U.S. patent application number 13/669945 was filed with the patent office on 2013-05-09 for control channel detection method and apparatus of mimo system.
This patent application is currently assigned to Samsung Electronics Co., Ltd.. The applicant listed for this patent is Samsung Electronics Co., Ltd.. Invention is credited to Joonyoung CHO, Hyoungju JI, Younsun KIM, Juho LEE.
Application Number | 20130114534 13/669945 |
Document ID | / |
Family ID | 48223632 |
Filed Date | 2013-05-09 |
United States Patent
Application |
20130114534 |
Kind Code |
A1 |
JI; Hyoungju ; et
al. |
May 9, 2013 |
CONTROL CHANNEL DETECTION METHOD AND APPARATUS OF MIMO SYSTEM
Abstract
A control channel transmission/reception method and apparatus
are provided. The control channel transmission method of a base
station includes acquiring a criterion for sorting control
channels, sorting the controls channels into at least two control
channel sets based on the criterion, configuring the control
channels by allocating at least one antenna port to each control
channel set, and transmitting the control channels as
configured.
Inventors: |
JI; Hyoungju; (Seoul,
KR) ; KIM; Younsun; (Seongnam-si, KR) ; LEE;
Juho; (Suwon-si, KR) ; CHO; Joonyoung;
(Suwon-si, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Samsung Electronics Co., Ltd.; |
Suwon-si |
|
KR |
|
|
Assignee: |
Samsung Electronics Co.,
Ltd.
Suwon-si
KR
|
Family ID: |
48223632 |
Appl. No.: |
13/669945 |
Filed: |
November 6, 2012 |
Current U.S.
Class: |
370/329 |
Current CPC
Class: |
H04L 5/0053 20130101;
H04L 5/0023 20130101; H04L 5/0094 20130101; H04W 72/0406
20130101 |
Class at
Publication: |
370/329 |
International
Class: |
H04W 72/04 20090101
H04W072/04 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 7, 2011 |
KR |
10-2011-0115276 |
Claims
1. A control channel transmission method of a base station, the
method comprising: acquiring a criterion for sorting control
channels; sorting the control channels into at least two control
channel sets based on the criterion; configuring the control
channels by allocating at least one antenna port to each control
channel set; and transmitting the control channels as
configured.
2. The method of claim 1, further comprising: determining the
criterion; and transmitting information on the criterion and
antenna ports allocated to each control channel set to a terminal
through higher layer signaling.
3. The method of claim 1, wherein the sorting comprises sorting the
control channels into the at least two control channel sets by
based on control information format.
4. The method of claim 1, wherein the sorting comprises sorting the
control channels into the at least two control channels sets based
on transmission mode.
5. The method of claim 4, wherein the transmission mode comprises
at least one of a beamforming transmission mode, a single antenna
transmission mode, and a transmission diversity mode.
6. A control channel reception method of a terminal, the method
comprising: acquiring a criterion for sorting control channels into
at least two control channel sets; acquiring allocation information
on at least one antenna port allocated to each control channel set
sorted by the criterion; and receiving the control channels based
on the criterion and allocation information.
7. The method of claim 6, further comprising receiving the
criterion and allocation information from a base station.
8. The method of claim 6, wherein the criterion is control channel
format of the control channels.
9. The method of claim 6, wherein the criterion is transmission
mode of the control channels.
10. The method of claim 9, wherein the transmission mode comprises
at least one of a beamforming transmission mode, a single antenna
transmission mode, and a transmission diversity mode.
11. A base station for transmitting control channels, the base
station comprising: a scheduler which acquires a criterion for
sorting the control channels and sorts the controls channels into
at least two control channel sets based on the criterion; a control
channel information generator which configures the control channels
by allocating at least one antenna port to each control channel
set; and a transmitter which transmits the control channels as
configured.
12. The base station of claim 11, wherein the scheduler determines
the criterion and transmits information on the criterion and
antenna ports allocated to each control channel set to a terminal
through higher layer signaling.
13. The base station of claim 11, wherein the scheduler sorts the
control channels into the at least two control channel sets by
control information format.
14. The base station of claim 11, wherein the scheduler sorts the
control channels into the at least two control channels sets by
transmission mode.
15. The base station of claim 14, wherein the transmission mode
comprises at least one of a beamforming transmission mode, a single
antenna transmission mode, and a transmission diversity mode.
16. A terminal for receiving control channels, the terminal
comprising: a controller which acquires a criterion for sorting
control channels into at least two control channel sets and
acquires allocation information on at least one antenna port
allocated to each control channel set sorted by the criterion; and
a receiver which receives the control channels based on the
criterion and allocation information.
17. The terminal of claim 16, wherein the receiver receives the
criterion and allocation information from a base station.
18. The terminal of claim 16, wherein the criterion is control
channel format of the control channels.
19. The terminal of claim 16, wherein the criterion is transmission
mode of the control channels.
20. The terminal of claim 19, wherein the transmission mode
comprises at least one of a beamforming transmission mode, a single
antenna transmission mode, and a transmission diversity mode.
Description
PRIORITY
[0001] This application claims the benefit under 35 U.S.C.
.sctn.119(a) of a Korean patent application filed on Nov. 7, 2011
in the Korean Intellectual Property Office and assigned Serial No.
10-2011-0115276, the entire disclosure of which is hereby
incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a Multiple Input Multiple
Output (MIMO) system. More particularly, the present invention
relates to a method and apparatus for detecting control channels in
a MIMO system.
[0004] 2. Description of the Related Art
[0005] Mobile communication systems are developed to provide
subscribers with voice communication services on the move. With the
rapid advance of technologies, the mobile communication systems
have evolved to support high speed data communication services as
well as the standard voice communication services. However, the
limited resource and user requirements for higher speed services in
the current mobile communication system spur the evolution to more
advanced mobile communication systems.
[0006] Long Term Evolution--Advanced (LTE-A) is a next generation
mobile communication standard under development to meet such user
requirements. LTE-A is being standardized by the 3.sup.rd
Generation Partnership Project (3GPP). LTE-A is a technology for
realizing high speed packet-based communication at up to about 1
Gbps. In an effort to achieve this, discussions are being held on
several schemes such as network multiplexing for deploying multiple
evolved Node Bs (eNBs) overlappingly in a specific area and
increasing the number of frequency bands supported by an eNB.
