U.S. patent application number 16/330514 was filed with the patent office on 2019-06-27 for methods and devices for determination of beamforming information.
The applicant listed for this patent is Telefonaktiebolaget LM Ericsson (publ). Invention is credited to Fredrik Huss, Jonas Karlsson, Oskar Mauritz, Christer Ostberg, Jacob Osterling, Jan Roxbergh, Alex Stephenne.
Application Number | 20190199379 16/330514 |
Document ID | / |
Family ID | 59295280 |
Filed Date | 2019-06-27 |
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United States Patent
Application |
20190199379 |
Kind Code |
A1 |
Osterling; Jacob ; et
al. |
June 27, 2019 |
Methods and Devices for Determination of Beamforming
Information
Abstract
There is presented mechanisms for obtaining information for
determining beamforming weights for terminal devices. A method is
performed by an RE of an access node. The RE has an interface to an
REC of the access node. The method comprises obtaining beamforming
information per direction from the REC over the interface. The
method comprises transforming the beamforming information per
direction to beamforming information per antenna, the beamforming
information per antenna representing the beamforming weights. The
method comprises applying the beamforming weights.
Inventors: |
Osterling; Jacob; (Jarfalla,
SE) ; Huss; Fredrik; (Sundbyberg, SE) ;
Karlsson; Jonas; (Upplands Vasby, SE) ; Mauritz;
Oskar; (Johanneshov, SE) ; Ostberg; Christer;
(Staffanstorp, SE) ; Roxbergh; Jan; (Sollentuna,
SE) ; Stephenne; Alex; (Stittsville, Ontario,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Telefonaktiebolaget LM Ericsson (publ) |
Stockholm |
|
SE |
|
|
Family ID: |
59295280 |
Appl. No.: |
16/330514 |
Filed: |
June 22, 2017 |
PCT Filed: |
June 22, 2017 |
PCT NO: |
PCT/SE2017/050690 |
371 Date: |
March 5, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62383871 |
Sep 6, 2016 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W 88/085 20130101;
H04B 10/25758 20130101; H03M 7/3068 20130101; H04W 88/02 20130101;
H04B 7/0617 20130101; H04B 1/0003 20130101 |
International
Class: |
H04B 1/00 20060101
H04B001/00; H04W 88/02 20060101 H04W088/02; H04W 88/08 20060101
H04W088/08; H04B 10/2575 20060101 H04B010/2575; H03M 7/30 20060101
H03M007/30 |
Claims
1-40. (canceled)
41. A radio equipment (RE) of an access node, the RE configured for
obtaining information for determining beamforming weights for
terminal devices, the RE having an interface to a radio equipment
controller (REC) of the access node and comprising processing
circuitry, wherein the processing circuitry is configured to cause
the RE to: obtain beamforming information per direction from the
REC over the interface; transform the beamforming information per
direction to beamforming information per antenna, the beamforming
information per antenna representing the beamforming weights; and
apply the beamforming weights.
42. The RE according to claim 41, wherein the beamforming weights
are applied at antennas of the RE.
43. The RE according to claim 41, wherein the beamforming
information per antenna is associated with a first dimensionality,
and wherein the beamforming information per direction is associated
with a second dimensionality that is smaller than the first
dimensionality.
44. The RE according to claim 41, wherein the beamforming
information per direction is obtained as a linear combination of
predetermined beamforming weights per direction.
45. The RE according to claim 41, wherein the beamforming
information is transformed using a Discrete Fourier Transform
(DFT).
46. The RE according to claim 41, wherein the processing circuitry
is configured to cause the RE to: obtain information appointing
fixed beam directions from the REC over the interface, and wherein
the beamforming information per direction is transformed to
beamforming information per antenna only for the appointed beam
directions.
47. A radio equipment controller (REC) of an access node, the REC
configured for providing information for determining beamforming
weights for terminal devices, the REC having an interface to a
radio equipment (RE) of the access node and comprising processing
circuitry, wherein the processing circuitry is configured to cause
the REC to: obtain beamforming information per antenna, the
beamforming information per antenna representing the beamforming
weights; transform the beamforming information per antenna to
beamforming information per direction; and provide the beamforming
information per direction to the RE over the interface.
48. The REC according to claim 47, wherein the beamforming
information per antenna is associated with a first dimensionality,
and wherein the beamforming information per direction is associated
with a second dimensionality that is smaller than the first
dimensionality.
49. The REC according to claim 47, wherein only the beamforming
information per direction having a signal quality measure above a
threshold is provided to the RE over the interface.
50. The REC according to claim 47, wherein the beamforming
information is transformed using a Discrete Fourier Transform
(DFT).
51. The REC according to claim 47, wherein the processing circuitry
causes the REC to: provide information to the RE over the interface
appointing which fixed beam directions to use when transforming the
beamforming information per direction to beamforming information
per antenna.
52. The REC according to claim 47, wherein the beamforming
information per antenna is obtained from at least one of the
terminal devices.
53. A radio equipment (RE) of an access node, the RE configured for
providing information for determining beamforming weights for
terminal devices, the RE having an interface to a radio equipment
controller (REC) of the access node and comprising processing
circuitry, wherein the processing circuitry is configured to cause
the RE to: obtain beamforming information per antenna from at least
one of the terminal devices, the beamforming information per
antenna representing the beamforming weights; transform the
beamforming information per antenna to beamforming information per
direction; and provide the beamforming information per direction to
the REC over the interface.
54. The RE according to claim 53, wherein the beamforming
information per antenna is associated with a first dimensionality,
and wherein the beamforming information per direction is associated
with a second dimensionality being smaller than the first
dimensionality.
55. The RE according to claim 53, wherein only the beamforming
information per direction having a signal quality measure above a
threshold is provided to the REC over the interface.
56. The RE according to claim 53, wherein the beamforming
information is transformed using a Discrete Fourier Transform
(DFT).
57. The RE according to claim 53, wherein the processing circuitry
is configured to cause the RE to: obtain updated beamforming
weights per direction from the REC over the interface; transform
the updated beamforming weights per direction to updated
beamforming weights per antenna; and apply the updated beamforming
weights per antenna.
58. The method according to claim 53, wherein the updated
beamforming weights are applied at antennas of the RE.
59. A radio equipment controller (REC) of an access node, the REC
configured for obtaining information for determining beamforming
weights for terminal devices, the REC having an interface to a
radio equipment (RE) of the access node and comprising processing
circuitry, wherein the processing circuitry is configured to cause
the REC to: obtain beamforming information per direction from the
RE over the interface; determine the beamforming weights per
direction based on the beamforming information per direction; and
provide the beamforming weights per direction to the RE over the
interface.
60. The REC according to claim 59, wherein only the beamforming
information per direction having a signal quality measure above a
threshold is used when determining the beamforming weights per
direction.
61. The REC according to claim 59, further comprising: obtaining
channel rank information from the RE over the interface, and
wherein the beamforming weights per direction are determined based
on the channel rank information.
Description
TECHNICAL FIELD
[0001] Embodiments presented herein relate to a method, an RE, a
computer program, and a computer program product for determining
beamforming weights or decoding user data for terminal devices.
Embodiments presented herein further relate to a method, an REC, a
computer program, and a computer program product for determining
beamforming weights or decoding user data for terminal devices.
BACKGROUND
[0002] In communications systems, there may be a challenge to
obtain good performance and capacity for a given communications
protocol, its parameters and the physical environment in which the
communications system is deployed.
[0003] For example, the introduction of digital beamforming antenna
systems in access nodes, such as radio base stations, etc., could
allow multiple simultaneous narrow beams to be used to provide
network access to, and thus server, multiple simultaneous served
terminal devices, such as user equipment (UE), etc. However, the
current split in the access nodes between a radio equipment
controller (REC) and a radio equipment (RE) as interconnected by
the Common Public Radio Interface (CPRI) may no longer be feasible
as passing the data for each individual radio chain over the CPRI
interface could drive prohibitively high data rates.
[0004] In more detail, the bit rate of the current CPRI interface
scales directly to the number of independent radio chains in the
RE. When having e.g., a 200 MHz carrier bandwidth and 128 physical
antenna elements in the beamforming antenna system, a bit rate of
530 Gbps would be needed for the CPRI interface with currently used
sample coding. A further potential drawback with CPRI is the extra
latency from uplink (UL; from terminal device to access node)
sampling to the time the data can be used in downlink (DL; from
access node to terminal device), as any information needs to loop
in the REC.
