U.S. patent application number 13/942967 was filed with the patent office on 2013-11-14 for methods and apparatus for coordination of sending reference signals from multiple cells.
The applicant listed for this patent is Qualcomm Incorporated. Invention is credited to Luo Tao.
Application Number | 20130303157 13/942967 |
Document ID | / |
Family ID | 43354324 |
Filed Date | 2013-11-14 |
United States Patent
Application |
20130303157 |
Kind Code |
A1 |
Tao; Luo |
November 14, 2013 |
METHODS AND APPARATUS FOR COORDINATION OF SENDING REFERENCE SIGNALS
FROM MULTIPLE CELLS
Abstract
Methods and apparatus for coordination of sending reference
signals in wireless network are disclosed. A network node may
select a cell ID based on a measurement of adjacent cells so as to
mitigate interference. A network node may communicate information
to another network node to control transmitted resources in a
protected interval so as to measure channel characteristics.
Inventors: |
Tao; Luo; (San Diego,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Qualcomm Incorporated |
San Diego |
CA |
US |
|
|
Family ID: |
43354324 |
Appl. No.: |
13/942967 |
Filed: |
July 16, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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12818464 |
Jun 18, 2010 |
|
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13942967 |
|
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Current U.S.
Class: |
455/423 |
Current CPC
Class: |
H04W 84/047 20130101;
H04W 72/0426 20130101; Y02D 70/442 20180101; H04W 4/00 20130101;
H04L 5/0037 20130101; H04L 5/0035 20130101; Y02D 70/1264 20180101;
H04L 5/0073 20130101; Y02D 70/1222 20180101; Y02D 70/146 20180101;
H04W 72/082 20130101; Y02D 70/168 20180101; H04W 24/02 20130101;
H04L 5/005 20130101; Y02D 70/144 20180101; Y02D 70/24 20180101;
H04L 5/0058 20130101; Y02D 70/1262 20180101; H04L 25/0228 20130101;
H04L 5/0048 20130101; H04B 7/024 20130101; Y02D 70/1242 20180101;
H04W 84/045 20130101; Y02D 30/70 20200801; H04L 5/0094 20130101;
Y02D 70/142 20180101 |
Class at
Publication: |
455/423 |
International
Class: |
H04W 72/08 20060101
H04W072/08 |
Claims
1. A method, comprising: determining a time variation in an
interference level experienced by a receiver; generating a first
channel estimate of a wireless communication channel as of a first
time; generating a second channel estimate of the wireless
communication channel as of a second time; weighting the first
channel estimate and the second channel estimate in accordance with
the time variation, thereby generating a first weighted channel
estimate and a second weighted channel estimate; and computing a
weighted channel estimate based upon the first weighted channel
estimate and the second weighted channel estimate.
2. The method of claim 1, wherein the determining includes
measuring a parameter of a first reference signal received from a
first network node and a parameter of a second reference signal
received from a second network node.
3. The method of claim 1, wherein the first time occurs during a
first sub-frame period and wherein the second time occurs during a
second sub-frame period.
4. The method of claim 1, further including adjusting a filter
responsive based on the first weighted channel estimate and the
second weighted channel estimate.
5. A computer program product comprising a computer readable medium
including codes for causing a computer to: determine a time
variation in an interference level experienced by a receiver;
generate a first channel estimate of a wireless communication
channel as of a first time; generate a second channel estimate of
the wireless communication channel as of a second time; weight the
first channel estimate and the second channel estimate in
accordance with the time variation, thereby generating a first
weighted channel estimate and a second weighted channel estimate;
and compute a weighted channel estimate based upon the first
weighted channel estimate and the second weighted channel
estimate.
6. The computer program product of claim 5, wherein the determining
includes measuring a parameter of a first reference signal received
from a first network node and a parameter of a second reference
signal received from a second network node.
7. The computer program product of claim 5, wherein the first time
occurs during a first sub-frame period and wherein the second time
occurs during a second sub-frame period.
8. The computer program product of claim 5, further including
adjusting a filter responsive based on the first weighted channel
estimate and the second weighted channel estimate.
9. An apparatus for use in a communication system, comprising: a
receiver module configured to receive a signal from a wireless
communications channel and determine a time variation in an
interference level in the channel; and a channel estimation module
configured to: generate a first channel estimate of a wireless
communication channel as of a first time and a second channel
estimate of the wireless communication channel as of a second time;
weight the first channel estimate and the second channel estimate
in accordance with the time variation, thereby generating a first
weighted channel estimate and a second weighted channel estimate;
and compute a weighted channel estimate based upon the first
weighted channel estimate and the second weighted channel
estimate.
10. The apparatus of claim 9, wherein the determining includes
measuring a parameter of a first reference signal received from a
first network node and a parameter of a second reference signal
received from a second network node.
11. The apparatus of claim 9, wherein the first time occurs during
a first sub-frame period and wherein the second time occurs during
a second sub-frame period.
12. The apparatus of claim 9, further including adjusting a filter
responsive based on the first weighted channel estimate and the
second weighted channel estimate.
13. An apparatus for use in a communication system, comprising:
means for receiving a signal from a wireless communications channel
and determining a time variation in an interference level in the
channel; and means for generating a first channel estimate of a
wireless communication channel as of a first time and a second
channel estimate of the wireless communication channel as of a
second time; means for weighting the first channel estimate and the
second channel estimate in accordance with the time variation,
thereby generating a first weighted channel estimate and a second
weighted channel estimate; and means for computing a weighted
channel estimate based upon the first weighted channel estimate and
the second weighted channel estimate.
14. The apparatus of claim 13, wherein the means for determining
includes means for measuring a parameter of a first reference
signal received from a first network node and a parameter of a
second reference signal received from a second network node.
15. The apparatus of claim 13, wherein the first time occurs during
a first sub-frame period and wherein the second time occurs during
a second sub-frame period.
16. The apparatus of claim 13, further including means for
adjusting a filter responsive based on the first weighted channel
estimate and the second weighted channel estimate.
Description
CLAIM OF PRIORITY UNDER 35 U.S.C. .sctn.119
[0001] The present application for patent is a Divisional
application of application Ser. No. 12/818,464, ENTITLED METHOD AND
APPARATUS FOR COORDINATION OF SENDING REFERENCE SIGNALS FROM
MULTIPLE CELLS, filed Jun. 18, 2010 which claims priority to
Provisional Application Ser. No. 61/219,354, entitled METHODS OF
COORDINATION OF SENDING REFERENCE SIGNALS FROM MULTIPLE CELLS,
filed on Jun. 22, 2009, the content of which is hereby incorporated
by reference herein in its entirety for all purposes.
FIELD
[0002] This application is directed generally to wireless
communications systems. More particularly, but not exclusively, the
application relates to methods and apparatus for coordination of
sending reference signals from multiple cells, such as in a long
term evolution (LTE) network, as well as adjusting receivers based
on measured interference.
BACKGROUND
[0003] Wireless communication systems are widely deployed to
provide various types of communication content such as voice, data,
video and the like, and deployments are likely to increase with
introduction of new data oriented systems such as Long Term
Evolution (LTE) systems. Wireless communications systems may be
multiple-access systems capable of supporting communication with
multiple users by sharing the available system resources (e.g.,
bandwidth and transmit power). Examples of such multiple-access
systems include code division multiple access (CDMA) systems, time
division multiple access (TDMA) systems, frequency division
multiple access (FDMA) systems, 3GPP Long Term Evolution (LTE)
systems and other orthogonal frequency division multiple access
(OFDMA) systems.
[0004] Generally, a wireless multiple-access communication system
can simultaneously support communication for multiple wireless
terminals (also know as user equipments (UEs), or access terminals
(ATs). Each terminal communicates with one or more base stations
(also know as access points (APs), EnodeBs or eNBs) via
transmissions on forward and reverse links. The forward link (also
referred to as a downlink) refers to the communication link from
the base stations to the terminals, and the reverse link (also
referred to as an uplink) refers to the communication link from the
terminals to the base stations. These communication links may be
established via a single-in-single-out, single-in-multiple out,
multiple-in-single-out or a multiple-in-multiple-out (MIMO) system.
In MIMO systems, multiple antennas are used in both transmitters
and receivers to improve communications performance without
requiring additional transmit power or bandwidth. Next generation
systems such as Long Term Evolution (LTE) allow for use of MIMO
technology for enhanced performance and data throughput.
[0005] As the number of mobile stations deployed increases, the
need for proper bandwidth utilization becomes more important.
Moreover, with the introduction of semiautonomous base stations for
managing small cells, such as femtocells, in systems such as LTE,
interference with existing base stations may become an increasing
problem.
SUMMARY
[0006] This disclosure relates generally to methods and apparatus
for coordination of sending reference signals from multiple cells,
such as in an LTE system.
[0007] In one aspect, the disclosure is directed to a method
comprising receiving transmission coordination information provided
by a first wireless network node and controlling wireless
transmission from a second wireless network node in accordance with
the transmission coordination information.
[0008] In another aspect, the disclosure is directed to a computer
program product comprising a computer readable medium including
codes for causing a computer to receive transmission coordination
information provided by a first wireless network node and control
wireless transmission from a second wireless network node in
accordance with the transmission coordination information.
[0009] In another aspect, the disclosure is directed to an
apparatus for use in a communication system comprising a
coordination module configured to receive coordination information
from a network node and a transmitter module configured to transmit
a signal during a protected interval responsive to the coordination
information.
[0010] In another aspect, the disclosure is directed to a method
comprising receiving a first reference signal transmitted by a
first network node, receiving a second reference signal transmitted
by a second network node and modifying a functionality of a
receiver based upon a relationship between the first reference
signal and the second reference signal.
[0011] In another aspect, the disclosure is directed to a computer
program product comprising a computer readable medium including
codes for causing a computer to receive a first reference signal
transmitted by a first network node, receive a second reference
signal transmitted by a second network node, and modify a
functionality of a receiver based upon a relationship between the
first reference signal and the second reference signal.