[0007] Meanwhile, LTE operates with control channels designed based
on a distributed transmission mode. The distributed
transmission-based design aims to reduce inter-cell interference,
distribute interference, and achieve frequency diversity gain.
[0008] However, LTE-A assumes there is an operating environment
with very short inter-cell distance and high inter-cell
interference. Accordingly, in the distributed transmission
mode-based control channel design, inter-cell interference is
inevitable.
[0009] LTE-A is also capable of adopting a control channel
transmission mode exploiting frequency-selective gain. This is
advantageous in that the control channel can be transmitted using a
lesser amount of resources, but is also disadvantageous in that the
terminal is likely to fail to receive the control channel,
especially when the channel varies frequently. The evolved system
supports both the related-art frequency diversity gain-oriented
transmission mode and frequency selective gain-oriented
transmission mode. The frequency-selective gain varies dynamically
according to the status of the terminal Also, there can be a
control channel to which only one of the two transmission modes is
employed, i.e., frequency-selective gain-oriented and frequency
diversity gain-oriented transmission modes.
[0010] Accordingly, the system should support both the
aforementioned transmission modes, frequency-selective
gain-oriented and frequency diversity gain-oriented transmission
modes, in control channel transmission without compromising
terminal complexity. This means that there is a need of a control
channel detection method for the terminal to acquire the
configuration information on the new control channel structure.
[0011] The above information is presented as background information
only to assist with an understanding of the present disclosure. No
determination has been made, and no assertion is made, as to
whether any of the above might be applicable as prior art with
regard to the present invention.
SUMMARY OF THE INVENTION
[0012] The present invention has been made in an effort to address
the above problems and it is an object of the present invention to
provide a control channel detection method and apparatus that is
capable of transmitting/receiving the control channels configured
with different reference signals and/or in different transmission
modes.
[0013] In accordance with an aspect of the present invention, a
control channel transmission method of a base station is provided.
The method includes acquiring a criterion for sorting control
channels, sorting the control channels into at least two control
channel sets based on the criterion, configuring the control
channels by allocating at least one antenna port to each control
channel set, and transmitting the control channels as configured.
In accordance with another aspect of the present invention, a
control channel reception method of a terminal includes acquiring a
criterion for sorting control channels into at least two control
channel sets, acquiring allocation information on at least one
antenna port allocated to each control channel set sorted by the
criterion, and receiving the control channels based on the
criterion and allocation information.
[0014] In accordance with an aspect of the present invention, a
control channel reception method of a terminal is provided. The
method includes acquiring a criterion for sorting control channels
into at least two control channel sets, acquiring allocation
information on at least one antenna port allocated to each control
channel set sorted by the criterion, and receiving the control
channels based on the criterion and allocation information.
[0015] In accordance with another aspect of the present invention,
a base station for transmitting control channels is provided. The
base station includes a scheduler which acquires a criterion for
sorting the control channels and sorts the controls channels into
at least two control channel sets based on the criterion, a control
channel information generator which configures the control channels
by allocating at least one antenna port to each control channel
set, and a transmitter which transmits the control channels as
configured.
[0016] In accordance with still another aspect of the present
invention, a terminal for receiving control channels is provided.
The terminal includes a controller which acquires a criterion for
sorting control channels into at least two control channel sets and
acquires allocation information on at least one antenna port
allocated to each control channel set sorted by the criterion, and
a receiver which receives the control channels based on the
criterion and allocation information.
[0017] Other aspects, advantages, and salient features of the
invention will become apparent to those skilled in the art from the
following detailed description, which, taken in conjunction with
the annexed drawings, discloses exemplary embodiments of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The above and other aspects, features, and advantages of
certain exemplary embodiments of the present invention will be more
apparent from the following description taken in conjunction with
the accompanying drawings, in which:
[0019] FIG. 1 is a diagram illustrating a control channel structure
of a subframe for use in a Long Term Evolution (LTE) system to
which exemplary embodiments of the present invention are
applied;
[0020] FIG. 2 is a diagram illustrating a control channel structure
of an LTE-Advanced (LTE-A) system according to an exemplary
embodiment of the present invention;
[0021] FIG. 3 is a diagram illustrating a control channel-resource
mapping mechanism according to an exemplary embodiment of the
present invention;
[0022] FIG. 4 is a diagram illustrating a mechanism of a control
channel transmission according to a first exemplary embodiment of
the present invention;
[0023] FIG. 5 is a diagram illustrating a mechanism of a control
channel detection according to a second exemplary embodiment of the
present invention;
[0024] FIG. 6 is a diagram illustrating a mechanism of a control
channel detection according to a third exemplary embodiment of the
present invention;
[0025] FIG. 7 is a flowchart illustrating a control channel
transmission method of an evolved Node B (eNB) according to an
exemplary embodiment of the present invention;
[0026] FIG. 8 is a flowchart illustrating a control channel
reception method of a User Equipment (UE) according to an exemplary
embodiment of present invention;
[0027] FIG. 9 is a block diagram illustrating a configuration of a
control channel transmission apparatus of an eNB according to an
exemplary embodiment of the present invention; and
[0028] FIG. 10 is a block diagram illustrating a control signal
reception apparatus of a UE according to an exemplary embodiment of
the present invention.
[0029] Throughout the drawings, it should be noted that like
reference numbers are used to depict the same or similar elements,
features, and structures.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0030] The following description with reference to the accompanying
drawings is provided to assist in a comprehensive understanding of
exemplary embodiments of the invention as defined by the claims and
their equivalents. It includes various specific details to assist
in that understanding but these are to be regarded as merely
exemplary. Accordingly, those of ordinary skill in the art will
recognize that various changes and modifications of the embodiments
described herein can be made without departing from the scope and
spirit of the invention. In addition, descriptions of well-known
functions and constructions may be omitted for clarity and
conciseness.
[0031] The terms and words used in this description and the
appended claims are not to be interpreted in common or lexical
meaning but, based on the principle that an inventor can adequately
define the meanings of terms to best describe the invention, to be
interpreted in the meaning and concept conforming to the technical
concept of the present invention.
