U.S. patent application number 14/672290 was filed with the patent office on 2015-07-23 for beamforming signaling in a wireless network.
This patent application is currently assigned to OFINNO TECHNOLOGIES, LLC. The applicant listed for this patent is Esmael Hejazi Dinan. Invention is credited to Esmael Hejazi Dinan.
Application Number | 20150207546 14/672290 |
Document ID | / |
Family ID | 48610039 |
Filed Date | 2015-07-23 |
United States Patent
Application |
20150207546 |
Kind Code |
A1 |
Dinan; Esmael Hejazi |
July 23, 2015 |
Beamforming Signaling in a Wireless Network
Abstract
A wireless receives at least one channel state input information
element (IE) from a first base station. The wireless device
computes a precoding matrix indicator (PMI) employing, at least in
part, the at least one channel state input IE and measurement of
signals received from a second base station. The wireless device
transmits the PMI to the first base station.
Inventors: |
Dinan; Esmael Hejazi;
(Herndon, VA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Dinan; Esmael Hejazi |
Herndon |
VA |
US |
|
|
Assignee: |
OFINNO TECHNOLOGIES, LLC
Herndon
VA
|
Family ID: |
48610039 |
Appl. No.: |
14/672290 |
Filed: |
March 30, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14536723 |
Nov 10, 2014 |
8995300 |
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14672290 |
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13716135 |
Dec 15, 2012 |
8885569 |
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14536723 |
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61577206 |
Dec 19, 2011 |
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61577208 |
Dec 19, 2011 |
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61577203 |
Dec 19, 2011 |
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Current U.S.
Class: |
375/267 |
Current CPC
Class: |
H04B 7/0473 20130101;
H04W 36/0058 20180801; H04W 36/0072 20130101; H04W 72/0406
20130101; H04W 72/046 20130101; H04L 5/0023 20130101; H04W 74/002
20130101; H04B 7/0617 20130101; H04J 11/0056 20130101; H04W 24/02
20130101; H04W 72/0426 20130101; H04W 88/08 20130101; H04W 28/0236
20130101; H04L 25/03955 20130101; H04W 36/0055 20130101; H04W
72/042 20130101; H04B 7/0456 20130101; H04W 36/08 20130101; H04B
7/0478 20130101; H04W 36/30 20130101; H04W 72/082 20130101; H04B
7/043 20130101; H04W 36/0005 20130101; H04B 7/0417 20130101; H04B
7/046 20130101; H04L 27/2646 20130101; H04L 5/0073 20130101; H04W
72/044 20130101; H04B 7/0639 20130101; H04L 5/0053 20130101; H04W
36/0094 20130101; H04W 36/24 20130101; H04W 72/0453 20130101; H04B
7/0626 20130101; H04B 7/0634 20130101; H04B 7/063 20130101 |
International
Class: |
H04B 7/04 20060101
H04B007/04; H04W 24/02 20060101 H04W024/02 |
Claims
1. A wireless device comprising: a) one or more communication
interfaces; b) one or more processors; and c) memory storing
instructions that, when executed, cause said wireless device to: i)
receive from a first base station a measurement information
message; ii) compute a precoding matrix indicator (PMI) employing,
in part: (1) at least one information element (IE) in said
measurement information message; (2) measurement of first signals
received from one or more antenna ports of said first base station;
and (3) measurement of second signals received from one or more
antenna ports of a second base station; iii) transmit channel state
information comprising said PMI to said first base station; and iv)
receive at least one data packet, transmission of said at least one
data packet employing beamforming according to a precoding matrix
identified by said PMI.
2. The wireless device of claim 1, wherein measurement of said
first signals comprises measurement of reference signals received
from said one or more antenna ports of said first base station.
3. The wireless device of claim 1, wherein measurement of said
second signals comprises measurement of reference signals received
from said one or more antenna ports of said second base
station.
4. The wireless device of claim 1, wherein said at least one IE is
generated by said first base station based, at least in part, on
one or more information elements received by said first base
station from said second base station.
5. The wireless device of claim 1, wherein said first base station
communicates with said second base station information about said
at least one IE.
6. The wireless device of claim 5, wherein said information is
related to at least one downlink resource block.
7. The wireless device of claim 5, wherein said information is
related to downlink signals transmitted by said first base station
or said second base station.
8. The wireless device of claim 1, wherein said channel state
information further comprises a rank indicator and a channel
quality indicator.
9. The wireless device of claim 1, wherein said wireless device
selects said PMI from a subset of a precoding codebook indicated by
a codebook subset restriction bitmap parameter.
10. The wireless device of claim 1, wherein said PMI is computed,
in part, to reduce downlink inter-cell interference received from
said second base station.
11. The wireless device of claim 1, wherein said wireless device
selects said PMI from a plurality of predetermined PMIs.
12. The wireless device of claim 1, wherein said PMI is computed
for a sub-band of a downlink carrier.
13. A first base station comprising: a) one or more communication
interfaces; b) one or more processors; and c) memory storing
instructions that, when executed, cause said first base station to:
i) transmit to a wireless device a measurement information message;
ii) receive from said wireless device channel state information
comprising a precoding matrix indicator (PMI) computed employing,
in part: (1) at least one information element (IE) in said
measurement information message; and (2) measurement of first
signals received by said wireless device from one or more antenna
ports of said first base station; and (3) measurement of second
signals received by said wireless device from one or more antenna
ports of a second base station; and iii) transmit signals to said
wireless device, said transmission employing beamforming according
to a precoding matrix identified by said PMI.
14. The first base station of claim 13, wherein said PMI is
selected from a plurality of predetermined PMIs employing, at least
in part, said measurement of signals to reduce downlink inter-cell
interference received from said second base station.
15. The first base station of claim 13, wherein measurement of said
second signals is related to computation of inter-cell interference
from said second base station.
16. The first base station of claim 13, wherein said wireless
device selects said PMI from a subset of a precoding codebook
indicated by a codebook subset restriction bitmap parameter.
17. The first base station of claim 13, wherein said channel state
information further comprises a rank indicator and a channel
quality indicator.
18. A method for use in a wireless network, the method comprising:
a) receiving, by a wireless device from a first base station, a
measurement information message; b) computing, by said wireless
device, a precoding matrix indicator (PMI) employing, in part: i)
at least one information element (IE) in said measurement
information message; ii) measurement of first signals received from
one or more antenna ports of a first base station; and iii)
measurement of second signals received from one or more antenna
ports of a second base station; c) transmitting, by said wireless
device to said first base station, channel state information
comprising said PMI; and d) receiving by said wireless device at
least one data packet, transmission of said at least one data
packet employing beamforming according to a precoding matrix
identified by said PMI.
19. The method of claim 18, further comprising said first base
station communicating with said second base station information
about said at least one IE.
20. The method of claim 18, wherein said at least one IE is
generated by said first base station based, at least in part, on
one or more information elements received by said first base
station from said second base station.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of application Ser. No.
14/536,723, filed Nov. 10, 2014, which is a continuation of
application Ser. No. 13/716,135, filed Dec. 15, 2012, now U.S. Pat.
No. 8,885,569, which claims the benefit of U.S. Provisional
Application No. 61/577,203, filed Dec. 19, 2011, and U.S.
Provisional Application No. 61/577,206, filed Dec. 19, 2011, and
U.S. Provisional Application No. 61/577,208, filed Dec. 19, 2011,
which are hereby incorporated by reference in its entirety.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0002] An exemplary embodiment of the present invention is
described herein with reference to the drawings, in which:
[0003] FIG. 1 is a diagram depicting example sets of OFDM
subcarriers as per an aspect of an embodiment of the present
invention;
[0004] FIG. 2 is a diagram depicting an example transmission time
and reception time for two carriers as per an aspect of an
embodiment of the present invention;
[0005] FIG. 3 is a diagram depicting OFDM radio resources as per an
aspect of an embodiment of the present invention;
[0006] FIG. 4 is a block diagram of a base station and a wireless
device as per an aspect of an embodiment of the present invention;
and
[0007] FIG. 5 is a block diagram depicting a system for
transmitting data traffic over an OFDM radio system as per an
aspect of an embodiment of the present invention;
[0008] FIG. 6 is a block diagram of a limited feedback system as
per an aspect of an embodiment of the present invention;
[0009] FIG. 7 is a block diagram of a limited feedback MIMO system
as per an aspect of an embodiment of the present invention;
[0010] FIG. 8 is a block diagram for beamforming information
exchange as per an aspect of an embodiment of the present
invention;
[0011] FIG. 9 depicts message flows between a base station and a
wireless device as per an aspect of an embodiment of the present
invention;
[0012] FIG. 10 depicts an example flow chart for a base station
employing beamforming as per an aspect of an embodiment of the
present invention;
[0013] FIG. 11 depicts an example flow chart for a base station
employing beamforming as per an aspect of an embodiment of the
present invention;
[0014] FIG. 12 depicts an example flow chart for a base station
employing beamforming as per an aspect of an embodiment of the
present invention; and
[0015] FIG. 13 depicts an example flow chart for a base station
employing beamforming as per an aspect of an embodiment of the
present invention.
DETAILED DESCRIPTION OF EMBODIMENTS
[0016] Example embodiments of the present invention enable
beamforming information to be exchanged between base stations.
Embodiments of the technology disclosed herein may be employed in
the technical field of wireless communication systems. More
particularly, the embodiments of the technology disclosed herein
may relate to enhancing the exchange of beamforming information
between base stations in a wireless communication system.
[0017] Example embodiments of the invention may be implemented
using various physical layer modulation and transmission
mechanisms. Example transmission mechanisms may include, but are
not limited to: CDMA (code division multiple access), OFDM
(orthogonal frequency division multiplexing), TDMA (time division
multiple access), Wavelet technologies, and/or the like. Hybrid
transmission mechanisms such as TDMA/CDMA, and OFDM/CDMA may also
be employed. Various modulation schemes may be applied for signal
transmission in the physical layer. Examples of modulation schemes
include, but are not limited to: phase, amplitude, code, a
combination of these, and/or the like. An example radio
transmission method may implement QAM (quadrature amplitude
modulation) using BPSK (binary phase shift keying), QPSK
(quadrature phase shift keying), 16-QAM, 64-QAM, 256-QAM, and/or
the like. Physical radio transmission may be enhanced by
dynamically or semi-dynamically changing the modulation and coding
scheme depending on transmission requirements and radio
conditions.
[0018] FIG. 1 is a diagram depicting example sets of OFDM
subcarriers as per an aspect of an embodiment of the present
invention. As illustrated in this example, arrow(s) in the diagram
may depict a subcarrier in a multicarrier OFDM system. The OFDM
system may use technology such as OFDM technology, SC-OFDM (single
carrier-OFDM) technology, or the like. For example, arrow 101 shows
a subcarrier transmitting information symbols. FIG. 1 is for
illustration purposes, and a typical multicarrier OFDM system may
include more subcarriers in a carrier. For example, the number of
subcarriers in a carrier may be in the range of 10 to 10,000
subcarriers. FIG. 1 shows two guard bands 106 and 107 in a
transmission band. As illustrated in FIG. 1, guard band 106 is
between subcarriers 103 and subcarriers 104. The example set of
subcarriers A 102 includes subcarriers 103 and subcarriers 104.
FIG. 1 also illustrates an example set of subcarriers B 105. As
illustrated, there is no guard band between any two subcarriers in
the example set of subcarriers B 105. Carriers in a multicarrier
OFDM communication system may be contiguous carriers,
non-contiguous carriers, or a combination of both contiguous and
non-contiguous carriers.
[0019] FIG. 2 is a diagram depicting an example transmission time
and reception time for two carriers as per an aspect of an
embodiment of the present invention. A multicarrier OFDM
communication system may include one or more carriers, for example,
ranging from 1 to 10 carriers. Carrier A 204 and carrier B 205 may
have the same or different timing structures. Although FIG. 2 shows
two synchronized carriers, carrier A 204 and carrier B 205 may or
may not be synchronized with each other. Different radio frame
structures may be supported for FDD (frequency division duplex) and
TDD (time division duplex) duplex mechanisms. FIG. 2 shows an
example FDD frame timing. Downlink and uplink transmissions may be
organized into radio frames 201. In this example, radio frame
duration is 10 msec. Other frame durations, for example, in the
range of 1 to 100 msec may also be supported. In this example, each
10 ms radio frame 201 may be divided into ten equally sized
sub-frames 202. Other subframe durations such as including 0.5
msec, 1 msec, 2 msec, and 5 msec may also be supported.
Sub-frame(s) may consist of two or more slots 206. For the example
of FDD, 10 subframes may be available for downlink transmission and
10 subframes may be available for uplink transmissions in each 10
ms interval. Uplink and downlink transmissions may be separated in
the frequency domain. Slot(s) may include a plurality of OFDM
symbols 203. The number of OFDM symbols 203 in a slot 206 may
depend on the cyclic prefix length and subcarrier spacing.
[0020] In an example case of TDD, uplink and downlink transmissions
may be separated in the time domain. According to some of the
various aspects of embodiments, each 10 ms radio frame may include
two half-frames of 5 ms each. Half-frame(s) may include eight slots
of length 0.5 ms and three special fields: DwPTS (Downlink Pilot
Time Slot), GP (Guard Period) and UpPTS (Uplink Pilot Time Slot).
The length of DwPTS and UpPTS may be configurable subject to the
total length of DwPTS, GP and UpPTS being equal to 1 ms. Both 5 ms
and 10 ms switch-point periodicity may be supported. In an example,
subframe 1 in all configurations and subframe 6 in configurations
with 5 ms switch-point periodicity may include DwPTS, GP and UpPTS.
Subframe 6 in configurations with 10 ms switch-point periodicity
may include DwPTS. Other subframes may include two equally sized
slots. For this TDD example, GP may be employed for downlink to
uplink transition. Other subframes/fields may be assigned for
either downlink or uplink transmission. Other frame structures in
addition to the above two frame structures may also be supported,
for example in one example embodiment the frame duration may be
selected dynamically based on the packet sizes.
[0021] FIG. 3 is a diagram depicting OFDM radio resources as per an
aspect of an embodiment of the present invention. The resource grid
structure in time 304 and frequency 305 is illustrated in FIG. 3.
The quantity of downlink subcarriers or resource blocks (RB) (in
this example 6 to 100 RBs) may depend, at least in part, on the
downlink transmission bandwidth 306 configured in the cell. The
smallest radio resource unit may be called a resource element (e.g.
301). Resource elements may be grouped into resource blocks (e.g.
302). Resource blocks may be grouped into larger radio resources
called Resource Block Groups (RBG) (e.g. 303). The transmitted
signal in slot 206 may be described by one or several resource
grids of a plurality of subcarriers and a plurality of OFDM
symbols. Resource blocks may be used to describe the mapping of
certain physical channels to resource elements. Other pre-defined
groupings of physical resource elements may be implemented in the
system depending on the radio technology. For example, 24
subcarriers may be grouped as a radio block for a duration of 5
msec.
[0022] Physical and virtual resource blocks may be defined. A
physical resource block may be defined as N consecutive OFDM
symbols in the time domain and M consecutive subcarriers in the
frequency domain, wherein M and N are integers. A physical resource
block may include M.times.N resource elements. In an illustrative
example, a resource block may correspond to one slot in the time
domain and 180 kHz in the frequency domain (for 15 KHz subcarrier
bandwidth and 12 subcarriers). A virtual resource block may be of
the same size as a physical resource block. Various types of
virtual resource blocks may be defined (e.g. virtual resource
blocks of localized type and virtual resource blocks of distributed
type). For various types of virtual resource blocks, a pair of
virtual resource blocks over two slots in a subframe may be
assigned together by a single virtual resource block number.