[0012] In another aspect, the disclosure is directed to an
apparatus for use in a communication system comprising a receiver
module configured to receive a first reference signal transmitted
by a first network node and a second reference signal transmitted
by a second network node, and a control module configured to modify
a functionality of a receiver based upon a relationship between the
first reference signal and the second reference signal.
[0013] In another aspect, the disclosure is directed to a method
comprising determining a time variation in a measurable parameter
of one or more reference signals and modifying a functionality of a
receiver based upon the time variation.
[0014] In another aspect, the disclosure is directed to a computer
program product comprising a computer readable medium including
codes for causing a computer to determine a time variation in a
measurable parameter of one or more reference signals and modify a
functionality of a receiver based upon the time variation.
[0015] In another aspect, the disclosure is directed to an
apparatus for use in a communication system comprising a receiver
module configured to determine a time variation in a measurable
parameter of one or more reference signals, and a control module
configured to modify a functionality of a receiver based upon the
time variation.
[0016] In another aspect, the disclosure is directed to a method
comprising determining a time variation in an interference level
experienced by a receiver, generating a first channel estimate of a
wireless communication channel as of a first time, generating a
second channel estimate of the wireless communication channel as of
a second time, weighting the first channel estimate and the second
channel estimate in accordance with the time variation, thereby
generating a first weighted channel estimate and a second weighted
channel estimate, and computing a weighted channel estimate based
upon the first weighted channel estimate and the second weighted
channel estimate.
[0017] In another aspect, the disclosure is directed to a computer
program product comprising a computer readable medium including
codes for causing a computer to determine a time variation in an
interference level experienced by a receiver, generate a first
channel estimate of a wireless communication channel as of a first
time, generate a second channel estimate of the wireless
communication channel as of a second time, weight the first channel
estimate and the second channel estimate in accordance with the
time variation, thereby generating a first weighted channel
estimate and a second weighted channel estimate, and compute a
weighted channel estimate based upon the first weighted channel
estimate and the second weighted channel estimate.
[0018] In another aspect, the disclosure is directed to an
apparatus for use in a communication system comprising a receiver
module configured to receive a signal from a wireless
communications channel and determine a time variation in an
interference level in the channel and a channel estimation module
configured to generate a first channel estimate of a wireless
communication channel as of a first time and a second channel
estimate of the wireless communication channel as of a second time,
weight the first channel estimate and the second channel estimate
in accordance with the time variation, thereby generating a first
weighted channel estimate and a second weighted channel estimate,
and compute a weighted channel estimate based upon the first
weighted channel estimate and the second weighted channel
estimate.
[0019] In another aspect, the disclosure is directed to a method
comprising receiving a reference signal transmitted by a first
network node in accordance with a first reference signal resource
pattern and selecting, for a second network node, a cell identifier
associated with a second reference signal resource pattern
different from the first reference signal resource pattern.
[0020] In another aspect, the disclosure is directed to a computer
program product comprising a computer readable medium including
codes for causing a computer to receive a reference signal
transmitted by a first network node in accordance with a first
reference signal resource pattern and select for a second network
node, a cell identifier associated with a second reference signal
resource pattern different from the first reference signal resource
pattern.
[0021] In another aspect, the disclosure is directed to an
apparatus for use in a communication system comprising a receiver
module configured to receive a reference signal transmitted by a
first network node in accordance with a first reference signal
resource pattern, and a reference signal selector module configured
to select a cell identifier associated with a second reference
signal resource pattern different from the first reference signal
resource pattern.
[0022] Additional aspects are further described below in
conjunction with the appended drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The present application may be more fully appreciated in
connection with the following detailed description taken in
conjunction with the accompanying drawings, wherein:
[0024] FIG. 1 illustrates details of a wireless communications
system including multiple cells;
[0025] FIG. 2 illustrates details of a wireless communications
system;
[0026] FIG. 3 is a diagram illustrating elements of a wireless
communications system configured for coordination for interference
mitigation;
[0027] FIG. 4 showns an example process for selecting a cell ID to
mitigate interference in a wireless communications system;
[0028] FIG. 5 shows an example process for coordination
transmissions to facilitate channel measurements in a wireless
communications system;
[0029] FIG. 6 shows an example process for controlling receiver
functionality based on interference levels;
[0030] FIG. 7 shows an example process for receiver adjustment
based on sub-frame interference measurement;
[0031] FIG. 8 shows a methodology for managing interference in a
wireless communication system such as shown in FIG. 1; and
[0032] FIG. 9 is an example base station (eNB or HeNB) and
associated user terminal (UE) for use in a communication
system.
DETAILED DESCRIPTION
[0033] This disclosure relates generally to interference
coordination and management in wireless communications systems. In
various embodiments, the techniques and apparatus described herein
may be used for wireless communication networks such as Code
Division Multiple Access (CDMA) networks, Time Division Multiple
Access (TDMA) networks, Frequency Division Multiple Access (FDMA)
networks, Orthogonal FDMA (OFDMA) networks, Single-Carrier FDMA
(SC-FDMA) networks, LTE networks, as well as other communications
networks. As described herein, the terms "networks" and "systems"
may be used interchangeably.
[0034] In one aspect, the disclosure is directed to a method
comprising receiving transmission coordination information provided
by a first wireless network node and controlling wireless
transmission from a second wireless network node in accordance with
the transmission coordination information.
[0035] In another aspect, the disclosure is directed to a computer
program product comprising a computer readable medium including
codes for causing a computer to receive transmission coordination
information provided by a first wireless network node and control
wireless transmission from a second wireless network node in
accordance with the transmission coordination information.
[0036] In another aspect, the disclosure is directed to an
apparatus for use in a communication system comprising a
coordination module configured to receive coordination information
from a network node and a transmitter module configured to transmit
a signal during a protected interval responsive to the coordination
information.
[0037] In another aspect, the disclosure is directed to a method
comprising receiving a first reference signal transmitted by a
first network node, receiving a second reference signal transmitted
by a second network node and modifying a functionality of a
receiver based upon a relationship between the first reference
signal and the second reference signal.
[0038] In another aspect, the disclosure is directed to a computer
program product comprising a computer readable medium including
codes for causing a computer to receive a first reference signal
transmitted by a first network node, receive a second reference
signal transmitted by a second network node, and modify a
functionality of a receiver based upon a relationship between the
first reference signal and the second reference signal.
[0039] In another aspect, the disclosure is directed to an
apparatus for use in a communication system comprising a receiver
module configured to receive a first reference signal transmitted
by a first network node and a second reference signal transmitted
by a second network node, and a control module configured to modify
a functionality of a receiver based upon a relationship between the
first reference signal and the second reference signal.
[0040] In another aspect, the disclosure is directed to a method
comprising determining a time variation in a measurable parameter
of one or more reference signals and modifying a functionality of a
receiver based upon the time variation.
[0041] In another aspect, the disclosure is directed to a computer
program product comprising a computer readable medium including
codes for causing a computer to determine a time variation in a
measurable parameter of one or more reference signals and modify a
functionality of a receiver based upon the time variation.
[0042] In another aspect, the disclosure is directed to an
apparatus for use in a communication system comprising a receiver
module configured to determine a time variation in a measurable
parameter of one or more reference signals, and a control module
configured to modify a functionality of a receiver based upon the
time variation.
[0043] In another aspect, the disclosure is directed to a method
comprising determining a time variation in an interference level
experienced by a receiver, generating a first channel estimate of a
wireless communication channel as of a first time, generating a
second channel estimate of the wireless communication channel as of
a second time, weighting the first channel estimate and the second
channel estimate in accordance with the time variation, thereby
generating a first weighted channel estimate and a second weighted
channel estimate, and computing a weighted channel estimate based
upon the first weighted channel estimate and the second weighted
channel estimate.
[0044] In another aspect, the disclosure is directed to a computer
program product comprising a computer readable medium including
codes for causing a computer to determine a time variation in an
interference level experienced by a receiver, generate a first
channel estimate of a wireless communication channel as of a first
time, generate a second channel estimate of the wireless
communication channel as of a second time, weight the first channel
estimate and the second channel estimate in accordance with the
time variation, thereby generating a first weighted channel
estimate and a second weighted channel estimate, and compute a
weighted channel estimate based upon the first weighted channel
estimate and the second weighted channel estimate.
[0045] In another aspect, the disclosure is directed to an
apparatus for use in a communication system comprising a receiver
module configured to receive a signal from a wireless
communications channel and determine a time variation in an
interference level in the channel and a channel estimation module
configured to generate a first channel estimate of a wireless
communication channel as of a first time and a second channel
estimate of the wireless communication channel as of a second time,
weight the first channel estimate and the second channel estimate
in accordance with the time variation, thereby generating a first
weighted channel estimate and a second weighted channel estimate,
and compute a weighted channel estimate based upon the first
weighted channel estimate and the second weighted channel
estimate.
[0046] In another aspect, the disclosure is directed to a method
comprising receiving a reference signal transmitted by a first
network node in accordance with a first reference signal resource
pattern and selecting, for a second network node, a cell identifier
associated with a second reference signal resource pattern
different from the first reference signal resource pattern.
[0047] In another aspect, the disclosure is directed to a computer
program product comprising a computer readable medium including
codes for causing a computer to receive a reference signal
transmitted by a first network node in accordance with a first
reference signal resource pattern and select for a second network
node, a cell identifier associated with a second reference signal
resource pattern different from the first reference signal resource
pattern.
[0048] In another aspect, the disclosure is directed to an
apparatus for use in a communication system comprising a receiver
module configured to receive a reference signal transmitted by a
first network node in accordance with a first reference signal
resource pattern, and a reference signal selector module configured
to select a cell identifier associated with a second reference
signal resource pattern different from the first reference signal
resource pattern.
[0049] Various other aspects and features of the disclosure are
further described below. It should be apparent that the teachings
herein may be embodied in a wide variety of forms and that any
specific structure, function, or both being disclosed herein is
merely representative. Based on the teachings herein one skilled in
the art should appreciate that an aspect disclosed herein may be
implemented independently of any other aspects and that two or more
of these aspects may be combined in various ways. For example, an
apparatus may be implemented or a method may be practiced using any
number of the aspects set forth herein. In addition, such an
apparatus may be implemented or such a method may be practiced
using other structure, functionality, or structure and
functionality in addition to or other than one or more of the
aspects set forth herein. Furthermore, an aspect may comprise at
least one element of a claim.
