D2D discovery or Type 2 D2D discovery.
7. The UE of claim 1, wherein the UE includes an antenna, a touch
sensitive display screen, a speaker, a microphone, a graphics
processor, an application processor, an internal memory, or a
non-volatile memory port.
8. A user equipment (UE) operable to perform device-to-device (D2D)
discovery, the UE comprising one or more processors configured to:
identify a D2D discovery resource that is M subframes in a time
domain, wherein M is a positive integer greater than one; generate
two demodulation reference signal (DMRS) sequences to be
transmitted from the UE for each subframe in the D2D discovery
resource; apply an orthogonal cover code (OCC) to each DMRS
sequence, wherein the OCC is randomly selected from a pool of OCCs,
wherein the OCCs in the pool are predefined based on a value of M;
and transmit the two DMRS sequences for each of the M subframes of
the D2D discovery resource.
9. The UE of claim 8, wherein the one or more processors are
further configured to transmit the two DMRS sequences in a D2D
discovery message using a physical uplink shared channel
(PUSCH).
10. The UE of claim 8, wherein the one or more processors are
further configured to randomly select the D2D discovery resource
from a D2D discovery resource pool allocated by an evolved node B
(eNB).
11. The UE of claim 8, wherein the one or more processors are
further configured to transmit the two DMRS sequences for each of
the M subframes.
12. A method for performing device-to-device (D2D) discovery, the
method comprising: identifying, at a user equipment (UE), a D2D
discovery resource that is M subframes in a time domain, wherein M
is a positive integer greater than one; generating K demodulation
reference signal (DMRS) sequences to be transmitted from the UE for
each subframe in the D2D discovery resource, wherein K is a
positive integer greater than two; applying an orthogonal cover
code (OCC) to each DMRS sequence, wherein the OCC is randomly
selected from a pool of OCCs, wherein the OCCs in the pool are
predefined based on a value of M and a value of K; and transmitting
the K DMRS sequences for each of the M subframes of the D2D
discovery resource from the UE.
13. The method of claim 12, wherein the K DMRS sequences for each
of the M subframes is transmitted using a physical uplink shared
channel (PUSCH).
14. The method of claim 12, wherein Type 1 D2D discovery or Type 2
D2D discovery is performed at the UE.
15. A user equipment (UE) operable to perform device-to-device
(D2D) discovery, the UE comprising: a selection module configured
to: select a first demodulation reference signal (DMRS) sequence
from a pool of DMRS sequences for D2D discovery; and select a first
D2D discovery resource from a first D2D discovery resource pool
allocated by an evolved node B, wherein the selection module is
stored in a digital memory device or is implemented in a hardware
circuit; and a communication module configured to transmit the
first DMRS sequence from the UE using the first D2D discovery
resource selected from the D2D discovery resource pool, wherein a
second DMRS sequence is subsequently transmitted from the UE using
a second D2D discovery resource that is selected from a second D2D
discovery resource pool allocated by the eNB, wherein the
communication module is stored in a digital memory device or is
implemented in a hardware circuit.
16. The UE of claim 15, wherein the selection module is further
configured to: randomly select the first DMRS sequence from the
pool of DMRS sequences; and select the second D2D discovery
resource based on the first D2D discovery resource.
17. The UE of claim 15, wherein the communication module is further
configured to transmit a DMRS sequence in each discovery subzone
within a configured discovery period.
18. The UE of claim 15, wherein the second DMRS sequence is
identical to the first DMRS sequence
19. The UE of claim 15, further comprising a generation module
configured to generate the second DMRS sequence by performing DMRS
sequence hopping on the first DMRS sequence, wherein the DMRS
sequence hopping utilizes at least one of: base sequence hopping,
cyclic shift hopping, or orthogonal code cover hopping, wherein the
generation module is stored in a digital memory device or is
implemented in a hardware circuit.
20. The UE of claim 15, wherein the selection module is further
configured to randomly select the first D2D discovery resource from
the D2D discovery resource pool, wherein the second D2D discovery
resource is deterministically associated with the first D2D
discovery resource.
21. The UE of claim 15, wherein the selection module is further
configured to randomly select the first DMRS sequence and the
second DMRS sequence at substantially a same time, wherein the
second DMRS sequence is distinguishable from the first DMRS
sequence.
22. The UE of claim 15, wherein the selection module is further
configured to randomly select the first D2D discovery resource and
the second D2D discovery resource at substantially a same time,
wherein the second D2D discovery resource is not associated with
the first D2D discovery resource.
23. The UE of claim 15, wherein the UE is configured to perform
Type 1 D2D discovery or Type 2 D2D discovery.
24. The UE of claim 15, further comprising a discovery module
configured to perform the D2D discovery using a subset of the pool
of DMRS sequences, wherein each DMRS sequence in the subset is
associated with a configured number of cyclic shift (CS) and a
configured number of orthogonal cover codes (OCCs), wherein the
discovery module is stored in a digital memory device or is
implemented in a hardware circuit.
Description
RELATED APPLICATIONS
[0001] This application claims the benefit of and hereby
incorporates by reference U.S. Provisional Patent Application Ser.
No. 61/990,643, filed May 8, 2014, with an attorney docket number
P67685Z.
BACKGROUND
[0002] Wireless mobile communication technology uses various
standards and protocols to transmit data between a node (e.g., a
transmission station) and a wireless device (e.g., a mobile
device). Some wireless devices communicate using orthogonal
frequency-division multiple access (OFDMA) in a downlink (DL)
transmission and single carrier frequency division multiple access
(SC-FDMA) in an uplink (UL) transmission. Standards and protocols
that use orthogonal frequency-division multiplexing (OFDM) for
signal transmission include the third generation partnership
project (3GPP) long term evolution (LTE), the Institute of
Electrical and Electronics Engineers (IEEE) 802.16 standard (e.g.,
802.16e, 802.16m), which is commonly known to industry groups as
WiMAX (Worldwide interoperability for Microwave Access), and the
IEEE 802.11 standard, which is commonly known to industry groups as
WiFi.
[0003] In 3GPP radio access network (RAN) LTE systems, the node can
be a combination of Evolved Universal Terrestrial Radio Access
Network (E-UTRAN) Node Bs (also commonly denoted as evolved Node
Bs, enhanced Node Bs, eNodeBs, or eNBs) and Radio Network
Controllers (RNCs), which communicates with the wireless device,
known as a user equipment (UE). The downlink (DL) transmission can
be a communication from the node (e.g., eNodeB) to the wireless
device (e.g., UE), and the uplink (UL) transmission can be a
communication from the wireless device to the node.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] Features and advantages of the disclosure will be apparent
from the detailed description which follows, taken in conjunction
with the accompanying drawings, which together illustrate, by way
of example, features of the disclosure; and, wherein:
[0005] FIG. 1 illustrates a device to device (D2D) discovery zone
within an LTE operation zone in accordance with an example;
[0006] FIGS. 2A-2C depict a set of orthogonal cover codes (OCCs)
for each value of demodulation reference signal (DMRS) sequences
within a single subframe in accordance with an example;
[0007] FIG. 3 illustrates discovery resource mapping in a device to
device (D2D) discovery zone in accordance with an example;
[0008] FIGS. 4A-4C depict a set of orthogonal cover codes (OCCs)
for each value of subframes within a device to device (D2D)
discovery resource in accordance with an example;
[0009] FIG. 5 depicts functionality of a user equipment (UE)
operable to perform device-to-device (D2D) discovery in accordance
with an example;
[0010] FIG. 6 depicts functionality of a user equipment (UE)
operable to perform device-to-device (D2D) discovery in accordance
with an example;
[0011] FIG. 7 depicts a flow chart of a method for performing
device-to-device (D2D) discovery in accordance with an example;
[0012] FIG. 8 depicts functionality of a user equipment (UE)
operable to perform device-to-device (D2D) discovery in accordance
with an example; and
[0013] FIG. 9 illustrates a diagram of a wireless device (e.g., UE)
in accordance with an example.