Virtual resource blocks of localized type may be mapped directly to
physical resource blocks such that sequential virtual resource
block k corresponds to physical resource block k. Alternatively,
virtual resource blocks of distributed type may be mapped to
physical resource blocks according to a predefined table or a
predefined formula. Various configurations for radio resources may
be supported under an OFDM framework, for example, a resource block
may be defined as including the subcarriers in the entire band for
an allocated time duration.
[0023] According to some of the various aspects of embodiments, an
antenna port may be defined such that the channel over which a
symbol on the antenna port is conveyed may be inferred from the
channel over which another symbol on the same antenna port is
conveyed. In some embodiments, there may be one resource grid per
antenna port. The set of antenna port(s) supported may depend on
the reference signal configuration in the cell. Cell-specific
reference signals may support a configuration of one, two, or four
antenna port(s) and may be transmitted on antenna port(s) {0}, {0,
1}, and {0, 1, 2, 3}, respectively. Multicast-broadcast reference
signals may be transmitted on antenna port 4. Wireless
device-specific reference signals may be transmitted on antenna
port(s) 5, 7, 8, or one or several of ports {7, 8, 9, 10, 11, 12,
13, 14}. Positioning reference signals may be transmitted on
antenna port 6. Channel state information (CSI) reference signals
may support a configuration of one, two, four or eight antenna
port(s) and may be transmitted on antenna port(s) 15, {15, 16},
{15, . . . , 18} and {15, . . . , 22}, respectively. Various
configurations for antenna configuration may be supported depending
on the number of antennas and the capability of the wireless
devices and wireless base stations.
[0024] According to some embodiments, a radio resource framework
using OFDM technology may be employed. Alternative embodiments may
be implemented employing other radio technologies. Example
transmission mechanisms include, but are not limited to: CDMA,
OFDM, TDMA, Wavelet technologies, and/or the like. Hybrid
transmission mechanisms such as TDMA/CDMA, and OFDM/CDMA may also
be employed.
[0025] FIG. 4 is an example block diagram of a base station 401 and
a wireless device 406, as per an aspect of an embodiment of the
present invention. A communication network 400 may include at least
one base station 401 and at least one wireless device 406. The base
station 401 may include at least one communication interface 402,
at least one processor 403, and at least one set of program code
instructions 405 stored in non-transitory memory 404 and executable
by the at least one processor 403. The wireless device 406 may
include at least one communication interface 407, at least one
processor 408, and at least one set of program code instructions
410 stored in non-transitory memory 409 and executable by the at
least one processor 408. Communication interface 402 in base
station 401 may be configured to engage in communication with
communication interface 407 in wireless device 406 via a
communication path that includes at least one wireless link 411.
Wireless link 411 may be a bi-directional link. Communication
interface 407 in wireless device 406 may also be configured to
engage in a communication with communication interface 402 in base
station 401. Base station 401 and wireless device 406 may be
configured to send and receive data over wireless link 411 using
multiple frequency carriers. According to some of the various
aspects of embodiments, transceiver(s) may be employed. A
transceiver is a device that includes both a transmitter and
receiver. Transceivers may be employed in devices such as wireless
devices, base stations, relay nodes, and/or the like. Example
embodiments for radio technology implemented in communication
interface 402, 407 and wireless link 411 are illustrated are FIG.
1, FIG. 2, and FIG. 3. and associated text.
[0026] FIG. 5 is a block diagram depicting a system 500 for
transmitting data traffic generated by a wireless device 502 to a
server 508 over a multicarrier OFDM radio according to one aspect
of the illustrative embodiments. The system 500 may include a
Wireless Cellular Network/Internet Network 507, which may function
to provide connectivity between one or more wireless devices 502
(e.g., a cell phone, PDA (personal digital assistant), other
wirelessly-equipped device, and/or the like), one or more servers
508 (e.g. multimedia server, application servers, email servers, or
database servers) and/or the like.
[0027] It should be understood, however, that this and other
arrangements described herein are set forth for purposes of example
only. As such, those skilled in the art will appreciate that other
arrangements and other elements (e.g., machines, interfaces,
functions, orders of functions, etc.) may be used instead, some
elements may be added, and some elements may be omitted altogether.
Further, as in most telecommunications applications, those skilled
in the art will appreciate that many of the elements described
herein are functional entities that may be implemented as discrete
or distributed components or in conjunction with other components,
and in any suitable combination and location. Still further,
various functions described herein as being performed by one or
more entities may be carried out by hardware, firmware and/or
software logic in combination with hardware. For instance, various
functions may be carried out by a processor executing a set of
machine language instructions stored in memory.
[0028] As shown, the access network may include a plurality of base
stations 503 . . . 504. Base station 503 . . . 504 of the access
network may function to transmit and receive RF (radio frequency)
radiation 505 . . . 506 at one or more carrier frequencies, and the
RF radiation may provide one or more air interfaces over which the
wireless device 502 may communicate with the base stations 503 . .
. 504. The user 501 may use the wireless device (or UE: user
equipment) to receive data traffic, such as one or more multimedia
files, data files, pictures, video files, or voice mails, etc. The
wireless device 502 may include applications such as web email,
email applications, upload and ftp applications, MMS (multimedia
messaging system) applications, or file sharing applications. In
another example embodiment, the wireless device 502 may
automatically send traffic to a server 508 without direct
involvement of a user. For example, consider a wireless camera with
automatic upload feature, or a video camera uploading videos to the
remote server 508, or a personal computer equipped with an
application transmitting traffic to a remote server.
[0029] One or more base stations 503 . . . 504 may define a
corresponding wireless coverage area. The RF radiation 505 . . .
506 of the base stations 503 . . . 504 may carry communications
between the Wireless Cellular Network/Internet Network 507 and
access device 502 according to any of a variety of protocols. For
example, RF radiation 505 . . . 506 may carry communications
according to WiMAX (Worldwide Interoperability for Microwave Access
e.g., IEEE 802.16), LTE (long term evolution), microwave,
satellite, MMDS (Multichannel Multipoint Distribution Service),
Wi-Fi (e.g., IEEE 802.11), Bluetooth, infrared, and other protocols
now known or later developed. The communication between the
wireless device 502 and the server 508 may be enabled by any
networking and transport technology for example TCP/IP (transport
control protocol/Internet protocol), RTP (real time protocol), RTCP
(real time control protocol), HTTP (Hypertext Transfer Protocol) or
any other networking protocol.
[0030] According to some of the various aspects of embodiments, an
LTE network may include many base stations, providing a user plane
(PDCP: packet data convergence protocol/RLC: radio link
control/MAC: media access control/PHY: physical) and control plane
(RRC: radio resource control) protocol terminations towards the
wireless device. The base station(s) may be interconnected with
other base station(s) by means of an X2 interface. The base
stations may also be connected by means of an S1 interface to an
EPC (Evolved Packet Core). For example, the base stations may be
interconnected to the MME (Mobility Management Entity) by means of
the S1-MME interface and to the Serving Gateway (S-GW) by means of
the S1-U interface. The S1 interface may support a many-to-many
relation between MMEs/Serving Gateways and base stations. A base
station may include many sectors for example: 1, 2, 3, 4, or 6
sectors. A base station may include many cells, for example,
ranging from 1 to 50 cells or more. A cell may be categorized, for
example, as a primary cell or secondary cell. When carrier
aggregation is configured, a wireless device may have one RRC
connection with the network. At RRC connection
establishment/re-establishment/handover, one serving cell may
provide the NAS (non-access stratum) mobility information (e.g.
TAI-tracking area identifier), and at RRC connection
re-establishment/handover, one serving cell may provide the
security input. This cell may be referred to as the Primary Cell
(PCell). In the downlink, the carrier corresponding to the PCell
may be the Downlink Primary Component Carrier (DL PCC), while in
the uplink, it may be the Uplink Primary Component Carrier (UL
PCC). Depending on wireless device capabilities, Secondary Cells
(SCells) may be configured to form together with the PCell a set of
serving cells. In the downlink, the carrier corresponding to an
SCell may be a Downlink Secondary Component Carrier (DL SCC), while
in the uplink, it may be an Uplink Secondary Component Carrier (UL
SCC). An SCell may or may not have an uplink carrier.
[0031] A cell, comprising a downlink carrier and optionally an
uplink carrier, is assigned a physical cell ID and a cell index. A
carrier (downlink or uplink) belongs to only one cell, the cell ID
or Cell index may also identify the downlink carrier or uplink
carrier of the cell (depending on the context it is used). In the
specification, cell ID may be equally referred to a carrier ID, and
cell index may be referred to carrier index. In implementation, the
physical cell ID or cell index may be assigned to a cell. Cell ID
may be determined using the synchronization signal transmitted on a
downlink carrier. Cell index may be determined using RRC messages.
For example, when the specification refers to a first physical cell
ID for a first downlink carrier, it may mean the first physical
cell ID is for a cell comprising the first downlink carrier. The
same concept may apply to, for example, carrier activation. When
the specification indicates that a first carrier is activated, it
equally means that the cell comprising the first carrier is
activated.
[0032] Embodiments may be configured to operate as needed. The
disclosed mechanism may be performed when certain criteria are met,
for example, in wireless device, base station, radio environment,
network, a combination of the above, and/or the like. Example
criteria may be based, at least in part, on for example, traffic
load, initial system set up, packet sizes, traffic characteristics,
a combination of the above, and/or the like. When the one or more
criteria are met, the example embodiments may be applied.
Therefore, it may be possible to implement example embodiments that
selectively implement disclosed protocols.
[0033] Example embodiments of the invention may enable beamforming
information to be exchanged between base stations. Other example
embodiments may comprise a non-transitory tangible computer
readable media comprising instructions executable by one or more
processors to cause beamforming information to be exchanged between
base stations. Yet other example embodiments may comprise an
article of manufacture that comprises a non-transitory tangible
computer readable machine-accessible medium having instructions
encoded thereon for enabling programmable hardware to cause a
device (e.g. wireless communicator, user equipment (UE), base
station, etc.) to exchange beamforming information between base
stations. The device may include processors, memory, interfaces,
and/or the like. Other example embodiments may comprise
communication networks comprising devices such as base stations,
wireless devices (or UE), servers, switches, antennas, and/or the
like.
[0034] According to some of the various aspects of embodiments,
base stations in a wireless network may be directly or indirectly
connected to each other to exchange signaling and data packets.
This interface in LTE and LTE-Advanced may be called an X2
interface. Other embodiments of the interface may also possible,
for example, using an S1 interface. The X2 user plane interface
(X2-U) may be defined between base stations. The X2-U interface may
provide non-guaranteed delivery of user plane packet date units
(PDUs). The transport network layer may be built on internet
protocol (IP) transport and GPRS tunneling protocol user plane
(GTP-U) may be used on top of user datagram protocol (UDP)/IP to
carry the user plane PDUs. The X2 control (X2-C) plane interface
may be defined between two neighbor base stations. The transport
network layer may be built on Stream Control Transmission Protocol
(SCTP) on top of IP. The application layer signaling protocol may
be referred to as X2 Application Protocol (X2-AP). A single SCTP
association per X2-C interface instance may be used with one pair
of stream identifiers for X2-C common procedures. A few pairs of
stream identifiers may be used for X2-C dedicated procedures. The
list of functions on the interface between the base stations may
include the following: mobility support, load management,
inter-cell interference coordination, and data exchange.
[0035] In order to establish an association between two base
stations, a first base station sends a first message to a second
base station to initiate an association between two endpoints. The
first initiation message may comprise multiple parameters such as
the following: initiate tag, advertised receiver window credit,
number of outbound streams, number of inbound streams, an initial
transmit sequence number, a combination thereof, and/or the
like.
[0036] According to some of the various aspects of the embodiments,
an initiation tag may be a 32-bits unsigned integer. The receiver
of the initiation message (the responding end) may record the value
of the initiate tag parameter. This value may be placed into the
verification tag field of SCTP packet(s) that the receiver of the
initiation message transmits within this association. In an
example, the initiation tag may be allowed to have any value except
zero.
[0037] According to some of the various aspects of the embodiments,
the advertised receiver window credit may be a 32-bit unsigned
integer. The sender of the initiation message may reserve a
dedicated buffer space defined by the number of bytes in
association with this window. During the life of the association,
the size of this buffer space may be maintained (e.g., dedicated
buffers taken away from this association); however, an endpoint may
change the value of window credit it sends in a packet. The number
of outbound streams may be represented by a 16-bit unsigned integer
which may define the number of outbound streams the sender of the
initiation message wishes to create during an association. The
number of inbound streams may be represented by a 16-bit unsigned
integer and may define the maximum number of streams the sender of
the initiation message may allow the peer end to create during the
association between the two base stations. The two endpoints may
use the minimum of requested and offered parameters rather than
negotiation of the actual number of streams. The initial transmit
sequence number may be represented by a 32-bit unsigned integer and
may define the initial transmit sequence number that the sender may
use. This field, for example, may be set to the value of the
initiate tag field.
[0038] According to some of the various aspects of embodiments, the
second base station may transmit an initiation acknowledgement
message to acknowledge the initiation of an SCTP association with
the first base station. The parameter part of the initiation
acknowledgement message may be formatted similarly to the
initiation message. The parameter part of the initiation
acknowledgement message may use two extra variable parameters: the
state cookie and the unrecognized parameter. The initiate tag may
be represented by a 32-bit unsigned integer. The receiver of the
initiation acknowledgement message may record the value of the
initiate tag parameter. This value may be placed into the
verification tag field of SCTP packet(s) that the initiation
acknowledgement message receiver transmits within this association.
According to some of the various aspects of the embodiments, the
advertised receiver window credit may represented by a 32-bit
unsigned integer. This value may represent the dedicated buffer
space, in terms of the number of bytes, that the sender of the
initiation acknowledgement message has reserved in association with
this window. During the life of the association, the size of this
buffer space may be maintained (e.g. not be lessened or taken away
from this association).
[0039] According to some of the various aspects of embodiments, the
number of outbound streams may be represented by, for example, a
16-bit unsigned integer. The number of outbound streams may define
the number of outbound streams the sender of the initiation
acknowledgement message wishes to create during this association
between base stations. The number of inbound streams may, for
example, be a represented in terms of a 16-bit unsigned integer. It
may define the maximum number of streams the sender of this
initiation acknowledgement message allows the peer end to create.
The two endpoints may use the minimum of requested and offered
parameters, rather than negotiation of the actual number of
streams. An initial transmit sequence number (TSN) may be a
represented by a 32-bit unsigned integer. The initial transmit
sequence number (TSN) may define the initial TSN that the
initiation acknowledgement message sender may use. This field may
be set to the value of the initiate tag field. The state cookie
parameter may contain the needed state and parameter information
required for the sender of this initiation acknowledgement message
to create the association between base stations. The state cookie
parameter may also include a message authentication code (MAC). An
unrecognized parameter may be returned to the originator of the
initiation message when the initiation message contains an
unrecognized parameter that has a value that indicates it should be
reported to the sender. This parameter value field may contain
unrecognized parameters copied from the initiation message complete
with, for example, parameter type, length, and value fields.
