Note: Descriptions are shown in the official language in which they were submitted.
CA 02786700 2012-07-06
METHOD AND APPARATUS FOR GENERATING A REFERENCE SIGNAL
SEQUENCE IN A WIRELESS COMMUNICATION SYSTEM
BACKGROUND OF THE INVENTION
Field of the Invention
[01] The present invention relates to wireless communication, and more
particularly, to a
method and apparatus for generating a reference signal sequence in a wireless
communication system.
. 10
Related Art
_
[02] Multiple-input multiple-output (MIMO) technology can be used to
improve the
efficiency of data transmission and reception using multiple transmission
antennas
and multiple reception antennas. MIMO technology may include a space frequency
block code (SFBC), a space time block code (STBC), a cyclic delay diversity
(CDD),
a frequency switched transmit diversity (FSTD), a time switched transmit
diversity
(TSTD), a precoding vector switching (PVS), spatial multiplexing (SM) for
implementing diversity. An MIMO channel matrix according to the number of
reception antennas and the number of transmission antennas can be decomposed
into
a number of independent channels. Each of the independent channels is called a
layer or stream. The number of layers is called a rank.
[03] In wireless communication systems, it is necessary to estimate an
uplink channel or a
downlink channel for the purpose of the transmission and reception of data,
the
acquisition of system synchronization, and the feedback of channel
information. In
wireless communication system environments, fading is generated because of
multi-
path time latency. A process of restoring a transmit signal by compensating
for the
distortion of the signal resulting from a sudden change in the environment due
to
such fading is referred to as channel estimation. It is also necessary to
measure the
state of a channel for a cell to which a user equipment belongs or other
cells. To
estimate a channel or measure the state of a channel, a reference signal (RS)
which is
known to both a transmitter and a receiver can be used.
- 1 -
CA 02786700 2012-07-06
4
[04] A subcarrier used to transmit the reference signal is referred to as a
reference signal
subcarrier, and a subcarrier used to transmit data is referred to as a data
subcarrier.
In an OFDM system, a method of assigning the reference signal includes a
method of
assigning the reference signal to all the subcarriers and a method of
assigning the
reference signal between data subcarriers. The method of assigning the
reference
signal to all the subcarriers is performed using a signal including only the
reference
signal, such as a preamble signal, in order to obtain the throughput of
channel
estimation. If this method is used, the performance of channel estimation can
be
improved as compared with the method of assigning the reference signal between
data subcarriers because the density of reference signals is in general high.
However, since the amount of transmitted data is small in the method of
assigning
_
the reference signal to all the subcarriers, the method of assigning the
reference
signal between data subcarriers is used in order to increase the amount of
transmitted
data. If the method of assigning the reference signal between data subcarriers
is
used, the performance of channel estimation can be deteriorated because the
density
of reference signals is low. Accordingly, the reference signals should be
properly
arranged in order to minimize such deterioration.
[05] A receiver can estimate a channel by separating information about a
reference signal
from a received signal because it knows the information about a reference
signal and
can accurately estimate data, transmitted by a transmit stage, by compensating
for an
estimated channel value. Assuming that the reference signal transmitted by the
transmitter is p, channel information experienced by the reference signal
during
transmission is h, thermal noise occurring in the receiver is n, and the
signal received
by the receiver is y, it can result in y=h=p+n. Here, since the receiver
already knows
õ
the reference signal p, it can estimate a channel information value h using
Equation
1 in the case in which a Least Square (LS) method is used.
[06] [Equation 1]
[0] h=y1p=h+nlp=h+n
õ
[08] The accuracy of the channel estimation value h estimated
using the reference
..
signal p is determined by the value n . To accurately estimate the value h,
the
value n must converge on 0. To this end, the influence of the value n has to
be
- 2 -
CA 02786700 2015-06-12
53456-58
minimized by estimating a channel using a large number of reference signals. A
variety of
algorithms for a better channel estimation performance may exist.
[09] In order to minimize inter-cell interference (ICI) in transmitting a
reference signal,
sequence group hopping (SGH) or sequence hopping (SH) may be applied to a
reference signal
sequence. When the SGH is applied, the sequence group index of a reference
signal sequence
transmitted in each slot may be changed.
[010] In a multi-user (MU) MIMO environment, in order to guarantee
orthogonality
between reference signals transmitted by a plurality of UEs, an orthogonal
covering code (OCC)
may be used. When the OCC is applied, the improvement of orthogonality and
throughput can be
guaranteed. Meanwhile, in an MU-MIMO environment, a plurality of UEs may use
different
bandwidths. If the OCC is applied while the SCH is performed on reference
signals transmitted
by the plurality of UEs having different bandwidths, the complexity of cell
planning is increased.
That is, it is difficult to guarantee orthogonality the reference signals
transmitted by the plurality
of UEs.
[011] Accordingly, there is a need for another method to indicate whether
to perform
SGH or SH on a reference signal sequence.
SUMMARY OF THE INVENTION
[012] The present invention provides a method and apparatus for
generating a reference
signal sequence in a wireless communication system.
[012a] According to one aspect of the present invention, there is provided
a method of
generating, by a user equipment (UE), a reference signal sequence in a
wireless communication
system, the method comprising: receiving a cell-specific sequence group
hopping (SGH)
parameter from a base station, the cell-specific SGH parameter being used to
enable a sequence
group hopping for a plurality of UEs in a cell; receiving a UE-specific SGH
parameter, specified
to the UE, from the base station, the UE-specific SGH parameter being used to
disable the
sequence group hopping, enabled by the cell-specific SGH parameter, for the
UE; and generating
the reference signal sequence based on a base sequence and a sequence group
number, wherein
the sequence group number is determined by the UE-specific SGH parameter.
- 3 -
CA 02786700 2015-06-12
53456-58
[012b] According to another aspect of the present invention, there is
provided a user
equipment (UE) for generating a reference signal sequence in a wireless
communication system,
the user equipment comprising: a radio frequency (RF) unit for transmitting or
receiving a radio
signal; and a processor, operatively coupled to the RF unit, and configured
for: receiving a cell-
specific sequence group hopping (SGH) parameter from a base station, the cell-
specific SGH
parameter being used to enable a sequence group hopping for a plurality of UEs
in a cell;
receiving a UE-specific SGH parameter, specified to the UE, from the base
station, the UE-
specific SGH parameter being used to disable the sequence group hopping,
enabled by the cell-
specific SGH parameter, for the UE; and generating the reference signal
sequence based on a base
sequence and a sequence group number, wherein the sequence group number is
determined by the
UE-specific SGH parameter.
[013] In another aspect, a method of generating, by a user equipment (UE),
a reference
signal sequence in a wireless communication system is provided. The method
includes receiving
a UE-specific sequence group hopping (SGH) parameter specified to the UE; and
generating the
reference signal sequence based on a base sequence for every slot, wherein the
base sequence is
classified according to a sequence-group number and a base sequence number
which are
determined for every slot by the UE-specific SGH parameter indicating whether
to perform SGH.
[014] In some embodiments, the UE-specific SGH parameter may be transmitted
through a higher layer.
[015] In some embodiments, the reference signal sequence may be a sequence
of a
demodulation reference signal (DMRS) that uses a physical uplink shared
channel (PUSCH)
resources and demodulates a signal.
[016] In some embodiments, when the UE-specific SGH parameter indicates
that SGH is
not performed, a sequence-group number of slots within one subframe and a base
sequence
number within a sequence group may be identical with each other.
[017] In some embodiments, when the UE-specific SGH parameter indicates
that
sequence hopping (SH) is not performed, a sequence-group number of slots
within one subframe
and a base sequence number within a sequence group may be identical with each
other.
- 4 -
CA 02786700 2015-06-12
53456-58
[018] In some embodiments, when the UE-specific SGH parameter indicates
that SGH is
not performed, sequence-group numbers of all slots within a frame may be
identical with each
other.
[019] In some embodiments, the method may further include receiving a cell-
specific
SGH parameter indicating whether to perform SGH or a cell-specific SH
parameter indicating
whether to perform SH. When the cell-specific GH parameter indicates that SGH
is performed,
the UE-specific SGH parameter may override the cell-specific SGH parameter in
indicating
whether to perform SGH. When the cell-specific SH parameter indicates that SH
is performed,
the UE-specific SGH parameter may override the cell-specific SH parameter in
indicating whether
to perform SH.
[020] In some embodiments, the method may further include transmitting the
reference
signal sequence by mapping the reference signal sequence to a subcarrier.
[021] In some embodiments, the reference signal sequence may be generated
further
based on a cyclic shift.
[022] In some embodiments, the base sequence may be based on a Zadoff-Chu
(ZC)
sequence.
[023] In some embodiments, an orthogonal covering code (OCC) may be
applied to the
reference signal sequence. Whether to apply the OCC may be indicated by an OCC
index
transmitted through a higher layer.