[0014] Reference will now be made to the exemplary embodiments
illustrated, and specific language will be used herein to describe
the same. It will nevertheless be understood that no limitation of
the scope of the invention is thereby intended.
DETAILED DESCRIPTION
[0015] Before the present invention is disclosed and described, it
is to be understood that this invention is not limited to the
particular structures, process steps, or materials disclosed
herein, but is extended to equivalents thereof as would be
recognized by those ordinarily skilled in the relevant arts. It
should also be understood that terminology employed herein is used
for the purpose of describing particular examples only and is not
intended to be limiting. The same reference numerals in different
drawings represent the same element. Numbers provided in flow
charts and processes are provided for clarity in illustrating steps
and operations and do not necessarily indicate a particular order
or sequence.
Example Embodiments
[0016] An initial overview of technology embodiments is provided
below and then specific technology embodiments are described in
further detail later. This initial summary is intended to aid
readers in understanding the technology more quickly but is not
intended to identify key features or essential features of the
technology nor is it intended to limit the scope of the claimed
subject matter.
[0017] A technology is described for a novel demodulation reference
signal (DMRS) sequence design for device to device (D2D) discovery.
When D2D discovery is performed by a user equipment (UE), the UE
can send a DMRS sequence using a discovery resource. The DMRS
sequence can be selected from a pool of DMRS sequences. When the
discovery resource spans multiple subframes, the UE can select a
novel orthogonal code cover (OCC) to be applied to the DMRS
sequences. When additional DMRS sequences are present within the
discovery resource of a single subframe, the UE can select a novel
OCC to be applied to the DMRS sequences. The application of the
novel OCC can result in an increased capacity of the DMRS
sequences. In one configuration, the DMRS sequence design can
enable the UE to perform repeated transmissions of a D2D discovery
signal within a discovery period. The UE can randomly select a
first DMRS sequence to be transmitted using a first discovery
resource, and then subsequent DMRS sequences that are associated
with the first DMRS sequence can be transmitted using subsequent
discovery resources that are associated with the first discovery
resource, thereby reducing a processing power at the UE. In one
configuration, the DMRS sequence design can be applicable to both
Type 1 D2D discovery and Type 2 D2D discovery. In addition, the UE
can utilize only a subset of the pool of DMRS sequences in order to
reduce DMRS blind detection complexity, and thereby, UE power
consumption.
[0018] Device to device (D2D) communication for 3GPP LTE networks,
such as an Evolved Universal Terrestrial Radio Access network
(E-UTRAN), is being standardized in 3GPP LTE Release 12. A D2D
communication is a direct communication between two devices, such
as two user equipments (UEs). The two devices (e.g., LTE-based
devices) can communicate directly with one another when the two
devices are in close proximity, but such D2D communications do not
use the cellular network infrastructure. D2D discovery is generally
the first step performed at the UE to enable a D2D service. One
particular application for D2D communications is related to public
safety services. Furthermore, D2D communication can allow direct
communication from one UE to one or more target or receiving UEs,
thus enabling group communication. Examples described herein can
refer to transmission to a target or receiving UE, but it should be
understood that this could also be a transmission to a group of
target or receiving UEs.
[0019] D2D can allow a direct link between two UEs that are using
the cellular spectrum. As a result, media or other data can be
transferred from one device to another device over short distances
and using a direct connection. By using D2D data communications,
the data can be communicated directly without being relayed to the
cellular network, thereby avoiding problems with lack of or poor
network coverage or with overloading the network. The cellular
infrastructure, if present can assist with other issues, such as
peer discovery, synchronization, and the provision of identity and
security information.
[0020] The use of D2D communication can provide several benefits to
users. For example, the devices can be remote from cellular
infrastructure. D2D can allow devices to communicate locally, even
when the cellular network has failed (e.g., during a disaster)
because D2D communication does not rely on the network
infrastructure. By using licensed spectrum, the frequencies used to
perform the D2D communications are less subject to interference. In
addition, if the two devices are in close proximity, then reduced
transmission power levels are used, thereby saving power at the
devices.
[0021] D2D communication features can be referred to as ProSe
(Proximity Services) Direct Commination in the 3GPP LTE standard.
D2D communications are primarily targeted for public safety use
cases, but can be used for other applications as well. The D2D
feature enables the direct communication between UEs over the
cellular radio spectrum, but without the data being carried by the
cellular network infrastructure. D2D communication can occur when
the UE is outside of the coverage of the cellular network, or
alternatively, when the UE in within coverage of the cellular
network. Within the access stratum of the UE, the D2D data can be
carried by a D2D radio bearer.
[0022] In one example, a UE can transmit a D2D discovery message in
order to perform D2D discovery. A physical uplink shared channel
(PUSCH) can be used to transmit the D2D discovery message. The D2D
discovery message can include a demodulation reference signal
(DMRS) sequence. In addition, D2D discovery can utilize a cyclic
redundancy code (CRC) between 16 and 24 bits, channel encoding
(e.g., turbo or tail-biting convolutional codes), rate matching for
bit size matching and the generation of multiple transmissions, and
scrambling for interference randomization. The UE can transmit the
D2D discovery message during a discovery period. For each discovery
period, the UE can transmit on a randomly selected discovery
resource. When the UE is within a coverage area of an evolved node
B (eNB), the discovery period and the amount of discovery resources
can be configured by the eNB. In one example, the discovery
resource can have a duration of at least one millisecond (ms). The
duration can be selected based on a size of a media access control
(MAC) protocol data unit (PDU), in which case the duration can be a
multiple of 1 ms and include consecutive D2D subframes. The
discovery resource can be used for a single transmission of a given
discovery MAC PDU by the UE.
[0023] When the UE is within network coverage, the eNB can
periodically allocate certain discovery resources in the form of
D2D discovery regions for the UE. The UE can use these discovery
resources in order to transmit discovery information. The discovery
information can include one or more DMRS sequences, which can be
used to perform channel estimation, and timing offset and frequency
offset estimation for uplink transmissions. The discovery
information can be in the form of a discovery packet with payload
information or a discovery packet preceded by a discovery preamble.
One or more resource blocks (RB) can be used for a discovery packet
transmission during D2D discovery, which is denoted as
L.sub.RB.sup.D2D, depending on a payload size and overall discovery
performance requirements.
[0024] FIG. 1 illustrates an exemplary device to device (D2D)
discovery zone within an LTE operation zone. The LTE operation zone
can be composed of periodic D2D discovery zones (DZ), wherein each
DZ includes a defined number of resource blocks (RBs) in a
frequency domain and a defined number of subframes in a time
domain. As shown in FIG. 1, N.sub.RB.sup.D2D, n.sub.RB.sup.start,
N.sub.SF.sup.D2D and n.sub.SF.sup.start are denoted as a number of
allocated RBs, a starting RB index, a number of subframes, and a
starting subframe index of each discovery zone, respectively.