[0040] According to some of the various aspects of embodiments,
when sending an initiation acknowledgement message as a response to
an initiation message, the sender of the initiation acknowledgement
message may create a state cookie and send it in the state cookie
parameter of the initiation acknowledgement message. Inside this
state cookie, the sender may include a message authentication code,
a timestamp on when the state cookie is created, and the lifespan
of the state cookie, along with the information needed for it to
establish the association. The following steps may be taken to
generate the state cookie: 1) Create an association transmission
control block (TCB) using information from both the received
initiation message and the outgoing initiation acknowledgement
messages, 2) In the TCB, set the creation time to the current time
of day, and the lifespan to the protocol parameter to a
pre-determined number, 3) From the TCB, identify and collect the
minimal subset of information needed to re-create the TCB, and
generate a MAC using this subset of information and a secret key,
and/or 4) Generate the state cookie by combining this subset of
information and the resultant MAC.
[0041] After sending the initiation acknowledgement with the state
cookie parameter, the sender may delete the TCB and any other local
resource related to the new association so as to prevent resource
attacks. The hashing method used to generate the MAC may be
strictly a private matter for the receiver of the initiation
message. The MAC may be used to prevent denial-of-service attacks.
The secret key may be random. The secret key may be changed
reasonably frequently, and the timestamp in the state cookie may be
used to determine which key should be used to verify the MAC. An
implementation of an embodiment may make the cookie as small as
possible to ensure interoperability.
[0042] According to some of the various aspects of embodiments, the
first base station may transmit at least one third message to the
second base station. One of the at least one third message may be a
cookie-echo message. The cookie-echo message may be used during the
initialization of an association. It may be sent by the initiator
of an association to its peer to complete the initialization
process. This cookie-echo message may precede any transport packet
message sent within the association and may be bundled with one or
more data transport packet in the same packet. This message may
contain the cookie received in the state cookie parameter from the
previous initiation acknowledgement message. The type and flags of
the cookie-echo may be different than the cookie parameter. Some
embodiments may make the cookie as small as possible to ensure
interoperability. A cookie echo may not contain a state cookie
parameter, but instead, the data within the state cookie's
parameter value becomes the data within the cookie echo's chunk
value. This may allow an implementation of an embodiment to change
the first two bytes of the state cookie parameter to become a
cookie echo message. The first base station may transmit at least
one application protocol message in the cookie echo message.
Alternatively, an implementation option may be for the base station
to transmit application protocol messages after the association is
complete and to not include application protocol messages in a
cookie-echo message.
[0043] The application protocol message may receive a cookie-ack
message from the second base station. This application protocol
message may be used during the initialization of an association.
The application protocol message may also be used to acknowledge
the receipt of a cookie-echo message. This application protocol
message may precede other data sent within the association and may
be bundled with one or more data packets in the same SCTP packet.
The second base station may transmit at least one application
protocol message in a cookie ack message. Alternatively, according
to one embodiment, the base station may choose to transmit
application protocol messages after the association is complete
rather than include application protocol messages in a cookie-ack
message.
[0044] After the initiation and initiation acknowledgement messages
are transmitted, the first base station or the second base station
may transmit an X2 setup message to cause an X2 application
interface to be configured. The first base station or the second
base station may wait until the association is complete to set up
an X2 application interface. Either the first base station or
second base station could start the setup of the X2 application.
The purpose of an X2 setup procedure could be to exchange
application level configuration data needed for two base stations
to interoperate correctly over the X2 interface. This procedure may
erase any existing application level configuration data in the two
nodes and replace the application level configuration data by the
one received by the X2 setup message. This procedure may also reset
the X2 interface.
[0045] A first base station or second base station may initiate the
X2 setup procedure by sending the X2 set up request message to a
candidate base station. The candidate base station may reply with
the X2 set up response message. The initiating base station may
transfer the list of served cells. The candidate base station may
reply with the complete list of its served cells.
[0046] FIG. 11 depicts an example flow chart for a base station
employing beamforming as per an aspect of an embodiment of the
present invention. According to some of the various aspects of
embodiments, a base station may receive a first application
protocol message, for example an X2 set up request message, as
shown in 1101. The X2 set up request message may include the
following information about the originator of the message: a global
base station identifier, the information about the served cells,
and a group identifier list. The group identifier list identifies
the pools to which the base station belongs to. Each row in this
list may include the public land mobile network (PLMN) ID and
mobility management entity (MME) group identifier. The information
about each served cell may include information about the served
cell configurations and may also include the list of neighbor cells
of the served cell including, for example: the cell global
identifier of the neighbor cell, the physical cell identifier of
the neighbor cell, and the frequency of the cells. The served cell
information may include at least one of the following parameters: a
physical cell ID, a global cell identifier, a tracking area code,
at least one broadcast PLMN, frequency division duplexing (FDD)
information (uplink and downlink frequencies, uplink and downlink
transmission bandwidth), time division duplexing (TDD) information
(transmission frequency, subframe assignment, special subframe
information, special subframe pattern, cyclic prefix for downlink
and uplink), number of antenna ports, physical random access
channel (PRACH) configuration, multicast broadcast single frequency
network (MBSFN) subframe info (radio frame allocation period, radio
frame allocation offset, subframe allocation), and a CSG
identifier. The X2 set up request or some other subsequent
application protocol messages may also include a beamforming
codebook comprising a plurality of beamforming codewords. Each of
the plurality of beamforming codewords may be identifiable by an
index. In an example implementation, the codebook may be
transmitted in the form of a look up table including rows, columns,
and/or the like. For example, each row may include the index and
the codeword corresponding to that index. A codeword in a row may
be identifiable by the index in the same row. In another example
implementation, the codewords in a codebook may be ordered
according to their index. Identifying a codeword by an index may be
performed implicitly according to codeword order or codeword
ranking in a list. The indexes may or may not be included in the
message transmitted on the X2 interface. The index(es) may be
employed in other messages in order to refer to the codeword. In an
example implementation, rows could be implemented as columns by
just transposing the implemented matrix or array. It is also
possible to implement a matrix, rows and/or columns of variables
using various techniques such as using pointers, object oriented
programing structures or other various programming structures
configured to store a list of interrelated variables.
[0047] The index may be presented by a number of bits in a
transmitted message between base stations or between a base station
and a wireless device. The number of bits may be greater than or
equal to log.sub.2(N), N being the number of the plurality of
beamforming codewords. The number of bits may be less than the
number of bits in a corresponding beamforming codeword.
[0048] The first base station may receive at least one fourth
message from a second base station. The at least one fourth message
may comprise a second beamforming codebook comprising a second
plurality of codewords. The base station may receive from a second
base station, at least one second application protocol message
comprising at least one index in the plurality of indexes as shown
in 1102. The at least one index may identify a subset of the
plurality of beamforming codewords. The first base station may
transmit signals to a plurality of wireless devices employing a
first plurality of beamforming codewords from a first beamforming
codebook as shown in 1103. The first plurality of codewords may be
selected, at least in part, employing the subset of the second
plurality of beamforming codewords.
[0049] The base station may transmit signals (data and/or control
packets) to a plurality of wireless devices using a first plurality
of beamforming codewords from a first beamforming codebook. The
first plurality of codewords may be selected based, at least in
part, on information received from the other base station. The
information may comprise indexes of codewords from the second
beamforming codebook. In some of the various embodiments, a first
base station may transmit X2 messages to cause configuration of a
table of codewords in a second base station. The first base station
may then refer to the index(es) in the same and/or subsequent
messages to refer to a codeword(s). The process may reduce the
number of bits transmitted on the X2 and/or air interfaces. In an
example embodiment, a codebook may include ten codewords. (N=10).
Each codeword may be a variable presented by fifty bits. The
indexes may be presented by k number of bits, k being a number
greater than or equal to four and less than fifty.
[0050] According to some of the various aspects of embodiments, a
first base station may transmit a first message to initiate an
association between the first base station and a second base
station in the plurality of base stations. The first message may
comprise a first initiation tag. The first base station may receive
a second message from the second base station. The second message
may comprise a second verification tag, a second initiation tag,
and a first state parameter. The second verification tag may be
equal to the first initiation tag. A first state parameter may
comprise at least one parameter related to operational information
of the association and a message authentication code generated as a
function of a private key.
[0051] The first base station may transmit at least one third
message to the second base station. The at least one third message
may comprise a first verification tag, a parameter, and a first
application protocol message. The first verification tag may be
equal to the second initiation tag. The parameter may comprise the
first state parameter. The first application protocol message may
comprise a unique identifier of the first base station, at least
one MME group identifier, and a first beamforming codebook. The
first beamforming codebook may comprise a first plurality of
beamforming codewords. Each of the first plurality of beamforming
codewords may be identifiable by an index. The index may be
presented by a number of bits. The number of bits may be greater
than or equal to log.sub.2(N), wherein N is the number of the
plurality of beamforming codewords. The number of bits may be
smaller than the number of bits in a corresponding beamforming
codeword. The first base station may receive at least one fourth
message from the second base station comprising an acknowledgement
for the receipt of the parameter. The second base station may
transmit signals to a plurality of wireless devices using a second
plurality of beamforming codewords from a second beamforming
codebook. The first plurality of codewords may be selected based,
at least in part, on information received from the first base
station. The information may comprise indices of codewords from
said first beamforming codebook.
[0052] FIG. 10 depicts an example flow chart for a base station
employing beamforming as per an aspect of an embodiment of the
present invention. According to some of the various aspects of
embodiments, a first base station may transmit a first message to
initiate an association between the first base station and a second
base station in the plurality of base stations as shown in 1001.
The first message may comprise a first initiation tag. The first
base station may receive a second message from the second base
station as shown in 1002. The second message may comprise: a second
verification tag, a second initiation tag, a first state parameter,
a combination thereof, and/or the like. The second verification tag
may be equal to the first initiation tag. The first state parameter
may comprise at least one parameter related to operational
information of the association, and a message authentication code
generated as a function of a private key. The first base station
may transmit at least one third message to the second base station
as shown in 1003. The at least one third message may comprise a
first verification tag and a parameter. The first verification tag
may be equal to the second initiation tag. The parameter may
comprise the first state parameter.
[0053] The first base station may receive at least one fourth
message from the second base station as shown in 1004. The at least
one fourth message may comprise an acknowledgement for the receipt
of the parameter, and a second application protocol message. The
second application protocol message may comprise a unique
identifier of the second base station, at least one MME group
identifier, and a second beamforming codebook. The second
beamforming codebook may comprise a second plurality of beamforming
codewords. Each of the second plurality of beamforming codewords
may be identifiable by an index. The index may be presented by a
number of bits. The number of bits may be greater than or equal to
log.sub.2(N), wherein N is the number of the plurality of
beamforming codewords. The number of bits may be smaller than the
number of bits in a corresponding beamforming codeword. The first
base station may transmit signals to a plurality of wireless
devices using a first plurality of beamforming codewords from a
first beamforming codebook as shown in 1006. The first plurality of
codewords may be selected based, at least in part, on information
received from the second base station as shown in 1005. The
information may comprise indices of codewords from the second
beamforming codebook.
[0054] According to some of the various aspects of embodiments, the
first initiation tag value may be selected in the first base
station using a pseudo-random process. The second initiation tag
value may be selected in the second base station using a
pseudo-random process. The first message may further comprise a
first base station transport address and a second base station
transport address. The first message may further comprise a first
advertised receiver window credit representing a dedicated buffer
space that the first base station reserves for a window of received
packets from the second base station. The first message may further
comprise a first initial transmission sequence number that the
first base station uses for transmission of data segments. The
first initial transmission sequence number may be equal to the
first initiation tag.
[0055] The second message may further comprise the first base
station transport address and the second base station transport
address. The second message may further comprise a second
advertised receiver window credit representing a dedicated buffer
space that the second base station reserves for a window of
received packets from the first base station. The second message
may further comprise a second initial transmission sequence number
that the second base station uses for transmission of data chunks.
The second initial transmission sequence number may be equal to the
second initiation tag. The at least one third message may further
comprise the first base station transport address and the second
base station transport address. The at least one third message may
further comprise a transmit sequence number, a stream identifier, a
stream sequence number.
[0056] The at least one fourth message may further comprise a
transmit sequence number, a stream identifier, and a stream
sequence number. The second base station may place the first
initiation tag in the verification tag of every transport layer
packet that it transmits to the first base station within the
association. The first base station may place the second initiation
tag in the verification tag of every SCTP packet that it transmits
to the second base station within the association. The association
may be an SCTP association. The at least one fourth message may
further comprise the first base station transport address and the
second base station transport address. The second application
protocol message may be an X2-Application Protocol Setup Request
message. The second application protocol message may be an
X2-Application Protocol Setup Response message. The at least one
third message may further comprise an X2-Application Protocol Setup
Request message. The at least one third message may further
comprise an X2-Application Protocol Setup Response message.
[0057] The first state parameter may further comprise a timestamp
on when the first state parameter is created. The first state
parameter may further comprise the lifespan of the first state
parameter. The message authentication code may further be a
function of at least one parameter related to operational
information of the association. The at least one third message may
further comprise a first application protocol message. The first
application protocol message may comprise a unique identifier of
the first base station, at least one MME group identifier, a
beamforming codebook comprising a first plurality of beamforming
codewords. Each of the first plurality of beamforming codewords may
be identifiable by an index. The index may be presented by the
first number of bits.
[0058] The first verification tag and the second verification tag
in the association may not change during the life time of the
association. A new verification tag value may be used each time the
first base station or the second base station tears down and then
reestablishes an association with the same node. The operational
information may comprise at least one of the following: a parameter
in the first message, a parameter in the second message, a state of
the association, a configuration parameter of the first base
station, a configuration parameter of the second base station, a
combination thereof, and/or the like. The first message and the
second message may further comprise a checksum for packet
validation. The first base station transport address and the second
base station transport address may comprise an IP address and a
port address.
[0059] The first message may further comprise a first number of
outbound streams that the first base station intend to create and a
first maximum number of inbound streams that the first base station
allows the second base station to create. The second message may
further comprise a second number of outbound streams that the
second base station intend to create, a second maximum number of
inbound streams the second base station allows the first base
station to create. The second number of outbound streams is smaller
than or equal to the first maximum number of inbound streams. The
first base station may further select a number equal or lower than
the minimum of the first number of outbound streams and the second
maximum number of inbound streams as the number of outbound streams
for the first base station.
[0060] The first base station may use the plurality of indexes in
communications with the second base station. Each of the plurality
of indexes may refer to a locally unique beamforming codeword. The
second application protocol message may further comprise the number
of antennas of each cell in the second base station. The second
application protocol message may further comprise a cell ID for
each cell in the second base station. The second application
protocol message may further comprise the frequency of each
downlink and uplink carrier of the second base station. The first
beamforming codebook and second beamforming codebook may be the
same. The first plurality of beamforming codewords may be selected
to reduce inter-cell interference from the second base station. The
first base station may use information received from at least one
wireless device to compute the inter-cell interference from the
second base station.
