U.S. patent application number 13/888320 was filed with the patent office on 2013-09-26 for synchronous tdm-based communication in dominant interference scenarios.
This patent application is currently assigned to QUALCOMM Incorporated. The applicant listed for this patent is QUALCOMM Incorporated. Invention is credited to Kapil Bhattad, Ravi Palanki.
Application Number | 20130250855 13/888320 |
Document ID | / |
Family ID | 41505093 |
Filed Date | 2013-09-26 |
United States Patent
Application |
20130250855 |
Kind Code |
A1 |
Bhattad; Kapil ; et
al. |
September 26, 2013 |
SYNCHRONOUS TDM-BASED COMMUNICATION IN DOMINANT INTERFERENCE
SCENARIOS
Abstract
Techniques for supporting communication in a heterogeneous
network are described. In an aspect, communication in a dominant
interference scenario may be supported by reserving subframes for a
weaker base station observing high interference from a strong
interfering base station. In another aspect, interference due to a
first reference signal from a first station (e.g., a base station)
may be mitigated by canceling the interference at a second station
(e.g., a UE) or by selecting different resources for sending a
second reference signal by the second station (e.g., another base
station) to avoid collision with the first reference signal. In yet
another aspect, a relay may transmit in an MBSFN mode in subframes
that it listens to a macro base station and in a regular mode in
subframes that it transmits to UEs. In yet another aspect, a
station may transmit more TDM control symbols than a dominant
interferer.
Inventors: |
Bhattad; Kapil; (San Diego,
CA) ; Palanki; Ravi; (San Deigo, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
QUALCOMM Incorporated |
San Diego |
CA |
US |
|
|
Assignee: |
QUALCOMM Incorporated
San Diego
CA
|
Family ID: |
41505093 |
Appl. No.: |
13/888320 |
Filed: |
May 6, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12499423 |
Jul 8, 2009 |
8172274 |
|
|
13888320 |
|
|
|
|
61080025 |
Jul 11, 2008 |
|
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Current U.S.
Class: |
370/328 |
Current CPC
Class: |
H04J 11/0069 20130101;
H04W 72/082 20130101; H04J 3/02 20130101; H04W 16/14 20130101; H04W
16/32 20130101; H04J 11/005 20130101 |
Class at
Publication: |
370/328 |
International
Class: |
H04J 3/02 20060101
H04J003/02 |
Claims
1. A method for wireless communication, comprising: identifying a
strong interfering station to a first station; determining a first
number of time division multiplexed (TDM) control symbols being
transmitting by the strong interfering station in a subframe; and
transmitting a second number of TDM control symbols by the first
station in the subframe, the second number of TDM control symbols
being more than the first number of TDM control symbols.
2. The method of claim 1, wherein the strong interfering station
and the first station are base stations with different transmit
power levels.
3. The method of claim 1, wherein the second number of TDM control
symbols comprise a maximum number of TDM control symbols allowed
for the first station.
4. The method of claim 1, wherein the second number of TDM control
symbols comprise three TDM control symbols.
5. The method of claim 1, further comprising: transmitting a
control channel indicating the second number of TDM control symbols
being transmitted by the first station in the subframe if the
strong interfering station is not present, and not transmitting the
control channel if the strong interfering station is present.
6. The method of claim 1, wherein the transmitting the second
number of TDM control symbols comprises: transmitting a control
channel in a first TDM control symbol at a first transmit power
level, and transmitting the control channel in at least one
additional TDM control symbol at a second transmit power level
higher than the first transmit power level.
7. The method of claim 1, wherein the transmitting the second
number of TDM control symbols comprises transmitting a control
channel in the second number of TDM control symbols on resource
elements selected to reduce collision with a reference signal from
the strong interfering station.
8. An apparatus for wireless communication, comprising: means for
identifying a strong interfering station to a first station; means
for determining a first number of time division multiplexed (TDM)
control symbols being transmitted by the strong interfering station
in a subframe; and means for transmitting a second number of TDM
control symbols by the first station in the subframe, the second
number of TDM control symbols being more than the first number of
TDM control symbols.
9. The apparatus of claim 8, further comprising: means for
transmitting a control channel indicating the second number of TDM
control symbols being transmitted by the first station in the
subframe if the strong interfering station is not present, and
means for not transmitting the control channel if the strong
interfering station is present.
10. The apparatus of claim 8, wherein the means for transmitting
the second number of TDM control symbols comprises: means for
transmitting a control channel in a first TDM control symbol at a
first transmit power level, and means for transmitting the control
channel in at least one additional TDM control symbol at a second
transmit power level higher than the first transmit power
level.
11. The apparatus of claim 8, wherein the means for transmitting
the second number of TDM control symbols comprises means for
transmitting a control channel in the second number of TDM control
symbols on resource elements selected to reduce collision with a
reference signal from the strong interfering station.
Description
[0001] The present application is a Divisional Application of U.S.
application Ser. No. 12/499,423, filed Jul. 8, 2009, entitled
SYNCHRONOUS TDM-BASED COMMUNICATION IN DOMINANT INTERFERENCE
SCENARIOS which claims priority to provisional U.S. Application
Ser. No. 61/080,025, entitled "ENABLING COMMUNICATIONS IN THE
PRESENCE OF DOMINANT INTERFERER," filed Jul. 11, 2008, assigned to
the assignee hereof and incorporated herein by reference.
BACKGROUND
[0002] I. Field
[0003] The present disclosure relates generally to communication,
and more specifically to techniques for supporting communication in
a wireless communication network.
[0004] II. Background
[0005] Wireless communication networks are widely deployed to
provide various communication services such as voice, video, packet
data, messaging, broadcast, etc. These wireless networks may be
multiple-access networks capable of supporting multiple users by
sharing the available network resources. Examples of such
multiple-access networks include Code Division Multiple Access
(CDMA) networks, Time Division Multiple Access (TDMA) networks,
Frequency Division Multiple Access (FDMA) networks, Orthogonal FDMA
(OFDMA) networks, and Single-Carrier FDMA (SC-FDMA) networks.
[0006] A wireless communication network may include a number of
base stations that can support communication for a number of user
equipments (UEs). A UE may communicate with a base station via the
downlink and uplink. The downlink (or forward link) refers to the
communication link from the base station to the UE, and the uplink
(or reverse link) refers to the communication link from the UE to
the base station.
[0007] A base station may transmit data and control information on
the downlink to a UE and/or may receive data and control
information on the uplink from the UE. On the downlink, a
transmission from the base station may observe interference due to
transmissions from neighbor base stations. On the uplink, a
transmission from the UE may cause interference to transmissions
from other UEs communicating with the neighbor base stations. The
interference may degrade performance on both the downlink and
uplink.
SUMMARY
[0008] Techniques for supporting communication in a dominant
interference scenario and for supporting operation of a relay
station in a heterogeneous network are described herein. The
heterogeneous network may include base stations of different
transmit power levels. In a dominant interference scenario, a UE
may communicate with a first base station and may observe high
interference from and/or may cause high interference to a second
base station. The first and second base stations may be of
different types and/or may have different transmit power
levels.
