U.S. patent application number 15/123436 was filed with the patent office on 2017-03-09 for method of receiving control information for receiving discovery reference signal and apparatus thereof.
The applicant listed for this patent is LG ELECTRONICS INC.. Invention is credited to Jonghyun PARK, Yunjung YI.
Application Number | 20170070312 15/123436 |
Document ID | / |
Family ID | 54055564 |
Filed Date | 2017-03-09 |
United States Patent
Application |
20170070312 |
Kind Code |
A1 |
YI; Yunjung ; et
al. |
March 9, 2017 |
METHOD OF RECEIVING CONTROL INFORMATION FOR RECEIVING DISCOVERY
REFERENCE SIGNAL AND APPARATUS THEREOF
Abstract
The present specification provides a method and UE for receiving
configuration usable for a discovery, which can be used in a small
cell scenario. In detail, the UE is configured for receiving
measurement configuration for a discovery signal, wherein the
discovery signal includes CRS, PSS, and SSS. In addition, the
discovery signal may further include CSI-RS depending on its
configuration. The measurement configuration may include at least
one set of configuration elements, each set of the configuration
elements being defined per a frequency of a corresponding cell. In
detail, the each set of the configuration elements indicates a
measurement period of the discovery signal, an offset of the
measurement period, and a measurement duration. The each set of the
configuration elements is applied to a plurality of cells having a
same frequency. The UE performs a measurement on the discovery
signal based on the received configuration.
Inventors: |
YI; Yunjung; (Seoul, KR)
; PARK; Jonghyun; (Seoul, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LG ELECTRONICS INC. |
Seoul |
|
KR |
|
|
Family ID: |
54055564 |
Appl. No.: |
15/123436 |
Filed: |
March 4, 2015 |
PCT Filed: |
March 4, 2015 |
PCT NO: |
PCT/KR2015/002099 |
371 Date: |
September 2, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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62004205 |
May 29, 2014 |
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61990657 |
May 8, 2014 |
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61974990 |
Apr 3, 2014 |
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61972386 |
Mar 30, 2014 |
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61953947 |
Mar 17, 2014 |
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61947444 |
Mar 4, 2014 |
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62037127 |
Aug 14, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W 72/0406 20130101;
H04W 4/06 20130101; H04W 72/042 20130101; H04W 88/02 20130101; H04L
5/14 20130101; H04W 72/08 20130101; H04L 5/001 20130101; H04J
11/0069 20130101; H04W 88/08 20130101; H04L 5/0048 20130101; H04W
72/082 20130101 |
International
Class: |
H04J 11/00 20060101
H04J011/00; H04W 72/08 20060101 H04W072/08; H04W 72/04 20060101
H04W072/04; H04L 5/00 20060101 H04L005/00 |
Claims
1-15. (canceled)
16. A method of receiving control information for receiving a
signal in a wireless communication system, the method performed by
a user equipment (UE) and comprising: receiving channel status
information-reference signal (CSI-RS) configuration including at
least one set of CSI-RS configuration elements used for a zero
power CSI-RS, wherein the zero power CSI-RS is included in a
discovery signal, which includes a cell-specific reference signal
(CRS), a primary synchronization signal (PSS), and a secondary
synchronization signal (SSS); and performing a rate matching on a
downlink channel by determining available resource elements (REs)
for the downlink channel based on the CSI-RS configuration for the
zero power CSI-RS.
17. The method of claim 16, wherein resource elements (REs)
configured for the zero power CSI-RS are not used for the downlink
channel.
18. The method of claim 16, wherein the CSI-RS configuration
includes a plurality set of CSI-RS configuration elements, each set
of CSI-RS configuration elements includes CSI-RS interval
information and CSI-RS offset information, and each set of CSI-RS
configuration elements is separately configured.
19. The method of claim 16, further comprising: receiving
measurement configuration for the discovery signal, wherein the
measurement configuration includes at least one set of
configuration elements, each set of the configuration elements is
defined per a frequency of a corresponding cell, the each set of
the configuration elements indicates a measurement period of the
discovery signal, an offset of the measurement period, and a
measurement duration during which the UE measures the discovery
signal in one period of the measurement period; and performing a
measurement on the discovery signal based on the measurement period
of the discovery signal, the offset of the measurement period, and
the measurement duration.
20. The method of claim 19, wherein the measurement configuration
for the discovery signal is received via a radio resource control
(RRC) message.
21. A user equipment (UE) for receiving control information for
receiving a signal in a wireless communication system, comprising:
a radio frequency (RF) unit configured for receiving a signal; and
a processor coupled to the RF unit and configured to: receive
channel status information-reference signal (CSI-RS) configuration
including at least one set of CSI-RS configuration elements used
for a zero power CSI-RS, wherein the zero power CSI-RS is included
in a discovery signal, which includes a cell-specific reference
signal (CRS), a primary synchronization signal (PSS), and a
secondary synchronization signal (SSS); and perform a rate matching
on a downlink channel by determining available resource elements
(REs) for the downlink channel based on the CSI-RS configuration
for the zero power CSI-RS.
22. The user equipment of claim 21, wherein resource elements (REs)
configured for the zero power CSI-RS are not used for the downlink
channel.
23. The user equipment of claim 21, wherein the CSI-RS
configuration includes a plurality set of CSI-RS configuration
elements, each set of CSI-RS configuration elements includes CSI-RS
interval information and CSI-RS offset information, and each set of
CSI-RS configuration elements is separately configured.
24. The user equipment of claim 21, wherein the processor is
further configured to: receive measurement configuration for the
discovery signal, wherein the measurement configuration includes at
least one set of configuration elements, each set of the
configuration elements is defined per a frequency of a
corresponding cell, the each set of the configuration elements
indicates a measurement period of the discovery signal, an offset
of the measurement period, and a measurement duration during which
the UE measures the discovery signal in one period of the
measurement period; and perform a measurement on the discovery
signal based on the measurement period of the discovery signal, the
offset of the measurement period, and the measurement duration.
25. The user equipment of claim 24, wherein the measurement
configuration for the discovery signal is received via a radio
resource control (RRC) message.
Description
TECHNICAL FIELD
[0001] This specification relates to a method of receiving control
information used for a discovery reference signal, more
specifically to a method of receiving configuration information
used for measuring a discovery reference signal in a user equipment
(UE).
BACKGROUND ART
[0002] The Third Generation Partnership Project (3GPP) Long Term
Evolution (LTE) which is a set of enhancements to the Universal
Mobile Telecommunications System (UMTS) is introduced as 3GPP
Release 8. The 3GPP LTE uses orthogonal frequency division multiple
access (OFDMA) for a downlink, and uses single carrier frequency
division multiple access (SC-FDMA) for an uplink, and adopts
multiple input multiple output (MIMO) with up to four antennas. In
recent years, there is an ongoing discussion on 3GPP LTE-Advanced
(LTE-A), which is a major enhancement to the 3GPP LTE.
[0003] The commercialization of the 3GPP LTE (A) system is being
recently accelerated. The LTE systems are spread more quickly as
respond to users' demand for services that may support higher
quality and higher capacity while ensuring mobility, as well as
voice services. The LTE system provides for low transmission delay,
high transmission rate and system capacity, and enhanced
coverage.
[0004] To increase the capacity for the users' demand of services,
increasing the bandwidth may be essential, a carrier aggregation
(CA) technology or resource aggregation over intra-node carriers or
inter-node carriers aiming at obtaining an effect, as if a
logically wider band is used, by grouping a plurality of physically
non-continuous bands in a frequency domain has been developed to
effectively use fragmented small bands. Individual unit carriers
grouped by carrier aggregation is known as a component carrier
(CC). For inter-node resource aggregation, for each node, carrier
group (CG) can be established where one CG can have multiple CCs.
Each CC is defined by a single bandwidth and a center
frequency.
[0005] Recently, a wireless access network configuration has been
changed such that various types of small cells having small sizes,
such as a pico cell, a femto cell, etc., interact with a macro cell
having a relatively large size. The wireless access network
configuration aims to provide a high data rate to final UEs and
thus increase Quality of Experience (QoE) for the final UEs in a
situation where multi-layer cells co-exist in a hierarchical
structure basically involving a macro cell.
[0006] According to one of the current 3rd Generation Partnership
Project (3GPP) standardization categories, Small Cell Enhancements
for E-UTRA and E-UTRAN SI; e.g., RP-122033, enhancement of
indoor/outdoor scenarios using low-power nodes is discussed under
the title of small cell enhancement. In addition, scenarios and
requirements for the small cell enhancement are described in 3GPP
TR 36.932.
[0007] Meanwhile, the usage of small cell is getting grown in many
fields nowadays, such as pico cells, small cells under dual
connectivity, etc. To properly perform communication between the
small cells and UEs, improvements related to conventional control
signals, such as reference signals and synchronous signals, have
been discussed
DISCLOSURE
Technical Problem
[0008] Recently, a number of issues regarding a discovery reference
signal (DRS) have been discussed. An object of the present
specification is to provide a method and apparatus for providing an
advanced scheme to support the DRS in a wireless communication. In
detail, the present specification proposes detailed embodiments
related to candidates which can be used as DRS. Further, the
present specification proposes a clarification and/or embodiment
with respect to alignment between a measurement gap and the DRS.
Further, the present specification proposes an embodiment of
configurations related to measurement timing of the DRS. In such
embodiment, detailed configuration elements are defined per each
frequency, which is corresponding to a cell. The present
specification proposes a clarification and/or embodiment with
respect to misalignment with respect to a number of cells. The
present specification also proposes a clarification and/or
embodiment with respect to enhanced Interference Mitigation &
Traffic Adaptation (eIMTA), which dynamically changes Time Division
Duplex (TDD) configuration in the context of DRS operations.
[0009] With respect to the above-mentioned objects of the present
specification, it should be noted that the present specification
now proposes a number of additional features and the
above-mentioned objects are introduced for exemplary purposes, and
thus the objects of the present specification are not limited to
the foregoing objects.
Technical Solution
[0010] An embodiment of the present specification is to provide a
method of receiving control information for receiving a signal in a
wireless communication system, the method performed by a user
equipment (UE). Further, the present specification also proposes a
wireless device, e.g., UE, to perform the proposed method.
[0011] Preferably, the UE is configured for receiving measurement
configuration for a discovery signal, wherein the discovery signal
includes a cell-specific reference signal (CRS), a primary
synchronization signal (PSS), and a secondary synchronization
signal (SSS).
[0012] In addition, the discovery signal may further include a
channel status information-reference signal (CSI-RS) depending on a
configuration of the CSI-RS.
[0013] The measurement configuration may include at least one set
of configuration elements, each set of the configuration elements
being defined per a frequency of a corresponding cell. In detail,
the each set of the configuration elements indicates a measurement
period of the discovery signal, an offset of the measurement
period, and a measurement duration during which the UE measures the
discovery signal in one period of the measurement period.
[0014] Preferably, the measurement configuration for a discovery
signal is received via a radio resource control (RRC) message.
Moreover, the RRC message is received at the UE being in an RRC
connected mode. The measurement on the discovery signal starts on a
first subframe carrying the SSS in one period of the measurement
period. Further, a set of the configuration elements defined for
one frequency contains a single measurement period, a single
offset, and a single measurement duration. The each set of the
configuration elements is applied to a plurality of cells having a
same frequency.
[0015] The UE is configured for performing a measurement on the
discovery signal based on the measurement period of the discovery
signal, the offset of the measurement period, and the measurement
duration.
[0016] Additionally, the UE may further comprising: receiving
measurement gap configuration indicating a length and a repetition
period of a measurement gap, wherein the measurement period of the
discovery signal is set to be a multiple of the repetition period
of a measurement gap.
[0017] Additionally, the UE may further comprising receiving
channel status information-reference signal (CSI-RS) configuration
including at least one set of CSI-RS configuration elements used
for a zero power CSI RS. The CSI-RS configuration includes a
plurality set of CSI-RS configuration elements, each set of CSI-RS
configuration elements includes CSI-RS interval information and
CSI-RS offset information, and each set of CSI-RS configuration
elements is separately configured.
[0018] Additionally, the UE expecting to receive MBMS subframe(s)
and/or MBMS service may not expect to receive discovery signal in a
corresponding subframe.
[0019] When performing the above embodiments, a system frame number
(SFN) of a macro cell of the UE is used as a reference for a
duration where the UE performs the measurement on the discovery
signal.
Advantageous Effects
[0020] According to the present specification, an advanced example
clarifying candidates which can be used as DRS is proposed.
Further, an advanced example clarifying alignment between a
measurement gap and the DRS is proposed in the present
specification. Further, an advanced example related configuration
related to measurement timing of the DRS is proposed. Further, an
advanced example related to configuration related to measurement
timing of the DRS is proposed. Further, an advanced example with
respect to misalignment with respect to a number of cells is
proposed. Also, an advanced example related to the eIMTA is
proposed in the present specification.
DESCRIPTION OF DRAWINGS
[0021] FIG. 1 shows a wireless communication system to which the
present specification is applied.
[0022] FIG. 2 shows an exemplary concept for a carrier aggregation
(CA) technology according to an exemplary embodiment of the present
specification.
[0023] FIG. 3 shows a structure of a radio frame to which the
present specification is applied.
[0024] FIG. 4 shows an example of a synchronization signal which is
used in a basic CP and an extended CP.
[0025] FIG. 5 shows a scheme of generating a code related to a
sub-synchronous signal (SSS).
[0026] FIG. 6 shows an example of a multi-node system.
[0027] FIG. 7 shows one example of a pattern in which a CRS is
mapped to an RB when a base station uses a single antenna port.
[0028] FIG. 8 shows one example of a pattern in which a CRS is
mapped to an RB when a base station uses two antenna ports.
[0029] FIG. 9 shows one example of a pattern in which a CRS is
mapped to an RB when a base station uses four antenna ports.
[0030] FIG. 10 shows an example of an RB to which a CSI-RS is
mapped.
[0031] FIG. 11 shows an example of UE measurement performed on the
DRS according to one example of the present specification.
[0032] FIG. 12 shows an example of PSS/SSS time-divisional
multiplexing.
[0033] FIG. 13 shows another example of PSS/SSS time-divisional
multiplexing.
[0034] FIG. 14 shows candidate locations of DRS-PSS and DRS-SSS
according to one aspect of the present specification.
[0035] FIG. 15 shows a DRS RS pattern based on CRS according to the
present specification.
[0036] FIG. 16 shows a number of measurement gap configurations
proposed by the present specification.
[0037] FIG. 17 shows an additional embodiments related to
measurement gap configurations proposed by the present
specification.
[0038] FIG. 18 shows the relationship between UE measurement on DRS
and measurement gap.
[0039] FIG. 19 shows a block diagram which briefly describes a
wireless communication system including an UE 1900 and a BS or cell
2000.
MODE FOR INVENTION
[0040] FIG. 1 shows a wireless communication system to which the
present specification is applied. The wireless communication system
may also be referred to as an evolved-UMTS terrestrial radio access
network (E-UTRAN) or a long term evolution (LTE)/LTE-A system.
[0041] The E-UTRAN includes at least one base station (BS) 20 which
provides a control plane and a user plane to an user equipment (UE)
10. The UE 10 may be fixed or mobile, and may be referred to as
another terminology, such as a mobile station (MS), a user terminal
(UT), a subscriber station (SS), a mobile terminal (MT), a wireless
device, etc. The BS 20 is generally a fixed station that
communicates with the UE 10 and may be referred to as another
terminology, such as an evolved node-B (eNB), a base transceiver
system (BTS), an access point, a cell, node-B, or node etc.
[0042] Multi-access schemes applied to the wireless communication
system are not limited. Namely, various multi-access schemes such
as CDMA (Code Division Multiple Access), TDMA (Time Division
Multiple Access), FDMA (Frequency Division Multiple Access), OFDMA
(Orthogonal Frequency Division Multiple Access), SC-FDMA (Single
Carrier-FDMA), OFDM-FDMA, OFDM-TDMA, OFDM-CDMA, or the like, may be
used. For uplink transmission and downlink transmission, a TDD
(Time Division Duplex) scheme in which transmission is made by
using a different time or an FDD (Frequency Division Duplex) scheme
in which transmission is made by using different frequencies may be
used.
[0043] The BSs 20 are interconnected by means of an X2 interface.
The BSs 20 are also connected by means of an S1 interface to an
evolved packet core (EPC) 30, more specifically, to a mobility
management entity (MME) through S1-MME and to a serving gateway
(S-GW) through S1-U.
[0044] The EPC 30 includes an MME, an S-GW, and a packet data
network-gateway (P-GW). The MME has access information of the UE or
capability information of the UE, and such information is generally
used for mobility management of the UE. The S-GW is a gateway
having an E-UTRAN as an end point. The P-GW is a gateway having a
PDN as an end point.