[0050] A CDMA network may implement a radio technology such as
Universal Terrestrial Radio Access (UTRA), cdma2000 and the like.
UTRA includes Wideband-CDMA (W-CDMA) and Low Chip Rate (LCR).
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).
[0051] An OFDMA network may implement a radio technology such as
Evolved UTRA (E-UTRA), IEEE 802.11, IEEE 802.16, IEEE 802.20,
Flash-OFDM and the like. UTRA, E-UTRA, and GSM are part of
Universal Mobile Telecommunication System (UMTS). In particular,
Long Term Evolution (LTE) is a release of UMTS that uses E-UTRA.
UTRA, E-UTRA, GSM, UMTS and LTE are described in documents provided
from an organization named "3rd Generation Partnership Project"
(3GPP), and cdma2000 is described in documents from an organization
named "3rd Generation Partnership Project 2" (3GPP2). These various
radio technologies and standards are known or are being developed
in the art. For example, the 3rd Generation Partnership Project
(3GPP) is a collaboration between groups of telecommunications
associations that aims to define a globally applicable third
generation (3G) mobile phone specification. 3GPP Long Term
Evolution (LTE) is a 3GPP project aimed at improving the Universal
Mobile Telecommunications System (UMTS) mobile phone standard. The
3GPP may define specifications for the next generation of mobile
networks, mobile systems, and mobile devices. For clarity, certain
aspects of the apparatus and techniques are described below for LTE
implementations, and LTE terminology is used in much of the
description below; however, the description is not intended to be
limited to LTE applications. Accordingly, it will be apparent to
one of skill in the art that the apparatus and methods described
herein may be applied to various other communications systems and
applications.
[0052] Logical channels in wireless communications systems may be
classified into Control Channels and Traffic Channels. Logical
Control Channels may comprise a Broadcast Control Channel (BCCH)
which is a downlink (DL) channel for broadcasting system control
information, a Paging Control Channel (PCCH) which is a DL channel
that transfers paging information and a Multicast Control Channel
(MCCH) which is a point-to-multipoint DL channel used for
transmitting Multimedia Broadcast and Multicast Service (MBMS)
scheduling and control information for one or several MTCHs.
Generally, after establishing a Radio Resource Control (RRC)
connection this channel is only used by UEs that receive MBMS. A
Dedicated Control Channel (DCCH) is a point-to-point bi-directional
channel that transmits dedicated control information and is used by
UEs having an RRC connection.
[0053] Logical Traffic Channels may comprise a Dedicated Traffic
Channel (DTCH) which is point-to-point bi-directional channel,
dedicated to one UE, for the transfer of user information, and a
Multicast Traffic Channel (MTCH) for Point-to-multipoint DL channel
for transmitting traffic data.
[0054] Transport Channels may be classified into downlink (DL) and
uplink (UL) Transport Channels. DL Transport Channels may comprise
a Broadcast Channel (BCH), Downlink Shared Data Channel (DL-SDCH)
and a Paging Channel (PCH). The PCH may be used for support of UE
power saving (when a DRX cycle is indicated by the network to the
UE), broadcast over an entire cell and mapped to Physical Layer
(PHY) resources which can be used for other control/traffic
channels. The UL Transport Channels may comprise a Random Access
Channel (RACH), a Request Channel (REQCH), an Uplink Shared Data
Channel (UL-SDCH) and a plurality of PHY channels. The PHY channels
may comprise a set of DL channels and UL channels.
[0055] In addition, the DL PHY channels may comprise the following:
[0056] Common Pilot Channel (CPICH) [0057] Synchronization Channel
(SCH) [0058] Common Control Channel (CCCH) [0059] Shared DL Control
Channel (SDCCH) [0060] Multicast Control Channel (MCCH) [0061]
Shared UL Assignment Channel (SUACH) [0062] Acknowledgement Channel
(ACKCH) [0063] DL Physical Shared Data Channel (DL-PSDCH) [0064] UL
Power Control Channel (UPCCH) [0065] Paging Indicator Channel
(PICH) [0066] Load Indicator Channel (LICH) [0067] The UL PHY
Channels may comprise the following: [0068] Physical Random Access
Channel (PRACH) [0069] Channel Quality Indicator Channel (CQICH)
[0070] Acknowledgement Channel (ACKCH) [0071] Antenna Subset
Indicator Channel (ASICH) [0072] Shared Request Channel (SREQCH)
[0073] UL Physical Shared Data Channel (UL-PSDCH) [0074] Broadband
Pilot Channel (BPICH)
[0075] The word "exemplary" is used herein to mean "serving as an
example, instance, or illustration." Any aspect and/or embodiment
described herein as "exemplary" is not necessarily to be construed
as preferred or advantageous over other aspects and/or
embodiments.
[0076] For purposes of explanation of various aspects and/or
embodiments, the following terminology and abbreviations may be
used herein: [0077] AM Acknowledged Mode [0078] AMD Acknowledged
Mode Data [0079] ARQ Automatic Repeat Request [0080] BCCH Broadcast
Control CHannel [0081] BCH Broadcast CHannel [0082] C- Control-
[0083] CCCH Common Control CHannel [0084] CCH Control CHannel
[0085] CCTrCH Coded Composite Transport Channel [0086] CP Cyclic
Prefix [0087] CRC Cyclic Redundancy Check [0088] CTCH Common
Traffic CHannel [0089] DCCH Dedicated Control CHannel [0090] DCH
Dedicated CHannel [0091] DL DownLink [0092] DSCH Downlink Shared
CHannel [0093] DTCH Dedicated Traffic CHannel [0094] FACH Forward
link Access CHannel [0095] FDD Frequency Division Duplex [0096] L1
Layer 1 (physical layer) [0097] L2 Layer 2 (data link layer) [0098]
L3 Layer 3 (network layer) [0099] LI Length Indicator [0100] LSB
Least Significant Bit [0101] MAC Medium Access Control [0102] MBMS
Multmedia Broadcast Multicast Service [0103] MCCH MBMS
point-to-multipoint Control CHannel [0104] MRW Move Receiving
Window [0105] MSB Most Significant Bit [0106] MSCH MBMS
point-to-multipoint Scheduling CHannel [0107] MTCH MBMS
point-to-multipoint Traffic CHannel [0108] PCCH Paging Control
CHannel [0109] PCH Paging CHannel [0110] PDU Protocol Data Unit
[0111] PHY PHYsical layer [0112] PhyCH Physical CHannels [0113]
RACH Random Access CHannel [0114] RLC Radio Link Control [0115] RRC
Radio Resource Control [0116] SAP Service Access Point [0117] SDU
Service Data Unit [0118] SHCCH SHared channel Control CHannel
[0119] SN Sequence Number [0120] SUFI SUper FIeld [0121] TCH
Traffic CHannel [0122] TDD Time Division Duplex [0123] TFI
Transport Format Indicator [0124] TM Transparent Mode [0125] TMD
Transparent Mode Data [0126] TTI Transmission Time Interval [0127]
U- User- [0128] UE User Equipment [0129] UL UpLink [0130] UM
Unacknowledged Mode [0131] UMD Unacknowledged Mode Data [0132] UMTS
Universal Mobile Telecommunications System [0133] UTRA UMTS
Terrestrial Radio Access [0134] UTRAN UMTS Terrestrial Radio Access
Network [0135] MBSFN Multicast broadcast single frequency network
[0136] MCE MBMS coordinating entity [0137] MCH Multicast channel
[0138] DL-SCH Downlink shared channel [0139] MSCH MBMS control
channel [0140] PDCCH Physical downlink control channel [0141] PDSCH
Physical downlink shared channel
[0142] A MIMO system employs multiple (N.sub.T) transmit antennas
and multiple (N.sub.R) receive antennas for data transmission. A
MIMO channel formed by the N.sub.T transmit and N.sub.R receive
antennas may be decomposed into N.sub.S independent channels, which
are also referred to as spatial channels. The maximum spatial
multiplexing N.sub.S if a linear receiver is used is min(N.sub.T,
N.sub.R), with each of the N.sub.S independent channels
corresponding to a dimension. This provides an N.sub.S increase in
spectral efficiency. A MIMO system can provide improved performance
(e.g., higher throughput and/or greater reliability) if the
additional dimensionalities created by the multiple transmit and
receive antennas are utilized. The special dimension may be
described in terms of a rank.
[0143] MIMO systems support time division duplex (TDD) and
frequency division duplex (FDD) implementations. In a TDD system,
the forward and reverse link transmissions use the same frequency
regions so that the reciprocity principle allows the estimation of
the forward link channel from the reverse link channel. This
enables the access point to extract transmit beamforming gain on
the forward link when multiple antennas are available at the access
point.
[0144] System designs may support various time-frequency reference
signals for the downlink and uplink to facilitate beamforming and
other functions. A reference signal is a signal generated based on
known data and may also be referred to as a pilot, preamble,
training signal, sounding signal and the like. A reference signal
may be used by a receiver for various purposes such as channel
estimation, coherent demodulation, channel quality measurement,
signal strength measurement and the like. MIMO systems using
multiple antennas generally provide for coordination of sending of
reference signals between antennas, however, LTE systems do not in
general provide for coordination of sending of reference signals
from multiple base stations or eNBs.
[0145] 3GPP Specification 36211-900 defines in Section 5.5
particular reference signals for demodulation, associated with
transmission of PUSCH or PUCCH, as well as sounding, which is not
associated with transmission of PUSCH or PUCCH. For example, Table
1 lists some reference signals for LTE implementations that may be
transmitted on the downlink and uplink and provides a short
description for each reference signal. A cell-specific reference
signal may also be referred to as a common pilot, a broadband pilot
and the like. A UE-specific reference signal may also be referred
to as a dedicated reference signal.