[0009] In an aspect, communication in a dominant interference
scenario may be supported by reserving subframes for a weaker base
station observing high interference from a strong interfering base
station. An eNB may be classified as a "weak" eNB or a "strong" eNB
based on the received power of the eNB at a UE (and not based on
the transmit power level of the eNB). A UE can then communicate
with the weaker base station in the reserved subframes in the
presence of the strong interfering base station.
[0010] In another aspect, interference due to a reference signal in
the heterogeneous network may be mitigated. A first station (e.g.,
a base station) causing high interference to or observing high
interference from a second station (e.g., a UE or another base
station) in the heterogeneous network may be identified. In one
design, interference due to a first reference signal from the first
station may be mitigated by canceling the interference at the
second station (e.g., the UE). In another design, interference to
the first reference signal may be mitigated by selecting different
resources for sending a second reference signal by the second
station (e.g., another base station) to avoid collision with the
first reference signal.
[0011] In yet another aspect, a relay station may be operated to
achieve good performance. The relay station may determine subframes
in which it listens to a macro base station and may transmit in a
multicast/broadcast single frequency network (MBSFN) mode in these
subframes. The relay station may also determine subframes in which
it transmits to UEs and may transmit in a regular mode in these
subframes. The relay station may send a reference signal in fewer
symbol periods in a subframe in the MBSFN mode than the regular
mode. The relay station may also send fewer time division
multiplexed (TDM) control symbols in a subframe in the MB SFN mode
than the regular mode.
[0012] In yet another aspect, a first station may transmit more TDM
control symbols than a dominant interferer in order to improve
reception of the TDM control symbols by UEs. The first station
(e.g., a pico base station, a relay station, etc.) may identify a
strong interfering station to the first station. The first station
may determine a first number of TDM control symbols being
transmitted by the strong interfering station in a subframe. The
first station may transmit a second (e.g., the maximum) number of
TDM control symbols in the subframe, with the second number of TDM
control symbols being more than the first number of TDM control
symbols.
[0013] Various aspects and features of the disclosure are described
in further detail below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 shows a wireless communication network.
[0015] FIG. 2 shows an exemplary frame structure.
[0016] FIG. 3 shows two exemplary regular subframe formats.
[0017] FIG. 4 shows two exemplary MBSFN subframe formats
[0018] FIG. 5 shows an exemplary transmission timeline for
different base stations.
[0019] FIGS. 6 and 7 show a process and an apparatus, respectively,
for mitigating interference in a wireless communication
network.
[0020] FIGS. 8 and 9 show a process and an apparatus, respectively,
for operating a relay station.
[0021] FIGS. 10 and 11 show a process and an apparatus,
respectively, for transmitting control information in a wireless
communication network.
[0022] FIG. 12 shows a block diagram of a base station or a relay
station and a UE.
DETAILED DESCRIPTION
[0023] The techniques described herein may be used for various
wireless communication networks such as CDMA, TDMA, FDMA, OFDMA,
SC-FDMA and other networks. The terms "network" and "system" are
often used interchangeably. A CDMA network may implement a radio
technology such as Universal Terrestrial Radio Access (UTRA),
cdma2000, etc. UTRA includes Wideband CDMA (WCDMA) and other
variants of CDMA. cdma2000 covers IS-2000, IS-95 and IS-856
standards. A TDMA network may implement a radio technology such as
Global System for Mobile Communications (GSM). An OFDMA network may
implement a radio technology such as Evolved UTRA (E-UTRA), Ultra
Mobile Broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX),
IEEE 802.20, Flash-OFDM.RTM., etc. UTRA and E-UTRA are part of
Universal Mobile Telecommunication System (UMTS). 3GPP Long Term
Evolution (LTE) and LTE-Advanced (LTE-A) are new releases of UMTS
that use E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A and GSM are
described in documents from an organization named "3rd Generation
Partnership Project" (3GPP). cdma2000 and UMB are described in
documents from an organization named "3rd Generation Partnership
Project 2" (3GPP2). The techniques described herein may be used for
the wireless networks and radio technologies mentioned above as
well as other wireless networks and radio technologies. For
clarity, certain aspects of the techniques are described below for
LTE, and LTE terminology is used in much of the description
below.
[0024] FIG. 1 shows a wireless communication network 100, which may
be an LTE network or some other wireless network. Wireless network
100 may include a number of evolved Node Bs (eNBs) 110, 112, 114
and 116 and other network entities. An eNB may be a station that
communicates with the UEs and may also be referred to as a base
station, a Node B, an access point, etc. Each eNB may provide
communication coverage for a particular geographic area. In 3GPP,
the term "cell" can refer to a coverage area of an eNB and/or an
eNB subsystem serving this coverage area, depending on the context
in which the term is used.
[0025] An eNB may provide communication coverage for a macro cell,
a pico cell, a femto cell, and/or other types of cell. A macro cell
may cover a relatively large geographic area (e.g., several
kilometers in radius) and may allow unrestricted access by UEs with
service subscription. A pico cell may cover a relatively small
geographic area and may allow unrestricted access by UEs with
service subscription. A femto cell may cover a relatively small
geographic area (e.g., a home) and may allow restricted access by
UEs having association with the femto cell (e.g., UEs in a Closed
Subscriber Group (CSG), UEs for users in the home, etc.). An eNB
for a macro cell may be referred to as a macro eNB. An eNB for a
pico cell may be referred to as a pico eNB. An eNB for a femto cell
may be referred to as a femto eNB or a home eNB. In the example
shown in FIG. 1, eNB 110 may be a macro eNB for a macro cell 102,
eNB 112 may be a pico eNB for a pico cell 104, and eNBs 114 and 116
may be femto eNBs for femto cells 106 and 108, respectively. An eNB
may support one or multiple (e.g., three) cells.
[0026] Wireless network 100 may also include relay stations. A
relay station is a station that receives a transmission of data
and/or other information from an upstream station (e.g., an eNB or
a UE) and sends a transmission of the data and/or other information
to a downstream station (e.g., a UE or an eNB). A relay station may
also be a UE that relays transmissions for other UEs. In the
example shown in FIG. 1, a relay station 118 may communicate with
macro eNB 110 and a UE 128 in order to facilitate communication
between eNB 110 and UE 128. A relay station may also be referred to
as a relay eNB, a relay, etc.
[0027] Wireless network 100 may be a heterogeneous network that
includes eNBs of different types, e.g., macro eNBs, pico eNBs,
femto eNBs, relays, etc. These different types of eNBs may have
different transmit power levels, different coverage areas, and
different impact on interference in wireless network 100. For
example, macro eNBs may have a high transmit power level (e.g., 20
Watts) whereas pico eNBs, femto eNBs and relays may have a lower
transmit power level (e.g., 1 Watt).
[0028] Wireless network 100 may support synchronous operation. For
synchronous operation, the eNBs may have similar frame timing, and
transmissions from different eNBs may be approximately aligned in
time. Synchronous operation may support certain transmission
features, as described below.
[0029] A network controller 130 may couple to a set of eNBs and may
provide coordination and control for these eNBs. Network controller
130 may communicate with the eNBs via a backhaul. The eNBs may also
communicate with one another, e.g., directly or indirectly via a
wireless or wireline backhaul.