[0045] Layers of a radio interface protocol between the UE and the
network can be classified into a first layer (L1), a second layer
(L2), and a third layer (L3) based on the lower three layers of the
open system interconnection (OSI) model that is well-known in the
communication system. Among them, a physical (PHY) layer belonging
to the first layer provides an information transfer service by
using a physical channel, and a radio resource control (RRC) layer
belonging to the third layer serves to control a radio resource
between the UE and the network. For this, the RRC layer exchanges
an RRC message between the UE and the BS.
[0046] More details, radio protocol architecture for a user plane
(U-plane) and a control plane (C-plane) are explained. A PHY layer
provides an upper layer with an information transfer service
through a physical channel. The PHY layer is connected to a medium
access control (MAC) layer which is an upper layer of the PHY layer
through a transport channel. Data is transferred between the MAC
layer and the PHY layer through the transport channel. The
transport channel is classified according to how and with what
characteristics data is transferred through a radio interface.
Between different PHY layers, i.e., a PHY layer of a transmitter
and a PHY layer of a receiver, data are transferred through the
physical channel. The physical channel may be modulated using an
orthogonal frequency division multiplexing (OFDM) scheme, and may
utilize time and frequency as a radio resource.
[0047] Functions of the MAC layer include mapping between a logical
channel and a transport channel and multiplexing/de-multiplexing on
a transport block provided to a physical channel over a transport
channel of a MAC service data unit (SDU) belonging to the logical
channel. The MAC layer provides a service to a radio link control
(RLC) layer through the logical channel.
[0048] Functions of the RLC layer include RLC SDU concatenation,
segmentation, and reassembly. To ensure a variety of quality of
service (QoS) required by a radio bearer (RB), the RLC layer
provides three operation modes, i.e., a transparent mode (TM), an
unacknowledged mode (UM), and an acknowledged mode (AM). The AM RLC
provides error correction by using an automatic repeat request
(ARQ).
[0049] Functions of a packet data convergence protocol (PDCP) layer
in the user plane include user data delivery, header compression,
and ciphering. Functions of a PDCP layer in the control plane
include control-plane data delivery and ciphering/integrity
protection.
[0050] A radio resource control (RRC) layer is defined only in the
control plane. The RRC layer serves to control the logical channel,
the transport channel and the physical channel in association with
configuration, reconfiguration and release of radio bearers (RBs).
An RB is a logical path provided by the first layer (i.e., the PHY
layer) and the second layer (i.e., the MAC layer, the RLC layer,
and the PDCP layer) for data delivery between the UE and the
network.
[0051] The setup of the RB implies a process for specifying a radio
protocol layer and channel properties to provide a particular
service and for determining respective detailed parameters and
operations. The RB can be classified into two types, i.e., a
signaling RB (SRB) and a data RB (DRB). The SRB is used as a path
for transmitting an RRC message in the control plane. The DRB is
used as a path for transmitting user data in the user plane.
[0052] When an RRC connection is established between an RRC layer
of the UE and an RRC layer of the network, the UE is in an RRC
connected state (it may also be referred to as an RRC connected
mode), and otherwise the UE is in an RRC idle state (it may also be
referred to as an RRC idle mode).
[0053] FIG. 2 shows an exemplary concept for a carrier aggregation
(CA) technology according to an exemplary embodiment of the present
specification.
[0054] Referring to FIG. 2, the downlink (DL)/uplink (UL) subframe
structure considered in 3GPP LTE-A (LTE-Advanced) system where
multiple CCs are aggregated (in this example, 3 carriers exist) is
illustrated, a UE can monitor and receive DL signal/data from
multiple DL CCs at the same time. However, even if a cell is
managing N DL CCs, the network may configure a UE with M DL CCs,
where M.ltoreq.N so that the UE's monitoring of the DL signal/data
is limited to those M DL CCs. In addition, the network may
configure L DL CCs as the main DL CCs from which the UE should
monitor/receive DL signal/data with a priority, either
UE-specifically or cell-specifically, where L.ltoreq.M.ltoreq.N. So
the UE may support one or more carriers (Carrier 1 or more Carriers
2 . . . N) according to UE's capability thereof.
[0055] A Carrier or a cell may be divided into a primary component
carrier (PCC) and a secondary component carrier (SCC) depending on
whether or not they are activated. A PCC is always activated, and
an SCC is activated or deactivated according to particular
conditions. That is, a PCell (primary serving cell) is a resource
in which the UE initially establishes a connection (or a RRC
connection) among several serving cells. The PCell serves as a
connection (or RRC connection) for signaling with respect to a
plurality of cells (CCs), and is a special CC for managing UE
context which is connection information related to the UE. Further,
when the PCell (PCC) establishes the connection with the UE and
thus is in an RRC connected mode, the PCC always exists in an
activation state. A SCell (secondary serving cell) is a resource
assigned to the UE other than the PCell (PCC). The SCell is an
extended carrier for additional resource assignment, etc., in
addition to the PCC, and can be divided into an activation state
and a deactivation state. The SCell is initially in the
deactivation state. If the SCell is deactivated, it includes not
transmit sounding reference signal (SRS) on the SCell, not report
channel-quality indicator (CQI)/precoding matrix indicator
(PMI)/rank indicator (RD/procedure transaction identifier (PTI) for
the SCell, not transmit on UL-SCH on the SCell, not monitor the
PDCCH on the SCell, not monitor the PDCCH for the SCell. The UE
receives an Activation/Deactivation MAC control element in this TTI
activating or deactivating the SCell.
[0056] To enhance the user throughput, it is also considered to
allow inter-node resource aggregation over more than one eNB/node
where a UE may be configured with more than one carrier groups. It
is configured PCell per each carrier group which particularly may
not be deactivated. In other words, PCell per each carrier group
may maintain its state to active all the time once it is configured
to a UE. In that case, serving cell index i corresponding to a
PCell in a carrier group which does not include serving cell index
0 which is a master PCell cannot be used for
activation/deactivation.
[0057] More particularly, if serving cell index 0, 1, 2 are
configured by one carrier group whereas serving cell index 3, 4, 5
are configured by the other carrier group in two carrier group
scenarios where serving cell index 0 is PCell and serving cell
index 3 is the PCell of the second carrier group, then only bits
corresponding 1 and 2 are assumed to be valid for the first carrier
group cell activation/deactivation messages whereas bits
corresponding 4 and 5 are assumed to be valid for the second
carrier group cell activation/deactivation. To make some
distinction between PCell for the first carrier group and the
second carrier group, the PCell for the second carrier group can be
noted as S-PCell hereinafter. Herein, the index of the serving cell
may be a logical index determined relatively for each UE, or may be
a physical index for indicating a cell of a specific frequency
band. The CA system supports a non-cross carrier scheduling of
self-carrier scheduling, or cross carrier scheduling.
[0058] FIG. 3 shows a structure of a radio frame to which the
present specification is applied.
[0059] Referring to FIG. 3, a radio frame includes 10 subframes,
and one subframe includes two slots. The time taken for one
subframe to be transmitted is called a Transmission Time Interval
(TTI). For example, the length of one subframe may be 1 ms, and the
length of one slot may be 0.5 ms.
[0060] One slot includes a plurality of OFDM symbols in the time
domain and includes a plurality of Resource Blocks (RBs) in the
frequency domain. An OFDM symbol is for representing one symbol
period because downlink OFDMA is used in 3GPP LTE system and it may
be called an SC-FDMA symbol or a symbol period depending on a
multi-access scheme. An RB is a resource allocation unit, and it
includes a plurality of contiguous subcarriers in one slot. The
number of OFDM symbols included in one slot may vary according to
the configuration of the CP (Cyclic Prefix). The CP includes an
extended CP and a normal CP. For example, if normal CP case, the
OFDM symbol is composed by 7. If configured by the extended CP, it
includes 6 OFDM symbols in one slot. If the channel status is
unstable such as moving at a fast pace UE, the extended CP can be
configured to reduce an inter-symbol interference. Herein, the
structure of the radio frame is only illustrative, and the number
of subframes included in a radio frame, or the number of slots
included in a subframe, and the number of OFDM symbols included in
a slot may be changed in various ways to apply new communication
system. This specification has no limitation to adapt to other
system by varying the specific feature and the embodiment of the
specification can apply with changeable manners to a corresponding
system.
[0061] The downlink slot includes a plurality of OFDM symbols in
the time domain. For example, one downlink slot is illustrated as
including 7 OFDMA symbols and one Resource Block (RB) is
illustrated as including 12 subcarriers in the frequency domain,
but not limited thereto. Each element on the resource grid is
called a Resource Element (RE). One resource block includes
12.times.7 (or 6) REs. The number NDL of resource blocks included
in a downlink slot depends on a downlink transmission bandwidth
that is set in a cell. Bandwidths that are taken into account in
LTE are 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, and 20 MHz. If the
bandwidths are represented by the number of resource blocks, they
are 6, 15, 25, 50, 75, and 100, respectively.
[0062] The former 0 or 1 or 2 or 3 OFDM symbols of the first slot
within the subframe correspond to a control region to be assigned
with a control channel, and the remaining OFDM symbols thereof
become a data region to which a physical downlink shared chancel
(PDSCH) is allocated. Examples of downlink control channels include
a Physical Control Format Indicator Channel (PCFICH), a Physical
Downlink Control Channel (PDCCH), and a Physical Hybrid-ARQ
Indicator Channel (PHICH).
[0063] The PCFICH transmitted in a 1st OFDM symbol of the subframe
carries a control format indicator (CFI) regarding the number of
OFDM symbols (i.e., a size of the control region) used for
transmission of control channels in the subframe, that is, carries
information regarding the number of OFDM symbols used for
transmission of control channels within the subframe. The UE first
receives the CFI on the PCFICH, and thereafter monitors the
PDCCH.
[0064] The PHICH carries acknowledgement (ACK)/not-acknowledgement
(NACK) signals in response to an uplink Hybrid Automatic Repeat
Request (HARQ). That is, ACK/NACK signals for uplink data that has
been transmitted by a UE are transmitted on a PHICH.
[0065] A PDCCH (or ePDCCH) is a downlink physical channel, a PDCCH
can carry information about the resource allocation and
transmission format of a Downlink Shared Channel (DL-SCH),
information about the resource allocation of an Uplink Shared
Channel (UL-SCH), paging information about a Paging Channel (PCH),
system information on a DL-SCH, information about the resource
allocation of a higher layer control message, such as a random
access response transmitted on a PDSCH, a set of transmit power
control commands for UEs within a certain UE group, the activation
of a Voice over Internet Protocol (VoIP), etc. A plurality of
PDCCHs may be transmitted within the control region, and a UE can
monitor a plurality of PDCCHs. The PDCCH is transmitted on one
Control Channel Element (CCE) or on an aggregation of some
contiguous CCEs. A CCE is a logical assignment unit for providing a
coding rate according to the state of a radio channel to a PDCCH.
The CCE corresponds to a plurality of resource element groups
(REGs). A format of the PDCCH and the number of bits of the
available PDCCH are determined according to a correlation between
the number of CCEs and the coding rate provided by the CCEs.
[0066] The wireless communication system of the present
specification uses blind decoding for Physical Downlink Control
Channel (PDCCH) detection. The blind decoding is a scheme in which
a desired identifier is de-masked from a CRC of a PDCCH to
determine whether the PDCCH is its own channel by performing CRC
error checking. An eNB determines a PDCCH format according to a
Downlink Control Information (DCI) to be transmitted to a UE.
Thereafter, the eNB attaches a cyclic redundancy check (CRC) to the
DCI, and masks a unique identifier (referred to as a radio network
temporary identifier (RNTI)) to the CRC according to an owner or
usage of the PDCCH. For example, if the PDCCH is for a specific UE,
a unique identifier (e.g., cell-RNTI (C-RNTI)) of the UE may be
masked to the CRC. Alternatively, if the PDCCH is for a paging
message, a paging indicator identifier (e.g., paging-RNTI (e.g.,
P-RNTI)) may be masked to the CRC. If the PDCCH is for system
information (more specifically, a system information block (SIB) to
be described below), a system information identifier and system
information RNTI (e.g., SI-RNTI) may be masked to the CRC. To
indicate a random access response that is a response for
transmission of a random access preamble of the UE, a random
access-RNTI (e.g., RA-RNTI) may be masked to the CRC.
[0067] Thus, the BS determines a PDCCH format according to a
Downlink Control Information (DCI) to be transmitted to the UE, and
attaches a cyclic redundancy check (CRC) to control information.
The DCI includes uplink or downlink scheduling information or
includes an uplink transmit (TX) power control command for
arbitrary UE groups. The DCI is differently used depending on its
format, and it also has a different field that is defined within
the DCI.
[0068] Meanwhile, an uplink subframe may be divided into a control
region to which a physical uplink control channel (PUCCH) that
carries uplink control information is allocated; the control
information includes an ACK/NACK response of downlink transmission.
A data region to which physical uplink shared channel (PUSCH) that
carries user data is allocated in the frequency domain.
[0069] Hereinafter, technical features related to synchronization
signals used in wireless communication system to which the present
specification is applied.
[0070] FIG. 4 shows an example of a synchronization signal which is
used in a basic CP and an extended CP.
[0071] The synchronization signal may be divided into a primary SS
(PSS) and a secondary SS (SSS) depending on the role and structure
thereof. As illustrated in FIG. 4, when the basic CP and the
extended CP are used, PSS/SSS is included in the preset subframe.
Specifically, the synchronization signals (SS) are respectively
transmitted from the second slots of subframe 0 and subframe 5 in
consideration of the GSM frame length 4.6 ms, and the boundary for
the radio frame may be detected through the SSS. The PSS is
transmitted in the last OFDM symbol of the slot, and the SSS is
transmitted in the OFDM symbol right before the PSS. The SS may
transmit a total of 504 physical cell IDs through the combination
of 3 PSSs and 168 SSSs. Further, the SS and the PBCH are
transmitted within central 6 RBs within the system bandwidth so
that the UE may be detected or decoded regardless of the
transmission bandwidth.
[0072] The detailed operation related with the PSS will be
described below.
[0073] Zadoff-Chu (ZC) sequence of length 63 is defined in the
frequency domain and is used as the sequence of the PSS. The ZC
sequence is defined by formula 1 below, and the sequence element
corresponding to the DC subcarrier, n=31, is punctured. In the
formula 1 below, Nzc=63.
d_u(n)=e (-j .pi.un(n+1)N_ZC) [Math Figure 1]
[0074] 9 remaining subcarriers among central 6RBs (=72 subcarriers)
are always transmitted with the value 0 and make the filter design
for synchronization easy. In order to define a total of 3 PSSs, in
formula 1, u=25, 29, and 34 are used.
[0075] At this time, 29 and 34 have the conjugate symmetry relation
and thus two correlations may be simultaneously performed. Here,
the conjugate symmetry refers to the relation of formula 2 (the
first formula is when Nzc is an even number, and the second formula
is when Nzc is an odd number), and the one shot correlator for u=29
and 34 may be implemented by using this characteristic, and the
overall amount of operations may be reduced by about 33.3%.
d.sub.u(n)=(-1).sup.n(d.sub.N.sub.ZC.sub.-u(n))*
d.sub.u(n)=(d.sub.N.sub.ZC.sub.-u(n))* [Math Figure 2]
[0076] The detailed operation related with SSS will be described
below.
[0077] FIG. 5 shows a scheme of generating a code related to a
sub-synchronous signal (SSS).
[0078] The sequence, which is used for SSS, performs interleaved
joining of two m-sequences of length 31 and combines the two
sequences so as to transmit 168 cell group ids. The m-sequence as
the sequence of the SSS is strong in the frequency selective
environment, and the amount of operations may be reduced by a high
speed m-sequence conversion which uses the fast Hadamard
transformation. Furthermore, configuring SSS with two short codes
has been suggested to reduce the amount of operations of the
UE.
[0079] FIG. 5 shows that two sequences in the logical region are
interleaved in the physical region so as to be mapped. When two
m-sequences, which are used for generation of SSS code, are defined
as S1 and S2, if the SSS of subframe 0 transmits the cell group ID
with (S1, S2) combination, SSS of subframe 5 swapped with (S2, S2)
so as to be transmitted, and thus 10 ms frame boundary may be
distinguished. At this time, the used SSS code uses a polynomial of
x.sup.5+x.sup.2+1, and may generate a total of 31 codes through
different circular shifts.
[0080] In order to enhance the receiving performance, the PSS-based
two different sequences are defined so as to be scrambled to the
SSS and are scrambled to different sequences to S1 and S2.