[0061] The first plurality of beamforming codewords may be selected
to reduce inter-cell interference to the second base station. The
first base station may use information received from at least one
wireless device to compute the inter-cell interference to the
second base station. The first beamforming codebook or the second
beamforming codebook may be defined for a maximum number of
transmit antennas and comprises a set of original codewords. Each
original codeword may have a number of rows or columns equal to the
maximum number of transmit antennas. Codewords for a smaller number
of transmit antennas may be constructed by using a subset of rows
or columns of the original codewords. The first beamforming
codebook or the second beamforming codebook may be defined for a
maximum number of layers and may comprise a set of codewords. Each
codeword may have a number rows or columns equal to the maximum
number of layers. Codewords for a smaller number of layers may be
constructed by using a subset of columns or rows of the original
codewords.
[0062] The first base station may exchange similar messages with a
plurality of second base stations. The first plurality of
beamforming codewords may be selected to reduce inter-cell
interference from a subset of the plurality of second base
stations. The first base station may use information received from
at least one wireless device to compute the inter-cell interference
from the subset of the plurality of second base stations. The first
plurality of beamforming codewords may be selected to reduce
inter-cell interference to a subset of the plurality of second base
stations. The first base station may use information received from
at least one wireless device to compute the inter-cell interference
to the subset of the plurality of second base stations. The second
base station may transmit the same second application protocol
message to a plurality of first base stations. The plurality of
first base stations may select their respective first plurality of
beamforming codewords based on information received from the second
base station in the second application protocol message.
[0063] FIG. 6 is a block diagram of a limited feedback system
according to an aspect of an embodiment of the present invention.
Wireless device 604 measures information about a wireless channel
(either perfect or imperfect) between the base station 602
transmitter and the wireless device 604 receiver. This receiver
channel information may be fed into a quantizer/encoder 605 that
returns a small number of feedback bits to be sent as overhead on
reverse link 606. The base station 602 transmitter may use the
received feedback bits to adapt the transmitted signal to forward
channel 607.
[0064] The limited feedback may be implemented in multiple antenna
wireless systems. Limited feedback may be a viable and beneficial
option for a system that adapts a spatial degree-of-freedom. The
degrees of freedom with multiple antenna systems may be exploited
to offer rate and diversity benefits as well as beamforming and
interference canceling capabilities. While the diversity gain may
be extracted without the need of channel state information at the
transmitter (CSIT) feedback (e.g., space time codes), CSIT may play
a role for beamforming and interference mitigation at the
transmitter.
[0065] A single-user narrowband multiple antenna system may be
represented by an expression of the form y[k]=H[k]x[k]+n[k] at the
k-th channel. Assuming M.sub.t transmit antennas and M.sub.r
receive antennas, y[k] may be an M.sub.r-dimensional receive
vector, H[k] may be an M.sub.r.times.M.sub.t channel response
matrix, x[k] may be an M.sub.t-dimensional transmit vector, and
n[k] may be M.sub.r-dimensional noise. The noise may be assumed to
have independent and identically distributed (iid) normalized
entries distributed according to CN(0, 1). As in the single antenna
case, the scenario where the receiver has access to H[k] may be
considered. Given this, there may be a variety of ways to design
x[k] if the transmitter is given access to some quantized
information relating to H[k]. Again, this analysis may depend on
the time evolution model of the channel. If we use notation of
block-fading, the t.sup.th channel block may satisfy
H[tKch]=H[tKch+1]= . . . =H[(t+1)Kch-1]=H(t) where Kch is the
length of the fading block.
[0066] When the transmitter and receiver both know the channel, the
ergodic capacity may be
R = E H [ log 2 Q : tr ( Q ) .ltoreq. 1 , Q * = Q , Q .gtoreq. 0
max det ( I + .rho. HQH * ) ] . ##EQU00001##
Here, Q may be the covariance of the transmitted signal for each
individual instantaneous channel realization. The covariance of the
transmitted signal may incorporate both the spatial power
allocation as well as unitary precoding. Spatial power allocation
may be needed for cases when the number of transmit antennas is
greater than the number of receive antennas. From an encoding point
of view, x[k]= {square root over (.rho.)}(Q[k]).sup.1/2s[k], k=0, .
. . , K.sub.b1-1 where Q[k] may solve the optimization (based on
channel feedback)
Q [ k ] = log 2 Q : tr ( Q ) .ltoreq. 1 , Q * = Q , Q .gtoreq. 0
argmax det ( I + .rho. HQH * ) . ##EQU00002##
and s[k] may the k-th channel use of an open-loop codeword.
[0067] For a limited rate feedback approach, the general idea may
be to use the fact that the receiver knows H[k] through procedures
such as training. Using this channel knowledge, the receiver may
quantize some function of H[k] using vector quantization (VQ)
techniques.
[0068] Naturally, the aspects of the channel that the transmitter
cares about are those that allow the design of the covariance for
the t.sup.th channel block. Using this line of reasoning, the
receiver may determine a rate maximizing covariance and feed this
back to the transmitter. Employing a codebook of possible
covariance matrices Q={Q.sub.1, . . . , Q.sub.2.sub.B} that may be
known to the transmitter and receiver, the receiver may search for
the codebook index.
[0069] The covariance codebook may be either fixed or randomly
generated (using a seed known to both the transmitter and
receiver). Designing a fixed covariance codebook to maximize the
average rate may be a challenging problem that depends on the
stationary distribution of the channel. Vector quantization
approaches may efficiently generate codebooks that achieve a large
rate. Random approaches for a covariance design may also be
possible. The rate loss with B bits of feedback may decrease with
the number of feedback bits.
[0070] While the codebook approach may be used for a block-to-block
independently fading channel, temporal correlation between channel
realizations may improve quantization. Feedback approaches based on
tracking the channel using gradient analysis may also be possible.
The use of switched codebooks, where the codebook is changed or
adapted over time may be implemented. Orientation and radius of a
localized codebook cap changing over time may be implemented with
beamforming codebooks which have adaptive localized codebook caps.
Models may be used to implement feedback compression. For example,
Markov chain compression may be employed to analyze the effects of
feedback delay and channel time evolution.
[0071] In an example embodiment, beamforming may be characterized
by the use of a rank one covariance matrix. Using a rank one Q
matrix may be useful whenever the single-user channel is itself
rank one. This may occur when the user terminal is equipped with a
single antenna. In this situation, the availability of CSIT may be
needed.
[0072] In beamforming, the single-user multiple input multiple
output (MIMO) expression in y[k]=H[k]x[k]+n[k] may be restricted so
that x[k]= {square root over (.rho.)}f[k]s[k] where f[k] is a
channel dependent vector referred to as a beamforming vector and
s[k] is a single-dimensional complex symbol chosen independently of
instantaneous channel conditions. In the multiple input single
output (MISO) case, there may be a single receive antenna. In this
case, y[k] may be reformulated as y[k]= {square root over
(.rho.)}h.sup.T[k]f[k]s[k]+n[k]. h[k] may be a column vector. With
this configuration, the receive SNR at channel use k (averaged with
respect to the transmitted signal and noise) may be given by
SNR[k]=.rho.|h.sup.T[k]f[k]|.sup.2.
[0073] For MIMO beamforming and combining, a receive-side combining
vector z[k] (sometimes, but not necessarily, unit norm) may be used
so that after processing y[k]= {square root over
(.rho.)}z*[k]H[k]f[k]s[k]+z*[k]n[k]. Conjugate transpose is denoted
by *. Various forms of combiners may be implemented.
[0074] The receiver may be allowed to send some feedback to assist
the transmitter's configuration. An example form of this feedback
may select a transmit antenna(s). In this scenario, the transmit
beamforming vector may be restricted such that one entry is
non-zero. With this kind of set-up in a MISO system, a solution may
be to send data on the antenna that substantially maximizes the
receiver SNR, meaning data (and power) may be sent on antenna
m.sub.opt[k]=.sub.1.ltoreq.m.ltoreq.M.sub.t.sup.argmax|h.sub.m[k]|.sup.2
[0075] h.sub.m[k] may denote the m.sup.th antenna entry of the
channel vector h[k]. Using this approach, the selected antenna may
be configured at the receiver and may be sent back to the
transmitter using [log.sub.2(M.sub.t)]bits. Error rates with
antenna selection for spatially uncorrelated set-ups may be
considered.
[0076] Antenna selection may be limited in terms of its benefits to
the overall capacity as it may not allow for the full beamforming
gain. If there exists a feedback link, more complicated forms of
channel dependent feedback may improve performance. The channel
vector may be quantized for a MISO system into a set of normalized
column vectors={h.sub.1, . . . , h.sub.2.sub.B}. Because the system
may have a single receive antenna, the channel vector h[k] may be
quantized over this set by selecting the codebook vector
h.sub.n.sub.opt[k] using a phase invariant distortion such that
n.sub.opt[k]=.sub.1.ltoreq.m.ltoreq.2.sub.B.sup.argmax|h*.sub.n-
h[k]|.sup.2.
[0077] The transmitter can then pick a beamforming vector that
solves
f [ k ] = log 2 f : .parallel. f .parallel. = 1 argmax ( 1 + .rho.
| h n opt [ k ] T f | 2 ) = ( h n opt [ k ] T ) * .parallel. h n
opt [ k ] T .parallel. 2 . ##EQU00003##
[0078] Equal gain approaches that attempt to co-phase the signals
received from various antennas may be implemented. This concept may
be implemented to quantize the phases of each h.sub.m[k], m=1, . .
. , M.sub.t, using uniform phase quantization on a unit circle.
[0079] The codebooks may allow the receiver to directly configure
the beamforming vector and send this vector back to the
transmitter. In one example embodiment, beamforming vector
quantization may be considered rather than channel quantization.
f[k] may be restricted to lie in a set or codebook F={f.sub.1, . .
. , f.sub.2.sub.B}. The receiver may use its channel knowledge to
pick the required vector from the codebook.
[0080] This kind of approach is demonstrated in FIG. 7 using the
interpretation that beamforming may be rank one precoding. FIG. 7
is a block diagram of a limited feedback linear precoded MIMO
system according to an embodiment. The receiver 702 in wireless
device 701 may use a channel estimate to pick the optimal
transmitter-side linear precoder from a codebook known to the
transmitter and receiver. The wireless device 701 may use
quantization 703 to calculate feedback. For a codebook of size
2.sup.B, the B-bit binary label of the chosen precoder may be sent
over feedback channel 705 to base station 704. Note that the rate
and/or SNR may also be known as side information to facilitate
communication and may be fed back to the base station.
[0081] The receiver now, in some sense, may control how the signal
is adapted to the channel. Phase quantization codebooks may be
implemented for MIMO beamforming and combining. This may jointly
quantize the phases across transmit antennas and implement
diversity. While equal gain approaches may be an option, a general
design framework may be useful. Determining favorable configuration
parameters for a spatially uncorrelated Rayleigh fading channel may
be a goal for outage minimizing, SNR maximizing, rate maximizing, a
combination thereof, and/or the like.
[0082] For a channel, the maximum diversity order may be when the
rank of the matrix [f.sub.1, . . . , f.sub.2.sub.B] constructed
from the set of beamforming vectors has a rank of M.sub.t. Receiver
SNR degradation may be analyzed. Insights from the problem of
Grassmannian line packing designs may be used to assist analysis.
Closed-form integral expressions may be obtained by modeling the
feedback problem as one of a correlated antenna selection. An
alternative approach to Grassmannian codebooks may be to construct
the codebooks using vector quantization (VQ) techniques. A
distortion function (usually related to rate loss or SNR loss) may
be formulated and the distortion function may be iteratively
minimized to obtain local solutions. Using multiple iterations with
different (possibly randomized) initial settings may yield an
approximately optimal codebook. Because of the unit vector
constraints on the beamforming vector set, this may be a problem in
spherical vector quantization. VQ designs also may have useful
analytical properties when the codebook size (or quantizer
resolution) increases. High resolution analysis and codebook design
may be leveraged to give new insight into codebook behavior.
[0083] Grassmannian and VQ limited feedback designs may assume
codebooks that are fixed and do not vary as the channel changes.
Another implementation may be to randomly generate the codebook at
each block (with the randomly generated codebook known to both the
transmitter and receiver). This sort of codebook design technique
may be based on random vector quantization (RVQ). The idea here is
to generate the 2.sup.B codebook vectors independently and all
identically distributed according to the stationary distribution of
the quantized beamforming vector.
[0084] For example, a MISO system with channel information at the
transmitter and receiver may use a beamforming vector
f [ k ] = ( h T [ k ] ) * .parallel. h [ k ] .parallel. 2
##EQU00004##
(known as maximum ratio transmission). When the channel
distribution is a spatially uncorrelated Rayleigh, the vector may
follow a uniform distribution on the unit sphere. Thus, the RVQ
codebook may be constructed by taking 2.sup.B independently and
uniformly generated points on the unit sphere. These kinds of
codebooks may have very asymptotic properties as the number of
antennas scales to infinity. Closed-form analysis may also be
possible when the channel follows a spatially uncorrelated Rayleigh
model. Several other codebook designs may be considered as
alternatives to Grassmannian line packings, vector quantization,
and RVQ. Equiangular frame based codebooks may be implemented based
on the observation that (in the real case) codebooks from
equiangular frames maximize the mutual information between the true
beamforming vector and the quantized precoding vector. In certain
cases Grassmannian line packing may lead to equiangular frames.
Codebooks may be generalized based on the Fourier concept for
limited feedback. The key idea is to recognize that the
non-coherent MIMO space-time code design problem may also be the
problem of finding packings on the Grassmann manifold. DFT
codebooks may introduce additional structure in Fourier codebooks,
further simplifying their design. Adaptive modulation may be
combined with beamforming codebooks. Techniques for dealing with
time variation of the channel during the feedback phase may be
considered in an example implementation.
[0085] Fourth generation (4G) and beyond cellular standards may use
MIMO-OFDM technology. Generalizing the input-output relation to
MIMO for the v.sup.th subcarrier yields {tilde over (y)}v[{tilde
over (k)}]={tilde over (H)}v[{tilde over (k)}]{tilde over
(X)}v[{tilde over (k)}]+nv[{tilde over (k)}] for OFDM channel use
{tilde over (k)}. In the formula, {tilde over (y)}v[{tilde over
(k)}] is an M.sub.r-dimensional received signal for subcarrier v,
{tilde over (H)}v[{tilde over (k)}] is an M.sub.r.times.M.sub.t
channel realization (in the frequency domain) for the v.sup.th
subcarrier, {tilde over (x)}v[{tilde over (k)}] is an
M.sub.t-dimensional transmitted signal for subcarrier v, and
nv[{tilde over (k)}] is M.sub.r-dimensional normalized additive
noise with iid CN(0, 1) entries.
[0086] MIMO channel adaptation may be done on a per-subcarrier
basis. For example, a linear precoded spatial multiplexing system
may set {tilde over (x)}v[{tilde over (k)}]= {square root over
(.rho.v)}{tilde over (F)}v[{tilde over (k)}]{tilde over
(s)}v[{tilde over (k)}], where .rho.v is the SNR on subcarrier v,
{tilde over (F)}v[{tilde over (k)}] is the M.sub.t.times.M precoder
on subcarrier v, and {tilde over (s)}v[{tilde over (k)}] is an
M-dimensional transmitted spatial multiplexing vector. The precoder
{tilde over (F)}v[{tilde over (k)}] may be adapted directly to
{tilde over (H)}v[{tilde over (k)}].
[0087] MIMO-OFDM feedback systems may send feedback for pilot
subcarriers v.sub.0, . . . , v.sub.K.sub.pilot-1 where K.sub.pilot
is a function of the number of pilots. For example, a precoding
system using limited feedback with a common codebook for all pilots
of F={F.sub.1, . . . , F.sub.2.sub.B} may send B bits for each
pilot subcarrier for a total feedback load of BK.sub.pilot bits per
channel block. Given this information, the precoders for non-pilots
may be determined.