[0030] UEs 122, 124 and 128 may be dispersed throughout wireless
network 100, and each UE may be stationary or mobile. A UE may also
be referred to as a terminal, a mobile station, a subscriber unit,
a station, etc. A UE may be a cellular phone, a personal digital
assistant (PDA), a wireless modem, a wireless communication device,
a handheld device, a laptop computer, a cordless phone, a wireless
local loop (WLL) station, etc. A UE may be able to communicate with
macro eNBs, pico eNBs, femto eNBs, relays, etc. In FIG. 1, a solid
line with double arrows indicates desired transmissions between a
UE and a serving eNB, which is an eNB designated to serve the UE on
the downlink and/or uplink. A dashed line with double arrows
indicates interfering transmissions between a UE and an eNB.
[0031] LTE utilizes orthogonal frequency division multiplexing
(OFDM) on the downlink and single-carrier frequency division
multiplexing (SC-FDM) on the uplink. OFDM and SC-FDM partition the
system bandwidth into multiple (K) orthogonal subcarriers, which
are also commonly referred to as tones, bins, etc. Each subcarrier
may be modulated with data. In general, modulation symbols are sent
in the frequency domain with OFDM and in the time domain with
SC-FDM. The spacing between adjacent subcarriers may be fixed, and
the total number of subcarriers (K) may be dependent on the system
bandwidth. For example, K may be equal to 128, 256, 512, 1024 or
2048 for system bandwidth of 1.25, 2.5, 5, 10 or 20 megahertz
(MHz), respectively. The system bandwidth may also be partitioned
into subbands. For example, a subband may cover 1.08 MHz, and there
may be 1, 2, 4, 8 or 16 subbands for system bandwidth of 1.25, 2.5,
5, 10 or 20 MHz, respectively.
[0032] FIG. 2 shows a frame structure used in LTE. The transmission
timeline for the downlink may be partitioned into units of radio
frames. Each radio frame may have a predetermined duration (e.g.,
10 milliseconds (ms)) and may be partitioned into 10 subframes with
indices of 0 through 9. Each subframe may include two slots. Each
radio frame may thus include 20 slots with indices of 0 through 19.
Each slot may include L symbol periods, e.g., L=7 symbol periods
for a normal cyclic prefix (as shown in FIG. 2) or L=6 symbol
periods for an extended cyclic prefix. The 2L symbol periods in
each subframe may be assigned indices of 0 through 2L-1.
[0033] The available time frequency resources may be partitioned
into resource blocks. Each resource block may cover N subcarriers
(e.g., 12 subcarriers) in one slot and may include a number of
resource elements. Each resource element may cover one subcarrier
in one symbol period and may be used to send one modulation symbol,
which may be a real or complex value. An eNB may transmit one OFDM
symbol in each symbol period. Each OFDM symbol may include
modulation symbols on subcarriers used for transmission and zero
symbols with signal value of zero on the remaining subcarriers.
[0034] In LTE, an eNB may send a primary synchronization signal
(PSS) and a secondary synchronization signal (SSS) in the center
1.08 MHz of the system bandwidth for each cell in the eNB. The
primary and secondary synchronization signals may be sent in symbol
periods 6 and 5, respectively, in each of subframes 0 and 5 of each
radio frame with the normal cyclic prefix, as shown in FIG. 2. The
synchronization signals may be used by UEs for cell search and
acquisition. The eNB may send a Physical Broadcast Channel (PBCH)
in symbol periods 0 to 3 in slot 1 of subframe 0 in certain radio
frames. The PBCH may carry certain system information.
[0035] The eNB may send a Physical Control Format Indicator Channel
(PCFICH) in the first symbol period of each subframe, as shown in
FIG. 2. The PCFICH may convey the number of symbol periods (M) used
for control channels in a subframe, where M may be equal to 1, 2 or
3 and may change from subframe to subframe. M may also be equal to
4 for a small system bandwidth, e.g., with less than 10 resource
blocks. The eNB may send a Physical HARQ Indicator Channel (PHICH)
and a Physical Downlink Control Channel (PDCCH) in the first M
symbol periods of each subframe (not shown in FIG. 2). The PHICH
may carry information to support hybrid automatic retransmission
(HARQ). The PDCCH may carry information on resource allocation for
UEs and control information for downlink channels. The first M OFDM
symbols of the subframe may also be referred to as TDM control
symbols. A TDM control symbol may be an OFDM symbol carrying
control information. The eNB may send a Physical Downlink Shared
Channel (PDSCH) in the remaining symbol periods of each subframe.
The PDSCH may carry data for UEs scheduled for data transmission on
the downlink. The various signals and channels in LTE are described
in 3GPP TS 36.211, entitled "Evolved Universal Terrestrial Radio
Access (E-UTRA); Physical Channels and Modulation," which is
publicly available.
[0036] LTE supports transmission of unicast information to specific
UEs. LTE also supports transmission of broadcast information to all
UEs and multicast information to a group of UEs. A
multicast/broadcast transmission may also be referred to as an
MBSFN transmission. A subframe used for sending unicast information
may be referred to as a regular subframe. A subframe used for
sending multicast and/or broadcast information may be referred to
as an MBSFN subframe.
[0037] FIG. 3 shows two exemplary regular subframe formats 310 and
320 that may be used to send unicast information to specific UEs on
the downlink. For the normal cyclic prefix in LTE, the left slot
includes seven symbol periods 0 through 6, and the right slot
includes seven symbol periods 7 through 13.
[0038] Subframe format 310 may be used by an eNB equipped with two
antennas. A cell-specific reference signal may be sent in symbol
periods 0, 4, 7 and 11 and may be used by UEs for channel
estimation. A reference signal is a signal that is known a priori
by a transmitter and a receiver and may also be referred to as
pilot. A cell-specific reference signal is a reference signal that
is specific for a cell, e.g., generated with one or more symbol
sequences determined based on a cell identity (ID). For simplicity,
a cell-specific reference signal may be referred to as simply a
reference signal. In FIG. 3, for a given resource element with
label R.sub.i, a reference symbol may be sent on that resource
element from antenna i, and no symbols may be sent on that resource
element from other antennas. Subframe format 320 may be used by an
eNB equipped with four antennas. A reference signal may be sent in
symbol periods 0, 1, 4, 7, 8 and 11.
[0039] In the example shown in FIG. 3, three TDM control symbols
are sent in a regular subframe with M=3. The PCFICH may be sent in
symbol period 0, and the PDCCH and PHICH may be sent in symbol
periods 0 to 2. The PDSCH may be sent in the remaining symbol
periods 3 to 13 of the subframe.
[0040] FIG. 4 shows two exemplary MBSFN subframe formats 410 and
420 that may be used to send broadcast/multicast information to UEs
on the downlink. Subframe format 410 may be used by an eNB equipped
with two antennas. A reference signal may be sent in symbol period
0. For the example shown in FIG. 4, M=1 and one TDM control symbol
may be sent in the MBSFN subframe. Subframe format 420 may be used
by an eNB equipped with four antennas. A reference signal may be
sent in symbol periods 0 and 1. For the example shown in FIG. 4,
M=2 and two TDM control symbols may be sent in the MBSFN
subframe.
[0041] In general, the PCFICH may be sent in symbol period 0 of an
MBSFN subframe, and the PDCCH and PHICH may be sent in symbol
periods 0 to M=1. Broadcast/multicast information may be sent in
symbol periods M through 13 of the MBSFN subframe. Alternatively,
no transmissions may be sent in symbol periods M through 13.