Thereafter, S1-based scrambling code is defined, and scrambling is
performed in S2. At this time, the code of the SSS is exchanged in
5 ms units, but the PSS-based scrambling code is not exchanged. The
PSS-based scrambling code is defined as 6 circular shifts version
according to the PSS index in the m-sequence which is generated
from the polynomial of x.sup.5+x.sup.3+1, and S1-based scrambling
code is defined as 8 circular shifts version according to the index
of S1 in the m-sequence which is generated from the polynomial of
x.sup.5+x.sup.4+x.sup.2+x.sup.1+1.
[0081] Hereinafter, the concept of multi-node system, which is
associated with coordinated multi-point (CoMP) transmission scheme,
is explained in detail.
[0082] To improve a performance of the wireless communication
system, a technique is evolved in a direction of increasing density
of nodes capable of accessing to an area around a user. A wireless
communication system having nodes with higher density can provide a
higher performance through cooperation between the nodes.
[0083] FIG. 6 shows an example of a multi-node system.
[0084] Referring to FIG. 6, a multi-node system 20 may consist of
one BS 21 and a plurality of nodes 25-1, 25-2, 25-3, 25-4, and
25-5. The plurality of nodes 25-1, 25-2, 25-3, 25-4, and 25-5 may
be managed by one BS 21. That is, the plurality of nodes 25-1,
25-2, 25-3, 25-4, and 25-5 operate as if they are a part of one
cell. In this case, each of the nodes 25-1, 25-2, 25-3, 25-4, and
25-5 may be allocated a separate node identifier (ID), or may
operate as if it is a part of an antenna group without an
additional node ID. In this case, the multi-node system 20 of FIG.
6 may be regarded as a distributed multi node system (DMNS) which
constitutes one cell.
[0085] Alternatively, the plurality of nodes 25-1, 25-2, 25-3,
25-4, and 25-5 may have separate cell IDs and perform a handover
(HO) and scheduling of the UE. In this case, the multi-node system
20 of FIG. 6 may be regarded as a multi-cell system. The BS 21 may
be a macro cell. Each node may be a femto cell or pico cell having
cell coverage smaller than cell coverage of a macro cell. As such,
if a plurality of cells is configured in an overlaid manner
according to coverage, it may be called a multi-tier network.
[0086] In FIG. 6, each of the nodes 25-1, 25-2, 25-3, 25-4, and
25-5 may be any one of a BS, a Node-B, an eNode-B, a pico cell eNB
(PeNB), a home eNB (HeNB), a remote radio head (RRH), a relay
station (RS) or repeater, and a distributed antenna. At least one
antenna may be installed in one node. In addition, the node may be
called a point. In the following descriptions, a node implies an
antenna group separated by more than a specific interval in a DMNS.
That is, it is assumed in the following descriptions that each node
implies an RRH in a physical manner. However, the present
specification is not limited thereto, and the node may be defined
as any antenna group irrespective of a physical interval. For
example, the present specification may be applied by considering
that a node consisting of horizontal polarized antennas and a node
consisting of vertical polarized antennas constitute a BS
consisting of a plurality of cross polarized antennas. In addition,
the present specification may be applied to a case where each node
is a pico cell or femto cell having smaller cell coverage than a
macro cell, that is, to a multi-cell system. In the following
descriptions, an antenna may be replaced with an antenna port,
virtual antenna, antenna group, as well as a physical antenna.
[0087] A coordinated multi-point (CoMP) transmission means a
cooperative communication scheme between nodes. In a multi-cell
distributed multi-node system, inter-cell interference may be
reduced by applying the CoMP transmission. In a single cell
distributed multi-node system, intra-cell inter-point interference
may be reduced by applying the CoMP transmission. A UE may receive
data from a plurality of nodes in common by performing the CoMP
transmission. Further, each node may simultaneously support at
least one UE by using the same radio frequency resource in order to
improve a performance of a system. In addition, the base station
may perform a space division multiple access (SDMA) scheme based on
state information of a channel between the base station and the
UE.
[0088] A main purpose of the CoMP transmission is to improve
communication performances of UEs located at cell boundary or node
boundary. In 3GPP LTE, CoMP transmission scheme may be classified
into two schemes.
[0089] 1) Joint processing (JP) scheme: JP scheme is a scheme of
transmitting data, which is shared by at least one node, for the
UE. The JP scheme includes a joint transmission (JT) scheme and a
dynamic point selection (DPS) scheme. The JP scheme is a scheme
where a plurality of nodes simultaneously transmits data to one UE
or a plurality of UEs in time-frequency resources. The plurality of
nodes transmitting the data may be all or a part of a group capable
of performing the CoMP transmission. The data may be transmitted
coherently or non-coherently. Accordingly, quality of a received
signal and/or a data throughput may be improved. The DSP scheme is
a scheme where one node in a group capable of performing the CoMP
transmission transmits data in time-frequency resources. In the DSP
scheme, even if the data can be transmitted by a plurality of nodes
simultaneously, but one node selected from the plurality of nodes
transmit the data. A node transmitting the data or a muting node
which does not transmit the data may be changed in a subframe unit.
Further, an RB pair used in a subframe may be also changed. The DSP
scheme may include a dynamic cell selection (DCS) scheme.
[0090] 2) Coordinated scheduling (CS)/coordinated beamforming (CB)
scheme: CS/CB scheme is a scheme in which only one serving node can
transmit data and the remaining nodes coordinate with the serving
node through scheduling or by reducing interference of a
transmission beam, due to a problem such as a limited backhaul
capacity. The CS/CB scheme includes a semi-static point selection
(SSPS) scheme. The SSPS scheme is a scheme in which one node
transmits data to a specific UE in a specific time. The node
transmitting the data may be changed by a semi-static scheme.
[0091] Hereinafter, the concept of quasi co-location (QCL) is
described.
[0092] In the CoMP situation in which one UE receives a downlink
channel from a plurality of transmission points, the UE may receive
a specific evolved PDCCH (EPDCCH) or a PDSCH scheduled by the
EPDCCH from a specific transmission point via specific time
resources and/or specific frequency resources or receive an EPDCCH
or a PDSCH scheduled by the EPDCCH from another transmission point
via other time resources and/or other frequency resources. At this
time, if the UE can determine from which transmission point the
channel is transmitted, channel reception performance can be
improved using several attributes observed from the transmission
point, e.g., large scale properties such as Doppler spread, Doppler
shift, average delay, delay spread or average gain.
[0093] The eNB may signal the transmission point, from which a
specific EPDCCH or a PDSCH scheduled by the specific EPDCCH are
transmitted. As an example, the eNB may notify the UE that a
specific EPDCCH or a PDSCH scheduled by the specific EPDCCH are
quasi co-located (QCL) with a specific reference signal such as a
CRS or a CSI-RS consistently transmitted by a specific transmission
point. Here, QCL may mean that the channel has the same channel
attributes as the specific reference signal in the long term. If
information about QCL is not provided, the UE may assume that all
channels are transmitted from a serving cell and are QCL with the
CRS of the serving cell.
[0094] Accordingly, resource mapping of a specific EPDCCH or a
PDSCH scheduled by the specific EPDCCH and transmission of other
control channels such as a PCFICH, a PHICH and a PDCCH are
selectively applicable depending on with which RS the channel is
QCL.
[0095] Hereinafter, the detailed features related to reference
signals (RSs) are described.
[0096] In general, a reference signal is transmitted as a sequence.
Any sequence may be used as a sequence used for an RS sequence
without particular restrictions. The RS sequence may be a phase
shift keying (PSK)-based computer generated sequence. Examples of
the PSK include binary phase shift keying (BPSK), quadrature phase
shift keying (QPSK), etc. Alternatively, the RS sequence may be a
constant amplitude zero auto-correlation (CAZAC) sequence. Examples
of the CAZAC sequence include a Zadoff-Chu (ZC)-based sequence, a
ZC sequence with cyclic extension, a ZC sequence with truncation,
etc. Alternatively, the RS sequence may be a pseudo-random (PN)
sequence. Examples of the PN sequence include an m-sequence, a
computer generated sequence, a Gold sequence, a Kasami sequence,
etc. In addition, the RS sequence may be a cyclically shifted
sequence.
[0097] A downlink RS may be classified into a cell-specific
reference signal (CRS), a multimedia broadcast and multicast single
frequency network (MBSFN) reference signal, a UE-specific reference
signal, a positioning reference signal (PRS), and a channel state
information reference signal (CSI RS). The CRS is an RS transmitted
to all UEs in a cell, and is used in channel measurement for a
channel quality indicator (CQI) feedback and channel estimation for
a PDSCH. The MBSFN reference signal may be transmitted in a
subframe allocated for MBSFN transmission. The UE-specific RS is an
RS received by a specific UE or a specific UE group in the cell,
and may also be called a demodulation reference signal (DMRS). The
DMRS is primarily used for data demodulation of a specific UE or a
specific UE group. The PRS may be used for location estimation of
the UE. The CSI RS is used for channel estimation for a PDSCH of a
LTE-A UE. The CSI RS is relatively sparsely deployed in a frequency
domain or a time domain, and may be punctured in a data region of a
normal subframe or an MBSFN subframe. If required, a channel
quality indicator (001), a precoding matrix indicator (PMI), a rank
indicator (RI), etc., may be reported from the UE through CSI
estimation.
[0098] A CRS is transmitted from all of downlink subframes within a
cell supporting PDSCH transmission. The CRS may be transmitted
through antenna ports 0 to 3 and may be defined only for
.DELTA.f=15 kHz. The CRS may be referred to Section 6.10.1 of 3rd
generation partnership project (3GPP) TS 36.211 V10.1.0 (2011-03)
"Technical Specification Group Radio Access Network: Evolved
Universal Terrestrial Radio Access (E-UTRA): Physical channels and
modulation (Release 8)."
[0099] FIG. 7 shows one example of a pattern in which a CRS is
mapped to an RB when a base station uses a single antenna port.
FIG. 8 shows one example of a pattern in which a CRS is mapped to
an RB when a base station uses two antenna ports. FIG. 9 shows one
example of a pattern in which a CRS is mapped to an RB when a base
station uses four antenna ports. The CRS patterns may be used to
support features of the LTE-A. For example, the CRS patterns may be
used to support coordinated multi-point (COMP)
transmission/reception technique, spatial multiplexing, etc. Also,
the CRS may be used for channel quality measurement, CP detection,
time/frequency synchronization, etc.
[0100] Referring to FIGS. 7 to 9, in case the base station carries
out multiple antenna transmission using a plurality of antenna
ports, one resource grid is allocated to each antenna port. "R0"
represents a reference signal for a first antenna port. "R1"
represents a reference signal for a second antenna port. "R2"
represents a reference signal for a third antenna port. "R3"
represents a reference signal for a fourth antenna port. Positions
of R0 to R3 within a subframe do not overlap with each other. l,
representing the position of an OFDM symbol within a slot, may take
a value ranging from 0 to 6 in a normal CP. In one OFDM symbol, a
reference signal for each antenna port is placed apart by an
interval of six subcarriers. The number of R0 and the number of R1
in a subframe are the same to each other while the number of R2 and
the number of R3 are the same to each other. The number of R2 or R3
within a subframe is smaller than the number of R0 or R1. A
resource element used for a reference signal of one antenna port is
not used for a reference signal of another antenna port. This is
intended to avoid generating interference among antenna ports.
[0101] The CRSs are always transmitted as many as the number of
antenna ports regardless of the number of streams. The CRS has a
separate reference signal for each antenna port. The frequency
domain position and time domain position of the CRS within a
subframe are determined regardless of UEs. The CRS sequence
multiplied to the CRS is also generated regardless of UEs.
Therefore, all of UEs within a cell may receive the CRS. However,
it should be noted that the CRS position within a subframe and the
CRS sequence may be determined according to cell IDs. The time
domain position of the CRS within a subframe may be determined
according to an antenna port number and the number of OFDM symbols
within a resource block. The frequency domain position of the CRS
within a subframe may be determined according to an antenna port
number, cell ID, OFDM symbol index (l), a slot number within a
radio frame, etc.
[0102] A two-dimensional CRS sequence may be generated by
multiplication between symbols of a two-dimensional orthogonal
sequence and symbols of a two-dimensional pseudo-random sequence.
There may be three different two-dimensional orthogonal sequences
and 170 different two-dimensional pseudo-random sequences. Each
cell ID corresponds to a unique combination of one orthogonal
sequence and one pseudo-random sequence. In addition, frequency
hopping may be applied to the CRS. The period of frequency hopping
pattern may be one radio frame (10 ms), and each frequency hopping
pattern corresponds to one cell identity group.
[0103] A CSI RS is transmitted through one, two, four, or eight
antenna ports. The antenna ports used for each case is p=15, p=15,
16, p=15, . . . , 18, and p=15, . . . , 22, respectively. The CSI
RS may be defined only .DELTA.f=15 kHz. The CSI RS may be referred
to Section 6.10.5 of the 3rd generation partnership project (3GPP)
TS 36.211 V10.1.0 (2011-03) "Technical Specification Group Radio
Access Network; Evolved Universal Terrestrial Radio Access
(E-UTRA): Physical channels and modulation (Release 8)."
[0104] A CSI RS sequences may be based on a pseudo-random sequence
which is generated from a seed based on a cell ID. Regarding
transmission of the CSI RS, a maximum of 32 configurations
different from each other may be taken into account to reduce
inter-cell interference (ICI) in a multi-cell environment,
including a heterogeneous network (HetNet) environment. The CSI RS
configuration is varied according to the number of antenna ports
within a cell and CP, and neighboring cells may have the most
different configurations. Also, the CSI RS configuration may be
divided into two types depending on a frame structure. The two
types include a type applied to both of FDD frame and TDD frame and
a type applied only to the TDD frame. A plurality of CSI RS
configurations may be used for one cell. For those UEs assuming
non-zero power CSI RS, 0 or 1 CSI configuration may be used. For
those UEs assuming zero-power CSI RS, 0 or more CSI configurations
may be used.
[0105] Configuration of the CSI RS may be indicated by a higher
layer, such as Radio Resource Control (RRC) signalling. In detail,
CSI-RS-Config information element (IE) transmitted via the higher
layer may indicate the CSI RS configuration.
[0106] The higher layer signalling can further define the period
and the offset of the subframe in which the CSI RS is transmitted
may be determined according to the CSI RS subframe
configuration.
[0107] FIG. 10 shows an example of an RB to which a CSI-RS is
mapped. In detail, FIG. 10 shows resource elements used for the
CSI-RS in a normal CP structure when CSI RS configuration index is
zero. Rp denotes resource elements used for CSI-RS transmission on
an antenna port p. Referring to FIG. 10, the CSI-RS for an antenna
port 15 and 16 are transmitted through resource elements
corresponding to a third subcarrier (subcarrier index 2) of a sixth
and seventh OFDM symbol (OFDM symbol index 5, 6) of a first slot.
The CSI-RS for an antenna port 17 and 18 is transmitted through
resource elements corresponding to a ninth subcarrier (subcarrier
index 8) of a sixth and seventh OFDM symbol (OFDM symbol index 5,
6) of the first slot. The CSI-RS for an antenna port 19 and 20 is
transmitted through the same resource elements as the CSI-RS for an
antenna port 15 and 16 is transmitted. The CSI-RS for an antenna
port 21 and 22 is transmitted through the same resource elements as
the CSI-RS for an antenna port 17 and 18 is transmitted.
[0108] Hereinafter, detailed features related to a discover
reference signal (DRS), which is associated with the
above-explained small cells, are introduced. Namely, the following
portions of the specification propose various features related to
DRS, which is also referred to as a discovery signal, or advanced
discovery signal. For instance, the present specification proposes
detailed embodiments related to candidates which can be used as
DRS. Further, the present specification proposes an embodiment with
respect to alignment between a measurement gap and the DRS, an
embodiment related to configuration related to measurement timing
of the DRS, an embodiment with respect to misalignment between a
number of cells, an embodiment with respect to enhanced
Interference Mitigation & Traffic Adaptation (eIMTA), which
dynamically changes Time Division Duplex (TDD) configuration in the
context of DRS operations.
[0109] Here, a number of desired characteristics of the DRS (or
interchangeably "advanced discovery signal") and a number of
candidates for the DRS are proposed in detail.
[0110] In a dense small cell scenario, it is likely that a UE is
connected with an overlaid macro and small cell may be used as for
data offloading. In such a case, it is desirable for a UE to
discover many cells within a communication range and then the
overlaid macro layer selects the best cell considering "loading"
information as well as other information. In other words, the best
cell for data offloading may not be the best cell based on
RSRP/RSRQ. Rather, a cell with low loading or many users may be
desirable from overall cell management perspective. Thus, an
advanced discovery procedure to allow detecting more cells than
conventional mechanism can be considered.