[0025] The UE can receive information regarding a partitioning of
the LTE operation zone (or D2D discovery regions) via
semi-statically signaling from the eNB. For example, the eNB can
use radio resource control (RRC) signaling to communicate the
information to the UE. In particular, the eNB can send the
information via a system information block (SIB) when the UE is
within a coverage area of the eNB. When the UE has partial network
coverage, information regarding the configuration of the discovery
resources (i.e., the partitioning of the LTE operation zone) can be
forwarded by one or a plurality of UEs that are within network
coverage to the UE with partial network coverage. When the UE is
out of network coverage, the discovery zone can be predefined or
broadcasted by a centralized D2D device or be associated with and
signaled by an independent synchronization source, with the
configuration further forwarded by other dependent/gateway
synchronization sources.
[0026] In one configuration, a legacy PUSCH structure with a DMRS
sequence can be used for a D2D discovery message transmission. In
previous techniques, multiple mutually orthogonal reference signals
can be generated by employing different cyclic shifts of Zadoff-Chu
sequence and applying orthogonal cover codes to two
reference-signal transmissions within a subframe. More
specifically, length-2 orthogonal cover codes [1 1] and [1 -1] can
be utilized.
[0027] In Type 1 D2D discovery, the UE can perform contention based
D2D discovery or D2D discovery with UE-autonomous selection of
discovery resources. In other words, the UE can select the
discovery resources used for transmitting D2D discovery messages
(e.g., a discovery packet), as opposed to the eNB selecting the
discovery resources. The UE can also be referred to as a ProSe
enabled device. The UE can randomly select the DMRS sequence when
transmitting the discovery packet. The DMRS sequence can be used to
perform channel estimation, and timing offset and frequency offset
estimation for uplink transmissions. Therefore, the DMRS sequence
can enable D2D discovery to be performed by the UE. The DMRS
sequence can include a base sequence, which can be common with a
plurality of other UEs or a function of the cell ID of the serving
cell for in-coverage UEs. In addition, the DMRS sequence can
include a random choice of the cyclic shift and/or the orthogonal
cover code (OCC) index. The discovering UEs can perform detection
of discovery preambles or packet detection in order to detect
whether the discovery packet is present in the discovery resource.
In addition, the discovering UEs can perform DM-RS identification
in order to ensure appropriate channel estimation and
timing/frequency offset compensation.
[0028] In legacy LTE solutions, 24 unique DMRS configurations are
available. The 24 unique DMRS configurations are derived from 12
cyclic shifts and 2 OCC indices. However, only a subset of the 24
DMRS sequences may be configured for D2D UEs in order to maintain
sufficient orthogonality between cyclic shifted versions of the
same DM-RS base sequence. In addition, using the subset of the 24
DMRS sequences can ensure robustness against delay spread
introduced by practical channels, and to reduce the DMRS blind
detection complexity. For instance, D2D UE can select only one of
the DMRS sequences for discovery packet transmission from a subset
of DMRS sequences with n.sub.cs.epsilon.{0,4,8} and
n.sub.oc.epsilon.{0,1}, where n.sub.cs is the cyclic shift index
and n.sub.oc is the orthogonal cover code index. In this example,
the D2D UE can select from a subset consisting of six DMRS
sequences.
[0029] In one example, the configuration of the subset of DMRS
sequences can be pre-configured or semi-statically signaled to the
UE by the eNB using RRC signaling, e.g., via system information
blocks (SIBs) when the UE is within network coverage. For a partial
network coverage scenario, the configuration can be forwarded by
one or a plurality of UEs that are in-coverage to the UEs that are
outside the network coverage area. For an out-of-network coverage
scenario, the configuration can be predefined or broadcasted by a
centralized D2D device. Alternatively, the configuration can be
associated with and signaled by an independent synchronization
source, with the configuration further forwarded by other
dependent/gateway synchronization sources.
[0030] In one configuration, whether the D2D discovery is for
public safety (PS) or non-PS can influence a size of the D2D
discovery message transmitted from the UE. In other words, the
message sizes for these two types of D2D discovery can be
different. To support D2D discovery with different message sizes,
the DMRS sequence can be used to carry one or more information bits
to signal a particular payload size. For example, one subset of
DMRS sequences with n.sub.cs.epsilon.{0,4,8} and
n.sub.oc.epsilon.{0} can be used to indicate a message size of X
bits, while another subset of DMRS sequences with
n.sub.cs.epsilon.{0,4,8} and n.sub.oc.epsilon.{1} can be used to
indicate a message size of Y bits.
[0031] The technology described herein relates to a novel DMRS
sequence design for D2D discovery. The DMRS sequence design can
account for three different scenarios: (1) a first scenario is for
when a D2D discovery resource is one subframe and a number of DMRS
sequences (or symbols) within the one subframe is at least three;
(2) a second scenario is for when the D2D discovery resource is at
least two subframes; and (3) a third scenario is for when the D2D
discovery resource is at least two subframes and the number of DMRS
sequences (or symbols) for each subframe is at least three.
[0032] With respect to the first scenario, a D2D discovery resource
of a single subframe can be modified to include additional DMRS
sequences (or symbols). The additional DMRS sequences can improve a
channel estimation performance, as well as timing and frequency
offset compensation. The D2D discovery resource of the single
subframe can be used by the UE to send a D2D discovery message. In
legacy solutions, only two DMRS sequences are within a single
subframe. In the technology described herein, the number of DMRS
sequences within a single subframe can be greater than two. The
number of DMRS sequences within the single subframe can be denoted
as K, wherein K is a positive integer greater than two. In one
example, a length-K Discrete Fourier Transform (DFT) based sequence
or Walsh-Hadamard based sequence can be utilized for a
predetermined orthogonal cover code (OCC) that is applied to each
DMRS sequence. The predetermined OCC can be selected based on a
value of K. The length-K DFT based sequence or the Walsh-Hadamard
based sequence can be utilized when the D2D discovery resource of
the single subframe is modified to include the additional DMRS
sequences. The UE can apply the predetermined OCC to each of the K
DMRS sequences, and then transmit the K DMRS sequences using the
D2D discovery resource of the single subframe. In one example, the
UE can transmit the K DMRS sequences in the D2D discovery message
using a physical uplink shared channel (PUSCH).
[0033] FIG. 2A is a table depicting a set of orthogonal cover codes
(OCCs) when the number (K) of DMRS sequences (or symbols) within a
D2D discovery resource of a single subframe is three (i.e., K=3).
The set of OCCs can be used for D2D discovery at the UE. The
orthogonal sequences can be based on a length-3 DFT code. The
orthogonal sequences can be represented as [w(o) . . . W(2)] when
K=3. Each orthogonal sequence can be associated with a particular
sequence index n.sub.oc. For example, when the sequence index is 0,
the orthogonal sequence is [1 1 1].
When the sequence index is 1, the orthogonal sequence is
[ 1 e j 2 .pi. / 3 e j 4 .pi. / 3 ] . ##EQU00001##
When the sequence index is 2, the orthogonal sequence is
[ 1 e j 4 .pi. / 3 e j 2 .pi. / 3 ] ##EQU00002##
Therefore, an appropriate orthogonal sequence can be applied to the
DMRS sequence when K=3.
[0034] FIG. 2B is a table depicting a set of orthogonal cover codes
(OCCs) when the number (K) of DMRS sequences (or symbols) within a
D2D discovery resource of a single subframe is four (i.e., K=4).
