U.S. patent application number 14/640680 was filed with the patent office on 2015-09-10 for method for extracting iterference signal information and apparatus for the same.
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 Sung-Yoon Cho, Dong-Hyun Kim, Jong-Han Lim, Seong-Wook SONG.
Application Number | 20150256292 14/640680 |
Document ID | / |
Family ID | 53786146 |
Filed Date | 2015-09-10 |
United States Patent
Application |
20150256292 |
Kind Code |
A1 |
SONG; Seong-Wook ; et
al. |
September 10, 2015 |
METHOD FOR EXTRACTING ITERFERENCE SIGNAL INFORMATION AND APPARATUS
FOR THE SAME
Abstract
A method and apparatus are provided for extracting interference
signal information. The method includes demodulating control
channel signals received from serving and adjacent cells; decoding
the control channel signals received from the serving cell to
extract control information; decoding the control channel signals
received from the adjacent cell; extracting, at each subframe, from
the decoded control channel signals received from the adjacent
cell, a terminal ID of the adjacent cell; accumulating the
extracted terminal IDs; filtering only a control channel signal
from among the control channel signals received from the adjacent
cell corresponding to a terminal ID having an accumulation count
that is greater than or equal to a threshold; determining a
reliability value of the filtered control channel signal;
identifying the filtered control channel signal as a first
interference signal, based on the reliability value; and extracting
interference signal information based on the first interference
signal.
Inventors: |
SONG; Seong-Wook; (Seoul,
KR) ; Kim; Dong-Hyun; (Seoul, KR) ; Cho;
Sung-Yoon; (Seoul, KR) ; Lim; Jong-Han;
(Seoul, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Samsung Electronics Co., Ltd. |
Gyeonggi-do |
|
KR |
|
|
Assignee: |
Samsung Electronics Co.,
Ltd.
|
Family ID: |
53786146 |
Appl. No.: |
14/640680 |
Filed: |
March 6, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61948873 |
Mar 6, 2014 |
|
|
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Current U.S.
Class: |
375/350 |
Current CPC
Class: |
H04L 1/0072 20130101;
H04B 7/0452 20130101; H04L 1/0061 20130101; H04L 1/0048
20130101 |
International
Class: |
H04L 1/00 20060101
H04L001/00; H04B 15/00 20060101 H04B015/00; H04B 7/04 20060101
H04B007/04 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 1, 2014 |
KR |
10-2014-0132612 |
Claims
1. A method for extracting interference signal information by a
terminal in a communication system, the method comprising:
demodulating control channel signals received from a serving cell
and an adjacent cell; decoding the control channel signals received
from the serving cell to extract control information; decoding the
control channel signals received from the adjacent cell;
extracting, at each subframe, from the decoded control channel
signals received from the adjacent cell, a terminal Identifier (ID)
of the adjacent cell; accumulating the extracted terminal IDs;
filtering only a control channel signal from among the control
channel signals received from the adjacent cell corresponding to a
terminal ID having an accumulation count that is greater than or
equal to a threshold, from among the accumulated extracted terminal
IDs; determining a reliability value of the filtered control
channel signal; identifying the filtered control channel signal as
a first interference signal, if the reliability value is greater
than or equal to a first predetermined value; and extracting
interference signal information based on the first interference
signal.
2. The method of claim 1, wherein extracting the terminal ID
comprises: extracting information bits and tail bits from the
decoded control channel signals received from the adjacent cell;
calculating a Cyclic Redundancy Check (CRC) from the information
bits; and extracting the terminal ID by performing an Exclusive OR
(XOR) operation on the calculated CRC and the tail bits.
3. The method of claim 1, further comprising: if the terminal
operates in a Multiuser Multiple Input Multiple Output (MU-MIMO)
transmission mode, extracting interference signal information from
a set of control channel signals having a same Downlink Control
Information (DCI) format as a DCI format of control information
extracted from the control channel signals of the serving cell.
4. The method of claim 3, wherein extracting the interference
signal information from the control channel signal of the serving
cell comprises: filtering a control channel signal having the same
DCI format as the DCI format of the extracted control information,
among the control channel signals of the serving cell; decoding the
filtered control channel signal of the serving cell; determining a
reliability value of the decoded filtered control channel signal of
the serving cell; identifying the decoded filtered control channel
signal as a second interference signal, if the reliability value is
greater than or equal to a second predetermined value; and
extracting the interference signal information based on the second
interference signal.
