U.S. patent application number 13/610464 was filed with the patent office on 2013-03-14 for dmrs association and signaling for enhanced pdcch in lte systems.
This patent application is currently assigned to RESEARCH IN MOTION LIMITED. The applicant listed for this patent is Shiwei Gao, Yongkang Jia, Amin Mobasher, Hua Xu. Invention is credited to Shiwei Gao, Yongkang Jia, Amin Mobasher, Hua Xu.
Application Number | 20130064216 13/610464 |
Document ID | / |
Family ID | 47829804 |
Filed Date | 2013-03-14 |
United States Patent
Application |
20130064216 |
Kind Code |
A1 |
Gao; Shiwei ; et
al. |
March 14, 2013 |
DMRS Association and Signaling for Enhanced PDCCH in LTE
Systems
Abstract
A method is provided for operating a UE in a wireless
communication network. The method comprises sending, by the UE, an
ACK/NACK message after receiving data on a PDSCH scheduled by an
E-PDCCH, wherein the sending is from at least one antenna port and
uses at least one physical resource, and wherein the at least one
physical resource is determined based at least partially on a
resource over which the E-PDCCH is received, and wherein the
resource over which the E-PDCCH is received consists of at least
one eCCE.
Inventors: |
Gao; Shiwei; (Nepean,
CA) ; Xu; Hua; (Ottawa, CA) ; Jia;
Yongkang; (Ottawa, CA) ; Mobasher; Amin;
(Santa Clara, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Gao; Shiwei
Xu; Hua
Jia; Yongkang
Mobasher; Amin |
Nepean
Ottawa
Ottawa
Santa Clara |
CA |
CA
CA
CA
US |
|
|
Assignee: |
RESEARCH IN MOTION LIMITED
Waterloo
CA
|
Family ID: |
47829804 |
Appl. No.: |
13/610464 |
Filed: |
September 11, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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61533470 |
Sep 12, 2011 |
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61541514 |
Sep 30, 2011 |
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61554582 |
Nov 2, 2011 |
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61576558 |
Dec 16, 2011 |
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61606839 |
Mar 5, 2012 |
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61611968 |
Mar 16, 2012 |
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61644089 |
May 8, 2012 |
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Current U.S.
Class: |
370/330 ;
370/329 |
Current CPC
Class: |
H04L 5/0053 20130101;
H04W 72/12 20130101; H04L 1/1861 20130101; H04L 5/0055 20130101;
H04L 5/0051 20130101; H04W 16/10 20130101; H04W 48/12 20130101;
H04B 7/024 20130101; H04B 7/0606 20130101; H04L 5/0035 20130101;
H04L 5/0026 20130101; H04L 5/0094 20130101; H04W 72/04 20130101;
H04L 5/0023 20130101; H04B 7/0417 20130101; H04L 5/0016 20130101;
H04L 5/0048 20130101 |
Class at
Publication: |
370/330 ;
370/329 |
International
Class: |
H04W 72/04 20090101
H04W072/04 |
Claims
1. A method of operating a user equipment (UE) in a wireless
communications network, the method comprising: sending, by the UE,
an acknowledgement/negative acknowledgement (ACK/NACK) message
after receiving data on a physical downlink shared channel (PDSCH)
scheduled by an extended physical downlink control channel
(E-PDCCH), wherein the sending is from at least one antenna port
and uses at least one physical resource, and wherein the at least
one physical resource is determined based at least partially on a
resource over which the E-PDCCH is received, and wherein the
resource over which the E-PDCCH is received consists of at least
one extended control channel element (eCCE).
2. The method of claim 1, further comprising using, by the UE, an
eCCE index of the at least one eCCE to derive the physical resource
for the ACK/NACK.
3. The method claim 1 further comprising using, by the UE, the
lowest index of the eCCE for the E-PDCCH transmission, plus a DMRS
port offset, to derive the physical resource for the ACK/NACK.
4. The method of claim 3, wherein the DMRS offset is the port index
difference between the DMRS port associated with the eCCE with the
lowest index and the DMRS port with which the E-PDCCH is
demodulated.
5. The method of claim 1, further comprising using, by the UE, a
signaling from a network element, wherein the signaling includes at
least one of an ACK/NACK resource offset and a seed identifier
(SCID) for DMRS sequence generation, for deriving the physical
resource for the ACK/NACK.
6. The method of claim 1, further comprising using, by the UE, a
transmit antenna port offset for deriving the physical resource for
the ACK/NACK transmitted on a second transmit antenna.
7. The method of claim 5, wherein the physical resource index for
the ACK/NACK is derived by a combination of one or more of the
following parameters: an eCCE index; a DMRS port offset; the
ACK/NACK resource offset; the SCID value; and a transmit antenna
port offset.
8. A method of operating an enhanced node B (eNB) in a wireless
communications network, the method comprising: detecting, by the
eNB, from a user equipment (UE), an acknowledgement/negative
acknowledgement (ACK/NACK) message after a physical downlink shared
channel (PDSCH) scheduled by an extended physical downlink control
channel (E-PDCCH) is transmitted to the UE, wherein the detection
of the ACK/NACK is over at least one physical resource, and wherein
the at least one physical resource is determined based at least
partially on a resource over which the E-PDCCH is transmitted, and
wherein the resource over which the E-PDCCH is transmitted consists
of at least one extended control channel element (eCCE).
9. The method of claim 8, wherein the physical resource for the
ACK/NACK is derived from an eCCE index of the at least one
eCCE.
10. The method claim 8 wherein the physical resource for the
ACK/NACK is derived from the lowest index of the eCCE for the
E-PDCCH transmission, plus a DMRS port offset.
11. The method of claim 10, wherein the DMRS offset is the port
index difference between the DMRS port associated with the eCCE
with the lowest index and the DMRS port with which the E-PDCCH is
transmitted.
12. The method of claim 8, further comprising the eNB using at
least one of an ACK/NACK resource offset and a seed identifier
(SCID) for DMRS sequence generation for deriving the physical
resource for the ACK/NACK.
13. The method of claim 8, wherein a transmit antenna port offset
is used for deriving a second physical resource for the ACK/NACK
when the ACK/NACK is also transmitted on a second transmit antenna
by the UE.
14. The method of claim 12, wherein the physical resource index for
the ACK/NACK is derived by a combination of one or more of the
following parameters: an eCCE index; a DMRS port offset; the
ACK/NACK resource offset; the SCID value; and a transmit antenna
port offset.
15. A method for operating an enhanced node B (eNB) in a wireless
communications network, the method comprising: determining, by the
eNB, an antenna port out of a set of antenna ports for sending a
user equipment (UE) an enhanced physical downlink control channel
(E-PDCCH), the determining being based at least partly on a time
and frequency resource for the E-PDCCH and an offset parameter; and
sending, by the eNB to the UE, the E-PDCCH and a demodulation
reference signal associated with the antenna port.
16. The method of claim 15, wherein the time and frequency resource
comprises one or more enhanced control channel elements (eCCEs),
and wherein each of the eCCEs comprises a plurality of resource
elements (REs) within a physical resource block (PRB) pair, and
wherein a PRB pair comprises a plurality of eCCEs.
17. The method of claim 16, wherein the eCCEs available for E-PDCCH
transmission for the UE are indexed starting from zero.
18. The method of claim 16 wherein the antenna port index is
determined by the following equation: Antenna port index=A starting
antenna port index of the set of antenna ports+function(the time
and frequency resource)+offset value indicated by the offset
parameter.
19. The method of claim 18, wherein the offset parameter has a
value of zero if the E-PDCCH is transmitted over one eCCE.
20. The method of claim 18, wherein the function is given by the
following equation: function(the time and frequency
resource)=(index of the first eCCE of the time and frequency
resource)mod(number eCCEs per PRB pair) wherein x mod(N) is a
modulo N operation on x.
21. The method of claim 18, wherein the offset parameter is
semi-statically signaled by the eNB to the UE through radio
resource control (RRC) signaling.
22. The method of claim 18, wherein the offset parameter is a
function of the UE's radio network temporary identifier (RNTI).
23. The method of claim 22, wherein the function is a modulo two
function.
24. The method of claim 18, wherein the offset parameter is a
function of both the UE's RNTI and the subframe number over which
the E-PDCCH is transmitted.
25. The method of claim 24, wherein the function is given by the
following equation: Offset parameter at subframe k=Y.sub.k mod(2)
wherein Y.sub.k=(AY.sub.k-1)mod D, Y.sub.k-1=n.sub.RNTI, A=39827,
D=65537, n.sub.RNTI is the value of RNTI.
26. A method of operating a user equipment (UE) in a wireless
communications network, the method comprising: determining an
antenna port of an enhanced physical downlink control channel
(E-PDCCH) candidate based at least partly on a time and frequency
resource for the E-PDCCH candidate and an offset parameter; and
receiving the E-PDCCH candidate using a demodulation reference
signal associated with the antenna port.
27. The method of claim 26, wherein the time and frequency resource
comprises one or more enhanced control channel elements (eCCEs),
and wherein each of the eCCEs comprises a plurality of resource
elements (REs) within a physical resource block (PRB) pair, and
wherein a PRB pair comprises a plurality of eCCEs.
28. The method of claim 27, wherein the eCCEs available for E-PDCCH
transmission in the network are indexed starting from zero.
29. The method of claim 27, wherein a number of the antenna port is
determined by the following equation: Antenna port index=A starting
antenna port index of the set of antenna ports+function(the time
and frequency resource)+offset value indicated by the offset
parameter.
30. The method of claim 29, wherein the offset parameter has a
value of zero if the E-PDCCH is received over one eCCE
31. The method of claim 29, wherein the function is given by the
following equation: function(the time and frequency
resource)=(index of the first eCCE of the time and frequency
resource)mod(number eCCEs per PRB pair) wherein x mod(N) is a
modulo N operation on x.
32. The method of claim 29, wherein the offset parameter is
semi-statically signaled by an enhanced node B (eNB) to the UE
through radio resource control (RRC) signaling.
33. The method of claim 29, wherein the offset parameter is a
function of the UE's radio network temporary identifier (RNTI).
34. The method of claim 33, wherein the function is a modulo two
function.
35. The method of claim 29, wherein the offset parameter is a
function of both the UE's RNTI and the subframe number over which
the E-PDCCH is to be received.
36. The method of claim 35, wherein the function is given by the
following equation: Offset parameter at subframe k=Y.sub.k mod(2)
wherein Y.sub.k=(AY.sub.k-1)mod D, Y.sub.k-1=n.sub.RNTI, A=39827,
D=65537, n.sub.RNTI is the value of RNTI.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority to U.S. Provisional
Application Nos. 61/533,470 filed Sep. 12, 2011; 61/541,514 filed
Sep. 30, 2011; 61/554,582 filed Nov. 2, 2011; 61/576,558 filed Dec.
16, 2011; 61/606,839 filed Mar. 5, 2012; 61/611,968 filed Mar. 16,
2012, and 61/644,089 filed May 8, 2012 by Shiwei Gao, et al.,
entitled "Enhanced PDCCH with Transmit Diversity in LTE Systems",
which are incorporated herein by reference as if reproduced in
their entirety.
FIELD OF THE DISCLOSURE
[0002] The present disclosure relates to a physical downlink
control channel in wireless telecommunications systems.
BACKGROUND
[0003] As used herein, the term "user equipment" (alternatively
"UE") might in some cases refer to mobile devices such as mobile
telephones, personal digital assistants, handheld or laptop
computers, and similar devices that have telecommunications
capabilities. Such a UE might include a device and its associated
removable memory module, such as but not limited to a Universal
Integrated Circuit Card (UICC) that includes a Subscriber Identity
Module (SIM) application, a Universal Subscriber Identity Module
(USIM) application, or a Removable User Identity Module (R-UIM)
application. Alternatively, such a UE might include the device
itself without such a module. In other cases, the term "UE" might
refer to devices that have similar capabilities but that are not
transportable, such as desktop computers, set-top boxes, or network
appliances. The term "UE" can also refer to any hardware or
software component that can terminate a communication session for a
user. Also, the terms "user equipment," "UE," "user agent," "UA,"
"user device," and "mobile device" might be used synonymously
herein.
[0004] As telecommunications technology has evolved, more advanced
network access equipment has been introduced that can provide
services that were not possible previously. This network access
equipment might include systems and devices that are improvements
of the equivalent equipment in a traditional wireless
telecommunications system. Such advanced or next generation
equipment may be included in evolving wireless communications
standards, such as long-term evolution (LTE). For example, an LTE
system might include an Evolved Universal Terrestrial Radio Access
Network (E-UTRAN) node B (eNB), a wireless access point, or a
similar component rather than a traditional base station. Any such
component will be referred to herein as an eNB, but it should be
understood that such a component is not necessarily an eNB. Such a
component may also be referred to herein as an access node or an
access point.
[0005] LTE may be said to correspond to Third Generation
Partnership Project (3GPP) Release 8 (Rel-8 or R8), Release 9
(Rel-9 or R9), and Release 10 (Rel-10 or R10), and possibly also to
releases beyond Release 10, while LTE Advanced (LTE-A) may be said
to correspond to Release 10 and possibly also to releases beyond
Release 10. As used herein, the terms "legacy", "legacy UE", and
the like might refer to signals, UEs, and/or other entities that
comply with LTE Release 10 and/or earlier releases but do not
comply with releases later than Release 10. The terms "advanced",
"advanced UE", and the like might refer to signals, UEs, and/or
other entities that comply with LTE Release 11 and/or later
releases. While the discussion herein deals with LTE systems, the
concepts are equally applicable to other wireless systems as
well.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] For a more complete understanding of this disclosure,
reference is now made to the following brief description, taken in
connection with the accompanying drawings and detailed description,
wherein like reference numerals represent like parts.
[0007] FIG. 1 is a diagram of a downlink LTE subframe, according to
the prior art.
[0008] FIG. 2 is a diagram of an LTE downlink resource grid in the
case of a normal cyclic prefix, according to the prior art.
[0009] FIG. 3 is a diagram of CRS, DMRS and CSI-RS ports in an LTE
subframe for a normal cyclic prefix, according to the prior
art.
[0010] FIG. 4 is a diagram of an MBSFN subframe, according to the
prior art.
[0011] FIG. 5 is a diagram of an example of an E-PDCCH region,
according to an embodiment of the disclosure.
[0012] FIG. 6 is a diagram of an example of a cell with a macro-eNB
and multiple low power node (LPNs) sharing the same cell ID,
according to the prior art.
[0013] FIG. 7 is a block diagram of transmit diversity supported in
an LTE system, according to the prior art.
[0014] FIG. 8 is a diagram of an example of using transmit
diversity with DMRS ports for demodulation, according to an
embodiment of the disclosure.
[0015] FIG. 9 is a diagram of another example of transmit diversity
over DMRS ports, according to an embodiment of the disclosure.
[0016] FIGS. 10a, 10b, and 10c are diagrams of examples of
four-port transmit diversity with different DMRS ports, according
to an embodiment of the disclosure.
[0017] FIG. 11 is a diagram of an example of a new DMRS for
E-PDCCH, according to an embodiment of the disclosure.
[0018] FIGS. 12a and 12b are diagrams of examples of E-PDCCH with
and without cross-interleaving, according to an embodiment of the
disclosure.
[0019] FIG. 13 is a diagram of an example of PDCCH transmission in
a cell with multiple LPNs sharing the same cell ID, according to an
embodiment of the disclosure.
[0020] FIG. 14 is a diagram of another example of PDCCH
transmission in a cell with multiple LPNs sharing the same cell ID,
according to an embodiment of the disclosure.
[0021] FIG. 15 is a diagram of an example of E-PDCCH transmission
from two transmission points, each with one transmission antenna,
according to an embodiment of the disclosure.
[0022] FIG. 16 is a diagram of an example of E-PDCCH transmission
with cross-transmission point transmit diversity, with each
transmission point having two transmission antennas, according to
an embodiment of the disclosure.
[0023] FIG. 17 is a flow chart of E-PDCCH transmission from two
transmission points with beamforming, according to an embodiment of
the disclosure.
[0024] FIG. 18 is a diagram of an example of E-PDCCH transmission
with cross-transmission point transmit diversity and per
transmission point beamforming, according to an embodiment of the
disclosure.
[0025] FIGS. 19a and 19b are diagrams of resource mapping based on
SFBC, according to an embodiment of the disclosure.
[0026] FIG. 20 is a diagram of another example of resource mapping
based on SFBC, according to an embodiment of the disclosure.
[0027] FIG. 21 is a diagram of an example of resource mapping based
on SFBC when both DMRS and CSI-RS are present, according to an
embodiment of the disclosure.
[0028] FIGS. 22a and 22b are diagrams of resource mapping based on
hybrid SFBC and STBC, according to an embodiment of the
disclosure.
[0029] FIGS. 23a and 23b are diagrams of other examples of resource
mapping based on hybrid SFBC and STBC in the presence of CSI-RS,
according to an embodiment of the disclosure.
[0030] FIGS. 24a and 24b are diagrams of examples of RE to REG
mapping in OFDM symbols containing DMRS, according to an embodiment
of the disclosure.
[0031] FIGS. 25a and 25b are diagrams of other examples of RE to
REG mapping in OFDM symbols containing DMRS, according to an
embodiment of the disclosure.
[0032] FIGS. 26a and 26b are diagrams of other examples of RE to
REG mapping in OFDM symbols containing DMRS, according to an
embodiment of the disclosure.
[0033] FIG. 27 is a diagram of transmission of an E-PDCCH from two
transmission points to a UE during UE transition from a first
transmission point to a second transmission point, according to an
embodiment of the disclosure.
[0034] FIG. 28 is a simplified block diagram of an exemplary
network element according to one embodiment.
[0035] FIG. 29 is a block diagram with an example user equipment
capable of being used with the systems and methods in the
embodiments described herein.
[0036] FIG. 30 illustrates a processor and related components
suitable for implementing the several embodiments of the present
disclosure.
[0037] FIG. 31 is a block diagram illustrating horizontal sub
physical resource block pair partition according to one
embodiment.
[0038] FIG. 32 is a block diagram illustrating horizontal sub
physical resource block pair partition according to another
embodiment.
[0039] FIG. 33 is a block diagram illustrating vertical sub
physical resource block pair partition according to yet another
embodiment.
[0040] FIG. 34 is a block diagram illustrating an example of eCCE
multiplexing with CDM in a PRB pair according to one
embodiment.
[0041] FIG. 35 is a block diagram illustrating an example of REGs
in a RB pair according to one embodiment.
[0042] FIG. 36 is a block diagram illustrating an example of DMRS
port assignment in which each eCCE in a PRB pair is allocated to a
different UE and each UE is assigned with a DMRS port according to
one embodiment.
[0043] FIG. 37 is a block diagram illustrating an example of
resource dependent DMRS port assignment in a PRB pair in which each
eCCE is associated with a different DMRS port according to one
embodiment.
[0044] FIG. 38 is a block diagram illustrating an example of common
DMRS port assignment for all UEs, in which only the DMRS within
each eCCE is used for demodulation of the eCCE according to one
embodiment.
[0045] FIG. 39 is a block diagram illustrating another example of
common DMRS port assignment for all UEs, where only the DMRS within
each eCCE is used for demodulation of the eCCE according to one
embodiment.
[0046] FIG. 40 is a table illustrating an example of eCCE
interleaving with N.sub.eCCE=kN according to one embodiment.
[0047] FIG. 41 illustrates an E-PDCCH region and corresponding
allocated eCCEs according to one embodiment.
[0048] FIG. 42 illustrates an example of DMRS port and eCCE
association according to one embodiment.
[0049] FIG. 43 illustrates an example of DMRS port assignment for
L=2 with different eCCE allocations for an E-PDCCH according to one
embodiment.
[0050] FIG. 44 illustrates an example of DMRS port assignment for
L=4 with different eCCE allocations for an E-PDCCH according to one
embodiment.
[0051] FIG. 45 illustrates an example of DMRS port assignment for
L=1/2/4 with different eCCE allocations for an E-PDCCH according to
one embodiment.