TABLE-US-00001 TABLE 1 Link Reference Signal Description Downlink
Cell Specific Reference signal sent by a Node B Reference Signal
and used by the UEs for channel estimation and channel quality
measurement. Downlink UE Specific Reference signal sent by a Node B
Reference Signal to a specific UE and used for demodulation of a
downlink transmission from the Node B. Uplink Sounding Reference
signal sent by a UE and Reference Signal used by a Node B for
channel estimation and channel quality measurement. Uplink
Demodulation Reference signal sent by a UE and Reference Signal
used by a Node B for demodulation of an uplink transmission from
the UE.
[0146] In some implementations a system may utilize time division
duplexing (TDD). For TDD, the downlink and uplink share the same
frequency spectrum or channel, and downlink and uplink
transmissions are sent on the same frequency spectrum. The downlink
channel response may thus be correlated with the uplink channel
response. A reciprocity principle may allow a downlink channel to
be estimated based on transmissions sent via the uplink. These
uplink transmissions may be reference signals or uplink control
channels (which may be used as reference symbols after
demodulation). The uplink transmissions may allow for estimation of
a space-selective channel via multiple antennas.
[0147] In LTE implementations orthogonal frequency division
multiplexing is used for the downlink--that is, from the base
station, access point or eNodeB to the terminal or UE. Use of OFDM
meets the LTE requirement for spectrum flexibility and enables
cost-efficient solutions for very wide carriers with high peak
rates, and is a well-established technology, for example OFDM is
used in standards such as IEEE 802.11a/g, 802.16, HIPERLAN-2, DVB
and DAB.
[0148] Time frequency physical resource blocks (also denoted here
in as resource blocks or "RBs" for brevity) may be defined in OFDM
systems as groups of transport carriers (e.g. sub-carriers) or
intervals that are assigned to transport data. The RBs are defined
over a time and frequency period. Resource blocks are comprised of
time-frequency resource elements (also denoted here in as resource
elements or "REs" for brevity), which may be defined by indices of
time and frequency in a slot. Additional details of LTE RBs and REs
are described in 3GPP TS 36.211.
[0149] UMTS LTE supports scalable carrier bandwidths from 20 MHz
down to 1.4 MHZ. In LTE, an RB is defined as 12 sub-carriers when
the sub-carrier bandwidth is 15 kHz, or 24 sub-carriers when the
sub-carrier bandwidth is 7.5 kHz. In an exemplary implementation,
in the time domain there is a defined radio frame that is 10 ms
long and consists of 10 sub frames of 1 ms each. Every sub frame
consists of 2 slots, where each slot is 0.5 ms. The subcarrier
spacing in the frequency domain in this case is 15 kHz. +Twelve of
these subcarriers together (per slot) constitutes an RB, so in this
implementation one resource block is 180 kHz. 6 Resource blocks fit
in a carrier of 1.4 MHz and 100 resource blocks fit in a carrier of
20 MHz.
[0150] In the downlink there are typically a number of physical
channels as described above. In particular, the PDCCH is used for
sending control, the PHICH for sending ACK/NACK, the PCFICH for
specifying the number of control symbols, the Physical Downlink
Shared Channel (PDSCH) for data transmission, the Physical
Multicast Channel (PMCH) for broadcast transmission using a Single
Frequency Network, and the Physical Broadcast Channel (PBCH) for
sending important system information within a cell. Supported
modulation formats on the PDSCH in LTE are QPSK, 16QAM and
64QAM.
[0151] In the uplink there are typically three physical channels.
While the Physical Random Access Channel (PRACH) is only used for
initial access and when the UE is not uplink synchronized, the data
is sent on the Physical Uplink Shared Channel (PUSCH). If there is
no data to be transmitted on the uplink for a UE, control
information would be transmitted on the Physical Uplink Control
Channel (PUCCH). Supported modulation formats on the uplink data
channel are QPSK, 16QAM and 64QAM.
[0152] If virtual MIMO/spatial division multiple access (SDMA) is
introduced the data rate in the uplink direction can be increased
depending on the number of antennas at the base station. With this
technology more than one mobile can reuse the same resources. For
MIMO operation, a distinction is made between single user MIMO, for
enhancing one user's data throughput, and multi user MIMO for
enhancing the cell throughput.
[0153] In 3GPP LTE, a mobile station or device may be referred to
as a "user device" or "user equipment" (UE). A base station may be
referred to as an evolved NodeB or eNB. A semi-autonomous base
station may be referred to as a home eNB or HeNB. An HeNB may thus
be one example of an eNB. The HeNB and/or the coverage area of an
HeNB may be referred to as a femtocell, an HeNB cell or a closed
subscriber group (CSG) cell (where access is restricted).
[0154] Attention is now directed to FIG. 1, which shows a wireless
communication system 100 with multiple user equipments (UEs) 104, a
home evolved NodeB (HeNB) 110, two evolved NodeBs (eNB) 102, 132, a
relay node 106, and a core or backhaul network 108. The eNB 102 may
be the central base station in a wireless communication system. The
eNB 132 may be an eNB in an adjacent macrocell (denoted as Macro
Cell 2), and may be associated with components such as those shown
in FIG. 1 in communication with Macro Cell 1 (components are
omitted from FIG. 1 for clarity). A UE 104 may also be called, and
may contain some or all of the functionality of, a terminal, a
mobile station, an access terminal, a subscriber unit, a station,
etc. A UE 104 may be a cellular phone, a personal digital assistant
(PDA), a wireless device, a wireless modem, a handheld device, a
laptop computer, etc.
[0155] The core network 108 may be the central piece of a
telecommunications network. For example, the core network 108 may
facilitate communications with the Internet, other UEs, etc. A UE
104 may communicate with the core network 108 through an eNB 102,
132 or an HeNB 110. Multiple UEs 104 may be in wireless
communication with an eNB 102 or an HeNB 110. eNBs 102 and 132, and
HeNB 110 may communicate with the core network and/or to each other
either directly or through the core network 108.
[0156] The term "eNB" may be used to refer to the eNB 102 or to the
HeNB 110, because the HeNB 110 may be considered to be one type of
eNB. The eNB 102 may be referred to as a macro-eNB 102 or macrocell
eNB 102. A macro-eNB 102 may have a much larger range than an HeNB
110. Furthermore, a macro-eNB 102 may provide unrestricted access
to UEs 104a subscribing to the core network 108 (i.e., in a non-CSG
configuration). In contrast, an HeNB 110 may provide restricted
access to UEs 104b belonging to a closed subscriber group (CSG). It
may be assumed that a UE 104 may only communicate with a single eNB
at a given time. Thus, a UE 104b communicating with an HeNB 110 may
not generally simultaneously communicate with a macro-eNB 102,
however, some communication may be performed to facilitate UE
management, inter-cell coordination, etc. This will generally
include transfer of control information but not data.
[0157] The coverage area of an eNB may be referred to as a cell.
Depending on sectoring, one or more cells may be served by the eNB.
The coverage area of a macroeNB 102 may be referred to as a
macrocell 112 or an eNB cell (shown as Macro Cell 1 in FIG. 1).
Likewise, the coverage area of an HeNB 110 may be referred to as an
HeNB-cell 114 or a femtocell. As shown in FIG. 1, multiple cells
may be adjacent to and/or overlapping. For example, in FIG. 1,
Macro Cells 1 and 2 overlap femtocell 114. Obviously, many other
variations of adjacent and/or overlapping cells are possible in
various system implementations.
[0158] Multiple eNBs may have a backhaul connection with each other
through the core network 108. For example, a backhaul connection
may exist between the HeNB 110 and eNBs 102 and 132. In a backhaul
connection, an eNB may communicate with the core network 108 and
the core network 108 may correspondingly communicate with the HeNB
110. A direct connection may also exist between multiple eNBs.
[0159] For example, a direct connection may exist between the HeNB
110 and the eNB 102. The direct connection may be an X2 connection
120. Details about an X2 interface may be found in, for example,
3GPP TS 36.423 X2-AP. Multiple eNBs may also have a connection 122,
124 through use of a relay node 106. In one configuration, the
relay node 106 may be the core network 108.
[0160] The coverage range for a macrocell 112 may be much larger
than the coverage range for an HeNB-cell 114. In one configuration,
the coverage range for a macrocell 112 may include the entire
coverage range for an HeNB-cell 114.
[0161] A UE 104 may communicate with a base station (e.g., the eNB
102 or the HeNB 110) via transmissions on an uplink 116 and a
downlink 118. The uplink 116 (or reverse link) refers to the
communication link from the UE 104 to a base station, and the
downlink 118 (or forward link) refers to the communication link
from the base station to the UE 104. Thus, a UE 104a may
communicate with the eNB 102 via the uplink 116a and downlink 118a.
Likewise, a UE 104b may communicate with the HeNB 110 via the
uplink 116b and downlink 118b.
[0162] The resources of the wireless communication system 100
(e.g., bandwidth and transmit power) may be shared among multiple
UEs 104. A variety of multiple access techniques are known,
including code division multiple access (CDMA), time division
multiple access (TDMA), frequency division multiple access (FDMA),
orthogonal frequency division multiple access (OFDMA),
single-carrier frequency division multiple access (SC-FDMA), and so
forth.
[0163] In some configurations, one or more macro-UEs 104a located
within an HeNB-cell 114 may cause interference so as to interfere
with or jam the HeNB-cell 114. For example, a macro-UE 104a located
within an HeNB-cell 114 may cause interference for communications
between an HeNB-UE 104b and the HeNB 110. Likewise, a macro-UE 104a
within the HeNB-cell 114 may not have macrocell 112 coverage due to
interference from other HeNBs or eNBs. Both uplink interference 130
and downlink interference 132 may occur.
[0164] If there are no UEs 104 in the CSG cell (e.g., HeNB cell
114), there may be no interference issues. In order to allow a
successful initial access by a UE 104 to the CSG cell, the CSG cell
may dynamically bias the open loop power control algorithm to
balance the effect of high interference. CSG cells may also add
noise to balance the uplink 116 and the downlink 118.
