U.S. patent application number 17/096283 was filed with the patent office on 2021-03-04 for methods, network nodes and user equipments in a wireless network for communicating an epdcch.
The applicant listed for this patent is Telefonaktiebolaget LM Ericsson (publ). Invention is credited to Erik Eriksson, Mattias Frenne, David Hammarwall, George Jongren.
Application Number | 20210068089 17/096283 |
Document ID | / |
Family ID | 48577206 |
Filed Date | 2021-03-04 |
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United States Patent
Application |
20210068089 |
Kind Code |
A1 |
Eriksson; Erik ; et
al. |
March 4, 2021 |
Methods, Network Nodes and User Equipments in a Wireless Network
for Communicating an EPDCCH
Abstract
A network node in a wireless communication network communicates
an enhanced Physical Downlink Control Channel (ePDCCH) to a user
equipment (UE). This begins with the transmission, to the UE, of a
configuration message that indicates the mappings of ePDCCH onto
resource elements for both a first ePDCCH set and a second ePDCCH
set. The mapping for the first ePDCCH set avoids the use of
resource elements already in use by a first type of signal (e.g., a
Cell-Specific Reference Signal or CRS), whereas the mapping for the
second ePDCCH set avoids the use of resource elements in use by a
second type of signal. The choice of an ePDCCH set for transmitting
data to a UE may then be dynamically made in order to avoid
interference caused by the first or second types of signal.
Inventors: |
Eriksson; Erik; (Linkoping,
SE) ; Frenne; Mattias; (Uppsala, SE) ;
Hammarwall; David; (Vallentuna, SE) ; Jongren;
George; (Sundbyberg, SE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Telefonaktiebolaget LM Ericsson (publ) |
Stockholm |
|
SE |
|
|
Family ID: |
48577206 |
Appl. No.: |
17/096283 |
Filed: |
November 12, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15899215 |
Feb 19, 2018 |
10841912 |
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17096283 |
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13885520 |
May 15, 2013 |
9913259 |
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PCT/SE2013/050340 |
Mar 27, 2013 |
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15899215 |
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61707555 |
Sep 28, 2012 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L 5/0053 20130101;
H04W 72/042 20130101; H04L 5/0094 20130101; H04L 5/001 20130101;
H04L 5/0048 20130101 |
International
Class: |
H04W 72/04 20060101
H04W072/04; H04L 5/00 20060101 H04L005/00 |
Claims
1. A method, performed by a user equipment (UE) in a wireless
communication network, for communicating an enhanced Physical
Downlink Control Channel (ePDCCH) with a network node providing
coverage to a serving cell, the method comprising: receiving a
configuration message from the network node, the configuration
message comprising: an indication of a first mapping of the ePDCCH
for the serving cell to resource elements belonging to a first
ePDCCH set, where the ePDCCH is mapped around resource elements of
the first ePDCCH set used for a first Cell-Specific Reference
Signal (CRS), the indication of the first mapping comprising an
indication of at least one of (a) the number of CRS ports for the
first CRS and (b) the CRS frequency shift for the first CRS, and an
indication of a second mapping of the ePDCCH for the serving cell
to resource elements belonging to a second ePDCCH set, where the
ePDCCH is mapped around resource elements of the second ePDCCH set
used for a second CRS, the indication of the second mapping
comprising an indication of at least one of (c) the number of CRS
ports for the second CRS and (d) the CRS frequency shift for the
second CRS; and monitoring ePDCCH candidates in the first ePDCCH
set according to the first mapping and monitoring ePDCCH candidates
in the second ePDCCH set according to the second mapping.
2. The method of claim 1, wherein the configuration message
comprises an indication of an ePDCCH start symbol for the first
ePDCCH set and an indication of an ePDCCH start symbol for the
second ePDCCH set.
3. The method of claim 2, wherein the indicated ePDCCH start symbol
for the first ePDCCH set is the same start symbol as scheduled for
a Packet Data Shared Channel (PDSCH) to be transmitted by the
network node.
4. The method of claim 1, wherein one or more of the following
configuration parameters are shared between the ePDCCH and a Packet
Data Shared Channel (PDSCH): a number of CRS antenna ports; a CRS
frequency shift; a start position; a Multicast/Broadcast Single
Frequency Network (MBSFN) subframe configuration; and a Zero Power
Channel State Information Reference Signal (CSI-RS) resource
configuration.
5. The method of claim 1, further comprising: receiving a message
from the network node comprising the ePDCCH allocated to a selected
one of the first ePDCCH set and the second ePDCCH set; decoding
ePDCCH candidates according to the first mapping and decoding
ePDCCH candidates according to the second mapping; detecting
whether the ePDCCH was allocated to the first ePDCCH set or the
second ePDCCH set.
6. The method of claim 1, wherein the first ePDCCH set consists of
N Physical Resource Block, (PRB) pairs, where N is 2, 4 or 8, and
the second ePDCCH set consists of N Physical Resource Block (PRB)
pairs, where N is 2, 4 or 8.
7. The method of claim 1, wherein the configuration message is
received in a Radio Resource Control (RRC) message.
8. A user equipment (UE) for use in a wireless communication
network, the UE being configured for communicating an enhanced
Physical Downlink Control Channel (ePDCCH) with a network node
providing coverage to a serving cell, the UE comprising: a
receiving circuit configured to: receive a configuration message
from the network node, the configuration message comprising an
indication of a first mapping of the ePDCCH for the serving cell to
resource elements belonging to a first ePDCCH set, where the ePDCCH
is mapped around resource elements of the first ePDCCH set used for
a first Cell-Specific Reference Signal (CRS), the indication of the
first mapping comprising an indication of at least one of (a) the
number of CRS ports for the first CRS and (b) the CRS frequency
shift for the first CRS, and an indication of a second mapping of
the ePDCCH for the serving cell to resource elements belonging to a
second ePDCCH set, where the ePDCCH is mapped around resource
elements of the second ePDCCH set used for a second CRS, the
indication of the second mapping comprising an indication of at
least one of (c) the number of CRS ports for the second CRS and (d)
the CRS frequency shift for the second CRS; and a monitoring
circuit configured to monitor ePDCCH candidates in the first ePDCCH
set according to the first mapping and monitoring ePDCCH candidates
in the second ePDCCH set according to the second mapping.
9. The UE of claim 8, wherein the configuration message comprises
an indication of an ePDCCH start symbol for the first ePDCCH set
and an indication of an ePDCCH start symbol for the second ePDCCH
set.
10. The UE of claim 9, wherein the indicated ePDCCH start symbol
for the first ePDCCH set is the same start symbol as scheduled for
a Packet Data Shared Channel (PDSCH) to be transmitted by the
network node or another network node.
11. The UE of claim 8, wherein the receiving circuit is further
configured to receive a message from the network node comprising
the ePDCCH allocated to a selected one of the first ePDCCH set and
the second ePDCCH set, the UE further comprising: a decoding
circuit configured to decode ePDCCH candidates according to the
first mapping and decode ePDCCH candidates according to the second
mapping; a detecting circuit configured to detect whether the
ePDCCH was allocated to the first ePDCCH set or to the second
ePDCCH set.
12. A method, performed by a network node providing coverage to a
serving cell of a wireless communication network, for communicating
an enhanced Physical Downlink Control Channel (ePDCCH) to a user
equipment (UE), the method comprising transmitting a configuration
message to the UE, the configuration message comprising: an
indication of a first mapping of the ePDCCH in the serving cell to
resource elements belonging to a first ePDCCH set, where the ePDCCH
is mapped around resource elements of the first ePDCCH set used for
a first Cell-specific Reference Signal (CRS), the indication of the
first mapping comprising an indication of at least one of (a) the
number of CRS ports for the first CRS and (b) the CRS frequency
shift for the first CRS, and an indication of a second mapping of
the ePDCCH in the serving cell to resource elements belonging to a
second ePDCCH set, where the ePDCCH is mapped around resource
elements of the second ePDCCH set used for a second CRS, the
indication of the second mapping comprising an indication of at
least one of (c) the number of CRS ports for the second CRS and (d)
the CRS frequency shift for the second CRS; selecting, according to
a selection criterion, one of the first ePDCCH set or the second
ePDCCH set for transmission of the ePDCCH in the serving cell to
the UE; allocating the ePDCCH to resource elements according to the
selected set; and transmitting the allocated ePDCCH in the serving
cell to the UE.
13. The method of claim 12, further comprising: performing the
first mapping of the ePDCCH to resource elements belonging to the
first ePDCCH set; and performing the second mapping of the ePDCCH
to resource elements belonging to the second ePDCCH set.
14. The method of claim 12, wherein the configuration message
comprises an indication of an ePDCCH start symbol for the first
ePDCCH set and an indication of an ePDCCH start symbol for the
second ePDCCH set.