[0042] FIGS. 3 and 4 show some subframe formats that may be used
for the downlink. Other subframe formats may also be used, e.g.,
for more than two antennas at the eNB.
[0043] An eNB or a relay may operate in a regular mode, an MBSFN
mode, and/or other operating modes. The eNB or relay may switch
mode from subframe to subframe, or at a slower rate. In the regular
mode, the eNB or relay may transmit using a regular subframe
format, e.g., as shown in FIG. 3. The regular mode may be
associated with certain characteristics such as a configurable
number of TDM control symbols, the reference signal being sent from
each antenna in two or more symbol periods of a subframe, etc. In
the MBSFN mode, the eNB or relay may transmit using an MBSFN
subframe format, e.g., as shown in FIG. 4. The MBSFN mode may be
associated with certain characteristics such as a minimum number of
TDM control symbols, the reference signal being sent from each
antenna in one symbol period of a subframe, etc. The eNB or relay
may transmit control information and reference signal in fewer
symbol periods in the MBSFN mode than the regular mode, e.g., as
shown in FIGS. 3 and 4. The eNB or relay may also transmit fewer
TDM control symbols in the MBSFN mode than the regular mode. The
MBSFN mode may thus be desirable under certain operating scenarios,
as described below.
[0044] A UE may be within the coverage of multiple eNBs. One of
these eNBs may be selected to serve the UE. The serving eNB may be
selected based on various criteria such as received power,
pathloss, signal-to-noise ratio (SNR), etc.
[0045] A UE may operate in a dominant interference scenario in
which the UE may observe high interference from one or more
interfering eNBs. A dominant interference scenario may occur due to
restricted association. For example, in FIG. 1, UE 124 may be close
to femto eNB 114 and may have high received power for eNB 114.
However, UE 124 may not be able to access femto eNB 114 due to
restricted association and may then connect to macro eNB 110 with
lower received power (as shown in FIG. 1) or to femto eNB 116 also
with lower received power (not shown in FIG. 1). UE 124 may then
observe high interference from femto eNB 114 on the downlink and
may also cause high interference to eNB 114 on the uplink.
[0046] A dominant interference scenario may also occur due to range
extension, which is a scenario in which a UE connects to an eNB
with lower pathloss and possibly lower SNR among all eNBs detected
by the UE. For example, in FIG. 1, UE 122 may detect macro eNB 110
and pico eNB 112 and may have lower received power for pico eNB 112
than macro eNB 110. Nevertheless, it may be desirable for UE 122 to
connect to pico eNB 112 if the pathloss for pico eNB 112 is lower
than the pathloss for macro eNB 110. This may result in less
interference to the wireless network for a given data rate for UE
122.
[0047] In an aspect, communication in a dominant interference
scenario may be supported by reserving subframes for a weaker eNB
observing high interference from a strong interfering eNB. A UE can
then communicate with the weaker eNB in the reserved subframes in
the presence of the strong interfering eNB. An eNB may be
classified as a "weak" eNB or a "strong" eNB based on the received
power of the eNB at a UE (and not based on the transmit power level
of the eNB). Furthermore, different eNBs may send their
synchronization signals such that interference from a dominant
interferer can be avoided.
[0048] In one design, eNBs and relays may be arranged into
different groups. Each group may include eNBs and/or relays that
are not dominant interferers of one another. For example, one group
may include macro eNBs, another group may include pico eNBs and
relays, and one or more groups may include femto eNBs. Relays may
have a similar transmit power level as pico eNBs and may thus be
grouped with the pico eNBs. Femto eNBs may be divided into multiple
groups if they are dominant interferers of one another. By having
each group includes eNBs that are not dominant interferers of one
another, outage scenarios may be avoided and the benefits of range
extension may be realized.
[0049] In one design, different groups of eNBs may be associated
with different subframe offsets. The timing of eNBs in different
groups may be offset from one another by an integer number of
subframes. For example, when macro eNBs in a first group transmit
subframe 0, pico eNBs in a second group may transmit subframe 1,
femto eNBs in a third group may transmit subframe 2, etc. The use
of subframe offset may allow eNBs and relays in different groups to
transmit their synchronization signals such that UEs can detect
these signals.
[0050] FIG. 5 shows an exemplary transmission timeline for four
groups of eNBs and relay. A first group may include macro eNB 110,
which may have its subframe 0 starts at time T.sub.0. A second
group may include pico eNB 112 and relay 118, which may have their
subframe 0 starts one subframe after time T.sub.0. A third group
may include femto eNB 114, which may have its subframe 0 starts two
subframes after time T.sub.0. A fourth group may include femto eNB
116, which may have its subframe 0 starts three subframes after
T.sub.0. In general, any number of groups may be formed, and each
group may include any number of eNBs and/or relays.
[0051] In one design, a strong interfering eNB may reserve or clear
some subframes for a weaker eNB to allow the weaker eNB to
communicate with its UEs. The interfering eNB may transmit as
little as possible in the reserved subframes in order to reduce
interference to the weaker eNB. In one design, the interfering eNB
may configure the reserved subframes as MBSFN subframes. The
interfering eNB may transmit only the PCFICH with M=1 and the
reference signal in the first symbol period of each reserved
subframe and may transmit nothing in the remaining symbol periods
of the subframe, e.g., as shown in FIG. 4. In another design, the
interfering eNB may operate in a 1-Tx mode with one transmit
antenna or a 2-Tx mode with two transmit antennas. The interfering
eNB may transmit the PCFICH with M=1 and the reference signal in
each reserved subframe, e.g., as shown in FIG. 3. In yet another
design, the interfering eNB may transmit the reference signal but
may avoid transmitting the PCFICH in the reserved subframes in
order to reduce interference to the weaker eNB. For the designs
described above, the interfering eNB may avoid transmitting other
control channels, such as the PHICH and PDCCH, as well as data in
each reserved subframe. In yet another design, the interfering eNB
may transmit nothing in each reserved subframe in order to avoid
causing any interference to the weaker eNB. The interfering eNB may
also transmit in the reserved subframes in other manners. The
interfering eNB may transmit the least number of modulation symbols
required by the LTE standard in each reserved subframe.
[0052] In the example shown in FIG. 5, macro eNB 110 reserves
subframes 1 and 6 for pico eNB 112 and transmits one TDM control
symbol with M=1 for the PCFICH in each reserved subframe. Femto eNB
114 (femto eNB A) reserves subframes 3 and 8 for macro eNB 110,
reserves subframes 4 and 9 for pico eNB 112, and reserves subframe
1 for femto eNB 116 (femto eNB B). Femto eNB 114 transmits one TDM
control symbol with M=1 for the PCFICH in each reserved subframe.
Femto eNB 116 reserves subframes 2 and 7 for macro eNB 110,
reserves subframes 3 and 8 for pico eNB 112, and reserves subframe
9 for femto eNB 114. Femto eNB 116 transmits one TDM control symbol
with M=1 for the PCFICH in each reserved subframe. As shown in FIG.
5, the subframes reserved for macro eNB 110 by femto eNBs 114 and
116 are time aligned and allow the macro eNB to transmit in its
subframes 0 and 5 with little interference from the femto eNBs. The
subframes reserved for pico eNB 112 by macro eNB 110 and femto eNBs
114 and 116 are time aligned and allow the pico eNB to transmit in
its subframes 0 and 5 with little interference from the macro and
femto eNBs.