[0165] Inter-cell interference coordination (ICIC) may be used to
prevent the uplink interference 130 and/or the downlink
interference 132. Frequency ICIC may be feasible for both
synchronous and asynchronous deployments. Time ICIC may be feasible
in synchronized deployments. Inter-cell interference coordination
and mitigation may be facilitated by coordination and control of
transmissions between combinations of eNBs and HeNBs, by
self-selection of cell ID, and/or by interference monitoring and
receiver adjustment.
[0166] In one aspect, interference management may be facilitated by
determining information associated with a cell node at the UE and
supplying the information to the node (eNB or HeNB). The
information may include spatial channel information, power level
information, or other information associated with the femtocell or
femtocell node. For example, the UE may determine Reference Signal
Received Power (RSRP), which for a particular cell may be the
average power measured (and the average between receiver branches)
of the resource elements that contain cell specific reference
signals. The UE may also determine Reference Signal Received
Quality (RSRQ) as the ratio of the RSRP and the E-UTRA Carrier
Received Signal Strength Indicator (RSSI), for the reference
signals. The UE may also determine other signal metrics. For
example, the UE may determine power used (power contribution) for
the resource elements that are used to transmit cell-specific
reference signals from an eNB or HeNB (in the system bandwidth).
The UE may also determine a Channel Quality Indicator (CQI), a Rank
Indicator (RI), and a Precoding Matrix Indicator (PMI). The CQI
provides information to the eNB or HeNB about the link adaptation
parameters the UE can support at the time. The CQI is a table
containing modulation and coding information. The RI is a UE
recommendation for the number of layers, i.e., streams, to be used
in spatial multiplexing. The UE may also determine received
interference power per physical resource block, as well as thermal
noise power over the system bandwidth.
[0167] Spatial channel information may be determined and composed
in a measurement report to be sent to an eNB or HeNB. The spatial
information and/or power information may then be used by the node
to coordinate transmissions from other nodes so as to mitigate
interference with the UE. Information may be communicated directl
between eNBs and/or HeNBs or may be relayed using backhaul
signaling.
[0168] In various implementations, power determination of the
adjacent channel may be based on particular components or
subcarriers of the adjacent channel signal, which may
correspondingly be based on the adjacent network type. For example,
the received power may be determined based on a particular
subcarrier or signal in the adjacent channel, such as a pilot
signal, with the determined power based on a measurement of the
pilot signal. The pilot signal may be a pilot signal in a dedicated
or allocated pilot sub-channel of the adjacent channel. For
example, reference signals, as are defined with respect to LTE, may
be used as a pilot signal and processed to determine power level.
In UTRA implementations, alternate pilot signals are used and these
may be used to determine adjacent network power metrics and levels.
Channel characteristics, such as fading characteristics, may be
determined through use of reference signals and may be reported to
eNBs or HeNBs.
[0169] In some implementations, an average or peak power level
measurement may be made on the adjacent channel signal. This may
be, for example, a power density determination made on the adjacent
channel signal. Other power determinations may also be used and/or
combined with those described above. For example, in one
implementation, a power density measurement may be combined with a
peak determination or pilot signal determination to generate a
power level metric.
[0170] In some implementations, the received signal power level
metric may be based on a Reference Signal Received Power (RSRP) per
resource element, with the determining including determining the
Reference Signal Received Power per resource element by measuring,
at the node, a Reference Signal transmitted on one of the adjacent
channels. In addition, the RSRP may be based on the average of RSRP
per resource element across multiple transmit antennas, such as in
a MIMO system.
[0171] FIG. 2 illustrates a wireless communication system 200 with
a macro-eNB 202 and multiple HeNBs 210. The wireless communication
system 200 may include an HeNB gateway 234 for scalability reasons.
The macro-eNB 202 and the HeNB gateway 234 may each communicate
with a pool 240 of mobility management entities (MME) 242 and a
pool 244 of serving gateways (SGW) 246. The HeNB gateway 234 may
appear as a C-plane and a U-plane relay for dedicated S1
connections 236. An S1 connection 236 may be a logical interface
specified as the boundary between an evolved packet core (EPC) and
an Evolved Universal Terrestrial Access Network (EUTRAN). The HeNB
gateway 234 may act as a macro-eNB 202 from an EPC point of view.
The C-plane interface may be S1-MME and the U-plane interface may
be S1-U.
[0172] The HeNB gateway 234 may act towards an HeNB 210 as a single
EPC node. The HeNB gateway 234 may ensure S1-flex connectivity for
an HeNB 210. The HeNB gateway 234 may provide a 1:n relay
functionality such that a single HeNB 210 may communicate with n
MMEs 242. The HeNB gateway 234 registers towards the pool 240 of
MMEs 242 when put into operation via the S1 setup procedure. The
HeNB gateway 234 may support setup of S1 interfaces 236 with the
HeNBs 210.
[0173] The wireless communication system 200 may also include a
self organizing network (SON) server 238. The SON server 238 may
provide automated optimization of a 3GPP LTE network. The SON
server 238 may be a key driver for improving operation and
maintenance (O&M) to the wireless communication system 200. An
X2 link 220 may exist between the macro-eNB 202 and the HeNB
gateway 234. X2 links 220 may also exist between each of the HeNBs
210 connected to a common HeNB gateway 234. The X2 links 220 may be
set up based on input from the SON server 238. An X2 link 220 may
convey ICIC information. If an X2 link 220 cannot be established,
the S1 link 236 may be used to convey ICIC information. Backhaul
signaling may be used in communication system 200 to manage
interference mitigation between macro-eNB 202 and HeNBs 210.
[0174] Attention is now directed to FIG. 3, which illustrates an
embodiment of a network 300 employing coordination components
configured to mitigate interference across a wireless network
310.
[0175] It is noted that the system 300 can be employed with an
access terminal or mobile device, and can be, for instance, a
module such as an SD card, a network card, a wireless network card,
a computer (including laptops, desktops, personal digital
assistants (PDAs)), mobile phones, smart phones, or any other
suitable terminal that can be utilized to access a network. The
terminal accesses the network by way of an access component (not
shown). In one example, a connection between the terminal and the
access components may be wireless in nature, in which access
components may be the base station and the mobile device is a
wireless terminal For instance, the terminal and base stations may
communicate by way of any suitable wireless protocol, including but
not limited to Time Divisional Multiple Access (TDMA), Code
Division Multiple Access (CDMA), Frequency Division Multiple Access
(FDMA), Orthogonal Frequency Division Multiplexing (OFDM), FLASH
OFDM, Orthogonal Frequency Division Multiple Access (OFDMA), or any
other suitable protocol.
[0176] Access components can be an access node associated with a
wired network or a wireless network. To that end, access components
can be, for instance, a router, a switch, or the like. The access
component can include one or more interfaces, e.g., communication
modules, for communicating with other network nodes. Additionally,
the access component can be a base station (or wireless access
point) in a cellular type network, wherein base stations (or
wireless access points) are utilized to provide wireless coverage
areas to a plurality of subscribers. Such base stations (or
wireless access points) can be arranged to provide contiguous areas
of coverage to one or more cellular phones and/or other wireless
terminals.
[0177] System 300 may correspond to the wireless networks shown in
FIGS. 1 and 2. System 300 may include one or more base stations 320
(also referred to as a node, evolvedNode B--eNB, serving eNB,
target eNB, femto station, pico station and the like) which can be
an entity capable of communication over the wireless network 310 to
various devices 330. For instance, each device 330 can be an access
terminal (also referred to as terminal, user equipment (UE),
mobility management entity (MME) or mobile device) or in some cases
may be an eNB or HeNB. For purposes of brevity, the device 330 will
be referred to here in as a UE and the base station 320 will be
referred to herein as an eNB or HeNB. The eNB 320 and UE 330 may
include coordination components 340 and 344 respectively, which may
comprise hardware, software, firmware or combinations of these
elements in various embodiments. It is to be appreciated that
coordination to mitigate interference may occur between base
stations, between base stations and devices, and/or between base
stations, devices, and other network components such as a network
manager or server. Coordination may include communicative
connections between mobile devices and base stations, base stations
and base stations, or mobile devices and mobile devices.
Communications may be via wireless links or may be via wired
connections such as backhaul connections.
[0178] As shown, the eNB 320 may communicate to the UE 330 (or UEs
330) via downlink 360 and may receive data via uplink 370. Such
designation as uplink and downlink is arbitrary as the UE 330 can
also transmit data via downlink and receive data via uplink
channels. It is noted that although two network components 320 and
330 are shown, that more than two components can be employed on the
network 310 in various configurations, with such additional
components also being adapted for reference signal coordination as
described herein.
[0179] In general, when the UE 330 cannot connect a desired cell
with the strongest downlink channel, it may see strong interference
in various downlink scenarios or applications. The strongest
downlink channel is generally the one with the strongest reference
signals. When a UE cannot connect to a desired cell with the
strongest downlink channel (for example, a UE in proximity to a
restricted HeNB, such UE 104 in proximity to HeNB 110 as shown in
FIG. 1), or where the downlink may be good but the uplink is not,
the UE may benefit from interference mitigation.
[0180] For systems deploying with varying transmitting power and/or
with restricted association, or where the eNB 330 tries to balance
loading by offloading some users from one cell to a different cell,
such as between macrocells 1 and 2 as shown in FIG. 1, the UE may
use interference cancellation or other advanced receivers to
improve the receiver performance. Channel estimates are important
for those advanced receivers. Channel estimation may be facilitated
in systems such as LTE systems through use of reference signals,
which may be arranged in resource blocks so as to allow a receiver
to determine channel characteristics such as fading, power levels
and the like by measuring and processing the received reference
signals.
[0181] Consequently, it is desirable that the reference signal does
not see strong interference, which may come from other components
of a network such as are shown in FIG. 1, including other eNBs
and/or HeNBs. Accordingly, in self organizing network
configurations (SONs), where deployment of HeNBs may be done in a
relatively uncontrolled fashion and/or may vary over time, the eNB
(or HeNB) 320 may choose a cell identity to prevent cell ID
collision with other cells such as other macro, pico, and/or
femtocells, for example. Alternately, or in addition, further cell
ID selection criteria may be enforced such that at least the
reference signal will not see strong interference (for example, by
halting data or control information transmission during
time-frequency resources allocated to the reference signals).