15. The method of claim 14, wherein the indicated ePDCCH start
symbol for the first ePDCCH set is the same start symbol as
scheduled for a Packet Data Shared Channel (PDSCH) to be
transmitted by the network node or another network node.
16. The method of claim 12, wherein one or more of the following
configuration parameters are shared between the ePDCCH and a Packet
Data Shared Channel (PDSCH): a number of Cell-specific Reference
Signal (CRS) antenna ports, a CRS frequency shift, a start
position, a Multicast/Broadcast Single Frequency Network (MBSFN)
subframe configuration, a Zero Power Channel State Information
Reference Signal resource configuration, and a Channel State
Information Reference Symbol (CSI-RS) resource configuration.
17. The method of claim 12, wherein the first CRS is a CRS
transmitted from a first network node, and the second CRS is a CRS
transmitted from a second network node, and wherein the selection
criterion is based upon whether the first CRS or the second CRS has
the highest signal strength at the UE.
18. The method of claim 12, wherein the configuration message is
transmitted in a Radio Resource Control (RRC) message.
19. A network node of a wireless communication network, configured
for providing coverage to a serving cell and for communicating an
enhanced Physical Downlink Control Channel (ePDCCH) to a user
equipment (UE), the network node comprising a transmitting circuit
configured to transmit a configuration message to the UE, the
configuration message comprising: an indication of a first mapping
of the ePDCCH in the serving cell to resource elements belonging to
a first ePDCCH set, where the ePDCCH is mapped around resource
elements of the first ePDCCH set used for a first Cell-specific
Reference Signal (CRS), the indication of the first mapping
comprising an indication of at least one of (a) the number of CRS
ports for the first CRS and (b) the CRS frequency shift for the
first CRS, and an indication of a second mapping of the ePDCCH in
the serving cell to resource elements belonging to a second ePDCCH
set, where the ePDCCH is mapped around resource elements of the
second ePDCCH set used for a second CRS, the indication of the
second mapping comprising an indication of at least one of (c) the
number of CRS ports for the second CRS and (d) the CRS frequency
shift for the second CRS; a selecting circuit configured to select
one of the first ePDCCH set or the second ePDCCH set for
transmission of the ePDCCH in the serving cell to the UE; and an
allocating circuit configured to allocate the ePDCCH to resource
elements according to the selected set, wherein the transmitting
circuit is further configured to transmit the allocated ePDCCH to
the UE.
20. The network node of claim 19, further comprising a performing
circuit adapted to perform the first mapping of the ePDCCH to
resource elements belonging to the first ePDCCH set and to perform
the second mapping of the ePDCCH to resource elements belonging to
the second ePDCCH set.
21. The network node of claim 19, wherein an indicated ePDCCH start
symbol for the first ePDCCH set is the same start symbol as
scheduled for a Packet Data Shared Channel (PDSCH) to be
transmitted by the network node or another network node.
22. The network node of claim 19, wherein one or more of the
following configuration parameters are shared between the ePDCCH
and a Packet Data Shared Channel (PDSCH): a number of Cell-specific
Reference Signal (CRS) antenna ports, a CRS frequency shift, a
start position, a Multicast/Broadcast Single Frequency Network
(MBSFN) subframe configuration, a Zero Power Channel State
Information Reference Signal resource configuration, and a Channel
State Information Reference Symbol (CSI-RS) resource
configuration.
23. The network node of claim 19, wherein the first CRS is a CRS
transmitted from a first network node, and the second CRS is a CRS
transmitted from a second network node, and wherein the selecting
of the first ePDCCH set or the second ePDCCH set is based upon
whether the first CRS or the second CRS has the highest signal
strength at the UE.
Description
TECHNICAL FIELD
[0001] The present disclosure relates generally to a method
performed by a network node and a network node, for communicating
an enhanced Physical Downlink Control Channel, ePDCCH, to a user
equipment, UE. The disclosure also relates to a method performed by
a UE and a UE, for communicating an ePDCCH with a network node.
Further, the disclosure relates to computer programs and computer
program products which when run in a network node or a UE, causes
the network node or the UE to perform the method mentioned
above.
BACKGROUND
[0002] 3GPP Long Term Evolution, LTE, technology is a mobile
broadband wireless communication technology in which transmissions
from base stations, referred to as eNBs, to mobile stations,
referred to as user equipments, UEs, are sent using orthogonal
frequency division multiplexing, OFDM. OFDM splits the signal into
multiple parallel sub-carriers in frequency. The basic unit of
transmission in LTE is a resource block, RB, which in its most
common configuration consists of 12 subcarriers and 7 OFDM symbols,
which is the same as one slot. A unit of one subcarrier and one
OFDM symbol is referred to as a resource element, RE. Thus, an RB
consists of 84 REs. An LTE radio subframe is composed of multiple
resource blocks in frequency with the number of RBs determining the
bandwidth of the system and two slots in time. Furthermore, the two
RBs in a subframe that are adjacent in time are denoted as an RB
pair. In the time domain, LTE downlink transmissions are organized
into radio frames of 10 ms, each radio frame consisting of ten
equally-sized subframes of length Tsubframe=1 ms.
[0003] The signal transmitted by the eNB in a downlink (the link
carrying transmissions from the eNB to the UE) subframe may be
transmitted from multiple antennas and the signal may be received
at a UE that has multiple antennas. The radio channel distorts the
transmitted signals from the multiple antenna ports. In order to
demodulate any transmissions on the downlink, a UE relies on
reference symbols, RS that are transmitted on the downlink. These
reference symbols and their position in the time-frequency grid are
known to the UE and hence can be used to determine channel
estimates by measuring the effect of the radio channel on these
symbols.
[0004] Messages transmitted over the radio link to users can be
broadly classified as control messages or data messages. Control
messages are used to facilitate the proper operation of the system
as well as proper operation of each UE within the system. Control
messages could include commands to control functions such as the
transmitted power from a UE, signaling of RBs within which the data
is to be received by the UE or transmitted from the UE and so
on.
[0005] In LTE Rel-8, the first one to four OFDM symbols, depending
on the configuration, in a subframe are reserved to contain such
control information. Furthermore, in LTE Rel-11, an enhanced
physical downlink control channel was introduced, ePDCCH, in which
PRB pairs are reserved to exclusively contain ePDCCH transmissions,
although excluding from the PRB pair the one to four first symbols
that may contain control information to UEs of releases earlier
than Rel-11. FIG. 1 shows a downlink subframe of 10 RB pairs. The
subframe is configured with three ePDCCH regions (marked with
black) of size 1 PRB pair each. The remaining PRB pairs may be used
for PDSCH transmissions.
[0006] Hence, the ePDCCH is frequency multiplexed with data
messages, i.e. with Packet Data Shared Channel, PDSCH,
transmissions contrary to the physical downlink control channel,
PDCCH, which is time multiplexed with PDSCH transmissions. Note
also that multiplexing of PDSCH and any ePDCCH transmission within
a PRB pair is not supported in LTE Rel-11.
[0007] Furthermore, two modes of ePDCCH transmission is supported,
localized and distributed ePDCCH transmission.
[0008] In distributed transmission, an ePDCCH is mapped to resource
elements in an EPDCCH set, containing N PRB pairs, where N=2, 4, or
8. In this way, frequency diversity can be achieved for the ePDCCH
message. FIG. 2 shows a downlink subframe with 4 parts belonging to
an ePDCCH. The parts are mapped to multiple of the enhanced control
regions known as PRB pairs, to achieve distributed transmission and
frequency diversity.
[0009] In localized transmission, an ePDCCH is mapped to one PRB
pair only, if the space allows, which is always possible for
aggregation level one and two and for normal subframes and normal
Cyclic Prefix, CP, length also for aggregation level four. In case
the aggregation level of the ePDCCH is too large, a second PRB pair
is used as well, and so on, using more PRB pairs, until all
enhanced Control Channel Elements, eCCE, belonging to the EPDCCH
has been mapped. FIG. 3 shows a downlink subframe where the 4 eCCEs
belonging to an ePDCCH is mapped to one of the enhanced control
regions, to achieve localized transmission.
[0010] To facilitate the mapping of eCCEs to physical resources
each PRB pair is divided into 16 enhanced resource element groups
and each eCCE is split into L=4 or L=8 enhanced Resource Element
Groups, eREGs, for normal and extended cyclic prefix, respectively.
An ePDCCH is consequently mapped to a multiple of four or eight
eREGs depending on the aggregation level.
[0011] These eREGs belonging to an ePDCCH resides in either a
single PRB pair, as is possible for localized transmission, or a
multiple of PRB pairs, as is possible for distributed transmission.