[0052] FIG. 46 illustrates an example of DMRS ports assignment for
E-PDCCHs supporting SU-MIMO according to one embodiment.
[0053] FIG. 47 illustrates an example of MU-MIMO for E-PDCCH
according to one embodiment.
[0054] FIG. 48 illustrates an example of DMRS port assignment for
L=2 with different eCCE allocations for an E-PDCCH according to one
embodiment.
[0055] FIG. 49 illustrates an example of DMRS port assignment for
L=4 with different eCCE allocations for an E-PDCCH according to one
embodiment.
[0056] FIG. 50 illustrates an example of DMRS port assignment for
L=1/2/4 with different eCCE allocations for an E-PDCCH according to
one embodiment.
[0057] FIG. 51 illustrates an example of DMRS port assignment for
E-PDCCHs supporting SU-MIMO according to one embodiment.
[0058] FIG. 52 illustrates an example of MU-MIMO for E-PDCCH
according to one embodiment.
[0059] FIG. 53 illustrates a comparison between implicit DMRS
signaling options according to one embodiment.
[0060] FIG. 54 illustrates an E-PDCCH search space and DMRS port
assignment for different ALs according to one embodiment.
[0061] FIG. 55 illustrates an eCCE index for a PUCCH ACK/NACK
resource according to one embodiment.
[0062] FIG. 56 illustrates an eNB procedure for a common control
channel and a UE-specific control channel with distributed
transmission in an E-PDCCH according to one embodiment.
[0063] FIG. 57 illustrates a UE procedure for a common control
channel and a UE-specific control channel with distributed
transmission in an E-PDCCH according to one embodiment.
[0064] FIG. 58 illustrates DMRS port allocation for L=2 according
to one embodiment.
[0065] FIG. 59 illustrates DMRS port allocation for L=4 according
to one embodiment.
[0066] FIG. 60 illustrates DMRS port allocation for L=8 according
to one embodiment.
[0067] FIG. 61 illustrates DMRS port allocation at different
aggregation levels according to one embodiment.
DETAILED DESCRIPTION
[0068] It should be understood at the outset that although
illustrative implementations of one or more embodiments of the
present disclosure are provided below, the disclosed systems and/or
methods may be implemented using any number of techniques, whether
currently known or in existence. The disclosure should in no way be
limited to the illustrative implementations, drawings, and
techniques illustrated below, including the exemplary designs and
implementations illustrated and described herein, but may be
modified within the scope of the appended claims along with their
full scope of equivalents. Embodiments are described herein in the
context of an LTE wireless network or system, but can be adapted
for other wireless networks or systems.
[0069] In an LTE system, a physical downlink control channel
(PDCCH) is used to carry downlink control information (DCI) from an
eNB to one or more UEs. DCI may contain a downlink (DL) data
assignment or an uplink (UL) data grant for a UE. By decoding
PDCCHs in a subframe, a UE knows whether there is a DL data
transmission scheduled to itself in the current DL subframe or a UL
resource assignment for itself in a future UL subframe.
[0070] FIG. 1 illustrates a typical DL LTE subframe 110. Control
information transmitted in a control channel region 120 and may
include a PCFICH (physical control format indicator channel), PHICH
(physical HARQ (hybrid automatic repeat request) indicator
channel), and PDCCH. The control channel region 120 includes the
first few OFDM (orthogonal frequency division multiplexing) symbols
in the subframe 110. The exact number of OFDM symbols for the
control channel region 120 is either dynamically indicated by
PCFICH, which is transmitted in the first symbol, or
semi-statically configured in the case of carrier aggregation in
LTE Rel-10.
[0071] A physical downlink shared channel (PDSCH), PBCH (physical
broadcast channel), PSC/SSC (primary synchronization
channel/secondary synchronization channel), and CSI-RS (channel
state information reference signal) are transmitted in a PDSCH
region 130. DL user data is carried by the PDSCH channels scheduled
in the PDSCH region 130. Cell-specific reference signals are
transmitted over both the control channel region 120 and the PDSCH
region 130.
[0072] The PDSCH is used in LTE to transmit DL data to a UE. The
PDCCH and the PDSCH are transmitted in different time-frequency
resources in a LTE subframe as shown in FIG. 1. Different PDCCHs
can be multiplexed in the PDCCH region 120, while different PDSCHs
can be multiplexed in the PDSCH region 130.
[0073] In a frequency division duplex system, a radio frame
includes ten subframes of one millisecond each. A subframe 110
includes two slots in time and a number of resource blocks (RBs) in
frequency as shown in FIG. 1. The number of RBs is determined by
the system bandwidth. For example, the number of RBs is 50 for a 10
megahertz system bandwidth.
[0074] An OFDM symbol in time and a subcarrier in frequency
together define a resource element (RE). A physical RB can be
defined as, for example, 12 consecutive subcarriers in the
frequency domain and all the OFDM symbols in a slot in the time
domain. An RB pair with the same RB index in slot 0 (140a) and slot
1 (140b) in a subframe can be allocated together to the same UE for
its PDSCH.
[0075] In LTE, multiple transmit antennas are supported at the eNB
for DL transmissions. Each antenna port can have a resource grid as
shown in FIG. 2. Each DL slot includes seven OFDM symbols in the
case of a normal cyclic prefix configuration and six OFDM symbols
in the case of an extended cyclic prefix configuration. To simplify
the following discussion, subframes with the normal cyclic prefix
configuration will be considered hereinafter, but it should be
understood that similar concepts are applicable to subframes with
an extended cyclic prefix.
[0076] FIG. 2 shows an LTE DL resource grid 210 within each slot
140 in the case of a normal cyclic prefix configuration. The
resource grid 210 is defined for each antenna port, i.e., each
antenna port has its own separate resource grid 210. Each element
in the resource grid 210 for an antenna port is an RE 220, which is
uniquely identified by an index pair of a subcarrier and an OFDM
symbol in a slot 140. An RB 230 includes a number of consecutive
subcarriers in the frequency domain and a number of consecutive
OFDM symbols in the time domain, as shown in the figure. An RB 230
is the minimum unit used for the mapping of certain physical
channels to REs 220.
[0077] In LTE, the set of antenna ports supported for DL
transmission depends on the reference signal configuration. Cell
specific reference signals (CRSs) support a configuration of one,
two or four antenna ports and are transmitted on antenna ports p=0,
p.epsilon.{0, 1}, and p.epsilon.{0, 1, 2, 3} respectively. CRS
signals are transmitted in all subframes and can be used for
channel measurement and PDSCH demodulation.
[0078] UE-specific reference signals, which can also be referred to
as demodulation reference signals (DMRS), are used for PDSCH
demodulation and are transmitted on antenna ports p=7, p=8, or one
or several of p.epsilon.{7, 8, 9, 10, 11, 12, 13, 14}. DMRSs are
transmitted only in the RBs upon which the corresponding PDSCH for
a particular UE is mapped.
[0079] Channel state information reference signals (CSI-RS) can be
configured as one, two, four or eight ports and are transmitted on
antenna ports p=15, p=15, 16, p=15, . . . , 18 and p=15, . . . ,
22, respectively. CSI-RSs can be transmitted only in certain
subframes.
[0080] An example of mapping CRS and DMRS to REs in a subframe is
shown in FIG. 3. It should be noted that DMRS ports {7, 8, 11, 13}
are multiplexed on the same group of REs with different orthogonal
codes. The same is true for DMRS ports {9, 10, 12, 14} The
orthogonal codes are applied in the time direction and are shown in
Table 1 below.
TABLE-US-00001 TABLE 1 Orthogonal codes assigned to DMRS ports for
normal cyclic prefix in LTE Antenna port p [ w.sub.p (0) w.sub.p
(1) w.sub.p (2) w.sub.p (3)] 7 [+1 +1 +1 +1] 8 [+1 -1 +1 -1] 9 [+1
+1 +1 +1] 10 [+1 -1 +1 -1] 11 [+1 +1 -1 -1] 12 [-1 -1 +1 +1] 13 [+1
-1 -1 +1] 14 [-1 +1 +1 -1]
[0081] A subset of the LTE DL subframes in a radio frame supporting
PDSCH transmission can be configured as Multimedia Broadcasting and
multicasting Single Frequency Network (MBSFN) subframes, as shown
in FIG. 4. An MBSFN subframe 410 includes two regions, a non-MBSFN
region 420, which spans the first one or two OFDM symbols, and an
MBSFN region 430 for the rest of the OFDM symbols. The non-MBSFN
region 420 is used for transmitting control information. The MBSFN
region 430 can be used for transmitting a multimedia broadcasting
signal. In LTE Rel-10, the MBSFN region 430 can also be configured
to transmit a PDSCH with a DMRS as the demodulation reference
signal. There is no CRS transmission in the MBSFN region 430.
[0082] The PDCCH region 120 shown in FIG. 1 may consist of up to
three symbols for a system bandwidth greater than 10 RBs and up to
four symbols for a system bandwidth less than or equal to 10 RBs.
In some cases, such as a secondary radio frequency carrier, a PDCCH
region may not be present in a subframe. The REs of each OFDM
symbol in the PDCCH region 120 are grouped into resource element
groups (REGs). An REG includes four neighbor REs not allocated for
CRS transmission. A PDCCH is transmitted on an aggregation of one
or several consecutive indexed control channel elements (CCEs),
where a CCE includes nine REGs. Up to eight CCEs may be allocated
to a PDCCH.
[0083] For a PDCCH region that spans 10 MHz bandwidth and three
OFDM symbols, the available CCEs in the case of four CRS ports are
in the range of 34 to 39 depending on the number of hybrid
automatic repeat request (HARQ) groups configured. Assuming an
equal resource partition between UL grants and DL assignments,
about 17 to 20 CCEs are available for each link. So the average
number of UEs that can be scheduled in a subframe could be less
than ten.
[0084] With the introduction of Multi-User Multiple Input and
Multiple Output (MU-MIMO) and future support of Machine-to-Machine
(M2M) communication, the current PDCCH capacity may not be enough
to support a large number of UEs in a cell. One approach for PDCCH
capacity enhancement is to transmit DCI in the legacy PDSCH region.
Similar to the situation with the R-PDCCH (Relay Physical Downlink
Control Channel) in which a number of RBs are reserved in the PDSCH
region for transmitting DCIs from an eNB to relay nodes (RNs), some
RBs in the traditional PDSCH region can be reserved for DCI
transmission to the UE. Hereinafter, a physical downlink control
channel transmitted in the PDSCH region will be referred to as an
enhanced or extended PDCCH (E-PDCCH). The set of RBs and OFDM
symbols reserved for this purpose can be referred as the E-PDCCH
region. One example is shown in FIG. 5. The time and frequency
resources of an E-PDCCH region 510 may be configurable. In
addition, the PDCCH region 120 in a subframe may not be present in
a subframe containing the E-PDCCH region.
[0085] One of the wireless network deployment scenarios under study
for LTE Rel-11 for system performance improvement through
coordinated scheduling is the deployment in a cell covered by a
macro-eNB of multiple low power nodes (LPNs) that share the same
cell ID with the macro-eNB. The LPNs might be relay nodes, remote
radio heads, or similar components. This scenario is also referred
as Coordinated Multi-Point (CoMP) Scenario 4 in some contexts. An
example is shown in FIG. 6. In this scenario, it may be more
efficient to transmit downlink data to a UE 610 from a transmission
point 620 or transmission points that provides the best signal
quality to the UE 610. The term "transmission point" (TP) may be
used herein to refer to either an LPN or a macro-eNB. As the LPNs
620b and 620c have the same cell ID as the macro-eNB 620a, only one
set of CRSs might be configured. The CRSs could be transmitted
either from the macro-eNB 620a only or from both the macro-eNB 620a
and the LPNs 620b and 620c. Because CRSs are required for legacy
PDCCH demodulation, the PDCCH has to be transmitted over the same
antenna ports as the CRS. As a result, the PDCCH can be transmitted
either from the macro-eNB 620a only or from both the macro-eNB 620a
and the LPNs 620b and 620c. To support DCI transmission only from
LPNs 620b and 620c, an E-PDCCH could be used instead, with DMRSs as
the reference signals for demodulation.
[0086] In a scenario where an E-PDCCH is transmitted in the MBSFN
subframes, the CRS is not available, and thus DMRSs may need to be
used for E-PDCCH demodulation.
[0087] A conceptual block diagram of data transmission with
transmit diversity in LTE systems is shown in FIG. 7. Let {d(0),
d(1), . . . , d(M.sub.symb-1)} be the symbols after modulation for
transmission. The symbols are first mapped to layers. For two-port
transmit diversity, the following mapping can be performed:
x.sup.(0)(i)=d(2i)
x.sup.(1)(i)=d(2i+1)
where i=0, 1, . . . , M.sub.symb.sup.layer-1;
M.sub.symb.sup.layer=M.sub.symb.
[0088] Precoding for transmit diversity can be combined with the
above layer mapping. The precoding for transmit diversity can be
defined for two and four antenna ports.
[0089] For transmission on two antenna ports {0, 1}, the output
y(i)=[y.sup.(0)(i) y.sup.(1)(i)].sup.T, i=0, 1, . . . ,
M.sub.symb.sup.ap-1 of the precoding operation can be defined
by:
[ y ( 0 ) ( 2 i ) y ( 1 ) ( 2 i ) y ( 0 ) ( 2 i + 1 ) y ( 1 ) ( 2 i
+ 1 ) ] = 1 2 [ 1 0 j 0 0 - 1 0 j 0 1 0 j 1 0 - j 0 ] [ Re ( x ( 0
) ( ) ) Re ( x ( 1 ) ( ) ) Im ( x ( 0 ) ( ) ) Im ( x ( 1 ) ( ) ) ]
##EQU00001##
for i=0, 1, . . . , M.sub.symb.sup.layer-1 with
M.sub.symb.sup.ap2M.sub.symb.sup.layer, where Re( ) and Im( )
indicate the real and imaginary part, respectively.
[0090] For four-port transmit diversity on antenna ports {0, 1, 2,
3}, the following layer mapping can be performed:
x ( 0 ) ( i ) = d ( 4 i ) ##EQU00002## x ( 1 ) ( i ) = d ( 4 i + 1
) ; ##EQU00002.2## x ( 2 ) ( i ) = d ( 4 i + 2 ) ; ##EQU00002.3## x
( 3 ) ( i ) = d ( 4 i + 3 ) ; i = 0 , 1 , , M symb layer - 1 ;
##EQU00002.4## M symb layer = { M symb / 4 if M symb mod 4 = 0 ( M
symb + 2 ) / 4 if M symb mod 4 = 0 ##EQU00002.5##
[0091] The output y(i)=[y.sup.(0)(i) y.sup.(1)(i) y.sup.(2)(i)
y.sup.(3)(i)].sup.T, i=0, 1, . . . , M.sub.symb.sup.ap-1 of the
precoding operation can be defined by:
[ y ( 0 ) ( 4 i ) y ( 1 ) ( 4 i ) y ( 2 ) ( 4 i ) y ( 3 ) ( 4 i ) y
( 0 ) ( 4 i + 1 ) y ( 1 ) ( 4 i + 1 ) y ( 2 ) ( 4 i + 1 ) y ( 3 ) (
4 i + 1 ) y ( 0 ) ( 4 i + 2 ) y ( 1 ) ( 4 i + 2 ) y ( 2 ) ( 4 i + 2
) y ( 3 ) ( 4 i + 2 ) y ( 0 ) ( 4 i + 3 ) y ( 1 ) ( 4 i + 3 ) y ( 2
) ( 4 i + 3 ) y ( 3 ) ( 4 i + 3 ) ] = 1 2 [ 1 0 0 0 j 0 0 0 0 0 0 0
0 0 0 0 0 - 1 0 0 0 j 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 j 0 0 0 0 0 0 0
0 0 0 1 0 0 0 - j 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0
j 0 0 0 0 0 0 0 0 0 0 0 0 - 1 0 0 0 j 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0
j 0 0 0 0 0 0 0 0 0 0 1 0 0 0 - j 0 ] [ Re ( x ( 0 ) ( ) ) Re ( x (
1 ) ( ) ) Re ( x ( 2 ) ( ) ) Re ( x ( 3 ) ( ) ) Im ( x ( 0 ) ( ) )
Im ( x ( 1 ) ( ) ) Im ( x ( 2 ) ( ) ) Im ( x ( 3 ) ( ) ) ]
##EQU00003## for i = 0 , 1 , , M symb layer - 1 with ##EQU00003.2##
M symb ap = { 4 M symb layer if M symb ( 0 ) mod 4 = 0 ( 4 M symb
layer ) - 2 if M symb ( 0 ) mod 4 .noteq. 0. ##EQU00003.3##
[0092] For maintaining orthogonality between the symbols, thus
achieving maximum diversity gain and allowing simple decoding, the
symbol pair {y.sup.(p)(2i), y.sup.(p)(2i+1)} (i=0, 1, . . . ,
M.sub.symb.sup.layer-1; p=0, 1, 2, 3) may need to be transmitted
over the same wireless channel. For this purpose, {y.sup.(p)(2i),
y.sup.(p)(2i+1)} could be mapped to two REs in close proximity in
either time or frequency. In LTE, each symbol pair is mapped to
consecutive REs in the same OFDM symbol.
[0093] In LTE Rel-8, DL transmit diversity only uses CRSs as the
reference signal for demodulation. When DMRSs are used as
demodulation reference signals, transmit diversity is not
supported. For PDCCH transmission, CRSs are used as demodulation
reference signals. Therefore, transmit diversity is used for PDCCH
transmission if more than one CRS port is present. For E-PDCCH
transmission, as DMRSs are likely configured as the demodulation
reference signals due to reasons such as E-PDCCH transmission in
MBSFN subframes or in the CoMP scenario as shown in FIG. 6, the
E-PDCCH transmission scheme is therefore left to either single
antenna port or beamforming transmission.
[0094] Beamforming transmission requires DL channel state
information (CSI) including precoding information, which is not
always available at an eNB. For example, under certain PDSCH
transmission modes in LTE, such as transmission modes 2 and 3, a UE
does not feed back precoding information to the eNB. In addition,
even if precoding information is reported by a UE, it may not
always be reliable under a fast fading channel with a high mobility
UE. In the situation that UE feeds back only wideband precoding
information, it may not be good enough to form a narrow beam.
[0095] Unlike in the PDSCH case where, with the support of HARQ,
retransmission can be performed by an eNB in the case of a PDSCH
decoding failure at a UE, any E-PDCCH decoding failure could lead
to the loss of a DL and/or UL packet because retransmission is not
possible for an E-PDCCH (as is also the case for the legacy PDCCH).
So it may be desirable to have more robust E-PDCCH transmissions
under even the worst case channel conditions and UE mobility.
Implementations of the present disclosure can address questions
that may arise regarding how to support E-PDCCH with transmit
diversity (TxD) for robust E-PDCCH detection performance using DMRS
as the demodulation reference signals.
[0096] The concept of an E-PDCCH has been discussed in a number of
publications. However, in all these discussions, E-PDCCH
transmission is limited to one of the following transmission
schemes: a single-port transmission with CRS as the demodulation
reference signal; a single-port transmission with DMRS as the
demodulation reference signal (this scheme supports
beamforming-based E-PDCCH transmission); transmit diversity using
SFBC (space frequency block coding) with CRS as the demodulation
reference signal; or Single User MIMO (SU-MIMO) or MU-MIMO with
DMRS as the demodulation reference signal. In the SU-MIMO case,
multiple data layers can be transmitted to a single user over the
same resource for increased data throughput with multiple
transmission antennas at the eNB and multiple reception antennas at
the UE. In the case of MU-MIMO, multiple E-PDCCHs, one to each UE,
can be transmitted over the same resource.
[0097] However, transmit diversity for E-PDCCH transmission with
DMRS as the demodulation reference signal has not been discussed.