[0005] One way to address the above-mentioned issues is to collapse
the CPRI based architecture by removing the CPRI interface and
putting the functionality of the REC in the RE. This approach has
at least two drawbacks. Firstly, due to faster technological
development of the REC compared to the RE, the technical lifetime
of the REC is assumed to be shorter than that of the RE. Replacing
the RE is more costly than replacing the REC. From this aspect it
could thus be beneficial to keep the functionality of the RE as
simple as possible. Secondly, the REC could be configured to make
decisions spanning over multiple REs in order to make coordinated
multi-sector decisions, e.g. when some REs represent coverage
regions of the access node within the coverage regions of other REs
(e.g. a so-called micro cell within a so-called macro cell). A
collapsed architecture loses this overarching coordination
possibility.
[0006] Hence, there is a need for an improved communication between
the REC and the RE.
SUMMARY
[0007] An object of embodiments herein is to provide efficient
communication between the REC and the RE.
[0008] According to a first aspect there is presented a method for
obtaining information for determining beamforming weights for
terminal devices. The method is performed by an RE of an access
node. The RE has an interface to an REC of the access node. The
method comprises obtaining beamforming information per direction
from the REC over the interface. The method comprises transforming
the beamforming information per direction to beamforming
information per antenna, the beamforming information per antenna
representing the beamforming weights. The method comprises applying
the beamforming weights.
[0009] According to a second aspect there is presented an RE of an
access node for obtaining information for determining beamforming
weights for terminal devices. The RE has an interface to an REC of
the access node and comprises processing circuitry. The processing
circuitry is configured to cause the RE to obtain beamforming
information per direction from the REC over the interface. The
processing circuitry is configured to cause the RE to transform the
beamforming information per direction to beamforming information
per antenna, the beamforming information per antenna representing
the beamforming weights. The processing circuitry is configured to
cause the RE to apply the beamforming weights.
[0010] According to a third aspect there is presented an RE of an
access node for obtaining information for determining beamforming
weights for terminal devices. The RE has an interface to an REC of
the access node and comprises processing circuitry and a computer
program product. The computer program stores instructions that,
when executed by the processing circuitry, causes the RE to perform
operations, or steps. The operations, or steps, cause the RE to
obtain beamforming information per direction from the REC over the
interface. The operations, or steps, cause the RE to transform the
beamforming information per direction to beamforming information
per antenna, the beamforming information per antenna representing
the beamforming weights. The operations, or steps, cause the RE to
apply the beamforming weights.
[0011] According to a fourth aspect there is presented an RE of an
access node for obtaining information for determining beamforming
weights for terminal devices. The RE has an interface to an REC of
the access node. The RE comprises an obtain module configured to
obtain beamforming information per direction from the REC over the
interface. The RE comprises a transform module configured to
transform the beamforming information per direction to beamforming
information per antenna, the beamforming information per antenna
representing the beamforming weights. The RE comprises an apply
module configured to apply the beamforming weights.
[0012] According to a fifth aspect there is presented a computer
program for obtaining information for determining beamforming
weights for terminal devices. The computer program comprises
computer program code which, when run on processing circuitry of an
RE, causes the RE to perform a method according to the first
aspect.
[0013] According to a sixth aspect there is presented a method for
providing information for determining beamforming weights for
terminal devices. The method is performed by an REC of an access
node. The REC has an interface to an RE of the access node. The
method comprises obtaining beamforming information per antenna, the
beamforming information per antenna representing the beamforming
weights. The method comprises transforming the beamforming
information per antenna to beamforming information per direction.
The method comprises providing the beamforming information per
direction to the RE over the interface.
[0014] According to a seventh aspect there is presented an REC of
an access node for providing information for determining
beamforming weights for terminal devices. The REC has an interface
to an RE of the access node and comprises processing circuitry. The
processing circuitry is configured to cause the REC to obtain
beamforming information per antenna, the beamforming information
per antenna representing the beamforming weights. The processing
circuitry is configured to cause the REC to transform the
beamforming information per antenna to beamforming information per
direction. The processing circuitry is configured to cause the REC
to provide the beamforming information per direction to the RE over
the interface.
[0015] According to an eighth aspect there is presented an REC of
an access node for providing information for determining
beamforming weights for terminal devices. The REC has an interface
to an RE of the access node and comprises processing circuitry and
a computer program product. The computer program stores
instructions that, when executed by the processing circuitry,
causes the REC to perform operations, or steps. The operations, or
steps, cause the REC to obtain beamforming information per antenna,
the beamforming information per antenna representing the
beamforming weights. The operations, or steps, cause the REC to
transform the beamforming information per antenna to beamforming
information per direction. The operations, or steps, cause the REC
to provide the beamforming information per direction to the RE over
the interface.
[0016] According to a ninth aspect there is presented an REC of an
access node for providing information for determining beamforming
weights for terminal devices. The REC has an interface to an RE of
the access node. The REC comprises an obtain module configured to
obtain beamforming information per antenna, the beamforming
information per antenna representing the beamforming weights. The
REC comprises a transform module configured to transform the
beamforming information per antenna to beamforming information per
direction. The REC comprises a provide module configured to provide
the beamforming information per direction to the RE over the
interface.
[0017] According to a tenth aspect there is presented a computer
program for providing information for determining beamforming
weights for terminal devices. The computer program comprises
computer program code which, when run on processing circuitry of an
REC, causes the REC to perform a method according to the sixth
aspect.
[0018] According to an eleventh aspect there is presented a method
for determining beamforming weights for terminal devices. The
method is performed by an RE of an access node. The RE has an
interface to an REC of the access node. The method comprises
obtaining beamforming information per antenna from at least one of
the terminal devices, the beamforming information per antenna
representing the beamforming weights. The method comprises
transforming the beamforming information per antenna to beamforming
information per direction. The method comprises providing the
beamforming information per direction to the REC over the
interface.
[0019] According to a twelfth aspect there is presented an RE of an
access node for determining beamforming weights for terminal
devices. The RE has an interface to an REC of the access node and
comprises processing circuitry. The processing circuitry is
configured to cause the RE to obtain beamforming information per
antenna from at least one of the terminal devices, the beamforming
information per antenna representing the beamforming weights. The
processing circuitry is configured to cause the RE to transform the
beamforming information per antenna to beamforming information per
direction. The processing circuitry is configured to cause the RE
to provide the beamforming information per direction to the REC
over the interface.
[0020] According to a thirteenth aspect there is presented an RE of
an access node for determining beamforming weights for terminal
devices. The RE has an interface to an REC of the access node and
comprises processing circuitry and a computer program product. The
computer program stores instructions that, when executed by the
processing circuitry, causes the RE to perform operations, or
steps. The operations, or steps, cause the RE to obtain beamforming
information per antenna from at least one of the terminal devices,
the beamforming information per antenna representing the
beamforming weights. The operations, or steps, cause the RE to
transform the beamforming information per antenna to beamforming
information per direction. The operations, or steps, cause the RE
to provide the beamforming information per direction to the REC
over the interface.
[0021] According to a fourteenth aspect there is presented an RE of
an access node for determining beamforming weights for terminal
devices. The RE has an interface to an REC of the access node. The
RE comprises an obtain module configured to beamforming information
per antenna from at least one of the terminal devices, the
beamforming information per antenna representing the beamforming
weights. The RE comprises a transform module configured to
transform the beamforming information per antenna to beamforming
information per direction. The RE comprises a provide module
configured to provide the beamforming information per direction to
the REC over the interface.
[0022] According to a fifteenth aspect there is presented a
computer program for determining beamforming weights for terminal
devices. The computer program comprises computer program code
which, when run on processing circuitry of an RE, causes the RE to
perform a method according to the eleventh aspect.
[0023] According to a sixteenth aspect there is presented a method
for obtaining information for determining beamforming weights for
terminal devices. The method is performed by an REC of an access
node. The REC has an interface to an RE of the access node. The
method comprises obtaining beamforming information per direction
from the RE over the interface. The method comprises determining
the beamforming weights per direction based on the beamforming
information per direction. The method comprises providing the
beamforming weights per direction to the RE over the interface.
[0024] According to a seventeenth aspect there is presented an REC
of an access node for providing information for obtaining
information for determining beamforming weights for terminal
devices. The REC has an interface to an RE of the access node and
comprises processing circuitry. The processing circuitry is
configured to cause the REC to obtain beamforming information per
direction from the RE over the interface. The processing circuitry
is configured to cause the REC to determine the beamforming weights
per direction based on the beamforming information per direction.