[0032] Although the description is directed to the exemplary case
of Long Term Evolution (LTE) and LTE-Advanced (LTE-A) systems, the
present invention can be applied to other radio communication
systems operating with base station scheduling.
[0033] Orthogonal Frequency Division Multiplexing (OFDM) is a
transmission technique for transmitting data using multiple
carriers, i.e., a multicarrier data transmission technique which
parallelizes the serial input stream into parallel data streams and
modulates the data streams onto the orthogonal multiple carriers,
i.e., sub-carrier channels.
[0034] The multicarrier modulation scheme originated in the late
1950's with microwave radio for military communication purposes,
and OFDM using orthogonal overlapping multiple subcarriers was
developed in 1970's. However, the implementation of such systems
was limited due to the difficultly of implementing orthogonal
modulations between multiple carriers. With the introduction of the
idea of using a Discrete Fourier Transform (DFT) for implementation
of the generation and reception of OFDM signals, by Weinstein, in
1971, OFDM technology began a period of rapid development.
Additionally, the introduction of a guard interval at the start of
each symbol and the use of a Cyclic Prefix (CP) addresses the
negative effects caused by multipath signals and delay spread.
[0035] Owing to such technical advances, the OFDM technology is
applied in various digital communications fields such as Digital
Audio Broadcasting (DAB), Digital Video Broadcasting (DVB),
Wireless Local Area Network (WLAN), and Wireless Asynchronous
Transfer Mode (WATM). That is, the implementation of OFDM could be
accomplished by reducing implementation complexity with the
introduction of various digital signal processing technologies such
as Fast Fourier Transform (FFT) and Inverse Fast Fourier Transform
(IFFT).
[0036] OFDM is similar to Frequency Division Multiplexing (FDM) but
much more spectrally efficient for achieving high speed data
transmission by overlapping multiple subcarriers orthogonally. Due
to the spectral efficiency and robustness to the multipath fading,
OFDM has been considered as a prominent solution for broadband data
communication systems.
[0037] Other advantages of OFDM are to control Inter-Symbol
Interference (ISI) using a guard interval and to reduce the
complexity of an equalizer in view of hardware as well as spectral
efficiency and robustness to the frequency selective fading and
multipath fading. OFDM is also robust to impulse noise so as to be
employed in various communication systems.
[0038] In wireless communications, high-speed, high-quality data
services are generally hindered by the channel environment. In
wireless communications, the channel environment suffers from
frequent changes not only due to Additive White Gaussian Noise
(AWGN), but also power variation of received signals, caused by a
fading phenomenon, shadowing, a Doppler effect brought by movement
of a User Equipment (UE) and a frequent change in a velocity of the
UE, interference by other users or multipath signals, etc.
Therefore, in order to support high-speed, high-quality data
services in a wireless communication system, there is a need to
efficiently address the above channel quality degradation
factors.
[0039] In OFDM, modulation signals are located in two-dimensional
time-frequency resources. Resources on the time domain are divided
into different OFDM symbols, and are orthogonal with each other.
Resources on the frequency domain are divided into different tones,
and are also orthogonal with each other. That is, the OFDM scheme
defines one minimum unit resource by designating a particular OFDM
symbol on the time domain and a particular tone on the frequency
domain, and the unit resource is referred to as a Resource Element
(RE). Since different REs are orthogonal with each other, signals
transmitted on different REs can be received without causing
interference to each other.
[0040] The physical channel is a channel defined on the physical
layer for transmitting modulation symbols obtained by modulating
one or more coded bit sequences. In an Orthogonal Frequency
Division Multiple Access (OFDMA) system, a plurality of physical
channels can be transmitted depending on the usage of the
information sequence or receiver. The transmitter and receiver
determine REs on which a physical channel is transmitted, and this
process is referred to as mapping.
[0041] The LTE system and LTE-A system evolved therefrom are the
representative systems adopting OFDM in a DownLink (DL). Meanwhile,
the LTE/LTE-A system adopts Single Carrier-Frequency Division
Multiple Access (SC-FDMA) in UpLink (UL).
[0042] FIG. 1 is a diagram illustrating a control channel structure
of a subframe for use in an LTE system to which exemplary
embodiments of the present invention are applied. The subframe of
FIG. 1 may be compatible in the LTE-A system.
[0043] Referring to FIG. 1, the entire downlink transmission
bandwidth 101 consists of a plurality of Resource Blocks (RBs)
(also referred to herein as Physical RBs (PRBs)). Each RB 103
consists of 12 frequency tones arranged in the frequency domain and
14 or 12 OFDM symbols arranged in the time domain. A RB is the
basic unit of resource allocation. FIG. 1 is directed to a subframe
consisting of 14 time symbols. Each subframe 105 spans 1 ms and
consists of two 0.5 ms slots 107.
[0044] Reference Signals (RSs) 113 and 115 are signals agreed upon
between an evolved Node B (eNB) and a User Equipment (UE) for use
in channel estimation. There are two types of reference signals,
i.e., a Common RS (CRS) 115 and a Dedicated RS (DRS) 113, defined
for use in the LTE system. The eNB with two antennas transmits CRS
through ports 0 and 1. The eNB with 4 antennas transmits the CRS
115 through ports 0, 1, 2, and 3. If there is more than one antenna
port, this means that a multi-antenna system is employed.
[0045] The RSs are arranged at fixed positions of the RB in a
cell-specific manner at a regular interval in the frequency domain.
That is, the RSs for the same antenna port are located on every
6.sup.th RB, and the reason why the absolute positions of the RSs
are determined differently per cell is to avoid collisions between
the RSs of different cells. The number of RSs differs according to
the antenna port. For the antenna ports 0 and 1, a total of 8 RSs
exist in a single RB or subframe, while for the antenna ports 2 and
3, a total of 4 RSs exist in a single RB or subframe. Since it has
to be received by all UEs, the CRS is transmitted in all RBs across
the entire downlink bandwidth.
[0046] The DRS 113 is a UE-specific reference signal transmitted in
the RB where the UE is scheduled. If the RB receiving the
corresponding RB 117 does not use DRS, no DRS is transmitted. The
DRS 115 can also be transmitted through multiple ports like the
CRS. Although it depends on the configuration, the LTE-A system may
use the same resource for two antenna ports differentiated with two
scrambling codes and may support up to 8 DRSs. The DRS is
transmitted in the data region 103 of a specific PRB assigned to a
specific UE but not across the entire downlink bandwidth 101.