Robust E-PDCCH transmission with transmit diversity using DMRS may
be needed for improved E-PDCCH detection performance in scenarios
where CRSs are either not available or cannot be used for E-PDCCH
demodulation. Examples of such scenarios include an E-PDCCH being
transmitted over an LPN located in a macro-cell coverage area and
sharing the same cell ID as the macro-cell, or an E-PDCCH being
transmitted in the MBSFN region in an MBSFN subframe.
[0098] In an implementation, transmit diversity is used for E-PDCCH
transmission with LTE Rel-10 DMRSs as demodulation reference
signals. Such implementations allow for more robust E-PDCCH
transmission to a UE from a nearby TP or TPs in a CoMP deployment
scenario where LPNs share the same cell ID as the macro-eNB. Terms
such as "near" a TP or "a nearby TP" or "close to" a TP are used
herein to indicate that a UE would have a better DL signal strength
or quality if the DL signal is transmitted to that UE from that TP
rather than from a different TP. Such implementations would also
allow for more robust E-PDCCH transmission to a UE in MBSFN
subframes where CRSs are not available in the MBSFN region. The UE
could use the received DMRS signals for channel estimation and
E-PDCCH demodulation.
[0099] Two resource mapping methods, one based on space frequency
block code (SFBC) and the other based on hybrid SFBC and space time
block code (STBC), are also provided for mapping of transmit
diversity precoded signals to resource elements.
[0100] Although the Rel-10 DMRS is discussed hereinafter, it should
be understood that the implementations described herein are not
limited only to the Rel-10 DMRS. For example, a new DMRS could be
defined for the same purpose.
[0101] An E-PDCCH could also be transmitted using beamforming,
where both the E-PDCCH and DMRS are precoded with the same
precoding vectors.
[0102] In an implementation, the configuration of E-PDCCH
transmission schemes for a UE can be implicitly signaled through
demodulation reference signal configuration for the UE. For
example, if multiple DMRS ports are configured for E-PDCCH
transmission to a UE, transmit diversity could be assumed by the UE
for E-PDCCH transmission. The UE could use the received DMRS
signals for channel estimation and E-PDCCH demodulation. This
concept is applicable to an E-PDCCH with or without
cross-interleaving. If a single DMRS port is configured for a UE, a
single port E-PDCCH transmission with the configured DMRS could be
used by the UE. Beamforming, which is transparent to the UE, could
be achieved by applying precoding to both the DMRS and E-PDCCH.
[0103] Alternatively, the configuration of E-PDCCH transmission
schemes could be explicitly signaled to a UE.
[0104] The same DMRS sequence and resources defined in LTE Rel-10
could be reused for the E-PDCCH. However, in the case of E-PDCCH
with cross-interleaving, the same DMRS ports could be shared by
different UEs for E-PDCCH demodulation. In this case, DMRS ports
could be viewed as TP-specific RS ports and precoding might not be
applied on the DMRS.
[0105] The transmit diversity method could also be used for PDSCH
transmission in MBSFN subframes with DMRS.
[0106] More specifically, a method for E-PDCCH transmission with
transmit diversity (TxD) using UE-specific reference signal (RS) or
demodulation RS (DMRS) ports for demodulation is provided for LTE
systems. E-PDCCH transmission with transmit diversity could enable
robust E-PDCCH transmissions to a UE from a nearby TP in a cell
where multiple LPNs are deployed that share the same cell ID as the
macro-eNB. Such robust E-PDCCH transmissions could also be provided
in an MBSFN subframe where CRSs are not available. In addition,
robust E-PDCCH transmissions could be made from multiple TPs with
increased transmit diversity, and thus improved robustness of
E-PDCCH decoding could be achieved.
[0107] An implementation of one such E-PDCCH transmission scheme is
illustrated in FIG. 8, where DMRSs are used together with existing
LTE Rel-8 TxD layer mapping and precoding for E-PDCCH transmission.
In this example, there is a one-to-one mapping between DMRS ports
and physical antenna ports.
[0108] Alternatively, DMRS may be precoded at the eNB as shown in
FIG. 9, where there is no one-to-one mapping between the DMRS ports
and the physical antennas. The number of physical antennas can be
larger than the number of DMRS ports. The precoding is transparent
to a UE. That is, the UE does not need to know whether or not
precoding is applied or what precoding vector is applied. Precoding
may provide additional benefits when there are more physical
antennas than two or four DMRS ports. For example, if there are
eight antennas and TxD with two or four DMRS ports is used, then
precoding may be applied to provide additional beamforming gain if
DL channel state information is available for a UE at the eNB.
[0109] It should be noted that the additional precoding 910 applied
in FIG. 9 after TxD precoding 920 could be an eNB implementation
issue. Namely, whether to apply the precoding and which precoding
vector to choose could be a decision made by the eNB. This
operation of additional precoding is also transparent to the UE. In
this sense, the examples shown in FIG. 8 and FIG. 9 are the same
from a UE's perspective.
[0110] A UE can be configured with either CRS or DMRS as the
demodulation reference signals for its E-PDCCH demodulation. When
CRS is configured for E-PDCCH demodulation, the number of CRS ports
is indicated in the Physical Broadcast Channel (PBCH) and thus no
additional signaling is needed for the CRS ports. If DMRS is
configured for E-PDCCH demodulation, the DMRS ports may need to be
signaled to the UE through UE-specific higher layer signaling.
[0111] The following Rel-10 DMRS ports may be configured for
E-PDCCH to a UE: a single DMRS port, i.e., port {7}, {8}, . . . ,
{14}; two DMRS ports, i.e., any two of the DMRS ports {7, 8, 9, 10,
11, 12, 13, 14}; or four DMRS ports, i.e., ports {7, 8, 11, 13},
{9, 10, 12, 14}, {7, 8, 9, 10}, {11, 12, 13, 14}, {7, 8, 12, 14},
or {9, 10, 11, 13}.
[0112] When the Rel-10 DMRSs are reused for E-PDCCH demodulation,
proper pairing of DMRS ports may be needed. For example, in the
case of two-port TxD, any pair of DMRS ports {7, 8}, {9, 10}, {11,
13}, or {12, 14} may be used to save DMRS overhead, because the
DMRS ports in each pair share the same time-frequency resource. In
addition, high mobility UEs can be supported because the DMRS
signals in each pair are orthogonal to each other over two adjacent
OFDM symbols. Further, due to the orthogonal covering code used for
each pair of ports, two separate channel estimations could be
derived, one for each slot. Therefore, good channel estimation can
be done as the channels do not change significantly over two
adjacent OFDM symbols, even for high mobility UEs. For very high
speed scenarios, it is possible to choose one DMRS port from {7, 8,
11, 13} and one from {9, 10, 12, 14} to improve channel estimation
at the cost of additional DMRS overhead, as these two ports of DMRS
occupy different resources and therefore will not cause
interference with each other in the situation of a UE with very
high mobility.
[0113] In the case of four-port TxD, DMRS ports {7, 8, 11, 13} or
{9, 10, 12, 14} may be used. With these two groups of DMRS ports,
the same DMRS resource is used on all the antenna ports in each
group. A drawback is that this grouping may not be good for high
mobility UEs because the DMRS signals of those ports are orthogonal
only if the channels do not change significantly over a subframe.
Otherwise, the orthogonality may not hold and large channel
estimation errors may occur.
[0114] An alternative option is to use DMRS ports {7, 8, 9, 10} or
{11, 12, 13, 14} instead, in which different frequency resources
are used for ports {7, 8} and {9, 10} and similarly for ports {11,
13} and {12, 14}. This option could provide better channel
estimation even in the high mobility case because orthogonality can
be maintained as long as the channels do not change between two
adjacent OFDM symbols. This condition can be satisfied even at high
mobility. A drawback is that more overhead may be needed for the
DMRS.
[0115] FIG. 10 shows some examples of different DMRS port groupings
for four-port TxD. FIG. 10(a) shows a DMRS port configuration that
can provide good performance for both low and high mobility UEs,
but more RS resource overhead may be required in this
configuration. FIG. 10(b) and FIG. 10(c) use fewer resources for
DMRS and may provide good performance for low mobility UEs.
[0116] The TxD schemes provided herein may be applied to an E-PDCCH
with DMRSs that are different from the ones defined in LTE Rel-10.
In fact, new DMRSs may be introduced for the E-PDCCH. Such an
example is shown in FIG. 11, where two DMRS ports could be code
division multiplexed (CDM) over the allocated DMRS resources along
the subcarrier indices. It should be noted that such a DMRS might
be used for TxD demodulation of an E-PDCCH for a particular UE or a
group of UEs. Therefore, unlike the CRS, the DMRS might be
transmitted only in assigned RBs for E-PDCCH transmission for a
particular UE or a group of UEs.
[0117] In some implementations, a set of N.sub.RB.sup.E-PDCCH RBs
could be configured for potential E-PDCCH transmission by Radio
Resource Control (RRC) signaling. The configured RBs may or may not
be adjacent in frequency. The location of a configured RB in the
two slots of an LTE subframe may or may not be the same. These RBs
are referred to as virtual RBs (VRBs) and the mapping from VRBs to
physical RBs (PRBs) in a subframe may be semi-statically configured
by RRC. The configured VRBs may be continuously numbered
n.sub.VRB.sup.E-PDCCH=0, 1, . . . , N.sub.RB.sup.E-PDCCH-1 such
that the smallest VRB number of n.sub.VRB corresponds to
n.sub.VRB.sup.E-PDCCH=0 and the largest VRB number of n.sub.VRB
corresponds to n.sub.VRB.sup.E-PDCCH=N.sub.RB.sup.E-PDCCH-1. In
some implementations, an E-PDCCH may be transmitted on one or
several VRBs without being cross-interleaved with other E-PDCCHs.
Alternatively, multiple E-PDCCHs may be cross-interleaved in one or
several VRBs. A conceptual diagram is shown in FIG. 12, where
VRB=PRB. E-PDCCH without cross-interleaving is shown in FIG. 12(a)
and E-PDCCH with cross-interleaving is shown in FIG. 12(b).
[0118] Without cross-interleaving, an E-PDCCH can be transmitted on
an aggregation of one or several VRBs. For the E-PDCCH example
without cross-interleaving shown in FIG. 12(a), one PRB or a number
of PRBs in the region are allocated to each E-PDCCH.
[0119] In the case of E-PDCCH with cross-interleaving, as shown in
FIG. 12(b), an RB in the E-PDCCH region can be used by multiple
E-PDCCHs in different symbols across a subframe. With
cross-interleaving, E-PDCCHs can be multiplexed in a manner similar
to that used for the PDCCH in the legacy LTE systems, with the
following exceptions: for the purpose of REG-to-RE mapping, the
downlink system bandwidth can be determined as
N.sub.RB.sup.E-PDCCH; a DMRS may be present in a PRB with or
without a CRS and may be used for E-PDCCH demodulation; and the REs
used for DMRS transmission can be assumed to be unavailable for
E-PDCCH traffic transmission.
[0120] The possible E-PDCCH transmission schemes that a UE can
assume under different E-PDCCH configurations are summarized in
Table 2 below. The E-PDCCH transmission scheme for a UE could be
semi-statically configured through demodulation RS
configuration.
TABLE-US-00002 TABLE 2 Relationship between E-PDCCH transmission
scheme and E-PDCCH demodulation reference signal configuration
E-PDCCH demodulation RS configuration E-PDCCH transmission scheme
Single DMRS port Single antenna port transmission Two or four DMRS
ports T .times. D CRS port {0} Single antenna port transmission CRS
port {0,1} or {0,1,2,3} T .times. D
[0121] When a UE is configured with a single CRS or DMRS port for
E-PDCCH demodulation, a single port transmission could be assumed
by the UE. When a UE is configured with two or four CRS or DMRS
ports, TxD could be assumed by the UE for its E-PDCCH demodulation.
The relation between the number of CRS and DMRS ports and the
transmission scheme could be used to save additional signaling for
E-PDCCH transmission scheme configuration.
[0122] Alternatively, when more than one DMRS port is configured
for E-PDCCHs, the use of either TxD or MIMO for the E-PDCCHs could
be explicitly signaled. For example, a TxD scheme or a multiple
layer spatial multiplexing or beamforming scheme could be
configured when multiple DMRS ports are configured.
[0123] An example of E-PDCCH transmission is shown in FIG. 13,
where two LPNs 1310a and 1310b are deployed in a cell covered by a
macro-eNB 1320 sharing the same cell ID. The E-PDCCH for UE0 1330a,
which is covered by the macro-eNB 1320, could be configured with
one of two options. In the first option, a CRS is used as the
E-PDCCH demodulation RS. In this case, E-PDCCHs to UE0 1330a could
be sent over the CRS ports using one of two transmission methods.
In the first method, single CRS port transmission is used if a
single CRS port is configured in a cell. In the second method, TxD
is used if two or four CRS ports are configured in a cell.
[0124] In the second option, DMRS is used as the E-PDCCH
demodulation RS. In this case, E-PDCCHs to UE0 1330a could be sent
over the configured DMRS ports using one of two transmission
methods. In the first method, single DMRS port transmission is used
if one DMRS port is configured. In the second method, TxD is used
if two or four DMRS ports are configured.
[0125] In the case of E-PDCCH transmission with cross-interleaving,
UE0 1330a can be cross-interleaved with UEs whose E-PDCCHs are also
transmitted from the same macro-cell. However, UE0 1330a cannot be
cross-interleaved with UE1 1330b or UE2 1330c if their E-PDCCHs are
transmitted from different TPs and their demodulation reference
signals are thus not the same.
[0126] It may be desirable to transmit an E-PDCCH to UE1 1330b,
which is close to TP1 1310a, only from TP1 1310a. In such a case,
the DMRS could be configured as the only E-PDCCH demodulation
reference signal. The E-PDCCH to UE1 1330b could then be
transmitted with one of two options: single DMRS port transmission
or transmit diversity. When single DMRS port transmission is used,
the E-PDCCH could be transmitted over one antenna port without
precoding or over more than one antenna with open-loop precoding or
close-loop precoding if DL CSI for UE1 1330b is available at TP1
1310a. If there are two or more antennas in TP1 1310a, the use of
transmit diversity could allow robust E-PDCCH transmission with two
or four DMRS ports from TP1 1310a to UE1 1330b.
[0127] An approach similar to that used for UE1 1330b and TP1 1310a
could be used for E-PDCCH transmission from TP2 1310b to UE2 1330c,
which is close to TP2 1310b.
[0128] Another example is shown in FIG. 14, where UE3 1410 is
covered by both TP1 1420a and TP2 1420b. In this case, different
DMRS ports could be configured for TP1 1420a and TP2 1420b to
support different transmission schemes. At least three different
configurations are possible in this deployment scenario. In the
first configuration, DMRS ports support cross-TP TxD transmission.
In this configuration, one DMRS port (e.g., port 7) could be
transmitted from TP1 1420a and a different DMRS port (e.g., port 8)
could be transmitted from TP2 1420b. UE3 1410 could be configured
with both DMRS ports (e.g., ports 7 and 8) for E-PDCCH
demodulation. E-PDCCHs to UE3 1410 could be sent from both TP1
1420a and TP2 1420b using two-port TxD for increased diversity and
robustness, as shown in FIG. 15.
[0129] Similarly, if TP1 1420a and TP2 1420b have two antenna ports
each, then TP1 1420a could transmit DMRS ports 7 and 8, and TP2
1420b could transmit DMRS ports 11 and 13. UE3 1410 could be
configured with DMRS ports {7, 8, 11, 13} and four-port TxD could
be used for E-PDCCH transmission to the UE 1410 from the two TPs
1420. Such an implementation is shown in FIG. 16.
[0130] In the second configuration, DMRS ports support joint
beamforming transmission. In this configuration, if E-PDCCH without
cross-interleaving is configured, then beamforming could be used to
transmit E-PDCCHs to the UE 1410 from the two TPs 1420 with
precoded DMRS if DL CSI regarding the two TPs 1420 to the UE 1410
is available at the eNB 1430. In this case, the UE 1410 could feed
back a precoding matrix indicator (PMI) for each of the two TPs
1420 and a single DMRS port could be configured for the UE 1410. An
example is shown in FIG. 17, where w1 and w2 are the precoding
vectors applied at TP1 1420a and TP2 1420b, respectively. For
better received E-PDCCH signal quality at the UE 1410, phase
information between the two PMIs may be fed back and applied at the
TPs 1420 for coherent addition of the E-PDCCH signals from the two
TPs 1420 at the UE 1410.
[0131] In the third configuration, DMRS ports support joint
beamforming and TxD transmission. In this configuration, a two-port
TxD can be used for E-PDCCH transmission to the UE 1410 from the
two TPs 1420, as shown in FIG. 18. At each TP 1420, TxD precoded
symbols together with the DMRS could be further precoded over two
antennas at each TP 1420 before transmission. A different DMRS port
may need to be configured for each TP. The UE 1410 could be
configured with the two DMRS ports and could decode the E-PDCCH
data assuming two-port TxD. The precoding vector at each TP 1420
may be obtained from UE feedback. Because the precoding operation
at each TP is generally beneficial for a specific UE, this option
may be applicable only to E-PDCCH without cross-interleaving.
[0132] TxD resource mapping for E-PDCCH will now be considered. Let
{y.sup.(p)(i), i=0, 1, . . . , M.sub.symb.sup.ap-1} be the output
modulation symbols after TxD precoding at port p, where p is one of
the two DMRS ports configured for two-port TxD, or p is one of the
four DMRS ports configured for four-port TxD. Then for each of the
DMRS ports used for the TxD transmission, the block of complex
symbols {y.sup.(p)(i), i=0, 1, . . . , M.sub.symb.sup.ap-1} can be
mapped to resource element (k,l) in OFDM symbols not containing
DMRS.
[0133] Unlike LTE Rel-8 to Rel-10, where DMRS is not present in RBs
over which TxD is performed, to support TxD with DMRS for E-PDCCH
transmission, new mapping may need to be defined in OFDM symbols
containing DMRS. Some mapping options will now be discussed. TxD
resource mapping for E-PDCCH without cross-interleaving will be
considered first, and then TxD resource mapping for E-PDCCH with
cross-interleaving will be considered.
[0134] An example of mapping of TxD precoded symbols {y.sup.(p)(i),
i=0, 1, . . . , M.sub.symb.sup.ap-1} to REs for two-port or
four-port TxD with DMRS ports using resource mapping based on space
frequency block code (SFBC) is shown in FIG. 19. TxD with DMRS
ports {7, 8, 11, 13} is shown in FIG. 19(a), and TxD with DMRS
ports {7, 8, 9, 10} is shown in FIG. 19(b). The mapping in the OFDM
symbols without DMRS is the same as that for the PDSCH in LTE
Release-8. In the OFDM symbols containing DMRS, the REs used for
DMRS transmission are assumed unavailable for TxD mapping. The rest
of the REs in the OFDM symbols containing DMRS may or may not be
used for TxD transmission. The TxD precoded symbol pair
{y.sup.(p)(i), y.sup.(p)(i+1)} is mapped to neighbor REs labeled
"1" and "2" in each OFDM symbol respectively, where i is an even
number. The mapping starts from the RE (k,l) with the lowest symbol
index l in the even numbered slot and the lowest frequency index k,
and increments first from frequency and then from time in the
allocated RBs. The maximum allowed separation between the RE for
y(i) and the RE for y(i+1) is one RE in this example.
[0135] Another option is that y(i) and y(i+1) are only allowed to
be mapped to adjacent REs. In this case, the unmapped REs would be
at the lowest frequency index in the OFDM symbols containing DMRS.
An example is shown in FIG. 20. An example of resource mapping when
CSI-RSs are present in a subframe is shown in FIG. 21.
[0136] In these SFBC-based TxD options, resource elements (k,l) in
an OFDM symbol containing DMRS can be used in the mapping if those
resource elements are not used for transmission of DMRS, if those
resource elements are not used for transmission of CSI-RS, and if
the complex symbols y.sup.(p)(i) and y.sup.(p)(i+1), where i is an
even number, are mapped to resource elements (k,l) and (k+n, l) in
the same OFDM symbol with, for example, n<3.