[0111] In terms of desired characteristics of the DRS may include
the following:
[0112] detect more cells than legacy PSS/SSS/CRS based cell
detection;
[0113] detect cells in a short time such as in a subframe;
[0114] perform measurement in a short time such as in a subframe;
and
[0115] support necessary measurement for fast time scale on/off
operation.
[0116] Further, the candidates which can be considered for advanced
discovery algorithm can include the following:
[0117] PSS/(SSS)+CRS;
[0118] PSS/(SSS)+CSI-RS;
[0119] PSS/(SSS)+PRS;
[0120] PSS+SSS+CRS+(CSI-RS);
[0121] Combination of one or more options of (1)-(3); and
[0122] PSS+SSS+CRS+(CSI-RS): in this case, a UE may assume that
CSI-RS is present only if configured with CSI-RS configuration such
as scrambling ID, the resource configurations for CSI-RS, etc. In
other words, a UE may perform transmission point (TP)
identification only if network assistance related to CSI-RS is
configured or the explicitly configured with the presence of CSI-RS
resource.
[0123] Although the candidates for the DRS are not limited to a
certain example, it is preferable that the DRS comprises the PSS,
SSS, and CRS. Further, the DRS may further comprise CSI-RS
depending on the CSI-RS configuration (e.g., interval, offset of
the CSI-RS).
[0124] It is expected that discovery signal (i.e., DRS) should be
used for coarse time/frequency tracking, measurement and Quasi
Co-Location (if necessary). Considering some of objectives, the
design of discovery signal should meet the following
requirements:
[0125] (1) Discovery signal should support coarse time
synchronization with assumption of very high initial timing error
(such as +-2.5 ms);
[0126] (2) Discovery signal should support coarse frequency
synchronization with assumption of very high initial frequency
error (such as 20 KHz);
[0127] (3) Discovery signal should support the detectability of at
least three cells (or transmission points); and
[0128] (4) Discovery signal should support sufficient accuracy of
measurement.
[0129] To support the items (1) and/or (2), it can be assumed that
PSS and/or SSS can be transmitted.
[0130] In terms of designing discovery signals, the following
questions should be answered:
[0131] (1) In the same frequency, cells transmitting advanced
discovery signal and cells not transmitting advanced discovery
signals can coexist or not;
[0132] (2) If a cell transmits advanced discovery signals, it will
transmit discovery signals in off-state as well as in
on-state?;
[0133] (3) From a UE measurement reporting perspective, a UE
reports both measurement reports based on legacy and advanced
discovery signals if available or report only one? When it reports
only one, what is the criteria to select one report?;
[0134] (4) Whether a UE can perform measurement based on advanced
discovery signal even in DRX mode ? (A) If this is supported, it
may be required that a UE shall wake-up even in DRX cycle (not in
OnDuration) to perform the measurement following DRS transmission
timing/configuration. For example, if DRS is transmitted in every
160 msec, a UE shall wake up every 160 msec to perform the
measurement;
[0135] (5) How does multiplexing between discovery signals from
different cells will be performed? Via TDM or FDM or CDM?;
[0136] (6) Any active data transmission in subframe where discovery
signal is transmitted? Without active data transmission, how to
measure RSSI?;
[0137] (7) Is there any necessity to increase the number of cell
IDs from 504 to?;
[0138] (8) What if SFN is not aligned among cells transmitting
discovery signals together for efficient UE performance?;
[0139] (9) What is CP length is not aligned among cells
transmitting discovery signals together for efficient UE
performance?;
[0140] (10) What if discovery signal has been scheduled in MBSFN
SF?;
[0141] (11) Discovery signal transmission period and resource
configuration should be configurable?; and
[0142] (12) How to transmit discovery signal in TDD.
[0143] For a possible configuration, the periodicity of advanced
discovery signals (i.e., the DRS) can be considered with the
following constraints:
[0144] (1) Multiple of measurement gap period: e.g., 40 msec, 80
msec, or 160 msec or 320 msec (if a new measurement gap period is
configured, multiple of those new periods can be also
considered);
[0145] (2) Align with DRX cycle: 10, 20, 32, 40, 64, 80, 128, 160,
256, 320, 512, 640, 1024, 1280, 2048, 2560 (this constraint can be
eliminated if a UE can measure using legacy signals for the serving
cell); and
[0146] (3) If PSS/SSS are transmitted in discovery signal, the
periodicity of discovery signal may be multiple of 5 msec so that
PSS/SSS transmitted for advanced discovery signal can be replaced
by PSS/SSS transmitted in on-state. If discovery signal is not
transmitted in on-state, this constraint can be eliminated. Or to
avoid impact on legacy UE, different periodicity not aligned with
PSS/SSS can be also considered such that PSS/SSS can be transmitted
during on-state while additional PSS/SSS can be also transmitted
for discovery signal transmission. If DRS-PSS and DRS-SSS are
additionally transmitted separately from PSS/SSS transmitted in
on-state, the cell ID between DRS-PSS/DRS-SSS can be different from
PSS/SSS. Also, QCL relationship between DRS-PSS/DRS-SSS and PSS/SSS
may not be assumed. In that case, a QCL relationship DRS-CSI-RS (or
DRS-CRS) and PSS/SSS and/or CRS can be configured where DRS-CSI-RS
can be used for PSS/SSS and/or CRS decoding/tracking. In that case,
the cell ID used for DRS-CSI-RS and PSS/SSS and/or CRS may be
assumed to be equal. If the cell ID used for DRS-PSS/DRS-SSS is
same to that of PSS/SSS, DRS-PSS/DRS-SSS can be replaced by SSS/SSS
if DRS-PSSS/DRS-SSS collide with PSS/SSS if two collide. Otherwise,
PSS/SSS may be dropped when two collide.
[0147] As discussed above, it is preferable the periodicity of the
DRS is set to be a multiple of the measurement gap period. In this
specification, the "multiple" also includes the same value.
Accordingly, if the measurement gap period is set to 40 ms and one
same measurement gap period is configured, it is preferable that
the periodicity of the DRS is set to one of 40 msec, 80 msec, 160
msec. Based on the present specification, UEs may measure the DRS
within the measurement gap, and thus the DRS period can be aligned
with the measurement gap if the periodicity of the DRS is set to be
a multiple of the measurement gap period.
[0148] Furthermore, in terms of feasible subframe where discovery
signal can be transmitted, both TDD and FDD, MBSFN subframes need
to be removed from the candidate list. Thus, discovery signal may
not be transmitted in MBSFN subframe based on another possible
aspect of the present specification.
[0149] Hereinafter, features related measurement gaps and
measurement requirements for a UE with the DRS are explained in
detail.
[0150] The motivation of making discovery signal aligned with
measurement gap period is to allow "same measurement gap"
applicable for inter-frequency measurement regardless of whether
the measurement is based on legacy signal or new discovery signal.
Otherwise, a UE may need to be configured with two different
measurement gap patterns which may not be desirable due to service
interruption and performance impact. When one or more additional
measurement gap are configured to UEs, some constraints can be
considered to limit the same amount of UE interruption time or not
to increase UE service interruption time from the current
requirement. This can be done in general by increasing measurement
interval or shorten the measurement gap. This needs to be
considered from two aspects. One from configuring measurement gaps
for discovery signals and the other from configuring measurement
gap for legacy discovery signals. Following current RAN4
requirement, a UE is required to detect a new FDD cell within the
following formula.
T Identify_Inter = T Basic_Identify _Inter 480 T Inter 1 N freq ms
[ Math Figure 3 ] ##EQU00001##
[0151] Where:
[0152] T_Basic_Identify_Inter=480 ms. It is the time period used in
the inter frequency equation where the maximum allowed time for the
UE to identify a new FDD inter-frequency cell is defined.
[0153] N_freq is defined in section 8.1.2.1.1 and T_inter1 is
defined in section 8.1.2.1 in 3GPP TS 36.133 V10.1.0 (2010-12).
[0154] The following table is defined in 3GPP standard
documents.
TABLE-US-00001 TABLE 1 Measure- Minimum available Measure- ment Gap
time for inter- mentGap Repetition frequency and inter- Gap Length
Period RAT measurements Pattern (MGL, (MGRP, during 480 ms period
Measurement Id ms) ms) (Tinter1, ms) Purpose 0 6 40 60 Inter-
Frequency E-UTRAN FDD and TDD, UTRAN FDD, GERAN, LCR TDD, HRPD,
CDMA2000 1x 1 6 80 30 Inter- Frequency E-UTRAN FDD and TDD, UTRAN
FDD, GERAN, LCR TDD, HRPD, CDMA2000 1x
[0155] For example, with measurement gap of 40 msec, a UE should
find a new frequency with 480*480/60*7=480*8*7. In other words, 8
measurements are used for inter-frequency measurement for a
frequency where 7 frequencies are searched. When discovery signal
(i.e., DRS) is introduced, a UE may be expected to perform cell
detection by reading one or a few discovery signals. In that case,
the requirement for a UE with discovery signal would be
480*(480*Number of DRS bursts required for detection/DRS
interval)*N_freq where *N_freq may represent either the number of
frequency layer with DRS only or both DRS and CRS.
[0156] Namely, when determining UE requirements associated with the
measurement latency on the DRS, the interval of the DRS (i.e.,
periodicity of the DRS) can be used.
[0157] In another aspect of the present specification, the
measurement gap can be defined in the following manners.
[0158] When discovery signal is introduced where the measurement
gap is not aligned with legacy UE, to meet the service interruption
time intact, the requirement on cell detection using legacy signals
would need to be tailored.
[0159] One approach is to use "minimum available time" for
inter-frequency for CRS based cell detection or other RAT can be
reduced (where the measurement interval or pattern may also
change).
[0160] For example, the following table can be proposed in the
present specification.
TABLE-US-00002 TABLE 2 Measure- Minimum available Measure- ment Gap
time for inter- mentGap Repetition frequency and inter- Gap Length
Period RAT measurements Pattern (MGL, (MGRP, during 480 ms period
Measurement Id ms) ms) (Tinter1, ms) Purpose 0 6 40 60 Inter-
Frequency E-UTRAN FDD and TDD, UTRAN FDD, GERAN, LCR TDD, HRPD,
CDMA2000 1x 1 6 80 30 Inter- Frequency E-UTRAN FDD and TDD, UTRAN
FDD, GERAN, LCR TDD, HRPD, CDMA2000 1x 2 6 160 15 Inter- Frequency
E-UTRAN FDD and TDD, UTRAN FDD, GERAN, LCR TDD, HRPD, CDMA2000 1x
(not based on discovery signal) 3 3 80 15 Inter- Frequency E-UTRAN
FDD and TDD, UTRAN FDD, GERAN, LCR TDD, HRPD, CDMA2000 1x (not
based on discovery signal)
[0161] For example, instead of configuring gap pattern 0 or 1 only,
new gap patterns can be considered as shown in above where the
minimum available time used for other procedures than DRS based
measurement can be limited which allows the remaining time used for
discovery signals. For example, during 480 msec, inter-frequency
measurement using discovery signals would require 6*2 (6 msec
measurement gap with 2 times of DRS detection) for a frequency is
needed and a UE needs to monitor 3 frequencies with DRS, the total
time used for DRS is 12*3=36 msec. Thus, available time for legacy
signal based measurement should be reduced (such as 2 or 3) by
either relaxing measurement gap period or measurement gap.
[0162] When DRX is configured, the similar requirement is
applicable.
[0163] Another option to determine requirement with DRS is to use
OTDOA requirement as shown in below. In other words, TPRS can be
changed to TDRS with the interval of DRS transmission and M can be
the number of samples to read.
[0164] All inter-frequency RSTD measurement requirements specified
in Sections 8.1.2.6.1-8.1.2.6.4 (of 3GPP TS 36.133) shall apply
when the measurement gap pattern ID #0 specified in Section 8.1.2.1
(of 3GPP TS 36.133) is used.
[0165] All inter-frequency RSTD measurement requirements specified
in Sections 8.1.2.6.1-8.1.2.6.4 (of 3GPP TS 36.133) shall apply
without DRX as well as for all the DRX cycles specified in 3GPP TS
36.331. More detailed features related to the above operation can
be referred to Section 8.1.2.6.1 of 3GPP TS 36.133 V10.1.0
(2010-12).
[0166] To align discovery signal transmissions from cells in a
frequency, similar to PRS, the following may be assumed. In detail,
the following "DRS" field can be further defined based on the
following language.
[0167] DRS
[0168] This field specifies the DRS configuration of the neighbour
cell.
[0169] When the EARFCN of the neighbour cell is the same as for the
assistance data reference cell (or another neighbor cell), the
target device may assume that each DRS occasion in the neighbour
cell at least partially overlaps with a DRS occasion in the
assistance data reference cell where the maximum offset between the
transmitted DRS occasions may be assumed to not exceed half a
subframe. Alternatively, the target device may assume each DRS
occasion in the neighbour cell does not overlap with the DRS
occasion when the DRS occasion is set to 1 msec.
[0170] Additionally or alternatively, the target device may assume
the DRS is transmitted during a DMTC duration whose maximum is set
to 6 msec as configured by a network via a high layer signalling.
Accordingly, the UE may assume that the DRS is transmitting with in
a window of 6 msec and further assume that the maximum of the
offset of the DRS is 5 ms.
[0171] When an evolved absolute radio-frequency channel number
(EARFCN) of the neighbour cell is the same as for the serving cell
(or other cell), the target may assume that this cell has the same
PRS periodicity (Tprs) as the assistance data reference cell.
[0172] In other words, a UE may assume that DRS transmissions from
multiple cells in a frequency is aligned in terms of period and
offset.
[0173] More specifically, triggering discovery signal based
measurement for inter-frequency may be configured only with
measurement gap pattern #0 where the network may align transmission
of discovery signals to be aligned with UE measurement gap
pattern.
[0174] If a UE is configured with both OTDOA and DRS, it would not
be easy to align all measurements by one measurement gap pattern.
Thus, in general, it is worthwhile to consider configuring one or
more measurement gap patterns for the UE which the serving cell
should be aware of. However, in this case, not to increase UE
overhead, relaxing legacy measurement including OTDOA (by extending
measurement period) may be necessary. Or, similar to OTDOA, a UE
should be configured with only one measurement gap which is used
for both DRS and CRS (as well as OTDOA) measurements if needed.
However, this may restrict the deployment use cases for DRS based
discovery procedure. Thus, in general, consideration of relaxing UE
measurement gap along with allowing multiple measurement
configurations are preferred where at least some coordination among
small cells within a cluster is assumed (i.e., the above-explained
assumption related to DRS occasion is also applicable here.). This
may be extended to the same frequency. Among different frequencies,
a UE may be configured with different offset of measurement gap
starting which the serving cell configures in multiple different
ways.
[0175] One is to change the measurement gap pattern such to include
multiple offset values with larger measurement period or a UE may
be configured with multiple measurement gaps.
[0176] Additionally or alternatively to the above operation, a UE
can be also configured with a set of DRS configurations which
includes information on period, offset, the duration, and
potentially RS type. In this case, period and duration can be
optional whereas offset may be mandated or optional (if the field
is not present, UE can assume SFN and subframe offset is aligned
between the target cells and the serving cell). If period is not
present, UE may assume a prefixed value such as 40 msec or 80
msec.
[0177] When a measurement gap (or multiple measurement gaps) are
configured, a UE can perform only DRS based measurement on those
configured gaps for discovery signal based measurements.
[0178] Detailed features related to the above operation are
explained as follows.
[0179] FIG. 11 shows an example of UE measurement performed on the
DRS according to one example of the present specification. As
depicted, a UE can be configured to measure at least one cell,
e.g., small cells supporting power on/off operations. In FIG. 11,
cell 1 is on-cell which is always "on" whereas cells 2-3 perform
periodic on/off operations. As discussed above, it is preferable
that the period of the DRS is aligned with the measurement gap, and
thus the UE can be configured to measure the DRS within the
measurement gap. Further, as discussed above, a length of the
measurement gap 1130 in FIG. 11 can be set to 6 ms and a repetition
period of the measurement gap can be set to 40 ms or 80 ms, and
thus a measurement period of the DRS 1140 in FIG. 11 can be set to
40 msec, 80 msec, or 160 msec. Since the candidates of the DRS may
include the PSS, SSS, CRS, and optionally CSI-RS, the UE can be
configured to measure the PSS, SSS, CRS, and CSI-RS during a
certain measurement duration based on the "DRS configurations"
delivered via an RRC message. Since the DRS configurations are
delivered via the RRC message, the DRS configurations are delivered
to the UE which is in an RRC connected mode.
[0180] As discussed above, each set of DRS configurations may
include information on period, offset, the duration used for DRS
measurement. The information on period included in each set of DRS
configurations may indicate a measurement period of the DRS, and an
offset of the measurement period. Accordingly, a starting point of
a duration where the UE possibly measures the DRS can be determined
based on the information on period and offset. However, actual
measurement on the DRS starts with SSS (depicted in 1120 of FIG.