The set of OCCs can be used for D2D discovery at the UE. The
orthogonal sequences can be based on a length-4 Walsh-Hadamard
code. The orthogonal sequences can be represented as [w(o) . . .
W(3)] when K=4. Each orthogonal sequence can be associated with a
particular sequence index n.sub.oc. For example, when the sequence
index is 0, the orthogonal sequence is [+1 +1 +1 +1]. When the
sequence index is 1, the orthogonal sequence is [+1 -1 +1 -1]. When
the sequence index is 2, the orthogonal sequence is [+1 +1 -1 -1].
When the sequence index is 3, the orthogonal sequence is [+1 -1 -1
+1]. Therefore, an appropriate orthogonal sequence can be applied
to the DMRS sequence when K=4.
[0035] FIG. 2C is a table depicting a set of orthogonal cover codes
(OCCs) when the number (K) of DMRS sequences (or symbols) within a
D2D discovery resource of a single subframe is five (i.e., K=5).
The set of OCCs can be used for D2D discovery at the UE. The
orthogonal sequences can be based on a length-5 DFT code. The
orthogonal sequences can be represented as [w(o) . . . W(4)] when
K=5. Each orthogonal sequence can be associated with a particular
sequence index n.sub.oc. For example, when the sequence index is 0,
the orthogonal sequence is [1 1 1 1 1]. When the sequence index is
1, the orthogonal sequence is
[ 1 e j 2 .pi. / 5 e j 4 .pi. / 5 e j 6 .pi. / 5 e j 8 .pi. / 5 ] .
##EQU00003##
When the sequence index is 2, the orthogonal sequence is
[ 1 e j 4 .pi. / 5 e j 8 .pi. / 5 e j 2 .pi. / 5 e j 6 .pi. / 5 ] .
##EQU00004##
When the sequence index is 3, the orthogonal sequence is
[ 1 e j 6 .pi. / 5 e j 2 .pi. / 5 e j 8 .pi. / 5 e j 4 .pi. / 5 ] .
##EQU00005##
When the sequence index is 4, the orthogonal sequence is
[ 1 e j 8 .pi. / 5 e j 6 .pi. / 5 e j 4 .pi. / 5 e j 2 .pi. / 5 ] .
##EQU00006##
Therefore, an appropriate orthogonal sequence can be applied to the
DMRS sequence when K=5.
[0036] The design principles described above can be extended when K
is greater than five DMRS sequences (or symbols), i.e., when
K>5.
[0037] The UE can be configured to perform either Type 1 D2D
discovery or Type 2 D2D discovery. In Type 1 D2D discovery, the eNB
can allocate a D2D discovery resource pool to the UE via a system
information block (SIB). The UE can randomly select the D2D
discovery resource (e.g., a single subframe) from the D2D discovery
resource pool and transmit the K DMRS sequences using the randomly
selected D2D discovery resource. In Type 2 D2D discovery, the UE
can receive an indication of the D2D discovery resource from the
eNB via radio resource control (RRC) signaling. In other words, in
Type 2 D2D discovery, the UE can receive an allocation for the D2D
discovery resource from the eNB, and then transmit the K DMRS
sequences using the allocated D2D discovery resource. The UE can
transmit the K DMRS sequences using the D2D discovery resource
(e.g., a single subframe) in order to perform channel estimation,
timing offset compensation, and frequency offset compensation for
D2D discovery. As previously described, a novel orthogonal cover
code can be applied to each of the K DMRS sequences prior to
transmission of the D2D discovery message with the DMRS sequence in
the single subframe.
[0038] With respect to the second scenario, a D2D discovery
resource of multiple subframes can be used to transmit the DMRS
sequences (or symbols) from the UE. The D2D discovery resource can
span multiple subframes and multiple physical resource blocks
(PRBs). The D2D discovery resource can be used by the UE to send a
D2D discovery message. In legacy solutions, the D2D discovery
resource would consist of only a single subframe. In the technology
described herein, the number of subframes within the D2D discovery
resource in a time domain can be greater than one. The number of
subframes within the D2D discovery resource can be denoted as M,
wherein M is a positive integer greater than one. Similar to the
legacy solution, the number of DMRS sequences (or symbols) for each
of the M subframes in this scenario is two.
[0039] In one example, a length-2M DFT based sequence or
Walsh-Hadamard based sequence can be utilized for a predetermined
orthogonal cover code (OCC) that is applied to each DMRS sequence.
The predetermined OCC can be selected when multiple subframes are
applied for discovery packet transmission. In other words, the
predetermined OCC can be selected based on a value of M. The first
length-2 sequence can applied for the DMRS symbols within the first
subframe, the second length-2 sequence can applied for the 2.sup.nd
subframe, and the M.sup.th length-2 sequence can applied for the
M.sup.th subframe.
[0040] In one configuration, the UE can generate two DMRS sequences
to be transmitted for each subframe of the D2D discovery resource,
wherein the D2D discovery resource can include multiple subframes.
A predetermined orthogonal cover code (OCC) can be applied to each
DMRS sequence, wherein the predetermined OCC is selected based on a
value of M. The UE can transmit the two DMRS sequences for each of
the M subframes of the D2D discovery resource using a physical
uplink shared channel (PUSCH). The two DMRS sequences can be
included in the D2D discovery message that is transmitted from the
UE. The UE can transmit the two DMRS sequences for each of the M
subframes in order to perform channel estimation, timing offset
compensation, and frequency offset compensation for D2D
discovery.
[0041] The UE can be configured to perform either Type 1 D2D
discovery or Type 2 D2D discovery. In Type 1 D2D discovery, the eNB
can allocate a D2D discovery resource pool to the UE via a system
information block (SIB). The UE can randomly select the D2D
discovery resource (e.g., multiple subframes) from the D2D
discovery resource pool and transmit two DMRS sequences using the
multiple subframes of the randomly selected D2D discovery resource.
In Type 2 D2D discovery, the UE can receive an indication of the
D2D discovery resource (e.g., multiple subframes) from the eNB via
radio resource control (RRC) signaling. In other words, in Type 2
D2D discovery, the UE can receive an allocation for the D2D
discovery resource from the eNB, and then transmit the two DMRS
sequences using the allocated D2D discovery resource of multiple
subframes. As previously described, a novel orthogonal cover code
can be applied to each DMRS sequence prior to transmission of the
D2D discovery message using the D2D discovery resource of the
multiple subframes.
[0042] FIG. 3 illustrates an example of discovery resource mapping
in a device to device (D2D) discovery zone. As previously
explained, the discovery resource can span multiple subframes and
multiple physical resource blocks (PRBs). In the example shown in
FIG. 3, the discovery zone can include the discovery resource
(i.e., the discovery resource can be mapped from the discovery
zone). For the discovery resource, the number of subframes in the
time domain (denoted as M) is two and the number of PRBs in the
frequency domain (denoted as N) is two. In each subframe, the
number of DMRS sequences can be two, as in a legacy PUSCH
transmission.
[0043] FIG. 4A is a table depicting a set of orthogonal cover codes
(OCCs) when a D2D discovery resource spans two subframe (i.e.,
M=2). The set of OCCs can be used for D2D discovery at the UE. The
orthogonal sequences can be based on a length-4 Walsh-Hadamard
based sequence. The orthogonal sequences can be represented as
[w(o) L W(3)] when M=2. Each orthogonal sequence can be associated
with a particular sequence index n.sub.oc. For example, when the
sequence index is 0, the orthogonal sequence is [+1 +1 +1 +1]. When
the sequence index is 1, the orthogonal sequence is [+1 -1 +1 -1].