[0137] With the above mapping rules, some REs in the OFDM symbols
containing DMRS are left un-mapped to any TxD precoded symbols,
resulting in some overhead. The overhead due to unmapped REs could
be reduced or eliminated by using STBC (space time block code)
based mapping in the OFDM symbols containing DMRS.
[0138] An example of such a mapping scheme for two-port or
four-port TxD with DMRS ports is shown in FIG. 22, where TxD with
{7, 8, 11, 13} is shown in FIG. 22(a) and TxD with ports {7, 8, 9,
10} is shown in FIG. 22(b). Symbol y.sup.(p)(i) is mapped to RE
(k,l) (i.e., an RE labeled "1") in the first OFDM symbol containing
DMRS and y.sup.(p)(i+1) is mapped to RE (k, l+1) (i.e., an RE
labeled "2") in the next OFDM symbol containing DMRS. The mapping
continues to the next resource element (k+1, l) and so on. With
this mapping, it can be seen that there are no longer any unmapped
REs. Another example of hybrid SFBC- and STBC-based resource
mapping in the presence of CSI-RS is shown in FIG. 23.
[0139] In these hybrid SFBC- and STBC-based resource mapping
options, resource elements (k,l) in an OFDM symbol containing DMRS
can be used in the mapping if those resource elements are not used
for transmission of DMRS and if those resource elements are not
used for CSI-RS.
[0140] In this hybrid SFBC- and STBC-based resource mapping option,
the mapping to resource element (k,l) in the OFDM symbols
containing DMRS on antenna port p not reserved for other purposes
can be in increasing order with first the index/over the adjacent
two OFDM symbols and then the index k over the assigned RBs for the
transmission.
[0141] TxD resource mapping for E-PDCCH with cross-interleaving
will now be considered. An REG may be defined in each OFDM symbol
in an E-PDCCH region supporting cross-interleaving. In OFDM symbols
that do not contain DMRS or CSI-RS, the same REG definition in
Rel-8 may be used. That is, an REG is composed of four
consecutively available REs in one OFDM symbol in an RB configured
for potential E-PDCCH transmission counted in ascending order of
subcarriers. An RE is assumed to be unavailable with respect to
mapping the E-PDCCH if the RE is used for transmission of CRS. If
CRS is configured for port 0, it can be assumed that REs for
transmission of CRS on antenna port 1 are unavailable for an REG.
Precoded TxD symbols for 2-tx and 4-tx could be mapped as defined
in Rel-8 within each REG. For example, a TxD precoded symbol pair
could be mapped to RE 1 and 2.
[0142] In OFDM symbols containing DMRS or CSI-RS, at least two
options for REG definition may exist. In the first option, an REG
is composed of four consecutively available REs in one OFDM symbol
in an RB configured for potential E-PDCCH transmission counted in
ascending order of subcarriers. An RE is assumed to be unavailable
with respect to mapping the E-PDCCH if the RE is used for the
transmission of DMRS or if the RE is configured for CSI-RS. For an
REG={RE(k0), RE(k1), RE(k2), RE(k3)}, where ki (i=0, 1, 2, 3) are
the subcarrier indices of the REs, the following conditions may be
satisfied:
k1-k0<3 and k3-k3<3.
One such example is shown FIG. 24. Alternatively, for an
REG={RE(k0), RE(k1), RE(k2), RE(k3)}, where ki (i=0, 1, 2, 3) are
the subcarrier indices of the REs, the following conditions may be
satisfied:
k1-k0=1 and k3-k3=1.
One such example is shown FIG. 25.
[0143] In the second option, an REG is composed of four neighboring
available REs in a RB in two consecutive OFDM symbols containing
DMRS and configured for potential E-PDCCH transmission counted in
ascending order of OFDM symbols first and then subcarriers. An RE
is assumed to be unavailable with respect to mapping the E-PDCCH if
the RE is used for the transmission of DMRS or if the RE is
configured for CSI-RS. One such example is shown FIG. 26.
[0144] With the above resource mapping, E-PDCCHs may be
multiplexed, scrambled, modulated, and/or mapped to layers and
precoded in a manner similar to that used for the legacy PDCCH,
with the following exceptions: TxD transmission uses DMRS ports for
demodulation; for the purpose of REG-to-RE mapping, the downlink
system bandwidth can be determined as N.sub.RB.sup.E-PDCCH;
N.sub.REG is the number of REGs in the E-PDCCH region; and
n.sub.PDCCH is the number of transmitted E-PDCCHs in the E-PDCCH
region.
[0145] It should be noted that for 4-tx TxD, the two pairs of TxD
precoded symbols of two pairs of antennas could be transmitted in
the same REG in E-PDCCH with cross-interleaving. In the case of
E-PDCCH transmission without cross-interleaving, the two pairs of
TxD precoded symbols of two pairs of antennas could be transmitted
alternatively along frequency and/or time.
[0146] The above examples show the mapping within an RB. If
multiple consecutive RBs are assigned for a UE or a group of UEs
for the E-PDCCH transmission, the mapping could be extended to
include all assigned RBs. For example, the mapping of a pair of
precoded TxD symbols does not need to be limited at the RB
boundary, and thus unused orphan REs at the RB boundary can be
avoided.
[0147] When E-PDCCH without cross-interleaving is configured in a
cell and DMRSs are configured as the E-PDCCH demodulation reference
signals for a UE, DMRS signals might be transmitted only on the
resource blocks where the corresponding E-PDCCH is transmitted for
the UE. The UE can perform channel estimation based on the
configured DMRS in the resources over which E-PDCCH detection is
performed.
[0148] When E-PDCCH with cross-interleaving is configured in a
cell, different E-PDCCHs could be multiplexed and transmitted on
the same E-PDCCH region. If DMRSs are configured as the E-PDCCH
demodulation reference signals, the same DMRS ports could be used
throughout a whole E-PDCCH region, and the DMRS signals may need to
be transmitted in the E-PDCCH region as long as there is E-PDCCH
transmission in the region. The DMRSs in this case can be shared
among UEs and can be considered TP-specific. As used herein, the
term "TP-specific" refers to a signal that is transmitted from a
transmission point but is not transmitted from other transmissions
points near that transmission point.
[0149] So when DMRSs are configured as E-PDCCH demodulation
reference signals for a UE and E-PDCCH with cross-interleaving is
configured in a cell, the UE can assume the same DMRS configuration
in the E-PDCCH region when performing channel estimation for
E-PDCCH detection. If CRS is configured for E-PDCCH demodulation at
a UE, the UE can assume that there is no DMRS transmission in the
RBs over which E-PDCCH detection is performed.
[0150] Each TP can be configured to have its own E-PDCCH region.
This configuration could reduce the required blind decodes at a UE
since only one E-PDCCH region would need to be searched. It is
generally desirable that the E-PDCCH regions configured with
cross-interleaving are non-overlapping with each other. A benefit
of non-overlapping E-PDCCH regions is that E-PDCCH interference
between TPs could be reduced. The E-PDCCH regions from different
TPs could have overlaps if the coverage of the TPs are
non-overlapping, i.e., there is no or very small interference with
each other. E-PDCCH regions configured with DMRS and without
cross-interleaving could overlap, and the interference among them
could be reduced or avoided through coordinated E-PDCCH
scheduling.
[0151] It may be preferable that an E-PDCCH region configured with
cross-interleaving and with CRS as the E-PDCCH demodulation RS do
not overlap with regions configured with DMRS as the E-PDCCH
demodulation RS, since a region configured with CRS as the E-PDCCH
demodulation RS might have UEs attached to the macro-eNB and
interference could occur with E-PDCCHs transmitted from LPNs due to
the large coverage of the macro-eNB.
[0152] When a UE leaves the coverage area of one TP and enters the
coverage of another TP, a reconfiguration of the E-PDCCH for the UE
may be needed. The reconfiguration could be done by higher layer
signaling, such as RRC signaling. Alternatively, the eNB could
transmit an E-PDCCH to the UE from the targeting TP when E-PDCCH
without cross-interleaving is used. Such mobility scenarios are
shown in FIG. 27, where two different E-PDCCH regions 2710 are
configured in TP1 2720a and TP2 2720b. TP1 2720a is the serving TP
while TP2 2720b is the targeting TP. During the UE's transition
period from TP1 2720a to TP2 2720b, the E-PDCCHs to the UE 2730
could be sent from both the TPs 2720 using the same DMRS ports and
on the same E-PDCCH region. It should be noted that such an E-PDCCH
could be transmitted in the PDSCH region of TP2 2720b, as before
handover to the targeting TP 2720b, UE1 2730 may not be aware of
the E-PDCCH region of the targeting TP 2720b. To achieve that, TP
2720b may need to avoid scheduled PDSCH on this region to avoid
collision with the E-PDCCH for UE1 2730. After handover is
completed for UE1 2730, the E-PDCCH region of TP 2720b could be
signaled to UE1 2730 where it will expect to receive its E-PDCCH in
the future. This transmission could be transparent to UE1 2730 as
well as other UEs served by TP2 2720b.
[0153] The SFBC-based or hybrid SFBC- and STBC-based transmit
diversity as described above can apply Alamouti coding on the
symbols of an E-PDCCH transmitted from multiple antennas, and
therefore can improve spatial diversity gain due to the fact that
after coding, the two data streams transmitted from each antenna
are orthogonal to each other. However, such transmit diversity may
require mapping for pairs of coded symbols onto neighbor REs.
[0154] Alternatively, channel independent beamforming or random
beamforming (RBF) can be used, in which precoding vectors (or
matrices) are randomly selected from a known codebook and applied
to an E-PDCCH. As in the situation of high mobility and a highly
dispersive channel, the feedback wideband CSI may be aging and not
able to match the variations of the channels. Therefore, instead of
relying on such unreliable and inaccurate CSI for the precoding,
some randomly chosen precoding vectors can be used to achieve some
spatial diversity gain. Several variations of RBF can be used for
E-PDCCH transmission, as follows.
[0155] In a first variation, symbol-based RBF may be used. In such
a method, each modulated symbol or a group of modulated symbols of
an E-PDCCH for a UE is precoded with a known precoding vector
(matrix) before transmission over multiple antennas. Different
precoding vectors (matrices) may be applied to different symbols or
different groups of symbols, and precoding vectors (matrices) in a
codebook can be cyclically used to precode different symbols or
groups of symbols.
[0156] For example, if there are N.sub.w precoding vectors
{w.sub.1, w.sub.2, . . . w.sub.N.sub.w} in a predefined codebook
known to both the transmitter and receiver, let {x(0), x(1), . . .
, x(k), . . . , x(M.sub.symb-1)} be the M.sub.symb modulated
symbols of the E-PDCCH to be sent to a UE over P transmit antennas
from an eNB or access point. The precoded symbols with random
beamforming to be mapped onto resources on each of the antennas are
given by:
[ y ( 0 ) ( i ) y ( 1 ) ( i ) y ( P - 1 ) ( i ) ] = v ( i ) x ( i )
, i = 0 , 1 , , M symb - 1. ##EQU00004##
where y.sup.(p)(i) is the ith precoded symbol to be transmitted
over the pth antenna. The precoding vector v(i) is of the size of
Px1 and is defined in one scenario as follows:
v(i)=w.sub.k,k=i mod N.sub.w+1
where mod is a modular function. In another scenario, v(i) can be
defined as:
v(i)=w.sub.k,k=(floor(i/L))mod N.sub.w+1
where L is the size of a group of symbols over which the same
precoding vector is applied. L is known to both the eNB and the
UE.
[0157] The mapping of the precoded symbols to REs can be along the
frequency direction first followed by the time direction or vice
versa. The starting precoding vector at the first symbol can vary
from subframe to subframe and/or from cell to cell to further
randomize possible interference in adjacent cells. One such example
of precoding vector selection is given below:
v(i)=w.sub.k,k=(floor(i/L)+f(n.sub.s+CellID))mod N.sub.w+1
where n.sub.s is a subframe number, cellID is a cell identifier,
and f( ) is a predefined function of n.sub.s and cellID.
[0158] This symbol-based RBF scheme can create a channel variation
from symbol to symbol and therefore can bring some potential
spatial diversity gain.
[0159] The precoding vector selection and mapping to the symbols
can be pre-defined so that the UE knows exactly the precoding
vector that is applied on each symbol for channel estimation
purposes. Alternatively, either dynamic or semi-static signaling
can be used to convey the pre-coding vector pattern to the UE.
[0160] When such RBF is used, any reference signals used for
channel estimation and E-PDCCH demodulation should not be precoded.
This may allow the UE to estimate the channel for each symbol
through the channel information from such reference signals and
corresponding precoding on each symbol. For example, if the
estimated channel for the ith symbol at a receive antenna
corresponding to the pth transmit antenna is h.sup.(p)(i) and the
known precoding vector is v(i), then the channel after precoding
for the ith symbol can be estimated as:
h(i)=[h.sup.(0)(i),h.sup.(1)(i), . . . ,h.sup.(P-1)(i)]v(i),i=0,1,
. . . ,M.sub.symb-1.
[0161] This channel estimate can then be used for equalization and
demodulation. An RS port is required for each of the transmit
antennas. CRS can be used for this purpose as it is not precoded.
Alternatively, DMRS without precoding can also serve this
purpose.
[0162] In a second variation, PRB-based RBF may be used. That is,
as an alternative to the per-symbol-based RBF, the random BF can
also be applied on a per-PRB basis for an E-PDCCH. Namely, the same
precoding vector (matrix) can be applied to the symbols of the
E-PDCCH to be mapped onto the same PRB (or PRB pair). A different
precoding vector is used for symbols of the E-PDCCH allocated to a
different PRB or PRB pair.
[0163] Alternatively, a single precoding vector can be applied to
symbols of the E-PDCCH to be mapped to a number of neighboring
PRBs. For example, if a number of consecutive PRBs are used for
E-PDCCH transmission for a UE or a group of UEs, the same randomly
selected precoding vector can be applied to the whole group of
PRBs.
[0164] A benefit of PRB-based RBF is that only one port of RS is
needed for channel estimation if the RS in a PRB is also precoded
with the same precoding vector used for the E-PDCCH in the PRB,
assuming one layer transmission for the E-PDCCH.
[0165] If DMRS is used for demodulation and the same precoding
vector applied to the E-PDCCH is also applied to the DMRS in the
same PRB, then the UE does not need to be informed separately of
the actual precoding vector used by the eNB, as such information is
carried by the DMRS already. Therefore such RBF may be totally
transparent to the UE.
[0166] However, if the RS used for demodulation cannot be precoded,
such randomly selected precoding vector information may need to be
conveyed to the UE. One way to do that is to pre-define the
precoding vectors for each PRB and PRB pair (or a group of PRBs and
PRB pairs). For example, a number of precoding vectors in a
codebook can be cyclically used over the PRB/PRB pairs (or a group
of PRBs/PRB pairs) starting from the lowest frequency to the
highest frequency of the system bandwidth. In order to provide more
patterns for precoding vectors for each PRB, there can be different
patterns based on subframe number or frame number. This order can
be pre-defined or signaled.
[0167] Such PRB-based RBF can be used in conjunction with other
diversity schemes such as frequency diversity. For example, in
frequency diversity transmission, the E-PDCCH from the same UE can
be distributed and transmitted over a number of non-consecutive
PRBs, and different precoding vectors can be applied to each of
such PRBs. To achieve more diversity gain, different precoding
vectors in the codebook can be selected cyclically for these
PRBs.
[0168] In a third variation, E-PDCCH-based RBF may be used. That
is, when multiple E-PDCCHs for different users need to share the
same resources (PRBs or PRB pairs), different precoding vectors can
be used for each E-PDCCH. For each E-PDCCH, the precoding vector
can be selected either randomly or using a pre-determined pattern
which may depend on the UE ID, subframe, PRB number, etc.
[0169] When the precoding vector for each E-PDCCH in a PRB or PRB
pair is either randomly selected (which the UE is unaware of) or is
determined based a predetermined pattern (which the UE is aware
of), a single port of precoded RS may be used for each E-PDCCH for
channel estimation and E-PDCCH demodulation. When a predetermined
pattern is used for precoding vector selection for each E-PDCCH,
un-precoded RS, one for each transmit antenna, can be shared by all
the E-PDCCHs for E-PDCCH demodulation. The precoding vector in this
case can vary from PRB to PRB or from symbol to symbol.
[0170] The multiplexing of multiple E-PDCCHs on a PRB (or PRB pair)
can be based on frequency division multiplexing (FDM), time
division multiplexing (TDM) or a mix of both. In one FDM case, each
PRB (or PRB pair) can be divided into three resource units. Each
resource unit includes four consecutive subcarriers in frequency
and all OFDM symbols in a slot or a subframe in time. Each of the
three resource units can be allocated to a different E-PDCCH, and
the modulated symbols in each resource unit can be precoded
independently. The DMRS symbols in each resource unit can be
precoded the same as the E-PDCCH transmitted on that resource unit
and used for E-PDCCH demodulation.
[0171] To summarize, randomly selected precoding vectors (matrices)
can be applied to an E-PDCCH on a modulated symbol or PRB (PRB
pair) or per-E-PDCCH channel basis. The precoding vectors can be
cyclically selected from a codebook and applied to modulated
symbols or PRB pairs. Both CRS and DMRS without channel independent
precoding can be used as RS for E-PDCCH demodulation.
[0172] Antenna port configuration for an E-PDCCH with non-precoded
RS will now be considered. Even though an E-PDCCH is transmitted in
the legacy PDSCH region, the number of transmit antennas configured
for E-PDCCH transmission may not follow that of the PDSCH. This is
because E-PDCCH transmission may have different requirements from
that of the PDSCH. In an embodiment, the same number of transmit
antenna ports is used as is used in the legacy PDCCH rather than
following that for the PDSCH transmission. By doing this, the
transmission of the E-PDCCH may be more in line with that of the
legacy PDCCH. For example, if the number of transmit antenna ports
for legacy PDCCH transmission as detected from the PBCH is two,
then the number of transmit antenna ports assumed for E-PDCCH
transmission is two. If the number of transmit antenna ports for
legacy PDCCH transmission as detected from the PBCH is four, then
the number of transmit antenna ports assumed for E-PDCCH
transmission is four. The number of transmit antenna ports can
determine the precoding vectors (matrices) used for precoding
operation. Alternatively, the number of transmit antenna ports of
the E-PDCCH can be independently configured and signaled to the UE
by higher layer signaling, such as RRC signaling. It may be
preferable that a maximum of four transmit antenna ports be
configured for E-PDCCH transmission.
[0173] After the number of transmit antenna ports for the E-PDCCH
is determined, other information that may need to be conveyed to
the UE might include the transmission mode to be used, whether BF
transmission or diversity transmission is to be used, and whether
such transmission modes are supported for E-PDCCH transmission.
Such transmission modes can be implicitly signaled to the UE
through the number of demodulation RS ports. For example, if one
demodulation RS port (CRS or DMRS) is configured for the E-PDCCH,
then BF transmission can be assumed, but if multiple demodulation
RS ports are configured, a diversity scheme such as SFBC-based
transmit diversity can be assumed by the UE. Alternatively, the
E-PDCCH transmission mode and the RS ports for a UE may be
explicitly signaled. Here, it is assumed that there is only one
layer transmission for the E-PDCCH. It should be mentioned that if
PRB-based RBF is used as the diversity scheme, then there is no
distinction between closed-loop BF and RBF from the UE's
perspective. In this case, switching between BF and RBF is totally
transparent to the UE (if DMRS with precoding is used for E-PDCCH
demodulation).
[0174] In summary, if non-precoded RS is used for demodulation of
the E-PDCCH, the number of transmit antennas used for E-PDCCH
transmission can be the same as that used for legacy PDCCH
transmission. Such a configuration can be inherited from that of
the legacy PDCCH transmission or can be signaled through a higher
layer. Beamforming or diversity transmissions can be either
implicitly signaled by the configured number of demodulation RS
ports or explicitly signaled to a UE. When non-precoded RS is used
for E-PDCCH demodulation, a UE can assume the same number of
transmit antennas as the legacy PDCCH transmission.