11). In detail, the measurement on the DRS starts on a first
subframe carrying the SSS in each period of the measurement period.
The UE's measurement on the DRS lasts during subframe(s) determined
based on the "duration" included in each set of DRS configurations.
In FIG. 11, the duration 1150 is set to 4 ms, and thus the
measurement on the DRS lasts during 4 subframes. The maximum of the
duration 1150 can be set to 5 ms in the present specification.
[0181] It is preferable that each set of DRS configurations is
defined per frequency. In other words, a single and same DRS
configuration can be defined for an individual frequency, and such
DRS configurations can be applicable to any cell using the same
frequency. Further, if the DRS configuration is defined for a
specific frequency among a plurality of available frequencies, the
UE may only perform DRS measurement for the specific frequency
configured for the DRS and perform legacy measurement for the
remaining frequencies. When performing legacy measurement for the
remaining frequencies, the UE's measurement is not restricted to
interval/offset/duration included in the DRS configuration.
Accordingly, UE may continuously (if possible) measure the
conventional PSS, SSS, CRS for the remaining frequencies, which are
not configured with the DRS measurement.
[0182] Another aspect to consider is DRX cycle which is more tricky
as it may not easy to setup a periodic discovery signal
transmission which is aligned with all DRX cycles. Thus, it can be
assumed that a UE may wake up during DRX cycle aligned with
discovery signal transmission interval such that it can perform
measurement. In other words, if a UE is configured with a
measurement gap (which may be additional measurement gap from the
measurement gap configured for inter-frequency measurement using
legacy signals), it may be assumed that UE will perform measurement
regardless of its DRX states. In this case, it can be further
assumed that a UE may select any discovery signal interval or
measurement gap to perform measurement with the constraint that at
least one measurement per DRX cycle is taken. For example, if DRX
cycle is 1280 msec where measurement gap is configured every 80
msec, whether the UE performs the measurement one or more time can
be up to the UE implementation as long as it performs the
measurement at least once per DRX cycle to satisfy the requirement.
When a UE can create autonomous gap, the timing information of
network assistance for advanced discovery procedure can be used to
determine when to perform the measurement.
[0183] 1. Design of PSS/SSS Sequence
[0184] First, the design choices of signal generation of PSS and/or
SSS are described.
[0185] To avoid detection of PSS/SSS by legacy UEs, it is desirable
to use different resource in terms of time and frequency between
legacy PSS/SSS and PSS/SSS for DRS in advanced discovery procedure.
Furthermore, it is also considerable to use different code shown in
the following table.
TABLE-US-00003 TABLE 3 N.sub.ID.sup.(2) Root index (off-state) Root
index (on-state) 0 a 25 1 b 29 2 c 34
[0186] Where a, b, and c are different numbers from 25, 29 and 34.
This would increase the complexity of advanced UE in terms of cell
search/synchronization. However, this will allow preventing legacy
UEs from detecting advanced discovery signals.
[0187] Furthermore, it may not be sufficient to perform coarse
time/frequency tracking using single-shot PSS transmission. Thus,
it would be desirable to consider multi-shot PSS transmission where
PSS transmission can be occurred in a burst fashion such that
consecutive PSS transmissions can be occurred over the multiple
subframes or a UE may acquire coarse time synchronization using
multiple incidents of PSS transmission. If the latter is used, the
periodicity of PSS transmission should not be very long. For
example, at least measurement gap interval (40 msec or 80 msec) may
be used as a periodicity such that PSS will be transmitted in every
40 mesc or 80 msec. If SSS is used for frequency tracking and/or
time tracking, the similar approaches for SSS can be applied as
well.
[0188] When PSS/SSS is transmitted, to enhance the cell detection
performance, a few approaches can be considered.
[0189] (1) SFN transmission of PSS and/or SSS from multiple cells
within a cluster
[0190] (2) Only a few cell transmits PSS and/or SSS
[0191] (3) PSS/SSS muting or ICIC: when discovery signal consists
of PSS/SSS/CSI-RS (for example, but not limited to this
combination), to enhance the multiplexing capability of PSS/SSS,
TDM approach among multiple cells can also be considered. For
example, if discovery signal is transmitted (cell ID detection
signals) every 200 msec where the measurement RS such as CSI-RS may
be transmitted more frequently such as 40 msec, PSS/SSS may be
transmitted in every 200 msec whereas CSI-RS is transmitted every
40 msec. In the first 40 msec interval, cell 1 may transmit
PSS/SSS/CSI-RS whereas other cells transmit only CSI-RS, in the
second 40 msec interval, cell2 may transmit PSS/SSS/CSI-RS whereas
other cells transmit only CSI-RS and so on. By this way, the
interference on PSS/SSS can be minimized where measurement can be
performed for a cell which is discovered by cell detection
procedure. This is similar to the case where PSS/SSS is transmitted
every 5 msec whereas CRS is transmitted in every subframe for
measurement. From a UE measurement perspective, a UE may select any
incidents of CSI-RS (or CRS) transmission for its measurement if
only one measurement is performed in every 200 msec. Instead of TDM
across subframes, TDM within a subframe or FDM can be also
considered where PSS/SSS can be transmitted in different OFDM
symbols by shift OFDM symbol per cell (or shift value may be tied
with cell ID) or shift the transmission frequency. The example is
shown in FIG. 12. Instead of transmitting PSS/SSS infrequently
only, all the RS can be transmitted infrequently where different
cell may take different interval to transmit the set of discovery
signals. For example, in the figure, cell1 may transmit
PSS/SSS/CSI-RS in first 40 msec interval whereas cell2 may transmit
PSS/SSS/CSI-RS in second 40 msec interval. If this approach is
used, the same CSI-RS configuration among different cells or CRS
pattern can be used where TDM is used among multiple cells to
increase the orthogonality. This can be viewed as "offset" with the
fixed discovery signal transmission period where discovery signal
transmission from each cell uses different offset value.
[0192] (4) Information for PSS and/or SSS cancellation ? the list
of cell IDs can be configured to a UE where a UE may perform PSS
and/or SSS cancellation within the list of cell IDs (which may
improve the cancellation performance).
[0193] Note that all proposed ideas here applicable to CSI-RS can
be applicable to CRS in case DRS consists of PSS/SSS/CRS.
[0194] Considering legacy UE impact on transmitting potentially
additional PSS/SSS which may be covered by legacy ZP CSI-RS
configuration, it is desirable to transmit PSS/SSS in OFDM symbol 2
and 3 in the second slot where the entire RB can be covered by a ZP
CSI-RS configuration for normal CP FDD/TDD. For normal CP TDD, OFDM
symbol 1 and 3 can be used where the entire RB can be covered by
non-ZP CSI-RS configurations (and thus a ZP CSI-RS configuration
can cover the PSS/SSS transmission for discovery signal). For
extended CP, OFDM symbol 4/5 for TDD/FDD can be considered and OFDM
symbol 1/3 can be considered for TDD in second slot. If CSI-RS is
not configured to a legacy UE, a ZP CSI-RS configuration is
configured according to discovery signal transmission interval (for
example, every 40 msec, a ZP CSI-RS configuration is configured).
When discovery signal consists of CSI-RS as well, there are a few
examples of transmitting discovery signal CSI-RS can be
considered.
[0195] (1) If system bandwidth is larger than 1.4 Mhz and CSI-RS is
transmitted over the entire system bandwidth or larger than 1.4 Mhz
bandwidth (for discovery signal transmission), it can be considered
to "omit" CSI-RS transmission when CSI-RS is colliding with PSS/SSS
(for a convenience, let's call DRS-CSI-RS as CSI-RS used for
discovery signal and DRS-PSS/DRS-SSS as PSS/SSS used for discovery
signal). This means that DRS-CSI-RS can be omitted if it collides
with DRS-PSS/DRS-SSS. Thus, DRS-CSI-RS will be transmitted over the
entire system bandwidth (or configured system bandwidth)
potentially except for the center 6PRBs where DRS-PSS/DRS-SSS is
transmitted. This will be applicable when DRS-CSI-RS will be
transmitted in the same OFDM symbol where DRS-PSS/DRS-SSS is
transmitted. The example is shown in FIG. 13. (In FIG. 13, a first
case where DRS-CSI-RS 1330 collides with DRS-PSS 1310 and DRS-SSS
1320 and a second case where DRS-CSI-RS 1330 does not collide with
DRS-PSS 1310 and DRS-SSS 1320 are depicted) If system bandwidth is
1.4 Mhz, to transmit DRS-CSI-RS with other signals, either
different CSI-RS configuration not colliding with other signals is
used or different subframe needs to be used for DRS-CSI-RS
transmission.
[0196] (2) Regardless of system bandwidth, always DRS-CSI-RS may
not be transmitted where DRS-PSS/DRS-SSS is transmitted in any PRB
in the same OFDM symbol. For example, if PSS is transmitted in OFDM
symbol 2 of second slot, CSI-RS configuration spanning OFDM symbol
2 of second slot will not be used for DRS-CSI-RS configuration.
[0197] In the above passage, DRS-PSS, DRS-SSS, DRS-CRS, DRS-CSI-RS,
and DRS-PRS indicate PSS, SSS, CRS, CSI-RS and PRS included in the
DRS, respectively. In one aspect of the present specification, the
above-mentioned RSs may be similar to conventional RSs in terms of
sequence-generation, but different waveforms may be used. In
detail, the conventional PSS and DRS-PSS can be transmitted via a
same waveform, whereas transmission scheme or resource allocation
may be differently applied to the both PSSs. Accordingly, depending
on the transmission scheme of the DRS-PSS, the UE may assume that
the DRS-PSS is same as the conventional PSS in some aspect. This is
also applicable to the conventional SSS and the DRS-SSS.
Accordingly, the conventional SSS and DRS-PSS may be different in
terms of sequence-generation and resource-allocation.
[0198] When CSI-RS is used for DRS, it is also feasible that a UE
can be configured with CSI-RS configuration mainly for CSI
measurement. If DRS-CSI-RS configuration and CSI-RS configuration
is the same for a specific cell, both CSI-RS may be used for CSI
measurement. Unless noted otherwise, a UE may assume that only
CSI-RS configuration configured for CSI measurement is used for CSI
measurement.
[0199] If DRS-CSI-RS is not transmitted when DRS-CSI-RS collides
with DRS-PSS or DRS-SSS, for measurement DRS-PSS and/or DRS-SSS can
be also used. For example, to measure RSRP, all the REs carrying
DRS can be used to perform measurement. For RSSI measurement, this
can be different where RSSI may be measured only in OFDM symbols
configured to measure RSSI or the entire subframe. However,
considering a case where DRS-PSS/DRS-SSS are transmitted in a SFN
manner by multiple cells (and thus the power is accumulated), it
can be also considered not to consider DRS-PSS and/or DRS-SSS in
RSRP-like measurement. Or, the behavior can be configured by the
network as well whether to include those REs for measurement or
not. Generally, if the cell ID used for DRS-CSI-RS and
DRS-PSS/DRS-SSS is identical, both RS may be used for measurement.
Otherwise, only one type of RS is used for measurement. In
different way is that the RS used for cell detection/verification
is used for measurement. If DRS-CSI-RS is used cell verification
finally where the partially DRS-PSS/DRS-SSS is used for cell ID
detection, only DRS-CSI-RS is used for measurement.
[0200] If CRS is used for discovery signal, this kind of problem
may not exist. Further to reduce the impact on legacy UEs, the
subframe where discovery signals are transmitted can be configured
as MBSFN subframes.
[0201] 2. Design of CRS or CSI-RS or PRS used for cell ID and
measurement
[0202] Even though PSS/SSS may be transmitted infrequently, CRS or
CSI-RS or PRS used for measurement may need to be transmitted more
often. Thus, when discovery signal consists of multiple signals
(e.g., PSS/SSS+CSI-RS), the interval/duration of transmitting one
signal can be different from the interval/duration of transmitting
another signal. In other words, the interval of discovery signal
transmission may be fixed, yet, whether multiple signals will be
present in one episode of discovery signal transmission or not can
be different. One example is to transmit one PSS/SSS in every 40
msec whereas CRS or CSI-RS will be transmitted in every subframe
(in relation to MBSFN SF) for m subframe (e.g., m=6). Or, more
specifically, PSS/SSS can be transmitted in every 40 msec of
subframe #0/#5 (i.e., twice per 40 msec) and CRS/CSI-RS may be
transmitted more frequently than PSS/SSS or following the current
configuration (e.g., CRS=continuous over m subframes, CSI-RS
following configured period).
[0203] When discovery signal (i.e., the DRS) consists of multiple
signals, QCL relationship among signals can be considered. For
example, if PSS/SSS and CRS or CSI-RS or PRS are used for discovery
signals, PSS/SSS antenna ports and CRS or CSI-RS or PRS antenna
ports can have QCL relationship w.r.t. large scale properties such
as average delay, delay spread, Doppler spread and Doppler shift
(or a subset of properties). In other words, if PSS/SSS included in
the DRS is used for coarse time/frequency tracking, the signals
used for coarse time/frequency tracking may have QCL relationship
with signals used for cell identification or measurement. Also, RS
for cell identification can have QCL relationship with RS used for
measurement. Explicit signaling of QCL relationship or behavior
(such as QCL behavior A or B) can be considered to a UE via higher
layer signaling. Or, a mapping between cell ID used by PSS/SSS and
CSI-RS or CRS or PRS can be signaled.
[0204] 3. Discovery Signal Design
[0205] Hereinafter, features related to signal designs of DRS are
explained in detail. The following features are beneficial when RSs
included in the DRS have modified features in view of the
conventional RSs.
[0206] When designing signals including PSS, SSS and CSI-RS, the
following issues should be considered: [0207] Due to heavy
interference on PSS/SSS, it would be considered to use "SFN-ed"
transmission of PSS/SSS if cancellation may not work perfectly or
PSS/SSS muting is not used; [0208] In other words, PSS/SSS are used
for time/frequency tracking and actual cell ID search may be
performed based on CSI-RS; [0209] To minimize the number of cell ID
detections (hypothesis), further consideration of shared cell ID
among cells in a small cell cluster where virtual cell ID can be
configured for CSI-RS where virtual cell ID can be driven by cell
ID used for PSS/SSS. For example, virtual cell ID would be
[physical cell ID+min_ID, physical cell ID+max_ID] where physical
cell ID is used for generating PSS/SSS; [0210] Depending on the
quality of SSS, either one or two (or more) SSS sequences can be
transmitted; and [0211] Considering the UE power consumption and
reliability, it can be further considered to transmit more than one
DRS-PSS and/or DRS-SSS pair in one discovery signal
transmission.
[0212] In terms of the location of DRS-PSS and/or DRS-SSS, to avoid
detection of DRS by legacy UEs, and also to enhance the
multiplexing capability, a new location different from Rel-8
PSS/SSS location can be considered. As shown in FIG. 13, one
example would be to utilize OFDM symbol 2/3 in second slot in
normal CP. To make a different gap from FDD, DRS-PSS/DRS-SSS can be
placed in OFDM symbol 2/3 respectively. Furthermore, since a UE
expects to receive system information via higher layer signaling or
by receiving system information broadcast once the cell is detected
(and the target cell wakes up), there is no need to take a
different gap between FDD/TDD. Thus, we propose to use the same gap
between DRS-PSS/DRS-SSS regardless duplex. Furthermore, instead of
DRS-PSS/DRS-SSS combination, the following combinations can be also
considered.
[0213] (1) DRS-PSS0/DRS-PSS1 where PSS0 and PSS1 can have different
code (generated by different root indices); and
[0214] (2) DRS-PSS/DRS-SSS0/DRS-SSS1 where SSS0 and SSS1 can be
generated as if it is transmitted in subframe #0/#5 in Rel-8 SSS
sequence generation.
[0215] Candidate locations of DRS-PSS/DRS-SSS would be to avoid
collision with:
[0216] (1) PDCCH (at least one or two OFDM symbols);
[0217] (2) CRS (at least for one antenna port);
[0218] (3) PSS;
[0219] (4) SSS: when SSS is transmitted and used for discovery
signal, either SSS0 or SSS1 (sequence transmitted in subframe#0 or
subframe #5 can be used. However, it is not desirable to use both
sequences unless the UE detects the subframe index or SFN of the
cell by reading two SSS sequences);
[0220] (5) Potentially considering to avoid collision with PBCH;
and
[0221] (6) Guard period.
[0222] FIG. 14 shows candidate locations of DRS-PSS and DRS-SSS
according to one aspect of the present specification.
[0223] In normal subframe, candidate locations would be as
follows.