When the sequence index is 2, the orthogonal sequence is [+1 +1 -1
-1]. When the sequence index is 3, the orthogonal sequence is [+1
-1 -1+1]. Therefore, an appropriate orthogonal sequence can be
applied to the DMRS sequence when M=2.
[0044] FIG. 4B is a table depicting a set of orthogonal cover codes
(OCCs) when a D2D discovery resource spans three subframe (i.e.,
M=3). The set of OCCs can be used for D2D discovery at the UE. The
orthogonal sequences can be based on a length-6 DFT code. The
orthogonal sequences can be represented as [w(o) L W(5)] when M=3.
Each orthogonal sequence can be associated with a particular
sequence index n.sub.oc. For example, when the sequence index is 0,
the orthogonal sequence is [1 1 1 1 1 1]. When the sequence index
is 1, the orthogonal sequence is
[ 1 e j .pi. / 3 e j 2 .pi. / 3 - 1 e j 4 .pi. / 3 e j 5 .pi. / 3 ]
. ##EQU00007##
When the sequence index is 2, the orthogonal sequence is
[ 1 e j 2 .pi. / 3 e j 4 .pi. / 3 1 e j 2 .pi. / 3 e j 4 .pi. / 3 ]
. ##EQU00008##
When the sequence index is 3, the orthogonal sequence is [1 -1 1 -1
1 -1]. When the sequence index is 4, the orthogonal sequence is
[ 1 e j 4 .pi. / 3 e j 2 .pi. / 3 1 e j 4 .pi. / 3 e j 2 .pi. / 3 ]
. ##EQU00009##
[0045] When the sequence index is 5, the orthogonal sequence is
[ 1 e j 5 .pi. / 3 e j 4 .pi. / 3 - 1 e j 2 .pi. / 3 e j .pi. / 3 ]
. ##EQU00010##
Therefore, an appropriate orthogonal sequence can be applied to the
DMRS sequence when M=3.
[0046] FIG. 4C is a table depicting a set of orthogonal cover codes
(OCCs) when a D2D discovery resource spans four subframe (i.e.,
M=4). The set of OCCs can be used for D2D discovery at the UE. The
orthogonal sequences can be based on a length-8 Walsh-Hadamard
based sequence. The orthogonal sequences can be represented as
[w(o) L W(7)] when M=4. Each orthogonal sequence can be associated
with a particular sequence index n.sub.oc. For example, when the
sequence index is 0, the orthogonal sequence is [+1 +1 +1 +1 +1 +1
+1 +1]. When the sequence index is 1, the orthogonal sequence is
[+1 -1 +1 -1 +1 -1 +1 -1]. When the sequence index is 2, the
orthogonal sequence is [+1 +1 -1 -1 +1 +1 -1 -1]. When the sequence
index is 3, the orthogonal sequence is [+1 -1 -1 +1 +1 -1 -1 +1].
When the sequence index is 4, the orthogonal sequence is [+1 +1 +1
+1 -1 -1 -1 -1]. When the sequence index is 5, the orthogonal
sequence is [+1 -1 +1 -1 -1 +1 -1 +1]. When the sequence index is
6, the orthogonal sequence is [+1 +1 -1 -1 -1 -1 +1 +1]. When the
sequence index is 7, the orthogonal sequence is [+1 -1 -1 +1 -1 +1
+1 -1]. Therefore, an appropriate orthogonal sequence can be
applied to the DMRS sequence when M=4.
[0047] The design principles described above can be extended when M
is greater than four subframes per D2D discovery resource i.e.,
when M>4.
[0048] With respect to the third scenario, a D2D discovery resource
can span multiple subframes and additional DMRS sequences (or
symbols) are included for each subframe of the D2D discovery
resource. The number of subframes in a time domain within the D2D
discovery resource can be denoted as M, wherein M is a positive
integer greater than one. The number of DMRS sequences for each
subframe within the D2D discovery resource can be denoted as K,
wherein K is a positive integer greater than two.
[0049] In one example, a length-MK DFT based sequence or
Walsh-Hadamard based sequence can be utilized for a predetermined
orthogonal cover code (OCC) that is applied to each DMRS sequence.
The predetermined OCC can be applied when the D2D discovery
resource spans multiple subframes and additional DMRS symbols are
included in each subframe. The first length-K sequence can be
applied for the first DMRS sequence within the first subframe, the
second length-K sequence can be applied for the second subframe,
and the M.sup.th length-K sequence can be applied for the M.sup.th
subframe.
[0050] In one configuration, the UE can generate K DMRS sequences
to be transmitted for each subframe of the D2D discovery resource,
wherein the D2D discovery resource can include multiple subframes.
A predetermined orthogonal cover code (OCC) can be applied to each
DMRS sequence, wherein the predetermined OCC is selected based on a
value of M and a value of K. The UE can transmit the K DMRS
sequences for each of the M subframes of the D2D discovery resource
using a physical uplink shared channel (PUSCH). The K DMRS
sequences can be included in the D2D discovery message that is
transmitted from the UE. The UE can transmit the K DMRS sequences
for each of the M subframes in order to perform channel estimation,
timing offset compensation, and frequency offset compensation for
D2D discovery. In this scenario, the total number of DMRS sequences
in one discovery resource can be calculated as M.times.K, wherein M
is the number of subframes for the discovery packet transmission
and K is the number of DMRS symbols within one subframe.
[0051] When M=2 and K=3, a length-6 DFT based sequence is utilized
for an orthogonal sequence, wherein the length-6 DFT based sequence
is similar to as described above.
[0052] When M=2 and K=4, a length-8 Walsh-Hadamard based sequence
is utilized for an orthogonal sequence, wherein the length-8
Walsh-Hadamard based sequence is similar to as described above.
[0053] The design principles described above can be extended when M
is greater than two subframes and/or K is greater than two DMRS
symbols, i.e., when M>2 and/or K>2.
[0054] In one configuration, the UE can perform a repeated
transmission of the DMRS sequences for Type 1 D2D discovery. A
novel DMRS sequence design for repeated transmissions is described
herein. The UE can repeatedly transmit (e.g., either contiguously
or non-contiguously) a given discovery MAC PDU within a discovery
period. The eNB can allocate a D2D discovery resource pool (or a
set of discovery resources) for the UE. The resources in the D2D
discovery resource pool can be used for the repeated transmissions
of the discovery MAC PDU. The UE can perform a random selection of
a first resource from the D2D discovery pool. The UE can use the
first resource for transmitting a first discovery MAC PDU. The UE
can subsequently use other resources for subsequent discovery MAC
PDU transmissions, wherein the other resources are
deterministically associated with the first resource.
Alternatively, the UE can perform random selection for each
resource in a D2D discovery resource pool (as opposed to the random
selection of only the first resource). The UE can be configured to
perform a defined number of repeated transmissions.