The processing circuitry is configured to cause the REC to provide
the beamforming weights per direction to the RE over the
interface.
[0025] According to a eighteenth aspect there is presented an REC
of an access node for obtaining information for determining
beamforming weights for terminal devices. The REC has an interface
to an RE of the access node and comprises processing circuitry and
a computer program product. The computer program stores
instructions that, when executed by the processing circuitry,
causes the REC to perform operations, or steps. The operations, or
steps, cause the REC to obtain beamforming information per
direction from the RE over the interface. The operations, or steps,
cause the REC to determine the beamforming weights per direction
based on the beamforming information per direction. The operations,
or steps, cause the REC to provide the beamforming weights per
direction to the RE over the interface.
[0026] According to an nineteenth aspect there is presented an REC
of an access node for obtaining information for determining
beamforming weights for terminal devices. The REC has an interface
to an RE of the access node. The REC comprises an obtain module
configured to obtain beamforming information per direction from the
RE over the interface. The REC comprises a determine module
configured to determine the beamforming weights per direction based
on the beamforming information per direction. The REC comprises a
provide module configured to provide the beamforming weights per
direction to the RE over the interface.
[0027] According to a twentieth aspect there is presented a
computer program for obtaining information for determining
beamforming weights for terminal devices. The computer program
comprises computer program code which, when run on processing
circuitry of an REC, causes the REC to perform a method according
to the sixteenth aspect.
[0028] According to a twenty first aspect there is presented a
computer program product comprises a computer program according to
at least one of the fifth aspect, the tenth aspect, the fifteenth
aspect, and the twentieth aspect and a computer readable storage
medium on which the computer program is stored. The computer
readable storage medium could be a non-transitory computer readable
storage medium.
[0029] Advantageously these methods, these REs, these RECs, and
these computer programs allows for efficient communications between
the RE and the REC when configuring resources for terminal
devices.
[0030] Advantageously these methods, these REs, these RECs, and
these computer programs allows for large-scale digital beamforming
in the access node without significantly upgrading the data rate of
the interface between the RE and the REC.
[0031] Other objectives, features and advantages of the enclosed
embodiments will be apparent from the following detailed
disclosure, from the attached dependent claims as well as from the
drawings.
[0032] Generally, all terms used in the claims are to be
interpreted according to their ordinary meaning in the technical
field, unless explicitly defined otherwise herein. All references
to "a/an/the element, apparatus, component, means, step, etc." are
to be interpreted openly as referring to at least one instance of
the element, apparatus, component, means, step, etc., unless
explicitly stated otherwise. The steps of any method disclosed
herein do not have to be performed in the exact order disclosed,
unless explicitly stated.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] The inventive concept is now described, by way of example,
with reference to the accompanying drawings, in which:
[0034] FIGS. 1, 2, 3, 4, 5, and 6 are schematic diagrams
illustrating an access node according to embodiments;
[0035] FIG. 7 is a schematic illustration of a time-frequency
resource grid according to embodiments;
[0036] FIG. 8 is a schematic illustration comparing energy in
antenna space and direction space;
[0037] FIG. 9 is a schematic illustration of a compression
subsystem according to an embodiment;
[0038] FIGS. 10, 11, 12, and 13 are flowcharts of methods according
to embodiments;
[0039] FIG. 14 is a schematic diagram showing functional units of
an RE according to an embodiment;
[0040] FIG. 15 is a schematic diagram showing functional modules of
an RE according to an embodiment;
[0041] FIG. 16 is a schematic diagram showing functional units of
an REC according to an embodiment;
[0042] FIG. 17 is a schematic diagram showing functional modules of
an REC according to an embodiment; and
[0043] FIG. 18 shows one example of a computer program product
comprising computer readable means according to an embodiment.
DETAILED DESCRIPTION
[0044] The inventive concept will now be described more fully
hereinafter with reference to the accompanying drawings, in which
certain embodiments of the inventive concept are shown. This
inventive concept may, however, be embodied in many different forms
and should not be construed as limited to the embodiments set forth
herein; rather, these embodiments are provided by way of example so
that this disclosure will be thorough and complete, and will fully
convey the scope of the inventive concept to those skilled in the
art. Like numbers refer to like elements throughout the
description. Any step or feature illustrated by dashed lines should
be regarded as optional.
[0045] FIG. 1 is a schematic diagram illustrating an access node
100 where embodiments presented herein can be applied. The access
node could be a radio base station such as a radio access network
node, base transceiver station, node B, evolved node B, or access
point. As disclosed above, the access node comprises at least one
Radio Equipment Controller (REC) 300 and at least one Radio
Equipment (RE) 200. In the illustrative example of FIG. 1 the
access node comprises one REC and two REs, where the REC has one
interface 700 to each of the REs. The REs are configured to perform
DL transmissions to, and UL receptions from, terminal devices boo
in beams 500 by using appropriate beamforming weights at the
antennas 400. The beamforming weights define at least the pointing
direction and the width of the beams. How to determine the
beamforming weights will be disclosed below.
[0046] As defined herein the REC does not send in-phase/quadrature
(I/Q) samples per physical radio branch to the RE, but rather
multiple-input multiple-output (MIMO) streams, i.e., I/Q samples
per layer. According to the current CPRI specification, the REC can
directly address the antennas in the RE, but in the herein
disclosed access node that is configured to perform beamforming,
the RE performs the functionality of mapping a MIMO stream to a set
of physical antenna elements in order to generate a wanted beam
form. Further, in order to enable efficient simultaneous multi user
beamforming, the Fast Fourier Transform (FFT) and Inverse Fast
Fourier Transform (IFFT) functions are performed in the RE. In
addition, the execution of the beamforming data plane functionality
is added to the RE. Further, the interface 700 between REC and RE
could be a packet-based interface, and hence no longer a streaming
interface, sending the (frequency domain) samples to the RE symbol
by symbol. This allows for quick and flexible allocation of
resources on the interface to different terminal devices. The REC
is configured to maintain knowledge about the terminal devices, and
schedules the air interface between the access node and the
terminal devices. The RE is configured to act on commands received
from the REC.
[0047] As an illustrative example, consider a communications system
having an air interface with a system bandwidth of 400 MHz and that
provides support for 4 MIMO streams and utilizes access nodes with
64 antennas for beamforming. Using CPRI interfaces between the REC
and the RE exposing all 64 antennas for the REC would require
approximately 54 CPRI interfaces of 10 Gbps, since a CPRI interface
carries about 480 MHz. Further, an interface using virtual antenna
ports would require 4 MIMO streams of 400 MHz, and would require
about 4 CPRI interfaces of 10 Gbps, since one 10 Gbps CPRI
interface still carries data for about 480 MHz. By also moving the
modulation DL to the RE, the 4 MIMO streams of 400 MHz would
require 7 Gbps (assuming 256QAM and 20 LTE 20 MHz carriers), or one
10 Gbps CPRI interface. A higher bitrate of the CPRI interface is
required in the UL if the whole system bandwidth is used, as
demodulation is still performed in the REC.
[0048] Consider the REC and RE illustrated in FIG. 2 where the REC
and RE are interconnected via an interface denoted RUI, for Radio
Unit Interface. In the DL direction the REC sends unmodulated bits
for each terminal device. The RE modulates the data, places it on
the correct subcarrier (thus performing resource mapping), applies
beamforming weights (individual per radio branch) defining e.g.
width and/or direction of the beams and finally convert it to time
domain and transmits it to the terminal devices. FIG. 2 shows 1-8
DL MIMO layers on 128 radio branches. In the UL direction the RE
samples the signals for each individual radio branch, converts it
to frequency domain, applies beamforming weights, combines the
signals from the different radio branches and sends a selection of
the modulated combined signal to the REC for further demodulation.
FIG. 2 shows 128 radio branches and 1-16 receive beams. The receive
beams weakly relates to UL MIMO branches as the more MIMO branches
the more receive beams are needed. Typically, more receive beams
than MIMO branches are required. FIG. 2 also shows beamforming as
performed before de-mapping in the RE. The two stages are
interlinked as the beamforming is performed individually per
terminal device. FIG. 2 further illustrates User Plane Control
(UPC) with its air interface scheduling and link adaptation placed
in the REC.