[0175] E-PDCCH multiplexing in a PRB pair will now be considered.
Sub-PRB pair resource unit partitioning will be considered first,
and then procedures for E-PDCCH resource assignment will be
considered.
[0176] Regarding sub-PRB pair resource unit partitioning, when
multiple E-PDCCHs are multiplexed in the same PRBs or PRB pairs,
one problem may be how to assign or allocate the DMRS to UEs. When
the symbol-based RBF approach is used, a non-precoded DMRS can be
used, and the DMRS can be shared by all UEs in a PRB. In this case,
the number of DMRS ports required equals the number of transmit
antennas at the eNB. In addition, the precoding vectors used for
RBF may need to be known at the UEs. An advantage is that an
E-PDCCH for a UE would be spread over multiple RBs, and thus both
potential spatial diversity and frequency diversity can be
achieved. In contrast, when the PRB-based RBF method is used, only
a single DMRS port with the same precoding may be needed, and the
precoding can be transparent to a UE. A drawback is that there may
not be enough spatial and frequency diversity because the resources
of one PRB pair may not be large enough for many E-PDCCHs.
[0177] On the other hand, the minimum resource allocation for the
legacy PDCCH is one CCE, which equals to 36 REs, or about the size
of a third of a PRB pair. So it may not be efficient in terms of
resource utilization when the minimum resource allocation for the
E-PDCCH is PRB pair-based. For example, in some high SNR and small
DCI scenarios, the required E-PDCCH performance may be achieved
with a resource allocation of one CCE, meaning that assigning one
PRB pair to one E-PDCCH may be a waste of resources. Therefore, it
may be more efficient to define a sub-PRB partition. Possible ways
of partitioning a PRB or PRB pair for E-PDCCH multiplexing and
transmission include a horizontal sub-PRB pair resource unit
partition and a vertical sub-PRB pair resource unit partition.
[0178] Regarding horizontal sub-PRB pair resource unit
partitioning, a PRB pair can be partitioned along frequency into
different resource units. In one embodiment, the PRB pair can be
partitioned into three resource units with equal size in frequency
as depicted in FIG. 31, where each resource unit takes four REs in
frequency. Roughly speaking, each resource unit contains resources
about the size of one CCE, i.e., 36 REs, which is the minimum
resource unit for PDCCH assignment.
[0179] An advantage of such a partition is that, in each resource
unit, a set of DMRS symbols can be precoded independently from
those in other resource units and thus can be used for E-PDCCH
demodulation transmitted in that resource unit.
[0180] In another embodiment, the PRB pair can be partitioned into
two resource units with equal size in frequency as depicted in FIG.
32, where each resource unit takes six REs in frequency. One or
more of such resource units may be allocated to an E-PDCCH. A UE
may be assigned with one DMRS port for E-PDCCH demodulation. When a
PRB or PRB pair is allocated to transmit two E-PDCCHs, one for a
different UE, two orthogonal DMRS ports can be allocated, one DMRS
port for each UE. For example, one UE could be assigned with DMRS
port 7 and the other UE with DMRS port 8. Channel estimation for
E-PDCCH demodulation can be performed using the DMRS REs over the
whole PRB or PRB pair. An advantage of this approach is that better
channel estimation can be achieved.
[0181] In another embodiment, vertical sub-PRB pair resource unit
partitioning may be used. That is, a PRB pair can be partitioned
into different resource units in the time domain. In one
embodiment, the PRB can be partitioned into two resource units in
time as depicted in FIG. 33. According to different lengths for the
legacy PDCCH region, different partitioning patterns are also
possible. This pattern can be fixed according to different PDCCH
lengths. As also depicted in the FIG. 33, the sub-PRB resource unit
may not be limited to a slot boundary.
[0182] Both types of partitioning can be used for close-loop
beamforming (CL-BF), RBF, DMRS-based TxD, and MU-MIMO
transmissions.
[0183] In summary, a PRB or PRB pair can be partitioned along
either the frequency domain or the time domain to create smaller
resource units. DMRS symbols in each resource unit can be used as
demodulation RS for the E-PDCCH transmitted in that resource unit.
If precoding is used, the same precoding vectors may be used as
those for the E-PDCCH transmitted in the same resource unit.
[0184] Procedures for E-PDCCH resource assignment will now be
considered. Partitioning a PRB pair in frequency or time to smaller
resource units provides finer granularity in terms of resource
mapping for the E-PDCCH compared to PRB pair-based resource
allocation. Each resource unit can be precoded individually and can
be allocated to different UE. In other words, when mapping and
multiplexing E-PDCCHs of different UEs, each UE can be assigned
with a number of resource units just as it was assigned with a
number of CCEs for a legacy PDCCH. The resource mapping of the
E-PDCCH for each UE can be localized or distributed. These
partitions may be particularly beneficial for CL-BF, as a smaller
resource may be needed for the E-PDCCH in many cases due to the
beamforming gain.
[0185] Similar to the CCE concept used for legacy PDCCH resource
allocation, the resource unit can be used in Rel-11 for E-PDCCH
resource assignment. The assignment procedure of the E-PDCCH for a
UE can follow a similar PDCCH assignment procedure as defined in
Rel-8. Namely, each resource unit can be viewed as a CCE and
assigned with an index. The assignment procedure of the E-PDCCH for
a particular UE can be determined by the possible number of
resource units used for the E-PDCCH, the number of E-PDCCH
candidates, and/or UE ID.
[0186] The DMRS symbols in those resource units can be used as
demodulation RS for the E-PDCCH transmitted in those resource
units. For example, frequency domain partitioning may be used to
partition a PRB pair into three resource units, and one resource
unit may be assigned to one UE while the remaining two resource
units may be assigned to another UE. Then, if DMRS port 7 is used
for demodulation of the E-PDCCH, the first UE can use DMRS symbols
of port 7 in the first resource unit for demodulation of its
E-PDCCH transmission, while the second UE can use DMRS symbols of
port 7 in the other two resource units for demodulation of its
E-PDCCH transmission.
[0187] Alternatively, each UE can be assigned with a different DMRS
port. For the previous example, DMRS port 7 within a PRB pair can
be assigned to the first UE for its E-PDCCH transmission, and DMRS
port 8 within a PRB pair can be assigned to the second UE for its
E-PDCCH transmission. With such assignments, a channel can be
estimated based on the DMRS symbols from the same port in the whole
PRB pair, which may improve the channel estimation accuracy, even
if the E-PDCCH of each UE is only transmitted from part of a PRB or
PRB pair. If E-PDCCHs from more than two UEs are transmitted in one
PRB pair, two additional scrambling sequences can be used to
scramble each DMRS port (such as port 7 and 8), as in the case of
MU-MIMO in Rel-10. That can allow the support of up to four
E-PDCCHs from different UEs in one PRB pair.
[0188] In summary, resources of an E-PDCCH for a UE can be assigned
based on resource units partitioned from a PRB pair. The resource
units can be used for E-PDCCH assignment, and the same assignment
procedure of the PDCCH in Rel-8 can be used for E-PDCCH assignment.
DMRS symbols of a DMRS port in a resource unit or in the whole PRB
pair can be assigned for demodulation of an E-PDCCH.
[0189] Several topics related to E-PDCCH operations will now be
considered. The topics include E-PDCCH configuration and signaling,
resource units for the E-PDCCH and their multiplexing, DMRS port
assignment for E-PDCCH demodulation, E-PDCCH transmission modes,
and the E-PDCCH search space and blind decoding.
[0190] Regarding E-PDCCH configuration and signaling, an E-PDCCH
region can be configured by an eNB and signaled by the eNB to a UE
semi-statically, for example using higher layer signaling such as
RRC signaling. Alternatively, the E-PDCCH region can be signaled by
the eNB to a UE dynamically, i.e., on a subframe-by-subframe basis
using, for example, PHY level signaling. The region can be
configured either UE-specifically or cell-specifically. There can
be more than one E-PDCCH region in the same subframe. Different
E-PDCCH regions could be configured together or separately.
[0191] Resource allocation for an E-PDCCH region can be either
localized or distributed. In a localized case, consecutive PRBs or
PRB pairs can be allocated. In a distributed case, non-consecutive
PRBs or PRB pairs can be allocated. In either a localized or
distributed case, a set of N_VRB Virtual RBs (VRBs) can be
allocated for an E-PDCCH region and for potential E-PDCCH
transmission. The resource allocation can be signaled using one of
the three existing resource allocation methods for the PDSCH as
specified in 3GPP TS 36.213, section 7.1.6.
[0192] The allocated VRBs can be indexed from 0 to N_VRB-1. For
resource allocation type 0 or type 1, the mapping from VRB to PRB
can be derived according to 3GPP TS 36.211, section 6.2.3. For
resource allocation type 2, the mapping can be configured through
RRC signaling.
[0193] More than one E-PDCCH region can be allocated in a subframe.
In one embodiment, if two E-PDCCH regions are allocated in the same
subframe and one has a localized resource allocation and the other
has a distributed resource allocation, some UEs can be configured
to use the E-PDCCH region with localized E-PDCCH resources, while
other UEs can be configured to use the E-PDCCH region with
distributed E-PDCCH resources. A UE may then only need to search
for its E-PDCCH in the E-PDCCH region for which it is configured.
In another embodiment, a UE may be configured with two E-PDCCH
regions, one region for carrying UE-specific E-PDCCHs and the other
region for carrying non-UE-specific information, such as E-PDCCHs
intended for multiple UEs or an E-PHICH.
[0194] Similar to the RRC signaling for an R-PDCCH, an example of
RRC signaling for an E-PDCCH region is shown below:
TABLE-US-00003 E-PDCCH-Config-r11 SEQUENCE {
resourceAllocationType-r11 ENUMERATED {type0, type1,
type2Localized, type2Distributed, spare4, spare3, spare2, spare1},
resourceBlockAssignment-r11 CHOICE { type01-r11 CHOICE { nrb6-r11
BIT STRING (SIZE(6)), nrb15-r11 BIT STRING (SIZE(8)), nrb25-r11 BIT
STRING (SIZE(13)), nrb50-r11 BIT STRING (SIZE(17)), nrb75-r11 BIT
STRING (SIZE(19)), nrb100-r11 BIT STRING (SIZE(25)) }, type2-r11
CHOICE { nrb6-r11 BIT STRING (SIZE(5)), nrb15-r11 BIT STRING
(SIZE(7)), nrb25-r11 BIT STRING (SIZE(9)), nrb50-r11 BIT STRING
(SIZE(11)), nrb75-r11 BIT STRING (SIZE(12)), nrb100-r11 BIT STRING
(SIZE(13)) }, ... }, multiplexingMethod-r11 CHOICE{ CCE, VRB, eCCE
with interleaving, eCCE without interleaving} demodulationRS-r11
CHOICE{ CCEbased-r11 ENUMERATED {crs,dmrs}, VRB based-r11
ENUMERATED {dmrs} eCCEbased-r11 ENUMERATED {dmrs} } TxMode CHOICE
{Txd, BF} }
[0195] The parameter or information element
"resourceAllocationType" represents the resource allocation used:
type 0, type 1, or type 2. Value type0 corresponds to type 0, value
type1 corresponds to type 1, value type2Localized corresponds to
type 2 with localized virtual RBs and type2Distributed corresponds
to type 2 with distributed virtual RBs.
[0196] The parameter or information element
"resourceBlockAssignment" indicates the resource block assignment
bits according to 3GPP TS 36.213, section 7.1.6. Value type01
corresponds to type 0 and type 1, and the value type2 corresponds
to type 2. Value nrb6 corresponds to a downlink system bandwidth of
6 RBs, value nrb15 corresponds to a downlink system bandwidth of 15
RBs, and so on.
[0197] In some embodiments, the existing RRC signaling method for
R-PDCCH configuration can be reused as semi-static signaling of an
E-PDCCH region configuration. The E-PDCCH region can contain
localized resource allocation or distributed resource allocation or
both. Multiple E-PDCCH regions can be configured in the same
subframe.
[0198] Resource units for the E-PDCCH and their multiplexing will
now be considered. The resource units are defined here as REs for
E-PDCCH transmission. Similar to the PDCCH, an E-PDCCH can include
one or multiple of such resource units. In this set of embodiments,
at least three options are available: a CCE-based option, a VRB- or
VRB pair-based option, and an eCCE-based or sub-PRB-based
option.
[0199] In the CCE-based option, the existing definition of CCE in
Rel-8 may be reused, where one CCE includes nine REGs and one REG
includes four consecutive REs in an OFDM symbol, excluding REs for
reference signals.
[0200] For E-PDCCH purposes, REGs may be defined over only the VRBs
allocated to an E-PDCCH region and indexed from the VRB with the
lowest index to the VRB with the highest index in each OFDM symbol,
and may then continue in the next OFDM symbol. An E-PDCCH channel
sent to a UE may include one or more CCEs.
[0201] RS for E-PDCCH demodulation are common to all UEs in the
corresponding VRBs. In this option, the VRBs allocated for an
E-PDCCH region cannot be shared with a PDSCH transmission unless
there is no E-PDCCH transmission in a subframe.
[0202] This CCE-based option can provide good frequency diversity
and can be good for carrying non-UE-specific E-PDCCHs.
[0203] Another option is to use either a VRB or a VRB pair as the
minimum E-PDCCH unit for E-PDCCH transmission. An E-PDCCH for a UE
may use one or more VRBs or VRB pairs. This option can be
advantageous for providing both frequency selective gain and
beamforming gain if channel state information is available at an
eNB. It is also good for resource utilization because a VRB that is
not scheduled for an E-PDCCH in a subframe can be used for PDSCH
transmission. A constraint of this option is that a VRB pair is
roughly equivalent to three CCEs, so it may be too coarse for
E-PDCCH resource allocation.
[0204] Instead of using a CCE or a VRB/VRB pair as the minimum
E-PDCCH unit for E-PDCCH transmission, a new unit may be defined,
which may be referred to herein as an extended CCE, an enhanced
CCE, or an eCCE. An eCCE has a finer granularity and occupies a
smaller time/frequency region compared to a VRB or VRB pair. This
may make it easy to use DMRS as demodulation reference signals for
the E-PDCCH. It may also allow multiple E-PDCCHs to be multiplexed
in a VRB/VRB pair.
[0205] There are a few options for eCCE definition in a VRB/VRB
pair. In one option, a VRB/VRB pair can be divided into a number of
eCCEs along the frequency domain. That is, eCCEs may be frequency
division multiplexed in a VRB/VRB pair as shown in FIG. 31. In
another option, eCCEs may be time division multiplexed in a VRB/VRB
pair as shown in FIG. 33.
[0206] In yet another option, the eCCEs can be code division
multiplexed (CDM) in a VRB/VRB pair. In this case, each eCCE is
assigned with an orthogonal cover code (OCC) over a VRB/VRB pair.
When an eCCE is allocated to an E-PDCCH, every symbol of the
E-PDCCH is spread by the corresponding OCC assigned to the eCCE and
mapped to a group of closely located REs in the VRB/VRB pair. The
groups of closely located REs for OCC spreading can be pre-defined,
using similar mapping options for REG description as described
above in connection with TxD resource mapping for the E-PDCCH. For
convenience, such groups of REs can be called a REG. A conceptual
example is shown in FIG. 34, where different eCCEs are separated by
an OCC.
[0207] Although multiplexing three eCCEs in one PRB is possible,
multiplexing two or four eCCEs in one PRB in CDM fashion can also
be possible, as the orthogonal code only has 1 or -1 element, thus
simplifying the computation in both the transmission and reception
sides. An example of REG groups for the case of multiplexing four
eCCEs in a RB pair is shown in FIG. 35, where a REG includes four
consecutive REs marked with "1," "2," "3," and "4" in an OFDM
symbol that does not contain any DMRS REs. For OFDM symbols
containing DMRS REs, REGs include the REs marked in the circles.
Four OCC codes can be defined for each E-PDCCH symbol to be mapped
to each REG. An example of such codes is shown in Table 3. The
index in each OCC code {w(1), w(2), w(3), w(4)} can also be used to
map spread symbols to the REG shown in FIG. 35. In the situation
where some OFDM symbols contain REs for CSI-RS, the above mapping
can be used, or alternatively, these OFDM symbols may not be used
to transmit the E-PDCCH.
TABLE-US-00004 TABLE 3 An example of OCC code OCC code index OCC
code: w = [w(1),w(2),w(3),w(4) ] 1 [+1 +1 +1 +1] 2 [+1 -1 +1 -1] 3
[+1 +1 -1 -1] 4 [+1 -1 -1 +1]
[0208] One advantage of the CDM-based eCCE multiplexing is that all
the eCCEs can have exactly the same number of resource elements in
each RB, and this may lead to simplified rate matching during
encoding. That is, only the information about the number of eCCEs
allocated to an E-PDCCH may be needed for rate matching during
channel encoding of the E-PDCCH. In addition, better diversity over
a PRB and similar channel estimation performance for each eCCE can
be achieved if the CDM method of eCCE multiplexing is used.
[0209] eCCEs in an E-PDCCH region can be indexed, i.e., {eCCE(0),
eCCE91), . . . , eCCE(N.sub.eCCE-1)}, where N.sub.eCCE is the total
number of eCCEs available in the E-PDCCH region. Within a VRB/VRB
pair, the index of an eCCE can ascend from lower time/frequency to
higher time/frequency in the case of FDM- or TDM-based eCCE
allocation within an RB. For CDM-based allocation, the index of an
eCCE can be linked to the OCC code index.
[0210] An E-PDCCH for a UE may include one or more eCCEs. In cases
where more than one eCCE is used, at least one of two options may
be used. In a first option, consecutive eCCEs are allocated to an
E-PDCCH, e.g., in closed-loop beamforming mode to achieve
beamforming gain. In a second option, interleaving may be performed
on the eCCEs first. That is, the indices of the eCCEs for an
E-PDCCH may not be contiguous after interleaving, e.g., in
open-loop beamforming or TxD mode to achieve frequency diversity
gain.
[0211] In some embodiments, E-PDCCH resource units can be defined
based on a CCE, a VRB/VRB pair, or an eCCE. The E-PDCCH resource
units can be multiplexed based on the FDM, TDM, or CDM methods.
Multiple eCCEs can be multiplexed with the CDM method in a PRB/PRB
pair with an orthogonal cover code.
[0212] DMRS port assignment for E-PDCCH demodulation will now be
considered. For the eCCEs defined in a VRB/VRB pair, at least three
options are available in assigning or associating DMRS ports to the
eCCEs. In the first option, DMRS ports are associated with UEs, in
the second option, DMRS ports are associated with eCCEs, and in the
third option, a DMRS RE is associated with its embedded eCCE.
[0213] In the first option, each UE can be configured with one or
multiple DMRS ports. A UE performs channel estimation based on the
assigned DMRS port for each of its eCCEs. The assigned DMRS port
can be precoded with the same precoder as that used for the E-PDCCH
data in each eCCE allocated for the E-PDCCH.
[0214] An example is shown in FIG. 36, where four eCCEs are defined
in a PRB pair in a FDM fashion and the four eCCEs are allocated to
four E-PDCCHs, each for a different UE. In this case, each of the
four eCCEs is allocated to a different UE and thus is allocated
with a different DMRS port. In this option, the eNB may need to
ensure that UEs allocated in the same PRB pair are assigned with
different DMRS ports. In demodulation of the E-PDCCH, each UE can
use all DMRS REs of the assigned DMRS port in the PRB/PRB pair for
the channel estimation.
[0215] In the second option, instead of signaling the DMRS port to
the UE, a fixed association can be used between a DMRS port and an
eCCE in a RB/RB pair. For example, each DMRS port can be associated
with an eCCE within a PRB or PRB pair. In the case of four eCCEs
per PRB pair, each of the four eCCEs in a PRB pair may be
associated with one of the four DMRS ports, e.g., DMRS ports 7-10.