[024] In another aspect, an apparatus for generating a reference signal
sequence is
provided. The apparatus includes a radio frequency (RF) unit configured to
receive a user
equipment (UE)-specific sequence group hopping (SGH) parameter, and a
processor coupled to
the RF unit and configured to generate the signal sequence based on a base
sequence for every
slot, wherein the base sequence is classified according to a sequence-group
number and a base
sequence number which are determined for every slot by the UE-specific SGH
parameter
indicating whether to perform SGH.
- 4a -
CA 02786700 2012-07-06
53456-58
[025] In some embodiments, in a MU-MIMO environment, orthogonality between a
plurality of UEs using different bandwidths can be guaranteed.
BRIEF DESCRIPTION OF THE DRAWINGS
[026] FIG. 1 shows a wireless communication system.
[027] FIG. 2 shows the structure of a radio frame in 3GPP LTE.
[028] FIG. 3 shows an example of a resource grid of a single downlink slot.
[029] FIG. 4 shows the structure of a downlink subframe.
[030] FIG. 5 shows the structure of an uplink subframe.
[031] FIG. 6 shows an example of the structure of a transmitter in an SC-FDMA
system.
[032] FIG. 7 shows an example of a scheme in which the subcarrier mapper maps
the
complex-valued symbols to the respective subcarriers of the frequency domain.
[033] FIG. 8 shows an example of the structure of a reference signal
transmitter for
demodulation.
[034] FIG. 9 shows examples of a subframe through which a reference signal is
transmitted.
[035] FIG. 10 shows an example of a transmitter using the clustered DFT-s OFDM
transmission scheme.
[036] FIG. 11 shows another example of a transmitter using the clustered DFT-s
OFDM
transmission scheme.
[037] FIG. 12 is another example of a transmitter using the clustered DFT-s
OFDM
transmission scheme.
[038] FIG. 13 shows an example where the OCC is applied to a reference signal.
[039] FIG. 14 is an example where a plurality of UEs performs MU-MIMO
transmission
using different bandwidths.
[040] FIG. 15 is an example where SGH and SH are not performed by the proposed
UE-
specific SGH parameter.
[041] FIG. 16 is an embodiment of a proposed method of generating a reference
signal
sequence.
[042] FIG. 17 is a block diagram showing a BS and UE in which the embodiments
of the
present invention are implemented.
- 5 -
CA 02786700 2012-07-06
*
DESCRIPTION OF EXEMPLARY EMBODIMENTS
[043] The following technique may be used for various wireless communication
systems
such as code division multiple access (CDMA), a frequency division multiple
access
(FDMA), time division multiple access (TDMA), orthogonal frequency division
multiple access (OFDMA), single carrier-frequency division multiple access (SC-
FDMA), and the like. The CDMA may be implemented as a radio technology such
as universal terrestrial radio access (UTRA) or CDMA2000. The TDMA may be
implemented as a radio technology such as a global system for mobile
_
communications (GSM)/general packet radio service (GPRS)/enhanced data rates
for
GSM evolution (EDGE). The OFDMA may be implemented by a radio technology
such as institute of electrical and electronics engineers (IEEE) 802.11 (Wi-
Fi), IEEE
802.16 (WiMAX), IEEE 802.20, E-UTRA (evolved UTRA), and the like. IEEE
802.16m, an evolution of IEEE 802.16e, provides backward compatibility with a
system based on IEEE 802.16e. The UTRA is part of a universal mobile
telecommunications system (UMTS). 3GPP (3rd generation partnership project)
LTE (long term evolution) is part of an evolved UMTS (E-UMTS) using the E-
UTRA, which employs the OFDMA in downlink and the SC-FDMA in uplink.
LTE-A (advanced) is an evolution of 3GPP LTE.
[044] Hereinafter, for clarification, LTE-A will be largely described, but the
technical
concept of the present invention is not meant to be limited thereto.
[045] FIG. 1 shows a wireless communication system.
[046] The wireless communication system 10 includes at least one base station
(BS) 11.
Respective BSs 11 provide a communication service to particular geographical
areas
15a, 15b, and 15c (which are generally called cells). Each cell may be divided
into
a plurality of areas (which are called sectors). A user equipment (UE) 12 may
be
fixed or mobile and may be referred to by other names such as MS (mobile
station),
MT (mobile terminal), UT (user terminal), SS (subscriber station), wireless
device,
PDA (personal digital assistant), wireless modem, handheld device. The BS 11
generally refers to a fixed station that communicates with the UE 12 and may
be
called by other names such as eNB (evolved-NodeB), BTS (base transceiver
system),
access point (AP), etc.
- 6 -
CA 02786700 2012-07-06
[047] In general, a UE belongs to one cell, and the cell to which a UE belongs
is called a
serving cell. A BS providing a communication service to the serving cell is
called a
serving BS. The wireless communication system is a cellular system, so a
different
cell adjacent to the serving cell exists. The different cell adjacent to the
serving cell
is called a neighbor cell. A BS providing a communication service to the
neighbor
cell is called a neighbor BS. The serving cell and the neighbor cell are
relatively
determined based on a UE.
[048] This technique can be used for downlink or uplink. In general, downlink
refers to
communication from the BS 11 to the UE 12, and uplink refers to communication
from the UE 12 to the BS 11. In downlink, a transmitter may be part of the BS
11
and a receiver may be part of the UE 12. In uplink, a transmitter may be part
of the
UE 12 and a receiver may be part of the BS 11.
[049] The wireless communication system may be any one of a multiple-input
multiple-
output (MIMO) system, a multiple-input single-output (MISO) system, a single-
input
single-output (SISO) system, and a single-input multiple-output (SIMO) system.
The MIMO system uses a plurality of transmission antennas and a plurality of
reception antennas. The MISO system uses a plurality of transmission antennas
and
a single reception antenna. The SISO system uses a single transmission antenna
and a single reception antenna. The SIMO system uses a single transmission
antenna and a plurality of reception antennas. Hereinafter, a transmission
antenna
refers to a physical or logical antenna used for transmitting a signal or a
stream, and a
reception antenna refers to a physical or logical antenna used for receiving a
signal or
a stream.
[050] FIG. 2 shows the structure of a radio frame in 3GPP LTE.
[051] It may be referred to Paragraph 5 of "Technical Specification Group
Radio Access
Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical
channels
and modulation (Release 8)" to 3GPP (3rd generation partnership project) TS
36.211
V8.2.0 (2008-03). Referring to FIG. 2, the radio frame includes 10 subframes,
and
one subframe includes two slots. The slots in the radio frame are numbered by
#0
to #19. A time taken for transmitting one subframe is called a transmission
time
interval (TTI). The TTI may be a scheduling unit for a data transmission. For
- 7 -
CA 02786700 2012-07-06
example, a radio frame may have a length of 10 ms, a subframe may have a
length of
1 ms, and a slot may have a length of 0.5 ms.
[052] One slot includes a plurality of orthogonal frequency division
multiplexing (OFDM)
symbols in a time domain and a plurality of subcarriers in a frequency domain.
Since 3GPP LTE uses OFDMA in downlink, the OFDM symbols are used to express
a symbol period. The OFDM symbols may be called by other names depending on a
multiple-access scheme. For example, when a single carrier frequency division
multiple access (SC-FDMA) is in use as an uplink multi-access scheme, the OFDM
symbols may be called SC-FDMA symbols. A resource block (RB), a resource
allocation unit, includes a plurality of continuous subcarriers in a slot. The
structure
of the radio frame is merely an example. Namely, the number of subframes
included in a radio frame, the number of slots included in a subframe, or the
number
of OFDM symbols included in a slot may vary.
[053] 3GPP LTE defines that one slot includes seven OFDM symbols in a normal
cyclic
prefix (CP) and one slot includes six OFDM symbols in an extended CP.
[054] The wireless communication system may be divided into a frequency
division duplex
(FDD) scheme and a time division duplex (TDD) scheme. According to the FDD
scheme, an uplink transmission and a downlink transmission are made at
different
frequency bands. According to the TDD scheme, an uplink transmission and a
downlink transmission are made during different periods of time at the same
frequency band. A channel response of the TDD scheme is substantially
reciprocal.
This means that a downlink channel response and an uplink channel response are
almost the same in a given frequency band. Thus, the TDD-based wireless
communication system is advantageous in that the downlink channel response can
be
obtained from the uplink channel response. In the TDD scheme, the entire
frequency band is time-divided for uplink and downlink transmissions, so a
downlink
transmission by the BS and an uplink transmission by the UE can be
simultaneously
performed. In a TDD system in which an uplink transmission and a downlink
transmission are discriminated in units of subframes, the uplink transmission
and the
downlink transmission are performed in different subframes.
[055] FIG. 3 shows an example of a resource grid of a single downlink slot.