[0055] For repeated transmission, ProSe-enabled UEs can transmit
multiple copies of the discovery packets within one D2D discovery
zone. In particular, each D2D discovery zone (DZ) can be divided
into N sub-DZs, and the D2D UEs can transmit one discovery packet
in each sub-DZ. There can be two scenarios with respect to repeated
transmissions of the discovery packets from the UE. In the first
scenario, the UE can randomly select the resource only for the
first transmission, and the resources for subsequent transmissions
are deterministically associated with the first resource. In other
words, a frequency and time location of the subsequent transmission
is determined by the initial transmission. The UE can randomly
select the resource from a D2D discovery resource pool that is
allocated by the eNB. In addition, the UE can randomly choose one
DMRS sequence for transmission within this selected discovery
resource. In other words, the UE can transmit the DMRS sequence
using the discovery resource selected from the D2D discovery
resource pool. The UE can subsequently transmit another DMRS
sequence that is related (or identical) to the initial DMRS
sequence. Even though the subsequent transmission can be performed
using another discovery resource that is selected from a separate
D2D discovery resource pool, the subsequent discovery resource can
be derived from the initial discovery resource. In the second
scenario, the UE can randomly select the resources for all the
transmissions. In other words, in this scenario, the resources that
are subsequently selected are not associated with the resource that
is initially selected. In addition, the UE can randomly select the
DMRS sequence for each of the randomly selected resources. In this
scenario, the subsequent DMRS sequences are not associated with the
initial DMRS sequence.
[0056] With respect to the first scenario, there are several
manners in which the UE can perform the DMRS sequence selection. In
one example, the UE can randomly select the DMRS sequences from a
DMRS sequence pool for the first transmission. The DMRS sequence
pool can be a subset of all available DMRS sequences and can be
predefined or configured by the network, or alternatively, the DMRS
sequence pool can be a full set of all available DMRS sequences.
The UE can perform the first transmission using a randomly selected
resource. The UE can randomly select the resource from a D2D
discovery resource pool that is allocated by the eNB. For the
subsequent transmission, the UE can choose an identical DMRS
sequence as the first transmission. Each subsequent transmission of
the DMRS sequence can be performed using discovery resources that
are selected from separate discovery resource pools allocated by
the eNB. Therefore, the discovering UE can combine the correlation
energy of multiple transmissions to improve DMRS detection
performance.
[0057] In another example, the UE can randomly select the DMRS
sequence from a DMRS sequence pool for the first transmission. The
UE can generate a subsequent DMRS sequence by performing DMRS
sequence hopping on the initial DMRS sequence (i.e., for the first
transmission). In other words, the subsequent DMRS sequence can be
associated with the initial DMRS sequence after DMRS sequence
hopping is performed, but the two DMRS sequences are not identical.
A DMRS sequence hopping pattern can be cell-specific or common
across the network to allow for efficient discovery. In some
examples, either base sequence hopping, or cyclic shift hopping or
orthogonal cover code hopping or any combination of the above
options can be utilized for DMRS sequence hopping. For instance,
for cyclic shift hopping, the UE can select a DMRS sequence for the
first transmission to have a cyclic shift index n.sub.cs. In the
subsequent transmission, the UE can transmit a DMRS sequence with
cyclic shift index of:
n.sub.cs(k)=(n.sub.cs+kL)mod N.sub.cs, wherein k is a repeated
transmission index, L is a hopping distance (which can be
predefined or signaled by a higher layer), and N.sub.cs is the
total number of cyclic shifts (e.g., 12 cyclic shifts). In another
example, the hopping pattern for the DMRS sequence can be the same
as the hopping pattern applied for resource hopping with respect to
repeated transmissions.
[0058] In yet another example, the UE can randomly select the DMRS
sequences for all of the transmissions. For this scheme, consistent
collision of DMRS sequence transmissions can be avoided. However,
the detection gain from combining multiple received copies of the
DMRS symbols cannot be realized.
[0059] With respect to the second scenario, the UE can randomly
select the resources for all of the transmissions. The UE can
randomly select the resources from a plurality of D2D discovery
resource pools allocated by the eNB. In this case, an initial
resource used for transmitting the discovery packet is not related
to or associated with a subsequent resource used for transmitting a
later discovery packet. In addition, the UE can randomly select the
DMRS sequences for all of the transmissions. Unlike the previous
scenario, an initial DMRS sequence selected for transmission is not
identical to or associated with a subsequent DMRS sequence that is
selected for transmission. The UE can transmit a first randomly
selected DMRS sequence using a first randomly selected discovery
resource, and then subsequently transmit a second randomly selected
DMRS sequence using a second randomly selected discovery resource,
wherein the DMRS sequence and discovery resource from the first
transmission is not related to the DMRS sequence and discovery
resource from the second transmission.
[0060] In one configuration, the UE can perform a repeated
transmission of the DMRS sequences for Type 2 D2D discovery. A
novel DMRS sequence design can be applicable for Type 2 D2D
discovery. Type 2 D2D discovery is a procedure where resources for
discovery signal transmissions are allocated on a per UE specific
basis. In Type 2A, resources are allocated for each specific
transmission instance of discovery signals. In Type 2B, resources
are semi-persistently allocated for discovery signal transmissions.
Type 2 discovery can be controlled by the eNB and not the UE. In
contrast, Type 1 D2D discovery is a discovery procedure where
resources for discovery signal transmissions are allocated on a
non-UE specific basis. The resources can be for all UEs or a group
of UEs. Type 1 D2D is for contention based D2D discovery, such that
the UE randomly chooses the D2D discovery resource for the
transmission. The utilization of DMRS base sequences for Type 2
discovery is subject to similar considerations as for Type 1
discovery. The DMRS sequences can either be network-common or
pre-configured or associated with a synchronization source
identity.
[0061] Several options can be considered for DMRS sequence design
for Type 2 discovery. In the first option, a D2D transmitter (Tx)
UE can randomly select a DMRS sequence with a defined cyclic shift
(CS) and a defined orthogonal cover code (OCC). The D2D Tx UE can
select the DMRS sequence for transmission in each discovery period
(for Type 2B discovery) or for each transmission instance (for Type
2A discovery). In the second option, the D2D Tx UE can apply DMRS
sequence hopping for the transmission in each discovery period (for
Type 2B discovery). An initial choice of the DMRS sequence can be
randomly chosen by the UE or assigned by the eNB. In the third
option, the D2D Tx UE can use the same DMRS sequence for the
transmission in each discovery period (for Type 2B discovery). An
initial choice of the DMRS sequence can be randomly chosen by the
UE or assigned by the eNB. When repeated transmissions are
configured or allowed for Type 2 discovery, similar options as
compared to Type 1 discovery can apply for DMRS sequence choices
within a discovery period.
[0062] In one configuration, for Type 1 discovery, a subset of DMRS
sequences can be configured for ProSe-enabled devices in order to
reduce DMRS blind detection complexity at the UE. A reduction of
DMRS blind detection complexity can result in power consumption
savings at the UE. To further improve the orthogonality and channel
separation, especially in the presence of practical impairment,
DMRS sequences with relatively large cyclic shift (CS) separation
and appropriate orthogonal cover codes (OCCs) can be
configured.
[0063] In one example, two OCCs with an identical CS may not be
configured for the DMRS sequence. For instance, OCC index 0 and 1
cannot be configured together with CS index 0. This is primarily
due to the fact that certain ambiguity occurs between phase
rotations of two DMRS symbols introduced by the OCC and large
frequency offset. In this case, discovering UE may be unable to
differentiate the OCC or estimate frequency offset correctly. As a
result, the discovering UE may be unable to identify the correct
DMRS sequences.