[0182] Generally, reference signal resource mappings in the
frequency domain are linked to the cell ID, where different cell
IDs may have different frequency shifts. There are limited number
of frequency locations that can be reused for reference signal. In
some implementations an eNB or HeNB may search and find a suitable
cell ID for itself. For example, the nodes may be part of a self
organizing network (SON), e.g., where a femto cell may search for a
suitable cell ID before configuring its respective cell ID. In an
exemplary embodiment, the cell ID is selected so that the
associated reference signals are orthogonal to another cell's
reference signals. This may be done based on the shifts as defined
in LTE, where in a 1 antenna MIMO system there are 6 available
shifts, and in a 2 antenna system there are 3 available shifts.
[0183] Accordingly, system 300 may be configured to mitigate
interference in wireless communications networks 310. In one
aspect, if a base station such as an HeNB or eNB locates a strong
adjacent cell, the eNB or HeNB can select a cell ID such that the
associated reference signal is selected to mitigate interference
with other known cells/reference signal patterns. For example, a
reference signal may be selected so that its signal mappings are
orthogonal to this strong cell, such as where a reference signal
occupies different frequency resources used by a non-CSG cell.
Different cell IDs may have different frequency shifts, however,
there are a limited number of frequency locations that can be
reused for reference signals.
[0184] Initial cell ID selection and assignment may be done in
different ways. For example, there may be a reserved set of cell
IDs assigned for femtocells (and associated HeNBs). When a new HeNB
is powered up, it may initially listen to determine whether there
are adjacent macrocells and/or or cells such as femtocells. Based
on this information, one of the reserved cell IDs may be assigned
to the new HeNB. However, if this initial cell ID corresponds with
reference signals that cause interference with adjacent cells, the
initial cell ID may subsequently be changed so as to address
interference issues, such as is further described below.
[0185] In some cases, an eNB may decide to apply the strategy above
based on the type of a cell which causes strong interference, e.g.,
whether the cell is a closed subscriber group (CSG) cell or non-CSG
cell. A CSG cell generally has a limited number of allowable
subscribers. Although a UE that is not associated with the CSG cell
may be able to communicate in a limited fashion with the CSG cell,
it may not be able to send or receive data. Femtocells may be CSG
or non-CSG. A so-called open femtocell may be controlled by a
carrier and may allow open access to any subscriber. Other
femtocells may be CSG, which only certain users may access.
[0186] For example, an HeNB (or in some implementations an eNB or
other base station) may initially listen to determine which other
cells are adjacent, and may then select a cell ID based on the
determination of cell ID/reference signals used and/or the type of
cell (HeNBs have UE listening functionality). An HeNB may select or
be assigned a particular cell ID if interference originates from a
CSG cell, however, it may choose not to do so if the interference
originates from a non-CSG cell. This selection may be based on a
table or other information stored in a memory or other data storage
device in the HeNB. For example, the HeNB may include a table or
algorithm to determine optimal orthogonal reference signals/cell
IDs based on other cells it detects at initiation and their
associated cell IDs/reference signal patterns. The optimal
reference signal may be selected based on the particularly
identified adjacent cell IDs/reference signals, cell type and/or
may also be based on other parameters such as power levels/signal
strength of the adjacent cell nodes, or other parameters. In some
implementations, the cell ID may be selected based on
communications with a core network and/or MME, such as are shown in
FIGS. 1 and 2, which may manage cell ID assignment. In some
implementations, the cell ID/reference signal selection process may
be periodically or asynchronously changed in response to changing
signal environments, such as where femtocells and associated HeNBs
are moved around in the environment and/or are turned on and
off.
[0187] In another aspect, multiple eNB's may coordinate the
data/control transmission such that over certain time duration
(contiguous or non-contiguous) or frequency band (contiguous or
non-contiguous), certain transmit signals are halted or omitted
(also denoted herein as a protected or restricted interval). For
example, in some cases no data and/or control signals (other than
reference signals) are transmitted to facilitate user equipment
(UE) measurement on reference signal. This coordination may be done
directly between two or more eNBs/HeNBs via wireless connection
and/or may be managed through other connections such as through a
backhaul connection to a core network as is shown in FIGS. 1 and
2.
[0188] In another aspect, a UE may measure the reference signal
strength (difference or ratio) to enable or disable certain
receiver functionality such as interference cancellation. For
example, the UE may use the reference signal strength variation
over time to determine whether to enable or disable certain
receiver functionality such as interference cancellation. Metrics
used may include RSPR, RSRQ, CQI Report (channel quality
indication), RLM (radio link monitoring, based on SNR of reference
signal) or other signal metrics. When reference signals do not
collide from different cells, the reference signal strength may
vary over time due to data and reference signal collision.
[0189] Nominally, the UE averages instant channel estimate (channel
estimate from that symbol and/or adjacent symbols) from different
sub frames or OFDM symbols by applying some filtering. Such
filtering is traditionally time-invariant or tunable based on
Doppler or signal-to-noise (SNR) information (i.e., fixed
filtering). Alternately, in accordance with another aspect, the UE
may use interference information to apply different weights on the
instant channel estimates over time. This may be done when there is
dynamic scheduling across different cells and each OFDM or subframe
may observe different interference.
[0190] Attention is now directed to FIG. 4 which illustrates one
embodiment of a process 400 for interference mitigation by
controlling cell IDs. At stage 410, a wireless network node, which
may be an eNB or HeNB, may monitor transmissions from other
wireless network elements, such as other eNBs, HeNBs or UEs. For
example, a newly installed or relocated HeNB may be initialized in
proximity to another wireless network, such as the various networks
as shown in FIG. 1. The node may initialize with a predefined cell
ID and may then initially listen before starting transmissions. The
node may then detect one or more adjacent cells, such as other
macrocells or femtocells. At stage 420, the node may then determine
a cell ID or IDs associated with the adjacent cells, and/or may
determine a reference signal pattern associated with the adjacent
cell or cells.
[0191] Based on this determination, the node may then select a new
cell ID and/or reference signal pattern at stage 430 such that the
selected reference signal will mitigate interference with the
adjacent cell or cells. This determination may be further based on
a power level metric associated with the adjacent cell or cells,
and a threshold may be predefined such that the cell ID and
associated reference signal is only changed when the interfering
signal exceeds a certain power level or other signal metric. The
determination may also be based on the type of adjacent cell, such
as, for example, whether it is a CSG or non-CSG cell. Assuming the
cell ID is to be updated, the selected reference signal may be
selected to be orthogonal to one or more received reference signals
associated with the other cell or cells. The selected cell ID may
be based on available cell ID information that may be stored in the
node, such as in a table in memory or other storage medium. The
selected cell ID may also be provided to the node through a
backhaul connection to a core network, such as core network 108 as
shown in FIG. 1 and/or using an MME or SGW pool as shown in FIG. 2.
This process may include consideration at the core network
regarding allocation of reference signals between various known
cells in the proximity of the node. In some embodiments, the node
may communicate with nodes associated with the adjacent cells to
select an appropriate cell ID and reference signal. This may be
done through a direct wireless communication link and/or via a
backhaul connection.
[0192] Once an appropriate selected cell ID and associated selected
reference signal has been determined at stage 430, the node may
then provide transmissions using the selected reference signal at
stage 440. The pattern associated with the selected reference
signal may then facilitate interference mitigation by being
selected to minimize interference or be orthogonal to the reference
signal pattern(s) of the adjacent cells, which may facilitate
processing in other network elements, such as UEs, for channel
estimation and/or other processing.
[0193] In some implementations, the channel may change over time,
for example, if new femtocells are added or removed. Consequently,
process 400 may include a decision step 450, where the process may
be repeated periodically or asynchronously depending on changes in
the operating environment. For example, certain adjacent cells may
create interference in the evening but not during daytime. In this
case, the cell ID of the node may be changed during times of
interference. Other periodic or asychronous re-scheduling of cell
ID and associated reference signals may also be used. In some
environments, femtocells may be added or removed either
periodically or at random. In these cases, two or more nodes
associated with the femtocells may communicate, either directly or
via a backhaul network, such as shown in FIGS. 1 and 2, to manage
reference signal assignments.
[0194] As noted previously, transmissions from adjacent cells can
affect performance of network components by creating interference.
For example, transmissions from one eNB or HeNB may affect
communications between another eNB or HeNB and a UE, or between
other network devices. FIG. 1 illustrates examples of such
interference. In accordance with one aspect, nodes such as eNBs and
HeNBs may communicate with each other to coordinate transmissions
so as to mitigate interference. This communication may be done
directly between nodes and/or may be done through a backhaul
connection, such as is shown in FIG. 1.
[0195] Attention is now directed to FIG. 5 which illustrates one
embodiment of a process 500 for providing such coordination between
network nodes. In particular, it may be desirable to perform
communication between two or more base stations, such as eNBS
and/or HeNBS, to coordinate so that an interfering node reserves
resources (i.e., halts or refrains from transmitting certain
signals during specified time, frequency or time/frequency
resources) during a protected interval so that other network
devices, such as UEs, can perform measurements or other signal
processing.
[0196] Initially, a first network node, such as an eNB or HeNB, may
be in communication with a UE (or other device), such as is shown
in FIGS. 1 and 2. The UE may be performing measurements such as
measuring power and/or channel characteristics or other signal
metrics associated with signals transmitted by the first network
node or other network nodes. Further, signals transmitted from the
second network node, which may likewise be an eNB or HeNB, may be
generating interference at the UE. It may be desirable to provide a
communication channel to the UE from the first network node that
has reduced interference from the second network node. To
facilitate this, communications of coordination information may be
provided between the first network node and the second network node
to establish this coordination. The coordination may result in
restraint or halting of transmission from the second network node
during a specified time period (also described herein as a
restricted time period), wherein signal transmissions from the
second (and/or other) nodes are restricted. The restriction may
include halting transmission of vary signal elements, such as by
halting transmission of data or control signals.