[0224] As depicted, in normal CP, OFDM symbol 2/3 of each slot may
be used. In extended CP, OFDM symbol 1/2 in second slot can be
used. In special subframe, OFDM symbol 2/3 in first slot or 1/2 in
first slot in normal/extended CP can be considered. If DRS-CSI-RS
is transmitted as well, to avoid collision with PSS/SSS, either
DRS-CSI-RS may not be transmitted at PRBs where DRS-CSI-RS collides
with PSS/SSS (it may impact discovery signal performance) or to
avoid performance impact, it can be further assumed that DRS-CSI-RS
will be transmitted in non-center-6PRB system only if the system
bandwidth is larger than 6PRB. Or, a discovery signal may be
transmitted only in subframe where PSS/SSS is not transmitted by
the network configuration and thus collision would not be occurred.
When DRS collides with PBCH, advanced UE may assume that DRS will
be transmitted regardless of PBCH (and thus PBCH will be rate
matched or punctured). Since legacy UE is not aware of DRS signal,
it may assume that PBCH will be transmitted where the performance
of legacy UE would be impacted as the DRS may override REs
colliding with PBCH.
[0225] Furthermore, when transmitting the DRS, the number of
antenna ports which may determine the RE density of DRS signal may
be determined regardless of actual antenna ports indicated by PBCH
antenna ports. To allow dense DRS transmission, it would be
desirable to fix 4 antenna ports (only for RE mapping) where actual
transmission may be done via single antenna ports or multiple
antenna ports. In terms of computing RSRP, a UE may assume that it
is transmitted from single antenna such that all REs can be used
for measurement. FIG. 15 shows a DRS RS pattern based on CRS
according to the present specification.
[0226] If CSI-RS is used for DRS, 4 antenna port can be assumed to
determine RE position where actual transmission may be done via
single port or multiple port if configured by higher layer or known
to the UE. In other words, CDM may not be utilized. The sequence
may be generated assuming single antenna port where the same
sequence is transmitted over the resource location where 4 antenna
ports are assumed in the current CSI-RS configuration as in the
Rel-11 specification. In other words, an example of mapping can be
based on the following formula. If the UE has not acquired any
information about antenna port, it may assume single antenna port
transmission.
k = k ' + 12 m + { - 0 , - 6 } fornormalCP , { - 0 , - 3 }
forextendedCP l = l ' + { l '' CSI reference signal configurations
0 - 19 , normal cyclic prefix 2 l '' CSI reference signal
configurations 20 - 31 , extended cyclic prefix l '' CSI reference
signal configurations 0 - 27 , extended cyclic prefix l '' = 0 , 1
m = 0 , 1 , , N RB DL_DRS - 1 m ' = m + N RB max , DL - N RB DL_DRS
2 [ Math Figure 4 ] ##EQU00002##
[0227] If PRS is used, the pattern with one or two antenna PBCH
ports is used for DRS where the density of PRS is higher than 4
ports.
[0228] 4. Multiplexing of DRS with Data Transmission
[0229] When a discovery signal (i.e., DRS) is transmitted, if the
cell is on-state or MBMS transmission occurs, data transmission may
be occurred. In terms of MBMS transmission, it is not desirable to
transmit MBMS transmission in subframes where discovery signals are
transmitted since it may occupy resources in MBMS region. Thus, a
UE expecting to receive MBMS may not expect to receive discovery
signal in a subframe. For instance, if the UE is configured to
receive MBMS services and/or MBMS subframes, the measurement on the
DRS may be performed in a corresponding subframe. For data
transmission in on-state, for advanced UE, a rate matching pattern
needs to be considered. A UE, if configured with one or more zero
power (ZP) CSI-RS configuration used for discovery signal, it may
assume that data will be rate-matched around those resource
elements. In other words, a muting or rate matching pattern can be
configured to a UE regardless of actual discovery signal
transmission. A UE further assumes that other signals such as
PSS/SSS, CSI-RS may be transmitted in those ZP CSI-RS
configurations where still the data will be rate matched around
those REs. The same rate matching can be applied to computing the
number of available REs for ePDCCH resource when EPDCCH is
configured in that subframe. In other words, those REs configured
by ZP CSI-RS configurations for discovery signal will not be
accounted for EPDCCH available REs and the necessary procedures to
determine the minimum aggregation level and resource mapping should
be taken.
[0230] If CP length used for discovery signal and data transmission
are different (e.g., extended CP for DRS and normal CP for data
transmission), when data transmission occurs, advanced UE shall
assume that CP used for DRS is used for data transmission as well
in that subframe including both data and ePDCCH transmission (and
also for PDCCH transmission).
[0231] Furthermore considering a case where DRS is transmitted only
via sub-band (not via entire system bandwidth), ZP CSI-RS
configuration can also include the list of PRBs or bandwidth where
ZP CSI-RS configuration can be applied.
[0232] Considering CoMP operation, when dynamic point selection
(DPS) is used, considering discovery signal transmission, more than
one ZP CSI-RS configuration may be configured per PQI entry where
one is to use for data rate matching for CSI-RS configurations (of
neighbor cells) and the other is used for data rate matching for
DRS configurations. Since the interval may be different between two
ZP-CSI-RS configuration, it would be better to configure different
ZP-CSI-RS configurations or at least two different interval/offset
configurations. This may be applicable only to advanced UEs.
Considering potentially hopping of CSI-RS resources of DRS signal,
if needed, a hopping pattern or configuration change can be
specified in a CSI-RS configuration used for DRS. In other words,
ZP-CSI-RS configuration configured for DRS may have subframe-index
dependent or SFN-dependent RE mapping or configuration mapping such
that actual ZP-CSI-RS RE positions may be changed over time
following a predetermined or higher-layer configured pattern. Or,
simply a ZP-CSI-RS configuration which consists of multiple
NZP-CSI-RS configurations for multiple DRS signals from multiple
neighbor cells can be configured to a UE where the actual mapping
between REs to DRS-CSI-RS from a specific cell may change over time
or over SFN. In other words, a cell ID=1 may transmit CSI-RS in
CSI-RS configuration #0 at one time where next time it may transmit
CSI-RS configuration #1. Regardless of actual location change, a UE
can assume REs configured in the ZP-CSI-RS configuration will be
rate matched.
[0233] The rate matching can be applied for SPS as well according
to the configuration per subframe where SPS-PDSCH is
transmitted.
[0234] As discussed above, at least two different interval/offset
configurations for ZP-CSI-RS configuration can be supported in the
present specification. In one example, the maximum number of the
different interval/offset configurations may be associated with the
duration during which the UE performs measurement on the DRS (as
illustrated in FIG. 11). As explained above, the maximum length of
the duration can be set to 5 ms, and thus the maximum number of the
different interval/offset configurations can be set to 5. Namely,
zero or a maximum of five different interval/offset configurations
used for ZP-CSI-RS can be used in the present specification. When
at least two interval/offset configurations are provided, the
interval/offset are separately configured.
[0235] 5. Misaligned SFN Among Cells
[0236] If cells transmitting discovery signals (i.e., DRS) in a
small cell cluster are not aligned in terms of SFN, there is a need
to select a cell which can be used as a `reference` to transmit
discovery signals in a same subframe. Or, an overlaid macro's SFN
is used as a reference. Also, it is possible that the serving cell
gives the offset value (between serving cell and target cell ? or
cells for discovery) can be configured to the UE along with
discovery signal timing information. Particularly, this would be
necessary if DRS is transmitted in a fixed subframe/SFN such as
every 40 msec with SFN %4=0 transmits DRS, then a UE needs to know
SFN and/or subframe index of the target cell (or cells to
discover). However, cells transmitting discovery signals may align
themselves within a measurement gap period such that a UE can
discovery multiple cells at one time attempt. Thus, this SFN and/or
subframe offset or actual value can be configured per frequency
rather than per cell. This may be applied in a measurement gap (or
similar configuration for discovery signal based measurement
object) where the offset can be used to indicate the offset value
between serving and neighbor cells for the discovery signal based
measurement. A UE however may not assume that discovery signals
from multiple cells may come in the same subframe.
[0237] As discussed above, in a case where a number of small cells
transmit DRSs there may occur misalignment between different DRSs,
and thus measurement period and offset of the DRS given to the UE
may not be sufficient information enabling the UE to determine
correct timing for the DRS measurement. Accordingly, UE is required
to a select a cell which can be used as a reference to transmit the
DRS in a same subframe. As discussed above, the macro cell (e.g.,
primary cell)'s system frame number (SFN) can be as the reference
for the misalignment.
[0238] 6. Not Aligned CP Among Cells
[0239] To protect discovery signals (i.e., DRS), it is desirable to
configure separate zero-power CSI-RS configurations covering
discovery signals transmitted by cells using different CP. For
example, for discovery signal related configuration, the used CP
can be indicated or more than one discovery signal related
configurations can be configured per each CP length. For example,
DRS-PSS/DRS-SSS may be transmitted in different OFDM symbols for
normal CP and extended CP. Thus, it is desirable to transmit in
different subframe of discovery signals. Or, one simple approach is
to use "extended CP" or "normal CP" regardless of actual CP used
for data transmission. In this case, actual CP used for data
transmission will be configured to a UE (or discovered by UE) upon
configuring the cell discovered. If this is used, a UE may not
assume that CP used for discovery signal is identical for CP used
for data transmission. This would be useful when DRS-PSS/DRS-SSS is
transmitted in a SFN manner and the time/frequency synchronization
accuracy may not be so high by one-shot of DRS-PSS/DRS-SSS and thus
transmitting DRS-CSI-RS or DRS-CRS using extended CP would be
beneficial for UE performance. However, this has a drawback where
multiplexing of data and discovery signal would become more
challenging particularly for legacy UEs. When only one type of CP
is used for DRS, to generate DRS signal, Ncp may not be used. In
general, subframe index and Ncp which may not be relevant for DRS
may not be used for sequence generation. This is particularly
important in a case when a UE does not know the SFN or slot index
of the target cell for detection or from where DRS is
transmitted.
[0240] 7. TDD Duplex
[0241] When TDD is used, depending on TDD DL/UL configurations, the
number of downlink subframes is limited. Considering subframe #0/#5
is used mainly for PSS/SSS and PBCH/SIB transmission and discovery
signal may be transmitted while the cell is on-state as well,
utilizing special subframe should be considered. In this case, for
a legacy UE, long guard period may be configured such that a legacy
UE may not expect to receive any RS in special subframes where
advanced UE can be configured with discovery signal transmission
along with different guard period configuration. For this, new
CSI-RS configuration in special subframe can be considered as well
as new ZP CSI-RS configuration covering those new CSI-RS
configurations specified in special subframes. For special subframe
configuration, a UE can be configured with special subframe
configuration used for discovery signal transmission and
potentially used for data transmission (for advanced UEs).
Alternatively, a UE may assume that guard period is same as
configured in SIB (same as to legacy UEs) whereas discovery signals
can be transmitted in those guard period following discovery signal
transmission configurations. In this case, ZP CSI-RS configurations
for DRS may not be necessary.
[0242] Note that a UE can be configured with duplex mode of each
frequency layer when network assistance information is available
such that a UE may assume a certain pattern of PSS/SSS and/or
CSI-RS/CRS per duplex type per each frequency. In other words,
blind decoding of different PSS/SSS location to determine duplex
mode may not be necessary if advanced discovery procedure is
utilized. Furthermore, a UE can be configured with CP length used
in each frequency (at least for DRS transmission) such that blind
decoding of CP length may not be necessary either with advanced
discovery procedure.
[0243] When TDD enhanced Interference Mitigation & Traffic
Adaptation (eIMTA) is used, it is possible that a subframe where
discovery signal has been scheduled is changed to uplink subframe.
To avoid this kind of situation, it is considerable to allow only
subframe configured as downlink subframe by a system information
block (SIB) can transmit discovery signals. Otherwise, a UE may
assume that discovery signal will not be present in subframes
changed to uplink subframe indicated by dynamic signaling. Or, it
is also possible that eNB will transmit DRS regardless of DL or UL
subframe according to the configured DRS transmission
configuration. This would be useful particularly for neighbor cell
measurement.
[0244] As discussed above, eIMTA is a scheme where a certain TDD
uplink subframe originally allocated for a certain transmission
(e.g., uplink) is dynamically allocated for another one (e.g.,
downlink). Accordingly, if eIMTA is used for a UE configured to
perform DRS measurement based on DRS configuration given by the
network, it should be clarified that which TDD subframes are
assumed to be carrying the DRS. To further improve the conventional
art, the present specification proposes to assume that a TDD
downlink subframe allocated by the SIB is only subframe(s) carrying
the DRS.
[0245] With respect to special TDD subframes (e.g., DwPTS and
UpPTS), the following improvement are further proposed by the
present specification.
[0246] For DwPTS region among neighbor cells, unless informed
otherwise, UE may assume the shortest DwPTS region. Or, it may
assume that the same DwPTS configuration is used among neighbor
cells from the serving cell. Or, DwPTS region can be configured per
frequency (along with potentially configuration of UL/DL).
[0247] In more detail, based on the conventional art, there is a
technical problem in which a UE does not know the exact length of
special TDD subframes of the neighbor cells when measuring the DRS.
Accordingly, the present specification proposes that the UE assumes
that a length of DwPTS region as a length of special TDD subframes
of the neighbor cells when measuring the DRS.
[0248] 8. Handling of Short-Term Measurement/Detection Accuracy
[0249] Considering a case where a UE may perform cell detection on
a cell infrequently (e.g., every 200 msec), it is important that a
UE can detect a cell in one attempt not to increase the latency of
cell detection or if DRS transmission occurs rather occasionally,
it is important to make it feasible to detect a cell in one
instance of DRS transmission. To enhance the cell detection and
measurement performance, some aspects should be considered. One is
that the accuracy of time/frequency tracking by one-shot PSS/SSS
transmission in a DRS transmission interval. It is therefore
necessary to consider a case where multiple shot of PSS/SSS
transmission may be necessary. To transmit multiple PSS/SSS, either
multiple transmission over multiple subframes or multiple
transmission in a subframe can be considered. The problem with
multiple transmission in a subframe is that it becomes challenging
to multiplex DRS with existing RS when the cell is on-state. Thus,
when it is used, OFDM symbol used for CRS transmission may not be
used for DRS signal transmissions. Or, in that case, since a UE can
use CRS for the same purpose, DRS colliding with existing signals
may be omitted. However, this may impact the performance of
neighbor cell detection which may not be aware of the cell state,
it is not desirable to change the DRS transmission depending on the
cell state. However, if there is a mechanism that UE can discover
the cell state, different DRS signal composition can be also
considered. When DRS transmission is occurred over multiple
subframes, considering potentially different TDD DL/UL
configurations and different duplex and collision with subframe #0,
the number of repetition may not exceed two subframes. Particularly
in TDD, if two subframes are used for DRS transmission, to work
with most special subframe configurations, it is desirable to
transmit DRS-PSS/DRS-SSS in a first slot rather than in second
slot. It means that the first DRS-PSS/DRS-SSS may be placed in
different OFDM symbol from second DRS-PSS/DRS-SSS. Or, only DRS-PSS
or DRS-SSS repetition can be further considered.
[0250] In terms of measurement, it would be still desirable to take
multiple measurements over the time to reflect channel condition
changes (e.g., fading, Doppler, etc.), thus, if repetition occurs,
it would be desirable to reduce the DRS signals used for
measurement (such as DRS-CSI-Rs) transmission interval. For
example, if DRS-PSS/DRS-SSS is transmitted in every 200 msec,
DRS-CSI-RS may be transmitted in every 40 msec where 5 samples of
DRS-CSI-RS can be accumulated for the measurement. It is however
considerable to repeat measurement RS over multiple subframes in a
DRS interval as well.
[0251] Considering a case where muting may be performed for PRB
locations where DRS is transmitted, in other words, PRBs in a
subframe may only carry DRS from potentially multiple cells, data
may not be scheduled in those PRBs in spite of cell is on-state,
DRS signals may use all the REs. One example is to use PRS
configuration format or repeated CRS or repeated CSI-RS
configurations. Furthermore, repeating PSS/SSS can be also
considered. When this is considered, still, the OFDM symbols used
for PDCCH may not be used for DRS as PDCCH needs to be spanned over
the entire system bandwidth. Also, if EPDCCH set is configured to a
subset of full PRBs used for DRS, handling of EPDCCH would be
necessary by not scheduling EPDCCH or by eNB scheduling. In other
words, if this is assumed that a UE may assume that DRS will be
transmitted regardless of data transmission or cell state or EPDCCH
configuration. Either the maximum OFDM symbols used for PDCCH is
assumed when DRS is designed (e.g., 3 for system bandwidth is
larger than 1.4 Mhz, 4 for 1.4 Mhz) or a UE may assume that PDCCH
will not be overlapped with DRS if configured where DRS may use all
OFDM symbols except for one or two OFDM symbols reserved for PDCCH
transmission.