The division of a PRB pair into eREGs is illustrated in FIG. 4,
which shows a PRB pair of normal cyclic prefix configuration in a
normal subframe. Each tile is a resource element where the number
corresponds to the eREG it is grouped within. The marked REs with
0, corresponds to the REs belonging to the same eREG indexed with
0.
[0012] Furthermore, how L=4 or L=8 eREGs respectively are grouped
into the eCCEs is described in [3GPP TS 36.213].
[0013] The ePDCCH resources may be UE specifically configured in
terms of ePDCCH sets. An ePDCCH set is a collection of N PRB pairs
containing 16N/L eCCE with the possible values of N=2, 4, 8. A UE
can be configured with K=1 or K=2 sets simultaneously and where the
value N can be different for each of the K sets. Each set may also
be configured to be of either localized or distributed type. For
example, a UE may be configured with K=2 and N.sub.1=4 and
N.sub.2=8 and where the first set is used for localized
transmission and the second for distributed transmission. The total
number of blind decodes, 32 in the case uplink multiple-input
multiple-output, MIMO, is not configured, is split between the K
sets. How this split is done is described in 3GPP [TS 36.213].
Hence, a UE will monitor Bi ePDCCH candidates in ePDCCH set i.
[0014] Each ePDCCH consists of AL eCCEs where AL is the aggregation
level of the message. Each eCCE in turn consists of L eREG where
L=4 or L=8. An eREG is a group of RE which is defined in 3GPP
specification TS 36.211. In each PRB pair there is 16 eREG. When
ePDCCH collides in mapping with own cell Cell-specific Reference
Signal, CRS, or own cell legacy control region, these signals have
priority and ePDCCH is mapped around these occupied REs and code
chain rate matching is applied. This means that the effective
number of available RE per eREG is usually less than the 9 RE but
there is no interference from the own cell CRS or own legacy
control region signals since the ePDCCH is mapped around these
signals.
[0015] The cell-specific reference signal, also known as the common
reference signal, is broadcasted periodically by LTE systems to
provide a UE the ability to measure the channel used for certain
downlink transmissions. The CRS is, for example, used to demodulate
the Physical Broadcast Channel, PBCH, but also to demodulate the
PDSCH for, for example, transmission modes 1-4, which are the
transmission modes that are primarily used for communication to any
LTE Rel-8 and Rel-9 UE. For these transmission modes, the CRS is
also utilized for the purpose of channel state information, CSI,
measurements, which are reported to the network for improved link
adaptation and MIMO downlink processing. Another application of CRS
is for mobility measurements.
[0016] Between cells, the CRS may be shifted in frequency domain.
This is often used in real-life deployments including conventional
homogenous deployments with macro nodes.
[0017] The different antenna ports of the CRS are mapped to
different sets of resource elements in the grid. Moreover, for all
resource elements assigned to a CRS port, the corresponding
resource elements may be muted, zero-power, on all other antenna
ports. The overhead of the CRS thus increases with increasing
number of transmitter antenna ports, 8, 16, and 24 resource
elements per PRB pair, for 1, 2 and 4 antennas, i.e. CRS antenna
ports, respectively.
[0018] The same enhanced control region, see for example FIG. 3,
can be used in different transmission points within a cell or
belong to different cells that are not highly interfering with each
other.
[0019] To reduce interference between different transmission
points, various interference coordination techniques may be used,
such as enhanced Inter-cell interference coordination, eICIC, or
Coordinated Multi Point, CoMP, operation introduced in LTE
Rel-11.
[0020] A heterogeneous network comprises a number of low-power
network nodes and a number of high-power network nodes, which
coverage areas may overlap each other partially and/or totally. A
low-power network node is a node providing coverage to a small
area, such as a pico node, e.g. a pico eNB. A high-power network
node is a node providing coverage to an area larger than the small
area, such as a macro node, e.g. a macro eNB. To increase the UE
pick-up area of a low-power node (i.e., the area in which a UE
would connect a pico node rather than a high power macro node),
cell range expansion, CRE, is a powerful tool where a UE is
prevented to make a handover to the high-power node unless the
received power from the high-power node exceeds the received power
of the low-power node by a configured CRE margin. This effectively
increases the "coverage area" of the low-power node. However, for
UEs in the so-called cell-range expansion area, i.e., the area
where UEs connect to the low-power node, but signals from the
high-power node are received with a stronger power than signals
from the low-power node, it is advantageous that the high-power
node minimizes the interfering signals in the subframes where the
network communicates with these UEs.
[0021] However, not all interference from the high-power node can
be muted in a subframe, such as the transmission of the CRS. In
particular, for cell-range expansion UEs to be able to accurately
estimate a propagation channel based on the CRS transmitted by the
low-power node, it is advantageous that the CRS of the macro node
does not collide with the CRS of the low-power node. This can be
ensured by configuring different CRS shift in frequency of the
high-power node and the low-power node.
[0022] Today, mapping of ePDCCH is performed such that the ePDCCH
is mapped around other signals, e.g. CRS or CSI-RS, of the same
cell as in which the ePDCCH is distributed, i.e. serving cell. In
other words, the resource elements, REs, used by the ePDCCH are not
coinciding with the REs used by the other signals of the same cell.
Thereby, there is no collision of the ePDCCH with the CRSs of the
same, serving, cell. The UE is implicitly informed on which REs the
other signals are situated. As an example, CRS positions are given
by the Cell-ID and CSI-RS is given by UE specific signaling using
the RRC protocol. However, it has been discovered that there are
use cases where other mappings may be needed, where REs different
than those occupied by the CRS and CSI-RS transmitted by the
serving cell need to be mapped around. For example, in
heterogeneous networks using CRE, a UE may be situated in the CRE
area and connected to a low-power node, and experience high
interference from a signal of a high-power network node. In that
case, the signal of the high-power node may need to be avoided in
the ePDCCH mapping in the serving cell of the low-power node, but
if the UE is situated closer to the low-power node, the signal from
the low-power node is the strongest and needs instead to be
avoided.
SUMMARY
[0023] It is an object of the invention to address at least some of
the problems and issues outlined above. It is an object to decrease
interference for ePDCCH signals. It is another object to decrease
interference for ePDCCH signals from other signals than CRS and
CSI-RS of the serving cell. It is another object to enable dynamic
allocation/mapping of an ePDCCH to REs. It is possible to achieve
these objects and others by using methods, network nodes, UEs and
computer programs as defined in the attached independent
claims.
[0024] According to a first aspect, a method performed by a network
node of a wireless communication network is provided. The method is
for communicating an enhanced Physical Downlink Control Channel,
ePDCCH, to a user equipment, UE. The method comprises transmitting
a configuration message to the UE. The configuration message
comprises an indication of a first mapping of the ePDCCH to
resource elements belonging to a first ePDCCH set, where the
resource elements of the first ePDCCH set are different from
resource elements used for a first type of signal The configuration
message further comprises an indication of a second mapping of the
ePDCCH to resource elements belonging to a second ePDCCH set, where
the resource elements of the second ePDCCH set are different from
resource elements used for a second type of signal, thereby
enabling dynamically mapping ePDCCH to the resource elements of the
first ePDCCH set or the second ePDCCH set.
[0025] According to a second aspect, a network node of a wireless
communication network is provided. The network node is configured
for communicating an ePDCCH to a UE. The network node comprises a
transmitting unit for transmitting a configuration message to the
UE. The configuration message comprises an indication of a first
mapping of the ePDCCH to resource elements belonging to a first
ePDCCH set, where the resource elements of the first ePDCCH set are
different from resource elements used for a first type of signal.
The configuration message further comprises an indication of a
second mapping of the ePDCCH to resource elements belonging to a
second ePDCCH set, where the resource elements of the second ePDCCH
set are different from resource elements used for a second type of
signal, thereby enabling dynamically mapping ePDCCH to the resource
elements of the first ePDCCH set or the second ePDCCH set.
[0026] According to a third embodiment, a computer program is
provided comprising computer readable code means, which when run in
a network node causes the network node to perform the step of
transmitting a configuration message to the UE. The configuration
message comprises an indication of a first mapping of the ePDCCH to
resource elements belonging to a first ePDCCH set, where the
resource elements of the first ePDCCH set are different from
resource elements used for a first type of signal. The
configuration message further comprises an indication of a second
mapping of the ePDCCH to resource elements belonging to a second
ePDCCH set, where the resource elements of the second ePDCCH set
are different from resource elements used for a second type of
signal, thereby enabling dynamically mapping ePDCCH to the resource
elements of the first ePDCCH set or the second ePDCCH set.