5. The method of claim 4, wherein identifying the decoded filtered
control channel signal as a second interference signal comprises:
extracting and distinguishing information bits and tail bits;
calculating a CRC from the information bits, and extracting the
terminal ID by performing an XOR operation on the calculated CRC
and the tail bits; extracting and accumulating the terminal ID
during the predetermined subframe; and filtering only a control
channel signal corresponding to a terminal ID, an accumulation
count of which is greater than or equal to a threshold, in a set of
the accumulated terminal IDs.
6. An apparatus for extracting interference signal information in a
communication system, the apparatus comprising: a receiver
configured to demodulate control channel signals received from a
serving cell and control channel signals received from an adjacent
cell; and a control channel decoder configured to: decode the
control channel signals received from the serving cell to extract
control information; decode the control channel signals received
from the adjacent cell; extract, at each subframe, from the decoded
control channel signals received from the adjacent cell, a terminal
Identifier (ID) of the adjacent cell; accumulate the extracted
terminal IDs; filter only a control channel signal from among the
control channel signals received from the adjacent cell
corresponding to a terminal ID having an accumulation count that is
greater than or equal to a threshold, from among the accumulated
extracted terminal IDs; determine a reliability value of the
filtered control channel signal; identify the filtered control
channel signal as a first interference signal, if the reliability
value is greater than or equal to a first predetermined value; and
extract interference signal information based on the first
interference signal.
7. The apparatus of claim 6, wherein the control channel decoder
comprises: an adjacent cell control channel decoding unit
configured to decode the control channel signals received from the
adjacent cell to extract information bits and tail bits; and a
terminal ID filtering unit configured to: calculate a Cyclic
Redundancy Check (CRC) from the information bits; extract the
terminal ID by performing an Exclusive OR (XOR) operation on the
calculated CRC and the tail bits; extract and accumulate the
terminal ID during the predetermined subframe; and filter only the
control channel signal corresponding to the terminal ID having the
accumulation count of that is greater than or equal to the
threshold.
8. The apparatus of claim 6, wherein if the terminal operates in a
Multiuser Multiple Input Multiple Output (MU-MIMO) transmission
mode, the control channel decoder is further configured to extract
interference signal information from a control channel signal
having a same Downlink Control Information (DCI) format as a DCI
format of control information extracted from the control channel
signals of the serving cell.
9. The apparatus of claim 8, wherein the control channel decoder
comprises: a DCI format filtering unit configured to filter the
control channel signal having the same DCI format as the DCI format
of the extracted control information, among the control channel
signals of the serving cell; a serving cell control channel
decoding unit configured to decode the filtered control channel
signal of the serving cell; and an interference control channel
determining unit configured to: determine a reliability value of
the decoded filtered control channel signal of the serving cell;
identify the decoded filtered control channel signal as a second
interference signal, if the reliability value is greater than or
equal to a second predetermined value; and extract the interference
signal information based on the second interference signal.
10. The apparatus of claim 9, wherein the serving cell control
channel decoding unit extracts information bits and tail bits; and
wherein the control channel decoder further includes a terminal ID
filtering unit configured to: calculate a CRC from the information
bits, and extract the terminal ID by performing an XOR operation on
the calculated CRC and the tail bits; extract and accumulate the
terminal ID during the predetermined subframe; and filter only a
control channel signal corresponding to a terminal ID, an
accumulation count of which is greater than or equal to a
threshold, among the accumulated terminal IDs.
Description
PRIORITY
[0001] This application claims priority under 35 U.S.C.
.sctn.119(a) to U.S. Provisional Patent Application Ser. No.
61/948,873, which was filed on Mar. 6, 2014, and Korean Patent
Application No. 10-2014-0132612, which was filed on Oct. 1, 2014,
the content of each of which is hereby incorporated.
BACKGROUND
[0002] 1. Field of the Disclosure
[0003] The present disclosure relates generally to a method and
apparatus for extracting interference signal information without
additional signaling from a network in a communication system.
[0004] 2. Description of Related Art
[0005] Generally, in a cellular-based communication system, a
terminal (e.g., a User Equipment (UE), a Mobile Station (MS), etc.)
may suffer from interference caused by a signal from another
terminal that uses the same resources in the same cell, and/or from
another terminal in an adjacent cell. In this case, the terminal
may detect or remove the interference signal from the signal that
the terminal should receive, using an interference detection
technique such as joint detection, thereby improving its signal
reception performance.