- 8 -
CA 02786700 2012-07-06
[056] A downlink slot includes a plurality of OFDM symbols in the time domain
and NRB
number of resource blocks (RBs) in the frequency domain. The NRB number of
resource blocks included in the downlink slot is dependent upon a downlink
transmission bandwidth set in a cell. For example, in an LTE system, NRB may
be
any one of 60 to 110. One resource block includes a plurality of subcarriers
in the
frequency domain. An uplink slot may have the same structure as that of the
downlink slot.
[057] Each element on the resource grid is called a resource element. The
resource
elements on the resource grid can be discriminated by a pair of indexes (k,l)
in the
_
slot. Here, k (k=0,...,NRBx12-1) is a subcarrier index in the frequency
domain, and 1
is an OFDM symbol index in the time domain.
[058] Here, it is illustrated that one resource block includes 7x12 resource
elements made
up of seven OFDM symbols in the time domain and twelve subcarriers in the
frequency domain, but the number of OFDM symbols and the number of subcarriers
in the resource block are not limited thereto. The number of OFDM symbols and
the number of subcarriers may vary depending on the length of a cyclic prefix
(CP),
frequency spacing, and the like. For example, in case of a normal CP, the
number
of OFDM symbols is 7, and in case of an extended CP, the number of OFDM
symbols is 6. One of 128, 256, 512, 1024, 1536, and 2048 may be selectively
used
as the number of subcarriers in one OFDM symbol.
[059] FIG. 4 shows the structure of a downlink subframe.
[060] A downlink subframe includes two slots in the time domain, and each of
the slots
includes seven OFDM symbols in the normal CP. First three OFDM symbols
(maximum four OFDM symbols with respect to a 1.4 MHz bandwidth) of a first
slot
in the subframe corresponds to a control region to which control channels are
allocated, and the other remaining OFDM symbols correspond to a data region to
which a physical downlink shared channel (PDSCH) is allocated.
[061] The PDCCH may carry a transmission format and a resource allocation of a
downlink shared channel (DL-SCH), resource allocation information of an uplink
shared channel (UL-SCH), paging information on a PCH, system information on a
DL-SCH, a resource allocation of an higher layer control message such as a
random
access response transmitted via a PDSCH, a set of transmission power control
- 9 -
CA 02786700 2012-07-06
commands with respect to individual UEs in a certain UE group, an activation
of a
voice over interne protocol (VoIP), and the like. A plurality of PDCCHs may be
transmitted in the control region, and a UE can monitor a plurality of PDCCHs.
The PDCCHs are transmitted on one or an aggregation of a plurality of
consecutive
control channel elements (CCE). The CCE is a logical allocation unit used to
provide a coding rate according to the state of a wireless channel. The CCE
corresponds to a plurality of resource element groups. The format of the PDCCH
and an available number of bits of the PDCCH are determined according to an
associative relation between the number of the CCEs and a coding rate provided
by
the CCEs.
[062] The BS determines a PDCCH format according to a DCI to be transmitted to
the UE,
and attaches a cyclic redundancy check (CRC) to the DCI. A unique radio
network
temporary identifier (RNTI) is masked on the CRC according to the owner or the
purpose of the PDCCH. I n case of a PDCCH for a particular UE, a unique
identifier, e.g., a cell-RNTI (C-RNTI), of the UE, may be masked on the CRC.
Or,
in case of a PDCCH for a paging message, a paging indication identifier, e.g.,
a
paging-RNTI (P-RNTI), may be masked on the CRC. In case of a PDCCH for a
system information block (SIB), a system information identifier, e.g., a
system
information-RNTI (SI-RNTI), may be masked on the CRC. In order to indicate a
random access response, i.e., a response to a transmission of a random access
preamble of the UE, a random access-RNTI (RA-RNTI) may be masked on the CRC.
[063] FIG. 5 shows the structure of an uplink subframe.
[064] An uplink subframe may be divided into a control region and a data
region in the
frequency domain. A physical uplink control channel (PUCCH) for transmitting
uplink control information is allocated to the control region. A physical
uplink
shared channel (PUCCH) for transmitting data is allocated to the data region.
I f
indicated by a higher layer, the user equipment may support simultaneous
transmission of the PUCCH and the PUSCH.
[065] The PUCCH for one UE is allocated in an RB pair. RBs belonging to the RB
pair
occupy different subcarriers in each of a 1st slot and a 2nd slot. A frequency
occupied by the RBs belonging to the RB pair allocated to the PUCCH changes at
a
slot boundary. This is called that the RB pair allocated to the PUCCH is
frequency-
- 10 -
CA 02786700 2012-07-06
hopped at a slot boundary. Since the UE transmits UL control information over
time through different subcarriers, a frequency diversity gain can be
obtained. 1n
the figure, m is a location index indicating a logical frequency-domain
location of the
RB pair allocated to the PUCCH in the subframe.
[066] Uplink control information transmitted on the PUCCH may include a HARQ
ACK/NACK, a channel quality indicator (CQI) indicating the state of a downlink
channel, a scheduling request (SR) which is an uplink radio resource
allocation
request, and the like.
[067] The PUSCH is mapped to a uplink shared channel (UL-SCH), a transport
channel.
Uplink data transmitted on the PUSCH may be a transport block, a data block
for the
UL-SCH transmitted during the TTI. The transport block may be user
information.
Or, the uplink data may be multiplexed data. The multiplexed data may be data
obtained by multiplexing the transport block for the UL-SCH and control
information. For example, control information multiplexed to data may include
a
CQI, a precoding matrix indicator (PMI), an HARQ, a rank indicator (RI), or
the like.
Or the uplink data may include only control information.
[068] FIG. 6 shows an example of the structure of a transmitter in an SC-FDMA
system.
[069] Referring to FIG. 6, the transmitter 50 includes a discrete Fourier
transform (DFT)
unit 51, a subcarrier mapper 52, an inverse fast Fourier transform (IFFT) unit
53, and
a cyclic prefix (CP) insertion unit 54. The transmitter 50 may include a
scramble
unit (not shown), a modulation mapper (not shown), a layer mapper (not shown),
and
a layer permutator (not shown), which may be placed in front of the DFT unit
51.
[070] The DFT unit 51 outputs complex-valued symbols by performing DFT on
input
symbols. For example, when Ntx symbols are input (where Ntx is a natural
number), a DFT size is Ntx. The DFT unit 51 may be called a transform
precoder.
The subcarrier mapper 52 maps the complex-valued symbols to the respective
subcarriers of the frequency domain. The complex-valued symbols may be mapped
to resource elements corresponding to a resource block allocated for data
transmission. The subcarrier mapper 52 may be called a resource element
mapper.
The IFFT unit 53 outputs a baseband signal for data (that is, a time domain
signal) by
performing IFFT on the input symbols. The CP insertion unit 54 copies some of
the
rear part of the baseband signal for data and inserts the copied parts into
the former
- 11 -
CA 02786700 2012-07-06
part of the baseband signal for data. Orthogonality may be maintained even in
a
multi-path channel because inter-symbol interference (1ST) and inter-carrier
interference (ICI) are prevented through CP insertion.
[071] FIG. 7 shows an example of a scheme in which the subcarrier mapper maps
the
complex-valued symbols to the respective subcarriers of the frequency domain.
Referring to FIG. 7(a), the subcarrier mapper maps the complex-valued symbols,
outputted from the DFT unit, to subcarriers contiguous to each other in the
frequency
domain. '0' is inserted into subcarriers to which the complex-valued symbols
are
not mapped. This is called localized mapping. In a 3GPP LTE system, a
localized
mapping scheme is used. Referring to FIG. 7(b), the subcarrier mapper inserts
an
(L-1) number of '0' every two contiguous complex-valued symbols which are
outputted from the DFT unit (L is a natural number). That is, the complex-
valued
symbols outputted from the DFT unit are mapped to subcarriers distributed at
equal
intervals in the frequency domain. This is called distributed mapping. If the
subcarrier mapper uses the localized mapping scheme as in FIG. 7(a) or the
distributed mapping scheme as in FIG. 7(b), a single carrier characteristic is
maintained.
[072] FIG. 8 shows an example of the structure of a reference signal
transmitter for
demodulation.
[073] Referring to FIG. 8, the reference signal transmitter 60 includes a
subcarrier mapper
61, an IFFT unit 62, and a CP insertion unit 63. Unlike the transmitter 50 of
FIG.6,
in the reference signal transmitter 60, a reference signal is directly
generated in the
frequency domain without passing through the DFT unit 51 and then mapped to
subcarriers through the subcarrier mapper 61. Here, the subcarrier mapper may
map the reference signal to the subcarriers using the localized mapping scheme
of
FIG. 7(a).
[074] FIG. 9 shows examples of a subframe through which a reference signal is
transmitted.