[0027] According to a fourth embodiment, a method performed by a UE
in a wireless communication network is provided. The method is for
communicating an ePDCCH, with a network node. The method comprises
receiving a configuration message from the network node. The
configuration message comprises an indication of a first mapping of
the ePDCCH to resource elements belonging to a first ePDCCH set,
where the resource elements of the first ePDCCH set are different
from resource elements used for a first type of signal. The
configuration message further comprises an indication of a second
mapping of the ePDCCH to resource elements belonging to a second
ePDCCH set, where the resource elements of the second ePDCCH set
are different from resource elements used for a second type of
signal.
[0028] According to a fifth embodiment, a UE is provided in a
wireless communication network. The UE is configured for
communicating an ePDCCH with a network node. The UE comprises a
receiving unit for receiving a configuration message from the
network node. The configuration message comprises an indication of
a first mapping of the ePDCCH to resource elements belonging to a
first ePDCCH set, where the resource elements of the first ePDCCH
set are different from resource elements used for a first type of
signal. The configuration message further comprises an indication
of a second mapping of the ePDCCH to resource elements belonging to
a second ePDCCH set, where the resource elements of the second
ePDCCH set are different from resource elements used for a second
type of signal.
[0029] According to a sixth embodiment, a computer program is
provided comprising computer readable code means, which when run in
a UE causes the UE to perform the step of receiving a configuration
message from a network node. The configuration message comprises an
indication of a first mapping of the ePDCCH to resource elements
belonging to a first ePDCCH set, where the resource elements of the
first ePDCCH set are different from resource elements used for a
first type of signal. The configuration message further comprises
an indication of a second mapping of the ePDCCH to resource
elements belonging to a second ePDCCH set, where the resource
elements of the second ePDCCH set are different from resource
elements used for a second type of signal.
[0030] Further possible features and benefits of this solution will
become apparent from the detailed description below.
BRIEF DESCRIPTION OF FIGURES
[0031] The solution will now be described in more detail by means
of exemplary embodiments and with reference to the accompanying
drawings, in which:
[0032] FIG. 1 is a schematic diagram of a downlink subframe.
[0033] FIG. 2 is another schematic diagram of a downlink
subframe.
[0034] FIG. 3 is a schematic diagram of a downlink subframe.
[0035] FIG. 4 is a schematic diagram of a mapping scheme for
mapping of physical resource blocks to resource elements.
[0036] FIG. 5 is a schematic view in perspective of an exemplary
wireless communication network in which the present invention may
be used.
[0037] FIG. 6 is a flow chart of a method performed by a network
node according to embodiments.
[0038] FIG. 7 is a schematic block diagram of a network node
according to embodiments.
[0039] FIG. 8 is a schematic block diagram of an arrangement in a
network node according to embodiments.
[0040] FIG. 9 is a flow chart of a method performed by a UE
according to embodiments.
[0041] FIG. 10 is a schematic block diagram of a UE according to
embodiments.
[0042] FIG. 11 is a schematic block diagram of an arrangement in a
UE according to embodiments.
[0043] FIG. 12 is a flow chart of a method in a network node.
[0044] FIG. 13 is a flow chart of a method in a UE.
DETAILED DESCRIPTION
[0045] For illustrative purposes, several embodiments of the
present invention will be described in the context of a Long-Term
Evolution, LTE, system, particularly an LTE system utilizing
carrier aggregation. Those skilled in the art will appreciate,
however, that several embodiments of the present invention may be
more generally applicable to other wireless communication systems,
including, for example, WiMax (IEEE 802.16) systems.
[0046] Today, mapping of ePDCCH is performed such that the ePDCCH
is mapped around other signals, e.g. CRS, CSI-RS or the legacy
control region, of the same cell as in which the ePDCCH is
distributed, i.e. serving cell. In other words, the resource
elements, REs, used by the ePDCCH are not coinciding with the REs
used by the other signals of the same cell. Thereby, there is no
collision of the ePDCCH with e.g. the CRSs of the same, serving,
cell. The UE is implicitly informed on which REs the other signals
are situated. As an example, CRS positions are given by the Cell-ID
and CSI-RS is given by UE specific signaling using the RRC
protocol. However, it has been discovered that there are use cases
where other mappings may be needed, where REs different than those
occupied by the CRS and CSI-RS transmitted by the serving cell need
to be mapped around. For example, in heterogeneous networks using
CRE, a UE may be situated in the CRE area and connected to a
low-power network node, and experience high interference from a
signal of a high-power network node. In that case, the signal of
the high-power node may need to be avoided in the ePDCCH mapping in
the serving cell of the low-power node, but if the UE is situated
closer to the low-power node, the signal from the low-power node is
the strongest and needs instead to be avoided . . . .
[0047] To be able to cater for such situations, the ePDCCH is,
according to an embodiment, dynamically selected to be mapped
around one out of a multiple of pre-configured set of REs used for
other signals. Dynamic selection of the mapping is possible by
associating a certain ePDCCH to RE mapping with an ePDCCH set. As
the UE monitors ePDCCH candidates in both sets, the eNodeB can
dynamically choose the mapping by selecting the corresponding
ePDCCH set for the ePDCCH transmission. An ePDCCH set may be a
group of resource elements used for ePDCCH monitoring. According to
3GPP TS 36.213, an ePDCCH set is a group of N=2, 4 or 8 Physical
Resource Blocks, PRB, configured for ePDCCH monitoring. The serving
eNodeB can then dynamically decide which mapping to use by
selecting which ePDCCH set to use for the ePDCCH transmission. In
this way the ePDCCH can be mapped around a signal that is
considered to be interfering. I.e. the eNodeB configures multiple
mappings and thereafter transmits the different mapping
configurations to the UE, such that the UE knows where to listen
for the ePDCCH. By transmitting information of the mapping
configuration to the UE, and associate each mapping with an ePDCCH
set, it is possible to dynamically map, or allocate, ePDCCH to REs,
around a signal that is problematic for the moment.
[0048] In a further aspect of the invention, each of these mappings
may correspond to the set of REs used by other signals in two or
more different eNodeBs. For instance, two eNodeBs may have
different CRS patterns, due to a difference in the number of CRS
antenna ports and/or the CRS frequency shift. Also the size of the
legacy control region (1, 2 or 3 OFDM symbols) could be different
between the two eNodeBs. By this arrangement, with a first ePDCCH
set mapping around other signals transmitted from a first eNodeB,
and a second ePDCCH set mapping around other signals transmitted
from a second eNodeB, the ePDCCH may dynamically be selected to be
transmitted from one of the eNodeBs, and have the ePDCCH mapped
correspondingly around the other signals of the corresponding
eNodeBs. Each eNodeBs is thus associated with one ePDCCH set in
this aspect of the invention.
[0049] An eNodeB is an example of a network node communicating with
a UE.
[0050] According to an embodiment, the effects of interference from
a nearby cell is reduced by configuring the UE to perform ePDCCH
mapping around the "other" signals transmitted in the interfering
cell instead of the "other" signals transmitted in the own cell.
With "other" signals may be meant other signals than the ePDCCH
signal, such as CRS signals. According to another embodiment,
dynamic switching of the node used for transmitting ePDCCH can be
performed even when participating nodes use different CRS shifts or
have different PDCCH control region sizes.
[0051] The configuration may be performed per ePDCCH set and may
include the number of CRS antenna ports and their location, e.g.
frequency shift. The configuration may also include the ePDCCH
start symbol so that the ePDCCH can be protected from interference
of legacy control transmissions from the interfering cell.
[0052] An exemplifying configuration could be K=2 sets of ePDCCH
where in a first set, ePDCCH is mapped around transmissions, e.g.
CRS transmissions, from the serving node (i.e. first network node)
and in a second set, ePDCCH is configured to be mapped around
transmissions, e.g. CRS transmissions, from an interfering
cell/node (i.e. second network node). When UE is close to its
serving node, CRS transmission power from its serving node is
dominating over CRS transmission power from the interfering node
and the first set is used for ePDCCH transmissions. When UE has a
large CRE bias, i.e. when the UE is located further away from the
serving node, and CRS transmission power from the interfering node
is dominating over CRS transmission power from the serving node,
the second set could instead be used for ePDCCH transmissions.
Hence, the ePDCCH is mapped around these highly interfering CRS RE
associated with the interfering node. The mentioned setup of ePDCCH
mapping sets can also be used for dynamically switching between
transmitting the ePDCCH from a first node and transmitting the
ePDCCH from a second node in general, and not only limited to the
described heterogeneous deployment scenario.