[0049] FIG. 3 shows an embodiment of an REC and an RE similar to
those in FIG. 2. In FIG. 3 the RE is configured to decode reference
symbols such as Sounding Reference symbols (SRS) in the UL, to
store information of how the reference symbols are best received
(e.g., what beamforming weights maximizes the SNR of the reference
symbols) and to use this stored information when performing
beamforming in the DL and UL. In FIG. 3 the RE could thus be
regarded as autonomous in this respect. To accomplish this, the RU
needs to maintain a storage of information identifying the best
beam shapes for each terminal device, and be configured to apply
that information when the corresponding terminal device is
scheduled. This minimizes the communication needed over the
interface between the REC and the RE with respect to beamforming,
but also hides the channel for the UPC.
[0050] The scheduling and the LA are based on the dimension reduced
information while further dimensions are used for the determination
of beamforming weights. This is equally applicable for UL and DL.
The radio channel should typically be dispersive to be able to gain
from adding more dimensions to the beam calculation.
[0051] FIG. 4 shows an embodiment of an REC and an RE similar to
those in FIG. 2. In FIG. 4 the beamforming control is performed
primarily by the UPC in the REC. The RE still receives the
reference symbols and determines information of how the reference
symbols are best received. This information is then sent to the
REC. The REC uses this information to make an optimal decision on
MIMO streams, link adaptation and coordinated scheduling with other
terminal devices, such as MU-MIMO or nulling.
[0052] To make the communication and functionality performed in the
UPC generic and not heavy dependent on the actual implementation of
the RE (e.g., in terms of number of branches, antenna layout, etc.)
or operating mode (e.g., power save, faulty branches, etc.), the
communications between the REC and the RE regarding beamforming
properties is expressed in beam direction space rather than antenna
element space. That is, instead of presenting a beam as a set of
weights of physical antenna elements the beam is presented as a
combination of a set of predetermined beams. This also allows for a
more compressed format for this communication, thus saving bit rate
on the interface between the REC and the RE. For instance, a linear
combination of 3 predetermined beams could be expressed as 3 times
24 bits (an 8-bit beam number+an 8-bit amplitude+an 8-bit phase)
rather than 128 times 16 bits (an 8-bit amplitude+an 8-bit phase
for each of the 128 physical antenna elements). The transformation
from the physical antenna element space to the beam direction space
is performed by a Dimensions Reduction entity, and the inverse
transformation is performed by a Beam Weight Transformation
entity.
[0053] The operations as performed by the REC and RE in FIG. 4
could be preferred when the load of the access node is
comparatively high and UPC needs to determine the channel state for
the best decision on link adaptation.
[0054] The operations as performed by the REC and RE in FIG. 4
could be preferred when MU-MIMO or nulling is used, as the UPC then
needs channel state information for the LA of the combination, and
to determine which users are suitable for simultaneous scheduling,
so called MU-MIMO scheduling. Note that nulling may also be applied
between terminal devices served by different REs, and is therefore
impossible to perform within one autonomous RE (as in FIG. 3).
[0055] FIG. 5 illustrates an embodiment of an REC and an RE
combining the functionality of the REC and RE in the embodiments of
FIG. 3 and FIG. 4. In comparison to FIG. 3 and FIG. 4, the
embodiment of FIG. 5 comprises a channel state memory, an UL/DL BF
coefficient calculation entity (where BF is short for beamforming),
an UL/DL quality calculation entity, an UL/DL SNR calculation
entity (where SNR is short for signal to noise ratio), and a CSI
feedback function (where CSI is short for Channel State
Information).
[0056] The channel state memory is configured to store reference
symbols since the reference symbols are not sent continuously. The
transmission rate of the reference symbols is controlled by the
access node, and different terminal devices could have different
transmission rates of the reference symbols to allow for the access
node to follow channel state changes. Although the channel state
memory is illustrated as storing data expressed in the beam space
in both the RE and the REC, the RE could instead have the channel
state memory storing data expressed in the physical antenna element
space.
[0057] The UL/DL BF coefficient calculation entity is configured to
determine beamforming weights based on the channel state memory and
possible other constraints (such as nulling and MU-MIMO) in the
RE.
[0058] The UL RX weights calculation entity (where RX is short for
reception) is configured to determine beamforming weights for the
uplink. The UL beamforming weight determination can be part of
maximum-ratio combining (MRC) in the UL demodulator/equalizer. The
UPC will order more beams than layers, and then the demodulation
will combine these to improve SNR or suppress interferers. In the
REC, the determination of beamforming weights could be performed in
conjunction with the link adaptation whereas in the case of
beamforming weights determined by the RE, the link adaptation is
done independently.
[0059] The UL/DL quality calculation entity is configured to
determine a quality estimate in respect of each terminal device
subject to MU-MIMO scheduling. This quality estimate should reflect
the spatial separation between wireless terminals as well as the
quality achieved when co-scheduling wireless terminals on the same
time/frequency resource. The quality estimate is based on the
information in the channel state memory.
[0060] The UL/DL SNR calculation entity is configured to determine
the beamforming weights for each terminal device, and to provide
the link adaptation function with estimates of the resulting SNR
for each of the terminal devices being scheduled, including the
mutual effect of co-scheduled terminal devices, so called MU-MIMO
scheduling. The UE feedback (CSI) entity is configured to extract
information about the channel provided by the terminal devices (in
the UL data plane). Especially, in the case of FDD, where the
reciprocity of the DL and UL of the channel to the terminal device
is not perfect, it can be beneficial for the terminal device to
send measurements (e.g., CSI) on the DL signal back to the access
node. The CSI reports are extracted by the REC and used in the
channel state memory and thus being considered in the determination
of the beamforming weights.
[0061] In configurations where the bitrate of the interface between
the REC and the RE is low (such as below a threshold), the
determination of beamforming weights is executed by the RE (as in
FIG. 3), otherwise the determination is executed by the REC (as in
FIG. 4). That is, in case of limited available capacity of the
interface between the REC and the RE, the REC (such as in the UPC)
determines that the determination of beamforming weights is to be
executed by the RE. Cell performance of the access node could be
maximized by determining the beamforming weights in the REC for all
co-scheduled terminal devices (within the same time and frequency
domain) in order to accomplish best link adaptation and
orthogonality. This requires that the RE sends extra information to
the REC to allow for such determination, and that the REC sends the
determined beamforming weights to the RE.
[0062] Still further, although the REC sends the determined
beamforming weights to the RE, the RE can determine beamforming
weights in parallel and thus combine these internally determined
beamforming weights with the beamforming weights received from the
REC. For access nodes where the interface between the REC and the
RE is constrained but not minimized, the dual loops (as defined by
the embodiment in FIG. 5) allow for the access node to select some
terminal devices which can be handled locally in the RE, thereby
making bitrate of the interface between the REC and the RE
available to handle terminal devices which are eligible to MU-MIMO
scheduling, e.g. terminal devices using a streaming service.
[0063] Having both loops also allows for efficient beamforming
coefficient compression. If a terminal device is note exposed to
constraints from the UPC, the beamforming coefficient calculation
in the REC will be the same as performed in the RE, and the REC can
send a minimal message requesting the RE to use its locally
calculated values. In case of heavy dimensioning reduction, this
may even improve the beamforming gain as the RE has uncompressed
channel estimation data. Correspondingly, if constraints have
changed any beamforming weights, it can be evaluated if the
constraints have less bits than the new beamforming weights, and
can be transferred instead.
[0064] Further aspects applicable to both the embodiments of the RE
and the REC will now be disclosed with reference to the embodiment
of REC and RE illustrated in FIG. 6. The description of those
entities already having been described with reference to any of
FIGS. 2-5 is omitted for brevity.
[0065] A reference symbol extraction entity is configured to
extract the reference symbols from the Resource Elements that are
provided by the UL OFDM FFT from all antenna ports.
[0066] The spatial Discrete Fourier Transform (DFT) entity and the
channel estimation entity are configured to collectively provide a
quality value for the fixed beam directions. The quality value is
typically based on a filtering of the reference symbols per
involved transmission antennas at the terminal device or MIMO layer
within the resource block or for a filtering of a further processed
channel estimate per involved transmission antennas at the terminal
device or MIMO layer and extracted reference symbols. The beam
direction space is provided by processing the reference symbols
from all antennas through the spatial DFT entity.
[0067] A Dimension Reduction entity is configured to reduce
dimension of data being inputted to the Dimension Reduction entity.
For beamforming weight determination performed via the REC, the
dimension of which fixed beam directions to use for the beamforming
is reduced in order to limit the processing load when calculating
the weights and the interface rate from the RE to the REC. The
dimension reduction is based on the quality values from the Spatial
DFT entity and the channel estimation entity. For beamforming
weight determination performed internally in the RE, more
dimensions can be stored, and thus providing better SNR in case of
SU-MIMO transmission.