The structure of a subframe in FIG. 9(a) shows a case of a normal CP. The
subframe includes a first slot and a second slot. Each of the first slot and
the second
slot includes 7 OFDM symbols. The 14 OFDM symbols within the subframe are
assigned respective symbol indices 0 to 13. Reference signals may be
transmitted
through the OFDM symbols having the symbol indices 3 and 10. The reference
- 12 -
CA 02786700 2012-07-06
signals may be transmitted using a sequence. A Zadoff-Chu (ZC) sequence may be
used as the reference signal sequence. A variety of ZC sequences may be
generated
according to a root index and a cyclic shift value. A BS may estimate the
channels
of a plurality of UEs through an orthogonal sequence or a quasi-orthogonal
sequence
by allocating different cyclic shift values to the UEs. The positions of the
reference
signals occupied in the two slots within the subframe in the frequency domain
may
be identical with each other or different from each other. In the two slots,
the same
reference signal sequence is used. Data may be transmitted through the
remaining
SC-FDMA symbols other than the SC-FDMA symbols through which the reference
signals are transmitted. The structure of a subframe in FIG. 9(b) shows a case
of an
extended CP. The subframe includes a first slot and a second slot. Each of the
first slot and the second slot includes 6 SC-FDMA symbols. The 12 SC-FDMA
symbols within the subframe are assigned symbol indices 0 to 11. Reference
signals
are transmitted through the SC-FDMA symbols having the symbol indices 2 and 8.
Data is transmitted through the remaining SC-FDMA symbols other than the SC-
FDMA symbols through which the reference signals are transmitted.
[075] Although not shown in FIG. 9, a sounding reference signal (SRS) may be
transmitted
through the OFDM symbols within the subframe. The SRS is a reference signal
for
UL scheduling which is transmitted from UE to a BS. The BS estimates a UL
channel through the received SRS and uses the estimated UL channel in UL
scheduling.
[076] A clustered DFT-s OFDM transmission scheme is a modification of the
existing SC-
FDMA transmission scheme and is a method of dividing data symbols, subjected
to a
precoder, into a plurality of subblocks, separating the subblocks, and mapping
the
subblocks in the frequency domain.
[077] FIG. 10 shows an example of a transmitter using the clustered DFT-s OFDM
transmission scheme. Referring to FIG. 10, the transmitter 70 includes a DFT
unit
71, a subcarrier mapper 72, an IFFT unit 73, and a CP insertion unit 74. The
transmitter 70 may further include a scramble unit (not shown), a modulation
mapper
(not shown), a layer mapper (not shown), and a layer permutator (not shown),
which
may be placed in front of the DFT unit 71.
- 13 -
CA 02786700 2012-07-06
[078] Complex-valued symbols outputted from the DFT unit 71 are divided into N
subblocks (N is a natural number). The N subblocks may be represented by a
subblock #1, a subblock #2, ..., a subblock #N. The subcarrier mapper 72
distributes the N subblocks in the frequency domain and maps the N subblocks
to
subcarriers. The NULL may be inserted every two contiguous subblocks. The
complex-valued symbols within one subblock may be mapped to subcarriers
contiguous to each other in the frequency domain. That is, the localized
mapping
scheme may be used within one subblock.
[079] The transmitter 70 of FIG. 10 may be used both in a single carrier
transmitter or a
multi-carrier transmitter. If the transmitter 70 is used in the single carrier
transmitter, all the N subblocks correspond to one carrier. If the transmitter
70 is
used in the multi-carrier transmitter, each of the N subblocks may correspond
to one
carrier. Alternatively, even if the transmitter 70 is used in the multi-
carrier
transmitter, a plurality of subblocks of the N subblocks may correspond to one
carrier.
Meanwhile, in the transmitter 70 of FIG. 10, a time domain signal is generated
through one IFFT unit 73. Accordingly, in order for the transmitter 70 of FIG.
10 to
be used in a multi-carrier transmitter, subcarrier intervals between
contiguous
carriers in a contiguous carrier allocation situation must be aligned.
[080] FIG. 11 shows another example of a transmitter using the clustered DFT-s
OFDM
transmission scheme. Referring to FIG. 11, the transmitter 80 includes a DFT
unit
81, a subcarrier mapper 82, a plurality of IFFT units 83-1, 83-2, ..., 83-N (N
is a
natural number), and a CP insertion unit 84. The transmitter 80 may further
include
a scramble unit (not shown), a modulation mapper (not shown), a layer mapper
(not
shown), and a layer permutator (not shown), which may be placed in front of
the
DFT unit 71.
[081] IFFT is individually performed on each of N subblocks. An nth IFFT unit
38-n
outputs an nth baseband signal (n=1, 2, .., N) by performing IFFT on a
subblock #n.
The nth baseband signal is multiplied by an nth carrier signal to produce an
nth radio
signal. After the N radio signals generated from the N subblocks are added, a
CP is
inserted by the CP insertion unit 314. The transmitter 80 of FIG. 11 may be
used in
a discontiguous carrier allocation situation where carriers allocated to the
transmitter
are not contiguous to each other.
- 14 -
CA 02786700 2012-07-06
[082] FIG. 12 is another example of a transmitter using the clustered DFT-s
OFDM
transmission scheme. FIG. 12 is a chunk-specific DFT-s OFDM system performing
DFT precoding on a chunk basis. This may be called Nx SC-FDMA. Referring to
FIG. 12, the transmitter 90 includes a code block division unit 91, a chunk
division
unit 92, a plurality of channel coding units 93-1, ..., 93-N, a plurality of
modulators
94-1, ..., 4914-N, a plurality of DFT units 95-1, ..., 95-N, a plurality of
subcarrier
mappers 96-1, ..., 96-N, a plurality of IFFT units 97-1, ..., 97-N, and a CP
insertion
unit 98. Here, N may be the number of multiple carriers used by a multi-
carrier
transmitter. Each of the channel coding units 93-1, ..., 93-N may include a
scramble
unit (not shown). The modulators 94-1, ..., 94-N may also be called modulation
mappers. The transmitter 90 may further include a layer mapper (not shown) and
a
layer permutator (not shown) which may be placed in front of the DFT units 95-
1, ...,
95-N.
[083] The code block division unit 91 divides a transmission block into a
plurality of code
blocks. The chunk division unit 92 divides the code blocks into a plurality of
chunks. Here, the code block may be data transmitted by a multi-carrier
transmitter,
and the chunk may be a data piece transmitted through one of multiple
carriers. The
transmitter 90 performs DFT on a chunk basis. The transmitter 90 may be used
in a
discontiguous carrier allocation situation or a contiguous carrier allocation
situation.
[084] A UL reference signal is described below.
[085] In general, the reference signal is transmitted in the form of a
sequence. A specific
sequence may be used as the reference signal sequence without a special limit.
A
phase shift keying (PSK)-based computer generated sequence may be used as the
reference signal sequence. Examples of PSK include binary phase shift keying
(BPSK) and quadrature phase shift keying (QPSK). Alternatively, a constant
amplitude zero auto-correlation (CAZAC) sequence may be used as the reference
signal sequence. Examples of the CAZAC sequence include a Zadoff-Chu (ZC)-
based sequence, a ZC sequence with cyclic extension, and a ZC sequence with
truncation. Alternatively, a pseudo-random (PN) sequence may be used as the
reference signal sequence. Examples of the PN sequence include an m-sequence,
a
computer-generated sequence, a gold sequence, and a Kasami sequence. A
cyclically shifted sequence may be used as the reference signal sequence.
- 15 -
CA 02786700 2012-07-06
[086] A UL reference signal may be divided into a demodulation reference
signal (DMRS)
and a sounding reference signal (SRS). The DMRS is a reference signal used in
channel estimation for the demodulation of a received signal. The DMRS may be
associated with the transmission of a PUSCH or PUCCH. The SRS is a reference
signal transmitted from a UE to a BS for UL scheduling. The BS estimates an UL
channel through the received SRS and uses the estimated UL channel in UL
scheduling. The SRS is not associated with the transmission of a PUSCH or
PUCCH. The same kind of a basic sequence may be used for the DMRS and the
SRS. Meanwhile, in UL multi-antenna transmission, precoding applied to the
DMRS may be the same as precoding applied to a PUSCH. Cyclic shift separation
is a primary scheme for multiplexing the DMRS. In an LTE-A system, the SRS
may not be precoded and may be an antenna-specific reference signal.
[087] A reference signal sequence ru,v(a)(n) may be defined based on a basic
sequence
bu,v(n) and a cyclic shift a according to Equation 2.
[088] [Equation 2]
[089] a)k(" v
r(14) = ejanh (n)
0 < n < MS
sc
[090] In Equation 2, mscas(1<m<NRBm'uL) is the length of the reference signal
sequence
and MscRs=m*NscaB. NseRB is the size of a resource block indicated by the
number
of subcarriers in the frequency domain. NRBma'cuL indicates a maximum value of
a
UL bandwidth indicated by a multiple of NseRB. A plurality of reference signal
sequences may be defined by differently applying a cyclic shift value a from
one
basic sequence.