[0053] According to a first embodiment, in the configuration of an
ePDCCH set to the UE, which configuration can be performed by RRC
signaling, the signaling may include information of one or more of
the following parameters, or equivalent parameters that allow the
corresponding REs to be avoided for ePDCCH transmission: [0054]
Presence or absence of CRS signals [0055] The number of CRS ports
[0056] The CRS frequency shift, v_shift [0057] The ePDCCH start
OFDM symbol, or number of ePDCCH symbols, in the subframe,
including start symbol zero, i.e. first symbol, in the subframe
[0058] Which subframes are configured as Multicast/Broadcast Single
Frequency Network, MBSFN, subframes, which impacts on which OFDM
symbols that have CRS present [0059] Zero Power, ZP, CSI-RS
configuration [0060] Non Zero Power, NZP, CSI-RS configuration
[0061] An OFDM start symbol, or ePDCCH start OFDM symbol, may be a
reference to a start position of an ePDCCH set in a data flow.
[0062] When an eNodeB transmits the ePDCCH in a PRB pair in a given
subframe, it may map the ePDCCH to the remaining RE when the RE
used by the signals configured by the parameters listed above have
been removed.
[0063] When a UE demodulates an ePDCCH it may likewise assume that
the RE used by the signals configured by the parameters listed
above have been removed from the RE used by the ePDCCH.
[0064] When multiple ePDCCH sets are configured to the UE, each set
may have different values of one, some or all of the parameters.
Since the UE has some blind decoding candidates in each of its
configured ePDCCH sets, the eNodeB can choose, by selecting which
set it uses to transmit the ePDCCH message, what mapping it want to
use for ePDCCH. The eNodeB could determine this based on
information of the interference situation of the UE, based on
downlink measurements on CSI-RS. Hence, when the UE is heavily
interfered by signals, e.g. CRS, from an adjacent cell, the mapping
of ePDCCH is performed around the signals transmitted from the
adjacent cell/eNodeB instead of the serving cell/eNodeB.
[0065] In a further embodiment a superset of configuration sets,
each containing a subset (or all) of the above parameters are
signaled to the UE. An ePDCCH set can next be assigned a specific
one of said superset of configurations sets.
[0066] In yet a further embodiment, said superset of configuration
sets may be shared for use relating to decoding/demodulating a data
channel, e.g., PDSCH, or another channel, and an ePDCCH. For
example, in the scheduling assignment of a PDSCH, one of said set
of configuration parameters for the PDSCH can be indicated for the
resource element mapping of the ePDCCH. Sharing a superset of
configurations between the ePDCCH and the PDSCH has the advantage
that the configuration message overhead can be reduced. That a
superset of configurations is shared between the ePDCCH and e.g.
the PDSCH may be interpreted such that the same configuration
parameter values as used for PDSCH are re-used for ePDCCH. For
example, the resource elements used by the ePDCCH and the PDSCH
within a PRB pair may be the same.
[0067] As mentioned, the ePDCCH start symbol in the subframe may be
configured by RRC signaling. Each ePDCCH set may have an individual
ePDCCH start symbol configuration and the value range may be any or
all of the values 0, 1, 2, 3 and 4. Further, the ePDCCH starting
symbol may not be dependent on the Physical Control Format
Indication Channel, PCFICH.
[0068] In a second embodiment, the network dynamically decides from
which network node the ePDCCH is to be transmitted from. The
network nodes that are candidates for ePDCCH transmission may be
associated with different ePDCCH sets, wherein the ePDCCH sets may
have mutually different parameters and/or different parameter
values. The parameters may be any of the parameters mentioned in
connection with the first embodiment. For example, two network
nodes with different CRS frequency shifts are the candidates and
they are associated with different ePDCCH sets configured to the
UE. When ePDCCH is transmitted in the first ePDCCH set, the ePDCCH
will be mapped around the CRS used in the first network node, and
when ePDCCH is transmitted in the second ePDCCH set, the ePDCCH
will be mapped around the CRS used in the second network node. This
is one example of dynamic switching of transmitting network node
for ePDCCH.
[0069] If there are more than two network nodes from which dynamic
switching of transmission can take place, network nodes with the
same CRS shift can be assigned the same ePDCCH set so that the
number of configured sets is minimized.
[0070] In a further embodiment, at least one of the network nodes
is using a non-backward compatible new carrier, which do not have
CRS transmissions and at least one other network node is using a
backward compatible carrier, with CRS transmissions and legacy
control signaling. In this case ePDCCH mapping in one of the ePDCCH
sets would assume no CRS is present and the ePDCCH start symbol
would be the first symbol in the subframe. Another ePDCCH set would
be configured with CRS present and CRS shift according to either
parameter signaling as in the first embodiment or derived from cell
ID, and the ePDCCH start symbol would be different than the first
ePDCCH symbol, hence corresponding to a backward compatible
node.
[0071] In a third embodiment, uplink grants and downlink
assignments are transmitted from different network nodes, wherein
the different network nodes may use mutually different parameters
and/or different parameter values. The parameters may be any of the
parameters mentioned in connection with the first embodiment. An
ePDCCH set is thus associated with a given network node and is
configured with the associated parameters that decides the ePDCCH
to RE mapping. Hence, uplink grants are transmitted in one ePDCCH
set and downlink assignments in another ePDCCH set. This is another
example of dynamic switching of transmitting network node for
ePDCCH.
[0072] When an ePDCCH belonging to a common search space, CSS, is
transmitted in an ePDCCH set), the UE advantageously needs to know
the configuration of the ePDCCH mapping without having been
configured to be able to receive control signals such as random
access response messages, paging, and system information. The
reason is that these control signals are broadcasted to multiple
UEs, which may have different configurations of the parameters
listed in connection with the first embodiment. The network does
not know the configuration since UE ID is unknown, as in the case
of random access response, or the UE has not been configured at
all, as in the case of paging in idle mode. Hence a default set of
parameters need to be used. CSS is proposed for ePDCCH in LTE
Rel-12.
[0073] In a further embodiment, the default parameters related to
CRS are obtained from the Cell ID of the serving cell and the
master information block, MIB, transmitted in the Physical
Broadcast Channel, PBCH, following LTE Rel-8 procedure. The ePDCCH
start symbol is either using a default value, e.g. the maximum
value 3 or 4 at the given system bandwidth, or is obtained by
decoding a control format indicator in the Physical Control Format
Indicator Channel, PCFICH. The UE can assume that no CSI-RS is
present, neither ZP or NZP, and that no MBSFN sub-frames are
present.
[0074] One or more of the described embodiments provides reduced
interference to control signaling when the ePDCCH is used.
[0075] In FIG. 5, an exemplary wireless communication network is
shown in which the present invention may be used. FIG. 5 shows a
part of an exemplary heterogeneous network 100 comprising a high
power network node 110 covering a high power network node area 111,
which may be a macro cell, and a low power network node 130
covering a low power network node area 131, which may be a pico
cell. The low power network node area 131 is usually limited to a
signal strength, SS, border 160. At the SS border 160, the downlink
SS from the high power network node 110 is more or less equal to
the downlink SS from the low power network node 130. A UE 150 may
be connected to the low power network node 130 if it is positioned
inside the low power network node area 131 and connected to the
high power network node 110 if it is positioned outside the low
power network node area 131 but inside the high power network node
area 111. When cell range expansion is employed for the low power
network node 130, the low power network node area 131 is extended
to include an extended low power network node area 132 limited at a
CRE border 170, where SS from the high power node is equal to SS
from the low power node added with a bias value When the UE 150 is
in the extended low power network node area 132 outside the low
power network node area 131 the UE is still connected to the low
power node 130 but experiences strong interference from the high
power network node 110. If the UE resides in the low power node
area 131, according to an embodiment it may be advantageous to map
the ePDCCH around signals from the low power network node 130, such
as CRS from the low power network node. If the UE resides in the
extended low power node area 132 outside the low power node area
131, it may, according to an embodiment, be advantageous to map the
ePDCCH around signals from the high power network node 110, such as
CRS from the high power network node, since the UE experiences
higher interference from the high power node 110 than the low power
node 130.
[0076] In FIG. 6 an embodiment of a method performed by a network
node 130 of a wireless communication network, for communicating an
enhanced Physical Downlink Control Channel, ePDCCH, to a UE is
described. The method comprises: transmitting 606 a configuration
message to the UE. The configuration message comprises an
indication of a first mapping of the ePDCCH to resource elements
belonging to a first ePDCCH set, where the resource elements of the
first ePDCCH set are different from resource elements used for a
first type of signal. The configuration message further comprises
an indication of a second mapping of the ePDCCH to resource
elements belonging to a second ePDCCH set, where the resource
elements of the second ePDCCH set are different from resource
elements used for a second type of signal. Thereby it is enabled to
dynamically map the ePDCCH to the resource elements of the first or
the second ePDCCH set.
[0077] By transmitting a configuration message to the UE comprising
two different ePDCCH mapping sets, it is possible for the network
node to dynamically select which of the ePDCCH sets to use when
allocating the ePDCCH to REs. The UE has thus been configured to
monitor ePDCCH candidates in both ePDCCH sets. Thereby the network
node can dynamically select which of the first and the second
signal that is to be mapped around, in other words if REs used for
the first signal is to be avoided or if REs used for the second
signal is to be avoided.