[0053] Referring back to FIG. 2, each eNB may transmit its
synchronization signals in subframes 0 and 5 and may also transmit
the PBCH in subframe 0. A UE may search for the synchronization
signals when detecting for eNBs and may receive the PBCH from each
detected eNB in order to communicate with the eNB. To allow UEs to
detect a weaker eNB, a strong interfering eNB may reserve or clear
subframes in which the synchronization signals and the PBCH are
transmitted by the weaker eNB. This clearing may be done for all
subframes or only some subframes in which the synchronization
signals and the PBCH are transmitted by the weaker eNB. The
clearing should be done such that UEs can detect the weaker eNB in
a reasonable amount of time.
[0054] Referring to the example shown in FIG. 5, subframes 0 and 5
of macro eNB 110 are cleared by femto eNBs 114 and 116 to avoid
interference to the synchronization signals and the PBCH from the
macro eNB. Subframes 0 and 5 of pico eNB 112 are cleared by macro
eNB 110 and femto eNBs 114 and 116 to avoid interference to the
synchronization signals and the PBCH from the pico eNB. Subframe 0
of femto eNB 114 is cleared by femto eNB 116, and subframe 0 of
femto eNB 116 is cleared by femto eNB 114.
[0055] In one design, the eNBs may communicate via the backhaul to
negotiate reservation/clearing of subframes. In another design, a
UE desiring to communicate with a weaker eNB may request an
interfering eNB to reserve some subframes for the weaker eNB. In
yet another design, a designated network entity may decide
reservation of subframes for the eNBs, e.g., based on data requests
sent by UEs to different eNBs and/or reports from the eNBs. For all
designs, subframes may be reserved based on various criteria such
as loading at the eNBs, the number of eNBs in the vicinity, the
number of UEs within the coverage of each eNB, pilot measurement
reports from the UEs, etc. For example, a macro eNB may reserve a
subframe to allow multiple pico eNBs and/or femto eNBs to
communicate with their UEs, which may provide cell splitting
gains.
[0056] Each eNB may transmit its reference signal on a set of
subcarriers determined based on its cell ID. In one design, the
cell ID space of strong interfering eNBs (such as macro eNBs) and
weaker eNBs (such as pico eNBs) may be defined such that the
reference signals of these eNBs are transmitted on different
subcarriers and do not collide. Some eNBs (such as femto eNBs and
relays) may be self-configuring. These eNBs may select their cell
IDs such that their reference signals do not collide with the
reference signals of strong neighboring eNBs.
[0057] A UE may communicate with a weaker eNB in a reserved
subframe and may observe high interference due to the PCFICH, the
reference signal, and possibly other transmissions from a strong
interfering eNB. In one design, the UE may discard each TDM control
symbol with high interference from the interfering eNB and may
process remaining TDM control symbols. In another design, the UE
may discard received symbols on subcarriers with high interference
and may process remaining received symbols. The UE may also process
the received symbols and the TDM control symbols in other
manners.
[0058] The UE may obtain a channel estimate for the weaker eNB
based on a reference signal transmitted by the weaker eNB. The
reference signal of the weaker eNB may be transmitted on different
subcarriers and may not overlap with the reference signal of the
strong interfering eNB. In this case, the UE may derive a channel
estimate for the weaker eNB based on the reference signal from this
eNB. If the reference signal of the weaker eNB collides with the
reference signal of the interfering eNB, then the UE may perform
channel estimation with interference cancellation. The UE may
estimate the interference due to the reference signal from the
interfering eNB based on known reference symbols sent by this eNB
and the known subcarriers on which the reference signal is
transmitted. The UE may subtract the estimated interference from
the received signal at the UE to remove the interference due to the
interfering eNB and may then derive a channel estimate for the
weaker eNB based on the interference-canceled signal. The UE may
also perform interference cancellation for control channels (e.g.,
the PCFICH) from the interfering eNB that collide with the
reference signal from the weaker eNB. The UE may decode each such
control channel from the interfering eNB, estimate the interference
due to each decoded control channel, subtract the estimated
interference from the received signal, and derive the channel
estimate for the weaker eNB after subtracting the estimated
interference. In general, the UE may perform interference
cancellation for any transmission from the interfering eNB which
can be decoded in order to improve channel estimation performance.
The UE may decode control channels (e.g., the PBCH, PHICH and
PDCCH) as well as the data channel (e.g., the PDSCH) from the
weaker eNB based on the channel estimate.
[0059] The weaker eNB may send control information and data to the
UE in a subframe reserved by the interfering eNB. The interfering
eNB may transmit only the first TDM control symbol in the subframe,
e.g., as shown in FIG. 4. In this case, the UE may observe high
interference on only the first TDM control symbol and may observe
no interference from the interfering eNB on the remaining TDM
control symbols in the subframe.
[0060] The weaker eNB may transmit control information in a manner
to facilitate reliable reception by the UE in the presence of the
interfering eNB. In one design, the weaker eNB may transmit three
TDM control symbols in a reserved subframe by setting M=3 for the
PCFICH. In another design, the weaker eNB may transmit a
predetermined number of TDM control symbols in the reserved
subframe. For both designs, the UE may be aware of the number of
TDM control symbols being transmitted by the weaker eNB. The UE
would not need to decode the PCFICH sent by the weaker eNB in the
first TDM control symbol, which may observe high interference from
the interfering eNB.
[0061] The weaker eNB may send three transmissions of the PHICH in
three TDM control symbols, one PHICH transmission in each TDM
control symbol. The UE may decode the PHICH based on the two PHICH
transmissions sent in the second and third TDM control symbols,
which may observe no interference from the interfering eNB. The UE
may decode the PHICH based further on a portion of the PHICH
transmission sent on subcarriers not used by the interfering eNB in
the first TDM control symbol.
[0062] The weaker eNB may also send the PDCCH in three TDM control
symbols. The weaker eNB may send the PDCCH to the UE such that
adverse impact due to interference from the interfering eNB can be
reduced. For example, the weaker eNB may send the PDCCH in TDM
control symbols without interference from the interfering eNB, on
subcarriers not used by the interfering eNB, etc.
[0063] The weaker eNB may be aware of the interference due to the
interfering eNB and may transmit the control information to
mitigate the adverse effects of the interference. In one design,
the weaker eNB may scale the transmit power of the PHICH, the
PDCCH, and/or other control channels to obtain the desirable
performance. The power scaling may account for the loss of part of
the control information due to puncturing by the high interference
from the interfering eNB.
[0064] The UE may decode the control channels (e.g., the PHICH and
PDCCH) from the weaker eNB with knowledge that some modulation
symbols in the first TDM control symbol may be lost or punctured
due to high interference from the interfering eNB. In one design,
the UE may discard received symbols with high interference from the
interfering eNB and may decode the remaining received symbols. The
discarded symbols may be replaced with erasures and given neutral
weight in the decoding process. In another design, the UE may
perform decoding with interference cancellation for the control
channels. The UE may estimate the interference due to the
interfering eNB in the TDM control symbols, remove the estimated
interference from the received symbols, and use the received
symbols after interference cancellation to decode the control
channels.