[0252] 9. Cell Detection Algorithms Using Multiple Signals for
DRS
[0253] When multiple signals are used for discovery signals, there
are multiple approaches of utilizing those signals for cell ID
detection, measurement, and so on. This section describes a few
alternative approaches and potential benefits and drawbacks of each
approach. For a convenience, let's assume that discovery signal can
consist of PSS, SSS and CSI-RS or PSS, SSS and CRS. Whether one DRS
transmission includes only one PSS, SSS and CSI-RS or PSS, SSS and
CRS or multiple can be used is not fixed. For a convenience, this
specification explains one example using one transmission of each
signal. However, it can be applied to multiple transmission of each
signal without the loss of generality.
[0254] First Category
[0255] Cell detection utilizes all three signals:
[0256] (1) A cell ID consists of [n_cid_1]*xy+[n_cid_2]*y+[n_cid_3]
where for example y is 17 and x is 10. PSS can carry n_cid_1 and
SSS can carry n_cid_2 and CSI-RS or CRS can carry n_cid_3 when
sequence is generated for each signal. More specifically, n_cid_2
can be used to indicate the location of CSI-RS
configuration/resource or CRS v-shift/resource. In other words,
n_cid_2 (second cell ID indicator) can be used to indicate the
location of CSI-RS or CRS resource. As an example, cell ID=308 can
be represented as n_cid 1, n_cid 2=6, n_cid 3=17 where if CSI-RS is
used and the total configurations used for CSI-RS are 10 sets,
configuration 6 can be used for carrying the DRS for the cell. The
location can be mapped or inferred from n_cid 1 and/or n_cid 2. The
exact function may be different. The principle of this approach is
to divide cell IDs in to multiple signals to reduce the number
candidates per signal and if CRS or CSI-RS which may have multiple
candidate resource locations, the partial or full cell ID can be
used to infer the resource location of those signals.
[0257] (2) A cell ID is same as Rel-8 PSS/SSS where CRS or CSI-RS
may carry the full cell ID: in this case, cell ID may not be
divided further and the same sequence for PSS and/or SSS can be
reused. However, cell ID detection can be done using multiple
signals. For example, instead of relying on PSS/SSS for cell
detection, all signals are used for detecting a cell ID. In this
case, detection of PSS can be same as Rel-8 implementation whereas
detection of cell ID using SSS may be slightly changed to utilize
SSS and/or CSI-RS (or CRS). In generating sequence, SSS and CSI-RS
may be used jointly such that the same scrambling can be used in
different resource locations. In terms of detecting correlation,
correlation of PSS and either from SSS or CSI-RS/CRS can be used
for cell detection.
[0258] Second Category
[0259] Cell detection utilizes only one signal such as CSI-RS
and/or CRS
[0260] (1) If this is used, frequency tracking or time tracking can
be accomplished via PSS and/or SSS. In terms of cell ID, a common
cell ID may be used. When network synchronization is not achieved
among small cells, and thus, transmission timing difference among
small cells may exceed 3 us, it may not be effective to use the
same cell ID for PSS/SSS. In that case, the same cell ID may be
shared only among cells synchronized. Thus, multiple cell IDs can
be detected by detecting PSS and/or SSS where each cell ID
represents different timing or grouping. The ID detected PSS/SSS
may not be tied with cell ID detected by CSI-RS or CRS. In other
words, sequence or scrambling used in time/frequency tracking may
not be used for cell ID detection. Alternatively, ID detected by
PSS/SSS can be used for scrambling CSI-RS or CRS as shown in above
approaches.
[0261] (2) To minimize the complexity increase, a UE may assume the
whole or partial network assistance such as duplex type or CP
length, etc.
[0262] In this category is used, the combination of discovery
signal can be as follows:
[0263] (1) PSS+CSI-RS assuming PSS is sufficient for time/frequency
tracking for CSI-RS cell detection. If the performance of
time/frequency tracking with PSS is not sufficient, frequency
tracking using CSI-RS can be further considered. In this case,
predetermine location of CSI-RS resource would be important to
guarantee the performance;
[0264] (2) PSS+PSS+CSI-RS where two PSS signals are used for
time/frequency tracking and CSI-RS is used for cell ID detection
and measurement;
[0265] (3) PSS+CRS;
[0266] (4) PSS+PSS+CRS; and
[0267] (5) PSS+SSS+CRS (+CSI-RS) in this case, a UE may assume that
CSI-RS is present only if configured with CSI-RS configuration such
as scrambling ID, the resource configurations for CSI-RS, etc.
[0268] When multiple PSS is transmitted, instead of transmitting
multiple signals in a same subframe, two or multiple subframes can
be utilized.
[0269] Third Category
[0270] Cell Detection Utilizes Only PSS/SSS:
[0271] (1) if this is used, cell detection can be performed as in
Rel-8 cell detection without assuming potentially aggregation of
multiple PSS/SSS over time (it can be aggregated depending on the
latency of cell detection requirement, yet, it is desirable to be
able to detect cell ID by one-shot PSS/SSS or one-burst of DRS);
and
[0272] (2) When this is used, measurement may be performed using
PSS/SSS as well or additional RS such as CRS or CSI-RS can be used
for measurement.
[0273] 10. Potential Network Assistance Information and
Signaling
[0274] In general, discovery signal transmission location can be
either fixed in a specification or configurable by higher layer. As
it is designed to allow higher multiplexing/orthogonality, it is
desirable to be able to configure the periodicity and/or offset of
discovery signal transmission. Furthermore, considering a case
where overlaid macro may not be aligned in terms of SFN, some
flexibility to configure the periodicity and offset can be
beneficial. However, it is still feasible to prefix the location of
discovery signal transmission.
[0275] Regardless of whether the discovery signal transmission
periodicity and offset are prefixed or configurable, some network
assistance information to help the network discovery would be
necessary. At least, some timing where a UE can find discovery
signals would be necessary and the timing and duration of those
timing can be determined based on the detection performance
requirement.
[0276] One example is to use the current measurement gap
configuration as it is where a UE needs to assume that discovery
signal may not be transmitted in other than configured measurement
gap. Thus, autonomous cell detection using discovery signal can be
more challenging. In this case, by proper network coordination, by
configuring measurement gap per UE, the periodicity and offset of
discovery signal can be given. However, it is feasible that each
frequency uses different offset, thus, a separate measurement gap
or periodicity/offset can be configured per frequency. Moreover, a
list of cell IDs per frequency and a list of candidate locations
where discovery signals are transmitted can be also signaled to
help the network discovery at a UE. A list of candidate locations
can be predetermined and thus the configuration may not be
necessary.
[0277] Alternatively, to consider multiple frequencies and
different offset per frequency, a measurement gap can be configured
such as:
[0278] Measurement interval: maximum discovery signal transmission
interval such as 200 msec
[0279] Measurement offset values
[0280] Set of {frequency, offset}
[0281] Where a UE can perform measurement on a certain frequency at
a given offset value. Not to incur too much overhead and
interruption, the offset value would be desirability multiple of
current measurement gap such as 40/80 mesc+delta_offset. In other
words, a UE can perform measurement on a set of frequencies near
every 40 msec or 80 msec and the discovery signal transmission
interval can be larger than typical measurement gap. Or, different
offset can be used per a set of cells. Thus, in that case,
[0282] Measurement interval: maximum discovery signal transmission
interval such as 200 msec
[0283] Measurement offset values
[0284] Set of {frequency, cell IDs, offset}
[0285] Furthermore, the location of DRS RSs can be also assisted.
One example is to give a configuration information about the
location of either `SSS` or `PSS` or additional `SSS` or additional
PSS' in terms of OFDM symbol or frequency. Furthermore, a gap used
between PSS and SSS according to each NCID(2) ? used for PSS
scrambling e.g., can be configured for all NCID values (or a
mapping table or an index to indicate mapping table). Or, if CSI-RS
type DRS is used, CSI-RS configuration or mapping between CSI-RS
resource position and cell ID can be configured. One example is
that the total number of CSI-RS configurations (e.g., 10 or 20)
where the starting offset can be given where each cell locates its
DRS in cell ID % max_configuration number+offset among feasible
configurations or resource positions. For example, if 10 CSI-RS
configurations are used with offset=0, cell ID % 10=0 will use
CSI-RS configuration #0, cell ID % 10=1 will use CSI-RS
configuration #0 and so on.
[0286] Also, mapping between cell ID and Vshift value can be
configured where for example if CRS with Vshift is used for
discovery signal, rather than following current specification,
different Vshift according to the mapping can be determined if
higher layer signaling is given.
[0287] Moreover, considering a case where network timing
information is not known among eNBs or cells, maximum uncertainty
in terms of timing can be also configured such that a UE may take
maximum uncertainty in terms of measurement gap application. Along
with maximum uncertainty, a UE may be configured with large
measurement gap to find discovery signals for the target cells. The
large measurement gap may be used once or only a few times. Once a
UE discovers the discovery signal transmission timing information,
a UE may report the discovered "offset" value to the serving cell
so that smaller measurement gap can be configured. For example, if
serving cell and target cells are "30 msec" off and the serving
cell does not know the timing information, it may configure the
maximum measurement gap of 40+6=46 msec assuming discovery signal
is transmitted in every 40 msec. Once a UE discovers that 30 msec
offset between serving cell and target cells discovery signal
transmission, it may inform the serving cell. Or, the UE reports
the subframe or SFN information of the serving cell when discovery
signal is detected. Or, eNB may configure multiple measurement gap
patterns where offset value may change per measurement interval.
For example, a measurement gap pattern can be given
TABLE-US-00004 {measurement gap pattern = 160 msec with 10msec gap
global_offset = 0 In every 40msec, offset value 1 = 10 offset value
2 = 20 offset value 3 = 30 offset value 4 = 40 }
[0288] where measurement interval would be 160 msec and each
measurement can be occurred in every 40 msec with different offset
values. In first 40 msec interval, the offset value 10 is used,
thus a UE starts measurement at 40 msec+10 msec (assuming starting
at 0 msec), the second offset value 20 is used for second 40 msec,
thus a UE starts measurement at 80 msec+20 msec (100 msec), and so
on. Assuming maximum uncertainly is 40 msec, this is to divide
search window per each measurement episode until a UE finds the
offset value. When a UE discovers the offset value, a new
measurement gap is configured or a UE may ignore sub-offset
values.
[0289] Since it is also feasible that some cells in a frequency may
transmit discovery signals whereas other cells may not transmit
discovery signals, it is desirable to know which cells are
transmitting discovery signals and thus a UE can use discovery
signals for measurement and cell detection. One simple approach is
to send a list of cell IDs which can be discovered/measured by
discovery signals. If the list of cell IDs is not known or
configured, a UE may assume that all the cells in the frequency
transmit DRS if DRS is configured for that frequency. In a case, a
measurement gap is used for inter-frequency covering both legacy
and DRS based cell detection and measurement, a UE may perform both
detection/measurement at each measurement gap. In that case, if a
UE detects a cell with the same ID with both legacy and DRS
measurement, it shall assume two cells are different even though
the cell ID is the same and reports both values (along with
potentially detection/measurement RS type). Alternatively, a UE may
assume that the cell ID is the same and takes only DRS-based
detection/measurement. If a UE is configured with a list of cell
IDs transmitting DRS, whether to detect other cells with legacy
signals would be up to UE implementation. Given that measurement
gap configuration, a UE is free to perform both detection
algorithms and reports them. However, if a DRS is configured for a
given frequency, a UE may not perform "legacy signal based
detection/measurement" other than configured subframes for
measurement/detection (e.g., measurement gap). This is to avoid a
case where a UE may detect legacy signals transmitted by ON-state
of the cell which transmits DRS and perform measurements on the
cell. If a UE performs measurement, it may report the RS type along
with results.
[0290] As discussed above, the present specification proposes that
if the cell is an unknown cell and configured with DRS
configuration for a certain frequency, a UE may assume that all the
cells in the frequency transmit DRS. Accordingly, a UE may assume
that a known cell, such as P-cell of the UE, does not transmit the
DRS. Further, as discussed above, DRS can be only configured for a
certain number of frequencies, the UE only performs the DRS
measurement for the configured frequencies and does not perform
legacy signal based measurement. Further, the UE may perform legacy
signal based measurement for un-configured frequencies.
[0291] When a UE is configured with event-triggered reports, it is
notable that a UE may be configured with different thresholds for
legacy based measurement vs. DRS-based measurement since RSSI
measurement can be different. The threshold values are up to the
network, or a single offset/delta value may be given to the UE
which will be used according to the measurement RS type or RSSI
measurement mechanism. In terms of computing RSSI, it is further
considerable to use either OFDM symbols or subframe which are not
carrying discovery RS. One example is to utilize RSSI on CRS-OFDM
symbols (#0/#4 in each slot in normal CP regardless of target cell
state) if DRS consists of PSS/(SSS)/CSI-RS. Another example is to
use non-DRS-subframe entire OFDM symbols for RSSI measurement in a
measurement gap. When RSSI is extremely low due to no data
transmission, RSRQ computation for the DRS can be done as
RSRP.times.N/{RSRP.times.N+RSSI} or similar fashion not to create
infinite value for RSRQ.
[0292] Based on the present specification, a single or multiple
measurement gaps can be configured for UEs. The following
embodiments are mainly related to a situation where multiple
measurement gaps are configured.
[0293] Handling multiple measurement gaps
[0294] As discussed above, a UE can be configured with one
measurement gap configuration for DRS-based measurement.
[0295] In case a UE is configured with a measurement gap due to
hardware restriction or eNB configuration for DRS based
measurement, measurement gap may follow legacy pattern or a new
pattern or a relaxed pattern (such as 40 msec periodicity with
delta offset value where a UE may be able to perform the
measurement m times of measurement gap every 200 msec).
[0296] FIG. 16 shows a number of measurement gap configurations
proposed by the present specification.
[0297] As depicted in FIG. 16, in case measurement gap is per
legacy pattern, the UE can be configured with only one measurement
gap.
[0298] Further, in case measurement gap is per the relaxed pattern,
the UE can be configured with up to two measurement gaps where one
with a legacy and the other one with the relaxed pattern. In this
case, a UE can assume that the relaxed pattern is overlapped with
the legacy pattern such that the relaxed pattern is a subset of the
legacy pattern. Or, a UE can ignore "non-overlap" measurement gap
(i.e., configured for the measurement gap for DRS-based
measurement, but not configured for the measurement gap for legacy
signal based measurement (or the legacy gap pattern), UE can ignore
those gaps for the measurement. Or, a UE is mandated to skip
measurement in those measurement gaps not aligned between two.
[0299] In case measurement gap is per a new pattern, the UE can be
configured with up to three measurement gaps where a UE should
assume that all three measurement gaps are somewhat aligned. The
three measurement gap can include a measurement gap for DRS-based
measurement, another gap for relaxed requirement (per relaxed
measurement gap pattern) and the last gap for the legacy
measurement gap. First, a UE may assume that the relaxed gap
pattern is a subset of the legacy measurement gap pattern. Then, a
UE may further assume that the measurement gap for DRS-based
measurement is a subset of either the relaxed measurement gap or
the legacy measurement gap (or both of them). Similar to the above
case, a UE may ignore "non-overlapped" gaps between the measurement
gap for DRS-based measurement with either relaxed or legacy
measurement gap configuration or a UE should not perform
measurement in those "non-overlapped" gaps. At the same time, a UE
may be able to request to perform the measurement on those gaps
even though are not aligned with other measurement gaps. Example is
shown in below.
[0300] Another possible way of configuring measurement gap for DRS
is to configure as "a multiple" of a legacy measurement gap such as
measurement gap following a legacy gap pattern every m-th gaps are
used for DRS based measurement.
[0301] Also, a gap for DRS based measurement can have shorter
measurement gap as shown in FIG. 16.
[0302] Alternatively, when multiple measurement gap is configured,
the total duration of measurement gap may be covered by Gap pattern
0 (40 msec with 6 msec gap).
[0303] For example, a legacy measurement gap of gap pattern 1 can
be configured for legacy signal based measurement and a new
measurement gap of gap pattern 1 can be configured for DRS based
measurement. Since the total service interruption time of both
measurement gaps would not exceed gap pattern 0, a UE can perform
the measurement. If two measurement gaps are colliding, a UE can
give high priority on DRS based measurement if both cannot be
attempted at the same time.
[0304] FIG. 17 shows an additional embodiments related to
measurement gap configurations proposed by the present
specification.