[0088] It may be possible to weight and sum together the feedback
beamforming vectors from the two nearest pilots. The weights may be
configured to maximize the receive SNR of the subcarrier halfway
between the two pilots. A transform domain quantization approach
may be implemented. The precoder interpolation problem may be
formulated as a weighted least squares problem. The weights may
correspond to the distance (in number of subcarriers) from
different pilot precoders. The technique may be generalized to
larger rank precoding interpolation techniques. A geodesic approach
(i.e., linear interpolation on the Grassmann manifold) may also be
used. Other interpolation ideas may also be available. Instead of
trying to interpolate, another implementation may be based on,
where a common precoder is chosen for several contiguous
subcarriers. The clustering implementation may yield an antenna
subset selection criterion when the cluster is extended to cover
all or most subcarriers (i.e., only one pilot) and the precoding
codebook has the
( M t M ) ##EQU00005##
antenna subset matrices.
[0089] The transmitter may recreate precoders employing precoder
feedback sent on a subset of the subcarriers in conjunction with
the channel correlation in the frequency domain. Clustering may
also be implemented. In this case, the transmitter and receiver may
divide (or cluster) the subcarriers in a predetermined way. All
narrowband channels within the cluster may use the same feedback
and use the same precoding matrix. The receiver may then design the
feedback to choose a precoder that is mutually beneficial (e.g.,
with respect to sum rate).
[0090] Alternative techniques besides clustering and interpolation
may also be implemented. For example, Trellis techniques for
precoder interpolation may be used. Successive beamforming taking
into account correlation in time and frequency may be implemented.
A reduced CSI feedback approach for MIMO-OFDM may take into account
that highly correlated channels may have highly correlated feedback
values; thus, the number of bits may be effectively reduced by
taking the actual correlation between binary sequences into
account.
[0091] The multi-mode precoding implementations may also be
quantized. In this scenario, both the matrix and the rank of the
matrix may evolve over the OFDM symbol subcarriers. An
interpolation framework for multi-mode precoding may be used.
[0092] 3GPP LTE and LTE-advanced may employ a MIMO-OFDMA physical
layer on the downlink and may support various single and multiple
user MIMO modes of operation. Several different single-user
codebook based limited feedback techniques may be used. Codebook
based precoding on the downlink may be implemented, for example,
with two, four, or eight transmit antennas. In the case of two
antennas, a beamforming codebook with six vectors (including two
corresponding to antenna selection) and a precoding codebook with
three matrices may be implemented. For four antennas, a four bit
codebook may be used for beamforming and precoding with two, three,
and four streams. The precoding codebooks may be built by taking
specific subsets of Householder reflection matrices generated from
the beamforming entries. The subsets may be chosen to have a nested
structure. For example, for a given generating vector, the two
stream codebook may include the original vector and an additional
vector. The three stream codebook may add an additional vector and
so on. This may facilitate multi-mode rank adaptation where the
base station may change the number of active streams, and may offer
some computational savings.
[0093] 3GPP codebooks may use a finite alphabet structure, which
may make them easy to store and may simplify computation.
[0094] A second base station may transmit to a first base station a
load indication message. The load indication message may be
transmitted periodically or regularly as needed. The first base
station may request a load indication message and indicate the
transmission period and duration. The load indication message may
comprise at least one of the following fields: an uplink
interference overload, an uplink high interference indication, a
transmit power parameter, and an almost blank subframe. The
transmitter of a load indication message may request a similar or
different load indication message from the base station receiving
the message. The invoke indication in the message may indicate
which type of information a base station requesting the other base
station may send back. A base station MAC and physical layer may
schedule and transmit downlink packets based, at least in part, on
the received load indication messages.
[0095] An uplink interference overload for the uplink carrier may
indicate the status of uplink interference. The uplink carrier may
comprise a plurality of uplink resource blocks. The uplink
interference overload may indicate a status of uplink interference
for each uplink resource block in the plurality of uplink resource
blocks. The status of uplink interference may be represented as one
of a plurality of predefined interference level indicators. The
uplink high interference indication may comprise a list of a target
carrier identifier and a status of uplink target interference. The
status of uplink target interference may indicate the status of
uplink target interference for each resource block in the plurality
of uplink resource blocks. The status of uplink target interference
may indicate a high interference sensitivity and/or low
interference sensitivity.
[0096] The transmit power parameter for the downlink carrier may
comprise a status of transmit power for each downlink resource
block, the number of antenna ports for the downlink carrier, PDCCH
information, beamforming information, a combination thereof, and/or
the like. The status of transmit power for downlink resource
block(s) may indicate a status of transmit power for downlink
resource block(s) in the plurality of downlink resource blocks. The
status of transmit power for a downlink resource block may be one
of a first value when transmit power of the downlink resource block
is below a pre-defined threshold and a second value when transmit
power of the downlink resource block is below or above the
pre-defined threshold. The PDCCH interference impact may be
presented by predicted number of occupied PDCCH OFDM Symbols. The
PDCCH interference impact may be one of 0, 1, 2, 3, and 4, wherein
value 0 indicates no prediction is available for load information
transmission;
[0097] FIG. 12 depicts an example flow chart for a base station
employing beamforming as per an aspect of an embodiment of the
present invention. According to some of the various aspects of
embodiments, a first base station may receive from a second base
station at least one application protocol message as shown in 1201.
The at least one application protocol message may be received, for
example from an X2 interface or an S1 interface. The first base
station and the second base station may be configured to
communicate with a plurality of wireless devices employing a
downlink carrier. The downlink carrier may comprise a plurality of
resource blocks. The at least one application protocol message may
comprise a downlink beamforming information element for at least
one resource block in the downlink carrier. In another
implementation at least one application protocol message may
comprise a plurality of downlink or uplink beamforming information
elements, each one for one or more resource blocks.
[0098] The downlink beamforming information element may indicate a
second beamforming codeword employed by the second base station for
the at least one resource block. In another example implementation
the downlink beamforming information element may indicate a
plurality of second beamforming codeword employed by the second
base station for the at least one resource block. The codewords are
employed for beamforming. In an example implementation, the second
beamforming codeword may have a number of rows or columns equal to
a number of antenna ports employed by the second base station for
beamforming on the downlink carrier. As described previously, an
array/matrix may be stored using multiple programming code
structures. The number of rows or columns refers to the information
in a codeword which can be stored using various methods. In another
example embodiment second beamforming codeword may have a number of
rows or columns less than a number of antenna ports employed by the
second base station for beamforming on the downlink carrier
[0099] The second beamforming codeword may be included in (be a
part of) a second beamforming codebook. In an example
implementation, the second beamforming codeword may be referenced
by an index. Instead of transmitting an entire codeword, the index
for the codeword may be transmitted. Correspondence between the
beamforming codeword and the index may be defined by an application
protocol message. The application protocol message may be received
prior to the at least one application protocol message
reception.
[0100] The first base station may select for the at least one
resource block, a first beamforming codeword from a first
beamforming codebook as shown in 1202. The selection may be based,
at least in part, on the downlink beamforming information element
received from the second base station. The first base station may
transmit, employing the first beamforming codeword, signals on a
subset of the at least one resource block to a wireless device as
shown in 1203. The signals may carry control or data packets for
one or more wireless devices.
[0101] According to some of the various aspects of embodiments, a
first base station may receive from a second base station at least
one application protocol message. The first base station and the
second base station may be configured to communicate with a
plurality of wireless devices employing a downlink carrier. The
downlink carrier may comprise a plurality of resource blocks. The
at least one application protocol message may comprise a downlink
beamforming information element for at least one resource block in
the downlink carrier. The downlink beamforming information element
may indicate a second beamforming codeword employed by the second
base station for the at least one resource block. The second
beamforming codeword may be referenced by an index. The second
beamforming codeword may be included in a second beamforming
codebook.
[0102] The first base station may select for the at least one
resource block, a first beamforming codeword from a first
beamforming codebook. The selection may be based, at least in part,
on the downlink beamforming information element received from the
second base station. The first base station may transmit, employing
the first beamforming codeword, signals on a subset of the at least
one resource block to a wireless device. The signals may carry
control or data packets for one or more wireless devices.
[0103] The at least one application protocol message may be
transmitted periodically. At least one application protocol message
may further comprise a load indication message. At least one
application protocol may comprise a transmit power parameter for
the downlink carrier. The transmit power parameter may comprise a
status of transmit power for each downlink resource block in the
plurality of downlink resource blocks. The status of transmit power
for a downlink resource block may be one of a first value when
transmit power of the downlink resource block is below a
pre-defined threshold and a second value when transmit power of the
downlink resource block is below or above the pre-defined
threshold.
[0104] The subset of the plurality of downlink resource blocks may
be selected based, at least in part, on the transmit power
parameter and the downlink beamforming information. The first
beamforming codebook and second beamforming codebook may be the
same. The first plurality of beamforming codewords may be selected
to reduce inter-cell interference from the second base station. The
first base station may use information received from at least one
wireless device to compute the inter-cell interference from the
second base station. The first base station may use a zero-forcing
criterion to select a subset of the first plurality of beamforming
codewords. The first base station may use a minimum mean squared
error criterion to select a subset of the first plurality of
beamforming codewords. The first plurality of beamforming codewords
may be selected to reduce inter-cell interference to the second
base station.
[0105] The first base station may use information received from at
least one wireless device to compute the inter-cell interference to
the second base station. The first base station may use a maximum
signal to leakage ratio criterion to select a subset of the
plurality of beamforming codewords. One skilled in the art may use
other criterions. The first beamforming codebook or the second
beamforming codebook may be defined for a maximum number of
transmit antennas and may comprise a set of original codewords.
Each original codeword may have a number rows equal to the maximum
number of transmit antennas. Codewords for a smaller number of
transmit antennas may be constructed by using a subset of rows of
the original codewords. The first beamforming codebook or the
second beamforming codebook may be defined for a maximum number of
layers and may comprise a set of original codewords. Each original
codeword may have a number columns (or rows) equal to the maximum
number of layers. Codewords for a smaller number of layers may be
constructed by using a subset of columns (or rows) of the original
codewords. The first base station may receive similar application
protocol messages from a plurality of second base stations.
[0106] The first plurality of beamforming codewords may be selected
to reduce inter-cell interference from a subset of the plurality of
second base stations. The first base station may use information
received from at least one wireless device to compute the
inter-cell interference from the subset of the plurality of second
base stations. The first base station may use a zero-forcing
criterion to select a subset of the first plurality of beamforming
codewords. The first base station may use a minimum mean squared
error criterion to select a subset of the first plurality of
beamforming codewords. The first plurality of beamforming codewords
may be selected to reduce inter-cell interference to a subset of
the plurality of second base stations. The first base station may
use information received from at least one wireless device to
compute the inter-cell interference to the subset of the plurality
of second base stations. The first base station may use a maximum
signal to leakage criterion to select a subset of the first
plurality of beamforming codewords. The second base station may
transmit the same second application protocol message to a
plurality of first base stations. The plurality of first base
stations may select their respective first plurality of beamforming
codewords based on information received from the second base
station in the second application protocol message.
[0107] FIG. 8 is a block diagram for beamforming information
exchange according to at least one embodiment. In an example
embodiment, a first base station 802 may comprise a communication
interface, a processor, and a memory storing instructions that,
when executed, cause the first base station to cause certain
functions. The first base station 802 may receive at least one
application protocol message from a second base station 801 using
interface 807. The second base station 801 may comprise a downlink
carrier comprising a plurality of downlink resource blocks. The at
least one application protocol message may comprise downlink
beamforming information for the downlink carrier. The downlink
beamforming information may indicate, for each downlink resource
block in the plurality of downlink resource blocks, a beamforming
codeword employed for the downlink resource block. The first base
station 802 may obtain channel state input information for a
wireless device based on, at least in part, processing the downlink
beamforming information. The first base station may transmit the
channel state input information 804 to the wireless device 803 in a
message, for example, a measurement information message. The
wireless device 803 may use the channel state input information to
compute a precoding matrix indicator. The first base station 802
may receive a channel state feedback 805 from the wireless device.
The channel state feedback may comprise the precoding matrix
indicator. Each of the beamforming codewords may be represented by
an index and may belong to a first beamforming codebook. The
correspondence between a beamforming codeword and an index may be
defined by an application protocol message received prior to the at
least one application protocol message reception. The base station
may transmit packets to the wireless device 803 using beamforming
transmission 806.
[0108] FIG. 9 depicts message flow between a base station 902 and a
wireless device 901, according to at least one embodiment. The
first base station 902 may receive at least one application
protocol message from a second base station in the plurality of
base stations. The second base station may comprise a downlink
carrier comprising a plurality of downlink resource blocks. The at
least one application protocol message may comprise the number of
antenna ports for the downlink carrier and downlink beamforming
information for the downlink carrier. The downlink beamforming
information may indicate, for each downlink resource block in the
plurality of downlink resource blocks, a beamforming codeword
employed for the downlink resource block. Each of the beamforming
codewords may depend on the number of antenna ports and may be
represented by an index and belonging to a first beamforming
codebook. The first base station may select a subset of the
downlink beamforming information for wireless device 901. The first
base station 902 may transmit a control message 903 to wireless
device 901. The control message may comprise an identifier of the
second base station, and the subset of the downlink beamforming
information. First base station 902 may receive a channel state
feedback 904 from the wireless device 901. The channel state
feedback may comprise a precoding matrix indicator. The wireless
device 901 may measure reference signals received from the second
base station and process the measured reference signals based, at
least in part, on the subset to compute the precoding matrix
indicator. The first base station 902 may transmit packets to the
wireless device 901 using beamforming transmission 905.
[0109] FIG. 13 depicts an example flow chart for a base station
employing beamforming as per an aspect of an embodiment of the
present invention. A first base station may receive from a second
base station at least one application protocol message as shown in
1301. The first base station and the second base station may be
configured to communicate with a plurality of wireless devices
employing a downlink carrier. The downlink carrier may comprise a
plurality of resource blocks. The at least one application protocol
message may comprise a downlink beamforming information element for
at least one resource block in the downlink carrier. The downlink
beamforming information element may indicate a second beamforming
codeword employed by the second base station for the at least one
resource block. The second beamforming codeword may be included in
(be a part of) a second beamforming codebook. The first base
station may compute a channel state input information element for a
wireless device based on, at least in part, processing the downlink
beamforming information element as shown in 1302. The first base
station may transmit the channel state input information element to
the wireless device for computing a precoding matrix indicator as
shown in 1303. The first base station may receive a channel state
feedback from the wireless device. The channel state feedback may
comprise the precoding matrix indicator as shown in 1304.
[0110] According to some of the various aspects of embodiments, a
wireless device may receive channel state input information from a
first base station. The wireless device may compute a precoding
matrix indicator using the channel state input information. The
wireless device may transmit a channel state information comprising
the precoding matrix indicator to the first base station.
[0111] According to some of the various aspects of embodiments, the
wireless device may receive channel state input information from a
first base station in the plurality of base stations. The first
base station may obtain the channel state input information based,
at least in part, on processing downlink beamforming information
received from a second base station in the plurality of base
stations. The first base station may compute a precoding matrix
indicator using the channel state input information. The first base
station may transmit a channel state information comprising the
precoding matrix indicator to the first base station.