[0065] The UE may decode the data channel (e.g., PDSCH) from the
weaker eNB, possibly with knowledge that some modulation symbols
may be punctured due to high interference from the interfering eNB.
In one design, the UE may discard received symbols with high
interference from the interfering eNB and may decode the remaining
received symbols to recover the data sent by the weaker eNB. In
another design, the UE may perform decoding with interference
cancellation for the data channel.
[0066] The UE may also decode the control and data channels from
the weaker eNB based on other techniques to improve performance in
the presence of high interference from the interfering eNB. For
example, the UE may perform detection and/or decoding by taking
into account high interference on certain received symbols.
[0067] The techniques described herein may be used to support
operation by relays, e.g., relay 118. In the downlink direction,
relay 118 may receive data and control information from macro eNB
110 and may retransmit the data and control information to UE 128.
In the uplink direction, relay 118 may receive data and control
information from UE 128 and may retransmit the data and control
information to macro eNB 110. Relay 118 may appear like a UE to
macro eNB 110 and like an eNB to UE 128. The link between macro eNB
110 and relay 118 may be referred to as a backhaul link, and the
link between relay 118 and UE 128 may be referred to as a relay
link.
[0068] Relay 118 typically cannot transmit and receive at the same
time on the same frequency channel or bandwidth. In the downlink
direction, relay 118 may designate some subframes as backhaul
downlink subframes in which it will listen to macro eNB 110 and
some subframes as relay downlink subframes in which it will
transmit to UEs. In the uplink direction, relay 118 may designate
some subframes as relay uplink subframes in which it will listen to
the UEs and some subframes as backhaul uplink subframes in which it
will transmit to macro eNB 110. In the example shown in FIG. 5, in
the downlink direction, relay 118 may transmit to its UEs in
subframes 0 and 5, which may be cleared by macro eNB 110, and may
listen to macro eNB 110 in subframes 1, 2, 3, 4 and 9. The
subframes for the uplink direction are not shown in FIG. 5.
[0069] In a range extension scenario, macro eNB 110 may be a strong
interfering eNB to UEs communicating with relay 118 as well as new
UEs that can be served by relay 118. For the relay downlink
subframes in which relay 118 transmits to the UEs, the timing of
relay 118 may be shifted by an integer number of subframes (e.g.,
by one subframe in FIG. 5) from the timing of macro eNB 110. Macro
eNB 110 may clear some subframes (e.g., subframes 1 and 6 in FIG.
5) for relay 118. Relay 118 may transmit its synchronization
signals and the PBCH in relay downlink subframes that coincide with
the subframes reserved by macro eNB 110. UEs can detect the
synchronization signals from relay 118. The UEs may be aware of
symbols punctured by macro eNB 110 and may make use of this
information to decode the control channels from relay 118, as
described above.
[0070] For the backhaul downlink subframes, relay 118 may desire to
only listen to macro eNB 110 and may not desire to transmit
anything to its UEs in these subframes. However, since relay 118 is
an eNB to its UEs, relay 118 may be expected to transmit some
signals to its UEs in the backhaul downlink subframes. In one
design, relay 118 may operate in the MBSFN mode for the backhaul
downlink subframes. In the MBSFN mode, relay 118 may transmit only
in the first symbol period of a backhaul downlink subframe and may
listen to macro eNB 110 in the remaining symbol periods of the
subframe. In the example shown in FIG. 5, relay 118 transmits in
only the first symbol period of subframes 1, 2, 3, 4 and 9, which
are subframes in which relay 118 listens to macro eNB 110.
[0071] In one design, macro eNB 110 may set the PCFICH to a
predetermined value (e.g., M=3) in subframes in which macro eNB 110
transmits to relay 118 (e.g., subframes 0 and 5 of macro eNB 110 in
FIG. 5). Relay 118 may know the predetermined value of the PCFICH
from macro eNB 110 and may skip decoding the PCFICH. Relay 118 may
transmit the PCFICH to its UEs in the first symbol period and may
skip decoding the PCFICH sent by macro eNB 110 in the same symbol
period. Macro eNB 110 may send three transmissions of the PHICH,
one transmission in each TDM control symbol. Relay 118 may decode
the PHICH from macro eNB 110 based on the PHICH transmissions in
the second and third TDM control symbols. Macro eNB 110 may also
send the PDCCH such that all or most of a PDCCH transmission for
relay 118 is sent in the second and third TDM control symbols.
Relay 118 may decode the PDCCH based on the portion of the PDCCH
transmission received in the second and third TDM control symbols.
Macro eNB 110 may boost the transmit power of the control channels
(e.g., the PHICH and/or PDCCH) intended for relay 118 to improve
reception of the control channels by relay 118 based on the part
sent in the second and third TDM control symbols. Macro eNB 110 may
also skip transmitting control information in the first TDM control
symbol to relay 118. Macro eNB 110 may send data to relay 118 in
symbol periods 3 through 13. Relay 118 may recover the data in the
normal manner.
[0072] Relay 118 may be unable to receive the reference signal from
macro eNB 110 in symbol period 0. Relay 118 may derive a channel
estimate for macro eNB 110 based on the reference signal that relay
118 can receive from macro eNB 110. When scheduling relay 118,
macro eNB 110 may make use of the information about which subframes
are likely to have better channel estimates by relay 118. For
example, relay 118 may listen to macro eNB 110 in two contiguous
subframes. In this case, the channel estimate for the first
subframe may be worse than the channel estimate for the second
subframe since the channel estimate for the first subframe may be
extrapolated whereas the channel estimate for the second subframe
may be interpolated and may have more reference symbols around it.
Macro eNB 110 may then send data to relay 118 in the second
subframe, if possible.
[0073] Relay 118 may not be able to operate in the MBSFN mode in
its subframes 0 and 5, which carry the synchronization signals. In
one design, relay 118 may skip listening to macro eNB 110 in
subframes 0 and 5 of relay 118, even if these subframes are
designated as backhaul downlink subframes, and may instead transmit
to its UEs. In another design, relay 118 may skip transmitting to
its UEs in subframes 0 and 5, even if these subframes are
designated as relay downlink subframes, and may instead listen to
macro eNB 110. Relay 118 may also perform a combination of both and
may transmit to its UEs in some of subframes 0 and 5 and may listen
to macro eNB 110 in some other subframes 0 and 5.
[0074] In the uplink direction, relay 118 may operate in a similar
manner as a UE in the backhaul uplink subframes in which relay 118
transmits data and control information to macro eNB 110. Relay 118
may operate in a similar manner as an eNB in the relay uplink
subframes in which relay 118 listens for data and control
information from UE 128. A scheduler at macro eNB 110 and/or a
scheduler at relay 118 may ensure that the uplink of relay 118 and
the uplink of UEs served by relay 118 are scheduled
appropriately.
[0075] FIG. 6 shows a design of a process 600 for mitigating
interference in a wireless communication network. Process 600 may
be performed by a UE, a base station/eNB, a relay station, or some
other entity. A first station causing high interference to or
observing high interference from a second station in a
heterogeneous network may be identified (block 612). The
heterogeneous network may comprise base stations of at least two
different transmit power levels and/or different association types.