[0078] The expression a "first type of signal" may be interpreted
as "a first signal" The expression "a second type of signal" may be
interpreted as "a second signal. The first type of signal is
different from the second type of signal, which means that the
first type of signal is a different signal than the second type of
signal. The first and the second type of signals may be the same
kind of signal, e.g. both may be CRS signals, but then they are
different CRS signals.
[0079] That the resource elements of the first ePDCCH set are
different from resource elements used for a first type of signal
means that the resource elements of the first ePDCCH set do not
coincide with the resource elements used for the first type of
signal. Similarly, the resource elements of the second ePDCCH set
are different from resource elements used for a second type of
signal means that the resource elements of the second ePDCCH set do
not coincide with the resource elements used for the second type of
signal. The first type of signal may be transmitted in the same
subframe or the same PBR pair as the ePDCCH. The first type of
signal may be received at the UE, and possibly also directed to the
UE. The second type of signal may be transmitted in the same
subframe, or the same PRB pair, as the ePDCCH. The second type of
signal may be received at the UE, and possibly also directed to the
UE. The second type of signal may be assumed to be different from
the first type of signal. The first type of signal and the second
type of signal may be any signal or type of signal other than the
ePDCCH (signal).
[0080] In addition or alternatively, the resource elements of the
first ePDCCH set may be different from resource elements used for a
first type of signal transmitted from a network node serving the
UE, and, the resource elements of the second ePDCCH set may be
different from resource elements used for a second type of signal
transmitted from a neighboring network node. The serving network
node may be a serving eNB providing coverage to a serving cell. The
neighboring network node may be a neighboring eNB providing
coverage to a neighboring cell. The serving and neighboring network
nodes may also be two transmission points within the same cell,
such as two remote radio heads. The first type of signals
transmitted from the serving network node may be CRS signals. The
second type of signals transmitted from the neighboring network
node may be CRS signals. The second type of CRS signals may have
different frequency shift than the first type of CRS signals. The
neighboring network node may be e.g. an eNB of which the
transmitted signals interfere with signals from the serving eNB at
the UE.
[0081] According to an embodiment, at least one resource element
belonging to the second ePDCCH set is not part of the resource
elements belonging to the first ePDCCH set.
[0082] According to an embodiment, the method further comprises
performing 602 the first mapping of the ePDCCH to resource elements
belonging to the first ePDCCH set, and performing 604 the second
mapping of the ePDCCH to resource elements belonging to the second
ePDCCH set. The steps of performing 602, 604 the first and the
second mapping may be performed before the configuration message
with the indication of the first and second mapping is transmitted
to the UE. The mapping may be performed by a separate network node
or by the same network node as transmits the configuration
message.
[0083] By the ePDCCH being mapped to resource elements that are
different from resource elements used for a first type of signal is
meant that the ePDCCH is mapped around the resource elements used
for the first type of signal.
[0084] By the ePDCCH being mapped to resource elements that are
different from resource elements used for a second type of signal,
the second signal at least partly using different resource elements
than used for the first type of signal is meant that the ePDCCH is
mapped around the resource elements used for the second type of
signal. Alternatively, the mapping of the first ePDCCH set may be
performed by a first network node and the mapping of the second
ePDCCH set may be performed by a second network node, different
from the first network node. That is, the ePDCCH may be transmitted
from different network nodes. This may be achieved through the use
of different ePDCCH sets, and the network, e.g. any of the involved
network nodes, can decide from which of the first and the second
network node the ePDCCH is to be transmitted from on a per subframe
basis, by selecting an ePDCCH set out of the first and second
ePDCCH set.
[0085] According to another embodiment, the configuration message
comprises an indication of an ePDCCH start symbol for the first
ePDCCH set and an indication of an ePDCCH start symbol for the
second ePDCCH set. Thereby, the different ePDCCH sets may be
allocated different ePDCCH start symbols which facilitates the
dynamic mapping and a diversification of the ePDCCH sets.
[0086] According to yet another embodiment, the indicated ePDCCH
start symbol is the same start symbol as scheduled for a Packet
Data Shared Channel, PDSCH, to be transmitted by the network node.
By using the same start symbol for ePDCCH as for PDSCH, less data
has to be sent in the configuration message for which reason
transmission overhead is decreased.
[0087] According to yet another embodiment, one or more of the
following configuration parameters: number of Cell-specific
Reference Signal, CRS, antenna ports, CRS frequency shift, start
position, Multicast/Broadcast Single Frequency Network, MBSFN,
subframe configuration, Zero Power Channel State Information
Reference Signal, CSI-RS, resource configuration CSI-RS resource
configuration, are shared between the ePDCCH and a Packet Data
Shared Channel PDSCH. By using the same configuration parameters
for ePDCCH as for PDSCH, less data has to be sent in the
configuration message for which reason transmission overhead is
decreased. For ePDCCH mapping, it may be enough just to send an
indication or reference to the PDSCH mapping. Also, the mapping may
be performed using less processor capacity.
[0088] The expression "one or more configuration parameters are
shared between the ePDCCH and the PDSCH" is to be interpreted such
that the same parameter values as used for PDSCH are re-used for
ePDCCH. For example, the resource elements used by the ePDCCH and
the PDSCH within a PRB pair may be the same.
[0089] According to yet another embodiment, the method may further
comprise selecting 608 one of the first ePDCCH set or the second
ePDCCH set for transmission of the ePDCCH to the UE according to a
criterion. The method may further comprise allocating 610 the
ePDCCH to resource elements according to the selected set. The
method may further comprise transmitting 612 the allocated ePDCCH
to the UE. Thereby, a dynamic selection of ePDCCH set is
realized.
[0090] According to yet another embodiment, the first type of
signal is a signal from a first network node 110, and the second
type of signal is a signal from a second network node 130. The
selecting criterion may be which of the signal from the first
network node and the signal from the second network node that has
the highest signal strength. Thereby it is possible to dynamically
map around signals from any of two network nodes, depending on
which network node's signal strength is the highest. This may be
advantageous in a heterogeneous network using CRE, for example when
a UE is moving into and out of the CRE area.
[0091] Another possible selection criterion may be to select first
or second ePDCCH set depending on type of message to be sent, e.g.
depending on whether the message is an Uplink grant message or a
Downlink assignment message. For example, if the network node is
intended to schedule uplink from the first ePDCCH set and downlink
from the second ePDCCH set, the network node will select the first
ePDCCH set if the message is an Uplink grant message and the second
ePDCCH set if the message is a Downlink assignment message. Another
selection criterion may be scheduling of different UEs depending on
scheduling priority. For example, for a first UE and a second UE to
be scheduled in the same subframe, the first UE may have a higher
scheduling priority than the second UE. It may be the best for both
the first UE and the second UE to be scheduled from the first
ePDCCH set, but since the first UE has a higher scheduling priority
than the second UE, the first UE is scheduled from the first ePDCCH
set, and the second UE is, consequently, scheduled from the second
ePDCCH set. This may be suboptimal for the second UE but from a
network perspective it may be advantageous since both the first UE
and the second UE may be scheduled in the same subframe.
[0092] According to another embodiment, the first network node is
an interfering network node 130 and the second network node is the
network node 110 performing the method.
[0093] According to another embodiment, the first type of signal
and the second type of signal is a Cell-specific Reference Signal,
CRS. Thereby it is possible to map around CRS signals.
[0094] According to another embodiment, the resource elements of
the first ePDCCH set comprises information of uplink grants and the
resource elements of the second ePDCCH set comprises downlink
assignments Uplink grants are scheduling information for uplink
transmissions. Downlink assignments are scheduling information for
downlink transmissions.
[0095] According to another embodiment, the configuration message
is transmitted 606 in a Radio Resource Control, RRC message. By
using an already existing message, or message structure, for
transmitting the configuration message, no or only small changes
have to be made to the network node for transmitting the
configuration message and to the UE for receiving the configuration
message.
[0096] FIG. 7 shows a network node 700 of a wireless communication
network according to an embodiment of the invention, configured for
communicating an ePDCCH to a UE. The network node may be an eNodeB
B of an LTE network. The network node 700 may be the low-power
network node 130 or the high power network node 110 of FIG. 5. The
network node 700 comprises a transmitting unit 702 for transmitting
a configuration message to the UE. The configuration message
comprises an indication of a first mapping of the ePDCCH to
resource elements belonging to a first ePDCCH set, where the
resource elements of the first ePDCCH set are different from
resource elements used for a first type of signal. The
configuration message further comprises an indication of a second
mapping of the ePDCCH to resource elements belonging to a second
ePDCCH set, where the resource elements of the second ePDCCH set
are different from resource elements used for a second type of
signal, thereby enabling dynamically mapping ePDCCH to the resource
elements of the first ePDCCH set or the second ePDCCH set.