[0006] However, if the terminal demodulates and decodes only the
target signal without information about the interference signal,
performance degradation caused by the interference signal may
increase, and this phenomenon may be more severe at the terminal in
the boundary of the cell. To combat this, the terminal may obtain
control channel information for the interference signal, and use it
for demodulation and decoding. In this case, however, the terminal
should separately receive information about the interference signal
from a base station (e.g., an evolved Node B (eNB), etc.) or should
perform blind detection. Using blind detection, the terminal may
reduce false alarms or misdetection probability with filtering
techniques, but it is difficult to make correct filtering
determinations, thereby limiting performance improvement of the
interference cancellation function.
[0007] Generally, when terminals attach to or connect to a base
station, the base station allocates a unique ID to each of the
terminals (hereinafter, referred to as a UE-ID). However, each
terminal may not know a UE-ID of another terminal since the
terminal receives only its own UE-ID through upper-level signaling.
In the 3GPP LTE system, the UE-ID is called an RNTI.
[0008] FIG. 1 illustrates an application of a UE-ID to a control
channel in a conventional LTE system.
[0009] Referring to FIG. 1, a base station generates DCI, and then
attaches a 16-bit Cyclic Redundancy Check (CRC) to the DCI, for
error detection at a terminal. That is, to distinguish a DCI of
each terminal, the base station may mask a 16-bit CRC with a UE-ID
through an Exclusive OR (XOR) operation, and then transmit the
masking results over a control channel (e.g., a Physical Downlink
Control Channel (PDCCH)).
[0010] A terminal may receive a control channel in every subframe,
and then find its own DCI through a blind decoding process in which
a terminal attempts decoding for all wireless resource units that
are available for each terminal in a control channel. For the
decoded control channel signals, the terminal determines whether a
DCI in the decoded control channel signals is its own DCI, using
its unique UE-ID.
[0011] FIG. 2 illustrates a conventional method of a terminal
receiving a control channel signal.
[0012] Referring to FIG. 2, the terminal decodes a received DCI,
and then generates a CRC with information bits, excluding 16 tail
bits corresponding to a CRC. If the decoded DCI matches a DCI of
the terminal, a UE-ID of the terminal may be derived when the XOR
operation is performed on the decoded tail bits and the CRC
generated by the terminal.
[0013] Therefore, if the UE-ID derived through the XOR operation
matches the UE-ID of the terminal (i.e., Success), the terminal may
demodulate and decode received data using the DCI information,
determining that the decoded DCI is its own DCI. However, if the
UE-ID derived through the XOR operation is different from the UE-ID
of the terminal (i.e., Fail), the terminal may discard the DCI,
determining that the decoded DCI is a DCI of another terminal.
[0014] FIG. 3 is a flowchart illustrating a conventional control
channel decoding process in a terminal.
[0015] Referring to FIG. 3, a terminal receives and demodulates a
control channel in step 301. In step 303, the terminal decodes the
demodulated control channel. In step 305, the terminal calculates a
CRC using information bits of the decoded control channel. In step
307, the terminal determines whether a value determined, i.e., a
determined UE-ID, by performing the XOR operation on the decoded
tail bits and the calculated CRC matches its own UE-ID previously
received from the base station. If the determined value is the same
as the terminal's own UE-ID, the terminal demodulates and decodes
information of a data channel using the DCI, determining that the
decoded data is its own DCI, in step 311. However, if it is
determined in step 307 that the determined value is not the same as
its own UE-ID, the terminal discards data of the decoded control
channel, determining that the decoded data is a DCI for another
terminal, in step 309.
[0016] After obtaining DCI information, the terminal may receive
downlink data from a base station in a cell to which the terminal
belongs. However, if there is a terminal that uses the same
frequency-time resources in the same cell as that of the terminal,
or if a base station of another cell is transmitting data to
another terminal using the same frequency-time resources, the
terminal may experience performance degradation due to the
interference problems, when receiving data. Although various
methods have been proposed to solve the interference problems in a
terminal, the actual performance improvement is limited if the
terminal does not have information as to whether a signal is an
interference signal.
[0017] For example, if a terminal has correct information about an
interference signal, the terminal may improve the reception
performance using a method of joint-detecting the signal the
terminal should receive, and the interference signal. However,
because a terminal generally does not know information about UE-IDs
of other terminals, the terminal may not extract a DCI of another
terminal, in which information about the interference signal is
present, so the terminal may not use an improved algorithm such as
joint detection.
[0018] Basically, in order for a terminal to know a UE-ID in an
interference signal, the base station should provide information
about the UE-ID through separate signaling, or the terminal should
directly detect the UE-ID. However, if the base station does
provide this information about the UE-ID in the interference
signal, this will increase the overhead of the control channel.
Accordingly, to address this issue, a blind decoding scheme has
been proposed, in which a terminal attempts decoding for allocation
of all possible control channels, and determines the validity of
the control channel using a soft metric and the like.