[0197] In particular, in the embodiment shown in FIG. 5, the first
network node may send a request at stage 520 to nodes associated
with the detected one or more adjacent cells (or to other nodes
known to be in proximity to the first network cell). Alternately,
or in addition, a communication link may have previously been
established between the first and second network nodes, or other
network nodes, to facilitate this communication. In some cases, the
request to initiate coordination may come initially from the second
network node to the first network node, or from a UE or other
network device.
[0198] In any case, the request may be received at the second
network node (and/or at additional network nodes that may be
adjacent and/or causing interference) at stage 530. The request may
include coordination information provided from the first network
node, such as cell ID, associated UEs, control information, timing
or other control or data information to facilitate coordination of
transmission. For example, the coordination information may include
information regarding possible time and/or frequency resources in a
resource block during which measurements wish to be made, which may
be in a specified protected interval or time period. These may be
time and/or frequency contiguous and/or non-contiguous. The
information may identify types of communications during which
transmission should be refrained, which may be transmission of
control and/or data information. Reference signals may be sent
during the specified time interval to facilitate measurements based
only on the reference signals during the protected interval.
[0199] Subsequent to receipt, the first and second network nodes
(and/or any other network nodes in communication) may further
exchange information regarding particular resources that may be
controlled so as to mitigate interference. This may involve, for
example, negotiation between the network nodes to determine
particular resource elements or other information to be
coordinated. This may also include information associated with
determinations made by agreement or by the second network node
regarding transmission controls, such as, for example, time and/or
frequency resources on which communications will be halted from the
second network node to facilitate measurement. As noted previously,
this may include certain restricted or protected time periods,
frequencies, or both, which may be contiguous or non-contiguous.
During these controlled time intervals, transmission of data and/or
control information may be halted.
[0200] At stage 540, the second network node will then control
transmissions to mitigate interference based on the transmission
coordination information during a protected interval. This may be
done to allow the UE to make measurements with respect to the first
network node in the absence of transmissions from the second
network node and/or to make other measurements or perform other
signal processing at stage 570. Information regarding the
controlled transmissions may be provided from the first network
node to the UE, which may then use this information to perform
targeted measurements and/or perform other processing during the
protected interval. In some case, the UE may operate independent of
knowledge of the controlled transmissions, and may provide data,
such as channel measurements, power levels, or other information,
to the first network node at stage 570, which may then share this
information with other network nodes, such as the second network
node, and/or the information may be used to control transmissions
from the second network node and/or other network nodes. In some
embodiments, this information may be used to determine a different
reference signal pattern to be used by the first or second wireless
network nodes, such as was described previously herein with respect
to FIG. 4. The node may resume normal operation at stage 550. In
some cases, process 500 may be repeatedly periodically or
asynchronously to facilitate additional measurements and
adjustments.
[0201] Measured information may further be used by the UE to
control device operation. For example, a UE may perform
measurements and/or other signal processing of signals received
from the first wireless network node (and/or other wireless network
nodes besides the second wireless network node) during the
protected interval period at stage 580. These may include various
metrics, such as RSRP, RSRQ, CQI information, radio link monitoring
(RLM), radio link failure monitoring (RLFM) and/or other signal
power metrics.
[0202] The UE may then use the information measured during the
protected interval to adjust receiver functionality and/or disable
or enable certain receiver functions at stage 590. For example, the
information obtained during the controlled transmission period may
be used by the receiver to turn on or off interference cancellation
functionality in the UE. If the interference level associated with
the second wireless network is high, interference cancellation may
be turned off at the UE to save battery power (assuming
interference cancellation would not be effective at high
interference levels). Conversely, if interference from the second
wireless network node is low or intermittent, interference
cancellation may be enabled. Other receiver functionality, such as
may be associated with the level of an interfering signal, may
correspondingly be controlled in response to measurements made
during the controlled transmission period.
[0203] In addition, a UE may measure reference signal strength over
time and may adjust receiver functionality based on variation over
time. For example, when reference signals from other cells collide
over time the received signals may vary. Accordingly, metrics such
as RSRP, RSPQ, CQI, radio link monitoring (RLM) measurements, radio
link failure monitor (RLFM) measurements, or other signal power
metrics may be used to enable or disable receiver functionality
over time. This may be based on, for example, a threshold level of
interference, above or below which functionality may be changed. In
an exemplary embodiment, a receiver sub-system in a UE (or other
network device) includes an interference cancellation (IC) module,
which consumes power when on. If the determined interference level
changes, the functionality of the IC module may be switched on or
off, depending on whether interference cancellelation would be
appropriate in the current environment.
[0204] FIG. 6 illustrates an embodiment of a process 600 for
performing dynamic functionality control. At stage 610 a receiver,
such as a UE, may monitor signals received from multiple cells,
with corresponding first and second cell reference signals. An
interference level may be generated at stage 620 based on this
monitoring, which may be, for example, a power level or signal
strength parameter such as RSRP, RSRQ, RLM, RLFM, CQI, and the
like, or another signal metric. At stage 630, the interference
level may be compared with one or more metrics, such as a threshold
value or range of values, a moving average value, or other value or
parameter associated with a receiver functionality. If the
interference level exceeds the threshold, a receiver functionality
may be controlled. For example, inteference cancellation may be
enabled or disabled in response to a dynamic interference level so
as to manage battery consumption.
[0205] It is noted that the terms "first wireless network node" and
"second wireless network node" are used above for purposes of
explanation, and that various specific nodes in particular systems
may correspond to the representative first and second wireless
network nodes described herein.
[0206] As noted previously, receiver functionality such as is
included in a UE performs instant channel estimates (i.e., channel
estimates from a particular symbol or a symbol and adjacent
symbols), which may be based on received reference signals.
Traditionally, these instant channel estimates are averaged over
multiple subframes or OFDM symbols, each of which have a reference
signal. This is often done by using a filter such as a FIR filter,
such as a 3 tap filter which may average over 2 milliseconds. The
filtering is normally time-invariant or tunable based only on
Doppler or signal to noise ratio (SNR) information.
[0207] In another aspect, different filtering for channel
estimation may be applied over different subframes, which may be
based on instant channel estimates associated with the subframes.
In particular, interference levels may vary between subframes based
on the particular characteristics of signals received during the
subframes. For example, subframes may be subject to significant
interference such as from adjacent networks, whereas other
subframes may be subject to less interference. To address this, a
UE (or other node implementing receiver functionality, may perform
instant channel estimates and collect interference information,
which may be time varying over intervals of sub-frames. Based on
this information, the UE may then generate different weightings for
the channel estimates and/or may apply different filtering based on
the instant estimates rather than an average taken over multiple
subframes.
[0208] FIG. 7 illustrates a process 700 for adjusting a receiver to
account for interference. The receiver may monitor interference
levels associated with multiple adjacent cells or devices at stage
710. In particular, this may include interference from multiple
reference signals from different nodes, which may increase or
decrease at the level of time resolution of sub-frames. A time
variation in the interference level, corresponding to subframe
levels may then be determined. For example, each OFDM symbol or
subframe may see different interference, which may be the case when
there is dynamic scheduling across different cells. Based on
detection of the interference, channel estimates may be weighted
accordingly so as to allow adjustment at the sub-frame level or
below at stage 730. A filter response may be adjusted based on the
weighting or on the instant channel estimate.
[0209] Attention is now directed to FIG. 8, which illustrates a
wireless communications methodology which may be implemented on a
system such as is shown in FIG. 1. While, for purposes of
simplicity of explanation, the methodology (and other methodologies
described herein) are shown and described as a series of acts, it
is to be understood and appreciated that the methodology is not
limited by the order of acts, as some acts may, in accordance with
one or more aspects, occur in different orders and/or concurrently
with other acts from that shown and described herein. In some
implementations some acts may be omitted, whereas in other
implementations some acts may be added. For example, those skilled
in the art will understand and appreciate that a methodology could
alternatively be represented as a series of interrelated states or
events, such as in a state diagram. Moreover, not all illustrated
acts may be utilized to implement a methodology in accordance with
the claimed subject matter.
[0210] At stage 810, reference mapping is employed. If a base
station such as an eNB (or HeNB) locates a strong cell, the eNB can
select a cell ID such that reference signal mapping are orthogonal
to this strong cell, where a reference signal occupies different
frequency resources used by this cell. The eNB may decide to apply
the strategy above based on the type of a cell which causes strong
interference, e.g., based on whether the cell is a closed
subscriber group (CSG) cell or non-CSG cell.
[0211] At stage 820, multiple eNB's (and/or HeNBs) may coordinate
data/control transmission such that over certain time periods
(contiguous or non-contiguous) or frequency bands (contiguous or
non-contiguous), no data and or control signal (other a reference
signal) are transmitted, so as to facilitate user equipment (UE)
measurements on the reference signal(s).
[0212] At stage 830, the UE may measure the reference signal
strength (difference or ratio) to enable or disable certain
receiver functionality such as interference cancellation. In
another aspect, the UE may use reference signal strength variations
over time to determine whether to enable or disable certain
receiver functionality, such as interference cancellation. When
reference signals do not collide from different cells, the
reference signal strength may vary over time due to data and
reference signal collision.
[0213] At stage 840, the UE may generate instant channel estimates
(channel estimates from the corresponding OFDM symbol and/or
adjacent symbols). The UE may use associated interference
information to apply different weights on the instant channel
estimates over time. This may be done when there is dynamic
scheduling across different cells and each OFDM or subframe may
observe different interference. By using this approach, receiver
performance may be enhanced over traditional methods that use
averaging of channel estimates.
[0214] Attention is now directed to FIG. 9, which illustrates a
block diagram of an embodiment of base station 910 (i.e., an eNB or
HeNB) and a terminal 950 (i.e., a terminal, AT or UE) in an example
LTE MIMO communication system 900. These systems may correspond to
those shown in FIGS. 1-3, and may be configured to implement the
processes illustrated previously herein in FIGS. 4-7.
[0215] Various functions may be performed in the processors and
memories as shown in base station 910 (and/or in other components
not shown), such as selection of cell ID based on adjacent node
information, output transmit control to provide protected intervals
based on coordination information received from other base
stations, as well as other functions as described previously
herein. UE 950 may include one or more modules to receive signals
from base station 910 to determine channel characteristics such as
channel estimates, demodulate received data and generate spatial
information, determine power level information, and/or other
information associated with base station 910.