[0305] Note there can be other possible options satisfying Proposal
7 (a UE should not have more service interruption time than
currently configurable measurement gap) without having the any
constraint that the configured measurement gap pattern for
DRS-based measurement should be a subset of the configured legacy
measurement gap pattern when two measurement gap patterns are
configured. While allowing independent measurement gap pattern
configurations for DRS-based and legacy-based measurement, there
can be one restriction that both of the two configured measurement
gap patterns (i.e., one for DRS-based and the other for
legacy-based measurement) should be covered by one legacy
measurement gap pattern in Table 8.1.2.1-1 in 3GPP TS 36.133. With
this one restriction, the measurement gap pattern for DRS-based
measurement can be newly defined, e.g., with shorter MGL and/or
longer MGRP.
[0306] Another approach to consider is to restrict the use of Gap
Pattern 0 when a UE is configured with more than one measurement
gap. For example, if a UE is configured with a measurement gap for
DRS and another measurement gap for legacy signal based
measurement, neither measurement gap pattern should be based on Gap
Pattern 0. By this restriction, the total service time of two or
measurement gaps may not exceed the measurement gap of Gap Pattern
0 (i.e., 6 msec per 40 msec). Along with this, a measurement gap
pattern for DRS should have longer periodicity than Gap Pattern 0
or 1 (i.e., 40 msec or 80 msec) and/or shorter gap duration (i.e.,
6 msec). Even with this, a gap pattern for the relaxed measurement
should be a subset of legacy gap pattern. For this, a UE shall not
expect to be configured with Gap Pattern 0, if the UE is configured
with a measurement gap pattern for DRS based measurement and a
measurement gap pattern for legacy based measurement. Or, a UE
shall not expect to be configured with Gap Pattern 0, if the UE is
configured with a measurement gap for discovery signal based
measurement.
[0307] Hereinafter, more detailed examples related to the
above-explained features are described.
[0308] A UE can be configured with a muting pattern per cell or TP.
In this case, muting is assumed in a RE-level.
[0309] For intra-frequency, if the serving cell in the same
frequency is activated, the UE shall not assume that CSI-RS based
measurement reporting is triggered.
[0310] As discussed in FIG. 11, a set of DRS configuration can be
provided via a higher layer signalling to UE in order for
signalling a period, offset, and duration for DRS measurement.
Examples of the DRS configuration can be defined as shown below. In
detail, the followings are for NZP-CSI-RS configurations. For
CSI-RS as DRS, we propose the following configurations in
below.
TABLE-US-00005 TABLE 4 CSI-RS-ConfigNZP-r11 ::= SEQUENCE {
csi-RS-ConfigNZPId-r11 CSI-RS-ConfigNZPId-r11,
antennaPortsCount-r11 ENUMERATED {an1, an2, an4, an8},
resourceConfig-r11 INTEGER (0..31), subframeConfig-r11 INTEGER
(0..154), scramblingIdentity-r11 INTEGER (0..503), qcl-CRS-Info-r11
SEQUENCE { qcl-ScramblingIdentity-r11 INTEGER (0..503),
crs-PortsCount-r11 ENUMERATED (n1, n2, n4, spare1},
mbsfn-SubframeConfigList-r11 CHOICE { release NULL, setup SEQUENCE
{ subframeConfigList MBSFN- SubframeConfigList } } OPTIONAL -- Need
ON } OPTIONAL, -- Need OR ... }
TABLE-US-00006 TABLE 5 MeasObjectEUTRA-R12 ::= SEQUENCE {
carrierFreq ARFCN- ValueEUTRA, allowedMeasBandwidth
AllowedMeasBandwidth, presenceAntennaPort1 PresenceAntennaPort1,
neighCellConfig NeighCellConfig, offsetFreq Q-OffsetRange DEFAULT
dB0, -- Cell list cellsToRemoveList CellIndexList OPTIONAL, -- Need
ON cellsToAddModList CellsToAddModList OPTIONAL, -- Need ON --
Black list blackCellsToRemoveList CellIndexList OPTIONAL, -- Need
ON blackCellsToAddModList BlackCellsToAddModList OPTIONAL, -- Need
ON cellForWhichToReportCGI PhysCellId OPTIONAL, -- Need ON ...,
Dmtc_config DMTCConfiguration mandatory {40, 0 default}
measSFPattern MeasSFPatternNeigh OPTIONAL triggerCSI-RS RSRP
Boolean {true to trigger CSI-RS RSRP, false not to trigger}
triggerCSI-RS RSRQ Boolean {true to trigger CSI-RS RSRP, false not
to trigger} DRS-CSI-RSConfigList DRS-CSI- RSConfigFormatList OPTION
(can present only if trigger CSI-RS RSRP or RSRQ is enabled)
[[measCycleSCell-r10 MeasCycleSCell-r10 OPTIONAL, -- Need ON
measSubframePatternConfigNeigh-r10
MeasSubframePatternConfigNeigh-r10 OPTIONAL -- Need ON ]],
[[widebandRSRQ-Meas-r11 BOOLEAN OPTIONAL -- Cond WB-RSRQ ]] }
TABLE-US-00007 TABLE 6 MeasPatternNeighb { Sequence of 5 bits
bitmap }
TABLE-US-00008 TABLE 7 DMTC config { Int periodity Int offset Int
duration Option, if not present assume as 5msec }
TABLE-US-00009 TABLE 8 DRS-CSI-RSConfigFormatList { a set of {cell
ID; A set of DRS_CSI-RS-ConfigNZP-r12; } }
TABLE-US-00010 TABLE 9 DRS_CSI-RS-ConfigNZP-r12 ::= SEQUENCE {
antennaPortsCount-r11 ENUMERATED {an1, an2, an4, an8},
resourceConfig-r11 INTEGER (0..31), subframeConfig-r11 INTEGER
(0..154), scramblingIdentity-r11 INTEGER (0..503), }
[0311] As shown in Table 7, each set of DRS configurations may
include a number of configuration elements, such as "periodicity"
indicating a measurement period of the DRS, "offset" indicating an
offset of the measurement period, and "duration" indicating a time
period during which the UE measures the DRS in one period of the
measurement period. Further, as shown in Table 5, each set of DRS
configurations are defined based on a frequency (e.g.,
"carrierFreq").
[0312] When a UE is configured with CSI-RS-RSRP or RSRQ triggered
without explicit signaling of CSI-RS configurations, the UE shall
assume that:
[0313] During a measurement duration or by MeasPatternNeighb, let's
assume "m" valid downlink subframe indexed 0 to m-1 starting from
the first DMTC subframe; and
[0314] For each subframe, except for the subframe where SSS is
transmitted (and/or PSS is transmitted), it can assume 20 CSI-RS
configurations or a prefixed set of CSI-RS configurations are used
and the scrambling identify of each CSI-RS can be determined by
function of F (subframe index=relative offset from DMTC starting
among m, CSI-RS RE configuration index).
[0315] More specifically, in DRS-CSI-RSConfigFormatList, it can be
configured as shown below.
TABLE-US-00011 TABLE 10 { a set of {cell ID; Boolean implicit {true
if DRS_CSI-RS-ConfigNZP-r1 is not present, 0 otherwise} A set of
DRS_CSI-RS-ConfigNZP-r12; OPTIONAL only if implicit is false. }
[0316] In this case, further indication of subframes where CSI-RS
is transmitted and some function mapping can be higher layer
configured per cell ID as well.
[0317] CSI-RS configuration applicability when the network is not
synchronized.
[0318] At least for FDD, to enhance the multiplexing/ICIC
capability, subframe-shift among clusters can be considered. In
this case, when NZP-CSI-RS like configuration is given, the
question arises how to apply subframe offset. This specification
proposes to apply the subframe offset as the following:
TABLE-US-00012 TABLE 11 For subframe index of QCL-ed SSS (same
scramling ID with QCL-ed CRS) m during a DMTC, If the subframe
offset is k, k = k % DMTC_Period; k = (m + k) % 5;
[0319] For example, subframe offset is 39, and SSS is transmitted
in second subframe of DMTC, CSI-RS is transmitted in 1st subframe
of DRS measurement timing configuration (DMTC) window.
[0320] Relationship between DMTC and measurement gap.
[0321] FIG. 18 shows the relationship between UE measurement on DRS
and measurement gap.
[0322] When a DRS measurement timing configuration (DMTC) is
configured per frequency, for a UE operating cell discovery based
on a measurement gap, it is necessary to further restrict the DMTC
configurations such that a UE can perform inter-frequency
measurements within a measurement gap. Mainly, all or a subset of
DMTC occurrence per each frequency should be aligned with a subset
of measurement gap pattern. FIG. 18 illustrates this
relationship.
[0323] When a UE is configured with multiple DMTC which may not be
aligned, in terms of UE requirement for discovering a cell, the
requirement should be defined that m*max_interval where
max_interval is the maximum interval value for a cell where a UE
can perform measurement. For example, DMTC at a frequency is per 80
msec and measurement gap is per 40 msec with the same offset, the
interval of measurement is 80 msec. On the other hand, if DMTC is
not aligned with measurement gap, and DMTC is overlapped with
measurement gap in every 3 measurement gaps, then, the interval of
measurement for that cell is 3*measurement gap interval. Among all
frequencies that UE needs to monitor, the interval is determined
and the requirement is specified by taking the maximum interval
among frequencies.
[0324] To avoid this, it is necessary to align DMTC duration and
measurement gap. Or, DMTC can be a multiple of measurement gap in
that case the requirement needs to be determined by DMTC interval
rather than measurement gap interval. Even in this case, it is
desirable to have the same DMTC periodicity for all frequencies not
to create complicated issue in measurement requirement. Also, it is
desirable to configure offset for DMTC and measurement gap such
that in a measurement gap, DMTC can be aligned (if present). Thus,
the maximum offset of a DMTC in terms of offset within a
measurement gap should be less than 4 msec allowing at least one
subframe for the measurement. Given that TDD can be also
configured, the overlap should be able to include subframe #0
and/or subframe #1 (or #5/#6).
[0325] Application of DRS-CSI-RS measurement and UE capability
[0326] It can be assumed that DRS-CSI-RS is used only for TP
identification which may be extended to other cases as well. In
other words, DRS-CRS based measurement is sufficient for cell
identification and measurement. In that case, from a UE capability
perspective, reporting capability or CSI-RS based measurement can
be a separate UE capability from DRS-based measurement capability.
In other words, a UE can report two different capabilities ? one
for DRS-CRS based measurement capability and the other for
DRS-CSI-RS based measurement capabilities. Alternatively, a UE
capability can be also associated with CoMP capability. For
example, when a UE supports Transmission Mode 10 (or enhanced TMs
to support CoMP like operation) and a UE supports DRS-based
measurements, it implies that a UE can support DRS-CSI-RS based
measurements. In that sense, if a UE does not support Transmission
Mode 10 (TM10), it is not very useful to configure DRS-CSI-RS based
measurements. Thus, a UE can assume that DRS-CSI-RS based
measurement can be configured only if it supports TM10. Otherwise,
the configuration may be ignored by the UE. More specifically, the
capability of TM10 is signaled per band and/or band-combination.
Thus, for a frequency configured by DMTC, a UE may assume that
DRS-CSI-RS can be configured only if the UE supports TM10 (or
enhanced TMs to support CoMP like operation or shared cell ID
operation) in that frequency or frequency band where the frequency
belongs. Since, CSI-RS based RSRP requires certain UE processing
burden, it is desirable to minimize the number of frequencies that
DRS-CSI-RS based measurements can be configured. This specification
proposes that a UE can be configured with maximum "m" frequencies
where DRS-CSI-RS based measurement can be performed. For example, m
can be fixed as 1 or can be also signaled by a UE capability. For
example, a UE can report the maximum number of frequencies where a
UE can perform DRS-CSI-RS based RSRP such that the network can
configure the frequencies of DRS measurement based on CSI-RS
accordingly. When a UE does not signal the capability, the network
may assume that a frequency band where TM10 is supported can also
be also configured for DRS-CSI-RS based measurements. Furthermore,
a number of TPs/cells searched by DRS-CSI-RS in a frequency can be
also configured to a UE in a DMTC configuration. For example, a UE
can be configured with the number of desired searching TPs/cells in
a frequency, that may limit a UE's processing burden as the UE does
not have to search all TPs/cells in that frequency. The number of
reported TPs/cells based on DRS-CSI-RS can be also specified in a
specification as a requirement of a UE.
[0327] In the meantime, in addition to the foregoing examples
related to DRS measurement interval, if a UE is configured with
CSI-RS, it is expected that the DMTC interval is either 40 msec or
80 msec. It is considered that 160 msec interval is not configured
with CSI-RS. Alternatively, 160 msec ZP-CSI-RS configuration can be
added. When a UE is configured with 160 msec DRS with CSI-RS, a UE
may assume ZP-CSI-RS configurations configured for data rate
matching for DRS measurement are applicable only in DMTC
durations.
[0328] FIG. 19 shows a block diagram which briefly describes a
wireless communication system including an UE 1900 and a BS or cell
2000. The UE 1900 and the BS 2000 may operate based on the
description as explained above. In view of downlink, a transmitter
may be a part of the BS 2000 and a receiver may be a part of the UE
1900. In view of uplink, a transmitter may be a part of the UE 1900
and a receiver may be a part of the BS 2000.
[0329] Referring to FIG. 19, the UE 1900 may include a processor
1910, a memory 1920 and a radio frequency (RF) unit 1930.
[0330] The processor 1910 may be configured to implement proposed
procedures and/or methods described in this application. For
example, the processor 1910 may operatively coupled to the RF unit
1930, wherein the processor 1910 is configured for transmitting
signals via the RF unit 1920 based on a scheduling for UL and/or
DL. The processor 1910 may perform single transmission of signal on
uplink and single reception of signal on downlink at one subframe
via the RF unit 1930.
[0331] The memory 1920 is coupled with the processor 1910 and
stores a variety of information to operate the processor 1910,
which includes data information and/or control information. The RF
unit 1930 is also coupled with the processor 1910.
[0332] The detailed operations of the UE 1900 are same as described
above.
[0333] The BS 2000 may include a processor 2010, a memory 2020 and
a RF unit 2030. Here, the BS may be PCell or SCell and the BS may
be a macro cell or small cell. The processor 2010 may be configured
to implement proposed procedures and/or methods described in this
application. For example, the processor 2010 may schedule UL and/or
DL.
[0334] The memory 2020 is coupled with the processor 2010 and
stores a variety of information to operate the processor 2010,
which includes data information and/or control information. The RF
unit 2030 is also coupled with the processor 2010. The RF unit 2030
may transmit and/or receive a radio signal.
[0335] The detailed operations of the BS 2000 are same as described
above.
[0336] The UE 1900 and/or the BS 2000 may have single antenna or
multiple antennas. The wireless communication system may be called
as multiple input/multiple output (MIMO) system when at least one
of the UE 1900 and the BS 2000 have multiple antennas.
[0337] As discussed, the UE 1900 in FIG. 19 performs the
above-explained technical features. In detail, the UE may receive
measurement configuration for a discovery signal (e.g., DRS). The
DRS candidates may include CRS, PSS, and SSS. Further, depending on
configuration of CSI-RS, the DRS may further includes CSI-RS.
Preferably, the measurement configuration includes at least one set
of configuration elements, and each set of the configuration
elements is defined per a frequency of a corresponding cell.
Further, the each set of the configuration elements indicates a
measurement period of the discovery signal, an offset of the
measurement period, and a measurement duration.
[0338] The UE 1900 in FIG. 19 performs a measurement on the
discovery signal based on the measurement period of the discovery
signal, the offset of the measurement period, and the measurement
duration. In the conventional arts, CRS measurement is performed in
every subframes without referring to any information on
periodicity/interval of the CRS. Also, PSS/SSS measurement is
performed without referring to any information on
periodicity/interval of PSS/SSS. However, to support communication
with small cells, which supports power on/off operations, the
present specification further proposes DRS configurations, each
being set for a certain frequency. Accordingly, the present
embodiments are distinctive over the conventional arts.
[0339] In the above exemplary systems, although the methods have
been described on the basis of the flowcharts using a series of the
steps or blocks, the present specification is not limited to the
sequence of the steps, and some of the steps may be performed at
different sequences from the remaining steps or may be performed
simultaneously with the remaining steps. Furthermore, the
above-described embodiments include various aspects of examples.
Accordingly, the present specification should be construed to
include all other alternations, modifications, and changes which
fall within the scope of the claims.
[0340] In the description regarding the present specification, when
it is said that one element is "connected" or "coupled" to the
other element, the one element may be directly connected or coupled
to the other element, but it should be understood that a third
element may exist between the two elements. In contrast, when it is
said that one element is "directly connected" or "directly coupled"
to the other element, it should be understood that a third element
does not exist between the two elements.
* * * * *