[0019] In the existing LTE system, a blind decoding method for
extracting a terminal's own control signal has limited the
complexity by allowing the terminal to attempt to decode only 44
detection locations, by limiting the detection locations using its
own RNTI that the terminal already knows. However, if the blind
decoding scheme used for decoding a control channel of another
terminal is applied, the terminal should perform decoding for all
the detection locations of the full band and the DCI formats
because the terminal does not know the RNTI of the other terminals,
increasing the likelihood of RNTI false alarms.
[0020] Specifically, in the LTE system, DCI information of each
terminal may be transmitted over a PDCCH including a plurality of
Control Channel Elements (CCEs), and the PDCCH may be divided into
four types of Aggregation Levels (ALs) and into a plurality of DCI
formats depending on the number of CCEs allocated to the terminal.
Therefore, if there are a total of, for example, 43 CCEs, there are
a total of 79 PDCCH candidates (including 43 PDCCH candidates for
AL=1, 21 PDCCH candidates for AL=2, 10 PDCCH candidates for AL=4,
and 5 PDCCH candidates for AL=8). If 6 formats exist for each of
the number of DCI cases, 474 candidates may be present in the DCI
information that is finally allocated to one terminal.
[0021] Therefore, a terminal may blind-decode all possible PDCCH
candidates to obtain a UE-ID and control channel information of
another terminal, and may use a soft metric-based filtering or
UE-ID based filtering method to decrease the false alarm
probability of falsely estimating a UE-ID.
[0022] The soft metric-based filtering method may use reliability
information of decoded data. If decoding is performed on all
possible DCIs, information about decoded data may be provided from
a decoder. The decoded data may be re-encoded to define a
difference or correlation between the re-encoded data and input
data as a reliability value, and the reliability values for all
possible DCIs may be calculated in order to determine whether a
PDCCH is valid for the DCIs having a high reliability value. That
is, in a good wireless channel environment, if a DCI has valid
information, a DCI value having a very high reliability value may
be calculated through the decoding and re-encoding process.
However, in the soft metric-based filtering scheme, even though a
soft metric value is large, a false alarm other than a desired
UE-ID value may be generated. In particular, if an AL is low, a
false alarm is likely to occur.
[0023] The UE-ID based filtering method uses CCEs of a PDCCH
determined by a UE-ID of a terminal. In the LTE system, for a PDCCH
having information about each terminal, locations of CCEs may be
determined by the UE-ID (i.e., RNTI) value of the terminal. If
there are 43 available CCEs and AL is 1, 2, 4, or 8, a PDCCH may
start at one of 6, 6, 2, or 2 CCE locations depending on the AL
value, respectively. As a result, it is possible to determine
whether the DCI and RNTI are valid information. For example,
assuming that a CRC is calculated using the results obtained by
decoding a PDCCH that has AL=1 and is located in CCE index=5, and a
UE-ID value determined by performing the XOR operation on the CRC
and the tail bits is represented by X, if CCE indexes which are
possible with X are {7, 8, 9, 10, 11, 12}, the CCE index=5 of the
decoded PDCCH may not be included in a set of CCE indexes possible
with X. Thus, a UE-ID X=5 would be considered invalid, and the
UE-ID and DCI information may be discarded. However, in the UE-ID
based filtering scheme, multiple RNTI candidates still exist, even
after undergoing filtering, so a possibility of the false alarm is
high. For example, assuming that there are four types of ALs (AL=1,
AL=2, AL=4, and AL=8), there are six types of DCI formats, and
there are 43 available CCEs, then the total number of possible
PDCCH candidates is 474. If the UE-ID based filtering is applied
thereto, 96 PDCCH candidates may remain on average. If the soft
metric-based filtering is additionally performed, 16 PDCCH
candidates may remain on average. That is, even though both of the
current two techniques are used, the false alarm possibility of
falsely estimating a UE-ID is high.
SUMMARY
[0024] An aspect of the present disclosure is to address at least
the above-mentioned problems and/or disadvantages and to provide at
least the advantages described below.
[0025] Accordingly, an aspect of the present disclosure is to
provide a method and apparatus for a terminal to directly extract
interference signal information from an interference control
channel by blind detection, without additional signaling from a
base station.
[0026] Another aspect of the present disclosure is to provide a
method and apparatus for increasing accuracy by using traffic
characteristics when directly decoding a control channel of an
interference signal to obtain information about the interference
signal.