[0112] According to some of the various aspects of embodiments, the
wireless device may receive channel state input information from a
first base station in the plurality of base stations. The first
base station may obtain the channel state input information based,
at least in part, on processing downlink beamforming information
received from a second base station in the plurality of base
stations. The second base station may comprise a downlink carrier
comprising a plurality of downlink resource blocks. The downlink
beamforming information may indicate a beamforming codeword
employed by the second base station for each downlink resource
block in the plurality of downlink resource blocks. The wireless
device may compute a precoding matrix indicator using the channel
state input information. The wireless device may transmit channel
state information comprising the precoding matrix indicator to the
first base station.
[0113] According to some of the various aspects of embodiments, the
wireless device may receive a control message from a first base
station in the plurality of base stations. The control message may
comprise an identifier of a second base station in the plurality of
base stations, and channel state input information. The channel
state input information may be a subset of downlink beamforming
information received from the second base station. The second base
station may comprise a downlink carrier comprising a plurality of
downlink resource blocks. The downlink beamforming information may
indicate a beamforming codeword employed by the second base station
for each downlink resource block in the plurality of downlink
resource blocks. The wireless device may measure reference signals
received from the second base station. The wireless device may
process the measured reference signals based, at least in part, on
the channel state input information to compute a precoding matrix
indicator. The wireless device may transmit channel state
information comprising the precoding matrix indicator to the first
base station. The processing of the measured reference signals may
comprise multiplying measured reference signal(s) by at least one
codeword in the channel state input information.
[0114] According to some of the various aspects of embodiments, a
wireless device may receive a control message from a first base
station. The control message may comprise an identifier of a second
base station in the plurality of base stations. The control message
may comprise a channel state input information element. The channel
state input information element may be based, at least in part, on
a downlink beamforming information element received by the first
base station from a second base station. The downlink beamforming
information element may indicate a beamforming codeword employed by
the second base station for at least one downlink resource block.
The wireless device may measure reference signals received from the
second base station. The wireless device may process the measured
reference signals based, at least in part, on the channel state
input information element to compute a precoding matrix indicator.
The wireless device may transmit a channel state information
comprising the precoding matrix indicator to the first base
station. The processing of the measured reference signals may
comprise multiplying measured reference signal by at least one
codeword in the channel state input information.
[0115] According to some of the various aspects of embodiments, a
wireless device may receive from a first base station a channel
state input information element. The channel state input
information element may be based, at least in part, on a downlink
beamforming information element received by the first base station
from a second base station. The downlink beamforming information
element may indicate a beamforming codeword employed by the second
base station for at least one downlink resource block. The wireless
device may compute a precoding matrix indicator employing the
channel state input information element. The wireless device may
transmit channel state information comprising the precoding matrix
indicator to the first base station.
[0116] The channel state input information may be a codebook subset
restriction bitmap parameter. The wireless device may select a
precoding matrix indicator from a subset of the precoding codebook
indicated by the codebook subset restriction bitmap parameter. The
processing of the measured reference signals may include vector
quantization and encoding. The processing of the measured reference
signals may comprise multiplying measured reference signal(s) by at
least one codeword in the downlink beamforming information. The
wireless device may further measure the data signals received from
the base station. The precoding matrix indicator may be calculated
to reduce downlink inter-cell interference. The channel state
feedback may further comprise a channel quality indicator. The
channel state feedback may further comprise a rank indicator. The
precoding matrix indicator may be selected from a plurality of
predetermined precoding matrix indicators.
[0117] The first base station may transmit a plurality of packets
to the wireless device. The plurality of packets may be transmitted
using the precoding matrix indicator. The precoding matrix
indicator may be computed for a sub-band of the downlink carrier.
The first base station may further transmit at least one control
message to the wireless device. The at least one control message
may configure measurement parameters of the wireless device. The
first base station may demodulate, despread, and decode the
received channel state feedback. The channel state feedback may be
modulated using SC-FDMA. The subset of the downlink beamforming
information may comprise a plurality of beamforming codewords
employed for a subset of the plurality of downlink resource blocks.
The wireless device may use a zero-forcing criterion to compute the
precoding matrix indicator. The wireless device may use a minimum
mean squared error criterion to compute the precoding matrix
indicator.
[0118] The subset of downlink beamforming information may comprise
beam information from the second base station that causes
substantial inter-cell interference to the wireless device. The
first beamforming codebook may be defined for a maximum number of
transmit antennas and may comprise a set of original codewords.
Each original codeword may have a number of rows (or columns) equal
to the maximum number of transmit antennas. Codewords for a smaller
number of transmit antennas may be constructed by using a subset of
rows (or columns) of the original codewords. The first beamforming
codebook may be defined for a maximum number of layers and comprise
a set of original codewords. Each original codeword may have a
number of columns (or rows) equal to the maximum number of layers.
Codewords for a smaller number of layers may be constructed by
using a subset of columns of the original codewords. The smaller
number of layers may be equal to a rank indicated by the wireless
device through a rank indicators field in the channel state
feedback.
[0119] According to some of the various aspects of embodiments, the
packets in the downlink may be transmitted via downlink physical
channels. The carrying packets in the uplink may be transmitted via
uplink physical channels. The baseband data representing a downlink
physical channel may be defined in terms of at least one of the
following actions: scrambling of coded bits in codewords to be
transmitted on a physical channel; modulation of scrambled bits to
generate complex-valued modulation symbols; mapping of the
complex-valued modulation symbols onto one or several transmission
layers; precoding of the complex-valued modulation symbols on
layer(s) for transmission on the antenna port(s); mapping of
complex-valued modulation symbols for antenna port(s) to resource
elements; and/or generation of complex-valued time-domain OFDM
signal(s) for antenna port(s).
[0120] Codeword, transmitted on the physical channel in one
subframe, may be scrambled prior to modulation, resulting in a
block of scrambled bits. The scrambling sequence generator may be
initialized at the start of subframe(s). Codeword(s) may be
modulated using QPSK, 16 QAM, 64 QAM, 128 QAM, and/or the like
resulting in a block of complex-valued modulation symbols. The
complex-valued modulation symbols for codewords to be transmitted
may be mapped onto one or several layers. For transmission on a
single antenna port, a single layer may be used. For spatial
multiplexing, the number of layers may be less than or equal to the
number of antenna port(s) used for transmission of the physical
channel. The case of a single codeword mapped to multiple layers
may be applicable when the number of cell-specific reference
signals is four or when the number of UE-specific reference signals
is two or larger. For transmit diversity, there may be one codeword
and the number of layers may be equal to the number of antenna
port(s) used for transmission of the physical channel.
[0121] The precoder may receive a block of vectors from the layer
mapping and generate a block of vectors to be mapped onto resources
on the antenna port(s). Precoding for spatial multiplexing using
antenna port(s) with cell-specific reference signals may be used in
combination with layer mapping for spatial multiplexing. Spatial
multiplexing may support two or four antenna ports and the set of
antenna ports used may be {0, 1} or {0, 1, 2, 3}. Precoding for
transmit diversity may be used in combination with layer mapping
for transmit diversity. The precoding operation for transmit
diversity may be defined for two and four antenna ports. Precoding
for spatial multiplexing using antenna ports with UE-specific
reference signals may also, for example, be used in combination
with layer mapping for spatial multiplexing. Spatial multiplexing
using antenna ports with UE-specific reference signals may support
up to eight antenna ports. Reference signals may be pre-defined
signals that may be used by the receiver for decoding the received
physical signal, estimating the channel state, and/or other
purposes.
[0122] For antenna port(s) used for transmission of the physical
channel, the block of complex-valued symbols may be mapped in
sequence to resource elements. In resource blocks in which
UE-specific reference signals are not transmitted the PDSCH may be
transmitted on the same set of antenna ports as the physical
broadcast channel in the downlink (PBCH). In resource blocks in
which UE-specific reference signals are transmitted, the PDSCH may
be transmitted, for example, on antenna port(s) {5, {7}, {8}, or
{7, 8, . . . , v+6}, where v is the number of layers used for
transmission of the PDSCH.
[0123] Common reference signal(s) may be transmitted in physical
antenna port(s). Common reference signal(s) may be cell-specific
reference signal(s) (RS) used for demodulation and/or measurement
purposes. Channel estimation accuracy using common reference
signal(s) may be reasonable for demodulation (high RS density).
Common reference signal(s) may be defined for LTE technologies,
LTE-advanced technologies, and/or the like. Demodulation reference
signal(s) may be transmitted in virtual antenna port(s) (i.e.,
layer or stream). Channel estimation accuracy using demodulation
reference signal(s) may be reasonable within allocated
time/frequency resources. Demodulation reference signal(s) may be
defined for LTE-advanced technology and may not be applicable to
LTE technology. Measurement reference signal(s), may also called
CSI (channel state information) reference signal(s), may be
transmitted in physical antenna port(s) or virtualized antenna
port(s). Measurement reference signal(s) may be Cell-specific RS
used for measurement purposes. Channel estimation accuracy may be
relatively lower than demodulation RS. CSI reference signal(s) may
be defined for LTE-advanced technology and may not be applicable to
LTE technology.
[0124] In at least one of the various embodiments, uplink physical
channel(s) may correspond to a set of resource elements carrying
information originating from higher layers. The following example
uplink physical channel(s) may be defined for uplink: a) Physical
Uplink Shared Channel (PUSCH), b) Physical Uplink Control Channel
(PUCCH), c) Physical Random Access Channel (PRACH), and/or the
like. Uplink physical signal(s) may be used by the physical layer
and may not carry information originating from higher layers. For
example, reference signal(s) may be considered as uplink physical
signal(s). Transmitted signal(s) in slot(s) may be described by one
or several resource grids including, for example, subcarriers and
SC-FDMA or OFDMA symbols. Antenna port(s) may be defined such that
the channel over which symbol(s) on antenna port(s) may be conveyed
and/or inferred from the channel over which other symbol(s) on the
same antenna port(s) is/are conveyed. There may be one resource
grid per antenna port. The antenna port(s) used for transmission of
physical channel(s) or signal(s) may depend on the number of
antenna port(s) configured for the physical channel(s) or
signal(s).
[0125] Element(s) in a resource grid may be called a resource
element. A physical resource block may be defined as N consecutive
SC-FDMA symbols in the time domain and/or M consecutive subcarriers
in the frequency domain, wherein M and N may be pre-defined integer
values. Physical resource block(s) in uplink(s) may comprise of
M.times.N resource elements. For example, a physical resource block
may correspond to one slot in the time domain and 180 kHz in the
frequency domain. Baseband signal(s) representing the physical
uplink shared channel may be defined in terms of: a) scrambling, b)
modulation of scrambled bits to generate complex-valued symbols, c)
mapping of complex-valued modulation symbols onto one or several
transmission layers, d) transform precoding to generate
complex-valued symbols, e) precoding of complex-valued symbols, f)
mapping of precoded complex-valued symbols to resource elements, g)
generation of complex-valued time-domain SC-FDMA signal(s) for
antenna port(s), and/or the like.
[0126] For codeword(s), block(s) of bits may be scrambled with
UE-specific scrambling sequence(s) prior to modulation, resulting
in block(s) of scrambled bits. Complex-valued modulation symbols
for codeword(s) to be transmitted may be mapped onto one, two, or
more layers. For spatial multiplexing, layer mapping(s) may be
performed according to pre-defined formula(s). The number of layers
may be less than or equal to the number of antenna port(s) used for
transmission of physical uplink shared channel(s). The example of a
single codeword mapped to multiple layers may be applicable when
the number of antenna port(s) used for PUSCH is, for example, four.
For layer(s), the block of complex-valued symbols may be divided
into multiple sets, each corresponding to one SC-FDMA symbol.
Transform precoding may be applied. For antenna port(s) used for
transmission of the PUSCH in a subframe, block(s) of complex-valued
symbols may be multiplied with an amplitude scaling factor in order
to conform to a required transmit power, and mapped in sequence to
physical resource block(s) on antenna port(s) and assigned for
transmission of PUSCH.
[0127] According to some of the various embodiments, data may
arrive to the coding unit in the form of two transport blocks every
transmission time interval (TTI) per UL cell. The following coding
actions may be identified for transport block(s) of an uplink
carrier: a) Add CRC to the transport block, b) Code block
segmentation and code block CRC attachment, c) Channel coding of
data and control information, d) Rate matching, e) Code block
concatenation. f) Multiplexing of data and control information, g)
Channel interleaver, h) Error detection may be provided on UL-SCH
(uplink shared channel) transport block(s) through a Cyclic
Redundancy Check (CRC), and/or the like. Transport block(s) may be
used to calculate CRC parity bits. Code block(s) may be delivered
to channel coding block(s). Code block(s) may be individually turbo
encoded. Turbo coded block(s) may be delivered to rate matching
block(s).
[0128] Physical uplink control channel(s) (PUCCH) may carry uplink
control information. Simultaneous transmission of PUCCH and PUSCH
from the same UE may be supported if enabled by higher layers. For
a type 2 frame structure, the PUCCH may not be transmitted in the
UpPTS field. PUCCH may use one resource block in each of the two
slots in a subframe. Resources allocated to UE and PUCCH
configuration(s) may be transmitted via control messages. PUCCH may
comprise: a) positive and negative acknowledgements for data
packets transmitted at least one downlink carrier, b) channel state
information for at least one downlink carrier, c) scheduling
request, and/or the like.
[0129] According to some of the various aspects of embodiments,
cell search may be the procedure by which a wireless device may
acquire time and frequency synchronization with a cell and may
detect the physical layer Cell ID of that cell (transmitter). An
example embodiment for synchronization signal and cell search is
presented below. A cell search may support a scalable overall
transmission bandwidth corresponding to 6 resource blocks and
upwards. Primary and secondary synchronization signals may be
transmitted in the downlink and may facilitate cell search. For
example, 504 unique physical-layer cell identities may be defined
using synchronization signals. The physical-layer cell identities
may be grouped into 168 unique physical-layer cell-identity groups,
group(s) containing three unique identities. The grouping may be
such that physical-layer cell identit(ies) is part of a
physical-layer cell-identity group. A physical-layer cell identity
may be defined by a number in the range of 0 to 167, representing
the physical-layer cell-identity group, and a number in the range
of 0 to 2, representing the physical-layer identity within the
physical-layer cell-identity group. The synchronization signal may
include a primary synchronization signal and a secondary
synchronization signal.
[0130] According to some of the various aspects of embodiments, the
sequence used for a primary synchronization signal may be generated
from a frequency-domain Zadoff-Chu sequence according to a
pre-defined formula. A Zadoff-Chu root sequence index may also be
predefined in a specification. The mapping of the sequence to
resource elements may depend on a frame structure. The wireless
device may not assume that the primary synchronization signal is
transmitted on the same antenna port as any of the downlink
reference signals. The wireless device may not assume that any
transmission instance of the primary synchronization signal is
transmitted on the same antenna port, or ports, used for any other
transmission instance of the primary synchronization signal. The
sequence may be mapped to the resource elements according to a
predefined formula.
[0131] For FDD frame structure, a primary synchronization signal
may be mapped to the last OFDM symbol in slots 0 and 10. For TDD
frame structure, the primary synchronization signal may be mapped
to the third OFDM symbol in subframes 1 and 6. Some of the resource
elements allocated to primary or secondary synchronization signals
may be reserved and not used for transmission of the primary
synchronization signal.