In the case of two eCCEs in a PRB pair, each of the two eCCEs may
be associated with one of the two DMRS ports, e.g., DMRS ports 7
and 8. In such an embodiment, a UE can use the DMRS port associated
with the eCCE to perform E-PDCCH demodulation during blind
decoding.
[0216] In each PRB pair, the DMRS can be precoded with the same
precoder as that for the E-PDCCH data in each associated eCCE. More
than one eCCE in one PRB or PRB pair can be allocated to one UE. An
example of this second option is shown in FIG. 37.
[0217] The first and second DMRS assignment options can also be
applied to eCCEs with CDM multiplexing, though the second option
can provide more flexibility in E-PDCCH scheduling in terms of
E-PDCCH multiplexing in a PRB/PRB pair. In addition, there is no
need to signal the DMRS port to a UE in the second option.
[0218] A difference between the first and second options may be
noted. In the first option, all DMRS REs of the DMRS port assigned
to a UE in a PRB/PRB pair can be used for channel estimation and
demodulation of the E-PDCCH in the PRB or PRB pair for that UE.
This means that the same precoding vector may be applied to all
eCCEs within the same PRB/PRB pair and assigned to that UE.
[0219] For the second option, however, either the same or different
precoding vectors can be applied to different eCCEs allocated to
the same UE within that PRB/PRB pair, as a different DMRS port is
associated with different eCCEs. Another merit of the second
option, as mentioned above, is that no signaling is needed to
inform the UE which DMRS port it can use. The UE may assume the
corresponding DMRS ports for the demodulation of an assigned
eCCE.
[0220] In the first two options, a total of four DMRS ports in a
PRB or PRB pair may be needed if four eCCEs are defined in a
PRB/PRB pair. For each eCCE, a DMRS port is used for its
demodulation. In the third option, the demodulation of the E-PDCCH
for each eCCE may use only the DMRS REs embedded in that eCCE. As a
result, only one legacy DMRS port may be needed for demodulation of
all eCCEs in a PRB/PRB pair, for example, DMRS port 7 as defined in
Rel-10.
[0221] The DMRS transmitted in the DMRS REs within an eCCE is
precoded with the same precoder as that used for the E-PDCCH data
in the eCCE. The DMRS transmitted in the DMRS REs in different
eCCEs of a PRB may be precoded differently if the eCCEs are
allocated to different UEs or even to the same UE.
[0222] A benefit for this option is that DMRS RE overhead can be
reduced compared to the first two options, as only the DMRS RE for
one DMRS port is used. If necessary, two DMRS ports (for example,
ports 7 and/or 8) can be assigned to each eCCE without additional
overhead. The two DMRS ports may be used for supporting two-port
TxD or for supporting MU-MIMO transmission for E-PDCCH.
[0223] One possible constraint for this option is that DMRS REs may
need to be present in each eCCE. So this option may be appropriate
only for the case of three eCCEs per PRB pair as shown in FIG. 38
as an example, or two eCCEs per PRB pair as shown in FIG. 39.
[0224] In some embodiments, a DMRS port for E-PDCCH demodulation
can be configured for a UE. In other embodiments, a unique DMRS
port is associated with each eCCE in a PRB or PRB pair for the
demodulation of E-PDCCH. In yet other embodiments, DMRS REs of a
DMRS port embedded in an eCCE can be used for the demodulation of
that particular eCCE.
[0225] E-PDCCH transmission modes will now be considered. Two
possible transmission modes can be used for E-PDCCH transmission:
beamforming (either close-loop or open-loop) and TxD.
[0226] For beamforming, a DMRS-based reference signal may be used.
The E-PDCCH and the corresponding DMRS are precoded with the same
precoder(s). This may be applicable to either VRB/VRB pair-based or
eCCE-based resource allocation.
[0227] For TxD, either CRS or un-precoded DMRS may be used. This
can be used for all three of the E-PDCCH resource allocation
methods, i.e., CCE, VRB/VRB pair, or eCCE based approaches. For
eCCE-based E-PDCCH resource allocation, either CRS or un-precoded
DMRS may be used as well. The REGs within an eCCE used for
2-antenna or 4-antenna TxD can be pre-defined following the
principle of using the closest neighboring REs in one block. A
similar approach for REG definition as described above can be
used.
[0228] The transmission mode for a UE may be semi-statically
configured through RRC signaling. The configuration can be either
explicit or implicit. In the case of implicit signaling, the
transmission mode can be linked to, for example, the resource
allocation type or resource unit for E-PDCCH scheduling. For
example, the reference signal for demodulation and the transmission
mode can be associated with the resource unit for E-PDCCH
scheduling in the following ways. If the resource unit for
scheduling is CCE-based, the reference signal for demodulation may
be CRS or DMRS and the transmission mode may be TxD. If the
resource unit for scheduling is VRB-based, the reference signal for
demodulation may be DMRS and the transmission mode may be
beamforming or TxD. If the resource unit for scheduling is
eCCE-based, the reference signal for demodulation may be DMRS and
the transmission mode may be beamforming or TxD.
[0229] The E-PDCCH search space and blind decoding will now be
considered. In one embodiment, after being configured with an
E-PDCCH region, a UE can try to detect a possible E-PDCCH in the
E-PDCCH region in each subframe. Similarly to what is done for the
legacy PDCCH, to reduce the number of blind decodings, a
UE-specific search space can be defined for each UE in the E-PDCCH
region. A UE-specific search space may include all the possible
resource allocations that may be used for E-PDCCH transmission to
the UE. In addition, a non-UE-specific search space may be defined
in the same E-PDCCH region or in a designated different E-PDCCH
region over which a multi-cast or broadcast E-PDCCH may be
transmitted to a group of or all UEs in a cell. The search space
may be defined according to different E-PDCCH resource
allocations.
[0230] For a search space for CCE-based resource allocation, the
same approach used for the PDCCH defined in Rel-8 and for the
R-PDCCH defined in Rel-10 can be used. This may include the
following: Four CCE aggregation levels (1, 2, 4, 8) can be defined.
The number of E-PDCCH candidates for each aggregation level and the
corresponding CCEs for each E-PDCCH candidate can be specified, for
example, (6, 6, 2, 2) E-PDCCH candidates for aggregation levels (1,
2, 4, 8), respectively. At each CCE aggregation level, a search
space can be defined to search for all the E-PDCCH candidates for
the aggregation level. The CCEs of an E-PDCCH candidate for each
aggregation level may be a function of the total number of CCEs in
the E-PDCCH region, the subframe index, and a UE's Radio Network
Temporary Identity (RNTI).
[0231] For a search space for VRB-based resource allocation, the
same RB-based search space approach used for the R-PDCCH defined in
Rel-10 can be used. This may include the following: Four VRB
aggregation levels (1, 2, 4, 8) may be defined. The number of
E-PDCCH candidates for each aggregation level and the corresponding
VRBs can be specified. At each aggregation level, a search space
may be defined for all the E-PDCCH candidates for the aggregation
level. The VRBs of an E-PDCCH candidate for each aggregation level
may be a function of the total number of VRBs in the E-PDCCH
region, the subframe index, and a UE's RNTI.
[0232] For a search space for eCCE-based resource allocation, the
search space can be defined using the following steps: In a first
step, assume a set of N.sub.VRB.sup.E-PDCCH VRBs is configured for
an E-PDCCH region for potential E-PDCCH transmission by higher
layers. The VRBs can be continuously numbered as {VRB.sub.0,
VRB.sub.1, . . . , VRB.sub.N.sub.VRB.sub.E-PDCCH.sub.-1}, where
VRB.sub.0 corresponds to the configured VRB with the lowest index
and VRB.sub.N.sub.VRB.sub.E-PDCCH.sub.-1 corresponds to the
configured VRB with the highest index. In a second step, the
available eCCEs in the E-PDCCH region may be indexed from 0 to
N.sub.eCCE-1, i.e., {eCCE(0), eCCE(1), . . . , eCCE(N.sub.eCCE-1)}.
In a third step, an E-PDCCH is transmitted on an aggregation of one
or several consecutive eCCEs. An E-PDCCH consisting of L eCCEs may
only start on an eCCE i fulfilling i mod L=0, where i is the eCCE
number. For example, L=1, 2, 4, 8 may be defined. In a fourth step,
for each aggregation level L, a number of E-PDCCH candidates,
denoted as M(L) can be defined. For example, {6, 6, 2, 2}
candidates may be defined for L=1, 2, 4, 8, respectively. The set
of the E-PDCCH candidates to monitor at an aggregation level
defines a search space at the aggregation level. In a fifth step, a
search space can be a function of the aggregation level, the
subframe number, the UE identity, and the total number of eCCEs in
the E-PDCCH region. For example, the eCCEs corresponding to E-PDCCH
candidates m of the search space at aggregation level L and
subframe k can be defined as follows:
L{(Y.sub.k+m)mod .left brkt-bot.N.sub.eCCE/L.right
brkt-bot.}+i,i=0,1, . . . ,L-1; m=1,2, . . . ,M(L)
where Y.sub.k is a variable depending on UE ID and subframe index
k.
[0233] In some embodiments, an eCCE based interleaving method for
the E-PDCCH can be used to exploit a higher level of frequency
diversity gain. The eCCEs may be interleaved or permuted such that
eCCEs for an E-PDCCH are spread over different VRBs for increased
frequency and time diversity. For example, the eCCEs can be
arranged into a matrix with N rows and k columns as shown in FIG.
40, where k and N are configurable numbers that satisfy the
condition of k(N-1)<N.sub.eCCE.ltoreq.kN. That is, kN is greater
than or equal to the total number of eCCEs in an E-PDCCH region
that is signaled to a UE. The eCCEs are written into the matrix row
by row starting with eCCE(0) in column 0 of row 0. When
kN>N.sub.eCCE, "Null"s are written in the rest of the last row
of the matrix after eCCE(N.sub.eCCE-1). The eCCEs are then read out
column by column from the matrix starting with eCCE(0) in row 0 of
column 0. Any "Null" in the matrix is ignored during the read-out.
The newly rearranged eCCEs are {eCCE(p(0)), eCCE(p(1)), . . . ,
eCCE(p(N.sub.eCCE-1))}, where p(i).epsilon.{0, 1, . . . ,
N.sub.eCCE-1} is the eCCE index at the ith location of the new eCCE
sequence. The eNB can then follow the above procedure in
transmitting an E-PDCCH to a UE. At the UE side, the UE can follow
the same procedure to search and detect the E-PDCCH.
[0234] The eCCEs {eCCE(p(i)), i=0, 1, . . . , N.sub.eCCE-1}, after
interleaving, can be mapped in increasing order of i to the VRBs in
the E-PDCCH region, where, if four eCCEs are configured in a PRB,
{eCCE(p(0)), . . . , eCCE(p(3))} are mapped to VRB.sub.0,
{eCCE(p(4)), . . . , eCCE(p(7))} are mapped to VRB.sub.1, and so
on, and {eCCE(p(N.sub.eCCE-4))), . . . , eCCE(p(N.sub.eCCE-1)))}
are mapped to VRB.sub.N.sub.VRB.sub.E-PDCCH.sub.-1.
[0235] The VRBs can be mapped to PRBs either through localized
resource allocation or distributed resource allocation. In
localized resource allocation, the VRBs are mapped to contiguous
PRBs, while in distributed resource allocation, the VRBs are mapped
to distributed PRBs across the system bandwidth.
[0236] In addition to the semi-static signaling of the E-PDCCH
region to a UE as discussed previously, the E-PDCCH multiplexing
method, the DMRS port assignment, and/or the E-PDCCH transmission
mode can be signaled to a UE semi-statically. For example, two bits
can be used to indicate the multiplexing method. That is, one of
the four options can be indicated: CCE-based, VRB-based, eCCE with
interleaving, or eCCE without interleaving. If CCE-based
multiplexing is selected, then one bit can be used to indicate one
of the two reference signals. That is, CRS or DMRS and TxD is
assumed as the transmission mode. Otherwise, if VRB-based or
eCCE-based multiplexing is selected, DMRS may be assumed as the
reference signal and one bit may be used to indicate one of the two
transmission modes, i.e., beamforming or TxD.
[0237] Further considerations regarding DMRS port assignment for
the E-PDCCH will now be provided. In some embodiments, similar to
the legacy PDCCH, an E-PDCCH can be transmitted on an aggregation
of one or several consecutive eCCEs, which may be indicated by
E-PDCCH formats. As shown in Table 4, multiple E-PDCCH formats can
be supported, and this may provide enough flexibility between
performance and resources. As shown in FIG. 41, the eCCEs available
in an E-PDCCH region can have an index from 0 to N_eCCE-1, i.e.,
{eCCE.sub.0, eCCE.sub.1, . . . , eCCE.sub.N.sub.eCCE.sub.-1}, where
N_eCCE is the total number of eCCEs in an E-PDCCH region configured
for the UE. An E-PDCCH consisting of L consecutive eCCEs, which is
also called aggregation level L, may only start at an eCCE
fulfilling i mod L=0, where i is the eCCE index.
TABLE-US-00005 TABLE 4 Example of E-PDCCH formats E-PDCCH format
Number of eCCEs 0 1 1 2 2 4 3 8
[0238] In one embodiment, a UE can monitor a set of E-PDCCH
candidates for control information in every non-DRX subframe, where
monitoring implies attempting to decode each of the E-PDCCHs in the
set according to all the monitored DCI formats. A search space is
defined for each UE, which includes a set of E-PDCCH candidates
with different aggregation levels in the range of {1, 2, 4, 8}.
[0239] The starting eCCE position of an E-PDCCH candidate for a UE
could be linked to its UE ID, i.e., RNTI, and the subframe index.
When an UE is configured to monitor the E-PDCCH, it can determine
the starting eCCE position of each E-PDCCH candidate first, and
then it will try to decode each of the E-PDCCH candidates.
[0240] One difference between decoding a legacy PDCCH and decoding
an E-PDCCH is related to the reference signals. For a PDCCH, CRS
may be used for channel estimation, while for eCCE, DMRS ports may
be used.
[0241] There can be generally two ways to assign the DMRS ports to
eCCEs; one is explicit and the other is implicit. In the case of
explicit assignment, RRC signaling can be used to tell a UE which
DMRS port or ports to use for E-PDCCH decoding. In this approach,
the same DMRS port or ports can be used by a UE during the
configuration. A drawback of this approach is that UEs assigned
with the same DMRS port or ports cannot be scheduled to transmit an
E-PDCCH on the same PRBs. This could introduce some scheduling
constraints and thus prevent efficient use of the eCCE
resources.
[0242] In the case of implicit assignment, a DMRS port can be
linked to the eCCE resources. For example, when an UE is trying to
decode an E-PDCCH on an eCCE, the UE may automatically know which
DMRS port it should use to decode the eCCE. Some implicit ways of
signaling DMRS ports will now be described.
[0243] The assignment of DMRS to eCCE may need to consider a number
of requirements, such as whether such an assignment is implicit or
explicit and the support of SU-MIMO and MU-MIMO. A goal may be to
provide enough flexibility and yet maximize the usage of the DMRS
ports.
[0244] In the following description, it is assumed that there are
four DMRS ports in one PRB pair as well, namely DMRS port 7-10. It
should be noted that the DMRS ports mentioned here are transmitted
in each PRB pair containing the eCCEs allocated to an UE.
Considering that multiple eCCEs could be allocated to one E-PDCCH,
in which one DMRS port is enough to decode the E-PDCCH, an implicit
signaling of the DMRS port for decoding such an E-PDCCH could be
that, for aggregation level L=1, i.e., if one eCCE,
eCCE.sub.m(m.epsilon.{0, 1, . . . , N.sub.eCCE-1}) is allocated to
an E-PDCCH, the DMRS port could be allocated as follows:
DMRS port number=m mod M.sub.eCCE+7
where M.sub.eCCE is the number of eCCEs in a PRB pair, which could
be four, for example. With this implicit assignment rule, if each
E-PDCCH is allocated with one eCCE, then the association between
DMRS port and corresponding eCCE could be as shown in FIG. 42,
where each eCCE is associated with a distinct DMRS port.
[0245] For aggregation level L>=2, i.e., if a set of
{eCCE.sub.m, eCCE.sub.m+1, . . . , eCCE.sub.m+L-1} are allocated to
an E-PDCCH, where m.epsilon.{0, 1, . . . , N.sub.eCCE-1} and m mod
L=0, the DMRS ports could be assigned as
DMRS port number=f(m,m+1, . . . ,m+L-1)mod M.sub.eCCE+7
where the aggregation level L can be, for example, 1, 2, 4, 8, . .
. , 2.sup.n, wherein n is an integer. f( . . . ) is a function of
eCCE indices allocated to an E-PDCCH.
[0246] At least two options are available for implicit DMRS port
signaling. In a first option, the max( . . . ) function is used in
the above implicit association to derive the DMTS port as
follows:
DMRS_port = max ( m , m + 1 , , , , m + L - 1 ) mod M eCCE + 7 = (
m + l - 1 ) mod M eCCE + 7 ##EQU00005##
where the aggregation level L can be, for example, 1, 2, 4, 8, . .
. , 2.sup.n, wherein n is an integer. m is the eCCE index,
m.epsilon.{0, 1, . . . , N.sub.eCCE-1} and m mod L=0. M.sub.eCCE is
the number of eCCEs in a PRB pair and M.sub.eCCE=4 is assumed in
the following discussion.
[0247] In the case when multiple eCCEs are allocated to the same
E-PDCCH, according to the above relation, one DMRS port may be
assigned, which may correspond to the eCCE with the largest index.
An example for L=2 is shown in FIG. 43 and for L=4 in FIG. 44.
[0248] An example of DMRS port assignments for E-PDCCHs with
different aggregation levels is shown FIG. 45.
[0249] When L>=2, if SU-MIMO with two layers is supported for
E-PDCCH transmission, then the above formula could be extended to
include both layers:
DMRS_port k = max ( m , m + 1 , , , , m + L - 1 ) mod M eCCE + 6 +
k - 1 = ( m + L - 1 ) mod M eCCE + 5 + k ##EQU00006##
where DMRS_port.sup.k is the DMRS port for layer k, k=1, 2. The
aggregation level L can be, for example, 1, 2, 4, 8, . . . ,
2.sup.n, wherein n is an integer. m is the eCCE index,
m.epsilon.{0, 1, . . . , N.sub.eCCE-1} and m mod L=0. M.sub.eCCE is
the number of eCCEs in a PRB pair and M.sub.eCCE=4 is assumed in
the following discussion. An example is shown in FIG. 46, where
two-layer SU-MIMO transmission is performed by all three
E-PDCCHs.
[0250] It can be seen that, in the situation where there is only
one eCCE assigned to an E-PDCCH, it may be difficult to assign
different orthogonal DMRS ports for different layers according to
the implicit DMRS assignment rule, and therefore, SU-MIMO
transmission may not be scheduled.
[0251] Multi-user MIMO (MU-MIMO) may also be supported for E-PDCCH
transmission. That is, two or more UEs may share or partially share
the same eCCE or eCCEs for E-PDCCH transmission. The same DMRS port
assignment rule can be used, and the MU-MIMO operation is
transparent to a UE. That is, a UE may not be aware of the eCCE
sharing with other UEs. An example is shown in FIG. 47, where eCCE2
is shared by both E-PDCCH3 and E-PDCCH5. Similarly, eCCE4 and eCCE5
are shared by E-PDCCH4 and E-PDCCH6, and eCCE6 is shared by
E-PDCCH4 and E-PDCCH7.
[0252] In a second option for implicit DMRS port signaling, min( .
. . ) could be used to derive the DMRS ports as follows:
DMRS_port = min ( m , m + 1 , , , , m + L - 1 ) mod M eCCE + 7 = (
m ) mod M eCCE + 7 ##EQU00007##
where the aggregation level L can be, for example, 1, 2, 4, 8, . .