[0216] In one embodiment, base station 910 may adjust output in
response to information received from UE 950 or from backhaul
signaling from another base station (not shown in FIG. 9) as
described previously herein. This may be done in one or more
components (or other components not shown) of base station 910,
such as processors 914, 930 and memory 932. Base station 910 may
also include a transmit module including one or more components (or
other components not shown) of HeNB 910, such as transmit modules
924. Base station 910 may include an interference cancellation
module including one or more components (or other components not
shown), such as processors 930, 942, demodulator module 940, and
memory 932 to provide interference cancellation functionality. Base
station 910 may include a coordination module including one or more
components (or other components not shown), such as processors 930,
914 and memory 932 to receive coordination information from other
network devices and manage the transmitter module based on the
coordination information. Base station 910 may also include a
control module for controlling receiver functionality, such as
turning on or off other functional modules such as the interference
cancellation module. Base station 910 may include a network
connection module 990 to provide networking with other systems,
such as backhaul systems in the core network or other components as
shown in FIGS. 1 and 2.
[0217] Likewise, UE 950 may include a receive module including one
or more components of UE 950 (or other components not shown), such
as receivers 954. UE 950 may also include a signal information
module including one or more components (or other components not
shown) of UE 950, such as processors 960 and 970, and memory 972.
In one embodiment, one or more signals received at UE 950 are
processed to estimate channel characteristics, power information,
spatial information and/or other information regarding
corresponding HeNBs, such as base station 910. Memories 932 and 972
may be used to store computer code for execution on one or more
processors, such as processors 960, 970 and 938, to implement
processes associated with channel measurement and information,
power level and/or spatial information determination, cell ID
selection, inter-cell coordination, interference cancellation
control, as well as other functions as are described herein.
[0218] In operation, at the base station 910, traffic data for a
number of data streams may be provided from a data source 912 to a
transmit (TX) data processor 914, where it may be processed and
transmitted to one or more UEs 950. The transmitted data may be
controlled as described previously herein so as to mitigate
interference or perform signal measurements at one or more UEs
950.
[0219] In one aspect, each data stream is processed and transmitted
over a respective transmitter sub-system (shown as transmitters
924.sub.1-924.sub.Nt) of base station 910. TX data processor 914
receives, formats, codes, and interleaves the traffic data for each
data stream based on a particular coding scheme selected for that
data stream so as to provide coded data. In particular, base
station 910 may be configured to determine a particular reference
signal and reference signal pattern and provide a transmit signal
including the reference signal and/or beamforming information in
the selected pattern.
[0220] The coded data for each data stream may be multiplexed with
pilot data using OFDM techniques. The pilot data is typically a
known data pattern that is processed in a known manner and may be
used at the receiver system to estimate the channel response. For
example, the pilot data may comprise a reference signal. Pilot data
may be provided to TX data processor 914 as shown in FIG. 9 and
multiplexed with the coded data. The multiplexed pilot and coded
data for each data stream may then be modulated (i.e., symbol
mapped) based on a particular modulation scheme (e.g., BPSK, QSPK,
M-PSK, M-QAM, etc.) selected for that data stream so as to provide
modulation symbols, and the data and pilot may be modulated using
different modulation schemes. The data rate, coding, and modulation
for each data stream may be determined by instructions performed by
processor 930 based on instructions stored in memory 932, or in
other memory or instruction storage media of UE 950 (not
shown).
[0221] The modulation symbols for all data streams may then be
provided to a TX MIMO processor 920, which may further process the
modulation symbols (e.g., for OFDM implementation). TX MIMO
processor 920 may then provide Nt modulation symbol streams to
N.sub.t transmitters (TMTR) 922.sub.1 through 922.sub.Nt. The
various symbols may be mapped to associated RBs for
transmission.
[0222] TX MIMO processor 920 may apply beamforming weights to the
symbols of the data streams and corresponding to the one or more
antennas from which the symbol is being transmitted. This may be
done by using information such as channel estimation information
provided by or in conjunction with the reference signals and/or
spatial information provided from a network node such as a UE. For
example, a beam B=transpose([b1 b2 . . . b.sub.Nt]) composes of a
set of weights corresponding to each transmit antenna. Transmitting
along a beam corresponds to transmitting a modulation symbol x
along all antennas scaled by the beam weight for that antenna; that
is, on antenna t the transmitted signal is bt*x. When multiple
beams are transmitted, the transmitted signal on one antenna is the
sum of the signals corresponding to different beams. This can be
expressed mathematically as
B1.times.1+B2.times.2+BN.sub.S.times.N.sub.S, where N.sub.S beams
are transmitted and xi is the modulation symbol sent using beam Bi.
In various implementations beams could be selected in a number of
ways. For example, beams could be selected based on channel
feedback from a UE, channel knowledge available at the eNB, or
based on information provided from a UE to facilitate interference
mitigation, such as with an adjacent macrocell.
[0223] Each transmitter sub-system 922.sub.1 through 922.sub.Nt
receives and processes a respective symbol stream to provide one or
more analog signals, and further conditions (e.g., amplifies,
filters, and upconverts) the analog signals to provide a modulated
signal suitable for transmission over the MIMO channel. N.sub.t
modulated signals from transmitters 922.sub.1 through 922.sub.Nt
are then transmitted from N.sub.t antennas 924.sub.1 through
924.sub.Nt, respectively.
[0224] At UE 950, the transmitted modulated signals are received by
N.sub.r antennas 952.sub.1 through 952.sub.Nr and the received
signal from each antenna 952 is provided to a respective receiver
(RCVR) 954.sub.1 through 952.sub.Nr. Each receiver 954 conditions
(e.g., filters, amplifies and downconverts) a respective received
signal, digitizes the conditioned signal to provide samples, and
further processes the samples to provide a corresponding "received"
symbol stream.
[0225] An RX data processor 960 then receives and processes the
N.sub.r received symbol streams from N.sub.r receivers 954.sub.1
through 952.sub.Nr based on a particular receiver processing
technique so as to provide N.sub.S "detected" symbol streams so at
to provide estimates of the N.sub.S transmitted symbol streams. The
RX data processor 960 then demodulates, deinterleaves, and decodes
each detected symbol stream to recover the traffic data for the
data stream. The processing by RX data processor 960 is typically
complementary to that performed by TX MIMO processor 920 and TX
data processor 914 in base station 910.
[0226] A processor 970 may periodically determine a precoding
matrix for use as is described further below. Processor 970 may
then formulate a reverse link message that may comprise a matrix
index portion and a rank value portion. In various aspects, the
reverse link message may comprise various types of information
regarding the communication link and/or the received data stream.
The reverse link message may then be processed by a TX data
processor 938, which may also receive traffic data for a number of
data streams from a data source 936 which may then be modulated by
a modulator 980, conditioned by transmitters 954.sub.1 through
954.sub.Nr, and transmitted back to base station 910. Information
transmitted back to base station 910 may include power level and/or
spatial information for providing beamforming to mitigate
interference from base station 910.
[0227] At base station 910, the modulated signals from UE 950 are
received by antennas 924, conditioned by receivers 922, demodulated
by a demodulator 940, and processed by a RX data processor 942 to
extract the message transmitted by UE 950. Processor 930 then
determines which pre-coding matrix to use for determining
beamforming weights, and then processes the extracted message.
[0228] In some configurations, the apparatus for wireless
communication includes means for performing various functions as
described herein. In one aspect, the aforementioned means may be a
processor or processors and associated memory in which embodiments
reside, such as are shown in FIG. 9, and which are configured to
perform the functions recited by the aforementioned means. The may
be, for example, modules or apparatus residing in UEs, HeNBs and/or
eNBs such as are shown in FIGS. 1-3 and FIG. 9. In another aspect,
the aforementioned means may be a module or any apparatus
configured to perform the functions recited by the aforementioned
means.
[0229] In one or more exemplary embodiments, the functions, methods
and processes described may be implemented in hardware, software,
firmware, or any combination thereof. If implemented in software,
the functions may be stored on or encoded as one or more
instructions or code on a computer-readable medium.
Computer-readable media includes computer storage media. Storage
media may be any available media that can be accessed by a
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 in the form of instructions or data
structures and that can be accessed by a computer. 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.
[0230] It is understood that the specific order or hierarchy of
steps or stages in the processes and methods disclosed are examples
of exemplary approaches. Based upon design preferences, it is
understood that the specific order or hierarchy of steps in the
processes may be rearranged while remaining within the scope of the
present disclosure. The accompanying method claims present elements
of the various steps in a sample order, and are not meant to be
limited to the specific order or hierarchy presented.
[0231] 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.
[0232] Those of skill would further appreciate that the various
illustrative logical blocks, modules, circuits, and algorithm steps
described in connection with the embodiments disclosed 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 disclosure.
[0233] The various illustrative logical blocks, modules, and
circuits described in connection with the embodiments disclosed
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.
[0234] The steps or stages of a method, process or algorithm
described in connection with the embodiments disclosed 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.
[0235] The claims are not intended to be limited to the aspects
shown herein, but is to be accorded the full scope consistent with
the language of the claims, wherein reference to an element in the
singular is not intended to mean "one and only one" unless
specifically so stated, but rather "one or more." Unless
specifically stated otherwise, the term "some" refers to one or
more. A phrase referring to "at least one of" a list of items
refers to any combination of those items, including single members.
As an example, "at least one of: a, b, or c" is intended to cover:
a; b; c; a and b; a and c; b and c; and a, b and c.
[0236] The previous description of the disclosed aspects is
provided to enable any person skilled in the art to make or use the
present disclosure. Various modifications to these aspects will be
readily apparent to those skilled in the art, and the generic
principles defined herein may be applied to other aspects without
departing from the spirit or scope of the disclosure. Thus, the
disclosure is not intended to be limited to the aspects shown
herein but is to be accorded the widest scope consistent with the
principles and novel features disclosed herein. It is intended that
the following claims and their equivalents define the scope of the
disclosure.
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