[0027] In accordance with an aspect of the present disclosure, a
method is provided for extracting interference signal information
by a terminal in a communication system. The method includes
demodulating control channel signals received from a serving cell
and an adjacent cell; decoding the control channel signals received
from the serving cell to extract control information; decoding the
control channel signals received from the adjacent cell;
extracting, at each subframe, from the decoded control channel
signals received from the adjacent cell, a terminal Identifier (ID)
of the adjacent cell; accumulating the extracted terminal IDs;
filtering only a control channel signal from among the control
channel signals received from the adjacent cell corresponding to a
terminal ID having an accumulation count that is greater than or
equal to a threshold, from among the accumulated extracted terminal
IDs; determining a reliability value of the filtered control
channel signal; identifying the filtered control channel signal as
a first interference signal, if the reliability value is greater
than or equal to a first predetermined value; and extracting
interference signal information based on the first interference
signal.
[0028] In accordance with another aspect of the present disclosure,
an apparatus is provided for extracting interference signal
information in a communication system. The apparatus includes a
receiver configured to demodulate control channel signals received
from a serving cell and control channel signals received from an
adjacent cell; and a control channel decoder configured to: decode
the control channel signals received from the serving cell to
extract control information; decode the control channel signals
received from the adjacent cell; extract, at each subframe, from
the decoded control channel signals received from the adjacent
cell, a terminal Identifier (ID) of the adjacent cell; accumulate
the extracted terminal IDs; filter only a control channel signal
from among the control channel signals received from the adjacent
cell corresponding to a terminal ID having an accumulation count
that is greater than or equal to a threshold, from among the
accumulated extracted terminal IDs; determine a reliability value
of the filtered control channel signal; identify the filtered
control channel signal as a first interference signal, if the
reliability value is greater than or equal to a first predetermined
value; and extract interference signal information based on the
first interference signal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] The above and other aspects, features, and advantages of
certain embodiments of the present disclosure will be more apparent
from the following description taken in conjunction with the
accompanying drawings, in which:
[0030] FIG. 1 illustrates an application of a UE-ID to a control
channel in a conventional LTE system;
[0031] FIG. 2 illustrates a conventional method of a terminal
receiving a control channel signal;
[0032] FIG. 3 is a flowchart illustrating a conventional control
channel decoding process in a terminal;
[0033] FIG. 4 illustrates a system configuration for extracting
interference signal information according to an embodiment of the
present disclosure;
[0034] FIG. 5 illustrates a control channel decoder according to an
embodiment of the present disclosure;
[0035] FIG. 6 illustrates an example of Radio Network Temporary
Identity (RNTI) allocation in a conventional LTE communication
network;
[0036] FIG. 7 illustrates a persistent UE-ID filtering unit
according to an embodiment of the present disclosure;
[0037] FIG. 8 illustrates frequency accumulation for each UE-ID
according to an embodiment of the present disclosure;
[0038] FIG. 9 illustrates an example of Multiuser Multiple Input
Multiple Output (MU-MIMO) Downlink Control Information (DCI) format
filtering according to an embodiment of the present disclosure;
and
[0039] FIG. 10 is a flowchart illustrating a process of determining
an interference signal according to an embodiment of the present
disclosure.
[0040] Throughout the drawings, like reference numerals will be
understood to refer to like parts, components, and structures.
DETAILED DESCRIPTION
[0041] The following description with reference to the accompanying
drawings is provided to assist in a comprehensive understanding of
various embodiments of the disclosure 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 disclosure. In addition, descriptions of well-known
functions and constructions may be omitted for clarity and
conciseness.
[0042] The terms and words used in the following description and
claims are not limited to their dictionary meanings, but, are
merely used to enable a clear and consistent understanding of the
disclosure. Accordingly, it should be apparent to those skilled in
the art that the following description of embodiments of the
present disclosure is provided for illustration purposes only and
not for the purpose of limiting the disclosure as defined by the
appended claims and their equivalents.
[0043] It is to be understood that the singular forms "a," "an,"
and "the" include plural referents unless the context clearly
dictates otherwise. Thus, for example, reference to "a component
surface" includes reference to one or more of such surfaces.
[0044] Although various embodiments of the present disclosure will
be described in detail below with reference to an LTE wireless
access network, the standard of which is established by 3.sup.rd
Generation Partnership Project (3GPP), it will be apparent to those
of ordinary skill in the art that the subject matter of the present
disclosure may be applied to any other communication systems having
the similar technical background with slight modifications, without
departing from the spirit and scope of the present disclosure.
[0045] In accordance with an embodiment of the present disclosure,
a method and apparatus are provided in which, for efficient
processing of an interference signal from a wireless terminal, a
terminal directly extracts interference signal information from an
interference control channel, without additional signaling from a
base station.