[0047] Typically, the common reference signal can be used for a
single antenna transmission or a Transmission Diversity (TD)
transmission mode for achieving frequency or antenna diversity
gain, along with a beamforming technique. Typically, the CRS is
receivable by all users within the cell and thus the signals are
carried in the CRS by all UEs.
[0048] In order to provide the frequency selective gain with the
DRS-based transmission, a beamforming technique is used. Since the
eNB performs transmission using the UE-recommended frequency
resource, it is possible for the UE to receive the signal with high
quality. However, there is a shortcoming in that it is vulnerable
to a fast channel varying environment.
[0049] The control channel signal of LTE is arranged at the
beginning of a subframe in the time domain. The control channel
signal can be located in the control channel region 109 in FIG. 1.
The control channel signal can be transmitted across N OFDM symbols
at the beginning of the subframe. N can be 1, 2, or 3. In the case
where the transmission bandwidth is narrow, n can be 2, 3, or 4.
FIG. 1 is directed to the case where the control channel region of
N=3. The control channel region 109 can be changed dynamically at
every subframe. If one OFDM symbol is sufficient due to there being
a small amount of control channel data, it is possible to allocate
the first OFDM symbol for the control channel signal transmission
(N=1) while the remaining 13 OFDM symbols are allocated for data
channel signal transmission. If the control channel amount
increases, the number of symbols available for data transmission
decreases. N is used as the basic information for allocated control
channel resource de-mapping and is especially used for interleaving
of the control channel. The reason for placing the control channel
signal at the beginning of the subframe is for early detection of
the control channel such that the UE determines whether to perform
a data channel reception operation depending on the presence of the
data channel signal addressed to the current UE. If there is no
data channel signal addressed to the UE, it is not necessary for
the UE to attempt data channel decoding, thereby avoiding the power
consumption caused by data channel reception. Also, by receiving
the control channel at the beginning of the subframe prior to the
data channel, it is possible to reduce scheduling delay.
[0050] In LTE, a Physical Dedicated Control Channel (PDCCH) is a
physical channel for transmitting a common control channel and a
dedicated control channel including data channel allocation
information, allocation information for system information
transmission or power control information. The eNB having one
antenna transmits the PDCCH in a single antenna transmission mode,
while the eNB having multiple antennas transmits the PDCCH in a
Transmit Diversity (TD) mode.
[0051] The eNB can configure the PDCCH with different channel
coding rates depending on the channel state of the UE. Since
Quadrature Phase Shift Keying (QPSK) is fixedly used for PDCCH
transmission, the resource amount is changed in order to change the
channel coding rate. The UE with a good channel condition uses a
high channel coding rate to reduce the amount of resources used for
transmission. Meanwhile, the UE with a bad channel condition uses a
low channel coding rate to ensure that the signal may be received
despite the use of a greater amount of resources. The amount of
resources for each PDCCH is determined depending on the unit of a
Control Channel Element (CCE). A CCE consists of a plurality of
Resource Element Groups (REGs). The REG of a PDCCH is interleaved
to ensure diversity and distribute inter-cell interference and then
mapped to the control channel region of PRBs across the entire
downlink bandwidth as denoted by reference number 101 and 109.
[0052] The interleaving is performed to all of the REGs of the
subframe that are determined by N. The output of the control
channel interleaving is designed to space the REGs of the control
channel allocated across one or more symbols far enough to acquire
diversity gain while avoiding inter-cell interference caused by use
of the same interleaver for the cells. Also, it guarantees uniform
distribution of the REGs constituting the same channel across the
per-channel symbols. Also, it is multiplexed with other control
channels.
[0053] In the advanced environment experienced in the recent LTE-A
system, however, it is assumed to deploy a large number of eNBs
that are different in size within an area as compared to the
related-art system. This increases interference per unit square
such that the PDCCH designed for preventing inter-cell interface
fails to adequately mitigate interference and is influenced more by
interference from neighbor cells, resulting in a reduction of UE
coverage.
[0054] Furthermore, the eNB adopting a Multi-User Multiple Input
Multiple Output (MU-MIMO) technique for scheduling a greater number
UEs and maximizing the system throughput lacks control channel
capacity while having a sufficiently large data channel, resulting
in a scheduling failure. In order to address this problem, there is
a need to study the transmission of a control channel using a
dedicated reference signal on the legacy data channel. In the case
of transmitting the control channel on the data channel, it is
possible to avoid inter-cell interference and utilize the dedicated
reference signal and, as a consequence, multiple antennas can be
used to transmit the control channel for multiple UEs on the same
resource, resulting in a maximization of the control channel
capacity. This new control channel is referred to as an enhanced
PDCCH (ePDCCH) and may, for example, be found in control channel
region 111 in FIG. 1.
[0055] FIG. 2 is a diagram illustrating a control channel structure
of an LTE-A system according to an exemplary embodiment of the
present invention. The control channel of LTE-A includes a PDCCH
transmitted with CRS 209 and an ePDCCH transmitted at locations in
the data region 207. Since the ePDCCH 213 is mapped to the
resources of the data region, it can be transmitted with DRS. The
ePDCCH 213 is also capable of being transmitted with CRS 209, a UE
group reference signal, or a sub-band reference signal. The UE
group reference signal denotes the common control channel shared by
a set of UEs. The sub-band reference signal is a common reference
signal but is smaller in the frequency or time domain than the CRS
209. The sub-band reference signal is carried in some RBs or
subframes 205.
[0056] The PDCCH is capable of being transmitted in the single
antenna transmission mode and/or the TD transmission mode. The
ePDCCH can be transmitted with various reference signals in at
least one of the beamforming transmission mode, the single antenna
transmission mode, and the TD transmission mode. The PDCCH is
mapped to the regions 211 distributed across the PRBs 203
constituting the entire downlink bandwidth 201. The eNB is capable
of restricting some resources to the frequency-selective region and
some resources to the frequency diversity-guaranteed region such
that the ePDCCH is transmitted in the region 213. The eNB is
capable of changing the ePDCCH transmission mode according to the
UE status, and the PDCCH reception probability also influences the
reception of the ePDCCH.