[0068] A Channel state memory is provided in the REC when
beamforming weight determination is performed via the REC. For the
terminal devices that are scheduled to be measured, the reference
symbol based channel estimates can be sent to the REC and stored in
the REC Channel State Memory. These stored channel estimates can
then be used for link adaption as well as determination of
beamforming weights. The content of the Channel state memory can be
used when the data channel is active and is updated for every new
measurement of reference symbols. In addition to this the Channel
state memory can also store a covariance matrix for all beam
directions that have been measured. Those values can be calculated
in the REC. If no MU-MIMO pairing shall be done the beam direction
related information does not need to be stored in the Channel state
memory, which will lower the demand on the interface between the
REC and the RE.
[0069] A Channel state memory is provided in the RE when
beamforming weight determination is performed internally in the RE.
For the reference symbols of the terminal devices that are
scheduled to be measured, the reference symbol based Channel
estimates are stored in the RE Channel State Memory. These stored
channel estimates can be used for determining beamforming weights.
The content of the Channel state memory can be used when the data
channel is active and could be updated for every new measurement of
reference symbols. If no MU-MIMO pairing is done, if no beam
direction related information is stored in the REC based channel
state memory, and if the covariance matrix will be used, the same
covariance matrix as described in the channel state memory in the
REC can instead be stored in the channel state memory in the
RE.
[0070] A Source Select entity is configured to select and/or
combine the beamforming weights that either originate from the REC
or locally from the RE. Even in the case where the channel estimate
is sent to the REC, a local copy of the channel estimate can be
stored in the RE. In case the REC will not send beamforming
weights, the RE will have to use beamforming weights as determined
internally. This can be due to the REC being satisfied with the
beamforming weights determined internally or that the beamforming
weights are not received properly by the RE (e.g., due to a lost
message). Further, as will be further disclosed below the local
stored channel estimates can be used to calculate a default setting
of the beamforming weights to which the REC sends differential
information, see the compression chapter below. The RE can signal
to the REC if it has stored a local copy of the channel estimate.
This allows the REC to know if such compression is possible. The RE
can run out of local memory, thus such a signalling is recommended
(but not mandated). Also, the REC can explicitly order the RE to
store a local copy. Also in case no complete channel estimate is
sent to the REC, a reduced channel estimate could be transmitted
from the RE to the REC to aid the link adaptation and rank
selection.
[0071] FIG. 7 gives an example of a time-frequency resource grid
1700 applicable to embodiments disclosed herein. The time-frequency
resource grid illustrates a possible allocation of resources to
terminal devices in terms of a scheduled entity comprising symbols,
where each symbol corresponds to a Resource Element. Each Resource
Element in time corresponds to one orthogonal frequency-division
multiplexing (OFDM) symbol and in frequency corresponds to a
subcarrier. One subframe comprises 7 symbols; one subcarrier group
comprises 24 subcarriers, one subcarrier chunk comprises 10
subcarrier groups; and one carrier comprises at least one
subcarrier chunk.
[0072] According to some aspects there are provided mechanisms for
efficient dimensions reduction for expressing beamforming weights
and information related to determining the beamforming weights.
[0073] Reference is now made to FIG. 10 illustrating methods for
determining beamforming weights for terminal devices as performed
by the RE of the access node according to embodiments.
[0074] As will be disclosed below, the REC in step S206 provides
beamforming information per direction to the RE 200 over the
interface 700. Hence, the RE 200 is configured to perform step
S102:
[0075] S102: The RE 200 obtains beamforming information per
direction from the REC 300 over the interface 700.
[0076] The beamforming information is to be applied not per
direction but per antenna. The RE 200 is therefore configured to
perform step S106:
[0077] S106: The RE 200 transforms the beamforming information per
direction to beamforming information per antenna. The beamforming
information per antenna represents the beamforming weights.
[0078] The beamforming weights are then applied. Thus, the RE 200
is configured to perform step S108:
[0079] S108: The RE 200 applies the beamforming weights.
[0080] Further aspects of determining beamforming weights for
terminal devices as performed by the RE will now be disclosed.
[0081] In general terms, the beamforming weights are to be applied
at antennas 400 of the RE 200.
[0082] In some aspects the number of beamforming weights in the
direction space is smaller than the number of beamforming weights
in the antenna space. In this aspect the transformation thus
results in an expansion of dimensionality of the of beamforming
information. That is, according to an embodiment the beamforming
information per antenna is associated with a first dimensionality,
and the beamforming information per direction is associated with a
second dimensionality being smaller than the first
dimensionality.
[0083] In some aspects the beamforming information is transmitted
between the RE 200 and the REC 300 as linear combinations of
predetermined beams. Particularly, according to an embodiment the
beamforming information per direction is obtained as a linear
combination of predetermined beamforming weights per direction.
[0084] There could be different ways to perform the transformation.
In some aspects the transformation is achieved based on using a
DFT. Particularly, according to an embodiment the beamforming
information is transformed using a DFT.
[0085] As will be further disclosed below, indices i.sub.0,
i.sub.1, . . . could be used that appoint which of the fixed beam
directions (as defined by the predetermined beams) to use.
Particularly, according to an embodiment the RE 200 is configured
to perform (optional) step S104:
[0086] S104: The RE 200 obtains information appointing fixed beam
directions from the REC 300 over the interface 100. The beamforming
information per direction is then transformed to the beamforming
information per antenna only for the appointed beam directions.
[0087] Reference is now made to FIG. 11 illustrating methods for
determining beamforming weights for terminal devices as performed
by the REC of the access node according to embodiments.
[0088] In general terms, beamforming information is applied per
antenna and beamforming information is therefore often determined
per antenna. Therefore the REC 300 is configured to perform step
S202:
[0089] S202: The REC 300 obtains beamforming information per
antenna. The beamforming information per antenna represents the
beamforming weights.
[0090] Beamforming information per direction could enable more
efficient transmission of the beamforming information to the RE 200
than when the beamforming information is per antenna. Therefore,
the REC 300 is configured to perform step S204:
[0091] S204: The REC 300 transforms the beamforming information per
antenna to beamforming information per direction.
[0092] The beamforming information is to be applied by the RE 200
and is therefore provided to the RE 200. That is, the REC 300 is
configured to perform step S206:
[0093] S206: The REC 300 provides the beamforming information per
direction to the RE 200 over the interface 100.
[0094] Further aspects of determining beamforming weights for
terminal devices as performed by the REC will now be disclosed.
[0095] The beamforming information per antenna could be obtained
from at least one of the terminal devices boo.
[0096] As disclosed above, in some aspects the number of
beamforming weights in the direction space is smaller than the
number of beamforming weights in the antenna space. That is, the
embodiment wherein the beamforming information per antenna is
associated with a first dimensionality, and wherein the beamforming
information per direction is associated with a second
dimensionality being smaller than the first dimensionality is also
applicable for the REC 300.
[0097] In some aspects only high quality beamforming information
per direction is provided. Particularly, according to an embodiment
only the beamforming information per direction having a signal
quality measure above a threshold is provided to the RE 200 over
the interface 700 in step S206. The beamforming information per
direction that does not fulfil the requirement defined by the
threshold is thus not transmitted over the interface 100, thus
enabling a reduction in bitrate in comparison to transmitting all
the beamforming information per direction or all the beamforming
information per antenna.
[0098] As disclosed above, in some aspects the transformation is
achieved based on using a DFT. That is, the embodiment wherein the
beamforming information is transformed using a DFT is also
applicable for the REC 300.
[0099] As disclosed above, in some aspects indices i.sub.0,
i.sub.1, . . . could be used that appoint which of the fixed beam
directions to use. That is, according to an embodiment the REC 300
is configured to perform (optional) step S208:
[0100] S208: The REC 300 provides information to the RE 200 over
the interface 700 appointing which fixed beam directions to use
when transforming the beamforming information per direction to
beamforming information per antenna.
[0101] Reference is now made to FIG. 12 illustrating methods
determining beamforming weights for terminal devices as performed
by the RE of the access node according to embodiments.
[0102] S302: The RE 200 obtains beamforming information per antenna
from at least one of the terminal devices boo. The beamforming
information per antenna represents the beamforming weights.
[0103] Beamforming information per direction could enable more
efficient transmission of the beamforming information to the REC
300 than when the beamforming information is per antenna.