. , 2.sup.n, wherein n is an integer. m is the eCCE index,
m.epsilon.{0, 1, . . . , N.sub.eCCE-1} and m mod L=0. M.sub.eCCE is
the number of eCCEs in a PRB pair and M.sub.eCCE=4 is assumed in
the following discussion.
[0253] For this case, if multiple eCCEs are allocated to one
E-PDCCH, the DMRS port corresponding to the smallest eCCE index
could be used for decoding the E-PDCCH.
[0254] An example for L=2 is shown in FIG. 48. Compared to FIG. 43,
it can be seen that DMRS port #7 is used for E-PDCCH1 and E-PDCCH3
instead of DMRS port #8. Similarly, DMRS port #9 is used for
E-PDCCH2 and E-PDCCH4 instead of DMRS port #10.
[0255] FIG. 49 shows an example of DMRS port allocation for
aggregation level 4, i.e., L=4, with this second option. It can be
seen that DMRS port #7 is allocated to E-PDCCH1 and E-PDCCH2
instead of DMRS port #10 as shown in FIG. 44 for the first
option.
[0256] An example of DMRS port assignments with the second option
for E-PDCCHs with different aggregation levels is shown in FIG.
50.
[0257] To support SU-MIMO transmission for E-PDCCH, the formula can
be extended for L>1 as follows:
DMRS_port k = min ( m , m + 1 , , , , m + L - 1 ) mod M eCCE + 6 +
k = ( m ) mod M eCCE + 6 + k ; k = 1 , 2. ##EQU00008##
where DMRS_port.sup.k is the DMRS port for layer k, k=1, 2. The
aggregation level L can be, for example, 1, 2, 4, 8, . . . ,
2.sup.n, wherein n is an integer. m is the eCCE index,
m.epsilon.{0, 1, . . . , N.sub.eCCE-1} and m mod L=0. M.sub.eCCE is
the number of eCCEs in a PRB pair and M.sub.eCCE=4 is assumed in
the following discussion. An example is shown in FIG. 51.
[0258] MU-MIMO transmission for E-PDCCH could also be scheduled for
this option. An example is shown in FIG. 52, where eCCE3 is shared
by E-PDCCH3 and E-PDCCH5, eCCE5 is shared by E-PDCCH4 and E-PDCCH6,
and eCCE6 and eCCE7 are shared by E-OPDCCH4 and E-PDCCH7. Compared
with FIG. 47, it can be seen that the eCCEs used for pairing two
E-PDCCHs are different. This is because the implicit rules for DMRS
assignment that need to be followed to assign different DMRS ports
for each E-PDCCH are different.
[0259] A comparison between the first and second options for
implicit DMRS port signaling is now provided. As described above,
the two options can be used as implicit signaling rules to
associate a DMRS port for decoding an E-PDCCH. They can also be
used to support SU-MIMO and MU-MIMO transmission of an E-PDCCH.
There are some subtle differences between these two options. One
example is shown in FIG. 53, where in MU-MIMO transmission of two
E-PDCCHs, E-PDCCH1 contains two eCCEs (i.e., aggregation level 2)
and E-PDCCH2 contains one eCCE (i.e., aggregation level 1). If the
implicit rule in the first option is used, E-PDCCH2 could be
scheduled on eCCE0 and could use DMRS port 7. However, for the
second option, as DMRS port 7 is already used for E-PDCCH1,
E-PDCCH2 can only be scheduled on eCCE1 and use DMRS port 8. As for
AL=1, the E-PDCCH candidates may start from eCCE0. The second
option may require the UE with E-PDCCH2 to conduct blind decoding
on eCCE0 first and then on eCCE1, resulting in one more blind
decoding in order to detect its E-PDCCH on eCCE1. In the case of
the first option, E-PDCCH2 would be decoded on eCCE0. Therefore, it
seems that the first option may be better than the second
option.
[0260] In some embodiments, other methods can be used for
allocating DMRS ports. Assume that N.sub.eCCE is the total number
of eCCEs configured in a subframe for a UE and that L is the
aggregation level. In addition, assume that P.sub.L is the number
of E-PDCCH candidates at the aggregation level L. The indices of
eCCEs {eCCE.sub.m, eCCE.sub.m+1, . . . , eCCE.sub.m+L-1} contained
in the E-PDCCH candidate p (p=0, 1, . . . , P.sub.L-1) at the
aggregation level L in subframe k are given by:
m=L(Y.sub.k+p)mod .left brkt-bot.N.sub.eCCE/L.right brkt-bot.
where Y.sub.k=(AY.sub.k-1) mod D, Y.sub.k-1=n.sub.RNTI,
A=n.sub.RNTI, A=39827, D=65537 k=.left brkt-bot..sub.s/2.right
brkt-bot.. n.sub.RNTI is the UE ID, i.e., RNTI, and n.sub.s
(n.sub.s=0, 1, . . . , 19) is the slot number.
[0261] For aggregation L>1, a DMRS port associated with an
E-PDCCH can be derived by a combination of E-PDCCH resource and UE
configuration as follows:
DMRS port#=m mod(M.sub.eCCE)+7+P.sub.offset
where P.sub.offset.epsilon.{0, 1} can be either implicitly or
explicitly signaled to a UE.
[0262] If P.sub.offset=0 is configured, for L=2, either DMRS port 7
or port 9 would be allocated to an E-PDCCH, depending on the
staring eCCE location of the E-PDCCH in a PRB pair, i.e., the value
of m mod(M.sub.eCCE). On the other hand, if P.sub.offset=1 is
configured, then either DMRS port 8 or port 10 would be allocated
to an E-PDCCH candidate. This is shown in FIG. 58. Note that the
allocation for P.sub.offset=0 is equivalent to the first option
discussed above, and the allocation for P.sub.offset=1 is
equivalent to the second option discussed above.
[0263] For L=4 and L=8, the allocation is shown in FIG. 59 and FIG.
60, respectively. It can be seen that either DMRS port 7 or port 8
is allocated, depending on whether P.sub.offset=0 or
P.sub.offset=1.
[0264] There can be a number of alternatives to determine and/or
signal the UE configuration P.sub.offset. In a first alternative,
P.sub.offset (or 7+P.sub.offset) is explicitly signaled to a UE by
RRC. In this case, the eNB directly controls the DMRS port
assignment to a UE, and the assignment can be changed
semi-statically.
[0265] In a second alternative, P.sub.offset is implicitly derived
from UE ID as follows:
P.sub.offset=n.sub.RNTI mod 2
where n.sub.RNTI is assigned by the eNB. In this alternative, there
is no additional signaling required. In certain cases, since the
assignment is linked to the RNTI, the assignment may not be changed
after the RNTI is assigned. Some UEs may not be paired for MU-MIMO
transmission for E-PDCCH if they have the same P.sub.offset
value.
[0266] In a third alternative P.sub.offset is implicitly derived
from Y.sub.k as follows:
P.sub.offset=Y.sub.k mod 2
This option may not require additional signaling. Furthermore,
since Y.sub.k changes from subframe to subframe, the DMRS port
assignment can also change from subframe to subframe. If two UEs
cannot be paired in one subframe for MU-MIMO transmission for
E-PDCCH, they can be paired for such operation in a different
subframe, where they have different P.sub.offset values and their
search spaces overlap. This may be an improvement to the second
alternative.
[0267] Note that, instead of signaling a value of P.sub.offset that
corresponds to a DMRS port number, a value of P.sub.offset may be
signaled to a UE to indicate the pre-defined set of DMRS ports. For
example, with P.sub.offset=0 and P.sub.offset=1, two sets of DMRS
ports can be defined at each aggregation level, and one bit can be
used to signal which set is to be used by a UE for E-PDCCH
transmission. For aggregation level two, the two sets of DMRS ports
are {7, 9} and {8, 10}. One of the two sets can be signaled to a UE
by using one bit. If the bit is zero, {7, 9} is selected; otherwise
{8, 10} is selected. One of the two DMRS ports within the selected
set is then assigned to an E-PDCCH according to the resource
location of the E-PDCCH.
[0268] Similarly, for an aggregation level greater than two, the
two sets of DMRS ports are {7} and {8}. In this case, each set
contains only one port. One of the two sets can be signaled to a UE
by using the same one bit. If the bit is zero, {7} is selected;
otherwise if the bit equals to one, {8} is selected.
[0269] An example of DMRS port allocation based on the third
alternative is shown in FIG. 61, where for aggregation levels
greater than one, the DMRS port allocation depends on Y.sub.k.
[0270] In summary, for an aggregation level greater than one, three
UE configurations can be used to determine the DMRS port
association with a corresponding an E-PDCCH transmission in
conjunction with an E-PDCCH resource. In a first alternative, the
UE configuration is semi-statically signaled to a UE through RRC
signaling, in a second alternative, the UE configuration is derived
from the UE's RNTI, and in a third alternative, the UE
configuration is derived from the UE's RNTI and subframe index.
[0271] Based on the above implicit DMRS signaling rules, the eNB
could schedule E-PDCCH transmission on different eCCEs, and also
use the associated DMRS ports for its transmission. That means the
same beamforming vector could be applied to all eCCEs assigned to
the E-PDCCH and corresponding DMRS ports. SU-MIMO and MU-MIMO
transmission of the E-PDCCH could also be scheduled. It should be
noted that, as seen from previous examples, SU-MIMO and MU-MIMO
transmission of the E-PDCCH may not always be able to be scheduled
on every eCCE, as orthogonal DMRS ports within a resource block or
resource block pair may not be available for that purpose due to
limited DMRS port resources and the implicit DMRS allocation rules.
But it is believed that loss due to such a limitation could be
small. In general, there may be a compromise between complexity in
DMRS port signaling and flexibility in scheduling the E-PDCCH. The
options discussed above can achieve such a compromise in a
favorable manner.
[0272] At the UE side, the UE may need to decode the E-PDCCH using
the associated DMRS port inferred by the implicit rule. The UE is
not aware of how many eCCEs are used for its E-PDCCH. That is, the
UE may not know the AL of the E-PDCCH and whether or not MU-MIMO
transmission is used for its E-PDCCH. The UE may need to try to
decode all candidate E-PDCCHs at every aggregation level. For
SU-MIMO transmission of the E-PDCCH, the UE could be configured
semi-statically or could find out this information blindly by
trying to decode the E-PDCCH in both cases, i.e., when SU-MIMO is
used or when SU-MIMO is not used.
[0273] All the E-PDCCH candidates at an aggregation level form a
search space for a UE at the aggregation level. The size of each
search space, i.e., the number of E-PDCCH candidates, may be
predefined. For example, six E-PDCCH candidates may be specified
for aggregation level 1, four candidates may be specified for
aggregation level 2, and two candidates may be specified for
aggregation levels 4 and 8. The size of the search spaces
determines the total number of blind decodings a UE may need to
perform in order to receive an E-PDCCH. FIG. 54 illustrates an
example of a search space of an E-PDCCH for a UE at different ALs.
Option 1 is applied for DMRS port assignment. There can be six
E-PDCCH candidates for AL=1, four E-PDCCH candidates for AL=2, and
two E-PDCCH candidates for AL=4 and AL=8. The UE could search such
candidates and use a corresponding DMRS port to decode its E-PDCCH
based on the implicit rule.
[0274] To facilitate the searching and better utilize the implicit
DMRS port assignment rule, some options are reiterated for
consideration here. The starting position of an E-PDCCH candidate
should align with the integer multiples of eCCEs contained in its
AL. Namely, the starting eCCE index m should satisfy m.epsilon.{0,
1, . . . , N.sub.eCCE-1} and m mod L=0. If an E-PDCCH is
transmitted across multiple PRB pairs, for example, for AL=8,
either the same or different precodings may be used for the DMRS
port and the E-PDCCH in different PRB pairs. The option of using
the same precoding may improve channel estimation under a flat
fading channel. Either the same precoding vector or different
precoding vectors may be assumed by the UE. When orthogonal DMRS
ports are not available, MU-MIMO transmission of E-PDCCH could be
supported for two E-PDCCHs with the same DMRS port but with
different DMRS scrambling sequences. The seed for different DMRS
scrambling sequences could be signaled to the UE with UE-specific
higher layer signaling in a semi-static manner. The implicit DMRS
port assignment may be applicable to localized transmission only
where consecutive eCCEs are allocated to an E-PDCCH. For
distributed transmission, non-consecutive eCCEs may be allocated to
an E-PDCCH. In this case, due to the limitation of the DMRS
resources and characteristics of the distributed E-PDCCH
transmission, it may be beneficial to support only a single layer
E-PDCCH transmission. For the distributed E-PDCCH transmission
based on the eCCE (namely, the smallest unit of distributed E-PDCCH
transmission is one eCCE), a separate DMRS port can be used for
each eCCE of an E-PDCCH. For example, the DMRS port for eCCE#m
allocated to an E-PDCCH can be derived as follows:
DMRS_port_for_eCCEm=(m)mod M.sub.eCCE+7
where m is the eCCE index. For example, if an E-PDCCH consists of
four eCCEs {eCCE0, eCCE5, eCCE10, eCCE15}, then the corresponding
DMRS ports can be obtained as DMRS ports {7, 8, 9, 10},
respectively. For MU-MIMO transmission of the E-PDCCH, different
DMRS scrambling sequences can be used for different E-PDCCHs. The
DMRS scrambling sequence could be signaled to the UE with
UE-specific higher layer signaling in a semi-static manner.
[0275] In summary, implicit DMRS port assignment may be used to
assign a DMRS port for each E-PDCCH. The DMRS ports assigned to an
E-PDCCH are a function of eCCEs assigned to the E-PDCCH. The DMRS
ports assigned to the E-PDCCH could be associated to the largest
assigned eCCE index in a PRB pair or could be associated to the
smallest assigned eCCE index in a PRB pair. SU-MIMO and MU-MIMO
transmission for E-PDCCH could be supported with orthogonal DMRS
ports assigned to different layers of the E-PDCCH from the same UE
or different E-PDCCHs from different UEs.
[0276] Referring back to FIGS. 38 and 39, for the eCCE definitions
shown in FIG. 38 and FIG. 39, the DMRS for an eCCE can be only
mapped to the DMRS REs within the time and frequency range of the
eCCE. An example is shown in FIG. 38.
[0277] In one embodiment, whether DMRS port 7 or port 8 is used by
a UE for E-PDCCH demodulation can be semi-statically signaled to
the UE by the eNB, for example using RRC signaling. The scrambling
ID associated with the DMRS port can also be semi-statically
signaled to the UE. The same scrambling ID can be used for all UEs
with a cell.
[0278] The benefits and features of this approach can include the
following: Only DMRS ports 7 and 8 are needed for E-PDCCH
demodulation purposes; thus DMRS overhead is reduced compared to
cases where DMRS ports 7 to 10 are used. The same DMRS port may be
assumed for all eCCEs allocated to the same UE. UEs with the same
DMRS port can still be multiplexed within the same PRB pair, as
different DMRS REs are used by different UEs. Therefore, there is
no scheduling constraint within a PRB pair in terms of which UEs
can be scheduled together. Any UEs can be scheduled within a PRB
pair. MU-MIMO can be supported for two UEs assigned with different
DMRS ports. For example, if DMRS port 7 is assigned to UE1 and DMRS
port 8 is assigned to UE2, then the two UEs can be paired to
perform MU-MIMO on the same eCCEs. MU-MIMO with orthogonal ports
can be supported for all aggregation levels and is not limited to
certain aggregation levels. SU-MIMO can be supported by assigning
both of the DMRS ports to the same UE. In this case, the UE may
always assume two-layer transmission. Each UE performs rate
matching based on the available REs in the allocated eCCEs by
assuming its own CSI-RS configuration. Therefore, there is no
ambiguity between the eNB and the UE.
[0279] In Rel-8, PUCCH resources for acknowledgements and negative
acknowledgements (ACK/NACK) can be derived based at least in part
on the first CCE of the PDCCH that schedules the corresponding
PDSCH. In Rel-11, with the introduction of the E-PDCCH, the PUCCH
resources for ACK/NACK can be based on the eCCE, which is the
smallest control channel element for the E-PDCCH. However, if
MU-MIMO transmission is supported for E-PDCCH transmission, such an
implicit mapping mechanism may have some issues. For example, as
shown in FIG. 47, where MU-MIMO transmission of an E-PDCCH is
illustrated, E-PDCCH3 and E-PDCCH5 both use eCCE2 as their first
eCCE. Therefore, if a Rel-8 implicit mapping rule is used, the
PUCCH resources for ACK/NACK for these two UEs can be the same. A
similar situation may apply to E-PDCCH4 and E-PDCCH6 in the same
figure, as they both use eCCE4 as the first eCCE.
[0280] To avoid this issue, the implicit mapping rule between a
PUCCH resource for ACK/NACK and the first CCE index may need to be
modified. In an embodiment, the PUCCH resource for ACK/NACK can be
linked to the eCCE index whose corresponding DMRS port is used for
E-PDCCH decoding. In general, if a set of {eCCE.sub.m,
eCCE.sub.m+1, . . . , eCCE.sub.m+L-1} are allocated to an E-PDCCH,
where m.epsilon.{0, 1, . . . , N.sub.eCCE-1} and m mod L=0, DMRS
ports for E-PDCCH decoding may be determined by the following
equation:
DMRS port number=f(m,m+1, . . . ,m+L-1)mod M.sub.eCCE+7
[0281] The PUCCH resource n.sub.PUCCH.sup.(1,p) on antenna port p
for ACK/NACK transmission using PUCCH format 1a/1b can be derived
based on the corresponding absolute eCCE index as described
below:
n.sub.PUCCH.sup.(1,p=p0)=f(m,m+1, . . . ,
m+L-1)+N.sub.PUCCH.sup.offset
where the aggregation level L can be, for example, 1, 2, 4, 8, . .
. , 2.sup.n, wherein n is an integer. N.sub.PUCCH.sup.offset is an
offset configured by a higher layer.
[0282] The above operation is performed because the DMRS ports
derived from the above formula would be different for different
E-PDCCHs paired for MU-MIMO, and their corresponding eCCE indices
used in deriving the DMRS ports are different.
[0283] To be more specific, in one example, a DMRS port can be
derived as follows:
DMRS_port = max ( m , m + 1 , , , , m + L - 1 ) mod M eCCE + 7 = (
m + L - 1 ) mod M eCCE + 7 ##EQU00009##
[0284] Then, the PUCCH resource for ACK/NACK can be derived based
on a corresponding f( . . . ) function as described below:
n.sub.PUCCH.sup.(1,p=p0)=m+L-1+N.sub.PUCCH.sup.offset
m.epsilon.{0,1, . . . ,N.sub.eCCE-1} and m mod L=0.
[0285] FIG. 55 shows an example where a number of E-PDCCHs are
paired for MU-MIMO transmission. Each E-PDCCH has an eCCE which
could be used to generate the PUCCH ACK/NACK. The eCCE used to
derive the PUCCH ACK/NACK resource index for each E-PDCCH is the
one used to derive the DMRS port assignment for the E-PDCCH and may
not necessarily be the first eCCE of the E-PDCCH. In the example,
the allocated eCCE with the highest index is used to derive the
PUCCH ACK/NACK resource index for each E-PDCCH. From the figure, it
can be seen that even with MU-MIMO transmission, the eCCEs used to
derive PUCCH ACK/NACK resources do not overlap with each other.
Therefore, the issue that two UEs may generate the same resource
for their PUCCH ACK/NACK signals if legacy mapping rules are used
may be avoided.
[0286] In another example, a DMRS port can be derived as
follows:
DMRS_port = min ( m , m + 1 , , , , m + L - 1 ) mod M eCCE + 7 = (
m ) mod M eCCE + 7 ##EQU00010##
[0287] Then, the PUCCH resource for ACK/NACK can be derived based
on a corresponding absolute eCCE index as described below:
n.sub.PUCCH.sup.(1,p=p0)=m+N.sub.PUCCH.sup.offset
[0288] In the situation of a MU-MIMO transmission of an E-PDCCH
where the same DMRS port but different scrambling identities
(SCIDs) are assigned to two E-PDCCHs, the eCCEs used to generate
the PUCCH ACK/NACK resource can be linked to the eCCEs generated
above plus an offset. For example, such offset can be the SCID to
generate the different sequences, which can be signaled to the UE
semi-statically using higher layer signaling. For example,
n.sub.PUCCH.sup.(1,p=p0)=f(m,m+1, . . .