[0132] According to some of the various aspects of embodiments, the
sequence used for a secondary synchronization signal may be an
interleaved concatenation of two length-31 binary sequences. The
concatenated sequence may be scrambled with a scrambling sequence
given by a primary synchronization signal. The combination of two
length-31 sequences defining the secondary synchronization signal
may differ between subframe 0 and subframe 5 according to
predefined formula(s). The mapping of the sequence to resource
elements may depend on the frame structure. In a subframe for FDD
frame structure and in a half-frame for TDD frame structure, the
same antenna port as for the primary synchronization signal may be
used for the secondary synchronization signal. The sequence may be
mapped to resource elements according to a predefined formula.
[0133] Example embodiments for the physical channels configuration
will now be presented. Other examples may also be possible. A
physical broadcast channel may be scrambled with a cell-specific
sequence prior to modulation, resulting in a block of scrambled
bits. PBCH may be modulated using QPSK, and/or the like. The block
of complex-valued symbols for antenna port(s) may be transmitted
during consecutive radio frames, for example, four consecutive
radio frames. In some embodiments the PBCH data may arrive to the
coding unit in the form of a one transport block every transmission
time interval (TTI) of 40 ms. The following coding actions may be
identified. Add CRC to the transport block, channel coding, and
rate matching. Error detection may be provided on PBCH transport
blocks through a Cyclic Redundancy Check (CRC). The transport block
may be used to calculate the CRC parity bits. The parity bits may
be computed and attached to the BCH (broadcast channel) transport
block. After the attachment, the CRC bits may be scrambled
according to the transmitter transmit antenna configuration.
Information bits may be delivered to the channel coding block and
they may be tail biting convolutionally encoded. A tail biting
convolutionally coded block may be delivered to the rate matching
block. The coded block may be rate matched before transmission.
[0134] A master information block may be transmitted in PBCH and
may include system information transmitted on broadcast channel(s).
The master information block may include downlink bandwidth, system
frame number(s), and PHICH (physical hybrid-ARQ indicator channel)
configuration. Downlink bandwidth may be the transmission bandwidth
configuration, in terms of resource blocks in a downlink, for
example 6 may correspond to 6 resource blocks, 15 may correspond to
15 resource blocks and so on. System frame number(s) may define the
N (for example N=8) most significant bits of the system frame
number. The M (for example M=2) least significant bits of the SFN
may be acquired implicitly in the PBCH decoding. For example,
timing of a 40 ms PBCH TTI may indicate 2 least significant bits
(within 40 ms PBCH TTI, the first radio frame: 00, the second radio
frame: 01, the third radio frame: 10, the last radio frame: 11).
One value may apply for other carriers in the same sector of a base
station (the associated functionality is common (e.g. not performed
independently for each cell). PHICH configuration(s) may include
PHICH duration, which may be normal (e.g. one symbol duration) or
extended (e.g. 3 symbol duration).
[0135] Physical control format indicator channel(s) (PCFICH) may
carry information about the number of OFDM symbols used for
transmission of PDCCHs (physical downlink control channel) in a
subframe. The set of OFDM symbols possible to use for PDCCH in a
subframe may depend on many parameters including, for example,
downlink carrier bandwidth, in terms of downlink resource blocks.
PCFICH transmitted in one subframe may be scrambled with
cell-specific sequence(s) prior to modulation, resulting in a block
of scrambled bits. A scrambling sequence generator(s) may be
initialized at the start of subframe(s). Block (s)of scrambled bits
may be modulated using QPSK. Block(s) of modulation symbols may be
mapped to at least one layer and precoded resulting in a block of
vectors representing the signal for at least one antenna port.
Instances of PCFICH control channel(s) may indicate one of several
(e.g. 3) possible values after being decoded. The range of possible
values of instance(s) of the first control channel may depend on
the first carrier bandwidth.
[0136] According to some of the various embodiments, physical
downlink control channel(s) may carry scheduling assignments and
other control information. The number of resource-elements not
assigned to PCFICH or PHICH may be assigned to PDCCH. PDCCH may
support multiple formats. Multiple PDCCH packets may be transmitted
in a subframe. PDCCH may be coded by tail biting convolutionally
encoder before transmission. PDCCH bits may be scrambled with a
cell-specific sequence prior to modulation, resulting in block(s)
of scrambled bits. Scrambling sequence generator(s) may be
initialized at the start of subframe(s). Block(s) of scrambled bits
may be modulated using QPSK. Block(s) of modulation symbols may be
mapped to at least one layer and precoded resulting in a block of
vectors representing the signal for at least one antenna port.
PDCCH may be transmitted on the same set of antenna ports as the
PBCH, wherein PBCH is a physical broadcast channel broadcasting at
least one basic system information field.
[0137] According to some of the various embodiments, scheduling
control packet(s) may be transmitted for packet(s) or group(s) of
packets transmitted in downlink shared channel(s). Scheduling
control packet(s) may include information about subcarriers used
for packet transmission(s). PDCCH may also provide power control
commands for uplink channels. OFDM subcarriers that are allocated
for transmission of PDCCH may occupy the bandwidth of downlink
carrier(s). PDCCH channel(s) may carry a plurality of downlink
control packets in subframe(s). PDCCH may be transmitted on
downlink carrier(s) starting from the first OFDM symbol of
subframe(s), and may occupy up to multiple symbol duration(s) (e.g.
3 or 4).
[0138] According to some of the various embodiments, PHICH may
carry the hybrid-ARQ (automatic repeat request) ACK/NACK. Multiple
PHICHs mapped to the same set of resource elements may constitute a
PHICH group, where PHICHs within the same PHICH group may be
separated through different orthogonal sequences. PHICH resource(s)
may be identified by the index pair (group, sequence), where
group(s) may be the PHICH group number(s) and sequence(s) may be
the orthogonal sequence index within the group(s). For frame
structure type 1, the number of PHICH groups may depend on
parameters from higher layers (RRC). For frame structure type 2,
the number of PHICH groups may vary between downlink subframes
according to a pre-defined arrangement. Block(s) of bits
transmitted on one PHICH in one subframe may be modulated using
BPSK or QPSK, resulting in a block(s) of complex-valued modulation
symbols. Block(s) of modulation symbols may be symbol-wise
multiplied with an orthogonal sequence and scrambled, resulting in
a sequence of modulation symbols
[0139] Other arrangements for PCFICH, PHICH, PDCCH, and/or PDSCH
may be supported. The configurations presented here are for example
purposes. In another example, resources PCFICH, PHICH, and/or PDCCH
radio resources may be transmitted in radio resources including a
subset of subcarriers and pre-defined time duration in each or some
of the subframes. In an example, PUSCH resource(s) may start from
the first symbol. In another example embodiment, radio resource
configuration(s) for PUSCH, PUCCH, and/or PRACH (physical random
access channel) may use a different configuration. For example,
channels may be time multiplexed, or time/frequency multiplexed
when mapped to uplink radio resources.
[0140] According to some of the various aspects of embodiments, the
physical layer random access preamble may comprise a cyclic prefix
of length Tcp and a sequence part of length Tseq. The parameter
values may be pre-defined and depend on the frame structure and a
random access configuration. In an example embodiment, Tcp may be
0.1 msec, and Tseq may be 0.9 msec. Higher layers may control the
preamble format. The transmission of a random access preamble, if
triggered by the MAC layer, may be restricted to certain time and
frequency resources. The start of a random access preamble may be
aligned with the start of the corresponding uplink subframe at a
wireless device.
[0141] According to an example embodiment, random access preambles
may be generated from Zadoff-Chu sequences with a zero correlation
zone, generated from one or several root Zadoff-Chu sequences. In
another example embodiment, the preambles may also be generated
using other random sequences such as Gold sequences. The network
may configure the set of preamble sequences a wireless device may
be allowed to use. According to some of the various aspects of
embodiments, there may be a multitude of preambles (e.g. 64)
available in cell(s). From the physical layer perspective, the
physical layer random access procedure may include the transmission
of random access preamble(s) and random access response(s).
Remaining message(s) may be scheduled for transmission by a higher
layer on the shared data channel and may not be considered part of
the physical layer random access procedure. For example, a random
access channel may occupy 6 resource blocks in a subframe or set of
consecutive subframes reserved for random access preamble
transmissions.
[0142] According to some of the various embodiments, the following
actions may be followed for a physical random access procedure: 1)
layer 1 procedure may be triggered upon request of a preamble
transmission by higher layers; 2) a preamble index, a target
preamble received power, a corresponding RA-RNTI (random
access-radio network temporary identifier) and/or a PRACH resource
may be indicated by higher layers as part of a request; 3) a
preamble transmission power P_PRACH may be determined; 4) a
preamble sequence may be selected from the preamble sequence set
using the preamble index; 5) a single preamble may be transmitted
using selected preamble sequence(s) with transmission power P_PRACH
on the indicated PRACH resource; 6) detection of a PDCCH with the
indicated RAR may be attempted during a window controlled by higher
layers; and/or the like. If detected, the corresponding downlink
shared channel transport block may be passed to higher layers. The
higher layers may parse transport block(s) and/or indicate an
uplink grant to the physical layer(s).
[0143] According to some of the various aspects of embodiments, a
random access procedure may be initiated by a physical downlink
control channel (PDCCH) order and/or by the MAC sublayer in a
wireless device. If a wireless device receives a PDCCH transmission
consistent with a PDCCH order masked with its radio identifier, the
wireless device may initiate a random access procedure. Preamble
transmission(s) on physical random access channel(s) (PRACH) may be
supported on a first uplink carrier and reception of a PDCCH order
may be supported on a first downlink carrier.
[0144] Before a wireless device initiates transmission of a random
access preamble, it may access one or many of the following types
of information: a) available set(s) of PRACH resources for the
transmission of a random access preamble; b) group(s) of random
access preambles and set(s) of available random access preambles in
group(s); c) random access response window size(s); d)
power-ramping factor(s); e) maximum number(s) of preamble
transmission(s); f) initial preamble power; g) preamble format
based offset(s); h) contention resolution timer(s); and/or the
like. These parameters may be updated from upper layers or may be
received from the base station before random access procedure(s)
may be initiated.
[0145] According to some of the various aspects of embodiments, a
wireless device may select a random access preamble using available
information. The preamble may be signaled by a base station or the
preamble may be randomly selected by the wireless device. The
wireless device may determine the next available subframe
containing PRACH permitted by restrictions given by the base
station and the physical layer timing requirements for TDD or FDD.
Subframe timing and the timing of transmitting the random access
preamble may be determined based, at least in part, on
synchronization signals received from the base station and/or the
information received from the base station. The wireless device may
proceed to the transmission of the random access preamble when it
has determined the timing. The random access preamble may be
transmitted on a second plurality of subcarriers on the first
uplink carrier.
[0146] According to some of the various aspects of embodiments,
once a random access preamble is transmitted, a wireless device may
monitor the PDCCH of a first downlink carrier for random access
response(s), in a random access response window. There may be a
pre-known identifier in PDCCH that indentifies a random access
response. The wireless device may stop monitoring for random access
response(s) after successful reception of a random access response
containing random access preamble identifiers that matches the
transmitted random access preamble and/or a random access response
address to a wireless device identifier. A base station random
access response may include a time alignment command. The wireless
device may process the received time alignment command and may
adjust its uplink transmission timing according the time alignment
value in the command. For example, in a random access response, a
time alignment command may be coded using 11 bits, where an amount
of the time alignment may be based on the value in the command. In
an example embodiment, when an uplink transmission is required, the
base station may provide the wireless device a grant for uplink
transmission.
[0147] If no random access response is received within the random
access response window, and/or if none of the received random
access responses contains a random access preamble identifier
corresponding to the transmitted random access preamble, the random
access response reception may be considered unsuccessful and the
wireless device may, based on the backoff parameter in the wireless
device, select a random backoff time and delay the subsequent
random access transmission by the backoff time, and may retransmit
another random access preamble.
[0148] According to some of the various aspects of embodiments, a
wireless device may transmit packets on an uplink carrier. Uplink
packet transmission timing may be calculated in the wireless device
using the timing of synchronization signal(s) received in a
downlink. Upon reception of a timing alignment command by the
wireless device, the wireless device may adjust its uplink
transmission timing. The timing alignment command may indicate the
change of the uplink timing relative to the current uplink timing.
The uplink transmission timing for an uplink carrier may be
determined using time alignment commands and/or downlink reference
signals.
[0149] According to some of the various aspects of embodiments, a
time alignment command may indicate timing adjustment for
transmission of signals on uplink carriers. For example, a time
alignment command may use 6 bits. Adjustment of the uplink timing
by a positive or a negative amount indicates advancing or delaying
the uplink transmission timing by a given amount respectively.
[0150] For a timing alignment command received on subframe n, the
corresponding adjustment of the timing may be applied with some
delay, for example, it may be applied from the beginning of
subframe n+6. When the wireless device's uplink transmissions in
subframe n and subframe n+1 are overlapped due to the timing
adjustment, the wireless device may transmit complete subframe n
and may not transmit the overlapped part of subframe n+1.
[0151] According to some of the various aspects of embodiments, a
wireless device may include a configurable timer
(timeAlignmentTimer) that may be used to control how long the
wireless device is considered uplink time aligned. When a timing
alignment command MAC control element is received, the wireless
device may apply the timing alignment command and start or restart
timeAlignmentTimer. The wireless device may not perform any uplink
transmission except the random access preamble transmission when
timeAlignmentTimer is not running or when it exceeds its limit. The
time alignment command may substantially align frame and subframe
reception timing of a first uplink carrier and at least one
additional uplink carrier. According to some of the various aspects
of embodiments, the time alignment command value range employed
during a random access process may be substantially larger than the
time alignment command value range during active data transmission.
In an example embodiment, uplink transmission timing may be
maintained on a per time alignment group (TAG) basis. Carrier(s)
may be grouped in TAGs, and TAG(s) may have their own downlink
timing reference, time alignment timer, and/or time alignment
commands. Group(s) may have their own random access process. Time
alignment commands may be directed to a time alignment group. The
TAG, including the primary cell may be called a primary TAG (pTAG)
and the TAG not including the primary cell may be called a
secondary TAG (sTAG).
[0152] According to some of the various aspects of embodiments,
control message(s) or control packet(s) may be scheduled for
transmission in a physical downlink shared channel (PDSCH) and/or
physical uplink shared channel PUSCH. PDSCH and PUSCH may carry
control and data message(s)/packet(s). Control message(s) and/or
packet(s) may be processed before transmission. For example, the
control message(s) and/or packet(s) may be fragmented or
multiplexed before transmission. A control message in an upper
layer may be processed as a data packet in the MAC or physical
layer. For example, system information block(s) as well as data
traffic may be scheduled for transmission in PDSCH. Data packet(s)
may be encrypted packets.
[0153] According to some of the various aspects of embodiments,
data packet(s) may be encrypted before transmission to secure
packet(s) from unwanted receiver(s). Desired recipient(s) may be
able to decrypt the packet(s). A first plurality of data packet(s)
and/or a second plurality of data packet(s) may be encrypted using
an encryption key and at least one parameter that may change
substantially rapidly over time. The encryption mechanism may
provide a transmission that may not be easily eavesdropped by
unwanted receivers. The encryption mechanism may include additional
parameter(s) in an encryption module that changes substantially
rapidly in time to enhance the security mechanism. Example varying
parameter(s) may comprise various types of system counter(s), such
as system frame number. Substantially rapidly may for example imply
changing on a per subframe, frame, or group of subframes basis.