[0057] The PDCCH can be classified into one of a common control
channel and a dedicated control channel. The common control channel
region is of a control channel to which all UEs attempt control
channel demodulation. The dedicated control channel region is of
the control channel to which a specific UE attempts control channel
demodulation. In the LTE system, the control channel has no fixed
code rate but its amount of information is determined according to
the aggregation level. The common control channel is limited to
aggregation levels 4 and 8, while the dedicated control channel is
limited to aggregation levels 1, 2, 4, and 8. The unit of
aggregation is CCE. The aggregation level 4 allows for the use of
up to 4 regions, while the aggregation 8 allows for the use of up
to 2 regions. Accordingly, the eNB is capable of transmitting the
common control channel at up to 6 regions. The number of
demodulations for the UE-specific control channel is also
determined according to the aggregation level. There can be up to 6
types for aggregation levels 1 and 2 and up to 2 types for
aggregation levels 4 and 8. The CCEs on which the modulation is
taken are identical with each other or not according to the
aggregation level. Table 1 shows the number of PDCCH candidates
according to the aggregation level and control channel type.
TABLE-US-00001 TABLE 1 Search space S.sub.k.sup.(L) # of PDCCH
Aggregation Size candidates Type level L [in CCEs] M.sup.(L) UE- 1
6 6 specific 2 12 6 4 8 2 8 16 2 Common 4 16 4 8 16 2
[0058] The control channel transmitted in the logical resource
region between the eNB and the UE is determined according to
Equation (1):
L{(Y.sub.k+m)mod .left brkt-bot.N.sub.CCE,k/L.right
brkt-bot.}+i,
m=0, . . . ,M.sup.(L)-1,i=0, . . . ,L-1 (1)
where L denotes aggregation level, and N.sub.cce,k denotes a total
number of CCEs existing in the k.sup.th subframe. With Equation
(1), the UE is capable of acquiring CCE index for blink
demodulation of the control channel transmitted by the eNB. Y.sub.k
denotes a random variable for distributing the control channels
over the entire control channel region per user to avoid collision
of control channels and changes at every subframe by Equation (2).
In the case of the common control channel, however, Y.sub.k is set
to 0 such that all UEs can receive. Y.sub.k starts with UE ID; and
A and D are 39826 and 65537 respectively.
Y.sub.k=(AY.sub.k-1)mod D (2)
[0059] FIG. 3 is a diagram illustrating a control channel-resource
mapping mechanism according to an exemplary embodiment of the
present invention. The common control channel 301 and UE-specific
control channel 303 are interleaved by the interleaver 305. The
interleaved signal is distributed across the entire bandwidth 307
in the unit of a REG The UE, using CRS port #0.about.#309 maps the
control channel resources into logical resources 310. The common
control channel 313 is located at the beginning of the logical
resource region 311 and is actually transmitted in the UE-specific
transmission region among the candidates of the resource region.
The UE-specific control channels 315 and 317 are transmitted in the
UE-specific transmission regions of the same logical resource
region. The UEs use different, overlapped, or the same logical
region at every subframe. This is to avoid repeated collisions of
the control channel regions of the UEs.
[0060] In the case of the PDCCH, since the UEs receive the control
channels with a common reference signal, all control channels are
transmitted in the region 315 or 317 in the same transmission mode
and with same reference signals. In the case of ePDCCH, however,
the control channels can be transmitted in different transmission
modes and with different resources, there is a need for configuring
respective transmission modes and determining respective search
spaces. A search space configuration method is proposed
hereinafter.
[0061] FIG. 4 is a diagram illustrating a mechanism of a control
channel transmission according to a first exemplary embodiment of
the present invention. According to the first exemplary embodiment
of the present invention, the eNB sorts the control channels mapped
to a control channel resource into sets by control channel format
or type and transmits the sets of different formats or types with
different reference signals or different reference signals ports.
The terminal receives the control channels of the sets of different
formats or types in the search regions for the different reference
signals or reference signal ports.
[0062] The control channel groups 401 and 411 sorted by control
channel format or control channel property are depicted. The eNB is
capable of sorting the control channels into groups by format. For
example, the eNB is capable of sorting the control channels into
3/3A, 1A, 1C, and other format groups. The eNB is also capable of
sorting the control channels into a group of control channels for
multiple UEs and a group of control channels for a single UE. The
control channels also can be sorted into a group of control
channels transmitted with a UE's unique Radio Network Temporary
Identifier (RNTI) and a group of control channels transmitted with
the RNTI for system information, paging, initial access, and power
control. The eNB may notify the UE of the identifiers of the
control channel groups through higher layer signaling. According to
a modified exemplary embodiment, the control channel group
identifiers can be stored in the memories of the UE and the eNB
according to a predetermined rule.
[0063] The control channel groups are encoded by the respective
encoders 403 and 413. The eNB arranges the control channels in a
resource group 405 signaled by the eNB. The eNB notifies the UE of
the information on the reference signals used in the respective
control channel groups. For example, the reference signal
information 407 is used for transmitting the control channel group
401, and the reference signal information 417 is used for
transmitting the control channel group 411. The control channel
groups can be transmitted via respective antennas 409 and 421 in
different transmission modes. Depending on the properties of the
control channel groups, one control channel group can transmitted
in a TD mode, while the other control channel group in a
beamforming mode. Here, the control channel groups 401 and 411, the
resource group 405, and the reference signal information 407 and
417, is collectively denoted as 410.
[0064] For another example, one control channel group can be
transmitted via antenna 409 as precoded by the precoder 408, while
the other control channel group can be transmitted via antenna 421
as precoded by the precoder 419. Although both the control channel
groups are processed in the same transmission mode, they may be
transmitted with different precodings. It is also possible for a
control channel group to be allocated one reference signal or
multiple reference signals. In the TD transmission mode, if two or
more reference signal groups are allocated to the control channel
group and beamforming is used, one or two reference signal groups
are allocated for the control channel group. The reference signal
information 407 and 417 can be notified through higher layer
signaling and, according to a modified exemplary embodiment, the UE
is capable of performing blind demodulation on the reference signal
information 407 and 417. In the blind demodulation, the terminal
attempts demodulation with the assumption of all available
combinations of the transmission modes and reference signals until
the control channel is received successfully.