[091] A basic sequence bõ,,(n) is divided into a plurality of groups. Here, u0
{0,1,...,29}
indicates a group index, and v indicates a basic sequence index within the
group.
The basic sequence depends on the length MscRs of the basic sequence. Each
group
includes a basic sequence (v=0) having a length of MseRs form (1<m<5) and
includes
2 basic sequences (v=0,1) having a length of MscRS for m(6<m<nRBmax,uLs.
) The
sequence group index u and the basic sequence index v within a group may vary
according to time as in group hopping or sequence hopping.
[092] Furthermore, if the length of the reference signal sequence is 3NscRB or
higher, the
basic sequence may be defined by Equation 3.
[093] [Equation 3]
- 16 -
CA 02786700 2012-07-06
RS RS
[094] ¨
bõ , (n) = x q (n mod Nzc ), 0 n < Mse
, '
[095] In Equation 3, q indicates a root index of a Zadoff-Chu (ZC) sequence.
NwRs is the
length of the ZC sequence and may be a maximum prime number smaller than
MscRs.
The ZC sequence having the root index q may be defined by Equation 4.
[096] [Equation 4]
.71-qm(m+1)
i RS
[097] Xq (M) = e Nzc , O_MN RS
zc ¨1
[098] q may be given by Equation 5.
[099] [Equation 5]
- q = Lq+1/2i+v=(-1)1_27]
RS
[0100] q = NZC = (11 + 1)/31
[0101] If the length of the reference signal sequence is 31\1scRB or less, the
basic sequence
may be defined by Equation 6.
[0102] [Equation 6]
0 < n< msRcS ¨1
b (n)= ej (n" ,
[0103] u,v
[0104] Table 1 is an example where cp(n) is defined when MscRs=NscRB.
[0105] [Table 1]
9(0), ...,y(11)
0 -1 1 3 -3 3 3 I 1 3 1 -3
3
1 1 1 3 3 3 -1 1 -3 -3 1 -3
3
2 1 1 -3 -3 -3 -1 -3 -3 1 -3
1 -1
3 -1 1 I 1 1 -1 -3 -3 1 -3
3 -1
4 -1 3 1 -1 1 -1 -3 -1 1 -I 1
3
5 1 -3 3 -1 -1 1 1 -1 -1 3 -3
1
6 -1 3 -3 -3 -3 3 1 -1 3 3 -3
1
7 -3 -1 -1 -1 1 -3 3 -1 1 -3
3 1
8 1 -3 3 1 -1 -1 -1 1 1 3 -1
1
9 1 -3 -1 3 3 -1 -3 1 1 1 1
I
10 -1 3 -1 1 1 -3 -3 -1 -3 -3
3 -1
11 3 I -1 -1 3 3 -3 I 3 1 3
3
12 1 -3 1 1 -3 1 1 1 -3 -3 -3
1
13 3 3 -3 3 -3 1 1 3 -1 -3 3
3
14 -3 1 -1 -3 -1 3 1 3 3 3 -1
1
15 3 -1 1 -3 -1 -1 1 I 3 1 -1
-3
16 I 3 1 -1 I 3 3 3 -1 -1 3 -
1
17 -3 1 1 3 -3 3 -3 -3 3 I 3 -
1
18 -3 3 1 1 -3 1 -3 -3 -1 -1
1 -3
19 -1 3 1 3 1 -1 -1 3 -3 -1 -
3 -1
-1 -3 1 1 I I 3 1 -1 1 -3 -1
-
- 17 -
CA 02786700 2012-07-06
21 -1 3 -1 1 -3 -3 -3 -3 -3 1
-1 -3
22 1 1 -3 -3 -3 -3 -1 3 -3 1
-3 3
23 1 1 -1 -3 -1 -3 1 -1 1 3 -1
1
24 1 1 3 1 3 3 -1 1 -1 -3 -3
1
25 1 -3 3 3 1 3 3 1 -3 -1 -I
3
26 1 3 -3 -3 3 -3 1 -1 -1 3 -1
-3
27 -3 -1 -3 -1 -3 3 1 -1 1 3
-3 -3
28 -1 3 -3 3 -1 3 3 -3 3 3 -I
-1
29 3 -3 -3 -1 -1 -3 -1 3 -3 3
1 -1
[0106] Table 2 is an example where y(n) is defined when MscR8=2*Nsc".
[0107] [Table 2]
y(0),...0(23)
0 -1 3 1 -3 3 -1 1 3 -3 3 1 3 -3 3 1 1 -1 1 3 -3 3 -3 -1 -3
1 -3 3 -3 -3 -3 1 -3 -3 3 -1 1 1 1 3 1 -1 3 -3 -3 1 3 1 1 -3
' 2 3 -1 3 3 1 1 -3 3 3 3 3 1 -1 3 -1 1 1 -1 -3 -1 -1 1 3 3
3 - 3 1 1 3 1 1 -3 -1 -I 1 3 1 3 1 -1 3 1 1 -3 1 -3 -1
4 - 1 -1 -3 -3 -1 1 1 3 3 -1 3 -1 1 - -3 1 -1 -3 -3 1 3 -1 -1
' 5 -3 1 1 3 -1 1 3 1 -3 1 -3 1 1 -1 -1 3 -1 -3 3 -3 -3 3 I 1
6 1 1 -1 -I 3 - -3 3 -3 1 -1 -1 1 -1 1 1 -1 -3 -1 1 -1 3 -1 -3
7 -3 3 3 -1 -1 -1 3 1 3 1 3 1 1 -1 3 1 -1 I 3 -3 1 -1 1
8 -3 1 3 -3 1 -3 3 -3 3 -1 -1 -1 -1 1 -3 -3 -3 1 -3 -3 3 1 -
3
9 1 1 -3 3 3 -3 -1 3 -3 3 3 3 -1 1 1 -3 1 -1 I 1 3 1 1
- 1 -3 -3 3 3 -1 -1 -3 -3 -1 -3 - 1 -1 1 3 3 -1 -
1 3
11 1 3 3 -3 -3 1 3 1 -1
-3 -3 3 3 -3 3 3 -1 -3 3 -1 1 -3 1
12 1 3 3 1 1 1 -1 -1 1 -3 3 -1 1 1 -3 3 3 -1 -3 3 -3 1 -3 -1
13 3 -1 -1 -1 -1 -1 3 3 1 -1 I 3 3 3 -1 1 1 -3 I 3 1 -3 3
14 - -3 3 1 3 1 -3 3 1 3 1 1 3 3 - -1 -3 1 -3 -1 3 1 1 3
- -1 I -3 1 3 -3 1 -1 -1 3 1 3 1 -1 -3 -3 -1 - -3 3 -3 -1
16 - -3 3 -1 -1 -1 1 1 3 1 3 3 1 -1 1 -3 1 -3 1 1 -3 -1
17 1 3 -I 3 3 -3 1 -1 3 3 3 -1
1 3 -1 -3 - 3 1 -1 -1
18 1 1 1 1 1 -1 3 -1 -3 1 1 3 -3 1 - -1 1 1 -3 -3 3 1 1 -3
19 1 3 3 1 -1 3 -1 3 3 3 -3 1 -I 1 -1 -3 -1 1 3 -1 3 -3 -3
- -3 3
21 - -3 1 1 -1 1 -1 1 -1 3 1 -3 -1 I -1 1 -1 -I 3 3 -3 1 1 -3
22 - -1 -3 3 1 - -3 -1 -3 -3 3 -3 3 -3 -1 1 3 I -3 1 3 3 -1 -3
23 - -1 -1 -1 3 3 3 1 3 3 -3 1 3 -1 3 -1 3 3 -3 3 1 1 3 3
24 1 -1 3 3 -1 -3 3 -3 -1 -1 3 -1 3 -1 -1 1 1 1 1 - -1 3 -1 3
1 -1 1 -1 3 -1 3 1 1 - -1 -3 1 1 -3 1 3 -3 1 1 -3 3 -1 -1
26 - -1 1 3 1 1 -3 -1 -1 -3 3 -3 3 1 -3 3 -3 1 -I 1 -3 1 1 1
27 - -3 3 3 1 1 3 -1 -3 - -1 -1 3 1 - -3 -1 3 -3 - -3 1 -3 -1
28 - -3 -1 -1 1 -3 -1 -1 1 -1 -3 1 1 -3 1 -3 -3 3 I 1 -1 3 -1 -1
29 1 1 -1 -1 -3 -1 3 -1 3 -1 1 3 1 -1 3 1 3 -3 -3 1 -1 -1 1 3
[0108] Hopping of a reference signal may be applied as follows.
[0109] The sequence group index u of a slot index ns may be defined based on a
group
5 hopping pattern fgh(ns) and a sequence shift pattern fõ according to
Equation 7.