[0064] In another example, two OCCs with a CS offset can be
configured for the DMRS sequence. As a non-limiting example, the
configuration can be DMRS Configuration I: CS and OCC index
{n.sub.cs, n.sub.occ}.epsilon.{{0,0}, {3,1}, {6,0},{9,1}}. In this
case, the total number of DMRS sequences is 4. As another
non-limiting example, the configuration can be DMRS Configuration
II: CS and OCC index {n.sub.cs, n.sub.occ} E {{0,0}, {2,1},
{4,0},{6,1},{8,0},{10,1}}. In this case, the total number of DMRS
sequence is 6. Although DMRS Configuration I can outperform DMRS
Configuration II in terms of DMRS blind detection performance, the
DM-RS collision probability can be higher for DMRS Configuration I
as compared to DMRS Configuration II.
[0065] In yet another example, only a CS with a single OCC index
can be configured for the DMRS sequence. Two non-limiting examples
of such configurations can be DMRS Configuration IA: CS and OCC
index {n.sub.cs, n.sub.occ}.epsilon.{{0,0}, {3,0}, {6,0},{9,0}} and
DMRS Configuration IIA: CS and OCC index {n.sub.cs,
n.sub.occ}.epsilon.{{0,0}, {2,0}, {4,0},{6,0},{8,0},{10,0}}.
[0066] Another example provides functionality 500 of a user
equipment (UE) comprising one or more processors configured to
perform device-to-device (D2D) discovery, as shown in the flow
chart in FIG. 5. The functionality can be implemented as a method
or the functionality can be executed as instructions on a machine,
where the instructions are included on at least one computer
readable medium or one non-transitory machine readable storage
medium. The one or more processors can be configured to identify a
D2D discovery resource of a single subframe, as in block 510. The
one or more processors can be configured to generate K demodulation
reference signal (DMRS) sequences to be transmitted from the UE
using the D2D discovery resource, wherein K is a positive integer
greater than two, as in block 520. The one or more processors can
be configured to apply an orthogonal cover code (OCC) to each DMRS
sequence, wherein the OCC is randomly selected from a pool of OCCs,
wherein the OCCs in the pool are predefined based on a value of K,
as in block 530. The one or more processors can be configured to
transmit the K DMRS sequences using the D2D discovery resource of
the single subframe, as in block 540.
[0067] In one example, the one or more processors are further
configured to transmit the K DMRS sequences in a D2D discovery
message using a physical uplink shared channel (PUSCH). In another
example, the one or more processors are further configured to
randomly select the D2D discovery resource from a D2D discovery
resource pool, wherein the D2D discovery resource pool is allocated
by an evolved node B (eNB) and indicated to the UE via a system
information block (SIB). In yet another example, the one or more
processors are further configured to receive an indication of the
D2D discovery resource from an evolved node B (eNB) via radio
resource control (RRC) signaling.
[0068] In one example, the one or more processors are further
configured to transmit the K DMRS sequences using the single
subframe of the D2D discovery resource. In another example, the UE
is configured to perform Type 1 D2D discovery or Type 2 D2D
discovery. In yet another example, the UE includes an antenna, a
touch sensitive display screen, a speaker, a microphone, a graphics
processor, an application processor, an internal memory, or a
non-volatile memory port.
[0069] Another example provides functionality 600 of a user
equipment (UE) comprising one or more processors configured to
perform device-to-device (D2D) discovery, as shown in the flow
chart in FIG. 6. The functionality can be implemented as a method
or the functionality can be executed as instructions on a machine,
where the instructions are included on at least one computer
readable medium or one non-transitory machine readable storage
medium. The one or more processors can be configured to identify a
D2D discovery resource that is M subframes in a time domain,
wherein M is a positive integer greater than one, as in block 610.
The one or more processors can be configured to generate two
demodulation reference signal (DMRS) sequences to be transmitted
from the UE for each subframe in the D2D discovery resource, as in
block 620. The one or more processors can be configured to apply an
orthogonal cover code (OCC) to each DMRS sequence, wherein the OCC
is randomly selected from a pool of OCCs, wherein the OCCs in the
pool are predefined based on a value of M, as in block 630. The one
or more processors can be configured to transmit the two DMRS
sequences for each of the M subframes of the D2D discovery
resource, as in block 640.
[0070] In one example, the one or more processors are further
configured to transmit the two DMRS sequences in a D2D discovery
message using a physical uplink shared channel (PUSCH). In another
example, the one or more processors are further configured to
randomly select the D2D discovery resource from a D2D discovery
resource pool allocated by an evolved node B (eNB). In yet another
example, the one or more processors are further configured to
transmit the two DMRS sequences for each of the M subframes.
[0071] Another example provides a method 700 for performing
device-to-device (D2D) discovery, as shown in the flow chart in
FIG. 7. The method can be executed as instructions on a machine,
where the instructions are included on at least one computer
readable medium or one non-transitory machine readable storage
medium. The method can include the operation of identifying, at a
user equipment (UE), a D2D discovery resource that is M subframes
in a time domain, wherein M is a positive integer greater than one,
as in block 710. The method can include the operation of generating
K demodulation reference signal (DMRS) sequences to be transmitted
from the UE for each subframe in the D2D discovery resource,
wherein K is a positive integer greater than two, as in block 720.
The method can include the operation of applying an orthogonal
cover code (OCC) to each DMRS sequence, wherein the OCC is randomly
selected from a pool of OCCs, wherein the OCCs in the pool are
predefined based on a value of M and a value of K, as in block 730.
The method can include the operation of transmitting the K DMRS
sequences for each of the M subframes of the D2D discovery resource
from the UE, as in block 740.
[0072] In one example, the K DMRS sequences for each of the M
subframes are transmitted using a physical uplink shared channel
(PUSCH). In another example, Type 1 D2D discovery or Type 2 D2D
discovery is performed at the UE.
[0073] FIG. 8 depicts functionality of a user equipment (UE) 800
operable to perform device-to-device (D2D) discovery. The UE 800
can include a selection module 802 configured to select a first
demodulation reference signal (DMRS) sequence from a pool of DMRS
sequences for D2D discovery. The selection module 802 can be
configured to select a first D2D discovery resource from a first
D2D discovery resource pool allocated by an evolved node B. The UE
800 can include a communication module 804 configured to transmit
the first DMRS sequence from the UE 800 using the first D2D
discovery resource selected from the D2D discovery resource pool,
wherein a second DMRS sequence is subsequently transmitted from the
UE 800 using a second D2D discovery resource that is selected from
a second D2D discovery resource pool allocated by the eNB
[0074] In one example, the selection module 802 can be further
configured to: randomly select the first DMRS sequence from the
pool of DMRS sequences; and select the second D2D discovery
resource based on the first D2D discovery resource. In another
example, the communication module 804 can be further configured to
transmit a DMRS sequence in each discovery subzone within a
configured discovery period. In yet another example, the second
DMRS sequence is identical to the first DMRS sequence
[0075] In one example, the UE 800 can include a generation module
806 configured to generate the second DMRS sequence by performing
DMRS sequence hopping on the first DMRS sequence, wherein the DMRS
sequence hopping utilizes at least one of: base sequence hopping,
cyclic shift hopping, or orthogonal code cover hopping. In another
example, the selection module 804 can be further configured to
randomly select the first D2D discovery resource from the D2D
discovery resource pool, wherein the second D2D discovery resource
is deterministically associated with the first D2D discovery
resource. In yet another example, the selection module 804 can be
further configured to randomly select the first DMRS sequence and
the second DMRS sequence at substantially a same time, wherein the
second DMRS sequence is distinguishable from the first DMRS
sequence.