[0097] The network node 700 may further comprise a communication
unit 710, which may be considered to comprise conventional means
for communication from and/or to other nodes or UEs of the wireless
network. In case the network node 700 is an eNodeB, the
communication unit 710 may comprise a wireless communication part
for communicating wirelessly with UEs, such as one or more
transceivers. The network node 700 may further comprise other
functional units (not shown) for providing e.g. regular network
node functions. The network node 700 may further comprise one or
more storage units 712.
[0098] The transmitting unit 702, the performing unit 704 and the
selecting unit 706 may be arranged in an arrangement 701. The
arrangement 701 could be implemented e.g. by one or more of: a
processor or a micro processor and adequate software and storage
therefore, a Programmable Logic Device (PLD) or other electronic
component(s)/processing circuit(s) configured to perform the
actions, or methods, mentioned above.
[0099] According to an embodiment, the network node 700 further
comprises a performing unit 704 for performing the first mapping of
the ePDCCH to resource elements belonging to the first ePDCCH set,
and for performing the second mapping of the ePDCCH to resource
elements belonging to the second ePDCCH set.
[0100] According to another embodiment, the configuration message
comprises an indication of an ePDCCH start symbol for the first
ePDCCH set and an indication of an ePDCCH start symbol for the
second ePDCCH set.
[0101] According to another embodiment the indicated ePDCCH start
symbol is the same start symbol as scheduled for a Packet Data
Shared Channel, PDSCH, to be transmitted by the network node.
[0102] According to another embodiment, one or more of the
following configuration parameters: number of Cell-specific
Reference Signal, CRS, antenna ports, CRS frequency shift, start
position, Multicast/Broadcast Single Frequency Network, MBSFN,
subframe configuration, Zero Power Channel State Information
Reference Signal, CSI-RS, resource configuration CSI-RS resource
configuration, are shared between the ePDCCH and a Packet Data
Shared Channel PDSCH.
[0103] According to another embodiment, the network node 700
further comprises a selecting unit 706 for selecting one of the
first ePDCCH set or the second ePDCCH set for transmission of the
ePDCCH to the UE according to a criterion. The network node 700
further comprises an allocating unit 708 for allocating the ePDCCH
to resource elements according to the selected set. Further, the
transmitting unit 702 is arranged to transmit the allocated ePDCCH
to the UE.
[0104] According to another embodiment, the first type of signal is
a signal from a first network node 110, and the second type of
signal is a signal from a second network node 130, and wherein the
selecting criterion is which of the signal from the first network
node and the signal from the second network node that has the
highest signal strength.
[0105] FIG. 8 schematically shows an embodiment of an arrangement
800 for use in a network node 700, which also can be an alternative
way of disclosing an embodiment of the arrangement 701 in a network
node 700 illustrated in FIG. 7. Comprised in the arrangement 800 is
a processing unit 806, e.g. with a Digital Signal Processor (DSP).
The processing unit 806 may be a single unit or a plurality of
units to perform different actions of procedures described herein.
The arrangement 800 may also comprise an input unit 802 for
receiving signals from other entities, and an output unit 804 for
providing signal(s) to other entities. The input unit 802 and the
output unit 804 may be arranged as an integrated entity.
[0106] Furthermore, the arrangement 800 comprises at least one
computer program product 808 in the form of a non-volatile or
volatile memory, e.g. an Electrically Erasable Programmable
Read-only Memory (EEPROM), a flash memory, a disk drive or a
Random-access memory (RAM). The computer program product 808
comprises a computer program 810, which comprises code means, which
when executed in the processing unit 806 in the arrangement 800
causes the arrangement and/or the network node 700 to perform the
actions of any of the procedures described earlier in conjunction
with FIG. 6.
[0107] The computer program 810 may be configured as a computer
program code structured in computer program modules. Hence, in an
exemplifying embodiment, the code means in the computer program 810
of the arrangement 800 comprises a transmitting module 810a for
transmitting a configuration message to the UE. The configuration
message comprises an indication of a first mapping of the ePDCCH to
resource elements belonging to a first ePDCCH set, where the
resource elements of the first ePDCCH set are different from
resource elements used for a first type of signal, and an
indication of a second mapping of the ePDCCH to resource elements
belonging to a second ePDCCH set, where the resource elements of
the second ePDCCH set are different from resource elements used for
a second type of signal, thereby enabling dynamically mapping
ePDCCH to the resource elements of the first ePDCCH set or the
second ePDCCH set.
[0108] The computer program may further comprise a performing
module 810b for performing the first mapping of the ePDCCH to
resource elements belonging to the first ePDCCH set, and for
performing the second mapping of the ePDCCH to resource elements
belonging to the second ePDCCH set. The computer program may
further comprise a selecting module 810c for selecting one of the
first ePDCCH set or the second ePDCCH set for transmission of the
ePDCCH to the UE according to a criterion. The computer program may
further comprise an allocating module 810d for allocating the
ePDCCH to resource elements according to the selected set. Further,
the transmitting module 810a may be arranged for transmitting the
allocated ePDCCH to the UE.
[0109] In FIG. 9, a method performed by a UE in a wireless
communication network is described, for communicating an ePDCCH,
with a network node. The method comprises receiving (902) a
configuration message from the network node. The configuration
message comprises an indication of a first mapping of the ePDCCH to
resource elements belonging to a first ePDCCH set, where the
resource elements of the first ePDCCH set are different from
resource elements used for a first type of signal, and an
indication of a second mapping of the ePDCCH to resource elements
belonging to a second ePDCCH set, where the resource elements of
the second ePDCCH set are different from resource elements used for
a second type of signal. Thereby, it is possible for the UE to
detect a later received ePDCCH if transmitted in either of the
first ePDCCH set or the second ePDCCH set. This enables dynamic
allocation of ePDCCH to REs.
[0110] According to an embodiment, the configuration message
comprises an indication of an ePDCCH start symbol for the first
ePDCCH set and an indication of an ePDCCH start symbol for the
second ePDCCH set.
[0111] According to another embodiment, the indicated ePDCCH start
symbol is the same start symbol as scheduled for a Packet Data
Shared Channel, PDSCH, to be transmitted by the network node.
[0112] According to another embodiment, one or more of the
following configuration parameters: number of Cell-specific
Reference Signal, CRS, antenna ports, CRS frequency shift, start
position, Multicast/Broadcast Single Frequency Network, MBSFN,
subframe configuration, Zero Power Channel State Information
Reference Signal, CSI-RS, resource configuration CSI-RS resource
configuration, are shared between the ePDCCH and a Packet Data
Shared Channel PDSCH.
[0113] According to another embodiment, the method further
comprises receiving 904 a message from the network node comprising
the ePDCCH allocated to a selected one of the first ePDCCH set and
the second ePDCCH set. The method further comprises decoding 906
ePDCCH candidates according to the first mapping and decoding
ePDCCH candidates according to the second mapping. The method
further comprises detecting 908 whether the ePDCCH was allocated to
the first ePDCCH set or the second ePDCCH set. The step of
detecting 908 may be performed by decoding a number of, for example
3, candidate REs in the first set and a number of candidate REs in
the second set. If there is a match the UE knows which of the two
sets that was used for the mapping. The UE may further detect
whether the message was intended for the UE or not. For this
reason, the UE may correlate the 16 CRC bits for each of the
decoded candidate REs with its UE identity. If there is a match the
UE knows that the ePDCCH message was intended for the UE.
[0114] According to an embodiment, the resource elements of the
first ePDCCH set comprises information of uplink grants and the
resource elements of the second ePDCCH set comprises information of
downlink assignments.
[0115] According to an embodiment, the configuration message is
received (902) in a RRC message.
[0116] FIG. 10 shows a UE 1000 in a wireless communication network,
configured for communicating an ePDCCH with a network node. The UE
1000 comprises a receiving unit 1002 for receiving a configuration
message from the network node. The configuration message comprises
an indication of a first mapping of the ePDCCH to resource elements
belonging to a first ePDCCH set, where the resource elements of the
first ePDCCH set are different from resource elements used for a
first type of signal, and an indication of a second mapping of the
ePDCCH to resource elements belonging to a second ePDCCH set, where
the resource elements of the second ePDCCH set are different from
resource elements used for a second type of signal.
[0117] The UE 1000 may further comprise a communication unit 1010,
which may be considered to comprise conventional means for
communication from and/or to network nodes, such as eNodeBs, of the
wireless network. The communication unit 1010 may comprise a
wireless communication part for communicating wirelessly with
network nodes, such as one or more transceivers. The UE 1000 may
further comprise other functional units (not shown) for providing
e.g. regular network node functions. The UE 1000 may further
comprise one or more storage units 1012.