[0110] [Equation 7]
[0111] U = (fgh (ns ) + As) mod30
- 18 -
CA 02786700 2012-07-06
[0112] 17 different group hopping patterns and 30 different sequence shift
patterns may
exist. Whether to apply group hopping may be indicated by a higher layer.
[0113] A PUCCH and a PUSCH may have the same group hopping pattern. A group
hopping pattern fgh(ns) may be defined by Equation 8.
[0114] [Equation 8]
0 if group hopping is disabled
[0115]
fgh (ns)= (E7 c(8n + i)=2 1) mod 30 if group hopping is enabled
i=0 s
[0116] In Equation 8, c(i) is a pseudo random sequence that is a PN sequence
and may be
defined by a Gold sequence of a length-31. Equation 9 shows an example of a
gold
sequence c(n).
[0117] [Equation 9]
c(n)= (xl(n+ T c)+ x2(n + N c)) mod 2
oci(n + 31) = (xl(n + 3) + xi(n)) mod 2
[0118] x2(n+ 31)=(x2(n+ 3)+ x2(n+2)+ xl(n+1)+xl(n)) mod 2
[0119] Here, Nc=1600, xi(i) is a first m-sequence, and x2(i) is a second m-
sequence. For
example, the first m-sequence or the second m-sequence may be initialized
according
to a cell identifier (ID) for every OFDM symbol, a slot number within one
radio
frame, an OFDM symbol index within a slot, and the type of a CP. A pseudo
random sequence generator may be initialized to _ Ne in the first of each
'nut ¨ 30
radio frame.
[0120] A PUCCH and a PUSCH may have the same sequence shift pattern. The
sequence
shift pattern of the PUCCH may be fsluccH=NID"11 mod 30. The sequence shift
pattern of the PUSCH may be fsspuscx=0;spuccx+Ass) mod 30 and As, El
{0,1,...,29}
may be configured by a higher layer.
[0121] Sequence hopping may be applied to only a reference signal sequence
having a
length longer than 6NseRB. Here, a basic sequence index v within a basic
sequence
group of a slot index ris may be defined by Equation 10.
[0122] [Equation 10]
= c(ns) if group hopping is disabled and sequence hopping is enabled
v
[0123] 0 otherwise
- 19 -
CA 02786700 2012-07-06
[0124] c(i) may be represented by an example of Equation 9. Whether to apply
sequence
hopping may be indicated by a higher layer. A pseudo random sequence generator
.rcen n
may be initialized to -AID 5 , PUSCH in the first of each radio
frame.
mit ¨ 30
c. = - ¨ = -r fss
[0125] A DMRS sequence for a PUSCH may be defined by Equation 11.
[0126] [Equation 11]
rPUSCH (in AARS ' n) = r(a) ,õ\
A' L sc u ,v
[0127]
[0128] In Equation 11, m=0,1,... and n=0,...,mscRs_i. mscRS=mscPUSCH.
[0129] a=27mes/12, that is, a cyclic shift value is given within a slot, and
ncs may be defined
by Equation 12.
[0130] [Equation 12]
(1)
[0131] )
ncs (nDmRs_,_ nD(2mits npRs (ns )) Mod 12
[0132] In Equation 12, npmR5(1) is indicated by a parameter transmitted by a
higher layer,
and Table 3 shows an example of a corresponding relationship between the
parameter and nDmRs(1).
[0133] [Table 3]
Parameter iipmRs
0 0
1 2
2 3
3 4
4 6
5 8
6 9
7 10
[0134] Back in Equation 12, nDmRs(2) may be defined by a cyclic shift field
within a DCI
format 0 for a transmission block corresponding to PUSCH transmission. The DCI
format is transmitted in a PDCCH. The cyclic shift field may have a length of
3 bits.
[0135] Table 4 shows an example of a corresponding relationship between the
cyclic shift
field and nDmRs(2).
[0136] [Table 4]
Cyclic shift field in DCI format 0 nDmiks(2)
000 0
001 6
010 3
011 4
100 2
- 20 -
CA 02786700 2012-07-06
101 8
110 10
111 9
[0137] If a PDCCH including the DCI format 0 is not transmitted in the same
transmission
block, if the first PUSCH is semi-persistently scheduled in the same
transmission
block, or if the first PUSCH is scheduled by a random access response grant in
the
same transmission block, npmRs(2) may be 0.
[0138] npRs(ns) may be defined by Equation 13.
[0139] [Equation 13]
[0140] nPRS
ns) ¨ L 7 0 c(8NsuLynib = ns +i). 2'
i=
[0141] c(i) may be represented by the example of Equation 9 and may be applied
in a cell-
specific way of c(i). A pseudo random sequence generator may be initialized to
[
Air . 25 f PUSCH in the first of each radio frame.
cina Ss
[0142] A DMRS sequence rPUSCH is multiplied by an amplitude scaling factor
PpuscH and
mapped to a physical transmission block, used in relevant PUSCH transmission,
from rPUSCH(0) in a sequence starting. The DMRS sequence is mapped to a fourth
OFDM symbol (OFDM symbol index 3) in case of a normal CP within one slot and
15 mapped to a third OFDM symbol (OFDM symbol index 2) within one slot in
case of
an extended CP.
[0143] An SRS sequence rsRs(n)=r,,(a)(n) is defined. u indicates a PUCCH
sequence
group index, and v indicates a basic sequence index. The cyclic shift value a
is
defined by Equation 14.
20 [0144] [Equation 14]
cs
a = nSRS
[0145] 8
[0146] rIsRscs is a value configured by a higher layer in related to each UE
and may be any
one of integers from 0 to 7.
[0147] Meanwhile, an orthogonal code cover (OCC) may be applied to a reference
signal
25 sequence. The OCC means a code which has different orthogonality and may
apply
to a sequence. In general, in order to distinguish a plurality of channels
from each
other, different sequences may be used, but the plurality of channels may be
distinguished from each other using the OCC.
- 21 -
CA 02786700 2012-07-06
[0148] The OCC may be used for the following purposes.
[0149] 1) The OCC may be applied in order to increase the amount of radio
resources
allocated to an uplink reference signal.
[0150] For example, assuming that the cyclic shift values of reference signals
transmitted in
a first slot and a second slot are allocated as a, a sign (-) may be allocated
to the
reference signal transmitted in the second slot. That is, a first user may
send a
reference signal, having a cyclic shift value of a and a sign (+), in the
second slot,
and a second user may send a reference signal, having a cyclic shift value of
a and a
sign (-), in the second slot. A BS may estimate the channel of the first user
by
adding the reference signal transmitted in the second slot and the reference
signal
transmitted in the first slot. Furthermore, the BS may estimate the channel of
the
second user by subtracting the reference signal transmitted in the second slot
from
the reference signal transmitted in the first slot. That is, if the OCC is
applied, the
BS can distinguish the reference signal transmitted by the first user from the
reference signal transmitted by the second user. Accordingly, the amount of
radio
resources can be doubled because at least two users use different OCCs while
using
the same reference signal sequence.
[0151] 2) The OCC may be applied in order to increase an interval between
cyclic shift
values allocated to the multiple antennas or the multiple layers of a single
user.
Cyclic shift values allocated to multiple layers are described below, but
cyclic shift
values allocated to multiple antennas may also be applied.
[0152] A uplink reference signal distinguishes channels from each other based
on cyclic
shift values. In order to distinguish a plurality of layers from each other in
a multi-
antenna system, different cyclic shift values may be allocated to reference
signals for
respective layers. The number of cyclic shift values to be allocated must be
increased according to an increase of the number of layers, and thus an
interval
between the cyclic shift values is reduced. Accordingly, channel estimation
performance is reduced because it is difficult to distinguish a plurality of
channels
from each other. In order to overcome this problem, the OCC may be applied to
each layer. For example, it is assumed that cyclic shift offsets 0, 6, 3, and
9 are
allocated to the respective reference signals of four layers. An interval
between the
cyclic shift values of the reference signals of the respective layers is 3.
Here, the
- 22 -
CA 02786700 2012-07-06
interval between the cyclic shift values of the reference signals of the
layers of
antennas may be increased to 6 by applying an OCC of a sign (-) to a third
layer and
a fourth layer. Accordingly, the performance of channel estimation can be
increased.
[0153] 3) The OCC may be applied in order to increase an interval between
cyclic shift
values allocated to a single user.
[0154] In an MU-MIMO system including a plurality of users having multiple
antennas, the
OCC may be applied to a cyclic shift value. For example, from a viewpoint of a
single user performing MIMO transmission, in order to distinguish a plurality
of
antennas or a plurality of layers from each other, a cyclic shift value having
a
distance interval between antennas or layers may be applied. From a viewpoint
of
multiple users, however, the cyclic shift interval between the users may be
narrowed.
In order to overcome this problem, the OCC may be used. When the OCC is
applied, the same cyclic shift value may be applied between the multiple users
according to a type of the OCC.