Encryption may be provided by a PDCP layer between the transmitter
and receiver, and/or may be provided by the application layer.
Additional overhead added to packet(s) by lower layers such as RLC,
MAC, and/or Physical layer may not be encrypted before
transmission. In the receiver, the plurality of encrypted data
packet(s) may be decrypted using a first decryption key and at
least one first parameter. The plurality of data packet(s) may be
decrypted using an additional parameter that changes substantially
rapidly over time.
[0154] According to some of the various aspects of embodiments, a
wireless device may be preconfigured with one or more carriers.
When the wireless device is configured with more than one carrier,
the base station and/or wireless device may activate and/or
deactivate the configured carriers. One of the carriers (the
primary carrier) may always be activated. Other carriers may be
deactivated by default and/or may be activated by a base station
when needed. A base station may activate and deactivate carriers by
sending an activation/deactivation MAC control element.
Furthermore, the UE may maintain a carrier deactivation timer per
configured carrier and deactivate the associated carrier upon its
expiry. The same initial timer value may apply to instance(s) of
the carrier deactivation timer. The initial value of the timer may
be configured by a network. The configured carriers (unless the
primary carrier) may be initially deactivated upon addition and
after a handover.
[0155] According to some of the various aspects of embodiments, if
a wireless device receives an activation/deactivation MAC control
element activating the carrier, the wireless device may activate
the carrier, and/or may apply normal carrier operation including:
sounding reference signal transmissions on the carrier, CQI
(channel quality indicator)/PMI(precoding matrix
indicator)/RI(ranking indicator) reporting for the carrier, PDCCH
monitoring on the carrier, PDCCH monitoring for the carrier, start
or restart the carrier deactivation timer associated with the
carrier, and/or the like. If the device receives an
activation/deactivation MAC control element deactivating the
carrier, and/or if the carrier deactivation timer associated with
the activated carrier expires, the base station or device may
deactivate the carrier, and may stop the carrier deactivation timer
associated with the carrier, and/or may flush HARQ buffers
associated with the carrier.
[0156] If PDCCH on a carrier scheduling the activated carrier
indicates an uplink grant or a downlink assignment for the
activated carrier, the device may restart the carrier deactivation
timer associated with the carrier. When a carrier is deactivated,
the wireless device may not transmit SRS (sounding reference
signal) for the carrier, may not report CQI/PMI/RI for the carrier,
may not transmit on UL-SCH for the carrier, may not monitor the
PDCCH on the carrier, and/or may not monitor the PDCCH for the
carrier.
[0157] A process to assign subcarriers to data packets may be
executed by a MAC layer scheduler. The decision on assigning
subcarriers to a packet may be made based on data packet size,
resources required for transmission of data packets (number of
radio resource blocks), modulation and coding assigned to data
packet(s), QoS required by the data packets (i.e. QoS parameters
assigned to data packet bearer), the service class of a subscriber
receiving the data packet, or subscriber device capability, a
combination of the above, and/or the like.
[0158] According to some of the various aspects of embodiments,
packets may be referred to service data units and/or protocols data
units at Layer 1, Layer 2 and/or Layer 3 of the communications
network. Layer 2 in an LTE network may include three sub-layers:
PDCP sub-layer, RLC sub-layer, and MAC sub-layer. A layer 2 packet
may be a PDCP packet, an RLC packet or a MAC layer packet. Layer 3
in an LTE network may be Internet Protocol (IP) layer, and a layer
3 packet may be an IP data packet. Packets may be transmitted and
received via an air interface physical layer. A packet at the
physical layer may be called a transport block. Many of the various
embodiments may be implemented at one or many different
communication network layers. For example, some of the actions may
be executed by the PDCP layer and some others by the MAC layer.
[0159] According to some of the various aspects of embodiments,
subcarriers and/or resource blocks may comprise a plurality of
physical subcarriers and/or resource blocks. In another example
embodiment, subcarriers may be a plurality of virtual and/or
logical subcarriers and/or resource blocks.
[0160] According to some of the various aspects of embodiments, a
radio bearer may be a GBR (guaranteed bit rate) bearer and/or a
non-GBR bearer. A GBR and/or guaranteed bit rate bearer may be
employed for transfer of real-time packets, and/or a non-GBR bearer
may be used for transfer of non-real-time packets. The non-GBR
bearer may be assigned a plurality of attributes including: a
scheduling priority, an allocation and retention priority, a
portable device aggregate maximum bit rate, and/or the like. These
parameters may be used by the scheduler in scheduling non-GBR
packets. GBR bearers may be assigned attributes such as delay,
jitter, packet loss parameters, and/or the like.
[0161] According to some of the various aspects of embodiments,
subcarriers may include data subcarrier symbols and pilot
subcarrier symbols. Pilot symbols may not carry user data, and may
be included in the transmission to help the receiver to perform
synchronization, channel estimation and/or signal quality
detection. Base stations and wireless devices (wireless receiver)
may use different methods to generate and transmit pilot symbols
along with information symbols.
[0162] According to some of the various aspects of embodiments, the
transmitter in the disclosed embodiments of the present invention
may be a wireless device (also called user equipment), a base
station (also called eNodeB), a relay node transmitter, and/or the
like. The receiver in the disclosed embodiments of the present
invention may be a wireless device (also called user equipment-UE),
a base station (also called eNodeB), a relay node receiver, and/or
the like. According to some of the various aspects of embodiments
of the present invention, layer 1 (physical layer) may be based on
OFDMA or SC-FDMA. Time may be divided into frame(s) with fixed
duration. Frame(s) may be divided into substantially equally sized
subframes, and subframe(s) may be divided into substantially
equally sized slot(s). A plurality of OFDM or SC-FDMA symbol(s) may
be transmitted in slot(s). OFDMA or SC-FDMA symbol(s) may be
grouped into resource block(s). A scheduler may assign resource(s)
in resource block unit(s), and/or a group of resource block
unit(s). Physical resource block(s) may be resources in the
physical layer, and logical resource block(s) may be resource
block(s) used by the MAC layer. Similar to virtual and physical
subcarriers, resource block(s) may be mapped from logical to
physical resource block(s). Logical resource block(s) may be
contiguous, but corresponding physical resource block(s) may be
non-contiguous. Some of the various embodiments of the present
invention may be implemented at the physical or logical resource
block level(s).
[0163] According to some of the various aspects of embodiments,
layer 2 transmission may include PDCP (packet data convergence
protocol), RLC (radio link control), MAC (media access control)
sub-layers, and/or the like. MAC may be responsible for the
multiplexing and mapping of logical channels to transport channels
and vice versa. A MAC layer may perform channel mapping,
scheduling, random access channel procedures, uplink timing
maintenance, and/or the like.
[0164] According to some of the various aspects of embodiments, the
MAC layer may map logical channel(s) carrying RLC PDUs (packet data
unit) to transport channel(s). For transmission, multiple SDUs
(service data unit) from logical channel(s) may be mapped to the
Transport Block (TB) to be sent over transport channel(s). For
reception, TBs from transport channel(s) may be demultiplexed and
assigned to corresponding logical channel(s). The MAC layer may
perform scheduling related function(s) in both the uplink and
downlink and thus may be responsible for transport format selection
associated with transport channel(s). This may include HARQ
functionality. Since scheduling may be done at the base station,
the MAC layer may be responsible for reporting scheduling related
information such as UE (user equipment or wireless device) buffer
occupancy and power headroom. It may also handle prioritization
from both an inter-UE and intra-UE logical channel perspective. MAC
may also be responsible for random access procedure(s) for the
uplink that may be performed following either a contention and
non-contention based process. UE may need to maintain timing
synchronization with cell(s). The MAC layer may perform
procedure(s) for periodic synchronization.
[0165] According to some of the various aspects of embodiments, the
MAC layer may be responsible for the mapping of multiple logical
channel(s) to transport channel(s) during transmission(s), and
demultiplexing and mapping of transport channel data to logical
channel(s) during reception. A MAC PDU may include of a header that
describes the format of the PDU itself, which may include control
element(s), SDUs, Padding, and/or the like. The header may be
composed of multiple sub-headers, one for constituent part(s) of
the MAC PDU. The MAC may also operate in a transparent mode, where
no header may be pre-pended to the PDU. Activation command(s) may
be inserted into packet(s) using a MAC control element.
[0166] According to some of the various aspects of embodiments, the
MAC layer in some wireless device(s) may report buffer size(s) of
either a single Logical Channel Group (LCG) or a group of LCGs to a
base station. An LCG may be a group of logical channels identified
by an LCG ID. The mapping of logical channel(s) to LCG may be set
up during radio configuration. Buffer status report(s) may be used
by a MAC scheduler to assign radio resources for packet
transmission from wireless device(s). HARQ and ARQ processes may be
used for packet retransmission to enhance the reliability of radio
transmission and reduce the overall probability of packet loss.
[0167] According to some of the various aspects of embodiments, an
RLC sub-layer may control the applicability and functionality of
error correction, concatenation, segmentation, re-segmentation,
duplicate detection, in-sequence delivery, and/or the like. Other
functions of RLC may include protocol error detection and recovery,
and/or SDU discard. The RLC sub-layer may receive data from upper
layer radio bearer(s) (signaling and data) called service data
unit(s) (SDU). The transmission entities in the RLC layer may
convert RLC SDUs to RLC PDU after performing functions such as
segmentation, concatenation, adding RLC header(s), and/or the like.
In the other direction, receiving entities may receive RLC PDUs
from the MAC layer. After performing reordering, the PDUs may be
assembled back into RLC SDUs and delivered to the upper layer. RLC
interaction with a MAC layer may include: a) data transfer for
uplink and downlink through logical channel(s); b) MAC notifies RLC
when a transmission opportunity becomes available, including the
size of total number of RLC PDUs that may be transmitted in the
current transmission opportunity, and/or c) the MAC entity at the
transmitter may inform RLC at the transmitter of HARQ transmission
failure.
[0168] According to some of the various aspects of embodiments,
PDCP (packet data convergence protocol) may comprise a layer 2
sub-layer on top of RLC sub-layer. The PDCP may be responsible for
a multitude of functions. First, the PDCP layer may transfer user
plane and control plane data to and from upper layer(s). PDCP layer
may receive SDUs from upper layer(s) and may send PDUs to the lower
layer(s). In other direction, PDCP layer may receive PDUs from the
lower layer(s) and may send SDUs to upper layer(s). Second, the
PDCP may be responsible for security functions. It may apply
ciphering (encryption) for user and control plane bearers, if
configured. It may also perform integrity protection for control
plane bearer(s), if configured. Third, the PDCP may perform header
compression service(s) to improve the efficiency of over the air
transmission. The header compression may be based on robust header
compression (ROHC). ROHC may be performed on VOIP packets. Fourth,
the PDCP may be responsible for in-order delivery of packet(s) and
duplicate detection service(s) to upper layer(s) after handover(s).
After handover, the source base station may transfer unacknowledged
packet(s)s to target base station when operating in RLC
acknowledged mode (AM). The target base station may forward
packet(s)s received from the source base station to the UE (user
equipment).
[0169] In this specification, "a" and "an" and similar phrases are
to be interpreted as "at least one" and "one or more." In this
specification, the term "may" is to be interpreted as "may, for
example," In other words, the term "may" is indicative that the
phrase following the term "may" is an example of one of a multitude
of suitable possibilities that may, or may not, be employed to one
or more of the various embodiments. If A and B are sets and every
element of A is also an element of B, A is called a subset of B. In
this specification, only non-empty sets and subsets are considered.
For example, possible subsets of B={cell1, cell2} are: {cell1},
{cell2}, and {cell1, cell2}.
[0170] Many of the elements described in the disclosed embodiments
may be implemented as modules. A module is defined here as an
isolatable element that performs a defined function and has a
defined interface to other elements. The modules described in this
disclosure may be implemented in hardware, software in combination
with hardware, firmware, wetware (i.e hardware with a biological
element) or a combination thereof, all of which are behaviorally
equivalent. For example, modules may be implemented as a software
routine written in a computer language configured to be executed by
a hardware machine (such as C, C++, Fortran, Java, Basic, Matlab or
the like) or a modeling/simulation program such as Simulink,
Stateflow, GNU Octave, or Lab VIEWMathScript. Additionally, it may
be possible to implement modules using physical hardware that
incorporates discrete or programmable analog, digital and/or
quantum hardware. Examples of programmable hardware comprise:
computers, microcontrollers, microprocessors, application-specific
integrated circuits (ASICs); field programmable gate arrays
(FPGAs); and complex programmable logic devices (CPLDs). Computers,
microcontrollers and microprocessors are programmed using languages
such as assembly, C, C++ or the like. FPGAs, ASICs and CPLDs are
often programmed using hardware description languages (HDL) such as
VHSIC hardware description language (VHDL) or Verilog that
configure connections between internal hardware modules with lesser
functionality on a programmable device. Finally, it needs to be
emphasized that the above mentioned technologies are often used in
combination to achieve the result of a functional module.
[0171] The disclosure of this patent document incorporates material
which is subject to copyright protection. The copyright owner has
no objection to the facsimile reproduction by anyone of the patent
document or the patent disclosure, as it appears in the Patent and
Trademark Office patent file or records, for the limited purposes
required by law, but otherwise reserves all copyright rights
whatsoever.
[0172] While various embodiments have been described above, it
should be understood that they have been presented by way of
example, and not limitation. It will be apparent to persons skilled
in the relevant art(s) that various changes in form and detail can
be made therein without departing from the spirit and scope. In
fact, after reading the above description, it will be apparent to
one skilled in the relevant art(s) how to implement alternative
embodiments. Thus, the present embodiments should not be limited by
any of the above described exemplary embodiments. In particular, it
should be noted that, for example purposes, the above explanation
has focused on the example(s) using FDD communication systems.
However, one skilled in the art will recognize that embodiments of
the invention may also be implemented in TDD communication systems.
The disclosed methods and systems may be implemented in wireless or
wireline systems. The features of various embodiments presented in
this invention may be combined. One or many features (method or
system) of one embodiment may be implemented in other embodiments.
Only a limited number of example combinations are shown to indicate
to one skilled in the art the possibility of features that may be
combined in various embodiments to create enhanced transmission and
reception systems and methods.
[0173] In addition, it should be understood that any figures which
highlight the functionality and advantages, are presented for
example purposes only. The disclosed architecture is sufficiently
flexible and configurable, such that it may be utilized in ways
other than that shown. For example, the actions listed in any
flowchart may be re-ordered or only optionally used in some
embodiments.
[0174] Further, the purpose of the Abstract of the Disclosure is to
enable the U.S. Patent and Trademark Office and the public
generally, and especially the scientists, engineers and
practitioners in the art who are not familiar with patent or legal
terms or phraseology, to determine quickly from a cursory
inspection the nature and essence of the technical disclosure of
the application. The Abstract of the Disclosure is not intended to
be limiting as to the scope in any way.
[0175] Finally, it is the applicant's intent that only claims that
include the express language "means for" or "step for" be
interpreted under 35 U.S.C. 112, paragraph 6. Claims that do not
expressly include the phrase "means for" or "step for" are not to
be interpreted under 35 U.S.C. 112, paragraph 6.
* * * * *