,m+L-1)+N.sub.PUCCH.sup.offset+SCID [0289] SCID={0, 1} is the seed
to generate the DMRS sequence.
[0290] In this situation, the eNB should properly schedule E-PDCCH
transmission to avoid any usage of f(m, m+1, . . . , m+L-1)+1 as an
eCCE index for PUCCH ACK/NACK resource generation.
[0291] For a two antenna port transmission case, the PUCCH resource
for antenna port p=p1 is given by:
n.sub.PUCCH.sup.(1,p=p1)=n=n.sub.PUCCH.sup.(1,p=p0)+1
[0292] Again, the eNB should try to avoid PUCCH ACK/NACK resource
collisions by proper E-PDCCH scheduling. In this case, for example,
the eNB may not schedule two aggregation level 1 E-PDCCHs in two
consecutive eCCEs.
[0293] In summary, in some embodiments, for E-PDCCH transmission,
the eCCE used to generate the PUCCH ACK/NACK resource is a function
of eCCE indices assigned for the E-PDCCH. The eCCE used to generate
the PUCCH ACK/NACK resource may be the one used to generate the
DMRS assignment for the E-PDCCH decoding. Alternatively or
additionally, the eCCE used to generate the PUCCH ACK/NACK resource
may be the one used to generate the DMRS assignment for the E-PDCCH
demodulation, plus the SCID, the seed to generate the DMRS
sequence.
[0294] Common control channels can also be configured and
transmitted in an E-PDCCH. Similar to the legacy PDCCH design, the
common control channels can be transmitted together with
UE-specific control channels over an E-PDCCH region with
distributed transmission. This is because common control channels
are used to carry common messages for multiple UEs and therefore
may not benefit from beamforming transmission. To enhance the
performance of common control channels, distributed transmission
may be used.
[0295] Similar to the legacy PDCCH design, a subset of the
resources in the E-PDCCH region configured for distributed
transmission can be used for common control channel transmission.
Common search spaces can be defined over the subset of such
resources for UEs to perform blind decoding of common control
channels. UE-specific search spaces can also be defined in the same
region for some or all UEs, and a UE can be configured through RRC
signaling regarding whether or not to use blind decoding to detect
UE-specific control channels in the region. As a result, both an
E-PDCCH region with localized transmission and an E-PDCCH region
with distributed transmission can be configured, and UE-specific
search spaces can be defined in each of the two regions.
[0296] For UEs that are configured for distributed transmission of
the E-PDCCH, the UE-specific E-PDCCH region with distribution
transmission can be viewed as a UE-specific search space (USS) with
distributed transmission. Such UE-specific search spaces along with
common search spaces in the distributed transmission region for the
E-PDCCH can be REG-based or eCCE-based. The REG-based transmission
may be similar to that designed in Rel-8, where a REG is the
smallest unit for resource mapping of control channels. The
eCCE-based transmission may use an eCCE as the smallest unit to
transmit each control channel.
[0297] At the eNB side, the transmission procedure of common
control channels and UE-specific control channels with distributed
transmission is illustrated in FIG. 56, which can be summarized as
follows: The common control channels and UE-specific control
channels may be placed in a queue. The common control channels can
be placed at the start of the queue, and the UE-specific control
channels can be placed after them. Alternatively, the available
eCCEs may be arranged in a queue starting from eCCE index 0. The
resources for the common control channels may be allocated in the
eCCEs at the start of the queue, and the number of eCCEs for that
purpose may be predefined. The resources for UE-specific control
channels at a subframe may be allocated to eCCEs determined by a UE
ID (e.g., an RNTI) and the subframe number. Thus, the possible
eCCEs used for UE-specific control channels may overlap with the
eCCEs for the common control channels. A common control channel, if
present, may be allocated first, and a UE-specific control channel
may be allocated after all common control channels have been
allocated. It is possible that a UE-specific control channel may
not be allocated in a subframe, as some or all of the possible
eCCEs that could be allocated for the UE-specific control channel
may have already been allocated to other common or UE-specific
control channels. The queue of eCCEs can go through an interleaving
process, which can change the order of eCCEs in the queue. The
interleaved eCCEs can be mapped to physical resources, which can be
allocated in multiple sub-bands distributed in the system
bandwidth.
[0298] At the UE side, the receiving procedure of common control
channels and UE-specific control channels with distributed
transmission is illustrated in FIG. 57, which is the reverse
procedure of that at the eNB. The procedure can be summarized as
follows: The physical eCCEs carrying common control channels and
UE-specific control channels with distributed transmission can be
mapped to logical eCCEs. The obtained queue of eCCEs can go through
a de-interleaving process, which is the reverse process of the
interleaving process at the eNB. The de-interleaved eCCEs in the
queue can be divided into CSS and USS, where CSS is at the
beginning of the queue, while USS can cover all the eCCEs. The UE
can search for the common control channels in the CSS and for
UE-specific control channels in the USS. The starting position of a
UE-specific control channel can be determined based on UE ID and
subframe index, and the aggregation level can be determined through
blind decoding.
[0299] In summary, in the E-PDCCH, eCCEs based on common control
channels and UE-specific control channels with distributed
transmission can be interleaved and mapped to physical eCCEs
distributed across the system bandwidth.
[0300] The concepts described above may be implemented by a network
element. A simplified network element is shown with regard to FIG.
28. In FIG. 28, network element 3110 includes a processor 3120 and
a communications subsystem 3130, where the processor 3120 and
communications subsystem 3130 cooperate to perform the methods
described above.
[0301] Further, the above may be implemented by a UE. One exemplary
device is described below with regard to FIG. 29. UE 3200 is
typically a two-way wireless communication device having voice and
data communication capabilities. UE 3200 generally has the
capability to communicate with other computer systems on the
Internet. Depending on the exact functionality provided, the UE may
be referred to as a data messaging device, a two-way pager, a
wireless e-mail device, a cellular telephone with data messaging
capabilities, a wireless Internet appliance, a wireless device, a
mobile device, or a data communication device, as examples.
[0302] Where UE 3200 is enabled for two-way communication, it may
incorporate a communication subsystem 3211, including a receiver
3212 and a transmitter 3214, as well as associated components such
as one or more antenna elements 3216 and 3218, local oscillators
(LOs) 3213, and a processing module such as a digital signal
processor (DSP) 3220. As will be apparent to those skilled in the
field of communications, the particular design of the communication
subsystem 3211 will be dependent upon the communication network in
which the device is intended to operate.
[0303] Network access requirements will also vary depending upon
the type of network 3219. In some networks network access is
associated with a subscriber or user of UE 3200. A UE may require a
removable user identity module (RUIM) or a subscriber identity
module (SIM) card in order to operate on a network. The SIM/RUIM
interface 3244 is normally similar to a card-slot into which a
SIM/RUIM card can be inserted and ejected. The SIM/RUIM card can
have memory and hold many key configurations 3251, and other
information 3253 such as identification, and subscriber related
information.
[0304] When required network registration or activation procedures
have been completed, UE 3200 may send and receive communication
signals over the network 3219. As illustrated in FIG. 29, network
3219 can consist of multiple base stations communicating with the
UE.
[0305] Signals received by antenna 3216 through communication
network 3219 are input to receiver 3212, which may perform such
common receiver functions as signal amplification, frequency down
conversion, filtering, channel selection and the like. Analog to
digital (A/D) conversion of a received signal allows more complex
communication functions such as demodulation and decoding to be
performed in the DSP 3220. In a similar manner, signals to be
transmitted are processed, including modulation and encoding for
example, by DSP 3220 and input to transmitter 3214 for digital to
analog (D/A) conversion, frequency up conversion, filtering,
amplification and transmission over the communication network 3219
via antenna 3218. DSP 3220 not only processes communication
signals, but also provides for receiver and transmitter control.
For example, the gains applied to communication signals in receiver
3212 and transmitter 3214 may be adaptively controlled through
automatic gain control algorithms implemented in DSP 3220.
[0306] UE 3200 generally includes a processor 3238 which controls
the overall operation of the device. Communication functions,
including data and voice communications, are performed through
communication subsystem 3211. Processor 3238 also interacts with
further device subsystems such as the display 3222, flash memory
3224, random access memory (RAM) 3226, auxiliary input/output (I/O)
subsystems 3228, serial port 3230, one or more keyboards or keypads
3232, speaker 3234, microphone 3236, other communication subsystem
3240 such as a short-range communications subsystem and any other
device subsystems generally designated as 3242. Serial port 3230
can include a USB port or other port known to those in the art.
[0307] Some of the subsystems shown in FIG. 29 perform
communication-related functions, whereas other subsystems may
provide "resident" or on-device functions. Notably, some
subsystems, such as keyboard 3232 and display 3222, for example,
may be used for both communication-related functions, such as
entering a text message for transmission over a communication
network, and device-resident functions such as a calculator or task
list.
[0308] Operating system software used by the processor 3238 may be
stored in a persistent store such as flash memory 3224, which may
instead be a read-only memory (ROM) or similar storage element (not
shown). Those skilled in the art will appreciate that the operating
system, specific device applications, or parts thereof, may be
temporarily loaded into a volatile memory such as RAM 3226.
Received communication signals may also be stored in RAM 3226.
[0309] As shown, flash memory 3224 can be segregated into different
areas for both computer programs 3258 and program data storage
3250, 3252, 3254 and 3256. These different storage types indicate
that each program can allocate a portion of flash memory 3224 for
their own data storage requirements. Processor 3238, in addition to
its operating system functions, may enable execution of software
applications on the UE. A predetermined set of applications that
control basic operations, including at least data and voice
communication applications for example, will normally be installed
on UE 3200 during manufacturing. Other applications could be
installed subsequently or dynamically.
[0310] Applications and software may be stored on any computer
readable storage medium. The computer readable storage medium may
be a tangible or in transitory/non-transitory medium such as
optical (e.g., CD, DVD, etc.), magnetic (e.g., tape) or other
memory known in the art.
[0311] One software application may be a personal information
manager (PIM) application having the ability to organize and manage
data items relating to the user of the UE such as, but not limited
to, e-mail, calendar events, voice mails, appointments, and task
items. Naturally, one or more memory stores may be available on the
UE to facilitate storage of PIM data items. Such PIM application
may have the ability to send and receive data items, via the
wireless network 3219. Further applications may also be loaded onto
the UE 3200 through the network 3219, an auxiliary I/O subsystem
3228, serial port 3230, short-range communications subsystem 3240
or any other suitable subsystem 3242, and installed by a user in
the RAM 3226 or a non-volatile store (not shown) for execution by
the processor 3238. Such flexibility in application installation
increases the functionality of the device and may provide enhanced
on-device functions, communication-related functions, or both. For
example, secure communication applications may enable electronic
commerce functions and other such financial transactions to be
performed using the UE 3200.
[0312] In a data communication mode, a received signal such as a
text message or web page download will be processed by the
communication subsystem 3211 and input to the processor 3238, which
may further process the received signal for output to the display
3222, or alternatively to an auxiliary I/O device 3228.
[0313] A user of UE 3200 may also compose data items such as email
messages for example, using the keyboard 3232, which may be a
complete alphanumeric keyboard or telephone-type keypad, among
others, in conjunction with the display 3222 and possibly an
auxiliary I/O device 3228. Such composed items may then be
transmitted over a communication network through the communication
subsystem 3211.
[0314] For voice communications, overall operation of UE 3200 is
similar, except that received signals may typically be output to a
speaker 3234 and signals for transmission may be generated by a
microphone 3236. Alternative voice or audio I/O subsystems, such as
a voice message recording subsystem, may also be implemented on UE
3200. Although voice or audio signal output is preferably
accomplished primarily through the speaker 3234, display 3222 may
also be used to provide an indication of the identity of a calling
party, the duration of a voice call, or other voice call related
information for example.
[0315] Serial port 3230 in FIG. 29 may normally be implemented in a
personal digital assistant (PDA)-type UE for which synchronization
with a user's desktop computer (not shown) may be desirable, but is
an optional device component. Such a port 3230 may enable a user to
set preferences through an external device or software application
and may extend the capabilities of UE 3200 by providing for
information or software downloads to UE 3200 other than through a
wireless communication network. The alternate download path may for
example be used to load an encryption key onto the device through a
direct and thus reliable and trusted connection to thereby enable
secure device communication. As will be appreciated by those
skilled in the art, serial port 3230 can further be used to connect
the UE to a computer to act as a modem.
[0316] Other communications subsystems 3240, such as a short-range
communications subsystem, is a further optional component which may
provide for communication between UE 3200 and different systems or
devices, which need not necessarily be similar devices. For
example, the subsystem 3240 may include an infrared device and
associated circuits and components or a Bluetooth.TM. communication
module to provide for communication with similarly enabled systems
and devices. Subsystem 3240 may further include non-cellular
communications such as WiFi or WiMAX.
[0317] The UE and other components described above might include a
processing component that is capable of executing instructions
related to the actions described above. FIG. 30 illustrates an
example of a system 3300 that includes a processing component 3310
suitable for implementing one or more embodiments disclosed herein.
The processing component 3310 may be substantially similar to the
processor 3120 of FIG. 28 and/or the processor 3238 of FIG. 29.
[0318] In addition to the processor 3310 (which may be referred to
as a central processor unit or CPU), the system 3300 might include
network connectivity devices 3320, random access memory (RAM) 3330,
read only memory (ROM) 3340, secondary storage 3350, and
input/output (I/O) devices 3360. These components might communicate
with one another via a bus 3370. In some cases, some of these
components may not be present or may be combined in various
combinations with one another or with other components not shown.
These components might be located in a single physical entity or in
more than one physical entity. Any actions described herein as
being taken by the processor 3310 might be taken by the processor
3310 alone or by the processor 3310 in conjunction with one or more
components shown or not shown in the drawing, such as a digital
signal processor (DSP) 3380. Although the DSP 3380 is shown as a
separate component, the DSP 3380 might be incorporated into the
processor 3310.
[0319] The processor 3310 executes instructions, codes, computer
programs, or scripts that it might access from the network
connectivity devices 3320, RAM 3330, ROM 3340, or secondary storage
3350 (which might include various disk-based systems such as hard
disk, floppy disk, or optical disk). While only one CPU 3310 is
shown, multiple processors may be present. Thus, while instructions
may be discussed as being executed by a processor, the instructions
may be executed simultaneously, serially, or otherwise by one or
multiple processors. The processor 3310 may be implemented as one
or more CPU chips.
[0320] The network connectivity devices 3320 may take the form of
modems, modem banks, Ethernet devices, universal serial bus (USB)
interface devices, serial interfaces, token ring devices, fiber
distributed data interface (FDDI) devices, wireless local area
network (WLAN) devices, radio transceiver devices such as code
division multiple access (CDMA) devices, global system for mobile
communications (GSM) radio transceiver devices, universal mobile
telecommunications system (UMTS) radio transceiver devices, long
term evolution (LTE) radio transceiver devices, worldwide
interoperability for microwave access (WiMAX) devices, and/or other
well-known devices for connecting to networks. These network
connectivity devices 3320 may enable the processor 3310 to
communicate with the Internet or one or more telecommunications
networks or other networks from which the processor 3310 might
receive information or to which the processor 3310 might output
information. The network connectivity devices 3320 might also
include one or more transceiver components 3325 capable of
transmitting and/or receiving data wirelessly.
[0321] The RAM 3330 might be used to store volatile data and
perhaps to store instructions that are executed by the processor
3310. The ROM 3340 is a non-volatile memory device that typically
has a smaller memory capacity than the memory capacity of the
secondary storage 3350. ROM 3340 might be used to store
instructions and perhaps data that are read during execution of the
instructions. Access to both RAM 3330 and ROM 3340 is typically
faster than to secondary storage 3350. The secondary storage 3350
is typically comprised of one or more disk drives or tape drives
and might be used for non-volatile storage of data or as an
over-flow data storage device if RAM 3330 is not large enough to
hold all working data. Secondary storage 3350 may be used to store
programs that are loaded into RAM 3330 when such programs are
selected for execution.
[0322] The I/O devices 3360 may include liquid crystal displays
(LCDs), touch screen displays, keyboards, keypads, switches, dials,
mice, track balls, voice recognizers, card readers, paper tape
readers, printers, video monitors, or other well-known input/output
devices. Also, the transceiver 3325 might be considered to be a
component of the I/O devices 3360 instead of or in addition to
being a component of the network connectivity devices 3320.
[0323] In an implementation, a method is provided for operating a
UE in a wireless communication network. The method comprises
sending, by the UE, an ACK/NACK message after receiving data on a
PDSCH scheduled by an E-PDCCH, wherein the sending is from at least
one antenna port and uses at least one physical resource, and
wherein the at least one physical resource is determined based at
least partially on a resource over which the E-PDCCH is received,
and wherein the resource over which the E-PDCCH is received
consists of at least one eCCE.
[0324] In another implementation, a method is provided for
operating an eNB in a wireless communication network. The method
comprises detecting, by the eNB, from a UE, an ACK/NACK message
after a PDSCH scheduled by an E-PDCCH is transmitted to the UE,
wherein the detection of the ACK/NACK is over at least one physical
resource, and wherein the at least one physical resource is
determined based at least partially on a resource over which the
E-PDCCH is transmitted, and wherein the resource over which the
E-PDCCH is transmitted consists of at least one eCCE.
[0325] In another implementation, a method is provided for
operating an eNB in a wireless communication network. The method
comprises determining, by the eNB, an antenna port out of a set of
antenna ports for sending a UE an E-PDCCH, the determining being
based at least partly on a time and frequency resource for the
E-PDCCH and an offset parameter; and sending, by the eNB to the UE,
the E-PDCCH and a demodulation reference signal associated with the
antenna port.
[0326] In another implementation, a method is provided for
operating a UE in a wireless communication network. The method
comprises determining an antenna port of an E-PDCCH candidate based
at least partly on at least one of a time and frequency resource
for the E-PDCCH candidate and an offset parameter; and receiving
the E-PDCCH candidate using a demodulation reference signal
associated with the antenna port.
[0327] The following are incorporated herein by reference for all
purposes: 3GPP Technical Specification (TS) 36.211, 3GPP TS 36.213,
3GPP TS 36.216, 3GPP TS 36.331, and 3GPP TR 36.819.
[0328] The embodiments described herein are examples of structures,
systems or methods having elements corresponding to elements of the
techniques of this application. This written description may enable
those skilled in the art to make and use embodiments having
alternative elements that likewise correspond to the elements of
the techniques of this application. The intended scope of the
techniques of this application thus includes other structures,
systems or methods that do not differ from the techniques of this
application as described herein, and further includes other
structures, systems or methods with insubstantial differences from
the techniques of this application as described herein.
[0329] While several embodiments have been provided in the present
disclosure, it should be understood that the disclosed systems and
methods may be embodied in many other specific forms without
departing from the scope of the present disclosure. The present
examples are to be considered as illustrative and not restrictive,
and the intention is not to be limited to the details given herein.
For example, the various elements or components may be combined or
integrated in another system or certain features may be omitted, or
not implemented.
[0330] Also, techniques, systems, subsystems and methods described
and illustrated in the various embodiments as discrete or separate
may be combined or integrated with other systems, modules,
techniques, or methods without departing from the scope of the
present disclosure. Other items shown or discussed as coupled or
directly coupled or communicating with each other may be indirectly
coupled or communicating through some interface, device, or
intermediate component, whether electrically, mechanically, or
otherwise. Other examples of changes, substitutions, and
alterations are ascertainable by one skilled in the art and could
be made without departing from the spirit and scope disclosed
herein.
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