[0155] FIG. 13 shows an example where the OCC is applied to a reference
signal.
[0156] Both a reference signal sequence for a layer 0 and a reference signal
sequence for a
layer 1 within one subframe are mapped to the fourth SC-FDMA symbol of a first
slot and the fourth SC-FDMA symbol of a second slot. The same sequence is
mapped to two SC-FDMA symbols in each layer. Here, the reference signal
sequence for the layer 0 is multiplied by an orthogonal sequence [+1 +1] and
then
mapped to the SC-FDMA symbol. The reference signal sequence for the layer 1 is
multiplied by an orthogonal sequence [+1 -1] and then mapped to the SC-FDMA
symbol. That is, when the reference signal sequence for the layer 1 is mapped
to
the second slot within the one subframe, the reference signal sequence is
multiplied
by -1 and then mapped.
[0157] If the OCC is applied as described above, a BS that receives a
reference signal may
estimate the channel of the layer 0 by adding a reference signal sequence
transmitted
in the first slot and a reference signal sequence transmitted in the second
slot.
Furthermore, the BS may estimate the channel of the layer 1 by subtracting the
reference signal sequence transmitted in the second slot from the reference
signal
sequence transmitted in the first slot. That is, a BS can distinguish
reference signals,
- 23 -
CA 02786700 2012-07-06
transmitted in respective layers, from each other by applying the OCC.
Accordingly, a plurality of reference signals can be transmitted using the
same
resources. If the number of possible cyclic shift values is 6, the number of
layers or
users that may be multiplexed using the OCC can be increased up to 12.
[0158] In this example, it is assumed that the binary format [+1 +1] or [+1 or
-1] is used as
the OCC, but not limited thereto and various kinds of orthogonal sequences may
be
used as the OCC. For example, orthogonal sequences, such as Walsh codes, DFT
coefficients, and CAZAC sequences, may be applied to the OCC. Furthermore,
reference signals can be multiplexed more easily between users having
different
bandwidths by applying the OCC.
[0159] A proposed method of generating a reference signal sequence is
described below.
[0160] As described above, whether to perform sequence group hopping (SGH) on
a
reference signal sequence in LTE re1-8 may be indicated by a signal that is
transmitted in a cell-specific way. The cell-specific signal indicating
whether to
perform SGH on a reference signal sequence is hereinafter called a cell-
specific GH
parameter. Although LTE re1-8 UE and LTE-A UE coexist within a cell, whether
to
perform SGH on a reference signal sequence is the same in the LTE Re1-8 UE and
the LTE-A UE. Currently defined SGH or sequence gopping (SH) may be
performed for every slot. The cell-specific GH parameter may be a group-
hopping-
enabled parameter provided by a higher layer. When the value of the group-
hopping-enabled parameter is true, SGH for a reference signal sequence is
performed,
but SH is not performed. When the value of the group-hopping-enabled parameter
is false, SGH for a reference signal sequence is not performed, and whether to
perform SH is determined by a cell-specific SH parameter, provided by a higher
layer and indicating whether to perform SH. The cell-specific SH parameter may
be a sequence-hopping-enabled parameter provided by a higher layer.
[0161] Meanwhile, In LTE-A, LTE re1-8 UE and LTE-A UE may perform MU-MIMO
transmission, or LTE-A UEs may perform MU-MIMO transmission. Here, in order
to support the MU-MIMO transmission of UEs having different bandwidths, the
OCC may be applied. When the OCC is applied, orthogonality between the UEs
performing the MU-MIMO transmission can be improved and the throughput can
also be improved. However, if UEs have different bandwidths and whether to
- 24 -
CA 02786700 2012-07-06
perform SGH or SH for a reference signal sequence is determined by a cell-
specific
GH or SH parameter defined in LTE re1-8, orthogonality between reference
signals
transmitted by the respective UEs may not be sufficiently guaranteed.
[0162] FIG. 14 is an example where a plurality of UEs performs MU-MIMO
transmission
using different bandwidths. In FIG. 14(a), a first UE UE1 and a second UE UE2
perform the same bandwidth. In this case, whether to perform SGH or SH for the
base sequence of a reference signal may be determined by a cell-specific GH or
SH
parameter defined in LTE re1-8. In FIG. 14(b), a first UE UE1 uses a bandwidth
which is the sum of bandwidths used by a second UE UE2 and a third UE UE3.
That is, the first UE, the second UE, and the third UE use different
bandwidths. In
this case, whether to perform SGH or SH for the base sequence of a reference
signal
transmitted by each UE needs to be determined using a new method.
[0163] Accordingly, a UE-specific SGH parameter may be newly defined in
addition to the
existing cell-specific GH parameter and the existing cell-specific SH
parameter.
The UE-specific SGH parameter is information for specific UE and may be
transmitted to only the specific UE. The UE-specific SGH parameter may be
applied to a DMRS transmitted using PUSCH resources allocated to specific UE.
That is, the UE-specific SGH parameter may indicate whether to perform SGH/SH
for the base sequence of a DMRS that is transmitted using PUSCH resources. For
convenience of description hereinafter, only an example where whether to
perform
SGH and SH for the base sequence of a reference signal is determined by the UE-
specific SGH parameter is described, but not limited thereto. Whether to apply
SH
for the base sequence of the reference signal may be determined by a UE-
specific SH
parameter different from the UE-specific SGH parameter. Furthermore, an
example
where the present invention is applied to the base sequence of a DMRS
transmitted
using PUSCH resources is described, but not limited thereto. The present
invention
may also be applied to a DMRS, an SRS, etc. which are transmitted using PUCCH
resources in various ways. Furthermore, an MU-MIMO environment in which a
plurality of UEs has different bandwidths is assumed, but the present
invention may
be applied to an MU-MIMO or SU-MIMO environment in which a plurality of UEs
has the same bandwidth.
- 25 -
CA 02786700 2012-07-06
-
,
[0164] When a value of the cell-specific GH parameter or the cell-specific SH
parameter is
true and thus SGH or SH is performed on the base sequence of a reference
signal,
SGH or SH of a slot level is in common performed on a DMRS using PUSCH
resources and a DMRS and STS using PUCCH resources. That is, the sequence
group index (or number) of the base sequence of the reference signal is
changed for
every slot, or a base sequence index (or number) is changed within a sequence
group.
Here, whether SGH or SH will be performed on the DMRS using PUSCH resources
may be indicated by a UE-specific SGH parameter again. In other words, the UE-
specific SGH parameter overrides the cell-specific GH parameter or the cell-
specific
- 10 SGH parameter. The UE-specific SGH parameter may be a
disable sequence-group
hopping parameter. That is, if a value of the UE-specific SGH parameter is
true,
SGH and SH may not be performed irrespective of the cell-specific GH parameter
or
the cell-specific SH parameter. More particularly, when a value of the UE-
specific
SGH parameter is true, SGH and SH for the base sequence of a reference signal
may
not be performed although to execute SGH or SH for the base sequence of the
reference signal is indicated by the cell-specific GH parameter or the cell-
specific SH
parameter. If SGH is not performed, a sequence group index of the base
sequence
of the reference signal may not be changed for every slot. Furthermore, as in
the
case where SGH is performed by the cell-specific GH parameter, a base sequence
index of the base sequence of the reference signal is not changed for every
slot
because SH is not performed. Here, two slots within a subframe send the base
sequences of the reference signals of base sequence indices, such as the same
sequence group index, because SGH and SH are not performed only within one
subframe, but SGH or SH may be applied between subframes. Alternatively, since
SGH and SH are not applied within all subframes, all slots may send the base
sequences of the reference signals of the same sequence group index and the
same
base sequence index. Meanwhile, when a value of the UE-specific SGH parameter
is false, SGH or SH for the base sequence of a reference signal may be
performed
according to the cell-specific GH parameter or the cell-specific SH parameter.
[0165] FIG. 15 is an example where SGH and SH are not performed by the
proposed UE-
specific SGH parameter. Referring to FIG. 15, when SGH and SH are performed in
LTE re1-8 or 9, a sequence group index or a base sequence index of base
sequence of
- 26 -
CA 02786700 2012-07-06
a reference signal transmitted in each slot is different. Approach 1 is a case
where
SGH and SH are not performed within a subframe according to a UE-specific SGH
parameter. Two slots within each subframe generate the base sequences of the
reference signals having the same sequence group index and the same base
sequence
index, and a sequence group index or a base sequence index is changed between
the
subframes. Approach 2 is a case where SGH and SH are not performed within all
subframes according to a UE-specific SGH parameter. Accordingly, all the
subframes generate the base sequences of the reference signals having the same
sequence group index and the same base sequence index.
= 10 [0166] FIG. 16 is an embodiment of a proposed method of
generating a reference signal
sequence.