Interference due to a first reference signal from the first station
may be mitigated by canceling the interference at the second
station, or interference to the first reference signal may be
mitigated by selecting different resources for sending a second
reference signal by the second station to avoid collision with the
first reference signal (block 614).
[0076] In one design, the first station may be a base station or a
relay station, and the second station may be a UE. For block 614,
the interference due to the first reference signal may be canceled
at the UE. In one design, the interference due to the first
reference signal may be estimated and subtracted from a received
signal at the UE to obtain an interference-canceled signal. The
interference-canceled signal may then be processed to obtain a
channel estimate for a base station or a relay station with which
the UE is in communication. The interference-canceled signal may
also be processed to obtain data and/or control information sent by
the base station or the relay station to the UE.
[0077] In another design, the first and second stations may
comprise (i) a macro base station and a pico base station,
respectively, (ii) two femto base stations, or (iii) some other
combination of macro, pico, and femto base stations and relay
station. For block 614, first resources used to send the first
reference signal by the first station may be determined. A cell ID
associated with second resources for sending the second reference
signal may be selected such that the second resources are different
from the first resources. The first resources may comprise a first
set of subcarriers, and the second resources may comprise a second
set of subcarriers, which may be different from the first set of
subcarriers. The second reference signal may be sent on the second
resources by the second station and may then avoid collision with
the first reference signal. A primary synchronization signal and a
secondary synchronization signal may be generated based on the
selected cell ID and may be sent by the second station in
designated subframes, e.g., subframes 0 and 5.
[0078] FIG. 7 shows a design of an apparatus 700 for mitigating
interference. Apparatus 700 includes a module 712 to identify a
first station causing high interference to or observing high
interference from a second station in a heterogeneous network, and
a module 714 to mitigate interference due to a first reference
signal from the first station by canceling the interference at the
second station or mitigate interference to the first reference
signal by selecting different resources for sending a second
reference signal by the second station to avoid collision with the
first reference signal
[0079] FIG. 8 shows a design of a process 800 for operating a relay
station in a wireless communication network. The relay station may
determine subframes in which it listens to a macro base station
(block 812). The relay station may transmit in an MBSFN mode in the
subframes in which it listens to the macro base station (block
814). The relay station may also determine subframes in which it
transmits to UEs (block 816). The relay station may transmit in a
regular mode in the subframes in which it transmits to the UEs
(block 818).
[0080] The relay station may send a reference signal in fewer
symbol periods in a given subframe in the MBSFN mode than the
regular mode. In one design, the relay station may transmit the
reference signal from each antenna in one symbol period of each
subframe in which the relay station listens to the macro base
station in the MBSFN mode, e.g., as shown in FIG. 4. The relay
station may transmit the reference signal from each antenna in
multiple symbol periods of each subframe in which the relay station
transmits to the UEs in the regular mode, e.g., as shown in FIG. 3.
In one design, the relay station may transmit the reference signal
in only the first symbol period or only the first two symbol
periods of each subframe in which the relay station listens to the
macro base station in the MBSFN mode. The relay station may
transmit the reference signal in more symbol periods across each
subframe in which the relay station transmits to the UEs in the
regular mode. The relay station may also transmit the reference
signal in other manners in the MBSFN mode and the regular mode.
[0081] In one design of block 814, the relay station may transmit a
single TDM control symbol and may transmit no data in each subframe
in which it listens to the macro base station. The relay station
may receive a maximum number of (e.g., three) TDM control symbols
from the macro base station in each subframe in which the macro
base station transmits to the relay station. The relay station may
decode at least one control channel (e.g., the PHICH and PDCCH)
from the macro base station based on the second and third TDM
control symbols.
[0082] FIG. 9 shows a design of an apparatus 900 for operating a
relay station. Apparatus 900 includes a module 912 to determine
subframes in which a relay station is listening to a macro base
station, a module 914 to transmit in an MBSFN mode by the relay
station in the subframes in which the relay station is listening to
the macro base station, a module 916 to determine subframes in
which the relay station is transmitting to UEs, and a module 918 to
transmit in the regular mode by the relay station in the subframes
in which the relay station is transmitting to the UEs.
[0083] FIG. 10 shows a design of a process 1000 for transmitting
control information in a wireless communication network. Process
1000 may be performed by a first station, which may be a base
station/eNB, a relay station, or some other entity. The first
station may identify a strong interfering station to the first
station (block 1012). The first station may determine a first
number of TDM control symbols being transmitted by the strong
interfering station in a subframe (block 1014). The first station
may transmit a second number of TDM control symbols in the
subframe, with the second number of TDM control symbols being more
than the first number of TDM control symbols (block 1016). The
second number of TDM control symbols may be the maximum number of
TDM control symbols allowed for the first station and may comprise
three TDM control symbols.
[0084] The first station and the strong interfering station may
have different transmit power levels. In one design, the first
station may be a pico base station, and the interfering station may
be a macro base station. In another design, the first station may
be a macro base station, and the interfering station may be a femto
base station, or vice versa. In yet another design, the first
station may be a femto base station, and the interfering station
may be another femto base station. The first station and the strong
interfering station may also be some other combination of macro
base station, pico base station, femto base station, relay station,
etc.
[0085] In one design, the first station may transmit a control
channel (e.g., the PCFICH) indicating the second number of TDM
control symbols being transmitted in the subframe if the strong
interfering station is not present. The first station may not
transmit the control channel if the strong interfering station is
present. In this case, a predetermined value may be assumed for the
second number of TDM control symbols.
[0086] In one design of block 1016, the first station may transmit
a control channel (e.g., the PHICH or PDCCH) in a first TDM control
symbol at a first transmit power level. The first station may
transmit the control channel in at least one additional TDM control
symbol at a second transmit power level, which may be higher than
the first transmit power level. In another design of block 1016,
the first station may transmit a control channel (e.g., the PHICH
or PDCCH) in the second number of TDM control symbols on resource
elements selected to avoid or reduce collision with a reference
signal from the strong interfering station. The first station may
also transmit the second number of TDM control symbols in other
manners to mitigate the effects of interference from the strong
interfering station.
[0087] FIG. 11 shows a design of an apparatus 1100 for transmitting
control information. Apparatus 1100 includes a module 1112 to
identify a strong interfering station to a first station, a module
1114 to determine a first number of TDM control symbols being
transmitted by the strong interfering station in a subframe, and a
module 1116 to transmit a second number of TDM control symbols by
the first station in the subframe, the second number of TDM control
symbols being more than the first number of TDM control
symbols.
[0088] The modules in FIGS. 7, 9 and 11 may comprise processors,
electronics devices, hardware devices, electronics components,
logical circuits, memories, software codes, firmware codes, etc.,
or any combination thereof.
[0089] FIG. 12 shows a block diagram of a design of a station 110x
and a UE 120. Station 110x may be macro base station 110, pico base
station 112, femto base station 114 or 116, or relay station 118 in
FIG. 1. UE 120 may be any of the UEs in FIG. 1. Station 110x may be
equipped with T antennas 1234a through 1234t, and UE 120 may be
equipped with R antennas 1252a through 1252r, where in general
T.gtoreq.1 and R.gtoreq.1.