Therefore, the RE 200 is configured to perform step 3204:
[0104] S304: The RE 200 transforms the beamforming information per
antenna to beamforming information per direction.
[0105] The beamforming information is then provided to the REC 300.
That is, the RE 200 is configured to perform step S306:
[0106] S306: The RE 200 provides the beamforming information per
direction to the REC 300 over the interface 700.
[0107] Further aspects of determining beamforming weights for
terminal devices as performed by the RE will now be disclosed.
[0108] As disclosed above, in some aspects the number of
beamforming weights in the direction space is smaller than the
number of beamforming weights in the antenna space. That is, the
embodiment wherein the beamforming information per antenna is
associated with a first dimensionality, and wherein the beamforming
information per direction is associated with a second
dimensionality being smaller than the first dimensionality is also
applicable for the RE 200.
[0109] As disclosed above, in some aspects only high quality
beamforming information per direction is provided. That is, the
embodiment wherein only the beamforming information per direction
having a signal quality measure above a threshold is provided to
the REC 300 over the interface 700 is also applicable for the RE
200.
[0110] As disclosed above, in some aspects the transformation is
achieved based on using a DFT. That is, the embodiment wherein the
beamforming information is transformed using a DFT is also
applicable for the RE 300.
[0111] As will be further disclosed below, in some aspects the REC
300 provide beamforming weights per direction to the RE 200 over
the interface 700.
[0112] Hence, according to an embodiment the RE 200 is configured
to perform (optional) step S308:
[0113] S308: The RE 200 obtains updated beamforming weights per
direction from the REC 300 over the interface 700.
[0114] The beamforming weights per direction are transformed to
beamforming weights per antenna. That is, according to this
embodiment the RE 200 is configured to perform (optional) step
S310:
[0115] S310: The RE 200 obtains transforms the updated beamforming
weights per direction to updated beamforming weights per
antenna.
[0116] The beamforming weights per antenna can then be used by the
RE 200. Particularly, according to this embodiment the RE 200 is
configured to perform (optional) step S312:
[0117] S312: The RE 200 applies the updated beamforming weights per
antenna.
[0118] The updated beamforming weights could be applied at antennas
400 of the RE 200.
[0119] Reference is now made to FIG. 13 illustrating a method for
determining beamforming weights for terminal devices as performed
by the REC of the access node according to embodiments.
[0120] As disclosed above, the RE 200 in step S306 provides
beamforming information per direction to the REC 300 over the
interface 700. Therefore, the REC 300 is configured to perform step
S402:
[0121] S402: The REC 300 obtains beamforming information per
direction from the RE 200 over the interface 700.
[0122] Beamforming weight to be applied at the RE 200 are then
determined. Particularly, the REC 300 is configured to perform step
S406:
[0123] S406: The REC 300 determines the beamforming weights per
direction based on the beamforming information per direction.
[0124] The beamforming weights are then provided to the RE 200.
Thus, the REC 300 is configured to perform step S408:
[0125] S408: The REC 300 provides the beamforming weights per
direction to the RE 200 over the interface 700.
[0126] As disclosed above, in some aspects only high quality
beamforming information per direction is used. That is, according
to an embodiment only the beamforming information per direction
having a signal quality measure above the threshold is used when
determining the beamforming weights per direction.
[0127] In some aspects the beamforming weights are determined based
on the rank of the radio channel, either for multiple users or a
single user (where each user is defined by a respective terminal
device 600). Therefore, according to an embodiment the REC 300 is
configured to perform (optional) step S404:
[0128] S404: The REC 300 obtains channel rank information from the
RE 200 over the interface 700. The beamforming weights per
direction are then determined based on the channel rank
information.
[0129] Particular aspects of efficient dimensions reduction of the
beamforming weights when communicating information of the
beamforming weights, such as beamforming information, between the
REC 300 and the RE 200 will now be disclosed in more detail.
[0130] The energy or Signal-to-Noise and Interference Ratio (SNIR)
of the signals is approximately the same for all the individual
antennas. However, since the received UL signals (or transmitted DL
signals) are associated with pointing directions due to the
beamforming weights, the energy or SNIR will be unevenly
distributed between different pointing directions. This is
illustrated in FIG. 8. At 1800a is illustrated energy per antenna
and at 1800b is illustrated energy per direction. The energy or
SNIR will be high in pointing directions from the access node to
the terminal devices and low in other directions. This motivates
beamforming information per direction to be communicated between
the RE 200 and the REC 300 in accordance with embodiments disclosed
above.
[0131] If the majority of the energy is located in a subset of all
possible pointing directions, and signals in other directions
contains mostly noise, it is possible to reduce the dimensionality
of the signals to process by only selecting the directions with
significant energy or SNIR. This motivates the above embodiments
wherein the beamforming information per antenna is associated with
a first dimensionality, and wherein the beamforming information per
direction is associated with a second dimensionality being smaller
than the first dimensionality.
[0132] In general terms, beam information, such as information
relating to the beamforming weights, can be transmitted between the
RE and the REC as linear combinations of predetermined beams.
Hence, in accordance with what has been disclosed above, the
beamforming information per direction could be represented by a
linear combination of predetermined beamforming weights per
direction
[0133] The UL OFDM FFT in FIG. 6 provides the output of Resource
Elements for all antennas with N.sub.a antenna elements used for
beamforming. The Resource Elements include either data or pre-known
Reference Symbols.
[0134] By extracting the same Reference Symbol from all N.sub.a
antennas elements and perform a transformation, e.g., a DFT, on the
thus N.sub.a Reference Symbols, a transformation to a beam
direction space from the antenna space is done. Each value in the
N.sub.a long output from the transform provides information about
the quality of the signal in one of the N.sub.a fixed beam
directions.
[0135] All beamforming weight calculation can thereby be made in
the beam direction space to minimize complexity. The beamforming
weights can be determined based on the rank of the radio channel
either for multiple users or a single user and be determined to
limit the influence of UL interference as well as spreading of
interference in the DL. This could be accomplished by combining
enough of the discrete beam directions properly weighted to capture
the majority of the energy that will result in a small throughput
loss on network level.
[0136] The beamforming weights in the direction space (of size
N.sub.d) for beam b are given by:
w.sub.d.sup.b,d=i.sub.0,i.sub.1, . . . ,i.sub.N.sub.d.sub.-1
[0137] When applying the weights to either the UL or DL digital
beamforming, they need to be transformed to the antenna space to
handle the Resource Elements with data that also is in the antenna
space.
[0138] The beamforming weights in the antenna space (of size
N.sub.a) for beam b are given by:
w.sub.a.sup.b,a=0,1, . . . ,N.sub.a-1
[0139] If the transformation matrix used for performing the inverse
transform (i.e. from the direction space to the antenna space) is
denoted F.sub.ad, then:
w.sub.a.sup.b=.SIGMA..sub.dF.sub.adw.sub.d.sup.b
[0140] The number of bits for per physical resource block (PRB)
group and beam is N.sub.aB.sub.weight, whilst the number of bits
for w.sub.d.sup.b per PRB group and beam is
N.sub.dB.sub.weight.
[0141] As disclosed above, in order to reduce the load on the
interface 700 between the REC 300 and the RE 200 the beamforming
weights can be transferred from the REC to the RE in the direction
space. The number of beamforming weights N.sub.d in the direction
space is smaller than the number of beamforming weights N.sub.a, in
the antenna space. That is, the beamforming information per antenna
is associated with a first dimensionality, and the beamforming
information per direction is associated with a second
dimensionality being smaller than the first dimensionality.
[0142] In addition to the beamforming weights in the direction
space the indices i.sub.0, i.sub.1, . . . appointing which of the
fixed beam directions to use are also transferred to the
beamforming weight transformation block. The number of bits to
transmit for the indices per PRB group and beam is
.ltoreq.N.sub.dB.sub.ind.
[0143] The beam weight transformation block also include a hardware
abstraction transformation function that hide the radio physical
implementation and is capable to handle different configurations of
number of antenna elements in the beamforming array antenna and
other implementation aspects and states. In more detail, since most
of the signal processing can be performed in the directional space,
it will be possible to hide some hardware properties from the
signal processing software. For example, this enables identical
signal processing software to be used for different number of
antennas but with the same number of used dimensions in the
directional space.
[0144] Particular aspects of efficient compression of beamforming
weights will now be disclosed in more detail.
[0145] Compression of the beamforming weights could be achieved by
applying different encoding techniques to reduce the channel
estimate in the UL direction and the beamforming weights in the DL
direction. For example, the encoding techniques could be based on
reducing the resolution of information in a transform domain,
and/or sending differential information.