[0065] The UE receives the control channel resource region
information transmitted by the eNB through higher layer signaling
and reconfigures the control channels into logical control channel
region 423. The terminal configures two search spaces based on the
information of the two control channel groups and the reference
signals for use in receiving the control channel groups. The first
search space is the search space 425 for the first control channel
group in which the UE searches for the control signal using the
reference signal group 407. The second search space is for second
control channel group in which the UE searches for the control
signal using the second reference signal group 417.
[0066] If the first control channel group is of controls channels
for multiple UEs, the UEs receive the control channels using the
same reference signal. The UEs receive the control channels 411
using different reference signals in the different control channel
search spaces 431, 427, and 429. In the case where the same
resource is allocated to the UEs as denoted by reference number 431
and 427, the control channels can be transmitted with different
reference signals. In the case where the different resources are
allocated to the UEs as denoted by reference number 431 and 429,
the control channel can be transmitted with the same reference
signal. In this way, the eNB is capable of transmitting the control
channels in different transmission modes according to the UE status
and type of the control channels. If the number of UEs which has to
receive the current control channel decreases to 1, the eNB is
capable of changing the transmission mode dynamically for the UE to
receive the control channel efficiently.
[0067] A description is made of the search space of the UE
according to the first exemplary embodiment with reference to
Equations (1) and (2). The UE is capable of acquiring a CCE index
for blind demodulation of the control channel transmitted by the
eNB using Equation (3). Y.sub.k denotes a random variable for
distributing the control channels regularly across the entire
control channel region by user in order to avoid collision. Y.sub.k
varies at every subframe according to Equation (2). The search
space for the first control channel group can be expressed as
Equation (3):
L{(Y.sub.k+m)mod .left brkt-bot.N.sub.CCE,k/L.right
brkt-bot.}+i,
m=0, . . . ,M.sup.(L)-1,i=0, . . . ,L-1
for common control channel with antenna port set #1
and Y.sub.k=(AY.sub.k-1)mod D (3)
where Y.sub.k denotes a common UE IDentifier (ID); and A and D are
39827 and 65537, respectively.
[0068] The search space for the second control channel group can be
expressed as Equation (4):
L{(Y.sub.k+m)mod .left brkt-bot.N.sub.CCE,k/L.right
brkt-bot.}+i,
m=0, . . . ,M.sup.(L)-1,i=0, . . . ,L-1
for UE specific control channel with antenna port set #2
and Y.sub.k=(AY.sub.k-1)mod D (4)
where Y.sub.k starts with the dedicated UE identifier (ID); and A
and D are 39827 and 65537, respectively.
[0069] According to Equations (3) and (4), the search spaces are
determined with different values of Y.sub.k. The first group is
determined with the UE group identifier, and the second group is
determined with a unique UE identifier. That is, the control
channel region for multiple UEs configured at the same location but
varies continuously at every subframe. The UE-specific control
channels for the respective UEs are transmitted at random
positions. In this way, it is possible to avoid repeated
collisions.
[0070] FIG. 5 is a diagram illustrating a mechanism of control
channel detection according to a second exemplary embodiment of the
present invention. Referring to FIG. 5, the eNB according to the
second exemplary embodiment of the present invention configures
different control channel transmission resources and maps the
logical control channel resources thereto respectively using the
same search space. The eNB transmits the control channels mapped to
the resources using different reference signals or different
reference signal ports. The terminal receives the control channels
mapped to the different control channel regions in the same search
space using the different reference signals or different reference
signal ports.
[0071] The second exemplary embodiment of the present invention can
be applied to the UE which is capable of receiving both the legacy
control channel and the newly introduced control channel. The
legacy control channel 501 transmitted in the control channel
region and the new control channel 509 transmitted in the new
control channel region are depicted in the FIG. 5. The control
channels 501 and 509 are coded by the respective encoders 503 and
511. The control channel 501 is transmitted via antenna 507 using
the reference signal or reference signal group 505 that has been
indicated to the UE. Here, the control channel 501 may be
transmitted with CRS generated by a CRS generator. The eNB
transmits the control channel 509 in the new control channel region
513 notified to the UE in advance through higher layer signaling.
The eNB transmits the control channel 509 via antenna 521 using the
reference signal or reference signal group 515 that has been
indicated to the UE. Herein, the new control channel region 513 and
the reference signal or reference signal group 515 are collectively
denoted as 517. In another example, the eNB transmits the control
channel 509 via antenna 521 as precoded by the precoder 419.
[0072] Such a control channel structure is designed to transmit the
control channel in the legacy control channel region and the new
control channel region dynamically. The eNB is capable of
transmitting the control channels in the legacy control channel
region in the case where the channel condition of the UE is bad or
in the new control channel region in the case where the channel
condition is good. This method is advantageous in that the eNB is
capable of changing the transmission region of the control channel
without extra signaling. Also, this method is advantageous in that
the UE is capable of receiving the control channel by applying the
same search space to different resources without additional search
space configuration. That is, the method of the second exemplary
embodiment allows the UE to receive the control channels mapped to
the different resources in the same search space with different
reference signals.
[0073] If the eNB transmits the control channels, the UE configures
the logical control channel resource 523. The common control
channel is received in the common control region 525. Each UE
determines UE-specific control channel regions 529, 527, and 531
using Equation (1) for search space determination. Afterward, the
UE maps the control channel region 533 for PDCCH transmission to
the logical control channel region 535 to receive the common
control channel and UE-specific control channel with CRS. At the
same time, the UE maps the resource region 537 for ePDCCH
transmission to the logical control channel region to receive the
ePDCCH in the UE-specific control channel region 539. The UE
receives the ePDCCH using the pre-notified reference signal group
515. In the case of ePDCCH, the resource 533 to which it is
actually mapped may have a different resource value. In contrast,
the resource 533 to which the PDCCH is mapped has the same resource
value. The control channel search space for the first control
channel group can be expressed by Equation (5):
L{(Y.sub.k+m)mod .left brkt-bot.N.sub.CCE,k(PDCCH)/L.right
brkt-bot.}+i,
m=0, . . . , M.sub.PDCCH.sup.(L)-1,i=0, . . . ,L-1
for dedicated control with CRS
and Y.sub.k=(AY.sub.k-1)mod D (5)
where Y.sub.k starts with the common UE identifier; and A and D are
39827 and 65537, respectively.