[0076] In one example, the selection module 804 can be further
configured to randomly select the first D2D discovery resource and
the second D2D discovery resource at substantially a same time,
wherein the second D2D discovery resource is not associated with
the first D2D discovery resource. In another example, the UE 800 is
configured to perform Type 1 D2D discovery or Type 2 D2D discovery.
In yet another example, the UE 800 can include a discovery module
808 configured to perform the D2D discovery using a subset of the
pool of DMRS sequences, wherein each DMRS sequence in the subset is
associated with a configured number of cyclic shift (CS) and a
configured number of orthogonal cover codes (OCCs).
[0077] FIG. 9 provides an example illustration of the wireless
device, such as a user equipment (UE), a mobile station (MS), a
mobile wireless device, a mobile communication device, a tablet, a
handset, or other type of wireless device. The wireless device can
include one or more antennas configured to communicate with a node
or transmission station, such as a base station (BS), an evolved
Node B (eNB), a baseband unit (BBU), a remote radio head (RRH), a
remote radio equipment (RRE), a relay station (RS), a radio
equipment (RE), a remote radio unit (RRU), a central processing
module (CPM), or other type of wireless wide area network (WWAN)
access point. The wireless device can be configured to communicate
using at least one wireless communication standard including 3GPP
LTE, WiMAX, High Speed Packet Access (HSPA), Bluetooth, and WiFi.
The wireless device can communicate using separate antennas for
each wireless communication standard or shared antennas for
multiple wireless communication standards. The wireless device can
communicate in a wireless local area network (WLAN), a wireless
personal area network (WPAN), and/or a WWAN.
[0078] FIG. 9 also provides an illustration of a microphone and one
or more speakers that can be used for audio input and output from
the wireless device. The display screen may be a liquid crystal
display (LCD) screen, or other type of display screen such as an
organic light emitting diode (OLED) display. The display screen can
be configured as a touch screen. The touch screen may use
capacitive, resistive, or another type of touch screen technology.
An application processor and a graphics processor can be coupled to
internal memory to provide processing and display capabilities. A
non-volatile memory port can also be used to provide data
input/output options to a user. The non-volatile memory port may
also be used to expand the memory capabilities of the wireless
device. A keyboard may be integrated with the wireless device or
wirelessly connected to the wireless device to provide additional
user input. A virtual keyboard may also be provided using the touch
screen.
[0079] Various techniques, or certain aspects or portions thereof,
may take the form of program code (i.e., instructions) embodied in
tangible media, such as floppy diskettes, compact disc-read-only
memory (CD-ROMs), hard drives, non-transitory computer readable
storage medium, or any other machine-readable storage medium
wherein, when the program code is loaded into and executed by a
machine, such as a computer, the machine becomes an apparatus for
practicing the various techniques. Circuitry can include hardware,
firmware, program code, executable code, computer instructions,
and/or software. A non-transitory computer readable storage medium
can be a computer readable storage medium that does not include
signal. In the case of program code execution on programmable
computers, the computing device may include a processor, a storage
medium readable by the processor (including volatile and
non-volatile memory and/or storage elements), at least one input
device, and at least one output device. The volatile and
non-volatile memory and/or storage elements may be a random-access
memory (RAM), erasable programmable read only memory (EPROM), flash
drive, optical drive, magnetic hard drive, solid state drive, or
other medium for storing electronic data. The node and wireless
device may also include a transceiver module (i.e., transceiver), a
counter module (i.e., counter), a processing module (i.e.,
processor), and/or a clock module (i.e., clock) or timer module
(i.e., timer). One or more programs that may implement or utilize
the various techniques described herein may use an application
programming interface (API), reusable controls, and the like. Such
programs may be implemented in a high level procedural or object
oriented programming language to communicate with a computer
system. However, the program(s) may be implemented in assembly or
machine language, if desired. In any case, the language may be a
compiled or interpreted language, and combined with hardware
implementations.
[0080] As used herein, the term processor can include general
purpose processors, specialized processors such as VLSI, FPGAs, or
other types of specialized processors, as well as base band
processors used in transceivers to send, receive, and process
wireless communications.
[0081] It should be understood that many of the functional units
described in this specification have been labeled as modules, in
order to more particularly emphasize their implementation
independence. For example, a module may be implemented as a
hardware circuit comprising custom very-large-scale integration
(VLSI) circuits or gate arrays, off-the-shelf semiconductors such
as logic chips, transistors, or other discrete components. A module
may also be implemented in programmable hardware devices such as
field programmable gate arrays, programmable array logic,
programmable logic devices or the like.
[0082] Modules may also be implemented in software for execution by
various types of processors. An identified module of executable
code may, for instance, comprise one or more physical or logical
blocks of computer instructions, which may, for instance, be
organized as an object, procedure, or function. Nevertheless, the
executables of an identified module need not be physically located
together, but may comprise disparate instructions stored in
different locations which, when joined logically together, comprise
the module and achieve the stated purpose for the module.
[0083] Indeed, a module of executable code may be a single
instruction, or many instructions, and may even be distributed over
several different code segments, among different programs, and
across several memory devices. Similarly, operational data may be
identified and illustrated herein within modules, and may be
embodied in any suitable form and organized within any suitable
type of data structure. The operational data may be collected as a
single data set, or may be distributed over different locations
including over different storage devices, and may exist, at least
partially, merely as electronic signals on a system or network. The
modules may be passive or active, including agents operable to
perform desired functions.
[0084] Reference throughout this specification to "an example" or
"exemplary" means that a particular feature, structure, or
characteristic described in connection with the example is included
in at least one embodiment of the present invention. Thus,
appearances of the phrases "in an example" or the word "exemplary"
in various places throughout this specification are not necessarily
all referring to the same embodiment.
[0085] As used herein, a plurality of items, structural elements,
compositional elements, and/or materials may be presented in a
common list for convenience. However, these lists should be
construed as though each member of the list is individually
identified as a separate and unique member. Thus, no individual
member of such list should be construed as a de facto equivalent of
any other member of the same list solely based on their
presentation in a common group without indications to the contrary.
In addition, various embodiments and example of the present
invention may be referred to herein along with alternatives for the
various components thereof. It is understood that such embodiments,
examples, and alternatives are not to be construed as defacto
equivalents of one another, but are to be considered as separate
and autonomous representations of the present invention.
[0086] Furthermore, the described features, structures, or
characteristics may be combined in any suitable manner in one or
more embodiments. In the following description, numerous specific
details are provided, such as examples of layouts, distances,
network examples, etc., to provide a thorough understanding of
embodiments of the invention. One skilled in the relevant art will
recognize, however, that the invention can be practiced without one
or more of the specific details, or with other methods, components,
layouts, etc. In other instances, well-known structures, materials,
or operations are not shown or described in detail to avoid
obscuring aspects of the invention.
[0087] While the forgoing examples are illustrative of the
principles of the present invention in one or more particular
applications, it will be apparent to those of ordinary skill in the
art that numerous modifications in form, usage and details of
implementation can be made without the exercise of inventive
faculty, and without departing from the principles and concepts of
the invention. Accordingly, it is not intended that the invention
be limited, except as by the claims set forth below.
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