[0146] FIG. 9 shows a compression subsystem 1900 according to an
embodiment where the interface 700 separates the REC 300 and the RE
200. The compression subsystem comprises a quantizer ("Quant.")
placed in the REC and respective compression memories ("Compression
DB" where DB is short for database) in the REC and RE. The
compression subsystem could be controlled by the UPC in the REC.
The use of beam direction space as disclosed above is optionally
part of the compression subsystem.
[0147] An embodiment of the quantizer of the compression subsystem
will now be disclosed. In general terms, the quantizer can apply
reduction of word widths, have variable length lists of
coefficients and/or apply other compression techniques. The
beamforming weights are applied per OFDM symbol. A first reduction
of the data is to use the same beamforming weights for a set of
consecutive OFDM symbols (e.g., a set of consecutive subcarriers)
in the time domain, typically for a complete transmission. A second
reduction is to use the same beamforming weights for a set of
consecutive OFDM symbols in the frequency domain. The REC could
then inform which beamforming weights to use for each N
subcarriers, and the RE could then perform interpolation for
determining the beamforming weights of the subcarriers between
these N subcarriers.
[0148] In some aspects the value of N is dependent on the channel
coherence. Thus, the channel estimate can be processed in order for
the REC to determine a value of N that is small enough to give
sufficient beamforming performance. Each value of N will give a
certain SNR performance, so the choice of N can be determined
jointly with other related parameters in the link adaptation, such
as output power and modulation and coding scheme (MCS).
[0149] An embodiment of the compression memories of the compression
subsystem will now be disclosed. In order to reduce the load of the
interface between the REC and the RE is for to the REC is to send
differential information of the beamforming weights rather than a
complete set of (quantized) beamforming weights to the RE. Two
sources of base information on which the differential information
can be based are previous transmissions of beamforming weights
between the REC and the RE and beamforming weights determined
internally in the RE. Previous transmissions of beamforming weights
between the REC and the RE can either be from the last transmission
(i.e., recent-most used beamforming weights), or as a continuous
incremental refinement of beamforming weights. For continuous
incremental refinement of beamforming weights, beamforming weights
are first transmitted with a coarse resolution and then more
refined, e.g. first using a large value N and then with
incrementally smaller values of N. In terms of beamforming weights
determined internally in the RE, the RE could be configured to
determine the beamforming weights from its locally stored channel
estimate. In the case that the REC is satisfied (e.g., the RE's
assumption of single-user transmission is correct; one example
where the REC is not satisfied is when it has received additional
information (e.g. about interference) that it wants to use to
create better beamforming weights) with the beamforming weights
determined by the RE (e.g. as optimized for single-user operation),
the REC can indicate this to the RE, thus requiring less signaling
on the interface between the REC and the RE than if beamforming
weight information is transmitted. This allows the REC to only send
beamforming weights for terminal devices which beamforming weights
have by the REC been modified (e.g. as optimized for multi-user
operation).
[0150] An advantage of using the herein disclosed compression
memories is that a communications system with stationary terminal
devices will have very little signaling relating to the beamforming
weights over the interface between the REC and the RE since such
stationary terminal devices could use the same beamforming weights
for two or more consecutive transmissions.
[0151] There are different ways of providing the differential
information. Examples relating thereto will be provided next. A
first example is to provide additive differential information
whereby differential beamforming weights are added to the stored
beamforming weights. A second example is to provide interpolating
differential information whereby complementary beamforming weights,
e.g. in frequency domain, are sent in order to improve the
resolution (of beamforming weights having been sent with lower
value of N) of the beamforming weights. A second example is to
provide multiplicative differential information whereby sending a
beam form to multiply the beamforming weights with in direction
space. Assuming that the beamforming weights are represented as
beamforming weight vectors, then each element of the beamforming
weight vector corresponds to one direction. Setting one of those
elements to zero (by multiply with zero) will create a beam pattern
with a null in that direction. This can be very efficient to
express a nulling, i.e. setting a restriction on a
transmission.
[0152] The transmission of information over the interface between
the REC and the RE in the UL generally is based on the same
features as for the DL, but with information relating to channel
estimates being transferred (instead of information relating to
beamforming weights).
[0153] The (S)RS channel estimation function is configured to set a
suitable value of N, and a suitable quatization. The UPC can, ahead
of a measurement, state the maximum amount to data to send, not to
overload the interface between the REC and the RE. One way is for
the UPC in the REC to provide the RE with a value of N and where
the RE then executes.
[0154] Particular aspects of efficient selection of UL beams will
now be disclosed in more detail.
[0155] It can here be assumed that the UL beams are selected based
on the channel state information. Selecting as a few beams as
possible could reduce the bit rate on the interface between the REC
and the RE. At the same time, more beams allow for more energy to
be received and better suppression of interferers.
[0156] The more terminal devices that are scheduled together and
the more angular spread of the beams needed to reach the terminal
devices, the more beams need to be selected in order to reach good
demodulation performance. Also the types of beams used (such as
beam widths and energy per beam) will affect the number of beams
needed. Beams with beamforming weights determined according to SVD
(so-called SVD-beams) will require fewer selected beams than beams
with beamforming weights determined according to a DFT (so-called
DFT-beams) but could require more computational resources to
compute. Hence there is a tradeoff between reduction of bitrate on
the interface between the REC and the RE and processing complexity
of the beam selection. DTF-beams imply that a fixed set of beams
that evenly cover the whole spatial view seen from the RE is used.
The DTF-beams can be spread out one-dimensionally (either spread
out vertically or horizontally) or they can be spread out
two-dimensionally (spread out both vertically and horizontally).
DFT is one example of creating fixed beams. As understood by the
person skilled in the art other methods for creating fixed beams,
optionally including uneven spread of the beams, are equally
applicable. SVD-beams imply that the set of beams are dynamically
decided depending on the received signals from the desired terminal
devices and optionally also dependent on received signals from the
interfering terminal devices. As understood by the person skilled
in the art other methods for creating dynamic beams are equally
applicable.
[0157] The selection of beams can be based on channel estimates of
reference symbol signals, or on channel estimates of demodulation
reference signals (DMRS) embedded in an LTE physical uplink shared
channel (PUSCH).
[0158] The selection of beams can be performed for each resource
block, or for groups of resource blocks, or even with one common
selection for the whole carrier bandwidth. The selection of beams
can be performed with one single, common, selection for the whole
carrier bandwidth, since the beams generally correspond to physical
directions and even though the phase of the radio propagation is
frequency dependent, the physical directions are not.
[0159] If multiple terminal devices are scheduled in the same
resource blocks, and the RE is connected to one single REC, the
selections can be made as the union of the beams needed for each
terminal device. If, for example, three beams are selected for a
first terminal device and three beams are selected for a second
terminal device and one of the beams is common for the first
terminal device and the second terminal device, then only five
beams need to be transferred from the RE to the REC. If, on the
other hand, the RE is connected to two RECs, and the first terminal
device is handled by one REC and the second terminal device is
handled by another REC, then three beams need to be sent to each
REC.
[0160] According to some aspects the maximum number of beams that
can be selected is controlled by the REC. The information about how
many beams that can be selected are then provided by the REC to the
RE over the interface. This information can be expressed in
different ways. According to a first example the information
specifies the maximum number of beams selected per terminal device.
According to a second example the information specifies the maximum
number of beams selected in total. According to a third example the
information specifies a combined restriction of both the maximum
number of beams selected per terminal device and the maximum number
of beams selected in total. Given these limitations, the RE will
decide how many beams that should be selected per terminal device.
This can be done by the RE comparing the signal quality for the
terminal devices in each of the beams, and select beams with the
given limitations. In additions to the limitations given by the
REC, the RE could also need to make the selection such that each
terminal gets at least M.gtoreq.1 number of beams selected.
[0161] FIG. 14 schematically illustrates, in terms of a number of
functional units, the components of an RE according to an
embodiment. Processing circuitry 210 is provided using any
combination of one or more of a suitable central processing unit
(CPU), multiprocessor, microcontroller, digital signal processor
(DSP), etc., capable of executing software instructions stored in a
computer program product 1810a (as in FIG. 18), e.g. in the form of
a storage medium 230. The processing circuitry 210 may further be
provided as at least one application specific integrated circuit
(ASIC), or field programmable gate array (FPGA).