[0167] At step S100, UE receives a UE-specific SGH parameter. The UE-specific
SGH
parameter may be given by a higher layer. At step S110, the UE generates a
reference signal sequence based on a base sequence for every slot. The base
sequence may be classified according to a sequence-group number and a base
sequence number which are determined for every slot by the UE-specific SGH
parameter indicating whether to perform SGH and SH.
[0168] The UE may be informed of whether to perform SGH and SH according to
the UE-
specific SGH parameter using various methods described below.
[0169] 1) A frequency hopping flag included in a DCI format for uplink
transmission may
play the role of the UE-specific SGH parameter. For example, if frequency
hopping
is enabled by the frequency hopping flag, SGH or SH of a slot level may be
performed. Furthermore, if the frequency hopping is disabled by the frequency
hopping flag, SGH and SH for the base sequence of a DMRS using PUSCH
resources may not be performed. Alternatively, SGH or SH may be performed for
every subframe.
[0170] 2) Whether to perform SGH and SH may be indicated by masking
information,
indicating whether to perform SGH and SH for the base sequence of a reference
signal, in a bit indicating a UE ID included in a DCI format for uplink
transmission.
[0171] 3) Whether to perform SGH and SH for the base sequence of a reference
signal may
be indicated when a specific index of a cyclic shift indicator included in a
DCI
format for UL transmission is designated.
- 27 -
CA 02786700 2012-07-06
[0172] 4) A UE-specific SGH parameter indicating whether to perform SGH and SH
for the
base sequence of a reference signal may be included in a DCI format for UL
transmission.
[0173] 5) A UE-specific SGH parameter may be transmitted to specific UE
through higher
layer signaling for the specific UE.
[0174] 6) If a clustered DFT-s OFDM transmission scheme is used, SGH and SH
for the
base sequence of a reference signal may not be performed.
[0175] Meanwhile, when SGH and SH for the base sequence of a reference signal
are not
performed according to a UE-specific SGH parameter, an OCC may be applied to
the
relevant reference signal. If SGH or SH for the base sequence of the reference
signal is performed, the OCC may not be applied.
[0176] A variety of methods may be used in order to indicate whether to apply
the OCC.
First, when a cyclic shift index is indicated through a DCI format and an OCC
index
indicating whether to apply an OCC is transmitted through a higher layer, if
SGH
and SH for the base sequence of a reference signal are not performed, whether
to
apply an OCC according to an OCC index may be used without change. For
example, an OCC may not be applied if an OCC index is 0, and an OCC may be
applied if an OCC index is 1. Alternatively, an OCC may not be applied if an
OCC
index is 1, and an OCC may be applied if an OCC index is 0. Furthermore, if
SGH
or SH for the base sequence of a reference signal is performed, whether to
apply an
OCC may be determined in an opposite way to the OCC index. For example, an
OCC may be applied if an OCC index is 0, and an OCC may not be applied if an
OCC index is 1. Alternatively, an OCC may be applied if an OCC index is I, and
an OCC may not be applied if an OCC index is 0.
[0177] Alternatively, an OCC index indicating whether to apply an OCC may not
be
separately defined, but a specific OCC may be indicated so that the specific
OCC is
applied to specific cyclic shift index by combining a cyclic shift index and
an OCC
index of 3 bits within a DCI format. Here, if SGH for the base sequence of a
reference signal is performed, an OCC index indicated by a relevant cyclic
shift
index may be reversed again, so that the OCC is not applied. Furthermore, if
SGH
and SH for the base sequence of a reference signal is not performed according
to a
UE-specific SGH parameter, the OCC may be applied by using an OCC index
- 28 -
CA 02786700 2012-07-06
indicated by a relevant cyclic shift index without change. Accordingly,
interference
between reference signals allocated to respective layers can be reduced.
[0178] In the above description, an example where whether to perform SGH and
SH for the
base sequence of a reference signal is determined by a UE-specific SGH
parameter
has been described. In an MU-MIMO environment, however, in order to further
guarantee orthogonality between the reference signals of UEs, a new parameter
indicating whether to perform SH may be further defined. The new parameter
indicating whether to perform SH may be a UE-specific SH parameter. The UE-
specific SH parameter may be applied using the same method as the UE-specific
SGH parameter. That is, the UE-specific SH parameter may override a cell-
specific
SH parameter. The above-described UE-specific SGH parameter may determine
only whether to perform SGH. That is, when a value of the UE-specific SGH
parameter is true, SGH for the base sequence of a reference signal is not
performed.
Furthermore, whether to perform SH for the base sequence of the reference
signal is
determined by the UE-specific SH parameter. When a value of the UE-specific SH
parameter is true, SH for the base sequence of the reference signal is not
performed.
When a value of the UE-specific SH parameter is false, whether to perform SH
for
the base sequence of the reference signal may be determined by a cell-specific
SH
parameter. The UE-specific SH parameter may be dynamically signalized
implicitly or explicitly using signaling through a PDCCH or may be given by a
higher layer, such as RRC signaling, implicitly or explicitly.
[0179] Meanwhile, in the above description, it has been described that the UE-
specific SGH
parameter, the UE-specific GH parameter, or the UE-specific SH parameter
override
the cell-specific GH parameter or the cell-specific SH parameter, irrespective
of a
UL transmission mode, but may be changed according to a transmission mode. In
LTE re1-8/9, a single antenna transmission mode is basically supported. In LTE-
A,
however, a multi-antenna transmission mode, a transmission mode for
discontinuous
allocation, etc. may be defined for the efficiency of UL transmission. Here,
whether to perform the UE-specific SGH parameter, the UE-specific GH
parameter,
or the UE-specific SH parameter may be determined according to the
transmission
mode. For example, in the single antenna transmission mode, although the UE-
specific SGH parameter overrides the cell-specific GH parameter or the cell-
specific
- 29 -
CA 02786700 2012-07-06
..
SH parameter, whether to perform SGH or SH for the base sequence of a
reference
signal may be determined by the cell-specific GH parameter or the cell-
specific SH
parameter.
[0180] FIG. 17 is a block diagram showing a BS and UE in which the embodiments
of the
present invention are implemented.
[0181] The BS 800 includes a processor 810, memory 820, and a radio frequency
(RF) unit
830. The processor 810 implements the proposed functions, processes, and/or
methods. The layers of a wireless interface protocol may be implemented by the
processor 810. The memory 820 is coupled to the processor 810, and it stores
* 10 various pieces of information for driving the processor 810.
The RF unit 830 is
coupled to the processor 810, and it sends a UE-specific SGH parameter to UE.
[0182] The UE 900 includes a processor 910, memory 920, and an RF unit 930.
The RF
unit 930 is coupled to the processor 910, and it receives a UE-specific SGH
parameter. The processor 910 implements the proposed functions, processes,
and/or methods. The layers of a wireless interface protocol may be implemented
by
the processor 910. The processor 910 is configured to generate a reference
signal
sequence based on a base sequence for every slot. The base sequence is
classified
according to a sequence-group number and a base sequence number which are
determined for every slot by a UE-specific SGH parameter indicating whether to
perform SGH. The memory 920 is coupled to the processor 910, and it stores
various pieces of information for driving the processor 910.
[0183] The processors 810, 910 may include application-specific integrated
circuit (ASIC),
other chipset, logic circuit and/or data processing device. The memories 820,
920
may include read-only memory (ROM), random access memory (RAM), flash
memory, memory card, storage medium and/or other storage device. The RF units
830, 930 may include baseband circuitry to process radio frequency signals.
When
the embodiments are implemented in software, the techniques described herein
can
be implemented with modules (e.g., procedures, functions, and so on) that
perform
the functions described herein. The modules can be stored in memories 820, 920
and executed by processors 810, 910. The memories 820, 920 can be implemented
within the processors 810, 910 or external to the processors 810, 910 in which
case
- 30 -
CA 02786700 2012-07-06
53456-58
those can be communicatively coupled to the processors 810, 910 via various
means
as is known in the art.
[0184] In view of the exemplary systems described herein, methodologies that
may be
implemented in accordance with the disclosed subject matter have been
described
with reference to several flow diagrams. While for purposed of simplicity, the
methodologies are shown and described as a series of steps or blocks, it is to
be
understood and appreciated that the claimed subject matter is not limited by
the order
of the steps or blocks, as some steps may occur in different orders or
concurrently
with other steps from what is depicted and described herein. Moreover, one
skilled
in the art would understand that the steps illustrated in the flow diagram are
not
exclusive and other steps may be included or one or more of the steps in the
example
flow diagram may be deleted without affecting the scope of the present
disclosure.
[0185] What has been described above includes examples of the various aspects.
It is, of
course, not possible to describe every conceivable combination of components
or
methodologies for purposes of describing the various aspects, but one of
ordinary
skill in the art may recognize that many further combinations and permutations
are
possible. Accordingly, the subject specification is intended to embrace all
such
alternations, modifications and variations that fall within the scope of the
appended claims.
- 31 -