[0074] The search space for the second control channel group can be
expressed by Equation (6):
L{(Y.sub.k+m)mod .left brkt-bot.N.sub.CCE,k(ePDCCH)/L.right
brkt-bot.}+i,
m=0, . . . ,M.sub.ePDCCH.sup.(L)-1,i=0, . . . ,L-1
for dedicated control with configured
DRS antenna port and Y.sub.k=(AY.sub.k-1)mod D (6)
where Y.sub.k starts with the common UE identifier; and A and D are
39827 and 65537, respectively. M.sub.PDCCH.sup.(L) and
M.sub.ePDCCH.sup.(L) denote the numbers of PDCCH and ePDCCH search
times, respectively. These parameters can be informed through
higher layer signaling. According to a modified exemplary
embodiment, the numbers of search times for the PDCCH and the
ePDCCH can be stored in the memories of the UE and the eNB in
advance.
[0075] FIG. 6 is a diagram illustrating a mechanism of a control
channel detection according to a third exemplary embodiment of the
present invention. The eNB according to the third exemplary
embodiment of the present invention configures a plurality of
control channel transmission resources and notifies the UE of
reference signals or reference signal groups for use in association
with the respective resources. The UE configures the plural control
channel transmission regions into the search spaces based on the
reference signals or reference signal groups informed by the eNB.
The UE receives the control channels based on the reference signals
or the reference signal groups mapped to the resources.
[0076] The control channels can be sorted into two groups 601 and
613. The two control channel groups 601 and 613 are the groups of
certain control channels and are coded by the respective encoders
603 and 615. The eNB is capable of configuring such that the
control channels are selectively transmitted via antennas 611 and
623 in the two control channel groups using the reference signals
or reference signal groups 607 and 619. The eNB notifies the UE of
the reference signals or reference signal groups 607 and 619 used
in resource regions commonly and independently. The resource region
605 for transmitting one control channel group and the reference
signal therefor and the resource region 617 for transmitting
another control channel group and reference signal therefor are
depicted in the drawing. Here, resource regions 605 and 617, and
reference signals or reference signal groups 607 and 619, are
collectively denoted as 625. In another example, the two control
channel groups 601 and 613 may be transmitted via antennas 611 and
623 as precoded by precoders 609 and 621.
[0077] The two resources 627 and 629 are the resources determined
according to the resource configuration method or transmission
method. For example, one resource can be the resource 639 for
transmitting the interleaved control channels while the other
resource can be the resource 641 for transmitting the
non-interleaved control channels. According to another exemplary
embodiment of the present invention, one resource can be the
control channel region 643 for the distributed transmission mode,
while the other resource can be the control channel region 645 for
the localized transmission mode. The eNB can configure the resource
regions such that the UE is capable of receiving the control
channels efficiently with or without application of the multiple
antenna transmission mode.
[0078] According to the third exemplary embodiment of the present
invention, two resources can be configured into a distributed
transmission resource or an interleaving transmission resource and
a localized transmission resource or a non-interleaving
transmission resource. The two resources can be configured
independently or in an overlapped manner. In the case where the
control channels are transmitted on the two resources, the eNB
performs transmission with different reference signals for the two
resources. The UE is capable of receiving the control channels with
different reference signals for the respective resources. Using the
resources configured with different reference signals, the eNB is
capable of configuring different transmission modes for the
respective resource regions. The eNB is capable of transmitting the
control channels to achieve at least one of frequency diversity
gain and antenna diversity gain according to the channel condition
of the UE. In this manner, the eNB is capable of supporting both
the resource configuration and multi-antenna transmission mode
simultaneously and switching among the transmission resources and
among the transmission modes dynamically.
[0079] Typically, the distributed transmission region or the
interleaving transmission region can be used for transmitting the
common control channel 631 or the UE-specific control channel 633
for the UE operating in a TD transmission mode. In contrast, the
localized transmission region or the non-interleaving transmission
region can be used for transmitting the dedicated reference signals
635 and 637 in the beamforming mode. However, the transmission
method can be changed depending on the number of UEs, eNB status,
and UE status. The search space for the first control channel group
can be expressed by Equation (7):
L{(Y.sub.k+m)mod .left brkt-bot.N.sub.CCE,k(Localized)/L.right
brkt-bot.}+i,
m=0, . . . ,M.sub.Localized.sup.(L)-1,i=0, . . . ,L-1
with DRS port set 1
and Y.sub.k=(AY.sub.k-1)mod D (7)
where Y.sub.k starts with the dedicated UE ID; and A and D are
39827 and 65537, respectively.
[0080] The search space for the second control channel group can be
expressed by Equation (8):
L{(Y.sub.k+m)mod .left brkt-bot.N.sub.CCE,k(distributed)/L.right
brkt-bot.}+i,
m=0, . . . ,M.sub.distributed.sup.(L)-1,i=0, . . . ,L-1
with DRS port set 2
and Y.sub.k=(AY.sub.k-1)mod D (8)
[0081] FIG. 7 is a flowchart illustrating a control channel
transmission method of the eNB according to an exemplary embodiment
of the present invention.
[0082] Referring to FIG. 7, the eNB transmits the configuration
information of ePDCCH through higher layer signaling at step 701.
This information includes at least one resource information and at
least one reference signal information for ePDCCH transmission as
proposed in the present disclosure. The eNB configures the control
channels of PDCCH and ePDCCH at step 703. Next, the eNB configures
the search spaces as the control channel transmission regions for
the control channel groups transmitted with multiple antenna port
sets and arranges the control channels in the search regions so as
to avoid collision between UE-specific control channels at step
705. The eNB transmits the control channels with the respective
reference signals in order for the UEs to receive the control
channels addressed thereto at step 707.
[0083] FIG. 8 is a flowchart illustrating a control channel
reception method of a UE according to an exemplary embodiment of
present invention. Referring to FIG. 8, the UE receives the
information about ePDCCH through higher layer signals at step 801.