[0162] Particularly, the processing circuitry 210 is configured to
cause the RE to perform a set of operations, or steps, S102-S108,
S302-S312, as disclosed above. For example, the storage medium 230
may store the set of operations, and the processing circuitry 210
may be configured to retrieve the set of operations from the
storage medium 230 to cause the RE to perform the set of
operations. The set of operations may be provided as a set of
executable instructions. Thus the processing circuitry 210 is
thereby arranged to execute methods as herein disclosed.
[0163] The storage medium 230 may also comprise persistent storage,
which, for example, can be any single one or combination of
magnetic memory, optical memory, solid state memory or even
remotely mounted memory.
[0164] The RE may further comprise a communications interface 220
for communications at least with the REC and the terminal devices.
As such the communications interface 220 may comprise one or more
transmitters and receivers, comprising analogue and digital
components.
[0165] The processing circuitry 210 controls the general operation
of the RE e.g. by sending data and control signals to the
communications interface 220 and the storage medium 230, by
receiving data and reports from the communications interface 220,
and by retrieving data and instructions from the storage medium
230. Other components, as well as the related functionality, of the
RE are omitted in order not to obscure the concepts presented
herein.
[0166] FIG. 15 schematically illustrates, in terms of a number of
functional modules, the components of an RE 200 according to an
embodiment. According to some aspects the RE 200 comprises an
obtain module 210a configured to perform step S102, an obtain
module 210b configured to perform step S104, a (optional) transform
module 210C configured to perform step S106, and an apply module
210d configured to perform step S108. According to some aspects the
RE 200 comprises an obtain module 210e configured to perform step
S302, a transform module 210 of configured to perform step S304, a
provide module 210g configured to perform step S306, an (optional)
obtain module 210h configured to perform step S308, a (optional)
transform module 210i configured to perform step S310, and an
(optional) apply module 210j configured to perform step S312.
[0167] In general terms, each functional module 210a-210j may be
implemented in hardware or in software. Preferably, one or more or
all functional modules 210a-210j may be implemented by the
processing circuitry 210, possibly in cooperation with functional
units 220 and/or 230. The processing circuitry 210 may thus be
arranged to from the storage medium 230 fetch instructions as
provided by a functional module 210a-210j and to execute these
instructions, thereby performing any steps of the RE as disclosed
herein.
[0168] FIG. 16 schematically illustrates, in terms of a number of
functional units, the components of an REC according to an
embodiment. Processing circuitry 310 is provided using any
combination of one or more of a suitable central processing unit
(CPU), multiprocessor, microcontroller, digital signal processor
(DSP), etc., capable of executing software instructions stored in a
computer program product 1810b (as in FIG. 18), e.g. in the form of
a storage medium 330. The processing circuitry 310 may further be
provided as at least one application specific integrated circuit
(ASIC), or field programmable gate array (FPGA).
[0169] Particularly, the processing circuitry 310 is configured to
cause the REC to perform a set of operations, or steps, S202-S208,
S402-S408, as disclosed above. For example, the storage medium 330
may store the set of operations, and the processing circuitry 310
may be configured to retrieve the set of operations from the
storage medium 330 to cause the REC to perform the set of
operations. The set of operations may be provided as a set of
executable instructions. Thus the processing circuitry 310 is
thereby arranged to execute methods as herein disclosed.
[0170] The storage medium 330 may also comprise persistent storage,
which, for example, can be any single one or combination of
magnetic memory, optical memory, solid state memory or even
remotely mounted memory.
[0171] The REC may further comprise a communications interface 320
for communications at least with the RE. As such the communications
interface 320 may comprise one or more transmitters and receivers,
comprising analogue and digital components.
[0172] The processing circuitry 310 controls the general operation
of the REC e.g. by sending data and control signals to the
communications interface 320 and the storage medium 330, by
receiving data and reports from the communications interface 320,
and by retrieving data and instructions from the storage medium
330. Other components, as well as the related functionality, of the
REC are omitted in order not to obscure the concepts presented
herein.
[0173] FIG. 17 schematically illustrates, in terms of a number of
functional modules, the components of an REC according to an
embodiment. According to some aspects the REC 300 comprises an
obtain module 310a configured to perform step S302, a transform
module 310b configured to perform step S304, a provide module 210C
configured to perform step S306, and a (optional) provide module
210d configured to perform step S308. According to some aspects the
REC 300 comprises an obtain module 310e configured to perform step
S402, an (option) obtain module 210f configured to perform step
S404, a determine module 310g configured to perform step S406, and
a provide module 310h configured to perform step S408.
[0174] In general terms, each functional module 310a-310h may be
implemented in hardware or in software. Preferably, one or more or
all functional modules 310a-310h may be implemented by the
processing circuitry 310, possibly in cooperation with functional
units 320 and/or 330. The processing circuitry 310 may thus be
arranged to from the storage medium 330 fetch instructions as
provided by a functional module 310a-310h and to execute these
instructions, thereby performing any steps of the REC as disclosed
herein.
[0175] The RE and REC may be provided as standalone devices or as a
part of at least one further device. For example, as disclosed
above the RE and REC may be provided in an access node.
Alternatively, functionality of the RE and the REC may be
distributed between at least two devices, or nodes.
[0176] Thus, a first portion of the instructions performed by the
RE or REC may be executed in a first device, and a second portion
of the of the instructions performed by the RE or REC may be
executed in a second device; the herein disclosed embodiments are
not limited to any particular number of devices on which the
instructions performed by the RE or REC may be executed.
[0177] Hence, the methods according to the herein disclosed
embodiments are suitable to be performed by an RE or REC residing
in a cloud computational environment. Therefore, although a single
processing circuitry 210, 310 is illustrated in FIGS. 14 and 16 the
processing circuitry 210, 310 may be distributed among a plurality
of devices, or nodes. The same applies to the functional modules
210a-210j, 310a-310h of FIGS. 15 and 17 and the computer programs
1820a, 1820b, 1820c, 1820d of FIG. 18 (see below).
[0178] FIG. 18 shows one example of a computer program product
1810a, 1810b, 1810c, 1810d comprising computer readable means 1830.
On this computer readable means 1830, a computer program 1820a,
1820c can be stored, which computer program 1820a, 1820c can cause
the processing circuitry 210 and thereto operatively coupled
entities and devices, such as the communications interface 220 and
the storage medium 230, to execute methods according to embodiments
described herein. The computer program 1820a, 1820c and/or computer
program product 1810a, 1820c may thus provide means for performing
any steps of the RE as herein disclosed. On this computer readable
means 1830, a computer program 1820b, 1820d can be stored, which
computer program 1820b, 1820d can cause the processing circuitry
310 and thereto operatively coupled entities and devices, such as
the communications interface 320 and the storage medium 330, to
execute methods according to embodiments described herein. The
computer program 1820b, 1820d and/or computer program product
1810b, 1810d may thus provide means for performing any steps of the
REC as herein disclosed.
[0179] In the example of FIG. 18, the computer program product
1810a, 1810b, 1810c, 1810d is illustrated as an optical disc, such
as a CD (compact disc) or a DVD (digital versatile disc) or a
Blu-Ray disc. The computer program product 1810a, 1810b, 1810c,
1810d could also be embodied as a memory, such as a random access
memory (RAM), a read-only memory (ROM), an erasable programmable
read-only memory (EPROM), or an electrically erasable programmable
read-only memory (EEPROM) and more particularly as a non-volatile
storage medium of a device in an external memory such as a USB
(Universal Serial Bus) memory or a Flash memory, such as a compact
Flash memory. Thus, while the computer program 1820a, 1820b, 1820c,
1820d is here schematically shown as a track on the depicted
optical disk, the computer program 1820a, 1820b, 1820c, 1820d can
be stored in any way which is suitable for the computer program
product 1810a, 1810b, 1810c, 1810d.
[0180] The inventive concept has mainly been described above with
reference to a few embodiments. However, as is readily appreciated
by a person skilled in the art, other embodiments than the ones
disclosed above are equally possible within the scope of the
inventive concept, as defined by the appended claims. For example,
although the embodiments mainly have been described in a time
division duplex (TDD) context, at least some of the embodiments are
also applicable for frequency division duplex (FDD). One difference
in FDD compared to TDD is that the UL measurements cannot for sure
be used for DL, due to the different frequencies UL and DL. In FDD
the terminal device sends information about what beam direction the
terminal device deems is best (from a raster of predetermined beams
that the access node is repeatedly transmitting, i.e. a "code
book"). In this case, the REC may need to provide beamforming
weights to the RE (thus defining the external information).
* * * * *