[0046] FIG. 4 illustrates a system configuration for extracting
interference signal information according to an embodiment of the
present disclosure.
[0047] Referring to FIG. 4, a terminal 400 receives a data channel
411 and a control channel 412 transmitted from a base station 410
of a serving cell, and receives a data channel 421 and a control
channel 422 transmitted from a base station 420 of an adjacent
cell. The data channel 421 and the control channel 422 transmitted
from the base station 420 of the adjacent cell act as interference
signals. The signals received from the base stations 410 and 420
are provided to a channel estimator 403, a control channel decoder
405, and a data channel demodulator 407 through a Radio Frequency
(RF) receiver 401. The channel estimator 403 estimates wireless
channels and provides the estimation results to the control channel
decoder 405 and the data channel demodulator 407. The control
channel decoder 405 decodes the control channel 412 received from
the base station 410 of the serving cell to obtain a DCI, and
provides the DCI to the data channel demodulator 407. The data
channel demodulator 407 demodulates the data channel 411 using the
channel estimation results of the channel estimator 403 and the DCI
provided from the control channel decoder 405, to obtain the data
from the data channel 411.
[0048] The control channel decoder 405 decodes the control channel
412 received from the base station 410 of the serving cell, and
then determines whether the received control channel 412 is a
control channel signal for the terminal itself, through a CRC
check. If the terminal operates in an MU-MIMO mode, the control
channel decoder 405 performs decoding to find a control channel of
another terminal that uses the same resources in the same serving
cell. The control channel decoder 405 may also perform decoding to
find a control channel of an interference signal transmitted from a
base station of an adjacent cell. The control channel decoder 405
decodes control channels received from the base stations of the
serving cell and the adjacent cell, in order to obtain reliability
information, and then determines the validity of the interference
signal using the obtained reliability information.
[0049] FIG. 5 illustrates a control channel decoder according to an
embodiment of the present disclosure.
[0050] Referring to FIG. 5, the control channel decoder 405
includes a first serving cell control channel decoder 501, a CRC
checker 503, an MU-MIMO DCI format filter 505, a second serving
cell control channel decoder 507, an adjacent cell control channel
decoder 509, an interference control channel determiner 511, and a
persistent UE-ID filter 513.
[0051] The first serving cell control channel decoder 501 decodes
the control channel received from the base station of the serving
cell, and the CRC checker 503 performs a CRC check on the control
channel decoded by the first serving cell control channel decoder
501. The adjacent cell control channel decoder 509 decodes the
control channel received from the base station of the adjacent
cell. The MU-MIMO DCI format filter 505, the second serving cell
control channel decoder 507, the interference control channel
determiner 511, and the persistent UE-ID filter 513 determine the
validity of the interference signal of the decoded control channel
according to an embodiment of the present disclosure.
[0052] According to different embodiments of the present
disclosure, two techniques, 1.) Persistent UE-ID Filtering and 2.)
MU-MIMO DCI Format Filtering, are provided to increase the accuracy
of the validity check for an interference signal.
[0053] Persistent UE-ID Filtering
[0054] Generally, a UE-ID is allocated when a terminal accesses a
base station to perform communication. The allocated UE-ID is often
transmitted through an upper layer, and kept until the
communication is terminated. Therefore, if a terminal persistently
receives data for a predetermined time, the UE-ID may be kept at
the same value. By using these characteristics, it is possible to
accurately estimate the UE-ID. A persistent UE-ID filtering scheme
according to an embodiment of the present disclosure may be used
independently, or may be used together with a soft metric-based
filtering scheme or an existing UE-ID based filtering scheme.
[0055] FIG. 6 illustrates an example of Radio Network Temporary
Identity (RNTI) allocation in a conventional LTE communication
network.
[0056] Referring to FIG. 6, if an RNTI is allocated to a terminal
during the presence of traffic to be transmitted from the base
station to the terminal, the same UE-ID is kept until the traffic
is terminated.
[0057] Therefore, using these characteristics, the persistent UE-ID
filtering unit 513 in the control channel decoder 405 according to
an embodiment of the present disclosure may estimate a UE-ID of the
interference signal.
[0058] FIG. 7 illustrates a persistent UE-ID filtering unit
according to an embodiment of the present disclosure.
[0059] Referring to FIG. 7, the persistent UE-ID filter 513
includes a UE-ID calculator 701, a UE-ID frequency accumulator 703,
and a UE-ID frequency comparator 705.