This information may include the control channel region information
and at least one reference signal information for receiving on the
respective resources. The UE estimates the channels based on the
reference signals and receives the information on the control
channel region in the data region based on the respective reference
signals at steps 809 and 803. The UE configures the search spaces
in the data region determined with the reference signal at steps
811 and 805. The UE demodulates the control channel of one control
channel resource region at step 811 and another control channel
resource region at step 805. The UE receives the control channel
information using the demodulated control channel at step 807.
[0084] FIG. 9 is a block diagram illustrating a configuration of a
control channel transmission apparatus of an eNB according to an
exemplary embodiment of the present invention.
[0085] Referring to FIG. 9, the scheduler 917 controls the PDCCH
generator 905 and the ePDCCH generator 907 to configure the control
channels based on the control channel information 901. The precoder
919 performs precoding on the ePDCCH, PDSCH 909, DRS 911, and CRS
913 according to the transmission mode. The resource mapper 921
maps the control channels to the reference signals using the
precoded signal. The Frequency Domain (FD) multiplexer 923
multiplexes the data channel and ePDCCH according to the scheduling
information of the scheduler 917. The resource mapper 915 maps the
PDCCH and CRS 903 to the resource. The Time Domain (TD) multiplexer
925 multiplexes the multiplexed ePDCCH and PDSCH signal with
multiplexed PDCCH signal in the time domain. The transmitter 927
transmits the time domain-multiplexed signal to the UE.
[0086] FIG. 10 is a block diagram illustrating a control signal
reception apparatus of a UE according to an exemplary embodiment of
the present invention.
[0087] Referring to FIG. 10, the receiver 1001 receives a signal.
The TD demultiplexer 1003 demultiplexes the received signal into
PDCCH transmission region and PDSCH transmission region. The
channel estimator 1007 estimates channels using the CRS 1005 in the
PDCCH transmission region. The PDCCH receiver 1009 receives PDCCH,
and the control channel detector 1011 detects the received PDCCH.
The FD demultiplexer 1021 demultiplexes the PDCCH region. The
resource de-mapper 1023 delivers the PDSCH to the PDSCH receiver
1015, the ePDCCH to the ePDCCH receiver 1013, and CRS 1025 and DRS
1017 to the channel estimator 1027. The channel estimator 1027
estimates channels. The PDSCH decoder 1019 and the control channel
detector 1011 receive the control channel using the estimated
control channel information.
[0088] According to an exemplary embodiment of the present
invention, the eNB is capable of transmitting to the UE the control
channels using multiple different reference signals with various
transmission modes in order to achieve frequency selective gain or
frequency diversity gain depending on the channel conditions
experienced by the UE. The UE is capable of configuring the search
spaces for receiving the control channels according to the type of
reference signal and/or allocated resource and receiving the
control channels based on the channel estimation information. The
UE is capable of receiving the control channels transmitted in
various transmission modes simultaneously without extra signaling.
The eNB is capable of transmitting the control channels with
different reference signals or in different transmission modes
according to the types of the control channels.
[0089] As described above, the control channel detection method and
apparatus of the exemplary embodiments of the present invention are
advantageous to transmit/receive control channels efficiently with
different reference signals or in different transmission modes.
[0090] It will be understood that each block of the flowchart
illustrations and/or block diagrams, and combinations of blocks in
the flowchart illustrations and/or block diagrams, can be
implemented by computer program instructions. These computer
program instructions may be provided to a processor of a general
purpose computer, special purpose computer, or other programmable
data processing apparatus to produce a machine, such that the
instructions, which execute via the processor of the computer or
other programmable data processing apparatus, create means for
implementing the functions/acts specified in the flowchart and/or
block diagram block or blocks. These computer program instructions
may also be stored in a non-transitory computer-readable memory
that can direct a computer or other programmable data processing
apparatus to function in a particular manner, such that the
instructions stored in the computer-readable memory produce an
article of manufacture including instruction means which implement
the function/act specified in the flowchart and/or block diagram
block or blocks. The computer program instructions may also be
loaded onto a computer or other programmable data processing
apparatus to cause a series of operational steps to be performed on
the computer or other programmable apparatus to produce a computer
implemented process such that the instructions which execute on the
computer or other programmable apparatus provide steps for
implementing the functions/acts specified in the flowchart and/or
block diagram block or blocks.
[0091] Furthermore, the respective block diagrams may illustrate
parts of modules, segments or codes including at least one or more
executable instructions for performing specific logic function(s).
Moreover, it should be noted that the functions of the blocks may
be performed in a different order in several modifications. For
example, two successive blocks may be performed substantially at
the same time, or may be performed in reverse order according to
their functions.
[0092] The term "module" according to the exemplary embodiments of
the present invention, means, but is not limited to, a software or
hardware component, such as a Field Programmable Gate Array (FPGA)
or Application Specific Integrated Circuit (ASIC), which performs
certain tasks. A module may advantageously be configured to reside
on the addressable storage medium and configured to be executed on
one or more processors. Thus, a module may include, by way of
example, components, such as software components, object-oriented
software components, class components and task components,
processes, functions, attributes, procedures, subroutines, segments
of program code, drivers, firmware, microcode, circuitry, data,
databases, data structures, tables, arrays, and variables. The
functionality provided for in the components and modules may be
combined into fewer components and modules or further separated
into additional components and modules. In addition, the components
and modules may be implemented such that they execute one or more
CPUs in a device or a secure multimedia card.
[0093] The foregoing disclosure has been set forth merely to
illustrate the exemplary embodiments of the present invention and
is not intended to be limiting. Since modifications of the
disclosed embodiments incorporating the spirit and substance of the
invention may occur to persons skilled in the art, the invention
should be construed to include everything within the scope of the
appended claims and equivalents thereof.
[0094] Although exemplary embodiments of the present invention have
been described in detail hereinabove with specific terminology,
this is for the purpose of describing particular embodiments only
and not intended to be limiting of the invention. While particular
embodiments of the present invention have been illustrated and
described, it would be obvious to those skilled in the art that
various other changes and modifications can be made without
departing from the spirit and scope of the invention.
* * * * *