[0118] The receiving unit 1002, the decoding unit 1004 and the
detecting unit 1006 may be arranged in an arrangement 1001. The
arrangement 1001 could be implemented e.g. by one or more of: a
processor or a micro processor and adequate software and storage
therefore, a Programmable Logic Device (PLD) or other electronic
component(s)/processing circuit(s) configured to perform the
actions, or methods, mentioned above.
[0119] According to an embodiment, the configuration message
comprises an indication of an ePDCCH start symbol for the first
ePDCCH set and an indication of an ePDCCH start symbol for the
second ePDCCH set.
[0120] According to another embodiment, the indicated ePDCCH start
symbol is the same start symbol as scheduled for a Packet Data
Shared Channel, PDSCH, to be transmitted by the network node.
[0121] According to another embodiment, one or more of the
following configuration parameters: number of Cell-specific
Reference Signal, CRS, antenna ports, CRS frequency shift, start
position, Multicast/Broadcast Single Frequency Network, MBSFN,
subframe configuration, Zero Power Channel State Information
Reference Signal, CSI-RS, resource configuration CSI-RS resource
configuration, are shared between the ePDCCH and a Packet Data
Shared Channel PDSCH.
[0122] According to another embodiment, the receiving unit 1002 is
further arranged to receive a message from the network node
comprising the ePDCCH allocated to a selected one of the first
ePDCCH set and the second ePDCCH set. The UE 1000 further comprises
a decoding unit 1004 for decoding ePDCCH candidates according to
the first mapping and for decoding ePDCCH candidates according to
the second mapping. The UE 1000 further comprises a detecting unit
1006 for detecting whether the ePDCCH was allocated to the first
ePDCCH set or to the second ePDCCH set.
[0123] According to another embodiment, the resource elements of
the first ePDCCH set comprises information of uplink grants and the
resource elements of the second ePDCCH set comprises information of
downlink assignments.
[0124] According to another embodiment, the receiving unit 1002 is
further arranged to receive the configuration message in a RRC
message.
[0125] FIG. 11 schematically shows an embodiment of an arrangement
1100 for use in a UE 1000, which also can be an alternative way of
disclosing an embodiment of the arrangement 1001 in the UE 1000
illustrated in FIG. 10. Comprised in the arrangement 1100 is a
processing unit 1106, e.g. with a Digital Signal Processor (DSP).
The processing unit 1106 may be a single unit or a plurality of
units to perform different actions of procedures described herein.
The arrangement 1100 may also comprise an input unit 1102 for
receiving signals from other entities, and an output unit 1104 for
providing signal(s) to other entities. The input unit 1102 and the
output unit 1104 may be arranged as an integrated entity.
[0126] Furthermore, the arrangement 1100 comprises at least one
computer program product 1108 in the form of a non-volatile or
volatile memory, e.g. an Electrically Erasable Programmable
Read-only Memory (EEPROM), a flash memory, a disk drive or a
Random-access memory (RAM). The computer program product 1108
comprises a computer program 1110, which comprises code means,
which when executed in the processing unit 1106 in the arrangement
1100 causes the arrangement and/or the UE 1000 to perform the
actions of any of the procedures described earlier in conjunction
with FIG. 9.
[0127] The computer program 1110 may be configured as a computer
program code structured in computer program modules. Hence, in an
exemplifying embodiment, the code means in the computer program
1110 of the arrangement 1100 comprises a receiving module 1110a for
receiving a configuration message from a network node, the
configuration message comprising an indication of a first mapping
of the ePDCCH to resource elements belonging to a first ePDCCH set,
where the resource elements of the first ePDCCH set are different
from resource elements used for a first type of signal, and an
indication of a second mapping of the ePDCCH to resource elements
belonging to a second ePDCCH set, where the resource elements of
the second ePDCCH set are different from resource elements used for
a second type of signal.
[0128] The computer program may further comprise a second receiving
module 1110b for receiving a message from the network node
comprising the ePDCCH allocated to a selected one of the first
ePDCCH set and the second ePDCCH set. The UE computer program may
further comprise a decoding module 1110c for decoding ePDCCH
candidates according to the first mapping and for decoding ePDCCH
candidates according to the second mapping. The computer program
may further comprise a detecting module 1110d for detecting whether
the ePDCCH was allocated to the first ePDCCH set or to the second
ePDCCH set.
[0129] FIG. 12 described a method performed by a network node of a
wireless communication network, for communicating an ePDCCH, to a
UE. The method comprises transmitting 1202 a configuration message
to the UE with indication of a number of sets of PDSCH to RE
mappings. The method further comprises transmitting 1204 a
configuration message to the UE with an indication of a first set
of ePDCCH to RE mapping, wherein the first set of ePDCCH to RE
mapping is the same as one of the number of sets of PDSCH to RE
mappings. The method further comprises allocating 1206 the ePDCCH
to REs of the first set. The method further comprises transmitting
1208 the allocated ePDCCH to the UE.
[0130] FIG. 13 described a method performed by a UE of a wireless
communication network, for communicating an ePDCCH with a network
node. The method comprises receiving 1302 a configuration message
from the network node with an indication of a number of sets of
PDSCH to RE mappings. The method further comprises receiving 1304 a
configuration message from the network node with an indication of a
first set of ePDCCH to RE mapping, wherein the first set of ePDCCH
to RE mapping is the same as one of the number of sets of PDSCH to
RE mappings. The method further comprises receiving 1306 a message
from the network node comprising the ePDCCH allocated to the first
ePDCCH set The method further comprises decoding 1308 the received
message according to the received first ePDCCH set.
[0131] The invention has been described in connection with two
different mappings and two different ePDCCH sets. Of course it is
possible to also use more than two different mappings and more than
two different ePDCCH sets.
[0132] It will be appreciated by the person of skill in the art
that various modifications may be made to the above described
embodiments without departing from the scope of the present
invention. For example, it will be readily appreciated that
although the above embodiments are described with reference to
parts of an LTE network, embodiments of the present invention will
also be applicable to like networks, such as a successor of the LTE
network, having like functional components, or a WiMax (IEEE
802.16) network. Therefore, in particular, the terms LTE and
associated or related terms used in the above description and in
the enclosed drawings and any appended claims now or in the future
are to be interpreted accordingly.
[0133] In the discussion, specific details of particular
embodiments of the present invention have been set forth for
purposes of explanation and not limitation. It will be appreciated
by those skilled in the art that other embodiments may be employed
apart from these specific details. Furthermore, in some instances
detailed descriptions of well-known methods, nodes, interfaces,
circuits, and devices are omitted so as not to obscure the
description with unnecessary detail. Those skilled in the art will
appreciate that the functions described may be implemented in one
or in several nodes. Some or all of the functions described may be
implemented using hardware circuitry, such as analog and/or
discrete logic gates interconnected to perform a specialized
function, ASICs, PLAs, etc. Likewise, some or all of the functions
may be implemented using software programs and data in conjunction
with one or more digital microprocessors or general purpose
computers. Where nodes that communicate using the air interface
have been described, it will be appreciated that those nodes also
have suitable radio communications circuitry. Moreover, the
technology can additionally be considered to be embodied entirely
within any form of computer-readable memory, including
non-transitory embodiments such as solid-state memory, magnetic
disk, or optical disk containing an appropriate set of computer
instructions that would cause a processor to carry out the
techniques described herein.
[0134] Hardware implementations may include or encompass, without
limitation, digital signal processor (DSP) hardware, a reduced
instruction set processor, hardware (e.g., digital or analog)
circuitry including but not limited to application specific
integrated circuit(s) (ASIC) and/or field programmable gate
array(s) (FPGA(s)), and (where appropriate) state machines capable
of performing such functions.
[0135] In terms of computer implementation, a computer is generally
understood to comprise one or more processors or one or more
controllers, and the terms computer, processor, and controller may
be employed interchangeably. When provided by a computer,
processor, or controller, the functions may be provided by a single
dedicated computer or processor or controller, by a single shared
computer or processor or controller, or by a plurality of
individual computers or processors or controllers, some of which
may be shared or distributed. Moreover, the term "processor" or
"controller" also refers to other hardware capable of performing
such functions and/or executing software, such as the example
hardware recited above
[0136] Examples of several embodiments of the present invention
have been described in detail above, with reference to the attached
illustrations of specific embodiments. Because it is not possible,
of course, to describe every conceivable combination of components
or techniques, those skilled in the art will appreciate that the
present invention can be implemented in other ways than those
specifically set forth herein, without departing from essential
characteristics of the invention. The present embodiments are thus
to be considered in all respects as illustrative and not
restrictive.
* * * * *