[0060] The UE-ID calculator 701 calculates a UE-ID by performing an
XOR operation on tail bits obtained from results of decoding
control channel candidates of a serving cell and adjacent cells,
and a CRC calculated from the decoded data.
[0061] The UE-ID frequency accumulator 703 accumulates the
frequency of each UE-ID that is calculated in every subframe, and
the UE-ID frequency comparator 705 compares the accumulated
frequency for each UE-ID with a predetermined threshold, determines
a UE-ID whose accumulated frequency is greater than or equal to the
threshold, as a valid UE-ID, and provides the determination results
to the interference control channel determiner 511. By adjusting
the buffer size of the UE-ID frequency accumulator 703 and the
threshold of the UE-ID frequency comparator 705 to suit the system
environment, for the accuracy of the UE-ID detection, it is
possible to properly adjust the false alarm or detection missing
probability.
[0062] After the demodulation of a control channel, if there is no
error, a UE-ID may be obtained by performing the XOR operation on
the CRC regenerated from the demodulated data and the tail bits.
However, in the common case, an error may occur in the demodulation
process. In this case, the regenerated CRC may be mismatched with
the CRC that is applied to the transmitted signal, so the UE-ID
detected through the XOR operation may have a meaningless random
pattern. However, when there is a terminal that accesses the base
station to perform communication according to an embodiment of the
present disclosure, if a UE-ID is continuously extracted over
several subframes, even though an error occurs in the decoding
process, the number of observations for a fixed UE-ID still higher
than the random pattern that is determined by calculating a UE-ID
only in one subframe.
[0063] FIG. 8 illustrates frequency accumulation for each UE-ID
according to an embodiment of the present disclosure.
[0064] Referring to FIG. 8, the UE-ID calculator 701 calculates a
UE-ID of control channel candidates in every subframe, and the
UE-ID frequency accumulator 703 stores, in its buffer, the
frequency for each UE-ID during the recent several subframes
corresponding to the buffer size. The UE-ID frequency comparator
705 compares the frequency of each UE-ID with a predetermined
threshold, and if the frequency of each UE-ID is greater than the
threshold, the UE-ID frequency comparator 705 provides the UE-ID to
the interference control channel determiner 511, determining that
the UE-ID is valid. Thereafter, the interference control channel
determiner 511 determines whether the control channel is valid as
an interference signal, using the reliability information of the
data decoded from the control channel having the UE-ID.
[0065] MU-MIMO DCI Format Filtering
[0066] If a terminal operates in an MU-MIMO transmission mode, the
number of decoding operations may be significantly reduced by
reducing the number of candidates for the DCI format that the
terminal can use. In the MU-MIMO transmission mode, the terminals
that receive signals using the same time-frequency resources in the
same serving cell may all operate in the same transmission mode,
and the signals that use the same DCI format and are transmitted to
another terminal may operate as interference signals to the
terminal. Therefore, if a terminal knows the DCI format used by its
own PDCCH and operates in the MU-MIMO transmission mode, the
terminal knows that another terminal that uses the same resources
in the same serving cell may also use the same DCI format.
[0067] Table 1 illustrates a relationship between DCI format sizes
and transmission modes used in MU-MIMO in the LTE communication
system.
TABLE-US-00001 TABLE 1 DCI format size [10 MHz] DCI format
Transmission mode 59 2B TM8 61 2C TM9
[0068] If MU-MIMO DCI format filtering according to an embodiment
of the present disclosure is applied, a terminal may perform
decoding on only the control channel candidates having the same DCI
format as its own DCI format, without having to decode the control
channel candidates having other DCI formats, thereby reducing the
number of decoding operations, compared with performing decoding
using multiple DCI formats. For example, if a terminal operates in
a dual-layer transmission mode, the terminal does not need to
perform blind decoding for the DCI format corresponding to a
single-layer transmission mode or a multi-layer transmission
mode.
[0069] Specifically, if the terminal operates in the MU-MIMO
transmission mode, the MU-MIMO DCI format filter 505, as
illustrated in FIG. 5, filters only the serving cell control
channel candidate(s) matching with its own DCI format among the
serving cell control channel candidates, using DCI format
information of the terminal, which is extracted from the CRC
checker 503, and provides the result value to the second serving
cell control channel decoder 507.
[0070] The second serving cell control channel decoder 507 decodes
the filtered serving cell control channel candidate and provides
the decoding results to the interference control channel determiner
511. The interference control channel determiner 511 determines
whether the control channel is valid as an interference signal,
using the reliability information of the filtered and decoded
serving cell control channel.
[0071] FIG. 9 illustrates an example of MU-MIMO DCI format
filtering according to an embodiment of the present disclosure.