[0090] At station 110x, a transmit processor 1220 may receive data
from a data source 1212 and control information from a
controller/processor 1240. The control information may be for the
PBCH, PCFICH, PHICH, PDCCH, etc. The data may be for the PDSCH,
etc. Processor 1220 may process (e.g., encode and symbol map) the
data and control information to obtain data symbols and control
symbols, respectively. Processor 1220 may also generate reference
symbols, e.g., for the PSS, SSS, and cell-specific reference
signal. A transmit (TX) multiple-input multiple-output (MIMO)
processor 1230 may perform spatial processing (e.g., precoding) on
the data symbols, the control symbols, and/or the reference
symbols, if applicable, and may provide T output symbol streams to
T modulators (MODs) 1232a through 1232t. Each modulator 1232 may
process a respective output symbol stream (e.g., for OFDM, etc.) to
obtain an output sample stream. Each modulator 1232 may further
process (e.g., convert to analog, amplify, filter, and upconvert)
the output sample stream to obtain a downlink signal. T downlink
signals from modulators 1232a through 1232t may be transmitted via
T antennas 1234a through 1234t, respectively.
[0091] At UE 120, antennas 1252a through 1252r may receive the
downlink signals from station 110x and may provide received signals
to demodulators (DEMODs) 1254a through 1254r, respectively. Each
demodulator 1254 may condition (e.g., filter, amplify, downconvert,
and digitize) a respective received signal to obtain input samples.
Each demodulator 1254 may further process the input samples (e.g.,
for OFDM, etc.) to obtain received symbols. A MIMO detector 1256
may obtain received symbols from all R demodulators 1254a through
1254r, perform MIMO detection on the received symbols if
applicable, and provide detected symbols. A receive processor 1258
may process (e.g., demodulate, deinterleave, and decode) the
detected symbols, provide decoded data for UE 120 to a data sink
1260, and provide decoded control information to a
controller/processor 1280.
[0092] On the uplink, at UE 120, a transmit processor 1264 may
receive and process data (e.g., for the PUSCH) from a data source
1262 and control information (e.g., for the PUCCH) from
controller/processor 1280. Processor 1264 may also generate
reference symbols for a reference signal. The symbols from transmit
processor 1264 may be precoded by a TX MIMO processor 1266 if
applicable, further processed by modulators 1254a through 1254r
(e.g., for SC-FDM, etc.), and transmitted to station 110x. At
station 110x, the uplink signals from UE 120 may be received by
antennas 1234, processed by demodulators 1232, detected by a MIMO
detector 1236 if applicable, and further processed by a receive
processor 1238 to obtain decoded data and control information sent
by UE 120. Processor 1238 may provide the decoded data to a data
sink 1239 and the decoded control information to
controller/processor 1240.
[0093] Controllers/processors 1240 and 1280 may direct the
operation at station 110x and UE 120, respectively. Processor 1240
and/or other processors and modules at station 110x may perform or
direct process 600 in FIG. 6, process 800 in FIG. 8, process 1000
in FIG. 10, and/or other processes for the techniques described
herein. Processor 1280 and/or other processors and modules at UE
120 may perform or direct process 600 in FIG. 6 and/or other
processes for the techniques described herein. Memories 1242 and
1282 may store data and program codes for station 110x and UE 120,
respectively. A scheduler 1244 may schedule UEs for data
transmission on the downlink and/or uplink.
[0094] Those of skill in the art would understand that information
and signals may be represented using any of a variety of different
technologies and techniques. For example, data, instructions,
commands, information, signals, bits, symbols, and chips that may
be referenced throughout the above description may be represented
by voltages, currents, electromagnetic waves, magnetic fields or
particles, optical fields or particles, or any combination
thereof.
[0095] Those of skill would further appreciate that the various
illustrative logical blocks, modules, circuits, and algorithm steps
described in connection with the disclosure herein may be
implemented as electronic hardware, computer software, or
combinations of both. To clearly illustrate this interchangeability
of hardware and software, various illustrative components, blocks,
modules, circuits, and steps have been described above generally in
terms of their functionality. Whether such functionality is
implemented as hardware or software depends upon the particular
application and design constraints imposed on the overall system.
Skilled artisans may implement the described functionality in
varying ways for each particular application, but such
implementation decisions should not be interpreted as causing a
departure from the scope of the present disclosure.
[0096] The various illustrative logical blocks, modules, and
circuits described in connection with the disclosure herein may be
implemented or performed with a general-purpose processor, a
digital signal processor (DSP), an application specific integrated
circuit (ASIC), a field programmable gate array (FPGA) or other
programmable logic device, discrete gate or transistor logic,
discrete hardware components, or any combination thereof designed
to perform the functions described herein. A general-purpose
processor may be a microprocessor, but in the alternative, the
processor may be any conventional processor, controller,
microcontroller, or state machine. A processor may also be
implemented as a combination of computing devices, e.g., a
combination of a DSP and a microprocessor, a plurality of
microprocessors, one or more microprocessors in conjunction with a
DSP core, or any other such configuration.
[0097] The steps of a method or algorithm described in connection
with the disclosure herein may be embodied directly in hardware, in
a software module executed by a processor, or in a combination of
the two. A software module may reside in RAM memory, flash memory,
ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a
removable disk, a CD-ROM, or any other form of storage medium known
in the art. An exemplary storage medium is coupled to the processor
such that the processor can read information from, and write
information to, the storage medium. In the alternative, the storage
medium may be integral to the processor. The processor and the
storage medium may reside in an ASIC. The ASIC may reside in a user
terminal. In the alternative, the processor and the storage medium
may reside as discrete components in a user terminal.
[0098] In one or more exemplary designs, the functions described
may be implemented in hardware, software, firmware, or any
combination thereof. If implemented in software, the functions may
be stored on or transmitted over as one or more instructions or
code on a computer-readable medium. Computer-readable media
includes both computer storage media and communication media
including any medium that facilitates transfer of a computer
program from one place to another. A storage media may be any
available media that can be accessed by a general purpose or
special purpose computer. By way of example, and not limitation,
such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM
or other optical disk storage, magnetic disk storage or other
magnetic storage devices, or any other medium that can be used to
carry or store desired program code means in the form of
instructions or data structures and that can be accessed by a
general-purpose or special-purpose computer, or a general-purpose
or special-purpose processor. Also, any connection is properly
termed a computer-readable medium. For example, if the software is
transmitted from a website, server, or other remote source using a
coaxial cable, fiber optic cable, twisted pair, digital subscriber
line (DSL), or wireless technologies such as infrared, radio, and
microwave, then the coaxial cable, fiber optic cable, twisted pair,
DSL, or wireless technologies such as infrared, radio, and
microwave are included in the definition of medium. Disk and disc,
as used herein, includes compact disc (CD), laser disc, optical
disc, digital versatile disc (DVD), floppy disk and blu-ray disc
where disks usually reproduce data magnetically, while discs
reproduce data optically with lasers. Combinations of the above
should also be included within the scope of computer-readable
media.
[0099] The previous description of the disclosure is provided to
enable any person skilled in the art to make or use the disclosure.
Various modifications to the disclosure will be readily apparent to
those skilled in the art, and the generic principles defined herein
may be applied to other variations without departing from the
spirit or scope of the disclosure. Thus, the disclosure is not
intended to be limited to the examples and designs described herein
but is to be accorded the widest scope consistent with the
principles and novel features disclosed herein.
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