[0072] Referring to FIG. 9, control channels transmitted to
terminals in a same serving cell may have a 47-bit DCI format, a
57-bit DCI format, and a 59-bit DCI format. If a terminal knows
that its own DCI format is a 57-bit DCI format, from its UE-ID,
then the terminal may decode only the control channels having the
same DCI format as its own DCI format, without decoding all the
control channels, when performing blind decoding to obtain
interference signal information of another terminal in the same
serving cell, efficiently reducing the number of decoding
operations.
[0073] In addition, the MU-MIMO DCI format filtering may be applied
together with the above-described persistent UE-ID filtering.
[0074] Referring again to FIG. 5, when the terminal operates in the
MU-MIMO transmission mode, if filtering is performed in the MU-MIMO
DCI format filter 505 and decoding on the control channel
candidates of the serving cell is performed in the second serving
cell control channel decoder 507, and then the decoded data is
provided to the persistent UE-ID filter 513, the persistent UE-ID
filter 513 may estimate a UE-ID for the control channel candidates
of the serving cell, which are filtered in the MU-MIMO DCI format,
in accordance with the method described in FIG. 7. The persistent
UE-ID filter 513 then provides the estimation results to the
interference control channel determiner 511. The interference
control channel determiner 511 determines whether the control
channel is valid as an interference signal, using the reliability
information of the data decoded from the control channel candidates
of the serving cell, which have the UE-ID.
[0075] FIG. 10 is a flowchart illustrating a process of determining
an interference signal according to an embodiment of the present
disclosure.
[0076] Although FIG. 10 illustrates a process in which both the DCI
format filtering and the persistent UE-ID filtering, according to
embodiments of the present disclosure, are both applied, the two
filtering methods may be applied separately. However, the DCI
format filtering is used in the MU-MIMO transmission mode.
[0077] Referring to FIG. 10, a terminal receives and demodulates
control channels of a serving cell and an adjacent cell in step
1001, and decodes the control channel of the adjacent cell and the
control channel of the serving cell in steps 1003 and 1005,
respectively.
[0078] In step 1007, the terminal performs a CRC check.
Specifically, the terminal calculates a CRC using information bits
of the decoded serving cell control channel, and determines if a
value obtained by performing the XOR operation on the decoded tail
bits and the calculated CRC is equal to its UE-ID received from the
base station.
[0079] In step 1008, the terminal determines a transmission mode.
If the transmission mode is not the MU-MIMO transmission mode and
if the value obtained by performing the XOR operation on the
decoded tail bits and the calculated CRC is equal to its UE-ID
received from the base station, the terminal extracts the UE-ID and
the DCI format as control information in step 1009.
[0080] If the terminal operations in the MU-MIMO transmission mode,
in step 1011, the terminal filters only the serving cell control
channels having a same DCI format, using the DCI format extracted
in step 1007, and decodes the filtered serving cell control
channels in step 1013.
[0081] In step 1015, the terminal filters the UE-IDs for the
serving cell control channels and for the adjacent cell control
channels using a persistent UE-ID filtering method, e.g., according
to the above-described embodiment of the present disclosure.
[0082] In step 1017, the terminal determines whether the control
channels are valid as an interference signal, using the reliability
information of the data decoded from the serving cell and adjacent
cell control channels having the filtered UE-ID. In step 1019, the
terminal outputs the valid channels as interference signal
information.
[0083] According to the above-described embodiments of the present
disclosure, a terminal may increase the accuracy when obtaining
control channel information about an interference signal, thereby
improving the interference signal cancellation and data reception
performances.
[0084] With the use of the persistent UE-ID filtering method
according to an embodiment of the present disclosure, a terminal
may directly extract interference signal information without the
base station providing information about the interference signal to
the terminal, saving resources of the control channels.
[0085] Further, with the use of the persistent UE-ID filtering
method according to an embodiment of the present disclosure, even
though a base station in a single cell transmits data to multiple
terminals at the same time using MU-MIMO, a terminal may extract
interference signal information as in the case of inter-cell
interference, efficiently processing the interference between
signals of the terminal. By applying the MU-MIMO DCI format
filtering technique according to an embodiment of the present
disclosure together with the persistent UE-ID filtering method in
the MU-MIMO environment, it is possible to extract the information
more accurately.
[0086] While the present disclosure has been shown and described
with reference to certain embodiments thereof, it will be
understood by those skilled in the art that various changes in form
and details may be made therein without departing from the spirit
and scope of the disclosure as defined by the appended claims and
their equivalents.
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